Validity of time-predictable seismicity model for Nepal and its adjoining regions

Abstract

Earthquake generation model for the Nepal Himalaya and its adjoining regions was studied using seismicity data from 1963 to 2004 reported in the catalogues of National Geophysical Data Centre, Colorado and U. S. Geological Survey. The earthquakes having a surface wave magnitude M_s≥5.1 were considered to establish the statistical relation. Four seismogenic sources based on clusters of earthquakes have been identified in the region. It is observed that the time interval between two consecutive main shocks depends on the preceding main shock magnitude (M_p) and not on the forthcoming main shock magnitude (M_f). The result supports the applicability of time-predictable model for Nepal and its adjoining regions. A linear relation is established connecting the logarithm of the inter-event times between two successive main shocks (T) and magnitude of preceding main shock in the form log T =cM_p + a where parameter a is a function of  the minimum  magnitude of the earthquake considered  and the tectonic loading, and c is a positive constant. The physical meaning of the model is that larger the magnitude of the preceding main shock the longer will be the time interval for the forthcoming earthquake. The values of constants c and a for Nepal Himalaya and its adjoining regions are computed to be 0.25 and -0.65 respectively. This result can be utilised to compute the time of occurrence of the impending strong earthquake within the delineated seismogenic sources and may be used for assessing the long-term seismic hazard in the region.