“…The depths where advection signals are observed occur where the borehole intersects the fault damage zone, an ~100-m-wide region identified in geophysical logging data and core samples with open faults and fractures within lithified mudstone above the <4.87-m-thick clay-rich uppermost candidate plate boundary fault, and other mudstones, siliceous clays, chert, and basalt within the downgoing Pacific plate (Chester et al, 2013a;Rabinowitz et al, 2015;Keren and Kirkpatrick, 2016). Depths near the bottom of the observatory array, around the main plate boundary fault and where the largest part of the frictional heat signal is observed, are largely unaffected by advection, which is consistent with the previous inference that the plate boundary fault has much lower permeability than the damage zone due to its composition of low-porosity scaly clay (Fulton et al, 2013;Chester et al, 2013b, Tanikawa et al, 2013. The location and relatively small magnitude of borehole transients are consistent with the interpretation of the broad long-lasting 0.3 °C signal at ~819 mbsf as conductive frictional heat.…”