GEOPHYSICAL STUDIES SITE B

GEOPHYSICAL STUDIES PROGRESS OSPER PROJECT SITE B

BRUCE SMITHROBERT BISDORFRAY HUTTONMARK TABACHECKROBERT HORTON

GEOPHYSICAL METHODS USED

• DC RESISTIVITY SOUNDING obtain variation in electrical resistivity as a function

of depth (to about 40 meters)

• ELECTROMAGNETIC PROFILING (EM31)obtain variation in electrical conductivity as a function of position (mapping lateral variations) 3 to 6 meters

• TOTAL FIELD MAGNETICS (not discussed) geologic mapping detect magnetic metallic objects (oil field pipes etc.)

• ELECTROMAGNETIC PROFILE (EM34…not discussed)depth to 40m but very noisy due to metallic pipes

DC RESISTIVITY

B SITE LOCATIONDC RESISTIVITY SOUNDINGS

DC SOUNDINGS SITE B

ELECTRICAL CROSS SECTION SITE B

RESISTIVITY (ohm meters) CONDUCTIVITY (millisiemens) ρ = 1000/σ(ms) σ(ms) = 1000/ρ

100 ohm meters = 10 ms

RESISTIVITY SOUNDING SITE B

1000 100 10 CONDUCTIVITY

WEATHERED BEDROCK

EM31 CONDUCTIVITY SURVEY

Vertical dipoles depth ~4.5m

Horizontal dipoles depth ~2.25m

EM31 HMD 2.25m depth map

EM31 VMD 4m depth map

EM31 HMD 4m 1960 Photo