Potential shallow aquifers characterization through an integrated geophysical method: multivariate approach by means of k-means algorithms

The need to obtain a detailed hydrogeological characterization of the subsurface and its interpretation for the groundwater resources management, often requires to apply several and complementary geophysical methods. The goal of the approach in this paper is to provide a unique model of the aquifer by synthesizing and optimizing the information provided by several geophysical methods. This approach greatly reduces the degree of uncertainty and subjectivity of the interpretation by exploiting the different physical and mechanic characteristics of the aquifer. The studied area, into the municipality of Laterina (Arezzo, Italy), is a shallow basin filled by lacustrine and alluvial deposits (Pleistocene and Olocene epochs, Quaternary period), with alternated silt, sand with variable content of gravel and clay where the bottom is represented by arenaceous-pelitic rocks (Mt. Cervarola Unit, Tuscan Domain, Miocene epoch). This shallow basin constitutes the unconfined superficial aquifer to be exploited in the nearly future. To improve the geological model obtained from a detailed geological survey we performed electrical resistivity and P wave refraction tomographies along the same line in order to obtain different, independent and integrable data sets. For the seismic data also the reflected events have been processed, a remarkable contribution to draw the geologic setting. Through the k-means algorithm, we perform a cluster analysis for the bivariate data set to individuate relationships between the two sets of variables. This algorithm allows to individuate clusters with the aim of minimizing the dissimilarity within each cluster and maximizing it among different clusters of the bivariate data set. The optimal number of clusters “K”, corresponding to the individuated geophysical facies, depends to the multivariate data set distribution and in this work is estimated with the Silhouettes. The result is an integrated tomography that shows a finite number of homogeneous geophysical facies, which therefore permits to distinguish and interpret the porous aquifer in a quantitative and objective way.

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Joint inversion of Rayleigh-wave dispersion and P-wave refraction data for laterally varying layered models

Geophysics ◽

10.1190/geo2013-0212.1 ◽

2014 ◽

Vol 79 (4) ◽

pp. EN49-EN59 ◽

Cited By ~ 14

Author(s):

Daniele Boiero ◽

Laura Valentina Socco

Keyword(s):

Rayleigh Wave ◽

Joint Inversion ◽

A Priori ◽

P Wave ◽

Inversion Method ◽

Model Parameters ◽

Data Set ◽

Wave Refraction ◽

Velocity Models ◽

Refraction Data

We implemented a joint inversion method to build P- and S-wave velocity models from Rayleigh-wave and P-wave refraction data, specifically designed to deal with laterally varying layered environments. A priori information available over the site and any physical law to link model parameters can be also incorporated. We tested and applied the algorithm behind the method. The results from a field data set revealed advantages with respect to individual surface-wave analysis (SWA) and body wave tomography (BWT). The algorithm imposed internal consistency for all the model parameters relaxing the required a priori assumptions (i.e., Poisson’s ratio level of confidence in SWA) and the inherent limitations of the two methods (i.e., velocity decreases for BWT).

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Application and evaluation of electromagnetic methods for imaging saltwater intrusion in coastal aquifers: Seaside Groundwater Basin, California

Geophysics ◽

10.1190/geo2012-0004.1 ◽

2013 ◽

Vol 78 (2) ◽

pp. B77-B88 ◽

Cited By ~ 13

Author(s):

Vanessa Nenna ◽

Daan Herckenrath ◽

Rosemary Knight ◽

Nick Odlum ◽

Darcy McPhee

Keyword(s):

