Test 2

plates are heated from below from _____ and _____
plates are heated from below by radioactive decay and earth accretion
fluids transfer heat _____
fluids transfer heat convectively 
plates transfer heat _____, meaning what
plates transfer heat conductively, meaning there is no flow  
which transfers heat more quickly, plates or liquid mantle?
the liquid mantle transfers heat more quickly than solid plates, becuase convective heat transfer is faster than conductive heat transfer
Fourier’s law as it applies to heat transfer in the earth

q=-k*(dT/dz)

q is heat flow 

k is thermal conductivity

dT/dz is temperature gradient 

which has a higher thermal conductivity, metal or styrofoam?
metal conducts heat better than styrofoam, it has a better thermal conductivity
units of heat flux
units of heat flux are watts/(meter2)
what do we add to Fourier’s law when we are examining heat flow in the earth?
when we are examining heat flow in the earth, we add a term for heat from radioactive decay, A*h. h is the thickness of the radioactive plate
what is worldwide heat loss on the scale of?
worldwide heat loss is on the scale of 1013 watts
what part of the earth makes up a disproportiontly large amount of heat loss for it’s area?
oceans cover 60% of the world’s surface but make up for 71% of the world’s total heat loss
what affects does change in temperature have on the lithosphere?
the lithosphere thickens as it cools
on what scale are variations in earth’s gravitational field 
variations in earth’s gravational field are on a scale of miligals 
lateral variations anywhere in the earth create _____
lateral variations anywhere in the earth create gravity anamolies 
application of micro-gravity data we talked about
we talked about using micro-gravity data for finding tombs and caves
what was the application of small-scale  gravity anamoly study we looked at?
we looked at using small-scale gravity anamoly study for mineral exploration 
isotasy relates what
isotasy relates the level that a solid floats at in a liquid to the density of the solid 
what principle would we use to relate the thickness of a crust to the height of the mountains on it?
isotasy is used to relate the thickness of a crust to the height of the mountains on it
what is the application of medium scale gravity anamoly study we looked at?
we looked at using medium scale gravity anamoly study to find salt domes during oil exploration
what are two large-scale gravity anamoly study applications we looked at?
we looked at using large-scale gravity anamoly study to study global ocean circulation, climate, and to estimate crustal thickness 
[image]

the curvy line is the geoid

the dotted line is the spheriod 

The distance between them is the geiod anamoly 

what is the reference ellipsoid 
the reference ellipsoid is the uniform oblate spheriod
what are the two forms of newton’s universal law of graviation that we learned?
[image]
whats the relation between the radius of the earth at the equator and the radius at the poles
radius of earth at equator = radius of earth at poles +21 km
when we look at a change in sea level caused by gravity, what information do we have that will help?
when we look at changes in sea level due to gravity, it is caused by a change in the density of what is below the sea at that point. We know the densities of sea water and the density of oceanic rock, so we have all the numbers we need to figure it out!
how does the geiod mathematically relate to the gravity field of the earth
the vertical derivative of the geiod is the gravity feild of the earth
what are the two gravity corrections we didn’t do any math with?

the two corrections to gravity we didn’t do math with are 1. instrumental drift 

2. tides

what is the international gravity formula

 

the internation gravity formula is

?g = gobserved – gtheoretical 

 

 

what is the equation for the free air correction?

the equation for the free air correction is 

FAC= (.3086*h)mgal

 

what is the free air anomaly?

the free air anomaly is the what you get when you apply the latitude and free-air corrections:

FAA = gobserved -gtheoretical + FAC

what is the word for the gravitional equilibrium between the lithosphere and the athenosphere?
the gravitational equilibrium betwee the lithosphere and the athenosphere is called isotasy
isotasy says what about heavier vs lighter mountains ranges?
isotasy says that heavier mountain ranges will sink deeper into the athenosphere than lighter mountains ranges.
what does the bouger correction assume about the mass below you that is affecting the gravitational pull on you?
the bouger correction assume that the mass below you is a giant cylinder with a finite height and a constant density
what do you do to the free air anomaly to get it to the bouger Anomaly
the free air anomaly minus the bouger correction yeilds the bouger anomaly
the assumption that gravity goes down as you go up is often cancelled out by the gravity provided by mountains as well as isotasy. In what cases does the assumption that gravity goes down as you go up more consistent?
the assumption that gravity goes down as you go up works better for short range topography
terrian correction for gravity
the terrian correction for gravity corrects for the fact that the bouger correction assumes a flat slab underneath the sensor. The terrian correction looks at small changes in terrian that deviate from this slab
what do we use to account for small changes in topography that don’t fit in with the infinite flat slab that the bouger correction assumes?
the bouger correction assumes an infinite flat slab, and small changes in topography deviate from this model, so we use a terrian correction 
if you have few data points for k when examining heat flow, what could you do to give yourself confidence?
if you have few data points, you can find the standard deviation, and use that to find a “low” and “high” limit, and do the calculations with those numbers and get a limit on the high and low of your answer
difference between gobs and gtheoretical is due to what
difference between gobs and gtheoretical is due to the flattening of the earth
sketch how isotasy effects a gravity diagram and how FAA and Bouger will cancel each other out
N/A
relationship between passive margin and gravity field
passive margins are zones on the interior of plates where the plates are “stretched.” the plate is thinner, less density from plate itself, less gravity field on passive margins
what is similar about choosing sample intervals between gravity and magnetic data sets?
in both gravity and magnetic data sets, you can’t choose to large a sample interval or else you lose information. too small a sample set and you aren’t getting any more information and you’re wasting time
station spacing needs to be less than ______
station spacing needs to be less than one half the body of interest
if you are trying to examine a subsurface body 28 meters below ground, what should your sample interval be?
if you are trying to examine a subsurface body 28 meters below ground, your sample interval should be less than 14 meters, because sample interval should be less than 1/2 the depth of the subsurface body
how do we reduce error when making a sample field?
redudancies reduce error when making a sample field
when making a sample field, what should the orientation of your profiles relative to the body of interest be?
when making a sample field, the profiles should be perpindicular to the body of interest
when making a sample field, how does one define error?
when making a sample field, error is the square root of the sum of the squares of each component erro
when making a sample field or any profile, where should station density be greatest?
when making a sample field or any profile, station density should be greatest in areas of steep gradients (of whatever you are measuring)
you want to make a station field and have some idea of the bodies/layers/anomalies you will be looking at. How do you determine relative station spacing between different areas on the map?
relative station spacing should be based on which areas have the biggest gradients of whatevery you are studying
what are 5 things to consider when making sample fields?

the 5 things to consider when planning a sample field is:

1. you want a consistent grid 

2. you want redundancies to reduce error 

3. you want profiles perpindicular to bodies of interest 

4. station spacing should be less than 1/2 the depth of the body of interest

5. station density should be greatest in areas of steep gradients 

if you are looking at a gravity anomaly field, what would a deep body show up as?
a deep body shows up as a wide, low amplitude anomaly on a gravity anomaly field
if you are looking at a gravity anomaly field, what would a shallow body show up as?
if you are looking at a gravity anomaly field, a shallow body would show up as a high amplitude, narrow anomaly.
as a body gets deeper, how does the resolution of it’s anomaly on a sample field change?
deeper bodies have lower resolution

what does the equation 

A*e-(2?z)/?

singify?

that equation shows how amplitude decreases as z, which is depth, goes up
four steps of constructing a forward model

the 4 steps of constructing a forward model:

1. propose a model

2. calculate it’s anomaly

3. see how observed anomaly fits data

4. adjust shape of model to the improved fit 

if I first predicted the gravity anomaly from a certain structure and then saw how my calcuations matched the data, what kind of modeling would this be?
if you first calculate what you would expect and then see how it matches reality, this is forward modeling 
if I looked at the data and then found a model to fit the data, what kind of modeling would this be?
looking at data first and then finding a model to fit the data is inverse modeling 
describe the two steps in inverse modeling

the two steps in inverse modeling are:

