近畿地方北西部地域の活構造 (2)

三田市西部での最終活動

抄録

Normal and reversed faults are observed at the outcrops of the western part of Sanda City, Hyogo Prefecture. Normal faults which are observed along the Sanda-Yamasaki tectonic line are discordant with the stress e stimated by the character of earthquakes. The results of the measurements of the crustal stress and the mechanism of the micro-earthquakes around these area indicate that the horizontal compressive stress acts in E-W direction around this region. This discordance is solved by the observation of a new outcrops in the western part of Sanda City, where that ground is prepared for housing. The movement of a fault, concealed underground, brings about various kinds of breaks on the loose sedimental layer.
The magnitude of earthquake occurred around here is estimated as about 7. The age of faulting is also estimated by ¹⁴C dating younger than 3340 years old and by the rice field older than 400 years old. This falt might be occurred Harima Earthquake in AD 868.