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seismology earthquake Seismic waves

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seismology

earthquake

Seismic waves

The study of earthquakes

Occur along fault lines

The shaking and trembling that results from movement of rock beneath the Earth’s surface

Most too small to notice

Caused by plate movement

Waves of energy that travel through the Earth

Similar to sound waves

Locating Earthquakes

Epicenter

focus

The point on the Earth’s surface directly above the focus of an EQ

The point inside the Earth where the EQ begins

P- waves

http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm?chapter_no=visualization

S-waves

Surface Waves

Primary wave

1st to arrive

Travels through liquid, solid & gas

Squeezing & stretching like accordian

Secondary wave

Second to arrive

Travels like an “s”

Travels through solids & gases, not liquids

Moves slower than P & S waves

Produces severe ground movement

Only on surface, up & down & in circles

Measuring Magnitude

Modified Mercalli Scale

Rates the amount of shaking from the earthquake

Uses peoples observations

Useful in areas w/o many instruments

Richter scale

Rates on size of EQ waves recorded by seismographs

Quakes get exponentially larger

Moment Magnitude

Rates total energy an EQ releases

Usually the number that is quoted on the news

Each point is approximately 32 x more energy

Below magnitude 5 not much damage

Above 6 can cause great damage

Above 8 is rare

Locating the Epicenter

Geologists use seismic waves to locate the epicenter

Using P & S waves

Read the distance of the seismic wave arrival

3 seismograms from 3 locations for the same EQ

Draw a circle of using the distance as a radius

Where 3 circles intersect = epicenter

Locating Earthquakes

Seismograph

The instrument that is used to track EQs & record seismic waves

The tracing motion is called a seismogram

Used to determine start time

Used to find where it started

Seismic waves cause the drum to vibrate – and a pen records the vibrations

The paper moves and the pen stays in place

Weight of seismograph resists moving

Must be very strong movement to trigger

Seismograms reveal patterns of earthquakes around the world, revealing patterns