Free‐field response from inclined SV‐ and P‐waves and Rayleigh‐waves

Abstract

AbstractTo identify the key features of the free‐field response for inplane motion, a vast parametric study is performed, varying the location of the control point, the nature of the wave pattern and the site properties. Harmonic excitation for a site consisting of a layer on bedrock is investigated.The nature of the wave pattern producing the site response is classified with respect to the apparent velocity of the motion propagating horizontally across the site. When the control point is selected at the outcrop of the bedrock, the amplification of the motion to the free surface of the site depends on the angle of incidence of the incoming wave in the bedrock. The amplification of the vertical motion for incident P‐waves hardly depends (with a tendency of being somewhat larger compared to vertical incidence) on the angle of incidence in the bedrock. The amplification of the horizontal motion for incident SV‐waves is affected strongly by the angle of incidence, being larger or smaller than for vertical incidence. Interpreting the two components of the motion at the free surface as arising from a combination of incident P‐ and SV‐waves leads to amplifications within the site (for the horizontal and vertical directions) which do not depend, from a practical point of view, on the angle of incidence and on the prescribed motion up to the fundamental frequency in the horizontal and vertical directions, respectively. The variation of the motion for the first Rayleigh‐mode with depth in the two directions bears comparison, in general, with that of vertically incident waves up to the corresponding fundamental frequency. The higher Rayleigh‐modes lead to a completely different variation with depth. In contrast to Rayleigh‐waves the attenuation of the motion in the horizontal direction for inclined body waves depends on the damping of only the bedrock. Rayleigh‐waves thus attenuate more strongly than body waves, especially in the higher‐frequency range. Generally, higher Rayleigh‐modes attenuate less than the first.