Tsunamis most frequently occur in countries bordering the Pacific Ocean around the Pacific Rim. This area also covers the region referred to as the Ring of Fire, a place known for severe tectonic-plate shifts. The earthquakes caused by the plates movement set the water in motion to create tsunami-strength waves.
The high frequency of tsunamis around the Ring of Fire occurs because earthquakes are the main triggers for tsunamis. However, they can also result from underwater mudslides, asteroid impacts and volcanoes, giving rise to rare tsunamis in the Caribbean and Mediterranean. About 80 percent of tsunamis occur along the Pacific Rim. Tsunami waves build bigger in shallow coastal waters than in deeper waters, as was seen along beaches in Thailand and Indonesia in 2004.
The areas most likely to see a tsunami are monitored by Deep-ocean Assessment and Reporting of Tsunamis buoys that measure pressure changes on the ocean floor and send tsunami warnings to vulnerable areas. As the tsunami approaches the coast, the water level on the shoreline retreats, signalling a warning of an incoming tsunami. Because tsunamis travel extremely fast, up to 500 mph, it's impossible for monitoring agencies to give long-term warnings. Typically between 6 to 7 tsunamis occur every century.