atquake

Eathquake musings

MH 370

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It’s hard not to get sucked into the Maylasian 370 story at some level… Although I mostly work on earthquakes, I started out and still am a sonar and seafloor mapping guy, so am interested in how it will be to search for this airplane.  The pinger contacts were on the west flank of Wallaby Ridge, also known as the Zenith Plateau.  Unfortunately this is a very rough area of seafloor that has never been mapped, much like most of the worlds oceans.  When you look on Google Earth, you get the impression that the ocean floor has been mapped everywhere, and in a way that is sort of true.  The Google earth image comes from Satellite altimetry, mapping the ocean surface.  Oddly, there is topography on the surface of the ocean caused by the gravitational pull of the seafloor mountains and trenches below. So mapping the surface gives you a sort of “pseudo gravity” map, which can then be converted to bathymetry with enough ground truth.  It looks great from a distance, but up close, you see that the smooth rolling hilly topography isn’t real, it’s mostly noise from the low resolution of the data.  Real mapping of the seafloor requires ships and underwater vehicles, and is very, very slow (and expensive) which is why it hasn’t been done globally.

Image

 

The pinger contacts from MH370 still leave a large area to search, but at least it’s possible, where without them, it was nearly hopeless.  The problem now is that the terrain there is very rough.  Even though it’s ~ 100 million years old, it has very little sediment cover, a few 10′s of meters most likely, of microfossil “ooze”.  the few swaths of multibeam sonar data nearby show a very rough terrain that will make finding even an intact airplane difficult, and there’s not much chance it’s intact.  A landing like the “miracle on the Hudson” might have been possible in perfect weather and a good pilot, but more likely the airplane is in small pieces.  Finding such pieces in a background of a mountainous, hard, rough, rocky bottom is a sonarmans nightmare.  There isn’t much contrast between the metal and the rocks from the sonar’s eye, and so you’d have to hope for a big recognizable piece to appear, like a wing.  If not, they will likely be chasing many many possible targets, and trying to photograph them with the AUV cameras, or with ROV cameras.  Hopefully they will get more vehicles there, as the one small AUV has a huge job.

One of the strangest stories in aviation history may take months, or even years to be told, but I think it will be told.

Written by eqgold

April 16, 2014 at 9:25 pm

Well, not completely dodged…

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While casualties and damage from the 8.2 quake near Iquique were thankfully light thanks to the smallish tsunami and good Chilean building codes, the local fishing fleet was heavily damaged.  Iquique is mostly a mining town, and the port there is a mostly man made fill expanding on several rock islands just offshore.  In the lee of this port facility, were numerous small fishing boats that were trapped in the open ended roadstead when he tsunami arrived.  I doubt the local fishermen would call the damage light.

Image

Fishing boats washed ashore by a tsunami sit in the waters of Iquique, Chile, on Wednesday, April 2. A magnitude-8.2 earthquake struck off the coast of northern Chile on Tuesday, April 1, triggering small landslides and prompting evacuations of coastal areas. At least six people were reported dead.

Wrecked boats in Iquique (AP photo)

This again reminded me of what would probably be a similar result to an earthquake of this size in the Pacific Northwest.  While we are well behind in preparedness, at least we know what to do.  Finding the will and the money is another matter.  But fishermen around the world are not so easily moved to higher ground, or at least their boats and livelihoods are not.  The same is true here in the northwest, in Japan, in Sumatra and wherever a subduction zone underlies the coast.  In first world countries, the answer is typically insurance, because there is no known cure for this problem. Well there is one cure, practiced in Japan, and that is massive tsunami walls and gates in some of the rivers and harbors. Elsewhere, not so much.

http://walrus.wr.usgs.gov/tsunami/japan/images/m-s4.jpg

River gate in Minami-Sanriku (USGS)

Written by eqgold

April 3, 2014 at 4:51 pm

Dodged a Bullet

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It looks like the Chileans and southern Peruvians dodged a bullet in the northern Chile seismic gap. The 8.2 earthquake yesterday didn’t fill the gap, and the tsunami maxed out locally at ~ 2.3 m or so. Some damage to the airport and container facilities at the mining port of Iquique, and a few casualties. Otherwise, the widespread evacuations were largely not needed, and damage was light.  The workshop I was at in Santiago in late January was focused on this exact spot, which probably was near the site of an M9 earthquake in 1868.  After Sumatra and Tohoku, areas previously though unlikely to generate M9 earthquakes are now suspect, and the not very well known 1868 Arica event is an example of a very large earthquake that never fit the older seismological models.

The 1868 Arica event generated a 12-16m tsunami locally, and one up to 7m in New Zealand!  Yikes.  But given the likely slip deficit, that is the seismic gap is not filled, there remains some possibility of another large event in the near future, triggered by this one and distinct from the aftershock sequence.  Something like this may have happened with two events in 1868 and 1877.

