detachment folding fold amplification and diapirism in thrust wedge experiments 1 the relations between detachment folding fold amplification and salt diapirism in contractional settings have been investigated by means of scaled analogue models the viscosity of the silicone layer simulating salt in nature and the shortening rates were combined in order to reproduce weak type 1 models and strong type 2 models decollements deformation patterns in the roof sequence exhibited two contrasting styles 1 outward propagation of detachment folding along the decollement ofp mode and 2 passive roof duplex prd mode in type 2 models detachment folding propagated away from the most external thrust in the floor sequence while in type 1 models long lived detachment folds almost invariably localized amplified above a floor thrust tip as a result of strain localization a silicone wall intruded occasionally into the crestal graben of detachment folds in type 1 and ofp models best fitting of transition models data points indicates nonlinear relations with regression curves close to the equilateral hyperbola equation for both ofp prd and amplified detachment folds box folds transitions a quantitative comparison of model results with nature has been attempted by plotting salt based fold and thrust belts data points on the scaled transition curves obtained from the modeling such a comparison relates shear stress products and ratios to the conditions favoring the amplification of detachment folds and the potential emplacement of ductile diapirs in their core by reducing the roof sequence strength pore fluid pressure b is inferred to shift the equilibrium of fold and thrust belts toward the field of ofp and diapirism

on the growth of normal faults and the existence of flats and ramps along the el asnam active fold and thrust system the combination of detailed topographic leveling on the southwest segment of the el asnam thrust fault with existing seismic and geologic data implies that the geometry of this fault involves shallow dipping flats and steep ramps the fault appears to be growing along strike toward the southwest end where the main shock initiated in 1980 from a depth of about 10 km the main thrust appears to ramp to the basement cenozoic cover interface on a plane striking n40 e and dipping 50 55 to the northwest along the southwest segment where folding has not yet developed the thrust continues steeply through the cenozoic cover to the near surface where it flattens causing normal faulting along the central and northeast segments which display a more evolved fold structure the deep thrust probably flattens at a depth of 5 6 km into a decollement along the cenozoic jurassic interface before ramping to the surface the sara el marouf and kef el mes anticlines have thus formed as fault propagation folds normal faults at beni rached probably branch with the thrust to maintain kinematic compatibility between the deep ramp and decollement the greater separation 7 km between the normal faults at beni rached and the thrust where it crosses oued cheliff than along the southwest segment 1 km reflects the greater depth of the ramp to flat bend we infer that the september 9 1954 earthquake activated only the central deep segment of the main thrust together with the beni rached normal faults while that of october 10 1980 activated the whole system of flat decollements ramp thrusts and compatibility normal faults further complexities of the faulting in map view are related to changes of strike of the thrust in particular north of oued cheliff

foredeeps versus subduction zones the geologic characteristics of foredeeps and accretionary wedges suggest that these features are distinguishable on the basis of the direction of the associated subduction east north east dipping subduction related accretionary wedges show high relief and broad outcrops of metamorphic rocks they are associated with shallow foredeeps with low subsidence rates in contrast west dipping subduction related accretionary wedges show low relief and involve mainly sedimentary cover the related foredeeps are deep and have high subsidence rates this differentiation is useful both for oceanic and continental subductions e g eastern vs western pacific subductions or east dipping alpine vs west dipping apenninec subductions in a cross section of the alps the ratio of the area of the orogen to the area of the foredeeps is at least 2 1 whereas this ratio is 0 22 1 for the apennines these ratios explain why foredeeps related to east or northeast dipping subduction are quickly filled and are bypassed by clastic rocks whereas foredeeps related to west dipping subduction maintain a deep water environment longer these differences support the presence of an eastward asthenospheric counterflow relative to the westward drift of the lithosphere detected in the hot spot reference frame even in the mediterranean where no hot spots are present in this interpretation the apennines foredeep was caused by the eastward push of the mantle acting on the subducted slab whereas the foredeeps in the alps were caused by the load of the thrust sheets and the downward component of movement of the upper adriatic plate these forces contrast with the upward component of the eastward mantle flow

on tangential longitudinal strain folding abstract intrinsic two dimensional analysis of the geometry of fold profiles originated by tangential longitudinal strain has allowed us to examine several features of this folding mechanism the strain distribution in the folded layers indicates that the direction of the strain ellipse axes has a deviation with respect to the directions normal and tangential to the boundaries of the folded layer which mainly depends on the curvature changes the geometry of the folded layers involves layer thickening in the hinge zone single hinge folds of class 1c and double hinge folds composed of classes 1a and 1c when migration of the neutral line is allowed layer thinning occurs in the hinge zone single hinge folds of class 1a and double hinge folds composed of classes 1c and 1a nevertheless in most cases the folds are close to parallel folds the bulk shortening due to tangential longitudinal strain mainly depends on the amplitude of the folds and scarcely depends on the shape of the folded surfaces when the original thickness of a layer is large in relation to the radius of curvature two gentle minor antiforms separated by a synform appear in the inner arc close to the hinge zone of the major antiform this minor folding involves local thickening in the hinge zone which is observed in some natural folds as a protuberance in the inner arc of the hinge zone

