from a deformed peri tethyan carbonate platform to a fold and thrust belt an example from the central apennines italy abstract in the central apennines of italy the relationships between the foreland deformation of a peri tethyan carbonate platform lazio abruzzi domain and the subsequent contractional pattern have been clearly documented by means of stratigraphic and structural evidence stratigraphic and structural data point out the occurrence of pre thrusting normal fault systems and allow us to define their relationships with contractional structures miocene normal faults are particularly well documented by thickness and facies variation of foredeep deposits and by structural evidence these faults controlled sedimentation during tortonian early messinian times foredeep stage and produced most of the accommodation space for clastic deposits in their hanging walls on the contrary the subsequent positive inversion appears to be quite limited and generally the hanging wall sequences are not uplifted above the regional clear evidence that normal faults formed first and were later cut and or rotated during thrusting is supported by analyses carried out along the main fault surfaces the restoration of a balanced geological section across the study area based on the inference of an extended foreland affected by later contraction provided a total small shortening value this is lower than the previous estimated by several authors for the same foreland fold and thrust belt

positive inversion tectonics in foreland fold and thrust belts a reappraisal of the umbria marche northern apennines central italy by integrating geological and geophysical data abstract unraveling the tectonic style in the outer zones of fold and thrust belts is generally puzzling because the basement cover relationships are often hidden in the subsurface as in the outer northern apennines of italy this study aims to reconstruct the deep setting of the northern apennine foreland thrust belt by integrating surface structural geological and subsurface seismic reflection profile and well data corroborated by a gravity magnetic modeling a remarkable mountain ridge the umbria marche apennine ridge umar which corresponds to a prominent area of structural and topographic elevation characterizes the morphology of the northern apennines this mountain ridge is constituted by meso cenozoic carbonates involved in neogene compressive structures and is surrounded by wide exposures of foredeep deposits the basement cover relationships are poorly constrained and both thin and thick skinned tectonic styles have been applied the interpretation of subsurface data allowed recognizing a thick pre jurassic sedimentary sequence filling a late paleozoic triassic symmetric fault bounded extensional basin lying directly below the umar this deep rooted basin underwent positive inversion during the neogene compression and thrust fold development the reconstructed thick skinned inversion tectonic model is consistent with both the modest amount of shortening and the remarkable structural elevation of the umar the outcomes of this study reveal that prominent mountain ridges occurring in foreland thrust belts are most likely related to the deep rooted basement involved positive inversion of pre existing extensional basins

seismicity triggered by fluid injection induced aseismic slip anthropogenic fluid injections are known to induce earthquakes the mechanisms involved are poorly understood and our ability to assess the seismic hazard associated with geothermal energy or unconventional hydrocarbon production remains limited we directly measure fault slip and seismicity induced by fluid injection into a natural fault we observe highly dilatant and slow 4 micrometers per second m s aseismic slip associated with a 20 fold increase of permeability which transitions to faster slip 10 m s associated with reduced dilatancy and micro earthquakes most aseismic slip occurs within the fluid pressurized zone and obeys a rate strengthening friction law 0 67 0 045ln v v with v 0 1 m s fluid injection primarily triggers aseismic slip in this experiment with micro earthquakes being an indirect effect mediated by aseismic creep

new insights into crustal structure cenozoic magmatism co2 degassing and seismogenesis in the southern apennines and irpinia region from local earthquake tomography we present high resolution vp and vp vs models of the southern apennines italy computed using local earthquakes recorded from 2006 to 2011 with a graded inversion scheme that progressively resolves the crustal structure from the large scale of the apennines belt to the local scale of the normal fault system high vp bodies defined in the upper crust and midcrust under the external apennines are interpreted as extensive mafic intrusions revealing anorogenic magmatism episodes that broadened on the adriatic domain during paleogene under the mountain belt a low vp region annular to the neapolitan volcanic district indicates the existence of a thermal fluid anomaly in the midcrust coinciding with a shallow moho and diffuse degassing of deeply derived co2 in the belt axial zone low vp vs gas pressurized rock volumes under the apulian carbonates correlate to high heat flow strong co2 dominated gas emissions of mantle origin and shallow carbonate reservoirs with pressurized co2 gas caps we hypothesize that the pressurized fluid volumes located at the base of the active fault system influence the rupture process of large normal faulting earthquakes like the 1980 mw6 9 irpinia event and that major asperities are confined within the high vp apulian carbonates this study confirms once more that preexisting structures of the pliocene apulian belt controlled the rupture propagation during the irpinia earthquake the main shock broke a 30 km long ne dipping seismogenic structure whereas delayed ruptures both the 20 s and the 40 s subevents developed on antithetic faults reactivating thrust faults located at the eastern edge of the apulian belt

