Understanding the Devastation of the Caraballeda Earthquake

On June 24, Caraballeda, Venezuela, was rocked by a severe earthquake that also affected Caracas and nearby coastal cities. This disaster resulted from a combination of factors that intensified its impact, causing extensive damage across the region, even far from the epicenter.

The “Doublet” Earthquake

One of the main reasons for the quake’s severity was the occurrence of two separate earthquakes in close succession, known as a “doublet.” The first quake had a magnitude of 7.2, followed by a stronger 7.5 magnitude quake, just 39 seconds later. According to David Oglesby, a geophysics professor at the University of California, Riverside, the initial earthquake likely triggered the latter one. Over 2,200 people perished, and more than 400 buildings were either destroyed or severely damaged.

Seismic Wave Direction

The seismic waves from the first earthquake spread in multiple directions. Notably, waves moving eastward reached a point on the San Sebastián fault, which was primed to slip, initiating the second quake. This rupture continued over 100 miles toward Caracas, the capital. According to William Barnhart from the United States Geological Survey, the direction the fault took was critical, as an alternative westward direction could have reduced the damage.

Ground Shifts

Satellite images showed significant ground shifting, particularly in coastal regions like La Guaira, where the fault runs close to the city. In these areas, the ground moved around 1.5 feet to the west. The San Sebastián fault is a strike-slip fault, which means the earth moves horizontally along it. For instance, at Simón Bolívar International Airport, the northern part shifted east while the southern part moved west. The satellite analysis revealed cracks in the ground, indicating significant displacement.

Impact of Directivity

The movement of the seismic rupture to the east possibly augmented the seismic waves’ amplitude, according to Dr. Oglesby. This phenomenon, known as “directivity,” may have intensified the shaking in Caracas and nearby areas, potentially making the difference between structural survival and collapse.

Shallow Quake Depth

The shallow depth of the quakes, approximately six miles below ground, intensified the destruction. The proximity of the quake’s energy release to the surface led to stronger ground shaking, as explained by Vitor Silva from the Global Earthquake Model Foundation. Besides, urban areas built on flat, sedimentary land further amplified these seismic waves.

Soil Conditions

These coastal areas generally sit on soft, sedimentary soil, which can amplify seismic waves. The softer the surface, the more likely it is to resonate with certain seismic waves, leading to greater damage. As per satellite analysis, over 150 buildings collapsed in Caraballeda alone, situated on loose soil that intensified the quake’s force.

Structural Factors

Though Venezuela’s seismic codes are considered among the best in Latin America, whether these were followed is questionable. The scale of destruction suggests many buildings may not have adhered to these standards. Some buildings showed weaknesses like “soft stories,” where a ground floor is less robust. In other buildings, structural failures indicated a lack of reinforcements.

Older structures, built before code improvements, often fared badly, leading to collapses. While some buildings became total losses, they allowed residents to escape, aligning with codes prioritizing life safety over structural preservation.