2018 Volume 2018 Issue 49 Pages 23-30
We described newly found fault exposures of the Shiraiwa and Ota faults and obtained dating materials from exposures including that of Senya fault, on which the surface ruptures appeared at the 1896 Rikuu earthquake. Based on radio-carbon dating and paleoseismic interpretation, we examined the event horizon of 1896 earthquake. We also estimated the exact trace of 1896 surface ruptures of Ota fault, using the comparison between before-and-after large scale topographic maps on artificial modification. Each of two new fault exposures and a previously reported fault exposure demonstrates the fault movement of a single event related to the 1896 earthquake. We confirmed that all faults in the exposures described here were activated at the 1896 earthquake and produced continuous fault scarps. The fault scarp of Shiraiwa fault on the foot of mountains is precisely identified along the boundary between higher farming fields and lower paddy fields depicted in the large scale topographic maps drawn before 2000s’ artificial modification.
