Letteratura scientifica selezionata sul tema "LANDSLIDE MICROZONATION"

Abstract. The probable mitigation and management issues of seismic hazard necessitate seismic microzonation for hazard and risk assessment at the local level. Such studies are preceded with those at a regional level. A comprehensive framework, therefore, encompasses several phases from information compilations and data recording to analyses and interpretations. The state-of-the-art methodologies involve multi-disciplinary approaches namely geological, seismological, and geotechnical methods delivering multiple perspectives on the prevailing hazard in terms of geology and geomorphology, strong ground motion, site amplification, site classifications, soil liquefaction potential, landslide susceptibility, and predominant frequency. The composite hazard is assessed accounting for all the potential hazard attributing features with relative rankings in a logic tree, fuzzy set or hierarchical concept.

The Ulu Manna area is classified as an area with high landslide potential because of its location and geological structure, which is hilly. The risk of landslides in the Ulu Manna area due to earthquakes in weak areas can be studied using ground shear strain (GSS). This study aimed to provide information on the potential of landslides in the Ulu Manna area, South Bengkulu Regency Indonesia. The data was collected using the Horizontal-to-Vertical Spectral Ratio (HVSR) method. The study area is 195.8 km2 and consists of 32 data collection points. The data processing was performed using WinMASW 5.2 HVSR and ArcGIS Desktop 10.8.2 software to obtain dominant frequency values, amplification values, subsurface soil vulnerability index values, maximum soil acceleration values, and soil shear strain values. The soil shear strain values obtained are on the order of 10-4 to 10-3, meaning that the dynamic characteristics of the soil in the study area are elastic-plastic. This plastic-elastic nature characterizes the area as an area with high landslide potential

The PARSIFAL (Probabilistic Approach to pRovide Scenarios of earthquake Induced slope FAiLures) method was applied to the survey of post-earthquake landslides in central Italy for seismic microzonation purposes. In order to optimize time and resources, while also reducing errors, the paper-based method of survey data sheets was translated into digital formats using such instruments as Tablet PCs, GPS and open source software (QGIS). To the base mapping consisting of Technical Regional Map (Carta Tecnica Regionale—CTRs) at the scale of 1:10,000, layers were added with such sensitive information as the Inventory of Landslide Phenomena in Italy (Inventario dei Fenomeni Franosi in Italia—IFFI), for example. A database was designed and implemented in the SQLite/SpatiaLite Relational DataBase Management System (RDBMS) to store data related to such elements as landslides, rock masses, discontinuities and covers (as provided by PARSIFAL). To facilitate capture of the datum on the ground, data entry forms were created with Qt Designer. In addition to this, the employment of some QGIS plug-ins, developed for digital surveying and enabling of quick annotations on the map and the import of images from external cameras, was found to be of considerable use.

Abstract. As concerns landslide prevention and mitigation policies at the urban scale, the ability of Geographical Information Systems (GIS) to combine multi-layered information with high precision enables technicians and researchers to devote efforts in managing multiple hazards, such as seismically induced instability in urbanized areas. As a matter of fact, many villages in the Italian Apennines, placed near high-energy seismic sources, are characterized by active sliding that are seasonally remobilized by rainfall. GIS tools can be useful whether accurate Digital Elevation Models (DEM) are available and detailed mechanical and hydraulic characterization of superficial deposits over significant portion of the urban territory is undertaken. Moreover, the classic methods for estimating the seismic-induced permanent displacements within natural slopes are drawn from the generalization of Newmark's method. Such method can be applied to planar sliding mechanism that can be considered still valid wherever shallow landslides are generated by an earthquake. The failure mechanism depends on the mechanical properties of the superficial deposits. In this paper, the town of Castelfranci (Campania, southern Italy) has been studied. This small town, hosting two thousand inhabitants, suffers from the seasonal reactivation of landslides in clayey soil deposits due to rainfall. Furthermore, the site is seismically classified by means of the peak ground acceleration (PGA) equal to 0.246 g with respect to a 475 yr return period. Several studies on the evolution of slopes have been undertaken at Castelfranci and maps have been drawn at the urban scale not taking into any account the seismic hazard. This paper shows possible seismically induced hazard scenarios within the Castelfranci municipal territory aimed at microzonation of level 2, by estimating the slope permanent displacements comparable to those caused by the strongest historical seismic event that hit this area: the 1980 Irpinia earthquake. To this aim, geotechnical characterization of local soils collected over the last 25 yr by local technicians have been used to predict possible permanent displacements by means of Newmark's sliding block approach. Two simplified relationships relating peak ground acceleration and Arias intensity to permanent displacements have been used and compared. Although similar results are drawn, the two analyses point out the most hazardous sectors of the Castelfranci urban area.

