Detailed Geophysical Fault Characterization in Yucca 

Flat, Nevada Test Site, Nevada 

By Theodore H. Asch, Donald Sweetkind, Bethany L. Burton, and Erin L. Wallin 

Open-File Report 2008–1346 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

KEN SALAZAR, Secretary 

U.S. Geological Survey 

Suzette M. Kimball, Acting Director 

U.S. Geological Survey, Reston, Virginia 2009

Prepared in cooperation with the U.S. Department of Energy, National Nuclear 

Security Administration Nevada Site Office under Interagency Agreement DEAI52-07NV28100 

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Asch, T.H., Sweetkind, D., Burton, B.L., and Wallin, E.L., 2009, Detailed geophysical fault characterization in 


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ii 

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Yucca Flat, Nevada Test Site, Nevada: U.S. Geological Survey Open-File Report 2008-1346, 64 p., plus two 


appendixes. 


 

Contents 


Introduction .........................................................................................................................................................................1 


Geologic Setting of Yucca Flat .........................................................................................................................................3 


Geophysical Surveys .........................................................................................................................................................6 


Electrical Properties of Rock..........................................................................................................................................13 


DC Resistivity Investigation ............................................................................................................................................14 


Magnetotelluric Investigation........................................................................................................................................15 


Yucca Flat Magnetotelluric Investigation ................................................................................................................18 


Vertical Gradient Magnetic Field Investigation ..........................................................................................................18 


DC Resistivity Results ......................................................................................................................................................19 


2005 Field Effort — Lines YFRESEW and YFRESNS................................................................................................19 


2006 Field Effort .............................................................................................................................................................24 


Near U–7cd — Lines 1 and 2 ................................................................................................................................24 


Near U–2gj — Lines 3 and 4 .................................................................................................................................27 


Audio Magnetotelluric Results .....................................................................................................................................30 


Two–dimensional Modeling Analysis of the AMT Data.........................................................................................33 


2005 Field Effort — Lines YFRESEW and YFRESNS ..............................................................................................36 


2006 Field Effort .............................................................................................................................................................42 


Near U–7cd — Lines 1 and 2 ..................................................................................................................................42 


Near U–2gj — Lines 3 and 4 ...................................................................................................................................45 


Vertical Gradient Magnetic Field Results ....................................................................................................................48 


Discussion..........................................................................................................................................................................50 


iii 
Geophysical Response Related to Varying Fault Offset ........................................................................................50 


Geophysical Response Related to Fault-Zone Geometry and Architecture......................................................51 


Conclusions .......................................................................................................................................................................58 


References Cited ..............................................................................................................................................................59 


Appendixes 

A. DC Resistivity Two–Dimensional Modeling 

B. AMT Data 

Figures 

1. Geophysical study locations at drill holes U–7cd and U–2gj in Yucca Flat .........................................................4 


2. Geophysical study locations on photo mosaic of northern Yucca Flat basin. ..................................................17 


3. Yucca Flat DC resistivity two–dimensional inversion modeling results for line YFRESEW ............................22 


4. Yucca Flat DC resistivity two–dimensional inversion modeling results for line YFRESNS. ............................23 


5. DC resistivity two–dimensional inversion modeling results for Line 1 of 2006 field effort..............................25 


6. DC resistivity two–dimensional inversion modeling results for Line 2 of 2006 field effort..............................26 


7. DC resistivity two–dimensional inversion modeling results for Line 3 of 2006 field effort..............................28 


8. DC resistivity two–dimensional inversion modeling results for Line 4 of 2006 field effort..............................29 


9. Two–dimensional AMT inversion modeling results for the TM mode along line YFRESEW. .........................37 


10. Two–dimensional MT inversion modeling results from regional Yucca Flat deep resistivity study .............38 


11. AMT two–dimensional inversion modeling results for the TM mode along Line YFRESNS ...........................40 


12. Two–dimensional AMT inversion modeling results for the TE mode along line YFRESEW............................41 


13. AMT two–dimensional inversion modeling results for Line 1 of 2006 field effort.............................................43 


iv 
14. AMT two–dimensional inversion modeling results for Line 2 of 2006 field effort.............................................44 


15. AMT two–dimensional inversion modeling results for Line 3 of 2006 field effort.............................................46 


16. AMT two–dimensional inversion modeling results for Line 4 of 2006 field effort.............................................47 


17. Bottom sensor total magnetic field data along lines YFRESEW and YFRESNS.................................................49 


18. Map of the Yucca fault and surface effects near drill hole U–7cd......................................................................53 


19. Three–dimensional perspective view of AMT profiles, Yucca fault and surface effects near

 drill hole U–7cd. ........................................................................................................................................................54 


20. Three–dimensional perspective view of DC resistivity profiles, 

 near drill hole U–7cd 

21. Three–dimensional perspective view of DC resistivity profiles and surface effects near

 drill hole U–2gj............................................................................................................................................................57 


Tables 

1. Location of drill holes U–7cd and U–2gj.....................................................................................................................6 


2. Coordinates of 2005 Line YFRESEW ............................................................................................................................7 


3. Coordinates of 2005 Line YFRESNS.............................................................................................................................8 


4. Coordinates of 2006 Line 1 ............................................................................................................................................9 


5. Coordinates of 2006 Line 2 ..........................................................................................................................................10 


6. Coordinates of 2006 Line 3 ..........................................................................................................................................11 


7. Coordinates of 2006 Line 4 ..........................................................................................................................................12 


8. DC resistivity two–dimensional inversion parameters ..........................................................................................20 


9. AMT profile azimuths and angles of rotation applied during processing..........................................................30 


10. AMT two–dimensional Inversion and Forward modeling mesh parameters .....................................................35 


v 

Yucca fault, and surface effects.

. .............................................................................................................................................56 

Conversion Factors 


Multiply By To obtain 

inch (in.) 2.54 centimeter (cm) 

inch (in.) 25.4 millimeter (mm) 

foot (ft) 0.3048 meter (m) 

mile (mi) 1.609 kilometer (km) 

centimeter (cm) 0.3937 inch (in.) 

millimeter (mm) 0.03937 inch (in.) 

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi) 

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD88). 


Horizontal coordinate information is referenced to either the North American Datum of 1927 (NAD 27) or 1983 (NAD83). 


Elevation, as used in this report, refers to distance above the vertical datum. 


vi 
Detailed Geophysical Fault Characterization in 

Yucca Flat, Nevada Test Site, Nevada 

By Theodore H. Asch, Donald Sweetkind, Bethany L. Burton, and Erin L. Wallin 

Introduction 

Yucca Flat is a topographic and structural basin in the northeastern part of the Nevada 

Test Site (NTS) in Nye County, Nevada (fig. 1). Between the years 1951 and 1992, 659 

underground nuclear tests took place in Yucca Flat (U.S. Department of Energy, 2000); most 

were conducted in large, vertical excavations that penetrated alluvium and the underlying 

Cenozoic volcanic rocks (U.S. Department of Energy, 2000). 

Radioactive and other potential chemical contaminants at the NTS are the subject of a 

long-term program of investigation and remediation by the U.S. Department of Energy (DOE), 

National Nuclear Security Administration, Nevada Site Office, under its Environmental 

Restoration Program. As part of the program, the DOE seeks to assess the extent of 

contamination and to evaluate the potential risks to humans and the environment from 

byproducts of weapons testing (Department of Energy, 2003). To accomplish this objective, the 

DOE Environmental Restoration Program is constructing and calibrating a ground-water flow 

model to predict hydrologic flow in Yucca Flat as part of an effort to quantify the subsurface 

hydrology of the Nevada Test Site. A necessary part of calibrating and evaluating a model of the 

flow system is an understanding of the location and characteristics of faults that may influence 

1
 
ground-water flow. Such influence may include fault offset that results in the juxtaposition of 

stratigraphic units with contrasting hydrologic properties (or special physical characteristics of 

the fault zones) such as brecciation and fracturing, that may cause specific parts of the zone to 

act either as conduits or as barriers to fluid flow. In addition, knowledge of fault-zone 

architecture and physical properties is a fundamental component of the containment of the 

contamination from underground nuclear tests (Carothers, 1995), should such testing ever 

resume at the Nevada Test Site. 

The goal of the present investigation is to develop a detailed understanding of the 

geometry and physical properties of fault zones in Yucca Flat. Such an understanding is essential 

in assessing the role of faults in the near-field ground-water flow environment and their 

importance in designing a successful containment strategy in Yucca Flat. Previous surface 

geologic mapping (Slate and others, 1999), geophysical studies, and data from hundreds of drill 

holes in Yucca Flat have defined the location and magnitude of offset of faults in the basin. A 

number of previous geophysical investigations using gravity data have defined the principal 

subsurface breaks within Paleozoic bedrock (Ferguson and others, 1988; Phelps and others, 

1999; Phelps and McKee, 1999); abundant drill-hole data (Covington and Berger, 1997) allow 

definition of the magnitude of offset across the faults in the Cenozoic units and changes in offset 

magnitude along fault strike. Geologic and geophysical data from Yucca Flat have previously 

been integrated to produce a three-dimensional framework model that incorporates fault location, 

dip and offset (Bechtel Nevada, 2006). 

The present study was designed to investigate faults in greater detail and to characterize 

fault geometry, the presence of fault splays, and the fault-zone width. Integrated, recent 

geological and geophysical studies have been designed and implemented to work toward this 

goal. 

2
 
This report describes, in detail, the geophysical surveys conducted near two drill holes in 

Yucca Flat, the data analyses performed, and the integrated interpretations developed from the 

suite of geophysical methodologies utilized in this investigation. Data collection for this activity 

started in the spring of 2005 and continued into 2006. A suite of electrical geophysical surveys 

was run in combination with ground magnetic surveys; these surveys resulted in high-resolution 

subsurface data that portray subsurface fault geometry at the two sites and have identified 

structures not readily apparent from surface geologic mapping, potential field geophysical data, 

or surface-effects fracture maps. 

Geologic Setting of Yucca Flat 

Yucca Flat is an elongate alluvial basin of Cenozoic age that formed consequent to 

regional crustal extension that was oriented generally east-west (Cole and others, 1997). Rocks 

exposed around the margins of the basin, and known in the subsurface from drill-hole data, 

include sedimentary rocks of Late Proterozoic to Mississippian age, local intrusive rocks of 

Mesozoic age, and volcanic and tuffaceous sedimentary rocks of Cenozoic age (fig. 1). The preCenozoic section includes Late Proterozoic through Lower Cambrian, predominantly siliciclastic 

rocks, a 4,500-m-thick Middle Cambrian through Middle Devonian carbonate-dominated 

succession, a 1,000- to 2,000-m-thick section of Upper Devonian through Mississippian shale, 

sandstone and minor limestone, and local Pennsylvanian and Lower Permian carbonate rocks 

(Ekren, 1968; Winograd and Thordarson, 1975). The Cenozoic rocks in Yucca Flat consist of a 

thick alluvial section underlain by Miocene volcanic rocks and rare, thin, prevolcanic 

sedimentary rocks. The Miocene volcanic rocks that form the lower part of the basin fill were 

erupted from source areas in the nearby southwestern Nevada volcanic field (Byers and others, 

1976; Sawyer and others, 1994). 

3
 
4
 
The volcanic rocks include variably welded ash-flow tuff, ash-fall tuff, and reworked tuff; the 

thickness and extent of these rocks vary greatly within the basin. The largely postvolcanic 

sedimentary basin fill consists of a mixture of loosely consolidated, coarse-grained alluvial and 

colluvial deposits that were derived from the surrounding Cenozoic silicic volcanic and 

Paleozoic siliciclastic and carbonate sedimentary rocks, fine-grained basin axis and playa 

deposits, and localized eolian sand and rare basalt flows (Byers and others, 1976; Sawyer and 

others, 1994). 

The pre-Cenozoic sedimentary rocks show evidence of contractile deformation related to 

generally east- and southeast-directing thrusting during Mesozoic time (Caskey and Schweickert, 

1992; Cole and Cashman, 1999). During late Cenozoic time, these rocks and the Cenozoic basin 

fill were affected by east-west extension that resulted in the formation of predominantly northstriking normal faults (Hinrichs, 1968). The Cenozoic volcanic units have been tilted west and 

have offset hundreds of meters by the major normal faults within the basin, including the 

Carpetbag, Topgallant, and Yucca faults (fig. 1); numerous faults with lesser offset exist as well 

(Hinrichs, 1968). Gravity models of the Yucca Flat basin define a Tertiary-Quaternary basin as 

much as 2,500 m deep to the east of the Carpetbag and Yucca faults, a midbasin high to the west 

of the Carpetbag fault, and a shallower basin to the west of the gravity high (Ferguson and 

others, 1988; Phelps and others, 1999). Movement along the Yucca fault in central Yucca Flat 

indicates deformation in the area has continued into the Holocene (Swadley and Hoover, 1990). 

