Study Warns Massive Quake Could Sink Pacific Coast Regions, Heighten Flood Risks

A series of new studies warn that a massive earthquake along the Cascadia subduction zone—from northern California to Washington and up to Vancouver Island—could cause significant land subsidence of up to 6.6 feet, dramatically expanding coastal floodplains and putting tens of thousands more people, structures, and miles of roads at risk of flooding. The earthquake could instantaneously reshape the shoreline, with the risk compounded by ongoing climate-driven sea level rise, leading to persistent and potentially irreversible flooding in low-lying areas. In the scenario of a major quake, flood-prone areas could expand by 116 square miles, tripling the number of residents and structures at risk, and severely compromising critical infrastructure such as bridges and power lines. Unlike gradual sea-level rise, changes from earthquake-induced subsidence would occur within minutes, leaving little time for adaptation or mitigation. The studies cite the 1700 Cascadia megaquake as a precedent for the scale of destruction possible, underscoring the urgent need for comprehensive planning and disaster preparedness among coastal communities. Experts emphasize that accounting for earthquake-triggered land sinking is essential for future flood hazard analyses and coastal resilience strategies.