Xinjiang China Earthquake

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Posting Date: February 24, 2003, 11:00:00 AM

A severe earthquake struck the western area of China on Monday, February 24, 2003, at about 10:03 a.m. local time (02:03 UTC). The U. S. Geological Survey (USGS) has initially estimated the moment magnitude (Mw) to be 6.3, with a focal depth of about 4 miles (6 km). The quake was centered at the western edge of Xinjiang province near the border with Kyrgyzstan, about 62 miles (100 km) from Kashi, Xinjiang. It was felt as far as 621 miles (1,000 km) to the northeast in the regional capital of Urumqi. Most of the damage was inflicted in Bachu County, which has a population of about 370,000. Preliminary indications suggest the earthquake occurred along the southern piedmont fault of the Tienshan mountain range (the southern Tienshan fault), which is the most active tectonic feature within the Eurasian continent. The fault is located where the Indian plate collides with the Eurasian plate, resulting in the rise of the world's highest plateau and mountain range, the Himalayas. The Tienshan mountain range lies at the northern edge of this plate boundary zone and accounts for roughly one half to one third of the total India-Eurasia plate motion (about 50 mm/yr). The Tarim basin thrusts underneath the Tienshan Mountains along this fault, and also accounts for roughly half of the total horizontal convergence (about 20 mm/yr) between the basin and the stable European plate in the north. Frequent moderate to large thrust earthquakes occur on this fault. There were eight earthquakes here with magnitudes of M > 6.0 during the last two decades, with the largest being a magnitude Mw = 6.9 event in 1985 that was located 124 miles (200 km) west. The largest historical earthquake in this area was a magnitude 8.2 event in 1902. While earthquakes are relatively common in the western part of China, today's was devastating. Initial reports indicate that damage was extensive, with more than 1,000 collapsed homes and school buildings. In the town of Chongku Qiake, every house in the area was damaged, according to one witness, and some 90% of the population were without shelter. The numbers of casualties and injured have continued to grow, reaching at least 257 killed and at least 1,000 injured as of Monday evening. Chinese officials consider today's earthquake to be the most severe to hit the Xinjiang region since 1949.

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Posting Date: February 24, 2003, 11:00:00 AM