Click the map (with no tool selected) to probe a point.
The science
Rigid plates on a sphere. Each plate rotates about an Euler pole: velocity at position r is v = omega x r R, so speed = omega R sin(theta), largest 90 degrees from the pole. 1 cm/yr = 10 km/Myr = 0.09 degrees per Myr. Here every plate is defined by its speed and heading at a seed point, which puts its pole 90 degrees away. The speed slider scales all plates together; the default 5 cm/yr is the Earth-like preset.
Boundaries from relative motion. At a boundary cell with unit normal n (pointing from plate A to plate B) the relative velocity v_rel = v_A - v_B splits into a normal part c = v_rel . n and a tangential part. c > 0.35 |v_rel| is convergent, c < -0.35 |v_rel| divergent, otherwise transform. The denser side subducts: oceanic crust older than the neighbour goes down; continent against continent collides.
Ocean floor. New crust forms at ridges (age 0) and ages as it moves away: age = distance / spreading rate. Depth follows 2600 + 350 sqrt(age) m for young crust and 5651 - 2473 exp(-0.0278 age) m for old crust (Stein and Stein 1992); a hotter mantle makes the ridge shallower (about 1.4 m per degree here, illustrative).
Mountains. Where plates converge, crust is thickened: uplift rate U = 40 m/Myr per cm/yr of convergence close to the boundary, falling by 0.62 per cell (about 111 km) away, and erosion removes relief with a 25 Myr time constant, so steady height = U x 25 Myr (about 5 km for 5 cm/yr). Trenches are dips up to 3.4 km deep on the subducting side.
Earthquakes. Each live snapshot is a synthetic catalogue drawn along the current boundaries, weighted by relative speed (convergent 1.0, transform 0.8, divergent 0.25). Magnitudes follow Gutenberg-Richter, log10 N = a - b M with b = 1, from M 3 up to a cap per boundary type. The count is calibrated to about 247 for the Earth-like start and then scales with total boundary activity; real catalogues are far larger.
Volcanoes. Arc volcanoes sit 100-250 km behind the trench on the overriding plate, above the depth (about 100 km) where the slab releases water; their number scales with exp(dT / 220 C) and sqrt(speed). Six fixed hotspots add island chains that ride the plate away from the plume at the plate speed. The active count is calibrated to about 42 at the start.
Simplifications. Plate territories are Voronoi cells of moving seeds (continents get a bonus so coastlines are not eaten), crust area is not conserved, there is no slab dynamics and no mantle convection model, one grid cell is 111 km, coastlines are coarse, relief is vertically exaggerated and the cross-section is schematic. The dashboard is a teaching model, not a forecast.