5
 
Geophysical Surveys 

In the spring of 2005 and 2006 the U.S. Geological Survey conducted geophysical 

investigations in the vicinity of two drill holes in Yucca Flat: U–7cd and U–2gj (table 1, fig. 2). 

These two sites were selected for their ease of access for the purposes of geophysical data 

collection, proximity to known or suspected faults, proximity to regional magnetotelluric (MT) 

survey sites (Asch and others, 2006), and the potential utility of the results from these sites to the 

government cooperator agencies. Drill hole U–7cd is in the immediate footwall of the Yucca 

fault (fig. 1), an east-dipping, east-side-down normal fault with 200 to 400 m of offset and a 

prominent easily observed topographic surface scarp. 

Table 1. Location of drill holes U–7cd and U–2gj. 

Well name Latitude NAD 27 Longitude NAD 27 NTS 

area 

Comment 

Station 1 37° 04' 51" 116° 02' 44" 7 Emplacement well U–7cd. 

Station 2 37° 08' 16" 116° 04' 25" 2 Emplacement well U–2gj. 

The initial fault investigation work in 2005 was for reconnaissance. One long traverse 

(table 2) was located so that it would possibly cross a couple of large faults, and a shorter 

traverse (table 3) was set perpendicular to the first to check for major lateral inhomogeneities. 

Line YFRESEW (fig. 2) is oriented approximately east-west (azimuth of 95 degrees), roughly 

perpendicular to the surface trace of the Yucca fault. The line is approximately 1,500 m in 

length, passes over the U–7cd pad and crosses the surface expression of Yucca fault on its 

eastern end (fig. 2). Line YFRESNS (fig. 2) is oriented approximately north-south, roughly 

parallel to the surface trace of the Yucca fault. The line is 500 m in length and is located about 

200 m west of well U–7cd (fig. 2). 

6
 
Table 2. Line YFRESEW, acquired in 2005. Coordinates are in NAD83, Universal Transverse 

Mercator Zone 11N, meters. All data are OPUS-corrected. 

Line YFRESEW - West end 

Easting Northing Elevation 

0 583872.81 4104401.44 1,256.32 

25 583897.50 4104398.98 1,255.94 

50 583922.35 4104396.65 1,255.89 

75 583947.29 4104394.40 1,255.65 

100 583972.09 4104391.70 1,255.42 

125 583996.80 4104389.39 1,255.33 

150 584021.68 4104386.70 1,255.02 

175 584046.50 4104383.98 1,254.77 

200 584071.21 4104380.90 1,254.84 

225 584095.97 4104378.51 1,254.28 

250 584120.66 4104375.88 1,253.75 

275 584145.43 4104373.29 1,253.25 

300 584170.17 4104370.41 1,253.29 

325 584194.94 4104368.06 1,253.15 

350 584219.67 4104365.63 1,253.03 

375 584244.55 4104362.82 1,252.96 

400 584269.12 4104359.94 1,252.82 

425 584293.83 4104357.20 1,252.79 

450 584318.58 4104354.19 1,252.81 

475 584343.61 4104351.94 1,252.50 

500 584368.35 4104349.31 1,252.33 

525 584392.71 4104345.97 1,252.31 

550 584417.79 4104343.16 1,252.36 

575 584442.53 4104340.22 1,252.25 

600 584467.37 4104337.65 1,252.22 

625 584491.94 4104334.35 1,252.12 

650 584516.92 4104331.91 1,252.05 

675 584541.79 4104329.04 1,251.77 

700 584566.46 4104327.01 1,251.82 

725 584591.38 4104324.13 1,251.40 

735 584601.29 4104323.02 1,251.80 

750 584616.13 4104321.28 1,251.41 

775 584640.88 4104318.95 1,251.87 

800 584665.57 4104316.13 1,252.67 

825 584690.19 4104312.68 1,253.39 

850 584715.02 4104309.72 1,254.19 

875 584739.75 4104306.70 1,254.61 

900 584764.61 4104304.54 1,254.91 

925 584789.40 4104302.55 1,255.23 

950 584814.20 4104299.88 1,255.31 

975 584839.12 4104297.21 1,255.25 

1,000 584863.68 4104294.77 1,255.13 

1,025 584888.59 4104292.89 1,255.01 

1,050 584913.51 4104291.10 1,254.89 

7
 
Table 2, Line YYRESNS-West End.—Continued 

Easting Northing Elevation 

1,075 584938.39 4104289.42 1,254.57 

1,100 584962.96 4104287.72 1,253.58 

1,125 584987.80 4104285.75 1,252.69 

1,150 585012.14 4104284.60 1,252.12 

1,175 585037.67 4104283.07 1,252.53 

1,200 585062.44 4104281.71 1,252.22 

1,225 585087.42 4104280.15 1,252.89 

1,250 585112.19 4104278.86 1,252.74 

1,275 585137.09 4104277.02 1,253.15 

1,300 585161.89 4104275.29 1,253.29 

1,325 585186.76 4104273.34 1,252.59 

1,350 585211.58 4104271.71 1,250.55 

1,375 585236.23 4104269.82 1,249.73 

1,400 585261.19 4104267.29 1,247.78 

1,425 585285.78 4104265.48 1,247.40 

1,450 585310.69 4104263.40 1,246.92 

1,475 585335.55 4104261.30 1,247.06 

1,500 585360.37 4104259.01 1,247.26 

Line YFRESEW - East end 

Table 3. Line YFRESNS, acquired in 2005. Coordinates are in NAD83, UTM Zone 11N, meters. All 

data are OPUS-corrected. 

Line YFRESNS - North end 

Easting Northing Elevation 

0 584555.77 4104576.88 1,253.52 

25 584555.85 4104551.96 1,252.92 

50 584555.50 4104527.34 1,252.44 

75 584556.05 4104502.16 1,252.81 

100 584556.23 4104477.10 1,252.87 

125 584556.34 4104452.20 1,252.72 

150 584556.10 4104427.42 1,252.59 

175 584556.37 4104402.32 1,252.29 

200 584556.53 4104377.43 1,252.24 

225 584556.45 4104352.37 1,251.99 

250 584556.61 4104327.58 1,251.58 

275 584556.72 4104302.95 1,251.51 

300 584556.96 4104278.07 1,251.20 

325 584557.16 4104253.15 1,250.98 

350 584557.33 4104228.21 1,250.81 

375 584557.40 4104203.33 1,250.61 

400 584557.50 4104178.07 1,250.28 

425 584557.56 4104153.44 1,250.29 

450 584557.69 4104128.21 1,250.03 

475 584557.80 4104103.56 1,249.86 

500 584558.01 4104078.51 1,249.73 

Line YFRESNS - South end 

8
 
The 2006 DC and AMT surveys were designed to examine, in greater detail, the 

subsurface geology of known fault zones in the vicinity of the two drill holes by using DC 

resistivity and AMT measurements. Near U–7cd, the Yucca fault escarpment, which was crossed 

in 2005 by line YFRESEW on its eastern terminus, was selected for investigation at a higher 

resolution. A pair of survey traverses (Lines 1 [240 m, table 4] and 2 [200 m, table 5], fig. 2) 

were approximately centered on Yucca fault in this area. The lines were separated by about 200 

m, and Line 2 is located north of Line 1. 

Table 4. Line 1, acquired in 2006. Coordinates are in North American Datum (NAD83), Universal 

Transverse Mercator Zone 11North, meters. All data are OPUS-corrected. 

Line 1 - West end 

Easting Northing Elevation 

1000 585105.60 4104275.73 1,248.28 

1010 585115.47 4104275.14 1,252.58 

1020 585125.44 4104274.67 1,252.69 

1030 585135.39 4104273.98 1,252.80 

1040 585145.35 4104273.53 1,252.98 

1050 585155.34 4104273.41 1,253.27 

1060 585165.30 4104272.87 1,253.27 

1070 585175.28 4104272.38 1,252.97 

1080 585185.22 4104272.06 1,252.69 

1090 585195.36 4104272.07 1,252.39 

1092 585197.08 4104272.03 1,252.28 

1098 585203.08 4104271.86 1,251.11 

1100 585204.87 4104271.91 1,250.83 

1110 585214.64 4104271.26 1,250.43 

1120 585224.82 4104270.89 1,250.18 

1130 585234.70 4104270.51 1,249.79 

1140 585244.46 4104270.32 1,248.90 

1150 585254.55 4104269.91 1,248.24 

1160 585264.32 4104269.28 1,247.73 

1170 585274.56 4104268.85 1,247.62 

1180 585284.46 4104268.47 1,247.54 

1190 585294.41 4104268.11 1,247.48 

1200 585304.29 4104267.93 1,247.25 

1210 585314.19 4104267.15 1,246.78 

1220 585324.13 4104266.52 1,246.90 

1230 585334.10 4104266.28 1,247.04 

1238 585342.23 4104266.17 1,247.21 

Line 1 - East end 

9
 
 

Table 5. Line 2, acquired in 2006. Coordinates are in North American Datum (NAD83), Universal 

Transverse Mercator Zone 11North, meters. All data are OPUS-corrected. 

Line 2 - West end 

Easting Northing Elevation 

2000 585071.71 4104451.11 1,254.73 

2010 585081.54 4104452.79 1,254.79 

2020 585091.45 4104454.42 1,254.96 

2030 585101.48 4104455.83 1,255.53 

2040 585111.11 4104457.39 1,254.69 

2050 585120.95 4104459.21 1,254.80 

2060 585130.80 4104460.57 1,254.48 

2070 585140.64 4104462.17 1,254.02 

2080 585150.51 4104463.36 1,253.62 

2090 585160.30 4104465.12 1,253.12 

2100 585170.01 4104466.74 1,251.32 

2110 585179.76 4104467.72 1,251.07 

2120 585189.61 4104469.19 1,250.90 

2130 585199.49 4104470.48 1,250.99 

2140 585209.37 4104472.05 1,250.74 

2150 585219.21 4104473.68 1,250.37 

2160 585229.15 4104474.91 1,249.75 

2170 585238.92 4104476.78 1,249.38 

2180 585248.72 4104478.49 1,249.31 

2190 585258.59 4104480.11 1,249.02 

2200 585268.43 4104481.60 1,248.71 

Line 2 - East end 

The second area investigated in 2006 centers around drill hole U–2gj. Asch and others 

(2006), using regional magnetotelluric measurements, reported that the structural geology in the 

vicinity of drill-hole U–2gj (stations 39 and 40, Asch and others, 2006) was complicated by a 

network of small faults. The 2006 data collection effort was designed to provide more detailed 

information on the nature of the faults in that area. Line 3 (200 m, table 6) was located so that it 

passed near regional MT station 39 of the Asch and others (2006) study. Both Lines 3 and 4 

(each 200 m long; see table 7) were located so that they would cross a known small fault (Slate 

and others, 1999) in the vicinity of the well pad of U–2gj. 

10
 
The observed and calculated results for the DC resistivity modeling are included in 

Appendix A, and the observed and calculated data for the AMT modeling are included in 

Appendix B. 

Table 6. Line 3, acquired in 2006. Coordinates are in North American Datum (NAD83), Universal 

Transverse Mercator Zone 11North, meters. All data are OPUS-corrected. 

