Posted on 12/10/2024 10:03:32 PM PST by Robert A Cook PE
Now, only 5 days after a Mag 7.0 earthquake shook the Cape Mendocino Fracture Zone offshore of the CA coast, aftershocks continue hourly. Over 420 earthquakes in this 110 km x 20 km region are already listed. More happen each hour.
Why do hundreds of small earthquakes offshore of northern California matter? Nobody lives there, no businesses nor voters nor industry is destroyed. No FEMA trailers nor FEMA money is needed of the earthquake is underwater.
The Cape Mendocino Fracture Zone is the southern border of three tectonic plates being pushed east underneath the US continental plate. The Gorda Plate is furthest south - pushing under northern California and south Oregon, then the larger Juan de Fuca plate pushes underneath Oregon and Washington State, then the Explorer Plate is furthest north - moving east underneath Seattle and Vancouver BC. These plates are divided by three east-west fracture zones: the Cape Mendocino Fracture Zone - hitting California at the end of the San Andres Fault north of San Francisco, the Blanco Fracture Zone is next, then the Sovanco Fracture Zone divides the Juan de Fuca and Explorer Plates.
When the Juan de Fuca ocean floor tectonic plate moves, the plate moves at these fracture zones on its borders, pushing the tectonic plates it collides with up out of its way. The horizontal movement is bad enough - creating Mag 8 to Mag 8.5 earthquakes on each border as the plates slide horizontally to each other. But it is the vertical movement as the Juan de Fuca plates slides under the continental plate that creates immense tsunami waves like the ones in Indonesia and Japan that kill tens of thousands coastal residences in minutes.
The frequency of 1000 km long earthquakes of Mag 9 and greater off of the BC-Washington-Oregon-CA coast has been increasing the past 4000 years. (Between each Mag 9 earthquake is a "smaller" Mag 8.0 or Mag 8.7 earthquake moving "only" 220 to 440 km of coastline homes.) Since 2200 BC, now some 19 such Mag 8 to Mag 9 earthquakes have struck these coastlines; on average less than 200 years between earthquakes and tsunamis.
Why should a US reader care?
Because a Japanese and British Columbia reader should care as well: The last large earthquake off of the Washington-Oregon-CA coastline occurred Jan 27 1700 - a date known because villages in Japan were destroyed by a tsunami later that day. Because every coastal tribe living near sea level in coastal BC-WA-OR-CA in January 1700 was killed, 104 years before Lewis and Clark reported only empty beaches and wilderness next to rivers flowing with clear water and plenty of fish.
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Me too.
But I’m willing to take one for the team if God decides to slide the whole west coast into the trench.
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