A Short Note on the Aftershock Duration of Strong to Major Himalayan Earthquakes

Abstract

Abstract Earthquakes of M ≥ 5 tend to be locally damaging, specifically when these are the aftershocks of larger earthquakes, as the main shock would have weakened the structures. For the rescue operations and general well-being of the local residents, it is helpful if an estimate is available as to how long M ≥ 5 aftershocks would continue to occur. Earthquakes M ≥ 6.5 tend to be followed by aftershocks of M ≥ 5. 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.