Under subcontract (DOE/UCCSN DE-FC28-98NV12081, Task 7) from the Seismological Laboratory of the University of Nevada-Reno, the University of California, San Diego (UCSD), has designed, installed, and operated a laser strainmeter (LSM) in the Exploratory Studies Facility (ESF) at Yucca Mountain, Nevada. This instrument provides precise deformation monitoring of the (proposed) repository block. This document describes the history of the installation, outlines the principles of operation of the system, documents the integral recording and control system and file formats used, and provides information on how QA has been implemented, with the aim of being a self-contained description which could be used (in conjunction with the data files at the TDMS) to understand the measurements made by the LSM. Appendix A gives the unique digital signatures for all data files submitted to the TDMS. The instrument was installed along the south wall of the tunnel, between 69+46 m and 65+41 m (tunnel coordinates). The resulting azimuth (91°) provides good sensitivity to the posited long-term strains from geologic sources. Designing an instrument for the tunnel was a challenge, as was installing it, given the usual, strict local operating procedures; these two elements combined to increase substantially the overall time to completion, though the experience gained has put us in a good position for further work in this setting. We have fully documented (SN) all aspects of the installation, and have complete engineering plans of the LSM available (Appendix B). The instrument began operating to QA standards on 2002:233 (August 21, 2002), and has recorded strain since that time, though with interruptions caused by the very strong shaking from the mining trains, which both caused sizeable gaps in the series and caused the lasers to degrade much more rapidly: both problems have been dealt with successfully. The instrument is producing quality records. Preliminary results from the laser strainmeter suggest that seismic waves and tides cause strains with no obvious anomalous response or nonlinearity; and that air-pressure changes can cause significant strains, with a response that depends on the spatial pattern of pressure applied. With the data so far available, we can constrain the long-term strain rate to be less than 0.2 /z£/yr. A longer-term record should greatly improve this constraint.
Earthquakes; Nevada – Yucca Mountain; Rock deformation; Strains and stresses
Earth Sciences | Geology | Geophysics and Seismology | Tectonics and Structure
Wyatt, F. K.,
Agnew, D. C.,
Brune, J. N.,
Smiecinski, A. J.
Longbase laser strainmeter measurements from the South Ramp of the Yucca Mountain facility.
Available at: http://digitalscholarship.unlv.edu/yucca_mtn_pubs/83