Earthquakes
Earthquakes release energy when rocks suddenly slip along faults.
About this topic
Earthquakes occur when stress built up in rocks along a fault is suddenly released, sending out seismic waves. The point of release underground is the focus, and the point above it on the surface is the epicentre. P-waves (fast, compressional) arrive first, S-waves (slower, shear) next, followed by the surface waves that do most damage.
Seismographs record them and the Richter or moment-magnitude scale measures size, a logarithmic scale. Tsunamis can result from undersea quakes. Earthquake-resistant buildings and early warning save lives.
Picture bending a stick until it snaps: the energy stored in the bending is released all at once, which is how a fault slips. A strong quake may slip by several metres along a fault tens or hundreds of kilometres long. Because the Richter and moment-magnitude scales are logarithmic, each whole number step means about 10 times larger ground motion and about 32 times more energy, so magnitude 7 releases roughly 1,000 times the energy of magnitude 5.
The time gap between P and S arrival gives the distance from a seismograph to the epicentre; using three stations, scientists triangulate the location. Early warning systems, like those in Japan and Mexico, use the fact that P-waves travel faster than the damaging S and surface waves, giving seconds to tens of seconds of notice to stop trains and shut gas lines. In an earthquake, remember to drop, cover and hold on. A common misconception is that the ground opens up and swallows people, or that we can predict exact times of quakes; scientists can estimate long-term probabilities but not specific dates. Magnitude measures energy, while intensity describes shaking effects at a place.
Key ideas
- Focus and epicentre
- P and S waves
- Magnitude and the Richter scale
Quick check
Use cases: where Earthquakes helps
- Homework: review the key idea behind Earthquakes before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Earthquakes without notes.
- Visual learning: play with the interactive lab to see how Earthquakes changes when you adjust its inputs.
- Teaching a friend: explain Earthquakes in your own words, then compare your version with the key ideas.
Earth science helps with weather forecasts, natural hazards, energy and climate planning.
Frequently asked questions
What is Earthquakes?
Earthquakes release energy when rocks suddenly slip along faults.
What will I learn in Earthquakes?
Focus and epicentre. P and S waves. Magnitude and the Richter scale.
Is Earthquakes part of Earth & Space?
Yes. It is one of 60 Earth & Space topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Earthquakes lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Earthquakes?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.