Test 1

Question 1

Displacement Hypothesis and Wegener Theory

Answer 1

Continents were together and glaciation occurred over a smaller area (most likely) Wegener also assembled paleoclimatic data showing the distribution of coal deposits(evidence of moist temperate zones), and salt, gypsum and desert sandstones(evidence of dry sandstones(evidence of dry climate) for several geological eras These reflected climatic belts like today’s, e.g. an equatorial tropical rain belt, two adjacent dry belts, two temperate belts and two polar ice caps

Question 2

Weakness in Wegener Theory

Answer 2

Wegener failed to address a convincing mechanism for continental drift
he proposed that the continents slide over ocean floor

Question 3

Paleoclimatology

Answer 3

Paleoclimatology is the study of climates for which direct measurements were not taken.

Question 4

Paleomagnetism

Answer 4

determination of direction and strength of magnetic field in old rocks
Old pole positions can then be determined (magnetic dip or inclination)

Question 5

Seafloor spreading and evidence to support it

Answer 5

Harry Hess(1962) proposed that besides continents, sea floor might also be moving

1. Marine Magnetic Anomalies
2. Fracture Zones and transform faults
3. Measuring plate motion directly w/ GPS

Question 6

Stages of Data Retrieval

Answer 6

1. Data Acquisition
2. Data Reduction
3. Data Processing
4. Data Interpretation

Question 7

Data Acquisition

Answer 7

Taking Measurements

Target: Anomalies

Question 8

Data Reduction

Answer 8

Converting Readings into a more useful form

Question 9

Noise

Answer 9

Unwanted variations in the quantities being measured

Question 10

Signal

Answer 10

The wanted quantities you want measured

Question 11

S/N Ratio

Answer 11

Repeat readings and take their average, also called stacking
You want high S/N ratio

Question 12

Inverse Modeling

Answer 12

to deduce the causative body directly from the results

Question 13

Forward Modeling

Answer 13

To “guess” a model, calculate the values it would produce, compare them with the observations, and then modify the model until it matches the results sufficiently well.
“Trial and error”

Question 14

Inversion Problem

Answer 14

Trying to deduce the form of the body from the anomaly

Not possible if more than one body could produce the results

Question 15

Resolution

Answer 15

stations may not be close enough to reveal all the details of the signal
i.e. Trying to define in a picture details smaller than the size of the pixels

Question 16

Data Interpretation

Answer 16

The physical model has to be translated into geological terms

Question 17

Data Processing

Answer 17

Fourier analysis
Harmonic analysis
Digital Filtering

Question 18

Fourier analysis

Answer 18

Sort features by their widths, from which we can then select the one we want

Question 19

Harmonic Analysis

Answer 19

Only certain wavelengths are used, such that 1, 2, 3,… half-wavelengths exactly fit the length of the profile; these are called harmonics
As more harmonics are added the approximation improves

Question 20

Harmonic analysis: residual anomaly

Answer 20

How well this recombined harmonics match the observed profile can be measured by showing their differences as a residual anomaly

Question 21

Harmonic Analysis: Considerations

Answer 21

1. usually contains a range of wavelengths, so separation of wanted/unwanted signals is only partial
2. Since the length of the profile are rather arbitrary, so are the harmonics
3. rejecting shorter wavelengths is often regarded as removing anomalies of bodies near the surface to leave deeper ones. (But whereas a narrow anomaly cannot be due to a deep body, the converse is not true)

Question 22

Digital Filtering: Low pass

Answer 22

they let pass through all wavelengths longer than some value, but reduce those shorter

Question 23

Digital Filtering: High pass

Answer 23

lets through only wavelengths shorter than some value

Question 24

Digital Filtering: Band pass

Answer 24

lets through only a range of intermediate wavelengths

Question 25

Aliasing

Answer 25

wavelengths that do not exist can appear to be that do not exist can appear to be present because of large intervals

Question 26

Nyquist wavelength

Answer 26

The critical wavelength(twice the sampling interval)

Question 27

Waves (Seismology)

Answer 27

Vibrations of Rocks

Question 28

4 Parts of Seismology

Answer 28

1. Global seismology and seismic waves
2. Refraction
3. Reflection
4. Earthquakes and seismotectonics

Question 29

Wave Fronts

Answer 29

compression travels spherically outwards (spherical surfaces)

Question 30

Rays

Answer 30

conforms a small portion of the wave front always perpendicular to it v=km/s

Question 31

Seismometers

Answer 31

More sensitive
Less Robust
used to measure weak signals (like distant earthquakes)

Question 32

Geophone

Answer 32

Used in small scale surveys

where highest sensitivity is not needed

Question 33

Earth symmetry analysis as based on epicentral angles

Answer 33

1. Times to travel all paths with the same epicentral angle are nearly the same (for both small and large angles), so the Earth is indeed spherically symmetrical
2. (gets faster with depth) Earth is not seismically uniform

Question 34

Refraction

Answer 34

When wave fronts cross obliquely into a rock with a higher seismic velocity they speed up, which causes them to change direction

Question 35

Snell’s Law

Answer 35

Determines degree of change of direction for refraction

Sin(i1)/v1 = sin(i2)/v2

Question 36

P-ray parameter

Answer 36

sin i1 / v1= sin i2 / v2= sin i3 / v3 … = constant = p= ray parameter. Used to deduce ray paths through Earth.

Question 37

Iasp91 Model

Answer 37

The model that displays P and S wave velocities throughout the depths of Earth

Question 38

P-ray shadow zone

Answer 38

98-144 degrees, caused by core refraction

Question 39

S-ray shadow zone

Answer 39

98-180 degrees, S-waves cannot travel through core

Question 40

Attenuation

Answer 40

Amplitude of seismic waves changes for two main reasons:
1. the wave front usually spreads out as it travels away from the source.

2. If wave energy is absorbed, such as if rock is not fully elastic or S-waves entering rocks with some liquid

Question 41

Elastic rebound theory

Answer 41

explains how rocks store energy until it is suddenly released in an earthquake: b) strain accumulates (elastically); c) elastic limit is exceeded, the fault slips releasing the pressure; d) surface rupture and surface offsets releasing the pressure; d)surface rupture, and surface offsets

Question 42

Earthquake location

Answer 42

Traces recorded at seismograms from seismometer stations used to deduce location or origin time
If we use only time of first arrivals If we use only time of first arrivals(P-waves) at different stations we can deduce location.

Question 43

Fault-plane solutions

Answer 43

It is also possible to deduce the orientation of the fault plane and the direction of displacement in that plane and the direction of displacement in that plane

Beach ball example, like lab. Compress= +, Dilation= -
Strike strip = basic quadrant
normal fault = +,-,+
Thrust fault = -,+,-

Question 44

Rupture and displacement Principles

Answer 44

The ruptured area of a fault due to a large earthquake has a length along strike that is usually much greater than its depth
Earthquakes have rupture lengths up to hundreds of km, widths up to tens of km, and displacements up to tens of m

Question 45

Measures of earthquake size

Answer 45

Intensity, Mercalli Scale

Magnitude, Richter Scale, uses Log scale

Question 46

Seismic moment (M0)

Answer 46

Value = to the product of shear force, displacement, and rupture area.
and/or
equals the product of the shear forces (F) and the perpendicular distance between them (b)