source parameters of the 1992 melilla spain mw 4 8 1994 alhoceima morocco mw 5 8 and 1994 mascara algeria mw 5 7 earthquakes and seismotectonic implications source mechanisms of the melilla alhoceima and mascara earthquakes including fault plane solutions waveform modeling and spectral analysis are presented strike slip solutions have been obtained for the melilla and alhoceima earthquakes and reverse faulting for mascara teleseismic p wave inversion using broadband data show a complex mechanism for the alhoceima earthquake formed by two subevents at very shallow depth 7 and 8 km and scalar seismic moments of 1 1 10e 17 n m and 4 8 10e 17 n m the mascara earthquake was a single event with a shallow depth 4 5 km and a scalar seismic moment of 3 3 10e 17 n m results of the alhoceima melilla and mascara earthquakes together with 53 focal mechanisms in the region show a regional stress regime that corresponds to horizontal compression in a nw se direction associated with the convergence between eurasia and africa a change of the stress regime in the plate boundary of the ibero maghrebian region has been found

reworked tsunami deposits by bottom currents circumstantial evidences from late pleistocene to early holocene in the gulf of cadiz abstract younger sand layers ysls have been identified in drill cores of a late glacial to early holocene muddy contourite succession from the gulf of cadiz in this study we evaluate the grain size characteristics of the ysl which display bi gradational grading with inverse grading from silt to fine or medium grained sand followed by normal grading from fine or medium grained sand to silt radiocarbon dating shows that the ysl formed at three distinct times 1 the bolling allerod sites u1387 and u1386 2 the younger dryas site u1390 and 3 the beginning of the boreal site u1389 ichnological analyses and radiocarbon dating of cores from drill site u1389c indicate that the ysls consist of reworked materials deposited at a high sedimentation rate the results of sedimentological analyses ichnological treatment spatial distributions and radiocarbon dating of the ysls suggest that the possibility of an origin of the ysls is tsunami related but later reworked by bottom current however the source areas of the sandy sediments remain unclear although our results show them to be variable and area dependent some sandy deposits are transported by the mediterranean outflow water mow from the proximal sector of the gulf of cadiz contourite depositional system cds which is close to the strait of gibraltar however in other cases it is more probable that local gravity flows which are the result of instability on adjacent margins provide the sandy material

a threshold based earthquake early warning system for offshore events in southern iberia the south of the iberian peninsula is situated at the convergence of the eurasian and african plates this region experiences large earthquakes with long separation in time the best known of which was the great 1755 lisbon earthquake which occurred sw of san vicente cape sw iberian peninsula the high risk of damaging earthquakes has recently led carranzaet al geophys res lett 40 2013 to investigate the feasibility of an eews in this region analysis of the geometry for the iberian seismic networks and the san vicente cape area led the authors to conclude that a threshold based approach which would not require real time location of the earthquake might be the best option for an eews in sw iberia in this work we investigate this hypothesis and propose a new eew approach that extends standard p wave threshold based single station analysis to the whole network the proposed method enables real time estimation of the potential damage at stations that are triggered by p waves and those which are not triggered with the advantage of greater lead times for release of alerts results of tests made with synthetic data mimicking the scenario of the great 1755 lisbon earthquake and those conducted by applying the new approach to available recordings indicate that an eew estimation of the potential damage associated with an event in the san vicente cape area can be obtained for a very large part of the iberian peninsula

a seismic reflection and gloria study of compressional deformation in the gorringe bank region eastern north atlantic seismic reflection and gloria side scan sonar data obtained on rrs charles darwin cruise cd64 reveal new information on the styles of deformation in the gorringe bank region at the eastern end of the azores gibraltar plate boundary previous studies suggest that gorringe bank was formed by the overthrusting of a portion of the african plate upon the eurasian plate the new seismic data show however that the most intensely deformed region is located south of gorringe bank on the northern flanks of a nw se trending submarine ridge which includes the ampere and coral patch seamounts the deformation is expressed as long wavelength up to 60 km large amplitude up to 800 m folds in the sediments and underlying acoustic basement which in places are associated with one or more reverse faults and as a fabric of short wavelength folds up to 3 km with a ne trend in contrast the same sedimentary units when traced beneath the flanking plains are undeformed except for some faults with a small throw 30 m some of which offset the seafloor gloria data show that recent deformation is broadly distributed over the region structural trends rotate from 45 in the west to 70 in the east of the region nearly perpendicular to the nw verging plate motion vectors as determined from plate kinematic models flexure modelling suggests that a portion of gorringe bank has loaded 152 ma oceanic lithosphere and that a maximum of 50 km of shortening has occurred at gorringe bank since the mid miocene our observations support a model in which there is no single plate boundary in the region rather that the deformation is distributed over a 200 330 km wide zone

an integrated geophysical investigation of recent seismicity in the al hoceima region of north morocco abstract data produced by the moroccan national seismological network and marine seismic reflection profiles are used to investigate the most seismically active region in morocco located on the mediterranean coast at the intersection of the rif mountain belt and the submarine alboran ridge this region in the vicinity of the city of al hoceima marks an east west transition in the marine and land deformation styles of the distributed plate boundary between africa and iberia and was the site of an m w 6 0 earthquake on 26 may 1994 the epicenter of the al hoceima earthquake is relocated onshore refining the initial submarine location close to the alboran ridge the spatial distribution of foreshocks and aftershocks shows a ne sw trend that continues partly offshore and is subparallel to the earlier yet still prominent miocene geologic structural trend the predominantly strike slip focal mechanism for the al hoceima event is characteristic of earthquakes in the region marine seismic reflection profiles that intersect the offshore region of seismicity image active high angle faults with possible strike slip components the seismicity trend is not directly related to the submarine alboran ridge or the geomorphologically prominent nekor fault deformation appears to be occurring on a number of subsidiary strike slip faults that together compose a ne sw zone of distributed shear the distributed strike slip and documented normal faulting taking place in the eastern rif mountains although characteristic of the rif region are in contrast to the thrusting style of deformation that occurs farther to the east in the algerian tell atlas this may be related to the reported lateral variations and evolution of the convergent plate boundary in these regions during the neogene and quaternary times

the role of continental margins in the final stages of arc formation constraints from teleseismic tomography of the gibraltar and calabrian arc western mediterranean abstract the deep seismicity and lateral distribution of seismic velocity in the central western mediterranean point to the existence under the alboran and tyrrhenian seas of two lithospheric slabs reaching the mantle transition zone gibraltar and calabrian narrow arcs correspond to the slabs similarities in the tectonic and mantle structure of the two areas have been explained by a common subduction and roll back mechanism in which the two arcs are symmetrical end members we present a new 3 d tomographic model at mantle scale for the calabrian arc and compare it with a recently published model for the gibraltar arc by monna et al 2013a the two models calculated with inversion of teleseismic phase arrivals have a scale and parametrization that allow for a direct comparison the inclusion in both inversions of ocean bottom seismometer broadband data improves the resolution of the areas underlying the seafloor networks this additional information is used to resolve the deep structure and constrain the reconstruction of the central western mediterranean geodynamic evolution the gibraltar tomography model suggests that the slab is separated from the atlantic oceanic domain by a portion of african continental margin whereas the calabrian model displays a continuous oceanic slab that is connected via a narrow passage 350 km to the ionian basin oceanic domain starting from the comparison of the two models we propose the following interpretation within the mediterranean geodynamic regime dominated by slab rollback the geometry of the african continental margin located on the lower plate represents a critical control on the evolution of subduction as buoyant continental lithosphere entered the subduction zones slab pull caused tears in the subducted lithosphere this tectonic response which occurred in the final stages of arc evolution and was strongly controlled by the paleogeography of the subducted plates explains the observed differences between the gibraltar and calabrian arcs

