magneto telluric s explained

8/18/2019 Magneto Telluric s Explained

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Magnetotellurics explained

through applications

Robert Hearst

Manager, Quantec Interpretation Group


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Geophysical Exploration Services Since

1986!

Over 2000 Projects completed worldwide!

Global Experience

> 100 employees> 40 geophysicists and engineers

Winner Best New Way to Find Minerals – 2004

Over 175 Titan Surveys CompletedOver 50 Minesite Titan Surveys Completed


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The Magnetotelluric Method (MT)


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What is magnetotellurics (MT) ?

Magnetotellurics (MT for short) is a remote sensingtechnique that can image the earth's electricalresistivity structure from depths of a few 100

metres to several 100 kilometres

What is magnetotellurics (MT) ?

Magnetotellurics (MT for short) is a remote sensingtechnique that can image the earth's electricalresistivity structure from depths of a few 100

metres to several 100 kilometres


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What are we measuring ?

• High frequency signals which originate from

lightning activity• Intermediate frequency signals come from

ionospheric resonances

• Low frequency signals are generated bysunspots

Natural electromagnetic waves that are

generated in the earths atmosphere by a range

of physical mechanisms. As these travel into the

Earth's interior they decay at a rate dependent

upon their wavelengths.


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From Magnetotelluric Research Overview / 6 April 2001 / [email protected]


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There is an electric field (E) and a magneticfield (M or H)

Requires coils that are orthogonal and matchedin frequency to the 3 sources of MT



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Spartan MT field equipment


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Line Length - 2400 m

24 Exsensors

12 Ey

sensors

2 B /Bx y sensors

LAN Link to central control

100m

potential electrode

Magnetometer site

2400m – 24 sites

current electrode

2 channel box

1 channel box

BxBy

2 ChannelBox

Battery

TypicalStationSet-up

Titan 24 DistributedSystem (MT only mode)

BxBy

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Spartan MT SystemSpartan MT System

Close‐up

of

6 channel

Spartan

Logger

Spartan

in

Operation

as

Tensor

MT

Unit

Spartan as Tensor MT System Spartan as Mini Titan MT System


13/34400 Hz to 0.01 Hz 20000 Hz to 0.1 Hz

‐

1 ohm‐m

‐

0.01 ohm‐m

‐

100 ohm‐m

‐

0 degrees

‐

45 degrees

‐

90 degrees

P H A S E D I F F E R E N C E

A

P P A R E N T R E S I S T I V I T Y

P H A S E D I F

F E R E N C E

A

P P A R E N T R E S I S

T I V I T Y

10kHz 100Hz 1Hz 0.01Hz 10kHz 100Hz 1Hz 0.01Hz

10kHz 100Hz 1Hz 0.01Hz 10kHz 100Hz 1Hz 0.01HzFREQUENCY FREQUENCY

FREQUENCY FREQUENCY

Spartan MT Sounding vs. Titan MT Sounding

Notice Upper Limit of

Frequency Bandwidth

of Spartan vs. Titan MT

Notice Lower Limit of

Frequency Bandwidth

of

Spartan

vs.

Titan

MT

i.e., Better Quality Data


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3 geophysicalparameters

Typical deliverablesTitan 24 DCIP & MTone survey line

Typical deliverablesTitan 24 DCIP & MTone survey line

MT Resistivity Model 0 1000m

DC Resistivity Model

Chargeability Model

2 electrical methods


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• 24 bit A/D distributed acquisition

• Linear sampled time series data• Highly linear, calibrated, simultaneity

• Broadband Remote Reference

(10kHz – 0.1Hz)

Titan24 system characteristics


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Raw MT Data - Time Series @48kHz

MT signal+ 60Hz noise


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MT Time Series - Unfiltered


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Filtered MT time Series @ 48kHz

MT signals


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Processing and Interpretation Flow

Time series

Resistivity

2-D Model

5 4 3 2 1 0 -1 -2 -3

-2

-1

0

1

2

3

4

5

Appa rent Resist ivit y line2_3450

LOG Frequency (Hz)RhoXY RhoYX5 4 3 2 1 0 -1 -2 -3

-2

-1

0

1

2

3

4

5

Appa rent Resis tivit y line2_3450

LOG Frequency (Hz)RhoXY RhoYX

4000

3000

2000

1000

0

2-D Model l2tm1

W E

N 70 E

|750 |

1050

|1350 |

1650

|1950 |

2250

|2550 |

2850

|3150 |

3450

|3750 |

4050

|4350 |

4650

|4950 |

5250

FEET

0 500 1000 1500 2000 2500 3000

Ohm-M

1

1.6

2.5

4

6.3

1016

25

40

63

100

160

250

400

630

1000

4000

3000

2000

1000

0

2-D Model l2tm1

W E

N 70 E

|750 |

1050

|1350 |

1650

|1950 |

2250

|2550 |

2850

|3150 |

3450

|3750 |

4050

|4350 |

4650

|4950 |

5250

FEET

0 500 1000 1500 2000 2500 3000

Ohm-M

1

1.6

2.5

4

6.3

10

16

25

40

63

100

160

250

400

630

1000


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Titan MT Curves - December, 2001

