DEVELOPMENT OF AN ENGINEERING MODEL OF THE AMPLITUDE AND DURATION EFFECTS OF BASIN GENERATED SURFACE WAVES

Basin waves are polarized predominantly in the directions parallel to and normal to the edge of the basin, consistent with the assumption made by Joyner (2000). There are significant differences between the amplitudes of the horizontal component parallel to the basin edge, which is predomi nantly Love waves, and the horizontal component perpendicular to the basin edge, which is predominantly Rayleigh waves, although these amplitudes will be affected by the relative strength of the incoming waves, which depends on focal mechanism and other factors. This is also consistent with the assumption made by Joyner (2000). There is a significant dependence of the ground motion amplitude and duration on basin depth. Basin depth dependence was not included in the Joyner (2000) model. When depth increases away from the basin edge (i.e. when basin depth and basin edge distance are correlated), this can cause ground motion amplitudes and durations to increase away from the basin edge. The Husid plot derived from the velocity waveform provides an appropriate duration measure that is independent of the absolute amplitude level.