The Dynamic EarthThe Dynamic EarthPart 1: Understanding EarthquakesPart 1: Understanding Earthquakes

The most common cause of Earthquakes is FAULTING. A Fault is a break in the earth’s crust. Earthquakes occur when rocks slip past each other along the fault line. This releases a tremendous amount of energy.

Studying EarthquakesStudying Earthquakes Seismology – the Seismology – the

study of study of earthquakes.earthquakes.

Seismograph – an Seismograph – an instrument used to instrument used to detect and measure detect and measure the shock (seismic) the shock (seismic) waves sent out by an waves sent out by an earthquake.earthquake.

Seismogram – a Seismogram – a recording of the recording of the three types of three types of seismic waves. (S, P seismic waves. (S, P and L)and L)

Seismograph

Types ofTypes ofSeismic WavesSeismic Waves

Primary Waves (P Waves) – Push / pull waves. (like a Primary Waves (P Waves) – Push / pull waves. (like a slinky) Can travel through solids liquids or gases. slinky) Can travel through solids liquids or gases. FASTEST WAVES!FASTEST WAVES!

Secondary Waves (S Waves) Move at right angles to Secondary Waves (S Waves) Move at right angles to the direction of the wave (like a rope) Can travel the direction of the wave (like a rope) Can travel through solids but not liquids or gases. Not as fast through solids but not liquids or gases. Not as fast as P waves. (Arrive after the P Wave)as P waves. (Arrive after the P Wave)

Surface Waves (L Waves) Travel like waves in Surface Waves (L Waves) Travel like waves in water. (up and down) Slowest wave but most water. (up and down) Slowest wave but most destructive kind of wave.destructive kind of wave.

SeismogramsSeismograms

P Waves arrive at the recording station first.

S Waves arrive after the P Wave.

The lag time between the arrival of the two waves is

called the S-P Interval

The Lag Time or S - P

Interval is 4 seconds.

Magnitude - 3.1Distance -34 km

(Only about 25 miles away from the epicenter.)

Earthquake TermsEarthquake Terms

Focus – the Focus – the point beneath point beneath the earth’s the earth’s surface where surface where the earthquake the earthquake occurs.occurs.

Epicenter – the Epicenter – the point on the point on the earth’s surface earth’s surface above the above the focus.focus.

Locating the EpicenterLocating the Epicenter

To locate the epicenter To locate the epicenter seismologists record the seismologists record the seismic waves from three seismic waves from three different recording different recording stations. They measure stations. They measure the time between the the time between the arrival of the P waves and arrival of the P waves and the S waves. Circles are the S waves. Circles are drawn based on this drawn based on this measurement. The measurement. The epicenter is located where epicenter is located where all three circles meet.all three circles meet.

Are We At Risk?Are We At Risk?New

Madrid Fault

New Madrid, Missouri

You You better better believe believe

it!it!

New Madrid Earthquakes 1811 - 1812

- Changed the course of the Mississippi River.- Created Reelfoot Lake in Tennessee.- Rang church bells as far away as Boston, Mass.

Several earthquakes occurred between December 1811 through February 1812. Estimated magnitudes as high as 8.1

United States Geological SurveyUnited States Geological Survey

QUAKES Activity

Finding the Finding the Epicenter Epicenter

of an of an EarthquakeEarthquake

When an earthquake occurs both P Waves and S Waves are sent out in all directions. Since P Waves travel faster than S Waves, the waves do not reach a distant point at the same time. This difference in time is known as the S/P Interval or Lag Time.

A P Wave travels through the earth at an average of 6.1 kilometers per second (km / sec.)

How many kilometers would a P wave travel in 6 seconds?

Multiply 6.1 times 6 seconds

36.6 km

6.1 km / sec.

X 6 sec.____________

An S Wave travels through the earth at an average of 4.1 km/sec.

How many kilometers would a S wave travel in 6 seconds?

Multiply 4.1 km / sec. times 6 seconds

24.6 km

4.1 km / sec.

X 6 sec.__________

If P Waves travel at an average of 6.1 km/sec. then in 16 Seconds a P Wave will travel about

100 km.

6.1 km / sec.

X 16 sec.__________

97.6(100 Km)

If S Waves travel at an average of 4.1 km/sec. then in 24 Seconds an S Wave

will travel about 100 km.

4.1 km / sec.

X 24 sec.__________

98.4(100 km)

Using this knowledge, we can see that the S-P Interval or Lag Time is about 8 seconds if the epicenter of

an earthquake is 100 km away.

This means that the epicenter is 12.5 km away for every single second of Lag Time

100 ÷ 8 = 12.5

Remember! It takes data from three recording stations to determine the epicenter of an earthquake.

An Earthquake has been detected…………………… Stand by for data

You will now begin the QUAKES Practice Activity.

Wait for further instructions.