EAPSI: The Role of Silica-redistribution in Healing Subduction-related Fault Rocks

Ramirez Gabrielle E, State College PA

Investigators

Abstract

This project will investigate subduction-related fault rocks in the Shimanto Belt of Japan in order to assess the role of silica redistribution in the healing of subduction zone fault rocks. These fault rocks record deformation that occurred at temperatures and depths that span the seismogenic zone (i.e., where most earthquakes originate). We hypothesize that silica redistribution is a viable process for fault healing on timescales relevant to earthquake (seismic) cycles and therefore can significantly impact the location, frequency, and magnitude of seismic events such as the destructive 2011 Tohoku-Oki earthquake. Understanding these healing processes has potential implications for seismic prediction and seismic hazard. Dr. Yoshitaka Hashimoto of Kochi University will serve as source of knowledge for my field areas and will also provide characterization equipment that will allow me to further our understanding of the role of silica redistribution and other geochemical processes that contribute to healing subduction-related fault rocks. This project will study subduction-related fault fabrics and veins in the Shimanto Belt from multiple mélanges that represent the seismogenic zone in order to assess the role of silica redistribution in healing fault rocks. The proposed research includes (1) field work to gather samples for analyses and to collect structural measurements (2) geochemical analyses of veins and slip surfaces (i.e. scaly fabrics) using characterization techniques (i.e., EPMA, FE-SEM) to investigate processes of dissolution and precipitation of silica and (3) petrographically characterizing the distribution and dimensions of veins and shear fabrics (i.e. spacing and thickness). The data from the proposed research will help to better constrain a kinetics model for silica redistribution that will assess timescales of subduction zone healing. Evaluating the timescales of fault healing along the subduction interface will allow us to investigate the connection between healing processes and the seismic cycle in subduction zones. This award, under the East Asia and Pacific Summer Institutes program, supports summer research by a U.S. graduate student and is jointly funded by NSF and the Japan Society for the Promotion of Science.