Resistivity image of the Philippine Sea Plate around the 1944 Tonankai earthquake zone deduced by Marine and Land MT surveys

Takafumi Kasaya,Kiyoshi Baba,Kiyoshi Suyehiro,Hisashi Utada,Hitoshi Mikada,Tada-Nori Goto

doi:10.1186/bf03351817

Abstract

Abstract The Nankai Trough is an active convergent region in southwest Japan and mega-thrust earthquakes have repeatedly occurred in some areas of its plate-boundary interface. Generation of mega-thrust earthquakes is inferred to be related to the existence of water. The resistivity structure is very sensitive to the existence of water. For that reason, it is important to obtain the resistivity image around the rupture area of mega-thrust earthquakes. We carried out land and marine magnetotelluric surveys in the Kii Peninsula and the offshore Kii Peninsula where the 1944 Tonankai earthquake occurred. We constructed a 2D resistivity model using an inversion technique. The modeled resistivity structure portrayed the Philippine Sea Plate as a resistive region. However, its resistivity becomes more conductive as the plate subducts, showing 10 Ω-m around the down-dip limit. These characteristics are considered to relate to the water. Therefore, we infer that water might control the generation of mega-thrust earthquakes.

Highlights

Nakanishi et al (2002) performed a wideangle seismic survey and constructed a crust and uppermost mantle P-wave velocity model across the Nankai Trough around the Tonankai earthquake rupture zone
The Nankai Trough is located offshore of the Kii Peninsula and is an active convergent region in southwest Japan
Multi-channel seismic (MCS) and ocean bottom seismometer (OBS) reflection surveys were carried out around the Nankai trough region to elucidate what occurred on the thrust earthquake rupture zone

Summary

Introduction

Nakanishi et al (2002) performed a wideangle seismic survey and constructed a crust and uppermost mantle P-wave velocity model across the Nankai Trough around the Tonankai earthquake rupture zone. Magneto-telluric (MT) surveys have been carried out to obtain electrical resistivity images of the subduction zone. In the ‘Electro Magnetic Study of the Lithosphere and Asthenosphere Beneath’ the Juan de Fuca Plate (EMSLAB) project, seafloor and land electromagnetic (EM) surveys were carried out in the area of the Juan de Fuca subduction system.

Results

Conclusion