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Most of us think of earthquakes as a purely random, almost unpredictable, natural event. Mankind's activities can rarely (if ever) cause an earthquake, but there some activities by mankind that can trigger (induce) an earthquake in a region where one is is prone.
If you want to know what is the risk of an earthquake anywhere in the United States, regardless of source, just see this federal earthquake risk map!
However, after the map referenced above was created, the USGS has added induced earthquakes, those presumed to have been initiated by manmade activities. This is shown in the map below. However, we would urge caurtion in interpreting this map. There are a lot of conditions associated with the map, so look at this page fopr the detailed information, which includes citations about the USGS statements about impacts from injection wells and fracking.
The USGS says:
To produce natural gas from shale formations, it is necessary to increase the interconnectedness of the pore space (permeability) of the shale so that the gas can flow through the rock mass and be extracted through production wells. This is usually done by hydraulic fracturing ("fracking"). Fracking causes extremely small earthquakes, but they are almost always too small to be a safety concern. In addition to natural gas, fracking fluids and salt water trapped in the same formation as the gas are returned to the surface. These wastewaters are frequently disposed of by injection into deep wells. The injection of wastewater and salt water into the subsurface can cause earthquakes that are large enough to be felt and may cause damage.
Translated into English, they are saying that Fracking itself does not induce earthquakes, but the injection of wastewaters afterwards can. The key word is "induce" neither fracking nor wastewater injection casue earthquakes. Earthquakes are created the existing stress in the Earth's crust due to pressure along fault lines, techtonic plate interactions and teh sublimation of crust. The theory is that the injection of the water increases the slippage and makes it easier for eartyhquakes to happen where the pressures already exist.
Of course, a rather obvious question that no one appears to be asking is, since earthquakes ordinarily occur when the pressure builds up to levels that the faultlines can no longer hold, does this deep water in jection increase or decrease the likelhood of a serious, large damaging earthquake? Or, is it possible, that a series of minor eatherquakes releases the pressure in a series of small, less damaging earthquakes, making a larger eathquake less likely?.
This page was updated on 4-Apr-2016