Scientific drilling in a central italian volcanic district

This article introduces the 350m scientific borehole performed in the Colli Albani area. It describes the technical features of the drilling and the on-site measurements, and summarizes the main ongoing researches on data and samples from the borehole

Studio multidisciplinare per la caratterizzazione ed identificazione di aree sismicamente attive in Appennino: metodi geologici, geofisici e statistici

Lo studio effettuato in questa tesi di Dottorato ha lo scopo di integrare metodologie di analisi diverse - geologiche, geofisiche e statistiche - per contribuire alla determinazione del potenziale sismico, che è la diretta espressione dell’attività del campo di stress attualmente agente e responsabile della sismicità. Queste tre diverse metodologie sono state applicate in due aree selezionate ubicate lungo la catena appenninica, in corrispondenza delle conche intramontane di origine tettonica. La scelta di queste aree si basa anche sul presupposto che esse possano avere un notevole potenziale sismico essendo caratterizzate da importanti eventi storici di elevata magnitudo. Tra le metodologie applicate in questo studio, i metodi geologici mirano alla comprensione dell’evoluzione quaternaria delle depressioni intrappenniniche con particolare riguardo al riconoscimento ed alla valutazione delle evidenze di tettonica attiva. I metodi geofisici sono stati applicati per studiare e definire meglio il campo di stress attraverso l’analisi dei dati di borehole breakout, dei meccanismi focali dei terremoti e del test di Leak-off. Tutte le tecniche sono volte a determinare le componenti relative al campo di stress quali orientazione (Shmin ed asse-T), tipo di regime (normale, trascorrente o inverso) e sua quantificazione (pressioni in MPa). È stato inizialmente affrontato uno studio della sismicità storica e strumentale, attraverso l’analisi dei vari cataloghi, per integrare le conoscenze sulla geodinamica dell’Appennino, sull’assetto geologico-strutturale profondo, sulla definizione delle strutture sismogeniche, sulla distribuzione e sul potenziale sismico delle aree campioni. È stata affrontata l’analisi delle sequenze sismiche per determinare la distribuzione areale ed in profondità degli eventi, l’orientazione ed il tipo di regime di stress e la stima del tensore dello stress regionale mediante il metodo di inversione di GEPHART & FORSYTH (1984). Infine, sono stati applicati due metodi statistici per studiare la distribuzione spazio-temporale dei terremoti tramite due approcci non-parametrici: l’analisi multivariata che implementa il dato di sismicità con quello geologico-strutturale (FAENZA et al., 2003) ed il metodo di TANNER & WONG, 1984) che utilizza solo i dati di sismicità relativi ad un campione omogeneo. Infine, è stata calcolata la probabilità di evento nelle due aree campioni

Contemporary and concurrent extension and compression in Italy

Contemporary and concurrent extension and compression in Italy Paola Montone1, M. Teresa Mariucci1 and Simona Pierdominici2 1-Istituto Nazionale di Geofisica e Vulcanologia, Rome , Italy 2 – GFZ GeoForschungsZentrum, Potsdam, Germany We present the latest updating and the complete collection of data on the contemporary stress orientations in Italy. Data are relative to different stress indicators: borehole breakouts from deep drillings, crustal earthquake focal mechanisms and fault data. With respect to the previous compilation, performed in 2004, 206 new entries complete the definition of the horizontal stress orientation and tectonic regime in the most part of the territory, and bring new information mainly in Sicily and along the Apenninic belt. With an increase of 37% with respect to the previous compilation, now the global Italian dataset consists of 499 records with a reliable quality for stress maps. The total dataset includes the following active stress indicators: 56% borehole breakouts, 39% single earthquake focal mechanisms, and 5% represented by formal inversions of focal mechanisms, faults and overcoring data. A quality ranking between A and E is assigned to each stress data, with A being the highest quality and E the lowest. Only A-, B- and C-quality stress indicators are considered consistent for analyzing stress patterns. Depth interval of the entire dataset is between 0 to 40 km. The results in map are reported in terms of minimum horizontal stress (Shmin) because most of earthquakes present an extensional regime. Concerning breakouts, their orientations correspond to Shmin; since all the considered faults are normal faults, we assume the Shmin direction as perpendicular to the fault strike when no information on slip direction is available. The achieved results can be summarized in 3 main points: i) in some areas of Italy (Sicily, Friuli and Po Plain in the northern Italy), the alignment of horizontal stresses closely matches the ~N-S direction of ongoing crustal motions with respect to stable European plate. This result can be associated to the first-order stress field that drives the plate movement; ii) along the entire Apenninic belt – from north to south- a diffuse extensional stress regime is clearly showed by a large dataset indicating a NE-SW direction of extension, probably related to a second-order stress field; iii) the stress rotations observed in some areas (i.e., Po Plain minor arcs and Gela thrust front) reflect a complex interaction between first order stress field and local effects, revealing the importance of the inherited tectonic structure orientations. In particular in this work the simultaneous occurrence of different stress regimes is discussed. Finally, we underline that this kind of map is very useful to those many users that work on this topic and/or related ones such as, for instance, geophysical modeling, seismic hazard assessment, rock mechanics laboratory experiments, deep drillings but also on oil and gas well production and construction of nuclear waste deposits

