Chikara KASAHARA

Consideration of earthquake ground motion level and Liquefaction in The 1987 East Off Chiba Prefecture Earthquake

Takaaki IKEDA

Heavy liquefaction occurred in Urayasu city, Chiba Prefecture, due to the 2011 off the Pacific coast of Tohoku Earthquake. However, according to the field survey with borehole drilling, liquefaction strength was not low. This result is contradictory liquefaction situation. We must survey of past earthquakes to solve in this problem.
We select from multiple earthquakes. In this research, we studied liquefaction in the 1987 East Off Chiba Prefecture Earthquake.
The Consideration procedure is as follows. 1) Survey on liquefaction situation, 2) Estimation of earthquake ground motion level, 3) Assessment of soil liquefaction, 4) Comprehensive evaluation, 
 The 1987 East Off Chiba Prefecture Earthquake with Mw6.7 have a 58 km depth. Many house damage occurred in this earthquake. Liquefaction was discovered in Urayasu city partially. Liquefaction level was evaluated from literature survey. 
Earthquake ground motion level was evaluated from attenuation equation. In this research, I used the formula of Hongjun SI and Saburoh MIDORIKAWA. We also modified the model compared to observed values. Observed values were obtained from research report based on strong motion records. However, it is not listed in the record longitude latitude of seismic station. We must find the location of the seismic station. So I used Google Earth for that.
Assessment of soil liquefaction was estimated by gFL methodh, result of boring survey and estimated ground motion level.
As a result, I can estimate maximum acceleration of Urayasu city that is 113cm/s/s, and in Urayasu city was estimated to be partially liquefied.