CNN News:美国阿拉斯加发生7.9级地震 已发布海啸预警

AZUZ: Just after midnight on Tuesday, the earth jolted beneath the Gulf of Alaska. This is a Pacific body of water surrounded by southern Alaska.
The earthquake that hit there was powerful, magnitude 7.9. The U.S. Geological Survey says only about three quakes that strong hit the earth in an average year. And it was felt about 175 miles away in the southern Alaska city of Kodiak.
Residents described the tremor as a long slow roll. And though siren sounded and classes were cancelled so schools could serve as emergency shelters, no major damage was reported. Still, people in Kodiak evacuated their homes and headed for high ground.
The reason: a tsunami warning. Earthquakes at sea don't just bring the threat of shaking. This one brought fears of dangerous tsunami waves from the Gulf of Alaska to Hawaii, and the west coast of the U.S. and Canada.
Some people in California were warned to avoid the coastline for 12 hours. Thankfully, the only tsunami waves actually seen were in Alaska and they were small, less than a foot high. Meteorologists say the type of quake that occurred yesterday was the result of a strike-slip fault, when two plates move horizontally against each other. It's not believed to be as dangerous as a thrust fault, when the plate jolts vertically. That can produce major tsunami waves.

SUBTITLE: What is a tsunami?
JENNIFER GRAY, AMS METEOROLOGIST: Tsunami waves or seismic sea waves are a series of waves, not just one that are created when there's an underwater disturbance, like an earthquake or a volcanic eruption.
When an earthquake strikes, the erratic movement of the ocean floor can generate a tsunami. The first wave in this series can occur within minutes of the earthquake or hours. Areas that are closest to the epicenter will experience the waves much sooner than areas far away.
One warning sign of a tsunami is water right along the coast rapidly receding. If you see this or find yourself in a tsunami warned area, seek higher ground immediately and get as far away from the coast as you can. Make sure you stay in that safe place until the tsunami threat has ended.