Download Earthquake Cornell Notes

Cues
Pages 162-181in your
textbook.
Earthquake Notes
Stress in Earth's Crust
Name the 3 types of force
and what kind of fault they
produce.
Faults in Earth's crust are caused by these same tectonic
forces:
1) tension – stretches a body and pulls it apart, located at
divergent plate boundaries, and creates a Normal fault. Ex.
rift valley (The Basin-and-Range province of Nevada, Utah,
and eastern Oregon is a region of strong extension that has
many normal faults cutting the crust, making fault-bounded
mountains and basins.)
2) compression - squeezes material inward and causes
shortening, located at convergent plate boundaries, and
creates a reverse or thrust fault and anticline/ syncline,
fault-block and folded mountains. Large mountain ranges
such as the Himalayas (active) and the Appalachians
(ancient), Sierra Nevada and Tetons were formed by strong
compression, which produced thrust and reverse faults and
many large folds.
What are seismic waves?
What are the two categories
and two types within each?
What kind of motion and
damage is made by each
type?
3) shearing - forces that push two sides of a body in opposite
directions (like the sliding deformation of a deck of
cards). Located at transform plate boundaries, creates a
strike-slip fault. ex. The San Andreas fault is a large active
strike-slip fault that poses significant earthquake hazards in
California.
seismic waves - waves of energy generated by an earthquake
2 categories of seismic waves:
A. Body Waves:
(1) primary waves - the first waves that move through Earth
causing particles to move back & forth in the same direction.
(ex. slinky) (P= push wave) (longitudinal wave) (travels
through solids and liquids)
(2) secondary waves - the second set of waves which
move through Earth causing particles to move at right angles
to the direction of the wave. (S wave) (ex. rope) (transversal
wave) (travel through solids only)
B. Surface Waves: Waves that travel on Earth's surface
causing the most damage of all waves. (L = last waves)
(1) Love waves - named after A.E.H. Love, a British
mathematician who worked out the mathematical model for
this kind of wave in 1911. It's the fastest surface wave and
moves the ground from side-to-side.
(2) Rayleigh Waves - named for John William Strutt, Lord
Rayleigh, who mathematically predicted the existence of this
kind of wave in 1885. A Rayleigh wave rolls along the ground
What is the difference
between the focus and the
epicenter?
just like a wave rolls across a lake or an ocean. Because it
rolls, it moves the ground up and down, and side-to-side in the
same direction that the wave is moving. Most of the shaking
felt from an earthquake is due to the Rayleigh wave, which
can be much larger than the other waves.
- focus - the point in the Earth’s interior where the earthquake
originates
Define seismologist,
seismograph, and
magnitude.
Name and describe 3 scales
used to describe
earthquakes.
- epicenter - the point on the Earth’s surface above the focus.
- seismologists - scientists who study earthquakes and seismic
waves.
- seismograph - an instrument which measures the three
types of earthquake (seismic) waves.
- magnitude - a measure of the amount of energy released
Earthquake Scales:
1) the Mercalli scale - invented by Giuseppe Mercalli in 1902,
this scale uses the observations of the people who
experienced the earthquake to estimate its intensity. The
amount of damage caused by the earthquake may not
accurately record how strong it was.
2) the Richter magnitude scale - developed in 1935 by
Charles F. Richter of the California Institute of Technology as
a mathematical device to compare the size of earthquakes.
The magnitude of an earthquake is determined from the
logarithm of the amplitude of waves recorded by
seismographs. Because of the logarithmic basis of the scale,
each whole number increase in magnitude represents a
tenfold increase in measured amplitude; as an estimate of
energy, each whole number step in the magnitude scale
corresponds to the release of about 31 times more energy
than the amount associated with the preceding whole number
value.
3) the Moment Magnitude scale is the measure of total
energy released by an earthquake. Moment magnitude is the
measurement and term generally preferred by scientists and
seismologists to the Richter scale because moment magnitude
is more precise. Moment Magnitude is not based on
instrumental recordings of a quake, but on the area of the fault
that ruptured in the quake. This means that the moment
magnitude describes something physical about an
earthquake. Moment Magnitude is calculated in part by
multiplying the area of the fault's rupture surface by the
distance the earth moves along the fault.
Name and describe 4 types
of earthquake hazards.
Earthquake Hazards
1) Soil Conditions and Liquifaction - The first main
earthquake hazard is the effect of ground shaking. Buildings
can be damaged by the shaking itself or by the ground
beneath them settling to a different level than it was before the
earthquake (subsidence). Loose soil shakes more than solid
rock. Liquefaction is the mixing of sand or soil and
groundwater (water underground) during the shaking of a
moderate or strong earthquake. When the water and soil are
mixed, the ground becomes very soft and acts similar to
quicksand. If liquefaction occurs under a building, it may start
to lean, tip over, or sink several feet. The ground firms up
again after the earthquake has past and the water has settled
back down to its usual place deeper in the ground.
Liquefaction is a hazard in areas that have groundwater near
the surface and sandy soil. This is the main hazard to the
Coastal Plain and Coastal Zone of South Carolina.
2) Ground Displacement - is ground movement along a fault.
If a structure (a building, road, etc.) is built across a fault, the
ground displacement during an earthquake could seriously
damage or rip apart that structure. Aftershocks are
earthquakes which occur from hours to months after a larger
earthquake. Aftershocks often topple already weakened
buildings.
3) Flooding - An earthquake can rupture (break) dams or
levees along a river. The water from the river or the reservoir
would then flood the area, damaging buildings and maybe
sweeping away or drowning people.
Tsunamis and seiches can also cause a great deal of
damage. A tsunami is what most people call a tidal wave, but
it has nothing to do with the tides on the ocean. It is a huge
wave caused by an earthquake under the ocean. Tsunamis
can be tens of feet high when they hit the shore and can do
enormous damage to the coastline. Seiches are like small
tsunamis. They occur on lakes that are shaken by the
earthquake and are usually only a few feet high, but they can
still flood or knock down houses, and tip over trees.
4) Fire - Fires can be started by broken gas lines and power
lines, or tipped over wood or coal stoves. They can be a
serious problem, especially if the water lines that feed the fire
hydrants are broken, too. For example, after the Great San
Francisco Earthquake in 1906, the city burned for three days.
Most of the city was destroyed and 250,000 people were left
homeless.
What are some safety
measures to take before,
during and after an
earthquake?
Earthquake safety:
During an Earthquake
If indoors:


Take cover under a piece of heavy furniture or against
an inside wall and hold on.
Stay inside. The most dangerous thing to do during the
shaking of an earthquake is to try to leave the building
because objects can fall on you.
If outdoors:


Move into the open, away from buildings, street lights,
and utility wires.
Once in the open, stay there until the shaking stops.
If in a moving vehicle:



Stop quickly and stay in the vehicle.
Move to a clear area away from buildings, trees,
overpasses, or utility wires.
Once the shaking has stopped, proceed with caution.
Avoid bridges or ramps that might have been damaged
by the quake.
After an Earthquake










Be prepared for aftershocks. Although smaller than the
main shock, aftershocks cause additional damage and
may bring weakened structures down. Aftershocks can
occur in the first hours, days, weeks, or even months
after the quake.
Help injured or trapped persons. Do not move seriously
injured persons unless they are in immediate danger of
further injury. Remember to help your neighbors who
may require special assistance -- infants, the elderly,
and people with disabilities.
Listen to a battery-operated radio or television for the
latest emergency information.
Stay out of damaged buildings. Return home only when
authorities say it is safe.
Use the telephone only for emergency calls.
Clean up spilled medicines, bleaches or gasoline or
other flammable liquids immediately. Leave the area if
you smell gas or fumes from other chemicals.
Open closet and cupboard doors cautiously.
Inspect the entire length of chimneys carefully for
damage. Unnoticed damage could lead to a fire.
Check for gas leaks--If you smell gas or hear blowing or
hissing noise, open a window and quickly leave the
building. Turn off the gas at the outside main valve if
you can. Gas should only be turned on by a
professional.
Look for electrical system damage--If you see sparks or
broken or frayed wires, or if you smell hot insulation,

How are most people injured
during an earthquake?
turn off the electricity at the main fuse box or circuit
breaker.
Check for sewage and water lines damage--If you
suspect sewage lines are damaged, avoid using the
toilets and call a plumber. If water pipes are damaged,
contact the water company and avoid using water from
the tap.
Most of the hazards to people come from things falling on
people.
Name 4 devices used in
buildings to make them
earthquake resistant.
How Buildings are Made Earthquake Resistant
Seismic devices:
1) shear walls - Triangular steel or concrete components may
be added to an existing building or designed into a new one.
These components are free to move in an earthquake, so the
wall may bend and crack, but won't break.
2) braced framing - Sometimes referred to as trussed
framing, bracing stretches diagonally within a bay to create a
triangulated vertical frame. As in roof trusses, the triangles are
able to handle stresses better than a conventional rectangular
frame. They also add stiffness.
3) shock-absorbing devices or dampers - There are four
basic types of dampers: visco-elastic, friction, metallic, and
viscous. Each employs some type of pumping component or
piston that operates against a friction device-pads or fluid-filled
chambers-to release energy in the form of friction or heat.
4) base isolation - the structure is build on a series of blocks
made of alternating layers of rubber and steel, enabling them
to move and absorb the energy from the earthquake. This
allows the structure to move independently of the shifting
ground below.
These may be used alone or, for tall buildings, in combination.
Why do we need at least 3
seismic stations to find the
epicenter of an earthquake?
How Earthquakes are located:
We observe earthquakes with a network of at least 3
seismometers on the earth's surface. When an earthquake
occurs, we observe the times at which the wave-front passes
each station. The seismograms are a recording of the time
(arrival & duration) and amplitude (intensity) of all three types
of seismic waves. We must find the unknown earthquake
source knowing these wave arrival times. The distance
between the beginning of the first P wave and the first S wave
tells you how many seconds the waves are apart. This number
will be used to tell you how far your seismograph is from the
epicenter of the earthquake.
To know exactly where the earthquake occurred, you'll need a
drawing compass and a map (with a scale of 1cm=1km).
Calculate the distance on the map using the scale. Using your
compass, draw a circle with a radius equal to the number you
came up with for each seismograph station. All of the circles
should overlap. The point where all of the circles overlap is the
approximate epicenter of the earthquake.
Can Earthquakes be predicted?
Many earthquakes give some kind of signal that precedes the
slip. There are a variety of precursors that have been noted:







ground deformation
foreshocks
hydrologic changes
low frequency radio waves
seismic wave velocity changes
electromagnetic changes
poorly understood observations such as strange animal
behavior.
Summaries