Quake Watch 2012

reply to post by PuterMan

Thank you for those details. Now I follow you.

You know, I think the information you've referenced tends to suggest that there is still some degree of uncertainty when it comes to dating the major events (pre the 1700 one). For example, in an article by Atwater et al entitled Earthquake Recurrence Inferred from Paleoseismology, published in Quaternary Science (2004), they identify seven specific major events in the past 3500 years (with one being on the Seattle fault), but there is a fair amount of range in dating some of them and far less with others: carbon dating for the older ones is actually more precise. (Pdf of article available here).

The Pratt et al article that I mentioned above -- Understanding the Seismotectonics of the Cascadia Subduction Zone -- has dating that's a little at variance with Atwater's in some cases but still suggests 7 major events in the past 3500 years.

I think the real conundrum here is one that both these and other researchers have raised: there is a great degree of variance in the intervals between great quakes in this region, with some (including Goldfinger, for example), stating recurrence times varying between less than two centuries and possibly as low as 100 years, up to 1,000 years. Some have stated an extreme interval of 1300 years but I think the more recent research tends towards one millennium as the longest period between two identified events.

Very roughly, if we go for a low interval of 200 years and a high of about 1,000 years, we are looking at rupture intervals that vary by around 500%. If we take the extremes of 100 and 1300 years then clearly, we have a 1300% variation. But let's use the lower figure.

This begs the question: why, or how is it possible that there can be such variance in time between major events? And what do any potential answers do to assumptions we try to make about when the next one may occur?

Granted, when considering a matter like this we need to make assumptions. You've done that and I applaud what you've put forward. I just wonder if we need to think more about some combinations of assumptions. (I have no doubt that you already have, I'm just putting this down, is all. )

For example, within your calculations, one of the basic assumptions is that the subduction zone can only withstand a certain amount of accumulated stress before it has to let go. That's probably an assumption we can accept and in fact, it's probably the most fundamental. Otherwise, we would have to discover a mechanism that allows the zone to build up stress in vastly variable amounts, sometimes rupturing and sometimes not. And I don't think anyone has suggested such a mechanism. So okay, let's accept a reasonably steady maximum allowable stress load before failure.

Next, you have mathematically modelled a fixed amount of stress being input into the system per given period of time. Also, by fair averaging, a given amount of stress is taken out by the lesser seismic events that occur, so the net gain can be determined and carried forward.

Obviously you've thought of this as well, but I'll voice it anyway: if the first and fundamental assumption is accepted, then by implication the second assumption cannot hold, because if the amount of stress entering the system is near-constant, and the stress limit is also, then the time interval between ruptures ought to be more or less the same -- perhaps give or take a century or so. However, as the interval varies much more than that, we have to ask why.

It seems to me that the scientists' assumption of movement at (roughly) a fixed rate per period of time (I recall around 5cm pa), just doesn't fit. Here's why: the evidence of the past events and when they occurred cannot be denied. They are facts and whatever scientists assume (in this case) must fit with those facts. We have very good reason to believe that the rupture will occur when the stress reaches the failure limit. Even allowing for variations in dating, there is about a 500% variation in time between failures. This is a fact and a vital one.

Why does the failure interval vary by that much? In my mind there can be only three possible answers. Perhaps the stress limit can vary by 500%, or perhaps a varying proportion of the stress is dispersed in some other way and not by a major rupture. Thirdly, perhaps the stress entering the system is nowhere near constant. On balance, I'd suggest that the latter is more likely the case.

And that's a problem, because it makes it difficult to achieve the end we all seek.

Having said all that, I appreciate what you're doing and I think it's vital to present it, as you have done.

Mike

reply to post by JustMike


Yes I would have to agree with you Mike that like all things scientific, except global warming, there are definitely elements of uncertainty.

I am still trying to find that original site because like you i was a little gobsmacked when I read it. This was not some blogger in the ether but a scientist on what I would call a private web site, i.e. not like ones provided by wordpress, blogger and the like.

