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EARTHQUAKE

An earthquake is a shaking of the ground caused by the sudden

breaking and movement of large sections (tectonic plates) of the

earth's rocky outermost crust. The edges of the tectonic plates are

marked by faults (or fractures). Most earthquakes occur along the

fault lines when the plates slide past each other or collide against each

other.

MEASURMENT OF EARTHQUAKE

There are two ways in which scientists quantify the size of

earthquakes: magnitude and intensity.

RICHTER SCALE

Magnitude is a measure of the amount of energy released during an earthquake. The Richter magnitude scale (also Richter scale) assigns a magnitude number to quantify the energy released by an earthquake. The Richter scale is a base-10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of the seismic waves to an arbitrary, minor amplitude.

THE MERCALLI SCALE

Another way to measure the strength of an earthquake is to use the Mercalli scale. Invented by Giuseppe Mercalli in 1902, this scale uses the observations of the people who experienced the earthquake to estimate its intensity.

The Mercalli scale isn't considered as scientific as the Richter scale, though. Some witnesses of the earthquake might exaggerate just how bad things were during the earthquake and you may not find two witnesses who agree on what happened; everybody will say something different. The amount of damage caused by the earthquake may not accurately record how strong it was either

http://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Decimalhttp://en.wikipedia.org/wiki/Logarithmic_scalehttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Seismic_wavehttp://en.wikipedia.org/wiki/Seismic_wavehttp://www.geo.mtu.edu/UPSeis/Mercalli.html

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Fig: 1 Basic Figure of Earth core with waves and Seismograph

Fig: 2 The tectonic plates of the world were mapped in the second half of the 20th century.

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PLATE TECHTONICS

Plate tectonics is a scientific theory that describes the large-scale

motion of Earth's lithosphere. This theoretical model builds on the

concept of continental drift which was developed during the first few

decades of the 20th century. The geoscientific community accepted

the theory after the concepts of seafloor spreading were later

developed in the late 1950s and early 1960s.

The lithosphere, which is the rigid outermost shell of a planet (on

Earth, the crust and upper mantle), is broken up into tectonic plates.

On Earth, there are seven or eight major plates (depending on how

they are defined) and many minor plates. Where plates meet, their

relative motion determines the type of boundary; convergent,

divergent, or transform. Earthquakes, volcanic activity, mountain-

building, and oceanic trench formation occur along these plate

boundaries. The lateral relative movement of the plates typically

varies from zero to 100 mm annually.

Tectonic plates are able to move because the Earth's lithosphere has

greater strength than the underlying asthenosphere. Lateral density

variations in the mantle result in convection. Plate movement is

thought to be driven by a combination of the motion of the seafloor

away from the spreading ridge (due to variations in topography and

density of the crust, which result in differences in gravitational forces)

and drag, with downward suction, at the subduction zones. Another

explanation lies in the different forces generated by the rotation of

the globe and the tidal forces of the Sun and Moon. The relative

importance of each of these factors and their relationship to each

other is unclear, and still the subject of much debate.

http://en.wikipedia.org/wiki/Scientific_theoryhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Lithospherehttp://en.wikipedia.org/wiki/Continental_drifthttp://en.wikipedia.org/wiki/Earth_sciencehttp://en.wikipedia.org/wiki/Seafloor_spreadinghttp://en.wikipedia.org/wiki/List_of_tectonic_plateshttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Transform_faulthttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Volcanohttp://en.wikipedia.org/wiki/Mountainhttp://en.wikipedia.org/wiki/Oceanic_trenchhttp://en.wikipedia.org/wiki/Asthenospherehttp://en.wikipedia.org/wiki/Mantle_convectionhttp://en.wikipedia.org/wiki/Earth%27s_gravity#Variation_in_gravity_and_apparent_gravityhttp://en.wikipedia.org/wiki/Drag_%28physics%29http://en.wikipedia.org/wiki/Suctionhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Moon

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TYPES OF EARTHQUAKE WAVES

Seismic Waves

Body Waves Surface Waves

P Waves S waves Love Waves Rayleigh

Waves

Earthquake shaking and damage is the result of three basic types of

elastic waves. Two of the three propagate within a body of rock. The

faster of these body waves is called the primary or P wave. Its motion

is the same as that of a sound wave in that, as it spreads out, it

alternately pushes (compresses) and pulls (dilates) the rock. These P

waves are able to travel through both solid rock, such as Granite

Mountains, and liquid material, such as volcanic magma and the water

of the oceans.

Fig: 3 P Waves

The slower wave through the body of rock is called the secondary or S

wave. As an S wave propagates, it shears the rock sideways at right

angles to the direction of travel. If a liquid is sheared sideways or

twisted, it will not spring back, hence S waves cannot propagate in the

liquid parts of the earth, such as oceans and lakes.

