多波多分量波场的地震物理模型观测

The observation of multiwave-multicomponent wave-field with seismic physical modeling.

在纵波震源激发的三分量记录中,经常在SH分量上得到P波或SV波的反射,通常认为这是地下不均匀或各向异性引起的,然而,均匀各向同性介质的三分量记录上也出现了各种波的反射同相轴。为此,在实验室进行了多波多分量地震物理模型实验,以解释这种现象出现的原因。采用纵波和横波换能器作为模型实验的震源和接收器,并通过将横波换能器的偏振方向转动90°来获得九分量的观测方式。设计了均匀各向同性层状介质和倾斜介质物理模型,利用纵测线和非纵测线得到了多波多分量的观测记录。对观测记录分析发现,平层模型纵测线观测时,在P-P,P-SV和SV-SV分量上都可以看到P波、转换SV波和SV波,这从另一方面说明,无论是P波震源还是S波震源都会产生P波和S波;平层模型采用非纵测线观测时,也能在各分量上得到各种波的反射;倾斜模型用P波震源激发,在SH分量上能接收到P波或SH波反射,这是因为P波和S波在SH分量上有振动分量。

P-wave or SV-wave reflection events can often be found in SH-component of three-component reflection records excited by P-wave source, which usually was thought to be cause by subsurface unhomogeneity or anisotropy. However, reflection events of all kinds of waves in threecomponent records can still be observed in homogeneous isotropic media. We use P-wave and S-wave transducers as source and receiver respectively, and we can acquire nine-component observation method by rotating the polarization direction of the S-wave transducer by 90°. Single-shot multiwave-multicomponent records are acquired on physical models of homogeneous isotropic stratified and oblique media with both in-line and out-of-line methods. The experiments indicate that when P- wave or S-wave source propagates in elastic media, S-wave or P-wave will be produced besides the main vibration P-wave or S-wave. Even in isotropic media, reflection events of these waves can still be obtained in records of various components when using out-of-line method on plane model. And the reason that P-wave or SH-wave reflection events can be found in SH component of three-component records excited by P-wave source on oblique model is that there is vibration component of reflection p-wave and S-wave on SH component.