This study demonstrates the effectiveness of applying Electrical Resistivity Tomography (ERT) to investigate the internal structure of an active alpine landslide. The use of two innovative systems - MultiSource and FullWaver - allowed for the acquisition of high-density 2D and 3D resistivity datasets, achieving investigation depths greater than 200 meters. The results revealed a well-defined conductive zone interpreted as a saturated, mechanically weak pelitic-marly complex, bounded by resistive carbonate formations. The 3D resistivity model confirmed the presence of a bowl-shaped sliding structure underlying the inhabited area of Cazzaso. These findings contribute significantly to the understanding of the geoelectrical and hydrogeological behavior of deep-seated landslides and provide a solid basis for future monitoring and mitigation strategies. The application of such advanced distributed ERT systems opens new possibilities for landslide characterization and risk management.

Abstract This paper presents the results of the interpretation of a set of high‐resolution seismic lines integrated with multibeam echosounder data acquired in a coastal area in the Northern Adriatic Sea. The aim of the study was to reconstruct the stratigraphic evolution of a late Quaternary sedimentary succession offshore the town of Bibione, North‐Eastern Italy, by recognising the key unconformities, identifying the main depositional units, dating them and reconstructing the depositional environments in relation to relative sea‐level variations. Specifically, four sedimentary units, separated by erosional unconformities associated with the development of deep channels, were identified and dated based on literature information. By interpreting the seismic data, sedimentary dynamics were reconstructed and palaeoenvironments identified. The lower unit corresponds to a paludal environment, showing abundant gas seeps and accumulations (bright spots); the two intermediate units correspond to fluvial deposits, filling the deep incisions that characterise the bounding surfaces. Finally, the shallowest unit, bounded by a wave‐ravinement surface incised by tidal currents, corresponds to the Holocenic progradation of the coastal wedge. In addition, several vertical gas chimneys were identified, ranging in width from a few metres to 20–30 m. These were present in all units, often reaching the sea floor. Finally, elongated mounds, about 300 m wide, at the sea floor were recognised. The bathymetric and seismic characteristics of these elongated bodies and their relationship to adjacent sedimentary bodies suggest that they are probably methane‐derived carbonate formations known as ‘Trezze’ or ‘Tegnùe’. These names recall the fact that the trawls of the local fishermen were often hindered (‘tegnù’ in the Venetian language) or even cut off by these formations.

Integrated geophysical analysis using different methods along with a priori information from wells, is a proven approach to investigate the geology and the petro-physical characteristics of subsoil. We collected seismic and geoelectric data in an area located on the Adriatic coast in North-Eastern Italy, aimed at characterizing the quaternary sediments and the shallow geological structures. Compressional and shear-wave data provided information about geometry and velocity of the quaternary sedimentary succession, while geoelectric data provided information about the resistivity in the shallower formation, which strongly depends on the presence of groundwater (brine) and on its salinity. Clustering analysis allowed us to subdivide the study area into subdomains showing similar values of resistivity and compressional- and shear-wave velocity, enabling for a better interpretation of the processed seismic sections. Then, we calculated the petro-physical properties of the investigated sediments, i.e., brine saturation and resistivity, porosity, and clay content, for each cluster. This inverse problem involves rock-physics theories and an optimization algorithm based on the simulated annealing global-search method. The results, validated using borehole stratigraphy, provided information about the salty water wedge intrusion.

We present two case studies of the application of seismic surveys to estimate the elastic properties of soil and rock in the shallow subsurface. The two sites present very different geological characteristics. The first test site is a town on the Croatian coast, not far from the city of Split, built on hard rock, where we acquired three seismic lines. The second site is located in the outskirts of the city of Ferrara, in Italy, in an alluvial plain, where two lines were acquired. In both sites, for detailed characterization, we acquired surface-, compressional- and shear-waves, further distinguishing the latter between horizontally (SH) and vertically (SV) polarized wavefields. We processed the data by performing a Multichannel Analysis of Surface Waves to compute a preliminary one-dimensional shear wave velocity profile. Then, we performed first-break tomography to compute P-, SH- and SV-velocity profiles. Such unusual acquisition allowed us to compute not only basic engineering parameters such as the equivalent shear-wave velocity of the first 30 m of subsurface (VS30) from the SH profiles but also other useful parameters such as the VP/VS and estimate the anisotropy of the medium thanks to the VSV/VSH. Given the level of detail of the results and their engineering value, we conclude that the method of investigation we applied in the two test sites is a valuable tool for characterizing the shallow subsurface.

