1946年南海地震の震源の位置

概要

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The hypocenter location of the 1946 Nankai earthquake is discussed based on observational results that most of large earthquake hypocenters obtained by recent seismic observation nets with high density and high accuracy in Japan are located in their respective aftershock distribution areas. However this argument is not applied to the hypocenter location generally given for the 1946 Nankai earthquake. Because the hypocenter and its aftershock distribution can not be accurately determined owing to the observation net biased to the inland and the poor time keeping of observation instruments at the time. Thus, to calculate the epicenter of the main shock we make use of the direction of seismic wave path to the epicenter obtained from the recorded amplitude of P first motions. Besides, we consider that the aftershock area of the 1946 Nankai earthquake corresponds to the focal distribution area of earthquakes which occur at present in the uppermost mantle of Shikoku and its vicinity. By comparing this aftershock distribution area with some main shock hypocenters currently proposed, it is concluded that two of those hypocenters are reasonable for the 1946 Nankai earthquake. One of them is located south off Shionomisaki in the tip of the Kii peninsula and another south off Tosa Bay. The latter hypocenter is appropriate to explain the large seismic disaster in the central and western regions of Kochi prefecture, Shikoku.
2002-12-25