In Cooperation with the Southern Nevada Water Authority (SNWA) 

Audiomagnetotelluric data from Spring, Cave, 

and Coyote Spring Valleys, Nevada 

By Darcy K. McPhee, Bruce A. Chuchel, and Louise Pellerin 

Open-File Report 2006–1164 

U.S. Department of the Interior 

U.S. Geological Survey
ii

Contents 

Abstract.........................................................................................................................................1 

Introduction ...................................................................................................................................2 

Audiomagnetotelluric Method........................................................................................................3 

Audiomagnetotelluric Survey.........................................................................................................5 

Audiomagnetotelluric Data ............................................................................................................6 

Acknowledgments .........................................................................................................................8

References Cited ..........................................................................................................................8 

Figures 

1. Topographic maps of study area showing locations of AMT profiles A, B, and E (A) and 

profile C (B). ................................................................................................................. ...10

Tables 

1. Description of AMT profiles. ....................................................................................................12 

2. Sounding numbers, locations and elevations of stations along four AMT profiles ..................12

Appendix 

A. Sounding curves .....................................................................................................................15
1

Audiomagnetotelluric data from Spring, Cave, 

and Coyote Spring Valleys, Nevada 

By Darcy K. McPhee1, Bruce A. Chuchel1, and Louise Pellerin2

Abstract 

Audiomagnetotelluric (AMT) data along four profiles in Spring, Cave, and Coyote Spring 

Valleys are presented here. The AMT method is used to estimate the electrical resistivity of the 

earth over depth ranges of a few meters to greater than one kilometer. This method is a valuable 

tool for revealing subsurface structure and stratigraphy within the Basin and Range of eastern 

Nevada, therefore helping to define the geohydrologic framework in this region. We collected 

AMT data using the Geometrics StrataGem EH4 system, a four-channel, natural and controlledsource tensor system recording in the range of 10 to 92,000 Hz. To augment the low signal in the 

natural field, an unpolarized transmitter comprised of two horizontal-magnetic dipoles was used 

from 1,000 to 70,000 Hz. Profiles were 1.4 – 12.6 km in length with station spacing of 100-400 m. 

Data were recorded with the electrical (E) field parallel to and perpendicular to the regional 

geologic strike direction. Station locations and sounding curves, showing apparent resistivity, 

phase data, and coherency data, are presented here. 

 

1

 U.S. Geological Survey, 345 Middlefield Rd., MS 989, Menlo Park, CA 94025 

2

 Green Engineering, Inc., 2215 Curtis St., Berkeley, CA 94702 
2

Introduction 

The Basin and Range province is an arid, mountainous, sparsely populated region of the 

western United States. Here, ground water is organized into extensive regional systems (Harrill 

and Prudic, 1998) where it can flow between adjacent topographic ranges and basins. Much of the 

structure that controls the hydrogeology of the valleys in eastern Nevada is obscured by sediments, 

hence geophysical investigations are underway to characterize the subsurface structures and 

stratigraphy influencing ground-water resources. The gravity method has been used to estimate the 

structure and depth of the basins in eastern Nevada (Mankinen et al., 2006; Scheirer, 2005), 

however densities of silicic ash-flow tuff units in the area may be comparable to the average 

density of basin sediment-fill causing difficulty in resolving the subsurface geometry between the 

basin-fill and volcanic rocks using the gravity method alone. 

In this study, the audiomagnetotelluric (AMT) method was tested in Spring, Cave, and 

Coyote Spring valleys (Figure 1) to see if it is a feasible approach for mapping geologic/tectonic 

structures and thus could contribute significantly to the regional hydrological model in a typical 

Basin and Range setting. During the fall of 2004 and summer of 2005 AMT data were acquired 

along four profile lines (Figure 1). The AMT data obtained in this study were acquired to delineate 

range-front faults, structure, and stratigraphy within the basins as well as the geometry of the basins 

as a framework for hydrogeological modeling. 

The purpose of this report is to release the AMT sounding data. No interpretation of the 

data is included. 

 
3

Audiomagnetotelluric Method 

The magnetotelluric (MT) method is a geophysical technique, which uses the earth's natural 

electromagnetic (EM) fields as a source to investigate the electrical resistivity structure of the 

subsurface (Vozoff, 1991). The resistivity of geologic units is largely dependent upon their fluid 

content, porosity, degree of fracturing, temperature, and conductive mineral content (Keller, 1989). 

