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Tsunami Hazard and Risk Assessment on the Global Scale

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... Anomaly data can be taken as a problem or rare events, which affects the regular pattern of the data [3]. When, these suspicious different patterns created into the data in majority cases, then we need to identify and remove them in different tasks, such as medical problem identification [4], condition monitoring [5], defective object or equipment failure in manufacturing or in nuclear power plants [6], and chemical identification [7], etc. These anomalies are analyzed to do risk assessment and decrease the future risk by removing these anomalies in future data. ...
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We present an updated global model of Earth's crustal structure. The new model, CRUST1.0, serves as starting model in a more comprehensive effort to compile a global model of Earth's crust and lithosphere, LITHO1.0. CRUST1.0 is defined on a 1-degree grid and is based on a new database of crustal thickness data from active source seismic studies as well as from receiver function studies. In areas where such constraints are still missing, for example in Antarctica, crustal thicknesses are estimated using gravity constraints. The compilation of the new crustal model initially follows the philosophy of the widely used crustal model CRUST2.0 (Bassin et al., 2000; http://igppweb.ucsd.edu/~gabi/crust2.html). Crustal types representing properties in the crystalline crust are assigned according to basement age or tectonic setting. The classification of the latter loosely follows that of an updated map by Artemieva and Mooney (2001) (http://www.lithosphere.info). Statistical averages of crustal properties in each of these crustal types are extrapolated to areas with no local seismic or gravity constraint. In each 1-degree cell, boundary depth, compressional and shear velocity as well as density is given for 8 layers: water, ice, 3-layer sediment cover and upper, middle and lower crystalline crust. Topography, bathymetry and ice cover are taken from ETOPO1. The sediment cover is essentially that of our sediment model (Laske and Masters, 1997; http://igppweb.ucsd.edu/~sediment.html), with several near-coastal updates. In the sediment cover and the crystalline crust, updated scaling relationships are used to assign compressional and shear velocity as well as density. In an initial step toward LITHO1.0, the model is then validated against our new global group velocity maps for Rayleigh and Love waves, particularly at frequencies between 30 and 40 mHz. CRUST1.0 is then adjusted in areas of extreme misfit where we suspect deficiencies in the crustal model. These currently include some near-coastal areas with thick sediment cover and several larger orogenic belts. Some remaining discrepancies, such as in backarc basins, may result from variations in the deeper uppermost mantle and remain unchanged in CRUST1.0 but will likely be modified in LITHO1.0. CRUST1.0 is available for download.
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The study of tsunami hazards in Thailand has been an ongoing topic of research. However, the hazards from tsunami sources based on probabilistic study and population risk are still unclear. In this study, potential tsunami sources along rupture zones were selected. A series of far-field tsunami simulations were performed with scaled fault parameters based on fault lengths from 100–600 km. The results show that within a few centuries, the maximum tsunami height could be 2–5 m at the west coast and less than 2 m at the east coast. The potential tsunami exposure (PTE) of populations in an estimated inundation zone was calculated using global population data in relation to tsunami height. The results show that much attention should be paid to fault ruptures longer than 300 km (≈ 8.5 moment magnitude, Mw) that originate from 4°–6° N and 14°–17° N for the Sumatra subduction zone and the Manila trench, respectively. A quarter of a million people are at risk of exposure to a maximum 9 m tsunami height after 100 min of the arrival of the first wave at the Andaman coast. One million people near the Gulf of Thailand are at risk of a tsunami height less than 3 m after 9 hr.
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Numerical model simulations, combined with tide-gauge and satellite altimetry data, reveal that wave amplitudes, directionality, and global propagation patterns of the 26 December 2004 Sumatra tsunami were primarily determined by the orientation and intensity of the offshore seismic line source and subsequently by the trapping effect of mid-ocean ridge topographic waveguides.
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Analysis of the earth's longest period normal modes shows that the December 2004 Sumatra-Andaman earthquake was much larger (Mw 9.3) than ini- tially inferred from surface-wave data and involved slip on a much longer fault than initially inferred from body-wave data. The seismic moment and relative excitation of the normal modes indicate that the entire aftershock zone ruptured, consistent with the large tsunami amplitudes in Thailand, Sri Lanka, and India. An apparent increase in seismic moment with period results from interference between parts of the fault. The earthquake resulted from subduction of the Indian plate beneath the Burma microplate, a sliver plate between the Indian and Sunda plates. Hence, the rate and direction of convergence depends on the motion of the Burma plate, which is not well known. Convergence would be highly oblique if the rate of motion between Burma and Sunda is that inferred from spreading in the Andaman Sea, and less if a slower rate is inferred from the Sagaing fault. The December earthquake was much larger than expected from a previously proposed relation, based on the idea of seismic coupling, in which such earthquakes occur only when young lithosphere subducts rapidly. Moreover, a global reanalysis finds little support for this correlation. Hence, we suspect that much of the apparent differences between subduction zones, such as some trench segments but not others being prone to Mw 8.5 events and hence oceanwide tsunamis, may reflect the short earthquake history sampled. This possi- bility is supported by the variability in rupture mode at individual trench segments.
