fault death a perspective from actively deforming regions abstract patterns of activity on large faults in regions of distributed continental deformation can change quite rapidly in less than 1 ma such changes include faults becoming permanently or temporarily inactive spatial migration of activity between different faults or faults sets within a deforming region and faults apparently going through episodes of intense activity separated by long quiescent periods greater knowledge of these changes combined with our increasingly detailed understanding of the geometry of large faults have implications for a variety of structural and tectonic issues such as 1 the nature of the interaction between neighbouring faults 2 the link between the discontinuous deformation on faults in the seismogenic upper crust and the more distributed deformation in the aseismic lithosphere beneath and 3 the relation between the instantaneous kinematics and the cumulative finite deformation examples from the active extensional province of central greece are used to illustrate the nature and possible significance of changing fault patterns

topographic expressions of mantle dynamics in the mediterranean abstract the surface of the earth is the ever changing expression of the dynamic processes occurring at depth and at or above its surface however our ability to read landscapes in terms of their underlying tectonic or climatic forcing remains rudimentary during the last decade particular attention has been drawn to the deep dynamic contributions to topography related to the stresses that are produced at the base of the lithosphere by mantle convection and their relevance compared to the iso static component of topography here we use examples from the mediterranean and estimate residual and dynamic topography we then compare those with surface uplift from geology for specific regions to disentangle the dynamic from the static components considering the different topographic signatures of tectonic processes e g actual residual and dynamic topography as well as uplift rates jointly provides a powerful way to distinguish between the contributions of mantle crustal and surface processes such an approach might bring us closer to reading topographic expressions in terms of their geological cause

human impact and slope dynamics evolutionary trends in the monoclinal relief of adriatic area of central italy abstract the present work deals with a large area of the marche abruzzi monoclinal relief which is made up of a clayey sediment succession with sandy conglomeratic levels alternating at varying stratigraphic heights the east verging monocline was generated by an intense quaternary tectonic uplifting it differs approximately in the west east and in the southern directions forming three wide morphostructures the deep fluvial down cutting disjointed the monoclinal relief into a succession of high hills which give the area a typical cuesta morphology with fronts facing the western quadrants the present study aims at contributing to the knowledge of recent slope morphodynamics by analyzing the spatial distribution and state of activity of fast hydro erosion processes and superficial mass movements correlations are made between these phenomena and the morphotectonic and lithological features of the various sectors in the area with particular reference to agricultural land use the present research underlines how the badlands represent the most spectacular form of fast erosion whereas the landslide phenomena which affect the prevalently loamy clayey eluvial colluvial covers are the most widespread processes despite the distribution density and recent or current evolutionary trends are generally associated with different morphostructural features of the various sectors of the area they prove to be strictly controlled by agricultural exploitation and by the connected techniques and types of cultivation

contemporaneous extension and compression in the northern apennines from earthquake fault plane solutions summary the northern apenninic arc belongs to the deformation zones surrounding the adriatic plate which behaves as a rigid block it is a ne verging fold and thrust belt which developed since the miocene with the migration of an extensional compressional pair previous seismological data are roughly in agreement with this deformation picture although the outer compressional front was not clearly defined by the few available solutions in this work we confirm the existence of two adjacent zones of contemporaneous extension and compression in the northern apennines defining the extent of these two zones and their interim1 deformation better than was previously done this is accomplished through the analysis of 125 new focal mechanisms of earthquakes 2 6 md 4 8 recorded by the national network of the lstituto nazionale di geofisica in the period 1988 1995 the two deformation zones are clearly separated and lie very close to each other with a partial overlapping in the emilian tuscan apennines strikeslip events are scattered in most of the study area thrust faulting earthquakes are located in the internal part of the most recently active thrust front middle upper pleistocene there is a general trend of the compressional p axes of thrust fault and strike slip solutions to be perpendicular to the apenninic direction in the external zone while the tensional axes of the normal fault and strike slip solutions in the belt do not show a uniform orientation however clearly evident is the ene direction of extension in the peri tyrrhenian region consistent with the direction of shmln in the quaternary volcanoes of this region inferred from borehole breakouts and microearthquake fault plane solutions we determined the orientation of the stress tensor in the two main deformation zones by inversion of the 125 fault plane solutions determined in this study we found that the external belt is characterized by ne sw compression ol horizontal oriented n45 e while a normal faulting regime with o3 e w oriented is characteristic of the umbria tuscany back arc region

fault generated mountain fronts in the central apennines central italy geomorphological features and seismotectonic implications the morphotectonic framework of the central apennines is given by faulted blocks bounded by normal faults mostly trending nw se nnw sse and ne sw which cut previous compressive structures such a structural setting is consistent with the lbcal mechanisms of the earthquakes which often occur in this area in this paper three lithologically different normal fault generated mountain fronts are analysed in order to assess the relations between their geomorphic features and active tectonics they border the norcia depression sibillini mts umbria the amatrice ampotosto plateau laga mts lazio and the fucino basin marsica mts abruzzi the norcia depression is bounded by a n20 w trending normal fault to the east and by a parallel antithetic fault to the west the main fault has a 1000 m throw and gives rise to a wide fault escarpment characterized by l sharp slope breaks due to low angle gravity faults 2 important paleolandslides and 3 several fault scarplets on the piedmont belt affecting quaternary deposits the amatrice ampotosto plateau is delimited by the western slope of mt gorzano which runs along a n20 w trending normal fault having a 1500m throw minor parallel faults dislocate quaternary landforms large scale massmovements also occur here e the fucino basin was struck by th e 1915 avezzano earthquake 0 xi mcs which produced extensive surface faulting along two parallel nw trending normal fault escarpments on the eastern border of the basin there is paleoseismrc evidence including buried gravity graben in late glacial gravels and tectonic dip slip striations on holocene calcitic crusts covering bedrock normal fault planes these data suggest that active extensional tectonics plays a major role in the slope morphogenesis of the central apennines and they indicate the importance of geomorphic analysis in seismic zonation of this area

the 1997 umbria marche italy earthquake sequence a first look at the main shocks and aftershocks a long sequence of earthquakes six with magnitudes between 5 and 6 struck central italy starting on september 26 1997 causing severe damages and loss of human lives the seismogenic structure consists of a nw se elongated fault zone extending for about 40 km the focal mechanisms of the largest shocks reveal normal faulting with ne sw extension perpendicular to the trend of the apennines consistently with the quaternary tectonic setting of the internal sector of the belt and with previous earthquakes in adjacent regions preliminary data on the main shocks and aftershocks show that extension in this region of the apennines is accomplished by normal faults dipping at low angle 40 to the southwest and confined in the upper 8 km of the crust these normal faults might have reactivated thrust planes of the pliocene compressional tectonics the aftershock distribution and the damage patterns also suggest that the three main shocks ruptured distinct 5 to 15 km long fault segments adjacent and slightly offset from one another

helium 3 anomalies and crust mantle interaction in italy abstract the distribution of primordial 3he in the crust of italy has been investigated through a survey of groundwaters hot springs exploration and production geothermal wells the mantle derived component varies from 0 to 60 and reaches a maximum at vulcano in the eolian islands 3he anomalies occur where the conductive heat flow is relatively high but the relationships between heat flow and anomaly are uncertain the distribution of 3he in the main reservoir and cap rock to the larderello geothermal system shows that the mantle derived 3he varies from 5 to 40 of total he and reaches a maximum in fluids extracted from a depth of ca 3 km within the basement bomb produced tritiogenic 3he appears to make a near negligible contribution well 107 at larderello has been monitored over a period of 17 months and the 3 he 4 he ratio r varies from 1 4 to 1 6 times the atmospheric ratio ra whilst he ne varies from 9 to 160 a model is proposed for the larderello geothermal system whereby mantle derived heat and volatiles are advected to shallow 6 8 km depths in association with melts and released into the main geothermal reservoir at larderello in a non uniform manner possibly associated with fracturing isotopic and elemental equilibrium of gaseous species c o h appears to have taken place in the basement to the main reservoir from where fluid with r ra 3 2 has been extracted

