continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

role of decollement material with different rheological properties in the structure of the aljibe thrust imbricate flysch trough gibraltar arc an analogue modelling approach abstract the miocene aljibe thrust imbricate flysch trough in the external zone of the gibraltar arc shows large changes in structural style towards the foreland rheological variation of the decollement rocks triassic evaporitic rocks and mesozoic limestones appears to be the main factor controlling the contrasts in structural style that characterise adjacent wedge domains in order to test this hypothesis we carried out analogue experiments involving three dimensional variations of decollement material a plate of viscous material was placed in the central part of the models at the base of the sand multilayers different geometries of the viscous plate were used experimental results show a strong link between the rheological properties of the decollement material and the structure of the overlying thrust wedge these results compare well with the internal geometry and vergence distribution in the aljibe thrust imbricate indeed the tectonic style of the wedge can be explained as a consequence of variations of rock type along the basal decollement

downdip segmentation of strike slip fault zones in the brittle crust outcrop scale field evidence from the southern san jacinto fault zone in southern california indicates that bedding parallel slip may be an important mechanism for transferring and accommodating slip within strike slip fault zones that cut across heterogeneous stratigraphy steeply dipping strike slip fault segments exposed in conglomeratic sandstones abruptly terminate at weaker shale layers where slip occurs on bedding parallel planes cross sections of fault related seismicity within the southern san jacinto fault zone reveal that events generally cluster within tabular steeply dipping fault parallel streaks that are limited in extent in the downdip direction the depths of the downdip terminations of shallow streaks tend to be roughly coincident with the depths of the updip terminations of deeper streaks these configurations define stepover geometries that range in character from sharp to diffuse the examples described herein provide evidence that downdip segmentation within strike slip fault zones may be common over a wide range of scales

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

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

the brittle plastic transition and the depth of seismic faulting a simple rheological model of shearing of the lithosphere that has gained wide acceptance is a two layer model with an upper brittle zone in which deformation takes place by frictional sliding on discrete fault surfaces and a lower plastic zone in which deformation takes place by bulk plastic flow the two are separated by an abrupt brittle plastic transition which is assumed to be indicated by the lower limit of seismicity experimental studies however as well as the deformation structures of mylonites indicate that a broad transitional field of semi brittle behavior lies between these extremes this is a field of mixed mode deformation with a strength that can be expected to be considerably higher than that predicted from the extrapolation of high temperature flow laws for quartzofeldspathic rocks the semi brittle field lies between t1 the onset of quartz plasticity at about 300 c and t2 feldspar plasticity at about 450 c a model is presented in which the transition t1 does not correspond to a transition to bulk flow but to a change from unstable velocity weakening friction to stable velocity strengthening friction t1 thus marks the depth limit of earthquake nucleation but large earthquakes can propagate to a greater depth t3 t3 t2 which corresponds to the lower limit of dynamic frictional behavior in the semi brittle field and approximately to the peak in strength the zone between t1 and t3 is one of alternating behavior with flow occurring m the interseismic period and with co seismic dynamic slip occurring during large earthquakes this zone is characterized by mylonites interlaced by pseudotachylytes and other signs of dynamic faulting the transition t1 is also marked by a change in the generation mechanism of fault rocks from abrasive wear above which produces cataclastites to adhesive wear below which is proposed as an important generation mechanism of mylonites in the upper part of the semi brittle field

neogene patterns of relative plate motion for africa europe some implications for recent central mediterranean tectonics a detailed relative motion picture for the neogene africa europe plate kinematics is presented the kinematic reconstruction was carried out using the finite difference solution between the rotation parameters determined for anomalies 7 to 2 in the africa north america europe plate motion circuit the analysis shows a motion of africa with respect to europe which is nne directed during late oligocene to burdigalian times becoming nnw trending from the langhian to the early tortonian from upper tortonian times onward the motion changes to a clear north west directed convergence major late neogene tectonic features of the central mediterranean region can to a large extent be explained within the context of the reconstructed major plate motions late tortonian to recent africa europe slip vectors are compatible with a variety of geological phenomenoa such as north west directed subduction beneath calabria south east translation of calabria and extension in the tyrrhenian sea north west trending slip vectors from thrust earthquakes between gibraltar and sicily and dextral strike slip across the north african margin

on the spatial and temporal distribution of near inertial energy in the southern ocean 1 we use an eddying realistic primitive equation model of the southern ocean to examine the spatial and temporal distribution of near inertial wind power input wpi and near inertial energy nie in the southern ocean we find that the modeled near inertial wpi is almost proportional to inertial wind stress variance iwsv while the modeled nie is modulated by the inverse of the mixed layer depth we go on to assess recent decadal trends of near inertial wpi from trends of iwsv based on reanalysis wind stress averaged over the southern ocean annual mean iwsv is found to have increased by 16 over the years 1979 2011 part of the increase of iwsv is found to be related to the positive trend of the southern annular mode over the same period finally we show that there are horizontal local maxima of nie at depth that are almost exclusively associated with anticyclonic eddies

