Abstract
Reconstrucion of paleoseismicity for a long period is very important for the progress of a repetition model of large earthquakes. Previous study (Naruhashi et al., 2004, 2008) successfully reconstructed middle to late Holocene activity of the Kuwana fault based on stepwise changes in the depositional rates of shallow marine sediments controlled by 14C dates and wide-spread tephras.
This study examined utility of grain size, electric conductivity (EC) and initial magnetic susceptibility as proxy to detect the faulting events of the Kuwana fault. As a result, the event horizons indicated by Naruhashi et al. (2004, 2008) can be recognized by specific changes in EC, initial magnetic susceptibility and grain size composition of the core samples. These changes reflect the burial process of the fault scarp formed by individual faulting event. Moreover, grain size, EC and initial magnetic susceptibility in the depth of 23-24m and 28-29m on the downthrown side of the fault show similar changes around faulting event horizons on the downthrown side as described above. This result implies that changes of the proxy could indicate two older unknown faulting events.
