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| Usme Fault | |
|---|---|
| Name | Usme Fault |
| Other names | Falla de Usme |
| Location | Colombia, Cundinamarca Department |
| Length km | 64 |
| Strike | NW-SE |
| Type | Oblique strike-slip and normal |
| Displacement | estimated mm/yr |
| Tectonic setting | Andean orogeny, North Andean Plate margin |
| Coordinates | 4°30′N 73°40′W (approx.) |
Usme Fault is an active, oblique strike-slip and normal fault system in the Eastern Cordillera of Colombia near the southern sector of Bogotá. It forms part of a network of Quaternary structures that accommodate deformation of the northern Andes and interacts with regional features around the Bogotá basin. The fault influences local topography, drainage patterns, and landslide susceptibility in populated zones adjacent to Bogotá and the Cundinamarca Department.
The Usme Fault cuts Neogene to Quaternary volcanic, sedimentary, and metamorphic rocks of the Eastern Cordillera exposed near the Bogotá savanna. It juxtaposes units correlated with the Villeta Group and the Guaduas Formation against uplifted remnants of the Santa Marta-Bucaramanga Fault domain. Lithologies along the trace includeandesitic and dacitic lavas linked to the Central Ranges volcanism, clay-rich lacustrine deposits related to paleo-Lake Humboldt fluctuations, and low-grade metamorphic schists comparable to those mapped in the Eje Cafetero. Fault gouge and breccia, together with colluvial wedges, indicate repeated Holocene surface-rupturing events similar to those documented for the Atrato Fault and Palermo Fault systems.
The fault trends northwest–southeast across the southern margin of the Bogotá savanna, crossing rural localities near Usme and extending toward the Sumapaz Páramo. Its western terminations approach the Humedal La Vaca wetlands and the eastern terminations link with folds and splays near the foothills of the Eastern Ranges. The trace influences major transport corridors connecting Bogotá with Villavicencio and pastoral lands in Sumapaz, and lies within the administrative boundaries of the Metropolitan Area of Bogotá and the Cundinamarca Department. Elevation along the rupture varies from high Andean páramo plateaus to lower intermontane valleys near urban fringes of Usme and Ciudad Bolívar.
The Usme Fault occupies a complex tectonic setting at the margin of the North Andean Plate where shortening, transcurrent motion, and vertical uplift accommodate convergence between the Nazca Plate and the South American Plate. It interacts with major crustal structures such as the Algeciras Fault and the regional splay network connecting to the Sinu Fault system. Seismicity in the region includes microseismic swarms, historical moderate earthquakes reported in archives for Bogotá and felt events correlated with activity on nearby thrusts like the Palomino Fault. Instrumental records from the Colombian Geological Survey and networks operated by the National University of Colombia show low-to-moderate seismic release consistent with oblique-slip faulting, with recurrence intervals similar to large active faults across the Andean foreland.
The Usme Fault is characterized by a combination of dextral strike-slip displacement and normal oblique components, producing a segmented trace with en echelon overlapping strands, releasing bends, and pull-apart basins comparable to those along the Buesaco Fault and Silos Fault. Surface expression includes linear scarps, offset terraces, shutter ridges, and aligned springs observed along the fault corridor, reminiscent of morphologic markers mapped at the Bucaramanga Fault. Crosscutting relationships demonstrate Quaternary offset of fluvial terraces and Holocene colluvium, indicating a significant component of horizontal shear accompanied by vertical subsidence. Kinematic indicators from slickensides, striations, and fault-plane solutions derived from focal mechanisms show predominantly strike-slip motion with normal dip-slip vectors, consistent with transtensional deformation linked to regional oblique convergence documented for the Andean back-arc.
Paleoseismic trenches and geomorphic mapping reveal evidence for late Pleistocene to Holocene surface-rupturing events, including displaced paleochannels and buried colluvial wedges similar to records from the Romeral Fault System. Historical chronicles from colonial Bogotá describe felt shaking and ground fracturing that researchers have tentatively associated with the Usme Fault or nearby structures. Instrumental earthquakes in the 20th and 21st centuries recorded by the Seismological Network of Colombia include events with locations and focal depths compatible with activity on the Usme Fault, though attribution remains complex due to the dense fault network of the Eastern Cordillera. Estimated slip rates, derived from geomorphic offsets and radiocarbon dating of organic horizons, suggest millimeters-per-year order motion, implying potential for damaging earthquakes comparable in scale to historic Andean events affecting Tunja and Zipaquirá regions.
Ongoing investigations by institutions such as the Colombian Geological Survey, National University of Colombia, Universidad de los Andes, and international collaborators employ paleoseismology, geomorphology, remote sensing from Landsat and Sentinel-2 satellites, and dense GPS campaigns to refine slip rates and hazard models. Urban seismic risk assessments led by the Mayor's Office of Bogotá integrate probabilistic seismic hazard analyses, building inventory studies, and scenario modeling used by emergency agencies like the National Unit for Disaster Risk Management (UNGRD). Geophysical surveys, including shallow seismic reflection and electrical resistivity tomography near populated sectors, aim to map blind splays and identify liquefaction-prone deposits analogous to those investigated after the Armero tragedy. Continued monitoring through accelerometer arrays and community-based early warning initiatives is prioritized to mitigate earthquake risk for populations in Curripio and other localities along the fault corridor.
Category:Geology of Colombia Category:Seismic faults of South America