The earthquake which struck China’s western province of Xinjiang on 12 February 2014 was, at magnitude 6.9 (M6.9) the strongest to occur in the country since the tremor of the same magnitude in April 2010.
According to the United States Geological Survey, the epicentre of the tremor occurred at the northern margin of the Tibetan Plateau, some 270km form the Chinese city of Hotan; several aftershocks of M4.4-M5.3 followed.
At the time of writing, there’s no information available from news media regarding any damage or injuries resulting from the earthquake. Initial data from the USGS do show, however, that local shaking was intense and the organisation’s ‘Pager’ impact estimates suggest a 35% probability of at least one fatality.
Tectonic Setting of the February 12 Tremor
Although subduction zones generate most major earth tremors, other areas of the world are by no means immune from significant earth movements – and collisions between continents are also responsible for generating major tremors. Here, thrust and strike slip faulting (depending on the angle of impact) dominate the fault movements – rather than movement along plate interfaces, as is more likely at a subduction zone.
The Himalayas, and the Tibetan Plateau to the north, are the result of the ongoing collision between the Indian continent and Eurasia. Although there’s no information currently available on the mechanism responsible for today’s ‘quake, fault maps of the region show that strike-slip faults, which accommodate lateral movement of around 30mm per year, dominate the region.
The main fault is the Altyn Tagh fault but there are also a number of broadly parallel subsidiary faults; it is likely that one of these was the source of today’s tremor.
Seismic History of South Western China
Large earthquakes are by no means uncommon in southern and western China, although most of the larger ones of recent years (most notably the M6.9 of 2010, M6.4 of October 2008 and the M7.9 which killed almost 90,000 people in 2008) occurred further east and closer to the northern edge of the Himalayas.
The last significant earthquake to strike in the region occurred in March 2008. That event, slightly further to the west, had a magnitude of M7.2 and displaced an estimated 46500 people, although again there was no reported loss of life. The USGS report on that event attributed it to normal faulting and noted that it “likely reflects the interplay amongst these major tectonic forces, dominated in this location by east-west extension.” The similarities between this and the most recent tremor imply that the source mechanism is likely to be much the same.
In the past China has been the location of many devastating earthquakes whose impact is attributable as much to the high-energy environment (steep slopes are more prone to landslides) and the density of population as to the size of the tremor itself. The collision of continents has caused major earthquakes in the past and will continue to do so in the future.