Active deformation of Sagami Bay triggered by approach of the Izu island arc
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ORIGINAL
Active deformation of Sagami Bay triggered by approach of the Izu island arc Ayanori Misawa 1
&
Juichiro Ashi 2 & Kenji Tara 3 & Mikiya Yamashita 1,4 & Masataka Kinoshita 4,5
Received: 23 December 2019 / Accepted: 28 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Sagami Bay in central Japan is known as the seismogenic and tsunamigenic zone of the 1703 and 1923 Kanto earthquakes that caused devastating damage in the Tokyo metropolitan area. However, the tsunamigenic structure within the frontal wedges of the subduction zone remains unresolved after the last disastrous events. In the present study, the detailed structural features of the shallowest structure of the Sagami Tectonic Line in Sagami Bay were revealed by seismic reflection, a deep-towed highresolution sub-bottom profiler, and swath bathymetry data. Based on our data, the middle segments of the Sagami Tectonic Line, which is distributed along the southwestern rim of the Miura Knoll, are considered highly likely to be an active fault that has been a repeatedly active feature. The trough-fill sediments of the south Sagami Bay are currently thought to be actively deformed by the compressive stress accompanying northwestward subduction of the tip of Izu-Ogasawara (Bonin) Arc crust on the Philippine Sea plate.
Introduction Since the Japan Islands coincide with multiple plates and plate boundaries, there are seismogenic and tsunamigenic zones, such as the Japan Trench and the Nankai and Sagami Troughs, which cause enormous damage to coastal cities. The Philippine Sea (PHS) plate is subducting beneath the southwest Japan arc along the Nankai and Sagami Troughs (Fig. 1a). In the Nankai Trough, accretionary complexes have been formed on the forearc region due to the subduction of the PHS plate (e.g., Moore et al. 1990), and the existence of a large number of active faults has been revealed in the forearc slope (e.g., Takahashi et al.
* Ayanori Misawa [email protected] 1
Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
2
Atmosphere and Ocean Research Institute, The University of Tokyo, Tokyo, Japan
3
JGI, Inc., Tokyo, Japan
4
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
5
Earthquake Research Institute, The University of Tokyo, Tokyo, Japan
2002; Gulick et al. 2004). Located on the south side of the trough, the Zenisu Ridge (Fig. 1a) is a topographic high with reverse faults distributed along its southern margin of the Zenisu Ridge. It is also suggested that one of the reverse faults reaches the Moho at the southern edge (Mazzotti et al. 2002). The Sagami Trough, which is located at the opposite side of the Nankai Trough over the IzuOgasawara (Bonin) Arc, is also a seismogenic and tsunamigenic zone adjacent to a metropolitan area of Japan. The fault distribution and geological structure of the Sagami Trough are not clear when compared with those of the Nankai Trough, however, and this area remains an
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