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Dipartimento di Geologia e Geofisica, Università di Bari, Italy
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- PublicationOpen AccessStudio dell'anisotropia elettrica nella zona della sorgente sismogenetica del terremoto dell’Irpinia del 1930(2007-11)
; ; ; ; ; ; ; ; ; ; ;Balasco, M.; Istituto per le Metodologie Applicate all’Ambiente - CNR, Marsico Nuovo (PZ), Italia ;Diaferia, I.; Dipartimento di Geologia e Geofisica, Università di Bari, Bari, Italia ;Di Bucci, D.; Dipartimento della Protezione Civile, Roma, Italia ;Fracassi, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Loddo, M.; Dipartimento di Geologia e Geofisica, Università di Bari, Bari, Italia ;Magrì, C.; Dipartimento di Geologia e Geofisica, Università di Bari, Bari, Italia ;Romano, G.; Istituto per le Metodologie Applicate all’Ambiente - CNR, Marsico Nuovo (PZ), Italia ;Schiavone, D.; Dipartimento di Geologia e Geofisica, Università di Bari, Bari, Italia ;Siniscalchi, A.; Dipartimento di Geologia e Geofisica, Università di Bari, Bari, Italia ;Tripaldi, S.; Dipartimento di Geologia e Geofisica, Università di Bari, Bari, Italia; ; ; ; ; ; ; ; ; L’area del terremoto dell’Irpinia del 1930 corrisponde in profondità all'avampaese Apulo, inflesso al di sotto delle unità alloctone accavallate nella porzione frontale del cuneo orogenico, ma non coinvolto nelle strutture dei cosiddetti duplex dell'Apula sensu Patacca and Scandone (2004). In particolare, le profondità ipocentrali del terremoto del 1930 corrispondono al basamento sottostante la successione della Piattaforma Carbonatica Apula. Il campo macrosismico e i dati strumentali disponibili (si veda la sorgente in DISS, 2007, con relativa bibliografia, e Pino et al., sottomesso) suggeriscono una sorgente sismogenetica con un’orientazione e una cinematica che rappresentano una sorta di transizione tra la direzione W-E a cinematica trascorrente destra, che caratterizza la sismicità propria delle aree di avampaese sia affiorante che sepolto, e la direzione NW-SE a cinematica normale, che caratterizza la sismicità connessa all'estensione lungo l'asse della catena Appenninica (si veda il terremoto del 1980). In questo quadro, l’obiettivo dello studio magnetotellurico è stato quello di investigare i volumi di crosta al di sotto della successione Apula per valutare l'eventuale presenza di direzioni preferenziali dell'anisotropia di resistività che fossero confrontabili con la direzione della sorgente del terremoto del 1930. Il verificarsi di tale evenienza avrebbe potuto essere infatti interpretato come indizio di una zona di debolezza regionale, che avrebbe condizionato le caratteristiche geometriche e cinematiche della sorgente del terremoto stesso. Partendo dall’area sismogenetica segnalata nel DISS per questo terremoto, sono stati effettuati in un’area di circa 1000 km2 sondaggi magnetotellurici in 15 siti, nell’intervallo di 0.009- 4000 s. Per ciascun sito si è proceduto alla misura delle tre componenti ortogonali del campo magnetico e di tre componenti del campo elettrico, di cui due lungo la stessa linea e ortogonali alla terza. Ciò ha consentito la stima dei parametri magnetotellurici per due sondaggi adiacenti, al fine di meglio controllare possibili problemi di rumore antropico o strumentale. Le stazioni, fino ad un massimo di tre, hanno operato in contemporanea fungendo l’una per l’altra da remote reference (Gamble et al., 1979). Va sottolineata la buona qualità dei dati acquisiti sia in termini di stime stabili con diverse tecniche di analisi, che per basso scattering delle curve di resistività apparente e fase. Le risposte sperimentali sono state poi comparate con i dati di pozzo disponibili, verificando un ottimo accordo. È stata inoltre eseguita un’analisi sulle proprietà fisiche e geometriche del tensore impedenza, adottando lo schema di decomposizione di Weaver et al. (2000) dal quale è derivato poi lo studio degli invarianti magnetotellurici per la definizione della dimensionalità delle strutture elettriche investigate ai vari periodi (ovvero alle varie profondità). Circa il 75% dei dati analizzati implica strutture assimilabili necessariamente a modelli tridimensionali e le quattro componenti del tensore impedenza sono significativamente diverse da zero. Per questo tipo di strutture, seguendo Weaver et al. (2000), è comunque possibile definire una direzione di eterogeneità elettrica. Ciò è stato fatto per ciascun sondaggio e per ciascun periodo di stima. Mediante la trasformazione di Niblett–Bostick è stato poi ottenuto lo strike elettrico in funzione della profondità stimata. Viene riportata la direzione di strike per i vari sondaggi alla profondità stimata nell’intervallo 8 - 16 km, riferibile quindi a una porzione di crosta al di sotto del resistivo che identifica le successioni della Piattaforma Apula.276 83 - PublicationOpen AccessShallow to intermediate resistivity features of the Colfiorito Fault System inferred by DC and MT survey(2008-04)
