Saturday, March 26, 2011

Earthquake Intensity

I just cannot imagine how bad was the earthquake when i read on newspaper 9.0...7.0...6.8... So I googled it and i found this... Good to know!


Modified Mercalli Scale, 1956 version
Intensity value Characteristics Richter
(note 1)
I Only detectable by seismographs. (note 2) <3.5
II Felt by persons at rest on upper floors or favorably placed. 3.5
III Felt indoors. Hanging objects swing. Vibration like passing of light trucks. Duration estimated. May not be recognized as an earthquake. 4.2
IV Hanging objects swing. Vibration like passing of heavy trucks. Windows, dishes, doors rattle. Parked cars rock. Glasses clink. Crockery clashes. In the upper range of IV, wooden walls and frames creak. 4.5
V Felt outdoors; direction estimated. Sleepers awakened. Liquids disturbed, some spilled. Small unstable objects displaced or upset. Doors swing, close, open. Shutters, pictures, move. Pendulum clocks stop; start, change rate. 4.8
VI Felt by all. Many frightened and run outdoors. Persons walk unsteadily. Windows, dishes, glassware broken. Knickknacks, books, etc. fall off shelves. Pictures fall off walls. Furniture moves or overturned. Weak plaster and masonry D cracked. Small bells ring (church, school). Trees, bushes sway visibly or are heard to rustle. 5.4
VII Difficult to stand. Noticed by drivers. Hanging objects quiver; furniture breaks; damage to masonry D, including cracks. Weak chimneys broken off at roof line. Fall of plaster, loose bricks, stones, tiles, cornices, unbraced parapets and architectural ornaments. Some cracks in masonry C. Waves on ponds, water turbid with mud. Small slides and caving in along sand and gravel banks. Large bells ring. Concrete irrigation ditches damaged. 6.1
VIII Steering of cars affected. Damage to masonry C and partial collapse; some damage to masonry B, none to masonry A. Fall of stucco and some masonry walls. Twisting, fall of chimneys, factory stacks, monuments, towers, elevated tanks. Frame houses moved on foundations if not bolted down; loose panel walls thrown out. Decayed piling broken off. Branches broken from trees. Changes in flow or temperature of springs and wells. Cracks in wet ground and on steep slopes. 6.5
IX General panic. Masonry D destroyed; masonry C heavily damaged, sometimes with complete collapse; masonry B seriously damaged. General damage to foundations. Frame structures, if not bolted down, shift off foundations. Frames racked. Serious damage to reservoirs. Underground pipes break. Conspicuous cracks in ground. In alluviated areas sand and mud ejected, earthquake fountains, sand craters. 6.9
X Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, and embankments. Large landslides. Water thrown on banks of canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly. 7.3
XI Rails bent greatly. Underground pipelines completely out of service. 8.1
XII Damage nearly total. Large rock masses displaced. Lines of sight and level distorted. Objects thrown into the air. >8.1

Masonry A: shows good workmanship, mortar and design; reinforced, especially laterally, and bound together using steel, concrete, etc.; designed to reduce lateral forces.

Masonry B: Good workmanship and mortar; reinforced, but not designed in detail to resist lateral forces.

Masonry C: Ordinary workmanship and mortar; no extreme weaknesses like failing to tie in at corners, but neither reinforced nor designed against horizontal forces.

Masonry D: Weak materials, such as adobe; poor mortar; low standards of workmanship; weak horizontally.

From: Elementary Seismology, by Charles F. Richter. Copyright © 1958 by W. H. Freeman and Company. Reprinted with permission.

Notes

1. Any Richter scale equivalent to a Mercalli intensity is at best approximate, since the two scales measure different things. The number given is an estimate of the Mercalli intensity experienced at or near the epicenter of the earthquake.

2. Intensity I is assigned to some quakes that actually were detected by people, if the people were very far from the epicenter and could feel the quake only because of exceptionally favorable circumstances. In 1964 a few people in Seattle, for example, felt the Alaska earthquake because they were up in the Space Needle, and some people in Houston skyscrapers felt the 1985 Mexican earthquake.

Source by: www.sizes.com

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