Project will monitor tremor activity beneath San Andreas Fault

BERKELEY — The Berkeley Seismological Laboratory will begin early next year to install earthquake detectors on the southern San Andreas Fault near the town of Cholame to study mysterious tremors discovered beneath the area. Tremors from deep underground have been detected in the area of Cholame, 32 kilometers southeast of Parkfield. The TremorScope project will install instruments in four 300-meter deep boreholes (red stars) and at four surface stations (orange open stars) to monitor these tremors and determine how they relate to earthquakes on the southern San Andreas Fault (SAF). The Cholame Segment (dashed arrow) forms the northernmost extent of the currently "locked" fault segment that last ruptured in California’s great magnitude 7. Fort Tejon earthquake, in 1857. The triangles and squares represent existing seismic stations, while the circles are the most active tremor areas. (TremorScope/UC Berkeley) Tremors are extremely faint and periodic rumblings originating 20-40 kilometers below ground – far beneath the zone where earthquakes occur – that appear to be associated with slipping rocks deep in the earth.