NSG2022 28th European Meeting of Environmental and Engineering Geophysics

In this paper, the triangular meshing parameter field is used to solve the problems of numerical scattering and the reduction of reflected wave resolution due to the fact that conventional rectangular meshing cannot accurately simulate the undulation shape of the formation. On this basis, triangular mesh division is introduced into VTI anisotropic traveltime tomography, and the sparseness of the triangular mesh model and the flexibility of the division are used to effectively reduce the computational cost and time during tomographic inversion. In addition, the ill-conditioned nature of the tomographic equation is improved, the difficulty of solving is reduced, and the parameter field established by the tomographic inversion is more accurate. In this paper, the sensitivity of the three parameters of anisotropy is tested, and the inversion strategy of using triangular grid tomographic inversion for the Vp0 field and the sequence inversion of ε and δ field rectangular grid tomographic inversion is formulated, and the model is used to verify the feasibility and correctness of the method.

This study aims to identify and locate subsoil areas containing archaeological remains in an important site located in south-eastern Sicily (Akrai archaeological site). Archaeological knowledge from the site suggests that the actual extension of the ancient city of Akrai should be greater than what has been discovered so far. Considering the location of the archaeological remains currently found at the site, in order to verify the existence of spatial continuity between them, were carried out different applied geophysical (magnetic and electromagnetic) surveys. The data obtained from the geophysical surveys have provided essential information to locate and delimit areas of interest where could be concentrated future archaeological digs.

Measurement of gravity in hydrocarbon wells has been possible since the mid 1960’s, however the use of the method was limited by the availability, cost and utility of the borehole gravimeter. The recent development of a new borehole gravimeter with upgraded 3D inversion software has made acquisition and interpretation of gravity data acquired in boreholes practical for both mining and hydrocarbon applications. Borehole gravity, combined with other geophysical methods, is effective to monitor CO2 sequestration into carbonate reefs and to locate serpentine for permanent storage by carbon mineralization.

In this work we investigate the problem of surface wave analysis and subtraction from seismic measurements generated with wide frequency band seismic vibrators. We apply a specific practical seismic processing workflow, derived by an f-k filtering method, to remove aliased, wide-band surface waves from the data. We also extract the surface waves dispersion curves associated to the fundamental propagation mode before and after the subtraction for QC purposes, and to assess the accuracy of our algorithm. Finally, we use the extracted dispersion curves for building a very high-resolution shear-wave velocity model of the very shallow subsurface. The ultimate goal of this project is to derive a high resolution image for near-surface characterization and geohazard prediction.

In this work, a new methodological approach based on electrical resistivity measurements is proposed to characterize the physical-chemical properties of cemented lightweight soils (LWCS) and to verify their mechanical performance. The electrical resistivity parameter, indeed, strongly depends on petrophysical properties (e.g., porosity, water content, grain size, orientation and pore structure) of soils, suggesting that it can be very helpful for analysing the physical-chemical behavior of LWCS. Therefore, the purpose has been to implement a non-destructive investigation technique to be applied for monitoring the physical and mechanical properties of LWCS. The effectiveness of the proposed approach has been validated by resistivity laboratory tests on lightweight cemented soil samples made with different amounts of foam. Our results show for the first time a possible correlation between the effect of the cementation products and the time variations of the resistivity values suggesting that the electrical resistivity could be one of the relevant parameters for in situ monitoring of LWCS to control the development of the cementation products, and the subsequent suitability of the treated material.

Electromagnetic induction (EMI) is a non-invasive and fast geophysical measurement technique that provides information about the uppermost meters of the subsurface with a spatial resolution in the submeter range. Frequency domain EMI systems measure the apparent electrical conductivity of the soil by inducing a time-varying primary electromagnetic field into the ground, which produces eddy currents that generate secondary electromagnetic fields. The secondary and primary fields are measured at a receiver. EMI data are known to be susceptible to measurement influences associated with time-varying external ambient factors. Temperature variation is one of the most prominent factors causing drift in EMI data, leading to poor predictive performance and non-reproducibility of results. An enhanced correction method is presented that models the dynamic characteristics of drift and later uses it for correction. The model is tested with a custom-made EMI device equipped with ten temperature sensors that simultaneously measure the internal ambient temperature across the device. The device was used to perform outdoor calibration measurements within a wide range of temperatures. In contrast to typical approaches involving static thermal ECa error correction based on a look-up table, this new approach models the dynamic thermal characteristics of the drift and actively uses it for correction.

Monitoring processes occurring in the subsurface, e.g., hydraulic head, moisture content, and salinity, remains a challenge for hydrology. Traditionally, direct methods have been applied to get insight into subsurface processes. However, they may offer limited spatial and temporal information or with very local sensitive volumes. Non-invasive geophysical methods applied in time-lapse approach show great promise to address this problem - capable of monitoring hydrological variables with higher temporal resolution. In this work, we demonstrate the suitability of the transient electromagnetic (TEM) method for time-lapse monitoring of groundwater dynamics in unconfined aquifers using a laterally constrained inversion scheme. Results from a synthetic experiment and a field study case are presented to highlight the feasibility of the TEM method in time-lapse studies.

Shallow seismic exploration in an urban area is slightly different from conventional land seismic exploration since survey design and field parameters are limited for determining survey profile directions and source types due to the cultural noise and artificial structures. If a river passes the survey site in the urban area, the cableless receivers and an airgun source are helpful for seismic exploration to reduce the obstacles. In this study, we designed a seismic acquisition method using a cableless seismic system and a small–scale single airgun source in the river. Receivers are set up on riverbank and source is hung beneath a small boat in the water. The airgun source volume is 50 in3. Shot gathers show direct waves, airwaves, and reflections, including multiple reflections. Since the source line is parallel to the receiver line, which is apart from 147 m, we applied a time delay static correction to keep the 2D processing procedures. Since the seismic acquisition method gives a higher signal-to-noise ratio without surface waves than vibroseis and weight-drop sources in the river, it will be one of the shallow seismic explorations in the urban area.

The Albanian orogen, is divided in two areas with different tectonic regimes: the external area with compressive regime, representing its offshore part and the internal area with expanding regime, representing the continental area. The main cause of Albanian seismicity is the collision of Adria microplate with the Albanian orogen. During the 2021, the seismic activity within the Albanian territory and its surroundings has been characterized by a normal seismic activity. Earthquakes foci are concentrated mostly along the five active fault zones: Durres – Rodon cape, Lezhe – Ulqin, Kurbnesh-Skavice-Prizren, Fier-Elbasan-Diber, Korce-Oher and Ionian fault zones. On the Albanian and its surrounding territory have been located 2359 earthquakes with a ranging magnitude from 0.6 to 4.8, with an average depth of 16 km and a maximum depth of 120 km, 110 of which were of magnitude ML> 3.0 (Richter), average depth 25 km and maximum depth 120 km, 18 of magnitude ML> 4.0 Richter and 2 of magnitude ML> 4.5. About 8 seismic events were felt by the population of Albania. The focal mechanism parameters of moderate earthquakes that have occurred during 2020 (ML>4.0) can be used to shed light on the seismotectonics of their areas and the current stress field.