a recent tectonic reorganization in the south central mediterranean abstract new geodetic data combined with seismicity geologic and geochemical information document a major tectonic reorganization in the central mediterranean around 0 8 0 5 ma when rapid trench migration and consequent tyrrhenian back arc extension which dominated the region s evolution since the tortonian 10 8 ma essentially stopped in response the african convergence in sicily was transferred to a back thrust in the southern tyrrhenian characterized by frequent m5 6 earthquakes in the last 20 years a diffuse transform boundary formed across northeastern sicily to connect the sicilian and calabrian plate boundaries causing opening of the messina straits home to large historical earthquakes and unusual volcanism in the aeolian island arc and the intraplate mount etna a divergence of the ionian region from the main part of africa with northeastward motions that reflect the joint influence of african push and hellenic slab pull and are transmitted to calabria and adria could explain motions observed in the sicily channel calabria and apulia as well as the high level of southeastern sicilian seismic activity

temperature and density of the tyrrhenian lithosphere and slab and new interpretation of gravity field in the tyrrhenian basin abstract the gravity anomaly field of the tyrrhenian basin and surrounding regions reflects the complex series of geodynamic events active in this area since the oligocene miocene they can resume in lithospheric thinning and asthenospheric rising beneath the tyrrhenian basin coexisting with the roll back subduction of the african plate margin westward sinking beneath the calabrian arc the geographic closeness between these processes implies an intense perturbation of the mantle thermal regime and an interference at regional scale between the related gravity effects a model of the litho asthenospheric structure of this region is suggested showing a reasonable agreement with both the evidences in terms of regional gravity anomaly pattern and the results concerning thermal state and petro physical features of the mantle the first phase of this study consisted of the computation of the isotherms in the crust mantle system beneath the tyrrhenian basin and afterwards of the density distribution within the partially melted upwelling asthenosphere the second phase consisted of a temperature density modelling of the slab subducting beneath the calabrian arc finally a 21 2 interpretation of gravity data was carried out by including as constraints the results previously obtained thus the final result depicts a model matching both gravity thermal and petrographic data they provide a a better definition of the thermal regime of the passive mantle rise beneath the tyrrhenian basin by means of the estimation of the moderate asthenospheric heating and b a model of lithospheric slab subducting with rates that could be smaller than generally suggested in previous works

dynamics of retreating slabs 2 insights from three dimensional laboratory experiments 1 a laboratory analogue of a three layer linear viscous slab upper mantle lower mantle system is established in a silicone putty honey and crystallized honey tank experiment the same setup as in the numerical investigation part 1 is used we focus on the interaction of the slab with the induced passive mantle flow by widely varying the mantle volume flux boundary conditions in our numerical experiments the lateral volume flux was set to zero in interpreting the results relative to the real earth the base of the box is taken as the bottom of the mantle convection system while the lateral boundaries may be associated with the presence of other nearby slabs dynamic force equilibrium assessed on the basis of an analytical review of forces is described for four different phases 1 the subduction initiation instability 2 the accelerating dynamic free fall phase of the slab 3 the dynamic interaction with the 660 km discontinuity and 4 a final phase of steady state trench retreat phase 3 is an important feature not observed in the numerical experiments this highly dynamic phase of interrupted trench retreat can therefore be attributed to boundary conditions on mantle volume flux on the basis of integration constants of force equilibrium in phases 2 and 4 we identify two different classes of volume flux one in which the lateral boundary can be considered open and the other class where it is closed closed boundary condition cases are obtained if any of the lateral box boundaries are 600 km away from the slab assuming a one to one relation between trench retreat and back arc spreading enigmatic observations of episodic opening of back arc basins can be explained by our experimental observations

