active crustal deformation from the azores triple junction to the middle east the co seismic crustal deformation along the africa eurasia eurasia arabia plate boundary from the azores triple junction 30 w up to the karliova triple junction 41 e is examined based on the moment tensor summation of mainly post 1964 earthquakes with ms 5 0 strain rates range from 10 8 yr to 10 6 yr while values exceeding 10 7 yr were calculated for the back arc aegean area and for the north anatolian fault zone a remarkable stability in the azimuth of the component of compression and of extension is observed in the area that extends west of italy 17 e up to the azores triple junction along this region the deformation is taken up by compression along a mean direction of n140 with rates from 1 1 to 2 8 mm yr and by extension along a mean direction of n50 with rates from 2 4 to 12 0 mm yr at the gloria fault and in the surrounding area dextral strike slip motion occurs at a rate of 11 mm yr from sicily up to the eastern end of the hellenic arc the crust is compressed at azimuths in the range n20 n31 with an average value of 26 5 this compression is occurring at a rate of 1 21 mm yr with an average value of 9 8 mm yr in the back arc aegean area extension is occurring along a mean azimuth of n156 with a rate of 5 2 3 8 mm yr the average shortening rate along the convex side of the hellenic arc is 12 mm yr from the eastern end of the north anatolian fault 41 e up to the northern aegean trough extension along n68 n179 and compression along n158 n89 occurs which results in dextral strike slip motion the rate of extension reduces from east to west from 30 mm yr to 5 mm yr while the rate of compression reduces from 17 mm yr to 5 mm yr the northwards motion of arabia results in a n31 trending compression at a rate of 7 mm yr along the east anatolian fault zone

source mechanism of mining induced seismic events resolution of double couple and non double couple models abstract traditional assumption about a seismic source as a double couple dc can represent a serious limitation for describing mechanisms of mining induced seismic events in mining conditions more general process than a shear slip can occur due to stress concentration on mined out areas we assume both non dc components within the dipole description of the source the moment tensor and a single force we processed five seismic events recorded at driefontein gold mine in south africa to demonstrate that waveform modeling is not successful enough due to poor information about the medium inversion of amplitudes of direct p and s waves is more prospective due to their smaller sensitivity to detail of the medium and possibility to correct them for ray bending and shear wave splitting prior to the inversion moreover we are able to estimate the error of the resulting mechanism due to neglect of ray bending all five events processed display non dc mechanisms which are significant at 95 considering the mismodelling of the rock mass by a homogeneous isotropic medium the source mechanisms are in agreement with the underground mining and geological structures one event has a sub vertical pressure single dipole complemented by an implosion which is the body force equivalent of a collapsing horizontal crack or a burst of a pillar supporting the hangingwall of a mined out area two events have mechanisms close to a pressure single couple all three events are located on pillars two out of these three events can be assigned with a downward single force as an alternative mechanism which matches the amplitude data successfully it is the force equivalent of a mined out area collapse when a rock mass falls from the hangingwall to the footwall the events are however rather strong which would require too large rock mass fallen one of the remaining events is a nearly horizontal tensile single couple corresponding to a vertical tensional fault it could be originated by a break of the hangingwall of a mined out area however the hypocenter of this event is deep into the footwall were there is no mining taking place the last event is mostly dc accompanied by a compensated compressive dipole which may be associated to nearly vertical dip slip along a fault in the hangingwall this event is located on the margin of a wide pillar which supports the interpretation

source analysis of the february 12th 2007 mw 6 0 horseshoe earthquake implications for the 1755 lisbon earthquake 1 while very large earthquakes are generally confined to subduction zones the sw iberian margin setting of the famous mw 8 5 8 7 1755 lisbon tsunami earthquake may be an exception to this rule evidence for active subduction is not conclusive here but instead plate convergence in old oceanic lithosphere with large brittle layer thickness can account for the occurrence of great earthquakes along moderate length faults we estimate the source parameters of the february 12th 2007 horseshoe earthquake regional moment tensor inversion yields an mw 6 0 reverse to strike slip faulting source in the upper mantle modelling teleseismic surface reflected body waves pp pwp sp indicates a source depth of 40 km beneath the seafloor analysing apparent source time functions allows identifying the preferred fault plane strike n245 e dip 55 rake 50 and estimating rupture area 53 km2 and average slip 0 27 m scaling the source characteristics to the size of the 1755 earthquake suggests a fault length of 230 315 km being compatible with the length of mapped faults in the area

geodynamic evolution of the lithosphere and upper mantle beneath the alboran region of the western mediterranean constraints from travel time tomography an edited version of this paper was published by the american geophysical union copyright 2000 agu see also http www agu org pubs crossref 2000 2000jb900024 shtml http atlas geo cornell edu morocco publications calvert2000 htm

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

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

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

efficient calculation of complete differential seismograms for laterally homogeneous earth models summary differential seismograms the sensitivity of the seismogram to perturbations of parameters of the earth model are essential for waveform modelling with iterative non linear optimization techniques the growing number of broad band highdynamic range fixed and portable stations provide a rich data set of regional distance events with accurate locations and source mechanisms that are ideal for modelling lithospheric structure an efficient technique for calculating differential seismograms for complete synthetic seismograms in laterally homogeneous earth models will significantly decrease the computational burden of seismic waveform inverse modelling the technique we present here is equivalent to computing three synthetic seismograms in multilayered models contrasted with n 1 seismograms for a typical brute force approach which reduces the work to 3 n 1 or about a 90 per cent saving for 30 layers the lateral homogeneity requirement will yield path averaged structures which may form the basis for later tomographic studies to resolve lateral variations

crust and upper mantle shear wave structure of northeast algeria from rayleigh wave dispersion analysis abstract we resolve the crust and upper mantle structure beneath northeast algeria at depths of 0 400 km using inversion of fundamental mode rayleigh wave our data set consists of 490 earthquakes recorded between 2007 and 2014 by five permanent broadband seismic stations in the study area applying a combination of different filtering technics and inversion method shear wave velocities structure were determined as functions of depth the resolved changes in vs at 50 km depth are in perfect agreement with crustal thickness estimates which reflect the study area s orogenic setting partly overlying the collision zone between the african and eurasian plates the inferred moho discontinuity depths are close to those estimated for other convergent areas in addition there is good agreement between our results and variations in orientations of regional seismic anisotropy at depths of 80 180 km negative vs anomalies at station cbbr suggest the existence of a failed subduction slab

point source inversion techniques abstract a variety of approaches for obtaining source parameters from waveform data using moment tensor or dislocation point source models have been investigated and applied to long period body and surface waves from several earthquakes generalized inversion techniques have been applied to data for long period teleseismic body waves to obtain the orientation time function and depth of the 1978 thessaloniki greece event of the 1971 san fernando event and of several events associated with the 1963 induced seismicity sequence at kariba africa the generalized inversion technique and a systematic grid testing technique have also been used to place meaningful constraints on mechanisms determined from very sparse data sets a single station with high quality three component waveform data is often sufficient to discriminate faulting type e g strike slip etc sparse data sets for several recent california earthquakes for a small regional event associated with the koyna india reservoir and for several events at the kariba reservoir have been investigated in this way although linearized inversion techniques using the moment tensor model are often robust even for sparse data sets there are instances where the simplifying assumption of a single point source is inadequate to model the data successfully numerical experiments utilizing synthetic data and actual data for the 1971 san fernando earthquake graphically demonstrate that severe problems may be encountered if source finiteness effects are ignored these techniques are generally applicable to on line processing of high quality digital data but source complexity and inadequacy of the assumed green s functions are major problems which are yet to be fully addressed

