An international study analyzed, down to the smallest detail, the dynamics of the avalanche that overwhelmed the hotel in Rigopiano in 2017, accurately reporting the chronology of what happened
On 18 January 2017, an avalanche in the locality of Rigopiano in Abruzzo devastated a Resort-hotel. The event, which led to the loss of some people, was observed only by two witnesses who, fortunately, were outside the building.
There are many questions and hypotheses that revolve around this tragic event. A multidisciplinary study by the National Institute of Geophysics and Volcanology, the Turin Polytechnic, the WSL Institute for Snow and Avalanche Research SLF in Davos (CH) and the Geophysics Observatory of the University of Monaco (DE) sought to provide answers on the timing and dynamics of the avalanche.
Research "Seismic signature of the deadly snow avalanche of January 18, 2017, at Rigopiano (Italy)”, just published in Scientific Reports magazine, has ascertained that everything happened in just under a minute and a half. The avalanche detached from Monte Siella at 15:41:59 (UTC time), on its way down the valley it entered a canyon and at around 15:43:20 it hit the hotel in Rigopiano at a speed of about 100 km/h.
To arrive at such a precise result, the researchers first analyzed the timing of the emergency calls as reported by the news and then evaluated numerous data including the analysis of the National Seismic Network and the numerical modeling of the avalanche, then elaborated in studies engineering and theoretical seismograms obtained through simulations.
This complex and multidisciplinary work highlights a new reading of the dynamics of the event suggesting, among other things, potential non-traditional uses of a seismic monitoring network.
"A First Hypothesis" says Thomas Braun, one of the authors of the research, “born from the observation of a suspicious seismic signal, was the one that this signal was given by the impact of the avalanche itself with the hotel. A more in-depth analysis revealed, however, the existence of three distinct seismic phases, which could support a second hypothesis, that the avalanche had spread downstream in three consecutive phases.
To achieve these results, we first narrowed down the time window in which the avalanche occurred." explains Thomas Braun, “To do this we relied on the history and content of emergency calls and messages sent by the hotel. At 15:30 (UTC time) the last call from the structure took place while at 15:54 there was an attempt to send a WhatsApp message requesting help from a person who was blocked by snow. We deduced that the avalanche occurred in this 24-minute time window. We then looked for seismic signals hypothetically generated by the avalanche. At that time we were in the middle of the seismic sequence of central Italy, with epicenters about 45 km west of Rigopiano. Analyzing the signals recorded by the seismic stations, we noticed that the GIGS station located under the Gran Sasso had recorded an anomalous signal in the 24 minutes identified as the time window of the avalanche detachment. Of this signal”, continues the researcher, “we then studied the spectral content and the direction of origin, thus observing three distinct seismic phases that occurred within a few seconds. The decisive question that arises from this observation is how an avalanche moving on the surface can transmit seismic energy underground.
On the basis of the topography of the place, taking into account the type, temperature and humidity of the snow, hundreds of numerical models were carried out to reconstruct the route and dynamics of the avalanche, which provided an answer to the question: along the trajectory of the avalanche there are three points where the "moment", given by the product of height and speed of the avalanche, becomes maximal. These points correspond to the passage of the avalanche in the canyon, exactly at the entrance and at the following two deflections. The work just published has therefore made it possible to synchronize the modeling with the observations and to estimate the times of the event.
"The reconstruction of the event”, adds Thomas Braun, “showed that the avalanche in its descent towards the valley covered a total of 2400 meters and overwhelmed trees and rocks, changing mass with a continuous increase in its specific weight. Today we know that the speed with which the avalanche hit the hotel was 28 meters per second, almost 100 km per hour. Researchers at the University of Munich have calculated theoretical seismograms which - compared with the signal recorded at the GIGS station - find greater coherence if it is assumed that the seismic signal was generated during the passage of the avalanche in the canyon.
Researchers from the Turin Polytechnic, on the other hand, studied in detail, from an engineering point of view, the impact, collapse and dislocation of the main hotel building and, together with the WSL Institute for Snow and Avalanche Research SLF of Davos, investigated the dynamics of the avalanche by analyzing the topography of the slope before and after the event.
