A review of Seismic hazard assessment of Gujarat: a highly active intra-plate region

Large intraplate earthquakes that occur in the interior of continental plates are rare and often very destructive. The Gujarat region of western India, that witnessed the deadly Mw 7.6 earthquake on January 26, 2001 and the Mw7.8 quake on June 16, 1819, is one of the most active intraplate regions of the world. The tragedy caused by the 2001 earthquake marked a turning point in the disaster awareness and preparedness in the region. In the aftermath of this earthquake, several workers investigated the important issue of mitigating seismic hazard through new knowledge based techniques of probabilistic and deterministic ground motion prediction, micro and macro zoning of vulnerable areas. This paper reviews the results of seismic hazard estimation in the Gujarat region from different methodologies. We note that the probabilistic seismic hazard estimates by different workers are not consistent even within the same region because of uncertainties in constraining the hazard parameters, akin to the global observations. Using a logical approach, we evaluate all the ground motion predictions from different methodologies and constrain the level of expected peak ground acceleration (PGA) by adjusting all the values onto a common platform. Our assessment reveals that the PGA values in Gujarat vary from 0.04 to 0.35g and 0.07 to 0.77g for 10% and 2% probability of exceedance in 50 years, at the engineering bedrock (Vs=760 m/s) level. The hazard values thus estimated in this study can be directly used to estimate the PGAs at the surface by incorporating local site effects, which in-turn can be utilized in planning and mitigating earthquake hazards. Further, the estimates of PGA from deterministic approaches range from 0.05 to 0.90g. We see that within Gujarat, the ground motion values obtained by deterministic and probabilistic methodologies do not show much variation. We affirm that we need to undertake such a logical approach to arrive at realistic probabilistic hazard values that are in conformity with the estimates from deterministic assessment. We also advocate the need to upgrade the classical methods of probabilistic and deterministic hazard assessment and incorporate the source and site complexities while estimating the hazard. Further, a comparison of the hazard values of Gujarat with those from other intraplate regions of the world, reveals that the hazard level in Gujarat is higher than in Australia, Brazil and Western Europe and comparable to North China, Eastern Canada and the New Madrid Seismic zone.

Research Highlights

Comparison of PSHA of Gujarat with different intraplate regions of the world for occurrence rate of 475 year (10% probability of exceedance in 50 years)

Further details:

Choudhury P., Chopra S., Kumar M. R. (2018) A review of seismic hazard assessment of Gujarat: A highly active intra-plate region, Earth-Science Reviews, 187, 205-218.

News

Detailed geophysical and geological investigations to identify copper lead and zinc mineralization around Ambaji, Banaskantha district are in progress.

ISR has initiated a project on imaging the shallow subsurface of the Kachchh district for delineation of ground water aquifers and fresh water-saline water interface.