2. How Does an Earthquake Work?
 An earthquake is a vibration that travels through the
3. Causes of Earthquakes
All kinds of things can cause earthquakes:
movements of the earth's plates
underground explosions (an underground nuclear
test, for example)
collapsing structures (such as a collapsing mine)
4. Steps to an Earthquake
 An Earthquake occurs about once every 11 seconds.
 There have been more than 1.5 million earthquake-
related fatalities in the last hundred years.
6. Plate Tectonics
 Seismology - 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.
 At 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
 transform boundaries (Plates slide against each
 Faults are formed where these plates meet
 Faults 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
9. Seismic Waves
 When 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
 A seismograph is a machine that registers the different
11. The Richter Scale
The 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.
12. The Richter Scale
 Earthquakes 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 fatalities
 Seismographs measure earthquakes