Localized compressional velocity decrease precursory to the kalapana, hawaii, earthquake.
A delay in the arrival times of compressional or P waves of 0.15 to 0.2 second from deep distant earthquakes has been detected at the closest seismograph station to the 20 November 1975 earthquake at Kalapana, Hawaii (surface-wave magnitude MS = 7.2). This delay appeared approximately 3.5 years prior to the quake, and travel times returned to normal several months before it. The P-wave arrival times at other nearby stations remained constant during this period, an indication that the decreased velocity implied by the delay in travel time was associated with this normal-faulting earthquake and was confined to distances less than 20 kilometers from the epicenter.
Johnston
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