Media Advisory: UC Berkeley begins monitoring tremors on San Andreas Fault

ATTENTION: Reporters covering science

WHAT: The first of four borehole seismometers will be installed underground in Central California to monitor faint tremors beneath the San Andreas Fault, part of the University of California, Berkeley’s TremorScope project to determine the link between tremors and earthquakes.

WHEN: 2 p.m. PDT Wednesday, May 6

WHERE: Cass Vineyard and Winery, 12 miles east of Highway 101 near Paso Robles, California. Click here for directions.

WHO: Peggy Hellweg, UC Berkeley project lead, research seismologist and Berkeley Seismological Laboratory operations manager

VISUALS: Photographers and videographers are invited to film the seismometers and capture them being lowered into the borehole, as well as view laptop displays of initial data from the sensors. The full video linked here and b-roll are available from Roxanne Makasdjian (roxannem@berkeley.edu).

DETAILS: Tremors are occasional and extremely faint rumblings that originate beneath the zone where earthquakes occur and appear to be associated with slipping rocks deep in the earth.

Seismologist Peggy Hellweg explains the TremorScope project, which involves four subsurface borehole seismometers and four surface seismometers to monitor faint tremors under the San Andreas Fault near Parkfield. Video by Roxanne Makasdjian and Phil Ebiner.

“Tremors are associated with big, very slow movements on the fault, and there is speculation that they might cause big earthquakes,” said UC Berkeley research seismologist Peggy Hellweg. “But we see tremor activity with earthquakes and earthquakes without tremor, so the connection is still unclear.”

TremorScope is designed to measure these tremors more precisely than ever before, using geophones sensitive to high-frequency ground movement and broadband seismometers able to record low-frequency rumblings. Geophones and broadband seismometers are to be installed in four deep boreholes drilled around an area of the San Andreas Fault near Parkfield that seems to be the center of tremor activity where the northern and southern segments of the fault meet. The borehole instruments, which can detect quieter tremors because of less noise underground, complement instruments already in place at four surface stations in the area.

A surface accelerometer was installed at the Cass Winery site in January; the borehole instruments will be installed about 900 feet underground May 6-7. The three other boreholes will be instrumented in coming months.

UC Berkeley seismologists discovered tremors just south of the Parkfield area of the San Andreas Fault in 2004, and subsequent studies suggest that changes in tremor activity may precede earthquakes. Tremors also have been detected in active earthquake zones in Japan, Washington state and other subduction zones around the world.

UC Berkeley seismologist Robert Nadeau studies tremors and noted that the Aug. 24, 2014, magnitude 6 Napa earthquake triggered tremors under the Parkfield region of the San Andreas Fault about 10 hours later, and that they lasted for about 100 days before dropping off.

“With the four surface seismometers now installed, TremorScope is already helping us to locate tremor,” he said. “The deeper borehole seismometers will be able to give us a range of frequencies at higher resolution to figure out what is going on underground.”

The project is funded by a $1.2 million grant from the Gordon and Betty Moore Foundation.

NOTE: Reporters interested in visiting the drill site and seismometer installation should contact Robert Sanders (rlsanders@berkeley.edu) or Peggy Hellweg (hellweg@seismo.berkeley.edu) in advance.