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

the crustal domains of the alboran basin western mediterranean the alboran basin in the westernmost mediterranean hosts the orogenic boundary between the iberian and african plates although numerous geophysical studies of crustal structure onshore iberia have been carried out during the last decade the crustal structure of the alboran basin has comparatively been poorly studied we analyze crustal scale images of a grid of new and reprocessed multichannel seismic profiles showing the tectonic structure and variations in the reflective character of the crust of the basin the nature of the distinct domains has been ground truthed using available basement samples from drilling and dredging our results reveal four different crustal types domains of the alboran basin a a thin continental crust underneath the west alboran and malaga basins which transitions to b a magmatic arc crust in the central part of the alboran sea and the east alboran basin c the north african continental crust containing the pytheas and habibas sub basins and d the oceanic crust in the transition towards the algero balearic basin the alboran basin crust is configured in a fore arc basin west alboran and malaga basins a magmatic arc central and east alboran and a back arc system in the easternmost part of the east alboran basin and mainly algero balearic basin the north african continental crust is influenced by arc related magmatism along its edge and was probably affected by strike slip tectonics during westward migration of the miocene subduction system the distribution of active tectonic structures in the current compressional setting generally corresponds to boundaries between domains possibly representing inherited lithospheric scale weak structures

are the seismological and geological observations of the al hoceima morocco rif 2004 earthquake m 6 3 contradictory abstract seismic hazard is associated with recent and present fault activity in mountain ranges in the betic rif alpine mountain chain tectonic activity started in the cretaceous and topographic uplift continues since tortonian times as a consequence of the nw se oblique convergence between africa and eurasia the deformation is active and produces seismicity that sometimes has catastrophic consequences the al hoceima earthquake february 24 2004 considered one of the largest earthquakes ever recorded instrumentally in the westernmost mediterranean m 6 3 caused great damage in the region seismological studies agree that the main shock was situated on land at the limit between the external and internal zones of the rif at a depth of 10 14 km the focal mechanism points to a strike slip solution with a nw se oriented p axis quite similar to those of the significant 1994 earthquake swarm located to the north the epicenter aftershocks distribution would signal the presence of a n s oriented sinistral fault activated by the nw se regional compression associated to plate boundary convergence in this setting the seismogenic fault ruptures related to these seismic events are expected to have reached the earth s surface however detailed field work carried out 1 month after the earthquake does not evidence any n s strike slip coseismic fault in the epicentral area the main observed effects were landslides damages to constructions and locally open cracks indicating an unexpected nw se extension scarce n s faults are normal the main ones being located several kilometers away from the epicentral area to explain this apparent contradiction between geological and seismological observations we propose a decoupled tectonic model with crustal detachments that separate a deep brittle crust from an upper crust undergoing uplift and the development of large folds and normal faults this geological setting common to internal zones of cordilleras may need to be taken into account in future paleoseismicity studies and in the assessment of seismic hazard

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

redistribution of energy available for ocean mixing by long range propagation of internal waves ocean mixing which affects pollutant dispersal marine productivity and global climate1 largely results from the breaking of internal gravity waves disturbances propagating along the ocean s internal stratification a global map of internal wave dissipation would be useful in improving climate models but would require knowledge of the sources of internal gravity waves and their propagation towards this goal i present here computations of horizontal internal wave propagation from 60 historical moorings and relate them to the source terms of internal waves as computed previously2 3 analysis of the two most energetic frequency ranges near inertial frequencies and semidiurnal tidal frequencies reveals that the fluxes in both frequency bands are of the order of 1 kw m 1 that is 15 50 of the energy input and are directed away from their respective source regions however the energy flux due to near inertial waves is stronger in winter whereas the tidal fluxes are uniform throughout the year both varieties of internal waves can thus significantly affect the space time distribution of energy available for global mixing

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

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

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

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

imaging the growth of recent faults the case of 2016 2017 seismic sequence sea bottom deformation in the alboran sea western mediterranean

the al hoceima morocco earthquake of 24 february 2004 analysis and interpretation of data from envisat asar and spot5 validated by ground based observations abstract the magnitude mw 6 3 earthquake in al hoceima morocco of 24 february 2004 occurred in the active plate boundary accommodating the oblique convergence between africa and eurasia three different sets of estimates of its source parameters have already been published we try to resolve the discrepancies between them by using additional data including two remote sensing satellite systems envisat and spot5 using a model with a dislocation in an elastic half space we constrain the source parameters the hypothesis of two subevents on distinct faults as inferred from seismological inversions is confirmed here by adopting a cross fault mechanism the rupture began on a left lateral strike slip fault striking at n10 azimuth with 90 cm of horizontal slip and then transferred to a right lateral strike slip fault striking at n312 azimuth with 85 cm of horizontal slip the first fault is at 500 m depth from the free surface and the second fault is at 3 km depth this model is consistent with ground based observations including gps seismology and mapped surface fissures the pair of faults activated in 2004 appears to constitute part of a complex seismogenic structure striking nne ssw that separates the rif tectonic blocks

