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Transcript of Earthquakes
Earthquakes are natural vibrations of the ground caused by movement along fractures in Earth’s crust, or sometimes, by volcanic eruptions.
Fractures: form when stress exceeds the strength of the rocks involved.A fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces
Stress is the forces per unit area acting on a material.
the fracture or system of fractures along which movement occurs.
Most earthquakes are caused by movements along faults.
Irregular surfaces in rocks can snag and lock, causing stress to build in the rocks.
When the rocks reach their elastic limit they break, and this produces an earthquake.
The vibrations of the ground during an earthquake are called seismic waves.
Every earthquake generates three types of seismic waves.
or P-waves, squeeze and pull rocks in the same direction along which the waves are traveling.
They arrive at a given point before any other type of wave
They travel through
S-Waves – Seismic waves that do not travel through the Earth as fast as P-waves do
S-waves arrive at a given point after P-waves do
S-waves travel through solids but not liquids and gases
travel along Earth’s surface, moving in two directions as they pass through rock.
L-waves: They are the slowest moving seismic waves
They arrive at a given point after P and S waves
They start at the epicenter and move along the Earth’s surface
Earth’s surface moves up and down like water waves do
They cause the most damage to the Earth because they bend and twist the surface
The focus of an earthquake is the point of failure of rocks at the depth where an earthquake originates.
The epicenter of an earthquake is the point on Earth’s surface directly above the focus.
Seismograph – An instrument that detects and measures seismic waves
The Richter Scale is an absolute scale; wherever an earthquake is recorded, it will measure the same on the Richter Scale. Second, the Modified Mercalli scales measures how people feel and react to the shaking of an earthquake
A huge wave caused by an earthquake on the floor of the ocean
They can travel at speeds of 700 to 800 MPH
They can reach Heights of 20 meters
The height of a 6 Story Building
Types of Volcanoes
Cinder Cones - made mostly of cinders and other rock particles that have been blown into the air
Form from explosive eruptions
Cones are not high
Narrow base & steep sides
largest in size
effusive eruptions; basalt
oceanic hot spots, oceanic rift zones
Composite Volcanoes – Built up of alternating layers of rock particles and lava
First is a violent eruption
intermediate in size (but still big)
explosive eruptions; andesite & rhyolite
subduction zones, continental hotspots, continental rift zones
At the top of a funnel-shaped pit or depression is a pit
If it becomes to large it is called a Caldera
The focus is the point within the earth where seismic waves originate; it is centered on the part of the fault that has the greatest movement. The epicenter is on the earth's surface directly above the focus.