不均匀无应力场地上地震动的放大和持时的增加
Amplification and Increased Duration of Earthquake Motion on Uneven Stress-Free Ground
摘要：
当平坦的无应力表面（即，地震学应用中的地面）将空气与各向同性的、均匀的或水平分层的固体基底分离，由入射在基底中的SH平面体波引起，基底中的响应是单个镜面反射体波。当通过引入{空间常数、非零表面阻抗}来放松等效于零表面阻抗的无应力条件时，基层中的响应再次是单个反射体波，其振幅小于无应力地面情况下的振幅。当无应力条件通过引入α {空间调制表面阻抗}而放松时，其模拟不均匀的作用（即，不是完全平坦）的地面，频域响应采取{平面体波}和{表面波}的频谱形式，并且在一个或多个表面波振幅可能变大的频率下产生{共振}。它示出，在谐振，振幅的一个，或几个，组件的运动在表面上可以被放大的情况下，其中表面阻抗是恒定的或消失。此外，当请求是脉冲状时，对于空间调制阻抗表面，表面位移的平方和速度的平方的积分时间历程可以更大，并且信号的持续时间可以比恒定或消失的阻抗表面长得多。
英文摘要：
When a flat stress-free surface (i.e., the ground in seismological applications) separating air from a isotropic, homogeneous or horizontally-layered, solid substratum is solicited by a SH plane body wave incident in the substratum, the response in the substratum is a single specularly-reflected body wave. When the stress-free condition, equivalent to vanishing surface impedance, is relaxed by the introduction of a {spatially- constant, non- vanishing surface impedance}, the response in the substratum is again a single reflected body wave whose amplitude is less than the one in the situation of a stress-free ground. When the stress-free condition is relaxed by the introduction of a a {spatially-modulated surface impedance}, which simulates the action of an uneven (i.e., not entirely-flat) ground, the frequency-domain response takes the form of a spectrum of {plane body waves} and {surface waves} and {resonances} are produced at the frequencies of which one or several surface wave amplitudes can become large. It is shown, that at resonance, the amplitude of one, or of several, components of the motion on the surface can be amplified with respect to the situation in which the surface impedance is either constant or vanishes. Also, when the solicitation is pulse-like, the integrated time history of the square of surface displacement and of the square of velocity can be larger, and the duration of the signal can be considerably longer, for a spatially-modulated impedance surface than for a constant, or vanishing, impedance surface.
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