Discovery of deep long period earthquakes beneath the volcanoes of the French Massif Central

Volcanic landscape of the Chaîne des Puys in the Puy-de-Dôme, Auvergne © jef 77 / Adobe Stock

A recent study conducted by scientists from Institut des Sciences de la Terre (ISTERRE-OSUG, CNRS / IRD / UGA / Univ. Savoie Mont-Blanc/ Univ. Gustave Effeil) [1] and published in Geophysical Research Letters, reveals unusual seismic signals beneath the volcanoes of the Massif Central. These signals, linked to the active presence of magma at depth, suggest that the magma reservoirs beneath the Chaîne des Puys and the Pavin maar may still be active, despite 6,700 years of volcanic dormancy.

Geological studies have shown that volcanic eruptions have affected the Massif Central over the past 65 million years, with the most recent eruption occurring 6,700 years ago, giving rise to the Pavin maar. Since then, the region has been in a state of volcanic quiescence, relying on the stability of presumed magma reservoirs in the crust and upper mantle.

A unique seismic survey carried out as part of the ANR MACIV project

As part of the project ANR MACIV (Multi-scale seismic imaging of the sources of volcanism in the Massif Central), which aims to probe the deep structure of the Massif Central, 100 broadband seismometers were temporarily installed between 2023 and 2024, complementing the. permanent broadband network (RLBP) of the Epos-France research infrastructure.

Identification of deep long-period (DLP) earthquakes

The data analysis made it possible to detect several deep long-period (DLP) earthquakes located near the crust-mantle boundary beneath the volcanoes of the Chaîne des Puys and the Pavin region.

These earthquakes, previously observed beneath many volcanoes worldwide, are interpreted as resulting from the presence of active magma at depth. Their discovery could therefore indicate that the deep magma reservoirs beneath certain volcanoes in the Massif Central are still active.

Given the geodynamic context, as well as the number and frequency of the detected events, the situation in the Massif Central resembles that of the Eifel volcanic massif in Germany, which has also been dormant for about ten thousand years but where signs of renewed magmatic activity have been observed.

Perspectives and challenges for monitoring the Massif Central

The detection of these deep long-period earthquakes sheds light on the state of the magmatic system beneath the Chaîne des Puys and the Pavin region. These findings represent a significant step forward in understanding the long-term evolution of volcanism in the Massif Central.

These new data will help complement observations from the permanent Epos-France RLBP seismological network to strengthen monitoring in this dormant yet potentially reactivatable volcanic region.

Learn more

🌐 SISMalp website, Alpine seismicity observation network
🌐 French Central Seismological Bureau website :
🗞️ News (18/08/2020) : “Deep long-period volcanic earthquakes linked to magma degassing”"

References :

Deep Long Period Earthquakes Beneath Volcanoes of the French Massif Central
N. M. Shapiro, C. Aubert, S. Chevrot, A. Mordret, A. Paul, M. Sylvander, M. Laumonier, G. Boudoire, D. Laporte, N. Cluzel, J. Battaglia, G. Scheiblin, H. Pauchet, T. Souriot, F. Brenguier, M. Campillo, B. Plazolles, L. Gailler, E. Thébault. Geophysical Research Letters, 18 June 2025. DOI : https://doi.org/10.1029/2025GL114904

This article was published by CNRS INSU.