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

relay ramps in active normal fault zones a clue to the identification of seismogenic sources 1688 sannio earthquake italy relay ramps commonly occur in areas of active extension they have relevance in terms of fault segmentation fault linkage and related seismic potential we propose consideration of field evidence of an active relay ramp in a seismic area as a clue to the definition of a seismogenic normal fault we have chosen the calore river valley as our study area it is located within the core of the apennine chain of the italian peninsula and is characterized by active extension and associated severe seismicity in particular a destructive earthquake struck the study area in 1688 we integrated data deriving from a geological field survey with original geomorphic and mesostructural analyses and new radiometric dating 40 ar 39 ar results indicate that brittle deformation detected in the northern part of mt camposauro could represent the surface expression of the ne dipping main fault of an active extensional system we refer to as the calore river fault system its structural connection with the neighboring boiano basin extensional fault system is marked by an area of complex deformation which links them and can be described as a stage 3 relay ramp given that the boiano basin fault system is a seismogenic source the identification of a relay ramp implies a seismogenic role also for the calore river fault system in turn these results allow us to suggest a new hypothesis for the seismogenic source of the 1688 sannio earthquake finally we discuss the implications on the seismic potential of two seismogenic structures linked by a relay ramp

geomorphological response of fluvial and coastal terraces to quaternary tectonics and climate as revealed by geostatistical topographic analysis geostatistical topographic analysis is widely recognized as a useful tool for the statistical reconstruction of planar geomorphic markers from relict surfaces this work is aimed at improving the geostatistical approach used in previous works and developing a method for evaluating the incision rates of rivers in their lower catchments during the late quaternary we chose the major valleys of the adriatic foothills central italy affected since late miocene by a differential tectonic uplift which is still active in particular i we applied the geostatistical analysis to reconstruct the original top surfaces of fluvial to coastal terrace bodies at the metauro river and cesano river mouths ii we performed correlations between the height distribution of the alluvial terrace sequences and the quaternary climatic curve to estimate the average long term fluvial incision rates in the lowermost reaches of the metauro cesano misa and esino rivers the obtained averaged incision rates have been interpreted also in the light of the stream length gradient index sl index steepness index ks and concavity index as proxies of the stream power per unit length results confirm that geostatistical and terrain analysis of topographic and geometric arrangements of fluvial and coastal terraces is an effective tool in detecting geomorphic and tectonic factors inducing perturbations on planar geomorphic markers in particular we better delineated the surface geometry and boundaries of well developed coastal fans at the mouths of the metauro and cesano rivers already recognized in previous works through sedimentological morphostratigraphic and chronological data moreover we found evidence for cut and fill phases that took place during and immediately after the river aggradation of the late quaternary glacial periods despite the slope area analysis evidenced a widespread influence of the regional differential uplift on single river basin configuration we observed some space and time variability of averaged incision rates for adjacent valleys mainly explained by physiographic configuration and dynamics of drainage network copyright 2011 john wiley sons ltd

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

the 1997 umbria marche italy earthquake sequence relationship between ground deformation and seismogenic structure a field survey performed during the 1997 umbria marche earthquake sequence led us to recognize ground and pavement ruptures associated with the three largest shocks mw 5 7 the ruptures are concentrated in narrow bands that in part are on and near previously mapped high angle normal faults the geometry of the ground deformation is consistent with the ne trending extension indicated by cmt focal solutions of the mainshocks the distribution of aftershocks suggests that the three mainshocks occurred on 40 sw dipping normal faults geological investigations modelling of expected coseismic elevation changes and seismic data suggest that the surface deformation is not the direct result of primary rupture of faults at depth

multi phase reactivations and inversions of paleozoic mesozoic extensional basins during the wilson cycle case studies from the north sea uk and the northern apennines italy

geomorphological paleontological and 87sr 86sr isotope analyses of early pleistocene paleoshorelines to define the uplift of central apennines italy abstract the eastern border of the middle valley of the tiber river is characterized by several plio pleistocene paleoshorelines which extend for about 100 km along the western margin of the central apennines italy we studied these paleoshorelines by the means of geological and paleontological analyses and new 87 sr 86 sr isotope analyses the youngest and uppermost paleoshorelines have been detected and mapped through detailed geologic and stratigraphic surveys which led to the recognition of nearshore deposits cliff breccias alignments of lithophaga borings fossil abrasion notches and wave cut platforms the altitude of these paleoshorelines decreases almost regularly in the nnw sse direction from 480 to 220 m a s l measurements of the 87 sr 86 sr isotope ratio have been conducted on corals and mollusks collected from sediments outcropping close to the paleoshorelines the isotopic dating results indicate numerical values that range between 0 70907 and 0 70910 all over the 100 km outcrop these results together with biostratigraphic data constrain the age of the youngest paleoshorelines to 1 65 1 50 ma these paleoshorelines are thus considered almost isochronous giving an estimated uplift rate of 0 34 0 17 0 03 mm a moving from nnw to sse shape length and continuity of the 100 km long observed movements indicate that the studied paleoshorelines are an important marker of the quaternary uplift of the central apennines

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

active normal faulting along the mt morrone south western slopes central apennines italy in the present work we analyse one of the active normal faults affecting the central apennines i e the mt morrone normal fault system this tectonic structure which comprises two parallel nw se trending fault segments is considered as potentially responsible for earthquakes of magnitude 6 5 and its last activation probably occurred during the second century ad structural observations performed along the fault planes have allowed to define the mainly normal kinematics of the tectonic structure fitting an approximately n 20 trending extensional deformation geological and geomorphological investigations performed along the whole mt morrone south western slopes permitted us to identify the displacement of alluvial fans attributed to middle and late pleistocene by means of tephro stratigraphic analyses and geomorphological correlations with dated lacustrine sequences along the western fault branch this allowed to evaluate in 0 4 0 07 mm year the slip rate of this segment on the other hand the lack of synchronous landforms and or deposits that can be correlated across the eastern fault segment prevented the definition of the slip rate related to this fault branch nevertheless basing on a critical review of the available literature dealing with normal fault systems evolution we hypothesised a total slip rate of the fault system in the range of 0 4 0 07 to 0 8 0 09 mm year moreover basing on the length at surface of the mt morrone fault system i e 22 23 km we estimated the maximum expected magnitude of an earthquake that might originate along this tectonic structure in the order of 6 6 6 7

geodetic and seismologic evidence for slip variability along a blind normal fault in the umbria marche 1997 1998 earthquakes central italy summary we analysed elevation changes induced by the 1997 1998 umbria marche central apennines italy earthquakes we employed data from a first order geodetic levelling line measured in 1951 1992 and 1998 the line bears a record of pre seismic and coseismic strains associated with the causative fault of the 1997 september 26 09 40 mainshock mw 6 0 a first level analysis performed under the assumption of slip homogeneity of coseismic slip shows misfits that cannot be reduced simply by altering the fault size and geometry a more detailed analysis based on a distribution of coseismic slip obtained from broad band seismograms provides a better fit and is in agreement with 1951 1992 elevation changes interpreted as precursory slip by previous investigators the levelling data sets new constraints on the location extent dip and depth of the fault in full agreement with seismological evidence and images from sar interferometry the data show no evidence for slip in the uppermost 3 km of the crust suggesting that a major and widely recognized normal fault that exists in the area is no longer active and showing a tendency of present tectonic strains to revert the current topographic setting

drainage systems and the development of normal faults an example from pleasant valley nevada abstract drainage systems in regions of active extension contain information about fault zone structure and development and particularly about the lateral growth of individual fault segments that is difficult to obtain by more conventional means such as the dating of sedimentary material we investigate drainage fault interaction in pleasant valley nevada where a large normal faulting earthquake occurred in 1915 we find geomorphological evidence for a propagation increase in length of several km at both ends of one of the 1915 fault segments at one end we estimate the propagation rate to be about 50 m per earthquake this estimate is uncertain but is within the range predicted by theoretical models of fault growth drainage along the axes of half graben in this region may be influenced by the spacing of tilted fault blocks the highest valleys are also the narrowest whether the axial streams succeed in reaching lower neighbouring sinks depends on whether sedimentation rates are able to keep basins filled to the levels of the basement highs that separate half graben of opposite polarity a knowledge of modern drainage fault interactions may help predict drainage systems and the position of potential syn rift reservoir sediments in older extensional terrains where fault configurations but not facies distributions are known from seismic reflection surveys

migration of activity within normal fault systems examples from the quaternary of mainland greece abstract we examine five areas of mainland greece where active extension occurs on sub parallel systems of normal faults and where geomorphological and stratigraphic evidence indicates that the faulting has migrated basinwards into the original hanging walls in several cases within the late quaternary by comparing fault slip rates estimated from geomorphological data with current extension rates known from geodetic measurements it appears that the newest faults can account for effectively all the present day motions fault migration of this sort is easy to recognize in young systems close to sea level because vertical movements of footwalls and hanging walls are obvious and reveal which faults are currently most active but is less easy to confirm away from reliable reference levels or in older terrains with poorer time resolution it is probably more common than is appreciated and has a profound effect on syn rift sedimentation and erosion patterns fault migration is probably an inevitable consequence of the interplay between stresses generated by the fault related topography and the ultimate strength of major faults it is likely to be further encouraged in places where lower crustal flow or rotations about a vertical axis are important however it is not clear why migration should preferentially occur into the hanging walls as observed in central greece

