broadband waveform inversion of moderate earthquakes in the messina straits southern italy abstract we report the first application of the cut and paste cap method to compute earthquake focal mechanisms in the messina straits area by waveform inversion of pnl and surface wave segments this application of cap has furnished new knowledge about low magnitude earthquake mechanics that will be useful for improved understanding of the local geodynamics this is possible because the cap inversion technique can be applied to small earthquakes for which traditional moment tensor inversion methods are not appropriate and p onset focal mechanisms in the study area fail because of a lack of sufficient observations we estimate the focal mechanisms of 23 earthquakes with local magnitudes in the range of 3 4 occurring in the 2004 2008 time period and recorded by the broadband stations of the italian national seismic network and the mediterranean very broadband seismographic network mednet run by the istituto nazionale di geofisica e vulcanologia ingv the solutions show that normal faulting is the prevailing style of seismic deformation in the northern part of the study area while co existence of normal faulting and strike slip has been detected in the southern part in the whole area of investigation the t axes of focal mechanisms display a preferential northwest southeast direction of extension combined with the findings of previous investigations this improved database of focal mechanisms allows us to better detail the transitional area between the extensional domain related to subduction trench retreat southern calabria and the compressional one associated with continental collision western central sicily the observed spatial change of seismic deformation regime offers new data to current seismotectonic and seismic hazard investigations in the area of messina straits where a magnitude 7 2 earthquake caused more than 60 000 casualties on 28 december 1908

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

seismicity and structure in central mexico evidence for a possible slab tear in the south cocos plate the morphology of the transition from flat to normal subduction in eastern central mexico is explored using intraslab earthquakes recorded by temporary and permanent regional seismic arrays observations of a sharp transition in slab dip near the abrupt end of the trans mexican volcanic belt tmvb suggest a possible slab tear located within the subducted south cocos plate the eastern lateral extent of a thin ultra slow velocity layer usl imaged atop the cocos slab in recent studies along the meso america subduction experiment array is examined here using additional data we find an end to this usl which is coincident with the western boundary of a zone of decreased seismicity and the end of the tmvb near the sharp transition in slab dip waveform modeling of the 2 d structure in this region using a finite difference algorithm provides constraints on the velocity and geometry of the slab s seismic structure and confirms the location of the usl analysis of intraslab seismicity patterns reveals clustering sudden increase in depth variable focal mechanism orientations and faulting types and alignment of source mechanisms along the sharp transition in slab dip the seismicity and structural evidence suggests a possible tear in the south cocos slab this potential tear together with the tear along the orozco fracture zone to the northwest indicates a slab rollback mechanism in which separate slab segments move independently allowing for mantle flow between the segments

seismotomography of the crust in the transition zone between the southern tyrrhenian and sicilian tectonic domains 1 a crustal tomography of seismic wave velocity was performed in the contact zone between the southern tyrrhenian sicilian and ionian tectonic units a zone where the lithospheric structure can be expected to furnish evident signatures of dynamics related to the tyrrhenian subduction process a dataset of 10241 p and 5597 s readings from 932 local earthquakes recorded between 1978 and 2001 by stations operating in sicily and calabria was inverted by the simulps12 algorithm for simultaneous computation of hypocenter parameters and vp and vp vs three dimensional distributions the study brought significant improvement in the knowledge of the local velocity structure furnishing new information useful to better identify the local tectonic units the results appear to be compatible with the most recent hypotheses regarding the geodynamics of the study region

