Modeling of Slow Slip Events at the Hikurangi Subduction Margin
Abstract
Slow slip events (SSEs) occur along nearly the entire Hikurangi subduction margin adjacent to the North Island, New Zealand. Long duration (1-2 years), deep (40- 60 km depth), large events (equivalent to Mw ~7.0) occur at the southern Hikurangi margin, while shallow (10-15 km depth), short (1-2 weeks), smaller events (equivalent to Mw ~6.5) occur at the northern and central Hikurangi margin. A recently-initiated shallow event (Castle Point) lies further to the south than previous shallow events and appears to be rupturing a portion of the plate interface that was previously thought to be locked. Since 2000, three major slow slip events have been identified at the southern Hikurangi margin; the 2003 Kapiti SSE, the 2004/2005 Manawatu SSE, and the 2007/2008 Kapiti SSE (which ended in early 2009). A repeat of the 2004/2005 Manawatu event is presently underway. In some cases, these SSEs may have triggered moderate seismicity within the subducting Pacific plate (e.g., Reyners and Bannister, 2007). To date, all of the inferred slip distributions for the SSEs have been obtained using elastic half-space dislocation models. Numerous recent studies of coseismic displacement fields have shown that variations in elastic properties and surface topography can influence the predicted deformation. In our initial work, we used a finite element model to evaluate the influence of material property variations on the predicted surface deformation field. Elastic properties were assigned based on a seismic velocity model, and slip distributions inferred from an elastic half-space model were applied. When compared to the elastic half- space model, we found that the heterogeneous models generally predict larger amounts of surface deformation, indicating that the half-space models may be overestimating the amount of slip. As the next phase in our study, we are using finite element models that include material property variations and topography to generate Green's functions for use in an inversion. In this study, we estimate the slip distributions for the 2010 Gisborne event (northern part of the margin) and the ongoing Castle Point event (southern part of the margin). The inversion work is the first step in an attempt to understand the factors controlling SSE occurrence along the Hikurangi Margin. We have also begun initial modeling of fluid flow in the vicinity of a subducting seamount (as is inferred for the Gisborne SSE events) to evaluate the effects of variations in pore fluid pressure on fault frictional parameters.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.S23B2282W
- Keywords:
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- 0545 COMPUTATIONAL GEOPHYSICS / Modeling;
- 7240 SEISMOLOGY / Subduction zones;
- 8118 TECTONOPHYSICS / Dynamics and mechanics of faulting