On Anomalous Time-Distance Curves Observed in Local Earthquakes

Abstract

The precise observations of local earthquakes were carried out in Wakayama District, Japan, for the purpose of studying the crustal structure and the nature of local shocks.

The travel-time anomalies were detected, and the anomalous time-distance curves were separable into two groups which seemed to be related with the directions of the initial motion of shocks recorded at their respective stations. The causes of the travel-time anomalies may reasonably be attributed to the condition of the hypocentre and mechanism of earthquake occurrence.