Geological and geophysical surveys were carried out in the eastward extended area of the Yamasaki fault. In this area, any faults have not been recognized, but many microearthquakes occur.
From the geological survey, three remarkable outcrops and some topographical evidences which show the existence of the fault were found in this area. The hidden fault was traced by γ-ray and ELF·MT surveys. γ-ray intensity was measured at 12sites. The places where high γ-ray intensities are obtained, are approximately on a straight line in the direction of N70°-80°W.
The ELF·MT surveys have been conducted in the Yashiro and Sanda regions. The spatial distribution of the obtained apparent resistivities reveals the existence of low resistivity belts along the fault which was inferred from the geological surveys. These belts have a width of more than 1.5km in both regions. The results of these surveys show that this new fault named the Yashiro fault, running from the Fukusaki to the Sanda regions in the Hyogo prefecture, is the eastward extension of the Yasutomi fault that is a part of the Yamasaki fault system. On the other hand, the results of the surveys also suggest that the Yashiro fault extends to the Jumantsuji fault which is one of the members of the Arima-Takatsuki tectonic line.
The large fault which consists of a series of three faults, Yasutomi, Yashiro, and Jumantsuji faults, bounds this region into two blocks. They show different patterns in each region in the topography, the distribution of active faults and the occurrence of microearthquakes.

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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.

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