The Eastern Frontal Fault System ( es, Sistema de Fallas de la Falla Frontal de la Cordillera Oriental) is a megaregional system of oblique and thrust faults cross-cutting Colombia from Ecuador in the south to Venezuela in the north. The system from south to north covers ten out of 32

departments Department may refer to: * Departmentalization, division of a larger organization into parts with specific responsibility Government and military *Department (administrative division), a geographical and administrative division within a country, ...

of Colombia; Nariño, Putumayo, Cauca, Huila, Caquetá, Cundinamarca,

Meta Meta (from the Greek μετά, '' meta'', meaning "after" or "beyond") is a prefix meaning "more comprehensive" or "transcending". In modern nomenclature, ''meta''- can also serve as a prefix meaning self-referential, as a field of study or ende ...

, Boyacá, Casanare and Arauca. The Eastern Frontal Fault System underlies and affects the capitals of Putumayo, Mocoa, Caquetá, Florencia, Meta, Villavicencio and Casanare,

Yopal Yopal () is a municipality and capital city of the department of Casanare in Colombia. History During the period of the Spanish colonization of the Americas, the land on which Yopal stands was occupied by the indigenous Achagua people. The ...

. The fault system has a total length of with a cumulative length of the faults of and runs along an average northeast to southwest strike of 042.1 ± 19 bordering and crossing the Eastern Ranges of the Colombian Andes. The fault system forms the boundary between the North Andes microplate and the

South American Plate The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-A ...

. Several segments of the fault system are active, with major

earthquakes An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

occurring in historical times. The 1827 Timaná (M_w 7.7), 1834 Sibundoy (M_w 7.0), 1917 Sumapaz (M_w 7.3), 1967 Neiva (M_w 7.2), 1995 Tauramena (M_w 6.5) and

2008 El Calvario earthquake The 2008 El Calvario earthquake occurred in central Colombia on 24 May and measured 5.9 on the moment magnitude scale. The earthquake occurred at 2:20:43 p.m. (19:20:43 UTC) at the epicenter (El Calvario, Meta). The depth was 35 km; it ...

s (M_w 5.6) are associated with movement of the fault system.

Etymology

The fault system is named after the Eastern Ranges, forming the front with the

Llanos The Llanos (Spanish ''Los Llanos'', "The Plains"; ) is a vast tropical grassland plain situated to the east of the Andes in Colombia and Venezuela, in northwestern South America. It is an ecoregion of the tropical and subtropical grasslands, sav ...

and Caguán-Putumayo Basins.

Description

The Eastern Frontal Fault System is one of the most active and continuous fault systems in Colombia. Several names have been given to it according to where it has been studied along its length. Local common fault names or "sections" from north to south are the Guaicáramo, Yopal, San José, Servitá-Santa Maria, Guayuriba, Algeciras, Mocoa, Florencia and Afiladores Faults. Other less common names include the Pajarito, Colepato, Acacías, and Colonia Faults. The fault system is probably an extension of the

Boconó Fault The Boconó Fault is a complex of geological faults located in the Eastern Ranges of northeastern Colombia and the Mérida Andes of northwestern Venezuela. The fault has a NE-SW orientation; it is a strike-slip fault and has a dextral relative ...

and associated faults of the

Mérida Andes Mérida or Merida may refer to: Places *Mérida (state), one of the 23 states which make up Venezuela *Mérida, Mérida, the capital city of the state of Mérida, Venezuela * Merida, Leyte, Philippines, a municipality in the province of Leyte * ...

in Venezuela and likely continues south as a dextral fault in the Republic of Ecuador. The Eastern Frontal Fault System is the main fault system bounding the Andean Ranges in the west and the lowlands or ''Llanos Orientales'' plains in the east. This fault system extends all the way south to the Jambali Graben in the Gulf of Guayaquil in Ecuador. It is considered to be the actual plate boundary of the South American Plate disconnecting it from the North Andes Block. The Eastern Frontal Fault System extends from near latitude 3°N, north into the Venezuelan Andes, close to San Cristóbal at about latitude 7.5°N. The fault system developed from an initial set of parallel fractures ( strike joints) arising from

distension Distension (spelled distention in many style regimens) generally refers to an enlargement, dilation, or ballooning effect. It may refer to: * Abdominal distension, typically a symptom of an underlying disease or dysfunction in the body, rather th ...

