Probabilistic Seismic Hazard Assessment for Amaravathi Region, Andhra Pradesh

This article explains an analytical attempt that estimates seismic hazard for Amaravathi city. The present study has been carried out contemplating the available faults and epicentral data within a radius of 300km of the Amaravathi region. The homogenous earthquake catalogue has been prepared for Amaravathi region by Steep’s method. The seismic hazard parameters ―a‖ and ―b‖ for Amaravathi city were evaluated by Gutenberg-Ritcher method. The ―a‖ and ―b‖ values obtained as 4.69, 0.6468 respectively. The total 353 epicenters and 31 faults were considered in this seismic analysis for the estimate of PSHA for Amaravathi. The ground motion produced by the faults at this site has been estimated by using the regionspecific Ground Motion Prediction Equation (GMPE) developed by the raghukanth and lyenger (2007). The probability of occurrence of different magnitude classes was estimated. The hazard curves and mean annual rate of exceedance for Peak Ground Acceleration were calculated by using ground motion estimated in this area. The Uniform Hazard Response Spectrum (UHRS) for the ranging time periods between 0.1 – 4 seconds was prepared. PGA values for Amaravati region was found to be in between 0.001g to 0.3g from seismic hazard map that was prepared in this study

Conditional Mean Spectra in Site-Specific Seismic Hazard Evaluation for a Major River Crossing in the Central United States

Current seismic design practice often relies on the use of the uniform hazard response spectrum (UHRS), which implicitly includes motions from multiple earthquake sources and envelops possible spectra, yet does not represent a single event. Seismic hazard analyses at the site of a major Mississippi River crossing near St. Louis, Missouri, showed bimodal seismic hazard dominated by small, nearby earthquakes at short periods and large, distant earthquakes in the New Madrid seismic zone at long periods. UHRS motions resulted in large seismic demands and predictions of pervasive liquefaction that were inconsistent with historical and geologic records. UHRS-compatible conditional mean spectra (CMS) were developed to bridge deterministic and probabilistic seismic hazard evaluations, and used to evaluate liquefaction, lateral spreading, and settlement potential. The computed response was consistent with the historical and geologic record. CMSs offer hazard-compatible alternatives to the UHRS and result in seismic demand consistent with historical and geologic evidence.

Evaluation of Peak Ground Acceleration and Response Spectra Considering the Local Site Effects

The local site effects play an important role in the evaluation of seismic hazard. The proper evaluation of the local site effects will help in evaluating the amplification factors for different locations. This article deals with the evaluation of peak ground acceleration and response spectra based on the local site effects for the study area. The seismic hazard analysis was done based on a probabilistic logic tree approach and the peak horizontal acceleration (PHA) values at the bed rock level were evaluated. Different methods of site classification have been reviewed in the present work. The surface level peak ground acceleration (PGA) values were evaluated for the entire study area for four different site classes based on NEHRP site classification. The uniform hazard response spectrum (UHRS) has been developed for the city of Bangalore and the details are presented in this work.