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约30年来,杰弗瑞斯一布伦(J-B)时距曲线被认为是最准确的标准时距曲线.但观测到的地震波走时在3—4秒时很少与J-B时距曲线所给定的值一致.在地震工作者中就爆破和地震所观测到的地震波走时不同的原因进行过争论,大多数学者认为走时之所以有差别是由于爆破时观测的精度较高所致.为了提高时距曲线的精度,也就是建立全球平均状态的时距曲线,必须考虑不同震中区的速度特点.而J—B时距曲线所利用的地震大多属于太平洋地震带,不能作为全球的平均值.1968年得出的时距曲线虽然用了278个地震和13个爆破的资料,但时距曲线在纵坐标中的位置是根据美国中部地区和上地幔构造模型确定的,因此,也不能作为全球的平均值.
The Jeffreys-Bruins (JB) time-span curve is considered to be the most accurate standard time-span curve for approximately 30 years, but the observed seismic wave travel times are rarely as large as 3-4 seconds for the JB time-distance curve The authors agree that the reason for the difference in travel time is due to the higher accuracy of observations during blasting.In order to improve the time-interval The accuracy of the curve, that is, the time-span curve for establishing the global average, must take account of the velocity characteristics of the different epicentral regions, whereas most of the earthquakes utilized by the J-B time-history curve belong to the Pacific Seismic Belt and can not be average globally. Although the time-history curves are based on data from 278 earthquakes and 13 explosions, the location of the time-distance curve in the ordinate is based on the US Central and Upper Mantle tectonics model and therefore can not be used as a global average value.