1. look at the data, then find a model that fits the data

2. use linear algebra to maximize fit in the “least squares sense”

what generates the earth’s magnetic field?
the earth’s magnetic field is generated by the liquid outer core that spins at a different speed than the solid layers bordering it
earth’s magnetic field is strongest at ____ and weakest at _____
earth’s magnetic field is strongest at the poles and weakest at the equator
3 applications of examining earth’s magnetic field

the 3 applications of examining the earth’s magnetic field:

1. finding metal objects

2. mapping the subsurface

3. mineral exploration 

2 steps to interpreting magnetic data

the two steps to interpreting magnetic data are:

1. geomagnetic correction: this is a latitude correction that account for the fact that the earth’s magnetic field is much stronger at the poles

2. diurnal correction: this corrects for charged particles from the sun, it is based on time

what magnetic anomaly data is based on time?
the diurnal correction for magnetic data corrects for charged particules coming from the sun, it is based on time
what magnetic anomaly correction is based on location?
the geomagnetic correction is based on the fact that the earth’s poles have a much stronger field than the equator. The geomagnetic correction is based on latitude
what do we look for when we have solved for the remanant field, which we get after accounting for magnetic anomaly data, if we are looking to see if subsurface rocks haved moved?
after we take into account the magnetic anomalies, we want to see if the remanant field is parallel or anti-parallel. if the remanant field is anti-parallel it is evidence that the rocks have moved
what does a circular magnetic signal indicate?
a circular magnetic singal suggests an instrusive body 
after we account for the two magnetic anomalies, what is left?
after we account for the two magnetic anomalies, what is left is called the remanent field
what kind of magnetic singal would an intrusive body create?
an intrusive body would create a circular magnetic signal on a signal field
what magnetic singal would a dike, shear zone, or isoclinal fold make?
a dike, shear zone, or isoclinal zone would should up on a magnetic signal map as a long, narrow anomaly
if you are looking at a magnetic field and you see a long, narrow signal, what geologic body might that indicate?
a long, narrow signal on a magnetic field indicates a dike, a shear zone, or an isoclinal fold
what kind of singal on a magnetic map would a basaltic lava flow make?
a basaltic lava flow would show up on a magnetic map as a high intensity area with no regular pattern of contours
you are looking at a magnetic singal map and you come across an area of strong magnetic field with no recognizable pattern of contours, what geologic body does this indicate?
a magnetic signal map that has an area of high intensity with no pattern of contours is caused by a basalt lava flow 
what kind of signal on a magnetic signal map do sedimentary rocks create?
sedimentary rocks result in a quiet zone with few changes on a magnetic signal map because the magnetically active rocks are buried far below
if you are looking at a magnetic signal map and you see a quiet area with few changes, what kind of geologic body does this indicate?
if you are looking at a magnetic signal map and you see a quiet area with few changes, this suggests layer(s) of sedimentary rock, because the magnetically active rocks are buried far below
at what rate does the amplitude of a gravity anomaly drop as the body cuasing it gets deeper?
the amplitude  of a gravity anomaly drops at a rate of 1/r3 where r is the depth of the body causing the anomaly
the magnetic anomaly caused by a dike of mostly iron will look like what at the equator?
the magnetic anomaly caused by a dike of mostly iron at the equator will look like a simple symmetrical curve that has a peak at the center of the dike
the magnetic anomaly of a dike of mostly iron will look like what at 45° latitude?
at 45° latitude, the magnetic anomaly of an iron dike will show a postive curve first followed by sharp dip to the negative, and then will flatten out from there
where on earth would you see the smallest gravity anomly in units of mgals for a subsurface iron body?
at the equator you see relatively weak signal for any magnetic anomaly because that is where the earth’s magnetic field is weakest
what are the two types of measurements we can make on magnetic fields?
we can measure the direction of magnetic fields (x,y) and the magnitude of the magnetic fields (z)
I didn’t make slides about the pros and cons of different magnometers
earth’s crustal field: the magnetism we “see” on the surface, is really a combination of these two field

the magnetism we “see” on earth is a combination of

1. earth’s internal field, generated by the liquid outer core

2. the external field generated by the sun (called “solar interferance”)

earth’s crustal field is the same as _____
the earth’s crustal field is what we called the remanent field before
in the mid to lower crust, rocks change in this way relating to magnetism
in the mid to lower crust, rocks get too hot to acquire magnetism
as bodies get deeper, wavelength of the signal goes down, and we lose ____
as bodies get deeper, the wavelength of the signal goes down, and we lose accuracy 
we can use gravity to examine these two things in volacanoes

