Transcript Ch. 19 - Earthquakes

Ch. 19 - Earthquakes
Earthquakes
are caused by gigantic fractures in the
Earth’s crust, which produce ground vibrations.

Video – Intro.
The
pressure (force/area) acting on the rocks involved
forms fractures when this stress exceeds the strength of
the rocks.
The deformation of materials in response to stress is
called strain.

3 Types  compression, tension, and shear.
1.
Compression occurs with a decrease in volume of
the material.
2. Tension occurs when the material pulls apart.
3. Shear occurs when the material twists.

Fig. 19-1 (pg. 496)
– movement of the Earth’s crust causing a
fracture or system of fractures.
 3 Types of Faults
 Fault



1. Reverse fault – occurs when land compresses
together horizontally
2. Normal fault – occurs when land separates from
one another horizontally.
3. Strike-slip fault – occurs when land slides left and
right of one another horizontally.
 Earthquakes
are caused by movements along
faults. As stress continues to build in these
rocks, they reach their elastic limit, break, and
produce an earthquake.

Video – Earthquake & Volcanoes
Types of Seismic Waves
 Seismic
waves are vibrations of the ground
during an earthquake.
 1. Primary waves (P waves) – rocks are
squeezed and pulled in the same direction in
which the waves are traveling.
 2. Secondary waves (S waves) – rocks move at
right angles in relation to the direction of the
waves.
 3. Surface waves move in two directions as
they pass through rock. Similar to an ocean
wave.

The point were an earthquake originates is the focus.

The focus is usually several kilometers below the Earth’s
surface.

The epicenter is the point directly above the focus at
the Earth’s surface.
 What is the study of earthquake waves?



Seismology
Seismic waves provide us with information to understand the
Earth’s interior.
What are seismometers or seismographs?



Instruments used to detect and record vibrations sent out
from earthquakes. They can shake the entire Earth.
The frame vibrates with the movement of the ground.
Video – Earthquakes & Plates
 The
seismogram is the paper portion of the
seismograph that records the vibrations

Fig. 19-8
A
travel-time graph displays the distance and
time it takes for p-waves and s-waves to travel.

Fig. 19-9
P
& S-waves travel through the crust and
mantle. Only the P-wave travels through the
outer and inner core of the Earth’s interior.

Fig. 19-10
 The
disappearance of S-waves allows scientists
to theorize that the Earth’s outer core must be a
liquid.
 Studies
of seismic waves shows that the
lithosphere (crust & upper mantle) is primarily
igneous rocks granite, basalt, (crust) and
peridotite (liquid – mantle).
 The Earth’s core and mantle are made up
similar components to that of a meteorite – iron
and nickel. Scientists study meteorites to
indirectly study the Earth’s core and mantle.
Measuring & Locating Earthquakes
 Approximately
1 million earthquakes occur
annually.

Little if any cause damage and are not felt.
 Magnitude
is the amount of energy released
during an earthquake. The magnitude is rated
on a scale called the Richter scale based on the
size of the largest seismic wave generated by
the quake.

A
1-10
magnitude of 8 is ten times larger than 7 and
100 times larger than 6.
 Moment
magnitude scale is rated on the size of
the fault rupture, the amount of movement
along the fault, and the rocks’ stiffness


Most seismologist use this scale.
The values are estimated from several seismic
waves rather than the largest generated.
 Modified
Mercalli scale rates the earthquake
based on the amount of damage done to the
structures involved. It uses Roman numerals I
to XII.

Table 19-1 – pg. 507
– page 508
 Video – earthquake simulation
 MiniLab
 Locating

an earthquake
Locations of several seismic stations (at least 3) are
used by plotting the radius or epicentral, which is
the distance away from the station which detects
the greatest seismic intensity with calculations. The
time it takes for the seismic waves to get to the
station can be used to calculate this also.
• Fig 19-14
 Seismic
belts are the global distribution of these
epicenters. Most of the seismic belts are
narrow regions.

Fig. 19-15 (pg. 510)
 Are
there any trend or patterns on the map?
Earthquakes & Society





Most of the damage produced by an earthquake is to
buildings and deaths may occur because of it. Brick,
stone, and concrete buildings damage easily
compared to wooden buildings.
Some buildings even rest on large rubber structures
that absorb most of the vibrations.
Pancaking – lower or ground floors of a building
collapse causing the upper levels to fall.
Structural failure – upper floors of a high building fail
causing the lower levels to collapse.
Soil Liquefaction – houses fall over due to the sinking
of the ground.

Tsunami – large ocean waves generated by vertical
motions of the seafloor during an earthquake.


The Indian Ocean tsunami of December 26, 2004 with a 9.0
magnitude.
The death toll exceeded 225,000.

Most of the earthquakes that are predicted are based
on probability from the history of earthquakes in an
area and the rate at which strain builds up in the
rocks.
 Seismic gaps are active faults that haven’t experience
significant earthquakes for a long period of time.

Lasers  Fig. 19-20
Video – earthquake danger
 Video – earthquake force
