Preprints
https://doi.org/10.5194/nhess-2021-339
https://doi.org/10.5194/nhess-2021-339

  12 Nov 2021

12 Nov 2021

Review status: this preprint is currently under review for the journal NHESS.

Brief communication: Seismological analysis of flood dynamics and hydrologically-triggered earthquake swarms associated with storm Alex

Małgorzata Chmiel1,2,6, Maxime Godano1, Marco Piantini3, Pierre Brigode1,5, Florent Gimbert3, Maarten Bakker3, Françoise Courboulex1, Jean-Paul Ampuero1, Diane Rivet1, Anthony Sladen1, David Ambrois1, and Margot Chapuis4 Małgorzata Chmiel et al.
  • 1Université Côte d’Azur, Observatoire de la Côte d’Azur, Géoazur, CNRS, IRD, Sophia Antipolis, France
  • 2Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zürich, Zürich, Switzerland
  • 3Institute for Geosciences and Environmental Research (IGE), CNRS/INSU, IRD, University Grenoble Alpes and Grenoble-INP, Grenoble, France
  • 4Université Côte d’Azur, CNRS, ESPACE, bd Edouard Herriot, 06204 Nice, France
  • 5Université Paris-Saclay, INRAE, UR HYCAR, 1 Rue Pierre-Gilles de Gennes, 92160 Antony, France
  • 6Swiss Federal Institute for Forest, Snow and Landscape Research, Zürich, Switzerland

Abstract. On October 2, 2020, the Maritime Alps in southern France were struck by the devastating storm Alex that caused locally more than 600 mm of rain in less than 24 hours. The extreme rainfall and flooding destroyed regional rain and stream gauges. That hinders our understanding of the spatial and temporal dynamics of rainfall-runoff processes during the storm. Here, we show that seismological observations from permanent seismic stations constrain these processes at a catchment scale. The analysis of seismic power, peak frequency, and backazimuth provide us with the timing and velocity of the propagation of flash-flood waves associated with bedload-dominated phases of the flood on the Vésubie river. Moreover, the combined short-term average to long-term average ratio and template matching earthquake detection reveal that 114 local earthquakes between local magnitude ML = −0.5 and ML = 2 were triggered by the hydrological loading and/or the resulting in-situ underground pore pressure increase. This study shows the impact of storm Alex on the Earth’s surface and deep layer processes and paves the way to future works that can reveal further details of these processes.

Małgorzata Chmiel et al.

Status: open (until 24 Dec 2021)

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Małgorzata Chmiel et al.

Małgorzata Chmiel et al.

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Short summary
On October 2, 2020, the French Maritime Alps were struck by storm Alex. Storm Alex caused extreme rainfall, hazardous flash floods, and large damage. Here, we use seismological observations from permanent seismic stations to resolve the flash flood propagation on the Vésubie river. We further describe increased seismic activity in the Tinée river associated with storm Alex. Our study also gives a base for future works that may reveal additional details of the processes described herein.
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