SEG Honorary Lecturer Near Surface 2013
(Politecnico di Torino, Italy)
"Surface wave analysis for near-surface characterization: Introduction, theme and variations"
(by Florian)We, the SGS, had the pleasure to welcome SEG Near Surface Lecturer Valentina Socco at the Freie Universität Berlin on the 03/09/13.
On the day before the lecture a group of students joint her for an evening meal at the "Paddenwirt" located in the historical Nikolaiviertel in Mitte. Besides the delicious feast the topics of the evening included our future plans, the coffee drinking habbits of italiens, the german universitarian system and also german history. At 11 a.m. the next day we showed her around the campus. We were also able to give a quick guided tour through our facilities including a presentation of the rock physics laboratory. After this experience the staff of the geophysical department decided to go for lunch and was joint by our group. Valentina used the possibility to get in contact with the PhDs during the meal.
At 2 p.m. the lecture took place. The number of attendees was higher than we expected it to be. Coming from TU, GFZ and Uni Potsdam 23 people, Bachelor, Master and PhD students, were following the 90 min informative lecture on surface wave analysis. After the talk the officers of the SEG Student Chapter were invited by Valentina to have a coffee with her. We used this opportunity to reflect on the presentation, giving feedback and having a nice conversation. We said goodbye at the Hauptbahnhof wishing all the best for the future lectures.
While seismologists have been using surface waves to image the Earth's crust since the ‘60s and geotechnical engineers developed surface-wave analysis methods to characterize the soil in the ‘80s, we have had to wait until the last decade to see surface-wave analysis becoming a standard method in seismic exploration. Nowadays, surface waves, which are traditionally considered noise in seismic gathers, have shown the potential of estimating the shear properties of the shallow subsurface. They are, hence, routinely used in many near-surface applications that range from seismic hazard studies to the building of weathering-layer velocity models for seismic reflection corrections.
Different kinds of surface waves can be gathered, according to the environment and the subsurface conditions: Rayleigh waves, from land surveys, Scholte waves, in marine environments, Love waves, when horizontally polarized sources and receivers are used, Lamb waves or P-guided waves, when very high-impedance contrasts are present. Regardless of the kind of waves, the most established analysis method is based on the inversion of the geometrical dispersion of surface waves. This approach, which exploits the relationship between the vertical distribution of the seismic properties in the subsurface and the phase velocity of different surface wave harmonics, only considers the kinematics of the propagation and is based on several simplified assumptions. I will examine the potentials and limitations of this approach and different technical solutions for acquisition, processing, and inversion in the context of different applications.
The most important assumptions that are usually made in surface-wave analysis are that the site is 1D and that the experimentally retrieved dispersion curve coincides with the surface-wave fundamental mode. Both assumptions are often violated and specific measures have to be taken to handle multimodal propagation in laterally varying environments. Several technical solutions have been proposed and I will discuss them to define the best practice for surface-wave analysis in complex geologic conditions. Recently, tomographic techniques, which are usually applied in seismology, have been adapted to active seismic data. Their potentials and requirements will be presented.
Content: Society of Exploration Geophysicists
Laura Valentina Socco is presently associate professor in Applied Geophysics at the Politecnico di Torino, where she obtained her PhD in environmental geo-engineering (1997) and her MSc in civil engineering (1992). She has been in charge of the Applied Geophysics Lab at the Politecnico since 2007. Her research work covers several near-surface geophysical methods and applications, and, over the last decade, has focused on surface-wave methods and geophysical data integration for near-surface characterization, with particular regard to the development of new processing and inversion approaches. She is author of about 100 peer-reviewed scientific publications in journals and for conferences and has been given an honorable mention for Best Paper in Geophysics in 2012. She is member of the EAGE Research Committee, and is vice-chairwoman of the EAGE Near Surface Division Committee. She is Associate Editor of Geophysics (since 2003) and Near Surface Geophysics (since 2006). She has been the principal investigator of many research projects financed by national and international institutions as well as by private companies. She teaches geophysical prospecting in the Petroleum Engineering MSc Program. She has been advisor of more than 40 MSc and of 5 PhD theses. She has been convener of several workshops at EAGE conferences and an invited speaker at international conferences and research institutions.
Content: Society of Exploration Geophysicists