Hello everyone. An earthquake can be described in two different ways. Through its magnitude linked to the released energy M and through the shaking intensity I. You already know the magnitude scale for instance, the moment magnitude proposed by Kanamori. The intensity of the seismic shaking characterizes at a given location the effect on people, ordinary objects, human structures, and the natural environment. Earthquake intensity is mainly controlled by three factors. The magnitude, that is how big is this earthquake, the distance from the epicenter D, since intensity varies from place to place, and local rock and soil conditions. Because seismic intensity is a subjective value depending on how you fill it, it is not so simple to assess this parameter. Many scales have been proposed from the beginning of the 19th century until today. Intensity scales have progressively evolved with respect to different criteria. Among the most famous scales is the scale of Sieberg becomes the foundation of all modern 12 degrees intensity scale. A later version proposed by Mercalli-Cancani-Sieberg scale, the so-called MCS scale, introduced in 1932. Modified Mercalli scale has been proposed in 1956. European Macroseismic scale as the last one to have been developed. Different in density scales are used today all over the world. Among the three most famous intensity scale in current use is the Modified Mercalli Intensity scale in USA, the Japanese Meteorological Agency scale in Japan, and the European Intensity scale introduced in 1992 and accepted in its revised version in 1998 in Europe. Let's focus today on the later to understand how it is built. Any intensity scale consists of a series of descriptions of the effects of different degree of earthquake shaking on a number of things that may be found in every days life. These things can be considered as sensor since their response to the shaking is used to measure its strength. These things are living bodies such as people and animals. As intensity increases, a greater proportion of people and animals notice the shaking and may be frightened by it. Ordinary objects. As intensity increases, a large number of ordinary domestic items, crockery, books begin to shake and may be thrown down. And buildings. Buildings are progressively more severely damaged as intensity increases. Several intensity scales describe also affects on natural environment like landslides, rockfalls. However, it is not taken into account in the EMS intensity scale. The main difference between the EMS-98 and the other intensity scale is in the details with which different criteria are defined. The European Macroseismic scale uses in particular three important terms. The building typology, the damage grades, and a quantity associated to each observed data; few, many, or most. Let's focus now on the building typology. The way in which a building deforms under earthquake loading depends on the building type. An earthquake does not have the same effect on a poorly built brick building and a reinforced concrete building. It is thus important to distinguish different types of buildings, particularly in areas showing a large diversity of building construction like Europe. This introduces the notion of vulnerability. Vulnerability is defined as a resistance of the building to earthquake generating shaking. It is described in this kind of vulnerability table. The first step is obviously to assess the type of structure corresponding to the left column of our table. The type of structure are subdivided in four classes. Masonry building, reinforced concrete building, steel and wood structures.. Each class is then detail into sub-classification, which is the first step in the vulnerability assessments. The sub-classification takes into account, the type of construction, material used and other factors used to evaluate our measure building resists to earthquake shaking. A vulnerability class is then assigned to each of these sub-classified group, and six classes of decreasing vulnerability are proposed: A, B, C, D, E, and F. A circle indicates the most likely vulnerability class. A black line shows a probable range of the vulnerability class. The dashed line is used where it is uncertain. Now let's focus on the masonry class. Here, you will find some of the most common building type in Europe. You can find masonry mainly with rubble stone or field stone. These are traditional construction in which undressed stone are used as a basic building material usually with poor quality mortar. These buildings are particularly heavy and have a little resistance to lateral loading. Floors are typically of wood, and provide no horizontal stiffening. Adobe construction is widely spread in the world. Bricks are built using clays. The strength of adobe construction against earthquake shaking depends on the quality of the bricks and the mortar. Simple stone construction differs from field stone construction in that the building stones have undergone some dressing prior to use and are arranged according to some techniques improving the strength of the structure. Buildings with very large stones possess great strengths. But take care to not use monumental buildings such as castle, church, or cathedral, which are not used in the European macro seismic scale because