Gravity and volcanoes: use gravity data to detect:

1. very small shape changes in volcanoes

2. magma bodies that have a different density than the rest of the volcanoe 

when you get magnetic data with amplitude on one axis and distance on the other, Cindy says we should concentrate on _____
when you get magnetic data with amplitude on one axis and distance on the other, we should be looking for the change in signal over time time aka the derivative aka the gradient 
why doesn’t the BGA correlate well with topography?
the BGA intentionally corrects for the topography
what is the gravity correction for altitude?
the gravity correction for altitude is .3086*h(m)
when you want to set up a magnetic survey, you should take these four things into account

when you want to set up a magnetic survey, you should take into account:

1. depth of body

2. orientation of body

3. where you are on the earth and how that relates to the earth’s magnetic field. the field has different strengths and points in different directions in different places on earth 

4. any objects in the survery field that will provide noise, any random metal objects will provide noise.

what is the Curie Isotherm?
the Curie isotherm is the heat at which rocks lose thier magnetic properties
what do we call the point at which rocks get too hot to maintain their magnetic properties?
the point at which rocks get to hot to maintan thier magnetic properties is called the curie isotherm
what is half-width?
half-width is the distance from the center of an anomaly at which the amplitude of the anomaly is half of the max
what do we call the distance from the center of an anomaly at which the amplitude of the anomaly has decreased to half it’s size?
the distance from the center of an anomaly at which the amlitude of the anomaly has decreased to half it’s size is called the half-width 
the bouger anomaly is the free air correction ____ the bouger correction
the bouger anomaly is the Free air correction minus the bouger correction. it is important to see it is minus not plus
the free air anomaly is the observed gravity _____ the latitude correction and ____ the free air correction
the free air anomaly is the observed gravity minus the latitude correction and plus the free air correction
name three long scale changes in the earth’s magnetic field

two long scale changes in the earth’s magnetic feild are:

1. movement of magnetic north

2. wobble around in the inclined rotation axis

3. reversals of polarization

what is the geomagnetic pole?
earth’s magnetic field is best represented by a dipole. this dipole has an axis the connects the two ends of the diple the geomagnetic pole is the position on earth’s surface intersected by this made-up axis
what is the magnetic pole of the earth?
the magnetic pole is where the earth’s magnetic field is vertical 
what is pearmeability?
permeability is a measure of the connectedness of pores in a rock
give an example of 1. something that is porous and permeable and 2. something that is porous and not permeable

1. sponges are porous and permeable 

2. when frothy magma cools, there are air pockets within crystalline rocks. So there is porosity but no permeability 

Darcy’s law assumes _____ flow paths
Darcy’s law assumes linear flow paths 
what is magnetic inclination?
magnetic inclination is the angle between the earth’s magnetic field and the earth’s surface (aka the horizontal)
what is magnetic declination?
magnetic declination is the angle between true north and the magnetic north from where you are standing
in the darcy equation, what does the symbol q represent? what are the units of q?
in the darcy equation, q is specific discharge, which is flow/area and has units of length/time. on the slides it was m/sec
what do we get when we divide flow by area?
flow/area gives specific discharge in units of length/time, meters/second in her example
when we look at darcy’s law, what is n?
when we look at darcy’s law, n is the effective porosity of the material we are looking at
what is the symbol for average linear velocity in the darcy equation?
average linear velocity in the darcy equation is “v”

write Darcy’s law. The write how to relate Q, p, v, and n in Darcy’s law

 

Darcy’s Law: Q=-k*A*(dH/dL)

Q/A=q

v=Q/(A*n)=q/n

what temperature is the curie isotherm?
the curie isotherm is usually 600° C, it ranges from 580-770° C