a multidisciplinary geophysical study in the betic chain southern iberia peninsula abstract the combined analysis of magnetotelluric measurements tomographic velocity models and deep seismic reflection images confirms that the betics orogen consists of the juxtaposition of two crustal domains characterized by distinctive physical properties at depth these data sets show evidence for a non coincidence of the petrological and the seismic moho beneath the betics chain the data sets reveal the geophysical properties of the alboran domain internal betics and the iberian massif external betics according to this the iberian crust features a relatively high seismic velocity is seismically transparent in the seismic reflection images and is electrically resistive the alboran domain crust is characterized by a low average velocity displays high reflectivity in the seismic reflection images and is electrically conductive the outcrops of the metamorphic complexes alpujarride and nevado filabride showing relatively high velocities coupled with low v p v s values 1 67 derived from the wadati slopes suggest the existence of rocks rich in silica beneath the alboran domain crust an interpreted detachment at 12 km depth imaged by deep seismic reflection suggests that these rocks could be related to the iberian upper crust partial melts and fluids are proposed to explain the high conductivity observed at deep crustal levels these would account also for the reflectivity and the low v p v s ratios mapped beneath the alboran domain

local stress fields and intraplate deformation of iberia variations in spatial and temporal interplay of regional stress sources tertiary to present deformation in the interior of the iberian peninsula reflects spatial and temporal variations of the activity of the plate boundaries local deformation patterns observed in many of the numerous intraplate tertiary basins and their borders such as the madrid basin and the sierra de altomira are at first sight incompatible with the regional stress field under which they were formed we demonstrate however that they can be explained as the effect of several stress fields that acted on the iberian peninsula from earliest tertiary onward data on local deformation can constrain both magnitudes and directions of forces acting on the plate boundaries of iberia enabling us to estimate the relative importance of the different plate driving and deforming mechanisms providing further constraints on the tectonic evolution of iberia

seismogenic stress field estimation in the calabrian arc region south italy from a bayesian approach a new high quality waveform inversion focal mechanism database of the calabrian arc region has been compiled by integrating 292 mechanisms selected from literature and catalogs with 146 newly computed solutions the new database has then been used for computation of posterior density distributions of stress tensor components by a bayesian method never applied in south italy before the present study the application of this method to the enhanced database has allowed us to provide a detailed picture of seismotectonic stress regimes in this very complex area where lithospheric unit configuration and geodynamic engines are still strongly debated our results well constrain the extensional domain of calabrian arc and the compressional one of the southernmost tyrrhenian sea in addition previously undetected transcurrent regimes have been identified in the ionian offshore the new information released here will furnish useful tools and constraints for future geodynamic investigations

2 d seismic modeling of the variscan foreland thrust and fold belt crust in nw spain from escin 1 deep seismic reflection data abstract the foreland thrust and fold belt cantabrian zone of the variscan belt in nw spain and the transition to the hinterland westasturian leonese zone was the location of a seismic experiment in 1991 the seismic reflection profile escin 1 is 140 km long and runs in an e w direction the interpretation and seismic modeling of the main reflective interfaces in the profile were made integrating available geological and geophysical data including surface geology deep seismic reflection data from escin 1 transmission velocities from a borehole refraction and laboratory data the geological and velocity model of the crust was tested obtaining synthetic seismograms and can be correlated with surface geology the velocity model images the main crustal structures interpreted from escin 1 the basal detachment of the foreland thrust and fold belt dips gently from 12 km in the easternmost part of the profile to 16 km in the transition to the hinterland to the west a new interpretation is proposed for the structure above the basal detachment in the eastern end of the profile where the basal detachment at a depth of 12 km is duplicated at 6 5 km by a n dipping alpine thrust that also duplicates part of the basement in the western part two deep reflective bands dip westward and the most conspicuous one can be followed from 16 27 km depth the two bands previously interpreted as crustal ramps join a reflective lower crust that is located between 25 and 29 km and fades westwards a reflective moho interpreted at the base of the reflective lower crust dips and fades in the same direction from 30 34 km

recent and present day stresses in the granada basin betic cordilleras example of a late miocene present day extensional basin in a convergent plate boundary the diffuse convergent boundary between the eurasian and african plates in the western mediterranean is associated with a seismicity zone more than 300 km wide although the two plates are converging nw se the betic and rif cordilleras contain extensional structures that have been active since the miocene the extensional tectonics in the region which occurred simultaneously with the uplift of the cordillera have been analyzed in the southeastern sector of the late miocene to recent granada basin using earthquake focal mechanisms the determination of paleostresses from the study of the orientation and kinematics of microfaults and the study of the major structures both the geological surface data and the focal mechanisms indicate present day regional conditions of ne sw extension with triaxial to prolate stress ellipsoids however the stress field is heterogeneous with local variations in stress over time with different stresses sometimes even acting simultaneously in adjacent areas the most frequent changes consist of pluridirectional or ne sw extension favored by the prolate character of the stress ellipsoids and nw se subhorizontal compression favored by the regional tectonic setting strike slip faults are scarce even though they are the most likely structure to be expected in a region with sw ne extension and nw se compression seismicity is concentrated in the upper crust and may correspond to the activity of low to high angle normal faults similar to the surface faults although they can not be correlated with them the lower cutoff of this seismicity probably coincides with the 300 c isotherm and suggests a low thermal gradient for the region present day regional stresses have 1 vertical at the surface but in depth plunge toward the sw

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

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

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

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

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

nucleation linkage and active propagation of a segmented quaternary normal dextral fault the loma del viento fault campo de dalias eastern betic cordillera se spain active faults from the campo de dalias se betic cordillera allow us to constrain the deformation styles involved in the development of segmented oblique slip faults this sector constitutes the widest outcrop of plio quaternary sediments in the northern boundary of the alboran sea it has emerged since the late pliocene and therefore provides recent deformation markers that are not disturbed by erosive processes the faults started to grow during the pleistocene reactivating previous hybrid joints with a normal dextral slip we present a detailed map of the largest fault in the area the loma del viento fault comprising six onshore segments based on field work and aerial photography the distributions of the contiguous joints have been mapped and the joints reactivated as faults are identified some of these fault segments are hard linked and fault slip enhances toward the linkage sectors between them with associated sedimentary depocenters an electrical tomography profile reveals the wedge geometry of a unit of pleistocene conglomerates and red silts that were coevally deposited during the fault movement long term slip rate in the central part of the fault is estimated at 0 07 0 03 mm y in addition a seismic crisis nucleated close to the loma del viento fault during november 2010 was recorded moment tensor analysis of the two mainshocks mw 3 5 and 4 2 provides a focal solution indicating a n120 e striking right lateral strike slip fault the corrugated morphology of the loma del viento fault may have influenced its seismic behavior some of the fault segments are oblique to the general motion of the fault these oblique segments would provide higher resistance against the general fault motion and could lock the fault leading to accumulate elastic energy

