Japan Geoscience Union Meeting 2018

Presentation information

[EE] Evening Poster

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

[S-CG53] Science of slow earthquakes: Toward unified understandings of whole earthquake process

Wed. May 23, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Satoshi Ide(Department of Earth an Planetary Science, University of Tokyo), Hitoshi Hirose(Research Center for Urban Safety and Security, Kobe University), Kohtaro Ujiie(筑波大学生命環境系, 共同), Takahiro Hatano(Earthquake Research Institute, University of Tokyo)

[SCG53-P18] Estimation of pore fluid overpressures for tensile cracking at depth of shallow slow earthquakes

*Makoto Otsubo1, Kohtaro Ujiie2, Jeanne L. Hardebeck3, Hanae Saishu1, Ayumu Miyakawa1, Asuka Yamaguchi4 (1.Geological Survey of Japan/AIST, 2.University of Tsukuba, 3.U.S. Geological Survey, 4.The University of Tokyo)

Keywords:Slow earthquake, Stress, Crack, Fluid, Subduction

Pore fluid pressure Pf is important for understanding slow earthquake mechanics. In this study, we estimated the pore fluid pressure during the formation of foliation-parallel quartz veins filling mode I cracks in the Makimine mélanges, eastern Kyushu, SW Japan. In the coastal region of the Makimine mélanges (Late Cretaceous Shimanto accretionary complex of SW Japan; temperature = 300–350°C, Palazzin et al., 2016), the mélange preserves quartz-filled shear, foliation-parallel veins and tension vein arrays. We applied the stress tensor inversion approach proposed by Sato et al. (2013) to estimate stress regimes by using foliation-parallel vein orientations. The estimated stress is a reverse faulting stress regime with a sub-horizontal σ1-axis trending NW–SE and a sub-vertical σ3-axis, and the driving pore fluid pressure ratio P* (P* = (Pf – σ3) / (σ1 – σ3)) is ~0.1. When the pore fluid pressure exceeds σ3, veins filling mode I cracks are constructed (Jolly and Sanderson, 1997). The pore fluid pressure that exceeds σ3 is the pore fluid overpressure ΔPfPf = Pf – σ3). To estimate the pore fluid overpressure, we used the poro-elastic model for extension quartz vein formation (Gudmundsson, 1999). Pf in the case of the Makimine mélanges are ~280 MPa (assuming depth = 10 km, density = 2750 kg/m3, tensile strength = 5 MPa and Young’s modulus = 7.5–15 GPa). The normalized pore pressure ratio λ* (λ* = (PfPh) / (PlPh), Pl: lithostatic pressure; Ph: hydrostatic pressure) is ~1.03 (Pf > Pl).