10 Earthquake News Terms Explained

Earthquake News Terms: Why 'Magnitude' Alone Doesn't Tell You the Damage

From magnitude and intensity to aftershocks, liquefaction, and tsunamis — ten official terms for reading earthquake news accurately.

The most common mistake in earthquake coverage is judging local damage or a building's safety from one number like 'magnitude 5.2.' Magnitude is a single figure for the energy released at the source, while intensity is how strongly the shaking was actually felt in a given place — it varies by distance from the epicenter and ground conditions even for the same quake. Mixing the two up lets one headline number badly mislead you.

This list untangles that with ten official terms: magnitude, intensity, hypocenter, and epicenter, then mainshock, foreshock, and aftershock, faults, seismic design, liquefaction, long-period ground motion, and tsunamis — each with its meaning, context, and a common misunderstanding. Order follows how often each shows up right after a quake, so read #1-4 after breaking news, or jump to #7 for building safety.

Selection criteria

Only terms official agencies actually use.
Ranked by frequency in breaking coverage and how foundational each is.
Each entry flags a common misreading.

Magnitude

Magnitude is a single number for the total energy an earthquake released at its source. Each one-point increase reflects a dramatically larger jump in energy, so even a small difference in the number means a much bigger difference in force. News reports use it to compare quakes, but the same magnitude can still produce very different local intensity.

Intensity

Intensity rates how strongly people and structures actually experienced shaking in a specific place, reported region by region. The closer an area is to the epicenter and the softer its ground, the higher intensity tends to register. The same quake can be reported at different intensity levels across regions, so read local figures with that in mind.

Hypocenter

The hypocenter is the point underground where a fault slipped and the rupture actually began. Its depth affects how strongly seismic waves reach the surface — a shallower hypocenter at the same magnitude often means stronger surface shaking. It's distinct from the epicenter, the surface point shown on maps.

Epicenter

The epicenter is the surface point directly above the hypocenter — the coordinate shown on earthquake maps or in phrases like 'waters near [region].' It isn't where the rupture itself started; the hypocenter usually sits deeper underground than the epicenter marked above it.

Mainshock, foreshock, and aftershock

Among quakes clustered close together along one fault, the largest is the mainshock, with earlier ones called foreshocks and later ones aftershocks. Whether a quake was a foreshock can't be known until a larger one hits, and aftershock timing and size can't be predicted — so stay prepared for continued shaking after a major quake.

Fault

A fault is a geological structure where rock has cracked and shifted out of alignment under stress. Earthquakes happen when built-up stress along a fault finally releases, which is why faults appear constantly in cause explanations and surveys — but a fault's existence alone doesn't reveal when or how large the next quake will be.

Seismic design

Seismic design means a building was engineered to withstand earthquake loads and resist collapse. You can estimate whether it applies from the occupancy approval date in the building registry, but actual condition also depends on maintenance and any retrofitting. The label alone doesn't let anyone judge a building's current safety.

Liquefaction

Liquefaction happens when loose, water-saturated sandy ground momentarily loses the strength holding its particles together under strong shaking. Investigators flag it when ground has subsided or sand and water have surfaced. It's worth remembering it doesn't occur in every soft-soil area during every earthquake.

Long-period ground motion

Long-period ground motion is slow, drawn-out shaking that continues rather than ending quickly, affecting tall structures more because their natural sway period is longer. Depending on ground conditions, it can amplify even far from the hypocenter, so magnitude alone can't tell you how a specific high-rise fared.

Tsunami

A tsunami is a series of waves reaching the coast after an undersea earthquake or seafloor shift moves a large body of ocean water. It's the concept behind coastal warnings, evacuation guidance, and all-clear notices — and it's a mistake to assume the first wave is always strongest, or that the sea must visibly recede first.

What to check, in order, during a quake

If you feel shaking, your body comes before any number. Drop and take cover under something sturdy, protect your head and neck, and move toward an exit only once shaking fully stops. Call 119 immediately for injury, fire, or collapse risk, and stay outside afterward in case of aftershocks (#5).

Once safe, check magnitude (#1) and intensity (#2) for how hard your area was hit, and watch for tsunami (#10) warnings near the coast. For building safety or liquefaction (#8) concerns, get a professional inspection rather than judging it yourself. Always follow official agency guidance first.

Frequently asked questions

What's the actual difference between magnitude and intensity?

Magnitude is a single value for the energy an earthquake released; intensity is how strongly people and buildings actually experienced the shaking in a specific place. The same quake can produce very different intensity readings depending on distance from the epicenter and local ground conditions, so check the region-by-region intensity report from your national weather agency.

Can you predict when or how strong an aftershock will be?

No — the exact timing and magnitude of aftershocks can't be reliably predicted in advance. After a major quake, prepare for continued shaking, but rely on ongoing updates from official agencies rather than any claim that pins down a specific date or size.

If a building has seismic design, is it automatically safe?

Seismic design means the structure was engineered to withstand earthquake loads — it doesn't by itself let anyone judge the building's current condition. Check the occupancy approval date and maintenance history in the building registry, and get a professional inspection when it matters.

What should I do when a tsunami warning is issued?

If you're in a low-lying coastal area, move to higher ground or a designated evacuation site as soon as a tsunami (#10) warning is issued. The first wave isn't always the weakest, and later waves can be larger, so don't return to the coast until an official all-clear is announced.

Where does liquefaction tend to happen?

It's most likely on soft ground like reclaimed land or riverside areas with loose, water-saturated sandy soil, when it experiences strong shaking. Ground subsidence or sand and water surfacing are the typical signs investigators look for, but soft ground doesn't guarantee liquefaction in every earthquake.

Why do high-rises sometimes shake hard from a distant earthquake?

Long-period ground motion (#9) can travel to locations far from the hypocenter, and when it resonates with a high-rise's own long natural sway period, the shaking can last longer or grow stronger. Even so, magnitude alone can't predict how a specific building will actually be affected.

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Selection criteria

MagnitudeUpvote

IntensityUpvote

HypocenterUpvote

EpicenterUpvote

Mainshock, foreshock, and aftershockUpvote

FaultUpvote

Seismic designUpvote

LiquefactionUpvote

Long-period ground motionUpvote

TsunamiUpvote