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1
Geersen, Jacob, Andrea Festa, and Francesca Remitti. "Structural constraints on the subduction of mass-transport deposits in convergent margins." Geological Society, London, Special Publications 500, no. 1 (December 19, 2019): 115–28. http://dx.doi.org/10.1144/sp500-2019-174.
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AbstractThe subduction of large and heterogeneous mass-transport deposits (MTDs) is discussed to modify the structure and physical state of the plate boundary and therewith exert an influence on seismicity in convergent margins. Understanding which subduction-zone architectures and structural boundary conditions favour the subduction of MTDs, primarily deposited in oceanic trenches, is therefore highly significant. We use bathymetric and seismic reflection data from modern convergent margins to show that a large landslide volume and long runout, in concert with thin trench sediments, increase the chances for an MTD to become subducted. In regions where the plate boundary develops within the upper plate or at its base (non-accretionary margins), and in little-sedimented trenches (sediment thickness <2 km), an MTD has the highest potential to become subducted, particularly when characterized by a long runout. On the contrary, in the case of a heavily sedimented trench (sediment thickness >4 km) and short runout, an MTD will only be subducted if the thickness of subducting sediments is higher than the thickness of sediments under the MTD. The results allow identification of convergent margins where MTDs are preferentially subducted and thus potentially alter plate-boundary seismicity.
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Lemenkova, Polina. "GEBCO and ETOPO1 gridded datasets for GMT based cartographic Mapping of Hikurangi, Puysegur and Hjort Trenches, New Zealand." Acta Universitatis Lodziensis. Folia Geographica Physica, no. 19 (December 30, 2020): 7–18. http://dx.doi.org/10.18778/1427-9711.19.01.
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The study focused on the comparative analysis of the submarine geomorphology of three oceanic trenches: Hikurangi Trench (HkT), Puysegur Trench (PT) and Hjort Trench (HjT), New Zealand region, Pacific Ocean. HjT is characterized by an oblique subduction zone. Unique regional tectonic setting consist in two subduction zones: northern (Hikurangi margin) and southern (Puysegur margin), connected by oblique continental collision along the Alpine Fault, South Island. This cause variations in the geomorphic structure of the trenches. PT/HjT subduction is highly oblique (dextral) and directed southwards. Hikurangi subduction is directed northwestwards. South Island is caught in between by the “subduction scissor”. Methodology is based on GMT (The Generic Mapping Tools) for mapping, plotting and modelling. Mapping includes visualized geophysical, tectonic and geological settings of the trenches, based on sequential use of GMT modules. Data include GEBCO, ETOPO1, EGM96. Comparative histogram equalization of topographic grids (equalized, normalized, quadratic) was done by module ’grdhisteq’, automated cross-sectioning – by ’grdtrack’. Results shown that HjT has a symmetric shape form with comparative gradients on both western and eastern slopes. HkT has a trough-like flat wide bottom, steeper gradient slope on the North Island flank. PT has an asymmetric V-form with steep gradient on the eastern slopes and gentler western slope corresponding to the relatively gentle slope of a subducting plate and steeper slope of an upper one. HkT has shallower depths < 2,500 m, PT is <-6,000 m. The deepest values > 6,000 m for HjT. The surrounding relief of the HjT presents the most uneven terrain with gentle slope oceanward, and a steep slope on the eastern flank for PT, surrounded by complex submarine relief along the Macquarie Arc. Data distribution for the HkT demonstrates almost equal pattern for the depths from -600 m to ₋2,600 m. PT has a bimodal data distribution with 2 peaks: 1) -4,250 to -4,500 m (18%); 2) -2,250 to -3,000 m, < 7,5%. The second peak corresponds to the Macquarie Arc. Data distribution for HjT is classic bell-shaped with a clear peak at -3,250 to -3,500 m. The asymmetry of the trenches resulted in geomorphic shape of HkT, PT and HjT affected by geologic processes.
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Hatheway, Darwin L., and William Ellis. "Subduction Trenches as Nuclear Dumps." Science News 144, no. 5 (July 31, 1993): 67. http://dx.doi.org/10.2307/3977778.
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Plunder, Alexis, Cédric Thieulot, and Douwe J. J. van Hinsbergen. "The effect of obliquity on temperature in subduction zones: insights from 3-D numerical modeling." Solid Earth 9, no. 3 (June 14, 2018): 759–76. http://dx.doi.org/10.5194/se-9-759-2018.
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Abstract. The geotherm in subduction zones is thought to vary as a function of the subduction rate and the age of the subducting lithosphere. Along a single subduction zone the rate of subduction may strongly vary due to changes in the angle between the trench and the plate convergence vector, i.e., the subduction obliquity, due to trench curvature. We currently observe such curvature in, e.g., the Marianas, Chile and Aleutian trenches. Recently, strong along-strike variations in subduction obliquity were proposed to have caused a major temperature contrast between Cretaceous geological records of western and central Turkey. We test here whether first-order temperature variation in a subduction zone may be caused by variation in the trench geometry using simple thermo-kinematic finite-element 3-D numerical models. We prescribe the trench geometry by means of a simple mathematical function and compute the mantle flow in the mantle wedge by solving the equation of mass and momentum conservation. We then solve the energy conservation equation until steady state is reached. We analyze the results (i) in terms of mantle wedge flow with emphasis on the trench-parallel component and (ii) in terms of temperature along the plate interface by means of maps and the depth–temperature path at the interface. In our experiments, the effect of the trench curvature on the geotherm is substantial. A small obliquity yields a small but not negligible trench-parallel mantle flow, leading to differences of 30 °C along-strike of the model. Advected heat causes such temperature variations (linked to the magnitude of the trench-parallel component of velocity). With increasing obliquity, the trench-parallel component of the velocity consequently increases and the temperature variation reaches 200 °C along-strike. Finally, we discuss the implication of our simulations for the ubiquitous oblique systems that are observed on Earth and the limitations of our modeling approach. Lateral variations in plate sinking rate associated with curvature will further enhance this temperature contrast. We conclude that the synchronous metamorphic temperature contrast between central and western Turkey may well have resulted from reconstructed major variations in subduction obliquity.
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Grevemeyer, Ingo, Cesar R. Ranero, and Monika Ivandic. "Structure of oceanic crust and serpentinization at subduction trenches." Geosphere 14, no. 2 (January 12, 2018): 395–418. http://dx.doi.org/10.1130/ges01537.1.
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Bykov, V. G., and T. V. Merkulova. "THE WAVE GEODYNAMIC IMPACT OF TECTONIC PROCESSES ON THE AMURIAN PLATE." Tikhookeanskaya Geologiya 40, no. 4 (2021): 72–86. http://dx.doi.org/10.30911/0207-4028-2021-40-4-72-86.
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The analysis of data on the migration of earthquakes and slow deformations from the Indo-Eurasian collision and the Western Pacific subduction zones is given, and the wave “geodynamic impact” of these tectonic processes on the Amurian plate and surrounding structures is shown. The interaction and a relative contribution of collision and subduction to the recent geodynamics of the Amurian plate are discussed. A scheme is constructed showing localizations of the slow strain wave manifestation in the areas of central and eastern Asia. The calculations are performed aimed at revealing a transverse migration of earthquakes (M ≥ 6.5) directed from the Japan and the Kuril-Kamchatka trenches toward the Asian continent during the time period from 1960 to 2015. The migration of earthquakes along the profile crossing Hokkaido Island occurs at velocities of 15 and 23 km/yr, whereas the migration velocity from the Kuril-Kamchatka Trench via Sakhalin Island is evaluated from 20 to 40 km/yr at different depths. We focus on an insufficient study of the influence of the Western Pacific subduction on the formation of the deformation field in continental Asia.
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Fryer, Patricia, and N. Christian Smoot. "Processes of seamount subduction in the Mariana and Izu-Bonin trenches." Marine Geology 64, no. 1-2 (March 1985): 77–90. http://dx.doi.org/10.1016/0025-3227(85)90161-6.
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Shatwell, Dave. "Mesozoic Metallogenesis of Peru: A Reality Check on Geodynamic Models." SEG Discovery, no. 124 (January 1, 2021): 15–24. http://dx.doi.org/10.5382/segnews.2021-124.fea-01.
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Abstract The Andean Cordillera is generally regarded as the product of easterly subduction of oceanic lithosphere below South America since the Late Triassic, but recent syntheses have challenged this paradigm. In one model, W-dipping oceanic subduction pulls the continent west until it collides with a ribbon continent that now forms the coastal region and Western Cordillera of the Peruvian Andes. A second model involves westerly oceanic subduction until 120 to 100 Ma, without the involvement of a ribbon continent, to explain deep, subducted slabs revealed by mantle tomographic images. Both assume that “Andean-style” E-dipping subduction did not exist during the Jurassic and Early Cretaceous. Another model, also involving mantle tomography, assumes that a back-arc basin opened inboard of the trench between 145 and 100 Ma, displacing the E-dipping subduction zone offshore without changing its polarity. This article examines the implications of these hypotheses for southern Peruvian metallogenesis during the Mesozoic, when marginal basins opened and closed and were thrust eastward and then were intruded, between 110 and ~50 Ma, by a linear belt of multiple plutons known as the Coastal Batholith. The earliest mineralization in southern Peru is located on the coast and comprises major iron oxide and minor porphyry copper deposits emplaced between 180 and 110 Ma. This was followed by Cu-rich iron oxide copper-gold deposits and a large Zn-rich volcanogenic massive sulfide (VMS) deposit between 115 and 95 Ma, then minor porphyry Cu deposits at ~80 Ma. A second episode of localized VMS mineralization followed at 70 to 68 Ma, then a group of at least five giant porphyry Cu-Mo deposits in southernmost Peru formed between 62 and 53 Ma. The conventional model of Andean-style subduction, which explains many features of Mesozoic Andean metallogenesis in terms of changing plate vectors and velocities, is a poor fit with mantle tomographic anomalies that are thought to record the paleopositions of ancient trenches. A ribbon-continent model requires some plutons of the Coastal Batholith to have been separated from others by an ocean basin. West-dipping oceanic subduction does not account for Jurassic mineralization and magmatism in southern Peru. A model involving a back-arc basin that opened inboard of the existing trench, forcing E-dipping subduction to retreat offshore between 145 and 100 Ma, seems to best explain the metallogenic and tomographic data.
