Slow Slip Events at the Hikurangi Subduction Margin, New Zealand, from 2006 to 2017

Abstract:

Slow slip events (SSEs) occur frequently along the Hikurangi Margin in New Zealand, and understanding these events is critical to our understanding of interseismic coupling, plate motion budgets, and the potential for damaging earthquakes. Along the Hikurangi, deeper and less frequent SSEs are observed along the southern part of the margin, while shallower and more frequent events are observed along the northern section. We have been compiling a catalog of Hikurangi SSEs covering the time period from 2006 to 2017 to help us understand the spatial and temporal patterns of slip along the Hikurangi Margin. Using this catalog, we can begin the process of characterizing the behavior of Hikurangi SSEs, looking at properties such as depth, peak slip rate, total slip, and recurrence interval. The catalogs will also allow us to explore possible scaling relationships, such as that between moment release and event duration.

We use the Network Inversion Filter (NIF) [Segall and Matthews,1997; McGuire and Segall, 2003; Miyazaki et al.,2006] to perform our time-dependent slip inversions. We generate the Green’s functions for our inversions using the PyLith finite element code [Aagaard et al., 2013] to allow consideration of elastic property variations provided by the New Zealand-wide seismic velocity model [Eberhart-Phillips et al., 2010]. Previous results [Williams and Wallace, 2015; 2018] have shown that SSE inversions that consider elastic heterogeneity provide significantly different results than inversions based on elastic half-space solutions. Incorporating these effects significantly improves the accuracy and reliability of our time-dependent inversions. Our inversions also include recent absolute pressure gauge (APG) data to constrain offshore vertical movement during a recent SSE observed in 2014. The catalog represents the most comprehensive to date for the Hikurangi Margin, and the usage of APG data and consideration of elastic heterogeneity effects will provide the best possible constraints on the predicted slip distributions.