Geologic Hazards on the Oregon Coast: A Look at New Tsunami Inundation and Evacuation Maps at Cannon Beach

 

The Department of Geology and Mineral Industries (DOGAMI) has been working with coastal communities on tsunami awareness and preparedness for over a decade, making Oregon a national leader in tsunami education and mitigation.

For example, working with Oregon Emergency Management (OEM) and local governments, 27 evacuation maps and brochures have been completed for coastal communities, with over 250,000 brochures printed in 2010.

But the 2004 Indian Ocean magnitude 9.3 Sumatra-Andaman Islands earthquake and subsequent tsunami led to a re-evaluation of our tsunami hazard mapping approach. Because of critical observations made about the Indian Ocean tsunami that killed over 250,000 people, DOGAMI decided to update the State tsunami hazard assessment technology. With the encouragement and support of NOAA, Dr. Robert C. Witter of DOGAMI is leading a technical team of researchers and scientists using the latest technology in terrain mapping (lidar) and computer simulation to produce new tsunami inundation and evacuation maps for the entire Oregon coast. Cannon Beach served as the initial test site for this effort. Below are Cannon Beach inundation and evacuation maps from this new approach (for data and details, see DOGAMI Special Paper 41 (Report only [28 MB]; zipped file of DVD [746 MB]); for a summary article see Confidence levels for tsunami-inundation limits in northern Oregon inferred from a 10,000-year history of great earthquakes at the Cascadia subduction zone (Natural Hazards. doi 10.1007/s11069-009-9453-5).

 
 
 

This new scenario-based inundation mapping expresses the variability of what could be expected from a tsunami impact on the Oregon coast in the event of a Cascadia subduction zone earthquake or a distant tsunami-generating earthquake, including a most likely case Cascadia event tsunami, a worst case Cascadia event tsunami, and a worst case distance tsunami.

This new map at Cannon Beach is based on exhaustive, state of the art, computer modeling and on the ground paleo-tsunami mapping field work aimed at identifying the extent of prehistoric tsunami deposits. Results from the Cannon Beach experiment are being combined with a similar test at Bradley Lake near Bandon to set the standards for re-mapping tsunami inundation for the entire Oregon coast.

It is hoped this new generation of tsunami inundation maps will be easily interpreted by both technical users and the general public and therefore more useful. DOGAMI will use this new research and mapping techniques to collaborate with coastal communities in also creating a new generation of tsunami evacuation brochures and maps. How these new maps are translated into public policy, land use planning, and are used for evacuation planning will probably be unique to each community.