[S-SS10] Strong Ground Motion and Earthquake Disaster

[SSS10-P12] Microtremor and gravity survey near the Yoshioka Fault caused by the 1943 Tottori Earthquake - Case of Ohtsuka area, Tottori City, Japan -

*Tatsuya Noguchi¹, Isamu Nishimura², Nao Yoshikawa¹, Honoka Ueda¹, Takao Kagawa¹ (1.Department of Management of Social Systems and Civil Engineering, Civil Engineering Course Graduate School of Engineering, Tottori University, 2.Graduate School of Engineering, Tottori University)

Keywords:Yoshioka fault , 1943 Tottori Earthquake , microtremor, gravity anomaly, subsurface structure

The Yoshioka fault is an earthquake fault that appeared due to the 1943 Tottori earthquake. At the faults, trench surveys, reconnaissance surveys, and interview surveys with residents are conducted as fault displacement surveys. For the subsurface structure, microtremor exploration and gravity exploration were carried out near the fault displacement.

In this study, we grasped the ground motion characteristics in the vicinity of the fault by using the results of dense microtremor and gravity observations at the fault displacement location and in the vicinity.

As a result, there was a difference in the shape of the microtremor H/V, predominate periods and particle motion of records between the front and the back of the fault displacement point. As the cause of this phenomenon, the correspondence between the results of microtremor observation and underground structure exploration suggests that the crush zone and step structure of the fault are in-volved in the characteristics of microtremor. The gravity observation results show that the gravity anomaly changes abruptly along the direction of the fault line near the fault line. From the density structure analysis of the two-layer model, we can estimate the drop-off of the south-falling base.