Geology Chapter 10: Crustal Deformation

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?

Anticlines are folds in which each half of the fold dips away from the crest. Signup and view all the answers

What are synclines?

Synclines are folds in which each half of the fold dips toward the trough of the fold. Signup and view all the answers

Contrast the movements that occur along normal and reverse faults. What type of stress is indicated by each fault?

Normal faults involve the hanging wall moving down relative to the footwall, indicating tensional stress; reverse faults involve the hanging wall moving up, indicating compressional stress. Signup and view all the answers

How are thrust faults different from reverse faults? How are they similar?

Thrust faults are at a lower angle than reverse faults and accommodate horizontal shortening; both types result from compressional stresses. Signup and view all the answers

What is elastic rebound?

Elastic rebound is the process by which energy is spread during earthquakes as rocks deform and accumulate stress until they break. Signup and view all the answers

What type of faults tend to produce the most destructive earthquakes?

Megathrust faults. Signup and view all the answers

List the major differences between P, S, and L waves. Which ones tend to cause the most damage and destruction?

P waves arrive first and have the lowest amplitude, S waves arrive second with greater amplitude, and L waves arrive last with the greatest amplitude, causing the most damage. Signup and view all the answers

What does the Modified Mercalli Scale tell us about an earthquake?

It measures the intensity of ground shaking during an earthquake. Signup and view all the answers

How much more energy does a magnitude 7.0 earthquake release than does a magnitude 6.0 earthquake?

A magnitude 7.0 earthquake releases 32 times more energy than a magnitude 6.0 earthquake. Signup and view all the answers

What is a tsunami and how is it generated?

A tsunami is a series of large waves generated by an abrupt movement on the ocean floor, such as an earthquake or underwater landslide. Signup and view all the answers

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.

<ol> <li>Soft sediment may amplify vibrations. 2. Liquefaction may occur. 3. Buildings may not be built to withstand strong vibrations.</li> </ol> Signup and view all the answers

Where does the greatest amount of seismic activity occur?

Along plate boundaries. Signup and view all the answers

Describe how a rock might change during metamorphism.

The rearrangement of mineral crystals occurs when heat and pressure change the environment of a rock. Signup and view all the answers

What is meant by the statement 'Every metamorphic rock has a parent rock'?

It means all metamorphic rocks originate from preexisting rocks. Signup and view all the answers

What are the three primary agents of metamorphism?

Heat, pressure, and chemically active fluids. Signup and view all the answers

Which feature would easily distinguish schist and gneiss from quartzite and marble?

The foliated texture. Signup and view all the answers

What is the place where slippage first occurs during an earthquake called?

Focus. Signup and view all the answers

Most earthquakes occur along or near the edges of what?

Earth's lithospheric plates. Signup and view all the answers

The San Andreas Fault in California is an example of what type of fault?

Strike-slip fault. Signup and view all the answers

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.