EARTHQUAKE Flashcards
For rocks to be deformed, they must be acted upon by stress
which can be classified into three (3) basic types; what are the 3 basic types?
Compression, Tension, Shear
pushes on rocks from opposite
directions which causes rocks to be shortened parallel to the stress applied
Compression
pulls rocks from opposite directions, resulting it to become stretched/lengthened
Tension
occurs when rocks are being pushed in an uneven manner, causing the rocks to be skewed
such that different sides of a rock body slide or move in opposite directions
shear
true or false? rock near the surface of the earth are elastic?
true
what is rock elasticity?
when a force
(stress) that is acting on
them is removed, the
rocks will return to their
original shape
what is elastic limit?
the point in which they no longer behave elastically and deformation becomes permanent
when rocks deform they often slide past one another along a fracture plane, the fracture is called?
fault
refer to vibrational waves that travel through solid earth
materials which may be magmatic, tectonic, or artificial in origin.
seismic waves
what are the two types of seismic waves? differentiate.
Body waves; travel trough the earth’s interior, spreading
outward from the hypocenter in all directions and surface waves; travel on the earth’s surface away from the
epicenter (like ripples on water); slowest wave
compressional waves; parallel
to direction the wave is travelling, causing rocks to
alternately compress and decompress as successive
waves pass through.
primary waves
type of body wave that transverse/ perpendicular
to direction of wave propagation
secondary wave
also known as ground roll, spread to the ground as ripples, similar to rolling waves on the ocean; move both vertically and horizontally in
a vertical plane pointed in the direction in which the
wave is travelling;
rayleigh waves
move the ground from side to side in a horizontal plane but at right angles to the direction
of propagation
love wave
the instrument used to detect
seismic waves
seismometer
a seismometer with a recording device that
produces a permanent record of earth motion, usually in the
form of wiggly line drawn on a moving strip of paper
seismograph
the paper record of earth vibration
seismogram
how do they locate earthquakes
- P and S waves start out from the hypocenter.
- As they travel, they gradually separate because of
their different speeds. - The interval of the time of arrival between P and S
waves increases with increasing distance of the
seismic stations from the focus and epicenter; the
longer the time, the greater the distance is.
true or false? The interval of arrival between S and P waves is used to calculate the distance of the seismograph station from the earthquake source.
true
how deep is shallow, intermediate and deep in classifying earthquakes?
- Shallow – 0.70 km
- Intermediate – 70-350 km
- Deep – 350-670 km
How were the major layers of Earth inferred?
through seismic method
when rocks are subjected under a force, also called
_____, they can become deformed and have a
corresponding change in their shape (distortion) or
volume (dilation), a process known as ______.
stress; strain
two types of earthquake? explain how this occur.
volcanic and tectonic earthquake
Based on the relationship between stress and strain
and the deformation of rocks, earth scientists have developed the ________________ that explains the occurrence of earthquakes.
elastic rebound theory
vibrational wave energy that
radiates outward and causes the ground to shake in
what is called an _____
earthquake
The release of energy generally begins at a point
called the focus/hypocenter whereas the point on
the earth’s surface directly above the hypocenter is
termed as _____
epicenter
This redistribution of strain
commonly produces a series of smaller earthquakes called ________, which may continue to occur for days or weeks after the primary earthquake, sometimes called the _____
aftershocks; main shock
In areas where tensional forces dominate the friction along faults is naturally low, allowing them to slip in an almost continuous process known as _________
fault creep.
It is often referred to as a _______ due to the network of interlocking faults located on either side.
fault zone
earthquake that forms when an oceanic plate is overridden by another plate
subduction zone earthquakes
Factors that affect Ground Shaking
- period, Natural Vibration Frequency, and
Resonance - Focal Depth and Wave Attenuation
- Ground Amplification
true or false “Smaller structure take shorter time to vibrate back and forth than larger structures”
true
Natural Vibration Frequency
refers to the vibration of a structure/building at a fixed
frequency; frequency is the number of times the motion is
repeated in a set amount of time.
The matching of frequency then leads to the phenomenon called _______, whereby the amplitudes of the individual waves combine
resonance
energy of the resulting seismic waves steadily decreases as they travel away from the focus, a process referred to as
________.
wave attenuation
what is ground amplification
When seismic waves
travel through weaker
materials, they slow down and
lose energy at a faster rate.
This, in turn, causes wave
amplitude to increase, creating
a phenomenon known as
ground amplification.
name secondary earthquake hazards
liquefaction
ground displacement
ground fissures
earthquake-induced mass wasting
fires
tsunamis
Who is the Italian seismologist who developed a means of comparing both modern and historical earthquakes through the use of firsthand human observations during
earthquakes? what is this called?
Giuseppe Mercalli; Mercalli Intensity scale
is a seismic scale used and developed by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) to measure the intensity of an earthquake.
PHILIPPINE EARTHQUAKE INTENSITY SCALE (PEIS)
Intensity scale ranges from ______.
I to X
they quantify the amount of ground motion during an earthquake and the energy that was released when the rocks ruptured.
Magnitude scales
Differentiate Moment Magnitude scale and Ritcher Magnitude scale?
Richter Scale is mostly effective for regional earthquakes no greater than M5. Moment Magnitude is more effective for large earthquakes Moment Magnitude uses more variables to calculate the energy released using seismic moment. Seismic moment combines the seismic energy with offset on the fault and rigidity of rock.
what are the classes of earthquakes based on their magnitude?
Great - 8 or more
Major - 7.0-7.9
Strong - 6.0-6.9
Moderate 5.0-5.9
Light - 4.0-4.9
Minor 2.0-3.9
Microearthquake 1.0-1.9
A Method of assessing earthquake where it is based mainly on the knowledge of
when and where earthquakes occurred in the past
long-term forecasting
study of prehistoric earthquakes
paleoseismology
a zone along a tectonically
active area where no
earthquakes have occurred
recently, but it is known that
elastic strain is building in
the rocks.
seismic gap
involves monitoring of processes
that occur in the vicinity of earthquake prone faults for activity that signify a coming earthquake.
short-term prediction
Anomalous events or processes that may precede an earthquake are called _________and might signal a coming earthquake
precursor events
Earthquake precursors
- increase in foreshocks
- slight swelling/uplift or tilting of the ground surface
- decreases electrical resistance
- Fluctuating water levels in wells
- increased concentration if radon gas in groundwater
- generation of radio signals
3 examples of non-conventional / intrusive methods
- Microtremor survey method
- Refraction Microtremor Method
- Horizontal-to-Vertical Spectral Ration Method
Reducing Earthquake Risks
Seismic engineering
Early warning systems
planning and education
earthquake control?
How long is the Philippine Fault?
1200-1250 km
Thrust Fault vs Reverse Fault
- Thrust Fault
o usually less than 45 degrees
o PHIVOLCS - <30o - Reverse Fault
o Steeper
▪ >45/30o
- a planar zone of seismicity corresponding with the down-going slab in a subduction zone
Wadati–Benioff zone
