EARTHQUAKES AND RELATED HAZARD Flashcards
is defined as a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath the earth’s surface.
earthquake
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
rocks are also considered to be _____, meaning that if the force (stress) is removed they will return to their original shape
elastic
brittle materials reach their elastic limit they undergo permanent deformation by _____, whereas ductile materials deform by ______
fracturing; flowing plastically
Two types of Earthquake
Volcanic and Tectonic
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 _____
earthquake
The release of energy generally begins at a point called the _____ whereas the point on the earth’s surface directly above the hypocenter is termed as ______.
focus/hypocenter; epicenter
When rocks become more ductile (less brittle) they tend to accumulate less strain, and instead undergo _____.
plastic deformation
why can’t earthquakes happen below 700 km the surface?
the higher temperatures cause the rocks to become so ductile that they deform only by plastic flow, hence do not rupture
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
- refer to vibrational waves that travel through solid earth materials which may be magmatic, tectonic, or artificial in origin.
seismic waves
two types of seismic waves
Body waves and surface waves
Body waves are subdivided into…
o Primary (P)-Waves
o Secondary (S)-Waves
travel trough the earth’s interior, spreading outward from the hypocenter in all directions (like sound in air). It is subdivided into;
body waves
- travel on the earth’s surface away from the epicenter (like ripples on water); slowest wave (typically at a speed that is 10% slower than S-waves), can cause more property damage compared to body waves.
surface waves
compressional waves; parallel to direction the wave is travelling, causing rocks to alternately compress and decompress as successive waves pass through
p-waves
transverse/ perpendicular to direction of wave propagation
s-waves
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 waves
Very fast at speeds of 4 to 7 km/sec; first wave to arrive at a station; can pass through solid and liquid
p-wave
Slow, at 2-5 km/sec; Arrives at a later time than P-wave does; Can pass through solid but not liquid
s-waves
– 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
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 ______ the time, the greater the distance is.
longer
The interval of arrival between S and P waves is used to calculate the _____ of the seismograph station from the earthquake source
distance
The intersection of the ____ pinpoints the location of the earthquake.
three circles
The depth of focus is determined in a similar procedure, and is used to classify earthquakes as:
- Shallow – 0-70 km
- Intermediate – 70-350 km
- Deep – 350-670 km
they measure the strength of the earthquakes by its
intensity
In 1902 an Italian seismologist named_______ developed a means of comparing both modern and historical earthquakes through the use of firsthand human observations during earthquakes.
Giuseppe Mercalli
earthquakes are ranked based on a set of observations most humans could report objectively, particularly the type of damage sustained by buildings I to XII
the 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
PHIVOLCS Earthquake Intensity Scale (PEIS)
PIES was developed as a response to the ________ (magnitude ___) and was adopted in the Philippines in 1996
1990 Luzon Earthquake ; 7.7
one of the first seismic scales developed by Michele Stefano de Rossi and Francois-Alphonse Forel in the late 19th century, to reflect earthquake intensities and was used for about two decades by some countries until the introduction of the Mercalli Intensity Scale in 1902.
Rossi-Forel Intensity Scale
Intensity scale of PEIS ranges from
I to X
magnitude scales are useful because they _____ the amount of ground motion during an earthquake, and the energy that was released when the rocks ruptured
quantify
rates earthquakes based on the size of their seismic waves, as measured by seismographs; governed by amplitude (wave height) and distance
Richter Magnitude Scale
based on similar types of seismogram measurements as Richter’s, but is more accurate over a wide range of magnitudes and geologic conditions; based on the total amount of energy released and is determined by measuring the surface area of the ruptured fault and how far the land moved along the fault
Moment Magnitude Scale
- Although a unit increase on the magnitude scale represents a 10-fold increase in ground motion, this corresponds to about a __-fold increase in energy released at the focus—recall that the release of stored elastic energy is what causes the shaking in the first place
30
two largest earthquake in san francisco area
1989 Loma Prieta earthquake and the great earthquake of 1906
calculate the difference in ground motion of EQ 1 with magnitude 7.8 and EQ 2 with magnitude 6.9
8x
An earthquake’s Richter’s rating and moment magnitude rating are always the same. true or false
false
Earthquakes are also divided into several classes based on their magnitude; a class with Major earthquake have ____ magnitude
7.0 to 7.9
what are the 8 classes of earthquales (based on their magnitude) rank from strongest to weakest (with magnitude)
Great - 8.0 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
rocks are much ____ under a compressional force compared to a tensional force
stronger
at convergent boundaries where compressive forces dominate, rocks are able to accumulate much more ____ before rupturing than at divergent boundaries where tensional forces are dominant
strain
- The other key factor in the ability of a rock body to store strain is the ___ of the faults
frictional resistance
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
San Andreas Fault is a ________transform fault that separates the Pacific and North American Plates.
