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HowHow Earthquakes work &Earthquakes work &Earthquake resistant Earthquake resistant buildingbuilding

Mgr. Ekaterina AndreevaThe Institute of Chemistry and Technology of Environmental Protection

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Content

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 Introduction to how earthquakes workhow earthquakes work

One of the most terrifying phenomena Until recently - unsubstantiated guesses as to what

caused earthquakes Today – much clearer understanding

o Identified forces of earthquakeso Technology that can tell an earthquake’s

magnitudeo Technology that can tell an origin

To find a way of predicting earthquakes To find way to protect people and property

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Shaking groundShaking ground

An earthquake is a vibration that travels through the earth's crust.o A large truck rumbling down the streeto Volcanic eruptiono Meteor impactso Underground explosionso Collapsing structureso Movements of the earth’s plates

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Earthquakes factsEarthquakes 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 tectonicsTheory of plate tectonics

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 theoryThe basic theory

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 happeno Plates slide against each othero Plates can move aparto Plates can push together

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FaultsFaults

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.

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

In these faults, which are also caused by compression, the rock of the hanging wall is actually pushed up on top of the footwall

This is the sort of fault that occurs in a converging plate boundary

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Reverse faultReverse 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

If this friction level is high enough, the two blocks become locked -- the friction keeps them from sliding against each other

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

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 wavesSeismic waves

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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SeismologySeismology 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

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

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 eathquakesPredicting eathquakes 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 earthquakesPredicting 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 earthquakesSo 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 byo 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 Strengthening Buildings for EarthquakesEarthquakes

Earthquakes cause sideways forces on buildings These are some of the structural systems used to

resist sideways forces

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Horizontal structural systemsHorizontal structural systems

Usually floors and roofs Usually floors and roofs

They share the sideways forces on the building They share the sideways forces on the building between its vertical between its vertical structural membersstructural members..

They include:They include:

Diaphragms Diaphragms TrussingTrussing

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Horizontal DiaphragmsHorizontal Diaphragms

Horizontal diaphragms are usually floors and roofs. Horizontal diaphragms are usually floors and roofs. They are made up from a horizontal frame covered by a They are made up from a horizontal frame covered by a floor or roof floor or roof deck.deck. When a diaphragm is stiff enough in its horizontal When a diaphragm is stiff enough in its horizontal plane, it can share the sideways earthquake forces on a plane, it can share the sideways earthquake forces on a building between the vertical building between the vertical structural membersstructural members, e.g. , e.g. the the columnscolumns and walls. and walls.

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Horizontal TrussingHorizontal Trussing

Horizontal Horizontal trussingtrussing is usually used in roofs where is usually used in roofs where there is not enough deck to allow the roof to act as a there is not enough deck to allow the roof to act as a stiff stiff horizontal diaphragmhorizontal diaphragm..The trussing transfers the sideways earthquake forces The trussing transfers the sideways earthquake forces on a building to its vertical on a building to its vertical structural membersstructural members e.g. the e.g. the columnscolumns and walls. and walls.

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Vertical structural systemsVertical structural systems

Made up from Made up from columns, , beams, walls and , walls and bracing. .

They transfer the sideways forces on the building to the ground. They transfer the sideways forces on the building to the ground.

They include:They include:

Braced framesBraced frames

Moment Moment

resisting framesresisting frames

Shear wallsShear walls

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Braced frames use Braced frames use trussingtrussing to resist sideways forces on to resist sideways forces on buildings. buildings. Trussing, or triangulation, is formed by inserting Trussing, or triangulation, is formed by inserting diagonal diagonal structural members into rectangular areas of a into rectangular areas of a structural frame. It helps stabilise the frame against sideways forces It helps stabilise the frame against sideways forces from earthquakes and strong winds.from earthquakes and strong winds.

Single diagonalsSingle diagonals Cross-bracingCross-bracing Other ways of bracing framesOther ways of bracing frames

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Other ways of bracing frames

Knee Bracing

V Bracing

K Bracing

Knee Bracing

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Moment Moment Resisting FramesResisting Frames

In moment resisting frames, the joints, or In moment resisting frames, the joints, or connections, between connections, between columns and and beams are are designed to be rigiddesigned to be rigidThis causes the columns and beams to bend This causes the columns and beams to bend during earthquakes. So these during earthquakes. So these structural members are designed to be strong in are designed to be strong in bending. . Moment resisting frames simply means frames Moment resisting frames simply means frames that resist forces by bending.that resist forces by bending.

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Shear WallsShear WallsShear walls are vertical walls that are used to stiffen Shear walls are vertical walls that are used to stiffen the structural frames of buildings. They help frames the structural frames of buildings. They help frames resist sideways earthquake forcesresist sideways earthquake forcesThe earthquake forces are transferred to the The earthquake forces are transferred to the ground mainly by shear forces in the wallsground mainly by shear forces in the wallsIt is better to use walls with no openings in them.It is better to use walls with no openings in them.Usually the walls around lift shafts and stairwells are Usually the walls around lift shafts and stairwells are usedused Walls on the sides of buildings that have no windows Walls on the sides of buildings that have no windows can be used.can be used.

