Modified from Liz LaRosa http://www.middleschoolscience.com Earthquakes Modified from Liz LaRosa http://www.middleschoolscience.com

What is an earthquake? A sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip Caused by: sudden stress changes in the earth volcanic or magmatic activity

Three Types of Faults Strike-Slip Thrust Normal Three types of faults Form depending on type of plate motion and complex reaction of earth’s lithospheric blocks Strike-slip Normal Thrust Normal

What causes Earthquakes? Tectonic plates move past each other causing stress. Stress causes the rock to deform Plastic deformation – does not cause earthquakes Elastic deformation – rock stretches then reaches a breaking point, causing an earthquake and releasing energy.

Elastic Rebound – after the earthquake, deformed rock goes back to its original shape http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Focus – point inside the Earth where an Focus – point inside the Earth where an earthquake begins Epicenter – point on Earth’s surface above focus

How Seismographs Work the pendulum remains fixed as the ground moves beneath it http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

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

Two Types of SeismicWaves Surface Waves Body Waves Primary (P Waves) Secondary (S Waves)

Primary Waves (P Waves) – Pressure Waves A type of seismic wave that compresses and expands the ground (longitudinal) The first wave to arrive at an seismic station Can travel through solids, liquids and gases http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

Secondary Waves (S Waves) –Shear Waves A type of seismic wave that moves the ground up and down or side to side (transverse) Arrives at the seismic station second Can’t travel through liquids 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 than S and P waves

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

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

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

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

How are Earthquakes Measured? Richter Scale

How are Earthquakes Measured? Mercalli Intensity Scale Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

Earthquake Waves & Earth’s Interior

Seismic Waves in the Earth http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

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

Formation of a tsunami http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

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