Coastal Aquifers ◽

Saltwater Intrusion ◽

Groundwater Resources ◽

Management Strategies ◽

Geophysical Methods ◽

Unconfined Aquifer ◽

Data Sets ◽

Data Set ◽

Aquifer System ◽

Spatial Coverage

Developing effective resource management strategies to limit or prevent saltwater intrusion as a result of increasing demands on coastal groundwater resources requires reliable information about the geologic structure and hydrologic state of an aquifer system. A common strategy for acquiring such information is to drill sentinel wells near the coast to monitor changes in water salinity with time. However, installation and operation of sentinel wells is costly and provides limited spatial coverage. We studied the use of noninvasive electromagnetic (EM) geophysical methods as an alternative to installation of monitoring wells for characterizing coastal aquifers. We tested the feasibility of using EM methods at a field site in northern California to identify the potential for and/or presence of hydraulic communication between an unconfined saline aquifer and a confined freshwater aquifer. One-dimensional soundings were acquired using the time-domain electromagnetic (TDEM) and audiomagnetotelluric (AMT) methods. We compared inverted resistivity models of TDEM and AMT data obtained from several inversion algorithms. We found that multiple interpretations of inverted models can be supported by the same data set, but that there were consistencies between all data sets and inversion algorithms. Results from all collected data sets suggested that EM methods are capable of reliably identifying a saltwater-saturated zone in the unconfined aquifer. Geophysical data indicated that the impermeable clay between aquifers may be more continuous than is supported by current models.

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Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

Journal of Environmental and Engineering Geophysics ◽

10.32389/jeeg9-067 ◽

2020 ◽

Vol 25 (3) ◽

pp. 415-423

Author(s):

Ahmed Lachhab ◽

El Mehdi Benyassine ◽

Mohamed Rouai ◽

Abdelilah Dekayir ◽

Jean C. Parisot ◽

...

Keyword(s):

Heavy Metals ◽

Seismic Velocity ◽

Seismic Refraction ◽

Geophysical Methods ◽

Low Frequency ◽

Electrical Current ◽

P Wave ◽

Low Resistivity ◽

Refraction Tomography ◽

Geophysical Surveys

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

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SEMIPARAMETRIC CLUSTERING METHOD FOR MICROARRAY DATA ANALYSIS

Journal of Bioinformatics and Computational Biology ◽

10.1142/s021972000800345x ◽

2008 ◽

Vol 06 (02) ◽

pp. 261-282 ◽

Cited By ~ 2

Author(s):

AO YUAN ◽

WENQING HE

Keyword(s):

Data Analysis ◽

Microarray Data ◽

Mixture Distribution ◽

Information Criterion ◽

Optimal Number ◽

Microarray Data Analysis ◽

Parametric Methods ◽

Clustering Methods ◽

Microarray Gene Expression ◽

Data Set

Clustering is a major tool for microarray gene expression data analysis. The existing clustering methods fall mainly into two categories: parametric and nonparametric. The parametric methods generally assume a mixture of parametric subdistributions. When the mixture distribution approximately fits the true data generating mechanism, the parametric methods perform well, but not so when there is nonnegligible deviation between them. On the other hand, the nonparametric methods, which usually do not make distributional assumptions, are robust but pay the price for efficiency loss. In an attempt to utilize the known mixture form to increase efficiency, and to free assumptions about the unknown subdistributions to enhance robustness, we propose a semiparametric method for clustering. The proposed approach possesses the form of parametric mixture, with no assumptions to the subdistributions. The subdistributions are estimated nonparametrically, with constraints just being imposed on the modes. An expectation-maximization (EM) algorithm along with a classification step is invoked to cluster the data, and a modified Bayesian information criterion (BIC) is employed to guide the determination of the optimal number of clusters. Simulation studies are conducted to assess the performance and the robustness of the proposed method. The results show that the proposed method yields reasonable partition of the data. As an illustration, the proposed method is applied to a real microarray data set to cluster genes.

