Questions and Answers
List the three types of differential stress and briefly describe the changes they impart to rock bodies.
Compressional stress squeezes rock mass together, tensional stress pulls rock apart, and shear stress causes rock to slide past one another.
Identify the plate boundary that is most commonly associated with each of the three types of differential stresses.
Compressive stress at convergent boundaries, tensional stress at divergent boundaries, and shear stress at transform boundaries.
How is brittle deformation different from ductile deformation?
Brittle deformation causes rocks to fracture, while ductile deformation allows rocks to bend without breaking.
What are anticlines?
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What are synclines?
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Contrast the movements that occur along normal and reverse faults. What type of stress is indicated by each fault?
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How are thrust faults different from reverse faults? How are they similar?
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What is elastic rebound?
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What type of faults tend to produce the most destructive earthquakes?
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List the major differences between P, S, and L waves. Which ones tend to cause the most damage and destruction?
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What does the Modified Mercalli Scale tell us about an earthquake?
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How much more energy does a magnitude 7.0 earthquake release than does a magnitude 6.0 earthquake?
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What is a tsunami and how is it generated?
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List at least three reasons an earthquake with a magnitude of 7.0 might result in more death and destruction than a quake with a magnitude of 8.0.
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Where does the greatest amount of seismic activity occur?
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Describe how a rock might change during metamorphism.
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What is meant by the statement 'Every metamorphic rock has a parent rock'?
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What are the three primary agents of metamorphism?
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Which feature would easily distinguish schist and gneiss from quartzite and marble?
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What is the place where slippage first occurs during an earthquake called?
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Most earthquakes occur along or near the edges of what?
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The San Andreas Fault in California is an example of what type of fault?
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Study Notes
Differential Stress Types
- Compressional stress: Squeezes rock masses together.
- Tensional stress: Pulls rock apart or elongates it.
- Shear stress: Causes rocks to shear, moving one part past another.
Plate Boundaries and Differential Stresses
- Compressional stress: Associated with convergent plate boundaries where plates collide.
- Tensional stress: Found at divergent plate boundaries where plates move apart.
- Shear stress: Occurs at transform boundaries with sliding plates.
Deformation Types
- Brittle deformation: Leads to faulting and folding, involves elastic recovery.
- Ductile deformation: Allows for bending and flow of rocks without rupturing.
Types of Folds
- Anticlines: Folds where each half dips away from the crest.
- Synclines: Folds where each half dips toward the trough.
Fault Movements
- Normal fault: Hanging wall moves down relative to footwall; associated with tensional stress.
- Reverse fault: Hanging wall moves up relative to footwall; associated with compressional stress.
Thrust vs Reverse Faults
- Thrust faults: Are a type of reverse fault with a lower angle (usually less than 45 degrees) accommodating horizontal shortening.
- Both faults result from strong compressional stresses and involve upward movement of rock.
Earthquake Mechanics
- Elastic rebound: Energy accumulates in rocks until the internal strength is exceeded, resulting in slippage and earthquakes.
Fault Types and Earthquake Destruction
- Megathrust faults: Most destructive earthquake-producing faults, typically occurring in subduction zones.
Seismic Wave Types
- P waves: Fastest, lowest amplitude; create least damage.
- S waves: Arrive second, greater amplitude; cause more damage.
- L waves: Slowest, greatest amplitude; result in the most destruction.
Modified Mercalli Scale
- Measures the intensity of ground shaking, indicating the severity of an earthquake's effects.
Energy Release Comparison
- A magnitude 7.0 earthquake releases 32 times more energy than a magnitude 6.0 earthquake.
Tsunami Generation
- Tsunamis are large waves generated by abrupt movements on the ocean floor, resulting from earthquakes, underwater landslides, or volcanic activity.
Earthquake Impact Factors
- Soft sediments can amplify vibrations.
- Liquefaction can lead to significant destruction.
- Buildings may be inadequately anchored or engineered to withstand powerful vibrations.
Seismic Activity Locations
- The greatest amount of seismic activity occurs along plate boundaries.
Metamorphism Process
- Rocks undergo metamorphism through the rearrangement of mineral crystals under heat, pressure, and chemically active fluids.
Parent Rock Concept
- The phrase "Every metamorphic rock has a parent rock" means that all metamorphic rocks originate from pre-existing rocks.
Agents of Metamorphism
- Heat: Increases temperature causing changes in mineral structure.
- Pressure: Alters rock texture and mineral alignment.
- Chemically active fluids: Facilitate mineral reactions and transformations.
Distinguishing Metamorphic Rocks
- Foliated texture: Distinguishes schist and gneiss from non-foliated rocks like quartzite and marble.
Earthquake Focus
- The focus is the initial point where slippage occurs during an earthquake.
Seismic Activity and Lithospheric Plates
- Most earthquakes occur along or near the edges of the Earth's lithospheric plates.
Fault Types
- The San Andreas fault in California exemplifies a strike-slip fault.
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Description
Test your knowledge on the different types of differential stress that affect rock bodies in geology. This quiz covers compressional, tensional, and shear stress, along with their definitions and effects. Perfect for students studying Chapter 10 of a geology course.