Predicting Earthquakes

　　Can earthquakes be predicted? 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 devised 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.

　　How do earthquakes occur? Earthquakes are caused by the shifting of rocks along cracks, 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 seismic 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 precede 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 radon 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. While this is a small start, it is still a beginning.

　　預測地震

　　地震可以預報嗎?科學家們正致力于研究預報何時何地會發(fā)生地震的計劃，他們希望開發(fā)一種早期報警系統(tǒng)用來預報地震，以挽救人們的生命。

　　地震是自然災害中最危險的最致命的，發(fā)生在世界許多地方。伊朗、中國、危地馬拉、智利、印度和阿拉斯加都有過大地震的記錄。有記載的最大兩次地震是發(fā)生在中國和阿拉斯加。這兩次地震經(jīng)測量約為里氏8.5級。里氏震級是1935年查爾斯·里克特發(fā)明的，用來比較地震的能量等級。里氏地震級測出的2 級地震可以感覺到，但幾乎沒什么破壞;測出的4.5級地震能夠造成輕微破壞，讀數(shù)超過7級的地震會帶來重大破壞。必須注意的是，讀數(shù)為4級的地震表明其強度是讀數(shù)為3級的10倍�？茖W家想預測那些讀數(shù)超過里氏4級的地震。

　　地震是怎么發(fā)生的呢?地震是由地殼中的裂縫，或稱斷層處的巖石發(fā)生移位而引起的。當鄰近巖石受到不同方向的拉力時便產(chǎn)生了斷層。北美洲最著名的斷層是位于美國加利福尼亞的圣安德烈亞斯斷層。積極參與地震預測計劃的國家包括日本、中國、俄羅斯和美國。這些國家在已知發(fā)生地震的地區(qū)建立了地震網(wǎng)絡，這些網(wǎng)絡一直處于戒備狀態(tài)，搜索著告警的跡象，這些跡象顯示出在地震前可能發(fā)生的巖層松動的狀況。這些網(wǎng)絡使用多種地震儀器來監(jiān)測地殼的運動。科學家還檢查深井里的水，觀察與斷層運動有關的水位與溫度的變化。

　　中國、俄羅斯和美國的科學家測量地下水的氡含量。氡是來自巖石中鐳輻射衰變而產(chǎn)生的氣體。這種氣體溢出地面并溶解到地下溪流和井里�？茖W家推測當巖層移位時，新巖石露出，產(chǎn)生更多的氮，這樣地層中的氡數(shù)量就增加了。中國和俄羅斯報告說壓力增加的地方，水中氡的含量也會增加。當水中氡的含量下降，回到正常讀數(shù)時，地震就可能發(fā)生。美國科學家也在地震區(qū)，特別是加利福尼亞，設置了檢測站。不過，所有的科學家都一致認為，需要更多的資料才能證明水中氡的含量和可能發(fā)生的地震有關。

　　地震預測仍然是一門年輕的科學。人們都認為地震不可能可靠地預測。科學家對引起地震的物理過程只是部分了解，還必須作更多的研究，必須找到新的和更先進的方法收集地震數(shù)據(jù)并加以分析。不過，科學家已經(jīng)在地震預測方面取得了一些成功：美國東部紐約州的幾次小地震就已預測到了，1975年中國科學家預測到了海城大地震，1978年俄羅斯科學家預測了加爾姆大地震。雖然這只是個小小的起步，但畢竟是一個開端