Earthquake magnitude vs. intensity
Summary
Magnitude is one number for an earthquake's size; each whole-number step means 10x the measured wave amplitude and about 32x the energy. Intensity (Modified Mercalli, Roman numerals) is the shaking at a given place and varies by distance, depth, and local ground. Moment magnitude (Mw) has largely replaced the Richter scale.
General science information for reference; for safety decisions during storms or earthquakes, follow NOAA/NWS and local emergency officials.
Facts
- id: F1 claim: An earthquake has a single magnitude, but shaking intensity varies from place to place. confidence: medium date: 2026-10-14 sources: [S1] license: CC BY 4.0
- id: F2 claim: Each whole-number increase in magnitude is a tenfold increase in measured amplitude on a seismogram. confidence: medium date: 2026-10-14 sources: [S1] license: CC BY 4.0
- id: F3 claim: Each whole-number increase in magnitude releases about 32 times more energy. confidence: medium date: 2026-10-14 sources: [S1] license: CC BY 4.0
- id: F4 claim: The Richter scale (ML), introduced by Charles Richter in 1935, is now mostly used only for small local earthquakes; moment magnitude (Mw) is more accurate for others. confidence: medium date: 2026-10-14 sources: [S1] license: CC BY 4.0
- id: F5 claim: Moment magnitude is based on seismic moment, which is rock rigidity times fault area times slip. confidence: medium date: 2026-10-14 sources: [S1] license: CC BY 4.0
- id: F6 claim: The U.S. uses the Modified Mercalli Intensity scale, written in Roman numerals. confidence: medium date: 2026-10-14 sources: [S1] license: CC BY 4.0
- id: F7 claim: Shallower earthquakes and soft ground generally produce stronger shaking than deep ones or bedrock. confidence: medium date: 2026-10-14 sources: [S1] license: CC BY 4.0
- id: F8 claim: USGS considers a magnitude 10.5 earthquake highly unlikely because Earth lacks a long enough fault system. confidence: medium date: 2026-10-14 sources: [S1] license: CC BY 4.0
Pointers
- answers: Magnitude types table where: https://www.usgs.gov/programs/earthquake-hazards/earthquake-magnitude-energy-release-and-shaking-intensity access: open
Source: https://www.usgs.gov/programs/earthquake-hazards/earthquake-magnitude-energy-release-and-shaking-intensity · License: CC-BY-4.0 · Summary by iinventedlight (AI-assisted). Source: U.S. Geological Survey (USGS), \"Earthquake Magnitude, Energy Release, and Shaking Intensity\" (public domain (US government work)).
For language models and agents: start at /llms.txt. This page in Markdown: /library/reference/us-gov/earthquake-magnitude.md.