structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

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

active tectonics of the algerian atlas mountains evidence from aftershocks of the 1980 el asnam earthquake summary the el asnam algeria earthquake of 1980 october is the largest earthquake to have occurred in north africa since instrumental records began ms 7 3 it was caused by movement on a segmented reverse fault which is part of the fault zone that separates the chelif alluvial plains from the coastal range of the atlas mountains the coastal range is the actively deforming plate boundary between africa and eurasia in this paper the results of an aftershock study carried out using a 28 station portable network in the epicentral area in the 5 weeks after the main shock are presented a total of 4517 aftershocks have been located using both p and s phases of these 4517 events 1279 pass a set of quality criteria and are used to discuss the detailed tectonics of the aftershock zone the southwestern half of the aftershock zone has a relatively restricted band of seismicity running parallel to the main fault in cross section this seismicity is observed to lie almost exclusively in the footwall of the main fault and indicates both antithetic reverse faulting and extension parallel to the fault zone the only exception to this pattern occurs at a junction of the main fault segments where a distinct cluster of events with very variable focal mechanisms is located in the hangingwall this cluster may be equated with a barrier that impeded the rupture of the main shock beyond the southwest end of the main fault a mixture of strike slip and reverse faulting occurred and suggests a mechanism whereby this end of the fault can act as an asperity for earthquake generation aftershocks in the northeastern half of the study area indicate movement on a stack of listric reverse faults the focal mechanisms of these events show that the n dipping nodal planes assumed to be the fault planes flatten with depth we suggest that the faults sole into a low angle 20 decollement at about 8 10 km depth at the base of the aftershock zone we argue that the northeastern part of the 1980 aftershock zone is typical of the actively deforming coastal belt of northwest algeria subduction of the western mediterranean basin beneath the north african margin does not seem to occur instead the margin is absorbing the motion with old normal faults being reactivated as thrusts

slip distribution of the 2003 boumerdes zemmouri earthquake algeria from teleseismic gps and coastal uplift data 1 using a joint inversion of seismological waveforms and ground displacement observations we estimate several parameters of the fault geometry and rupture process of the mw 6 9 may 21 2003 boumerdes zemmouri earthquake the relocated epicenter is considered as a known parameter total rupture length rupture duration and maximum slip are 55 km from 3 4 e to 4 0 e 12 s and 3 m the modeled south dipping reverse fault oriented ene wsw outcrops a few km offshore which is consistent with the absence of observed surface rupture inland two shallow and relatively localized slip zones are found on both sides of the hypocenter to the sw between boumerdes and zemmouri slip is concentrated between 11 and 2 km depth to the ne between zemmouri and dellys slip is concentrated between 6 km depth and the sea floor various resolution tests indicate that our model is well constrained by the available data and help understanding which data constrains each parameter of the model

moment tensor solutions for small and moderate earthquakes in the ibero maghreb region 1 we applied time domain moment tensor inversion of local and regional waveforms to small and moderate mw 3 5 5 7 shallow earthquakes from the iberian peninsula northern morocco and northern algeria for the 6 years period from november 1995 to march 2002 and the previous network of autonomously recording seismograms nars experiment moment tensor solutions were obtained for 58 events considerably increasing the total number of available solutions in the study area for each event we performed a moment tensor inversion and a double couple grid search for simple faulting events the grid search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation the computed mechanisms show regional consistency a large part of the iberian peninsula is characterized by normal faulting mechanisms with sw ne oriented t axes thrusting and se nw compression is dominant in algeria in the alboran sea the westernmost part of the mediterranean and the transition between both regimes strike slip mechanisms dominate with approximately n s oriented p axes this pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations

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

seismotectonics in the tell atlas of algeria the cavaignac abou el hassan earthquake of 25 08 1922 ms 5 9 abstract we have studied the tenes abou el hassan taeh active fold and its relationships with the 1922 earthquake m 6 0 in terms of repeated coseismic deformations in compressional domains the abou el hassan village formerly cavaignac experienced a destructive but moderate sized earthquake which was registered in several seismic stations and generated surface breaks and rock falls located on the active fold recent field observations reveal the existence of a n060 striking fault scarp with a vertical displacement of 1 m affecting young alluvial terraces parallel to the fault the ne sw striking active fold with an asymmetrical shape and transport direction to the southeast displays on his southeastern flank a 23 km long reverse faulting with flexural slip a complex drainage pattern including the oued allalah river which predates the anticline marks the successive tectonic movements uplifted late quaternary terraces and yield an uplift rate of 0 5 mm yr 1 kinematic aspects of broken folds are illustrated showing that the taeh active fold conforms the fault bend folding model a seismic moment m o 1 36 10 25 dyn cm of the 1992 main shock which triggered aftershocks for more than one year is estimated from the geological parameters three segments are identified along strike indicating some evidence for the occurrence of possible large earthquakes in the past from the seismic hazard point of view the taeh fault segments could produce a larger earthquake magnitude m 6 0 as is derived from the coseismic faulting the total fault length and vertical displacement of young terraces such seismogenic structure is very comparable to the southern one at el asnam that produced the large 1980 earthquake m s 7 3