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

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

an upper bound on the rate of strain in the central apennines italy from triangulation measurements between 1869 and 1963 italy is covered by a first order triangulation network that was established between 1869 and 1908 and re measured in patches between 1936 and 1963 we analyse the measurements made in the central part of italy to form an estimate of the rate of strain in the central apennines we conclude that the rate of strain in this region is too small to detect from the repeated triangulation measurements this result places an upper bound of about 10 7 yr on the strain rate of the central apennines and implies that the maximum rate of extension across the region is no higher than about 3 mm yr

extensional basins in the tectonically bimodal central apennines fold thrust belt italy response to corner flow above a subducting slab in retrograde motion the apennines fold thrust belt has developed over the past 20 m y in response to southeastward retrograde migration of the adriatic trench in a region of ongoing subduction but little plate convergence the orogenic belt is characterized by a gently sloping southwestern flank in a state of regional extensional collapse and a steeply sloping northeastern flank in regional contraction in any given area in the central apennines the chronologies of thrusting and subsequent extension provide an estimate of the time required for attainment of high elevation 2 5 3 0 km the time between initial extension and eruption of local ultramafic lavas provides an estimate of the time required to collapse by regional crustal thinning these estimates suggest that the northeastern contractional flank of the range is rising at least twice as fast as the southwestern flank is collapsing we propose that the bimodal state of stress in the apennines is maintained by corner flow in the mantle wedge beneath the crest of the range

vertical gps ground motion rates in the euro mediterranean region new evidence of velocity gradients at different spatial scales along the nubia eurasia plate boundary we use 2 5 to 14 years long position time series from 800 continuous global positioning system gps stations to study vertical deformation rates in the euro mediterranean region we estimate and remove common mode errors in position time series using a principal component analysis obtaining a significant gain in the signal to noise ratio of the displacements data following the results of a maximum likelihood estimation analysis which gives a mean spectral index 0 7 we adopt a power law white noise stochastic model in estimating the final vertical rates and find 95 of the velocities within 2 mm yr with uncertainties from filtered time series 40 smaller than from the unfiltered ones we highlight the presence of statistically significant velocity gradients where the stations density is higher we find undulations of the vertical velocity field at different spatial scales both in tectonically active regions like eastern alps apennines and eastern mediterranean and in regions characterized by a low or negligible tectonic activity like central iberia and western alps a correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area glacial isostatic adjustment and weathering processes do not completely explain the measured rates and a combination of active tectonics and deep seated geodynamic processes must be invoked excluding areas where localized processes are likely or where subduction processes may be active mantle dynamics is the most likely process but regional mantle modeling is required for a better understanding

the holocene paleoearthquakes on the 1915 avezzano earthquake faults central italy implications for active tectonics in the central apennines abstract extensive paleoseismological research was conducted in the fucino plain central italy in order to better understand the seismogenic characteristics of the fault responsible for the 1915 avezzano earthquake ms 7 0 and improve the general knowledge regarding active tectonics in the central apennines evidence for late pleistocene holocene surface faulting events was obtained through the study of thirteen sites across four different fault branches the paleoseismological analysis outlined the occurrence of ten surface faulting events in the past 33 000 years seven of which occurred during the holocene radiocarbon thermoluminescence and archaeological dating permitted the definition of an event chronology and the estimation of a recurrence interval for surface faulting events ranging between 1400 and 2600 years on the basis of the observed offsets it was possible to calculate vertical slip rates for the individual fault branches ranging between 0 24 mm yr 1 and 0 5 mm yr 1 and an extension rate across the fucino plain ranging between 0 6 and 1 mm yr 1 the chronology of surface faulting events appears linearly distributed in time and the observed recurrence times are similar to those inferred by other paleoseismological studies along different active apennine faults the general consequence of the large time span between strong earthquakes is that even a 2000 year long historical record such as the italian earthquake catalogue does not cover the entire seismic cycle of all the active apennine faults a comparison of the extension rate across the fucino plain with that across the entire central apennines as inferred from the sum of seismic moments of earthquakes which occurred in the interval 1000 1992 shows a seismicity deficit in the period indicated this confirms that a number of seismogenic faults were not active during the past 1000 years

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

the september 26 1997 colfiorito italy earthquakes modeled coseismic surface displacement from sar interferometry and gps the largest events of the 1997 umbria marche seismic sequence were the two september 26 earthquakes of mw 5 7 00 33 gmt and mw 6 0 09 40 gmt which caused severe damage and ground cracks in a wide area around the epicenters we created an ers sar differential interferogram where nine fringes are visible in and around the colfiorito basin corresponding to 25 cm of coseismic surface displacement gps data show a maximum horizontal displacement of 14 1 8 cm and a maximum subsidence of 24 3 cm we used these geodetic data and the seismological parameters to estimate geometry and slip distribution on the fault planes modeled fault depths and maximum slip amplitudes are 6 5 km and 47 cm for the first event and 7 km and 72 cm for the second one in good agreement with those derived from the seismological data

mechanics of continental rift architecture continental rifts are long narrow features bounded on one or both sides by normal faults along which several kilometers of displacement has occurred resulting in deep rift valleys that form sedimentary basins continental rifts all share the same geometrical features they have widths that are characteristic of the region in which they form they are predominantly asymmetric and they are segmented along axes at a length scale that is also characteristic of the region we describe a very simple mechanical model to explain these three features the rift initiates with the formation of a conjugate set of normal faults that intersect at the center of the seismogenic layer one of these becomes the boundary fault system the other the failed conjugate fault being offset by the former becomes locked early in the rifting history hence an asymmetric graben is formed which is the basic building block of rifts the failed conjugate fault has distinctive properties that allow it to be easily distinguished from other faults examples of these faults from the tanganyika and malawi rifts show excellent agreement with predictions about their positions with respect to the boundary fault system and their net displacement and slip history the width of the asymmetric graben is a simple function of seismogenic thickness the net displacement on the boundary fault system is limited by the resistive friction and the flexural restoring force we calculate this limiting boundary fault system displacement and using the displacement length scaling law for normal faults suggest that this controls the along axis segmentation length both maximum fault slip and segmentation length are functions of the seismogenic thickness and the effective elastic thickness of the crust these calculations agree very well with observations of segmentation from the african rifts and the maximum length of range fronting normal faults in nevada

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

effects of lateral variations of crustal rheology on the occurrence of post orogenic normal faults the alto tiberina fault northern apennines central italy abstract the northern apennines na are characterized by formerly compressive structures partly overprinted by subsequent extensional structures the area of extensional tectonics migrated eastward since the miocene the youngest and easternmost major expression of extension is the alto tiberina fault atf we estimate 2d rheological profiles across the na and conclude that lateral rheological crustal variations have played an important role in the formation of the atf and similar previously active faults to the west lithospheric delamination and mantle degassing resulted in an easterly migrating extension compression boundary coinciding at present with the atf where i the thickness of the upper crust brittle layer reaches a maximum ii the critical stress difference required to initiate faulting at the base of the brittle layer is at a minimum and iii the total strengths of both the brittle layer and the whole lithosphere are at a minimum although the location of the fault is correlated with lithospheric rheological properties the rheology by itself does not account for the low dip 20 of the atf two hypotheses are considered a the low dip of the atf is related to a rotation of the stress tensor at the time of initiation of the fault caused by a basal shear stress 100 mpa possibly related to corner flow associated with delamination or b the low dip is associated to low values of the friction coefficient 0 5 coupled with high pore pressures related to mantle degassing our results establishing the correlation between crustal rheology and the location of the atf are relatively robust as we have examined various possible compositions and rheological parameters they also provide possible general indications on the mechanisms of localized extension in post orogenic extensional setting the hypotheses to account for the low dip of the atf on the other hand are intended simply to suggest possible solutions worthy of further study

