When earthquakes are discussed on the news, reporters always state the location of the quake’s epicenter with such certainty. But in fact, there is a large margin of error associated with earthquake locations derived from then-available seismic monitoring systems.
As EnergyMakers Advisory Group’s Laura Capper writes in her recent article in Shale Play Water Management magazine, the true epicenter, or more precisely the hypocenter (the subsurface location where an earthquake initiates), could be off the reported value by several miles—up or down, and side to side.
A study of individual hypocenter locations assigned by the United States Geological Survey (USGS) for Texas earthquakes between 2000 and 2017 showed that the actual locations could be as far as +/- 4.1 miles away horizontally and +/- 10.2 miles vertically, from the reported locations. The same study on Oklahoma earthquakes showed a narrower, but still significant, margin of error (+/- 3.7 miles horizontally and +/- 6.3 miles vertically).
These errors are collectively caused by unknowns related to distance traveled, rate of energy transfer, unknown pathways, concurrent activities and the inherent margin of error with monitoring networks. Nonetheless, circumstantial data such as proximity to oilfield activities should be adequate to develop sound mitigation programs that minimize seismicity in many cases.
This phenomenon is discussed in more detail in EnergyMakers’ exclusive industry report, US Class II Subsurface Injection Wells: Injection and Seismicity Operational Risk Factors. This first-of-its-kind, comprehensive study of injection wells in major shale plays across the US is an essential reference guide for operators, leaseholders, service companies, midstream companies, private equity/venture capital firms, and law firms—basically, anyone who needs to understand the risks and complexities associated with the industry’s current reliance on Class II injection and disposal wells.
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