Download Faults

How Earthquakes work &
Earthquake resistant building
Mgr. Ekaterina Andreeva
The Institute of Chemistry and Technology of Environmental Protection
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Content
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Introduction to how earthquakes work
Shaking ground
Earthquakes facts
Theory of plate tectonics
Faults
Seismic waves
Seismology
Seismometer
Richter Scale rating and Mercalli Scale
rating
Predicting earthquakes
Earthquake Resistant Buildings
Earthquake in the world
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Introduction to
how earthquakes work
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One of the most terrifying phenomena
Until recently - unsubstantiated guesses as to what
caused earthquakes
Today – much clearer understanding
o Identified forces of earthquakes
o Technology that can tell an earthquake’s
magnitude
o Technology that can tell an origin
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To find a way of predicting earthquakes
To find way to protect people and property
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Shaking ground
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An earthquake is a vibration that travels through
the earth's crust.
o A large truck rumbling down the street
o Volcanic eruption
o Meteor impacts
o Underground explosions
o Collapsing structures
o Movements of the earth’s plates
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Earthquakes facts
According to the United States
Geological Survey, more than three million earthquakes
occur every year
 That's about 8,000 a day, or one every 11 seconds
 The vast majority of these 3 million quakes are extremely
weak
 It is the big quakes that occur in highly populated areas
that get our attention
 It's not the shaking ground itself that claims lives -- it's
the associated destruction of man-made structures and
the instigation of other natural disasters, such as
tsunamis, avalanches and landslides
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Theory of plate tectonics
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Scientific breakthrough in the history of seismology
To explain a number of peculiar phenomenon on earth
o the apparent movement of continents over time
o the clustering of volcanic activity in certain areas
o the presence of huge ridges at the bottom of the
ocean
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The basic theory
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The surface layer of the earth -- the lithosphere -- is
comprised of many plates that slide over the lubricating
athenosphere layer
At the boundaries between these huge plates of soil and
rock, three different things can happen
o Plates slide against each other
o Plates can move apart
o Plates can push together
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Faults
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Faults -- breaks in the earth's
crust where the blocks of
rock on each side are moving
in different directions
Earthquakes are much more
common along fault lines than
they are anywhere else on the
planet
Few types of faults,
characterized by the position
of the fault plane, the break
in the rock and the movement
of the two rock blocks
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In a normal fault, the fault plane is nearly vertical
 The hanging wall, the block of rock positioned above
the plane, pushes down across the footwall, which is
the block of rock below the plane
 The footwall, in turn, pushes up against the hanging
wall
 These faults occur where the crust is being pulled
apart, due to the pull of a divergent plate boundary.
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The fault plane in a reverse fault is also nearly
vertical, but the hanging wall pushes up and the
footwall pushes down.
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This sort of fault forms where a plate is being
compressed
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Thrust fault moves the same way as a reverse fault,
but the fault line is nearly horizontal
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In these faults, which are also caused by
compression, the rock of the hanging wall is actually
pushed up on top of the footwall
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This is the sort of fault that occurs in a converging
plate boundary
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Reverse fault
In
a strike-slip fault, the blocks of rock move in opposite
horizontal directions
These
faults form when the crust pieces are sliding against
each other, as in a transform plate boundary
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The different blocks of
rock push very tightly
together, creating a good
deal of friction as they
move
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If this friction level is
high enough, the two
blocks become locked -the friction keeps them
from sliding against each
other
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When this happens, the
forces in the plates
continue to push the rock,
increasing the pressure
applied at the fault
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If the pressure increases to a high enough level,
then it will overcome the force of the friction, and
the blocks will suddenly snap forward
 To put it another way, as the tectonic forces push
on the "locked" blocks, potential energy builds
 When the plates are finally moved, this built-up
energy becomes kinetic. Some fault shifts create
visible changes at the earth's surface, but other
shifts occur in rock well under the surface, and so
don't create a surface rupture.
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The initial break that creates a fault, along with
these sudden, intense shifts along already formed
faults, are the main sources of earthquakes
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Most earthquakes occur around plate boundaries,
because this is where the strain from the plate
movements is felt most intensely, creating fault zones,
groups of interconnected faults
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Seismic waves
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When a sudden break or shift occurs in the earth's
crust, the energy radiates out as seismic waves
In every earthquake, there are several different
types of seismic waves
Body waves move through the inner part of the
earth
Surface waves travel over the surface of the earth.
Surface waves -- sometimes called long waves, or
simply L waves -- are responsible for most of the
damage associated with earthquakes, because they
cause the most intense vibrations. Surface waves
stem from body waves that reach the surface.
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There are two main types of body waves.
o Primary waves, also called P waves or
compressional waves, travel about 1 to 5 miles
per second, depending on the material they're
moving through
o This speed is greater than the speed of other
waves, so P waves arrive first at any surface
location
o They can travel through solid, liquid and gas, and
so will pass completely through the body of the
earth.
o As they travel through rock, the waves move tiny
rock particles back and forth -- pushing them
apart and then back together -- in line with the
direction the wave is traveling
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P-waves
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o Secondary waves, also called S waves or shear waves,
lay a little behind the P waves
o As these waves move, they displace rock particles
outward, pushing them perpendicular to the path of
the waves
o This results in the first period of rolling associated
with earthquakes. Unlike P waves, S waves don't move
straight through the earth
o They only travel through solid material, and so are
stopped at the liquid layer in the earth's core.
