paleomagnetism of jurassic to miocene sediments from the apenninic carbonate platform southern apennines italy evidence for a 60 counterclockwise miocene rotation abstract the tectonic evolution of the apennine belt southern tyrrhenian sea system is addressed through a paleomagnetic study of lias to langhian sediments from the apenninic carbonate platform southern apennines italy reliable paleomagnetic data gathered from 21 sites document a regional scale post langhian 80 counterclockwise ccw rotation since previous studies of the plio pleistocene clays spread over the orogen had shown a 20 ccw rotation we conclude that the southern apennines rotated by 60 during middle late miocene our data provide evidence that the southeastward drift of calabrian block and synchronous spreading of the southern tyrrhenian sea induced saloon door like deformation of the southern apennines and sicily which underwent similar magnitude although opposite in sign orogenic rotations a paleomagnetically derived paleogeographic reconstruction shows that at 15 ma late langhian the alpine apennine belt collided with a nne oriented carbonate platform corridor surrounded by oceanic basins we speculate that both the end of the corsica sardinia rotation and the eastward jump of the locus of back arc extension from the liguro provencal to the tyrrhenian sea may have been consequences of this event

state of stress in the southern tyrrhenian subduction zone from fault plane solutions summary in this paper we present revised locations and original focal mechanisms computed for intermediate and deep earthquakes that occurred within the southern tyrrhenian subduction zone between 1988 and 1994 in order to improve our knowledge of the state of stress for this compressional margin in particular we define the stress distribution within a large portion of the descending slab between 40 and about 450 km depth the seismicity distribution reveals a continuous 40 50 km thick slab that abruptly increases its dip from subhorizontal in the ionian sea to a constant 70 dip in the tyrrhenian we computed focal mechanisms for events with magnitudes ranging from 2 7 and 5 7 obtaining the distribution of p and t axes for many events for which centroid moment tensor cmt solutions are not available thus enabling the sampling of a larger depth range compared to previous studies we define three portions of the slab characterized by different distributions of p and t axes a general down dip compression is found between 165 and 370 km depth whereas in the upper part of the slab 40 165 km depth the fault plane solutions are strongly heterogeneous below 370 km the p axes of the few deep events located further to the north have a shallower dip and are not aligned with the 70 dipping slab possibly suggesting that they belong to a separated piece of subducted lithosphere there is a good correspondence between the depth range in which the p axes plunge closer to the slab dip 70 and the interval characterized by the highest seismic energy release 190 370 km

the puglia uplift se italy an anomaly in the foreland of the apenninic subduction due to buckling of a thick continental lithosphere the apenninic foreland shows two distinct structural signatures comparing the central adriatic sea and the puglia region during the pliocene pleistocene the central adriatic underwent high subsidence rates due to the eastward rollback of the hinge of the west dipping apenninic subduction the puglia region and the bradanic foredeep are located southward along strike in the same foreland but in contrast with the central adriatic after pliocene early pleistocene subsidence they underwent uplift since the middle pleistocene the geometry and the kinematics of the frontal accretionary wedge and related foreland changed from that moment on between the two areas at the front of the central northern apennines off scraping and subsidence continued whereas the foredeep and foreland of the southern apennines were buckled those differences are interpreted as being due to the larger subduction hinge rollback rate since middle pleistocene of the central adriatic lithosphere 70 km thick with respect to the thicker puglia 110 km the different thicknesses of the continental crust and lithosphere were inherited from the mesozoic rifting that disrupted the adriatic plate the different thicknesses appear to have controlled the variable degree of flexure of the lithosphere and its asthenospheric penetration rate the tremiti e w alignment is the right lateral lithospheric transfer zone of those different tectonic regimes the consequent different dip of the subduction in the two sections steeper west of puglia could also explain the lower elevation of the southern apennines compared to their central northern sector

teleseismic tomography of the southern tyrrhenian subduction zone new results from seafloor and land recordings 1 teleseismic traveltime data recorded by temporary ocean bottom seismographs deployed in tyrrhenian sea around the aeolian islands tyrrhenian deep sea experiment tyde have been used for the first time in italy to refine the 3 d model for the deep p wave velocity structure of the southern tyrrhenian subduction zone the arrival times of 35 teleseisms have been combined with those recorded by the italian national network in order to obtain a more complete azimuthal coverage of teleseismic rays 80 events recorded by land stations from 1990 to 2002 have been included in the data set in total 2904 p and 314 pkpdf phases 1300 recorded by ocean bottom instruments have been collected the upper mantle structure is reconstructed down to 500 km by a nonlinear inversion of the relative residuals computed with respect to the reference 1 d velocity model ak135 the obtained tomographic model has a higher resolution than those previously published thanks to the recordings of tyde seafloor stations tomographic results confirm the presence of the tyrrhenian slab imaged as a high velocity body extending from the uppermost mantle down to the bottom velocity model with dip 70 75 nw the model better defines the geometry of the seismogenic part of the slab its lateral extension is about 200 km in the depth interval 150 300 km where most of the deep seismicity is concentrated at uppermost mantle depths the fast structure has smaller lateral dimensions about 100 km the inversion also points out a wide well resolved low velocity zone completely surrounding the steeply dipping fast structure from the lower crust down to about 300 km this feature suggests the presence of a three dimensional circulation of asthenospheric flow around the ionian slab caused by retreat and roll back of the slab our results are in agreement with recent laboratory experiments mantle anisotropy studies geochemical and isotopic analyses and modeling based on residual topography

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

crustal velocity structure in italy from analysis of regional seismic waveforms abstract in this article we use regional seismic waveforms recorded by the recently installed istituto nazionale di geofisica e vulcanologia ingv national network and the mediterranean very broadband seismographic network mednet stations to develop 1d crustal velocity models for the italian peninsula about 55 000 p wave and 35 000 s wave arrival times from 4727 events are used to derive average seismic parameters in the crust and uppermost mantle we define four regions according to geological constraints and recent travel time tomography results based on the average seismic parameters we combine broadband seismic waveforms and travel times of regional phases to model crustal structures for the four regions by applying the genetic algorithm our results indicate smooth velocity gradients with a depth beneath the apennines and a deep moho beneath the central alps green s functions from the regionalized 1d velocity models are used to determine source depths and focal mechanisms for 37 events with a magnitude larger than 3 5 by a grid search technique our results show that normal and strike slip faulting source mechanisms dominate the apenninic belt and that most thrust faulting events occur in the adriatic sea and the outer margin of the northern apennines

