论文部分内容阅读
在密西西比南部应用垂直地震剖面法(VSP)进行的垂直波试验进一步证实,视多次波不但可能包括转换波而且也包括多次反射纵波。震源附近所观察到的P波和S波传播的深度很大,P波向S波的转换在深部和浅部都是明显的。P波反射与根据声测井所作的合成记录的预测是一致的。上行P波在地面以下一小段距离的低速层底部被反射,然后作为下行P波被在200英尺深度上的垂直排列所接收。在200英尺以下,跟在初至P波波列后面的主要能量似乎是下行P波,不能追踪这些波回到上行P波的反射。子波的连续性表明,震源附近产生的强下行S波,在800和1400英尺之间的范围内某处通过S-P转换而产生P波。用单个地震检波器或少量地震检波器组合接收,以炸药爆炸作为震源所得到的记录上的干扰通常都具有低频特性,因此可用高通滤波器改善信噪比(S/N)。当使用长度范围为100英尺的散布型炸药作震源时,不用滤波器也能使记录上的干扰大大减少。用散布型炸药在P波的反射频带内所产生的S波能量很少,就证明在应用集中型炸药震源时所遇到的干扰是由于震源附近产生的S波的缘故。选择散布型炸药作震源可以有效地消除次生反射(伴随波),这是一种不需要的多次反射波的形式。
Vertical wave tests using vertical seismic profiling (VSP) in southern Mississippi further confirm that apparent multiple waves may include not only converted waves but also multiple reflected longitudinal waves. The P and S waves observed near the source have a large depth of propagation and the P to S wave transitions are evident both in the deep and shallow parts. The P-wave reflection is consistent with the prediction of composite recordings based on acoustic logging. The upgoing P-wave is reflected at the bottom of the low-velocity layer a short distance below the ground and then received as a down-going P wave in a vertical arrangement at a depth of 200 feet. At 200 feet below, the primary energy behind the P-wave arrives at the beginning of the P wave appears to be a descending P-wave that can not be traced back to the up-going P-wave reflections. The continuity of the wavelet shows that the strong descending S-wave generated near the hypocenter generates P waves somewhere between 800 and 1400 feet by S-P conversion. High-pass filters can be used to improve the signal-to-noise ratio (S / N) by recording with a single geophone or a small number of geophones in combination and the resulting interference recorded on the explosives as a source of vibration typically has low frequency characteristics. When using dispersive explosives with a length of 100 feet as the source, the interference on the recording can be greatly reduced without the use of filters. The small amount of S-wave energy produced by the scattered explosives in the reflection band of the P-wave proves that the disturbance encountered in the application of concentrated explosives is due to the S-wave generated near the source. The choice of dispersive explosives as a source of vibration can effectively eliminate secondary reflections (accompanying waves), an unwanted form of multiple reflections.