intermediate and deep earthquakes in spain recent improvements in the seismological networks on the ibero maghrebian region have permitted estimation of hypocentral location and focal mechanisms for earthquakes which occurred at south spain alboran sea and northern morocco of deep and intermediate depth with magnitudes between 3 5 and 4 5 intermediate depth shocks range from 60 to 100 km with greater concentration located between granada and malaga fault plane solutions of 5 intermediate shocks have been determined they present a vertical plane in ne sw or e w direction seismic moments of about 1015 nm and dimensions of about 1 km have been determined from digital records of spanish stations p wave forms are complex this may be explained by the crustal structure near the station discontinuities in the upper mantle and inhomogeneities near the source deep activity at about 650 km has only 3 shocks since 1954 1954 1973 1990 shocks are located at a very small region fault plane solutions show a consistent direction of the pressure axis dipping 45 in e direction for the 1990 shock seismic moment is 1016 nm and dimensions 2 6 km thep waves are of simpler form with a single pulse the intermediate and deep activities are not connected and no activity has been detected between 100 and 650 km the intermediate shocks may be explained in terms of a recent subduction from africa under iberia in se direction the very deep activity must be related to a sunk detached block of lithospheric material still sufficiently cold and rigid to generate earthquakes

recent large fold nucleation in the upper crust insight from gravity magnetic magnetotelluric and seismicity data sierra de los filabres sierra de las estancias internal zones betic cordillera abstract rheological heterogeneities in the upper crust have a close relationship with the fold position where rigid bodies could constitute initial perturbations that allow the nucleation of folds consequently establish the position and geometry of anomalous rocks located in the upper crust by geophysical studies help to understand the folded structure observed on surface new geological observations in the field along with gravity magnetic magnetotelluric and seismicity data reveal the subsurface structure in the sierra de los filabres sierra de las estancias folded region part of the alpine belt in southern spain the geometry of the upper crust is determined by geological field data 2d gravity models 2d magnetic models and 2d mt resistivity model while seismicity evidences the location of the deep active structures these results allow us to propose that a basic rock body at 4 to 9 km depth has determined the nucleation and development of the sierra de los filabres kilometric antiform n vergent large late folds are subjected to a variable present day stress field earthquake focal mechanisms suggest the presence in depth of a regional nw se compressive stress field however most of the seismogenetic structures do not extend up to the surface where nw se and wnw ese outcropping active normal faults are observed thus indicating a ne sw extension in the upper crust simultaneous to orthogonal nw se compression related to reverse faults and minor folds developed in the eastern almanzora corridor and in the nearby huercal overa basin the recent and active tectonic studies of cordilleras hinterland subjected to late folding greatly benefits from the integration of surface observations together with geophysical data

the inorganic geochemistry of cretaceous black shales dsdp leg 41 in comparison to modern upwelling sediments from the gulf of california

moment tensor inversion for iberia maghreb earthquakes 2005 2008 abstract we present and discuss a set of 77 moment tensor solutions for earthquakes in the iberia maghreb region from mid 2005 to the end of 2008 with moment magnitudes ranging from 3 2 to 6 0 inversion is based upon full three component intermediate period waveforms recorded at regional seismic broadband stations following the recent densification of permanent broadband networks and large scale temporary deployments at present more than 150 stations are recording in spain portugal and morocco this unprecedented station density allows analysis of small events from available short distance recordings and in general leads to more reliable source estimates due to data redundancies that permit elimination of waveforms affected by noise or complicated propagation effects the solutions for 2005 2008 constitute an important upgrade of the iberia maghreb moment tensor inventory to 225 solutions to date enhancing the image of seismotectonics at the compressive n algerian margin in the betic alboran shear zone and at the transpressive sw iberian margin as well as providing valuable constraints on seismic deformation in the western betics and the iberian foreland where little information has been previously available new solutions for the foreland and three recent seismic series in the western betics show strike slip and reverse faulting style contrasting with the dominance of normal faulting in the adjacent areas towards east in these areas as well as at the sw iberian margin faulting orientations are heterogeneous including solutions with opposite kinematics this indicates control by local stress conditions and points to fault interaction along the n algerian margin a counterclockwise rotation of slip vectors of thrust events from east to west becomes apparent several solutions for the area offshore cape st vincent are located at sub moho depths between 40 and 60 km supporting a large brittle layer thickness in the oceanic lithosphere

simulations of strong ground motion in sw iberia for the 1969 february 28 ms 8 0 and the 1755 november 1 m 8 5 earthquakes i velocity model summary this is the first paper of a series of two concerning strong ground motion in sw iberia due to earthquakes originating from the adjacent atlantic area the aim of this paper is to build and calibrate a velocity model that will be used in the companion paper for seismic intensity modelling of the 1969 m s 8 0 and 1755 m 8 5 8 7 earthquakes taking into account the geological evolution of the region since the palaeozoic we build a 3 d velocity model down to the moho discontinuity substantially different from a simple 1 d layered model the velocity model presented in this paper is built a priori using information originating from a variety of geological and geophysical studies its resolution is sufficient to simulate realistically seismic wave propagation in the low frequency f 0 5 hz range which is the most significant for the study of the destructive effects of large earthquakes at a regional scale to validate the model we compute synthetic seismograms for three recent earthquakes of moderate magnitudes 4 6 m w 5 3 located offshore in the most seismically active area in the region synthetics are generated using a wave propagation code based on the finite difference method which was chosen for its simplicity and accuracy in the frequency range considered in this study 0 1 0 5 hz we compare simulated waveforms with threecomponent seismograms for 9 different stations traveltimes of the direct p waves and the amplitude of ground motion are accurately reproduced at all stations the frequency content of the seismograms fits the observations especially for the lowest frequencies investigated 0 1 0 3 hz for each earthquake the estimated seismic moment is in good agreement with values obtained by other authors using different methods we conclude that the velocity model provides encouraging results for the computation of low frequency seismograms in the region and can be used for the study of larger earthquakes for which the radiated wavefield has a predominant low frequency spectrum

