Term
| plates are heated from below from _____ and _____ |
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Definition
| plates are heated from below by radioactive decay and earth accretion |
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Term
| fluids transfer heat _____ |
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Definition
| fluids transfer heat convectively |
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Term
| plates transfer heat _____, meaning what |
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Definition
| plates transfer heat conductively, meaning there is no flow |
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Term
| which transfers heat more quickly, plates or liquid mantle? |
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Definition
| the liquid mantle transfers heat more quickly than solid plates, becuase convective heat transfer is faster than conductive heat transfer |
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Term
| Fourier's law as it applies to heat transfer in the earth |
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Definition
q=-k*(dT/dz)
q is heat flow
k is thermal conductivity
dT/dz is temperature gradient |
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Term
| which has a higher thermal conductivity, metal or styrofoam? |
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Definition
| metal conducts heat better than styrofoam, it has a better thermal conductivity |
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Term
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Definition
| units of heat flux are watts/(meter2) |
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Term
| what do we add to Fourier's law when we are examining heat flow in the earth? |
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Definition
| 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 |
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Term
| what is worldwide heat loss on the scale of? |
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Definition
| worldwide heat loss is on the scale of 1013 watts |
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Term
| what part of the earth makes up a disproportiontly large amount of heat loss for it's area? |
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Definition
| oceans cover 60% of the world's surface but make up for 71% of the world's total heat loss |
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Term
| what affects does change in temperature have on the lithosphere? |
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Definition
| the lithosphere thickens as it cools |
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Term
| on what scale are variations in earth's gravitational field |
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Definition
| variations in earth's gravational field are on a scale of miligals |
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Term
| lateral variations anywhere in the earth create _____ |
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Definition
| lateral variations anywhere in the earth create gravity anamolies |
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Term
| application of micro-gravity data we talked about |
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Definition
| we talked about using micro-gravity data for finding tombs and caves |
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Term
| what was the application of small-scale gravity anamoly study we looked at? |
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Definition
| we looked at using small-scale gravity anamoly study for mineral exploration |
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Term
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Definition
| isotasy relates the level that a solid floats at in a liquid to the density of the solid |
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Term
| what principle would we use to relate the thickness of a crust to the height of the mountains on it? |
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Definition
| isotasy is used to relate the thickness of a crust to the height of the mountains on it |
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Term
| what is the application of medium scale gravity anamoly study we looked at? |
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Definition
| we looked at using medium scale gravity anamoly study to find salt domes during oil exploration |
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Term
| what are two large-scale gravity anamoly study applications we looked at? |
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Definition
| we looked at using large-scale gravity anamoly study to study global ocean circulation, climate, and to estimate crustal thickness |
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Term
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Definition
the curvy line is the geoid
the dotted line is the spheriod
The distance between them is the geiod anamoly |
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Term
| what is the reference ellipsoid |
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Definition
| the reference ellipsoid is the uniform oblate spheriod |
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Term
| what are the two forms of newton's universal law of graviation that we learned? |
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Definition
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Term
| whats the relation between the radius of the earth at the equator and the radius at the poles |
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Definition
| radius of earth at equator = radius of earth at poles +21 km |
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Term
| when we look at a change in sea level caused by gravity, what information do we have that will help? |
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Definition
| 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! |
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Term
| how does the geiod mathematically relate to the gravity field of the earth |
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Definition
| the vertical derivative of the geiod is the gravity feild of the earth |
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Term
| what are the two gravity corrections we didn't do any math with? |
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Definition
the two corrections to gravity we didn't do math with are 1. instrumental drift
2. tides |
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Term
what is the international gravity formula
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Definition
the internation gravity formula is
Δg = gobserved - gtheoretical
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Term
| what is the equation for the free air correction? |
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Definition
the equation for the free air correction is
FAC= (.3086*h)mgal
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Term
| what is the free air anomaly? |
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Definition
the free air anomaly is the what you get when you apply the latitude and free-air corrections:
FAA = gobserved -gtheoretical + FAC |
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Term
| what is the word for the gravitional equilibrium between the lithosphere and the athenosphere? |
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Definition
| the gravitational equilibrium betwee the lithosphere and the athenosphere is called isotasy |
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Term
| isotasy says what about heavier vs lighter mountains ranges? |
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Definition
| isotasy says that heavier mountain ranges will sink deeper into the athenosphere than lighter mountains ranges. |
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Term
| what does the bouger correction assume about the mass below you that is affecting the gravitational pull on you? |
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Definition
| the bouger correction assume that the mass below you is a giant cylinder with a finite height and a constant density |
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Term
| what do you do to the free air anomaly to get it to the bouger Anomaly |
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Definition
| the free air anomaly minus the bouger correction yeilds the bouger anomaly |
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Term
| 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? |
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Definition
| the assumption that gravity goes down as you go up works better for short range topography |
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Term
| terrian correction for gravity |
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Definition
| 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 |
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Term
| 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? |
