Mapping the pre and post seismic crustal stress heterogeneity analogous to 2016, Mw 7.8, Kaikoura quake, New Zealand

Abstract

Heterogeneity of pre and post seismic stress states associated to any earthquake play a primary role in understanding the earthquake mechanism and hazard assessment of a seismically dynamic region. The Mw 7.8, November 14, 2016 Kaikoura, New Zealand earthquake offer an unprecedented possibility to observe the heterogeneity in stress field over a very complex fault system wherein subduction zone converges with the strike slip faults system. Here we report the pre and post seismic stress field asperity first time in terms of spatial and temporal variations of b-values associated to the Kaikoura main-shock. Pre seismic spatial disparity of b-value indicates the existence of two prominent low b-value clusters, one towards southwest closer to the epicenter and other to the north of the rupture zone. During co seismic period, owing to the stress release near the epicentral area, the pattern of prominent low b-value pattern has become negligible in the post seismic period. However, the pattern of low b-value in the north of the rupture zone remains similar in the post seismic period indicates the unreleased strain energy in the province. The temporal evaluation of the earthquakes frequency magnitude distributions over a period of two decades also showed an analogous pattern that the b-values were decreased considerably before the large earthquakes in the expanse, which could spawn a larger future earthquakes in the vicinity.