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65 Cards in this Set
- Front
- Back
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Earthquake
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the vibration of Earth produced by the rapid release of energy
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When an earthquake occur what 3 major things happen?
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A. energy released radiates in all directions from its source, the focus
B. energy is in the form of waves C. sensitive instruments around the world record the event. |
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Faults
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movements that produce earthquakes are usually associated with large fractures called... doesn't always go to surface.
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How can most of the motion along faults be explained?
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Plate Tectonics Theory
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Epicenter
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area above the source of the Earthquake, not where actual earthquake occurs. It is 90 degrees above the focus
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Focus
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Where acutal earthquake occurs
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Who first explained mechanism for earthquakes
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H.F. Reid
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Elastic rebound
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A. rocks on both sides of an existing fault are deformed by tectonic forces.
B. Rocks bend and store elastic energy C. Frictional resistance hoding the rocks together is overcome |
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Earthquake mechanism
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A. slippage at the weakest point(focus) occurs
B. Vibrations (earthquakes) occur at the deformed rock "springs back" to its original shape (elastic rebound) |
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Where does it break
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weakest point (the focus)
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Aftershocks
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adjustments that follow a major earthquake often generate smaller earthquakes
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Foreshocks
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Small earthquakes often precede a major earthquake by days or, in some cases, by as much as several years.
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What is the most studied fault system in the world?
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San Andreas
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San Andreas
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Displacement occurs along discrete segments 100 to 200 kilometers long (62 to 120 miles)
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Fault Creep
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San Andreas- Some portions exhibit slow, gradual displacement
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San Andreas regualary produce small earthquakes in other segments by
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slip
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Where is the New Madrid Fault
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S.E. Missouri and Tennessee
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Still other segments along the San Andreas fault store what type of energy before ruptureing in great earthquakes
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Elastic. and the process is called stick-slip motion.
Great earthquakes should occur about every 50 to 200 years along these sections. |
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What are the 3 types of displacements along the San Andreas Fault?
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1. Slow, graded displacement know as fault creep
2. Regualr slip producing small earthquakes 3. store elastic energy for hundereds of years before rupturing in great earthquakes called stick-slip. |
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In the stick-slip motion how often whoupd great earthquakes occur?
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50 to 200 years
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The study of earthquake waves is called
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seismology
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How far back does seismology date back to
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almost 2000 years ago to the Chinese
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instruments that record seismic waves.
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seismographs
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How does a seismograph work?
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it records the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape.
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More than one type of seismograph is needed to record what types of ground motion?
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vertical and horizontal
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What are the records that are obtained from a seismograph called?
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seismogram
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What are the 2 types of seismic waves
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Body waves-P, S can travel through Earth's surface.
Surface waves- L (surface)cannot travel through Earth's surface. |
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P waves
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Primary, Push-Pull, 1st to be detected, least powerful, fastest, can go through anything.
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S waves
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Secondary, Side to Side (shake), 2nd fastest, 2nd wave to be detected, 2nd powerful, travel only through solids
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L waves
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Surface or Long waves, most powerful, last to be discovered, slowest wave, cannot travel through earth, greatest amplitude and slowest velocity. actually ripple the earth
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THe place within Earth where earthquake waves originate.
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Focus
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Location on the surface directly above the focus
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Epicenter
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How is the Epicenter located?
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using the difference in velocities of P and S waves
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Generally in any solid material, P waves are how much faster than S waves?
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1.7 times
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The 5 steps to locating the Epicenter
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1. THree station recordings are needed to locate an epicenter
2. Each station determines the time interval between the arrival of the first P wave and the First S wave at their locaiton 3. A travel-time graph is used to determine each station's distance to the epicenter 4. A circle with a radius equal to the distance to the epicenter is drawn around each station 5. The point where all three circles intersect is the earthquake epicenter. |
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About 95 percent of the energy released by earthquakes originates in a few relatively narrow zones that wind around the globe. these are known as
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Earthquake belts
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Major Earthquake zones include:
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Circum -Pacific belt (ring of fire), Meiterranean Sea region tothe Himalayan complex (where Asia is still pusing), adn the oceanic ridge system (only in Atlantic)
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Earthquakes originate at depths ranging from
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5 to nearly 700 kilometers. They are classified as Shallow , Intermediate, and Deep
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Shallow Earthquake
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surface to 70 kilometers (less than 50 miles deep)
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Intermediate Earthquakes
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between 70 and 300 kilometers. 180 miles down to mantle
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Deep Earthquakes
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over 300 kilometers
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Concerning Earthquake depth where do shallow focus occur
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along oceanic ridge system
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Concerning Earthquake depth where do almost all deep-focus earthquakes occur?
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circum-Pacific belt. particularly in regions situated landward of deep-ocean trenches.
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What are the two measurements that describe the size of an earthquake
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Intensity and Magnitude
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a measure of the degree of earthquake shaking at a given locale based on the amount of damage
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intensity
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measure that estimates the amount of energy released at the source of the earthquake
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magnitude
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Which system is better Magnitude or Intensity scales
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Magnitude
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What Intensity scale was developed using California buildings as its standard
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Modified Mercalli Intensity Scale
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What is the drawback of intensity scales
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destruction may not be a true measure of the earthquake's actual severity
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Who first introduced the concept of the Richter magnitude scale?
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Charles Richter in 1935
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How does Richter scale work?
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1. Based on the amplitude of the largest seismic wave recorded.
2. Accounts for the decrease in wave amplitude with increased distance. |
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What is the largest magnitude recorded on a Wood-Anderson seismograph
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8.9
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Magnitude less than what are not felt by humans?
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2.0
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Concerning intensity each unit of the Richter magnitude increase coressponds to
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10 fold increase in a wave amplitude.
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Concening magnitude each unit of the Richter magnitude increase corresponds to
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32 fold energy increase
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Amounts fo structural damage attributable to earthquakes vibrations depends on
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1. Intensity and duration of the vibrations
2. Nature of the material upon which the structure rests 3. Design of the structure |
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Concerning ground shaking, regions within what distance of the epicenter will experience about the same intensity of ground shaking.
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withing 20 to 50 kilometers (up to 30 miles) of the epicenter
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Concerning ground shaking destruction varies considerably mainly due to what?
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the nature of the ground on which the structures are built.
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Destruction from seismic vibrations can include unconsolidated materials saturated with water turn into a mobile fluid. in other words, soil with a lot of moisture will behave like water. this is called
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liquefaction of the ground
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the rhythmic sloshing of water in lakes, reservoirs, and enclosed basins where waves can weaken reservoir walls and cause destruction is called
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seiches
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destruction waves that are often inappropriately called "tidal waves". THey result from vertical displacement along a fault located on the ocean floor or a large undersea landslide triggered by an earthquake
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Tsunamis, or seismic sea waves
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How high do Tsunamis usually get in the open ocean?
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less than one meter
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Concernign Tsunamis,in shallower coastal waters how high can water piles get up to
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can occasionally exceed 30 meters
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WHat are the types of destruction from seismic vibrations?
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Liquefaction of the ground, Seiches, Tsunamis, Landslides and ground subsidence, and Fire
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Earthquake safety
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only run for door if close, get under heavy object (such as a desk), if run outside get out of the way of falling things
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