Ten misconceptions about seismic risk

Earthquakes in France are rare... so much the better ! Not so long ago, however, some earthquakes reminded us that Western Europe was an active area, producing moderate and diffuse but very real seismicity. The mystery surrounding earthquakes has always favoured the emergence of hazardous theories, far-fetched observations, preconceived ideas..... Since the 1960s, seismology has grown considerably, mainly because of the need to explain the phenomena observed and felt, and also because of the desire to know the depths of the earth. The knowledge acquired since then has made it possible to remove some ambiguities about the seismic reality of France and the Rhône-Alpes region, and about the representation and observation of seismic phenomena. There are still preconceived ideas that this document tries to clarify. They are the expression of a diffuse knowledge of the major seismological concepts such as magnitude, seismic waves, site effects or seismic regulations, which are taken up and illustrated.

NB : following documents are available only in french.

Idée reçue N° 1 : Il n’y a pas de séismes pouvant provoquer des victimes en France - L’intensité macrosismique

Idée reçue N° 2 : Les séismes, on ne peut rien y faire - La réglementation parasismique

Idée reçue N° 3 : Il n’y a pas de séisme en Rhône-Alpes - Risque sismique en Rhône-Alpes : mythe ou réalité ?

Idée reçue N° 4 : L’échelle de magnitude de Richter contient dix niveaux - La magnitude des séismes

Idée reçue N° 5 : Les bâtiments anciens ne résistent pas aux séismes - Vulnérabilité sismique du bâti existant

Idée reçue N° 6 : Un bâtiment construit sur du rocher sera plus sûr - Les effets de site

Idée reçue N° 7 : Les séismes ne font pas de bruit - Surveillance sismologique

Idée reçue N° 8 : Les constructions en béton armé résistent mieux - Conception parasismique

Idée reçue N° 9 : Les séismes destructeurs se produisent tous les 475 ans - Zonage sismique de la France.

Idée reçue N° 10 : Les grandes catastrophes sont derrières nous - La sismologie urbaine

These documents are a simplified and educational support intended to shed light on certain aspects and concepts about earthquakes, with particular attention to the Rhône-Alpes region. They are intended for people who need to handle notions of seismology, engineering seismology and seismic engineering, but do not master all aspects of them. They should enable secondary school students, university undergraduates and professionals confronted with seismic problems to appreciate the richness of these phenomena and to decipher the seismic reality of France and the Rhône-Alpes region.

Earthquakes are, at their origin, natural phenomena that generate complex processes. It is illusory to want to give a complete and precise explanation in a few pages. As a result, some concepts and vocabularies may appear too complicated here, but references and cross-references to more comprehensive resource materials will allow readers to enrich and deepen their knowledge.

These documents were produced with the support of the European Community’s Alcotra programme as part of the project RiskNat

These documents are based on the results of research, experiments and observations carried out at the Institut des Sciences de la Terre de Grenoble by the members of the Risk team and as part of its involvement with the Observatoire des Sciences de l’Univers de Grenoble. In particular, it is the work carried out by Pierre-Yves Bard, Céline Beauval, Emmanuel Chaljub, Cécile Cornou, Fabrice Cotton, Philippe Guéguen, François Thouvenot and Marc Wathelet.