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GLE 2024 (Day 3) > GEOPHYSICS (SEISMOLOGY) > Flashcards

GEOPHYSICS (SEISMOLOGY) Flashcards

1
Q

Seismlogy caused by NATURAL SEISMIC WAVE of EQUAKES and derives infor on physical properties, composition and the gross internal structure of Earth

A

Equake Seismology

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2
Q

Waves are caused by artificial balsts such as detonating explosives on land and non explosive vibroseis or compressed air (Marine) at selected sites to infer info about regional/local structures

A

Explosion Seismology

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3
Q

Main purpose

A

?Interpret the interfaces of rock boundaries
?Layered sed Sequence
?Location of Watertable
?Oil and Gas Exploration

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4
Q

Main premise of the survey

A

Waves are propagated to travel in rock media and which the subsurface is assumed to be homogenous and isotropic to simplify wave propagatig resulting in interpretato of the measured effect at the plane of discontnuity

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5
Q

Strain that causes change in shape

A

Shear or distortional strain

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6
Q

Strain that changes the volume without change in shape

A

Dilataion or Contraction

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7
Q

The ratio between longitudinal stress and longitudinal strain

A

E Young’s Modulus

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8
Q

The ratio of Uniform compressive stress to fractional change in Volume

A

K Bulk Modulus

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9
Q

the measure of the stress/strain in the case of simple tangential shear

A

u Rigiity stress

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10
Q

measure of the geometrical change in the shape of a clastic body or the compressibility of a material

A

Poissons Ratio

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11
Q

Fastest of all seismic waves
longitudinal
Travels to all media (S,L,G)
Propagate by compressional and dilational uniaxial strain (Forward backward) or alterate compression and dilation)

A

Pwaves, compressonal

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12
Q

Transverse waves which VIBRATE about their fixed mean position in a plane PERPENDICULAR to the direction of wave propagatio (Up down)
Slower than P waves
Cannot travel thrugh the outer core because they cannot exist in fluids (Air, Water, and Molten Rock)

A

S waves, shear

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13
Q

Formed when particle motion is a combination of both longitudinal and transverse vibration thus giving an ELLIPTICAL RETROGRADE MOTION (CCW) in the vertical plane along the direction of travel

A

Rayleigh Waves

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14
Q

Major type of surface wave having a horizontal motion that is shear or transverse/Perpendicular to the direction of the propagation

A

Love Waves

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15
Q

Velocity or progpagation is equal to?

A

Elastic Moduli and densities

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16
Q

Velocity of P wave

A

Square root (4/3 Shear Modulus + Bulk Modulus)/Density)

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17
Q

Velocity of S wave

A

Square root of shear modulus / density

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18
Q

What is being measured of waves as they return after rfraction or reflection

A

Travel times

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19
Q

Variation of velocity with density

A

The higher the density the higher the velocity

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20
Q

Which will travel faster P or S?

A

P

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21
Q

Rocks with best linera relationship between velocity and densiy

A

Sed Rocks (Isipin mo na lang na lagi syang ginagamit sa petroleum kaya sed rocks

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22
Q

Rocks with velocities that increase with depth of burial and with age

A

Sandstone and shale (The more the burial, the denser the rocks, the higher the velocity)

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23
Q

Porosity and weathering effect on seismic velocity

A

The higher the porosity and weathering, the lower the velocity since density decreases

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24
Q

Materials in increasing Vp (Basic-Acidic Ign, Coarse to Fine grained Met, Sed Rocks)

A

Gabbro
Iron
Granite
Gneiss
Slate
Sandstone limestone
Water

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25
Q

In reflection, angle of incidence is equal to

A

Angle of refraction

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26
Q

In refraction, angle of incidence

A

Snells law
Sin I / Sin R = V1/V2

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27
Q

A particular angle of incidence when velocity is higher in the underlying layer for which angle of refraction is at 90 deg and which gives rise to critically refracted ray that travales along the interface at higher velocity

A

Critical Angle

28
Q

Th perturbation caused by the passage of the critically refracted ray along the top of the lower layer which travels at velocity which is higher than that of the upper layer

A

Headwave

29
Q

P wave velocity as a function of time

A

P = 1.47 [Depth (km) T (Age in Ma)]^1/6

30
Q

Detonated in shallow holes of 6-30m and has a depth of over 10m

A

Explosives

31
Q

Non explsisve source that uses COMPRESSED AIR which is release in the form of HIGH PRESSURE BUBBLES

