EARTHQUAKE Sarada Mandal Associate Professor in Geography Teacher-in-Charge PRABHU JAGATBANDHU COLLEGE Andul, Howrah.

EARTHQUAKEEARTHQUAKE

Sarada MandalSarada Mandal

Associate Professor in GeographyAssociate Professor in Geography

Teacher-in-ChargeTeacher-in-Charge

PRABHU JAGATBANDHU COLLEGEPRABHU JAGATBANDHU COLLEGE

Andul, HowrahAndul, Howrah

EARTHQUAKEEARTHQUAKE

Definition of Earthquake Definition of Earthquake

An earthquake is the sudden, sometimes violent An earthquake is the sudden, sometimes violent movement of the earth's surface from the release movement of the earth's surface from the release of energy in the earth's crust. Earthquakes occur of energy in the earth's crust. Earthquakes occur when energy stored within the Earth, usually in when energy stored within the Earth, usually in the form of strain in rocks, suddenly releases. the form of strain in rocks, suddenly releases. This energy is transmitted to the surface of the This energy is transmitted to the surface of the Earth by earthquake waves. The study of Earth by earthquake waves. The study of earthquakes and the waves they create is called earthquakes and the waves they create is called seismologyseismology (from the Greek (from the Greek seismosseismos, “to shake”). , “to shake”). Scientists who study earthquakes are called Scientists who study earthquakes are called seismologists.seismologists.

FOCUS AND EPICENTREFOCUS AND EPICENTRE

The point within the Earth along the rupturing geological fault The point within the Earth along the rupturing geological fault where an earthquake originates is called the focus, or where an earthquake originates is called the focus, or hypocenter. hypocenter.

The point on the Earth’s surface directly above the focus is The point on the Earth’s surface directly above the focus is called the epicenter. called the epicenter.

Earthquake waves begin to radiate out from the focus and Earthquake waves begin to radiate out from the focus and subsequently form along the fault rupture. If the focus is near subsequently form along the fault rupture. If the focus is near the surface—between 0 and 70 km (0 and 40 mi) deep—the surface—between 0 and 70 km (0 and 40 mi) deep—shallow-focus earthquakes are produced. shallow-focus earthquakes are produced.

If it is intermediate or deep below the crust—between 70 and If it is intermediate or deep below the crust—between 70 and 700 km (40 and 400 mi) deep—a deep-focus earthquake will 700 km (40 and 400 mi) deep—a deep-focus earthquake will be produced. be produced.

Shallow-focus earthquakes tend to be larger, and therefore Shallow-focus earthquakes tend to be larger, and therefore more damaging, earthquakes. This is because they are closer more damaging, earthquakes. This is because they are closer to the surface where the rocks are stronger and build up to the surface where the rocks are stronger and build up more strain.more strain.

Earthquake WavesEarthquake Waves

Earthquake wavesEarthquake waves

There are four kinds of wave produced by an earthquake. Two move There are four kinds of wave produced by an earthquake. Two move over the surface, causing damage, and two pass through the Earth over the surface, causing damage, and two pass through the Earth itself: body waves. itself: body waves.

By studying body waves, scientists have worked out what the Earth By studying body waves, scientists have worked out what the Earth is like inside:is like inside:

Body waves tell us a great deal about what we cannot see inside the Body waves tell us a great deal about what we cannot see inside the planet. planet.

-          P-waves: Primary waves are longitudinal waves that push and -          P-waves: Primary waves are longitudinal waves that push and pull the earth. They are the fastest body wave, averaging speeds of pull the earth. They are the fastest body wave, averaging speeds of about 6 km/s and so arrive first. about 6 km/s and so arrive first.

-          S-waves: Secondary waves are transverse waves, which make -          S-waves: Secondary waves are transverse waves, which make the earth shake from side to side. Slower than P waves, they average the earth shake from side to side. Slower than P waves, they average about 4 km/s and so arrive second. about 4 km/s and so arrive second.

