Download Earthquakes Seismic Waves

Earthquakes
Earthquakes!
• Chapter 10
• One of most destructive forces on Earth
• Natural rapid shaking of the ground due to
friction from sliding faults
(Ex: rubbing your hands)
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Results in displaced rocks
Causes energy to dissipate outward
Energy travels through Earth in seismic waves
When reaches the surface, moves the ground!
On ocean floor, form tidal waves or tsunamis
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Copyright © 2008 Thomson Delmar Learning, a division of Thomson Learning, Inc.
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Copyright © 2008 Thomson Delmar Learning, a division of Thomson Learning, Inc.
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Seismic Waves
• Seismic Waves can be detected using a
seismograph
http://earthsci.org/education/teacher/basicge
ol/earthq/seismograph.gif
– Uses series of springs and weights
• Types of seismic waves:
1) P-waves (compressional Primary wave)
• Move like sound waves
• Fastest type of seismic wave
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92/5103423.JPG
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2) S-waves (Secondary waves)
– Travel in an up-and-down pattern
– Can only travel through solid material
Surface wave —> interaction of P- and S- waves
– Results in a rolling motion of the ground
Source of waves is called the focus
http://earthquakes.usgs.gov/learning/faq.
php?categoryID=5&faqID=26
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Area directly above focus called
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epicenter
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http://www.astro.virginia.edu/class/oconnell/astr121/im/seismic-waves-crossec-CM.jpg
Epicenter Location
• Determined by arrival of P- and S-waves
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Using a seismograph
Locates the distance to the epicenter
Use difference in arrival times
Data from three
seismograph
stations needed
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Earthquake Measurement
Strength measured using:
– Richter scale — measures equivalent energy
produced
• Scale of 0 to 9
• Every increase in number means ten fold
(10 x) increased magnitude
• 5 is equivalent of medium-sized atomic bomb!
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Earthquake
Measurement
• Or the MM scale, which
measures destruction.
• The Modified Mercalli
Intensity (MM) scale is a
means of categorizing the
effects of shaking on people,
structures and the
environment.
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http://data.gns.cri.nz/geoatlas/images/mercalli.jpg
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Volcanoes !
Formation of a Volcano
• Where molten rock flows from beneath crust
– Molten rock is called lava
• Location associated with convergent tectonic
plate boundaries
– Where subducting plate begins to descend
underneath another plate.
– Sinking plate brings in seawater making steam
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Types of Volcanoes
• Volcanoes are classified by type of
eruption
• Eruption — release of lava, ash, steam,
and gases
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Quiet Eruption Volcanoes
• Quiet eruptions from volcanoes called
shield cones
– Formed when lava flows from a central vent
• Lava cools at surface and solidifies
forming a shield
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Explosive Eruption Volcanoes
• Fissure eruption
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Long crack in Earth’s crust
Produces large amounts of lava
Cool to form huge sheets or plateaus
Deccan lava flows in India
Columbia River plateau
• Much more violent
• Greatest threat to human life and property
• Composite cone — mountain-like structures
– Fire-broken rocks that were blasted apart
– Usually surround one central vent
– Near subduction zones with convergent
plate boundaries
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• Caldera — volcanic crater (a small canyon)
– Left behind after composite cone is destroyed
– Crater Lake in Oregon
Explosive eruption with lightning at
Sakurajima Volcano
Cinders were issued up to >2,500 m high
(23:03 on18 May 1991; taken by SVO)
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– One of world’s largest in Yellowstone Park
– Heats water
• Produces geysers, mud pots, and hot springs
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Geyser in Yellowstone
Caldera A large, usually circular depression at the summit of a
volcano formed when magma is withdrawn or erupted from a
shallow underground magma reservoir.
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• Lava dome
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• Cinder cone
Smaller mounds, hardened lava covering a vent
Grow slowly
Build up great pressure
After Mount St. Helens in 1980
• Formed small lava dome in its crater
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– Small mound of lava, ash,
and pyroclastic material
– Smallest type of volcano
– When lava breaks through for first time
– Resulting eruption spews lava into air
– Forms a volcanic bomb
• Lava hardens before hitting the ground
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Volcanic Hazards
• Most dangerous result is pyroclastic flow
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Moves at speeds of more than 100 mph
Contains hot gases, water, ash, and debris
Destroys everything in its path
Mount Vesuvius in A.D. 79
• Destroyed Pompeii
• Volcanic ash enters atmosphere
and travels miles!
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• Ash mixes with water, causes mudflows
• Release of toxic gas
– Sulfur dioxide and water forms sulfuric acid
• Mount Pinatubo in 1991
– Mudflow 650 feet deep
• Debris flows called lahars
– When snow melts suddenly at high elevations
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