A

Air Gun

32
Q

Truck mounted Vribrator which punds 50k-60K output

A

Vibroseis

33
Q

Other Non explosive seismic sources

A

Weight Drop
Hammer
Actual Earthquake
Shotgun, Rifles
Bufallo Gun

34
Q

A marine seismic source which uses explosive mixture of gases instead of High pressure ubbles

A

Water Guns

35
Q

Devices that converts electrical energy into acoustic energy and which the pulse is generated by the discharge of a large capacitor bank directly into the sea waters

A

Sparkers

36
Q

A rigid aluminum plate attached below heavy duty electrical coil by a spring loaded mounting typically towed behind survey vessel in a catamaran mounting

A

Boomers

37
Q

Small ceramic piezoelectric transducers mounted in a towing fish w/c when activated by electrical impulse will emit a very short, high frequencey acoustic pulses of low energy

A

Pingers

38
Q

Electro mechanical transducers that produce an extended repeatable source wave form w/c allows greater energy outpur

A

Chirps

39
Q

Converts ground motion to electrical signal

A

Transducers

40
Q

Devices used on land to detect seismic ground motions

A

Geophones or Seismometers

41
Q

Most common seismometer

A

Moving Coil Geophone

42
Q

Used to detect passage of compreesonal seismic waves marked by transcent pressire canges in sea waeter

A

Hydrophones

43
Q

Siesmic Wave Recorders

A

Seismographs

44
Q

Any vibration which is not part of the signal

A

Noise

45
Q

A noise generated by the shot itself like swaves, surface waves and reflections from near surface irregularities

A

Coherent Noise

46
Q

Noise not generate by the shot itself such as traffic, livestock, pople that can be controlled

A

Random Noise

47
Q

Most widely sed technique and well known geophysical technique that aborb more than 90% money spent worldwide on applie geophysics

Carried out in areas with SHALLOW DIPPING SED SEQUENCES

A

Reflection Surveys

48
Q

What is the vertical scale of a seismic reflection profile?

A

Time not depth

49
Q

Limitations

A

Costly
Computer intensvive w/c requires super computers
Data processing is tedious

50
Q

Seismic survey that utilizies seismic energy that returns to the surface after traveling through a ground along refracted ray paths

A

Siesmic Refraction Survey

51
Q

if Vlayer 1>V layer 2

A

Use snells Law

52
Q

if Vlayer 2>V layer 1

A

Sin Critical Angle = V1/V2

53
Q

Ray that travels along a straight line through the top of the upper layer from source to detector at velocity V1

A

Direct Ray

54
Q

Obliquely incident to the interface and is reflected back through the top layer to the detector travalling along its entire path to top with layer velocy V1

A

Reflected Ray

55
Q

Travels obliquiley down to the interface at velocity V1 then along the segment of the interface at V2 and back up through the upper layer at V1

A

Refracted Ray

56
Q

The distance at which the refracte ray overtakes the direct ray

A

Cross over distance

57
Q

The distance at which the travel tmes of the reflected and refracte rays coincid because they follo the same path

A

Critical distance

58
Q

First arrivals at the critical distance

A

Direct Rays

59
Q

First arrivals at the cross voer distance

A

Refracted Ray

60
Q

Minimum line length of refraction

A

10x of depth of horizon of interest

61
Q

Reflection line length

A

Same order as reflctor depth of interest (Equal lang)

62
Q

Differentiate Spread and Array

A

Spread pertains to a line of geophones laid out for a refraction survey while array is reserved for geophone feeing a single recording channel

63
Q

Mining and Econ Geol

A

Hydrocarbons (offshore and onshore)

64
Q

Structural

A

High Res studies of Shallow Geology (Quat Sed Sequence, Bedrock Mapping)
Crustal and lithospheric studies

65
Q

Structural

A

Regional Investiogation of internal structure and thickess of crust

66
Q

Hydrogeol

A

Exploration for Underground water supplies in sed sequences w/ ER

67
Q

Environmental and Engg

A

Foundation studies to map bedrock surfaces
Estimation of bulk and shear moduli from P and S Waves

GLE 2024 (Day 3) (48 decks)

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