SEISMICITY OF WESTERN HIMALAYA

Abstract

Himalaya is the one of the youngest mountain belt having active tectonic discontinuities, complex geological setup, and zones of variable seismic density. The western part of Himalaya faced catastrophe due to great Kangra earthquake (32.3oN, 76.25oE) of April 4, 1905 of magnitude 8 and the recently occurred Mw 7.6 Muzaffarabad earthquake of October 8, 2005.The process of removing the group of dependent earthquakes events, form the seismicity catalog, is termed 'declustering' of seismic catalog. There are many available declustering algorithms that have been proposed over the years but, most users have use either the algorithm of Gardner and Knopoff (1974) or Reasenberg (1985). The incompleteness of an earthquake dataset that comes in because of the non-uniformity of the seismic networks with time is investigated generally by fitting a Gutenberg-Richter model to the frequency magnitude distribution (FMD). The FMD described the relationship between the frequency of occurrence and magnitude of earthquakes as 𝑙𝑜𝑔𝑁(𝑀) = 𝑎 − 𝑏(𝑀). However, in practice as said earlier the available catalogs of earthquakes are not complete particularly for smaller magnitude events i.e. catalog is biased against small events. Objective of this work is declustering of Merged Homogenized earthquake catalog of study area, Estimation of a value, b value and Magnitude of completeness (Mc) of Merged Homogenized catalog (MH Catalog) and Merged Homogenized Declustered (MHD Catalogs) catalogs, calculation of return period of earthquake for several magnitudes, completeness analysis of MH Catalog and MHD Catalog, division study area into seismic source zones and Estimation of a value, b value, Magnitude of completeness (Mc) and return period.