ゑびの・吉松地震調査報告

Abstract

On the 21st of Feb. 1968, an earthquake swarm including the destructive earthquake, whoseMagnitude is 6.1, began to occur near the borderland between Miyazaki and Kagoshima pre-fecture.In the past, similar earthquake swarm often attacked this area, and some volcanoes in Kin-shima Volcanic Belt successively erupted following it in some cases. Therfore, recent earthquakeswarm awoke our volcanological interests so much.We carried out the multipatite seismometric observation in small area from 1st to 7th of Marchfor the investigation of the natures of this earthquake swarm. The results of our investigation canbe summarized as follows:1) Hypocenters of observed earthquakes distribute forming the belt which is extending east andwest direction between Yoshimatsu and Kyomachi.2) The push-pull distribution of P wave showes the clear regularity for the azimuth. Consideringthis fact in connection with the data concerning the initial motion of the earthquakes so varsousobservatory, it may be possible to draw nodal line near north and south direction.3) The area closing the observed hypocenters is smaller than that expected from the empenicalformula of Utsu and Seki in the case of an earthquake whose magnitude is 6.1.4) The coefficient of Ishimoto-lida's emperical formula is as follows:m=2.02±0.19 (Feb. 29-Mar.24)m=l.80±0.24 (Mar. 25-May 31)