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Using published cross-sections and a series of geological constraints, a 3D geological model of an important area of the Adriatic sector of peninsular Italy—i.e., the Marche region—was developed. Then, an analytical procedure, taking into account the heat rising from the mantle and the radiogenic heat produced by the crust, was applied on the pre-built structural model, in order to obtain the 3D geothermal setting of the entire region. The results highlighted the key role played by the Moho geometry, particularly as a step of ~10 km occurs between the Adriatic Moho of the subducting plate to the west and the new Tyrrhenian Moho characterizing the back-arc area to the west. The comparison between our results and available borehole data suggests a good fit between the applied analytical methodology and published datasets. A visible anomaly is located at a specific site (i.e., the coastal town of Senigallia), where it may be envisaged that fluid circulation produced a local surface heat flow increase; this makes the Senigallia area a promising feature for the possible exploitation of geothermal systems.

In this work we examine the seismicity of Montefeltro, a historical region of central Italy located between the northern Apennines and the Republic of San Marino towards the northern Adriatic coast...

The Zagros thrust belt formed due to the convergence between the Arabian and Eurasian plates during the closure of the Neo-Tethys Ocean. GPS measurements show that the northward relative motion of ...

To unravel how and where coseismic and interseismic deformation impacts the spatial and temporal patterns of rock uplift of the Lurestan sector of the Zagros Mountains, we performed an investigation of the large‐scale features of topography and river network coupled with 2‐D finite element modeling. Geomorphological analysis and constraints from parameters such as elevation, local relief, normalized channel steepness index (ksn), river longitudinal profiles, and transformed river profiles (chi plots) were used to unravel the time‐space distribution of vertical motions. Whereas the much longer timescale over which topography grows and/or rivers respond to tectonic or climatic perturbations with respect to even multiple seismic cycles, the outputs of the finite element model yield fundamental information on the source of the late part of the spatiotemporal evolution of surface uplift recorded by the geomorphology. Model outputs shed new light into the processes controlling relief evolution in an actively growing mountain belt underlain by a major blind thrust. The outputs illustrate how coseismic slip controls localized uplift of a prominent topographic feature—the Mountain Front Flexure—located above the main upper crustal ramp of the principal basement thrust fault of the region, while continuous displacement along the deeper, aseismic portion of the same basement fault controls generalized uplift of the whole crustal block located farther to the NE, in the interior of the orogen.

The 2018 Gulf of Alaska earthquake (Mw 7.9) occurred in a region of the Pacific plate southwest of the Alaskan subduction zone. The earthquake was a strike-slip event, with the hypocenter located at a depth of about 25 km and a seismic moment equal to 0.96 × 1021 Nm. Two observed moment rates have been obtained by the Geoscope Observatory, France, and by the United States Geological Survey (USGS). Both of them can be interpreted as due to the failure of two asperities on the fault surface. We consider a discrete fault model, with two asperities of different areas and strengths, and show that the observed moment rates can be reproduced by appropriate values of the model parameters, as inferred from the available data. A good fit to the observed moment rates is obtained by a sequence of three dynamic modes of the system, including a phase of simultaneous slip of the asperities. The two moment rates are however characterized by different initial conditions, in terms of different initial shear stress distributions on the fault. Shear stresses on the asperities are calculated as functions of time during the event and show a similar evolution in the two cases, but with different final values. The model results show that the presence of simultaneous asperity motion can significantly increase the seismic moment of a large earthquake.

Using an analytical methodology taking into account heat flow density data, frictional heating, temperature variations due to the re-equilibrated conductive state after thrusting and geological constrains, we calculated surface heat flow, geotherms and isotherms along a balanced and restored regional geological cross-section. Our results highlight the impact of frictional heating produced by thrusts on the thermal structure of the study area, leading to a raising of the isotherms both in the inner Albanides to the E and in the Adriatic sector offshore. Minimum values of Qs in the surroundings of Tirana and the reconstructed 2D thermal structure suggest less favorable conditions for exploitation of geothermal energy, besides the direct use (Borehole Heat Exchanger-Geothermal Heat Pump systems). Nevertheless, the occurrence of the “Kruja geothermal zone”, partially overlapping this area and including hot spring manifestations, emphasize the structural control in driving hot fluids to the surface with respect to the regional thermal structure.

A geothermal model for the area of the Val d’Agri oil fields has been obtained by an analytical procedure. The model takes into account both the temperature variation due to the re-equilibrated conductive state after thrusting and frictional heating. Input parameters include heat flow density data and a series of geologically derivedconstraints - thrust depth, timing of thrusting, slip rate - obtained by the integration of surface and subsurface datasets. The results of this work, representing a first attempt to reconstruct a geothermal 3D model for the Val d’Agri zone of the Basilicata region, emphasize two main regional features: (i) the isotherms relative to temperatures lower than 350 °C are roughly parallel and sub-horizontal across thewhole study area, tending to deepen just along the NE-most edge of the investigated region; (ii) the isotherms relative to temperatures greater than 350 °C tend to deepen toward the center of the valley. Therefore, while the thermal structure at mid crustal depths appears to be perturbed and roughly mirroring the surface valley, the seismogenic upper crust of the study area is characterized by an unperturbed, roughly homogeneous and regular thermal structure.

