West Coast USA: Pay Attention, Cascadia May Be Ready to Rupture

Originally posted by yourmaker
reply to post by Olivine

 

all of those red dots in the north by surrey/vancouver are recent quakes?

No, not really.

All those red dots represent slow "grinding" on the subduction zone interface. These slow slip episodes can last minutes, hours or days--but you cannot feel them. They are tiny--most lower than Mag 1. And relatively deep, 30-40km down. It's not like a normal earthquake which is a supersonic rupture.

You can read more about ETS (episodic tremor & slip) at the following links:

Central Washington University ETS page
Natural Resources Canada ETS page
Pacific Northwest Seismic Network tremor page -- click on FAQ

ETA: Hi John. Yesterday must have been hectic. Are you and your team still trying to "untangle" and review the seismograms--they are messy!

reply to post by nonnez


1. See quake #1 offshore Oregon

2. See quake #2 offshore Oregon

3. See quake #1 move out to sea.

4. See quake #2 move out to sea.

5. Learn not to even bother with quakes posted by USGS offshore Oregon, because they will be moved. For the zillionth time!

6. Let this thread die a miserable failed death. And thank God for that. If there is one.

reply to post by TrueAmerican


Been feeling these in the area for the last few months.
theextinctionprotocol.wordpress.com...

USGS warning Humbolt county in February of more that were to come,
and then there is always this worry of the Nuclear plant.

yournec.org...

Not enjoying the ride.

reply to post by TrueAmerican


Yes, an analyst got the wrong range on those off-Oregon quakes again, and we had to fix them. We're working on training them to get the S waves right so that the quakes are placed the proper distance off shore. Eventually, we'll surround them with offshore instrumentation, but not any time soon.

reply to post by Olivine


Hectic yesterday, then a radio station called at 7am this morning, but it's been smooth sailing since then.

reply to post by AuntB


Not much concern. There were no foreshocks and no aftershocks big enough for us to see, so it looks like a one-and-done sequence. If more small seismicity appears, then we would pay more attention.

reply to post by JohnVidale


So in a general sense, and I know this is anyone's guess, but do you think there would be smaller activity in the locked zone or in other areas prior to the CSZ giving way? Or do you think that it will just all of a sudden go boom with no warning? Some subduction zones seem to give away their intent, as in Chile 1960, with all those foreshocks. The New Madrid did this as well, even though it is not a subduction zone. But given what you know of the geology of the CSZ area, is it more or less likely that there will be foreshocks (and warning) prior to a massive rupture? And is there any consensus on that?

reply to post by TrueAmerican


Great question. I'd guess there is a better than usual chance of some foreshocks, maybe 50%?, but still no way to tell the events were foreshocks until after the fact. Generally, if seismicity is swarmy - tends to come in clumps - one might expect foreshocks more often, and seismicity, what little there is on the plate interface, looks moderately swarmy.

reply to post by JohnVidale




I am still confused. So are you saying that because this recent activity is "moderately swarmy," that means chances are we WOULD see some foreshock activity prior to an M9 on the CSZ?

reply to post by TrueAmerican


Yes, when there are swarms (for whatever reason, maybe some aseismic slip going on, maybe some local fluid pressure fluctuation on the fault, maybe both, or something else driving activity) it is more likely that one event can lead to another, or point out that the odds of another are higher than normal.

So if the mainshock activity is NOT swarmlike, there is not likely to be an event to give us an idea some activity is ongoing before the big quake strikes.

reply to post by JohnVidale


Ok, you mentioned before in this thread that so far there is nothing in this current activity seems particularly troubling. What about something like an M6 or so right in the locked zone? Would that get the worry meters up? It would seem that might imply it's starting to slip?

reply to post by TrueAmerican


Yes, we'd worry in proportion to the size of an event and its proximity to the subduction fault. And similarity in mechanism to motion on the fault. And specifically proximity to where we think the fault is locked.

reply to post by JohnVidale


Interesting. Thanks for all the answers. I am amazed at the lack of people asking you questions, to be honest. It took years to even get someone like you here, and now that you're here, there's only a handful of us asking you any questions!

:shk:

So would a specific event, or series of events on the CSZ actually cause you guys to issue a formal warning to authorities of an impending M9 quake? That would be pretty rare, would it not, if it occurred?

In any case, there you have it folks. I guess don't worry unless something big lights up right near the locked zone. What little comfort from that you can take, to those living there, you better take it. Looks like things are probably going to be OK. For now.

This fault line is capable of a 10.0. It’s time for me to email my insurance agent and add earthquake protection and stock up on beach front property furniture. I live several hundred miles inland but according to the map I’d have an ocean view. I never want to see Seattle or L.A slide in to the ocean. The big one is over-due.

Edit to add poor Japan would have another really huge Tsunami.

reply to post by TrueAmerican


Yes, we'd issue some statements if activity was sufficiently alarming. There are no set criterion for "sufficiently alarming", we'd just convene, or maybe someday we'll formulate specific criteria. It's tough because of the variety potential scenarios and our evolving understanding.

reply to post by JohnVidale


I have a question;

Ive been told that it is virtually impossible for the west coast to actually slip in to the ocean, even though it has happened before. Is it logical to believe this could happen today?

reply to post by wonderworld


Slipping into the ocean sounds like a landslide, certainly possible but only affecting a small stretch of coast.

The greatest earthquake slip seen is about 40m, usually it is much less. So that is one limit on how much land might submerge.

Further, the big faults along the San Andreas Fault Zone (CA-Mexico border up to Cape Mendocino) are strike slip, moving sideways rather than vertically, so the coastline would NOT submerge much along that stretch.

Cascadia, the stretch of coast from Cape Mendocino to Vancouver Island, is a subduction, and prone to M9 earthquakes, and might see 20-40m of fault motion in the worst case. However, most of the motion would consist of the shoreline moving laterally outward, with vertical uplift or down drop of only a few meters.

So there will not be a big change in the location of the beachfront property.

reply to post by TrueAmerican

It took years to even get someone like you here, and now that you're here, there's only a handful of us asking you any questions!

Well, you're doing such a great job with the questions and I can't think of any you haven't covered that would be worthwhile in asking...

I do appreciate the conversations though and have learned quite a bit, so keep it up. If I am able to formulate a coherent question on the topic, I will certainly speak up.

reply to post by JohnVidale


Thanks for that answer.

I have another question if you dont mind, rather a few;

If the Cascadia fault line actually ruptured would a Tsunami hit the City of Seattle and do significant structural damage and loss of life? If this were to occur could it set off a chain reaction to ignite the whole ring of fire simultaneously, therefore setting off the Volcanoes? I lived through Mount St. Helens that was sure something! I suppose Yellowstone is most scary. Do you have any clue about that?

I love geology but dont much about the scientific nature of these things. I can see where Mount Borah was lifted a couple feet at the base.

reply to post by wonderworld


Not much of a tsunami would be generated inland by the Puget Sound from a coastal quake, and volcanoes could be set off, but it is unlikely. Got to run.

John