報告書番号

U99029

タイトル（和文）

釜石鉱山の地下深部における地震動特性

タイトル（英文）

Characteristics of seismic ground motion observed at the Kamaishi Mine

概要 （図表や脚注は「報告書全文」に掲載しております）

釜石鉱山において約8年間に得られた344個の地震記録を解析した結果、以下のことが明らかになった。(1)震源の深さが30 kmより浅い地震の最大加速度は、既往の距離減衰式から予測される加速度の値とほぼ同レベルか下回る傾向にある。しかし、震源が60 kmよりも深い地震の場合、最大加速度の観測値は予測値を上回り、震源距離やマグニチュードが同じであれば、震源が深い地震ほど最大加速度は大きくなる。(2)速度応答スペクトルの平均は震源の深さに依存し、震源が60 kmよりも深い地震の速度応答スペクトルが最も大きく、30 km以浅の地震のものが最も小さい。震源距離やマグニチュードが同じであれば、震源が深い地震の速度応答スペクトルは大きくなる。(3)最大加速度振幅は、地表から140mの地中でおよそ1/2に低減するが、それ以深ではほぼ一定である。実効値の低減率は、最大加速度振幅の場合よりもばらつきは小さい。

概要 （英文）

In about 8 years since seismic observations were started in February 1990 at the Kamaishi Mine, a total of 344 seismic data were obtained.These records were analyzed, obtaining the following results:(1)The average magnitude of earthquakes observed is 4.5.The average hypocentral distance and focal depth are 107km and 59km, respectively.Eleven earthquakes with their Magnitude being greater than 7 were observed, including M = 8.1 (earthquake off the east of Hokkaido in 1994).The maximum acceleration amplitude is 52gal in EW component on the ground surface.A total of 32 earthquakes that exceeded 10 gal on the ground surface were observed, including this earthquake.(2)The maximum acceleration of earthquakes whose focal depth is shallower than 30km has a tendency to be at the same level as or lower than the acceleration which is estimated from the attenuation relation.However, it can be recognized as a clear tendency that if the focal depth is deeper than 60km, the observed value of maximum acceleration is higher than the estimated value and if the hypocentral distance or magnitude is the same, the deeper the hypocenter the larger becomes the maximum acceleration.(3)The average of velocity response spectra obtained from seismic records in the Kamaishi Mine shows a value smaller than the estimated value of velocity response spectra.Also, the average of response spectra obtained is dependent on the focal depth, and the velocity response spectrum of the earthquake whose hypocenter is deeper than 60km is largest, while the response spectrum of the earthquake shallower than 30km is smallest. As in the case of maximum acceleration amplitude, if the hypocentral distance or magnitude is the same, the velocity response spectrum of a deep-hypocenter earthquake becomes larger.(4)The maximum acceleration amplitude attenuate to approximately 1/2 in the ground of 140m from the surface, though in the area deeper than that these values are almost constant.

報告者

キーワード