Historical seismicity of the Mont Dore volcanic province (Auvergne, France) unraveled by a regional lacustrine investigation: New insights about lake sensitivity to earthquakes

Abstract

Lake sediments are relevant natural seismographs over long time scale. However, because tectonic events are not systematically recorded in lake sediments, one forthcoming challenge for paleoseismology is to better assess lake sensitivity to earthquakes. To this end, a limnogeological investigation, including hydroacoustic mapping techniques, core sampling and multi-proxy sediment analyses, has been conducted within four small volcanic lakes located in the Mont Dore province (Auvergne, France), an area with a moderate seismo-tectonic activity. Results show the existence of several gravity reworking processes in the lakes over the last millennium. Around AD 1300, the occurrence of synchronous events in lakes Pavin, Chauvet, Montcineyre and Guéry (100km2 area) highlights an undocumented earthquake as a common trigger for slope failures in disconnected basins. At regional scale, the record of this tectonic event may have been favored by human-induced increase in sediment load (Chauvet and Montcineyre) and/or after an abrupt lake-level drop (Pavin) affecting the sediment stability. In addition, synchronous turbidites and mass-wasting deposits (MWD) recorded in lakes Pavin and Guéry provide evidence for a seismic activity during the XIXth century. Potential triggers are historical earthquakes that occurred either in the Mont Dore area or in the southern part of the Limagne fault at this time. Despite moderate seismic activity in this intraplate volcanic domain, these results highlight the role of tectonics as a major trigger in the sedimentary processes dominating these lacustrine infills. Within the diversity of studied sites, it appears that lake sensitivity to earthquakes was not constant over time. This sensitivity can be expressed as a combination of external factors, namely earthquake magnitude and lake-epicenter distance and internal factors such as lake morphology, nature of sediment, lake-level fluctuations and human-induced changes in catchment sedimentary load.