segmentation and differential post rift uplift at the angola margin as recorded by the transform rifted benguela and oblique to orthogonal rifted kwanza basins abstract we analyse tectonic and sedimentary field and subsurface data for the angola onshore margin together with free air gravity anomaly data for the offshore margin this enables us to characterize the mode of syn rift tectonism inherited from the precambrian and its impact on the segmentation of the angola margin we illustrate that segmentation by the progressive transition from the benguela transform rifted margin segment to the oblique rifted south kwanza and orthogonal rifted north kwanza margin segments the spatial variation in the intensity of post rift uplift is demonstrated by the study of a set of geomorphic markers detected in the post rift succession of the coastal benguela and kwanza basins upper cretaceous to cenozoic uplifted palaeodeltas erosional unconformities palaeovalleys quaternary marine terraces and perched gilbert deltas the onshore benguela transform margin has a distinctive mainly progradational stratigraphic architecture with long term sedimentary gaps and high elevation marine terraces resulting from moderate upper cretaceous cenozoic to major quaternary uplifting i e 775 1775 mm ky or m ma by contrast repeated synchronous episodes of minor cenozoic to quaternary uplift occurred along the orthogonal rifted north kwanza segment with its cenozoic aggradational architecture short term sedimentary gaps and low elevation pleistocene terraces margin style likewise governs spatial variations in the volume of offshore sediment dispersed in the associated deep sea fans along the low lying north kwanza margin sedimentation of the broad cenozoic to pleistocene kwanza submarine fan was probably governed by the width of the kwanza interior palaeodrainage basin combined with the wet tropical neogene climate along the high rising benguela margin the small size of the benguela deep sea fan is related to the interplay between moderate continental sediment dispersal from long lived small catchments and a warm very arid neogene climate however the driving forces behind the epeirogenic post rift uplift of the angola coastal bulge remain a matter of speculation

evidence of large scale deformation patterns from gps data in the italian subduction boundary abstract we present the velocity field in italy derived from over 300 continuous gps stations operated in the 1998 2009 time span the gps network maps the whole country with a mean inter site distance of about 50 km and provides a valuable source of data to study the ongoing deformation processes in the central mediterranean the estimated horizontal and vertical velocity fields show major significant features and also less known second order kinematic features a general uplift characterizes the whole apennines and alpine belts that follow the topographic ridge whereas the po plain shows a gradually increasing subsidence from west to east the apennines belt displays a distinctive extension 50 80 10 9 yr 1 while compressive tectonic regimes characterize northern sicily eastern alps and the northeast front of the northern apennines 25 50 10 9 yr 1 second order deformation patterns on large scale wavelength 100 km have been detected on the accretionary prism of central and southern apennines that are highly correlated with other geophysical data vp anomalies seismic anisotropy etc and related to deep rooted sections 70 100 km marked by different subduction regimes apparently at this scale length the observed deformations are governed by the lithosphere as a whole we interpret these deformations as a result of different subduction mechanisms such as variations of the subduction rollback velocity affecting different segments of the subduction zone and or to mantle flows in proximity of the slab edges further south in central southern sicily we detect a contraction of 1 1 0 2 mm yr that probably accommodates part of the africa eurasia convergence on the outer thrust front of the apennines maghrebides belt this hypothesis agrees with an independent analysis of the seismicity associated to the sicilian basal thrust thought to be still active the itrf2005 estimates of the new gps velocity field are available also in sinex format as supplementary file s1

centroid depth and mechanism of trench outer rise earthquakes trench outer rise earthquakes occur by reactivation or creation of normal faults caused as the oceanic lithosphere approaches a subduction zone and bends into the deep sea trench these faults may cut deep enough into the mantle to allow sea water to penetrate into the lithosphere causing serpentinization the amount of water carried into the mantle is linked to the maximum depth that the tensional faults cut into the lithosphere which in turn is directly linked to the maximum focal depths of outer rise normal faulting earthquakes we analysed teleseismic p and s waves of seven earthquakes from the trench outer rise offshore of central america using teleseismic waveform inversion of broad band data for the computation of green s functions for waveform inversion probabilistic earthquake locations were calculated to study the rupture process earthquake centroid depths and focal mechanisms for a sequence of subevents were calculated both hypocentral depths from the relocation process and the estimated centroid depths from the waveform inversion show that all events occur at shallow depths 30 km furthermore the locations of the subevents relative to each other suggest that fault planes for mw 6 are in the order of 50 km in length and only 5 10 km in width rupture generally propagates downdip and the focal mechanisms change for most events from normal faulting to strike slip or oblique thrusting with time the depth at which this mechanism change is observed may represent the depth of the nodal plane between tensional and compressional regions in the incoming plate

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

three dimensional instantaneous mantle flow induced by subduction 1 we conduct three dimensional subduction experiments by a finite element approach to study flow around slabs which are prescribed based on a transient stage of upper mantle subduction from a laboratory model instantaneous velocity field solutions are examined focusing on the toroidal vs poloidal components as a function of boundary conditions plate width and viscosity contrast between slab and mantle we show how the slab to mantle viscosity ratio determines the strength of toroidal flow and find that the toroidal flow component peaks for slab mantle viscosity ratios 100 independent of slab width or geometry

seismic source modeling seismic source modeling is taken to mean the modeling of seismograms to investigate kinematic properties of the earthquake source current trends such as the use of other data types e g geodetic measurements of coseismic deformation and the explicit consideration of source dynamics when modeling seismograms are beginning to blur this definition but i will adhere to it in this review i have divided seismic source modeling into teleseismic regional and near source modeling teleseismic modeling has the advantage of global coverage for earthquakes of magnitude 5 5 and larger but does not provide much more than point source parameters regional distance modeling has the advantage of a more rapid assessment of earthquake source properties but is complicated by relatively complex wave propagation the coverage is also limited to areas of broadband regional networks typically continental areas of developed countries near source modeling has the potential for detailed imaging of source properties but very few earthquakes occur in regions with sufficient instrumentation to allow this i have also included a section on historical earthquakes because of the additional issues that seismologists face in working with pre wwssn data and because of the important issues such as earthquake recurrence that require historical data in addition to reviewing the progress in seismic source modeling during the last four years i have also briefly reviewed some of the progress in understanding earthquake physics and hazards that has come about because of basic research in earthquake source modeling

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

body wave inversion moment tensors and depths of oceanic intraplate bending earthquakes this paper develops a moment tensor inversion technique suited for analysis of long period body waves from distant shallow earthquakes in addition to the moment tensor the procedure resolves precise source depths 5 km and estimates the duration of faulting the technique is applied to digital sro dwwssn recordings of outer rise intraplate earthquakes these earthquakes result from bending of oceanic plates prior to subduction bending induces horizontal tension near the top of the lithosphere and horizontal compression near its base a neutral surface separates compressional from tensional regimes an examination of 11 bending earthquakes in the period january 1981 to july 1982 indicates that the depth to the neutral surface is not geographically uniform although the seismicity sample is very small the depth of the neutral surface appears to correlate with the position of the trench arc in the evolutionary sequence of uyeda and kanamori 1979 in particular neutral surfaces at strongly coupled chilean type plate boundaries are elevated as much as 15 km above those at weakly coupled mariana type boundaries this correlation implies that nonuniformities in neutral surface height are created by variations in regional compressive stress resulting from contrasts in plate plate coupling to account for the observed heights maximum interplate compressive stresses must be comparable with stresses derived from bending

rupture extent of the 1978 miyagi oki japan earthquake and seismic coupling in the northern honshu subduction zone underthrusting at subduction zones can cause large earthquakes at shallow depths but is always accommodated by aseismic creep below a certain depth this transition depth is referred to as the depth of seismic coupling and can be directly observed in a subduction zone as the lower depth extent of significant moment release of the deepest large underthrusting earthquakes in 1978 a large ms 7 5 earthquake occurred off the coast of miyagi prefecture in northern honshu its focal mechanism represents underthrusting of the pacific plate beneath honshu since the hypocenter is located 150 km landward from the trench and there are no other large interplate earthquakes further landward from the trench axis this event defines the maximum depth of the coupled zone the lower limit of significant moment release of the miyagi oki earthquake is obtained by analysis of the long period p waves the deconvolved source time function consists of a dominant single pulse with peak moment release at 12 s and a total duration of 18 s the rupture extent of this dominant pulse does not extend deeper than 40 km thus the transition from coupled to uncoupled in northern honshu occurs at or above 40 km depth

