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Topic:Earthquake
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The crustal plates of the Earth are being deformed by
stresses from deep
within the Earth.
The ground first
bends, then, upon
reaching a certain
limit, breaks and
"snaps" to a new
position. In the
process of breaking
or "faulting,"
vibrations are set
up that are the
earthquakes. Some of the vibrations are of very low
frequency, with many seconds between waves, whereas
other vibrations are of high enough frequency to be in
the audible range.
The vibrations are of two basic types, compression
waves and transverse or shear waves. Since the
compression waves travel faster through the Earth, they
arrive first at a distant point; they are known as primary
or "P" waves. The transverse waves arriving later are
referred to as shear or "S" waves. In an earthquake,
people may note first a sharp thud, or blast-like shock,
that marks the arrival of the P wave. A few seconds later,
they may feel a swaying or rolling motion that marks the
arrival of the S wave.
From:http://pubs.usgs.gov/gip/earthq3/whatearth.html
The first, or inner, part of the Earth is the inner core,
which is solid and composed mostly of iron and nickel.
Although, scientists cannot actually get to the inner core
to test it because it is over 5000 km below the Earth's
surface, scientist have predicted that the inner core is
solid. The second layer, going from the inside outward, is
the outer core, which is molten — or liquid iron and
nickel. It lies from 2891 to 5150 km inside the Earth. The
third layer that makes up most of the Earth is the mantle.
The mantle ranges from 40 to 2900 km deep. It is made
of molten rock, which is lighter than the iron and nickel
core, but heavier than the Earth's crust — the fourth and
final
layer of the Earth. The crust is 15 - 200 km thick and is
made of light materials, which stay on the surface of the
Earth. Figure 2 illustrates the different layers of the
Earth.
Figure 2. The layers of the Earth Copyright ©
http://pubs.usgs.gov/publications/text/ unanswered.html
About 30 years ago, geologists developed the theory of
plate tectonics — the theory that the crust of the Earth is
divided into large plates called tectonic plates, which lock
together like the pieces of a puzzle. The tectonic plates
are between 200 km (under landmasses) and 15 km
(under the ocean) thick. Geologists believe that the
tectonic plates are floating on the molten rock of the
mantle and moving around very slowly. Each continent
has its own tectonic plate (see Figure 3), and the
continual slow movement of the plates subsequently
causes movement of the continents— called continental
drift.
Figure 3. The world's
http://pubs.usgs.gov/
tectonic
plates.
Copyright
©
Scientists believe that convection currents in the molten
rock under the crust account for the movement of the
continents. Convection currents are currents, or
movements, of liquid that occur because of differences in
temperature. As the hot molten rock closest to the outer
core of the Earth rises toward the crust, it cools slightly.
The cooler molten rock is denser, so it sinks, creating a
circular current similar to a pot of boiling soup.
The boundaries where the tectonic plates meet are the
areas of the world with the most violent natural
earthquake activity. When the plates grind against each
other along plate boundaries, the rocks are under so
much pressure that sometimes they heat up and fold,
creating mountain ranges, hills and valleys. The intense
pressure at plate boundaries can also cause rocks to snap
and break — forming cracks in the Earth, or faults.
When faults are formed, a tremendous amount of
energy is released, which shakes the Earth and causes
earthquakes.
There are three main types of faults: transcurrent,
normal and reverse faults. Transcurrent faults move
sideways creating earthquakes. The San Andreas Fault
in California is an example of a transcurrent fault. In
normal faults, the tectonic plates either move apart from
one another or towards each other causing a block of
Earth to fall between the two plates. With a reverse fault,
a block of Earth is pushed upwards and sometimes over
the tectonic plate.
The U.S. Geological Survey has created a map of the
United States to help identify areas that are naturally
prone to more earthquake activity (see Figure 4).
Through their historical assessment of earthquake
activity, they are able to predict which areas of the U.S.
are likely to experience high, medium, low or little to
no earthquake activity. Such a map assists engineers in
developing the best structure to withstand these
naturally occurring events.
Earthquake occurred in the world
Figure 4. An earthquake hazard map. Copyright ©
http://earthquake.usgs.gov
From:http://www.teachengineering.com/view_lesson.php?url=http://
www.teachengineering.com/collection/cub_/lessons/cub_earth/cub_e
arth_lesson01.xml
Earthquakes occurred recently in the world
(the most updated news)
From:cse.ssl.berkeley.edu/.../ QuakesEng3.html
What the earthquake’s prediction should state?