anthropogenic contribution to the geological and geomorphological record a case study from great yarmouth norfolk uk abstract reconstruction of artificial or anthropogenic topographies sediment thicknesses and volumes provides a mechanism for quantifying anthropogenic changes to sedimentary systems in the context of the proposed anthropocene epoch we present a methodology for determining the volumetric contribution of anthropogenic deposits to the geological and geomorphological record and apply it to the great yarmouth area of norfolk uk 115 boreholes drilled to a maximum depth of 6 m below ground level were used to determine the thickness and distribution of seven geo archaeological units comprising natural and anthropogenic deposits in the central great yarmouth area this was supplemented by additional depth information derived from 467 existing ground investigation boreholes and published 1 50 000 scale geological maps the top and base of each geo archaeological unit were modelled from elevations recorded in the borehole data grids were produced using a natural neighbour analysis with a 25 m cell size using mapinfo 8 0 vertical mapper 3 1 to produce palaeotopographical surfaces maximum minimum and average elevations for each geo archaeological unit generally increase with decreasing age with the exception of the early medieval palaeotopographical surface which locally occurs at higher elevations than that of the younger late medieval unit the total sediment volume for the combined modern post medieval late medieval and early medieval geo archaeological units is 10 91 10 5 m 3 the total sediment volume for the aeolian river terrace and marine geo archaeological units combined is 65 58 10 5 m 3 anthropogenic sedimentation rates were calculated to increase from 590 m 3 yr during the early medieval period 1500 m 3 yr during the post medieval period and 2300 m 3 yr during the modern period it is estimated that the combined anthropogenic geo archaeological units contribute approximately 15 of the total volume of sediments that would have been traditionally considered natural holocene deposits in the great yarmouth area the results indicate that an approach combining geological and archaeological deposit modelling can be used to quantify anthropogenic landscape impact and its associated sediment flux

a tomographic study of the lithosphere beneath the pyrenees from local and teleseismic data a tomographic image of the pyrenean lithosphere from the surface down to 200 km is deduced from the propagation of the seismic waves recorded at the regional pyrenean seismograph network crustal and subcrustal models are derived independently from the inversion of two different data sets p and s velocity models for the crust are obtained from the propagation of local earthquakes the upper crust appears very heterogeneous and exhibits sharp velocity contrasts in the uppermost 7 km an east west trending zone with velocities up to 6 higher than the surrounding material is observed all along the pyrenees this zone coincides in most places with the exposure of the paleozoic rocks of the axial zone low velocities are observed on both sides of this high velocity zone at the surface they coincide with well known sedimentary basins but dip down to about 11 km depth toward the axis of the range in the central and eastern pyrenees two large high velocity bodies stand out in the north pyrenean zone and extend down to the base of the upper crust they coincide with large positive gravity anomalies and are interpreted as lower crust or upper mantle blocks uplifted into the upper crust the lower crust is poorly resolved but appears to be less heterogeneous than the upper crust moreover the lower crustal structure is almost uncorrelated with the upper crustal structure the major feature of the lower crust is a low velocity anomaly which stretches along the north pyrenean fault in the western pyrenees and beneath the axial zone in the central pyrenees its location nearly coincides with the distribution of the seismicity in the upper mantle p models are derived from the travel times of the remote events recorded at the pyrenean stations the most important feature is the presence in the eastern and central pyrenees of a vertical low velocity heterogeneity south of the north pyrenean fault down to 80 100 km this structure exhibits a 2 velocity contrast with respect to the surrounding structures and is interpreted as lower crustal material subducted during the pyrenean convergence this heterogeneity is not observed in the western pyrenees suggesting that the crustal shortening has been completely accommodated by several thrusts in the thinned aquitaine crust

the dynamics of back arc extension an experimental approach to the opening of the tyrrhenian sea the e w opening tyrrhenian sea developed after the cretaceous palaeogene alpine collision nearly perpendicular to the motion of the african plate as a back arc of the adria ionian westward subduction three driving mechanisms have been proposed to explain the dynamic evolution of the tyrrhenian apennine system 1 the northward indentation of the african plate 2 the retreating subduction of the adria ionian lithosphere and 3 the gravitational collapse of the alpine post collisional wedge in order to define the relative contribution of each of these mechanisms in the neogene dynamic of the tyrrhenian apennine system we performed 3 d laboratory experiments in which we simulated a retreating subduction process in a compressional regime oriented perpendicularly to the direction of subduction in this framework we also tested the influence of the gravitational collapse of the overriding plate experiments were constructed using dry sand and silicone putties to simulate brittle upper crust and ductile lower crust upper mantle respectively these layers floated on a high density low viscosity glucose syrup which simulated the asthenosphere the main conclusion of our experiments is that large scale continental extension similar to that observed in the tyrrhenian area could be reproduced perpendicular to the shortening direction induced by the indentation of the african plate in this framework extensional processes are indeed possible if the trench retreat velocity is higher than the rate of shortening induced by the advancing african plate our experimental results indicate that this high trench retreat velocity could be explained by the coexistence of the gravitational collapse of the post alpine wedge with a slab pull process linked to the retreating subduction of the adria ionian plate while the first mechanism is predominant in the northern tyrrhenian area the second one seems to be important in the latest stage of extension and oceanic accretion of the southern tyrrhenian area

timing of normal faulting along the indus suture in pakistan himalaya and a case of major 231 pa 235 u initial disequilibrium in zircon we report age data by tims u pb la icp ms and 39ar 40ar techniques for main magmatic events in the lower swat region of pakistan in order to constrain the tectonic evolution of the northwestern himalaya the pre himalayan history of the indian continent is documented by single zircon u pb results from the peraluminous choga granite gneiss which yielded a 468 5 ma lower concordia intercept interpreted to approximate the time of magmatic emplacement the presence of a well defined 870 7 ma inherited component upper intercept suggests a plutonic or volcanic protolith residing at unexposed levels of the indian crust zircon data for the swat granite gneiss from the northern part of the loe sar dome give an emplacement age of 267 6 3 ma which is at variance with earlier correlations favoring an early paleozoic origin subsequent to metamorphic overprint by the himalayan orogeny the swat granite was intruded by late kinematic alkali granite dykes single zircons from one of these dykes show reproducible 206pb 238u data giving a precise mean age of 29 26 0 12 ma whereas the 207pb 235u ages scatter between 34 and 81 ma pointing to huge and variable enrichment in 207pb the unsupported 207pb can be explained by incorporation of 231pa an intermediate long lived daughter nuclide in the 235u decay chain in excess of the secular equilibrium ratio la icp ms measurements confirm the presence of unsupported 207pb but do not show any correlation between the latter and other selected trace element concentrations in these zircons a concordant ar ar muscovite age of 28 4 1 1 ma obtained for the same dyke postdates regional mica cooling ages and indicates a lack of younger regional events capable of resetting the k ar system in muscovite because the dyke is pre to synkinematic relative to normal faulting and related north vergent folds its emplacement age provides a maximum age for this event or reflects already ongoing local extension a lower limit of 15 ma has previously been established by apatite fission track analysis the 29 15 ma age bracket for normal faulting is coeval with extension along the south tibetan detachment system stds on the north side of the high himalaya this suggests that the indus suture in pakistan has acted as a western continuation of the stds and that related faulting was roughly contemporaneous over most of the himalaya

