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UCR Studying Previously Unknown Fault Underneath Ridgecrest


A UC Riverside scientist is studying a previously unknown fault underlying the two large earthquakes that shook the town of Ridgecrest in July.

Dr. Abhijit Ghosh is an associate professor of geophysics at UCR.

On July 6, just a day after the 7.1 earthquake in Ridgecrest, Ghosh drove out to the city to install 25 seismometers in the ground.

Seismometers are instruments that measure vibrations in the ground and record them into a data log that can be used to analyze earthquakes.

Ghosh will use this data to map the structure of the still-unnamed fault in three dimensions.

He’ll also use it to answer some fundamental questions.

Ghosh: “One question to ask is whether the 6.4 has a role to play to trigger that 7.1 and if so, how? What is the mechanism of that triggering? That would be a very important science question to ask because if we can understand how it operates, trigger a larger earthquake, then we can apply that knowledge in other places. And that would be very critical information.”

Credit UCR
This map shows all of the seismic stations measuring the Ridgecrest-area aftershocks.

Another question is how the Ridgecrest earthquakes affected nearby faults, like the Garlock fault in the Mojave Desert.

Ghosh: “So one question this dataset would be suitable to answer is that how these different faults, that is not too far from the 7.1 epicenter, is affected. Because when you rupture a fault, producing earthquakes, it changes the stress pattern in the surrounding area, not just in that fault but also in the surrounding area and if those areas include large faults like the one near Ridgecrest, for example, Garlock, then it also changes the stress in those faults. We have evidence that Garlock fault shows heightened activity, small earthquakes, after the 7.1. earthquake.”

Ghosh says all of this is important information to know as Southern California prepares for the Big One.

Ghosh: “It's not a question of whether, it's a question of when. It is inevitable, it is going to happen, we just don't know exactly when. But again I don't want to sound an alarm, this is a natural hazard, earthquake is a natural hazard, so treat it like any other natural hazards like no matter where you go there are natural hazards - tornadoes, hurricane, flood, wildfire, landslides - so this is another natural hazard, earthquake. And the key is to be prepared. So know what to do during strong ground shaking, between earthquakes, so that is, drop, cover, and hold on. Do not try to run outside. Drop, cover, and hold on. And get an earthquake kit. And inform and educate your family and friends. So those are the critical things to remember.”

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