As with any of these things there is room for error but if the minimum period discovered is ~200 years that still puts it in the time frame for a biggie.


I have recalculated with the 1600 one removed and a couple of 8.5 quakes added since there does appear to be evidence for that. Still very difficult to calculate as it makes many assumptions but I believe there is still right at this moment sufficient energy for a Mag 8.887

It may not be a Mag 9 but it sure as hell would give the good folk of Cascadia more than a nasty jolt.

reply to post by PuterMan

Would love to see that scientist's website. Please let me know if you are able to locate it again.

And yes, as researchers such as Satake, Atwater, Goldfinger and Nelson all agree, the CSZ could basically let go at any time. True, it might sit quiet for several centuries yet, but the odds are that it won't.

I feel that in a way, both residents and authorities in the region have been given a golden opportunity to take stock and do what they can to lessen the devastating effects of the next great quake and the huge tsunami it will most likely produce. The one in 1700 is estimated to have gone ashore on the Oregon and BC coast up to 30 metres high... Worse even than the mean height of Japan's tsunami last year.

I do hope it stays quiet there for some time longer.

It's quite remarkable, really. Considering that it's only been a couple of decades since experts have even begun to develop a fair understanding of what the CSZ can do (and relatively speaking, how often), people living in the region these days have been incredibly lucky. Based on past events, the thing could have let go even a hundred years ago -- or yesterday. But it's holding for now and thank goodness that it has. At least it should not be a total surprise when it finally happens. Not scientifically, at least.

But for the people? There's time to educate them and I just hope that's being done as well as it should be.

MIke

reply to post by JustMike

Obviously you've thought of this as well, but I'll voice it anyway: if the first and fundamental assumption is accepted, then by implication the second assumption cannot hold, because if the amount of stress entering the system is near-constant, and the stress limit is also, then the time interval between ruptures ought to be more or less the same -- perhaps give or take a century or so. However, as the interval varies much more than that, we have to ask why.

There actually is no problem with variable incidences. Whilst we can compute an average amount of stress that is going in and an average amount of stress coming out what we don't know is the conditions under which the rupture occurs.

It is perfectly possible for stress to build, rupture to occur, stress to build again but no rupture at the same point because of another mechanism that means it has stuck in which case it has to build sufficient to overcome the sticking point.

Then, does it release all the stress or only part of the stress? You could get a good release but still have sufficient left in the system for another.

One place that is good for 2 quakes of around the same size is Vanuatu. 7.1, 7.2 last year for example with a 6.5 in between. Is this a stuck fault building up 2 quakes worth?

Of course as you also mention the stress input may not be constant and the factors that affect this are many and not limited to, for example, stress being released on other areas of the plate.

Did Japan increase or decrease the stress on Cascadia I wonder?

Banda Aceh seemed to have a marked effect on Santa Cruz/Vanuatu which went very quiet (relatively) immediately after that big one for almost a year.

Whilst the slip is mechanical it is not clockwork and there will be many factors that contribute to the lubrication or not of the fault. These are all unknowns in a simplistic calculation like this.

Originally posted by JustMike

It's quite remarkable, really. Considering that it's only been a couple of decades since experts have even begun to develop a fair understanding of what the CSZ can do (and relatively speaking, how often), people living in the region these days have been incredibly lucky.

In 1969 I left San Francisco for Humboldt and Mendocino counties to get away from the threat of the big one, and eventually settled down in Ferndale, probably the most dangerous location on the west coast, knowing what we now know, and moved in thinking 'boy it feels good not having to think about earthquakes"

reply to post by zworld


I'm always at least a day late & a dollar short! Just remembered this tonight!
I posted this back on page 27 I think it was.
It has Japan earthquakes back to January 2008. I spent a couple of hours going throught it when someone mentioned a big swarm right before the big one. Pages & pages & pages of eq's! I only found 40 of them I think it was. But the smallest I found anywhere was a 2.3. I list them in that post.
I tried to copy the post, but it copied something completely different!
There's an English option, top right. Hope this isn't too late!

quake.twiple.jp...

