August 16, 2007
Construction of the final pair of PBO long baseline (laser) strainmeters, near Cholame, California, is making impressive progress. These 400-meter long instruments are being sited over a region of recently discovered seismic tremor activity. The instruments will also detect strain changes in the Parkfield area to the north, and on the locked section of the San Andreas Fault nearby, which last ruptured 150 years ago. The first of the PBO longbase (laser) strainmeters, DHL2, is located at the other end of the southern San Andreas Fault, some 500 km distant; that highly strained segment of the fault has not ruptured in over 300 years and is estimated to be supporting over seven meters of slip-deficit. The photograph shows the endpoints of the East-West instrument during the drilling of the optical-fiber anchoring systems which are emplaced in paired 25 meter deep boreholes. When the strainmeter construction is completed there will be small buildings at each end for the optics and electronics, with an above-ground evacuated pipe providing a stable pathway for laser light running between them.
The companion North-South instrument is nearby, also running parallel to the local country road. PBO has been able to use this ideal location thanks to the cooperation of the site landowner, Mr. Bill Vogel, a local rancher who has also permitted the installation of GPS systems and two borehole strainmeters.
Last modified: Sunday, 11-May-2014 18:01:06 UTC