marine resistivity: a tool for characterizing sediment zones
TRANSCRIPT
Marine Resistivity: Marine Resistivity: a Tool for a Tool for
Characterizing Characterizing Sediment ZonesSediment Zones
MotivationMotivation Beach NourishmentBeach Nourishment
Large Scale FeaturesLarge Scale Features Sand vs. claySand vs. clay
from USACE Philadelphia (2003)
ProblemProblem VibracoreVibracore
Large area Large area lots of lots of samplessamples
Heterogeneities Heterogeneities lots of sampleslots of samples
Could a geophysical Could a geophysical method guide point method guide point measurements?measurements?
From Waldner et al. (2008)
Geophysical MethodsGeophysical Methods
SeismicSeismic Reflections due to different wave Reflections due to different wave
velocitiesvelocities Identify geologic structuresIdentify geologic structures
C15
2
C78
1
Dep
th (
ms)
25
0
50
Sea Surface
WaterBottomSeismic Line 350
1km
From Waldner et al. (2008)
Geophysical MethodsGeophysical Methods
ResistivityResistivity Responds to electrical conductivity of Responds to electrical conductivity of
sedimentsediment Map sediment type directly based on resultsMap sediment type directly based on results
Bedrock Clay
From Heaney (2007)
ResistivityResistivity How materials conduct electricityHow materials conduct electricity
Current is injected into the groundCurrent is injected into the ground Measure changes in electric potential Measure changes in electric potential
From Peake (2005)
ResistivityResistivity
Potential Targets Potential Targets PorosityPorosity Pore fluid Pore fluid
conductivityconductivity LithologyLithology
From http://earthnet-geonet.ca
21 1 1
w s
a b
From Rhoades et al. (1976).
Terrestrial Resistivity Terrestrial Resistivity ApplicationsApplications
Groundwater Groundwater explorationexploration
Pollution monitoringPollution monitoring Void detectionVoid detection
From agiusa.com
Archeological Archeological surveyssurveys
Borehole loggingBorehole logging Dam investigationsDam investigations
Towed Resistivity Towed Resistivity SurveysSurveys
Rapid data Rapid data collectioncollection ~3 km/hr~3 km/hr
Electrodes at Electrodes at water surfacewater surface ~ 30 m ~ 30 m
penetration penetration
Towed Resistivity ResultsTowed Resistivity Results
20
10
0
20
0
10
9180 9200 9220 9240 9260
Distance (m)
C7
81
2360 2380 2400 2420 244020
10
0
Distance (m)
Dep
th (m
)
20
0
10
C1
52
C7
81
C1
52
Water
SandWater
Clay0.5
0.6
0.8
0.9
1.1
1.2
1.3
1
Near Clay Core Near Sand Core
From Waldner et al. (2008)
Towed Resistivity ResultsTowed Resistivity Results
Resistivity in ohm-m
Ohm-m
Towed Resistivity ResultsTowed Resistivity Results
SummarySummary Towed resistivityTowed resistivity
Responds directly to lithology/clay contentResponds directly to lithology/clay content Rapid data collection supplements vibracoreRapid data collection supplements vibracore
GoalsGoals Refine/expand existing borrow areasRefine/expand existing borrow areas Map changes between existing vibracoreMap changes between existing vibracore Guide placement of future vibracoreGuide placement of future vibracore