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Some scientists believe that when one monster quake hits, others may follow.
Geologists used to answer with an emphatic “No” when asked if mega-earthquakes can trigger temblors on the other side of the globe. Today, some experts are not so sure. Evidence is mounting that large earthquakes can rattle geologic formations more than 1000 miles away—and perhaps even set off volcanic eruptions days, months or years later.
There’s also an intriguing hint that major earthquakes might occur in clusters: Nearly one-third of the biggest quakes of the past century struck during a 20-year span between 1950 and 1970. In 1952 and 1957, two major quakes hit eastern Russia and Alaska. These same areas also experienced a major quake each year from 1963 to 1965.
Herb Dragert, a research scientist for the Geological Survey of Canada, and his American counterparts operate a network of GPS sensors throughout the western North American region. The instruments can detect stress at the Cascadian subduction zone—the 600-mile-long offshore region where the ocean floor is diving under the continental plate.
“If we suddenly had a very large earthquake in Alaska, and I saw displacement in my GPS instruments, then I would begin to worry,” he says.
Contagious disasters?
When undersea plates snap apart and trigger an earthquake, the dislocation almost certainly increases stress and strain on adjacent geological faults and plate boundaries. Geologists call the phenomenon “contagion” because it raises the odds of subsequent earthquakes like an influx of germs raises the risk of infection.
Scientists have long known about the contagion effect, which can extend for 100 miles or so from the epicenter of a major quake. It’s the phenomenon that’s responsible for the after-shocks that follow many major quakes. But most experts were stunned in 1992 when a magnitude 7.2 quake struck the Mojave Desert in Southern California, and was almost immediately followed by more than a dozen quakes as far away as Wyoming.
Seismic connections
“As people around the world look more carefully, they’re seeing more examples of this kind of (long - distance) effect,”said David Hill, a US Geological Survey (USGS) geophysicist stationed at Menlo Park, California, “At this point there’s really no doubt that it happens.”
Generally, the triggered earthquakes are smaller than the original, though there’s no reason to believe that larger earthquakes couldn’t be kicked off this way as well. The effect seems to be caused by seismic waves that radiate out from the epicenter of an earthquake, along the surface of the ground. Imperceptible to people, these waves cover a lot of distance. But a fault or plate boundary must already be on the verge of slipping or breaking for the surface waves to push it over the edge.
There’s still no detailed explanation for the way that happens, though, Hill said. “In a way, it’s frustrating to be doing research on this,” he said, “because we can’t do it in the lab and repeat the experiment. We’ve got to wait for the earth to do it, and then have good recording networks in the field.”
Lack of solid evidence
Garry Rogers, a seismologist at the Geological Survey of Canada in British Columbia, says major earthquakes are far too rare and the historical record far too short to be able to draw any conclusion about clusters or large-scale connections. “In any random process, you will get clusters,” he said.
Hill believes that more data will eventually solve the mystery—and will probably reveal patterns and links no one understands today. “My own hunch is that there are lots of instances of clusters that are, in fact, related physically,” he said. “We just don’t know yet what the details might be.”
