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How do we use geophysics and what to we find with it?
We use the properties of rocks to find density and velocity.
What are the five major areas of geophysics?
- .1. Rock properties
- .2. Seismology
- .3. Gravity
- .4. Magnetism
- .5. Electromagnetic Methods
What did people use to find oil first?
What is seismology?
Measures the elastic properties of the rock.
What is stress?
Force applied to an object
What does stress result in?
What is strain?
deformation resulting from stress?
What are the 3 different types of strain and define each?
- Elastic strain- temporary deformation, when strain is removed object goes back into orginal state.
- Plastic strain-Strain is applied and deformes the object without breaking it.
- Brittle strain- Strain is applied then object breaks.
Where does elastic strain happen?
At the microscopic level.
What is Bulk Modulus?
The measure of change in volume with the change in pressure.
What is the symbol for bulk modulus?
What is Shear modulus?
It is a measure of distortion.
What is youngs modulus?
The change in the length of a cylinder with addition of pressure.
What is poisson's ratio?
The measure of the change in width of a cylinder after the addition of pressure.
What are the 4 elastic constants?
- Poission's ratio
- Youngs modulus
- Bulk modulus
- Shear modulus
What do elastic constants tell us?
They determine how a rock will behave when energy is applied to it.
That is the period of a wave?
The time required to go through one wave cycle units time.
What is frequency?
Number of wave cycles per second.
What are units for frequency?
What are units for period of a wave?
What is velocity?
Distance divided by time.
What are the 4 types of seismic waves?
- P waves
- S waves
- Love waves
- Reyligh waves
What are body waves?
P and W waves.
Why are body waves called such?
Because they move through the body of the earth.
What are surface wave?
Love and reyleigh.
Why are surface wave called such?
Because the waves energy stays close to the surface.
P waves can move through what type of material?
Any solid, liquid, or gas.
Which is faster P or S waves?
How do s waves travel?
Only through solids.
how do we create p waves?
Hitting side of rock with hammer.
How do we create s waves?
glancing blow to side of rock with hammer.
What are rays?
Energy moving out in a straight line.
What is the incident ray?
What are the two types of s waves and define them.
- Sh-Hoizontal s wave
- Sv- Vertical s waves
What is Critical refration?
Angle of refraction is 90 degrees and runs down the boundery.
What is Huygen's Principle?
Every point on a wave front is a source of new waves.
What does Feramats principle say?
Seismic waves travel along the fastest path.
How does the Reyliegh wave move?
In an retrograde eliptical motion.
How does a love wave move?
In a back and forth motion crossing the motion of the wave.
What is noise?
Any unintended signal in data.
What is omgea?
Energy of source.
What is geometric spreading?
Same amount of energy from source is distributed over a wider area as wave moves.
What is absorption?
The converstion of seismic energy into heat energy.
What is the reflection coeffient?
How much seismic energy is reflected ar a boundary.
What is transmission coeffient?
How much seismic energy is refracted across a boundary.
What are some examples of sources for making seismic energy?
- vibroseis truck
What is the process to recording seismic waves?
- set of geophones
- Geophone cable
- Computer system
What is Snell's Law?
V2 will have a higher velocity thean v1, and v3 will have a higher velocity than v2.
What is a wave guide?
The lowest speed layer.
When doing a gravity survey what are we measuring?
density of rock
When doing a seismic survey what are we measuring?
When doing a magnetic survey what are we measuring?
Magnetism of the rock.
Seismic refraction is used of what size of scale?
Seismic refraction is used to what?
Calculate how deep layers are.
What is a first arrival?
the first seismic wave to reach the geophone.
What is Condition of Reciprocity?
If there is no dip, data will be exactly the same ither way you shoot.
Which is prefered reflection or refraction surveying?
What scale is reflection surveying?
What is reflection surveying typically used for?
Deeper subsurface, Hydrocarbon exploration.
What is reflection?
When waves reflect off layers in the subsurface.
What are some seismic sources for reflection surveying?
- Weight drop
- betsy gun
- Impact vibration source
- Vibroseis truck
What is used for marin reflection surveys?
What are geophones?
What is the Dix equation used for?