We study the effects of friction heterogeneity on the dynamics of a seismogenic fault. To this aim, we consider a fault model containing two asperities with different static frictions and a rate-dependent dynamic friction. We consider the seismic events produced by the consecutive failure of the two asperities and study their properties as functions of the ratio between static frictions. In particular, we calculate the moment rate, the stress evolution during fault slip, the average stress drop, the partitioning of energy release, the seismic energy, the far-field waveforms and the spectrum of seismic waves. These quantities depend to various extent on the friction distribution on the fault. In particular, the stress distribution on the fault is always strongly heterogeneous at the beginning of the seismic event. Seismic energy and frictional heat decrease with increasing friction heterogeneity, while seismic efficiency is constant. We obtain an equation relating seismic efficiency to the parameters of the friction law, showing that the efficiency is maximum for smaller values of dynamic friction. The seismic spectrum depends on the friction distribution as to the positions and the values of the minima. However, under the model assumption that the slip durations are the same for both asperities, the corner frequency is independent of the friction distribution, but it depends on the friction law and on the coupling between asperities. The model provides a relation between the total radiated energy and the seismic moment that is consistent with the empirical relation between the two quantities. The fault model with one asperity is also considered as a particular case. The model is applied to the 1965 Rat Islands (Alaska) earthquake and shows the role of fault heterogeneity in controlling the spatial distribution of stress drop as well as the time dependence and the final amount of radiated energy.

Esiste un ampio dibattito sia sulla struttura profonda dell'Appennino meridionale, sia sulla geometria e cinematica dei sistemi di faglia che controllano la deformazione attiva e la sismicit�. Il prisma d�accrezione degli Appennini forma un elemento alloctono sovrapposto sugli strati carbonatici dell'avampaese, continui con quelli esposti nel promontorio Apulo a NE. La porzione tettonicamente sepolta della Piattaforma Apula � stata coinvolta nelle fasi finali del raccorciamento, generando ampie pieghe associate a faglie inverse. Tali pieghe ad elevata lunghezza d'onda formano le trappole per gli idrocarburi che caratterizzato gli importanti giacimenti petroliferi nell'Italia meridionale. Recenti studi geofisici hanno evidenziato che il basamento � coinvolto nella deformazione associata al raccorciamento crostale, mentre l'interpretazione di profili sismici ad alta risoluzione e il bilanciamento di sezioni geologiche favoriscono modelli di inversione tettonica con riattivazione delle preesistenti faglie normali (principalmente Permo-Triassiche) presenti nel basamento. La zona di m�lange interposta tra i carbonati della Piattaforma Apula sepolta e le unit� alloctone di superficie gioca un ruolo rilevante nella evoluzione tettonica dell�orogene. Tale zona di m�lange rappresenta, infatti, un efficiente livello di scollamento tra i livelli strutturali superficiali e quelli profondi. Mentre questi ultimi sono dominati dalle principali faglie radicate in profondit�, le unit� superficiali sono dissecate da numerose strutture fragili che si sono formate in diverse fasi durante l'evoluzione tettonica degli Appennini. D'altra parte, le principali strutture fragili presenti nei carbonati sepolti della Piattaforma Apula e nel sottostante basamento rappresentano importanti zone di faglia che hanno accumulato notevoli rigetti in tempi geologici, costituendo pertanto strutture sismogenetiche in grado di enucleare grandi terremoti in caso di loro riattivazione all�interno del campo di stress attuale. L�analisi e la modellazione numerica di tali strutture e degli associati stress e strain rates richiedono una definizione soddisfacente della struttura termica della crosta. In questo studio ci si propone di realizzare un modello termico lungo un transetto dall�alta Val d�Agri (Basilicata) a Bari (Puglia), basandoci sulle attuali conoscenze tettono-stratigrafiche della zona in esame. Gli effetti termici sono analizzati utilizzando la soluzione proposta da Dragoni et al. (1996), per la Piattaforma Apula, e da Molnar et al. (1983), per il bacino del fiume Agri. La geoterma per la zona della Valle del Sauro e quella per la zona della Val d�Agri sono state ottenute per mezzo di una procedura analitica che tiene conto delle strutture della Piattaforma Apula sepolta, che costituisce il reservoir degli idrocarburi del giacimento di Tempa Rossa. Viene evidenziato come il coinvolgimento del basamento nei processi di raccorciamento tettonico determina la necessit� di utilizzare diverse procedure analitiche per la limitrofa area dell�Alta Val d�Agri, nel cui sottosuolo un�importante faglia inversa si approfondisce verso SW con una rampa che coinvolge il basamento sottostante i carbonati che costituiscono il reservoir degli idrocarburi del giacimento di Monte Alpi. I risultati ottenuti in questo studio permettono in ogni caso di ottenere una soddisfacente descrizione della struttura termica dell�Appennino meridionale dall�avampaese apulo sino alla zona assiale della catena.

