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Correlation Day 3 > Geophysics > Flashcards

Geophysics Flashcards

1
Q

Asthenosphere comes from the Greek word ________ meaning weak or sick; mechanically weak.

A

“asthenia”

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2
Q

This is where differential movements between plates occur.

A

Seismic Belts

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3
Q

Which among the following geophysical methods can directly locate chromite deposits.

A

a. Magnetic

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4
Q

It refers to the degree to which a rock can be
magnetized by a external magnetic field.

A

Magnetic Susceptibility

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5
Q

The ratio of the remanent magnetization to the induced magnetization.

A

Königsberger ratio

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6
Q

The measurement of the inclination of cooled lava or sediment can provide the magnetic latitude during the time of its formation.

A

Paleolatitude

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7
Q

It refers to the plot of the paleomagnetic pole positions of rocks of different ages in the same continent. It also shows how the magnetic pole moved
relative to that continent.

A

Polar Wander Path

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8
Q

Thisrefers to a rock that is rich in magnetite that was known by the Greeks by 800 BC due to its magnetic behaviour.

A

Lodestone

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9
Q

By the Tang dynasty (500 AD), the Chinese discovered that magnetic north was not the same as astronomically defined north. This angle of deviation is called __________.

A

Declination

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10
Q

In 1544, Hartmann discovered that a magnetised needle would point north, but would be tilted from the horizontal. The angle of tilt is called the __________.

A

Inclination

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11
Q

It is used as a timescale for magnetic reversals observed.

A

Reversal Timescale

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12
Q

Reversal Timescale is started from middle Jurassic to present. Why was it used up to middle Jurassic only?

A

Because old oceanic sediment only dates back to Jurassic.

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13
Q

These magnetometers use changes in the frequency splitting of optical spectral lines of elements such as rubidium, caesium or potassium to measure the magnetic field. This is governed by the Zeeman effect.

A

Alkali Vapour Magnetometer

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14
Q

High resolution aeromagnetic (HRAM) surveys are now the standard field technique and they use a _________ and _________ to give detailed information about subtle, sub-nanotesla magnetic field anomalies.

A

Dense Line Spacing, Low Flight Elevation

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15
Q

This law describes the linear relationship between density and seismic velocity.

A

Birch’s Law

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16
Q

Enumerate and differentiate the different types of plate boundaries.

A

1) Divergent – accreting, constructive; mid‐ocean‐ridge system 2) Convergent – consuming, destructive; oceanic trench, island arc systems 3) Conservative – neither created nor destroyed; transform faults

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17
Q

Prerequisite for gravity anomaly is _____________.

A

Lateral Density Contrast

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18
Q

An alpha particle emitted from the nucleus during radioactive decay of a parent isotopeis composed of

A

2 protons and 2 neutrons

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19
Q

Sedimentary rocks is usually _______.

A

c. Non-Magnetic

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20
Q

Differentiate the two types of free oscillations.

A
  1. Spheroidal (S) – radial and tangential components 2. Toroidal or torsional (T) – perpendicular to the radius vector; confined to surfaces of concentric spheres within Earth; crust and mantle only (outer core cannot sustain shear); do not change shape or volume
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21
Q

Explain the mechanism of induced magnetization/magnetic polarization.

A

It refers to magnetization that is acquired when a material is placed in an external magnetic field; lost when the field is removed.

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22
Q

Provide 6 common causes of magnetic anomalies in sedimentary-covered areas.

A
  1. Dykes 2. Faulted/Folded Sills 3. Lava Flows 4. Basic Intrusions 5. Metamorphic Basement Rocks 6. Magnetite Ore Bodies
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23
Q

Give two spatial corrections in a magnetic survey.

A
  1. Elevation and Terrain Corrections 2. Geomagnetic Corrections
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24
Q

Which of the following is only possible if using ground magnetic survey.

A

C. Diurnal Corrections

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25
Q

Why can’t S-waves propagate through fluids?