al forces. These dipped westwards, forming the eastern border of a huge Paleozoic to Cretaceous sedimentary basin. Later in the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

, regional uplift and shortening of the crust gave rise to the Eastern Ranges of Colombia. The initial normal faults reversed motion and became thrust faults in the ''Borde Llanero''. The Guaicáramo Fault System deforms late Neogene deposits and is characterised by neotectonic morphology that is some of the most outstanding and continuous in the country.

Segments

The fault system is subdivided into multiple segments.

Guaicáramo Fault System

The Guaicáramo Fault System is composed of three sections of faults, the northern Guaicáramo section of , the central Guaicáramo section of , and the southern Guaicáramo section of .

Yopal Fault

The long Yopal Fault is the easternmost active geologic thrust fault known in northeastern Colombia. North of the city of

, it places

rocks on the west against

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

alluvial deposits of the

Llanos Basin The Llanos Basin ( es, Cuenca Llanos) or Eastern Llanos Basin ( es, Cuenca de los Llanos Orientales) is a major sedimentary basin of in northeastern Colombia. The wikt:onshore, onshore foreland basin, foreland on Mesozoic rift basin covers the dep ...

on the east.

San Pedro-Cumaral Fault

The long San Pedro-Cumaral system is formed by the parallel San Pedro and Cumaral Faults. The faults form well defined fault scarps on Tertiary and

sedimentary rocks that form hilly landscapes, upwarping and tilting of terraces, deflected streams, linear fault ridges, and narrowing of streams on the eastern sides of the faults.

Servitá-Santa María Fault

The long Servitá-Santa María Fault extends close to the east margin of the Eastern Colombian Ranges near the Guaicáramo Fault, east of

Bogotá Bogotá (, also , , ), officially Bogotá, Distrito Capital, abbreviated Bogotá, D.C., and formerly known as Santa Fe de Bogotá (; ) during the Spanish period and between 1991 and 2000, is the capital city of Colombia, and one of the larges ...

. The combined fault is grouped in a system because of their morphologic similarity, geometric characteristics and

activity and includes the Servitá Fault to the south and Santa María and San Pedro de Jagua Faults to the north. Thrusting of Paleozoic rocks over younger formations is seen along faults of this group. The faults offset Jurassic, Cretaceous and Tertiary strata and deform

strata.

Guayuriba Fault

The long Guayuriba Fault is located to the southeast the Servitá-Santa María section. It lies south of and close to the city of Villavicencio, at the base of the eastern front of the Eastern Ranges, and extends along the change of slope between the uplifted range and the flat plains of the

Algeciras Fault

The long Algeciras Fault crosses the southward narrowing Eastern Ranges at an oblique angle, with its southern extension following the western flank. The fault displaces

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

crystalline shield rocks and Mesozoic granites. Neotectonic deformation is suggested by the formation of a narrow and long

pull-apart basin In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments. A pull-apart basin is a structural basin where two overlapping (en echelon) strike-slip faults or a fault bend creates an area of cru ...

filled with

sediments. Younger faults cross the basin diagonally. The fault is part of a set of major strike-slip faults that farther north probably join the Guayuriba Fault, which borders the Eastern Ranges to the northeast.

