Earthquake simulator and intensity scale
An online tool for working out how strongly an earthquake would be felt: set a magnitude and focal depth, drop the epicentre on the map, and see the intensity that reaches each city, what the record looks like on a seismograph, and what buildings of different heights do about it. Intensity comes from published USGS models rather than from guesswork, so the numbers can be checked against the real earthquakes in the list.
How to use it
Drag the magnitude and depth, or pick one of the real earthquakes — that loads its actual coordinates, depth and published rupture dimensions.
Click anywhere on the map. The contours redraw at once: white dashes show the rupture, coloured lines the boundaries between intensity degrees.
Search for it or press "Locate me". The card below then reports the intensity that reaches you and how many seconds it takes to arrive.
The seismogram shows the shape of the shaking, and the three buildings beneath it show why the same intensity means different things to a two-storey block and a twenty-two-storey tower.
Place an epicentre on the map and see how hard your city shakes
1The earthquake
2How far it reaches
The lines are isoseismals — boundaries between zones of equal shaking. For a large earthquake they stretch along the rupture rather than forming circles, because the energy leaves a long strip of fault rather than a point. The white dashes mark the rupture at the surface.
3What you would feel
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Settlements of 15,000 people and above (GeoNames): villages are absent, so an empty patch on the map does not mean nobody lives there. These figures are EXPOSURE — how many people fall inside each zone — not a forecast of casualties or damage.
4What it looks like on a seismogram
The record is synthetic: its shape and frequency content are computed from the seismic moment by Boore's stochastic method, and its level is pinned to the peak acceleration from the empirical chain. It is one plausible realisation rather than a prediction — "another realisation" shows how much two records differ at the same magnitude and distance. Measure the gap between the P and S marks, multiply by 8.2, and you have the distance to the source: that is genuinely how it is found.
5What buildings do about it
All three buildings are driven by the same record. Each answers at its own natural period — roughly a tenth of a second per storey — and if the record carries energy at that period, the building sways further than the ground did. That is why "how dangerous is it" has no single answer: in one earthquake a low block and a tower are having different experiences. The percentages are drift: roof displacement over height. The sway is exaggerated so it can be seen; the percentages are real.
6Energy and rupture
One unit of magnitude is 31.6 times the radiated energy and ten times the amplitude on a seismogram. So M7 is not "twice" M3.5 — it is nearly 180,000 times. Rupture dimensions come from the Wells & Coppersmith regressions; the real earthquakes above carry their published source dimensions instead.
7The intensity scale, degree by degree
| Degree | MMI | Acceleration | What happens |
|---|---|---|---|
| 1 | I | 0.05 %g | Not felt by people; recorded by instruments only. |
| 2 | II | 0.14 %g | Felt by a few people at rest, mostly on upper floors. |
| 3 | III | 0.62 %g | Felt indoors by some — much like a passing lorry. Hanging objects swing slightly. |
| 4 | IV | 2.8 %g | Felt by many indoors, by a few outdoors. Windows and dishes rattle, doors creak, parked cars rock. |
| 5 | V | 6.2 %g | Felt by nearly everyone; sleepers wake. Unstable objects overturn, small items fall, thin cracks appear in plaster. |
| 6 | VI | 11.5 %g | Felt by all, many run outdoors. Heavy furniture moves, plaster falls, weak buildings take slight damage. |
| 7 | VII | 21.5 %g | Cracks in masonry walls, tiles and cornices fall. Well-built structures are barely harmed; poorly built ones are damaged considerably. |
| 8 | VIII | 40.1 %g | Large cracks in walls, chimneys and cornices collapse, heavy furniture overturns. Some buildings become uninhabitable. |
| 9 | IX | 74.7 %g | Walls and floors collapse, weak buildings are destroyed, strong ones badly damaged. Buildings shift off their foundations. |
| 10 | X | 139.2 %g | Most buildings collapse, ground cracks open up to a metre wide, landslides start, bridges and dams are damaged. |
| 11 | XI | > 190 %g | Almost no masonry structure remains standing, bridges are destroyed, rails bend, underground services are cut. |
| 12 | XII | > 190 %g | Damage is total, the landscape itself changes, river courses shift, objects are thrown into the air. |
MMI — and its near-twin МСК-64, the scale used across the post-Soviet world — measure how hard the ground shook where you stood. Magnitude is a different quantity entirely: how much energy the source released, one number for the whole earthquake. That is why "magnitude 6 — how many degrees is that?" has no single answer: VIII–IX above the source, III two hundred kilometres away.
Models: intensity — Allen, Wald & Worden (2012); acceleration and velocity — Worden et al. (2012); rupture dimensions — Wells & Coppersmith (1994); record synthesis — the stochastic method of Boore (2003) with the two-corner source of Atkinson & Silva (2000). Cities — GeoNames (CC BY 4.0). Site conditions are not modelled.
