correlations between surface chlorophyll and sea surface height in the tropical pacific during the 1997 1999 el nino southern oscillation event correlations between sea viewing wide field of view sensor seawifs surface chlorophyll and topex sea surface height ssh are examined in the tropical pacific 30 s 30 n using empirical orthogonal function eof analysis both separately and jointly on the two fields this analysis is done on data from september 1997 the start of data from the seawifs satellite through december 1999 a time period dominated by the el nino southern oscillation four distinct biological responses are observed the dominant response is a symmetric off equatorial chlorophyll increase during la nina that extends between 2 and 18 latitude from the eastern pacific to the date line the chlorophyll mode is tightly correlated to ssh suggesting that the chlorophyll increase is a result of the shoaling thermocline which increases the surface nutrient supply the better known equatorial decrease in chlorophyll during el nino is seen in a separate eof mode using acoustic doppler current profiler data from the tropical atmosphere ocean triton array it is shown that the cessation of the el nino equatorial chlorophyll minimum is tied to the recommencement of the iron rich equatorial undercurrent which occurs several months prior to the termination of the el nino there is an off equatorial bloom during the peak of the el nino between 120 w 180 w and 8 n 15 n this bloom occurs within the area covered by the previously mentioned la nina bloom but it is more localized and its fluctuations appear correlated with changes in the north equatorial counter current the shoaling thermocline in the western warm pool during el nino results in a chlorophyll bloom that extends from the philippines to 155 e between 0 n and 15 n this bloom terminates in unison with the end of the el nino when elevated ssh is reestablished in the western basin

le bassin de tizi n test haut atlas maroc exemple d evolution d un segment oblique au rift de l atlantique central au trias detailed mapping completed by a microtectonic study of the tizi n test triassic basin located along the tizi n test fault zone in the moroccan high atlas has allowed us to improve the knowledge on the geometry of the structures and the activity of faults during the triassic extensional events related to the rifting of the central atlantic the latter are reflected by the development of a rift at present inverted and deformed by the collision of africa and europe comprising kilometric scale grabens and half grabens bounded by major faults trending ene wsw with a dip towards the nnw and a dip slip syndepositional motion inverse analysis of fault slickenside populations shows a heterogeneous triassic state of stress however in the most significant measurement sites the maximum horizontal stress 1 is vertical while the minimum stress 3 is horizontal with a nw se trend the strike slip component appears to be very small during the triassic a noticeable fact because of the obliquity of the basin w

process studies on the po river plume north adriatic sea the coastal processes in the adriatic sea and in particular the development and evolution of the po river plume are studied with a three dimensional primitive equation model experiments are performed to examine the buoyancy driven flow and the interaction with topography wind stress and ambient stratification the pathways of particles released from the po are computed to simulate the transport of land drained materials in the absence of wind forcing the po river plume consists of an offshore bulge that occupies most of the north part of the basin and a southward coastal current that is confined within the narrow coastal region along the italian peninsula when all adriatic rivers are included basinwide buoyancy driven cyclonic coastal flow is established that diminishes the seaward removal of po waters and promotes their southward advection through the coastal current wind stress modifies the above winds that are downwelling favorable for the po discharge site like bora restrict offshore plume development enhance the southward coastal current and confine the plume within the narrow western adriatic shelf conversely upwelling favorable winds like scirocco eliminate the baroclinic coastal current and advect low salinity po waters toward the shallow parts of the northern adriatic when preexisting stratification of basin waters is described the density field is influenced by both temperature and salinity during winter when the coastal waters tend to be colder and fresher than offshore waters the cyclonic circulation is sustained owing to input from rivers and particularly the po the intense spatial and temporal variability of wind stress and river runoff and the resulting variability in the circulation of the coastal adriatic sea are elaborated through a realistic simulation during january 1994

fault reactivation control on normal fault growth an experimental study field studies frequently emphasize how fault reactivation is involved in the deformation of the upper crust however this phenomenon is generally neglected except in inversion models in analogue and numerical models performed to study fault network growth using sand silicon analogue models we show how pre existing discontinuities can control the geometry and evolution of a younger fault network the models show that the reactivation of pre existing discontinuities and their orientation control i the evolution of the main fault orientation distribution through time ii the geometry of relay fault zones iii the geometry of small scale faulting and iv the geometry and location of fault controlled basins and depocenters these results are in good agreement with natural fault networks observed in both the gulf of suez and lake tanganyika they demonstrate that heterogeneities such as pre existing faults should be included in models designed to understand the behavior and the tectonic evolution of sedimentary basins

geology geochronology and rift basin development in the central sector of the main ethiopia rift based on stratigraphic relationships and k ar dating of volcanic rocks from both of the escarpments flanking plateaus and from the rift floor of the central sector of the main ethiopian rift six major volcanic episodes are recognized in the rift9s development over a time span from the late oligocene to the quaternary using the k ar data correlation of volcanic units from the six periods of activity throughout the study area forms the basis for establishing six time stratigraphic chronozones for the central sector that are related to volcanism in the ethiopian cenozoic volcanic province the oldest basalt and rhyolite flows exposed along the rift margins of the central sector are time correlative to or older than those in river canyons for example blue nile on the adjacent northwest plateau a thinned mesozoic stratigraphic sequence along the guraghe western rift margin suggests that doming may have preceded volcanism and rifting of the cenozoic by late miocene time at least by 8 3 ma and 9 7 ma the eastern and western faulted margins respectively of the rift had formed at guraghe and at agere selam as indicated by containment of flows of that age within the rift wall during eruption a paroxysm of calc alkaline ignimbrite activity produced voluminous flows nearly fully contained within the rift during the pliocene epoch the munesa crystal tuff 3 5 ma a prominent marker tuff exposed on both rift margins is present at depth in a geothermal well beneath the rift floor and indicates a minimum of 2 km of downthrow in the central sector since its eruption structural and stratigraphic relationships in the central sector indicate a two stage rift development this is characterized by an early phase late oligocene or early miocene of a series of alternating opposed half grabens along the rift with alternating polarity such as that in the present gregory and western rifts of east africa and symmetrical rifts that evolved from these grabens in late miocene or early pliocene time thus evolution from alternating half graben to a full symmetrical graben with a medially located neovolcanic zone that is bifurcated to marginal grabens in the northern part of the study area may be a fundamental part of the rifting process the study indicates that there are major petrologic and tectonic differences between the main ethiopian rift and the gregory kenyan rift

latest pleistocene and holocene river network evolution in the ethiopian lakes region abstract river network geomorphologic paleohydrologic stratigraphic and sedimentologic analyses document a dramatic reorganization of the drainage pattern in the northern part of the main ethiopian rift mer during latest pleistocene and early holocene the river network modification was induced by tectonic deformation volcanic activity and by the arid conditions connected with the last glacial maximum lgm this arid phase triggered the shrinking of a pleistocene megalake that formerly flooded large part of the main ethiopian rift the northern tributaries paleo awash and paleo mojo rivers extended following the lake shore retreat and incised the fesesa koye and cheleleka sulula hafa paleovalleys through the pleistocene deposits at the beginning of the holocene humid conditions induced a water level rise in the lacustrine basin ziway shala basin supplied from the north by the large awash mojo meki fluvial system a well exposed cross section of the cheleleka paleovalley at the confluence with the meki river and the use of paleohydrological methods allowed to infer the bankfull paleo discharge of the larger awash mojo river system tectonic events allowed the awash and mojo rivers to divert their courses to the east toward the afar depression depriving the ziway shala lacustrine basin of large volumes of water supply this and the further increase in aridity during the late holocene led to the separation of the ziway shala paleolake into the present four lakes ziway langano abjiata shala this study indicates that in the main ethiopian rift climatic changes cannot be inferred from lake level variations alone because changes in water supply are also influenced by the tectonic induced rearrangement of the fluvial drainage networks

influence of pre existing pervasive fabrics on fault patterns during orthogonal and oblique rifting an experimental approach abstract pervasive mechanical anisotropy e g metamorphic foliation in the pre rift basement rocks often appears to control the orientation of new faults in natural rift systems and thus tend to influence formation of fault bounded sedimentary basins however the extent to which this influence works in nature has remained debatable and contrasting ideas exist regarding the issue of structural inheritance in natural rifts like the east african rift system earlier experimental works have investigated different kinematic aspects of faulting in simulated orthogonal and oblique rift systems including the role of a crustal scale pre existing zone of weakness on continent scale rifting these experiments have tested the influence of discrete pre existing weak zones e g pre existing faults or an ancient orogenic belt on localization of subsequent rifting but have not considered the control of pervasive fabric anisotropy e g metamorphic foliation etc in pre rift basement rocks on the fault patterns during rifting here we present a series of simple roughly scaled analog model experiments where pervasive strength anisotropy in the basement was created by brushing plaster of paris on a viscous pitch substratum this way a transverse anisotropy of tensile strength was generated in the plaster of paris layer due to thickness variation across the brush marks the basement was overlain by a dry sand pack simulating weak sedimentary rocks overlying a foliated crystalline basement orthogonal and oblique extension of the models at various angles and with differently oriented strength anisotropy exhibited the control of the anisotropy on the orientations of new faults in the sand layer in general anisotropy could significantly control the fault pattern only when it was at a high angle 45 with respect to the maximum instantaneous horizontal stretching direction e h1 otherwise they largely disregarded the anisotropy and formed orthogonal to e h1 faults never formed orthogonal to the displacement vector d in oblique rifting unless the fault controlling anisotropy was perpendicular to d faults strongly following the anisotropy were much longer than those not following that trend faults oblique to the anisotropy were short segmented and tortuous in nature and mainly grew by segment linkage the experimental results support many field observations made in the east african rift system and are likely to be applicable to other rift systems like gondwana basins of india where field data on such structural inheritance are meager

