Determination of Site Specific Response Spectra for Site Class D and E for Guwahati City, NE India Region

For the construction of earthquake (EQ) resistant structures, the most important information required for a particular region is the design response spectrum. This design response spectrum is generally obtained from seismic hazard analysis (SHA) for that particular region. Though many researchers have performed SHA for the NE India region, either the response spectra are obtained for bedrock level or the Site Class (SC A) condition. Obtaining this response spectrum for other SCs such as C, D, and E is necessary to form a basis for designing EQ resistant structures on the mentioned SCs. This can be achieved by combining SHA and local site effects (LSE) for a particular SC collectively. In the present study, the SC A level response spectrum for Guwahati city is determined based on deterministic seismic hazard analysis (DSHA). Further, an attempt has been made to quantify Local Site Effect (LSE) for SCs D and E numerically for Guwahati city by carrying out equivalent linear ground response analysis (ELGRA) using 30 globally recorded ground motions. For the purpose, 20 borehole data belonging to SC D and SC E is collected for Guwahati city. Results are obtained in the form of 5% damped response spectra at the ground surface and at the bedrock level. In addition, average normalized (surface/SC A) response spectra for SC D and SC E are determined separately based on results obtained from ELGRA. The normalized response spectra (or site coefficients) are then used along with the SC A level response spectrum obtained from DSHA for the region to determine the surface level response spectrum for a particular SC.