The 1976 Songpan–Pingwu earthquake that struck Songpan and Pingwu counties in Sichuan, China consisted of three mainshocks on the 16th, 21st, and 23rd (UTC) of August. A 1984 report gave the magnitudes as 7.2, 6.7, and 7.2, respectively (scale not specified). The magnitudes were subsequently recalculated as 6.7, 6.3, and 6.4 on the Mw scale, and 7.0, 6.6, and 6.7 on the Ms scale. These were preceded by an earthquake swarm lasting three years. During the period from August 16 to August 31 there were over 400 aftershocks of magnitude 3.0 or greater.