the dynamics of the coastal region of the northern adriatic sea abstract the northern half of the adriatic sea is constituted by the continental shelf with very shallow depths 20 m in the northernmost extremity in particular the new coastal region adjacent to the italian coastline forms a shallow strip with isobaths running parallel to the coast and a topography gently increasing towards the interior of the basin in the region immediately south of the po river delta the major source of fresh water input into the adriatic important eutrophication phenomena have recently occurred in summer the controversial question thus arises whether these eutrophication phenomena are to be ascribed to nutrient inputs from local sources or from the po river waters carried southward parallel to the italian coastline in the general cyclonic gyre characterizing the adriatic yearly average circulation the dynamically important question is then whether and how a localized source of freshwater drives the nearcoastal shelf circulation to answer this question a multi level hydrodyn

interaction between normal faults and pre existing thrust systems in analogue models the influence of pre existing thrusts on the development of later normal faults was investigated using scaled laboratory analogue models experiments consisted of a phase of shortening followed by extension at variable angles of obliquity a to the shortening direction results suggest that the angle a has a major influence on the surface fault pattern and on the interaction between shortening related structures and later extensional structures three different modes of interactions were identified depending upon the extension kinematics 1 for orthogonal extension a 1 4 08 shortening related fold and thrust structures strongly influence the development of normal faults graben structures nucleate within anticlines and the normal faults reactivate thrusts at depth branching at depth mode of interaction 2 for highly oblique extension a 458 shortening related structures exert no influence on normal faults as extension related steeply dipping faults characterized by an oblique component of movement displace early thrusts no interaction mode 3 for intermediate obliquity angles a 1 4 158 308 an intermediate mode of interaction characterizes the experiments where the no interaction and branching at depth modes coexist in different regions of models modelling results can be used to infer regional extension directions as is shown for the northern appenines italy it has been shown that in many cases pre existing thrust systems play an important role in controlling the architecture of superimposed normal faults mechanical theory suggests that the probability of reactivation of pre existing thrust faults depends on their orientation with respect to the superimposed extensional stress field e g sibson 1985 the process was investigated in previous analogue models krantz 1991 faccenna et al 1995 and references therein suggesting that the initial dip of thrust faults has a major control on the development of successive normal faults both studies started with a phase of shortening that resulted in progressively steeper thrust faults prior to extension model results suggested that three different types of interactions between pre existing thrusts and successive normal faults may arise e g faccenna et al 1995 1 no interaction occurs in case of low dip thrusts 328 18 and normal faults form independently displacing pre existing thrusts 2 branching at depth of normal faults with thrusts is observed for intermediate dip angles 328 182 418 18 3 total reactivation occurs on thrusts dipping at angles higher than 418 18 these three basic mode of interaction between normal faults and thrust systems have been recognized and described in natural systems such as the central apennines italy and the north sea region faccenna et al 1995 active extensional structures interacting with early thrust systems have been also recognized in the northern apennines e g finetti et al 2001 in this fold and thrust belt the early compressive structures show a prominent curvature along strike and the successive normal faults display strong variations in terms of trend arrangement and kinematics in different sectors of the chain fig 1 in particular where thrusts are orthogonal to the regional ne sw extension direction e g mugello basin fig 1 normal faults are long and linear display a mainly pure dip slip kinematics and from buiter s j h schreurs g eds 2006 analogue and numerical modelling of crustal scale processes geological society london special publications 253 65 78 0305 8719 06 15 00 the geological society of london 2006 are subparallel to the early compressive structures delle donne et al 2003 conversely where thrusts are slightly oblique to the extension garfagnana lunigiana area fig 1 normal faults are arranged en echelon are characterized by an oblique slip kinematics and display a mean peak in distribution oriented at about 108 with respect to the earlier thrusts piccardi et al 1999 in case of high obliquity e g martani mounts terni basin area fig 1 normal faults are linear are characterized by an important locally dominant strike slip component of movement and form at an angle of 208 to the pre existing structures bonini et al 2003 these features suggest that the different orientation of thrusts with respect to the direction of extension may have exerted an important control on the pattern of successive extensional structures this influence is investigated in this study by means of analogue models we present a series of experiments on polyphase deformation consisting of orthogonal shortening followed by extension at variable angles of obliquity

space and time variability of the surface color field in the northern adriatic sea a time series of coastal zone color scanner images for the years 1979 and 1980 was used to observe the spatial and temporal variability of bio optical processes and circulation patterns of the northern adriatic sea on monthly seasonal and interannual scales the chlorophyll like pigment concentrations derived from satellite data exhibited a high correlation with sea truth measurements performed during seven surveys in the summer of both years comparison of the mean pigment fields indicates a general increase in concentration values and larger scales of coastal features from 1979 to 1980 this variability may be linked to the different patterns of nutrient influx due to coastal runoff in the 2 years the distribution of surface features is consistent with the general cyclonic circulation pattern the pigment heterogeneity appears to be governed by fluctuations of freshwater discharge while the dominant wind fields do not appear to have important direct effects the po river presents a plume spreading predominantly in a southeastern direction with scales positively correlated with its outflow the spatial scales of the western coastal layer in contrast are negatively correlated with this outflow and the plume scales both results are consistent with and may be rationalized by recent theoretical and experimental results involving a dynamical balance between nonlinear advection and bottom friction with alternate predominance of one of the two effects

the phytoplankton bloom in the northwestern arabian sea during the southwest monsoon of 1979 the biological variability of the northwestern arabian sea during the 1979 southwest monsoon has been investigated by the synthesis of satellite ocean color remote sensing with analysis of in situ hydrographic and meteorological data sets and the results of wind driven modeling of upper ocean circulation the phytoplankton bloom in the northwestern arabian sea peaked during august september extended from the oman coast to about 65 e and lagged the development of open sea upwelling by at least 1 month in total the pigment distributions hydrographic data and model results all suggest that the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore ekman pumping coastal upwelling was evident from may through september yielded the most extreme concentrations of phytoplankton biomass and along the arabian coast was limited to the continental shelf in the promotion of high concentrations of phytoplankton upward ekman pumping to the northwest of the somali jet axis stimulated the development of a broad open sea phytoplankton bloom oceanward of the oman shelf vertical mixing during the 1979 southwest monsoon was apparently not a primary cause of the regional scale phytoplankton bloom

influence of hegenshan heihe suture on evolution of late mesozoic extensional structures in wunite depression erlian basin inner mongolia china we integrate previous work on the hegenshan heihe suture with our interpretation of geomagnetic anomaly and seismic reflection data to investigate the role of the hegenshan heihe suture in the evolution of late mesozoic extensional structures in the wunite depression of the erlian basin sags in the wunite depression present as ne50 trending in the western sector n0 ne30 trending in the central sector and ne45 trending in the eastern sector our results highlight the importance of the pre existing hegenshan heihe suture in the evolution of the late mesozoic rift system and reveal the following details 1 the ne50 extent sags in the western sector are controlled by the c ne50 trending suture moreover the extensional deformation of the reactivated suture during early cretaceous time resulted in a further vertical and horizontal extension of major border faults 2 the n0 ne30 extent sags in the central sector are influenced by the c ne75 trending suture the sinistral strike slip component of the reactivated suture during early cretaceous time resulted in a strike rotation of major border faults from nee trending following the suture to nne trending 3 because of strike slip deformation which resulted from the deformation of the reactivated suture accrued in major border faults light dip slip deformation led to less vertical offset 4 the ne45 trending sags in the eastern sector are controlled by the c ne45 trending suture moreover the extensional deformation of the reactivated suture during early cretaceous time facilitated a further vertical and horizontal prolongation of major border faults

earthquakes in the davie ridge madagascar region and the southern nubian somalian plate boundary the largest earthquake sequence mb up to 6 4 and m0 up to 5 1018 nm to have struck eastern africa within the past 60 years occurred in may and june of 1985 off the coast of the tanzania mozambique border the epicenters are located on the northern extension of the davie ridge a prominent north south trending bathymetrie feature accompanied by distinct gravity anomalies a joint hypocenter location of the 14 largest events in this sequence appears as a cluster of epicenters with no apparent lineation al teleseismic distances p and sh waves generated by the two largest events of this sequence have nearly identical waveforms on the long period records of the worldwide standard seismograph network a formal inversion of the data shows a pure normal faulting mechanism on nodal planes striking slightly west of north at least two point sources are necessary to model each event one at a depth of 40 10 km and the other at about 20 5 km on a regional scale normal faulting seems to characterize the scattered seismicity throughout the region between madagascar and the eastern arm of the east african rift zone even though oceanic lithosphere dominates part of the region and no topographic expression of a rift system can be identified since normal faulting events of up to 25 5 km deep also characterize the scattered seismicity west of the topographic expression of the western arm of the rift zone at about the same latitude we propose that the southern termination of the nubian somalian plate boundary consists of a diffuse zone of east west extension up to 2000 km wide