deep structure and tectonics of the northern central apennines as seen by regional scale tomography and 3 d located earthquakes 1 in this study we present new high resolution regional scale vp and vp vs models of the northern central apennines along with accurate 3 d locations of a large set of local earthquakes the main velocity anomalies are consistent with the surface geology in the shallow layers and present evidence for fluids stored within the basement at greater depths beneath the extensional belt the adria and tyrrhenian mantle are defined by positive velocity anomalies below 30 km depth while a low vp high vp vs region in between indicates the existence of a hydrated wedge the results yield new constraints on active processes in the apennines and more generally envisage the evolution of a postcollisional belt velocity anomalies and earthquakes are consistent with a complex system of delamination and sinking of the adria continental lithosphere with the peeling of the crust identified by intermediate depth seismicity change of seismicity and structural patterns along the belt indicates that this tectonic process is diachronous and that fluids released by sunken lithosphere are stored within the crust conditioning the occurrence of seismicity and the onset of extension

pore pressure migration along a normal fault system resolved by time repeated seismic tomography in this study we outline the space and time variations of body wave velocities during one of the best documented series of normal faulting earthquakes the 1997 umbria marche sequence in central italy we show the first ever observations of rock fracturing and fluid overpressure propagation along a fault system by using space time resolved variations of vp vs anomalies four dimensional variations that accompany earthquake migration and precede large aftershocks the vp vs increase observed before the mid october earthquakes was related to a pore pressure increase on fluid filled cracks in the volume around the fault we also document that such variations are measurable only by using s and p wave arrival times

tectonic subsidence modelling and gondwana source rock hydrocarbon potential northwest bangladesh modelling of kuchma singra and hazipur wells abstract the northwestern part of bangladesh is in terms of hydrocarbon exploration still under explored this paper presents the basin development from a structural point of view and includes the results of thermal and maturity modelling using numerical tools of basin modelling one regional seismic section and three exploration wells have been investigated to unravel a conceptual model for the subsidence and thermal history of the region according to the findings it is very likely that up to 2900 m of triassic jurassic and partly permian sediments have been eroded prior to the break up of gondwana during continental break up a peak heat flow is considered this was necessary for calibrating maturity profiles using vitrinite reflectance vr derived from modelled wells a significant gas generation phase during lower jurassic is predicted at modelled well locations although renewed subsidence occurred during tertiary to present day a second phase of gas generation has not occurred as past maximum temperatures were not exceeded according to the interpreted regional seismic sections in the region the area southeast of the hinge zone can be regarded as the main kitchen area for gas generation from the gondwana source rock the petroleum system in the northwestern part of bangladesh remains high risk due to uncertainties in source rock distribution and generation

carbon dioxide earth degassing and seismogenesis in central and southern italy 1 we present the first regional map of co2 earth degassing from a large area most of central and south italy derived from the carbon of deep provenance dissolved in the main springs of the region the investigation shows that a globally significant amount of deeply derived co2 10 of the estimated global co2 emitted from subaerial volcanoes is released by two large areas located in western italy the anomalous flux of co2 suddenly disappears in the apennine in correspondence to a narrow band where most of seismicity concentrates here at depth the gas accumulates in crustal traps generating co2 overpressurized reservoirs which induce seismicity

seismic interpretation of the laga basin constraints on the structural setting and kinematics of the central apennines abstract the messinian laga basin is the largest foreland basin within the central apennines fold and thrust belt italy this area actively investigated in the 1980s and 1990s for hydrocarbon resources is considered a valuable analogue for clastic reservoirs developed in confined structural settings furthermore it represents a key area for understanding the evolution of the apennines as it links the internal structurally uplifted early miocene fold and thrust belt of the western central apennines with the more external and recent belt to the east despite several papers published on this area the only reconstruction of the substratum structure is an internal and classified industry report during the present study we had access to a seismic database comprising 200 km of seismic profiles that were collected between 1983 and 1990 these data allowed us to reconstruct the structural setting of the laga basin substratum define the lateral continuity of the main compressional structures within the basin construct a balanced cross section and define the shortening values