A

Because the shear modulus for liquids is zero. Therefore, in S-waves, there is no shear strain.

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26
Q

What is the modern monitoring standard used to detect toxic metal pollution in sediments and in the environment as well?

A

Geochemical Anomaly Cut-off

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27
Q

Strong magnetism is exhibited by magnetite to a lesser extent by

A

a. Pyrrhotite

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28
Q

Minerals with smaller atoms and ions tend to be:

A

Malleable

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29
Q

Telluric currents are Earth’s natural currents which are utilized in the application of:

A

Radiometric survey

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30
Q

In a gravity survey, correction due to topography is known as:

A

Bouguer or Terrain Corrections

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31
Q

The acceleration of gravity in the equator is __________ compared to the acceleration of gravity in the poles.

A

Less

32
Q

The most effective geophysical technique to employ in searching for ground water is ______.

A

Resistivity

33
Q

Magnetic Force is _________ proportional to the square of the polar distance.

A

Inversely

34
Q

The most accurate space-based geodetic technique at large observation station distances.

A

GPS

35
Q

Explain the mechanism of Rayleigh scattering.

A

Rayleigh scattering refers to the scattering of light by particles in its path of size up to one-tenth the wavelength of the light and occurs without any loss of energy or change of wavelength. Being wavelength dependent, this phenomenon gives us nature’s blue sky because of the increased scattering of blue light.

36
Q

Explain TRM or thermoremanent magnetization.

A

It refers to the magnetization acquired when a rock cools through the Curie temperature of its magnetic minerals.

37
Q

The most appropriate technique in locating porphyry copper deposit is ____________.

A

Electromagnetic

38
Q

Differentiate magnetic equator from geographic equator.

A

At the magnetic equator, the dip or inclination is zero. Unlike Earth’s geographic equator, the magnetic equator is not fixed, but slowly changes.

39
Q

Differentiate s-waves from p-waves.

A

P-wave involves compression and rarefaction as it passes through a medium. While s-wave involve shearing of the medium as it passes through.

40
Q

Differentiate diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic and ferrimagnetic.

A

Diamagnetic - full orbitals, no unpaired electrons, weak and negative. Paramagnetic - electron shells are incomplete, electrons unpaired, weak but positive. Ferromagnetic - parallel dipoles, Fe, Co, Ni. Antiferromagnetic - antiparallel but equal dipoles, Hematite. Ferrimagnetic - antiparallel and unequal dipoles, Magnetite.

41
Q

How do radioisotope dating works?

A

Measuring the abundance of (ordinarily rare) decay products of unstable isotopes.

42
Q

Explain the mechanism of “Photodissociation”.

A

Photodissociation is a process in which a photon from the Sun fragments an atmospheric atom or molecule into new atomic or molecular components.

43
Q

Enumerate and define the different corrections for magnetic data.

A

a. Normal Magnetic Corrections (corresponds to latitude correction of gravity values) - Designed to remove the spatial variations of magnetic intensity due to the earth’s inner field b. Diurnal Variations (due to the combined effects of the sun and the moon) - attributed to a regular cyclic change in the magnetic elements of a period of about 24 hours, upon which irregular disturbances are superimposed c. Secular Variations - Refers to the variation of intensity and direction of magnetization with time.
d. Artificical Variation - mainly due to man-made activities (coherent and cultural noises) e. Magnetic Storms - Depends upon the location with respect to auroral zones. f. Geomagnetic Corrections - takes into account variations of main field with latitude, longitude and time; computed using the International Geomagnetic Reference Field (1995 version).

44
Q

Enumerate the different geophysical noise and provide each remedy.

A

a. Disturbance Field Noise (i. natural - lightning, magnetic storms, earthquakes, typhoons; ii. artificial - powerlines, buried metal pipes, metallic objects on the ground) Remedy: (natural) discontinue measurements; (artificial) stay away from sources of noise. b. Geologic Noise – variable thickness of overburden, presence of non-economical minerals in the overburden or overlying layers. Remedy: mathematical corrections. c. Topographic Noise – ground surface varies in elevation. Remedy: mathematical corrections.