Abstract The Northridge, California, earthquake of 17 January 1994 (Mw = 6.7) caused widespread damage in the San Fernando valley and adjacent areas. In many places, the earthquake motion was amplified or strongly modified by the local ground response, but the most localized and extreme site effect occurred at Tarzana, a small hill of gentle topography at the northern edge of the Santa Monica mountains where strong amplification (horizontal peak acceleration of 1.82g) and other unusual site effects were recorded at a CDMG accelerograph. The anomalous site effect was confined to a small area 50 m in radius around the station, beyond which the ground shaking was down to its theoretically expected level. If strong ground motion can vary so much in such a small scale, microzonation of urban areas may be an impossible goal at worst or, at best, only reliable at those sites where ground response has previously been measured. Hence, to clearly understand the dynamic response of the ground at the Tarzana site has become an important problem in earthquake hazard assessment and microzonation. This article reports results on the characteristics of the seismic response of the Tarzana site based on the investigation of aftershock data recorded on a local array and recorded accelerograms. Preliminary results strongly suggest that the Tarzana hill is formed by an old landslide of the Modelo formation. Such a structure is consistent with the anomalous resonant behavior at C00, the observed resonant frequencies, and the complex body wave recordings observed throughout the local array. The results also suggest that the 1.82g peak acceleration at C00 could have been caused by a small (Mw = 1.3) earthquake, located some 60 m from the station, generated by a downslope sliding of the hill with a maximum displacement of 4 cm over a circular area of nearly 50 m in radius. The slide was triggered by the Northridge mainshock.

The Mw 7.2 Fiordland earthquake of August 21 2003 was the largest shallow earthquake to occur in New Zealand for 35 years. Because of its location in an unpopulated area, it caused only minor damage to buildings, roads and infrastructure. It triggered numerous landslides on steep slopes in the epicentral region, where intensities reached MM9. Deployments of portable seismographs, strong motion recorders and GPS receivers in the epicentral region immediately after the event have established that the earthquake involved thrusting at the shallow part of the subduction interface between the Australian and Pacific plates. Recently installed strong motion recorders of the GeoNet network have ensured that the earthquake is New Zealand's best recorded subduction interface event. Microzonation effects are clear in some of the records. Current peak ground acceleration attenuation relationships for New Zealand subduction interface earthquakes underprediet the ground motions recorded during the earthquake, as was the case for previous large events in Fiordland in 1993 and 1989. The four portable strong motion recorders installed in the epicentral region have provided excellent near-field data on the larger aftershocks, with recorded peak ground accelerations ranging up to 0.28g from a nearby ML 6.1 event.

The goal of the multi-year seismic microzonation mapping project for Greater Vancouver, British Columbia, Canada, is to produce seismic hazard maps inclusive of local site effects, in particular seismic hazard specific to one-dimensional site response and three-dimensional Georgia sedimentary basin amplification, as well as liquefaction and landslide hazard potential. We explore the variability in key seismic site characterization measures most often used for seismic microzonation mapping to evaluate the impact on mapping and communication of seismic microzonation of Greater Vancouver. This study focuses on the comparison of seismic microzonation maps of Greater Vancouver based on up to three seismic site term parameters and their associated classification schemes: 1) the time-averaged shear-wave velocity (Vs) of the upper 30 m (Vs30) and associated Canadian National Building Code (NBC) site class; 2) Vs30-based site classification proposed for the updated Eurocode 8; 3) site period (T0) determined from microtremor site amplification spectra; and 4) a hybrid site classification based on T0 and the average Vs and thickness of soil. 810 Vs30 and 2,200 T0 values are determined to evaluate sub-regional differences in these important seismic site parameters in Greater Vancouver. We find that the seismic microzonation of Greater Vancouver depends on the chosen seismic site parameter (Vs30, T0, or a combination of parameters) and that classification schemes with greater class divisions are beneficial to communicating the great variability in seismic site conditions in Greater Vancouver. We recommend that either one hybrid classification map or two classification maps of Vs30 and T0 together are required for effective communication of the seismic microzonation of Greater Vancouver.

