Berkeley Seismological Laboratory installing seismometers to study link between tremors and earthquakes

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Robert Sanders/UC Berkeley/Courtesy

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On Wednesday, the Berkeley Seismological Laboratory began installing the first of four underground seismometers designed to measure faint tremors occurring below the San Andreas Fault.

The installation of the first seismometer, located in Cass Vineyard and Winery near Paso Robles, will be completed Thursday, while the other three devices will become operational in the next few months.

These new seismometers are part of UC Berkeley’s TremorScope project — funded by a $1.2 million grant from the Gordon and Betty Moore Foundation — that aims to determine the link between small tremors and major earthquakes along the San Andreas Fault. According to Peggy Hellweg, the UC Berkeley project leader, the exact nature of this link is not yet known.

“Tremors are associated with big, very slow movements on the fault, and there is speculation that they might cause big earthquakes,” Hellweg said in a Monday press release. “But we see tremor activity with earthquakes and earthquakes without tremor, so the connection is still unclear.”

By installing the seismometers in boreholes at depths of approximately 900 feet, the researchers will be able to analyze tremors — which are often difficult to detect from near the earth’s surface due to extraneous noise from wind and traffic — with unprecedented precision.

“These new seismometers are deeper and more advanced than any other devices that are already in place,” said Robert Nadeau, a research seismologist involved in the project who is an expert on nonvolcanic tremors. “They’ll allow us to monitor the tremors’ frequencies very accurately in real time.”

Tremors have been connected with several recent earthquakes, including those in the Parkfield region of the San Andreas Fault that were triggered by the Napa earthquake in August 2014.

Tremors may also precede earthquakes, which is part of what the TremorScope project hopes to determine.

The Berkeley Seismological Laboratory is currently working on a number of projects to study and prepare for earthquakes, such as an advanced early warning system.

“When we detect the primary wave of an earthquake, our system electronically notifies everyone when the more damaging secondary waves will arrive,” Nadeau said. “BART actually relies on this system to stop trains if a large earthquake is coming.”

According to city spokesperson Matthai Chakko, Berkeley analyzed its buildings in the wake of the large 1994 Northridge earthquake and found that 321 of them were structurally weak. By requiring property owners to post signs indicating that their buildings were unsafe, the city effected the retrofitting of 112 of these buildings, while the remaining seismically dangerous properties will be retrofitted by the end of 2018.

“Berkeley’s efforts have been so successful that it’s been used as a model for other cities,” Chakko said. “Berkeley has really been on the forefront of addressing these issues.”

Contact Logan Goldberg at [email protected].