Understanding earthquakes caused by hydraulic fracturing

Induced earthquakes is the process by which human activities trigger an earthquake. Hydraulic fracturing is a technique used by the petroleum industry to create small cracks in rocks using pressurized fluids, allowing hydrocarbon production. Understanding earthquakes due to hydraulic fracturing is important due to their influence as a geographic hazard, especially in areas that were previously seismically calm. A recent article in Geophysics Reviews presents the current state of knowledge regarding earthquake-induced hydraulic fracturing. Here, one of the authors provides an overview of earthquakes caused by hydraulic fracturing, and how they are measured and managed.

How does hydraulic fracturing cause earthquakes?

It has been known for decades that any injection of liquid into the Earth’s interior can cause earthquakes. However, hydraulic fracturing has only been recognized as a source of induced earthquakes only recently.

In the simplest conceptual model, fluids injected into a well below the surface of the earth must be connected in error through some permeable pathways. This allows the fluid pressure within the fault to increase during stimulation, and the crack opening hydraulically. While opening hydraulically, the low ‘clamping’ force on the crack makes it more prone to slip.

The left panel shows a map of the hydraulic fracturing pad, with four wells and sixteen stages. The right panel shows a depth-section of a well, with only two phases on the far right intersecting the rift. The inset shows the entry of hydrocarbons into the wellbore, via newly stimulated fractions. Credit: Ryan Schultz

How common, frequent and large are earthquakes caused by hydraulic fracturing?

Typically less than 1 percent of hydraulically fractured wells cause induced earthquakes, and less than 1 percent of hydraulically fractured wells typically cause earthquakes. This scarcity appears to be related to the unlikely scenario of having all the right geological conditions together in the same place: tectonic, geomechanical, and hydrological. In other words, pressurized “cracking” fluids may cause earthquakes only if the phase occurs to be connected to a sensitive fault.

Earthquakes caused by hydraulic fracturing occur frequently during hydraulic stimulation processes. The stimulation of all phases in a single well / pillow can take days or weeks, with only some (or none) of the phases causing earthquakes. If earthquakes do occur, the vast majority occur within this time frame. However, earthquakes can persist after hydraulic fracturing is complete – for periods of weeks or months. In some cases, the largest earthquakes occurred after the well was completed.

The largest fracturing earthquake of magnitude observed was 5.7, and the largest fracking earthquake of magnitude 5.7 occurred in the Sichuan Basin in China on December 16, 2018. Some North American plays have hosted events greater than 4.0 degrees as well (at For example, Duvernay, Montney, and Eagle Ford).

The left panel displays a map of earthquake situations caused by hydraulic fracturing, with the date and magnitude of the largest earthquake in each area. The right panel shows the number of hydraulic fracturing wells stimulated in each zone. Credit: Ryan Schultz

What are the main physical properties of earthquakes caused by hydraulic fracturing?

It appears that the physical properties of these earthquakes do not differ from their natural counterparts. Earthquakes caused by hydraulic fracturing exhibit the same characteristics that are often associated with natural earthquakes related to fluid flow: swarm-like sequences, temporal relationship to injection source, spatial proximity to fluid source, and linear relationship between volume injected and the number of induced earthquakes. Because of this similarity, this type of induced earthquake provides an opportunity to better understand natural earthquakes related to fluid flow.

How can scientists work effectively with industry to shape regulatory and mitigation efforts?

Transparency is the key to effective regulation and mitigation. In this regard, scientists can work to build trust relationships with the industry, specifically those that facilitate open sharing of data, and transparency is the key to effective regulation and mitigation. In this regard, scientists can work to build trust relationships with the industry, especially those that facilitate open data sharing.

Certainly, the large-scale publication of seismic data was an important part of creating more comprehensive earthquake catalogs, using various newly developed techniques. Examining indexes in many jurisdictions is beginning to show some evidence supporting when and where these types of earthquakes occurred.

This open post should also include geophysical, geological, and complementary engineering data. Many of the unresolved (and unrecognized) problems with induced earthquakes are interdisciplinary and will benefit from multiple perspectives.

What are some unresolved questions that require more research, data, or modeling?

Some of the important but not yet resolved questions relate to effective management – what kinds of conditions allow these earthquakes to occur and what kinds of operational changes can reduce their risk? Increasing knowledge of how to identify vulnerable areas before fracturing begins, along with confidence in management tools for when earthquakes strike can build significant trust with the general public. In one example, recent research efforts have focused on a better understanding of the precise catalytic mechanism responsible for reactivating sensitive errors; While the physical process that controls how defects begin to slip is still a matter of debate, the flow of fluids along portions of these defects appears to be an important factor.

– Ryan Schultz ([email protected]; 0000-0002-1796-9622), Stanford University, USA

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