When an earthquake strikes, the instinct of many Californians is to ask: What fault has it fallen – Newport-Inglwood, Hayward, the mighty San Andreas?
But more and more scientists say it's not so simple.
New research shows that the July 2005 earthquake in Ridgecrest has torn at least two dozen faults. This is the latest evidence of how small faults can be joined together to cause a major earthquake and how these earthquakes can span a wider area than expected.
Discoveries are important to understand how earthquakes can increase in the seconds after a rift breaks when two blocks of land are moving away from each other. In areas littered with a crisis model of faults, an earthquake with a smaller fault can destabilize the larger ones, initiating a process that results in a much stronger earthquake.
In the case of Ridgecrest, some subsequent earthquakes came seconds after; the largest came about 34 hours later.
It is only in recent decades that earthquake scientists have come to understand how smaller fractures in California come together to create a more powerful earthquake.
After the Landers earthquake in 1
Over the years, more evidence has accumulated that earthquakes can and do occur with multiple faults – such as the 7.1 Hector earthquake, about 20 miles east of the Landers earthquake and 7.2 magnitude on Sunday, 2010. near Mexicali.
Detailed observations recently outlined in the journal Science by Caltech experts and NASA's Jet Propulsion Laboratory highlight how scientists' understanding of earthquake destruction has evolved.
Researchers discovered the Fourth of July at the Ridcrest Tabler are actually three different earthquakes. – magnitudes 6.1, 6.2 and 6.2 – of the trio of errors. Taken together, they produce enough energy to create a 6.4-timbler magnitude, said Zahari Ross, associate professor of Kaltech geotechnics, lead author of the article. The first two earthquakes split at right angles to each other, forming the capital letter L: the first to the northwest and the southeast, the second to the southwest. The third earthquake also tore to the southwest. The errors broke in 12 seconds.
"This is something we have not seen so far and is described on such a small scale in detail," says Caltech seismologist Egil Huxson, a co-author and expert on seismology in Southern California.
The second major earthquake, on July 5, was actually made up of four smaller events that broke out in 22 seconds, producing an event of magnitude 7.1, the most powerful in California in the last 20 years. At the same event, at least 20 smaller faults that intersected the major faults also collapsed, according to a study that made the land area of peaks with rolling faults wider than expected.
"The geometry of this fault network is just incredibly complex," Ross said. "These mistakes have not been rectified … many of them are at right angles to each other; they intersect each other. In its central part they are located a few kilometers, like dominoes. There are 20 of them in a row. This 7.1 is torn apart by all this. ”
The results provide even more evidence to support the notion that California faults, once considered limited by their individual lengths, can actually be joined together in a much more massive earthquake.
For example, as cited in a 1993 study in the journal Science, co-authored with Howson, previous estimates suggest that only earthquakes of magnitude 6.9 or less are expected in the Landers area. The magnitude 7.3 earthquake, which struck, tripled the startling energy as expected.
"The point is that the Landers earthquake and this earthquake are daisies that were previously thought to be self-destructive, and this is an important observation," said Hawkson. "These earthquakes are interconnected segments that were thought to have been independent before, but it has now been proven that they actually connect in a major earthquake."
Thus, instead of the earthquake strain being relieved by many magnitude 6 on a number of faults, "you could just do it with magnitude 7, with the destruction moving upwards and jumping from one error to another," said Hawkson.
Modest damage, which begins to move in an earthquake, can facilitate the destruction of a neighbor, said Huxon. In Ridgecrest, the Fourth of July earthquakes likely lingered on knocking strong spots on seismically-charged faults, until on July 5, the larger magnitude 7.1 collapsed, Hawkson said.
The study raises the possibility that previous earthquakes may actually have been larger than previously thought. A prehistoric earthquake, which is currently being identified by fracturing in one place, could lead to even greater force if scientists did not yet find other segments of the fracture that collapsed in the same event, the study says .
This may sound ominous. But there is a silver lining, according to seismologist Lucy Jones, who did not participate in the study.
If super large earthquakes are more likely, this means that there will be less harmful timbre for each given period of time. "You won't need to have another earthquake for much longer," Jones said.
"What's worse, one 8 or six 7.5?", Jones asked. "It is not clear that one 8 is worse than six 7.5. There is a lot of damage that happens in every single event. "
And at great magnitudes, only so much can shake the earth before the rocks break; so that the worst shaking caused by a magnitude 7 and magnitude 8 earthquake is not so different. An earthquake of magnitude 8 however, it will cause devastating shaking in a much larger area of California and will be longer.
The Ridcrest study and information obtained from other recent earthquakes also emphasized the importance of understanding how multiple faults can break affected broader
In New Zealand, scientists were amazed at the bizarre map of the rifts, torn apart by the magnitude 7.8 of the 2016 Kaikoura earthquake, resembling a three-tooth with its head downwards aimed at the silhouette of an eagle. Kaikoura ” width=”840″ height=”887″/>
A map showing where fractures on the surface of a 7.8 magnitude earthquake in Kaikoura, New Zealand were broken in 2016.
area … and it's kind of mind-blowing, "said Huxson. "And this is important because it means that many more people are affected – the destruction of the surface and the shaking of the surface of the earth are spread over a much wider area."
At a practical level, studies highlight the potential limitations of earthquake zones. in the state to prevent new construction directly on faults, said Hawkson. If a major fault can be prevented by much shorter perpendicular faults and employees want to avoid new construction on active faults, the areas may need to be larger than they are now.
Additional analysis is needed to determine whether the 20 cross-errors identified in the Ridgecrest study using computer analysis of shaking records actually broke ground on the surface, according to Tim Dawson, a senior engineering geologist at California geological survey.
Ridgecrest earthquakes have occurred through a region that is already known to be very complex, with many structurally immature baby bugs intersecting each other, said James Dolan, a professor of earth sciences at USC.
"It's just very, very interesting to see one of these errors on the web. all are destroyed at the same time by a major earthquake, "said Dolan.
A significant achievement of this study, said Dolan, was to be able to imagine what faults look like deep bowels ound, at the depths where earthquakes begin. that the structural complexity of surface defects is simplified more deeply; what this study proves is that structural complexity continues deep underground where earthquakes begin, Dolan said.
That's important, Dolla said. Because it can help scientists determine where to stop future earthquakes, which tends to happen when devastation become structurally complicated.