View Full Version : How earth quakes occur

01-05-2005, 02:45 PM
To understand how earth quakes occur we need to understand how earth was formed....

I started my college life as a Geological student..but due to some reasons i left the course in 8 months..but still i could capture what was taught to us long back..

There are lot of theories ..on earth formation

Approximate age of earth and solar system: is said to be in 4.5-5 billion years.

Two common theories on earth formation are Nebular theory and Big bang theory

Nebular theory:

Diffuse cloud of matter rotating in space, formed a disk shaped body, which later formed into sun and planets. Planets are cooled and condensed gases that surrounded the sun.
Two range of planets were formed inner and outer planets....

Inner planets: Mercury, Venus, Earth, Mars. Rocky planets. Volatiles removed

Outer planets: Jupiter, Saturn, Uranus, Neptune. Mostly hydrogen and helium.
Pluto: mixture of gas, ice & rock

Big bang theory

According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions.


Next we will go thru the layers of earth.....

01-05-2005, 03:34 PM
:clap: :clap: :clap: :clap: :clap:

romba nandri katteri, thanks for all the info u will be providing us.. :) its important to know these things right?


01-05-2005, 04:09 PM
The earth can be classified into three layers..
Core-Central part
Mantle- middle layer
Crust- outer part where we live this extends to a depth of 10 km.

There are around 100 elements in the earth but only 8 elements form 99% of earth total mass.
Whole Earth:(Includes crust, core and mantle)
Fe>O>Si>Mg>Ni>S>Ca>Al (others constitute < 1%)

Earth's crust
O>Si>Al>Fe>Mg>Ca>K>Na (other constitute <1%)

01-05-2005, 04:15 PM

Some geologist classify earth as 4 layers, they bifurcate mantle into outer and inner mantle

Crust is the layer where we live..

The mantle is much hotter and has the ability to flow.

The Outer and Inner Cores are hotter still with pressures so great that you would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth

01-05-2005, 04:19 PM

The outermost layer of the Earth is the crust. This comprises the continents and ocean basins. The crust has a variable thickness, being 35-70 km thick in the continents and 5-10 km thick in the ocean basins. The crust is composed mainly of alumino-silicates

The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, plastic mantle which is located below the crust. These plates usually move along smoothly but sometimes they stick and build up pressure. The pressure builds and the rock bends until it snaps. When this occurs an Earthquake is the result!

The seven continents and ocean plates basically float across the mantle which is composed of much hotter and denser material

The next layer is the mantle, which is composed mainly of ferro-magnesium silicates.

It is about 2900 km thick, and is separated into the upper and lower mantle.

This is where most of the internal heat of the Earth is located.

Large convective cells in the mantle circulate heat and may drive plate tectonic processes.

01-05-2005, 04:23 PM
:( sorry appo appo question kaekuraen okvaa..

Large convective cells in the mantle circulate heat and may drive plate tectonic processes.

Whats tectonic process.. actually the one that caused thsi tsunami too was due to some movement of plates and as there were 3 plates there, it caused such disasternu padichaen..


01-05-2005, 04:47 PM
Tsunamic wave are cuased due to earth quakes..

Plate tectonics is again a theory which states the various geological activities.According to this theory earth consists on many plates , the sizes and position of the plates change over a period of time...
When the edges of the plate interact u can expect either a earth quake, volcanoes or a mountain building..

The mechanism of plate tectonics is a combinational movements of ocean floor spreading and continental drifting. (7 continents nu solram ilaa athu ..these continents move as they are on crust )

Continental drift is the movement of continents over the Earth's surface and in their change in position relative to each other. Sea-floor spreading is the creation of new oceanic crust at mid-ocean ridges and movement of the crust away from the mid-ocean ridges.


This animated image will explain how the continents have undergone changes in last 750 million years

01-05-2005, 04:57 PM
intha imagela animation varalaiyae enakku :(


01-05-2005, 04:58 PM
oops sorry, enakku load aanathuku appuram final image thaan first therinchathu, once i refreshed it, i was able to see.. sorry katteri !!


01-05-2005, 05:18 PM
[video width=400 height=350:e17777f4dd]http://www.ucmp.berkeley.edu/geology/tecall1_4.avi[/video:e17777f4dd]
ippaa neenga paarkalam.....

Athu mattum illaa intha plate tectonics aala than Inida african continent le irunthu Asian continet ku vanthuchu...

Plate split apart due to volcanic eruption so a single plate may be split into two or many number depending on the intensity of forces.

Three types of convergence:
Ocean-ocean conevrgence:
Continent -continet convergence
Ocean-continet convergence,

Ocean -ocean first parpom:

When two oceanic plates try to coneverge one goes down and other flows sideways...
pacific ocean la mariana trench ippadi than aachu...


interaction of ocean plates with continetal plates

Continental-continental convergence.