the m w 5 0 hammam melouane earthquake north central algeria of 17 july 2013 in the context of the tellian atlas seismicity on 17 july 2013 03 00 gmt a new moderate earthquake of magnitude 5 0 happened in the tell belts of northern algeria more precisely near the village of hammam melouane algeria 30 km south of algiers the capital of algeria the main shock parameters and aftershocks activity analysis reveal that the earthquake occurred on a 5 km long dextral strike slip fault oriented n114 e a conjugate strike slip fault of the major ne sw reverse fault system of the neogene mitidja basin this event caused damage to houses and social infrastructures but no fatalities were reported onland the earthquake triggered rock falls and minor landslides along the hammam melouane river the occurrence of the hammam melouane in the northern limit of the tell belts is representative of the african eurasiatic interplate seismicity of northern algeria where major seismic events could occurred as the previous boumerdes event of may 21st 2003 m w 6 8

lithospheric structure beneath the alboran basin results from 3d gravity modeling and tectonic relevance a three dimensional gravity modeling combined with integrated heat flow and elevation modeling is conducted to map out the crustal and lithospheric mantle thickness in the alboran basin in the westernmost mediterranean a sediment corrected bouguer anomaly has been derived using a depth to the basement map and densities determined from well logs and seismic data the gravity effect of the base of the lithosphere has been removed from the sediment corrected bouguer anomaly to obtain a crustal bouguer anomaly which has been inverted for crustal thickness the resulting lithospheric structure is further constrained by elevation data under the assumption of local isostasy the low residual elevation anomalies obtained 100 m in average suggest that the area is in local isostasy particularly the medium and long wavelength topography features variations in crustal thickness range from 36 km underneath the betic and rif chains to 12 km beneath the easternmost part of the alboran sea basin in the transition to the south balearic basin in western alboran the moho lies at a rather constant depth of 18 km deepening sharply toward the gibraltar strait down to 30 32 km the base of the lithosphere shallows from 140 km depth in the gibraltar strait to 45 km depth in the easternmost alboran sea lithospheric thinning penetrates to the southeastern side of the iberian margin crosscutting topographic highs of the central and eastern betic chain our results favor mantle delamination produced by detachment and subsequent peeling away of the lithospheric mantle rather than convective removal of the lithospheric mantle either by orogenic collapse or detachment and sinking of a lithospheric slab

p wave tomographic images in the central betics alboran sea south spain using local earthquakes contribution for a continental collision to investigate the relationship between shallow and intermediate depth earthquakes and the crust and upper mantle structure beneath the betic cordillera and alboran sea region we have applied seismic tomography to 2569 p wave arrival times from 367 microearthquakes recorded by both permanent and temporary seismic stations deployed in the region these earthquakes occurred in the depth range of 0 to 110 km beneath the central betic cordilleras and alboran sea our results have revealed significant structural heterogeneities in the crust and upper mantle beneath the study area in the upper crust there is a high velocity anomaly at sierra gorda western boundary of the granada basin penetrating to 15 km depth which is in good agreement with the aeromagnetic anomaly in the granada basin a low velocity anomaly is located in the middle crust which coincides with a previously detected greater cutoff depth of seismicity and are considered to be associated with a highly fractured zone generated by an intracrustal detachment the northern boundary of the alboran sea malaga coast is well imaged as low velocities from 50 to 90 km depths this low velocity zone in the upper mantle is associated with the intermediate depth seismicity which outline a section of continental crust related to the collision subduction beneath the northern part of the alboran sea southern part of the central betics

seismotectonics of portugal and its adjacent atlantic area abstract a study of focal mechanisms of earthquakes and stress indicators are presented for portugal and its adjacent atlantic margins recently riberio et al 1996 published a work on this subject in this study we introduce new focal mechanisms of nine earthquakes we use these results together with 12 other focal mechanisms and the main tectonic features in the region to define more accurately the type of mechanism and the stress pattern of the region all the focal mechanisms used in this study differ partially but are compatible with the regional stress field the stress indicators resulting from focal mechanisms and other geological and geophysical data show that the portugal continental and its atlantic margins are under horizontal pressure in nnw sse direction with a greater proportion of strike slip and reverse oblique mechanisms for the whole area

holocene earthquake record offshore portugal sw iberia testing turbidite paleoseismology in a slow convergence margin the sw margin of the iberian peninsula hosts the present day boundary between the eurasian and african plates convergence 4 5 mm yr is accommodated through a wide deformation zone characterized by moderate magnitude seismic activity this zone has also been the source of the most important seismic events in western europe such as the 1755 lisbon earthquake and tsunami and 1969 horseshoe earthquake despite efforts to identify active seismogenic structures in the gulf of cadiz in the last ten years little is known about its paleoseismic history the turbidite paleoseismology approach was applied for the first time in a low rate convergent margin to determine the recurrence interval of large earthquake events that occurred in sw iberia during the holocene four sediment cores collected at strategically located sites offshore portugal i e tagus abyssal plain infante don henrique basin and horseshoe abyssal plain reveal that these deep sea basins preserve a record of episodic deposition of turbidites in the sw iberian margin excluding special climatic events earthquakes are the most likely triggering mechanism for synchronous widely spaced distributed turbidites during the holocene when the sea level was relatively stable age correlation together with textural mineralogical physical properties and geochemical signatures of the new cores complemented by pre existing multicores and gravity cores reveals a total of 7 widespread turbidite events for the holocene precise dating of the most recent turbidite event e1 based on

laboratory drilling under martian conditions yields unexpected results 1 current plans to drill boreholes in the surface of mars suppose that diamond drill bits will be used on drilling equipment developing drilling power of 100 w or less such drilling produces very fine cuttings at martian ambient pressure it has been shown that quite small gas flows are capable of clearing these cuttings from the hole for example the release of 1 l of gas compressed to 50 torr is capable of removing 25 g of cuttings from a borehole 50 mm in diameter and at least 250 mm deep generating such volumes of gas by compressing the martian atmosphere would not be difficult alternatively the required volume of gas could be provided by the sublimation of ice trapped in the pore spaces of soil or rock in the martian surface once heated by the friction of the drill bit the ice transforms into vapor and blows the cuttings out of the hole since the cuttings are in effect freeze dried they do not choke the drill bit or hole with the result that the drilling efficiency is much greater than under terrestrial pressures and temperatures

goringe alboran tell tectonic zone a transpression system along the africa eurasia plate boundary neotectonic structures distributed from the goringe bank to the tell atlas mountains show that the africa eurasia plate boundary in the western mediterranean corresponds to an east west trending deforming zone goringe alboran tell main pliocene and quaternary tectonic structures of the northern atlas mountains are northeast southwest striking fault related folds similar to that of el asnam and are related to north south to northwest southeast compressional movements active tectonics in agreement with the main seismicity distribution and focal mechanisms also support an oblique plate convergence and the existence of a 50 100 km wide transpression zone from goringe across alboran to the tell atlas mountains a kinematic model shows the interaction between dextral transcurrent faults and left lateral faults with block rotations and no lateral extension pinned model shortening and lateral movement rates during the quaternary are estimated to be 1 0 2 3 mm yr and block rotation rate is estimated as 2 5 3 9 m y the plate boundary may correspond to a transpression zone active thrust faults being controlled by deep seated dextral transcurrent faults

