Earthquakes and Ground Motions - Earthquake Engineering for Structural Design - page 277

Fracture of weak crust Collision of two Fracture, collision

continental plate and subduction

faults faults

Figure 7.54 Histograms for intensity in three European countries: Germany,
Switzerland and Greece (after Pinto, 2000)

In the last few years, the understanding of earthquakes that occur in low to
moderate zones has improved, as Eastern North America, Central and Northern
Europe, South of China and Eastern Australia, made progress in the establishment
of the main characteristics of these earthquake types (Mooney et al, 2004, Schulte
and Mooney, 2005, 2007). Consequently, the results derived from these analyses
show that the recorded intraplate earthquakes were generally different from the
interplate-recorded earthquakes. Unfortunately, the information referring the
characteristics of these intraplate earthquakes remains until now very reduced in
comparison with that existing for interplate earthquakes.
Although only about 5% of the global seismic energy is released in continental
interiors by intraplate earthquakes, some of the most damaging earthquakes
occurred there (see Tangshan and Sishuan-China and Bhuj-India), due to the near-
source effects and the local site conditions in the urbanized areas. The great limit in
the structural design for moderate earthquakes is that the results obtained for the
other earthquake types, mainly for interplate earthquakes, are normally extended
also to these earthquakes. In the last decades a significant progress has been
reached in the understanding of the seismic risk for intraplate earthquakes,
especially based on studies of earthquakes that have occurred in Central United
States and Northern Europe (Gioncu, 2008).

7.6.2 Low-to-moderate Near-source Ground Motions of Intraplate
Earthquakes

First of all, one must mention that the following characteristics of intraplate
earthquakes refer only to the ones produced by rifts. When the intraplate