the ionian and alfeo etna fault zones new segments of an evolving plate boundary in the central mediterranean sea highlights plate boundary re organization in the central mediterranean sea segmentation of the subduction complex along lithospheric transverse faults step faults in the ionian sea pleistocene active faulting and mt etna formation abstract the calabrian arc is a narrow subduction rollback system resulting from africa eurasia plate convergence while crustal shortening is taken up in the accretionary wedge transtensive deformation accounts for margin segmentation along transverse lithospheric faults one of these structures is the nnw sse transtensive fault system connecting the alfeo seamount and the etna volcano alfeo etna fault aef a second nw se crustal discontinuity the ionian fault if separates two lobes of the ca subduction complex western and eastern lobes and impinges on the sicilian coasts south of the messina straits analysis of multichannel seismic reflection profiles shows that 1 the if and the aef are transfer crustal tectonic features bounding a complex deformation zone which produces the downthrown of the western lobe along a set of transtensive fault strands 2 during pleistocene times transtensive faulting reactivated structural boundaries inherited from the mesozoic tethyan domain which acted as thrust faults during the messinian and pliocene 3 the if and the aef and locally the malta escarpment accommodate a recent tectonic event coeval and possibly linked to the mt etna formation regional geodynamic models show that whereas aef and if are neighboring fault systems their individual roles are different faulting primarily resulting from the ese retreat of the ionian slab is expressed in the northwestern part of the if the aef on the other hand is part of the overall dextral shear deformation resulting from differences in africa eurasia motion between the western and eastern sectors of the tyrrhenian margin of northern sicily and accommodating diverging motions in the adjacent compartments which results in rifting processes within the western lobe of the calabrian arc accretionary wedge as such it is primarily associated with africa eurasia relative motion

fast geodetic strain rates in eastern sicily southern italy new insights into block tectonics and seismic potential in the area of the great 1693 earthquake abstract along the 500 km long sicily calabria segment of the nubia eurasia plate boundary gps data highlight a complex and debated kinematic pattern we focus on eastern sicily where the style of crustal deformation rapidly changes in the space of few tens of kilometers in southeastern sicily struck by the 1693 m w 7 4 earthquake gps measurements highlight a steep velocity gradient with 2 4 mm yr of n s shortening in 10 km changing to broader extension 3 mm yr in 60 km in northern sicily and shortening in the southern tyrrhenian sea gps data and kinematic elastic block models highlight a complex fragmentation of the sicilian domain into three tectonic blocks which move independently from nubia describing an overall clockwise rotation of this crustal domain with respect to eurasia shortening in southeastern sicily is associated with a system of high angle reverse faults resulting from tectonic inversion of extensional faults at the northern tip of the hyblean plateau extension in northern sicily occurs on a broader deformation belt developed on the former kumeta alcantara line extending west of mount etna toward the southwestern tyrrhenian sea accommodating the faster rotation of the northeastern sicily block with respect to central sicily although the seismic potential of inland faults is not negligible our results strengthen the hypothesis that the malta escarpment is the likely source of the large 1693 earthquake and tsunami the observed kinematics appears only subordinately driven by the nubia eurasia convergence and the dynamics of the mediterranean subduction system is likely playing a major role in governing block motions and active tectonics in sicily

development of the palaeogeography of pangaea from late carboniferous to early permian abstract old and new well and poorly known lithofacies data of moscovian and artinskian age in the area limited by the arctic sea and central africa the atlantic ocean and the ural mountains have been plotted on present day maps the facies mapped and related environments allow the recognition of a series of different palaeogeographic palaeotectonic units including the late carboniferous to early permian deep sea to palaeo tethyan ocean west siberia kazakhstan continent and uralian kazakhstan tienshan arc uralian foredeep up to the closing arms of the uralian ocean precaspian basin russian platform donets rift basin caucasian moesian dobrogean polish oslo basinal belt syn tectonic hercynian foreland basin intramontane post hercynian basins iran anatolian hellenic dinaric carnic basin branching into the hungarian seaway apennine basin branching into the cantabrian and south portuguese basins oman iraq levantine sicily deep basin and inferred oceanic sea way south peri tethyan platform basins east arabian cratonic basin and north african intracratonic basins the subsidence sedimentation trends of these units were correlated and compared through lithostratigraphic logs bathymetric curves and uncorrected cumulative stratigraphic curves the sets of original and processed data were used to test two different palaeodynamic models a pangaea a model static from late carboniferous to triassic and a mobile pangaea b model with different dextral displacements between laurussia and gondwanaland in the same time interval the best fit for our data requires a strike slip offset of about 800 km from moscovian to artinskian time this model implies a first quasi pangaea or pangaea b assembly at the carboniferous permian transition an ephemeral pangaea b break up driven by an early permian oblique rift across the mediterranean to caribbean areas and a final pangaea a assembly in the mid to late permian the two palinspastic maps describing the model have been cross checked by comparison with an independent set of biogeographic features of late carboniferous and early permian overall floral reptile and marine benthic organism distribution is consistent with the early permian trans pangaea seaway inferred from facies and palaeodynamic analyses

active thrust tectonics in western sicily southern italy the 1968 belice earthquake sequence the 1968 belice earthquake sequence characterized by six main shocks with 5 m 5 4 represents the strongest seismic event recorded in western sicily in historical times the epicentral area is located in the belice valley a region lacking any topographic lineament likely to result from a fault with significant offsets of any kind instrumental data show that hypocentres of the major shocks are distributed along a roughly n dipping plane extending from about 36 km to 1 km depth fault plane solutions show pure thrusting mechanisms on n dipping ene trending planes or oblique slip with a right lateral component of motion along steep wsw dipping planes both as a result of approximate n s shortening the observed destruction indicates that isoseismal areas are elongated in an ene direction similarly the epiccntral distribution of events with m 4 outlines a roughly elliptical ene elongated area located 20 km nw of the sciacca rocca ficuzza thrust front this ene striking structure representing the regional morphotectonic feature closest to the epicentral area consists of two main imbricate fan systems in the southernmost system quaternary deposits tentatively dated as 1 0 0 7 myr old are involved in a large ramp anticline uplifting them to a maximum altitude of 346 m the occurrence of holocene lacustrine piggy back basins on the rear of this structure also indicates late quaternary activity of the underlying thrust seismological structural and morphotectonic observations suggest that multiple ruptures might have occurred during the 1968 sequence on a blind crustal thrust ramp located beneath the epicentral area slip propagated southwards along the shallow ramp flat system characterizing the thin skinned foreland fold and thrust belt of southwestern sicily being dispersed in flexural folding processes and diffuse strain along this path

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

the influence of dynamically supported topography on estimates of te abstract the effective elastic thickness t e of continental lithosphere can be estimated from the relationship between gravity and topography in the spectral domain two methods have been used one of which depends on the coherence between bouguer gravity anomalies and topography whereas the other uses the transfer function commonly known as the admittance between the free air gravity and topography the two methods give estimates of t e which differ by as much as an order of magnitude in those continental regions where variations in elevation are small this problem has led to much controversy an important concern is the extent to which estimates of t e are affected by dynamically maintained gravity and topography arising from mantle convection and postglacial recovery unlike elastically supported anomalies these processes can generate gravity and topographic long wavelength 500 km anomalies if such anomalies are modelled as being supported by elastic forces the resulting values of t e are overestimated often by a large amount

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

importance of model parameterization in finite fault inversions application to the 1974 mw 8 0 peru earthquake the spatial and temporal slip distributions for the october 3 1974 mw 8 0 peru subduction zone earthquake and its largest aftershock on november 9 ms 7 1 are calculated and analyzed in terms of the inversion parameterization and tectonic significance teleseismic long period world wide standard seismograph network p and sh waveforms are inverted to obtain the rupture histories we demonstrate that erroneous results are obtained if a parameterization is used that does not allow for a sufficiently complex source involving spatial variation in slip amplitude risetime and rupture time the inversion method utilizes a parameterization of the fault that allows for a discretized source risetime and rupture time well located aftershocks recorded on a local network have the same general pattern as teleseismically determined hypocenters and help to constrain the geometry of the subduction zone for the main shock a hinged fault is preferred having a shallow plane with a dip of 11 and a deeper landward plane with a dip of 30 the preferred nucleation depth lies between 11 and 15 km a bilateral rupture is obtained with two major concentrations of slip one 60 to 70 km to the northwest of the epicenter and a second 80 to 100 km to the south and southeast of the epicenter for these source regions risetimes vary from 6 to 18 s our estimates of risetimes are consistent with the time for the rupture to traverse the dominant local asperity the slip distribution for the november 9 aftershock falls within a conspicuous hole in the main shock rupture pattern near the hypocenter of the main shock the november 9 event has a simple risetime function with a duration of 2 s aftershocks recorded by the local network are shown to cluster near the hypocenter of the impending november 9 event and downdip from the largest main shock source region slip during the main shock is concentrated at shallow depths above 15 km and extends updip from the hypocenter to near the plate boundary at the trench axis the large amount of slip at shallow depths is attributed to the absence of any significant accretionary wedge of sediments and the relatively young age and high convergence rate of the subducted plate which results in good seismic coupling near the trench axis

