We discuss the results of seismic survey to delineate temporal and spatial changes of frozen layer in Alpine environments. The seismic characterization allows us to detect changes of soil deformability properties related to the temperature effect on subsoi

Arato, Alessandro

Garofalo, Flora

Godio, Alberto

Socco, Laura

Théodule, A.

English

PORTO Publications Open Repository TOrino

Geophysical Research Abstracts
Vol. 14, EGU2012-5835, 2012
EGU General Assembly 2012
© Author(s) 2012
P-wave and surface wave survey for permafrost analysis in alpine regions
A. Godio (1), L.V. Socco (1), F. Garofalo (1), A. Arato (1), and A. Théodule (2)
(1) Politecnico di Torino, DIATI, Italy (alberto.godio@polito.it), (2) Fondazione Montagna Sicura - Montagne Sûre - Villard
de la Palud 1 - 11013 Courmayeur (Italy)
In various high mountain environments the estimate of mechanical properties of slope and sediments are relevant
for the link of the geo-mechanical properties with the climate change effects.
Two different locations were selected to perform seismic and georadar surveying, the Tsanteleina glacier (Gran
Paradiso) and the Blue Lake in Val d’Ayas in the massif of Monterosa. The analysis of the seismic and GPR lines
allowed to characterize the silty soil (top layer) and underlying bedrock. We applied seismic survey in time lapse
mode to check the presence of “active” layer and estimate the mechanical properties of the moraines material
and their sensitivity to the permafrost changes. Mechanical properties of sediments and moraines in glacial areas
are related to the grain-size, the compaction of the material subjected to the past glacial activity, the presence of
frozen materials and the reactivity of the permafrost to the climate changes.
The test site of Tsanteleina has been equipped with sensors to monitor the temperature of soil and air and with
time domain reflectometry to estimate the soil moisture and the frozen and thawing cycle of the uppermost
material. Seismic reflections from the top of the permafrost layer are difficult to identify as they are embedded
in the source-generated noise. Therefore we estimate seismic velocities from the analysis of traveltime refraction
tomography and the analysis of surface wave. This approach provides information on compressional and shear
waves using a single acquisition layout and a hammer acts as source. This reduces the acquisition time in complex
logistical condition especially in winter period.
The seismic survey was performed using 48 vertical geophones with 2 m spacing. The survey has been repeated
in two different periods: summer 2011 and winter 2011. Common offset reflection lines with a 200 MHz GPR
system (in summer) permitted to investigate the sediments and obtain information on the subsoil layering.
The processing of seismic data involved the tomographic interpretation of traveltime P-wave first arrivals by
considering the continuous refraction of the ray-paths. Several surface-wave dispersion curves were extracted in
f-k domain along the seismic line and then inverted through a laterally constrained inversion algorithm to obtain a
pseudo-2D section of S-wave velocity.
Georadar investigation (about 2 km of georadar lines in the first site) confirmed the presence both of fine and
coarse sediments in the uppermost layer; the seismic data allowed the moraines to be characterized down to
20-25 meters of depth. At the elevation of 2700 m asl, we observed a general decrease of the P-wave traveltimes
collected in November, when the near surface layer was in frozen condition, respect to the data acquired in
June. The frozen layer is responsible of the inversion of P-wave velocity with depth; the higher velocity layer
(frozen) cannot be detected in the tomographic interpretation of refraction tomographic of the P-wave arrivals.
Compressional wave velocity ranges from 700 m/s on the uppermost part, to 2000-2500 m/s in the internal part of
the sediments reaching values higher than 5000 m/s at depth about 20 m. The analysis of surface wave permit-
ted to estimate a slight increase from summer to winter of the S-wave velocity, in the depth range between 0 to 5 m.


