A magnitude 5.8 earthquake occurred on September 3, 2016, just northwest of Pawnee in Oklahoma. The earthquake caused moderate to severe damage to buildings located nearby. This was the biggest earthquake ever recorded in Oklahoma.
This earthquake was a result of the rapid increase in seismic activity in the central United States since 2009, which is associated with an increase in underground wastewater disposal from oil and gas operators. The Pawnee earthquake and other incidents in the region raised public concern and led government agencies to shut down wastewater injection wells and create new regulations regarding wastewater injecting.
While earthquakes caused by humans have been known for over a century, the increasing number of reports worldwide has attracted much attention from scientists, politicians, and social activists. These earthquakes can be attributed to industrial activities like mining, the construction of dams, and injections of liquids, including wastewater, carbon dioxide, and oil.
The number of earthquakes caused by humans is expected to increase in the coming years. The artificial causes of some of the most destructive and large earthquakes in the last few years include the 2008 Wenchuan earthquake and the 2015 Nepal earthquake.
Most of the time, industrial activities don’t cause earthquakes. This becomes a problem when industrial activities are near active faults. Even small stresses caused by human-made activities underground can cause faults to destabilize, causing earthquakes.
Fluid injections that are not correct
Fluid injections can cause earthquakes to occur days, months, or even years later.
Drilling site near Basel in Switzerland. Keystone/Georgios Kefalas/Giorgos Michas, Author provided
In the figure above, as the fluid pressure in the well Basel 1 increased during injection (purple line), the rate of induced seismicity also increased (blueish bars). The bottom figure shows the average square of the distances of the induced seismicity from the well. This illustrates the complex spread of seismicity over time. The biggest earthquakes (shown with stars and a magnitude greater than 3) occurred after injection.
These problems, as well as the lack of information about the exact stress and faulting situations below ground, make it difficult to predict or manage earthquakes.
The public is more concerned about artificial earthquakes in Europe than it is in the United States. In the well-known case of Basel in Switzerland, which took place in 2006, approximately 11,500 cubic meters of water at high pressure were injected into a 5 km deep well to enable the extraction of geothermal power. During the injection stage, over 10,000 earthquakes occurred, some of which were strong enough to be felt in Basel. This caused public outrage and concern, which led to the cancellation of the project. More than $9 million was spent on damage claims.
Nature’s Work
In Southern Europe, where there is a greater risk of naturally occurring earthquakes, the public’s tolerance for induced earthquakes caused by industrial activities has been reduced even further. Based on the closeness of the earthquake epicenters to an oilfield, the deadly 2012 Emilia earthquake sequence (Italy) became the subject of a sustained public and political debate.
While no link was established between oil extraction and regional seismicity, it wasn’t ruled out. Some studies have concluded that earthquakes are an event.
Castor, a gas storage facility located in the Gulf of Valencia (Spain), is another recent example. In 2014, the Spanish government terminated the US$2 billion project following an explosion of seismic activity in the region immediately after the start of gas injection operations and public concern.
European Seismic Risk Map. Georgios Michas, the Author, provided
The European Seismic Hazard Map above shows the seismically dangerous areas in Europe, measured by the maximum ground acceleration that can be expected during a quake. There is a 10% chance of reaching or exceeding this level in 50 years. The green color indicates a relatively low hazard value of PGA less than 0.1g. Yellow to orange indicate a moderate hazard of 0.1-to-2.25g. And red shows hazard levels of PGA greater than 0.25.
The challenges that lie ahead
These cases highlight some of the challenges that artificial seismic events will face. In seismically active areas, it can be hard or impossible to differentiate between human-induced and natural earthquakes. In other cases, the risks associated with industrial activity are greatly underestimated. These problems present new challenges to risk mitigation and economic development, particularly in seismically active regions like Southern Europe.
Map of 50-year seismicity for Greece, including large and moderate earthquakes. Also shows the blocks in Greece that are licensed or have been for oil and gas exploration. Giorgos Michas, the Author, provided
The image shows that drilling and extraction activities may be conducted near or in seismically active areas, increasing the risks of activating faults or accelerating earthquakes which would normally occur sometime in the future.
Regulations are needed to reduce these hazards. These regulations must include hazard modeling and assessment both before and during any industrial activity that could disrupt regional stress fields. In North America, such regulations have been issued, including in California, Oklahoma, and Texas, as well as Canada and the United States. The EU has yet to issue any rules in Europe. However, guidelines have been issued by some countries who have experienced earthquakes. These include the Netherlands, Switzerland and the UK.