the 1994 2004 al hoceima morocco earthquake sequence conjugate fault ruptures deduced from insar abstract we study the may 26 1994 mw 6 0 and february 24 2004 mw 6 4 earthquakes that affected the al hoceima region of northern morocco these events are the two strongest earthquakes recorded in this region yet the exact location kinematics and relationships between these earthquakes are poorly known since neither of them produced surface ruptures using synthetic aperture radar interferometry insar we mapped the surface displacement field of the two earthquakes to characterize their seismic source parameters analysis of the interferograms constructed from ascending and descending orbits for both earthquakes and subsequent elastic modeling using slip inversions on triangular fault patches suggest that the two mainshocks occurred on blind conjugate strike slip faults the 1994 earthquake being associated with n23 e trending left lateral fault and the 2004 earthquake with n45 w trending right lateral fault this result contradicts previous inferences on the kinematics location and rupture geometry of the earthquakes deduced from conventional analyses of seismic waveforms and aftershocks distribution the insar analysis reveals the fragmentation of the rif mountain throughout a complex network of conjugate blind faults consistent with the transpression tectonics along the plate boundary in north africa although the two earthquakes took place in the rif thrust and fold belt the late quaternary deformation indicates e w extension in agreement with the nw se and ne sw trending conjugate strike slip faulting

the offshore yangsan fault activity in the quaternary se korea analysis of high resolution seismic profiles abstract the nne trending dextral yangsan fault is a 190 km long structure in the korean peninsula traced to the southeastern coast the scarcity of quaternary deposits onland precludes any detailed investigation of the quaternary activity and structure of the yangsan fault using seismic reflection profiling we acquired offshore high resolution seismic profiles to investigate the extension of the yangsan fault and constrain its quaternary activity using stratigraphic markers the seismic profiles reveal a nne trending fault system consisting of a main fault and an array of subsidiary faults that displaced quaternary sequences stratigraphic analysis of seismic profiles indicates that the offshore faults were activated repeatedly in the quaternary the up to the east sense of throw on the main fault and plan view pattern of the fault system are explained by dextral strike slip faulting the main fault when projected toward the korean peninsula along its strike aligns well with the yangsan fault we suggest that the offshore fault system is a continuation of the yangsan fault and has spatial correlation with weak but ongoing seismicity

submarine fault scarps in the sea of marmara pull apart north anatolian fault implications for seismic hazard in istanbul earthquake scarps associated with recent historical events have been found on the floor of the sea of marmara along the north anatolian fault naf the marmarascarps cruise using an unmanned submersible rov provides direct observations to study the fine scale morphology and geology of those scarps their distribution and geometry the observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north marmara extensional step over between the strike slip ganos and izmit faults smaller strike slip segments and pull apart basins alternate within the main step over commonly combining strike slip and extension rapid sedimentation rates of 1 3 mm yr appear to compete with normal faulting components of up to 6 mm yr at the pull apart margins in spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief sets of youthful earthquake scarps extend offshore from the ganos and izmit faults on land into the sea of marmara our observations suggest that they correspond to the submarine ruptures of the 1999 izmit mw 7 4 and the 1912 ganos ms 7 4 earthquakes while the 1999 rupture ends at the immediate eastern entrance of the extensional cinarcik basin the 1912 rupture appears to have crossed the ganos restraining bend into the sea of marmara floor for 60 km with a right lateral slip of 5 m ending in the central basin step over from the gulf of saros to marmara the total 1912 rupture length is probably about 140 km not 50 km as previously thought the direct observations of submarine scarps in marmara are critical to defining barriers that have arrested past earthquakes as well as defining a possible segmentation of the contemporary state of loading incorporating the submarine scarp evidence modifies substantially our understanding of the current state of loading along the naf next to istanbul coulomb stress modeling shows a zone of maximum loading with at least 4 5 m of slip deficit encompassing the strike slip segment 70 km long between the cinarcik and central basins that segment alone would be capable of generating a large magnitude earthquake mw 7 2 other segments in marmara appear less loaded