有些科学家认为一个巨大地震发生后，其他一些地震可能尾随而至。
以前，地质学家被问到大地震是否会引发地球另一端的地震时，都会用坚定的口气回答： “不会”。今天，有些专家已经不那么有把握了。愈来愈多的证据显示，大规模的地震可能会打乱远在一千英里之外的地质结构，甚至可能造成数天、数月或数年之后的火山爆发。
还有一个耐人寻味的迹象显示大型的地震可能会接踵而来：过去一个世纪内，近1/3最剧烈的地震都发生在1950-1970年这20年之间。1952年和1957年，有两次强烈地震袭击俄罗斯东部及阿拉斯加。这个地区在1963-1965年间，每年也都发生过一次强烈地震。
加拿大地质调查局的研究科学家赫布·德雷珀特与他在美国的合作伙伴，管理一套涵盖整个北美西部地区的全球卫星定位系统感应器网络。这些仪器可以测定卡斯卡迪亚地层潜没带的压力。卡斯卡迪亚地层潜没带是海床潜入大陆板块下方，长达600英里的近海区域。
他说： “如果阿拉斯加突然发生大地震，我又在我的全球卫星定位系统仪器上看到位移，那么我就会开始担心了。”
具有传染性的灾难？
海底的板块突然断裂分开并造成地震时，错位极可能会增加邻近地质断层及板块边界的压力及负担。地质学家将这种现象称为“感染”，因为它会增加后续地震发生的可能性，就好像一群蜂拥而至的细菌会增加感染的风险一样。
科学家很早以前就知道这种会自强震震中延伸至约百英里之外的感染效应，这也正是造成许多大规模地震之后的余震的现象。但在1992年，当强度达7.2级的地震袭击南加州的莫哈维沙漠、而遥远的怀俄明州竟几乎立刻就出现10余次的地震时，大多数科学家还是十分震惊。
地震的关联
派驻在加州门洛帕克市的美国地质调查局地球物理学家大卫·希尔表示：“全球各地的人更谨慎注意此事时，会看到愈来愈多类似这种（长距离）效应的例子。就目前而言，这种现象真的毫无疑问会发生。”
虽然没有理由相信较大规模的地震一定不会被原来的地震激发，但一般而言，被引发的地震会比原来的地震规模小。这种引发效应似乎是由震中沿着地表向四面八方传送出的震波所造成的。这些震波人类无法察觉，而影响的范围极广，但是断层或是板块边界必定已经濒临滑落或断裂，才可能会被地表的震波推落到边缘之外。
不过，对于这种接踵而来的地震发生的方式，到现在还没有更详尽的解释。希尔说：“就某种角度来说，做这方面的研究让人感到很沮丧，因为我们不能在实验室里做并重复试验。我们只能等待地球行动，而且那时在当地还要有良好的记录网络。”
缺乏有力证据
不列颠哥伦比亚省加拿大地质调查局的地震学家加里·罗杰斯表示，大型地震过于罕见，而历史纪录又太短，无法从中得出结论，证明其与地震连续发生或大规模地震之间有什么样的关联性。他指出：“在任何一个随机过程中，都可以看到连续发生的地震。”
希尔相信，更多的资料最后终将解开谜团，也可能会揭露一些今天还没有人能够了解的模式和联系。他说：“我自己的直觉是许多接踵而来的地震的实例其实在物理学上是有关联的，我们只是还不知道详细的内容可能是什么罢了。”
Geologists used to answer with an emphatic “No” when asked if mega-earthquakes can trigger temblors on the other side of the globe. Today, some experts are not so sure. Evidence is mounting that large earthquakes can rattle geologic formations more than 1000 miles away—and perhaps even set off volcanic eruptions days, months or years later.
There’s also an intriguing hint that major earthquakes might occur in clusters: Nearly one-third of the biggest quakes of the past century struck during a 20-year span between 1950 and 1970. In 1952 and 1957, two major quakes hit eastern Russia and Alaska. These same areas also experienced a major quake each year from 1963 to 1965.
Herb Dragert, a research scientist for the Geological Survey of Canada, and his American counterparts operate a network of GPS sensors throughout the western North American region. The instruments can detect stress at the Cascadian subduction zone—the 600-mile-long offshore region where the ocean floor is diving under the continental plate.
“If we suddenly had a very large earthquake in Alaska, and I saw displacement in my GPS instruments, then I would begin to worry,” he says.
Contagious disasters?
When undersea plates snap apart and trigger an earthquake, the dislocation almost certainly increases stress and strain on adjacent geological faults and plate boundaries. Geologists call the phenomenon “contagion” because it raises the odds of subsequent earthquakes like an influx of germs raises the risk of infection.
Scientists have long known about the contagion effect, which can extend for 100 miles or so from the epicenter of a major quake. It’s the phenomenon that’s responsible for the after-shocks that follow many major quakes. But most experts were stunned in 1992 when a magnitude 7.2 quake struck the Mojave Desert in Southern California, and was almost immediately followed by more than a dozen quakes as far away as Wyoming.
Seismic connections
“As people around the world look more carefully, they’re seeing more examples of this kind of (long - distance) effect,”said David Hill, a US Geological Survey (USGS) geophysicist stationed at Menlo Park, California, “At this point there’s really no doubt that it happens.”
Generally, the triggered earthquakes are smaller than the original, though there’s no reason to believe that larger earthquakes couldn’t be kicked off this way as well. The effect seems to be caused by seismic waves that radiate out from the epicenter of an earthquake, along the surface of the ground. Imperceptible to people, these waves cover a lot of distance. But a fault or plate boundary must already be on the verge of slipping or breaking for the surface waves to push it over the edge.