slip distributions on active normal faults measured from lidar and field mapping of geomorphic offsets an example from l aquila italy and implications for modelling seismic moment release surface slip distributions for an active normal fault in central italy have been measured using terrestrial laser scanning tls in order to assess the impact of changes in fault orientation and kinematics when modelling subsurface slip distributions that control seismic moment release the southeastern segment of the surface trace of the campo felice active normal fault near the city of l aquila was mapped and surveyed using techniques from structural geology and using tls to define the vertical and horizontal offsets of geomorphic slopes since the last glacial maximum 15 3 ka the fault geometry and kinematics measured from 43 sites and throw heave measurements from geomorphic offsets seen on 250 scarp profiles were analysed using a modification of the kostrov equations to calculate the magnitudes and directions of horizontal principal strain rates the map trace of the studied fault is linear except where a prominent bend has formed to link across a former left stepping relay zone the dip of the fault and slip direction are constant across the bend throw rates since 15 3 ka decrease linearly from the fault centre to the tip except in the location of the prominent bend where higher throw rates are recorded vertical coseismic offsets for two palaeo earthquake ruptures seen as fresh strips of rock at the base of the bedrock scarp also increase within the prominent bend the principal strain rate calculated by combining strike dip slip direction and post 15 3 ka throw rate decreases linearly from the fault centre towards the tip the strain rate does not increase across the prominent fault bend the above shows that changes in fault strike whilst having no effect on the principal horizontal strain rate can produce local maxima in throw rates during single earthquakes that persist over the timescale of multiple earthquakes 15 3 ka detailed geomorphological and structural characterisation of active faults is therefore a critical requirement in order to properly define fault activity for the purpose of accurate seismic hazard assessment we discuss the implications of modelling subsurface slip distributions for earthquake ruptures through inversion of gps insar and strong motion data using planar fault approximations referring to recent examples on the nearby paganica fault that ruptured in the mw 6 3 2009 l aquila earthquake

active tectonics in the central apennines and possible implications for seismic hazard analysis in peninsular italy abstract the central apennines fault system cafs of peninsular italy overprints earlier structures of a neogene fold and thrust belt and includes segments characterized by diffuse seismicity distributed within a nnw sse trending zone 50 60 km wide the system has been analysed by means of morphotectonic and structural analysis of exposed active fault segments the resulting fault structure consists of an interconnecting network of roughly n s trending left lateral strike slip segments and mostly nw se oriented transtensional to normal faults evidence for recent activity of cafs structures is provided by faulted middle pleistocene holocene deposits including 30 40 ka old pyroclastites and 40 ka old palustrine sediments fresh scarps in both bedrock and late quaternary continental deposits and decametric lateral offsets locally affecting the post wurmian drainage pattern of the area the regional stress field responsible for the development and evolution of the cafs as inferred from fault slip data is characterized by a nw se compression and by a ne sw extension the cafs pattern and its present day kinematics have been related to left lateral strike slip motion on north south trending crustal faults the existence of deep seated strike slip faults in the central apennines has implications for seismic hazard analysis motion along these structures suggests in fact that coseismic surface faulting is distributed and that cumulative displacements include normal transtensional and strike slip components the seismogenic potential of cafs structures can therefore be best described by multiple rupture models and be better analysed in terms of partial contributions of lower rank features constituting congruent structural associations within the system

plio quaternary vertical motion of the northern apennines insights from dynamic modeling we test the effects of different geodynamic mechanisms on the pliocene to present day dynamics and in particular on the vertical motions of the northern apennines system by means of two dimensional finite element models we show that the pliocene features of the northern apennines exhumation of deep rocks in western italy and fast subsidence rates in the adriatic foredeep can be adequately reproduced by a model slab characterized by the passive sinking of a negatively buoyant adriatic slab and by the upwelling of buoyant asthenosphere beneath western italy model slab is however not able to account for the quaternary and present day pattern of vertical motion of eastern italy and of the adriatic basin a deep configuration of the system characterized by a detached slab model detach may explain the vertical motions of these areas constrained by uplift of the eastern portions of the apenninic chain by an eastward shift of the foredeep depocenter and by lower subsidence rates in the adriatic basin the tectonic and stratigraphic data showing major differences between the tertiary and the quaternary evolution of the northern apennines are discussed

deep seated gravitational slope deformation large scale rock failure and active normal faulting along mt morrone sulmona basin central italy geomorphological and paleoseismological analyses abstract active faulting is one of the main factors that induce deep seated gravitational slope deformations dgsds in this study we investigate the relationships between the tectonic activity of the nw se normal fault system along mt morrone central apennines italy and the evolution of the associated sackung type dgsd the fault system is considered to be the source of m 6 5 7 earthquakes our investigations have revealed that the dgsd began to affect the mt morrone sw slope after the early pleistocene this was due to the progressive slope instability arising from the onset of the younger western fault with the older eastern fault acting as the preferred sliding zone paleoseismological investigations based on the excavation of slope deposits across gravitational troughs revealed that the dgsd was also responsible for the displacement of late pleistocene holocene sediments accumulated in the sackung troughs moreover we observed that the investigated dgsd can evolve into large scale rock slides therefore as well as active normal faulting the dgsd should be considered as the source of a further geological hazard overall our approach can be successfully applied to other contexts where active normal faults control the inception and evolution of a dgsd

late pleistocene differential uplift inferred from the analysis of fluvial terraces southern apennines italy abstract the stratigraphic architecture and morphological assemblage of the pleistocene fluvial terraces contained in two contiguous fluvial valleys are used to understand the spatial distribution and the timing of the differential uplift that affected two different geological and geomorphological settings of an active orogen the study areas both placed in the eastern sector of the southern apennines of italy are the sant arcangelo sedimentary basin and the valsinni ridge anticline pleistocene uplift rate of 0 7 0 9 mm y 1 and historical earthquakes affecting those areas suggest active tectonics based on the synthem units used to classify the fluvial deposits in the field several strath fill and fill cut terraces have been mapped in the middle valleys of the agri and sinni rivers four middle pleistocene high terraces qes are found in the sant arcangelo basin and cut its infill and three late pleistocene low terraces qt are found at both the agri and sinni valley flanks the agri and sinni rivers cross cut the nw se oriented fold and thrust belt of the southern apennines from w to e producing a transverse drainage as a result ten to hundred metre deep gorges and wide floodplains were created in the middle reach of the river valleys computation of the bedrock incision rates from the qes1 qes4 and sqt1 terraces corresponding to 1 2 0 2 mm y 1 at 400 240 ka and 0 8 0 2 mm y 1 in the last 240 ka together with the terrace profile arrangements in the agri and sinni valleys allow for the documentation of i the differential uplift of the study area and ii the age of terrace abandonment corresponding to the beginning age of the vertical incision in the valley floor sediments to form the qt terraces the differential uplift is subsequently discussed in a space and time sequence evolution of the late pleistocene to assess the complex morphotectonic development that occurred in the eastern threshold of the basin the differential uplift of both the sant arcangelo basin and valsinni ridge would appear to indicate that buried fold and thrust structures that affect the mesozoic cenozoic sedimentary nappes are still active and they also controlled the slab retreat processes in the mediterranean region during the late pleistocene

active crustal extension in the central apennines italy inferred from gps measurements in the interval 1994 1999 we present the first gps estimate of crustal extension in the central apennines italy through the analysis of the deformation of a sub network of the national gps geodetic network igm95 in the interval 1994 1999 the selected sub network spans the entire active deformation belt perpendicularly to its axis and allows the evaluation of 1 the total extension rate absorbed in this sector of the apennines and 2 the seismogenic potential of the normal faults active in the late pleistocene holocene interval within the network results of this reoccupation are consistent with an extensional strain rate of 0 18 10 6 yr 1 concentrated in an area of about 35 km width giving an average extension rate of 6 2 mm yr across the central apennines the pattern of active deformation suggests active elastic strain accumulation on the westernmost of the two fault systems active in the late pleistocene holocene interval and may also suggest the presence of another active fault system not recognized so far

the use of the stream length gradient index in morphotectonic analysis of small catchments a case study from central italy abstract the aim of this work is to test an integrated quantitative geomorphic approach based on stream length gradient index sl index analysis within the small catchment of the tarugo river in the northern marchean apennines central italy the tarugo river basin 92 km 2 wide strikes sw ne across the marchean ridge and the western sector of marchean piedmont the area is characterized by a series of nw se trending ne verging thrust folds affecting the meso cenozoic bedrock that pass upward from dominantly carbonate to dominantly terrigenous rocks the area investigated has been affected since the pliocene by extensional tectonics accompanying a regional uplift decreasing in rate north eastwards in this work the sl index analysis has been integrated with the spatial analysis of the amplitude of relief a r and compared to geological and geomorphological field data results of this work indicate that the sl index is a valid tool to detect the long wavelength structural effect on topography as well as the incipient local response to regional processes i e regional uplift that is often undetectable by other morphotectonic parameters in contrast the sl index analysis seems not be a valid tool for discriminating the local lithological influence from the tectonic one

grouping and migration of surface faulting and variations in slip rates on faults in the great basin province abstract nonuniformity of the occurrence of large slip events producing surface ruptures on seismogenic faults and variations in slip rate probably characterize seismogenic faulting in the great basin province western united states examples include the grouping of faulting events along the lost river fault idaho changes in tilt rates of the east range and cortez mountains nevada extension of slip along a fault on the northwest flank of the humboldt range nevada and migration or shifting of slip back and forth from one fault to another along subparallel range front faults in dixie valley nevada

