BOSTON, July 22, 2013 – According to catastrophe modeling firm AIR Worldwide, rural communities in northwest China’s Gansu province experienced a devastating earthquake on July 21 at 23:45:56 UTC (July 21, 7:45 a.m. local time). Because of its low population and agricultural economy, there is little exposure in Gansu province and insurance take-up rates are low. While damage is likely to be serious and potentially widespread, AIR does not expect significant insured losses from this event.
The magnitude of the earthquake has been estimated as 6.6 by the China Earthquake Data Center, 5.9 by the United States Geological Survey, and 6.0 by the European Alert System. Tremors were felt in the provincial capital of Lanzhou 177 km (110 mi) north, and as far away as Xi’an, 400 km (250 mi) to the east. It was a shallow event, occurring at a depth of about 10 km (6 mi), and has been followed by a series of at least seven aftershocks, including one of M5.6.
“The event occurred in the west Qingling Mountain Range in Gansu province,” said Dr. Bingming Shen-Tu, senior principal scientist at AIR Worldwide. “The epicenter is about 230 km (143 mi) north-northwest of the Longmenshan fault, which ruptured during the 2008 M7.9 Wenchuan earthquake. It falls within the North-South Seismic Belt in central China. The tectonics of the epicentral area are poorly understood
because of its mountainous topography. Several large earthquakes, including two events of M8 in 1654 and 1879, were located within 150 km (93 mi) of this event. But none of these large events have been associated with any mapped active faults, and none of the active faults in this area have been mapped well enough to provide insight into the seismogenic activities in this region.”
According to the Xinhua News Agency, eight towns in remote and mountainous areas have been seriously damaged in the earthquake and the flooding and mudslides that followed. Landslides have blocked the major railway linking Longxi County and
Tianshui City and several roads, cutting off 13 townships and obstructing rescue and
recovery work. The continuing heavy rain in the region is also hampering rescue
operations and increasing the need to provide shelter.
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Dr. Shen-Tu noted, “The rupture occurred in an arid and hilly farming area on the border of Minxian County and Zhangxian County in the city of Dingxi. This is a lightly-populated region of mountains, desert and pastureland. The agricultural area around Dingxi however, which is about the size of New Jersey, has rolling hills terraced for crops and fruit trees and a more concentrated population of about 2.7 million.”
According to AIR, Gansu is one of the poorest provinces in China, and it has many old buildings, typically of adobe or unreinforced masonry (brick) with tiled roofs. Structures of this type are highly vulnerable to ground shaking. Gansu Television reported that 20% of buildings in the earthquake-stricken zone have collapsed and that 60% show cracks. The Dingxi city government website claims that nearly 2,000 homes have been badly damaged or destroyed. Residents of Dingxi reported however that the shaking there lasted about one minute, and wasn’t strong enough to cause major damage in urban areas, where buildings are more solidly constructed.
Telephone service to many communities was cut and over 14,000 households lost their power supply. Hundreds of troops have been sent to the area to aid rescue operations and the Chinese Red Cross has sent 200 tents, 1,000 sets of household items, and 2,000 jackets as well as teams of rescue workers from Lanzhou and Beijing.
AIR will continue to monitor the situation and will provide updates as warranted.