Academic literature on the topic 'Andaman-Nicobar Islands - Earthquake'

The damage sustained by buildings and structures in the Andaman and Nicobar islands area was due to earthquake shaking and/or giant tsunami waves. While damage on Little Andaman Island and all the Nicobar Islands was predominantly tsunami-related, damage on islands north of Little Andaman Island was primarily due to earthquake shaking even though tsunami waves and high tides were also a concern. In general, the building stock consists of a large number of traditional and non-engineered structures. Many traditional structures are made of wood, and they performed well under the intensity-VII earthquake shaking sustained along the islands. However, a number of new reinforced concrete (RC) structures suffered severe damage or even collapse. Also, extensive damage occurred to the coastal and harbor structures in the Andaman and Nicobar islands.

Boats and ships are the major modes of transportation among the Andaman and Nicobar group of islands. The Andaman Trunk Road also forms an important part of the transportation system in the Andaman Islands north of Port Blair. The harbor structures in the islands were the most affected during the ground shaking; the result heavily disrupted the lives of the island residents. These transportation systems are expected to be in working condition after a major disaster, to facilitate the search and rescue operations and the relief work in the affected areas. A reconnaissance team surveyed the damage that the 2004 earthquake and tsunami caused to the transportation structures in the islands. Damage was observed in all transportation systems, including harbors, highways, airports, and hangars.

Plate tectonics after the 26 December 2004 Great Sumatra earthquake resulted in major topological changes in the Andaman and Nicobar islands. Aerial and land reconnaissance surveys of those islands after the earthquake provide evidence of spectacular plate tectonics that took place during the earthquake. Initial submergence of the built environment and the subsequent inundation upon arrival of the tsunami wave, as well as emergence of the new beaches along the islands—particularly on the western rims of the islands and in the northern islands—are the major signatures of this Mw=9.3 event.

The potential areas of upcoming earthquakes were investigated along the Northern segment of the Sumatra–Andaman Subduction Zone according to the b-value of the frequency-magnitude distribution. After enhancing the completeness of the earthquake catalogue, two datasets, those recorded during (i) 1980–1994 and (ii) 1980–2003, were tested in order to verify the effective correlation between precursory b-values and the location of subsequent earthquakes. The results confirmed that areas with low b-values agreed well with the locations of the subsequent earthquakes in that region. Accordingly, the present-day dataset from 1980–2010 was carefully evaluated to determine the b-values across the region. Within this spatial investigation, three areas of low b-values and so potential hazards were found. These consisted of the (i) West coast of Myanmar, and (ii) North and (iii) South of the Nicobar Islands. From 2010–2012, a major earthquake with magnitude 7.5 mb was recorded as being generated in the region South of the Nicobar Islands. Thus, attention should be paid to the remaining two until now quiescent areas, and mitigation plans should be raised for both seismic and tsunami hazards.

The rescue and relief work undertaken in the Andaman and Nicobar islands and in mainland India after the 26 December 2004 Indian Ocean tsunami was massive. A number of new initiatives undertaken by the government and nongovernmental agencies were innovative and successful. Also, since the tsunami was not a typical disaster for India, it raised a number of new concerns related to reconstruction along the coast.

AbstractObjective:The objective of this study was to compare the psychiatric morbidity between the displaced and non-displaced populations of the Andaman and Nicobar Islands during the first three months following the 2004 earthquake and tsunami.Methods:The study was conducted at the 74 relief camps in the Andaman and Nicobar Islands. Port Blair had 12 camps, which provided shelter to 4,684 displaced survivors. There were 62 camps on Car-Nicobar Island, which provided shelter to approximately 8,100 survivors who continued to stay in their habitat (non-displaced population). The study sample included all of the survivors who sought mental health assistance inside the camp. A psychiatrist diagnosed the patients using the ICD-10 criteria.Results:Psychiatric morbidity was 5.2% in the displaced population and 2.8% in the non-displaced population. The overall psychiatric morbidity was 3.7%. The displaced survivors had significantly higher psychiatric morbidity than did the non-displaced population.The disorders included panic disorder, anxiety disorders not otherwise specified, and somatic complaints. The existence of an adjustment disorder was significantly higher in the non-displaced survivors. Depression and post-traumatic stress disorder (PTSD) were distributed equally in both groups.Conclusions:Psychiatric morbidity was found to be highest in the displaced population. However, the incidence of depression and PTSD were distributed equally in both groups. Involvement of community leaders and survivors in shared decision-making processes and culturally acceptable interventions improved the community participation. Cohesive community, family systems, social support, altruistic behavior of the community leaders, and religious faith and spirituality were factors that helped survivors cope during the early phase of the disaster.