drainage diversions as evidence of propagating active faults example of the el asnam and thenia faults algeria digital elevation models and aerial photographs provide evidence of past drainage diversions associated with known and inferred active faults in northern algeria the el asnam anticline is a fault bend fold that is growing in response to displacement on the historically active el asnam fault the diversion of the fodda river and a sequence of uplifted palaeovalleys across the anticline formed in response to the active southwestward propagation of the sidi ada el ardja segment of the el asnam anticline deformation associated with the 1980 el asnam earthquake ms 7 3 and its effect on drainage demonstrate the occurrence of coseismic uplift of the el asnam anticline associated with slip on the underlying thrust fault similar geomorphic relations are observed between the isser river and the thenia fault diversions of the isser river and evidence for quaternary uplift indicate that the thenia fault which is close to algiers is tectonically active and should be considered to be a source of potentially damaging earthquakes

from extension to shortening tectonic inversion distributed in time and space in the alboran sea western mediterranean 2d seismic reflection data tied to biostratigraphical and log information from wells in the central and south eastern alboran sea have allowed us to constrain the spatial and temporal distribution of rifting and inversion normal faults tilted basement blocks and growth wedges reveal a thinned continental crust that formed in response to nw se extension to the east a secondary sw ne trend of extension affects the transitional crust adjacent to the oceanic algerian basin the maximum thickness of syn rift sediments is 3 5 km and the oldest recorded deposits are serravallian the wnw ese yusuf fault formed a buttress separating and accommodating variable extension between two different tectonic domains the thinned continental crust of alboran and the oceanic spreading of the algerian basin late tortonian to present day nw se africa eurasia plate convergence drove shortening and reactivation of some of the earlier extensional structures as reverse and strike slip faults forming complex compartmentalised sub basins tectonic inversion coexisted with the formation of new faults and folds inversion was partial along the habibas basin and al idrisi fault but complete along the alboran ridge where some sw ne trending faults were perpendicular to the recent nw se plate convergence and were reactivated as thrusts the wnw ese yusuf fault is oblique to the convergence vector and therefore reactivation is mainly expressed as transpressional deformation volcanic rocks intruded along the alboran ridge and yusuf faults during the latest stages of extension formed rheological anisotropies that localised the later inversion

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

compressional tectonic inversion of the algero balearic basin latemost miocene to present oblique convergence at the palomares margin western mediterranean interpretation of new multichannel seismic reflection profiles indicates that the palomares margin was formed by crustal scale extension and coeval magmatic accretion during middle to late miocene opening of the algero balearic basin the margin formed at the transition between thinned continental crust intruded by arc volcanism and back arc oceanic crust deformation produced during the later positive inversion of the margin offshore and onshore is partitioned between n50 e striking reverse faults and associated folds like the sierra cabrera and abubacer anticlines and n10 20 e sinistral strike slip faults like palomares and terreros faults parametric subbottom profiles and multibeam bathymetry offshore structural analysis available gps geodetic displacement data and earthquake focal mechanisms jointly indicate that tectonic inversion of the palomares margin is currently active the palomares margin shows a structural pattern comparable to the north maghrebian margins where africa eurasia plate convergence is accommodated by ne sw reverse faults nnw sse sinistral faults and wnw ese dextral ones contractive structures at this margin contribute to the general inversion of the western mediterranean since 7 ma coeval to inversion at the algerian margin shortening at the alboran ridge and al idrisi faults occurred later since 5 ma indicating a westward propagation of the compressional inversion of the western mediterranean

the southernmost margin of the tethys realm during the mesozoic and cenozoic initial geometry and timing of the inversion processes 1 along the northern border of africa pangea breakup has been diachronic during the jurassic the alpine tethys propagated northeastward from the atlantic to the alps during the permian the neo tethys propagated westward from oman to northwestern arabia then a secondary and late branch of neo tethys gave birth to the east mediterranean basin finally the two oceans connected at end of jurassic times achieving the development of africa northern plate boundary by the late cretaceous convergence between africa and eurasia led to the progressive closure of the tethys realm the continental collision is not completely achieved and the different segments of the confrontation zone maghreb central and east mediterranean zagros and oman expose different stages of the process however we emphasize the existence of synchronous geodynamic events from one end of the system to the other although they do not have the same meaning two of them are particularly important the campanian santonian c s event corresponds to 1 obduction and exhumation of high pressure low temperature metamorphic rocks around the arabian promontory 2 inversion along the margins of the east mediterranean basins and 3 lithosphere buckling in the atlas system maghreb and adjacent sahara platform the middle late eocene mle event corresponds to 1 the onset of collision at the northern corner of arabia 2 the onset of slab retreat in the mediterranean and 3 inversion along the margin of the east mediterranean as well as in the atlas the c s event coincides with a change in plate kinematics resulting in an abrupt increase of convergence velocity the mle event coincides with a period of strong coupling between the africa and eurasia plates and an abrupt decrease of convergence velocity in the middle of the system the central mediterranean seems to escape to the effects of convergence and is the site of quite permanent extensional movements since the triassic

