Seismic Waves

Seismic Waves

Waves of energy that travel through the earth after rock has been elastically deformed

1. The crust layer is stressed and begins to deform

2. If the crust breaks it releases energy

3. The energy waves travel through the earth to the surface

The seismic waves have names

Body waves – seismic waves that travel through the earth’s interior which include:

1. Primary waves (P) 2. Secondary waves

(S) Surface waves (L) –

Long waves, travel on the surface

Primary Waves – also called P waves

Waves that spring back and forth until the rock goes back to its original or new shape

Travel through solids, liquids and gasses

Are the fastest First to be

detected

Secondary Waves – also called “shear waves”

Waves travel side to side after rock is back in original or new position

Second fastest Cannot travel

through liquids or gasses

Called secondary or shear waves

Surface waves – also called L waves

L WAVES = LAST TO ARRIVE!

Waves travel along the surface

Travel more slowly but are more destructive

Most damage comes from surface waves

Move the ground up and down and in circles

SURFACE WAVES = L WAVES

A Seismogram is a printout of the P,S, and L waves

Seismographs are instruments that record the seismic waves

How seismographs work …

Seismograms are used to calculate when and where an earthquake started

EPICENTER AND FOCUS

SEISMOGRAPH – RECORDS SEISMOGRAMS

The FOCUS is the earthquakes starting point

The EPICENTER is the point on the earth’s surface directly above the starting point (focus)

How do scientists find the epicenter of an earthquake?

• Scientists collect several seismograms of the same earthquake from different locations

They calculate the arrival time difference between the S and P waves

They plot these differences on a time distance graph to determine the distance of the epicenter to the recording seismograph

TIME/ DISTANCE GRAPH

Finding the epicenter …

Using the data from the time distance graph scientists can calculate the radius of the area the waves travel

Then scientists construct the diameter of each area and where they all overlap is the epicenter

After shock!

When another earth- quake occurs at the same epicenter shortly after the first earth quake

Not usually as strong

Sometimes occur a few days after the initial earthquake

Can cause damage!

Complete P, S and L wave worksheet!