The Chixoy-Polochic Fault, also known as Cuilco-Chixoy-Polochic Fault, is a major

fault zone In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectoni ...

Guatemala Guatemala ( ; ), officially the Republic of Guatemala ( es, República de Guatemala, links=no), is a country in Central America. It is bordered to the north and west by Mexico; to the northeast by Belize and the Caribbean; to the east by Hon ...

and southeast

Mexico Mexico (Spanish language, Spanish: México), officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the so ...

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

Chiapas Chiapas (; Tzotzil and Tzeltal: ''Chyapas'' ), officially the Free and Sovereign State of Chiapas ( es, Estado Libre y Soberano de Chiapas), is one of the states that make up the 32 federal entities of Mexico. It comprises 124 municipalities ...

, following the deep valleys of the

Polochic River The Polochic River () is a river in eastern Guatemala. It flows eastwards through a deep valley and flows into Lake Izabal at . The river is navigable for to Panzós. It was used many years ago to transport coffee and timber Lumber is w ...

Chixoy River The Chixoy River or Río Chixoy 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 (located at ), where the Río Salamá and Ri ...

and

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 Cu ...

Extent, slip rate and total displacement

The Chixoy-Polochic Fault is a large, dominantly strike-slip, left-lateral fault that runs largely parallel to the

Motagua Fault The Motagua Fault (also, Motagua Fault Zone) 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. It is conside ...

situated some 45 km to its south. Both fault zones are onshore extensions of the Bartlett Deep, or

Cayman Trench __NOTOC__ The Cayman Trough (also known as the Cayman Trench, Bartlett Deep and Bartlett Trough) is a complex transform fault zone pull-apart basin which contains a small spreading ridge, the Mid-Cayman Rise, on the floor of the western Caribb ...

of the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexic ...

, which marks the tectonic boundary between the

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. Roughly 3.2 million square kilometers (1.2 million square miles) in area, the Caribbean Plate border ...

and the

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Paci ...

. Both faults connect at sea west of the Guatemalan coast. To the west, the Polochic fault may branch onto the Tonala fault of western Chiapas. It does not continue at sea across the Pacific coastal plain and marine shelf. The Chixoy-Polochic fault has total displacement of 125 km, well constrained by the offset of Paleocene or Eocene laramide folds and thrusts. Fault velocity has been estimated at 4.8 ± 2.3 mm/y over the past 10 ky, 2.5–3.3 mm/y over the last 7–10

Myr The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...

, and less than 5 mm/y during the current interseismic cycle.

Seismicity

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. The magnitude 7.5–7.8 M_w 1816 Guatemala earthquake of western Guatemala has been ascribed to the Polochic Fault, although this has been disputed. Most recent recorded fault activity includes at least for slip events between 17 ka and 13 ka BP, and aseismic

surface rupture In seismology, surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a fault affects the Earth's surface. Surface rupture is opposed by buried rupture, where th ...

over some of the past 5 centuries. One or several intermediate to large earthquakes between 850 CE and 1,400 CE, including a cluster of 4 earthquakes over 60 years during the Classic Maya collapse. The fault display a 5 km to 10 km deep zone of microseismicity which may represent a locked zone. Only ≤ 5.6 M_w earthquakes have occurred on the fault since the beginning of regional instrumental records (1920 CE).

References

{{Faults Chixoy Geographic areas of seismological interest Geology of Guatemala Seismic faults of Guatemala