Scientific earthquake predictions should state where,
when, how big, and how probable the predicted event is,
and why the prediction is made. The National
Earthquake Prediction Evaluation Council reviews such
predictions, but no generally useful method of predicting
earthquakes has yet been found.
Damage caused by earthquake
From:geot.civil.metro-u.ac.jp/.../
eq/95kobe/m/035.jpg
How to predict earthquake?
There are some methods to predict the earthquake:
1. Scientists study the past frequency of large
earthquakes in order to determine the future likelihood of
similar large shocks.
For example, if a region has experienced four magnitude
7 or larger earthquakes during 200 years of recorded
history, and if these shocks occurred randomly in time,
then scientists would assign a 50 percent probability (that
is, just as likely to happen as not to happen) to the
occurrence of another magnitude 7 or larger quake in the
region during the next 50 years.
2. Study how fast strain accumulates.
What is strain accumulates?
When plate movements build the strain in rocks to a
critical level, like pulling a rubber band too tight, the
rocks will suddenly break and slip to a new position.
Scientists measure how much strain accumulates along
a fault segment each year, how much time has passed
since the last earthquake along the segment, and how
much strain was release in the last earthquake.
This information is then used to calculate the time
required for the accumulating strain to build to the
level that results in an earthquake.
To conclude:
Because of their devastating potential, there is great
interest in predicting the location and time of large
earthquakes. Although a great deal know about where
earthquakes are likely, there is currently no reliable way
to predict the days or months when an event will occur
in any specific location. It is because when a damaging
earthquake will occur, because when enough strain has
built up, a fault may become inherently unstable, and
any small background earthquake may or may not
continue rupturing and turn into a large earthquake.
While it may eventually be possible to diagnose
accurately the strain state of faults, the precise timing
of large events may continue to elude us.
Follows can be a conjunctive paragraph
with the causes and effects of earthquake:
Scientific understanding of earthquakes is of vital
importance to the Nation. As the population increases,
expanding urban development and construction works
encroach upon areas susceptible to earthquakes. With
a greater understanding of the causes and effects of
earthquakes, we may be able to reduce damage and
loss of life from this destructive phenomenon.
Damaged caused by earthquake
From:www-ed.fnal.gov/.../
earthquake%20photo4.jpg
Earthquake Severity
Richter
Magnitudes
Earthquake Effects
Less than 3.5
Generally not felt,but recorded
3.5-5.4
Often felt,but rarely causes damage
Under 6.0
At most slight damage to well-designed
buildings.Can cause major damage to poorly
constructed buildings over small regions.
6.1-6.9
Can be destructive in areas up to about 100 km
across where people live.
7.0-7.9
Major earthquake.Can cause serious damage over
larger areas
8 or greater
Great earthquake.Can cause serious damage in
areas several hundred km across.
Richter showed that, the larger the intrinsic energy of
the earthquake, the larger the amplitude of ground
motion at a given distance. He calibrated his scale of
magnitudes using measured maximum amplitudes of
shear waves on seismometers particularly sensitive to
shear waves with periods of about one second. The
records had to be obtained from a specific kind of
instrument, called a Wood-Anderson seismograph.
Although his work was originally calibrated only for
these specific seismometers, and only for earthquakes in
southern California, seismologists have developed scale
factors to extend Richter's magnitude scale to many
other types of measurements on all types of
seismometers, all over the world. In fact, magnitude
estimates have been made for thousands of Moonquakes and for two quakes on Mars
The diagram below demonstrates how to use Richter's
original method to measure a seismogram for a
magnitude estimate in Southern California:
From:http://www.seismo.unr.edu/ftp/pub/louie/clas
s/100/magnitude.html
The cause by human activities was the injection of fluids into
deep wells for waste disposal and secondary recovery of oil,
and the use of reservoirs for water supplies. Most of these
earthquakes were minor. And nuclear detonations have not
been linked to earthquake activity. Energy from nuclear blasts
dissipates quickly along the Earth's surface.
Earthquakes are part of a
global tectonic process that
generally occurs well beyond
the influence or control of
humans. The focus (point of
origin) of earthquakes is
typically tens to hundreds of
miles underground. The scale
and force necessary to
produce earthquakes are well
beyond our daily lives.
We cannot prevent
earthquakes; however, we
can significantly mitigate
their effects by identifying
hazards, building safer
structures, and providing
education on earthquake
safety.
Shallow crevasses can form during earthquake induced
landslides, lateral spreads, or other types of ground failures.
Faults, however, do not open up during an earthquake.
Movement occurs along the plane of a fault, not
perpendicular to it. In the field, one can readily see this
displacement along modern and ancient faults. If faults
opened up, no earthquake would occur because friction would
be lacking.
