The initial jolt rocked Qinghai province on August 28 with a magnitude of 6.2 at a relatively shallow depth of only 6 miles.
China’s state-run Xinhua news agency reports that tunnels in a coal mine very near the epicenter caved in during Friday’s temblor.
It noted that all of the miners were above ground when the quake struck.
The main quake and strongest of the 350 aftershocks also triggered landslides that blocked a main road in the district of Da Qaidam.
Shaking was felt strongly in the large cities of Delingha and Golmud, according to the China Earthquake Administration.
The area near the epicenter is seismically active and home to ethnic Mongolians and Tibetan farmers and herdsmen. Numerous coal, tin, lead, zinc and copper mines are scattered across the remote region.
A 6.3 magnitude quake there last November injured three people and caused more than 10,000 houses to collapse or be severely damaged.