Examples of relocated foreshock sequences.
Observed prior to the a, 4 February 1975 M = 7.3 Haicheng, China earthquake1 (study no. 1, see Fig. 2 and Table S1), b, 28 June 1992 M = 7.3 Landers, California earthquake26 (study no. 6) and c, 16 October 1999 M = 7.1 Hector Mine, California earthquake27 (study no. 16). N and n are the numbers of foreshocks above and below the M − 3.0 lines, respectively. Almost all foreshock magnitudes are below M − 3.0. An aseismic slip origin of foreshocks is suggested in the three cases1,26,27. The Haicheng earthquake has been successfully predicted based on foreshock information2. The three studies imply that far fewer events are observed prior to the foreshock sequences above mmin.