Title: EARTHQUAKES Chapter 12
1EARTHQUAKESChapter 12
- Section 1
- How and Why Earthquakes Happen
- Pages 295-300
2REVIEW
- LITHOSPHERE is the
- the ROCKY outer layer of Earth including
- the CRUST the rocky outer part of
- the MANTLE
- UNDER the lithosphere is the weak sphere, the
putty-like plastic layer called the - ASTHENOSPHERE
3NEED to KNOW from chapter 11
- Lithosphere moves up and down depending on the
balance of pressure between what is above,
either ________ crust or ______ crust - CONTINENTAL
OCEANIC - and what is below
- the
ASTHENOSPHERE
4LITHOSPHERE MOVEMENT
- Since the polar icecaps are melting due to golabl
climate change, the ocean levels are rising
making the ocean (lighter or heavier), so the
lithosphere under the ocean will _____ -
SINK - Since the polar icecaps are melting, the ice on
the land is decreasing making land (lighter or
heavier), so the lithosphere under the land will
______ -
RISE
5CAUSES of STRESS
- As the lithosphere moves in this way, or as it
moves as a result of tectonic plate movement it
puts STRESS on rocks. - STRESS is a result of
- FORCE exerted on rock.
- STRESS is
- the AMOUNT of FORCE exerted
- on an area of rock.
6CAUSES of STRESS
- The types of tectonic plate movement that cause
stress are - 1) CONVERGENCE which causes
- COMPRESSION stress
- 2) DIVERGENCE which causes
- TENSION stress
- 3) GRINDING/TRANSFORM which causes
- SHEAR stress
7RESULT of STRESS
- Sometimes stress cause rock to DEFORM
- DEFORMATION is when the crust
- bends, tilts, or breaks
- ch 11 deform.html
8RESULT of STRESS
- Sometimes stress cause rock to FOLD.
- (Read about FOLDS in chapter 11 and take notes
for extra credit.)
9RESULT of STRESS
- Sometimes stress causes rock to BREAK.
- There are 2 kinds of breaks
- Rock breaks ? broken pieces do NOT move
- called a FRACTURE
- 2) Rock breaks ? broken pieces DO MOVE
- called a FAULT
10FAULTS
- The BIGGEST type of FAULT that we already studied
are the CRACKS BETWEEN - TECTONIC PLATES which are called
- BOUNDARIES
- There are 3 types of boundaries
- CONVERGENT
- DIVERGENT
- TRANSFORM
11Chapter 12 EARTHQUAKES
- An EARTHQUAKE is
- MOVEMENTS OF THE GROUND CAUSED BY SUDDEN RELEASE
OF ENERGY WHEN ROCKS ALONG A FAULT MOVE. - And a FAULT is
- a CRACK between moving rocks!
12WHY earthquakes do NOT happen
- If the rocks along a fault are LOCKED then
earthquakes do NOT happen! - A fault is LOCKED when
- the ROCKS are PREVENTED from MOVING by
- FRICTION
13WHY earthquakes DO happen
- If the rocks along a fault build up enough stress
they suddenly grind past each other. - This sudden grinding slip is an earthquake.
- "The ground seemed to twist under us like a top
while it jerked this way and that, and up and
down and every way," wrote a person describing
the experience of being in the large 1906
earthquake in San Francisco, CA.
14WHY earthquakes DO happen
- The expression on solid ground is often used to
describe something as stable. Usually the solid
ground underfoot seems very stable. But sometimes
it is not. - EARTHQUAKES are defined as
- MOVEMENTS OF THE GROUND THAT ARE CAUSED BY A
SUDDEN RELEASE OF ENERGY WHEN ROCKS ALONG A FAULT
MOVE.