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Gamage, S. S. N. "Seismic Activity near the Sunda and Andaman Trenches in the Sumatra Subduction Zone." International Journal of Multidisciplinary Studies 4, no. 2 (December 28, 2017): 49. http://dx.doi.org/10.4038/ijms.v4i2.22.
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Barbot, S., and J. R. Weiss. "Connecting subduction, extension and shear localization across the Aegean Sea and Anatolia." Geophysical Journal International 226, no. 1 (February 27, 2021): 422–45. http://dx.doi.org/10.1093/gji/ggab078.
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SUMMARY The Eastern Mediterranean is the most seismically active region in Europe due to the complex interactions of the Arabian, African, and Eurasian tectonic plates. Deformation is achieved by faulting in the brittle crust, distributed flow in the viscoelastic lower-crust and mantle, and Hellenic subduction, but the long-term partitioning of these mechanisms is still unknown. We exploit an extensive suite of geodetic observations to build a kinematic model connecting strike-slip deformation, extension, subduction, and shear localization across Anatolia and the Aegean Sea by mapping the distribution of slip and strain accumulation on major active geological structures. We find that tectonic escape is facilitated by a plate-boundary-like, trans-lithospheric shear zone extending from the Gulf of Evia to the Turkish-Iranian Plateau that underlies the surface trace of the North Anatolian Fault. Additional deformation in Anatolia is taken up by a series of smaller-scale conjugate shear zones that reach the upper mantle, the largest of which is located beneath the East Anatolian Fault. Rapid north–south extension in the western part of the system, driven primarily by Hellenic Trench retreat, is accommodated by rotation and broadening of the North Anatolian mantle shear zone from the Sea of Marmara across the north Aegean Sea, and by a system of distributed transform faults and rifts including the rapidly extending Gulf of Corinth in central Greece and the active grabens of western Turkey. Africa–Eurasia convergence along the Hellenic Arc occurs at a median rate of 49.8 mm yr–1 in a largely trench-normal direction except near eastern Crete where variably oriented slip on the megathrust coincides with mixed-mode and strike-slip deformation in the overlying accretionary wedge near the Ptolemy–Pliny–Strabo trenches. Our kinematic model illustrates the competing roles the North Anatolian mantle shear zone, Hellenic Trench, overlying mantle wedge, and active crustal faults play in accommodating tectonic indentation, slab rollback and associated Aegean extension. Viscoelastic flow in the lower crust and upper mantle dominate the surface velocity field across much of Anatolia and a clear transition to megathrust-related slab pull occurs in western Turkey, the Aegean Sea and Greece. Crustal scale faults and the Hellenic wedge contribute only a minor amount to the large-scale, regional pattern of Eastern Mediterranean interseismic surface deformation.
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Kiratzi, A. A. "THE 16 APRIL 2015 MW6.1 EARTHQUAKE SEQUENCE NEAR KASOS ISLAND AT THE EASTERN HELLENIC SUBDUCTION ZONE." Bulletin of the Geological Society of Greece 50, no. 3 (July 27, 2017): 1163. http://dx.doi.org/10.12681/bgsg.11822.
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Broad band seismic waveforms are used to determine the source model of the 16 April 2015 (UTC 18:07:44) earthquake, Mw6.1, which occurred 14 km SW of Kasos Island, in the eastern Hellenic subduction zone. The mainshock is connected with oblique leftlateral motion on a reverse fault, dipping to SE. Most of the aftershocks are compatible with strike-slip or oblique normal faulting, with the T-axes showing along arc extension. A finite fault slip inversion was performed, allowing for the rake angle to vary across the fault, to capture the variation in the slip vectors. The rupture initiated in the lower crust, at a centroid depth of 23 km, and propagated mainly towards SW. The slip is confined in depth within ~17km and 27km, mainly in a single asperity, with the peak slip of the order of 60 cm. The slip model provided synthetic seismograms which matched satisfactory the observed, and with forward modelling the ShakeMap was calculated. The 2015 Kasos earthquake sequence is compatible with shear motions parallel to the strike of the subduction zone. It provides evidence that part of the deformation in the eastern Hellenic subduction is taken up by the simultaneous operation of reverse faulting and of minor strike-slip and oblique normal faulting, with slip vectors aligned ~ parallel to the Pliny and Strabo Trenches and the long axis of the local bathymetry.
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Gurnis, Michael. "Depressed continental hypsometry behind oceanic trenches: A clue to subduction controls on sea-level change." Geology 21, no. 1 (1993): 29. http://dx.doi.org/10.1130/0091-7613(1993)021<0029:dchbot>2.3.co;2.
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Fiala-Médioni, A., J. Boulègue, S. Ohta, H. Felbeck, and A. Mariotti. "Source of energy sustaining the Calyptogena populations from deep trenches in subduction zones off Japan." Deep Sea Research Part I: Oceanographic Research Papers 40, no. 6 (June 1993): 1241–58. http://dx.doi.org/10.1016/0967-0637(93)90136-q.
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Lemenkova, Polina. "SUBMARINE TECTONIC GEOMORPHOLOGY OF THE PLINY AND HELLENIC TRENCHES REFLECTING THE GEOLOGICAL EVOLUTION OF SOUTHERN GREECE." Rudarsko-geološko-naftni zbornik 36, no. 4 (2021): 33–48. http://dx.doi.org/10.17794/rgn.2021.4.4.
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Mapping seafloor geomorphology is a complex task requiring the integration of advanced cartographic technologies and high-resolution spatial data. This paper provides a comparative geomorphological analysis of the Hellenic Trench (HT) and the Pliny Trench (PT) located in the Eastern Mediterranean Sea, southern Greece. These trenches were formed as a result of the tectonic plate subduction in the Eastern Mediterranean Sea: the northward motion of the African and Arabian plates, complicated by the regional geological settings, such as active faults and earthquakes, which resulted in their different geomorphological forms and bathymetric shapes. Technically, this paper presents an example of the advanced scripting mapping by scripting the cartographic toolset of Generic Mapping Tools (GMT), which performs mapping through shell scripts. The maps are based on the high-quality topographic, geological and geophysical data: GEBCO, EGM96, geoid, and marine free-air gravity fields. The GMT builds upon the modules used for data processing. The region was subsetted by ‘grdcut’, analysed by the Geospatial Data Abstraction Library (GDAL) (gdalinfo utility), and visualized by ‘grdimage’. Two segments of the trenches formed in a condition of varying geological and geophysical settings, have been modelled, visualized and compared, as representative cross-sections. As a result of the automated digitizing, spatial interpolation and sequential aggregating of GMT codes, the segments of the cross-sections were represented. The HT (Ionian segment) has an asymmetric one-sided shape; a steepness of 56.8° on the NE side and 7° on the SW flank. The PT has a more symmetric view; a steepness of 42.14° on its NW flank and 26.66° on its SE flank. The PT has a clear peak of the depths at -2600 to -2800 m and the most representative data range at -5000 to -6000 m. The HT has a bimodal data distribution with two peaks. The most frequent data for HT is -3200 m to -3400 m. Compared to PT, the HT is deeper. The histogram shows the peak of data for HT in the interval between -3200 to -3400 m (135 samples) while the PT shows the peak of data in the interval at -2600 to -2800 m (310 samples). Besides, 105 samples of the HT have depths exceeding 4000 m, while only 20 samples were recorded for PT in the same interval. This paper contributes to the geomorphological studies of the general Eastern Mediterranean Sea region, particularly relating to regional seafloor mapping of the Hellenic and Pliny trenches.
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Rowley, David B., Alessandro M. Forte, Christopher J. Rowan, Petar Glišović, Robert Moucha, Stephen P. Grand, and Nathan A. Simmons. "Kinematics and dynamics of the East Pacific Rise linked to a stable, deep-mantle upwelling." Science Advances 2, no. 12 (December 2016): e1601107. http://dx.doi.org/10.1126/sciadv.1601107.
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Earth’s tectonic plates are generally considered to be driven largely by negative buoyancy associated with subduction of oceanic lithosphere. In this context, mid-ocean ridges (MORs) are passive plate boundaries whose divergence accommodates flow driven by subduction of oceanic slabs at trenches. We show that over the past 80 million years (My), the East Pacific Rise (EPR), Earth’s dominant MOR, has been characterized by limited ridge-perpendicular migration and persistent, asymmetric ridge accretion that are anomalous relative to other MORs. We reconstruct the subduction-related buoyancy fluxes of plates on either side of the EPR. The general expectation is that greater slab pull should correlate with faster plate motion and faster spreading at the EPR. Moreover, asymmetry in slab pull on either side of the EPR should correlate with either ridge migration or enhanced plate velocity in the direction of greater slab pull. Based on our analysis, none of the expected correlations are evident. This implies that other forces significantly contribute to EPR behavior. We explain these observations using mantle flow calculations based on globally integrated buoyancy distributions that require core-mantle boundary heat flux of up to 20 TW. The time-dependent mantle flow predictions yield a long-lived deep-seated upwelling that has its highest radial velocity under the EPR and is inferred to control its observed kinematics. The mantle-wide upwelling beneath the EPR drives horizontal components of asthenospheric flows beneath the plates that are similarly asymmetric but faster than the overlying surface plates, thereby contributing to plate motions through viscous tractions in the Pacific region.