separating natural and anthropogenic vertical movements in fast subsiding areas the po plain n italy case the geological and the anthropogenic components of vertical movement act on different time scales millions to thousands years and hundreds to tens of years respectively this peculiarity has been used in order to separate the factors controlling sea level changes in the po plain area the component due to long term geological processes is calculated from stratigraphic data commercial wells and seismic lines adding to this long term component the contribution of pleistocene deglaciation obtained from analytical models an estimate of the total natural component of vertical velocities is obtained the validity of these values is confirmed by comparison with velocities obtained from archaeological data and detailed palynological and paleontological analyses the anthropogenic components can be inferred by comparison between the total natural vertical velocities we calculate and vertical velocities obtained from other data sets two applications are proposed using tide gauge records and geodetic data respectively

segmentation and configuration of subducted lithosphere in italy an important control on thrust belt and foredeep basin evolution the apennine foredeep basin system located on continental crust consists of four roughly parallel basin segments each containing a flexural outer rise and an inner trough that deepens continuously toward the thrust belt flexural modeling of subsidence data across the basin indicates that this foredeep basin results mainly from deep subsurface loads acting on the subducted slab from within the subduction zone rather than from the topographic load of the apennine mountains the geometry of the four basin segments observed within the apennine foredeep is thus inferred to reflect subduction of segmented lithosphere where each lithospheric segment corresponds to a segment of the foredeep basin beneath the basin and in the foreland the lithosphere is continuous segmentation occurs only at depth beneath the thrust belt this pattern olf segmentation of the subducted lithosphere at depth is reflected in the large scale geometry of the outer part of the apennine thrust belt and appears to control it similarly the pattern of segmentation also appears to control the position of the eastern limit of back arc type extension in western italy these relations strongly suggest a genetic relation between subduction zone processes foredeep basin geometry and thrust belt evolution in which the configuration of the subducted lithosphere largely controls the large scale surface deformation observed in the apennine system

mechanical constraints on the chronology of fracture activation in folded devonian sandstone of the western moroccan anti atlas the three dimensional meter scale fracture networks observed on exposed folds between the towns of tata and akka western moroccan anti atlas consist mostly of planar discontinuities which are sub perpendicular to the bedding and partitioned in three main sets the chronology of their activation is proposed in five stages since the hercynian orogeny stage 1 predates folding and involves the horizontal compression of the emsian sandstone it involves fracture set i composed of systematic joints parallel to the direction of compression stages 2 4 correspond to the folding and are marked in the outer arc by the activation of fracture set ii composed mainly of joints parallel to the fold axial plane stage 5 is a regional shear event during which sets i and iii separated by an angle close to 608 are activated in a conjugate manner to throw light on the recurrent difficulty in discriminating between activation of inherited and new fractures an elasto plastic model is used to construct a stress path in the pervasively fractured medium idealized as a continuum each fracture set obeys the mohr coulomb criterion truncated in tension to describe both sliding and opening activations finite element simulations of a simple buckling event accounting for the field fracture sets are presented it is shown that set i cannot be generated by folding and thus does belong to stage 1 set ii is activated at a later stage of folding than expected from the field interpretation set iii cannot be activated during stage 2 confirming its role in stage 5 the advantages and limitations of the proposed modeling are finally discussed q 2002 elsevier science ltd all rights reserved

late quaternary uplift and valley evolution in the northern apennines lamone catchment abstract the topographic evolution of mountain chains is fundamentally dictated by the balance of erosional and tectonic processes in the northern apennines several questions about the late holocene to present deformation style and uplift rates are still open we consider a typical ne facing drainage basin focusing on all the geomorphic markers capable of supplying direct or indirect information regarding tectonic forcing on the landscape characteristics of altitude and relief drainage pattern river profile and fluvial response expressions were found to be in good agreement indicating that the most recent tectonic activity consists of a general persistent uplift of the chain associated with an extensional regime where different sectors are distinguished through differential uplift such differences have been found to act both along and transverse to the chain causing similar coherent patterns of response in erosional processes the geomorphology of the catchment displays several features which together with the long sustained tectonic forcing indicate the near attainment of a dynamic equilibrium between the rates of tectonic forcing and erosional processes creating steady state topography

