IF YOU FEEL AN EARTHQUAKE GET TO HIGH GROUND! TSUNAMI HAZARD MAPS FOR WASHINGTON COMMUNITIES

Thousands of Washington residents and visitors live, work, and play on or near coastal areas and are at risk from tsunamis. Tsunami deposits found along many Washington beaches provide us with evidence of large earthquakes that have caused tsunamis here in the past. The Washington Geological Survey works with state and local emergency managers to develop inundation and evacuation products. These publications inform people about tsunami hazard areas, designated evacuation routes, estimated walking time to high ground, and assembly locations. We recently published tsunami inundation and current velocity maps representing the effects of a magnitude 9.0 Cascadia Subduction Zone earthquake (L1 scenario after Witter and others, 2011). These maps are now available for Southwest Washington Anacortes, Bellingham, Port Townsend, and Port Angeles. Tsunami inundation is highly variable along the outer coast and within Puget Sound. Modeled inundation depths range from less than a foot to over 60 feet in some locations. Current velocities are highly variable, with extreme currents >9 knots along hooks, peninsulas, and near mouths to major rivers and bays. These map products are critical for decision-making and public preparation for an L1 scenario earthquake and ensuing tsunami.

The Survey is also creating pedestrian evacuation maps that depict the amount of time needed to walk to high ground or to a vertical evacuation shelter. Pedestrian evacuation maps are currently in development for the greater Aberdeen and Anacortes areas, and for the towns of Bellingham, Port Townsend, and Port Angeles. Several areas on these maps were identified as “unable to evacuate”, either at a slow walk pace, or even at a fast run in some cases. In some cases this is due to high ground being far away or the result of an assumed failure of critical infrastructure (such as bridges) during the earthquake. Such a failure would isolate certain areas, making evacuation impossible in the model scenario. These pedestrian evacuation maps inform emergency managers where they may have stranded or at-risk populations and are a useful tool in planning vertical evacuation structures or hardening evacuation routes and other critical infrastructure.