source parameters of the mw 6 1 1910 adra earthquake southern spain summary we examine and model analogue recordings from 6 early mechanical seismographs for the 1910 june 16 earthquake at adra southern spain modern standard time domain analysis techniques were applied to the historical data to estimate the source parameters of the event the regional sparse network data were inverted for the deviatoric seismic moment tensor the best moment tensor solution corresponds to a m0 1 50 1018 nm mw 6 1 oblique strike slip event at 16 km depth our preferred faulting solution is strike 122 dip 80 rake 137 in very good agreement with available neo and seismotectonic data the source time function of this earthquake was estimated by deconvolving recordings of a mw 5 5 aftershock that occurred the same day the time function indicates a total rupture time of 4 5 s corresponding to estimates for mainshock rupture length of 12 km and stress drop of 29 bar

mechanism of the 1992 erzincan earthquake and its aftershocks tectonics of the erzincan basin and decoupling on the north anatolian fault summary the 1992 march 13 erzincan earthquake ms 6 8 affected the erzincan basin on the eastern part of the north anatolian fault naf this event occurred on the eastern tip of a westward propagating series of major north anatolian earthquakes between 1939 and 1967 ambraseys 1970 it is located within a key region of eastern anatolia which displays both expulsion of the anatolian block towards the west and regional n s convergence due to the arabian eurasian collision philip et al 1989 a reinterpretation of the tectonics of the erzincan basin is made from field information and the analysis of satellite images a model explaining the development of the basin is proposed it combines a pull apart on the naf with the effect of two compressional wedges one is formed by the northeast anatolian fault neaf and the naf the other around pulumur is limited by the ovacik fault of and the naf both e w extension and n s compression occur according to this model normal faulting on the southwestern border and extension related quaternary rhyolitic volcanic domes along the northeastern boundary of the basin support the proposed e w extension the block limiting the southern side of the basin is uplifted and displaced left laterally along the of suggesting southward growth of the basin a kinematic model of the 1992 erzincan earthquake combines aftershock field information neotectonic observations satellite image interpretation and bodywaveform inversion the complex earthquake rupture starts on the naf and propagates bilaterally westward rupture propagation progresses along the northern border of the basin eastward propagation is shifted on a segment of the naf south of the euphrates and ends within the pulumur wedge both branches are connected by a system of normal faults the main focal mechanism is strike slip with a slight normal component o 122 63 164 the strongest aftershock mechanism is compatible with n s compression within the pulumur wedge aftershock mechanisms and stress tensor analyses give detailed insight into the earthquake sequence the 1992 erzincan earthquake is located between two segments of the naf that suffered large destructive earthquakes in the past the 1939 earthquake ms 8 2 ruptured 370 km west of erzincan the last major earthquake east of the erzincan basin occurred in 1784 rupturing a segment of at least 75 km length this area has displayed a seismic gap since then the mechanism of the main shock and the absence of aftershock activity east of tanyeri indicate decoupling between the 1992 event and the 1784 gap aftershocks within the pulumur wedge suggest that the probability of the occurrence of a future earthquake is higher on the of than in the 1784 earthquake gap

european mediterranean regional centroid moment tensors 1997 2000 the mediterranean region is seismically very active and undergoing rapid deformation earthquakes as strong as m 6 are present but relatively rare on the other hand moderate magnitude seismicity 4 5 m 5 5 is widespread and often damaging an improved knowedge of moderate magnitude earthquakes can contribute significantly to a better understanding of active tectonics in the region harvard centroid moment tensors cmt today represent the most widely used reference for reliable source mechanisms but modelling seismic sources with the cmt technique for earthquakes with magnitude less than m 5 5 5 is quite difficult since 1997 we are using an extension of the standard cmt algorithm to compute regional centroid moment tensors rcmt for moderate magnitude earthquakes mw as low as 4 0 analyzing intermediate period surface waves from regional and teleseismic seismograms we routinely apply the algorithm to european mediterranean seismicity to produce a catalog of seismic moment tensors for events with magnitude between 4 5 and 5 5 which generally are not included in the harvard cmt catalog in this paper we show the results for earthquakes that occurred between 1997 and 2000 consisting of 252 solutions and we discuss the characteristics of the catalog and the areas where these new data are most relevant

scenarios for earthquake generated tsunamis on a complex tectonic area of diffuse deformation and low velocity the alboran sea western mediterranean the tsunami impact on the spanish and north african coasts of the alboran sea generated by several reliable seismic tsunamigenic sources in this area was modeled the tectonic setting is complex and a study of the potential sources from geological data is basic to obtain probable source characteristics the tectonic structures considered in this study as potentially tsunamigenic are the alboran ridge associated structures the carboneras fault zone and the yusuf fault zone we characterized 12 probable tsunamigenic seismic sources in the alboran basin based on the results of recent oceanographical studies the strain rate in the area is low and therefore its seismicity is moderate and cannot be used to infer characteristics of the major seismic sources these sources have been used as input for the numerical simulation of the wave propagation based on the solution of the nonlinear shallow water equations through a finite difference technique we calculated the maximum wave elevations and tsunami travel times using the numerical simulations the results are shown as maps and profiles along the spanish and african coasts the sources associated with the alboran ridge show the maximum potential to generate damaging tsunamis with maximum wave elevations in front of the coast exceeding 1 5 m the carboneras and yusuf faults are not capable of generating disastrous tsunamis on their own although their proximity to the coast could trigger landslides and associated sea disturbances the areas which are more exposed to the impact of tsunamis generated in the alboran sea are the spanish coast between malaga and adra and the african coast between alhoceima and melilla

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

moment tensor resolvability application to southwest iberia abstract we present a method to assess the uncertainty of earthquake focal mechanisms based on the standard theory of linear inverse problems we compute the uncertainty of the moment tensor m then map it into uncertainties of the strike dip and rake the inputs are source and station locations crustal model frequency band of interest and an estimate of data error the output is a six dimensional 6d error ellipsoid which shows the uncertainty of the individual parameters of m we focus on the double couple dc part of m the method is applicable both with and without waveforms the latter is particularly useful for network design as an example we present maps of dc resolvability for earthquakes in southwest europe computed without waveforms we find that the resolvability depends critically on frequency range and source depth shallow dc sources 10 km are theoretically better resolved than deeper sources 40 km and 60 km the dc resolvability of a 40 km deep event improves considerably when the portuguese network is supplemented by stations in spain and morocco the dc resolvability can be further improved by using a few ocean bottom seismometer obs stations or a dense land network a dense land network is able to resolve m well in spite of the large azimuthal gap which spans 200 the theoretical resolution analysis also explains the success of single station inversions when using a broad frequency range as exemplified by an application using waveforms of a m w 6 earthquake offshore iberia

seismicity analysis at the prestige oil tanker wreck area galicia margin nw of iberia an evaluation of the geological hazard related to the sinking of the prestige oil tanker in november 2002 in the galicia margin nw of iberia was supported by the spanish research agency it included a specific seismic study of the local activity and of the regional seismicity in this margin results of which are presented here published global catalogues show that diffuse seismicity of moderate magnitude events up to 5 6 mb can be associated with the northern flank of the galicia margin with a roughly e w distribution however event locations in this area are poorly constrained due to the inappropriate geometry of permanent seismic networks we collected and analyzed new data from a dense deployment of 10 obs around the wreck site and from a network of 12 land stations at the nw corner of iberia during a 7 months operation period the land network permitted location of 120 events with magnitudes ranging from 1 6 to 4 8 more than 30 of which were not reported by the spanish permanent array confirming the existence of a moderate seismicity in this area five new focal solutions have been obtained for events on land providing additional information about the active faults in the region the obs network ran for 1 month and allowed the location of three earthquakes of magnitude 2 5 near the sinking site four more events have been identified with just a rough determination of their epicenters based on polarization of the p wave arrivals besides these earthquakes the obs data recorded numerous seismic events of different types they include i groups of very short and regularly spaced pulses that can be explained as acoustic calls generated by finback whales ii a large number of short duration seismic events 2 3 s long identified only at individual obs iii local intense monochromatic signals lasting for up to 4 h that can be described as harmonic tremors these last two types of seismic events might be related to hydrothermal activity within the uppermost sediments and deserve additional studies to appropriately establish the seismic hazard of this area 2007 elsevier b v all rights reserved

