How are Earthquakes Recorded?

Educational Materials and Videos are made by:Giovanna Perrone

and Alexandra Mair

SEYS 753 Spring 2008

Professor Brain Murfin

Dynamic CrustDynamic Crust• Do Now:

– Watch the following clip and describe what you are seeing.

– http://www.youtube.com/watch?v=m9RF5eRdG9c

The following clip is a demonstration of how earthquakes occur and they are recorded. Using the following worksheet, earthquake video worksheet, answer the questions using the information from the video. After the video, have a class discussion on the notes as the lesson will reiterate the concepts of the video. (click the warning to begin the video)

Earthquakes • Earthquakes: a violent shaking of the earth’s crust

caused by the movement of landmasses along faults and/or subduction zones

Fault: it is the first place where movement occurs between the plates A fault line is where an earthquake occurs

EarthquakesEpicenter: is the location on the earth’s surface that

is directly above the focus of an earthquake. This is where the seismic waves first reach the surface.

Seismic Waves: Seismic waves the energy that an earthquake release and goes in ALL DIRECTIONS

Richter Scale• The Richter scale is widely used to measure the

magnitude (or the amount) of energy of an earthquake. There is no limit as to how strong an earthquake may be.

Mercalli Scale• Mercalli Scale is used to determine how

much observable damage, also called the intensity, was done by an earthquake

Seismograph vs. Seismogram• Seismograph is an instrument that is used to detect

(measure) seismic waves • Seismic waves are recorded on a seismogram• A seismogram is a piece of paper that records

seismic waves

http://www.thetech.org/exhibits/online/quakes/seismo/images/seismograph.gif

How to Read a Seismogram

http://ww2.lafayette.edu/~malincol/Geol120/earthquaketopics.html

Earthquake Waves• P-waves – also called primary waves, or

compressional waves– P-waves travel faster – They always reach the seismic stations first– P-waves cause particles to vibrate back and

forth in the direction that a P-wave moves (← →)

– P-waves can travel through solids, liquids, and gases

Earthquake Waves• S-waves – also called secondary waves,

or shear waves.– S-waves travel slower than P-waves and

reach seismic stations second.– S-waves cause particles to vibrate at right

angles (up and down motion) to the direction that S-waves move. (↑↓)

– S-waves can only travel through solids - NEVER through liquids

Shadow zones are created due to secondary waves cannot pass through the liquid outer core. These are areas where no seismic recording occurs.

Notice the vertical axis

This represents TIME (in minutes!)

Let’s enlarge a small section

Between each minute, we notice that there are 3 segments.

If there are 60 seconds in a minute, each one of these segments must be ________seconds.

What would this time be?

Notice the horizontal axis

This represents DISTANCE (in thousands

of Kilometers!)Let’s enlarge a small section

There are also two curves on this chart that display the way different earthquake waves behave.

This chart can be used for answering many different questions!

How long does it take an S-Wave to travel 5,000km?

The recording station tells us it took 6 minutes and 20 seconds for the P-Wave to reach them. How far away from the epicenter of the earthquake must they be?

I know that there was a 7 minute difference in the arrival of my P and S waves. How far away from the epicenter must I be?

Mark off 7 minutes on scrap paper…

Slide your scrap paper up until the tick marks match up with the curves…