Evaluating Seismic Stability of Embankment Dams - Multiscale Geomechanics: From Soil to Engineering Projects - page 345

− Reservoir induced earthquake (RIE) : whose impact on nearby engineering
structures has to be examined during the project. The seismic level in France does
not require this study.
− Operating basis earthquake (OBE) after which the dam and connected
engineering works must stay in an operational state. This level assures the owner
that his or her structure remains in operation after the earthquake. Even if the
ICOLD proposes an average return period of 145 years, in accordance with the 50%
probability of over 100 years, the final decision concerning the retained criterion
belongs to the owner (for example, a 5% probability over the period of back
investment, that is over 200 to 500 years).
− Maximum design earthquake (MDE) after which the dam must keep its
stocking capacity and all its functions, and ensure population safety. The annual
probability of such an event is between 1,000 and 10,000 years.
− Maximum credible earthquake (MCE) : treated on a case by case level,
depending on the stakes and associated costs. For engineering works of significant
importance, this level is the same as the one corresponding to the MDE. It is
noteworthy that in Japan [JAP 02], it is recommended that two levels of MCE are
estimated: level 1, applied to common engineering works, which must induce
admissible seismic loads as computed by classical methods; and level 2, applied to
the most important or most exposed structures, which induces irreversible but
acceptable damages computed by more elaborate methods. Level 2 is similar to
MCE (the largest seismic ground motions that ever occurred and may occur in the
future at a given site).
10.4.3. Choiceoftheseismiccharacteristics
In France, the MCE is called séisme maximal de dimensionnement or séisme de
référence . It is determined by intra-continental seismicity. The earthquakes induced
by the encounter of the African and Eurasian plates are too far from France to be
taken into consideration. Japan, in comparison, is shaken by earthquakes of
magnitude 8 every 100 to 200 years at the bottom of the Pacific Ocean, and
earthquakes of magnitude 6 to 7 along the active faults with a return period of 1,000
years. The convergence of the plates is 2 cm/year in France compared to 6 cm/year
in Algeria. Furthermore, the successive and various orogeneses did not produce an
important stress concentration within the French territory. These data as well as the
seismic events, numbering 6,000, have been put into a database called Sisfrance .
The epicentral depths are statistically located between 5 and 20 km.