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Fig: 4 S Waves

The actual speed of P and S seismic waves depends on the density and

elastic properties of the rocks and soil through which they pass. In

most earthquakes, the P waves are felt first. The effect is similar to a

sonic boom that bumps and rattles windows. Some seconds later, the

S waves arrive with their up-and-down and side-to-side motion,

shaking the ground surface vertically and horizontally. This is the wave

motion that is so damaging to structures.

The third general type of earthquake wave is called a surface wave,

reason being is that its motion is restricted to near the ground surface.

Such waves correspond to ripples of water that travel across a lake.

Surface waves in earthquakes can be divided into two types. The first

is called a Love wave. Its motion is essentially that of S waves that have

no vertical displacement; it moves the ground from side to side in a

horizontal plane but at right angles to the direction of propagation.

The horizontal shaking of Love waves is particularly damaging to the

foundations of structures.

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Fig: 5 Love Waves

The second type of surface wave is known as a Rayleigh wave. Like

rolling ocean waves, Rayleigh waves wave move both vertically and

horizontally in a vertical plane pointed in the direction in which the

waves are travelling.

Fig: 6 Rayleigh Waves

Surface waves travel more slowly than body waves (P and S); and of

the two surface waves, Love waves generally travel faster than

Rayleigh waves. Love waves (do not propagate through water) can

effect surface water only insofar as the sides of lakes and ocean bays

pushing water sideways like the sides of a vibrating tank, whereas

Rayleigh waves, because of their vertical component of their motion

can affect the bodies of water such as lakes.

P and S waves have a characteristic which effects shaking: when they

move through layers of rock in the crust, they are reflected or

refracted at the interfaces between rock types. Whenever either wave

is refracted or reflected, some of the energy of one type is converted

to waves of the other type. A common example; a P wave travels

upwards and strikes the bottom of a layer of alluvium, part of its

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energy will pass upward through the alluvium as a P wave and part will

pass upward as the converted S-wave motion. Noting also that part of

the energy will also be reflected back downward as P and S waves.

BODY/PARTS OF EARTHQUAKE

FOCUS

The focus is also called the hypocenter of an earthquake. The vibrating

waves travel away from the focus of the earthquake in all directions.

The waves can be so powerful they will reach all parts of the Earth and

cause it to vibrate like a turning fork.

EPICENTRE

Directly above the focus on the Earth's surface is the earthquake

epicenter. Earthquake waves start at the focus and travel outward in

all directions. Earthquake waves do not originate at the epicenter.

MAGNITUDE

Earthquake size is a quantitative measure of the size of the

earthquake at its source. The Magnitude indicates the amount of

energy released at the source (or epicentre). The Richter Magnitude

Scale measures the amount of seismic energy released by an

earthquake.

INTENSITY

The severity of earthquake shaking is assessed using a descriptive

scale. The intensity of an earthquake at a particular locality indicates

the violence of earth motion produced there by the earthquake. It is

determined from reported effects of the tremor on human beings,

furniture, buildings, geological structure, etc. The Modified Mercalli

Intensity Scale is used to measure the intensity.

http://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-difference-between-Magnitude-and-Intensity/The-Richter-Magnitude-Scalehttp://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-difference-between-Magnitude-and-Intensity/The-Richter-Magnitude-Scalehttp://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-difference-between-Magnitude-and-Intensity/The-Modified-Mercalli-Intensity-Scalehttp://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-difference-between-Magnitude-and-Intensity/The-Modified-Mercalli-Intensity-Scale

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EFFECT OF EARTHQUAKE

MASONRY STRUCTURES

Masonry buildings are brittle structures and one of the most

vulnerable of the entire building stock under strong earthquake

shaking. Ground vibrations during earthquakes cause inertia forces at

locations of mass in the building. These forces travel through the roof

and walls to the foundation.

The walls are most vulnerable to damage caused by horizontal

forces due to earthquake. A wall topples down easily if pushed

horizontally at the top in a direction perpendicular to its plane (termed

weak direction), but offers much greater resistance if pushed along its

length (termed strong direction).

The ground shakes simultaneously in the vertical and two

horizontal directions during earthquakes. However, the horizontal

vibrations are the most damaging to normal masonry buildings.

Horizontal inertia force developed at the roof transfers to the walls

acting either in the weak or in the strong direction. If all the walls are

not tied together like a box, the walls loaded in their weak direction

tend to topple.

