The Chixoy-Polochic Fault, also known as Cuilco-Chixoy-Polochic Fault, is a major fault zone in Guatemala and southwestern Mexico. It runs in a light arc from the east coast of Guatemala to Chiapas, following the deep valleys of the Polochic River, Chixoy River and Cuilco River.
The Chixoy-Polochic Fault runs largely parallel to the Motagua Fault situated some 80 km to its south. Both fault zones are onshore extensions of the Bartlett Deep, or Cayman Trench of the Caribbean Sea, which marks the tectonic boundary between the Caribbean Plate and the North American Plate.
The Chixoy-Polochic fault separates the largely crystalline rocks of the Sierra de Chuacús and Sierra de las Minas to the south, from the sedimentary rocks of the Sierra de los Cuchumatanes and the Sierra de Chamá to the north. The fault zone was particularly active during the Laramide orogeny which occurred during the early Tertiary. 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 Mw.
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