The earthquake of magnitude 7.4 that has shaken Colombia this Monday comes just a few weeks after the devastating double seismic event in Venezuela, where two earthquakes of magnitude 7.2 and 7.5 separated by only 39 seconds ended up causing one of the largest recent natural disasters in South America. Although the magnitudes are comparable, the initial assessments show very different scenarios.
In Colombia, the movement has had its epicenter in San José del Palmar, in Chocó, and has caused serious damage in cities such as Cali, Pereira, Quibdó, and Manizales. Authorities continue to evaluate buildings, assist injured people, and search for possible trapped individuals. In Venezuela, on the other hand, the combination of two consecutive and very shallow earthquakes triggered massive destruction that, almost a month later, had already surpassed 5,000 fatalities.
An almost identical magnitude
On paper, the three movements belong to a similar category. The Colombian earthquake has reached a magnitude of 7.4, while the two that struck Venezuela on June 24 were 7.2 and 7.5.
But magnitude alone does not determine the level of destruction.
In Venezuela, a particularly rare phenomenon occurred: a "double" seismic event, that is, two earthquakes of similar size occurring almost in the same place and in an extremely short time interval. The first, of magnitude 7.2, was followed just 39 seconds later by another of 7.5.
This meant that buildings and infrastructures hit by the first movement had virtually no chance to stabilize before receiving a second shock that was even stronger.
Depth makes a decisive difference
One of the main known differences between both episodes lies underground.
The Venezuelan earthquakes were very shallow. According to the USGS, the first had an approximate depth of 22 kilometers and the second of just 10 kilometers.
The Colombian earthquake occurred much deeper. The estimates released during the first hours have been revised, although sources agree on placing it at several tens of kilometers below the surface. Associated Press reports a depth of about 107 kilometers; the Colombian Geological Service has been reviewing its parameters throughout the day.
This difference is relevant because, in general terms, a shallow earthquake can transmit a much more intense shake to the areas close to the epicenter than another of similar magnitude originating at greater depth.
In the Colombian case, the greater depth also helps explain why the movement could be felt over a huge geographical area, from Bogotá and Medellín to Ecuador.
Venezuela suffered two blows in less than a minute
The Venezuelan sequence was especially destructive due to the combination of magnitude, shallow depth, and temporal proximity.
The two earthquakes occurred on the northern coast, near Morón, in an area linked to the boundary between the Caribbean and South American plates. The second movement, of magnitude 7.5, came when the buildings had already suffered the first shake.
La Guaira became one of the most affected areas. Entire buildings collapsed, there were power outages, the country's main airport had to close temporarily, and thousands of people were trapped or missing during the first days.
The toll continued to rise for weeks. By mid-July, Venezuelan authorities had already counted more than 5,000 dead, 16,740 injured, and 17,907 people without housing. In addition, 856 buildings had been damaged and 190 had completely collapsed.
Colombia continues assessing the damages
In Colombia, it is still too early to establish a definitive comparison in terms of victims.
The earthquake has caused serious structural damage. In Cali, there have been landslides with people trapped, while in Quibdó the governor of Chocó has reported injuries and severe damage. Collapses have also been documented in Pereira and the fall of part of a tower of the cathedral of Manizales.
President Abelardo de la Espriella has directly taken charge of coordinating the emergency and has announced the installation of a Unified Command Post in San José del Palmar.
For now, there is no comparable toll to that of Venezuela, and Colombian authorities continue conducting inspections, rescues, and assessments.
Two distinct seismic scenarios
There is also an important tectonic difference.
The double Venezuelan earthquake was the result of a lateral slip movement on faults near the boundary between the Caribbean and South American plates, according to the USGS.
Colombia is located, for its part, in a tectonically very complex region where the plates of Nazca, South American, and Caribbean interact, in addition to numerous continental fault systems. For this reason, it registers seismic activity much more frequently. The earthquake this Monday occurred in western Colombia, in one of the areas of greatest seismic activity in the country.
The magnitude is not enough to measure a catastrophe
The comparison between both episodes allows us to understand why two earthquakes with similar magnitudes can produce radically different consequences.
Venezuela suffered two large movements separated by less than a minute, both very shallow and near densely populated areas. Colombia has so far recorded a single main earthquake, of comparable magnitude but considerably deeper.
To this, other factors are added that can only be analyzed when there is a definitive balance: the quality and age of the constructions, the distance of the cities to the epicenter, the duration of the shaking, the local geology, and the response capacity of emergency services.
For this reason, a 7.4 does not automatically equate to another 7.4. The magnitude informs of the energy released, but the level of destruction depends on how, where, and at what depth that energy is released.
Just a few weeks separate both events. Venezuela is still facing the consequences of a tragedy that has left thousands dead and tens of thousands affected, while Colombia is now beginning to measure the real extent of its own earthquake.