A powerful earthquake in western China killed at least 400 people, injured 10,000 and left many others buried under debris on Wednesday, Chinese state media reported. The quake, which struck at 7:49 a.m. in Qinghai Province, had a magnitude of 7.1, according to China’s earthquake agency. The China Earthquake Networks Administration said the quake struck in Yushu County, a remote and mountainous area sparsely populated by farmers and herdsmen, most of them ethnic Tibetans. The region, pocked with copper, tin and coal mines, is also rich in natural gas. More than 90,000 people live in the county, which borders Tibet and is about a 12-hour drive from the provincial capital, Xining. A seismologist, Gu Guohua, said in an interview with the national broadcaster CCTV that 90 percent of the homes in the county seat, Jeigu, had collapsed. The houses, he said, were of “quite poor quality,” with many constructed of wood, mud and brick.