TSUNAMI MODELING ON THE PACIFIC NORTHWEST COAST OF OREGON: PRESENT AND FUTURE

Considerable geologic data from estuaries, coastal lakes and offshore turbidite records document the occurrence of 19 great earthquakes that ruptured the full margin of the Cascadia Subduction Zone (CSZ) over the past 10,200 years, producing catastrophic tsunami; the most recent event occurred on 26 January 1700, striking the coast within minutes. The occurrence of such an event today would be catastrophic with potentially thousands of lives lost. To facilitate public safety, the Oregon Department of Geology and Mineral Industries (DOGAMI), in collaboration with scientists at Oregon Health and Science University (OHSU), Oregon State University, and the Geological Survey of Canada, developed a new modeling approach guided by paleotsunami data and knowledge of CSZ geophysics to produce a suite of next-generation tsunami hazard maps for Oregon.

With the completion of inundation mapping in 2013, our ongoing efforts to build community resilience is based on three needs: tsunami evacuation modeling to assist local government with evacuation route planning and wayfinding; development of ‘Beat the Wave’ evacuation speed maps that explicitly define how fast the public need to travel to reach safety; and, maritime modeling in major estuaries such as the Columbia River (CR). The CR experiences considerable maritime traffic (e.g. transoceanic container ships) from the Pacific Ocean to the Ports of Portland and Vancouver. Modeling in the CR explores a suite of parameters including frictional effects, dynamic tides and river flows to determine the effects of both local and distant tsunamis and associated evacuation responses for vessels on the river.

In the future, tsunami hazard mapping will remain focused on evacuation modeling. These data remain critical for guiding people out of harm’s way and for exploring scenario and land-use planning that could include building vertical evacuation shelters. Additional areas in need of attention could include probabilistic CSZ tsunami hazard assessments, and the incorporation of dynamic landscape responses in future inundation models. The latter is likely to be important since initial model results undertaken on the US East Coast suggest that allowing dunes to erode in response to the tsunami produces greater inundation, suggesting that current methods may not be appropriate.