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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.
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.
What does an EQ release rapidly?
The source of the released energy
The technological tool used for seismology?
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.
What kind of waves does a seismograph record?
the internal movements generate waves that travel through Earth's interior and across Earth's surface
The major layers of Earth consists of:
- Inner core
A wave's speed depends on ..____.
The medium through which it travels.
Seismographs record on ________.
Seismograms are then used to determine:
- -time of occurance
- -to define internal structure of Earth
What are the 3 basic types of seismic waves
P waves, S waves, and surface waves
Which types of waves travel thru Earth?
P and S waves while surface waves only travel along the outer layer.
Which of the three waves has the greates velocity and therefore arrives at the seismograph station first?
Which arrive last to the seismograph station?
Which wave has the shortest AMP and shortest PERIODs?
P waves have smaller amplitude and periods that S and surface waves
EQ foci have been recorded to depths as great as
from a few miles to 680 km
The point on Earth's surface directly above the focus
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.
Seismic waves are made up of:
Which type of waves are the last to register?
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.
- (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
Which type of wave?
Which type of wave?
Can go thru solids, liquids, and gases
P wave (body wave)
Which type of wave?
Only goes thru solids
The focus where EQ's originate
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
Times of the EQ tie directly with
What does the intensity of an EQ mean?
- The degree of shaking based on amount of damage (subjective)
- NOT MAGNITUDE
Modified Mercalli Scale
Scale for measuring intensity of an EQ
Magnitude (Charles Richter 1935)
- Based on the largest amplitude of largest wave
- e/a unit is roufly equivalent to 32 fold increase in energy
Process of denser objects sinking
What factors affect destruction?
- Nature of foundation
- Design of structures
- Liquification of soild (saturated material turns fluid, underground objects will float to surface).
- Tsunami from EQs
- Ground subsidence (sinking)
- Damage to nuclear power plants
What magnitude is considered an intense EQ?
- 5 magnitue or higher.
- Remember, 32 fold increase for each level
Earthquakes are used as tool for?
Viewing layers of Earth. (Crust, matnle, core)
Moment magnute scale
Most accurate way to measure magnitude of EQ
Earthquakes are strongly associated with
Movements along faults
Faults provide evidence of the _____ theory.
Plate tectonic theory
As energy travels to Earth's surface, the ground _________.
Shakes and moves, e.i. EARTHQUAKEs
Most earthquakes are related to Earth's tectonic movement.
What produces strain the rocks?
Interaction at plate boundries creates stress.
A fracture along which visible displacement of one side relative to the other can be detected.
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.
Transfrom plate boundry
A plate boundry where two plates are sliding HHorizontally past each other, without appriciable verticle movement.
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.
What happens with continued stress at rocks at depth?
They begin to store up elastic energy
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.
Faults have a certain amount of strenght to resist ____.
- 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.
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.
What happens to the epicenter as the cause of an EQ?
strain often occurs, seen as brittle deformation of the crust.
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.
Interplate areas are ____.
Zones of weakness
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.
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.
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.
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.
Devestating earthquakes can occur with what kind of faults?
All three types: reverse, normal, and strike-slip
The more castroptropic/severe EQ have occured along what kind of fault and why?
REVERSE FAULTS (usually those at subduction zones)
Types of surface waves
Rayleigh and Love waves