奄美大島の地震活動

Abstract

To study the seismic activity near and at Amami-Oshima, 3 conponents electro-magnetictype seismographs were set up at Naze city in Feb., 1969. Soon after then, a distructive earthquakeattacked this region and gave a comsiderable dameges in inhabitants.In this paper, the modes of the seismic activity before and after this distructive earthquake arediseussed from the results of the seismic observation. The main results are as followes.1) Before this earthquake the number of earthquakes in this region was not so many, but the greatmany after-shockes followed the main-shock.2) The decreament of the after-shockes was slowly untill 20 days after the main-shock, but afterthen it was normal, that is, the value of p in the reformula for Omori's one, which was proposed byUtsu, n(t)=A/(t+c)p, was 1.15.3) The epicenters of the after-shocks distributed in 10-15 km apart to NW from Naze.4) The value of m in Ishimoto-lida's emperical formula was 2.06 before this earthquake, and was1.81 for the after-shockes.