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

palaeoseismicity in the gran sasso massif abruzzo central italy abstract the upper maone and venacquaro valleys on the northern side of the gran sasso massif apennines central italy have been studied in detail from the geological and geomorphological standpoints to date the activity of the faults that produced spectacular fault scarps in the late glacial and holocene sediments and morphological features the faults that produced the studied scarps have been active at least four times during the last 18 000 years and each time on the basis of the indications emerging from the study of the scarp heights displacements of similar size were probably produced the first faulting seems datable to a period slightly more recent than 18 000 years ago the second faulting occurred after the moraines of the second apennine stage these preceding a lacustrine deposit dated 11 760 160 bp could be put in the older portion of the period between 16 000 and 13 000 years ago the third faulting must be more recent than 6000 7000 years ago and slightly older than 5450 170 and 6110 180 bp a fourth phase is appreciably later than 3490 160 bp and older than the year 1000 a d for the venacquaro valley the size of the displacements more recent than 18 000 years ago indicated by the height of the fault scarps and by geophysical data is about 16 18 m for the val maone the size of the displacements more recent than the moraines of the second apennine stage is 10 11 m the respective slip rates are 0 88 1 mm year for the venacquaro valley and approximately 0 67 0 78 mm year for the maone valley it is very probable that the fault activity occurred during a seismic event or events that took place during a short time the intervals between the seismic events or seismic periods although these cannot be defined with precision appear longer than 2500 3000 years and shorter than 6000 7000 years it is possible that also in the gran sasso as in other parts of the abruzzo apennines seismic activity is characterized by events of great magnitude with long return periods

the colle curti mammal site in the colfiorito area umbria marchean apennine italy geomorphology stratigraphy paleomagnetism and palynology abstract an approximately 90 m thick sequence has been studied in the colle curti basin colfiorito area umbria marchean apennine it was deposited in a drainage system characterized by a mature landscape without a clear watershed separating the adriatic and tyrrhenian sides close to the end of the early pleistocene this landscape was dismembered by the activation of extensional faults linked to an uplifting of the chain that reached its greatest magnitude at the beginning of the middle pleistocene from a sedimentological point of view the sequence can be roughly divided into three parts with gravel deposition in a braidplain environment dominating the lower and upper parts and a phase of clay deposition in a lacustrine environment separating these an ar ar analysis on the sanidine contained in a vertisol in the upper part of the sequence gave an age not older than 427 ka an early galerian fauna was collected in clay layers where the jaramillo paleomagnetic event was recognized cold periods are documented in the lower and upper part of the sequence although in the latter the intense weathering caused by the development of a soil with tropical features precludes further investigations the palynological data supported by sedimentological and palaeomagnetic evidence indicate that the sequence can be related to a large part of the bavelian and part of the menapian in the middle part where clay layers outcrop two cool and humid phases are followed by colder and drier periods biological and geological evidence suggests that around 1 my the basin of colle curti was probably located at an elevation of about 600 m

the relationship between topography and gravity on earth and venus abstract the measurement of the admittance between the topography and the gravity of a planet as a function of wavelength provides important constraints on its interior processes a detailed discussion of the influence of noise on such measurements shows that at long wavelengths the admittance is best determined in the frequency domain using gravity as input and topography as output this procedure is used to estimate the admittance in the pacific and indian oceans the observed values are reduced by volcanism above plumes which produces a contribution to the long wavelength compensated topography when this effect is taken into account there is little evidence that the admittance is reduced by the presence of a low viscosity zone in the upper mantle a similar study of venus shows an excellent correlation between gravity g and topography h for wavelengths greater than 700 km with an admittance of about 50 mgal km 1 this value agrees well with that expected from numerical axisymmetric models of plumes and can be used to construct maps of residual topography by calculating h g 50 where h is in kilometers and g in milligals the power spectrum of the gravity field and its skewness with positive anomalies covering a smaller area but being larger than the negative ones are also in agreement with those of the numerical models of the major topographic features only aphrodite and ishtar terrae behave differently with a value of admittance of about one third of other large structures this difference requires their topography to be partly supported by variations in crustal thickness by analogy with similar structures on earth both are likely to be supported by volcanically thickened crust on top of rising plumes though the observed relationships do not rule out other models the behavior of the admittance at long wavelengths is important because it can constrain the thickness of the convecting layer at wavelengths of more than 3000 km the gravity data provides some evidence that the layer depth is about 1000 km over the center of beta and phoebe regiones there are short wavelength anomalies of residual topography produced by crust that is thinner than that elsewhere flanked by positive anomalies of thicker crust the regions of thin crust occur beneath rift zones this behavior can be explained if crust flows down the flanks of elevated regions above plumes and can generate coronae when the plume support disappears

geologic evolution and aspects of the petroleum geology of the northern east china sea shelf basin analysis of multichannel seismic reflection profiles reveals that the northern east china sea shelf basin experienced two phases of rifting followed by regional subsidence the initial rifting in the late cretaceous created a series of grabens and half grabens filled by alluvial and fluviolacustrine deposits regional uplift and folding yuquan movement in the late eocene early oligocene terminated the initial rifting rifting resumed in the early oligocene while alluvial and fluviolacustrine deposition continued to prevail a second phase of uplift in the early miocene terminated the rifting marking the transition to the postrift phase the early postrift phase early miocene late miocene is characterized by regional subsidence and westward and northwestward marine transgression inversion longjing movement in the late miocene interrupted the postrift subsidence resulting in an extensive thrust fold belt in the eastern part of the area the entire area entered a stage of regional subsidence again and has become a broad continental shelf source rocks include synrift lacustrine facies fluvial shales and coal beds synrift fluvial lacustrine and deltaic deposits postrift littoral and or shallow marine sandstones and fractured basement have the potential to provide reservoirs various types of hydrocarbon traps e g faulted anticlines overthrusts rollover anticlines faults unconformity traps combination structural stratigraphic traps weathered basement and stratigraphic traps are recognized but many of these traps have not been tested

geomorphic significance of postglacial bedrock scarps on normal fault footwalls the existence of well preserved holocene bedrock fault scarps along active normal faults in the mediterranean region and elsewhere suggests a dramatic reduction in rates of rock weathering and erosion that correlates with the transition from glacial to interglacial climate we test and quantify this interpretation using a case study in the italian central apennines holocene rates are derived from measurements of weathering pit depth along the magnola scarp where previous cosmogenic cl 36 analyses constrain exposure history to estimate the average hillslope erosion rate over similar to 10 5 years we introduce a simple geometric model of normal fault footwall slope evolution the model predicts that the gradient of a weathering limited footwall hillslope is set by fault dip angle and the ratio of slip rate to erosion rate if either slip or erosion rate is known the other can be derived applying this model to the magnola fault yields an estimated average weathering rate on the order of 0 2 0 4 mm yr more than 10 times higher than either the holocene scarp weathering rate or modern regional limestone weathering rates a numerical model of footwall growth and erosion in which erosion rate tracks the oxygen isotope curve reproduces the main features of hillslope and scarp morphology and suggests that the hillslope erosion rate has varied by about a factor of 30 over the past one to two glacial cycles we conclude that preservation of carbonate fault scarps reflects strong climatic control on rock breakdown by frost cracking

