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通常首波被认为是以下层高速度沿着平坦界面传播的折射波。然而,沿着不规则界面首波的传播路径至今仍不明确。在这里,我们将利用重叠单元(SEMO)方法以模拟的方式来研究这个问题。之所以选择重叠单元方法,是因为这种方法可以准确地计算出沿不规则界面传播的界面波。然后我们利用时间窗将首播从界面波中分离出来,并分析首播沿不规则界面传播进程中能量的变化和走时的变化。分析结果表明,与平坦的界面上首播的传播情况不同,沿不规则界面传播的首播由两种机制产生:折射机制和透射机制,也就是说,首播可能是沿界面传播的折射波或高速介质中向低速介质的透射波。关于首播的这种认识将有助于我们建设更加精确的首播反演方法,例如建立更为精确的首波旅行时层析成像,并由此获得更准确的地下结构模型,这对于研究认识一些特殊地区(如青藏高原)的形成机制是非常重要的。
Often the first wave is considered as a refracted wave propagating along a flat interface at high velocity. However, the propagation path of the first wave along the irregular interface is still not clear yet. Here, we will use the overlap unit (SEMO) method to simulate the way to study this issue. The reason for choosing overlapping elements is because this method can accurately calculate the interface waves propagating along the irregular interface. Then, we use the time window to separate the premiere from the interface wave and analyze the changes in energy and travel time in the first broadcast along the irregular interface. The analysis shows that, unlike the first broadcast in a flat interface, the first broadcast transmitted along an irregular interface is generated by two mechanisms: the refraction mechanism and the transmission mechanism. That is, the premiere may be a refracted wave propagating along the interface or a high-speed medium Medium to low-speed transmission medium wave. This understanding of premiere will help us to build more accurate inversions, such as more accurate first-wave travel-time tomography and more accurate subsurface structure models, The formation mechanism of special areas (such as the Qinghai-Tibet Plateau) is very important.