Fast hypocenter determination in an inhomogeneous velocity structure using a 3D travel-time table

The computer processing time required for raytracing and hypocentre determination in a 3D inhomogeneous velocity structure is too great for the method to be used to locate a large number of hypocenters or for interactive processing. In this study, hypocenter determinations were conducted using 3D travel-time tables (3D-TTs) to reflect travel times of a 3D inhomogeneous velocity structure in event locations, and the results were compared with those achieved using the 3D raytracing method. The use of 3D-TTs reduced the calculation time by a factor of about 1800 compared with the raytracing method. Whereas minor differences between interpolated travel times and the raytracing method caused some corresponding location differences, the travel-time table was effective for correction of hypocenter locations according to an inhomogeneous velocity-structure model.