Seismic Waves – Grade 10 Science Class Notes

Opening Elements

  • Catholic prayers integrated into class routine
    • Apostle’s Creed recited at start
    • Invocation of Mary, the Immaculate Conception ("Pray for us")
  • Closing prayer: Act of Contrition with commitment to amend life and ask grace
    • Reinforces school’s faith-based ethos and daily structure

Administrative Items

  • Day of lesson: Tuesday
  • Teacher: Ms. Janiene C. Coraza
  • Grade level: Grade 10 Science
  • Attendance check performed before lesson
  • Ice-breaker activities
    • “Science Trivia” prompt (no trivia content given)
    • “WORD SCRAMBLE / GUESS THE WORD” mini-game
    • Target words and correct unscrambles:
      • EPICENTER (from “I N C E P T R E E”) – location on Earth’s surface directly above earthquake focus
      • FOCUS (from “U C S O F”) – point within Earth where seismic rupture starts
      • SEISMIC (from “I C S M I S E”) – relating to earthquakes or Earth vibrations
      • SURFACE (from “F A S E R U C”) – outermost Earth layer where certain waves travel
      • PRIMARY (from “M A R P R I Y”) – first arriving body waves (P-waves)

Core Content – Seismic Waves

Fundamental Concepts
  • Earthquake energy travels in seismic waves that propagate through Earth’s interior and along its surface.
    • Waves originate at a fault (fracture where blocks of crust slip).
  • Waves classified by location of travel:
    • Body waves – move through Earth’s interior.
    • Surface waves – confined to Earth’s exterior layers.
  • Waves carry information about Earth’s internal structure and are responsible for earthquake damage.
Detection & Measurement
  • Seismograph / Seismometer
    • Instrument that detects, amplifies, and records ground motion.
    • Captures wave strength (amplitude) and duration (time) for analysis.
Detailed Comparison of Seismic Wave Types
  • (Repeated table in slides; speeds for crustal rocks.)

Body Waves

  • P-wave (Primary wave)

    • Speed: 5–8 km/s5\text{–}8\,\text{km/s} in continental crust – fastest of all seismic waves.
    • Medium: Solids, liquids, gases ⟶ travels through entire Earth (outer core included).
    • Particle motion: Compressional / longitudinal – push-pull parallel to propagation.
    • First to arrive at seismic stations; useful for early-warning.
    • Diagram notes: X-axis propagation, Y-axis particle displacement shown as alternating compressions & rarefactions.

  • S-wave (Secondary wave)

    • Speed: 3–4.5 km/s3\text{–}4.5\,\text{km/s} (≈60–70 % of P-wave speed).
    • Medium: Solids only (absorbed by liquids; stops at outer core) – provides evidence for liquid outer core.
    • Particle motion: Shear / transverse – side-to-side or up-and-down, perpendicular to propagation.
    • Arrives after P-waves; causes stronger shaking than P-waves.

Surface Waves

  • Love wave (L-wave)

    • Speed: slower than S-waves; confined to surface layers.
    • Medium: uppermost solid crust.
    • Particle motion: horizontal, side-to-side (transverse) with no vertical component.
    • High amplitude; very destructive to rigid structures (shear-type damage).
    • Slide mislabeled particle-motion box “S WAVE” but pertains to Love wave.

  • Rayleigh wave

    • Speed: slowest of common seismic waves.
    • Medium: solid surface layers.
    • Particle motion: elliptical rolling (retrograde) analogous to ocean waves – ground moves both vertically and horizontally.
    • Produces long-duration undulations; notorious for structural collapse.
Tabulated Summary (verbatim values)
Type of Wave | Speed               | Medium                  | Particle Motion
-------------|--------------------|-------------------------|-----------------------------
P (Primary)  | 5–8 km/s (fastest) | Solids, liquids, gases  | Compressional (parallel)
S (Secondary)| 3–4.5 km/s         | Solids only             | Shear (perpendicular)
Love         | < S-wave           | Surface (solids only)   | Horizontal, side-to-side
Rayleigh     | Slowest            | Surface (solids only)   | Rolling, elliptical
Conceptual Connections & Significance
  • Time lag between P- and S-wave arrivals allows epicenter distance calculation (triangulation using three or more stations).
  • Absence of S-waves beyond 104∘104^{\circ} arc (S-wave shadow zone) indicates fluid outer core – foundational discovery for internal Earth layers.
  • Surface waves correlate with observed earthquake destruction; underscores importance of building codes.
  • Seismic methods employed in mineral & oil exploration; analogous wave behavior used in ultrasound & sonar.
Example / Hypothetical Scenario
  • If a station records P-wave at t0t_0 and S-wave 40 s40\,\text{s} later, and average Δv=2 km/s\Delta v = 2\,\text{km/s}, then epicentral distance ≈ 80 km80\,\text{km} (simple difference-in-travel-time method).

Seatwork – True or False (with keys & explanations)

  1. “The Primary wave is the slowest wave among the seismic waves.” – False (it is fastest).
  2. “The Secondary wave can travel through all states of matter.” – False (solids only).
  3. “The most destructive wave is the Surface wave.” – True (Love & Rayleigh cause maximum damage).
  4. “The Primary wave is the first wave that can be detected.” – True (arrives first).
  5. “The two types of Surface waves are the Primary waves and Love waves.” – False (Surface waves are Love & Rayleigh; Primary is a body wave).

Practical / Ethical / Safety Implications

  • Early detection of P-waves enables Earthquake Early Warning (EEW) systems providing seconds to minutes for protective action.
  • Engineering: Design structures to withstand shear forces from S- and Love waves and vertical undulations from Rayleigh waves.
  • Disaster preparedness curricula integrate both scientific knowledge and value formation (e.g., prayer component) to foster holistic resilience.

Quick-Reference Equations

  • Wave speed relation: v=distancetimev = \dfrac{\text{distance}}{\text{time}}
  • Arrival-time difference method: Δt=t<em>S−t</em>P,D≈(v<em>P⋅v</em>S)/(v<em>S−v</em>P)⋅Δt\Delta t = t<em>S - t</em>P,\quad D \approx (v<em>P \cdot v</em>S)/(v<em>S - v</em>P) \cdot \Delta t (simplified two-station formula)

Suggested Study Path

  • Memorize properties (speed, medium, motion) of P, S, Love, Rayleigh waves.
  • Practice reading seismograms: identify P- and S-wave onsets, compute Δt\Delta t.
  • Use real earthquake data (USGS) to apply triangulation.
  • Reflect on ethical responsibilities of scientists: informing the public, improving infrastructure, and integrating cultural/religious context in outreach.