The other Big One

Almost everyone is familiar with the idea of a major earthquake for southern California when the south end of the San Andreas fault slips. Less known is the Cascadia Subduction Zone off the coast of Washington and Oregon. The last major quake there was in 1700. The locals still talked of it in their oral traditions and told the first European settlers arriving in the region about it. A quake of magnitude 8 or 9 is to be expected every 300-400 years.

"Observations suggest the spring is sourced from water 2.5 miles beneath the seafloor at the plate boundary, regulating stress on the offshore fault…Observations from later cruises show the fluid leaving the seafloor is 9°C (16°F) warmer than the surrounding seawater. Calculations suggest the fluid is coming straight from the Cascadia megathrust…

“Loss of fluid from the offshore megathrust interface through these strike-slip faults is important because it lowers the fluid pressure between the sediment particles and hence increases the friction between the oceanic and continental plates… Fluid released from the fault zone is like leaking lubricant, Solomon said. That’s bad news for earthquake hazards: Less lubricant means stress can build to create a damaging quake.”



We sure know about the Cascadia Subduction Zone here on the Olympic Peninsula. Active measures are in process, including building an emergency coordination center, posting tsunami evacuation route signs and organizing community response teams since it will take a while for professional first responders to reach the scattered neighborhoods.

We assume that the Hood Canal Bridge will be destroyed, cutting off the road over which our food is brought in. I have a month’s worth of food and water in my basement pantry.

DH and I live on a ridge so we are safe from tsunamis. Hard to predict what will happen to the house.



Brother and I both rebuillt at least one bedroom in our homes to be safe against anything short of a nuclear weapon going off nearby. We taught his three boys to quickly carefully make their way or simply to sleep in their central shared “big bedroom” of bunk beds and desks during earthquakes. Sure helped us all sleep better.

The Cascadia tsunami risk is truly terrifying. My brightest cousin is a geologist and her house is 200 feet up above Puget Sound with amazing views of the Olympics, and she tells me the coming Cascadia would very likely take out her home,

david fb


How high is the ridge?


Years ago a doomsayer said that a tsunami would wipe out Caracas, elevation 3,000 feet above sea level. :wink:

The Captain

52 meters (170 feet) at our house which is about 1.5 miles away from the Strait of Juan de Fuca.