Some Problems on Poisson’s Ratio in the Earth‘s Crust

Instead of the time-distance graph, the P-S diagram is effectively employed to estimate the value of Poisson’s ratio in the earth’s crust. This diagram is advantageous, especially to detect its local anomaly or distribution. The obtained results are as follows:

1. Applying this method to eighteen earthquakes occurring in south-western Japan, the domain with anomalously large Poisson’s ratio was found in the Kyushu district. This hints to the possibility of an existence of a local magmatic reservoir.
2. The azimuthal distribution of the crustal Poisson’s ratio in case of earthquake occurrence was investigated and it was found to be considerably different in the push- and pull-zone of initial seismic motion. This may be related to the state of stress accumulation causing the earthquake occurrence.