right-lateral (dextral)
In ______where the San Andreas fault moves offshore the boundary of the North American plate changes from a transform (shear) setting to one of convergence (compression).
northern California
an earthquake that forms when an oceanic plate is overridden by another plate
subduction zone earthquakes
reason subduction zone earthquakes are capable of releasing unusually large amounts of energy is partly due to
(1) the way the overriding plate buckles and becomes locked.
(2) the surface area over which the slippage or rupture occurs can be quite large compared to that in other plate settings.
(3) the descending oceanic plate is relatively cool, which makes the rocks more brittle and capable of accumulating more strain before rupturing.
(4) some of this energy can be transferred to the ocean, creating tsunamis that reach heights of 100 feet (30 m) as they crash into coastal areas.
earthquakes that occur far from a plate boundary or active mountain belt and are generally believed to be related to tectonic forces that are being transmitted through the rigid plates.
Intraplate Earthquakes
example of a intraplate earthquake
1976 Tangshan disaster (7.5)
___, is the leading cause of death and property damage in most earthquakes
failure of buildings and other manmade structures
engineers design a structure they take into account the fact that the structure must be able to withstand a range of different forces, with ___ being the most important.
GRAVITY
surface waves are the most destructive due to the fact they cause the ground to vibrate in a _____direction, and at the same time, roll up and down like an ocean wave
lateral
Once a floor becomes free, it naturally falls onto the one below, which can cause additional floors to fail in a cascading manner that engineers call ____
pancaking
Another important type of structural failure in earthquakes is the sudden ______
rupture of steel reinforced concrete columns
refers to the vibration of a structure/building at a fixed frequency
Natural vibration frequency
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
the most dangerous earthquakes tend to be those with a combination of ____ magnitude and ___ focal depth
large; shallow
Seismic waves experience different amounts of wave attenuation, depending on the types of geologic materials the waves pass through. true or false?
true
Loose materials and rocks of lower density will absorb more energy from passing seismic waves compared to rocks that are ____rigid and dense
more
areas of rigid rocks, seismic waves are able to retain more of their energy as they travel farther. Because the waves undergo ____attenuation, they therefore have the potential to cause damage farther from the focus
less
what earthquake wherein seismic waves from these earthquakes were able to retain enough energy to ring church bells as far as way as Boston, Massachusetts due to the rigid rocks throughout this region
8 mag earthquake, New Madrid
When seismic waves travel through weaker materials, they slow down and lose energy at a faster rate. causes wave amplitude to increase, creating a phenomenon known as
Ground Amplification
SECONDARY EARTHQUAKE HAZARDS
fires, landslides, and saturated ground that suddenly turns into a liquid (liquefaction)
the displacement of lithospheric plates along subduction zones can generate devastating ___
tsunamis
compacted sand-rich layers of sediment that are normally in contact with one another behave as fluid
Liquefaction
The increased water pressure within the saturated sediment can also cause geysers of liquefied sand to erupt onto the surface, creating what are called
sand blows
rocks on either side of a fault move way from each other horizontally and/or vertically.
Ground displacement
are large open cracks that typically develop close to the surface in loose sediment where there is little resistance to the rolling and stretching motion associated with surface waves
ground fissures
earthquakes provide one of the basic triggering mechanisms for the downslope movement of earth materials due to gravity such as landslide (debris slump), rock falls, and mudflows.
Earthquake-induced mass wasting
underground gas lines are easily broken when surface waves roll through a city and are likely to be ignited by sparks from countless electrical shorts in damaged buildings and downed power lines
fire
a series of ocean waves that form when energy is suddenly transferred to the water by an earthquake, volcanic eruption, landslide, or asteroid impact.
tsunami
EARTHQUAKE PRECURSORS
- Increase in foreshocks
- Slight swelling or tilting of the ground surface
- Decreased electrical resistance
- Fluctuating water levels in wells
- Increased concentration of radon gas in groundwater
- Generation of radio signals
Sections of an active fault where strain has not been released for an extended period of time are called _____ which can be useful in predicting what areas are most likely to experience a large earthquake.
seismic gaps
3 ways of reducing Earthquake risk
- Seismic Engineering
- Early Warning Systems
- Planning and Education
