Cascadia MegaThrust Fault Goes Active

Thank you for the extra info...makes for a much better mind meal when there's a bit more "meat" on the bones of a story. The darn thing about earthquakes is that you never know if it's just starting (bad thing), or getting rid of a bit of pressure that has already built up.(good thing) I hope it's the latter in this case.

Here is what I think I don't get about these type of threads.

If these faults, zones and volcano-activity areas are shaking.....that means they are releasing the energy/pressure build up. Which would suggest these are not going to have a big shake. The energy for it is being released in small ones.

An active line that isn't shaking for an extended period of time, I would find quite concerning possibly.

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.

[atsimg]http://files.abovetopsecret.com/images/member/394d51a2a56d.jpg[/atsimg]

Also, here is the USGS earthquake map.

[atsimg]http://files.abovetopsecret.com/images/member/4aa7e75dfe97.jpg[/atsimg]

“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.”
Source: www.pnsn.org...

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.”
Source: en.wikipedia.org...

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."
Source: www.pnsn.org...

“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).”

Source: en.wikipedia.org...

"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 rupture."
Source: www.pnsn.org...


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!

Just another angle of DOOM for those who CRAVE doom.

Yes, you have no degree or formal study in earthquakes and yet, you think you're qualified to claim that one is going to hit soon?

reply to post by The Sword


I didn't say I was qualified to say anything. As a matter of fact I stated clearly that I wasn't a specialist or anything. However, if you have read all the literature and scientific, and geological studies, they are experts and they expect exactly that. As a matter of fact there has been documentaries on History and Science channel stating exactly that. All I said is these quakes can trigger what the scientists say could happen at any time in the next few decades, or tomorrow. Earthquake prediction is not possible at this time.

Maybe you should learn to think before spouting off some drivel sounding like a moron!

the last one to happen was in 1700 which was 311 years ago and that was an estimated 9.0.
the region wasn't explored until 1792.
they supposedly happen in the pacific northwest every 200-800 years. they know it happened because of native stories and destruction of coastal japan.
7.0 occur a lot more frequently and a lot closer to the surface. the last one of recent memory was february 2001
a 7.3 in washington state, felt in BC, i was in class. should a 9.0 hit now, it would be unlike anything the region has ever seen and you'd all be watching youtube destruction videos for weeks afterwards.

Originally posted by yourmaker
they supposedly happen in the pacific northwest every 200-800 years. they know it happened because of native stories and destruction of coastal japan.

Yes, that and the geological evidence. I watched a couple of documentaries on it. They even took core samples of dead trees and determined the time was the same timeframe when the Japanese wrote in the records what was called an "Orphan Tsunami" because there was no earthquake associated with it that was close enough for them to feel. They wanted to make sure younger generations realized that tsunamis can come unexpectedly. The geologist in one of the documentaries showed the various layers of sediment and fine sand petinas where the tsunami carried in sand inland. They made a good case for the cycles of these megathrust earthquakes.

reply to post by spirit_horse


I've been watching that area for a couple of years now, mainly because the plates could/would be locked-up around there. And given how close any major quake there could be, we would expect to see a Tsunami reach the mainland in minutes.

MAP 5.0 2011/03/08 01:26:59 44.246 -129.391 17.8 OFF THE COAST OF OREGON

Same place at the other 4's. Just had to add it.

reply to post by spirit_horse


This getting somewhat worrisome. I think it is building up more pressure because the quakes are happening along the Blanco zone....if they were happening along the subduction zone, closer to shore, they would be releasing the pressure, no? And with the perigee coming, this could be something to keep an eye on. I'll be watching this thread. Good info. S&F

It is always a good idea to keep an eye on the Juan de Fuca plate, as it seems to be kind of active lately.

I just finished watching a television program online about earthquake hazards in the Pacific Northwest, if anyone is interested in learning more.

It is called - On Shaky Ground:Earthquakes in the Pacific Northwest

Link

reply to post by Tasty Canadian

Yea, with the Pacific Ring of Fire so active I figured that we should see earthquakes off the West coast. But there hasn't been any of significance. With Chile, the Baha, and Alaska being real active, it would seem that at some point this area needs to release stress. Since I am not an expert, that theory may not be right. But if the Pacific plate is moving and causing big quakes and volcanic activity around the entire edge, we should expect some large quakes off the West coast and this subduction zone where the Juan de Fuca plate is would probably be one of the worst case scenarios for the West coast. Now some of the stuff I have read in the last couple of days says that big quakes happen in the fracture zones where the latest quakes have been coming in. But, according to the experts the timeframe of the cycle of large megathrust quakes indicates we are in prime time to be expecting it to go off again. That isn't a good thing with the way the Pacific is rattling and blowing off steam.

