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What are earthquakes?
- Vibrations of earth.
- An earthquake is the shaking or trembling of the ground that happens when rock under Earth's surface moves or breaks.
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When does an earthquake occur?
When the rigid materials of the lithosphere is strained beyond their limit, yield, and spring back to their orignial shape.
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What does an EQ release rapidly?
Stored energy
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Focus
The source of the released energy
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The technological tool used for seismology?
Seismograph instrument
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Where are seismograph's located and what are they used for?
Throughout the world. They amplify and record the ground motions produced by passing seismic waves.
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What kind of waves does a seismograph record?
Seismsmic waves
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Seismic waves
the internal movements generate waves that travel through Earth's interior and across Earth's surface
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The major layers of Earth consists of:
- Crust
- Mantle
- Outercore
- Inner core
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A wave's speed depends on ..____.
The medium through which it travels.
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Seismographs record on ________.
Seismograms
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Seismograms are then used to determine:
- -time of occurance
- -location
- -to define internal structure of Earth
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What are the 3 basic types of seismic waves
P waves, S waves, and surface waves
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Which types of waves travel thru Earth?
P and S waves while surface waves only travel along the outer layer.
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Which of the three waves has the greates velocity and therefore arrives at the seismograph station first?
P waves
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Which arrive last to the seismograph station?
Surface waves
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Which wave has the shortest AMP and shortest PERIODs?
P waves have smaller amplitude and periods that S and surface waves
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EQ foci have been recorded to depths as great as
from a few miles to 680 km
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Epicenter
The point on Earth's surface directly above the focus
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What makes it possible for locating the epicenter of an earthquake?
The difference in velocites of P and S waves. Both P and S waves leave the EQ focus at the same instant. The greater the difference in arrival time of the first waves compared to the first S wave.
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Seismic waves are made up of:
released energy
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Which type of waves are the last to register?
Surface waves
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Prediction of waves
- Earthquakes and fault movement occur with little or no warning and are thus very difficult to predict.
- Sometimes their is a foreschock, most def. an afterschock, which both have less magnitude than EQ
- No formal method exists (short term).
- Some animals "unofficially" give short term warning.
- Earthquakes are repitative
- Based on past occurances in the target area.
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H.F. Reid
- (Early 1990s)During the previous generation European scientists had begun to wonder
- if faults were related to earthquakes, and vice-versa, but it was Harry
- Fielding Reid who established that there was a clear and dynamic
- relationship
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Which type of wave?
Low speed
Complex motion
Surface waves
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Which type of wave?
Compression waves
Can go thru solids, liquids, and gases
P wave (body wave)
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Which type of wave?
Shaking motion
Only goes thru solids
S waves
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Rupture zone
The focus where EQ's originate
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How is the epicenter located?
- Using data from 3 different reporting stations
- Method: calculate difference between P+S arrival times.
- Find the point of intersection
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Times of the EQ tie directly with
distance
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What does the intensity of an EQ mean?
- The degree of shaking based on amount of damage (subjective)
- NOT MAGNITUDE
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Modified Mercalli Scale
Scale for measuring intensity of an EQ
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Magnitude (Charles Richter 1935)
- Based on the largest amplitude of largest wave
- e/a unit is roufly equivalent to 32 fold increase in energy
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Process of denser objects sinking
Differiantation
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What factors affect destruction?
- Intensity
- Duration
- Nature of foundation
- Design of structures
- Liquification of soild (saturated material turns fluid, underground objects will float to surface).
- Tsunami from EQs
- Landslides
- Ground subsidence (sinking)
- Fires
- Damage to nuclear power plants
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What magnitude is considered an intense EQ?
- 5 magnitue or higher.
- Remember, 32 fold increase for each level
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Earthquakes are used as tool for?
Viewing layers of Earth. (Crust, matnle, core)
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Moment magnute scale
Most accurate way to measure magnitude of EQ
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Earthquakes are strongly associated with
Movements along faults
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Faults provide evidence of the _____ theory.
Plate tectonic theory
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As energy travels to Earth's surface, the ground _________.
Shakes and moves, e.i. EARTHQUAKEs
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Most earthquakes are related to Earth's tectonic movement.
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What produces strain the rocks?
Interaction at plate boundries creates stress.
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Fault
A fracture along which visible displacement of one side relative to the other can be detected.
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Convergent plate boundry
A plate boundry where tectonic plates move toward one another: an aear of compressive stress where lithosphere is recycled into the mantle, or shortened by folding and faulting.
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Transfrom plate boundry
A plate boundry where two plates are sliding HHorizontally past each other, without appriciable verticle movement.
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Divergent plate boundry
A plate boundry where lithospheric plates move away from one another-- a spreading center; an area of tensional stress where new lithospheric crust is formed.
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What happens with continued stress at rocks at depth?
They begin to store up elastic energy
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When does a fault form?
When the buidlup stress (at depth) exceeds the rock's elastic limit, the rock suddenly breaks and slips into a new position--a fault forms.
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Faults have a certain amount of strenght to resist ____.
- Slipage.
- Fault surfaces are not smooth; rocks on opposite sides of the fault become interlocked.
When the strengh of the fault is exceeded, it breaks suddenly.
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After sudden rupturing and releasing of energy, rocks on both sides of the fault rebound to ____.
- Their original shapes.
- This snapping back into shape is an earthquake.
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What happens to the epicenter as the cause of an EQ?
strain often occurs, seen as brittle deformation of the crust.
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How come Earthquakes do'nt always occur at plate boundires? (even though most earthquakes occur at plate boundires)
- Earth is very old and plate boundries can change over geological time.
- Faults and EQs can also be found on interplates----areas that were once closer to plate boundries.
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Interplate areas are ____.
Zones of weakness
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How does subduction affect volcanic acitivity?
Subduction occurs around the Pacific ocean, and around the pacific ocean is the "Ring of Fire"
- Subduction is related to volcanic activity.
- What is subduction and why does this mean an increase in volcanic activity.
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Degree of the earthquake if it occurs at a divergent plate boundry.
- Mild and shallow
- A plate boundry where lithospheric plates move away from one another-- a
- spreading center; an area of tensional stress where new lithospheric
- crust is formed.
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Degree of EQ if it occurs at transform plate boundary.
- MILD TO moderate
- A plate boundry where two plates are sliding HHorizontally past each
- other, without appriciable verticle movement.
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Degree of EQ if it occurs at convergent plate boundary:
- Moderate to very strong.
- A plate boundry where tectonic plates move toward one another: an aear
- of compressive stress where lithosphere is recycled into the mantle, or
- shortened by folding and faulting.
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Devestating earthquakes can occur with what kind of faults?
All three types: reverse, normal, and strike-slip
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The more castroptropic/severe EQ have occured along what kind of fault and why?
REVERSE FAULTS (usually those at subduction zones)
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Types of surface waves
Rayleigh and Love waves
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