Summary We present the application of an innovative survey technique for in-depth characterisation of the elastic properties of the shallow subsurface. The novelty of the method lies in the fact that we acquired along the same line surface-, as well as P-, SH- and SV-waves. First, we perform multichannel analysis of surface waves to estimate a preliminary 1D VS profile, which served as reference for further analyses. Then, we performed first-break tomography on both lines, for all wavefields, obtaining velocity profiles. Thanks to the unusual acquisition, from these profiles we are able to compute not only basic engineering parameters like the VS30, but also geotechnical parameters like VP / VSH and VSV / VSH (i.e. estimate the anisotropy of the medium). We then perform a cluster analysis based on the VP / VS and map the sediments accordingly, obtaining further useful information like the position of the water table.

The acquisition of S-wave seismic data, separating S H (orthogonal to the seismic line) and S V (parallel to the seismic line) wavefields on the same seismic line, is not so frequent. However, this type of acquisition allows obtaining important information on the investigated area; in particular the anisotropy of the sediments, which can be detected from the differences between the corresponding two velocity fields. In this work, we analysed the S V - and S H -wave data in order to answer two questions: how can we estimate anisotropy from the comparison of the velocities of the S V and S H wavefields? What information can be obtained about the dip and strike angles of the anisotropic layers from this analysis? For this purpose, we used the travel time tomography to obtain the two velocity fields ( V SV and V SH ) and to exploit the computed ray paths from which we can know the directions of each ray segment crossing the model, associated with each V S component. We, then, used them, together with the V SV / V SH values obtained from the tomography, to estimate the anisotropy and the orientation of the anisotropic layer, defined by the slope (dip) and the azimuth angle (strike). Furthermore, we tried to define a possible relationship between the V SV and V SH components with the anisotropy parameters, the direction of the rays and the geometry of the anisotropic layer.

In mineral exploration, a detailed description of the near-surface is important when seismic reflection is applied, because the heterogeneity of the shallow layers can influence the imaging of deeper targets. The use of surface waves can provide valuable information about the shallow subsurface but multichannel methods might be limited by the existence of lateral variations in the subsurface. On the contrary, surface-wave tomography has the potential to locate more accurately subsurface heterogeneities and lateral variations without lacking penetration depth. We apply surface-wave tomography on the mining site of Blötberget (Ludvika Mines, Sweden). A checkerboard test provides information about the resolution and is used for the parameterization of the initial model for the tomographic inversion. The results provide a detailed description of the shallow subsurface, showing the potential of using surface-wave tomography in seismic exploration, also for challenging data from mining sites.

Summary We propose a workflow to obtain the path-average dispersion curves, which are the input of SW tomography, from 3D ambient noise records. The workflow starts with a pre-processing step, which separates the time windows at which significant surface-wave energy has been recorded and sorts them, based on the azimuthal direction of the SW origin. For each direction, aligned pairs of receivers are found and the path-average dispersion curves are extracted for each pair. The availability of long records allows stacking, improving the data quality. We applied the proposed workflow on a dataset recorded in 2018 in the Siilinjärvi mining site in Finland, with the purpose of increasing the knowledge of the extension of the phosphate mineralization. Comparison with active dispersion curves proves the reliability of our results and indicates that the passive data allow deeper investigation, increasing the possibility of mapping deeper mineralization targets.

Summary We present an in-depth characterization of the shallow subsurface in a coastal area of the northern Adriatic. In this research, we integrated the results from the processing of active seismic data (P-, SH-, SV- wavefields, and surface waves) with those obtained from electrical resistivity tomography. Seismic data analysis provided stacked sections as well as velocity profiles from first-break tomography. Furthermore, surface-wave analysis was performed to obtain a S-wave velocity model. The results show a highly heterogeneous subsurface, due to changes in water saturation, as well as in the properties of the sediments. This is consistent with the geology of the area, characterized by sand deposits and clay sediments.