Oru example oda solren...

Wheat flour irukku illa athai ball mathiri urutti vaipeenga chapthi kuu..
keep one ball in each hand..
Now try to bring in line both the balls and apply enorumous pressure...enna aagaum the balls loose their shape and then they look like a mountain...

Ithai padinga india eppadi vanthuchu nu theriyum...
Approximately 20 million years ago India was connected to the southeastern tip of Africa. Stresses in the earth's crust resulted in the development of a rift between them. India broke free and began drifting north as part of the Indo-Australian Plate. The leading edge of the plate was oceanic crust. Several millions of years later this leading oceanic edge collided with the Eurasian Plate and began to be thrust upward. Eventually, the deep sea-floor of the Indo-Australian Plate rose above sea level, and the Himalayas were born.

Today, India continues it's push northward. The Himalayas, once the deep sea-floors of an ancient sea, are now a majestic terrestrial mountain range. Imagine the surprise of geologists when they discovered the fossilized remains of ancient sea creatures at the top of the world. The mid-ocean ridge visible in the lower left of the image is largely responsible for India's northerly movement.

01-05-2005, 05:22 PM
Mellaa avi file irukku illaa athai slow va paarunga at end of every 100 million years india oda position...

01-05-2005, 06:07 PM
etho geography lecture poi okandha madhiri irukku katz. very nice information. konja vishayam erkanavey therinchurundhaalum niraya vishayam pudhusa irukku.. thanx for the lecture Ram.


01-05-2005, 07:24 PM
Enakku oru sandheham katteri. Arambatthula Indiavum srilankavum onna thaane irundhicchu. Appuram thaane pirinjuthu. Aana indha pictrure-la arambatthulerndhe Srilanka separate-a irukka maadiri kaamicchurukkaangale?

01-05-2005, 07:36 PM
Priyankaaa of course india and srilanka were together... intha picture le sernthu than irukku .. ungallukkku innum doubt theeralai na ...

avi file irukku illaa athai 20 million years before la puase panni printscreen edunkaa appuram srilanka location zoom in panni parungaa ..i tried its tied to india.....

01-05-2005, 07:49 PM
thanks a lot katteri, eppo thaan antha plates concept purinchathu :b: wow.. suddena so interested to know more about our earth !!! jollya poitu vanthutu irukoom daily, ennaennamoo irukku inside this beautiful earth :)


01-05-2005, 07:55 PM

Wonderful pictures and superb animation.... and too good an explanation... Understood the concepts very clearly... Thanks :)

01-05-2005, 08:16 PM
Priyankaaa of course india and srilanka were together... intha picture le sernthu than irukku .. ungallukkku innum doubt theeralai na ...

avi file irukku illaa athai 20 million years before la puase panni printscreen edunkaa appuram srilanka location zoom in panni parungaa ..i tried its tied to india.....

Oh! Aamam katz. Serndhu dhaan irukku.

Very very nice pictures and beautiful pictures. Oru chinna kuzhandhaikku kooda puriyaraa maadiri beautiful-a explain panniyirukkeenga. Simply superb. :clap:

01-06-2005, 01:22 AM
great explanation Mr vampire :clap: :clap: :clap:

01-06-2005, 06:02 AM
Katteri! Enakku sila doubts. If you dont mind avatrai clarify panna mudiyuma?

1) Earth-oda inner layers patthi ellaam scientists-ala eppadi kandu pudikka mudinjuthu. Athai patthi konjam solla mudiyuma?

2) About the picture of world map starting from 750 years ago. Ippadi thaan irundhirukkumnu nambaraangalaa illainna nejamaave appadi thaan irundhiccha? 750 million years munnaadi earth eppadi irundhucchunnu eppadi solla mudiyum ivangalaala?

3) Ippo sameebatthula nadandha earth-quake naalaiyum tsunaaminaalaiyum earth-e tilt aayiducchunnum athanaala oru naalaikku 24 hours-a vida sila micro seconds koodiducchu appadinna ellaam padicchen. Ithu entha alavukku unmai? Ethukku kekkarenna inga local channels-la ellam athai patthi onnum solla kaanome?

01-06-2005, 02:06 PM
How tsunami warning system works

http://newsimg.bbc.co.uk/media/images/40685000/gif/_40685733_tsunami_detection2_i nf416.gif

The pressure sensors are installed on the sea bed , these sensors capture any varitions in the pressure
P=density*head(height of water level)*g

If the head of the water rises these pressure sensor can capture the varitons and sent an initial warning.

Problem here is:
To have accurate information we need to install many sensors across the sea bed over a wide spread area.
Second is to monitor the information continously.
Cost of operation and maintenance high.

