沖縄県地方における地震危険度について

概要

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The rational approach to the aseismic design for buildings and structures has to be based on the seismic hazard in the area concerned. This paper deals with the seismicity in Okinawa area by using the data for intensities of earthquakes observed in eight meteorological stations, and magnitudes and seismic centers of earthquakes caused annual maximum earthquake motions. The adequacy of the 'zone factor' in the aseismic design code is discussed by the estimated maximum accerelation on ground surface after Kanai's formula.It is found out that the seismisity in Miyako and Yaeyama, among many islands of Okinawa, is to be comparatively high. The probability distribution of the logarithm of annual maximum acceleration is well-fitted by Gumbel's third distribution function. The expected annual maximum acceleration on ground surface in return period of 100 years is estimated 60 to 90 gal for Okinawa main island area, and 90 to 140 gal for Miyako and Yaeyama area. It is concluded that the application of the different 'zone factor', i. e., 0.5 for Okinawa main island area, 0.7 for Miyako and Yaeyama excluding Yonaguni island, and 0.9 for Yonaguni island is more adequate, instead of appling 0.7 in conventional code over the entire area of Okinawa Prefecture.
1994-09-01