A seismic study was conducted in a historical town in Croatia to characterize the shallow subsurface and evaluate the response to an earthquake for engineering purposes. The study involves three seismic lines acquired along the existing roads of the town. For each of the lines, we acquired vertical compressional P and two horizontally polarized, S-wavefields; SH and SV, respectively orthogonal and parallel to the direction of the seismic line. We processed the data from these three wavefields with both first-break tomography, to obtain wave-velocity profiles, and reflection seismic imaging, to obtain stacked sections, and integrated the results. From such analyses, we obtained an in-depth characterization of the shallow subsurface. Specifically, we obtained standard engineering parameters like the equivalent shear-wave velocity of the upper 30 m of the subsurface (VS30), which indicates A-class soil, and compressional to shear-wave velocity ratio (VP/VS), which gives an indication regarding the presence of fractures in the rock. In addition to this, we evaluated the presence of anisotropy thanks to the SH- and SV-wave tomography inversions, which allowed to notice that VSV > VSH on most of the area. The presence of anisotropy is consistent with the known geological features of the area, in particular the subvertical bedding of the flysch, of which we were able to estimate the bedding plane orientations (dip and strike angles). Finally, by superimposing the stacked sections obtained from reflection seismic imaging with the velocity profiles computed with the traveltime tomography, we confirmed the reliability of the tomographic velocity models.

In mineral exploration, increased interest towards deeper mineralizations makes seismic methods attractive. One of the critical steps in seismic processing workflows is the static correction, which is applied to correct the effect of the shallow, highly heterogeneous subsurface layers, and improve the imaging of deeper targets. We showed an effective approach to estimate the statics, based on the analysis of surface waves (groundroll) contained in the seismic reflection data, and we applied it to a legacy seismic line acquired at the iron-oxide mining site of Ludvika in Sweden. We applied surface-wave methods that were originally developed for hydrocarbon exploration, modified as a step-by-step workflow to suit the different geologic context of hardrock sites. The workflow starts with the detection of sharp lateral variations in the subsurface, the existence of which is common at hard-rock sites. Their location is subsequently used, to ensure that the dispersion curves extracted from the data are not affected by strong lateral variations of the subsurface properties. The dispersion curves are picked automatically, windowing the data and applying a wavefield transform. A pseudo-2D time-average S-wave velocity and time-average P-wave velocity profile are obtained directly from the dispersion curves, after inverting only a reference curve. The time-average P-wave velocity profile is then used for the direct estimation of the one-way traveltime, which provides the static corrections. The resulting P-wave statics from the field data were compared with statics computed through conventional P-wave tomography. Their difference was mostly negligible with more than 91% of the estimations being in agreement with the conventional statics, proving the effectiveness of the proposed workflow. The application of the statics obtained from surface waves provided a stacked section comparable with that obtained by applying tomostatics.

Summary In this work we present an analysis of P, Sv and Sh seismic velocities using the tomographic inversion of the first arrivals. The data used in this study are four 2D seismic lines, acquired in the urban area of Kaštela, (Croatia). For each line we picked and inverted the first arrivals of P, Sv and Sh components obtaining the corresponding velocity sections. Then, we analyzed the ratio between these velocities to better characterize the underground sediments of the inversigated area. The results showed the presence of a consolidated subsoil combined with an anisotropic effect of the buried layers, in particular the general high VSv/VSh ratio, obtained from this analysis, suggests a possibile sub-vertical trend of the flysch under the quaternary coverage characterized by an averaged strike perpendicular to the main tectonic movement direction of the area.

ABSTRACTIn order to assess the feasibility and validity of surface‐wave tomography as a tool for mineral exploration, we present an active seismic three‐dimensional case study from the Siilinjärvi mine in Eastern Finland. The aim of the survey is to identify the formation carrying the mineralization in an area south of the main pit, which will be mined in the future. Before acquiring the data, we performed an accurate survey design to maximize data coverage and minimize the time for deployment and recollection of the equipment. We extract path‐averaged Rayleigh‐wave phase‐velocity dispersion curves by means of a two‐station method. We invert them using a computationally efficient tomographic code which does not require the computation of phase‐velocity maps and inverts directly for one‐dimensional S‐wave velocity models. The retrieved velocities are in good agreement with the data from a borehole in the vicinity, and the pseudo three–dimensional S‐wave velocity volume allows us to identify the geological contact between the formation hosting most of the mineralization and the surrounding rock. We conclude that the proposed method is a valid tool, given the small amount of equipment used and the acceptable amount of time required to process the data.

