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PBO Core/Log/Strain Workshop Held at UNAVCO

Overview

The installation of the first ten PBO borehole strainmeters (BSMs) represents a major accomplishment for the EarthScope community. These instruments provide high resolution geodetic data spanning the frequency band from seismic data to GPS data, giving scientists good insight into processes with durations of hours to weeks. For example, strain associated with a Cascadia episodic slip event in September, 2005, was recorded by at least one and probably several of the BSMs. To date there are eight months of data available from the first four PBO BSMs, and up to six months of data from five other instruments.

In the process of installing these first strainmeters, PBO collected core samples and borehole logging data to help characterize the environment in which the instruments were installed. UNAVCO held a Core/Log/Strain workshop in Boulder on January 23-24, 2006, to discuss the strain data, cores, and logging results and their implications for future installation procedures. The main goals of the meeting were to review data from the PBO strainmeters deployed to date at six Pacific Northwest sites, develop hypotheses to explain for performance issues that originate with the characteristics of the rock and borehole in which the instrument is installed, and look for an optimal approach to borehole characterization that provides necessary information about strainmeter performance at acceptable cost. The meeting began on Monday with discussions on developing criteria for assessing strainmeter performance and how the presently deployed PBO strainmeters perform relative to these criteria, and continued through Tuesday with examination of the cores and logging data.

Summarized below are the recommendations that resulted from the two-day meeting:

  • Recommendation #1: It is not necessary to core strainmeter boreholes (however spot core where possible).
  • Recommendation #2: In lieu of coring, it is necessary to obtain a full site of geophysical logs, specifically: acoustic televiewer; optical side-scan vide; caliper; combination sonic; gamma; resistivity; temperature; inclination and sp.
  • Recommendation #3: UNAVCO should lease/purchase equipment to do the geophysical logging and the logging should be carried out by the UNAVCO personnel.

For more information please contact Greg Anderson or Kathleen Hodgkinson.

Meeting participants included: Greg Anderson, Mike Hasting, Kathleen Hodgkinson, Mike Jackson, Bob Mueller, Evelyn Roeloffs, Amy Day-Lewis, Roger Bilham, Chuck Meertens, David Mencin, and Will Prescott.


Last modified: Sunday, 11-May-2014 18:01:18 UTC

 

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