Abstract
The Chiu-chiu-feng area is located about 20km southwest of Taichung city in the midwesten in part of Taiwan. This area consists of manny narrow ridges of a relatively large height. In the surrounding area of the Chiu-chiu-feng area, there was acceleration of 500-600 gal cased by the Chi-chi earthquake in September 1999. The ridge of the The Chiu-chiu-feng area were strongly accelerated by this earthquake, and many shallow slope failures occured around the ridge over the whole area. In December of that year, broken pieces of cobble were discovered by an investigation of the ridge. It was confirmed that the cobble had broken by a drop test of cobble on the ridge. Also, acceleration of about 1 -3 times that of gravitational acceleration might have arisen, as determined from the results of the earthquake response analysis of the narrow ridge of the survey site. It is liky that slope failures and sliding down of soil were triggerd by the strong acceleration which was in the manner of lifting and breaking cobbles on the rige.
