earthquake locations by 3 d finite difference travel times abstract we present a new method for locating earthquakes in a region with arbitrarily complex three dimensional velocity structure called quake3d our method searches a gridded volume and finds the global minimum travel time residual location within the volume any minimization criterion may be employed the l1 criterion which minimizes the sum of the absolute values of travel time residuals is especially useful when the station coverage is sparse and is more robust than the l2 criterion which minimizes the rms sum employed by most earthquake location programs on a unix workstation with 8 mbytes memory travel time grids of size 150 by 150 by 50 are reasonably employed with the actual geographic coverage dependent on the grid spacing location precision is finer than the grid spacing earthquake recordings at six stations in bear valley are located as an example using various layered and laterally varying velocity models locations with quake3d are nearly identical to hypoinverse locations when the same flat layered velocity model is used for the examples presented the computation time per event is approximately 4 times slower than hypoinverse but the computation time for quake3d is dependent only on the grid size and number of stations and independent of the velocity model complexity using quake3d with a laterally varying velocity model results in locations that are physically more plausible and statistically more precise compared to flat layered solutions the earthquakes are more closely aligned with the surface fault trace are more uniform in depth distribution and the event and station travel time residuals are much smaller hypocentral error bars computed by quake3d are more realistic in that the trade off of depth versus origin time is implicit in our error estimation but ignored by hypoinverse

geodynamic implications of earthquake data in the southern tyrrhenian sea abstract data from short period seismic stations operating in calabria sicily and the aeolian islands have been used to investigate earthquake properties of the southern tyrrhenian lithosphere the results have been analyzed taking into account other geophysical and geological information available in the literature for the same region with the main purpose of contributing to the definition of local geodynamic processes space distribution and focal mechanisms of earthquakes support the hypothesis of southeastward migration of the southern tyrrhenian lithosphere shared by several authors in their tectonic modelling of the area we find that most seismicity appears to be related to two main faults crossing the aeolian island archipelago sisifo and vulcano and propose that these faults are important dislocation structures associated with the lithosphere migration process we also give a detailed picture of the seismic behaviour of the above mentioned fault systems by analyzing the earthquake depth distribution focal mechanisms seismic clustering and strain release some degree of activity was also detected at the eastern boundary of the southern tyrrhenian area calabrian arc in particular our results demonstrate that in this highly stressed zone of contact between different tectonic units tyrrhenian and ionian basins strain is released under seismic form up to depths of the order of 25 km in the crust and not just in the shallowest structures as proposed by other authors

neogene tectonostratigraphy and kinematics of calabrian basins implications for the geodynamics of the central mediterranean abstract a new structural model for the calabrian arc southern italy is presented based on a systematic analysis of basin kinematics combined with a review of the literature on basement structure three tectonic patterns can be distinguished a nw se trending oblique thrust zones determining a set of n130 trending segments b sw ne to e w trending thrust zones and c radial and concentric tensional fault systems in the southern tyrrhenian back arc area these faults combined with dome shaped uplift centres determine the actual arc patterns a and b can be regarded as the on shore representation of the calabrian accretionary wedge system the kinematics of various types of basins such as piggy back pull apart and complex oblique strike slip basins are connected to these patterns the patterns a and b can be linked to the middle miocene early pliocene development of oblique convergent crustal shear zones strike slip cycle whereas pattern c can be linked to the pleistocene collapse of the southern tyrrhenian basin and concentric uplift of the arc our structural model has considerable implications for the understanding of the kinematic evolution of the central mediterranean we propose a model in which the evolution is characterized by an alternation of the translation of the calabrian lithosphere element either to the southeast gravitationally or to the northeast compression combining a our analyses of basin evolution b the structural model and c some considerations concerning kinematics of the central mediterranean with the geodynamic mechanisms as proposed in literature we present a model which consists of a geodynamic cycle comprising the following three stages 1 a tension stage with back arc basin opening related to the diapiric inflow of asthenosphere material and roll back of the subducted ionian slab resulting in gravitational displacement of the calabrian element to the southeast 2 a transpression stage with oblique overthrusting towards the northeast upon the southern apennines and 3 a compression stage with ne sw compression due to oblique dextral shear along the north african margin plate rupture lithosphere split and back arc basin collapse

new unspiked k ar ages of volcanic rocks of the central and western sector of the aeolian islands reconstruction of the volcanic stages abstract a geochronological study of the filicudi salina lipari and vulcano islands aeolian archipelago using the unspiked potassium argon technique provides new age data which combined with stratigraphic correlation better constrain the temporal evolution of volcanism the unspiked k ar age of the oldest exposed lavas on filicudi 219 5 ka is significantly younger than the previous estimation of 1 02 ma in the general context of aeolian volcanism this new date suggests that the volcanism of the western sector of the aeolian archipelago is younger than previously thought geochronological data point out on the rapid transition from calc alkaline to potassic volcanism the distribution of the k ar ages within the salina lipari vulcano group shows that the volcanism started on lipari and propagated over time northward on salina and southward on vulcano geochronological and geophysical data suggest that the onset of volcanism in the central sector of the aeolian arc may be due to a mantle upwelling structure located below lipari a change in the style of the eruptions occurred in the salina lipari vulcano system at about 100 ka from the present low energy magmatic eruptions occurred between 188 and about 100 ka from about 100 ka to the present higher energy eruptions and low energy events due to magma water interaction also occurred this change in the style of activity together with the appearance of evolved products i e rhyolites during the last 50 ka is consistent with the formation of magmatic reservoirs located at shallower depth with respect to those of the 188 100 ka period the new geochronological data and available petrological models reveal that a change in the deep source of the primary magmas occurred in a relatively short time interval

