Last Week's Earthquakes May Have Exposed A New Fault Line
Given Southern California's history of quakes, the unrelenting media coverage every time the ground moves, and all the premier research institutions based here, you might assume we know everything about earthquakes.
The Little Lake fault zone -- where the two quakes took place -- wasn't on many lists as a top contender for a big rupture. Then, the re-rupture of the same fault just a day later caught even scientists off guard. On top of that, that re-repture might have revealed a whole new fault.
Scientists are busy prowling around the Mojave Desert looking for revelations large and small right now, but here's some of what they've already figured out -- and what they haven't.
WE MAY HAVE JUST FOUND A NEW FAULT LINE
Before the massive earthquake in Ridgecrest, scientists didn't know about the roughly 30-mile long continuous, straight, fault that looks like it runs right through the region.
"The maps of faults we had prior to the event show a whole bunch of little sections, but not exactly this huge, long throughgoing fault that seems to have ruptured," said Morgan Page, a geophysicist with the U.S. Geological Survey. "We're not really sure why this wasn't in the maps and how this fault could link up with other faults that we do know about in the area."
The 6.4-magnitude quake on July 4 only ruptured a small part of the bigger fault that the 7.1-magnitude quake revealed the next day.
It's interesting, Page said, that "a big earthquake had already happened, and that wasn't enough to completely remove all of the stress on that portion of the fault. It was still able to re-rupture in a bigger event."
If you think it's strange that the long fault might be a surprise, just know that it's not the first time this has happened. Back in 1994, we were unaware of the Northridge fault until it crippled swaths of Los Angeles.
"It's just a humbling reminder that when it comes to earthquakes 7 and smaller, it's very difficult to make sure you've inventoried everything that can happen," said Ross Stein, an emeritus scientist with the USGS and CEO of Temblor, a business that evaluates earthquake risk.
GEOLOGISTS ARE HAVING A FIELD DAY, LITERALLY
After a quake of this magnitude, there's a big rush to document changes to the earth as quickly as possible because it's only a matter of time before weather, crowds, and additional earthquakes obscure the pristine data out in the field.
The desert around Ridgecrest is dry and undeveloped with clear evidence of seismic activity across the surface. All of which means it lends itself to study.
Brian Olson, an engineering geologist with the California Geological Survey, was already close by when the 7.1 struck; he'd already rushed out to survey the area after the 6.4 foreshock.
"We gathered our stuff, went outside into the parking lot and you've never seen so many geologists with big smiles," he said.
Using measuring tapes, Olson and his colleagues documented the size and offset at a break in the road. They then sprayed white lines across the break, so they could track how far each side moved in the coming days.
More from our #RidgecrestEarthquake coverage: DOC Drone footage south of Ransberg Road captures surface rupture. Photo: Roadway surface displacement - right-lateral offset approx. 6.5 ft and 3' vertical. Offset bottom of pic 5' ~ Footage: Nathaniel Roth. Photo: @mrbrianolson pic.twitter.com/6kDX8Tcc1e— California Department of Conservation (@CalConservation) July 10, 2019
In the days since the quakes, scientists have continued to gather information from high-precision GPS instruments, seismometers, drone flyovers and satellites, all of which document the earth as it continues to shift and settle.
The research has been complicated by the fact that a lot of the fault runs beneath the Naval Air Weapons Station China Lake, which means scientists had to be escorted through restricted areas areas by unexploded ordnance specialists.
ANOTHER QUAKE IS ALWAYS COMING
The Garlock is a sleeping giant. It bisects central California and is capable of producing an earthquake above a magnitude 7, USC earthquake geologist James Dolan said. He added that there's a remote possibility that a quake on the Garlock could trigger a quake on the San Andreas fault.
However, there's no indication as of yet, that any of these earthquakes increased the risk of a rupture on either one of the faults.
Scientists are continuing to study how last week's quakes changed the earth around the fault and whether other faults in the region have been impacted.
On Monday, researcher David Sandwell and his colleagues from the Scripps Institute of Oceanography were doing just that, driving around the desert checking on what they call "monuments."
This is a monument. A reference point - concrete poured onto bed rock with a metal rod - that will help scientists measure the movement of earth over time. Helps them figure out what level of strain has been distributed to earth around the faults. That’s a GPS unit stuck on top. pic.twitter.com/u8PcpV9xvo— Jacob Margolis (@JacobMargolis) July 8, 2019
"We want to get the state of stress in the entire region surrounding the fault," he said. "It's all part of trying to forecast earthquakes. Where's the next earthquake going to be, how big is it going to be?"
THE BIG ONE IS COMING. GET PREPARED
We don't want to scare you, but the Big One is coming. We don't know when, but we know it'll be at least 44 times stronger than Northridge and 11 times stronger than Friday's quake. To help you get prepared, we've compiled a handy reading list