kinematics of the western africa eurasia plate boundary from focal mechanisms and gps data summary the western mediterranean displays a complex pattern of crustal deformation distributed along tectonically active belts developed in the framework of slow oblique plate convergence we used earthquake and global positioning system gps data to study the present day kinematics and tectonics of the africa eurasia plate boundary in this region crustal seismicity and focal mechanisms analysed in terms of seismic moment release and seismic deformation outline the geometry of major seismic belts and characterize their tectonics and kinematics continuous gps data have been analysed to determine euler vectors for the nubian and eurasian plates and to provide the global frame for a new mediterranean gps velocity field obtained by merging continuous and campaign observations collected in the 1991 2005 time span gps velocities and displacements predicted by the nubia eurasia rotation pole provide estimates of the deformation accommodated across the tectonically active belts the rather simple deformation occurring in the atlantic region characterized by extension about perpendicular to the middle atlantic and terceira ridges and right lateral motion along the gloria transform fault turns into a complex pattern of deformation occurring along broader seismic belts where continental lithosphere is involved our analysis reveals a more complex fragmentation of the plate boundary than previously proposed the roughly e w trending mainly compressive segments i e southwestern iberia northern algeria and southern tyrrhenian where plate convergence is largely accomodated across rather localized deformation zones and partially transferred northward to the adjacent domains i e the algero balearic and tyrrhenian basins are interrupted by regions of more distributed deformation i e the rif alboran betics tunisia libya and eastern sicily or limited seismicity i e the strait of sicily which are characterized by less homogeneous tectonics regimes mainly transcurrent to extensional in correspondence of the observed breaks tectonic structures with different orientation interfere and we find belts with only limited deformation i e the high and middle atlas the tunisian atlas and the offshore tunisia libya belt that extends from the plate boundary into the nubian plate along pre existing tectonic lineaments our analysis suggest that the sicilian pelagian domain is moving independently from nubia according to the presence of a right lateral and extensional decoupling zone corresponding to the tunisia libya and strait of sicily deformation zone despite the space variability of active tectonic regimes plate convergence still governs most of the seismotectonic and kinematic setting up to the central aeolian region in general local complexities derive from pre existing structural features inherited from the tectonic evolution of the mediterranean region on the contrary along calabria and the apennines the contribution of the subducted ionian oceanic lithosphere and the occurrence of microplates i e adria appear to substantially modify both tectonics and kinematics finally gps data across the gibraltar arc and the tyrrhenian calabria domain support the hypothesis that slab rollback in these regions is mostly slowed down or stopped

estimates of stress directions by inversion of earthquake fault plane solutions in sicily summary the tectonic stress orientation is estimated in the lithosphere of northern sicily the southern tyrrhenian sea and southern calabria and in the wadati benioff zone below the tyrrhenian by inversion of fault plane solutions of earthquakes covering a magnitude range from 2 5 to 7 1 focal mechanisms of 97 earthquakes are taken from the literature after a critical evaluation of their data quality an average misfit of f 13 indicates that the set of all shallow 50 km earthquakes is generated by a heterogeneous stress field for three subsets based on regional and magnitude separation f was small enough 2 8 lfs5 9 to support the assumption of a homogeneous stress direction for an additional subset with f 7 4 such a condition is close to being fulfilled even though some heterogeneity appears to be present the number of earthquakes in these subsets ranged from nine to 22 and the uncertainties of the principal stress directions were generally of the order of 20 at the 90 per cent confidence level the earthquakes with a425 define a regional stress field with the greatest principal stress ul dipping at a shallow angle to the south in north eastern sicily and south western calabria the stress field estimated by earthquakes is extensional with o3 in a direction of wnw and a near vertical ol in agreement with the graben tectonics mapped geologically in this area in western sicily the c1 direction is oriented wnw but this result is judged less reliable than the others based on the broader confidence limits of the solution and the average misfit of 7 4 the earthquakes in the wadati benioff zone define ol dipping at about 70 to the nw subparallel to the zone with o2 horizontal and striking parallel to the zone