subduction kinematics and dynamic constraints the kinematics of subduction zones shows a variety of settings that can provide clues for dynamic understandings two reference frames are used here to describe the simple 2d kinematics of subduction zones in the first the upper plate is assumed fixed whereas in the second frame upper and lower plates move relative to the mantle relative to a fixed point in the upper plate u the transient subduction hinge h can converge diverge or be stationary similarly the lower plate l can converge diverge or be stationary the subduction rate vs is given by the velocity of the hinge h minus the velocity of the lower plate l vs vh vl the subduction rate 1 increases when h diverges and 2 decreases when h converges combining the different movements at least 14 kinematic settings can be distinguished along the subduction zones variable settings can coexist even along a single subduction zone as shown for the 5 different cases occurring along the apennines subduction zone apart from few exceptions the subduction hinge converges toward the upper plate more frequently along e or ne directed subduction zone whereas it mainly diverges from the upper plate along w directed subduction zones accompanying backarc extension before collision orogen growth occurs mostly at the expenses of the upper plate shortening along e ne directed subduction zones whereas the accretionary prism of w directed subduction zones increases at the expenses of the shallow layers of the lower plate the convergence shortening ratio is 1 along e or ne directed subduction zones whereas it is 1 along accretionary prisms of w directed subduction zones backarc spreading forms in two settings along the w directed subduction zones it is determined by the hinge divergence relative to the upper plate minus the volume of the accretionary prism or in case of scarce or no accretion minus the volume of the asthenospheric intrusion at the subduction hinge since the volume of the accretionary prism is proportional to the depth of the decollement plane the backarc rifting is inversely proportional to the depth of the decollement on the other hand along e or ne directed subduction zones few backarc basins form e g aegean andaman and can be explained by the velocity gradient within the hangingwall lithosphere separated into two plates when referring to the mantle the kinematics of subduction zones can be computed either in the deep or in the shallow hotspot reference frames the subduction hinge is mostly stationary being the slab anchored to the mantle along w directed subduction zones whereas it moves w or sw ward along e or ne directed subduction zones surprisingly along e or ne directed subduction zones the slab moves out of the mantle i e the slab slips relative to the mantle opposite to the subduction direction kinematically this subduction occurs because the upper plate overrides the lower plate pushing it down into the mantle as an example the hellenic slab moves out relative to the mantle i e sw ward opposite to its subduction direction both in the deep and shallow hotspot reference frames in the shallow hotspot reference frame upper and lower plates move westward relative to the mantle along all subduction zones this kinematic observation casts serious doubts on the slab negative buoyancy as the primary driving mechanism of subduction and plate motions w directed subduction zones rather provide about 2 3 times larger volumes of lithosphere re entering into the mantle and the slab is pushed down this opposite behavior is consistent with the down dip extension seismicity along e ne directed subduction zones and the frequent down dip compression along the w directed subduction zones subduction kinematics shows that plate velocity is not dictated by the rate of subduction along the w directed subduction zones the rate of subduction is rather controlled i by the hinge migration due to the slab interaction with the easterly trending horizontal mantle wind along the global tectonic mainstream ii by the far field plate velocities and iii by the value of negative buoyancy of the slab relative to the country mantle alternatively e ne nne directed subduction zones have rates of sinking chiefly determined i by the far field velocity of plates and ii by the value of negative buoyancy of the slab relative to the country mantle along this type of subduction the subduction hinge generally advances e ne ward toward the upper plate decreasing the subduction rate but it moves w sw ward relative to the mantle all this indicates that subduction zones have different origin as a function of their geographic polarity and the subduction process is more a passive feature rather than being the driving mechanism of plate motions a rotational component combined with mantle density and viscosity anisotropies seems more plausible for generating the global tuning in the asymmetry of subduction zones

fault parameters in the messina strait southern italy and relations with the seismogenic source abstract the messina strait is characterized by strong deformations in pliocene and pleistocene times but considering the historical seismicity significant uncertainity exists as to whether any of the surface fault systems reflects the location geometry and mechanisms of the seismogenic source based on field data and structural analyses the parameters length l displacement d age of activity t minimum slip rate min and total geological moment m g have been derived for all the faults exposed on the sicilian and calabrian sides of the strait the analysis of these parameters shows that the highest rates of activity pertain to interconnected faults of different orientation and length which bound the uplifted crystalline basement relative to the pliocene pleistocene foundered zones of the calabrian side the comparison between the fault slip rates and the regional uplift rates shows that each single fault contributes for a limited fraction only to the whole deformation release in the area the contribution of the whole fault population expressed as cumulative m g release is still one order of magnitude less than the seismic moment release taking into account the underestimation of the geological parameters the lack of information on the offshore faults and the role of anelastic deformation by aseismic creep the data suggest that the long term recurrence of seismic breaks is partitioned at the surface in a complex array of interconnected faults some of these faults might represent basement inherited structures repeatedly and preferentially reactivated over geological time

ionian marine terraces of southern italy insights into the quaternary tectonic evolution of the area 1 new detailed morphotectonic analyses of a well exposed flight of marine terraces along the ionian coast of southern italy has been carried out the area represents a key transect for investigating the middle late quaternary evolution of the southern apennines chain foredeep foreland geodynamic system a major result of the research is the reconstruction of a virtually complete 3d geometry of the marine surfaces along a coastal sector of ca 70 km which 1 documents the occurrence of 18 paleo shorelines and 2 provides evidence for a strong regional uplift affecting the investigated area following a systematic critical review of literature relating to geochronological data integrated with a morphogenetic model based on the interaction between tectonic uplift and eustatic sea level changes the different terraces are correlated to as many highstand sea level peaks dating the highest oldest terrace to ca 600 ka mis 15 the vertical and horizontal distribution of the terraces show a general convergence of the paleo shorelines toward nne which indicates a decreasing trend in differential uplift in that direction ranging from almost 2 mm a in the southwestern sector to about 0 2 mm a in the northeastern sector detailed mapping and 3d reconstruction also emphasize the partitioning of the area into three distinct sectors characterized by different tilting rates this behavior is likely caused by the combined role and activity of three major tectonic structures working at different scales and rates including 1 the reactivation of an out of sequence thrust 2 sliding along the basal detachment of the external apennines wedge and 3 a lithospheric scale duplexing crustal or deeper as a major conclusion within the external sector of the southern apennines chain and its foredeep regional shortening and a contractional tectonic regime persisted throughout the whole quaternary and it is probably still active

