生野鉱山内の山はねによる震動

Abstract

Rock burst occurred at the Ikuno mine in the central part of Hyogo prefecture on Jan. 26, 1970.Coincidently, ground tremors were also observed by the network for micro-earthquake observationstations in the prefecture and it is evident that the origin of tremors coincided with the rock burstarea.Energy release in the origin estimated as 3 x 10" ergs from the analysis of microseismogram andthis value coincides almost with the strain energies estimated from the situation of the brokendomain and the strength of rocks.An exact source-mechanism for the tremors could not be obtained. However it seems that thedirection of the principal stress (E-W) inferred from the seismic data was perpendicular to thevein-plane near the scene and a null vector of focal sphere was within the plane.Moreover, the E-W direction was the same as that of the tectonic forces in the prefecture.It is interesting to note the frequency of the rock burst and the active epoch of the seismic belt nearIkuno coincided with each other.