Ryohei Nishida

RELATIONSHIP BETWEEN SEISMIC GROUND MOTION AND SUBSURFACE STRUCTURE BY ANARYSIS OF INSTRUMENTAL SEISMIC INTENSITY IN TOTTORI PREFECTURE, SOUTHWEST JAPAN

A dataset of instrumental seismic intensities recorded at 50starions in Tottori Prefecture, southwest Japan, including 1464 events (4833 records) has been compiled. An average difference between the seismic intensities obtained from the observation and those estimated by using the attenuation was defined as an index representing the site amplification; a standard deviation and the number of observations were also used. The relationship between the index and the subsurface ground structure was studied. There was a correlation of the index with AVS30. On the closed two stations in Sakaiminato City, we analyzed the difference of instrumental seismic intensities by using the same method. The case of the difference between the two stations was found in this analysis.

Study of Focal Mechanisms in Eastern and Central Areas of Tottori Prefecture

The tectonic stress, which was found from focal mechanisms of earthquakes in the eastern and the central area of Tottori prefecture, were investigated. Focal mechanisms in this area were the strike slip type of WNW-ESE compression, which is nearly agreed with the mechanism of the 1943 Tottori earthquake. Tectonic stress in this area has conserved the same pattern as the Tottori earthquake, 1943. But the seismic activity near the Yoshioka-Shikano faultsystem shows lower than the other regions. Though their focal mechanisms show a large irregularity, the averaged P-axis indicates NW-SE compression compatible with the strike of the Yoshioka-Shikano faultsystem. This may be attributed to the situation that this area agrees approximately with the bright spots of the 1943 Tottori earthquake.