The Zagros thrust belt is a large orogenic zone located along the southwest region of Iran. To obtain a better knowledge of this important mountain chain, we elaborated the first 3-D model reproducing the thermal structure of its northwestern part, i.e., the Lurestan arc. This study is based on a 3-D structural model obtained using published geological sections and available information on the depth of the Moho discontinuity. The analytical calculation procedure took into account the temperature variation due to: (1) The re-equilibrated conductive state after thrusting, (2) frictional heating, (3) heat flow density data, and (4) a series of geologically derived constraints. Both geotherms and isotherms were obtained using this analytical methodology. The results pointed out the fundamental control exerted by the main basement fault of the region, i.e., the Main Frontal Thrust (MFT), in governing the thermal structure of the crust, the main parameter being represented by the amount of basement thickening produced by thrusting. This is manifested by more densely spaced isotherms moving from the southwestern foreland toward the inner parts of orogen, as well as in a lateral variation related with an along-strike change from a moderately dipping crustal ramp of the MFT to the NW to a gently dipping crustal ramp to the SE. The complex structural architecture, largely associated with late-stage (Pliocene) thick-skinned thrusting, results in a zone of relatively high geothermal gradient in the easternmost part of the study area. Our thermal model of a large crustal volume, besides providing new insights into the geodynamic processes affecting a major salient of the Zagros thrust belt, may have important implications for seismotectonic analysis in an area recently affected by a Mw = 7.3 earthquake, as well as for geothermal/hydrocarbon exploration in the highly perspective Lurestan region.

We study the dynamics of a fault containing two asperities having different strengths and subject to a constant strain rate. The fault is modeled by a discrete dynamical system with two degrees of freedom that are the slip deficits of the asperities. The radiation of elastic waves during the slipping modes is taken into account by introducing a term proportional to slip rate in the equations of motion. We give a complete analytical solution of the four dynamic modes of the system. Any seismic event can be expressed as a sequence of modes, for which the moment rate, the spectrum and the total seismic moment can be calculated. We consider the energy budget of the event and calculate the seismic efficiency. The presence of radiation may remarkably change the evolution of the system from a given state, since it moves the boundaries between the different subsets of the sticking region. In addition, the slip amplitude in a seismic event is smaller, while the slip duration is longer in the presence of radiation. The shape of the moment rate function depends on the seismic efficiency and the seismic moment decreases with increasing efficiency, at constant radiated energy. As an application of the model, we consider the 1964 Great Alaska earthquake and calculate the mode durations, the slip distribution, the moment rate function and the seismic moment of the earthquake, obtaining values that are consistent with observations.

The Val d'Agri area provides the opportunity to analyse active structures in a seismic region for which a large amount of subsurface data is available. This area, which was struck in 1857 by one of the most destructive earthquakes in Italy (MW = 7.03), represents a unique natural laboratory to gain new insights into geometry, modes and rates of faulting controlling crustal deformation in an actively extending orogen. In this study, a crustal geological section through the southern Apennines is discretized into a finite element model (FEM). We present a 2D elastoplastic FEM that reproduces stress perturbations and strain field around the Val d'Agri active fault system. The influence of fault strand activity on interseismic crustal deformation is tested by a series of computer models, whose predictions are compared with the horizontal velocity components of continuous GPS sites in the region and with stress directions and geological data. The best fit with available geological and geophysical constraints is obtained with a 300 km long, 29 km deep model formed by a multilayer including three components having different rheological characteristics and including several shallow, locked fault segments, which branch into a freely slipping major basement fault at depth. Finite element modelling provides new insights into the controversial and widely debated active tectonic setting of the study area, pointing out the fundamental role played by a structural reactivation process involving inherited, long-lived, mature fault systems at depth. Our FEM, reconciling apparently contrasting geological and geophysical constraints from the study area, points to maximum stress build up and strain accumulation at a depth of 15 ± 5 km. Such a depth range is suggested as the most likely one for the nucleation of large events such as the 1857 Val d'Agri earthquake.

A geothermal model for the area of the Basilicata oil fields has been obtained by an analytical procedure. The model takes into account both the temperature variation due to the re-equilibrated conductive state after thrusting and frictional heating. Input parameters include heat flow density data and a series of geologically derived constraints – thrust depth, timing of thrusting, slip rate – obtained by the integration of surface and subsurface datasets. For the top 5 km of the crust, the resulting geothermal curve shows a remarkably good fit with temperatures recorded from deep oil wells. The new geotherm provides a fundamental constraint for rheological and stress accumulation modelling in the seismically active study area. Furthermore, the analytical solution provided in this study may be used as a basis to calculate the relevant geotherm for further areas and/or tectonic settings.

