Monitoring the mechanics of mountain permafrost using ambient noise seismology
Authors: Guillemot Antoine , Larose Eric , Baillet Laurent , Helmstetter Agnès , Bodin Xavier , Delaloye Reynald 
Published: March 2024

Since last decades, coda wave interferometry (CWI) from ambient seismic noise has become an efficient method to probe continuous temporal changes of mechanical properties of the subsurface and crust. This method has successfully been used for environmental seismology issues, in a view of investigating the response of subsurface to environmental changes, in particular hydrological and thermal forcings (2). More, it has contributed to monitoring instabilities such rock slopes or landslides (3). Applying these methods to permafrost is then relevant to assess and monitor its mechanical response to environmental forcings.As lobate or tongue-shaped superficial landforms composed of frozen rock debris, active rock glaciers are widespread features of mountain permafrost (4), potentially causing emerging hazards linked to permafrost thawing and debris flows.Passive seismic instrumentation has been deployed for several years at Gugla, Tsarmine (Valais, Switzerland) and Laurichard (Hautes-Alpes, France) rock glaciers.CWI has been applied to compute daily averaged dV/V (or relative change in velocity of the surface waves). For the three sites studied, seasonal variations of shear stiffness have been measured, associated with freeze-thawing cycles (5) (6). We located these daily fluctuations in depth by using a 1D coda wave inversion scheme. We also tracked water-induced power spectral density (PSD) and we detected microseismic events, highlighting the role of water inputs in changing the mechanical state, thus accelerating the whole rock glacier body. Also, we developed a viscoelastic model to explain the seasonal variability of the kinematics of rock glaciers. Combined with other geophysical methods, environmental seismology paves hence the way to deeply understand the mechanical response of mountain permafrost landforms to thermo-hydrological forcings.&#160;ReferencesRichter, T., Sens&#8208;Sch&#246;nfelder, C., Kind, R., &amp; Asch, G. (2014). Comprehensive observation and modeling of earthquake and temperature&#8208;related seismic velocity changes in northern Chile with passive image interferometry.&#160;Journal of Geophysical Research: Solid Earth,&#160;119(6), 4747-4765
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