In situ observations of earthquake-driven fluid pulses within the Japan Trench plate boundary fault zone

Transient fluid flow within faults is suspected to be an important component of the earthquake cycle and subduction zone evolution. However, an understanding of the mechanisms and time scales involved has been limited due to a paucity of direct measurements. Here we report on in situ observations that appear to capture the thermal signature of earthquake-driven fluid pulses within the damage zone of the Japan Trench plate boundary fault. The data are from a sub-seafloor temperature observatory installed through the fault following the March 2011 Mw 9.0 Tohoku-oki earthquake as part of the Integrated Ocean Drilling Program’s Japan Trench Fast Drilling Project (JFAST). High-resolution temperature time series data reveal spatially correlated transients in response to earthquakes that are indicative of advection by transient fluid flow. We interpret the observed phenomenon as reflecting pressure redistribution in a fault zone and a potential mechanism for earthquake triggering and episodic heat and chemical transport.