GEOPHYSICS (SEISMOLOGY)

Question 1

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

Answer 1

Equake Seismology

Question 2

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

Answer 2

Explosion Seismology

Question 3

Main purpose

Answer 3

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

Question 4

Main premise of the survey

Answer 4

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

Question 5

Strain that causes change in shape

Answer 5

Shear or distortional strain

Question 6

Strain that changes the volume without change in shape

Answer 6

Dilataion or Contraction

Question 7

The ratio between longitudinal stress and longitudinal strain

Answer 7

E Young’s Modulus

Question 8

The ratio of Uniform compressive stress to fractional change in Volume

Answer 8

K Bulk Modulus

Question 9

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

Answer 9

u Rigiity stress

Question 10

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

Answer 10

Poissons Ratio

Question 11

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)

Answer 11

Pwaves, compressonal

Question 12

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)

Answer 12

S waves, shear

Question 13

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

Answer 13

Rayleigh Waves

Question 14

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

Answer 14

Love Waves

Question 15

Velocity or progpagation is equal to?

Answer 15

Elastic Moduli and densities

Question 16

Velocity of P wave

Answer 16

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

Question 17

Velocity of S wave

Answer 17

Square root of shear modulus / density

Question 18

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

Answer 18

Travel times

Question 19

Variation of velocity with density

Answer 19

The higher the density the higher the velocity

Question 20

Which will travel faster P or S?

Answer 20

P

Question 21

Rocks with best linera relationship between velocity and densiy

Answer 21

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

Question 22

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

Answer 22

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

Question 23

Porosity and weathering effect on seismic velocity

Answer 23

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

Question 24

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

Answer 24

Gabbro
Iron
Granite
Gneiss
Slate
Sandstone limestone
Water

Question 25

In reflection, angle of incidence is equal to

Answer 25

Angle of refraction

Question 26

In refraction, angle of incidence

Answer 26

Snells law Sin I / Sin R = V1/V2

Question 27

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

Answer 27

Critical Angle

Question 28

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

Answer 28

Headwave

Question 29

P wave velocity as a function of time

Answer 29

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

Question 30

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

Answer 30

Explosives

Question 31

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

Answer 31

Air Gun

Question 32

Truck mounted Vribrator which punds 50k-60K output

Answer 32

Vibroseis

Question 33

Other Non explosive seismic sources

Answer 33

Weight Drop Hammer Actual Earthquake Shotgun, Rifles Bufallo Gun

Question 34

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

Answer 34

Water Guns

Question 35

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

Answer 35

Sparkers

Question 36

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

Answer 36

Boomers

Question 37

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

Answer 37

Pingers

Question 38

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

Answer 38

Chirps

Question 39

Converts ground motion to electrical signal

Answer 39

Transducers

Question 40

Devices used on land to detect seismic ground motions

Answer 40

Geophones or Seismometers

Question 41

Most common seismometer

Answer 41

Moving Coil Geophone

Question 42

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

Answer 42

Hydrophones

Question 43

Siesmic Wave Recorders

Answer 43

Seismographs

Question 44

Any vibration which is not part of the signal

Answer 44

Noise

Question 45

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

Answer 45

Coherent Noise

Question 46

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

Answer 46

Random Noise

Question 47

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

Answer 47

Reflection Surveys

Question 48

What is the vertical scale of a seismic reflection profile?

Answer 48

Time not depth

Question 49

Limitations

Answer 49

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

Question 50

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

Answer 50

Siesmic Refraction Survey

Question 51

if Vlayer 1>V layer 2

Answer 51

Use snells Law

Question 52

if Vlayer 2>V layer 1

Answer 52

Sin Critical Angle = V1/V2

Question 53

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

Answer 53

Direct Ray

Question 54

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

Answer 54

Reflected Ray

Question 55

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

Answer 55

Refracted Ray

Question 56

The distance at which the refracte ray overtakes the direct ray

Answer 56

Cross over distance

Question 57

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

Answer 57

Critical distance

Question 58

First arrivals at the critical distance

Answer 58

Direct Rays

Question 59

First arrivals at the cross voer distance

Answer 59

Refracted Ray

Question 60

Minimum line length of refraction

Answer 60

10x of depth of horizon of interest

Question 61

Reflection line length

Answer 61

Same order as reflctor depth of interest (Equal lang)

Question 62

Differentiate Spread and Array

Answer 62

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

Question 63

Mining and Econ Geol

Answer 63

Hydrocarbons (offshore and onshore)

Question 64

Structural

Answer 64

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

Question 65

Structural

Answer 65

Regional Investiogation of internal structure and thickess of crust

Question 66

Hydrogeol

Answer 66

Exploration for Underground water supplies in sed sequences w/ ER

Question 67

Environmental and Engg

Answer 67

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