quaternary oblique extensional tectonics in the ethiopian rift horn of africa abstract the ethiopian rift extends in a northeasterly direction from southern ethiopia to the afar region it shows a complex fault pattern characterised by the interplay of a n30 e n40 e trending border fault system with the quaternary wonji fault belt which is constituted by right stepping en echelon n s to n20 e trending faults the wonji fault belt affects mainly the rift floor but it also overlaps with some segments of the margins its en echelon arrangement indicates a left lateral component of displacement along the rift trend the general fault pattern of the ethiopian rift as well as mesoscopic fault analyses and structural features of some key areas indicate the occurrence of a roughly e w extension which is compatible with the sinistral shear component of motion along the rift this paper proposes that oblique rifting related to the e w direction of extension has been active since the beginning of the quaternary and that it came after an earlier phase of roughly pure extension orthogonal to the rift trend

neotectonic development of the el salvador fault zone and implications for deformation in the central america volcanic arc insights from 4 d analog modeling experiments the el salvador fault zone esfz is an active approximately 150 km long and 20 km wide segmented dextral strike slip fault zone within the central american volcanic arc striking n100 e although several studies have investigated the surface expression of the esfz little is known about its structure at depth and its kinematic evolution structural field data and mapping suggest a phase of extension at some stage during the evolution of the esfz this phase would explain dip slip movements on structures that are currently associated with the active dominantly strike slip and that do not fit with the current tectonic regime field observations suggest trenchward migration of the arc such an extension and trenchward migration of the volcanic arc could be related to slab rollback of the cocos plate beneath the chortis block during the miocene pliocene we carried out 4 d analog model experiments to test whether an early phase of extension is required to form the present day fault pattern in the esfz our experiments suggest that a two phase tectonic evolution best explains the esfz an early pure extensional phase linked to a segmented volcanic arc is necessary to form the main structures this extensional phase is followed by a strike slip dominated regime which results in intersegment areas with local transtension and segments with almost pure strike slip motion the results of our experiments combined with field data along the central american volcanic arc indicate that the slab rollback intensity beneath the chortis block is greater in nicaragua and decreases westward to guatemala

the somalia plate and the east african rift system present day kinematics summary the motion of the somalia plate relative to the nubia africa arabia and antarctica platcs is re evaluated using a new inversion method based on a monte carlo technique and a least absolute value misfit criterion a subset of the nuvel 1 data set with additional data along the levant fault and in the red sea is used the results confirm that the motion of arabia with respect to africa is significantly different from the motion relative to somalia it is further shown that the data along the sw indian ridge are compatible with a pole of relative motion between africa and somalia located close to the hypothetical diffuse triple junction between the ridge and thc east african rift the resulting africa somalia motion is then compatible with the geological structures and seismological data along the east african rift system assuming a separate somalia plate thus solves kinematic and geological problems around the afar triple junction and along the east african rift

geostrophic circulation patterns in the northeastern adriatic sea and the effects of air sea coupling may september 2003 1 ctd data were collected weekly during 20 cruises from may to september 2003 over a 19 station grid in a coastal region of the northeastern adriatic sea as part of the adriatic sea integrated coastal areas and river basin management system pilot project adricosm relative geostrophic velocities indicated fine scale circulation patterns in the area consisting of two pronounced circulation cells of cyclonic and anticyclonic character and that were present in the area for most of the investigated period these motions were induced primarily by spatial variations in the temperature field and may be strengthened during episodes of very strong northeasterly bora wind when the investigated region is not heated cooled uniformly

three dimensional laboratory modelling of rifting application to the baikal rift russia abstract continental rifting is treated as a mechanical instability developing under horizontal tectonic tension the instability results in strain localization and the formation of a neck which is interpreted as a rift zone at the scale of the whole lithospheric plate this process occurs in plane stress conditions and can therefore be modelled to a first approximation by a one layer plate whose properties represent integral over thickness properties of the real lithosphere we have designed a scaled experimental single layer lithosphere model having elasto plastic rheology and lying upon a liquid substratum to study its behaviour under axial horizontal tension in a homogeneous plate the instability develops along a linear zone oriented at an angle of 60 to the tension axis this orientation is preserved even when the divergent displacement of the plate boundaries is not plain parallel but rotational in the latter case the strain localization zone is rapidly propagating when the plate length to width ratio is less than 2 5 the necking develops along two branches conjugated at an angle of about 120 which is frequently observed in actual rift systems if the model contains a local weak zone hot spot or fault zone the rift junction is located at this zone in the lithospheric models comprising strong cratonic and weak segments strain localization depends on the configuration of the boundary between different lithospheres the necking starts to form within the weak segment in the vicinity of the cratonic promontories and propagates in opposite directions again at an angle of ca 60 to the tension axis in the models containing both a strong lithosphere and local weak zones the rift configuration depends on their shape and relative positions with necking always going through the weak zones in a set of models we have reproduced the geometry of the boundary between the siberian craton and the thermally much younger 100 ma sayan baikal lithosphere in the baikal rift area in these models we were able to obtain the well known three branch configuration of the baikal rift system only by introducing a weak zone in the area of lake baikal such a zone simulates the paleozoic suture existing in this area as in nature two wide outer branches eastern and western are oblique to the regional tension axis whereas the central one is narrow and orthogonal to the tension direction in nature and in the model rifting starts in the central branch corresponding to lake baikal the modelling also predicts the formation of a fourth oblique ns trending branch to the south of baikal although poorly expressed in the field this branch has some seismotectonic and magmatic manifestations the orientations of all four branches with respect to each other and with respect to the regional tension direction are remarkably similar in nature and in the model

cenozoic extension in coastal dhofar southern oman implications on the oblique rifting of the gulf of aden a detailed analysis of fault populations that affect the paleocene to early miocene sedimentary succession of southern dhofar allows the definition of a time sequence of paleostresses and the reconstruction of the rifting history of the eastern gulf of aden two distinct phases of n20j and n160j trending extensions took place during the deposition of the synrift dhofar group from late priabonian 35 ma to middle burdigalian 18 ma a period of tectonic instability preceded these events marked by normal and strike slip faulting as early as the mid eocene the two main directions of extension also recorded in southern yemen developed respectively oblique and normal to the n75e trend of the gulf of aden an anticlockwise succession of the two episodes from n20 to n160 only established in yemen accounts for the observed synrift fault pattern which is consistent with the type and geometry of faults predicted in analogue models of oblique rifting a latest phase of ns compression marked by strike slip faulting may represent a far echo of the arabia eurasia collision d 2002 elsevier science b v all rights reserved

observations of gulf stream induced and wind driven upwelling in the georgia bight using ocean color and infrared imagery ocean color and infrared imagery from aircraft and satellite sensors are combined with in situ measurements of currents chlorophyll temperature salinity coastal winds and sea level to study upwelling events in the georgia bight where the gulf stream and continental shelf waters strongly interact these interactions were observed over an 8 day period in april 1980 during which five independent upwellings occurred the upwellings included a nearshore wind driven upwelling enhanced by topographic effects three gulf stream filament induced upwellings and what appears to have been a gulf stream meander induced event the chlorophyll distributions as inferred from the imagery are found to be reliable tracers which indicate filamentary circulation and propagation and advective routes by which nearshore water moves offshore the propagation of two of the filaments and the meander are studied in detail using the imagery and mooring array temperature time series both techniques yield nearly identical results for the phase speeds of each event there is evidence that one of the filaments accelerated as it entered into the charleston bump area where the gulf stream deflects offshore the other filament exhibited a steady deceleration as it moved past cape canaveral and eventually lost any semblance of wave motion also includedmore are data from april 1979 which offer corroborating evidence of filamentary structure and circulation intercomparisons of field measurements and the nimbus 7 coastal zone color scanner estimates of surface pigment concentrations show excellent agreement over the range of 0 1 7 0 mg m sup 3 54 references 22 figures 6 tables less

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

pigment distribution in the caribbean sea observations from space abstract the caribbean is a semi enclosed tropical sea which is generally considered oligotrophic but that is influenced by nearly 20 of the annual discharge of the world s rivers amazon and orinoco rivers and by seasonal upwelling along the southern margin to investigate the role of these nutrient sources on the productivity of the region we mapped the distribution of pigments in the eastern caribbean east of 80 w using a series of coastal zone color scanner czcs images collected between november 1978 and december 1982 five additional images were examined for the period 1983 1986 the images revealed a seasonal cycle in the spatial structure of near surface pigment during january may there were high pigment concentrations 0 5 mg m 3 along the continental margin south of 14 n where upwelling occurred very little pigment 3 105 km2 this plume reached puerto rico around september october and drifted westward slowly losing its color signature we estimate that the discharge of the orinoco contributes 2 12 of the daily nitrogen requirements of the phytoplankton growing in the river plume and leads to the fixation of 7 29 105 tons of carbon per year the rest of the nitrogen demand appears to be met by nitrogen cycling the large scale 100 km pigment distribution patterns in the caribbean sea seem to be controlled by wind stress flux of water through the basin and river discharge westward advection of atlantic water probably dominates the flow during the first half of the year restricting the dispersal of blooms to the southern half of the caribbean while flushing the central and northern portions as the influx of atlantic water decreases in the second half of the year local ekman transport driven by the trade winds becomes dominant and surface waters drift northwestward throughout the basin the seasonal sequence of changes in pigment distribution patterns was consistent from year to year except in 1980 and 1984 when wind conditions in the caribbean were anomalous close scrutiny of the 4 years of czcs images did not reveal any evidence of large scale 300 km eastward flowing currents in the central caribbean this supports the view that previous observations of countercurrents were based on partial sampling of eddies of 100 250 km diameter

