Veronica Cañas barely she managed to grab her 6-year-old son and put on her shoes before running out of her Caracas apartment. As she ran down the stairs, the walls began to crack and part of the facade began to crumble. A few kilometers away, in Altamira, 50-year-old Eduardo Burger watched as one building swayed and another crumbled.
What neither of them knew was that it wasn’t just a single terrible earthquake, but a occasional occurrence. On June 24, Venezuela experienced a seismic doublet, with magnitude 7.2 and 7.5 earthquakes occurring just 39 seconds apart. The first tremors occurred at the epicenter in Yaracuy. Just seconds later, an even more intense earthquake shook the same region again.
Both occurred at shallow depths from 10 to 20 kilometers (6 and 12 miles), which caused the energy to reach the surface with greater intensity and allowed seismic waves to be felt as far away as Colombia, northern Brazil, and several Caribbean islands such as Aruba, Bonaire, and Curaçao. Although one single fire would have caused damage, it was the double-whammy effect that created the conditions that demolished so many buildings and made it hard to rescue survivors as the death toll mounted.
Technical explanation: tectonic plates, damage and resonance
“The table in the dining room started shaking… We thought it was shaking, then it started shaking much more violently. The walls were cracking and pieces of the ceiling were falling. We thought it was going to collapse on us,” Cañas says.
She and her family managed to make it to the sports field across from the building, where other neighbors began to gather. There they were hit by another shock.
“We were all scared and hugged each other because we are not used to it. In Mexico and Chile, there is a culture of earthquake preparedness and people are already prepared when the alarm goes off or they feel certain movements, but we are not,” he says.
Cañas’ experience highlights one of the main differences between Venezuela and other countries with higher seismicity. Although the country straddles the boundary between the Caribbean Plate and the South American Plate, earthquakes of this magnitude are relatively occasional.
Alan Damián Sánchez Pulido, a structural engineer at Mexico’s Ibero-American University and a specialist in structural damage assessment, explains that the position and movement of the plates determine why earthquakes are not as common as in other regions and why they are so powerful when they do occur.
“In Venezuela, the interaction between the Caribbean and South American plates involves parallel movement, which could have caused two earthquakes of significant magnitude that occurred in such a short space of time,” he notes.
Unlike Mexico, where the Cocos Plate is sliding under the North American Plate, in Venezuela, lateral movement leads to different results. “It’s a very rare phenomenon, but the probability is not zero. It can occur anywhere in the world where there is interaction between tectonic plates,” says Sánchez Pulido.
What was surprising was not only that there were two vast earthquakes, but also that the second one occurred just 39 seconds after the first. According to Sánchez Pulido, it was this tiny pause that made the series of quakes so devastating.
“Many structures suffered some type of damage from the first earthquake. This does not mean that the damage was extensive, but any damage changes the original behavior for which they were designed. When another earthquake of similar magnitude occurs immediately afterwards, there is no longer any way to strengthen, test or repair the structure. As a result, it no longer functions as intended,” he says.