Teizo Fujiwara

Local site amplification and damage to wooden houses in Shimoenoki, Tottori, Japan, by the 2000 Western Tottori Earthquake

The degree of damage to wooden houses in the vicinity of the source area of the 2000 Western Tottori Earthquake was very low compared to the 1995 Hyogo-ken Nanbu Earthquake. Shimoenoki in Hino Town, however, suffered remarkable damage compared to other villages, particularly to residential wooden houses. Furthermore, although Shimoenoki is a small area of only 300 × 400 m2, the damage varied markedly from the foot of the mountains through central Shimoenoki to the Hino River. From the damage distribution based on a survey of all wooden houses, the local site-amplification characteristics estimated from aftershock records, and the transfer functions of wooden houses evaluated using microtremors, the spatial variation of damage appears to be attributed to the variation in site-amplification factors at frequencies between 2 and 5 Hz, which is close to the first natural frequency of wooden houses.

Soil Condition and Seismic Characteristics in Shiga Prefecture, Japan

The seismic observation network in Shiga prefecture iscomposed of four systems.All the observation data obtained were used to estimatethe dynamic characteristicsof the surface soils around the lake and the seismichazard for Hikone City. Since1995, 21 records have been obtained at the USP site ofwhich those for the 1999Shigaken-Hokubu Earthquake and 1999 Wakayarnaken-HokubuEarthquake wereused in this study. Transfer functions of the surfacesoil in each ward of ShigaPrefecture based on the Mt. Kojin site (KJY), whichhas relatively hard soil, werecalculated from the records of the two earthquakes.Assuming a scenario earthquakeat the Hyakusaiji fault close to Hikone City, maximumground motions were obtainedfor 15 city blocks in order to establish a damageestimation for that city. The numberof collapsed wooden houses and the damage ratiowere calculated based on the distributionof construction of wooden houses by year. Blockswith a larger ratio of old, wooden housesin Hikone showed a close correlation with blockswith a large ratio of aged persons inthem, indicative that weak persons, such as theelderly, may find themselves in a severesituation during a natural disaster.