Most of California's Big Earthquakes Are Preceded by Ghostly 'Foreshocks' Weeks in Advance
大多数加州大地震发生前几周都有鬼魅般的前震
By Brandon Specktor
Foreshocks — the tiny, sometimes imperceptible tremors that precede massive earthquakes — are way more common than we thought.
(Image: © Shutterstock)
布兰登 · 斯佩克特前震ーー大规模地震前微小的、有时难以察觉的震动ーー比我们想象的要常见得多。 (图片: Shutterstock)
How do earthquakes begin? It's an ancient question — and while scientists have ruled out the vengeful gods blamed over the past few millennia, agreeing that tremors are more a matter of grinding plate tectonics than of Poseidon's wrath, many facets of this seismic puzzle remain murky.
地震是如何开始的？ 这是一个古老的问题。虽然科学家们已经排除了过去几千年来复仇心切的神灵的可能性，并同意地震更多是一种磨盘构造的问题，而不是波塞冬的愤怒，但这个地震谜题的许多方面仍然是个谜。
One ongoing mystery is the phenomenon of foreshocks, small, sometimes imperceptible tremors that can precede larger quakes in the same area by several days or weeks. Studies have found that anywhere from 10% to 50% of large earthquakes follow these minishocks. This has led many researchers to wonder whether foreshocks are a geophysical fluke or a standard feature of big quakes that modern instruments just aren't sensitive enough to detect with certainty.
一个持续的谜团是前震现象---- 在同一地区发生大地震之前，可能会发生几天或几周的小规模、有时甚至是难以察觉的地震。 研究发现，在任何地方都有10% 到50% 的大地震发生在这些微型岩块之后。 这使得许多研究人员怀疑前震是地球物理上的侥幸，还是大地震的标准特征，现代仪器不够灵敏，无法准确地探测到。
A study published July 30 in the journal Geophysical Research Letters offers compelling new evidence for the second hypothesis. Using the most comprehensive catalogue of earthquake activity in Southern California ever assembled, a team of researchers found that roughly 72% of large (magnitude 4.0 or greater) quakes in the region between 2008 and 2017 followed distinct foreshocks that hit up to a month before the event.
7月30日发表在《地球物理研究通讯志上的一项研究为第二种假设提供了令人信服的新证据。 利用南加州有史以来收集的最全面的地震活动目录，一组研究人员发现，2008年至2017年间，该地区大约72% 的大型(4.0级或以上)地震都是在地震发生前一个月发生的明显的前震之后发生的。
"We're hoping that these observations will help inform improved physical models of how earthquakes get started," lead study author Daniel Trugman, a seismologist at Los Alamos National Laboratory in New Mexico, told Live Science. "With this improved physical understanding, we'll eventually be able to improve earthquake forecasting as well."
首席研究作者，新墨西哥州洛斯阿拉莫斯国家实验室的地震学家 Daniel Trugman 告诉《生活科学》 : “我们希望这些观测将有助于改进地震开始的物理模型。”。 “随着物理认识的提高，我们最终也将能够改进地震预报。”
Trugman and his colleagues began their hunt for foreshocks by compiling a catalogue of some 284,000 earthquakes detected by various monitoring stations around Southern California between 2008 and 2017. Using a technique called quake template matching (QTM), the researchers trained a computer to recognize the distinct waveform these quakes created, then scoured the records for hints of smaller quakes showing those same vibrational patterns, hints that lay hidden in the constant, rumbling background noise of Earth.
特鲁格曼和他的同事们在2008年到2017年间，通过收集南加利福尼亚各监测站探测到的大约284,000次地震的目录，开始搜寻前震。 利用一种叫做地震模板匹配(QTM)的技术，研究人员训练计算机识别这些地震产生的不同波形，然后从记录中搜寻那些显示相同振动模式的较小地震的迹象，这些迹象隐藏在地球持续不断的隆隆背景噪音中。
The team turned up more than 1 million additional earthquakes, many of them magnitude 0.0 or less (seismologists measure earthquake magnitude on a logarithmic scale, so a magnitude 0.0 quake would be about 10,000 times weaker than a magnitude 4.0 quake). In total, the researchers expanded their catalogue to include 1.81 million earthquakes, or an average of one quake every 3 seconds over the last 10 years, Trugman said.