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P-wave backazimuth anomalies observed by a small-aperture seismic array at Pinyon Flat, southern California: Implications for structure and source location

Bulletin of the Seismological Society of America ◽

10.1785/bssa0860020470 ◽

1996 ◽

Vol 86 (2) ◽

pp. 470-476 ◽

Cited By ~ 1

Author(s):

Cheng-Horng Lin ◽

S. W. Roecker

Keyword(s):

Southern California ◽

Seismic Array ◽

P Wave ◽

Small Aperture ◽

Data Set ◽

Single Interface ◽

Seismic Networks ◽

Dense Seismic Array ◽

Beamforming Technique

Abstract Seismograms of earthquakes and explosions recorded at local, regional, and teleseismic distances by a small-aperture, dense seismic array located on Pinyon Flat, in southern California, reveal large (±15°) backazimuth anomalies. We investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating backazimuth with an array using three different techniques: the broadband frequency-wavenumber (BBFK) technique, the polarization technique, and the beamforming technique. While each technique provided nearly the same direction as a most likely estimate, the beamforming estimate was associated with the smallest uncertainties. Backazimuth anomalies were then calculated for the entire data set by comparing the results from beamforming with backazimuths derived from earthquake locations reported by the Anza and Caltech seismic networks and the Preliminary Determination of Epicenters (PDE) Bulletin. These backazimuth anomalies have a simple sinelike dependence on azimuth, with the largest anomalies observed from the southeast and northwest directions. Such a trend may be explained as the effect of one or more interfaces dipping to the northeast beneath the array. A best-fit model of a single interface has a dip and strike of 20° and 315°, respectively, and a velocity contrast of 0.82 km/sec. Application of corrections computed from this simple model to ray directions significantly improves locations at all distances and directions, suggesting that this is an upper crustal feature. We confirm that knowledge of local structure can be very important for earthquake location by an array but also show that corrections computed from simple models may not only be adequate but superior to those determined by raytracing through smoothed laterally varying models.

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Source dynamics of the 1979 Imperial Valley earthquake from near-source observations (of ground acceleration and velocity)

Bulletin of the Seismological Society of America ◽

10.1785/bssa07206a1957 ◽

1982 ◽

Vol 72 (6A) ◽

pp. 1957-1968

Author(s):

Mansour Niazi

Keyword(s):

Particle Acceleration ◽

Particle Velocity ◽

High Frequency ◽

Observation Point ◽

P Wave ◽

Imperial Valley ◽

Ground Acceleration ◽

Data Set ◽

Ground Shaking ◽

Fault Surface

abstract Two sets of observations obtained during the 15 October 1979 Imperial Valley earthquake, MS 6.9, are presented. The data suggest different dynamic characteristics of the source when viewed in different frequency bands. The first data set consists of the observed residuals of the horizontal peak ground accelerations and particle velocity from predicted values within 50 km of the fault surface. The residuals are calculated from a nonlinear regression analysis of the data (Campbell, 1981) to the following empirical relationships, PGA = A 1 ( R + C 1 ) − d 1 , PGV = A 2 ( R + C 2 ) − d 2 in which R is the closest distance to the plane of rupture. The so-calculated residuals are correlated with a positive scalar factor signifying the focusing potential at each observation point. The focusing potential is determined on the basis of the geometrical relation of the station relative to the rupture front on the fault plane. The second data set consists of the acceleration directions derived from the windowed-time histories of the horizontal ground acceleration across the El Centro Differential Array (ECDA). The horizontal peak velocity residuals and the low-pass particle acceleration directions across ECDA require the fault rupture to propagate northwestward. The horizontal peak ground acceleration residuals and the high-frequency particle acceleration directions, however, are either inconclusive or suggest an opposite direction for rupture propagation. The inconsistency can best be explained to have resulted from the incoherence of the high-frequency radiation which contributes most effectively to the registration of PGA. A test for the sensitivity of the correlation procedure to the souce location is conducted by ascribing the observed strong ground shaking to a single asperity located 12 km northwest of the hypocenter. The resulting inconsistency between the peak acceleration and velocity observations in relation to the focusing potential is accentuated. The particle velocity of Delta Station, Mexico, in either case appears abnormally high and disagrees with other observations near the southeastern end of the fault trace. From the observation of a nearly continuous counterclockwise rotation of the plane of P-wave particle motion at ECDA, the average rupture velocity during the first several seconds of source activation is estimated to be 2.0 to 3.0 km/sec. A 3 km upper bound estimate of barrier dimensions is tentatively made on the basis of the observed quasiperiodic variation of the polarization angles.

