Décollement geometry controls on shallow Very Low Frequency Earthquakes

Yoshitaka Hashimoto (Kochi University), Shigeyuki Sato (Kochi University), Gaku Kimura (JAMSTEC), Masataka Kinoshita (ERI, University of Tokyo), Ayumu Miyakawa (AIST), Gregory F. Moore (University of Hawai‘i), Masaru Nakano (JAMSTEC), Kazuya Shiraishi (JAMSTEC) and Yasuhiro Yamada (Kyushu University)

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 and Yasuhiro Yamada, Scientific Reports (2022) https://doi.org/10.1038/s41598-022-06645-2

 Slow earthquakes are widely observed in subduction zones in the circum-Pacific area. Slow earthquake is a slip along subduction plate interface much slower than regular earthquakes and faster than normal plate convergence rate. Understanding of the mechanism of slow earthquake can be connected to understandings of large earthquakes, which could lead to mitigations of future disaster by large earthquakes. A heterogenetic distributions of material properties and/or stress on subduction plate interfaces are proposed for a possible mechanism of slow and fast slips. The natural example of the heterogenetic distribution, however, has not been examined yet.

 In this study, a geometry of the shallow subduction plate interface was obtained from the 3D seismic survey data in Nankai Trough off Kii Peninsula, and combined it with the regional stress state, distributions of slip and dilation tendencies on the plate interface were mapped. In the result, the high slip tendency area distributes in NNE-SSW trend. Shallow Very Low Frequency Earthquakes (VLFE: one of slow earthquakes) are observed in the same area, which aligned mostly parallel to the high slip tendency area. This consistency suggests that the high slip tendency area contributes the VLFE occurrence.

 The slip and dilation tendencies were estimated only from the geometry of plate interface and the regional stress state without any material properties. Therefore, the parallel distribution between high slip tendency area and VLFE suggests that the geometry of plate interface is the primal control of the VLFE excitations.

left:3D seismic survey area in Nankai Trough off Kii Peninsula (red line), VLFE distribution (red area), and area of the examined plate interface (black box); center: Distribution of slip tendency on shallow subduction plate interface; right: VLFE distribution in the study area. NNE-SSW alignments of VLFE are observed.