1966年イカ地震(ペルー)前後の土地の異常変動

Abstract

The international cooperative observations of the crustal movements related to seismic activi-ties were commenced in the lea region, Peru, at the end of 1965. OnJune 7th in the next year, theearthquake of magnitude around 6 occurred off the coast of lea, accompanying a foreshock and alarge number of aftershocks.At that time the observations had not got to stable conditions, however, anomalous groundtilts had been observed at the three observation stations for a few months before the occurrence ofthe series of earthquakes. The vectors of anomalous ground tilts had the same direction as thestrike of the faults in the region. At the nearest station, Zamaca, characteristic changes of groundstrains, extending in the E-W component and contracting in the N-S component, also began 20 daysbefore the occurrence of main shock and continued to the termination of aftershock activities. Itshould be noticed that the ground tilts preceded the ground strains there.Examining these observed facts, in detail, it may be suggested that accumulated energy inthe crust is first consumed with block movements or deformation of the ground surface and thenconcentrates in the focal region, in the case of a mosaic structure as expected from the faultingsystem in this region.