Summary We present a feasibility study for surface wave tomography for mineral exploration. We apply a typical seismological approach, the Two Station Method to a hard-rock site, at exploration scale. Even with this method, we are able to separate the two propagation modes typical of these sites. After windowing the traces by picking one propagation mode in the group velocity matrix, we pick the phase velocity dispersion curve in the cross-multiplication matrix. We finally propose a plot consisting of slices of tomographic pseudo volumes, which allows us to understand the penetration depth we can have. Furthermore, it gives us a first indication of the velocity anomalies in the area.

Summary Near-surface velocity models are important for deep imaging of mineral deposits with seismic exploration. The near-surface can be quite complex from loose, highly heterogeneous materials to stiff, fractured rocks. Surface-wave analysis can be an effective method to image the shallow subsurface of such challenging environments. Here, we propose a workflow that includes several processing and inversion steps. Initially, for the optimization of the processing parameters, we assess the presence of sharp lateral variations with a method based on the measured energy of Rayleigh waves. Then, using a moving window of receivers, we extract Rayleigh-wave dispersion curves along the acquisition line as the maxima of the f-k spectrum. Finally, the dispersion curves are inverted using a laterally constrained inversion scheme. The proposed methodology has been tested on legacy data from a mining field.

Introduction. Geological storage of carbon dioxide has been proven to be a viable, yet partial, solution to the excessive carbon present in the atmosphere due to human activities. Deep saline aquifers appear to be the geological setting with the highest storage capacities, since the injected supercritical CO2 dissolves in the brine. The presence of the gas in the bulk fluid changes the elastic properties of the medium, therefore it is possible to monitor the propagation of the CO2 in the formation by means of an active seismic experiment. In this work, we present a synthetic, yet realistic, 2D anticlinal formation suitable for CO2 injection, monitored with a cross-hole seismic experiment. Modeling consists of 4 steps: i) Propagation of the CO2 plume via a 2-phase flow simulator ii) Computation of the pand s-wave velocities via White’s model iii) Computation of the synthetic seismograms iv) Tomographic inversion of the synthetic seismograms using cat3d software. Geological setting and numerical discretization. We consider a 2D sandstone aquifer with shale intrusions, as in Carcione et al. (2012), with shale above and below such formation. The formation is located from 0.7 to 1.5 km depth and is 800 m long in the horizontal direction. The depth has been chosen so that carbon dioxide is in supercritical state and better dissolves in the

CO2 injection in saline aquifers is one solution to avoid the emission of this greenhouse gas to the atmosphere. This process induces a pore-pressure build-up around the borehole that generates tensile and shear micro-earthquakes which emit P and S waves if given pressure thresholds are exceeded. Here, we develop a simple model to simulate micro-seismicity in a layer saturated with brine, based on an analytical solution of pressure diffusion and an emission criterion for P and S waves. The model is based on poroelasticity and allows us to obtain estimations of the hydraulic diffusivity on the basis of the location of the micro-earthquakes (defining the CO2 plume) and the triggering time. Wave propagation of P and S waves is simulated with a full-wave solver, where each emission point is a source proportional to the difference of the pore pressure and the tensile and shear pressure thresholds. Finally a reverse-time migration algorithm is outlined to locate the asynchronous sources induced by the fluid flow, determinated by the maximum amplitude at each cell versus the back propagation time. (C) 2015 Elsevier Ltd. All rights reserved.

ABSTRACTThe link of spectral anomalies of microtremors to underlying hydrocarbon reservoirs is very controversial, as field experiments support both positive and negative opinions, and there is not a solid theory supporting this work hypothesis. We conducted field tests at different sites, with and without oil and gas presence, to add new experimental data to the ongoing studies. Microtremor information may become repeatable (and so physically meaningful) only when the observation duration exceeds a few days, but even in this case, factors such as topography and active faults may severely bias the signal.Ocean waves impinging the coasts provide natural background noise, which stands out clearly when the observation time exceeds a dozen days or so, in such a way that human noise is stacked out statistically over time.Microtremors recorded in (relatively) deep wells may provide useful information about ongoing production in a reservoir, and may link well data and seismic surveys, as their interferometric analysis can provide information comparable to Vertical Seismic Profiles.

Summary Surface-wave tomography is usually applied at regional or planetary scale but represent an interesting approach also for near surface applications. We present a surface wave dispersion tomography that does not require the construction of phase or group velocity maps and which inverts path-specific dispersion data directly for 3-D S-wave velocity variations. To compare it with classical multichannel surface-wave analysis we here present the application to a 2D seismic line.