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This paper outlines the main contributions to the definition and evaluation of tsunami hazard and risk resulting from studies undertaken in Italy in recent years and emphasises that adopting characteristic cases or scenarios is a very useful and advantageous technique. Three main cases are given as valuable examples, that is the 1627 Gargano tsunami, the 1693 eastern Sicily tsunami and the 1908 Messina Straits tsunami, since: (1) they characterise three distinct tsunamigenic regions; (2) they are instances of destructive events; and (3) they have been extensively studied in the last decade. The paper elucidates the state-of-the-art of the research on these events, clarifies the chief points of agreement and disagreement among scientists, and illustrates the main issues that are to be addressed by future research to provide reliable assessment of tsunami risk and to implement efficient countermeasures to defend the life of people, coastal structures and the coastal environment against the attacks of tsunamis.
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We investigate the tsunami hazard associated with the Catalina Fault off-shore of southern California. Realistic faulting parameters are used to match coseismic displacements to existing sea 炉oor topography. Several earthquake scenarios with moment magnitudes ranging between 7.0 and 7.6 are used as initial conditions for tsunami simulations, which predict runup of up to 4 m. Normalizing runup with the maximum uplift identifies areas susceptible to tsunami focusing and amplification. Several harbors and ports in southern California lie in areas where models predict tsunami amplification. Return periods are estimated by dividing the modeled sea炉oor uplift per event by the observed total uplift of the Santa Catalina Island platform multiplied by the time since the uplift began. The analysis yields return periods between 2,000 to 5,000 years for the Catalina Fault alone, and 200 to 500 years when all offshore faults are considered. [DOI: 10.1193/1.1773592]
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ABSTRACT This paper introduces a method for the evaluation of the seismic risk at the site of an engineering project. The results are in terms of a ground,motion parameter (such as peak acceleration) versus average,return period. The method,incorporates the influence of all potential sources of earthquakes and the average activity rates assigned to them. Arbitrary geographical relationships between,the site and po- tential point, line, or areal sources can be modeled with computational ease. In the range of interest, the derived distributions of maximum annual ground motions are in the form of Type I or Type II extreme value distributions, if the more com- monly assumed magnitude,distribution and attenuation laws are used.
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An approximate method to estimate the maximum lateral deformation demands in multistory buildings responding primarily in the fundamental mode when subjected to earthquake ground motions is presented. This method permits a rapid estimation of the maximum roof displacement and of the maximum interstory drift for a given acceleration time history or for a given displacement response spectrum. A multistory building is modeled as an equivalent continuum structure consisting of a combination of a flexural cantilever beam and a shear cantilever beam. The simplified model is used to investigate the ratio of the spectral displacement to the roof displacement and the ratio of the maximum interstory drift ratio to the roof drift ratio. The effect of the distribution of lateral forces along the height of the building and of the ratio of overall flexural and shear deformations is examined. Lateral deformation demands of a 10-story steel building computed with the simplified method when subjected to various earthquake ground motions are compared with those computed using step-by-step time history analyses. It is shown that the method provides good approximations, which are useful for the preliminary design of new buildings or for a rapid evaluation of existing buildings.
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We evaluate far-field tsunami hazard in the Indian Ocean Basin based on hydrodynamic simulations of ten case studies of possible mega earthquakes at the major seismic zones surrounding the basin. They represent worst-case scenarios of seismic rupture along the full extent of seismogenic faults having supported large earthquakes in the historical record. In a series of numerical experiments in which the source parameters of the 2004 Sumatra tsunami are allowed to vary one by one, while keeping the seismic moment and the fault orientation unchanged, we document that the main patterns of far-field tsunami amplitudes are remarkably robust with respect to nominal variations in such parameters as hypocentral depth, exact centroid location, and slip distribution on the fault plane. These results validate the concept of modelling case scenarios of potential future earthquakes whose source is by definition imprecise. We consider seismic sources located at the extremities of the 2004 Sumatra–Andaman rupture, namely along the southern coast of Sumatra and in the Andaman–Myanmar province; along the Makran coast of Pakistan and Iran; and also along the southern coast of Java, where the possibility of a large interplate thrust earthquake cannot be entirely dismissed. The results of our hydrodynamic simulations indicate that the distribution of maximum amplitudes in the Indian Ocean Basin is primarily controlled by the classical effect of source directivity, and additionally by refraction and focusing along bathymetric features. As a result, many provinces in the basin could be threatened by higher tsunami amplitudes than in 2004. This pattern is particularly important along the coast of East Africa, from Somalia to and including South Africa, in Madagascar and the Mascarene Islands, especially under a South Sumatra scenario involving an earthquake comparable to, or even possibly larger than, the 1833 event, whose epicentral area is widely believed to be under enhanced seismic risk as a result of stress transfer from the 2004 and 2005 ruptures to the northwest, possibly even in the wake of the 2007 Bengkulu earthquakes.