Wide-angle OBS velocity structure along the SAHKE transect, lower North Island, New Zealand
Abstract
As part of the Seismic Array HiKurangi Experiment (SAHKE), we acquired wide-angle reflection / refraction seismic data using ocean bottom seismometers (OBSs) along a transect across the southern North Island of New Zealand, where the Hikurangi Plateau subducts eastward beneath Wellington. The SAHKE project was designed to investigate the physical parameters controlling locking at the plate interface beneath the southern North Island and characterize slip processes in a major segment of the Hikurangi system. We deployed 16 OBSs with 5 km spacing off the east coast and 4 OBSs with 10 km spacing off the west coast. Controlled airgun sources were shot at every 100 m along a 350 km onshore-offshore transect. Although data from OBSs at shallow depths (~100 m) contain large amplitude ambient noise, first arrivals from the airgun sources can be traced up to over 100 km offset on record sections of most OBSs. We applied first-arrival travel-time inversion in order to obtain P-wave velocity structure along the 80 km-long OBS profile off the east coast. The velocity structure to ~20 km depth was resolved, and the down going slab was clearly imaged. We picked travel times of reflected waves, and projected reflection points by applying a travel-time migration method using the velocity model. Reflection interfaces including the plate interface, the Moho interface of the Hikurangi Plateau and a possible interface between the upper and lower crusts are imaged. The plate interface reflections in the east appear smooth as opposed to its rough appearance in the west of the profile. This may reflect large structural heterogeneity in the overriding crust as its thickness increases landward.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.T11C..05M
- Keywords:
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- 7270 SEISMOLOGY / Tomography;
- 8170 TECTONOPHYSICS / Subduction zone processes