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我们观察了在纵波和横波地震数据中超临界反射的有趣的例子。数据是1977—1978年间由孔诺科(Conoco)横波组合爆炸计划在得克萨斯的米德兰盆地(Midland Basin)记录到的。正如资料中所观察,纵波和横波的临界角现象十分相似。在炮检距超过大约2000英尺以后,同相轴的振幅很小或不能检测出来,但排列在2500英尺到3600英尺之间时,其振幅又高于别的同相轴。在临界距离处出现的首波是微弱的,但可以观察到。纵波和横波同相轴的超临界部份的长程多次反射以预料到的倍数和炮检距出现。借助常速度时差校正可以确定它们. 声测井与岩性知识的结合使得纵波临界角现象的模型制作成为可能。当我们假定柱面波前时,模型的结果与数据的一致性是不错的。如所预期的,基于平面波的模型与所观察到的相位和振幅情况是不能一致的。勘探与数据处理中的临界反射的许多潜在应用确实来自于这样的思想,即许多超临界反射是与不同距离的相对高振幅记录有关,这里,震源产生的噪声是低的。特别对横波而言,接近临界炮检距时,在振幅上所观察到的上跳现象是非常突然的。这样就可推之,高振幅的波跳变化对于掌握反射界面处的速度对比的变化可能是有用的。
We observe interesting examples of supercritical reflections in longitudinal and shear wave seismic data. The data were recorded in the Midland Basin, Texas, from 1977 to 1978 by the Conoco shear-wave combined explosion program. As observed in the data, the critical angles of P-wave and S-wave are very similar. After an offset of more than about 2000 feet, the amplitudes of the events are either small or undetectable, but with amplitudes higher than the other events at altitudes between 2500 and 3600 feet. The first wave at the critical distance is weak, but observable. Long-range multiple reflections of the supercritical portion of the compressional and shear-wave events occur at expected multiples and offset distances. They can be identified by means of constant velocity time difference correction, and the combination of acoustic logging and lithology makes modeling of the critical angle of P-wave possible. When we assume the wavefront of a cylinder, the consistency of the results of the model with the data is good. As expected, the plane wave based model is not consistent with the observed phase and amplitude conditions. Many of the potential applications of critical reflections in exploration and data processing do come from the idea that many supercritical reflections are related to relatively high amplitude recordings at different distances where the noise generated by the source is low. Especially for shear waves, the jump observed in amplitude is very abrupt when approaching the critical offset. As such it can be deduced that a high amplitude wave jump change may be useful for grasping the change in speed contrast at the reflecting interface.