Both S and P waves travel throughout the body of the earth, and can Both S and P waves travel throughout the body of the earth, and can be picked up by seismometers - machines that record earthquakes - be picked up by seismometers - machines that record earthquakes - anywhere in the world. anywhere in the world.

However, it turns out that S waves cannot travel through the core, However, it turns out that S waves cannot travel through the core, and only P waves are recorded in some places: and only P waves are recorded in some places:

Earthquake wavesEarthquake waves

Causes of Earthquake Causes of Earthquake

Plate tectonicsPlate tectonics Elastic Rebound theory – Propounded Elastic Rebound theory – Propounded

by Harry Fielding Reid in 1911by Harry Fielding Reid in 1911 Occurrence of FaultOccurrence of Fault VolcanismVolcanism Actions of ManActions of Man

PLATE TECTONICSPLATE TECTONICS

Most Earthquakes are caused by Plate Tectonics. The Most Earthquakes are caused by Plate Tectonics. The earth's crust consists of a number of sections or plates earth's crust consists of a number of sections or plates that float on the molten rock of the mantle. These that float on the molten rock of the mantle. These plates move on convection currents caused by heat plates move on convection currents caused by heat rising from the center of the earth. The hot magma rising from the center of the earth. The hot magma rises and spreads out on the surface, creating new rises and spreads out on the surface, creating new crust. The crust spreads out forming a new plate until it crust. The crust spreads out forming a new plate until it meets another plate. One of the plates will be pushed meets another plate. One of the plates will be pushed down into the interior of the earth and reabsorbed into down into the interior of the earth and reabsorbed into the mantle. Plates can also be compressed to push up the mantle. Plates can also be compressed to push up mountains when they collide or move sideways along mountains when they collide or move sideways along transform faults. transform faults.

PLATE TECTONICSPLATE TECTONICS

PLATE TECTONICSPLATE TECTONICS

FAULTSFAULTS

Most earthquakes are caused by the sudden slip along Most earthquakes are caused by the sudden slip along geologic faults. The faults slip because of movement of geologic faults. The faults slip because of movement of the Earth’s tectonic plates. This concept is called the the Earth’s tectonic plates. This concept is called the elastic rebound theory. The rocky tectonic plates move elastic rebound theory. The rocky tectonic plates move very slowly, floating on top of a weaker rocky layer. As very slowly, floating on top of a weaker rocky layer. As the plates collide with each other or slide past each the plates collide with each other or slide past each other, pressure builds up within the rocky crust. other, pressure builds up within the rocky crust. Earthquakes occur when pressure within the crust Earthquakes occur when pressure within the crust increases slowly over hundreds of years and finally increases slowly over hundreds of years and finally exceeds the strength of the rocks. Earthquakes also exceeds the strength of the rocks. Earthquakes also occur when human activities, such as the filling of occur when human activities, such as the filling of reservoirs, increase stress in the Earth’s crust.reservoirs, increase stress in the Earth’s crust.

