Download Earthquakes! - Westerville City Schools

Earthquakes!
Earth is never still!

Every year there are 500,000 detectable
earthquakes

100,000 of them can be felt

Only 100 cause damage
http://earthquake.usgs.gov/eqcenter/recenteqsww/
Ohio Earthquake Facts

Last earthquake
occurred January
26, 2008

Magnitude 1.8

Largest quake
occurred March 9,
1937

Magnitude 5.4
Causes of Earthquakes
 All
rocks have an elastic limit.
 If
the forces acting on these rocks exceed
this limit or overcome friction between
blocks, the crust snaps and an earthquake
occurs.
 This
phenomenon is known as the elastic
rebound theory.
Causes of Earthquakes
 The
most common cause of earthquakes is
faulting.
Causes of Earthquakes
 As
rocks slide past one another large
amounts of energy that has been built up
over time is finally released, causing an
earthquake.
 The
point inside the Earth where rock first
breaks or moves in called the focus of the
earthquake.
Classifying Earthquakes

Shallow focus earthquakes originate
between the Earth’s surface at a depth
of 70 km.

Intermediate focus earthquakes
originate between 70-300 km.

Deep focus earthquakes originate
between 300-700 km.
Classifying Earthquakes
Seismic Waves

When an earthquake occurs, energy
moves away from the focus in the forms
of waves called seismic waves.
Seismic Waves

Primary (P) waves are the fastest
seismic waves.

They compress and expand like a
slinky.

P waves can travel through solid and
liquid rock.
Seismic Waves

Secondary (S) waves are the second
fastest seismic wave.

They vibrate up and down and side to
side.

S waves can only travel through solid
rock.
Seismic Waves

Surface (L)
waves are the
slowest seismic
waves.

L waves travel in
a rolling motion
along the
surface of the
Earth.
Studying Earthquakes

Scientists use sensitive instruments
called seismographs to measure and
record seismic waves.

The seismograph’s record of waves is
called a seismogram.

A scientist who studies earthquakes is
called a seismologist.
Studying Earthquakes
Studying Earthquakes

The epicenter is
the place on the
surface of the
Earth directly
above the focus
of the
earthquake.
Studying Earthquakes

Lag time is
the difference
between the
arrival of the P
and S waves.
Studying Earthquakes

Seismologists
need to take
readings form
3 stations in
order to locate
the epicenter
of an
earthquake.
Studying Earthquakes
1000 km
500 km
epicenter
400 km
Studying Earthquakes

The magnitude of an earthquake is
the total amount of energy released.
Studying Earthquakes

The Richter scale is a logarithmic scale used
to determine the strength of an earthquake
(1-10) based on the energy that is released.

Humans cannot feel any earthquake activity lower
than a 3.

Those that measure 6 or more are considered
major earthquakes.

The strongest earthquake recorded occurred in
Chile in 1960 and had a magnitude 9.5.
Studying Earthquakes
Studying Earthquakes

The Mercalli scale is a method of
describing describing the strength of an
earthquake in terms of damage that is
done to surrounding structures.

The measure of damage done by an
earthquake is called intensity.
Earthquake Damage

The effect of an earthquake in a given region
depends greatly on the local surface and
underground geologic conditions.
1985 Mexico City earthquake
Earthquake Damage

Loss of human life during earthquakes
is usually attributed to falling buildings
and fires.
1994 Northridge earthquake
Earthquake Damage
1906 San Francisco earthquake
Earthquake Damage
1994 Northridge earthquake
Earthquake Damage

Earthquakes also occur on the floor of
the ocean, which often produce
displacement of water called tsunami.

Tsunami can travel at speeds up to
700-800 km per hour and can reach
heights of up to 20 meters - that is the
height of a 6 story building!
Earthquake Damage
Earthquake Damage
2004 Indonesian tsunami
Earthquake Damage
2004 Indonesian Tsunami