the dynamics of back arc extension an experimental approach to the opening of the tyrrhenian sea the e w opening tyrrhenian sea developed after the cretaceous palaeogene alpine collision nearly perpendicular to the motion of the african plate as a back arc of the adria ionian westward subduction three driving mechanisms have been proposed to explain the dynamic evolution of the tyrrhenian apennine system 1 the northward indentation of the african plate 2 the retreating subduction of the adria ionian lithosphere and 3 the gravitational collapse of the alpine post collisional wedge in order to define the relative contribution of each of these mechanisms in the neogene dynamic of the tyrrhenian apennine system we performed 3 d laboratory experiments in which we simulated a retreating subduction process in a compressional regime oriented perpendicularly to the direction of subduction in this framework we also tested the influence of the gravitational collapse of the overriding plate experiments were constructed using dry sand and silicone putties to simulate brittle upper crust and ductile lower crust upper mantle respectively these layers floated on a high density low viscosity glucose syrup which simulated the asthenosphere the main conclusion of our experiments is that large scale continental extension similar to that observed in the tyrrhenian area could be reproduced perpendicular to the shortening direction induced by the indentation of the african plate in this framework extensional processes are indeed possible if the trench retreat velocity is higher than the rate of shortening induced by the advancing african plate our experimental results indicate that this high trench retreat velocity could be explained by the coexistence of the gravitational collapse of the post alpine wedge with a slab pull process linked to the retreating subduction of the adria ionian plate while the first mechanism is predominant in the northern tyrrhenian area the second one seems to be important in the latest stage of extension and oceanic accretion of the southern tyrrhenian area

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

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

the lithosphere asthenosphere system in the calabrian arc and surrounding seas southern italy a fairly detailed structural model of the lithosphere asthenosphere system thickness s and p wave velocities of the crust and of the uppermost mantle layers has been defined in the calabrian arc region southern tyrrhenian sea calabria and the northwestern part of the ionian sea in southern italy using seismic data from literature as a priori constraints of the nonlinear inversion of surface wave data

source parameters of the 1908 messina straits italy earthquake from geodetic and seismic data 1 we carry out a nonlinear joint inversion of p wave first motion polarities and coseismic surface displacement data of the 1908 messina earthquake we model the earthquake using a single planar fault slip is at first assumed to be uniform across the whole fault then independent in a small set of coplanar subfaults and finally smoothly variable across the fault the first two steps are accomplished using a global minimization technique the main features of the retrieved model are very robust and independent of the seismic velocity profile of the presence of questionable bench marks and of the assumed residual distribution the along strike component of slip is about half the along dip component in agreement with the direction of the extensional stress axis retrieved from geological observations surface vertical displacement is consistent with tsunami data and with the morphology of the messina straits

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

seasonal variability in winds in the north polar region of mars abstract surface features near mars polar regions are very active suggesting that they are among the most dynamic places on the planet much of that activity is driven by seasonal winds that strongly influence the distribution of water ice and other particulates morphologic features such as the spiral troughs chasma boreale and prominent circumpolar dune fields have experienced persistent winds for several myr therefore detailing the pattern of winds throughout the year is an important step to understanding what processes affect the martian surface in contemporary and past epochs in this study we provide polar focused mesoscale simulations from northern spring to summer to understand variability from the diurnal to the seasonal scales we find that there is a strong seasonality to the diurnal surface wind speeds driven primarily by the retreat of the seasonal co 2 until about summer solstice when the co 2 is gone the fastest winds are found when the co 2 cap boundary is on the slopes of the north polar layered deposits providing a strong thermal gradient that enhances the season long katabatic effect mid summer winds while not as fast as spring winds may play a role in dune migration for some dune fields late summer wind speeds pick up as the seasonal cap returns

spatial relation between the 1908 messina straits earthquake slip and recent earthquake distribution 1 we re analyze coseismic surface displacement data of the 1908 messina earthquake taking into account both correlated and uncorrelated uncertainties to re determine the slip distribution on the fault plane using a data set of earthquakes occurred at crustal depth in the messina straits between july 1988 and december 2004 we evidence a peculiar recent seismicity distribution inside the fault volume of the 1908 messina straits earthquake with respect to other regions in the area an unusually large number of earthquakes is found in regions smoothly ringing slipped areas our results seem consistent with static coulomb stress variations inside the fault volume and regional strain rate from gps data but could also suggest that in the last 15 20 years the 1908 earthquake source has been releasing strain accumulated in portions of it which did not rupture during the 1908 event

