Earthquakes and Earthquake Waves

What causes earthquakes? Earthquakes are caused by sudden movements in the Earth’s crust Fractures in the crust are also called faults The energy for quakes builds up for many years

What causes earthquakes? There are different type of faults depending on the motion. Two common ones are normal (vertical) and strike/slip (horizontal sliding)

Strike/Slip http://earthquake.usgs.gov/learning/animations/animation.php?flash_title=Strike-Slip+Fault&flash_file=strikeslip&flash_width=240&flash_height=310

What causes earthquakes? 90% of the quakes occur on plate margins where plates are colliding or subducting or transforming (moving toward, sliding under or sliding past one another)

Earthquake Measurement Earthquakes are measured by their magnitude, the size of the seismic wave. This is recorded at an earthquake station with a seismograph. (Richter Scale) Earthquake intensity (Modified Mercali Scale) measures the amount of damage to an area and is determined by the damage of an earthquake.

Earthquake Waves There are two types of waves in an earth quake: Surface Waves (l for love) – just what you would expect Body Waves – vibrational waves that travel through the earth Body waves are divided into shear (s for secondary) and compression (p for primary) waves. P waves travel through the core.

Surface Waves

P Waves

S waves

Magnitude Recording This is a picture of a seismogram recording an earthquake

How to know where an earthquake happened: The seismograph records the arrival of the different l, s and p waves. Since p waves travel faster, they get there first. S waves get there later. The interval between arrival times lets seismologists know how far away the earthquake was.

Seismograph Recordings

Seismograph Recordings One seismogram location can only give you the distance or radius of the earthquake – that is not enough to find it You need three seismogram centers to pin point the exact location – this is called triangulation

Earthquake Triangulation

Earthquake Vocabulary The location on the surface where the earthquake occurs is called the epicenter The place inside the earth where the earthquake originated is called the focus Aftershock –readjustment of the crust in an area that has experienced a quake or mainshock

Pictures of Earthquake Damage – very powerful energy!

Cool Internet Site http://www.thetech.org/exhibits/online/quakes/ I got many of my animations here, it has way more cool stuff. The main site also has other science stuff! If you have a way to get there, do it as homework.