Which earthquake sequence is known for producing the most aftershocks of a major event?

Major megathrust earthquakes commonly generate long aftershock sequences as the crust settles into a new stress balance. The 2011 Tōhoku earthquake, for example, produced thousands of aftershocks, including many strong ones in the days and months after the mainshock. The 2004 Sumatra earthquake also triggered a prolonged sequence across a huge section of the plate boundary. Aftershocks can cause additional damage, complicate rescue efforts, and increase the risk to already weakened buildings. They are a normal but dangerous part of the earthquake cycle.