Statistical analysis of earthquake catalogue and magnitude of completeness for Northern and Southwestern Pakistan

Abstract

A historical and instrumental earthquake catalogue is prepared for the Northwest Himalayan Fold and Thrust Belt and Makran Subduction Zone Pakistan from 1960 to 2019 with homogenized moment magnitude. The local and some international published sources were utilized for the preparation of catalogue. This earthquake catalogue contained numbers of duplicate, repeated, dependent and independent events. Declustering process was opted to remove the dependent events such as foreshock and aftershock from catalogue to separate the mainshock only in term of distance and time space window. The declustering found 2714 clusters of earthquakes with total of 19512 (57.19 %) events out of 34112. Only cluster events which contained the mainshock or independent events were drawn on seismicity map with color identification. Maximum likelihood method was used to compute the value of magnitude of completeness i.e., Mc = 3.8 with estimation of a and b-values. Years vise magnitude of completeness was also computed to check the time period variation. The completeness of magnitude for different intervals of time indicates the impartial approximation of previous recorded seismicity. Temporal and spatial maps were also drawn to investigate the slope “b” and rate of productivity “a” in the study region. It is noted that b-values varied from 0.2 to 2.0 due to stress and intensive tectonic setting whereas a value increases due to increase the seismicity rate with respect to region. Seismotectonic map was drawn to delineate the major faults, seismicity pattern and tectonic activities. This work further can be used for single value hazard assessment for any region and their response spectra to update buildings and bridges codes.