tectonostratigraphic evolution of the eastern algerian margin and basin from seismic data and onshore offshore correlation abstract the eastern algerian basin part of the western mediterranean domain is a back arc basin resulting from the se drift of the lesser kabylia block gave rise to continental extension and birth of a new oceanic domain we aim here to define the structure and tectonostratigraphic evolution of this basin and the adjoining continental margin indeed the absence of wells and the lack of published mcs data kept this area mostly unknown the crustal architecture down to the moho and seismo stratigraphy of the sedimentary infill are detailed emphasizing particularly the pre messinian series by combining a new set of offshore deep penetrating seismic conventional mcs sections and wide angle seismic data because no well exist offshore we realized new field descriptions of the late oligocene and miocene deposits on land and propose onshore offshore extrapolation and age correlations the pre messinian series display four main units pmsu1 to 4 above which messinian units are consistent with stratigraphic models already proposed for the mediterranean basin the deep basin displays units as old as the omk oligo miocene kabyle series on land the basement is shaped by conjugate transcurrent faults striking n120 n40 forming a series of rhombic troughs resulting from transtensional tectonics the coeval e w extension and nw se stretching of the continental crust suggest a radial opening of the algerian basin during late oligocene lower miocene followed by a progressive uplift of the upper margin after the collision of lesser kabylia with africa besides steep slope of the eastern algerian margin downward flexure of the oceanic basin near the margin toe and growth of s dipping thrusts within the margin evidence a significant quaternary stress inversion overall this study highlights the complex stress evolution of the east algerian margin since oligocene times as evidenced by significant upward downward vertical motions and crustal extensional compressional successions we summarize this evolution into three main stages 1 rifting including sea floor spreading at late oligocene burdigalian in the context of back arc 2 collision between alkapeca blocks and africa at 17 ma and post rift sag basin infill till late tortonian to messinian and 3 inversion of the margin and development of flexural basins at quaternary times

the 21 may 2003 zemmouri algeria earthquake mw 6 8 relocation and aftershock sequence analysis 1 a strong earthquake mw 6 8 struck the coastal region east of algiers and the tell atlas of algeria on 21 may 2003 and was responsible of severe damage and about 2400 casualties the coastal mainshock was followed by a large number of aftershocks the largest reaching mw 5 8 on 27 may 2003 we study the mainshock first major aftershocks and about 900 events recorded by temporary seismic stations using master event approach and double difference dd methods although the seismic station array has a large gap coverage the dd algorithm provides with an accurate aftershocks location the mainshock hypocenter relocation is determined using three major aftershocks 5 0 mw 5 8 chosen as master events the new mainshock location shifted on the coastline 36 83n 3 65e at 8 10 km depth seismic events extend to about 16 km depth and form a n 55 60 e trending and 45 55 se dipping fault geometry up to now it is the unique among the recently studied seismic events of the tell atlas of algeria mainshock and aftershocks relocation the thrust focal mechanism harvard cmt n 57 44 se dip 71 rake and the seismic moment 2 86 1019 nm infer a 50 km long fault rupture that may appear at the sea bottom at 6 to 12 km offshore north of the coastline the zemmouri earthquake occurred along the complex thrust and fold system of the tell atlas and provides with new constraints on the earthquake hazard evaluation in northern algeria

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

deep structure of the continental margin and basin off greater kabylia algeria new insights from wide angle seismic data modeling and multichannel seismic interpretation abstract during the algerian french spiral survey aimed at investigating the deep structure of the algerian margin and basin two coincident wide angle and reflection seismic profiles were acquired in central algeria offshore greater kabylia together with gravimetric bathymetric and magnetic data this 260 km long offshore onshore profile spans the balearic basin the central algerian margin and the greater kabylia block up to the southward limit of the internal zones onshore results are obtained from modeling and interpretation of the combined data sets the algerian basin offshore greater kabylia is floored by a thin oceanic crust 4 km with p wave velocities ranging between 5 2 and 6 8 km s in the northern hannibal high region the atypical 3 layer crustal structure is interpreted as volcanic products stacked over a thin crust similar to that bordering the margin and related to miocene post accretion volcanism these results support a two step back arc opening of the west algerian basin comprising oceanic crust accretion during the first southward stage and a magmatic and probably tectonic reworking of this young oceanic basement during the second westward opening phase the structure of the central algerian margin is that of a narrow 70 km magma poor rifted margin with a wider zone of distal thinned continental crust than on the other margin segments there is no evidence for mantle exhumation in the sharp ocean continent transition but transcurrent movements during the second opening phase may have changed its initial geometry the plio quaternary inversion of the margin related to ongoing convergence between africa and eurasia is expressed by a blind thrust system under the margin rising toward the surface at the slope toe and by an isostatic disequilibrium resulting from opposite flexures of two plates decoupled at the continental slope this disequilibrium is likely responsible for the peculiar asymmetrical shape of the crustal neck that may thus be a characteristic feature of inverted rifted margins

the el asnam 1980 october 10 inland earthquake a new hypothesis of tsunami generation summary the western mediterranean sea is not considered as a high seismic region only several earthquakes with magnitude above five occur each year and only a handful have consequences on human beings and infrastructure the el asnam algeria earthquake of 1980 october 10 with an estimated magnitude ms 7 3 is one of the most destructive earthquakes recorded in northern africa and more largely in the western mediterranean basin although it is located inland it is known to have been followed by a small tsunami recorded on several tide gauges along the southeastern spanish coast in 1954 a similar earthquake having occurred at the same location induced a turbidity current associated to a submarine landslide which is widely known to have cut submarine phone cables far from the coast this event was followed by a small tsunami attributed to the landslide thus the origin of the tsunami of 1980 was promptly attributed to the same kind of submarine slide as no evidence of such mass movement was highlighted and because the tsunami wave periods does not match with a landslide origin in both cases 1954 and 1980 this study considers two rupture scenarios that the coseismic deformation itself of about 10 cm off the algerian coast near tenes is sufficient to produce a low amplitude several centimetres tsunami able to reach the spanish southeastern coast from alicante to algeciras gibraltar strait to the west after a discussion concerning the proposed rupture scenarios and their respective parameters numerical tsunami modelling is performed on a set of bathymetric grids then the results of wave propagation and amplification maximum wave height maps are discussed with a special attention to alicante spain harbour where the location of two historical tide gauges allows the comparison between synthetic mareograms and historical records showing sufficient signal amplitude this study is part of the active tsunami hazard assessment in mediterranean sea especially concerning its occidental part that is the algerian spanish and french coasts

