Transcript Earth`s Dynamic Crust and Interior: small scale crustal changes

Earth’s Dynamic Crust and Interior:
small scale crustal changes
 Movements of the crust is based on the concept of
original horizontality. This concept assumes that
sedimentary rocks and some extrusive igneous rocks, form
in horizontal layers parallel to the Earth’s surface.
 Rock layers that no longer show their original
horizontality are called deformed layers. Some are folded,
tilted and faulted.
 Folded rock layers are bent or curved.
 Faulted rock layers are offset. (A fault is a crack in a
mass of rock along which there has been displacement or
movement.)
 Rocks can also be uplifted, meaning the land has been
raised.
Folding, Faulting, and Tilting
Earthquakes and Igneous Activity,
Including Volcanoes
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An earthquake is a natural rapid shaking of the
lithosphere caused by the release of energy stored in
rocks.
Most earthquakes are caused by the movement along
faults.
During an earthquake the potential energy stored in
rocks is given off as seismic waves.
The location within the Earth, in which the earthquake
originates is called the focus.
The location on Earth’s surface directly above the focus
is called the epicenter.
Earthquakes are recorded using a seismograph and
they produce a recording of “wiggles” called a
seismogram
Earthquake Waves
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There are three different types of seismic
waves:
1) P-waves: primary waves, cause particles
they travel through to vibrate in the direction
the waves are moving.
2) S-waves: secondary waves, cause
particles they travel through vibrate at right
angles to the direction the waves are moving.
3) Surface waves: produced when a pwave or s-wave comes to Earth’s surface.
These waves cause much of the surface shaking
and damage of an earthquake.
Properties of Earthquake Waves
In any one material, P-waves travel the fastest.
 The velocity of the seismic waves is dependent
upon the material they travel through.
Generally, the more dense a material, the
faster the velocity will be. Waves will become
bent if they travel through different material
with different densities.
 P-waves pass through solids, liquids and gases.
S-waves will only pass through solids.
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Location of an Epicenter
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Epicenters are located by using the velocity differences between
the P-waves and S-waves.
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Since P-waves move faster than S-waves, the farther an observer is
from an epicenter, the larger the time interval between the arrival of
the P and S waves.
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To find the position of the epicenter, at least three seismograph
stations must be used. For each of the three locations, the epicenter
distance is then used as a radius and circles are drawn on a map.
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The place where all three
circles intersect is the
epicenter of the earthquake.
Finding the Origin Time of Earthquakes
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In the ESRT (earth science reference tables), use the Earthquake Pwave and S-wave Travel Time on page 11.
Examples:
1)If the S-wave first arrived at a
station at 10 hr: 12 min: 30 sec,
and the seismograph is 5500
km away from the epicenter,
when did the earthquake
occur?
9 hr: 56 min: 30 sec
2)What is the time interval
between the P and S wave if
the epicenter is 3000 km away?
4 min: 20 sec
Magnitude of the Earthquake
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Scientists often use an earthquake magnitude scale to measure the
strength of the quake. Magnitude scales use the height of the
“wiggles” produced on the seismogram.
The lowest value of magnitude is less than 1 and the highest value is
about 9.5
Tsunamis
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If there are strong earthquakes on the ocean floor
they can produce a seismic sea wave called a Tsunami
(Japanese word for “wave in the harbor”)
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The disruption creating the earthquake can be caused
by the faulting, a volcanic eruption or a rapid landslide.
Igneous Activity and Volcanoes
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When magma reaches the surface it is called lava. If the
lava forms a significant mound with a slope of at least a
few degrees, the mass is called a volcano.
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A volcano is composed of extrusive igneous rocks.
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A volcanic eruption is the giving off of gases, lava, and/or
lava rock onto the Earth’s surface and into the
atmosphere through the opening of a vent of a volcano.
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Major areas of uplift, sinking, earthquakes, and volcanic
eruptions are often found together.
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The “Ring of Fire” (region surrounding the Pacific Ocean)
is where the majority of these related events occur
Ring Of Fire