Emergency communication plan for: reuniting after the earthquake if family members are
separated from one another ask a relative or friend as the “ contact person” after the
disaster. Make sure everyone in the family knows the name, address, and the phone
number of the contact personDuring an earthquake: If inside: take cover under a desk or
against the wall and stay there dont leave the building during the earthquakeIf outside:
Stay away from buildings, street lights, and overpasses stay there until the shaking stopsIf
driving: stop quickly and pull to the side of the road stay in the vehicle avoid bridges or
ramps that are damaged by the quake once the shaking has stoppedIf in a public area: do
not panic move away from shelvesAfter an earthquake: be prepare for aftershocks dont
move seriously injured persons unless they need are in immediate danger listen to radio or
television for the latest information stay our of damaged buildingsChecking for damage in
your home: Gas leaks: if you smell gas or hear a hissing or exploding noise, open a
window and leave the building quickly call gas company to turn off the gas NEVER turn
off the gas yourself unless you are a professionalElectrical system damage: if you see
sparks, broken wires, smell hot insulation, turn off the electricity at the fuse box or circuit
breakerSewage and water lines: dont use the toilet if the sewage line is damaged call the
water company if the water pipes are damaged
earthquakes
Colombian Fear
Have you ever lived through an earthquake? Earthquakes are among the
most destructive and powerful forces in nature(McNally 33). Just recently, people in
Colombia lived and many died in an earthquake. This earthquake overwhelmed and
literally shook up the people of Armenia. First, the unexpected earthquake shocked the
people with its high magnitude. For example, authorities said, Mondays quake
measuring 6. 0 on the open-ended Richter scale, also destroyed buildings and triggered
landslides(Colombian Earthquake 1). This shows that for such a big earthquake people
need time to prepare, but the Colombians had no warning. The innocent people of
Armenia thought that day was going to be an ordinary day but they were unfortunately
wrong. In addition, Earthquakes of magnitude 5. 5 or above are the ones that usually do
damage(Fradin 27). The word damage is an understatement; the earthquake left most
of the people buried under rubble. The damage that was done by this force of nature was
too much for these people to handle. The number 6. 0 seems like a little number, but when
you see the damage that was done it doesnt seem so little. Next, many peoples lives were
greatly affected by this sudden tragedy. There are more than 1, 000 dead, perhaps more
than 2, 000 in Armenia alone(Whitbeck 2). Many people lost their family members and
friends that they deeply cared about. One minute people are happy and enjoying life and
the next minute 2, 000 of those happy people are dead. It left over two-thirds of Armenia
in total ruin, and rural village decimated in addition to the loss of life, the injuries and the
damage to the infrastructure(Moreno 20). There was practically none of the towns left. It
all was demolished by the quake. This left many people homeless without safety and
warmth. This disaster made people lose their lives and homes; it left so many people
empty-handed. Finally, the governments effort to aid the situation at hand lacked merit.
Henry Gomez, the governor said, We dont have enough coffins to bury the
dead(Whitbeck 3). The government needs to provide the dead with coffins because it is
just disrespectful not to. The deceased people deserve a proper burial to end their lives
right. In addition, there was little coordination between the Red Cross, Civil Defense
and firefighters, and accused each group of operating like a separate club(Whitbeck 1).
All the rescue teams needed to work together because the unorganization caused chaos. It
is ridiculous that when citizens are really in need of help, other people have to be stubborn
and unhelpful. The government should have done their job and been there for their people.
Colombia was shocked when the earthquake rocked their country and affected so many
people. Since the quake, Colombia is trying to recover from this tragedy that has greatly
impacted their lives. Hopefully, the victims can pick up the pieces left of their lives and put
them back together.
Earthquake San Francisco- 1906
On the morning 12 past 5: 00 San Francisco suffered a major earthquake that killed 3000
people, the earthquake lasted for about 40 seconds and was recorded at 8. 3 on the Richter
Scale.
People ran from there houses and some stayed inside the buildings and were crushed. The
people who ran in the streets were killed by toppled buildings falling from above. There
fire department was efficient but the water pipes that go down the San Andreas Fault were
severed. The fire could not be stopped because there were now water until the next couple
of days. Gas mains blew and caused massive fires all around the city. The city was in the
middle of a great economic boom and almost all was lost on that day. The old buildings
were never made to withstand earthquakes and easily crumbled and fell crushed people.