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

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

a 550 km long moho traverse in the tyrrhenian sea from o b s recorded pn waves six obs deployed on a 550 km line in the tyrrhenian sea furnish reversed and overlapping profiles from 43 shots at 12 km intervals head waves recorded from a 8 km s refractor the moho permitted the computation of the crustal thickness which shows this basin to be underlain by an oceanic type of crust at least in two 100 km wide regions variations of pn arrival times mirror strong topographical changes of the moho differences in dips at the extremities towards corsica and calabria are documented

crustal structure and seismicity of southern tyrrhenian basin abstract in this paper all the travel time data from crustal earthquakes that occurred in the period 1978 1991 along the southern tyrrhenian sea have been re examined in particular 410 local earthquakes recorded at a minimum number of seven seismic stations and 52 shots fired on sea have been utilized to infer a tomographic image of the velocity model beneath a region located in the domain 37 41 39 10 n and 14 10 16 44 e these earthquakes are selected from a database containing about 1000 local earthquakes the results from the inversion of about 9000 travel times confirm the strong lateral variations of the velocity model relative to compressional and shear waves below the volcanic center of the aeolian islands in the upper crust several low velocity bodies are found in agreement with features inferred from seismicity and other geophysical data the 3 d velocity images also show a thickening of the crust from the center of the tyrrhenian sea towards the coasts of sicily and calabria finally hypocenter locations derived from inversion which appear to be significantly less scattered than using 1 d velocity models help to identify with some accuracy two notable fault systems of the southern tyrrhenian basin

fault plane solutions and seismicity of the italian peninsula abstract a new fault plane solution map of the italian peninsula is presented in this paper the earthquakes analyzed are included in the period 1905 1980 with magnitudes ranging 4 7 75 earthquakes are located in the crust while 31 are related to the deep and intermediate zone of the calabrian arc the large seismic events of the italian peninsula are generally associated with normal faulting while strike slip motion is mostly related to small earthquakes located along lateral segments of the mountain chain the deep and intermediate earthquakes of the tyrrhenian sea indicate predominant down dip compression and strike slip motion at the boundaries of this benioff zone this last is interpreted as a remnant of a subduction zone active since oligocene extending to 500 km depth with a very small lateral size about 300 km the present tectonics of this benioff zone is strongly conditioned by the lateral bending more so than the gravitational sinking process the coexistence of thrust and normal faulting motion associated to the earthquakes within a few tens of kilometers of each other seems to be explained by the strong lateral inhomogeneities of the crustal rocks present in this region more so than to the depth of the seismogenetic zone and the nature of the faulting process

new data and hypothesis on the development of the tyrrhenian basin abstract among those basins which developed during the neogene and quaternary at the rear of the perimenditerranean mountain chains the tyrrhenian basin is the most recently formed comparing the available geological and geophysical data the tyrrhenian domain and its neighbourhoods can be divided into more or less homogeneous sectors namely northern and southern tyrrhenian apenninic chain maghrebides chain apulian and iblean african foreland ionian foreland for each sector the different phenomena involved and the crustal characteristics are discussed the evolution of the domain has been explained by the application of a crustal stretching model developed for continental margins this approach predicts the formation of basinal areas as a result of the europe africa collisional movements within a plastic rigid deformation model taking into account the mass redistribution after collision the model explains both the distension developed within the collisional system and the penecontemporaneous development of compressive and distensive phases as a consequence of the intraplate stresses horizontal shearings affecting the whole lithosphere at different levels occur with delaminations asthenosphere uprising and gradual collapse in the upper crust e w trending and strike slip dextral faults played a primary role in the evolution of the tyrrhenian basin inducing the largest tearings at the end of the major transcurrent systems such an evolution is complicated by the migrating motion of the shear zone from n to s and by the penecontemporaneous stop in the extension from the northern towards the southern domains of outstanding importance is the shear zone which borders the southern tyrrhenian enabling the opening of the basin and allowing the development of the major group of en echelon sub basins with a nw se trend

continental collision and basin opening in southern italy a new plate subduction in the tyrrhenian sea an analysis of the spatial distribution of the seismicity of the southern tyrrhenian sea is presented with the aim of putting constraints on the geometry of the complex benioff zone of this area by relocating the earthquakes that occurred in the period 1985 1990 the data set used in this analysis is based on information from ing isc and neis databases in order to ensure the quality of epi hypocentral locations we based our selection of earthquakes on both the available number of p and s readings at least eight p and two s pickings and the epicentral distances of the stations reporting the event 5 such a selection enabled us to obtain a catalogue of 450 well located events with focal depths of up to 500 km the seismogenetic volumes estimated from the distribution of hypocentres of the whole seismicity analysed were interpreted according to a recent geodynamic model proposed for this area this has led us to the hypothesis of an active nw se oriented subduction of the lithosphere generated and stressed by the opening of the tyrrhenian basin