fold uplift versus regional subsidence and sedimentation rate abstract fold uplifts compete during their development with regional subsidence in the frontal parts of thrust belts and accretionary wedges two cases exist in frontal thrust belts in the first more common case the uplift rate of the external folds is higher than the subsidence rate of the foredeep in the second case the fold uplift is less than the regional subsidence the total fold uplift may be considered as the fold uplift rate minus the regional subsidence rate this value can be either positive or negative positive total fold uplift occurs when folds rise faster than regional subsidence and the envelope of the fold crest rises towards the hinterland of the accretionary wedge in the opposite case negative total fold uplift the envelope dips towards the hinterland because folds rise more slowly than regional subsidence in the first positive case the folds are deeply eroded and the onlap of the growing strata moves away from the fold crest if the sedimentation rate is lower than the fold uplift rate in marine or alluvial environments in the second negative case where folds rise at lower rates than the regional subsidence the onlap moves towards the fold crest if the sedimentation rate is higher than the fold uplift rate this is also the more favorable case for hydrocarbon traps where growth strata can seal the fold moreover the fast subsidence rates in the foredeep provide a higher thermal maturation this second tectonic setting is commonly associated with accretionary wedges forming along westdirected subduction zones which are characterized by high subsidence rates in the foredeep or trench due to the fast eastward roll back of the subduction hinge e g apennines carpathians banda arc

compaction induced stress variations with depth in an active anticline northern apennines italy 1 it is shown that the stress field can vary with depth even within a homogeneous tectonic setting as documented for the active mirandola fault related fold along the buried front of the northern apennines analyses of borehole breakouts and other well data integrated with seismological information and field evidence show that extension perpendicular to the fold axis above approximately 1200 m changes to a strike slip stress field and finally to compression near the main detachment at depth similar along depth strain variations recognized in non active anticlines are usually explained by invoking tangential longitudinal strain folding i e stretching above and shortening below a neutral surface or gravitational instabilities however in this study we propose that differential compaction may play a significant and generally overlooked role with the aid of numerical modeling it is shown that where fold limbs are onlapped by highly compactable deposits as in the mirandola area differential compaction induces stretching at shallow 1 2 km depths the amount of stretching is a function of the shape of the fold and of the thickness of the syn tectonic sediments we conclude that in the mirandola case study the stress variations observed with depth are the result of a combination of a regional compression at depth and local tension driven by differential compaction of growth strata on the limbs of the anticline with respect to its crest

the mw 5 4 reggio emilia 1996 earthquake active compressional tectonics in the po plain italy summary we have analysed the seismic sequence that occurred in october 1996 near the town of reggio emilia on the southern edge of the po plain the onset of the sequence was marked by a 5 4 moment magnitude main shock located at 15 km depth the main shock focal mechanism is a reverse solution with a strike slip component and the scalar moment is 1 46 1017 n m we used broad band digital recordings from a borehole station located at about 70 km from the epicentre for a spectral analysis in order to estimate attenuation and source parameters for the main shock in addition the empirical green s function method has been applied to evaluate the source time function in terms of both moment rate and stress rate we infer an asperity like rupture process for the main shock as suggested by the short duration of the stress release with respect to the overall duration of the moment rate function this analysis also allows us to estimate the average dynamic stress drop of the main shock 600 bar we analysed the digital recordings of the temporary local seismic network deployed after the main shock and of a permanent local network maintained by the italian petroleum agency agip during 15 days of field experiments we recorded more than 800 aftershocks which delineate a 9 km long ne elongated distribution confined between 12 and 15 km depth suggesting that the basement is involved in the deformation processes 102 focal mechanism of aftershocks have been computed from p wave polarities showing mainly pure reverse solutions we calculate the principal stress axes from a selected population of earthquakes providing a constraint on the stress regime of this part of the po plain the focal mechanisms are consistent with a n s subhorizontal 1 all the seismological data we have analysed confirm that this region is undergoing active compressional tectonics as already inferred from recent earthquakes geomorphological data and other stress indicators moreover the elongation of the reggio emilia aftershock sequence is consistent with the regional direction of the thrust fronts cropping out in the area suggesting that they are still active

