抄録
The 1586 M~8 Tensho earthquake might have been one of the largest inland earthquakes in Japan. Historical documents and geologic evidence suggest that there might be a composite rupture process involving more than a couple of active faults. To retrospectively evaluate such a possibility of distant cascading ruptures with stress transfer hypothesis, here I compute the static Coulomb stress changes under two representative scenarios. One is the Shogawa fault, Atera fault, and Yoro-Kuwana-Yokkaichi fault zone have been the sources(Sangawa’s scenario), while the other is a movement of the norther Shogawa fault followed by the Yoro fault or Isewan fault (Matsu’ura’s scenario). To assess the imminency and instability of their earthquakes in 1586, I also take the 30-yr earthquake probabilities of the causative faults into account. Computed stress transfer in five out of six combinations in the Sangawa’s scenario suggests that Coulomb stress on the subsequent rupturing fault is loaded by the previous earthquake by up to 0.5 MPa. On the Matsu’ura’s scenario, amount of stress transfer by the northern Shogawa fault to the Yoro or Isewan fault would be smaller than 0.01 MPa. But such small stress perturbation including possible effect of dynamic shaking might have been enough to trigger the Isewan fault which had been on the verge of the next rupture. Although there are still large uncertainties to assign fault parameters, my preliminary computations imply both scenarios can be supported by the recent consensus of static stress transfer hypothesis.