magnetotelluric evidence for thick skinned tectonics in central taiwan taiwan is the type example of an arc continent collision numerous tectonic models have been proposed for this orogen and include both thin skinned and thick skinned lithospheric deformation these models predict very different structures at middle and lower crustal depths but insuffi cient geophysical data exist to unequivocally distinguish between them long period magnetotelluric mt data were collected in central taiwan in 2006 2007 to constrain the crustal resistivity structure a two dimensional inversion of these mt data revealed a prominent electrical conductor that extends across the decollement predicted by the thin skinned model this feature is interpreted to be due to 1 2 saline fl uids and is inconsistent with the thin skinned model in contrast the thick skinned model predicts this feature since fl uids are generated in the crustal root through metamorphism quantitative correlation of the resistivity and seismic velocity models supports small volume high salinity fl uids in a thickened crust as the cause of this conductor

crustal rheology and faulting at strike slip plate boundaries 2 effects of lower crustal flow we present a numerical model of deformation at a strike slip plate boundary within a linear viscoelastic crust which is driven by far field plate motions and basal mantle velocities the crust is assumed to have uniform elastic properties but continuously varying viscosity as a function of depth brittle faulting is represented by static elastic dislocations that are imposed when stresses exceed a critical threshold for fracture or frictional sliding the locations and depth extents of faults in this model are not prespecified but instead are governed by stress evolution within the crust we find that when a primarily elastic upper crust is underlain by a low viscosity lower crustal layer the deformation zone broadens in time to encompass many parallel strike slip faults in an interacting network in contrast when the entire crust behaves elastically the deformation zone remains narrow and focused on a single plate bounding fault reflecting imposed mantle motions surface strain rate patterns within the interacting fault network are complex and reflect significant faulting related strain rate perturbations that decay over timescales of postseismic relaxation in the lower crust 10 100 years the fault network has a characteristic spacing with complex fault interactions and with the depth extents of faults increasing with time to a maximum depth governed by crustal rheology the maximum depth of faults is limited by stress relaxation and large scale viscous flow in the lower crust which confines brittle failure to shallow and midcrustal levels

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

ground deformation patterns at white island volcano new zealand between 1967 and 2008 deduced from levelling data article i nfo since 1967 levelling measurements have been conducted in the main crater of white island volcano interpretation of these data using numerical modelling reveals that shallow pressure sources 200 600 m deep extending up to the subsurface dominated the long term deformation pattern consisting of inflation deflation cycles the time sequence of height changes magnetic changes and fumarole temperature and chemistry reveal that surface changes were caused by increasing temperature below the main crater reflecting the presence of magma at shallow depth the uplift and subsidence are interpreted in terms of increase or decrease in fluid pore pressure in response to changes of the heat and gas flux the subsidence during and following eruptions could be also linked with removal of material at depth to feed the eruptions

crustal structure of the central sector of the betic cordillera se spain deep seismic reflection gravimetric and magnetometric data allow the main features of the deep structure of the central sector of the betic cordillera to be established the moho is horizontal or dips slightly toward the s below the mountain chain and its morphology has no direct relationship with the region s topography the deep reflectors are not deformed by the neogene kilometric scale folds that produced the main topographic features probably due to the existence of detachment levels in the crust the crust is slightly thickened in the betic cordillera almost 35 km and has an abrupt transition to the thin crust of the alboran sea 15 km in the central alboran sea along an e w oriented narrow band subparallel to the coast line where the moho dips more than 60 n the neogene evolution of the mountain chain caused compressive deformation in the external zones in the internal zones pre tortonian low angle normal faults developed after the alpine metamorphism and later high and low angle normal faults and strike slip faults occurred up to the quaternary geophysical and field geology data can be used to establish a geological model for the recent evolution of the crustal deformation in this model the recent evolution of the region is probably determined by thrusting of the thin continental crust of the alboran sea toward the nw over the southern margin of the iberian massif this deformation could be a consequence of the oblique convergent movement between the african and eurasian plates which may have uplifted the entire region causing regressions in the sedimentary basins and the formation of folds and extensional structures in the upper part of the thickened crust