Saline fluids within the pore spaces and fracture openings can reduce resistivities in a rock matrix. 

Resistivity can be lowered by the presence of conductive clay minerals, carbon, and metallic 

mineralization. Increased temperatures cause higher ionic mobility and mineral activation energy, 

reducing rock resistivities significantly. Unaltered, unfractured igneous rocks are normally very 

resistive, with values typically 1,000 ohm-m or greater. Fault zones can appear as low resistivity 

units of less than 100 ohm-m when they are comprised of rocks fractured enough to have hosted 

fluid transport and consequent mineralogical alteration (Eberhart-Phillips and others, 1995). 

Carbonate rocks are moderately to highly resistive, with values of hundreds to thousands of ohm-m 

depending upon their fluid content, porosity, fracturing, and impurities. Marine shale, mudstone, 

and clay-rich alluvium are normally very conductive – a few ohm-m to tens of ohm-m. Unaltered, 

metamorphic, non-graphitic rocks are moderately to highly resistive. Tables of electrical resistivity 

for a variety of rocks, minerals and geological environments may be found in Keller (1987) and 

Palacky (1987). 

Using the same theory, the audiomagnetotelluric (AMT) method is used to estimate the 

electrical resistivity of the Earth over depth ranges of a few meters to greater than one kilometer 

(Zonge and Hughes, 1991). The Geometrics StrataGem EH-4 system, used in this study, utilizes 

both natural and man-made electromagnetic signals to obtain a continuous electrical sounding of 

the Earth beneath the measurement site (Geometrics, 2000). AMT systems are used to estimate the 
4

electrical impedance at the Earth’s surface from a series of simultaneous measurements of local 

electrical (E) and magnetic (H) field fluctuations made over a period of several minutes. The 

surface impedance is a complex function of frequency where higher-frequency data are influenced 

by shallow or nearby features, and lower-frequency data are influenced by structures at greater 

depth and distance. An AMT sounding provides an estimate of vertical resistivity beneath the 

receiver site and also indicates the geoelectric complexity at the sounding site. In areas where the 

resistivity distribution does not change rapidly from station to station, the resistivity sounding is a 

reasonable estimate of the geoelectric layering beneath the site. 

The Stratagem system consists of two basic components; a receiver and a transmitter 

(Geometrics, 2000). The natural source is worldwide lightning, but in the frequency range above 

1,000 Hz, natural signals are typically weak and a transmitter is used to augment the natural field 

and improve data quality. The unpolarized transmitter is comprised of two horizontal-magnetic 

dipoles and transmits signals from 1,000 to 70,000 Hz. The battery-powered system is compact 

and portable. Data are recorded in the range of 92,000 to 10 Hz. Surface impedance results are 

immediately displayed as a resistivity sounding. Data are subsequently modeled using twodimensional inversion algorithms. 

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

directions. The tensor impedance, parameterized as apparent resistivity and phase, are obtained 

from the time-series signals. Signals are converted to complex cross-spectra using a Fouriertransform technique. A least-squares, cross-spectral analysis (Geometrics, 2000) is then used to 

solve for a transfer function (impedance) that relates the observed electric fields to the magnetic 

fields under the assumption that the earth consists of a two-input, two-output, linear system with 

the magnetic fields as input and the electric fields as output. 
5

For a two-dimensional (2-D) earth, the diagonal terms of the impedance tensor are zero. 

The off-diagonal terms are decoupled into transverse electric (TE) and transverse magnetic (TM) 

modes. When the geology satisfies the 2-D assumption, the MT and AMT data for the TE mode 

measures electric field parallel to geologic strike, and the data for the TM mode measures electric 

field perpendicular to geologic strike. Data are processed with a fixed rotation parallel and 

perpendicular to regional strike. The MT and AMT methods are 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 

EM fields are responding to subsurface terranes of 1-, 2-, or 3-dimensions. For more information 

on this technique, see Telford and others (1991) for an introduction to the MT method and Vozoff 

(1991) for a more advanced treatment. 