Line 3 – Northwest end 

Easting Northing Elevation 

3000 582180.24 4109659.78 1,302.61 

3010 582189.03 4109655.44 1,302.47 

3020 582198.20 4109651.27 1,302.35 

3030 582207.27 4109647.15 1,302.20 

3040 582216.12 4109643.01 1,302.13 

3050 582225.35 4109638.57 1,301.89 

3060 582234.58 4109634.63 1,301.68 

3070 582243.51 4109630.50 1,301.59 

3080 582252.80 4109626.49 1,301.39 

3090 582261.92 4109622.42 1,301.20 

3100 582271.09 4109618.48 1,300.83 

3110 582280.00 4109614.19 1,300.75 

3120 582288.98 4109609.92 1,300.57 

3130 582298.00 4109605.69 1,300.37 

3140 582307.10 4109601.55 1,300.10 

3150 582316.11 4109597.26 1,299.95 

3160 582325.17 4109593.01 1,300.00 

3170 582334.15 4109588.84 1,299.98 

3180 582343.27 4109584.52 1,299.87 

3190 582352.37 4109580.28 1,299.69 

3200 582361.39 4109576.17 1,299.43 

Line 3 - Southeast end 

Although the Yucca Flat fault is generally north-striking, it is distinctly sinuous in detail, 

probably as a result of en-echelon linked segments. Geophysical traverses were designed to cross 

the trace of the fault, evaluate the extent of footwall damage, and investigate possible hanging 

wall splay faults. Farther to the north, drill hole U–2gj is roughly equidistant (2 km) from the 

Yucca fault and the Carpetbag/Topgallant fault system (fig. 1). Surficial geologic mapping (Slate 

and others, 1999) and analysis of surface effects (Grasso, 2001) suggest the presence of small11
 
offset faults. Geophysical surveys at this location were designed to investigate minor faults 

distant from the major mapped normal faults in the basin. 

Table 7. Line 4, acquired in 2006. Coordinates are in North American Datum (NAD83), Universal 

Transverse Mercator Zone 11North, meters. All data are OPUS-corrected. 

Line 4 - West end

 Easting Northing Elevation 

4000 582323.42 4110702.61 1,312.28 

4010 582333.31 4110701.77 1,312.25 

4020 582343.23 4110700.93 1,312.15 

4030 582353.17 4110700.18 1,312.09 

4040 582363.15 4110699.69 1,312.04 

4050 582372.86 4110698.80 1,311.26 

4060 582382.98 4110698.03 1,311.66 

4070 582392.94 4110697.34 1,311.64 

4080 582402.94 4110696.68 1,311.60 

4090 582412.87 4110696.02 1,311.39 

4100 582422.82 4110695.29 1,311.39 

4110 582432.80 4110694.83 1,311.36 

4120 582442.73 4110694.06 1,311.48 

4130 582452.69 4110693.26 1,311.46 

4140 582462.63 4110692.41 1,311.42 

4150 582472.60 4110691.54 1,311.37 

4160 582482.49 4110690.81 1,311.33 

4170 582492.53 4110689.94 1,310.67 

4180 582502.52 4110689.36 1,310.53 

4190 582512.28 4110688.66 1,310.41 

4200 582522.27 4110687.57 1,310.34 

Line 4 - East end 

The geophysical studies described in this report collected 6-channel 3–D tensor audiomagnetotelluric (AMT) data, shallow DC resistivity data, and total magnetic field and vertical 

gradient magnetic field data near drill-hole U–7cd only. DC resistivity would provide enhanced 

near-surface resolution (2-m to 90-m depth). The AMT data would complement the DC 

resistivity data in the near-surface and then provide greater resolution vertically down to 

approximately 600-m to 800-m depth (depending on how conductive or resistive the subsurface 

materials are and on the quality of the data). The surveys were located such that the data could 

then be compared with the results of a previous regional MT study that had resolution to almost 

12
 
10 km (Asch and others, 2006). A Leica 1200 Global Positioning System (GPS) was used to 

locate all data-measurement stations in this investigation. 

Electrical Rock Properties 

Electromagnetic geophysical methods detect variations in the electrical properties of 

rocks — in particular, electrical resistivity, or its inverse, electrical conductivity. Electrical 

resistivity can be correlated with geologic units on the surface and at depth using lithologic logs 

to provide a three-dimensional (3–D) picture of subsurface geology. In the upper crust, the 

resistivities of geologic units are largely dependent upon their fluid content, pore-volume 

porosity, interconnected fracture porosity, and conductive mineral content (Keller, 1989). While 

there is not a one-to-one relationship between lithology and resistivity, there are general 

correlations that can be made using typical values, even though values can be found at other 

localities that may fall outside of the ranges presented herein (Palacky, 1987). Fluids within the 

pore spaces and fracture openings, especially if saline, can reduce electrical resistivities in what 

would otherwise be a resistive rock matrix. Resistivity can also be lowered by the presence of 

electrically conductive clay minerals, graphitic carbon, and metallic mineralization. It is 

common, for example, for altered volcanic rocks to contain replacement minerals that have 

resistivities 10 times lower than those of the surrounding rocks (Nelson and Anderson, 1992). 

Fine-grained sediments, such as clay-rich alluvium, marine shales, and other mudstones, are 

normally conductive from a few ohm-meters to a few tens of ohm-meters (Keller, 1987; Palacky, 

1987). Metamorphic rocks (nongraphitic) and unaltered, unfractured igneous rocks are normally 

moderately to highly resistive (a few hundreds to thousands of ohm-meters). Carbonate rocks can 

have similarly high resistivities depending on their fluid content, porosity, and impurities (Keller, 

1987; Palacky, 1987). Fault zones may be moderately conductive (tens of ohm-meters) when 

13
 
composed of rocks fractured enough to have hosted fluid transport and consequent mineralogical 

alteration (Eberhart-Phillips and others, 1995). Higher subsurface temperatures cause higher 

ionic mobility that reduces rock resistivities (Keller, 1987; Palacky, 1987). Tables of electrical 

resistivity for a variety of rocks, minerals, and geological environments are in Keller (1987) and 

Palacky (1987). 

DC Resistivity Investigation 

The DC resistivity data were collected using the Advanced Geosciences Inc. (AGI). 

SuperSting R8 system (Advanced Geosciences, Inc., 2003). The SuperSting is an 8-channel 

multielectrode resistivity and IP imaging system. The R8 reads eight potential differences for 

each 200-W current injection using 24-V batteries. A multichannel Swift dual-mode automatic 

multielectrode cable with outtakes to stainless-steel electrodes brings the data into the system. 

Internal memory can store up to 79,000 measurements. The survey setup was to lay out 100 

stainless-steel electrodes at a set distance in a straight line. Watering each electrode reduced the 

contact resistance. Inverse Schlumberger array data were collected. For a single measurement 

using this array, the instrument simultaneously uses from 4 to 18 electrodes, one half on either 

side of a central point. The inner two electrodes transmit current into the earth, whereas the outer 

electrodes measure the potential difference in the earth. The instrument sequentially switches the 

transmitter and receiver electrodes along the survey line following instructions in a user-defined 

command file. One 100-electrode setup acquires data along 500 m of the traverse. For the longer 

traverses, at the end of each data run, 20 electrodes were moved from the end of the line to the 

front of the line and a new data set recorded. This process was repeated until the full length of a 

line, such as line YFRESEW (fig. 2), was surveyed. 

14
 
In 2005, resistivity stations were located every 5 m along orthogonal lines that were 

about 1,500 m long in the east-west direction (line YFRESEW, fig. 2) and 500 m long in the 

north-south direction (line YFRESNS, fig. 2). A 5-m electrode spacing with the R8 DC 

resistivity system resulted in an investigation depth of approximately 90 m. In 2006, electrode 

spacings were shortened to 2 m and were used along 200-m lines (100 electrodes) centered on 

the surface expression of the Yucca fault in the vicinity of U–7cd (Lines L1 and L2, fig. 2). This 

electrode spacing resulted in a depth of investigation of approximately 40 m. 

Magnetotelluric Investigation 

The MT method is a passive surface geophysical technique that uses the Earth's natural 

electromagnetic fields to investigate the electrical resistivity structure of the subsurface from 

depths of tens of meters to tens of kilometers (Vozoff, 1991). Natural variations of the Earth's 

magnetic and electric field are measured and recorded at each MT station. Worldwide lightning 

activity at frequencies of 10,000 to 1 hertz (Hz) and geomagnetic micropulsations at frequencies 

of 1 to 0.001 Hz provide the majority of the signal sensed by the MT method. The natural 

electromagnetic waves propagate vertically in the Earth because the large resistivity contrast 

between the air and the Earth causes a vertical refraction of the electromagnetic wave transmitted 

into the Earth (Vozoff, 1972). 

The natural electric and magnetic fields are recorded in two orthogonal, horizontal 

directions as well in the vertical direction (named, in magnetotelluric parlance, the “tipper”). The 

resulting time-series signals are used to derive tensor apparent resistivities and phases by first 

converting them to complex cross-spectra using Fourier transform techniques. Then a 

least-squares, cross-spectral analysis (Bendat and Piersol, 1971) is used to solve for a transfer 

function that relates the observed electric fields to the observed magnetic fields. Before 

15
 
conversion to apparent resistivity and phase, the tensor is normally rotated into principal 

directions that usually correspond to the direction of maximum and minimum apparent 

resistivity, or the tensor may be rotated perpendicular to the survey traverse. 

For a 2–D Earth, in which the Earth’s resistivity structure varies with depth and in one 

lateral direction, the MT fields can then be decoupled into transverse electric (TE) and 

transverse-magnetic (TM) modes. Two-dimensional (2–D) resistivity modeling is generally 

computed to fit both modes. When the geology satisfies the 2–D assumption and the MT survey 

is perpendicular to the geologic strike, the MT data for the TE mode represent the electric field 

parallel to geologic strike, and the data for the TM mode represent the electric field across strike. 

The MT method is well suited for studying complicated geological environments because the 

electric and magnetic relations are sensitive to vertical and horizontal variations in resistivity. 

The method is capable of establishing whether the electromagnetic fields are responding to 

subsurface rock bodies of effectively 1, 2, or 3 dimensions. An introduction to the MT method 

and references for a more advanced understanding are in Dobrin and Savit (1988) and Vozoff 

(1991). 

16
 
Figure 2. Geophysical study locations on photo mosaic of northern Yucca Flat basin, Nevada Test 

Site, Nevada. Dark blue lines represent data acquisition in 2005 (Lines YFRESEW and YFRESNS) 

and the lighter blue lines represent field data acquired in 2006 (Lines 1, 2, 3, and 4). Green dots 

and labels indicate 2005 regional MT sounding locations in this area. AMT, audiomagnetotelluric; 

MT, magnetotelluric; DC, direct current; NTS, Nevada Test Site. 

17
 
Yucca Flat Magnetotelluric Investigation 

In 2005 the AMT data were acquired with Electromagnetic Instruments, Inc., MT–1 

Magnetotelluric system (EMI, 1996). This is a 5-channel, 16-bit, high-frequency (10 Hz to 100 

kHz) 3–D tensor MT receiver that uses high-frequency magnetic coils (three EMI BF–6 coils) 

and titanium electrodes. AMT recording stations were established every 100 m along the same 

lines as the 2005 DC resistivity traverses, resulting in 27 soundings. Electric field dipole lengths 

were 25 m with, for YFRESEW, Ex positive along the line pointing east and Ey positive pointing 

south and, for YFRESNS, Ex positive along the line pointing south and Ey positive pointing 

west. The magnetic field induction coils were oriented parallel to the corresponding electric field 

components plus the one vertical magnetic field component. 

In 2006 Schlumberger/EMI’s new MT24/HF, a 6-channel, 24-bit, remote-referencecapable, high-frequency (10 Hz to 100 kHz) 3–D tensor MT receiver was used for the AMT 

investigation. EMI BF–6 and BF–16 high-frequency (10 Hz to 100 kHz) magnetic induction 

coils and buffered (amplified, filtered) stainless-steel electrodes are used with this AMT system. 

The receiver was set up every 20 m along each of the 200-m lines (240 m for Line 1) with an 

effective station spacing, and electric field dipole lengths, of 10 m. Two adjacent electric field 

dipoles used one set of magnetic field induction coils in order to save station installation time. 

For all the 2006 AMT lines, Ex was positive in an easterly direction and Ey positive in a 

southerly direction. 

Vertical Gradient Magnetic Field Investigation 

In 2005, along with the DC resistivity and AMT, magnetic field data were acquired along 

three parallel transects with the center transect coincident with the 2005 east-west AMT and 

resistivity survey lines and the side transects located approximately 10 m to either side of the 

18
 
center transect. Two Geometrics G–858 magnetometers (self-oscillating split-beam cesium vapor 

[nonradioactive Cs133]) were configured into a vertical array with a 0.5-m separation. The 

magnetic field survey consisted of continuously recording, at 10-Hz sampling, the total magnetic 

field and the vertical gradient of the magnetic field in the vicinity of U–7cd. 