And one more time for the record, I am no expert in quakes and volcanos, I just read the experts literature and am a little concerned and interested. I am not trying to fear monger or anything. I would suspect that it would be better for people to be aware of what is there ESPECIALLY if you live on the West coast.

MAP 4.1 2011/03/07 15:59:27 44.446 -129.049 10.0 OFF THE COAST OF OREGON

I missed this one Monday afternoon. I thought I would add it in. There has been 6 total. This was before the 5.0 above.

reply to post by spirit_horse


hmmmm.....
so OP, is this all normal for this area? is there anything else to this activity?

reply to post by spirit_horse


If you want to examine all of the related quakes, than you need to take a more comprehensive look:



MAP 5.0 2011/03/08 01:26:59 44.246 -129.391 17.8 OFF THE COAST OF OREGON
MAP 4.1 2011/03/07 15:59:27 44.446 -129.049 10.0 OFF THE COAST OF OREGON
MAP 3.9 2011/03/07 02:22:02 44.299 -129.136 10.8 OFF THE COAST OF OREGON
MAP 4.9 2011/03/06 22:23:15 44.334 -129.473 10.2 OFF THE COAST OF OREGON
MAP 4.8 2011/03/06 21:35:47 44.372 -129.346 10.9 OFF THE COAST OF OREGON
MAP 4.5 2011/03/06 13:46:37 40.404 -125.363 24.7 OFFSHORE NORTHERN CALIFORNIA
MAP 2.1 2011/03/05 08:33:50 48.425 -122.944 17.2 14 km ( 9 mi) SSE of Friday Harbor, WA
MAP 4.0 2011/03/03 03:55:05 50.417 -129.914 10.0 337 km (209 mi) W of Campbell River, Canada

MAP and SOURCE

Those are all the quakes located on this plate in the past week.

You should also check out this interactive quake map for the PNW...LINK


And don't forget to take into consideration the deep tremors:LINK


I just don't have the time tonight to get into all my theories...but you seem to be interested in this region, so you might enjoy looking through some of my threads. The links are in my sig line...but I have been talking about my region and my various theories for awhile now, as well as the deep tremors and rumblings that have been heard by many lately. Check it out!

reply to post by westcoast


Thanks I'll check those out. I was looking in the last couple of days because I was looking at the world quake map 2.5 for the week.

I think another quake just happened off the coast, same rough spot, but smaller- like 3 to 4 range. At about 7:21 UTC


Wow, now another it appears at about 7:31 UTC, same rough size as above. Waiting on USGS, as usual...

earthquake.usgs.gov...

reply to post by wingsfan


That area has been pretty quiet since I have been watching it in the last year, but the literature says is has quakes there every 5 years or so in the 5-7 Mag range on the Blanco Fracture Zone. It could be a 5 year cycle on that particular fracture zone. However, with all the activity around the Pacific Ring of Fire there is probably no telling how much additional stress is building on the West coast including the Juan de Fuca plate. And it is in the time frame when there could be a megathrust quake on the subduction zone. There really is no predicting earthquakes, even with the quakes happening in the area. But, taking all things into consideration, I am interesting in keeping tabs on it.

reply to post by TrueAmerican


Yup...I was just jumpin on to say the same. What station are you looking at?

4.4

I think there was another one though too. Notice this is a bit shallower, if that depth sticks.


Magnitude 4.4
Date-Time Tuesday, March 08, 2011 at 07:19:33 UTC
Monday, March 07, 2011 at 10:19:33 PM at epicenter

Location 44.335°N, 129.250°W
Depth 10.3 km (6.4 miles)
Region OFF THE COAST OF OREGON
Distances 409 km (254 miles) W (272°) from Yachats, OR
411 km (256 miles) WNW (287°) from Barview, OR
412 km (256 miles) W (270°) from Waldport, OR
490 km (305 miles) W (276°) from Eugene, OR
537 km (334 miles) WSW (258°) from Portland, OR

Location Uncertainty horizontal +/- 21.5 km (13.4 miles); depth +/- 0.4 km (0.2 miles)
Parameters NST=169, Nph=171, Dmin=476.4 km, Rmss=1.25 sec, Gp=169°,
M-type=body wave magnitude (Mb), Version=4
Source U.S. Geological Survey, National Earthquake Information Center:
World Data Center for Seismology, Denver

Event ID usb0001qp1