Hilly regions are highly prone to natural disasters. Natural disasters like floods, forest fires, slope failures, erosion, and landslides are common phenomena in hilly terrains. Landslide is a disastrous phenomenon that is responsible for economic losses and loss of lives. Landslides are responsible for huge economic loss which makes them 3rd largest natural disaster after floods and earthquakes. The planners and engineers require information about the possibility of the occurrence of landslides in working regions. So, the landslide hazards must be planned carefully to avoid losses. Microzonation of landslides or slopes which are susceptible to failure is an important task for understanding and planning the mitigation measures for landslides. Microzonation of landslides is the identification of the potential occurrence of landslides in different areas. The microzonation maps of landslides represent the landslide susceptibility and distribution of previously occurred landslides. The main objective of the thesis is to implement and compare the mixed methods and quantitative techniques of landslide susceptibility mapping. Due to the high subjectivity of the opinion of the experts, the qualitative techniques give lesser accuracy as compared to the statistical method. So, it is also attempted to propose a hybrid technique for enhancing the accuracy of expert-based methods.In this thesis, causative factors of landslides are identified using historical landslide data. The causative factors of landslides considered in this study are slope gradient, slope aspect, relative relief, topographic wetness index (TWI), lithology, drainage density, proximity to the road, proximity to faults/lineament and land use of the study area. The causative factors of the landslides are divided into simpler sub-categories. For example, the slope is divided into sub-categories like 0º to 15º, 15º to 30º, etc. Slope, aspect, relative relief and TWI are extracted by processing the vi CARTOSAT DEM. The parameters that are not extracted from the digital elevation model (DEM) are converted into the digital format using the geographic information system (GIS). The impact of these causative factors on the occurrence of landslides is evaluated using an expert-based approach and mathematical approach. In this study, four models are implemented for the microzonation of landslides in the study area. A landslide inventory containing more than 1500 landslide events is prepared using previous literature, news reports, Geological Survey of India (GSI) practical sheets, google imagery and field survey. Analytic hierarchy process (AHP), frequency ratio (FR) and Shannon’s entropy models are used for landslide susceptibility mapping and a new technique by hybridization of Shannon’s entropy and AHP model is proposed taking a case study of Shimla region in Himachal Pradesh (H.P). However, the analytic hierarchy process (AHP) is a semi-qualitative model and an improvement over expert-based techniques, the rest three models are mathematical models. The weightage of causative factors and sub-factors are determined based on expert opinion and are checked for consistency in AHP. The weightage of causative factors and sub-factors in the other three models is obtained using mathematical relationships. Four landslide susceptibility maps for the study area are prepared and the performance of each method is evaluated using the receiver operation characteristics (ROC) curve. It can be observed that the frequency ratio (FR) model is the most effective approach in predicting the landslide susceptibility while the analytic hierarchy process (AHP) remained the least productive. The hybrid model i.e. SE-AHP model performed better as compared to the analytic hierarchy process (AHP) model. Shannon’s entropy model assigns weightage to the causative vii factors and sub-factors both, but still, the model’s accuracy is lesser compared to the frequency ratio (FR) model. The mathematical models require a well-distributed landslide inventory while it is not essential for the expert-based models. It is observed that the accuracy of the results in mathematical methods depends upon the distribution and accuracy of the landslide inventory while the accuracy depends upon the expert’s judgment in the case of expert-based methods. Some work has been reported related to mathematical and expert-based models but Shannon’s entropy has been used very rarely. The performance of the AHP model is improved significantly by the hybridization of AHP with Shannon’s entropy. The results of the study revealed that realistic weightage can be obtained only from an accurate and well-distributed inventory. Finally, the thesis presents a comparison of expert-based methods and mathematical methods for landslide susceptibility mapping. The study helps in identifying the contribution of causative factors in the occurrence of landslides. The output of the study helps in the demarcation of the zones of high landslide potential. This study also provides information that can be used by the researchers in understanding and choosing the suitable method for landslide susceptibility mapping. The newly proposed mixed technique in this study can reduce the subjectivity in the expert-based methods and improve the accuracy of the AHP model. The results of the study will also help the planners and risk managers for understanding the landslide potential in the study area.