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And Defining Earthquakes • Shaking and trembling of the earth’s crust. • The waves travel in all directions • More than 1,000,000 occur a year or one every 30 seconds • Faulting is the most common cause • Earthquakes continue until all the energy is used up • TSUNAMIS- earthquake on the ocean floor: causing waves to become greater than 20 meters high Three Types of Faults Strike-Slip Thrust Normal What is the Elastic Rebound Theory? • 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 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, releasing energy. Elastic Rebound – deformed rock goes back to its original shape http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Focus – point inside the Earth where an earthquake begins Epicenter – point on Earth’s surface above focus Seismic Waves • FOCUS- underground point of origin • EPICENTERaboveground of origin; most violent shaking occurs at the epicenter • The three main types of seismic waves are: P waves, S waves, and L waves P Waves • Primary waves • Arrive first at the epicenter • Can travel through solids, liquids, and gases • They are pushpull waves S Waves • Secondary waves • Can travel through solids, but NOT through liquids and gases • Move in up-down motion Comparing Seismic Waves R and L Waves • • • • Surface waves Slowest moving seismic waves Travel on top of Earth’s surface Cause most of damage to Earth, because they bend and twist the surface Surface Waves: R and L waves • 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 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 How is an Earthquake’s Epicenter Located? 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. John Milne- 1893 • Seismograph-measures and detects seismic waves • Seismogram- Paper record of waves • Seismologist- scientist who study earthquakes • Richter Scale- a scale that allows scientists to determine earthquake strength based on many readings • 1-10 levels at which an earthquake is measured on amount of damage caused; Above a 6 is very destructive Typical Seismogram http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt How are Earthquakes Measured? Richter Scale How are the Size and Strength of an Earthquake Measured? • Magnitude – Richter scale measures total amount of energy released by an earthquake; independent of intensity – Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open-ended logarithmic 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 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 VOLCANOES • Volcano- place on Earth’s surface that allows magma and other material to erupt • Magma- found beneath the Earth’s surface, it is liquid rock • Lava- magma that reaches the Earth’s surface Volcanic Fragments • Volcanic Dust- less that 0.25 mm in diameter (flour) • Volcanic Ash- more than 0.25 less than 5 mm (rice) • Volcanic Bombsfew cm to several meters. • Cinders- volcanic bombs the size of golf balls Types of Volcanoes • Cinder Cones- made of mostly of cinders; formed from explosive eruptions • Shield- Made of quiet lava flows • Composite- made up of alternating layers of rock particles; explosive eruptions, then quite lava flows Volcanic Terminology • Crater- funnel shaped • Dormant- sleeping pit, or depression at volcano top of volcano • Extinct- not known to • Caldera- when a have erupted in crater becomes too modern history large, it collapses: • Active- Erupts fairly also can form when regularly the top of a volcano collapses or explodes Ring of Fire Zones • There are 3 zones: • Ring of Fire- Extends nearly all the way around the edge of the Pacific Ocean • Mediterranean Sea- Italy, Greece, Turkey • Iceland and Atlantic Ocean- Mid Atlantic Ridge EXTRA! EXTRA! • Mount St. Helens is a volcano is Washington State • San Andreas Fault in California • New Madrid Fault is where we live