Estimation of temperature rise in a shallow slip zone of the megasplay fault in the Nankai Trough

A megasplay fault branching from the subduction boundary megathrust in the Nankai Trough is thought to have caused large tsunamis associated with past Tonankai earthquakes. Because the temperature recorded in the fault can constrain parameters of seismic slip, we evaluated several temperature proxies (fluid-mobile trace element concentrations, Sr isotopes, magnetic minerals, inorganic carbon content, and Raman spectra of carbonaceous material) in material from a localized slip zone, sampled at Site C0004 by Integrated Ocean Drilling Program Expedition 316. Our results showed that the shallow part of the megasplay fault has not experienced temperatures above 300 °C. We also found that in addition to shear stress and slip distance, slip rate and porosity are effective parameters for frictional heat, as demonstrated by numerical analysis incorporating thermal diffusion. The slip rate estimated through these proxies may indicate that the fault did not slip with high velocity near the seafloor.