FAULTSFAULTS

Elastic Rebound Theory Elastic Rebound Theory

In 1911 American seismologist Harry Fielding Reid studied the In 1911 American seismologist Harry Fielding Reid studied the effects of the April 1906 California earthquake. He proposed the effects of the April 1906 California earthquake. He proposed the elastic rebound theory to explain the generation of certain elastic rebound theory to explain the generation of certain earthquakes that scientists now know occur in tectonic areas, earthquakes that scientists now know occur in tectonic areas, usually near plate boundaries. This theory states that during an usually near plate boundaries. This theory states that during an earthquake, the rocks under strain suddenly break, creating a earthquake, the rocks under strain suddenly break, creating a fracture along a fault. When a fault slips, movement in the crustal fracture along a fault. When a fault slips, movement in the crustal rock causes vibrations. The slip changes the local strain out into the rock causes vibrations. The slip changes the local strain out into the surrounding rock. The change in strain leads to surrounding rock. The change in strain leads to aftershocksaftershocks (smaller (smaller earthquakes that occur after the initial earthquake), which are earthquakes that occur after the initial earthquake), which are produced by further slips of the main fault or adjacent faults in the produced by further slips of the main fault or adjacent faults in the strained region. The slip begins at the focus and travels along the strained region. The slip begins at the focus and travels along the plane of the fault, radiating waves out along the rupture surface. On plane of the fault, radiating waves out along the rupture surface. On each side of the fault, the rock shifts in opposite directions. The each side of the fault, the rock shifts in opposite directions. The fault rupture travels in irregular steps along the fault; these sudden fault rupture travels in irregular steps along the fault; these sudden stops and starts of the moving rupture give rise to the vibrations stops and starts of the moving rupture give rise to the vibrations that propagate as seismic waves. After the earthquake, strain begins that propagate as seismic waves. After the earthquake, strain begins to build again until it is greater than the forces holding the rocks to build again until it is greater than the forces holding the rocks together, then the fault snaps again and causes another earthquake.together, then the fault snaps again and causes another earthquake.

Human ActivitiesHuman Activities

Fault rupture is not the only cause of earthquakes; human Fault rupture is not the only cause of earthquakes; human activities can also be the direct or indirect cause of activities can also be the direct or indirect cause of significant earthquakes. Injecting fluid into deep wells for significant earthquakes. Injecting fluid into deep wells for waste disposal, filling reservoirs with water, and firing waste disposal, filling reservoirs with water, and firing underground nuclear test blasts can, in limited underground nuclear test blasts can, in limited circumstances, lead to earthquakes. These activities increase circumstances, lead to earthquakes. These activities increase the strain within the rock near the location of the activity so the strain within the rock near the location of the activity so that rock slips and slides along pre-existing faults more that rock slips and slides along pre-existing faults more easily. While earthquakes caused by human activities may be easily. While earthquakes caused by human activities may be harmful, they can also provide useful information. Prior to the harmful, they can also provide useful information. Prior to the Nuclear Test Ban treaty, scientists were able to analyze the Nuclear Test Ban treaty, scientists were able to analyze the travel and arrival times of P waves from known earthquakes travel and arrival times of P waves from known earthquakes caused by underground nuclear test blasts. Scientists used caused by underground nuclear test blasts. Scientists used this information to study earthquake waves and determine this information to study earthquake waves and determine the interior structure of the Earth.the interior structure of the Earth.

Volcanic Earthquakes Volcanic Earthquakes

Volcanic earthquakes occur near active volcanoes Volcanic earthquakes occur near active volcanoes but have the same fault slip mechanism as tectonic but have the same fault slip mechanism as tectonic earthquakes. Volcanic earthquakes are caused by earthquakes. Volcanic earthquakes are caused by the upward movement of magma under the the upward movement of magma under the volcano, which strains the rock locally and leads to volcano, which strains the rock locally and leads to an earthquake. As the fluid magma rises to the an earthquake. As the fluid magma rises to the surface of the volcano, it moves and fractures rock surface of the volcano, it moves and fractures rock masses and causes continuous tremors that can masses and causes continuous tremors that can last up to several hours or days. Volcanic last up to several hours or days. Volcanic earthquakes occur in areas that are associated earthquakes occur in areas that are associated with volcanic eruptions, such as in the Cascade with volcanic eruptions, such as in the Cascade Mountain Range of the Pacific Northwest, Japan, Mountain Range of the Pacific Northwest, Japan, Iceland, and at isolated hot spots such as Hawaii.Iceland, and at isolated hot spots such as Hawaii.

