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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]

We focused on validation of applicability of semi-empirical technique (spectral models and stochastic simulation) for the estimation of ground-motion characteristics in the northeastern region (NER) of India. In the present study, it is assumed that the point source approximation in far field is valid. The one-dimensional stochastic point source seismological model of Boore (1983) (Boore, DM. 1983. Stochastic simulation of high frequency ground motions based on seismological models of the radiated spectra. Bulletin of Seismological Society of America, 73, 1865–1894.) is used for modelling the acceleration time histories. Total ground-motion records of 30 earthquakes of magnitudes lying betweenMW4.2 and 6.2 in NER India from March 2008 to April 2013 are used for this study. We considered peak ground acceleration (PGA) and pseudospectral acceleration (response spectrum amplitudes) with 5% damping ratio at three fundamental natural periods, namely: 0.3, 1.0, and 3.0 s. The spectral models, which work well for PGA, overestimate the pseudospectral acceleration. It seems that there is a strong influence of local site amplification and crustal attenuation (kappa), which control spectral amplitudes at different frequencies. The results would allow analysing regional peculiarities of ground-motion excitation and propagation and updating seismic hazard assessment, both the probabilistic and deterministic approaches. [ABSTRACT FROM PUBLISHER]

We analyzed the within-earthquake correlation (peak ground acceleration PGA and velocity PGV) in Japan by taking into account local geological conditions. The database includes more than 23,700 records (K-NET and the KiK-net networks) from 84 events (M 4.2–7.4) occurring in 1999–2011. The correlation structure was investigated for residuals obtained using two recently developed ground-motion models for Japan. We have shown that the level of within-earthquake correlation may vary significantly depending on site classes, general geological conditions and earthquake magnitude. The results of the analysis are in general agreement with the findings obtained recently for Taiwan (Sokolov et al. in Bull Earthq Eng 10(5):1401–1429, 2012 . doi: 10.1007/s10518-012-9368-5 ). The high level of ground-motion correlation reflects the presence of a non-random component in the residuals that may be caused by the joint influence of surface soil and thick sediments, and this influence depends on the earthquake magnitude. Therefore, a single generalized model of within-earthquake correlation across geologically heterogeneous regions may not be adequate. The application of empirical correction factors, which may be a function of earthquake magnitude, source-to-site distance, site class, and average shear-wave velocity for a given station, allows for effective reduction in the level of within-earthquake correlation. [ABSTRACT FROM AUTHOR]

We analysed the within-earthquake correlation of ground motion using the strong-motion records accumulated by the TSMIP (Taiwan Strong Motion Instrumentation Program) network in Taiwan during 1993-2009. Two ground-motion prediction equations, which were recently developed for peak ground acceleration (PGA) in the region and based on moment and local magnitude and hypocentral distance, were used for the calculation and analysis of ground-motion residuals. We also used the database containing shear-wave velocity data averaged for the top 30 m of the soil column (Vs30) for the TSMIP stations. We showed that the within-earthquake correlation may vary significantly depending on site classes, gross geological features of the area, and magnitude of earthquakes, records of which dominate the analysed dataset. On the one hand, there is a prominent correspondence between the within-earthquake correlation of PGA residuals and spatial correlation of Vs30 values, which was estimated for particular geological structures (e.g., sedimentary filled basins and large plain areas). On the other hand, the high level of ground-motion correlation (or significant non-random component of residuals) may be caused by the joint influence of soft surface soil and thick sediments and by the path or azimuthal effects. The point-source approximation of extended fault and neglected hanging- and foot-wall effects may also result in non-random residuals. The application of empirical correction factors, which consider the magnitude of earthquakes, source-to-site distance and Vs30 value for given stations, allows for the effective reduction in the level of within-earthquake correlation, as well as the within-earthquake standard deviation. The results of the analysis may be used in practical estimates of seismic hazard, damage and loss for spatially distributed structures (portfolios, lifelines) in Taiwan, as well in other regions with similar geological characteristics. [ABSTRACT FROM AUTHOR]

The August 17, 1999 Kocaeli earthquake ruptured the earth’s surface along 145 km and produced a magnitude ofM w=7.4. As expected for such an event Modified Mercalli intensities of typically IX and X in the vicinity of the fault were determined. Yet the observed accelerations at the five near-fault sites remained amazingly small with horizontal PGA values of 0.14 g to 0.4 g. We attempt to resolve the enigma by modeling surface ground motion with a finite-difference algorithm, utilizing two different rupture and slip histories derived from the strong-motion observations and ‘translate’ the computed horizontal motion in intensity values. We can show that (a) in a given simple crustal velocity model different slip distributions result in significantly different ground motion distributions in the vicinity of the fault even though both slip distributions fit the observed accelerometer data quite well. (b) Both slip distributions ‘project’ high ground motion into areas adjacent to the fault where no accelerometer was located. (c) Both slip distributions are not fully compatible with observed intensity observations around the fault, although this could be partly attributed to the lack of knowledge regarding to the crustal structure. In the light of our results it would thus be misleading if the few strong-motion observations around the Kocaeli earthquake fault were taken as typical or representative for the entire area and for potential future events. [ABSTRACT FROM AUTHOR]