Some sailers on the coast tried to leave but the waves flew the boats around like toys. The
buildings were made out of unreined forced brick or wood which couldn’t withstand a
earthquake of that magnitude.
After the earthquake, they noticed that the San Andreas Fault shifted a 250-mile long
section witch tore roads and fences. Rivers, roads and power lines were severed and not
aligned with its surroundings. A road across the fault ended up 21 feet north of the road to
the east same with the rivers and creeks.
The earthquake’s most damage were in Los Bonas 30km east of the fault yet there was
little damage along towns to the east side of San Francisco Bay such as Berkely, 25km
east of the fault. And the capital of California Sacramento that was 120km east of the
rupture showed no damage.
Scientists found out that the earthquake originated north of Oregon and south to Los
Angeles a total of 1170 Km.
Knowing now that buildings could not withstand a earthquake with unreiforced brick, the
new San Francisco would have buildings that can handle major earthquakes by
constructing them so that they sway back and fourth rather than just simply crumbling to
the ground killing people.
The San Andreas fault is formed by the Pacific plate sliding north and the North American
plate running South. The two slide together caused the earthquake.
The most recent earthquake in that area today, was in 1990 in San Francisco which
measured around 8. 3 on the richter scale but it wasn’t a bad as the one in 1906.
earthquake
trembling or shaking movement of the earth’s surface. Most earthquakes are minor
tremors. Larger earthquakes usually begin with slight tremors but rapidly take the form of
one or more violent shocks, and end in vibrations of gradually diminishing force called
aftershocks. The subterranean point of origin of an earthquake is called its focus; the point
on the surface directly above the focus is the epicenter. The magnitude and intensity of an
earthquake is determined by the use of scales, e. g., the and the Mercalli scale.
Causes of Earthquakes
Most earthquakes are causally related to compressional or tensional stresses built up at the
margins of the huge moving lithospheric plates that make up the earth’s surface (see ). The
immediate cause of most shallow earthquakes is the sudden release of stress along a , or
fracture in the earth’s crust, resulting in movement of the opposing blocks of rock past one
another. These movements cause vibrations to pass through and around the earth in wave
form, just as ripples are generated when a pebble is dropped into water. Volcanic
eruptions, rockfalls, landslides, and explosions can also cause a quake, but most of these
are of only local extent.
See also .
Seismic Waves
There are several types of earthquake waves including P, or primary, waves, which are
compressional and travel fastest; and S, or secondary, waves, which are transverse, i. e.,
they cause the earth to vibrate perpendicularly to the direction of their motion. Surface
waves consist of several major types and are called L, or long, waves. Since the velocities
of the P and S waves are affected by changes in the density and rigidity of the material
through which they pass, the boundaries between the regions of the earth known as the
crust, mantle, and core have been discerned by seismologists, scientists who deal with the
analysis and interpretation of earthquake waves (see ). Seismographs (see ) are used to
record P, S, and L waves. The disappearance of S waves below depths of 1, 800 mi (2, 900
km) indicates that at least the outer part of the earth’s core is liquid.
Damage Caused by Earthquakes
The effects of an earthquake are strongest in a broad zone surrounding the epicenter.
Surface ground cracking associated with faults that reach the surface often occurs, with
horizontal and vertical displacements of several yards common. Such movement does not
have to occur during a major earthquake; slight periodic movements called fault creep can
be accompanied by microearthquakes too small to be felt. The extent of earthquake
vibration and subsequent damage to a region is partly dependent on characteristics of the
ground. For example, earthquake vibrations last longer and are of greater wave amplitudes
in unconsolidated surface material, such as poorly compacted fill or river deposits;
bedrock areas receive fewer effects. The worst damage occurs in densely populated urban
areas where structures are not built to withstand intense shaking. There, L waves can
produce destructive vibrations in buildings and break water and gas lines, starting
uncontrollable fires.
Damage and loss of life sustained during an earthquake result from falling structures and
flying glass and objects. Flexible structures built on bedrock are generally more resistant to
earthquake damage than rigid structures built on loose soil. In certain areas, an earthquake
can trigger mudslides, which slip down mountain slopes and can bury habitations below. A
submarine earthquake can cause , damaging waves that ripple outward from the
earthquake epicenter and inundate coastal cities.