Results of EarthquakeResults of Earthquake

LandslideLandslide Soil liquefactionSoil liquefaction FireFire Tsunami waves and floodingTsunami waves and flooding DiseasesDiseases

Major belts of Earthquake Major belts of Earthquake of the Worldof the World

Average number of Average number of Earthquakes per year Earthquakes per year

LEVELLEVEL RICHTER RICHTER MAGNITUDEMAGNITUDE

FREQUENCY/YEARFREQUENCY/YEAR

GREATGREAT +8.0+8.0 11

MAJORMAJOR 7.0-7.97.0-7.9 1818

LARGE/LARGE/DESTRUCTIVEDESTRUCTIVE

6.0-6.96.0-6.9 120120

MODERATE/ MODERATE/ DAMAGINGDAMAGING

5.0-5.95.0-5.9 10001000

MINORMINOR 4.0-4.94.0-4.9 60006000

GENERALLY FELTGENERALLY FELT 3.0-3.93.0-3.9 4900049000

POTENTIALLY POTENTIALLY PERCEPTIBLEPERCEPTIBLE

2.0-2.92.0-2.9 300,000300,000

IMPERCEPTIBLEIMPERCEPTIBLE <2.0<2.0 +600,000+600,000

Seismograph Seismograph

A seismometer records the vibrations from A seismometer records the vibrations from earthquakes. Mechanical versions work by way of a earthquakes. Mechanical versions work by way of a large mass, freely suspended. large mass, freely suspended.

In the example on the right, a rotating drum records a In the example on the right, a rotating drum records a red line on a sheet of paper. If the earth moves (in this red line on a sheet of paper. If the earth moves (in this case from left to right) the whole machine will vibrate case from left to right) the whole machine will vibrate too. too.

However, the large mass tends to stay still, so the However, the large mass tends to stay still, so the drum shakes beneath the pen, recording a squiggle. drum shakes beneath the pen, recording a squiggle.

The confiner prevents the mass from bouncing around The confiner prevents the mass from bouncing around all over the place. all over the place.

Incidentally, a Incidentally, a seismographseismograph is the graph that a is the graph that a seismometer draws seismometer draws

SeismographSeismograph

Magnitude of Earthquake Magnitude of Earthquake

FIGURE 1 - CHARLES RICHTER STUDYING A SEISMOGRAM

Magnitude of EarthquakeMagnitude of Earthquake

One of Dr. Charles F. Richter's most valuable contributions was to One of Dr. Charles F. Richter's most valuable contributions was to recognize that the seismic waves radiated by all earthquakes can recognize that the seismic waves radiated by all earthquakes can provide good estimates of their magnitudes. . He collected the provide good estimates of their magnitudes. . He collected the recordings of seismic waves from a large number of earthquakes, recordings of seismic waves from a large number of earthquakes, and developed a calibrated system of measuring them for and developed a calibrated system of measuring them for magnitude. magnitude.

Richter showed that, the larger the intrinsic energy of the Richter showed that, the larger the intrinsic energy of the earthquake, the larger the amplitude of ground motion at a given earthquake, the larger the amplitude of ground motion at a given distance. He calibrated his scale of magnitudes using measured distance. He calibrated his scale of magnitudes using measured maximum amplitudes of shear waves on seismometers particularly maximum amplitudes of shear waves on seismometers particularly sensitive to shear waves with periods of about one second. The sensitive to shear waves with periods of about one second. The records had to be obtained from a specific kind of instrument, called records had to be obtained from a specific kind of instrument, called a Wood-Anderson seismograph. Although his work was originally a Wood-Anderson seismograph. Although his work was originally calibrated only for these specific seismometers, and only for calibrated only for these specific seismometers, and only for earthquakes in southern California, seismologists have developed earthquakes in southern California, seismologists have developed scale factors to extend Richter's magnitude scale to many other scale factors to extend Richter's magnitude scale to many other types of measurements on all types of seismometers, all over the types of measurements on all types of seismometers, all over the world. In fact, magnitude estimates have been made for thousands world. In fact, magnitude estimates have been made for thousands of Moon-quakes and for two quakes on Mars. of Moon-quakes and for two quakes on Mars.