thermo mechanical model of the dead sea transform abstract we employ finite element thermo mechanical modelling to study the dynamics of a continental transform boundary between the arabian and african plates marked by the dead sea transform dst that accommodated ca 105 km of relative transform displacement during the last 20 myr we show that in the initially cold lithosphere expected at the dst shear deformation localizes in a 20 40 km wide zone where temperature controlled mantle strength is minimal the resulting mechanically weak decoupling zone extends sub vertically through the entire lithosphere one or two major faults at the top of this zone take up most of the transform displacement these and other modelling results are consistent with geological observations and lithospheric structures imaged along the desert seismic line suggesting that the arava valley segment of the dst is an almost pure strike slip plate boundary with less than 3 km of transform perpendicular extension modelling suggests that the location of the arava valley segment of the dst has been controlled by the minimum in lithospheric strength possibly associated with margin of the arabian shield lithosphere and or by regionally increased crustal thickness models also show that heating of the arabian shield mantle adjacent to the dst inferred independently by petrological and seismological studies is required to explain asymmetric late cenozoic uplift in the area

a high electrical conductive zone at lower crustal depth beneath the betic chain spain abstract magnetotelluric data with periods of up to 2000 s were collected and the conductivity structure of the crust and upper mantle was imaged in the central betic chain interpretation of the impedance tensor components and the geomagnetic transfer functions was made in terms of a two dimensional resistivity model along a nw se profile from the guadalquivir foreland basin and across the boundary between the external and the internal betics elongated high conductivity zones in the upper and middle crust related to fluid circulation along both sediments and faults were detected the conductors in the upper crust coincide with the areal distribution of the cenozoic and mesozoic sedimentary rocks from the guadalquivir basin and the external betics and the conductors in the middle crust with the major miocene extensional detachments affecting the basement rocks of the internal betic zone a high conductivity zone at lower crustal levels beneath the outer internal betics was also detected next to an area where earlier seismic reflection data had imaged a duplication of the reflective moho this conductor was interpreted as partial melting of a southeast dipping subducted iberian lower crust the geodynamic significance of this subduction depends mainly on whether the overthrusting lower crust belongs to the alboran domain or to the iberian plate in the former case it would correspond to a major plate boundary and in the latter to an intraplate feature

evaluation of deep sediment velocity structure in the new madrid seismic zone detailed knowledge of the physical properties of the sediments filling the mississippi embayment has proven critical to both unravel the tectonic frame work operating in the region and assess the seismic hazards posed by the new madrid seismic zone in this article we show that independent geotechnical estimates for p and s wave velocities are compatible with a sedimentary model of k feldspar clasts embeded in water and we test its validity by modeling receiver functions at a number of broadband stations by constraining the bulk sediment thicknesses beneath each station from independent reflection profiling estimates we have been able to recover the depth to the top of the cretaceous from the receiver function data at individual stations our receiver function modeling thus provides confidence in the velocity and density structures extrapolated from in situ geotechnical measurements in the upper mississippi embayment

great slave lake shear zone canadian shield reconstructed vertical profile of a crustal scale fault zone abstract the great slave lake shear zone gslsz of the northwestern canadian shield a 25 km wide early proterozoic transcurrent dextral mylonite zone is a type example of a crustal scale fault zone profile with time 1 1 the metamorphic grade decreased from granulite to greenschist facies 2 2 the locus of high strain narrowed and jumped laterally abandoning relatively older mylonites progressively younger mylonites represent both cooler temperatures and lower pressures thus the sequence of narrowing mylonite belts represents a series of progressively shallower seated sections through the gslsz 3 3 deformation evolved through the brittle ductile transition initially producing non dilational penetrative breccias followed first by discrete non dilational faulting and subsequently by dilational quartz stockworks developing crustal scale shear zones grow to an optimum width dictated by the requirement of minimum geologically reasonable strain rates for given conditions of wall rock rheology and displacement rate independent of variations in relative plate motion mature shear zones change width and migrate laterally as a function of inferred thermally activated rheological changes within the wall rocks

moho depth and poisson s ratio in the western central alps from receiver functions summary current knowledge about deep crustal structure of the alpine orogen has mainly been derived from p wave velocity models obtained from active and passive seismic experiments a complementary s wave model to provide lithological constraints necessary for unique structural interpretation has been missing to date in this paper we present important new information on s wave velocity model in the alps we applied the receiver function method using 6 yr of high quality data from 61 permanent and temporary stations sampling the western central alps we determined first order crustal features moho depth h and average vp vs ratio with the h stacking technique that uses timing of direct and multiple p to s converted phases from the moho interface synthetic tests reveal a dipping moho interface expected beneath an orogen causes a systematic bias of h and potentially leading to misinterpretation we thus applied corrections determined from synthetic data to remove the bias providing better fit of recovered moho depths with active seismic estimates for each site we also obtained independent h and estimates based on the timing of the strong ps phase our results show a gently south southeast dipping european moho at a depth of 24 30 km beneath the northern alpine foreland steepening rapidly towards the europe africa suture zone to reach a maximum depth of 55 km south of the suture the moho of the adriatic crust promontory of the african plate is at 35 45 km depth in the previously ill constrained western alps we found the european moho at 30 km depth beneath the more external units dipping east northeast to reach 50 55 km in the inner core of the alps the poisson s ratio clearly correlates with the tectonic units that comprise the alps average crustal values in the european alpine foreland are close to 0 25 in the alps we observe low values 0 22 in the highly deformed nappes of the mesozoic helvetic and southern alps indicating a thickening of felsic upper crustal material in contrast the poisson s ratio is significantly higher 0 26 in the penninic and austroalpine units near the suture zone this rapid and significant change marks a clear rupture between the alpine forelands and the suture domain we assign this high poisson s ratio to doubling of mafic lower crust consistent with results from previous active seismic experiments a continuation of the lower crustal wedge into the central part of the western alps however seems unlikely based on low observed poisson s ratios