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

faulting parameters of the 1999 mula earthquake southeastern spain abstract the seismicity of southern spain is characterized by low to moderate earthquake activity magnitudes

end member modelling as an aid to diagnose remagnetization a brief review remagnetization of a palaeomagnetic signal is difficult to recognize independently of directional information the situation becomes more complex when remagnetized rocks pass palaeomagnetic field tests for example when the remagnetization of a rock sequence has occurred before folding it is evident that palaeogeographic reconstructions are seriously flawed when actu ally remagnetized rocks are not identified as such here we discuss the merits and pitfalls of so called end member modelling of acquisition curves of the isothermal remanent magnetization irm to recognize remagnetized strata the technique requires no a priori information about the irm acquisition curves the algorithm unmixes a set of irm acquisition curves into a number of invariant curves termed end members and calculates the mixing proportions of the end members for each sample since primary natural remanent magnetization nrm and remag netized nrm are acquired by different processes their signatures can be recognized from subtle differences in the magnetic properties we illustrate the potential of the approach by three case studies one from spain and two from turkey in which the magnetic properties of remagnetized and non remagnetized rocks are evaluated the natural remanent magnetization nrm of a rock is described asremagnetized when itrepresents apalaeomagnetically younger age thanthe sediment age of the rock formation under study remagneti zation interferes with palaeogeographic reconstruc tions asisincreasinglybeingappreciated the late palaeozoic remagnetization event was firmly rec ognized in the appalachians in the usa in the early 1980s e g mccabe et al 1983 see the review of van der voo torsvik 2012 while the implica tionsoflatepalaeozoicremagnetizationineuropean

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

the recent upper miocene to quaternary and present tectonic stress distributions in the iberian peninsula a general synthesis of the recent and present stress situation and evolution in the iberian peninsula was obtained from microstructural and seismological analysis the stress evolution was deduced from 1 fault population analysis fpa from 409 sites distributed throughout the iberian peninsula 2 paleostress indicators given by 324 stations taken from the bibliography and 3 seismic data corresponding to 161 focal mechanisms evenly spread in the studied region the application of fpa together with the determination of stress tensors and focal mechanisms for the whole iberian microplate has provided two main results 1 the iberian peninsula is undergoing a nw se oriented compression except for the northeastern part pyrenees ebro basin and iberian chain where it is n s to ne sw and the gulf of cadiz where it seems to be e w and 2 the main trends of the stress field have remained almost constant since the upper miocene the analysis performed by zones suggests the presence of local heterogeneities in the stress field

seismic source and structure estimation in the western mediterranean using a sparse broadband network we present a study of regional earthquakes in the western mediterranean geared toward the development of methodologies and path calibrations for source characterization using regional broadband stations the results of this study are useful for the monitoring and discrimination of seismic events under a comprehensive test ban treaty as well as the routine analysis of seismicity and seismic hazard using a sparse array of stations the area consists of several contrasting geological provinces with distinct seismic properties which complicates the modeling of seismic wave propagation we started by analyzing surface wave group velocities throughout the region and developed a preliminary model for each of the major geological provinces we found variations of crustal thickness ranging from 45 km under the atlas and betic mountains and 37 km under the saharan shield to 20 km for the oceanic crust of the western mediterranean sea which is consistent with earlier works throughout most of the region the upper mantle velocities are low which is typical for tectonically active regions the most complex areas in terms of wave propagation are the betic cordillera in southern spain and its north african counterparts the rif and tell atlas mountains as well as the alboran sea between spain and morocco the complexity of the wave propagation in these regions is probably due to the sharp velocity contrasts between the oceanic and continental regions as well as the the existence of deep sedimentary basins that have a very strong influence on the surface wave dispersion we used this preliminary regionalized velocity model to correct the surface wave source spectra for propagation effects which we then inverted for source mechanism we found that this method which is in use in many parts of the world works very well provided that data from several stations are available in order to study the events in the region using very few broadband stations or even a single station we developed a hybrid inversion method which combines p nl waveforms synthesized with the traditional body wave methods with surface waves that are computed using normal modes this procedure facilitates the inclusion of laterally varying structure in the green s functions for the surface waves and allows us to determine source mechanisms for many of the larger earthquakes m 4 throughout the region with just one station we compared our results with those available from other methods and found that they agree quite well the epicentral depths that we have obtained from regional waveforms are consistent with observed teleseismic depth phases as far as they are available we also show that the particular upper mantle structure under the region causes the various p n and s n phases to be impulsive which makes them a useful tool for depth determination as well thus we conclude that with proper calibration of the seismic structure in the region and high quality broadband data it is now possible to characterize and study events in this region both with respect to mechanism and depth with a limited distribution of regional broadband stations

testing the sensitivity of geomorphic indices in areas of low rate active folding eastern betic cordillera spain abstract active deformation structures have an incidence in topography that can be quantified by using geomorphic indices most of these indices have been checked in faulted regions with high deformation rates the application of several geomorphic indices hypsometric curve analysis normalized stream length gradient and valley width to valley height ratio to the drainage network of the southern limb of the sierra de las estancias antiform internal zones eastern betic cordillera where low rate active folding has been recognized allows us to investigate the suitability of these indices to identify active structures in such a scenario hypsometric curves clearly identify regions with recent uplift and young topography but they do not provide any constraint on the location of active folds local valley width to valley height index variations have been detected just coinciding whit the position of ene wsw active folds normalized stream length gradient index serves to locate active folds in areas of hard rock substratum but not in those areas with soft sediments neogene quaternary sedimentary basins this is most likely due to the fact that in the basins erosion is much more intense than in the hard rock sectors in view of these results we consider that geomorphic indices constitute a valuable tool for identifying sectors affected by low rate uplift related to active folding with the best results obtained in hard rock areas

a deep seismic sounding investigation of lithospheric heterogeneity and anisotropy beneath the iberian peninsula abstract the dimensions of the iberian peninsula the facility of firing large charges in the surrounding waters the well known and relatively uniform geology and prior knowledge of the crustal structure resulted in it being chosen as a study area for the investigation of the seismic structure of the lower lithosphere via refraction wide angle reflection seismic profiling the iberian lithosphere heterogeneity and anisotropy experiment iliha with a star shaped arrangement of six long range dss profiles was carried out in october 1989 the models derived from a first interpretation of the recorded data are presented three crustal profiles cover the same western and central part of the hercynian massif as the mantle profiles the resulting interpretations all include a middle as well as a lower crustal layer above the mantle the velocities of the layers in all three models are similar however the layer depths vary beneath the profiles interpretation of the mantle derived data suggests a layered lower lithosphere one reversed line and an intersecting unreversed line indicate the layering penetrates to at least 90 km depth the homogeneity of these layers contrasts strongly with the heterogeneous hercynian surface geology velocities derived from reflected data from the deep layers suggest the constituent materials are either anisotropic or that the layers suffer a slight regional dip

