Hypocentre determination offshore of eastern Taiwan using the Maximum Intersection method

The maximum intersection (MAXI) method, which derives from the master station method (MSM), determines within a 3-D velocity model the absolute hypocentral location based on observed arrival times. First, the spatial node that better satisfies the arrival time differences computed at all station pairs, plus or minus an error tolerance value (in seconds), is defined as the preliminary hypocentral solution (PRED). Second, because PRED depends neither on the estimate of origin time nor on the residual root mean square (rms), residual outliers are objectively detected and cleaned out from the original data set without any iterative process or weighting. Third, a statistical minimization (residual rms) is conducted in a small domain around the PRED node, which results in a unique FINAL solution. The MAXI method is applied to the determination of earthquake hypocentres (with the proper station correction terms) in the southernmost extremity of the Ryukyu subduction zone, where several dense seismic clusters occur near the seismogenic plate interface. The location of earthquakes, recorded at both the Taiwanese and Japanese networks, is obtained for about a thousand events (between 1992 and 1997). The process uses a detailed 3-D velocity model based on multiple geophysical data sources obtained in the junction area between subduction and collision (east of Taiwan). The earthquake clustering and the significant drop in residual statistics (1.20, 0.80 and 0.35 s, for Taiwanese catalogue, MSM and MAXIM solutions respectively) indicate the accuracy of the method, which can be used to routinely determine absolute hypocentre location based on observed arrival times.