Seismic Wave Lab - Interactive Science Simulation

Focus Depth: 25 km

Magnitude-like (M): 6.5

Sim Speed:

P-Wave S-Wave Surface

Earth Crust & Mantle Cross-Section View

Focus (Hypocenter) Epicenter Stations (A, B, C)

Tap/click rock to reposition the model Focus

Elapsed: 0.0 s

Virtual Station Seismograms

Synthetic Feeds

Station A (Hypo dist: 120 km) Waiting for waves...

Station B (Hypo dist: 240 km) Waiting for waves...

Station C (Hypo dist: 380 km) Waiting for waves...

P-WAVE SPEED 6.0 km/s

S-WAVE SPEED 3.5 km/s

SURFACE SPEED 3.0 km/s

Primary (P) Waves

Compressional body waves. Particle motion is parallel to propagation. In this teaching model they are the fastest phase; compressional waves can propagate through solids and fluids.

Secondary (S) Waves

Shear body waves. Particle motion is perpendicular to propagation. They travel more slowly than P waves and require shear rigidity, so they do not propagate through liquids.

L/R

Surface Waves

Rayleigh and Love waves propagate along or near Earth’s surface. They are generally slower than body waves and can produce large, long-duration ground motion; actual damage depends on source, distance, frequency content, site conditions, and structures.

P–S Arrival Interval & Distance Calculation

Because P waves travel faster than S waves, the S–P lag ($\Delta t = T_s - T_p$) generally grows with source distance. This exercise uses constant speeds and a straight-ray distance proxy; real earthquake locations use travel-time models/curves.

Interactive Station Trace Reader Use the sliders to place P and S arrival markers on the synthetic trace

P-Wave Arrival ($T_p$): 0.0 s

S-Wave Arrival ($T_s$): 0.0 s

Arrival Measurements Exercise

P–S Time Lag ($\Delta t$): 0.0 s

Distance Formula:

$$d = \Delta t \times \frac{v_p \cdot v_s}{v_p - v_s}$$

With this lab’s constant values ($v_p = 6.0$ km/s, $v_s = 3.5$ km/s), each second of S–P lag corresponds to 8.4 km of straight-ray model distance. This is not a substitute for real travel-time curves or a layered-Earth location solution.

Calculated Distance: 0 km

Estimate model distance (km) & verify:

Epicenter Triangulation

In this idealized 2D exercise, each station supplies a distance circle. A third circle usually resolves the two-circle ambiguity and gives one common epicenter intersection when the synthetic distances are consistent.

Regional Station Map Grid (800 x 600 km) Completed: 0

Station Seismogram Data

Station Alpha Lag: 25s

100 km

Station Beta Lag: 40s

100 km

Station Gamma Lag: 30s

100 km

For this exercise only: distance ≈ S–P lag × 8.4 km. Set each radius from its displayed lag.

Why a Third Distance Circle Helps:

1 station: An ideal distance constraint places the epicenter somewhere on a circle.
2 stations: Two circles can have zero, one, or two intersections; in the common two-intersection case the location remains ambiguous.
3 stations: With consistent idealized distances, a third circle can select the common intersection. Real networks solve arrival times with velocity models and uncertainty rather than perfect circles.

Seismic Physics Parameter Explorer

Modify constant model wave speeds, station geometry, focus depth, and the magnitude-like display control to explore how this simplified model changes arrival times and synthetic waveform gain.

Physical Variables

P-Wave Speed ($v_p$): 6.0 km/s

S-Wave Speed ($v_s$): 3.5 km/s

Focus Depth ($Z$): 20 km

Epicentral Distance ($X$): 150 km

Magnitude ($M$): 6.0

HYPOTENUSE DISTANCE 151.3 km

P-WAVE TIME 25.2 s

S-WAVE TIME 43.2 s

P–S LAG ($\Delta t$) 18.0 s

Synthetic Waveform Preview Visual gain only — not a magnitude, energy, or ground-motion calculation

Model Simplifications Highlighted:

• Homogeneous medium: Real Earth has layered, laterally variable velocities and curved/refracted ray paths. This lab uses uniform speeds and straight-line travel-time arithmetic.

• Attenuation/geometric spreading: Real amplitudes depend on wave type, geometry, frequency, material attenuation, and site response. A simple universal $1/r^2$ amplitude rule is not used here.

• Wave Dispersion: Surface wave speed in reality depends on frequency/wavelength.

• Single Rupture Point: Real fault line ruptures extend across many kilometers rather than a single point focus.

Best Quiz Score: 0%

Focus vs. Epicenter

The hypocenter (focus) is the subsurface source location assigned to an earthquake-location solution; real ruptures occupy a finite fault area rather than a mathematical point. The epicenter is the surface point directly above the hypocenter.

Core Concept

P-Waves (Primary)

P waves are compressional body waves (push-pull motion). They are normally the first seismic phase to arrive because they travel faster than S waves. Their speed varies substantially with material and depth; the 6.0 km/s value used here is only a local teaching constant.

Speed Leader

S-Waves (Secondary)

S waves are shear body waves. They travel more slowly than P waves and require shear rigidity, so they do not propagate through the liquid outer core. The 3.5 km/s value used here is an illustrative crustal constant, not a global speed.

Solid Only

Surface Waves

Rayleigh and Love waves propagate along or near the surface and are generally slower than body waves. They can have large amplitudes and long durations and often contribute strongly to damaging shaking, but damage is controlled by many source, path, site, and structural factors.

Potentially Strong Surface Motion

Seismograph Mechanics

Seismographs rely on inertia. A heavy suspended weight stays still while Earth and the instrument frame shake around it, recording ground motion onto a rotating drum or digital sensor array.

Principle of Inertia

Triangulation & Travel Curves

S–P intervals are related to source distance through travel-time models or curves. Classroom circle intersection is a useful geometric approximation; operational earthquake locations use many phase arrivals, station geometry, velocity models, and uncertainty estimates.

Location Method

Question 1 of 5 Score: 0

Seismic Wave Lab EDUSIM v2.5

Virtual Station Seismograms

Primary (P) Waves

Secondary (S) Waves

Surface Waves

P–S Arrival Interval & Distance Calculation

Arrival Measurements Exercise

Epicenter Triangulation

Station Seismogram Data

Why a Third Distance Circle Helps:

Seismic Physics Parameter Explorer

Physical Variables

Model Simplifications Highlighted:

Focus vs. Epicenter

P-Waves (Primary)

S-Waves (Secondary)

Surface Waves

Seismograph Mechanics

Triangulation & Travel Curves

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