Quakes – Special CSZ Monitor Page

DON’T Panic!

Just to Monitor nothing happening!

Quakes Hemisphere Map centered on Cascadia and off shore

Quakes Hemisphere Map centered on Cascadia and off shore

Original Map with Clickable areas for details

This page is for Catherine Clark (and anyone else with family and friends where the Cascadia Seismic Zone could cause them harm). There is no quake there, as I type this. But that can be seen as “ominous”. So I’m making a page that looks in some detail at that area. The maps are all live, so you can see if anything starts to happen. The best use of this page is as a bookmark you can click on to see that nothing has happened, yet.

OK, next up is the North American View, then we’ll do a set of “close ups” along the whole plate structure:

North America

North America and Mid Atlantic Ridge Quake Map

North America and Mid Atlantic Ridge Quake Map

Original with clickable details

From Alaska to California in Closeups

Alaska / Canada Coastal Earthquake 10 Degree Map

Alaska / Canada Coastal Earthquake 10 Degree Map

Original with clickable details

Canada / PNW Coastal 10 Degree Earthquake Map

Canada / PNW Coastal 10 Degree Earthquake Map

Original with clickable details

Offshore Washington / Oregon 10 Degree Earthquake Map

Offshore Washington / Oregon 10 Degree Earthquake Map

Original with clickable details

Washington / Oregon On Shore 10 Degree Earthquake Map

Washington / Oregon On Shore 10 Degree Earthquake Map

Original with clickable details

Northern California Coastal 10 Degree Earthquake Map

Northern California Coastal 10 Degree Earthquake Map

Original with clickable details

Live USA Quake Map

Live USA Quake Map

Original Image

California Map

Action Closer to Me

Current quake map in California

Current quake map in California

Original Image, with captions and description. The original is interactive with clickable regions for ‘close ups’.

The Rest of the World Earthquakes

Here is a Pacific centric view:

With quite a bit of action North of New Zealand and Australia. It looks like it’s ‘cooled off’ to 5.x range aftershocks.

Pacific Centric Quake Map

Pacific Centric Quake Map

Original Image with Clickable Details

Both Hemispheres

A view of Earthquakes from the South Pole

A view of Earthquakes from the South Pole

Original Image with Clickable Details

North Polar Earthquake Map

North Polar Earthquake Map

Original Image with Clickable Details

There are also some informational pages on the Cascadia Seismic Zone (or Cascadia Subduction Zone):


While this page is particularly interesting as it describes the strain being built up and detected in ground deformation as seen in this graph:

Ground Deformation Showing Strain Buildup

Ground Deformation Showing Strain Buildup

You can see that the land nearer the ocean is moving inland rather a lot. The land inland is not moving so much. Somthing has got to give… it’s that old “two objects in one space” problem.

The Pacific Northwest Seismic Network has a nice 3-D image of the fault structure on this page:

Plate Structure of CSZ

Plate Structure of CSZ

( Formerly from: http://www.pnsn.org/INFO_GENERAL/INFOSHEET/plates.gif that is now a broken link)

( http://www.pnsn.org/INFO_GENERAL/eqhazards.html )

Used to point to this text:

The seismology lab at the University of Washington records roughly 1,000 earthquakes per year in Washington and Oregon. Between one and two dozen of these cause enough ground shaking to be felt by residents. Most are in the Puget Sound region, and few cause any damage. However, based on the history of past damaging earthquakes and our understanding of the geologic history of the Pacific Northwest, we are certain that damaging earthquakes (magnitude 6 or greater) will recur in our area, although we have no way to predict whether this is more likely to be today or years from now. A map and list of selected historic earthquakes shows that while the most damaging events were fairly deep, many moderate sized earthquakes are fairly shallow. Several detailed Earthquake Scenarios, projecting likely effects from large quakes, are available.

Earthquakes are driven by geologic processes which produce stresses in the earth. In the Pacific Northwest, oceanic crust is being pushed beneath the North American continent along a major boundary parallel to the coast of Washington and Oregon. This boundary, called the “Cascadia Subduction Zone” lies about 50 miles offshore and extends from the middle of Vancouver Island in British Columbia past Washington and Oregon to northern California.