the tyrrhenian apennines system structural setting and seismotectogenesis abstract the available geological geophysical and seismological data of the tyrrhenian apennines system are briefly reviewed and synthesized in a number of sketch maps integrating and comparing these data a large scale simple shear kinematic model is proposed for the tyrrhenian apennines system that is here interpreted as an oblique asymmetric passive continental margin developed during the progressive counterclockwise rotation of the adriatic foreland from the late miocene to the present in the frame of this working hypothesis the thinning and stretching of the tyrrhenian crust were accommodated by progressive eastward motion of extensional allochthonous slices bounded by low angle west dipping oblique shear zones rotating above a common detachment that penetrates into the mantle lithosphere at any given time the most external eastward moving slice is bounded by a transtensional shear zone at the top and by a transpressional one at the bottom the displacement within the hanging wall of the transtensional shear zone is accommodated by high angle normal faults and en echelon grabens the displacement within the hanging wall of the transpressional shear zone is instead accommodated by co axial en echelon sets of folds thrusts and high angle strike slip faults thus the development of the late miocene pliocene pleistocene contractional strain field of the apennines of italy might not be a consequence of complex subduction processes but subordinate to the deformation processes that lead to the progressive opening of the tyrrhenian sea the seismicity of the crustal apennines of italy is analyzed in the frame of the above history of progressive deformation and a seismotectogenetic model is outlined

relationships among crustal structure volcanism and strike slip tectonics in the lipari vulcano volcanic complex aeolian islands southern tyrrhenian sea italy abstract the lipari vulcano volcanic complex lvvc aeolian arc southern tyrrhenian sea italy develops along a strike slip fault system that bisects the aeolian arc the lvvc crustal structure is investigated by applying seismic methods to two data sets p wavefronts generated by local and distant events constrain the shallow velocity structure dss data provide shape and depth of the main crustal discontinuities the obtained velocity model shows that the lvvc shallow structure is characterized by the presence of two sharp lateral discontinuities the northern discontinuity bounds a low velocity basin like structure including the la fossa caldera and mt guardia caldera depressions the southern discontinuity coincides with the southern boundary of a high velocity diffractor located beneath the la fossa cone direct modeling of dss data define three crustal discontinuities showing a complex geometry the intra crustal interfaces and the moho discontinuity show an upheaval beneath the lvvc central sector the estimated crustal velocities are lower than those generally reported for the continental crust this feature is due to the high heat flux and fluid circulation affecting the lvvc area the ratio between the thickness of the upper and lower crust and the presence of the moho upheaval are consistent with that reported for continental areas affected by extensional strain the collected geophysical data combined with volcanological and structural information indicate that a the mt guardia and la fossa caldera depressions represent the surface expression of a single structure whose formation is mainly due to tectonic processes b the lvvc crustal structure and the evolution of the volcanism are consistent with those recognized in zones of transition from arc related to rift volcanism in addition results of a preliminary mechanical analysis based on the available structural data indicate low values of the ratio between magmatic overpressure and tectonic stress this suggests a passive mechanism of mantle upwelling the mantle upwelling is due the post collisional normal strike slip tectonics affecting the aeolian arc

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

travel time residuals and three dimensional velocity structure of italy jeffreys bullen p and pkp travel time residuals observed at more than 50 seismic stations distributed along italy and surrounding areas in the time interval 1962 1979 indicate the complex velocity pattern of this region strong lateral velocity inhomogeneities and low velocity zones are required to explain the observed pattern of residuals in particular late arrivals of about 1 sec are observed in the apenninic mountain range requiring both greater crustal thickness and low velocity layers coherent with seismic refraction data and surface wave dispersion measurements the seismic stations located in the western and eastern alps indicate the presence of high velocities in the western alps the strong azimuthal variation of residuals and the high values of early arrivals have a close relationship to the ivrea body an intrusive crustal complex characterized by a velocity as high as 7 7 2 km sec a travel time inversion performed with theaki et al 1977 block model confirms the peculiar characteristics and the sharp variations in the lithosphere of the whole italian region with values of velocity perturbations between many adjacent blocks ranging in size from 50 to 100 km and independent from the earth parametrization chosen reaching values up to 10 in the lithospheric part and 5 in the asthenosphere 3 d inversion requires also high velocity along the tyrrhenian coastal margin equivalent to an uprise of major crustal and lithospheric discontinuities along this part of the italian peninsula moreover low velocity material must be present in the northern part of the adriatic foreland in the lithosphere asthenosphere system closely related to the stress and seismicity pattern and the lateral bending of the lithosphere in the same region