trench investigations of the 1915 fucino earthquake fault scarps abruzzo central italy geological evidence of large historical events earthquake hazard analyses in italy are mainly based on historical seismic catalogs however the completeness of the italian catalog which spans more than 2000 years progressivcly decreases going back in time in the fucino basin historical research has not produced evidence of large earthquakes before the january 13 1915 event m s 7 0 33 000 people killed this event generated surface faulting along at least two parallel quaternary normal faults bounding the eastern side of the basin the celano gioia and parasano cerchio faults over an end to end length of about 23 km with a downthrow of 30 90 cm toward southwest to improve geological aspects of the seismic history of this area we trenched onc of the coseismic scarps along the celano gioia fault at a trench site near the village of san benedetto de marsi the fault traverses the area formerly covered by the fucino lake drained for farming in 1875 a d the evidence collected in the trenchcs suggests at least two large events in historical times before 1915 radiocarbon dates constrain the age of event b between the 6th and the 9th centuries a d possibly coinciding with the cvent felt in rome in 801 a d molin arid guidoboni 1989 event a probably occurred after the 10th ccntury a d and almost certainly before the 1349 a d earthquake because historical studies show 1 that event a was not produced during the earthquake sequence that occurred in central italy in 1349 a d molin and guidoboni 1989 and 2 that the post 1349 seismic catalog can be regarded as complete for surface faulting earthquakes surface displacements determined for events a and b compared to the 1915 surface faulting indicate that m 6 5 earthquakes were associated with each rupturc these obscrvations suggest that the return period for large earthquakes in the fucino basin is shorter than that indicated by the historical record alone the fucino example clearly shows that thc cxceptionally long historical record in italy is still inadequate for a comprehcnsive seismic hazard characterization

the effect of a shallow low viscosity zone on the apparent compensation of mid plate swells abstract a simple model for mid plate swells is that of convection in a fluid which has a low viscosity layer lying between a rigid bed and a constant viscosity region finite element calculations have been used to determine the effects of the viscosity contrast the layer thickness and the rayleigh number on the flow and on the perceived compensation mechanism for the resulting topographic swell as the viscosity decreases in the low viscosity zone the effective local rayleigh number for the top boundary layer of the convecting cell increases also because the lower viscosity facilitates greater velocities in the low viscosity zone the low viscosity layer produces proportionally greater horizontal flow near the conducting lid causing the base of the conducting lid to appear like a free boundary the change in the local rayleigh number and in the effective boundary condition both cause the top boundary layer to thin through a green s function analysis we have found that the low viscosity zone damps the response of the surface topography to the temperature anomalies at depth whereas it causes the gravity and geoid response functions to change sign at depth counteracting the positive contributions from the shallower temperature variations by increasing the viscosity contrast the conbined effects of the thinning of the boundary layer and the behaviour of the response functions allow the apparent depth of compensation to become arbitrarily small therefore shallow depths of compensation cannot be used to argue against dynamic support of mid plate swells furthermore we compared the distribution of the effective compensating densities which is used to obtain the geoid to that of pratt compensation which is often used to calculate the depth of compensation from geoid and topography data for mid plate swells for all of our calculations including those with no low viscosity layer the effective gravitational mass distribution is more complex than assumed in simple pratt models so that the pratt models are not an appropriate gauge of the compensation mechanism

deformation of the 125 ka marine terrace in italy tectonic implications in peninsular italy marine terraces and shorelines created during oxygenisotope substage 5e known historically as the tyrrhenian highstand provide a reliable and homogeneous datum of vertical motions during the past 125 000 years published accounts of 121 locations on the tyrrhenian inner edge were reinterpreted and used to calculate both local and regional uplift rates the data show arching of southern italy between the tyrrhenian and the adriatic coasts and of the calabrian arc between the sangineto and the longi taormina tectonic lineaments at rates of up to 1 2 mm yr for the past 125 ka they also suggest that the present configuration of the southern apennines is the product of post early pleistocene regional uplift superimposed on tortonian to early pleistocene thrusting uplift patterns are characterised by different wavelength in different geodynamic settings suggesting a close link with the depth of the causative tectonic sources

relations between normal fault geometry tilting and vertical motions in extensional terrains an example from the southern gulf of suez abstract earthquakes and data from subsurface oil exploration suggest that large active normal faults in the southern gulf of suez are approximately planar with dips of 30 40 from the surface to around 10 km depth these faults and the blocks they bound appear to rotate about a horizontal axis as they move causing tilting this tilting is seen both in young vertical movements of the coastline such as raised beaches and marshlands and in the distribution of middle miocene marine rocks which are uplifted to elevations of 400 500 m in footwalls of faults and found at depths of around 3500 m in the adjacent grabens the absolute amplitude of the observed vertical motions can be approximately modelled by planar rotating normal faults that impose a saw tooth topography on a regional subsidence caused by crustal and lithospheric thinning the observations required for this simple model are the present day fault dip the amount of tilting and the width of the rotating blocks the virtues of the model are its simplicity and its compatibility with our knowledge of how large active normal faults move elsewhere on the continents

pliocene and pleistocene exhumation and uplift of two key areas of the northern apennines application of different thermochronological methods to two areas of pronounced relief apuane alps and mt falterona of the northern apennines chain documents an average exhumation rate of about 0 7m m yr this result suggests that the general exhumation of the chain is driven mainly by erosion nevertheless the long term exhumation trend seems to be perturbed by shortterm events at higher exhumation rates the time of increased exhumation rates coincides with onset of intramontane sedimentation documenting a contribution of tectonics local normal faulting to the surface uplift the data indicate an eastward shifting of the onset of topographic relief early pliocene in the apuane alps and early pleistocene in the mt falterona area r 2002 elsevier science ltd and inqua all rights reserved

temporary seismic quiescence se turkey summary the border zone that is the contact of the arabian plate with the three plates of turkey eurasia and iran to the north has been remarkably aseismic during this century by extending the period of observation backwards in time by a few centuries it is shown that this seismicity is atypical of the long term behaviour of the zone and due to a quiescent period in the activity of the area during the 20th century in turn this implies that short term data alone do not provide a reliable assessment of earthquake hazard

connecting seismically active normal faults with quaternary geological structures in a complex extensional environment the colfiorito 1997 case history northern apennines italy 1 the northern apennines of italy are characterized by a complex tertiary tectonic history where superposed compressional and extensional deformation occurred in such regions characterized by low active extensional strain rate the coseismic surface ruptures are rare and often a matter of much debate resulting in a difficult connection between geological faults i e faults which can be mapped at the surface and seismological faults i e faults which actually generate earthquakes the availability of detailed geological mapping and high resolution seismological data for the colfiorito area struck in 1997 by a sequence of six 5 mw 6 normal faulting earthquakes allow us to compare and verify the existence of geometric and kinematic correspondence between the mapped geological quaternary faults and the activated structures in map view the earthquakes distribution reflects the fault pattern mapped at the surface the length of activated and mapped faults is quite similar 7 10 km the coseismic subsided region imaged by interferometric synthetic aperture radar data is located in the hanging wall of the mapped normal faults that bound the quaternary basins in section view there is a geometric connection between mapped normal faults and the aftershock alignments used to image fault geometry at depth comparison of striated fault planes and aftershock focal mechanism solutions show a strong kinematic consistency this study points out that the quaternary tectonosedimentary evolution and the present day geological and geomorphologic setting of the colfiorito area can be interpreted as the result of repeated extensional earthquakes similar to the 1997 events occurring on nw se trending normal faults our data also show that the main shocks of the colfiorito sequence nucleated close to the intersections between the normal faults and the preexisting compressional transpressional structures which in 1997 acted as lateral barriers to rupture propagation and consequently constrained the fault size

a healing reloading feedback control on the growth rate of seismogenic faults spatial and temporal variations in the growth rates of faults are explained in terms of a stress feedback mechanism operating in the seismogenic upper crust it is based on the idea that seismic rupture of a fault perturbs the surrounding stress field advancing the occurrence of future earthquakes on some faults that are optimally oriented while relaxing stress levels on others if post slip healing is geologically rapid then the earthquakes that are thus induced will contribute to reloading along the earlier rupture zone because of the symmetry of the optimal geometry a positive feedback is set up so that even in areas that are undergoing uniform tectonic straining some faults develop higher displacement rates and grow more rapidly while others experience reduced rates or become inactive using a thin plate elastic model for lithospheric scale faulting it is shown that this healing reloading feedback mechanism drives rapid localisation and the formation of major through going faults moving at plate boundary velocities enhanced displacement rates compared to an isolated fault develop shortly after the onset of deformation along those faults which are optimally positioned in the overall fault population thus the formation of a new plate boundary fault zone is predetermined and is a consequence of rather than the precursor of preferentially high displacement rates also fault segments located at points of rupture symmetry e g the central portion of a fault zone are reloaded more frequently and develop higher displacement rates and consequently have longer segment lengths and or larger displacement to length ratios episodic fault movement through time is a general feature of the model these predictions are consistent with available field observations over a wide range of scales thus elastic brittle failure and healing appear to be important rheological components of the lithosphere on long time scales 104 106 y as well as on the time scale of earthquake recurrence