tectonic evolution of a low angle extensional fault system from restored cross sections in the northern apennines italy 1 broad geological and geophysical documentation is available on regional extensional systems driven by low angle normal faults however little information exists about the three dimensional geometry and the offset distribution of such extensional structures we present a new set of balanced geological sections across the extensional fault system driven by the altotiberina low angle normal fault in the northern apennines of italy we document this extensional system throughout a large set of surface field surveys and geological maps and subsurface data seismic reflection profiles and boreholes the subsurface data allowed us to define the fault deep geometry and to obtain its structural contours the fault geometry is characterized by both along dip and along strike irregularities in cross section the fault displays a staircase trajectory with the shallowest part being dome shaped and flattened to horizontal this bending could be due to the footwall uplift triggered by a footwall uploading greater than about 115 mpa the sequential restoration of five geological cross sections yields a maximum extension of about 10 km accumulated over approximately 3 ma the resulting long term slip rate is about 3 mm yr which is of the same order as the present day extensional rate measured by gps 2 5 3 0 mm yr suggesting an almost steady state extension over the last 3 ma the distribution of the extension values along the fault strike is bell shaped as expected for a continuous surface

overpressure detection from compressional and shear wave data by analyzing experimental data we show that in many room dry rocks the poisson s ratio pr decreases with decreasing differential pressure confining minus pore pressure this means that in gas saturated rocks pr decreases with increasing pore pressure we confirm the generality of the observed effect by theoretically reproducing it via effective medium modeling this effect can be used as a new tool for overpressure detection from surface seismic cross well sonic logs and measurements ahead of the drill bit

monitoring and numerical modelling of riverbank erosion processes a case study along the cecina river central italy riverbank retreat along a bend of the cecina river tuscany central italy was monitored across a near annual cycle autumn 2003 to summer 2004 with the aim of better understanding the factors influencing bank changes and processes at a seasonal scale seven flow events occurred during the period of investigation with the largest having an estimated return period of about 1 5 years bank simulations were performed by linking hydrodynamic fluvial erosion groundwater flow and bank stability models for the seven flow events which are representative of the typical range of hydrographs that normally occur during an annual cycle the simulations allowed identification of i the time of onset and cessation of mass failure and fluvial erosion episodes ii the contributions to total bank retreat made by specific fluvial erosion and mass wasting processes and iii the causes of retreat the results show that the occurrence of bank erosion processes fluvial erosion slide failure cantilever failure and their relative dominance differ significantly for each event depending on seasonal hydrological conditions and initial bank geometry due to the specific planimetric configuration of the study bend which steers the core of high velocity fluid away from the bank at higher flow discharges fluvial erosion tends to occur during particular phases of the hydrograph as a result fluvial erosion is ineffective at higher peak discharges and depends more on the duration of more moderate discharges slide failures appear to be closely related to the magnitude of peak river stages typically occurring in close proximity to the peak phase preferentially during the falling limb but in some cases even before the peak while cantilever failures more typically occur in the late phase of the flow hydrograph when they may be induced by the cumulative effects of any fluvial erosion copyright 2008 john wiley sons ltd

seismotectonic zoning in east central italy deduced from an analysis of the neogene to present deformations and related stress fields this paper concerns the space time evolution of the late miocene to present contractional and extensional deformations within east central italy with an analysis of the pattern and orientation of the related stress field an insight into the cover basement relations and a discussion of the seismotectonic implications the pattern and orientation of the deformation and stress fields have remained unchanged since late miocene time and have been always characterized by the coexistence and parallelism in contiguous areas in a given time of shortening to the east and elongation to the west with time during a multistage deformation history both the contraction and the extension fields have moved eastward basement involved tectonics with a west dipping multiple detachment system would have allowed the progressive eastward shift of crustal slices corresponding at the surface to well defined tectonic domains with consequent crustal thinning in the tuscan zone and crustal thickening beneath the apennine mountain chain by comparing macroseismic epicenters hypocenters and focal mechanisms with crustal structure and independently known active faults it appears evident that the pattern frequency and distribution of the crustal seismicity are tectonically controlled and that a contraction extension pair is active also at the present time in fact along the adriatic coastline contractional deformation prevails with involvement of pleistocene layers whereas beneath the apennine range extensional deformation prevails both t axes in the inner domain and p axes in the outer domain are oriented southwest northeast or west south west east northeast and this coaxiality reflects the situation depicted by the geologic stress field on this basis we have produced a seismotectonic zoning of east central italy with three distinct domains intramountain seismic zone isz foothills seismic zone fsz and coastal seismic zone csz a plausible explanation for the genesis of the active seismic deformations of east central italy is that the locally intense extensional upper crustal seismicity of the intramountain seismic zone is confined to the hanging wall of a major west dipping active extensional discontinuity whereas the less frequent contractional seismic activity of the coastal seismic zone is within the hanging wall of an outer major active west dipping contractional discontinuity an area of overlap between these two zones is represented by the foothills seismic zone where superposed epicentral patterns from different surfaces of weakness at different depths are the predictable result of the asymmetry of the deformation

