Bäckström, E.

Colombero, C.

Da Col, F.

Malehmir, A.

Marsden, P.

Papadopoulou, M.

Socco, L. V.

English

Socco L. V.

Papadopoulou M.

Da Col F.

Colombero C.

Bäckström E.

Marsden P.

Malehmir A.

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

04 August 2020POLITECNICO DI TORINORepository ISTITUZIONALESurface wave dispersion analysis in hard rock sites: challenges and opportunities / Socco, L. V.; Papadopoulou, M.; DaCol, F.; Colombero, C.; Bäckström, E.; Marsden, P.; Malehmir, A.. - In: GEOPHYSICAL RESEARCH ABSTRACTS. -ISSN 1607-7962. - 21(2019), p. EGU2019-18283. ((Intervento presentato al convegno EGU General Assembly 2019tenutosi a Vienna (Austria) nel 7-12 April 2019.OriginalSurface wave dispersion analysis in hard rock sites: challenges and opportunitiesPublisher: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: 11583/2746474 since: 2019-08-06T20:13:07ZCopernicus GmbHGeophysical Research AbstractsVol. 21, EGU2019-18283, 2019EGU General Assembly 2019© Author(s) 2019. CC Attribution 4.0 license.Surface wave dispersion analysis in hard rock sites: challenges andopportunitiesLaura Valentina Socco (1), Myrto Papadopoulou (1), Da Col Federico (1), Colombero Chiara (1), BäckströmEmma (2), Marsden Paul (2), and Malehmir Alireza (3)(1) Politecnico di Torino, DIATI, Italy (valentina.socco@polito.it), (2) Nordic Iron Ore AB, (3) Uppsala UniversityAnalysis of surface wave (SW) dispersion data is widely used for exploring the subsurface at various scales. Morethan 95% of published examples, however, refer to soft sites characterized by soil layers. In these conditions,SW exhibit smooth, broadband, often multimodal dispersion patterns. On stiff sites, characterized by very thinoverburden above shallow or even outcropping rocks, SW data become noisy and higher modes can prevail over thefundamental mode (Bergamo et al., 2011). Moreover, local fractures and heterogeneities can generate scatteringand back reflections in a certain frequency band (Pileggi et al., 2011). On the other hand, high phase velocitiesof rock materials produce long wavelengths that make the investigation depth significant also for band limited data.We show using synthetic and real data from a hard rock mining site the typical spectral patterns that canbe expected on hard rock sites and the effect of having or not having a thin soft overburden with high impedancecontrast with the underlying bedrock. In case of overburden, two well separated dispersive wavetrains aregenerated on top and on bottom of the overburden. The slow event generated on top of the overburden followsthe theoretical fundamental mode of Rayleigh waves, while the fast event generated at the top of the hard rockcoincides with the theoretical first higher mode. They can be separated and muted both in t-x domain and in f-kor f-v domains. For outcropping rock, the slow event is not present and a poorly dispersive high-energy event isgenerated. This propagation mode is very similar to the higher mode in case of overburden and corresponds to thefundamental mode of Rayleigh wave propagation. The clear interpretation of the nature of dispersive events is ofparamount importance for their inversion.We present a processing workflow based on muting and multi-stage inversion to handle hard rock SW dataand obtain reliable pseudo-2D VS models. Spectral energy vs. offset is used to identify different environmentsfor wave propagation (Colombero et al, 2018) and a method based on skin depth of surface wave (Socco andComina, 2017) is used to estimate Poisson’s ratio and transform the VS models into VP models. This leads to acomprehensive site characterization in hard rock environments using surface wave data.Acknowledgements: Smart Exploration has received funding from the European Union’s Horizon 2020 re-search and innovation programme under grant agreement No.775971.ReferencesBergamo, P., Comina, C., Foti, S. and Maraschini, M.: Seismic characterization of shallow bedrock sites withmultimodal Monte Carlo inversion of surface wave data, SDEE, 31, 8530-534, 2011.Colombero, C., Papadopoulou, M., Socco, V. and Comina, C.: Multifold optimization of surface-wave methodsfor imaging of sharp lateral variations, SEG Technical Program 2018, 4723-4727, 2018Pileggi, D., Rossi, D., Lunedei, E. and Albarello, D.: Seismic characterization of rigid sites in the ITACA databaseby ambient vibration monitoring and geological surveys, BEE, 9, 1839-1854, 2011. doi: 10.1007/s10518-011-9292-0Socco, V. and Comina, C.: Time-average velocity estimation through surface-wave analysis: Part 2 – P-wavevelocity, Geophysics, 82, 3, U61-U73,

Surface wave dispersion analysis in hard rock sites: challenges and opportunities

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Surface wave dispersion analysis in hard rock sites: challenges and opportunities

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