TSUNAMI HAZARD MAP OF TACOMA, WASHINGTON: MODEL RESULTS FOR SEATTLE FAULT AND TACOMA FAULT EARTHQUAKES

Numerical modeling of tsunamis generated by Magnitude 7.3 earthquakes on either the Seattle fault and the Tacoma fault show that Tacoma would be subjected to larger and more damaging waves from a Seattle fault earthquake, even though the Seattle fault is considerably more distant. This is because the Seattle fault traverses Puget Sound in much deeper water and can therefore displace more water. The results show that a repeat of the Seattle fault earthquake of about A. D. 935 would generate inundation depths of more than 2 meters in much of the Puyallup delta. Although the port of Tacoma has experienced substantial dredging and filling, there is still natural ground along the main stem of the Puyallup River in Fife and in Hylebos Waterway. Both of these channels have significant areas with modeled inundation depths of more than 5 meters for a Seattle fault event and more than 4 meters from a Tacoma fault event. These models will provide useful guidance for paleoseismology investigations of ~A. D. 935 tsunami deposits and perhaps also the last Tacoma fault earthquake and tsunami, which was also about 1,000 years ago but is less well constrained.