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

seismic exploration of continental strike slip zones abstract seismic exploration of both palaeozoic and active strike slip zones shows strike slip faults that penetrate all or most of the crust offsets on the moho are evident particularly at young and active zones with a component of compression such as the alpine fault of new zealand where a change in crustal thickness of about 20 km is observed moho offsets for the old palaeozoic strike slip zones are usually much less prominent careful migration of crustal seismic reflection data from some of these zones shows that instead of sharp offsets the moho structure consists of a localized keel type crustal thickening of a few kilometres in amplitude and occurs over a zone approximately 10 km wide the large moho offsets of young strike slip zones may in some cases partially decay with time active strike slip zones are becoming an important focus of study but seismic exploration is hampered by complex near surface geology 3d structure and the difficulty of imaging steeply dipping structure in the subsurface in order to meet this challenge a wide range of seismic techniques is now being deployed these include wide angle seismic reflection refraction p wave delays and the study of guided s waves results from california give geophysical images of vertical strike slip faults that penetrate to the moho in contrast the alpine fault of new zealand appears to be a surface manifestation of an inclined 40 ramp extending down to the lower crust and along which uplift and exhumation of the continental crust and possibly strike slip motion is taking place

40ar 39ar age of the cabo de gata volcanic series and displacements on the carboneras fault zone se spain the sw ne trending carboneras fault zone of se spain separates a terrain comprising uplifted massifs of the metamorphic basement of the betic cordilleras and intervening neogene sedimentary basins from the cabo de gata volcanic series along the southeastern boundary of the carboneras fault burdigalian marls and tuffs mark the beginning of the volcanic episode rest unconformably on the basement and were tilted to the vertical during the earliest stages of movement on the fault zone 40 ar 39 ar dating of hornblende grains and igneous clasts from the tuffs constrain the onset of the volcanic episode at 21 ma some 4 ma earlier than previously reported volcanic rocks higher in the sequence that overstep unconformably onto the southern edge of the fault zone yielded an age of 11 ma thus constraining the earliest episode of motion on the fault zone between these age limits the main phase of left lateral strike slip movement on the carboneras fault may be later than this time movements on more northerly strands of the fault zone including the uplift of the sierra cabrera basement block to the nw continued at least through pliocene times the onset of volcanism is broadly coeval with the unroofing of the orogen by extensional collapse and supports earlier inferences of very rapid rates of uplift and cooling of the basement rocks

lithospheric transition from the variscan iberian massif to the jurassic oceanic crust of the central atlantic abstract a 1000 km long lithospheric transect running from the variscan iberian massif vim to the oceanic domain of the northwest african margin is investigated the main goal of the study is to image the lateral changes in crustal and lithospheric structure from a complete section of an old and stable orogenic belt the variscan iberian massif to the adjacent jurassic passive margin of sw iberia and across the transpressive and seismically active africa eurasia plate boundary the modelling approach incorporates available seismic data and integrates elevation gravity geoid and heat flow data under the assumptions of thermal steady state and local isostasy the results show that the variscan iberian crust has a roughly constant thickness of 30 km in opposition to previous works that propose a prominent thickening beneath the south portuguese zone spz the three layers forming the variscan crust show noticeable thickness variations along the profile the upper crust thins from central iberia about 20 km thick to the ossa morena zone omz and the ne region of the south portuguese zone where locally the thickness of the upper crust is