present day stress field and deformation in eastern austria we analysed fault plane solutions and borehole breakouts in the eastern part of the eastern alps and found a heterogeneous stress field which we interpret as a transition zone of three different stress provinces the western european stress province with nw to nnw sh orientation and mainly strike slip faulting regime the adriatic stress province with a radial stress pattern and thrust faulting to strike slip faulting regime and the dinaric pannonian stress province with ne sh orientation and strike slip faulting regime the western pannonian basin seems to be a part of the transition zone with wnw to nw sh orientation a stress regime stimulating strike slip faulting prevails in the eastern alps the south bohemian basement spur as a major tectonic structure with a high rheological contrast to surrounding units has a strong influence on the stress field and exhibits the highest seismicity at its tip due to stress concentration from a constructed vertical stress orientation profile we found stress decoupling of the northern calcareous alps from the underlying european foreland both the molasse and the flysch helvetic zone are considered as candidates for decoupling horizons due to stress orientation observations and due to their rheological behaviour from seismological and rheological data we suggest a horizontal stress decoupling across the eastern alps caused by a weakened central alpine lithosphere

subsidence rates in the po plain northern italy the relative impact of natural and anthropogenic causation abstract the central eastern po plain in northern italy is a rapidly subsiding sedimentary basin that hosts about 30 of the italian population and 40 of italy s total productive activities subsidence rates range from 0 to 70 mm year the maximum occurring in synclinal areas at the po delta and near bologna the minimum located at the top of buried probable tectonically active anticlines mirandola ferrara we show that modern subsidence is at least an order of magnitude higher than due solely to long term natural processes this implies that most subsidence in the po plain has been induced by human activities as previously noted we suggest that the main factor controlling modern subsidence is water withdrawal which was particularly intense during the second half of the 20th century coinciding with accelerating economic growth we also evaluate the impact of rapid subsidence on floods in low areas by comparing subsidence velocity maps with flood maps this shows that there is a clear cut correlation between flood frequency and rapid subsidence in contrast few floods occurred in low subsidence areas which generally correspond with the top of buried anticlines we finally note that the anthropic caused increase in subsidence has now greatly increased the potential for additional floodings

paleosols from the groups of burial mounds provide paleoclimatic records of centennial to intercentennial time scale a case study from the early alan cemeteries in the northern caucasus russia abstract buried soil chronosequences under a series of early alan kurgans burial mounds in the vladikavkazkaya depression of the northern caucasus russia were studied to derive a high resolution paleoclimatic record from the variations of the selected paleosol properties haplic chernozems occur under kurgans and on the actual land surface three kurgan cemeteries brut 1 brut 2 and beslan dated from the end of the second to the beginning of the seventh centuries ad have been studied the cemeteries are situated close to each other under similar lithological and geomorphological conditions but differed in the paleosols preservation the brut 2 site has been recently altered due to annual ploughing and intensive irrigation for more than 30 years the background soils and paleosols of the brut 2 site have been compared with synchronous soils of non irrigated brut 1 and beslan sites to detect pedogenic properties that are less changed by irrigation and thus comprise the soil memory stronger black color of humus horizon increase of humus content and decrease of humus 13c values clear signs of biological activity absence of morphological and analytical signs of solonetz properties diffused carbonate white soft spots in the bca horizon and decreasing carbonate content are thought to be related to the comparatively humid climatic conditions in the region on the contrary relatively low humus content tongue like lower boundary of humus horizon increase of humus 13c values morphological signs of solonetz properties together with high content of exchangeable na relatively large and clearly shaped carbonate white soft spots in the paleosols of the brut 2 site as well as increase of density thickness of the carbonate pseudomicellium and high carbonate content in the upper part of profiles in the paleosols of the non irrigated brut 1 site are assumed to be xeromorphic features indicating comparatively drier climatic conditions the paleosols of the earliest chronointerval of burial the end of the second to the beginning of the third centuries ad demonstrate clear xeromorphic properties which indicate a relatively dry climate with a mean annual precipitation 50 100 mm less than today the estimated duration of the period with such climatic conditions is thought to be not less than 100 years in addition those paleosols have some weak signs of humid conditions indicating that between the end of the first and the middle of the second centuries ad the climate was getting more moist mean annual precipitation became equal or slightly higher than today the paleosols buried in the first half of the fifth century ad again demonstrate the gradual enhancement of xeromorphic properties reflecting the next stage of droughts thus the period with favourable humid climate when the early alan culture flourished in the northern caucasus was relatively short about 400 years studying the detailed chronosequence in the non irrigated brut 1 site the records of intercentennial time scale soil properties variability produced by comparatively fast pedogenic processes typical for the steppe zone i e humus formation and accumulation bioturbation carbonate accumulation and transformation and solonetzization have been provided

