Crustal Movements Related to the Earthquake on March 18, 1987 in Hyuganada

Abstract

Crustal deformations associated with the earthquake of magnitude 6.6 on March 18, 1987, in Hyuganada east of Kyushu in Japan are investigated. Of nine extensometers at three observatories around Hyuganada, only one extensometer at Miyazaki, where the epicentral distance is 62km, recorded an irregular strain change just before the earthquake hidden in the data behind the disturbance due to rainfall. Co-seismic strain steps observed are compared with calculated strains by a dislocation theory. Observed strain steps in five components at two stations agree well with theoretical ones. Post-seismic aftereffects were observed at all observatories. They cannot be attributed to the source property, but probably due to the viscoelasticity around the observatories, as well as to more local or instrumental effects.