Raw ApparentResistivitySounding

Raw Phase

Sounding

4 3 2 1 0 -1 -2

0

1

2

3

4

5

Apparent Resis tiv ity ex9750

L O G R H O ( O H M

- M )


4 3 2 1 0 -1 -2

-180

-135

-90

-45

0

45

90

135

180

Phase ex9750

P H A S E A N G L E ( D E G )

LOG Frequency (Hz)PhsXY PhsYX


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Raw ApparentResistivityPseudosection

Raw Phase

Pseudosection

-2

-1

0

1

2

3

4

Apparent Resistivity Freq Section - RhoXY L108_noremote

L O

G F r e q u e n c y ( H z )

W E

E-W

|

9750 |9850

|

9950 |10050

|

10150 |10250

|

10350 |10450

|

10550 |10650

|

10750 |10850

|

10950 |11050

|

11150 |11250

|

11350 |11450

|

11550 |11650

|

11750 |11850

|

11950 |12050

METERS0 500 1000 1500

Ohm-M

10

18

32

56

100

180

320

560

1000

1799.

3200.

5600

10000

17999.

31999.

-2

-1

0

1

2

3

4

Phase Freq Section - PhsXY L108_noremote

L O G F r e q u e n c y ( H z )

W E

E-W

|9750 |

9850|

9950 |10050

|10150 |

10250|

10350 |10450

|10550 |

10650|

10750 |10850

|10950 |

11050|

11150 |11250

|11350 |

11450|

11550 |11650

|11750 |

11850|

11950 |12050

METERS

0 500 1000 1500

Degrees

0

6

12

18

24

30

36

42

48

54

60

66

72

78

84

-2

-1

0

1

2

3

4

Apparent Resistivity Freq Section - RhoYX L108_noremote

L O G F r e q

u e n c y ( H z )

W E

E-W

|

9750 |9850

|

9950 |10050

|

10150 |10250

|

10350 |10450

|

10550 |10650

|

10750 |10850

|

10950 |11050

|

11150 |11250

|

11350 |11450

|

11550 |11650

|

11750 |11850

|

11950 |12050

METERS0 500 1000 1500

Ohm-M

10

18

32

56

100

180

320

5601000

1799.

3200.

5600

10000

17999.

31999.

-2

-1

0

1

2

3

4

Phase Freq Section - PhsYX L108_noremote

L O G F r e q u e

n c y ( H z )

W E

E-W

|

9750 |9850

|

9950 |10050

|

10150 |10250

|

10350 |10450

|

10550 |10650

|

10750 |10850

|

10950 |11050

|

11150 |11250

|

11350 |11450

|

11550 |11650

|

11750 |11850

|

11950 |12050

METERS

0 500 1000 1500

Degrees

-180

-174

-168

-162

-156

-150-144

-138

-132

-126

-120

-114

-108

-102

-96



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4 3 2 1 0 -1 -2

0

1

2

3

4

5

Apparent Resis tiv ity l108_9750

L O G R H O ( O H M

- M )


4 3 2 1 0 -1 -2

-180

-135

-90

-45

0

45

90

135

180

Phase l108_9750

P H A S E A N G L E ( D E G )

LOG Frequency (Hz)PhsXY PhsYX

Dead Band

Dead Band

Apparent

ResistivitySounding

PhaseSounding

Results demonstratehigh level of data qualityachieved in spite ofproximity of mine andwinter season



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Final ApparentResistivityPseudosection

Final Phase

Pseudosection

-2

-1

0

1

2

3

4

Apparent Resistivity Freq Section - RhoXY L108

L O G

F r e q u e n c y ( H z )

W E

E-W

|

9750 |9850

|

9950 |10050

|

10150 |10250

|

10350 |10450

|

10550 |10650

|

10750 |10850

|

10950 |11050

|

11150 |11250

|

11350 |11450

|

11550 |11650

|

11750 |11850

|

11950 |12050

|

12150

METERS0 500 1000 1500

Ohm-M

10

18

32

56

100

180

320

560

1000

1799.

3200.

5600

1000017999.

31999.

-2

-1

0

1

2

3

4

Phase Freq Section - PhsXY L108

L O G F

r e q u e n c y ( H z )

W E

E-W

|9750 |

9850|

9950 |10050

|10150 |

10250|

10350 |10450

|10550 |

10650|

10750 |10850

|10950 |

11050|

11150 |11250

|11350 |

11450|

11550 |11650

|11750 |

11850|

11950 |12050

|12150

METERS

0 500 1000 1500

Degrees

0

6

12

18

24

30

36

42

48

54

6066

72

78

84

-2

-1

0

1

2

3

4

Apparent Resistivity Freq Section - RhoYX L108

L O G F r e q u

e n c y ( H z )

W E

E-W

|

9750 |9850

|

9950 |10050

|

10150 |10250

|

10350 |10450

|

10550 |10650

|

10750 |10850

|

10950 |11050

|

11150 |11250

|

11350 |11450

|

11550 |11650

|

11750 |11850

|

11950 |12050

|

12150

METERS0 500 1000 1500

Ohm-M

10

18

32

56

100

180

320

560

1000

1799.

