the limits of seaward spreading and slope instability at the continental margin offshore mt etna imaged by high resolution 2d seismic data highlights analysis of a combined new high resolution 2d seismic and bathymetric data set offshore mt etna extensional domains are mapped at the shallow subsurface of the continental margin compressional structures are mapped at the toe of the continental margin a coupled volcano edifice continental margin instability is proposed mount etna is the largest active volcano in europe instability of its eastern flank is well documented onshore and continuously monitored by geodetic and insar measurements little is known however about the offshore extension of the eastern volcano flank defining a serious shortcoming in stability models in order to better constrain the active tectonics of the continental margin offshore the eastern flank of the volcano we acquired a new high resolution 2d reflection seismic dataset the data provide new insights into the heterogeneous geology and tectonics at the continental margin offshore mt etna the submarine realm is characterized by different blocks which are controlled by local and regional tectonics a compressional regime is found at the toe of the continental margin which is bound to a complex basin system both the clear link between on and offshore tectonic structures as well as the compressional regime at the easternmost flank edge indicate a continental margin gravitational collapse as well as spreading to be present at mt etna moreover we find evidence for the offshore southern boundary of the moving flank which is identified as a right lateral oblique fault north of catania canyon our findings suggest a coupled volcano edifice continental margin instability at mt etna demonstrating first order linkage between on and offshore tectonic processes

the results of the taormina 2006 seismic survey possible implications for active tectonics in the messina straits abstract the straits of messina and its surroundings are considered as one of the most tectonically active area of the mediterranean but in spite of their hazard potential modern geophysical data aimed at investigating their hidden structures are lacking in order to bridge this gap we carried out a marine multichannel seismic survey primarily aimed at i studying the regional fault pattern in the area of the messina 1908 earthquake and ii checking the existence of a potentially seismogenic fault the taormina fault which many authors locate offshore along the coast between taormina and messina our seismic profiles show a great structural complexity within the messina straits with the best imaged faults occurring on the calabrian side in particular a more than 30 km long nw trending fault located at the sw tip of calabria is cutting the sea floor moreover our data did not image any extensional fault plane attributable to the taormina fault rather the whole slope has been tilted east ward the geodynamic implication is that extension in south eastern sicily on the ionian side of the hyblean plateau and extension in southern calabria and messina straits belong to two different tectonic systems and cannot be mechanically linked

a numerical model study of the alboran sea gyre abstract reduced gravity and two layer numerical models have been used to study the circulation in the westernmost basin of the mediterranean sea the alboran sea circulation is forced by flow through a 20 km wide port in the western boundary representing the strait of gibraltar the reduced gravity model domain is a rectangle measuring 600 km 160 km with 10 km 5 km grid resolution when forced by an eastward on northeastward inflow the model solutions evolve to a steady state which exhibits a meandering current the first meander of the current forms the northern boundary of an anticyclonic gyre horizontal dimensions of the gyre are strongly dependent upon the inflow angle vorticity associated with the incoming current magnitude of the incoming transport and the north south extent of the basin the meandering current is considered a standing rossby wave with a highly distorted vorticity trajectory due to the interaction of the current with the northern and southern boundaries when velocity transport is increased the wavelength increases approximately as v as a result the anticyclonic gyre shifts east as velocity increases and west as velocity decreases these solutions show that bottom topography winds and coastline features are not necessary mechanisms for the formation of the gyre two layer model solutions were obtained using realistic topography geometry and a westward moving lower layer the addition of the lower layer flow and topography distorted the circulation in the upper layer particulary in the southern half of the basin this is caused by the large topographically steered currents along the southern shelf the high variability of the horizontal dimensions and location of the gyre has been observed both experimentally and through satellite imagery model results show that the high variability is caused by variations in the inflow velocity drifter tracks both observational and model derived help determine the circulation in both layers of the alboran sea the close comparison between model and experimental drifters lends credibility to the model circulation and dynamics

the deformation offshore of mount etna as imaged by multichannel seismic reflection profiles abstract despite the clear evidence of active flank dynamics that is affecting the eastern side of mount etna the contribution of tectonic processes has not been yet understood so far the various models proposed to explain the observed flank deformation have been based on onshore structural data coming from the volcanic edifice the ionian offshore of mount etna has been only recently investigated using multichannel seismic profiles and offers the opportunity to image the structural features of the substrate of the unstable flank of the volcano this contribution aims at describing the deformation located offshore mount etna using multichannel seismic profiles recently acquired during three seismic surveys the onshore flank deformation of mount etna appears to be laterally confined by two tectonic guidelines trending roughly e w located to the north and south of the deforming flank the northern guideline in particular takes the surface expression of a sharp fault pernicana fault though often assumed that these boundary structures continue offshore as linear features connected to a frontal thrust ramp the occurrence of this simple offshore structural system has not been imaged in fact seismic data show a remarkable degree of structural complexity offshore mount etna the pernicana fault for instance is not continuing offshore as a sharp feature rather the deformation is expressed as ene wsw folds located very close to the coastline it is possible that these tectonic structures might have affected the offshore of mount etna before the pernicana fault system was developed less than 15 ka ago the southern guideline of the collapsing eastern flank of the volcano is poorly expressed onshore and does not show up offshore in fact seismic data indicate that the catania canyon a remarkable e w trending feature does not reflect a tectonic control seismic interpretation also shows the occurrence of a structural high located just offshore the edifice of mount etna whereas a complex deformation affects the boundary of this offshore bulge it shows only limited internal deformation part of the topography of the offshore bulge pre existed the constructional phase of mount etna being an extension of the hyblean plateau only in the northern part the bulge is a recent tectonic feature being composed by plio quaternary strata that were folded before and during the building of mount etna the offshore bulge is bounded by a thrust fault that can be related to the intrusion of the large scale magmatic body below mount etna