Active stress field in central Italy: a revision of deep well data in the Umbria region

In this area the active stress from borehole breakout analysis shows a prevalent NE-SW extension, perpendicular to the main tectonic structures, in agreement with stress inferred from earthquake focal mechanisms and with the strain velocity field. A detailed analysis of active stress data allows to infer the influence of active structures on the local stress field orientations. San Donato 1 well shows a minimum horizontal stress orientation N55±22°, in agreement with the regional trend and with the local one influenced by its vicinity to the Alto Tiberina Fault. Whereas Monte Civitello 1 well shows a quite different orientation, N12±29°, due to its different location, more to the east, and to the structures that it crosses. Although the angular difference between the two directions is within the error, to estimate the regional active stress field many borehole data should be analysed or smoothing maps should be evaluated. In fact, each borehole dataset could be influenced by local stress conditions that in some case can be different from the regional trend. The two breakout orientations perfectly depict the regional extension along the axis of the Apennines and also the minimum horizontal stress rotation moving eastward to the area where compression is predominant

Comparison between active stress field and tectonic structures in Northern Italy, Lombardy Region

The aim of this work is to understand the complex pattern of active stress field orientations revealed by borehole breakout analysis with respect to the tectonic structures in a wide region of Northern Italy. The area is located in the central-western part of the Po Plain between the south verging Southern Alps structures and the north verging buried folds and thrusts of the Monferrato and Emilia arcs. Little information concerning the active stress field is available because of the low seismicity level and the thick layer of sediments that covers the entire zone. A detailed borehole breakout analysis has been performed in 36 wells with depths ranging from 2.2 to 7.3 km, whose data have been supplied by Eni. Breakout analysis determined the minimum and maximum horizontal stress directions (Shmin and SHmax). The results show a very complex pattern, pointing out that the stress field is not uniform. In this area the regional stress field seems not «strong» enough, compared to the local one, so most of the wells detect only the local field. This work contributes to clarify the various Shmin orientations observed in this area, pointing out at wide scale, a general compression in NNE-SSW direction in this complex region

Hydrogeological study of the monti sibillini north-western sector: a contribution to the official hydrogeologic mapping

This work underlines the importance of experimental data and integrates the hydrogeological mapping methods. The work has analyzed the lithological features of the outcropping rocks and their attitude to be crossed by the meteoric waters. Geologic-structural analysis has allowed to identify elements that can constitute the hydraulic barriers and the hydrogeological complexes that can contain the aquifers. A detailed analysis of base flow was carried out through hydrogeological survey directly performed in the river. The hydrogeological survey has allowed us: 1) to appraise the river's base flow; 2) to identify the punctual and linear springs; 3) to quantify the water resource on average drained; and 4) to determine the discharge regime of springs and rivers. The Conceptual Hydrogeological Model for each individual aquifer have been derived from geologic-structural analysis and hydrogeological studies. The Conceptual Hydrogeological Models allowed us to calculate the Mean Effective Infiltration (Ieff) of every aquifer. The values of Ieff are gathered in classes. All merged information has been used in the preparation of Hydrogeological Complexes and Natural Springs Map. The manifold hydrogeological information cannot be represented in one document only; so the Experimental Hydrogeological Mapping has been prepared as the overlap of different informative levels: Hydrogeological Complexes and Natural Springs Map (principal document), Surface Hydrology Map and Conceptual Hydrogeological Models of several recognized aquifers (complementary elements)

A Methodology for a Comprehensive Probabilistic Tsunami Hazard Assessment: Multiple Sources and Short-Term Interactions