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

construction of a seismotectonic model the case of italy procedures for constructing a seismotectonic model of italy designed to be used as a basis for hazard assessment are described the seismotectonic analysis has essentially been based on a gis aided cross correlation of three data sets concerning the 3 d structural model of italy and surrounding areas the space distribution of historical and present seismicity the kinematic model of the central mediterranean region referred to the last 6 ma and including the available information on the present day plate motion and stress field the seismicity pattern in the study area is controlled by a quite complex geodynamic framework which includes continent continent convergence alps and dinarides with development of a neutral arc bordering the plate margins plate divergence across margins characterized by passive slab sinking northern apennines and calabrian arc with development of backarc basins northern tyrrhenian sea and southern tyrrhenian sea flanked by forelandward migrating thrust belt foredeep systems plate divergence across a margin previously characterized by lithosphere sinking and afterwards discharged from the subducted slab southern apennines with development of quite peculiar rift processes within the inactive thrust belt transpression northern sicily due to the combined effect of plate convergence africa europe and high rate flexure hinge retreat of an intervening plate adria microplate with high angles between the respective slip vectors intraplate strain partition and fault activity mainly combined strike slip and thrust motions possibly in correspondence of inverted structures the results of the seismotectonic analysis are synthesized in a zonation of italy in which every delimited zone corresponds to the surface projection of a kinematically homogeneous segment of a seismogenic fault system in cornell type hazard evaluations every polygon should be considered as a homogeneous source zone seat of randomly distributed earthquakes a homogeneous mechanical behaviour of an entire zone and a random earthquake distribution within a single source zone obviously represent oversimplified assumptions since every zone includes one or more master fault segments responsible for the greatest events in the area and several second order associated faults responsible for the background minor seismicity therefore major faults and background seismicity should be treated separately nevertheless the oversimplified assumption of homogeneous seismic zones was the price the authors consciously paid to produce in a reasonably short time a homogeneous product relative to the entire national territory suitable for earthquake hazard evaluation and for decisions regarding risk mitigatiton

the origin of the apenninic arcs abstract the apennine area is composed of a variety of arcs some of them forming the mountain chain and some of them being submerged below the po plain and the adriatic sea the structure of the apennine mountain belt is that of a succession of northeast east and southeastward directed arcs corresponding to single thrust sheets each arc is limited by n s oriented dextral transcurrent faults data from volcanology gravimetry and reflection seismic surveys show that an important section of the upper mantle is involved in these features the geodynamic reconstruction during neogene times i e the period of apenninic up building suggests that a unique arc existed from oligocene to middle miocene times as a result of the rotation of the sardo corso continental block this arc was successively disrupted in several segments which advanced and shortened differentially as a function of the resistance to the orogenic expansion opposed by the rigid adriatic foreland this new tectonic phase which is responsible for most of the apenninic features has been triggered by the differential evolution of anomalous mantle domes in the tyrrhenian area from post middle miocene times onwards

structural evolution of the tyrrhenian back arc basin abstract the tyrrhenian basin has developed as a marginal basin through drifting of the calabrian sicilian arc system towards the east southeast the main structural features of the basin result from this movement the tensional structures normal faults of the margins are mainly aligned n10 to n30 e the transform faults are oriented n110 n120 e except for a previous structuralization linked to the western mediterranean rifting and drifting the first extensional movements affected the tyrrhenian area as early as lower miocene time during the post burdigalian nevertheless the main rifting phase which led to oceanic accretion was initiated during the late tortonian the narrow central oceanic area generated mainly around the early pliocene is restricted to the rift s axis the marginal basin type of evolution of the tyrrhenian sea is most probably directly linked to subduction of the ionian lithosphere nevertheless interferences between collision in the surrounding apennines calabria or sicilides and subduction processes have dominated this special back arc basin evolution since late tortonian time the tyrrhenian arc shows a regional n120 e oriented tensional pattern short compressional events occur briefly in middle pliocene and middle pleistocene times correlated with brief paroxysmal phases of extension and subsidence the deformation depends on the presence of a subduction zone parallel to the calabrian arc swell which allows the migration of the unblocked segments of the arc in a n120 e direction

interpretation of heat flow density of the apennine chain italy the apennine chain is a consequence of the continental collision between europe and africa characterized by several compressive phases with events of intense shortening during one of these phases from early oligocene to early miocene the continental crust broke into various segments which became packed one over the other forming an adriatic verging structure of imbricated listric wedges this event is thermally modeled in the southern apennines by the successive overthrust of two slabs of 7 km total thickness and explains the low heat flow density hfd 40 mw m 2 observed there in the northwestern apennines modeling is on the basis of the overthrusting of a slab 10 km thick which reduced the hfd of the steady lithosphere 63 mw m 2 observed on the iblean platform to 50 4 mw m 2 from the late miocene onwards tensional tectonism developed in the internal areas of the chain application of mckenzie s simple stretching model shows that the high regional heat flow 100 mw m 2 obtaining by filtering the observed data is explained by a stretching of the lithosphere of a factor 3 1

