Minor earthquakes caused by human activities are known as induced seimicity.
In the past several years the central U.S. has undergone an overall increase in seismic events. The increased seismicity is, however, limited to a few areas. There is emerging evidence that some of the seismicity in these areas may be the result of the disposal of fluids (wastewater) related to oil and gas production deep underground in what are known as injection wells.
Induced seismicity can be reported incorrectly by the media and consequently the public and policy makers may have an incorrect or incomplete understanding of when, how, and why it occurs. Although some have focused on the process of hydraulic fracturing as a source of induced seismicity, evidence now indicates that it has a far lower potential to induce a seismic event than injection wells.
However, most injection wells do not pose a hazard for induced seismicity. Any direct link between injection wells and seismicity is highly complex and due to a variety of site-specific factors.
Following are some of the key observations from our on-going work:
Hydraulic fracturing can cause induced seismicity in rare instances but most of the induced seimicity in the U.S. is rather the likely result of deep underground disposal of wastewater.
Underground injection disposal wells are being linked by some scientists and state officials to minor earthquakes because injected wastewater is thought to lubricate faults and accelerate movement that can cause seismic events.
Underground injection remains in many regions the cheapest way to dispose of wastewater from oil and gas production and their use is likely to continue until recycling becomes a viable cost competitive alternative.
All breakouts at underground injection wells should be documented even if no environmental damage or harm occurs in order to better understand how and why they occur as well as inform future efforts to prevent them.
Due to broad geologic differences, a one-size-fits-all regulatory approach for managing and mitigating risks of induced seismicity is not appropriate – individual impacted states should develop science-based approaches for assessing and managing seismicity risk.