San Jacinto fault, more active than San Andreas, could produce damaging quake sooner than thought
Trapped under rubble for 30 hours: Mexico quake survivor's story Video provided by AFP
The San Jacinto fault may not be shaking yet, but it's trembling. And if it goes, according to one study, it could rupture along with the San Andreas fault--producing a catastrophic earthquake.
Scientists at the University of California, Riverside have been using new technology to track faint movements deep inside the San Jacinto fault. This week, they've published the results of a project tracking "tectonic tremors."
The finding, said UCR earthquake seismologist Abhijit Ghosh may mean "the next damaging earthquake may be sooner than we previously thought." But he added: "To quantify these aspects, we need more data, more analysis."
The San Jacinto fault, which cuts through the southern edge of the Coachella Valley, is not as large as the more well-known San Andreas fault, which many Californians have learned to fear for its potential to produce a devastating earthquake coined "the big one".
While the San Andreas fault encompasses the space where the North American and the Pacific plate meet, the San Jacinto fault is a fracture within the Pacific plate. However, the San Jacinto fault should not be underestimated when it comes to its potential to cause damaging earthquakes.
"It's more active in terms of earthquake activity than the San Andreas fault," says Abhijit Ghosh, earthquake seismologist at UC Riverside.
Additionally, a 2016 study by CSU Northridge professor Julian Lozos found that the 7.5 earthquake of 1812 began on the San Jacinto fault and then "propagated" to the San Andreas fault.
Lozos' revelation makes the UCR research on the San Jacinto all the more important in predicting "The Big One."
Together with graduate student Alexandra Hutchinson, Ghosh has used a new sophisticated technology called "multibeam backprojection", to detect seismic signals previously undetectable by regular seismic instruments.
"It allows us to detect this very faint signal that we previously couldn't detect," Ghosh said. The signals they detected are called tectonic tremors, faint movements measurable in the shallow parts of the tectonic plate.
Just like the tremors some humans experience at a higher age, making it hard to hold a pencil or play an instrument, the reasons for the subtle shaking movement measured by Ghosh and Hutchinson lie deep beneath the surface.
"Typically an earthquake is a sudden release of energy," Ghosh says. In the case of tectonic tremors, the underlying movement takes place in deeper levels of the tectonic plate. "Instead of a sudden slip and a quick release of energy, it slips slowly," Ghosh explains.
In their research, Ghosh and Hutchinson focused on a specific area of the San Jacinto fault, the Anza gap.
"In the past one- to two-hundred years, San Jacinto fault has produced damaging earthquake along the entire faultline, except for one section: the Anza gap," Ghosh says.
The gap is not a physical gap, but rather an area, close to the small town of Anza, California, which has been unusually quiet. "That's why we call it Anza gap, because its a gap in earthquake activity," Ghosh explains.
Still waters run deep, and so does the Anza gap.
"It can not be silent indefinitely, it has to break," Ghosh warns. "One way to do that is through earthquake activity."
It is not clear whether these findings increase the probability of an earthquake in the near future, but they show that there is an important factor which has not been taken into account before.
In 2004, tectonic tremors occurred leading up to a 6.0 earthquake in Parkfield, California, nicknamed "the earthquake capital of the world" for its frequent seismic activity.
Scientists back then did not have the technology to identify tectonic tremors, but researchers were able to retroactively analyze the data leading up to the quake.
The data did not provide conclusive results to clearly identify a relationship between tremors and eventual earthquakes.
"We did not see anything that stood out from the regular activity before the Parkfield earthquake," said research geophysicist David Shelly.
Still, Shelly is excited about the additional information the analysis of tectonic tremors may provide for researchers in the future.
Until scientists are able to clearly identify any patterns - if they exist- which could help predict earthquakes, Southern Californians need to be vigilant in their earthquake preparation.
"In SoCal we live in earthquake country," says Ghosh. "Just like a flash flood, a wildfire, we can't predict it, we can only prepare for it."