crustal and upper mantle responses to lithospheric segmentation in the northern apennines lithospheric tear faults are expected to develop in response to along strike variations in the rates of slab rollback however the exact geometry of such structures and their crustal and upper mantle expressions are still debated we present an analysis of seismic structural and morphological features that possibly represent the expression of lithospheric segmentation in the northern apennines geophysical observations show evidence for the existence of a discontinuity in the lithospheric structure beneath the northern apennines characterized by a change in the spatial distribution of intermediate depth seismicity along strike variations in the pattern of crustal seismicity and a bend in the moho topography the near surface expression of this discontinuity is associated with an abrupt change in the morphology and exhumation history of the northern apennines in the proximity of the livorno sillaro lineament we interpret these features as evidence for incipient tearing of the lithospheric slab beneath the northern apennines marking the boundary between domains that underwent contrasting styles of lithospheric deformation which are either associated with different rates of slab rollback or a transition from underplating to retreat we suggest that similar types of structures may play a crucial role in the evolution of convergent plate boundaries allowing segmentation of orogenic belts and facilitating the development of orogenic curvatures ultimately further tearing along such structures could potentially lead to the occurrence of tear related magmatism and the formation of slab windows

polyphase tectonic evolution of fore arc basin related to step fault as revealed by seismic reflection data from the alboran sea w mediterranean 25 pages 14 figures 1 table seismic reflection and bathymetric data collected during the marlboro and saras cruises are stored at sismer and seanoe sea scientific open data edition https doi org 10 17600 11480100 https doi org 10 17600 12450090 and https campagnes flotteoceanographique fr campagnes 12000010

fault pattern and seismotectonic potential at the south western edge of the ionian subduction system southern italy new field and geophysical constraints abstract the south western edge of the calabrian arc in southern italy has been investigated throughout a joint analysis of field marine and geophysical data which provided constraints on the fault pattern and on the seismotectonic potential the study was focused on a poorly known sector of a larger belt of seismically active faults slicing across the ne corner of sicily the so called tindari fault system our data pointed out that the investigated area including the mainland and the ionian offshore is deformed by oblique faulting with a general nw se tectonic trend earthquake distribution and seismic profiles pointed out active deformation in the offshore while the mainland is characterized by the occurrence of a nw se oriented 20 km long structural belt however scarce seismicity has been recorded in the last 30 years alongside this tectonic structure accounting for a possible silent segment of the larger fault system tomographic images revealed that the moho discontinuity is deformed by a ne dipping lithospheric tectonic structure which has been here retained the main mode of deformation and responsible for coseismic displacement in the area as a whole field and geophysical data agree with a general nw se trend segmented pattern of recent active faults that have the potentiality of generating magnitude 6 5 7 earthquakes

chaotic transport of mass and potential vorticity for an island recirculation the method of lobe analysis is used and extended to analyze a time dependent boundary trapped recirculation the recirculation gyre occurs in a numerical model of wind driven flow around an island but the underlying geometry of the gyre is similar to persistent eddies such as the alboran gyre and the great whirl even in the steady weak forcing limit the gyre leaks fluid due to the fact that the surface ekman pumping above it is directed downward the authors show that this leakage is rapidly superseded by chaotic transport into and out of the gyre when time dependence sets in variations of the traditional turnstile approach to transport are used to study the dynamics of the gyre a lagrangian recirculation boundary consisting of pieces of stable and unstable manifolds joined by a gate allows straightforward calculation and visualization of potential vorticity flux

propagation of a lithospheric tear fault step through the western boundary of the calabrian accretionary wedge offshore eastern sicily southern italy the rollback of a segmented slab of oceanic lithosphere is typically accompanied by vertical lithospheric tear fault s along the lateral slab edge s and by strike slip movement in the upper plate defined as a step fault subduction tear edge propagator the neogene evolution of the central mediterranean is dominated by the interaction between the slow africa eurasia convergence and the se ward rollback of the ionian slab that leads to the back arc opening of the tyrrhenian sea here we present post stack time migrated and pre stack depth migrated archimede 1997 multichannel seismic lines that were acquired offshore eastern sicily at the foot of the malta escarpment first we identify the recent deformation along the lateral ramp of the calabrian accretionary wedge towards the east the calabrian wedge is formed by the accretion of the post evaporitic sediments above a decollement at the base of the messinian evaporites at the latitude of syracuse 50 km east of the malta escarpment a major n150 degrees e trending crustal scale and vertical fault slices through the entire accretionary wedge this fault cuts by several kilometers through the pre evaporitic messinian sediments and into the basement the vertical offset along this vertical fault decreases from north to south and the fault is no longer observed on the seismic lines 50 km se of the alfeo seamount a previously published moho depth isocontour map offshore sicily and the recent gps data combined with the presence of strike slip movements ne onshore sicily allow us to identify this 200 km long crustal scale fault as the surface expression of a step fault the presence of syntectonic pleistocene sediments on top this crustal scale fault suggests a recent lithospheric vertical movement of the step fault in response to the rollback of the ionian slab and to the se ward advance of the calabria peloritan block