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

neotectonic fault mapping at the gibraltar strait tunnel area bolonia bay south spain abstract a map of fault activity has been developed for preliminary engineering planning related to the construction of an underwater fixed link route between africa and europe at the gibraltar strait sector in south spain the gibraltar tunnel main criteria used in fault activity evaluation have been seismicity surface faulting geomorphology of fault traces identification of paleoseismic ground failures and evaluation of differential uplift rates on coastal segments separated by large scale inland faults the aim of this work is the development of comprehensive methodology for the graphic representation chart format of geo hazards related to ground conditions seismicity and fault activity the criteria management is mainly focused on the establishment of the seismic or aseismic character of individual fault traces for this the age of the last deformational event and slip rates where possible are taken into account but their classification as active or inactive structures is avoided from this study the cabo de gracia strike slip fault ne sw can be catalogued as active during at least the last 128 ka bp and as a probable seismic source of moderate events mb

multiplet focal mechanisms from polarities and relative locations the iznajar swarm in southern spain abstract in april 1998 a swarm of 1800 microearthquakes near the village of iznajar southern spain was recorded at the granada basin short period seismic network focal mechanisms from local p wave polarities are poorly constrained and cannot characterize the seismotectonics of the series here we combine polarity information and multiplet relocation to address this issue we use waveform cross correlation on p and s arrivals to identify events with highly similar seismograms group our detections into multiplet clusters and invert the cross correlation time delays to obtain precise relative locations relative locations have errors of several tens to a few hundreds of meters horizontally and vertically and define strike and dip of active fault patches with an accuracy of 20 30 we introduce the multiplet fault plane orientations into focal mechanism inversion now yielding mostly well constrained solutions in addition to resolving the nodal plane symmetry we observe mainly north south left lateral strike slip faulting and a few north northwest south southeast normal faulting solutions illustrating the kinematic complexity of the swarm and pointing to a local deformation style different from the nearby granada basin

moment tensor inversion with single component historical seismograms the 1909 benavente portugal and lambesc france earthquakes summary moment tensor inversion of early xx century mechanical seismograph recordings offers the opportunity to estimate source parameters for a number of important earthquakes this knowledge is crucial for understanding regional tectonics and estimating seismic hazard but processing of the historical seismograms is often difficult especially the rotation of horizontal seismograms into radial p sv and transverse sh components tends to fail for example if one polarity is wrong if the alignment of the seismograms is not correct or if one component is lost to avoid these kind of problems we use a moment tensor inversion scheme that processes the original single component horizontal traces without rotation and rotates the theoretical green s functions instead we show how this approach simplifies the analysis and allows a better use of available data we present moment tensor solutions for two destructive earthquakes in southwestern europe in 1909 the april 23 earthquake near benavente in the lower tagus valley portugal had a moment magnitude mw 6 0 and an estimated centroid depth of 10 km our preferred moment tensor solution indicates reverse faulting nodal planes have strike dip rake of n51 e 52 83 and n242 e 38 99 we propose a blind thrust beneath the tagus valley sediment basin as the responsible fault the june 11 earthquake near lambesc provence france was found to be slightly smaller mw 5 5 and related to oblique reverse faulting at 4 km depth nodal planes of the preferred solution have strike dip rake of n80 e 53 53 and n311 e 50 128 subparallel to the trevaresse fold

lateral variation of the crust in the iberian peninsula new evidence from the betic cordillera abstract new results from a seismic refraction wide angle reflection survey carried out in the betic cordillera in autumn 1989 contribute to a better picture of its deep structure one nw se profile cuts across the iberian massif the external and internal betics the structure of the crust in the iberian massif shows characteristics similar to those found in previous experiments the lower crust is found as a distinct layer 12 km thick with an average velocity of 6 8 km s 1 the moho is found at about 35 km depth this structure extends southeastward until a 3 4 km upwelling of the moho about 30 km north of the present day surface boundary between the external and internal betic units further southeast the moho deepens to 38 km and the lower crust is no longer seismically detected the absence of differentiated lower crust beneath part of the external betics may be related with the mesozoic rifting of the south iberian passive margin instead this absence under the internal betics may be caused by rifting in conjunction with the collisional evolution of the orogen a wnw ese profile lying in the internal betics shows the presence of a prominent reflector at 10 12 km depth this seems to be a widespread feature in the internal betics and may be interpreted as a detachment surface the moho is found at 38 km depth rising strongly in the easternmost betics seismic data suggest a thin crust in the offshore area southwest of malaga probably containing a massive zone of high velocity rocks which is also supported by available geophysical and geological data

crust mantle coupling in the gulf of cadiz sw iberia 1 in the gulf of cadiz and cape st vincent region at the sw iberian margin seismic catalogues report seismicity down to 100 km depth according to structural models for the region this includes earthquakes that occur in the uppermost continental mantle we invert regional waveforms to estimate moment tensors and centroid depths for moderate earthquakes obtaining eight solutions mw 3 8 to 5 3 between 6 and 60 km depth moment tensor solutions and previous source estimates show predominately reverse and strike slip faulting style with nnw sse oriented p axes close to plate convergence between africa and eurasia we obtain similar stress tensor estimates from crustal and upper mantle earthquakes both with sub horizontal nnw 1 axes this indicates analogous deformation in both domains and that earthquakes are unrelated to any subduction process

directivity detection and source properties of the 11 may 2011 mw 5 2 lorca spain earthquake a kinematic finite source study of the 11 may 2011 m w 5 2 lorca spain earthquake has been performed using broadband data from the spanish national network the nodal plane ambiguity of the double couple solution was resolved from finite source analysis and a rupture velocity of 1 8 km s 1 and the northeast southwest striking northwest dipping plane was found to best fit the data this fault plane corresponds to the central sector of the alhama de murcia fault amf the resulting slip distribution has a maximum of 19 3 cm and a total seismic moment of 6 25 1016 n m a jackknife test has been performed to estimate the fault plane errors and their consequences in the slip distribution also synthetic tests have been performed to evaluate the errors in the finite source modeling from this model a prediction of the strong ground motion near the fault corrected for soil amplification is given in terms of peak ground velocity pgv which fits with the observed value at the accelerograph in the city of lorca we also compared the pgv converted to modified mercalli intensity at the surface with the intensity distribution also showing good agreement finally we extracted the directivity pulse from the strong ground motion record at lorca with 0 5 s period in the transverse component to the amf direction and 33 cm s 1 pgv to further analyze the directivity effect we estimate the duration and azimuthal amplitude distribution of the source time functions finding them to be shorter and of greater amplitude in the direction of rupture and longer and smaller in amplitude in the opposite direction