RCC STRUCTURES

A typical RC building is made of horizontal members (beams and slabs)

and vertical members (columns and walls), and supported by

foundations that rest on ground. The system comprising of RC

columns and connecting beams is called a RC Frame. The RC frame

participates in resisting the earthquake forces. Earthquake shaking

generates inertia forces in the building, which are proportional to the

building mass. Since most of the building mass is present at floor

levels, earthquake-induced inertia forces primarily develop at the

floor levels. These forces travel downwards - through slab and beams

to columns and walls, and then to the foundations from where they

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are dispersed to the ground. As inertia forces accumulate downwards

from the top of the building, the columns and walls at lower storeys

experience higher earthquake-induced forces

Fig: 8 Floor Bends with the Beam but Fig: 9 Earthquake shaking reverses

Moves all columns at the level together Tension & Compression in members.

NEPAL EARTHQUAKE

MAP/PHOTOS

Before Fig: 10 Field After

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Fig: 11 Map

Before Fig: 12 Bhaktapur Durbar Square After

Before Fig: 13 Bastantapur Getty Omar Havana After

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Before Fig: 14 Narayan Hiti Palace After

Before Fig: 15 Dharahara Tower After

The 2015 Nepal earthquake, also called the Gorkha earthquake

and Nepal Greater Earthquake occurred at 11:56 NST on 25 April,

killing at least 6,700 people and injuring more than twice as many as

of 1 May 2015 with a moment magnitude 7.9. Its epicenter lay in

Barpak village of Gorkha district and its hypocenter was at a depth of

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approximately 15 km. Some casualties have also been reported in the

adjoining areas of India, China, and Bangladesh.

A major aftershock of magnitude 6.7occurred on 26 April 2015

in the same region at 12:55 NST, with an epicenter located about

17 km south of Kodari, Nepal. The aftershock caused fresh avalanches

on Mount Everest and was felt in many places in northern India

including Kolkata, Siliguri, Jalpaiguri and Assam. The aftershock caused

a landslide on the Koshi Highway which blocked the section of the road

between Bhedetar and Mulghat.

INDIA SUPPORTED NEPAL (AS OF 28 APRIL 2015)

India aided $500 million to Nepal

hundreds of tons of food and dry rations

5,000 vials of insulin

3 tons of relief material

1 tons of blankets

Several tons of stretchers, tents

2 tons of medical supplies

Potable water (non-bottled and over 100,000 bottles)-Indian

Railways

Helicopters Mi-17, Cheetah, HAL Dhruv ALH

Unmanned Aerial Vehicles (UAVs)

8 member medical team

4 bed health camp (Lagankhel)

Light vehicles

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REFERENCES

http://www.vtaide.com/png/George/earthquake.htm

http://tremor.nmt.edu/faq/how.html

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

http://www.geo.mtu.edu/UPSeis/intensity.html

http://pubs.usgs.gov/gip/earthq1/measure.html

http://www.azosensors.com/Article.aspx?ArticleID=7

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

http://allshookup.org/quakes/wavetype.htm

http://www.kids-fun-science.com/earthquake-focus.html

http://www.gns.cri.nz/Home/Learning/Science-

Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-

questions/What-is-the-difference-between-Magnitude-and-

Intensity

http://www.iitk.ac.in/nicee/EQTips/EQTip12.pdf

http://articles.architectjaved.com/earthquake_resistant_structures

/how-earthquakes-affect-reinforced-concrete-buildings/

http://www.bbc.com/news/world-asia-32479909

http://en.wikipedia.org/wiki/2015_Nepal_earthquake

http://www.vtaide.com/png/George/earthquake.htmhttp://tremor.nmt.edu/faq/how.htmlhttp://en.wikipedia.org/wiki/Richter_magnitude_scalehttp://www.geo.mtu.edu/UPSeis/intensity.htmlhttp://pubs.usgs.gov/gip/earthq1/measure.htmlhttp://www.azosensors.com/Article.aspx?ArticleID=7http://en.wikipedia.org/wiki/Plate_tectonicshttp://allshookup.org/quakes/wavetype.htmhttp://www.kids-fun-science.com/earthquake-focus.htmlhttp://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-difference-between-Magnitude-and-Intensityhttp://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-difference-between-Magnitude-and-Intensityhttp://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-difference-between-Magnitude-and-Intensityhttp://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Monitoring-Earthquakes/Other-earthquake-questions/What-is-the-difference-between-Magnitude-and-Intensityhttp://www.iitk.ac.in/nicee/EQTips/EQTip12.pdfhttp://articles.architectjaved.com/earthquake_resistant_structures/how-earthquakes-affect-reinforced-concrete-buildings/http://articles.architectjaved.com/earthquake_resistant_structures/how-earthquakes-affect-reinforced-concrete-buildings/http://www.bbc.com/news/world-asia-32479909http://en.wikipedia.org/wiki/2015_Nepal_earthquake

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