造成海地地震的原因

Haiti Earthquake Science: What Caused the DisasterBy Andrea Thompson, LiveScience Senior Writer

posted: 13 January 2010 12:46 pm ET
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The major earthquake that struck Haiti Tuesday may have shocked a region unaccustomed to such temblors, but the devastating quake was not unusual in that it was caused by the same forces that generate earthquakes the world over. In this case, the shaking was triggered by much the same mechanism that shakes cities along California's San Andreas fault.
星期二的大地震沉重地打擊了海地，震憾了罕見這樣地震的地區(qū)。不過，世界各地由同樣的力量引發(fā)的這種災難性地震并不罕見。如此說來，是震動了沿加利福尼亞圣安德烈亞斯斷層帶城市的相同機制觸發(fā)了這次地震。

The 7.0-magnitude Haiti earthquake would be a strong, potentially destructive earthquake anywhere, but it is an unusually strong event for Haiti, with even more potential destructive impact because of the weak infrastructure of the impoverished nation.
海地的7.0級地震發(fā)生在任何地方都是具強大潛在破壞性的地震，但是，對海地來說這是異常嚴重的事件，可能具有更大的破壞性影響，因為這個貧困國家的基礎設施非常薄弱。

While reports from the ground on the effects of the quake are spotty because of downed communication lines, geologists can use worldwide measurements of the event as well as their general knowledge of how earthquakes work to piece together a picture of what happened in Haiti.
盡管因為通訊線路中斷，來自當地的地震影響報告各不相同，但是地質學家能夠運用全球通用的評價地震影響的方法，以及他們的地震原理知識拼湊出海地地震事件的面貌。

Sliding plates滑動的板塊

Earthquakes typically occur along the jigsaw-puzzle pieces of Earth's crust, called plates, which move relative to one another, most of the time at an imperceptibly slow pace. In the case of the Haiti quake, the Caribbean and North American plates slide past one another in an east-west direction. This is known as a strike-slip boundary.
地震一般發(fā)生在犬牙交錯的一塊塊地殼（板塊）間。這些板塊相向運動，大部分時間我們察覺不到它們的移動。在這次海地的地震中，加勒比海和北美板塊東西相向滑動。這種滑動稱為走滑邊界（strike-slip boundary）。

Stress builds up in points along the boundary and along its faults where parts of the crust stick; eventually that stress is released in a sudden, strong movement that causes the two sides of the fault to move and generate an earthquake. The fault system that ruptured to cause this quake is called the Enriquillo-Plantain Garden fault system.
壓力沿邊界各點以及地殼部分粘連的斷層增強；最終，壓力在強大的運動中突然釋放，導致斷層的兩面移動，引發(fā)地震。因破裂而引發(fā)地震的斷層系，被稱為恩里基洛－芭蕉園斷層系（Enriquillo-Plantain Garden fault system）。

Major earthquakes are rare in this part of the world in part because the Caribbean is a minor plate, with a fault system that isn't as long as, say, the San Andreas, which is at the boundary between two of the world's largest plates – the Pacific and North American plates.
世界的這部分地區(qū)很少見大地震，其部分原因是加勒比海板塊較小，其斷層系和圣安德烈亞斯不一樣長，處在世界最大的板塊——太平洋和北美板塊之間的邊界上。

The unusually high magnitude of Tuesday’s quake for this region is part of the reason it has likely caused enormous damage to Haiti.
有可能對海地造成巨大破壞的部分原因，是該地區(qū)星期二發(fā)生的異乎尋常的高震級地震。

Intensity and infrastructure 基礎設施的強度

Another factor in the damage that a quake can cause is it intensity. While magnitude is a measurement of how much energy is released by an earthquake, intensity is "simply an estimate or a measure of how strongly that earthquake was felt," said Don Blakeman, an earthquake analyst with the United States Geological Survey.
地震能造成破壞的另一個因素是其強度。震級是測量地震釋放了多少能量的方法，而強度“只是人們感覺地震有多強的估計或測量。”美國地質調查局的地震分析師唐·布萊克曼（Don Blakeman）說。

One factor that influences earthquake intensity is the distance to the epicenter of those who feel the earthquake's effects. In the case of the Haiti quake, the epicenter of the quake was only 10 miles (15 km) southwest of the capital Port-au-Prince and just 6.2 miles (10 km) below the Earth's surface, "which for earthquakes is very shallow," Blakeman told LiveScience.
影響地震強度的一個因素是人們感覺到地震影響的震中距離。海地地震的震中距首都太子港（Port-au-Prince）西南部只有10英里（15公里），在地表以下只有6.2英里（10公里），“對地震而言，這是很淺的。”布萊克曼對LiveScience說。

"So everyone in Port-au-Prince is basically within 30 to 40 km [18 to 25 miles] of the earthquake," he added.
他補充說，“因此，太子港的所有人距震中基本上都在30至40公里（18至25英里）之內。