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Grevemeyer, Ingo, Norbert Kaul, Juan L. Diaz-Naveas, Heinrich W. Villinger, Cesar R. Ranero, and Christian Reichert. "Heat flow and bending-related faulting at subduction trenches: Case studies offshore of Nicaragua and Central Chile." Earth and Planetary Science Letters 236, no. 1-2 (July 2005): 238–48. http://dx.doi.org/10.1016/j.epsl.2005.04.048.
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Celebi, M., J. Prince, C. Dietel, M. Onate, and G. Chavez. "The Culprit in Mexico City—Amplification of Motions." Earthquake Spectra 3, no. 2 (May 1987): 315–28. http://dx.doi.org/10.1193/1.1585431.
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Mexico City has repeatedly suffered from the long-distance effects of the earthquakes that originate as far away as the subduction trenches near the Mexican Pacific Coast. The Michoacan, Mexico earthquake of 19 September 1985 was no exception and caused extensive damage to property and numerous loss of lives. The unique subsurface condition resulting from the historical lakebed has distinct resonant low frequencies around 0.5 Hz. The strong earthquake motions from long distances as well as the locally originating weak motions cause large amplifications at resonant low frequencies in the subsurface environment of Mexico City lakebed. In this paper, the resonant frequencies and associated amplification of motions in Mexico City are quantified in terms of spectral ratios using 19 September 1985 strong-motion data and weak motions recorded in January, 1986. These ratios confirm that the amplification of motions at resonant frequencies due to the subsurface conditions is indeed the culprit.
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SUÁREZ, MANUEL, RITA DE LA CRUZ, MICHAEL BELL, and ALAIN DEMANT. "Cretaceous slab segmentation in southwestern Gondwana." Geological Magazine 147, no. 2 (September 16, 2009): 193–205. http://dx.doi.org/10.1017/s0016756809990355.
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AbstractThe Mesozoic Austral Basin of Patagonia, in southwestern Gondwana, experienced a major tectonic segmentation during Aptian times. Sometime between 121 and 118 Ma (Aptian), the northern part of the Austral Basin, known as the Aisén Basin or Río Mayo Embayment, was inverted, with the sediments overlain by calc-alkaline subaerial volcanic rocks of Aptian to Maastrichtian age. In the southern segment of the Austral Basin, known as the Magallanes Basin, predominantly marine sediments accumulated until Cenozoic times in a back-arc position, relative to a magmatic arc located to the west. The subduction-related N–S-trending volcanic chains of both segments were geographically displaced during Aptian to Late Cretaceous times. In the Aisén segment north of ~49–50° S, the volcanic chain was located further east than the coeval arc in the Magallanes segment. A transform fault connected the trenches of both segments, with the Aisén segment dipping at a shallower angle than the Magallanes segment.
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Sallarès, Valentí, Manel Prada, Sebastián Riquelme, Adrià Meléndez, Alcinoe Calahorrano, Ingo Grevemeyer, and César R. Ranero. "Large slip, long duration, and moderate shaking of the Nicaragua 1992 tsunami earthquake caused by low near-trench rock rigidity." Science Advances 7, no. 32 (August 2021): eabg8659. http://dx.doi.org/10.1126/sciadv.abg8659.
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Large earthquake ruptures propagating up to areas close to subduction trenches are infrequent, but when they occur, they heavily displace the ocean seafloor originating destructive tsunamis. The current paradigm is that the large seafloor deformation is caused by local factors reducing friction and increasing megathrust fault slip, or prompting the activation of ancillary faults or energy sources. As alternative to site-specific models, it has been proposed that large shallow slip could result from depth-dependent rock rigidity variations. To confront both hypotheses, here, we map elastic rock properties across the rupture zone of the MS7.0-MW7.7 1992 Nicaragua tsunami earthquake to estimate a property-compatible finite fault solution. The obtained self-consistent model accounts for trenchward increasing slip, constrains stress drop, and explains key tsunami earthquake characteristics such as long duration, high-frequency depletion, and magnitude discrepancy. The confirmation that these characteristics are all intrinsic attributes of shallow rupture opens new possibilities to improve tsunami hazard assessment.
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Marotta, A. M., F. Restelli, A. Bollino, A. Regorda, and R. Sabadini. "The static and time-dependent signature of ocean–continent and ocean–ocean subduction: the case studies of Sumatra and Mariana complexes." Geophysical Journal International 221, no. 2 (January 16, 2020): 788–825. http://dx.doi.org/10.1093/gji/ggaa029.
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SUMMARY The anomalous density structure at subduction zones, both in the wedge and in the upper mantle, is analysed to shed light on the processes that are responsible for the characteristic gravity fingerprints of two types of subduction: ocean–continent and ocean–ocean. Our modelling is then performed within the frame of the EIGEN-6C4 gravitational disturbance pattern of two subductions representative of the above two types, the Sumatra and Mariana complexes, finally enabling the different characteristics of the two patterns to be observed and understood on a physical basis, including some small-scale details. A 2-D viscous modelling perpendicular to the trench accounts for the effects on the gravity pattern caused by a wide range of parameters in terms of convergence velocity, subduction dip angle and lateral variability of the crustal thickness of the overriding plate, as well as compositional differentiation, phase changes and hydration of the mantle. Plate coupling, modelled within a new scheme where the relative velocity at the plate contact results self-consistently from the thermomechanical evolution of the system, is shown to have an important impact on the gravity signature. Beyond the already understood general bipolar fingerprint of subduction, perpendicular to the trench, we obtain the density and gravity signatures of the processes occurring within the wedge and mantle that are responsible for the two different gravity patterns. To be compliant with the geodetic EIGEN-6C4 gravitational disturbance and to compare our predictions with the gravity at Sumatra and Mariana, we define a model normal Earth. Although the peak-to-peak gravitational disturbance is comparable for the two types of subductions, approximately 250 mGal, from both observations and modelling, encompassing the highest positive maximum on the overriding plates and the negative minimum on the trench, the trough is wider for the ocean–ocean subduction: approximately 300 km compared to approximately 180 km for the ocean–continent subduction. Furthermore, the gravitational disturbance pattern is more symmetric for the ocean–ocean subduction compared to the ocean–continent subduction in terms of the amplitudes of the two positive maxima over the overriding and subducting plates. Their difference is, for the ocean–ocean type, approximately one half of the ocean–continent one. These different characteristics of the two types of subductions are exploited herein in terms of the different crustal thicknesses of the overriding plate and of the different dynamics in the wedge and in the mantle for the two types of subduction, in close agreement with the gravity data.
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Wolfe, John A. "Arc magmatism and mineralization in North Luzon and its relationship to subduction at the East Luzon and North Manila Trenches." Journal of Southeast Asian Earth Sciences 2, no. 2 (January 1988): 79–93. http://dx.doi.org/10.1016/0743-9547(88)90011-6.
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Lynner, Colton. "Anisotropy-revealed change in hydration along the Alaska subduction zone." Geology 49, no. 9 (June 3, 2021): 1122–25. http://dx.doi.org/10.1130/g48860.1.
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Abstract Megathrust earthquake behavior in subduction zones is controlled by a variety of factors including the hydration state of the subducting slab. Increased hydration reduces the occur-rence of great, damaging earthquakes by diminishing the strength of the material along the interface between tectonic plates. Understanding variations in hydration in subductions zones is necessary for properly assessing the overall hazard posed by each region. Fortunately, seismic anisotropy is strongly dependent upon hydration of the subducting crust and litho-sphere. I present shear-wave splitting measurements that illuminate changes in anisotropy, and therefore hydration, of the subducting Pacific plate beneath the Alaska subduction zone (northern Pacific Ocean). Variations in shear-wave splitting directly correlate to changes in the behavior of great, megathrust earthquakes. My measurements show that the Shumagin seismic gap is characterized by a hydrated subducting slab, explaining the long-term lack of great earthquakes. Observations in the immediately adjacent Semidi segment, which experiences great events regularly, indicate a far less hydrated slab. These results are driven by the preferential alignment of paleo-spreading fabrics of the Pacific plate. Where fabrics are more closely aligned with the orientation of the trench, outer-rise faulting and plate hydration is enhanced. These results highlight the importance of changes in preexisting slab structures and subsequent hydration in the production of great, damaging earthquakes.
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Wolfe, John A. "Arc magmatism and mineralization in North Luzon and its relationship to subduction at the East Luzon and North Manila Trenches: reply." Journal of Southeast Asian Earth Sciences 4, no. 1 (January 1990): 71–72. http://dx.doi.org/10.1016/0743-9547(90)90028-c.
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Knittel, Ulrich. "Comment on “Arc magmatism and mineralization in North Luzon and its relationship to subduction at the East Luzon and North Manila Trenches”." Journal of Southeast Asian Earth Sciences 4, no. 1 (January 1990): 69–70. http://dx.doi.org/10.1016/0743-9547(90)90027-b.
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Guillaume, B., L. Husson, F. Funiciello, and C. Faccenna. "The dynamics of laterally variable subductions: laboratory models applied to the Hellenides." Solid Earth 4, no. 2 (July 10, 2013): 179–200. http://dx.doi.org/10.5194/se-4-179-2013.