File:USS Wateree (1863).jpg

The focal mechanism for the April 2014 event is as expected, a shallow thrust well aligned with the strike of the Nazca-S. America megathrust:

 

April 1, 2014, NEAR COAST OF NORTHERN CHILE, MW=8.1

Meredith Nettles
Goran Ekstrom

CENTROID-MOMENT-TENSOR  SOLUTION
GCMT EVENT:     C201404012346A  
DATA: II LD IU DK CU MN IC G  GE
 KP 
L.P.BODY WAVES:159S, 393C, T= 50
MANTLE WAVES:  159S, 451C, T=200
SURFACE WAVES: 142S, 199C, T= 50
TIMESTAMP:      Q-20140401232631
CENTROID LOCATION:
ORIGIN TIME:      23:47:29.1 0.1
LAT:19.77S 0.01;LON: 70.98W 0.01
DEP: 21.9  0.4;TRIANG HDUR: 26.9
MOMENT TENSOR: SCALE 10**28 D-CM
RR= 0.940 0.004; TT=-0.037 0.002
PP=-0.903 0.003; RT= 0.595 0.023
RP=-1.270 0.030; TP= 0.201 0.001
PRINCIPAL AXES:
1.(T) VAL=  1.702;PLG=61;AZM= 58
2.(N)      -0.024;     6;    159
3.(P)      -1.678;    28;    252
BEST DBLE.COUPLE:M0= 1.69*10**28
NP1: STRIKE=357;DIP=18;SLIP= 109
NP2: STRIKE=157;DIP=73;SLIP=  84

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Full Circle!

with 7 comments

It’s a big Deal!  That’s what a 2nd grader shouted when the assembly of K-5 kids were asked why worry about earthquakes when they are so rare?  This was yesterday at Central Elementary School in Albany, a 100 + year old URM school which has just been retrofitted with shear walls, a steel fire escape and other features to make it more earthquake resistant.  There are about 1000 schools in Oregon that fall into this risky category in earthquake country.  So far about 13 have been upgraded…. A long way to go, but it’s a start.

When I first came to OSU as a grad student, I wasn’t sure what aspect of geology I wanted to gravitate too, but after a couple of years, active tectonics, and later earthquakes rise to the top for me, as things we could observe directly, and also as things that actually mattered to people, which seemed like a plus, though not a requirement for me.  As time went on, and I started working on the Cascadia subduction zone, it was an odd enigmatic place seemingly devoid of earthquakes, and that alone made it interesting.  Then the evidence for past great earthquakes began to come out, which answered some questions but raised others.  The enigma was still there, the lack of small earthquakes, even though the riddle of the absence of any earthquakes faded.   When Hans Nelson and I started working on paleoseismology, it became more and more clear that regular and very large earthquakes punctuate the recent history in Cascadia.  I bought earthquake insurance.

The earthquake story evolved, but remained a scientific issue for me until 2004, when the 2004 earthquake and tsunami hit Banda Aceh, Thailand and places all around the Indian Ocean. In the blink of an eye, this was no longer academic, and there I was talking to CNN on live TV from the wave lab the day after Christmas.    Few had ever actually seen a large destructive tsunami and lived to tell about it, let along watch it on TV.  But like millions of others, I watched it, and the reality of it was there for all to see.

Suddenly,  Cascadia was no longer academic either.  8 years later, we put the finishing touches on the paper that pulled together a decade of paleoseismology and calculated new odds for earthquakes.  The numbers got bigger.  The enormity of the Pacific Northwest having to actually do something to prepare for this coming earthquake became much more apparent.  The Tohoku earthquake put triple exclamation points on it.

Two years ago, a parent in Portland sent me an email asking about 1906 URM school her daughter goes to might be a problem in an earthquake.  She said a retrofit was planned but not completed and she felt she was getting the run round from school officials.   I told her what any earthquake person would, yes it’s a problem.  I suggested she bypass the local officials and write some letters to people starting with state legislators on up.   She did better than that  and started an organization, and Amanda Gersh and Ted Wolf became involved and instrumental in pushing for changes. Two years later, a bond measure for seismic retrofit passed to retrofit schools on Portland.

Then yesterday, at Central Elementary School, I went to see  the dedication of the seismic retrofit and said a few words to the kids along with the folks who made it happen.  It was pretty cool really to see this come full circle.

