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EARTHQUAKE

Vibration of the earth on earth surface is called as

earthquake

Earthquakes are the shaking, rolling or sudden shock of the earth’s surface.

They are the Earth's natural means of releasing stress.

Earthquakes can be felt over large areas although they usually last less than one minute.

Earthquakes cannot be predicted, although scientists are working on it.

As the plates move they put forces on themselves and each other. When the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy, which moves through the Earth in the form of waves, which we feel and call an earthquake.

• AN EARTHQUAKE IS THE VIBRATION OF EARTH PRODUCED BY THE RAPID RELEASE OF ENERGY.

ENERGY RADIATES IN ALL DIRECTIONS FROM ITS SOURCE, THE FOCUS ENERGY MOVES LIKE WAVES SEISMOGRAPHS RECORD THE EVENT

A fault is an area of stress in the earth where broken rocks slide past each other, causing a crack in the Earth's surface.

There are 4 major types of faults which are as follows: dip-slip normal, dip-slip reverse, strike-slip, and oblique-slip.

STRIKE AND DIP

Strike intersection w horizontal, dip perpendicular, angle from horizontal down toward surface

Strike is long line, dip is short lineNote the angle of dip given 45o

VERTICAL MOVEMENT ALONG DIP-SLIP FAULTS

Divergent

Convergent

HORIZONTAL MOVEMENT ALONG STRIKE-SLIP FAULT

Normal Fault Quake - NevadaReverse Fault Quake - Japan

Strike Slip Fault Quake - California

DEMO – Types of faults

Reverse Fault Quake - Japan

Strike Slip Fault Quake - California

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Earthquakes are caused by sudden release of accumulated strain energy along Faults

Rocks on sides of fault are deformed by tectonic forces

Rocks bend and store elastic energy

Frictional resistance holding the rocks together is overcome by tectonic forces

• Earthquakes often occur when tectonic plate collide • When two plates collide head-on, they push each other up and form

mountains. That's how the Himalayas and other great mountain ranges (including the Rockies, long ago) were created.

These zones mark of edges of tectonic plates

LIQUEFACTION

EFFECTS Fires Liquifaction Landslides

•The point beneath the Earth's surface where the rocks break and move is called the focus of the earthquake. •The focus is the underground point of origin of an earthquake. Directly above the focus, on the Earth's surface, is the epicenter.

• STUDY OF SEISMIC WAVES IS CALLED AS SEISMOLOGY

Seismometers - instruments that record seismic waves Records the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape

• Earthquake waves are known as seismic waves

EARTHQUAKES IS MEASURED ON RICHTER SCALE

The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air..

TYPES OF WAVES

S WAVES (SURFACE WAVES)

(Theses produce all the damage!)

Love WavesThe first kind of surface wave is called a Love wave, named after A.E.H. Love, a British mathematician who worked out the mathematical model for this kind of wave in 1911. It's the fastest surface wave and moves the ground from side-to-side.

Rayleigh WavesThe other kind of surface wave is the Rayleigh wave, named for John William Strutt, Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves.

COMPARING SEISMIC WAVES

SEISMIC GAP ALONG HIMALAYAS

2005

What Controls the Level of Shaking?

Magnitude The more energy released, the greater potential for damage, regardless of all other factors (and greater areal extent).

Distance Shaking decays with distance

Local soils and bedrock geologySoil characteristics may amplify the shaking.

(seasonal climatic variations can impact this)

Complex geology tends to dampen waves

FACTORS EFFECTING THE DESTRUCTIVENESS OF AN EARTHQUAKE

Earthquakes: Facts and Fiction

Fiction: Earthquakes usually happen in the morning. Fact: Earthquakes happen in both the day and the night. There is no pattern.

Fiction: There is such a thing as "earthquake weather." Fact: There is no connection between earthquakes and weather. Remember, earthquakes happen deep in the earth, far away from the weather!

Fiction: Earthquakes are on the increase. Fact: It may seem like we’re having more earthquakes because there are more reporting stations, but the truth is we’re not.

Fiction: We can prevent earthquakes from happening. Fact: No. You can protect yourself by doing things to secure buildings, like your home, but earthquakes can’t be prevented -- or predicted.

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