Earthquake Hazard Update in Central Himalaya

Abstract

To gauge the risk of future earthquakes, one must first understand the earthquake hazard and related earthquake engineering determinations; which usually need estimate of return periods, probabilities of exceedance of specific levels of design load criteria or extremal safety conditions. Himalayan region 29°N - 33°N latitude and 75°E - 81°E longitude which exclusively include Himachal Pradesh and Uttarakhand adjoining have been considered for potential earthquake hazard analyses. This region is one of the most seismically active due to Indian and Eurasian plate collision where large to great earthquakes have occurred in the past. Fifty five years of earthquake data from the year 1963 to 2017 with Mw≥4.0 have been taken from the catalogue of USGS and ISC. The analyses indicate that the earthquake occurrences agree with the Gumbel’s Type I extreme distribution function applied to those maximum magnitude data with novel correlation (0.87). Hazard in the region have been quantified in terms of return periods and probabilities of occurrence of earthquake of any given magnitude. The line of expected extremes (LEE) based on 55 years (1963-2017) of seismicity for the region has been plotted. The medium to large size earthquakes have been predicted. Study indicates that the most probable largest annual earthquakes are close to 4.9 and the most probable earthquake that may occur in an interval of 50 years is estimated to be 7.3.