University of Wisconsin-Madison engineers have increased understanding of how one earthquake’s seismic magnitude may influence another’s.
The study, led by Jesse Hampton, an assistant professor of civil and environmental engineering at UW-Madison, and then-postdoctoral researcher Qiquan Xiong, published in the journal Nature Communications in April 2023.
The research demonstrates the existence of multiple earthquakes with similar seismic magnitudes, clustered in time and across various distances ranging from laboratory scales to spans of hundreds of miles. While previous studies have reported correlations in the magnitudes of sequential earthquakes, those findings have been questioned due to concerns about incomplete earthquake catalogs.
To conduct their study, Hampton and Xiong analyzed data from the Southern California Catalog, which encompasses information on more than 400,000 earthquakes recorded between 1985 and 2001. They also examined catalogs containing data on induced seismic events from hydraulic fracturing sites in Harrison County, Ohio, as well as wastewater disposal cases near Guthrie in central Oklahoma and in the Delaware Basin in west Texas.
Assistant professor Jesse Hampton, left, and postdoctoral researcher Qiquan Xiong, looked into old catalogs with decades of data to research how earthquake magnitudes cluster. Their findings show that the strength of one seismic event may influence subsequent ones. Submitted photo.
Throughout their analysis of these catalogs and laboratory experiments, Hampton and Xiong discovered that clustering in earthquake magnitudes was more pronounced when earthquakes occurred within shorter time intervals and closer geographical proximity. They found that in order to recreate the same magnitude clustering signature seen in the field and laboratory catalogs, synthetic catalogs required up to 20% repeating events.
“There’s been this debate for a really long time about whether magnitudes cluster,” Hampton says. “We’ve been able to show in the laboratory and field catalogs that it does exist. Now that we can start to see that clustering of magnitudes is prevalent and we can begin to assign some physical meaning to that, we may one day be able to start including magnitudes in earthquake forecasting models that already account for space and time.”
Such capabilities could be valuable in regions that are vulnerable to powerful earthquakes, especially if subsequent aftershocks are likely to be of similar strength. For example, on Feb. 6, 2023, a magnitude 7.8 earthquake hit south-central Turkey and northwest Syria. A few hours later, a magnitude 7.5 earthquake struck the same region. The two earthquakes caused widespread devastation and triggered storms of aftershocks. Several of those aftershocks were stronger than magnitude 6.0.
These quakes are an example of how predictive magnitude modeling could prove useful, if we know that one seismic event might trigger another of similar strength.
“After the main shock, you can have aftershocks, which can potentially cause more casualties than the initial earthquake” says Xiong, who now is a research scientist in Hampton’s group. “That’s because buildings may have collapsed and you can have search-and-rescue efforts underway. If we could predict an aftershock of similar magnitude, that could be crucial in reducing additional risks to human life.”
Hampton is continuing research to build upon what he and Xiong have already laid out in this paper. He hopes their research will provide a foundation that other researchers can work from to continue deepening our understanding of earthquake magnitude, branching influences from one seismic event to the next and, ultimately, how earthquakes happen.
And it may even have implications for broader civil engineering applications.
“For instance with mine pillars, tunnels or concrete bridges,” Hampton says. “If we can non-destructively listen to the cracks that are occurring and then process them, possibly in real time, to look at some of these connections between events, we might be able to say something about the imminent failure of a structure.”
The research, with its potential implications for the future of earthquake forecasting, might not have happened if not for the COVID-19 pandemic. In 2020, as the world shut down to try to slow the spread of the COVID-19 virus, Hampton and Xiong—who are both experimentalists—were forced to reconsider how to do their work without access to laboratory equipment.
“If the university is locked down, how can you do tests?” Xiong says. “It was an incentive that forced me to go deeper into the old data. It was like digging for gold in an old mine. This publication in Nature Communications is thanks to us having the chance to look through all of this old data that’s been compiled across decades.”
Top photo caption: Assistant professor Jesse Hampton’s research into earthquake magnitude clustering may help shed light on how to predict the strength of earthquakes in the future. Submitted photo.