“Through our analyses”, concludes the researcher, “it was also possible to determine the exact time when the avalanche was generated and when the hotel was hit.
By applying this multidisciplinary methodology, one can therefore imagine a potential use of the network of seismic stations, specially configured for mountain areas, to monitor avalanches in remote and inaccessible places, useful for a more complete understanding of the phenomenon".
#ingv #politecnicoditorino #WSL #avalanche #retesismicanazionale #universitadimonaco
Rigopiano: identified the characteristics and the exact timing of the avalanche
By means of an international study, the dynamics of the avalanche that hit the hotel at Rigopiano in 2017 has been analyzed down to the smallest detail, accurately reporting the event chronology
On 18 January 2017, an avalanche in the municipality of Rigopiano in Abruzzo devastated a Resort-hotel. The event, which caused the loss of some people, was observed only by two witnesses who stayed fortunately outside the building.
Many are the questions and hypotheses around this tragic event. A multidisciplinary study conducted by the National Institute of Geophysics and Volcanology, the Polytechnic University of Turin, the WSL Institute for Snow and Avalanche Research SLF in Davos (CH) and the Geophysical Observatory of the University of Munich (DE) tried to provide responses on the timing and on the dynamics of the avalanche.
The research"Seismic signature of the deadly snow avalanche of January 18, 2017, at Rigopiano (Italy)", just published in Scientific Reports, revealed that everything happened in less than one and a half minutes. The avalanche detached from Mt. Siella at 15:41:59 (UTC), on its way down to the valley entered a canyon and hit the hotel approximately at 15:43:20 at a speed of about 100 km per hour.
To achieve such a precise result, the researchers first analyzed the timing of the emergency calls as reported in the news and evaluated then numerous data, like the analysis of the National Seismic Network and the numerical modeling of the avalanche, subsequently elaborated in engineering studies and theoretical seismograms obtained through simulations.
This complex and multidisciplinary work evidences a new interpretation concerning the dynamic of the event, suggesting, moreover, potential non-traditional use of a seismic monitoring network.
"A first hypothesis", affirms Thomas Braun, one of the authors of the research, "born from the observation of a suspicious seismic signal, was that this signal would have been generated by the impact of the avalanche with the hotel. An in-depth analysis revealed, however, the existence of three distinct seismic phases, which could support a second hypothesis, that the avalanche would have propagated in three consecutive phases.
To achieve these results, we first restricted the time window in which the avalanche occurred", Thomas Braun explains, "To do this, we relied on the chronology and contents of the calls and emergency messages sent from the hotel. At 3:30 pm (UTC time) the last call from the facility took place while at 3:54 pm there was an attempt to send a WhatsApp message requesting help from a person blocked by the snow.We deduced that the avalanche occurred in this 24-minute time window.We then looked for seismic signals hypothetically generated by the avalanche.In those days we were in the midst of the central Italy seismic sequence, with epicentres about 45 km west of Rigopiano.Analysing the signals recorded by the seismic stations, we noticed that GIGS station located under the Gran Sasso, had recorded an anomalous signal within the 24 minutes identified as the time window of the avalanche release. Concerning this signal”, continues the researcher, “we then studied its spectral content and the direction of origin, thus observing three distinct seismic phases which occurred a few seconds apart. The decisive question that arises from this observation is how an avalanche, moving on the surface, can transmit seismic energy in the subsoil.
On the basis of the topography of the place, taking into account the type, temperature and humidity of the snow, hundreds of numerical modeling were carried out to reconstruct the path and dynamics of the avalanche, which provided an answer to the question: along the avalanche trajectory there are three points where the "moment" (given by the product of height by velocity of the avalanche) becomes maximum. These points correspond to the passage of the avalanche through the canyon, exactly, at the entrance, and the two subsequent deflections. The work just published has therefore made it possible to synchronize the modeling with the observations and to estimate the timing of the event.
