reply to post by Aeons
I have been studying the area and its various faults and have found some interesting information that is directly related to this topic. As I said
before, I am no Earthquake specialist, but have an interest in this area because of it potential to cause untold death and destruction.
First, here is another map that shows the individual faults in the Cascadia network of faults.
Also, here is the USGS earthquake map.
“The Blanco Fracture Zone is one of several seismically active transform faults off the coast of Oregon. The Blanco FZ offsets the Juan de Fuca
(JDF) Ridge from the Gorda Ridge (ridges are spreading centers where new ocean floor is created). “
“Over the past 20 years, a magnitude 6.0-7.0 earthquake has occurred on the Blanco Fracture Zone every 5 years or so. Each year, there are several
earthquakes in the magnitude 5.0 to 6.0 range.”
The earthquakes along the Blanco Fracture Zone will not in themselves cause a tsunami and they are not usually felt . The other earthquake is located
further South on the Mendocino Fracture Zone. Note map above. The Mendocino Fault is an extension of the San Andreas Fault, but is called Mendocino as
it goes offshore apparently.
The problem is the Subduction Zone where the Juan de Fuca plate is subducting under the North American plate. It is Locked and building up enormous
pressure. If the earthquakes along the Fracture Zones Blanco and Mendocino cause the subduction zone to release it energy in what is called a
Megathrust Earthquake, then it will cause enormous damage to the cities of Seattle, Tacoma, etc. and also it is highly likely it will cause a huge
Tsunami as has happened before. The geologic studies in the last decade have shown this has happened on a cycle.
“The last known great earthquake in the northwest was in January 1700, the Cascadia Earthquake. Geological evidence indicates that great earthquakes
may have occurred at least seven times in the last 3,500 years, suggesting a return time of 300 to 600 years.”
HOW BIG ARE CASCADIA SUBDUCTION ZONE QUAKES?
"Great Subduction Zone earthquakes are the largest earthquakes in the world, and can exceed magnitude 9.0. Earthquake size is proportional to fault
area, and the Cascadia Subduction Zone is a very long sloping fault that stretches from mid-Vancouver Island to Northern California. It separates the
Juan de Fuca and North America plates. Because of the very large fault area, the Cascadia Subduction Zone could produce a very large earthquake,
magnitude 9.0 or greater, if rupture occurred over its whole area."
“Recent findings concluded the Cascadia subduction zone was more hazardous than previously suggested. The feared next major earthquake has some
geologists predicting a 10 to 14% probability that the Cascadia Subduction Zone will produce an event of magnitude 9 or higher in the next 50 years,
although the most recent studies suggest that this risk could be as high as 37%.Geologists have also determined the Pacific Northwest is not prepared
for such a colossal earthquake. The tsunami produced may reach heights of approximately 30 meters (100 ft).”
"The width of the Cascadia Subduction Zone fault varies along its length, depending on the temperature of the subducted oceanic slab, which heats up
as it is pushed deeper beneath the continent. As it becomes hotter and more molten it eventually loses the ability to store mechanical stress and
generate earthquakes. The "locked" zone is storing up energy for an earthquake, and the "transition" zone, although somewhat plastic, could probably
So, although these quakes are releasing energy, the Subduction Zone where the Juan de Fuca plate is subducting under the North American plate remains
LOCKED and building up stress which will be released in a Megathrust earthquake.
Basically, releasing stress along the fracture zone is not in itself releasing the stress on the Subduction Zone, but could trigger the release and
that is why I am watching this area.
I hope this explains my reasons on this. This is my first real attempt at a thread. The first one or two I would rather forget I tried. It is more
work than some think to get the right info out here and back it u with documents, maps, etc. I have a much greater respect for these guys and gals
doing threads of certain complexity. Next time, I will do all this first!
edit on 7/3/11 by spirit_horse because: spell check