Chaman Fault

The Chaman Fault is a major, active geological fault in Pakistan and Afghanistan that runs for over 850 km.^[1] Tectonically, it is actually a system of related geologic faults that separates the Eurasian Plate from the Indo-Australian Plate. It is a terrestrial, primarily transform, left-lateral strike-slip fault. The slippage rate along the Chaman fault system as the Indo-Australian Plate moves northward (relative to the Eurasian Plate) has been estimated at 10 mm/yr or more.^[1] In addition to its primary transform aspect, the Chaman fault system has a compressional component as the Indian Plate is colliding with the Eurasian Plate. This type of plate boundary is sometimes called a transpressional boundary.^[2]

From the south, the Chaman fault starts at the triple junction where the Arabian Plate, the Eurasian Plate and the Indo-Australian Plate meet, which is just off the Makran Coast of Pakistan. The fault tracks northeast across Balochistan and then north-northeast into Afghanistan, runs just to the west of Kabul, and then northeastward across the right-lateral-slip Herat fault, up to where it merges with the Pamir fault system north of the 38º parallel.^[3] The Ghazaband and Ornach-Nal faults are often included as part of the Chaman fault system. South of the triple junction, where the fault zone lies undersea and extends southwest to approximately 10ºN 57ºE, it is known as the Owen Fracture Zone.

While there is general agreement that the fault is slipping at a rate of at least 10 mm/yr, there is a report of volcanic rocks in Pakistan dated to 2 m.y. BP which have been offset such as to indicate a slip rate of 25–35 mm/yr.^[4] Offsets have been described throughout the fault in Pakistan that are young enough that “only the alluvium of the bottom of active dry washes is not displaced.”^[5]

The parallel mountain ranges of eastern Balochistan, (east to west) the Kirthar Mountains, the Khude Mountains, the Zarro Mountains, the Pab Mountains and the Mor Mountains, are a result of the compressional plate boundary and are aligned parallel to the Chaman fault movement. The fault itself is west of these ranges.

Significant earthquakes along the fault

• 1505, 5 July or 6th – An earthquake created a 60 km long surface rupture along a transverse fault in the Chaman system with several meters of vertical offset. This transverse fault is sometimes called the Paghman fault.^[6]
• 1892, 20 December –^[6][7]
• 1935, 31 May – The 7.7 M_w 1935 Balochistan earthquake along the Ghazaband portion of the fault system killed upwards of 35,000 people.^[8]
• 1978, 16 March – A 6.4 M_w earthquake created a 5 km long rupture with up to 4 cm of left-lateral offset, and a smaller amount of vertical slip as the eastern wall of the fault dropped down.^[9]

Notes

1. ^ ^{a b} "USGS Unveils How Earthquakes Pose Risks to Afghanistan" News Release, 30 May 2007, United States Geological Survey
2. ^ "Earthquakes Pose a Serious Hazard in Afghanistan" Fact Sheet 2007–3027, April 2007, United States Geological Survey
3. ^ Fig.2 Chaman fault System associated with Indian Plate Boundary (April 2008) "Chaman Fault System (CFS) – a Prominent Seismo-tectonic Feature In Pakistan" Cowasjee Earthquake Study Centre Ned Newsletter 8(1): pp. 2–3, p.2
4. ^ not viewed, cited by Lawrence , R. D.; Khan, S. Hasan and Nakata, T. (1992) "Chaman fault, Pakistan-Afghanistan" In Bucknam, R. C. and Hancock, P. L. (eds.) (1992) Major active faults of the world—Results of IGCP project 206 Annales Tectonicae 6(supplement): pp. 196–223
5. ^ Lawrence, R. D.; Khan, S. Hasan and Nakata, T. (1992) "Chaman fault, Pakistan-Afghanistan" In Bucknam, R. C. and Hancock, P. L. (eds.) (1992) Major active faults of the world—Results of IGCP project 206 Annales Tectonicae 6(supplement): pp. 196–223, p. 204
6. ^ ^{a b} Quittmeyer, R. C. and Jacob, K. H.(1979) "Historical and modern seismicity of Pakistan, Afghanistan, northwestern India, and southeastern Iran" Bulletin of the Seismological Society of America 69: pp. 773–823, p.791
7. ^ Wheeler, Russell L.; Bufe, Charles G.; Johnson, Margo L. and Dart, Richard L. (2005) "Seismotectonic map of Afghanistan, with annotated bibliography" U.S. Geological Survey Open-File Report 2005-1264, p.9
8. ^ Carayannis, George Pararas (2007) "The Earthquake of 30 May 1935 in Quetta, Balochistan"
9. ^ Yeats, R. S.; Lawrence, R. D.; Jamil-Ud-Din, Syed and Khan, S. H. (1979) "Surface effects of the 16 March 1978 earthquake, Pakistan-Afghanistan border" In Farah, Abul and DeJong, Kees A. (eds.) (1979) Geodynamics of Pakistan Geological Survey of Pakistan, Quetta, pp. 359–361

External links

• Photograph of the surface expression of the Chaman fault by Hiroyuki Tsutsumi

See also

• 2008 Pakistan earthquake

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