When an earthquake occurs, many Californians have to ask themselves: what mistake has been made – the Newport-Inglewood, the Hayward, the mighty San Andreas?
But scientists are increasingly saying that it's not that easy.
New research shows that the Ridgecrest earthquakes that started in July caused at least two dozen faults. This is the latest evidence of how small faults join together to form a large earthquake and how these quakes can cover a larger area than expected.
The results are important to understand how earthquakes can occur in the seconds after a break when two earth blocks separate. In areas with crossed perturbation patterns, an earthquake on a smaller disturbance can destabilize larger earthquakes and trigger a process that results in a much stronger earthquake.
In the case of Ridgecrest, some subsequent earthquakes occurred seconds later. the largest came about 34 hours later.
Only in the last few decades have earthquake researchers understood how smaller disturbances in California combine to form a stronger earthquake.
After the Landers earthquake in 1
Over the years, more and more evidence has accumulated that earthquakes can and do occur with multiple faults – such as the magnitude 7.1 earthquake at the Hector Mine, about 20 miles east of the Landers Quake, and the earthquake of magnitude 7.2 at Easter Sunday 2010 near Mexicali.
Detailed observations recently described in the journal Science by experts at Caltech and NASA's Jet Propulsion Laboratory demonstrate the scientists' understanding of earthquake fractions – sizes 6.1, 6.2, and 6.2 – with three errors. Taken together, they produced enough energy to produce a 6.4-gauge Temblor, said Zachary Ross, Caltech Assistant Professor of Geophysics, the lead author of the paper. The first two quakes burst at right angles to each other and formed the shape of the capital letter L: the first in the northwest and southeast, the second in the southwest. The third quake also broke out in the southwest. The errors broke within 12 seconds.
"This is something we have not seen before, and it's detailed on such a small scale," said Caltech seismologist Egill Hauksson, a co-author and expert on seismology in Southern California.
The July 5th earthquake consisted of four minor events that exploded within 22 seconds, producing a magnitude 7.1 event. It was the strongest in California in the last 20 years. In the same event, the study found at least 20 smaller faults overlapping the major faults, causing the land zone to broaden on moving faults than expected.
"The geometry of this bug network is just incredibly complicated," said Ross. "These mistakes are not pictured … many of them are at right angles to each other. they overlap. In the middle they are like dominoes a few miles apart, 20 of them in a row. This 7.1 has overcome all these problems. "
The results provide even more evidence to suggest that California errors, once considered limited by their individual length, can actually lead to a much more massive earthquake.
For example, previous estimates, as quoted in a 1993 study published in the journal Science co-authored by Hauksson, had only expected 6.9 or less magnitude earthquakes in the Landers area. The magnitude 7.3 earthquake that occurred quadrupled the expected trembling energy.
"The point is that Lander's earthquake and earthquake concatenate errors that were previously thought to break only by themselves, and that's an important observation," Hauksson said. "These earthquakes have linked segments that were previously considered independent, but are now actually connected to a large earthquake."
"You could just do it in a magnitude 7 by moving the fraction up and out of error jump to the next, "said Hauksson.
A modest error that begins to move in a quake can facilitate the rupture of a neighboring fault, Hauksson said. In Ridgecrest, the July 4th earthquakes have likely struck strong points along seismic-laden faults until the magnitude 7.1 magnitude burst on July 5, Hauksson said.
The study raises the possibility that past earthquakes could actually have been larger than previously thought. A prehistoric earthquake, which is currently identified by a failure in a site fault, could have been more powerful if scientists had not discovered other fault segments that had burst in the same event, the study said.
That may sound threatening. However, according to seismologist Lucy Jones, who was not involved in the study, there is a silver lining.
If oversized earthquakes are more likely, it means there will be less dithering in a given period of time. "They will not need another earthquake for a much longer time," Jones said.
"What's worse, an 8 or six 7.5?" Jones asked. "It's not clear that an 8 is worse than six-7.5. There's a lot of damage done to every single event."
And at high levels, the ground can only shake so hard before the rocks break , The worst tremor caused by a magnitude 7 earthquake and a magnitude 8 quake is not much different. However, a magnitude 8 earthquake would cause destructive shaking in a much larger area of California, and its duration would be longer.
The Ridgecrest study and information obtained from other recent quakes have also shown how important it is to understand how cracks occur along multiple quakes. Errors can affect a larger area.
In New Zealand, scientists were baffled by the bizarre map of the faults that occurred in the magnitude 7.8 earthquake in Kaikoura in 2016. Map shows where from the magnitude 7.8 Kaikoura earthquake in New Zealand in 2016 the surface has occurred.