neogene tectono sedimentary interaction between the calabrian accretionary wedge and the apulian foreland in the northern ionian sea abstract the structural setting of the northern ionian sea is the result of the collision between the calabrian accretionary wedge caw and the adjacent foreland i e the apulian carbonate platform the caw represents a sector of the apennine accretionary system extending in the ionian sea bounded to the west by the malta escarpment and to the east by the apulia escarpment this work presents the results of the interpretation of new seismic and bathymetric data acquired on the north eastern edge of the caw in the n ionian sea the data interpretation has identified four main structural domains from ne to sw 1 the apulian carbonate platform consisting of foreland shelf and transitional mesozoic cenozoic carbonate deposits 2 a narrow foredeep basin filled by a very thick plio quaternary succession 3 a deformed domain at the front of the caw incorporating thrusted foredeep sequences and a carbonate block of the apulian platform transpressed apulian block tab 4 a highly deformed pre pliocene accretionary wedge a mid pliocene unconformity interpreted on both the caw and apulian foreland suggests that a regional tectonic event occurred at that time related to the evolution of calabrian arc moving on the subducting oceanic ionian slab before the collision this event would correspond to a main tilting and faulting phase of the apulian foreland during the diachronous oblique collision with the caw the collision and the presence of a remnant of ionian foreland at the southern front of the accretionary prism caused a gradual transition to a transpressional tectonics which produced the uplift of the tab the tab would be the south east continuation of the amendolara ridge transpressed structure which forms the offshore extension of the pollino range this transpressed shear zone involving the apulian foreland developed above the transition between the adriatic continental crust and the subducting ionian oceanic crust

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

crustal structure variations and transcurrent faulting at the eastern and western margins of the eastern mediterranean abstract crustal structure variations within the crust of the eastern mediterranean as well as within the continental crust of the land areas east and west of the basin have caused segmentation of the collision zones which extend from sicily through the calabrian arc the hellenic arc and the cyprian arc to the taurus chain on both sides of the eastern mediterranean in southeastern sicily and in the levant similar tectonic features have developed hinge faults exist along both continental margins due to the different modes of collision between the land areas and the adjacent oceanic areas landward of the margins two large transcurrent fault systems the scicli fault zone and the dead sea rift have developed due to the existence of unique crustal units within the continental crust adjacent to the margins on both sides these units are more buoyant than the adjacent crust and resist underthrusting the initial faulting along both transcurrent fault systems probably started at the collision zone in the north and propagated to the south where large extensional areas the pantelleria rift and the red sea exist

active tectonics of the calabrian subduction revealed by new multi beam bathymetric data and high resolution seismic profiles in the ionian sea central mediterranean highlights dextral strike slip faulting occurs offshore e sicily above a lateral slab tear fault proposed dextral ionian fault becomes sinistral to the south in external wedge compressional folding and thrusting tectonics occur throughout the wedge morpho tectonics indicate ongoing subduction and advance of calabrian backstop the detailed morphology and internal structure of the calabrian accretionary wedge and adjacent eastern sicily margin are imaged in unprecedented detail by a combined dataset of multi beam bathymetry and high resolution seismic profiles the bathymetric data represent the results of 6 recent marine geophysical surveys since 2010 as well as a compilation of earlier surveys presented as a 2 arc sec 60 m grid several distinct morpho tectonic provinces are identified including the deeply incised malta hyblean escarpment numerous submarine canyons broad regions of relatively flat seafloor dominated by fields of sediment waves the gently undulating anticlinal fold and thrust belts of the external calabrian accretionary wedge and the adjacent portion of the western mediterranean ridge the calabrian arc can be divided into 4 domains from se to nw 1 the undeformed ionian abyssal plain 2 the external evaporitic wedge 3 the internal clastic wedge 4 the calabrian backstop variscan crystalline basement the calabrian accretionary wedge can also be divided laterally into two major lobes the ne and the sw lobes and two minor lobes the kinematics of the limit between the two major lobes is investigated and shown to be sinistral in the external evaporitic wedge a network of radial slip lines within the southernmost external wedge unequivocally demonstrate ongoing dextral displacement of a rigid indenter representing the corner of the clastic wedge into the evaporitic wedge thereby confirming the geodynamic model of an active lateral slab tear fault here off eastern sicily the slab tear produces a series of major sub parallel dextral strike slip faults offshore mt etna and south of the straits of messina consistent with the relative motions between calabria and the peloritan domain ne sicily abundant strike slip faulting and wide spread folding and thrusting observed throughout the entire accretionary wedge indicate regional shortening between the ionian abyssal plain foreland and the calabrian peloritan backstop caused by active subduction

outer rise earthquakes and seismic coupling outer rise earthquakes can be separated into two basic categories based on focal mechanism compressional and tensional events reflecting compressional and tensional outer rise stress regimes we propose a model that connects the stress regime in the outer rise to the behavior of large subduction earthquakes and explains the focal mechanisms and both the temporal and spatial occurrence of outer rise earthquakes we find that compressional outer rise events tend to occur oceanward of seismic gaps in seismically coupled subduction zones or equivalently just prior to large subduction zone earthquakes the compressional stress regime is probably caused by slip in adjacent subduction zone segments there are two modes of occurrence for tensional outer rise earthquakes depending on whether they occur in coupled or uncoupled subduction zones in coupled subduction zones tensional events tend to occur after large subduction events as tensional stress from slab pull is temporarily transmitted to the outer rise in subduction zones that are inherently uncoupled tensional events can occur at any time therefore in uncoupled subduction zones the outer rise is always in tension and only tensional outer rise events occur there while in coupled subduction zones the outer rise is in a compressional state prior to large subduction earthquakes and a tensional state afterwards due to the large displacements

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

structural and tectono stratigraphic review of the sicilian orogen and new insights from analogue modeling abstract the apennines sicilian maghrebian fold and thrust belt originated from the subduction of the alpine tethys and the later collision of drifted continental blocks against the african and apulian paleomargins from north to south the sicilian fold and thrust belt sftb is divided in four main tectono stratigraphic domains 1 the calabro peloritani terrane drifted from the european margin 2 the remnants of the alpine tethys accretionary wedge atw related to the subduction of the tethys 3 the folded and thrusted platform panormide and deep water imerese sicanian series of the offscrapped african margin and 4 the african foreland hyblean unfortunately scarce quality seismic lines and outcrops of key tectono stratigraphic units make the structure and dynamic evolution of the central eastern part of the sftb controversial first this study outlines through a review of the tectono stratigraphic evolution of the central eastern sector of the sicilian orogen the major remaining issues concerning 1 the occurrence of inferred alpine tethys units far from the region where the remnants of the atw outcrop nebrodi mountains both in a forearc position above the peloritani block to the north and in an active foreland context along the present day southern front of the belt and 2 the diverging tectonic styles from stacked large scale tectonic nappes to foreland imbricated thrust systems rooted into a main basal decollement secondly new constraints are given using analogue modeling to test mechanically the hypothesized structural and tectono stratigraphic evolution of the sftb the experiment simulates the orogenic evolution of the sftb at crustal scale from the oligocene tethys subduction to the middle miocene late pliocene continental collision between the european and african paleomargins the tectono stratigraphic synthesis is used to model the first order mechanical stratigraphy of the sedimentary units involved in the sicilian belt as well as the imprint of the african margin structural inheritance the experiments succeed in reproducing the general structure and tectono stratigraphic evolution of the sftb in particular the models support field observations hypothesing a gravity driven origin of the inferred alpine tethys units intercalated within the forearc and foreland syntectonic sedimentation moreover the model testifies of the main tectonic steps that led to the sftb building first a low tapered accretionary wedge was accreted above the alpine tethys oceanic crust from the oligocene to the early miocene the following underthrusting of the stretched african continental margin and its frontal panormide platform shortened and thickened the accretionary wedge this phase provided favorable conditions for significant pulses of reworked alpine tethys units that intercalated within the forearc and foredeep successions during the middle miocene the decollement of the african meso cenozoic cover panormide platform and imerese sicanian deep water basin enhanced a deep seated deformation phase along with duplexing of the panormide platform beneath the alpine tethys wedge leading to its emersion since the late messinian activation of basement faults led to a generalized emersion of the orogenic units through large wavelength fold culminations accompanied by syn tectonic deposition at their southern limbs concurrently the prism front was partly indented to the southeast by the thick and locally already emerged hyblean platform

regional deformation and offshore crustal local faulting as combined processes to explain uplift through time constrained by investigating differentially uplifted late quaternary palaeoshorelines the foreland hyblean plateau se sicily

