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Ground-motion models (GMMs) are a key driver for the results of probabilistic seismic hazard analyses and their uncertainty. GMMs that bridge seismological and empirical approaches are an effective tool to represent the distribution of ground motion and its uncertainty in seismic hazard assessment. A methodology is presented that uses ground-motion data recorded at seismograph sites in eastern North America and shows how they can be used to calibrate simple scalable seismological models of ground-motion generation and propagation. Such GMMs can directly account for the gross features of source scaling (magnitude and stress parameter), attenuation, site response, and kappa effects. It is shown that, by application of appropriate GMM strategies, sigma (aleatory uncertainty) could be greatly reduced, resulting in lower calculated hazard for nuclear plants founded on rock. This reduction in sigma requires that high-quality seismic monitoring (e.g., broadband seismograph stations) be installed and operated over a period of years (in addition to strong-motion stations), and that an ongoing investment be made in data analysis and targeted GMM development using the data. [ABSTRACT FROM AUTHOR]

Earthquake time series are widely used to characterize the main features of seismicity and to provide useful insights into the dynamics of the seismogenic system. Properties such as intermittency and non-stationary clustering are common in earthquake time series such that multifractal concepts seem essential to describe the temporal clustering variability. Here we use a multifractal approach to study the time dynamics of the recent earthquake activity in the Corinth rift. The results indicate the degree of heterogeneous clustering and correlations acting at all time scales that suggest non-Poissonian behavior. Additionally, the multifractal analysis in different time periods showed that the degree of multifractality exhibits strong variations with time, which are associated with the dynamic evolution of the earthquake activity in the rift and the transition between periods of high and low seismicity. [ABSTRACT FROM AUTHOR]

The Kumaon Himalaya region in India has accumulated considerable seismic risk potential from moderate to high seismicity due to ongoing tectonic evolutionary processes. To assess conditions of high seismic risk arising from local site effects at populated locations, we applied the empirical horizontal to vertical ( H/ V) spectral amplitude ratio method ( Nakamura in Quarterly Reports of the Railway Technical Research Institute Tokyo, 30:25-33, ) using ambient seismic noise recorded by a network of 32 digital broadband seismographs from June 2005 to June 2008. The data and the estimated parameters were subjected to stability tests to assess the effect of seasonal variations. Seasonal variations in the ambient noise data seemed to show a lesser effect on fundamental frequency estimates and a slightly greater effect on the peak H/ V amplitudes. Validation of the ambient noise results was done by complementary tests using H/ V ratios of local and regional earthquakes. The 'peak' corresponding to the fundamental resonance frequency is prominently present in both the ambient noise and the earthquake datasets. The study locations showed distinct H/ V curve topologies, corresponding to the effects of both velocity contrast at well-defined frequencies and characteristic topographic effect around a certain frequency range. The clearly indicated 'peaks' in the H/ V curves possibly correspond to velocity contrasts created by weathered sediments overlying hard rock basements in rocky hills. Our study indicates high site responses at many populated locations near the surface trace of the seismically active Main Central Thrust (MCT) and other fault boundaries. The fundamental resonance frequencies estimated from the site response studies at the 32 locations could be useful in preliminary site characterization, ground motion prediction and seismic hazard analysis. [ABSTRACT FROM AUTHOR]