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geophysics exam 2 > powerpoints > Flashcards

powerpoints Flashcards

1
Q

earthquakes cause….

A

vibration of the Earth & permanent deformation

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2
Q

in what mediums do earthquakes exist?

A

They exist in space and time

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3
Q

Elastic Rebound Model

A

You begin with unbent rocks, over time stress builds up and rocks bend (strain) and store elastic energy. Eventually rock breaks sending seismic waves through the earth.

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4
Q

Earthquake strain

A

Abrupt movement occurs along a fault. (No movement across fault for many years, then as much as
several meters of plate movement in a few seconds)

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5
Q

tectonic creep

A

In some areas tectonic movement is slow + continuous. There is no earthquake in these areas.

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6
Q

Where do earthquakes begin?

A

beneath the surface at the hypocenter or focus.

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7
Q

Location directly above focus at Earth’s surface

A

epicenter

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8
Q

surface rupture

A

Slip that reaches all the way to the surface

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9
Q

Average location of

energy release

A

centroid

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10
Q

local magnitude

A

Determined by amount of ground movement recorded.

magnitude = log (Amp./Period) + f (depth, distance)

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11
Q

moment magnitude

A

Determined by size of fault and the amount of slip. More accurate for energy release that local magnitude.
Mw = (log (M0) / 1.5) – 10.73

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12
Q

What type of relationship is there between earthquake size and energy released?

A

logarithmic.

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13
Q

Besides local and moment magnitude what are other ways that earthquake sizes can be determined?

A
  • Human reports

* Instrumental recordings

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14
Q

seismology

A

study of the origin of ground vibration

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15
Q

What are some important applications of seismology?

A
  • Hazard mitigation
  • Exploration of resources
  • check for nuclear testing
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16
Q

seismometer

A

instrument that measures ground shaking.

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17
Q

seismoscope

A

Inverted pendulum with mechanical linkage. A historic way of measuring size of earthquakes.

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18
Q

Parts of a simple seismograph

A
  • Metal frame + recording device connected to Earth
  • Recording device is moving paper (on rotating drum)
  • Heavy metal object with pen suspended from beam
  • Inertia: Mass essentially fixed while frame moves
  • Pen fixed while paper moves, producing written signal
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19
Q

modern electronic seismometer

A
  • Suspended heavy weight now has a magnet
  • Wire coil surrounding magnet connected to earth
  • When earth moves, magnet induces current in coil
  • Voltage = velocity * magnetic field * wire length
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20
Q

DAS

A

Data Acquisition System- a specially designed computer. . records time and voltage from modern electronic seismometers.

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21
Q

energy radiates away from an earthquake in the form of…

A

seismic waves

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22
Q

P waves

A
  • body waves
  • begin at earthquake focus and move away in all directions
  • compressional waves (push-pull movement)
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23
Q

S-waves

A
  • secondary waves
  • slower than p waves
  • shear waves
  • usually larger than p-waves
  • only travel through solids
24
Q

Surface waves

A
  • slowest waves
  • last to arrive
  • generate greatest amount of wave movement
  • move only along earth’s surface.
25
Q

How do we locate earthquake epicenters

A
  • we use that fact that p and s waves travel at different distances.
  • Get info from at least 3 stations and triangulate location.
26
Q

S waves have what two orientations?

A

horizontal (SH) and

vertical (SV) polarization

27
Q

How are waves propagated from an earthquake epicenter?

A

*travel in spherical wave fronts (circles) away from the source

28
Q

What happens when seismic waves interact between layers?

A

reflection and refraction

29
Q

fast velocities cause a bend towards

A

the surface

30
Q

critical angle

A

the refracted wave is horizontal

31
Q

how do wave velocities react within each layer of the earth?

A

they increase with each layer.

32
Q

using the slope of a travel time curve to determine velocity

A

slope = 1/velocity

33
Q

shadow zones

A

A low velocity zone causes a set of distances where

no arrivals are recorded. Caused by top of the asthenosphere and the outer core.

34
Q

waveform modeling

A

Utilize full information of seismogram (waveform) to

interpret velocity structure, not just arrival times.

35
Q

synthetic seismograms

A
  • predicted from a velocity structure

* compare with recorded seismograms

36
Q

Forward modeling of velocity

A
  • Make educated guesses about velocity structure;
  • compare predicted seismogram with observed. This can show areas we correctly knew what was going on, and others where we needed improvement.
37
Q

Seismic travel time tomography

A
  • CAT scan of earth using seismic rays.
  • Divides earth into boxes, looks at travel times of boxes. Determine if each box is fast or slow.
  • Create a 3d model of velocity anomalies.
38
Q

When look at seismic vectors blue means

A

cooler and faster than average.

39
Q

when looking at seismic vectors red means

A

hotter and slower than average

40
Q

What do cool temperatures do to seismic velocities?

A

raise seismic velocities.

41
Q

What do warm temperatures do to seismic velocities?

A

slow seismic velocities.

42
Q

Issues with tomography

A

weakness of data set (not uniform coverage, unknown quality of arrival times)
weakness of technique (inversions are non-unique, do not give uncertanties, solutions are only for the earth’s interior at that particular time)

43
Q

equation for stress

A

stress equals strain/area

44
Q

normal stress

A

perpindicular to surface

45
Q

shear stress

A

parallel to surface

46
Q

strain

A

material deformation due to stress. (Change in shape of material)

47
Q

Types of deformation

A

elastic, ductile, brittle

48
Q

elastic strain

A

not permanent

49
Q

brittle strain

A

permanent. stress exceeds strength of material.

50
Q

ductile strain

A

some strain is permanent.

51
Q

shaded areas on “beach balls” represent

A

compression quadrants

52
Q

The double-couple model

A
  • In an elastic body, fault slip (ie., EQ) causes a 4-quadrant pattern of compression-waves.
  • Collect first motion measurements from EQ. Use this information to define compressional and dilational quadrants.
  • allows you to find 2 nodal planes.
53
Q

Lynn Sykes

A
  • Slip of earthquakes between MOR
  • Opposite of apparent offset between ridge segments
  • Proof for Wilson’s transform fault
  • Birth of seismotectonics
54
Q

When the compression or shaded are of “beach ball” is in the center what type of faulting do you get?
How does this look in cross-section?

A

Thrust or pure reverse faulting.

Shaded quadrants on top and bottom

55
Q

strike slip faulting in cross section

A

Only 3 quadrants visible

56
Q

Oblique faulting

A

Mixture of strike slip and dip slip faulting

geophysics exam 2 (2 decks)

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