WOQ


Just found an English option on your HiNet link. It's up near the top right. A bright blue rectangle in the black bar.
That takes you to a list of eq's with English numbers. Only latitudes & longitudes with no place names though. Found a list of seismos, but no graphs yet. Those weren't 'clickable'. Some of the pages have English numbers, but the words aren't in English!
Some of the pages have the word 'English' option on them after you get in there farther.

www.jamstec.go.jp...

Some interesting stuff in there. Even code of conduct for research activities! I just kept clicking on anything that was blue! It's after 2 AM here or I would look around some more! Hope this helps!

Uhhh... Iceland?

Icelandic Met Office Reykjanes Ridge

[http-en.vedur.is-earthquakes-and-volcanism/earthquakes/reykjanesridge/

sorry ,not sure how to link properly - anyone?

reply to post by 5senses


en.vedur.is...

You just copy and post the link in the thread.

And yeah, that's a pretty darn good swarm they got going there on the ridge. Good catch.

Lots of action near Mexico in the past 36 hours.

Magnitude 4.6 - OAXACA, MEXICO
2012 February 09 09:21:57 UTC
16.300°N, 96.905°W
Depth
34.5 km (21.4 miles)
Region
OAXACA, MEXICO
Distances
33 km (20 miles) W (264°) from Miahuatlán, Oaxaca, Mexico

MAP 4.6 2012/02/09 09:21:58 16.300 -96.905 34.5 OAXACA, MEXICO
MAP 4.4 2012/02/09 02:20:47 15.273 -94.305 38.8 OFFSHORE CHIAPAS, MEXICO
MAP 4.5 2012/02/08 21:24:59 14.963 -94.258 29.0 OFF THE COAST OF CHIAPAS, MEXICO
MAP 5.0 2012/02/08 13:06:46 15.050 -94.022 47.7 OFFSHORE CHIAPAS, MEXICO
MAP 4.5 2012/02/08 09:39:14 16.053 -94.088 112.4 OFFSHORE CHIAPAS, MEXICO
MAP 4.6 2012/02/07 22:30:34 14.738 -93.356 64.6 OFFSHORE CHIAPAS, MEXICO

USGS

reply to post by TrueAmerican


A ha. THAT'S how you link. Thank you.
I 've been watching them build over the last few days and don't remember when there were that many plus mag 3's. Worth keeping a continued eye on...

I have a couple of questions for the general earthquake studying community.

Based on plate tectonic theory, specifically oceanic-continental subduction zones, there seems to be a few different major mechanisms at play:
1. the "push" on the subducting oceanic plate from the associated spreading ridge.
2. the "pull" on the oceanic plate from the portion sinking into the mantle. (probably stronger on a steeply-dipping plate (ie. the Marianna trench area) vs. a shallow-dipping plate (ie. Juan de Fuca).
3. the convergent movement of the over-riding continental plate.

Take the Cascadia subduction zone, for example. The Juan de Fuca is being "pushed" by the speading ridge to its west. It's being pulled ENE by the portion diving under North America. And the NA continent is slowly moving SW over the Juan de Fuca (and Gorda) plates.

So, my questions are: Which mechanism is strongest? And which do you think is the "spark" that most often initiates a megathrust earthquake?
I can't seem to find an acceptable answer after scouring the internets. Even a proportional breakdown of relative importance would be helpful.

Just curious as to all of your thoughts...thanks in advance.

reply to post by Olivine


Perhaps PuterMan should answer that question, seeing as he doesn't believe in tectonics theory.

But good luck trying to pin down an answer to that one. The mechanics all probably work together to create the stress needed to initiate a rupture. Considering that it takes all elements present, I don't know that you could really define one element as the most important.