recent movements along the main boundary thrust of the himalayas normal faulting in an over critical thrust wedge abstract the main boundary thrust mbt is one of the major himalayan thrusts occurring during the cainozoic and it is presently incorporated within the himalayan thrust wedge lesser and outer himalayas displaced above the indian lithosphere nonetheless the mbt shows recent normal displacement along most of its length we suggest that the orientation of the major principal stress within the himalayan thrust wedge deviates significantly from the horizontal and when this deviation exceeds the dip of the vectors normal to back tilted thrusts the normal component of displacement may act along these faults steep north dipping segments of the mbt therefore show a normal component of displacement if a geometrical definition is used but they are faults in a compressional regime where the major principal stress axis has deviated from the horizontal micro structural data recorded along the surkhet ghorahi segment of the mbt are consistent with a strong deviation of the state of stress the presence of such peculiar normal faulting along the mbt is used to calibrate the mechanical characteristics of the belt considered as a coulomb wedge the following characteristics are suggested a very poor strength contrast between basal decollement and rocks in the wedge body b a high pore fluid pressure ratio probably close to 0 8 0 9 and a higher fluid pressure ratio close to 1 0 along the active normal faults if a high internal friction angle close to the byerlee value is considered the strong deviation in principal stress direction may have recently increased due to a taper of the himalayan wedge exceeding the stability boundary and may be controlled by erosion and isostatic uplift rebound of the himalayan range

development of crestal normal faults associated with deepwater fold growth deepwater anticlines during their early stages of development approximately between interlimb angles of 180 and 140 grow and accumulate weak fine grained and poorly lithified sediment on their crests growth of the anticlines induced gravitational instability within the syn kinematic sediments and development of a range of shallow gravity driven failure mechanisms in addition to shallow tens of metres depth to detachment rotational landslides deeper seated normal fault swarms also affect the fold crests and upper fold limbs these faults tend to penetrate to depths between 200 and 800 m are 100s of metres to a few kilometres long planar to weakly curved in cross section and display throws in the order of tens of metres the faults do not sole out into a detachment but die out downwards they can occur as single sets or tiers of faults that have developed at different times in map view the fault patterns range from straight to anastamosing to highly curved with complex cross cutting relationships the number and orientation of faults corresponds to the maximum slope dip and direction and consequently the faults are inferred to be mainly the product of gravity induced deformation although tangential stresses arising from outer arc bending of a fold or crestal collapse in response to a mobile sedimentary unit may contribute to some extent

the italian cmt dataset from 1977 to the present abstract the ingv harvard european mediterranean regional centroid moment tensor rcmt catalog collects solutions routinely computed since 1997 for earthquakes with moderate magnitude 4 5 m 5 5 in the mediterranean region the database represents an extension to smaller magnitudes of the harvard global cmt catalog based on analysis of seismograms recorded at regional distance and modeling of intermediate period surface waves the catalog includes about 600 events 200 of which in the italian region this study extends the catalog back in time for the italian region as long as made possible by available digital data i e since 1977 with the same analysis and inversion method used for current seismicity as a result we present here 65 new moment tensors for years between 1977 and 1997 these solutions represent 45 of the total number of events analyzed the existing seismograms being often too scarce to allow a stable solution the new dataset includes events in many seismic zones where moderate seismicity had previously been scarcely documented e g the po plain the central to southern apennines and the adriatic sea the complete dataset including previously determined rcmts and cmts represents the seismic deformation in the italian area during the last 25 years

grain size of fluvial deposits and late quaternary climate a case study in the po river valley italy by stacking the grain size data interpreted from many logs of borings down to 200 m deep in a sector of the po river valley we have obtained a curve of the clay silt fraction vs depth that matches the oxygen isotope curve of paleotemperatures for the late quaternary contour maps and plots for selected subzones show that the northern half of the study area is characterized by this correlation whereas the southern part adds only a random low amplitude noise to the curve the suggested dependence of grain size of fluvial deposits on climate in a part of the study area would provide an indirect way to date these not otherwise datable sediments allowing an evaluation of the sedimentation rates and of the total subsidence since the last interglacial

modelling of piggyback basin stratigraphy record of tectonic evolution abstract the tectono stratigraphic evolution of foreland basins is influenced by processes acting on local regional and global scale in this paper the effects of these processes on the basin evolution are investigated using a forward reconstruction model based on the principles of balanced cross section the modelling incorporates the consequences of thrust deformation sedimentation erosion basement subsidence and sealevel changes on the basin stratigraphy basement subsidence due to lithospheric loading is the main cause of foreland basin formation but appears to have minor implications for the occurrence of angular unconformities in the stratigraphie record of piggyback basins thrusting is probably the dominant factor in the control of the stratigraphie evolution of piggyback basins overprinting the effect of eustasy detailed analyses of stratigraphie data enable the reconstruction of the structural evolution of the underlying thrust system modelling of the northern apenninic po basin shows that neogene stratigraphie sequences of the proximal part of the basin can be explained by tectonic activity of the apenninic fold and thrust belt strong basement subsidence accompanied with deep seated mid pliocene thrusting controls the stratigraphie record of the po piggyback basins

