 By the end of this unit, you should be able to:  Discuss stress and strain and their roles in earthquakes  Know the differences between elastic and plastic deformation  Compare and contrast the three types of faults and three different seismic waves  Explain the process of locating an earthquakes epicenter  Discuss the relationship between plate tectonics, stresses and earthquakes

 The shaking or trembling caused by the sudden release of energy  Usually associated with faulting or breaking of rocks  Continuing adjustment of position results in aftershocks

 Explains how energy is stored in rocks  Rocks bend until the strength of the rock is exceeded  Rupture occurs and the rocks quickly rebound to an undeformed shape  Energy is released in waves that radiate outward from the fault

 Stress occurs when there is a force on the rocks.  Strain is the response to stress  1. Compression-squeeze together  2. Tension-pull apart  3. Shear-distortion

 Elastic deformation- low stress, material bends and stretches (pulling of rubber band- goes back into shape  Plastic deformation- stress builds past elastic point, causes permanent deformation  Failure occurs when there is a rupture

 Crack in the earth where plates moves  Types of Faults  Reverse  Horizontal and vertical pressure that squeezes the rock or land together  Seen at convergent boundaries

 Normal Fault  Movement is vertical and horizontal  Caused by tension  Divergent boundary

 Strike Slip Fault  Also known as a transform fault  Caused by horizontal sheering  Example  San Andreas Fault in California

 Chapter 19.1  Pg

 Energy that is released by an earthquake  Energy travels in the form of waves  Two types:  Body waves  P and S  Surface waves

 Body waves  P or primary waves  fastest waves  travel through solids, liquids, or gases  compression wave, material movement is in the same direction as wave movement

 S or secondary waves  slower than P waves  travel through solids only  shear waves - move material perpendicular to wave movement

 Surface Waves  Travel just below or along the ground’s surface  Slower than body waves; rolling and side- to-side movement  Especially damaging to buildings

 Earth’s internal structure  Waves change speed and direction depending on the material they go through  S Waves do not go through the outer core  When the waves change scientists can gain information about the consistency and density of our earth’s layers  Shadow zone is created where no P or S waves travel

 Focus  The point within Earth where faulting begins is the focus---below the surface  Epicenter  The point directly above the focus on the surface

Seismic wave behavior  P waves arrive first, then S waves, then L and R  Average speeds for all these waves is known  After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.

 Three seismograph stations are needed to locate the epicenter of an earthquake  A circle where the radius equals the distance to the epicenter is drawn  The intersection of the circles locates the epicenter

 Magnitude  Richter scale measures total amount of energy released by an earthquake; independent of intensity  Amplitude tells us the size of the seismic wave  The greater the amplitude the stronger the earthquake  Intensity  Modified Mercalli Scale  subjective measure of the kind of damage done and people’s reactions to it  isoseismal lines identify areas of equal intensity

 ~ 80% of all earthquakes occur in the circum-Pacific belt  most of these result from convergent margin activity  ~15% occur in the Mediterranean-Asiatic belt  remaining 5% occur in the interiors of plates and on spreading ridge centers  more than 150,000 quakes strong enough to be felt are recorded each year

Damage in Oakland, CA, 1989 Building collapse Fire Tsunami Ground failure