earthquake measurement assignment

8/2/2019 Earthquake Measurement Assignment

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EARTHQUAKE MEASUREMENT

Earthquakes are measured with a device called a seismograph. The Richter scale

measures the magnitude (size) of an earthquake on a scale of 1 to 10 using a seismograph. Each

step in the scale indicates a tenfold increase in the energy of the earthquake.

The Richter scale was devised in the 1930s by an American geophysicist called Charles

Richter (1900 - 1985). The most powerful earthquake ever recorded was in Chile in 1960, which

regidtered 9.5 on Richter scale. Between 10 and 20 earthquakes each year reach 7 on the Richter

scale.

The Modified Mercalli scale assesses an earthquake's severity according to its effects on

a scale of 1 to 12 in Roman numerals (I - XII). A Mercalli scale I earthquake is one that is only

detectable with special instruments. A Mercalli scale XII earthquake causes almost total

destruction of cities and reshapes the landscape.

RICHTER MAGNITUDE SCALE

The expression Richter magnitude scale refers to a number of ways to assign a single

number to quantify the energy contained in an earthquake. In all cases, the magnitude is a base-

10 logarithmic scale obtained by calculating the logarithm of the amplitude of waves measured

by a seismograph. An earthquake that measures 5.0 on the Richter scale has a shaking amplitude

10 times larger and corresponds to an energy release of √1000 ≈ 31.6 times greater than one that

measures 4.0

The Richter magnitude of an earthquake is determined from the logarithm of the

amplitude of waves recorded by seismographs (adjustments are included to compensate for the

variation in the distance between the various seismographs and the epicenter of the earthquake).The original formula is: where A is the maximum excursion of the Wood-Anderson

seismograph, the empirical function A0 depends only on the epicentral distance of the station, δ.

In practice, readings from all observing stations are averaged after adjustment with station-

specific corrections to obtain the ML value.

http://en.wikipedia.org/wiki/Earthquake

http://en.wikipedia.org/wiki/Base-10


http://en.wikipedia.org/wiki/Logarithmic_scale

http://en.wikipedia.org/wiki/Amplitude

http://en.wikipedia.org/wiki/Seismometer

http://en.wikipedia.org/wiki/Logarithm


http://en.wikipedia.org/wiki/Epicentral_distance

http://en.wikipedia.org/wiki/Epicentral_distance


http://en.wikipedia.org/wiki/Logarithm

http://en.wikipedia.org/wiki/Seismometer


http://en.wikipedia.org/wiki/Logarithmic_scale






Because of the logarithmic basis of the scale, each whole number increase in magnitude

represents a tenfold increase in measured amplitude; in terms of energy, each whole number

increase corresponds to an increase of about 31.6 times the amount of energy released, and each

increase of 0.2 corresponds to a doubling of the energy released. Events with magnitudes greater

than about 4.6 are strong enough to be recorded by a seismograph anywhere in the world, so long

as its sensors are not located in the earthquake's shadow

The following describes the typical effects of earthquakes of various magnitudes near the

epicenter. The values are typical only and should be taken with extreme caution, since intensity

and thus ground effects depend not only on the magnitude, but also on the distance to the

epicenter, the depth of the earthquake's focus beneath the epicenter, and geological conditions

(certain terrains can amplify seismic signals).

Magnitude Description Earthquake effectsFrequency of

occurrence

Lessthan

2.0Micro Micro earthquakes, not felt. Continual

2.0 – 2.9

Minor

Generally not felt, but recorded. 1,300,000 per year (est.)

3.0 – 3.9 Often felt, but rarely causes damage. 130,000 per year (est.)

4.0 – 4.9 LightNoticeable shaking of indoor items, rattling

noises. Significant damage unlikely.13,000 per year (est.)

5.0 – 5.9 Moderate

Can cause major damage to poorly

constructed buildings over small regions. At

most slight damage to well-designed

buildings.

