We apply a grid-search waveform inversion technique to determine moment tensors for 73 small-to-moderate earthquakes that occurred in the Yunnan–Sichuan region of China in 2003 and 2004 and were recorded by a PASSCAL deployment together with 6 small-to-moderate events recorded by the Yunnan province digital seismic network (YDSN) that occurred in 2000 to 2001. The advantage of studying these earthquakes down to an Mw 3.03 is that the large number of solutions present a picture of the interaction of the four tectonic blocks in the region. We find distinct patterns in the orientation of the maximum compressive stress axes derived from the moment tensor solutions. They are compatible with the clockwise rotation of the Eastern Himalayan syntaxis, northeastward compressive motion, and the south-southeast movement of the east Tibetan Plateau crustal material and the counterclockwise rotation at the east of the Red River fault. We also find a subtle variation in source depth for crustal sources across the region.