研究小组又发现了超过100万个地震，其中许多都是0.0级或更低的地震(地震学家在对数尺度上测量地震的震级，所以0.0级的地震要比4.0级的地震弱10000倍)。 特鲁格曼说，研究人员总共扩大了他们的目录，包括了181万次地震，或者说在过去10年中平均每3秒钟发生一次地震。
From this expanded list, the researchers picked 46 quakes with magnitude 4.0 or higher to study for foreshock activity. But first, the team had to calculate the average number of earthquakes near each fault line in Southern California.
从这个扩展的名单中，研究人员挑选了46次4.0级或更高的地震来研究前震活动。 但是首先，研究小组必须计算南加州每条断层线附近地震的平均次数。
"If you pick any point in Earth's crust, especially near an active fault zone, there's going to be a background rate of seismicity," Trugman said. "To show that there are foreshocks, you have to demonstrate that there are more earthquakes than you'd expect leading up to the larger event."
特鲁格曼说: “如果你选择地壳中的任何一个点，特别是在活动断裂带附近，地震活动的背景频率就会出现。”。 “为了证明存在前震，你必须证明存在着比你预期的更多的地震，从而导致更大规模的地震。”
Armed with these seismic averages, the researchers showed a statistically significant increase in foreshock activity shortly before 33 of the 46 big quakes. Foreshocks activity spiked anywhere from three to 35 days before a mainshock hit, with the average increase in rumbling occurring about 16 days before the big event.
根据这些平均地震数据，研究人员显示，在46次大地震中，有33次发生前，前震活动在统计上显著增加。 前震活动在主震袭击前3到35天达到峰值，隆隆声的平均增加发生在大震前16天左右。
"The results suggest that foreshock occurrence in nature is more prevalent than previously thought," the researchers concluded in their study.
研究人员在他们的研究中得出结论: “研究结果表明，自然界中前震的发生比以前认为的更为普遍。”。
And what about the 28% of quakes that lacked a surge in foreshock activity? Trugman said it's likely that many of those quakes did see foreshocks as well but the researchers just couldn't define them with "99% certainty."
那么28% 没有前震活动激增的地震又如何呢？ 特鲁格曼说，很可能许多这样的地震确实发生过前震，但研究人员只是不能“99% 肯定”地给它们下定义
"There are a number of cases where there is an increase in seismic activity, but we're not sure it's statistically significant," Trugman said. As seismic-monitoring equipment improves, so too should foreshock detection, he said.
特鲁格曼说: “有很多地震活动增加的例子，但我们不确定这在统计学上是否有意义。”。 他说，随着地震监测设备的改进，前震探测也应该得到改进。
Still, Trugman added, some of the big quakes clearly missed such a spike in foreshocks before the heavy rumbling began. And, on the flipside, a vast majority of the tiny quakes he and his team discovered did not precede large earthquakes at all, meaning that simply seeing an increase in seismic activity along a given fault line is not a reliable predictor of a bigger earthquake to come.
尽管如此，特鲁格曼补充说，一些大地震显然没有在隆隆声开始之前的前震中达到这样的峰值。 另一方面，他和他的团队发现的绝大多数小地震根本就不是大地震的前兆，这意味着仅仅看到某条断层线上地震活动的增加并不能作为未来更大地震的可靠预报。
"What we show in this paper is that most if not all mainshocks are preceded by elevated seismic activity that cannot be explained as simple background seismicity," Trugman said. "But that is a very different statement from saying that 'most upticks in seismicity are foreshocks that signal that a mainshock is impending'."
特鲁格曼说: “我们在这篇论文中所展示的是，大多数(如果不是所有的)主震发生之前，都有不能简单解释为背景地震活动的升高地震活动。”。 “但这是一个非常不同的说法，不同于‘大多数地震活跃性上升是预示主震即将到来的前震’。”
This all shows that the processes that initiate earthquakes are "quite variable," Trugman said, reminding us that seismologists are still a good ways away from being able to forecast earthquakes with any certainty. Perhaps we shouldn't let Poseidon off the hook yet after all.
这一切都表明，引发地震的过程是“相当多变的” ，特鲁格曼说，这提醒我们，地震学家距离能够准确预测地震还有很长的路要走。 也许我们还是不应该让波塞冬逍遥法外。 |
