Verónica Cañas barely had time to grab her 6-year-old son and put on her shoes before running out of her apartment in Caracas. As she ran down the stairs, the walls began to crack, and part of the facade started to crumble. A few kilometers away in Altamira, 50-year-old Eduardo Burger watched as one building swayed while another fell apart.

Neither knew that this was not just a single terrible earthquake but instead a rare phenomenon. On June 24, Venezuela experienced a seismic doublet that saw earthquakes of magnitude 7.2 and 7.5 occur just 39 seconds apart. The first tremor occurred with its epicenter in Yaracuy. Just a few seconds later, an even more intense earthquake shook the same region again.

Both occurred at a shallow depth of between 10 and 20 kilometers (6 and 12 miles), which caused the energy to reach the surface with greater intensity and allowed the seismic waves to be felt as far away as Colombia, northern Brazil, and several Caribbean islands such as Aruba, Bonaire, and Curaçao. While one alone would have caused damage, it was the one-two punch that created the conditions that brought down so many buildings and made it hard to rescue survivors as the death toll mounts.

The Technical Explanation: Tectonic Plates, Damage, and Resonance

“The dining room table started to shake … We thought it was a tremor; then it started shaking much more violently. The walls were cracking, and pieces of the ceiling were falling,” Cañas says.

She and her family managed to make it to a sports field across from the building, where other neighbors were beginning to gather. There, they were hit by another tremor. “We all hugged each other, terrified, because we’re not used to this. In Mexico and Chile, there’s an earthquake-preparedness culture, and people are already prepared when an alarm goes off or they feel certain movements, but we aren’t,” she says.