Human Induced Earthquake Increased Dramatically

The number of earthquakes has changed over the past several years within central and eastern United States. Nearly 450 earthquakes scale 3.0 and higher happened in the four years from 2010-2013, an average of over 100 each year, compared with an average rate of 20 earthquakes each year noticed from 1970-2000. 

Seismicity of the coterminous United States and surrounding areas, 2009–2012. Black spots represent earthquakes with a magnitude ≥ 3.0 are shown; bigger spots represent events with a magnitude ≥ 4.0. Background colors show earthquake threat levels from the US National Seismic Hazard Map (NSHM).

Credit:USGS

This changed magnitude in earthquakes reminds two important questions: Are they natural, or human induced earthquake? In addition, what should be done in the future as we deal with the causes and effects of these actions to decrease associated risks? USGS researchers have been examining the changes in earthquakes as well as the likely causes, and they have some answers.

USGS researchers have discovered that at some locations the increased in seismicity correlates with the hypodermic injection of wastewater in deep disposal wells. Much of this wastewater is a by-product of oil and gas production and is regularly disposed by hypodermic injection into wells designed for this objective.

Review Content on Injection-Induced Earthquakes

U.S. Geological Study geophysicist Bill Ellsworth examined the issue of injection-induced quakes in a July 2013 study released in the journal science. This content focused on the hypodermic injection of liquids into deep wells as a common practice for disposal of wastewater, and talks about latest actions and key scientific difficulties for analyzing this threat and continuing to move ahead to decrease associated threats.

What is Induced Seismicity?

Although it may seem like science fiction, human induced earthquakes have been a reality for decades. It has lengthy been recognized that earthquakes can be induced by impoundment of water in reservoirs, surface and subterranean exploration, drawback of liquids and gas from the subsurface, and hypodermic injection of liquids into subterranean structures.

Cumulative count of earthquakes with a scale ≥ 3.0 in the central and eastern United States, 1970-2013. The dashed line matches to the long-term rate of 20.2 earthquakes each year, with a rise in the rate of earthquake events starting around 2009.

What is Wastewater Disposal?

Water that is high sodium or contaminated by substances needs to be discarded in a manner that stops it from damaging freshwater resources. Often, it is most economical to geologically sequester such wastewater by injecting it underground, deep below any aquifers that offer drinking water.

Wastewater can result from various processes, including those relevant to energy production. For example, water is usually present in stone structures containing oil and gas and therefore will be co-produced during oil and gas manufacturing. Wastewater can also occur as flow back from hydraulic breaking works that involve injecting water under high-pressure into a rock formation to activate moving oil and gas to a well for manufacturing.

Wastewater injection increase the underground pore pressure, which may, in effect, lubricate nearby mistakes by weakening them. If the pore pressure increases enough, the damaged fault will slip, launching stored tectonic pressure 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 circumstances underground are correct.

Although the disposal procedure has the prospective to induce earthquakes, not every wastewater disposal well produces earthquakes. In fact, few of the more than 30,000 water wells developed for these objective cause earthquakes.

Hydraulic Fracturing

Many concerns have been raised about whether hydraulic breaking — commonly known as “fracking”— is responsible for the latest increased of earthquakes. USGS’s research suggests the hydraulic fracturing procedure is only rarely the direct cause of sensed earthquakes. While hydraulic fracturing works by making thousands of little “micro earthquakes,” they are, with just a few exclusions, too little to be felt; none have been huge enough to cause structural damage. As mentioned previously, underground disposal of wastewater co-produced with oil and gas, allowed by hydraulic fracturing works, has been linked to induced earthquakes.

Unknowns and Questions Moving Forward

House damage in Central Oklahoma from the scale 5.6 earthquake on Nov. 6, 2011. Research performed by USGS geophysicist Elizabeth Cochran and her university-based colleagues shows that this earthquake was induced by injection into deep disposal water wells in the Wilzetta North field.

Photo Credit: Brian Sherrod, USGS

USGS researchers are dedicated to gaining a better knowing of the geological circumstances and industrial methods associated with induced earthquakes, and to finding out how seismic threat can be managed.

One risk-management approach outlined in Ellsworth’s article involves setting seismic action limits for safe operation. Under this “traffic light” system, if seismic action surpasses predetermined limits, decrease in injection would be made. If seismicity continues or gets worse, operations could be revoked.

The current regulating structure for wastewater disposal wells was developed to protect drinking water from pollution and does not deal with earthquake safety. Ellsworth mentioned that one outcome is that both the quantity and timeliness of details on injection volumes and pressures reported to the regulating organizations is far from ideal for managing earthquake threat from injection activity.

Thus, improvements in the collection and confirming of injection data to regulating organizations would offer much-needed details on circumstances potentially associated with induced seismicity. In particular, said Ellsworth, daily reporting of injection volumes, peak and average injection pressures would be a step in the right direction, as would measurement of the preinjection water pressure and tectonic pressure.

Importance of Understanding Risks and Hazards

There is a growing interest in knowing the threats associated with injection-induced earthquakes, especially in the areas of the country where, before the modern boom in oil and gas manufacturing, earthquakes huge enough to be sensed were rare.

For example, wastewater disposal be relevant to the magnitude-5.6 earthquake that hit nonurban central Oklahoma in 2011 leading to a few injuries and harm to more than a dozen homes. Damage from an earthquake of this scale would be much worse if it were to happen in a more largely populated area.

The USGS and Oklahoma Geological Study (OGS) have performed research quantifying the changes in earthquake rate in the Oklahoma Town area, analyzing and evaluating possible links between these earthquakes and wastewater disposal relevant to oil and gas manufacturing activities in the area. In a joint declaration {http://www.usgs.gov/newsroom/article.asp?ID=3710}, USGS and OGS recognized wastewater injection as a contributing aspect for this year's earthquake swarm and damaging scale 5.6 events.

Studies show one to three scale 3.0 earthquakes or bigger happened each year from 1975 to 2008, while the common grew to around 40 earthquakes each year from 2009 to mid-2013.

“We’ve mathematically examined the latest earthquake amount changes and discovered that they do not seem to be due to typical, unique variations in natural seismicity rates,” said Bill Leith, USGS seismologist. “These studies need significant changes in both the background rate of events and earthquake leading to properties needed to have happened to be consistent with the noticed increased in seismicity. This is in contrast to what is typically discovered when modeling natural earthquake swarms.”

The Oklahoma analysis shows that a contributing reason in the increased in earthquakes incident may be from injection-induced seismicity from activities such as wastewater disposal. The OGS has examined the behavior of the seismicity through the state analyzing the model fault orientations and pressures within the area of increased seismicity, particularly the uncommon behavior of the swarm just east of Oklahoma City.

Oil field waste comes by tanker truck at a wastewater disposal facility near Platteville, Colorado. After removal of solids and oil, the wastewater is injected into a deep well for permanent storage underground. This disposal procedure has the prospective to induced earthquakes, but few wastewater disposal wells produce earthquakes. No earthquakes are associated with injection at the site in this picture. Photo taken on Jan. 15, 2013.

Photo Credit: William Ellsworth, USGS

Start with Science

As the use of injection for disposal of wastewater increases, the significance of knowing the associated threats also develops. To meet these difficulties, the USGS hopes to increase research initiatives to understand the causes and effects of injection-induced