佐渡海盆東縁断層と2007年中越沖地震

抄録

We show locations of active submarine faults near the focal area of the 2007 Chuetsu-oki earthquake in detail, and investigate fault structure based on tectonic landforms and sounding profiles obtained by Tokyo Electric Power Company. There are several active submarine faults in the area. The Plio-Pleistocene series are cumulatively deformed by reverse faulting. The Sado Basin lies between the Eastern-boundary fault dipping southeast and the Western-boundary fault dipping northwest. The former is an active reverse fault over 50-km long. Tectonic geomorphic features indicate that the Eastern-boundary fault branches upward into two faults at a certain depth with a ramp and flat structure next to the focal area. The Eastern-boundary fault B merges downward into the southwestern half of the Eastern-boundary fault A extending into the swarm of the aftershocks associated with the earthquake. The 2007 Chuetsu-oki earthquake has resulted from the reverse faulting in the southwestern half of the fault A. Although the magnitude of this recent quake was only 6.8, the Easternboundary fault A, over 50-km long reverse fault, is capable of generating a much greater earthquake. The largest nuclear power plant suffered considerable damage from the earthquake. This is because the active submarine faults have been slurred over. We should correct the inappropriate fault assessments in Japan's nuclear society.