Several active and seismic faults are sporadically distributed in the San'in (northern Chugoku) District in the western part of Honshu, Japan. As the detailed surveys including trench excavations for these active faults have been recently carried out, common characteristics among these faults have clarified as follows:
1) The features of the fault morphology in this district are not so obvious, and cum u lative offsets are always smaller than a few hundreds of meters.
2) All active faults are strike-slip type, in w hich arcuate ENE-WNW trending ones are dextral, and NNWSSE trending are sinistral. These are distributed within the active moble zone between the north s i d e of the Chugoku Mountains and the southern Japan Sea fault zone (SJSFZ).
3) Each active fault (zone) is composed of a few to several fault s arranged with en echelon segment or accompanies the diverged branch. Although linear or slightly curving trace extends continuously, th e total length of each fault is shorter than 25km.
4) The fault shattered zone is usually not w i de and narrower than a few 10 cm. And these faults do not indicate the reactivity along the pre-existed wide shattered zone
5) The newly developed active fault system has been form e d under the stress field with maximum compressional axis of WNW-ESE direction since the middle Quaternary. The matuarity of ea c h fault is lain under the young stage.
6) As even indistinct lin e a ment or active fault has potential to produce large earthquake of M7 class in this district, the careful further more detailed surveys are required.
7) This centennial is the seismically active period in this district after the quiescent recurrence interval of about one thousand of years.
