TWO DISTINCT PHASES IN THE INITIAL P-WAVE GROUP OF THE NIIGATA EARTHQUAKE OF 1964 AND OF THE TAIWAN-OKI EARTHQUAKE OF 1966

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In general, it is not adequate to analyze the form of body waves radiated by a shallow earthquake, because the initial P-wave group may be contaminated by various complicated phases. But in the cases of the Niigata earthquake (h=12 km by ISS) of 1964 and the Taiwan-oki earthquake (h=42 km) of 1966, the initial P-wave form on seismograms has two distinct phases. One of these phases can be thought to be the stopping phase and the other to be the break-out phase. It is possible to obtain the seismic parameters by analyzing these two phases and to determine the fault plane of the earthquake.