late quaternary deformation history of the volcanic edifice of panarea aeolian arc italy a series of raised palaeoshorelines is documented along the emergent coastal slopes of panarea and surrounding islets at elevations of 115 palaeoshoreline ia and 100 m a s l ib 62 5 m ii 35 m iii 12 m iv 10 12 va and 5 m vb according to stratigraphic constraints and cross cutting relationships these palaeoshorelines are correlated with discrete high sea level stillstands during marine oxygen isotope stages mis 5e 5c 5a and 3 coastal elevation changes suggest the occurrence of a long term sustained uplift trend of the volcanic edifice since the last interglacial last 124 ka the uplift rates are not constant but display a progressive deceleration from maximum values of 1 5 1 58 m ka in the period between 124 and 100 ka down to the lowest values of 0 66 0 69 m ka which tend to be constant starting from 81 ka bp the long term deformation pattern of panarea suggests that a transitory volcano related component of uplift interplayed with the regional tectonic component affecting the sub volcanic basement which has undergone a persistent and widespread uplift since the mid pleistocene the volcano related component of uplift prevailing between 124 and 100 81 ka is interpreted as the result of visco elastic deformation mechanisms which characterize the progressive re equilibration of the shallow magmatic system following the incoming quiescence of the volcanic edifice the long term uplift values at panarea are higher than in the main portion of the western central aeolian arc where a mean uplift rate of 0 34 m ka was estimated since the last interglacial last 124 ka such a pattern of deformation on a regional scale may be a response to active deformation processes connected with the southeastward rollback of the subducting ionian slab which is still active only in correspondence with the eastern sector of the aeolian arc including panarea in the short term a localized submergence trend has been documented at the nearby islet of basiluzzo for the last 2 000 years likely connected to neo tectonic movements along main ne sw trending faults

an experimental setup for fluid venting in unconsolidated sediments new insights to fluid mechanics and structures abstract focused outflow of water at the seafloor termed seepage or fluid venting is a widely recognized global phenomenon in an effort to better understand the mechanisms by which fluid flow related structures form we performed laboratory seepage experiments using samples representing a broad range of grain sizes and hydraulic conductivities 10e 3 to 10e 7 m s detailed observations led to the recognition of a typical often repeated progression of fluid flow structures that form during processes of increasing and decreasing hydraulic gradients the development of fluid flow structures like macro pores conduits and pipes is strongly dependant upon cohesion but is unrelated to grain size variations from sample to sample partial liquefaction leads to permanent changes in the grain fabric and to an increase in hydraulic conductivity our observations explain the longevity of seep sites and systematic relationships between hydraulic gradients grain fabric appearance and hydraulic conductivity that could be used to estimate flow rates based on structural findings

crayfish burrows from late jurassic late cretaceous continental deposits of patagonia argentina their palaeoecological palaeoclimatic and palaeobiogeographical significance abstract the trace fossil loloichnus baqueroensis igen and isp nov from late jurassic late cretaceous continental deposits of patagonia argentina includes thickly lined mostly passively filled and y branched burrows other important features of this ichnofossil are the inner surface texture of lining showing transversal elongated and adjacent grooves and less commonly the pelletal filling of burrows l baqueroensis is recorded from the bajo grande bajo tigre punta del barco and laguna palacios formations which were deposited in different volcaniclastic environments of the deseado massif and san jorge basin geological provinces respectively the described burrows are found in many levels of palaeosols developed in reworked piroclastic deposits where they are the main component of the ichnofabrics in association with meniscate and thinly lined burrows and a diffuse and complex boxwork of small diameter burrows root traces are also present and in many cases occur inside l baqueroensis considering general morphology surface texture filling types palaeoenvironments in which they occur and comparisons with extant and fossil decapod burrows the likely trace makers of l baqueroensis were crayfishes decapoda astacidea probably parastacidae the producers of l baqueroensis inhabited soils where their burrows probably reached the water table and contained roots that were used for feeding considering climatic preferences of extant parastacids it is proposed a temperate climate for central patagonia during the deposition of the studied units the widespread presence of crayfishes during late jurassic late cretaceous times in central patagonia supports the monophyletic origin of this group during the triassic and suggests that the present restricted geographic distribution in southern south america is a relict of a broader one

seismic strain and seismogenic stress regimes in the crust of the southern tyrrhenian region abstract an investigation has been performed to identify and characterize the seismic deformation zones active over the last decades in the region of italy that has experienced the strongest seismicity during the last centuries the study is based on the estimate of hypocenter locations fault plane solutions seismogenic stress and seismic strain tensor orientations carried out using the entire dataset of the national and local seismic networks and the recently improved three dimensional 3d crustal velocity model of the study area a series of simulation tests have been performed to evaluate the significance of the earthquake space distribution obtained and whether it was influenced by network geometry problems related to the sea and the lack of ocean bottom seismometers in the sectors where hypocentral location was synthetically proved to be reliable space distributions of earthquakes located with epicenter and focal depth errors less than 3 and 4 km respectively have been compared with local geology in order to identify seismogenic faults the dataset of 32 fault plane solutions estimated with fault parameter errors less than 20 has been used to investigate space variations of seismogenic stress and seismic strain orientations over the study area stress was found to be uniform in the messina strait and southern calabria where inversion of the available set of 11 fault plane solutions showed clear evidence of an extensional regime the different orientations of the minimum compressive stress and strain found in this sector together with the information available on local geology and tectonics lead us to propose that the seismicity occurring over the last decades in the messina strait and southern calabria was not in general produced at the main faults but at minor faults activated by the main tectonic stress field acting in the area to the west in the sector including western etna the nebrodi chain and the western aeolian islands analysis of the available set of 16 fault plane solutions revealed a certain degree of stress heterogeneity with an apparent prevalence of north south compression this east to west change of stress strain regimes is evaluated in the light of current hypotheses regarding the geodynamics of the study region