oligo miocene rift of sardinia and the early history of the western mediterranean basin the geodynamic evolution of the western mediterranean basin in spite of many studies is still uncertain there is some consensus for interpreting this basin as a kind of small oceanic marginal basin its opening has generally been related to a subduction process which was active during the oligocene miocene somewhere east of sardinia corsica1 7 as the margins of the basin are deeply buried below miocene to present sediments direct lithological and stratigraphical data which could explain the events responsible for its formation are rare8 10 or missing altogether to obtain such data detailed field studies have been undertaken in sardinia fig 1 and the first results are presented here this approach is justified by the fact that in that island oligocene and miocene sediments were deposited in a rift fossa tettonica sarda of verdabasso11 which is the easternmost arm of the complex rift system that affected the european plate during oligocene and miocene times one of these arms evolved towards a small oceanic basin the western mediterranean or algero provencal basin while others such as the gulf of valencia and the sardinia rift aborted and remained at the rift stage its exceptional exposures make it possible to examine the sardinia rift to clarify the sequence of events which created it and to establish a sedimentological model which we believe is directly applicable to the western mediterranean basin

long term behaviour of the late quaternary normal faults in the straits of messina area calabrian arc structural and morphological constraints abstract the calabrian arc is located in the peri tyrrhenian orogenic belt of southern italy and is characterised by intense post collision dynamics this consists of rapid regional uplifting combined with active normal faulting affecting the tyrrhenian side of calabria and the ionian coast of sicily the siculo calabrian rift zone the effects of the two combined processes are well exposed in the straits of messina area that represent a major transfer zone located between two opposing sets of normal faults characterising the southern calabria and the northeastern sicily branches of the rift in the straits of messina region the distribution and elevation of the upper quaternary marine terraces suggest a southward propagation of the normal fault belt from calabria to sicily it occurred at about 125 ka after a long period of tectonic quiescence and was triggered by huge elastic releases in southern calabria the long term behaviour recorded on the distinct fault segments of the rift is to relate to the presence of a crustal barrier that influenced both the geometry and the fault propagation along the rift zone

seismotectonics of the nubia plate compressive margin in the south tyrrhenian region italy clues for subduction inception 1 seismological and structural data are used to constrain the active tectonics of the nubia plate compressive margin in southern italy in this region compressional displacements have resumed at the rear of the maghrebian orogenic wedge since about 700 500 ka and are presently accommodated along a seismic belt in the south tyrrhenian area where a passive margin has developed during late neogene quaternary times earthquake data from the south tyrrhenian belt are analyzed with bayloc a probabilistic nonlinear location method results show that the seismic belt is segmented and involves a series of ne sw and nw se elongated clusters the ne sw clusters are interpreted as high angle reverse fault zones verging toward the southeast whereas the perpendicular clusters are interpreted as possible strike slip fault zones transferring the contractional displacements to advanced segments of the belt in the southeast brittle deformations observed in the quaternary volcanic island of ustica are consistent with the geometry and kinematics of the seismic belt deduced from the seismological data the south tyrrhenian active belt may constitute an early stage of subduction of the tyrrhenian oceanic crust beneath sicily a similar scenario has been hypothesized also for the westward prolongation of the south tyrrhenian belt off the algerian coast by integrating instrumental and historical seismic data with tectonic evidences we infer that the south tyrrhenian belt is probably capable of producing earthquakes with a maximum size close to magnitude 7 the analyzed data suggest a multifault system behavior for the studied compressional belt this inference is important to estimate and mitigate the seismic and tsunamic hazards in such a densely populated region

sea level and climate changes during ois 5e in the western mediterranean palaeontological geomorphological and sedimentological data supported by isotopic dating on oxygen isotopic stage ois 5e deposits from the spanish mediterranean coast are interpreted with the aim of reconstructing climatic instability in the northern hemisphere data point to marked climatic instability during the last interglacial ois 5e with a change in meteorological conditions and consequently in the sedimentary environment the oolitic facies generated during the first part of ois 5e ca 135 kyr shift into reddish conglomeratic facies during the second part ca 117 kyr sea surface temperature sst and salinity are interpreted mainly on the basis of warm senegalese fauna which show chronological and spatial differential distribution throughout the western mediterranean present hydrological and meteorological conditions are used also as modern analogues to reconstruct climatic variability throughout the last interglacial and this variability is interpreted within the wider framework of the north atlantic record all the available data indicate an increase in storminess induced by an increase in the influence of northwesterlies a slight drop of sst in the northern western mediterranean and an important change in meteorological conditions at the end of ois 5e 117 kyr these changes correlate well with the decrease in summer insolation and with the climatic instability recorded in north atlantic high latitudes

seismic anisotropy reveals the long route of the slab through the western central mediterranean mantle abstract in the south eastern corner of the tyrrhenian basin in the central mediterranean sea a tight alignment of earthquakes along a well defined benioff zone marks one of the narrowest active trenches worldwide where one of the last fragment of the former tethys ocean is consumed seismic tomography furnishes snapshot images of the present day position of this slab and seismic anisotropy allows to reconstruct the past kinematics of the subduction process using seismic anisotropy fast directions as a proxy for the present and past mantle flow we look backward for the seismic traces of the slab motion through the western central mediterranean mantle from the starting locus of subduction toward its present day position the result of combining independent data sets provides a coherent pattern of anisotropy that illustrates an example of slab rollback from its initiation point to its present day position

