Hypocentral parameter inversion for regions with poorly known velocity structures

The determination of accurate hypocentral parameters is crucial in seismic monitoring, and is highly dependent on the accuracy of the implemented velocity model in conventional methods. A method to determine accurate hypocentral parameters based on an approximate velocity model is desirable. We introduce an iterative velocity updating scheme that can be readily combined with conventional hypocentral inversion methods. The algorithm searches for an optimum velocity model in a prescribed velocity range that minimizes the traveltime residuals. The hypocentral parameters are determined using the optimum velocity model. The proposed scheme reduces the dependence on a given velocity model in hypocentral inversion, providing reasonable hypocentral parameters based on an approximate velocity model. The feasibility and accuracy of the algorithm are tested with synthetic and field data. The scheme yields hypocentral parameters that are as accurate as those from full inversion methods but with approximately 70 times lower cost in terms of computational time. The proposed scheme can be readily implemented in any conventional method that is based on a fixed velocity model.