# What Causes Earthquakes?

> Earthquakes happen when stress built up in the Earth's crust is suddenly released along faults. This guide explains plate tectonics, how magnitude is measured, and the safety steps that genuinely help.

*Section: Science — By Dr. Nadia Okoro (Science & Health Writer) — Published January 15, 2026 — 4 min read*

Canonical URL: https://dailyjunction.co.uk/science/what-causes-earthquakes
Tags: earthquakes, plate tectonics, geology, magnitude, seismology

## Key takeaways

- Most earthquakes occur when rock under stress suddenly slips along a fault, releasing energy as seismic waves.
- The driving force is plate tectonics: the slow movement of the large plates that make up Earth's outer shell.
- Magnitude measures the energy released and is logarithmic, so each step up is a large jump in size.
- The focus is where the quake starts underground; the epicentre is the point directly above it on the surface.
- Simple preparation, such as 'Drop, Cover and Hold On', meaningfully improves safety during shaking.

An earthquake is the sudden shaking of the ground caused by the rapid release of energy stored in the Earth's crust. That energy builds up slowly over years or centuries as giant slabs of rock push against one another, and is let go in seconds when the rock finally slips.

## What an earthquake is

An **earthquake** is a sudden release of energy within the Earth that creates **seismic waves** — vibrations that travel through the ground and make it shake. Most earthquakes are caused by the movement of rock along a **fault**, a fracture in the Earth's crust where two blocks of rock can move past each other.

To understand why faults slip, you have to start with the structure of the planet itself.

## Plate tectonics: the engine behind earthquakes

The Earth's rigid outer shell, called the **lithosphere**, is not one continuous piece. It is broken into about a dozen large pieces, plus many smaller ones, known as **tectonic plates**. These plates float on the hotter, slowly flowing rock of the mantle beneath, and they move — only a few centimetres a year, about as fast as your fingernails grow, but relentlessly.

Most earthquakes happen at or near the **boundaries** where plates meet. There are three main kinds of boundary:

- **Convergent** — plates push together; one may dive beneath the other. These produce some of the largest earthquakes.
- **Divergent** — plates pull apart, often along the ocean floor, allowing new crust to form.
- **Transform** — plates slide horizontally past each other, such as along California's San Andreas Fault.

At these boundaries, friction can lock the rock so the plates do not slide smoothly. Stress builds. When the stress exceeds the strength of the rock, it ruptures and slips suddenly — and that is an earthquake. The same slow plate movements that cause quakes also build mountains and drive volcanic activity.

> Think of bending a wooden ruler. It resists, stores energy, then snaps all at once. The Earth's crust does something similar, on an enormous scale.

## Focus, epicentre and aftershocks

Two terms describe where a quake happens:

- The **focus** (or hypocentre) is the point underground where the rupture begins.
- The **epicentre** is the point on the surface directly above the focus — usually where shaking is strongest.

After a large earthquake, a sequence of smaller quakes called **aftershocks** often follows as the crust adjusts. These can continue for days, weeks or longer, and occasionally cause additional damage to already weakened buildings.

## Measuring earthquakes: magnitude and intensity

People often talk about earthquakes in terms of the "Richter scale", but seismologists today generally use the **moment magnitude scale**, which better captures the size of large quakes.

The crucial thing to understand is that magnitude is **logarithmic**. Each whole number up represents roughly:

- about **10 times** more ground shaking, and
- about **32 times** more energy released.

| Magnitude | Typical effect |
| --- | --- |
| Below 2.0 | Not felt; recorded by instruments only |
| 2.0 to 3.9 | Often felt, rarely causes damage |
| 4.0 to 5.9 | Felt widely; can cause minor to moderate damage |
| 6.0 to 6.9 | Can be destructive in populated areas |
| 7.0 and above | Major earthquake; serious, widespread damage possible |

Magnitude is one number for the whole quake. **Intensity**, by contrast, describes how strongly shaking is felt at a specific place, and depends on distance from the epicentre, the depth of the focus, and local ground conditions — soft ground can amplify shaking considerably.

## Can earthquakes be predicted?

Not in the way people often hope. Scientists cannot reliably forecast the exact time, location and size of a future earthquake. What they can do is map fault zones, study past activity, and estimate the long-term probability of quakes in a region. This is enough to inform **building codes**, land-use planning and emergency preparedness, which save lives even without precise prediction.

Some areas also have **early warning systems** that detect the first, faster seismic waves and send alerts seconds before the stronger shaking arrives — a short window that can be enough to take cover or halt trains.

## Staying safe

Preparation genuinely reduces harm. The internationally promoted advice for when shaking begins is:

1. **Drop** to your hands and knees so you are not knocked over.
2. **Cover** your head and neck, and shelter under sturdy furniture if you can.
3. **Hold on** to that shelter until the shaking stops.

Other sensible steps include securing heavy furniture to walls, knowing how to turn off utilities, keeping an emergency kit, and avoiding windows and exterior walls during a quake. Do not run outside while the ground is moving — most injuries come from falling objects.

Like other natural hazards, earthquakes are part of the larger story of how a dynamic planet behaves, a story that also includes [the greenhouse effect](/environment/what-is-the-greenhouse-effect) and the deep-time processes behind [evolution](/science/the-theory-of-evolution-explained).

## The bottom line

Earthquakes are caused by the sudden release of stress that builds up as the Earth's tectonic plates grind against one another, usually along faults near plate boundaries. Magnitude measures the energy released on a logarithmic scale, while intensity describes the shaking felt at a given spot. We cannot predict individual quakes, but plate tectonics explains where they cluster — and simple preparation, summed up as Drop, Cover and Hold On, makes a real difference. The forces involved are the same ones that shape continents and mountains, part of the broader study of how matter and gravity behave across the universe — from the ground beneath our feet to [black holes](/science/what-is-a-black-hole) in deep space.

## Frequently asked questions

### What actually causes an earthquake?

The Earth's outer shell is broken into moving plates. Where they meet, friction can lock the rock in place while stress builds. When that stress exceeds the strength of the rock, it slips suddenly along a fault and releases energy as seismic waves, which we feel as an earthquake.

### What is the difference between magnitude and intensity?

Magnitude measures the energy released at the source and is a single number for each quake. Intensity describes how strongly the shaking is felt at a particular place, which varies with distance, depth and local ground conditions.

### Can scientists predict earthquakes?

Scientists cannot yet predict the exact time, place and size of an individual earthquake. They can, however, identify high-risk zones and estimate long-term probabilities, which is why building codes and preparedness matter so much.

### What should I do during an earthquake?

The widely recommended advice is to Drop to the ground, take Cover under sturdy furniture, and Hold On until the shaking stops. Stay away from windows, and do not run outside while the ground is moving.

## Sources

- [United States Geological Survey: Earthquakes](https://www.usgs.gov/programs/earthquake-hazards)
- [British Geological Survey: Earthquakes](https://www.bgs.ac.uk/discovering-geology/earth-hazards/earthquakes/)
- [Great ShakeOut Earthquake Drills](https://www.shakeout.org/)

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