Abstract. Throughout the world, the tsunami generation potential of some large under-sea earthquakes significantly contributes to regional seismic hazard, which gives rise to significant risk in the near-shore provinces where human settlements are in sizeable population, often referred to as coastal seismic risk. In this context, we show from the pertinent GPS data that the transient stresses generated by the viscoelastic relaxation process taking place in the mantle is capable of rupturing major faults by stress transfer from the mantle through the lower crust including triggering additional rupture on the other major faults. We also infer that postseismic relaxation at relatively large depths can push some of the fault segments to reactivation causing failure sequences. As an illustration to these effects, we consider in detail the earthquake sequence comprising six events, starting from the main event of Mw = 7.5, on 10 August 2009 and tapering off to a small earthquake of Mw = 4.5 on 2 February 2011 over a period of eighteen months in the intensely seismic Andaman Islands between India and Myanmar. The persisting transient stresses, spatio-temporal seismic pattern, modeled Coulomb stress changes, and the southward migration of earthquake activity has increased the probability of moderate earthquakes recurring in the northern Andaman region, particularly closer to or somewhat south of Diglipur.

Trinket cattle is a highly endangered feral cattle of Trinket Island, linked with the colonial history of Andaman and Nicobar Islands. Danish people during their colonial time introduced these cattle in Trinket Island. Great Sumatra earthquake and Indian Ocean Tsunami in 2004 has forced these cattle to become feral in nature. Due to negligence, the cattle is at the brink of extinction and only around 150 of descendants of the cattle are reported. In the present study, the haematology, serum biochemistry and mineral profiles of Trinket cattle were evaluated. Study indicated that all the values were under the normal physiological range. These findings of this study may serve as reference values in which alterations due to metabolic, nutrient deficiency, physiological and health status can be compared for diagnostic and therapeutic purpose.

Abstract. The primary background for the present study was a project to assist the authorities in Thailand with development of plans for how to deal with the future tsunami risk in both short and long term perspectives, in the wake of the devastating 26 December 2004 Sumatra-Andaman earthquake and tsunami. The study is focussed on defining and analyzing a number of possible future earthquake scenarios (magnitudes 8.5, 8.0 and 7.5) with associated return periods, each one accompanied by specific tsunami modelling. Along the most affected part of the western coast of Thailand, the 2004 tsunami wave caused a maximum water level ranging from 5 to 15 m above mean sea level. These levels and their spatial distributions have been confirmed by detailed numerical simulations. The applied earthquake source is developed based on available seismological and geodetic inversions, and the simulation using the source as initial condition agree well with sea level records and run-up observations. A conclusion from the study is that another megathrust earthquake generating a tsunami affecting the coastline of western Thailand is not likely to occur again for several hundred years. This is in part based on the assumption that the Southern Andaman Microplate Boundary near the Simeulue Islands constitutes a geologic barrier that will prohibit significant rupture across it, and in part on the decreasing subduction rates north of the Banda Ache region. It is also concluded that the largest credible earthquake to be prepared for along the part of the Sunda-Andaman arc that could affect Thailand, is within the next 50–100 years an earthquake of magnitude 8.5, which is expected to occur with more spatial and temporal irregularity than the megathrust events. Numerical simulations have shown such earthquakes to cause tsunamis with maximum water levels up to 1.5–2.0 m along the western coast of Thailand, possibly 2.5–3.0 m on a high tide. However, in a longer time perspective (say more than 50–100 years) the potentials for earthquakes of similar magnitude and consequences as the 2004 event will become gradually larger and eventually posing an unacceptable societal risk. These conclusions apply only to Thailand, since the effects of an M 8.5 earthquake in the same region could be worse for north-western Sumatra, the Andaman and Nicobar Islands, maybe even for Sri Lanka and parts of the Indian coastline. Moreover, further south along the Sunda arc the potentials for large ruptures are now much higher than for the region that ruptured on 26 December 2004.