heterogeneity in southern central indian ridge morb implications for ridge hot spot interaction between the rodrigues triple junction and the marie celeste fracture zone basalts from the central indian ridge cir exhibit an enrichment in incompatible elements that increases in intensity northward in addition h2o tio2 al 8 and dy yb ratios increase while na 8 remains unchanged and fe 8 decreases evolution of the enriched magma appears to be affected by elevated water contents which lower the mantle solidus thereby increasing the initial depth of melting as well as delaying plagioclase crystallization however the enrichment affecting the northern samples is not a just function of hydrous mantle melting and crystallization instead of trending toward a small melt fraction from the mantle as predicted by hydrous melting models the cir samples lie on a mixing line between n morb and a source component that closely resembles present day reunion hot spot lavas thus it appears that while hydrous melting and crystallization affect the cir the enriched and wet mantle originates from the reunion hot spot where it migrates eastward toward the cir against the direction of motion of the lithosphere

active faulting offshore se spain alboran sea implications for earthquake hazard assessment in the southern iberian margin the southern margin of the iberian peninsula hosts the convergent boundary between the european and african plates the area is characterised by low to moderate magnitude shallow earthquakes although large historical events have also occurred in order to determine the possible sources of these events we recently acquired swath bathymetry tobi sidescan sonar and high resolution seismic data on the almeria margin eastern alboran sea the new dataset reveals the offshore continuation of the ne sw trending carboneras fault a master fault in the eastern betic shear zone and its associated structures n150 and ns faults these structures are active since they cut the late quaternary sedimentary units the submarine carboneras fault zone is 100 km long 5 10 km wide and is divided into two n045 and n060 segments separated by an underlapping restraining stepover geomorphic features typically found in subaerial strike slip faults such as deflected drainage water gaps shutter ridges pressure ridges and ben echelonq folds suggest a strike slip motion combined with a vertical component along the submarine carboneras fault considering the nnw sse regional shortening axis a left lateral movement is deduced for the carboneras fault whereas right lateral and normal components are suggested for the associated n150 and ns faults respectively the offshore portion of this fault is at least twice as long as its onshore portion and together they constitute one of the longest structures in the southeastern iberian margin despite the fact that present day seismicity in the almeria margin seems to be associated with the n150 to ns faults the carboneras fault is a potential source of large magnitude mw 7 2 events hence the carboneras fault zone could pose a

surface deformation associated with the mw 6 4 24 february 2004 al hoceima morocco earthquake deduced from insar implications for the active tectonics along north africa we study the surface deformation associated with the 24 february 2004 al hoceima earthquake mw 6 4 that recently affected the rif mountains of mo rocco the coseismic displacement field is mapped using synthetic aperture radar interferometry insar with the envisat esa satellite data acquired in the ascend ing and descending modes our analysis and modeling of insar data suggest that the earthquake is associated with a northwest southeast trending right lateral ap parently blind strike slip fault with a seismic moment reaching 6 8 10 18 n m this result is in contrast with the north northeast south southwest left lateral fault mech anism inferred from the modeling of seismic waves thrust and fold structures of the rif mountains developed during the tertiary period but the recent significant seismic events and late quaternary deformation indicate east west extension accom modated by north south trending normal and northwest southeast and northeast southwest trending conjugate strike slip faults the active deformation illustrates the fragmentation of the rif mountain range due to the africa iberia collision and west southwestward escape tectonics

source analysis of the mw 6 3 2004 al hoceima earthquake morocco using regional apparent source time functions 1 we use small and moderate aftershocks of the 24 february 2004 al hoceima earthquake as empirical greens functions egfs to retrieve the rupture history of the main event the magnitude depth and geometry of faulting were estimated for the main shock and 20 small and moderate aftershocks mw between 3 9 and 5 2 computing moment tensor solutions for the main shock we obtain a moment magnitude of mw 6 3 and a nearly pure double couple source 4 compensated linear vector dipole with predominately strike slip faulting the preferred fault plane has a strike of n11 e a dip of 72 and a rake of 17 fourteen aftershocks having depths 4 km and faulting geometries 11 for the strike of the preferred plane similar to the ones found for the main event were used as egfs apparent source time functions astfs of the al hoceima event were retrieved at twelve regional stations using an iterative time domain deconvolution on the p waveforms at each station time functions are enhanced by stacking of the deconvolved waveforms for different egfs astfs show total durations of 5 to 6 s two consecutive subevents separated by about 3 s and only a weak effect of directivity we further investigate the source history by inverting the set of astfs for the distribution of fault slip and rupture propagation two different source models were selected for presentation one involving one single fault plane and the other involving two parallel fault planes the two fault model fits more accurately the observations and leads to a more plausible slip distribution we estimate rupture dimensions of about 10 10 km2 and 8 8 km2 and moment magnitudes of mw 6 2 and 6 0 for the first and second subevent respectively

