Abstract
An earthquake of magnitude 6.1 occurred off the Atsumi Peninsula on January 5, 1971. A few foreshocks and many aftershocks were recorded at many seismological stations of both the Wakayama Micro-earthquake and the Inuyama Seismological Observatories. The distribution of hypocenters and nodal plane solutions were examined with the following results:
1) The epicenters of foreshocks, the main and large aftershocks were located along the line N 60°W-S 60°E across the Median Tectonic Line. The foreshocks occurred in the northern side of the Median Tectonic Line were very shallow as deep as 2km. However, the main shock and most of the aftershocks occurred in the southern side of the Median Tectonic Line were rather deep, about 30km in depth. But some of focal depths of aftershocks occurred near the largest foreshock were about 5km.
2) It seems that there were two types of earthquake mechanism in this region. The mechanisms of foreshocks and the aftershocks which occurred in the foreshock region were dip-slip-fault type with the pressure axes of N 90°W. On the contrary, those of the main shock and the deep aftershocks which occurred near the main shock were strike-slip-fault type with the pressure axes of N 30°W.
3) The daily frequency distribution of aftershocks was well represented by the Omori's formula N (t) =k. t-p for the first fifteen days, where p=1.2.
