Here I am, sitting all alone on Christmas Day, very early, waiting for everybody to wake up. The earthquakes in ENA have always been a mystery, mainly because very little effort was put into studying them. Over the 30-40 years I've been looking at this, Eastern North America (ENA) was the poor cousin to California. Even in Canada, all the effort was on the giant Quebec City zone, and 30 years ago nobody looked at Toronto and such.
I managed to change that in Canada, at least. We were looking at new nuclear plants, and I couldn't live with this lack of interest. It allowed wild theories to come up and take over the media (yes, they were interested in this at one time when they had money). They were making up 'magnetic lineaments' and we had the famous 'Fault Under Pickering'. So, to my great satisfaction, I drank from the firehose of wasted company money and extracted a small percentage for seismic studies. When put outside for the academic community, this was a huge Christmas package.
I always partnered with notable academics and had no control over the output. The only influence I had was to direct the studies, since somebody had to do it. Dealing with academics is like herding cats. I didn't do any of these 'bespoke studies' as consultant reports, as was done with the Bruce Black Hole. For this type of study a famous consultant once told us "Tell me what you want to hear, and I'll see if I can live with it.".
I engineered the seismic monitoring to be unstoppable and totally open. Nobody can hide inconvenient earthquakes, and we did the best monitoring in ENA. With all the other studies, I was not so lucky, since we got poleaxed by the NDP election, and all such records were slated to be destroyed. I hid them in my desk and eventually could get them back into official records where they could be lost forever. A portion of the studies made it out to papers securely hidden behind the 'paywall' where the Bruce Thing could safely ignored them.
These were all the geophysics studies we made before we were shut down. They went into vast government archives, but we all know what happened to that under Harper. These studies told me everything I wanted to know about the mechanism of eastern earthquakes. All the scientists involved were muzzled by having no Harper money, and went into retirement. They are all running their farms.
These marvellous studies clearly showed the role of Precambrian megathrusts, and the massive earthquake activity around Toronto. The seismic monitoring showed the importance of fresh water seeping into the faults. We flew a magnetic study so detailed, it showed all the individual farmer transformers, and shipwrecks in Lake Ontario. Nobody has ever duplicated that anywhere.
In those old days, the company was divided into the "Force", and "Darkness". You can guess what side I was on - Design and Development. We lived on debt for new plants, and all that shut down. Everything went dark when when the 'Factory' took over -- all they were interested in were Soviet production numbers at any cost. You can see the result with the early destruction of Darlington, and no hope with the refurb.
I had one last hurray when we drilled the famous 'Fault under Pickering'. Just like California, somebody put great stock into a visible surface fault. We drilled it and found out it was only shallow and the main bedrock was undisturbed. I knew all this, but I needed the money. :)
My last days were under great depression, and I never did anything interesting, but I retired as soon as I could, and it took two years to heal. But then I felt great, and decided to review all this in order to clarify the great mystery of ENA earthquakes.
What finally woke me up was the injection of fracking wastes in Arkansas.
As I was saying, Arkansas was my 'Eureka" moment. We had observed that all the earthquakes in southern Ontario were under the lakes. Thus, all our historical seismicity was wrong. It was simple: No water, no earthquakes.
Fracking was going ballistic, and there was something like 2 million gallons of water per hole. All of this had to go some place, and that was deep underground. Arkansas had the advantage of being close to New Madrid, so it was partially covered by a intense seismic monitor array.
I noticed right away that they were getting earthquakes, and they were forming a pattern. The first earthquakes were lining up on a NW line, and then came a very long NE line. This was the exact same pattern as New Madrid! It was also the proper pattern for rock failure along the megathrusts, which have a very strong NE direction in horizontal stress. Yahoo!
There were some injection earthquakes in Ohio, but the lack of seismic monitoring meant no clear patterns.
There had been the M5.6 Oklahoma earthquake, but I was not following the pattern at that time. In retrospect, the reprocessed locations showed a very strong NW line.
Thus, the rock was acting as though it were in a giant rock testing machine. Using the testing machine analogy, all California earthquakes were acting as if there were a very weak, lubricated cut in the rock sample, and the machine turned on. As the rock was compressed, the fault slid.
On the other hand, the earthquakes in ENA were completely the opposite; they acted as though the rock sample was compressed and you were weakening the rock with acid. There was a major difference in the way the surrounding rock acted, and those California guys didn't have a clue.
Now, Arkansas and Ohio did not do their bit for Science since they chickened out at M4 and banned direct injection into the Precambrian. As well, we had the Virginia earthquake, which was very poorly covered by seismometers, but the later aftershocks showed a NE trend, and some association with a dammed lake.
Fortunately, we have other desperate states who are dying to prove my theories. If we are very lucky, they should go all the way to a New Madrid M7+, since they just can't give up all that money.
For the final bit, we digress into the whole story about the Precambrian under our feet. This a new story to most, since all the geological people ignore the deep structure, and when they plot earthquakes and faults, they stick to the shallows.
