MMI Scale › Level IV

Light

Light shaking · None damage potential

PGA

1.4 – 3.9 %g

PGV

3.4 – 8.1 cm/s

I II III IV V VI VII VIII IX X

Felt by many indoors, few outdoors. At night some awakened. Sensation like a heavy truck striking the building.

Effects

People & Response

Felt by many indoors, few outdoors during the day
Some people awakened at night
No general alarm; mostly surprise

Objects & Furnishings

Dishes and windows rattle alarmingly
Hanging objects swing noticeably
Liquids slightly disturbed in open containers
Small bells ring

Structures & Environment

Walls creak noticeably
Cars rock noticeably
No structural damage

Also at this level, in other versions of the scale

Sensation like a heavy truck striking the building USGS, The Modified Mercalli Intensity Scale (table image on that page)

Simulated at this level

Our physics animations of familiar objects, shaken by the ground motion estimated for a city at intensity IV.

Lone Juniper Ranch

M4.1 2 km ESE of Frazier Park, CA

Frazier Park

M4.1 2 km ESE of Frazier Park, CA

Typical PGA (ShakeMap) 1.4 – 3.9 %g

Typical PGV (ShakeMap) 3.4 – 8.1 cm/s

PGA/PGV ranges are approximate; values overlap between adjacent levels. See Instrumental Intensity for details.

Video Example

Watch on YouTube ↗

← III Weak Moderate V →

Descriptions are verbatim from the USGS MMI Scale, based on Wood & Neumann (1931) and Richter (1958). Source: USGS Modified Mercalli Intensity Scale .

Instrumental intensity values and PGA/PGV ranges from USGS ShakeMap V4 Technical Documentation (Worden et al.). Intensity Lab reports MMI derived via the Worden et al. (2012) GMICE, interpolated from USGS ShakeMap. PGA/PGV ranges are approximate; actual values overlap between adjacent levels.