Geophysical Methods as Support to Aquifer Recharge

AbstractIn the framework of WAter Re-BOrn Project a large pond in Mereto (upper Friuli plain) was chosen as artificial recharge test site. Several geophysical investigations (GPR, Electrical Resistivity Tomography and High Resolution Seismic) were carried out to study and to characterize the vadose zone of this large infiltration basin. These geophysical integrated methods supplied us many information to characterize the vadose zone and the unconfined aquifer in the study area. The geophysical information greatly reduces the hydrogeological knowledge gaps and was used to improve the three-dimensional Finite Element numerical model to predict the effect of the artificial recharge

Aquifer Characterization and Monitoring by Active and Passive Seismic Surveys

AbstractA 3D active and passive seismic survey was carried over an aquifer in Italy. We used 1-component vertical receivers in a fine areal grid of 100x100 m. Furthermore, two orthogonal linear profiles were acquired with 3-component receivers, recording the signal of a directional vibrator in the x, y and z direction, so getting a 9-component wave field. The data allow studying the elastic propagation effects of seismic waves in the aquifer, getting independent measurements of direct P, SH and SV arrivals. The elastic parameters they provide allow exploiting the Rayleigh wave velocities obtained by passive seismic for aquifer monitoring

Basal and Frontal Accretion Processes versus BSR Characteristics along the Chilean Margin

Multichannel seismic reflection data recorded between Itata (36°S) and Coyhaique offshores (43°S) were processed to obtain seismic images. Analysis of the seismic profiles revealed that weak and discontinuous bottom simulating reflectors were associated to basal accretion processes, while strong and continuous bottom simulating reflectors were associated to frontal accretion processes. This can be explained considering that during basal accretion processes, extensional tectonic movements due to uplifting can favour fluid escapes giving origin to weaker and most discontinuous bottom simulating reflectors. During frontal accretion processes (folding and thrusting), high fluid circulation and stable tectonic conditions however can be responsible of stronger and most continuous bottom simulating reflectors. Along the Arauco-Valdivia offshores, steep accretionary prisms, normal faults, slope basins, and thicker underplated sediment bed were associated to basal accretion, while along the Itata, Chiloe and Coyhaique offshores, small accretionary prisms, folding, and thinner underplated sediment bed were associated to frontal accretion

A crustal seismic profile across Sicily

A crustal reflection seismic profile, more than 100 km long, was recorded across central Sicily, from the Tyrrhenian shore to the Sicily Channel, to understand the deep structures and the collision mechanisms between Europe and Africa and the subsequent geodynamic evolution. The profile was acquired using explosive sources and 240 active channels recorded by a Sercel 408-XL, 24 bits A/D converter, with a 12 km spread and a 24-fold coverage. The data were processed following a non-conventional procedure in order to preserve the relative amplitudes of the reflections and to better investigate the Sicily deep structures down to the Moho. The main highlighted structures are the dramatic flexure of the Iblean crust, the huge, deeper than expected, trough of Caltanissetta consisting of deep seated thrusts and nappes, and the imbricate thrust system of rigid bodies characterizing the northern Maghrebian chain. We designed an ad hoc acquisition and processing in order to highlight these main geological features in the seismic stacked section. Moreover, the deepest parts of the Caltanissetta trough are imaged for the first time, and its bottom is now fixed at more than 7 s TWT. The giant crustal wedge flexuring the Iblean foreland and the Moho geometries are examinated

Gas hydrates and active mud volcanism on the South Shetland Trench, Antarctic Peninsula

During the Antarctic summer 2003\u20132004, new geophysical data were acquired aboard R/V OGS Explora in the BSR area discovered in 1996\u20131997 along the South Shetland continental margin, Antarctic Peninsula. The objective of the program was to verify the existence of a potential gas hydrate reservoir and to reconstruct the tectonic setting of the margin, controlling extent and character of the diffused and discontinuous bottom simulating reflections. The new dataset, multibeam bathymetry, seismic profiles, and gravitycores, analysed by computer-aided tomography and for gas composition and content, clearly shows active mud volcanism sustained by hydrocarbon venting: several vents, located mainly close to mud volcanoes, were imaged during the cruise and their occurrence identified in the sediment samples. Mud volcanoes, vents and recent slides border the gas hydrate reservoir. The cores are composed of stiff silty mud. In core GC01, collected close to a mud volcano ridge, the following gases were identified (maximum contents in brackets): methane (46 \u3bcg/kg), pentane (45), ethane (35), propane (34), hexane (29) and butane (28). In core GC02, collected on the flank of the Vualt mud volcano, the corresponding data are methane (0 \u3bcg/kg), pentane (45), ethane (22), propane (0), hexane (27) and butane (25)

REGIONAL VERSUS DETAILED VELOCITY ANALYSIS TO QUANTIFY HYDRATE AND FREE GAS IN MARINE SEDIMENTS: THE SOUTH SHETLAND MARGIN CASE STUDY

The presence of gas hydrate and free gas within marine sediments, deposited along the South Shetland margin, offshore the Antarctic Peninsula, was confirmed by low and high resolution geophysical data, acquired during three research cruises. Seismic data analysis has revealed the presence of a bottom simulating reflector that is very strong and continuous in the eastern part of the margin. This area can be considered as a useful site to study the seismic characteristics of sediments containing gas hydrate, with a particular focus on the estimation of gas hydrate and free gas amounts in the pore space. Pre-stack depth migration and tomographic inversion were performed to produce a regional velocity field of gas-phase bearing sediments and to obtain information about the average thickness of gas hydrate and free gas layers. Using these data and theoretical models, the gas hydrate and free gas concentrations can be estimated. Moreover, the common image gather semblance analysis revealed the presence of detailed features, such as layers with small thickness characterised by low velocity alternating with high velocity layers, below and above the bottom simulating reflector. These layers are associated with free gas trapped within the hydrate stability zone and deeper sediments. Thus, the use of the detailed and the regional velocity field analysis is important to give a more reliable estimate of gas content in the marine sediments.Non UBCUnreviewe