b-value Estimation and Extreme Magnitude Assessment in the Source Region of Past Earthquakes in Central Himalaya and Vicinity.

The Gutenberg-Richter (GR) and Gumbel methodologies were applied to analyze seismic activity parameters (specifically, b-values) in the central Himalaya region, covering latitudes between 26° and 31° E and longitudes between 80° and 88° N during the time frame from 1964 to 2021. Additionally, Gumbel's techniques were utilized to gauge the frequency of occurrence for moderate-tolargemagnitude earthquakes. Within a circular area with a diameter of 250 kilometers, we determined the b-values for the primary source regions of the ten past major earthquakes. The estimated b-value based on GR relation varies from 0.82±0.06 to 1.02±0.10, whereas the b-value based on Gumbel's method ranges from 0.86±0.30 to 1.88±0.32. The results indicate that Gumbel's distribution approach is effective for regions where large earthquake data is available, and the b-values, estimated from the GR method, are found to be more appropriate for the tectonics of the source regions. The Lo-Mustang earthquake region and Bajhang earthquake regions are identified as probable regions for the occurrence of a large earthquake in less than 100 years, which also supports the existence of a western Nepal seismic gap between Uttarakhand, India, and central Nepal. The findings describe the seismic risk in the epicenters of previous earthquakes in terms of b-value, recurrence intervals, and earthquake probability for each magnitude. [ABSTRACT FROM AUTHOR]