Together San andreas fault Near the city of Parkfield, California, an incredibly sensitive array of seismic and GPS devices have been detecting something strange for years: Earthquake It comes down when California has the most seismic movement.
These earthquakes cannot be felt on the surface, but they are tricky because this section of San Andreas near the city of Parkfield also shines with magnitude-6 or earthquakes every 20 or 40 years – damaging buildings. Strong enough to pose a threat to nearby people. And these deep shocks can be associated with surface templars.
Now, new research reveals the root of these silent, deep earthquakes. They can occur when rocks slide against each other to a depth of more than 10 miles (16 kilometers). Collision) Is sufficient to melt, which enables them to slide rapidly and cause tremors. These shocks can also relieve stress in a way that affects the upper crust.
related: Photo Journal: The Magnificent San Andreas Fault
“There is a possibility that these shocks may play an important role to trigger large earthquakes near the surface,” said Sylvain Barbot, a geophysicist at the University of Southern California, who led the research.
Secret of parkfield
San Andreas in Parkfield is probably the best monitored section of the fault. Scientists began to focus on monitoring the area around Parkfield due to their relative forecasts. He hoped to be able to predict the first successful earthquake on this stream of fault, An expectation that collapsed in 1993 When the fault failed to repeat one of its magnitude-6. Instead, the mistake was caught on September 28, 2004, Generate a magnitude 6.0 6.0.
In 2004, researchers drilled seismometers into the fault zone to set 1.2 to 1.8 miles (2 to 3 km) deep to better detect the movements of San Andreas. With GPS devices, which allow scientists to measure ground deformation that does not create tremors – or aseismic movement – these devices allow for detailed monitoring of fault, even earthquakes that show Cannot be detected otherwise.
These shocks are 10.5 miles (17 km) below the surface of Emeaning, More than a mile (2 km) higher than seismic activity elsewhere in California.
“We are studying them [small quakes] Because these earthquakes occur every few months, “Barbot told Live Science,” so it gives us a chance to understand them with a lot of data, but these findings apply to understanding large earthquakes. ”
Barbot and his colleague Lifeng Wang of the China Earthquake Administration in Beijing used a computer model to mimic a real-life mistake and its movements. They found that temperature is an important metric in reproducing regularly, almost monthly, that shocks deep below the fault. As the rocks slide against each other, they heat up and begin to melt. Depending on the type of rock, this melting occurs between 1,100 ° F and 1650 F (600 to 900 ° C).
Gooey rocks move more easily, create even more friction, are even hotter and move faster. This positive feedback loop creates deep earthquakes detected by seismic monitoring. The researchers published their findings in the journal on 4 September Science advance.
It is possible that these deep shocks play a role in triggering strong earthquakes to surface in Parkfield, Barbot said. This relationship can also work the other way, with higher speeds in the crust to help drive deeper vibrations.
Barbot and his colleagues hope to discover signs of this melting on rocks that now surface. If they can learn more about rocks that are erratically down and what happens to them as they melt, researchers may be able to improve their models and better predict how San Andreas will behave.
“In general, we understand that earthquakes are actually part of a wider spectrum of things that can happen on a fault, from completely asymmetrical to mild to seismic to extremely seismic and dangerous,” Barbot said. “We are trying to understand the whole spectrum of this behavior.”
Originally published on Live Science.