Major Earthquakes
Notable earthquakes have occurred at Lisbon (1755), Charleston, S. C. (1886), Assam,
India (1897 and 1950), California (1906), Messina (1908), Gansu, China (1920), Japan
(1923), Chile (1960), Iran (1962), Guatemala (1976), Hebei, China (1976), and Armenia
(1988). The Lisbon and Chilean earthquakes were accompanied by tsunami. On Good
Friday, 1964, one of the most severe North American earthquakes ever recorded struck
Alaska, measuring 8. 4 to 8. 6 on the Richter scale. Besides elevating some 70, 000 sq mi
(181, 300 sq km) of land and devastating several cities, it generated tsunami that caused
damage as far south as California. In Feb., 1971, movement of the San Fernando fault near
Los Angeles rocked the area for 10 sec, thrust parts of mountains 8 ft (2. 4 m) upward,
killed 64 persons, and caused damage amounting to 500 million dollars; in 1989, the Loma
Prieta earthquake above Santa Cruz shook for 15 seconds at 7. 1 on the Richter scale,
killed 67 people, and toppled buildings and bridges. Managua, the capital of Nicaragua,
was almost totally destroyed by a severe earthquake that struck in Dec., 1972. An
earthquake measuring 7. 8 on the Richter scale devastated northern Japan in July, 1993. It
is estimated that in the last 4, 000 years over 13 million deaths were caused by
earthquakes.
Earthquakes are happening almost everyday all over the world. Most of the time
earthquakes are not strong enough to be felt by people, but the shaking caused by an
earthquake is recorded by a seismogram. These are located all over the world at different
points. Only occasionally will a larger magnitude earthquake strike and cause damage to
the region. Around the world there are many faults, depending where these faults are plays
a major factor in determining where an earthquake will happen. It is these faults that are
the reason for earthquakes. The type of fault will also determine how often an earthquake
will happen.
A mid-ocean ridge occurs under the sea at a divergent boundary. This is where two plates
are been pulled apart because of tension. This then allows new oceanic crust to be made in
the divergent boundary, as magma rises and eventually sets on the sea floor.
If the plates on either side of the divergent boundary continue to spread then the ocean
slowly becomes larger in width, a process called seafloor spreading. Mid-ocean ridges are
characterised by a crack like valley at the divergent boundary. This crack like valley is
caused by the tension pulling the plates apart, causing normal faulting to occur a number
of times in the divergent boundary.
It is these normal faults that are the cause and therefore the origin of earthquakes at
divergent boundaries. When the tension pulling apart the two plates becomes too much
then the oceanic crust will fracture. This fracturing is caused by many normal faults
happening as shown in the diagram. The normal faults happen because the crust is been
extended. When the tension becomes too much the faults slip vertically. They move a large
distance in a relatively short space of time, this is the cause of the earthquakes at divergent
boundaries.
Divergent boundaries mostly occur on the sea floor and therefore the earthquakes that
happen at these boundaries are distributed along the boundary. This means that the
distributions of earthquakes at divergent boundaries are at shallow depths, where the crust
is been pulled apart. The earthquakes happen at shallow depths because the normal
faulting occurs near the sea floor, as a result of the tension. The normal faults are the
cause of the earthquakes at these divergent boundaries.
The seafloor sees the most intense tectonic activity in the world, meaning that at the sites
of mid-ocean ridges the frequency of earthquakes is very high.
An example of a mid-ocean ridge is the Mid-Atlantic ridge, there the seafloor is spreading
at a rate of about 3cm per year. The frequency of earthquakes at a mid-ocean ridge will
depend on how much tension is happening at that point. The more tension means the more
seafloor spreading, resulting in a higher frequency of earthquakes at a particular
mid-ocean ridge.
Four major oceans make up most of the water in the world, The Atlantic (north ; south),
The Pacific, The Antarctic and The Indian Ocean. Within the basins of these oceans
earthquakes can happen without been caused at Mid-ocean ridges, or a Subduction Zones.
When the earths crust is under tensional forces the crust will become much thinner than
normal, if there is no fault. This means that the crust becomes weaker as it is thinner than
normal. This can happen to the oceanic crust in the ocean basins, but will only cause an
earthquake with a hot spot. A hot spot is an abnormal hot rising area of the mantle that
supplies the lava for volcanoes. If at the same time a hot spot is directly below a thinned
crust then the magma in the hot spot may hold too much pressure to be held by the thinner
weakened crust. If this is the case then the magma can penetrate the lithosphere, and
eventually erupt on the surface. The action of the magma forcing its way up can trigger
earthquakes as it breaks through the crust. When its breaks through the crust at the sea
bed eventually a volcanic island will be formed in the middle of the ocean. Due to plate
movements this can lead to the creation of mid-plate chains of basaltic volcanic islands,
e. g. Hawaii.