a correlation between schmidt hammer rebound numbers with impact strength index slake durability index and p wave velocity the main objective of this study was to establish statistical relationship between schmidt hammer rebound numbers with impact strength index isi slake durability index sdi and p wave velocity these are important properties to characterize a rock mass and are being widely used in geological and geotechnical engineering due to its importance schmidt hammer rebound number is considered as one of the most important property for the determination of other properties like isi sdi and p wave velocity determination of these properties in the laboratory is time consuming and tedious as well as requiring expertise whereas schmidt hammer rebound number can be easily obtained on site which in addition is non destructive so in this study an attempt has been made to determine these index properties in the laboratory and each index property was correlated with schmidt hammer rebound values empirical equations have been developed to predict isi sdi and p wave velocity using rebound values it was found that schmidt hammer rebound number shows linear relation with isi and sdi whereas exponential relation with p wave velocity to check the sensitivity of empirical relations student s t test was done to verify the correlation between rebound values and other rock index properties

on the upper layer circulation in the alboran sea we present new experimental results and assemble them with previous results in order to develop an improved picture of the upper layer circulation in the alboran sea it is suggested that the key idea to understanding this upper layer circulation is the tendency of the atlantic jet aj to have negative curvature local interactions with the western alboran gyre wag or the african coast can however counterbalance this tendency and modify the anticyclonic path of the aj it is also proposed that the density gradients in the wag can be maintained in part by means of an intermittent surface cross gyre current which results in an input mixing and renewal of atlantic water the static stability at the bottom of the gyre increases because of the mixing of atlantic water with western mediterranean deep water which is uplifted close to the african coast this mixing process thereby acts as a local source of potential vorticity we also report the existence in the alboran sea of subsurface anticyclonic eddies located between 100 and 400 m of relatively cold water that appear to be detached from the iberian shelf regarding the large scale variability of the aj wag system we present evidence of an eastward migration of the wag and the subsequent formation of a new anticyclonic gyre in the western alboran basin on a timescale of 1 month this eastward gyre migration process temporarily allows the simultaneous presence of three anticyclonic gyres in the alboran sea

tectonic expression of an active slab tear from high resolution seismic and bathymetric data offshore sicily ionian sea subduction of a narrow slab of oceanic lithosphere beneath a tightly curved orogenic arc requires the presence of at least one lithospheric scale tear fault while the calabrian subduction beneath southern italy is considered to be the type example of this geodynamic setting the geometry kinematics and surface expression of the associated lateral slab tear fault offshore eastern sicily remain controversial results from a new marine geophysical survey conducted in the ionian sea using high resolution bathymetry and seismic profiling reveal active faulting at the seafloor within a 140 km long two branched fault system near alfeo seamount the previously unidentified 60 km long nw trending north alfeo fault system shows primarily strike slip kinematics as indicated by the morphology and steep dipping transpressional and transtensional faults available earthquake focal mechanisms indicate dextral strike slip motion along this fault segment the 80 km long sse trending south alfeo fault system is expressed by one or two steeply dipping normal faults bounding the western side of a 500 m thick 5 km wide elongate syntectonic plio quaternary sedimentary basin both branches of the fault system are mechanically capable of generating magnitude 6 7 earthquakes like those that struck eastern sicily in 1169 1542 and 1693

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

slake durability study of shaly rock and its predictions more than 35 of the earth s crust is comprised of clay bearing rocks characterized by a wide variation in engineering properties and their resistance to short term weathering by wetting and drying phenomenon the resistance to short term weathering can be determined by slake durability index test there are various methods to determine the slake durability indices of weak rock the effect of acidity of water slaking fluid on slake durability index of shale in the laboratory is investigated these methods are cumbersome and time consuming but they can provide valuable information on lithology durability and weather ability of rock fuzzy set theory fuzzy logic and artificial neural networks ann techniques seem very well suited for typical complex geotechnical problems in conjunction with statistics and conventional mathematical methods a hybrid method can be developed that may prove a step forward in modeling geotechnical problems during this investigation a model was developed and compared with two other models i e neuro fuzzy systems combination of fuzzy and artificial neural network systems and artificial neural network system for the prediction of slake durability index of shaly rock to evaluate the performance of its prediction capability

seismotectonics of northeastern sicily and southern calabria italy new constraints on the tectonic structures featuring in a crucial sector for the central mediterranean geodynamics