"The reconstruction of the event", adds Thomas Braun, "showed that the avalanche on its descent into the valley covered a total of 2400 meters and swept over trees and rocks, changing mass with a continuous increase in its specific weight. Today we know that the speed with which the avalanche hit the hotel was 28 meters per second, almost 100 km per hour. The researchers of the University of Munich calculated theoretical seismograms which - compared with the signal recorded at station GIGS – are more coherent, when assuming that the seismic signal was generated during the passage through the canyon.
The researchers of the Polytechnic University of Turin, however, supported the detailed study from an engineering point of view, focusing on the impact, collapse and displacement of the main building of the hotel and, together with the WSL Institute for Snow and Avalanche Research SLF of Davos, investigating the dynamics of the avalanche by comparing the topography of the slope before and after the event.
"Through our analyses", concludes the researcher, "it was also possible to determine the exact moment when the avalanche was generated and when the hotel was hit.
By applying this multidisciplinary methodology it is possible to imagine a potential use of a seismic network, specifically configured for mountain areas, to monitor avalanches in remote and inaccessible places, useful for a more complete understanding of the phenomenon".
#ingv #UniversityofTurin #WSL #University of Munich #seismicmonitoringnetwork #avalanche
caption: Figure 1: (a) Seismic stations of the INGV network (triangles) installed in Abruzzo. Yellow asterisks indicate the earthquakes of January 18, 2017 with epicenters near Campotosto, which occurred at UTC 09:25:40 (Mw5.1), 10:14:09 (Mw 5.5), 10:25:23 ( Mw 5.4), and 13:33:36 (Mw 5.0). Only the GIGS station, located 17 km west of Rigopiano, recorded a seismic signal, which can be associated with the avalanche that hit the hotel. (b) The avalanche caused the displacement of the first floor of the hotel by 48 m in the direction of 70°N and a rotation of ~13° counterclockwise.
caption: Figure 1: (a) Seismic stations of the INGV-network (triangles) installed in the Abruzzo area. The yellow stars indicate the earthquakes on January 18, 2017, with epicenters near Campotosto, which occurred at UTC 09:25:40 (Mw5.1), 10:14:09 (Mw 5.5), 10:25:23 (Mw 5.4 ), and 13:33:36 (Mw 5.0). Only station GIGS, situated at 17 km W of Rigopiano, recorded a seismic signal related to the avalanche that hit the hotel. (b) The avalanche caused a dislocation of the hotel's upper floor by 48 m in ~70°N direction and a ~13° anticlockwise rotation.
caption: Figure 2: Seismic traces recorded at the GIGS station: (a) a 24 min time window around the avalanche event, (b) 20 s zoom of the moving trace, indicating three distinct phases generated by the avalanche, (c ) spectrogram of the E component (GIGS station) illustrated for the time window of 20 s indicated in Fig. 2b.
caption: Figure 2: Seismic traces recorded at station GIGS: (a) a time window of 24 min around the avalanche event, (b) 20 s zoom of the displacement trace, indicating three distinct phases T1,T2 T3 generated by the avalanche, (c) spectrogram of the E-component (GIGS station) plotted for the 20 s-time window of Figure 2b.
caption Figure 3:
Simulation of the trajectory of the avalanche of 18 January 2017 in Ricopiano and comparison with the seismic signal: (a) progression of the "momentum" modeled along the path of the avalanche. At the canyon entrance (T1), and the deflection points (T2, T3) maximal moment values are expected. (b) Elevation of the route (black line), speed of the avalanche (red line) and the corresponding time (s) following the release, as a function of the distance from the release area. (c) Component E of the seismic record, indicating the arrival times of the three seismic transients (at 15:42:38, 45 and 51 UTC). The avalanche reaches the hotel after about 81 s.
caption: Figure 3:
Track simulation of the Rigopiano avalanche of January 18, 2017, and comparison with the seismic signal: (a) progression of the modeled momentum along the avalanche track. At the entrance into the canyon (T1), and the deflection points (T2, T3) maximum momentum changes are expected. (b) Track elevation (black line), avalanche velocity (red line) and corresponding Time (s) after nucleation, as function of distance from the release area. (c) E-component of seismic recording, indicating the onset times of the three seismic transients (at 15:42:38, 45 and 51 UTC). The avalanche reaches the Hotel after approximately 81 s