Modified Mercalli Intensity III MMI III: Weak shaking
MMI III is weak shaking. Felt quite noticeably by persons indoors. Many people do not recognize it as an earthquake. Vibrations similar to the passing of a truck. Typical peak ground acceleration is 0.3–1.4% of gravity, and it causes no damage.
What MMI III does
- Perceived shaking
- Weak
- Damage potential
- None
- Peak acceleration
- 0.3–1.4% g
- Peak velocity
- 1.1–3.4 cm/s
What people feel
- Felt noticeably indoors, especially on upper floors
- Many do not recognize it as an earthquake
- Duration of shaking can be estimated
What objects do
- Chandeliers and hanging objects shake
- Vibration similar to passing heavy truck
- Dishes and windows may rattle slightly
What happens to buildings
- Standing cars rock slightly
- No structural damage
Sources: the USGS Modified Mercalli Intensity scale (Wood and Neumann, 1931; Richter, 1958); ground-motion ranges from the USGS ShakeMap documentation (Worden et al., 2012), approximate and overlapping between neighbouring levels. See instrumental intensity. An older example: MMI III on YouTube.
Recently at MMI III in our region
Earthquakes in the western United States and northern Mexico whose strongest shaking at a named place reached this level.
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M3.8
8 km NNE of Delta, B.C., MX
2026-11-03 · Ejido Saltillo, MMI 3.3 III -
M4.0
10 km N of Lake Pillsbury, CA
2026-10-28 · Redwood Valley, MMI 2.7 III -
M3.8
4 km SE of Piru, CA
2026-09-30 · Fillmore, MMI 3.1 III -
M3.9
6 km WNW of Wauna, Washington
2026-09-29 · Home, MMI 3.1 III -
M3.6
7 km WSW of Hermosa Beach, CA
2026-09-27 · Hermosa Beach, MMI 3.4 III
Seen on camera: no clips yet
Each clip is rated from the effects it shows. A rating describes one camera at one place, not a whole town.
How MMI III is estimated
From instruments
USGS ShakeMap converts peak ground acceleration and velocity recorded at seismic stations into intensity. About 0.3–1.4% g of acceleration corresponds to MMI III.
From people's reports
USGS Did You Feel It? turns answers from thousands of people into a community intensity for each place. If you felt an earthquake, report it there.
From footage
We rate each clip with questions built from the scale's own statements: what people, objects and buildings do on camera. A rating describes one camera at one place.
Common questions
What magnitude causes MMI III?
It depends on distance and ground conditions, not magnitude alone. In our region, MMI III has come from earthquakes such as M3.8 near Delta, B.C., MX (2026); M4.0 near Lake Pillsbury, CA (2026); M3.8 near Piru, CA (2026).
What does MMI III feel like?
Felt noticeably indoors, especially on upper floors. Many do not recognize it as an earthquake. Duration of shaking can be estimated.
How strong is the ground motion at MMI III?
Peak ground acceleration is typically 0.3–1.4% g and peak velocity 1.1–3.4 cm/s.
How is intensity different from magnitude?
Magnitude measures the energy an earthquake releases and is one number per earthquake. Intensity describes the shaking at one place, so a single earthquake produces many intensities, strongest near the fault and weaker with distance.