Audiomagnetotelluric Survey 

AMT sounding data were acquired along four profile lines in eastern Nevada (Figure 1). A 

description of each line is given in Table 1. In addition to these profiles, a fifth transect, Profile D, 

was attempted in Coyote Spring Valley (Figure 1). However, this line was aborted due to the 

distortion of the data from nearby power lines, and the data are not presented here. Access to all but 

a few stations was with a truck along dirt roads. All soundings were collected with a Geometrics 

StrataGem EH-4 system (Geometrics, 2000). Horizontal electric fields were measured using Model 

BE-26 Buffered Active High Frequency dipoles and stainless steel electrodes in an X-shaped array 

with nominal dipole lengths of 40 m. The two, horizontal and orthogonal components of the 

magnetic field are measured in the same direction as the electric-field array with permalloy-cored 
6

BF-10 induction coils. Data were acquired in two frequency bands: 92,000 to 800 Hz and 1000 to 

10 Hz. 

Through experimentation we found that the optimal transmitter distance, at which the 

measurement site is located in the transmitter’s far field and yet receives adequate signal power, 

was 200 to 300 m from the receiver array, and we were able to acquire two stations for each 

transmitter location. 

Table 2 shows the AMT station locations and elevations for lines A, B, C, and E. Locations 

and elevations were recorded using a Garmin global positioning system during field acquisition. 

 

Audiomagnetotelluric Data 

After transforming the recorded time-series data to the frequency domain, standard 

processing (Geometrics, 2000) was employed to determine apparent resistivity and phase tensor at 

each site. Apparent resistivity is the ratio of one component of the electric field magnitude over 

the orthogonal component of the magnetic field magnitude, normalized by the frequency and the 

magnetic susceptibility for free space. The impedance phase is the arctangent of the unnormalized 

ratio. The apparent resistivity and phase are related through a Hilbert transform; the phase is 

proportional to the slope of the apparent resistivity curve on a log-log plot, but from a baseline of 

45 degrees (Vozoff, 1991). 

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 E-predicted coherency plots. 
7

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

levels. 

Anthropomorphic noise, such as power lines, power generators, moving vehicles and trains, 

can produce an incoherent noise mainly affecting frequencies above 1 Hz. An ungrounded, barbed 

wire fence along Profile A did not influence the data. Noise sources were absent from Profiles B 

and E. Data along Profile C were noisier than the other profiles: A power line located over 10 km 

away from Profile C was the only known source of noise in the area, and we do not have 

explanations for the increased broadband noise on several soundings. 

Several soundings were recorded at each station. The best sounding from each station is 

presented here and will be used in subsequent modeling of the data. The unedited data presented 

here are not rotated, but fixed at specific azimuths as acquired in the field (Table 1). The ExHy 

mode is the nominal TM and the EyHx the TE mode. Scalar data as calculated in the Imagem 

presentational software (Geometrics, 2000) are presented. For each station, three separate plots are 

given in Appendix A: 

1. Apparent Resistivity for the TM and TE modes at a fixed direction. 

2. Impedance Phase for the TM and TE modes at a fixed direction. 

3. E-Predicted Coherencies are (ExHy * Conj(ExHy)) / (Hy * Conj(Hy) * Ex * 

Conj(Ex)) and (EyHx * Conj(EyHx)) / (Hx*Conj(Hx) * Ey * Conj(Ey)), where Conj 

indicates complex conjugation. 

Electronic data are available upon request in two formats: Geometrics Z Impedance files 

(Geometrics, 2000; Appendix A) and the Electronic Data Interchange (EDI), which was established 

in 1987 by the Society of Exploration Geophysicists (SEG) as a standard format for the interchange 

of MT data (Wright, 1988). 
8

Acknowledgments 

This study was performed in cooperation with the Southern Nevada Water Authority 

(SNWA) whose support is greatly appreciated. We are grateful to Janet Tilden for her help in the 

field, and to Gary Dixon, Jeff Johnston, and Ester Falgás Parra for contributing their expertise and 

advice. We also thank Ed Mankinen and Vicki Langenheim for their helpful reviews. 

References Cited 

Eberhart-Phillips, D., Stanley, W.D., Rodriguez, B.D. and Lutter, W.J., 1995, Surface seismic and 

electrical methods to detect fluids related to faulting: Journal of Geophysical Research, vol. 100, 

no. B7, p. 12,919-12,936. 

Geometrics, 2000, Operation Manual for Stratagem systems running IMAGEM, Ver. 2.16: 

Geometrics, San Jose, California. 

Harrill, J.R., and Prudic, D.E., 1998, Aquifer systems in the Great Basin region of Nevada, Utah 

and adjacent states – summary report: U.S. Geological Professional Paper, 1409A, 61p. 