crustal structure of northern latium central italy from receiver functions analysis new evidences of a post collisional back arc margin evolution abstract the crustal velocity structure in a region of central apennines of italy at the hinge between the highly stretched portion of the monte argentario promontory and the magmatic province of the tolfa domes complex northern latium is discussed in this study s wave velocities at depth have been constrained by the modeling of p wave receiver functions rf from both temporary and permanent broadband seismic stations the computer 3d vs models show a thin crust 19 25 km made of a shallow and thin sedimentary cover a very high velocity and anisotropic layer related to a metamorphic basement and a low vs anisotropic layer in the middle lower crust above a shallow moho discontinuity modeled at about 20 km depth the volcano tectonic evolution of this portion of tyrrhenian back arc margin has been strongly influenced by its peculiar crustal architecture the low vs layer acted as a shear zone in the middle lower crust during the tyrrhenian extension also helping the development of plio quaternary magmatism our findings potentially give new constraints on the evolution of the area and to the general comprehension of back arc development in collisional regions

compressional velocity structure and anisotropy in the uppermost mantle beneath italy and surrounding regions travel times of about 39 000 pn arrivals recorded from regional earthquakes by the italian telemetered seismic network and by stations of nearby countries are inverted to image lateral variations of seismic velocity and anisotropy at subcrustal depth in italy and surrounding regions this method allows simultaneous imaging of variations of pn velocity and anisotropy as well as crustal thickness variations the po plain the adriatic sea and the ionian sea have normal to high pn velocities in contrast lower velocities 7 9 8 0 kin s are imaged in italy beneath the western alps the northern apennines and eastern sicily and nearby calabria as well as in northern albania and beneath the pannonian basin low pn velocities beneath the northern apennines correlate with present day extension and may have resulted from thermal anomalies in the uppermost mantle possibly due to delamination processes low velocities are consistent with the high attenuation zone inferred in the uppermost mantle beneath the internal apennine units and the tyrrhenian margin of the peninsula by mele et al 1996 1997 on the contrary low velocities beneath the western alps may be an apparent effect due to the abrupt thickening of the crustal roots pn velocity is anisotropic in the study area with a maximum amplitude of 0 2 km s the largest anisotropic velocity anomalies are observed along the major arc structures of italy i e the northern apennines and the calabrian arc indicating that these features are controlled by uppermost mantle processes the anisotropy anomaly along the calabrian arc extends as far as albania but ends abruptly north of this area suggesting that a lithospheric discontinuity is present along the northern albanian border

seismic anisotropy beneath the northern apennines italy and its tectonic implications we examined shear wave splitting in sks and s phases from 22 teleseisms at 10 temporary stations on a transect across the northern apenninic arc the array near 43 n spans from corsica island across the tyrrhenian region and the apenninic belt to the adriatic coast we applied particle motion covariance matrix decomposition and cross correlation methods to estimate the polarization direction of the fast split shear wave and the delay time between split phases t most of the analyzed shear waves show clear evidence of splitting the in the adriatic foreland and in the apennines are approximately parallel to the strike of the mountain belt nw se the largest t correspond to the highest elevations suggesting that anisotropy is related to the compressional tectonics which built the apennines and that this tectonic compression involved at least the entire lithosphere in the tyrrhenian area we observe oriented about e w suggesting a reorientation of the mantle fabric due to astenospheric flow responsible for the e w post orogenic extension observed at the surface

2d coda and direct wave attenuation tomography in northern italy abstract a 1d coda method was proposed by mayeda et al 2003 in order to obtain stable seismic source moment rate spectra using narrowband coda envelope measurements that study took advantage of the averaging nature of coda waves to derive stable amplitude measurements taking into account all propagation site and s to coda transfer function effects recently this methodology was applied to microearthquake data sets from three subregions of northern italy i e western alps northern apennines and eastern alps because the study regions were small ranging between local to near regional distances the simple 1d path assumptions used in the coda method worked very well the lateral complexity of this region would suggest however that a 2d path correction might provide even better results if the data sets were combined especially when paths traverse larger distances and complicated regions the structural heterogeneity of northern italy makes the region ideal to test the extent to which coda variance can be reduced further by using a 2d q tomography technique the approach we use has been developed by phillips et al 2005 and is an extension of previous amplitude ratio techniques to remove source effects from the inversion the method requires some assumptions such as isotropic source radiation which is generally true for coda waves our results are compared against direct s wave inversions for 1 q and results from both share very similar attenuation features that coincide with known geologic structures we compare our results with those derived from direct waves as well as some recent results from northern california obtained by mayeda et al 2005 that tested the same tomographic methodology applied in this study to invert for 1 q we find that 2d coda path corrections for this region significantly improve upon the 1d corrections in contrast to california where only a marginal improvement was observed we attribute this difference to stronger lateral variations in q for northern italy relative to california

crustal and uppermost mantle structure in italy from the inversion of p wave arrival times geodynamic implications summary in this paper we present a 3 d image of the p wave velocity structure in the crust and uppermost mantle beneath italy obtained by inverting p wave arrival times of crustal earthquakes we used about 48000 arrival times at stations close to the epicentres within 200 km to mitigate the eiects of both reading errors and intrinsic complexity for long distance ray paths due to the scale of heterogeneities in the earth structure beneath italy whereas two of the inverted layers located in the lower crust and beneath the moho are well resolved by the data the upper crustal layer has regions of relatively poor resolution beneath the central apennines due to the sparse station spacing we made several attempts varying the moho geometry to obtain reliable and stable results without introducing too complex and unconstrained ap rioriinformation one of the most important results is the discovery of low velocity anomalies at 38 km depth beneath the northern apenninic and calabrian arcs which we interpret as subducted crustal material of the adriatic and ionian lithospheres in the lower crust beneath the entire apennines a pronounced low velocitybelt is present suggesting high temperatures in front of the bent adriatic lithosphere based on our results and on those previously obtained from seismic tomography we propose amodel for the geodynamic evolution of the apenninic system in which the present day scenario re ects lateral heterogeneities in the subducting ionian oceanic and adriatic continental lithosphere