A fault made of two coplanar asperities subject to a constant strain rate is considered. The fault is modelled as a discrete dynamical system made of two blocks coupled by a spring and pulled at constant velocity on a rough plane. Such a system exhibits a variety of slipping modes, including the slip of single asperities and the simultaneous slip of both asperities. The associated source function can be expressed by the seismic moment rate as a function of time. The moment rate depends on the state of the system preceding the earthquake, which can be described by a single variable expressing the difference between the stresses imposed to the two asperities. We present a systematic study of the moment rate as a function of this variable and show how the moment rate changes as a function of the model parameters. The observed source function of the 2010 Maule (Chile) earthquake, that was the result of the failure of two main asperities, is interpreted in the framework of the proposed model.

The recent earthquake sequences of 2012 (northern Italy) and 2013 (Marche offshore) provided new, fundamental constraints to the active tectonic setting of the outer northern Apennines. In contrast to the Po Plain area, where the 2012 northern Italy earthquakes confirmed active frontal thrusting, the new focal mechanisms obtained in this study for the 2013 Marche offshore earthquakes indicate that only minor thrust fault reactivation occurs in the Adriatic domain, even for a theoretically favourably oriented maximum horizontal compression. Recent seismicity in this domain appears to be mainly controlled by transcurrent crustal faults dissecting the Apennine thrust belt. The along-strike stress field variation from the Po Plain to the Adriatic area has been quantitatively investigated by applying the multiple inverse method (MIM) to the analysis of the entire seismicity recorded from January 1976 to August 2014, from the top 12 km of the crust (fault plane solutions from 127 earthquakes with MW ≥ 4), allowing us to obtain a comprehensive picture of the state of stress over the outer zone of the fold and thrust belt. The present-day stress field has been defined for 39 cells of 1.5° × 1.5° surface area and 12 km depth. The obtained stress field maps point out that, although the entire outer northern Apennines belt is characterized by a sub-horizontal maximum compressive axis (σ1), the minimum compression (σ3) is sub-vertical only in the Po Plain area, becoming sub-horizontal in the Adriatic sector, thus confirming that the latter region is dominated by an active tectonic regime of strike-slip type.

Studio della composizione litologica delle rocce circostanti i Laboratori sotterranei del Gran Sasso: valutazione di peso atomico, numero atomico e densita.Al fine di ottimizzare l’analisi dei risultati di alcuni esperimenti condotti nei laboratori sotterranei del Gran Sasso, si e reso necessario valutare l'interazione con i raggi cosmici dei materiali rocciosi per definire il rapporto tra il flusso di energia incidente e il flusso di energia dei raggi cosmici rilevata. L’analisi della stratigrafia e la definizione della composizione litologica sono fondamentali al fine di ottenere peso atomico (Z), numero atomico (A) e densita (ρ) del materiale che un raggio cosmico attraversa prima di essere intercettato dai rivelatori dei laboratori sotterranei. Allo scopo, sono state studiate otto sezioni geologiche attraverso i volumi rocciosi intorno ai laboratori, tracciate come i raggi di una ruota rispetto ad un azimut. In altre parole si considera un cerchio con i Laboratori Nazionali del Gran Sasso al centro: ogni sezione e un diametro del cerchio. Queste sezioni sono distribuite in tutta la gamma degli angoli di azimut (360°), con ogni sezione alla stessa distanza angolare (22° 30') dalle altre adiacenti. Le otto sezioni hanno consentito di determinare la litologia attraversata dai raggi cosmici in funzione degli angoli di zenit e di azimut, quindi di ottenere le caratteristiche fisiche delle rocce del Gran Sasso intorno ai laboratori. Le informazioni suddette hanno inoltre permesso di calcolare la media ponderata di peso atomico, numero atomico e densita per i raggi cosmici rilevati con un angolo zenitale di 70°, 80° e 90°. In tal modo si e potuto evidenziare come le variazioni della litologia, per elevati angoli di zenit, sono in grado di determinare notevoli variazioni del peso atomico, del numero atomico e dei valori di densita e di conseguenza variazioni significative nella valutazione del flusso di energia rilevato.

The availability of a large amount of surface geological data and subsurface information gathered by the oil industry, together with seismic and geodetic data, allowed us to define and analyse the active structures in the Val d'Agri area of the southern Apennines. Taking into account that the study of interseismic deformation can be significant to identify locked fault areas that can potentially slip, in this study we present 2D elastoplastic finite-element models to reproduce interseismic characteristics of the study area. This hosts the largest Europe's onshore oil field and is characterised by an active extensional tectonic regime, as inferred from earthquake focal mechanisms and fault slip data from late Quaternary structures. Based on high-quality seismic profiles tied with deep well logs, we constructed a detailed geological section across the study area. Outcropping units are dissected by numerous brittle structures that formed at various stages during the tectonic evolutionof the Apennines, while the deep ones are dominated by deeply rooted major faults. The rheological behaviour has been constrained by the reconstruction of the thermal structure of the fold and thrustbelt, using available information from the foreland Apulian Platform and from temperature data from a series of wells. Starting from the geological model, we reproduced interseismic deformation by means of finite-element numerical modelling, varying boundary conditions and unlocking different fault segments. Our numerical models provide new insights into the controversial and widely debated active tectonic setting of the Val d'Agri area, confirming the major role played by structural inheritance and reactivation processes. In fact, recent low-magnitude seismicity tends to illuminate fault segments consisting of pre-existing reverse faults reactivated as normal faults in the present-day stress field.These long-lived, mature fault systems occurring in the buried Apulian Platform carbonates (and underlying basement) represent major brittle structures that cumulated displacements of up to a few kilometres over geologic time. As a result of their reactivation within the late Quaternaryextensional stress field, these long-lived crustal structures are capable of nucleating also moderate- to large-magnitude earthquakes. The decoupling between deep and shallow structural levels, and the different inherited structures affecting them, explain the apparent contrast between the subdued surface expression of active fault systems and the known occurrence of large magnitude seismic events in the study area, thus reconciling apparently contrasting geological and geophysical constraints.

