15). Quake Research on Solid Ground

Text 15

Quake Research on Solid Ground 地震研究

Pre-reading Activities

1. Have you ever heard of an earthquake? If you have, say something about it.

2. Do you know which country in the world has the most earthquakes?

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1. Geophysicist Dr. Andrea Donnellan of NASA's Jet Propulsion Laboratory, Pasadena, Calif., remembers the morning of January 17, 1994, like few others. Like millions of other Southern California residents, she was shaken from her sleep in her normally tranquil foothill community home as a large earthquake caused a mountain, located just 30 miles away, to grow nearly 15 inches higher, all in a matter of seconds.

安德莉.唐娜伦博士是加利福尼亚州帕萨德纳NASA实验室的地球物理学家.和其他人一样,她清楚地记得1994年1月17日的那个早晨.同千千万万南加州的居民一样,她在一贯很静的家中从睡梦中被摇醒.强烈地震使30英里外的大山隆起了约15英寸高.所有这一切都发生在一瞬间.

2. “Large earthquakes are always disconcerting," she said. "Being a geophysicist I was immediately interested in how large the earthquake was and where it had occurred."

“强烈的地震通常令人心神不安,”她说,”作为地球物理学家,我急于想知道震级和震源.”

3. Within minutes, news reports confirmed that Los Angeles' San Fernando Valley had taken a direct hit from an earthquake comparable in size to the damaging 1972 San Fernando earthquake. More than 60 people were killed in each earthquake and thousands were injured. The latter event became one of the costliest natural disasters ever to strike the United States. Only the pre-dawn time of day and the fact that it was a holiday kept the death toll from being much higher.

几分钟后新闻报道证实了洛杉矶的圣弗尔南多山谷是地震中心,与1972年该地区遭受的地震危害差不多.在这两次地震中,各有超过60人遇难,数千人受

伤.1972年的地震成为美国历史上因自然灾害而损失最惨重的一次.地震发生在黎明前,而且是节假日,这使死亡率没有继续上升.

4. Less than two months before that fateful day, Donnellan and colleagues from the Massachusetts Institute of Technology had published a landmark paper in the journal Nature on ground distortion north of LA's San Fernando Valley. Six years of relatively sparse data from a fledgling network of Global Positioning System (GPS)

deformation monitors, that had been developed and installed around Southern California by scientists at JPL and other organizations, had detected that Earth's crust was being squeezed closed across the Ventura Basin. The data showed the area's faults were accumulating strain , and they gave the scientists clear indications of the style and relative size of an earthquake that might strike there, even though the faults there do not all break the surface. They placed no time frame on when such a temblor might occur, however.

地震发生前不到两个月,唐娜伦和麻省理工学院的同行在《自然》杂志上发表了关于洛杉矶圣费尔南多山谷北部地层发生变形的文章.这篇文章在地震研究领域具有里程碑的意义.通过全球定位系统监控仪，喷气推进实验室以及其他机构的科学家将这一系统安装在南加利福尼亚。提供的六年不太充分的数据已经表明地壳在温图瑞盆地附近受到挤压.数据显示了这一地带的断层正受到更大的压力,尽管断层没有使表层完全断裂,但这也给科学家明显的暗示,这里很可能发生地震,以及地震的类型和震级.然而他们没有确定地震发生的时间.

5. "The Northridge GPS measurements solidified in many scientists' minds how valuable data from space-based instruments could be for collecting precise measurements of Earth's crustal movements," said Donnellan. "We knew that something was up because an earthquake had not occurred there historically and yet a large amount of strain needing to be released had accumulated. After the earthquake, additional GPS data made it possible to rapidly and uniquely determine where the fault ruptured and to measure how the earthquake had deformed Earth's surface. " “GPS(全球定位系统)的测量使科学家们更加确定,来自太空测量仪器的数据可以作为研究地壳运动的原始资料.”唐娜伦说, “我们知道会有事情发生,因为历史上那里从来没发生过地震.然而巨大的压力积聚在那里等待释放.地震以后,更多的GPS数据使人们有可能测定断层在哪里破裂,以及地震如何改变地球表层.”

6. In the decade since Northridge, a high-tech, GPS-based ground deformation network was installed within Southern California. Called the Southern California Integrated GPS Network, it provides a continuous measurement of ground deformation at 250 locations with a precision of a few millimeters, measuring the slow buildup of deformation along faults. In addition, advances in satellite-based radar Interferometric Synthetic Aperture Radar (InSAR) and lidar are now used in combination with the GPS measurements to provide images of ground deformation for the entire Southern California earthquake region. Theses new technologies, coupled with powerful new computer modeling capabilities, have revitalized research in understanding earthquakes and earthquake processes. The new technologies will substantially refine earthquake hazard maps.

自从南加利福尼亚安装了高科技全球定位系统综合网,它可以持续测量250个地点的地层变形,和测量断层缓慢形成的形变,而且能精确到毫米.此外卫星雷达干涉测量仪和GPS一起使用,提供了南加利福尼亚地震带地表变形的全部资料.这