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(yù)測(cè)地震

　　地震可以預(yù)報(bào)嗎?科學(xué)家們正致力于研究預(yù)報(bào)何時(shí)何地會(huì)發(fā)生地震的計(jì)劃，他們希望開(kāi)發(fā)一種早期報(bào)警系統(tǒng)用來(lái)預(yù)報(bào)地震，以挽救人們的生命。

　　地震是自然災(zāi)害中最危險(xiǎn)的最致命的，發(fā)生在世界許多地方。伊朗、中國(guó)、危地馬拉、智利、印度和阿拉斯加都有過(guò)大地震的記錄。有記載的最大兩次地震是發(fā)生在中國(guó)和阿拉斯加。這兩次地震經(jīng)測(cè)量約為里氏8.5級(jí)。里氏震級(jí)是1935年查爾斯·里克特發(fā)明的，用來(lái)比較地震的能量等級(jí)。里氏地震級(jí)測(cè)出的2 級(jí)地震可以感覺(jué)到，但幾乎沒(méi)什么破壞;測(cè)出的4.5級(jí)地震能夠造成輕微破壞，讀數(shù)超過(guò)7級(jí)的地震會(huì)帶來(lái)重大破壞。必須注意的是，讀數(shù)為4級(jí)的地震表明其強(qiáng)度是讀數(shù)為3級(jí)的10倍�？茖W(xué)家想預(yù)測(cè)那些讀數(shù)超過(guò)里氏4級(jí)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(chēng)斷層處的巖石發(fā)生移位而引起的。當(dāng)鄰近巖石受到不同方向的拉力時(shí)便產(chǎn)生了斷層。北美洲最著名的斷層是位于美國(guó)加利福尼亞的圣安德烈亞斯斷層。積極參與地震預(yù)測(cè)計(jì)劃的國(guó)家包括日本、中國(guó)、俄羅斯和美國(guó)。這些國(guó)家在已知發(fā)生地震的地區(qū)建立了地震網(wǎng)絡(luò)，這些網(wǎng)絡(luò)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(dòng)的狀況。這些網(wǎng)絡(luò)使用多種地震儀器來(lái)監(jiān)測(cè)地殼的運(yùn)動(dòng)。科學(xué)家還檢查深井里的水，觀察與斷層運(yùn)動(dòng)有關(guān)的水位與溫度的變化。

　　中國(guó)、俄羅斯和美國(guó)的科學(xué)家測(cè)量地下水的氡含量。氡是來(lái)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(xué)家推測(cè)當(dāng)巖層移位時(shí)，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(guó)和俄羅斯報(bào)告說(shuō)壓力增加的地方，水中氡的含量也會(huì)增加。當(dāng)水中氡的含量下降，回到正常讀數(shù)時(shí)，地震就可能發(fā)生。美國(guó)科學(xué)家也在地震區(qū)，特別是加利福尼亞，設(shè)置了檢測(cè)站。不過(guò)，所有的科學(xué)家都一致認(rèn)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(guān)。

　　地震預(yù)測(cè)仍然是一門(mén)年輕的科學(xué)。人們都認(rèn)為地震不可能可靠地預(yù)測(cè)。科學(xué)家對(duì)引起地震的物理過(guò)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(jìn)的方法收集地震數(shù)據(jù)并加以分析。不過(guò)，科學(xué)家已經(jīng)在地震預(yù)測(cè)方面取得了一些成功：美國(guó)東部紐約州的幾次小地震就已預(yù)測(cè)到了，1975年中國(guó)科學(xué)家預(yù)測(cè)到了海城大地震，1978年俄羅斯科學(xué)家預(yù)測(cè)了加爾姆大地震。雖然這只是個(gè)小小的起步，但畢竟是一個(gè)開(kāi)端

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