DC Resistivity Results 

2005 Field Effort — Lines YFRESEW and YFRESNS 

The DC resistivity data acquired along these lines were processed and analyzed using 

AGI’s EarthImager 2D modeling and inversion program, (Advanced Geosciences, Inc., 2006). 

Processing of the DC resistivity consisted of editing out noisy and bad data and checking for 

abnormal outliers, and determinations were made as to why the outliers exist. The data were then 

either retained or deleted from the modeling and interpretation process. The resistivity data were 

collated with the GPS station location and elevation data. The 2–D inversion process was 

monitored for unusual results caused by accidental inclusion of bad data and for the inversion 

program’s proclivity to include nonexistent conductors that were solely used to reduce the 

statistical error. Field processing included preliminary 2–D inversions, and the final inversions 

were topographically corrected. The observed data and calculated model pseduosections are 

presented in Appendix A along with data misfit pseudosections for each model. 

Table 2 lists the 2–D DC inversion modeling parameters for both the 2005 and 2006 field 

events. Forward modeling followed up the inversions to verify features in the inverted model that 

were required by the measured field data. 

19
 
 

 

Table 8. DC resistivity two–dimensional inversion parameters. [Min, minimum; Max, maximum; :-m,

ohm-meters; V, volts; I, amperes; mV, millivolts; %, percent; NTSL, Nevada Test Site Line; --, 

no data; horiz., horizontal; vert., vertical; abs, absolute value] 

DC inversion parameters YFRESEW NTSL01 NTSL02 NTSL03 NTSL04 

Mesh thickness incremental factor 1.1 

Depth factor 1.1 

Min number mesh cells between electrodes 2 

Min voltage accepted (mV) 0.2 

Min abs (V/I) accepted (Ω) 0.0005 

Max repeat error accepted (%) 3 

Min apparent resistivity accepted (Ω-m) 1 

Max apparent resistivity accepted (Ω-m) 10,000 

Inversion method Robust 

Max number of iterations 10 

Max RMS model error (%) 3 

Starting model (Ω-m) 113.81 265.84 283.29 231.97 164.43 

Min output resistivity (Ω-m) 10 

Max output resistivity (Ω-m) 1,000 

Horiz./Vert. Roughness Ratio 0.1 

Stabilizing factor (Lagrange multiplier) 100 

Damping factor 100 

Model parameter width (horiz. smoothing) 1 

Model parameter height (vert. smoothing) 1 

Resolution factor (rough conditioner) 0.2 

Robust data conditioner (εD) 1 

Robust model conditioner (εM) 1 

Data points removed from misfit 

histogram (%) 

--

3.2 3.7 1.0 1.3 

Data misfit cutoff (%) -- 20 20 10 8 

The modeling results for the 2005 DC resistivity survey along line YFRESEW, presented 

in figure 3, show that the western end of the DC resistivity inversion has a 100–200 ohm-m unit 

from the beginning to approximately a 300-m distance along the line. The projected surface trace 

of the Topgallant fault crosses the section between about 100 and 200 m. There are slight 

changes in resistivity at this location; DC resistivity is complex between 200 and 300 m, possibly 

as a result of fault effects. From the 300-m mark to around 1,100–1,200 m, the near-surface 

geology is somewhat electrically conductive, about 50–100 ohm-m; at depth, there is a distinct 

20
 
change to a more resistive unit, from about the 950-m to 1,200-m mark, that appears to dip west 

at about 20 degrees. Based on lithology intercepted in drill hole U–7cd, the resistivity change 

with depth appears to correspond to a lithology change from porous gravels above to coarse sand 

below; the dip of this surface is consistent with the dip in the underlying tuff units. East of 1,200 

m distance, the near-surface geology becomes generally more resistive; two mapped splays of 

the Yucca fault cross the section in this area. 

The DC resistivity results for the shorter north to south line, YFRESNS, are presented in 

figure 4. It appears that no major geologic structural features were crossed except possibly the 

electrically conductive structure located between 60 m and 100 m. This short line is located in 

the footwall of the Yucca fault, well to the west of the fault trace. The results from this line are 

consistent with the somewhat electrically conductive (around 50–100 ohm-m) central part of the 

east-west line YFRESEW. 

21
 
Figure 3. Yucca Flat DC resistivity two–dimensional inversion modeling results for line YFRESEW acquired in 2005 

Nevada. Black dashed lines indicate interpreted fault crossings. Location of drill hole U–7cd indicated with a blacalong the traverse. [m, meters; ohm-m, ohm-meters, NAVD88, North American Vertical Datum of 1988] 

22
 
Figure 4. Yucca Flat DC resistivity two–dimensional modeling and inversion results for YFRESNS, the north–south 

2005 at the Nevada Test Site, Nevada. [Ohm-m, ohm-meters; m, meters; NAVD88, North American Vertical Datum 

23
 
2006 Field Effort 

The DC resistivity results from lines 1 and 2 near the southern drill hole, U–7cd, are 

presented first, followed by results from lines 3 and 4 from near the northern drill hole, U–2gj. 

Near U–7cd — Lines 1 and 2 

The DC resistivity results for Line 1 are presented in figure 5. All the survey traverses 

progressed from west to east (left to right in the figures). There is a rapid change in topography 

at the location of the Yucca fault escarpment, which is approximately located at 100-m distance 

in figure 5. To the west of the Yucca fault escarpment the DC resistivity results indicate thin 

resistive material (500–1,000 ohm-m) overlying more conductive material (100–200 ohm-m). 

There is a discontinuity in the conductive material at the approximate location of the Yucca fault 

surface expression and again at the 160-m distance along the line. The conductivity change at the 

160-m distance (more pronounced than the break at 100–110 m) is likely an expression of 

another subsurface fault that appears to be an en-echelon splay of the Yucca fault zone. 

The DC resistivity inversion results (fig. 6) for Line 2 show a marked conductivity 

contrast across the location of the surface expression of the Yucca fault (around 100-m distance 

along the line). There is a smaller conductivity contrast at approximately the 150-m distance 

along the line that could represent a northern extension of the eastern fault observed on Line 1 at 

the 160-m distance. 

24
 
Figure 5. DC resistivity two–dimensional inversion results for Line 1 (fig. 2) of 2006 field effort at the Nevada Test S

Nevada; NTS, Nevada Test Site; ohm-m, ohm-meters; NAVD88, North American Vertical Datum of 1988] 

25
 
Figure 6. DC resistivity two–dimensional inversion results for Line 2 (fig. 2) of 2006 field effort at the Nevada Test S

Nevada; NTS, Nevada Test Site; ohm-m, ohm-meters; NAVD88, North American Vertical Datum of 1988] 

26
 
Near U–2gj — Lines 3 and 4 

Line 3 is located south of drill hole U–2gj (fig. 2) in the northern end of Yucca Flat basin. 

The DC resistivity inversion results (fig. 7) for line 3 show slight conductivity contrasts (between 

the green (150–200 ohm-m) and blue colors (300–400 ohm-m) along the traverse that may be 

due to near-surface shallow faulting. Possible fault locations along the line are at distances 48 m, 

85 m, 115 m, 140 m, and 155 m. The slight conductivity contrasts indicate that the faulting is 

likely within the same or closely related lithological unit. 

Line 4 is located just north of drill hole U–2gj (fig. 2). The DC resistivity inversion 

results for line 4 are presented in figure 8. As with line 3, only slight conductivity contrasts in the 

near surface could be related to traces of shallow faulting. Possible faults are located at 38 m, 82 

m, 100 m, and 147 m along the traverse. It was observed during data acquisition along line 4 that 

a shallow trench had been cut across a fault at a distance along the line of about 100 m. This 

trench forms the basis for the faults in the subsurface indicated in figure 8. 

27
 
Figure 7. DC resistivity two–dimensional inversion results for Line 3 (fig. 2) of 2006 field effort at the Nevada Test S

Nevada; NTS, Nevada Test Site; ohm-m, ohm-meters; NAVD88, North American Vertical Datum of 1988] 

28
 
Figure 8. DC resistivity two–dimensional inversion results for Line 4 (fig. 2) of 2006 field effort at the Nevada Test S

Nevada; NTS, Nevada Test Site; ohm-m, ohm-meters; NAVD88, North American Vertical Datum of 1988] 

29
 
Audio Magnetotelluric Results 

In this investigation, the recorded time-series data were transformed to the frequency 

domain and processed to determine a 2–D apparent resistivity and phase tensor at each site. 

Time-series data sets were selected for optimal signal-to-noise characteristics prior to the crosspower calculations. Cross-power files were created with Egbert’s (1997) multiple-station, 

remote-reference magnetotelluric data-processing algorithms used in single-station local remote 

reference mode. During the analysis and interpretation process, each station was rotated to a 

fixed angle determined by the given nominal profile orientation. Rotation of the impedance 

tensor allows for decoupling into the TE and TM modes. Table 9 lists the nominal line azimuths 

and the fixed, orthogonal angles of rotation for each profile. The 2005 time-series data were 

edited with EMI’s MTR15 MT data-processing program and the 2006 data with ACQ24, EMI’s 

24-bit MT data-analysis program (EMI, 2002), to remove noisy data points and calculate spectral 

crosspowers. The different programs were used because two different MT systems acquired the 

data. The data recorded in 2006 with the new MT24/HF were generally quite noisy, and in some 

cases, a few stations were not used in the inversion analysis along the profiles. 

Table 9. AMT profile azimuths and angles of rotation applied during processing. 

Profile number MT stations Profile azimuth Fixed angle of rotation 

in profile (degrees) (degrees) 

2005 YFRESEW 16 95 5 

2005 YFRESNS 6 180 90 

2006 Line 1 24 90 0 

2006 Line 2 20 90 0 

2006 Line 3 20 109 19 

2006 Line 4 20 89 –1 

30
 
The effects of near-surface resistivity anomalies can cause what are known as “static 

shifts” in the data (Sternberg and others, 1988). Cultural features also can affect the measured 

magnetotelluric responses. These include fences, pipelines, communication lines, railways, and 

other manmade conductors. The data acquired near the tower at U–7cd were somewhat affected 

by the infrastructure. There were no cultural issues near U–2gj. Otherwise, cultural features were 

not an issue during this investigation. 

The raw and model controlled source AMT data are presented in Appendix B. For each 

station, the following images are presented: Apparent Resistivity, Impedance Phase, E-Predicted 

Coherencies, Impedance Skew, Impedance Polar Plots, Rotation Angle, Tipper Magnitude, and 

Tipper Strike. Error bars (],[) on the Apparent Resistivity and the Impedance Phase plots 

represent probable errors within one standard deviation of the sample variance (Gamble and 

others, 1979). 

Apparent resistivity is the approximate ratio of the electric field strength to the magnetic 

field strength at a given frequency. The impedance phase is proportional to the slope of the 

apparent resistivity curve on a log-log plot, but from baselines at ±45 degrees (Vozoff, 1991). A 

measure of the dimensionality for MT data is provided by the impedance skew of the impedance 

tensor (Vozoff, 1972). If the effective measured resistivity response to the geology beneath an 

MT station truly is one or two dimensional, then the skew will be zero. Instrument and 

environmental sources of electrical noise can cause nonzero skew values. Skew values typically 

are small (about 0.1) for relatively low noise recordings. Higher skews (above 0.2) are an 

indication of either the resistivity response to 3–D geology or higher levels of noise. Manmade 

electrical noise, such as power lines, power generators, and moving vehicles and trains, can have 

a negative effect on MT data quality. All of these local disturbances can produce incoherent 

noise that mainly affects frequencies above 1 Hz. Other manmade electrical noise, such as direct 

31
 
 

current electric trains and active cathodic protection of pipelines, produces coherent 

electromagnetic signals that mainly affect frequencies below 1 Hz. 

In the survey area, noise from a number of small power lines and small moving vehicles 

was negligible at distances greater than 0.4 km from the noise source. Power-line signal levels 

were measured at each site and typically were less than 20 percent of the maximum recordable 

signals. Noise from larger power lines, power generators, pipelines, and trains was negligible at 

distances greater than 5 km. Local lightning, wind, and rainstorms also can degrade data quality. 

Burying the magnetic induction coils and the electric dipole wires minimized wind noise. 

