Tsunami Lab

Rupture the seafloor and follow a real shallow-water wave simulation across the basin, up the shelf and onto the beach.

Playback speed 10 min / s

Source and seafloor

Source type Magnitude / uplift M8.5 · 3.9 m Ocean depth 4,000 m

Shelf width 150 km Coast slope 0.5 %

Drag on the map to move the epicentre. Changing a slider restarts the event.

Readouts

Hover depth: —
Wave speed: —
Wavelength: —
Wave period: —
Max run-up (coast): —
Run-up at town: —
Predicted arrival at town: —
Warning time: —

Warning time = predicted arrival minus ~10 min for detection and alerting.

Tide gauges (0/4)

Switch to “Click: tide gauge” (or Shift+click) and click the water to place up to four gauges.

Show

Arrival contours Distance rings Max-height envelope Absorbing zone

What am I seeing?

A tsunami is a long wave: its wavelength (tens to hundreds of km) is far larger than the ocean depth, so the whole water column moves together and the wave speed is c = √(g·h). At 4,000 m that is about 700 km/h, a jet airliner. At 10 m it drops to about 36 km/h.
The simulation solves the nonlinear shallow-water equations on a 200 × 140 staggered grid (8 km cells) with a forward-backward finite-difference scheme, a CFL-limited time step, Manning friction and simple wetting and drying at the shore.
Shoaling: as depth falls the wave slows, its front compresses, and energy conservation makes the height grow roughly as h^−1/4 (Green’s law). A 0.5 m open-ocean wave can reach several metres at the coast. Watch the amplitude in the cross-section view.
Refraction: the part of a wavefront over shallower water slows first, so fronts bend towards the coast and around seamounts and islands. Arrival-time contours are computed with an eikonal solver on the same depth map.
Run-up: the wave pushes up the beach. Steeper coasts reflect more, gentle shelves slow and amplify more. Wider shelves give a later but often larger arrival.
The open sides of the basin are absorbing (sponge layers). The coast reflects, so waves bounce back and trap along the shelf for hours. The first wave is often not the largest.
Educational model: no dispersion, no tides, no real bathymetry. Cell size (8 km) is much coarser than a real beach, so run-up is indicative only, and the magnitude, uplift and period scalings are simplified.