1,319 per year

6.0 – 6.9 StrongCan be destructive in areas up to about 160

kilometers (99 mi) across in populated areas.134 per year

http://en.wikipedia.org/wiki/Seismic_shadowing

http://en.wikipedia.org/wiki/Seismic_shadowing



7.0 – 7.9 Major Can cause serious damage over larger areas. 15 per year

8.0 – 8.9

Great

Can cause serious damage in areas several

hundred kilometers across.1 per year

9.0 – 9.9Devastating in areas several thousand

kilometers across.1 per 10 years (est.)

10.0+ Massive

Never recorded, widespread devastation

across very large areas; see below for

equivalent seismic energy yield.

Extremely rare

(Unknown/May not be

possible)

MAGNITUDE MEASUREMENT

Earthquakes can be measured in several ways. The first way is to describe the

earthquake's intensity. Intensity is the measure, in terms of degrees, of damage to the surface and

the effects on humans. Intensity records only observations of effects on the crust, not actual

ground motion or wave amplitudes which can be recorded by instruments. While intensity helps

to determine how large of an area was effected, it is not an accurate measure of the earthquake

for many reasons. Two such reasons are: only the effect on an area showing the greatest intensity

is reported, which can imply a greater or lesser intensity than what actually occurred, and the

way in which seismic waves travel varies as they pass through different types of rocks, so some

areas near by may feel nothing because they are built on faulted rock, while other areas quite a

distance from the foci will feel the effects because they are built on compact homogenous rocks.

The second type of measurement is the magnitude of the earthquake. Magnitude does not

depend on population and effects to ground structures, but rather on wave amplitude and

distance. Magnitude is determined using mathematical formulae and information from

seismograms. One such magnitude scale is the Richter scale. This magnitude scale is

logarithmic, meaning each step in magnitude is exponentially greater than the last.

http://scign.jpl.nasa.gov/learn/glossary.htm#thirtyfive

http://scign.jpl.nasa.gov/learn/glossary.htm#fortytwo




http://scign.jpl.nasa.gov/learn/glossary.htm#thirtyfive



To determine the Richter magnitude, information collected by seismometers is used.

Using a seismogram, the time difference between the recording of the P wave and the S wave is

determined and matched to a corresponding distance value. The single maximum amplitude

recorded on the seismogram is calculated and a line is drawn between the amplitude scale and

the distance scale. The line crosses another scale, which corresponds to the magnitude. While

this type of measurement is the most well known, the Richter scale is not as accurate a

measurement as believed. Originally designed specifically for California, the Richter magnitude

scale becomes an approximation in other states and countries. Also, the type of wave whose

amplitude is to be measured is not specified, and it does not distinguish between deep and

shallow foci.

Below is a chart that shows how to measure Richter magnitude by an "eyeball" fit. First,the amplitude of the surface wave is measured on a seismogram produced by a Wood-Anderson

seismometer (a specfic type of seismometer) and then it is compared with distance from the

earthquake or the S-P time (which is the amount of time between the P-wave and S-wave arrival)

to yield a magnitude.

There are many other magnitude measurements. In addition to Richter magnitude, there is

also body wave magnitude and surface wave magnitude. These magnitude scales differ by the

type of wave amplitude that is measured from the seismogram and the mathematical formula

used to determine the magnitude. They are all, however, logarithmic scales.

A third type of measurement is called the seismic moment. Using the seismic waves and

field measurements that describe the fault area, the moment, a parameter related to the angular

leverage of the forces that produce slip on a fault, can be measured. This moment can be related

to a corresponding magnitude for easier interpretation, called the moment magnitude. The benefit

of this type of measurement is that it gives a consistent and uniform measure of the size of an

earthquake of any magnitude anywhere in the world, and because it takes into account fault

geometry. Along with this new type of measurement, the individual amplitudes of body and

surface waves are being measured as well.

