Revealing Hidden Deformation Sources in New Zealand: a Novel Inversion of GPS Data for Non-Prescriptive Physics-Based Surface Forces and High-Precision Strain Rates
Abstract
Monitoring strain accumulation in active deformation zones is vital for studying and preparing for earthquake hazards. New Zealand straddles the complicated boundary between the obliquely converging Australian and Pacific plates. The motion is accommodated largely along the Alpine Fault in the south, through the Marlborough fault system and onto the Hikurangi trench in the north. In addition, a significant component of the motion is distributed on smaller, poorly characterized faults. Dimitrova et al. (2012) showed that the vertical derivatives of horizontal stress (VDoHS) rates are a substantially higher resolution expression of subsurface sources of ongoing deformation than the GPS velocities or GPS derived strain rates. We expand this method to solve the horizontal force balance equations for the VDoHS in 2-D to obtain the highest possible resolution picture of the surface deformation pattern in New Zealand. We invert GPS data from campaign GPS observations spanning from 1995 to 2012 for the VDoHS that best fit the GPS velocities, without prescribing sources or zones of deformation, while fully accounting for the physics of the problem. Using the VDoHS rates we identify (1) areas of deformation due to well-known active faults, (2) areas of poorly characterized deformation, e.g. deformation along faults without slip rate information mapped from palaeo-seismicity, (3) areas of previously unknown deformation, potentially on hidden faults, and (4) areas undergoing post-seismic deformation. The VDoHS are integrated to produce the highest resolution to-date maps of strain rates. We identify an area of extensional areal strain between the Alpine fault and the Main Divide of the central Southern Alps indicating possible gravitational collapse of the Southern Alps. Relationships between the VDoHS and strain rates allow us to calculate the variation in fault slip rate and locking depth for the identified faults, and we show selected results for the Alpine Fault and the smaller, previously-uncharacterized faults. The latter account for 0-50% of the plate motion depending on location (detailed results will be shown in accompanying by Haines et al.). We characterize the transfer of slip further north through the Marlborough and Wellington Fault Systems. In the North Island,we highlight the deformation related to upper plate faults, such as the Wairarapa fault, as well as signals related to the Hikurangi subduction interface, the Taupo Volcanic Zone and broad-scale extension within the Raukumara Peninsula region.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.G41A0920D
- Keywords:
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- 1209 GEODESY AND GRAVITY Tectonic deformation;
- 1240 GEODESY AND GRAVITY Satellite geodesy: results;
- 8150 TECTONOPHYSICS Plate boundary: general;
- 8168 TECTONOPHYSICS Stresses: general