Earthquakes And Volcanoes

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

Seismic Waves FOCUS- underground point of origin EPICENTER- aboveground 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 push-pull 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 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 Bombs- few 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 pit, or depression at top of volcano Caldera- when a crater becomes too large, it collapses: also can form when the top of a volcano collapses or explodes Dormant- sleeping volcano Extinct- not known to have erupted in modern history Active- Erupts fairly regularly

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