acquisition and processing of wide aperture ground penetrating radar data a 40 channel wide aperture ground penetrating radar gpr data set was recorded in a complicated fluvial aeolian environment in eastern canada the data were collected in the multichannel format usually associated with seismic reflection surveys and were input directly into a standard seismic processing sequence filtering static corrections common midpoint gathering velocity analysis normal and dip moveout corrections stacking and depth migration the results show significant improvements over single channel recordings in noise reduction and depth of penetration by stacking and in spatial positioning and reduction of diffraction artifacts by migration these characteristics increase the potential for reliable interpretation of structural and stratigraphic details thus without having to develop any new software gpr data processing technology is brought to the same level of capability flexibility and accessibility that is current in seismic exploration

erratum to thermoluminescence dating tests of pleistocene sediments from uplifted marine shorelines along the southwest coastline of the calabrian peninsula southern italy palaeogeogr palaeoclimatol palaeoecol 130 1997 25 41

the role of slab detachment processes in the opening of the western central mediterranean basins some geological and geophysical evidence abstract a review of the geological and geophysical data from the central and western mediterranean region and the present day upper mantle structure derived from tomographic studies are utilized in order to define the oligocene recent geodynamic evolution for the area in line with previous work we suggest that the miocene quaternary opening of the western and central mediterranean basins is the result of back arc extension due to the roll back toward the southeast of a northwestward subducting african slab in a geodynamic setting pinned between the alpine and betic collisional zones we find however that this general pattern is complicated by four different detachment events which occurred beneath the alps early oligocene the betic chain aquitanian northern africa langhian and the apennines late miocene pliocene we show that each of these events determines a major tectonic reorganization within the european plate

toroidal mantle flow around the calabrian slab italy from sks splitting 1 sks wave birefringence is likely caused by ongoing and or fossil mantle flow splitting parameters in the southern tyrrhenian subduction zone define a quite complex pattern of fast directions with large delay times up to 2 7 s fast directions are prevalently trench parallel below the slab and rotate to trench normal at the western edge of the slab depicting a ring around it we interpret these anisotropic patterns also observed in laboratory experiment as toroidal mantle flow induced by rollback subduction

sea level fluctuations due to subduction the role of mantle rheology by means of a stratified viscoelastic earth model we study the effect of sinking slabs on the dynamic topography the non hydrostatic geoid and the long term sea level variations sea level fluctuations due to subduction are found to be sensitive to the nature of the 670 km seismic discontinuity and to the rheological layering of the mantle the response of our model to both a single subduction and a realistic distribution of slabs is studied by a numerical simulation based on a simplified approach consistent with previous results we find that an upper bound to relative sea level time variations associated with the initiation of a new subduction in the upper mantle is 0 1 mm yr relative sea level changes driven by the dynamic readjustment of internal mass heterogeneities may thus be comparable with those attributed to other changes in the tectonic regime on a large scale this confirms the relevance of subduction as an important contributor to long term sea level fluctuations copyright 1997 by the american geophysical union

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

narrow subducting slabs and the origin of backarc basins abstract both tectonic and seismic data suggest that horizontally wide in the direction parallel to the axis of the trench dipping subducting slabs typically move stably at fixed angles to the horizontal and that their associated trenches migrate very slowly or not at all in contrast where backarc basins babs exist the associated trenches typically migrate at rates of several cm year this behavior may be related to the finite width of the slabs under babs analysis shows that hydrodynamic suction created by the downdip motion of a wide slab is sufficient to balance the pull of gravity on the heavy slab however for a narrow slab sideways asthenospheric flow into the slab overriding plate corner effectively eliminates the suction which results in the rapid sinking of the slab hydrodynamic modeling is used to quantify this hypothesis modeling is used also to show that wide slabs are stable in their inclined position not because of the gravitational wing like sliding but due to the lifting force produced by the negative pressure suction in the slab overriding plate corner finally the model results confirm that for relatively narrow slabs this lifting force is small and cannot counterbalance gravity therefore when bending moments in a narrow slab exceed the plastic yield limit the slab becomes unstable this instability can cause the rapid migration of the slab s hinge and the associated arc at rates of 10 20 cm year and thus form the bab

fault activity and marine terracing in the capo vaticano area southern calabria during the middle late quaternary abstract the capo vaticano peninsula is a structural high bordered by several normal fault segments mainly striking ne sw and wnw ese and belonging to the so called siculo calabrian rift zone both the two fault systems extend in the tyrrhenian offshore and show recent activity in the capo vaticano peninsula six orders of marine terraces with their preserved paleoshorelines and a top surface have been recognised they form a continuous set of morphological elements ascribed to the last seven principal high stands of the eustatic curve occurred from 330 to 60 kyr on the basis of new chronological data available in the recent literature the morphotectonic analysis of the paleoshorelines allowed recognition of a deformation pattern characterised by a northeastward tilting of the area and to quantify the uplift rates moreover vertical slip rates ranging between 0 25 and 2 5 mm yr have been calculated for a wnw ese trending fault segment the coccorino fault in this structural framework the late quaternary uplift of the capo vaticano peninsula can be related to the activity of both the ne sw and wnw ese striking normal fault systems added to the regional component of uplift the recent activity of these structures is also suggested by the 1905 seismic event that occurred offshore of the capo vaticano peninsula