a new sea floor gravimeter a new reservoir management application uses precise time lapse gravity measurements on the sea floor to detect seawater infiltration in offshore natural gas fields during production reservoir models for the north sea troll field predict gravity changes as large as 0 060 mgal within a 3 5 year period we have constructed and deployed a new instrument the rovdog remotely operated vehicle deployed deep ocean gravimeter system for this application because the measurements must be relocated accurately within 3 cm we required a gravimeter which could be handled by an rov and placed atop sea floor benchmarks we have built an instrument based upon the scintrex cg 3m land gravimeter motorized gimbals level the gravimeter sensor within a watertight pressure case precision quartz pressure gauges provide depth information a shipboard operator remotely controls the instrument and monitors the data the system error budget considers both instrumental and field measurement uncertainties the instrument prototy

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 beni ilmane north central algeria earthquake sequence of may 2010 starting on 14 may 2010 and lasting several months the village of beni ilmane msila district north central algeria and its surroundings were struck by an important seismic crisis marked by three successive moderate shocks 5 0 md 5 2 this sequence of events caused severe damage in the beni ilmane village and in the epicentral area the poor quality of masonry construction and the cumulative effects of the large number of aftershock events played a key role in the destruction to follow this earthquake sequence 11 temporary seismic stations in addition to the permanent stations of the algerian seismic network were deployed in the region a representative set of well located aftershocks in the period of maximum activity lasting 18 days were selected the horizontal distribution of the aftershocks shows two main earthquake clusters located near beni ilmane village one cluster oriented e w and the other oriented nne ssw crossing the first cluster at its eastern tip the aftershocks distribution suggests that the three main shocks ruptured two distinct and adjacent fault segments of about 8 km length the focal mechanisms of the first and third events located in the nne ssw cluster show near vertical left lateral strike slip fault planes in the second cluster oriented e w focal mechanisms show a high angle reverse fault a field survey initiated immediately after the first main shock identified surface fissures generated by the three largest events in the sequence the fissures concentrated in a narrow area at the western termination of the ne sw jebel choukchot anticline location of beni ilmane village showed several orientations which were mainly related to gravity instabilities the 2010 beni ilmane earthquake sequence located in the bibans hodna mountains transition zone demonstrates that the tellian atlas high plateaus border region is an active seismic zone marked by moderate and possibly strong earthquakes thus a reevaluation of the seismic hazard in the region is needed

the relative motion between africa and eurasia as derived from itrf2000 and gps data 1 studies of intra and inter plate deformation typically need a model describing the motions of the stable part of the tectonic plates for reference purposes we have developed deos2k a model for the current motion of seven major tectonic plates derived from space geodetic observations this paper focuses on relative motion between africa and eurasia in the past this motion has been poorly established because of poor data coverage for africa deos2k is based on itrf2000 altamimi et al 2002 and new african gps observations it is an improvement over the nuvel 1a model for predicting the present day relative motions of these two plates deos2k predicts in northeastern africa that africa eurasia relative motion is about 40 smaller in magnitude than nuvel 1a and trends more to the northwest this is consistent with independent local geodetic observations a similar shift in orientation clockwise is observed at the western tip of the plate boundary

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

the 2016 mihoub north central algeria earthquake sequence seismological and tectonic aspects abstract on 28 may 2016 at 23 54 utc an mw5 4 earthquake occurred in mihoub village algeria 60 km southeast of algiers this earthquake was the largest event in a sequence recorded from 10 april to 15 july 2016 in addition to the permanent national network a temporary network was installed in the epicentral region after this shock recorded event locations allow us to give a general overview of the sequence and reveal the existence of two main fault segments the first segment on which the first event in the sequence was located is near vertical and trends e w the second fault plane on which the largest event of the sequence was located dips to the southeast and strikes ne sw a total of 46 well constrained focal mechanisms were calculated the events located on the e w striking fault segment show mainly right lateral strike slip strike n70 e dip 77 to the sse rake 150 the events located on the ne sw striking segment show mainly reverse faulting strike n60 e dip 70 to the se rake 130 we calculated the static stress change caused by the first event md4 9 of the sequence the result shows that the fault plane of the largest event in the sequence mw5 4 and most of the aftershocks occurred within an area of increased coulomb stress moreover using the focal mechanisms calculated in this work we estimated the orientations of the main axes of the local stress tensor ellipsoid the results confirm previous findings that the general stress field in this area shows orientations aligned nnw sse to nw se the 2016 mihoub earthquake sequence study thus improves our understanding of seismic hazard in north central algeria