a 125 kyr long geological record of seismic source repeatability the messina straits southern italy and the 1908 earthquake ms7 2 the occurrence of characteristic earthquakes along segments of major active belts has been described as early as the beginning of the century the large 1908 messina straits blind normal faulting earthquake provides an opportunity to investigate the repetition of characteristic earthquakes and the persistency of the main features of the fault zone over a time scale in the order of 100 kyr we have compared seismological and geodetic descriptions of the 1908 rupture process with long term crustal deformation recorded at different stratigraphic levels by marine terraces marine sedimentary units and landscape features the wealth of elevated coastal features in and around a region affected by large normal faulting earthquakes indicates that coseismic strain is superimposed on much faster uplift on a regional scale we investigated in detail the pattern of deformation of the 125 kyr old lowest emergent terrace and found that it mimics the pattern of elevation changes observed following the earthquake this suggests 1 that the 1908 earthquake is characteristic 2 that its segment boundaries have been stationary during the past 125 kyr and 3 that even the locations of the regions of largest coseismic release do not change through many seismic cycles based on a comparison between observed heights of the 125 kyr terrace and 1908 displacements we estimated an average repeat time of 1000 yr for a 1908 type earthquake we also investigated the height position age and state of deformation of older terraces and found 1 that uplift of the region started about 1 ma and has since continued rather uniformly at 0 9 1 4 mm yr 1 2 that during this time the straits have narrowed at a rate of 10 20 mm yr 1 and 3 that all the main geomorphic features of the messina straits result from the interaction of fast regional uplift 1908 type coseismic subsidence and global sea level fluctuations

geodetic measurements of crustal deformation in the western mediterranean and europe geodetic measurements of crustal deformation over large areas deforming at slow rates 5 mm yr over more than 1000 km such as the western mediterranean and western europe are still a challenge because 1 these rates are close to the current resolution of the geodetic techniques 2 inaccuracies in the reference frame implementation may be on the same order as the tectonic velocities we present a new velocity field for western europe and the western mediterranean derived from a rigorous combination of 1 a selection of sites from the itrf2000 solution 2 a subset of sites from the european permanent gps network solution 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy on the order of 1 mm yr or better its analysis shows that central europe behaves rigidly at a 0 4 mm yr level and can therefore be used to define a stable europe reference frame in that reference frame we find that most of europe including areas west of the rhine graben the iberian peninsula the ligurian basin and the corsica sardinian block behaves rigidly at a 0 5 mm yr level in a second step we map recently published geodetic results in the reference frame previously defined geodetic data confirm a counterclockwise rotation of the adriatic microplate with respect to stable europe that appears to control the strain pattern along its boundaries active deformation in the alps apennines and dinarides is probably driven by the independent motion of the adriatic plate rather than by the africa eurasia convergence the analysis of a global gps solution and recently published new estimates for the african plate kinematics indicate that the africa eurasia plate motion may be significantly different from the nuvel1a values in particular geodetic solutions show that the convergence rate between africa and stable europe may be 30 60 slower than the nuvelia prediction and rotated 10 30 counterclockwise in the mediterranean

