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タイトル: Accuracy of the Initial Phase and the Phase Velocity of Surface Waves with Special Reference to the Single-Station Method
その他のタイトル: 表面波の初期位相と位相速度の精度 : 特に一観測点法に関連して
著者: Yoshida, Mitsuru
著者(別言語): 吉田, 満
発行日: 1983年3月31日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第57冊第4号, 1983.3.31, pp. 627-652
抄録: Initial phase of surface waves, which depends on such earthquake source parameters as depth, source-type and -orientation, source time function and medium property near the source, is investigated specially with respect to accuracy. The effects of small errors in the solution of the earthquake mechanism and uncertainties of the local underground structure near the source region on the initial phase of surface waves are quantitatively examined on the basis of the dislocation theory. By assuming the errors of source parameters and by using different medium models, the errors of the initial phase and surface wave velocity are evaluated. Against an error of ±5° in the dip and slip angles of the fault plane at the source, the space phase error in the initial phase is negligible in most parts of the azimuth except the minimum amplitude direction. Against an error of the source time function, the phase error of 0.1 radian or so may be caused at the period 40 sec and it decreases as the period increases. If we assume an earthquake with the magnitude 6 to be a point source, a phase error of maximum 0.4 radian in the initial phase due to the finite fault length will be produced at the azimuth just opposite to the rupture direction. It can be said that the space phase error due to uncertainties of the medium property near the source is negligible as far as we use a reasonable model representing the source region. Among the three phase factors of the initial phase, the error of the rupture propagation phase is largest, and the initial phase error decreases as the period increases. The total error of the initial phase seems not to exceed 0.6 radian at the period 40 sec and 0.3 radian at 100 sec, when an earthquake with the magnitude 6 or less is used and the station is carefully chosen in order to select the azimuth of the stable portion of the initial phase, by taking the amplitude radiation pattern of surface waves at the source into consideration. For an error in the initial phase of 0.6 radian at the periods 40 and 100 sec, for the path length of about 9000 km, the phase velocity error of Rayleigh waves is estimated to be 0.007 km/sec (0.17%) and 0.018 km/sec (0.44%) respectively.
URI: http://hdl.handle.net/2261/12861
ISSN: 00408972


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