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Oklahoma Yin Yang

With 2016 coming to a close, GG thought we might want to see just how things are shaking out in Oklahoma, home of the great induced earthquake experiment. And there is something for everybody, depending on how you want to look at it.

For the optimists hoping that Oklahoma’s actions to slow wastewater injection will end the plague of induced earthquakes, we have plot number one: number of quakes with a magnitude of 3.0 or higher by month:

ok2016eqsmgt3

Earthquakes within Oklahoma, by month, 2016, from U.S. Geological Survey

The rate of such earthquakes dropped from nearly 4 a day in January to about one a day this month. And you could hope that this had something to do with this:

okinjection16

Monthly averaged daily injection volumes of Arbuckle disposal wells in the Area of Interest for Triggered Seismicity, from Oklahoma Corporation Commission, Oil and Gas Division. (December decline probably because of incomplete reporting).

The 25% reduction during the year in the rate of injection in the area where triggered seismicity has been observed might be responsible for this.  But there are other things to watch as well.  First, these are still pretty high volumes of water going back into the Arbuckle, and all the water that went down earlier is still making its way through the subsurface.  Second, presumably a lot of produced water is going to other wells, either in the Arbuckle outside the area of interest or into other formations. Third, a decrease in the number of M3+ events is not the same thing as a decline in seismic moment:

ok2016eqmoment

Seismic moment release in Oklahoma in 2016, derived from USGS catalog.

The 9/3/2016 M5.8 Pawnee, Oklahoma earthquake put a big damper on any celebration of a decrease in seismicity. The overall moment release of 7.8 x 1024 dyne cm is the largest single year moment release in Oklahoma history. As we noted before, this isn’t unexpected: the Rocky Mountain Arsenal sequence in the 1960s produced its largest quakes after the injection ended.

So we enter 2017 on a note of caution.  If you bought earthquake insurance in Oklahoma, don’t let it lapse just yet. You might get shaken a bit less often, but when you do get a quake, it might still be pretty big.

P.S.: there are a couple of nice visualizations out there.  Tulsa World put together an interactive map a year ago showing how produced water injection was varying over time and by county. The Oklahoma state government has an interactive figure with recent earthquakes and disposal well locations.

Single Quake Slip Partitioning?

UPDATE 2 11/22: GNS has assembled quite a lot of information, and the puzzlement deepens. It appears from the satellite and ground analysis that the bulk of the motion–up to 11 m of slip–was more nearly strike-slip and not the thrusting that appears in the focal mechanism (below). But the uplift of some areas of the coast by 6 meters (!) seems to suggest there is something more.

UPDATE 11/18: A considerable amount of information was put in an article on stuff.co.nz.  This includes a map from GNS showing where the faults are that ruptured, a good deal of geodetic information.

Yesterday’s M7.5/7.8 Kaikoura earthquake in New Zealand is one of the more bizarre large earthquakes we have seen in some time. On the face of it, this appears to mostly be rupture of a subduction zone under northeasternmost part of the South Island of New Zealand. But there is a lot of other stuff going on….

First, the main focal mechanism as reported by the USGS:

kaikouramt

Now this beachball would suggest a fault dipping to the NW while paralleling the coast. But the appearance that a toddler was not coloring in the lines tells you that there is something more here.

Some of that became apparent when the New Zealand’s GNS Science group went looking to see if there was any slip on earthquake faults.  This is what they found:

Rapid field reconnaissance indicates that multiple faults have ruptured:

  • Kekerengu Fault at the coast – appears to have had up to 10m of slip
  • Newly identified fault at Waipapa Bay
  • Hope Fault – seaward segment – minor movement
  • Hundalee Fault

I’ve tried to sketch these out from my copies of geologic maps of New Zealand:

kaikouramap

(The base map is from Google).

This is where the other shoe drops. The Hope and Kekerengu faults are mapped as strike-slip.  Now minor slip on the Hope Fault might not mean much, but 10m on the Kekerengu means there was a lot of slip (I’ve assumed above it is strike-slip, but perhaps there is a thrust component).  Plus, the epicenter of the quake–where it started–is somewhere between Cheviot and Rotherham, well to the south (this is why initially this was called the Cheviot earthquake). Toss in a very odd slip history (the moment release was low for a minute and then things really broke) and you get the impression that a relatively small earthquake on an unnamed fault southeast of Rotherham started tripping things off to the north, which eventually tripped off a big rupture.

That big rupture probably is not on the map.  It is likely offshore, in the very southern end of the Hikurangi Trench (which is in part responsible for the whale watching that is so popular at Kaikoura).  This is the northeast trending thrust fault that the focal mechanism captured and is responsible for the large slip amounts found on the finite-fault map the USGS shares. This is probably also the reason for the ~1m uplift of the seashore at Kaikoura, which led to many photos of paua and crawfish out of the ocean (though uplift at the southwest end of the big strike-slip fault is also possible).

