A goal-oriented adaptive finite-element approach for plane wave 3-D electromagnetic modelling

We have developed a new full-waveform groundpenetrating radar (GPR) multicomponent inversion scheme for imaging the shallow subsurface using arbitrary recording configurations. It yields significantly higher resolution images than conventional tomographic techniques based on first-arrival times and pulse amplitudes. The is formulated as nonlinear least squares problem in which misfit between observed modeled data minimized. modeling implemented by means of finite-difference time-domain...

Predictive groundwater modeling requires accurate information about aquifer characteristics. Geophysical imaging is a powerful tool for delineating properties at an appropriate scale and resolution, but it suffers from problems of ambiguity. One way to overcome such limitations adopt simultaneous multitechnique inversion strategy. We have developed methodology characterization based on structural joint multiple geophysical data sets followed by clustering form zones subsequent zonal...

This paper investigates the relative merits and effectiveness of cross‐hole resistivity tomography using different electrode configurations for four popular arrays: pole–pole, pole–bipole, bipole–pole bipole–bipole. By examination two synthetic models (a dipping conductive strip a dislocated fault), it is shown that besides pole–pole array, some specified three‐ four‐electrode configurations, such as pole–bipole AM – N , B bipole–bipole BN with their multispacing profiling scanning surveys,...

The hydrogeological properties and responses of a productive aquifer in northeastern Switzerland are investigated. For this purpose, 3D crosshole electrical resistivity tomography (ERT) is used to define the main lithological structures within (through static inversion) monitor water infiltration from an adjacent river. During precipitation events subsequent river flooding, increases. As consequence, characteristics infiltrating can be as natural tracer delineate preferential flow paths...

Abstract The interior of the Earth is quite complex due to actual geometrical structure and presence rheological materials, including viscoelastic rocks, porous sediments anisotropy. Seismic wavefield forward modeling in such media forms basis most wave equation‐based methods for investigating processing imaging seismic data, e.g., full waveform inversion. Numerical using Biot's equations that describe physics poroelasticity provides a useful framework investigate attenuation dispersion....

We developed a novel parallel domain-decomposition approach for 3D large-scale electromagnetic induction modeling in the earth. used edge-based finite-element method and unstructured meshes. Unstructured meshes were divided into sets of nonoverlapping subdomains. curl-curl electric field equation to carry out analysis. In each subdomain, was discretized by first-order vector shape functions along edges tetrahedral elements. The tangential components magnetic on interfaces subdomains defined...

We provide a six-component (6-C) polarization model for P-, SV-, SH-, Rayleigh-, and Love-waves both inside an elastic medium as well at the free surface. It is shown that single-station 6-C data comprised of three components rotational motion translational opportunity to unambiguously identify wave type, propagation direction, local P- S-wave velocities receiver location by use analysis. To extract such information conventional processing three-component (3-C) would require large dense...

Abstract Enigmatic lunar seismograms recorded during the Apollo 17 mission in 1972 have so far precluded identification of shear‐wave arrivals and hence construction a comprehensive elastic model shallow subsurface. Here, for first time, we extract information from active seismic data using novel waveform analysis technique based on spatial wavefield gradients. The star‐like recording geometry experiment lends itself surprisingly well to compute gradients rotational ground motion as function...

Abstract Tectonic earthquakes are usually thought to be the result of stick-slip frictional instability along a pre-existing fault. As result, large rarely nucleate at shallow depths. In present study, we relocated 8 September 2019 Ms 5.4 Earthquake in Weiyuan, Sichuan, China, and 943 aftershocks. The results suggest rather surprisingly that these seismic events occurred depth less than 3.5 km, rupturing relay zone between two active thrust faults. Prior earthquake, ruptured ramp was...

The control and manipulation of waves in optical and/or acoustic science engineering are widespread. Recently, despite reported studies on high frequency via time modulated media, none these approaches has demonstrated success with broadband exceeding that the mechanical system, all them were not able to emit ultralow waves. There both fundamental practical issues. Achieving ultra-low underwater wave interfaces remains a major challenge for integrated devices. Here, we explore design marine...