deformation processes at fast to ultra fast oceanic spreading axes mechanical approach abstract the morphology of fast to ultra fast oceanic spreading ridges such as the east pacific rise epr is characterized by an axial dome 5 10 km wide culminating at 300 500 m above the surrounding seafloor this dome is bounded by lateral grabens that develop systematically 2 to 6 km apart from the spreading axis a large summit trough 200 m to 2 km wide locally notches the axial high only where the dome is inflated indicative of a time average robust magma supply this summit trough is thought to represent an elongated axial summit caldera asc created as a result of the subsidence of the top of the axial magma chamber amc such subsidence is likely caused by a temporary decrease in melt supply into the shallow magma reservoir suffering continuous regional extension analog experiments using small scale modeling have been performed in order to better constrain the tectonic evolution of the axial region the experimental apparatus includes an elongated balloon filled with water as an analog of the magma reservoir set in a central groove in a table it is capped with a silicone layer representing hot rocks below the brittle ductile transition and is covered by a sand layer representing the brittle crust the experiments integrate withdrawal of the balloon and extension at the boundary of the model by the mean of two mobile walls three experimental setups allowed us to study independently the mechanical parameters controlling the axial tectonic evolution extension without withdrawal withdrawal without extension withdrawal and synchronous extension we show that the morphology of the epr axis can be considered as the result of both horizontal and vertical movements two symmetrical lateral grabens develop on both sides of a non deformed axial dome when single extension is applied to a model with a thin silicone layer normal faults of the lateral grabens are rooted on two divergent velocity zones dvzs located on the edges of the groove this situation is regarded as an analog of the natural case where the top of the amc acts as a stress free boundary that fails to transmit the extensional stresses to the upper brittle layer an important deflation of the balloon without extension results in the creation of a central collapse trough limited by reverse faults during synchronous extension and withdrawal the initiation of the lateral grabens is favored by a balloon deflation even if such deflation is unable to generate a superficial collapse this last case is considered as representative of the evolution of epr segments showing little variations in melt supply into the amc higher deflation rates under continuous extension correspond to epr segments undergoing strong variations in melt supply in such experiments the lateral grabens are created together with a central collapse trough developing in a way similar to that of experiments involving only balloon deflation finally we show that dvzs located at the brittle ductile boundary are the key mechanical elements which may explain the structural evolution of the axial region of fast to ultra fast spreading ridges the distance from axis and the width of the dvzs directly control the location and the distribution of the lateral grabens

control of rift obliquity on the evolution and segmentation of the main ethiopian rift the main ethiopian rift has evolved in two stages with successive activation of differently oriented fault systems analogue modelling of the earth s lithosphere demonstrates that such a rift evolution requires neither magma weakening nor a change in plate kinematics the main ethiopian rift is an active rift in the break up stage and it marks the incipient boundary between the nubia and somalia plates1 rifting started with the activation of large boundary faults and diffuse volcanism followed by focused magmatism and faulting in the rift floor along step like segments oblique to the rift axis that now act as a protoridge for future seafloor spreading2 this concentration of volcano tectonic activity has been thought to be either magma assisted2 3 or controlled by a change in rift kinematics with a late oblique rifting phase that would have caused the development of the step like fault segments that focused magma upwelling4 5 geodetic6 7 seismic8 and stress field9 data confirm current oblique rifting kinematics but plate kinematics models do not predict a change in nubia somalia motion in the past 11 million years10 here i use lithospheric scale analogue models of oblique rifting to analyse the development of the main ethiopian rift i find that neither magma weakening nor a change in plate kinematics are required to simulate a two phase evolution with successive activation of differently oriented fault systems i conclude that rift evolution and segmentation are controlled by rift obliquity independent of magmatic processes

structural evolution of lake malaŵi africa over 2 000 km of seismic reflection profiles have been collected in lake mala i nyasa the southernmost of the east african rift lakes these studies reported here reveal a severely faulted lake floor bounded by rift structures of pliocene or greater age faults that penetrate the uppermost sedimentary units and numerous earthquakes1 attest to continuing activity in the rift inter basinal differences in fault spacing orientation and sedimentary thicknesses have led to a subdivision of lake mala i into four discrete structural provinces these provinces only now are linked by faults attributed to the most recent episodes of extension an evolutionary sequence of 1 initial block faulting and subsidence 2 fragmentation of fault blocks 3 uplift and 4 renewed subsidence and rotation of fault blocks is proposed for the central part of the mala i rift

oblique extensional tectonics in the malawi rift africa the malawi rift is the southern segment of the western branch of the east african rift system there has been little agreement as to whether this rift is opening perpendicularly or obliquely to its north south axis and little agreement on a mechanism for the formation of the asymmetric basins that make up the rift our analysis combines landsat image interpretation and field measurement of the latest slip direction on faults to produce a kinematic model of rift evolution the fault slip data are consistently compatible with a late cenozoic northwest southeast directed divergence between the nubian and somalian blocks plates across the rift the northwest striking livingstone fault at the northern limit of the malawi rift and the northwest striking zambezi fault zone to the south serve as dextral intracontinental transform zones between left stepping segments of the western branch of the east african rift system within the rift second order northwest striking transfer faults separate adjacent asymmetric basins the transform and transfer faults form a pattern that is similar to overlapping right stepping strike slip faults with a releasing geometry fault surfaces with two sets of striations indicate a progression from predominantly strike slip toward oblique normal faulting we hypothesize that during initial rift formation most northwest striking faults were dextral and that fault interaction between these structures resulted in curved stress trajectories and a pull apart component arcuate north to northeast striking border faults and subsiding basins then formed between these northwest striking faults in response to the right stepping dextral shear the maximum distance over which fault interaction is significant may control basin dimensions as opening of the rift proceeds slip partitioning and gravity failure result in increasing normal slip perpendicular to major escarpments and decreasing strike slip parallel to them

wind driven upwelling in the vicinity of cape finisterre spain observations and numerical simulations of upwelling along the galician coast of spain during april 1982 are presented in situ measurements include shipboard determinations of hydrographic and biological parameters from a grid of stations covering the continental shelf from cape finisterre to ria de vigo sea level data from vigo and la coruna and wind stress estimates derived from the ship winds and from surface pressure charts sea surface temperature information and pigment concentration information have been obtained from a sequence of satellite images from the noaa 7 advanced very high resolution radiometer and the nimbus 7 coastal zone color scanner respectively since the cape finisterre sector of the iberian peninsula is characterized by an abrupt change in coastline orientation wind driven upwelling can occur in that region over a 270 range of wind direction these data document the evolution of upwelling and the resultant coastal circulation in response to two wind events that occurred over a 10 day period salient features of the circulation include a southward coastal jet and a northward flow further offshore along the western coast numerical simulations of the coastal currents the vertical excursion of a density interface from a static equilibrium position and coastal sea level are conducted using a wind patch characterized by constant direction and negative curl the simulations show that during these wind events the greatest upwelling will occur either at cape finisterre or along the northern coast as was observed in this case and as has been reported by others it is suggested on the basis of the analysis of the sea level records and on the numerical simulations that wave disturbances propagate northward along the coast at a speed of 120 160 km day finally it is speculated that much of the organic material formed during upwelling events north of the cape finisterre is advected out to sea northwest of the cape

3d seismic analysis of the ak fault orange basin south africa implications for hydrocarbon leakage and offshore neotectonics abstract a high resolution 3d reflection seismic dataset was used to achieve a detailed description of the half graben bounded ak fault in the ibhubesi gas field of the offshore orange basin seismic analysis of the fault involved the combination of both the conventional seismic interpretation and seismic attributes the main objective of the study was to provide insights into hydrocarbon leakage and neotectonic activity along the west coast shelf of south africa the ak fault is among the several half graben bounded faults that formed in the late jurassic to early cretaceous during the separation of the south american and the african continents the ak fault consists of five seismically detectable segments whose evolution reflects characteristics of both the coherent and the isolated end members model of segmented fault origin diapiric structures that are direct indicators of vertical fluid movement were also observed along the ak fault system providing evidence of significant roles that the fault plays in promoting the vertical migration of hydrocarbon in the orange basin recent reactivation of the fault has also occurred along an oblique extensional regime that is dominated by normal dip slip faulting with minor shear components along the tips

growth and linkage of a complex oblique slip fault zone in the pearl river mouth basin northern south china sea abstract oblique slip faults are ubiquitous in sedimentary basins but have been largely neglected relative to their dip slip counterparts case studies of oblique slip faults are very limited in this study we used 3d seismic data tied to well control to investigate the geometry kinematic characteristics growth and linkage and tempo spatial evolution of a complex oblique slip growth fault zone in the pearl river mouth basin prmb of the northern continental margin south china sea scs the e w oriented 30 5 km long fault zone consists of two superimposed oblique slip fault systems the lower fault system is an integrated zig zag fault consisting of three ene wsw to e w striking right stepping sinistral en echelon fault segments which were hard linked by two nw se trending fault segments while the upper fault system is composed of nine wnw ese striking left stepping dextral en echelon component faults which had overlapping fault tips and were partly hard linked by breaching of the relay zones the lower and upper fault systems were activated in the eocene and the oligocene to pliocene which respectively correspond to the syn rift and post rift stages in the prmb the fault throws up to 288 m and activity rates up to 34 5 m ma of the upper fault system are overall much less than those of its lower counterpart reactivation of the lower syn rift fault system shows clear influence on the development of post rift en echelon fault segments a four stage evolution model of the oblique slip fault zone was presented