So, billions of years ago we had our Earth and oceans. The Galactic Seeders had come and gone, leaving a rich bacterial ecosystem. The amazing thing is that as the plates subducted with all the water, it cooked some rocks that were rich in silicates, and wanted to float like pond scum on the dark basalts. This scum became our continents, and North America was slowly built up by having huge island arc complexes, with their fresh silicates smashing up and pasting themselves like a big snowball rolling down the hill.
A billion years ago when this was in full swing, Toronto was under mountain ranges, up to the limits of rock strength. They were built up by sliding on huge megathrusts that extended in straight lines, NE to SW. You can see this type of linear range in the Rockies. The pressure eased off and these mountains slid back down. Eventually, erosion carved the landscape into something you see up in Cottage Country.
So, for a few hundred million years we had this Precambrian surface which was not flat, as some people would have you believe. Then the plates shifted over a cold spot and the whole thing sank beneath the sea. Although silicates are less dense than the ocean basalts, they will sink if cold enough. They just sank enough for shallow seas, which built up sediments and sank more.
This is all the limestone and such, full of little critters. The Appalachian collision shoved up more sediments, and everybody forgot about the Precambrian, which held us up. :)
The amazing thing about the Precambrian is that it takes all the strain of the plate moving about. There have been several collisions and separations, and that rock keeps us alive. Of course, we humans are only a blip on the geological time scale, but we should respect our elders. The last Atlantic collision had all the continents together and it was a great time for the Earth's heat flow to cook out all that buried carbon dioxide and water. The result was the dinosaurs and a very hot world. The Precambrian was stretched to its limit.
All that heat, and then the continents separated to form the Atlantic. NA slid to a colder spot, which is like pressing a thumb on a beachball, and it settled into a dimple. It uniformly compressed the Precambrian on all sides, yet only a strong NE-SW trending horizontal stress remains. What could have happened? Does anybody in the USGS think of this?
It's all in the grain of ENA, which is strong down the spine of the megathrusts, and weak in the NW direction. In order for the stress to be so strongly polarized, a lot of displacement had to happen in the NW direction. This crunched up the Paleozoic over the megathrusts, and caused things such as the gigantic Paleo-collapse up at the Bruce Black Hole, which has conveniently been left out in the reports.
Now we are left with the strong NE horizontal stress, which kills us when we have a water seep such as New Madrid.
So now we know we have these huge megathrusts forming bands of good and bad rock. Good rock is what we drilled with our deep holes at Darlington -- high stress, extremely tight. The rock came out in 10 foot solid sections that you could use as baseball bats. No fractures, no water.
Bad rock is right at the faults, and it is fractured all the way up. It is what was chosen for the Bruce Black Hole. The fractures go all the way down to the Moho. Recent studies have show there are oceans of billion year old water in those fractures, along with bacteria, probably from the very beginning of life. A whole ecosystem, probably as alien to us as anything on Mars.
All this water lives in perfect harmony with the rock, since it's been there long enough. Once in a while there have been huge earthquakes to accommodate the shifting of the plates, but the whole thing is in chemical equilibrium.
The one thing that disturbs this happiness is a seep of fresh water. This water is aggressive to the strong points of quartz that are holding the little NW stress that remains. Over the millennia, natural seeps have caused local earthquake hotspots along the megathrusts. We are mainly aware of New Madrid, because it happened in historic times, and it still has aftershocks. There could be many other spots.
Seeps happen when lots of surface water accumulates. Lakes Erie and Ontario have them, and there are some in Quebec, wherever that is. :) New Madrid is still sucking in the water.
Natural seeps may be very well and good, but what if you want to create a New New Madrid in a hurry? You inject surface water directly into the Precambrian and upset all that balance. The fascinating thing about earthquakes is their chaotic nature. And you never know the initial conditions. Yeah, that makes them impossible to predict on the fine scale required for humans. You can predict that if you inject you will get earthquakes, but you'll never know how big and how soon.
Initial conditions depend on earthquakes past, and so a minor seep such as Virginia can almost instantly produce an M6 from a dammed lake. The M5.6 Oklahoma happened quickly, as well. That is to say, the fault was all primed up and Ready to Rumble.
On the other hand, you can have something as slow as the main OK mechanism. Massive injection of billions of barrels of water has only brought things to M4.8 so far. That means the area may be generally destressed. Earthquakes are also fascinating in that they are self-similar (fractal) between two limits - the very large, and the very small (grain size). So, if you looked at a picture of fractured rock, you wouldn't be able to tell the scale, unless there was a scale, like a person standing in front of it. Some satellite photos look like they were taken with a magnifying glass.
This self-similarity produces the classic straight log-log plot between Magnitude and frequency of occurrence. So, there are a lot of little earthquakes for one of the next bigger size. The slope of this curve is related to fractal roughness. OK has a high fractal roughness, and California is probably very low.
OK has developed a full mechanism, just like New Madrid. We just don't know how long it will take to get to M7's. At any time we could have a 7 or it may take decades. The same is true for the natural seeps, such as Toronto. Who knows? It would be prudent for all these areas to have a good earthquake plan, but they just go on and party. Ce la vie!