they belong to a very specific and restricted typology. These are other types of masonry, mixing bricks, reinforced concrete floor, or reinforced elements which increases strengths of the building. Damage to building is also classified. The degree of damage to buildings is expressed as a number from 1 to 5. For the assignment of this degree, a distinction is made between reinforced concrete buildings and masonry buildings. Grades 1-5 should ideally represent a linear increase in the strength of shaking, but in practice, they do this only approximately. The degree of damage describes both structural and non-structural damage. In grade 1 there is only slight non-structural damage as this fallen small pieces of plaster or loose stones from upper parts of buildings in very few cases. In grade 2, there is only slight structural damage like some cracks in many walls and moderate non-structural damage like full of fairly large pieces of plaster and partial collapse of chimney as shown in this picture. In grade 3, moderate structural damage like large extensive cracks in most walls and also heavy non-structural damage like the detachment of loose ties, fracture of chimneys. And, in this picture you can observe some large cracks even if they are not so severe. In grade 4, there are heavy structural damage, very heavy non-structural damage. This example show large diagonal cracks in the wall. We particularly see the loss of connection between the external walls, which indicates heavy structural damage. Finally, grade 5 corresponds to the destruction of the structure, as you can see in this picture, the whole ground floor has collapsed. The seismic intensity is assigned from most of damage building. It is necessary to assign some statistical elements in the intensity scale. This statistical elements are confined to broad term. Few, if the number of observed data belongs to a value range between 0-20 percent. The term many is defined to value range from 20-60 percent and most from 60-100 percent. You can notice there is 10 percent of overlapping of the three intervals. Let's see how the European Macroseismic Scale (EMS) works in practice in the field. There are 12 degrees. Let's describe a few. From degree 1 to degree 4, there is no building damage, but the effects of the shaking is increasing. As an example for degree 4, the shaking is weak; the earthquake is felt indoors by many and it's felt outdoors only by very few; a few people are awaked; the level of vibration is not frightening; observer feels a slight trembling or swinging of the building room or beds. Hanging objects swing. Light furniture shakes visibly in a few cases, and woodwork cracks in a few cases, but there is still no damage. In degree 5 the earthquake is felt indoors by most and outdoors by a few. A few people are frightened and run outdoors. Many sleeping people awake and observer feels a strong shaking or rocking of the whole building room or furniture. Hanging objects swing considerably and small, top-heavy, and precariously supported objects may be shifted or fall down. Doors and windows swing open or shuts. In a few cases, window panes brakes, and liquid oscillate and they spill from well-filled containers. Animals indoor may become uneasy. We also notice the very first damage. Damage of grade 1 to a few buildings of vulnerability class A and B. Degree 6 is slightly damaging for buildings. Degree 7 is heavily damaging. First, many people find it difficult to stand even outdoors. Furniture may be overturned. Objects like TV sets, typewriters, photographs, tombstones may be occasionally be displaced, twisted, or overturned. Waves may be seen on very soft grounds. 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 and a few of grade 3. A few buildings of class D sustain damage of great 2. Degree 9 is destructive. There is general panic, people may be forcibly thrown to the ground floor, and many monuments and column fall or are twisted. Waves can be seen on soft ground also. Many buildings of class A sustain damage of grade 5. Building of vulnerability class B suffer damage of grades 4 and a few of grade 5. Many buildings of vulnerability class C suffer damage of grade 3 and a few of grade 4. Many buildings of class D suffer damage of grade 2 and a few of grade 3. A few building of class A sustain damage of grade 2. The description of degree 10, 11, and 12 only focus on building damage. All vulnerability classes are involved with higher proportion than the previous degrees. In this sequence, we have seen there are two different ways to describe an earthquake. Earthquake magnitude, which is a single value describing energy released by the full system, and earthquake intensity describes the shaking at specific location. In the European Macroseismic Scale, the degree is assigned from the observed effects of shaking on current things like people reaction, effects on ordinary objects, response of buildings. The European Macroseismic Scale detects particularly the building response. We have introduced three parameters to establish the intensity degree: vulnerability class of the observed building, the damage degree, and the quantity of observed data. If you want to know more about the European Macroseismic Scale, do not hesitate to consider a dedicated guide in open access.