Presumably the large strike-slip faulting on the Hope and Kekerengu faults is what has contaminated the focal mechanism, making it a composite of complex motions instead of the clean double-couple. (Pure strike-slip faulting is seen in many aftershocks.) As such, it seems this earthquake might well have captured both major thrust motion on the subduction zone and strike-slip on the upper plate faults, a form of slip-partitioning in a single event that is quite striking.

It will be interesting to see how the seismological and geological analysis continues; the main seismological slip appears north of these faults and so there could well be more to be found.  But rain is in the forecast, which tends to ruin the easiest of signals to see.

Oklahoma Dreamin’

Back in September, Oklahoma had a M5.6.  Some of you might recall the difference in opinion between USGS scientist Dan McNamara, who expected continued seismicity, and Oklahoma Geological Survey director Jeremy Boak, who said “I’d be surprised if we had another 5.0 this year.”

Well, Director Boak hopefully was in the vicinity to be surprised in person by the M5.0 today that damaged buildings in Cushing, OK, site of the largest oil storage facility in the country (which at least apparently escaped any damage). Yeah, once more wishful thinking trumped by actual scientific examination….increasingly it seems the branch McNamara has climbed out on is the real stout one while the hopes of the Oklahoma injection operators rest on thin reeds.

At least nobody has died, but when you are evacuating a senior housing facility in the night and cancelling school, you know you are playing with fire.

And hey, we aren’t even done with 2016 yet.

Overthrowing the model

Recently we mentioned how you don’t want to mistake a model’s assumption for a result. A new paper in Science by Inbal et al. makes some claims about deformation in the mantle that are interesting, but it is something totally outside their field of view that makes this of interest here.

Back in the 1980s, after the Coalinga earthquake of 1983 showed that fold could pose a seismic hazard as much as surface faults, some researchers tried to see what kinds of hazardous faults might be hiding at depth.  Tom Davis and Jay Namson, two consulting geologists, were particularly enthused and soon had a model for Southern California. When GG was a postdoc at Caltech, one of the authors came up to show us the model; it looked something like the version published in 1989:

davislabasin

SSW to NNE section across the Los Angeles Basin, Davis et al., JGR, 1989

It is hard to see (you can click here for a bigger version), but the area where the shaded horizon is deepest is under the Los Angeles Basin.  The red highlight is where the trend of the Newport-Inglewood fault passes through, and below that is a detachment fault extending all the way from the San Gabriel Mountains on the right to offshore Palos Verdes on the left. The orange section in particular is of interest here, as it suggests that the Newport Inglewood fault is cut at depth. When this was presented to us at Caltech, GG asked, why is that orange segment required? At the time, this was being presented as a seminal threat to Los Angeles.  The short answer really came to be: the means by which this model is constructed require it, but after some hemming and hawing there was the admission that you could have two detachments, one rooting to the right, one to the left.  Nevertheless, this is what was published.

How does a paper on faulting into the mantle come into this?

Read More…

Horses, barns and earthquakes

Well, it appears that the state of Oklahoma finally bought into the connection of earthquakes to deep injection wells as the recent M5.6 earthquake led them to shut down injection wells in the vicinity of the epicenter [and once again we learn the national media still cannot discern between fracking, which is not the cause here, and injection of waste water, which is the likely culprit]. Interestingly, there are two views on how Oklahoma seismicity is varying: Dan McNamara of the USGS argues that seismicity is still on the rise, while Oklahoma Geological Survey director Jeremy Boak is quoted by the Tulsa World that “I still expect to see declining figures over the rest of the year just because we’ve decreased the (wastewater) injection so much.”

Given how long the Oklahoma survey dragged its feet on acknowledging the problem, their credibility is kind of at a low point. McNamara in November said that more M5s were likely, and two more have happened since. McNamara made a plot of seismic moment over time that is pretty damning:

moment_release_OK_daniel_mcnamara

The big decrease in seismicity Boak was excited about is the somewhat shallower slope of moment increase in early 2016, a decrease now obliterated by this latest quake.

The problem is that fluid injection of this magnitude over this amount of time has probably not reached any kind of equilibrium yet. The overall upward concavity of this plot suggests that we aren’t at the end of increasing rates of moment release. Hopefully it will come as a boatload of small-impact M4s and low M5 events, but M6 events don’t seem implausible. If you look at a much smaller example, the likelihood of earthquakes continuing for decades is substantial–even if injection stops.

Back in the 1960s the Army injected wastewater at the Rocky Mountain Arsenal into basement.  This caused a bunch of earthquakes and eventually the injection was stopped–but two years later some of the largest quakes in the sequence happened. At the time the interpretation was that the pressure wave from the injection was propagating outward and so could have a substantial time lag. Regardless of mechanism, it should concern Oklahoma residents that in a similar case with much, much smaller volumes of water being injected that earthquakes continued long after injection ceased.