The finite element method is a powerful tool for 3 D DC resistivity modelling and inversion. solution accuracy computational efficiency are critical factors in using the imaging. This paper investigates of two common type schemes: trilinear interpolation within regular 8 node solid parallelepiped, linear interpolations six tetrahedral bricks same block. Four iterative solvers based on pre conditioned conjugate gradient (SCG, TRIDCG, SORCG ICCG), one elimination solver called banded Choleski...

Polarization analysis can be achieved efficiently by treating a time window of single‐station triaxial recording as matrix and doing singular value decomposition (SVD) this seismic data matrix. SVD the produces an eigenanalysis covariance (cross‐energy) rotation onto directions given (Karhunen‐Loève transform), all in one step. provides complete principal components window. Selection is crucial to success governed three considerations: should contain only arrival; such that signal‐to‐noise...

First‐break traveltimes can be accurately computed by the finite‐difference solution of eikonal equation using a new corner‐node discretization scheme. It offers accuracy advantages over traditional cell‐centered node A substantial efficiency improvement is achieved incorporation wavefront tracking algorithm based on construction minimum traveltime tree. For scheme, an accurate average value for local squared slowness found to crucial in stabilizing numerical scheme models with large...

Fluid that fills boreholes in crosswell electrical resistivity investigations provides the necessary contact between electrodes and rock formation but it is also source of image artifacts standard inversions do not account for effects boreholes. The distortions can be severe large contrasts borehole fluid diameters. We have carried out 3D finite-element modeling using an unstructured-grid approach to quantify magnitude different contrasts, diameters, electrode configurations. Relatively...

The infiltration of river water into aquifers is high relevance to drinking-water production and a key driver biogeochemical processes in the hyporheic riparian zone, but distribution quantification infiltrating are difficult determine using conventional hydrological methods (e.g., borehole logging tracer tests). By time-lapse inverting crosshole ERT (electrical resistivity tomography) monitoring data, we imaged groundwater flow patterns driven by perialpine gravel aquifer northeastern...

SUMMARY From 1998 May to September a portable array of 40 short-period digital seismograph stations was operated in western Victoria, southeast Australia, across the end midPaleozoic Lachlan Foldbelt and Newer Volcanic Province. Consisting four parallel, almost W‐E-oriented receiver lines, covered an area about 270 × 150 km 2 . The major aim LF98 (Lachlan survey 1998) project is map lateral variations P-wave speeds (Vp) crust upper mantle using teleseismic arrival time tomography, primarily...

We investigate a simple scheme for full‐waveform amplitude spectrum inversion of crosshole seismic data with an unknown source wavelet. The method is based on our 2D/2.5D finite‐element acoustic‐wave modeling. normalized data, defined as the spectral ratio original trace to average entire common shot gather, are used in frequency domain. In essence, normalization amplitudes removes wavelet and easily carried out time domain or from surveying. Two synthetic models, simulating, respectively,...

New derivations for the conventional linear and parabolic τ-p transforms in classic continuous function domain provide useful insight into discrete transformations. For filtering of unwanted waves such as multiples, derivation transform should define inverse first, then compute forward transform. The usually requires a p‐direction deconvolution to improve resolution that direction. It aids wave by improving separation events domain. is required both curvilinear transformations...

This paper presents in a general form the most popular local minimization search solutions for geophysical inverse problems—the Tikhonov regularization solutions, smoothest model and subspace from which inter-relationships between these are revealed. For solution, variety of forms exist—the iterative formula, linearized scheme, Levenberg–Marquardt version, conjugate gradient solver (CGS) local-search quadratic approximation CGS. It is shown here that first three equivalent just specified...

We present an accurate 3D ray-tracing algorithm based on a modified (more flexible and economical) shortest-path method (SPM). Unlike the regular SPM in case, which uses only primary nodes at corners of each cell whose accuracy depends actual size, new can work with much larger sizes by introducing secondary along all bounding surfaces cell. This increases ray angular coverage permits detailed specification velocity field. The simultaneously calculates first-arrival times gradually locates...

Seismic full-waveform inversion (FWI) is often based on forward modeling in the computationally attractive 2D domain. This implies assumption of a line source extended out-of-plane medium invariant direction, with far-field amplitudes decaying inversely square root distance. Realistic point sources, however, generate that decay approximately inverse Conventionally, practitioners correct for this amplitude difference and associated phase shift by transforming recorded 3D field data to...