on the mesozoic ionian basin summary new seismic reflection profiles of the italian deep crust project crop provide new insights on the structure of the ionian sea in spite of the apennines and hellenides neogene subduction zones two conjugate passive continental margins are preserved at the margins of the ionian sea along the malta escarpment to the southwest and the apulian escarpment to the northeast the ionian sea is likely to be a remnant of the mesozoic tethys ocean confined by these two conjugate passive continental margins the transition from continental to oceanic crust appears sharper to the northeast than to the southwest the basin between southeast sicily and southwest puglia was about 330 km wide and suggests a low spreading rate the inferred oceanic ridge should have been flattened by thermal cooling and buried by later sediments based on stratigraphic and structural constraints to the north in the apennines belt the ocean continued to the northwest this palaeogeography is supported by the seismicity of the apennines slab underneath the southern tyrrhenian sea which implies downgoing oceanic lithosphere the adjacent absence or paucity of deep seismicity does not imply absence of subduction but rather it can be interpreted as due to the more ductile behaviour of the subducted continental lithosphere surprisingly we note that where the oceanic inherited basin is subducting underneath the apennines in the hangingwall of the subduction hinge there are outcropping slices of continental crystalline basement previously deformed by the alpine orogen

new structural and seismological evidence and interpretation of a lithospheric scale shear zone at the southern edge of the ionian subduction system central eastern sicily italy we performed an integrative analysis of geological gravimetric and seismological data analyzed data depicted a not well known wrench zone in the central eastern sicily our findings enabled us to interpret this shear zone as a plio pleistocene step fault

plate detachment asthenosphere upwelling and topography across subduction zones this study analyzes the topography across subduction zones considering the separate contributions of the crust and the mantle lithosphere to the observed surface elevation we have found a transition from a region where the overriding plate is coupled to the descending slab and pulled down along with it to a region where the overriding plate floats freely on the asthenosphere when the subducting slab retreats oceanward rapidly this transition is abrupt and the edge of the overriding plate is uplifted we propose that at some point during rapid slab rollback the overriding plate detaches and rebounds like a boat released from its keel this event is associated with suction of asthenospheric material into the gap that is opened between the plates up to the base of the crust as a result the forearc uplifts and magmatism in the arc increases

crustal structure and seismotectonics of central sicily southern italy new constraints from instrumental seismicity summary in this paper we propose a new model of the crustal structure and seismotectonics for central sicily southern italy through the analysis of the depth distribution and kinematics of the instrumental seismicity occurring during the period from 1983 to 2010 and its comparison with individual geological structures that may be active in the area the analysed data set consists of 392 earthquakes with local magnitudes ranging from 1 0 to 4 7 we defined a new detailed 1 d velocity model to relocate the earthquakes that occurred in central sicily and we calculated a moho depth of 37 km and a mean vp vs ratio of 1 73 the relocated seismic events are clustered mainly in the area north of caltanissetta e g mainland sicily and in the northeastern sector madonie mountains of the study area only minor and greatly dispersed seismicity is located in the western sector near belice and along the southern coast between gela and sciacca the relocated hypocentral distribution depicts a bimodal pattern 50 per cent of the events occur within the upper crust at depths less than 16 km 40 per cent of the events occur within the middle and depth crust at depths between 16 and 32 km and the remaining 10 per cent occur at subcrustal depths the energy release pattern shows a similar depth distribution on the basis of the kinematic analysis of 38 newly computed focal plane solutions two major geographically distinct seismotectonic domains are distinguished the madonie mountain domain with prevalent extensional and extensional oblique kinematics associated with upper crust late pliocene quaternary faulting and the mainland sicily domain with prevalent compressional and compressional oblique kinematics associated with thrust faulting at mid to deep crust depth along the north dipping sicilian basal thrust sbt the stress inversion of the mainland sicily focal solutions integrated with neighbouring mechanisms available in the literature highlights a regional homogeneous compressional tensor with a subhorizontal nnw sse striking 1 axis in addition on the basis of geodetic data the mainland sicily domain may be attributed to the sse ward thrusting of the mainland sicily block along the sbt plane seismogenic shearing along the sbt at mid crustal depths was responsible for the unexpected belice 1968 earthquake mw 6 1 with evident implications in terms of hazard assessment

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

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

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

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

the depth of the october 1981 off chile outer rise earthquake ms 7 2 estimated by a comparison of several waveform inversion methods the determination of source depth of the october 1981 ms 7 2 outer rise earthquake off the chilean coast has important implications for the stress state of the subducting plate we analyze the chile earthquake using three different waveform inversion methods in order to check the consistency of these methods and to estimate the source depth the methods we used are 1 1 honda and seno s 1989 inversion method in which we incorporate both long period p waves and surface waves 2 2 nab lek s 1984 body wave inversion methods for long period p and sh waves 3 3 seno and honda s 1988 deconvolution method in which we assume vertically distributed point sources and use long period p waves these methods give consistent results which suggest that the centroid depth and depth extent of the chile earthquake lies between 20 to 45 km measured from the sea surface this conclusion is contradictory to those obtained by the previous workers who prefer a shallow 25 km source depth we found that the gdsn long period data alone cannot constrain the source depth well the shape of deconvolved source time function is found to be strongly dependent on the assumption of point and distributed sources and the crustal structure used in the deconvolution the source depth obtained in this study shows that the 1981 chile outer rise earthquake possibly occurred because of the compression associated with the bending of the subducting plate

analysis of the trade off between hypocentral depth and source time function focal depth determination for shallow 60 km intermediate size ms 6 5 to 7 5 earthquakes continues to be problematic for these events the depth phases i e pp and sp are not distinctly separated in time and thus synthetic modeling of wave shapes becomes necessary unfortunately the uniqueness of the solution is not easily determined because of the trade off between various focal parameters we have investigated the trade off between depth and source function both theoretically and experimentally the changes in the green s function caused by an incorrect assumed depth can almost always be compensated by changes in the source function producing the same observed seismogram thus there is considerable trade off between depth and the source function perturbing the depth from the true depth leads to a more complicated source function the simplest source function then pinpoints the true depth we have used two different measures of simplicity the varimax norm v max and the half absolute moment time t 1 2 both measures successfully characterize the complications that appear in the source functions for incorrect assumed depths the true depth of an event can be interpreted from the resultant v max versus depth and t 1 2 versus depth curves thus we have a technique that determines the depth range of faulting in a systematic quantitative fashion our observations from the synthetic study have been applied to an outer rise event off the coast of central chile 16 october 1981 ms 7 2 to an event in southern mexico 24 october 1980 ms 7 0 and to the borrego mountain event in southern california 9 april 1968 ms 6 4 resulting in faulting depth ranges of 0 to 20 5 km 60 to 70 5 km and 10 to 14 5 km respectively

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

inelastic models of lithospheric stress 11 implications for outer rise seismicity and dynamics summary outer rise seismicity and dynamics are examined using inelastic models of lithospheric deformation which allow a more realistic characterization of stress distributions and failure behaviour we conclude that thrust and normal faulting outer rise earthquakes represent substantially different states of stress within the oceanic lithosphere specifically the normal faulting events occur in response to downward plate bending which establishes the standard bending dominated state of outer rise stress and the thrust faulting events occur in response to an elevated level of in plane compression which develops only in response to exceptional circumstances this interpretation accounts for the observation that normal faulting outer rise earthquakes occur more frequently and are more widely distributed than their thrust faulting counterparts an observation for which the simple bending model offers no explanation in addition attributing both thrust and normal faulting outer rise earthquakes to plate bending implies that both classes of events should occur within relatively close lateral proximity to one another because both are allegedly a manifestation of the same bendingdominated stress distribution whereas in reality this is not observed we propose that the tendency for thrust faulting outer rise earthquakes to exhibit greater source depths than their normal faulting counterparts an observation that is frequently cited in support of the bending interpretation of the former is merely a consequence of the fact that bending induced tension is confined to the upper lithosphere our model predicts that outer rise in plane force variations may promote thrust faulting outerrise activity prior to an underthrusting interplate subduction earthquake and normalfaulting outer rise activity following such an earthquake but that both forms of outerrise activity are unlikely to be associated with the same subduction earthquake a corollary implication of our model is that subduction earthquakes are likely to be either preceded by or followed by an absence of large outer rise earthquakes levels of in plane compression necessary to generate thrust faulting outer rise earthquakes are attributed to stress concentrations within the subducting plate that are induced by relatively localized resistance to regionally distributed plate driving forces resistance of this nature may result from either the attempted subduction of relatively buoyant i e isostatically compensated bathymetric features or the existence of strong interplate