45
Q

Provide the different types of surveying on geophysical data and their total covered area in terms of kilometers.

A
  1. Reconnaissance (over 10 to >100 km) 2. Focused mapping (1 to 10 km) 3. High resolution mapping (<1 km) (e.g. microgravity surveys at 50-60 m intervals)
46
Q

Explain the magnetic susceptibility variations based on rock types.

A

1.In igneous rocks, magnetic property decreases with increasing acidity. 2.Metamorphic rocks have variable magnetic properties. 3.Sedimentary rocks are effectively non-magnetic unless they contain a significant amount of magnetite in their heavy mineral fraction.

47
Q

Explain the density variations based on rock types.

A

1.Sedimentary rocks exhibit the greatest range of density variation (mineral composition, cementation, porosity, pore fluid type). 2. Density of igneous rocks is controlled primarily by the silica content.

48
Q

What operative physical property does an induced polarization survey measure?

A

Electrical Capacitance

49
Q

It is a mathematical operation defining the change of shape of a waveform resulting from its passage through a filter.

A

Convolution

50
Q

If you want to show on a map even the smaller details or features of a certain area, which of the following scales will you use?

A

1:5,000

51
Q

The distance between two points on a 1:10,000 map is 5 centimeters. What is the real distance on the ground?

A

500 meters. 1/x = Map Distance/Real World Distance 1/10,000 = 5 cm/RWD RWD = 50,000cm or 500m

52
Q

The economical mineral in chromium ore is chromite (FeO•Cr2O3). Commercial chromium ores usually contain how much percent of Cr2O3?

A

40%

53
Q

What is the last phase in a petroleum exploration program?

A

Resource Estimation

54
Q

A correlation coefficient of ± .81 to ± 0.99 indicates _________ linear relationship.

A

Very Strong

55
Q

In variograms, this represents the maximum distance which sample pairs can be said to have some relationship to their separation distance.

A

Range

56
Q

The ________ the wavelength, the lower the frequency. The ______ the wavelength, the higher the frequency.

A

longer, shorter

57
Q

Define histogram.

A

This is a visual representation of the data distribution represented through vertical rectangles or bars where mode and possible outliers can be easily determined.

58
Q

Compare and contrast a vector data from a raster data.

A

Vector data represents geographic data symbolized as points, lines, or polygons. Raster data represents geographic data as a matrix of cells that each contains an attribute value. While the area of different polygon shapes in a data set can differ, each cell in a raster data set is the same cell

59
Q

Define isogal.

A

These are isolines in maps that indicate equal gravitational acceleration.

60
Q

Define exsolution.

A

Process in which minerals that form natural solid solutions in each other, and at determined lower temperatures unmix to yield distinguishable mineral intergrowths.

61
Q

Describe what a histogram is.

A

It is a statistical term that refers to a graph of frequency vs. value.

62
Q

Differentiate XRD from XRF.

A

XRD can determine the presence and amounts of minerals species in sample, as well as identify phases. XRF will give details as to the chemical composition of a sample but will not indicate what phases are present in the sample.

63
Q

What do you mean by TIN (Triangular Irregular Network) Models and what was it made for?

A

A vector-based data structure made for storing terrain information in digital terrain modelling in which each sample point has xy coordinate and a height, or z value. All the points are connected by edges to form a network of non-overlapping triangles that collectively represent the terrain surface.

64
Q

Differentiate electromagnetic and magnetic geophysical methods.

A

Electromagnetic (EM) survey, both airborne and ground, is one of the most commonly used methods in mineral exploration. The technique is proficient in direct detection of conductive sulfide deposits, in which large conductivity contrasts exist between the orebodies and country/host rocks or thin overburden cover. The magnetic method can be used for large scale geology mapping (often from the air using airplane or helicopter mounted sensors) or for detecting buried metallic objects such as underground storage tanks, pipes, utilities, or landfills. Magnetic methods can also detect some geologic features, such as lava tubes.

