Earthquake simulator
Put an epicentre anywhere on Earth, choose a magnitude, and watch the shaking spread over a real map — with an estimate of how many of the people living there it would kill.
Open the earthquake simulatorWhat this simulator does
Click any point on the map — a city centre, a fault line, the middle of nowhere — and set a magnitude between 4.0 and 9.5. The simulator places the quake 8 km below the point you clicked and draws five rings around it, one for each level of shaking on the Modified Mercalli scale, from intensity V (everyone feels it) to IX and above (buildings collapse).
It then counts the towns inside each ring, takes their real population from OpenStreetMap, and estimates a death toll. You can run the same magnitude on Tokyo, Istanbul, Lima and San Francisco in under a minute and see how differently the numbers land.
Why buildings matter more than magnitude
Earthquakes do not kill people; collapsing buildings do. That is why the simulator asks you to choose the construction quality, and why it changes the answer so violently:
- Modern codes — deaths multiplied by 0.06
- Average — deaths multiplied by 1
- Poor — deaths multiplied by 7
The real world supplies the proof. In 1994 a magnitude 6.7 quake struck Northridge, California, and killed 57 people. In 2010 a magnitude 7.0 hit near Port-au-Prince, Haiti, and killed somewhere between about 46,000 and 316,000, depending on whose estimate you trust. The Haitian quake released roughly twice the energy; it killed a thousand times more people.
Magnitude is not intensity
These two numbers get mixed up constantly, and the difference is the whole point of the map.
Magnitude measures the energy released at the source. There is one magnitude per earthquake, and each whole step up is about 32 times more energy: a magnitude 8 releases roughly a thousand times the energy of a magnitude 6.
Intensity describes how hard the ground actually shakes at one particular place, on a scale of I to XII, and it falls off with distance. A magnitude 7.5 quake can be intensity IX at the epicentre, VII in a city 50 km away and barely noticeable 300 km further on. The coloured rings on the map are intensity, which is why they get weaker as they spread.
Scenarios worth trying
Each link opens the simulator with the scenario already loaded:
- Magnitude 7.9 under Tokyo — the 1923 Great Kantō magnitude, but under today's building codes
- Magnitude 7.4 under Istanbul — the quake seismologists expect on the North Anatolian Fault
- Magnitude 7.0 near Port-au-Prince — the 2010 catastrophe
- Magnitude 7.9 under San Francisco — a repeat of 1906
What is behind the numbers
Shaking weakens with distance using the site's own attenuation formula, which trades precision for the ability to run instantly in a browser. Population and town boundaries come from OpenStreetMap. Each intensity ring carries a share of people killed, multiplied by the construction factor above.
What the model deliberately leaves out: a large real earthquake does not rupture a point but a fault tens or hundreds of kilometres long; soft sediment can double the shaking while hard rock damps it; landslides, liquefaction, fires and tsunamis often kill more people than the shaking itself. Treat every number as an order of magnitude, not a forecast, and never as a judgement about a particular building.
The full method, with every constant, is written out on the how it works page.
Questions
Can this predict an earthquake?
No, and nothing else can either. Seismologists can say which faults are loaded and roughly how often they break, but not when. This tool is for comparing scales, not for forecasting.
What is the largest earthquake possible?
The largest ever recorded was magnitude 9.5 in Chile in 1960, which is why the slider stops there. Magnitude is limited by how much fault can break at once, and only the longest subduction zones — Chile, Alaska, Cascadia, Japan, Sumatra — can produce a 9.
Why does my city show zero deaths?
Either the shaking never reaches the intensity that hurts people, or OpenStreetMap has no population for the towns inside the rings. Sparsely mapped regions will under-report.
Does depth matter?
Enormously, and the simulator fixes it at 8 km — a shallow crustal quake, the kind that does the most damage. A magnitude 7 at 600 km depth is felt over a huge area but rarely destroys anything.
Further reading: The strongest and deadliest earthquakes — and how magnitude really works
Open the earthquake simulator