均匀介质背景中三维异常体的面波波场响应及其动力学特征分析

Surface wave wavefield and dynamic analysis for three-dimensional abnormal structures with homogenous background velocity model

除介质各向异性之外,地球内部介质的横向非均匀性也是控制面波速度变化的重要因素.本文基于振型耦合和多重散射的地震波传播理论,数值模拟并分析了在具有均匀介质背景的三维异常体——上地幔横向非均匀介质中传播时.地震面波的振幅与偏振等动力学响应参数;其中分别模拟了不同周期入射、不同角度入射和不同尺度非均匀介质模型等多种情形下面波波场,并对横向非均匀性诱导的面波偏振异常进行了分析.结果表明,相对于长周期面波而言.短周期面波的振幅和偏振方向受横向非均匀性的影响更大,特别是偏振方向对地球结构的非均匀性更为敏感;切向分量存在横向非均性引起的Rayleigh与Love面波耦合现象;异常体边界处表现出强的面波波场响应.

Besides anisotropy, lateral heterogeneity in the earth is also one important factor affecting surface wave velocities. Based on the theory of mode coupling and scattering of seismic waves, the amplitude and polarization anomalies of surface waves propagating in a 3D heterogeneous model are numerically computed. Surface wave wavefields have been simulated for several different incident situations. That is to say, the incident waves have different periods, different back-azimuths by rotating the structure in horizontal plane and different sizes of heterogeneity. Emphases were laid on the investigations of the importance of amplitude and polarization anomalies of surface waves, which are induced by lateral heterogeneity. We can conclude that amplitudes, especially polarization anomalies, of short-period surface waves are more sensitive to the lateral heterogeneity than those of long-period waves. Coupling between Rayleigh waves and Love waves occurs on transverse components because of the existence of lateral heterogeneity. Larger amplitudes of surface waves locate in the boundary of the lateral heterogeneity structure.