The Tachikawa fault, which is the only active fault in the Tokyo Metropolis, is expected to be the source of shallow intra-plate earthquakes in the future. We performed additional trenching surveys at the northwestern part of the fault to obtain the paleoseismological parameters for evaluating earthquake potential caused by the fault. Trench wall observation, radiocarbon dating, and tephra analyses constrained the last surface-rupturing event at the Tachikawa fault between about 13, 700 cal yBP and 12, 800 cal yBP. The vertical separation of the event is estimated to be more than 2.6 meters.
