Faults and Earthquakes - Earthquake Engineering for Structural Design - page 182

- Crustal intraplate earthquakes, are produced in the interior crust of a tectonic
plate, far from the boundaries, in the diffuse zones (see Section 5.3). In this case,
the ground movements are caused by the previous rupture, or by a new one, due to
the reaching of the rock bearing capacity. Thus, generally, an intraplate
earthquake occurs in the same seismic area but not in the same place, as in the
case of interplate earthquakes. So, the position of an intraplate earthquake is,
generally, very difficult to determine beforehand.
- Intraslab (inslab) earthquake, affected by thermal phenomena, the earthquake
occurs in slab (subducted oceanic plate), at shallow or deep depth. It is situated in
a slab, in a zone under the Earth crust, where the solid rock begins to be
transformed into molten-lava, due to the high temperatures and pressures.
Therefore, very special features, different from the cases presented above,
characterize this source type.
Generally, a seismic zone is composed by one or more source types. The best
case to exemplify this fact, is given by the European territory, which is composed
by four distinct zones (Fig. 6.2). The first zone is the Mediterranean basin, where
the Northern zone (along the Alps) is dominated by crustal interplate earthquakes
and the Southern zone (along North Africa, Sicily and Greece) by crustal
interplate and intraslab earthquakes. The second zone is the Central Europe,
characterized by crustal intraplate earthquakes (France, Belgium and Germany).
The third zone is the Northern area (UK and Norway), which is dominated also by
the intraplate earthquakes. The last important zone is the Carpathian one
(Romania), characterized by intraslab earthquakes.
Figure 6.2 European seismically active zones (Gioncu, 2006)