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Abstract. We designed three-dimensional dynamically self-consistent laboratory models of subduction to analyse the relationships between overriding plate deformation and subduction dynamics in the upper mantle. We investigated the effects of the subduction of a lithosphere of laterally variable buoyancy on the temporal evolution of trench kinematics and shape, horizontal flow at the top of the asthenosphere, dynamic topography and deformation of the overriding plate. Two subducting units, which correspond to a negatively buoyant oceanic plate and positively buoyant continental one, are juxtaposed via a trench-perpendicular interface (analogue to a tear fault) that is either fully-coupled or shear-stress free. Differential rates of trench retreat, in excess of 6 cm yr−1 between the two units, trigger a more vigorous mantle flow above the oceanic slab unit than above the continental slab unit. The resulting asymmetrical sublithospheric flow shears the overriding plate in front of the tear fault, and deformation gradually switches from extension to transtension through time. The consistency between our models results and geological observations suggests that the Late Cenozoic deformation of the Aegean domain, including the formation of the North Aegean Trough and Central Hellenic Shear zone, results from the spatial variations in the buoyancy of the subducting lithosphere. In particular, the lateral changes of the subduction regime caused by the Early Pliocene subduction of the old oceanic Ionian plate redesigned mantle flow and excited an increasingly vigorous dextral shear underneath the overriding plate. The models suggest that it is the inception of the Kefalonia Fault that caused the transition between an extension dominated tectonic regime to transtension, in the North Aegean, Mainland Greece and Peloponnese. The subduction of the tear fault may also have helped the propagation of the North Anatolian Fault into the Aegean domain.
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Noda, Atsushi, Hiroaki Koge, Yasuhiro Yamada, Ayumu Miyakawa, and Juichiro Ashi. "Subduction of trench-fill sediments beneath an accretionary wedge: Insights from sandbox analogue experiments." Geosphere 16, no. 4 (June 17, 2020): 953–68. http://dx.doi.org/10.1130/ges02212.1.
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Abstract Sandy trench-fill sediments at accretionary margins are commonly scraped off at the frontal wedge and rarely subducted to the depth of high-pressure (HP) metamorphism. However, some ancient exhumed accretionary complexes are associated with high-pressure–low-temperature (HP-LT) metamorphic rocks, such as psammitic schists, which are derived from sandy trench-fill sediments. This study used sandbox analogue experiments to investigate the role of seafloor topography in the transport of trench-fill sediments to depth during subduction. We conducted two different types of experiments, with or without a rigid topographic high (representing a seamount). We used an undeformable backstop that was unfixed to the side wall of the apparatus to allow a seamount to be subducted beneath the overriding plate. In experiments without a seamount, progressive thickening of the accretionary wedge pushed the backstop down, leading to a stepping down of the décollement, narrowing of the subduction channel, and underplating of the wedge with subducting sediment. In contrast, in experiments with a topographic high, the subduction of the topographic high raised the backstop, leading to a stepping up of the décollement and widening of the subduction channel. These results suggest that the subduction of stiff topographic relief beneath an inflexible overriding plate might enable trench-fill sediments to be deeply subducted and to become the protoliths of HP-LT metamorphic rocks.
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Taber, J. John, and B. T. R. Lewis. "Crustal structure of the Washington continental margin from refraction data." Bulletin of the Seismological Society of America 76, no. 4 (August 1, 1986): 1011–24. http://dx.doi.org/10.1785/bssa0760041011.
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Abstract Refraction data were collected in an onshore-offshore experiment in 1978 near Grays Harbor, Washington. Two-dimensional raytracing and synthetic seismograms were used to model the data along the refraction lines. The resulting velocity model uses a broad-scale subduction zone geometry to explain the major features of the data. The three main contributions of the onshore-offshore model are: (1) evidence for an approximately 9° dip of the subducting oceanic lithosphere; (2) a clear indication of the point at which the subducting slab begins to bend beneath the margin; and (3) confirmation of the continuity of the slab from the buried trench offshore to beneath Puget Sound. The model also helps explain the distribution and stress orientation of earthquakes within the subduction zone.
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Bessat, Annelore, Thibault Duretz, György Hetényi, Sébastien Pilet, and Stefan M. Schmalholz. "Stress and deformation mechanisms at a subduction zone: insights from 2-D thermomechanical numerical modelling." Geophysical Journal International 221, no. 3 (February 21, 2020): 1605–25. http://dx.doi.org/10.1093/gji/ggaa092.
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SUMMARY Numerous processes such as metamorphic reactions, fluid and melt transfer and earthquakes occur at a subducting zone, but are still incompletely understood. These processes are affected, or even controlled, by the magnitude and distribution of stress and deformation mechanism. To eventually understand subduction zone processes, we quantify here stresses and deformation mechanisms in and around a subducting lithosphere, surrounded by asthenosphere and overlain by an overriding plate. We use 2-D thermomechanical numerical simulations based on the finite difference and marker-in-cell method and consider a 3200 km wide and 660 km deep numerical domain with a resolution of 1 km by 1 km. We apply a combined visco-elasto-plastic deformation behaviour using a linear combination of diffusion creep, dislocation creep and Peierls creep for the viscous deformation. We consider two end-member subduction scenarios: forced and free subduction. In the forced scenario, horizontal velocities are applied to the lateral boundaries of the plates during the entire simulation. In the free scenario, we set the horizontal boundary velocities to zero once the subducted slab is long enough to generate a slab pull force large enough to maintain subduction without horizontal boundary velocities. A slab pull of at least 1.8 TN m–1 is required to continue subduction in the free scenario. We also quantify along-profile variations of gravitational potential energy (GPE). We evaluate the contributions of topography and density variations to GPE variations across a subduction system. The GPE variations indicate large-scale horizontal compressive forces around the trench region and extension forces on both sides of the trench region. Corresponding vertically averaged differential stresses are between 120 and 170 MPa. Furthermore, we calculate the distribution of the dominant deformation mechanisms. Elastoplastic deformation is the dominant mechanism in the upper region of the lithosphere and subducting slab (from ca. 5 to 60 km depth from the top of the slab). Viscous deformation dominates in the lower region of the lithosphere and in the asthenosphere. Considering elasticity in the calculations has an important impact on the magnitude and distribution of deviatoric stress; hence, simulations with increased shear modulus, in order to reduce elasticity, exhibit considerably different stress fields. Limiting absolute stress magnitudes by decreasing the internal friction angle causes slab detachment so that slab pull cannot be transmitted anymore to the horizontal lithosphere. Applying different boundary conditions shows that forced subduction simulations are stronger affected by the applied boundary conditions than free subduction simulations. We also compare our modelled topography and gravity anomaly with natural data of seafloor bathymetry and free-air gravity anomalies across the Mariana trench. Elasticity and deviatoric stress magnitudes of several hundreds of MPa are required to best fit the natural data. This agreement suggests that the modelled flexural behaviour and density field are compatible with natural data. Moreover, we discuss potential applications of our results to the depth of faulting in a subducting plate and to the generation of petit-spot volcanoes.
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Suchoy, Lior, Saskia Goes, Benjamin Maunder, Fanny Garel, and Rhodri Davies. "Effects of basal drag on subduction dynamics from 2D numerical models." Solid Earth 12, no. 1 (January 20, 2021): 79–93. http://dx.doi.org/10.5194/se-12-79-2021.
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Abstract. Subducting slabs are an important driver of plate motions, yet the relative importance of different forces in governing subduction motions and styles remains incompletely understood. Basal drag has been proposed to be a minor contributor to subduction forcing because of the lack of correlation between plate size and velocity in observed and reconstructed plate motions. Furthermore, in single subduction system models, low basal drag leads to subduction behaviour most consistent with the observation that trench migration velocities are generally low compared to convergence velocities. By contrast, analytical calculations and global mantle flow models indicate basal drag can be substantial. In this study, we revisit this problem by examining the drag at the base of the lithosphere, for a single subduction system, in 2D models with a free trench and composite non-linear rheology. We compare the behaviour of short and long plates for a range of asthenospheric and lithospheric rheologies. We reproduce results from previous modelling studies, including low ratios of trench over plate motions. However, we also find that any combination of asthenosphere and lithosphere viscosity that produces Earth-like subduction behaviour leads to a correlation of velocities with plate size, due to the role of basal drag. By examining Cenozoic plate motion reconstructions, we find that slab age and plate size are positively correlated: higher slab pull for older plates tends to be offset by higher basal drag below these larger plates. This, in part, explains the lack of plate velocity–size correlation in observations, despite the important role of basal drag in the subduction force balance.
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Prytkov, A. S., and N. F. Vasilenko. "The March 25, 2020 MW 7.5 Paramushir earthquake." Geosystems of Transition Zones 5, no. 2 (2021): 113–27. http://dx.doi.org/10.30730/gtrz.2021.5.2.113-120.121-127.
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The strong earthquake with moment magnitude Mw = 7.5 occurred on March 25, 2020, in the North Kurils to the southeast of the Paramushir Island. The hypocenter of the earthquake was located under the oceanic rise of deep-sea trench in the subducting Pacific lithospheric plate. This earthquake has been the strongest seismic event since 1900 for an area about 800 km long of the outer rise of the trench. It also was the strongest earthquake for the 300-kilometer long area of the Kuril-Kamchatka subduction zone adjacent to the epicenter. The article summarizes the data on the Paramushir earthquake. Tectonic position of the earthquake, source parameters, features of the aftershock process development, as well as coseismic displacement of the nearest continuous GNSS station are considered. The performed analysis did not allow us to clearly determine the rupture plane in the source. Nevertheless, the study of the features of the outer-rise earthquake is a matter of scientific interest, since the stress state of the bending area of the subducting Pacific lithospheric plate reflects the interplate interaction in the subduction zone.