15WHY earthquakes DO happen
- Geologists think earthquakes are a result of the
rock which has been deformed by stress suddenly
being able to return to its UNdeformed shape. - This springing back to previous shape is called
- ELASTIC REBOUND
16ANATOMY of an EARTHQUAKE
- The location within the Earth along a fault where
the first motion of an earthquake begins is
called the - FOCUS or the HYPOCENTER
- In addition to PAY ATTENTION CONCENTRATE, FOCUS
means THE CENTRAL POINT, as in The FOCUS of
this lesson is earthquakes. - HYPO means BELOW, so the hypocenter is the below
ground center of the earthquake.
17ANATOMY of an EARTHQUAKE
- The point directly ABOVE the FOCUS, on the
surface of the Earth, is called the - EPICENTER
- EPI means OVER or UPON
- (Your EPIdermis is the top layer of your
dermis/skin) - So the EPIcenter is the point OVER the FOCUS of
an earthquake thats UPON the Earths surface
18This diagram shows an earthquake along a fault.
The focus of the earthquake is where the energy
is released underground. The epicenter is the
spot on the Earths surface directly above the
focus.
19ANATOMY of an EARTHQUAKE
- The FOCUS of an earthquake can be
- SHALLOW, INTERMEDIATE, or DEEP
- Which one causes the most damage?
- SHALLOW
- Why?
- The energy of deeper earthquakes is spread out or
dissipated as it moves to the surface. - The energy of a surface earthquake does not
spread out or get used up moving TO the surface.
- Its already HERE where we and our houses are!
20The ENERGY from EARTHQUAKES
- As rocks along a fault slip, they release energy
in the form of vibrations called - SEISMIC WAVES
- These waves ripple outward through the Earth from
the focal point in a _________ pattern -
CIRCULAR - as when you drop a stone in a pool.
21This diagram shows an earthquake along a fault.
The focus of the earthquake is where the energy
is released underground. The epicenter is the
spot on the Earths surface directly above the
focus.
22SEISMIC WAVES
- There are 2 MAIN kinds of seismic waves
- and each type has 2 subtypes
- BODY waves include
- either P waves or S waves
- SURFACE waves include
- either LOVE waves or RALEIGH
waves
23- P waves
- BODY WAVES
- S waves
- LOVE waves
- SURFACE WAVES
- RALEIGH waves
24- P waves primary , fast
- BODY WAVES compression
waves - S waves secondary / shear
- second fastest
side to side
25(No Transcript)
26-
- LOVE waves slower but damaging
- SURFACE WAVES sideways rocking
motion - RALEIGH waves slower but damaging
- ellipitical rolling motion
27Love waves top / Raleigh waves bottom
28SEISMIC WAVES EARTHS INTERIOR
- The MORE DENSE the material they are passing
through the (slower or faster) seismic waves
move. - FASTER
- Can you run faster on concrete or on sand?
- CONCRETE is (more or less) dense than sand.
- MORE
- So, MORE DENSE FASTER
29SEISMIC WAVES EARTHS INTERIOR
- The waves that go THROUGH the CENTER of the Earth
are the two types of _________ waves. -
BODY - The 2 types of BODY waves are
- S waves P
waves
30SEISMIC WAVES EARTHS INTERIOR
- Can the BODY waves go through ALL the parts of
Earths interior? - NO
- They can NOT go through the
- LIQUID
__________ CORE -
OUTER
31SEISMIC WAVES EARTHS INTERIOR
- Since BODY waves can NOT go through the liquid
OUTER CORE there is a ______zone on the other
side of the Earth that does NOT feel the waves. - SHADOW
ZONE - YOUR shadow is a place where there is no _____
- LIGHT
- In the seismic shadow zone there are no _______
- SEISMIC WAVES
32Are faults always clean breaks?
- Faults (do or do not) usually consist of a
single, break. - do NOT
- So, we refer to the complex network of cracks as
- a FAULT ZONE
33What are tectonic plates doing to cause
earthquakes?
- -oceanic oceanic crust DIVERGE
- -oceanic oceanic crust CONVERGE
- -continental continental crust DIVERGE
- -continental continental crust CONVERGE
- -continental continental crust GRIND(transform)
34Are earthquakes always on plate boundaries?
