DIVERSITY OF SOLUTIONS OF THE PROBLEM OF EARTHQUAKE FAULTING INVERSION - APPLICATION TO SH-WAVES FOR THE GREAT 1989 MACQUARIE RIDGE EARTHQUAKE

We use the SH waves generated by the great 1989 Macquarie Ridge earthquake to investigate the non-uniqueness of the inverse problem of earthquake faulting. The details of the method of linear programming developed for this problem of solution of a constrained set of equations is described. Protective measures necessary to remove loss of accuracy when solving the problem for large numbers of unknowns and constraints are developed. It is shown that solutions which look very different fit the data almost equally well. A method is presented for choosing solutions with desirable properties (e.g. with the most uniformly distributed moment along the fault, or with the most concentrated moment release on the fault) from among available solutions. The results show that the data may equally well be interpreted as representing an asperity model of faulting or a propagating crack model of faulting. The common feature of all the models is that the hypocentral region is a region of low moment release, with regions of higher release being located to its northeast and its southwest along the fault. Clearly, this earthquake did not initiate by the rupture of an asperity.