tomography of the source area of the 1995 kobe earthquake evidence for fluids at the hypocenter seismic tomography revealed a low seismic velocity 5 and high poisson s ratio 6 anomaly covering about 300 square kilometers at the hypocenter of the 17 january 1995 magnitude 7 2 kobe earthquake in japan this anomaly may be due to an overpressurized fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake

fault lubrication and earthquake propagation in thermally unstable rocks experiments performed on dolomite or mg calcite gouges at seismic slip rates v 1 m s and displacements d 1 m show that the frictional coefficient decays exponentially from peak values m p 0 8 in the byerlee9s range to extremely low steady state values ss 0 1 attained over a weakening distance d w microstructural observations show that discontinuous patches of nanoparticles of dolomite and its decomposition products periclase and lime or portlandite were produced in the slip zone during the transient stage d w these observations integrated with co 2 emissions data recorded during the experiments suggest that particle interaction in the slip zone produces flash temperatures that are large enough to activate chemical and physical processes e g decarbonation reactions t 550 c during steady state d d w shear strength is very low and not dependent upon normal stresses suggesting that pressurized fluids co 2 may have been temporarily trapped within the slip zone at this stage a continuous layer of nanoparticles is developed in the slip zone for d d w a slight but abrupt increase in shear strength is observed and interpreted as due to fluids escaping the slip zone at this stage dynamic weakening appears to be controlled by velocity dependent properties of nanoparticles developed in the slip zone experimentally derived seismic source parameter w b i e breakdown work the energy that controls the dynamics of a propagating fracture 1 matches w b values obtained from seismological data of the a d 1997 m6 colfiorito italy earthquakes which nucleated in the same type of rocks tested in this study and 2 suggests similar earthquake scaling relationships as inferred from existing seismological data sets we conclude that dynamic weakening of experimental faults is controlled by multiple slip weakening mechanisms which are activated or inhibited by physicochemical reactions in the slip zone

on the increase of background seismicity rate during the 1997 1998 umbria marche central italy sequence apparent variation or fluid driven triggering abstract we investigate the temporal evolution of background seismicity rate in the umbria marche sector of the northern apennines that was struck by the 1997 1998 colfiorito seismic sequence specifically we apply the epidemic type aftershock sequences etas model to separate the background seismicity rate from the coseismic triggered rate of earthquake production analyzed data are extracted from the catalogo della sismicita italiana csi1 1 catalog of italian seismicity 1981 2002 which contains for the study area 12 163 events with m l 1 5 the capability of the etas model to match the observed seismicity rate is tested by analyzing the model residuals and by applying two nonparametric statistical tests the runs and the kolmogorov smirnov tests to verify the fit of residuals to poisson hypothesis we first apply the etas model to the seismicity that occurred in the study area during the whole period covered by the csi1 1 catalog our results show that the etas model does not explain the temporal evolution of seismicity in a time interval defined by change points identified from time evolution of residuals and encompassing the colfiorito seismic sequence we therefore restrict our analysis to this period and analyze only those events belonging to the 1997 1998 seismic sequence we again obtain the inadequacy of a stationary etas model with constant background rate to reproduce the temporal pattern of observed seismicity we verify that the failure of the etas model to fit the observed data is caused by the increase of the background seismicity rate associated with the repeated colfiorito mainshocks we interpret the inferred increase of background rate as a consequence of the perturbation to the coseismic stress field caused by fluid flow and or pore pressure relaxation in particular we show that the transient perturbation caused by poroelastic relaxation can explain the temporal increase of background rate that therefore represents a fluid signal in the seismicity pattern