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Suyehiro, Kiyoshi, Hitoshi Mikada, and Kenichi Asakawa. "Japanese Seafloor Observing Systems: Present and Future." Marine Technology Society Journal 37, no. 3 (September 1, 2003): 102–14. http://dx.doi.org/10.4031/002533203787537230.
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We describe in this article Japanese efforts toward building and operating long-term seafloor observing systems. Greater details are given to those systems in which the authors have been involved. The main impetus for obtaining long-term time-series from the ocean floor in Japan has been earthquake monitoring for risk assessment and hazard mitigation. Most of the earthquake energy is released near and along the oceanic trenches offshore Japan, and large inter-plate earthquakes recur at decades to 100-year intervals, which are a great threat to the society. The first cabled observatory was laid in 1978 by the Japan Meteorological Agency to monitor seismicity in an area where a M-8 earthquake has been expected to occur. Since then, national agencies and universities established more cabled observing systems (8 systems as of 2003). The very reason of seismic activity is the plate subduction, which causes numerous geophysically interesting activities including fluid vents, biological communities, and magma movements. Realizing all these processes require long-term monitoring to lead to eventual understanding of their dynamics, efforts were made particularly at JAMSTEC to establish multiple-sensor observing systems. There are now certain directions towards the future. One is establishing monitoring systems in deep ocean boreholes, which will become possible by the new Integrated Ocean Drilling Program (2003-). Another is enabling many sensors to be deployed at an appropriate spatial density so that networks realized on land can be extended over the surrounding oceans. The third is establishing observatories as components of global networks.
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Jaxybulatov, K., I. Koulakov, and N. L. Dobretsov. "Segmentation of the Izu-Bonin and Mariana slabs based on the analysis of the Benioff seismicity distribution and regional tomography results." Solid Earth 4, no. 1 (January 31, 2013): 59–73. http://dx.doi.org/10.5194/se-4-59-2013.
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Abstract. We present a new model of P and S velocity anomalies in the mantle down to a depth of 1300 km beneath the Izu-Bonin and Mariana (IBM) arcs. This model is derived based on tomographic inversion of global travel time data from the revised ISC catalogue. The results of inversion are thoroughly verified using a series of different tests. The obtained model is generally consistent with previous studies by different authors. We also present the distribution of relocated deep events projected to the vertical surface along the IBM arc system. Unexpectedly, the seismicity forms elongated vertical clusters instead of horizontal zones indicating phase transitions in the slab. We propose that these vertical seismicity zones mark zones of intense deformation and boundaries between semi-autonomous segments of the subducting plate. The P and S seismic tomography models consistently display the slab as prominent high-velocity anomalies coinciding with the distribution of deep seismicity. We can distinguish at least four segments which subduct differently. The northernmost segment of the Izu-Bonin arc has the gentlest angle of dipping which is explained by backward displacement of the trench. In the second segment, the trench stayed at the same location, and we observe the accumulation of the slab material in the transition zone and its further descending to the lower mantle. In the third segment, the trench is moving forward causing the steepening of the slab. Finally, for the Mariana segment, despite the backward displacement of the arc, the subducting slab is nearly vertical. Between the Izu-Bonin and Mariana arcs we clearly observe a gap which can be traced down to about 400 km in depth. Based on joint consideration of the tomography results and the seismicity distribution, we propose two different scenarios of the subduction evolution in the IBM zone during the recent time, depending on the reference frame of plate displacements. In the first case, we consider the movements in respect to the Philippine Plate, and explain the different styles of the subduction by the relative backward and forward migrations of the trench. In the second case, all the elements of the subduction system move westward in respect to the stable Asia. Different subduction styles are explained by the "anchoring" of selected segments of the slab, different physical properties of the subducting plate and the existence of buoyant rigid blocks related to sea mount and igneous provinces.
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Sasmi, Annisa Trisnia, Andri Dian Nugraha, Muzli Muzli, Sri Widiyantoro, Zulfakriza Zulfakriza, Shengji Wei, David P. Sahara, et al. "Hypocenter and Magnitude Analysis of Aftershocks of the 2018 Lombok, Indonesia, Earthquakes Using Local Seismographic Networks." Seismological Research Letters 91, no. 4 (May 27, 2020): 2152–62. http://dx.doi.org/10.1785/0220190348.
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Abstract The island of Lombok in Indonesia is located between the Indo-Australian and Eurasian subduction trenches and the Flores back-arc thrust, making it vulnerable to earthquakes. On 29 July 2018, a significant earthquake Mw 6.4 shook this region and was followed by series of major earthquakes (Mw>5.8) on 5, 9, and 19 August, which led to severe damage in the northern Lombok area. In this study, we attempt to reveal the possible cause of the sequences of the 2018 Lombok earthquakes based on aftershock monitoring data. Twenty stations were deployed to record earthquake waveform data from 4 August to 9 September 2018. In total, 3259 events were identified using 28,728 P- and 20,713 S-wave arrival times during the monitoring. The aftershock hypocenters were determined using a nonlinear approach and relocated using double-difference method. The moment magnitude (Mw) of each event was determined by fitting the displacement spectrum amplitude using a Brune-type model. The magnitudes of the aftershocks range from Mw 1.7 to 6.7. The seismicity pattern reveals three clusters located in the Flores oceanic crust, which fit well with the occurrences of the four events with Mw>6. We interpret these events as the main rupture area of the 2018 Lombok earthquake sequence. Furthermore, an aseismic zone in the vicinity of Rinjani extending toward the northwestern part of Lombok was observed. We propose that the crust in this area has elevated temperatures and is highly fractured thus inhibiting the generation of large earthquakes. The aseismic nature is therefore an artifact of the detection threshold of our network (Mw 4.6).
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Guillaume, B., L. Husson, F. Funiciello, and C. Faccenna. "The dynamics of laterally variable subductions: laboratory models applied to the Hellenides." Solid Earth Discussions 5, no. 1 (April 9, 2013): 315–63. http://dx.doi.org/10.5194/sed-5-315-2013.
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Abstract. We design three-dimensional dynamically self-consistent laboratory models of subduction to analyze the relationships between overriding plate deformation and subduction dynamics in the upper mantle. We investigate the effects of the subduction of a lithosphere of laterally variable buoyancy on the temporal evolution of trench kinematics and shape, horizontal flow at the top of the asthenosphere, dynamic topography and deformation of the overriding plate. The interface between the two units, analogue to a trench-perpendicular tear fault between a negatively buoyant oceanic plate and positively buoyant continental one, is either fully-coupled or shear-stress free. Differential rates of trench retreat, in excess of 6 cm yr−1 between the two units, trigger a more vigorous mantle flow above the oceanic slab unit than above the continental slab unit. The resulting asymmetrical sublithospheric flow shears the overriding plate in front of the tear fault, and deformation gradually switches from extension to transtension through time. The consistency between our models results and geological observations suggests that the Late Cenozoic deformation of the Aegean domain, including the formation of the North Aegean Trough and Central Hellenic Shear zone, results from the spatial variations in the buoyancy of the subducting lithosphere. In particular, the lateral changes of the subduction regime caused by the Early Pliocene subduction of the old oceanic Ionian plate redesigned mantle flow and excited an increasingly vigorous dextral shear underneath the overriding plate. The models suggest that it is the inception of the Kefalonia Fault that caused the transition between an extension dominated tectonic regime to transtension, in the North Aegean, Mainland Greece and Peloponnese. The subduction of the tear fault may also have helped the propagation of the North Anatolian Fault into the Aegean domain.
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Schellart, W. P., and V. Strak. "Geodynamic models of short-lived, long-lived and periodic flat slab subduction." Geophysical Journal International 226, no. 3 (April 1, 2021): 1517–41. http://dx.doi.org/10.1093/gji/ggab126.
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SUMMARY Flat slab subduction has been ascribed to a variety of causes, including subduction of buoyant ridges/plateaus and forced trench retreat. The former, however, has irregular spatial correlations with flat slabs, while the latter has required external forcing in geodynamic subduction models, which might be insufficient or absent in nature. In this paper, we present buoyancy-driven numerical geodynamic models and aim to investigate flat slab subduction in the absence of external forcing as well as test the influence of overriding plate strength, subducting plate thickness, inclusion/exclusion of an oceanic plateau and lower mantle viscosity on flat slab formation and its evolution. Flat slab subduction is reproduced during normal oceanic subduction in the absence of ridge/plateau subduction and without externally forced plate motion. Subduction of a plateau-like feature, in this buoyancy-driven setting, enhances slab steepening. In models that produce flat slab subduction, it only commences after a prolonged period of slab dip angle reduction during lower mantle slab penetration. The flat slab is supported by mantle wedge suction, vertical compressive stresses at the base of the slab and upper mantle slab buckling stresses. Our models demonstrate three modes of flat slab subduction, namely short-lived (transient) flat slab subduction, long-lived flat slab subduction and periodic flat slab subduction, which occur for different model parameter combinations. Most models demonstrate slab folding at the 660 km discontinuity, which produces periodic changes in the upper mantle slab dip angle. With relatively high overriding plate strength or large subducting plate thickness, such folding results in periodic changes in the dip angle of the flat slab segment, which can lead to periodic flat slab subduction, providing a potential explanation for periodic arc migration. Flat slab subduction ends due to the local overriding plate shortening and thickening it produces, which forces mantle wedge opening and a reduction in mantle wedge suction. As overriding plate strength controls the shortening rate, it has a strong control on the duration of flat slab subduction, which increases with increasing strength. For the weakest overriding plate, flat slab subduction is short-lived and lasts only 6 Myr, while for the strongest overriding plate flat slab subduction is long-lived and exceeds 75 Myr. Progressive overriding plate shortening during flat slab subduction might explain why flat slab subduction terminated in the Eocene in western North America and in the Jurassic in South China.