successive orthogonal and oblique extension episodes in a rift zone laboratory experiments with application to the ethiopian rift small scale modeling was performed to examine the effects of the superposition of two successive extensional phases from orthogonal to oblique type 1 and from oblique to orthogonal type 2 in both the type 1 and type 2 models faults produced during the first stage strongly control fault development during the second stage in type 1 models the oblique faults developed during the second oblique phase are confined within a first phase graben whereas in type 2 models the oblique faults produced during the first phase continue to develop during orthogonal extension and connect with each other to give sigmoidal fault blocks type 1 models are compared with the structural setting of the ethiopian rift the evolution of the rift is related to a recent extensional event whose principal direction of stretching trends at around 50 to preexisting major normal faults type 1 laboratory models are fairly comparable to the northern sector of the ethiopian rift referred to here as mer they account for both the development of the en echelon oblique faults of the wonji fault belt and the sinistral shear gradient running parallel to the eastern border of the mer which formed during an oblique rifting extension the statistical analysis of the whole ethiopian rift fault pattern by reference to the experimental data allows the determination of a n100 n110 mean direction of stretching

a note on the charleston gyre the deflection of the gulf stream caused by a topographic feature the charleston bump located offshore of savannah georgia results in a quasi stationary cyclonic eddy the charleston gyre which is situated over the continental slope east of charleston and cape romain occasionally the upwelling associated with this eddy produces an enhancement in the surface layer primary production that is great enough to be detected by the nimbus 7 coastal zone color scanner czcs in this note a czcs image with simultaneous hydrography current and wind observations is presented that documents an unusual manifestation of the gyre in addition to the czcs image a seasat synthetic aperture radar sar image is included that clearly indicates the presence of the eddy adjacent to the gulf stream front

continental rift architecture and patterns of magma migration a dynamic analysis based on centrifuge models 1 small scale centrifuge models were used to investigate the role of continental rift structure in controlling patterns of magma migration and emplacement experiments considered the reactivation of weakness zones in the lower crust and the presence of magma at moho depths results suggest that surface deformation which reflects the weakness zone geometry exerts a major control on patterns of magma migration in the case of a single rift segment the experimental lower crust and magma were both transferred in an extension parallel direction toward the rift flanks this lateral migration reflected the dominance of far field stresses over extension induced buoyancy forces local pressure gradients favored the raise of experimental magma in correspondence of marginal grabens the lateral migration gave rise to major accumulations below the footwall of major boundary faults providing the magma source able to feed off axis volcanoes in nature as inferred for the main ethiopian rift in the case of two offset rift segments a major transfer zone developed this transfer zone was characterized by prominent experimental lower crust doming and strong magma accumulation dynamic analysis showed that the transfer zone development caused a strong pressure difference in a rift parallel direction which dominated over the far field thinning owing to this pressure gradient almost all the underplated experimental magma collected below the lower crust dome suggesting a rift parallel extension orthogonal migration this process has a direct relevance for the localization of magmatic activity at transfer zones in natural continental rifts such as in the western branch of the east african rift system

northwest to north northwest extension direction in the ethiopian rift deduced from the orientation of extension structures and fault slip analysis northeast to north northeast trends of eruptive centers some of which formed at the termination of faults and en echelon extension fractures the largest one of which is 0 1 km wide up to 1 km long and at least 50 m deep exist between lat 7 n and 9 n in the ethiopian rift on systeme probatoire d9observation de la terre spot imagery the extension fractures form scars in the rift floor border faults of the rift are generally oriented northeast to north northeast two fault systems observed on land sat multi spectral scanner mss cross the rift the bilate weyira fault with a north northwest strike and the wonji fault belt with a north northeast trend north northwest striking faults cutting across the rift are interpreted to be transfer faults that cut the rift into rhomboid shaped basins extension fractures and rows of eruptive centers collectively referred to as extension structures are used in the paper to infer the direction of plate motion in the ethiopian rift northwest to north northwest extension of the rift is deduced by assuming that the direction of opening of extension structures is also the orientation of the minimum principal stress 3 fault slip inversion on faults that cut post miocene volcanic rocks confirms this interpretation

metallogenic age and hydrothermal evolution of the jidetun mo deposit in central jilin province northeast china evidence from fluid inclusions isotope systematics and geochronology abstract the jidetun deposit is a large porphyry mo deposit that is located in central jilin province northeast china the mo mineralization occurs mainly at the edge of porphyritic granodiorite as well as the adjacent monzogranite field investigations cross cutting relationships and mineral paragenetic associations indicate four stages of hydrothermal activity to determine the relationships between mineralization and associated magmatism and better understand the metallogenic processes in ore district we have undertaken a series of studies incluiding molybdenite re os and zircon u pb geochronology fluid inclusions microthermometry and c h o s pb isotope compositions the molybdenite re os dating yielded a well defined isochron age of 168 9 1 9 ma mswd 0 34 that is similar to the weighted mean 206 pb 238 u age of 173 5 1 5 ma mswd 1 8 obtained from zircons from the porphyritic granodiorite the results lead to the conclusion that mo mineralization occurred in the middle jurassic 168 9 1 9 ma was spatially temporally and genetically related to the porphyritic granodiorite 173 5 1 5 ma rather than the older monzogranite 180 1 0 6 ma fluid inclusion and stable c h o isotope data indicate that the initial h 2 o nacl fluids of mineralization stage i were of high temperature and high salinity affinity and exsolved from the granodiorite magma as a result of cooling and fractional crystallization the fluids then evolved during mineralization stage ii into immiscible h 2 o co 2 nacl fluids that facilitated the transport of metals mo cu and fe and their separation from the ore bearing magmas due to the influx of abundant external co 2 and heated meteoric water subsequently during mineralization stage iii and iv increase of ph in residual ore forming fluids on account of co 2 escape and continuous decrease of ore forming temperatures caused by the large accession of the meteoric water into the fluid system reduced solubility and stability of metal clathrates thus facilitating the deposition of polymetallic sulfides

scales and variability of the sea surface temperature distribution in the adriatic sea 1 scales and variability of the adriatic sea surface temperature sst distribution in the period january 1991 to december 2000 are studied by means of 8 day composite 4 km resolution sst data scales of the sst are defined as scales of the sst autocorrelation function assuming an exponential correlation model scales of the sst are quantified as e folding times and distances of the sst autocorrelation function variability in the sst is analyzed through empirical orthogonal function eof analysis from summer to winter spatial scales of the sst in the along basin direction remain unchanged while in the across basin direction they decrease resulting in scales that are slightly shorter 10 15 in winter than in summer the spatial distribution of temporal scales displays two patterns the first characterized by low values is located in the northern part of the basin and along the italian coast and the second characterized by high values covers the rest of the basin the sst variability is dominated by the annual signal which explains 45 of the overall variance the main structures of the adriatic circulation leave their signature on the first three eofs whose spatial variability occurs on wavelengths longer than 200 km in the along basin direction and in the across basin direction in the band 25 50 km and at 80 and 100 km eof coefficients are characterized by oscillating components with periods of 20 days to 6 months

a block model of distributed deformation by faulting it is clear from palaeomagnetic evidence that large and hitherto unexpected rotations about a vertical axis are common in regions of distributed continental deformation we propose a simple two dimensional model to illustrate how fault movement and block rotation within a zone of distributed deformation may be related to the relative motion of the rigid plates that bound the zone one surprizing feature of this model is that the component of strike slip motion on the faults within the deforming zone is in the opposite sense to the strike slip component across the zone as a whole thus slip vectors within the zone are not the same as that between the bounding rigid plates in contrast to deformation at oceanic plate boundaries examples of active fault geometries similar to those of our model can be seen in greece iran and the western usa

experiments on fault reactivation in strike slip mode abstract experiments were undertaken to investigate how faults reverse or normal in a cover sequence become reactivated when an underlying basement fault is itself reactivated in strike slip mode physical models properly scaled for gravity were deformed in a large 2 1 5 m apparatus divided into two halves one half can be moved laterally or vertically past the other models were constructed with a coulomb layer sand overlying a newtonian ductile layer silicone three different configurations of the basement fault reverse normal or vertical defined three series of experiments each consisted of 1 brittle model 6 cm of sand and 2 brittle ductile models 5 cm of sand overlying 1 cm of silicone or 4 cm of sand overlying 2 cm of silicone each model was deformed in two steps 1 a pure dip slip stage and 2 a reactivation in pure strike slip mode in surface views little reactivation was observed but in all cases the deformation imposed during the strike slip episode was localized by pre existing dip slip structures in cross sections however faults were seen reactivated at depth on the basis of these experiments we suggest that 1 a previously faulted zone can control the deformation of a strike slip zone and 2 reactivation of faults in strike slip mode can occur at depth without being visible at the surface we attribute the higher probability of reactivation at depth to the mechanical properties of the sand especially cohesion

temporal variations of particle fluxes in the deep subtropical and tropical north atlantic eulerian versus lagrangian effects the flux of particles measured by sediment traps in the deep water of the sargasso sea and western tropical north atlantic undergoes pronounced temporal variation in the sargasso sea the variability is largely due to seasonal changes in mixed layer depth and attendant changes in primary productivity affecting a wide region by contrast the variability in the western tropical atlantic appears to be caused by patches of elevated nutrient and pigment concentrations which have their origin in the plumes of the amazon and orinoco rivers coastal zone color scanner scenes demonstrate the great seasonal and interannual differences in the direction and dispersal patterns of the plumes the river plumes break up into irregular patches which may pass through the catchment area of a sediment trap at varying rates thereby creating the impression of almost random temporal flux variability at a fixed trap site

