Bulletin of the Seismological Society of America · 1979 · 33 citations · 7 references
Geodetic Tilt MeasurementsEngineeringMeasurementEducationGeophysical Signal ProcessingBench Mark ArraysEarth ScienceGeophysicsSatellite MeasurementCalibrationEarthquake SourceInstrumentationBorehole Tiltmeter SitesGeodesyGeophysical InterpretationGeographyRadiation MeasurementCentral CaliforniaSan Andreas FaultEarthquake RuptureSpace WeatherTectonicsFault GeometryAperture 300Space Geodesy
abstract Changes in tilt have been measured by annual or semi-annual spirit level surveys of small-aperture (40 to 400 m) bench mark arrays located at borehole tiltmeter sites along the San Andreas Fault in California. Because there are six or more bench marks in most arrays, the tilt is overdetermined, and realistic estimates of uncertainties can be made. The large arrays (aperture 300 m) afford a precision (two standard deviations) of about 3 μrad in measuring tilt, and the measured tilt remains constant to within ±5 μrad over periods of up to 5 years. The small arrays (aperture 10 μrad) in tilt within periods on the order of a year, but the best tiltmeters exhibit a stability comparable to that obtained from surveys of the large-aperture bench mark arrays.
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