- The seismic risk in France
- Build your house in a seismic risk zone
- How is one built in seismic risk zone?
60% of the French municipalities are concerned by the seismic risk. Quite regularly enough small shakes come to remind us that, even if metropolitan France remains a country of moderate seismicity, the risk for buildings and people is present.
House construction and seismic risk
The seismic risk in France
The earthquakes that have occurred in recent decades in metropolitan France are distributed along areas of faults and folds very old. The most affected areas are the Pyrenees, the Alps, the Jura, the Rhenish ditch and to a lesser extent, the Armorican Massif and the Massif Central. The Paris Basin and Aquitaine pose a very low risk.
These findings led to the establishment of seismic zoning of the territory:
- Seismicity zone 1: very low risk
- Seismicity zone 2: low risk
- Seismicity zone 3: moderate risk
- Seismicity zone 4: average risk
- Zone of seismicity 5: strong risk
The seismic risk was taken into account by the State and resulted in the drawing up of a regularly updated earthquake plan. The evolution of scientific knowledge concerning the earthquake and the implementation of the European code of earthquake-resistant construction (Eurocode 8 or EC8), have led to an update of the zoning since January 2015.
Build your house in a seismic risk zone
In seismic risk zones, buildings must meet seismic standards. These standards are intended to preserve the occupants of a building. In case of strong shaking, it must not collapse.
To know which standards to apply, all constructions are classified into different categories. Residential buildings are considered "normal risk" works of importance category II. In concrete terms, this means that the damaging consequences of an earthquake " are circumscribed to the occupants and their immediate neighborhood "- Article R563-3 of the Environment Code.
In zone 1, no seismic standard is recommended.
From zone 2 "Preventive measures, including rules of construction, planning and seismic operations, are applied to buildings - Article R563-5 of the Environment Code". But for the construction of individual houses standards are simplified.
These standards apply to new buildings, the creation of new surfaces (addition, elevation) and significant changes to the structure of existing buildings.
How is one built in seismic risk zone?
A seismic construction takes into account the characteristics of the soil. A geotechnical study is needed to determine how the soil will behave during an earthquake. Sandy soil will aggravate the consequences of an earthquake on the building. It is imperative protect the building from falling rocks or landslide following an earthquake.
The shape of the building itself also plays an important role. Simple and compact forms are preferred. They are more resistant to shaking.
Construction standards also address this concern to avoid the collapse of the building with chainings (at floor and corner levels), framing of openings (doors, windows, bay windows) reinforced and bracing to ensure the stability of the building.
How to know the seismic risk in my commune?
Article D 563.8.1 of the Code of the Environment accessible on legifrance.gouv.fr details by department and by commune the level of risk. The portal prim.net: my common face to the risks allows to know all the risks for each municipality.