GPS Measurements of Interseismic,Coseismic, and Postseismic Deformation in Puysegur Subduction Zone, New Zealand

Abstract:

A combination of continuous and campaign style geodetic measurements from sites on the South Island of New Zealand help us to constrain long-term and short-term deformation adjacent to the Puysegur subduction zone, offshore Fiordland, New Zealand. We update an elastic block model for the region that consists of an array of microplates bounded by active faults. We invert GPS velocities, and long-term fault slip rates and earthquake slip vectors for tectonic block rotations, fault coupling coefficients, and permanent block strain. Three large subduction interface earthquakes, 2003 Secretary Island (Mw 7.2), 2007 George Sound (Mw 6.7), and 2009 Dusky Sound (Mw 7.8) complicate interpretation of the GPS time series over the last decade in the Fiordland region. To deal with this, we also conduct time-dependent inversions for coseismic and postseismic slip in those earthquakes using TDefnode (McCaffrey, 2009), fitting the campaign and continuous GPS timeseries with the best-fitting coseismic and postseismic slip models for those events. We evaluate the interseismic coupling model for the Puysegur subduction zone in the context of the recent earthquakes, and in particular find that the source region of the Mw 7.8 Dusky Sound earthquake was interseismically coupled prior to 2009. Overall, the campaign and continuous GPS are well-fit by a partially locked subduction interface undergoing seismic and aseismic slip as well as distributed (likely permanent) deformation east of the main plate boundary fault.