Predicted values of the electric field can be computed from the measured values of the 

magnetic field (Vozoff, 1991). The coherence of the predicted electric field with the measured 

electric field is a measure of the signal-to-noise ratio provided in the multiple coherency plots. 

Values are normalized between 0 and 1; values at 0.5 signify signal levels equal to noise levels. 

For this data set, coherencies generally were at an acceptable level, except at times in the 

frequency ranges of 0.01 to 5 Hz (often referred to as the “dead band”). 

These controlled source AMT data include some scatter and very poor signal-to-noise 

ratios. Spectral results were inspected visually for noisy data, and the best signal-to-noise field 

data were combined into the final plots and spectral data sets. In some cases most of the data at a 

site was almost totally removed from the analysis. This occurred primarily with the 2006 data as 

a new system, the MT24/HF, was being field tested for the first time; therefore many acquisition 

issues became evident as the data were acquired. 

The magnetotelluric impedance polar plots provide a measure of MT data dimensionality 

(Reddy and others, 1977). For 1–D resistivity structures, the principal impedance polar diagram 

(dashed line) is a circle. For 2–D or 3–D resistivity structures, the principal impedance polar 

diagram (dashed line) elongates either parallel or perpendicular to strike direction. Over resistors, 

32
 
the principal impedance polar diagram elongates perpendicular to strike direction, and over 

conductors, it elongates parallel to strike direction. For 2–D resistivity structures, the additional 

impedance polar diagram (solid line) attains the shape of a symmetric cloverleaf. For 3–D 

resistivity structures, the additional impedance polar diagram (solid line) elongates in one 

direction, and its amplitude is comparable to that of the principal impedance polar diagram 

(dashed line). 

The magnetotelluric “tipper” is calculated from the vertical component of the magnetic 

field. The tipper magnitude is a measure of the “tipping” of the magnetic field out of the 

horizontal plane (Vozoff, 1991). It will be equal to zero for the 1–D case. Typically, the tipper 

value is between 0.1 to 0.5 and seldom approaches 1.0. The tipper responds primarily to vertical 

and subvertical structures. The tipper magnitude of the stations discussed in this report ranged 

from 0.1 to 0.6 over the lower frequencies. This indicates some lateral contacts or vertical 

structure at depth. The tipper strike is used to help resolve the 90-degree ambiguity in the 

impedance rotation angle. The HzHx and HzHy coherency is a measure of the signal-to-noise 

ratio of the vertical magnetic field with respect to each of the orthogonal, horizontal magnetic 

field components. Values are normalized between 0 and 1; values at 0.5 signify signal levels 

equal to noise levels. These three-component magnetic field coherencies provide a check on the 

signal-to-noise ratio of the measured values in the tipper magnitude and tipper strike plots. 

Two–Dimensional Modeling Analysis of the AMT Data 

A two-dimensional modeling analysis of the Yucca Flat CSAMT data has been 

performed. Wannamaker (1983) found that while some MT responses in the Basin and Range 

region are fundamentally three-dimensional (3–D) in nature, for elongated structures, 2–D 

modeling could be used to construct reasonable estimates of the resistivity cross sections along 

each profile. Wannamaker and others (1984) demonstrated that approximating 3–D structure 

33
 
beneath a centrally located profile with 2–D modeling is best achieved when fitting the TM 

curve, even at the expense of a poor fit of the TE curve. However, because TM data are 

relatively insensitive to the depth extent of a subsurface body (Eberhart-Phillips and others, 

1995), the depths to the base of the bodies in the model are not well constrained. Hence, 

clarifying the model limits with 3–D resistivity modeling may be necessary. 

Two dimensional resistivity models were constructed for each profile. First, 2–D 

inversions of the audio magnetotelluric data were conducted using the computer program, 

RLM2DI (Mackie and others [1997] and Rodi and Mackie [2001]), from within GEOTOOLS 

(Geotools, 1998), a shell program specifically designed to process and interpret MT and AMT 

data. This was followed by the application of the 2–D forward modeling algorithm program, 

PW2D, developed by Wannamaker and others (1987). The results of the RLM2DI 2–D inversion 

were used as the initial input model for the forward modeling, PW2D, where a sensitivity 

analysis was performed on the conductive structures derived from the inversion results. 

RLM2DI uses a finite-difference network analog to the Maxwell’s equations governing 

magnetotellurics to calculate the forward solution and a nonlinear conjugate gradient 

optimization approach that is applied directly to the minimization of the objective function for 

the inverse problem. PW2D is a stable finite-element algorithm that simulates transverse electric 

and magnetic fields using a linear basis across each finite element. The inversion algorithm, 

RLM2DI, was usually allowed to batch run 25 iterations in order to reduce the root mean square 

(RMS) error to a reasonable value between the field data and the numerical model. The number 

of iterations of forward modeling (PW2D) necessary depended on how complex the profile 

inversion results were from RLM2DI. 

Table 10 lists the number of horizontal and vertical nodes that were used in the modeling 

for each profile. The variability in the number of nodes from profile to profile is due to the 

34
 
different number of MT stations along each profile. In all cases the number of horizontal and 

vertical nodes necessary for the iterative forward modeling (PW2D) algorithm to accurately 

model the Yucca Flat subsurface resistivity distribution is greater than the number of nodes 

required by the inversion algorithm (RLM2DI). This is a function of some fundamental 

differences between how finite-difference and finite-element algorithms handle the numerical 

boundary conditions and, subsequently, how the electric and magnetic fields are calculated 

across the mesh. 

Table 10. Inversion (RLM2DI) and forward (PW2D) numerical model meshes for each profile. The 

number of horizontal (Horiz) nodes and vertical (Vert) nodes in each model mesh are listed. [-, 

PW2D not run] 

Profile RLM2DI PW2D 

no. Horiz Vert Horiz Vert 

YFRESEW 69 59 94 63 

YFRESNS 69 59 85 59 

Line 1 116 50 140 50 

Line 2 100 59 100 59 

Line 3 88 59 89 56 

Line 4 91 59 - -

The edges of the model were extended horizontally and vertically to minimize edge 

effects. The resolution of the resistivity boundaries used for each model is somewhat subjective. 

If different resistivities were used, then boundary positions and layer depths would have to be 

adjusted to achieve similar fits to the observed data. The extreme case would be to use a model 

with a "continuous" resistivity gradient from low to high resistivities. The resolution of the 

resistivity boundaries is also, in part, a function of the model grid mesh design. We have 

attempted to keep each model simple. The MT profiles models’ depths are relative to the Earth’s 

surface. Nine additional vertical nodes are usually added to model the overlying air layer. 

35
 
2005 Field Effort — Lines YFRESEW and YFRESNS 

The AMT interpreted resistivity model for the TM mode for line YFRESEW, acquired in 

2005, is presented in figure 9. The AMT and DC resistivity inversion models (figs. 9 and 3, 

respectively) for line YFRESEW appear to agree over the 100-m depth at which the resistivity 

models overlap. In this depth range, a generally conductive section is disrupted on the west end 

of the section (between 200 and 300 m) by the Topgallant fault; a distinct change in resistivity 

east of 1,100 m is related to offset on the Yucca fault. A resistive section in figure 9 between 0 m 

and 300 m along the line at depths of 100 m to 225 m may represent an alluvial unit. The most 

conductive part of the section occurs between 300- and 600-m depth and corresponds to the 

partly welded parts of Timber Mountain Group rocks. The Topgallant fault is interpreted to cut 

the electrically resistive alluvium and more conductive volcanic units on the western end of the 

generally east-west line, and Yucca fault is interpreted to cross the section on the eastern end of 

the line. There is no surface expression of faulting on the western end of the line. However, 

surface offset is observed at approximately 1,350 m at the eastern end of the line where Yucca 

fault crosses the profile. Another subsurface fault may cross the section at 950 m along the 

profile (indicated in the figure) just beneath U–7cd. The thin red line in figure 9 at approximately 

90-m depth indicates the interpreted depth of the DC resistivity inversion presented in figure 3. 

The 2005 east-west AMT and DC resistivity transects, lines YFRESEW, are 

approximately co-linear with a longer magnetotelluric profile from a regional study of the 

resistivity structure of the Yucca Flat basin (Asch and others, 2006). Line YFRESEW is located 

near station 33 (fig. 2) in that study. The regional interpreted resistivity model (fig. 10) shows 

good agreement with the detailed AMT fault study interpretation (fig. 9) in the near surface. The 

top of the generally more conductive volcanic section appears in both profiles at about 500-m 

36
 
depth, overlain by more resistive alluvium and, in the case of the MT data, shown to be underlain 

by resistive Paleozoic carbonate rocks (fig. 10). 

Figure 9. Yucca Flat detailed fault study — two–dimensional AMT inversion modeling results 

for the transverse-magnetic (TM) mode along line YFRESEW. The interpreted positions of the Topgallant 

and Yucca faults are indicated by dashed black lines. The depth overlapping with the DC 

resistivity results (fig. 3) is demarcated with a red dashed line at approximately 100-meter depth. 

A black arrow indicates the location of drill hole U–7cd. 

37
 
Figure 10. Two–dimensional MT inversion and forward modeling results from the Yucca Flat 

regional deep resistivity study (Asch and others, 2006) at the Nevada Test Site, Nevada. Inferred 

faults are indicated by dashed black lines. Abbreviations indicate major lithologic subdivisions, 

based in part on hydrogeologic nomenclature of Winograd and Thordarson (1975). The red line 

indicates the extent of the east-west detailed profile shown in figure 9. 

38
 
 

 

The AMT inversion result for the TM mode for the north to south line acquired in 2005, 

YFRESNS, is presented in figure 11. This figure shows an electrically conductive section 

(approximately 10 to 22 ohm-m) for the first 100-m depth with more resistive units (100 to 500 

ohm-m) developing under stations 0, 100, 400 and 500 along the line. The interpreted geology 

under the station at 200 m along the line is more conductive (10 ohm-m) than the surrounding 

material at the same depth (22–50 ohm-m). Line YFRESEW crosses line YFRESNS at 

approximately 240 m along the traverse. 

Compare this north-south section (fig. 11) at 240 m to the TE mode results for line 

YFRESEW presented in figure 12. Line YFRESNS crosses line YFRESEW at approximately 

690 m as shown in the figure. Both figures show similar conductive and resistive depth sections 

at their respective locations. This illustrates the expected orthogonal relationship between the 

TM and TE modes of magnetotelluric surveying. 

However, it should be noted that the inferred fault under hole U–7cd and Yucca fault are 

likely affecting the natural electrical current flow that is being observed along line YFRESNS. 

The proximity of this line to these faults and the orientation of line YFRESNS, approximately 

north to south, is affecting exactly what is being recorded as the observed MT signal. The effect 

is that what should be the TE mode data on line YFRESNS (that is, current flow perpendicular to 

the traverse direction) is more likely an approximate representation of the TM mode, and the 

reverse, because of the restriction of current flow by the fault. 

39
 
Figure 11. Two–dimensional AMT inversion modeling results for 2005 line YFRESNS, at the Nevada 

Test Site, Nevada. Line YFRESEW crosses this line at approximately 240 meters along the traverse. 

40
 
Figure 12. Two–dimensional AMT inversion modeling results for the TE mode on line YFRESEW. Line 

YFRESNS (fig. 11), which crosses this line at approximately 690 meters along the traverse, presents a 

similar resistivity-depth section at 240 meters along that traverse. 

41
 
2006 Field Effort 

The AMT results for data acquired in 2006 are presented in figures 13 through 16. As 

with the DC resistivity modeling, the results for AMT Lines 1 and 2 near the southern drill hole 

U–7cd are presented first followed by results from Lines 3 and 4 which were located near the 

northern drill hole, U–2gj. 

Near U–7cd — Lines 1 and 2 

The AMT results for Line 1, presented in figure 13, compared with the DC resistivity 

results shown in figure 5, indicate several subsurface geologic contacts that may possibly be 

faults. As with the DC resistivity surveys, these survey traverses progressed from west to east 

(left to right in the figures). While there is a rapid change in the surface topography at the 

location of the Yucca fault escarpment that is approximately located near station 110 in figure 

13, the noted topographic exposure is only on the scale of about 4 m. Given the scale of figure 13 

(down to 600 m), such a small change in topography is not very evident. 