- NO
- Big earthquakes occurred in Missouri (1811
1812). - Are the tectonic plates weve been studying
converging, diverging, or transforming in
Missouri? - NONE of these! So why the
earthquakes? - An ancient fault (600 million years old) is
buried beneath the rocks and sediment in
Missouri.
35ALWAYS on FAULTS?
- While it is not as common, there are also some
faults in the middle of plates. Movement along
those faults can cause earthquakes too. - For example, many strong earthquakes shook the
Mississippi River Valley between December 1811
and March 1812. - Although this area is in the middle of the North
American plate, there is a large fault. Its
called the New Madrid Fault and movement along it
caused the 1811-1812 earthquakes.
36Animation Where do earthquakes happen?
- http//www.windows.ucar.edu/tour/link/earth/geolo
gy/quake_2.html
37PREVIOUS EARTHQUAKES
- The animation shows where earthquakes happened
between 1960 and 1995. Each earthquake is shown
on the map as a yellow dot. Did you see a pattern
to where the dots are found? - Earthquakes do not happen at random locations.
They are not equally spaced. Some areas have many
earthquakes while other areas have few. - Since earthquakes happen along faults and most
faults are near plate boundaries, the yellow dots
in the animation are found mostly at the
boundaries between Earths tectonic plates.
38Where did earthquakes happen this week?
- http//earthquake.usgs.gov/eqcenter/recenteqsww/Ma
ps/region/N_America.php
39REVIEW EARTHQUAKES
- Earthquakes happen as large blocks of the Earths
crust move suddenly past one another because of
the force of plate tectonics. These blocks of the
Earths crust meet at cracks called faults.
Sometimes those pieces do not slide smoothly past
one another.
40REVIEW FAULTS
- There can be friction along the fault jagged
edges that snag the blocks of rock. This makes it
difficult for them to move past each other. - Sometimes they get stuck together temporarily.
41REVIEW FAULTS
- a FAULT or FAULT LINE is
- A BREAK IN A BODY OF ROCK ALONG WHICH THE ROCK ON
ONE SIDE CAN MOVE WITH RESPECT TO THE ROCK ON THE
OTHER SIDE. - A fault that runs along the boundary between two
tectonic plates is called a
transform fault.
42REVIEW EARTHQUAKES
- When the pieces of rock overcome the snags caused
by friction, energy is released. - The release of energy causes shaking at the
ground surface called an EARTHQUAKE.
43How Where Earthquakes Happen
- Each year, more than a million earthquakes occur
worldwide. Most of these are so small that people
do not feel the shaking. But some are large
enough that people feel them, and a few of those
are so large that they cause significant damage.
44REVIEW FOCUS EPICENTER
- The location inside the Earth where an earthquake
begins is called the focus. - The point at the Earths surface directly above
the focus is called the epicenter. - The strongest shaking happens at the epicenter.
45REVIEW EARTHQUAKES
- Earthquakes happen when rock below the Earths
surface moves abruptly. Usually, the rock is
moving along large cracks in Earths crust called
faults. Most earthquakes happen at or near the
boundaries between Earths tectonic plates
because thats where there is usually a large
concentration of faults. Some faults crack
through the Earth because of the stress and
strain of the moving plates. Other, large faults
are at the boundary between plates, such as the
San Andreas Fault on the North American west
coast.
46PREVIEW Section 3
- Earthquakes can cause damage to things like
buildings, bridges, and roads. Earthquakes can
cause landslides and mudslides, too. If a large
earthquake happens under the ocean it can cause a
tsunami a giant ocean wave or series of waves. - Scientists can figure out whether an earthquake
is likely to happen in a place by studying plate
tectonics, the faults underground, and the
history of the areas earthquakes. However,
unlike weather events, earthquakes can not be
forecast ahead of time.