upper crustal tomographic images of the amiata vulsini geothermal region central italy we computed the three dimensional p wave velocity structure of the upper crust beneath the adjacent amiata and vulsini quaternary volcanoes central italy inverting local earthquake arrival times we used 676 selected earthquakes out of more than 3000 in the m range 1 5 4 0 located between 1977 and 1992 by two contiguous microseismic networks operated by ente nazionale energia elettrica to monitor three geothermal areas namely latera torre alfina and mount amiata the resolving capability of the data set has been verified both with a priori synthetic tests and an a posteriori analysis of the resolution matrix we find a 40 25 7 h km3 crustal volume where we can resolve details as small as 2 to 4 km our analysis is favored by numerous geological and geophysical data collected for geothermal exploration these independent data give us specific constraints for both choosing a starting model and interpreting tomographic results we find high velocity anomalies in the upper 3 km of the crust beneath latera torre alfina and mount amiata geothermal fields related to uplifted limestone units the lateral extension of limestone units is defined by the three dimensional velocity pattern a negative anomaly clearly identifies the radicofani graben a plio quaternary depression filled with low velocity clayey sediments between 1 and 3 km depth a sharp gradient between high velocities 6 9 km s in the northern region and lower velocities in the southern one is recovered at 7 km depth this feature may indicate the transition between the tuscan province uplifted metamorphic crust and thickened carbonate series of the latium province

automatic seismic phase picking and consistent observation error assessment application to the italian seismicity summary accuracy of seismic phase observation and consistency of timing error assessment define the quality of seismic waves arrival times high quality and large data sets are prerequisites for seismic tomography to enhance the resolution of crustal and upper mantle structures in this paper we present the application of an automated picking system to some 600 000 seismograms of local earthquakes routinely recorded and archived by the italian national seismic network the system defines an observation weighting scheme calibrated with a hand picked data subset and mimics the picking by an expert seismologist the strength of this automatic picking is that once it is tuned for observation quality assessment consistency of arrival times is strongly improved and errors are independent of the amount of data to be picked the application to the italian local seismicity documents that it is possible to automatically compile a precise homogeneous and large data set of local earthquake pg and pn arrivals with related polarities we demonstrate that such a data set is suitable for high precision earthquake location focal mechanism determination and high resolution seismic tomography

passive seismology and deep structure in central italy in the last decade temporary teleseismic transects have become a powerful tool for investigating the crustal and upper mantle structure in order to gain a clearer picture of the lithosphere asthenosphere structure in peninsular italy between 1994 and 1996 we have deployed three teleseismic transects in northern central and southern apennines in the framework of the project geo modap european community contract ev5v ct94 0464 some hundreds of teleseisms were recorded at each deployment which lasted between 3 and 4 months although many analyses are still in progress the availability of this high quality data allowed us to refine tomographic images of the lithosphere asthenosphere structure with an improved resolution in the northern and central apennines and to study the deformation of the upper mantle looking at seismic anisotropy through shear wave splitting analysis also a study of the depth and geometry of the moho through the receiver function technique is in progress tomographic results from the northernmost 1994 and the central 1995 teleseismic experiments confirm that a high velocity anomaly hva does exist in the upper 200 250 km and is confined to the northern apenninic arc this hva already interpreted as a fragment of subducted lithosphere is better defined by the new temporary data compared to previous works based only on data from permanent stations no clear high velocity anomalies are detected in the upper 250 km below the central apennines suggesting either a slab window due to a detachment below southern peninsular italy or a thinner perhaps continental slab of adriatic lithosphere not detectable by standard tomography we found clear evidence of seismic anisotropy in the uppermost mantle related to the main tectonic processes which affected the studied regions either ne sw compressional deformation of the lithosphere beneath the mountain belt or arc parallel asthenospheric flow both giving nw se fast polarization direction and successive extensional deformation e w trending in the back arc basin of northern tyrrhenian and tuscany preliminary results of receiver function studies in the northern apennines show that the moho depth is well defined in the tyrrhenian and adriatic regions while its geometry underneath the mountain belt is not yet well constrained due to the observed high complexity

gravity modelling along the ecors crop vertical seismic reflection profile through the western alps abstract new gravity data from 500 stations and results from all previous surveys on the western alps are used to compile a detailed profile along the ecors crop vertical seismic profile the bouguer anomaly consists of two approximately two dimensional regional features namely a wide negative anomaly occurring on the central part of the belt and the pronounced positive anomaly of the geophysical ivrea zone at the border between the alps and the po plain the results of a wide angle seismic campaign and the preliminary line drawing from the vertical seismic have been the main constraints for the modelling of the anomaly two models are proposed their common feature is a piling up of the crust upper mantle units in the penninic zone of maximum crustal thickness as well as in the ivrea zone the contribution of the apulian lower crust to the positive anomaly is greater than formerly suggested several hypotheses are put forward for the zones where reasonable seismic information is available as an illustration of the uncertainties surrounding their geological interpretation the density models are consistent with the hypothesis of lithospheric accretionary processes for the collision between the european and apulian plates

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

the southern tyrrhenian subduction zone deep geometry magmatism and plio pleistocene evolution abstract we report on a high resolution vp vp vs and qp model of the southern tyrrhenian subduction zone obtained by the inversion of p and s wave arrival times and t values from intraslab seismicity the arcuate shape of the southern apennines calabrian arc sicilian maghrebides is perfectly mirrored by two rather continuous low and high vp bands lying beneath the belt system at ca 25 and 100 km respectively between 100 and 300 km two independent high vp slabs lie beneath the neapolitan region and the southern tyrrhenian sea separated by unperturbed mantle we suggest that the ca 150 km wide slab window beneath the southern apennines opened after a tear occurring within a composite subduction system formed by the apulian continental lithosphere and the ionian oceanic slab the abrupt slab rupture induced ultrafast southeastward retreat of the ionian slab and the 19 cm yr spreading of the back arc oceanic marsili basin between ca 2 1 and 1 6 ma ago the 25 km low vp zone beneath the arc denotes continental upper crustal rocks below the chain its striking continuity requires a unique orogenic wedge at 25 km depth below the southern apennines the calabrian arc and the sicilian maghrebides the alternative explanation would imply the ubiquitous occurrence of autochthonous lower plate rocks at 25 km depth i e a puzzling autochthonous continental calabria the ionian slab beneath calabria shows high vp high qp and low vp vs anomalies typical of old oceanic lithosphere intermediate depth seismicity is concentrated within its thin oceanic crust suggesting the occurrence of vigorous metamorphism the slab dehydration promotes the melting of the overlying mantle as testified by high vp vs and low qp anomalies between the slab and the aeolian magmatic arc