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Definition
| the bouger correction assumes an infinite flat slab, and small changes in topography deviate from this model, so we use a terrian correction |
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Term
| if you have few data points for k when examining heat flow, what could you do to give yourself confidence? |
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Definition
| 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 |
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Term
| difference between gobs and gtheoretical is due to what |
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Definition
| difference between gobs and gtheoretical is due to the flattening of the earth |
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Term
| sketch how isotasy effects a gravity diagram and how FAA and Bouger will cancel each other out |
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Definition
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Term
| relationship between passive margin and gravity field |
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Definition
| 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 |
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Term
| what is similar about choosing sample intervals between gravity and magnetic data sets? |
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Definition
| 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 |
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Term
| station spacing needs to be less than ______ |
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Definition
| station spacing needs to be less than one half the body of interest |
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Term
| if you are trying to examine a subsurface body 28 meters below ground, what should your sample interval be? |
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Definition
| 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 |
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Term
| how do we reduce error when making a sample field? |
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Definition
| redudancies reduce error when making a sample field |
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Term
| when making a sample field, what should the orientation of your profiles relative to the body of interest be? |
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Definition
| when making a sample field, the profiles should be perpindicular to the body of interest |
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Term
| when making a sample field, how does one define error? |
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Definition
| when making a sample field, error is the square root of the sum of the squares of each component erro |
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Term
| when making a sample field or any profile, where should station density be greatest? |
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Definition
| when making a sample field or any profile, station density should be greatest in areas of steep gradients (of whatever you are measuring) |
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Term
| 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? |
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Definition
| relative station spacing should be based on which areas have the biggest gradients of whatevery you are studying |
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Term
| what are 5 things to consider when making sample fields? |
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Definition
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 |
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Term
| if you are looking at a gravity anomaly field, what would a deep body show up as? |
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Definition
| a deep body shows up as a wide, low amplitude anomaly on a gravity anomaly field |
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Term
| if you are looking at a gravity anomaly field, what would a shallow body show up as? |
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Definition
| if you are looking at a gravity anomaly field, a shallow body would show up as a high amplitude, narrow anomaly. |
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Term
| as a body gets deeper, how does the resolution of it's anomaly on a sample field change? |
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Definition
| deeper bodies have lower resolution |
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Term
what does the equation
A*e-(2∏z)/λ
singify? |
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Definition
| that equation shows how amplitude decreases as z, which is depth, goes up |
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Term
| four steps of constructing a forward model |
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Definition
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 |
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Term
| 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? |
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Definition
| if you first calculate what you would expect and then see how it matches reality, this is forward modeling |
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Term
| if I looked at the data and then found a model to fit the data, what kind of modeling would this be? |
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Definition
| looking at data first and then finding a model to fit the data is inverse modeling |
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Term
| describe the two steps in inverse modeling |
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Definition
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" |
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Term
| what generates the earth's magnetic field? |
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Definition
| the earth's magnetic field is generated by the liquid outer core that spins at a different speed than the solid layers bordering it |
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Term
| earth's magnetic field is strongest at ____ and weakest at _____ |
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Definition
| earth's magnetic field is strongest at the poles and weakest at the equator |
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Term
| 3 applications of examining earth's magnetic field |
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Definition
the 3 applications of examining the earth's magnetic field:
1. finding metal objects
2. mapping the subsurface
3. mineral exploration |
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Term
| 2 steps to interpreting magnetic data |
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Definition
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 |
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Term
| what magnetic anomaly data is based on time? |
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Definition
| the diurnal correction for magnetic data corrects for charged particules coming from the sun, it is based on time |
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Term
| what magnetic anomaly correction is based on location? |
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Definition
| 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 |
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Term
| 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? |
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Definition
| 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 |
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Term
| what does a circular magnetic signal indicate? |
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Definition
| a circular magnetic singal suggests an instrusive body |
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Term
| after we account for the two magnetic anomalies, what is left? |
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Definition
| after we account for the two magnetic anomalies, what is left is called the remanent field |
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Term
| what kind of magnetic singal would an intrusive body create? |
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Definition
| an intrusive body would create a circular magnetic signal on a signal field |
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Term
| what magnetic singal would a dike, shear zone, or isoclinal fold make? |
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Definition
| a dike, shear zone, or isoclinal zone would should up on a magnetic signal map as a long, narrow anomaly |
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Term
| if you are looking at a magnetic field and you see a long, narrow signal, what geologic body might that indicate? |
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Definition
| a long, narrow signal on a magnetic field indicates a dike, a shear zone, or an isoclinal fold |
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Term