Richter Magnitude of Richter Magnitude of EarthquakeEarthquake

The equation for Richter Magnitude is: The equation for Richter Magnitude is:

MML = logL = logA(mm)A(mm) + + (Distance correction factor)(Distance correction factor) Here Here AA is the amplitude, in millimeters, measured directly is the amplitude, in millimeters, measured directly from the photographic paper record of the Wood-Anderson from the photographic paper record of the Wood-Anderson seismometer, a special type of instrument. The seismometer, a special type of instrument. The distance distance factorfactor comes from a table that can be found in Richter's comes from a table that can be found in Richter's (1958) book (1958) book Elementary SeismologyElementary Seismology. .

In the 'Richter scale'. An increase of one unit represents a In the 'Richter scale'. An increase of one unit represents a thirty-fold increase in energy, so an earthquake like the one thirty-fold increase in energy, so an earthquake like the one that ruined Kobe in Japan in 1995 (magnitude nearly 7) was that ruined Kobe in Japan in 1995 (magnitude nearly 7) was about 900 times as powerful as the earthquake felt in England about 900 times as powerful as the earthquake felt in England and Wales in 1990 (magnitude about 5).and Wales in 1990 (magnitude about 5).

Disadvantage of Richter Disadvantage of Richter scalescale

Over-dependence on instrumental Over-dependence on instrumental readingreading

No scope for physiographic and tectonic No scope for physiographic and tectonic parametersparameters

Seismic Moment Seismic Moment

Seismologists have more recently developed a standard magnitude Seismologists have more recently developed a standard magnitude scale that is completely independent of the type of instrument. It is scale that is completely independent of the type of instrument. It is called the moment magnitude, and it comes from the seismic moment. called the moment magnitude, and it comes from the seismic moment.

To get an idea of the seismic moment, we go back to the elementary To get an idea of the seismic moment, we go back to the elementary physics concept of torque. A torque is a force that changes the angular physics concept of torque. A torque is a force that changes the angular momentum of a system. It is defined as the force times the distance momentum of a system. It is defined as the force times the distance from the center of rotation. Earthquakes are caused by internal torques, from the center of rotation. Earthquakes are caused by internal torques, from the interactions of different blocks of the earth on opposite sides from the interactions of different blocks of the earth on opposite sides of faults. After some rather complicated mathematics, it can be shown of faults. After some rather complicated mathematics, it can be shown that the moment of an earthquake is simply expressed by:that the moment of an earthquake is simply expressed by:

Seismic MomentSeismic Moment

The formula above, for the moment of an earthquake, is fundamental to seismologists' The formula above, for the moment of an earthquake, is fundamental to seismologists' understanding of how dangerous faults of a certain size can be. understanding of how dangerous faults of a certain size can be.

Next let's take the energy we found for the Double Spring Flat earthquake and Next let's take the energy we found for the Double Spring Flat earthquake and estimate its magnitude:estimate its magnitude:

Seismic Energy Seismic Energy

Both the magnitude and the seismic moment are related to the amount of Both the magnitude and the seismic moment are related to the amount of energy that is radiated by an earthquake. Richter, working with energy that is radiated by an earthquake. Richter, working with Dr. Beno Dr. Beno GutenbergGutenberg, early on developed a relationship between magnitude and , early on developed a relationship between magnitude and energy. Their relationship is: energy. Their relationship is:

loglogEES = 11.8 + 1.5S = 11.8 + 1.5MM

giving the energy giving the energy EES in S in ergergs from the magnitude s from the magnitude MM. Note that . Note that EES is not S is not the total ``intrinsic'' energy of the earthquake, transferred from sources the total ``intrinsic'' energy of the earthquake, transferred from sources such as gravitational energy or to sinks such as heat energy. It is only the such as gravitational energy or to sinks such as heat energy. It is only the amount radiated from the earthquake as seismic waves, which ought to amount radiated from the earthquake as seismic waves, which ought to be a small fraction of the total energy transfered during the earthquake be a small fraction of the total energy transfered during the earthquake

process. process. More recently, More recently, Dr. Hiroo KanamoriDr. Hiroo Kanamori came up with a relationship between came up with a relationship between seismic moment and seismic wave energy. It gives: seismic moment and seismic wave energy. It gives:

