Validating a full-waveform inversion velocity model at the north Hikurangi subduction margin using IODP drilling data

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Author(s): Bell, Rebecca E.; Gray, Melissa; Morgan, Joanna V.; Henrys, Stuart A.; Barker, Daniel H. N.; Bangs, Nathan L.; Barnes, Philip; Wallace, Laura M.; Saffer, Demian M.; Petronotis, Katerina E.
International Ocean Discovery Program (IODP), Drilling Expedition 375 Scientific Team
Author Affiliation(s): Primary:
Imperial College London, Department of Earth Science and Engineering, London, United Kingdom
GNS Science, New Zealand
University of Texas at Austin, United States
National Institute of Water & Atmospheric Research, New Zealand
Pennsylvania State University, United States
International Ocean Discovery Program, United States
Volume Title: AGU 2018 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2018; American Geophysical Union 2018 fall meeting, Washington, DC, Dec. 10-14, 2018. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The north Hikurangi subduction plate boundary, offshore the east coast of northern New Zealand, exhibits a range of slip behaviors, including shallow slow slip events at depths of <2 km to 15 km. Although the shallow structure is clearly imaged with seismic reflection data, these data provide limited information about physical properties of the sediments being subducted, the overriding plate and the plate boundary fault zone itself. Full-waveform inversion (FWI) is an imaging technique which incorporates the full seismic wavefield rather than just travel times to produce seismic velocity models with a resolution an order of magnitude better than conventional models. In FWI, a source wavelet, derived from the observed data, is propagated through a smooth starting velocity model, and a residual is calculated between the synthetic and true seismic data. A back-propagated residual is used to update the velocity model so that the match between the real and synthetic waveforms improves. Here, we have used 2D FWI of streamer data to resolve the P-wave velocity structure of the north Hikurangi margin in the region of IODP drilling, up to 2 km below the sea-bed. Drilling of the north Hikurangi margin to depths of up to ∼1 km took place in 2017-2018 during International Ocean Discovery Program (IODP) Expeditions 372 and 375, which included sampling across a shallow splay fault. Logging while drilling (LWD), wireline and core data were collected, providing an excellent opportunity to test the FWI velocity model. Sonic logging data show a good match with the FWI velocities at the drill sites, particularly in terms of improvements to velocity gradients over the starting velocity model. The validated FWI model reveals fine-scale geological features, including fault-zones associated with low P-wave velocities, which may represent damage zones that act as fluid conduits. In 2017-2018 new 3D seismic data was collected optimally for 3D FWI in a joint UK, US, Japan and New Zealand funded venture. These data will allow extrapolation of rock physical properties away from drill sites in three-dimensions in the future.
Year of Publication: 2018
Research Program: IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; Crust; Expedition 372; Expedition 375; Fault zones; Faults; Hikurangi Margin; International Ocean Discovery Program; Lithosphere; Oceanic crust; Oceanic lithosphere; Pacific Ocean; Plate tectonics; Seismicity; Seismotectonics; South Pacific; Southwest Pacific; Subduction; Subduction zones; Tectonics; West Pacific
Coordinates: S385830 S384330 E1790800 E1782830
S390300 S384100 E1791600 E1783500
Record ID: 2019050430
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