EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Early results from 3D full-waveform inversion imaging of the slow slip region at the shallow Hikurangi Subduction Margin

Richard Davy1, Laura Frahm1, Rebecca Bell1, Joanna Morgan1, Ryuta Arai2, Nathan Bangs3, Stuart Henrys4, and Daniel Barker4
Richard Davy et al.
  • 1Imperial College London, Earth Science and Engineering, London, United Kingdom
  • 2Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
  • 3University of Texas Institute for Geophysics, Austin, TX, United States of America
  • 4GNS Science, Lower Hutt, New Zealand

The northern Hikurangi subduction margin hosts shallow slow-slip events (SSEs) and multiple historic tsunami earthquakes. The physical mechanisms and properties of the subduction interface which enable these dual modes of fault rupture remain largely enigmatic. In 2017-2018, the NZ3D seismic experiment was conducted offshore of Gisborne to image the structure of the overriding plate and subduction interface and infer the physical properties within the region of shallow SSEs. This experiment included a 3D seismic volume collected with four 6 km long streamers, ocean-bottom seismometers, and land stations. Early results from this project have demonstrated the successful application of 2D full-waveform inversion (FWI) to high frequencies along selected seismic inlines.

Here, we present the initial results of acoustic 3D FWI on the collected streamer data. Compared with 2D FWI, 3D FWI benefits from greater azimuthal coverage and the ability to relocate out-of-plane arrivals accurately but is restricted by increased calculation times and file sizes. Velocity models reveal a complex system of thrust faulting, horst and graben structures and bottom-simulating reflectors within the accretionary prism, as well as the decollement below the accretionary prism. Velocity inversions across the imaged thrust faults in the accretionary prism indicate the presence of fluids, potentially supporting the hypothesis that the subduction interface has elevated pore-fluid pressures, which are drained along some thrust faults. Velocity inversions are also observed across bottom-simulating reflectors, which indicate the presence of gas hydrates and free gas. Imaging the shallow decollement reveals an acoustically transparent region of low velocity contrasts in the inferred location of a subducted seamount.

How to cite: Davy, R., Frahm, L., Bell, R., Morgan, J., Arai, R., Bangs, N., Henrys, S., and Barker, D.: Early results from 3D full-waveform inversion imaging of the slow slip region at the shallow Hikurangi Subduction Margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6589,, 2022.