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

fast kinematic waveform inversion and robustness analysis application to the 2007 mw 5 9 horseshoe abyssal plain earthquake offshore southwest iberia an m w 5 9 earthquake occurred beneath the horseshoe abyssal plain hap offshore southwest iberia on 12 february 2007 the region where the earthquake occurred has a high seismogenic and tsunamigenic potential the purpose of this paper is twofold 1 to extract information about the source of the earthquake that contributes to the understanding of regional tectonics and 2 to evaluate the applicability of a fast algorithm to study a moderate earthquake offshore mainland portugal we employed the kiwi tools which implement a multistep inversion algorithm to infer both the point and finite source properties of the earthquake in order to assess the robustness of our solutions we performed independent sets of inversions that take different datasets and assumptions e g green s functions passbands wave types as inputs we also performed bootstrap analyses in order to appraise the robustness of the source parameters we concluded that the 2007 hap earthquake centroid is located at 35 841 n 10 611 w at a depth of 39 km scalar moment m is consistently retrieved with an average value of graphic 1 moment magnitude m w 5 9 the finite fault parameters are difficult to resolve given the existing data approximately 70 of our bootstrap solutions indicate a true rupture plane that trends west northwest east southeast strike 128 dip 46 and rake 138 the location and strike of this fault plane coincide with the southwest iberian margin swim faults however the 46 dip is difficult to reconcile with the subvertical nature of the swim faults online material inversion results using teleseismic data prem and body waves only 1 embed inline graphic 1 gif

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

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

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

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

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

eurid a regionalized 3 d seismological model of europe abstract this paper presents a 3 d regionalized model of the european crust and mantle velocity structure down to depths of approximately 300 km the model is entirely based upon the existing geological and geophysical literature and it incorporates topographic and bathymetric features the resulting model which we call eurid european i data set consists of approximately 6400 1 d vertical structures having an average separation of about 100 km eurid is compared quantitatively with eur s91 a recent s wave velocity tomographic model obtained from body and surface wave waveform inversion zielhuis a nolet g 1994 shear wave velocity variations in the upper mantle beneath central europe geophys j int 117 695 715 it is found that the s wave velocities in eurid and in eur s91 zielhuis and nolet 1994 do not differ by more than about 4 over most of the area to validate eurid surface wave dispersion analysis is performed along some selected paths the fundamental mode group velocity curves obtained using 1 d average models derived from eurid are found in good agreement with those determined from observations broadband waveform synthetics are also calculated along the same paths and compared with the observed time series overall we believe that eurid is representative of our current knowledge of the crust upper mantle structure beneath europe and it can be used to model realistically ground motion for periods above 10 s within structurally homogeneous regions the first digital version of this structure database is available for public use

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

stress relations in three recent seismic series in the murcia region southeastern spain abstract in this work we study the relation between the seismicity belonging to three recent seismic series in the murcia region southeastern spain with the coseismic stress changes due to their largest shocks the first series occurred in 1999 near the town of mula with a mainshock magnitude of mw 5 1 the second series occurred in 2002 in the region of bullas 35 km sw from the 1999 series with events of magnitudes mw 5 0 the last one occurred three years later 2005 5 km se from the 2002 series with magnitudes of events mw 4 8 for the analysis we relocated the seismicity of each series next we computed the coseismic stress change produced by its main events and a foreshock and finally tested the possible stress relations inside and among the series based on the coulomb failure stress changes our results show that the mula 1999 main earthquake associated in different publications to the crevillente fault was positively influenced for triggering by the foreshock we also find that the 1999 series aftershocks were jointly influenced for triggering by both the foreshock and the mainshock events from a comparative analysis of p wave arrivals the series seems to be associated to different neighbouring seismogenic zones belonging to the crevillente system for the bullas 2002 and the bullas la paca series we found that it is unlikely that any of them have been triggered by the previous mula 1999 event but it appears that the main event in 2002 had an important influence on the triggering of its aftershock activity and the promotion of the mainshock and aftershock seismicity in the zone of the 2005 series summing the effects of the last two main events it may have been produced different zones of high stress increase on the aftershock area of the 2002 and 2005 series finally the seismicity of the two latest series could be associated to different neighbouring seismogenic zones

present day state of stress in northern morocco from focal mechanism analysis abstract the use of focal mechanisms of micro earthquakes and moderate teleseisms in the al hoceima area northern morocco enables the determination of the state of stress in the southern part of the gibraltar arc two different states of stress were determined 1 a ene wsw extension in the imzouren area probably with similar magnitudes of 2 and 1 which may be controlled by pre existing structures and 2 a strike slip regime in beni boucetta tamassint and beni abdallah areas 1 nnw sse 3 ene wsw in the two first areas and 1 ne sw 3 nw se in the latter contrary to recently proposed ideas the mean state of stress determined with the help of moderate teleseisms corresponds to a strike slip regime with a nnw sse oriented main compressional axis and a ene wsw horizontal extension similar to the stress field determined from neotectonic studies and somewhat different from that determined from the el asnam aftershock sequence of 1980

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

zemmouri earthquake rupture zone mw 6 8 algeria aftershocks sequence relocation and 3d velocity model 1 we analyze the aftershocks sequence of the zemmouri thrust faulting earthquake 21 may 2003 mw 6 8 located east of algiers in the tell atlas the seismic sequence located during 2 months following the mainshock is made of more than 1500 earthquakes and extends ne sw along a 60 km fault rupture zone crossing the coastline the earthquake relocation was performed using handpicked p and s phases located with the tomodd in a detailed 3d velocity structure of the epicentral area contrasts between velocity patches seem to correlate with contacts between granitic volcanic basement rocks and the sedimentary formation of the eastern mitidja basin the aftershock sequence exhibits at least three seismic clouds and a well defined se dipping main fault geometry that reflects the complex rupture the distribution of seismic events presents a clear contrast between a dense sw zone and a ne zone with scattered aftershocks we observe that the mainshock locates between the sw and ne seismic zones it also lies at the nns sse contact that separates a basement block to the east and sedimentary formations to the west the aftershock distribution also suggests fault bifurcation at the sw end of the fault rupture with a 20 km long n 100 trending seismic cluster with a vertical fault geometry parallel to the coastline juxtaposed another aftershock cloud may correspond to 75 se dipping fault the fault geometry and related sw branches may illustrate the interference between pre existing fault structures and the sw rupture propagation the rupture zone related kinematics and velocity contrasts obtained from the aftershocks distribution are in agreement with the coastal uplift and reflect the characteristics of an active zone controlled by convergent movements at a plate boundary

evidence for active subduction beneath gibraltar comment and reply reply we welcome the opportunity to discuss the geodynamics of the rif betic region and will address the points in the order raised in the comment 1 there is no rigid alboran plate instead a portion of the upper plate the gibraltar block is pulled westward by hydrostatic suction induced by the

geomorphology and neogene tectonic evolution of the palomares continental margin western mediterranean abstract the palomares continental margin is located in the southeastern part of spain the margin main structure was formed during miocene times and it is currently part of the wide deformation zone characterizing the region between the iberian and african plates where no well defined plate boundary occurs the convergence between these two plates is here accommodated by several structures including the left lateral strike slip palomares fault the region is characterized by sparse low to moderate magnitude mw

