Seismic Site Classification of Recording Stations in Tarai Region of Uttarakhand, from Multiple Approaches

Abstract

Repeated earthquakes (EQs) are clear indication of alarming seismicity which can be witnessed across Indian subcontinent. Increase in population density with inappropriate construction practice repeatedly rise alarm that in comparison to damage scenarios experienced during previous major to great EQs in India, future catastrophes would be manifold. Performing regional seismic hazard as well as site response studies can possibly help in accurate estimation of probable future seismic scenario. Site class (SC) of EQ recording stations is an important part of both seismic hazard as well as site response analyses. In seismic hazard analysis, suitable attenuation relations are often selected based on comparison of recorded ground motion with proposed ground motion as per selected attenuation relation for the same SC. Thus, unless SC of recorded ground motions is known, suitability of selected attenuation relation cannot be validated. In addition, recent studies suggest that for same soil column, ground motion may amplify at the surface from minimal to very high depending upon input motion characteristics. Thus again, unless SC of recording station is not known, recorded ground motion cannot be considered with confidence as outcrop or base motion for region specific site response studies. In the present work, SC of eight recording stations located in Tarai region of Uttarakhand, India located adjacent to the Himalayan belt and which are part of PESMOS database, are established by three different methods namely; equivalent linear ground response analysis, generalized inversion technique and horizontal to vertical spectral ratio method. Collectively all these three methods suggest same SC for each of the eight recording stations including Roorkee, Rishikesh, Dehradun etc. Further, obtained SC based on the present study is considerably different from available SC as per PESMOS database. However, present findings are matching with recent published work. Obtained results can be very helpful in developing surface seismic hazard using regional ground motion records towards minimizing future EQ induced damages.