Feature article

Databases to improve knowledge of seismic risks

With the exception of its Caribbean islands, France is not a country with high seismic risk. However, it still registers nearly 500 minor earth tremors every year. On the initiative of the Ministry for Ecology and several scientific bodies, work has been undertaken to develop databases. For more than thirty years, BRGM has been recording the history of past earthquakes and enriching and managing its databases.

2 April 2008

Cover of the thematic file.

The 29 November 2007 earthquake in Martinique reminds us that seismic activity persists in the West Indies. In mainland France, earthquakes are relatively frequent but of moderate intensity with an average of one highly destructive earthquake and four earthquakes responsible for severe damage per century over a thousand years of history. However, the risk should not be underestimated.

Large inhabited areas, vulnerable infrastructures (dams, nuclear power plants and Installations Classified for the Protection of the Environment) could be seriously impacted by an earthquake. This explains why several databases track not only current earthquakes but also those of the past in order to better quantify and locate them.

Nearly 6,000 tremors in 1,000 years

The construction of nuclear power plants in the 1970s was accompanied by a programme to gain knowledge of the "seismic past". Back in 1975, BRGM, EDF (the electricity utility) and the Institut de Radioprotection et de Sûreté Nucléaire joined forces to launch SIRENE, a system to register past earthquakes. Managed by BRGM, this database, now called SisFrance, still benefits from permanent updates to provide the best possible knowledge of macroseismicity (i.e. tremors whose effects can actually be felt). This database has been accessible on line since 2002.

SisFrance has recorded nearly 6,000 tremors: it lists all earthquakes with an intensity greater than or equal to degree 4 on the macro-seismic intensity scale, 1,800 epicentres with their date, intensity, exact location and nearly 100,000 observations or localities affected.. The database also offers 10,000 bibliographical references testifying to the activity of earthquakes over time, the first mentioned dating from the year 463 AD in the Dauphinois lowlands.

Since 2002, the SisFrance site has been a great success with nearly one million visitors including the general public, professionals and design offices. Over the months, SisFrance has been going back in time to complete its data. Eventually, this database could be further developed and enriched by integrating regulatory data.