evolution of the calabrian accretionary wedge central mediterranean 1 the neogene tectonics of the central mediterranean are related to the subduction and trench rollback of the ionian basin under eurasia causing the opening of the liguro provencal and tyrrhenian back arc basins and the formation of the calabrian accretionary wedge the calabrian accretionary wedge is a partially submerged accretionary complex located in the ionian offshore and laterally bounded by the apulia and malta escarpments while the history of the back arc extension process is fairly well defined the structure and evolution of the wedge are still poorly known we have analyzed and interpreted the available reflection multichannel and single channel seismic profiles in the ionian offshore and integrated them with other geological and geophysical data acquired in the last 40 years here we present unpublished seismic profiles to provide a new map of the tectonic structure of the ionian offshore and to define the structure of the wedge and its evolution during the last 15 myr our reconstruction points out that the messinian salinity crisis represents an important break in the evolution of the wedge as the basal decollement ramps up onto the messinian salt deposits producing a dramatic and fast forward propagation of the frontal thrust and resulting underplating of the underlying crustal ionian sequence during progressive trench rollback our results provide new insight into the style of accretion in a weakly converging setting which is typical for the mediterranean region

ten years of marine current measurements in espartel sill strait of gibraltar more than 10 year of acoustic doppler current profiler observations collected at the westernmost sill espartel sill of the strait of gibraltar by a monitoring station have been carefully processed to provide the most updated estimation of the mediterranean outflow a comprehensive quality control of the factors affecting the uncertainty of the measurements has been carried out and great care has been paid to infer the current at the bottom layer where direct observations are lacking the mean outflow in the southern channel of the sill section has been estimated as 0 82 sv 1 sv 1 106 m3 s 1 with an average contribution of the eddy fluxes of 0 04 sv this figure is an overestimation as the mooring measurements assumed valid for the whole section ignore the lateral friction on the other hand it only gives the flow through the southern channel and disregards the fraction flowing through shallower northern part both drawbacks have been addressed by investigating the cross strait structure of the outflow from hindcasts produced by the mitgcm numerical model run in a high resolution domain covering the gulf of cadiz and alboran sea basins an overall rectifying factor of 1 039 was found satisfactory to correct the first estimate so that the final mean outflow computed from this data set is 0 85 sv complemented with an uncertainty of 0 03 sv based on the interannual variability of the series the temporal analysis of the series shows an outflow seasonality of around the 8 of the mean value with maximum outflow in early spring

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

chaotic advection in an archipelago abstract techniques from dynamical systems theory have been applied to study horizontal stirring of fluid in the philippine archipelago the authors analysis is based on velocity fields produced by two high resolution 3 and 6 km numerical models particular attention is paid to identifying robust surface flow patterns and associating them with dominant lagrangian coherent structures lcss a recurrent wind driven dipole in the lee of the coastline is considered in detail the associated lcss form a template for stirring exchange and biological transport in and around the dipole chaotic advection is argued to provide a relevant framework for interpreting mesoscale horizontal stirring processes in an archipelago as a whole implications for the formation of filaments the production of tracer variance and the scale at which stirring leads to mixing are discussed in connection with an observed temperature record

the schmidt hammer weathering and rock surface roughness measures of the differential relief of adjacent feldspar and pyroxene grains provide the first clear negative correlation of schmidt hammer rebound r values and degree of weathering however weathering and roughness are intimately related so the latter cannot be seen simply as a source of error limiting the utility of the schmidt hammer only where surfaces had similar textures prior to weathering can r values be compared directly even where surface texture is well controlled differences in r values should be viewed critically rather than assigned indiscriminately to differences in degree of weathering

circulation in the alboran sea as determined by quasi synoptic hydrographic observations part i three dimensional structure of the two anticyclonic gyres abstract the circulation and dynamics of the modified atlantic water have been studied using data from an intensive field experiment carried out between 22 september and 7 october 1992 data included 134 ctd casts adcp and satellite imagery a well defined wavelike front was observed with two significant anticyclonic gyres in the western and eastern alboran sea smaller scale cyclonic eddies were also observed the front separates the more saline older modified atlantic water s 38 in the northern region from the fresher more recent modified atlantic water s 36 8 in the south the associated baroclinic jet had a mean transport of 1 sv and maximum geostrophic velocities of 1 0 ms 1 the three dimensional structure and spatial scales of both gyres were similar that is 90 km long and 220 m deep in the eastern alboran northeast of oran the origin of the algerian current was also detected with an eastward transport of 1 8 sv the general picture can be presented as a structure formed by a wavelike

measurement and calibration of weathering using the schmidt hammer on wave washed moraines on the upper norrland coast sweden the schmidt hammer has for some years been used to measure the hardness of different rock surfaces and to date relatively boulders in moraine deposits in this paper applications on isostatically raised boulder beaches and rocky shores are described the research area is the northern swedish bothnian coast where present isostatic uplift is between 0 8 1 0 cm year 1 elevations above sea level can be converted to a timescale rebound values r of the schmidt hammer are correlated with the altitude and the degree of rock weathering can be estimated for each site eight sites with boulder beaches and nine sites with rocky shores have been analysed for boulder beaches correlation coefficients of 0 82 0 97 for weathering values r and the elevations above sea level were obtained for the rocky shores these values were calculated to 0 75 0 97 this method has applications in both geomorphology and archaeology for example a deep layer of weathered dolerite in the nordingra region which previously has been regarded as a post weichselian formation can be shown to be of pre weichselian origin several archaeological applications are also mentioned in the paper