in situ stress data from the jura mountains new results and interpretation recently completed in situ stress measurements using the borehole slotter at 33 new test sites within the swiss and french jura mountains are presented when combined with previously published stress data these new measurements allow a detailed description of the contemporary state of stress in this fold and thrust belt and the adjacent foreland the data now allow the recognition of five stress provinces within which two general and different orientations of maximum horizontal stress sh can be distinguished the central and the southwest provinces with a nnw sse to nne ssw orientation and the east northwest and southeast provinces orientated e w to nw se each province has its own characteristic orientation measurements in three study areas are presented for comparison with already published acoustic anisotropy measurements borehole breakout data overcoring tests and triangulation measurements the results show a generally good agreement with the new borehole slotter measurements the tectonic implications of these stress data are discussed in terms of a large scale stress reorientation of the nw se orientated contemporary central european stress field in the foreland of the western alpine arc

water chemistry and heavy metal distribution in an amd highly contaminated river environmental impacts of acid mine drainage amd from dexing copper mine the largest open pit copper mine in asia on le an river were well documented 10 years ago however ore production of the mine has increased fourfold and the contamination situation of the river now is unknown our studies indicated that heavy metal concentrations in riverwaters dissolved suspended solids ss and sediments all showed highly localized distribution patterns closely associated with two amd contaminated tributaries dawu river and ji river and are significantly different from the previous findings compared with the previous reports most of the sampling sites in le an river displayed lower contents of sediments of 2005 because several historical upstream and downstream heavy metal sources disappeared or became unimportant the surprised decrease of copper contents in sediments at the mixing location with dawu river was mainly due to dilution from the sufficient input of poor copper ore 0 3

a new active tectonic model for the construction of the northern apennines mountain front near bologna italy 1 we integrate existing and new geologic data retreating trench extension and accretion tectonics retreat project particularly on the origin growth and activity of the mountain front at bologna italy into a new model that explains apennine orogenesis in the context of a slab rollback upper plate retreat process the bologna mountain front is an actively growing structure driving rock uplift 1 mm year cored by a midcrustal flat ramp structure that accommodates ongoing shortening driven by adria subduction at a rate of 2 5 mm year the data we use are assembled from river terraces and associated pleistocene growth strata geodesy including releveling surveys reinterpretation of published reflection lines and a new high resolution reflection line these data constrain a simple trishear model that inverts for blind thrust ramp depth dip and slip apennine extension is recognized both in the foreland as high angle normal faults and modest stretching in the carapace of the growing mountain front and in the hinterland with larger normal faults that accomplish some crustal thinning as the upper plate retreats this coevolution of extension and shortening shares some notable characteristics with other basement involved collisional orogens including the early tertiary laramide orogeny in the american west and the oligocene to miocene evolution of the alps we propose a possible relationship between underplating and the development of the po as a sag basin as a quaternary phenomenon that may also apply to past periods of apennine deformation tortonian continued shortening on the structure beneath the bologna mountain front represents by far the most important and underappreciated seismogenic source in the front of the northern apennines

geomorphic evidence for an emergent active thrust along the edge of the po plain the broni stradella fault 1 we present here geomorphic evidence for an emergent active thrust along the northwestern apennine front about 50 km south of milano fieldwork combined with spot image analysis attests to the presence of a 35 km long en echelon cumulative fault scarp that cuts e w across quaternary surface deposits from casteggio to sarmato the scarp offsets vertically alluvial fans and terraces emplaced by tributaries of the po river that flow northward from the apennines incision by such tributaries occurs only south of the scarp valleys of smaller streams stand in hanging position to the northeast the buried east dipping pavia lateral ramp bounds the san colombano anticline we interpret the montebello sarmato scarp to result from the emergence of an active thrust fault dipping south the stradella thrust which splays eastward from that ramp total station profiles leveled perpendicular to the stradella thrust show variable cumulative surface throws ranging from 2 to 25 m scarp degradation analysis indicates fairly recent offset of the terrace surfaces 10 100 kyr suggesting a minimum uplift rate of 0 3 mm yr the underlying fault might thus be one of the most active thrust ramps along this segment of the apennines n s to n15 w shortening is consistent with both the e w strike of this thrust ramp and with coeval oblique sinistral motion on the nne ssw trending pavia lateral ramp the vogherese bobbiese earthquake of 1828 i ix south of casteggio and broni may have activated one segment of this lateral ramp rather than the stradella thrust other historical events i 7 that caused damage in pavia piacenza lodi and milano in the last 2000 years 290 a d 1249 a d 1276 a d 1473 a d may have occurred on the broni stradella thrust or on the blind san colombano and lodi thrusts farther north this makes detailed paleoseismological studies and trenching across its trace mandatory

