Earthquakes

What Is An Earthquake? Click here to find out

What is an earthquake?• Used to describe both sudden slip on a fault, and the resulting

ground shaking and radiated seismic energy caused by the slip• Caused by volcanic or plate activity,

The map above shows the distribution of earthquakes with magnitudes greater than 5.0 that occurred between 1965 and 1995.

http://eqseis.geosc.psu.edu

Three Types of Faults

Strike-Slip

Normal

Reverse

Animation of fault movement

Normal fault

Pulls on the crust stretching rock so that it becomes thinner (like pulling on bubble gum) = tensionOccurs when plates are moving apart

Results in hanging wall slipping downward

Hanging wall

Foot wall

animation

What type of fault?

Hanging wallFoot wall

http://www.bgs.ac.uk/eqr/GeoD_Structures.htm

normal

What causes earthquakes?

• Tectonic plates move past each other causing stress. Stress causes the rock to deform– What type of fault boundary is this?– What type of stress is shown?

transform

shearing

Strike – slip fault

Rocks on either side of fault slip past each other sideways with little up or down motion -

Animation of strike-slip motion

Occurs at a plate boundarytransform

shearingWhat type of stress is produced?

Fault rupture across road in western Kaynasli, right-lateral strike slip displacement was about 4.0 m (13 feet) at this location http://www.geerassociation.org/GEER_Post%20EQ

%20Reports/Duzce_1999/kaynasli1.htm

Reverse fault

Pushes on the crust squeezing rock until it folds or breaks (like a trash compactor) = Occurs when plates are moving together

Results in hanging wall slipping upward

Hanging wall

Foot wall

animation

compression

What type of fault?

Hanging wall

Foot wall

http://geologicalintroduction.baffl.co.uk

reverse

What type of fault?

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

– 1. point inside the Earth where an earthquake begins

– 2. point on Earth’s surface above focus where earthquake is FELT most strongly

Epicenter

Focus

1

2

How Seismographs Work

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

the pendulum remains fixed as the ground moves beneath it

A seismograph is an instrument used for recording the intensity and duration of an earthquake.

Earthquakes

• How are earthquakes measured?

Seismograph machine

Seismogram – seismic wave display record

Seismic Waves

Primary Waves (P Waves)

• A type of seismic wave that compresses and expands the ground

• The first wave to arrive at an earthquakehttp://daphne.meccahosting.com/~a0000e89/insideearth2.htm

Secondary Waves (S Waves)

• A type of seismic wave that moves the ground up and down or side to side

http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

Comparing Seismic Waves

Surface Waves

• Move along the Earth’s surface• Produces motion in the upper crust

– Motion can be up and down– Motion can be around– Motion can be back and forth

• Travel more slowly than S and P waves• More destructive

Animation of wave types

How do scientists calculate how far a location is from the epicenter of an earthquake?

• Scientists calculate the difference between arrival times of the P waves and S waves

• The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

Typical Seismogram

http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

start finish

How much time elapsed between the arrival of the P wave (start) and the arrival of the S wave (finish)?

Locating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Locating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Now you are going to be seismologists and locate an Earthquake

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Go to: http://tinyurl.com/11quake13

Click here to go to virtual earthquake site

National Geographic earthquake information

How are Earthquakes Measured? Richter Scale

A logarithmic scale used to express the total amount of energy released ___________ of an earthquake. Its values typically fall between 0 and 9, with each increase of 1 representing a _________ increase in energy.

magnitude

10-fold

How are Earthquakes Measured? Mercalli Intensity Scale

Click for Interactive Demo Go to http://tinyurl.com/13quake13

A scale of earthquake intensity based on ___________and ranging from I (detectable only with instruments) to XII (causing almost total destruction).

observed effects

Earthquake Waves & Earth’s Interior

Seismic wave animation

Seismic Waves in the Earth

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Click here for animation

Tsunamis

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Click here for explanation of a tsunami

Formation of a tsunami

http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

PBS –tsunami animation

a large ocean wave usually caused by an underwater earthquake or a volcanic explosion.

Click here for Japan helicopter view of tsunami

With typical waves, water flows in circles, but with a tsunami, water flows straight. This is why tsunamis cause so much damage!

Tsunami Warning System

http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

Review Questions

1. A large ocean wave usually caused by an underwater earthquake or a volcanic explosion.

tsunami

2. Used to describe both a sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip

earthquake

How are Earthquakes Measured?

3. Which one uses a logarithmic scale to express the total amount of energy released or magnitude of an earthquake.

Richter Scale

4. Which uses a scale of earthquake intensity based on observed effects and ranging from I (detectable only with instruments) to XII (causing almost total destruction).

Modified Mercalli Scale

What type of fault is shown by each picture?

1.2.

3.

NormalReverse

Transverse or strike-slip

Which type of wave travels through solids only?

S-wave

Which type of wave causes the most destruction?

Surface or Love waves

What type of fault?

AHanging wall has moved

http://geologicalintroduction.baffl.co.uk B

Source: indiana.edu

Reverse fault

upwardStrike –slip or transverse fault

– 1. point inside the Earth where an earthquake begins

– 2. point on Earth’s surface above focus where earthquake is FELT most strongly

Epicenter

Focus

1

2

People walk along a damaged road in the province of Bohol on Tuesday, October 15, 2013.

Do you think this was a major earthquake? Why or why not?

Yes, it was a major quake.It crumbled a number of buildings

Such as this church

7.1 magnitude earthquake hit the Philippines

Earthquakes

5. __________ machine

____________ seismic wave display record

Seismograph

P-wave

Surface

2.

3.

4.

1. S-wave

Seismogram