The Finicky Nature of Earthquake Shaking‐Triggered Submarine Sediment Slope Failures and Sediment Gravity Flows

Since 2011, seafloor temperatures, pressures, and seismic ground motions have been measured by the seafloor cabled Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET) on the Nankai margin. These measurements, high‐resolution bathymetry, and abundant contextual information make the DONET region seem ideally suited to provide constraints on seismic shaking‐triggered sediment slope failures and gravity flows, particularly since numerous published studies have linked paleo‐ to modern earthquakes to failures and flows within the DONET. The occurrences of the local 2016 M6.0 Mie‐ken and regional M7.0 Kumamoto earthquakes within and at regional distances, respectively, from the DONET data set provided an opportunity to explore this potential. We used DONET seismic recordings of the posited triggering shaking and to search for submarine slide signals and continuous temperature and pressure data to detect pulses of warm and densified water indicative of passing flows. We developed and applied a variety of analytical methods to eliminate signals generated by water column processes, while leaving slope failures and sediment gravity flow anomalies as residuals. Our explorations yielded no evidence that earthquake shaking initiated either phenomenon, which we suggest reflects the finicky nature both of the detection of and the physical processes that contribute to slope failures and flows (i.e., both require satisfying precise suites of conditions). Nonetheless, this negative result, our analyses, and the estimates of physical properties we derived for them, provide useful lessons and inputs for future studies. Plain Language Summary Since 2011, measurements of both seafloor displacements caused by deformation within the Earth and motions of the water column above the seafloor have been made by the seafloor cabled Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET) in the offshore region of the Nankai subduction zone, Japan. These measurements, the occurrence in 2016 of a magnitude M6.0 earthquake within the DONET footprint and another M7.0 in southern Japan, and a rich repository of other information make the DONET region seem ideally suited to learn about how earthquake shaking triggers submarine landslides and rapidly flowing currents that carry sediments downslope. We analyzed DONET measurements but found no evidence that earthquake shaking initiated either phenomenon, which we suggest reflects the finicky nature both of detecting