Molly Zurheide

1
(No Transcript)
2
Molly Zurheide The Basin, NH
3
Marc Massie Saas Fee Switzerland
4
Olivia Sher Amazon River
5
EFFECTS OF EARTHQUAKES
SEICHES (pronounced sayshes)
Seismic waves cause water in an enclosed
basin to oscillate. Can occur miles from
the focus or epicenter of the earthquake.
6
EFFECTS OF EARTHQUAKES
TSUNAMI
Translated from Japanese means harbor wave. Not
a tidal wave. TSUNAMI is a very long
wavelength, high-speed ocean wave, produced by
earthquakes. Wavelength can be up to 160
km. Velocities reach 800 km/hr (500
mph). Generally imperceptible at sea, crest only
1 m high. Water bunches up when the wave feels
bottom. Wave height can reach 65 m (210).
7
EFFECTS OF EARTHQUAKES
TSUNAMI
Produced by large, rapid displacement of sea
floor due to submarine faulting. Can also be
produced by submarine landslides.
Tsunami hitting Hawaii following an earthquake in
Alaska in 1946
8
EFFECTS OF EARTHQUAKES
TSUNAMI
1964 Anchorage Earthquake
9
EFFECTS OF EARTHQUAKES
FIRE
Fire is not directly a result of earthquakes, but
fire certainly accompanies earthquakes in
industrialized setting. Earthquakes rupture gas
mains, oil tanks and power lines. They also
break water mains which makes fire
fighting difficult.
10
EFFECTS OF EARTHQUAKES
FIRE
1906 San Francisco Earthquake
11
(No Transcript)
12
(No Transcript)
13
EFFECTS OF EARTHQUAKES
Anchorage, AK
FIRE
Kobe, Japan
14
PRINCIPAL EARTHQUAKE ZONES
15
PRINCIPAL EARTHQUAKE ZONES
Most earthquakes happen at plate boundaries.
Divergent Boundaries
Have shallow focus and low magnitude.
16
PRINCIPAL EARTHQUAKE ZONES
Transform Boundaries
Have shallow focus and high magnitude.
17
PRINCIPAL EARTHQUAKE ZONES
Convergent Boundaries
Have deep focus and high magnitude. Deeper focus
due to subduction (depths up to 700 km).
18
PRINCIPAL EARTHQUAKE ZONES
Benioff-Wadati Zone
19
PRINCIPAL EARTHQUAKE ZONES
Intraplate Earthquakes
Generally have shallow focus and low
magnitude. Lower strain due to location away from
plate margins. However... Intraplate rocks are
older and colder and more brittle. Less fractured
at mid-continent. Thus they transmit seismic
waves more efficiently.
20
PRINCIPAL EARTHQUAKE ZONES
Intraplate Earthquakes
New Madrid, MO Largest recorded earthquake in
North America. Occurred in 1811, lasted 53
DAYS! Three main quakes had magnitudes of
8.5! 1500 aftershocks. Moved position of
Mississippi River Rang church bells in BOSTON!
21
PRINCIPAL EARTHQUAKE ZONES
Intraplate Earthquakes
New Madrid, MO
22
PRINCIPAL EARTHQUAKE ZONES
Intraplate Earthquakes
New Madrid, MO (1811) vs. San Francisco, CA (1906)
23
OTHER EARTHQUAKE FEATURES
SEISMIC GAP
Parts of faults stick. Friction prevents
movement in that part of the fault. Force is
applies, rocks are stressed. When friction is
overcome, fault movement occurs. Areas where
major earthquakes could occur.
24
SEISMIC GAP
25
OTHER EARTHQUAKE FEATURES
TECTONIC CREEP
Fault has continuous movement over time. Allows
stress to be released without building up.
26
TECTONIC CREEP
Hayward Fault, CA
27
A COMPARISON
A joule is a measure of stored energy, similar
to calories.
28
What do we know about the interior of the Earth?
Most comes from interpretation of SEISMIC
WAVES. Generally waves travel in a straight line
and at an unchanging velocity when passing
through a homogeneous medium at constant
temperature and pressure. Seismic waves speed up
and slow down. Indicates variation in conducting
medium. Allowed interpretation of the Earths
interior.
29
PRIMARY OR P-WAVES
P-waves travel through solid, liquid, and
gas. Travel fastest through solid. Velocity
varies with medium. Shadow zones exist
because of this. Due to refraction of p-waves
through different media (i.e., the Earths
three layers, crust, mantle and core)
30
SECONDARY OR S-WAVES
S-waves do not go through liquid. In early
investigations it was noted that p-waves
always arrived at the seismograph
station, but sometimes S-waves
didnt. Produced a larger shadow zone than
for p-waves.
31
(No Transcript)
32
Seismic waves allow us to view the interior of
the Earth. Indicates that crust is thinner
under ocean basins than under continents. Change
in P-wave velocity indicates a change in
composition between crust and mantle. Boundary
is called the MOHOROVICIC DISCONTINUITY or MOHO.
33
(No Transcript)
34
P-waves go through the upper mantle faster than
those that go through the crust. Velocity also
slows down as they go through the
aesthenosphere. Produces Low Velocity Zone.
P-waves also determined that there was a
boundary between the mantle and the core.
35
S-waves helped to determine that the outer
core was liquid. Observed through the shadow
zone for S-waves.
36
ISOSTASY
Lithosphere floats on the underlying denser,
heat- softened, partially melted
aesthenosphere. Areas with greater mass sink
deeper into the aesthenosphere. Equilibrium
between lithospheric segments (plates) and
aesthenosphere beneath them is called ISOSTASY.
37
ISOSTASY
Water
38
ISOSTASY
39
ISOSTASY
Lithosphere, because of its lower density
floats or sinks to find its own isostatic
equilibrium. Continental lithosphere is less
dense so a larger proportion of it floats
above the aesthenosphere. Changes in mass cause
it to rise and fall. Similar to a boat unloading
or loading cargo. Removal of mass causes it to
rise. Addition of mass causes it to sink. Rise
after removal of mass is called
ISOSTATIC REBOUND.
40
ISOSTASY
41
EARTHS MAGNETIC FIELD
Penetrates and surrounds the Earth. Extends into
space approximately 60,000 km.
42
EARTHS MAGNETIC FIELD
Obvious cause would be the Earths iron
core. But, the core is too hot to be a permanent
magnet. However, magnetic fields such as those
that surround the Earth can be produced by an
electrical current. So, we think of the Earth now
as a giant electromagnet. The electrical field is
produced by the movement of electrons through
the molten iron of the liquid outer core.
43
EARTHS MAGNETIC FIELD
The rotation of the Earth sets the liquid in
motion. Moving currents generate the magnetic
field. This, then, generates more electrical
currents. Produces a SELF-EXCITING DYNAMO.
44
MAGNETIC REVERSALS
Magnetic pole moves around all the time, but in
general it is in close proximity to the
geographic pole. Earths magnetic field reverses
occasionally. Magnetic north and south poles
switch position. Happens every 500,000
years. We think it takes 1000 to 5000 years to
switch, but evidences suggest it can be only
100. How do we know..
45
MAGNETIC REVERSALS
46
MAGNETIC REVERSALS
Normal is when magnetic pole is in the northern
hemisphere. Reversed is when magnetic pole is in
the southern hemisphere.