Two massive earthquakes that struck Venezuela on June 24, just 39 seconds apart, had epicenters slightly apart in north-central Venezuela. The first (M7.2) near San Felipe, and the second (M7.5) near Yumare, killing thousands and injuring thousands more. According to government officials. But beyond the devastation, the sequence opened up a rare scientific opportunity: Researchers believe the unusual “earthquake repetitions” could provide new insights into how large fault systems interact and how some of the most destructive earthquakes grow.
Big Earthquake This is usually followed by smaller shocks. But particularly intense events can also change the stress on nearby faults or on the same fault, causing another, larger earthquake.
These scenarios are rare but not unprecedented. 2023 sequence in Kahramanmaraş, Türkiyeand this Double earthquake in Harnai, Pakistan in 1997There are two famous examples.
The Venezuela sequence also reinforces an emerging consensus among seismologists: that treating faults as isolated structures may underestimate the destructive power of earthquakes in areas where multiple tectonic faults meet, as they do in both Venezuela and around California’s San Andreas Fault System. This is a problem, because many seismic hazard models in California do not account for those multiple-fault interactions.
A natural laboratory for understanding major earthquakes
The fault system involved in the Venezuela earthquake – which includes the Bocono, Moron, San Sebastián, and El Pilar faults – shares several key features with the San Andreas fault. Both are right-lateral strike-slip fault systems – in which crustal blocks move horizontally past each other – located along the boundary between two tectonic plates: the South American and Caribbean plates in Venezuela, and the Pacific and North American plates in California.
Despite these similarities, researchers caution that the two systems differ in important ways.
“The main difference is that the Venezuelan plate boundary has a much more complex fault architecture,” Julian Garcia Mayordomoa senior scientist in the department of geological hazards and climate change at Spain’s Geological and Mining Institute told Live Science.
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The difference largely arises from the Maracaibo block, whose interaction with surrounding faults creates a far more complex plate boundary than California’s.
“The other difference is the speed at which the plates move,” García Mayordomo explained.
In Venezuela, tectonic plates move past each other at a rate of about 0.8 inches (20 millimeters) per year, while along the San Andreas Fault the rate is about 1.2 inches (30 millimeters). Faster plate motion causes tectonic stress to accumulate more quickly, which affects how often large earthquakes occur over long time scales, but not when the next earthquake will occur.
Aerial view of the San Andreas Fault in California.
(Image credit: Kevin Schafer/Getty Images)
Earthquakes of magnitude 7 or larger occur on average every time the San Andreas Fault 100 to 200 yearsHowever the frequency of repetition varies according to the defect. The last major earthquake in Southern California was the magnitude 7.9 Fort Tejon earthquake in 1857. In Venezuela, estimated slip rates suggest a recurrence interval of one to two centuries. The region experienced two devastating earthquakes in 1812, part of a multiple-rift sequence. 7.5, 7.2 and 6.5 magnitude eventsand a 2018 study concluded that enough pressure had already accumulated in the Bokono Fault to trigger another major earthquake.
However, these are statistical averages. The recurrence of large earthquakes is highly irregular and depends on many factors, many of which we still do not fully understand. So a major event could happen in 100 years – or even tomorrow.
looking beyond personal faults
This uncertainty is one of the reasons why Venezuela’s seismic recurrence is generating so much interest among seismologists.
“This is the kind of natural phenomenon that can accelerate and test dissection-interaction hypotheses that paleoclimate models like ours can only indirectly infer,” he said. Lillian BurkhardA geologist and geophysicist at the University of Bern and first author of recent study Suggest that the junction between the San Andreas and San Jacinto faults in Southern California is experiencing Some of its highest tectonic stress levels in the last 1,000 yearsTold Live Science.
“Our Cajon Pass work relies on paleoclimatic reconstructions spanning centuries to explore how stress evolves and what cracks may form between fault systems,” Burkhardt told Live Science. But it doesn’t give geologists real-time data, captured by seismic instruments, that shows how different faults react during an earthquake, he said.
Venezuela Doublet offers exactly this opportunity. The main lesson for California, Burkhardt said, is that interactions between neighboring faults can play an important role in the development of large earthquakes.
“Whether it’s the Cajon Pass where the San Andreas and San Jacinto systems meet or the Bocono-San Sebastian in Venezuela, these are exactly the places where single-fault hazard models break down because the actual behavior depends on how stress is shared and transferred between adjacent structures,” she said.
Many times the winner is not the boxer who punches the hardest, but the one who continues punching for the longest period of time.
Julián García Mayordomo, Senior Scientist at the Geological and Mining Institute
Nevertheless, the two systems are quite different. The Venezuela sequence represents a different type of cascading rupture than that described in Burkhardt’s research. At Cajon Pass, the “earthquake door” concept explores whether a single rupture can move from one fault system to another during the same earthquake, in tens of seconds of rupture propagation along the continuous fault trace. Venezuela’s repetition, in contrast, “looks like two separate ruptures on two separate fault structures, triggered in close succession,” Burkhardt said.
For Burkhardt, the Venezuela earthquake reinforces the need for seismic hazard models to move beyond treating faults as isolated structures and instead represent them as interconnected networks. This challenge is particularly relevant in California, where nearly 300 active faults may interact in ways that traditional hazard models do not capture.
New Zealand has already incorporated this text. After the 2016 Kaikoura earthquake ruptured at least 12 faults in a single event, New Zealand revised its national seismic hazard model to include complex multifault ruptures.
García Mayordomo argues that both Venezuela and the United States should incorporate these complex rupture scenarios into seismic hazard assessments and building codes. Earthquakes along multiple faults can produce long-lasting aftershocks that increase structural fatigue and, ultimately, increase the risk of collapse.
“It’s like a boxing match,” Garcia Mayordomo said. “Many times the winner is not the boxer who punches the hardest, but the one who continues punching the longest.”
Still, researchers cautioned against drawing broad conclusions from a single earthquake.
“Each earthquake gives us a possible scenario,” Judith Hubbarda Cornell University seismologist and structural geologist told Live Science. “The range of earthquake behavior is wide.”