Deep Earthquakes: The three most recent damaging earthquakes in Washington, in 2001 (magnitude 6.8, near Olympia), 1965 (magnitude 6.5, located between Seattle and Tacoma), and in 1949 (magnitude 7.1, near Olympia), were roughly 40 miles deep and were in the oceanic plate where it lies beneath the continent. Each earthquake caused serious damage, and was felt as far away as Montana. No aftershocks were felt following the 1965 and 1949 earthquakes, and only 2 small aftershocks were felt after the 2001 quake. Other sizable events which were probably deep occurred in 1882, 1909, and 1939.

Shallow crustal earthquakes: The largest historic earthquake in Washington or Oregon occurred in 1872 in the North Cascades. This earthquake had an estimated magnitude of 7.4 and was followed by many aftershocks. It was probably at a depth of 10 miles or less within the continental crust. In 1993, a magnitude 5.6 earthquake in the Willamette Valley caused $28 million in damages (including damage to the Oregon State Capitol in Salem), and a pair of earthquakes near Klamath Falls, OR (magnitudes 5.9 and 6.0) caused two fatalities and $7 million in damages. Many other crustal sources in Washington and Oregon could also produce damaging earthquakes. Recent studies have found geologic evidence for large shallow earthquakes 1,100 years ago within the central Puget Basin. Massive block landslides into Lake Washington, marsh subsidence and tsunami deposits at West Point in Seattle, tsunami deposits at Cultus Bay on Whidbey Island, and large rock avalanches on the southeastern Olympic Peninsula have all been dated to approximately 1,100 years ago.

Subduction Zone earthquakes: Although no large earthquakes have happened along the offshore Cascadia Subduction Zone since our historic records began in 1790, similar subduction zones worldwide do produce “great” earthquakes – magnitude 8 or larger. These occur because the oceanic crust “sticks” as it is being pushed beneath the continent, rather than sliding smoothly. Over hundreds of years, large stresses build which are released suddenly in great earthquakes. Such earthquakes typically have a minute or more of strong ground shaking, and are quickly followed by damaging tsunamis and numerous large aftershocks. The Alaskan earthquake of 1964 was a great subduction zone earthquake. Geologic evidence shows that the Cascadia Subduction Zone has also generated great earthquakes, and that the most recent one was about 300 years ago. Large earthquakes also occur at the southern end of the Cascadia Subduction Zone (in northern California near the Oregon border) where it meets the San Andreas Fault system; including a magnitude 7.1 earthquake in 1992, and a magnitude 6.8 (estimated) earthquake in 1873.

Although scientists have tried for decades to predict earthquakes, no one has discovered a method which can be applied with regular success. For some areas with well-understood patterns of seismicity, it may be possible to forecast decades-long time windows when large earthquakes are likely to occur. However, the Pacific Northwest has only been monitored for a couple of decades; not long enough to allow us to see what patterns, if any, exist here. Seismologists are still trying to understand what types of earthquakes are possible here, and what kind of shaking we will experience from future earthquakes (depending on the earthquake location and size, and the site geology and topography). Earthquake hazards can be reduced by advance preparation; such as coordinating emergency communications and activities across jurisdictional lines, preparing personal emergency plans, and considering seismic hazards in land use plans, building codes, and planning for medical, utility, and emergency facilities.

They have redone their web site, so who knows where all the interesting links are now. You can fish for more here:


The Oregon State Geologist has a nice pdf write up about it, and the risks, here:


And, of course, the Wiki for those who might be interested in it:


I may add some more resources as time and interest permit. If you have one you particularly like, please post a comment including a link.

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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44 Responses to Quakes – Special CSZ Monitor Page

  1. Missing Link says:

    Apologies for being off-topic but I’ve just been reading your articles over the past day or so, and feel compelled to give you more feedback than just leaving an IP address in a web server log. The clarity of your writing makes it a real pleasure to read.

    So, thank you from some random new internet fan :)

    (I’ll understand if you have to move or delete this comment due to it’s off-topic-ness.)

