Modified Mercalli (MM) Scale, Table 1 Modified Mercalli intensity scale of 1931 (From Wood and Neumann 1931)

I

Not felt – or, except rarely under especially favorable circumstances

Under certain conditions, at and outside the boundary of the area in which a great shock is felt:

Sometimes birds, animals, reported uneasy or disturbed;

Sometimes dizziness or nausea experienced;

Sometimes trees, structures, liquids, bodies of water, may sway –doors may swing, very slowly

II

Felt indoors by few, especially on upper floors, or by sensitive, or nervous persons

Also, as in grade I, but often more noticeably:

Sometimes hanging objects may swing, especially when delicately suspended;

Sometimes trees, structures, liquids, bodies of water, may sway; doors may swing, very slowly;

Sometimes birds, animals, reported uneasy or disturbed;

Sometimes dizziness or nausea experienced

III

Felt indoors by several, motion usually rapid vibration

Sometimes not recognized to be an earthquake at first

Duration estimated in some cases

Vibration like that due to passing of light, or lightly loaded trucks, or heavy trucks some distance away

Hanging objects may swing slightly

Movements may be appreciable on upper levels of tall structures. Rocked standing motor cars slightly

IV

Felt indoors by many, outdoors by few

Awakened few, especially light sleepers

Frightened no one, unless apprehensive from previous experience. Vibration like that due to passing of heavy, or heavily loaded trucks. Sensation like heavy body striking building, or falling of heavy objects inside

Rattling of dishes, windows, doors; glassware and crockery clink and clash

Creaking of walls, frame, especially in the upper range of this grade

Hanging objects swung, in numerous instances

Disturbed liquids in open vessels slightly

Rocked standing motor cars noticeably

V

Felt indoors by practically all, outdoors by many or most: outdoors direction estimated

Awakened many or most

Frightened few – slight excitement, a few ran outdoors

Buildings trembled throughout

Broke dishes, glassware, to some extent

Cracked windows – in some cases, but not generally

Overturned vases, small or unstable objects, in many instances, with occasional fall

Hanging objects, doors, swing generally or considerably

Knocked pictures against walls, or swung them out of place. Opened, or closed, doors, shutters, abruptly

Pendulum clocks stopped, started or ran fast, or slow

Moved small objects, furnishings, the latter to slight extent. Spilled liquids in small amounts from well-filled open containers. Trees, bushes, shaken slightly

VI

Felt by all, indoors and outdoors

Frightened many, excitement general, some alarm, many ran outdoors. Awakened all

Persons made to move unsteadily

Trees, bushes, shaken slightly to moderately

Liquid set in strong motion

Small bells rang – church, chapel, school, etc

Damage slight in poorly built buildings

Fall of plaster in small amount

Cracked plaster somewhat, especially fine cracks in chimneys in some instances

Broke dishes, glassware, in considerable quantity, also some windows

Fall of knickknacks, books, pictures

Overturned furniture in many instances

Moved furnishings of moderately heavy kind

VII

Frightened all – general alarm, all ran outdoors

Some, or many, found it difficult to stand

Noticed by persons driving motor cars

Trees and bushes shaken moderately to strongly

Waves on ponds, lakes, and running water

Water turbid from mud stirred up

Incaving to some extent of sand or gravel stream banks

Rang large church bells, etc

Suspended objects made to quiver

Damage negligible in buildings of good design and construction, slight to moderate in well-built ordinary buildings, considerable in poorly built or badly designed buildings, adobe houses, old walls (especially where laid up without mortar), spires, etc

Cracked chimneys to considerable extent, walls to some extent. Fall of plaster in considerable to large amount, also some stucco. Broke numerous windows, furniture to some extent

Shook down loosened brickwork and tiles

Broke weak chimneys at the roofline (sometimes damaging roofs). Fall of cornices from towers and high buildings

Dislodged bricks and stones

Overturned heavy furniture, with damage from breaking

Damage considerable to concrete irrigation ditches

VIII

Fright general – alarm approaches panic

Disturbed persons driving motor cars

Trees shaken strongly – branches, trunks, broken off, especially palm trees

Ejected sand and mud in small amounts

Changes: temporary, permanent; in flow of springs and wells; dry wells renewed flow; in temperature of spring and well waters

Damage slight in structures (brick) built especially to withstand earthquakes

Considerable in ordinary substantial buildings, partial collapse: racked, tumbled down, wooden houses in some cases; threw out panel walls in frame structures, broke off decayed piling

Fall of walls

Cracked, broke, solid stone walls seriously

Wet ground to some extent, also ground on steep slopes

Twisting, fall of chimneys, columns, monuments also factory stacks, towers

Moved conspicuously, overturned, very heavy furniture

IX

Panic general

Cracked ground conspicuously

Damage considerable in (masonry) structures built especially to withstand earthquakes:

Threw out of plumb some wood-frame houses built especially to withstand earthquakes;

Great in substantial (masonry) buildings, some collapse in large part; or wholly shifted frame buildings off foundations, racked frames; serious to reservoirs; underground pipes sometimes broken

X

Cracked ground, especially where loose and wet, up to widths of several inches; fissures up to a yard in width ran parallel to canal and stream banks

Landslides considerable from river banks and steep coasts

Shifted sand and mud horizontally on beaches and flat land

Changed level of water in wells

Threw water on banks of canals, lakes, rivers, etc

Damage serious to dams, dikes, embankments

Severe to well-built wooden structures and bridges, some destroyed

Developed dangerous cracks in excellent brick walls

Destroyed most masonry and frame structures, also their foundations

Bent railroad rails slightly

Tore apart, or crushed endwise, pipe lines buried in earth

Open cracks and broad wavy folds in cement pavements and asphalt road surfaces

XI

Disturbances in ground many and widespread, varying with ground material

Broad fissures, earth slumps, and land slips in soft, wet ground. Ejected water in large amounts charged with sand and mud

Caused sea waves (“tidal” waves) of significant magnitude

Damage severe to wood-frame structures, especially near shock centers

Great to dams, dikes, embankments, often for long distances

Few, if any (masonry), structures remained standing

Destroyed large well-built bridges by the wrecking of supporting piers, or pillars

Affected yielding wooden bridges less

Bent railroad rails greatly, and thrust them endwise

Put pipe lines buried in earth completely out of service

XII

Damage total – practically all works of construction damaged greatly or destroyed

Disturbances in ground great and varied, numerous shearing cracks. Landslides, falls of rock of significant character, slumping of river banks, etc., numerous and extensive

Wrenched loose, tore off, large rock masses

Fault slips in firm rock, with notable horizontal and vertical offset displacements

Water channels, surface and underground, disturbed and modified greatly

Dammed lakes, produced waterfalls, deflected rivers, etc

Waves seen on ground surfaces (actually seen, probably, in some cases). Distorted lines of sight and level

Threw objects upward into the air