Estimation of propagation direction of earthquake ground motion near ground surface based on array observation data

The three-dimensional propagation directions of earthquake ground motion near ground surface are estimated for eight earthquakes. By the NIOM method, three dimension (3-D) oriental angles are resulted in determining the arrival time of an incident wave and a reflective wave. In this study, the estimation method of 3-D propagation directions is developed rationally and confirmed reliably with the independent data of Chiba array in Japan. The propagation directions are equivalent numerically to the geographical position of plural spots in horizontal and vertical, and the theoretical result obtained by the structural model of global horizontal layer velocity.