Borehole Tilt Measurements at the Charlevoix Observatory, Quebec.
Final technical rept. 12 Sep 79-31 Dec 82,
DALHOUSIE UNIV HALIFAX (NOVA SCOTIA) DEPT OF OCEANOGRAPHY
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An array of three Bodenseewerk Gbp10 borehole tiltmeters was established to measure tidal, transient and secular tilting of the Earths surface in the Charlevoix region of Quebec. Two of the tiltmeters operate at a depth of 47m and the third at 110m. They are placed at the corners of a roughly equilateral triangle with side lengths of 70-90m. The Charlevoix region is an area of high intraplate seismic activity and the location of the tiltmeter array is primarily designed to investigate the relationship between earthquake activity, the tectonic stress that induces it, and the tilting of the Earths surface. Tilt observation for about 1 year from each of the 47m boreholes were analyzed. The results show that 1 the long period secular tilt is strongly correlated with the piezometric pressure measured in the nearby water wells 2 there are tilt step offsets at the time of local earthquakes but these are probably a site effect 3 the mean M2 and O1 load tide admittances are in reasonably good agreement with the predictions of a model of loading by the marine tides in the nearby St. Lawrence estuary and 4the observations show significant variations in tidal admittance with time but it is not known whether these merely reflect time changes in the marine tide admittance or whether the solid earth response to tidal forces is changing.