Application of a seismograph network and electronic computer in near earthquake studies

Abstract

A description is given of the application of a close network of seismograph stations and of an IBM 650 computer program to the study of a sequence of near earthquakes in southeastern Australia. The epicenters, depths, and origin times of a moderate sized earthquake and its aftershocks were determined with unusual accuracy, revealing an interesting pattern of foci. The position and origin time of the main shock were then used to study arrivals at more distant stations; Pn arrivals were found to fit a linear travel-time equation closely to a distance of 15 degrees, with a surface velocity of 8.16 ± 0.03 km/sec. The Sn phase was not clear and gave an approximate velocity of 4.7 ± 0.2 km/sec. The possibility of a small velocity decrease in the upper mantle below eastern Australia is discussed.