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Morphological evolution of the middle and lower Seine valley during the Quaternary period.

10.5194/egusphere-egu21-12502 ◽

2021 ◽

Author(s):

Kim Genuite ◽

Carole Nehme ◽

Daniel Ballesteros ◽

Dominique Todisco ◽

Damase Mouralis

Keyword(s):

Morphological Evolution ◽

Glacial Cycle ◽

Seine River ◽

Quaternary Period ◽

Alluvial Deposits ◽

Last Glacial ◽

Fluvial Terraces ◽

Elevation Model ◽

Fluvial Dynamic ◽

Alluvial Terraces

The Seine river (France) drains today a catchment area of 80,000 km2 covering almost the northern part of France. Despite its importance, few studies focused on the Seine catchment and its landscape evolution, unlike the Somme basin, which remains a European reference for the&#160;Quaternary, because of to the numerous archaeological sites it contains. The middle and lower Seine valley in Normandy shows nevertheless a particular meandering fluvial dynamic and a succession of fluvial terraces over 120 m height, dated back to Early Quaternary. Previous works focused on the stratigraphy of alluvial sequences and led to the accurate characterization&#160;of lower fluvial and estuarine levels from Marine Isotope Stage (MIS) 1 to MIS 11. The alluvial terraces comprise also various&#160;Acheulean industries, showing human settlements in the valley for at least 400,000 years. Such archaeological remnants were retrieved&#160;in&#160;Saint-Pierre-L&#232;s-Elbeuf, Tourville-la-Rivi&#232;re, Vernon and La Celle.Nowadays, the Seine connects to the drowned lower Seine course which continues in the Channel. This submerged part was subaerial during the last glacial cycle. Presently, the lower Seine course is still under the influence of marine tidal effects up to la Bouille (around 30 km from the coast). Additionally, estuarine deposits filled the valley up to Les Andelys (around 80 km from the coast) during the Holocene transgression and cover the penultimate and last glacial alluvial terraces. Nevertheless, the dynamic of the Seine river is broadly identified with few chronological constraints, but without any morphometric analysis combined with stratigraphical study.This work provides a review of the stratigraphy of the quaternary alluvial deposits in the lower part of the Seine Valley, together with new morphometrical analysis of the paleo-meanders located at higher altitudes. The analysis of the paleo-morphologies compared with high-resolution digital elevation model (DEM), provides new means for constraining the fluvial incision and deposition over long distances and periods, and helps to discuss the river evolution related with quaternary uplift, catchment evolution and glacio-eustatic dynamics.

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Shear‐wave velocity and density estimation from PS-wave AVO analysis: Application to an OBS dataset from the North Sea

Geophysics ◽

10.1190/1.1444833 ◽

2000 ◽

Vol 65 (5) ◽

pp. 1446-1454 ◽

Cited By ~ 33

Author(s):

Side Jin ◽

G. Cambois ◽

C. Vuillermoz

Keyword(s):

Wave Velocity ◽

North Sea ◽

Random Noise ◽

P Wave ◽

S Wave ◽

Data Set ◽

Avo Analysis ◽

The North ◽

Avo Inversion ◽

The North Sea

S-wave velocity and density information is crucial for hydrocarbon detection, because they help in the discrimination of pore filling fluids. Unfortunately, these two parameters cannot be accurately resolved from conventional P-wave marine data. Recent developments in ocean‐bottom seismic (OBS) technology make it possible to acquire high quality S-wave data in marine environments. The use of (S)-waves for amplitude variation with offset (AVO) analysis can give better estimates of S-wave velocity and density contrasts. Like P-wave AVO, S-wave AVO is sensitive to various types of noise. We investigate numerically and analytically the sensitivity of AVO inversion to random noise and errors in angles of incidence. Synthetic examples show that random noise and angle errors can strongly bias the parameter estimation. The use of singular value decomposition offers a simple stabilization scheme to solve for the elastic parameters. The AVO inversion is applied to an OBS data set from the North Sea. Special prestack processing techniques are required for the success of S-wave AVO inversion. The derived S-wave velocity and density contrasts help in detecting the fluid contacts and delineating the extent of the reservoir sand.

