Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG52] Intraslab and intraplate earthquakes

Tue. May 22, 2018 10:45 AM - 12:15 PM A03 (Tokyo Bay Makuhari Hall)

convener:Saeko Kita(International Institute of Seismology and Earthquake Engineering, BRI), Tomohiro Ohuchi(Geodynamics Research Center, Ehime University), Thomas P. Ferrand (東京大学地震研究所, 共同), Keishi Okazaki(Japan Agency for Marine-Earth Science and Technology), Chairperson:Ferrand Thomas(ENS), Okazaki Keishi(JAMSTEC)

11:45 AM - 12:00 PM

[SCG52-11] Isolated intermediate-depth seismicity: Implications for local slab hydration

*Junichi Nakajima1 (1.Department of Earth and Planetary Sciences, Tokyo Institute of Technology)

We analyzed an isolated seismic cluster in a depth range of 40–90 km located 100 km north of the Izu peninsula. We relocated 40 earthquakes by hypoDD using catalogue-derived arrival time differences and determined 7 focal mechanism solutions A total of 37 earthquakes occurred in the subducting Philippine Sea (PHS) plate. Based on the focal mechanism solution, the largest earthquake (M3.1) is interpreted as a thrust earthquake along the upper surface of the PHS plate. Locations of other earthquakes relative to the largest event suggest that most occur within the subducting PHS plate. Our results suggest that the PHS plate north of Izu peninsula has temperatures low enough to facilitate thrust and intraslab earthquakes at depths of 60–90 km. Earthquakes are likely to occur where pore pressures are locally high, which weakens pre-existing faults.