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

application of genetic algorithms to constrain near source velocity structure for the 1989 sichuan earthquakes abstract when a complex earthquake source process is studied using broadband body waveforms a common problem is finding an adequate layered velocity model for the near source structure tests with several existing crustal models are not sufficient or objective but an enumerative search scheme to search through a whole possible model space is not practical we study the feasibility of applying genetic algorithms ga to rapidly and effectively explore the model space to find an optimal model for the near source structure our data set consists of multi station broadband body waveforms of a simple event recorded at teleseismic distances the near source velocity structure is approximated by a layered model and the model parameters include the layer thicknesses and velocities as well as the source depth forming a multi parameter search space test results with synthetic data indicate that optimal models can be found using ga depending on the noise level when the noise level is low optimal models are well recovered with small uncertainty results with the data of the 1989 earthquakes of sichuan province china indicate that a three layer velocity model obtained with ga is in agreement with regional models and better explains the observed waveforms

locating and modeling regional earthquakes with two stations 1 we developed a new technique caploc to retrieve full source parameters of small seismic events from regional seismograms which include origin time epicenter location depth focal mechanism and moment magnitude despite rather complicated propagation effects at short periods a simple localized one dimensional model can well explain signals of periods 3 10 s if we break the three component records into different segments and allow differential time shifts among them these differential time shifts once established from a calibration process or a well determined tomographic map can be used together with p wave travel times to refine an event s location in this study we tested whether our new method could produce satisfactory results with as few as two stations so that we can improve source estimates of poorly monitored events with sparse waveform data we conducted the test on 28 events in the tibetan plateau the focal mechanisms and locations determined from only two stations agree well with those determined from a whole passcal array in particular our new method produces better locations than international seismological centre with the average mislocation error reduced from 16 to 5 km we also tested whether an event s depth and mechanism can be determined separately from its epicenter relocation in a two step approach we find that the two step approach does not always give the correct solution but the reliability of a solution can be evaluated using a reduced chi square value

reply to comments on the paper are the source models of the m 7 1 1908 messina straits earthquake reliable insights from a novel inversion and sensitivity analysis of levelling data by aloisi et al 2012

seismotectonics of western turkey from high resolution earthquake relocations and moment tensor determinations 1 we have relocated 364 earthquakes in western turkey between 2002 and 2003 using more than 45 000 accurate p and s differential travel times we also have determined moment tensors for 71 of these earthquakes using their broadband regional waveforms after relocation the events are highly concentrated in three clusters and delineate two nearly vertical faults their strikes agree with the strike of one of the fault planes of the averaged fault plane solution of the cluster which allowed us to pick the true fault plane and the slip direction we identified a nnw striking left lateral strike slip fault near buldan that connects the gediz graben in the north and the eastern end of the buyuk menderes graben in the south the other right lateral strike slip fault near izmir strikes ene wsw direction our results indicate that part of the n s extension occurring in western turkey is accommodated by strike slip faults and is accompanied by e w shortening

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

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

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

tectonic stress and seismogenic faulting in the area of the 1908 messina earthquake south italy 1 stress inversion of the twenty best quality earthquake fault plane solutions available in the area of the 1908 messina earthquake showed a nearly uniform extensional regime with min constrained between n284 e and n312 e coinciding with the direction of extension derived from geostructural data the misfits of earthquake nodal planes and related slip vectors to the stress tensor allowed us to identify the fault planes of thirteen of the earthquakes used for inversion in particular the fault plane of 1908 earthquake was found in the north trending east dipping nodal plane of the focal mechanism these findings and strain tensor estimates performed with the same dataset lead us to propose that in spite of stress uniformity detected over the study area the seismic strain orientations change significantly in the crustal volume under investigation due to different fault orientations in the different sectors however when comparing strong earthquakes with background seismicity in a given sector the strain orientations are found to be similar

real time determination of seismic moment tensor for the italian region this work has been funded by the 2005 2007 dpc s4 and 2008 2010 dpc s3 italian civil protection contracts

