Abstract

Abstract

Abstract

Abstract
The fast development of field, data processing equipment and software has allowed the use of geophysical methods to an ever increasing range of applications. Hence nowadays it is much easier to conduct massive field surveys combining different methods, to obtain more accurate and denser data, so that complex modeling and interpretation at limited costs can be carried out. Landfills have been targeted by geophysical methods in order to investigate their environmental impacts. In fact, landfills have been the classic way to deposit domestic and industrial waste and have generated a large range of negative environmental impacts in groundwater and soils. These problems often persist even after the effective use of the landfills and subsequent recovery processes. Owing to their characteristics, landfills are difficult to access and because of the general lack of accurate information regarding the shape, nature of the refuse, history and development of the landfill, non-invasive, nondestructive methods and sometimes autonomous data acquisition devices must be used to monitor impacts and to investigate and prevent groundwater and soil contamination. Geophysical methods can be applied to investigate a wide range of aspects related with the assessment of the environmental impact of landfills. Problems such as geometry definition, geological settings, contamination plume location and monitoring investigation of internal structure and refuse zoning, determination of fluid flow direction and paths or the determination of sealing conditions and leakage may be more successfully evaluated if a carefully chosen geophysical survey is part of any investigation program. Because of the nature and complexity of the problems to investigate, only multidisciplinary approaches, involving geophysics, hydrochemical, hydrogeological and geological information, can provide meaningful results for a thorough assessment of the landfills impact on the environment. This work intends to demonstrate the application of geophysical methods in the investigation of the environmental impacts, as described above, of industrial and domestic landfills during their life time and after closure. Thus, several examples will be discussed illustrating the use of 2D, 3D and time lapse resistivity, electromagnetic, ground probing radar, self-potential, magnetic, gravity surveys and airborne thermal mapping. Most of the geophysical data will be presented and shortly discussed together with information from boreholes, geology, hydrogeology and hydrochemical data. As it will be shown, it is clear that only a judicious combination of methods and information from different nature can provide tools for the diagnosis and assessment of the impact of landfills in the environment, for the investigation of the best engineering solutions to remediate them and for the possible recovery of refuse with economic interest.

Abstract
Scientific models are considered to be fundamental in scientific research and in science education. In true inquiry activities the focus is not to confirm ideas that have already been presented but to promote a serious inquiry action that involves student-centered exploration and problem solving. Models provide students with a broader framework to undertake inquiry activities. Modelling is a process that reflects the spirit of sciences by mirroring scientific entrepreneurship. One kind of models that can be used to develop inquiry in geoscience higher education is replicas of historical models used to collect evidences and to discover new knowledge. Replicas of historical models always help students to identify the problem, formulate questions, decide the factors involved in the questions, understand the investigation and record modelling activities notes. Within this framework, it was built a replica of a shaking table founded in a Collection of Glass Plate Negatives which belonged to Professor John Milne, now in Carisbrooke Castle Museum, Isle of Wight. A PowerPoint presentation and modelling activities with the shaking table were applied to a non-random selection of participants. The convenience sample was constituted by 31 students from a graduation in Geoscience: 19 (61,3%) females and 12 (38,7%) males with 21,9 age average. A pre-experimental study was undertaken, with the application of a validated questionnaire, before and after the two hours modelling workshop. During the workshop it was discussed particular model problems, resorting to a problem-based learning approach, having as the starting point a scenario referring to the research studies conducted by J. Milne in the XIX century. The pre-experimental study was used to do a follow up validation of the questionnaire and also to evaluate if students understood the role of models and of modelling activities in teaching and learning geosciences. After the workshop, the Wilcoxon test was used to verify whether the average difference of the pre and post questionnaire was statistically significant. The group showed an improvement of the average in the questionnaire, increasing from 13,7 to 14,9. The difference that was obtained was statistically significant (Wilcoxon Z = - 1.929; p = 0,03). Considering the main objective of this study, we consider that it was proved that modelling is significant in an inquiry based teaching.

Abstract
Propagation of surface waves can occur with complex energy distribution amongst the various modes. It is shown that even simple Vs (shear-wave velocity) profiles can generate velocity spectra that, because of a complex mode excitation, can be quite difficult to interpret in terms of modal dispersion curves. In some cases, Rayleigh waves show relevant differences depending on the considered component (radial or vertical) and the kind of source (vertical impact or explosive). Contrary to several simplistic assumptions often proposed, it is shown, both via synthetic and field datasets, that the fundamental mode of Rayleigh waves can be almost completely absent. This sort of evidence demonstrates the importance of a multi-component analysis capable of providing the necessary elements to properly interpret the data and adequately constrain the subsurface model. It is purposely shown, also through the sole use of horizontal geophones, how it can be possible to efficiently and quickly acquire both Love and Rayleigh (radial-component) waves. The presented field dataset reports a case where Rayleigh waves (both their vertical and radial components) appear largely dominated by higher modes with little or no evidence of the fundamental mode. The joint inversion of the radial and vertical components of Rayleigh waves jointly with Love waves is performed by adopting a multi-objective inversion scheme based on the computation of synthetic seismograms for the three considered components and the minimization of the whole velocity spectra misfits (Full Velocity Spectra - FVS - inversion). Such a FVS multi-component joint inversion can better handle complex velocity spectra thus providing a more robust subsurface model not affected by erroneous velocity spectra interpretations and non-uniqueness of the solution.