At 10:42 a.m. local time a M=5.2 earthquake struck central Colombia. Fortunately, strong shaking was not felt at the surface because the earthquake struck at a depth of 113 km. But it was widely felt, including in the capital city of Bogota approximately 150 km away, as well as Medellin and Cali, which combined, are home to over 12 million people. Despite the fact that this earthquake occurred close to an active convergent plate boundary, we know that this earthquake was extensional in nature. The earthquake struck very close to where a M=6.6 event occurred in 1995, which was also extensional. This suggests to us that in this location, the Pacific slab might be bending downward as it descends beneath Colombia.
Additionally, based on the map above, we know that this region is no stranger to large earthquakes. The map shows historic large earthquakes from the ISC-GEM catalog in Colombia. One can see that just to the south of today’s event, there are numerous M=6+ events in the past few decades, highlighting the earthquake hazard of the country.
Further illustrating the seismicity of Colombia is the map below from the Servicio Geologico Colombiano. This map shows the last 2.5 weeks of earthquakes around the country, colored by depth. While the majority of the deep earthquakes throughout the country likely pose no risk to residents, if a large, shallow magnitude earthquake were to strike, damage could be significant.
The message of the past century of large shocks (the ISC-GEM catalog), and from the past weeks of small ones (Colombian Seismic Network), is that this is a highly active seismic corridor that produces both deep and shallow shocks, all of which can be much larger than today’s M=5.2. The deep events appear to be tensional in nature, perhaps related to the downward bending of the subducting slab as it plunges into the earth’s mantle. The shallow shocks strike on the oblique strike-slip reverse faults. Our explanation of the mechanism of the deep shocks is speculative, but the existence of a long history of large shocks is irrefutable.
Fortunately, many in Colombia have recognized their seismic hazard and have taken measures to limit their risk. For example, Manizales, which lies just to the south of today’s epicenter, built an insurance program to protect its residents (Marulanda et al., 2012). So, while great (M≥8) events in Colombia are probably confined to the coastal subduction zones, we are reminded today that large (M≤7) damaging events can occur 500 km east of the Colombia-Ecuador trench in the high Andes. Given this likelihood, the earthquake insurance program adopted by Manizales seems to us both prudent and prescient. More cities—and not only those in Latin America—should work to find affordable solutions to reduce the financial impact of future shocks. And more homeowners should protect themselves by strengthening their homes and insuring them, so they can enjoy living in these majestic ranges free of worry.
Servicio Geologico Colombiano
M. C. Marulanda, A.H. Barbat, O. D. Cardona, M. G. Mora, Design and Implementation of a Collective Insurance Program based on Cross Subsidies for Recovery of Low Income Homeowners, 15 WCEE Lisbon 2012