  2. George says:

    There has been some interesting monitoring of “slow” quakes that can last for weeks in the CSZ, I will attempt to find the actual link to the research, I used to see it regularly when I went to the old Mt. St. Helens site but they have changed it.

    Here is a recent AP article describing it:


    Probably somewhere around here:


    Has to do with this:

    http://www.ess.washington.edu/SEIS/PNSN/WEBICORDER/DEEPTREM/summer2010.html (scroll down the page, lots of links there … the “deep tremor” stuff is what I had been watching a few years ago.).

    This “deep tremor” can last for days or weeks and you can’t feel it at the surface.

  3. George says:

    Ah, here is the page I was looking for:


  4. George says:

    And this page linked from the previous:


  5. Catherine Clark says:

    This is very cool – thanks! I knew about slow tremors, and in Japan sometimes they seem to presage EQ’s along the coastal subduction areas, but there doesn’t seem to be a pattern that I can discern. I love all these links! EQ research fascinates me. Thanks!!!!!

  6. PhilJourdan says:

    Damn! My in laws just had a martini shaker (Brawley 2.4).

    I am book marking that site! Cool!

  7. George says:

    This page seems to be rather high resolution for EQ activity in that region:


  8. E.M.Smith says:


    Very Nice!

    Don’t see an easy way to make an embed of it, though, so folks will need to click the link…

  9. Catherine Clark says:

    Hmmm…..not close to the plate boundary, but the first offshore quake I have ever seen off WA state. What does anyone make of this???

    Earthquake Details
    This event has been reviewed by a seismologist.
    Magnitude 2.7
    Date-Time Thursday, January 20, 2011 at 03:04:53 UTC
    Wednesday, January 19, 2011 at 07:04:53 PM at epicenter

    Location 46.796°N, 124.288°W
    Depth 38.4 km (23.9 miles) set by location program
    Distances 15 km (9 miles) W (261°) from Grayland, WA
    16 km (10 miles) WSW (239°) from Cohassett Beach, WA
    17 km (11 miles) SW (232°) from Westport, WA
    22 km (14 miles) SSW (207°) from Ocean Shores, WA
    147 km (92 miles) WSW (251°) from Tacoma, WA
    174 km (108 miles) WSW (239°) from Seattle, WA

    Location Uncertainty horizontal +/- 2.1 km (1.3 miles); depth fixed by location program
    Parameters NST= 29, Nph= 29, Dmin=39 km, Rmss=0.35 sec, Gp=223°,
    M-type=duration magnitude (Md), Version=1
    Source Pacific Northwest Seismograph Network

    Event ID uw01200304

  10. E.M.Smith says:

    @Catherine Clark:

    My take on it is that it’s a ‘dinky’ and doesn’t mean much. All the mountains of the west coast are the result of consistent uplift over a very long time. That uplift is still happening. That means you get the odd creak and crack pretty much everywhere from the Rocky Mountains out to sea from time to time. It’s when a pattern develops that it has meaning.

    So one ‘dinky’ and it’s just a ‘watch a bit’. A bunch of dinky, with a few ‘small’ and one ‘medium’ showing up? Start packing and making plans… A couple of 5+ and it’s time for a short vacation… You are a long ways from that.

  11. E.M.Smith says:

    Well, somethings started up on the Cascadia… how big is yet to be determined… Time to watch more closely…

    h/t Boballab in https://chiefio.wordpress.com/2011/01/18/quakes-7-2-pakistan/#comment-12633

    Magnitude 5.2 – OFF THE COAST OF OREGON

    This event has been reviewed by a seismologist.Magnitude 5.2
    Date-Time Tuesday, February 08, 2011 at 22:02:01 UTC
    Tuesday, February 08, 2011 at 02:02:01 PM at epicenter
    Time of Earthquake in other Time Zones
    Location 43.405°N, 127.119°W
    Depth 10.1 km (6.3 miles)
    Distances 235 km (145 miles) W of Coos Bay, Oregon
    275 km (170 miles) NW of Brookings, Oregon
    280 km (175 miles) WSW of Newport, Oregon
    370 km (230 miles) WSW of SALEM, Oregon
    Location Uncertainty horizontal +/- 22.3 km (13.9 miles); depth +/- 0.8 km (0.5 miles)
    Parameters NST= 88, Nph= 95, Dmin=234.9 km, Rmss=0.96 sec, Gp=241°,
    M-type=body wave magnitude (Mb), Version=7
    Source USGS NEIC (WDCS-D)
    Event ID usb0001atx

  12. George says:

    That quake is on the spreading center between the Pacific Plate and the Gorda plate. Usual place for earthquakes of that size.

