Earthquakes - SEISMIC WAVES AND PLATE TECTONICS Flashcards
three basic types of stress that are acted upon on rocks for them to deform
compression; tension; shear
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
a type of stress that pulls rocks from opposite direction, resulting it to become stretched/lengthened
tensional stress
occurs when rocks are being pushed in an uneven manner, causing the rocks to be skewed
shear
in a shear stress, different sides of a rock body slide or move in ______ directions
opposite
rocks near the surface of the earth are ____
elastic
when a force (stress) acted on rock is removed, they will ____
return to their original shape
t or f: all elastic materials have elastic limit
T
the point in which materials no longer behave elastically and deformation becomes permanent
elastic limit
a fracture plane where rocks slide past one another
fault
t or f: all faults involve slippage while fractures do not
T
what type of fault is north bohol fault?
reverse fault with minor right and left lateral displacement
which direction of displacement is more dominant in NBF?
right lateral displacement
when was bohol earthquake and what magnitude
October 15, 2013, Mag 7.2
thrust faults are low angle reverse fault with what angle according to phivolcs?
<30 degrees
where is the surface manifestations of NBF be found?
Brgy. Anonang, Inabanga, Bohol
how high was the vertical displacement of the NBF? and what is it composed of?
1-2m high ; it was an uplifted marine platform
when was the Luzon 1990 earthquake and what magnitude was it?
July 16, 1990 ; Mag 7.8
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)
what caused 1990 Luzon earthquake?
movement of the NW portion of the PFZ and it splay, the Digdig Fault
how long is the PFZ and what is its estimated age?
1,200 km-long ; less than 5 mya
slip rate of the PFZ
approx 2-2.5 cm/yr
t or f: the PFZ and Digdig fault are both sinistral type of strike-slip fault
T
t or f: the Luzon 1990 earthquake was linked to the succeeding 1991 Mt. Pinatubo Eruption
T
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
T
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
T
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
T
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
T
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
T
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
T
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
T
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
- overriding plates buckle and becomes locked
- greater slippage or rupture surface area
- oceanic plates descend and cool down, making them brittle
- 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
