A Measurement of Long-Term Tilt in Colorado and Wyoming.
Abstract
Borehole tiltmeters are conceptually attractive for monitoring long-period crustal deformation and the spatial variations of tidal tilt response due to crustal inhomogeneties. A major part of this research has been devoted to the development and testing of comparatively inexpensive instruments suitable for deployment in standard 6-inch diameter cased holes drilled to industrial tolerance (vertical to within 5 degrees), and also sufficiently sensitive and stable for earth tide studies. The present system is composed of a stainless steel capsule, six feet in length, pressed by flat springs against a stainless steel casing section at the bottom of a hole cased with standard steel pipe. The capsule contains two tilt sensors on a leveling platform. Each sensor is composed of a pendulum whose position is sensed by means of a capacitance bridge. Most of the electronics are installed with the sensor at depth to reduce the temperature sensitivity of the system. Field tests have shown that surfician effects are large at a depth of 20 feet, that these effects are negligible at 100 feet, and that no further improvement is apparent at 200 feet. Measurement of the azimuthal orientation is made with a series of alignment rods. As it is difficult to extend this method to instruments deeper than 100 feet, that depth has been selected for standard installation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1980
- Accession Number
- ADA091720
Entities
People
- J Levine
- J. C. Harrison
Organizations
- University of Colorado Boulder