1906 San Francisco Earthquake - 23.8.1 | 23. Elastic Rebound | Earthquake Engineering - Vol 2
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23.8.1 - 1906 San Francisco Earthquake

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Interactive Audio Lesson

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Introduction to the 1906 San Francisco Earthquake

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0:00
Teacher
Teacher

Today, we’re going to explore the 1906 San Francisco earthquake, a pivotal event in the study of earthquakes. Who can tell me what they know about it?

Student 1
Student 1

Wasn't it one of the most significant earthquakes in the U.S.?

Teacher
Teacher

Absolutely! It was a major earthquake that struck on April 18, causing extensive damage. And can anyone tell me what was observed regarding fault movement?

Student 2
Student 2

I think there was about 6 meters of movement?

Teacher
Teacher

Correct! Approximately 6 meters of fault movement occurred. This is where the elastic rebound theory comes in. Let's delve into what that means. Remember, elastic rebound refers to how energy builds up in deformed rocks until it is released suddenly.

Mechanics of Elastic Rebound

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0:00
Teacher
Teacher

Let’s discuss how elastic rebound theory works. As stress accumulates in rocks due to tectonic forces, what happens next?

Student 3
Student 3

Do they deform until they can’t hold anymore?

Teacher
Teacher

Exactly! They store elastic energy, and once the stress exceeds their strength, a sudden rupture occurs at the fault line. This is how earthquakes happen. Does anyone remember the types of waves produced?

Student 4
Student 4

There are P-waves, S-waves, and surface waves!

Teacher
Teacher

Right again! Those waves carry the energy released during the rupture. This event was instrumental in shaping our understanding of seismic hazards.

Impact and Implications

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0:00
Teacher
Teacher

Now, let's talk about the implications of the 1906 earthquake. Why is it important in today’s understanding of earthquakes?

Student 1
Student 1

Because it helped develop the elastic rebound theory, right?

Teacher
Teacher

Exactly! It provided a real-world example of the theory in action. Understanding this earthquake has helped improve seismic hazard assessments and our ability to predict future seismic activity.

Student 2
Student 2

So, is that why we monitor plate movements now?

Teacher
Teacher

Yes! Monitoring crustal deformation helps us prepare for potential future events. Remember, knowledge of past events can mitigate risks in the future.

Introduction & Overview

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Quick Overview

The 1906 San Francisco earthquake demonstrates the elastic rebound theory, showcasing significant fault movement and ground displacement.

Standard

The 1906 San Francisco earthquake, caused by the rupture along the San Andreas Fault, exhibited approximately 6 meters of fault movement. This event is a classic example of the elastic rebound theory, which describes how accrued stress in the Earth's crust is suddenly released as seismic energy, leading to ground displacement.

Detailed

1906 San Francisco Earthquake

The 1906 San Francisco earthquake is one of the most significant seismic events in U.S. history. It illustrates the principle of elastic rebound theory, which explains the sudden release of accumulated strain energy in the Earth's crust. On April 18, 1906, the San Andreas Fault experienced a catastrophic rupture, resulting in approximately 6 meters of fault movement. Geologist Harry Fielding Reid observed the land displacement and formulated the elastic rebound theory to describe the mechanics behind it.

Key Points:

  • Fault Movement: The earthquake resulted in approximately 6 meters of movement along the San Andreas Fault, emphasizing the significant energy release during the seismic event.
  • Elastic Rebound Theory: This theory elucidates how stored elastic energy in deformed rocks is released suddenly when the strength exceeds the frictional resistance, causing rapid faulting.

The understanding of the elastic rebound theory and events like the 1906 earthquake has led to advancements in assessing seismic hazards and improving earthquake prediction methodologies.

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Fault Movement Observed

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  • Fault movement of ~6 meters observed.

Detailed Explanation

The 1906 San Francisco earthquake resulted in a significant fault movement, measured to be approximately 6 meters. This means that the ground on either side of the San Andreas Fault shifted by about that distance during the earthquake. Such shifting is a direct result of the buildup of strain along the fault line, which suddenly released during a seismic event.

Examples & Analogies

Imagine a rubber band that you are pulling. As you stretch the band, it builds up tension. If you pull it too far, it snaps back to its original position suddenly. In this analogy, the rubber band is like the Earth's crust, and the snapping back represents the fault movement during the earthquake.

Elastic Rebound Explanation

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  • Elastic rebound explains sudden rupture and ground displacement.

Detailed Explanation

The elastic rebound theory provides a framework for understanding how the sudden rupture occurred during the 1906 San Francisco earthquake. According to this theory, rocks on either side of the fault accumulate stress over time as tectonic forces continue to act on them. When the stress surpasses the strength of the rocks, a rupture occurs, releasing the stored energy in the form of seismic waves. This sudden release results in ground displacement, which was observed during the earthquake.

Examples & Analogies

Think about a child playing with a slingshot. When the child pulls back the rubber band of the slingshot, they are storing potential energy. Once they release it, the energy converts into motion, and the projectile flies off at high speed. Similarly, the stored energy in the Earth's crust is released during an earthquake, leading to ground shaking and displacement.

Definitions & Key Concepts

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Key Concepts

  • Elastic Rebound Theory: Describes the process whereby accumulated stress in rocks is suddenly released during an earthquake.

  • Fault Movement: Refers to the displacement along a fault line that occurs as a result of tectonic stress and strain.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • The significant ground shaking and destruction in San Francisco, resulting from the release of energy during the fault movement.

  • Harry Reid’s observations of the land displacement leading to the formulation of elastic rebound theory.

Memory Aids

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🎵 Rhymes Time

  • Tectonic plates move with might, / When they shift, the earth ignites. / Stress builds high, and then it snaps, / Creating waves like mighty claps.

📖 Fascinating Stories

  • Imagine a tightly stretched rubber band. The pressure builds as you stretch it further and further until it finally snaps back – just like how the earth behaves during the elastic rebound process during an earthquake.

🧠 Other Memory Gems

  • Remember 'S.E.R.' – Stress builds, Elastic energy stored, Rupture occurs.

🎯 Super Acronyms

F.R.I.S.K. – Fault movement Results in Instantaneous Seismic Kinetics.

Flash Cards

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Glossary of Terms

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  • Term: Elastic Rebound Theory

    Definition:

    A theory explaining how energy is stored in deformed rock masses and released suddenly during an earthquake.

  • Term: Fault Movement

    Definition:

    The displacement that occurs along a fault line during an earthquake.