Earthquake impact in Germany
The earthquake hazard in Germany is described by an earthquake zone map (with zoning from 0 to 3). Areas not assigned to earthquake zones 1 to 3 are classified as areas of very low seismicity, so that no earthquake verification is required for structures in these areas. The reference return period is 475 years, which corresponds to a probability of occurrence of 10% in 50 years.
The boundaries of the earthquake zones correspond to intensity limits of 6.0, 6.5, 7.0 and 7.5 according to the EMS scale, with a reference peak value of ground acceleration agR assigned to each zone in DIN EN 1998-1.
Ground and sub ground classes
The influence of the subsurface conditions on the strength of possible earthquakes is taken into account both with regard to the nature of the existing foundation soil and with regard to the geological subsurface conditions ("deep geology"). For this purpose, the subsoil is assigned to one of the intended subsoil classes A, B and C. With regard to the geological subsoil, a distinction is made between classes R, S and T, the spatial distribution of which is also described by the map shown above.
|Ground classes (≤ 20m Depth)||Ground classes (≥ 20m Depth)|
unweathered (freshly mined) solid rocks with high strength;
dominant shear wave velocities are higher than about 800 m/s;
|R||Solid rock areas|
|B||moderately weathered bedrock or bedrock with lower strength or coarse-grained or mixed-grained unconsolidated rocks with high frictional properties in dense storage or with a bedding or in solid consistency (e.g., glacially preloaded unconsolidated rocks). Dominant shear velocities velocities are between 350 m/s and 800 m/s;||S||Area of shallow sedimentary basins and transition zones|
|C||strongly to completely weathered solid rock or -coarse-grained or mixed-grained unconsolidated rocks in medium-dense bedding or of at least stiff consistency ; dominant shear wave velocities are approximately between 150 m/s and 350 m/s.||T||Areas of deep sedimentary basins|
With the soil acceleration and the soil and subsoil class, the design response spectra required for the structural design can be established. The following figure shows the response spectra for different subsoil combinations and a soil acceleration ag of 0.8 m/s2.