Tsunami hazards were greatly underestimated along the coasts of countries bordering the northeastern Indian Ocean until the occurrence of the 26 December 2004, Mw 9.2 earthquake and its ensuing tsunami. Sourced off the coast of northern Sumatra, on the plate boundary between the Indo-Australian and Eurasian plates, the rupture of the 2004 earthquake propagated ~1300 km northward. The magnitude of this earthquake and the reach of its tsunami exceeded all known precedents, based on instrumental and historic records. The coseismic deformational and post-tsunami depositional features facilitated opportunities to conduct tsunami geology studies along the coasts of countries bordering the Indian Ocean. Several questions are being posed, the answers of which have implications for tsunami hazard assessment. How did this plate boundary behave prior to and after the great earthquake? Was the 2004 earthquake the first of its kind on the Sumatra-Andaman plate boundary? If it had a predecessor, when did it occur and was it a true predecessor in terms of its rupture dimensions and tsunamigenic potential? What types of depositional evidence are preserved and how can we use them to develop the history of past tsunamigenic earthquakes? Researchers are exploring the affected regions and using the imprints left by the 2004 event, to address these questions. There are two components to this study: one, a seismotectonic analysis of the region from the perspective of plate driving forces and their relative roles in the interseismic and post-seismic phases. This study uses global data catalogs like the NEIC PDE (National Earthquake Information Centre Preliminary Determination of Epicenters) and the Global Centroid Moment Tensor (CMT) solutions for earthquake source parameters to understand the along-strike variations in seismicity patterns before and after the 2004 earthquake. The 2004 experience was unprecedented in South Asia. Unaffected by tsunami hazards in the past, tsunami geology is a nascent field for most South Asian researchers. Very little background field data is available on the deformational features of great earthquakes along this plate boundary and the depositional characteristics of extreme coastal surges, such as tsunamis and storms. Where do we begin our search for evidence of past tsunamigenic earthquakes? How best can we use the 2004 tsunami and its deposits as a proxy? What problems are encountered in the interpretations? This thesis addresses these questions in part and presents observations from the Andaman Islands (the ~400 km, northern segment of the Sumatra-Andaman subduction zone) and the southeast coast of India, towards developing a reliable database of tsunami geology for 2004-type events. The premise is that regions affected by the 2004 earthquake are more likely to conserve signatures from older events. Based on the stratigraphic context of the proxy and quality of age estimates, this work presents evidence for past earthquake related deformation and tsunami deposition. In this work we use deformational and depositional features from the Andaman Islands, falling within the 2004 rupture zone and from one location on the Tamil Nadu coast of India (Kaveripattinam). From a perceptive understanding of the features related to tectonic deformation of the Sumatra-Andaman subduction zone, we have selected the Andaman segment that demonstrates explicit evidence for deformation and tsunami deposition through geomorphological and stratigraphic features, which are key to our exploration. A gist of each chapter is given below. The introduction (chapter 1) presents the background, motivation and scope of this work and the organization of this thesis, also summarizing the contents of each chapter. Chapter 2 provides a review of literature on subduction zone earthquakes and updates on tsunami geology, to place this study in the global context. The next two chapters discuss the seismotectonics of the Sumatra-Andaman plate boundary, the important earthquakes and their source processes. In chapter 3 we discuss the Andaman segment (from 10–15° N), characterized by relatively lower level seismicity, but distinctive, as it falls within the northern limit of the 2004 rupture. The deformational and depositional features here are better exposed due to availability of land straddling the hinge line separating the areas of 2004 uplift and subsidence. Here, the pre-2004 earthquakes used to occur along a gently dipping subducting slab, up to a depth of about 40 km. Post-2004, the earthquakes moved up-dip, extending also to the outer-rise and outer-ridge regions, expressing post-earthquake relaxation [Andrade and Rajendran, 2011]. The southern Nicobar segment (5–10° N) differs from the Andaman segment in its style of deformation and seismic productivity. The decreasing obliquity of convergence, the likely influence of a subducting ocean ridge on the subducting plate and the character of the subducting oceanic plate make this segment distinctly different. In chapter 4 we present an analysis of its seismotectonic environment based on the well-constrained focal mechanisms of historic and recent earthquakes. We report that left-lateral strike-slip faulting on near N-S oriented faults control the deformation and the style of faulting is consistent to ~80 km within the subducting slab [Rajendran, K. et al., 2011]. The 11 April 2012 sequence of earthquakes on the subducting oceanic plate, between the Sumatra Trench and the Ninety East Ridge are the more recent among the oceanic intraplate earthquakes that demonstrate the reactivation of N-S oriented fossil fractures. The limited availability of land and the 2004 coseismic deformation dominated by subsidence, followed by prolonged waterlogging makes exploration difficult in the Nicobar segment. Thus, we focus on the Andaman Islands for deformational and depositional evidence, using observations that can be corroborated through multiple proxies and depositional environments that are not prone to other coastal surges, such as cyclones and storms. The criteria for selection of sites, evaluation of deposits and determination of limiting ages are discussed in chapters 5 through 9. In chapter 5 we discuss different types of coastal environments and their response to high-energy sea surges. We also give a brief review of the comparative analyses of storm and tsunami deposits, a highly debated issue and then discuss important characteristics of these two deposits, using examples from the 2004 tsunami and the 2011 Thane cyclone that affected parts of the Tamil Nadu coast. An important component of tsunami geology is the ability to identify and select datable material from tsunami deposits and chose an appropriate method for dating (chapter 6). The types of material used vary from peat layers, peat-rich soil, gastropod shells, wood, charcoal, organic remains such as bones, coral fragments, pottery sherds and buried soil. Techniques such as AMS Carbon-14 and Thermoluminescence are commonly used with appropriate calibrations and corrections. In addition to the dates generated in this study (based on wood and shell dates) we use some previous dates from the entire stretch of the rupture within the Indian Territory and assign a relative grading to these ages, based on the quality criterion evolved in this study. We believe that this is the first attempt to segregate age data obtained from coastal deposits, and assign them a specific quality grading based on their environment of deposition and the type of material dated. Chapter 7 presents results of our investigations in the Andaman Islands, which cover ~30% of the rupture area. A coseismically subsided mangrove from Rangachanga (Port Blair, east coast of South Andaman) led us to a former subsidence during AD 770–1040, which we believe is the most convincing evidence for a previous tectonic event. Data based on inland deposits of coral and organic debris yielded a younger age in the range of AD 1480–1660. Both these dates fall in the age brackets reported from other regions of this plate boundary (mainly Sumatra) as well as distant shores of Sri Lanka, Thailand and mainland India. To understand the nature of distant deposits, we present observations from Kaveripattinam, an ancient port city on the east coast of India, where a high-energy sea surge deposit, found 1 km inland is attributed to a paleotsunami. The inland location of this archeological site at an elevation of 2 m and characteristics of the deposit that help discriminate it from typical storm deposition provide clinching evidence in favor of a 1000-year old regional tsunami (chapter 8). In chapter 9 we discuss the results of our study. We evaluate the nature of deformation/deposition and the calibrated age data in the context of their environments. Ages based on the organic material associated with coral debris (at Hut Bay and Interview Island) and the remains of mangrove roots, 1 m below the present ground level (at Port Blair) are considered as reliable estimates, due to their sheltered inland location and the in situ root horizon used for dating. Age data from Kaveripattinam is also considered reliable, based on its inland location beyond the reach of storm surges, sediment characteristics typical of tsunami deposition and ages based on multiple methods and samples. The age data based on the sites presented in this thesis are more conclusive about the 800 to 1100 AD and 1250 to 1450 AD tsunamis, and the former is represented from regions closer to the 2004 source as well as distant shores reached by its tsunami. Chapter 10 presents our conclusions and the scope for future studies. We present this as the first study of its kind in the northeastern Bay of Bengal, wherein the coseismic vertical coastal deformation features along an interplate subduction boundary and a variety of tsunami deposits are used to categorize depositional environments and ages of paleoearthquakes and tsunamis. To our knowledge, this is the first study of its kind where the effects of a recent tsunami have been used to evaluate paleodeposits based on their respective environments of occurrence. Our results have implications for tsunami geology studies in coastal regions prone to tsunami hazard.