Damaged caused by
earthquake
From:news.bbc.co.uk/1/hi/
world/south_asia/4126971.stm
Generally, during an earthquake you will feel a swaying
motion, then a slight pause, followed by a more intense
rolling or jerking motion. The duration of the shaking you
feel depends on the earthquake's magnitude, your
distance from the epicenter, and the geology of the
ground under your feet. Shaking at a site with soft
sediments, for example, can last 3 times as long as shaking at a
stable bedrock site such as one composed of granite. If the site
we consider is in a building, then the height of the building and
type of material it is constructed from are also factors. For
minor earthquakes, ground shaking usually lasts only a few
seconds. Strong shaking from a major earthquake usually lasts
less than one minute.
The largest recorded earthquake in the world was a
magnitude 9.5 (Mw) in Chile on May 22, 1960
The first "pendulum seismoscope" to measure the
shaking of the ground during an earthquake was
developed in 1751, and it wasn't until 1855 that faults
were recognized as the source of earthquakes.
The hypocenter of an earthquake is the location
beneath the earth's surface where the rupture of the
fault begins. The epicenter of an earthquake is the
location directly above the hypocenter on the surface
of the earth.
Landslides caused by
earthquake
From:www.santegidio.or
g/.../ salvador/foto1.htm
It is estimated that there are 500,000 detectable
earthquakes in the world each year. 100,000 of
those can be felt, and 100 of them cause damage.
The core of the earth was the first internal
structural element to be identified. In 1906 R.D.
Oldham discovered it from his studies of earthquake
records. The inner core is solid, and the outer core is
liquid and so does not transmit the shear wave
energy released during an earthquake.
Most earthquakes occur at depths of less than 80
km (50 miles) from the Earth's surface.
From:http://earthquake.usgs.gov/4kids//
1. DO NOT turn on the gas again if you turned it off;
let the gas company do it
2. DO NOT use matches, lighters, camp stoves or
barbecues, electrical equipment, appliances UNTIL
you are sure there are no gas leaks. They may
create a spark that could ignite leaking gas and
cause an explosion and fire
3. DO NOT use your telephone, EXCEPT for a medical
or fire emergency. You could tie up the lines needed
for emergency response. If the phone doesn't work
send someone for help
4.DO NOT expect firefighters, police or paramedics to
help you. They may not be available.
1. If you are INDOORS--STAY THERE! (Get under a
desk or table and hang on to it, or move into a
hallway or get against an inside wall. STAY CLEAR
of windows, fireplaces, and heavy furniture or
appliances. GET OUT of the kitchen, which is a
dangerous place (things can fall on you). DON'T run
downstairs or rush outside while the bldg is shaking
or while there is danger of falling and hurting
yourself or being hit by falling glass or debris.
2. If you are OUTSIDE-- get into the OPEN, away from
bldgs, power lines, chimneys, and anything else
that might fall on you.
3.If you are DRIVING--stop, but carefully. Move your
car as far out of traffic as possible. DO NOT stop on
or under a bridge or overpass or under trees, light
posts, power lines, or signs. STAY INSIDE your car
until the shaking stops. When you RESUME driving
watch for breaks in the pavement, fallen rocks, and
bumps in the road at bridge approaches.
4.If you are in a MOUNTAINOUS AREA--watch out for
falling rock, landslides, trees, and other debris that
could be loosened by quakes.
Only if you live in an old, unreinforced adobe house. In
modern homes doorways are no stronger than any
other parts of the house and usually have doors that
will swing and can injure you. YOU ARE SAFER
PRACTICING THE DUCK, COVER, AND HOLD under a
sturdy piece of furniture.
1. Fire extinguisher
2. Adequate supplies of medications that you or family
members are taking
3. Crescent and pipe wrenches to turn off gas and
water supplies
4. First-aid kit and handbook
5. Flashlights with extra bulbs and batteries
6. Portable radio with extra batteries
7.Water for each family member for at least 3 days
(allow at least 1 gallon per person per day) and
purification tablets or chlorine bleach to purify
drinking water from other sources
8.Canned and package foods, enough for several days
and MECHANICAL can opener. Extra food for pets if
necessary
9.Camp stove or barbecue to cook on outdoors (store
fuel out of the reach of children)
10.Waterproof, heavy-duty plastic bags for waste
disposal.