P-wave and surface wave survey for permafrost analysis in alpine regions

We discuss the results of seismic survey to delineate temporal and spatial changes of  frozen layer in Alpine environments. The seismic characterization allows us to detect changes of soil deformability properties related to the temperature effect on subsoil

GODIO, Alberto

SOCCO, LAURA

GAROFALO, FLORA

ARATO, ALESSANDRO

A. Théodule

PORTO@iris (Publications Open Repository TOrino - Politecnico di Torino)

04 August 2020POLITECNICO DI TORINORepository ISTITUZIONALEP-wave and surface wave survey for permafrost analysis in alpine regions / A. Godio; L.V. Socco; F. Garofalo; A. Arato;A. Théodule. - ELETTRONICO. - 14(2012), p. EGU2012-5835. ((Intervento presentato al convegno EuropeanGeosciences Union, general Assembly 2012 tenutosi a Vienne nel April.OriginalP-wave and surface wave survey for permafrost analysis in alpine regionsPublisher:PublishedDOI:Terms of use:openAccessPublisher copyright(Article begins on next page)This article is made available under terms and conditions as specified in the  corresponding bibliographic description inthe repositoryAvailability:This version is available at: 11583/2502712 since: 2015-12-09T23:55:28ZGeophysical Research AbstractsVol. 14, EGU2012-5835, 2012EGU General Assembly 2012© Author(s) 2012P-wave and surface wave survey for permafrost analysis in alpine regionsA. Godio (1), L.V. Socco (1), F. Garofalo (1), A. Arato (1), and A. Théodule (2)(1) Politecnico di Torino, DIATI, Italy (alberto.godio@polito.it), (2) Fondazione Montagna Sicura - Montagne Sûre - Villardde la Palud 1 - 11013 Courmayeur (Italy)In various high mountain environments the estimate of mechanical properties of slope and sediments are relevantfor the link of the geo-mechanical properties with the climate change effects.Two different locations were selected to perform seismic and georadar surveying, the Tsanteleina glacier (GranParadiso) and the Blue Lake in Val d’Ayas in the massif of Monterosa. The analysis of the seismic and GPR linesallowed to characterize the silty soil (top layer) and underlying bedrock. We applied seismic survey in time lapsemode to check the presence of “active” layer and estimate the mechanical properties of the moraines materialand their sensitivity to the permafrost changes. Mechanical properties of sediments and moraines in glacial areasare related to the grain-size, the compaction of the material subjected to the past glacial activity, the presence offrozen materials and the reactivity of the permafrost to the climate changes.The test site of Tsanteleina has been equipped with sensors to monitor the temperature of soil and air and withtime domain reflectometry to estimate the soil moisture and the frozen and thawing cycle of the uppermostmaterial. Seismic reflections from the top of the permafrost layer are difficult to identify as they are embeddedin the source-generated noise. Therefore we estimate seismic velocities from the analysis of traveltime refractiontomography and the analysis of surface wave. This approach provides information on compressional and shearwaves using a single acquisition layout and a hammer acts as source. This reduces the acquisition time in complexlogistical condition especially in winter period.The seismic survey was performed using 48 vertical geophones with 2 m spacing. The survey has been repeatedin two different periods: summer 2011 and winter 2011. Common offset reflection lines with a 200 MHz GPRsystem (in summer) permitted to investigate the sediments and obtain information on the subsoil layering.The processing of seismic data involved the tomographic interpretation of traveltime P-wave first arrivals byconsidering the continuous refraction of the ray-paths. Several surface-wave dispersion curves were extracted inf-k domain along the seismic line and then inverted through a laterally constrained inversion algorithm to obtain apseudo-2D section of S-wave velocity.Georadar investigation (about 2 km of georadar lines in the first site) confirmed the presence both of fine andcoarse sediments in the uppermost layer; the seismic data allowed the moraines to be characterized down to20-25 meters of depth. At the elevation of 2700 m asl, we observed a general decrease of the P-wave traveltimescollected in November, when the near surface layer was in frozen condition, respect to the data acquired inJune. The frozen layer is responsible of the inversion of P-wave velocity with depth; the higher velocity layer(frozen) cannot be detected in the tomographic interpretation of refraction tomographic of the P-wave arrivals.Compressional wave velocity ranges from 700 m/s on the uppermost part, to 2000-2500 m/s in the internal part ofthe sediments reaching values higher than 5000 m/s at depth about 20 m. The analysis of surface wave permit-ted to estimate a slight increase from summer to winter of the S-wave velocity, in the depth range between 0 to 5 m.

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P-wave and surface wave survey for permafrost analysis in alpine regions

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