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 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.

• 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 ${\displaystyle M_{\mathrm {w} }}$ 1935 Quetta earthquake along the Ghazaband portion of the fault system killed upwards of 35,000 people.^[8]
• 1978, 16 March – A 6.4 ${\displaystyle M_{\mathrm {w} }}$ 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]

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

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