The creation of these islands around the world has happened in other places. Frequent
large earthquakes do not happen along the Hawaiian chain, it is an essentially an asesimic
ridge. Therefore the frequency of earthquakes caused in ocean basins by hot spots is very
low.
The distributions of these earthquakes that do occur happen at shallow depths. This is
because the origin is in the crust, which has been thinned because of tension.
A subduction zone is where two plates collide and one is forced below the other, they
occur at convergent boundaries. They collide because of compression forces, pushing
them into each other. One plate is subducted below the other into the mantle, where it will
be recycled. An example of this is shown below with the Pacific plate subducting under the
Eurasian plate.
The two plates want to travel in opposite directions, they want to go straight into each
other. This causes the pressure to build up over a long period of time, as the two plates
push at each other. As time progresses one of the plates will start to be bent downward
under the other one because of the extreme force, however does not slip, just bends. This
is because of the friction between the two plates is enough to allow them to bend, without
slipping. This is a very slow but continuous movement, maybe only a few millimetres
every year. Every fraction moved by the plates increases the build-up of elastic strain
energy within the rock. The rock continues to store this energy from a few decades to a
few thousand years. An earthquake will happen when the strain in the rocks exceeds that
of the limit of the rocks. The fault then ruptures, moving a large distance in a short space
of time. The plates then snap back into a new position, forcing the already undercutting
plate to dive down even further under the other. The collisions of two plates generally
produce large forces in the plates. These forces result in the triggering of the earthquakes
within the subduction zones.
The frequency of earthquakes in Subduction zones is about the same as that in the
mid-ocean ridges. This is because the plates cover the globe, and if they separate in one
place then in another place one-plate sinks below another. This means that the triggering
of an earthquake at a divergent boundary triggers an earthquake at a convergent plate.
Meaning that the frequency of earthquakes at Subduction zones is the same as at
Mid-ocean ridges, which is very high.
The earthquakes at convergent boundaries are distributed at different points. The deep
focus earthquakes occur along the already subducted plate. Shallow focus earthquakes
occur just at the point where one plate starts to be thrust under the other. These
earthquakes tend to be more common than the deeper earthquakes. This is shown on the
diagram on the left. The red dots show the distribution of earthquakes at a convergent
boundary.
Continental shields are extensively flat tectonically stable interiors of the continents,
composed of ancient rocks. Most of the stress that builds up by tectonic movements is
released in earthquakes at the plate boundaries. However stress can also build up in the
interiors of plates. Old fault lines in the plates are weaker than the surrounding rocks,
these old fault lines cover many continents, crossing all over each other. The old faults can
slip if the stress becomes too much from recent plate movements, which will cause an
unexpected earthquake. This can be a problem as many old fault lines are not known, and
many are away from modern plate boundaries that exist today. This is potentially
dangerous as many modern settlements may be at risk from earthquakes, even though they
are not near modern day faults.
The distribution of earthquakes at continental shields is not yet known, as scientists do not
know whether these earthquakes will strike the same region within a plate.
The strength of these inter-plate earthquakes are relatively small, compared to boundary
earthquakes. The frequency is also very small, the last major inter plate earthquake was in
Latur-India in 1993. However they can catch regions totally unexpected because they can
affect areas with no previous earthquake history. Also the energy of the earthquake is
spread out further without losing as much. Due to the older hard rocks that transmit
energy better, than the deformed broken younger rocks. This can cause more damage to a
larger region.
Earthquakes are common events and are happening all the time. They can be caused by
many different factors within the earths interior. Depending on the type of area that they
happen in will determine the strength of the earthquake, and the frequency of earthquakes
within the region. The distribution of earthquakes within an area will much depend upon
what caused the earthquake to happen in the first place. We understand today how
earthquakes are caused, and we can record where they happen every day of the year. This
has helped us to learn and understand about earthquakes in much detail. We now only
miss one important factor that we all would like to know, when and where the next one
will be. In truth it must be said that today we are still not close to predicting earthquakes
even with all the technology that is available.
Bibliography
Understanding Earth 2nd edition by Frank Press and Raymond Siever.
Microsoft Encarta Encyclopaedia 1998.
