Venezuela’s June 24 Earthquake: What Made it a Catastrophe

The Double Earthquake

On June 24, a devastating earthquake hit the coastal region of Caraballeda, Venezuela. The disaster resulted from two earthquakes striking in quick succession, a phenomenon known as a “doublet.” These quakes struck the populated areas of Caracas and surrounding cities, leading to severe effects.

The first earthquake, measuring 7.2 in magnitude, came first, followed by a more powerful quake of 7.5, just 39 seconds later. The doublet’s impact was catastrophic, causing buildings to endure prolonged and intense shaking. According to David Oglesby, a geophysics professor at the University of California, Riverside, the first quake likely triggered the second one.

The impact was disastrous, with over 2,200 people reported dead as per the Venezuelan government, and more than 400 buildings were destroyed.

The Rupture Direction and Faults

Seismic waves from the first quake spread in all directions, but the waves traveling east triggered further activity on the San Sebastián fault, causing the second earthquake. This rupture extended over 100 miles east toward Caracas, intensifying the impact.

William Barnhart from the U.S. Geological Survey noted that the fault could have shifted either west or east. Unfortunately, it moved toward the densely populated areas of Caracas. The initial rupture occurred on the Boconó fault, part of a system known for substantial past earthquakes.

Satellite imagery revealed that the second quake traveled east along the San Sebastián fault, affecting the areas severely.

Ground Displacement and Soil Effects

Scientists compared pre- and post-quake satellite images to measure ground shifts. The coastal areas like La Guaira saw ground displacement of up to 1.5 feet westward. This region is directly above or near the offshore fault line. The San Sebastián fault is characterized as a strike-slip fault, meaning the Earth’s movement is primarily horizontal along it.

The ground shifted in different directions in areas built directly on top of the fault. Simón Bolívar International Airport, for instance, experienced noticeable displacement between its northern and southern halves.

Directivity and Shallow Depth

Another factor worsening the situation was the directivity effect. Dr. Oglesby explained that as the rupture advanced east, it possibly heightened the seismic waves’ strength, akin to how waves pile up before a moving boat. This effect likely intensified the shaking toward Caracas.

The shallowness of the quakes further amplified the destruction. Occurring just about six miles below ground, they produced strong surface shaking. Dr. Vitor Silva, from the Global Earthquake Model Foundation, indicated this shallow depth allowed the energy to impact the built environment vigorously.

Urban areas often sit on sedimentary, soft ground that magnifies seismic waves. This phenomenon was evident in Caraballeda and other regions near the epicenter.

Structural Vulnerabilities

The earthquake’s full impact was most visible in low-lying coastal areas. In Caraballeda alone, satellite analysis confirmed that at least 152 buildings were destroyed, highlighting the vulnerability of constructions on soft, unconsolidated soil.

Engineering practices and building codes come into question following the disaster. Venezuela’s seismic codes are recognized as among the best in Latin America. However, whether these regulations were adhered to remains uncertain. The collapse of buildings, in many cases, may indicate issues like soft story structures or inadequately reinforced columns.

Older buildings that predate seismic code updates also suffered significant damage. Some structures that did not collapse completely allowed occupants to escape, aligning with codes prioritizing human life over structural integrity.