1. WEAR STURDY SHOES to avoid injury from broken
glass and debris. Expect aftershocks
2. CHECK FOR INJURIES (if a person is bleeding, put
direct pressure on the wound, use clean gauze or
cloth if available; If a person is not breathing
administer CPR; DO NOT attempt to move seriously
injured persons unless they are in further danger of
injury; COVER injured persons with blankets to keep
warm; SEEK medical help for serious injuries
3.CHECK FOR HAZARDS (Fire hazards--put out fires in
your home or neighborhood immediately, call for help;
Gas leaks--shut off main gas valve ONLY if you
suspect a leak because of broken pipes or odor;
Damaged electrical wiring--Shut off power at the control
box if there is any danger to house wiring; Downed or
damaged utility lines--do not touch downed power lines
or any objects in contact with them; SPILLS--clean up
any spilled medicines, drugs, or other harmful materials
such as bleach, lye, gas; DOWNED OR DAMAGED
CHIMNEYS--Approach with caution--don't use damaged
chimney (it could start fire or let poisonous gases into
your house; FALLEN ITEMS--beware of items tumbling
off shelves when you open doors of closets and
cupboards; (4) CHECK FOOD AND WATER SUPPLIES--Do
not eat or drink anything from open containers near
shattered glass; If power is off,plan meals to use up
foods that will spoil quickly or frozen foods (food in the
freezer should be good for at least a couple of days;
Don't light your kitchen stove if you suspect a gas leak;
USE BBQ or camp stoves, outdoors only for emergency
cooking; If your water is off you can drink supplies from
water heaters, melted ice cubes or canned vegetables
(AVOID drinking water from swimming pools or
especially spas--it may have too many chemicals in it to
be safe.)
1. Estimate what EQ of what size are likely to occur
(geology)
2. Given the EQ size we then estimate what the shaking
will be (seismology)
3.Given the shaking we estimate the response of
different types of buildings (EQ engineering). Only
with all these steps can we take steps as society to
enact bldg. codes and retrofitting programs to make
our community safer.
From:http://earthquake.usgs.gov/faq/prepare.html
Some news about the earthquake
Quake on L.A. Fault Would Be Calamity
By ALICIA CHANG, AP Science Writer Thu May 26, 9:04 PM ET
A major earthquake on a little-known fault buried under downtown Los
Angeles would cause the most catastrophic natural disaster in U.S.
history, killing thousands of people and causing up to $250 billion in
damage, scientists said Wednesday.
Despite the doomsday forecast, the likelihood of the Puente Hills fault
generating a large temblor in the next 50 years is slim.
First discovered in 1999, the fault has ruptured at least four times in the
last 11,000 years, creating quakes with estimated magnitudes of 7.2 to 7.5.
If a temblor of similar magnitude were to occur today, it would cause
between 3,000 and 18,000 deaths and 120,000 injuries, according to
estimates by the U.S. Geological Survey and the Southern California
Earthquake Center.
The projections are meant to help structural engineers, emergency
planners and first responders better understand the potential risks if a
Puente Hills quake were to occur, scientists said.
The consequences would be far more damaging during a major Puente
Hills quake because it would hit the urban core of downtown Los
Angeles. Unlike the Northridge quake, which shook mostly wood-frame
houses, the Puente Hills fault snakes beneath older and more vulnerable
commercial and industrial buildings.
The estimated casualty and damage numbers are based on the quake
striking on a weekday afternoon, when most people are at work. The
death toll would be lower if the quake struck at night.
Scientists calculated the losses based on software developed by USGS
and the Southern California Earthquake Center and models from the
Federal Emergency Management Agency. Results appear in the May
issue of the journal Earthquake Spectra.
The Puente Hills fault, which runs about 25 miles from downtown Los
Angeles to northern Orange County, is formed by the collision of the
Pacific and North American plates.
On the Net:
U.S. Geological Survey: http://www.usgs.org
Southern California Earthquake Center: http://www.scec.org
Earthquakes shake southwestern Japan
Agence France-Presse
Tokyo, June 3, 2005
Earthquakes measuring 4.8 and 3.5 on the Richter scale
shook Japan's southwestern Kyushu island early on
Friday but there were no reports of major damage, the
Meteorological Agency and police said.The initial temblor
took place at 4:16 am (1916 GMT Thursday), centring
about 10 kilometres (6.2 miles) underground in the
island's central Kumamoto prefecture, the agency said.It
was followed by an aftershock of 3.5 at 7:31 (2231 GMT),
the agency said.
Police received no reports
of major damage or
casualties."A 73-year-old
woman sustained a slight
head injury as she fell
from her bed ... but we
have received no other
reports," a Kyushu police
spokesman said.There was
no danger of tsunami
seismic waves.