roots of etna volcano in faults of great earthquakes abstract results from several seismic methods allow us to sketch the deep structure of etna and its ionian margin under etna a volume of high velocity material is found in a structurally high position the emplacement of this suggests spreading of the surrounding medium just offshore down to the east normal faults penetrate through the upper crust the deeper crustal structure beneath appears upwarped from the basin towards etna juxtaposed with the crust of sicily a thinner crust reaches from the ionian basin under etna and the mantle is upwarped in such a structure magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth rather than in an intracrustal chamber this reduces the conflict between estimates of its volume from excess output of volatiles and short residence times a link in time is indicated between volcanic and seismic activity at a large scale over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 earthquakes which caused destruction in southeastern sicily several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of catania and augusta which may be fault planes for such large earthquakes they expand and prolongate the system of the timpe faults on the eastern flank of etna thus linking large scale tectonics offshore with the volcano etna developed together with normal faulting upwarp and spreading during the recent evolution of the former ionian subduction activation of the material at depth at the lateral edge of the slab by vertical motion with extension above could produce the peculiar type of etna magmatism

high frequency wave propagation from mantle earthquakes in the tyrrhenian sea new constraints for the geometry of the south tyrrhenian subduction zone propagation of shear waves produced by 25 mantle earthquakes 80 600 km depth in the subduction zone of the south tyrrhenian sea southern italy has been investigated to infer the geometry and extent of the descending lithosphere from all hypocentral depths high frequency high amplitude shear waves are recorded at most of the stations in southern italy and easternmost sicily this shear wave energy is interpreted to travel as a guided wave within the descending slab in contrast shear waves are either not recorded at all or they are recorded as low frequency low amplitude signals at stations located in the peninsular part of italy north of the calabrian arc in western sicily and in sardinia this systematic s wave attenuation is interpreted in terms of an active and continuous slab correlated with and limited to the calabrian arc

a simple criterion for gyre formation by the surface outflow from a strait with application to the alboran sea a survey of relevant numerical laboratory and observational studies combined with our own laboratory experiments suggests that the surface outflow from a strait generally forms a gyre in the adjacent sea if the exit corner is sharp the gyre grows from an initial separation bubble of radius u f where u is the current speed and f the coriolis frequency the criterion for the maintenance of a coastal jet along a curved coast instead of separation and gyre formation seems to be that the rossby number u frw 1 1 with rw the radius of curvature of the exit corner so that the coriolis force can hold the current to the coast this synthesis disregards factors such as the variation of u across the current but applied to the flow through the strait of gibraltar into the alboran sea suggests that a gyre should always form as the exit corner is sharp we suggest though that the relevant curvature is that where the interface between the two layers intersects the seafloor rather than where the sea surface meets the coast if this is the case supercritical flow or some subcritical flows at the eastern end of the strait should still always lead to gyre formation but the observed replacement of the gyre by a coastal jet along the moroccan coast could be related to subcritical flow that is reduced below its normal value by a barotropic fluctuation or by changes in the interface depth in the mediterranean

comment on geometry of the deep calabrian subduction central mediterranean sea from wide angle seismic data and 3 d gravity modeling by dellong et al

malta escarpment fault zone offshore eastern sicily pliocene quaternary tectonic evolution based on new multichannel seismic data 1 the malta escarpment represents the dominant morphological feature offshore eastern sicily linking the deep ionian basin to the east with the hyblean carbonate platform to the west interpretation of purposely acquired multichannel seismic data allows division of the malta escarpment into two portions characterized by different tectonic structures along the segment south of siracusa the malta escarpment is not affected by recent faulting and appears as a steep surface that flattens out toward the ionian basin a recent deformation characterized by a broad area of uplift occurs 20 30 km east from the slope along a nnw sse trend the segment of the malta escarpment extending north of siracusa on the other hand is characterized by the presence of nnw sse east dipping recent extensional faults and related sedimentary basins the observed structural features support the occurrence of a lithospheric tear between the ionian oceanic basin and the hyblean plateau

comment on the article propagation of a lithospheric tear fault step through the western boundary of the calabrian accretionary wedge offshore eastern sicily southern italy by gallais et al 2013 tectonophysics abstract the oceanic lithosphere of the ionian sea is subducted under the calabrian arc and it has been proposed that the ionian lithosphere has been torn apart step fault sensu govers and wortel 2005 on its western side close to the malta escarpment a major morphological feature inherited from the mesozoic palaeogeography in a recent paper gallais et al tectonophysics 2013 have traced a right lateral strike slip fault that extends from south of the alfeo seamount all the way to the tyrrhenian sea they also argue that the position of the step fault is distinct from and located ca 50 km east of the malta escarpment gallais et al document with some additional details a fault segment that was already reported in the literature and that is located south of the alfeo seamount however gallais et al have little constraints to trace the step fault further to the north in this sector a belt of surface deformation that can be related to the step fault has been mapped from a denser grid of seismic profiles and is located west ward close to the malta escarpment argnani and bonazzi 2005 this undermines the conclusion of gallais et al that the lithospheric tear is distinct from the malta escarpment it is therefore likely that surface deformation associated with the lithospheric tear fault is more complex and is not represented by a single strike slip fault

