日向灘地殻活動総合観測線による地殻変動連続観測と地震活動

Abstract

1996年10月19日, および12月3日に日向灘中部でM6.9, M6.7の地震が続けて発生した。一方宮崎観測所の地殻変動連続観測においては, 歪の経年変化に数ヶ月前からそれまで(記録開始から地震前20年間)見られない変動が現れている。また, 地震後の歪の経年変化は, 2つの地震が発生した日向灘中央部の最も地震活動が活発な地域の積算地震数の変化と良い関係を示している。

Two earthquakes occurred with magnitude 6.9 and 6.7 at the central part of Hyuganada Sea, east off Kyushu, on October and December, 1996. Seismic activities and crustal movement before and after these earthquakes are examined by using data at Miyazaki Observatory, DPRI, Kyoto Univ., where 52 km and 19 km respectively apart from the epicenters of each event.Secular variations of continuous strain observations revealed increase in strain rate at 13 months before the occurrence of the first event.The major axis of the principal strain rate is expansion of 2.17E-6/year in north-south direction that is seven times of the value before the appearance of this acceleration of strain accumulation.It is reported about the change after that crustal deformations and the recent earthquake activities of the Hyuganada region, and examined about the one with the relation of the crustal movement and the earthquake activities.