Surface potential and gravity changes due to internal dislocations in a spherical earth-II. Application to a finite fault

Abstract

SUMMARY We present a numerical formulation for computing elastic deformations caused by a dislocation on a ¢nite plane in a spherically symmetric earth. It is based on our previous work for a point dislocation (Sun & Okubo 1993). The formulation enables us to compute the displacement, potential and gravity changes due to an earthquake modelled as spatially distributed dislocations. As an application of the ¢nite-fault dislocation theory, we make a case study of the theoretical and observed gravity changes. The computed results are in excellent agreement with the observed gravity changes during the earthquake. The gravity changes in the near ¢eld can reach some 100 ]gal, which can be easily detected by any modern gravimeter. In the far ¢eld they are still signi¢cantly large:jdgj > 10 ]gal within the epicentral distance h 1 ]gal within h 0:1 ]gal within h 0:01 ]gal globally. We also calculate the geoid height changes caused by the 1964 Alaska earthquake and by the same earthquake with revised parameters and an assumed barrier. We ¢nd that the earthquake should have caused geoid height changes as large as 1.5 cm.