http://scign.jpl.nasa.gov/learn/glossary.htm#sixtyfive

http://scign.jpl.nasa.gov/learn/glossary.htm#fortysix

http://scign.jpl.nasa.gov/learn/glossary.htm#fortysix

http://scign.jpl.nasa.gov/learn/glossary.htm#sixtyfive



RICHTER'S FIRST SCALE

The pioneering seismologist Charles Richter started in the 1930s by simplifying

everything he could think of. He chose one standard instrument, a Wood-Anderson seismograph,

used only nearby earthquakes in Southern California, and took only one piece of data — the

distance A in millimeters that the seismograph needle moved. He worked up a simple adjustment

factor B to allow for near versus distant quakes, and that was the first Richter scale of local

magnitude M L:

M L = log A + B

A graphical version of his scale is reproduced on the Caltech archives site.

You'll notice that M L really measures the size of earthquake waves, not an earthquake's total

energy, but it was a start. This scale worked fairly well as far as it went, which was for small and

moderate earthquakes in Southern California. Over the next 20 years Richter and many other

workers extended the scale to newer seismometers, different regions, and different kinds of

seismic waves.

BODY-WAVE MAGNITUDE

mb = log( A / T ) + Q( D,h)

where A is the ground motion (in microns), T is the wave's period (in seconds), and Q( D,h) is a

correction factor that depends on distance to the quake's epicenter D (in degrees) and focal depth

h (in kilometers).

SURFACE-WAVE MAGNITUDE

M s = log( A / T ) + 1.66 log D + 3.30

mb uses relatively short seismic waves with a 1-second period, so to it every quake source that is

larger than a few wavelengths looks the same. That corresponds to a magnitude of about 6.5. M s

uses 20-second waves and can handle larger sources, but it too saturates around magnitude 8.

http://archives.caltech.edu/pictures/1.46.1-17.jpg

http://archives.caltech.edu/pictures/1.46.1-17.jpg



MOMENT MAGNITUDE

M w = 2/3 log( M o) - 10.7

This scale therefore does not saturate. Moment magnitude can match anything the Earth canthrow at us. The formula for M w is such that below magnitude 8 it matches M s and below

magnitude 6 it matches mb, which is close enough to Richter's old M L. So keep calling it the

Richter scale if you like — it's the scale Richter would have made if he could.

MEASURING EARTHQUAKES

Seismologists use two main devices to measure an earthquake: a seismograph and aseismoscope. The seismograph is an instrument that measures seismic waves caused by an

earthquake. The seismograph has three main devices, the Richter Magnitude Scale, the Modified

Mercalli Intensity Scale, and the Moment-Magnitude Scale. The seismoscope is an instrument

that measures the occurrence or the time of an occurrence of an earthquake (―Inventors‖).

Unlike other measuring devices, the seismoscope is a simple device without any technological

background. The seismoscope is the oldest and most accurate instrument for measuring

direction.

First invented in 132 AD, the Dragon Jar was the first instrument for determining the

direction of an earthquake Chang Heng, a Chinese scientist, developed the Dragon Jar. The

Dragon Jar consists of a large jar with eight dragons protruding around the top. Each

dragonhead holds a ball in its mouth while a frog sits with its mouth open directly underneath.

Behind each dragonhead lies a trigger. Down the center of the jar is a thin stick that is loosely

secured. The tremors of an earthquake cause the stick to fall on one of the eight triggers. When

the trigger is set off, the dragonhead linked to the trigger drops the ball into the frog’s mouth.The sound of the ball dropping into the frog’s mouth indicated an earthquake had just occurred.

By looking at which ball dropped, the direction of the earthquake could be determined. Heng’s

seismoscope was not only the first seismoscope but also very accurate and precise. In 138 AD,

Heng’s seismoscope detected an earthquake 1,000 miles away (―Chinese‖). Wang Zhenduo



recreated Chang Heng’s seismoscope in 1951. Instead of a thin stick loosely secured in the

center of the jar, Zhenduo replaced it with a copper pendulum shaft that connected to eight

copper arms (―Zhang Heng‖). Like the seismoscope, other devices used to gather information on

earthquakes were also first developed outside the United States.