central and eastern u s surface pressure variations derived from the usarray network abstractlarge magnitude pressure signatures associated with a wide range of atmospheric phenomena e g mesoscale gravity waves convective complexes tropical disturbances and synoptic storm systems are examined using a unique set of surface pressure sensors deployed as part of the national science foundation earthscope usarray transportable array as part of the usarray project approximately 400 seismic stations were deployed in a pseudogrid fashion across a portion of the united states for 1 2 yr then retrieved and redeployed farther east surface pressure observations at a sampling frequency of 1 hz were examined during the period 1 january 2010 28 february 2014 when the seismic array was transitioning from the central to eastern continental united states surface pressure time series at over 900 locations were bandpass filtered to examine pressure perturbations on three temporal scales meso 10 min 4 h subsynoptic 4 30 h and synoptic 30 h 5 days scales case studies of strong pressure pe

interpretation of radon anomalies in seismotectonic and tectonic gravitational settings the south eastern crati graben northern calabria italy the study area is located in the south eastern part of the crati valley northern calabria italy which is a graben bordered by n s trending normal faults and crossed by nw se normal left lateral faults numerous severe crustal earthquakes have affected the area in historical time present day seismic activity is mainly related to the n s faults located along the eastern border of the graben in this area much seismically induced deep seated deformation has also been recognised in the present paper radon concentrations in soil gas have been measured and compared with a lithology b quaternary faults c historical and instrumental seismicity and d deep seated deformation the results highlight the following a there is no evidence of a strong correlation between lithology and the radon anomalies b a clear correlation between the n s geometry of radon anomalies and the orientation of main fault systems has been recognised except in the southernmost part of the area where the radon concentrations are strongly affected by the superposition of the n s and the nw se fault systems c epicentral zones of instrumental and historical earthquakes correspond to the highest values of radon concentrations probably indicating recent activated fault segments in particular high radon values occur in the zones struck by earthquakes in 1835 1854 and 1870 d deep seated gravitational deformation generally coincides with zones characterised by low radon concentrations in the studied area the anisotropic distribution of radon concentrations is congruent with the presence of neotectonic features and deep seated gravitational phenomena the method used in this study could profitably contribute towards either seismic risk or deep seated gravitational deformation analyses

spreading pulses of the tyrrhenian sea during the narrowing of the calabrian slab the opening of the tyrrhenian sea has been punctuated by short lived episodes of oceanic accretion on separate small backarc basins during early pliocene vavilov basin and early pleistocene marsili basin time these spreading pulses are related to slab rollback and are synchronous with the reduction of the subduction zone width during the formation of the narrow calabrian arc using laboratory models we investigated the long term and transient effects of the reduction of slab width on the subduction kinematics we found that the abrupt reduction in slab width results in a pulse of acceleration of the trench retreat velocity as the balance between driving and resisting forces acting on the slab is temporarily modified our findings also show that the time scale and amplitude of spreading observed in the tyrrhenian sea can be experimentally fitted if the scaled viscosity of the uppermost part of the mantle ranges between 10 19 and 10 20 pa s

thermomechanical modelling of slab detachment abstract slab detachment or breakoff is appreciated as an important geological process as shown by recent tomographic imaging using a 2 d upper mantle model 660 km deep and 2000 km wide we have investigated with a 2 d finite difference and marker in cell numerical technique the multi resolutional character of the thermomechanical phenomena related to this complex geological process our experiments show that this process can be initiated in form of slab necking by a prolonged 8 30 my period of slab weakening due to thermal diffusion 60 c my due to strong positive thermal feedback from shear heating detached slab fragments sink rapidly with a tendency for coherent rotation the influence of temperature and pressure dependent thermal conductivity on the process of thermal weakening of the slab is quite significant this supports the idea that the breakoff process is triggered by thermal diffusion on a time scale linearly dependent on heat conductivity rapid topographic changes and increasing volcanic activities due to the melting of subducted oceanic crust are possible scenarios of this vigorously driven geodynamic process

raised pleistocene marine terraces of the crotone peninsula calabria southern italy facies analysis and organization of their deposits abstract wide marine terraces well known in the italian literature are present in the crotone peninsula ionian calabria they are related to the interplay between pleistocene sea level changes and the progressive uplift of the calabrian arc from the middle pleistocene onwards we present a description of facies organization and stratigraphical characteristics of the terrace deposits along with a new geological map of the area all the marine terraces unconformably overlie a plio pleistocene slope succession known as cutro clay the oldest and highest terrace named cutro terrace is placed between 90 and 200 m of elevation and is gently inclined south eastwards four younger terraces placed at progressively lower elevations and dipping seawards at low angles have been recognized the sedimentary deposits of the terraces are represented by mixed carbonate and siliciclastic bodies up to 10 m thick algal reefs and grainstone to rudstone deposits are common in the south eastern part of the study area whereas mostly siliciclastic sandstone units of shoreface environments are more abundant northwards and westwards the deposits of some terraces are made up of minor cycles bounded by subaerial transgressive and flooding surfaces referred to minor sea level fluctuations nne ene e and wnw trending normal fault systems are present within the study area and dissect the marine terraces specifically the activation of ene trending faults took place after the formation of the oldest terrace but prior to the formation of the younger terraces

