About 10 minutes after the S-wave's arrival and while surface waves were still being recorded, a M 2.8 event occurred south of Lassen Peak. Film records showed 9 more earthquakes in the first hour, and 22 events were identified during the first 24 hours. Although most were M 1 or smaller, at least two and perhaps as many as four were of magnitude greater than or equal to 2. Nine were detected by the RTP system. Three more small events occurred SW of Lassen Peak two days after the M 7.5 earthquake, with two additional events on 5 July.
Squares mark seismic stations.
Courtesy of S. Walter.