The 2004 Indian Ocean earthquake was an undersea, megathrust earthquake that occurred on 26 December 2004, with an epicentre off the west coast of Sumatra, Indonesia, triggering a series of devastating tsunamis along coastal fringes of the Indian Ocean. Nagapattinam district was the most affected part of Tamil Nadu, accounting for 6,064 off the 8,009 casualties in the state. Sirkazhi remained mostly unaffected by the tsunami, but the groundwater quality deteriorated where aquifers were close to the water bodies. There was heavy salt water intrusion inland.