Quick answer
Magnitude describes the size of an earthquake at its source. Depth describes where the rupture starts below the surface. Intensity describes shaking at a particular place. These are different measurements: neither a magnitude nor a depth alone tells you what happened to a building or community.
Use this overview to choose a focused guide, then explore source records on the earthquake map. For local historical comparisons, browse earthquakes by city.
Magnitude and intensity are not the same
Compare three questions: how large was the source, how deep did it start, and how strong was the shaking here? A source report can give one preferred magnitude while an intensity map contains many local values. Read the intensity scale guide for the distinction.
What the Richter scale actually measures
Local magnitude, ML, was developed for recordings made under particular instrument and distance conditions. “Richter” is often used casually for every magnitude, but that hides meaningful differences between methods. See Richter versus moment magnitude.
Why moment magnitude Mw is preferred for large earthquakes
Moment magnitude describes earthquake size through seismic moment and remains useful for very large ruptures where some older wave-amplitude scales saturate. USGS can report several magnitude types. The magnitude scale guide explains what to compare.
How seismic moment and Mw are calculated
Seismic moment combines rock rigidity, rupture area and average slip: M₀ = μ × A × D. Moment magnitude is a logarithmic conversion of that moment. These are source estimates with uncertainty, not a direct measurement of damage. The measurement guide explains the observations behind them.
Why a one-unit magnitude increase is a large change
One unit corresponds approximately to ten times wave amplitude and about 32 times energy in the usual comparison. Those ratios do not mean ten or 32 times the damage. Exposure, depth, distance and construction matter separately; the energy illustration above compares source size only.
Why several magnitude types still exist
ML, mb, Ms and Mw use different observations or calibrations. Negative magnitudes are possible for small signals relative to the scale’s reference level; they do not mean negative energy. Keep the source’s magnitude type when comparing records and avoid relabeling every value “Richter.”
How earthquake depth is measured
Depth belongs to the hypocentre, the underground starting point of rupture. The epicentre is its surface projection. Networks estimate depth together with location and origin time; some solutions use constrained depths. Read epicentre versus hypocentre.
Shallow, intermediate and deep earthquakes
A common grouping is shallow below 70 km, intermediate from 70 to 300 km, and deep beyond 300 km. These are depth categories, not danger categories. Borderline values and preliminary solutions may change. The earthquake depth guide provides more context.
Why depth changes the shaking people experience
Depth influences how seismic waves reach the surface, but the resulting shaking also depends on rupture geometry, distance, ground conditions and buildings. A deeper event is not automatically harmless, and equal magnitudes do not guarantee equal effects.
Intensity scales: MMI, JMA and EMS-98
MMI, Japan’s JMA intensity scale and EMS-98 describe local shaking or its observed effects using different definitions. Their numbers are not interchangeable with magnitude, and matching numerals do not establish a direct conversion between scales.
ShakeMap, Did You Feel It? and PAGER
ShakeMap combines observations and models of ground motion. Did You Feel It? uses submitted experiences. PAGER estimates potential impacts using shaking and exposure information; it is not an earthquake magnitude. Read how to interpret a USGS report.
Volcano scales: VEI, alert levels and aviation color codes
VEI describes explosive eruption size, whereas volcano alert levels and aviation colour codes communicate different source-defined conditions. An activity notice is not proof of an eruption. Keep the issuing authority and timestamp attached rather than converting these systems into one universal risk score.
Why GDACS colors mean something different
GDACS colours concern its own humanitarian-impact assessment framework. They do not convert directly into MMI, magnitude, VEI or a local warning. Earthquake24’s current production pipeline does not ingest GDACS; the methodology identifies the active sources.
How to read an Earthquake24 event
Start with the source time, magnitude type, reported depth and review status. Open the original record to examine revisions and available products. On our globe, marker size represents magnitude; a selected pulse is only a visual cue, not a measured felt area or damage boundary.
Common questions
Does reviewed mean final?
No. Sources can revise reviewed records as new evidence arrives.
Does a missing field mean zero?
No. An unavailable intensity, felt-report count or impact product must not be presented as proof that nothing was felt or affected.
Where should I go next?
Browse all earthquake guides, learn about aftershocks or return to the live earthquake tracker. Earthquake24 provides source-attributed information, not predictions or official alerts.