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EarthquakesEarthquakes

• By: Momina AfzaliBy: Momina Afzali

What are Earthquakes?What are Earthquakes?

• Earthquakes are the Earth’s natural Earthquakes are the Earth’s natural means of releasing stressmeans of releasing stress

• When the Earth’s plates move When the Earth’s plates move against each other, stress is put on against each other, stress is put on the lithospherethe lithosphere

• When this stress is great enough, the When this stress is great enough, the lithosphere breaks or shiftslithosphere breaks or shifts

What are Earthquakes? What are Earthquakes? continuedcontinued

• As the plates move they put forces As the plates move they put forces on themselves and each otheron themselves and each other

• When the force is large enough, the When the force is large enough, the crust is forced to breakcrust is forced to break

• When the break occurs, the stress is When the break occurs, the stress is released as energy which we feel and released as energy which we feel and call an earthquakecall an earthquake

ForcesForces

• A force can be thought of as a push A force can be thought of as a push or pullor pull

• Force has both magnitude and Force has both magnitude and direction, therefore it is a vectordirection, therefore it is a vector

• From physics and Newton’s 2From physics and Newton’s 2ndnd law, law, we know that force is equal to a we know that force is equal to a change in an object’s momentum change in an object’s momentum which describes the quantity of which describes the quantity of motionmotion

Forces……. continuedForces……. continued

• When a force is applied to an object, When a force is applied to an object, the object is said to be under stress the object is said to be under stress

• Stress is the deforming force per areaStress is the deforming force per area• Stress and strain are related, so it is Stress and strain are related, so it is

easy to determine one from the other easy to determine one from the other if you know value of proportianality, a if you know value of proportianality, a constant value that relates strain to constant value that relates strain to stress, of the substance that is being stress, of the substance that is being deformeddeformed

What causes stress?What causes stress?