seismostratigraphy and tectonic architecture of the carboneras fault offshore based on multiscale seismic imaging implications for the neogene evolution of the ne alboran sea in the se iberian margin which hosts the convergent boundary between the european and african plates quaternary faulting activity is dominated by a large left lateral strike slip system referred to as the eastern betic shear zone this active fault system runs along more than 450 km and it is characterised by low to moderate magnitude shallow earthquakes although large historical events have also occurred the carboneras fault is the longest structure of the eastern betic shear zone and its southern termination extends further into the alboran sea previously acquired high resolution data i e swath bathymetry tobi sidescan sonar and sub bottom profiler show that the offshore carboneras fault is a ne sw trending upwarped zone of deformation with a length of 90 km long and a width of 0 5 to 2 km which shows geomorphic features typically found in subaerial strike slip faults such as deflected drainage pressure ridges and en echelon folds however the neotectonic depth architecture and neogene evolution of carboneras fault offshore are still poorly known in this work we present a multiscale seismic imaging of the carboneras fault i e topas high resolution multichannel seismic reflection and deep penetration multichannel seismic reflection carried out during three successive marine cruises from 2006 to 2010 the new dataset allowed us to define a total of seven seismostratigraphic units from tortonian to late quaternary above the basement to characterise the tectonic architecture and structural segmentation of the carboneras fault and to estimate its maximum seismic potential we finally discuss the role of the basement in the present day tectonic evolution of the carboneras fault and explore the northern and southern terminations of the fault and how the strain is transferred to nearby structures

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

crustal scale transcurrent fault development in a weak layered crust from an integrated geophysical research carboneras fault zone eastern betic cordillera spain new magnetotelluric and receiver transfer function studies provide insights from the upper to the lower crust of the eastern betic cordillera which is deformed by large folds normal faults and a major transcurrent left lateral fault the carboneras fault zone cfz receiver function analysis determines a nnw dipping moho reaching 20 that increases in depth from 20 km south of the cfz up to 34 km in the sierra de los filabres in addition seismic discontinuities determined in the upper crust are interpreted as major contacts between metamorphic complexes that are detached and folded the mt inversion model reveals a conductive zone also representing a crustal seismic discontinuity associated with the alpujarride nevado filabride contact and fitting the n vergent geometry of the sierra alhamilla antiform a small flexure at moho coincides with the cfz as revealed by the bouguer anomaly trend in agreement with the receiver function results moreover the bahr strike and tipper angle at the stations placed closest to the cfz clearly reveal the continuity of the cfz at least down to approximately 15 km in depth crossing all the detected crustal discontinuities up to the moho the lack of a clear moho offset associated with the carboneras fault supports the idea that some large strike slip faults tend to accommodate the deformation by a broadening fault zone at lower crustal levels its nucleation could occur at the base of a thin crust where melting processes critically reduced the lithospheric strength during the late miocene to then propagate upward reaching the topographic surface northward the lithosphere comprised moderately larger strength and the crustal discontinuities favored the development of larger folds with kilometric amplitude instead of strike slip faults since the late miocene

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

geodynamic implications for the formation of the betic rif orogen from magnetotelluric studies 1 magnetotelluric data from the central betics mountains spain have been used to determine the electrical resistivity of the crust after a three dimensional 3d interpretive approach at shallow levels 3 km the most striking and well resolved feature of the model is an upper middle crust conductive body located at the core of the internal betics antiform this approximately 14 km thick body is interpreted as basic or ultrabasic rocks containing a conducting mineral phase its structural location above the sole thrust of the betic orogen and beneath the nevado filabride complex confirms the presence of a major suture zone between this complex and the autochthonous iberian plate this suture may correspond to an ancient oceanic or transitional domain developed between iberia and the alboran domain during the opening of the tethys ocean partially subducted and closed during the development of the betic orogen the possible geodynamic scenarios for the betics have been reconsidered taking into account this new constraint

magnetotelluric transect across the niigata kobe tectonic zone central japan a clear correlation between strain accumulation and resistivity structure 1 we obtained an electrical transect image of the niigata kobe tectonic zone nktz several major active faults are located in this zone of concentrated deformation the main features of the final two dimensional model are a thick resistive block in the upper crust with a thinned out portion beneath the atotsugawa fault and a strong conductor in the lower crust that intrudes upward into the upper resistor the upper crustal resistive zone corresponds well to the spatiality of the nktz and relatively conductive zones sandwiching this resistor may contribute to observed changes in displacement rates the overlapping locations of the conductor and the low velocity body in the lower crust indicate that the conductor represents a zone that was weakened by fluids given that microearthquakes are localized in the regions between the resistive and conductive zones we suggest that the distribution of earthquakes is influenced by intrusions of fluid derived from the conductor