; ; ; ; ;Diaferia, I.; Dipartimento di Geologia e di Geofisica, Università degli Studi di Bari, Italy ;Loddo, M.; Dipartimento di Geologia e di Geofisica, Università degli Studi di Bari, Italy ;Schiavone, D.; Dipartimento di Geologia e di Geofisica, Università degli Studi di Bari, Italy ;Siniscalchi, A.; Dipartimento di Geologia e di Geofisica, Università degli Studi di Bari, Italy; ; ; Over the last decade electromagnetic (EM) measurements have provided new constraints on the upper-crustal structure of the major fault zones in the world, both when they act as conduit and as a barrier, due to strong sensitivity of resistivity to fluids circulation and mineralization. On the track of a high impact magnetotelluric (MT) study performed across the San Andreas Fault, high resolution EM data were collected in the Colfiorito epicentral area along profiles crossing some main fault lineaments. Being the study focussed both on shallow that on intermediate resistivity distribution in the brittle upper-crust, a MT profile was integrated by several electrical resistivity tomographies (ERT). The latter were successful in locating faults even where the structures are buried by a wide covering of Quaternary deposits and in the recognition of different electrical signatures of the faults. MT resistivity model crossing Mt. Prefoglio normal fault clearly imaged the typical thrust structures of the area and a high conductive zone spatially related to the fault. Seismicity seems to be located outside such conductive area, whose behaviour suggests a fluidised and altered zone incapable of supporting significant stress internally.205 241 - PublicationRestrictedA critical revision of the seismicity of Northern Apulia (Adriatic microplate - Southern Italy) and implications for the identification of seismogenic structures(2007-03-03)
; ; ; ; ; ; ;Del Gaudio, V.; Dipartimento di Geologia e Geofisica, University of Bari ;Pierri, P.; Dipartimento di Geologia e Geofisica, University of Bari ;Frepoli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Calcagnile, G.; Dipartimento di Geologia e Geofisica, University of Bari ;Venisti, N.; Dipartimento di Geologia e Geofisica, University of Bari ;Cimini, G. B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; ; ; ; ; Northern Apulia is an emerged portion of the Adriatic microplate, representing the foreland–foredeep area of a stretch of the Apennine chain in southern Italy. The interaction between the relatively rigid microplate and the contiguous more deformable domains is responsible for the intense seismicity affecting the chain area. However strong, sometimes even disastrous, earthquakes have also hit northern Apulia on several occasions. The identification of the causative faults of such events is still unclear and different hypotheses have been reported in literature. In order to provide guidelines and constraints in the search for these structures, a comprehensive re-examination and reprocessing of all the available seismic data has been carried out taking into consideration 1) the characteristics of historical events, 2) the accurate relocation of events instrumentally recorded in the last 20 years, 3) the determination of focal mechanisms and of the regional stress tensor. The results obtained bring to light a distinction between the foreland and foredeep areas. In the first region there is evidence of a regional stress combining NWcompression and NE extension, thus structures responsible for major earthquakes should be searched for among strike–slip faults, possibly with a slight transpressive character. These structures could be either approximately N–S oriented sinistral or E–Wdextral faults. In the foredeep region there is a transition toward transtensive mechanisms,with strikes similar to those of the previous zone, or maybe also towardsNWoriented normal faults,more similar to those prevailing in the southern Apennine chain in relation to a dominant NE extension; this appears to be the effect of a reduction of the NW compression, probably due to a decrease in efficiency of stress transmission along the more tectonised border of the Adriatic microplate.225 28 - PublicationOpen AccessEvidence of Apulian crustal structures related to low energy seismicity (Murge - Southern Italy)(2001-10)