There’s still no detailed explanation for the way that happens, though, Hill said. “In a way, it’s frustrating to be doing research on this,” he said, “because we can’t do it in the lab and repeat the experiment. We’ve got to wait for the earth to do it, and then have good recording networks in the field.”
Lack of solid evidence
Garry Rogers, a seismologist at the Geological Survey of Canada in British Columbia, says major earthquakes are far too rare and the historical record far too short to be able to draw any conclusion about clusters or large-scale connections. “In any random process, you will get clusters,” he said.
Hill believes that more data will eventually solve the mystery—and will probably reveal patterns and links no one understands today. “My own hunch is that there are lots of instances of clusters that are, in fact, related physically,” he said. “We just don’t know yet what the details might be.”
有些科学家认为一个巨大地震发生后，其他一些地震可能尾随而至。
以前，地质学家被问到大地震是否会引发地球另一端的地震时，都会用坚定的口气回答： “不会”。今天，有些专家已经不那么有把握了。愈来愈多的证据显示，大规模的地震可能会打乱远在一千英里之外的地质结构，甚至可能造成数天、数月或数年之后的火山爆发。
还有一个耐人寻味的迹象显示大型的地震可能会接踵而来：过去一个世纪内，近1/3最剧烈的地震都发生在1950-1970年这20年之间。1952年和1957年，有两次强烈地震袭击俄罗斯东部及阿拉斯加。这个地区在1963-1965年间，每年也都发生过一次强烈地震。
加拿大地质调查局的研究科学家赫布·德雷珀特与他在美国的合作伙伴，管理一套涵盖整个北美西部地区的全球卫星定位系统感应器网络。这些仪器可以测定卡斯卡迪亚地层潜没带的压力。卡斯卡迪亚地层潜没带是海床潜入大陆板块下方，长达600英里的近海区域。
他说： “如果阿拉斯加突然发生大地震，我又在我的全球卫星定位系统仪器上看到位移，那么我就会开始担心了。”
具有传染性的灾难？
海底的板块突然断裂分开并造成地震时，错位极可能会增加邻近地质断层及板块边界的压力及负担。地质学家将这种现象称为“感染”，因为它会增加后续地震发生的可能性，就好像一群蜂拥而至的细菌会增加感染的风险一样。
科学家很早以前就知道这种会自强震震中延伸至约百英里之外的感染效应，这也正是造成许多大规模地震之后的余震的现象。但在1992年，当强度达7.2级的地震袭击南加州的莫哈维沙漠、而遥远的怀俄明州竟几乎立刻就出现10余次的地震时，大多数科学家还是十分震惊。
地震的关联
派驻在加州门洛帕克市的美国地质调查局地球物理学家大卫·希尔表示：“全球各地的人更谨慎注意此事时，会看到愈来愈多类似这种（长距离）效应的例子。就目前而言，这种现象真的毫无疑问会发生。”
虽然没有理由相信较大规模的地震一定不会被原来的地震激发，但一般而言，被引发的地震会比原来的地震规模小。这种引发效应似乎是由震中沿着地表向四面八方传送出的震波所造成的。这些震波人类无法察觉，而影响的范围极广，但是断层或是板块边界必定已经濒临滑落或断裂，才可能会被地表的震波推落到边缘之外。
不过，对于这种接踵而来的地震发生的方式，到现在还没有更详尽的解释。希尔说：“就某种角度来说，做这方面的研究让人感到很沮丧，因为我们不能在实验室里做并重复试验。我们只能等待地球行动，而且那时在当地还要有良好的记录网络。”
缺乏有力证据
不列颠哥伦比亚省加拿大地质调查局的地震学家加里·罗杰斯表示，大型地震过于罕见，而历史纪录又太短，无法从中得出结论，证明其与地震连续发生或大规模地震之间有什么样的关联性。他指出：“在任何一个随机过程中，都可以看到连续发生的地震。”
希尔相信，更多的资料最后终将解开谜团，也可能会揭露一些今天还没有人能够了解的模式和联系。他说：“我自己的直觉是许多接踵而来的地震的实例其实在物理学上是有关联的，我们只是还不知道详细的内容可能是什么罢了。”