non linear behaviour of electrical parameters in porous water saturated rocks a model to predict pore size distribution

SUMMARY In this paper, two separate but related goals are tackled. The first one is to demonstrate that in some saturated rock textures the non-linear behaviour of induced polarization (IP) and the violation of Ohm's law not only are real phenomena, but they can also be satisfactorily predicted by a suitable physical-mathematical model, which is our second goal. This model is based on Fick's second law. As the model links the specific dependence of resistivity and chargeability of a laboratory sample to the injected current and this in turn to its pore size distribution, it is able to predict pore size distribution from laboratory measurements, in good agreement with mercury injection capillary pressure test results. This fact opens up the possibility for hydrogeophysical applications on a macro scale. Mathematical modelling showsthatthechargeabilityacquiredinthefieldundernormalconditions,thatisatlowcurrent, will always be very small and approximately proportional to the applied current. A suitable field test site for demonstrating the possible reliance of both resistivity and chargeability on current was selected and a specific measuring strategy was established. Two data sets were acquired using different injected current strengths, while keeping the charging time constant. Observed variations of resistivity and chargeability are in agreement with those predicted by the mathematical model. These field test data should however be considered preliminary. If confirmedbyfurtherevidence,thesefactsmayleadtochangingtheprocedureofacquiringfield measurements in future, and perhaps may encourage the design and building of a new specific geo-resistivity meter. This paper also shows that the well-known Marshall and Madden's equations based on Fick's law cannot be solved without specific boundary conditions

Installation of a very broad band borehole seismic station in Ferrara (Emilia)

The Istituto Nazionale di Geofisica e Vulcanologia (INGV) is the Italian agency devoted to monitor in real time the seismicity on the Italian territory. The seismicity in Italy is of course variable in time and space, being also very much dependant on local noise conditions. Specifically, monitoring seismicity in an alluvial basin like the Po one is a challenge, due to consistent site effects induced by soft alluvial deposits and bad coupling with the deep bedrock (Steidl et al., 1996). This problem was tackled by INGV first with the Cavola experiment (Bordoni et al., 2007), where a landslide was seismically characterized using a seismic array and also down-hole logging of P- and S-wave travel times at a borehole drilled within the array; later, with an ad hoc project in 2000-2001, with the first installation of a broad band seismic station nearby Ferrara in a borehole of 135 meters depth. Comparison of recordings with a surface seismic station indicated a noise reduction of 2 decades in power spectral density at frequencies larger than 1.0 Hz (Cocco et al., 2001). The instrumentation in Ferrara has been working for several months but after that the seismic station was discontinued due to lack of maintenance manpower. The Centro di Ricerche Sismologiche (CRS, Seismological Research Center) of the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italian National Institute for Oceanography and Experimental Geophysics) in Udine (Italy) after the strong earthquake of magnitude M=6.4 occurred in 1976 in the Italian Friuli-Venezia Giulia region, started to operate the Northeastern Italy (NI) Seismic Network: it currently consists of 15 very sensitive broad band and 21 simpler short period seismic stations, all telemetered to and acquired in real time at the OGS-CRS data center in Udine (Fig. 1). Real time data exchange agreements in place with other Italian, Slovenian, Austrian and Swiss seismological institutes lead to a total number of about 100 seismic stations acquired in real time, which makes the OGS the reference institute for seismic monitoring of Northeastern Italy. Since 2002 OGS-CRS is using the Antelope software suite on several workstations plus a SUN cluster as the main tool for collecting, analyzing, archiving and exchanging seismic data, initially in the framework of the EU Interreg IIIA project “Trans-national seismological networks in the South-Eastern Alps”. SeisComP is also used as a real time data exchange server tool (Bragato et al., 2011). Among the various Italian institution with which OGS is cooperating for real time monitoring of local seismicity there is the Regione Veneto (Barnaba et al., 2012). The Southern part of the Veneto Region stands on the Po alluvial basin: earthquake localization and characterization is here again affected in this area by the presence of soft alluvial deposits. OGS ha already experience in running a local seismic network in difficult noise conditions making use of borehole installations (Priolo et al., 2012) in the case of the monitoring of a local storage site for the Italian national electricity company ENEL. Following the ML=5.9 earthquake that struck the Emilia region around Ferrara in Northern Italy on May 20, 2012 at 02:03:53 UTC, a cooperation of INGV, OGS, the Comune di Ferrara and the University of Ferrara lead to the reinstallation of the very broad band borehole seismic station in Ferrara. The aim of the OGS intervention was on one hand to extend its real time seismic monitoring capabilities toward South-East (Fig. 1), including Ferrara and its surroundings, and on the other hand to evaluate the seismic response at the site. As concerns the superficial geology of the area where the borehole seismic station has been installed, the outcropping materials are represented by alluvial deposits of different environments, like channel and proximal levee, inter-fluvial, meander and swamps deposits. As a consequence, the outcropping deposits are everywhere Holocene in age substantially loose or poorly compacted in the first meters-decameters and granulometrically could vary from clay to coarse sand. Two preliminary reports prepared by the Italian Department of Civil Defense (Dipartimento Nazionale di Protezione Civile) in collaboration with other institutions describe the data recorded by the national accelerometric network and complemented by additional data recorded by a number of temporary stations (Dolce et al., 2012a; Dolce et al., 2012b). These reports bear witness of strong ground motion values with an acceleration peak of about 0.9 g in the vertical component recorded during the ML=5.8 earthquake of May 29, 2012 by the Mirandola station, located at about 2 km from the epicentre. The analysis of the seismic noise recorded at some stations shows a quite pronounced peak of the horizontal-to-vertical spectral ratio (H/V) in the frequency range of 0.6 – 0.9 Hz common to all stations. Finally, strong evidence of liquefaction phenomena are reported at several sites (e.g.: S. Carlo, S. Agostino and Mirabello), most of which have been attributed to the occurrence of saturated sandy layer(s) at shallow depth deposited along an abandoned reach of the Reno River (Papathanassiou et al., 2012). Details of the station configuration and installation will be outlined, with first results

