Quiz 5 Flashcards
Thought to cause earthquakes before plate tectonics
Angry gods, mythical creatures, magma movement, tidal forces, compressed air
Interplate earthquakes and an example of where they occur
Occur in plate interiors due to ancient rifts or fault zones. Fluids moving along fault zones can often cause movement
New Madrid Seismic Zone: made up of reactivated faults that formed when what’s now North America began to split/rift apart during the breakup of the supercontinent Rodinia
Hypocenter
Also called the focus. It’s the exact position on the fault, including the depth, where slippage began
Epicenter
The map position of the earthquake (on the surface), directly above the focus
Types of earthquake faults
Normal fault, thrust fault, and strike-slip fault
Normal fault
Caused by tension; one plate slides down (divergent boundaries) from tension forces (forces moving apart)
Thrust fault
One block moves up over the other from compression forces
Strike-slip fault
At a transform boundary; blocks/plates moving past each other from shearing forces
The stored energy that earthquakes release
Seismic waves
Body waves include
P waves (primary/compression waves) and S waves (secondary/shear waves)
Surface waves include
Love waves and Rayleigh waves
What do body and surface waves, respectively, tell us?
Body waves tell us where earthquakes might originate
Surface waves tell us about where damage might be done
For surface waves, _______ decreases with ______
Amplitude; depth
Particle motion of P waves
Alternating compression and dilation. Material returns to its original shape after wave passes
Particle motion of S waves
Up-and-down motion that propagates through. Material returns to its original shape after wave passes
Particle motion of Rayleigh waves
Elliptical motion (generally retrograde elliptical). Material returns to its original shape after wave passes
Particle motion of Love waves
Side-to-side motion that propagates through. Material returns to its original shape after wave passes
The difference between the arrival times of the P and S waves at a recording station is a function of
The distance from the epicenter
Scale based on the amount of energy released by the earthquake
Richter Magnitude Scale
The amount of energy released by an earthquake is based on measurements of what
The amplitude and the P-S wave distance
Scale measuring force, based on the damage done and human perception
Modified Mercalli Intensity Scale
Magnitude
The amount of energy released by an earthquake
Intensity
Measure of damage and death that an earthquake causes
Each whole number increase in magnitude represents
10-fold increase in the measured amplitude on a seismogram
32-fold increase in the energy released by the earthquake
Factors affecting earthquake intensity/Mercalli Scale variables
Magnitude
Distance away from the focus/epicenter
Foundation materials
Building style
Duration of shaking
Intensity of ground motion depends on
Geology (loose, unconsolidated sediments are subject to more intense shaking than solid bedrock is)
Size of earthquake (larger earthquake = more intense shaking and longer duration)
Distance of earthquake away from epicenter (more severe near epicenter)
Damage due to earthquakes can be caused from a variety of factors (i.e. what other disasters can an earthquake cause?)
Collapse
Fire damage
Landslides
Flood
Liquefaction
Tsunami
Liquefaction
Unconsolidated materials are saturated with water, earthquake vibrations can turn stable soil into a mobile fluid
Why could fire damage occur after an earthquake?
Power lines knocked down
Natural gas line ruptures
Broken water lines (can’t put out fire)
Why could flooding occur after an earthquake?
Dams can give way during/after an earthquake
Factors of Seismic Risk (list, no definitions)
Hazard, Vulnerability, Value
Hazard
The chance that the building will experience strong shaking, soil liquefaction, or a landslide
Vulnerability
The likelihood that the building will collapse due to those geological hazards
Value
The number of lives potentially affected
Mean Recurrence Interval (MRI)
Average time between earthquakes, calculated by 1/avg number of earthquakes
If earthquake number over 30 years is unknown, then plot out previous MRIs
To calculate the probability of an earthquake occurring over any number of years
1 - (probability of an earthquake NOT occurring)^years
To calculate the probability that an earthquake will occur over the course of a year
1/MRI, not to exceed 1 or 100%
Brittle building materials
Concrete and masonry
Flexible building materials
Wood and steel
Materials that are particularly prone to damage
Wood and unreinforced masonryS
Ways to make buildings more safe against earthquakes
Lower height
Move weight to lower floors
Change building shape
Change building materials
Shear walls
Braced frames
Base isolation
Retrofit older structures
Seismic dampeners (reduces the maximum amplitude of a wave passing through the object)
Vulnerability factors include:
Soft stories
Unreinforced masonry (brick/concrete without reinforcement)
Vertical irregularity (different building parts at different heights) or plan irregularity (deviation from a box shape)
Rough steps to the formation of an ocean basin
- Upwelling of ocean mantle material, causing the crust above it to thin and upwarp, which later leads to the faulting and breaking of rocks
- The crust is broken and stretched, producing a rift valley
- Continental rifting eventually produces a linear sea
- If spreading continues, the sea will develop into a full-on ocean
What types of rocks are you likely to find at oceanic ridges?
Igneous, mafic, fine-grained rocks: mainly basalt, but sometimes gabbro if cooling occurs below the ocean floor
What are two methods for volcanic monitoring?
Seismic monitoring; measuring deformation and tilt
Equipment needed for measuring deformation and tilt
Tilt meter, GPS
Equipment needed for seismic monitoring
Seismogram, seismometer
Data collected from seismic monitoring
Seismograph
Data collected from measuring deformation and tilt
GPS station motion
“Signature” of volcanic eruption about to occur, from a seismic monitoring standpoint
Earthquakes, which develop into longer tremors with more sustain (much larger earthquakes occur before the eruption, with a much longer duration seismogram)
Continuous release of seismic energy from magma moving
“Signature” of volcanic eruption about to occur, from the standpoint of measuring tilt and deformation
Magma causes the surface to transform (bulges and moves upward)
The tilt of the surface changes
___ is released before a volcanic eruption
Gas
Explain why divergent plate boundaries do(n’t) cause tsunamis
They don’t cause earthquakes – divergent plate boundaries make more space for water, so even with earthquakes, you won’t get tsunamis at that location.
Additionally, the upward force causing tsunamis comes from convergent boundaries.
