根据一项研究，今年早些时候震动南加州的一系列地震可能增加了一条主要休眠断层线部分的压力，该断层线自记录开始以来没有产生任何重大活动。
爱荷华大学的科学家们研究了所谓的脊峰地震，它始于7月4日莫哈韦沙漠的6.4级前震，第二天又发生了7.1级地震——这是南加州二十年来最大的一次地震。此外，记录了10多万次较小的余震。
通过分析卫星图像和地震仪器收集的数据，研究人员能够计算出这一系列地震是如何影响加尔洛克断层的——加尔洛克断层从臭名昭著的圣安地列斯断层向西延伸185英里至死亡谷。
这个断层似乎处于休眠状态，因为它至少已经一个世纪没有发生大地震了——科学家们第一次开始测量该地区的地震活动。然而，专家表示，它仍然对南加州构成地震风险。
该研究的主要作者比尔·巴恩哈特在一份声明中说:“加洛克断层已经平静了很长时间。”。“但是有地质证据表明那里发生过大地震。这是一条主要的断层线。”
根据发表在杂志上的研究地球物理研究快报——脊峰地震在加洛克断层特定的12至16英里范围内造成了一种被称为“抗震蠕变”的现象。
这个术语指的是尽管没有产生地震，断层还是滑动的时候，它可以表示应力的增加。
巴恩哈特说:“无震蠕变告诉我们，加尔洛克断层对应力变化很敏感，应力仅在断层的有限区域增加。”。
根据主要作者的说法，这些结果既令人惊讶又不足为奇。
“仅在加州，这种情况就被观察过几次，”巴恩哈特告诉记者新闻周刊。"因此，看到加尔洛克断层上的断层蠕动并不一定令人惊讶."
他说:“令人惊讶的是，断层蠕动区域与我们估计加洛克断层上应力增加的区域对应得有多好。”。“这几乎是一对一的关系，非常强烈地表明加尔洛克断层对附近的地震很敏感并做出反应。”
主要作者认为，这一证据揭示了断层未来可能发生地震的地方。
“所以，如果——这是一个很大的假设——这个地区在未来的地震中会滑动，我们正在显示这可能发生在哪里，”巴恩哈特说。
2019年7月7日，加州里奇雷斯特附近，里奇雷斯特居民检查了该地区两次大地震后最近的断层破裂。
幸运的是，该小组发现加尔洛克断层的其余部分没有受到脊峰地震的同样影响。事实上，大部分都显示出压力有所减轻——巴恩哈特称之为“好消息”
然而，该研究表明，由该小组确定的应力剖面的潜在破裂可能导致6.7至7.0级的地震。
“这将是一场脊峰级的地震，”巴恩哈特说。“那意味着它会很大。你会觉得洛杉矶有些摇晃，但不会有7.8级更具破坏性。”
“与此同时，地震通常会在加州附近的断层上引发蠕动，但不会导致更大的地震，所以我们在加尔洛克断层上发现的蠕动绝对不意味着大地震即将来临，”他说。
EARTHQUAKES IN SOUTHERN CALIFORNIA PUT STRESS ON A MAJOR FAULT LINE THAT'S BEEN DORMANT SINCE RECORDS BEGAN
Aseries of earthquakes which shook Southern California earlier this year may have increased stress on parts of a major dormant fault line which has not produced any significant activity since records began, according to a study.
Scientists from the University of Iowa examined the so-called Ridgecrest earthquakes, which began with a 6.4 magnitude foreshock in the Mojave Desert on July 4, followed the next day by a 7.1 magnitude quake—the largest in Southern California for two decades. In addition, more than 100,000 smaller aftershocks were recorded.
By analyzing satellite imagery and data collected by seismic instruments, the researchers were able to work out how this series of earthquakes affected the Garlock Fault—which stretches east to west for 185 miles from the infamous San Andreas Fault to Death Valley.
This fault appears to be lying dormant given that it has not produced a major earthquake for at least a century—when scientists first began measuring seismic activity in the area. Nevertheless, experts say that it still poses an earthquake risk to Southern California.
"The Garlock Fault has been quiet for a long time," lead author of the study Bill Barnhart said in a statement. "But there's geologic evidence that there have been large earthquakes on it. It's a major fault line."
According to the study—which is published in the journal Geophysical Research Letters—the Ridgecrest earthquakes caused a phenomenon known as "aseismic creep" across a specific 12-to-16-mile section of the Garlock Fault.
This term refers to when a fault slips despite not producing an earthquake, and it can indicate an increase in stress.
"The aseismic creep tells us the Garlock Fault is sensitive to stress changes, and that stresses increased across only a limited area of the fault," Barnhart said.
These results were both surprising and unsurprising, according to the lead author.
"This is has been observed several times in California alone," Barnhart told Newsweek. "So to see fault creep on the Garlock fault was not necessarily a surprise."
"What was surprising was how well the region of fault creep corresponded to the region where we estimate that stresses increased on the Garlock fault," he said. "It was almost a one-to-one relationship that very strongly suggests that the Garlock fault is sensitive to and responds to nearby earthquakes."
The lead author argues that this evidence reveals where a future earthquake at the fault could occur.
"So, if—and that's a big if—this area were to slip in a future earthquake, we are showing where that might happen," Barnhart said.
Ridgecrest residents inspect a recent fault rupture following two large earthquakes in the area on July 7, 2019 near Ridgecrest, California.
Fortunately, the team found that the rest of the Garlock Fault had not been affected by the Ridgecrest quakes in the same way. Most of it actually exhibited a decrease in stress—something Barnhart describes as "good news."
Nevertheless, the study suggests that the a potential rupture of the stressed section identified by the team could result in an earthquake with a magnitude of between 6.7 and 7.0.
"It would be an earthquake of the magnitude of the Ridgecrest sequence," Barnhart said. "That means it would be big. You'd feel some swaying in Los Angeles, but it wouldn't be a magnitude 7.8 that could be more damaging."
"At the same time, earthquakes commonly trigger creep on nearby faults in California without leading to a bigger earthquake, so the creep that we found on the Garlock fault absolutely does not mean that a big earthquake is imminent," he said.
