Seismic risk refers to the likelihood of an earthquake occurring. It depends on the geographical location of the institution in question and is an important factor for determining its seismic vulnerability. The DIN 4149 standard divides Germany into four seismic zones, from Z0 with the lowest risk to Z3 with the highest risk. Click on the link below to check which zone your institution is in.

German earthquake zones and subsoil classes

Ground acceleration greatly depends on the type of subsoil. Stone or solid rock can be considered a good foundation for construction, while shallow sediment basins and transitional zones are less favorable. Deep sediment basins are the least favorable. Knowing the characteristics of the subsoil is therefore important for assessing risk and specifying the necessary preventive measures. According to DIN 4149, subsoil is classified in one of three geological subsoil classes:
R - regions predominantly characterized by bedrock
S - regions with a soft subsoil, deep basin structures with thick sedimentary filling
T - transitional areas between regions of subsoil classes R and S and regions with relatively shallow sediment basins.

German earthquake zones and subsoil classes

Earthquake events can trigger subsidence in mining regions. This can happen even many years after mining operations have ceased in former mining areas. The type of subsoil is also a factor. Certain types of rock can absorb the stresses better than others, so the Saarland (Germany) is more prone to such events than the German Ruhr region for example.

Vaulted ceilings supported by masonry walls are vulnerable to earthquake damage. To provide resistance against earthquakes, it is advisable to have tie rods between the supports.

Photo: Barrel-vaulted structure with tie rods

Wooden ceilings increase the seismic vulnerability of a masonry building, especially with respect to the walls tilting, as the walls cannot be adequately fixed to the wooden beams. To stop walls from tilting over, wooden beam ceilings should be reinforced with tie rods or a thin layer of reinforced concrete, or the ceilings should be connected to the walls using steel ties.

In the event of an earthquake, a compact floor plan is advantageous. A rectangular floor plan is considered compact, whereas an L-shaped floor plan is considered to be irregular. An irregular floor plan increases seismic vulnerability, and is especially problematic if the ceilings are made of reinforced concrete. To prevent stress cracks, expansion joints can be inserted. These allow independent movement between adjoining structural members.

Floor plan design: compact and irregular floor plans

A symmetrical distribution of walls can better absorb the forces released by an earthquake (no torsional stress). A bracing wall must be of a certain thickness in order to absorb (vertical and horizontal) forces.

Favorable and unfavorable distribution of walls

Part of a wall tipping over

Buildings with a large number of stories are more at risk during earthquakes than low buildings.

The elevation is the vertical view of a building. The structure of the building can be easily discerned in views, especially cross-sectional ones. A building is considered to have a regular elevation if the supporting structures (walls are more important for earthquake resistance) are directly above one another, the stories are of equal height and the ceilings are contiguous. The seismic behavior of a building with an irregular elevation can be very unfavorable, especially if the irregularity is on the lower stories.

Regular and irregular elevations

In the event of an earthquake, religious buildings, such as churches and cathedrals, and entrance halls such as commonly found in museums, are particularly at risk because there is a lot of weight high up in the building (e.g. vaulted ceilings). This and other characteristics (few walls, high walls, irregular elevation and floor plan) are very unfavorable for earthquake resistance.

Towers, e.g. church spires, are particularly sensitive to earthquakes because they are tall and narrow. In zones of moderate seismicity the very top of a tower is particularly at risk because it is subject to high horizontal acceleration. It is rare for the rest of a tower to be badly damaged.

The supporting framework of a half-timbered house is generally made of wood, with a wattle and daub or brick infill. This method of construction is advantageous in the event of an earthquake.

Row houses often share main load-bearing walls, which can be favorable from the point of view of earthquake resistance. However, the position of the individual building within the group should be taken into account as this is also a factor when assessing earthquake resistance. For an individual building in the group, the connection between the walls and the ceilings should be examined, as unconnected walls can tip over.

Sketch: Row of houses/building group

Steel supporting structures are favorable from the point of view of earthquake resistance as they are normally ductile (up to 25 % deformable). The ductility of the connections must be checked by an earthquake engineer. The frequency of inspection depends on the type of supporting structure and its condition.

Suspended ceilings and light fixtures often fall down during an earthquake. To protect cultural artifacts, they must be securely attached to the ceiling.

Free-standing objects are vulnerable to earthquakes, especially if they are not attached firmly to a pedestal or to the floor, and/or if the pedestal is not fixed to the floor. There is a high risk that they will fall over.

Earthquakes can cause movable objects to fall over. Bars, glass panes or other fixtures should be fitted to stop objects falling off shelves. As shelves can also tip over, they should be bolted to load-bearing walls.

Tremors can cause non-load bearing walls to tilt and objects to be damaged or destroyed.

Buildings hit by earthquakes are usually damaged, i.e. walls are cracked, windows are broken, rooms are full of debris and broken glass, and alarm systems malfunction. It will therefore be necessary to take movable cultural artifacts to a safe place where they can be protected.

Since wall paintings form part of the surface of a wall, they can be damaged if masonry walls become cracked. Cracks in masonry walls are among the first damage to be caused by earthquakes. There are not many ways of protecting wall paintings. In some cases, it may be worthwhile separating the murals from the wall. It is also possible to reinforce the walls (e.g. with prestressing). It may also be possible to separate wall paintings from the supporting structure in order to avoid deformation or cracking.

During an earthquake there is no time to flee from a building so you should take shelter under a table or in a doorway. By contrast, it is extremely important that people are able to leave a damaged building quickly after an earthquake.

Many people do not know what to do if an earthquake occurs. It is advisable to inform staff what they should do to help visitors in the event of an earthquake.

Safety of visitors and staff in the event of an earthquake (in german)