The Chixoy-Polochic Fault, also known as Cuilco-Chixoy-Polochic Fault, is a major fault zone in Guatemala

Guatemala

Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...

 and southwestern Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

. It runs in a light arc from the east coast of Guatemala to Chiapas

Chiapas

Chiapas officially Estado Libre y Soberano de Chiapas is one of the 31 states that, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 118 municipalities and its capital city is Tuxtla Gutierrez. Other important cites in Chiapas include San Cristóbal de las...

, following the deep valleys of the Polochic River

Polochic River

The Polochic River is a 194 km long river in eastern Guatemala. It flows eastwards through a deep valley and flows into Lake Izabal at . The river is navigable for length of 30 km to Panzós. It was used many years ago to transport coffee and timber, but most commercial transport in the river valley...

, Chixoy River

Chixoy River

The Chixoy River or Río Negro is a river in Guatemala. The river is called Río Negro from its sources in the highlands of Huehuetenango and El Quiché until it reaches the Chixoy hydroelectric dam , where the Río Salamá and Rio Carchela converge with the Río Negro...

 and Cuilco River

Cuilco River

Río Cuilco is a river in Guatemala. The river's sources are located in the Sierra Madre just north of Cajolá where it is called Río Blanco. The Río Blanco joins the Las Manzanas River which in turn joins the San Isidro River to form the Cuilco river...

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The Chixoy-Polochic Fault runs largely parallel to the Motagua Fault

Motagua Fault

The Motagua Fault is a major, active left lateral-moving transform fault which cuts across Guatemala. It forms part of the tectonic boundary between the North American Plate and the Caribbean Plate...

 situated some 80 km to its south. Both fault zones are onshore extensions of the Bartlett Deep, or Cayman Trench of the Caribbean Sea

Caribbean Sea

The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....

, which marks the tectonic boundary between the Caribbean Plate

Caribbean Plate

The Caribbean Plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the north coast of South America....

 and the North American Plate

North American Plate

The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

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The Chixoy-Polochic fault separates the largely crystalline rocks of the Sierra de Chuacús

Sierra de Chuacús

The Sierra de Chuacús is situated in the central highlands of Guatemala, and runs southeast from El Quiché to Baja Verapaz. Its northwestern border is marked by the Chixoy River basin in Uspantán, which separates it from the Sierra de los Cuchumatanes. Its eastern border is marked by the Salamá...

 and Sierra de las Minas

Sierra de las Minas

Sierra de las Minas is a mountain range in eastern Guatemala, extending 130 km west of the Lake Izabal. It is 15–30 km wide and bordered by the valleys of the rivers Polochic in the north and the Motagua in the south. Its western border is marked by the Salamá River valley which separates it...

 to the south, from the sedimentary rock

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

s of the Sierra de los Cuchumatanes

Sierra de los Cuchumatanes

The Sierra de los Cuchumatanes is the highest non-volcanic mountain range in Central America. Its elevations range from 500 m to over 3,800 m, and it covers a total area of ±16,350 km². With an area of 1,500 km² situated above 3,000 m, it is also the most extensive highland region in Central...

 and the Sierra de Chamá to the north. The fault zone was particularly active during the Laramide orogeny

Laramide orogeny

The Laramide orogeny was a period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute, as is the cause. The Laramide...

 which occurred during the early Tertiary

Tertiary

The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...

. While recent seismic activity is more prominent in the Motagua fault, some studies suggest the Chixoy-Polochic Fault is still capable of producing major earthquakes, like the 1816 Guatemala earthquake with an estimated magnitude of 7.5 - 7.8 M_w

Moment magnitude scale

The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...

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