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.