Seismic signature of the deadly snow avalanche of January 18, 2017, at Rigopiano (Italy)

Thomas Braun,Joachim Wassermann,Perry Bartelt,Daniela Famiani,Bernardino Chiaia,Barbara Frigo

doi:10.1038/s41598-020-75368-z

Abstract

Most snow avalanches occur unobserved, which becomes particularly dramatic when human lives are involved. Seismological observations can be helpful to unravel time and dynamics of unseen events, like the deadly avalanche of January 18, 2017, that hit a Resort-hotel at Rigopiano in the Abruzzi (Italy). Particle motion analysis and spectrograms from data recorded by a close seismic broadband station, calculation of synthetic seismograms, as well as simulation of the flow, allowed us to construct the dynamics of the snow avalanche that buried alive 40 people, killing 29. Due to the bad weather conditions, no visual observation was made, thus making it impossible to determine the exact moment of the avalanche and to report necessary observations of the dramatic event. On-site inspections revealed that the hotel was horizontally cut by shear forces and dislocated by 48 m in 70°N direction, once the increasing avalanche pressure exceeded the structural shear strength of the building. Within an eligible 24 min time range of the avalanche, we found three weak seismic transients, starting at 15:42:38 UTC, recorded by the nearest operating station GIGS located in the Gran Sasso underground laboratory approximately 17 km away. Particle motion analysis of the strongest seismic avalanche signal, as well as of the synthetic seismograms match best when assuming a single force seismic source, attacking in direction of 120°N. Simulation of the avalanche dynamics—calculated by using a 2D rapid mass movement simulator—indicates that the seismic signals were rather generated as the avalanche flowed through a narrow and twisting canyon directly above the hotel. Once the avalanche enters the canyon it is travelling at maximum velocity (37 m/s) and is twice strongly deflected by the rock sidewalls. These impacts created a distinct linearly polarized seismic “avalanche transient”s that can be used to time the destruction of the hotel. Our results demonstrate that seismic recordings combined with simulations of mass movements are indispensable to remotely monitor snow avalanches.

Highlights

Seismology provides useful tools that can help to better understand the dynamics of seismic events, different from earthquakes, as e.g. volcanic eruptions, rock falls or huge landslides[1,2,3,4,5]
We investigated a 15 s-lasting seismic signal, recorded at station GIGS that occurred at approximately the same time as the catastrophic event at Rigopiano and that cannot be associated to any earthquake of the Central Apennines seismic sequence
On-site inspection clearly revealed that the avalanche caused a sudden horizontal shearing of the hotel building’s second floor, which collapsed after accumulation of the snow masses along the external wall of the ground floor redirecting the avalanche to the second floor collapsing subsequently by shearing without affecting the foundation and without an efficient coupling into the ground

Summary

Introduction

Seismology provides useful tools that can help to better understand the dynamics of seismic events, different from earthquakes, as e.g. volcanic eruptions, rock falls or huge landslides[1,2,3,4,5]. RAMMS considered further the process of the entrainment (snowpack erosion, variability of density, temperature and humidity of the snow in motion along the path)[24] and allowed to calculate for the two-avalanche components pressure, velocity, density and flow height for each point of the running slope.

Results

Conclusion