Objectives

Seismic risk assessment

The objectives of the seismic risk work developed in our team are multiple, ranging from hazard estimation to soil or structure response to earthquakes:

  • The team is conducting research on seismic hazard study, from the failure process to probabilistic seismic hazard estimation, to improve ground motion predictions.
  • The team is developing new techniques for simple and inexpensive underground reconnaissance.
  • The team’s work also aims to better understand and quantify the importance of spatial variability of the incident wave field on deformation and structural damage.

Gravity risk study

Gravitational instabilities are responsible for nearly 10,000 victims per year. They are therefore a major issue in many mountain regions. The factors that trigger these instabilities are multiple: rain, earthquake, frost... The understandinag of the triggering processes is still limited. The team’s work in this area is to:

  • develop methods to characterize the volume and mechanical properties of gravity movements by combining ground displacement measurements (RFID) or satellites and geophysical measurements (active seismic, background noise, electrical).
  • study the different environmental forcings (frost/degel, earthquakes, rain) on the deformation mechanisms of gravitational movements based on temporal monitoring of temperature, deformation, variation in seismic wave velocities.
  • detect precursors at rupture from seismological listening.
  • quantitatively evaluate the hazard of falling blocks from the statistical study of rockfall databases.

Coupling between the environment and solid earth

Solid earth is continuously subjected to various stresses that are likely to affect its subsurface mechanical and geophysical properties. The densification of instruments, the increase in their sensitivity, but also the emergence of massive data processing techniques now make it possible to measure minute variations induced by environmental forcings, particularly with seismic waves.

External forcings include temperature and precipitation, anthropogenic forcing, biological forcing (root development, bioturbation).

Internal forcing includes damage, gravity effect, tectonic loading.
The quantification of these forcings is essential for understanding the dynamic mechanisms that occur in the Earth’s crust. However, none can be studied without its effects being isolated or dissociated from the effects of other forcings.

The team’s objectives are to quantify these forcings with geophysical observations, particularly seismic observations, but also to discriminate between reversible and irreversible evolutions, and to dissociate external and internal forcings.

Activities in Southern countries

The team has a particular sensitivity to the scientific issues related to the reduction of seismic and gravity risk in the countries of the South.

In Ecuador, contributions to the catalogue, tectonic zoning recurrence models and PSHA analysis led to the new official seismic zoning.

In Peru, efforts have focused on

  • assistance for the construction of a seismic microzoning project in Lima,
  • the determination of the average dynamic parameters of buildings in Peru, leading to the revision of the local seismic code.
  • the implementation of monitoring of the Maca landslide (South Peru, Arequipa region)
  • mapping landslides triggered by earthquakes

In Algeria, several aspects of the use of ambient vibrations in site studies (H/V and networks) were addressed, with results on the existence of significant topographic effects at Boumerdès even for gently sloping slopes, the 3D geometry of the seismic bedrock, and details on the alignment of two faults under the city.

In Lebanon, efforts initially focused on local seismic hazard analysis in Beirut have expanded to include regional hazard estimation for the whole of Lebanon, vulnerability studies in Beirut, and surface structure imaging at two scales (very dense: 1ha area, and Beirut city).