Geological evidence for repeated slip-to-the-trench style megathrust earthquakes at the Japan Trench

Deformation of trench-fill sediments at the central Japan Trench axis confirms that coseismic slip during the 2011 CE M_w 9.1 Tōhoku-oki earthquake extended to the shallowest part of the megathrust fault, contributing to the unexpectedly large tsunami that followed. Understanding the recurrence of “slip-to-the-trench” style earthquakes is therefore essential for diagnosing future hazard at the Japan Trench (and other subduction zones). Thermal biomarkers from the décollement indicate that similar shallow slip has occurred repeatedly, but the timing has not yet been linked to specific past earthquakes. We examine the sedimentary sequence of a trench-fill basin at 38.75°N (just north of the Tōhoku-oki slip zone) to investigate archives of past deformation caused by slip to the trench. Reprocessed seismic reflection and sub-bottom profiler data image several stratigraphic intervals of imbricate thrust wedge formation and paleo-seafloor uplift consistent with compression induced by locally enhanced coseismic slip along the décollement. The uplifted paleo-seafloor topography is onlapped by thick seismoturbidites that have been cored and dated by International Ocean Discovery Program Expedition 386, thus providing chronostratigraphic tie points. With this, we link the youngest coseismic deformation of trench-fill sediments to the 869 CE Jogan earthquake, indicating that rupture extended farther north and closer to the trench than previously estimated. Documenting slip to the trench for this historical megathrust event is proof of concept for our core-to-seismic correlation approach to constrain shallow slip in past earthquakes. Hence, we infer the several deeper intervals of imbricate thrust faulting and turbidites contain the means to unlock an extensive history of slip-to-the-trench style earthquakes and quantify the recurrence of shallow, tsunamigenic slip at the Japan Trench.