The scale was initially formalized by the China Earthquake Administration (CEA) in 1980, therefore often referred to by its original title as "China Seismic Intensity Scale (1980)". It was later revised, and adopted as a national standard, or Guobiao, series GB/T 17742-1999 by then National Quality and Technology Supervision Administration (now General Administration of Quality Supervision, Inspection, and Quarantine of P.R.C., AQSIQ) in 1999. The standard was set for revision not long before the 2008 Sichuan earthquake.
Unlike the magnitude scales that objectively estimate the released seismic energy, liedu denotes how strongly an earthquake affects a specific place. It is determined by a combination of subjective evaluations (such as human senses and building damages) and objective kinetic measures. Building damages are further refined with a combination of descriptive qualifiers and a numeric evaluation process.
The following is an unofficial translation of the Appendix I of GB/T 17742-1999.
|Liedu (Intensity)||Senses by people on the ground||Degree of building damage||Other damages||Horizontal motion on the ground|
|Damages||Mean damage index||Peak acceleration m/s2||Peak speed m/s|
|II||Sensible by very few still indoor people|
|III||Sensible by a few still indoor people||Slight rattle of doors and windows||Slight swing of suspended objects|
|IV||Sensible by most people indoors, a few people outdoors; a few wake up from sleep||Rattle of doors and windows||Obvious swing of suspended objects; vessels rattle|
|V||Commonly sensible by people indoors, sensible by most people outdoors; most wake up from sleep||Noise from vibration of doors, windows, and building frames; falling of dusts, small cracks in plasters, falling of some roof tiles, bricks falling from a few roof-top chimneys||Rocking or flipping of unstable objects||0.31 |
(0.22 - 0.44)
(0.02 - 0.04)
|VI||Most unable to stand stably, a few scared to running outdoors||Damages - Cracks in the walls, falling of roof tiles, some roof-top chimneys crack or fall apart||0 - 0.10||Cracks in river banks and soft soil; occasional burst of sand and water from saturated sand layers; cracks on some standalone chimneys||0.63 |
(0.45 - 0.89)
(0.05 - 0.09)
|VII||Majority scared to running outdoors, sensible by bicycle riders and people in moving motor vehicles||Slight destruction - localized destruction, crack, may continue to be used with small repairs or without repair||0.11 - 0.30||Collapse of river banks; frequent burst of sand and water from saturated sand layers; many cracks in soft soils; moderate destruction of most standalone chimneys||1.25 |
(0.90 - 1.77)
(0.10 - 0.18)
|VIII||Most swing about, difficult to walk||Moderate destruction - structural destruction occurs, continued usage requires repair||0.31 - 0.50||Cracks appear in hard dry soils; severe destruction of most standalone chimneys; tree tops break; death of people and cattle caused by building destruction||2.50 |
(1.78 - 3.53)
(0.19 - 0.35)
|IX||Moving people fall||Severe destruction - severe structural destruction, localized collapse, difficult to repair||0.51 - 0.70||Many cracks in hard dry soils; possible cracks and dislocations in bedrock; frequent landslides and collapses; collapse of many standalone chimneys||5.00 |
(3.54 - 7.07)
(0.36 - 0.71)
|X||Bicycle riders may fall; people in unstable state may fall away; sense of being thrown up||Most collapse||0.71 - 0.90||Cracks in bedrock and earthquake fractures; destruction of bridge arches founded in bedrock; foundation damage or collapse of most standalone chimneys||10.00 |
(7.08 - 14.14)
(0.72 - 1.41)
|XI||Wide spread collapse||0.91 - 1.00||Earthquake fractures extend a long way; many bedrock cracks and landslides|
|XII||Drastic change in landscape, mountains, and rivers|
Notes about Qualifiers: "very few" - <10%; "few" - 10% - 50%; "most" - 50% - 70%; "majority" - 70% - 90%; "commonly" - >90%.
Historic local seismic liedu is an important reference in quake proofing existing and future buildings. The national standard Code for Seismic Design of Buildings (GB 500011-2001) published in 2001 and partially revised shortly after the 2008 Sichuan Earthquake includes a list of liedu that each building in designated cities is expected to resist.