Human Bocavirus Infection among Children, Jordan

Human bocavirus was detected in 57 (18.3%) of 312 children with acute respiratory infection (ARI) who required hospitalization in Jordan. It was also detected in 30 (21.7%) of 138 children with severe ARI, in 27 (15.5%) of 174 with mild or moderate disease, and in 41 (72%) of 57 with other pathogens

Imaging Cultural Heritage at Different Scales: Part I, the Micro-Scale (Manufacts)

Applications of non-invasive sensing techniques to investigate the internal structure and surface of precious and delicate objects represent a very important and consolidated research field in the scientific domain of cultural heritage knowledge and conservation. The present article is the first of three reviews focused on contact and non-contact imaging techniques applied to surveying cultural heritage at micro- (i.e., manufacts), meso- (sites) and macro-scales (landscapes). The capability to infer variations in geometrical and physical properties across the inspected surfaces or volumes is the unifying factor of these techniques, allowing scientists to discover new historical sites or to image their spatial extent and material features at different scales, from landscape to artifact. This first part concentrates on the micro-scale, i.e., inspection, study and characterization of small objects (ancient papers, paintings, statues, archaeological findings, architectural elements, etc.) from surface to internal properties

Imaging cultural heritage at different scales : part I, the micro-scale (manufacts)

Applications of non-invasive sensing techniques to investigate the internal structure and surface of precious and delicate objects represent a very important and consolidated research field in the scientific domain of cultural heritage knowledge and conservation. The present article is the first of three reviews focused on contact and non-contact imaging techniques applied to surveying cultural heritage at micro- (i.e., manufacts), meso- (sites) and macro-scales (landscapes). The capability to infer variations in geometrical and physical properties across the inspected surfaces or volumes is the unifying factor of these techniques, allowing scientists to discover new historical sites or to image their spatial extent and material features at different scales, from landscape to artifact. This first part concentrates on the micro-scale, i.e., inspection, study and characterization of small objects (ancient papers, paintings, statues, archaeological findings, architectural elements, etc.) from surface to internal properties.peer-reviewe

Geophysical characterization of liquefied terrains using the electrical resistivity and induced polarization methods: The case of the Emilia earthquake 2012

