Recurrence Interval of the Kuwana Fault Reconstructed from Holocene Synfaulting Shallow Marine Sediments on the Western Margin of the Nobi Plain, Central Japan

Holocene activity of the Kuwana Fault was reconstructed based on 82 AMS 14C datings and on stepwise changes in the depositional rates of shallow marine sediments in four drilled cores. Depositional rates on the footwall and hanging wall are nearly equal during the interseismic period. Depositional rate on the footwall becomes markedly larger than that of the hanging wall just after the appearance of the vertical displacement of the fault. Six probable and one possible paleo-seismic events, including the last two historical earthquakes, were detected during the last 7, 000 years as stepwise changes of depositional rate on both sides of the fault. Timing of faulting events was estimated from depositional curves of four drilling cores. Probable ages of seismic events are approximately 6, 200cal BP, 5, 700cal BP, 4, 000cal BP, 2, 100cal BP, AD 745, and AD 1586. Average recurrence interval of the Kuwana Fault calculated from these data is about 1, 000 years. Average vertical slip rate of the fault is at least 1mm/y during the last 7, 000 years.