Richter

magnitudeearthquake effects

less than 3.5 Generally not felt, but recorded.

3.5-5.4 Often felt, but rarely causes damage.

At most slight damage to well-designed

buildings. Can cause major damage to poorly

constructed buildings over small regions.

6.1-6.9Can be destructive in areas up to about 100

kilometers across where people live.

7.0-7.9Major earthquake. Can cause serious damage

over larger areas.

8 or greaterGreat earthquake. Can cause serious damage

in areas several hundred kilometers across.

I instrumental People do not feel any Earth movement.

II lightestA few people might notice movement if they are at rest and/or on the upper floors of tal

buildings.

III lightMany people indoors feel movement. Hanging objects swing back and forth. People

outdoors might not realize that an earthquake is occurring.

IV mediocre

Most people indoors feel movement. Hanging objects swing. Dishes, windows, and door

rattle. The earthquake feels like a heavy truck hitting the walls. A few people outdoors may

feel movement. Parked cars rock.

V strongly

Almost everyone feels movement. Sleeping people are awakened. Doors swing open o

close. Dishes are broken. Pictures on the wall move. Small objects move or are turned over

Trees might shake. Liquids might spill out of open containers.

VI much fort Everyone feels movement. People have trouble walking. Objects fall from shelves. Picture



fall off walls. Furniture moves. Plaster in walls might crack. Trees and bushes shake

Damage is slight in poorly built buildings. No structural damage.

VII strong

People have difficulty standing. Drivers feel their cars shaking. Some furniture breaks

Loose bricks fall from buildings. Damage is slight to moderate in well-built buildings

considerable in poorly built buildings.

VIII violent

Drivers have trouble steering. Houses that are not bolted down might shift on thei

foundations. Tall structures such as towers and chimneys might twist and fall. Well-buil

buildings suffer slight damage. Poorly built structures suffer severe damage. Tree branche

break. Hillsides might crack if the ground is wet. Water levels in wells might change.

IX disastrous

Well-built buildings suffer considerable damage. Houses that are not bolted down move of

their foundations. Some underground pipes are broken. The ground cracks. Reservoirs suffe

serious damage.

Xmost

disastrous

Most buildings and their foundations are destroyed. Some bridges are destroyed. Dams are

seriously damaged. Large landslides occur. Water is thrown on the banks of canals, rivers

lakes. The ground cracks in large areas. Railroad tracks are bent slightly.

XI catastrophicMost buildings collapse. Some bridges are destroyed. Large cracks appear in the ground

Underground pipelines are destroyed. Railroad tracks are badly bent.

XII

great

catastrophe

Almost everything is destroyed. Objects are thrown into the air. The ground moves in waves

or ripples. Large amounts of rock may move.

MERCALLI INTENSITY SCALE

The Mercalli intensity scale was invented in 1902 by the Italian scientist Giuseppe

Mercalli. It is based upon the observation of earthquake damage at a particular location. The

intensity of a quake differs greatly from place to place. It depends upon such factors as the

distance from the epicenter, the design and quality of construction of local buildings, and the

type of surface beneath the buildings.



Number Name Description

I Instrumental Detected by seismographs, usually not felt.

II Feeble A few people might notice movement if they are at rest and/or on the

upper floors of tall buildings.

III Slight Felt by many, often mistaken for a passing vehicle. Shaking felt

indoors; hanging objects swing back and forth. People outdoors might

not realize that an earthquake is occurring.

IV Moderate Most people indoors feel movement. Hanging objects swing, parked

cars might rock. Dishes, windows, and doors rattle. The earthquake

feels like a heavy truck hitting the walls. A few people outdoors mayfeel movement.

V Rather strong Almost everyone feels movement. Sleeping people are awakened.

Doors swing open or closed, dishes are broken, pictures on the wall

move. Cracked walls, trees disturbed.

VI Strong Felt by all. Many run outdoors. Slight damage occurs. Stronger

shaking can cause people to fall over and walls and ceilings to crack.

