The earthquake at a destructive plate boundary is what caused the 2004 Boxing day Tsunami. A destrucive Boundary is when an Oceanic plate is forced down beacuse it is more denser than the continet boundary plate that its is being pushed againts. At one point the oceanic plate gets pushed down a lot suddenly due to an earthquake and the water fills in the gap but then gets forced back up causing waves. When the waves get closer to land they start to rise up because the oceanic floor becomes higher this makes the wave become taller and into a Tsunami.

The earthquake happend at 7.59 UTC after the Indian plate (part of the Indo-Australian plate) suddenly subdected under the Burma plate (which is part of the Euroasian plate.) where rocks collided and held the plates still but due to the pressuare built up they suddenley broke apart causing the earthquake. The earthquake is what caused most of the fatality with just 200,000 deaths but the tsunami claimed another 40,000 with a total of 280,000 deaths