Keller, G.V., 1987, Rock and mineral properties, in Electromagnetic Methods in Applied 

Geophysics Theory: M.N. Nabighian, Ed., Society of Exploration Geophysicists, Tulsa, 

Oklahoma, v.1, p. 13-51. 

Keller, G.V., 1989, Electrical properties, in Carmichael, R.S., Ed., Practical handbook of physical 

properties of rocks and minerals: CRC Press, Boca Raton, Florida, p. 359-427. 

Mankinen, E.A., Roberts, C.W., McKee, E.H., Chuchel, B.A., and Moring, B.C., 2006, 

Geophysical data from the Spring and Snake valleys area, Nevada and Utah: U.S. Geological 

Survey Open-File Report 2006-1160, 42 p. 
9

Palacky, G.J., 1987, Resistivity characteristics of geologic targets, in Electromagnetic Methods in 

Applied Geophysics Theory: M.N. Nabighian, Ed., Society of Exploration Geophysicists, Tulsa, 

Oklahoma, vol. 1, p. 53-129. 

Scheirer, D.S., 2005, Gravity studies of Cave, Dry Lake, and Delamar Valleys, east-central 

Nevada: U.S. Geological Survey Open File Report, 2005-1339, 36p. 

Telford, W.M., Geldart, L.P.., and Sheriff, R.E., 1991, Applied Geophysics (2nd Edition): 

Cambridge University Press, 790 p. 

Vozoff, K., 1991, The magnetotelluric method, in Electromagnetic methods in applied geophysics: 

M.N. Nabighian, Ed., Society of Exploration Geophysicists, Tulsa, Oklahoma, vol. 2, part B, p. 

641-711. 

Wright, D.E., 1988, The SEG Standard for Magnetotelluric Data: presented at the Society of 

Exploration Geophysicists Annual Meeting, November. Available through 

http://www.geophysics.dias.ie/mtnet/docs/ediformat.txt. 

Zonge, K.L. and Hughes, L.J., 1991, Controlled source audio-frequency magnetotellurics, in 

 Electromagnetic methods in applied geophysics: M.N. Nabighian, Ed., Society of Exploration 

 Geophysicists, Tulsa, Oklahoma, vol. 2, part B, p. 713-809. 
Profile A

Profile E

Lake Valley

Cave Valley

Spring Valley

Hamlin Valley

Limestone

Hills

Profile B

38° 38°10' 38°20' 38°30' 38°40' 38°50' 39°

-115° -114°50' -114°40' -114°30' -114°20' -114°10' -114°

10 km

Sidehill

Pass

Fortification 

Range

Nevada

Utah

Salt Lake City

Las Vegas

10

Figure 1A. Topographic map of study area showing location of profiles A,B, and E.
36°50' 37°

-115° -114°50'

5 km

Coyote Spring Valley

Sheep Range

Meadow Valley Mountains

Kane Springs Wash

Profile C

Nevada

Utah

Salt Lake City

Las Vegas

Figure 1B. Topographic map of study area showing location of profile C.

11

Profile D 

(aborted)
12

Table 1. Description of AMT profiles. 

[Azimuth refers to the magnetic orientation of the x-direction, which remained fixed throughout each profile] 

Profile Length Azimuth 

(x-direction) 

Station 

Spacing 

Number of 

Stations 

Comments 

A 12.6 km 80o 200m 64 Across southern Spring Valley from 

the Fortification Range (west) to the 

Limestone Hills (east). 

B 2.2 km 80o 200-400m 9 North of Fortification Range, west 

side of Spring Valley 

C 1.4 km 100o 100-200m 9 Eastern Coyote Spring Valley near 

Kane Springs Wash 

D N/A N/A N/A N/A Aborted due to power line 

interference 

E 3.0 km 100o 200-400m 14 Cave Valley west of Sidehill Pass 

Table 2. Sounding numbers, locations and elevations of stations along four AMT 

profiles. 

 [Distance indicates distance along profile in meters, where positive is east. Latitude and longitude are in NAD 27 

decimal degrees. Universal Transverse Mercator (zone 11N) units are in meters. Horizontal locations are accurate to 

approximately 3 m (10 ft.) Station elevation is given in meters and feet and are accurate to approximately 7 m (23 ft.).] 