gps velocity and strain fields in sicily and southern calabria italy updated geodetic constraints on tectonic block interaction in the central mediterranean 1 we present an improved rendition of the geodetic velocity and strain fields in sicily and southern calabria obtained through the analysis of 18 years of gps observations from continuous and survey station networks the dense spatial coverage of geodetic data provides precise quantitative estimates of previously established first order active kinematic features including i a narrow east west elongated belt of contraction 1 1 5 mm yr extending offshore northern sicily from ustica to stromboli across the aeolian islands ii a narrow east west trending contractional belt located along the northern rim of the hyblean plateau in southern sicily with shortening at up to 4 4 mm yr iii right motion 3 6 mm yr on the aeolian tindari letojanni fault atlf system a main shear zone extending from the aeolian islands to the ionian coast of sicily with significant transpression and transtension partitioned between discrete sectors of the fault iv transtension 1 mm yr across the sicily channel between sicily and north africa we use geodetic observations coupled to geological constraints to better elucidate the interplay of crustal blocks revealed in the investigated area in particular we focus on the atlf which forms the primary boundary between the sicilian and calabrian blocks the atlf juxtaposes north south contraction between sicily and the tyrrhenian block with northwest southeast extension in northeastern sicily and calabria contraction between sicily and tyrrhenian blocks probably arises from the main europe nubia convergence although sicily has a component of lateral motion away from nubia we found that convergence is not restricted to the northern offshore as commonly believed but is widely accommodated between the frontal belt and the northern rim of the hyblean foreland in southern sicily geodetic data also indicate that active right shear on the atlf occurs to the southeast of the mapped fault array in northern sicily suggesting the fault cuts through till the ionian coast of the island the small geodetic divergence between the hyblean and apulian blocks rimming on both sides the calabria block and subjacent ionian slab coupled with marine geophysical evidences in the ionian sea lends credit to the proposed deep root of the atlf and to a fragmentation of the ionian domain

uplift histories of africa and australia from linear inverse modeling of drainage inventories this is the final version it first appeared at http onlinelibrary wiley com wol1 doi 10 1002 2014jf003297 abstract

rupture process of large earthquakes in the northern mexico subduction zone the cocos plate subducts beneath north america at the mexico trench the northernmost segment of this trench between the orozco and rivera fracture zones has ruptured in a sequence of five large earthquakes from 1973 to 1985 the jan 30 1973 colima event m s 7 5 at the northern end of the segment near rivera fracture zone the mar 14 1979 petatlan event m s 7 6 at the southern end of the segment on the orozco fracture zone the oct 25 1981 playa azul event m s 7 3 in the middle of the michoacan gap the sept 19 1985 michoacan mainshock m s 8 1 and the sept 21 1985 michoacan aftershock m s 7 6 that reruptured part of the petatlan zone body wave inversion for the rupture process of these earthquakes finds the best earthquake depth focal mechanism overall source time function and seismic moment for each earthquake in addition we have determined spatial concentrations of seismic moment release for the colima earthquake and the michoacan mainshock and aftershock these spatial concentrations of slip are interpreted as asperities and the resultant asperity distribution for mexico is compared to other subduction zones the body wave inversion technique also determines the moment tensor rate functions but there is no evidence for statistically significant changes in the moment tensor during rupture for any of the five earthquakes an appendix describes the moment tensor rate functions methodology in detail

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

seismic moment tensors and source depths determined by the simultaneous inversion of body and surface waves we present a linear moment tensor inversion method that incorporates both body and surface wave data the source coordinates are fixed during the inversion and the source depth is determined by applying the inversion at several depths and taking the depth that produces the minimum residual the inversion is carried out in the time domain for body wave data and in the frequency domain for surface wave data the fundamental rayleigh waves at the period of 256 s from ida stations and the long period p waves from wwssn and gdsn stations whose angular distances are from 30 to 90 are used as the data the simultaneous inversion of both body and surface wave data sets has several merits because of the body wave constraints the present method gives reasonable solutions at shallow depths 30 km where long period surface wave inversions become unstable although the inversion using only body wave data is unstable in the sense that it allows for a variety of solutions with a slight change in the assumed depth probably because of the noise present and poor coverage of body wave data to determine the source mechanisms the inclusion of surface wave data makes the solution stable this is because the surface wave data constrain nodal plane strikes we may also expect better resolution in source depth by including the body wave data because the local crustal structure above the source can be taken into account to generate the green s function we applied our method to two large earthquakes one occurring at the triple junction off boso peninsula central honshu on 18 september 1984 and another at the outer rise area off the chile trench on 16 october 1981 the scalar moments of the boso oki and chile earthquakes are estimated to be 3 2 1026 dyn cm and 6 3 1026 dyn cm respectively the ratio of the minimum absolute eigenvalue of the moment tensor to the maximum which may measure the non double couple component is less than 10 for both earthquakes this suggests that their sources are essentially a double couple the source depths of both events are determined as 30 km the boso oki event is indicative of hinge faulting within the pacific slab at the triple junction the chile event is consistent with compressional bending stress in the deeper part of the lithosphere at the trench outer rise area off chile

seismicity seismotectonics and crustal velocity structure of the messina strait italy abstract the messina strait is the most important structural element interrupting the southernmost part of the alpine apenninic orogenic belt known as the calabro peloritan arc it is being a narrow fan shaped basin linking the ionian sea to the tyrrhenian sea this region is affected by considerable seismic activity which mirrors the geodynamic processes due to the convergence between the african and the eurasian plates in the last four centuries a significant number of disastrous earthquakes originated along the arc among these the most noteworthy event occurred on december 28 1908 known as the reggio calabria messina earthquake in the messina strait area and caused a large tsunami and more than 100 000 casualties in this research we focus on the relationships between the general tectonic setting which characterize the messina strait and adjacent areas seismicity patterns and the crustal structure we analyzed a dataset consisting of more than 300 events occurring in the years from 1999 to 2007 having a magnitude range from 1 0 to 3 8 this dataset was exploited in a local earthquake tomography by carrying out a simultaneous inversion of both the three dimensional velocity structure and the distribution of seismic foci we applied the tomoadd algorithm which uses a combination of absolute and differential arrival times and a concept of self adapting grid geometry accounting for ray density encountered across the volume with this method the accuracy of event locations is improved and velocity structure near the source region is resolved in more detail than standard tomography fault plane solutions were obtained for the major and best recorded earthquakes the obtained velocity images highlight vertical and lateral heterogeneities that can be associated with structural features striking from nne ssw to ne sw these results are consistent with important tectonic elements visible at the surface and the pattern delineated by earthquake locations and focal mechanisms

a reassessment of outer rise seismicity and its implications for the mechanics of oceanic lithosphere we use body waveform modelling to constrain the source parameters of earthquakes occurring globally in oceanic lithosphere beneath the subduction zone outer rise and outer trench slope these data are then used to map the stress state in the lithosphere of the downgoing plate as it bends into the subduction zone our results provide new constraints on the faulting of oceanic lithosphere at the outer rise which is important for understanding the transmission of plate driving forces through the subduction system in all cases shallow normal faulting earthquakes are observed at the top of the plate and are separated in depth from any deeper thrust faulting earthquakes no temporal variation associated with large thrust faulting earthquakes on the subduction interface is seen in the depth extent of each type of faulting at the outer rise the transition depth from trench normal extension to compression is found to vary in agreement with models in which deformation is driven by the combination of in plane stresses and bending stresses resulting principally from slab pull combining the seismologically derived constraints on the thickness of the elastic core of the plate with estimates of the plate curvature we place upper bounds on the strength of the lithosphere at the outer rise which is required to be 300 mpa for a constant yield stress model or governed by an effective coefficient of friction of 0 3

depth extent of rupture of the 1981 chilean outer rise earthquake as inferred from long period body waves we have investigated how well the depth extent of rupture can be determined for a shallow dip slip earthquake from long period wwssn body waves the 16 october 1981 chilean outer rise earthquake mw 7 2 is analyzed as an example calculation of the resolution matrix for the vertical distribution of displacement rate on the fault plane shows that the depth extent of rupture cannot be resolved better than 20 km even when the data set consists of both p and s waves although the depth extent of rupture of the 1981 earthquake is too small to be resolved it is possible to infer some constraints from the point source depth in combination with the source duration while inversion for the depth extent of rupture can be formulated as a linear problem determination of the point source depth is nonlinear and a formal resolution study cannot be conducted the point source depth estimate for the 1981 earthquake is 28 to 32 km 80 confidence interval the source duration is 8 sec assuming a rupture velocity of 3 km sec we have explored several rupture models in a synthetic experiment to shed light on the relation between point source depth and centroid depth the experiments show that point source depths agree with the centroid depth given that there is poor resolution of the depth extent of rupture of the 1981 earthquake we conclude from the synthetic experiments that the earthquake may have ruptured updip to a depth as shallow as 17 km or downdip to a depth as deep as 43 km

new insights on 3d crustal structure in southeastern sicily italy and tectonic implications from an adaptive mesh seismic tomography abstract the adaptive mesh double difference tomography algorithm tomoadd was applied to absolute and differential p s and s p data to determine three dimensional v p v s and v p v s variations and event locations in southeastern sicily italy the obtained velocity images highlight vertical and lateral heterogeneities that can be associated with different geological units and main tectonic features in particular the sharp velocity contrasts are consistent with previously recognized active faults allowing us to better determine their shapes and geometries at depth moreover a striking correspondence between areas ruptured by earthquakes and velocity anomalies is observed in fact seismicity is mostly confined in the high velocity volumes and or along the high low velocity boundaries at mid crustal depths whereas it tends to avoid regions with lower than average v p and v s values and higher v p v s ratios

crustal structure and deformation across a mature slab tear zone the case of southern tyrrhenian subduction italy we compute s velocity profiles of the crust across the messina strait italy the tear zone at the southern end of the ionian subduction zone separating sicily from calabria the messina strait hosted some of the strongest earthquakes to ever occur in italy here the motion of the ionian slab with respect to sicily creates a complex tectonic setting characterized by lithospheric tearing we show velocity models of the crust computed from teleseismic receiver function inversion outlining the differences between sicily and calabria strong deformation across the messina strait between 10 15 and 30 km depth is expressed by strong anisotropy up to 10 developed in a ductile shear zone of the crust the top of these ductile weaker layers could limit the depth extent of future ruptures

