Along-strike variation of incoming plate to the Hikurangi seismogenic zone: results from Seismogenesis at Hikurangi Integrated Research Experiment (SHIRE)
Abstract
The Hikurangi margin is one of the best subduction zones to investigate factors controlling slip behavior in a shallow megathrust because onshore-offshore earthquake and geodetic monitoring reveals a clear along-strike transition from a stick-slip dominated margin (southern Hikurangi) to creep and slow slip dominated margin (northern Hikurangi). From October to November 2017, an international large-scale active-source seismic survey was carried out as a principal component of Seismogenesis at Hikurangi Integrated Research Experiment (SHIRE), which aims to assess the physical mechanisms controlling megathrust slip behavior. Wide-angle OBS data and multichannel seismic reflection data were acquired along four major profiles during the survey: two E-W profiles at the northern (Line 1) and the southern (Line 2) Hikurangi margin and two N-S profiles along the forearc shelf (Line 3) and across the Hikurangi Plateau east of the trench (Line 4). For data acquisition of the wide-angle seismic data, 114 OBS from JAMSTEC were deployed and recovered by R/V Tangaroa, and R/V Marcus G. Langseth shot the 6,600 cu. in. airgun array. In this study, we present observed data of Line 4, a 490 km-long profile, along which 30 OBS were deployed. Overall quality of the OBS data is good. Refraction phases from the uppermost mantle (Pn) and strong reflection phases from the Moho (PmP) are clearly observed at most of the OBS. Pn phases become first arrivals at 35km offsets and 60-70 km offsets at OBSs situated at the northern and southern part of the profile, respectively. These observations indicate a variation of a thickness of the incoming crust. A preliminary velocity image from forward travel-time modeling shows that the depth of the Moho is shallower than 20 km below sea level throughout the profile and tends to be deeper toward the south. Although further analysis is required, the tentative structural model is consistent with a result from a previous active-source profile crossing the southern Hikurangi margin, but the crustal thickness is found to be less than that of the subducted Hikurangi Plateau ( 35km thick) which is deduced from an earthquake study.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T51I0283K
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITYDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8170 Subduction zone processes;
- TECTONOPHYSICSDE: 8185 Volcanic arcs;
- TECTONOPHYSICS