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Subsurface characterization of a quick-clay vulnerable area using near-surface geophysics and hydrological modelling

Solid Earth ◽

10.5194/se-10-1685-2019 ◽

2019 ◽

Vol 10 (5) ◽

pp. 1685-1705

Author(s):

Silvia Salas-Romero ◽

Alireza Malehmir ◽

Ian Snowball ◽

Benoît Dessirier

Keyword(s):

Large Scale ◽

Geophysical Methods ◽

Hydrological Modelling ◽

P Wave ◽

Coarse Grained ◽

Near Surface ◽

Reflection Seismic ◽

Geotechnical Investigations ◽

Quick Clay ◽

Near Surface Geophysics

Abstract. Quick-clay landslides are common geohazards in Nordic countries and Canada. The presence of potential quick clays is confirmed using geotechnical investigations, but near-surface geophysical methods, such as seismic and resistivity surveys, can also help identify coarse-grained materials associated with the development of quick clays. We present the results of reflection seismic investigations on land and in part of the Göta River in Sweden, along which many quick-clay landslide scars exist. This is the first time that such a large-scale reflection seismic investigation has been carried out to study the subsurface structures associated with quick-clay landslides. The results also show a reasonable correlation with radio magnetotelluric and travel-time tomography models of the subsurface. Other ground geophysical data, such as high magnetic values, suggest a positive correlation with an increased thickness of the coarse-grained layer and shallower depths to the top of the bedrock and the top of the coarse-grained layer. The morphology of the river bottom and riverbanks, e.g. subaquatic landslide deposits, is shown by side-scan sonar and bathymetric data. Undulating bedrock, covered by subhorizontal sedimentary glacial and postglacial deposits, is clearly revealed. An extensive coarse-grained layer (P-wave velocity mostly between 1500 and 2500 m s−1 and resistivity from approximately 80 to 100 Ωm) exists within the sediments and is interpreted and modelled in a regional context. Several fracture zones are identified within the bedrock. Hydrological modelling of the coarse-grained layer confirms its potential for transporting fresh water infiltrated in fractures and nearby outcrops located in the central part of the study area. The modelled groundwater flow in this layer promotes the leaching of marine salts from the overlying clays by seasonal inflow–outflow cycles and/or diffusion, which contributes to the formation of potential quick clays.

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Crustal velocity structure of the Apennines (Italy) from P-wave travel time tomography

Annals of Geophysics ◽

10.4401/ag-4042 ◽

1996 ◽

Vol 39 (6) ◽

Author(s):

C. Chiarabba ◽

A. Amato

Keyword(s):

Velocity Structure ◽

P Wave ◽

Depth Interval ◽

Low Velocity ◽

Data Set ◽

Arrival Times ◽

Velocity Anomaly ◽

Minimum Number ◽

Velocity Images ◽

Lower Crustal

In this paper we provide P-wave velocity images of the crust underneath the Apennines (Italy), focusing on the lower crustal structure and the Moho topography. We inverted P-wave arrival times of earthquakes which occurred from 1986 to 1993 within the Apenninic area. To overcome inversion instabilities due to noisy data (we used bulletin data) we decided to resolve a minimum number of velocity parameters, inverting for only two layers in the crust and one in the uppermost mantle underneath the Moho. A partial inversion of only 55% of the overall dataset yields velocity images similar to those obtained with the whole data set, indicating that the depicted tomograms are stable and fairly insensitive to the number of data used. We find a low-velocity anomaly in the lower crust extending underneath the whole Apenninic belt. This feature is segmented by a relative high-velocity zone in correspondence with the Ortona-Roccamonfina line, that separates the northern from the southern Apenninic arcs. The Moho has a variable depth in the study area, and is deeper (more than 37 km) in the Adriatic side of the Northern Apennines with respect to the Tyrrhenian side, where it is found in the depth interval 22-34 km.

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