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See why Venezuela’s earthquakes were so deadly
Any major earthquake can be dangerous, but residents of Caracas and Venezuelan coastal cities like La Guaira and Catia la Mar have been victims of several unlucky factors.
Two earthquakes in rapid succession, a fault that exploded toward more populated areas, soft ground and the shallow depth of the quake all combined to make the June 24 disaster particularly severe, even for areas that were miles from the epicenter.
And here’s what made it so deadly.
“double”
First and most important: There was not one earthquake, but two earthquakes, only 39 seconds apart. Seismologists call this “double.”
The first was smaller, measuring 7.2 degrees; The second was much stronger at 7.5.
This duo means that buildings have to withstand chaotic vibrations for much longer than they would in a normal earthquake.
“What almost certainly happened is that the first earthquake triggered the second,” said David Oglesby, a professor of geophysics at the University of California, Riverside.
The earthquakes killed more than 2,200 people, according to the Venezuelan government. More than 400 buildings were destroyed, and hundreds more were damaged.
Direction
Seismic waves from the first earthquake spread outward in all directions. But it was the waves that were traveling east that eventually reached a point on the San Sebastian Fault that was ready to slide. This led to the second earthquake. The secession continued eastward, more than 100 miles toward the capital, Caracas.
“There were two directions this fault could have gone,” said William Barnhart, a geophysicist with the USGS Earthquake Hazards Program. He added: “It could have gone west, or east towards Caracas. They could have been lucky if it had gone the other way.”
Dr. Barnhart said the initial rupture occurred on what is known as the Pocono Fault, part of the system that produced a massive earthquake in the 1800s.
Satellite images show that the second quake then moved east along a known seam between two of Earth’s tectonic plates – the San Sebastian Fault.
“We know that the fault extended as far as Caracas, and that partly explains why there was so much shaking there,” Dr. Barnhart said.
Ground shift
Scientists compared satellite images before and after the earthquake to measure how much the ground had changed. In coastal areas like La Guaira — where the fault extends only a few miles offshore or directly under the city — the ground has moved as much as 1.5 feet to the west.
San Sebastian is a strike-slip fault, which means the ground moves mainly horizontally along it. During the earthquake, areas north of the fault slid eastward, while areas south of the fault moved west.
In built-up areas directly above the fault, displacement is illustrated by satellite analysis.
For example, the northern half of Simón Bolívar International Airport was moved to the east, with the southern half pushed in the opposite direction. The San Sebastian fault extends along the contact line between the two displacement directions.
Dr. Barnhart said that although cracks appeared in the airport floor in the post-earthquake images, satellite analysis indicates that the crack did not reach the ground surface in that area. He said that if this had happened, the contradiction between the two trends of displacement would have been clearer.
Directional effect.
Dr. Oglesby said another factor may have increased the strength of the shaking east of the rupture.
As the rupture moved eastward, it may have increased the amplitude or strength of seismic waves, piling up like waves in front of a boat, or sound in front of a speeding motorcycle. It is possible that the impact, known as “directivity”, amplified the strength of the shaking towards Caracas, although more data is needed to confirm this.
“It is very likely that the directionality contributed to the strong ground motion in Caracas and the region in general,” Dr Oglesby said. “This can make the difference between an existing, damaged building and one that is completely collapsed.”
“Shallow as it gets”
The depth of the earthquakes, or more accurately the lack thereof, may have exacerbated the devastation.
The quakes started only six miles below the Earth’s surface, so the shaking was felt particularly strongly at the surface. “This is as sketchy as it can be,” said Vitor Silva, head of risk engineering at the Global Earthquake Model Foundation.
As with an underground bomb explosion, a shallower explosion results in greater shaking at the surface, Dr. Silva said. “There is a very short distance between the areas where the energy is released and the built environment,” he said.
Built-up areas in the region, as in many parts of the world, also tend to sit on relatively flat terrain, which is often soft sedimentary material that can amplify seismic waves.
As the second rupture moved eastward, it moved about 110 miles toward populated areas such as Caraballeda, La Guaira, and Caracas, sending seismic waves radiating outward along its path, which explains why the strong shaking extended far from the epicenter.
The worst damage was seen in low-lying areas along the coast.
Soft soil
Another process that seismologists study is how shock waves reach the surface. In the simplest terms, a hard rock surface tends to dampen waves, while a softer sedimentary surface amplifies them.
Humans tend to build on flat sedimentary areas — former lake beds and sea floors — that don’t behave well in earthquakes. The situation is no different in Venezuela.
The exact frequencies, or wavelengths, that are amplified by sediment depend on details, such as its thickness or precise composition. If those amplified waves match the swaying natural frequency of a nearby building, they resonate. This can cause the building to shake more violently, resulting in more damage.
Earthquake engineers must take all of this into account when designing buildings to resist what may push from the ground beneath them.
In Caraballeda, satellite analysis showed that at least 152 buildings were destroyed, with dozens more damaged. Most of these buildings were located along low-lying coastline, and were built on areas of non-solid soil that could exacerbate shaking.
Many high-rise buildings collapsed in the built-up area along the coast.
Near the Playa Grande neighborhood, at least 246 buildings were destroyed and almost all of them were built on top of the same soft soil. The San Sebastian Fault extends directly beneath this area.
Other factors
Engineers say Venezuela’s seismic codes are among the best in Latin America. The question is whether they were followed up or not.
From the scale of the devastation, it appears that some and perhaps many of the buildings were not built up to code, though experts said a full accounting would have to wait until the search for survivors was over.
More study will be needed to understand why and how so many buildings collapsed in Venezuela. Some collapses may be the result of so-called soft stories, where one floor – often the ground floor – is not as strong or well designed as other floors in the same building.
In other cases, columns appear to have given way throughout entire buildings, suggesting that they lacked proper reinforcement or that the contractors underestimated the amount of steel.
Older buildings may have collapsed and fallen simply because they predated newer code upgrades in Venezuela.
There are also buildings that have been a complete loss – walls and contents falling to the ground – but are still standing. Which allowed the residents to flee. Results like these would presumably be consistent with rules that prioritize human survival over structural preservation.
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Sources 2/ https://www.nytimes.com/interactive/2026/07/03/world/americas/venezuela-earthquakes-epicenter-maps.html The mention sources can contact us to remove/changing this article |
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