地下爆炸Rg波低谷点激发机理

Generation of null in Rg wave by underground explosions

目前普遍认为Rg_S散射是地下核爆炸短周期Lg波的主要能量来源,其主要依据为由线性偶极补偿源(CLVD)激发的Rg波谱的低谷点随深度变化的特征与区域震相Lg波谱的低谷点随深度变化的特征具有一致性.本文利用简正振型理论,分析了Rg波谱中低谷点的形成机理,给出了各种速度模型下CLVD源深度与低谷点频率之间的关系,并分析了利用公式hCLVD=V (16fNull)估计震源深度的局限性.本文的研究结果进一步支持了CLVD源是激发Lg波的主要因素的观点,并得到重要结论:CLVD源形式下的本征位移函数及其导数的叠加所形成的极小值,即源的空间分布特征,是形成Rg波低谷点的原因,而不能仅用水平向基频本征位移函数过零点来解释.

It is widely accepted that the near-source scattering of explosion-generated Rg into S is the primary contributor to the low-frequency Lg from nuclear explosions, because the prominent low-frequency spectral null in Lg coincides with that in Rg from a compensated linear vector dipole (CLVD) source. In this study, the mechanism of the excitation of the spectral null of Rg generated by the CLVD source is analyzed in detail with the normal mode method. The most important result in this study is that the spectral null is due to a combination of displacement eigenfunction and its derivative of the fundamental-mode Rayleigh wave controlled by CLVD source, not only the zero-crossing can fully explain the excitation of the spectral null.