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

interannual variability in phytoplankton blooms observed in the northwestern arabian sea during the southwest monsoon interannual changes in the strength and seasonal evolution of the 1979 through 1982 surface level southwest monsoon winds have been related to variations in the summer phytoplankton bloom of the northwestern arabian sea by synthesis of satellite ocean color remote sensing with analysis of in situ hydrographic and meteorological data sets the 1979 1981 southwest monsoon phytoplankton blooms in the northwest arabian sea peaked during august september extended from the omani coast to about 65 e and appeared to lag the development of open sea upwelling by at least 1 month in all 3 years the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore ekman pumping coastal upwelling was evident from may through september yielded the most extreme concentrations of phytoplankton biomass and along the omani coast was limited in its impact on upper ocean biological variability to the continental shelf ekman pumping stimulated the development of a broad open ocean component of the southwest monsoon phytoplankton bloom oceanward of the omani shelf phytoplankton biomass on the omani continental shelf was increased during both the early and late phases of the 1980 southwest monsoon due to stronger coastal upwelling under the most intense southwesterly winds of the four summers investigated diminished coastal upwelling during the early phase of the weak 1982 southwest monsoon resulted in a coastal bloom that reached a mean phytoplankton pigment concentration that was 28 of that seen in 1980 the lack of a strong regional northwestern arabian sea bloom in late summer 1982 is attributed to the development of persistent shallow temperature stratification that rendered ekman pumping less effective in driving upward nutrient fluxes

structural and geochronological implications of the fentale volcanics at a nascent passive margin of the main ethiopian rift constraints from magnetostratigraphy study at the kereyou lodge ethiopia abstract we sampled twenty four cooling units for magnetostratigraphic study from a 110 m thick early pleistocene volcanic section near kereyou lodge in the main ethiopian rift seven samples were used from each site for analysis of remanent magnetization using thermal and alternating field demagnetization techniques the natural remanent magnetization nrm direction comprises two vector components in most samples the first low stability component is isolated generally by heating to 100 c 250 c or by demagnetization using an alternating field intensity of 10 15 mt after these steps most magnetization directions define straight lines directed towards the origin and record the primary nrm or chrm characteristic remanent magnetization magnetization decay curve analyses show the possible magnetic minerals to be titanomagnetite magnetite titanohematite and hematite paleomagnetic site mean directional analyses revealed that upper 18 flows are of reversed polarity and the bottom 4 flows are normal using available age information the normal interval is correlated to the olduvai subchron on the geomagnetic polarity time scale gpts of cande kent 1995 and the flows at the polarity transition are dated to be 1 77 ma the overall declination and inclination differences calculated d 4 8 4 4 i 0 8 4 2 are consistent with the 7 counterclockwise reported kidane et al 2009 site mean inclinations show a systematic change with flow position inclinations get progressively shallower with depth for the top 17 volcanic flows and progressively steeper for the bottom 4 flows consistent with progressive backward and rift ward block tilting mechanisms respectively

role of weak zone orientation in continental lithosphere extension 1 lithosphere extension and continental breakup axes are often sub parallel to orogenic belts and suture zones in an attempt to understand the relation between weak zone orientation and extension direction a 3 d numerical model is developed with which the following aspects are studied the relation between weak zone axis and axis of maximum crustal deformation the amount and distribution of crustal thinning and subsequent implications for rift a symmetry the results suggest that upon oblique extension rifts develop within the weak zone that individually cross the inherited structure while as a group they follow the weak trend this results in an alternating rift asymmetry the pattern of crustal thinning topography and thermal structure are not symmetric around the rift axes of the major rift zones and change along axis over such a rift this is a possible explanation for alternating asymmetric rift structures such as observed in the east african rift system

complex rift geometries resulting from inheritance of pre existing structures insights and regional implications from the barmer basin rift abstract structural studies of the barmer basin in rajasthan northwest india demonstrate the important effect that pre existing faults can have on the geometries of evolving fault systems at both the outcrop and basin scale outcrop exposures on opposing rift margins reveal two distinct non coaxial extensional events on the eastern rift margin northwest southeast extension was accommodated on southwest and west striking faults that form a complex zig zag fault network on the western rift margin northeast southwest extension was accommodated on northwest striking faults that form classical extensional geometries combining these outcrop studies with subsurface interpretations demonstrates that northwest southeast extension preceded northeast southwest extension structures active during the early previously unrecognised extensional event were variably incorporated into the evolving fault systems during the second in the study area an inherited rift oblique fault transferred extension from the rift margin to a mid rift fault rather than linking rift margin fault systems directly the resultant rift margin accommodation structure has important implications for early sediment routing and depocentre evolution as well as wider reaching implications for the evolution of the rift basin and west indian rift system the discovery of early rifting in the barmer basin supports that extension along the west indian rift system was long lived multi event and likely resulted from far field plate reorganisations

structure and evolution of the eastern gulf of aden conjugate margins from seismic reflection data the gulf of aden is a young and narrow oceanic basin formed in oligo miocene time between the rifted margins of the arabian and somalian plates its mean orientation n75 e strikes obliquely 50 to the n25 e opening direction the western conjugate margins are masked by oligo miocene lavas from the afar plume this paper concerns the eastern margins where the 19 35 ma breakup structures are well exposed onshore and within the sediment starved marine shelf those passive margins about 200 km distant are non volcanic offshore during the encens sheba cruise we gathered swath bathymetry single channel seismic reflection gravity and magnetism data in order to compare the structure of the two conjugate margins and to reconstruct the evolution of the thinned continental crust from rifting to the onset of oceanic spreading between the alula fartak and socotra major fracture zones two accommodation zones trending n25 e separate the margins into three n110 e trending segments the margins are asymmetric offshore the northern margin is narrower and steeper than the southern one including the onshore domain the southern rifted margin is about twice the breadth of the northern one we relate this asymmetry to inherited jurassic cretaceous rifts the rifting obliquity also influenced the syn rift structural pattern responsible for the normal faults trending from n70 e to n110 e the n110 e fault pattern could be explained by the decrease of the influence of rift obliquity towards the central rift and or by structural inheritance the transition between the thinned continental crust and the oceanic crust is characterized by a 40 km wide zone our data suggest that its basement is made up of thinned continental crust along the southern margin and of thinned continental crust or exhumed mantle more or less intruded by magmatic rocks along the northern margin abstract from author

development of the north viking graben inferences from laboratory modelling abstract the north viking graben is a classic sedimentary basin in the north sea that has been thoroughly studied over the last decade despite the amount and quality of seismic and well data now available the processes of extension remain unclear and the relationship between sedimentation and deformation is still a matter of debate we present the results of small scale laboratory modelling the models are made with sand and silicone putty to simulate brittle and ductile behaviour on a crustal scale the experiments were designed to study the effects of a the degree of coupling between brittle and ductile layers b the obliquity of extension and c the reactivation of inherited crustal scale structures the results are used to discuss the symmetry of extensional processes on crustal and lithospheric scales as well as the relationship between sedimentation and deformation it is proposed that the asymmetry of faulting in the upper crust and the nearly symmetric thinning of the whole crust are not mutually exclusive a model involving nearly pure shear on the lithospheric scale is used to explain the development of an asymmetrical basin at shallow level in addition this model accounts for the nearly horizontal stratification of lower cretaceous sediments the basal cretaceous unconformity which caps many of the normal faults and the localization of deformation to the west of the graben during the lower cretaceous

shear test results for cohesion and friction coefficients for different granular materials scaling implications for their usage in analogue modelling abstract laboratory tests have been carried out on dry granular materials such as quartz sand glass microspheres and sugar with different grain size rounding and sphericity the measurements have been made with a simple shear test machine for different values of normal stress 50 900 pa shear stress has been plotted against normal stress in order to determine the cohesion and coefficient of internal friction for the investigated materials resulting values of cohesion and coefficient of internal friction are mainly dependent on rounding and sphericity while grain size has a less significant influence further the behaviour of the materials for very small normal stresses 0 400 pa is more complex than previously assumed the fracture envelopes for all materials investigated are convex outward for this small range and converge towards a straight failure envelope with increasing normal stress finally in extensional faulting experiments there is no significant change in fault dip with increasing depth therefore the non linear behaviour for small normal stresses is best described as a dependence of the cohesion on the normal stress and not as a dependence of the coefficient of internal friction on the normal stress values for cohesion increase from 0 pa 15 pa at zero normal stress to 137 247 pa 15 pa for normal stresses greater than 250 400 pa the results show that well rounded spherical material is better suited to model brittle behaviour of rocks in crustal and lithospheric scale analogue models than less well rounded material since it has a smaller cohesion and a coefficient of internal friction which is closer to values of natural rocks

