The coastal region of Caraballeda, Venezuela, experienced a devastating earthquake on June 24 that affected many residents in nearby areas such as Caracas, La Guaira, and Catia La Mar. Several factors contributed to the disaster’s severity.
The Doublet Earthquake
The earthquake consisted of two significant tremors occurring in rapid succession, separated by just 39 seconds. Seismologists refer to this as a ‘doublet.’ The first tremor had a magnitude of 7.2, while the second was more powerful at 7.5. This prolonged shaking stressed buildings for an extended period. According to Professor David Oglesby from the University of California, Riverside, the initial quake likely triggered the second one. The earthquakes resulted in over 2,200 deaths and significant structural damage, including the destruction of more than 400 buildings.
Direction of Seismic Waves
The seismic waves from the first tremor radiated outward, but the ones traveling east triggered the second earthquake along the San Sebastián fault. This rupture moved towards Caracas, exacerbating the situation. Dr. William Barnhart from the United States Geological Survey explained that the rupture could have gone in either direction, west or east, with east being toward Caracas.
Ground Shifting
Satellite imagery helped scientists measure ground displacement. In coastal areas like La Guaira, the earth moved approximately 1.5 feet to the west. This displacement affected buildings, including Simón Bolívar International Airport, where different sections shifted in opposite directions. Although cracks are visible, the fault did not reach the surface at the airport.
The Directivity Effect
Dr. Oglesby noted that directivity likely amplified the seismic waves as they moved east, increasing the shaking’s strength in Caracas. This amplification might have affected how buildings responded to the quake.
Shallow Depth of the Quake
The earthquakes occurred about six miles below the surface, making the shaking felt even more on the ground. According to Dr. Vitor Silva from the Global Earthquake Model Foundation, shallow tremors result in greater surface shaking. The quake’s eastward movement toward populated areas further extended its impact.
Impact of Soft Soil
Soft, sedimentary ground can amplify seismic waves. Many affected buildings were constructed on these unstable surfaces. Engineers are aware that flat, sedimentary areas tend to behave poorly during earthquakes and require considerations in building designs.
Satellite analysis in Caraballeda showed extensive destruction of structures built on unconsolidated soil. Sources such as Copernicus and Microsoft noted at least 152 buildings were destroyed in low-lying coastal areas.
Construction and Building Codes
Venezuela is known for having strong seismic building codes, yet the extent of the destruction indicates that not all buildings adhered to these regulations. Experts will need further investigation to understand the structural failures, which could be due to issues like inadequate reinforcement or outdated building codes.
The aftermath of the earthquake calls for a comprehensive review of construction practices and adherence to building codes in Venezuela. Although buildings were lost, many still stand, allowing residents to escape safely.