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

geophysical evidence for a transform margin offshore western algeria a witness of a subduction transform edge propagator for the first time a deep seismic data set acquired in the frame of the algerian french spiral program provides new insights regarding the origin of the westernmost algerian margin and basin we performed a tomographic inversion of traveltimes along a 100 km long wide angle seismic profile shot over 40 ocean bottom seismometers offshore mostaganem northwestern algeria the resulting velocity model and multichannel seismic reflection profiles show a thin 3 4 km thick oceanic crust the narrow ocean continent transition less than 10 km wide is bounded by vertical faults and surmounted by a narrow almost continuous basin filled with miocene to quaternary sediments this fault system as well as the faults organized in a negative flower structure on the continent side marks a major strike slip fault system the extremely sharp variation of the moho depth up to 45 3 degrees beneath the continental border underscores the absence of continental extension in this area all these features support the hypothesis that this part of the margin from oran to tenes trending n65 n70 degrees e is a fossil subduction transform edge propagator fault vestige of the propagation of the edge of the gibraltar subduction zone during the westward migration of the alboran domain

spectral analysis of the gravity and elevation along the western africa eurasia plate tectonic limit continental versus oceanic lithospheric folding signals large scale folding is a key mechanism of lithospheric deformation and has been described in many parts of the earth both for the continental and oceanic lithospheres some aspects of this process such as the presence of coupling decoupling between the crustal deformation and the mantle lithosphere or between different lithospheres make it necessary to accurately control the periodic characteristics of the elevation and of the gravity signal 1d spectral analysis of gravity and topography profiles is sensitive to a series of factors the location length and orientation of the profiles as well as the number of samples taken we carry out a systematic analysis of the periodicities in the topography and gravity both 1d and 2d along the western border of the africa eurasia plate tectonic boundary we analyze the sensitivity of the 1d and 2d spectral analysis in order to compare the results along a plate boundary where oceanic and continental lithospheres are in contact with different tectonic kinematic and rheological aspects our 1d spectral results indicate that the greater the profile length the longer the wavelength peaks that are found nevertheless there are some periodic signals that appear in almost all the analyzed profiles 100 250 km for the n s profiles across oceanic plate boundary and 150 250 km where the plate boundary is developed over continental lithospheres the 2d spectral analysis avoids the problems found in relation to the particular location of the profile but the resulting wavelengths are slightly higher than those obtained from the 1d spectral analysis the wavelengths estimated for both oceanic and continental lithospheres at the africa eurasia boundary n250 km show low values of mean mantle strength b1013 pa m he presence of lithospheric folds means that the continental and oceanic lithospheres are mechanically oupled this had previously been suggested for iberia but not for the limit between s iberia and the terceira riple junction the orientation of the lithospheric folds is nw se at the contact between continental lithospheres and nne ssw at the contact between oceanic lithospheres this difference is also reflected in the signal anisotropy and must be related to the rotation of the tectonic stresses in the same direction a large periodic signal wavelength n600 km was also detected both in 1d and 2d spectral results after drawing the filtered values the resulting maps indicate that this signal is related to the transition between continental and oceanic lithospheres and to the significant changes in crustal and or lithospheric thickness from the mid atlantic ridge to the continental margins of western eurasia

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

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

the alhama de murcia fault se spain a seismogenic fault in a diffuse plate boundary seismotectonic implications for the ibero magrebian region received 20 december 2002 revised 15 september 2003 accepted 26 september 2003 published 2 january 2004 1 the shortening between the african and the iberian plates is absorbed by a number of faults distributed over a very wide zone with very low slip rates and long periods of seismic loading thus a seismotectonic map based only on faults associated with seismicity or with expressive geomorphic features is incomplete it is possible to characterize seismogenic faults using paleoseismology first paleoseismological results based on trenching analysis in the eastern betics lorca totana segment of the alhama de murcia fault are presented the main paleoseismic parameters of this fault segment are 1 a minimum of two to three mw 6 5 7 earthquakes in the last 27 kyr shortly before 1650 a d between 830 and 2130 b c and shortly before 16 7 ka respectively with a mean recurrence period of 14 kyr and a very short elapsed time and 2 a net slip rate of 0 07 0 6 mm yr during the last 30 kyr these results were extrapolated to the rest of the known active faults in the eastern betics and were added to the slip rates of the active faults at the african margin the total slip rate of the transect which crosses de alhama de murcia fault in spain and reaches the cheliff basin algeria would represent 21 82 of the total shortening between africa and eurasia estimated from plate motion models and seismic moment summation a number of factors could account for this discrepancy 1 hidden seismogenic faults in the emerged areas 2 absence of correlation between current and late pleistocene slip rates 3 extensive small faults that are undetected and that absorb a significant amount of the deformation and 4 possible overestimation of the convergence rates index terms 7221 seismology paleoseismology 7230 seismology seismicity and seismotectonics 7215 seismology earthquake parameters 8150 tectonophysics plate boundary general 3040 keywords eastern betics alhama de murcia fault paleoseismology trenching seismotectonics plate boundary

significance of non double couple components of deep and intermediate depth earthquakes implications from moment tensor inversions of long period seismic waves abstract analysis of long period seismic waves suggests that non double couple components in source moment tensors of intermediate depth and deep earthquakes are significant and appear to respond to the state of predominant strain release within slabs the strain regime is partially or fully induced by the sources themselves or by slab structures near the sources we observe consistency in the non double couple components from three different seismic wave inversions among 21 earthquakes studied 17 events have the same sign in the three non double couple components and the signs show a correlation with the state of strain release within the slabs the effects of unmodeled propagation structure and instability of the inversion procedure are unlikely to be responsible for the consistent non double couple components because the suites of seismic waves traverse different paths and the various inversion schemes have the different resolvabilities of the moment tensors

regional moment tensor determination in the european mediterranean area initial results the broadband seismic network in the european mediterranean area provides high quality data we invert these regional three component data for the source parameters of moderate to strong earthquakes in the entire european mediterranean area regional seismograms have a good signal to noise ratio even for moderate sized events that are too small for teleseismic analysis the magnitude threshold for source parameter determination can thus be significantly lowered the threshold depends on the average event station distances within dense broadband networks we analyze mw 3 0 earthquakes in areas far from broadband seismic stations the lower bound is mw 4 5 4 8 still considerably lower than the teleseismic analysis threshold about mw 5 0 5 3 for larger events we perform rapid moment tensor analysis using near real time data solutions are posted within hours after event occurrence in a second step we merge near real time and later available data to obtain a regional moment tensor catalog of moderate to large earthquakes for the entire european mediterranean area within less than 1 year we have analyzed 67 earthquakes ranging in size from mw 2 9 to 7 5 the solutions cover the seismically active areas of the european mediterranean area particularly important are solutions for slowly deforming regions where large earthquakes that could be analyzed with teleseismic data occur infrequently the solutions are reliable for events with independent source parameter estimates the agreement is generally high the solutions are robust variations in epicentral parameters source depth or exact choice of stations do not affect source parameter estimates strongly the moment magnitudes provide a unified estimate of earthquake size for the european mediterranean area we perform regression analyses to link our moment magnitudes with local body and surface wave magnitudes

uncertainty assessment for the seismic hazard map of spain abstract the uncertainty assessment for the development of the new seismic hazard maps of spain is explained in this work a detailed description of how uncertainties are considered in the different phases followed for the probabilistic seismic hazard assessment study is presented special emphasis is given to the characterization of the uncertainty of earthquake size parameters contained in the catalog and their propagation to subsequent phases of the analysis such as catalog homogenization completeness and declustering aleatory and epistemic uncertainties are examined and assessed using monte carlo simulations and a logic tree respectively the final impact of uncertainty in hazard estimates is evaluated through coefficient of variation maps showing the areas where larger and lower variability is obtained the hazard maps developed in this work are intended to be the basis for the future revision of the spanish seismic code

