Tuesday, April 30, 2013

Impact finite elements for seismic analysis

I'm quite happy, that I got Impact-fem working again!  I had a lot of trouble before, and the modelling gave me a headache.  After a couple of years, the project appears very active, and it is much improved.

This is just a cantilever springboard and the colours show the strain.  You can let it go and watch it go whappy-whappy.  This is much like a building on the side on a shake table, and it is showing the fundamental mode of vibration.  I encourage everybody to start playing with this.  You will soon realize that the existing conventions of seismic engineering are crap, once you add more reality.  For example, I will put a stiff building on a stiff half-space (the ground), and propagate a realistic seismic wave.  There is no major amplification in the building because seismic energy radiates back out into the ground.  It is not a shake table.

Now, why would one care?  This old conventions are one reason why the effect of soft ground is grossly underestimated by a factor of 10.  They are also responsible for using PGA (peak ground acceleration) for scaling, which is hogwash.  Better to use PGV.

Finally, they are rebuilding Darlington nuclear plant from the ground up, because they operated it so badly.  This is going to cost billions of dollars.  At least one billion will be wasted if they use the 40-year-old seismic conventions to seismically qualify new equipment.  Although this will be covered up, it is still a shame.  Comon' people, have some fun!  Do this.  I'll be doing some more modelling in the future.

Friday, April 26, 2013

Georgia Dam-Triggered Earthquakes

As far as I can tell, Georgia has no injection wells.  These are probably dam-triggered, much like Virginia, and Arkansas.  Very tiny for now, but it opens up the possibility of a Virginia-style M6.  I wouldn't hold my breath, though.

Thursday, April 25, 2013

Lots more Oklahoma earthquakes

As we all know by now, these earthquakes are triggered by irresponsible injection into the Precambrian megathrust.  These are huge features that run right through Eastern North America, although you would never know it from any US geology.  The megathrusts are highly stressed, and only lacking in water to make good earthquakes.

So, you can tickle the tails of these tigers to trigger small earthquakes, but how big can you get?  OK now has the record at M5.6.  But access to deep water is not totally caused by Man, it can happen naturally as well.  Thus, we must include the larger M7's of New Madrid.

Anyway, I wasn't going to write any more about this until my expected M5.  This will open up the central thrust zone, and start a full growing baby New Madrid.  In the meantime, the injector people are enjoying the fact that the fractures are opening up to accept more water.  They are making money hand over fist.

Friday, April 19, 2013

M6.9 earthquake China

Ok, I was completely wrong about Iran, but this is shallow, and has to be compression, right at the bulldozer end of the India push.  So I'm guessing this is a high PGV earthquake.  There are always lots of people everywhere in China, so it's a bad combination.  We'll wait for some news.

Update:  Huge rocks near the epicentre may indicate a high PGV, but there are lots of pictures of weak housing still standing.  We may never know the ground motion.

Update2:  All the videos show standard damage.  If there was a 'hammer zone' for a super-quake, it would be in the mountains.

M7.2 deep Pacific earthquake

Absolutely nothing exceptional about this earthquake except that it is smack dab in the middle of the next subduction curve up from the last big Japan earthquake.  That little curve produced an M9, this one is three times longer so it can get up to an M9.3.  The shaking wouldn't do anything, since it is so isolated, but it would make one heck of a tsunami!  Besides, I really like this picture.  :)  As I have said before, you can only get these beautiful landforms by having M9's pop off every few hundred years.  Otherwise,they would all fill in with goop.

Thursday, April 18, 2013

Caribbean earthquakes - a distorted cluster

I'm sad to say that I put a little more work into this than I am prone to do, and have found that my wonderful cluster is grossly distorted by a gold-plated USGS array in Puerto Rico.  I find they love to go places where it is sunny.  :)

So, in formal terms, if you drew a selectivity plot of the area, you would find it exactly matches this cluster.  So, 2's are detected close, then there is a ring of and 3's, and outside that you have 4's.  That means the same amount of activity could be elsewhere, but we wouldn't see it.

Oh well.

Wednesday, April 17, 2013

Oklahoma earthquakes - the beginning of a mechanism

Ok, OK had me rubbing my temple for a long time.  It is obvious they are injecting into the Precambrian like stink on cheese, and it is obvious they are on the last Grenville Front megathrust.  But why no mechanism?  Our earthquakes are caused by a static high horizontal stress, and weakening faults.  Not at all like California, which has weak faults and a building of stress.

A sustaining mechanism is one which grows to encompass more rock stress.  The biggest one is New Madrid.

It requires a central thrust zone and 2 shear wings.  My intelligent readers would know that this huge mechanism wasn't just placed there in all its glory.  No, it had to grow into the role.  Now it is confined by geology, and may be dying of old age.

But never fear, we can grow new ones!  Arkansas was the perfect proof of this concept.  It started with a central thrust zone, and was growing fine shear wings.  Had they kept injecting, the central thrust zone would have grown, and formed new shear wings.  All to capture more strain energy.

But with OK, we don't have to worry that they will stop injecting!  They had that one M5.6 out on the hanging wall, but that was isolated.  In response to the strain release, more activity appeared on the main megathrust under the city which was starting to form a shear wing.  This was a disconnected system, and under natural conditions, might have died.  But they kept injecting!

Now we suddenly have this huge rip, forming the necessary thrust zone.