reliability of earthquake location procedures in heterogeneous areas synthetic tests in the south western alps italy abstract the accuracy of procedures for locating earthquakes and tomographically imaging 3 d velocity structures is influenced by factors such as network geometry errors in picking seismic phases modeling errors and velocity model uncertainties the main purpose of this study is to investigate the importance of different error sources through synthetic experiments the synthetic data sets were generated for a realistic 3 d velocity model of the south western alps adopting a precise raytracing technique the actual station configuration and recorded seismicity during the passive seismological experiment geofrance3d alps conducted between august 1996 and february 1997 were used the station configuration corresponded to an enhancement of the regional networks operating in the area with the addition of temporary stations in addition synthetic data sets were corrupted by applying different error schemes furthermore to assess the locating capabilities of the regional networks synthetic data sets were constructed for synthetic events placed in correspondence to the nodes of a regular three dimensional 3 d grid we mimicked the actual data management scheme for synthetic data processing we re located the earthquakes performed an inversion for a minimum 1 d velocity model with station corrections and then ran a complete 3 d velocity model inversion one of the main results confirming earlier studies was that earthquake locations in strongly heterogeneous areas obtained using a regional 1 d model can have significant errors even a minimum 1 d model with station corrections does not significantly improve the accuracy of parameter locations in the south western alps for high precision locations a 3 d model is needed however a 3 d model cannot be reconstructed from noise contaminated data recorded by a sparse regional network

probing the sources of ambient seismic noise near the coasts of southern italy 1 in this study we probe the source of ambient noise in the southern apennines and the calabrian arc by crosscorrelating two months of ambient seismic noise records collected during the calabria apennine tyrrhenian subduction collision acretion network cat scan project significant rayleigh wave energy is observed on the vertical component of the noise correlation stacks and reveals multiple sources of ambient noise in southern italy the most dominant noise sources are found along 1 the tyrrhenian coast of northern calabria southern campania and 2 the adriatic sea near the gargano promontory enhanced ocean currents evident from buoy records during the study period could be responsible for the observed microseisms we validate the source locations using earthquake records and the consistency between noise and earthquake correlation functions supports the observed dominant directions of ambient seismic noise citation gu y j c dublanko a lerner lam k brzak and m steckler 2007 probing the sources of ambient seismic noise near the coasts of southern italy geophys res lett 34 l22315 doi 10 1029 2007gl031967

a 3d vs model of the upper mantle beneath italy insight on the geodynamics of central mediterranean abstract we compute a high resolution vs model of the upper mantle underneath italy by inverting relative residuals of s wave arrivals from teleseisms recorded at the italian broad band national seismic network we also present a model of vp vs perturbations obtained from similarly resolved p and s wave velocity models the joint analyses of vs and vp vs models suggests that compositional variations concur with temperature variations to generate the observed velocity patterns giving deeper insight into the upper mantle structure the investigation of coherent high vs and high vp anomalies permits a comprehensive picture of the main oceanic domains involved in the puzzling subduction system of the central mediterranean slab windows and tears developed in the ionian slab are highlighted by regions of low vp low vs and high vp vs anomalies the adria continental lithosphere is characterized by high vp high vs and low vp vs anomalies that trace the sinking of eclogitized material underneath the apennines and the eastern alps chains the overall tomographic results yield the development of a new conceptual model for the alps and apennines formation in which three basic processes occurred in different time and different locations all around the alpine apennines system continental collision slab break off and delamination of the upper plate lithosphere

interactions between mantle upwelling drainage evolution and active normal faulting an example from the central apennines italy summary in this paper we show that the processes that have shaped the quaternary surface development of the apennines in central italy are all consequences of a single subcrustal process the upwelling of the mantle the relationship between gravity and topography shows that mantle convection is responsible for a long wavelength 150 200 km topographic bulge over the central apennines and stratigraphic evidence suggests this bulge developed in the quaternary active normal faulting is localized at the crest of this bulge and produces internally draining fault bounded basins these basins have been progressively captured by the aggressive headward erosion of major streams that cut down to the sea on the flanks of the regional bulge the only surviving closed basins are those on the apennine watershed most distant from the marine base level where continued normal faulting is still able to provide local subsidence that defeats their capture by the regional drainage network understanding the competition between regional capture and local fault related subsidence of intermontane basins is crucial for recognizing potentially hazardous active faults in the landscape and also for interpreting the sediment supply to adjacent offshore regions central italy provides a good modern analogue for processes that are probably common in the geological record particularly on rifted margins and intracontinental rifts but may not have been fully appreciated

new evidence for the serpentinization of the palaeozoic basement of southeastern sicily from joint 3 d seismic velocity and attenuation tomography

application of revised ray tracing migration to imagine lateral variations of seismic fabric corresponding to different tectonic styles in the northern apennines abstract migration of zero offset seismic sections of deep crust can be done with methods based on ray tracing we modify the classical ray tracing migration method rtm introducing a consistency check to control whether back propagated rays satisfy the condition of strict normal incidence at the migrated reflector a synthetic test shows the effectiveness of the method in particular the control of normal incidence allows elimination of physically inconsistent reflectors from the migrated section then rtm is applied to a crustal seismic profile acquired in central italy using a velocity model obtained from wide angle data that reproduces the gross structures of the apenninic crust the lateral variation of the seismic fabric shown from the migrated section reveals the presence of coexisting extensional and compressional tectonic regimes kinematic diffraction modelling gives additional information about both the distribution of seismic velocities and major active geodynamic processes in the upper lithosphere the migrated section supports the subdivision of northern apennines in two tectonic regions a stretched upper plate tuscany and northern thyrrenian supported by a rise of the asthenosphere and a downwarped lower plate adria subducted below the mountain belt

three dimensional p and s wave velocity structures beneath taiwan deep structure beneath an arc continent collision the island of taiwan is a byproduct of one of the few active collisions between a continent represented by the eurasian continental shelf and an island arc represented by the northern extension of the luzon arc on the philippine sea plate to understand better the evolution and current tectonics of this collision we selected 1260 well recorded earthquakes from an initial set of 50 000 located by the taiwan telemetered seismograph network for the determination of one and three dimensional p and s wave velocity structures beneath the island the results for both structures and earthquake relocations reveal that the island is divided tectonically into three distinct zones in the east the philippine oceanic plate is underthrusting the eurasian plate east of a north south boundary that is well defined by both seismic activity and a region of high velocity in the south the eurasian continental plate is underthrusting the philippine sea plate south of an east west boundary at about 23 n that is sharply defined by both subcrustal seismicity and a zone of relatively low velocities the dip of the subducted continent is shallow until it reaches the luzon island arc 50 km east of the main island structure under the main part of the island north of 230n reveals a shallow dipping zone of low velocities in the west above 25 km depth that narrows and steepens below that depth to at least 50 km beneath the central range the dip of this low velocity region is outlined by a narrow zone of seismicity that extends to depths of 100 km this seismic zone lies in a velocity saddle and marks an apparent offset in the central low velocity region at 24 n evidence for the subduction of the eurasian continent beneath taiwan therefore exists everywhere beneath the island and the low velocity regions in the mantle support but do not require the subduction of some 6 16 km of lower continental crust to depths of at least 50 km the distinct change in both the velocity structure and the seismic activity at 23 n and the offset of the low velocity regions at 24 n argue for abrupt changes in the nature of subduction across these latitudes these changes may be caused by an interaction of the luzon island arc with the subducted continental shelf that mimics a similar interaction evident at the surface finally the velocity structure of the subducting philippine sea plate suggests that the earthquakes beneath 70 km depth are not occurring within the highest velocity regions of the plate but are probably located near the upper edge of the plate there is also evidence from earthquake locations and velocity structure that suggests that the subducting plate is segmented and that subduction is presently occurring as far south as 22 n

