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We analyze the results of a Probabilistic Seismic Hazard Assessment obtained for Saudi Arabia using a spatially smoothed seismicity model. The composite up-to-date earthquake catalog is used to model seismicity and to determine earthquake recurrence characteristics. Different techniques that are frequently used for the analysis of input data are applied in the study. The alternative techniques include the declustering procedures for catalog processing, statistical techniques for estimation the magnitude-frequency relationship (MFR), and the seismicity smoothing parameter. The scheme represents epistemic uncertainty that results from an incomplete knowledge of earthquake process and application of alternative mathematical models for a description of the process. Our calculations that are based on the Monte Carlo technique include also a consideration of the aleatory uncertainty related to the dimensions and depths of earthquake sources, parameters of MFR, and scatter of ground-motion parameter. The hazard maps show that the rock-site peak ground acceleration (PGA) is the highest for the seismically active areas in the north-western (Gulf of Aqaba, PGA > 300 cm/s for return period 2475 years) and south-western (PGA > 100 cm/s for return period 2475 years) parts of the country. We show that the procedures for catalog declustering have the highest influence on the results of hazard estimations, especially for high levels of hazard. The choice of smoothing parameter is a very important decision that requires proper caution. The relative uncertainty that is ratio between the 85th and 15th percentiles may reach 50-60% for the areas located near the zones of high-level seismic activity. [ABSTRACT FROM AUTHOR]

An approach to seismic hazard assessment that is based on consideration of spatial distribution of possible earthquakes with maximum credible magnitudes is proposed. A set of catalogs consisting in a large number of the earthquakes randomly distributed inside seismic source areas is generated using Monte Carlo technique. Magnitudes and parameters of the earthquake sources are considered as random variables with corresponding probability distribution functions. The modeling takes into account inherent uncertainty in location, magnitude, size of faulting and other characteristics of future large earthquakes. The ground-motion parameters at the point of interest are calculated from all events in the catalogs using ground motion prediction equations taking into account ground-motion variability. Seismic hazard for every site is described by a set of possible values of the ground-motion parameters, from which probability density function and cumulative distribution function are determined. The approach is discussed in application to region of western Saudi Arabia which is characterized by various levels of seismicity. Such type of seismic hazard analysis may be useful to constrain the expected level of maximum ground motion to be considered in design, seismic risk mitigation and reinsurance, bearing in mind necessity for estimations of ground motions from large rare earthquakes. [ABSTRACT FROM AUTHOR]

The results of classical probabilistic seismic hazard analysis (PSHA) contain no information about simultaneous ground motions at different sites during a particular earthquake. Seismic risk analysis for distributed critical structures requires estimates of the level of earthquake shaking that are likely to occur concurrently at multiple locations: whether the vulnerable elements of a lifeline system are likely to be simultaneously affected by shaking of sufficient strength to disable them and whether the shaking at any one of critical points may be sufficient to cause failure of the whole system. While the analysis of lifeline performance requires multiple-location estimations, the sparsely located elements of a network or critical facilities are designed on the basis of point-wise PSHA. In this paper we study specific features of multiple-location PSHA, as compared with the classical point-wise PSHA, using Monte Carlo simulations. We analyze the level of ground motion (PGA) that will be exceeded at any site inside a particular area or at several sites simultaneously with reference annual probability. The analysis has been performed for regions of Western and South-Western Germany, Northern and Eastern Taiwan, which represent different levels of seismicity (low, moderate and high, respectively). The relationship between the multiple-location and point-wise estimations are analyzed and quantified. Results of the study may be used to decide whether it may be possible to utilize the procedure of point-wise PSHA in particular cases of multiple-location PSHA, i.e. for assessment of maximum level of ground motion among several sites, or for estimation a reasonable lower safety level when considering simultaneous exceedances. [ABSTRACT FROM AUTHOR]

Taipei, the capital of Taiwan, suffered from destructive earthquakes four times during the 20th century ( ML = 7.3 on April 15, 1909; ML = 6.8 on November 15, 1986; the Chi–Chi ML = 7.3 earthquake on September 21, 1999; and ML = 6.8 on March 31, 2002). Analysis of recorded data shows a strong dependence of spectral amplification in the Taipei Basin on earthquake depth and azimuth. At low frequencies ( f < 3 Hz) significant larger amplifications are observed for shallow earthquakes as compared to intermediate depth events. The former ones also display strong azimuthal dependence. As structures with large response periods such as bridges and tall buildings are sensitive to these low frequencies the understanding of the associated wave effects within the basin and their role for site effect amplification is critical. The tool we employ is 3D finite-difference modeling of wave propagation of incident wave fronts. The available detailed model of the basin allows studying the wave effects. Modeling clearly reveals that basin edge effects as observed in data are related to surface wave generation at the basin edges with a high degree of azimuthal dependency. The reproduced site amplification effects are in qualitative agreement with the observations from strong motion data. [ABSTRACT FROM AUTHOR]