People walk unsteadily; windows break; pictures fall off walls.

Furniture moves. Trees and bushes shake

VII Very strong Everyone runs outdoors. Poorly built buildings suffer severe damage.

Slight damage everywhere else. Difficult to stand; plaster, bricks, and

tiles fall; large bells ring. Drivers feel their cars shaking. Some

furniture breaks. Loose bricks fall from buildings. People fall over.

VIII Destructive Tall buildings sway, furniture breaks, cars swerve. Everyone runs

outdoors. Moderate to major damage. Minor damage to specially

designed buildings. Chimneys and walls collapse. Drivers have trouble

steering. Houses that are not bolted down might shift on their

foundations. Tree branches break. Hillsides might crack if the ground

is wet. Water levels in wells might change.



IX Ruinous Ground cracks, well-constructed buildings damaged, pipes break. All

buildings suffer major damage. General panic; damage to foundations;

sand and mud bubble from ground. Reservoirs suffer serious damage.

X Disastrous Landslides, ground cracks widely. Major damage. Most buildings and

their foundations are destroyed. Some bridges are destroyed. Water is

thrown on the banks of canals, rivers, and lakes. Railroad tracks are

bent slightly.

XI Very disastrous Bridges and buildings destroyed, large fissures open. Almost all

structures fall. Very wide cracks in ground. Railway tracks bend; roads

break up; rocks fall. Underground pipelines are destroyed.

XII Catastrophic Rocks moved, objects thrown about. Total destruction. Ground surface

waves seen. River courses altered. Large amounts of rock may move.

SEISMOGRAM

A seismogram is a graph output by a seismograph. It is a record of the ground motion at a

measuring station as a function of time. Seismograms typically record motions in three cartesian

axes (x, y, and z), with the z axis perpendicular to the Earth's surface and the x- and y- axes

parallel to the surface. The energy measured in a seismogram may result from an earthquake or

from some other source, such as an explosion.

Historically, seismograms were recorded on paper attached to rotating drums. Some used

pens on ordinary paper, while others used light beams to expose photosensitive paper. Today,

practically all seismograms are recorded digitally to make analysis by computer easier. Some

drum seismometers are still found, though, especially when used for public display.

Seismograms are essential for finding the location and magnitude of earthquakes.

http://en.wikipedia.org/wiki/Seismograph


http://en.wikipedia.org/wiki/Explosion

http://en.wikipedia.org/wiki/Explosion


http://en.wikipedia.org/wiki/Seismograph



Figure: A typical seismogram.

The P wave will be the first wiggle that is bigger than the rest of the little ones (the

microseisms). Because P waves are the fastest seismic waves, they will usually be the first ones

that your seismograph records. The next set of seismic waves on your seismogram will be the Swaves. These are usually bigger than the P waves.If there aren't any S waves marked on your

seismogram, it probably means the earthquake happened on the other side of the planet. S waves

can't travel through the liquid layers of the earth so these waves never made it to your

seismograph.



The surface waves (Love and Rayleigh waves) are the other, often larger, waves marked on the

seismogram. They have a lower frequency, which means that waves (the lines; the ups-and-

downs) are more spread out. Surface waves travel a little slower than S waves (which, in turn,

are slower than P waves) so they tend to arrive at the seismograph just after the S waves. For

shallow earthquakes (earthquakes with a focus near the surface of the earth), the surface waves

may be the largest waves recorded by the seismograph. Often they are the only waves recorded a

long distance from medium-sized earthquakes.



INTRODUCTION OF EARTHQUAKE ENGINEERING

ASSIGNMENT 01

SUBMITTED BY

M.MOHAMED AQIL

08CER045

CIVIL-A



INTRODUCTION OF EARTHQUAKE ENGINEERING

ASSIGNMENT 01

SUBMITTED BY

K.M.NAGOOR MEERAN

08CER047

CIVIL-A

earthquake measurement assignment

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