Download Earthquakes

Earthquakes
Types of Stress
• Stress: a force that acts on rock to change its shape or volume.
– Because stress is a force, it adds energy to the rock. The energy is stored in
the rock until the rock changes shape or breaks.
– Most changes in the crust occur so slowly that they cannot be observed
directly. But if you could speed up time so a billion years passed by in
minutes, you could see the crust bend, stretch, break, tilt, fold, and slide.
• Tension: pulls on the crust, stretching rock so that it becomes thinner in
the middle.
– Occurs when two plates are moving apart (divergent boundary), but can also
happen inside a plate, such as the Great Basin (Basin and Range region) in
Nevada and Utah’s western boarder.
• Compression: squeezes rock until it folds or breaks.
– Occurs when two plates are moving together (example Himalayas, convergent
boundary) and during folding and faulting inside the plates.
• Shearing: stress that pushes a moss of rock in two opposite directions.
– Occurs when two plates are moving pass each other in opposite directions
(transform boundary). Also can happen during faulting and folding in a
smaller size scale.
Types of Stress
Earthquake features
• Hang and foot wall
– The blocks of rock involved in faults
– Hanging wall: touch you head on
– Foot Wall: walk on
Earthquake features Continues
• Fault Scarp
– When the energy build up enough the fault will
cause a break in the Earth’s crust, and a fault scarp
can occur.
Type of Earthquakes
• Most faults occur along plate boundaries, where the forces of plate
motion push or pull the crust so much that the crust breaks.
• Normal fault:
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tension in Earth’s crust pulls rock apart
Happens at an angle
Footwall moves up while the hanging wall moves down
Example: Wasatch Front, Yes where you live!
• Reverse fault
– Compression pushes rock together
– Footwall moves down while the hanging wall moves up
– Example: northern Rocky mountains in the western United states and Canada.
• Strike-Slip fault
– Rocks on either side of the fault slip past each other sideways, with little up or
down motion.
– Shear stress
– Right lateral and left lateral
– Example: San Andreas fault in California
Types of Faults
Changing Earth’s Surface
• Folding of Earth’s Crust
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Folds are caused by compression, which cause rocks to bend without breaking
Anticline: when the rock folds upward into an arch
Syncline: when the rock folds downward to form a valley
Examples of folds:
• Appalachian Mountains in Pennsylvania are folded mountains made up of parallel
ridges(anticlines) and valleys (synclines)
• Himalayas in Asia and Alps in Europe: formed when pieces of the crust folded during the
collision of two plates.
• Stretching Earth’s Crust
– Fault-block mountain forms when two normal faults cut through a block of
rock.
– Happens when tension forces pull two plates apart creating many normal
faults. When two of these normal faults parallel each other, a block of rock is
left lying between them.
– Example: Great Basin
• Uplifting Earth’s Crust
– Force the raise mountains can also uplift plateau
• Plateau: is a large are of flat land elevated high above sea level. Has many different flat
layers and is wider than it is tall.
• Example: Colorado Plateau
Types of folds
Question
• What conditions would allow older
sedimentary rock to lie in layers above
younger sedimentary rock?
– A. rocks that formed in desert environments
– B. places where fossils were located
– C. areas that were underwater for long periods of
time
– D. areas of faulting and folding
• Which location shows older rocks above
younger rocks?
– A.
– B.
– C.
– D.
A
B
C
D
A
C
B
D
• Based on the diagram, what force most likely
created the changes to the bottom three layers?
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A.
B.
C.
D.
compression causing folding
compression causing stretching
tension causing faulting
tension causing waving
A
C
B
D
General information about
Earthquakes
• Earthquakes: shaking and trembling that results
from the movement of rock beneath Earth’s
surface.
• Being in the lithosphere within about 100
kilometers of the Earth’s surface
• Focus: is the area beneath Earth’s surface where
rock that is under stress breaks, triggering an
earthquake. This is the point in which the stored
energy is released in the form of waves.
• Epicenter: the point on the surface directly above
the focus
Focus and Epicenter
Types of Seismic waves
• Types:
– Primary: P waves
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First waves to be felt
Faster than the S waves
Compress and expand the ground
Move through solids and liquids
– Secondary: S waves
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Second waves to be felt
Slower than the P waves
Vibrate from side to side as well as up and down
Can only move through solids
– Surface wave
• A surface wave is a seismic wave that is trapped near the surface of the earth.
• Two types
– Rayleigh waves: is a seismic surface wave causing the ground to shake in an elliptical
motion, with no transverse, or perpendicular, motion.
– Love wave: is a surface wave having a horizontal motion that is transverse (or
perpendicular) to the direction the wave is traveling.
Type of Seismic Waves
Recording Earthquakes-Energy
• Geologist use a seismograph to record energy released
by an earthquake onto a seismogram.
• From this data scientist can see when the P and S
waves arrived, which they then use to pin point where
the earthquake started in a process know as
triangulation.
– Triangulation requires three different location in which the
earthquake was felt.
– Also requires the difference in time between the P and S
wave arrive. Remember the P wave is the fastest of the
two.
• Greater the difference in time the further the epicenter is and the
shorter the difference of time the closer the epicenter is.
Seismogram
Triangulation
Measuring Earthquakes
•
Mercalli Earthquake Intensity Scale
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Developed to measure the level of damage at a give place
12 steps
Richter Magnitude Scale
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Is a rating of an earthquake’s magnitude based on the size of the
earthquake’s seismic waves.
Waves are measured by a seismograph
Works well for nearby earthquakes, but not as well for large or distant
earthquakes
• The Moment Magnitude Scale
– A rating system that estimates the total energy released by an earthquake
– Often used today because it can measure far and near earthquakes
– Most the time the new will quote the Richter scale, but most the time it is
actually the Monument Magnitude Scale they are reading.
– Helps to determine how much movement was along the fault and the strength
of the rocks that broke when the fault slipped.
Earthquake map
http://earthquake.usgs.gov/
earthquakes/recenteqsus/
Maps/US2/40.42.-113.111.php