Part 2 Intro to Earthquakes for Test 2

Overview of Seismic Faults and Waves

• Reference to the San Andreas Fault

  • Discussion of the previously left topic, revisiting it for clarity.

• Horizontal Faults

  • Identification: Classified as right lateral strike-slip faults.

  • Visual Reference: Observing river movement relative to the fault (e.g., river flows to the right when crossing the fault).

  • Contextual Note: Many faults in Southern California exhibit similar characteristics as the Cenotrace fault.

Seismic Waves

• Introduction to Seismic Waves

  • Transitioning to the subject of seismic waves after discussing fault types.

  • Seeking volunteers to interactively simulate seismic activities (suggestion of humor post-test).

Seismic Energy Dynamics

• Understanding the Epicenter

  • Definition: The point on the earth's surface directly above the earthquake's focus.

  • Illustration: Cross-sectional view of the Earth showcasing the earthquake's depth and the focus' significance.

• Energy Release:

  • Explanation of seismic energy generated at the focus and its propagation towards the surface in all directions.

  • Impact: Epicenter experiences seismic energy first.

Types of Seismic Waves

• Classification of Waves

  • Primary categories: Body Waves and Surface Waves.

  • Clarification: Each earthquake produces both body waves and surface waves.

Body Waves

• P-Wave (Primary Wave):

  • Description: The first wave felt during an earthquake, characterized by a push-pull movement (compressional wave).

  • Speed: Fastest among seismic waves; first to be detected at seismograph stations.

  • Characteristics: Can travel through all states of matter (solids, liquids, gases).

  • Layers of Earth Traversed:

    • Lithosphere

    • Asthenosphere

    • Mesosphere

    • Outer Core (not applicable for S-waves)

    • Recognized impact: Travel through oceans and atmosphere, producing sound.

• S-Wave (Secondary Wave):

  • Description: Follows P-waves; second wave felt during earthquakes, characterized by an up-and-down motion (shear wave).

  • Speed: Slower than P-waves, cannot travel through liquids.

  • Layers of Earth Traversed:

    • Lithosphere

    • Asthenosphere

    • Mesosphere

    • No travel through outer core, atmosphere, or oceans due to liquid nature.

Surface Waves

• Characteristics:

  • Arise from the energy that reaches the surface after body waves.

  • Typically more destructive due to their longer duration and ground motion intensity.

• Love Wave:

  • Description: A shear wave moving side-to-side, discovered by scientists named Love; capable of causing severe damage to upright structures.

  • Characteristics: Can destroy buildings as they shear off foundations, travel only through solids.

• Rayleigh Wave:

  • Description: Characterized by a rolling motion resembling ocean waves but rather moves in an elliptical motion.

  • Impact: Felt as a pervasive rolling movement that also causes significant structural damage.

Summary of Wave Characteristics

• P-waves are the fastest and least damaging, moving parallel to wave propagation.

• S-waves, while slower and only move through solids, exhibit perpendicular motion relative to wave propagation.

• Surface waves (Love and Rayleigh) are slower, cause the most damage, and create complex ground movements.

Analogies for Understanding Waves

• P-Wave Analogy: Represented by a slinky being pushed and pulled.

• S-Wave Analogy: Comparable to shaking a rope where movement occurs perpendicular to the wave direction.

• Surface Wave Visuals:

  • Love waves akin to a side-to-side shake, illustrative of slithering actions.

  • Rayleigh waves are depicted as rolling waves, showcasing carpet-like undulations.

Seismology Essentials

• Seismographs and Seismograms

  • Definition of Seismographs: Instruments designed to record seismic activity, assessing various wave dynamics.

  • Definition of Seismograms: Chart output illustrating various seismic waves – P, S, and surface waves.

  • Wave Recognition:

    • P-waves produce initial minor bumps followed by significant S-wave activity characterized by greater amplitude peaks due to extensive surface interactions.

• Amplitude: Defined as the height of the wave above the reference line, vital in measuring earthquake intensity and destruction potential.

Travel Time and Wave Propagation

• Travel Time Curve: Represents the relationship between time elapsed since a quake and distance from the epicenter.

  • P-waves are faster than S-waves;

  • Example Scenario: Cars analogy - a faster car (P-wave) vs. a slower car (S-wave) illustrates the increasing time gap as distance from the epicenter increases.

Conclusion

• Behavior of Waves Upon Distance

  • As proximity to epicenter increases, simultaneous detection of waves occurs; as distance increases, sequential wave detection is noted.

  • Summary: The importance of seismology is evident as it helps anticipate and analyze seismic behaviors, preparing for real-world implications, especially in earthquake-prone regions.