Abstract

Multiple faults with different paleoseismic histories sometimes rupture simultaneously, resulting in a larger earthquake than expected. To test behavioral models for a fault involved in a multiple-fault rupture, we performed detailed tectonic-geomorphological mapping along the Neodani fault, central Japan, one of several faults that ruptured simultaneously during the devastating 1891 Mw 7.5 Nobi earthquake. Our mapping showed that the along-strike distributions of the long-term rates of left-lateral and vertical slips generally mimic in shape those of the 1891 slip, implying that the slip-patch behavior, in which smaller more frequent earthquake ruptures fill in low-slip portions of the 1891 rupture, does not apply to the Neodani fault. If the earthquake recurrence interval estimated from a previous paleoseismic trench is correct, however, the Neodani fault should not be characterized by repetition of same slip-function earthquake ruptures or the characteristic slip-function behavior. The observations can instead be explained by the semicharacteristic slip-function behavior, in which a similarly shaped slip distribution is repeated independently of the rupture of adjacent faults, but the amount of slip varies. Nonetheless, characteristic slip-function behavior may still be a valid interpretation if some of the paleoseismic events identified in the trench are minor sympathetic-slip events. Although we found that the shape of the slip distribution has been quite stable through successive earthquakes, including a multiple-fault rupture earthquake, further paleoseismic efforts are warranted to examine the stability in the amount of slip.

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