Friday, 20 December 2013

Magnitude 5.6 Earthquake in northwest Sindh Province, Pakistan.

The United States Geological Survey recorded a Magnitude 5.6 Earthquake at a depth of 5.9 km roughly 45 km to the northwest of Nasirabad in northwest Sindh Province, Pakistan, slightly before 0.30 am local time on Friday 20 December 2013 (slightly before 7.30 pm on Thursday 19 December GMT). This is a large quake, in an area where few buildings are quakeproofed, and has the potential to be quite dangerous. There are no reports of any damage or casualties at the current time (roughly 4.30 hours after the event), but the United States Geological Survey estimate that there is a 35% chance of fatalities having occurred as a result of this quake.

The approximate location of the 20 December 2013 Sindh Earthquake. Google Maps.

The quake occurred slightly to the east of the boundary between the Indian Plate, to the southeast and the Eurasian Plate to the west. The Indian Plate is moving northwards at a rate of 5 cm per year, causing it to impact into Eurasia, which is also moving northward, but only at a rate of 2 cm per year. When two tectonic plates collide in this way and one or both are oceanic then one will be subducted beneath the other (if one of the plates is continental then the other will be subducted), but if both plates are continental then subduction will not fully occur, but instead the plates will crumple, leading to folding and uplift (and quite a lot of Earthquakes). The collision of the Indian and Eurasian plates has lead to the formation of the Kirthar Mountains as well as Himalayan Mountains, the Tibetan Plateau, and the mountains of southwest China, Central Asia and the Hindu Kush.

In addition to this the Arabian Plate is being subducted along the Makran Subduction Zone to the south of Balochistan, passing under the province, which sits on the southern Eurasian Plate, as it sinks into the Earth. The two plates do not move past one another smoothly, but continuously break apart and then stick together until the pressure builds up sufficiently to cause another break, leading to Earthquakes in the process. In addition to this the Eurasian Plate is scraping sedimentary material off the leading edge of the Arabian Plate as it is subducted, forming an accretionary prism of material over the subduction zone up to 7.5 km think in places. This takes the form of a series of parallel folded hill ranges running east to west across the province and Sistan & Baluchistan Province in neighbouring Iran.


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