In this study, aftershock sequences of seven earthquakes of magnitude M ≥ 6.5 were analyzed. Six among these are in the Himalayan region and the remaining one is in the near vicinity in China. The analysis suggests that the number of M ≥ 5 aftershocks and the duration of their occurrence decrease with the decrease of the mainshock magnitude. For the 2008 Sichuan earthquake of M 7.9 there were 136 M ≥ 5 aftershocks, while for 1975 Kinnaur earthquake of M 6.8 there were only 9. The aftershock duration of the Himalayan region earthquakes obeys the exponential law T = AecM, where the A and c are constants associated with regional fault settings. This relation is helpful in providing an estimate of the time for which M ≥ 5 aftershock activity would continue after the occurrence of a M ≥ 6.5 earthquakes.
Figure: Large Himalayan earthquakes and their aftershock sequences
Harsh K. Gupta and Rajesh Rekapalli (2022) Jour. Geol. Soc. India (2022) 98:611-614 https://doi.org/10.1007/s12594-022-2034-x