the alboran sea western mediterranean revisited with a view from the moroccan margin this paper presents a new depth to acoustic basement map based on a grid of seismic profiles in the western alboran basin the basement is more than 10 km deep an examination of a seismic profile of this region suggests that late oligocene early miocene 5 km thick synrift formation has been accumulated in this basin this west alboran basin has been formed in an extensional setting but in a fore arc position south of the balearic islands then westwards transported behind a subduction zone

fault identification for buried strike slip earthquakes using insar the 1994 and 2004 al hoceima morocco earthquakes summary the 1994 m w 6 0 and 2004 m w 6 5 al hoceima earthquakes are the largest to have occurred in morocco for 100 yr and give valuable insight into the poorly understood tectonics of the area bodywave modelling indicates the earthquakes occurred on near vertical strike slip faults with the nodal planes oriented nw se and ne sw distinguishing between the primary fault plane and auxiliary planes using either geodetic or seismic data is difficult due to the spatial symmetry in deformation fields and radiation pattern of moderately sized buried strikeslip earthquakes preliminary studies using aftershock locations and surface observations have been unable to identify the orientation of the primary fault plane for either earthquake conclusively we use radar interferometry and aftershock relocation of the earthquake sequence to resolve the ambiguity for the 2004 earthquake inverting the interferograms for a uniform slip model based either of the two potential nodal planes results in similar misfits to the data however the ne sw best fit fault plane has an unrealistically high fault slip to length ratio and we conclude the nw se striking nodal plane is the primary fault plane and slip was right lateral we carry out tests on synthetic data for a buried strike slip earthquake in which the orientation of the fault plane is known a priori independent of geometry missing data and correlated noise models produced assuming the auxiliary plane to be the fault plane have very high fault slip to length ratios the 1994 earthquake had a smaller magnitude and comparisons of model misfits and slip to length ratios do not conclusively indicate which of the nodal planes is the primary fault plane nonetheless the insar data provides valuable information by improving the accuracy of the earthquake location by an order of magnitude we carry out a multiple event relocation of the entire earthquake sequence including aftershocks making use of the absolute locations for the 1994 and 2004 main shocks from our insar study the aftershock locations are consistent with a nw se orientated fault plane in 2004 and suggests that the 1994 earthquake occurred on a ne sw fault perpendicular to the fault which ruptured in 2004 previous tectonic models of the area proposed a bookshelf model of block rotation with nne ssw left lateral faults this model requires modification to accommodate the observation of right lateral slip on a nw se fault plane for the 2004 earthquake and we prefer to interpret the fault orientations as due to a zone of distributed shear with a right lateral fault striking at 115 and conjugate clockwise rotating left lateral faults striking at 25

active tectonics of the western mediterranean geodetic evidence for rollback of a delaminated subcontinental lithospheric slab beneath the rif mountains morocco surface deformation in morocco derived from five years of global positioning system gps survey observations of a 22 station network four continuously recording gps cgps stations and four international gnss service igs stations in iberia indicates roughly southward motion 3 mm yr of the rif mountains morocco relative to stable africa motion of the rif is approximately normal to the direction of africa eurasia relative motion which is predominantly strike slip and results in shortening of the rif and subsequent crustal extension of the adjacent alboran sea region the sense and the n s asymmetry of the observed deformation i e no evidence for north directed shortening in the betic mountains north of the alboran sea cannot be easily explained in terms of crustal plate interactions suggesting that dynamic processes below the crust are driving the recent geologic evolution of the western mediterranean the model that best fits the observations involves delamination and southward rollback of the african lithospheric mantle under the alboran and rif domains