I will say this though- after studying Chile 1960 a lot more, I think the 9.5 could possibly have been stress triggered from the several massive 7+, and one 8.1 foreshocks. That was such an incredible amount of energy released in mere hours near the same spot, that it could have sent an otherwise locked stress point over the edge into creating the 9.5 - and rupturing 1000 km of fault area in total. A similar thing could happen in Cascadia, if several large quakes happened in a short period of time, and broke a critical point.

Originally posted by Olivine
I have a couple of questions for the general earthquake studying community.

Based on plate tectonic theory, specifically oceanic-continental subduction zones, there seems to be a few different major mechanisms at play:
1. the "push" on the subducting oceanic plate from the associated spreading ridge.
2. the "pull" on the oceanic plate from the portion sinking into the mantle. (probably stronger on a steeply-dipping plate (ie. the Marianna trench area) vs. a shallow-dipping plate (ie. Juan de Fuca).
3. the convergent movement of the over-riding continental plate.

Take the Cascadia subduction zone, for example. The Juan de Fuca is being "pushed" by the speading ridge to its west. It's being pulled ENE by the portion diving under North America. And the NA continent is slowly moving SW over the Juan de Fuca (and Gorda) plates.

So, my questions are: Which mechanism is strongest? And which do you think is the "spark" that most often initiates a megathrust earthquake?
I can't seem to find an acceptable answer after scouring the internets. Even a proportional breakdown of relative importance would be helpful.

Just curious as to all of your thoughts...thanks in advance.

I can't answer the first bit of your question, in fact, I'm just adding to it if anything. With Cascadia, the oceanic crust has been sinking beneath the continent for what, 100-200 million years or something at a rate of 40mm a year I've read.

With the Juan de Fuca, you're taking a dense rock that is sliding underneath a continent of thick and lighter rock. The megathrust spark comes down to when the weakened portion crumbles away at the limit of stress after so much heating, which can cause the land to perform a quick snap-back motion or elastic rebound dramatically.

There have been at least 7 quakes in the past 3,500 years, so they're looking at 300-600 years, since the apparent date of sometime in the early 1700s. It could happen in the next 200-300 years, but imo, 200+ seems unlikely. I would give it the next 100 years, but I'm going by nothing real when I say that. The long build up might be indicating an unusually large build up of stress...

Reference Number 3656029
Universal Time February 9 2012 at 9:57:02
NZ Daylight Time Thursday, February 9 2012 at 10:57 pm
Latitude, Longitude 40.98°S, 174.87°E
Focal Depth 40 km
Richter magnitude 3.9
Region Wellington

offshore Pukerua Bay 12.4 km from my house, was asleep, didn't feel it, but 346 others did
felt reports

Not sure if it was the Wairau Fault, looks too far offshore to be on the Pukerua Bay Fault. The Wairau F is a weird one, runs from the South Island across Cook Strait up the west coast and through between Kapiti Island and Raumati Beach, there was also a 4.995ML on 2010/2/12 @13:41:35 and 62.27km deep on the same fault 2km from my house and didn't feel that one either.
Sound sleeper

Also a swarm at Lake Rotoma, Bay of Plenty yesterday morning, 30 quakes, 29 from 1.562 to 3.468, and one undetermined magnitude, mostly shallow 0-29km, but one 2.76ML @ 139km. Volcanic




also ....................... another 5+, after that swarm, offshore SE of Mayor Island

Mag:5.147ML
Ref:3655733
Lat/Long:-37.426, 176.56709,
UTC: 2012/2/8 20:15:54
Depth: 223km

Originally posted by wasobservingquietly
reply to post by zworld

 

I'm always at least a day late & a dollar short! Just remembered this tonight!
I posted this back on page 27 I think it was.
It has Japan earthquakes back to January 2008. I spent a couple of hours going throught it when someone mentioned a big swarm right before the big one. Pages & pages & pages of eq's! I only found 40 of them I think it was. But the smallest I found anywhere was a 2.3. I list them in that post.
I tried to copy the post, but it copied something completely different!
There's an English option, top right. Hope this isn't too late!

quake.twiple.jp...

