sci

The Layers of the Earth!

*Crust

*Mantle

*Outer core

*Inner core

The Lithosphere

•The rigid, outermost shell on Earth.

•It is composed of hard, brittle rock

•The lithosphere is composed of part of the crust and the upper part of the mantle (the top 100 km).

•behaves elastically on time scales of thousands of years or greater.

The Crust

* The Earth’s crust is the outermost surface. 

*It is a very thin layer of solid rock.  It is the thinnest layer of the Earth.

*The crust is 5-35km thick beneath the land and 1-8km thick beneath the oceans.

* The crust of the Earth is broken into many pieces called plates.  The movement of these plates causes earthquakes.


Two types of Crust:

 1. Oceanic Crust- It is found under the

ocean floor. The oceanic crust is heavier

than the continental crust.

7- 10 kilometers thick which its average thickness is 8 kilometers.


2. Continental Crust- it is found under the land masses and is made of dense rocks such as granite.

The Continental crust is mainly made up Silicon, oxygen, and Aluminum , Calcium, Sodium and Potassium.


Mohorovicic Discontinuity

•the boundary between the crust and the mantle.                                                                                                                                                                                                                                                       

•discovered in 1909 by Andrija Mohorovicic, a Croatian seismologist

The Mantle

The mantle is the largest layer of the Earth.  It is 2900km thick.

*It includes the lithosphere and athenosphere.

*It is relatively flexible—it flows like very viscous liquid.

*It is very hot—1600°F at the top and 4000°F towards the center of the Earth.

       The Asthenosphere

The asthenosphere is the part of the mantle underneath the lithosphere. 

* It is made of molten rock and metal so that it “flows” like hot asphalt.

* The asthenosphere is the part of the mantle that moves and causes the tectonic plates of the crust to move as well.



The Core

*The core of the Earth is like a ball of very hot metals.  The core is divided into 2 layers—Outer and Inner.

* The core is SO hot and has SO much pressure that if you were to go there—you would be squished into something even smaller than a marble.

The Outer Core

*The outer core is liquid metal iron and nickel with 10% sulfur and/or oxygen.

* It is very hot—4000-9000°F.

•The outer core is 2,250km thick.

•Responsible for the Earth’s magnetic field

Earthquake

  • An earthquake is the result of a sudden release of energy in the earths crust that creates seismic waves.

  • The seismic activity of an area refers to the frequency type and size of earthquakes experienced over a period of time.

Focus ( hypocenter)

Focus is the point on the fault where rupture occurs and the location from which seismic waves are released.


Epicenter 

Epicenter is the point on the earth’s surface that is directly above the focus, the point where an earthquake or underground explosion originates.




Fault line -surface trace of a fault, the line of intersection between the earths surface.

Fault plane - the cracked or sudden slips of the land.

Fault scrap - the topographic expression of faulting attributed to the displacement of the land surface by movement along the faults.


CLASSIFICATION OF FAULTS

Normal fault 

  • hanging wall downward and footwall upward 

  • Dip slip fault in which the block above the fault has moved downward relative to the block below

  • Extensional stress

Thurst (reverse)

  • A dip slip fault in which the upper block, above the fault plane, moves up and over the lower back.

  • Hanging wall upward and footwall downward

  • Compression stress

A left lateral strike slip fault

  • It is the one on which the displacement of the far block is to the left when viewed from either side

  • Shear stress

A right lateral strike slip fault

  • It is the one on which the displacement of the far block is to the right when viewed from either side

  • Shear stress


Body wave - it travels through the interior(body) of the earth as they leave the focus.

 


Surface wave - waves travels parallel to the earths surface and these waves are slowest and most damaging.



STRENGTH OF EARTHQUAKE

The intensity and strength of an earthquake is measured on RICHTER SCALE, the scale invented by CHARLES RICHTER california, USA in 1935. Which categories earthquake on the basis of energy released.


“ the logarithm to base ten of the maximum seismic-wave amplitude recorded on a standard seismograph at a distance of 100 kilometers from the earthquake epicenter”


Scientists measure the strength of earthquakes using machines known as seismographs.


Seismology is the scientific study of earthquakes and the propagation of elastic waves through the earth.


Seismometers

  • Are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and otherseismic sources.

  • May be deployed at earth’s surface, in shallow vaults, in boreholes or underwater.


TRIANGULATION METHOD - is a method used by seismologists to determine the location of earthquake epicneter using 3 seismic stations


 

D = td/ 8 sec (100 km)

Wherein: 

D = distance 

Td = time difference or lag time.