Tectonic Plates
Seven major plates plus the largest of the minor plates. Tap any plate.
Plate Boundaries
Three flavors. Each produces a distinctive seismic and volcanic signature.
Earthquakes
Magnitude vs intensity, focal mechanisms ('beachballs'), and a list of the largest recorded.
Magnitude (logarithmic)
Each whole-number magnitude step releases ~32× more energy than the previous one. M9.0 → M8.0 means 32× weaker, not 12% weaker.
M3: rarely felt · M5: indoor objects shaken · M7: serious damage · M8+: destructive over hundreds of km · M9+: mega-thrust, only at convergent boundaries.
Intensity (Modified Mercalli, MMI)
Rates effects at a specific location, I (not felt) → XII (total destruction). One quake has many MMI values — strongest near the epicenter, weaker farther away.
Magnitude is the source's energy; intensity is how it shook a given place. A small shallow quake right under your feet can produce higher MMI than a deep distant M8.
Largest recorded earthquakes
Focal mechanism ("beachball")
Beachballs encode fault geometry. The four quadrants alternate compressional (filled) and tensional (white) — the geometry tells you whether the fault was strike-slip, normal, or reverse.
Strike-slip
Lateral motion. San Andreas, North Anatolian.
Reverse / thrust
Compression. Subduction megathrusts, Himalaya.
Normal
Extension. Mid-ocean ridges, basin & range.
Volcanoes
Five main types and the VEI scale. Eruption style depends on silica content and dissolved gas.
Geologic Time Scale
Earth is 4.6 billion years old. The whole of recorded human history takes the last ~5,000 years — the thickness of a hair on this scale.
Key events
Continental Drift
Drag the slider to scrub from Pangaea to today. Plate motion is centimetres a year, but compounded over hundreds of millions of years it rearranges the world.
Time: 250 Ma
Drill
Plate from feature, boundary type, period from event, volcano type.
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Daily Challenge
Eight questions. Same set for everyone, new at midnight local time.
Today's set
Question 1 / 8