Profile A (SVNA) 

Sounding Distance 

(m) 

Latitude Longitude Easting 

(m) 

Northing 

(m) 

Elevation 

(m) 

Elevation 

(ft) 

4 0 38.6459 -114.4465 722154 4280566 1898 6228 

5 200 38.6463 -114.4440 722368 4280617 1891 6204 

6 400 38.6465 -114.4420 722542 4280652 1888 6193 

7 600 38.6469 -114.4398 722737 4280694 1884 6180 

8 800 38.6474 -114.4375 722931 4280755 1880 6169 

10 1000 38.6477 -114.4353 723126 4280799 1868 6128 

12 1200 38.6481 -114.4330 723320 4280846 1878 6161 

15 1400 38.6484 -114.4307 723519 4280891 1858 6097 

17 1600 38.6488 -114.4285 723713 4280933 1847 6060 

54 1800 38.6492 -114.4263 723902 4280990 1853 6078 

18 2000 38.6496 -114.4240 724099 4281035 1848 6062 

56 2200 38.6499 -114.4217 724296 4281078 1848 6063 

19 2400 38.6503 -114.4195 724487 4281126 1839 6035 
13

57 2600 38.6507 -114.4173 724682 4281178 1843 6045 

20 2800 38.6511 -114.4150 724878 4281225 1836 6024 

58 3000 38.6515 -114.4128 725072 4281270 1836 6025 

21 3200 38.6519 -114.4105 725269 4281319 1832 6009 

59 3400 38.6523 -114.4083 725461 4281369 1831 6007 

23 3600 38.6526 -114.4060 725661 4281412 1825 5988 

60 3800 38.6530 -114.4037 725856 4281457 1826 5992 

24 4000 38.6533 -114.4015 726047 4281502 1818 5964 

61 4200 38.6537 -114.3992 726243 4281550 1820 5970 

25 4400 38.6541 -114.3970 726434 4281600 1811 5943 

62 4600 38.6545 -114.3948 726630 4281647 1812 5944 

26 4800 38.6548 -114.3925 726823 4281692 1799 5902 

63 5000 38.6552 -114.3903 727017 4281742 1810 5937 

28 5200 38.6556 -114.3880 727216 4281791 1806 5924 

64 5400 38.6560 -114.3858 727405 4281836 1812 5946 

30 5600 38.6562 -114.3835 727606 4281864 1805 5922 

65 5800 38.6567 -114.3813 727795 4281932 1802 5911 

32 6000 38.6571 -114.3790 727990 4281976 1823 5980 

67 6200 38.6574 -114.3768 728187 4282020 1803 5915 

34 6400 38.6579 -114.3745 728380 4282074 1803 5915 

68 6600 38.6582 -114.3722 728578 4282117 1816 5959 

35 6800 38.6586 -114.3700 728770 4282168 1815 5955 

69 7000 38.6590 -114.3678 728963 4282213 1812 5946 

95 7200 38.6593 -114.3655 729159 4282260 1828 5997 

70 7400 38.6597 -114.3633 729350 4282309 1819 5967 

39 7600 38.6601 -114.3610 729550 4282358 1826 5992 

71 7800 38.6605 -114.3588 729742 4282403 1830 6005 

40 8000 38.6608 -114.3565 729935 4282450 1832 6010 

72 8200 38.6612 -114.3543 730133 4282494 1832 6012 

41 8400 38.6616 -114.3520 730327 4282545 1834 6016 

74 8600 38.6620 -114.3498 730520 4282593 1837 6028 

43 8800 38.6623 -114.3475 730717 4282638 1843 6045 

75 9000 38.6627 -114.3453 730909 4282685 1848 6062 

45 9200 38.6631 -114.3430 731105 4282731 1853 6078 

77 9400 38.6635 -114.3408 731297 4282781 1855 6086 

46 9600 38.6638 -114.3385 731493 4282820 1860 6104 

78 9800 38.6642 -114.3363 731688 4282872 1866 6121 

47 10000 38.6646 -114.3336 731923 4282930 1872 6142 

80 10200 38.6649 -114.3318 732076 4282965 1875 6152 

49 10400 38.6653 -114.3295 732273 4283012 1878 6162 

82 10600 38.6657 -114.3273 732468 4283059 1884 6180 

51 10800 38.6660 -114.3250 732663 4283107 1888 6195 

83 11000 38.6664 -114.3228 732858 4283151 1895 6218 

52 11200 38.6668 -114.3205 733055 4283201 1896 6219 

84 11400 38.6671 -114.3182 733254 4283242 1904 6247 

98 11600 38.6671 -114.3158 733458 4283245 1913 6277 

87 11800 38.6671 -114.3135 733663 4283248 1915 6282 

94 12000 38.6686 -114.3121 733857 4283221 1959 6246
14

88 12200 38.6671 -114.3090 734054 4283260 1914 6279 

93 12400 38.6670 -114.3067 734255 4283259 1929 6329 

102 12600 38.6670 -114.3040 734489 4283264 1911 6270 

Profile B (SVNB) 