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

spatial variations of seismogenic stress orientations in sicily south italy abstract seismogenic stress orientations are estimated in the lithosphere of sicily by inversion of 131 local earthquake focal mechanisms fms selected from the literature an average misfit f 14 5 between stress tensor and fms indicates that the entire set of earthquakes is generated by a highly heterogeneous stress field detailed analysis of stress tensors and related earthquake misfits obtained for tens of subsets based on spatial separation of data allowed us to identify two main stress domains in the study region i a compressional domain including etna western sicily and the southern tyrrhenian sea offshore sicily where the 1 orientation roughly changes from nw se in the etna area and western sicily to nne ssw at the northeastern edge of the domain eolian islands and ii an extensional domain in northeastern sicily between the eolian islands and etna where 3 is oriented analogously to previously estimated in the easterly confining extensional area of the messina straits general agreement is found between this stress pattern and the gps crustal displacement vectors reported in the most recent literature for the study region moreover stress inversion enables us to locate the extensional domain more accurately than the presently available gps data finally the stress orientations estimated in the southern and western sectors of the study area etna and western sicily on and offshore match well with the displacement fields predicted for sicily by large scale models of plate motion conversely a mismatch is observed in the northeastern sector eolian islands and northeastern sicily we suggest that the joint action of africa eurasia convergence and ionian subduction trench retreat rollback of the subducting slab may explain the stress pattern detected in sicily in the present study work for computation of a finite element regional geodynamic model based on geophysical and geological data collected over the last few years has recently started with the purpose of quantitatively checking this hypothesis

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

subduction initiation along the inherited weakness zone at the edge of a slab insights from numerical models summary a preexisting weakness zone in the lithosphere is required to initiate subduction here we focus on a new type of weakness zone a subduction transform edge propagator step fault which is inherited from a tear along the edge of a slab using coupled thermal mechanical models we show that step fault perpendicular convergence results in a dipping shear zone in any tectonic setting at a continental margin this shear zone dips towards the continent which is an excellent starting condition for ocean continent subduction if far field convergence persists step faults become new subduction boundaries the trench moves landward during the earliest stages of convergence when slab pull becomes a dominant driving force after 80 km convergence trench roll back commences the initial geometry and mechanical properties of the sub crustal step fault zone affect the results subduction initiation is facilitated by a wide 100 km and low viscosity weakness zone incipient subduction is easier for young oceanic lithosphere due to its lower flexural rigidity and is insensitive to the far field convergence rate as step faults are commonly associated with young oceanic lithosphere subduction initiation is thus relatively easy along them of particular interest are continent ocean margins where step faulting has occurred

structural evidence for neogene rotations in the eastern sicilian fold and thrust belt abstract a geological and structural analysis carried out on a sector of the eastern sicilian fold and thrust belt pointed out the occurrence of two systems of structural associations typical of collisional fronts in particular the mesozoic serravallian succession of the mt judica unit outcropping in three w e to wnw ese striking distinct ridges is characterized by two fold systems with sub perpendicular axes the first plunging towards 010 040 at angles of 30 55 the second one with sub horizontal axes trending 090 115 the different angular values of plunging suggest that the folds of the first system underwent the effects of severe tectonic deformation following their formation moreover the distinct ridges were uplifted by south verging thrusts and relative back thrusts coaxial to the second system of folds conversely the upper tortonian lower pliocene deposits of mt pulicara show only one fold and thrust system wnw ese trending roughly coaxial to the second system recognized in the mt judica unit succession the structural analysis carried out in the two areas compared with published eastern central sicily palaeomagnetic data suggest that the mesozoic serravallian succession of the mt judica unit recorded both major 70 langhian late tortonian clockwise rotations and locally 30 pliocene clockwise rotations so the structures formed during the first deformation stage were totally rotated up to 100 conversely structures of the mt pulicara upper tortonian lower pliocene deposits were involved only in the pliocene clockwise rotation from a geodynamic point of view the neogene clockwise rotation in the eastern sicily fold and thrust belt is related to the regional framework of the africa europe convergence

stress transfer and seismic phenomena in coupled subduction zones during the earthquake cycle an elementary mechanical model of a coupled subduction zone is presented it is used to study the transfer of extensional stresses along the underthrusting plate and shear stress interactions between the plate itself and its thrust contact zone with the overriding plate during the earthquake cycle the model assumes an elastic plate which deforms one dimensionally has shear drag interactions treated approximately by the elsasser procedure with a maxwellian viscoelastic mantle and is subject to steady gravitational sinking forces great thrust earthquakes are simulated as sudden stress relieving displacements at the contact zone between the slab and overriding plate the model allows analysis of the space and time variable stresses in the main thrust zone the adjacent oceanic plate and the subducting slab over each earthquake cycle stress variations leading to outer rise events are discussed as well as stress changes responsible for intraplate seismicity downdip from the main thrust zone based on simulations of periodic great earthquakes the results of simulated slow progression of deformation slip from below into the thrust contact zone are also presented such preslip occurring over a time scale that is small in comparison with the whole seismic cycle e g of the order of a tenth or so is shown to transiently slow the rate of buildup of or even relieve extensional stresses in the slab in the absence of preslip those stresses build up steadily in time during the latter part of the cycle the results have implications for induction of sesimic quiescence as well as for explaining patterns of seismicity in relation to spatial position along the underthrusting plate and to time throughout the cycle correlations are reported between the model simulations and seismicity observations from coupled subduction zones around the world the observations include tensional outer rise events after large subduction earthquakes and compressional ones in the latter parts of the cycle normal tensional intraplate earthquakes preceding the main thrust events and positioned downdip from the thrust zones and interlaced periods of seismic activity in the lower part of the main thrust zone and in the descending slab

age dependence of oceanic intraplate seismicity and implications for lithospheric evolution we have determined depths for 16 oceanic intraplate earthquakes using body wave modeling a data set composed of these and 11 other well constrained depths shows that the maximum depth of seismicity deepens with increasing lithospheric age and appears to be bounded by a 700 800 c isotherm the maximum depth to which intraplate earthquakes occur is approximately equal to the flexural elastic thickness but much less than the seismic thickness from surface wave dispersion the maximum faulting depth is consistent with the predictions of rapid weakening at high temperatures for dry olivine rheologies determined by experimental rock mechanics oceanic intraplate earthquakes can occur at greater depths and temperatures than has previously been reported for continental crustal events presumably because oceanic lithosphere is stronger at high temperatures both the number of earthquakes and the cumulative seismic moment decrease with lithospheric age the cause of this trend is unclear possibilities include nonrandom location of preexisting weak zones with respect to the age provinces fault strengthening with age or a decrease in the stress level a decrease in intraplate stress with age is opposite that expected from ridge push stresses which increase with age but may result either from thermoelastic stresses which are greatest in young lithosphere or near ridge stress concentrations due to local heterogeneities in the spreading process

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

convergence vs retreat in southern tyrrhenian sea insights from kinematics 1 the tyrrhenian sea is an extensional basin opened by trench retreat and back arc extension during subduction of the calabrian slab in the last 10 12 my subduction is still active beneath the semost part of the tyrrhenian sea as testified by seismicity down to 500 km depth by analyzing seismicity and geodetic data together with recent tomographic images we define the present day situation an evident n s compressional regime prevails in the tyrrhenian region west of the aeolian archipelago while east of them a nnw sse extension is documented by focal mechanisms and gps data with a much smaller strain rate with respect to the past the transition between these two domains is accommodated by a n s discontinuity zone which runs from aeolian islands to mt etna with an extensional to strike slip deformation

uplift histories from river profiles 1 longitudinal river profiles where elevation of a river bed is plotted as a function of distance along the river bed contain information about uplift rate when a region adjacent to a reference level e g sea level is uplifted a rapid change in gradient occurs near the river mouth the erosional process causes this change in gradient to migrate upstream thus a river profile is effectively a tape recording of the uplift rate history provided that the erosional process can be adequately parameterized here we use a non linear equation to relate the shape of a river profile z x to uplift rate history u t if erosion is assumed to be dominated by knickpoint retreat an inverse model can be formulated and used to calculate uplift rate histories our model builds upon standard stream profile analysis which focuses on the relationship between profile slope and drainage area we have applied this analytical approach to river profiles from the bie dome angola calculated uplift rate histories agree with independent geologic estimates