EnergyEnergy = ( = (MomentMoment)/20,000)/20,000

Earthquake IntensityEarthquake Intensity

GIUSEPPE MERCALLI

Evolution of the Mercalli Evolution of the Mercalli scalescale

The Mercalli scale originated with the widely used simple ten-The Mercalli scale originated with the widely used simple ten-degree Rossi-Forel scale, which was revised by Italian degree Rossi-Forel scale, which was revised by Italian volcanologist Giuseppe Mercalli in 1883 and 1902. The terms volcanologist Giuseppe Mercalli in 1883 and 1902. The terms Mercalli intensity scaleMercalli intensity scale or or Mercalli scaleMercalli scale should not be used should not be used unless one really means the original ten-degree scale of 1902.unless one really means the original ten-degree scale of 1902.In 1902 the ten-degree Mercalli scale was expanded to twelve In 1902 the ten-degree Mercalli scale was expanded to twelve degrees by Italian physicist Adolfo Cancani. It was later degrees by Italian physicist Adolfo Cancani. It was later completely re-written by German geophysicist August Heinrich completely re-written by German geophysicist August Heinrich Sieberg and became known as the Mercalli-Cancani-Sieberg Sieberg and became known as the Mercalli-Cancani-Sieberg (MCS) scale. The Mercalli-Cancani-Sieberg scale was later (MCS) scale. The Mercalli-Cancani-Sieberg scale was later modified and published in English by Harry O. Wood and Frank modified and published in English by Harry O. Wood and Frank Neumann in 1931 as the Mercalli-Wood-Neuman (MWN) scale. It Neumann in 1931 as the Mercalli-Wood-Neuman (MWN) scale. It was later improved by Charles Richter, the father of the Richter was later improved by Charles Richter, the father of the Richter magnitude scale. The scale is known today as the Modified magnitude scale. The scale is known today as the Modified Mercalli Scale and commonly abbreviated MM.Mercalli Scale and commonly abbreviated MM.

Modified MercalliModified Mercalli

The lower degrees of the MM scale generally The lower degrees of the MM scale generally deal with the manner in which the earthquake deal with the manner in which the earthquake is felt by people. The higher numbers of the is felt by people. The higher numbers of the scale are based on observed structural scale are based on observed structural damage. The table below is a rough guide to damage. The table below is a rough guide to the degrees of the the degrees of the Modified Mercalli ScaleModified Mercalli Scale. The . The colors and descriptive names shown here differ colors and descriptive names shown here differ from those used on certain shake maps in from those used on certain shake maps in other articles.other articles.

Modified MercalliModified MercalliI.I. InstrumentalInstrumental Not felt except by a very few Not felt except by a very few

under especially favorable conditionsunder especially favorable conditionsII.II. Feeble Feeble Felt only by a few persons at rest, Felt only by a few persons at rest,

especially on upper floors of buildings. especially on upper floors of buildings. Delicately suspended objects may swing.Delicately suspended objects may swing.

III.III. Slight Slight Felt quite noticeably by persons Felt quite noticeably by persons indoors, especially on the upper floors of indoors, especially on the upper floors of buildings. Many do not recognize it as an buildings. Many do not recognize it as an earthquake. Standing motor cars may rock earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of slightly. Vibration similar to the passing of a truck. Duration estimated.a truck. Duration estimated.