Garzón-Pitalito Fault

The long Garzón-Pitalito Fault extends along the western slope of the Eastern Ranges southeast from the city of Neiva and crosses the upper part of the Magdalena Valley. In the northern half, the fault places Jurassic to Triassic sedimentary rocks on the eastern side in contact with

alluvium and colluvium on the western side. Along its southern half, the fault places Jurassic-Triassic rocks in contact with Cretaceous rocks. The Garzón-Pitalito Fault strikes toward and merges with the Algeciras Fault to the north. To the south, it passes the towns of Garzón, Altamira, Timaná,

Pitalito Pitalito is a Colombian town and municipality located to the south of the Department of Huila, Colombia over the Valley of the Rio Grande de la Magdalena, 188 km from Huila's capital, Neiva. It is referred to as "''The Valley of Laboyos''" ...

and San Agustín. In Pitalito, it creates a

. The fault appears to dextrally displace the Suaza Fault. The place of the offset is marked by a large shutter ridge near where the

Suaza River Suaza () is a town and municipality in the Huila Department Huila () is one of the departments of Colombia. It is located in the southwest of the country, and its capital is Neiva, Colombia, Neiva. Demography and Ethnography Huila is a de ...

was dammed by huge landslides as a result of the earthquake of November 16, 1827.

Suaza Fault

The long Suaza Fault crosses the western slope of the Eastern Ranges, close to the Upper Magdalena Valley. It puts

crystalline rocks on the east against Jurassic and Cretaceous sedimentary rocks on the west. Mesozoic granites are also displaced by the fault. A broad and long valley along the fault is filled with

sediments. Near the town of

Suaza Suaza () is a town and municipality in the Huila Department, Colombia Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as w ...

, exposures show at least two episodes of neotectonic deformation: 1) early thrusting of Jurassic rocks over older Quaternary deposits, and 2) later deformation affecting the Jurassic rocks, old Quaternary deposits, and the relatively young Quaternary sediments. Most of the fault trace south of the Upper Magdalena valley is poorly located and documented. On the basis of regional correlations, it is believed that the Garzon-Pitalito Fault, the Suaza Fault, and the Algeciras Fault all are continuous southward extensions of the Guaicáramo Fault sections.

Mocoa Fault

The long Mocoa Fault strikes close to the base of the eastern side of the mountain front of the central mountains and coincides with the abrupt change in slope between the Andean Range on the west and the dense forest-covered hilly lowlands on the east. The fault places Cretaceous and Jurassic sedimentary rocks and Tertiary to

volcanics Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...

on the west against

crystalline rocks on the east.

Sibundoy Fault

The long Sibundoy Fault is located in the "Cordillera Centro-Oriental" to the east of the city of Pasto, which is south of where the cordillera splits in two ranges (Eastern and Central Ranges), this location is known as

Colombian Massif The Colombian Massif (from the Spanish Macizo Colombiano), also known colloquially as ''Nudo de Almaguer'', refers to a group of mountains within the Andes of south central Colombia. The massif is mainly within the area of the Cauca, Huila, and ...

. The Sibundoy Fault is probably the southward extension of the Suaza Fault and may well be part of the Afiladores Fault to the south. At the Sibundoy Valley (the locality where the Sibundoy Fault is best studied), the fault displaces

, Jurassic and Cretaceous rocks, and deforms

topographic features.

Afiladores Fault

The long Afiladores Fault runs through a geographic area of the Andes where the

Central Central is an adjective usually referring to being in the center of some place or (mathematical) object. Central may also refer to: Directions and generalised locations * Central Africa, a region in the centre of Africa continent, also known as ...

and Eastern Ranges merge into a single range known as the "Cordillera Centro-Oriental de Colombia". The fault offsets

gneisses and schists, metamorphic Paleozoic rocks, Mesozoic

granitic rocks A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quart ...

, and Tertiary sedimentary deposits. The fault extends south into the Republic of Ecuador and probably connects with the Chingual Fault.

Activity

Several segments of the fault system are active, with major earthquakes occurring in historical times. The 1827 Timaná (Mw 7.7), 1834 Sibundoy (Mw 7.0), 1917 Sumapaz (Mw 7.3), 1967 Neiva (Mw 7.2), 1995 Tauramena (Mw 6.5) and

s (Mw 5.6) are associated with movement of the fault system.