What caused the christmas day tsunami? what kinds of geographic forces were involved in creating the tsunami? why were so many people caught unprepared?

The Christmas Day Tsunami was caused by a very strong earthquake that has the same impact of the Hiroshima atomic bombing in Japan.

Because of the strong tectonic movement, it had displacement plates and thus created a major wiped out among the cities of Sumatra and Sri Lanka

Many of the citizens were not prepared because there was no advice from the government of the impending tsunami. Many people have died because of the tsunami waves in the affected areas.