In this study, we elaborated a 2D model that reproduces the thermal structure of the central-northern Adriatic offshore and adjacent onshore area of the Italian peninsula. Based on the crustal structure along the trace of the CROP-03 deep section, the geotherms offshore Gabicce (northern Marche region) were obtained by an analytical procedure taking into account the role of thrusting within the sedimentary cover. Basement involvement at depth beneath the neighbouring Mondaino area to the SW, where a crustal thrust ramp dips towards the hinterland, required the use of a different analytical procedure. The results obtained in this study allowed us to define a satisfactory description of the thermal state of the northern Marche coastal area and adjacent Adriatic offshore. These results, integrated with those obtained by previous studies, confirm that the isotherms of 250°C and 400°C are placed in the stable Adriatic lithosphere at depths of about 11 km and 22 km, respectively. Furthermore, the 400°C isotherm is deeper in the onshore area, reaching a depth of about 30 km in the zone comprised between Gabicce and Mondaino, whereas the 250°C isotherm deepens towards the SW along the Adriatic Sea sector, to reach a maximum depth of 13 km in coastal area, rising again at a depth of 11 km in the innermost sector of the studied section.

A fault with two asperities is modelled as a system made of two blocks coupled by a spring and sliding on a plane under the same values of static and dynamic friction. An analytical solution is given for the simultaneous motion of the blocks and the corresponding orbits are plotted in the phase space. It is proven that, whichever the initial state is, the long-term behaviour of the system is one of an infinite number of limit cycles, characterized by a particular pattern of forces. The region where the system is located when the blocks are stationary can be divided into narrow stripes corresponding to different orbits of the points belonging to them. This implies that the system is sensitive to perturbations and has relevant implications for a fault, which is subject to stress transfers from earthquakes generated by neighbouring faults. In this case, the fault may experience a larger earthquake, with the simultaneous failure of the two asperities, which restores a stress distribution compatible with periodic behaviour. The seismic moment associated with simultaneous asperity failure is always greater than the maximum value that can be released in a limit cycle. For strongly coupled asperities, the moment can be several times larger.

By means of a 2D finite-element procedure, we tested how heterogeneities at the scale of seismogenic fault affect the displacement. We defined one or more slip distributions for two typical normal-faulting earthquakes in the Central Apennines, computed the displacement occurred within different structures including lateral heterogeneities, and compared the different displacement profiles to isolate the effect of the crustal structure. To understand at what magnitude the heterogeneities affect the observation significantly, we compared the predicted coseismic displacement with GPS and DInSAR data for the Colfiorito 1997 earthquake. We find that heterogeneities significantly affect the observable horizontal coseismic displacement for the larger magnitudes, whereas for smaller quakes, they affect horizontal displacement close to the fault trace only.

We develop a model of lava flow in a cylindrical tube with elliptical cross section. The lava is considered an isothermal, incompressible Newtonian fluid. We solve analytically the steady-state Navier–Stokes equation under a constant driving force, given by the component of gravity along the axis of the tube and obtain the velocity and stress field components in the fluid. The ratio between the flow rate of the elliptical tube and that of a circular tube, having the same cross sectional area, is found to be always less than 1 and to depend only on the value of eccentricity. The ratio decreases rapidly when the eccentricity becomes lower than about 0.5. The average flow velocity in a partially filled tube is calculated under the assumption of constant flow rate. In an elliptical tube, the shear traction is not uniform on the wall of the tube, but changes periodically with the position. It is maximum at the intersections with the minor axis and minimum at the intersections with the major axis, the ratio between the maximum and the minimum value being equal to the ratio between the lengths of the two axes. Assuming that the erosion rate of the wall of the tube is proportional to shear traction, we calculate the erosion of the wall as a function of time and find that its effect is such as to make the tube cross section closer to the circular shape.

