SURFACE-POTENTIAL AND GRAVITY CHANGES DUE TO INTERNAL DISLOCATIONS INA 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 e arth. It is based on our previous work for a point dislocation (Sun & Okubo 1993). The formulation enables us to compute the displacement, p otential and gravity changes due to an earthquake modelled as spatiall y distributed dislocations. As an application of the finite-fault disl ocation theory, we make a case study of the theoretical and observed g ravity changes. The computed results are in excellent agreement with t he observed gravity changes during the earthquake. The gravity changes in the near field can reach some 100 mu gal, which can be easily dete cted by any modern gravimeter. In the far field they are still signifi cantly large: \delta g\ > 10 mu gal within the epicentral distance the ta < 6 degrees; \delta g\ > 1 mu gal within theta < 16 degrees; \delta g\ > 0.1 mu gal within theta < 40 degrees; and \delta g\ > 0.01 mu ga l globally. We also calculate the geoid height changes caused by the 1 964 Alaska earthquake and by the same earthquake with revised paramete rs and an assumed barrier. We find that the earthquake should have cau sed geoid height changes as large as 1.5 cm.