We propose a methodological approach for a comprehensive and total probabilistic tsunami hazard assessment (TotPTHA), in which many different possible source types concur to the definition of the total tsunami hazard at given target sites. In a multi-hazard and multi-risk perspective, the approach allows us to consider all possible tsunamigenic sources (seismic events, slides, volcanic eruptions, asteroids, etc.). In this respect, we also formally introduce and discuss the treatment of interaction/cascade effects in the TotPTHA analysis and we demonstrate how the triggering events may induce significant temporary variations in short-term analysis of the tsunami hazard. In two target sites (the city of Naples and the island of Ischia in Italy) we prove the feasibility of the TotPTHA methodology in the multi-source case considering near submarine seismic sources and submarine mass failures in the study area. The TotPTHA indicated that the tsunami hazard increases significantly by considering both the potential submarine mass failures and the submarine seismic events. Finally, the importance of the source interactions is evaluated by applying a triggering seismic event that causes relevant changes in the short-term TotPTHA

A proposal for compiling quantitative hydrogeological maps

An innovative approach to hydrogeological mapping based on quantitative analysis is shown in this paper. It gives some cartographical solutions for an immediate evaluation of the groundwater resources and their spatial distribution. All relevant aquifers, springs and their regime, geological and structural setting and their hydraulic role should be shown in several understandable and clear hydrogeological maps where all hydrogeological information is reported in detail in the “Hydrogeological experimental Map” composed by a. “Hydrogeological Complexes and Natural Springs Map”, b. “Surface Hydrology Map”, c. “Conceptual Hydrogeological Model” and d. “Hydrogeological sections”. The cartographical solutions adopted for representing all these documents are proposed in this paper. Some graphical solutions have been proposed for improving the Italian official guidelines of hydrogeological mapping at scale 1:50.000, explain the legends symbols and illustrate the structure of a hydrogeological GIS database. An application of this approach has been carried out in north-western sector of Sibillini Mts. (Marche, Italy)

Fracture Logging of the AND-2A Core, ANDRILL Southern McMurdo Sound Project, Antarctica

Fractures in AND-2A drillcore were documented in this study. Over 4100 fractures of all types were logged. A population of 510 steeply-dipping, petal, petal-centreline and core-edge induced fractures is present, reaching a maximum density of c. 10 fractures/metre. Subhorizontal induced extension fractures are also abundant. There are 1008 natural fractures in the core, including faults, brecciated zones, veins and sedimentary intrusions. Kinematic indicators document dominant normal faulting, although reverse faults are also present. The natural fractures occur in strata ranging in age from the Miocene to the Plio-Pleistocene

Borehole breakout analysis: results from the AND-2A Well

To define the present-day stress field in the upper crust and to understand the recent tectonic activity in Antarctica, a study of breakout measurements along AND-2A well was performed. The borehole breakout is an important indicator of horizontal stress orientation and occurs when the stresses around the borehole exceed that required to cause compressive failure of the borehole wall (Bell and Gough, 1979; Zoback et al., 1985, Bell, 1990). The enlargement of the wellbore is caused by the development of intersecting conjugate shear planes that cause pieces of the borehole wall to spall off. Around a vertical borehole, stress concentration is greatest in the direction of the minimum horizontal stress (Shmin), hence, the long axes of borehole breakouts are oriented approximately perpendicular to the maximum horizontal stress orientation (SHmax). The orientation of breakouts along the AND-2A well was measured using acoustic (BHTV) and mechanical (Four-Arm Caliper) tools. Borehole televiewer (BHTV) provides an acoustic "image" of the borehole wall (360 degree coverage) and gives detailed information for investigation of fractures and stress analysis. The four-arm caliper is the oldest technique for borehole breakout identification and it is included in routine dipmeter logs. A quality value has been assigned to the well results in agreement with the World Stress Map quality ranking scheme (Zoback, 1992; Heidback et al., 2010) based mainly on the number, accuracy, and length of breakout measurements. The result is presented as rose diagram of the breakout directions where the length of each peak is proportional to the frequency and the width to the variance of its gaussian curve. We have analyzed the following curves to recognize the breakout: the azimuth of Pad 1 (P1az), the drift azimuth (HAZI), the two calipers with respect to the bit size (BZ) curve and the curve relative to the deviation of the well. The AND-2A Four-Arm Caliper data cover a depth interval between 637 down to 997 mbsl, that corresponds to 360 m of logged interval. We have distinguished breakouts and some washouts only in the interval from 753 to 825 mbsl. From borehole televiewer images, we have data from 398 mbsl down to 1136 mbsl. The BHTV worked well showing a lot of interesting features such as many bedding, lamination and fractures (natural and induced) but poor breakouts. The rare breakouts have also a small size (called protobreakouts) but they are consistent with induced features. Considering the breakout result from caliper and BHTV, the AND-2A borehole is unfortunately classified as D quality. This means that to obtain a reliable active stress field of the area it is necessary to compare this result with other available data