A travel-time study made in the Hidaka region,Hokkaido,Japan,on the "source" of series of earthquakes of the Usu volcano.

Abstract

The source of natural earthquakes poses an intrinsic problem of loss of precision in a travel-time study. For example, the loss-of-precision problem is, in particular, a result of inherent low accuracies of source parameters of origintime and hypocentral coordinates for an earthquake occurring in a sparse seismological network. Hitherto, such demerits have been overemphasized even if greater seismic wave energy can usually be generated than with an artificial earthquake caused by an explosion.