WOQ


Just found an English option on your HiNet link. It's up near the top right. A bright blue rectangle in the black bar.
That takes you to a list of eq's with English numbers. Only latitudes & longitudes with no place names though. Found a list of seismos, but no graphs yet. Those weren't 'clickable'. Some of the pages have English numbers, but the words aren't in English!
Some of the pages have the word 'English' option on them after you get in there farther.

www.jamstec.go.jp...

Some interesting stuff in there. Even code of conduct for research activities! I just kept clicking on anything that was blue! It's after 2 AM here or I would look around some more! Hope this helps!

edit on 9-2-2012 by wasobservingquietly because: Stumbled upon this!

Thank you very much wasobservingquietly. Excellent. You made my day.

Originally posted by murkraz

There have been at least 7 quakes in the past 3,500 years, so they're looking at 300-600 years, since the apparent date of sometime in the early 1700s. It could happen in the next 200-300 years, but imo, 200+ seems unlikely. I would give it the next 100 years, but I'm going by nothing real when I say that. The long build up might be indicating an unusually large build up of stress...

edit on 9/2/12 by murkraz because: (no reason given)

Once again the MTJ and Gorda plate are the wildcard. We have a return interval of big ones every 270+ years, as opposed to the 500+ for the northern JDF.

However, due to the fact that the ring of fire has been so active in the last 100 years while excluding the CSZ and the Mexico TJ makes me think that things have built to the breaking point everywhere in our area. If it is true that the lithosphere is tectonically connected and functions as a separate mass from the rest of the earth, which everything points towards, then tectonic energy released anywhere in the world goes somewhere, and it seems to all point to us.

Just waiting for the shoe to drop we are. And here is the mind blower. most peeps in this area dont have a clue what could happen, and are totally unprepared for the lights going out let alone a massive 9+ shaker. Japan taught us very little

Before is news.

TextMagnitude mb 5.4 Region MACQUARIE ISLAND REGION Date time 2012-02-09 18:52:49.4 UTC Location 58.18 S ; 157.55 E Depth 2 km Distances 1623 km SW Dunedin (pop 114,347 ; local time 07:52:49.4 2012-02-10) 1497 km SW Invercargill (pop 47,287 ; local time 07:52:49.4 2012-02-10) 1477 km SW Bluff (pop 1,938 ; local time 07:52:49.4 2012-02-10)

source(www.emsc-csem.org...

Magnitude mb 5.2
Region WESTERN XIZANG-INDIA BORDER REG.
Date time 2012-02-09 19:17:31.0 UTC
Location 31.04 N ; 78.41 E
Depth 10 km
Distances 85 km NE Dehra dun (pop 522,081 ; local time 00:47:31.5 2012-02-10)
35 km NW Uttarkashi (pop 17,123 ; local time 00:47:31.5 2012-02-10)
32 km NE Barkot (pop 7,725 ; local time 00:47:31.5 2012-02-10)

EMSC

reply to post by muzzy


Yup busy day yesterday
heres the NZ interactive map for the 8th UTC

couple of 4's on Banks Peninsula too

not sure who is keeping the score but just for the heck of it I had a look

last 24 hours;

Japan - 378
California - 51
Aegean (Greece) - 47
Turkey - 40
Iceland - 31
New Zealand - 13 (51 yesterday)

and in the cricket ODI
NZ 373/8 , Zimbabwe 171 all out (44 overs)

reply to post by diamondsmith

and another;
5.1 2012/02/09 19:21:02 -58.303 158.022 13.8 MACQUARIE ISLAND REGION

usgs had
5.8 2012/02/09 18:52:47 -58.325 157.870 3.9 MACQUARIE ISLAND REGION
for your emsc 5.4, which they have now downgraded even further to 5.3 (mb)

FWIW, GFZ had 5.7Mw for that first one