Complex seismic patterns in east-central Colombia have kept seismologists baffled for years. Finally, researchers have explained it all in a paper identifying the “Caldas tear.”
Carlos Alberto Vargas of the Universidad Nacional de Colombia and Paul Mann of the University of Houston published their paper “Tearing and breakoff of the subducted slabs as the result of a collision of the Panama arc-indenter with northwestern South America,” in the June edition of the Bulletin of the Seismological Society of America.
The duo used a database of more than 100,000 seismic events along with tomographic data, gathered by sending waves or pulses into the earth to identify the prominent gash separating the Nazca and Panama plates.
Colombia sits on top of three tectonic plates: the Caribbean plate in the north, the Panama plate in the center, and the Nazca plate in the south.
These plates are moving in a very complex pattern. The northern Caribbean plate is subducting or being forced under Colombia, but at a very shallow angle, the Panama plate is colliding with Colombia in the center, and the Nazca plate is subducting at a shallow angle from the west in southern Colombia.
The Caldas tear is a break in a slab separating the two subduction zones where the plates are moving underneath and slipping into the mantle.
Mann describes the Panama plate as an indenter, or “a block of thick crust” that is colliding and pushing into Colombia “like a fist.”
The piece of crust that went ahead of this fist, or indenter, is being ripped apart as it refuses to slide easily below Colombia. This is causing what the researchers term the “Bucamaranga Nest,” a hotbed of seismic activity at only 140km depth.
“The deformation is proceeding on a regional scale in Colombia,” said Mann.
While the Caribbean plate crust to the north is also subducting at a very shallow angle and at a slower rate than the southern Nazca plate, it produces very little deep seismic activity, which Vargas suggests could mean there is an “accumulation of stresses” that could trigger stronger events in the future because of the collision of the Panamanian plate against Colombia.
The Caldas tear is an “incredibly important feature” for Colombia in assessing its earthquake hazard, according to the researchers.
The effects of the Caldas Tear are evident in Colombia’s landscape. Even the famed Magdalena river, running north, changes from broad bottomed valleys to steep gorges as it crosses the tear, which leads the researchers to believe that the tear may reach all the way to the surface.
The tear causes mineral deposits, hydrocarbon occurrences and geomorphological anomalies on the surface above it. The small volcanoes along the Caldas tear are also different in composition to those in the south, like Colombia’s most active volcano el Ruiz.
The researchers say that although there have been many earthquakes in the last two decades, none have been too major, despite the complex activity beneath the ground
- Caldas tear resolves puzzling seismic activity beneath Colombia (Science Daily)
- Caldas tear beneath Colombia (Phys Org)