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of two plates. Fault zones such as
the San Andreas represent key
areas at which earthquakes oc-
cur. Strong vibrations are gener-
ated inside the Earth as a result
of earthquakes which causes
the ground to shake. The various
types of plate tectonics move-
ments on which an earthquake
can occur are discussed below:

Strike-Slip Faults. A strike-slip
(or transform) fault results when
two plates move sideways and
past each other. Examples of
earthquakes caused by strike-slip
Earthquake faults include the San Andreas
and Haywards faults in California.
Dip-Slip Faults. A Dip-slip fault
occurs when a plate moves verti-
cal in respect to another plate or
when two plates move vertical
past each other. There are two
types of Dip-Slip Faults, normal
and reverse. A Normal Fault oc-
curs when the plate on the bottom
side of the fault slides down. A Re-
verse Fault occurs when the plate
on the top side of the fault slides
up. The Sierra Nevada fault, in
Eastern California, is an example
of a Dip-Slip Fault.

Oblique - Slip Faults. Oblique
Facts about Earthquakes slip faults occur when two plates
significantly slide both vertically
The Earth’s top layer, the crust, the dense but fluid mantle, they and horizontally against each
rests on the mantle. The crust move around. When two tecton- other.
is more like a puzzle than one ic plates get close, one may try
solid landmass. It has a number to slip underneath or rise above How are Earthquakes Mea-
of plates that fit together, and the other. Sometimes the friction sured?
the plates are made of rock and caused by the two plates jockey- Scientists use a piece of equip-
other solid materials. The Earth ing for position results in a great ment known as a “seismograph”
has seven major plates and doz- release of kinetic (movement) en- to measure earthquake activ-
ens of minor plates. The seams in ergy, causing an earthquake. ity and strength. A seismograph
between each of these plates are measures three distinct pieces of
called “fault lines.” Faults information: the size (magnitude)
Faults are generally categorized of the earthquake, the depth of
Why do Earthquakes happen? as a type of boundary either within the earthquake and the location
As tectonic plates sit on top of a continental plate or at the edges of the earthquake.
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