Japan Geoscience Union Meeting 2023

Presentation information

[E] Online Poster

S (Solid Earth Sciences ) » S-EM Earth's Electromagnetism

[S-EM14] Electric, magnetic and electromagnetic survey technologies and scientific achievements

Wed. May 24, 2023 1:45 PM - 3:15 PM Online Poster Zoom Room (4) (Online Poster)

convener:Kiyoshi Baba(Earthquake Research Institute, The University of Tokyo), Tada-nori Goto(Graduate School of Science, University of Hyogo), Yuguo Li(Ocean University of China), Wiebke Heise(GNS Science, PO Box 30368, Lower Hutt, New Zealand)

On-site poster schedule(2023/5/23 17:15-18:45)

1:45 PM - 3:15 PM

[SEM14-P13] Plate coupling at the northern Hikurangi margin: new results from magnetotellurics

*Wiebke Heise1, Ted Bertrand1, Grant Caldwell1, Yasuo Ogawa2, Stephen Bannister1, Stewart Bennie1, Rory Hart1, Neville Palmer1, Kuo Hsuen Tseng2,4, Masato Fukai2,5, Masaki Ishikawa2, Kaori Seki2,6, Tatsuji Nishizawa2,7, Jack McGrath3 (1.GNS Science, PO Box 30368, Lower Hutt, New Zealand, 2.Volcanic Fluid Research Center, Tokyo Institute of Technology, Tokyo, Japan, 3. School of Earth and Environment, University of Leeds, UK, 4.Sumiko Resources Exploration & Development Co., Ltd., Japan, 5.Nittetsu Mining Consultants Co., Ltd., Japan, 6.Kokusai Kogyo Co., Ltd.,Japan, 7.Mount Fuji Research Institute, Yamanashi Prefectural Government, Japan)

Keywords:subduction, magnetotellurics, plate coupling, Hikurangi margin

At the Hikurangi subduction margin, on the east coast of New Zealand’s North Island, the inter plate coupling changes from locked in the south to weakly coupled in the north. In the weakly coupled area, a complicated pattern of slip behaviour (and resistivity) is observed. The change in coupling and slip behaviour is attributed to structural and physical changes at the plate interface, in particular the fluid content of the subduction interface shear zone.
3-D inversion modelling of magnetotelluric (MT) data from a 300 km long segment of the Hikurangi margin shows that the electrical resistivity of the subduction interface shear zone is heterogenous, however, the degree of heterogeneity decreases from north to south. The resistivity heterogeneities correlate well with the distribution of near-plate interface seismicity, vp/vs values and the pattern of areal stain rate derived from GPS data and are consistent with variations in the fluid content of the subduction interface shear zone. In the northern part of this segment, conductive areas interpreted to be fluid rich occur where seismicity is sparse, vp/vs ratios are high and the areal strain rate is extensional. In contrast, where the areal strain rate is compressional the plate interface is more resistive, and seismicity is more abundant suggesting inter-plate friction is greater. In the south, the resistivity of the plate interface is more homogenous, and the overlying plate is more resistive at shallower levels than in the north. Our analysis further supports the hypothesis that the fluid and/or hydrated clay content of the subduction interface shear zone is correlated with plate coupling.