Earthquake Guide
Earthquakes strike without warning — pick a topic above, or start with the safety guide.
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What is an earthquake?
An earthquake is the sudden slip of rock along a fault — a fracture in the Earth's crust where stress has been building for years to centuries. When the stress exceeds the strength of the rock, it releases in seconds as seismic waves that radiate outward and shake the ground.
The rupture starts at the hypocenter (focus) at depth; the point on the surface directly above it is the epicenter — the location shown on our live map.
Our network locates an event by comparing wave arrival times across many stations — with enough stations, an epicenter can be published in under 90 seconds.
P waves & S waves
P waves arrive first, S waves follow with the stronger shaking — the gap between them is what makes early warning possible.
Where earthquakes happen
The Earth's outer shell is broken into a dozen large tectonic plates that move a few centimeters per year — about as fast as fingernails grow. Nearly all earthquakes occur on the boundaries where plates meet, which is why events on the live map trace such clear lines.
- Convergent (subduction) — plates collide and one dives beneath the other. Produces the planet's biggest quakes and tsunamis (Japan, Chile, Sumatra).
- Divergent (ridges) — plates pull apart at mid-ocean ridges. Frequent but mostly moderate, shallow events (Mid-Atlantic Ridge).
- Transform (strike-slip) — plates slide past each other. Shallow quakes that can be very damaging near cities (San Andreas, North Anatolian).
Magnitude vs Intensity an earthquake's "size" and its "impact" are different things
- The energy released at the source
- Same value worldwide, measured by seismometers
- +1 magnitude ≈ 32× more energy
- How strongly people and buildings feel it
- Different at every location
- Fades with distance and depth
We report moment magnitude (Mw), today's standard scale. It is logarithmic: each whole step means about 10× larger ground motion and ~32× more energy — so an M 7 releases roughly 1,000× the energy of an M 5.
The magnitude scale
Typical effects and how often each class occurs worldwide.
| Class | M | Typical effects | Per year |
|---|---|---|---|
| Minor | 2–3.9 | Often felt, rarely causes damage | > 100,000 |
| Light | 4–4.9 | Noticeable shaking, minor damage | ~ 13,000 |
| Moderate | 5–5.9 | Damage to weak structures | ~ 1,300 |
| Strong | 6–6.9 | Destructive near the epicenter | ~ 130 |
| Major | 7–7.9 | Serious damage over wide areas | ~ 15 |
| Great | 8+ | Catastrophic; can trigger tsunamis | ~ 1 |
Key Terms
The vocabulary you'll meet on this platform and in the news.
Frequently Asked Questions
Why do earthquakes happen?
Tectonic plates constantly push against each other, storing stress in the rock along faults. When the stress exceeds the rock's strength, the fault slips suddenly — releasing the stored energy as seismic waves. That slip is the earthquake.
Can earthquakes be predicted?
No — no method reliably predicts the exact time, place, and size of a future quake. What science can do is forecast probabilities (like aftershock forecasts) and issue early warnings seconds before strong shaking arrives, using the fast P wave.
How do earthquake alerts work?
Stations near the epicenter detect the first P waves, estimate location and magnitude within seconds, and broadcast a warning that races ahead of the slower, damaging S waves — giving seconds to tens of seconds of notice.
How long do aftershocks last?
Days to months — occasionally years after a very large mainshock. They become less frequent with time, but a large aftershock can still damage buildings weakened by the mainshock, so stay cautious around damaged structures.
Do many small quakes prevent a big one?
Unfortunately not. Magnitude is logarithmic: it takes about 32,000 M 3 events to release the energy of a single M 6. Small quakes barely relieve the stress that drives large ones.
Does earthquake-resistant design really work?
Yes — it is the single most effective way to save lives. Modern seismic codes let buildings flex and dissipate energy instead of collapsing, which is why similar quakes cause vastly different damage in different countries.
Small habits now build big safety later.
Earthquakes are hard to predict — but easy to prepare for. Know what to do in each situation and keep your emergency kit ready.
Get under a sturdy table, protect your head, and hold on until the shaking stops. Stay away from windows.
Move away from façades, glass, and power lines to open space — falling debris causes most street injuries.
Stop clear of bridges, overpasses, and tunnels. Stay in the car until the shaking ends, then drive carefully.
Press every floor button, exit at the first floor that opens, and use the stairs — never an elevator — to evacuate.
Emergency Kit Checklist
Prepare it together with your family — check what you already have.
Is your home ready?
Three things to check this week.