Chaman Fault Explained

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 38° 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 10°N 57°E, 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]

See also

• List of faults in Pakistan
• 2008 Ziarat earthquake
• 2013 Balochistan earthquakes

External links

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

Notes and References

1. http://www.usgs.gov/newsroom/article.asp?ID=1685 "USGS Unveils How Earthquakes Pose Risks to Afghanistan"
2. http://pubs.usgs.gov/fs/2007/3027/pdf/FS07-3027_508.pdf "Earthquakes Pose a Serious Hazard in Afghanistan"
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. 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