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Choe, Hanjin, and Jerome Dyment. "Fading magnetic anomalies, thermal structure and earthquakes in the Japan Trench." Geology 48, no. 3 (January 17, 2020): 278–82. http://dx.doi.org/10.1130/g46842.1.
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Abstract Early magnetic studies of the Japan Trench showed that seafloor spreading magnetic anomalies progressively fade away and disappear during subduction, reflecting the increasing distance to magnetized sources and the removal of their remanent magnetization with alteration and increasing temperature. An improved magnetic anomaly map derived from both scalar and vector magnetic anomaly data, coupled with a better knowledge of the slab geometry in one hand, of the magnetic structure of the oceanic crust on the other hand, allow us to constrain the thermal structure of the subducting slab. We, for the first time, identify two steps in the anomaly disappearance: first the magnetization of extrusive basalt is rapidly erased between 9 and 12 km, where titanomagnetite reaches its blocking temperature between 150 °C and 350 °C, then the magnetization of deeper crustal layers slowly decreases down to ∼20 km, reflecting the progressive slab heating toward the Curie temperature of magnetite, 580 °C. The resulting slab temperatures are higher than predicted by most thermal models. Recent observations and models suggest rejuvenated hydrothermal activity triggered by lithospheric flexure before subduction that may significantly heat up the subducting oceanic crust through thermal blanketing and possibly serpentinization, with consequences on the depth of the seismogenic zone.
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Jolivet, Laurent, Romain Augier, Claudio Faccenna, François Negro, Gaetan Rimmele, Philippe Agard, Cécile Robin, Federico Rossetti, and Ana Crespo-Blanc. "Subduction, convergence and the mode of backarc extension in the Mediterranean region." Bulletin de la Société Géologique de France 179, no. 6 (November 1, 2008): 525–50. http://dx.doi.org/10.2113/gssgfbull.179.6.525.
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Abstract 30-35 Ma ago a major change occurred in the Mediterranean region, from a regionally compressional subduction coeval with the formation of Alpine mountain belts, to extensional subduction and backarc rifting. Backarc extension was accompanied by gravitational spreading of the mountain belts formed before this Oligocene revolution. Syn-rift basins formed during this process above detachments and low-angle normal faults. Parameters that control the formation and the kinematics of such flat-lying detachments are still poorly understood. From the Aegean Sea to the Tyrrhenian Sea and the Alboran Sea, we have analysed onshore the deformation and P-T-t evolution of the ductile crust exhumed by extension, and the transition from ductile to brittle conditions as well as the relations between deep deformation and basin formation. We show that the sense of shear along crustal-scale detachments is toward the trench when subduction proceeds with little or no convergence (northern Tyrrhenian and Alboran after 20 Ma) and away from the trench in the case of true convergence (Aegean). We tentatively propose a scheme explaining how interactions between the subducting slab and the mantle control the basal shear below the upper plate and the geometry and distribution of detachments and associated sedimentary basins. We propose that ablative subduction below the Aegean is responsible for the observed kinematics on detachments (i.e. away from the trench). The example of the Betic Cordillera and the Rif orogen, where the directions of stretching were different in the lower and the upper crust and changed through time, is also discussed following this hypothesis.
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Qiu, Qiang, Linlin Li, Ya-Ju Hsu, Yu Wang, Chung-Han Chan, and Adam D. Switzer. "Revised earthquake sources along Manila trench for tsunami hazard assessment in the South China Sea." Natural Hazards and Earth System Sciences 19, no. 7 (July 31, 2019): 1565–83. http://dx.doi.org/10.5194/nhess-19-1565-2019.
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Abstract. Seismogenic tsunami hazard assessments are highly dependent on the reliability of earthquake source models. Here in a study of the Manila subduction zone (MSZ) system, we combine the geological characteristics of the subducting plate, geometry, and coupling state of the subduction interface to propose a series of fault rupture scenarios. We divide the subduction zone into three rupture segments: 14–16, 16–19, and 19–21.7∘ N inferred from geological structures associated with the down-going Sunda plate. Each of these segments is capable of generating earthquakes of a magnitude between Mw=8.5+ and Mw=9+, assuming a 1000-year seismic return period as suggested by previous studies. The most poorly constrained segment of the MSZ lies between 19 and 21.7∘ N, and here we use both local geological structures and characteristics of other subduction zone earthquakes around the world, to investigate the potential rupture characteristics of this segment. We consider multiple rupture modes for tsunamigenic earthquake and megathrust-splay fault earthquakes. These rupture models facilitate an improved understanding of the potential tsunami hazard in the South China Sea (SCS). Hydrodynamic simulations demonstrate that coastlines surrounding the SCS could be devastated by tsunami waves up to 10 m if large megathrust earthquakes occur in these segments. The regions most prone to these hazards include west Luzon of Philippines, southern Taiwan, southeastern China, central Vietnam, and Palawan Island.
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Haberland, Christian, Mohammad Mokhtari, Hassan Ali Babaei, Trond Ryberg, Mehdi Masoodi, Abdolreza Partabian, and Jörn Lauterjung. "Anatomy of a crustal-scale accretionary complex: Insights from deep seismic sounding of the onshore western Makran subduction zone, Iran." Geology 49, no. 1 (August 13, 2020): 3–7. http://dx.doi.org/10.1130/g47700.1.
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Abstract The Makran subduction zone has produced M 8+ earthquakes and subsequent tsunamis in historic times, hence indicating high risk for the coastal regions of southern Iran, Pakistan, and neighboring countries. Besides this, the Makran subduction zone is an end-member subduction zone featuring extreme properties, with one of the largest sediment inputs and the widest accretionary wedge on Earth. While surface geology and shallow structure of the offshore wedge have been relatively well studied, primary information on the deeper structure of the onshore part is largely absent. We present three crustal-scale, trench-perpendicular, deep seismic sounding profiles crossing the subaerial part of the accretionary wedge of the western Makran subduction zone in Iran. P-wave travel-time tomography based on a Monte Carlo Markov chain algorithm as well as the migration of automatic line drawings of wide-angle reflections reveal the crustal structure of the wedge and geometry of the subducting oceanic plate at high resolution. The images shed light on the accretionary processes, in particular the generation of continental crust by basal accretion, and provide vital basic information for hazard assessment and tsunami modeling.
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Cramer, Chris H., and Eric Jambo. "Impact of a Larger Fore‐Arc Region on Earthquake Ground Motions in South‐Central Alaska Including the 2018 M 7.1 Anchorage Inslab Earthquake." Seismological Research Letters 91, no. 1 (December 11, 2019): 174–82. http://dx.doi.org/10.1785/0220190183.
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Abstract The thermal state of the crust and mantle in subduction zones is controlled by the depth of the subducting plate. With low‐angle subduction, like at the eastern end of the Alaska subduction zone, the less attenuating fore‐arc is extended farther from the trench and can effect ground motions in addition to source and site effects. Recent crustal and subduction earthquakes in south‐central Alaska, including the 2018 M 7.1 Anchorage event, demonstrate these effects. Inslab earthquake waves in the subducting plate can propagate up the slab to the fore‐arc region with less attenuation, causing an increase in observed ground motions. Long‐period ground motions from the 2018 M 7.1 Anchorage earthquake are significantly higher than predicted ground motions from current subduction ground‐motion models within 50–100 km of the epicenter. At short periods, ground motions show reduced amplitudes due to nonlinear sediment effects in the Anchorage area, reducing the damage potential of the earthquake. At long periods, ground motions are little affected by sediment nonlinearity and remain higher than expected. The duration of shaking was too short for widespread liquefaction effects, unlike during the 1964 M 9.2 earthquake. Other historical earthquakes have produced similar increases in ground motions in the Cook Inlet and Kenai Peninsula region. At both short and long periods, ground motions from the 2016 Iniskin M 7.1 inslab earthquake are higher than expected in the Cook Inlet region. The 2015 Redoubt M 6.3 inslab earthquake also shows increased ground motions in the Cook Inlet region at all periods. Crustal Q estimates from Lg waves show less attenuation in south‐central Alaska at longer periods. In the larger south‐central Alaska region crustal Q(f)=336f0.34 compared to Q(f)=217f0.84 for all of Alaska with most of the decrease in attenuation at frequencies below 2 Hz.
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Dilek, Yildirim, and Yujiro Ogawa. "Subduction zone processes and crustal growth mechanisms at Pacific Rim convergent margins: modern and ancient analogues." Geological Magazine 158, no. 1 (December 11, 2020): 1–12. http://dx.doi.org/10.1017/s0016756820001326.
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AbstractContinents grow mainly through magmatism, relamination, accretionary prism development, sediment underplating, tectonic accretion of seamounts, oceanic plateaus and oceanic lithosphere, and collisions of island arcs at convergent margins. The modern Pacific–Rim subduction zone environments present a natural laboratory to examine the nature of these processes. The papers in this special issue focus on the: (1) modern and ancient accretionary margins of Japan; (2) arc–continent collision zone in the Taiwan orogenic belt; (3) accreting versus non-accreting convergent margins of the Americas; and (4) several examples of ancient convergent margins of East Asia. Subduction erosion and sediment underplating are important processes, affecting the melt evolution of arc magmas by giving them special crustal isotopic characteristics. Oblique arc–continent collisions cause strong deformation partitioning that results in orogen-parallel extension, crustal exhumation and wrench faulting in the hinterland, and thrust faulting–folding in the foreland. Trench-parallel widths of subducting slabs exert major control on slab geometries, the degree of coupling–decoupling between the lower and upper plates, and subduction velocity partitioning. An initially large width of the subducting Palaeo-Pacific Plate against East Asia caused flat subduction and resistance to slab rollback during the Triassic Period. These conditions resulted in shortening across SE China. Foundering and delamination of the flat slab during the Early Jurassic Epoch led to slab segmentation and reduced slab widths, followed by slab steepening and rollback. This pull-away tectonics induced lithospheric extension and magmatism in SE China during Late Jurassic – Cretaceous time. Melting of subducted carbonaceous sediments commonly produces networks of silicate veins in CLM that may subsequently undergo partial melting, producing ultrapotassic magmas.
