lecture recording on 13 March 2025 at 11.51.39 AM

Chapter 1: Introduction to Earthquakes

• Experience with Earthquakes

  • Many have experienced earthquakes; important to understand them for preparation.

  • Knowing what to do before, during, and after can alleviate fear.

• Quote from Dr. Seth Stein

  • "Our ability to predict earthquakes is, quite frankly, lousy."

  • Unlike volcanoes, earthquake prediction isn’t reliable; alarms activate post-event.

• Understanding Earthquakes

  • Importance of understanding risks and hazards.

  • Overview: Definitions, causes, types of faults, and earthquake waves.

  • An earthquake = the earth shaking; scientifically, it's a release of energy.

    • Energy radiates from a localized point, analogous to ripples in a pond.

• Earthquake Frequency

  • Occur daily; over a million detectable earthquakes in a year.

  • Small earthquakes often go unnoticed; media highlights significant ones.

  • Seismicity: Term for overall earthquake activity in an area.

Chapter 2: A Preexisting Fault

• Seismicity Causes

  • Earthquakes can be caused by:

    • Creation of new faults or movement along existing ones.

    • Sudden mineral structure changes.

    • Magma movement under volcanoes.

    • Landslides, meteor impacts, and nuclear detonations.

    • The most common cause is sudden slip along a preexisting fault.

• Role of Plate Tectonics

  • Plate movements (divergence, convergence, transformation) lead to slips and resultant earthquakes.

• Displacement

  • Definition: Movement that alters the original position of rocks.

  • Cumulative displacement can help estimate the age of a fault.

Chapter 3: The Hanging Wall

• Fault Definition

  • A fault is a planar break in rock where movement occurs between two sides.

  • Most faults are not vertical; they typically have angles, creating footwall and hanging wall distinctions.

• Measurable Displacement

  • Displacement must be quantifiable (e.g., a specific distance moved).

  • Offset is similar to displacement but includes measurement.

Chapter 4: Occupants of Faults – Sandy

• Introducing Sandy

  • Imaginary figure (a miner) used to help visualize faults.

  • Helps identify footwall (ground) and hanging wall (above ground).

• Normal Faults

  • Definition: Hanging wall moves down, footwall moves up (caused by tensional forces).

  • Example locations: Yellowstone, Nevada, Utah.

Chapter 5: Characteristics of Faults

• Identifying Faults

  • Using Sandy's position, we can determine which side is the footwall and which is the hanging wall.

• Reverse Faults

  • Definition: Hanging wall moves up, footwall moves down (caused by compressional forces).

  • Reverse faults typically exhibit steep angles.

• Illustration of Movement

  • Movement can be observed through surface features or rock layers.

Chapter 6: Right Lateral Fault

• Strike-Slip Faults

  • Vertical, allowing horizontal movement (no up and down motion).

  • Identify types of motion: left lateral or right lateral.

  • Importance of perspective when using Sandy to identify motion direction.

• Left/Right Lateral Motion

  • If a block moves left relative to Sandy, it's a left lateral fault; if right, a right lateral fault.

Chapter 7: Conclusion

• Practice Session

  • In-class activity to identify different types of faults by drawing (using Sandy as a reference).

  • Emphasize understanding the characteristics of faults and their movements.