Modified Mercalli Intensity IX MMI IX: Violent shaking
MMI IX is violent shaking. General panic. Well-designed structures thrown out of plumb; great damage in substantial buildings with partial collapse. Buildings shifted off foundations. Typical peak ground acceleration is 65–124% of gravity, and the damage potential is heavy.
What MMI IX does
- Perceived shaking
- Violent
- Damage potential
- Heavy
- Peak acceleration
- 65–124% g
- Peak velocity
- 116–219 cm/s
What people feel
- General panic; widespread fear
- Difficult or impossible to stand outdoors
What objects do
- Water reservoirs seriously damaged
- Underground pipes broken
What happens to buildings
- Well-designed frame structures thrown out of plumb
- Buildings shifted off foundations; walls collapse
- Ground cracked conspicuously
- Considerable damage even in specially designed structures
Also at this level, in other versions of the scale
- Damage great in substantial buildings, with partial collapse USGS, The Modified Mercalli Intensity Scale (table image on that page)
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 IX on YouTube.
Simulated at MMI IX
Our animations of named places where the estimated shaking reached this level, driven by simulated or recorded ground motion.
Recently at MMI IX in our region
Earthquakes in the western United States and northern Mexico whose strongest shaking at a named place reached this level.
-
M7.2
The 2010 Sierra El Mayor, B.C., Mexico Earthquake
2010-04-04 · Ejido Durango, MMI 8.5 IX -
M6.7
Northridge, California, earthquake
1994-01-17 · Northridge, MMI 8.6 IX
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 IX is estimated
From instruments
USGS ShakeMap converts peak ground acceleration and velocity recorded at seismic stations into intensity. About 65–124% g of acceleration corresponds to MMI IX.
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 IX?
It depends on distance and ground conditions, not magnitude alone. In our region, MMI IX has come from earthquakes such as M7.2 The 2010 Sierra El Mayor, B.C., Mexico Earthquake (2010); M6.7 Northridge, California, earthquake (1994).
What does MMI IX feel like?
General panic; widespread fear. Difficult or impossible to stand outdoors.
How strong is the ground motion at MMI IX?
Peak ground acceleration is typically 65–124% g and peak velocity 116–219 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.