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Magni, V., J. van Hunen, F. Funiciello, and C. Faccenna. "Numerical models of trench migration in continental collision zones." Solid Earth Discussions 4, no. 1 (March 1, 2012): 429–58. http://dx.doi.org/10.5194/sed-4-429-2012.
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Abstract. Continental collision is an intrinsic feature of plate tectonics. The closure of an oceanic basin leads to the onset of subduction of buoyant continental material, which slows down and eventually stops the subduction process. We perform a parametric study of the geometrical and rheological influence on subduction dynamics during the subduction of continental lithosphere. In 2-D numerical models of a free subduction system with temperature and stress-dependent rheology, the trench and the overriding plate move self-consistently as a function of the dynamics of the system (i.e. no external forces are imposed). This setup enables to study how continental subduction influences the trench migration. We found that in all models the trench starts to advance once the continent enters the subduction zone and continues to migrate until few million years after the ultimate slab detachment. Our results support the idea that the trench advancing is favoured and, in part provided by, the intrinsic force balance of continental collision. We suggest that the trench advance is first induced by the locking of the subduction zone and the subsequent steepening of the slab, and next by the sinking of the deepest oceanic part of the slab, during stretching and break-off of the slab. The amount of trench advancing ranges from 40 to 220 km and depends on the dip angle of the slab before the onset of collision.
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Kassaras, I., V. Kapetanidis, A. Karakonstantis, and P. Papadimitriou. "Deep structure of the Hellenic lithosphere from teleseismic Rayleigh-wave tomography." Geophysical Journal International 221, no. 1 (January 8, 2020): 205–30. http://dx.doi.org/10.1093/gji/ggz579.
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SUMMARY This research provides new constraints on the intermediate depth upper-mantle structure of the Hellenic lithosphere using a three-step Rayleigh-wave tomography. Broadband waveforms of about 1000 teleseismic events, recorded by ∼200 permanent broad-band stations between 2010 and 2018 were acquired and processed. Through a multichannel cross-correlation technique, the fundamental mode Rayleigh-wave phase-velocity dispersion curves in the period range 30–90 s were derived. The phase-velocities were inverted and a 3-D shear velocity model was obtained down to the depth of 140 km. The applied method has provided 3-D constraints on large-scale characteristics of the lithosphere and the upper mantle of the Hellenic region. Highlighted resolved features include the continental and oceanic subducting slabs in the region, the result of convergence between Adria and Africa plates with the Aegean. The boundary between the oceanic and continental subduction is suggested to exist along a trench-perpendicular line that connects NW Peloponnese with N. Euboea, bridging the Hellenic Trench with the North Aegean Trough. No clear evidence for trench-perpendicular vertical slab tearing was resolved along the western part of Hellenic Subduction Zone; however, subcrustal seismicity observed along the inferred continental–oceanic subduction boundary indicates that such an implication should not be excluded. The 3-D shear velocity model supports an N–S vertical slab tear beneath SW Anatolia that justifies deepening, increase of dip and change of dip direction of the Wadati-Benioff Zone. Low velocities found at depths <50 km beneath the island and the backarc, interrelated with recent/remnant volcanism in the Aegean and W. Anatolia, are explained by convection from a shallow asthenosphere.
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Patria, Adi, and Atin Nur Aulia. "STRUCTURAL AND EARTHQUAKE EVALUATIONS ALONG JAVA SUBDUCTION ZONE, INDONESIA." RISET Geologi dan Pertambangan 30, no. 1 (July 20, 2020): 65. http://dx.doi.org/10.14203/risetgeotam2020.v30.1072.
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Java Subduction is a zone of trench perpendicular convergence of Australian Plate and Southeast Asia in the south of Java. It is characterized by an almost E-W trending trench with an eastward increase of convergence velocity. Three major earthquakes with tsunamis have been caused by deformation along this subduction zone. Although many studies have undertaken to understand the nature of the subduction system, a clear relationship between structures and earthquake activities remains poorly explained. In this study, we used bathymetry, residual bathymetry, and published seismic reflection profiles to evaluate structural and morphological elements, then link the observations to earthquake activity along Java Subduction Zone. Based on seafloor morphology, characteristics of the accretionary wedge and forearc basin varies along the trench in response to the variation of seafloor morphology. Features such as seamounts and ridges which were observed in the oceanic basin may be subducted beneath accretionary wedge and disrupt the morphology of accretionary wedge, forearc basin, and trench. Earthquake activities are generally dominated by normal fault solutions in the trench, which is attributed to plate bending faults while thrust fault solution is observed in the forearc basin area. Thrust fault activities in accretionary wedge are decreased to the east, where there is no thrust fault solution observed in the eastern end of the subduction zone. Few strike-slip focal mechanisms are observed and mainly located within the subducting oceanic plate. Structures and subducting oceanic features may control the earthquake activity where deformation occurred at the edge of these features. The two largest thrust fault earthquakes in 1994 and 2006 are interpreted as a result of deformation along with plate interface on soft or unconsolidated sediment above the incoming plate. The largest normal fault earthquake with a magnitude 8.3 is possibly caused by a crustal scale-fault that breaks the entire oceanic crust.ABSTRAK - Evaluasi struktur dan gempa bumi di sepanjang zona subduksi Jawa, Indonesia. Subduksi Jawa adalah zona konvergensi yang tegak lurus palung antara Lempeng Australia dan Asia Tenggara di selatan Jawa. Hal ini ditandai dengan palung berarah hampir barat–timur dengan peningkatan kecepatan konvergensi ke arah timur. Tiga gempa bumi besar dengan tsunami disebabkan oleh deformasi di sepanjang zona subduksi ini. Meskipun banyak penelitian telah dilakukan untuk memahami sifat sistem subduksi, hubungan antara struktur dan kegiatan gempa bumi masih kurang jelas. Dalam studi ini, kami menggunakan batimetri, batimetri residual, dan profil refleksi seismik untuk mengevaluasi elemen struktur dan morfologi, kemudian menghubungkan pengamatan dengan aktivitas gempa bumi di sepanjang zona subduksi Jawa. Berdasarkan morfologi dasar laut, karakteristik prisma akresi dan cekungan busur muka bervariasi di sepanjang palung sebagai respon terhadap variasi morfologi dasar laut. Fitur seperti seamount dan punggungan yang diamati di cekungan samudera menunjam di bawah prisma akresi dan mengganggu morfologi prisma akresi, cekungan busur muka, dan palung. Aktivitas gempa bumi umumnya didominasi oleh patahan normal di palung, yang dikaitkan dengan patahan tekukan lempeng sedangkan patahan naik diamati di daerah cekungan busur muka. Aktivitas sesar naik di dalam prisma akresi berkurang ke arah timur, di mana tidak ada patahan naik yang teramati di ujung timur zona subduksi. Beberapa mekanisme patahan mendatar diamati dan terutama terletak di dalam lempeng samudera yang menunjam. Struktur dan fitur di kerak samudra yang menunjam dapat mengontrol aktivitas gempa bumi di mana deformasi terjadi di tepian fitur ini. Dua gempa bumi besar dengan sifat patahan naik pada tahun 1994 dan 2006 ditafsirkan sebagai hasil dari deformasi di sepanjang antarmuka lempeng pada sedimen lunak atau tidak terkonsolidasi di atas lempeng yang masuk. Gempa bumi besar dengan sifat sesar normal magnitude 8,3 mungkin disebabkan oleh patahan skala-kerak yang menghancurkan seluruh kerak samudera.
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Meighan, Hallie E., and Jay Pulliam. "Seismic anisotropy beneath the northeastern Caribbean: implications for the subducting North American lithosphere." Bulletin de la Société Géologique de France 184, no. 1-2 (January 1, 2013): 67–76. http://dx.doi.org/10.2113/gssgfbull.184.1-2.67.
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Abstract Active plate boundaries in the Caribbean form a complex tectonic environment that includes transform and subduction zones. The Caribbean-North American plate boundary is one such active margin, where subduction transitions from arc- to oblique-type off the northeast coast of Puerto Rico. Understanding mantle flow in this region will not only help determine the nature of tectonic activity and mantle dynamics that control these margins, but will also aid our understanding of the fate of subducting lithosphere. The existence of tears, windows, and gaps in subducting slabs has been proposed at various locations around the world but few have been confirmed. Since mantle flow and crustal deformation are believed to produce seismic anisotropy in the asthenosphere and lithosphere, searching for changes in, for example, SKS splitting parameters can help identify locations at which subducting slabs have been disrupted. Several lines of evidence support the notion of a slab tear within the subducting North American plate at this transition zone, including the counter-clockwise rotation of the Puerto Rico microplate over the past ~10 Ma, clusters of small seismic events, and trench collapse initiating ~3.3 m.y. Here we present results from a detailed investigation of seismic anisotropy from 28 stations across six networks in the Northeast Caribbean that support the hypothesis of a significant slab gap in the vicinity of the U.S. and British Virgin islands. A regional synthesis of our results reveals fast shear wave polarizations that are generally oriented parallel to the plate boundary with intermediate to high SH-SV delay times. For example, polarization directions are oriented roughly NE-SW along the bulk of the Lesser Antilles, E-W along the Puerto Rico trench and the northern Lesser Antilles, and NW-SE beneath Hispaniola. Beneath the U.S. and British Virgin Islands, however, the fast polarization direction differs markedly from the regional pattern, becoming almost perpendicular to the plate boundary. Stations on Anegada, British Virgin islands and St. Croix, U.S. Virgin islands show a fast polarization direction that is oriented nearly NNE-SSW and smaller delay times than surrounding stations. These results suggest that mantle flow is redirected NE-SW at this location through a gap in the subducted lithosphere of the North American plate.
