In December 2004, tsunamis (ocean waves created by an undersea earthquake) spread throughout the Indian Ocean from Thailand to Somalia, killing over 200,000 people and injuring thousands more along the affected shores. Tsunamis generated by earthquakes can travel at speeds up to 600 miles (970 kilometers) per hour. The earthquake, measuring 9.0 on the Richter Scale, resulted from a rupture in Earth's crust more than 600 miles (960 kilometers) long. The earthquake's epicenter was about 100 miles (160 kilometers) off the north coast of Indonesia's Sumatra island at a depth of about 6 miles (9 kilometers). It was the strongest earthquake since 1964 and tied a 1952 quake in Kamchatka, Russia, as the fourth strongest since such measurements began in 1899.
Earthquakes are among the most powerful events on earth, and their results can be terrifying. A severe earthquake may release energy 10,000 times as great as that of the first atomic bomb. Rock movements during an earthquake can make rivers change their course. Earthquakes can trigger landslides and tsunamis that cause great damage and loss of life.
On average, a powerful earthquake occurs less than once every two years. At least 40 moderate earthquakes cause damage somewhere in the world each year. Scientists estimate that more than 8,000 minor earthquakes occur each day without causing any damage. Of those, only about 1,100 are strong enough to be felt.
World Book editors have compiled a collection of articles that examine earthquakes, the damage they cause, and how to minimize their destruction.
Photo: A tsunami that devastated coastal areas bordering the Indian Ocean in December 2004 killed more than 200,000 people and destroyed property in dozens of countries, including these buildings in Phi Phi, Thailand. The tsunami resulted from a massive earthquake on the floor of the Indian Ocean.
©Lana Slivar, Reuters