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When stresses inside the Earth make rocks slide and break quickly past each
other along fault lines, earthquakes are formed. The quick movement of these
plates causes the ground to shake which is what happens during an earthquake.
This motion occurs 40 miles below the surface, or at the focus.
Body waves branch out from the focus, which causes tremors miles away. There
are three types of surface waves. The primary waves take only twenty minutes
to reach there destination. That is called compressional. Transverse are
the secondary waves.They move at a slower pace and take twice as long to
reach the same place as primary waves. Movement is faster in dense, rigid
rock and slower in lighter liquid materials like the atmosphere.
Differences in the state of matter from layer to layer affect the behavior
of waves. Waves are also influenced by the kind of boundary the plates lie
A triple junction is where three plates meet. These types of faults are
the most complex and the most important in terms of long-term translations.
Even though there are sixteen possible combinations, only six different
kinds are found on Earth today. The Gulf of California is the intersection
of all three of the types of plates. It is the result of plate activity
at the triple junction of the Pacific, Nazca,
and North American plates. The Galapagos Islands and the East Pacific Rise
are thought of as the simplest example of a triple junction.
Oceanic ridge boundaries are very narrow
bands of shallow earthquakes. These earthquakes are caused by tensile stresses
that follow the crest of the 48,000-mile-long, active mid-ocean ridges.
These plates move in opposite directions. This creates crust.
The cracks in these rift zones fill up with lava. The lava eventually cools
and forms rock bodies called dikes. Volcanoes, faulting, escarpments, mountains,
and shallow earthquakes happen here. There are many examples of oceanic
ridges. In Iceland, the southwest Mid-Atlantic-Ridge has risen above water.
Thingvellir Graben is a rift in southwest Iceland where lava erupts to form
new crust. The Red Sea was made by Africa splitting from Arabia. The Gulf
of California and the Gulf of Aqaba were formed by this process. and will
probably be oceans in the future.
A subduction zone is the opposite of the mid-oceanic-ridge.
These boundaries include all of the world's deep trenches and young mountains,
but they are more spread out. Along these boundaries, crust is destroyed
where the edge of one plate goes under the edge of another. Continental
crust along these boundaries is more buoyant
and lighter than oceanic crust. Here, mountain chains are made with earthquakes,
sediment, and volcanic activity. The Himalayas were made 100 million years
ago when India collided with Asia. The border between Nepal and Tibet is
made up of the Himalayas which were created by the Eurasian and Indian plates.
The Alps were formed by crust pilling up in a subduction zone.
Transform faults happen in places where ridges are offset. Much more violent
earthquakes occur here. They result from plates on either side of the faults
grinding sideways in different directions. The crust here is conserved.
These long faults make steep slopes and cliffs thousands of feet high going
deep into the crust. Most of the transform faults cut the ocean floor.
San Andreas Fault
San Andeas Fault
The San Andreas is a transform fault that is
1,000 miles long. The western plate moves north along the fault two inches
every year. This fault connects the Juan de Fuca ridge with the ridge in
the Gulf of California. California, New Zealand, and Pakistan are faults
cut into the ocean floor.