  13. E.M.Smith says:


    When one place is spreading, somewhere else is subducting.
    When one place is moving, other places are being shaken.
    So when this place pops a 5.x, it’s time to watch the area. Not panic. Not “expect at it”. Just watch more closely.

    For what to watch?

    Action that accellerates. 2 today, 4 tomorrow, 5 next week,…
    Action that spreads. Middle today, each end tomorrow, adjacent subduction zone next week.
    “Empty Spaces”. Action on each side of a long locked chunk of fault that ‘is due’ (showing build up of stresses in that section).

    So yes, you are correct, this is nothing ‘out of the ordinary’; but it is a reminder to ‘watch here’ for a while. To assure that it stays nothing out of the ordinary.

    Just like each time we get a 5.x to 6 on the San Andreas I check my water barrels (and often ‘freshen’ the water), make sure no glass objects have wandered to the tops of bookcases and that the ‘quake kit’ isn’t burried under 200 lbs of hockey gear in the garage, and fill the cars gas tanks (and ‘freshen’ the fuel in the generator fuel can… i.e. dump the old into a car and refill it.)

    I ‘expect’ to do that the rest of my life and never have any benefit from it other than peace of mind.


    If my expectations are wrong, I’ll still have peace of mind…

    FWIW, I have a general attitude about “expecting at” things and the tendency of people to “expect at” markets and / or “expect at” me. I try to never “expect at” things. Of course, no one can completely avoid it. But it’s a good thing to work toward.

    Folks “expect me” to do or not do certain things, or to believe or not believe certain things (or they ‘expect at me’ that if I’ve said “Facisim is a form of Socialism” that I have some baggage about it or an agenda; when the reality is that it’s more an abstract economic theory thing for me… I’m an Economist by training and it’s rather like a botanist deciding what genus a plant ought to be in… interesting, but not exactly a big deal.) And expectations usually cloud clarity. So I try not to ‘expect at’ the world.

    What does this have to do with quakes?

    Your statement implies that others are ‘expecting’ this quake means “the big one is coming” or that I’m ‘expecting’ this quake means the big one is more likely. The reality is a bit different.

    I’m not ‘expecting’ that the big one is coming. I am however aware that large quakes are often preceeded by ‘foreshocks’ and that the only oportunity you have to get your preparedness gear in order is in that gap, should it happen, between a fore shock and the main event. 99%+ of the time you will be preparing for nothing. I’m not ‘expecting at’ the fault that it do anything. I am very much expecting that folks will not periodically check on their gear and fuel (or even go buy their gear and fuel) without some reminder of why they ought to do it. I’m also expecting that folks don’t look at this page every day (even folks interesed in The Cascadia) and that a 5.x is a reason to remind them to ‘watch here’.

    In some ways it’s rather like watching moles. I have a few spots that the dermatoligist regularly watches. Don’t ever expect them to become skin cancer. But when one gets a little darker or larger, we watch it. Is the edge getting ragged? Is it showing signs of changing character? I expect to do this the rest of my life and die of something else. But I also realize that “expecting at” my moles and freckles will not change what they do, or become, and that having a look when one darkens is “a good thing”, despite my expectation that it’s most likely the result of a weekend gardening in the sun…

    (FWIW, I once had a spot ‘blossom’ to about 3/4 the diameter of a dime… though it was still a bit lighter in color and had no other indicia. The Dr. decided to send it off to the lab… The pathology report said it was nothing. The procedure description was, roughly translated, “freckle-ectomy” ;-)

    So what do I “expect at” the Cascadia? A LOT of “frecklectomy” and some reminders to ‘be prepared’.