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Surface waves are something like the waves in a body of
water -- they move the surface of the earth up and down
This generally causes the worst damage because the
wave motion rocks the foundations of manmade
structures
L waves are the slowest moving of all waves, so the most
intense shaking usually comes at the end of an
earthquake.
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Seismology
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The exact speed of P and S waves varies depending on the
composition of the material they're traveling through, the
ratio between the speeds of the two waves will remain
relatively constant in any earthquake. P waves generally
travel 1.7 times faster than S waves.
Using this ratio, scientists can calculate the distance
between any point on the earth's surface and the
earthquake's focus, the breaking point where the vibrations
originated
They do this with a seismograph, a machine that registers
the different waves
To find the distance between the seismograph and the
focus, scientists also need to know the time the vibrations
arrived
With this information, they simply note how much time
passed between the arrival of both waves and then check a
special chart that tells them the distance the waves must
have traveled based on that delay.
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Richter Scale rating and Mercalli Scale
rating
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These two ratings describe the power of the
earthquake from two different perspectives.
o The Richter Scale is used to rate the magnitude
of an earthquake -- the amount of energy it
released
o This is calculated using information gathered by
a seismograph.
 Richter ratings only give you a rough idea of the
actual impact of an earthquake
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The extent of damage is rated on the Mercalli Scale
An earthquake's destructive power varies depending on
the composition of the ground in an area and the design
and placement of manmade structures
Mercalli ratings, which are given as Roman numerals, are
based on largely subjective interpretations
A low intensity earthquake, one in which only some people
feel the vibration and there is no significant property
damage, is rated as a II
The highest rating, a XII, is applied only to earthquakes
in which structures are destroyed, the ground is cracked
and other natural disasters, such as landslides or
Tsunamis, are initiated
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Another Intensity scales
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European Macroseismic Scale
Medvedev-Sponheuer-Karnik scale
INQUA Scale (International Union for
Quaternary Research)
Japan Meteorological Agency seismic intensity
scale
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Predicting eathquakes
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They are caused by fundamental, powerful geological
processes that are far beyond our control
These processes are also fairly unpredictable, so it's not
possible at this time to tell people exactly when an
earthquake is going to occur
The first detected seismic waves will tell us that more
powerful vibrations are on their way, but this only gives
us a few minutes warning, at most
Scientists can say where major earthquakes are likely to
occur, based on the movement of the plates in the earth
and the location of fault zones
They can also make general guesses of when they might
occur in a certain area, by looking at the history of
earthquakes in the region and detecting where pressure
is building along fault lines
Scientists have had more success predicting aftershocks,
additional quakes following an initial earthquake. These
predictions are based on extensive research of
aftershock patterns
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Predicting earthquakes
Another area of study is the relationship between
magnetic and electrical charges in rock material and
earthquakes
 Some scientists have hypothesized that these
electromagnetic fields change in a certain way just
before an earthquake
 Seismologists are also studying gas seepage and the
tilting of the ground as warning signs of
earthquakes. For the most part, however, they can't
reliably predict earthquakes with any precision
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So what can we do about earthquakes
The major advances over the past 50 years have
been in preparedness -- particularly in the field of
construction engineering
 Strengthening support material as well as designing
buildings so they are flexible enough to absorb
vibrations without falling or deteriorating
 Another component of preparedness is educating
the public.
 The United States Geological Survey (USGS) and
other government agencies have produced several
brochures explaining the processes involved in an
earthquake and giving instructions on how to
prepare your house for a possible earthquake, as
well as what to do when a quake hits.
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Earthquake Resistant Buildings
Earthquakes can cause buildings to vibrate
 Every building has a number of ways, or modes, in
which it can vibrate naturally. In each mode, the
building vibrates to and fro with a particular
distorted shape called its mode shape.
 Earthquakes usually make buildings vibrate most
strongly in their fundamental mode, the mode of
vibration with the lowest frequency
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The vibrations die out because of damping which
removes energy from the moving building.
 The damping can be caused by
o Friction as different parts of the building move
against each other.
o Internal friction in the materials making up the
structural members and other parts of the
building.
o Damage in the building, for example, cracking in
concrete or brickwork or permanent distortions
in steel.
Engineers can design buildings to have extra damping,
by adding dampers to the structural frame.
The dampers absorb energy from a vibrating building,
so that its movement is not as violent
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When the ground shakes during an earthquake, it does not
have one frequency of vibration, but it is made up from a
mixture of frequencies.
A building will vibrate more strongly when any of those
frequencies are close to its fundamental frequency
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Strengthening Buildings for
Earthquakes
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Earthquakes cause sideways forces on buildings
These are some of the structural systems used to resist
sideways forces
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Horizontal structural systems
Usually
floors and roofs
They
share the sideways forces on the building
between its vertical structural members.