| what kind of singal on a magnetic map would a basaltic lava flow make? |
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Definition
| a basaltic lava flow would show up on a magnetic map as a high intensity area with no regular pattern of contours |
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Term
| 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? |
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Definition
| a magnetic signal map that has an area of high intensity with no pattern of contours is caused by a basalt lava flow |
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Term
| what kind of signal on a magnetic signal map do sedimentary rocks create? |
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Definition
| sedimentary rocks result in a quiet zone with few changes on a magnetic signal map because the magnetically active rocks are buried far below |
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Term
| 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? |
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Definition
| 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 |
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Term
| at what rate does the amplitude of a gravity anomaly drop as the body cuasing it gets deeper? |
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Definition
| the amplitude of a gravity anomaly drops at a rate of 1/r3 where r is the depth of the body causing the anomaly |
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Term
| the magnetic anomaly caused by a dike of mostly iron will look like what at the equator? |
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Definition
| 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 |
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Term
| the magnetic anomaly of a dike of mostly iron will look like what at 45° latitude? |
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Definition
| 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 |
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Term
| where on earth would you see the smallest gravity anomly in units of mgals for a subsurface iron body? |
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Definition
| at the equator you see relatively weak signal for any magnetic anomaly because that is where the earth's magnetic field is weakest |
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Term
| what are the two types of measurements we can make on magnetic fields? |
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Definition
| we can measure the direction of magnetic fields (x,y) and the magnitude of the magnetic fields (z) |
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Term
| I didn't make slides about the pros and cons of different magnometers |
|
Definition
|
|
Term
| earth's crustal field: the magnetism we "see" on the surface, is really a combination of these two field |
|
Definition
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") |
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Term
| earth's crustal field is the same as _____ |
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Definition
| the earth's crustal field is what we called the remanent field before |
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Term
| in the mid to lower crust, rocks change in this way relating to magnetism |
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Definition
| in the mid to lower crust, rocks get too hot to acquire magnetism |
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Term
| as bodies get deeper, wavelength of the signal goes down, and we lose ____ |
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Definition
| as bodies get deeper, the wavelength of the signal goes down, and we lose accuracy |
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Term
| we can use gravity to examine these two things in volacanoes |
|
Definition
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 |
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Term
| when you get magnetic data with amplitude on one axis and distance on the other, Cindy says we should concentrate on _____ |
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Definition
| 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 |
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Term
| why doesn't the BGA correlate well with topography? |
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Definition
| the BGA intentionally corrects for the topography |
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|
Term
| what is the gravity correction for altitude? |
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Definition
| the gravity correction for altitude is .3086*h(m) |
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Term
| when you want to set up a magnetic survey, you should take these four things into account |
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Definition
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. |
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Term
| what is the Curie Isotherm? |
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Definition
| the Curie isotherm is the heat at which rocks lose thier magnetic properties |
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Term
| what do we call the point at which rocks get too hot to maintain their magnetic properties? |
|
Definition
| the point at which rocks get to hot to maintan thier magnetic properties is called the curie isotherm |
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Term
|
Definition
| half-width is the distance from the center of an anomaly at which the amplitude of the anomaly is half of the max |
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Term
| 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? |
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Definition
| 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 |
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Term
| the bouger anomaly is the free air correction ____ the bouger correction |
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Definition
| the bouger anomaly is the Free air correction minus the bouger correction. it is important to see it is minus not plus |
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Term
| the free air anomaly is the observed gravity _____ the latitude correction and ____ the free air correction |
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Definition
| the free air anomaly is the observed gravity minus the latitude correction and plus the free air correction |
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|
Term
| name three long scale changes in the earth's magnetic field |
|
Definition
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 |
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|
Term
| what is the geomagnetic pole? |
|
Definition
| 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 |
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|
Term
| what is the magnetic pole of the earth? |
|
Definition
| the magnetic pole is where the earth's magnetic field is vertical |
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|
Term
|
Definition
| permeability is a measure of the connectedness of pores in a rock |
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|
Term
| give an example of 1. something that is porous and permeable and 2. something that is porous and not permeable |
|
Definition
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 |
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|
Term
| Darcy's law assumes _____ flow paths |
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Definition
| Darcy's law assumes linear flow paths |
|
|
Term
| what is magnetic inclination? |
|
Definition
| magnetic inclination is the angle between the earth's magnetic field and the earth's surface (aka the horizontal) |
|
|
Term
| what is magnetic declination? |
|
Definition
| magnetic declination is the angle between true north and the magnetic north from where you are standing |
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|
Term
| in the darcy equation, what does the symbol q represent? what are the units of q? |
|
Definition
| 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 |
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|
Term
| what do we get when we divide flow by area? |
|
Definition
| flow/area gives specific discharge in units of length/time, meters/second in her example |
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|
Term
| when we look at darcy's law, what is n? |
|
Definition
| when we look at darcy's law, n is the effective porosity of the material we are looking at |
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|
Term
| what is the symbol for average linear velocity in the darcy equation? |
|
Definition
| average linear velocity in the darcy equation is "v" |
|
|
Term
write Darcy's law. The write how to relate Q, p, v, and n in Darcy's law
|
|
Definition
Darcy's Law: Q=-k*A*(dH/dL)
Q/A=q
v=Q/(A*n)=q/n |
|
|
Term
| what temperature is the curie isotherm? |
|
Definition
| the curie isotherm is usually 600° C, it ranges from 580-770° C |
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