    So when a 5.x goes off, it’s not a time to ignore it. It’s a time to watch it… Then when nothing else happens, ignore it for a while.

  14. boballab says:

    The thing is it just wasn’t one quake, there was a 4.7 less then 24 hrs prior to it at the same depth and within 40 miles of it. The thing about big quakes is they typically don’t just pop off in isolation, they have preshocks in the weeks and months leading up to it.

    As I put it in my original comment this could be the Cascadia working itself up or the 5.2 was the “event” that the 4.7 was a precursor to.

  15. E.M.Smith says:

    And one of the ‘fun bits’ is the official definition of a ‘preshock’ vs a ‘main quake’. The last largest quake is the “main shock’ right up until a larger one comes along… then it’s the ‘preshock’ ;-)

    No, really… In geology class years and years ago the prof went to great lengths to make it clear that the period of time was rather fuzzy (but on the scale of months) and that a quake was a main quake until it was a fore shock and that after shocks were after shocks as long as they were getting smaller but after some ill defined months they become fore shocks again as soon as a main quake happens (unless it, too, is followed by a larger shock… then all of them become foreshocks…) Clear?

    In other words it’s all ex post facto pattern matching… and only becomes stable after enough ‘facts’ are ‘post’…

    Which is WHY we watch when a 5 goes off. To gather the ‘post facto’s to know who was a what…

  16. George says:

    Quakes along the spreading center are fairly common and don’t really have much to do with anything in the subduction zone other than that is where the subduction stress originates. The main difference is that you can expect quakes all the time at the spreading center. They will probably be fairly well-distributed over time. A major CSZ quake wouldn’t change the behavior at the spreading center much. Now, I would pay attention to subduction zone quakes. Actually, I would pay attention to a lack of them. If the “slow” background movement stops for an extended period of time, I would begin to become concerned.

    So it isn’t quakes that bother me so much in the CSZ, it would be the lack of them. A lack of “slow” deep quakes accompanied with deformation (in particular, ground rising along the subduction zone) would cause the hair on the back of my neck to stand up.

  17. Catherine Clark, Illinois says:

    More quakes just West of the CSZ. Makes me wonder if these small quakes are just adding more stress to the area. We have seen in Japan how earthquakes can spread stress along other faults. It was seen also in China and can bee seen in Turkey, among others.

  18. E.M.Smith says:

    @Catherine Clark:

    I presume you mean this one:

    Magnitude 4.6 – OFF THE COAST OF OREGON
    2011 May 22 07:21:37 UTC

    This event has been reviewed by a seismologist.Magnitude 4.6
    Date-Time Sunday, May 22, 2011 at 07:21:37 UTC
    Saturday, May 21, 2011 at 11:21:37 PM at epicenter
    Time of Earthquake in other Time Zones
    Location 43.494°N, 127.054°W
    Depth 10.1 km (6.3 miles)
    Distances 229 km (142 miles) W of Coos Bay, Oregon
    271 km (168 miles) WSW of Newport, Oregon
    277 km (172 miles) NW of Brookings, Oregon
    359 km (223 miles) WSW of SALEM, Oregon
    Location Uncertainty horizontal +/- 18.8 km (11.7 miles); depth +/- 4.5 km (2.8 miles)
    Parameters NST=305, Nph=314, Dmin=267.2 km, Rmss=0.98 sec, Gp=180°,
    M-type=body wave magnitude (Mb), Version=9
    Source USGS NEIC (WDCS-D)
    Event ID usc0003l3u

    While in general George is correct, what that does not cover is that quakes along the spreading center mean more movement pushing things over toward the subduction zone ( IMHO). So when the spreading center is active, and the subduction zone is not (as we see in the frames above) I get more nervous while George says “where is there a problem?”…

    Basically, my money is no the notion of a repeat of the 1700’s where Japan and CSZ both “went” inside a few years of each other in Great Quakes.

    But the “signature” ought to be a sudden swarm of very small quakes along the CSZ as the locked section starts to crumble. So I’m watching for:

    1) Persistent moderate quakes along the spreading zone off shore (where that last one was).