seismic sources on the iberia african plate boundary and their tectonic implications the plate boundary between iberia and africa has been studied using data on seismicity and focal mechanisms the region has been divided into three areas a the gulf of cadiz b the betics alboran sea and northern morocco and c algeria seismicity shows a complex behavior large shallow earthquakes h 30 km occur in areas a and c and moderate shocks in area b intermediate depth activity 30 h 150 km is located in area b the depth earthquakes h 650 km are located to the south of granada moment rate slip velocity andhvalues have been estimated for shallow shocks and show similar characteristics for the gulf of cadiz and algeria and quite different ones for the central region focal mechanisms of 80 selected shallow earthquakes 8 mb 4 show thrust faulting in the gulf of cadiz and algeria with horizontal nnw sse compression and normal faulting in the alboran sea with e w extension focal mechanisms of 26 intermediate depth earthquakes in the alboran sea display vertical motions with a predominant plane trending e w solutions for very deep shocks correspond to vertical dip slip along n s trends frohlich diagrams and seismic moment tensors show different behavior in the gulf of cadiz betic alboran sea and northern morocco and northern algeria for shallow events the stress pattern of intermediate depth and very deep earthquakes has different directions vertical extension in the nw se direction for intermediate depth earthquakes and tension and pressure axes dipping about 45 o for very deep earthquakes regional stress pattern may result from the collision between the african plate and iberia with extension and subduction of lithospheric material in the alboran sea at intermediate depth the very deep seismicity may be correlated with older subduction processes

postseismic deformation at el asnam algeria in the seismotectonic context of northwestern algeria summary we use a combination of seismicity tectonic features focal mechanisms seismic strain and postseismic movement to study the western part of north algeria the el asnam region and its surrounding area in particular a seismotectonic map of this part of algeria delimited by the mediterranean sea in the north and the tellian mountains in the south was built from available geological and seismological data an examination of this map shows that the most significant earthquakes are concentrated along tectonic features and quaternary basins elongated in an east west direction suggesting nnw sse compressional movements during the large el asnam earthquake of 1980 october 10 m 7 1 vertical movement was measured along a 40 km northeastsouthwest thrust fault these movements were determined geodetically in 198 1 with reference to a basic network previously measured in 1976 in order to control postseismic movement and to ensure the monitoring of the seismic area a dense geodetic network has been regularly measured since 1986 both in planemetry and altimetry the results of the altimetric remeasurements show significant vertical movements the elevation changes of the benchmarks have been deduced from precise levelling measurements a remarkable uplift 5 1 5 1 9 mm yr of the northwestern block during the 1986 91 period has been observed whereas the southeastern block is seen to be relatively stable the sar el maiirouf anticline situated along the central segment of the el asnam surface breaks appears to be growing with a maximum postseismic slip rate of 9 6 1 4 mm yr i the mean uplift rates computed for the northwestern block support the view that the 1954 earthquake did not occur on the same reverse fault as the 1980 event

multifractal images of the seismicity in the ibero maghrebian region westernmost boundary between the eurasian and african plates abstract the earthquake occurrence has a scale invariant behavior that can be analyzed by means of a set of non integer dimensions the capacity dimension is related to the number of spatially distributed earthquakes that is to what extent the data space is full while the dimensions of entropy and correlation are related to the mode in which the data fill the space i e how data are ordered and how data are clustered respectively the behavior of the multifractal spectrum is asymptotic at the ends of its variation range the difference between the extreme values of the spectrum called multifractal spectrum slope is used to investigate how the earthquakes and its energy are spatially distributed in this paper we explain the fractal geometry of the seismicity in the ibero maghrebian region which is located in the westernmost end of the contact between the eurasian and african plates this region presents an unevenly spatially distributed seismic activity with areas of strong earthquakes beside others where the seismicity is weaker the present day stress field the fault systems and the characteristic seismicity of the zone make the contact between the eurasian and african plates an open problem to address this issue we have mapped the spatial variation of the fractal dimensions of capacity entropy correlation and the multifractal spectrum slope which are calculated from positions and energies of earthquakes with focal depth between 0 and 120 km the multifractal approach allows shedding light on the filling ordination and clustering of the spatially distributed earthquakes and the released energy the existence of lithospheric faults in response to the strong interaction between plate edges seems to be the cause of the observed shallow and intermediate seismicity and the rupture of the plate boundary in the betic rif alboran area

evidence of bias in estimations of earthquake size magnitudes of earthquakes determined using traditional methods show systematic deviations dependent on tectonic setting from accurate estimates of earthquake size magnitudes are overestimated for most of the continental earthquakes underestimated for mid oceanic ridges and differences of varying sign are obtained for subduction zones this is important in evaluating the seismic risk or consideration of effects such as the seismic versus aseismic strain release as seismic moments determined from magnitudes can be wrong by as much as a factor of four

probabilistic tsunami hazard in the northeast atlantic from near and far field tectonic sources in this article we present the first study on probabilistic tsunami hazard assessment for the northeast ne atlantic region related to earthquake sources the methodology combines the probabilistic seismic hazard assessment tsunami numerical modeling and statistical approaches we consider three main tsunamigenic areas namely the southwest iberian margin the gloria and the caribbean for each tsunamigenic zone we derive the annual recurrence rate for each magnitude range from mw 8 0 up to mw 9 0 with a regular interval using the bayesian method which incorporates seismic information from historical and instrumental catalogs a numerical code solving the shallow water equations is employed to simulate the tsunami propagation and compute near shore wave heights the probability of exceeding a specific tsunami hazard level during a given time period is calculated using the poisson distribution the results are presented in terms of the probability of exceedance of a given tsunami amplitude for 100 and 500 year return periods the hazard level varies along the ne atlantic coast being maximum along the northern segment of the morocco atlantic coast the southern portuguese coast and the spanish coast of the gulf of cadiz we find that the probability that a maximum wave height exceeds 1 m somewhere in the ne atlantic region reaches 60 and 100 for 100 and 500 year return periods respectively these probability values decrease respectively to about 15 and 50 when considering the exceedance threshold of 5 m for the same return periods of 100 and 500 years

morphotectonics of the gorringe bank summit eastern atlantic ocean based on high resolution multibeam bathymetry abstract high resolution swath bathymetry of the gorringe bank located along the europe africa obliquely convergent plate boundary offshore sw portugal allowed investigation of its shallow depth morphotectonic structure as a contribution to understanding the interplay of sea level changes and active deformation of the region dominant ene wsw to nne wsw and subordinate nw se trending morphologic alignments were mapped on the digital terrain model dtm built from multibeam data for both the gettysburg and ormonde summits of the bank based on appraisal of regional structural and seismological data the dominant and subordinate sets are interpreted to reflect dip slip to left oblique reverse faults and normal faults or dyke like joints respectively several terrace remnants were mapped on the dtm and were grouped into five orders at depths ranging from 40 to 120 m morphological features suggest that the terraces were formed in a coastal environment likely during middle late pleistocene sea level changes the terraces are probably polycyclic implying minor vertical tectonic motion however the whole terrace set except the deeper and younger one which was mainly shaped during the lgm lowstand is consistently up to 10 m lower at ormonde in the east relative to gettysburg in the west suggesting displacement across a nne ssw striking fault mapped in the saddle between the two seamounts the structure assemblage is argued to represent the shallow splay system of a crustal scale fault ramp underlying the bank the ene wsw reverse faults have a southward polarity and together with the overall northwest tilt of the bank point to displacement toward the horseshoe abyssal plain to the south at least at upper crustal levels

