A reader writes:
Friedman's optimistic reading is baseless. First of all, the small quakes we're talking about here are mostly around magnitude-2 events (see Oklahoma Geophysical Survey's catalog). The amount of energy released by an earthquake jumps by a factor of ~32 for each successive magnitude. In order to release the same amount of energy as a magnitude-7 earthquake, you'd need about 30 million magnitude-2 earthquakes. So 1047 small earthquakes make hardly a dent in terms of energy release, and an increased frequency of small earthquakes is not something we can tout as a feature.
Energy gets stored up around a fault because the blocks on either side want to move in different directions, but are prevented from doing so by friction on the fault surface. The force due to friction along any surface is proportional to the force applied perpendicular to that surface (called the "normal force"). Imagine pressing your hands together lightly — it's quite easy to rub your hands, right? If you press your hands together firmly, you have raised the normal force and thus increased the force of friction — it's now more difficult to rub your hands together.
Fracking centers around the injection of highly pressurized fluids into rock. These fluids don't like being compressed, and they want to expand. In addition to propagating fractures in rock and increasing access to fossil fuels, the pressurized fluid reduces normal stresses along a fracture surface by "pushing out" against both sides of the fault. In turn, the friction along a fault surfaces drops, promoting fault rupture. There's no way of knowing whether a fault with a lot of stored energy vs. little stored energy will be affected. That's why the increased frequency of small earthquakes is worrisome – magnitude aside, it indicates that the injection of pressurized fluids is actually enough to promote fault rupture. If you're going to talk about net benefits vs. risks, I think the risks outweigh the benefit (?) of releasing an absurdly small amount of energy.
I'll note that I'm a geochemist, not a seismologist, but you know who had a job in Harvard's seismology group in the '80s? Jonathan Franzen. He worked on some highly-cited earthquake catalogs while writing (I believe) his first novel – his total citation count is higher than most Earth science faculty.
Another reader:
Regarding David Friedman’s optimistic take on fracking, the idea of pumping water into faults to relieve the built up force by triggering lots of small ones is an old idea that has been studied and considered by geologists who specialize in seismology. I think it best these questions be answered by scientists, not economists. This is from the website of the USGS:
Q: Can you prevent large earthquakes by making lots of small ones, or by "lubricating" the fault with water or another material?
A: Seismologists have observed that for every magnitude 6 earthquake there are 10 of magnitude 5, 100 of magnitude 4, 1,000 of magnitude 3, and so forth as the events get smaller and smaller. This sounds like a lot of small earthquakes, but there are never enough small ones to eliminate the occasional large event. It would take 32 magnitude 5's, 1000 magnitude 4's, 32,000 magnitude 3's to equal the energy of one magnitude 6 event. So, even though we always record many more small events than large ones, there are never enough to eliminate the need for the occasional large earthquake.
As for "lubricating" faults with water or some other substance, injecting high pressure fluids deep into the ground is known to be able to trigger earthquakes to occur sooner than would have been the case without the injection. However this would be a dangerous pursuit in any populated area, as one might trigger a damaging earthquake.
The Dish 