Deterministic seismic hazard analysis considering different seismicity levels for the state of Goa, India

Deterministic seismic hazard analysis (DSHA) is carried out for the state of Goa, which is a small but one of the most popular touristic places on the west coast of peninsular India. Goa state is located about 250 km from Koyna region which experienced a 6.3 magnitude earthquake in 1967 and about 350 km from Latur which witnessed a 6.3 magnitude earthquake in 1993. Hence, it is important to carry out the seismic hazard analysis for Goa, such studies being scarce in literature till date. In this paper, DSHA for Goa is carried out by considering a 350 km distance from the state boundary taking into account the historic seismicity and identifying active faults and lineaments. Seven attenuation relationships developed for intraplate regions and shallow crustal earthquakes including one developed specifically for peninsular India are used. Three earthquake scenarios representing three levels of seismic activity are considered using the logic tree approach. The maximum magnitude estimated by empirical relations and the same from past earthquake events are considered in two scenarios for carrying out the DSHA, and the third scenario is derived from the previous two scenarios using equal weightage. The peak ground acceleration (PGA) values are obtained by considering a grid of 0.1 degrees x 0.1 degrees (i.e., 11.1 km x 11.1 km) covering the entire state of Goa. The deterministic seismic hazard map showing contours of PGA are developed for the state of Goa for the three scenarios. For the mildest scenario 2, highest hazard with PGA of 0.15 g is found at localized areas in the southwest of Goa. The hazard maps for the severe scenarios indicate high hazard in the central band of the state. The deterministic spectra are developed for five major cities of Goa and compared with the spectra given in Indian seismic code IS 1893-Part 1 (Criteria for Earthquake resistant design of structures. Bureau of Indian standards, New Delhi, 2002). PGA map and the spectra will be very useful for seismic design of important structures in Goa.