crustal shortening and duplication of the moho in the northern apennines a view from seismic refraction data abstract a reappraisal of the dss refraction seismic campaigns of 1978 and 1974 in the northern apennines and the northern tyrrhenian sea after digitization of the original analog data and a new interpretation of crustal structures are presented in this paper the layering of the adria crust consists of a low velocity lower crust topped by a 6 7 km s horizon and an upper crust again formed by a low velocity layer capped by a faster one in the tuscany sector the crust mantle boundary and lower crust show attenuated velocities and a reduced thickness with respect to the adriatic counterpart these differences are due to the extensional tectonics restricted to tuscany and occurred in a high heat flow regime related to an uplifting astenosphere it has been confirmed that a deep thrust is responsible for moho doubling in correspondence with the zero bouguer anomaly line the tuscan moho overlaps the umbro marchean one for a length of about 30 km it is hypothesized that another shallower thrust involves upper crust in the mid tuscany range mt cetona and perugia massifs had their roots in the mantle and that subsequent extensional tectonics obliterated every trace of thrusting in lower crust and mantle rocks no conclusive proof of the existence of a european moho below a tuscan one in the area underneath elba has yet been found revision of dss data excludes the presence of a refractor reflector 60 km deep the same data however are compatible with the existence of a crust mantle boundary at 30 35 km depth

continental subduction and three dimensional crustal structure the northern south island new zealand the three dimensional vp and vp vs structure of a region where subduction transitions to oblique transform faulting has been determined using arrival times from 579 local earthquakes recorded during a temporary deployment and 3146 earthquakes have been relocated between 40 km and 100 km depth the subducted plate is imaged as a relatively low velocity feature in the uppermost mantle reflecting the continental nature of the subducted crust in this region an increase in amplitude of this low velocity feature from northeast to southwest can be related to an increase in the thickness of the crust of the subducted plate in this direction velocity variations within the subducted and overlying plates show some spatial correlation this suggests an interaction between the plates which extends well beyond the plate interface and is consistent with other geophysical and geological evidence that the plate interface beneath marlborough is currently not accommodating much active subduction in the overlying plate the awatere fault is a major structural feature associated with a low velocity zone extending to 23 km depth there is a marked change in structure near this fault with seismic velocities being lower to the southeast a relatively high level of seismicity occurs in this region of lower seismic velocities suggesting a relationship between the two a possible explanation for this is elevated pore pressures caused by fluids derived from dehydration of the continental subducted crust the low velocity region in the overlying plate coincides with the region of most intense active deformation suggesting it is relatively weak

mapping the moho of the western alps by wide angle reflection seismics abstract a new picture of the moho beneath the western alps could be obtained using wide angle reflection seismic data this picture in addition to its increased sharpness clearly shows how the moho deepens down to the root zone of the chain 55 km a 25 30 km deep reflector with upper mantle characteristics is discovered under the brianconnais zone where it overlies the autochthonous moho this unit does not seem to connect to the so called ivrea body situated much shallower and farther into the chain it supports a hypothetical flaking of the european lithosphere beneath the western alps farther east the moho beneath the po plain is clearly mapped too with a crustal thickness increasing in steps from 25 to 35 km this p wave moho picture is compared with an s wave picture and major differences appearing in the middle crust are discussed finally the seismic response of the moho is investigated and is shown to be shifted towards low frequencies in the inner zones of the chain this could partly explain why the ecors crop vertical seismic line equipped with high frequency geophones faltered over the identification of the deep alpine moho

seismic moment summation for historical earthquakes in italy tectonic implications tectonic deformation rates in and around the apennine mountains of italy are studied using seismic moments estimated from macroseismic effects of historical earthquakes northeastward extension in the northern apennines north of 42 5 n accompanies shortening along their northeast flank since the seventeenth century the sparse seismicity in these two zones has included no earthquake with magnitude 6 5 or seismic moment above 6 1018 n m their spatially averaged deformation rates are only 0 3 mm yr 1 but are equal such that the extension and shortening balance with no relative motion between their external surroundings in contrast the numerous historical earthquakes in the central and southern apennines with magnitude 7 and seismic moment 20 1018 n m require northeastward relative velocity across the deforming zone up to 5 mm yr 1 matching the expected relative motion of their surroundings this relative velocity is taken up in part by extension and in part by strike slip depending on the trend of the deforming zone and is not accompanied by en echelon shortening elsewhere in italy the northern apennines thus show different senses and rates of deformation from localities farther south and are thus technically distinct at present in contrast with previous interpretations

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

crustal structures in the central eastern alpine sector a revision of the available dss data abstract in the alpine sector east of the giudicarie line the investigation of crustal structure is less developed than in the western and central sectors because seismic near vertical reflection nvr profiles are not yet available however it is felt that a revision by a complete homogeneous reinterpretation of several refraction wide angle reflection profiles or deep seismic soundings dss recorded during different phases of the early exploration will help in defining a model of the deep crust and of the moho boundary in the whole area from the central to the eastern alps six interpretative cross sections are proposed as the final output of the seismic modelling as well as a map of the crust mantle boundary the main results of this investigation are the following the lower crust and the moho beneath the northern alps show a fairly homogeneous structure the seismic velocity of the european lower crust is anomalously low while in the north the southward dip of the bottom of the european crust is of about 12 in the center of the investigated area its dip is reduced to about 6 in this zone of flatter moho a complex crust mantle transition is observed the northern strip of the adriatic crust appears highly fragmented into small blocks each block dipping in different directions n ne nw as far as the relationship between the surface tectonic features and the deep crustal structure is concerned it is found that while the edge of the adriatic moho is fairly coincident with the periadriatic lineament in its western sector tonale line it appears to be strongly displaced in the eastern one pustertal line also in the eastern alps in agreement with the interpretation of the european geotraverse crossing eastern swiss alps and lombardian southern alps a wedge of the adriatic lower crust overrides the more ductile european crust protruding northwards beyond the edge of the adriatic moho these results can help to better investigate the complex interactions between the european and adriatic plates as well as to study the relationships between deep and surface structures

