HR: 10:50h
AN: S42B-03    [Abstracts]
TI: Aseismic Slip on the Hikurangi Subduction Zone, New Zealand.
AU: * Douglas, A
EM: douglaanne@student.vuw.ac.nz
AF: School of Earth Sciences , Victoria University of Wellington, PO Box 600, Wellington, 6015 New Zealand
AU: Beavan, J
EM: j.beavan@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Wallace, L
EM: l.wallace@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Townend, J
EM: john.townend@vuw.ac.nz
AF: School of Earth Sciences , Victoria University of Wellington, PO Box 600, Wellington, 6015 New Zealand
AU: Smith, E
EM: euan.smith@vuw.ac.nz
AF: School of Earth Sciences , Victoria University of Wellington, PO Box 600, Wellington, 6015 New Zealand
AB: In October 2002, an aseismic slip event of 20--25 mm magnitude was observed on two continuous GPS (CGPS) instruments near Gisborne, North Island, New Zealand. This event was the first of its kind to be documented with CGPS in New Zealand. It occurred over approximately ten days and is interpreted to be the result of about 20 cm of reverse slip on the Hikurangi subduction interface offshore of the north-eastern North Island. Since October 2002, smaller aseismic slip events (of 4--8 mm magnitude) have been recorded on CGPS stations near Gisborne, and Hastings to the south. Using campaign GPS data from the region we are attempting to better constrain the Gisborne 2002 event and quantify the distribution, frequency and magnitude of silent earthquakes on the northern Hikurangi subduction margin. We have analysed nearly ten years of regional campaign GPS records (1995--2004) in conjunction with recent CGPS and seismic data. We use station position time-series as the primary means of identifying transient behaviour, as would be expected from an aseismic slip event. The large October 2002 aseismic slip event is not obviously discernible in any of the campaign time-series, indicating that such events may occur on a more regular basis than previous geodetic data have revealed. Work is underway to investigate a possible correlation between the October 2002 aseismic slip event and an anomalous seismic swarm above the Hikurangi subduction margin offshore from Gisborne. We also intend to analyse broadband seismic records for low-frequency tremor that may be associated with the aseismic slip events. By combining recent, high-quality CGPS data with campaign data spanning ten years and regional seismicity data, we are able to re-evaluate existing models of deformation for the northern Hikurangi margin, and propose new models based on the known occurrence of aseismic slip. Greater understanding of the role of aseismic slip in accommodating relative plate motion on the northern Hikurangi margin will lead to more accurate assessment of seismic hazard posed by this subduction zone to New Zealand.
UR: http://www.geonet.org.nz
DE: 7230 Seismicity and seismotectonics
DE: 1200 GEODESY AND GRAVITY
DE: 1242 Seismic deformations (7205)
DE: 1299 General or miscellaneous
SC: Seismology [S]
MN: 2004 AGU Fall Meeting