Sounding Distance 

(m) 

Latitude Longitude Easting 

(m) 

Northing 

(m) 

Elevation 

(m) 

Elevation 

(ft) 

107 -200 38.7644 -114.5394 713791 4293294 1805 5922 

103 0 38.7654 -114.5375 713952 4293411 1789 5871 

108 200 38.7664 -114.5356 714114 4293527 1790 5874 

104 400 38.7672 -114.5335 714293 4293623 1783 5850 

109 600 38.7677 -114.5314 714481 4293681 1770 5807 

105 800 38.7677 -114.5280 714698 4293696 1769 5803 

106 1200 38.7676 -114.5240 715118 4293691 1765 5792 

111 1600 38.7674 -114.5195 715514 4293675 1764 5786 

112 2000 38.7672 -114.5149 715911 4293665 1761 5777 

Profile C (SVNC) 

Sounding Distance 

(m) 

Latitude Longitude Easting 

(m) 

Northing 

(m) 

Elevation 

(m) 

Elevation 

(ft) 

16 -600 36.9962 -114.8911 687590 4096521 871 2856 

27 -400 36.9955 -114.8890 687778 4096450 876 2873 

19 -200 36.9947 -114.8869 687965 4096365 875 2870 

21 0 36.9944 -114.8847 688165 4096333 863 2831 

33 100 36.9937 -114.8842 688212 4096264 871 2857 

32 200 36.9933 -114.8830 688314 4096217 887 2911 

23 400 36.9920 -114.8815 688456 4096075 888 2915 

25 600 36.9918 -114.8791 688668 4096058 875 2870 

30 800 36.9912 -114.8770 688854 4095993 882 2895 

Profile E (SVNE) 

Sounding Distance 

(m) 

Latitude Longitude Easting 

(m) 

Northing 

(m) 

Elevation 

(m) 

Elevation 

(ft) 

16 -1800 38.3802 -114.8546 687319 4250168 1819 5972 

14 -1400 38.3787 -114.8503 687698 4250011 1821 5979 

13 -1000 38.3772 -114.8462 688063 4249858 1820 5976 

12 -800 38.3765 -114.8441 688243 4249782 1823 5986 

10 -600 38.3758 -114.8421 688426 4249711 1835 6024 

7 -400 38.3750 -114.8400 688612 4249628 1820 5976 

41 -200 38.3743 -114.8378 688799 4249554 1825 5991 

4 0 38.3734 -114.8358 688978 4249459 1820 5974 

39 200 38.3727 -114.8337 689163 4249385 1826 5996 

19 400 38.3721 -114.8316 689352 4249319 1825 5990 

23 600 38.3714 -114.8295 689539 4249249 1821 5978 

36 800 38.3708 -114.8273 689729 4249180 1822 5982 

26 1000 38.3701 -114.8253 689910 4249110 1828 6002 

27 1200 38.3694 -114.8231 690100 4249042 1834 6022 

 
15

Appendix 

A. Sounding curves 

The “Audiomagnetotelluric Data” section in this report contains an explanation for three separate 

plots for each station: 

1. Apparent Resistivity for x-directed profile line such that the nominal TM mode is ExHy 

 (red diamond) and TE is EyHx (blue square). 

2. Impedance Phase for x-directed profile line such that the nominal TM mode is ExHy (red 

 diamond) and TE is EyHx (blue square). 

3. Multiple E-Predicted Coherencies, defined as (ExHy * Conj(ExHy)) / (Hy * Conj(Hy) * 

 Ex * Conj(Ex)) (red diamond) and (EyHx * Conj(EyHx)) / (Hx * Conj(Hx) * Ey * 

 Conj(Ey)) (blue square) 

Sounding curves are named by profile name, distance along the profile (m) and sounding number, 

respectively. Note that for the distance along the profile, the positive direction trends eastward and 

the negative direction trends westward.