three dimensional p velocity structure in the region of the ms 6 9 irpinia italy normal faulting earthquake abstract we have calculated the three dimensional velocity structure in the epicentral region of the 1980 irpinia southern italy earthquake using thurber s inversion technique for hypocenter and velocity parameters particular care was given to the evaluation of the resolution of the models because of the poor reading accuracy of the analog stations operating at that time we analyzed the averaging vector for each node of the model in order to estimate the degree of smearing within the final tomographic image this approach is suitable for determining the best parametrization to use i e the minimum grid spacing and for evaluating the region where the computed velocities are meaningful the results show that the main rupture occurred along a sharp nw se trending velocity contrast which probably reflects a crustal discontinuity the velocity variations along the fault probably due to lithological heterogeneities account for the complex character of this earthquake based on the velocity distribution at depth the secondary rupture that started about 40 s after the mainshock is interpreted to be the result of reactivation of an old thrust as a normal fault

upper crustal structure of the benevento area southern italy fault heterogeneities and potential for large earthquakes summary the benevento region is part of the southern apennines seismogenic belt which experienced large destructive seismic events both in historical and in recent times the study area lies at the northern end of the irpinia fault which ruptured in 1980 with a ms 6 9 normal faulting event which caused about 3000 casualties the aims of this paper are to image lateral heterogeneities in the upper crust of the benevento region and to try to identify the fault segments that are expected to generate such large earthquakes this work is motivated by the recognition that lithological heterogeneities along major fault zones inferred from velocity anomalies reflect the presence of fault patches that behave differently during large rupture episodes in this paper we define the crustal structure of the benevento region by using the background seismicity recorded during 1991 and 1992 by a local seismic array these data offer a unique opportunity to investigate the presence of structural discontinuities of a major seismogenic zone before the occurrence of the next large earthquake the main result that we obtained is the delineation of two nw trending high velocity zones hvzs in the upper crust beneath the matese limestone massif these high velocities are interpreted as high strength regions that extend for 30 40 km down to at least 12 km depth the correspondence of these hvzs with the maximum intensity regions of historical earthquakes 1688 ad 1805 ad suggests that these anomalies delineate the extent of two fault segments of the southern apenninic belt capable of generating m 6 5 7 earthquakes the lateral offset observed between the two segments from tomographic results and isoseismal areas is possibly related to transverse right lateral faults

crustal structure and moho geometry beneath the northern apennines italy 1 we used receiver functions rfs from broad band seismic stations to investigate the crustal structure of the northern apennines italy additionally we use data obtained in this study to provide initial constraints for a map of the moho depth of italy ten stations were deployed along a transect n75 e during the 1994 geomodap project rf analysis shows the presence of lateral variations in the crust we observed patterns of symmetric and anti symmetric converted phases from radial and tangential rfs vs back azimuth these patterns can be explained by the presence of dipping interfaces and or anisotropy within the crust we then inverted rfs following the inversion scheme proposed by sambridge 1999 the results show the presence of s velocity inversions in the lower crust beneath the apennines the upwelling of moho in the tyrrhenian area and its progressive deepening from the tyrrhenian sea toward the adriatic coast

two ship deep seismic soundings in the basins of the eastern mediterranean sea pasiphae cruise summary new results from a two ship refraction and oblique reflection deep seismic cruise are presented to discuss the nature of the crust in the ionian sirte and herodotus abyssal plains these expanding spread profiles were processed and analysed in both the x t and p domains arrival times of reflected and refracted branches are matched by ray tracing in both domains in spite of a shallow evaporitic sequence messinian evaporites deposited on top of a thick sedimentary pile responsible for velocity inversions on many profiles we obtain excellent velocity control down to moho depth pmp and pn 8 4 8 6 km s 1 arrivals are observed the three basins have a relatively thin crust 8 to 11 km overlain by a thick sedimentary cover up to 10km in the herodotus abyssal plain the moho boundary and main crustal units identified in the basins can be followed beneath the calabrian prism to the west and beneath the mediterranean ridge to the east the crustal structure is of oceanic type for both the ionian and sirte basins where typical oceanic layer 2 and 3 are recognized the thin crust of the herodotus basin may be interpreted either as oceanic or thinned continental crust about 10 km thick the top of the crust of the herodotus basin is much deeper therefore the herodotus basin is probably significantly older than the ionian basin triassic versus early cretaceous in age

seismicity and p wave velocity image of the southern tyrrhenian subduction zone summary this paper focuses on the deep earth structure and earthquake distribution within the southern tyrrhenian subduction zone we discuss seismological observations which provide insight into the mechanics of subduction processes for an unusual compressional margin the motivation for this work derives from the recognition that little is known about one of the most intriguing geodynamic features of the italian peninsula and the fact that a large amount of information can be extracted from data collected by the istituto nazionale di geofisica national seismic network we show that the hypocentres of intermediate and deep earthquakes that have occurred since 1988 image a nw dipping plane continuous from the ionian sea to the tyrrhenian down to 450 km depth we also present a 3 d model of the deep structure beneath southern italy derived using deep earthquake seismic tomography tomographic images reveal a high velocity body dipping from the apulian and iblean forelands towards the tyrrhenian basin in the crust and upper mantle at least down to 320 km depth this high velocity body may be related to the cold subducted ionian lithosphere earthquake hypocentres are confined within the high velocity body delineating the subduction beneath the calabrian arc

seismicity in central and northern apennines integrating the italian national and regional networks abstract in this paper we present and discuss an improved picture of the seismicity distribution of the umbria marche abruzzi apennines as obtained through the integration of the national and the regional seismic networks operating from 2002 to 2006 during this period both the istituto nazionale di geofisica e vulcanologia ingv national seismic network and the regional networks have been greatly improved we compare the results of the integrated catalogue obtained in this study with the catalogue of the italian seismicity between 1981 and 2001 castello b selvaggi g chiarabba c amato a 2006 csi catalogo della sismicita italiana 1981 2002 versione 1 1 ingv cnt roma http legacy ingv it csi confirming the basic known features of the seismic activity in the region but also evidencing some original and interesting results in particular the new data set allows us to better define the geometry and kinematics of the crustal seismicity which is confined to the upper 20 km and shows a clear general deepening from west to east in the crust we find additional evidence of extensional seismicity below the central portion of the belt and thrust reverse faulting mechanisms at the outer fronts of the apennines looking at the seismicity along the belt it is also possible to observe aseismic regions which could be due to either locked or creeping portions of the apenninic fault system at greater depth the west dipping seismicity distribution down to about 70 km confirms the hypothesis of a slab of adriatic lithosphere subducted below the apennines but also suggests that there are strong lateral heterogeneities and possibly tears in the slab

the deep seismicity of the tyrrhenian sea the deep seismicity of the tyrrhenian sea is analysed using data from a new instrumental catalogue of the seismicity of the italian area we use algorithms for the determination of absolute and relative hypocentral locations and for the evaluation of the geometry and coherence of the state of stress within the subducting slab the structure of the benioff zone although simpler than previously indicated reveals anomalous traits both in the seismicity distribution and in the stress geometry confirming that standard subduction models cannot be applied in the tyrrhenian region the velocity anomaly and the location of few isolated events indicate that the subducted slabs extend to the north along the apenninic chain approximately to the latitude of the irpinia region in central italy 42 n

