Pre- and Post-seismic Crustal Stress Heterogeneity Analogous to 14 November 2016, Mw 7.8, Kaikoura Earthquake, New Zealand.

The 14 November 2016, M_w 7.8 Kaikoura, New Zealand earthquake offers an unprecedented opportunity to observe the heterogeneity in stress field over a very complex fault system where the subduction zone converges with the strike-slip faults system. Here, we report the pre- and post-seismic stress field asperity for the first time in terms of the b value variations associated to the Kaikoura earthquake. Pre-seismic disparity of b values indicates the existence of two prominent low b value clusters, one in the neighborhood of the epicenter and the other just to the northeast of the earthquake rupture zone. Owing to the co-seismic stress release near the epicentral area, the pattern of low b value has become negligible in the post-seismic period. However, the pattern of low b value in the northeast of the rupture zone remains unchanged in the post-seismic period and indicates the unreleased strain energy in the province. The stress fields inferred from the inversion of the focal mechanism during pre- and post-seismic periods of the event suggest a strike-slip mechanism with a horizontal maximum stress axis (σ1) in the WNW-ESE direction. Nevertheless, before and after the earthquake, the stress field direction did not change significantly, indicating that the energy released during the Kaikoura event was insufficient to alter the stress orientations in the complex fault system. [ABSTRACT FROM AUTHOR]