Relative Hypocenter Location Algorithm by Registering Past Earthquakes (hypoTD): Method and Application to Earthquakes Beneath the Japanese Islands
By Shigeki Horiuchi, Shuken Wada, Yuko Sato, Minoru Yoshida, Yoshiharu Hirayama, Hiroyuki Fujiwara

ABSTRACT
We developed a new method for determining relative hypocenter locations by registering all past earthquakes or relatively large ones. We conducted a relocation of 4.1 million hypocenters of earthquakes that have occurred in and around the Japanese Islands over the last 22 yr. We compare hypocenter distributions obtained by the present method and by the hypoDD method. We also compare the root mean square of travel‐time residuals and values of the migration of hypocenters due to changes in the parameters and velocity structure used in hypocenter determination. These comparisons indicate that the hypocenters determined via the present method appear to be better constrained than those determined via hypoDD. It would have been better to compare the results to another more recent method such as the double‐pair double‐difference or the tomoDD methods. On the other hand, hypoDD is still being widely used.
  
KEY POINTS
· We developed a new method of relative hypocenter location.
· Hypocenters determined via the present method appear to be better constrained than those determined via hypoDD.
· It is available for the real-time monitoring of precise seis-mic activity over a wide area.