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19 Cards in this Set
- Front
- Back
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Learning Goals |
1) Describe how earthquakes are distributed across the planet as a function of plate tectonics. 2) Compare the types of seismic waves generated during an earthquake. 3) Describe how earthquakes are measured and located. 4) Compare earthquake magnitude and intensity and how they are affected by local geology. 5) Describe how seismic waves are used to image the interior of the Earth. |
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Earthquake |
Shaking or vibration of the ground caused by rocks undergoing deformation suddenly breaking along a fault
Most found at tectonic plate margins, where friction and faulting are most intense
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Pacific Ring of Fire |
Zone characterized by subduction zones. Friction from subduction produces large and destructive quakes so earthquakes here are violent |
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What causes an earthquake? |
Along a fault, large masses of rock move past each other because of tectonic forces. Friction causes them to lock.
Stress builds up to a critical point.
Accumulated stress > friction
Brittle rupture/failure along fault |
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Focus or Hypocenter |
Originating point of earthquake on the fault plane |
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Epicenter |
Point on surface directly above focus |
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Body waves |
Transmit energy through Earth's interior in all directions from earthquake's focus
Can be either P-waves or S-waves |
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Surface waves |
Transmit energy along Earth's surface causing the Earth's surface to vibrate
Can be either Love or Rayleigh waves |
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P-waves |
Stands for primary
Travel through solids and liquids
Material is displaced parallel to waves' travel path
Faster than S-waves |
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S-waves |
Stands for secondary
Travel only through solids
Material is displaced perpendicular to waves' travel path
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Love waves |
Surface waves that cause sideways shaking of the ground
Travel only through solids
Slower than S-waves |
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Rayleigh waves |
Surface waves that produce rolling motion, like ripples in a pond
Travel through solids and liquids
Slower than S-waves and Love waves |
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Seismometers |
Sensors located in underground vaults that detect seismic activity |
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Seismograph |
Instrument that measures ground movement in 1 direction. Built in clusters of 3 to record principal directions of movement in 3-D |
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How is the epicenter located? |
Difference in wave arrival times at a seismograph station: waves travel at different velocities
P-waves arrive first, then S-waves, then L- and R-
Farther away from epicenter a seismograph is, the larger the interval between wave arrivals
Three seismograph stations are needed to locate the epicenter of an earthquake (see slides 20 - 25) |
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Intensity |
Subjective measure of an earthquake's size based on damage and people's reaction to the quake using the Modified Mercalli Intensity Scale
Varies as a function of distance from epicenter, local geology, etc |
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Factors influencing intensity |
1) Total energy released at focus 2) Distance of focus to the surface 3) Underlying geology in an area (solid bedrock will inhibit large damage, whereas poorly consolidated soils have more potential for damage) 4) Building construction and population density |
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Magnitude |
Quantitative measure of total energy released at an earthquake's source using the Richter Magnitude Scale
Fixed value for an earthquake (while intensity varies) |
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Richter Scale |
Amplitude of larges wave is corrected for distance and assigned number on the scale.
Base 10 logarithmic scale: each magnitude increase represents 10 fold increase in shaking amplitude, which equates to 30 fold increase in energy released |
