SHAFAQNA – The Grand Ayatollah Sistani answered questions about the Salaatal-Ayaat for aftershocks (smaller earthquakes following the main shock of a large earthquake).
Question 1: In areas prone to earthquakes where frequent aftershocks occur; is it Wajib to perform the Salaatal Ayaat for every aftershock?
Question 2: How long after the earthquake, must the Salaatal-Ayaat be performed?
Answer 1: If it is felt and they are separated from one another which customarily/usually is counted as another earthquake, according to Wajib precaution must perform the Salaat.
Answer 2: After a moderate amount of time which is usually connected to the time of the earthquake, about 20 minutes after the earthquake.
Source: PERSIAN SHAFAQNA