What are 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
What is the Elastic Rebound Theory?
*Explains how energy is stored in rocks
-Rocks bend until the strength of the rock s exceeded
-Rupture occurs and the rocks
The focus and epicenter of an earthquake
*The point within Earth where faulting begins is the focus
*The point directly above the focus on the surface is the epicenter
*record earthquake events
-At convergent boundaries, focal depth increases along a dipping seismic zone called a Benioff zone
Where do earthquakes occur and how often?
-80% of all earthquakes occur around the Pacific Plate
-Most of these result from convergent plate 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 string enough to be
The economics and societal impacts of EQ's
What are Seismic Waves?
*Response of material to the arrival of energy fronts released by rupture
-Body waves (Inside the Earth)
*P and S
-Surface waves (Surface of the Earth)
*R and L
Body Waves: P and S waves
-P or primary waves
*travel through solids, liquids, or gases
*compressional 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 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
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
What causes volcanoes to erupt?
*The shift in the Earth's plates are what causes volcanoes to form.
*As the plates join or separate some of the molten rock is exposed
resistance of a fluid to flow.
Where do volcanoes erupt??
convergent plate boundaries
Convergent plate boundaries
where two of Earth's plates join together
Divergent plate boundaries
where two of the Earth's plates move apart RING OF FIRE!!
active areas below the earth's crust
the molten, or liquid-like, rock within the Earth
magma that reaches Earth's surface
an opening through which molten rock flows onto Earth's surface
How many vents do volcano's have?
Volcanoes always have one central vent, but also have several smaller side vents
Types of Volcanoes
Shield volcanoes, composite volcanoes, cinder cone volcanoes
the magma inside a shield volcano is rich in iron magnesium and is very fluid.
how long does the magma flow>
since the magma is very fluid, the lava coming out of the volcano tends to flow great distances.
what happens when the shield volcanoes erupt?
the flowing lava gives the volcano the shpae of a gently sloping mountain,
how often do shield volcanoes erupt?
Mild and occur several times.
Example: Mauna Loa in Hawaii is a shield volcano
the magma inside a composit volcano is rich in silica and much thicker than magma from a shield volcano
eruptions from composite volcanoes
they can be flowing lava or explosions. the explosive eruptions come from the trapped gases and produce cinders and ash.
Examples of composite volcanoes
Mount Fuji in Japan and Mount St. Helens in USA
What makes the composite volcanoes alternating layers of lava and cinders?
The different type of eruptions