Severe Earthquake in Caraballeda
On June 24, Caraballeda, Venezuela, experienced a significant earthquake disaster. The event struck coastal regions including Caracas and cities like La Guaira and Catia La Mar. Several elements made the situation particularly catastrophic.
Earthquake Doublet
The most critical factor was the occurrence of two earthquakes in rapid succession, referred to as a “doublet.” The first quake was 7.2 magnitude, followed 39 seconds later by a stronger 7.5 magnitude tremor. This sequence prolonged the chaotic shaking.
“Almost certainly, what happened was that the first earthquake triggered the second one,” stated David Oglesby, geophysics professor at UC Riverside.
These earthquakes resulted in over 2,200 fatalities as reported by the Venezuelan government, with more than 400 buildings destroyed.
Direction of the Rupture
Seismic waves from the first earthquake radiated in all directions, but waves traveling east triggered the second earthquake along the San Sebastián fault. This rupture continued more than 100 miles toward Caracas.
“It could have gone to the west, or the east toward Caracas,” noted William Barnhart, geophysicist at the US Geological Survey.
Satellite imagery indicates the second quake traveled along a known seam between tectonic plates, affecting regions built directly on top of fault lines.
Ground Shift
Scientists measured ground shifts using satellite imagery. In coastal areas like La Guaira, the ground moved 1.5 feet to the west. This fault is strike-slip, meaning horizontal movement primarily occurred.
The displacement was evident in areas like Simón Bolívar International Airport, where one half shifted east and the other west due to the fault line.
Directivity Effect
Directivity amplified seismic waves toward Caracas, worsening the shaking. Dr. Oglesby explained how directivity likely contributed to stronger ground motion.
“Directivity very likely contributed to the strong ground motion in Caracas and the area overall,” he said.
Depth and Soil Conditions
The earthquakes were shallow, beginning around six miles below the surface, increasing surface shaking. Vitor Silva explained the greater impact shallow quakes have on surface structures.
Built-up regions located on soft, sedimentary soil tend to amplify seismic waves, contributing to extensive damage in low-lying areas along the coast.
Structural Failures
Many buildings were not constructed to Venezuela’s seismic code, despite its strength. Experts anticipate further study to understand the failures contributing to such widespread destruction.
This ongoing analysis may reveal issues like inadequate reinforcements in columns and outdated buildings, contributing to the damage experienced.
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