Unit 10, Chapter 28

Integrated Science

28.3 Earthquakes As tectonic plates move, friction

causes rock at plate boundaries to stretch or compress, this causes rocks to store energy.

When the rocks break, change shape, or decrease in volume, the stored energy is suddenly converted to kinetic energy and an earthquake occurs.

28.3 Earthquakes A seismograph measures

earthquakes, and seismologists use seismic waves to study Earth’s internal structure.

This is similar to how a doctor uses X rays to look at bone structure.

28.3 Earthquakes The majority of

earthquakes occur at the plate boundaries.

Earthquakes also occur at a fault.

Fault - a place crack in rocks along which movement occurs.

Earthquake TermsEpicenter –

point on earth’s surface where the EQ waves touch surface first.

Focus – point inside crust where the EQ movement first occurred.

Northridge, California in January

1994.

Seismic waves – common name given to all EQ waves.

Hawaii earthquake damage

Worldwide EarthquakesNotice- most earthquakes occur on plate boundaries.

2 Categories ofSeismic Waves

Body & Surface

P waves Short for Primary waves

Fastest and First body wave recorded by a seismograph

Travel through solids and liquids (generate

sound)

Faster through more rigid material

They are Compression waves— Cause rock particles to move

together and apart along the direction of the waves

P-Wave movement

S waves short for Secondary WavesSecond body wave recorded by a seismograph

Only travel through solids

Can’t be detected on the side of the earth opposite the earthquake’s epicenter.

They are Shear waves— Cause rock particles to move up &

down or side to side (right angle) to the direction in which the waves are traveling

S-Wave movement

Surface WavesSlowest moving wave & last to be recorded by seismograph

Travel similar to ocean waves

Cause the surface to rise, fall, turn and twist

Very destructive: especially in loose earth

2 Types of Surface wavesLove Waves

Fastest kind of surface wave is called a Love wave , (named for A.E.H. Love, a British mathematician)

Love worked out the mathematical model for this kind of wave in 1911.

It moves the ground from side-to-side.

2 Types of Surface wavesRayleigh Waves

Slower kind of surface wave (named for John William Strutt, Lord of Rayleigh

Rayleigh predicted mathematically the existence of this kind of wave in 1885.

It moves the ground up & down and side-to-side rolling the ground like waves on water.

Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves

Surface Waves movements

28.3 Earthquakes in the U.S.The west coast of U.S.

experiences most earthquakes because of the San Andreas fault a boundary between Pacific and North American Plate, and the 10,000 + smaller faults.

The Midwest and Eastern U.S. does experience EQ but they are more rare.

28.3 Earthquakes in the U.S. Minor earthquakes release

stored energy in small, less destructive amounts.

Rocks in areas that do not experience frequent small earthquakes may have a lot of stored potential energy.

When this potential energy is finally converted to kinetic energy, the earthquake could be big.

28.3 Earthquake SafetyGet outside to an open area (if possible), far

from buildings and objects that could fall. Sit down to avoid falling.

If you are inside: Drop, cover, and hold.

28.3 Preparing for Earthquakes A huge wave generated by an underwater earthquake or

landslide is called a tsunami. The speed at which this wave travels can be about 700

kilometers per hour. (435MPH)

28.3 Earthquakes

Key Question: What mechanical factors affect earthquakes?

*Read text section 28.3 BEFORE Investigation 28.3