"The depth of this earthquake in Haiti was very shallow meaning that the energy that was released is very close to the surface," said Carrieann Bedwell of the USGS and NEIC.
美國地質勘探局（USGS）和國家地震信息中心（NEIC）的凱瑞恩·貝德威爾（Carrieann Bedwell）說，“海地地震的深度非常淺，就是說，其釋放的能量離地面非常近。”

In contrast, areas like the Fiji Islands in the South Pacific can experience earthquakes that originate hundreds of miles down in the Earth's crust, which would already put them hundreds of miles away from the earthquake, Blakeman explained. Earthquakes are much deeper in this the South Pacific because instead of two plates sliding past one another, one is descending deep into the Earth below the other, allowing earthquakes to originate much farther down below the surface. This is called a subduction zone.
布萊克曼解釋說，與此相反，南太平洋上的斐濟群島能夠經歷來自地殼以下數百英里的地震，那已經使他們距震中數百英里了。在南太平洋發(fā)生的地震深很多，是因為兩個板塊不是相向交錯滑動，而是其中之一在另一板塊底下沉入地下很深處，使得地震在地表以下深得多的地方引發(fā)地震。這被稱為俯沖帶（subduction zone）。

Another unfortunate factor in the intensity equation for Haiti is the infrastructure involved.
對海地來說，強度公式中的另一個不幸因素是相關的基礎設施。

The 1989 Loma Prieta earthquake that struck San Francisco just before Game 3 of the 1989 World Series was also about a 7.0-magnitude quake. While it killed scores of people and caused billions of dollars in property damage, the relatively high construction standards in the city kept the devastation much lower than what will likely be the case in Haiti.
1989年在當年世界大賽第三場比賽之前襲擊舊金山的洛馬普列塔地震（Loma Prieta earthquake）也是約7.0級地震。雖然地震奪走了許多人的生命，而且導致數十億美元的財產損失，但是，這座城市較高的建筑標準使其遭受的災難比可能發(fā)生在海地的災難低的多。

Haiti is a poor country with lax building standards and high population density, which makes buildings more likely to crumble, according to Blakeman. "Unfortunately that's going to be a lot of the factor here," he said.
據布萊克曼說，海地是個貧窮的國家，建筑標準松散，人口高度密集，其建筑更有可能倒塌。“不幸的是，那將是這里遭災的很大因素。”他說。

Experts have estimated that the death toll will likely reach into the thousands, with untold numbers homeless.
專家估計，那里的死亡人數可能達到數千人，但沒有說流離失所的人數。

Another problem is the relative rareness of major earthquakes in the area coupled with poor public communication and education, which likely means that most Haitians were not prepared for such a disaster, as many Californians might be.
另一個問題是，該地區(qū)相對罕見的大地震加上薄弱的公共通訊和教育，這可能意味著海地人沒有像加利福尼亞人那樣做好應對這種災難的準備。

Waiting for answers
等待回音

Information from the earthquake will help scientists better understand the future quake threat that exists for Haiti and the rest of the Caribbean by providing information that isn't available from the previously known major quakes in the region, which occurred in the 18th and 19th centuries.
來自震區(qū)的信息將有助于科學家通過提供從18和19世紀發(fā)生在當地的所謂大地震中得不到的信息，更好地了解存在于海地和加勒比海其它地區(qū)的未來地震威脅。

Just how bad the destruction from the quake will be remains to be seen and likely will not be known fully for days, as reports trickle in from the crippled island nation. The United Nation and Red Cross have both mobilized emergency efforts.
地震的破壞到底有多嚴重仍有待觀察，可能幾天內都不會完全清楚，因為來自這個傷殘島國的報告逐步升級。聯(lián)合國和紅十字會都動員了緊急行動。

"There is no doubt that we are facing a major humanitarian emergency and that a major relief effort will be required," said United Nations Secretary-General Ban Ki-moon.
“毫無疑問，我們正面對著一場嚴重的人道主義突發(fā)事件，需要更多的救援努力。”聯(lián)合國秘書長潘基文說。

Compounding the problems of the quake aftermath will likely be the numerous aftershocks that accompany any major earthquake. Though aftershocks are typically several orders of magnitude below the original temblor, they can still cause further damage, especially with the precarious building situation in Haiti.
震后的問題中可能還有伴隨大震而來的無數余震。雖然余震一般比原震低幾級，仍然可能造成進一步的破壞，特別是因為海地建筑處于危險的狀況。

The USGS has already measured more than 40 aftershocks above a 4.0 magnitude (including a 5.9 and 5.5 magnitude) and many more below that, Bedwell said. More aftershocks are anticipated in the coming days and weeks as the restive fault continues to react to the jolt that set it off in the first place.
貝德威爾說。美國地質勘探局已經估計將有4.0級以上（包括5.9級和5.5級）余震40多次，還有許多震級更低的余震。預計今后幾天或幾周內會發(fā)生更多余震，因為不穩(wěn)定的斷層會繼續(xù)對將其移離原位的震蕩作出反應。

"We like to think they are more repositioning of the faults in the area because of the larger earthquake," Bedwell said.
貝德威爾說，“我們這樣想，它們在為斷層在該地區(qū)重新定位，因為這次地震更大。”