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

odp leg 107 in the tyrrhenian sea insights into passive margin and back arc basin evolution leg 107 of the ocean drilling program drilled a west northwest east southeast transect of seven sites across the tyrrhenian sea the youngest of the sub basins of the mediterranean sea sites 654 653 652 and 656 document the rifting and subsidence of the sardinia passive continental margin on the upper margin site 654 we cored a classic transgressive sequence subaerial conglomerates overlain by oyster bearing sands overlain by marine marl comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are tortonian late miocene to messinian latest miocene in age whereas synrift sediments on the lower margin are messinian to pliocene in age during the messinian desiccation of the mediterranean sites 654 and 653 now on the upper sardinian margin apparently occupied a basinal setting where they received nannoplankton bearing clays interbedded with laminated gypsum sites 656 and 652 now on the lower sardinia margin were apparently higher standing during the desiccation event their messinian facies are subaerial and lacustrine respectively we infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a rolling back subduction zone or in terms of extension of continental crust by shear along a deep detachment fault sites 655 651 and 650 were drilled into two small basalt floored basins of the central and eastern tyrrhenian emplacement of basaltic crust in the central tyrrhenian vavilov basin apparently began more than a million years before emplacement of basaltic crust in the eastern tyrrhenian marsili basin this observation is compatible with previous suggestions that the tyrrhenian has grown southeastward in response to rollback of the down going slab that currently dips northwestward under the toe of italy at the easternmost site high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2 500 m it has apparently subsequently subsided to its present depth of 4 100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid ocean ridge

seismic coupling and outer rise earthquakes variation of interplate seismic coupling at subduction zones is a major factor controlling the size of the largest underthrusting events this variation also has a profound effect on the regional intraplate stresses in the vicinity of the subduction zone outer rise seismicity is strongly correlated with variations in interplate coupling reflecting the stress state of the interplate coupled zone over 200 outer rise earthquakes with known focal mechanisms are used to investigate the relationship between stresses in the outer rise and interplate seismic coupling these events occur within the downgoing i e oceanic plate near the bathymetric trench axes and generally fall into the categories of tensional normal or compressional thrust with their tensional or compressional stress axes oriented approximately horizontal and perpendicular to the trench in uncoupled subduction zones only tensional outer rise earthquakes occur which indicates that the outer rise is dominated by tensional stresses associated with plate bending and or slab pull forces in strongly coupled subduction zones both tensional and compressional outer rise events are found these events are related both spatially and temporally to the distribution of large underthrusting earthquakes and are thus an integral part of the earthquake cycle in the strongly coupled regions tensional outer rise events follow large underthrusting events as the outer rise is temporarily in tension due to the underthrusting motion compressional outer rise events take place as compressional stress slowly accumulates oceanward of locked sections of the interplate zone in four instances compressional outer rise earthquakes have been followed by large underthrusting events which have occurred 2 4 7 and 19 years after the associated outer rise event the remaining compressional outer rise events are located in regions that are either known seismic gaps or in regions where the seismic potential is unknown the occurrence of compressional outer rise earthquakes suggests that compressional stress is accumulating in the adjacent interplate region and that there is the potential for a future large underthrusting event in the region thirty compressional outer rise events have been located in trench segments of middle and south america the kurile islands the tonga and kermadec islands the new hebrides arc and the solomon islands regions in both the southern kamchatka and northern new hebrides regions the outer rise seismicity indicates that the stress regimes in the outer rise have changed with time from tensional following a previous large underthrusting event to compressional at present thus three stages of the cycle from underthrusting to tensional outer rise regime to compressional outer rise regime are present requiring only the occurrence of the next underthrusting event to complete the cycle the occurrence of compressional outer rise events is useful for assessing the seismic potential of a region on an intermediate time scale

late cenozoic subduction complex of sicily abstract besides remnants of hercynian deformations in the peloritani nappe and of pre oligocene alpine structures in the troiani nappe most compressive structures observed in the sicilian accretionary wedge result from the late cenozoic tortonian to present continental subduction of the apulia iblei block and are thus synchronous with distensive structures related to the opening of the tyrrhenian sea syntectonic deposits fill southward migrating foredeeps in a sequential fashion and the dating of these deposits helps to constrain the timing of deformation similarly plio quaternary sediments eroded from the accreted units rest on top of the allochthon in either compressive piggy back depressions or extensional basins the age and configuration of these overlap deposits constrain our reconstructions of the subsurface geometry of the underlying peri tyrrhenian detachment faults or s verging thrust faults post depositional erosion normal faulting and syntectonic filling of basins contribute to maintaining the critical taper of the prism whose geometry is continuously altered owing to frontal accretion underplating and isostatic uplift

foreland segmentation along an active convergent margin new constraints in southeastern sicily italy from seismic and geodetic observations abstract we performed an in depth analysis of the ongoing tectonics of a large sector of southern sicily including the hyblean foreland and the front of the maghrebian chain as well as the ionian sea offshore through the integration of seismic and gps observations collected in the nearly two decades in particular a dataset consisting of more than 1100 small to moderate magnitude earthquakes 1 0 ml 4 6 has been used for local earthquake tomography in order to trace the characteristics of the faulting systems and for focal mechanisms computation to resolve the current local stress field and to characterise the faulting regime of the investigated area in addition gps measurements carried out on both episodic and continuous stations allowed us to infer the main features of the current crustal deformation pattern main results evidence that the hyblean plateau is subject to a general strike slip faulting regime with a maximum horizontal stress axis nw se to nnw sse oriented in agreement with the eurasia nubia direction of convergence the plateau is separated into two different tectonic crustal blocks by the left lateral strike slip scicli ragusa fault system the western block moves in agreement with central sicily while the eastern one accommodates part of the contraction arising from the main eurasia nubia convergence furthermore we provided evidences leading to consider the hyblean maltese escarpment fault system as an active boundary characterised by a left lateral strike slip motion separating the eastern block of the plateau from the ionian basin all these evidences lend credit to a crustal segmentation of the southeastern sicily

multi trace deconvolution with unknown trace scale factors omnilinear inversion of p and s waves for source time functions seismic source and wave propagation theories allow seismologists to compute long period synthetic seismograms that commonly match even subtle details of observed waveshapes but the overall trace amplitudes must be scaled by arbitrary factors to emphasize the excellent waveshape correspondence this unexplained amplitude scatter causes considerable difficulties when formally inverting observed waveforms for seismic source parameters omnilinear inversion simultaneously determines the linear model parameters and trace scaling factors to minimize the mismatch between observed and synthetic seismograms omnilinear inversion is applied to source time function deconvolution from long period p and sh waves a simulation with synthetic data shows that omnilinear inversion finds the proper scaling factors and the source time function and focal depth are better determined than for standard linear inversion omnilinear inversion is then applied to a data set of seven p waves and one sh wave from the underthrusting earthquake of july 5 1968 ms 6 6 in northern honshu japan omnilinear inversion produces a best fit focal depth of 36 km with a single pulse time function of 6 s duration and seismic moment of 4 1018 n m mw 6 4 this focal depth supports the notion that the seismically coupled plate interface extends no deeper than 40 km in northern honshu

seismicity in the outer rise offshore southern chile indication of fluid effects in crust and mantle we examine the micro earthquake seismicity recorded by two temporary arrays of ocean bottom seismometers on the outer rise offshore southern chile on young oceanic plate of ages 14 ma and 6 ma respectively the arrays were in operation from december 2004 january 2005 and consisted of 17 instruments and 12 instruments respectively approximately 10 locatable events per day were recorded by each of the arrays the catalogue which is complete for magnitudes above 1 2 1 5 is characterized by a high b value i e a high ratio of small to large events and the data set is remarkable in that a large proportion of the events form clusters whose members show a high degree of waveform similarity the largest cluster thus identified consisted of 27 similar events average inter event correlation coefficient 0 8 for a 9 5 s window and waveform similarity persists far into the coda inter event spacing is irregular but very short waiting times of a few minutes are far more common than expected from a poisson distribution seismicity with these features high b value large number of similar events with short waiting times is typical of swarm activity which based on empirical evidence and theoretical considerations is generally thought to be driven by fluid pressure variations because no pronounced outer rise bulge exists on the very young plate in the study region it is unlikely that melt is accessible from decompression melting or opening of cracks a fluid source related to processes at the nearby ridge is conceivable for the younger segment but less likely for the older one we infer that the fluid source could be seawater which enters through fractures in the crust most of the similar earthquake clusters are within the crust but some of them locate significantly below the moho if our interpretation is correct this implies that water is present within the mantle hydration of the mantle is also indicated by a decrease of pn velocities below the outer rise seen on a refraction profile through one of the arrays contreras reyes e grevemeyer i flueh e r scherwath m heesemann m 2007 alteration of the subducting oceanic lithosphere at the southern central chile trench outer rise geochem geophys geosyst 8 q07003 the deepest events within the array on the 6 ma old plate occur where the temperature reaches 500 600 c consistent with the value observed for large intraplate earthquakes within the mantle 650 c suggesting that the maximum temperature at which these fluid mediated micro earthquakes can occur is similar or identical to that of large earthquakes