Written by eqgold

April 26, 2013 at 2:56 am

Posted in Uncategorized

Wierd Thrust Earthquake Somewhere Near the Queen Charlotte Fault

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Was watching a movie last night when the Mw7.7 earthquake went off somewhere near the Queen Charlotte Fault.  The USGS location is under land, the islands now called Haida Gwaii (Formerly Queen Charlotte).  I think the fault is still the Queen Charlotte Fault though.  The Harvard location is on the fault, different than all four of the other network locations on NEIC Image

(see the image, the red thingy is the USGS location, the pushpin is the Harvard solution).  Given the location, even though it was big, I went back to the movie, assuming it was a strike slip earthquake like the 1949 one (Mw 8.1!!) and there would be no tsunami.  But then saw the warnings coming through and the evacuation of Hawaii in the middle of the big Halloween party going on in Honolulu.  That seemed a bit overcautious given the strike slip fault.  But low and behold, it turned out to be a thrust earthquake, so the warnings were warranted, though that wasn’t known at the time.  Can you say strain partitioning?   How long had this strike-slip fault been saving up compressional strain to produce this earthquake?  The 1949 earthquake in the same areas was almost pure strike slip, and 500 km long.   Small increments of compressional strain could have been accumulating there for many hundreds, maybe thousands of years, something like the way Tohoku accumulated more and more compressional strain, all the while having M7.8-8.5 earthquakes for over 1000 years before the big one let go.  Every one of these things has lessons for us….

Here’s  a brief phone interview with Daily Planet about this earthquake:  http://www.youtube.com/watch?v=_B65voERptc&feature=youtu.be

 
Today Jeff Beeson and I ran a Coulomb stress model to see what sort of stress change might be expected from this earthquake on the northern tip of the Cascadia/Explorer megathrust.  With reasonable guesses about some of the parameters, the stress transfer might be 0.01-0.02 bars, a very small increase that’s in the noise.

Here’s the mechanism:

October 28, 2012, QUEEN CHARLOTTE ISLANDS REGION, MW=7.7

Meredith Nettles
Goran Ekstrom

CENTROID-MOMENT-TENSOR  SOLUTION
GCMT EVENT:     C201210280304A  
DATA: II LD IU DK CU MN G  IC GE
L.P.BODY WAVES:149S, 387C, T= 50
MANTLE WAVES:  150S, 405C, T=150
SURFACE WAVES: 153S, 408C, T= 50
TIMESTAMP:      Q-20121028073457
CENTROID LOCATION:
ORIGIN TIME:      03:04:39.2 0.1
LAT:52.47N 0.00;LON:132.13W 0.01
DEP: 15.0  0.2;TRIANG HDUR: 18.2
MOMENT TENSOR: SCALE 10**27 D-CM
RR= 4.120 0.015; TT=-2.560 0.011
PP=-1.560 0.009; RT= 2.900 0.123
RP=-0.906 0.110; TP= 2.140 0.006
PRINCIPAL AXES:
1.(T) VAL=  5.205;PLG=70;AZM=  3
2.(N)      -0.058;    10;    122
3.(P)      -5.147;    17;    215
BEST DBLE.COUPLE:M0= 5.18*10**27
NP1: STRIKE=320;DIP=29;SLIP= 111
NP2: STRIKE=116;DIP=63;SLIP=  79

            -----------           
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    ####################-------   
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  -#############   ########------ 
  --############ T ##########---- 
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      -- P ------------------     
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Written by eqgold

October 28, 2012 at 5:28 pm

Posted in Uncategorized

Seismology refutes global clustering of M9 earthquakes. Really?

with 2 comments

Two recent papers (Shearer and Stark, 2011; Michael 2011) unfortunately perpetuate a long-standing notion that statistical analysis of the ~ 100 year instrumental earthquake catalog informs us about clustering of M~9 subduction earthquakes.  This fallacy, perpetuated now for decades, has misled us into categorizing subduction zones by seismic capacity based on plate age and convergence rate.  Shearer and Stark (2011) make the same error committed in the 1970’s by turning to the instrumental catalog to “test” the possibility of clustering of M9 earthquakes.  There are a number of serious flaws in this approach.  With regard to the greatest earthquakes, recurrence times can be many hundreds of years.  Cascadia varies from 240-500 years, with gaps as long as 1200 years.  Cascadia has likely had two superquakes in 10,000 years, with long term cycling and clustering of events that is now becoming apparent (Goldfinger et al., 2011;submitted).  NE Japan likely had its penultimate M~9 event in the year 869, (Minoura et al. 2001).  During the intervening ~1000 years, numerous smaller earthquakes in the 8.2-8.4 range used only a small fraction of the accumulated strain, requiring the eventual superquake of March 2011 (forecast by  Ikeda, 2005).   The Sumatran subduction zone (Sieh et al., 2008), Cascadia and NE Japan apparently each have long term energy cycling, with groups of smaller events punctuated by larger events and long time gaps in their histories.  These three zones are the only three with paleoseismic records long enough to make these observations.