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Yoshida, Masaki. "Trench dynamics: Effects of dynamically migrating trench on subducting slab morphology and characteristics of subduction zones systems." Physics of the Earth and Planetary Interiors 268 (July 2017): 35–53. http://dx.doi.org/10.1016/j.pepi.2017.05.004.
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Walker, James A., and Esteban Gazel. "Igneous Rock Associations 13. Focusing on the Central American Subduction Zone." Geoscience Canada 41, no. 1 (March 4, 2014): 57. http://dx.doi.org/10.12789/geocanj.2014.41.036.
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Central America has recently been an important focus area for investigations into the complex processes occurring in subduction zones. Here we review some of the new findings concerning subduction input, magma production and evolution, and resultant volcanic output. In the Nicaraguan portion of the subduction zone, subduction input is unusually wet, likely caused by extensive serpentinization of the mantle portion of the incoming plate associated with bending-related faulting seaward of the Middle America trench. The atypical influx of water into the Nicaraguan section of the subduction zone ultimately leads to a regional maximum in the degree of mantle melting. In central Costa Rica, subduction input is also unusual in that it includes oceanic crust flavored by the Galapagos plume. Both of these exotic subduction inputs are recognizable in the compositions of magmas erupted along the volcanic front. In addition, Nicaraguan magmas bear a strong chemical imprint from subducting hemipelagic sediments. The high-field-strength-element depletions of magmas from El Salvador through Costa Rica are related to local variations in the depth to the subducting Cocos plate, and, therefore, to segmentation of the volcanic front. Minor phases, probably amphibole or rutile, control these variable depletions. Silicic magmas erupted along the volcanic front exhibit the same along-arc geochemical variations as their mafic brethren. This and their mantle-like radiogenic isotopic compositions suggest the production of juvenile continental crust all along the Central American subduction zone. Punctuated times of enhanced magmatic input from the mantle may aid in crustal development.SOMMAIREL’Amérique centrale a récemment été le lieu de recherches sur les processus complexes se produisant dans les zones de subduction. Ici nous passons en revue certaines découvertes sur nature des intrants de subduction, la production et l’évolution des magmas, ainsi que les extrants volcaniques résultants. Dans le segment nicaraguayen de la zone de subduction, les intrants de subduction sont exceptionnellement humides, probablement à cause de la serpentinisation généralisée de la portion mantélique de la plaque en subduction, fissurée par flexure dans partie marine de la fosse océanique de l’Amérique centrale. L'afflux atypique en eau dans le segment nicaraguayen de la zone de subduction induit ultimement un maximum régional de la proportion de fusion du manteau. Dans la portion centrale du Costa Rica l’intrant de subduction est lui aussi atypique en ce qu’il comprend une croûte océanique teintée par le panache des Galápagos. Ces deux intrants de subduction atypiques sont répercutés dans la composition des magmas éjectés le long du front volcanique. En outre, les magmas nicaraguayens affichent une forte empreinte chimique héritée des sédiments hémipélagiques en subduction. Les appauvrissements en éléments à fortes liaisons atomiques des magmas, du El Salvador jusqu’au Costa Rica, sont liés à des variations localisées de la profondeur de la plaque en subduction de Cocos, et donc, à la segmentation du front volcanique. Des phases mineures, probablement amphibole et rutile, déterminent ces appauvrissements variables. Les magmas siliceux éjectés le long du même front volcanique montrent les mêmes variations géochimiques le long de l’arc que leur contrepartie mafique. De plus, les compositions radiogéniques de leurs contreparties mantéliques évoquent la production d’une croûte continentale juvénile le long de la zone de subduction de l’Amérique centrale. Des épisodes d’accroissements ponctuels des intrants magmatiques du manteau peuvent contribuer au développement d’une croûte.
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Jaxybulatov, K., I. Koulakov, and N. L. Dobretsov. "Segmentation of the Izu-Bonin and Mariana plates based on the analysis of the Benioff seismicity distribution and regional tomography results." Solid Earth Discussions 4, no. 2 (July 5, 2012): 823–50. http://dx.doi.org/10.5194/sed-4-823-2012.
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Abstract. We present a new model of P- and S-velocity anomalies in the mantle down to 1300 km depth beneath the Izu-Bonin and Mariana (IBM) arcs. This model is derived based on tomographic inversion of global travel time data from the revised ISC catalogue. The results of inversion are thoroughly verified using a series of different tests. The obtained model is generally consistent with previous studies of different authors. We also present the distribution of relocated deep events projected to the vertical surface along the IBM arc. Unexpectedly, the seismicity form elongated vertical clusters instead of horizontal zones indicating phase transitions in the slab. We propose that these vertical seismicity zones mark zones of intense deformation and boundaries between semi-autonomous segments of the subducting plate. The P- and S-seismic tomography models consistently display the slab as prominent high-velocity anomalies coinciding with the distribution of deep seismicity. Based on joint consideration of the tomography results and the seismicity distribution we propose a scenario of the subduction evolution in the IBM zone during the recent time. We can distinguish at least four segments which subduct differently. The northernmost segment of the Izu-Bonin arc has the gentlest angle of dipping which is explained by backward displacement of the trench. In the second segment, the trench stayed at the same location, and we observe the accumulation of the slab material in the transition zone and its further descending to the lower mantle. In third segment, the trench is moving forward that causes steepening of the slab. Finally, for the Mariana segment, despite the backward displacement of the arc, the subducting slab is nearly vertical. We propose that it might be due to the high density of the slab which is responsible for turning any inclined subduction to the vertical position. Between the Izu-Bonin and Mariana arcs we clearly observe a gap which is traced down to about 400 km depth.
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Shi, Huiyan, Tonglin Li, Rui Sun, Gongbo Zhang, Rongzhe Zhang, and Xinze Kang. "Insights from the P Wave Travel Time Tomography in the Upper Mantle Beneath the Central Philippines." Remote Sensing 13, no. 13 (June 23, 2021): 2449. http://dx.doi.org/10.3390/rs13132449.
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In this paper, we present a high resolution 3-D tomographic model of the upper mantle obtained from a large number of teleseismic travel time data from the ISC in the central Philippines. There are 2921 teleseismic events and 32,224 useful relative travel time residuals picked to compute the velocity structure in the upper mantle, which was recorded by 87 receivers and satisfied the requirements of teleseismic tomography. Crustal correction was conducted to these data before inversion. The fast-marching method (FMM) and a subspace method were adopted in the forward step and inversion step, respectively. The present tomographic model clearly images steeply subducting high velocity anomalies along the Manila trench in the South China Sea (SCS), which reveals a gradual changing of the subduction angle and a gradual shallowing of the subduction depth from the north to the south. It is speculated that the change in its subduction depth and angle indicates the cessation of the SCS spreading from the north to the south, which also implies that the northern part of the SCS opened earlier than the southern part. Subduction of the Philippine Sea (PS) plate is exhibited between 14° N and 9° N, with its subduction direction changing from westward to eastward near 13° N. In the range of 11° N–9° N, the subduction of the Sulu Sea (SS) lies on the west side of PS plate. It is notable that obvious high velocity anomalies are imaged in the mantle transition zone (MTZ) between 14° N and 9° N, which are identified as the proto-SCS (PSCS) slabs and paleo-Pacific (PP) plate. It extends the location of the paleo-suture of PSCS-PP eastward from Borneo to the Philippines, which should be considered in studying the mechanism of the SCS and the tectonic evolution in SE Asia.
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Nettesheim, Matthias, Todd A. Ehlers, David M. Whipp, and Alexander Koptev. "The influence of upper-plate advance and erosion on overriding plate deformation in orogen syntaxes." Solid Earth 9, no. 6 (November 5, 2018): 1207–24. http://dx.doi.org/10.5194/se-9-1207-2018.
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Abstract. Focused, rapid exhumation of rocks is observed at some orogen syntaxes, but the driving mechanisms remain poorly understood and contested. In this study, we use a fully coupled thermomechanical numerical model to investigate the effect of upper-plate advance and different erosion scenarios on overriding plate deformation. The subducting slab in the model is curved in 3-D, analogous to the indenter geometry observed in seismic studies. We find that the amount of upper-plate advance toward the trench dramatically changes the orientation of major shear zones in the upper plate and the location of rock uplift. Shear along the subduction interface facilitates the formation of a basal detachment situated above the indenter, causing localized rock uplift there. We conclude that the change in orientation and dip angle set by the indenter geometry creates a region of localized uplift as long as subduction of the down-going plate is active. Switching from flat (total) erosion to more realistic fluvial erosion using a landscape evolution model leads to variations in rock uplift at the scale of large catchments. In this case, deepest exhumation again occurs above the indenter apex, but tectonic uplift is modulated on even smaller scales by lithostatic pressure from the overburden of the growing orogen. Highest rock uplift can occur when a strong tectonic uplift field spatially coincides with large erosion potential. This implies that both the geometry of the subducting plate and the geomorphic and climatic conditions are important for the creation of focused, rapid exhumation.