(5 12 09) how earthquakes work

How Earthquakes Work

Jordan ChairesP.4.

5-12-09

How Does an Earthquake Work?An earthquake is a vibration that travels

through the earth's crust.

Causes of EarthquakesAll kinds of things can cause earthquakes:movements of the earth's platesvolcanic eruptions meteor impacts underground explosions (an underground

nuclear test, for example) collapsing structures (such as a collapsing

mine)

Steps to an Earthquake

Plate Movement

s

Seismic

Waves

Destruction to

families, homes,

and contries

FactsAn Earthquake occurs about once every 11

seconds.There have been more than 1.5 million

earthquake-related fatalities in the last hundred years.

Plate TectonicsSeismology - the study of earthquakes The basic theory is that the surface layer of

the earth (lithosphere) is comprised of many plates that slide over the athenosphere layer.

CollideAt the boundaries between these huge plates

of soil and rock, three different things can happen: divergent plate boundary (Plates can move

apart)convergent plate boundaries (Plates can

push together)transform boundaries (Plates slide against

each other)

FaultsFaults are formed where these plates meetFaults are breaks in the earth's crust where

the blocks of rock on each side are moving in different directions

Earthquakes are most common along fault lines

Seismic WavesWhen a sudden break or shift occurs in the

earth's crust, the energy radiates out as seismic waves, just as the energy from a disturbance in a body of water radiates out in wave form.Primary waves – can travel through solid, liquid

and gas, and so will pass completely through the body of the earth. Typically arrive at the surface as an abrupt thud.

Secondary waves - don't move straight through the earth. They only travel through solid material, and so are stopped at the liquid layer in the earth's core

SeismographA seismograph is a machine that registers the

different waves.

The Richter ScaleThe Richter Scale is used to rate the amount of energy it released.

The wave amplitude increases 100 times between a level 7 earthquake and a level 9 earthquake. The largest earthquake on record registered an 9.5 on the currently used Richter Scale.

The Richter Scale

ConclusionEarthquakes are mainly formed by the

movements of the earth's plates. They occur all the time but not all of them

result in major destruction or fatalitiesSeismographs measure earthquakes