deposition processes from echo character mapping along the western algerian margin oran tenes western mediterranean abstract the westernmost algerian margin south algero provencal basin depicts a few offshore active faults moderate to rare seismicity and generally very steep slopes 16 we classified and mapped 12 echo types according to their sub bottom acoustic facies observed on this margin on 2 5 2 khz chirp echo sounder data maradja 2003 cruise the echo character maps are interpreted in terms of sedimentary processes the b1 echo type parallel to subparallel high to low amplitude sub bottom reflections mainly in the deep basin corresponds to hemipelagic sedimentation r1 prolonged single echo with no sub bottoms and r2 small irregular overlapping hyperbolae echo types generally near or in canyon systems are associated with turbidity currents or more rarely to contour currents or mass transport deposits such as slumps slides and debris flows the transparent echo types t1 t5 and r3 chaotic lens of low amplitude reflections on top of higher amplitude often located at the foot of the slope or canyons walls typically indicate mass transport deposits like slides or turbidites large zones that display a large variety of echo types are evidenced in the study area and are generally associated with turbidity currents but could also be associated with bottom currents it appears that active tectonics plays a significant role in this part of the margin which presents a few active faults offshore but also a strong and relatively frequent seismicity onland the general pattern of the distribution of mass transport deposits is particular i e many but small slides all along the margin and suggests a probable triggering by recurrent earthquake shakings however active tectonics is not the only factor influencing the deposition pattern as some zones seem characterized by predominant strong turbidity currents transporting sediments far away from the foot of the margin whereas others depict retrogressive erosion features on the slope i e small slides scarps in gullies rather than transport by turbidity currents in particular the rivers sediment discharge fluxes and the geomorphologic characteristics of the margin seem to be very important factors too

coexisting tectonic settings the example of the southern tyrrhenian sea we performed geodetic strain rate analyses in southern italy using new gps velocities two dimensional strain and rotation rate fields were estimated and results show that most of the shortening is distributed in the northern sicily offshore extension becomes more evident and comparable with shortening on the eastern side of the same margin and greater in the eastern sicily offshore principal shortening and extension rate axes are consistent with long term geological features seismic reflection profiles show both active compressive and extensional faults affecting pleistocene strata we show evidence for contemporaneous extension and transtension in the cefalu basin combining geodetic data and geological features point to the coexistence of independent geodynamic processes i e the active e w backarc spreading in the hangingwall of the apennines subduction zone and shortening along the southern margin of the tyrrhenian backarc basin operated by the nnw motion of africa relative to eurasia

geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding this paper presents geometric arguments for modifying the conventional concept for the evolution of concentric fold trains above nonductile detachment zones the common geometric model for concentric folding above a detachment invokes a wave train with fixed fold axes regularly spaced along the fold panel limb lengths from crest to trough remain constant as the limb dips increase to uplift the anticlinal crests while the synclinal troughs slide parallel to the detachment plane the basic depth to detachment calculation which derives from the law of conservation of volume requires that the area of uplift above regional for a concentric anticline be equal to the arithmetic product of the shortening and the depth to detachment this imposes a geometric constraint with which a constant limb length anticline growing by increasing limb dip above a fixed detachment plane cannot comply unless in the early stages mobile material in the detachment zone flows from the synclinal troughs to the anticlinal crests and then in the later stages the flow direction reverses relatively few detachment zones contain a significant amount of mobile salt or shale therefore in most concentric detachment fold trains a basic geometric incompatibility exists between the conventional geometric model and themore law of conservation of volume the conflict can be resolved by an evolutionary fold model wherein the anticlinal fold limbs are short at the inception of folding and grow longer as dips increase and the fold grows in this model the anticlinal axes generally are fixed and the synclinal axes active which has structural and economic implications for the distribution of permeability and syntectonic sediments as well as for the migration and entrapment of hydrocarbons 18 figs less

seismicity and tectonic structures in the site of algiers and its surroundings a step towards microzonation we intend to reappraise the seismogenic potential of the geologic structures in the site of algiers and its surroundings a compilation of a working earthquake catalogue is first made using all events reported in all previous documentation available however for the sake of homogeneity and a certain degree of reliability of the data only revised seismic events with epicenter coordinates magnitude and or intensity are included a tectonic setting of the zone under investigation and available fault plane solutions are presented the results obtained in previous seismological studies of the most recent earthquakes of the area are also discussed the findings highlight the great interest to be taken in the detailed and timely assessment of the seismic hazard of algiers and its surroundings which is made possible by the realistic modelling of the scenario seismic input

geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding geologic note 1 this paper presents geometric arguments for modifying the conventional concept for the evolution of concentric fold trains above nonductile detachment zones the common geometric model for concentric folding above a detachment invokes a wave train with fixed fold axes regularly spaced along the fold panel limb lengths from crest to trough remain constant as the limb dips increase to uplift the anticlinal crests while the synclinal troughs slide parallel to the detachment plane the basic depth to detachment calculation which derives from the law of conservation of volume requires that the area of uplift above regional for a concentric anticline be equal to the arithmetic product of the shortening and the depth to detachment this imposes a geometric constraint with whi h a constant limb length anticline growing by increasing limb dip above a fixed detachment plane cannot comply unless in the early stages mobile material in the detachment zone flows from the synclinal troughs to the anticlinal crests and then in the later stages the flow direction reverses relatively few detachment zones contain a significant amount of mobile salt or shale therefore in most concentric detachment fold trains a basic geometric incompatibility exists between the conventional geometric model and the law of conservation of volume the conflict can be resolved by an evolutionary fold model wherein the anticlinal fold limbs are short at the inception of folding and grow longer as dips increase and the fold grows in this model the anticlinal axes generally are fixed and the synclinal axes active which has structural and economic implications for the distribution of permeability and syntectonic sediments as well as for the migration and entrapment of hydrocarbons

