Buesaco-Aranda Fault

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Buesaco-Aranda Fault
Falla Buesaco-Aranda
Map showing the location of Buesaco-Aranda Fault
Map showing the location of Buesaco-Aranda Fault
Etymology Buesaco & vereda Aranda
Country  Colombia
Region Andean
State Nariño
Cities Pasto
Range Central Ranges, Andes
Part of Romeral Fault System
Length 29 km (18 mi)
Strike NE-SW
Dip Vertical
Displacement 1–5 mm (0.039–0.197 in)/yr
Plate North Andean
Status Active
Earthquakes 1995 Pasto (ML 5.0)
Type Strike-slip fault
Movement Dextral
Age Quaternary
Orogeny Andean

The Buesaco-Aranda Fault (Spanish: Falla Buesaco-Aranda) is a dextral strike-slip fault in the department of Nariño in southwestern Colombia. The fault has a total length of 29 kilometres (18 mi) and runs along an average northeast to southwest strike in the Central Ranges of the Colombian Andes. The 1995 Pasto earthquake is associated with the active fault showing high amounts of displacement. The earthquake caused seven fatalities.


The fault is named after Buesaco and Aranda, a vereda of Pasto.[1] Other sources call the fault by the general name of Silvia-Pijao Fault.[2]


The Buesaco-Aranda Faults, which are parallel, extend in a north-northeast to northeast direction from near the Galeras Volcano in southwestern Colombia. The Buesaco Fault is located 5 kilometres (3.1 mi) to the west of the Aranda Fault. On the eastern block of the Buesaco Fault, the basement rock consists of basic volcanic, andesite and dark sedimentary rocks which probably developed in a marginal basin environment during Early Cretaceous time. On the western block of the fault are a group of low-grade metamorphic rocks which consist of greenschist, amphibolite, quartzite and black schist, all of Paleozoic age. The area is mostly covered by a Pliocene blanket of pyroclastic rocks and calc-alkaline lavas, Quaternary lahar deposits and fluvio-glacial deposits.[1]

The Buesaco-Aranda Fault has a very outstanding fault line trace, strongly deformed landforms of Pleistocene-Holocene age, clear break on slopes of eroded fault scarps, and fault scarps facing either southeast or northwest, which are characteristic of transcurrent faults. Systematic right lateral deflections of some stream gullies, river channels, and ridges are visible. Offset features in confined alluvial deposits and in recent alluvial fans have fresh scarp morphology. The net cumulative horizontal slip calculated is 188 ± 14 metres (617 ± 46 ft), with 160 ± 10 metres (525 ± 33 ft) of displacement in offset landforms along the Aranda Fault.[1] The Morasurco volcano is enclosed by the Buesaco and Aranda Fault segments.[3]


The last strong seismic event occurred on the Buesaco Fault near Pasto at 18:23 on March 4, 1995; the magnitude of the biggest shock was M 5.0.[4] Seven people died as a result of the earthquake and the aftershocks.[5]

See also


  1. ^ a b c Paris et al., 2000a, p.26
  2. ^ Plancha 5-18, 2015
  3. ^ Tibaldi & Romero, 2000, p.360
  4. ^ (in Spanish) El sismo del 4 de marzo 1995, Pasto
  5. ^ (in Spanish) Siete muertos dejaron cuatro sismos en Pasto - El Tiempo


  • Paris, Gabriel; Michael N. Machette; Richard L. Dart, and Kathleen M. Haller. 2000a. Map and Database of Quaternary Faults and Folds in Colombia and its Offshore Regions, 1–66. USGS. Accessed 2017-09-18.
  • Tibaldi, Alessandro, and Jaime Romero León. 2000. Morphometry of late Pleistocene-Holocene faulting and volcanotectonic relationship in the southern Andes of Colombia. Tectonics 19. 358–377. Accessed 2017-09-24.


  • Paris, Gabriel; Michael N. Machette; Richard L. Dart, and Kathleen M. Haller. 2000b. Map of Quaternary Faults and Folds of Colombia and Its Offshore Regions, 1. USGS. Accessed 2017-09-18.
  • Gómez Tapias, Jorge; Nohora Emma Montes Ramírez; Álvaro Nivia Guevara, and Hans Diederix. 2015. Plancha 5-18 del Atlas Geológico de Colombia 1:500,000, 1. Servicio Geológico Colombiano. Accessed 2017-09-21.
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