Seismic Reflection Character of the Hikurangi Subduction Interface, New Zealand, in the Region of Repeated Gisborne Slow Slip Events
Abstract
Changes in reflection character and geometry of the Hikurangi subduction interface offshore the east coast of North Island, New Zealand, observed in deep (8-12 s twt) 2D prestack time migrated seismic reflection data may relate to changing seismogenic properties and can potentially help define locations of slow slip. Slow slip events have been recorded on the Hikurangi subduction interface in the Gisborne area, every two years since the installation of continuous Global Positioning System (CGPS) instruments in 2002. Preliminary inversion of CGPS displacements suggest the slow slip occurs on the subduction interface with a down-dip limit of 15 km. However, the other dimensions of the slow sliding segment are poorly constrained. The subduction interface offshore Gisborne includes subducting seamount asperities (capable of building up seismic stress) coupled with fluid-rich subduction erosion material (increased pore-pressures promote more stable slip) and may potentially provide an explanation why slow slip is constrained within this area. Margin perpendicular profiles image the subduction interface beneath the minor accretionary wedge and outer arc high as a narrow band of reflectivity overlying a subducting seamount on the down-going plate. Landward of the subducting seamount the subduction interface is defined as the top-most reflector of a 1 s wide band of high amplitude reflectivity which terminates up-dip against the seamount. This seismic character terminates down-dip when the subduction interface steps down to a lower level of 15 km at a distance of ~20 km offshore, coincident with the CGPS constrained down-dip limit of slow slip. The step-up in decollement level and introduction of a wedge of high amplitude reflections on the down-going plate is likely to be related to the accumulation of fluid-rich material that has been eroded from the accretionary wedge and/or overlying plate due to seamount subduction. The mapped region of the subduction interface with this reflection character is interpreted to potentially facilitate slow slip and has been inverted with the CGPS displacements for slow slip events in 2002, 2004 and 2006 to model the amount of slip on this surface during each event.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T23A1995B
- Keywords:
-
- 1242 Seismic cycle related deformations (6924;
- 7209;
- 7223;
- 7230);
- 3025 Marine seismics (0935;
- 7294);
- 3060 Subduction zone processes (1031;
- 3613;
- 8170;
- 8413);
- 7240 Subduction zones (1207;
- 1219;
- 1240);
- 8170 Subduction zone processes (1031;
- 3060;
- 3613;
- 8413)