palaeoenvironmental analysis of early pleistocene brackish marshes in the rieti and tiberino intrapenninic basins latium and umbria italy using ostracods crustacea abstract recent palaeontological and sedimentological studies on the upper pliocene lower pleistocene continental deposits of the rieti and tiberino basins latium and umbria italy showed the existence of brackish marshes influenced by the early pleistocene tyrrhenian sea the micropaleontological analyses carried out on five sections cropping out in the northern sector of the rieti basin and on one section cropping out in the southwestern branch of the tiberino basin showed the repeated alternance of two ostracod assemblages the first is characterized by a very abundant ostracod association dominated by cyprideis torosa typical of brackish waters the second one is less rich in specimens and dominated by several species of freshwater candoninae this alternance allowed the recognition of several changes in the water salinity that could be related to many early pleistocene sea level changes palaeosalinities were estimated for both the tiberino and the rieti basin using the morphological analysis of the shell of cyprideis torosa ornamentation nodosities and percentages of sieve type pore canals the obtained palaeosalinity values ranging from freshwater to oligohaline show slightly higher salinities for the tiberino basin located nearer the ancient coastline than for the rieti basin

seismic deformation in the mediterranean area estimated by moment tensor summation summary theoretical relationships allow the distributed deformation due to seismic activity to be quantified on the basis of the analysis of moment tensors we apply this method to a data set consisting of seismic events that have occurred in the past 85 yr 1908 1992 along the most important seismogenic zones of the mediterranean region we use the centroid moment tensor cmt catalog prepared at harvard university covering the last 16yr and older data from jackson mckenzie 1988 we determine the seismic deformation and compare it to estimates of the overall deformation as obtained from global plate motion and geological studies we generally find that the geometry of seismic deformation is similar to tectonic predictions even though spanning a shorter time interval the cmt catalog often gives a better estimate of deformation geometry than the whole data set 85yr seismic deformation generally ranges from less than 10 per cent to more than 90 per cent of the total deformation uncertainties arise because data sets may not be representative of the long term seismic behaviour of each zone more reliable estimates for comparison with geodynamic processes should result from analysis of a longer time period for which no instrumental data are available the similarity of the deformation geometry using cmt data with tectonic expectations suggests for several zones the possibility of using historical data to infer longer term deformation rates based on current deformation geometry

surface faulting of the 6 april 2009 mw 6 3 l aquila earthquake in central italy this paper documents evidence of surface faulting associated with the 6 april 2009 moderate sized earthquake ml 5 8 mw 6 3 in the central apennines of italy which caused major damage to the town of l aquila and its surroundings coseismic surface ruptures were mapped for a minimum distance of 2 6 km along the paganica fault a fault still poorly investigated relative to the other active faults nearby which bound much wider range fronts surface rupture length srl and maximum displacement parameters 2 6 km minimum and 10 15 cm respectively are in agreement with what is expected for an mw 6 3 event in the italian apennines tectonic environment different viewpoints exist on the amount of srl and the number of activated faults we propose a pattern of sympathetic and secondary slip on an array of faults around the master seismogenic structure past seismicity and evidence for larger holocene offsets on this and other capable faults nearby prove that the 2009 event is not a good reference event for assessing the seismic hazard of the region nevertheless the 2009 l aquila earthquake once more confirmed the importance of detailed geological studies for a proper seismic hazard assessment and it clearly illustrates the need to pay attention to moderate events and supposedly minor active faults indeed this type of earthquake is rather frequent in the whole mediterranean region and is potentially much more destructive than in the past due to the expanding urban centers and infrastructures inside their epicentral regions and even right above the traces of capable faults

inversion of source parameters from near and far field observations an application to the 1915 fucino earthquake central apennines italy we use a nonlinear inversion approach for determining source parameters of the fucino m s 6 9 earthquake that occurred along central apennines italy in 1915 taking into account both near field surface deformations and far field first motion polarities this event was one of the most destructive in italy this century causing over 30 000 casualties altitude and leveling measurements were performed before 1862 and after 1917 the event along a circular route consisting of 18 benchmarks polarities of first arrivals do not constrain a unique fault plane solution while the one obtained by inverting geodetic data with relevant constraints provided by neotectonic data disagrees with p wave polarities our joint inversion based on a robust fitting technique has resulted in only one well defined solution satisfying geophysical data as well as surface faulting distribution and paleoseismological information

decoding temporal and spatial patterns of fault uplift using transient river long profiles we present detailed observations of rivers crossing active normal faults in the central apennines italy where excellent constraints exist on the temporal and spatial history of fault movement we demonstrate that rivers with drainage areas 10 km2 and crossing faults that have undergone an increase in throw rate within the last 1 my have significant long profile convexities in contrast channels that cross faults that have had a constant slip rate for 3 my have concave up profiles and have similar concavities and steepness indices to rivers that do not cross any active fault structures this trend is consistent across the central apennines and cannot be explained by appeal to lithology or regional base level change the data challenge the belief that active faulting must always be reflected in river profiles instead the long profile convexities are best explained as a transient response of the river system to a change in tectonic uplift rate moreover for these rivers we demonstrate that the height of the profile convexity as measured from the fault scales with the magnitude of the uplift rate increase on the fault and we establish that this relationship holds for throw rate variation along strike for the same fault segment as well as between faults these findings are shown to be consistent with predictions of channel response to changing uplift rate rates using a detachment limited fluvial erosion model and they illustrate that analysis of the magnitude of profile convexities has considerable predictive potential for extracting tectonic information we also demonstrate that the migration rate of the profile convexities varies from 1 5 10 mm y and is a function of the slip rate increase as well as the drainage area this is consistent with n 1 for the slope exponent in a classical detachment limited stream power erosion law but could potentially be explained by incorporating an erosion threshold or an explicit role for sediment in enhancing erosion rates finally we show that for rivers in extensional settings where the response times to tectonic perturbation are long in this case 1 my attempts to extract tectonic uplift rates from normalised steepness indices are likely to be flawed because topographic steady state has not yet been achieved

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

estimating the compensation depth of the hawaiian swell with linear filters broad areas of anomalously shallow seafloor surround regions of active or recently active hot spot volcanism the cause of these midplate swells has been modeled both as elevated temperatures in a convecting layer and as thermal expansion within the conducting portion of the lithosphere according to the former explanation we would expect the low density material compensating the swell to lie beneath the conducting lid whereas the latter model allows compensation at shallower depths we present a technique based on the application of linear filters for determining the compensation depth of midplate swells given observations of topography and geoid or gravity anomalies our method does not require an a priori estimate of swell height or width nor does it assume complete spatial or spectral separation between the swell topography and the signal from the hot spot volcanoes which are compensated by flexure of the oceanic moho rather we exploit the difference in the predicted sign and amplitude of the moho deflection beneath elevated topography produced by loading above versus loading below the elastic plate in order to separate the two effects an application of these linear filters to residual topography and geoid data from the region surrounding the hawaiian hot spot yields a compensation depth of 70 10 km within the lower lithosphere

constraints on the seismotectonics of the central mediterranean from very long baseline interferometry summary very long baseline interferometry vlbi determined site velocities from seven stations in western europe reveal a stable continental platform north of the alps deformations between sweden germany and spain can not exceed 2 mm yr south of the alps significant motions are occurring with respect to stable europe two sites east of the apennine mountains on peninsular italy have north easttrending velocities which increase from 2 mm yr l in the north at medicina to 6 mm yr l in the south at matera in contrast the vlbi site in the south eastern corner of sicily is moving 7 mm yr i to the north north west these velocities are largely explained if southern sicily is attached to a north westerly moving african plate and the eastern portion of the italian peninsula forms part of a hypothesized adriatic sea crustal block which is rotating counter clockwise with respect to europe about a pole near the alps such an explanation is consistent with the styles of the larger historical earthquakes of the region which show ne sw extension across the apennines north south convergence across the alps and ne sw compression in coastal yugoslavia the adria plate model generates 1 5 2 2 x 10l8 nm yr l of potential earthquake moment along the northern and central apennines historical records suggest that 30 60 per cent of this moment is released seismically based on a direct strain rate measurement recurrence intervals for italian earthquakes south of medicina are estimated to be 12 46 yr for m6 5 quakes and 35 143 years for m7 0 quakes

