Detecting smaller earthquakes can improve predictions of larger tremors

Using machine learning techniques on ten years of seismic data from Oklahoma and Kansas, researchers have identified faults that can generate large earthquakes.

By Laura Vattaroso, Simpson Strong Tie Fellow (@labtalk_laura)

Citation: Fattaruso, L., 2022, Detection of Smaller Earthquakes Can Improve Prediction of Large Earthquakes, Temblor, http://doi.org/10.32858/temblor.282

Oil pump in Hanna, Oklahoma. Credit: Meganjin, CC BY 2.0, via Wikimedia Commons.

Advances in machine learning have helped seismologists find ever smaller earthquakes. By re-locating exactly where these small earthquakes come from, researchers are now able to see previously hidden faults that can lead to larger, more damaging earthquakes. A recent study in The Seismic Record shows how researchers using these techniques were able to identify 80% of the faults that hosted earthquakes of magnitude 4.0 or greater in Oklahoma and Kansas from 2010 to 2019.

“If we can find these small earthquakes, could that pre-illuminate fault structures that later hosted larger earthquakes?” asks Youngsoo Park, lead author of the study, which he worked on as a doctoral student at Stanford University. “If that is the case, perhaps the larger earthquakes will not be as complete a surprise as they used to be.”

Park and co-authors evaluated data from 420 seismic stations in Oklahoma and Kansas. Using new computational methods that automatically detect earthquakes in seismic data, they found many more quakes than previously observed. For example, in one region, they identified and reported 13,231 earthquakes from 2010 to 2016, a significant increase from previous research. Studies conducted in 2017 and 2019 found only 880 and 3,141 earthquakes during the same time period.

The careful detection of smaller and smaller earthquakes has enabled researchers to find hidden structures in Oklahoma and Kansas. The same area is shown in Oklahoma with data analyzed in 2017 (left), 2019 (middle), and 2022 (right) showing how advances in earthquake detection have led to better definition of fault zones. (Adapted from Park et al., 2022)

The increasing number of earthquakes detected has allowed the researchers to see connected fault structures where data previously was scattered and discrete. Larger faults can accommodate larger earthquakes and new connections have shed light on many of these potential regional hazards.

“The main message here is that monitoring small earthquakes is important,” says Park.

According to Park, almost all observed earthquakes in the area occurred on previously unmapped faults. Of the 60 faults that hosted magnitude 4.0 earthquakes over the past decade, 48 faults were able to be imaged as small earthquakes that occurred before the large earthquake.

“[The study] It is an innovative way to combine machine learning with what we know about the relationships between fault magnitude and earthquake magnitude. You can’t intend a magnitude 6.0 earthquake on a one-kilometer-long fault, explains Folarin Kolawole, a structural geologist at the Lamont-Doherty Earth Observatory in Columbia, who was not involved in the study.

Monitor small earthquakes for signs of larger ones

Oklahoma and Kansas experienced “unprecedented seismic activity” due to hydrofracking and related sewage injection, according to the study authors. Hydrofracking is used to take advantage of unconventional petroleum resources – natural gas trapped in the small pore spaces of oil shale. Extracting the gas requires large amounts of water mixed with sand and chemicals, which are pumped deep below the surface to force open pore space. After the extraction process, operators are left with waste water, which is stored in the now empty pore space. Injecting large amounts of wastewater into deep wells stresses pre-existing, unmapped faults, sometimes causing earthquakes.

In 2011, Oklahoma experienced one such event, a 5.7-magnitude earthquake, the strongest earthquake ever recorded in the state up to that point, until it was hit by a 5.8-magnitude earthquake in 2016. Both earthquakes led to lawsuits against petroleum. that were operating in the area at the time.

To avoid causing more of these large earthquakes, wastewater injection processes used a “stop” system based on the rate of detected earthquakes. When the number of earthquakes hitting in a certain period of time starts to increase, the stop light changes from green to yellow or red. Operators will then throttle the wastewater injection. Park suggests that, based on his research, industry and regulators should consider the magnitude of illuminated faults as well as the amounts of observed earthquakes when analyzing seismic hazards.

The method could also have the potential to better predict earthquakes in other regions, but it depends on having a lot of data. This is what made Oklahoma and Kansas ideal settings for testing them – the large number of smaller induced earthquakes, as well as the large number of monitoring stations. In most places, Kolawole explains, it will take much longer to collect data on many earthquakes. “If you don’t have enough events, you don’t have enough data to work with. [This method] It could be applied elsewhere, but the use of devices will be critical.”

Laura Vattaroso is a classmate of Temblor’s Strong Tie Simpson. They have a Ph.D. candidate at U Mass Amherst, where they study how rocks fracture to better understand seismic processes (laurafattaruso.com). Simpson Strong Tie sponsors a Science Writing Fellow to cover important earthquake news around the world.

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