; ; ; ; ; ; ; ; ; ;Del Gaudio, V.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Festa, V.; Dipartimento Geomineralogico, Università di Bari, Italy ;Ripa, R. R.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Iurilli, V.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Pierri, P.; Osservatorio Sismologico, Università di Bari, Italy ;Calcagnile, G.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Moretti, M.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Pieri, P.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Tropeano, M.; Dipartimento di Scienze Geologiche, Università della Basilicata, Potenza, Italy; ; ; ; ; ; ; ; The discovery of recent co-seismic sedimentary structures and the detection of low energy seismic activity in the Murgian plateau (Apulia - Southern Italy) motivated a more detailed examination of the tectonics in this part of the Apulian plate commonly believed to be aseismic. In particular, we examined the north-western zone where a seismic sequence with maximum magnitude 3.2 and tensional focal mechanism occurred in 1991. The analysis of the existing gravimetric data, integrated by three new profiles carried out across the epicentral area, disclosed an anomaly possibly due to an old tensional tectonic structure located within the upper crust. Even though the depth and the age hypothesised for the anomaly source would exclude a direct causal connection with the observed seismicity, this structure could be a shallower expression of a tectonic structure extending down to the crystalline basement: it could represent a zone of relative «weakness» where the regional stress, due to the interactions between Apennines and Apulian plate, encounters conditions facilitating the release of seismic energy.175 369 - PublicationOpen AccessQuaternary tectonic activity of the Murge area (Apulian foreland -Southern Italy)(1997-10)
; ; ; ; ;Pieri, P.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Festa, V.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Moretti, M.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Tropeano, M.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy; ; ; Integration of structural, stratigraphical, and sedimentological data and instrumental records of some recent low-energy seismic events in the Murge area allow us to suggest a new seismotectonic picture of this region, generally considered an aseismic and stable sector of the Apulian foreland.134 1026 - PublicationOpen AccessIs the dependence on the temperature of the friction important in stress triggering phenomena? The case of the 2000 Iceland seismic sequence(2012-04)
; ; ; ; ;Bizzarri, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Crupi, P.; Università degli Studi di Bari ;de Lorenzo, S.; Università degli Studi di Bari ;Loddo, M.; Università degli Studi di Bari; ; ; We perform numerical experiments by using a mass–spring fault model subject to an external coseismic stress perturbation due to a remote seismic event happening on another fault, the causative fault. In particular, the aim of this study is to investigate the instantaneous fault interaction and possible triggering that happens when a fault perturbed by a stress change fails before the so–called unperturbed instability. As a realistic example we focus our attention on the instantaneous dynamic triggering phenomena occurred during the 17 June 2000 south Iceland seismic sequence in the South Iceland Seismic Zone (SISZ, Reykjanes Peninsula). The main event (Ms 6.6) was followed by three large events within a few tens of seconds (8, 26 and 30 s, respectively) located in a neighborhood of several tens of km. Among them the 26 s event was the best constrained (Bizzarri and Belardinelli, 2008). In the present study, conditions to simulate the instantaneous dynamic triggering connected to the former three events, have been investigated using the simple 1–D spring–slider analogue model representing a fault governed by the rate– and state–dependent friction laws. In previous studies suitable constitutive parameters of the modeled fault which allow