用均匀等价层模拟地表低速层SH波波动特征的有效性问题

THE EFFECTIVENESS OF AN EQUIVALENT MODEL APPLICATION TO SIMULATE SEISMIC SH WAVE CHARACTERISTICS IN WEATHERING LAYERS

针对地表低速层对勘探反射地震波到时和波形的改造作用,这里探索了用一个简单等价模型来计算低速层对反射波影响的有效性问题。这里先介绍等价模型的构建方法,然后分别对原模型与等价模型模拟计算了从0到511Hz共512个频率的简谐SH波场,并对之进行了比较研究。结果表明,用等价模型模拟计算得到的反射波场的低速层时延是正确的。子波波形前面部份与原模型的结果相似,但波形在整体形状和幅值上都相差很大。因此,用等价模型来模拟计算低速层的静校时差,以及对子波波形的前面部份是有效的,但还不能完整地反映低速层对子波波形的改造作用。

This paper explores the effectiveness of a simple equivalent model application to study the effects of weathering layers on seismic reflected waveforms. The construction of the equivalent model is first described. Then 512 harmonic wavefields with frequencies from 0 to 511 Hz are simulated using the both of the original and equivalent models. The comparison of the two sets of synthetic seismic data shows that the time delay calculated using the equivalent model is correct and the first part of its wavelet waveform is similar to that of the original model. However the shape of the total waveform and its amplitude are very different from the original model. Therefore it is valid to use the equivalent model for calculating time delays, but invalid for determining the total effects of the weathering layer on the waveforms.