Décollement geometry controls on shallow very low frequency earthquakes

Yoshitaka Hashimoto; Shigeyuki Sato; Gaku Kimura; Masataka Kinoshita; Ayumu Miyakawa; Gregory F Moore; Masaru Nakano; Kazuya Shiraishi; Yasuhiro Yamada

doi:10.1038/s41598-022-06645-2

Décollement geometry controls on shallow very low frequency earthquakes

Sci Rep. 2022 Feb 17;12(1):2677. doi: 10.1038/s41598-022-06645-2.

Authors

Yoshitaka Hashimoto¹, Shigeyuki Sato², Gaku Kimura³, Masataka Kinoshita⁴, Ayumu Miyakawa⁵, Gregory F Moore⁶, Masaru Nakano³, Kazuya Shiraishi³, Yasuhiro Yamada⁷

Affiliations

¹ Department of Global Environment and Disaster Prevention, Faculty of Science and Technology, Kochi University, Akebonocho 2-5-1, Kochi, 780-8520, Japan. hassy@kochi-u.ac.jp.
² Department of Global Environment and Disaster Prevention, Faculty of Science and Technology, Kochi University, Akebonocho 2-5-1, Kochi, 780-8520, Japan.
³ Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan.
⁴ Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan.
⁵ Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba City, Ibaraki, 305-8567, Japan.
⁶ Department of Earth Sciences, University of Hawai'i, Mānoa, 1680 East-West Road, Honolulu, HI, 96822, USA.
⁷ Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University, Motooka 774, Fukuoka, 819-0395, Japan.

Abstract

Recent studies have documented the occurrence of shallow very low frequency earthquakes (VLFE) in subduction zones. The heterogeneity of the materials or stresses that act on the plate interface results in the variable slip rate. Stress on the décollement can be controlled by the décollement geometry and the regional stress, which is also able to control the material properties. We determined the distribution of stress along the shallow portion of the décollement in the Nankai Trough using a three-dimensional (3D) seismic survey and regional stress analysis to construct maps of normalized slip tendency (T_s') and dilation tendency (T_d). Alignments of VLFEs trend parallel to the trends of [Formula: see text] and [Formula: see text]. On the other hand, very low [Formula: see text] and [Formula: see text] areas probably act as barriers that limit the number of VLFEs that can migrate towards the trench. Because the [Formula: see text] and [Formula: see text] distributions are derived only from the décollement geometry and the regional stress without incorporating any data on sediment properties, the consistency between the trends suggests that the décollement geometry is the primary control on VLFE activity.