European Macroseismic Scale 1998 (EMS-98)
Currently, the macroseismic intensity of earthquakes perceived in Catalonia is assessed according to the European Macroseismic Scale (Grünthal, 1998). The EMS-98 scale, published in 1998 as an update of the MSK scale, considers 12 degrees of intensity to classify the severity of the seismic shaking according to the observed effects.
In addition to the description of the degrees of intensity, the scale defines the terms of quantity, types of constructions and degrees of damage that it uses.
Quantity definitions
The quantity terms used in the definitions of the intensity degrees correspond approximately to the following percentages:
- Few: 1 - 15 %.
- Many: 15 - 55 %
- Most: 55 - 100 %
Percentages used to define the quantity terms of the intensity degrees.
Classification of structures (buildings) according to its seismic vulnerability (vulnerability table)
The masonry types of structures are to be read as, for example, “rubble stone masonry”, while the reinforced concrete structure types are to be read as, for example, “reinforced concrete frame” or “reinforced concrete walls”.
Classification of structures (buildings) according to their vulnerability.
Damage classification
The way in which a building deforms under earthquake loading depends on the building type. In a broad categorization two main types of buildings can be identified: masonry buildings and reinforced concrete buildings.
Classification of damage to masonry buildings
Grade 1: Negligible to slight damage (no structural damage, slight non-structural damage)
Hair-line cracks in very few walls. Fall of small pieces of plaster only. Fall of loose stones from upper parts of buildings in very few cases.
Grade 2: Moderate damage (slight structural damage, moderate non-structural damage)
Cracks in many walls. Fall of fairly large pieces of plaster. Partial collapse of chimneys.
Grade 3: Substantial to heavy damage (moderate structural damage, heavy non-structural damage)
Large and extensive cracks in most walls. Roof tiles detach. Chimneys fracture at the roof line. Failure of individual non-structural elements (partitions, gable walls).
Grade 4: Very heavy damage (heavy structural damage, very heavy non-structural damage)
Serious failure of walls. Partial structural failure of roofs and floors.
Grade 5: Destruction (very heavy structural damage)
Col·lapse total o quasi total.
Classification of damage to reinforced concrete buildings
Grade 1: Negligible to slight damage (no structural damage, slight non-structural damage)
Fine cracks in plaster over frame members or in walls at the base. Fine cracks in partitions and infills.
Grade 2: Moderate damage (slight structural damage, moderate non-structural damage)
Cracks in columns and beams of frames and in structural walls. Cracks in partition and infill walls; fall of brittle cladding and plaster. Falling mortar from the joints of wall panels.
Grade 3: Substantial to heavy damage (moderate structural damage, heavy non-structural damage)
Cracks in columns and beam column joints of frames at the base and at joints of coupled walls. Spalling of concrete cover, buckling of reinforced rods. Large cracks in partition and infill walls, failure of individual infill panels.
Grade 4: Very heavy damage (heavy structural damage, very heavy non-structural damage)
Large cracks in structural elements with compression failure of concrete and fracture of rebars; bond failure of beam reinforced bars; tilting of columns. Collapse of a few columns or of a single upper floor.
Grade 5: Destruction (very heavy structural damage)
Collapse of ground floor or parts (e. g. wings) of buildings.
Intensity degrees definitions
The description of the intensity degrees of the EMS-98 scale is organized in the following order and each letter indicates the type of effect described.
a) Effects on humans.
b) Effects on objects and on nature (effects on ground and ground failure are dealt with especially in another section of the EMS-98).
c) Damage to buildings.
For the purposes of intensity assessment, it is considered that each intensity degree may also include the effects of shaking from lower intensity degrees, although these effects are not explicitly mentioned. The 12 degrees of intensity considered in EMS-98 are described below.
Grade I - Not felt
a) Not felt, even under the most favorable circumstances.
b) No effect.
c) No damage.
Grade II – Scarcely felt
a) The tremor is felt only at isolated instances (<1%) of individuals at rest and in a specially receptive position indoors.
b) No effect.
c) No damage.
Grade III - Weak
a) The tremor is felt only at isolated instances (<1%) of individuals at rest and in a specially receptive position indoors.
b) Hanging objects swing slightly.
c) No damage.