the role of small scale fold and fault development in seismogenic zones example of the western huercal overa basin eastern betic cordillera spain the nw se shortening between the african and the eurasian plates is accommodated in the eastern betic cordillera along a broad area that includes large n vergent folds and kilometric ne sw sinistral faults with related seismicity we have selected the best exposed small scale tectonic structures located in the western huercal overa basin betic cordillera to discuss the seismotectonic implications of such structures usually developed in seismogenic zones subvertical ese wnw pure dextral faults and e w to ene esw dextral reverse faults and folds deform the quaternary sediments the la molata structure is the most impressive example including dextral ese wnw neogene faults active southward dipping reverse faults and associated ene wsw folds a molar m1 assigned to mimomys savini allows for precise dating of the folded sediments 0 95 0 83 ma strain rates calculated across this structure give 0 006 mm a 1 horizontal shortening from the middle pleistocene up until now the widespread active deformations on small scale structures contribute to elastic energy dissipation around the large seismogenic zones of the eastern betics decreasing the seismic hazard of major fault zones copyright 2009 john wiley sons ltd

seismic moment tensor resolution on a local scale simulated rockburst and mine induced seismic events in the kopanang gold mine south africa seismic records contain information about the effect of the source as well as the effect of wave propagation through the rock mass the effect of wave propagation is usually not well known as only simplified models of geological structures are available therefore the information about the source retrieved by inverting seismograms may include errors due to incomplete knowledge of the rock mass along the propagation path which in turn cause a distortion in the calculated moment tensor mt the distortion of the mt on a local scale was observed by inverting records of a simulated rockburst conducted at the kopanang gold mine in south africa a dominant isotropic component of the explosive characteristics was found from the inversion the deviatoric components retrieved from the blast are spurious a test of their stability indicated that they are not significant assuming an uncertainty above 5 for velocities and 10 for attenuation within the homogeneous model available for the mine thus the retrieval of the mt from records of local networks in mines using a homogeneous model of the rock mass seems to be feasible however the homogeneous model of the rock mass can only be applied to close stations within a few kilometers of the source the seismic records from distant stations were too complex to be modelled by a homogeneous rock mass records of six mine induced seismic events recorded at the kopanang gold mine were also inverted a vertical linear dipole along the pressure p axis was found for three of the events suggesting a pillar burst the mechanism of two events contains an isotropic implosion together with a nearly vertical dip slip and seems to indicate a combination of a cavity collapse with a down dip slip along a nearly vertical fault one event corresponds to a dipole along the tensional t axis however it is vertical thus its association with tensile faulting of the hangingwall is uncertain

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

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

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

automatic regional moment tensor inversion in the european mediterranean region summary we produce fast and automatic moment tensor solutions for all moderate to strong earthquakes in the european mediterranean region the procedure automatically screens near real time earthquake alerts provided by a large number of agencies each event with magnitude m 4 7 triggers an automatic request for near real time data at several national and international data centres moment tensor inversion is performed using complete regional long period 50 100 s waveforms initially the data are inverted for a fixed depth to remove traces with a low signal tonoise ratio the remaining data are then inverted for several trial depths to find the best fitting depth solutions are produced within 90 min of an earthquake we analyse the results for the period 2000 april to 2002 april to evaluate the performance of the procedure for quality assessment we compared the results with the independent swiss regional moment tensor catalogue srmt and divided the 87 moment tensor solutions into three groups 38 a quality solutions with well resolved m w depth and focal mechanism 21 b quality solutions with wellresolved m w and 28 unreliable c quality solutions the non homogeneous station and event distributions varying noise level and inaccurate earthquake locations affected solution quality for larger events m w 5 5 we consistently obtained a quality solutions for m w 4 5 5 5 we obtained a and b quality solutions solutions that pass empirical rules mimicking the a posteriori quality for our data set are automatically disseminated

effects of axially variable diking rates on faulting at slow spreading mid ocean ridges abstract magma supply for dike injection can be highly variable within a segment of a slow spreading mid ocean ridge but the tectonic impact of this variability is not fully understood here we use three dimensional numerical models to quantify the effects of variable diking rates on the faulting mode at a 20 km long slow spreading ridge segment in addition to end member faulting modes in which long lived detachment faults or short lived normal faults form along the whole segment we newly identify a transitional mode in which a detachment and a short lived normal fault form simultaneously but in respective domains separated by a transfer fault different faulting modes can be better correlated with the average dike intrusion rate rather than the highest or lowest rate along the segment along axis stress coupling tends to homogenize fault offset along the segment inhibiting the domination of a particular faulting mode associated with an extreme local diking rate this homogenizing effect explains why detachment faults can sometimes form even in the regions previously considered as unfavorable our results further suggest that a long 15 km and continuous detachment partially overlain by younger faults can create an oceanic core complex when faults weaken fast and diking rate is low when faults weaken slow and diking rate is moderate however faulting occurs in the transitional mode producing a detachment over only a part of the segment length

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

moment tensor solutions for the iberian maghreb region during the iberarray deployment 2009 2013 abstract we perform regional moment tensor inversion for 84 earthquakes that occurred in the iberian maghreb region during the second and third leg of iberarray deployment 2009 2013 during this period around 300 seismic broadband stations were operating in the area reducing the interstation spacing to 50 km over extended areas we use the established processing sequence of the iag moment tensor catalogue increasing to 309 solutions with this update new moment tensor solutions present magnitudes ranging from mw 3 2 to 6 3 and source depths from 2 to 620 km most solutions correspond to northern algeria where a compressive deformation pattern is consolidated the betic rif sector shows a progression of faulting styles from mainly shear faulting in the east via predominantly extension in the central sector to reverse and strike slip faulting in the west at the sw iberia margin the predominance of strike slip and reverse faulting agrees with the expected transpressive character of the eurasian nubia plate boundary new strike slip and oblique reverse solutions in the trans alboran shear zone reflect its left lateral regime the most significant improvement corresponds to the atlas mountains and the surroundings of the gibraltar arc with scarce previous solutions reverse and strike slip faulting solutions in the atlas system display the accommodation of plate convergence by shortening in the belt at the gibraltar arc several new solutions were obtained at lower crustal and subcrustal depths these mechanisms show substantial heterogeneity covering the full range of faulting styles with highly variable orientations of principal stress axes including opposite strike slip faulting solutions at short distance the observations are not straightforward to explain by a simple geodynamic scenario and suggest the interplay of different processes among them plate convergence in old oceanic lithospheric with large brittle thickness at the sw iberia margin as well as delamination of thickened continental lithosphere beneath the betic rif arc

what caused the great lisbon earthquake in 1755 the great lisbon earthquake estimated magnitude 8 7 killed 60 000 people in southern iberia and northwest morocco and generated a 5 to 10 m high tsunami wave in his perspective gutscher discusses the current research on the tectonic source of the earthquake recent evidence suggests that an eastward dipping subduction zone beneath gibraltar may have caused the earthquake though no interplate earthquakes have been recorded here evidence from mud volcanoes seismic images of deformed sediments and heat flow data suggest that subduction is active and that the seismogenic fault zone may be locked numerous cruises planned in 2004 and 2005 may help to provide a definitive answer

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