a model for the 1908 messina straits italy earthquake by inversion of levelling data abstract the 28 december 1908 messina earthquake was a normal faulting event which produced considerable vertical displacements three levelling surveys having an overall extension of 125 km in calabria and sicily were performed by the igmi italian military geographical institute shortly before the occurrence of the main event and during the first months of 1909 vertical subsidence up to 70 cm was measured at bench marks located close of messina the inversion of the observed displacements has been performed by using a model consisting of uniform dislocation on one or more rectangular faults and the mathematical formalism developed by matsu9ura and hirata 1982 results indicate that the observed displacements are well modeled by a normal fault oriented about ns with a dislocation of 1 5 m dipping 39 e this fault is located beneath the messina straits with the upper end at 1 km depth and crossing to the city of messina this model gives a seismic moment m o 4 9 0 8 10 26 dyne cm and shows a good agreement with the fault plane solution derived from the long period p wave first arrivals

transpressive strain on the lipari vulcano volcanic complex and dynamics of the la fossa cone aeolian islands sicily revealed by gps surveys on a dense network abstract ground deformation resulting from the last two gps surveys carried out in march 2006 and september 2007 on the lipari vulcano volcanic complex are analyzed data inversion was performed by genetic algorithms approach using the horizontal strain measured on 258 gps baselines in order to avoid bias due to the ambiguity in fixing the reference system and to disregard the vertical deformation of the la fossa cone there are two networks in this area the main lipari vulcano network and the denser vulcano nord one surveying strategies adopted for the main network during the latest surveys allowed long baselines from lipari and vulcano to the surrounding permanent stations in the southern tyrrhenian to be processed with reliable accuracy the fast static strategy was instead adopted to survey the vulcano nord network data from the main lipari vulcano network has been processed in the itrf05 frame and also in a local reference frame together with the vulcano nord data a significant northward motion of vulcano island with respect to the itrf05 has been detected this motion abruptly decreases in the northern part of vulcano suggesting a decoupling of the main vulcano island from the rest of the volcanic complex the analysis in the local reference frame evidenced a relative sse ward motion of lipari and northern part of vulcano with respect to the central and southern vulcano this comparison also highlights a local uplift of the la fossa cone in addition a strain tensor analysis was performed which highlighted a main nne ssw contraction and a minor ese wnw extension detected only on the southern part of vulcano this results are in agreement with a transpressive kinematics of the lipari vulcano volcanic complex with a main dextral component of displacement along a nw se striking structure

a land locked back arc basin preliminary results from odp leg 107 in the tyrrhenian sea abstract the odp leg 107 drilled a series of eleven holes across the tyrrhenian sea probably one of the youngest of the mediterranean sea sub basins four sites have documented the evolution of the sardinia passive type continental margin and shown that tilting and subsidence occurred earlier on the upper margin than on the present lower margin three sites have been drilled into the two small deep basins of the central tyrrhenian the results show that both basins are floored by basaltic basements and strongly support the model of back arc basin growth by seaward southeast in this case retreat of the downgoing hinge line plate

different styles of deformation in the calabrian arc southern italy implications for a seismotectonic zoning abstract the most recent seismic profiles in southern italy show the existence of a sudden thinning of the crust at the boundary between the chain and the tyrrhenian margin the abrupt change in thickness can be followed along a zone which has the same geometry in plan as the calabrian arc by considering these data and the gravimetric anomalies it is possible to associate this crustal anomaly with a deep seated shear zone which determines a crustal shortening of about 40 60 km which can only be a consequence of post tortonian tectonics the surface equivalents of the deep seated shear zone can be recognized from north to south in the alignment of the intra apenninic basins vallo di diano san arcangelo potenza in the crati mesima graben and in the mount kumeta alcantara fault zone the distribution of the seismicity and its connection with the surface structures shows that the largest earthquakes occur along the deep shear zone in particular shocks with the highest magnitude and the longest recurrence intervals are located in those areas where the deep shear zone is at an angle of about 90 with the direction of maximum shortening crati mesima graben the fault zones nearly parallel to the regional compression axis e g mount kumeta alcantara fault zone are characterized by earthquakes of lower magnitude taking into account the neotectonic evolution of the regional structures as well as the orientation of the stress field and its connection with the deep seated shear zone it is possible to distinguish the following seismotectonic zones upper crati mesima graben transverse throughs mount pollino mount raparo fault zone external ionian area san arcangelo basin zone of the external flysch sicani mountains mount kumeta alcantara fault zone caltanissetta basin and iblean plateau bradanic trough murge ridge the definition of the geometry of the shear zone at depth is one of the most important but still unresolved problems

