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The stronger the spatial clustering, the larger the influence of small earthquakes on stress changes at the location of a future event as well as earthquake triggering. If earthquake magnitudes follow the Gutenberg-Richter law with b>D/2, small earthquakes collectively dominate stress transfer and earthquake triggering, because their greater frequency overcomes their smaller individual triggering potential.
Because large earthquakes modify stress over a much larger area than smaller ones, and because computing Coulomb stress changes requires a good model of slip distribution available only for large earthquakes, most studies have neglected the influence of “small” earthquakes.
• A triggered earthquakes size is independent of the magnitude of the triggering event (“mainshock”) as suggested by [Helmstetter, 2003]. This implies that the crust is everywhere close to failure, such that any small earthquake, triggered by a previous small one, can grow into an event much larger than its trigger
emphasis mine
These results imply that a small earthquake can trigger a much larger earthquake. It thus validates our hypothesis that the size of a triggered earthquake is not determined by the size of the trigger, but that any small earthquake can grow into a much larger one [Kagan, 1991b; Helmstetter, 2003; Felzer et al., 2004]. The magnitude of the triggering earthquake controls only the number of triggered quakes
emphasis mine
Although large earthquakes are much more important than smaller ones for energy release, small quakes have collectively the same influence as large ones for stress changes between earthquakes, due to seismic spatial clustering.
I didn't realize this was only about hydraulic fracturing, sorry.
I’m not the one who put “only” in capitals
LITTLE ROCK — The Arkansas Geological Survey says it is stepping up its monitoring of seismic activity in central Arkansas after dozens of small earthquakes in the region.
Six minor quakes were recorded Friday near Quitman, the latest of more than 50 temblors in October. The Friday tremors began with a 2.0-magnitude quake around 7:45 a.m. and peaked with a 2.5 quake later in the morning.
The shaking follows more than 1,000 earthquakes centered between Guy and Greenbrier from September 2010 to July of this year, when the Arkansas Oil and Gas Commission ordered four gas disposal wells shut down and voted to create a large moratorium area in which no future disposal wells could be drilled.
Geologists said the activity - which involves injecting pressurized liquid into the ground - was likely contributing to the shaking.
The quakes between Guy and Greenbrier tailed off significantly in August, but more quakes began occurring in October closer to Quitman. It sits about 10 miles northeast of Guy.
That distance is potentially concerning, warned Scott Ausbrooks, geohazards supervisor for the Arkansas Geological Survey. The Quitman quakes are occurring along the same line as the Guy-Greenbrier ones, but there's a miles-long gap between Guy and Quitman in which no quakes have been recorded.
Originally posted by JustMike
reply to post by MamaJ
Hi MamaJ,
many thank for posting that information and link.
Near the end of the part of the article you posted, where it says that there is a stretch of some miles between the two quake areas that has not had any quakes.
What I thought when I read that was: "Yeah. That stretch has not had any quakes. Yet."
Sometimes I wonder if Ausbrooks is doing his best to drop hints. He is a bit limited in what he can say; he certainly can't make statements as openly as he might like, I feel. I think that like Robin and doubtless many of us, he is concerned that the fault line in that area may not only be longer than first thought, but could be capable of producing larger seismic events than originally believed.
I also wonder how many other less-known or unknown faults there may be throughout that entire region of the US, faults that have been basically quiescent because over long periods of time, they had settled down and pretty much balanced their energies, if I can put it that way. But with the very unnatural rates of change being forced on and into the earth in that region (as in many others), what was so long in balance may rapidly be slipping into a new state of flux and the whole energy-balancing process will have to start up again.
Mike
ATLANTA — Researchers in a nationwide study of earthquakes will soon place instruments beneath the Georgia red clay and in other eastern states as they seek to learn more about what causes them and where they might strike.
Woodward says he's excited about the potential for discoveries in Georgia and states in the Appalachian mountains.
He's also hoping the broader USArray project will improve understanding of a region in southeast Missouri, where a series of ferocious earthquakes struck in 1811 and 1812 in an area known as the New Madrid fault. There's been debate among scientists over the potential for another devastating strike there, which could threaten modern skyscrapers, historic buildings and millions of people in cities such as Memphis and St. Louis.
"The question now is, is that area reloading for another one?," Woodward said. "Scientifically it's quite an interesting debate," he said. "I'm certainly hopeful that all the instruments may shed some light on it."