Earthquakes - SEISMIC WAVES AND PLATE TECTONICS Flashcards by J Shane

three basic types of stress that are acted upon on rocks for them to deform

compression; tension; shear

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it is a type of stress that pushes on rocks from opposite directions which causes rocks to be shortened parallel to the stress applied

compressional stress

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a type of stress that pulls rocks from opposite direction, resulting it to become stretched/lengthened

tensional stress

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occurs when rocks are being pushed in an uneven manner, causing the rocks to be skewed

shear

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in a shear stress, different sides of a rock body slide or move in ______ directions

opposite

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rocks near the surface of the earth are ____

elastic

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when a force (stress) acted on rock is removed, they will ____

return to their original shape

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t or f: all elastic materials have elastic limit

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the point in which materials no longer behave elastically and deformation becomes permanent

elastic limit

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a fracture plane where rocks slide past one another

fault

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t or f: all faults involve slippage while fractures do not

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what type of fault is north bohol fault?

reverse fault with minor right and left lateral displacement

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which direction of displacement is more dominant in NBF?

right lateral displacement

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when was bohol earthquake and what magnitude

October 15, 2013, Mag 7.2

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thrust faults are low angle reverse fault with what angle according to phivolcs?

<30 degrees

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where is the surface manifestations of NBF be found?

Brgy. Anonang, Inabanga, Bohol

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how high was the vertical displacement of the NBF? and what is it composed of?

1-2m high ; it was an uplifted marine platform

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when was the Luzon 1990 earthquake and what magnitude was it?

July 16, 1990 ; Mag 7.8

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how long was the surface rupture during the Luzon 1990 earthquake? in what location does it extend from and to?

125 km-long ; from Dingalan, Aurora to Kayapa, Nueva Viscaya

(Imugan, Nueva Viscaya yung may rice paddies na na displace)

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what caused 1990 Luzon earthquake?

movement of the NW portion of the PFZ and it splay, the Digdig Fault

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how long is the PFZ and what is its estimated age?

1,200 km-long ; less than 5 mya

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slip rate of the PFZ

approx 2-2.5 cm/yr

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t or f: the PFZ and Digdig fault are both sinistral type of strike-slip fault

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t or f: the Luzon 1990 earthquake was linked to the succeeding 1991 Mt. Pinatubo Eruption

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a scotting geologist who systematized the knowledge on the geometry and stress fields of various faults

Ernest Masson Anderson

the direction of maximum principal stress along normal fault is:

vertical downward

the direction of maximum principal stress along reverse fault is:

horizontal

the direction of maximum principal stress along strike-slip fault is:

horizontal, depending on the direction of the displacement

a weathered fault scarp is called a ____

fault line scarp

what is a transpressional fault

compression and strike-slip

what is a transtensional fault

tensional and strike-slip

seismic waves may be _____, _____, or _____ in origin

tectonic, magmatic, or artificial

refers to vibrational waves that travel through earth's materials

seismic waves

two general types of seismic waves

body waves ; surface waves

two types of body waves:

primary waves ; secondary waves

this type of wave travel through the earth's interior and radiates outward a hypocenter in all directions

Body wave

primary waves have _______ movement that is ____ to the direction that the wave is travelling

compressional ; parallel

transverse/perpendicular to the direction of wave propagation

secondary waves (s-waves)

travels on the earth's surface away from the epicenter

surface waves

surface wave is ____ slower than secondary waves

10%

two types of surface waves

rayleigh and love waves

also known as ground roll, spread to the ground as ripples, similar to rolling waves in the ocean

rayleigh waves

rayleigh waves move both ___ and ____ in a ____ plane

vertically and horizontally ; vertical plane

love waves move the ground from ____ in a _____ plane but at _____ to the direction of propagation

side to side ; horizontal plane ; right angles

velocity of primary waves

4-7 km/sec

velocity of secondary waves

2-5 km/sec

it is a type of wave that can only travel through solids

secondary (s) waves

a type of wave that is particularly damaging to the foundation of the structure

love waves

the instrument used to detect seismic waves

seismometer

a seismometer makes use of a _____ held as motionless as possible, suspended by ____ or hanging it as a ______

heavy suspended mass ; springs ; pendulum

the ____ of the heavy mass in a seismometer keeps it from moving and act as a _____ in determining the amount of ________

inertia ; point of reference ; ground motion

t or f: a seismometer determine the amount of ground motion as well as records it

F (does not record)

a seismometer with a recording device that produces a permanent record of the earth motion

seismograph

the paper record of the earth vibration

seismogram

T or F: seismic waves arrive at seismic station in this order: P waves ; S waves ; Surface waves

analysis of the seismograms can reveal the _____ and ____ of the earthquake

location ; strength

t or f: the longer the time of arrival interval between p and s waves, the greater the distance the seismograph is from the epicenter