    2) Lack of quakes along the subjuction zone at the shore.

    Semi-Check. It has slowed down some, but we HAVE had a batch recently (in geologic terms). Still, less action than at the spreading zone so stress is going somewhere…

    3) A swarm of 1 to 3 sized events along the CSZ in the course of a week or two.

    Nope, not even close.

    That, to me, says we need a longer ‘quiet time’ at the CSZ. I would expect that sometime in the next 5 to 10 years we will see a block of “nothing happens” for a year or so, then “the swarm”… At that point, I’d get out of town fast.

    Still, as that could be wrong, it is worth watching for that swarm even without the precursor ‘dead time’. It’s had 400 years to build to the breaking point so who knows if it is ready, or needs another decade, or if it will warn with a ‘quiet time’ or had it 80 years ago…

    Basically, there are two “modes” that I’d watch for. The “dead silent” when things just lock up (a common feature) and the “small swarm” that is an occasional feature. You don’t know in advance which signature you will get. The “small swarm” must be in the context of a generally quieter fault. Very active faults are sites of very frequent “small swarms” as stress is continuously released (see that Baja to Salton Sea section). That’s a good thing and means “no problem”. It’s the “small swarm” on a “not moving” block that indicates it’s at the breaking point AND has been locked long enough to matter. (Why I’m watching the activity on the Hayward / Calaveras system so closely) These sometimes come just a day or two or even just hours before it breaks. Sometimes months. Watch for building intensity. A couple of 1’s then 2, then a 4 or even a 5….

    Right now it looks, to me, like the CSZ is mostly loaded from 400 years of “no big one” but has some creep preventing the final break. Either signature would send me packing. Dead silent or a “swarm”. But I think it’s likely got a few more years of “build” before it’s fully ready to rumble…

  19. Catherine Clark says:


    Is this the foreshock? It looks to be on or very close to CSZ.

  20. boballab says:

    @ Catherine

    According to the map it is not dead on the major fault lines but that might not mean much. However i don’t remember a series of smaller quakes in that location prior to that 6.4.

  21. Catherine Clark says:

    What is a little unsettling is that prior to the big one in Indonesia they had what is now termed a prequake (I think) a couple of years earlier that was a 6 or 7 magnitude. No, it is not dead on, but I don’t think it has to be. The big one in Japan last Spring wasn’t dead on, and neither was the Indonesian quake if my memory serves me.

  22. P.G. Sharrow says:

    That Vancouver quake was felt in Chico,CA. This looks to me to be a prequake. We shall see if they get a few more in the next few weeks. pg

  23. Catherine Clark, Illinois says:

    Of course, the word I needed escaped me at the time! I really meant foreshock. I haven’t seen any aftershocks, which is pretty typical for the area. I was in the 1965 EQ that was a 6.5 magnitude and there were no aftershocks and from my understanding and talking to family members who experienced the 1949 EQ (epicenter same or very, very close) there were no aftershocks then, either. This will need an eye kept on it for the next few years to see what tranpires. I hope it isn’t a true foreshock because the implications of a foreshock on the CSZ give me the willies.

  24. Jeff Alberts says:

    Didn’t feel anything of the Vancouver quake in Mt Vernon, WA, probably less than 100 miles away. I only heard about it after the fact.

  25. E.M.Smith says:

    I’d count it as a likely preshock. It’s in the place where the plate is subducting under the continent margins. (The fault is not directly vertical, but is more like a tilted plane, so it’s not on the place where the plane intersects the surface, but could be easily where the plane is deeper…)

    @Jeff Alberts:

    I drove though a 5.x and didn’t even notice as the car isolated me from it. I was right on top of it too. A lot depends on where you are at the time and the type of geology between you and it. (Also if you are on a line along the fault, you get more than if you are perpendicular form it, most of the time).

    At any rate, we’ll see… Nice cluster of dinky ones near the California end too…

  26. Catherine Cklark says:

    I would be happy if this is an isolated shock and not a foreshock or preshock; I would like the big one to wait a few years. I do find a quake that size so near to the CSZ a bit unsettling. Have any geologists come out and said anything?