imaging active faulting in a region of distributed deformation from the joint clustering of focal mechanisms and hypocentres application to the azores western mediterranean region abstract the matching between linear trends of hypocentres and fault planes indicated by focal mechanisms fms is frequently used to infer the location and geometry of active faults this practice works well in regions of fast lithospheric deformation where earthquake patterns are clear and major structures accommodate the bulk of deformation but typically fails in regions of slow and distributed deformation we present a new joint fm and hypocentre cluster algorithm that is able to detect systematically the consistency between hypocentre lineations and fms even in regions of distributed deformation we apply the method to the azores western mediterranean region with particular emphasis on western iberia the analysis relies on a compilation of hypocentres and fms taken from regional and global earthquake catalogues academic theses and technical reports complemented by new fms for western iberia the joint clustering algorithm images both well known and new seismo tectonic features the azores triple junction is characterised by fms with vertical pressure p axes in good agreement with the divergent setting and the iberian domain is characterised by nw se oriented p axes indicating a response of the lithosphere to the ongoing oblique convergence between nubia and eurasia several earthquakes remain unclustered in the western mediterranean domain which may indicate a response to local stresses the major regions of consistent faulting that we identify are the mid atlantic ridge the terceira rift the trans alboran shear zone and the north coast of algeria in addition other smaller earthquake clusters present a good match between epicentre lineations and fm fault planes these clusters may signal single active faults or wide zones of distributed but consistent faulting mainland portugal is dominated by strike slip earthquakes with fault planes coincident with the predominant nne ssw and wnw ese oriented earthquake lineations clusters offshore sw iberia are predominantly strike slip or reverse confirming previous suggestions of slip partitioning

discussion of origins of hinterland basins to the rif betic cordillera and carpathians abstract the hinterland basins of the rif betic cordillera western alboran sea and the carpathians pannonian basin are in part composed of a thick in excess of 3 4 km thermal sag basin sequence the underlying crust has been thinned to 25 km in parts of the pannonian basin and to 15 km in parts of the alboran sea modern tectonic models for these areas envision tectonic collision and thickening of the crust followed by crustal thinning either by gravitational collapse back arc extension or a combination of the two contemporaneous with thrusting basin and range type extension has been envisioned for parts of these extensional collapse systems extensional features are common and they interact in a complex way with strike slip systems flexural cantilever modelling agrees with earlier mckenzie type pure shear modelling of the extensional systems in suggesting that extension alone cannot generate sufficient thermal decay to explain the great thickness of the sag basins associated with the alboran sea and pannonian basin consequently it is suggested that uplift of the asthenosphere accompanying subduction roll back is an important factor in the evolution of these basins roll back of the mantle lithosphere permits hot asthenospheric mantle to upwell and lie close to the base of the crust initially uplift and erosion of the crust overlying the asthenosphere occurs as the thermal perturbation cools the crust thermally subsides to produce a large sag basin

active transfer fault zone linking a segmented extensional system betics southern spain insight into heterogeneous extension driven by edge delamination pliocene and quaternary tectonic structures mainly consisting of segmented northwest southeast normal faults and associated seismicity in the central betics do not agree with the transpressive tectonic nature of the africa eurasia plate boundary in the ibero maghrebian region active extensional deformation here is heterogeneous individual segmented normal faults being linked by relay ramps and transfer faults including oblique slip and both dextral and sinistral strike slip faults normal faults extend the hanging wall of an extensional detachment that is the active segment of a complex system of successive wsw directed extensional detachments which have thinned the betic upper crust since middle miocene two areas which are connected by an active 40 km long dextral strike slip transfer fault zone concentrate present day extension both the seismicity distribution and focal mechanisms agree with the position and regime of the observed faults the activity of the transfer zone during middle miocene to present implies a mode of extension which must have remained substantially the same over the entire period thus the mechanisms driving extension should still be operating both the westward migration of the extensional loci and the high asymmetry of the extensional systems can be related to edge delamination below the south iberian margin coupled with roll back under the alboran sea involving the asymmetric westward inflow of asthenospheric material under the margins

seismic hazard in terms of spectral accelerations and uniform hazard spectra in northern algeria seismic hazard in terms of spectral acceleration sa has been estimated for the first time in northern algeria for this purpose we have used the spatially smoothed seismicity approach the present paper is intended to be a continuation of previous work in which we have evaluated the seismic hazard in terms of peak ground acceleration pga using the same methodology to perform these evaluations four complete and poissonian seismic models have been used one of them considers earthquakes with magnitudes above ms 6 5 in the last 300 years that is the most energetic seismicity in the region firstly seismic hazard maps in terms of sa at periods of 0 1 0 2 0 3 0 4 0 5 1 0 1 5 and 2 0 sec with 39 3 and 10 probability of exceedance in 50 years have been obtained therefore uniform hazard spectra uhs are computed and examined in detail for twelve of the most industrial and populated cities in northern algeria all the reported results in this study are for rock soil and 5 of damping it is noteworthy that in the seismic hazard maps as well as in the uhs plots we observe maximum sa values in the central area of the tell the higher values are reached in the chleff region previously el asnam specifically around the location of the destructive earthquakes of september 9 1954 ms 6 8 and october 10 1980 ms 7 3 these maximum values 0 4 g and 1 0 g are associated with periods of about 0 2 and 0 3 sec for return periods of 100 and 475 years respectively

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

spatial variation of present day stress field and tectonic regime in tunisia and surroundings from formal inversion of focal mechanisms geodynamic implications for central mediterranean we compiled 123 focal mechanisms from various sources for tunisia and adjacent regions up to sicily to image the current stress field in the maghrebides chain from tunisia to sicily and its foreland stress inversion of all the available data provides a first order stress field with a n150 e horizontal compression shmax and a transpressional tectonic regime but the obtained stress tensor poorly fit to the data set we separated them into regional subsets boxes in function of their geographical proximity kinematic regime homogeneity of kinematic orientations and tectonic setting their respective inversion evidences second and third order spatial variations in tectonic regime and horizontal stress directions the stress field gradually changes from compression in the maghrebides thrust belt to transpression and strike slip in the atlassic and pelagian foreland respectively where preexisting nw se to e w deep faults system are reactivated this spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data the major slab transfer edge propagator faults i e north south axis hammamet relay and malte escarpment which laterally delimit the subducting slabs play an active role in second and third order lateral variations of the tectonic regime and stress field orientations over the tunisian sicilian domain the past and current tectonic deformations and kinematics of the central mediterranean are subordinately guided by the plate convergence i e africa eurasia controlled or influenced by lateral slab migration segmentation and by deep dynamics such as lithosphere mantle interaction