Modified MercalliModified Mercalli iv. Moderateiv. Moderate Felt indoors by many, outdoors by few Felt indoors by many, outdoors by few

during the day. At night, some awakened. Dishes, during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. Dishes and Standing motor cars rocked noticeably. Dishes and windows rattle alarmingly.windows rattle alarmingly.

V. Rather StrongV. Rather Strong Felt by nearly everyone; many Felt by nearly everyone; many awakened. Some dishes and windows broken. awakened. Some dishes and windows broken. Unstable objects overturned. Clocks may stop.Unstable objects overturned. Clocks may stop.

VI. StrongVI. Strong Felt by all; many frightened and run Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, outdoors, walk unsteadily. Windows, dishes, glassware broken; books off shelves; some heavy glassware broken; books off shelves; some heavy furniture moved or overturned; a few instances of furniture moved or overturned; a few instances of fallen plaster. Damage slight.fallen plaster. Damage slight.

Modified MercalliModified Mercalli

VII. Very StrongVII. Very Strong Difficult to stand; furniture broken; damage Difficult to stand; furniture broken; damage negligible in building of good design and construction; negligible in building of good design and construction; slight to moderate in well-built ordinary structures; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed considerable damage in poorly built or badly designed structures; some chimneys broken. Noticed by persons structures; some chimneys broken. Noticed by persons driving motor carsdriving motor cars

VIII. DestructiveVIII. Destructive Damage slight in specially designed Damage slight in specially designed structures; considerable in ordinary substantial buildings structures; considerable in ordinary substantial buildings with partial collapse. Damage great in poorly built with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture moved.monuments, walls. Heavy furniture moved.

IX. RuinousIX. Ruinous General panic; damage considerable in specially General panic; damage considerable in specially designed structures, well designed frame structures designed structures, well designed frame structures thrown out of plumb. Damage great in substantial thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off buildings, with partial collapse. Buildings shifted off foundationsfoundations

Modified MercalliModified MercalliX. DisastrousX. Disastrous Some well built wooden structures Some well built wooden structures

destroyed; most masonry and frame structures destroyed; most masonry and frame structures destroyed with foundation. Rails bent.destroyed with foundation. Rails bent.

XI. Very DisastrousXI. Very Disastrous Few, if any masonry Few, if any masonry structures remain standing. Bridges destroyed. structures remain standing. Bridges destroyed. Rails bent greatly.Rails bent greatly.

XII. CatastrophicXII. Catastrophic Total damage - Almost Total damage - Almost everything is destroyed. Lines of sight and everything is destroyed. Lines of sight and level distorted. Objects thrown into the air. The level distorted. Objects thrown into the air. The ground moves in waves or ripples. Large ground moves in waves or ripples. Large amounts of rock may move.amounts of rock may move.

EXAMPLES OF OTHER EXAMPLES OF OTHER INTENSITY-SCALEINTENSITY-SCALE

MSK-64(Medvedev-Sponheur-Karnik MSK-64(Medvedev-Sponheur-Karnik scale)scale)

MSK-81MSK-81 EMS (European Macro-seismic) Scale EMS (European Macro-seismic) Scale

Disadvantages of Disadvantages of intensity scaleintensity scale

Depth of focusDepth of focus Under-lying structuresUnder-lying structures Nature of buildingsNature of buildings Perception of the affected peoplePerception of the affected people

Relationship between Relationship between magnitude and intensitymagnitude and intensity

Richter MagnitudeRichter Magnitude Energy in ergEnergy in erg Frequency / yearFrequency / year Intensity according to Intensity according to MM ScaleMM Scale

