Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

S (Solid Earth Sciences ) » S-SS Seismology

[S-SS12] Crustal Structure

Thu. May 30, 2019 1:45 PM - 3:15 PM A05 (TOKYO BAY MAKUHARI HALL)

convener:Kazuo Nakahigashi(Tokyo University of Marine Science and Technology), Chairperson:Yoshio Murai(Hokkaido University), Genti Toyokuni(東北大学)

2:30 PM - 2:45 PM

[SSS12-04] Seismic imaging of the eastern Japan forearc region using S-net data

*Genti Toyokuni1, Dapeng Zhao1, Naoki Uchida1, Takashi NAKAYAMA1 (1.RCPEVE, Tohoku Univ.)

Keywords:Seismic tomography, Offshore Northeast Japan, S-net, 3-D velocity structure

The great 2011 Tohoku-oki earthquake (Mw 9.0) occurred off the Pacific coast of Northeast Japan, where the Pacific plate is subducting beneath the Okhotsk plate. The S-net (the Seafloor observation network for earthquakes and tsunamis along the Japan Trench), initiated in 2016, is a large-scale, permanent, ocean-floor seismograph network with cabled 150 stations, which covers a wide oceanic region off Northeast Japan (Kanazawa, 2013). In this study, we aim to reveal the 3-D seismic velocity structure beneath the forearc region covered by the S-net.

We carefully picked 3754 first P-wave arrival times of 63 local earthquakes (M3.5–6.2) in the Tohoku forearc region from the continuous S-net records. Then, the newly picked data are integrated with the existing arrival-time data (Zhao et al., 2012) of 360 teleseismic and 1,180 local earthquakes recorded at 3,205 Hi-net stations on the Japanese land areas. These combined data are inverted to obtain a new 3-D P-wave velocity (Vp) model beneath the entire Northeast Japan arc by using the seismic tomography method of Zhao et al. (2012).

In this work we focus on the obtained 3-D images at depths < 40 km below the region covered by the S-net. The major results are summarized as follows.
(1) Prominent low-Vp anomalies are revealed in the off-Iwate and off-Fukushima areas. These features are consistent with those revealed by previous works (e.g., Zhao et al., 2011; Huang & Zhao, 2013; Liu and Zhao, 2018), indicating that our hand-picked arrival-time data are quite accurate and robust.
(2) A significant high-Vp anomaly is revealed along the Japan Trench especially beneath the off-Miyagi region where the 2011 Tohoku-oki earthquake (Mw 9.0) occurred, which may reflect that the sedimentary layer is very thin above the subducting Pacific plate.

Huang, Z., D. Zhao (2013) JAES, 70–71, 160–168.
Kanazawa, T. (2013) Underwater Technology Symposium (UT), 2013 IEEE International.
Liu, X., D. Zhao (2018) Science Advances 4, eaat4396.
Zhao, D. et al. (2011) GRL 38, L17308.
Zhao, D. et al. (2012) GJI 190, 816–828.