J. J. Sweeney, D. Felske, R. Mellors (LLNL) J. Louie (U. Nevada - - PowerPoint PPT Presentation

LLNL-PRES-637058

This work was performed under the auspices of the U.S. Department

• f Energy by Lawrence Livermore National Laboratory under contract

DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

June 17, 2013

• J. J. Sweeney, D. Felske, R. Mellors (LLNL)
• J. Louie (U. Nevada Reno) and S. Pullammanappallil (Optim, Inc.)

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The views expressed here do not necessarily reflect the views of the United States Government, the United States Department of Energy, or Lawrence Livermore National Laboratory. The work presented here was made possible through support of the United States Department of Energy, National Nuclear Security Agency.

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On Site Inspection Continuation Period of the CTBT begins after the initial inspection period (up to 25 days duration). Some inspection techniques can only be used during the Continuation Period [active seismic, resonance seismic, magnetic, gravity, and electrical methods] — the so-called Continuation Period Technologies (CPT). CPT can be divided into shallow and deep methods; shallow methods are commonly used in environmental, archaeological, and resource studies. The objective of deep CPT methods is to detect an anomaly caused by a possible underground explosion (deep rubble zone or cavity).

There is little experience with using deep CPT methods to look for anomalies caused by explosions

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The goal is to apply electrical methods and active seismic methods over a known underground nuclear explosion (UNE) test location in order to assess their application for OSI. Methods used: dipole-dipole resistivity survey, induced polarization (IP) survey, controlled source audiomagnetotelluric (CSAMT) survey, and an active seismic survey using both shear (S) and compressional wave (P) sources.

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High desert climate (Nevada, 2000 m elevation, former nuclear test site) Deep water table (> 600 m depth) Layered volcanic rock (Cenozoic tuff, welded and non-welded) Relatively flat topography and easy access at surface Test conducted in 1985: Working point depth 608 m; yield < 150 kT; cavity radius ~ 60 m; no surface crater; rubble chimney estimated to extend up to 200 m depth

Quartz-bearing rhyolite lavas Tuffs, welded and non-welded

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Dipole-dipole and IP are useful for tracking the depth to the saturated zone down to ~ 200 m. These methods were not expected to see effects of the UNE; we wanted to study the “noise” environment of a test location (effects of well casing, cables lying on the surface,

• ther artifacts).

CSAMT can “see” to depths of up to 1000 m or more, but resistivity contrast was not expected to be very large in rubble zone. Resistivity of a cavity immediately after a UNE test may be much different — there may be a conductive anomaly due to presence of hot fluids and steam, but this will be much different 28 years later.

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Survey lines for dipole-dipole and CSAMT surveys Dipole-dipole/IP: 20 m spacing, to n = 15 CSAMT: 10 m spacing, current source located 5 km east of site

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Dipole-dipole survey results S-N line; depth resolved is about 150 m W-E line; depth resolved is about 150 m

Borehole casing (GZ)

water pipe segments

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W-E CSAMT survey results Method “sees” to ~ 800 m depth; large effects of emplacement hole casing and wires lying on the surface

Borehole casing (GZ)

wires on surface

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Shorter W-E CSAMT line offset by 40 m south from the longer W-E line This still sees some effect of casing

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Receivers 3 component 4.5 Hz geophones wireless digitizer and internal GPS. Source Mini-vibe with waffle plate P wave (vertical) shear-wave (transverse and radial [w.r.t line]) 5-6 sweeps per location Setting Flat topography Some weathered tuff at surface

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300 stations Deployment 1 Roughly linear 30 m spacing on line; 40 on cross-lines Deployment 2 Star pattern with circle source

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Data were processed using two types of analysis:

• Surface wave dispersion

Love and Rayleigh Refraction microtremor

• Standard reflection processing

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Expected cavity Rhyolite lava? Expected top of chimney No clear reflections or features P-P stack S-S stack P-S stack

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data frequency/slowness dispersion model

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Away from rubble zone Above rubble zone

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Cavity Vs=905 Cavity Vs=817

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Dipole-dipole, IP, and CSAMT surveys used a 3-

person (experienced) crew and took about 6 days each.

Data processing electrical was overnight, or 1-2

days.

Active seismic used a 4-person (experienced)

crew and 7 days; processing took several weeks.

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• 1. Dipole-dipole and IP electrical performed as expected —

revealed some artifacts (borehole casing, pipes) and good representation of geology.

• 2. CSAMT was able to image deep enough, but borehole casing

masked possible effects of rubble zone. Some artifacts were also revealed.

• 3. In this setting, volcanic tuff, it was essentially impossible to

image a known cavity at a depth of 300-500 m using standard reflection processing. Possibly a more energetic source might work better.

• 4. Surface wave dispersion did produce a good result. The lateral

extent of the cavity was evident but vertical extent (bottom) was difficult to image.