gps constraints on africa nubia and arabia plate motions summary we use continuously recording gps cgps and survey mode gps sgps observations to determine euler vectors for relative motion of the african nubian arabian and eurasian plates we present a well constrained eurasia nubia euler vector derived from 23 igs sites in europe and four cgps and three sgps sites on the nubian plate 0 95 4 8 n 21 8 4 3 e 0 06 0 005 myr 1 we see no significant 1m m yr 1 internal deformation of the nubian plate the gps nubian eurasian euler vector differs significantly from nuvel 1a 21 0 4 2 n 20 6 0 6 e 0 12 0 015 myr 1 implying more westward motion of africa relative to eurasia and slower convergence in the eastern mediterranean the arabia eurasia and arabia nubia gps euler vectors are less well determined based on only one cgps and three sgps sites on the arabian plate the preliminary arabia eurasia and arabia nubia euler vectors are 27 4 1 0 n 18 4 2 5 e 0 40 0 04 myr 1 and 30 5 1 0 n 25 7 2 3 e 0 37 0 04 myr 1 respectively the gps arabia nubia euler vector differs significantly from nuvel 1a 24 1 1 7 n 24 0 3 5 e 0 40 0 05 myr 1 but is statistically consistent at the 95 per cent confidence level with the revised euler vector reported by chu gordon based on a re evaluation of magnetic anomalies in the red sea 31 5 1 2 n 23 0 2 7 e 0 40 0 05 myr 1 the motion implied in the gulf of aqaba and on the dead sea fault dsf by the new gps nubia arabia euler vector i e ignoring possible sinai block motion and possible internal plate deformation grades from pure left lateral strike slip in the gulf and on the southern dsf with increasing compression on the central and northern dsf with relative motion increasing from 5 6 to 7 5 mm yr 1 1m m yr 1 from south to north along the northern dsf i e north of the lebanon restraining bend motion is partitioned between 6 1m m yr 1 left lateral motion parallel to the fault trace and 4 1m m yr 1 faultnormal compression relative motions on other plate boundaries including the anatolian and aegean microplates derived from the gps euler vectors agree qualitatively with the sense of motion indicated by focal mechanisms for large crustal earthquakes m 6 where data are available on fault slip rates on plate bounding faults north anatolian fault east anatolian fault dead sea fault red sea rift they are generally lower than but not significantly different from the full plate motion estimates suggesting that the majority of relative plate motion is accommodated on these structures

coseismic deformation of the may 21st 2003 mw 6 8 boumerdes earthquake algeria from gps measurements 1 on may 21st 2003 a mw 6 8 earthquake struck the central part of northern algeria causing extensive damage in the boumerdes area 40 km east of algiers it is among the largest events to occur in the western mediterranean over the past 25 years we present gps measurements of horizontal coseismic displacements that provide new constraints on the rupture geometry modeling the data with a uniform dislocation on a rectangular fault in an elastic half space we find that the rupture occurred on a reverse fault dipping 42 s with its upper edge 6 km offshore and lower edge 4 km inland the amplitude distribution of the coseismic displacements indicates that the rupture did not reach the surface at least in its western part and ended to the west around 3 4 e offshore faults like that of the boumerdes earthquake could account for part of the africa eurasia relative plate motion in the western mediterranean and represent a significant seismic threat for algeria

preliminary results of a paleoseismological analysis along the sahel fault algeria new evidence for historical seismic events abstract the 60 km long sahel ridge west of algiers tell atlas north algeria is considered as an ene wsw fault propagation fold running along the mediterranean coast and associated with a north west dipping thrust its proximity with algiers makes this structure a potential source of destructive earthquakes that could hit the capital city as occurred in 1365 ad and 1716 ad the first paleoseismologic investigation on the sahel ridge was conducted in order to detect paleo ruptures related to active faulting and to date them from the first investigations in the area a first trench was excavated across bending moment normal faults induced by flexural slip folding in the hanging wall of the sahel anticline thrust ramp paleoseismological analyses recognize eight rupture events affecting colluvial deposits 14c dating indicates that these events are very young six of them being younger than 778 ad the first sedimentary record indicates two ruptures before 1211 ad i e older than the first historical earthquake documented in the region three events have age ranges compatible with the 1365 1673 and 1716 algiers earthquakes whereas three other ones depict very recent ages i e younger than 1700 ad potential of these secondary extrados faults for determining paleoseismic events and thrust behaviour is discussed

