Seismologists say they have detected small tremors deep beneath the San Jacinto Fault zone in the San Andreas Fault system which indicate there could be a massive earthquake in the region anytime soon. According Professor Abhijit Ghosh and graduate student Alexandra Hutchinson, in a new study published in the Bulletin of the Seismological Society of America , new sensitive measurements based on the multi-beam back projection technique have detected for the first time evidence of small tectonic tremors deep below the Earth’s surface which indicate that slow earthquakes are occurring deep below the fault system.
The San Jacinto Fault zone, a part of the San Andreas Fault system in Southern California, is the area where the stress which has been accumulating between the North American Plate and Pacific Plate is expected to be released. The researchers noted that a part of the San Jacinto Fault zone, a 20-km area known as the Anza Gap, is showing a greater level of seismic activity than previously suspected and that a massive earthquake could strike in the region at any moment.
The discovery is significant because it changes the perception that the San Jacinto Fault zone in Southern California has been relatively quiet in the past two centuries. It means that contrary to previous belief, the North American Plate and the Pacific Plate up to 14 miles below the Earth’s surface have been moving for decades and accumulating stress that could release a massive earthquake at any moment.
The researchers confirmed that the tremors are harbingers of an impending major quake. According to Ghosh, there is a link between slow earthquakes occurring deep below the surface and damaging earthquakes occurring close to the surface.
“While relatively little is known about tectonic tremors, in part because they have historically been difficult to detect, we know that these tremors are being caused by slow slips deep in the fault,” said Abhijit Ghosh, an expert in earth sciences at the College of Natural and Agricultural Sciences at University of California, Riverside.
“For that reason, many experts suspect that this area is ripe to produce a damaging earthquake.”
Ghosh noted that long before the detection of the small tremors, seismologists had been suspicious of the apparent lack of seismological activity in the Anza Gap region in the past two centuries because it raised unanswered questions about how the area was managing the stress building up due to the movement of the North American Plate and the Pacific Plate.
However, the researchers tried to calm fears that the results of the new study indicate imminent disaster. According to Ghosh, rather than view the deep slow tremors as harbingers of imminent catastrophe, scientists see them as offering a new way of forecasting major earthquakes more accurately.
The ability to predict future earthquakes will help to improve our ability to reduce the toll on human populations.
However, more research is needed before they can be used to forecast earthquakes.
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