Another major problem is communicating the warnings to the people which countires in south asia are not so good...

Unless we communicate the warnings to people and start evacuating the area the warning system doesnt meet the purpose.

People shd be trained to respond to tsunamis , thats how japanese survive..

01-06-2005, 02:23 PM
Priyanka unga first kelvi. ku answer..

unga thirs kelviku...pathil theriyalai...but first i was able to find answer.

Scientist mostly used seismic imaging to determine the structure of the earth.

intha search potta thu ku answer:

How did scientists decide what the Earth's structure is?
Scientists have determined the structure of the Earth through many methods. Different qualities of the Earth, such as the fact that it has a magnetic field, have been used to figure out some of its composition.
The main clue for scientists has been the behavior of seismic waves, waves caused by Earthquakes. Two types of seismic waves that travel through the Earth are P waves and S waves. S waves cannot pass through a liquid, and P waves can but are refracted when moving between liquids and solids. So, scientists use this information and knowledge that S waves can only be observed on the same side of the Earth as an Earthquake occured on, and P waves can make it to the far side, but there is a predictably sized dohnut shaped area called a shadow zone, where no P waves can be measured.

What this tells scientists is that there is an outer core which is liquid (blocking S waves), and a solid inner core determined by differences in where P waves are refracted

S and P wave pathi appuram parpom......

01-06-2005, 02:41 PM
Second ku:
How geological scales were formed?
Radiometric dating, stratigraph principles are used to establish the time scales.

Much of the Earth's geology consists of successional layers of different rock types, piled one on top of another. The most common rocks observed in this form are sedimentary rocks (derived from what were formerly sediments), and extrusive igneous rocks (e.g., lavas, volcanic ash, and other formerly molten rocks extruded onto the Earth's surface). The layers of rock are known as "strata", and the study of their succession is known as "stratigraphy". Fundamental to stratigraphy are a set of simple principles, based on elementary geometry, empirical observation of the way these rocks are deposited today, and gravity.

Its an direct way of finding the time scales..but to validate the findings people have used different methods to check the results.

01-06-2005, 02:45 PM
For more information abt second pls go thru foll pages




01-06-2005, 02:53 PM
Unga third question ku munndai?
Y earth is tilted num matha reason um parpomaa??

Earth travels in space at a speed of 18.4 miles per second (average speed than)..
it also rotating on its axis at 1,070 miles per hour (speed at the equator)....
Seasonal changes eppadi:
The Earth is tilted 23.5 degrees on its axis, a straight line through the planet from the North Pole to the South Pole. The Earth spins around, or rotates, on this axis as it orbits the sun. The key here is that as the Earth orbits the sun, different regions on Earth are tilted both towards and away from the sun depending on the region's respective hemisphere. This causes the sun's light and energy to hit the different regions of the Earth at different angles throughout the course of one orbit, or one full year.

Athanala than southern hemisphere winter a irukkum pothu northen hemisphere la summer and vice versaaa..

If the Earth was not Tilted....

If the Earth's axis were parallel to the Sun and not tilted, the Sun would remain positioned exactly halfway between the North and South Poles, and there would be no seasonal changes on Earth. Each area on Earth would maintain the same relative climate and same amount of daylight throughout the entire year.

01-06-2005, 03:00 PM

You see, the earth is tilted from it's axis because it got hit by meteoroids and other stuff when the planets first formed (or at least that's what scientists think). So, as the tilted earth orbits the sun, sometimes it is tilted toward the sun and sometimes away from the sun

Summer = More Sunlight & More Concentrated


Winter = Less Sunlight & less Concentrated

01-08-2005, 10:09 AM
Some thoughts:

Earthquakes tend to occur in the winter than the summer, usually when there is a surge of unusually warm weather

There is evidence suggesting that earthquakes are more likely to occur when the moon is closest to Earth. Apparently, the moon’s gravitational pull, which is responsible for our tides, may also affect earth’s tectonic plates. Yet another theory suggests that the earth shakes because of solar winds caused when sun flares reach large heights.

Animals have also been used as indicators of coming earthquakes. Horses have been known to act up, rearing and racing away before a tremor strikes. Fish and pheasants in Japan and China have also been valued for their ability to sense coming earthquakes. Pheasants supposedly scream in alarm before a tremor, while fish jump out of the water. Pet cats have run away and snakes and rats come out of their hiding places. In Turkey, it is said that the appearance of bats during the day signals an impending tremor. Residents around the Kamchatka Peninsula in Russia are alerted when the normally inactive bears begin to act more energetic than usual.

02-13-2005, 08:14 PM
There are other links from HowStuffWorks.com which explain Tsunami's and earthquakes and the warning systems....