Andaman and Nicobar Islands (ANI’s) being situated in the Tropical zone is the cradle of multi-disasters viz., cyclones, floods, droughts, land degradation, runoff, soil erosion, shallow landslides, epidemics, earthquakes, volcanism, tsunami and storm surges. Mangroves are one of the first visible reciprocators above land and sea surface to cyclonic storms, storm surges, and tsunamis among the coastal wetlands. The Indian Ocean 2004 tsunami was denoted as one of the most catastrophic ever recorded in humankind’s recent history. A mega-earthquake of Magnitude (9.3) near Indonesia ruptured the Andaman-Sunda plate triggered this tsunami. Physical fury, subsidence, upliftment, and prolonged water logging resulted in the massive loss of mangrove vegetation. A decade and half years after the 2004 tsunami, a study was initiated to assess the secondary ecological succession of mangrove in Tsunami Created Wetlands (TCWs) of south Andaman using Landsat satellite data products. Since natural ecological succession is a rather slow process and demands isotope techniques to establish a sequence of events succession. However, secondary ecological succession occurs in a short frame of time after any catastrophic event like a tsunami exemplifying nature’s resilience. Band-5 (before tsunami, 2003) and Band-6 (after tsunami, 2018) of Landsat 7 and Landsat-8 satellite respectively were harnessed to delineate mangrove patches and TCWs in the focus area using ArcMap 10.5, Geographic Information Systems (GIS) software. From the study, it was understood that Fimbrisstylis littoralis is the pioneering key-stone plant followed by Acrostichum aureum and Acanthus ilicifolius facilitating Avicennia spp/Rhizopara spp for ecological succession in the TCWs.