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include:
Diaphragms
Trussing
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Horizontal Diaphragms
Horizontal
diaphragms are usually floors and roofs. They
are made up from a horizontal frame covered by a floor or
roof deck.
When a diaphragm is stiff enough in its horizontal plane, it
can share the sideways earthquake forces on a building
between the vertical structural members, e.g. the columns
and walls.
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Horizontal Trussing
Horizontal
trussing is usually used in roofs where there is
not enough deck to allow the roof to act as a stiff
horizontal diaphragm.
The trussing transfers the sideways earthquake forces on
a building to its vertical structural members e.g. the
columns and walls.
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Vertical structural systems
Made up from columns, beams, walls and bracing.
They transfer the sideways forces on the building to the
ground.
They include:
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Braced frames
Moment
resisting frames
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Shear walls
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Braced
frames use trussing to resist sideways forces on
buildings.
Trussing, or triangulation, is formed by inserting diagonal
structural members into rectangular areas of a structural
frame.
It helps stabilise the frame against sideways forces from
earthquakes and strong winds.
 Single diagonals
 Cross-bracing
 Other ways of bracing frames
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Other ways of bracing frames
K Bracing
V Bracing
Knee Bracing
Knee Bracing
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Moment Resisting Frames
In
moment resisting frames, the joints, or
connections, between columns and beams are designed
to be rigid
This causes the columns and beams to bend during
earthquakes. So these structural members are
designed to be strong in bending.
Moment resisting frames simply means frames that
resist forces by bending.
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Shear Walls
Shear
walls are vertical walls that are used to stiffen the
structural frames of buildings. They help frames resist
sideways earthquake forces
The earthquake forces are transferred to the ground
mainly by shear forces in the walls
It is better to use walls with no openings in them.
Usually the walls around lift shafts and stairwells are used
 Walls on the sides of buildings that have no windows can
be used.
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Isolating building
Base
isolation systems reduce building
vibrations during earthquakes.
Normally, a building is supported directly on
its foundations, and it is said to have a fixedbase. When base isolation is used, special
structural bearings are inserted between the
bottom of the building and its foundation.
These bearings are not very stiff in the
horizontal direction, so they reduce the
fundamental frequency of vibration of a
building.
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During an earthquake, a fixed-base building can sway
from side to side. When a base isolation system is
used, the sideways movement occurs mainly in the
bearings
There are many types of bearings used for base
isolation. Here are two of them.
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Rubber bearings
Rubber
bearings are made from layers of rubber with thin
steel plates between them, and a thick steel plate on the
top and bottom.
The bearings are placed between the bottom of a building
and its foundation .
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bearings are designed to be very stiff and strong for
vertical load, so that they can carry the weight of the
building. However, they are designed to be much weaker for
horizontal loads, so that they can move sideways during an
earthquake.
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Friction Pendulum Bearings
Friction
pendulum bearings are made from two horizontal
steel plates that can slide over each other because of their
shape and an additional articulated slider.
They
are designed to be very stiff and strong for vertical
load, so that they can carry the weight of the building.
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Adding Dampers
Dampers
can be installed in the structural frame of a
building to absorb some of the energy going into the
building from the shaking ground during an earthquake.
The
dampers reduce the energy available for shaking
the building. This means that the building deforms
less, so the chance of damage is reduced.
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are many types of dampers that can be
installed in buildings. Here are some of them:
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Metallic Dampers
Metallic
dampers are usually made from steel.
They are designed to deform so much when the building
vibrates during an earthquake that they cannot return to
their original shape.
This permanent deformation is called inelastic deformation,
and it uses some of the earthquake energy which goes into
building.
X - Plate Metallic Damper
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Friction Dampers
Friction
dampers are designed to have moving parts
that will slide over each other during a strong
earthquake.
When the parts slide over each other, they create
friction which uses some of the energy from the
earthquake that goes into the building.
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The damper is made up from a set of steel plates, with
slotted holes in them, and they are bolted together. At
high enough forces, the plates can slide over each other
creating friction.
The plates are specially treated to increase the friction
between them.
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Viscous fluid dampers
Viscous
fluid dampers are similar to shock absorbers in
a car. They consist of a closed cylinder containing a
viscous fluid like oil.
A piston rod is connected to a piston head with small
holes in it. The piston can move in and out of the cylinder.
As it does this, the oil is forced to flow through holes in
the piston head causing friction.
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Viscous fluid dampers
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The friction converts some of the earthquake energy
going into the moving building into heat energy.
The damper is usually installed as part of a building's
bracing system using single diagonals. As the building
sways to and fro, the piston is forced in and out of the
cylinder.
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Earthquakes in the world
As
the Nation's largest water, earth, and biological science
and civilian mapping agency, the U.S. Geological Survey
(USGS) collects, monitors, analyzes, and provides scientific
understanding about natural resource conditions, issues, and
problems.
Earthquake Hazards Program
Latest earthquake in the world
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Thank You for attention
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