Japan Geoscience Union Meeting 2016

Presentation information

International Session (Poster)

Symbol S (Solid Earth Sciences) » S-SS Seismology

[S-SS02] Frontier studies on subduction zone megathrust earthquakes and tsunamis

Tue. May 24, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Kyuichi Kanagawa(Graduate School of Science, Chiba University), Demian Saffer(Department of Geosciences, The Pennsylvania State University, USA), Michael Strasser(University of Innsbruck), James Kirkpatrick(McGill University), Shuichi Kodaira(R&D Center for Earthquake and Tsunami Japan Agency for Marine-Earth Science and Technology), Ryota Hino(Graduate School of Science, Tohoku University), Yasuhiro Yamada(Japan Agency for Marine-Earth Science and Technology (JAMSTEC), R&D Center for Ocean Drilling Science (ODS)), Kohtaro Ujiie(Graduate School of Life and Environmental Sciences, University of Tsukuba), Yoshihiro Ito(Disaster Prevention Research Institute, Kyoto University)

5:15 PM - 6:30 PM

[SSS02-P16] Faulting-promoted illitization along the megasplay fault in the Nankai Trough

*Hirokazu Masumoto1, Jun Kameda1, Yohei Hamada2, Yujin Kitamura3 (1.Graduate School of Science, Hokkaido University, 2.Japan Agency for Marine-Earth Science and Technology Kochi Institute for Core Sample Research, 3.Department of Earth and Environmental Sciences, Graduate School of Science and Engineering, Kagoshima University)

Keywords:Subduction zone, Fault gouge, Frictional heating

The transformation of smectite to illite is thought to have important role on faulting because illitization can change friction strength and produce fluid overpressure by dehydration reaction. We performed X-ray diffraction analyses of sediment samples around the megasplay fault in the Nankai accretionary prism, recovered from Integrated Ocean Drilling Program (IODP) Expedition 316 Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). Quantitative analysis of the illite fraction in illite–smectite mixed layers (I-S) crystallites shows that the dark gouge has ~10% more illite content than that in the host rock. If applying a kinetic expression obtained under a static condition from the previous works, the observed mineralogical anomaly requires an event of frictional heating that have caused temperature rise to an extraordinarily high level around the dark gouge. We combined data from XRD analyses with modified kinetic simulations of illitization to quantify effect of mechanochemical processes. As a result, if we applied an activation energy ~30% lower than the value from the previous works, illitization can be reasonably explained by frictional heating. These results suggest that seismic slip helped to overcome kinetic barrier due to mechanochemical processes in the fault zone.