Geochemical approach to understanding fluid-rock interactions associated with slow earthquakes

Abstract

Slow earthquakes that occur at the subduction plate boundary are of great importance, including their close relationship to the large earthquakes. Although it is still unclear what geological process is related to the slow earthquakes, it is believed that fluid-rock interactions are important for their occurrence. Deep slow earthquakes that occur at greater depths beyond the seismogenic zone in subduction zones such as SW Japan may be associated with high-temperature fluid-rock interactions, and can be studied using geochemical approaches. We show that the Arima-type deep fluids can be candidates for such slow earthquake-related fluids, as some of them are observed in the region under which deep slow earthquakes frequently occur. We also show preliminary results that mélange rocks of the Shimanto accretionary complex, which have been proposed to represent the deep slow earthquake-related rocks, have geochemical characteristics consistent with high-temperature fluid-rock interactions at >300 deg. C.