The AMT results indicate several changes in conductivity along the line. One occurs at a 

distance of approximately 100 m along the traverse (near station 110) which corresponds with 

the surface expression of the Yucca fault. Other possible faults may be present at distances 

approximately 170 m (under station 117) and 210 m (station 121). Another fault, which is not 

marked in the figure, may be present at approximately 20 to 30 m along the line (under stations 

102 and 103). 

The AMT 2–D inversion results for Line 2, presented in figure 14, show a resistivity 

discontinuity at approximately 100 m along the line (under station 210) that may be another 

expression of Yucca fault. Another smaller fault may exist just to the left of the conductive zone 

42
 
at approximately 140 to 150 m along the line (under stations 214 and 215) and another small 

fault under station 218. 

Figure 13. AMT two–diminsional inversion modeling results for Line 1 (fig. 2) of 2006 field effort at the 

Nevada Test Site, Nevada. 

43
 
Figure 14. AMT two–dimensional inversion modeling results for Line 2 (fig. 2) of 2006 field effort at 

the Nevada Test Site, Nevada. 

A conclusion that may be drawn from a comparison between the DC resistivity results 

shown in figures 5 and 6 and those for the AMT in figures 13 and 14 is that the AMT technique 

does not have as high a lateral resolution as the DC technique. This is not a total surprise since 

the DC electrode spacing was 2 m between spacings and the AMT station spacing was 10 m, 

44
 
with one set of magnetic field readings used for two adjacent stations. While this was not an 

unusual setup for AMT measurements because the magnetic fields are known to vary slowly 

over a small area, it still indicates a limitation of the AMT technique to delineate small changes 

in resistivity over a small area. 

Near U–2gj — Lines 3 and 4 

As described above, Line 3 is located south of drill hole U–2gj (fig. 2) in the northern end 

of Yucca Flat basin. The Line 3 AMT inversion results (fig. 15) indicate slight conductivity 

contrasts (from 250 ohm-m to 400 ohm-m) in the subsurface at shallow depths at similar 

locations to those observed in the DC resistivity modeling (fig. 7). A few more small faults are 

inferred along the AMT profile than along the DC resistivity profile. Along the line, these small 

faults are located at 22 m (station 302), 52 m (station 305), 78 m (station 308), 103 m (station 

310), 126 m (station 313), 137 m (station 314), 159 m (station 316), and at 176 m (station 318). 

Line 4 is located just north of drill hole U–2gj (fig. 2). As with the DC resistivity 

inversion results for Line 4 (fig. 8), the AMT inversion results (fig. 16) do not present a very 

great resistivity contrast in the subsurface. Possible faults are located at 15 m (between stations 

401 and 402), 34 m (between stations 403 and 404), and 182 m along the traverse (between 

stations 418 and 419). Note that there is no indication, in this AMT section, of a fault under 

station 410 that is noted in the trench on the surface at this site. 

45
 
Figure 15. AMT two–dimensional inversion modeling results for Line 3 (fig. 2) of 2006 field effort at 

the Nevada Test Site, Nevada. 

46
 
Figure 16. AMT two–dimensional inversion modeling results for Line 4 (fig. 2) of 2006 field effort at 

the Nevada Test Site, Nevada. 

47
 
Vertical Gradient Magnetic Field Results 

As previously described a magnetic field survey was conducted along lines YFRESEW 

and YFRESNS to check for a magnetic susceptibility contrast across the traversed faults. The 

magnetic field survey results presented in figure 17 have been corrected for diurnal variations 

and indicate changes in the magnetic field up to 200 nanoteslas (nT) across Yucca fault on the 

eastern end of line YFRESEW and, possibly, up to 50 nT in the vicinity of Topgallant fault on 

the western end, though this amplitude variation is not very clear. The large high- and lowamplitude signals in the vicinity of easting 584600 are related to proximity to the U–7cd tower 

and the associated buildings and cables on top of and underneath the ground in that area. The 

vertical gradient of the measured magnetic fields did not show any large changes across the 

faults, likely due to the size of the structures involved. 

48
 
Figure 17. Bottom sensor total magnetic field data near drill hole U–7cd, Yucca Flat, Nevada Test Site, Nevada. L

near easting 584800 along the line of the east-west profile. DC resistivity lines 1 and 2 are indicated, as are the 

fault and Topgallant fault. [nT, nanoteslas] 

49
 
Discussion 

The goal of the present investigation is to develop, through geophysical study, an 

understanding of the geometry and architecture of fault zones at various scales in Yucca Flat. To 

this end, geophysical profiles were conducted across faults with various lengths and magnitude 

of offset. Line YFRESEW and Lines 1 and 2 (fig. 2) were collected across Yucca fault, a mature 

fault with about 300 m of displacement (Ferguson and others, 1988) and one of the major 

structures in Yucca Flat. Line 3 data were collected across a small mapped fault (Slate and 

others, 1999) to the south of drill hole U–2gj (fig. 2). Geologic cross-sections across the northern 

part of Yucca Flat that were tied to well and seismic data (IT Corporation, 1996) portray this 

small fault as an antithetic splay with about 30 m of west-side-down offset in the hanging wall of 

the Carpetbag fault. Line 4 data were collected across the northern projection of the same fault 

trace in an area where there are no mapped surface faults except for that uncovered in the trench 

at center of the line. 

Geophysical Response Related to Varying Fault Offset 

The location and magnitude of offset along major faults such as Yucca fault were 

previously determined by integration of results from gravity studies (Ferguson and others, 1988; 

Phelps and others, 1999; Phelps and McKee, 1999), regional magnetotelluric profiles (Asch and 

others, 2006), surface mapping (Slate and others, 1999; Grasso, 2001), abundant drill-hole data 

(Covington and Berger, 1997), and previous subsurface interpretations (IT Corporation, 1996; 

Bechtel Nevada, 2006). Fault offset along Yucca fault is suggested from the AMT models (figs. 

9, 13, and 14) as a result of juxtaposition of lithologic units, such as alluvial fill and partly 

welded ash-flow tuff, which have differing resistivity. Geologic cross sections across the central 

50
 
part of Yucca Flat that were tied to well and seismic data (IT Corporation, 1996) portray Yucca 

fault as two subparallel strands; this geometry is supported by the detailed AMT data (figs. 13 

and 14). The DC resistivity data across Yucca fault show clear offsets at even in the shallow 

subsurface where lithologic contrast across the fault would be expected to be low in the alluvium 

(figs. 5 and 6). 

Geophysical profiles across the small mapped fault (Slate and others, 1999) to the south 

of drill hole U–2gj portray a complicated response interpreted to be the result of several small 

faults (figs. 7 and 15). Relatively slight conductivity contrasts indicate that the faulting is likely 

within the same or closely related lithological unit, consistent with the relatively small amount of 

offset expected. The northernmost line (Line 4) shows the smallest conductivity contrasts, and 

only a few limited faults can be inferred (figs. 8 and 16). 

Geophysical Response Related to Fault Zone Geometry and Architecture 

Field mapping and seismic studies have demonstrated that fault zones result from 

displacements along numerous discrete segments (Segall and Pollard, 1980; Stewart and 

Hancock, 1991). Fault segments tend to be linked together in map and cross-section view, but the 

overall geometry of the fault zone is more complex than a single planar feature. As fault 

displacement proceeds (either vertically or horizontally), segments may coalesce into a longer, 

geometrically simple feature (Segall and Pollard, 1980; Peacock and Sanderson, 1991). 

Additionally, most faults can be described as having an internal architecture (Caine and others, 

1996; Kim and others, 2004) consisting of the following general elements: (1) a protolith of 

relatively undamaged rock, (2) a damage zone of fractured and brecciated fault rock, and (3) a 

fault core composed of gouge or cataclastic rock. The width and distribution of fault rocks in a 

fault zone are known to be related to the type and magnitude of fault displacement (Hull, 1988), 

51
 
rock type, geometry of the fault-zone segments, and the physical environment (Sibson, 1986). 

Geophysical profiles were conducted at a variety of scales in an attempt to characterize 

individual fault segments and to identify the extent of damage zones associated with fault offset. 

Yucca fault has a generally north-south surface trace but is broadly sinuous (fig. 1) along 

its 32-km length. Subsequent to underground nuclear testing near the fault, large fractures 

formed in the alluvium along Yucca fault where no fractures were noted prior to testing (Barosh, 

1968). Mapping of surface effects in Yucca Flat (Grasso, 2001) reveals a variety of features 

including collapse sinks, craters, cracks, fractures, faults, and pressure ridges, many of which are 

related to postexplosion collapse and expansion. However, the fractures along and near the trace 

of Yucca fault (fig. 18) are interpreted to be the surface expression of faults in the alluvial fill, 

these faults being the result of induced reactivation of an older, much larger bedrock feature 

(fault structure?) (Barosh, 1968). Topographically, the surface expression of the fault is generally 

an eastward-facing scarp about 3 m high. The fractures along Yucca fault form an en-echelon 

pattern along the fault with curving, northwest and northeast trends (fig. 18). These fractures 

appear to represent linked fault segments that initiated in the alluvium above the deeper bedrock 

fault. 

2006 AMT Lines 1 and 2 were collected across the surface scarp of Yucca fault (fig. 19) 

near a point where two fault segments are linked. Line 1 is just north of a northeast-striking fault 

segment; Line 2 is along a segment that strikes north-northwest. The AMT results (fig. 19) are 

consistent with the location and complexity of the surface trace, including the presence of 

multiple fault surfaces. The relatively gentle dips of the fault strands in Line 2 (fig. 19) may be 

the result of curved, low-angle relay structures that transfer displacement between fault 

segments. Alternatively, the far resistive block east of Yucca fault at the eastern end of Line 2 

may be seeing the collapse effects of a moderate-sized crater to the east of the profile. 

52
 
Figure 18. Map of Yucca fault and surface effects near drill hole U–7cd on Yucca Flat at the 

Nevada Test Site, Nevada. [AMT, audio magnetotelluric; DC, direct current; NTS, Nevada Test 

Site]. 

53 
Figure 19. Schematic three–dimensional perspective view of AMT profiles, Yucca fault and surface effects near d

Yucca Flat at the Nevada Test Site, Nevada. [Ohm-M, ohm-meters] 

54 
Surface fractures in alluvium that formed as a result of underground nuclear tests 

originally extended to a depth of as much as 30 m; most were widest at the surface and narrowed 

with depth (Carr, 1965). These fractures have largely filled in over the past decades and can no 

longer be seen. However, the DC resistivity profiles still appear to respond to the presence of 

these relief fracture zones, presumably because of the differing resistivity of the alluvium and the 

fracture-filling material. When the DC resistivity profiles are compared with the surface-effects 

map (fig. 20), there appears to be a nearly one-to-one correspondence; each surface feature 

appears to correspond to a change in resistivity along the profile. Irregular, complex variations in 

resistivity are present within about 20 m of each fault plane (figs. 5 and 6). This may represent 

the extent of fault-related damage associated with each fault trace. While this may be the case in 

the upper 10 m for 5-m electrode spacings, the response deeper than 10 m could represent a loss 

of resolution during the inversion, resulting in inversion artifacts. Overlap and steps between 

adjacent fault traces may increase the width of the disturbed zone to as much as 50 m, as seen on 

the surface-effects map (fig. 18). Changes in conductivity in the welded volcanic layers as Yucca 

fault is approached in AMT line YFRESEW (fig. 9) may also be the result of footwall damage 

adjacent to the fault. 

DC resistivity data from the northern geophysical profiles near drill hole U–2gj again are 

consistent with the surface-effects map (fig. 21), but the resistivity structure is much less variable 

adjacent to each fault, indicating that the fault-associated damage may be much narrower or less 

pronounced because of fracture-filling material that has an electrical resistivity that is similar to 

the alluvium overburden. 

55
 
Figure 20. Three–dimensional perspective view of DC resistivity profiles, the Yucca fault, and surface effects near 

[ohm-m, ohm-meters] 

56 
Figure 21. Three–dimensional perspective view of DC resistivity profiles and surface effects near drill-hole U–

Transverse Mercator] 

57 
Conclusions 


Detailed geophysical investigations near fault zones at Yucca Flat have revealed 

geophysical responses at a variety of scales of observation. At the most general scale, MT data 

provide information on the location of deeper crustal structures and general information on the 

attitude of the structure. AMT data provide a higher resolution set of observations confined to 

within about 1 km of the surface. These data allow for the delineation of multiple fault strands, 

understanding geometric relations at fault stopovers and intersections. The AMT data are best 

interpreted in areas with abundant drill-hole control because of the high degree of variability in 

lithology in the upper 1 km of section at Yucca Flat. DC resistivity data provide higher 

resolution imaging of the uppermost portions of fault zones than the AMT data and show a high 

degree of correspondence with fault-related surface fracturing. The magnetic field data indicated 

a clear change across the Yucca fault but not as strong a change across the Topgallant fault. 