quaternary normal faulting in southeastern sicily italy a seismic source for the 1693 large earthquake summary we present geological and morphological data combined with an analysis of seismic reflection lines across the ionian ovshore zone and information on historical earthquakes in order to yield new constraints on active faulting in southeastern sicily this region one of the most seismically active of the mediterranean is avected by wnw ese regional extension producing normal faulting of the southern edge of the siculo calabrian rift zone our data describe two systems of quaternary normal faults characterized by diverent ages and related to distinct tectonic processes the older nw se trending normal fault segments developed up to 400 kyr ago and striking perpendicular to the main front of the maghrebian thrust belt bound the small basins occurring along the eastern coast of the hyblean plateau the younger fault system is represented by prominent nnw sse trending normal fault segments and extends along the ionian ovshore zone following the ne sw trending avola and rosolini ispica normal faults these faults are characterized by vertical slip rates of 0 7 3 3 mm yr 1 and might be associated with the large seismic events of january 1693 we suggest that the main shock of the january 1693 earthquakes m 7 could be related to a 45 km long normal fault with a right lateral component of motion a long term net slip rate of about 3 7 mm yr 1 is calculated and a recurrence interval of about 550 50 yr is proposed for large events similar to that of january 1693

lithosphere tearing at step faults response to edges of subduction zones abstract slab edges are a relatively common feature in plate tectonics two prominent examples are the northern end of the tonga subduction zone and the southern end of the new hebrides subduction zone near such horizontal terminations of subduction trenches ongoing tearing of oceanic lithosphere is a geometric consequence we refer to such kinks in the plate boundary as a subduction transform edge propagator or step other steps are the north and south ends of the lesser antilles trench the north end of the south sandwich trench the south end of the vrancea trench and both ends of the calabria trench volcanism near steps is distinct from typical arc volcanism in some cases slab edges appear to coincide with mantle plumes using 3d mechanical models we establish that step faults are stable plate tectonic features in most circumstances in the probably rare cases that the resistance to fault propagation is high slab break off will occur relative motion along the transform segment of the plate boundary often is non uniform and the step is not a transform plate boundary in the rigid plate tectonics sense of the phrase step propagation may result in substantial deformation rotation topography and sedimentary basins with a very specific time space evolution surface velocities are substantially affected by nearby steps

crustal structure of the ionian margin of sicily etna volcano in the frame of regional evolution abstract crustal imaging could be achieved on normal incidence reflection profiles offshore eastern sicily by using industrial grade reflection seismic with improved marine sources thick recent sediments a reflective pile including the mesozoic deposits a transparent upper crust and a band of low frequency reflections attributed to the lower crust are imaged in the seismic sections the structure of the crust and its thickness show features inherited from the mesozoic evolution as a passive margin by which ionian basin crust was formed around the hyblean continental promontory of africa to constitute the southern plate in the later convergence with europe the seismic images are also marked by the lithospheric deformation due to the neogene overriding of the northern part of this paleomargin by the calabro peloritan block of european continental crust this transpressive motion may have been guided along the northern part of this paleomargin where the seismic profiles evidence a hinge line between the northward upslope of the moho of that old passive margin and its downslope to the present slab under the tyrrhenian sea etna volcano is located at the intersection of this mantle upwarp by a zone of active sea bottom normal faults which cut across the formerly constructed compressional belt the onset of its volcanic activity is roughly coeval with that of the cessation of interplate thrusting and could hence be related to a change of the coupling of the ionian slab this slab is now probably disconnected from the overriding plate and rolled back in front of the expanding hot tyrrhenian asthenospheric dome with the mobilisation of a viscous mantle material at depth an active lithospheric fault is here imaged which cuts over more than 100 km into the ionian basin the fault runs from the tyrrhenian margin in the sse direction of etna updip of the southwestern lateral edge of this slab leaving north eastward the extruded calabrian block and on its south westward edge the uplifted crust and mantle structures of etna along it the crust including the mesozoic and deeper layers has sagged vertically in the segment in front of the slab with a finite throw across the fault increasing from the basin towards etna

evolution of the southern tyrrhenian slab tear and active tectonics along the western edge of the tyrrhenian subducted slab abstract the evolution of the southern tyrrhenian subduction has been possibly controlled by distinct episodes of slab break off as indicated by a critical review of the geological literature and by the analysis of purposely acquired multichannel seismic profiles within the proposed interpretation the first episode occurred from 8 5 to 4 0 ma and affected the segment of the slab located in the sardinia channel causing the abandonment of the adventure thrust front in western sicily the second episode occurred between 2 5 and 1 6 ma affecting the segment of slab located north of sicily and was preceeded by rifting in the strait of sicily the space and time location of these episodes appear controlled by discontinuities pre existing within the subducted african plate that trend at high angle to the advancing subduction front these discontinuities delimit segment of subducted slab that can be affected by slab break off and can act as wayouts for magma and mantle derived he the major of these discontinuities the malta escarpment has been reactivated in the quaternary as a trench perpendicular tear step faults ultimately the hierarchy in strength of these trench perpendicular features could have affected the timing and amount of trench retreat and backarc opening