Liquefaction phenomenon results in high water pressure being exerted on the soil particles due to earthquake shaking. Under certain condition this may result in permanent deformations leading to the formation of fractures, sand boils, lateral spreading on gently sloping landforms and landslides in highly sloping terrains. Some factors are known to affect liquefaction of saturated sands and silty sands such as materials type (i.e. compositional characteristics: particle size, shape, gradation, and relative density), in addition to, duration and amplitude of the dynamic excitation of one or several successive earthquakes. The geo-lithological factors are known also to affect other physical properties such as shear wave velocity, electrical resistivity and polarizability which constitute the backbone of seismic and electric geophysical methods. In this work, I highlighted the importance of subsurface electrical imaging in liquefaction related studies. Special emphasis has been given to usefulness of the IPT technique in localizing lithologic heterogeneities in alluvial plain lands where their presence is the rule and not the exception. The employment of the IPT completes and adds more independent information about the subsurface lithology which aid in the reconstruction of realistic geo-hydrogeological models. In addition, the gained information help in capturing post-seismic modifications. In particular, the IPT succeeded in mapping ruptures depth extension as well as the probable pathways followed during excess pore water pressure dissipation. It was interesting to note, in the second example (site B), how the liquefied sediments had moved horizontally due to the presence of a thick impermeable crust. This crust has facilitated the lateral dissipation of excess pore water pressure. Of course, this crust was removed to allow for the construction of the industrial building that had suffered a lot of damage leading to its demolition. The observed resistivity and IP anomalies are related to porosity and permeability modifications following liquefaction. These modifications can be easily explained by invoking the Archie (1942) empirical equation which explains that effective porosity, related to permeability, is inversely proportional to the formation factor (F defined as the ratio of formation resistivity and water resistivity) of clean sand (fine percent <10 %). The intrusion of liquefied sand mixed with water and fine materials has contributed in the increment of the IP response. The ERT/IPT may also be used to map and control consolidation effects normally used to mitigate the liquefaction risk. This last issue, however, requires further tests and analyses in order to evaluate possibilities and limitations. I think that the IPT technique may be used as a permanent monitoring tool to complement standard tools used for pressure monitoring in the future. The advantage of using these techniques resides in the fact that they can cover large volumes of subsurface materials. Hence reducing costs the society has to pay for post-seismic event reconstruction phase. I do believe that the best way to mitigate earthquake risk is to increase citizens perception to this type of risk that is related not only to the construction and its continuous maintenance but also to the spatial distribution ofsubsurface sediments. Such integration contributes in the process of smart underground monitoring of sites highly vulnerable to liquefaction. Last, the possibility to use the IPT to investigate the subsurface conditions of existing building is feasible and can be easily realized by installing the electrodes around the building itself. In this case, full 3D data acquisition protocols can be set up and acquired data can be processed using available 3D codes for data inversion

Il monitoraggio geofisico dell'intrusione salina di aree costiere subsidenti: esempi dalla costa emiliano-romagnola. Tecniche geofisiche per il monitoraggio di acquiferi.

La salinizzazione degli acquiferi costieri rappresenta un’emergenza ben nota, dovuta essenzialmente a due motivi: l’attività antropica connessa al proprio fabbisogno idrico e la subsidenza. Lo studio di questo problema richiede una conoscenza approfondita del modello idrogeologico concettuale che costituisce pertanto la base essenziale per poter effettuare scelte corrette non solo per il monitoraggio delle risorse idriche sotterranee, ma anche per la loro gestione e risanamento. Tale operazione può essere ottenuta mediante tecniche d’indagine che usino metodi diretti e/o indiretti. I metodi geofisici sono particolarmente indicati sia perché non invasivi e facilmente ripetibili sia perché veloci nell’investigazione di aree molto vaste. Tra i metodi geofisici più impiegati, il metodo geoelettrico di resistività eseguito in diverse modalità e utilizzando diverse sorgenti, sia in corrente continua che alternata (metodi geoelettrici od elettromagnetici). Nella presente nota si riportano sinteticamente i risultati salienti di una prospezione geoelettrica di resistività (DC) eseguita in modalità tomografica (Earth Resistivity Tomography-ERT) in diverse aree lungo la fascia costiera alluvionale delle Province di Ferrara e Rovigo. L’analisi dei modelli di resistività integrati con dati diretti di taratura provenienti da sondaggi geognostici specificamente effettuati, hanno portato a stabilire una corrispondenza tra la granolumetria dei sedimenti sciolti saturi di acqua salata e la resistività elettrica. Dal punto di vista pratico, questa corrispondenza permette di localizzare i percorsi preferenziali attraverso i quali avviene il processo di salinizazzione contribuendo così alla corretta programmazione dei successivi interventi di protezione degli acquiferi ed il loro riprestino ambientale

Guardare all’interno delle murature. Caratterizzazione di murature storiche con la tecnica della tomografia della resistività elettrica. Esempi e linee guida.

