Estimation of Seismic Hazard and Amplification of Strong Ground Motions in Indo-Gangetic Plains

In India, many regions under high seismic risk are located on deep soil deposits extending up to several hundred meters of depth. Deep sedimentary deposits are more prone to earthquake hazard. The Indo-Gangetic Basin (IGB) is located in the vicinity of Himalayan Frontal Fault (HFT) and the presence of thick alluvium makes it more vulnerable to seismogenic sources and hence, its characterization is required. In the present study, six sites in Uttarakhand are characterized by using the joint fit Inversion method from the data obtained from Multi Channel Analysis of Surface Waves (MASW) technique with a combination of Horizontal-to-Vertical Curve (H/V) from microtremor studies. Further, seismic hazard assessment for a scenario earthquake (Mw= ۸.۰) is performed to study the behavior of IGB. There is an increase in spectral acceleration at sites with deep soil profiles and amplification also increases due to the presence of deep soil deposits in this region. This indicates that these sites suffer from high liquefaction potential as compared to shallow soilprofiles. Moreover, peak ground horizontal accelerations at bedrock level are computed by dividing the study area into seven seismogenic source zones. On a regional scale, the b value is relatively high for seismic zone VI indicating high locally concentrated stress and fracturing. Also, the value of l is highest in seismic zone IV and lowest in seismic zone II. The estimated return periods for R۶.۰, R۷.۰ and R۸.۰, represents the seismic zone IV as the most active in the whole region. The estimated hazard parameters are possibly in agreement with the reported hazard parameters in the literature. Seismic characteristics of seismogenic source zones may be used for earthquake engineering purposes, e.g. assigning the severity of input motions for earthquake resistant construction.

Keywords:

Deep Soil , MASW , H/V , Seismogenic Source Zone , Amplification