The ground beneath you feels like the most solid thing in existence — until, in seconds, it ripples like water, buildings sway, and the most fundamental assumption of daily life collapses. Earthquakes are the planet reminding us that the “solid” ground is a thin, cracked shell floating on a churning interior. What causes them is a story of colossal forces, stuck faults, and sudden release — and it is more comprehensible than you might think.
The engine: plate tectonics
Earth’s outer shell — the lithosphere, roughly 100km thick — is broken into about a dozen major tectonic plates that drift on the hot, slowly flowing mantle below, moving a few centimetres a year (about as fast as your fingernails grow). This motion is driven by the planet’s internal heat. Where plates meet, interact and grind, stress accumulates — and earthquakes are what happens when that stress finally overcomes friction.
The classic analogy: bend a stick slowly. It flexes, storing elastic energy, until it snaps — releasing the energy all at once. Faults do exactly this. Two blocks of rock locked together by friction bend over decades or centuries as plates push, then rupture in seconds, slipping metres in an instant. The rupture point underground is the focus (or hypocentre); the point on the surface above it is the epicentre. The slipping releases seismic waves that radiate outward — the shaking you feel.
The three types of plate boundary
Convergent (colliding): plates push together; one dives beneath the other in subduction. These produce the monsters — the 2004 Sumatra (magnitude 9.1) and 2011 Japan (9.1) quakes, both subduction events that generated devastating tsunamis. Divergent (spreading): plates pull apart, as in Iceland and mid-ocean ridges — frequent but usually smaller quakes. Transform (sliding past): plates grind sideways, as along California’s San Andreas Fault — capable of major quakes when long-locked segments rupture.
Measuring the violence: magnitude vs intensity
Magnitude measures energy released at the source — each whole number is about 32 times more energy (a magnitude 7 releases roughly 32 times the energy of a 6). The moment magnitude scale has no upper limit, though Earth’s rocks cannot store enough stress for much beyond 9.5 (Chile, 1960). Intensity measures shaking effects at a location — the same quake is violent near the epicentre and a gentle sway far away. Depth matters enormously: a shallow magnitude 6 under a city devastates; a deep magnitude 7 under the ocean may barely be felt.
Foreshocks, aftershocks and swarms
Big quakes rarely come alone. Foreshocks sometimes precede the mainshock (but are only identifiable afterwards — a cruel limitation). Aftershocks — the fault settling into its new position — can continue for months or years, occasionally rivalling the mainshock. The 2011 Japan quake produced thousands. This sequence is why earthquake response is a marathon: the danger does not end when the first shaking stops.
Do earthquakes happen in the UK?
Yes — about 200–300 are detected in the UK each year, though most are too small to feel. Britain sits mid-plate, far from boundaries, but ancient faults still occasionally release stress. The largest in recent times: the 2008 Market Rasen quake (magnitude 5.2), felt across England and Wales, damaging chimneys and walls. The UK’s biggest historical quake, the 1931 Dogger Bank event (magnitude 6.1), was offshore. British building codes and geology make damaging quakes rare, but not impossible — the British Geological Survey monitors them continuously.
If you travel to quake-prone regions — Japan, California, Turkey, Greece, Italy, New Zealand — know the drill: drop, cover and hold on under sturdy furniture; stay indoors away from windows; if outside, move to open ground away from buildings. Never run outside during shaking (falling masonry kills). After: expect aftershocks, check for gas leaks, and follow local guidance. The British Red Cross publishes emergency preparedness advice for travellers. Travellers should also know the practicalities — our guide to what to do if your passport is lost abroad covers the document chaos that follows any travel disruption, and claiming compensation for delayed flights applies when quakes close airports.
Can we predict earthquakes?
Honestly: no, not in any useful way. Seismologists can forecast probabilities over decades (“a 60% chance of a major quake in this region in 30 years”) but cannot predict the day, hour or exact location. Promising avenues — foreshock patterns, animal behaviour, electromagnetic signals — have all failed rigorous testing. What works is early warning: seismic waves travel slower than electronic signals, so systems in Japan, Mexico and California give seconds to tens of seconds of warning — enough to stop trains, halt surgery and take cover. Seconds save lives when millions get them.
The real defence is engineering: strict building codes, retrofitted masonry, flexible foundations. The difference between a magnitude 7 in Haiti (2010: ~200,000 dead) and a similar one in Japan is almost entirely buildings. Earthquakes do not kill people; collapsing buildings do — which makes earthquake safety, at heart, a construction problem we know how to solve.
Tsunamis: when quakes move the sea
The deadliest earthquake effect is often not shaking but water. When a subduction-zone quake vertically displaces the seafloor — one side of the fault lurching upward by metres — it shoves the entire water column above it. That displacement becomes a tsunami: not a single wave but a series, travelling at jet speeds (up to 800 km/h) in deep ocean with barely a ripple on the surface, then rearing up to devastating heights as the seafloor shoals near coast. The 2004 Indian Ocean tsunami killed ~230,000 people across 14 countries; Japan 2011’s reached 40 metres in places. Warning signs: strong shaking lasting more than 20 seconds near the coast, or the sea suddenly receding — if you see the ocean pull back, run to high ground immediately; do not wait for sirens. The UK’s tsunami risk is minimal (the 1755 Lisbon quake sent a small wave to Cornwall), but British travellers to the Pacific Ring of Fire, Indonesia and the Indian Ocean should know the signs — they are the difference between life and death.
Earthquake apps and alerts
For travellers to quake-prone regions, a few free tools add real safety. QuakeFeed and the USGS Earthquake Map show global seismic activity in near real-time — useful for situational awareness after a tremor. MyShake (California) and Japan’s Yurekuru Call deliver early-warning alerts seconds before shaking arrives — seconds that matter. The British Geological Survey’s website lets you report UK tremors you felt, contributing to citizen seismology. Download and configure these before you travel, not during the emergency.
Frequently Asked Questions
What causes earthquakes?
Stress building up along faults as tectonic plates move, released suddenly when friction is overcome. The rupture sends seismic waves outward — the shaking. Most occur at plate boundaries; some occur mid-plate on ancient faults.
What is the difference between magnitude and intensity?
Magnitude measures energy released at the source (each whole number ≈ 32× more energy). Intensity measures shaking effects at a given location, which depend on distance, depth and local geology.
Can scientists predict earthquakes?
No — not the time, place and size of specific quakes. Long-term probability forecasts work, and early-warning systems give seconds of alert after a quake starts, but reliable short-term prediction remains impossible.
Does the UK get earthquakes?
Yes — 200–300 detected yearly, though rarely felt. The 2008 Market Rasen quake (magnitude 5.2) was the largest recent one. The UK’s mid-plate position makes damaging quakes uncommon but not impossible.
What should I do during an earthquake?
Drop, cover and hold on under sturdy furniture, away from windows. Do not run outside during shaking. If outdoors, move to open ground away from buildings. Expect aftershocks afterwards.