The mechanism is off and running!  We should expect at least an M5 on this zone, and then the formation of a new shear wing.  Only time will tell if I'm full of it!  :)

*Note, why doesn't the US see this?  They are full of these little state geological surveys who only focus on their feet.  Couldn't see a continental pattern if it hit them on the nose.  The USGS is too busy tanning in California, and everybody is just trying to stay alive.

Update:  In g+ I thought of my new physics-based game "Grand Theft Injection".  Here's my kickstarter trailer.

You take the role of Rico, a corrupt geologist in the seedy city.  You started working for the Injection Mob when you realized it was the only way you could make money with a general geology degree.  In a first for games, the physics engine goes full 3-D right down to the Moho!  You must bribe corrupt politiciians, hide relevant data, and avoid falling buildings.  The more the Mob gets to inject, the more money you make, and the more earthquakes.  You can also make money as a shady contractor!  Lots of fun and laughs!

Something about the name seems familiar,  hmmm ....

Tuesday, April 16, 2013

Big Spray of Earthquakes Hits Oklahoma

Actually of more interest to me than a super quake in Iran, is this unbelievable spray of M4's and 3's in Okie-land.  They continue to inject and are now setting themselves up for another M6 right under the city.

These earthquakes have captured more strain energy up the megathrust.  In other words it is growing, just like a baby New Madrid.  If they can inject 30 km of the fault, we might break the record for a triggered earthquake and get up to an M7!  The church bells will ring in Boston!  Don't you just love pig-headedness.  :)

Update:  And still they come.

Update2:  Another 3.6!  These aren't aftershocks, this is something new ripping.

M7.8 Earthquake Iran

This is set in an area of pure compression, as the African Plate and Indian both jam up.

And therefore, we get a 'beachball' of pure compressional thrust.  Very shallow.  Most likely this was a 'super quake', similar to Kobe or Armenia.  That is when the fault rupture velocity exceeds the shear wave velocity, and essentially forms a shock wave of compression.  When that hits the surface, rocks fly in the air, and the PGV probably exceeds 2 m/s.  Nobody has been around to actually measure one of these things, so we don't know.

Update:  Pooey!  The beachball shows normal faulting.  Always get that wrong!  Forget the super-quake then, it's just average, which is enough to knock all the rubble houses down.

Update2:  I take that back.  A shallow thrust super-quake could totally screw up the beach!  I would have to double-check Armenia, if I wanted to do work.  :)

Update3:  Blah, deep extension earthquake, with no PGV.  This area is like the Sea of Japan, being wrenched apart by 2 plates with different vectors.

Tuesday, April 9, 2013

M4 earthquake Caribbean

I'm only reporting these earthquakes when they get to M4.  Unlike the Alaska cluster, these seem to be very closed at the M3-ish level.  That is very non-fractal, so it could be deep fluids.  If these earthquakes start curving around Anguilla, then there is a clearer mechanism.  There has been lots of earthquake action in the past

And looking at this, I'm probably blowing smoke about any concern of a cluster.

Still, it's fun.

Friday, April 5, 2013

Alaska M4.9 earthquake

I did say they would have to be over M5, and in the right zone.  This was almost there.  I don't really count the outer zone, but I am very fascinated on what is happening near the armpit.  The earthquakes here are operating at full fractal, which means a straight line log-log plot of frequency - mag (which is log).  That means there are x number of M3's for an M4, and x again for M4 to M5, etc.  I am still expecting the last M7.5 on the right strike-slip track to hit the armpit by the end of this year.

*as always, the uncertainties always swamp any human concept of time.  :)

M6.2 earthquake Russia and Japan Sea

Nothing much to this quake, but the picture and the tectonics of the Japan Sea are fascinating.  The sea is being ripped apart by the action of two subducting plates - Pacific and Philippine.  The crust is very thin here, so the action should be on the boundaries.

Mexico earthquake M5.4 - a little spice

They've been getting a few now.  This coast usually spits out M8's, with the capability for a doozy M9.  The last big Mexico City earthquake was around here.  That basin is deep soft soil inside a soft rock basin.  It is capable of amplifying PGV by a 100 times.  Of course, it doesn't amplify PGA, so nobody cares.  :(   It's just one of those many cities with zero seismic capacity, with the same odds for a big earthquake.  Most likely the next big earthquake won't be here.

Wednesday, April 3, 2013

M3.1 earthquake at Arkansas lake

Wow, can the Fish predict them or what?  I just did a blog of the earthquakes around the lake, and this pops up.  As with Virginia, larger earthquakes should be farther away from the source, since they need more room (fault area).  This was what I was looking for, namely a sustaining mechanism.

With a lot of earthquakes, they spring the 'rat trap' of high stresses, and then become locked out.  In other  words, the stress release is in the form of an isolated 'bubble'.  No more action is expected.  However, where there is a steady supply of water, as in a river, lake or injection, every earthquake will provide a channel for flow.   The best mechanism was the original Arkansas injection sequence, and I expect big things from this one.  :)

Update:  Downgraded to an M2.8, but now we have three of them at this location.  The only other possibility is injection.

Update2:  Up to 4 earthquakes now.

Tuesday, April 2, 2013

Arkansas lake effect earthquakes

The earthquakes continue around the dammed lake.  Looks fairly random and I can't see a mechanism developing.  Nevertheless, we should all remember Virginia.  As I was tracking this earthquake and aftershocks there was a pattern to that lake, indicating a trigger.  However, for the life of me, I can't find a good map of all the earthquakes there.  A time sequence would be nice, as well.  Just think of this basement rock as full of big rat traps, baited and ready to go, just waiting for a little bit of water.  :)