3.0 -- 3.93.0 -- 3.9 9.59.5×10×101515 -- 4×10 -- 4×101717 49,00049,000 II - IIIII - III

4.0 -- 4.94.0 -- 4.9 66×10×101717 – 8.8×10 – 8.8×101818 6,0006,000 IV - VIV - V

5.0 – 5.95.0 – 5.9 9.59.5×10×101818 -- 4×10 -- 4×102020 800800 VI -- VIIVI -- VII

6.0 – 6.96.0 – 6.9 66×10×102020 – 8.8×10 – 8.8×102121 120120 VII -- VIIIVII -- VIII

7.0 – 7.97.0 – 7.9 9.59.5×10×102222 -- 4×10 -- 4×102323 1818 IX -- XIX -- X

8.0 – 8.98.0 – 8.9 66×10×102323 – 8.8×10 – 8.8×102424 11 XI -- XIIXI -- XII

Mapping of EarthquakeMapping of Earthquake

Mapping for several earthquakesMapping for several earthquakese.g. superimposition of Plate Margins and e.g. superimposition of Plate Margins and

locations of the epicenters of 100 major locations of the epicenters of 100 major earthquakes all over the Worldearthquakes all over the World

Or showing the locations, magnitudes, Or showing the locations, magnitudes, depth and time for several earthquakes depth and time for several earthquakes by different symbolsby different symbols

Or loss estimation for several earthquakes.Or loss estimation for several earthquakes.

Mapping of EarthquakeMapping of Earthquake

Mapping for a single earthquakeMapping for a single earthquake Mapping by drawing Mapping by drawing isoseismal isoseismal lines, lines,

identification of intensity zones and identification of intensity zones and epicentersepicenters

Mapping by showing loss and damage Mapping by showing loss and damage for different intensity zonesfor different intensity zones

Mapping of EarthquakeMapping of Earthquake

Mapping by showing level of earthquake-Mapping by showing level of earthquake-proneness of different regions of a proneness of different regions of a

country (e.g. India)country (e.g. India)

Mapping by showing level of Mapping by showing level of earthquake-proneness of different earthquake-proneness of different regions of a country (e.g. India)regions of a country (e.g. India)

Collect the data for the locations and Collect the data for the locations and magnitudes of earthquakes in Andaman and magnitudes of earthquakes in Andaman and Nicobar islands for the time period of last 100 Nicobar islands for the time period of last 100 yearsyears

Divide the area by grids of latitude and Divide the area by grids of latitude and longitude ( say by 10 minutes )longitude ( say by 10 minutes )

Identify the highest magnitude as the Identify the highest magnitude as the representative value for a particular year representative value for a particular year ( say1910 )( say1910 )

Mapping by showing level of Mapping by showing level of earthquake-proneness of different earthquake-proneness of different regions of a country (e.g. India)regions of a country (e.g. India)

Identify the representative values for Identify the representative values for each year in the total time periodeach year in the total time period

Calculate the number of representative Calculate the number of representative values in each gridvalues in each grid

Consider two types of variables in each Consider two types of variables in each grid : a) the number of yearsgrid : a) the number of years

b) the number of highest b) the number of highest magnitudes of earthquakesmagnitudes of earthquakes

Mapping by showing level of Mapping by showing level of earthquake-proneness of different earthquake-proneness of different regions of a country (e.g. India)regions of a country (e.g. India)

Do Do time series analysistime series analysis of those variables of those variables for each grid by for each grid by Least Square MethodLeast Square Method

ΣΣy=Na + b y=Na + b ΣΣ x x

ΣΣxy = axy = aΣΣ x + b x + bΣΣ x x22

b=Mb=M11=maximum observed magnitude on =maximum observed magnitude on

regression relationregression relation

Draw isopleth lines by these b valuesDraw isopleth lines by these b values

Mapping by showing level of Mapping by showing level of earthquake-proneness of different earthquake-proneness of different regions of a country (e.g. India)regions of a country (e.g. India)

Calculate a/b values for each gridCalculate a/b values for each grid a/b= Ma/b= M22 = M = Mmaxmax = Expected upper = Expected upper

magnitude level of earthquakesmagnitude level of earthquakes Draw isopleth lines by these values and Draw isopleth lines by these values and

identify the zonesidentify the zones