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Instrumentation; Part 1

Instrumentation; Part 1. Creepmeters (all use LVDT as the displacement sensor) Legacy instruments – 10 to 30 meter Invar wire crossing the fault @ 30 degrees – measure change in distance between two piers

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Instrumentation; Part 1

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  1. Instrumentation; Part 1 • Creepmeters (all use LVDT as the displacement sensor) • Legacy instruments – 10 to 30 meter Invar wire crossing the fault @ 30 degrees – measure change in distance between two piers • Bilham designed – In SF Bay area (5 sites) uses either carbon fibre or quartz rods; Piers are typically helical piles augured to ~5 to 10 meters depth. From R. Bilham

  2. Instrumentation; Part 2Borehole strain • Dilatometers (first installed in 1980s @ Parkfield); uses lvdt to measure volume change of fluid filled chamber that is ~2 meters long • 5 – Parkfield • 5 – SF Bay • 2 – S. Calif • 4 – Long Valley • GTSM (Legacy or prototype PBO strainmeters) Uses capacitor transducers to measure length change of 4 extensometers – length of each extensometer is ~ few cm; averaging area in borehole a few cm. • 1 – SF Bay • 1 – San Juan Bautista • 1 – S. Calif (???) • 2 – Parkfield – failed • Mini-PBO, 3-component strainmeters; uses 3 vertical chambers each spanning a 120 deg. sector. Otherwise similar to dilatometer • 5 – SF Bay (one not functioning as we are still waiting with UCB to have AC power restored

  3. Instrumentation; Part 2Borehole strain – continued • Simultaneous retirement of personnel from borehole strainmeter project one year ago! • Deformation project in Menlo Park only retained partial expertise

  4. USGS Strain and Creepweb urls: • Locations, data plots and data archive: • http://earthquake.usgs.gov/monitoring/deformation/data/ • http://earthquake.usgs.gov/monitoring/deformation/data/plots/ Low resolution in strain – but does show site locations • http://earthquake.usgs.gov/monitoring/deformation/data/download/ Data archive • High resolution plots of strain data; http://escweb.wr.usgs.gov/share/langbein/Web/USGS_strain/

  5. Locations S.F. Bay San Juan Bautista

  6. Locations Parkfield Southern Calif.

  7. Operations, Part 1: • Only funded to continue operations of Bay Area creep and strain. • Working with NCSN and UCB to upgrade their telemetry to accommodate the borehole strain data (which for the 3-component, mini-PBO includes tilt and pore pressure). Data come in as mini-seed at 100 to 200 sps; raw data available at NCEDC; clean data available at USGS • Once complete, we would remove the low-sample rate, satellite telemetry from these sites. • NCSN and UCB would maintain telemetry (along with co-located seismic equipment) • There is a proposal to upgrade the Parkfield strainmeter sites to continuous, high-rate telemetry • No plans to change creep telemetry from low-sample rate telemetry to higher sample rate • Separate from the telemetry, it is not clear about the future of maintenance to strainmeters – assumption is to operate until the 'die'. How do you define death to a strainmeter? Bad battery??? failure of up-hole electronics? Failure downhole? Where is the expertise?

  8. Operations; part 2 • O & M for central Calif. sites (creep and strain) relies upon having a employee located in Parkfield; that individual also takes care of SAFOD related problems. • O & M for Southern Calif; nothing planned.

  9. Processing and Archiving • Both currently done at USGS Menlo Park • Depends upon availability of Langbein • Could this be transferred to UNAVCO?

  10. 1-month GPS and borehole straincomparison High-rate GPS Daily sampled GPS Assumes 10KM distance between GPS stations Borehole strain 1-day

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