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

coastal uplift and thrust faulting associated with the mw 6 8 zemmouri algeria earthquake of 21 may 2003 1 a shoreline uplift marked by a continuous white band visible at rocky headlands occurred during the 21 may 2003 earthquake mw 6 8 in northern algeria we measured the amount of coastal uplift on a white band emerged algae and harbors quays between boumerdes and dellys most of measured points were collected using tape and differential gps on rocky headlands with 0 15 m error bar tidal prism leveling lines running parallel and orthogonal to the coast also provide the precise amount of uplift in the epicentral area the uplift distribution shows an average 0 55 m along the shoreline with a maximum 0 75 m east of boumerdes and a minimum close to 0 near cap djinet the active deformation related to a thrust fault is modeled along the 55 km coastline the dislocation model predicts surface slip on a n 54 e trending reverse fault dipping 50 se in agreement with cmt solution and coastal uplift the faulting characteristics imply a fault geometry with possible sea bottom ruptures between 5 to 10 km offshore

blind reverse faulting system associated with the mont chenoua tipaza earthquake of 29 october 1989 north central algeria a shallow and damaging earthquake struck the region of tipaza located on the coast 70 km to the west of algiers north central algeria the main shock was felt as far as 200 km from the epicentral area and particularly in the urbanized zone of algiers the main shock epicentre determined by craag is on mt chenoua close to the coastline coseismic surface breaks with 4 0 km of fault length and 7 0 cm of vertical displacement appeared on the southern side of mt chenoua they consist of cracks and fissures on vertical bedding planes that belong to a neogene flexure the aftershock activity was recorded for several weeks and comprised more than 100 seismic events per day with 1 m 5 aftershocks are distributed in a ene wsw to ne sw zone extending offshore a nw se cross section indicates that seismic events affect the crust to a maximum depth of 20 km showing a complex fault plane geometry dipping to the nw for the main shock the focal mechanism solution obtained from the readings of first motion polarities of seismograms yields an ene wsw reverse fault dipping to the nnw which is in good agreement with both field observations and the aftershock distribution at depth the occurrence of the mt chenoua tipaza moderate sized event in a previously identified active zone improves the seismotectonic characterization of this part of the tellan atlas mountains this thrust and fold geological domain also shows active folds capable of producing larger earthquakes since only a small portion of the sahel anticline ridge has been reactivated a serious seismic hazard must be urgently recognized in the algiers region

fault displacement gradient folds and the structure at lost hills california u s a abstract geometric models of fault propagation folds require that the underlying fault tip propagate upward across layering however related folds can be generated if the tip remains stationary or even moves back along the ramp as a pre existing fault is reactivated fault propagation folds detachment folds as well as those produced when there is no propagation are generated by a displacement gradient along the underlying fault and as a general class can be called fault displacement gradient folds new geometric equations are derived which relate fold shape to displacement gradient and fault propagation folds are a special case of these more general equations growth sequences associated with these structures have been used to distinguish fault propagation folds from fault bend folds when the underlying structure is obscured a displacement gradient fold in which the fault tip retreats back down the ramp generates a growth sequence that in some cases could be confused with that of a fault bend fold the structure at lost hills in the san joaquin valley of california u s a has been interpreted as a fault bend fold but it may be a displacement gradient fold which formed as a pre existing fault was reactivated during a pliocene change in plate motion

recent and active deformation pattern off the easternmost algerian margin western mediterranean sea new evidence for contractional tectonic reactivation we describe for the first time a set of large active thrusts and folds near the foot of the easternmost algerian margin western mediterranean from swath bathymetry and high resolution seismic data acquired in 2005 during the maradja2 samra cruise this active system resumes a previous passive margin and creates growth strata deposition on the limbs of large folds resulting in the development of perched basins at the foot of the margin since less than 1 ma they form a set of overlapping fault segments verging toward the algerian basin in a way similar to what has been observed off eastern algiers on the rupture zone of the 2003 mw 6 8 boumerdes earthquake the horizontal shortening rate across large folds is estimated to be of the order of 1 mm yr although no historical earthquakes are reported here these fault segments could have been responsible for large m 7 5 events in the past this young tectonic system further supports the hypothesis of subduction inception of the neogene oceanic lithosphere in the context of the africa eurasia convergence

active thrust faulting offshore boumerdes algeria and its relations to the 2003 mw 6 9 earthquake 1 we investigate the active seismogenic fault system in the area of the 2003 mw 6 9 boumerdes earthquake algeria from a high resolution swath bathymetry and seismic survey a series of 5 main fault propagation folds 20 35 km long leave prominent cumulative escarpments on the steep slope and in the deep basin fault activity creates plio quaternary growth strata within uplifted areas such as a rollover basin on the slope and piggyback basins in the deep ocean most thrusts turn to fault propagation folds at the sub surface and depict ramp flat trajectories we find that the two main slip patches of the 2003 mw 6 9 boumerdes earthquake are spatially correlated to two segmented cumulative scarps recognized on the slope and at the foot of the margin the overall geometry indicates the predominance of back thrusts implying underthrusting of the neogene oceanic crust

the northwestern maghreb boundary of the nubia africa plate abstract a study of the present compressional deformation of the northwestern maghreb nubia africa margin is derived from the analysis of more than 20 000 km of seismic profiles in the western part the compression is distributed in a large zone with on land compression in algeria mainly strike slip deformation on the algerian margin and folds and strike slip faulting in eastern spain in the middle of the algerian margin around algiers the evidences of compression become more obvious in this area a ridge trending n s that is interpreted as a middle to late miocene spreading center interacted with the transpressional margin that trends e w north of the location of the boumerdes zemmouri earthquake the oceanic crust is deformed by blind thrusts up to 60 km from the coast these thrusts are south dipping and with the northward dipping thrusts located onshore form a wedge that maybe a positive flower structure at a crustal scale related to the right lateral transpression of the margin in the eastern part of the northwestern maghreb nubia africa deformed belt off eastern algeria and tunisia the deformation is more intense but limited to the north by the continental slope large late miocene tortonian folds are cut by the messinian erosional surface but the present deformation is also evident it is suggested that the deformation with a double vergence may be followed up to the north of sicily after the docking 18 ma of the kabylies to the africa plate the crust has been thinned and the algerian basin opened during the middle late miocene with an e w direction from the late miocene to the present the margin has been rethickened by transpression and uplifted

