Thirty years of paleoseismic research in metropolitan France

Olivier Bellier,Edward Marc Cushing,Michel Sébrier

doi:10.5802/crgeos.102

Abstract

A critical review is conducted of a selection of paleoseismic works published on, or close to, metropolitan France over the last 30 years. The evolution of these works may be subdivided into three periods: dawn of French paleoseismic studies (≈1990–1995), beginning of a multidisciplinary paleoseismologic approach, and paleoseismic studies in the first decades of the 21st century. This review of the most interesting paleoseismic studies at nine trench sites indicates that it is often difficult to associate Quaternary surface deformations with a well-identified fault. However, these studies also provided important results demonstrating that even in regions of low seismicity, seismic ruptures can repeat on the same low slip rate fault, thus providing evidence that historical seismicity is not sufficient to assess seismic hazard in metropolitan France. Finally, recommendations are provided for future paleoseismic investigations in low-seismicity regions.

Highlights

Paleoseismology was developed by US geologists, at the turn of the 1960s and 1970s to address the lack of historical earthquake records in the western states, with the goal of identifying and characterizing past earthquakes beyond the scope of instrumental seismicity
Results brought by paleoseismology in metropolitan France: toward a paleoseismic approach for low-seismicity regions
A lot of efforts have been made in the western European paleoseismology community to improve active fault identification

Summary

Introduction

The overall methodology used to identify paleoseismic events can be summarized as the search for evidence (or clues) preserved in Late Quaternary sedimentary deposits associated with their cumulative effects on the landscape These paleoearthquakes are determined either directly through the discovery and analysis of their past ruptures at or near the surface, or indirectly, through changes in the past geological and geomorphic environments. Paleoseismology requires the identification of active faults in order to associate past surface ruptures with their seismogenic characteristics (past earthquake locations, magnitudes, average return periods, etc.) These paleoearthquake data permit to extend the temporal scales provided by the instrumental and historical seismicity to the prehistoric time period. Paleoseismic studies allow for improved the hazard analyses (e.g., prior to the construction of nuclear facilities) This method was first used in regions characterized by moderate to high level of seismicity (i.e., the central and western United States). These researches have spread worldwide among seismic regions and many studies are conducted each year (average of ∼100/year of published works worldwide since 2003, Figure 1)

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Conclusion