the instantaneous triggering of the three events, have been found (Antonioli et al., 2006) and, furthermore, it was also shown how the dynamics of the 26 s event strongly depends on the assumed constitutive law and stress conditions (Bizzarri and Belardinelli, 2008) by considering the Dieterich–Ruina (DR henceforth) and the Ruina–Dieterich (RD henceforth) governing laws. In this context take place the present study original contribution that is to better understand if the conditions of instantaneous dynamic triggering (focusing on the case of the 26 s triggered event) provide any significant differences if modeled with a different rate– and state–dependent governing equation, the Chester and Higgs law (CH henceforth; see Chester and Higgs, 1992; Bizzarri, 2010b; Bizzarri, 2010c) which accounts for the thermal effect for frictional heating which may occur during seismic sliding.125 98 - PublicationOpen AccessMagnetotelluric investigation in a seismogenic source area: Evidences from the 1930 Irpinia earthquake area(2008-08)
; ; ; ; ; ; ; ; ; ; ;Siniscalchi, A.; Dipartimento di Geologia e Geofisica, Università di Bari ;Balasco, M.; CNR - IMAA, Potenza ;Diaferia, I.; Dipartimento di Geologia e Geofisica, Università di Bari ;Di Bucci, D.; PCM - Dipartimento Protezione Civile, Roma ;Fracassi, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Loddo, M.; Dipartimento di Geologia e Geofisica, Università di Bari ;Magrì, C.; Dipartimento di Geologia e Geofisica, Università di Bari ;Romano, G.; CNR - IMAA, Potenza ;Schiavone, D.; Dipartimento di Geologia e Geofisica, Università di Bari ;Tripaldi, S.; Dipartimento di Geologia e Geofisica, Università di Bari; ; ; ; ; ; ; ; ; On 23 July 1930, the Irpinia region in southern Italy experienced a destructive (M 6.7) earthquake that struck the eastern sector of the southern Apennines moutain belt. Previous studies suggest that this earthquake was caused by a seismogenic source having oblique right-lateral kinematics and striking at an angle between the general trend of NE-verging large dip-slip faults in the southern Apennines (~ NW-SE) and the E-W near-vertical, strike-slip right lateral faults that have been recently discovered in the foreland, east of the main extensional axis. Also, the ~14 km hypocentral depth of the 1930 earthquake that has been calculated in previous studies is likely located within the basement below the Apula carbonate platform succession. This puts the source of the 1930 earthquake not only in an intermediate region between pure normal (NW-SE) and strike-slip right-lateral (E-W) large seismogenic faults in the southern Apennines, but also at an hypocentral depth between the 12-13 km depth of the earthquakes caused by normal faulting (like the Irpinia 23 Nov. 1980, M 6.9 one) and the 15-20 km depth of the earthquakes caused by strike-slip faulting in the foreland (like the 31 Oct.-1 Nov. 2002, M 5.8 Molise ones). In this framework, we performed a magnetotelluric (MT) study to investigate the evidence of preferential direction in resistivity anisotropy and to compare it with the strike of the 1930 seismogenic fault.311 1837 - PublicationOpen AccessIntegrated geophysical survey for the geological structural and hydrogeothermal study of the North-western Gargano promontory (Southern Italy)(1996-01)
; ; ; ;Loddo, M.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Quarto, R.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Schiavone, D.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy; ; A multimethodological geophysical survey was performed in the north-western part of the Gargano promontory to study the geological structural setting and the underground fluid flow characteristics. The area has a complex tectonics with some magmatic outcrops and shallow low-enthalpy waters. Electrical, seismic reflection, gravimetric and magnetic surveys were carried out to reconstruct the geological structures; and in order to delineate the hydrogeothermal characteristics of the area, the self-potential survey was mainly used. Moreover magnetic and self-potential measurements were also performed in the Lesina lake. The joint three-dimensional interpretation of the geophysical data disclosed a large horst and graben structure covering a large part of the area. In the central part of the horst a large ramified volcanic body was modelled. The models show some intrusions rising from it to or near to the surface. The main structures are well deep-seated in the Crust and along them deep warm fluids rise as the SP data interpretation indicates.194 680 - PublicationOpen AccessThe Siena Graben: combined interpretation of DES and MT soundings(1996-01)