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

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

from collisional to rifted basins an example from the southern calabrian arc italy structural interpretation of available geological and geophysical data carried out along a regional transect extending across the southern calabrian arc from the tyrrhenian margins to the ionian off shore demonstrates that a complex interplay between compressional and extensional processes has controlled the evolution of upper miocene pleistocene sedimentary basins developing in this region our data indicate that an upper miocene lower pliocene succession outcropping in the southern calabrian arc represents the infilling of perched basins developed between crystalline basement thrust sheets a similar tectonic pattern characterises the plio pleistocene basins occurring on the frontal part of the arc in the ionian off shore upper pliocene pleistocene sediments outcropping along the tyrrhenian side of the arc reveal that they in fact represent the infilling of extension related basins time space migration of compressional and extensional related sedimentary basins can be explained as the result of different tectonic processes developing on the upper plate as a result of the underplating of the ionian domain beneath the calabrian block in this framework upper miocene lower pliocene and upper pliocene pleistocene perched basins represent therefore fore arc basins developed on the frontal accretionary wedge and or on the hangingwall buttress of the arc during its southeastwards migration late pliocene early pleistocene extensional tectonics occurring along the tyrrhenian side of the arc may indeed be related to accommodation processes which characterised the rear of the wedge to maintain a stable geometry as a result of the underplating of the ionian crust

subcrustal earthquakes in the northern apennines italy evidence for a still active subduction previously unreported subcrustal earthquakes have been located up to 90 km depth beneath the northern apennines italy these earthquakes occur beneath a zone of abundant upper crustal seismicity mostly confined to the upper 20 km of the crust although there are relatively few well located subcrustal earthquakes there appears to be a general southwestward deepening of the hypocenters from the adriatic to the tyrrhenian sea consistent with other geophysical data which suggest that the adriatic lithosphere is presently subducting beneath the northern apennines

deep structure of the alps what do we really know abstract in the last five decades the deep structure of the alps has been probed by every geophysical method applicable and the resulting amount of data is unmatched for any other orogen in this study an attempt is made to review the data and the proposed structural models with the aim of separating the certain from the probable and from the speculative information this can be achieved by first reviewing the theoretical resolving power and ambiguity of the applied interpretation methods and then analysing the proposed models the methods reviewed are inversion of surface wave data teleseismic and local earthquake seismic tomography near vertical reflection seismology wide angle reflection and refraction seismology and gravity modelling all information about the moho rated as certain is combined to give a moho map of the alpine area the information rated as certain and probable and additional qualitative arguments are used to discuss a crustal model of the western and central alps represented by two cross sections major structural elements in this crustal model are a thick overthrust penninic nappe system wedging at mid to lower crustal levels a discontinuous moho and strong variations along the strike of the orogen whereas the structures of the european upper crust and of the penninic nappe system are well constrained only few and isolated lower crustal structural elements are rated as certain finally the shape of the lower lithosphere in the alps is discussed by review and comparison of the results from surface wave teleseismic travel time residual and tomographic studies qualitative arguments suggest the existence of a lithospheric root or slab beneath the alps probable tomographic information suggests a south vergent european lithospheric slab beneath the southern alps and the po plain despite the considerable number of studies aimed at resolving the deepest part of alpine orogeny the available quantitative information on the sub moho structure cannot be rated as certain

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km

understanding the structural setting in the southern apennines italy insight from gravity gradient tensor abstract the lucania apennines form the frontal part of the apennines in southern italy this orogenic belt was formed in response to late miocene early pleistocene shortening and allochthon emplacement toward the northeast and was subsequently affected by extensional faulting which migrated to northeast ahead of the thrust system as a result contraction structures are found associated to pliocene early pleistocene thrust top basins in the ne part of the area whereas extensional faults shape middle pleistocene holocene basin on the sw sector the main structural grain of the belt is nw se but e w structures are widespread in the area as a result of phases of non coaxial thrusting and strike slip faulting the analysis one by one of the components of the gravity gradient tensor ggt has proved to yield a fine image of the structural setting of the investigated area ggt is a second rank tensor containing the second spatial derivatives of the gravity potential and in this paper is used instead than the more traditional gravity data the tzz component allows an accurate description of the location and of the shape of basins and other structures but different components of the ggt provide even more detailed insights for such structures in particular we found that the tzy and tyy locate well those structures trending closer to the e w direction for both thrust top and extensional basins and their termination against the main nw se structures the combined use of components of ggt provides a finer definition of the anomaly sources particularly if a good knowledge of their strike and depth is independently estimated with other geological and geophysical investigations

crustal structure and moho depth profile crossing the central apennines italy along the n42 parallel 1 we present results from a teleseismic receiver function study of the crustal structure in the central apennines italy data from 15 stations deployed in a linear transect running along the n42 parallel were used for the analysis a total number of 364 receiver functions were analyzed the crustal structure has been investigated using the neighborhood algorithm inversion scheme proposed by sambridge 1999a obtaining crustal thicknesses bulk crustal vp vs ratio and velocity depth models in each inversion the degree of constraint of the different parameters has been appraised by the bayesian inference algorithm by sambridge 1999b the study region is characterized by crustal complexities and intense tectonic activity recent volcanism orogenesis active extensional processes and these complexities are reflected in the receiver functions however the relatively close spacing among the seismometers about 20 km helped us in the reconstruction of the crustal structure and moho geometry along the transect crossing the apennines from west to east the moho depth varies by more than 20 km going from a relatively shallow depth around 20 km on the tyrrhenian side deepening down to about 45 km depth beneath the external front of the apenninic orogen and rising up again to about 30 km depth in correspondence of the adriatic foreland despite the strong variability of the crustal thickness the average crustal vs values show little variation along the transect fluctuating around 3 km s the average vp values obtained from the vs and vp vs are generally lower than 6 km s