orogens and slabs vs their direction of subduction abstract subduction zones appear primarily controlled by the polarity of their direction i e w directed or e to nne directed probably due to the westward drift of the lithosphere relative to the asthenosphere the decollement planes behave differently in the two end members in the w directed subduction zone the decollement of the plate to the east is warped and subducted whereas in the e to nne directed it is ramping upward at the surface there are w directed subduction zones that work also in absence of active convergence like the carpathians or the apennines w directed subduction zones have shorter life 30 40 ma than e or ne directed subduction zones even longer than 100 ma the different decollements in the two end members of subduction should control different ptt paths and therefore generate variable metamorphic assemblages in the associated accretionary wedges and orogens these asymmetries also determine different topographic and structural evolutions that are marked by low topography and a fast eastward migrating structural wave along w directed subduction zones whereas the topography and the structure are rapidly growing upward and expanding laterally along the opposite subduction zones the magmatic pair calc alkaline and alkaline tholeiitic volcanic products of the island arc and the back arc basin characterise the w directed subduction zones magmatic rocks associated with e or ne directed subduction zones have higher abundances of incompatible elements and mainly consist of calc alkaline shoshonitic suites with large volumes of batholithic intrusions and porphyry copper ore deposits the subduction zones surrounding the adriatic plate in the central mediterranean confirm the differences among subduction zones as primarily controlled by the geographic polarity of the main direction of the slab the western margin of the adriatic plate contemporaneously overridden and underthrust europe toward the west to generate respectively the alps and the apennines while the eastern margin subducted under the dinarides hellenides these belts confirm the characters of the end members of subduction zones as a function of their geographic polarity similarly to the pacific subduction zones

continental depositional systems of the quaternary of the po plain northern italy abstract the po plain is a molasse foredeep bounded by two mountain chains apennines and alps apenninic thrusting is still active whereas the alpine one ended by early pliocene times the continental deposits form a veneer at the surface and form the topset of a prograding complex the po river divides the plain into two sectors with different sedimentary facies and body geometries to the south the alluvial fan and plain deposits are small embedded in clays and show elongate shapes to the north sedimentary bodies are laterally extensive tabular and with minor amounts of fine grained sediments this difference could be due to a different climatic conditions during quaternary ice ages on the two sides of the basin b different structural settings in the two sectors of the basin that produce a higher subsidence rate to the south c different lithologies in the source areas i e alps and apennines

sedimentary basins formed and carried piggyback on active thrust sheets small sedimentary basins that formed on the apennine southern margin of the po basin complex northern italy have been studied using borehole and seismic reflection information and their evolution can be dated using the largely marine biostratigraphy of the miocene to quaternary sediments these studies show that the basins formed and were filled while being carried on moving thrust sheets and they are therefore named piggyback basins each of these basins corresponds to the active phase of a different thrust front ramp on the pyrenean northern margin of the ebro basin complex northern spain similar piggyback basins formed between eocene and mid miocene time they have since been uplifted and eroded and may therefore be studied in outcrop in northern spain much of the basin fill sediment was deposited in nonmarine environments

along depth stress rotations and active faults an example in a 5 km deep well of southern italy 1 we have analyzed a 1500 m section at 3 9 to 5 4 km depth in a well of the southern apennines in order to better characterize the local active stress field and its correlation with tectonic structures in this paper we present and discuss the results obtained from the comparison between breakouts and structural analysis from dipmeter data we have found that the mean breakout direction is in agreement with the regional stress field that in this area is characterized by normal faulting 1 v with ne sw trending extension horizontal 3 since the regional stress field is relatively well known in this region we could detect and study some anomalous horizontal stress directions along the well which we interpret as due to faults crosscutting the borehole a detailed comparison between the breakout inferred stress variations along depth and the faults identified by the dipmeter analysis reveals that some of these faults are associated with stress rotations whereas others do not show any variation the former can be interpreted either as open fractures or as faults that slipped recently with a near complete stress drop and the latter can be interpreted as sealed faults in particular we found that the main thrust faults of the area mainly active in pliocene times appear to be sealed whereas e w trending high angle normal faults determine strong stress rotations suggesting that they are the main active structures of the region this suggests that the study area is located in a transfer zone between the two main apenninic nw se trending fault systems which ruptured in the last 150 years this study has shown that a detailed analysis of the structural and geometrical characteristics of deep wells can be used for the reconnaissance of active structures this approach can contribute to seismic hazard studies and if carried out in an oil bearing section can help to maximize the hydrocarbon production