The Central Apennines, Italy, are characterized by moderate seismic activity on normal faults, oriented in directions parallel to the Apenninic chain. The subject of this study is the Umbria-Marche Apennines, a segment approximately 200-km long, where three main seismic events occurred in the last three decades. The 1979 Norcia earthquake was a Mw = 5.8 event, taking place at the south end of the considered segment. The 1984 Gubbio earthquake was a Mw = 5.6 event which took place at the north end. The 1997-1998 Colfiorito sequence constituted 8 main shocks with magnitudes Mw between 5 and 6 and epicenters located between the Gubbio and the Norcia earthquake areas. A model made of an elastic half-space is considered, in which the seismic sources are represented by rectangular dislocations which have the appropriate values of source parameters, and in which the static stress field produced by each event is calculated. The analysis of the Coulomb stress change as a function of time shows that the coseismic stress transfer and fault interaction played an important role in the region during the past three decades: 7 earthquakes of the 9 considered took place where then stress change is positive. Such an interaction has been confirmed by the analysis of the aftershocks in the Colfiorito zone post September 26, 1997: about the 61% of the aftershocks considered took place where the stress change is positive. The comparison between the Coulomb stress change due to the coseismic stress transfer and the rate of change due to the tectonic stress allows us to quantify the time advance of the earthquakes. The pattern of coseismic Coulomb stress change shows positive values in two areas that can be regarded as historical seismic gaps.

The Altotiberina low-angle normal fault in central Italy has been a focus of many recent studies. Although the existence of this fault has long been known, its seismicity and relationship to other faults are still debated. We present a 2D elastoplastic finite-element model that reproduces the interseismic deformation of the Altotiberina Fault. The model predictions are compared to observed geodetic velocities, stress orientations and geological data. The influence of the Altotiberina Fault on interseismic evolution is tested by building several models with different boundary conditions. The best model is 180 km long, 40 km deep and contains two layers with different rheological parameters, two ramps, two faults and four freely slipping segments. The main factors contributing to the large-scale interseismic deformation include basal traction, rheology and the Altotiberina Fault itself, whereas the local, small-scale variations are due to two secondary high-angle faults.

Subduzione e collisione continentale in Appennino meridionale: vincoli da due sezioni crostali.Mediante l’integrazione di dati geologici di superficie e sottosuolo, sono state realizzate due sezioni crostali attraverso il sistema catena-avanfossa-avampaese dell’Appennino meridionale. Di tali sezioni, quella settentrionale e stata elaborata dall’interpretazione del profilo sismico a riflessione CROP 04, mentre quella meridionale attraversa i giacimenti petroliferi della Val d’Agri e di Tempa Rossa, in Basilicata. Le due sezioni mostrano la presenza, nel sottosuolo del Cilento, di unita di basamento continentale coinvolte nella strutturazione della catena appenninica. Queste evidenze suggeriscono che, dopo l’iniziale fase di subduzione oceanica, l’evoluzione tettonica dell’Appennino meridionale e stata caratterizzata da due eventi di subduzione continentale alternati a due stadi di collisione continentale.

In order to obtain new insights into the active tectonic setting of the Italian territory and surrounding regions, the Multiple Inverse Method (MIM) has been applied to the analysis of fault plane solutions from more than 700 earthquakes with M w ≥ 4. The active stress field in the top 40 km of the lithosphere has been defined for four 10 km-thick layers, each including 810 square cells of 1.5° side. The obtained stress field maps point out that most of the upper crustal seismicity of the Western and Central Alps is controlled by a strike-slip regime, which is dominant also in part of the Dinarides, Albanides and Hellenides and in a large sector encompassing eastern Sicily and the Malta area to the eastern Tunisia offshore. On the other hand, the well-known extensional belt occurring in the interior of the Apennines appears to extend well beyond the backbone of Italy, potentially reaching the outer foothills of the northern Marche region, while the adjacent Adria block (extending to the eastern Po Plain and the outer Dinarides) sticks out as a major area characterised by dominant thrust faulting in the upper crust. A similar regime characterises also a large sector of the western Tyrrhenian Sea, from NE Tunisia through western Sicily and the west coast of Sardinia, to the Provence coast. Besides lateral variations, our analysis also points out a significant vertical heterogeneity of the stress field, the deeper levels (20 to 40 km) investigated in this study being characterised by dominant horizontal maximum compression even in areas of upper crustal extension. The application of the MIM to a large seismological dataset, providing basic information for the compilation of active stress maps, contributes to a better understanding of active tectonic processes and may be used for improving seismotectonic zoning and reservoir management.

SUMMARY An effusive volcanic eruption results from a sequence of different processes, such as the pressurization of a magma chamber, the propagation of a dyke and the flow of lava at the Earth' surface. The aim of this paper is to establish relationships between the different quantities describing such processes. We consider a spherical magma chamber filled with a low-viscosity magma and included in a homogeneous and isotropic elastic half-space. We assume that, as a result of the inflow of fresh magma or a phase transition, the pressure in the chamber increases slowly during a finite time interval. Assuming that the pressure increase is linear in time, we calculate the stress field generated in the surrounding medium considering the chamber as a centre of dilation. We assume that a vertical tensile fracture originates at the top of the magma chamber after the rock strength is exceeded. The fracture is assumed to propagate quasi-statically along a vertical plane, driven by the stress distribution: both the cases of positive and negative buoyancy force are considered. The problem is solved in two dimensions by considering the fracture as a tensile Somigliana dislocation and expanding the associated stress release into Chebyshev polynomials. The fracture may reach the Earth's surface or not, depending on the depth and radius of the magma chamber, the rate and duration of pressure increase, the rock and magma densities and the rock strength. When the fracture reaches the Earth's surface, we assume that it becomes a vertical conduit. Magma pours out from the vent, driven by the pressure gradient in the conduit. Under the assumption of laminar flow of a Newtonian fluid, we evaluate the initial effusion rate as a function of the relevant model parameters. The flow rate is found to be a non-linear function of the density contrast. We also establish a relationship between the flow rate in the conduit and the initial thickness of the ensuing lava flow, in the case of effusion on a steep slope.

