(5 12 09) How Earthquakes WorkPresentation Transcript
How Does an Earthquake Work?
An earthquake is a vibration that travels through the
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)
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.
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
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
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.
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