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

compression along the northern apennines evidence from the mw 5 3 monghidoro earthquake in this paper we present the seismological data recorded during the deployment of a dense three component seismic network installed a few hours after the 2003 mw 5 3 monghidoro earthquake in northern apennines the main shock focal solutions derived from polarities distribution and body wave modelling of regional broadband data show a ne sw striking reverse mechanism accurate relative locations of aftershocks and the inversion of focal mechanisms show that earthquakes occurred on a nw dipping backthrust within the adria lithosphere under a nw trending horizontal compression the observed compression is a secondary process possibly explained by differential motion within the adriatic lithosphere fault geometry and kinematics is controlled by pre existing structures

tomographic constraints on the geodynamic evolution of the italian region in this paper we present p wave tomographic images of the mantle beneath italy obtained by inverting 6000 teleseismic p and pkp wave arrival times accurately repicked recorded in the time period 1988 1994 by the stations of the national seismic network of the istituto nazionale di geofisica we pay great attention in the data selection and picking procedure of seismic phases to obtain a very high quality data set the data were inverted with the well established aki christofferson husebye tomographic technique different reference models and residuals computation have been tried to verify the stability of the results the high quality of the repicked arrival times allows us to enhance the definition of the deep structures beneath both the alps and the apennines looking for their lateral and vertical continuity down to 800 km depth the main finding of this study is a continuous high velocity body located between 250 and 670 km depth beneath the entire apenninic system dipping toward the tyrrhenian area which continues upward segmented in two main anomalies in the northern apenninic and the calabrian arcs we interpret this high velocity feature as the subducted oceanic lithosphere between the eurasian and african plates dipping down to the upper lower mantle boundary beneath the tyrrhenian sea the retrieved images of the lithosphere subducting beneath apennines are reliable in terms of thickness about 80 90 km and p wave velocity contrast 2 4 higher than the normal mantle furthermore our tomographic images which focus on the deep geometry and continuity of the velocity structures provide new keys to understanding the geodynamic evolution of the italian region the segmentation of the high velocity slab upward suggests a complex evolution of the arc trench system and the initially continuous subduction of the ionian adriatic plate progressively developed in subordinate arcs probably due to lateral heterogeneity of the subducting lithosphere

the role of fractures in the structural interpretation of sheep mountain anticline wyoming the development of fractures in the sedimentary layers of sheep mountain anticline a laramide asymmetric fault cored fold of the bighorn basin is documented and interpreted to constrain the kinematic evolution of the fold the fracture pattern is interpreted to identify five main fracture sets a fracture set striking 110 set i oblique to the future fold trend is interpreted as a regional fracture set that predates laramide compression a joint set set ii striking 045 and present in the hinge and backlimb is related to the ne oriented laramide compression just prior to and during initial anticline growth joints striking 135 set iii parallel to the fold trend are found within the hinge and are interpreted to have developed in response to the bending of layers the two youngest fracture sets are attributed to a late stage of fold growth a joint set set iv in the backlimb striking parallel to the set i fractures but vertical and a fracture set in the forelimb consisting of set i fractures reactivated as reverse faults the relative chronology mode of formation opening vs shearing and structural locations of these fractures suggest the following kinematics of folding at sheep mountain anticline little or no lateral fold propagation no hinge migration and limb rotation with only minor limb flexure and stretching

decollement depth versus accretionary prism dimension in the apennines and the barbados 1 along representative cross sections of the apennines and the northern barbados accretionary prisms we measured the area the decollement depth the angle a of the upper envelope and the angle b of the dip of the regional monocline the continental sections of the apennines accretionary prism have a deeper decollement than the oceanic sections of the northern barbados 6 10 km depth and 1 km depth respectively because the sediment pile is thinner on the incoming barbados plate and its denser oceanic structure is more easily subducted considering the frontal 50 km the apennines have an average cross sectional area of 500 km 2 and the northern barbados ridge of 100 km 2 the total area is a function of the depth of the decollement plane therefore at a given amount of subduction the deeper the decollement depth is the bigger the area of the wedge will result assuming negligible compaction and erosion as a consequence the larger area volume and higher elevation of the apennines with respect to the barbados is determined by the apenninic deeper decollement despite these differences the geometry of both decollements is in some cases comparable in particular close to the boundary between the crystalline crust and the sediment pile where the main density and strength contrasts are concentrated variations in depth of the decollement occur moving along strike in both accretionary prisms the geometry of the prisms is further controlled by the different values of a and b their sum and the distance of the accretionary prism relative to the subduction hinge index terms 8099 structural geology general or miscellaneous 8150 tectonophysics evolution of the earth plate boundary general 3040 8122 tectonophysics dynamics gravity and tectonics keywords decollement depth accretionary prism apennines barbados citation bigi s f lenci c doglioni j c moore e carminati and d scrocca decollement depth versus