Regional time-predictable modeling in the Hindukush–Pamir–Himalayas region

Abstract

The seismic characteristic of Hindukush–Pamir–Himalaya (HPH) and its vicinity is very peculiar and has experienced many widely distributed large earthquakes. Recent work on the time-dependent seismicity in the Hindukush–Pamir–Himalayas is mainly based on the so-called “regional time-predictable model”, which is expressed by the relation log T= cM p+ a, where T is the inter-event time between two successive main shocks of a region and M p is the magnitude of the preceded main shock. Parameter a is a function of the magnitude of the minimum earthquake considered and of the tectonic loading and c is positive (∼0.3) constant. In 90% of the cases with sufficient data, parameter c was found to be positive, which strongly supports the validity of the model. In the present study, a different approach, which assumes no prior regionalization of the area, is attempted to check the validity of the model. Nine seismic sources were defined within the considered region and the inter-event time of strong shallow main shock were determined and used for each source in an attempt at long-term prediction, which show the clustering and occurrence of at least three earthquakes of magnitude 5.5≤ M s≤7.5 giving two repeat times, satisfying the necessary and sufficient conditions of time-predictable model (TP model). Further, using the global applicability of the regional time- and magnitude-predictable model, the following relations have been obtained: log T t=0.19 M min+0.52 M p+0.29 log m 0−10.63 and M f=1.31 M min−0.60 M p−0.72 log m 0+21.01, where T t is the inter-event time, measured in years; M min the surface wave magnitude of the smallest main shock considered; M p the magnitude of preceding main shock; M f the magnitude of the following main shock; and m 0 the moment rate in each source per year. These relations may be used for seismic hazard assessment in the region. Based on these relations and taking into account the time of occurrence and the magnitude of the last main shock in each seismogenic source, time-dependent conditional probabilities for the occurrence of the next large ( M s≥5.5) shallow main shocks during the next 20 years as well as the magnitudes of the expected main shocks are determined.