I keep hearing people say that a Cascadia zone mega quake is about to happen or will happen within the next 50 years. I am not so sure. But while I am not sure I still recommend people know the signs and have an emergency plan and prepare, build buildings with a mega quake in mind because one will happen and in geologic times that will be soon. But I doubt it will be that soon.
The reason I say this is like all of the other people out there prognosticating that a quake will happen I am looking at the evidence. Part of the evidence of a mega quake is the stratification of the soils in the salt marshes inland of the west coast. These areas have layers of mud and sand and dead vegetation including trees. Each layer is the sand brought in by a mega tsunami then a layer of salt marsh buildup then regular soil and trees. Live trees that died when the ground subsides and became a salt marsh again. These trees always get to the point of being mature trees if the dead trees in the current marsh and the remains of dead trees in lower layers is anything to go by. There are currently dead trees standing in the briny waters and soil of the marsh.
As the pressure builds this area is raised up by the pressure to the height that it is no longer a salt marsh but fresh water and then pine trees and ceders start to grow and by the looks of the trees there now get to at least 60 or so years old. The area is starting to raise now and trees will start to grow once the salt water is gone. But that will be at least 100 years from now, it shows at least 20 cm of clean salt free soil needed for the trees to start to grow. This pattern repeats with little deviation in each of the layers of mega tsunami/salt swamp/trees cycle.
So yes prepare, build for the quake that is undoubtedly coming but if it doesn’t happen in the next 20 to 50 years do not say it’s not coming because it is, in possibly about 100 years.
- FEMA program models Northwest megaquake (bendbulletin.com)