We present here the results from dynamical and thermal models that describe a channeled lava flow as it cools by radiation. In particular, the effects of power-law rheology and of the presence of bends in the flow are considered, as well as the formation of surface crust and lava tubes. On the basis of the thermal models, we analyze the assumptions implicit in the currently used formulae for evaluation of lava flow rates from satellite thermal imagery. Assuming a steady flow down an inclined rectangular channel, we solve numerically the equation of motion by the finite-volume method and a classical iterative solution. Our results show that the use of power-law rheology results in relevant differences in the average velocity and volume flow rate with respect to Newtonian rheology. Crust formation is strongly influenced by power-law rheology; in particular, the growth rate and the velocity profile inside the channel are strongly modified. In addition, channel curvature affects the flow dynamics and surface morphology. The size and shape of surface solid plates are controlled by competition between the shear stress and the crust yield strength: the degree of crust cover of the channel is studied as a function of the curvature. Simple formulae are currently used to relate the lava flow rate to the energy radiated by the lava flow as inferred from satellite thermal imagery. Such formulae are based on a specific model, and consequently, their validity is subject to the model assumptions. An analysis of these assumptions reveals that the current use of such formulae is not consistent with the model.

The study of surface deformation due to seismic activity is often made using dislocations with uniform slip and simple geometries. A better modeling of coseismic and postseismic surface displacements can be obtained by using dislocations with variable slip and nonregular shapes. This is consistent with the asperity model of fault surfaces, assuming a friction distribution on faults made of locked zones with much higher friction than surrounding zones. In this paper we consider the 1997–1998 Colfiorito seismic sequence. The coseismic surface displacements in the Colfiorito zone are used in order to infer the slip distribution on the fault surface at different stages of the sequence. The displacement field has been modeled varying the slip distribution on the fault, and comparing the deformation observed by SAR and GPS techniques with model results. The slip distribution is calculated by Monte Carlo simulations on a normal fault with the dip angle equal to 40°. A good approximation is obtained by using square asperity units of 1.5 times 1.5 km2. In the first stage, we employed a simplified model with uniform slip, in which each asperity unit is allowed to slip a constant amount or not to slip at all, and in the second stage, we evaluate the slip distribution in the dislocation area determined by the Monte Carlo inversion: in this case we allow unit cells to undergo different values of slip in order to refine the initial dislocation model. The results show that the 1997 seismic events of the sequence can be modeled by irregular dislocations, obtaining a good fit to the DInSAR and GPS observations. The model also confirms the results of previous studies by a different methodology, defining the distribution of asperities on the fault plane using the fault geometry, the geodetic data and the seismic moment of the 1997–1998 Colfiorito seismic sequence. Furthermore, the analysis of 1997 aftershocks in the seismogenic region shows a strong correlation between most events and the asperity distribution, which can be considered as an independent test of the validity of the model.

The 1964 Alaska earthquake was the second largest seismic events in the 20th century. The aim of this work is the use of surface deformation data to determine asperity and slip distributions on the fault plane of the Alaska earthquake: these distributions are calculated by a Monte Carlo method. To this aim, we decompose the fault plane in a large number of small square asperity units with a side of 25 km; this allows us to obtain plane surfaces with an irregular shape. In the first stage, each asperity unit is allowed to slip a constant amount or not to slip at all, providing the geometry of the dislocation surface that best reproduces the observed displacements. To this purpose, a large number of slip distributions have been tried by the use of the Monte Carlo method. The slip amplitude is the same for all the asperities and is equal to the average fault slip inferred from the seismic moment. In the second stage, we evaluate the slip distribution in the dislocation area determined by the Monte Carlo inversion: in this case, we allow unit cells to undergo different values of slip in order to refine the initial dislocation model. The results confirm the previous finding that the slip distribution of the great Alaska earthquake was essentially made of two dislocation areas with a higher slip, the Prince William Sound and the Kodiak asperities. Analysis of the post-1964 seismicity in the rupture region shows a strong correlation between the larger earthquakes (Mw≥6) and the distribution of locked asperities following the 1964 event, which can be considered as an independent test of the validity of the model. We do not find slip values higher than 25 m for any of the patches, and we determine two separate high-slip zones: one correspondent to the Prince William Sound asperity, and one (∼18 m slip) to the Kodiak asperity. The slip distribution connected with the 1964 shock appears to be consistent with the following seismicity in the region.