The tectonic framework of the Indian Plate started to evolve since the break-up of Gondwanaland in the Late Triassic. It evolved mainly during the time between its separation from the African plate in the Early-Cretaceous and its collision with the Eurasian plate on the north in Late-Middle Eocene and with the Burmese plate in the northeast in Late-Oligocene. Present active tectonic zones, responsible for earthquake generation, were created by the collision pattern and subsequent plate motion. Continued subduction and plate motion due to ridge push and slab pull are responsible for the activation of primordial faults in the inherent structural fabric of the craton depending on the related stress field. Major tectonic zones of the Indian continental plate are related to the collision fronts and the reactivated intra-cratonic faults along the resurgent paleo-sutures between the proto-cratons. Major Tectonic Zones (TZ) are Himalayan TZ, Assam-Arakan TZ, Baluchistan- Karakoram TZ, Andaman-Nicobar TZ, and Stable Continental Region (SCR) earthquake zone. The structure of the continental margins developed during the break-up of Gondwana continental fragments. Western margin evolved during the sequential separation of Africa, Madagascar, and Seychelles since the Late-Triassic to Late Cretaceous time. The Eastern margin structure evolved during the separation of Antarctica in Mid Cretaceous. The orogenic belt circumscribing the northern margin of Indian plate is highly tectonised as the subduction of the plate continues due to northerly push from the Carlsberg Ridge in the SW and slab-pull towards northeast and east along the orogenic and island arc fronts in the NE. This stress pattern induced an anticlockwise rotatory plate motion. The back thrust from the collision front in the direction opposite to the ridge push put the plate under an overall compressive stress. This stress pattern and the plate motion are responsible for the reactivation of the major intra-cratonic faults. While the tectonised orogenic belts are the zones for earthquake nucleation, the reactivated faults are also the strained mega shear zones across the plate for earthquake generation in SCR. These faults trending WNW-ESE are apparently the transform faults that extend across the continent from Carlsberg ridge in the west to the collision zones in the northeast. As such, they are described here as the ‘trans-continental transform faults’. Three such major fault zones from north to south are (i) North Kathiawar fault - Great Boundary fault (along the Aravalli belt) zone, (ii) South Saurashtra fault (extension of Narmada fault) – SONATA-Dauki-Naga fault zone, and (iii) Tellichery-Cauvery-Eastern Ghat-T3-Hail Hakalula-Naga thrust zone. All these trans-continental faults, which are mega-shear zones, are traceable from western offshore to the northeastern orogenic belts along mega tectonic lineaments across the continent. The neotectonic movements along these faults, their relative motion, and displacement are the architect of the present geomorphic pattern and shape of the Indian craton. The overall compressive stress is responsible for strain build-up within these fault zones and consequent earthquake nucleation. The mid-continental Sonata-Dauki shear zone follows the Central Indian Suture Zone between Bundelkhand Proto Continent (BPC) and Deccan Proto Continent (DPC). With the reactivation of this shear zone, the two proto-cratonic blocks are subjected to relative movement as the plate rotates anticlockwise. The kinematics of these movements and their implications are discussed here with a special reference to the recent 2001 Bhuj earthquake.