dynamic equilibrium among erosion river incision and coastal uplift in the northern and central apennines italy erosion river incision and uplift rates in the northern and central apennines italy since 0 9 ma are determined from new cosmogenic nuclide data beryllium 10 concentrations in modern and middle pleistocene sediments indicate erosion rates from 0 20 to 0 58 mm yr these rates are similar to estimates of sediment yield 0 12 0 44 mm yr river incision 0 35 mm yr and uplift 0 01 1 0 mm yr rates inferred from other methods that integrate landscape process rates since the early pleistocene these rates of landscape change are significantly lower than long term exhumation rates of 1 2 mm yr since ca 4 5 ma inferred from thermochronometry collectively these data suggest that hillslope erosion and river incision rates in the northern and central apennines have balanced local uplift rates for 1 my but that exhumation rates have slowed significantly since emergence of the mountain chain in the pliocene this condition of dynamic equilibrium was potentially achieved within ca 3 ma similar to some model predictions of hillslope and fluvial system adjustment

incipient extension along the active convergent margin of nubia in sicily italy cefalu etna seismic zone 1 recent geodetic data are compatible with nne ssw tectonic extension at a rate of 5 mm yr in sicily southern italy within a broader region of net active compression along the nubian plate margin northern africa the structures that accommodate such extensional regime and its cause are still unknown from field structural surveys and seismological analyses the geometry kinematics structural architecture and seismic potential of an extensional seismic zone linking cefalu and mount etna in central eastern sicily are defined the zone includes high angle wnw striking normal and right lateral strike slip faults and subordinate north and nne striking strike slip faults either right or left lateral the occurrence of small discontinuous faults and the absence of related depressions and sedimentary basins suggest that the extensional regime is still in an incipient stage the ongoing seismic activity possibly reactivates preexisting faults instrumentally and historically recorded earthquakes are lower than about 6 in magnitude and destructive events are historically unknown since at least 1300 a d this apparent upper bound of earthquake magnitudes is consistent with the maximum magnitude values estimated from the length of the longest mapped faults and sources of seismic swarms which all together suggest a value between 6 and 6 5 as the maximum expected magnitude that can be proposed at the present stage of investigation for earthquakes in the study area lateral extension on preexisting faults and upwelling of melt mantle material beneath mount etna are considered viable processes to explain at least in part the active extensional tectonics along the cefalu etna seismic zone strike slip seismic faulting beneath mount etna may be part of a previously proposed diffuse transfer zone affecting northeastern sicily and including the tindari fault

influence of trench width on subduction hinge retreat rates in 3 d models of slab rollback subduction of tectonic plates limited in lateral extent and with a free trailing tail i e free subduction is modeled in a three dimensional 3 d geometry the models use a nonlinear viscoplastic rheology for the subducting plate and exhibit a wide range of behaviors depending on such plate characteristics as strength width and thickness we investigate the time evolution of this progressive rollback subduction measure the accompanying return flow in the upper mantle and quantify the plate kinematics due to the 3 d geometry flow is allowed to accompany slab rollback around the lateral edges of the slab the toroidal component as opposed to 2 d geometry where material is forced to flow underneath the slab tip the poloidal component a simple force balance is provided which relates the speed of backward trench migration to the resistive forces of generating flow and weakening the plate our results indicate most of the gravitational energy of the system i e the negative buoyancy of the subducting slab is converted into a toroidal flow 69 a much smaller amount goes into weakening the plate 18 and the remaining amount goes into driving flow parallel to displacement of the slab 13 for the trench widths w we investigate 1500 km a maximum trench retreat rate occurs for trenches 600 km wide which is attributed to the interaction between a plate of finite width and the induced flow which has a lengthscale in the horizontal direction these numerical results quantitatively agree with comparable 3 d laboratory experiments using analogue models with a purely viscous plate material schellart 2004a 2004b including correlations between increasing retreat rate with increasing plate thickness trench width for maximum retreat rate 500 km and estimated amount of slab buoyancy used to drive rollback induced flow 70 several implications for plate tectonics on earth result from these models such as rollback subduction providing a physical mechanism for ephemeral slab graveyards situated above the more viscous lower mantle and endothermic phase transition prior to a flushing event into the lower mantle mantle avalanche

