Faults and Earthquakes - Earthquake Engineering for Structural Design - page 201

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Crust
fracture
earthquakes

Figure 6.21 Seismotectonic map of Belgium (after Camelbeek, 2005)

Germany and Switzerland (Western zones) seismicity is influenced by the
Lower Rhine and Upper Rhine grabens, respectively (Fig. 6.22). Modern
earthquakes in the Rhine Valley have not exceeded magnitude M 6.0, but
geological studies reveal that its border faults are capable of producing magnitudes
M 6.0-6.5 earthquakes and generating ground rupture. On 1356 the most
damaging intraplate earthquake known to have occurred in Central Europe
devastated the city of Basel, Switzerland (RMS, 2006). Events of this magnitude
(estimated between M 6.0 to 6.9) are very rare in Central Europe, because the
seismic activity in this area is characterized by low levels of seismicity.
Austria, Slovakia, Hungary, Serbia, Croatia and Western Romania territories
are characterized by the presence of many active faults, which produce low to
moderate earthquakes (Fig. 6.23a). The best example is the Banat (Western
Romania) earthquake, produced by a network of faults (Fig. 6.23b).
Northern area considers the Scandinavian countries. The intraplate areas of
Scandinavia have only experienced small earthquakes. The most famous
Norwegian earthquake occurred in 1904 having the magnitude M 5.4. But almost
one hundred years earlier, in 1819, an even more powerful earthquake occurred,
being estimate with a magnitude M 5.8 to 6.0 (Norsar 2004, Gregersen, 2006). A
map of known earthquakes above M 3.0 is shown in Figure 6.23. Stress
accumulation in the crust is caused by forces related to the relative movements of
the tectonic plates: from the Mid-Atlantic Ridge stresses are imposed on the
Eurasian Plate where Norway is located.