crustal types and tertiary tectonic evolution of the alboran sea western mediterranean multichannel seismic reflection images across the transition between the east alboran and the algero balearic basins show how crustal thickness decreases from about 5 s two way traveltime twtt 15 km thick in the west east alboran basin to 2 s twtt typical of oceanic crust 6 km thick in the east algero balearic basin we have differentiated three different crustal domains in this transition mainly on the basis of crustal thickness and seismic signature boundaries between the three crustal domains are transitional and lack evidence for major faults tilted blocks related to extension are very scarce and all sampled basement outcrops are volcanic suggesting a strong relationship between magmatism and crustal structure stratigraphic correlation of lithoseismic units with sedimentary units of southeastern betic basins indicates that sediments onlap igneous basement approximately at 12 ma in the eastern area and at 8 ma in the western area linking seismic crustal structure with magmatic geochemical evidence suggests that the three differentiated crustal domains may represent from west to east thin continental crust modified by arc magmatism magmatic arc crust and oceanic crust middle to late miocene arc and oceanic crust formation in the east alboran and algero balearic basins respectively occurred during westward migration of the gibraltar accretionary wedge and shortening in the betic rif foreland basins arc magmatism and associated backarc oceanic crust formation were related to early to middle miocene subduction and rollback of the flysch trough oceanic basement subduction of this narrow slab beneath the alboran basin was coeval with collision of the alboran domain with the iberian and african passive margins and subsequent subcontinental lithosphere edge delamination along the betic rif margins

new gps constraints on active deformation along the africa iberia plate boundary abstract we use velocities from 65 continuous stations and 31 survey mode gps sites as well as kinematic modeling to investigate present day deformation along the africa iberia plate boundary zone in the western mediterranean region the gps velocity field shows southwestward motion of the central part of the rif mountains in northern morocco with respect to africa varying between 3 5 and 4 0 mm yr consistent with prior published results stations in the southwestern part of the betic mountains of southern spain move west southwest with respect to eurasia 2 3 mm yr the western component of betics motion is consistent with partial transfer of nubia eurasia plate motion into the southern betics the southward component of betics motion with respect to iberia is kinematically consistent with south to southwest motion of the rif mountains with respect to africa we use block modeling constrained by mapped surface faults and seismicity to estimate the geometry and rates of strain accumulation on plate boundary structures our preferred plate boundary geometry includes one block between iberia and africa including the sw betics alboran sea and central rif this geometry provides a good fit to the observed motions suggesting a wide transpressive boundary in the westernmost mediterranean with deformation mainly accommodated by the gloria azores fault system to the west and the rif tell lineament to the east block boundaries encompass aspects of earlier interpretations suggesting three main deformation styles i extension along the ne sw trending trans alboran shear zone ii dextral strike slip in the betics corresponding to a well defined e w seismic lineament and iii right lateral strike slip motion extending west to the azores and right lateral motion with compression extending east along the algerian tell we interpret differential motion in the rif alboran betic system to be driven both by surface processes related the africa eurasia oblique convergence and sub crustal dynamic processes associated with the long history of subduction of the neotethys ocean lithosphere the dextral slip identified in the betic mountains in southern spain may be related to the offshore fault that produced the great 1755 lisbon earthquake and as such may represent a significant seismic hazard for the west mediterranean region

microearthquake seismicity and fault plane solutions around the nekor strike slip fault morocco abstract three hundred and twenty eight earthquakes recorded in the course of 5 weeks in 1989 in the central rif of northern morocco provided no evidence for activity on the nekor fault the principal geological structure in the region itself most of the seismicity is located northwest of the nekor fault most of the 41 fault plane solutions show mainly strike slip motion left lateral on n s striking planes with p axes trending n145 this deformation is consistent with the n s trending normal faults caused by the e w quaternary extension and with the present relative nw se convergence between africa and europe the active deformation around the eastern rif is better represented by a distributed shear zone than by a strike slip fault

extensional tectonics graben development and fault terminations in the eastern rif bokoya ras afraou area abstract westward motion of the alboran domain between the eurasian and african plate boundaries determined crustal thickening along the southern border of the gibraltar arc forming the rif cordillera this process developed major sinistral ne sw to ene wsw faults such as the nekor fault inactive since the late miocene however the neogene quaternary boudinar and nekor basins underwent very intense recent tectonic and seismic activity related to n s faults kinematics of this fault set changes with depth while at 10 km faults have a sinistral strike slip kinematics they become normal to normal oblique at surface sfeha trougout and boudinar faults their different kinematics could be explained by the existence of a crustal detachment separating two differently pre structured domains shallow transtensive n s faults trend orthogonal to the coastline decreasing their slip southwards until disappearing paleostress analysis shows a progressive change from e w extension near the coastline up to radial extension in southern areas of major fault terminations the behavior of each fault bounded block is conditioned by its inherited rheological features the sequence of horsts bokoya ras tarf ras afraou corresponds mainly to resistant rocks volcanics or limestones whereas the grabens nekor and boudinar basins are generally floored by weak metapelites and flysch the presence of liquefaction structures interpreted as seismites underlines the continued recent seismic activity of the region the recent structures deforming the two alboran sea margins come to support the continuity at present of orogenic processes undergone by the eastern internal regions of the gibraltar arc involving regional e w extension in the framework of nw se to n s eurasian african convergence