simultaneous magma and gas eruptions at three volcanoes in southern italy an earthquake trigger this study was partly funded by the deutsche forschungsgemeinschaft wa 1642 1 4 and protezione civile project ingv dpc v2

late oligocene to recent episodes of magmatism in and around the tyrrhenian sea implications for the processes of opening in a young inter arc basin of intra orogenic mediterranean type abstract five episodes of magmatic activity as deduced from geochronological data affected the tyrrhenian and peri tyr rhenian areas from the late oligocene 32 ma to recent times the episodes of w e migration of magmatism from the islands of sardinia and corsica to the eolian islands and the roman comagmatic region of central italy are related to the anti clockwise drift movements of the apenninic chain and clockwise drifting of the sicilian part of the maghrebian chain magmatic activity in the tyrrhenian sea initiated in late miocene times 8 5 6 5 ma in concomitance with a significant change of the geodynamic regime from compressional to tensional the tyrrhenian bathyal plain was affected by two episodes of spreading the first episode occurred around 7 ma and the second from about 1 9 to 1 3 ma these spreading events apparently developed during times of magmatic quiescence in the peri tyrrhenian areas two subsequent episodes of volcanism of the seamount type occurred in the bathyal plain one from 5 to 1 8 and the other from 1 3 to recent they are contemporaneously with extensive manifestations in the peri tyrrhenian areas the different types of magmatism of the late miocene back arc spreading in the central bathyal plain and acidic manifestations of intra crustal anatectic origin in the northern continental platform and slope i e islands of capraia elba and montecristo and seamount vercelli are possibly related to movements of upwelling of the astenosphere which in the southern tyrrhenian sea developed with a much stronger intensity timing of the volcanism in relationship with the overall structural evolution through time in the basin and neighbouring lands is considered

the seismicity in the southern tyrrhenian area and its neural forecasting the southern tyrrhenian basin is a region characterized by complex tectonics and large scale geodynamic deformations and its seismicity has been recently recognized as following fractal laws in its five dimensional set magnitude time and space in particular the time occurrences of earthquakes are found to follow a significant fractal clustering within the interval ranging from 16 minutes to 24 hours for longer intervals the time clustering regime was not significantly different from that of a random process an artificial neural network is applied here to the same seismicity data set and further evidence of the nonlinear dynamic process for which the fractal approach failed is obtained the monthly values of magnitude predicted by extrapolation are found to be in fair agreement with the historical data

deformation pattern in the central mediterranean and behavior of the african adriatic promontory abstract the adriatic platform has been described in the literature both as an africa promontory moving in close connection with the main continent and as an independent microplate this evident incongruity is mainly due to the wide spectrum of kinematic hypotheses proposed on the basis of paleomagnetic data and to the fact that the adriatic africa transition is not marked by any clear decoupling fracture or by any interruption of lithological facies along the marginal belts apennines maghrebides and dinarides hellenides in this work it is argued that the counterclockwise rotation of the adriatic plate driven by africa pushing beneath the calabrian arc and southern tyrrhenian may coherently account for all major plio quatemary events in the central mediterranean

source parameters of earthquakes in the strait of messina italy during this century abstract basic source parameters of earthquakes that have occurred in the seismogenic source region of the strait of messina southern italy are analyzed from seismological data and vertical ground displacements in particular faulting parameters associated with the 1908 ms 7 1 messina earthquake have been analyzed through inversion of coseismic displacements and available seismograms this normal faulting earthquake was located in the upper 15 km of the crust and had a source dislocation of 1 5 m on a fault plane striking n s and dipping 40 e this seismogenic region was quiescent before 1908 and later on this century but its surroundings i e the southern segment of calabrian arc is one of the most seismically active regions of italy with sequences of large earthquakes m 7 7 5 in 1638 1693 1783 and 1905 probably also associated with normal faulting as suggested by the regional tectonics during this century in the strait of messina small earthquakes occurred in 1952 ml 4 5 1961 ml 4 7 1975 ml 4 7 and in 1985 ml 4 1 this last being the first documented swarm sequence hypocenter distribution fault plane solutions seismic moments and stress drops have been computed from the data of a local seismic network consisting of up to eight stations the scaling law of the swarm events seems to show a departure from self similarity with earthquakes having a constant source radius of about 300 m

influence of fault plane heterogeneity on the seismic behavior in the southern kurile islands arc the seismic behavior in the southern kurile islands arc is strongly influenced by spatial heterogeneity in the mechanical properties of the plate interface maps showing sites of maximum seismic moment release for the great underthrusting earthquakes of 1958 1963 1969 and 1973 provide a first order image of the major regions of enhanced strength or asperities hypocenters of these and an additional 83 smaller earthquakes with mb 5 3 and known underthrusting mechanisms were recomputed using the method of joint hypocenter determination in order to assess better the influence that the strength distribution exerts on the interplate seismicity patterns nearly all of the smaller magnitude earthquakes locate outside of the principal asperities of the great earthquakes this observation is consistent with substantial release of accumulated strain energy in asperity regions during the great earthquakes and a redistribution of stress in adjacent areas following their rupture an along dip depth dependent component of strength heterogeneity appears to influence the seismicity patterns the asperities of the 1958 and 1973 great earthquakes and hypocenters of most of the ms 7 earthquakes occur near the downdip edge of the 100 km wide seismically active plate interface this would be expected if shear resistance on the interface increases monotonically with lithostatic pressure up to the brittle ductile or stick slip stable slip transition that defines the base of the seismogenic zone the asperities of the 1963 and 1969 earthquakes however appear to be located well above the downdip edge of the coupled plate interface the occurrence of large asperities in middepth ranges of the seismogenic interface suggests the influence of along dip changes in other parameters besides lithostatic pressure that control shear resistance along strike segmentation of the kurile islands thrust zone may be a consequence of along strike alternation in the location of the largest asperities between the deep interface and the midinterface

