Heterogeneous structure around the rupture area of the 2003 Tokachi-oki earthquake (Mw = 8.0), Japan, as revealed by aftershock observations using Ocean Bottom Seismometers

Yuya Machida, Masanao Shinohara, Tetsuo Takanami, Yoshio Murai, Tomoaki Yamada, Naoshi Hirata, Kiyoshi Suyehiro, Toshihiko Kanazawa, Yoshiyuki Kaneda, Hitoshi Mikada, Shin'ichi Sakai, Tomoki Watanabe, Kenji Uehira, Narumi Takahashi, Minoru Nishino, Kimihiro Mochizuki, Takeshi Sato, Ei'ichiro Araki, Ryota Hino, Kouichi Uhira & 2 others Hajime Shiobara, Hiroshi Shimizu

Research output: Contribution to journalArticle

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Abstract

Large earthquakes have repeatedly occurred in the area off southeastern Hokkaido Island, Japan, as the Pacific Plate subducts beneath the island, which is on the North American Plate. The most recent large earthquake in this area, the 2003 Tokachi-oki earthquake (Mw = 8.0), occurred on September 26, 2003. In order to investigate aftershock activity in the rupture area, 47 Ocean Bottom Seismometers (OBSs) were quickly deployed after the main shock. In the present study, we simultaneously estimate the hypocenters and 3-D seismic velocity models from the P- and S-wave arrivals of the aftershocks recorded by OBSs. The subducting plate is clearly imaged as a northwest dipping zone in which Vp is greater than 7 km/s, and the relocated hypocenters also show the subducting Pacific Plate. The aftershock distribution reveals that the dip angle of the plate boundary increases abruptly around 90 km from the Kuril Trench. The bending of the subducting plate corresponds to the southeastern edge of the rupture area. The island arc crust on the overriding plate has P-wave velocities of 6-7 km/s and a Vp/Vs of 1.73. A region of Vp/Vs greater than 1.88 was found north of the epicenter of the main shock. The depth of the high Vp/Vs region extends about 10 km upward from the plate interface. The plate boundary just below the high Vp/Vs region has the largest slip at the main rupture. A high Vp anomaly (~ 7.5 km/s) is found in the island arc crust in northeast part of the study area, which we interpret as a structural boundary related to the arc-arc collisional tectonics of the Hokkaido region, as the rupture of the main shock terminated at this high Vp region. We suggest that the plate interface geometry and the trench-parallel velocity heterogeneity in the landward plate are principal factors in controlling the rupture area of the main shock.

Original languageEnglish
Pages (from-to)164-176
Number of pages13
JournalTectonophysics
Volume465
Issue number1-4
DOIs
Publication statusPublished - Feb 20 2009

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ocean bottom seismometer
ocean bottom
seismographs
aftershock
rupture
Japan
earthquakes
earthquake
Pacific plate
plate boundary
P-wave
island arc
trench
crust
shock
North American plate
island arcs
seismic velocity
earthquake epicenter
P waves

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Earth-Surface Processes

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Heterogeneous structure around the rupture area of the 2003 Tokachi-oki earthquake (Mw = 8.0), Japan, as revealed by aftershock observations using Ocean Bottom Seismometers. / Machida, Yuya; Shinohara, Masanao; Takanami, Tetsuo; Murai, Yoshio; Yamada, Tomoaki; Hirata, Naoshi; Suyehiro, Kiyoshi; Kanazawa, Toshihiko; Kaneda, Yoshiyuki; Mikada, Hitoshi; Sakai, Shin'ichi; Watanabe, Tomoki; Uehira, Kenji; Takahashi, Narumi; Nishino, Minoru; Mochizuki, Kimihiro; Sato, Takeshi; Araki, Ei'ichiro; Hino, Ryota; Uhira, Kouichi; Shiobara, Hajime; Shimizu, Hiroshi.

In: Tectonophysics, Vol. 465, No. 1-4, 20.02.2009, p. 164-176.

Research output: Contribution to journalArticle

Machida, Y, Shinohara, M, Takanami, T, Murai, Y, Yamada, T, Hirata, N, Suyehiro, K, Kanazawa, T, Kaneda, Y, Mikada, H, Sakai, S, Watanabe, T, Uehira, K, Takahashi, N, Nishino, M, Mochizuki, K, Sato, T, Araki, E, Hino, R, Uhira, K, Shiobara, H & Shimizu, H 2009, 'Heterogeneous structure around the rupture area of the 2003 Tokachi-oki earthquake (Mw = 8.0), Japan, as revealed by aftershock observations using Ocean Bottom Seismometers', Tectonophysics, vol. 465, no. 1-4, pp. 164-176. https://doi.org/10.1016/j.tecto.2008.11.009
Machida, Yuya ; Shinohara, Masanao ; Takanami, Tetsuo ; Murai, Yoshio ; Yamada, Tomoaki ; Hirata, Naoshi ; Suyehiro, Kiyoshi ; Kanazawa, Toshihiko ; Kaneda, Yoshiyuki ; Mikada, Hitoshi ; Sakai, Shin'ichi ; Watanabe, Tomoki ; Uehira, Kenji ; Takahashi, Narumi ; Nishino, Minoru ; Mochizuki, Kimihiro ; Sato, Takeshi ; Araki, Ei'ichiro ; Hino, Ryota ; Uhira, Kouichi ; Shiobara, Hajime ; Shimizu, Hiroshi. / Heterogeneous structure around the rupture area of the 2003 Tokachi-oki earthquake (Mw = 8.0), Japan, as revealed by aftershock observations using Ocean Bottom Seismometers. In: Tectonophysics. 2009 ; Vol. 465, No. 1-4. pp. 164-176.
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AU - Machida, Yuya

AU - Shinohara, Masanao

AU - Takanami, Tetsuo

AU - Murai, Yoshio

AU - Yamada, Tomoaki

AU - Hirata, Naoshi

AU - Suyehiro, Kiyoshi

AU - Kanazawa, Toshihiko

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AU - Mikada, Hitoshi

AU - Sakai, Shin'ichi

AU - Watanabe, Tomoki

AU - Uehira, Kenji

AU - Takahashi, Narumi

AU - Nishino, Minoru

AU - Mochizuki, Kimihiro

AU - Sato, Takeshi

AU - Araki, Ei'ichiro

AU - Hino, Ryota

AU - Uhira, Kouichi

AU - Shiobara, Hajime

AU - Shimizu, Hiroshi

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