A second problem is the authors, who are well aware of the problems with short records, attempt to circumvent what we consider to be a brick wall by using smaller earthquakes with higher frequencies.  This approach simply does not address the question of whether clustering of M9 earthquakes exists, but instead answers an entirely different question, that is have global rates of M> 7 earthquakes clustered in the 20th century.   We see no direct connection between these two distinct questions.  One need look no further than Cascadia, which has a b value of near zero, to see the fallacy of this assumption.

A third problem is that the basic observation that M9 events have clustered twice in the 1957-1965 period, and again 2004-2011 is questioned because a mechanism is not known.   Numerous arguments have been made against both static and dynamic triggering, the only two obvious options, and tests of both of them have been made as well using, again, smaller earthquakes.  Geology has a rather sordid history of throwing out observations for lack of a good mechanism.  Plate Tectonics and the Missoula Floods come to mind.  Lack of a mechanism is not evidence, it’s simply a neutral observation that may or not be relevant.

To evaluate global clustering of M9 earthquakes, long paleoseismic records from more subduction zones are required, and it is unlikely that seismology can address this question.  Statistical tests do not address this problem because they use a much larger range of earthquake magnitudes, addressing a different question.  As with plate tectonics, the current absence of evidence for a mechanism, is not evidence of absence of global clustering.

References

Goldfinger, C., Nelson, C.H., Morey, A., Johnson, J.E., Gutierrez-Pastor, J., Eriksson, A.T., Karabanov, E., Patton, J., Gracia, E., Enkin, R., Dallimore, A., Dunhill, G., and Vallier, T., 2011, Turbidite Event History: Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone, USGS Professional Paper 1661-F, Reston, VA, U.S. Geological Survey,  332 p, 64 Figures.

Goldfinger, C., Ikeda, Y., and Yeats, R.S., 2011, Superquakes and Supercycles, AGU fall meeting and submitted paper.

Ikeda, Y., 2005, Long-term and short-term rates of horizontal shortening over the Northeast Japan arc, Hokudan International Symposium on Active Faulting: January 17-24 2005, Hokudan City, Japan.

Michael, A. J., 2011, Random variability explains apparent global clustering of large earthquakes, Geophys. Res. Lett., 38, L21301, doi:10.1029/2011GL049443.

Minoura, K., Imamura, F., Sugawara, D., Kono, Y., and Iwashita, T., 2001, The 869 Jogan tsunami deposit and recurrence interval of large-scale tsunami on the Pacific coast of northeast Japan: Journal of Natural Disaster Science, v. 23, p. 83-88.

Shearer, P.M., and Stark, P.B., 2011, Global risk of big earthquakes has not recently increased: Proceedings of the National Academy of Sciences,  published ahead of print December 19, 2011, doi:10.1073/pnas.1118525109.

Shishikura, M., Sawai, Y., Okamura, Y., Komatsubara, J., Tin Aung, T., Ishiyama, T., Fujiwara, O., and Fujino, S., 2007, Age and distribution of tsunami deposit in the Ishinomaki plain, Northeast Japan: Annual Report on Active Fault and Paleoearthquake Researches, p. 31-46.

Sieh, K., Natawidjaja, D.H., Meltzner, A.J., Shen, C.-C., Cheng, H., Li, K.-S., Suwargadi, B.W., Galetzka, J., Philibosian, B., and Edwards, R.L., 2008, Earthquake Supercycles Inferred from Sea-Level Changes Recorded in the Corals of West Sumatra: Science, v. 322, p. 1674-1678.

Written by eqgold

December 23, 2011 at 9:12 pm

Short Memories

with 2 comments

It seems that the more “advanced” a society becomes, the shorter it’s memory.  The Andaman Islanders did  better in the 2004 quake than anyone else, and the previous big quake was hundreds of years prior.  Native Americans not only have a memory of the last Cascadia earthquake 311 years ago, they have a memory of the explosion of Mt Mazama (Crater Lake) ~ 7600 years ago.    We on  the other hand can’t remember much that happened before Twitter and Facebook.

Modern societies intentionally discard anything old.  So instead, we have to rely on science, not social memory for fill in what we have forgotten.  Even in Japan, the stone tablets warning of past great tsunamis (see http://www.google.com/hostednews/ap/article/ALeqM5hnlFOddxHicXMy-m1x3Lnd5OfLtg?docId=3186d9e8c263410eb1c1e60efabc62b1) were ignored mostly, and even they were not old enough to record the even larger tsunamis of the past, as many of them were washed away by the recent one.

Subduction zone earthquakes may have recurrence times of 500-1000 years, so human memory is really of little use.  In Cascadia, the 1700 AD earthquake was the most recent one, but not at all the largest.  The largest event probably occurred ~ 5900 years ago, and may have been ~ three times the energy of 1700.

Written by eqgold

April 9, 2011 at 2:34 pm

Posted in Uncategorized

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