The simulation demonstrates the profound effect the Seattle basin has on ground shaking produced by earthquakes. The relatively unconsolidated material in the basin amplifies the ground shaking and also traps seismic energy to prolong the duration of ground motion. The simulation is for 38 sec of ground motion. Vertical cross section. The top edge is the ground surface and depth is shown on the vertical axis.
North is to the left and south to the right.
The black curved lines in the cross section represent the configuration of the Seattle basin. The upper curve is the top of the bedrock and the lower curve is the top of the basement rocks at the bottom of the Seattle basin. The Seattle fault is located in the lower right hand portion of the cross section, at about 8-11 km depth. The colors denote the ground velocity caused by the seismic waves that radiate from the fault, analogous to waves in a pond generated when a pebble is dropped. Red values indicate the largest ground velocities.