variable crustal structure of strike slip fault zones as observed on deep seismic reflection profiles seismic reflection profiling across strike slip faults has revealed a distinct variation in deep crustal structure profiles across the san andreas great glen and bray faults depict a near vertical reflection free zone that appears to truncate and in some cases offset reflections interpreted to have originated from the base of the crust a near vertical crustal penetrating fault zone is suggested for these continental transform faults in contrast reflection profiles across intra plate strike slip fault systems such as the northern walker lane and garlock faults suggest that they are decoupled in the middle crust by subhorizontal detachments these detachments are inferred from reflections that are traceable below the surface faults without disruption such detachments in the middle crust may act to ease the rotation of upper crustal blocks adjacent to strike slip fault zones as observed in paleomagnetic studies furthermore moderately dipping reflections interpreted to be from the fault zone project to the surface traces of the northern walker lane faults and the frontal faults of the wichita uplift indicating that these strike slip faults with large components of dip slip displacement are not vertical but dip moderately into the mid crust although the available data sets are still few they suggest that there is a primary variation in fault geometry that is related to the different behavior of transform versus intra plate strike slip fault systems

the betic segment of the lithospheric trans alboran shear zone during the late miocene abstract the betic sinistral transcurrent shear zone betic cordilleras crosses the southeastern part of spain the study of the geodynamics of this area is approached from tectonic sedimentary magmatic and geophysical data large strike slip movements tectono sedimentary processes and magmatic events are seen at the boundary between two different lithospheric slabs they are located in a thinned compartment with a high geothermal gradient the large scale movements vertical and horizontal and the intensity of magmatic activity are the expression of the mechanical behaviour of this hot and thin crust all the geological events from the late miocene to recent are integrated in a crustal scale cross section which shows that the betic sinistral transcurrent shear zone widely affects the lithosphere it appears that subduction zones are not the only geodynamic context in which calc alkaline magmatism occurs

a deep seismic reflection survey across the betic chain southern spain first results abstract two land seismic reflection profiles across the betic chain have imaged the deep structure of the crust belonging to two different crustal domains to the north one profile samples the crust of the variscan iberian massif that underlies the sedimentary cover of both the guadalquivir foreland basin and the south iberian crustal domain the upper crust is non reflective along the profile but the lower crust is reflective in the northern half of the profile between 7 and 12 s two way travel time in this segment of the profile the mono is also well imaged the quality of the data diminishes significantly as the profile enters the neogene guadix baza basin a second profile crossing the alpine metamorphic complexes of the betics reveals a reflective lower crust and a conspicuous reflection in the upper crust that is continuous for about 10 km at 11 s a distinct reflection has been interpreted as the reflection moho deeper reflections are also seen in the central part of the profile in a segment about 10 km long comparison with available refraction and wide angle reflection data shows some differences in both the crustal configuration and in the depth to the moho

localized ductile shear below the seismogenic zone structural analysis of an exhumed strike slip fault austrian alps 1 the miocene salzachtal ennstal mariazell puchberg semp strike slip fault in austria allows study of the internal structure of a fault zone from the near surface to 30 km depth as it enters the tauern window along the rinderkarsee shear zone the semp fault passes from a dominantly brittle to a dominantly ductile structure the shear zone consists of three 1 to 100 m wide zones of brittle ductile and ductile deformation separated by 500 m wide zones of less deformed rocks the southern shear zone is mylonitic with ductile amphibole and plagioclase weak crystal preferred orientations imply that the main deformation mechanism was dislocation accommodated grain boundary sliding the northern and central shear zones are characterized by discrete millimeter wide shear zones with ductile quartz muscovite and biotite and brittle feldspar shear zone nucleation at the grain scale involved dislocation creep and the transformation of plagioclase to muscovite strain then localized in muscovite rich grain boundary shear zones that linked to form throughgoing shear zones

fracture zones in the north atlantic from combined geosat and seasat data we present a new tectonic fabric map of the northern and central north atlantic ocean floor from 10 s to 66 n based on combined geosat and seasat altimetry data short wavelength vertical gravity along track was derived by hilbert transforming and high pass filtering geosat and seasat deflection of the vertical profiles the along track gravity data were used in conjunction with magnetic anomaly data to locate a large number of fracture zones as well as extinct spreading ridges and v shaped structures we traced many fracture zones more continuously and closer to adjacent continental margins than was previously possible we also mapped a number of unnamed fracture zones and fracture zone segments many of which were previously uncharted we have evaluated the agreement between the mapped fracture zones and synthetic flow lines as predicted from recent plate models for the opening of the north central north and south atlantic most fracture zones in this area correlate quite well with synthetic flow lines supporting the proposition that geosat seasat altimetry data serve as a useful tool to map fracture zones where insufficient bathymetric data are available many fracture zones including some small offset fracture zones in the central north atlantic have been stable and follow tectonic flow lines for tens of millions of years however many other fracture zones do not reflect a railroad track pattern of plate motions the geometry of many small and medium offset fracture zones indicates that the ridge axis discontinuities that produce them can migrate along the ridge causing off axis traces that deviate from tectonic flow lines velocity space diagrams constructed using a recent relative and absolute present day plate motion model indicate that some low angle v shaped troughs and ridges are likely formed by migration of the plate boundary relative to a mesospheric reference frame other low angle v shaped structures reflect slow migrations oscillations of small offset ridge axis discontinuities that are distinct from both tectonic flow lines and v shapes reflecting absolute plate motions high angle v shaped structures are the result of fast migrating ridge axis discontinuities propagating rifts

