Diapositiva 1
EARTHQUAKESAnearthquake is the result of a sudden release of
energy in theEarth'scrustthat createsseismic waves.
Theseismicity,seismismorseismic activityof an area refers to the
frequency, type and size of earthquakes experienced over a period
of time.ELSTIC-REBOUND THEORY
Theelastic rebound theoryis an explanation for howenergyis
spread duringearthquakes. As rocks on opposite sides of afaultare
subjected to force and shift, they accumulate energy and slowly
deform until their internal strength is exceeded. At that time, a
sudden movement occurs along the fault, releasing the accumulated
energy, and the rocks snap back to their original undeformed
shape.Elastic rebound theory
SEISMIC CYCLEThe seismic "cycle" refers to the observation that
earthquakes repeatedly rupture a given part of a fault. The term
"cycle" does not however imply that earthquakes are a periodic or
regularly repeating event
An area where there is already been an earthquake should have
reached a period of equilibrium that means seismic tranquility. The
tectonic forces that may deform the crust will again accumulate
energy with the consequence of a new earthquake. This process take
the name of seismic cycle
SEISMIC WAVESSeismic wavesare the waves of energy caused by the
sudden breaking of rock within the earth or an explosion. They are
the energy that travels through the earth and is recorded on
seismographs.
P WAVESThe first kind of body wave is theP waveorprimary wave.
This is the fastest kind of seismic wave, and, consequently, the
first to 'arrive' at a seismic station. The P wave can move through
solid rock and fluids, like water or the liquid layers of the
earth. It pushes and pulls the rock it moves through just like
sound waves push and pull the air.
S WAVESThe second type of body wave is theS waveorsecondary
wave, which is the second wave you feel in an earthquake. An S wave
is slower than a P wave and can only move through solid rock, not
through any liquid medium. It is this property of S waves that led
seismologists to conclude that the Earth'souter coreis a liquid. S
waves move rock particles up and down, or
side-to-side--perpindicular to the direction that the wave is
traveling in
Travelling only through the crust,surface wavesare of a lower
frequency than body waves, and are easily distinguished on a
seismogram as a result. Though they arrive after body waves, it is
surface waves that are almost enitrely responsible for the damage
and destruction associated with earthquakes. This damage and the
strength of the surface waves are reduced in deeper
earthquakes.