Il volume, avente per oggetto la tecnica della tomografia della resistività elettrica, fornisce una descrizione di base di questa tecnica, che può essere alternativa e/o complementare alle altre due nel fornire una descrizione dettagliata della morfologia muraria. Dopo la descrizione del metodo, basata anche su risultati di laboratorio, sono fornite delle schede che riportano i risultati di alcune applicazioni sulle murature per definire alcuni difetti ed anomalie e la presenza e diffusione di miscele di iniezione nell’applicazione di riparazioni mediante la tecnica predetta. Successivamente ne sono descritte le basi teorico-metodologiche per lo studio 3D; infine vengono fornite delle linee guida per la scelta della strumentazione, la progettazione e l’esecuzione di misure di resistività elettrica e le modalità di utilizzo dei risultati, essendo quest’ultimo l’aspetto più delicato del metodo. Infine sono allegate delle appendici con la breve descrizione delle altre due tecniche e cioè dell’indagine radar e sonica, nonchè una lista di normative esistenti

TECNOLOGIE NON INVASIVE PER LA DEFINIZIONE DELLE CONTAMINAZIONI in Corso Siti contaminati: strategie e valutazione degli impatti

Negli ultimi decenni nelle aree di pianura, prossime ad importanti corsi d’acqua, si sono sviluppate in Italia attività antropiche (spesso industriali) a forte impatto ambientale, lasciando una pesante eredità in termini di inquinamento dei suoli e delle acque sotterranee, oltre che dell’aria e delle acque di superficie. Mentre è relativamente semplice monitorare la qualità di queste ultime, molto più difficile e quindi costoso risulta controllare lo stato di degrado dei suoli e delle acque sotterranee. Il sottosuolo, nei terreni alluvionali, può essere caratterizzato da un’estrema variazione della composizione mineralogica, del contenuto di sostanza organica (torbe) della permeabilità e dei caratteri strutturali - tessiturali dei sedimenti presenti, variazioni che influenzano la capacità di scambio fra suolo e sostanze inquinanti. Strategie di raccolta di campioni rappresentativi delle eterogeneità del sottosuolo, della distribuzione dell’inquinamento e quindi del degrado, per quanto attentamente programmate, rischiano purtroppo di non riuscire a descrivere il sistema. Dati puntuali, benché di elevata precisione, non riescono a definire l’esatta geometria della distribuzione degli inquinanti nel sottosuolo, e i progettisti sono costretti ad ampliare l’area d’intervento per non lasciarsi sfuggire volumi significativi di contaminanti, criterio cautelativo che comporta un inutile aggravio dei costi oltre che un notevole impatto sugli ecosistemi presenti. Ideale è quindi disporre di tecniche che, a costi contenuti, permettano di delimitare le aree contaminate fornendo un’informazione proporzionale all’entità della contaminazione ed alla sua migrazione in profondità (immagine 3D). Queste tecniche rientrano tra quelle che la Geofisica Applicata negli ultimi anni sta sviluppando per lo studio dello stato ambientale del sottosuolo, trasferendo le conoscenze acquisite per il reperimento di georisorse (principalmente il petrolio, i minerali metallici, le risorse idriche sotterranee) all’analisi dei siti inquinati

Direct Interpretation of Phase Lags (DIPL) of MASW data: An example for evaluation of (Jet grouting) for soil stiffening enhancement against soil liquefaction

The evaluation of the soil stiffness is routinely performed by direct investigation, using geotechnical tests such as CPT-CPTu. A low cost complement to the direct investigation would be the use of seismic surface wave methods such as, for example, the “Spectral Analysis of Surface Waves” (SASW) or the more updated “Multi-channel Analysis of Surface Waves” (MASW) which use the dispersive nature of surface waves to retrieve the shear velocity (Vs) profile of the subsurface. Unfortunately, available inversion algorithms assume the subsurface model as a stack of homogeneous parallel layers hence of limited practical use when subsoil is known to be laterally heterogeneous. In the following, we shall introduce a novel strategy based on the Direct Interpretation of Phase Lags (DIPL) among pairs of seismic signals, based on a combination of SASW and MASW work-flows, which aims to retrieve the 2-D Vs subsurface profile and in particular to tackle the lateral heterogeneity issue. As an example of application we shall retrieve the 2-D Vs profiles before and after a Jet-Grouting (JG) intervention performed at a test site studied in the context of the reconstruction and prevention phase following the seismic sequence that struck the Emilia Region (Northern Italy) in 2012. Soil stiffening due to the cement mixture injection is then retrieved in term of Vs increase