Week 2 Flashcards
It is a point at which three lithospheric plates meet.
Triple Junction
Who invented the system of longitude and latitude and made a map of the spherical world?
Eratosthenes of Cyrene
This theorem is described to be the most general displacement of a rigid body with a fixed point is equivalent to a rotation about an axis through that fixed point.
Euler’s Fixed Point Theorem
What process allows rocks to record the Earth’s past magnetic field?
A. Sedimentation
B. Magnetization
C. Paleomagnetism
D. Crystallization
C. Paleomagnetism
What is the main function of a fluxgate magnetometer in magnetic surveying?
A. Detecting seismic waves
B. Measuring magnetic anomalies
C. Inducing magnetization
D. Elevation correction
B. Measuring magnetic anomalies
What law states, “for relatively small deformations of an object, the displacement or size of the deformation is directly proportional to the deforming force or load”?
Hooke’s Law
What is the primary characteristic of a dipole field in Earth’s magnetic field?
A. Complex structure
B. Multi-polarity
C. Simple, largely dipolar
D. Chaotic orientation
C. Simple, largely dipolar
It is aligned at 11.5 ° to the earth’s geographic north-south axis (spin axis).
A. Geomagnetic North
B. Best-fitting dipole
C. Dipole field
D. Geomagnetic South
B. Best-fitting dipole
How often is the IGRF updated?
5 years
The ratios between the sine of each angle and their corresponding velocity are equal to a constant called?
Ray parameter
A mountain in isostatic equilibrium must be compensated by a ______ between the surface and compensation depth.
mass deficiency
Which among the following is true about ground magnetic surveys?
A. Covers a relatively small area with 10 to 100 kilometer station spacing
B. Avoid metallic objects and power lines
C. Is cost-effective compared to other magnetic survey methods
D. All of the above
B. Avoid metallic objects and power lines
These are zones of charged particles trapped by the Earth’s magnetic field, providing a protective shield against harmful radiation.
Van Allen Radiation Belts
This triple junction is always unstable.
FFF
If four (4) or more plates meet at one point, the configuration is always ______ and the system will evolve into two (2) or more triple junctions.
unstable
Define geoid.
Reference surface equivalent to sea level.
What are the Geomagnetic North and Geomagnetic South?
Geomagnetic North – 79◦N, 71◦W
Geomagnetic South – 79◦S, 109◦E
What is the IGRF?
International Geomagnetic Reference Field (IGRF) – The internationally agreed values of the geomagnetic field.
What are the plates involved in the Galapagos triple junction?
Cocos Plate, the Nazca Plate, and the Pacific Plate
Define the term magnetic (dip) poles.
The two points on the Earth’s surface at which the magnetic field is vertical and has no horizontal component.
Any changes in the solar wind, and hence in the magnetic field, can allow these charged particles
to enter the upper atmosphere, causing:
Northern Lights - Aurora Borealis
Southern Lights - Aurora Australis
Describe the term Eötvös correction.
Correction applied to gravity data taken on moving vehicles.
In aeromagnetic surveys, aircrafts can use a fixed “stinger” (aircrafts tail) in order to?
Compensate for the aircraft’s magnetic field
What is space weather?
Space weather involves active processes and interactions between the magnetosphere and solar wind.
Differentiate magnetic declination and magnetic inclination.
Magnetic inclination - angle between the earth’s surface and the magnetic field lines
Magnetic declination - angle between the magnetic north of the compass and the true north
What is the VMM hypothesis?
VMM Hypothesis states that magnetic stripes are caused by seafloor spreading. It was proposed by F.J. Vine, D.H. Matthews, and L.W. Morley.
What do the black and white magnetic stripes infer?
Black Stripe – strong record, normal polarity
White Stripe – low record, reversal occurred
What does the Königsberger Ratio mean?
It is the proportion of remanent magnetization relative to induced magnetization in natural rocks.
What is a magnetosphere?
It is the magnetic field that envelops the Earth.
What does Absolute Motion mean?
The motions of the plates relative to some imaginary fixed point; to calculate hotspot since hotspot is fixed.
What are the coordinates of the present North and South Magnetic Poles?
North Magnetic Pole (present) – 76◦N, 101◦W
South Magnetic Pole (present) – 66◦S, 141◦E
Differentiate magnetosheath and magnetopause.
Magnetosheath – turbulent zone w/n the bow shock
Magnetopause – inner boundary of magnetosheath
What is Airy’s Hypothesis?
When isostatic equilibrium is achieved by mountains having deep roots and ocean basins have anti‐roots.
Explain Terrain Correction.
Correction due to topography – only applied to rugged terrain
Define isostasy.
The state of balance/equilibrium between the lithosphere and asthenosphere.
Assume pc= 2800 kg/m^3, pm= 3100 kg/m^3, D= 30 km. What crustal density p1 is needed to explain the 5km high Tibetan Plateau?
Discuss the stability of the TTT triple junction. Provide illustration and example.
Simply explain the difference between dextral and sinistral faults. Give an example that occurred in the country.
Dextral - right-lateral (Ex. Marikina Valley Fault System)
Sinistral - left-lateral (Ex. Philippine Fault)
What does it mean when a triple junction is always stable? Give examples.
When the relative motions of the 3 plates and the azimuth of their boundaries are such that the configuration of the junction does not change with time. Examples: Galapagos, Azores, Afar
Expound the configuration and findings in the Mendocino triple junction. Provide the plates involved.
Configuration - Unstable (an FFT)
Findings - deformation, high magnitudes
Plates - Juan de Fuca, Pacific, North America
Expound the term hotspot volcanism and give an example.
It is a place where melt rises from deep in the mantle and formed volcanic islands as the plate moved over. Example: Hawaiian-Emperor seamount chain
What does Magnetic Gradiometers measure? Provide examples.
- measures horizontal and vertical magnetic gradients
1. Ground surveys
2. Aeromagnetic surveys
3. Marine surveys
Discuss the use of magnetic surveying and provide one (1) instrumentation and data collection technique for magnetic exploration.
- investigates the anomalies of the earth’s magnetic field caused by the magnetic properties of rocks in the subsurface
Instruments/Techniques:
- Fluxgate Magnetometer
- Proton Magnetometer (Nuclear Precession)
- Optically Pumped Magnetometer (Alkali Vapour Magnetometer)
- Magnetic Gradiometers
Illustrate and discuss Pratt’s Hypothesis.
Pratt’s hypothesis states that the density of the lithosphere is not uniform. Isostatic compensation is achieved by a lateral variation of density beneath surface features.
Calculate the mass of Earth.
Show how direct wave, head wave, and reflected wave behave in a ray path illustration.
Illustrate a model about Airy’s Hypothesis on isostasy.
Find the Free-Air Correction using the following values:
go = 9.81 m/s2
R = 6371 km
h = 1 m
Discuss the principles behind the Optically Pumped Magnetometer (Alkali Vapour Magnetometer) and its application in magnetic exploration.
Optically pumped magnetometer uses evaporated alkali in a glass cell energized by light, measuring changes in the frequency splitting.
