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.