source mechanisms of earthquakes near mid ocean ridges from body waveform inversion implications for the early evolution of oceanic lithosphere to investigate the early tectonic evolution of oceanic lithosphere we present a synthesis of the characteristics of near ridge earthquakes i e earthquakes which occur off the axis of major mid ocean spreading centers but in lithosphere less than 35 m y old near ridge seismicity for the past two decades has been rather evenly distributed along the major ridge systems with the exception of the central indian ocean and the eastern part of the cocos plate which have experienced a high rate of earthquake activity during that time for 32 near ridge earthquakes we determined the double couple orientation seismic moment centroid depth and source time function using a formal inversion technique based on matching synthetic and observed p and sh waveforms all types of faulting styles are observed seismogenic deformation in young oceanic lithosphere is concentrated in the first 15 m y and occurs almost entirely in the uppermost mantle from just below the moho to depths at which the temperature estimated from standard thermal models exceeds 800 c thrust faulting is not observed at depths greater than 10 km below the seafloor the deepest near ridge earthquakes are generally characterized by normal faulting focal mechanisms with the t axis oblique or perpendicular to the local spreading direction most of these earthquakes occur in the central indian ocean the transition from mechanisms characteristic of ridge axes to those characteristic of the near ridge environment occurs within the first few million years for lithosphere less than 35 m y old horizontal compressive stress associated with the cooling and subsidence of the lithosphere ridge push does not appear to be the dominant source of stress released in earthquakes this result may be used to place a lower bound of several hundred bars on the typical stress difference in young oceanic lithosphere this bound together with the observed depth of faulting implies that the strain rate associated with seismic deformation is locally at least 10 15 s 1 we propose that thermoelastic stresses associated with plate cooling play an important role in near ridge earthquakes this source of stress can account for the mechanisms and depths of many near ridge earthquakes and for the concentration of activity in very young lithosphere the comparative aseismicity of the oceanic crust may reflect the concentration of thermoelastic stress below the moho due to different material properties for the crust and upper mantle or the early release of thermoelastic stresses through hydrothermal circulation and cracking throughout the crust at or near the ridge axis the higher level of near ridge seismicity in the indian ocean may be the result of modification or enhancement of the more typical near ridge stress state by such local processes as the continental collision between india and asia or active secondary convection beneath the young lithosphere of the indian plate

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

crustal structure of central sicily abstract we processed crustal seismic profile siripro acquired across central sicily to improve the seismic image we utilized the wave equation datuming technique a process of upward or downward continuation of the wave field between two arbitrarily shaped surfaces wave equation datuming was applied to move shots and receivers to a given datum plane removing time shifts related to topography and to near surface velocity variations the datuming procedure largely contributed to attenuate ground roll enhance higher frequencies increase resolution and improve the signal noise ratio processed data allow recognizing geometries of crust structures differentiating seismic facies and offering a direct image of ongoing tectonic setting within variable lithologies characterizing the crust of central sicily migrated sections underline distinctive features of hyblean plateau foreland and above all a crustal thinning towards the caltanissetta trough to the contact with a likely deep permo triassic rifted basin or rather a zone of a continent to oceanic transition inhomogeneity and fragmentation of sicily crust with a distinct separation of central sicily basin from western and eastern blocks appear to have guided the tectonic transport inside the caltanissetta crustal scale syncline and the accumulation of allochthonous terrains with south and north verging thrusts major tectonic stack operated on the construction of a wide anticline of the maghrebian chain in northern sicily sequential south verging imbrications of deep elements forming the anticline core denote a crust wedge indenting foreland structures deformation processes involved multiple detachment planes down to decoupling levels located near crust mantle transition supporting a presence of high density lenses beneath the chain interrelated to a southwards push of tyrrhenian mantle and asthenosphere

tectonics from fluvial topography using formal linear inversion theory and applications to the inyo mountains california tectonic activity generates topography and the variability of tectonic forcing is responsible for topographic patterns and variability of relief in fluvial landscapes despite this basic relation the inverse problem by which features of the topography are used for inferring tectonic uplift rates has proven challenging here we develop formal linear inversion schemes to infer a record of the rate of relative uplift as a function of space and time from the long profiles of rivers the relative uplift rate is the difference between the rates of rock uplift and of the base level change the inversion schemes are based on a closed form analytic solution to the transient linear stream power model and to increase model resolution they make use of the multiplicity of information made available by multiple rivers and their tributaries the distribution of the fluvial response time to tectonic perturbations is a key component of the inversion scheme as this determines which tectonic events are preserved in the topography we develop two inversion parameterizations that differ in their assumptions about the tectonic forcing space invariant and time space variability with an assumed spatial distribution the inversion schemes are applied to the inyo mountains an uplifted block along the western boundary of the basin and range province in california inversion results indicate that the range has been experiencing an acceleration of the relative uplift in the past 2 3 ma we use the inversion results to constrain the paleotopography and paleo erosion rate along the range and to recover the throw rate history along the fault that bounds the inyo range

forearc extension and slow rollback of the calabrian arc from gps measurements 1 here we describe the horizontal velocities of continuous gps stations in the calabrian arc ca and surrounding regions the appropriate reference frame to evaluate the crustal motion of the ca is considered by assessing the internal deformation and the relative motion of the crustal blocks in the foreland of the apennines ionian maghrebides subduction system we propose that the motion of ca relative to the subducting ionian lower plate is most properly assessed by minimizing the gps velocities in apulia in this reference frame the significant 2 mm yr southeastward motion of the stations on the ionian flank of the ca shows that the arc is still moving towards the trench in agreement with the observations of active shortening in the ioanian wedge this southeastward migration is associated to 1 4 0 3 mm yr e w extension of the forearc in northern calabria comparable with the seismic strain averaged in the last 500 years the limited subaerial exposure decreases the resolution on locking of the subduction interface but the distribution and direction of crustal extension along the ca impose important constraints on geodynamic interpretations of the area

seismic coupling along the chilean subduction zone underthrusting at subduction zones can cause large earthquakes at shallow depths but is accommodated by aseismic creep below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding we have determined the maximum depth of the coupled zone and its variability along the chilean subduction zone the maximum depth of seismic coupling is defined by the depth of large m 6 underthrusting earthquakes that have occurred at the downdip edge of the coupled plate interface earthquake depth is determined with omnilinear waveform inversion of long period p waves the statistical uncertainty in the depth is estimated using bootstrapping omnilinear inversion formally accounts for the scaling incompatibility between the p waveforms and decreases the uncertainty in the depth estimate we have found the depths of 27 earthquakes in the time period from 1961 to 1987 seismic coupling in chile extends down to 48 53 km there is a resolvable change in the maximum depth of coupling around 28 s the region immediately north of this latitude has a coupled zone that extends no deeper than 36 41 km while south of this latitude coupling extends down to 48 53 km this transition is not simply related to the oceanic lithospheric age and plate convergence rate but coincides with a change in several geophysical and geological phenomena with respect to shallower north and deeper south coupling there is a change from active volcanos to no volcanos the dip of the deep slab changes from steep to shallow the thickness of trench sediments changes from thin to thick and the depth of the oceanic basement changes from deeper to shallower at 28 s due to the multiplicity of changes at 28 s there is no clear unique interpretation of what physical mechanism controls the variability in the maximum depth of the seismically coupled zone in chile

active thrusting as a possible seismogenic source in sicily southern italy some insights from integrated structural kinematic and seismological data abstract this paper proposes a new seismogenic interpretation of mainland and central southern sicily based on an integrated structural kinematic seismological approach through analysis of available structural and geophysical data the tectonic setting the major kinematic units and the crust geometry of the sicilian southward verging fold and thrust belt system are schematized in sections and in map form the depth contour lines of the outermost basal thrust plane which dates back to plio pleistocene times with some evidence of holocene activity are reconstructed this plane here named sicilian basal thrust sbt emerges along the southward convex sciacca gela catania front and reaches the base of the crust at a depth of about 30 km beneath northern sicily additionally an important regional upper crust splay with the same arched shape has been identified some kilometres northward in order to detect any possible indication of seismogenic activity linked to ongoing deformation of the sbt and its splay we analyzed the distribution and kinematics of the instrumental seismicity in the period between 1981 and 2006 particular attention was given to the background seismicity ml up to 4 6 located beneath the sedimentary cover at mt etna as it allows individuating a northward deepening seismogenic volume undergoing an average n s compression which corresponds well with the sbt geometry in section view a merged dataset of all the known major historical and instrumental events moment magnitude 4 5 that occurred above the sbt 0 to 30 km depth contour lines from 217 b c to 2006 was compiled and analyzed based on information from instrumental data and or on speculations on the shape and extent of the historical earthquake macroseismic fields two major ranges of hypocentral depths have been schematically identified within the merged dataset an upper crust range in average