vp and vp vs images in the mw 6 0 colfiorito fault region central italy a contribution to the understanding of seismotectonic and seismogenic processes 1 in 1997 the umbria marche apennines central italy was struck by a series of moderate magnitude normal faulting earthquakes accompanied by a prolonged sequence of aftershocks seismological analysis revealed a 40 km long nw trending structure composed by several low angle normal fault segments in this paper we present the three dimensional 3 d vp and vp vs structure of the fault zone determined by the inversion of p and s wave arrival times from 1982 aftershocks the high resolution tomographic images reveal strong heterogeneity along and across the fault zone and allow us along with the 3 d location of earthquakes to define the fault geometry at depth and to improve our understanding on the seismotectonics of this part of the northern apennines thrust and fold belt the relocated aftershocks suggest that the main ruptures occurred on planes slightly steeper than previously hypothesized and at depths shallower than those evidenced by 1 d locations we find that the preexisting structure which developed during the neogene compressional tectonics plays an important role in the earthquake generation and rupture evolution of the normal faulting events we propose that the main shocks whose hypocenters are all located at 6 km depth originated along a shallow decollement of the meso cenozoic cover thrust over the metamorphic basement geometrical discontinuities and lateral steps along the inherited structures control the lateral fault extent and determine fault segmentation this study offers a good example of how lithological heterogeneities and the complexity of the upper crust structure strongly affect the faulting process

normal faults and thrusts reactivated by deep fluids the 6 april 2009 mw 6 3 l aquila earthquake central italy 1 on 6 april 2009 a mw 6 3 earthquake occurred in the central apennines italy damaging the city of l aquila and the surrounding country we relocate the october 2008 to 6 april 2009 foreshocks and about 2000 aftershocks occurred between 6 and 30 april 2009 by applying a double difference technique and determine the stress field from focal mechanisms the events concentrate in the upper 15 km of the crust three main nw se to nnw sse striking 30 45 and 80 90 dipping faults were activated during the seismic sequence among these a normal fault and a thrust were reactivated with dip slip movements in response to ne sw extension the structural maturity of the seismogenic fault system is lower than that displayed by other systems in southern apennines because of the lower strain rate of the central sector of the chain with respect to the southern one vp vs increases progressively from october 2008 to the 6 april 2009 main shock occurrence along a nw se strike because of an increment in pore fluid pressure along the fault planes pore pressure diffusion controls the space time evolution of aftershocks a hydraulic diffusivity of 80 m2 s 1 and a seismogenic permeability of about 10 12 m2 suggest the involvement of gas rich co2 fluids within a highly fractured medium suprahydrostatic high fluid pressure about 200 mpa at 10 km of depth within overpressurized traps bounded by preexisting structural and or lithological discontinuities at the lower upper crust boundary are required to activate the april 2009 sequence traps are the storage zone of co2 rich fluids uprising from the underlying about 20 km deep metasomatized mantle wedge these traps easily occur in extensional regimes like in the axial sector of apennines but are difficult to form in strike slip regimes where subvertical faults may cross the entire crust in the apennines fluids may activate faults responsible for earthquakes up to mw 5 6 deep fluids more than tectonic stress may control the seismotectogenesis of accretionary wedges

deep structural heterogeneities and the tectonic evolution of the abruzzi region central apennines italy revealed by microseismicity seismic tomography and teleseismic receiver functions abstract the crustal structure of central apennines italy is still poorly defined leaving uncertainties on the tectonic style thin or thick skinned responsible for the development of the thrust and fold belt the today active extension which replaced compression since early quaternary is presumably influenced by the pre existing structure that yields location and segmentation of the fault system to focus on such issues we computed p and s wave velocity models of the crust by using the independent methodologies of local earthquakes tomography and teleseismic receiver function we document strong lateral and vertical heterogeneities that define shallow imbricate sheets of the mesozoic cover that overlay exceptionally high vp and high vs bodies these bodies can be interpreted as either dolomitic or partially hydrated mafic rocks the two alternative interpretations respectively imply an ultra thick deposition of dolomitic rocks in the hanging wall of triassic normal fault or a deep exhumation of the pre mesozoic basement during the early mesozoic sin rift tectonic in both cases these bodies influenced the evolution of the thrust and fold belt very remarkably active normal faults like those ruptured during the still ongoing 2009 l aquila sequence concentrate at the border of these bodies suggesting that they have an active role in the segmentation of the normal fault system the rheological behavior of such high vp high vs bodies weak or strong is still uncertain but of utmost importance to understand the risk of future normal faulting earthquakes