What may the following mega-earthquake on California’s infamous San Andreas fault appear like?
Would it not be a repeat of 1857, when an earthquake estimated at magnitude 7.7 to 7.9 ruptured the fault from Monterey County during Los Angeles County? Would it not be extra akin to the good 1906 San Francisco earthquake, which started simply offshore of town and ruptured in two instructions, towards Humboldt County and Santa Cruz County?
Don’t wager on an equivalent sequel.
That’s the implication of a examine revealed Monday within the journal Proceedings of the Nationwide Academy of Sciences. The report, coauthored by scientists at Caltech in Pasadena, studied a large earthquake that ruptured within the southeast Asian nation of Myanmar on March 28 — on a fault identified for being eerily just like the San Andreas.
The earthquake ended up rupturing a for much longer part of the fault than scientists anticipated, given the seismology of the area.
The implications of this examine are that “earthquakes by no means come again precisely the identical means,” Solene L. Antoine, a postdoctoral fellow at Caltech and the examine’s lead creator, stated in an interview.
An area man drives a bike previous a broken constructing, within the aftermath of an earthquake in Naypyidaw, Myanmar, on March 30.
(Aung Shine Oo / Related Press)
“It got here as a shock that you would get such a protracted rupture,” stated Jean-Philippe Avouac, a coauthor of the examine and a professor of geology and mechanical and civil engineering at Caltech.
March’s Mandalay earthquake devastated Myanmar, killing at the least 3,791 folks and an extra 63 folks in Thailand. Excessive-rise buildings have been broken as distant as Ho Chi Minh Metropolis in Vietnam and houses have been broken within the Ruili space of China. Harm was estimated at $1.9 billion, in line with the U.S. Geological Survey.
It was probably the most highly effective earthquake in Myanmar in at the least 79 years.

“Violent” and “excessive” shaking, proven in crimson, was felt all alongside the 317 miles of the ruptured Sagaing fault in Myanmar throughout a magnitude 7.7 earthquake in March.
(U.S. Geological Survey)
The magnitude 7.7 earthquake ruptured an astonishing 317 miles of the Sagaing fault, a discovering primarily based on Antoine’s evaluation of satellite tv for pc knowledge exhibiting earth motion after the quake. That’s the longest seismic rupture ever documented on a continent.
By comparability, California’s 1906 earthquake ruptured 296 miles of the San Andreas fault; and the 1857 earthquake, 225 miles. Longer seismic ruptures have been discovered solely on subduction megathrusts deep beneath the ocean.
What’s clear from the examine is that whereas California’s subsequent “Massive One” could share some traits of beforehand documented devastating quakes, it’s unlikely to be a precise replay. Because the current expertise in Myanmar reveals, even well-documented faults can behave in stunning methods.
The following step is to develop a mannequin simulating earthquakes over many millennia for the San Andreas fault, which the authors plan to do sooner or later. However the San Andreas fault “is way extra complicated,” Avouac stated. “It’s not going to return quickly, as a result of it’s fairly a heavy calculation.”
Nonetheless, such simulations would offer a mannequin of “all doable situations in order that we’ve got a greater view of the vary of doable ruptures that might occur.”

Rescuers work on the website of a high-rise constructing underneath building in Bangkok, Thailand, that collapsed after a magnitude 7.7 earthquake centered in Myanmar on March 28.
(Wason Wanichakorn / Related Press)
For example, possibly the San Andreas fault will rupture in smaller, separate earthquakes, Avouac stated.
Or it could possibly be a a lot bigger earthquake — rupturing the fault not simply from Monterey to Los Angeles counties, however maybe all the way in which into San Bernardino, Riverside and Imperial counties, which might exceed magnitude 8. Such a quake could be the biggest simultaneous catastrophe in trendy California historical past, with large swaths of the state wracked by highly effective seismic shaking all of sudden.
By comparability, the 1994 Northridge earthquake’s footprint was comparatively constrained, severely affecting solely a portion of Los Angeles County, particularly the San Fernando Valley — associated to its comparatively smaller magnitude of 6.7.
However whereas modeling earlier exercise on the San Andreas fault will present a glimpse into the big selection of doable outcomes, it is not going to pinpoint exactly when the following nice quake will strike.
“We will’t simply anticipate the very same factor to occur,” Antoine stated. “It’s a matter of simply exhibiting what situations are doable, the variety of situations and seeing what are the implications of every of these situations.”

A Buddhist monk walks close to a collapsed pagoda on March 30 after an earthquake in central Myanmar.
(Thein Zaw / Related Press)
Generally, Avouac stated, “it’s quiet for a very long time, nothing occurs … stress is increase, the fault is locked for a very long time, nothing occurs, after which, increase, you’ve a big earthquake.”
“After which you’ve different durations throughout which you’ve loads of [seismic] exercise, however these earthquakes are all smaller,” Avouac stated.
However “smaller” earthquakes, within the minds of researchers, are nonetheless large to the layperson. Within the examine’s simulations, there are durations the place earthquakes round magnitude 7.7 are frequent. In different durations, earthquakes max out at magnitude 7.5 or so, however are extra frequent.
The complete size of the Sagaing fault — together with areas that didn’t rupture within the March earthquake — is 750 miles, north to south, from the Himalayas to the Andaman Sea, and helps accommodate the northward push of the Indian tectonic plate.
The truth that 317 miles of the Sagaing fault ruptured in March was stunning to scientists. Solely about 170 miles had been quiet seismically for greater than a century, having final ruptured in 1839.

(Solene Antoine / Caltech)
Scientists name these “seismic gaps” — specific areas of a fault that haven’t just lately ruptured.
Typically, scientists would’ve anticipated solely this long-dormant 170-mile piece of the Sagaing fault to rupture, Avouac stated, however no more just lately ruptured sections. That features a 100-mile stretch that ruptured in giant earthquakes in 1929 and 1930, and a 50-mile stretch that went off in a pair of quakes in 1946 and 1956.
As a substitute, even these fault segments ruptured within the large March earthquake.
So what provides?
A doable rationalization is the Sagaing fault’s extraordinary smoothness. “And other people have noticed that when the fault could be very easy, the rupture … tends to propagate at a velocity” so quick that it ends in an “extraordinarily elongated rupture,” Avouac stated.
The examine additionally revealed the outcomes of a pc mannequin simulation how earthquakes may rupture alongside sections of all the 750-mile lengthy Sagaing fault. The code, developed by examine coauthor Kyungjae Im of Caltech, means that over a hypothetical 1,400-year interval, there could be no repeatable patterns.
In different phrases, earthquakes didn’t appear to re-occur like clockwork, rupturing the identical stretch of fault in a repeatable, predictable sample.
“There may be complexity right here. And it is because every time you’ve an earthquake, it redistributes the stress on the fault, which goes to affect the following earthquake,” Avouac stated. “There’s a self-induced complexity within the course of, and that results in a little bit of randomness.”
There may be one certainty, which is certain to disappoint anybody who shares the hope {that a} “Massive One” merely received’t ever strike California once more.
“There will probably be an earthquake sooner or later,” Antoine stated. “If there may be stress increase on the fault, the fault received’t maintain eternally.”
Additional analysis and observations are important to refine fashions of future doable earthquakes, together with from the Sentinel satellites, that are operated by the European Area Company, the authors stated.
The opposite coauthors of the examine are Rajani Shrestha and Chris Milliner of Caltech; Chris Rollins of Earth Sciences New Zealand; Kang Wang of the Washington-based EarthScope Consortium; and Kejie Chen of the Southern College of Science and Know-how in Shenzhen, China.