Spatiotemporal relationships between tectonic tremor, microseismicity, and slow-slip induced stress changes along the northern Hikurangi Margin, New Zealand

Abstract:

We investigate the spatiotemporal relationships between slow slip, tectonic tremor, and earthquakes along the northern Hikurangi Margin, New Zealand. The northern Hikurangi Margin plays host to some of the shallowest (<15km depth) slow slip events (SSEs) in the world, thus providing a unique window into the shallow subduction zone environment. There have been numerous observations of SSEs showing a diverse range in behavior that varies along strike. Working within the framework of existing observations, we use the recently quantified geometry of the Hikurangi subduction interface and PyLith, a sophisticated finite-element crustal deformation modeling tool, to simulate the largest well-recorded northern Hikurangi SSEs located near Gisborne in 2010 and 2014. We then analyze the spatial extent of slip from each SSE and compute the changes in Coulomb failure stress imparted on the megathrust with respect to tremor and seismicity.

To investigate the effects of slow slip induced Coulomb stress changes on local seismicity, earthquakes from the GeoNet catalog were relocated using NonLinLoc, a probabilistic, non-linear, 3D earthquake location tool. Relocated events within 5 km depth of the subduction interface were then plotted against the changes in Coulomb failure stress to look at the spatial relationship between slow slip and earthquakes. We also looked at the spatial relationship between slow slip and tremor using a modified version of the popular envelope cross-correlation method to detect tremor during the 2010 and 2014 SSEs. Tremor locations were visually examined with respect to slow slip imparted stress changes. Both seismicity and tremor are concentrated at the down-dip extent of the slow slip rupture patches in regions of Coulomb stress increase.