Modified Mercalli Seismic Intensity Scale

1. Not felt except by a very few under especially favorable circumstances.

Marginal and long-period effects.

2. Felt only by a few persons at rest, or favorably placed.

Delicately suspended objects may swing.

3. Felt quite noticeably especially on upper levels.

Many people do not recognize it.

Hanging objects swing.

Standing motorcars may rock slightly.

Vibration like passing of heavy trucks.

Duration estimated.

4. During the day felt indoors by many.

At night some awakened.

Sensation of jolt like heavy ball striking the walls.

Dishes, windows, doors disturbed.

Glasses clink.

Crockery clashes.

Wooden walls and frames creak.

Standing motorcars rocked noticeably.

5. Felt by nearly everyone.

Sleepers awakened.

Liquids disturbed.

Unstable objects overturned.

Windows broken.

Disturbance of poles and other tall objects noticed.

Doors swing, close, open.

Pendulum clocks stop.

6. Felt by all.

Many run outdoors.

Persons walk unsteadily.

Windows, dishes, glassware broken.

Books off shelves.

Pictures off walls.

Furniture overturned.

Weak masonry cracked.

Trees heard to rustle.

Small bells ring.

7. Everybody runs outdoors.

Difficult to stand.

Noticed by drivers.

Hanging objects quiver.

Furniture broken.

Damage considerable in poorly built structures.

Fall of plaster, bricks, stones, tiles and architectural

ornament.

Waves on ponds.

Water turbid with mud.

Large bells ring.

8. Damage great in poorly built structures.

Partial collapse.

Sand and mud ejected in small amounts.

Changes in well water.

Twisting, fall of factory stacks, monuments, towers.

Branches broken from trees.

Persons driving cars disturbed.

9. General panic.

Damage considerable in specially designed structures.

Well designed structures thrown out of plumb.

General damage to foundations.

Structures shifted off foundations.

Frames racked.

Sand and mud ejected.

10. Most structures destroyed with their foundation Some bridges destroyed.

Serious damage to dams, embankments.

Water thrown on banks of canals, rivers, lakes.

11. Few, if any, structures remain.

Bridges destroyed.

Broad fissures.

Pipelines completely out of service.

Earth slumps. Land slips.

12. Damage total.

Waves seen on ground surface.

Lines of sight and level distorted.

Objects thrown into the air.

Related

From “Detroit Seen,” FE #312, Spring, 1983: “As word gets back to us about the last issue, it seems as though many people didn’t understand why we printed the “Modified Mercalli Seismic Intensity Scale” on page 2. The actual scale is for measuring the intensity of earthquakes empirically rather than numerically such as on the Ricter scale, and we thought it provided a poetic metaphor for revolution. Guess we all have our flops, but save it for the coming quakes, particularly you readers in California.”