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Isolating buildingIsolating building

Base isolation systems reduce building Base isolation systems reduce building vibrations during earthquakes.vibrations during earthquakes.Normally, a building is supported directly Normally, a building is supported directly on its on its foundations, and it is said to have a fixed-base. 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 These bearings are not very stiff in the horizontal direction, so they reduce the horizontal direction, so they reduce the fundamental frequency of vibrationfundamental frequency of vibration of a of a building. building.

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During an earthquake, a fixed-base building can During an earthquake, a fixed-base building can sway from side to side. When a base isolation sway from side to side. When a base isolation system is used, the sideways movement occurs system is used, the sideways movement occurs mainly in the bearingsmainly in the bearings

There are many types of bearings used for base There are many types of bearings used for base isolation. Here are two of them.isolation. Here are two of them.

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Rubber bearingsRubber bearingsRubber bearings are made from layers of rubber with Rubber bearings are made from layers of rubber with thin steel plates between them, and a thick steel plate thin steel plates between them, and a thick steel plate on the top and bottom. on the top and bottom. The bearings are placed between the bottom of a The bearings are placed between the bottom of a building and its foundation . building and its foundation .

The bearings are designed to be very The bearings are designed to be very stiffstiff and strong and strong for for vertical loadvertical load, so that they can carry the weight of , so that they can carry the weight of the building. However, they are designed to be much the building. However, they are designed to be much weaker for horizontal loads, so that they can move weaker for horizontal loads, so that they can move sideways during an earthquake.sideways during an earthquake.

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Friction Pendulum BearingsFriction Pendulum Bearings

Friction pendulum Friction pendulum bearingsbearings are made from two are made from two horizontal steel plates that can slide over each other horizontal steel plates that can slide over each other because of their shape and an additional articulated because of their shape and an additional articulated slider. slider.

They are designed to be very stiff and strong for They are designed to be very stiff and strong for vertical loadvertical load, so that they can carry the weight of the , so that they can carry the weight of the building. building.

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Adding DampersAdding Dampers

Dampers can be installed in the Dampers can be installed in the structural framestructural frame of a building to absorb some of the energy going of a building to absorb some of the energy going into the building from the shaking ground during into the building from the shaking ground during an earthquake. an earthquake.

The dampers reduce the energy available for The dampers reduce the energy available for shaking the building. This means that the building shaking the building. This means that the building deformsdeforms less, so the chance of damage is reduced. less, so the chance of damage is reduced.

There are many types of dampers that can be There are many types of dampers that can be installed in buildings. Here are some of them:installed in buildings. Here are some of them:

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Metallic DampersMetallic Dampers

Metallic dampers are usually made from steel. Metallic dampers are usually made from steel. They are designed to deform so much when the They are designed to deform so much when the building vibrates during an earthquake that they cannot building vibrates during an earthquake that they cannot return to their original shape. return to their original shape. This permanent deformation is called This permanent deformation is called inelastic inelastic deformationdeformation, and it uses some of the earthquake , and it uses some of the earthquake energy which goes into building. energy which goes into building.

X - Plate Metallic Damper

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Friction DampersFriction Dampers

Friction dampers are designed to have moving Friction dampers are designed to have moving parts that will slide over each other during a strong parts that will slide over each other during a strong earthquake. earthquake. When the parts slide over each other, they create When the parts slide over each other, they create friction which uses some of the energy from the friction which uses some of the energy from the earthquake that goes into the building. earthquake that goes into the building.

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The damper is made up from a set of steel plates, The damper is made up from a set of steel plates, with slotted holes in them, and they are bolted with slotted holes in them, and they are bolted together. At high enough forces, the plates can slide together. At high enough forces, the plates can slide over each other creating friction. over each other creating friction.

The plates are specially treated to increase the The plates are specially treated to increase the friction between them.friction between them.

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Viscous fluid dampers Viscous fluid dampers Viscous fluid Viscous fluid dampersdampers are similar to shock are similar to shock absorbers in a car. They consist of a closed cylinder absorbers in a car. They consist of a closed cylinder containing a containing a viscous fluidviscous fluid like oil. like oil. A piston rod is connected to a piston head with A piston rod is connected to a piston head with small holes in it. The piston can move in and out of small holes in it. The piston can move in and out of the cylinder. As it does this, the oil is forced to flow the cylinder. As it does this, the oil is forced to flow through holes in the piston head causing through holes in the piston head causing friction.friction.

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Viscous fluid dampersViscous fluid dampers

The friction converts some of the earthquake energy The friction converts some of the earthquake energy going into the moving building into heat energy.going into the moving building into heat energy.

The damper is usually installed as part of a building's The damper is usually installed as part of a building's bracingbracing system using system using single diagonalssingle diagonals. As the building . As the building sways sways to and froto and fro, the piston is forced in and out of the , the piston is forced in and out of the cylinder.cylinder.

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Earthquakes in the worldEarthquakes in the world

As the Nation's largest water, earth, and biological As the Nation's largest water, earth, and biological science and civilian mapping agency, the U.S. science and civilian mapping agency, the U.S. Geological Survey (USGS) collects, monitors, analyzes, Geological Survey (USGS) collects, monitors, analyzes, and provides scientific understanding about natural and provides scientific understanding about natural resource conditions, issues, and problems. resource conditions, issues, and problems. Earthquake Hazards ProgramEarthquake Hazards ProgramLatest earthquake in the worldLatest earthquake in the world

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