new gps constraints on the kinematics of the apennines subduction abstract we present the velocity field of the italian area derived from continuous gps observations from 2003 to 2007 the gps sites were installed by different institutions and for different purposes they cover the whole country with a mean inter site distance of about 60 km and provide a valuable source of data to map the present day kinematics of the region the absolute itrf2005 rotation poles and rates of eurasia africa and adriatic plates are estimated to study the kinematics along their boundaries in the apennines belt the corsica sardinia block coherently moving as the eurasia plate is used as reference of the upper plate for the apennines subduction zone we apply a simple kinematic model to estimate the rates and spatial pattern of the subduction along the apennines we identify at least four different independently moving lower plates i e the adriatic diverging and internally segmented ionian sicily and africa converging plates with different subduction rates the conservative estimates of the subduction rate are 5 mm yr in the calabrian arc 1 5 mm yr in sicily and 0 9 mm yr in the northern apennines this variegate mixture of behaviors seems to reflect the variable lithospheric thickness and composition of the lower plates inherited from the mesozoic rifting an unexpected along strike contraction is observed along the western side of the central northern apennines velocities are estimated both relative to eurasia and relative to the deep and shallow hotspot reference frames hsrf the hotspot representation seems more coherent with the geophysical and geological constraints along the subduction system in which the adriatic and ionian plates move sw ward and their deeper slab portions provide an obstacle to the opposite relative mantle flow all these patterns better reconcile if the subduction process is conceived as a passive feature controlled by the far field plate velocities and the relative eastward mantle flow acting on a disrupted slab

regional waveform calibration in the pamir hindu kush region twelve moderate magnitude earthquakes m b 4 5 5 in the pamir hindu kush region are investigated to determine their focal mechanisms and to relocate them using their regional waveform records at two broadband arrays the kyrgyzstan regional network knet and the 1992 pakistan himalayas seismic experiment array pakh in northern pakistan we use the cut and paste source estimation technique to invert the whole broadband waveforms for mechanisms and depths assuming a one dimensional velocity model developed for the adjacent tibetan plateau for several large events the source mechanisms obtained agree with those available from the harvard centroid moment tensor cmt solutions an advantage of using regional broadband waveforms is that focal depths can be better constrained either from amplitude ratios of pnl to surface waves for crustal events or from time separation between the direct p and the shear coupled p wave spn spmp for mantle events all the crustal events are relocated at shallower depths compared with their international seismological centre bulletin or harvard cmt depths after the focal depths are established the events are then relocated horizontally using their first arrival times only minor offsets in epicentral location are found for all mantle events and the bigger crustal events while rather large offsets up to 30 km occur for the smaller crustal events we also tested the performance of waveform inversion using only two broadband stations one from the knet array in the north of the region and one from the pakh array in the south we found that this geometry is adequate for determining focal depths and mechanisms of moderate size earthquakes in the pamir hindu kush region

active tectonics of the adriatic region from gps and earthquake slip vectors 1 to investigate the kinematics of the adriatic region we integrate continuous and episodic gps measurements with mw 4 5 earthquake slip vectors selected from the regional centroid moment tensor catalogue coherent motion of gps sites in the po valley in apulia and in the hyblean plateau allows us to estimate geodetically constrained angular velocities for these regions the predictions of the gps inferred angular velocities are compared with the earthquake slip vectors showing that the seismically expressed deformation at the microplate boundaries is consistent with the observed geodetic motion the remarkable consistency between geodetic seismological and geological evidence of active tectonics suggests that active deformation in the central adriatic is controlled by the relative motion between the adria and apulia microplates the microplates angular rotation rates are then compared with the rotation rates calculated with a simple block model supporting the hypotheses 1 that apulia forms a single microplate with the ionian sea and possibly with the hyblean region and 2 that adria and apulia rotate in such a way as to accommodate the eurasia nubia relative motion we suggest that the present day microplate configuration follows a recent fragmentation of the adriatic promontory that during the neogene rigidly transferred the africa motion to the orogenic belts that now surround the adriatic region

