A Hypocenter-Determination Method Using Station Corrections as a Function of Hypocenter Coordinates

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  • HURUKAWA Nobuo
    International Institute of Seismology and Earthquake Engineering, Building Research Institute
  • OHMI Shiro
    National Research Institute for Earth Science and Disaster Prevention

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  • 震源座標の関数としての観測点補正値を用いた震源決定方法
  • シンゲン ザヒョウ ノ カンスウ トシテノ カンソクテン ホセイチ オ モチイ

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A simple method to determine hypocenters of earthquakes taking account of a lateral heterogeneity of the Earth is proposed. In this method we calculate a hypocenter using station corrections as a function of hypocenter coordinates (x, y, z). The lateral heterogeneity is corrected by these station corrections. We assume that station correction SCj at a j-th station is represented as follows: SCj=aj+bjx+cjy+djz+ejxy+fjyz+gjzx+hjx2+kjy2+ljz2. Where aj, bj, …, lj are constant.<br>Coefficients aj, bj, …, lj are obtained as follows: Dividing a whole region into many sub-regions, we relocate earthquakes in each sub-region by the method of joint hypocenter determination. We regard station corrections obtained in this sub-region as those at the center of the sub-region. Obtaining station corrections at all sub-regions, we interporate them by a function that is a quadratic form of x, y and z. Station correction SCij at the j-th station obtained at the i-th sub-region is represented as follows: SCij=aj+bjxi+cjyi+djzi+ejxiyi+fjyizi+gjzixi+hjxi2+kjyi2+ljzi2. Where xi yi and zi are x, y and z coordinates of the center of the i-th sub-region, respectively.<br>Obtaining station corrections at 41 stations of the Kanto network of the National Research Institute for Earth Science and Disaster Prevention, we relocated earthquakes in the Kanto district. Since the effect of the lateral heterogeity is taken account of, there is no magnitude dependence of hypocenters, which obscures spacial distribution of earthquakes determined by the previous method. We can obtain a fine distribution map of hypocenters.

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