  27. E.M.Smith says:

    I’ve not seen anything, but I would not expect anything either.

    In my geology class on quakes, the professors took great glee in explaining that you could only know something was a foreshock in retrospective analysis.

    “It is an isolated quake until it is followed by a larger one, then it’s a foreshock” and “It becomes the main shock when followed by enough aftershocks of lower magnitude. Unless a larger shock then follows, when it gets called a foreshock”.

    When I asked “how long is long enough” and “how big is a ‘larger one’?”… I got “Well, that kind of depends. The bigger they are the longer the window to make it a foreshock. Sometimes a year. Sometimes not.”

    And “Never call it a foreshock until after a larger quake happens”.

    So at best you will get the “It’s not a foreshock until it is” lecture…

    I’d expect to see something like this “soonish” at best:

    Click to access NEPEC_051807_10_Wilson_Communication.pdf

    So basically geologists are trained to never predict that anything is a foreshock until after a larger quake happens… but to run off and watch the shake recorders and hope…

    There are some minor things that can be a bit clueful. Is the shock ‘clean’, like a simple break before a major rumbly slide event? Is the shock very similar in size and placement to prior foreshocks? But none of it is definitive.

    So, in my experience, the foreshocks come as an isolated event, somewhat ‘brittle’ in character (short, sharp event). The main shock often has some minor quakes that precede it (a minor swarm of 1 and 2 events) then the big one with some rumble and slide to it (longer duration, more variation of motion, a bit more ‘rolling’). Except for when it isn’t and doesn’t ;-)

    At any rate, I’d avoid ‘beach time’ for a year or so…

  28. Jeff Alberts says:


    It’s possible I was in my van at the time, not sure.

    When I first moved out to Western Washington in 2002, there was a 5.2 quake near Orcas Island, about 30 miles straight line distance from me, maybe a little more. I felt that, but was sitting watching TV.

  29. Catherine Clark says:

    Well, I was way off base about the aftershocks; there have been a few. I still find it unsettling to have an EQ that close to the zone.

  30. PhilJourdan says:

    Interesting development on the 5.8 in Virginia. While we do not often think of a magnitude 5.x causing any appreciable damage, it has managed to shut down 2 schools for the year (and of course the national Cathedral and the Obelisk).

    But we had a fix-it guy on the radio this past weekend, who had a chimney expert come in and examine his chimney for damage. And the results were both surprising and cause for concern! Most houses on this side of the nation have brick chimneys (most just for that homey feeling). And even a slight jolt like that did significant damage to the chimneys! It has spurred me to get mine inspected!

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  35. E.M.Smith says:

    Worth note that in the last few days there have been two 4.x quakes on the subduction fault side of the plate. One just off the coast of California and one up at the top:

    Magnitude 4.7 – HAIDA GWAII REGION, CANADA
    2012 January 13 19:46:09 UTC

    Earthquake Details
    This event has been reviewed by a seismologist.Magnitude 4.7
    Date-Time Friday, January 13, 2012 at 19:46:09 UTC
    Friday, January 13, 2012 at 11:46:09 AM at epicenter
    Time of Earthquake in other Time Zones
    Location 51.262°N, 130.361°W
    Depth 15 km (9.3 miles)
    Distances 182 km (113 miles) WSW of Bella Bella, British Columbia, Canada
    215 km (133 miles) WNW of Port Hardy, British Columbia, Canada
    561 km (348 miles) WNW of Vancouver, British Columbia, Canada
    593 km (368 miles) NW of VICTORIA, British Columbia, Canada
    Location Uncertainty horizontal +/- 22.4 km (13.9 miles); depth +/- 10.8 km (6.7 miles)
    Parameters NST=238, Nph=240, Dmin=187 km, Rmss=0.88 sec, Gp=158°,
    M-type=body wave magnitude (Mb), Version=6
    Source Magnitude: USGS NEIC (WDCS-D)
    Location: USGS NEIC (WDCS-D)
    Event ID usc0007kg9