surface circulation in the alboran sea western mediterranean inferred from remotely sensed data 1 in this study for the first time at regional scale the combined use of remote sensing data altimetry and sea surface temperature records provides a description of the persistent recurrent and transient circulation regimes of the alboran sea circulation the analysis of 936 altimeter derived weekly absolute dynamic topography adt and surface geostrophic current maps for 1993 2010 reveals the presence of a dominant annual signal and of two interannual modes of variability the winter spring phase is characterized by two stable gyral scale features the well known western anticyclonic gyre within the western area and the central cyclonic gyre a new structure not identified in former studies occupying the central and eastern parts of the alboran sea a double anticyclonic gyre regime constitutes the stable circulation system of the summer autumn period when the eastern anticyclonic gyre is formed within the eastern alboran basin in this case the central cyclonic gyre is narrower and located closer to the western anticyclonic gyre they represent two stable states of the system robust at the decadal time scale whereas transient changes reflect perturbations on these stable states and are mainly observed at an interannual scale the circulation variability and the gyral features development may be dynamically linked to the corresponding changes of the gibraltar transport rates citation renault l t oguz a pascual g vizoso and j tintore 2012 surface circulation in the alboran sea western mediterranean inferred from remotely sensed data j geophys res 117 c08009 doi 10 1029 2011jc007659

transport in an idealized three gyre system with application to the adriatic sea abstract motivated by observations of surface drifters in the adriatic sea transport in a three gyre system is studied with the aid of dynamical systems techniques particular attention is paid to the issue of intergyre transport the velocity field is assumed to be two dimensional and incompressible and composed of a steady three gyre background flow on which a time dependent perturbation is superimposed two systems of this type are considered 1 an observationally motivated analytically prescribed model consisting of a steady background on which a multiperiodic time dependent perturbation is superimposed and 2 an observationally based model of the adriatic sea consisting of the mean surface circulation derived from surface drifter trajectories on which a time dependent altimetry based perturbation velocity field is superimposed it is shown that for a small perturbation to the steady three gyre background two of the gyres exchange no fluid with the third gyre when the perturbation strength excee

in situ and satellite observations of the eastward migration of the western alboran sea gyre during october 2003 an intensive oceanographic survey biomega was carried out in the alboran sea coinciding with a migration event of the western alboran sea gyre wag the observations gathered during that cruise constitute the first field evidence of a migrated stage of the wag in this work we present the main differences between the 3d hydrodynamic fields observed during biomega and those corresponding to a wag located at its usual position the migration of the gyre was followed by satellite altimetry and sea surface temperature imagery the causes of the gyre migration are explored in terms of the quasi geostrophic tendency equation in particular of the dynamics governing scales larger than the rossby radius of deformation it is shown that the steady state gyre must be almost equivalent barotropic and that the key process to break down the stationarity would be a density advection at gyre scale the mechanisms to explain the migration of the wag proposed by previous authors are discussed in light of the explanation proposed in this work

pattern of deformation around the central aeolian islands evidence from multichannel seismics and gps data the tectonics of the central aeolian islands which are located within the tyrrhenian backarc basin has been investigated through a marine seismic reflection survey we find that compressional structures dominate around the islands whereas extensional faults occur only to the north of salina and filicudi towards the marsili basin this pattern of deformation although different from previously reported is in agreement with the strain field and stress regime obtained from gps measurements and seismological data age constraints suggest that contractional deformation was active since middle pleistocene being coeval with the building of the volcanic edifices of the aeolian islands and is superimposed on pre existing extensional deformation compressional and extensional regimes therefore can coexist within a backarc setting seismic profiles show that the tindari letojanni fault considered as a major tectonic element does not extend to the north towards the island of vulcano as a throughgoing fault rather deformation is accommodated in a broader belt displaying greater structural complexity

sea surface transport in the western mediterranean sea a lagrangian perspective 2 we study the sea surface transport in the western mediterranean sea from a lagrangian point of view in particular the alboran and the north western subbasins the study is carried out through the analysis of 3 years of surface velocity model data through finite size lyapunov exponents residence time and virtual particle trajectories complementing the classical eulerian approach the spatiotemporal variability of the main transport processes is inferred from the empirical orthogonal function modes of the lyapunov exponents being the most relevant modes discussed and physically interpreted results indicate that some of the variability in the surface transport patterns in the western mediterranean can be explained by specific modes which provide an indication of connectivity among subbasins like the inflow of atlantic waters through the ibiza channel

