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Borehole Strainmeters

Borehole Strainmeters. Evelyn Roeloffs USGS. Topics. Cascadia Slow Slip Events as Seen on an Earthscope PBO borehole strainmeter Sacks- Evertson New Design Three-component borehole strainmeters installed 2011 . Cascadia Slow Slip: PBO BSM B004.

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Borehole Strainmeters

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  1. Borehole Strainmeters Evelyn Roeloffs USGS

  2. Topics • Cascadia Slow Slip Events as Seen on an Earthscope PBO borehole strainmeter • Sacks-Evertson New Design Three-component borehole strainmeters installed 2011

  3. Cascadia Slow Slip: PBO BSM B004

  4. Seasonal variations are as large as the slow slip events... …but at B004, seasonal signals are common to all gauges, which allows them to be removed

  5. Compare Maximum Shear Strain from Data and Model

  6. Adjust Propagation Speed

  7. Sacks-Evertson New Design 3-component Borehole Strainmeter • Horizontal cross-section • 3 “strain” channels are each total volume change in two opposite sensing chambers • Chambers have elliptical cross-section and are 3 meters long

  8. Two Sacks-Evertson BSM’s Installed 2011 B947 “Valdez” near San Juan Bautista, 546’-556’ in hard sandstone/siltstone B948 “Gold Hill 3” near Parkfield, 493’-503’ in hard diorite/granodiorite with healed fractures

  9. B947: Long-term Data

  10. B948: Long-term Data

  11. M8.2 Earthquake Off SumatraApril 11, 2012 B948 B947

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