Coseismic frictional heating and fluid-rock interaction in a slip zone within a shallow accretionary prism and implications for earthquake slip behavior

Abstract

To understand the relation between seismic events and the geological structure in a shallow accretionary prism, we investigated a major reverse fault in a fossil accretionary prism, the Emi Group (burial depth, 1-4 km), Boso Peninsula, Japan. We examined the slip zone rocks and the surrounding host rocks microscopically and analyzed their trace elements and isotopes. Using the fluid-mobile trace element spectrum, which is sensitive to fluid-rock interaction at high temperatures, we estimated that the slip zone experienced frictional heating of >350°C caused by high-velocity sliding. By numerical analysis of the frictional heating and thermal diffusion using various values for slip displacement, the frictional coefficient, depth, and fault dip, we determined the conditions sufficient for producing the estimated high-temperature frictional heating at shallow depth (1-2 km). The results suggest that such faulting in a shallow accretionary prism could potentially generate huge tsunamis. © 2011 by the American Geophysical Union.