An earthquake is a tremor of the earth's surface usually triggered by the release of underground stress along fault lines. This release causes movement in masses of rock and resulting shock waves. In spite of extensive research and sophisticated equipment, it is impossible to predict an earthquake, although experts can estimate the likelihood of an earthquake occurring in a particular region.
In 1935, American seismologist (地震学家) Charles Richter developed a scale that measures the magnitude of seismic waves. Called the Richter scale, it rates earth tremors on a scale from 1 to 9, with 9 being the most powerful and each number representing an increase of ten times the energy over the previous number. According to this scale, any quake that is higher than 4.5 can cause damage to stone buildings; quakes rated a magnitude of 7 and above are considered very severe. A less-known scale, the Mercalli scale (麦氏震级), was devised by Italian seismologist Giuseppe Mercalli to measure the severity of an earthquake in terms of its impact on a particular area and its inhabitants and buildings.
Some earthquakes are too small to be felt but can cause movement of the earth, opening up holes and displacing rocks. Shock waves from a very powerful earthquake can trigger smaller quakes hundreds of miles away from the epicenter. Approximately 1,000 earthquakes measuring 5.0 and above occur yearly. Earthquakes of the greatest intensity happen about once a year and major earthquakes (7.0-7.9) occur about 18 times a year. Strong earthquakes (6.0-6.9) occur about 10 times a month and moderate earthquakes (5.0-5.9) happen more than twice daily. Most earthquakes are not even noticed by the general public, since they happen either under the ocean or in unpopulated areas. Sometimes an earthquake under the ocean can be so severe, it will cause a tsunami, responsible for far greater damage.
The greatest danger of an earthquake comes from falling buildings and structures and flying glass, stones and other objects.
If you live in an earthquake-prone area, here are some steps that can be taken to minimize risks:
Affix bookcases, cabinets, refrigerators and furniture to the walls. 将书架、橱柜、冰箱和家具固定在墙上。California and Japan sell silicone putty kits that can be used to stick dishes and other breakables to the walls.
Fit cabinets with "childproof locks," so doors will remain closed and items won't fly out. 锁好橱柜。
Have a backpack prepared and attached to the bed, containing shoes, a flashlight and batteries, keys, money, first-aid supplies and medicines, a knife, food, water, ID and insurance information. Attaching the pack to the bed helps to insure that it will not be thrown around during an earthquake. 准备好应急包。
Keep shoes next to your bed, so you can put them on as soon as a quake begins. 将鞋放在床边。
Have a family evacuation plan including phone numbers and a safe place to which to evacuate. 做应对地震的演习。
Establish escape routes from each room in the house. 确定逃跑路线。
If you are in an earthquake:
If you are indoors, find a secure location to wait out the quake, such as under a heavy table or desk, or in an interior hallway where you can brace yourself between two walls. Doorways are among the safest places to stand, thanks to the strong beams overhead. However, watch out for swinging doors. Stay away from windows. 如在室内，躲在安全的地方。
If you are outdoors, try to get into an open area, away from falling buildings, power lines, trees, etc. 如在室外，紧急疏散到空旷地带。
If you are in a crowded public area, crouch down, with your hands protecting your head and neck. 如在人口密集的地方，蹲在地上，保护住头颈。
If you are in your car, pull over to the side, away from power lines and overpasses, and stay inside the car until the shaking has subsided. 如在车内，躲着一角，避开电线和车顶，直到震动停止。
Be sure to put on shoes immediately, to avoid injury from stepping on broken glass and objects. 穿好鞋，以防被玻璃和其他物件所伤。
Check yourself and others for injuries. 检查伤口。
Check for gas and water leaks and damage to electrical wires. 关闭煤气、水管和电线。
Survey the exterior of your home for structural damage to the chimney, roof, foundation and walls. 检查房屋状况。
Do NOT use your automobile unless there is an emergency. 除非紧急，不要用汽车。
If you must leave the area, try to leave word where you can be contacted. 如果必须离开，留下你的联系信息。
REMEMBER that there may be aftershocks, which can also cause great damage to your surroundings. Be prepared! 小心余震！
（来源：answers.com 英语点津 Annabel 编辑）