apparently deep events in the middle atlas resolved to be shallow implications for lithospheric deformation abstract the occurrence of intermediate depth seismicity in intracontinental settings is rare but it has been postulated with various degrees of certainty in several regions one such region is the middle atlas of morocco since 1960 75 intermediate depth earthquakes have been reported in this region by spain s national geographic institute ign the apparent deep nature of these events is hard to reconcile with well established geophysical evidence of a thin lithosphere under the middle atlas but has been associated with mantle delamination processes we relocate 4 events with ign reported depths 80 km that were recorded by a relatively dense temporary deployment using a recent regional 3d velocity model obtained through teleseismic body and surface wave tomography the relocation procedure uses a grid search approach to minimize the mean normalized misfit where each travel time misfit is normalized by the estimated pick uncertainty we find that our observed arrivals are much better fit by shallow 80 km we propose that these shallow foci earthquakes are the result of regional crustal deformation of this region caused by the present convergence between africa and eurasian plate we infer that if there are any ongoing delamination processes in the area they are aseismic this study is an example of how local earthquake locations in tectonically complex areas can be significantly improved by using a dense local seismic array and a well constrained 3 d velocity model

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

tearing of the mantle lithosphere along the intermediate depth seismicity zone beneath the gibraltar arc the onset of lithospheric delamination the intermediate depth seismicity ids beneath the gibraltar arc is enigmatic so far there is no general consensus on its relationship with the ongoing tectonic processes we analyzed s wave receiver functions srfs with data recorded by a dense n s seismic profile deployed across the sierra nevada in southern spain srf piercing points at depths of the lithosphere asthenosphere boundary lab sample an area of the ids zone providing an ideal opportunity to study the lithospheric structure at the ids zone we observe an abrupt change in the lab depth along a profile from north to south across the northern branch of the ids the lab depth changes from 90 to 100 km north of the ids to 130 km south of it we propose that the ids marks a tear in the iberian mantle lithosphere along its entire length implying an ongoing lithospheric delamination process that produces the seismicity at its onset

active continental subduction beneath the betic cordillera and the alboran sea p and s wave seismic tomography detect a low velocity anomaly in the upper mantle beneath the betic cordillera and the alboran sea region the anomaly is associated with the intermediate depth seismicity h

seismotectonics of the ibero maghrebian region abstract a study of the seismotectonics of the ibero maghrebian region is presented as deduced from main geological features seismicity and focal mechanism data the hypocentral distribution of shallow intermediate depth and deep earthquakes is analyzed the direction of the stress distribution is inferred from the focal mechanism of 24 selected events a seismotectonic framework summarizing these results together with the main geological features shows that a nw se general direction of horizontal compressive stresses is present in the region with a localized zone of horizontal tensions in the betics and the alboran sea the presence of intermediate depth and deep earthquakes is tentatively explained as caused by two consecutive processes of subduction

kinematics of the iberia maghreb plate contact from seismic moment tensors and gps observations the iberian peninsula and the maghreb experience moderate earthquake activity and oblique nw se convergence between africa and eurasia at a rate of 5 mm yr coeval extension in the alboran basin and a n35 e trending band of active left lateral shear deformation in the alboran betic region are not straightforward to understand in the context of regional shortening and evidence complexity of deformation at the plate contact we estimate 86 seismic moment tensors mw 3 3 to 6 9 from time domain inversion of near regional waveforms in an intermediate period band those and previous moment tensors are used to describe regional faulting style and calculate average stress tensors the solutions associated to the trans alboran shear zone show predominantly strike slip faulting and indicate a clockwise rotation of the largest principal stress orientation compared to the regional convergence direction 1 at n350 e at the n algerian and sw iberian margins reverse faulting solutions dominate corresponding to n350 e and n310 e compression respectively over most of the betic range and intraplate iberia we observe predominately normal faulting and wsw ene extension 3 at n240 e from gps observations we estimate that more than 3 mm yr of african nubian eurasian plate convergence are currently accommodated at the n algerian margin 2 mm yr in the moroccan atlas and 2 mm yr at the sw iberian margin 2 mm yr is a reasonable estimate for convergence within the alboran region while alboran extension can be quantified as 2 5 mm yr along the stretching direction n240 e superposition of both motions explains the observed left lateral transtensional regime in the trans alboran shear zone two potential driving mechanisms of differential motion of the alboran betic gibraltar domain may coexist in the region a secondary stress source other than plate convergence related to regional scale dynamic processes in the upper mantle of the alboran region as well as drag from the continental scale motion of the nubian plate along the southern limit of the region in the atlantic ocean the 3 5 mm yr westward motion of the gibraltar arc relative to intraplate iberia can be accommodated at the transpressive sw iberian margin while available gps observations do not support an active subduction process in this area

three dimensional s velocity of the mantle in the africa eurasia plate boundary region from phase arrival times and regional waveforms 1 a new model of the three dimensional shear velocity structure of the africa eurasia plate boundary is presented the new model is derived by jointly inverting different types of seismic data the two main sources of information are regional waveforms and teleseismic s wave arrival times we show that it is possible to find a model that fit the different data types nearly as well as when inverting solely one type of data the main improvement in resolving power is achieved between depths of 300 and 700 km though the improvements are not limited to this depth range our model reflects the complicated evolution of this plate boundary area the transition zone is dominated by high velocity anomalies which we infer to represent a mix of lithosphere that subducted relatively recently or is not sufficiently cold and dense to traverse the 660 km discontinuity the only low velocity zone in the transition zone is beneath the ionian sea the high velocity hellenic slab is continuous throughout the upper mantle and into the lower mantle to about 1200 km most likely representing subducted neo tethys lithosphere the uppermost mantle is dominated by low velocities consistent with the high level of tectonic activity low velocity regions are relatively strong beneath the mid atlantic ridge turkey and the dead sea region the region s current lithosphere is relatively thin except beneath the adriatic and ionian seas and the easternmost atlantic ocean