    2012 January 17 09:55:00 UTC
    Earthquake Details
    This event has been reviewed by a seismologist.Magnitude 4.3
    Date-Time Tuesday, January 17, 2012 at 09:55:00 UTC
    Tuesday, January 17, 2012 at 01:55:00 AM at epicenter
    Time of Earthquake in other Time Zones
    Location 40.528°N, 124.782°W
    Depth 24 km (14.9 miles) (poorly constrained)
    Distances 44 km (28 miles) W (263°) from Ferndale, CA
    48 km (30 miles) WNW (298°) from Petrolia, CA
    54 km (34 miles) W (263°) from Fortuna, CA
    60 km (37 miles) WSW (241°) from Eureka, CA
    359 km (223 miles) NW (309°) from Sacramento, CA
    Location Uncertainty horizontal +/- 0.5 km (0.3 miles); depth +/- 31.6 km (19.6 miles)
    Parameters Nph= 72, Dmin=38 km, Rmss=0.17 sec, Gp=227°,
    M-type=regional moment magnitude (Mw), Version=7
    Source California Integrated Seismic Net:
    Event ID nc71718846

    Not a big deal on their own. But certainly enough to say “Watch Here” for a while. If we start to see a pattern of more activity, it would be a good time to check the “bug out bag”, put gas in the car, stock up the food supply, fill the water barrel, etc.

    Most likely, it’s a big ‘nothing’ (as 4.x are common and it’s a few hundred years of ‘common’ before you get a Great Quake); but it doesn’t hurt to check the preparation kits and watch the charts a bit more often for a week or two…

  36. George says:

    Different plates, though. Well, the one at the Mendocino triple junction is on the Pacific plate and the one up North is on the Gorda plate.

  37. E.M.Smith says:


    Just eyeballing the maps, it looks like they are both on the N. American Plate (then again, without adjusting for depth that could just be a ‘projection’ error).

    So do you have a place to spot the ‘plate name’ or is it just the depth making it on the ‘other side of the red line’ vs the maps?

  38. Pingback: Quakes – Cascadia and Asia Pacific « Musings from the Chiefio

  39. E.M.Smith says:

    Well, we had a 5.6 inland N. California from where the fault heads out to sea, and now a 6.0 off the coast of Oregon (and others in past months).

    Somebody is being shaky in Cascadia…. So time to check the preparedness kits, but an extra $100 in the wallet, gas up the car, etc. etc. Not a prediction, just that IF it progresses, next stop is 7.0 or greater… and that is damage land. If it goes back to sleep, at least you know your kits are in good condition…

  40. Pingback: Quakes – California and South America | Musings from the Chiefio

  41. Pingback: Quakes – Mexico 7.6 | Musings from the Chiefio

  42. Pingback: Quakes – Odd Cascadia Cluster | Musings from the Chiefio

  43. E.M.Smith says:

    There’s an odd series of small quakes running up from the triple junction of the subduction and spreading zones on the Cascadia system.

    I would hope it is just random chatter, but it also looks a little bit like early pre-quake activity spreading… One of them is a 3.4, so getting big enough to matter.


    Earthquake Details

    This event has been reviewed by a seismologist.

    Magnitude 3.4

    Sunday, June 10, 2012 at 06:55:50 UTC
    Saturday, June 09, 2012 at 11:55:50 PM at epicenter
    Time of Earthquake in other Time Zones

    Location 40.985°N, 124.832°W
    Depth 24.5 km (15.2 miles)

    59 km (36 miles) W (262°) from Trinidad, CA
    60 km (37 miles) WNW (294°) from Bayview, CA
    60 km (37 miles) WNW (298°) from Humboldt Hill, CA
    60 km (38 miles) WNW (291°) from Eureka, CA
    394 km (245 miles) NW (314°) from Sacramento, CA

    Location Uncertainty horizontal +/- 1.2 km (0.7 miles); depth +/- 16.5 km (10.3 miles)
    Parameters Nph= 62, Dmin=70 km, Rmss=0.31 sec, Gp=220°,
    M-type=local magnitude (ML), Version=9

    California Integrated Seismic Net:

    Event ID nc71799216

  44. Well, that last post just gave me chills. Not sure why, but it did. I have been watching this activity.

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