By Albert Leonardo Aguilar Suarez, Ph.D. candidate, Stanford University, and Ross S. Stein, Ph.D., Temblor, Inc.
Evacuations in Bogotá and the suspension of transportation systems followed a magnitude-6.2 earthquake, which struck on or near where the North Andean Block grinds against South American Plate. The mainshock was followed just 15 minutes later by a magnitude-5.7 aftershock. Further large aftershocks remain a possibility.
Citation: Albert L. Aguilar and Ross S. Stein (2019), Largest Colombian crustal earthquake in 50 years strikes on Christmas Eve, Temblor, http://doi.org/10.32858/temblor.061
The Christmas Eve gift from the Earth to the people of Colombia was a reminder of Earth’s immense power and destructive potential. A magnitude-6.2 earthquake struck near the town of Mesetas, Meta just after 2 pm local time on December 24. This event was followed 15 minutes later by a magnitude-5.7 aftershock. Both were widely felt in Bogotá, Villavicencio, Cali and other big cities in the country. The shaking caused evacuations in Bogotá and the suspension of transportation systems. Fortunately, no injuries have been reported, but many buildings were damaged near the epicentral region. Damages in Mesetas include cracking of the school, the police station and many houses.
More to come
Following a large earthquake, many smaller earthquakes, called aftershocks, occur because of stress changes caused by the mainshock. In the 48 hours following the magnitude-6.2 earthquake, the National Seismological Network of Colombia (RSNC for its initials in Spanish) reported more than 300 aftershocks.
In a typical aftershock sequence, earthquakes will become less frequent with time. That is observed here, with the aftershock sequence including several earthquakes greater than magnitude-4.5. These aftershocks will continue for weeks to years, but most will be too small to be felt or cause damage, although we cannot rule out the possibility of a larger event.
Unsurprising, naturally occurring earthquakes
The magnitude-6.2 is the largest crustal earthquake that has occurred in Colombia in the last 20 years, but its size and location are not surprising for earthquake scientists. The epicenter is located on the eastern side of the Eastern Cordillera of Colombia, where the Algeciras fault system acts as the boundary between the South American plate and the North Andean Block [Velandia et al., 2005; Veloza et al., 2012]. The Algeciras fault system is as a right-lateral strike slip fault, meaning that whichever side of the fault you’re on, the opposite side moves to the right (see the green arrows on the map below). The Algeciras fault system was also responsible for the largest historical crustal earthquake in Colombia—the 1967 magnitude-7.0 Huila earthquake [Dimaté et al.,2005].
The eastern cordillera of Colombia and the faults that run through it are responsible for more than half of the shallow seismicity (i.e. depth < 30 km) reported by RSNC. Small earthquakes happen every day, but for the most part, their shaking is too small to be felt. However, more than two years ago, a magnitude-4.7 earthquake took place ~20 km NE of the epicenter of the magnitude-6.2 Christmas earthquake, which is why the location of the Christmas quake is no surprise at all.
In recent years, seismic activity surged near the town of Colombia (a town with the same name as the country). Three earthquakes greater than magnitude-5.0 struck the town in October 2016, February 2017 and July 2018, and were felt in major cities. These earthquakes also had a rich sequence of aftershocks, as shown by Aguilar & Prieto . There, the Altamira and Nazareth faults were responsible for the sequence, which occurred near the intersection of the two. At the time, these three quakes were the largest to occur close to Bogotá, after the 2008 magnitude-5.9 Quetame earthquake.
This seismicity is naturally occurring, a consequence of the interactions of the geological faults that are building the Eastern Cordillera. They are unrelated to industrial oil and gas activities as many people have falsely claimed on social media. Furthermore, there is no relation between these earthquakes and the so-called ‘activation of the Pacific ring of fire’, which is a headline that goes viral after any notable earthquake near the edge of the Pacific Ocean.
An opportunity for advancement
The RSNC recently deployed additional seismometers, including two new stations close to the recent earthquakes—station URMC in Uribe, Meta, installed in March 2018, and station CLBC in Colombia, Huila that started recording on February 2019. These additional seismometers will allow a higher resolution image of seismicity, especially for small quakes that are hidden in the shadow of bigger ones.
Aguilar & Prieto  and Aguilar et al.  revisited the data recorded by RSNC near Colombia-Huila. Through a systematic search for small earthquakes, they tripled the number of events in the catalog for the years 2016, 2017 and 2018. They also clarified the geometry of these faults via precise relocations. The work in the following weeks and months will be pivotal for gaining further insights into the geometry of the faults and the mechanisms of these earthquakes, as well as the seismic hazard near Bogotá, the largest city in Colombia.
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Aguilar, A. and Prieto, G. (2018), Spatial and temporal evolution of source properties in the Colombia-Huila seismic sequence. Seismology of the Americas. Available at: https://www.seismosoc.org/wp-content/uploads/2018/06/poster_AA.pdf
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Aguilar, A., Prieto, G., Pedraza, P., Pulido, N. and Beroza, G. (2019), The recent seismicity of the Eastern Cordillera of Colombia. American Geophysical Union Fall Meeting.
Velandia, F., Acosta, J., Terraza, R. and Villegas, H. (2005), The current tectonic motion of the Northern Andes along the Algeciras Fault System in SW Colombia, Tectonophysics, doi:10.1016/j.tecto.2004.12.028.
For the Spanish translation of this article, go here.