The 6.9 earthquake late on Sunday night caused widespread damage and has so far killed almost 100 people, mostly in northern Lombok, east of Bali.
GNS Science seismologist John Ristau says the largest aftershocks are often around one magnitude less - so possibly up to a 6, which could further damage weakened buildings.
He says it may not happen at all - or it could take months, as in Christchurch's major 6.2 earthquake.
Ristau says it could have been a result of the 7.1 magnitude quake five months earlier in Canterbury.
