Well it may have something to do with it being under 5,000 feet or more of bedrock.
Okay, so just taken at your word, an average frack generates enough force to lift the entire bedrock if the layers of the frack are as little as 4. Which is a serious quake in itself.
At any higher number of layers though, the fracks fly far into the realm of man made earth quakes.
One cubic inch of stone weighs about a pound. (1.0833 #) With 60,000 # above each 1 square inch per level of frack, and the frack pressure at 15,000 P.S.I., one can clearly see that a 5 layer can cause a massive earthquake, creating 20% more force than that required to lift the entire thickness of bedrock above it.
Eventually on of these purposeful earthquakes will act as a trigger for a massive earthquake, obviously. Please don't try to argue that it will not happen. It is just a matter of time.
http://en.wikipedia.org/wiki/Hydraulic_fracturing
Seismicity
Hydraulic fracturing routinely produces
microseismic events much too small to be detected except by sensitive instruments. These microseismic events are often used to map the horizontal and vertical extent of the fracturing.[SUP]
[192][/SUP] However, as of late 2012, there have been three instances of hydraulic fracturing, through
induced seismicity, triggering quakes large enough to be felt by people: one each in the United States, Canada, and England.[SUP]
[9][/SUP][SUP]
[193][/SUP][SUP]
[194][/SUP]
A 2012 US Geological Survey study reported that a "remarkable" increase in the rate of M ≥ 3 earthquakes in the US midcontinent "is currently in progress", having started in 2001 and culminating in a 6-fold increase over 20th century levels in 2011. The overall increase was tied to earthquake increases in a few specific areas: the Raton Basin of southern Colorado (site of coalbed methane activity), and gas-producing areas in central and southern Oklahoma, and central Arkansas.[SUP]
[195][/SUP] While analysis suggested that the increase is "almost certainly man-made", the USGS noted: "USGS’s studies suggest that the actual hydraulic fracturing process is only very rarely the direct cause of felt earthquakes." The increased earthquakes were said to be most likely caused by increased injection of gas-well wastewater into disposal wells.[SUP]
[196][/SUP] The injection of waste water from oil and gas operations, including from hydraulic fracturing, into saltwater disposal wells may cause bigger low-magnitude
tremors, being registered up to 3.3 (M[SUB]w[/SUB]).[SUP]
[197][/SUP]
Induced seismicity from hydraulic fracturing
The
United States Geological Survey (USGS) has reported earthquakes induced by hydraulic fracturing and by disposal of hydraulic fracturing flowback into waste disposal wells in several locations. Bill Ellsworth, a geoscientist with the U.S. Geological Survey, has said, however: “We don’t see any connection between fracking and earthquakes of any concern to society.”[SUP]
[198][/SUP] The National Research Council (part of the National Academy of Sciences) has also observed that hydraulic fracturing, when used in shale gas recovery, does not pose a serious risk of causing earthquakes that can be felt.[SUP]
[199][/SUP] In 2013, Researchers from Columbia University and the University of Oklahoma demonstrated that in the midwestern United States, some areas with increased human-induced seismicity are susceptible to additional earthquakes triggered by the seismic waves from remote earthquakes. They recommended increased seismic monitoring near fluid injection sites to determine which areas are vulnerable to remote triggering and when injection activity should be ceased.[SUP]
[9][/SUP][SUP]
[200][/SUP]
A British Columbia Oil and Gas Commission investigation concluded that a series of 38 earthquakes (magnitudes ranging from 2.2 to 3.8 on the
Richter scale) occurring in the Horn River Basin area between 2009 and 2011 were caused by fluid injection during hydraulic fracturing in proximity to pre-existing faults. The tremors were small enough that only one of them was reported felt by people; there were no reports of injury or property damage.[SUP]
[201][/SUP]
A report in the UK concluded that hydraulic fracturing was the likely cause of two small tremors (magnitudes 2.3 and 1.4 on the
Richter scale) that occurred during hydraulic fracturing of shale.[SUP]
[202][/SUP][SUP]
[203][/SUP][SUP]
[204][/SUP]
Induced seismicity from water disposal wells
According to the USGS only a small fraction of roughly 40,000 waste fluid disposal wells for oil and gas operations in the United States have induced earthquakes that are large enough to be of concern to the public.[SUP]
[205][/SUP] Although the magnitudes of these quakes has been small, the USGS says that there is no guarantee that larger quakes will not occur.[SUP]
[206][/SUP] In addition, the frequency of the quakes has been increasing. In 2009, there were 50 earthquakes greater than magnitude 3.0 in the area spanning Alabama and Montana, and there were 87 quakes in 2010. In 2011 there were 134 earthquakes in the same area, a sixfold increase over 20th century levels.[SUP]
[207][/SUP] There are also concerns that quakes may damage underground gas, oil, and water lines and wells that were not designed to withstand earthquakes.[SUP]
[206][/SUP][SUP]
[208][/SUP]
Several earthquakes in 2011, including a
4.0 magnitude quake on New Year's Eve that hit
Youngstown, Ohio, are likely linked to a disposal of hydraulic fracturing wastewater,[SUP]
[9][/SUP] according to seismologists at
Columbia University.[SUP]
[209][/SUP] A similar series of small earthquakes occurred in 2012 in Texas. Earthquakes are not common occurrences in either area. Disposal and injection wells are regulated under the
Safe Drinking Water Act and UIC laws.[SUP]
[210][/SUP]