Grade IV - Largely observed
a) The earthquake is felt indoors by many and felt outdoors only by very few. A few people are awakened. The level of vibration is not frightening. The vibration is moderate. Observers feel a slight trembling or swaying of the building, room or bed, chair etc.
b) Crockery, glasses, windows and doors rattle. Hanging objects swing. Light furniture shakes visibly in a few cases. Woodwork creaks in a few cases.
c) No damage.
Grade V - Strong
a) The earthquake is felt indoors by most, outdoors by few. A few people are frightened and run outdoors. Many sleeping people awake. Observers feel a strong shaking or rocking of the whole building, room or furniture.
b) Hanging objects swing considerably. China and glasses clatter together. Small, top-heavy and/or precariously supported objects may be shifted or fall. Doors and windows swing open or shut. In a few cases windowpanes break. Liquids oscillate and may spill from well-filled containers. Animals indoors may become uneasy.
c) Damage of grade 1 to a few buildings of vulnerability class A and B.
Grade VI - Slightly damaging
a) Felt by most indoors and by many outdoors. A few persons lose their balance. Many people are frightened and run outdoors.
b) Small objects of ordinary stability may fall and furniture may be shifted. In few instances dishes and glassware may break. Farm animals (even outdoors) may be frightened.
c) Damage of grade 1 is sustained by many buildings of vulnerability class A and B; a few of class A and B suffer damage of grade 2; a few of class C suffer damage of grade 1.
Grade VII - Damaging
a) Most people are frightened and try to run outdoors. Many find it difficult to stand, especially on upper floors.
b) Furniture is shifted and top-heavy furniture may be overturned. Objects fall from shelves in large numbers. Water splashes from containers, tanks and pools.
c) Many buildings of vulnerability class A suffer damage of grade 3; a few of grade 4.
Many buildings of vulnerability class B suffer damage of grade 2; a few of grade 3.
A few buildings of vulnerability class C sustain damage of grade 2.
A few buildings of vulnerability class D sustain damage of grade 1.
Grade VIII – Heavily damaging
a) Many people find it difficult to stand, even outdoors.
b) Furniture may be overturned. Objects like TV sets, typewriters etc. fall to the ground. Tombstones may occasionally be displaced, twisted or overturned. Waves may be seen on very soft ground.
c) c) Many buildings of vulnerability class A suffer damage of grade 4; a few of grade 5.
Many buildings of vulnerability class B suffer damage of grade 3; a few of grade 4.
Many buildings of vulnerability class C suffer damage of grade 2; a few of grade 3.
A few buildings of vulnerability class D sustain damage of grade 2.
Grade IX- Destructive
a) General panic. People may be forcibly thrown to the ground.
b) Many monuments and columns fall or are twisted. Waves are seen on soft ground.
c) Many buildings of vulnerability class A sustain damage of grade 5.
Many buildings of vulnerability class B suffer damage of grade 4; a few of grade 5.
Many buildings of vulnerability class C suffer damage of grade 3; a few of grade 4.
Many buildings of vulnerability class D suffer damage of grade 2; a few of grade 3.
A few buildings of vulnerability class E sustain damage of grade 2.
Grade X - Very destructive
c) Most buildings of vulnerability class A sustain damage of grade 5.
Many buildings of vulnerability class B sustain damage of grade 5.
Many buildings of vulnerability class C suffer damage of grade 4; a few of grade 5.
Many buildings of vulnerability class D suffer damage of grade 3; a few of grade 4.
Many buildings of vulnerability class E suffer damage of grade 2; a few of grade 3.
A few buildings of vulnerability class F sustain damage of grade 2.
Grade XI - Devastating
c) Most buildings of vulnerability class B sustain damage of grade 5.
Most buildings of vulnerability class C suffer damage of grade 4; many of grade 5.
Many buildings of vulnerability class D suffer damage of grade 4; a few of grade 5.
Many buildings of vulnerability class E suffer damage of grade 3; a few of grade 4.
Many buildings of vulnerability class F suffer damage of grade 2; a few of grade 3.
Grade XII - Completely devastating
c) All buildings of vulnerability class A, B and practically all of vulnerability class C are destroyed. Most buildings of vulnerability class D, E and F are destroyed. The earthquake effects have reached the maximum conceivable effects.