ダム貯水と地震活動 (1)

日本の大ダムの場合

抄録

The present paper is a macroscopic and qualitative research for the change of seismicity in and around dam sites before and after the impounding.
Dams sampled in this research are forty three dams with the height of dam crest more than eighty meters where the impoundment started during 1963-1976.
Seismic data used are taken from “The Seismological Bulletin of the Japan Meteorological Agency (January 1926 to October 1980)”.
Seismic activities within the hypocentral distance of fifty kilometers from the centers of dams are surveyed by dividing the periods into two before and after the impounding.
The nature of seismic activity for forty three dam sites can be divided into the following three classes:
(1) Seven dam sites where seismic activity became active after the impounding.
(2) Twenty one dam sites where seismic activity did not change through before and after the impounding.
(3) Fifteen dam sites where the change of seismic activity is hard to be clearly recognized by the impounding.
In some of these dam sites, earthquake swarm followed after the impounding. These earthquake swarms, however, are difficult to be connected to the impounding, because the hypocentral distances are too far as thirty to fifty kilometers. This is a subject to be solved in future.
It has generally been considered that induced seismicity is closely related to geological structure of the dam site. But, the present paper does not discuss about it and left it to a future study too.