Transient response of ground surface due to incident SH waves

摘要

The amplification of ground motion on the surfaces of two semi-elliptical alluvial valleys due to incident SH waves in homogeneous and layered half-spaces is investigated in time as well as in frequency domains by using a hybrid method combining the finite element discretization of the near-field with boundary integral representation of the far-field outside a contour enclosing completely the scatterers. First, the response in frequency domain is obtained from solving a set of large sparse unsymmetric complex matrix equations, which are stored in a compacted data structure, by the biconjugate gradient method with good initial guess, and then it is transformed into the time domain by using FFT. An efficient quadrature scheme is adopted to compute the Green's functions in a layered half-space. The study shows that an important role is played by the trapped surface waves (Love waves) that produce much larger amplification than the disturbance associated with the direct incident signal. These Love waves can propagate inside the valley back and forth resulting in a long duration when the impedance contrast is high. In the lower impedance contrast case, the Love waves produce disturbances on the outer sides of the valley. The P and SV cases will be presented in another paper.