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

We present a numerical formulation for computing elastic deformations caused by a dislocation on a finite 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 finite-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 field can reach some 100 μgal, which can be easily detected by any modern gravimeter. In the far field they are still significantly large: |δg|>10 μgal within the epicentral distance θ<6° ; |δg|>1 μgal within θ<16° ; |δg|>0.1 μgal within θ<40° ; and |δg|>0.01 μgal 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 find that the earthquake should have caused geoid height changes as large as 1.5 cm.