crustal image of the ionian basin and its calabrian margins abstract previous seismic investigation of the crustal structure in the ionian basin has been limited to shallow penetration seismics of the 1970 s characterized by inadequate source power and low fold earlier obs and esp seismic refraction experiments have not been able to firmly resolve one of the principal scientific problems for this region which is whether the ionian basin is floored by oceanic crust or by highly attenuated continental crust a second elusive problem is the nature of the transition of the boundaries between the ionian basin and its margins in this paper we describe and interpret new deep seismic reflection and wide angle data collected in the western ionian sea and the calabria region of italy one of the principal features of our multichannel reflection data beneath the ionian basin is a band of layered high amplitude reflections near the base of the crust this band shows a quasi monochromatic ca 8 to 10 hz frequency and a traveltime thickness of 1 to 1 5 s these images contrast with the well known reflection patterns of mesozoic oceanic crust investigated in the atlantic ocean there is evidence that the low frequency band dips down towards the edge of the malta escarpment me where landward dipping reflectors separate continental and intermediate type crust in the central tract of the me the increased traveltimes of the lower crustal reflectors and moho from the basin towards the southern and eastern margins of southern calabria could be partially due to the velocity pull down effect of the sedimentary pile of the arc although a true dip of 15 to 18 over 60 km distance can be substantiated moreover the reflecting band maintains its reflectivity and thickness until its abrupt termination beneath the ionian continuation of the calabrian compressional crustal structures the coincident acquisition of wide angle seismic data and marine reflection seismic data provided a landward extension of the survey which will complement existing geologic information on the deep framework of the ionian basin and its calabrian margin

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

variations in the structure of the anticyclonic gyres found in the alboran sea historical satellite aircraft and in situ data have shown that two anticyclonic gyres the western and eastern alboran gyres are major ocean features of the alboran sea an examination of several years of satellite imagery indicates that large variations in the surface expression of these two gyres occur and that on occasion one or the other gyre disappears the disappearance of both gyres at the same time was not seen the initial disappearance of either gyre occurs on a time scale of a week to 2 weeks whereas the return may take from 3 weeks to 2 months various forcing mechanisms i e winds mass flux inflow through the straits of gibraltar and sicily and or density have been used in numerical ocean circulation models to study the dynamics of the western mediterranean sea various model results show relationships similar to those shown by the satellite imagery however no single forcing mechanism has been positively identified as the source of the disappearances and the events may be a result of a combination of forcing mechanisms

active upper crust deformation pattern along the southern edge of the tyrrhenian subduction zone ne sicily insights from a multidisciplinary approach abstract using a multidisciplinary dataset based on gravimetric seismic geodetic and geological observations we provide an improved picture of the shallow structure and dynamics of the southern edge of the tyrrhenian subduction zone with a local earthquake tomography we clearly identify two main crustal domains in the upper 15 km characterized by different p wave velocity values a high velocity domain comprising southeasternmost tyrrhenian sea ne sicily and messina straits and a low velocity domain comprising mt etna and eastern sicily the transition between the two domains shows a good spatial correspondence with a wider set of faults including the taormina fault system tfs and the aeolian tindari letojanni fault system atlfs two nearly se striking fault systems crossing northeastern sicily and ending on the ionian shoreline of sicily according to many investigators within this set of faults most of the deformation seismicity occurs along the northern and central segments of atlfs compared to low activity along tfs a lack of seismicity both recent and historical is observed in the southern sector of atlfs where however geodetic data reveal significant deformation our multidisciplinary dataset including offshore observations suggests the southeastward continuation of the atlfs into the ionian sea until joining with the faults cutting the ionian accretionary wedge described in the recent literature our findings imply the existence of a highly segmented crustal shear zone extending from the aeolian islands to the ionian abyssal plain that we believe plays the role of accommodating differential motion between the southern tyrrhenian unit and the western compressional domain of sicily the atlfs which is a main part of the inferred shear zone behaves similarly to what often observed at the edges of retreating subduction slabs where the overriding plate drifts with a highly non uniform transform motion along the lateral borders

a laboratory model of exchange and mixing between western boundary layers and subbasin recirculation gyres chaotic advection is suggested as a possible mechanism for fluid exchange and mixing among a western boundary current and subbasin recirculation gyres applications include the north atlantic deep western boundary current and its adjacent mesoscale recirculation gyres visualization and quantification of certain aspects of chaotic advection in a laboratory analog are described depending on the strength of the forcing recirculating fluid offshore of the western boundary layer may be contained in a single gyre not favorable for chaotic advection or twin gyre with a figure eight geometry favorable for chaotic advection when time dependence is imposed on these steady flows by varying the forcing periodically the resulting fluid exchange stirring and mixing is most dramatic in the case of the twin gyre a template for these processes can be formed by highlighting certain material contours invariant manifolds using dye and other techniques these objects can be used to identify blobs of fluid turnstile lobes that are carried into and out of the gyres the associated transports and flushing times can be estimated the preferential stirring and mixing in the twin gyre case is quantified by calculating the effective diffusivity of the flow field based on snapshots of the dye fields at longer times the experiment suggests how tracers in a western boundary current might be transported into and out of neighboring recirculations and where regions of strong zonal or meridional transport might occur