Finding the velocities of reflected waves.
What is multiplexing?
1 file for each shot string data together in a single file for storage.
What is demultiplexing?
Seperating records for each geophone.
What is NMO?
Normal Move Out is taking time out for not being directly above.
What is measured in a potential field survey?
Some property of the Earth that always exisits.
What are the 4 things that effect gravity?
- Rotation Speed
What is the shape of the Earth?
An Oblate Spheroid.
What 4 things effect gravity surveys?
- Rock Type
What are Gravity Reductions?
- Latitude Correction
- Elevation (free air correction)
- Bouguer Correction( Excess mass)
- Terrain Correction(Hammer)
What is the Eotvos Correction used for?
Adjusts for speed and direction of the ship.
When doing a magnetism study, we often do another kind of study with it, what is this study?
What can we use magnetism to find?
- Igneous bodies
- metal ore bodies
If you have a magnet, then sprinkle metal flakes over it, the shape you get is called what?
Is magnetism a retractive or attractive force?
mew is what?
Magnetic permeability of medium in which magnetic field is being measured.
______________ exist in 3-D and have direction.
Where is magnetism measured?
At the Earth's surface or in areial surface.
What types of magnetism are there?
Diamagnetic, Paramagnetic, Ferromagnetic, Antiferromagnetic, or non-magnetic.
In what way does Earth's magnetic field change?
Changes ion long and short time scales.
What are outside influences on magnetism?
- Solar Wind
- Corneal masses
- Solar flares
How is earth most often modeled?
As a bar magnent.
More accurate magnetism of Earth is modeled by how many bar magnets?
Magnetisim is measured in what?
Gammas and nanoteslas.
What is magnetic field inclination?
Vertical angle of field lines.
What i s magnetic field declination?
angle between true north and magnetic north.
What seems to be the main effect belived to cause Earth's Magnetism, explain?
Dynamo Effect, it is the interaction between liquid outer core and solid inner core.
A Sphere is a model of what?
A horizontal Cylinder is a model of what?
Tunnels, dikes, grabbbens, caves.
Veritcal cylinder is a model of what?
What is the shape of earth magnetic field.
Asymetrical because it is stronger on one side than the other.
What does magnetism depend on?
- How suspetible is a material to becoming magnetized.
- Intensity of magnetization.
- How strongly magnetized is it?
Magnetic moment is when?
Product of pole strength multiplyed by the length seperating the poles.
What is diamagnetic?
electrons orbit in a way that produces a weak magnetic field that opposes the applied field.
Paramagnetic Magneitc is what?
moment alingn themsleves to the same direction, produces weak positive susceptibilty.EX, Garnet, aphibole,olivine, edt.
What is ferromagnetic?
Strong reaction between adjacent atoms and overlap of elecrton orbits.
What is the curie temp?
Temp at which magnetic material gains or loses magnetic properties.
What does higher temp do to magnetism?
Makes is weaker.
What is fluxgate magnometers used for?
Seterming permentant magnetism in rock.
What does Bouger correct for?
what is the energy required to keep positive and negative charges seperate?
How does electrical current flow?
from pos to neg.
Resistivity surveying is what?
Create a circut with the Earht used a the resistor.
What is current density?
How crowded the current is in given area.
What is apparent resistivity?
The weighted average of resistivites in different zones
What is G Geometrical factor?
A function of electrode configuration.
What are resistivity units?
What is profiling?
Fixed electrode spacing to gather dat at a constant depth.
Azuthal resistivity is what?
turning study with 4 pins.
What is sounding?
Expand electode spacing to survey carious depths.
Wenner Array is what?
Evenspacing between all electrodes.
What is Schlumberger Array?
2 different electorode spacing. sink and scource.
What is the barnes layer method?
Idea is that since wach survey depth is weighted agverage of the material abouve. You subtact whats above you end up with data primarly from the depth of interest.
What are Electromagnetic survey used to find?
Em-31 is good for finding what?
- Contaminant plumes
- Metal objects
EM-61 one can find what?
Pipes, drum, UXO's.
Ground penetrating Radar is what?
Operates like seismic but with radar waves.