The Redwood Coast Tsunami Work Group: Addressing the Earthquake and Tsunami Threat on California's North Coast

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

North Coast California and the adjacent offshore area is the most seismically active region of the contiguous 48 states and is at risk of tsunamis generated from nearby and elsewhere in the Pacific. 41 earthquakes of M6 or larger have been recorded in instrumental times, and 67 earthquakes have caused damage. 39 tsunamis have been detected since a tide gauge was installed in 1933, including five that caused damage. However, only three of the regionally felt earthquakes produced tsunamis, and all the damaging tsunamis came from the far-field. The relative frequency of strongly-felt earthquakes and the complexity of the tsunami threat has posed challenges in developing consistent, understandable messaging and regional preparedness efforts. It is further complicated by differences in messaging and products from neighboring states at risk of Cascadia earthquakes and the lack of full understanding of how the Gorda region of the Cascadia subduction zone differs from its characteristics in the Juan de Fuca portion. The frequency of both earthquakes and tsunamis and the relative isolation of California’s North Coast has led to regional mitigation efforts and strong partnerships between the North Coast and state/federal agencies. The (Redwood Coast Tsunami Work Group (RCTWG) an organization of local, state and federal partners, has become the lead regional organization coordinating hazard mapping with state partners, TsunamiReady community development, sign and siren placement, annual tsunami communication drills, evacuation drills and ShakeOut participation, and development of risk-communication products. Some areas in which the RCTWG approach differs from other parts of Cascadia include more emphasis on the likely shaking impacts, using shaking duration to distinguish potentially tsunamigenic earthquakes from the more frequent ones that don’t pose a tsunami threat, and emphasizing that because of source proximity, the first surges could arrive in as little as ten minutes.

Presenting Author: Lori Dengler

Authors