oblique rifting at oceanic ridges relationship between spreading and stretching directions from earthquake focal mechanisms the relationship between spreading and stretching directions is investigated at oblique spreading oceanic ridges using earthquake focal mechanisms the stretching direction at ridge axes corresponds to the direction of the greatest principal strain 31 taken as the mean trend of the seismic t axes of extensional earthquake focal mechanisms it is compared with the spreading direction provided by global plate motion models we find that the stretching direction trends approximately halfway between the spreading direction and the normal to the ridge trend a result in line with analogue experiments of oblique rifting this result is satisfactorily accounted for with an analytical model of oblique rifting for which the direction of 31 is calculated with respect to rifting obliquity for different amounts of stretching using continuum mechanics for low stretching factors typical of incremental seismic deformations 31 obliquity is two times lower than rifting obliquity for higher stretching factors the stretching and spreading directions become parallel 2006 elsevier ltd all rights reserved

salt flow and diapirism related to extension at crustal scale abstract the analysis of the structure and history of salt diapirs in large ancient evaporitic basins such as the southeastern north sea basin suggests that diapirism is controlled by crustal scale extension laboratory experiments on small scale models designed to simulate configurations comparable to the southeastern north sea basin show that diapirs which grow in a sedimentary cover during basement extension can develop close to basement normal faults or at a significant distance from them if the displacement on the basement faults is transfered horizontally along the salt layer for given values of salt viscosity strain rate and friction coefficient in brittle rocks the pattern of salt diapirism in a particular area depends on the ratio of cover thickness to salt thickness as well as the absolute thicknesses of cover and salt layers the experiments give criteria for identifying different types of diapirs and provide models of horizontal flow in a salt layer undergoing extension and diapir development some dynamic implications of the experiments are applied to the southeastern north sea basin

extension direction re orientation in the oceanic rift of iceland and comparison with continental rifts abstract in this study we report the results of a structural analysis carried out on fault systems that form the active rift segments of two areas of iceland namely 1 the northern part of the eastern rift segment northern volcanic zone nvz and 2 the western rift segment that include the western volcanic zone thingvellir area and the reykjanes peninsula in the n s trending nvz mainly krafla volcanic area the obtained extension directions trend around ese at thingvellir the extension directions trend ca nw se and are perpendicular to the main ne sw trending faults in the ene wsw trending tectono magmatic segments of the reykjanes peninsula our data show a marked difference with the gps data and spreading directions the extension directions trend roughly orthogonal to the strike of the boundary faults in all the investigated sectors extension shows an overall southward increase in divergence from the regional directions indicated by gps vectors this behavior has been compared with the continental main ethiopian rift of east africa where structural studies show a re orientation of the extension direction between the rift margins and the internal sectors resulting in a divergence between local and regional extension directions aimed at investigating the causes of these differences we performed a new series of analogue models by varying different parameters such as rift obliquity and width our findings suggest that rift width exerts a primary control on the boundary axis variation of the extension direction in particular significant differences in fault orientation and local direction of extension between the margins and the rift axis are observed in wider rift valleys e g continental rift of ethiopia conversely fault orientation and local extension direction are much more homogeneous in narrower rift valleys e g rifts of iceland where a variations in the direction of extension from the margins to the rift axis are not observed

coupling of coastal zone color scanner data to a physical biological model of the southeastern u s continental shelf ecosystem 1 czcs data description and lagrangian particle tracing experiments nine coastal zone color scanner czcs images from the southeastern u s continental shelf area during april 1980 were processed and the resulting chlorophyll distributions were analyzed in conjunction with concurrent flow and temperature fields which were obtained from an optimal interpolation of current meter measurements from 17m the chlorophyll distributions obtained from the czcs showed high chlorophyll concentrations over the shelf and low chlorophyll concentrations over the offshore shelf region the variance of the czcs derived chlorophyll distributions was highest at the shelf break region the chlorophyll patterns at the shelf break varied with time and space and showed shapes characteristic of typical gulf stream frontal eddies high chlorophyll bands that were oriented along shelf isolated high chlorophyll patches and simple waveforms each event observed in the chlorophyll patterns corresponded with a gulf stream frontal eddy event that could be identified in the optimally interpolated flow and temperature fields lagrangian particle tracing experiments were also conducted to track the movement of the features observed in the czcs images the particles traced in these experiments showed movement that was consistent with the evolution of the patterns observed in the czcs chlorophyll distributions results of the lagrangian experiments indicate that the optimal interpolation of the current meter measurements reproduced the flow between successive czcs images these experiments provide evidence that the high chlorophyll bands seen in the czcs chlorophyll distributions were produced by the passing of gulf stream frontal eddy events

slip history of the la cruz fault development of a late miocene transform in response to increased rift obliquity in the northern gulf of california abstract the gulf of california rift has accommodated oblique divergence of the pacific and north america plates in northwestern mexico since miocene time due to its infancy its rifted margins preserve a rare onshore record of early continental break up processes and an opportunity to investigate the role of rift obliquity in strain localization we map rift related structures and syn tectonic basins on southern isla tiburon a proximal onshore exposure of the rifted north america margin we integrate analysis and geochronology of syn tectonic sedimentary basins and mapping of crosscutting relationships to characterize the style and timing of fault activity on southern isla tiburon an early phase of extension initiated between 19 17 ma and 12 2 ma subsequently these normal faults and related basins were cut by the la cruz strike slip fault and buried by deposits of the la cruz basin an elongate fault controlled trough coextensive with the la cruz fault crosscutting relationships show that the nw striking la cruz fault accrued 5 2 km of dextral slip 8 4 ma the la cruz fault and parallel tiburon transform were kinematically linked to detachment faulting that accommodated latest miocene to pliocene oblique opening of the offshore upper tiburon pull apart basin the onset of strike slip faulting on isla tiburon was synchronous with the 8 6 ma onset of transform faulting and basin formation along 1000 km of the reconstructed pacific north america plate boundary this transition coincides with the commencement of a clockwise azimuthal shift in pacific north america relative plate motion that increased the obliquity of the gulf of california rift and formed the gulf of california shear zone the record from the proto gulf of california illustrates how highly oblique rift geometries where transform faults are kinematically linked to pull apart basins enhance the ability of continental lithosphere to rupture and ultimately hasten the formation of new oceanic rift basins

insights into the effects of oblique extension on continental rift interaction from 3d analogue and numerical models abstract continental rifts often develop from linkage of distinct rift segments under varying degrees of extension obliquity these rift segments arise from rift initiation at non aligned crustal heterogeneities and need to interact to develop a full scale rift system here we test the effects of 1 oblique extension and 2 initial heterogeneity seed offset on continental rift interaction with the use of an improved analogue model set up x ray computer tomography ct techniques are used to analyse the 3d models through time and the results are compared with additional numerical models and natural examples the experimental results reveal that increasing extension obliquity strongly changes rift segment structures from wide rifts in orthogonal settings to narrower rifts with oblique internal structures under oblique extension conditions to narrow strike slip dominated systems towards the strike slip domain we also find that both decreasing seed offset and increasing extension obliquity promote hard linkage of rift segments through the formation of continuous rift boundary faults at the surface initial soft linkage through the formation of relay ramps is more likely when seed offset increases or extension is more orthogonal rather than linking at depth the rift boundary faults curve around each other at depth and merge towards the surface to form a continuous trough orthogonal extension promotes the formation of intra rift horsts which may provide hydrocarbon traps in nature

oblique rifting at tempe fossae mars this work shows the results of a structural study of the faults observed at the tempe rift northeastern tharsis region mars a new detailed map of faults and fault systems was used to geometrically characterize the fracture architecture of the tempe rift and to measure fault length displacement and spacing data to analyze the spatial distribution of fault centroids and to investigate the fractal nature of fault trace maps a comparison with analog models and the use of conventional techniques of fault population analysis show that the tempe rift was most probably generated under sinistral oblique rifting processes which highlights the importance of the presence of inherited fractures in the tectonic evolution of the noachian crust the angle between the extension direction and the rift axis varies along the tempe rift ranging from 50o 60o at its central southern part to 66o 88o to the southwest fault scaling relationships are similar to those found at midocean ridges on earth with exponential fault length frequency distributions localized inhomogeneous deformation generated weakly interacting faults spanning the entire thickness of the mechanical layer this thickness decreased from southwest to northeast along the rift along with distance from the central part of the tharsis dome

oblique slip and the geometry of normal fault linkage mechanics and a case study from the basin and range in oregon abstract map patterns of normal fault linkages near summer lake oregon show a systematic relationship between echelon step sense oblique slip sense and the position of linking faults where the step sense is the same as the sense of oblique slip e g left step and left oblique slip the faults are linked in the lower part of their relay ramp where the step sense and slip sense are opposite e g left step and right oblique slip the faults are linked in the upper part of the ramp a boundary element code is used to calculate the stress field around echelon normal faults during oblique slip and the model results reveal a relationship similar to the field observations if step sense and oblique slip sense are the same there is a greater potential for deformation ahead of the tip of the front fault and in the lower part of the ramp if step sense and oblique slip sense are opposite there is a greater potential for deformation ahead of the tip of the rear fault and in the upper part of the ramp the field model comparison confirms that oblique slip modifies the mechanical interaction among fault segments and thus influences fault growth and the geometry of fault linkage

