A Holelock for Deployment of Two Streckeisen Long-Period Seismometers in a Single Borehole
Unusual for a Global Seismograph Network (GSN) borehole station, MSVF (Monasavu, Fiji) includes only a single 100 m borehole, which hosts the station's primary seismometer. Despite high seismic noise levels there, MSVF thus offers no noise environment comparable to that of the primary sensor where a traditionally-installed secondary seismometer can be deployed. However, a non-traditional installation of the secondary sensor---in the borehole's unoccupied upper portion---is possible. But can it be done without loss of primary seismometer data quality and without risking the removal of either sensor?
Here we report on the successful testing and evaluation of a new holelock designed to allow the installation of a Streckeisen STS-5A or STS-6A seismometer above a previously-deployed seismometer. The holelock, which does not require power to operate, features a massive and robust all-mechanical fail-safe design that also provides for safe management of cables from the downhole sensor.
A prototype of the new holelock was lab tested by Project IDA at UCSD in late Fall 2019. In late November, along with a Streckeisen STS-5A, it was deployed at the XPFO test facility at Pinyon Flat, California, at a depth of 10 m in a 100 m cased borehole already occupied by a Streckeisen STS-6A near the bottom. Noise spectra from the two sensors are consistent with their relative vertical positioning in the borehole, and the noise performance of the downhole STS-6A noise remains unchanged. Deconvolved waveforms from the 15 December 2019 M6.8 Magsaysay (Philippines) event at a distance of 109 deg are essentially identical, with R2 > 0.99.
The deployment of these two sensors and holelocks at MSVF is scheduled to take place during the second calendar quarter of 2020. This installation method offers simplicity in addition to logistical and cost benefits and could serve as a model for network operators when considering future seismic stations.
Presenting Author: C W. Ebeling
Additional Authors
C W Ebeling cebeling@ucsd.edu Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States Presenting Author
Corresponding Author
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Guillermo Naranjo gdnaranjo@gmail.com Kinemetrics, Pasadena, California, United States |
Joseph M Steim steim@quanterra.com Quanterra, Shirley, Massachusetts, United States |
Ian M Standley Ian_Standley@kmi.com Kinemetrics, Pasadena, California, United States |
Kevin Brook kevinb@quanterra.com Quanterra, Shirley, Massachusetts, United States |
Christopher Sites csites@ucsd.edu Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States |
James Conley jdconley@ucsd.edu Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States |
Jon Berger jberger@ucsd.edu Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States |
Peter Davis pdavis@ucsd.edu Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States |
A Holelock for Deployment of Two Streckeisen Long-Period Seismometers in a Single Borehole
Category
Recent Advances in Very Broadband Seismology