Seismic signal delays documented in 1975 earthquake


  • Anonymous


A major (magnitude 7.2) earthquake which struck Kalapana, Hawaii, in 1975 was preceded by a seismic velocity decrease, according to Arch C Johnston of the Cooperative Institute for Research in Environmental Sciences. In comparing the arrival times of seismic waves from the active Fiji and Tonga island chains, Johnston found that beginning about 3½ years before the Kalapana earthquake, a given signal from one of the Fiji quakes took about a fifth of a second longer to reach the station nearest the Kalapana epicenter than had previous signals. The travel time returned to normal a few months before the quake occurred.