Present-day horizontal and vertical crustal motion of New Zealand
Abstract
We present horizontal velocities in a well-defined reference frame from ~800 campaign GPS and ~120 continuous GPS stations in New Zealand, and relative vertical velocities from ~120 continuous GPS stations, by linear fits to daily GPS coordinate solutions. We use data spanning 1996 through 2012, though velocities in much of the South Island omit data from mid-2009 onwards to avoid major coseismic and postseismic effects. The period 1996-2012 (1996-2009 in the South Island) was free of major earthquakes, with the exception of two earthquakes south and west of the South Island whose coseismic and postseismic effects can be corrected. The resulting velocities can therefore be taken as average interseismic velocities, though admittedly only estimated over a 13-16 year time period. In the southern and eastern North Island and northeasternernmost South Island, many time series are non-linear due to slow slip events (SSEs) occurring on the Hikurangi subduction interface. Some of the velocities derived from these time series will be biased because they don't sample multiple repeats of the SSEs. We compare present-day vertical rates around the coastline with geological estimates of long-term (mainly 125,000 year) rates. There is general consistency except in the region affected by strong coupling on the subduction interface, where the present-day rates are as much as an order of magnitude faster and of opposite sign to the long-term rates. When we compare the observed vertical rates with rates predicted by a subduction-coupling model based largely on campaign GPS horizontal velocities we find general agreement, except for a possible uniform bias of ~1 mm/yr. The present-day vertical rates are fast enough (up to ~4 mm/yr subsidence) that we expect them to contribute significantly to the effects of future relative sea-level rise in the eastern and southern North Island, at least until such time as the interseismic strain is relieved by a major earthquake on the subduction megathrust. In the spirit of the SCEC Crustal Motion Map of California, we are making these New Zealand crustal velocity fields publicly available.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.G22B..01B
- Keywords:
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- 1209 GEODESY AND GRAVITY / Tectonic deformation;
- 7230 SEISMOLOGY / Seismicity and tectonics;
- 8158 TECTONOPHYSICS / Plate motions: present and recent