normal vs strike slip faulting during rift development in east africa the malawi rift kinematic analysis of neogene and quaternary faults demonstrates that the direction of extension in the malawi rift rotated from east northeast to southeast rift development commenced with the formation of half grabens bounded by northwest north and northeast striking normal faults owing to slightly oblique rifting the northwest striking faults in the northernmost rift segment show a small dextral oblique slip component whereas north and northeast oriented faults in the central part of the rift display a sinistral oblique slip component this first event resulted in block faulting and basin subsidence which is largely responsible for the present day basin morphology of lake malawi a major change in fault kinematics occurred because of rotation of the extension direction and permutation of the principal compressive and intermediate axes the structural pattern inherited from the first rifting phase was no longer suitably oriented to accommodate extensional deformation and strike slip faulting assumed a major role the strike slip regime amplified uplift of basement ridges within the rift in regions of local transpression but it also created alluvial basins because of local transtension this new kinematic style is compatible with the recent seismicity older faults that show mainly the first deformational increment are restricted to the outermost parts of the rift toward the center the faults depict an increase in strike slip components of movement suggesting deformation propagation toward the rift center which results in a narrowing of the active rift environments with time

constraining the african pole of rotation abstract in the absence of well defined transform faults in the east african rift system for constraining the plate kinematic reconstruction the pole of relative motion for the african nubian and somalian plates has been determined from residual motion if africa and somalia are to continue to drift apart along the east african rift system which would then evolve into a series of ridges offset by transform faults then incipient transform faults that may reflect the direction of relative motion should already be in place along the east african rift system the incipient transforms along the east african rift system are characterized by shear zones such as the zambezi shear zone in the south and the aswa and hamer shear zones in the north some of these shear zones have been associated with recent strike slip faulting in the nw se direction during periods of earthquakes provided that these consistently nw se oriented strike slip movements in the shear zones give the direction of relative motion of the adjacent plates then they can be used to constrain the position of the africa somalia euler pole due to the fact that identifying transform faults in the east african rift system is difficult and because the genesis of transform faults characterizing a plate boundary at an inception stage is not well known the discussion here is limited to the northern segment of the east african rift system where shear zones are better characterized by the existing geophysical data the characterizing features vary with latitude indicating the complexity of the problem of the genesis of transform faults i believe however that the relatively well defined intra continental transform fault in the northern east african rift system which is characterized by strike slip faulting and earthquakes constrains the pole of relative motion for the african and somalian plates to a position near 1 5 s and 29 0 e

the influence of preexisting structure on the evolution of the cenozoic malawi rift east african rift system this paper analyzes the importance of preexisting structure for the evolution of the cenozoic malawi rift which constitutes the southernmost part of the western branch of the east african rift system kinematic analyses demonstrate that the regional extension direction rotated clockwise from ene to se during rifting cenozoic rift faults of dip oblique and strike slip character rejuvenated crustal structures whenever those were properly oriented with respect to the extension directions depending on these boundary conditions the rift attempts to find the easiest pathway in order to develop in a mechanically modest way proterozoic basement structures represent the basic anisotropy which already influenced pre cenozoic rifts and also the cenozoic malawi rift amongst these basement structures pan african retrograde to cataclastic strike slip shear zones have the strongest influence on later rift structures rift related transfer faults appear as differently striking passive structures and their orientation seems to be controlled by a variety of steep basement structures retrograde shear zones foliation planes and fracture arrays

empirical orthogonal function analysis of cloud containing coastal zone color scanner images of northeastern north american coastal waters empirical orthogonal function eof analyses were performed on 36 coastal zone color scanner czcs images of the mid atlantic bight and gulf of maine taken from february 28 1979 through july 9 1979 the eof procedure was modified to allow images with significant portions of data missing because of clouds to be included in the analysis analyses performed both with the temporal and with the spatial means removed from the data produced similar results a strong gradient existed in the temporal mean from high pigment concentrations nearshore to much lower pigment concentrations offshore the first mode of the temporally averaged analysis explained 21 5 of the variance and showed a south to north pattern corresponding to an april mid atlantic bight bloom and a june bloom over nantucket shoals and platts bank the second temporally averaged mode explained 18 3 of the variance and corresponded to a shelf wide phytoplankton bloom that resulted in increased pigment concentrations through the spring the first mode of the spatially averaged analysis explained 59 1 of the variance and had a pattern similar to the temporal mean the second mode explained an additional 13 2 of the variance and was almost identical to the first mode in the temporally averaged analysis the inclusion of cloud containing images introduced some small scale spatial noise into the eof analyses however the inclusion of these images in the eof analysis allowed postanalysis image reconstruction that provided estimates of pigment concentrations beneath the clouds

oblique rifting in a slow spreading ridge in oceanic rifts the spreading direction is usually nearly perpendicular to the ridge axis but at the reykjanes1 and mohns2 4 ridges this direction is highly oblique 30 to 40 to the axis these ridges possess axial valleys containing oblique raised features highs corresponding to second or third order ridge axis discontinuities5 at the reykjanes ridge searle and laughton1 observed small highs which they interpreted as volcanic domes here we present a fault map of the mohns ridge obtained from image processing of seabeam data we argue that the oblique highs in this ridge are of tectonic origin the axial valley is interpreted as the surface trace of a deformable band of oceanic lithosphere inherited from an earlier stage of perpendicular spreading we describe laboratory experiments on brittle ductile models which support this interpretation in which stretching at 30 to a deformable band reproduces the en echelon horst and graben pattern of the mohns ridge

patterns of faulting in the ethiopian rift valley abstract some typical and some unusual fault patterns are described from the ethiopian rift valley they include arcuate faults convex in plan towards the downthrown side lines of obliquely tilted faulted blocks up horsts horizontally stratified rhomb horsts athwart tilted strata faults whose polarity switches in conjunction with development of small horsts intersecting fault sets and re entrant and semi circular faults explanations remain wanting for many of these phenomena which show that crustal extension can be complex at the meso scale

fault growth and interactions in a multiphase rift fault network horda platform norwegian north sea abstract physical models predict that multiphase rifts that experience a change in extension direction between stretching phases will typically develop non colinear normal fault sets furthermore multiphase rifts will display a greater frequency and range of styles of fault interactions than single phase rifts although these physical models have yielded useful information on the evolution of fault networks in map view the true 3d geometry of the faults and associated interactions are poorly understood here we use an integrated 3d seismic reflection and borehole dataset to examine a range of fault interactions that occur in a natural multiphase fault network in the northern horda platform northern north sea in particular we aim to i determine the range of styles of fault interaction that occur between non colinear faults ii examine the typical geometries and throw patterns associated with each of these different styles and iii highlight the differences between single phase and multiphase rift fault networks our study focuses on a ca 350 km 2 region around the 60 km long n s striking tusse fault a normal fault system that was active in the permian triassic and again in the late jurassic to early cretaceous the tusse fault is one of a series of large 1500 m throw n s striking faults forming part of the northern horda platform fault network which includes numerous smaller 2 10 km long lower throw nd stage nw se striking faults grew interacted and linked with the n s striking tusse fault documenting a range of interaction styles including mechanical and kinematic isolation abutment retardation and reactivated relays our results demonstrate that i isolated and abutting interactions are the most common fault interaction styles in the northern horda platform ii pre existing faults can act as sites of nucleation for 2 nd stage faults or may form mechanical barriers to propagation iii the throw distribution on reactivated 1 st stage faults will be modified in a predictable manner if they are intersected or influenced by 2 nd stage faults iv sites of fault linkage and relay breaching associated with the first phase of extension can act as preferential nucleation sites for 2 nd stage faults and v the development of fault intersections is a dynamic process involving the gradual transition from one style to another

structure of the rift basins in the central gulf of california kinematic implications for oblique rifting abstract we use structural and seismostratigraphic interpretation of multichannel seismic reflection data to understand the structure and kinematic history of the central gulf of california our analysis reveals that oblique strain in the central gulf formed two tectono sedimentary domains during distinct deformation stages the eastern domain offshore sonora is bounded by the east and west pedro nolasco faults that may constitute the southernmost segments of the tiburon fault system within this domain the dip slip yaqui fault controlled deposition of 3 9 km of sediments in the half graben yaqui basin the western domain offshore baja california is bounded by the guaymas transform fault which controlled the accumulation of 1 45 km of sediments within a half graben that formed the early guaymas basin the tectono sedimentary activity offshore sonoran likely ranges from late miocene pliocene to late pliocene time while activity in the guaymas basin commenced in late pliocene time extinction of the main faults offshore sonora was nearly coeval to the initiation of the guaymas transform fault our results suggest that oblique strain has been accommodated by strain partition since the onset of rifting in the central gulf the guaymas basin is now a nascent spreading center but prior to this it evolved as a half graben controlled by the guaymas transform fault such drastic transition is not constrained but likely occurred during the pleistocene time and must be localized

faulting and block rotation in the afar triangle east africa the danakil crank arm model several domains of contrasted extensional deformation have been identified in the southern afar triangle east africa from fault patterns analyzed with panchromatic stereoscopic spot systeme probatoire d9observation de la terre images stretching directions and statistical orientation and offset variations of faults fit with the danakii crank arm model of sichler a 10 sinistral rotation of the danakil block explains the fault geometry and dextral block rotation in the southern part of the afar triangle as well as the oblique extension in the tadjoura gulf analogue modeling supports this interpretation