1,720,970 research outputs found
Joint Inversion of P-waves refraction travel times and surface wave dispersion curves
No full textRayleigh wave dispersion curves and P refraction travel times are jointly inverted through a damped least square algorithm which accounts simultaneously for both datasets, solving for common thicknesses and respective VP and VS values. The velocities are coupled through the introduction of P-wave velocity values that are used for both the refraction and the surface wave forward modelling. Since the sensitivity of surface waves to P-wave velocity is low, the problem is strongly coupled on the thicknesses and weakly coupled on the velocities. The surface wave - P-wave refraction joint inversion algorithm is effective in solving hidden layer problem, which would lead to big interpretational errors in the case of individual inversion of P dromocrones. The approach is effective for inversion of 1D layered models as shown in one example for the inversion of experimental data, leading to better results than individual inversions also in the case of surface wave
Improved Monte Carlo 1D-Inversion of vertical electrical sounding and time-domain electromagnetic data
No full textThis work deals with a robust and reliable global search inversion tool for vertical electrical sounding (VES) and time-domain electromagnetic (TDEM) data, able to take into account the data quality and the dimensionality of the problem. The approach is an importance sampling method that exploits a scale property of the solution to move the random population of models closer to the solution. We obtain a more efficient sampling of the model parameter space with respect to a pure Monte Carlo method. The application of the scale properties overcomes some of the problems encountered when using optimization methods (e.g., simulated annealing), which are based on transition probability rules barely related to the specific problem or that require tuning of control parameters or training procedures (e.g., neural networks). Furthermore, the scale properties reduce the bias related to the initial definition of the boundaries of the model parameter space. A statistical test that accounts for the data uncertainties and the degrees of freedom of the problem is adopted to draw inference on the results. Synthetic and field data show that the algorithm is able to concentrate the sampling in high probability density zones of the model parameter space and to supply a reliable picture of the non-uniqueness and equivalence problem
Constrained 1D joint inversion of seismic surface waves and P-refraction traveltimes
No full textWe present a joint inversion scheme that couples P-wave refraction and seismic surface-wave data for a layered subsurface. An algorithm is implemented with a damped least-squares approach. The estimated parameters are S- and P-wave velocities and layer thicknesses, while densities are assumed constant during inversion. The coupling is both geometric and physical: layer thicknesses are the same for Sand P-wave velocity profiles and P-wave velocities enter in both forward algorithms. Sensitivity analysis, performed on synthetic data, reveals that surface-wave dispersion curves can be sensitive also to P-wave velocity of some layers (especially for Poisson's ratio values smaller than about 0.35), allowing synergic resolution of this parameter. Applications on both synthetic and field data show that the proposed approach mitigates the hidden layer problem of seismic refraction and leads to more accurate results than individual inversions also for surface waves. Additional constraints on the objective function on a priori Poisson's ratio values allow unrealistic and not admissible VP and VS values to be avoided; such constraints were applied in one field case considering the a priori information available about water-table depth. It is also shown that estimation of porosity can help the selection of the proper constraint on a priori Poisson's rati
Building 3D shear velocity models using surface wave testing: the Tarcento Basin case history
No full textThe paper reports on the use of surface‐wave testing for the construction of a three‐dimensional (3D) shear‐wave velocity model of an alluvial basin. The town of Tarcento (Italy) is located in a region with a high level of seismic hazard and was strongly affected by the two Friuli earthquakes in 1976.
The seismic surveys were performed with surface‐wave multistation methods using a combination of active‐source and passive‐source experimental setup. Experimental data were collected at 16 sites, and inversion of the data is based on an innovative procedure for spatially constrained inversion with a single objective function in which a priori information is included. The method provides an improvement in the robustness of the solution, mitigating solution nonuniqueness. Available borehole logs at different locations are integrated into the data set in terms of a priori bedrock information. Three independent cross‐hole tests are used for a posteriori comparison of the inverted one‐dimensional (1D) profiles.
Three‐dimensional interpolation of the obtained profiles leads to a shear‐wave velocity model that is internally consistent and complies with a priori information, cross‐hole results, and suitable boundary profiles. The model is intended for numerical simulations of the seismic response of the basin
Seismic body and surface wave data integration for near surfacecharacterisation
No full textSeismic methods are widely used in near surface characterisation and very often different seismic datasets relative to body and surface waves are acquired at the same site. These data are, in the majority of the cases, acquired and interpreted separately to provide different information disregarding the synergies between different methods both in acquisition and inversion. In particular the joint or constrained inversion of different datasets may overcome intrinsic limitations of individual techniques and provide a more reliable and consistent final velocity model. Moreover, different
information coming from different datasets provide a comprehensive site characterisation
Integrazione di dati sismici, geologici e geognostici per la costruzione del modello di velocità delle onde di taglio della conca di Tarcento (Friuli)
No full textLaterally constrained inversion of surface wave data for the characterization of Tarcento basin in Italy
No full textNew Site Specific CPT-based Suction Bucket Jacket Installation Coefficients from Field Measurements
No full textMagnetic, electrical, and GPR waterborne surveys of moraine deposits beneath a lake: A case history from Turin, Italy
Full text linkBathymetry and bottom sediment types of inland water basins provide meaningful information to estimate water reserves and possible connections between surface and groundwater. Waterborne geophysical surveys can be used to obtain several independent physical parameters to study the sediments. We explored the possibilities of retrieving information on both shallow and deep geological structures beneath a morainic lake by means of waterborne nonseismic methods. In this respect, we discuss simultaneous magnetic, electrical, and groundpenetrating radar (GPR) waterborne surveys on the Candia morainic lake in northerly Turin (Italy).We used waterborne GPR to obtain information on the bottom sediment and the bathymetry needed to constrain the magnetic and electrical inversions. We obtained a map of the total magnetic field (TMF) over the lake from which we computed a 2D constrained compact magnetic inversion for selected profiles, along with a laterally constrained inversion for one electrical profile. The magnetic survey detected some deep anomalous bodies within the subbottom moraine. The electrical profiles gave information on the more superficial layer of bottom sediments. We identify where the coarse morainic material outcrops from the bottom finer sediments from a correspondence between high GPR reflectivity, resistivity, and magnetic anomalie
Improved Monte Carlo Inversion of Resistivity Data
No full textInversion of 1D technique (VES and TDEM) by using Global Search Procedures (GSPs) as proved to be effective in evidencing local minima and equivalence problems, evaluating non-uniqueness in the solution, and estimating the values and uncertainties of the model parameters. The proposed approach is based on a Monte Carlo algorithm optimised through the application of the scale properties of the apparent resistivity curves. A statistical test selects a limited number of final models according to data uncertainties, model parameterisation and a chosen level of confidence
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