抄録
We present reflection profiles of the Kannonji Fault (Yamagata Prefecture), the Senya Fault (Akita Prefecture), and the Torigoe Fault (Niigata Prefecture) obtained by using a simple observation system, which consists of a 4kg wood hammer source and a 12ch ( or 24ch ) recording device. Reflecting surfaces can be seen down to the two way travel time of 200ms for the Kannonji Fault and the Senya Fault. The reflection profile of the Kannonji Fault implies that the faulting has formed a wide flexure zone, and that of the Senya Fault reveals a fault surface between the Miroku and the Senya formations. These features found in this study are very similar to those obtained by large scale reflection surveys conducted across these faults by Yamagata Prefecture (1998) and Satoet al. (1997). We set two survey lines at the Torigoe Fault, one is across a flexure scarp on the eastern limb of the Torigoe anticline, and the other crosses a flexure on Holocene lowland. The detailed subsurface structure obtained by this survey seems to contribute for investigating the formation of the Torigoe Fault System. Thus we suggest that such a simple observation system is useful to grasp a structure of an active fault near the surface.