It is great that the Corporation Commission in Oklahoma has acted to shut down a number of injection wells.  Too bad some of this didn’t come before the billions of barrels of produced water were injected into the Arbuckle Formation.  We will see if this closing of a barn door caught the horse or not.  The problem may be that the pasture gates need closing too: the production of oil is not likely to shut down at the same rate as injection well capacity; produced water will probably be rerouted to wells that have not yet been shut down.  And while many wells probably pose no risk of inducing earthquakes, some probably do. So this might simply migrate the problem even farther afield.

One reality is that the duration of time needed to really see if this helps–probably on the order of years at this point–is almost certainly beyond the ability of government overseers to keep operators from applying political pressure to resume operations at some level. The only really good solution is some kind of processing of these waters so they can be released at the surface, but such purification is expensive and would require creation of infrastructure that doesn’t yet exist.

Well, of course, there is another solution: quit pumping oil. Don’t hold your breath wait for that one. And if you live in Oklahoma, you might just want to see how much that earthquake insurance is.  And find those webpages Californians have perused for years on how to make your house more quake-proof.

Italian tectonics, corrected

With the earthquake in Italy last night (our time) come some of the most ham-handed tectonic explanations ever (this is stuff that makes the Grumpy Geophysicist officially grumpy).  The official USGS explanation is:

The August 24, 2016 normal faulting earthquake is an expression of the east­west extensional tectonics that now dominate along the Apennine belt, primarily a response to the Tyrrhenian basin opening faster than the compression between the Eurasia and Africa plates.

This is totally off the wall and so of course has been repackaged by the BBC:

The Tyrrhenian Basin, or Sea, which lies to the west of Italy, between the mainland and Sardinia/Corsica, is slowly opening up.

Scientists say this is contributing to extension, or “pull-apart”, along the Apennines. This stress is compounded by movement in the east, in the Adriatic.

The result is a major fault system that runs the length of the mountain range with a series of smaller faults that fan off to the sides. The foundations of cities like Perugia and L’Aquila stand on top of it all.

OK, here’s the problem with this explanation.  If the Tyrrhenian Sea is opening up, something else must be closing (Earth is not expanding, sorry Carey fans).  The general picture, as has been put forward by Malinverno and Ryan or Wiki Royden, goes like this: the ocean floor to the east of Italy (the Adriatic) is sinking into the mantle.  The subduction zone (where the Adriatic goes under Italy) is basically moving to the east, dragging Italy along for the ride.  To compensate for this, new ocean floor is opening up on the west side of Italy (the Tyrrhenian Sea).  This was drawn by Malinerno and Ryan like this:

Apennines

East-west section from the Tyrrhenian Sea (at left, pattern 2) across Italy, with the Apennine accretionary prism (pattern 5) and on into the Adriatic (Ad, at right). Oldest section at top, youngest at the bottom. Apennines are mainly stuff scraped off the Adriatic plate. From Malinverno and Ryan, Tectonics, 1986.

If the Tyrrhenian Sea was opening faster than the convergence on the east side of Italy, then you should see compression (thrust faulting) all the way across, but you do not.  Instead, this earthquake and others in the area are extensional, north-south trending normal faults. However, these are paralleling thrust faults farther east, so some additional thought is needed.

Now given the thrust faults on the east edge of Italy, the normal faults of the Apennines seem strange, but in fact this happens in many places.  Here, the buildup of the mountains  has produced gravitational stresses in the Apennines that favor normal faulting.  The fact the sub-Adriatic lithosphere is driving the subduction zone to the east is what prevents the lithosphere from being in compression, so the relatively low potential energy in the Apennines can be expressed as normal faulting (in contrast, the very high compressional stresses from the Indian-Asian collision require very high mountains before you see any extensional faulting, and there the extensional faults are perpendicular to the thrust belt, not parallel as in Italy).

Look, it is probably a bit more complex that “it is caused by the Tyrrhenian Sea opening” but not so much that it excuses such a misleading explanation.

This is, by the ways, an example of a style of tectonics that probably produced the late Paleozoic Antler orogeny in the western U.S.  Similar stuff goes on behind “retreating” subduction zones in parts of the western Pacific, but lacking the continental material to reproduce Italy in quite the same way.

As they sow…

Well, the chickens have come home to roost in Oklahoma.  After spending years obfuscating and denying any role in creating earthquakes in the Sooner State, the oil and gas industry has burned through their political cover and now are being told to cut way back on injecting waste from oil and gas wells into deeper strata.

Had industry taken a more proactive stance some years ago and invested some time and money in determining which wells, under which circumstances, were causing earthquakes, they might not today be facing a downturn in production.  It is quite likely that many of the 411 wells told to cut back were not part of the problem, but figuring that out now is probably very difficult.  Meantime, the fluid already injected over the past several years is likely going to continue to produce earthquakes for some time to come.