GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 3.2 428 Conclusions Ambient seismic noise parameters measured at the potentially unstable tower top showed reversible fluctuations mainly driven by air temperature. Precipitation amounts were not found to directly influence resonance frequency values and velocity changes, but temporary modifications in spectral amplitude were detected in periods with frequent or intense precipitations. A general change in the seismic event type, rate and released energywas identified in the same timewindows. A clear match between the microseismic observations and the on-site measured displacement was found. No irreversible modifications uncorrelated with meteorological parameters, indicating an acceleration towards the tower collapse, were recorded during the monitored period. Despite the simple geometry of the tower, groundmotion analyses and 3D numerical modeling highlighted a more complex vibration pattern with respect to literature studies on nearly 2D rock columns and prisms, more similar to 3D case studies. The joint interpretation of ambient noise and microseismicity data enabled to follow daily and seasonal modifications in the site response to external modifications. Acknowledgements We thank Diego Franco for his support in network installation and maintenance. We are also grateful to Lorenzo Bidone, Osvaldo Pirchio and Gabriele Calabrese (PASI s.r.l. and Iridium Italia s.a.s.) for the commitment in the development of the seismic instrumentation used for this study. We are sincerely grateful to ARPA Piemonte, Daniele Bormioli and Giuseppina Moletta, for the support and permission to publish displacement and meteorological data. References Bottelin, P., Lévy, C., Baillet, L., Jongmans, D., Guéguen, P., 2013. Modal and thermal analysis of Les Arches unstable rock column (Vercors massif, French Alps) . Geophys. J. Int., 194, 849–858. Colombero, C., Baillet, L., Comina, C., Jongmans, D., Vinciguerra, S., 2017. Characterization of the 3-D fracture setting of an unstable rock mass: from surface and seismic investigations to numerical modeling . J. Geophys. Res. Solid Earth, 122(8), 6346–6366. Colombero, C., Baillet, L., Comina, C., Jongmans, D., Larose, E., Valentin, J., Vinciguerra, S., 2018a. Integration of ambient seismic noise monitoring, displacement and meteorological measurements to infer the temperature-controlled long-term evolution of a complex prone-to-fall cliff . Geophys. J. Int., 213(3), 1876–1897. Colombero, C., Comina, C., Vinciguerra, S., Benson, P.M., 2018b. Microseismicity of an unstable rock mass: From field monitoring to laboratory testing . J. Geophys. Res. Solid Earth, 123(2), 1673–1693. Colombero, C., Jongmans, D., Fiolleau, S., Valentin, J., Baillet, L., Bièvre, G., 2021. Seismic noise parameters as indicators of reversible modifications in slope stability: a review . Surveys in Geophysics, 42, 339–375. Fiolleau, S., Jongmans, D., Bièvre, G., Chambon, G., Baillet, L., Vial, B., 2020. Seismic characterization of a clayblock rupture in Harmalière landslide, French Western Alps . Geophys. J. Int., 221(3), 1777–1788. Lévy, C., Jongmans, D., Baillet, L., 2011. Analysis of seismic signals recorded on a prone-to-fall rock column (Vercors massif, French Alps) . Geophys. J. Int., 186, 296–310 Mainsant, G., Larose, E., Brönnimann, C., Jongmans, D., Michoud, C., Jaboyedoof, M., 2012. Ambient seismic noise monitoring of a clay landslide: toward failure prediction . J. Geophys. Res. Earth. Surf., 117, F01030. Valentin, J., Capron, A., Jongmans, D., Baillet, L., Bottelin, P., Donze, F., Larose, E., Mangeney, A., 2017. The dynamic response of prone-to-fall columns to ambient vibrations: comparison between measurements and numerical modelling . Geophys. J. Int., 208, 1058–1076. Corresponding author: chiara.colombero@polito.it