far field tsunami simulations of the 1755 lisbon earthquake implications for tsunami hazard to the u s east coast and the caribbean article i nfo the great lisbon earthquake of november 1st 1755 with an estimated moment magnitude of 8 5 9 0 was the most destructive earthquake in european history the associated tsunami run up was reported to have reached 5 15 m along the portuguese and moroccan coasts and the run up was significant at the azores and madeira island run up reports from a trans oceanic tsunami were documented in the caribbean brazil and newfoundland canada no reports were documented along the u s east coast many attempts have been made to characterize the 1755 lisbon earthquake source using geophysical surveys and modeling the near field earthquake intensity and tsunami effects studying far field effects as presented in this paper is advantageous in establishing constraints on source location and strike orientation because trans oceanic tsunamis are less influenced by near source bathymetry and are unaffected by triggered submarine landslides at the source source location fault orientation and bathymetry are the main elements governing transatlantic tsunami propagation to sites along the u s east coast much more than distance from the source and continental shelf width results of our far and near field tsunami simulations based on relative amplitude comparison limit the earthquake source area to a region located south of the gorringe bank in the center of the horseshoe plain this is in contrast with previously suggested sources such as marques de pombal fault and gulf of cadiz fault which are farther east of the horseshoe plain the earthquake was likely to be a thrust event on a fault striking 345 and dipping to the ene as opposed to the suggested earthquake source of the gorringe bank fault which trends ne sw gorringe bank the madeira tore rise mtr and the azores appear to have acted as topographic scatterers for tsunami energy shielding most of the u s east coast from the 1755 lisbon tsunami additional simulations to assess tsunami hazard to the u s east coast from possible future earthquakes along the azores iberia plate boundary indicate that sources west of the mtr and in the gulf of cadiz may affect the southeastern coast of the u s the azores iberia plate boundary west of the mtr is characterized by strike slip faults not thrusts but the gulf of cadiz may have thrust faults southern florida seems to be at risk from sources located east of mtr and south of the gorringe bank but it is mostly shielded by the bahamas higher resolution near shore bathymetry along the u s east coast and the caribbean as well as a detailed study of potential tsunami sources in the central west part of the horseshoe plain are necessary to verify our simulation results

moment magnitudes for early 1923 1961 instrumental iberian earthquakes a collection of 18 iberian earthquakes felt with epicentral intensity i 0 vi msk in the iberian peninsula during the period 1923 1961 just before the introduction of the wwssn stations in 1962 have been investigated through digital reconstruction of old seismograms recorded in four spanish seismological observatories alicante almeria ebro and toledo spectral analysis of the seismic waves recorded at the different stations has been performed and the seismic moment of the early instrumentally recorded earthquakes considered has been calculated according to the model of brune 1970 and applying corrections by instrumental response anelastic attenuation free surface and radiation pattern a seismic moment magnitude relation has been obtained and the result has been compared with other regressions obtained for different seismo active regions in spain and in the world the moment magnitudes of the earthquakes considered have been calculated according to the scale of kanamori 1977 and hanks and kanamori 1979 finally a magnitude correction for the conversion of surface wave magnitude to moment magnitude has been proposed m 0 96 m a t 0 36 this conversion should be considered valid for the 4 0 6 0 surface wave magnitude interval which spans well the characteristic range for the moderate seismic activity in the iberian peninsula

seismicity source mechanisms and tectonics of the azores gibraltar plate boundary abstract a study and partial revision of the seismicity and source mechanisms of earthquakes are presented for the oceanic plate boundary of eurasia and africa from the azores islands to the strait of gibraltar focal mechanisms of 36 earthquakes wave form modelling of 4 and seismic moments and dimensions of 28 have been calculated these results indicate that the boundary is divided into three sections with different characteristics the azores the central section and the east section the azores section has high seismicity of moderate magnitude and a low slip rate 0 76 cm yr the predominant mechanism is normal or transform faulting with horizontal tensions on average in a n25 e direction in the central section large earthquakes occur with strike slip right lateral motion along faults in an e w direction there is a high slip rate 3 39 cm yr the east section is of more complex nature large earthquakes also occur but the predominant mechanism is reverse faulting with a horizontal pressure axis in the n30 w direction resulting in underthrusting of africa from the slip vectors the pole of rotation for the african plate is located at 28 2 n 21 1 w nearer to the boundary than previous locations close to the continent there is a continuation in the ocean crust of some structural features of the iberian peninsula

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

comparing seismic parameters for different source zone models in the iberian peninsula abstract seismical parameters of five seismogenic zonings for the iberian peninsula have been determined in this work for that purpose this research has two key goals the first is to generate a seismic catalog the second to calculate the seismical parameters of all the zones of the seismogenic zonings selected the first key goal has been the creation of a catalog of earthquakes for the iberian peninsula and adjacent areas first the national geographic institute of spain s catalog has been completed and reviewed with the information from other catalog reviews and specific studies second all magnitude calculations have been homogenized third all dependent data have been eliminated through declustering finally the year of completeness for each magnitude has been considered the quaternary active faults database of iberia has also been used as input data all of this information has been integrated into a geographic information system the second key aim is the calculation of the seismical parameters the first parameter obtained has been the b value a method which considers different years of completeness in accordance with the magnitude has been used also the annual rate of earthquakes per square kilometer has been calculated moreover the maximum magnitude known that quaternary active faults might generate and maximum magnitude recorded in the catalog have been determined finally based solely on the statistical parameters obtained a critical discussion of the seismogenic zonings of the iberian peninsula has been conducted the results show that some zonings possess insufficient data for a proper calculation of the seismic parameters from a statistical point of view

seismic anisotropy of northeastern algeria from shear wave splitting analysis abstract there are few studies of internal deformation under northern africa here we present such a study we analyze teleseismic shear wave splitting for northeast algeria to improve our knowledge of lithospheric and asthenospheric deformation mechanisms in this region we study waveform data generated by tens of teleseismic events recorded at five recently installed broadband bb stations in algeria these stations cover an area 2 across extending from the tellian geological units in the north to the saharan atlas units in the south analysis of sks wave splitting results insignificant spatial variations in fast polarization orientation over a scale length of at most 100 km the seismic anisotropy shows three clear spatial patterns a general ene wsw orientation is observed under the stations in the north this polarization orientation follows the direction of the tell atlas mountain chain which is perpendicular to the convergence direction between africa and eurasia delay times vary significantly across the region between 0 6 and 2 0 s at several stations there is an indication of a wnw ese polarization orientation which is apparently related to a later geodynamic evolutionary phase in this region a third pattern of seismic anisotropy emerges in the south with an orientation of roughly n s we discuss these observations in light of geodynamic models and present day geodetic motion

seismological evidence for a delamination process in the lithosphere under the alboran sea summary the continental collision between the african and eurasian plates in the iberian peninsula is solved with a nw se compression with an extensional basin the alboran sea to explain this paradox several models have been proposed including the subduction process of a lithospheric plate in this study a relocation of the seismicity of the area using a jhd algorithm for the period 1950 1995 has been performed which shows a specific hypocentre pattern that is not compatible with plate subduction in addition the direction of the stresses acting in the area has been determined through a comprehensive study of all existing focal mechanisms together with calculations for 19 new earthquakes with sufficient data to determine the focal solution after considering all these data the absence of intermediate shocks in the central part of the alboran basin and the predominantly thrusting mechanisms at the borders of the basin with pressure axes perpendicular to the front we consider a delamination process as a possible mechanism acting in the area

