Mercalli (Modified Mercalli) intensity scale

Scale and typical effects

The scale uses Roman numerals I through XII. Brief, generalized descriptions for each level help observers and investigators assign an intensity rating to a place:

• I. Instrumental: Recorded by seismographs but not felt by people indoors.
• II. Weak: Barely felt by a few people at rest, especially on upper floors; hanging objects may sway slightly.
• III. Weak to light: Felt indoors by many; stable objects do not move appreciably; vibration like passing trucks.
• IV. Light: Felt by most indoors, some outdoors; windows, dishes and doors rattle; noticeable but little or no damage.
• V. Moderate: Felt by nearly everyone; sleepers awakened; dishes and books may fall; light nonstructural damage possible.
• VI. Strong: Many frightened; furniture moves; some plaster or masonry cracking; slight structural damage to vulnerable buildings.
• VII. Very strong: Considerable damage to poorly built structures; chimneys and parts of buildings fall; ground may crack.
• VIII. Severe: Partial collapse of ordinary buildings; heavy furniture overturned; serious damage to substantial structures with partial failures.
• IX. Violent: General panic; substantial buildings shifted off foundations; ground conspicuously cracked; underground pipes broken.
• X. Extreme: Many well-built structures destroyed; ground badly fissured; rails bent; large landslides.
• XI. Very extreme: Few structures remain standing; bridges and broad infrastructures heavily damaged; large ground displacements.
• XII. Catastrophic: Near total destruction; objects thrown into the air; landscape altered; visible waves on ground surface in some materials.

History and variants

The original scale was developed by the Italian volcanologist Giuseppe Mercalli in the late 19th century as a ten-degree, descriptive scale. Later extensions and revisions by other scientists increased the range to twelve degrees and refined the descriptions; historical names for versions include the Mercalli–Cancani–Sieberg (MCS) scale. An English translation and adaptation by Harry O. Wood and Frank Neumann produced what became widely known as the Modified Mercalli scale. Further regional adaptations, such as the European Macroseismic Scale (EMS), have updated descriptions to reflect modern building types and engineering knowledge.

Assigning intensities

Intensity assignments result from field surveys, eyewitness and community reports, and study of structural damage. Investigators collect observations, photographs and damage assessments and compare them with standard descriptions to assign an intensity level for each locality. Modern practice often supplements traditional surveys with crowdsourced reports, online questionnaires and instrumental shaking measurements to improve spatial coverage. Those compiled local intensities can be contoured to produce isoseismal maps that show the distribution of shaking around an event.

Uses and limitations

The Mercalli approach is particularly valuable for mapping shaking patterns, assessing historical earthquakes that predate seismographs, guiding emergency response to damaged areas, and informing building vulnerability studies. However, it has intrinsic limitations: intensity is subjective and depends on population density, time of day, local construction practices and site amplification of seismic waves. The same earthquake will often produce different intensity ratings within short distances where ground conditions change. Intensity does not directly quantify the energy of an earthquake; magnitude scales such as the Richter scale or modern magnitude measures estimate size and energy release, and they complement intensity-based assessments. For discussion of the physical energy involved in earthquakes, see material on seismic energy.

Practical notes

In practice, seismologists and emergency planners use both magnitude and intensity information to form a fuller picture: magnitude provides a single measure of source size, while intensity maps localize damage and human impact. There is no simple universal conversion between magnitude and Mercalli intensity because local site effects and distance strongly influence observed damage. Nevertheless, intensity records remain an indispensable resource for historical research, post‑event response, and efforts to improve resilience of buildings and infrastructure.