Seismic Site Response of Regions in Northern Bihar

Due to the proximity of northern Bihar to the great Himalayan collision arc, the region has been exposed to hundreds of moderate to great earthquakes (EQs) since prehistoric times, leading to devastating effects. Understanding of such regions in the light of seismic site response is critical. To do so, initially, Multichannel Analysis of Surface Wave (MASW) and Standard Penetrationtesting (SPT) are coupled in understanding the subsurface properties of selected sites. The obtained shear wave velocity (𝑉𝑉𝑠𝑠) profiles and borelog data from the site are extrapolated to a depth of 100 m. Further, 12 synthetic bedrock motions are generated using EXSIM due to the lack of regional ground motion (GM) records for the locality. These extrapolated dynamic soil properties and synthetic ground motions (SGMs) are incorporated into the equivalent linear site response analysis (ELSRA) algorithm. Based on the analysis, the influence of Peak horizontal acceleration (PHA) and impedance contrast (IC) on amplification factors (AFs) are discussed. Furthermore, the impact of variation of depth on surface manifestation is highlighted. Such understanding of site response to EQs, influences the choice of ground improvement techniques and subsequent seismic hazard mitigation activities.

Keywords: Synthetic ground motion, Equivalent linear site response, Site investigation, Amplification factor.