3200.

5600

10000

17999.

31999.

-2

-1

0

1

2

3

4

Phase Freq Section - PhsYX L108

L O G F r e q u e n

c y ( H z )

W E

E-W

|9750 |

9850|

9950 |10050

|10150 |

10250|

10350 |10450

|10550 |

10650|

10750 |10850

|10950 |

11050|

11150 |11250

|11350 |

11450|

11550 |11650

|11750 |

11850|

11950 |12050

|12150

METERS

0 500 1000 1500

Degrees

-180

-174

-168

-162

-156-150

-144

-138

-132

-126

-120

-114

-108

-102

-96



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QUANTEC

MIRA

DATA COLLECTION

MT 2-D Smooth Model

Advanced E VA

Processing

GOCAD

EVA Smooth

Model Inversion

Wannamaker 2-D MT

UBC or PW 2D IP

UBC 2-D IP Inversion

Time Series Processing

In-FieldProcessing

Acquisition and Processing Flow

Post ProcessingToronto Office


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MT surveysare employed for;

• Large area target potential evaluation• Targeting of Titan surveys

• Basin mapping (depth of cover)• Shallow crustal scale evaluation for

hydrocarbon and geothermal exploration

• Deep crustal regional scale structuralmapping• Resistivity logs for Lithological

determinations


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32:00:00

32:01:53

32:03:45

1 1 0 : 0 3 : 4 5 W

1 1 0 : 0 1 : 5 3 W

1 1 0 : 0 0 : 0 0 W

drag_002drag_004

drag_008

drag_009

drag_010

drag_016

drag_017

drag_018

drag_019dr ag_020

drag_021

drag_022

drag_023

drag_024drag_025

drag_026drag_027

drag_028

drag_029

drag_030

drag_031

drag_032

drag_033

drag_034drag_035

drag_037drag_038

drag_039

drag_043

drag_044

drag_057

drag_097

drag_098drag_099

METERS

0 1000 2000 3000 4000

drag-all

75

105

135

165

195

225

255

285

315

345

375

405

435

465

495

qcl409Date: 07/27/05

Projection: UTM 12

C Merid: -111:00:00.00

Northing: 0.0

Easting: 500000

Scale: N/A

RhoYX AT 10 Hz

SET: drag-all

Porphyry Exploration


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Deep crustal studies

• Deep transect over 300km traverse, basin and rangesetting, northwest Nevada

• Soundings distributed at 3-4km intervals

• Data inverse modelled to 25km depth

• Basin and range geologic setting


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Station location map for the NW-NV Dixie Valley transect

240km


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50000

40000

30000

20000

10000

0

-10000

-20000

-30000

2-D Model l1rlm

D e p t h ( M E T E

R S )

W E

S 71 E

|

001|002

|

003 |004

|

005 |006

|

007 |008

|

009 |010

|

011|012

|

013|014

|

015 |016

|

017|018

|

019|020

|

021|022

|

023 |024

|

025 |026

|

027 |028

|

029|030

|

031|032

|

033|034

|

035|036

|

037|038

|

039|040

|

041|042

|

043|044

|

045|046

|

048|049

|

050

METERS0 20000 40000 60000 80000 100000

Ohm-M

1

1.84

3.41

6.31

11.6

21.539.8

73.5

135.

251.

464.

857.

1584.

2928.

5411.

10000

20000

10000

0

2-D Model l1rlm

D e p t h ( M E T E R S )

W E

S 71 E

|034

|

035 |036

|

037 |038

|

039 |040

|

041 |042

|

043 |044

|

045 |046

|

048 |049

|

050

METERS0 5000 10000 15000 20000 25000 30000

Ohm-M

1

1.84

3.41

6.31

11.6

21.5

39.8

73.5

135.

251.

464.

857.

1584.2928.

5411.

10000


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l

,

,

ValmyValmy-- Siliceous UnitsSiliceous Units

ValmyValmy -- Carbonaceous,Carbonaceous,

pyritic Shales pyritic ShalesTuffaceous MudstoneTuffaceous Mudstone

Pillow BasaltPillow Basalt

MT 2D INVERSIONMT 2D INVERSION

Bottom of MT Section 2000m depthBottom of MT Section 2000m depth

Section Courtesy Placer Dome, Peter Kowalczyk presentation, PDAC 2001

Black Massive LimestoneBlack Massive Limestone

Interbedded ChertInterbedded Chert,

Chert Beds In LimestoneChert Beds In Limestone


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Questions

magneto telluric s explained

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