P and S waves start out from the _____, as they travel they gradually ____ because of their ______

hypocenter ; separate ; different speeds

t or f: a single seismograph can record only the distance but not the direction to an earthquake

in triangulation method, seismograph stations are the _____ and the corresponding distances from the earthquake is the ______

centers ; radii

classification of earthquake based on depth

shallow - 0 to 70km intermediate - 70-350 km deep - 350-670 km

how were the major layers of the earth inferred?

through seismic waves and discontinuities of the earth

it is the property of the mantle in which the seismic waves aren't in uniform velocity because of the alignment of iron minerals

seismic anisotropy

deformation corresponding to change in shape

distortion

deformation corresponding to change in volume

dilation

the maximum amount of strain a material can accumulate before fracturing or undergoing plastic deformation

elastic limit

brittle materials deform by

fracturing

ductile materials deform by

plastic deformation

earthquake is defines as:

shaking or trembling of the ground caused by the sudden release of energy stored in rocks beneath the erath's surface

two types of earthquake

volcanic ; tectonic

earthquakes caused by volcanic activities

volcanic earthquakes

earthquakes caused by the movement of rocks past one another along faults

tectonic earthquakes

refers to the theory that explains the occurrence of earthquakes

elastic rebound theory

elastic rebound theory is based on the relationship between

stress and strain, and the deformation of rocks

strain released when a material reaches elastic limit is transformed into

vibrational wave energy

the release of energy begins at the point called the _____

focus / hypocenter

the point of surface directly above the hypocenter

epicenter

at what depth earthquakes can no longer occur

435 miles (700 km)

redistribution of strain commonly produces a series of smaller earthquakes called

aftershocks

t or f: aftershocks may continue for days or weeks

the primary earthquake is sometimes called the

main shock

t or f: fore shocks are only considered to be fore shocks right after the main shock happen

cotabato fault system is a _____ type of fault

strike-slip

cotabato series earthquakes

oct 16 - Mag 6.3 oct 29 - Mag 6.6 and 6.1 oct 31 - Mag 6.5

rocks are much stronger under a ______ force compared to _____ force

compressional ; tensional

t or f: at convergent boundaries, where compressive forces dominate, rocks accumulate less strain

F (rocks accumulate more strain)

at divergent boundaries, tensional forces are dominant over ______

frictional forces

the other key factor in the ability of a rock body to store strain is the _________

frictional resistance of the faults

t or f: high frictional resistance of fault generate larger earthquakes

a process where faults slip continuously because of low frictional resistance

fault creep

t or f: when a rock body experiences fault creep, it can build up more strain therefore generating larger earthquake

FALSE (it cannot build up high amount of strain, therefore cannot generate large earthquakes)

what kind of fault is the San Andreas fault

dextral transform fault

it is a network of interlocking faults on either side of a main fault

fault zone

small branches of larger fault

SPLAY

strain relieved along one fault can disrupt the ________ within the fault zone, triggering additional earthquakes

delicate balance of relationships

planar zone of seismicity corresponding with the down-going slab of a subduction zone

Wadati-Benioff zone

in Northern California, where the San Andreas fault moves offshore the boundary of the _______, it changes from a ______ setting to ______

North American Plate ; transform (shear) ; convergence (compression)

the ________ starts to override a series of relatively small oceanic plates along what geologist call the _______

North American Plate ; Cascadia Subduction Zone

Cascadia subduction zone produces volcanic arcs known as the _______, it also generates _______

Cascade Mountain Range ; subduction zone earthquakes

subduction zone earthquakes are formed when

an oceanic plate is overridden by another plate

t or f: subduction zones generate extremely powerful and devastating earthquakes

of the ten largest earthquake ever recorded, how many was subduction zone earthquakes? how many were more than a magnitude of 9?

9 subduction zone earthquakes ; 4 of those having a magnitude of greater than 9

four factors why subduction zone earthquakes are stronger

1. overriding plates buckle and becomes locked 2. greater slippage or rupture surface area 3. oceanic plates descend and cool down, making them brittle 4. tsunami up to 100 feet (30m)

when was the last major earthquake to occur in cascadia subduction zone?

1700

earthquakes that occur far from a plate boundary or active mountain belts are generally called

intraplate earthquakes

how are intraplate earthquakes formed?

tectonic forces travel through rigid bodies into the interior of the earth, in which strain are accumulated and eventually released along buried fault systems

of considerable interest in the US are the _____ and _____ seismic zones because they have a history of producing powerful intraplate earthquake

Charleston and New Madrid