Yesterday's magnitude 7.8 earthquake in southeastern Iran, the most powerful in that country in more than 50 years, occurred near the Pakistan border in a region of complex plate tectonics. Caught between the Arabian Plate, which is moving northward to collide with the Eurasian Plate, and the Indian Plate, which has been colliding with the Eurasian Plate for at least 55 million years, a fragment of oceanic crust, known as the Makran Wedge, is forced to subduct beneath the Iran-Pakistan border region.
The opening of the Red Sea, which began about 40 million years ago, split the Arabian Plate from the African Plate. This rifting extended eastward, forming the Gulf of Aden, about 20 million years ago, and southward through Africa to produce the East African Rift, which will eventually split that continent. As the Red Sea and Gulf of Aden continue to open, the Arabian Plate is forced northward, closing both the Persian Gulf and the Gulf of Oman. Caught between the Arabian and Indian Plates and forced northward as well, the Makran Wedge began to subduct beneath southern Eurasia during the Miocene Period (about 20-15 million years ago), producing the Baluchistan Volcanic Arc across southeastern Iran and eastern Pakistan.
While most Iranian earthquakes arise from compression between the Arabian and Eurasian Plates and most earthquakes in Pakistan result from the collision of the Indian and Eurasian Plates, yesterday's earthquake developed within the Makran subduction zone, about 50 miles deep, where that oceanic wedge continues to dive beneath the southern edge of Eurasia. Tremors from the powerful quake were felt throughout much of the Middle East.
