earthquake waves chapter 6-2. focus and epicenter actual location of fault up to 700 km below...

Earthquake WavesChapter 6-2

Focus and epicenter

Actual location of faultUp to 700 km below surface

Focus and epicenter

Surface location directly above the focus

Actual location of faultUp to 700 km below surface

P-waves

Primary waves- Compression waves

- Travel in a horizontal direction

- First to arrive at a distant location

S-waves

• Secondary waves

- vibrate at right angles

to p-wave

- particles move back

and forth but wave

moves forward

- second to arrive at

distant location

Surface Waves

• Surface waves- travel parallel to Earth’s surface- have greatest height- move like an ocean

wave- last to arrive at

distant location

- are responsible for damage

Locating Epicenter• Time lag between P-wave and S-wave indicate

how far the earthquake is from a seismograph station.

Lag Time

Locating Epicenter

• The lag time tells us how far we are from an earthquake but not from which direction

Epicenter can be any where on radius of the circle

Locating Epicenter

• At least ____ seismograph stations are needed to pinpoint the epicenter of an earthquake

Infinite number of possibleepicenters

Locating Epicenter

• At least ____ seismograph stations are needed to pinpoint the epicenter of an earthquake

Possibleepicenter

Possibleepicenter

Two seismograph stations narrow possible epicenters down to two

Locating Epicenter

• At least three seismograph stations are needed to pinpoint the epicenter of an earthquake

Three epicenters narrows possible locations down to one

epicenter

DEMO

Measuring Earthquakes

• Mercalli Scale- rates earthquake

according to level of

damage at a given

location

- 12 steps to scale

- same earthquake can

have different rating at

different locations

Measuring Earthquakes

• Richter Scale- rates earthquake’s

magnitude based

on size of seismic

waves

- works well with

small, nearby

quakes

- waves are

measured by a

seismograph

Measuring Earthquakes• Moment Magnitude

Scale- estimates the total

energy released by an earthquake

- can rate all earthquakes- scientists look at type

and strength of waves, amount of movement, and strength of rocks that broke

Video

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