We show the results of application of Differential SAR Interferometry to the MW 7.4, August 17, 1999, Izmit earthquake, Western Turkey. The differential interferogram is obtained using an interferometric ERS2 ascending pair with a time interval of 35 days (August 13th - September 17th). The fringe pattern clearly defines the coseismic displacement field extended in an area of about 100 km N-S and 120 km E-W. The analysis of the interferogram shows the right-lateral strike-slip movement on the activated section of the North Anatolian fault system. The maximum SAR-detected displacement ranges between 117.6 cm and 134.4 cm in the proximity of Gölcük. We invert SAR data for uniform dislocation on a single fault plane using a Montecarlo procedure, with the aim of testing a large set of a priori possible asperity distributions on the fault. We then use a forward modeling approach to evaluate the slip variability for the dislocation using additional constraints as surface offsets and seismicity distribution: in this case we allow unit cells to undergo different values of slip in order to refine the initial dislocation model. Misfits between SAR data and modeled slant range displacements are generally low for all our models (~ 12 cm). Our results indicate that slip is concentrated in the central-western part of the fault, in the upper 10-15 km, tapering to the fault tips. For the Izmit case, we note that a well constrained fault model can be obtained only integrating DInSAR data with additional observations. This is mainly due to an undersampling of the displacement field by DInSAR, caused by decorrelation and lack of image data.

A power-law, viscoelastic constitutive equation for lithospheric rocks, is considered. The equation is a nonlinear generalization of the Maxwell constitutive equation, in which the viscous deformation depends on the n-th power of deviatoric stress, and describes a medium which is elastic with respect to normal stress, but relaxes deviatoric stress. Power-law exponents equal to 2 and 3, which are most often found in laboratory experiments, are considered. The equation is solved by a perturbative method for a viscoelastic layer subjected to a constant, extensional or compressional, strain rate and yields stress as a function of time, temperature and rock composition. The solution is applied to an ideal extensional boundary zone and shows that the base of the crustal seismogenic layer may be deeper than predicted by a linear rheology.

A model is proposed describing the mechanical evolution of a shear zone along compressional and extensional plate boundaries, subject to constant strain rate. The shear zones are assumed as viscoelastic with Maxwell rheology and with elastic and rheological parameters depending on temperature and petrology. Stress and strain are computed as functions of time and depth. For both kinds of boundaries the model reproduces the existence of a shallow seismogenic zone, characterized by a stress concentration. The thickness of the seismogenic layer is evaluated considering the variations of shear stress and frictional strength on faults embedded in the shear zone. Assuming that a fault dislocation takes place, the brittle-ductile transition is assumed to occur at the depth at which the time derivative of total shear stress changes from positive to negative values. The effects of different strain rates and geothermal gradients on the depth of the brittle-ductile transition are studied. The model predictions are consistent with values inferred from seismicity data of different boundary zones. © 1993 Birkhäuser Verlag.

In the Umbria-Marche region, space and time variations concerning the b value were studied by instrumental seismicity from January 1987 to May 1999, according to the Bender method. Data were divided into two partially independent data sets. The first set, (January 1987 - December 1996), does not include the Colfiorito seismic sequence that occurred in the autumn of 1997. The second data set includes all events from January 1987 to May 1999. Using square cell dimensions of 80, 40 and 20 km, the examined area was divided respectively into three grids. The b value was estimated for each cell using the first data set, thus allowing us to reveal b value space variations and determine the resolution. To evaluate the stability of our result we estimated the b value on the basis of historical seismicity within the region. Several synthetic tests were also performed to estimate the stability of the Bender method and to verify its consistency with respect to other methods commonly used. Finally we estimated the b values using the second data set to prove the time variations. Results from the area examined show that the lowest possible spatial resolution of the b value is about 40 km and that there is a correlation between the b value pattern and the main active tectonic structures of the area. The most important time variations occur within the Colfiorito area, in which the b value drops significantly within the second data set. Results suggest two different ways of strain release: the first one produces continuous seismicity that spreads all over the examined area, while the second, which concerns stronger earthquakes, is localized.

In recent years, the recovery of some historical documents has permitted us to operate the seismographs used by Alessandro Serpieri (1823-1885) at the Observatory of the University of Urbino in the XIX century. The space-time concept of sensor network was already clear to Serpieri and he tried to apply this concept to the analysis of seismic phenomena in Italy. This paper reviews the history of the Urbino Observatory from Serpieri's age to present times. The historical region of Montefeltro, where Urbino is the main town, is affected by seismicity with typical magnitudes between 2.2 and 2.5. Most of these events occur in the upper 15 km of the crust. The seismicity of the neighbouring regions is mainly concentrated in three zones: Northern Rimini, the Apennine belt and the Sibillini Mountain area. From the overall data, it is possible to infer that there is a basin characterised by microseismicity and essentially dominated by a compressive tectonic regime in the Montefeltro area. Furthermore seismological data seem to show a "quiet" segment, separating the extension area from the compression area, characterised by a low concentration of seismic events.