Additional insights into the nature of faulting at Yucca Flat could be gained through threedimensional AMT or DC resistivity surveys that might capture along-strike variations in fault 

characteristics. 

While one of the goals of this study was to determine if the faults and fractures could be 

conduits or barriers to ground-water flow, the acquired data do not indicate one way or another if 

the faults studied would hinder or allow flow of ground water. This may be a function of when 

the data were acquired (early summer). Additional data collection during late winter or early 

spring, when more ground water was flowing in the near surface, could help resolve this issue. 

Any new electrically conductive or resistive anomalous zones could be investigated with shallow 

boreholes and the physical properties of these zones determined. 

58
 
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Winograd, I.J., and Thordarson, William, 1975, Hydrogeologic and hydrochemical framework, 

south-central Great Basin, Nevada-California, with special reference to the Nevada Test Site: 

U.S. Geological Survey Professional Paper 712–C, 126 p. 

64
 
Appendix A — DC Resistivity Two–Dimensional (2–D) Modeling 

Figure A-1. 2–D robust inversion for 2005 line YFRESEW from 0 to 760 m west-east 

along the line with data misfit. 

Figure A-2. 2–D robust inversion for 2005 line YFRESEW from 230 to 990 m west-east 

along the line with data misfit. 

Figure A-3. 2–D robust inversion for 2005 line YFRESEW from 460 to 1,500 m westeast along the line with data misfit. 

Figure A-4. 2–D robust inversion for 2005 line YFRESNS from 0 to 500 m north-south 

along the line with data misfit. 

Figure A-5. 2–D robust inversion for 2006 line 1 from 0 to 240 m west-east along the 

line with data misfit. 

Figure A-6. 2–D robust inversion for 2006 line 2 from 0 to 200 m west-east along the 

line with data misfit. 

Figure A-7. 2–D robust inversion for 2006 line 3 from 0 to 200 m west-east along the 

line with data misfit. 

Figure A-8. 2–D robust inversion for 2006 line 4 from 0 to 200 m west-east along the 

line with data misfit. 

A-1 
Appendix A – 2-D DC Resistivity Modeling 

Figure A-1. 2–D robust inversion for 2005 line YFRESEW from 0 to 760 meters west-east along the li

A-2 
Appendix A – 2-D DC Resistivity Modeling 

Figure A-2. 2–D robust inversion for 2005 line YFRESEW from 230 to 990 meters west-east along the 

A-3 
Appendix A – 2-D DC Resistivity Modeling 

Figure A-3. 2–D robust inversion for 2005 line YFRESEW from 460 to 1,500 meters west-east along t

A-4 
Appendix A – 2-D DC Resistivity Modeling 

Figure A-4. 2–D robust inversion for 2005 line YFRESNS from 0 to 500 meters north-south along the 

A-5 
Appendix A – 2-D DC Resistivity Modeling 

Figure A-5. 2–D robust inversion for 2006 line 1 from 0 to 240 meters west-east along the line with da

A-6 
Appendix A – 2-D DC Resistivity Modeling 

Figure A-6. 2–D robust inversion for 2006 line 2 from 0 to 200 meters west-east along the line with da

A-7 
Appendix A – 2-D DC Resistivity Modeling 

Figure A-7. 2–D robust inversion for 2006 line 3 from 0 to 200 meters west-east along the line with da

A-8 
Appendix A – 2-D DC Resistivity Modeling 

Figure A-8. 2–D robust inversion for 2006 line 4 from 0 to 200 meters west-east along the line with da

A-9 
APPENDIX B – AMT Data 

For each line: 

2-D Inversion model with and without model mesh 

Apparent Resistivity 

Impedance Phase 

E-Predicted Coherencies 

Impedance Skew 

Impedance Polar Plots 

Impedance Strike, Rotation, and Tipper Strike 

2005 AMT Data: 

Line YFRESEW - Figures B-1 through B-28 

Line YFRESNS - Figures B-29 through B-40 

2006 AMT Data: 

Line 1 – Figures B-41 through B-66 

Line 2 – Figures B-67 through B-92 

Line 3 – Figures B-93 through B-118 

Line 4 – Figures B-119 through B-146 

B-1 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-1. 7ZR±GLPHQVLRQDO2–D TM mode inversion model for 2005 east-west line, YFRESEW. 

ZLWKRXWWKHfinite difference mesh. 

B-2 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-2. Two–dimensional (2–D) TM mode forward and inversion model for 2005 east-west line, 

YFRESEW. with mesh. 

B-3 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-3. Apparent resistivity field and TM mode model data for 2005 east-west line, 

YFRESEW, sites 1 to 9. 

B-4 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-4. Apparent resistivity field and TM mode model data for 2005 east-west line, 

YFRESEW, sites10 to 16. 

B-5 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-5. Impedance phase field and TM mode model data for 2005 east-west line, 

YFRESEW, sites 1 to 9. 

B-6 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-6. Impedance phase field and TM mode model data for 2005 east-west line, 

YFRESEW, sites 10 to 16. 

B-7 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-7. Two–dimensional TE mode inversion model for 2005 east-west line, YFRESEW. without 

the finite difference mesh. 

B-8 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-8. Two–Gimensional TE mode forward and inversion model for 2005 east-west line, 

YFRESEW. with mesh. 

B-9 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-9. Apparent resistivity field and TE mode model data for 2005 east-west line, 

YFRESEW, sites 1 to 9. 

B-10 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-10. Apparent resistivity field and TE mode model data for 2005 east-west line, 

YFRESEW, sites10 to 16. 

B-11 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-11. Impedance phase field and TM mode model data for 2005 east-west line, 

YFRESEW, sites 1 to 9. 

B-12 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-12. Impedance phase field and TE mode model data for 2005 east-west line, 

YFRESEW, sites 10 to 16. 

B-13 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-13. Coherency data for 2005 east-west line, YFRESEW, sites 1 to 4. 

B-14 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-14. Coherency data for 2005 east-west line, YFRESEW, sites 5 to 8. 

B-15 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-15. Coherency data for 2005 east-west line, YFRESEW, sites 9 to 12. 

B-16 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-16. Coherency data for 2005 east-west line, YFRESEW, sites 13 to 16. 

B-17 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-17. Impedance skew data for 2005 east-west line, YFRESEW, sites 1 to 4. 

B-18 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-18. Impedance skew data for 2005 east-west line, YFRESEW, sites 5 to 8. 

B-19 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-19. Impedance skew data for 2005 east-west line, YFRESEW, sites 9 to 12. 

B-20 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-20. Impedance skew data for 2005 east-west line, YFRESEW, sites 13 to 16. 

B-21 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-21. Polar impedance plots for 2005 east-west line, YFRESEW, sites 1 to 4. 

B-22 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-22. Polar impedance plot for 2005 east-west line, YFRESEW, sites 5 to 8. 

B-23 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-23. Polar impedance plots for 2005 east-west line, YFRESEW, sites 9 to 12. 

B-24 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-24. Polar impedances for 2005 east-west line, YFRESEW, sites 13 to 16. 

B-25 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-25. Impedance strike and rotation angle and tipper strike for 2005 east-west line, 

YFRESEW, sites 1 to 4. 

B-26 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-26. Impedance strike and rotation angle and tipper strike for 2005 east-west line, 

YFRESEW, sites 5 to 8. 

B-27 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-27. Impedance strike and rotation angle and tipper strike for 2005 east-west line, 

YFRESEW, sites 9 to 12. 

B-28 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-28. Impedance strike and rotation angle and tipper strike for 2005 east-west line, 

YFRESEW, sites 13 to 16. 

B-29 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-29. Two–dimensional inversion model for 2005 north-south line, YFRESNS. without the 

finite difference mesh. 

B-30 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-30. 7ZR±GLPHQVLRQDO forward and inversion model for 2005 north-south line, YFRESNS. 

B-31 

with mesh. 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-31. Apparent resistivity field and model data for 2005 north-south line, YFRESNS, 

sites 1 to 6. 

B-32 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-32. Impedance phase field and model data for 2005 north-south line, YFRESNS, sites 1 

to 6. 

B-33 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-33. Coherency data for 2005 north-south line, YFRESNS, sites 1 to 4. 

B-34 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-34. Coherency data for 2005 north-south line, YFRESNS, sites 5 to 6. 

B-35 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-35. Impedance skew data for 2005 north-south line, YFRESNS, sites 1 to 4. 

B-36 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-36. Impedance skew data for 2005 north-south line, YFRESNS, sites 5 to 6. 

B-37 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-37. Polar impedance plots for 2005 north-south line, YFRESNS, sites 1 to 4. 

B-38 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-38. Polar impedance plot for 2005 north-south line, YFRESNS, sites 5 to 6. 

B-39 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-39. Impedance strike and rotation angle and tipper strike for 2005 north-south line, 

YFRESNS, sites 1 to 4. 

B-40 
Appendix B – AMT Data, 2005 Lines YFRESEW and YFRESNS 

Figure B-40. Impedance strike and rotation angle and tipper strike for 2005 north-south line, 

YFRESNS, sites 5 to 6. 

B-41 
Appendix B – AMT Data, 2006 Line 1 

Figure B-41. Two–dimensional inversion model for 2006 Line 1, no finite difference mesh. 

B-42 
Appendix B – AMT Data, 2006 Line 1 

Figure B-42. Two–dimensional inversion model for 2006 Line 1 with finite difference mesh. 

B-43 
Appendix B – AMT Data, 2006 Line 1 

Figure B-43. Apparent resistivity data for 2006 Line 1, sites 1 to 9. 

B-44 
Appendix B – AMT Data, 2006 Line 1 

Figure B-44. Apparent resistivity data for 2006 Line 1, sites 10 to 18. 

B-45 
Appendix B – AMT Data, 2006 Line 1 

Figure B-45. Apparent resistivity data for 2006 Line 1, sites 19 to 24. 

B-46 
Appendix B – AMT Data, 2006 Line 1 

Figure B-46. Impedance phase data for 2006 Line 1, sites 1 to 9. 

B-47 
Appendix B – AMT Data, 2006 Line 1 

Figure B-47. Impedance phase data for 2006 Line 1, sites 10 to 18. 

B-48 
Appendix B – AMT Data, 2006 Line 1 

Figure B-48. Impedance phase data for 2006 Line 1, sites 19 to 24. 

B-49 
Appendix B – AMT Data, 2006 Line 1 

Figure B-49. Coherency data for 2006 Line 1, sites 1 to 4. 

B-50 
Appendix B – AMT Data, 2006 Line 1 

Figure B-50. Coherency data for 2006 Line 1, sites 5 to 8. 

B-51 
Appendix B – AMT Data, 2006 Line 1 

Figure B-51. Coherency data for 2006 Line 1, sites 9 to 12. 

B-52 
Appendix B – AMT Data, 2006 Line 1 

Figure B-52. Coherency data for 2006 Line 1, sites 13 to 16. 

B-53 
Appendix B – AMT Data, 2006 Line 1 

Figure B-53. Coherency data for 2006 Line 1, sites 17 to 20. 

B-54 
Appendix B – AMT Data, 2006 Line 1 

Figure B-54. Coherency data for 2006 Line 1, sites 21 to 24. 

B-55 
Appendix B – AMT Data, 2006 Line 1 

Figure B-55. Polar impedance plots for 2006 Line 1, sites 1 to 4. 

B-56 
Appendix B – AMT Data, 2006 Line 1 

Figure B-56. Polar impedance plots for 2006 Line 1, sites 5 to 8. 

B-57 
Appendix B – AMT Data, 2006 Line 1 

Figure B-57. Polar impedance plots for 2006 Line 1, sites 9 to 12. 

B-58 
Appendix B – AMT Data, 2006 Line 1 

Figure B-58. Polar impedance plots for 2006 Line 1, sites 13 to 16. 

B-59 
Appendix B – AMT Data, 2006 Line 1 

Figure B-59. Polar impedance plots for 2006 Line 1, sites 17 to 20. 