distributed deformation in the lower crust and upper mantle beneath a continental strike slip fault zone marlborough fault system south island new zealand converted phases from teleseisms recorded by a seismic array spanning the northern half of the marlborough fault system south island new zealand show a continuous unbroken moho underlying a seismically anisotropic lower crust beneath the two north ernmost faults of the fault system these observations suggest that distributed deforma tion not slip on a narrow vertical fault accommodates displacement in the lower crust below the 120 480 km of right lateral slip across the wairau fault one splay of the marl borough fault system and the northward continuation of the alpine fault beneath the wairau fault the moho dips 258 308 southeast from a depth of 26 km northwest of the fault to a depth of 34 km southeast of the fault farther to the southeast ps conversions from the moho continue under the awatere fault 34 6 10 km of slip with a constant amplitude and depth of 34 km across the two faults converted energy from 16 20 km depth varies with back azimuth in a manner suggesting the presence of anisotropy in the lower crust these observations imply that one of the tenets of plate tectonics that faults defining plate boundaries pass through both crust and upper mantle does not apply to new zealand or to continents in general

mode of extensional tectonics in the southeastern betics se spain implications for the tectonic evolution of the peri alboran orogenic system the gibraltar arc which closes the westernmost part of the mediterranean basin is a miocene a type subduction arc formed by the continental collision of various pre miocene terranes in the major zone of collision between the iberian and african cratons the hanging wall block known as the alboran domain has undergone more than 300 km migration from a more easterly position where it was the continuation of the alpine cretaceous paleogene orogen contemporaneous with thin skinned thrusting in the footwall the alboran domain underwent two episodes of nearly orthogonal extension in which extensional systems developed with directions of extension varying from a nnw sse system orthogonal to the belt axis in the late burdigalian langhian to a wsw directed orogen parallel one in the serravallian the superposition of these two systems resulted in a chocolate tablet megastructure this extensional pattern is not satisfactorily explained in previously proposed models for the evolution of the arc orthogonal extension is plausible in a process of the gravitational collapse of an overthickened crust nevertheless orogen parallel extension is more difficult to explain in this context we advocate that the wsw directed low angle normal faults formed during large scale extension in connection with important westward arc migration the driving force of extension in a general context of convergence is controversial and varies between a convective removal model and a delamination model constraints on both the timing and the kinematics of extension as presented in this paper seem to support the contribution of both mechanisms convective removal may have started the process but continued n s convergence could have resulted in westward tectonic escape and asymmetric lateral inflow of asthenospheric material accompanying lithospheric delamination

vertical extent of the newborn san andreas fault at the mendocino triple junction three dimensional seismic refraction data reveal the structure of the plate boundaries at the mendocino triple junction first arrival traveltimes were inverted to obtain a three dimensional seismic velocity model the tomography results indicate a strong lateral velocity contrast in the lower crust this velocity contrast is beneath the surface trace of the san andreas fault and tracks along the fault to the triple junction and then along the mendocino fracture zone velocity values appropriate for mafic rocks are more than 5 km shallower on the pacific plate than east of the san andreas fault and 1 3 km shallower than under the cascadia accretionary prism the model suggests that the san andreas fault which is growing as the triple junction migrates northward cuts steeply through the entire crust pacific oceanic crust does not extend beneath north america at this location the slabless window south of the triple junction and east of the san andreas fault must be filled with upwelling asthenosphere the sharp corner of the pacific plate migrates northward displacing the cascadia accretionary prism and forcing the prism material to move north or east

seismic reflection evidence for the evolution of a transcurrent fault system the norumbega fault zone maine a seismic reflection profile in east central maine reveals a steeply dipping fault zone that terminates in diffraction hyperbolae that are associated with an offset of the moho when combined with data from geologic mapping the seismic data imply mesozoic or post mesozoic dip slip reactivation of the norumbega fault zone hitherto interpreted as a locus of mid to late paleozoic dextral offset this finding highlights the value of seismic reflection data in determining the history of fault displacement and warns of the complexities that arise in attempts to seismically characterize faults in polygenic tectonic regimes

