Dealing with man-made earthquakes

disposal takes place near faults, and underground conditions are right, earthquakes may be more likely to occur, Ellsworth’s research showed. Specifically, an earthquake can be triggered by the well-understood mechanism of raising the water pressure inside a fault. If the pressure increases enough, the fault may fail, releasing stored tectonic stress in the form of an earthquake.

Even faults that have not moved in millions of years can be made to slip and cause an earthquake if conditions underground are right.

While the disposal process has the potential to trigger earthquakes, not every wastewater disposal well produces earthquakes. In fact, very few of the more than 30,000 wells designed for this purpose appear to cause earthquakes.

Hydraulic fracturing
Many questions have been raised about whether hydraulic fracturing, commonly known as “fracking,” is responsible for the recent increase of earthquakes. USGS’s studies suggest that the actual hydraulic fracturing process is only very rarely the direct cause of felt earthquakes. While hydraulic fracturing works by making thousands of extremely small “microearthquakes,” they are rarely felt and are too small to cause structural damage. As noted previously, wastewater associated with hydraulic fracturing has been linked to some, but not all, of the induced earthquakes.

Unknowns and questions moving forward
USGS says its scientists are dedicated to gaining a better understanding of the geological conditions and industrial practices associated with induced earthquakes, and to determining how seismic risk can be managed.

One risk-management approach highlighted in Ellsworth’s article involves the setting of seismic activity thresholds for safe operation. Under this “traffic-light” system, if seismic activity exceeds preset thresholds, reductions in injection would be made. If seismicity continued or escalated, operations could be suspended.

The current regulatory framework for wastewater disposal wells was designed to protect drinking water sources from contamination and does not address earthquake safety. Ellsworth noted that one consequence is that both the quantity and timeliness of information on injection volumes and pressures reported to the regulatory agencies is far from ideal for managing earthquake risk from injection activities.

Thus, improvements in the collection and reporting of injection data to regulatory agencies would provide much-needed information on conditions potentially associated with induced seismicity. In particular, said Ellsworth, daily reporting of injection volumes, and peak and average injection pressures would be a step in the right direction, as would measurement of the pre-injection water pressure and tectonic stress.

Importance of understanding hazards and risks
There is a growing interest in understanding the risks associated with injection-induced earthquakes, especially in the areas of the country where damaging earthquakes are rare.

For example, wastewater disposal appears to have induced the magnitude-5.6 earthquake that struck rural central Oklahoma in 2011, leading to a few injuries and damage to more than a dozen homes.

Damage from an earthquake of this magnitude would be even worse if it were to happen in a more densely populated area.

The USGS notes that as the use of injection for disposal of wastewater increases, the importance of knowing the associated risks also grows. To meet these challenges, the USGS says it hopes to increase research efforts to understand the causes and effects of injection-induced earthquakes.

— Read more in William L. Ellsworth, “Injection-Induced Earthquakes,” Science 341, no. 6142 (12 July 2013) (DOI: 10.1126/science.1225942); see also David J. Hayes, “Is the Recent Increase in Felt Earthquakes in the Central US Natural or Manmade?” (U.S. Department of the Interior, 11 April 2012)