evidence for a post 3 16 ma change in nubia eurasia north america plate motions we combine updated gps velocities from the nubian nu eurasian eu and north american na plates with 500 new 3 16 myr average seafloor spreading rates and nine transform fault azimuths from the northern atlantic and arctic basin seafloor spreading centers to estimate and test for changes in the relative motion between these plates the numerous new seafloor spreading rates and gps velocities improve our ability to detect recent changes in the relative motions of these plates the angular velocity vector that best fits the eu na gps velocities lies significantly north of the 3 ma average pole in accord with previously published geologic evidence that the eu na pole has migrated northward since v3 ma although we also find evidence for a significant post 3 ma change in nu na motion it is less compelling because the nubian plate gps velocity field is sparse and nu na seafloor spreading rates appear to have remained steady within the 1 mm yr 31 uncertainties if we systematically decrease the seafloor spreading rates to correct for outward displacement of seafloor spreading magnetic lineations the nu eu pole derived from gps site velocities lies more than 30 angular degrees south of the tightly constrained 3 ma average estimate and predicts significantly slower and more oblique present day nu eu convergence in the mediterranean both models for nu eu motion pass a key test for their accuracy namely they correctly predict strike slip motion along the well mapped gloria fault east of the azores the change to more oblique nu eu motion may reflect increasing difficulty in maintaining margin normal convergence within this continent continent collision zone 8 2003 published by elsevier b v

aeromagnetic investigation of southern calabria and the messina straits italy tracking seismogenic sources of 1783 and 1908 earthquakes southern calabria and the ne corner of sicily italy were struck in 1783 and 1908 a d by two of the most catastrophic earthquakes ever in european history although it is generally acknowledged that the seisms were yielded by normal faults rupturing the upper crust of the calabria peloritani terrane no consensus exists on seismogenic source location and orientation here we report on a high resolution low altitude aeromagnetic survey of southern calabria and messina straits in southern calabria we document a broad weakly positive 5 10 nt anomaly zone interrupted by three en echelon sw ne null to negative magnetic anomaly corridors euler deconvolution and magnetic modeling show that the anomaly pattern is produced by a 1 1 5 km thick crustal layer located within 3 km depth this layer is offset by a 25 km long ne trending fault that corresponds to the armo normal fault recently inferred to be the source for the 1908 earthquake few kilometers to the south we also document a subparallel and previously unrecognized fault entering the messina straits and likely joining the armo fault at depth further east we model a 40 km long normal fault probably extending northeastward for additional 40 km running along the south calabria axis from aspromonte to the serre mountains and partly following the 18 km long surface rupture witnessed by deodat de dolomieu after the 1783 earthquake thus aeromagnetic data suggest that the sources of the 1783 and 1908 earthquakes are en echelon faults belonging to the same nw dipping normal fault system straddling the whole southern calabria

moment tensor analysis of the central italy earthquake sequence of september october 1997 the larger earthquakes in the umbria marche central italy seismic sequence of september october 1997 are analyzed using long period seismograms from the mediterranean seismographic network mednet and additional data from the global seismographic network gsn we modify the harvard centroid moment tensor cmt algorithm to allow moment tensor inversion of long period waveforms primarily rayleigh and love waves for small earthquakes at local to regional distances 5 5 in the sequence moment tensors have previously been determined using teleseismic waveforms and standard methods of analysis our results agree well with those of earlier studies we determine additional moment tensors for the largest foreshock and 10 aftershocks with mw 4 2 the earthquakes are characterized by normal faulting mechanisms with a ne sw tension axis and the presumed fault plane dips towards the sw only one of the fourteen events studied has a different faulting geometry indicating instead right lateral strike slip faulting on a plane oriented approximately e w or left lateral faulting on a plane oriented n s the september 26 mainshock 09 40 ut accounts for only approximately 50 of the total moment release in the sequence

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

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

reservoir imaging using low frequencies of seismic reflections there are numerous laboratory and field examples in which low frequency components of reflected seismic waves show surprising imaging capabilities ironically such components are often filtered out as useless in conventional data processing however as we demonstrate below this part of the signal contains the most important information about the reservoir

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