structure and kinematics of the south iberian paleomargin and its relationship with the flysch trough units extensional tectonics within the gibraltar arc fold and thrust belt western betics abstract the superposition of structures observed in a selected area of the external zones of the betic orogen situated in the westernmost segment of the peri mediterranean mountain belt reveals an alternation of compressional and extensional events during the overall convergence of the african and eurasian plates that bound the system an early miocene compressional event produced the formation of the so called gibraltar arc fold and thrust belt formed by the units derived from the south iberian paleomargin and the flysch trough this wedge constitutes the footwall of the gibraltar thrust whose hanging wall corresponds to the alboran domain the outward migration of the compressional front w to nwward in the south iberian segment was followed by the outward migration of the extensional locus related to the middle miocene rifting that led to the alboran basin subsidence the tectonic inversion of the gibraltar thrust was accompanied by normal faulting of the innermost part of the paleomargin and the flysch trough units finally the alboran region underwent n s to nw se compression from late miocene onwards which caused the uplift of the gibraltar arc area

the geometry and evolution of a transpressional strike slip system the carboneras fault se spain the carboneras fault system is a 40 km long 1 km wide neogene ne sw trending left lateral transpressional strike slip fault system which is part of the trans alboran shear zone in se spain the carboneras fault system is an anastomosing array of sub vertical individual fault planes or fault zones which surround pods or lenses of less intensely strained rocks displacements along the individual fault planes exhibit reverse components of slips and form positive flower structures faults have either sharp boundaries or wider bands of gouge typically a few metres thick and are hundreds of metres in length second order fault splays are well developed and usually exhibit p shear rather than riedel shear orientations these are interpreted to be related to the transpressional displacement and may also characterize other oblique convergent zones elsewhere the second order faults are interpreted to have formed as shear strain increased along the first order fault and was transferred laterally to branch segments this process produced pods or shear lenses bounded by the fault segments the length to width aspect ratios of the shear lenses were found to be scale independent across five orders of magnitude with the most common values between 3 l and 6 l a model is proposed for the development of the fault zone by incremental finite displacements along the segmented fault surfaces this model is based on field evidence that displacement switched with time from one fault strand to another

deformation style and controlling geodynamic processes at the eastern guadalquivir foreland basin southern spain the tectonic structure of the guadalquivir foreland basin becomes complex eastwards evolving from a single depocenter to a compartmented basin the deformation pattern within the eastern guadalquivir foreland basin has been characterized by combining seismic reflection profiles boreholes and structural field data to output a 3d model high dipping nne ssw to ne sw trending normal and reverse fault arrays deform the variscan basement of the basin these faults generally affect tortonian sediments which show syntectonic features sealed by the latest miocene units curved and s shaped fault traces are abundant and caused by the linkage of nearby fault segments during lateral fault propagation preexisting faults were reactivated either as normal or reverse faults depending on their position within the foreland at tortonian time reverse faults deformed the basin forebulge while normal faults predominated within the backbulge along strike variation of the betic foreland basin geometry is supported by an increasing mechanical coupling of the two plates alboran domain and variscan basement towards the eastern part of the cordillera thus subduction would have progressed in the western betics while it would have failed in the eastern one there the initially subducted iberian paleomargin nevado filabride complex was incorporated into the upper plate promoting the transmission of collision related compressional stresses into the foreland since the middle miocene nowadays compression is still active and produces low magnitude earthquakes likely linked to nne ssw to ne sw pre exiting faults reactivated with reverse oblique slip kinematics seismicity is mostly concentrated around fault tips that are frequently curved in overstepping zones

a rheologic model for wet crust applied to strike slip faults the strength and stability of crustal faults are not adequately addressed by the widely used two mechanism rheologic models of the crust based on byerlee s law and power law creep the models neglect the fluid assisted mechanisms of deformation that are important to strength of the crust and do not describe the variation in rate dependence of friction that governs the stability of fault slip several distinct mechanisms of frictional slip are defined on the basis of variations in frictional behavior and microfabric of simulated fault gouge in laboratory experiments state variable constitutive relations are used in a multiple mechanism formulation to describe the rate and temperature dependence of three friction mechanisms in wet quartz gouge at elevated temperatures this multimechanism description of friction is substituted for byerlee s law in the two mechanism models to generate a multimechanism rheologic model for the crust the multimechanism model is used to predict the rate and temperature dependence of crustal strength and the slip rate and depth temperature conditions over which each mechanism dominates application of the model to strike slip faults in the crust illustrates that the thickness of the actively shearing zone within faults is a critical parameter governing fault strength and stability the model predicts that frictional strength at midcrustal depths is significantly reduced relative to byerlee s law only for thick fault zones the reduction in strength is due to the operation of a strain rate sensitive friction mechanism involving combined cataclasis and solution transfer the rheologic model predicts that only very thin faults display the rate dependent characteristics necessary for initiation of seismic slip to any significant depth in the crust