evidence for active subduction beneath gibraltar we report on a marine seismic survey that images an active accretionary wedge west of gibraltar ramp thrusts offset the seafloor and sole out to an east dipping decollement indicating ongoing westward vergent tectonic shortening new traveltime tomographic re sults image a slab of oceanic lithosphere descending from the atlantic domain of the gulf of cadiz passing through intermediate depth 60 120 km seismicity beneath the west ernmost alboran sea and merging with a region of deep focus earthquakes 600 660 km below granada spain together these new data provide compelling evidence for an active east dipping subduction zone

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

development of asymmetric basins along continental transform faults abstract many basins associated with wrench or transform faults are asymmetrical both longitudinally and laterally the sense of basin asymmetry changes along the strike of transform faults geophysical data from the dead sea rift and other transforms indicate that wrench induced asymmetric basins are bounded on only one side by a transform fault this implies that during the evolution of such basins maximum compression was parallel to the transform the direction of extension can change during the geologic evolution of a basin a possible explanation of this observation takes the strength of the fault into into consideration in the case of a weak fault in a strong crust the horizontal principal stresses would probably rotate to orientations parallel and perpendicular to the fault thus minimizing the shear stress on the main fault basins formed by regional extension such as in the east african rift system sometimes show similar features recent studies have shown that these basins often undergo oblique extension this suggests that the asymmetry in these basins may result from simultaneous strike slip motion and fault normal extension similar to the way asymmetry is produced in large transform basins periods of oblique extension can alternate with periods of orthogonal extension the asymmetry formed during periods of oblique extension is often preserved in the stratigraphic record

high resolution imagery of active faulting offshore al hoceima northern morocco abstract two recent destructive earthquakes in 1994 and 2004 near al hoceima highlight that the northern moroccan margin is one of the most seismically active regions of the western mediterranean area despite onshore geodetic seismological and tectonic field studies the onshore offshore location and extent of the main active faults remain poorly constrained offshore al hoceima high resolution seismic reflection and swath bathymetry have been recently acquired during the marlboro 2 cruise these data at shallow water depth close to the coast allow us to describe the location continuity and geometry of three active faults bounding the offshore nekor basin the well expressed normal left lateral onshore trougout fault can be followed offshore during several kilometers with a n171 e 3 trend westward the bousekkour aghbal normal left lateral onshore fault is expressed offshore with a n020 e 4 trending fault the n030 e 2 bokkoya fault corresponds to the western boundary of the plio quaternary offshore nekor basin in the al hoceima bay and seems to define an en echelon tectonic pattern with the bousekkour aghbal fault we propose that these three faults are part of the complex transtensional system between the nekor fault and the al idrissi fault zone our characterization of the offshore expression of active faulting in the al hoceima region is consistent with the geometry and nature of the active fault planes deduced from onshore geomorphological and morphotectonic analyses as well as seismological geodetic and geodynamic data

la marge meridionale de la mer d alboran caracteres structuro sedimentaires et evolution recente abstract high resolution seismic reflection profiles 2000 km were collected across the southern continental margin and major structural trends of the alboran sea seismic units are dated on the basis of well known marine neogene onshore sections and offshore dredged samples a better assessment of margin structuration and neogene chronology is made a conformable succession of pliocene quaternary and older series provides evidence for the non evaporitic nature of the upper miocene similar to the facies from the onshore neogene boudinar and melilla basins it also suggests that alboran ridge is in part sedimentary rather than only volcanic this ridge appears as an en echelon anticlinal complex conformable upper miocene and lower pliocene quaternary strata are folded and faulted primarily important manifestation of the movements is dated as pliocene but the main vertical relative movements are of quaternary to recent age as emphasized by well developed divergent strata lying above submarine volcanism probably miocene in age often controls the morphology and structure of the eastern moroccan continental margin and adjacent south alboran basin the latter one is characterised by a thick sedimentary accumulation it is tectonically bounded except on the southwestern part seaward of the bokkoyas cliffs vertical movements occur during much of plio quaternary time prevailing during the quaternary the structure and related morphology of the study area are mainly the result of neotectonic events