late holocene emergence in calabria italy abstract a field survey along the coasts of calabria has found little evidence of holocene emergence the greatest being no more than 1 0 1 5 m in elevation a former shoreline a thick crust of calcareous algae in growth position at about 0 6 m capping an elevated beachrock slab was dated 2990 60 yr b p this emergence is recent if compared to the time of the climatic optimum and relatively slight if late pleistocene uplift rates which in some cases exceed 1 mm yr are considered this apparent discrepancy can be explained by taking into account glacio and hydroisostatic effects of the last glaciation which have produced subsidence at decreasing rates during the late holocene in a wide area around the former scandinavian ice sheet which includes most of the mediterranean according to isostatic modelling the average subsidence rate during the last 6000 5000 years was between 0 4 and 1 mm yr near the coasts of calabria if global sea level changes can be neglected it is only when the subsidence rate of glaciohydro isostatic origin became slower than the local uplift that emergence at a slower rate than that of the tectonic uplift trend could have begun such emergence is therefore a recent phenomenon in the holocene and its rate is still much slower than that of tectonic uplift predominating in calabria over a longer time scale

controls on trench topography from dynamic models of subducted slabs a finite element method with constrained elements and lagrange multipliers is used to study tectonic faults in a viscous medium a fault representing the interface between overriding and subducting plates has been incorporated into a viscous flow model of a subduction zone in which both thermal buoyancy and the buoyancy associated with the phase change from olivine to spinel are included the fault causes stress to concentrate in its vicinity giving rise to a weak plate margin and a mobile plate if a power law rheology is used surface dynamic topography with either a newtonian or a power law rheology and with typical subduction zone parameters is characterized by a narrow and deep trench and a broadly depressed back arc basin this suggests that oceanic trenches and back arc basins over subduction zones are dynamically compensated by viscous flow our models show that trench depth increases with fault dip angle slab dip angle slab length and age of oceanic lithosphere just prior to subduction the influence of fault dip angle and age of lithosphere on trench depth is greater than the influence of slab dip angle and slab length these relationships of trench depth versus subduction zone parameters explain well the statistics of observed trench depths for those subduction zones with oceanic lithosphere on both sides of the trench observed trench depths have been corrected for fault and slab dip angles based on the relationships from the dynamic models after correction to a common set of parameters trench depth correlates linearly with age of lithosphere prior to subduction with a slope which is close to what models having high viscosities within the transition zone and lower mantle predict comparison between the trench depths corrected for fault and slab dip angles and model trench depths suggests that the resisting tangential stress on faults in subduction zones may range from 15 mpa to 30 mpa depending on model details

topography of the calabria subduction zone southern italy clues for the origin of mt etna 1 calabria represents an ideal site to analyze the topography of a subduction zone as it is located on top of a narrow active wadati benioff zone and shows evidence of rapid uplift we analyzed a pattern of surface deformation using elevation data with different filters and showed the existence of a long wavelength 100 km relatively positive topographic signal at the slab edges the elevation of mis 5 5 stage marine terraces supports this pattern although the record is incomplete and partly masked by the variable denudation rate we performed structural analyses along the major active or recently reactivated normal faults showing that the extensional direction varies along the calabrian arc and laterally switches from arc normal within the active portion of the slab to arc oblique or even arc parallel along the northern and southern slab edges this surface deformation pattern was compared with a recent high resolution p wave tomographic model showing that the high seismic velocity anomaly is continuous only within the active wadati benioff zone whereas the northern and southwestern sides are marked by low velocity anomalies suggesting that large scale topographic bulges volcanism and uplift could have been produced by mantle upwelling we present numerical simulations to visualize the three dimensional mantle circulation around a narrow retreating slab ideally similar to the one presently subducting beneath calabria we emphasize that mantle upwelling and surface deformation are expected at the edges of the slab where return flows may eventually drive decompression melting and the mount etna volcanism

neogene uplift of central eastern patagonia dynamic response to active spreading ridge subduction the chile triple junction ctj episodically migrated northward during the past 14 ma from 54 s to its present day position at 46 30 s as different almost trench parallel spreading segments entered in subduction this migration resulted in the opening of an asthenospheric window below patagonia inducing a disturbance in the regional mantle convection on the overriding plate the middle miocene time corresponds to a major change in the central patagonian basin dynamics with a transition from subsidence to generalized uplift the detailed mapping and the morphological study of post middle miocene terraces evidence regional scale trench parallel tilt histories that differ depending on latitude south of 46 30 s the slopes of the fluvial terraces indicate a change from northward to southward tilt during late miocene terraces younger than the early pliocene do not show any trench parallel tilt north of 46 30 s in contrast only northward tilt active until the pleistocene is recorded we use a semianalytical model of dynamic topography which suggests that the northward migration of the chile triple junction should be accompanied by a dynamic uplift of the central patagonian basin uplift would cause both north directed and south directed tilt north and south of the triple junction respectively with values of 0 1 0 2 500 km east of the trench tilt measured in the southeastern part of the central patagonian basin 0 1 is comparable to values predicted using the semianalytical model the dynamic topography associated to the chile ridge subduction may have exerted a major control on the neogene dynamics of patagonia

