Study of a Crater Structure found in the south of Takamatsu City, Kagawa Prefecture, Japan Professor

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A crater-like structure was found in the south of Takamatsu city, Kagawa prefecture, western Japan. This may be the first finding of an impact crater in Japan.The structure was firstly detected by a abnormal value of gravity which is obtained in a course of regional gravity measurements over the Japanese Islands by us. After several tens of gravity measurements around the anomalous data point, depression of gravity anomaly appeared clearly. This crater was named as the Takamatsu crater. Topography around the crater is nearly flat and no geographical manifestation to indicate a crater-like structure beneath the earth's surface.More than 500 gravity measurements, geomagnetic anomaly measurements at more than 100 points and 2 sections of reflecting seismic wave measurements were carried out over and around the crater.Gravity and seismological analysis revealed that the crater is 4 km in diameter and 1.5 km in depth. The structure presumably buried by about 100 m thick Quaternary sediments.There are two hypothesis about origin of the Takamatsu crater. One is meteorite impact origin, i.e., impact crater. The other is volcanic eruption origin, i.e., caldera.Already some characteristic minerals are found from the crater area suggesting meteoritic impact origin.This crater also contains great amount of underground water. Since the crater has not only scientific values but also economical values, we hope that deep drillings undertaken in this crater.