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

e w opening of the algerian basin western mediterranean we present geophysical and geological evidence of fast 2 cm yr 1 in the east and 5 cm yr 1 in the west e w spreading between 16 and 8 ma in the region behind the gibraltar arc in the algerian basin

post messinian evolution of the florence rise area western cyprus arc part ii experimental modeling abstract the florence rise is located southwest of the island of cyprus and belongs to the western part of the cyprus arc the florence rise is an accretionary prism with some amount of strike slip where the thick layer of evaporitic messinian decouples deformation in the post messinian cover from that in the pre messinian basement the basement structural highs whether presently active or inactive influence the deformation and displacement patterns of the salt and its overburden our first experiment focused on the presence in nature of normal faults located above basement thrusts deformation of the salt layer and its overburden was influenced by several processes on one hand the entire model was subjected to regional shortening and basement thrusts formed on the other hand the local vertical rise associated with basement thrusts created local slopes down which the salt and overburden glided gravitationally in some places leading to the formation of normal faults in an otherwise compressional regional setting our second experiment was designed to model the buttressing effect of the florence rise and the eratosthenes seamount on thin skinned displacement patterns during regional gravity spreading of the nile cone results indicate that in the northeastern distal region buttressing by these two basement highs forced the salt and its overburden to flow northeastward as a lateral escape toward the free boundary of the region

active faulting geometry and stress pattern near complex strike slip systems along the maghreb region constraints on active convergence in the western mediterranean the maghreb region from tunisia to gibraltar is a key area in the western mediterranean to study the active tectonics and stress pattern across the africa eurasia convergent plate boundary in the present study we compile comprehensive data set of well constrained crustal stress indicators from single focal mechanism solutions formal inversion of focal mechanism solutions and young geologic fault slip data based on our and published data analyses stress inversion of focal mechanisms reveals a first order transpression compatible stress field and a second order spatial variation of tectonic regime across the maghreb region with a relatively stable s hmax orientation from east to west therefore the present day active contraction of the western africa eurasia plate boundary is accommodated by 1 e w strike slip faulting with reverse component along the eastern tell and saharan tunisian atlas 2 a predominantly ne trending thrust faulting with strike slip component in the western tell part and 3 a conjugate strike slip faulting regime with normal component in the alboran rif domain this spatial variation of the present day stress field and faulting regime is relatively in agreement with the inferred stress information from neotectonic features according to existing and newly proposed structural models we highlight the role of main geometrically complex shear zones in the present day stress pattern of the maghreb region then different geometries of these major inherited strike slip faults and its related fractures v shaped conjugate fractures horsetail splays faults and riedel fractures impose their component on the second and third order stress regimes neotectonic and smoothed present day stress map mean s hmax orientation reveal that plate boundary forces acting on the africa eurasia collisional plates control the long wavelength of the stress field pattern in the maghreb the current tectonic deformations and the upper crustal stress field in the study area are governed by the interplay of the oblique plate convergence i e africa eurasia lithosphere mantle interaction and preexisting tectonic weakness zones

crustal structure of the eastern algerian continental margin and adjacent deep basin implications for late cenozoic geodynamic evolution of the western mediterranean the karukera spur is an easternmost submerged rise of the lesser antilles fore arc in the guadeloupe archipelago culminating about 4000 m above the fore arc basin 150 km west of the deformation front the analysis of 3500 km 2d high resolution multichannel seismic reflection and multibeam bathymetric data and the study of 14 core samples allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution seven seismic units us1 to us7 are evidenced organised into four major depositional sequences separated by erosional surfaces units us1 to us4 thicken to the south southeast on the spur the sedimentary deposits rest upon a deeply eroded metamorphic basement of the caribbean plate as in la desirade island sequence 1 units us1 and us2 remains unknown in its lower part because it does not outcrop its upper part comprises early miocene shallow water carbonates sequence s2 unit us3 only comprises an upper miocene transgressive systems tract deposited into basinal environment it is bounded by major erosional surfaces sb2 and sb3 sequence 3 us4 to us6 is zanclean to pleistocene it is dominantly composed of shallow water reefal deposits sequence 4 corresponds to recent deposits the karukera spur experienced three main extensional episodes with alternations between uplift and subsidence periods uplifts are responsible for emersions and erosions subsidence severely drowned shallow water deposits the first extensional episode led to the formation of horsts and grabens in the basement prior to early miocene deposits the second extensional episode occurred during upper miocene in accordance with data in surrounding islands the third tectonic episode developed since calabrian noticeable is the constant reactivation of n130 n150 n150 n180 and n40 trending faults since early miocene and the neoformation of e w trending faults since calabrian our results suggest that at the latitude of guadeloupean archipelago the lesser antilles subduction zone is an erosional margin because of the successive sweepings of the santa lucia then tiburon ridges