観測点から逆伝播する波面の重複点検出による簡易震源決定法

抄録

When a large earthquake occurs, understanding general earthquake activity immediately is important. However, arrival-time classifications, which involve grouping by earthquake and seismic phase discrimination are difficult to perform. Hence, we developed a new simple hypocenter determination method without these classifications. Only the arrival time was used. In our method, both the P and S phase wavefronts propagate reversely from the P and S arrival times from the seismic stations. The location where many wavefronts overlap is the seismic source, that is, a hypocenter. The wavefront is an isochronous surface of the travel time calculated using the ray tracing method. The target space-time volume was discretized, and travel times at all grid points in the volume from all seismic stations were calculated in advance. One point was added to the grid points at which each wavefront was present. The grid point of the local maximum score, where the wavefronts overlapped, was searched and extracted as a seismic source. Assigning points only to grid points on wavefronts is important to significantly reduce the computing time. We applied manually picked arrival time datasets of four typical seismic activities in Japan from Hi-net to our method, and successfully extracted sufficient source locations to understand the general distribution within an acceptably short computation time for each dataset.