B-60 
Appendix B – AMT Data, 2006 Line 1 

Figure B-60. Polar impedance plots for 2006 Line 1, sites 21 to 24. 

B-61 
Appendix B – AMT Data, 2006 Line 1 

Figure B-61. Impedance strike, rotation, and tipper strike for 2006 Line 1, sites 1 to 4. 

B-62 
Appendix B – AMT Data, 2006 Line 1 

Figure B-62. Impedance strike, rotation, and tipper strike for 2006 Line 1, sites 5 to 8. 

B-63 
Appendix B – AMT Data, 2006 Line 1 

Figure B-63. Impedance strike, rotation, and tipper strike for 2006 Line 1, sites 9 to 12. 

B-64 
Appendix B – AMT Data, 2006 Line 1 

Figure B-64. Impedance strike, rotation, and tipper strike for 2006 Line 1, sites 13 to 16. 

B-65 
Appendix B – AMT Data, 2006 Line 1 

Figure B-65. Impedance strike, rotation, and tipper strike for 2006 Line 1, sites 17 to 20. 

B-66 
Appendix B – AMT Data, 2006 Line 1 

Figure B-66. Impedance strike, rotation, and tipper strike for 2006 Line 1, sites 21 to 24. 

B-67 
Appendix B – AMT Data, Line 2 

Figure B-67. Two–dimensional inversion model for Line 2 no finite difference mesh. 

B-68 
Appendix B – AMT Data, Line 2 

Figure B-68. Two–dimensional inversion model for Line 2 with finite difference mesh. 

B-69 
Appendix B – AMT Data, Line 2 

Figure B-69. Apparent resistivity data for Line 2, sites 1 to 10. 

B-70 
Appendix B – AMT Data, Line 2 

Figure B-70. Apparent resistivity data for Line 2, sites 11 to 20. 

B-71 
Appendix B – AMT Data, Line 2 

Figure B-71. Phase data for Line 2, sites 1 to 10. 

B-72 
Appendix B – AMT Data, Line 2 

Figure B-72. Phase data for Line 2, sites 11 to 20. 

B-73 
Appendix B – AMT Data, Line 2 

Figure B-73. E-predicted coherencies for Line 2, sites 1 to 5. 

B-74 
Appendix B – AMT Data, Line 2 

Figure B-74. E-predicted coherencies for Line 2, sites 6 to 9. 

B-75 
Appendix B – AMT Data, Line 2 

Figure B-75. E-predicted coherencies for Line 2, sites 10 to 13. 

B-76 
Appendix B – AMT Data, Line 2 

Figure B-76. E-predicted coherencies for Line 2, sites 14 to 18. 

B-77 
Appendix B – AMT Data, Line 2 

Figure B-77. E-predicted coherencies for Line 2, sites 19 to 20. 

B-78 
Appendix B – AMT Data, Line 2 

Figure B-78. Impedance skews for Line 2, sites 1 to 5. 

B-79 
Appendix B – AMT Data, Line 2 

Figure B-79. Impedance skews for Line 2, sites 6 to 9. 

B-80 
Appendix B – AMT Data, Line 2 

Figure B-80. Impedance skews for Line 2, sites 10 to 13. 

B-81 
Appendix B – AMT Data, Line 2 

Figure B-81. Impedance skews for Line 2, sites 14 to 18. 

B-82 
Appendix B – AMT Data, Line 2 

Figure B-82. Impedance skews for Line 2, sites 19 to 20. 

B-83 
Appendix B – AMT Data, Line 2 

Figure B-83. Polar impedance plots for Line 2, sites 1 to 5. 

B-84 
Appendix B – AMT Data, Line 2 

Figure B-84. Polar impedance plots for Line 2, sites 6 to 9. 

B-85 
Appendix B – AMT Data, Line 2 

Figure B-85. Polar impedance plots for Line 2, sites 10 to 13. 

B-86 
Appendix B – AMT Data, Line 2 

Figure B-86. Polar impedance plots for Line 2, sites 14 to 18. 

B-87 
Appendix B – AMT Data, Line 2 

Figure B-87. Polar impedance plots for Line 2, sites 19 to 20. 

B-88 
Appendix B – AMT Data, Line 2 

Figure B-88. Impedance strike, rotation, and tipper strike for Line 2, sites 1 to 5. 

B-89 
Appendix B – AMT Data, Line 2 

Figure B-89. Impedance strike, rotation, and tipper strike for Line 2, sites 6 to 9. 

B-90 
Appendix B – AMT Data, Line 2 

Figure B-90. Impedance strike, rotation, and tipper strike for Line 2, sites 10 to 13. 

B-91 
Appendix B – AMT Data, Line 2 

Figure B-91. Impedance strike, rotation, and tipper strike for Line 2, sites 14 to 18. 

B-92 
Appendix B – AMT Data, Line 2 

Figure B-92. Impedance strike, rotation, and tipper strike for Line 2, sites 19 to 20. 

B-93 
Appendix B – AMT Data, Line 3 

Figure B-93. Two–dimensional inversion model for Line 3 without the finite difference mesh. 

B-94 
Appendix B – AMT Data, Line 3 

Figure B-94. Two–dimensional inversion model for Line 3 with the finite difference mesh. 

B-95 
Appendix B – AMT Data, Line 3 

Figure B-95. Apparent resistivity data for Line 3, sites 1 to 12. 

B-96 
Appendix B – AMT Data, Line 3 

Figure B-96. Apparent resistivity data for Line 3, sites 13 to 20. 

B-97 
Appendix B – AMT Data, Line 3 

Figure B-97. Phase data for Line 3, sites 1 to 12. 

B-98 
Appendix B – AMT Data, Line 3 

Figure B-98. Phase data for Line 3, sites 13 to 20. 

B-99 
Appendix B – AMT Data, Line 3 

Figure B-99. E-predicted coherencies for Line 3, sites 1 to 7. 

B-100 
Appendix B – AMT Data, Line 3 

Figure B-100. E-predicted coherencies for Line 3, sites 8 to 11. 

B-101 
Appendix B – AMT Data, Line 3 

Figure B-101. E-predicted coherencies for Line 3, sites 12 to 15. 

B-102 
Appendix B – AMT Data, Line 3 

Figure B-102. E-predicted coherencies for Line 3, sites 16 to 19. 

B-103 
Appendix B – AMT Data, Line 3 

Figure B-103. E-predicted coherencies for Line 3, site 20. 

B-104 
Appendix B – AMT Data, Line 3 

Figure B-104. Impedance skews for Line 3, sites 1 to 7. 

B-105 
Appendix B – AMT Data, Line 3 

Figure B-105. Impedance skews for Line 3, sites 8 to 11. 

B-106 
Appendix B – AMT Data, Line 3 

Figure B-106. Impedance skews for Line 3, sites 12 to 15. 

B-107 
Appendix B – AMT Data, Line 3 

Figure B-107. Impedance skews for Line 3, sites 16 to 19. 

B-108 
Appendix B – AMT Data, Line 3 

Figure B-108. Impedance skews for Line 3, site 20. 

B-109 
Appendix B – AMT Data, Line 3 

Figure B-109. Polar impedance plots for Line 3, sites 1 to 7. 

B-110 
Appendix B – AMT Data, Line 3 

Figure B-110. Polar impedance plots for Line 3, sites 8 to 11. 

B-111 
Appendix B – AMT Data, Line 3 

Figure B-111. Polar impedance plots for Line 3, sites 12 to 15. 

B-112 
Appendix B – AMT Data, Line 3 

Figure B-112. Polar impedance plots for Line 3, sites 16 to 19. 

B-113 
Appendix B – AMT Data, Line 3 

Figure B-113. Polar impedance plots for Line 3, site 20. 

B-114 
Appendix B – AMT Data, Line 3 

Figure B-114. Impedance strike, rotation, and tipper strike for Line 3, sites 1 to 7. 

B-115 
Appendix B – AMT Data, Line 3 

Figure B-115. Impedance strike, rotation, and tipper strike for Line 3, sites 8 to 11. 

B-116 
Appendix B – AMT Data, Line 3 

Figure B-116. Impedance strike, rotation, and tipper strike for Line 3, sites 12 to 15. 

B-117 
Appendix B – AMT Data, Line 3 

Figure B-117. Impedance strike, rotation, and tipper strike for Line 3, sites 16 to 19. 

B-118 
Appendix B – AMT Data, Line 3 

Figure B-118. Impedance strike, rotation, and tipper strike for Line 3, site 20. 

B-119 
Appendix B – AMT Data, Line 4 

Figure B-119. Two–dimensional inversion model for Line 4 without finite difference mesh. 

B-120 
Appendix B – AMT Data, Line 4 

Figure B-120. Two–dimensional inversion model for Line 4 with finite difference mesh. 

B-121 
Appendix B – AMT Data, Line 4 

Figure B-121. Apparent resistivity data for Line 4, sites 1 to 9. 

B-122 
Appendix B – AMT Data, Line 4 

Figure B-122. Apparent resistivity data for Line 4, sites 10 to 18. 

B-123 
Appendix B – AMT Data, Line 4 

Figure B-123. Apparent resistivity data for Line 4, sites 19 and 20. 

B-124 
Appendix B – AMT Data, Line 4 

Figure B-124. Impedance phase data for Line 4, sites 1 to 9. 

B-125 
Appendix B – AMT Data, Line 4 

Figure B-125. Phase data for Line 4, sites 10 to 18. 

B-126 
Appendix B – AMT Data, Line 4 

Figure B-126. Phase data for Line 4, sites 19 and 20. 

B-127 
Appendix B – AMT Data, Line 4 

Figure B-127. E-predicted coherencies for Line 4, sites 1 to 4. 

B-128 
Appendix B – AMT Data, Line 4 

Figure B-128. E-predicted coherencies for Line 4, sites 5 to 8. 

B-129 
Appendix B – AMT Data, Line 4 

Figure B-129. E-predicted coherencies for Line 4, sites 9 to 12. 

B-130 
Appendix B – AMT Data, Line 4 

Figure B-130. E-predicted coherencies for Line 4, sites 13 to 16. 

B-131 
Appendix B – AMT Data, Line 4 

Figure B-131. E-predicted coherencies for Line 4, sites 17 to 20. 

B-132 
Appendix B – AMT Data, Line 4 

Figure B-132. Impedance skews for Line 4, sites 1 to 4. 

B-133 
Appendix B – AMT Data, Line 4 

Figure B-133. Impedance skews for Line 4, sites 5 to 8. 

B-134 
Appendix B – AMT Data, Line 4 

Figure B-134. Impedance skews for Line 4, sites 9 to 12. 

B-135 
Appendix B – AMT Data, Line 4 

Figure B-135. Impedance skews for Line 4, sites 13 to 16. 

B-136 
Appendix B – AMT Data, Line 4 

Figure B-136. Impedance skews for Line 4, sites 17 to 20. 

B-137 
Appendix B – AMT Data, Line 4 

Figure B-137. Polar impedance plots for Line 4, sites 1 to 4. 

B-138 
Appendix B – AMT Data, Line 4 

Figure B-138. Polar impedance plots for Line 4, sites 5 to 8. 

B-139 
Appendix B – AMT Data, Line 4 

Figure B-139. Polar impedance plots for Line 4, sites 9 to 12. 

B-140 
Appendix B – AMT Data, Line 4 

Figure B-140. Polar impedance plots for Line 4, sites 13 to 16. 

B-141 
Appendix B – AMT Data, Line 4 

Figure B-141. Polar impedance plots for Line 4, sites 17 to 20. 

B-142 
Appendix B – AMT Data, Line 4 

Figure B-142. Impedance strike, rotation, and tipper strike for Line 4, sites 1 to 4. 

B-143 
Appendix B – AMT Data, Line 4 

Figure B-143. Impedance strike, rotation, and tipper strike for Line 4, sites 5 to 8. 

B-144 
Appendix B – AMT Data, Line 4 

Figure B-144. Impedance strike, rotation, and tipper strike for Line 4, sites 9 to 12 

B-145 
Appendix B – AMT Data, Line 4 

Figure B-145. Impedance strike, rotation, and tipper strike for Line 4, sites 13 to 16 

B-146 
Appendix B – AMT Data, Line 4 

Figure B-146. Impedance strike, rotation, and tipper strike for Line 4, sites 17 to 20. 

B-147