; ; ; ; ;Giammetti, S.; Dipartimento di Geofisica e Vulcanologia, Università «Federico II», Napoli, Italy ;Patella, D.; Dipartimento di Geofisica e Vulcanologia, Università «Federico II», Napoli, Italy ;Siniscalchi, A.; eomare Sud, Istituto di Geologia Marina del C.N.R., Napoli, Italy ;Tramacere, A.; Dipartimento di Geofisica e Vulcanologia, Università «Federico II», Napoli, Italy; ; ; The Siena Graben study area is located in Tuscany, Central Italy. The local geological structures were extensively studied in the frame of the Italian National Research Council (CNR) and the Commission of the European Communities (CEC) geothermal projects. Axial dipole-dipole geoelectrical soundings (DES) were also performed. Recently we carried out 13 broadband magnetotelluric (MT) soundings, most of which were located very close to the station sites of the mentioned DES. For six of them we made a DES-MT combined interpretation in order to put in evidence resistivity frequency dispersion effects. Indeed, four sites showed DES-MT anomalous responses, in the frequency range 1 ¸ 102 Hz, which can be properly explained as due to dispersion effects in shallow layers. Three of these anomalous sounding sites are located on the neoautochthonous clayey formation, while the fourth is located on the eastern boundary of the graben over an extensive outcrop of the «Macigno» complex. The dispersion-affected soundings are all located in the northern part of the graben, while there is no evidence of such effects in the southern part. This circumstance, together with the estimate of very low time constants of the fitting Cole-Cole dispersion model, can be tentatively explained as due to local and shallow lithological effects (clay-like membrane polarization) rather than to deep geothermal effects (sulphide-like electrode polarization). Moreover, the MT soundings delineated a conductive zone in the upper crust below the resistive geoelectrical basement, located in the northern part of the graben, which appears at present difficult to interpret. Furthermore, the combined analysis of the DES and MT soundings in the same sites has allowed us to resolve one of the most intriguing ambiguities concerning the determination of the depth to the graben basement. The result is a remarkable reduction of the depth to the basement top, especially in the northern part of the graben. Finally, the easternmost MT soundings, located on the resistive outcrops of the massive calcareous formations of the basement and of the «Macigno» complex, permitted us to investigate almost all the lithospheric slab, thanks to the locally greater skin depth penetration. The lithosphere-asthenosphere transition is very well delineated, whereas the crust-mantle transition seems not to have an evident electrical signature.172 254 - PublicationOpen AccessGeneration of synthetic wide-band electromagnetic time series(2002)
; ; ; ;Loddo, M.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Schiavone, D.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Siniscalchi, A.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy; ; The estimation of the earth transfer functions in MT prospecting method poses the greatest difficulty. As in the seismic prospecting method this task requires the development of advanced processing techniques. In order to assess the performance of each technique, controlled synthetic data and different noise types, which simulate the observed signals, are required. This paper presents a procedure to generate a wide-band noise-free electromagnetic field to be used both for magnetotelluric and audio-magnetotelluric studies. Furthermore, an effort was made to extend the simulation procedures to generally stratified and simple inhomogeneous earth structures. The discrete-time magnetic field values are generated through the inverse Fourier transform of a continuous amplitude spectrum and a sampling procedure. The electric field time series are obtained by the convolution of the magnetic field time series, calculated in the interested frequency band, with a non-causal impedance impulse response. Polarized fields, which are important when inhomogeneous media are considered, are also generated.182 203
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