Seismic Characteristics and Seismic Hazard Assessment: Source Region of the 2015 Nepal Earthquake Mw 7.8 in Central Himalaya

Abstract

Seismicity and seismic characteristics like b value, fractal dimension, energy release and recurrence period are assessed for the region (80°E–89°E and 26°N–31°N), which includes the 2015 large Nepal earthquake Mw 7.8 in central Himalaya. The International Seismological Centre (ISC) catalogue of earthquakes with mb ≥ 3.8 for the period August 1964 – January 2013 are used. The b values are estimated using the maximum likelihood and least square methods. The fractal dimension is estimated using the correlation integral method. The events are also used for estimating radiated energy in the region. The probability of occurrence of moderate earthquakes (mb ≥ 5.0 using ISC data and Mw ≥ 6.0 using USGS data for the period 1964–2015) during a specified interval of time is estimated on the basis of three probabilistic models, namely, Weibull, gamma and lognormal. The model parameters are estimated by the maximum likelihood estimates. It is found that there is a 99% probability for occurrence of at least one earthquake mb ≥ 5.0 in this region in a time window of 2–3 years from the year 2013, and in 20–30 years for an earthquake Mw ≥ 6.0 from the year 2015. The b value maps identified variable stressed zones, and the fractal dimension maps fractal characteristics of the active fault zones. The energy release map identified the zones of higher and lower energy release. The percent probability maps, prepared using the Poisson distribution, identify the zones of higher- and lower-probability earthquakes and thus indicate the areas of future probable earthquakes.