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

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

recent crustal deformations and tectonics of the messina strait area summary the tectonics of the region at the convergence of the tyrrhenian and ionian basins is very complicated the seismicity is particularly interesting in the area 38 39 30 n 14 30 16 30 e where both deep events occur with compressive mechanism and crustal events with predominant normal faulting in excess of magnitude 7 0 the tectonic origin of this apparently contradictory behaviour can be traced to a remanent downgoing slab in the southern tyrrhenian basin which is now inactive but is still undergoing considerable horizontal bending sedimentological studies suggest the bending to be accompanied by a marked uplift of calabira reaching its highest rates in the area of the strait of messina we performed a spirit levelling campaign in the strait and found that a differential uplift of the inner lands with respect to coastlines took place in the period 1970 82 the question regarding the possibilities of either an absolute uplift of inner lands or a subsidence of coastlines can only be resolved after detailed tidal studies the available tidal data seem to support the uplift hypothesis but they are substantially incomplete the apparent pattern of vertical deformations seems to be a marked steady uplift with episodic subsidence periods in connection with large normal faulting earthquakes furthermore our measurements and the results of a recently completed trilateration campaign tend to confirm the hypothesis of the existence of an angular graben in the strait and a southnorth right lateral slip of sicily with respect to calabria

recent deformations and the seismogenic source in the messina strait southern italy abstract the relationships between mechanisms and mode of faulting in pliocene and pleistocene times and seismic release are the basis for an interpretation of the growth of deformation energy in the messina strait the major fault systems trending in ne sw nw se and e w directions divide blocks subjected to high mobility in concurrence with greater uplifting of the calabrian side with respect to sicily across the two sides of the strait as revealed by structural analyses the tectonic features of the area are dominated by normal faulting many synsedimentary features seem to indicate repeated and intermittent pulses of high velocity fault slippage possibly related to seismic shaking when considering the seismic record it seems that the strongest shocks are generated by preferential strain accumulations along the nne ssw fault systems from a geological standpoint it seems clear that the largest events may be alternately related to either the nne ssw e w or nw se fault systems which dissect an extremely cataclastic upper crust the recent deformations of the messina strait can be related to the large scale processes induced by the overthrusting of the thinned tyrrhenian crust over the thickened african crust as suggested by seismic refraction profiles along the inner margin of the calabrian arc the deep deformation mechanisms are reflected by contrasting vertical movements between a stretched and downfaulted tyrrhenian domain and an uplifted chain with resulting large strain accumulations and seismic failure in the brittle upper crust

character of the stress field in the calabrian arc and southern apennines italy as deduced by geological seismological and volcanological information abstract three crustal sections located in key zones of the calabrian arc and southern apennines have been drawn on the basis of the available geological geophysical seismological and volcanological data the purpose is to gather information on the state of stress at different crustal levels and to test to which extent data sampled at different time intervals may be consistently compared the analysis allows for the individualization of the following sectors 1 1 peri tyrrhenian belt marked by a tensional state of stress down to the moho depth 2 2 apenninic chain subjected to tension only in its shallow portions and to a compressive regime at depth 3 3 external chain internal foretrough characterized by a deep compressive regime which is expressed at the surface in its outermost zone only 4 4 external foretrough foreland with tensional processes in the whole crust compressional processes are linked to the activity of a deep shear zone which causes the thrusting of the tyrrhenian crust over the adriatic crust and which seems to control the present distortion of the calabrian arc the analysis suggests a change in the stress field and deformation mechanisms from the uppermost to the lowermost levels of the crust and an eastward migration with time of the compressional events these facts would explain the contrasting evidence sometimes given by stress constraints derived from geological seismological and volcanological data

ground deformation of the southern sector of the aeolian islands volcanic arc from geodetic data abstract the deformation pattern and the dynamics of the southern sector of the aeolian archipelago are investigated a study on the ground deformation measured over the last 20 years in the trilateration geodetic network between the islands of vulcano and lipari has been conducted analysis of the relative displacements and the uniform strain tensor parameters as well as the comparison between areal dilatation and the vertical variations deduced by precise levelling allow distinguishing different phases associated both with the regional dynamics and the local volcanic context of the area these phases however appear to be closely interrelated the analysis of the deformation pattern allows to constrain the predominance of a roughly e w trending extension and a n s contraction at a regional scale this regime is consistent with right lateral movements along a nw se striking fault system