10:00 AM - 10:15 AM
[SSS08-11] Cumulativeness of “triggered” surface rupture in north-western area of outer rim of Aso caldera and its impact for active fault evaluation
Keywords:Kumamoto Earthquake, SAR interferometry, surface rupture, triggered fault, cumulativeness
From the geomorphological point of view, the fault shows reverse fault scarp cutting flat surface of alluvial fan, and a low fault scarplet of 1 m - 3 m of relative elevation continues at the bottom of the scarp. By SAR interferometry, there supposed to have about 10 cm of vertical displacement associated with the 2016 Kumamoto Earthquake. From the observation of the trench wall, a clear fault displacement is not found, but a sediment layer with pyroclastic materal is deformed vertically at least 70 cm dipping to south with a sharp boundary to upper layer, suggesting that a repetitive faulting activities occurred resulting the layer displaced cumulatively. The result of GPR survey also indicates a consistent structure.
Extension of the Matoishi Bokujo 1 Fault is about 2 km, with the clear displaced topography cutting the low relief surface which seems Aso 4 pyroclastic flow depositional surface. This fault is shown on an active fault map of GSI "Aso" (Suzuki et al. 2017) as an active fault. If such passive, "triggered" or "accompanied" crustal deformation without generating a major seismicity contributes to at least one part of formation of active fault topography, we should reconsider the evaluation method for activities in the active fault where the recurrence of the earthquake is presumed from the history of displacing events from a trench excavation.