1. Lecture 15 Resistivity-GPR

2. Death Valley Basin

4. Furnace Creek Fault

5. Resistivity
SYSCAL R1 Plus – resistivity meter for medium-depth exploration
can be used for:
geological mapping
groundwater exploration

6. Put 48 stainless steel electrodes in the ground every five meters
Attach the electrodes to the cable with clips
Press start on the box

7. Ohm’s Law + -
Battery
current
resistance + - V I R

8. Resistivity
Double length double R
Double area halve R
R proportional to length/area
Area
current
length

9. Archie’s law

10. Wenner Array a=2πa ΔV/I Ohm’s law V=IR Apparent resistivity
Voltage (V)
Current (I)
Resistance (R)
a=2πa ΔV/I
Electric Sounding
Shallowest = a
Deepest = spacing*(round down((number of electrodes -1) /3))

11. Field Data

12. Theory r1 r2 V I r3 r4

13. Wenner array

14. Two Layer Model Wenner Spread

15. Mtlab Program for 2 Layer Resistivity
%Resistivity function from Pages 529 Telford et al., Applied Geophysics
%Second Edition
clear f
aarray=x; %meters
rho1=a(1);
rho2=a(2);
z=a(3);
k=(rho2-rho1)/(rho2+rho1);
%Equation 8.38
for i=1:length(aarray);
aa=aarray(i);
m=1:10000;
D=sum( k.^m./((1+(2*m*z./aa).^2).^0.5) )-sum( k.^m./((4+(2*m*z./aa).^2).^0.5) );
rhoa=rho1*(1+4*D);
f(i)=rhoa;
end
figure(1)
plot(log10(aarray),log10(f),log10(aarray), log10(y),'*')

18. Pseudosections Roughly how resistivity varies vertically and laterally
Electrical imaging creates ‘true’ section using tomographic theory

19. Turkey Flat Modeled Resistivity

20. Middle Mountain Resistivity
Line 1
Line 2
Two resistivity lines were laid out for Middle Mountain
The anomaly colored yellow is most likely the water table dammed by the faults
From the 1st line to the 2nd line the water table increases in size likely due to the increase in distance between the fault splays

24. Furnace Creek Fault

26. SAF
Splay
Map view
Model to explain increase in size of water table