mantle unrooting in collisional settings abstract we present a two dimensional numerical model to study the thermo mechanical evolution of the lithosphere under a convergence regime in order to define the conditions that lead to lithospheric mantle break up and consequent unrooting a newtonian rheology with a temperature dependent viscosity is considered the system is not closed and horizontal flow through lateral boundaries is permitted a horizontal velocity is imposed at the top of the model to simulate compression whereas velocity vanishes at the bottom of the model the initial conditions correspond to a homogeneous lithosphere with a constant heat production in the crust the analysis of variations of maximum shear stress strain rate and total kinetic energy allowed us to define four major stages during the mantle unrooting process orogenic growth initiation of gravitational instability until lithospheric failure sinking of the detached lithosphere and relaxation of the system numerical results also show that the conditions for lithospheric unrooting strongly depend on the convergence velocity the wideness of the deformation zone and the imposed rheology

recent and active tectonics in the calabrian arc southern italy normal faulting which has developed since the middle pleistocene with an overall ese wnw extension is the dominant mode of deformation which has characterized the calabrian arc up to the present quaternary normal faults extend for a total length of about 180 km along the inner side of the arc the different normal fault segments which during the pleistocene controlled the evolution of the main marine sedimentary basins are varying in length from 10 to 20 km and have fault escarpments showing a very young morphology which define the fronts of the major mountain ranges of the arc the morphological features of the fault escarpments suggest slip rates of 0 8 1 1 mm yr for the last 700 k y and values of 0 6 0 9 mm yr for the last 120 k y indicating a uniform rate of faulting since the middle pleistocene crustal seismicity and the mesoseismic areas of historical large events 6 5 m 7 1 which occurred in the calabrian arc are located within a narrow belt along the hanging walls of the quaternary normal fault segments this suggests that the normal faults which dissect the inner side of the calabrian arc may be seismically active

tectonics and seismicity of the tindari fault system southern italy crustal deformations at the transition between ongoing contractional and extensional domains located above the edge of a subducting slab 1 the tindari fault system southern tyrrhenian sea italy is a regional zone of brittle deformation located at the transition between ongoing contractional and extensional crustal compartments and lying above the western edge of a narrow subducting slab onshore structural data an offshore seismic reflection profile and earthquake data are analyzed to constrain the present geometry of the tindari fault system and its tectonic evolution since neogene including the present seismicity results show that this zone of deformation consists of a broad nnw trending system of faults including sets of right lateral left lateral and extensional faults as well as early strike slip faults reworked under late extension earthquakes and other neotectonic data provide evidence that the tindari fault system is still active in the central and northern sectors and mostly accommodates extensional or right lateral transtensional displacements on a diffuse array of faults from these data a multiphase tectonic history is inferred including an early phase as a right lateral strike slip fault and a late extensional reworking under the influence of the subduction related processes which have led to the formation of the tyrrhenian back arc basin within the present regional geodynamic context the tindari fault system is interpreted as an ongoing accommodation zone between the adjacent contractional and extensional crustal compartments these tectonic compartments relating to the complex processes of plate convergence occurring in the region the tindari fault system might also be included in an incipient oblique extensional transfer zone linking the ongoing contractional belts in the calabrian ionian and southern tyrrhenian compartments

origin and evolution of the west philippine basin a new interpretation abstract combined analyses of the magnetic lineations and seafloor structures of the west philippine basin show that it was formed by spreading from the central basin spreading center in two distinctly different spreading phases before and after subduction was initiated along the palau kyushu trend at 45 ma b p these episodes are recognized by differences in the strike of the magnetic lineations spreading rates density and strike of fracture zones and basement relief from 60 45 ma b p spreading was ne sw relative to present orientations at a half rate of 44 mm a at about 45 ma b p the spreading direction changed to a more n s direction with a reconfiguration of the central basin spreading center into numerous short e w segments offset by closely spaced n s transform faults spreading slowed to a half rate of 18 mm a and ceased at 35 ma b p thus the west philippine basin originated at 45 ma b p by the trapping of normal ocean crust west of the initial subduction along the palau kyushu trend the 45 35 ma b p period represents the dying phase of spreading on the central basin spreading center following isolation of the west philippine basin from the plate driving forces of the pacific

morphometric analysis and amino acid geochronology of uplifted shorelines in a tectonic region near reggio calambria south italy the tectonic coastline of the calabrian peninsula provides an opportunity to study the morphology and history of elevated marine shorelines near capo dell armi eleven shorelines are preserved between sea level and 256 m with some correlation difficulties posed by the dissection of the area by intermittent streams we are able to correlate several of the shorelines across the entire study area with the support of correlations provided by amino acid geochronology we have identified four shorelines dating from the last interglacial period isotope stage 5 the oldest two both contain the strombus bubonius fauna and are of indistinguishable early last interglacial ages stage 5e aminozone e ca 125 ka the highest terrace vii is associated with a shoreline at 157 m and the lower with a shoreline around 125 105 m a s l of the two younger stage 5 without strombus bubonius the higher v lies at about 90 100 m and produces amino acid ratios slightly younger than but statistically indistinguishable from those of aminozone e however the youngest last interglacial shoreline deposits iv have produced amino acid ratios correlated to late stage 5 5a elsewhere in the mediterranean basin amino acid and geomorphic data have shown that uplift varies the study area from 0 85 to 1 03 m ka and suggeststhat constant uplift along any one traverse is unlikely