65
Q

Enumerate the two electrical geophysical surveying methods and explain what parameters they measure and their operative physical property.

A

a. Resistivity - measure the Earth’s resistance. Operative physical property = Electrical Conductivity. b. Induced Polarization - measure polarization voltage or frequency-dependent ground resistance. Operative physical property = Electrical Capacitance.

66
Q

Describe anomaly.

A

It is a deviation from an expected geophysical background measurement.

67
Q

What is Vertical Electrical Sounding (VES)?

A
  • Used mainly for the study of horizontal to near-horizontal interfaces. - Current and potential electrodes maintained at same relative spacing while whole spread is progressively expanded at a fixed point. - Readings taken as current penetration becomes deeper. - Use Schlumberger electrode configuration (Used in geotechnical surveys to determine overburden thickness and hydrogeology to define porous horizontal zones)
68
Q

Enumerate the limitations of resistivity method.

A
  • Interpretations are ambiguous
  • Interpretations are limited to simple structural configuration
  • Topography and near-surface effects can mask deeper signal
  • Depth of penetration (practical maximum or about 1 km) is limited by the maximum power transmitted into the ground and the practical difficulties of laying out long cables
69
Q

Why Geophysics Instead of Drilling?

A

— Even though prone to major interpretation ambiguities. It’s relatively rapid and cost-effective in getting subsurface geology information. Capable of detecting and delineating local features of potential interest. — Doesn’t do away with drilling but optimizes exploration programs by maximizing ground coverage rate and minimizing expensive drilling

70
Q

Explain the mechanism of a ground-penetrating radar and how it works as a geophysical instrument.

A

GPR works by sending a tiny pulse of energy into a material and recording the strength and the time required for the return of any reflected signal. A series of pulses over a single area make up what is called a scan. It can be used to map subsurface features such as depth to bedrock, depth to the water table, depth and thickness of soil and sediment strata (including under freshwater bodies), buried stream channels, and the location of cavities and fractures in bedrock.

71
Q

Explain how Eötvös correction (EC) is applied to gravity reduction anomalies.

A

It is a correction on a gravity survey that is applied to gravity data taken on moving vehicles.

72
Q

What do you mean by Aeromagnetic and marine surveys and how does it work?

A
  • Sensor towed in a housing known as a “bird” (for aeromagnets) and “fish” (for marine) to remove it from the magnetic effects of the vehicle. Aircraft can also use a fixed “stinger” (aircrafts tail) where inboard coils compensate for the aircraft’s magnetic field. - Aeromagnetic surveys are rapid and cost effective (40% less than ground surveys). - Majority of surveys are airborne.
73
Q

Explain the mechanism of an electrical resistivity instrument and how it works in conducting geological studies.

A
  • Artificially-generated currents (DC and low frequency AC) are introduced into the ground (via electrodes) and the resulting potential differences are measured. - Deviations from potential difference patterns expected from homogenous ground provide information on the form and electrical properties of subsurface inhomogeneities.
74
Q

What do you mean by SHRIMP and how does it work?

A

Scientists use the SHRIMP or sensitive high-resolution ion microprobe to measure the ration of lead to uranium (Pb/U) in order to calculate the age of the mineral grain. It enables the accurate determination of the uranium-lead age of the mineral zircon, and this has revolutionized the understanding of the isotopic age of formation of zircon-bearing igneous granitic rocks.

75
Q

Explain how an electrical profiling works in geophysical studies.

A
  • Used to determine lateral variations of resistivity.
  • Current and potential electrodes maintained at fixed spacing and progressively moved along a profile.
  • Use Wenner electrode configuration.
  • Used in mineral exploration to locate faults or shear zones and to detect localized bodies of anomalous conductivity.
  • Used also in geotechnical surveys to determine bedrock depth variations and presence of deep discontinuities.

Correlation Day 3 (3 decks)

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