The “double” earthquakes that struck Venezuela were probably one large earthquake. Here’s why science is important

On Wednesday evening, Venezuela was hit by the largest earthquakes in more than a century. Authorities said on Friday that floods destroyed buildings and killed more than 500 people. This event, according to the US Geological Survey, was a rare phenomenon called a “double” that contained not one but two large earthquakes.

Twin earthquakes occur when two earthquakes of the same magnitude occur in close succession, potentially causing more damage than a single earthquake. In this case, a 7.2-magnitude earthquake shook northern Venezuela, followed by a 7.5-magnitude earthquake just 39 seconds later.

“Double earthquakes are very devastating,” said Raul Pérez Lopez, a seismologist at the Institute of Geology and Mining in Madrid, Spain. “The main difference is that double earthquakes have similar energy, whereas (a) single earthquake and (smaller) aftershocks are lower in energy.”

However, some researchers expect that additional data over the coming days could reveal that the event was caused by one large earthquake rather than two. The difference between a single long earthquake and a double earthquake may not matter in terms of human consequences, but it can teach scientists a lot about this uncommon event and predict the severity of earthquakes.

“It may take a few days or more for seismologists to really understand the event, and then they may not have a definitive idea whether it was one earthquake or two earthquakes,” said Judith Hubbard, a seismologist at Cornell University who has analyzed recent seismic activity.

Binaries are rare, although this area is no stranger to them. Weaker twin quakes — magnitude 6.2 and 6.3 — struck there in September 2025, according to the US Geological Survey.

“We don’t really have a good idea which errors produce double copies and which don’t — or even whether there is a type of error that produces double copies,” Hubbard said. “It doesn’t happen frequently enough for us to come up with a general rule.”

Earthquakes occur when two moving tectonic plates stick together, building tension and then suddenly releasing pent-up energy. Wednesday’s tremors occurred at the boundary between the Caribbean and South American plates, which has been sliding at a rate of about 20 mm per year. Northern Venezuela is often hit by large, damaging earthquakes, but over the past century, the region has only experienced seven earthquakes of magnitude 6 or greater.

Because of the rapid succession of Wednesday’s quakes, Hubbard said confirming two quakes may be difficult based on preliminary data — and there are other possible explanations for what scientists are currently seeing on seismometers.

For starters, large earthquakes of magnitude 7.5 don’t usually happen all at once. Such a large earthquake starts at one location and propagates along the fault, tearing apart different parts at different times. In the case of Venezuela, the first pulsation — responsible for the 7.2 magnitude earthquake — could have set off a domino effect of pulsations that turned into a larger sequel.

An earthquake typically takes about 30 to 40 seconds to complete, but “because that larger pulse occurred during the first quake’s shaking, it was really hard to see” in the current data, she said.

If those two pulses were from a single rupture, Hubbard said the event could be equivalent to a 7.6-magnitude earthquake.

However, in preliminary reports so far, the USGS has painted a picture of two separate quakes about 5 to 10 kilometers (3 to 6 miles) apart — raising the possibility that one could trigger the other. Despite the proximity, the agency noted that the faults behind the quakes slid with opposite movements.

“The seismic data is ambiguous,” Hubbard said. “You can’t tell the difference between fault trends and slip trends” until more data comes in.

Several less intense aftershocks have since occurred near Caracas, which could provide clarity. If aftershocks rupture in patterns similar to the initial tremors, she said, it could confirm whether the proposed trends are accurate.

Confirming what happened on the ground may be difficult amid the damage. Subterranean sediments, especially in the area around Caracas, may have slowed and amplified seismic waves, resulting in increased destructive power. In addition, subsidence can cause additional damage to a building’s foundation. The region lacks large-scale seismic networks, and power outages in major centers may delay efforts. Satellite data, which should be available in the coming days, may reveal fault movements and provide more clues about which faults have ruptured.

Although rare, double earthquakes are interesting when they occur. In 2023, two earthquakes measuring 7.8 and 7.7 struck Turkey and Syria. They occurred nine hours apart and caused widespread damage.

Hubbard expects this event to be studied intensively in the scientific community, and could help scientists better estimate how large an earthquake could grow from the first few seconds of rupture.

“Everything we know about earthquakes comes from case studies of large earthquakes like this,” Hubbard said. “Even when there was very little data, we were able to learn a lot of things.”

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