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

active oblique extension in the central apennines italy evidence from the fucino region the fucino basin is a flat quaternary depression within the central apennines it is surrounded by active normal faults with small oblique slip components surface faulting was observed along the east side of the basin during the ms 7 0 avezzano earthquake of 1915 in order to understand the kinematics of recent strain better and to assess the seismic hazard of this region we carried out a detailed geomorphic and structural study of the faults around the basin fault scarp heights were accurately measured with total station profiles and vertical slip rates were estimated assuming slope offsets to post date the end of periglacial abrasion 14 4 kyr bp to the north the most prominent fault the magnola fault appears to have an average postglacial throw rate of 0 7 0 3 mm yr 1 and together with the velino fault to be capable of generating earthquakes of maximum magnitudes of 6 9 7 3 with recurrence intervals of 1000 3000 yr east of the basin the serrone parasano and ventrino faults form a right stepping horsetail of the giovenco fault current vertical slip rates on the three former faults appear to be between 0 5 and 1 4 0 5 and 1 0 and 0 3 and 1 1 mm yr 1 respectively infrequent maximum magnitude earthquakes on them may also exceed 7 particularly in the case of coupled rupture with loosely constrained recurrence intervals up to several thousand years the right lateral slip components implied by the most recent slickensides and by geomorphic offsets on the nw se trending normal faults of the area suggest that the blocks they bound rotate counterclockwise consistent with oblique left slip on the nnw sse trending giovenco and ovindoli faults to the east sinistral shear parallel to the latter faults the maximum relief across the magnola fault and the postglacial slope offsets measured suggest that the extension rate across the central apennines might be of the order of 6 3 mm yr 1 in a n20 10 e direction more northerly than hitherto inferred

the role of pre existing thrust faults and topography on the styles of extension in the gran sasso range central italy abstract structural analysis and field mapping together with simple geometrical and flexural elastic models document that two styles of quaternary extensional tectonics characterized the gran sasso range central apennines italy in the western part of the range extension took place on 10 15 km long range front normal faults with associated 600 1000 m high escarpments showing evidence of late glacial holocene activity this topography has been reproduced with a thin elastic plate subjected to the isostatic forces induced by the movement along high angle 55 65 planar normal faults in the eastern part of the belt extension occurred on shallow dipping normal faults 30 35 which reactivated progressively deeper pre existing thrusts in this area antithetic domino faults formed to accommodate the mechanical adjustment of the hanging wall over a variably dipping major fault surface the eastward increase in shortening due to the earlier compressional phase documented in the gran sasso belt by previous authors accounts for the more developed zones of weakness and high topographic relief in the eastern sector this setting could explain the different styles of extension and the more advanced northeastern limit of normal faulting in the eastern sector this work suggests that normal faults can originate either with low or high angle geometry in the upper crust according to the pre existing tectonic setting and that topography could be important in controlling the geometry and pattern of migrating normal faulting

morphotectonic study of the lower sangro river valley abruzzi central italy abstract this work analyses the morphotectonic setting of the adriatic piedmont of central italy in order to outline the role of tectonics in the development of the fluvial landscape in this area particularly it focuses on the sangro river which flows in the southern abruzzi from the apennines through the piedmont to the adriatic coast the piedmont area developed in a marine environment from the pliocene to the early pleistocene resulting in the deposition of a clayey sandy sequence afterwards regional uplift processes with ne tilting led to the deposition of a regressive conglomeratic sequence as the area evolved into a continental environment this work is based on the qualitative and quantitative study of drainage patterns and on the analysis and correlation of selected morphological evidence of tectonics on fluvial terraces in order to define the role of tectonics in the geomorphological evolution of the lower sangro river valley the drainage network and its statistical azimuthal distributions are analysed the distribution and the transverse and longitudinal profiles of fluvial terraces are investigated and the morphological evidence for tectonics is then assessed river bends linear valleys beheaded and hanging valleys counterflow confluences of streams space and time correlation of these features allows us to highlight the effects of regional uplift tilting and local tectonics on drainage development following the emergence of the piedmont area middle pleistocene uplift and tilting determined a sw ne consequent and parallel drainage progressive incision shaped the sangro valley as a consequent valley local tectonics along nnw sse and wnw ese faults and fractures resulted in the incision of linear valleys beheading the previous sw ne drainage and controlled the development of a rectangular drainage network late middle pleistocene the drainage network was then rearranged by selective erosion processes maintaining a strong inheritance from of its middle pleistocene configuration

shear wave attenuation in the lithosphere beneath italy and surrounding regions tectonic implications more than 700 waveforms produced by 51 shallow earthquakes and recorded at regional distances 250 1400 km by the italian seismic network have been analyzed to characterize the amplitude and frequency contents of the crustal and uppermost mantle shear waves lg and sn respectively the crustal phase lg efficiently propagates through the relatively stable adriatic continental crust while it is not observed along propagation paths crossing major physiographic features like the apennine chain and the basinal domain of the tyrrhenian and ionian seas similar to lg efficient sn propagation is observed in the uppermost mantle beneath the po plain and the adriatic sea efficient sn transmission is also observed across the northern ionian sea and sicily and in the area between sardinia and the northern coasts of africa sn are efficiently transmitted across the sicily channel and rather efficient sn propagate beneath the ligurian sea on the contrary inefficient sn transmission characterizes the uppermost mantle beneath the apennines the western margin of the italian peninsula and the southern tyrrhenian sea shear wave attenuation suggests the presence of asthenospheric material in the uppermost mantle probably related to the present day extension along the apennine chain and in the tyrrhenian basin this interpretation is consistent with the presence of extensive neogene and quaternary volcanic activity in these areas and related high heat flow proposed lithospheric delaminatioh processes beneath the apennines and subduction beneath the tyrrhenian sea can reasonably explain the observed high attenuation zones in the uppermost mantle in contrast a high strength mantle lid is inferred to underlay the po plain the adriatic sea and the northern ionian sea the available waveforms also indicate that a continuous mantle lid is present beneath sicily and the extensional domain of the sicily channel as well as in the marine area south of sardinia

lateral variations of pn propagation in italy evidence for a high attenuation zone beneath the apennines pn phases recorded by 40 stations of the italian seismic network are analyzed using the spectral ratio technique to estimate the q structure of the uppermost mantle beneath the italian peninsula and nearby adriatic sea a total of 344 digital waveforms are analyzed from 22 earthquakes that occurred within distances of 300 to 1600 km the calculated apparent q values are grouped into two categories q 800 characterizes the adriatic side of the italian peninsula indicating that the adriatic lithosphere is very efficient in propagating pn phases through the uppermost mantle q 600 characterizes the uppermost mantle beneath the apennines and western italy indicating less efficient wave propagation the presence of asthenospheric mantle material at shallow depths beneath the apennines can explain the observed q

paleoseismicity of the ovindoli pezza fault central apennines italy a history including a large previously unrecorded earthquake in the middle ages 860 1300 a d geomorphic and trenching investigations along the ovindoli pezza fault show that this normal fault is one of the major seismogenic faults in the central apennines we found clear geological evidence for three holocene surface faulting earthquakes on this fault the most recent earthquake occurred in the middle ages between 860 and 1300 a d the penultimate occurred about 1900 b c or shortly after and the oldest probably occurred between 3300 and 5000 b c although the most recent surface faulting earthquake occurred during historical time no evidence for it have been found in the historical record slip per event ranges between 2 and 3 m and the length of the rupture is at least 12 20 km suggesting m 6 5 7 0 for the paleoearthquakes the dip slip rate determined from trenching is 0 7 1 2 mm yr and is consistent with the long term slip rate of 0 9 2 5 mm yr lower values preferred obtained from displaced geomorphic features trench data combined with long term slip rate estimates suggest the recurrence interval is longer than a millennium and possibly as long as 3300 years the time elapsed since the most recent earthquake is 700 1130 years the seismic behavior of the ovindoli pezza fault is consistent with other well known seismogenic faults of the central and southern apennines the lack of mention or mislocation of the most recent event on the ovindoli pezza fault in the historical record of the past two millennia should be attributed mainly to the unsettled cultural and social conditions and poor economic state that characterized the middle ages especially in thinly populated regions such as the central apennines this example highlights an intrinsic limit of the historical data and raises the possibility that other regions considered seismically quiet on the basis of a long historical record may in reality have had large earthquakes that were not recorded