probabilistic mapping of earthquake induced submarine landslide susceptibility in the south west iberian margin abstract the sw iberian continental margin is well recognized as a tectonically active area where major canyons and mass wasting events are both present earthquake triggered submarine landslides may cause tsunami and result in catastrophic damage to bordering coastal areas in this setting submarine landslide susceptibility mapping represents a major step towards a regional risk mitigation strategy landslide susceptibility mapping in large offshore areas presents significant challenges as a result of the limited information on controlling variables large uncertainties in triggering mechanisms and limited geotechnical data in this study a geotechnical model based approach has been followed that narrows the range of controlling factors and within a probabilistic framework allows a systematic treatment of parameter uncertainties this model based analysis covers the whole sw iberian margin increasing by three orders of magnitude the areal extent of precedent offshore slope stability susceptibility studies this jump in spatial scale is facilitated by application of a systematic bayesian updating procedure to combine geotechnical information from global databases and that available from regional sites seismic shaking is estimated using an available regional database of seismogenic faults these tools are implemented within a gis to generate via montecarlo simulations probabilistic landslide susceptibility maps based on two different analytical seismic infinite slope stability models these models differ mainly in the form of their final results either as distributions of slope stability safety factors or as distributions of seismic triggered slope displacements receiving operator curves are used to assess the different landslide susceptibility predictions obtained against a comprehensive regional database of submarine landslides it turns out that the models analyzed correctly predict 92 and 82 of the mapped landslide subset chosen for validation for pseudo static and displacement based method respectively this suggests that within the limits of the currently available databases seismic events are the dominant factor at the origin of the submarine landslides mapped in the study area an advantage of the framework presented is that it can quickly incorporate new regional geotechnical information or better regional landslide databases as they become available

seismicity and focal mechanisms in south spain abstract recent improvements in regional seismological networks allow a better definition of the seismicity and the determination of focal mechanisms in south spain this region is part of the lithospheric plate boundary between africa and eurasia and shows a continuous seismic activity of moderate magnitude m h h 650 km earthquakes also occurring in the region eight fault plane solutions have been determined that can be related to the tectonics of the area the solutions for the shallow shocks are compatible with regional stresses with horizontal compressions in nw se direction and tensions in e w direction that produce normal faulting along the n30 to 60 w and n10 to 30 e systems of faults the mechanisms of the intermediate depth shocks can be explained in terms of a subduction zone from africa in a nw direction that is under compression

waveform inversion of small to moderate earthquakes located offshore southwest iberia summary in this paper we apply the kinematic waveform inversion kiwi tools to the study of smallto moderate earthquakes in southwest sw iberia the earthquakes have magnitudes in the range ml 3 5 4 9 with the exception of one earthquake with magnitude ml 6 0 most events are located offshore are recorded with a large azimuthal gap and generate waves that travel throughastronglyheterogeneous crustalstructure weobtainnewestimatesofcentroid depth seismic moment strike dip and rake for 12 of the 29 studied events the earthquakes whose waveforms we cannot successfully model are 1 located too far from the stations 2 have small magnitude hence low signal to noise ratio or 3 are located within the cadiz basin which is a major sedimentary basin that affects wave propagation notably our results indicate that onshore earthquakes occur at shallow depths 15 km whereas offshore earthquakes occur deeper down to 46 km focal mechanisms indicate transpressive faulting

plio quaternary reactivation of the neogene margin off nw algiers algeria the khayr al din bank the algiers region northern algeria is known to be seismically active with recurrent large m 6 earthquakes because of the lack of high resolution bathymetry the offshore structures remained for a long time poorly known thanks to a new marine data base maradja 2003 cruise the offshore part of the margin is accurately mapped and new active and recent structures are described west of the bay of algiers the margin enlarges forming the khayr al din bank interpreted as a tilted block of the passive margin born during the opening of the algero provencal basin at the slope break a 80 km long fault tip quaternary fold namely the khayr al din fault extends at the foot of the margin off nw algiers and represents the largest active structure of the coastal area together with the sahel anticline we also map for the first time a set of overlapping en echelon active folds in the upper part of the khayr al din bank located off previously known active structures on land most of these faults represent actually a threat for the algiers region in terms of seismic hazard but also geological hazards such as tsunamis as most of them depicts significant dimensions and slip rates the highest long term horizontal shortening rate is found on the khayr al din fault and is estimated at 0 5 0 1 mm yr with a maximal magnitude of 7 3 which provides one of the highest seismogenic potential in the region a new tectonic framework for the algiers region is proposed in which the main south dipping offshore structure of opposite vergence relative to most thrusts on land appears to be nowadays the main driving fault system as also found further east in the boumerdes m 6 8 2003 rupture zone the overall apparent pop up structure of the recent and active faults may result from a progressive migration of the plate limit from the late miocene north dipping suture zone on land to the quaternary south dipping main khayr al din fault at sea suggesting a process of subduction inception

the 1980 1997 and 1998 azores earthquakes and some seismo tectonic implications abstract we have studied the focal mechanisms of the 1980 1997 and 1998 earthquakes in the azores region from body wave inversion of digital gdsn global digital seismograph network and broadband data for the 1980 and 1998 shocks we have obtained strike slip faulting with the rupture process made up of two sub events in both shocks with total scalar seismic moments of 1 9 1019 nm mw 6 8 and 1 4 1018 nm mw 6 0 respectively for the 1997 shock we have obtained a normal faulting mechanism with the rupture process made up of three sub events with a total scalar seismic moment of 7 7 1017 nm mw 5 9 a common characteristic of these three earthquakes was the shallow focal depth less than 10 km in agreement with the oceanic type crust from the directivity function of rayleigh lr waves we have identified the nw se plane as the rupture plane for the 1980 and 1998 earthquakes with the rupture propagating to the se slow rupture velocity about of 1 5 km s has been estimated from directivity function for the 1980 and 1998 earthquakes from spectral analysis and body wave inversion fault dimensions stress drop and average slip have been estimated focal mechanisms of the three earthquakes we have studied together with focal mechanisms obtained by other authors have been used in order to obtain a seismotectonic model for the azores region we have found different types of behaviour present along the region it can be divided into two zones zone i from 30 w to 27 w zone ii from 27 w to 23 w with a change in the seismicity and stress direction from zone i in zone i the total seismic moment tensor obtained corresponded to left lateral strike slip faulting with horizontal pressure and tension axes in the e w and n s directions respectively in zone ii the total seismic moment tensor corresponded to normal faulting with a horizontal tension axis trending ne sw normal to the terceira ridge the stress pattern for the whole region corresponds to horizontal extension with an average seismic slip rate of 4 4 mm yr

thin shell modeling of neotectonics in the azores gibraltar region we applied the thin shell neotectonic modeling method to study the neotectonics of the africa eurasia plate boundary in the azores gibraltar region the plate boundary consists of a simple fault system running from azores to the gorringe bank where it branches along the betics and rift tell thrust fronts major faults in west iberia and nw africa have also been incorporated results are compared with seismic strain rates fault slip rates and stress orientations the best estimate for the fault friction coefficient is 0 1 0 15 meaning that the plate boundary is only about 1 4 as strong as the adjacent lithosphere the largest fault slip rates 1 5 mm yr are obtained along the gloria fault strike slip and the betic transpressive and rif tell compressive thrust systems whereas tectonic activity in the atlas region is comparable to that obtained along the plate boundary the fault slip rates in the west iberia fault systems are one order of magnitude less