Scientists are working on programs to predict where and when an earthquake will occur. They hope to develop an early warning system that can be used to forecast earthquakes so that lives can be saved.
Earthquakes are the most dangerous and deadly or all natural events. They occur in many parts of the world. Giant earthquakes have been recorded in Iran， China， Guatemala， Chile， India， and Alaska. Two of the biggest earthquakes that were ever recorded took place in China and Alaska. These earthquakes measured about 8.5 on the Richter Scale. The Richter Scale was devised① by Charles Richter in 1935， and compares the energy level of earthquakes. An earthquake that measures a 2 on the scale can be felt but causes little damage. One that measures 4.5 on the scale can cause slight damage， and an earthquake that has a reading of over 7 can cause major damage. It is important to note that a reading of 4 indicates an earthquake ten times as strong as one with a reading of 3. Scientists want to be able to predict those earthquakes that have a reading of over 4 on the Richter Scale.
Earthquakes are caused by the shifting of rocks along cracks②， or faults， in the earth’s crust. The fault is produced when rocks near each other are pulled in different directions. The best—known fault in North America is the San Andreas fault in the state of California in the United States.
The nations that are actively involved in earthquake prediction programs include Japan， China， Russia， and the United States. These countries have set up seismic③ networks in areas of their countries where earthquakes are known to occur. These networks are on the alert for warning signs that show the weakening of rock layers that can precede④ an earthquake. Many kinds of seismic instruments are used by the networks to monitor the movements of the earth’s crust. The scientists also check water in deep wells. They watch for changes in the water level and temperature that are associated with movement along faults.
Scientists in China， Russia， and the United States measure radon in ground water. Radon is a gas that comes from the radioactive decay of radium in rocks. The gas flows through the ground and dissolves in underground streams and wells. Scientists speculate that the amount of radon increases in the ground when rocks layers shift， exposing new rock， and thus more radon. Chinese and Russian scientists have reported that in places where stress is building up， the radon levels of the water build up too. When the radon levels of the water subside and drop back to normal readings， an earthquake may occur. United States scientists have also placed radon⑤ monitoring stations in earthquake zones， particularly California. However， all the scientists agree that more data is necessary to prove that radon levels in water are associated with the possible birth of an earthquake.
Earthquake prediction is still a young science. Everyone agrees that earthquakes cannot be predicted with any reliability. Scientists have only a partial understanding of the physical processes that cause earthquakes. Much more research has to be done. New and more up-to-date methods have to be found for collecting earthquake data and analyzing it. However， scientists have had some success in predicting earthquakes. Several small earthquakes were predicted in New York State， in the eastern part of the United States. Chinese scientists predicted a major one in Haicheng in 1975， and Russian scientists predicted a major one in Garm in 1978.
① devisev. 设计；发明；策划；想出
② crackn. 裂缝，裂痕
③ seismicadj. 地震的；因地震而引起的
④ precedev. (顺序，位置或时间上)处在……之前
⑤ radonn. ［化］氡
预测地震
科学家们正致力于研究预报何时何地会发生地震的计划，他们希望开发一种早期报警系统用来预报地震，以挽救人们的生命。
地震是自然灾害中最危险的最致命的，发生在世界许多地方。伊朗、中国、危地马拉、智利、印度和阿拉斯加都有过大地震的记录。有记载的最大两次地震是发生在中国和阿拉斯加。这两次地震经测量约为里氏8.5级。里氏震级是1935年查尔斯·里克特发明的，用来比较地震的能量等级。里氏地震级测出的2级地震可以感觉到，但几乎没什么破坏；测出的4.5级地震能够造成轻微破坏，读数超过7级的地震会带来重大破坏。必须注意的是，读数为4级的地震表明其强度是读数为3级的10倍。科学家想预测那些读数超过里氏4级的地震。
地震是由地壳中的裂缝，或称断层处的岩石发生移位而引起的。当邻近岩石受到不同方向的拉力时便产生了断层。北美洲最著名的断层是位于美国加利福尼亚的圣安德烈亚斯断层。
积极参与地震预测计划的国家包括日本、中国、俄罗斯和美国。这些国家在已知发生地震的地区建立了地震网络，这些网络一直处于戒备状态，搜索着告警的迹象，这些迹象显示出在地震前可能发生的岩层松动的状况。这些网络使用多种地震仪器来监测地壳的运动。科学家还检查深井里的水，观察与断层运动有关的水位与温度的变化。
中国、俄罗斯和美国的科学家测量地下水的氡含量。氡是来自岩石中镭辐射衰变而产生的气体。这种气体溢出地面并溶解到地下溪流和井里。科学家推测当岩层移位时，新岩石露出，产生更多的氮，这样地层中的氡数量就增加了。中国和俄罗斯报告说压力增加的地方，水中氡的含量也会增加。当水中氡的含量下降，回到正常读数时，地震就可能发生。美国科学家也在地震区，特别是加利福尼亚，设置了检测站。不过，所有的科学家都一致认为，需要更多的资料才能证明水中氡的含量和可能发生的地震有关。
地震预测仍然是一门年轻的科学。人们都认为地震不可能可靠地预测。科学家对引起地震的物理过程只是部分了解，还必须作更多的研究，必须找到新的和更先进的方法收集地震数据并加以分析。不过，科学家已经在地震预测方面取得了一些成功：美国东部纽约州的几次小地震就已预测到了，1975年中国科学家预测到了海城大地震，1978年俄罗斯科学家预测了加尔姆大地震。
