General Geological Setting
Colombia is located in the northwestern corner of the South American plate, where it meets the Nazca and Caribbean plates. This collision of tectonic plates has produced a subduction zone beneath the Pacific coast and shallow crustal faults within the interior of Colombia. Although the subduction earthquakes are potentially very damaging, they occur in an area of the Pacific coast that is sparsely populated.
The shallow crustal faults however, can produce significant damage because of their proximity to major population centers. For example, a relatively small magnitude shallow crustal event occurred on March 1983 near the city of Popanyan measuring only M5.4, yet causing US$400 million of damage. One particularly hazardous shallow crustal fault zone called the Frontal Fault system runs along the eastern boundary of the Cordillera Oriental mountain range. Segments of this fault have the potential to produce M8.0 events that could result in extensive damage to many cities including Bogota.
>The collision of oceanic and continental plates. One plate is thrust or subducted under the other plate so that a deep ocean trench is produced. Along the Peru - Chile trench, the Nazca plate is being subducted under the South American plate which responds by crumpling to form the Andes.<
>The oceanic crust is pushed downwards and forms deep ocean trenches along the plate margin. The pressure created by the frontal collision between the two plate systems, forces the continental plate material to buckle and rise, forming young folded mountain ranges. The classic example of such activity can be found along the west coast of South America where the Nazca plate is being forced below the westward moving American plate. The sub-ducting Nazca plate forms a deep ocean trench running north to south off the coast of Chile whilst the pressure buckling of the American plate has formed the Andes mountain range. Ocean/continental plate margins are characterised as Andean margins. < (St. Vincent College-Updated: August 1999)