a new look at the saturn system the voyager 2 images voyager 2 photography has complemented that of voyager i in revealing many additional characteristics of saturn and its satellites and rings saturn s atmosphere contains persistent oval cloud features reminiscent of features on jupiter smaller irregular features track out a pattern of zonal winds that is symmetric about saturn s equator and appears to extend to great depth winds are predominantly eastward and reach 500 meters per second at the equator titan has several haze layers with significantly varying optical properties and a northern polar collar that is dark at short wavelengths several satellites have been photographed at substantially improved resolution enceladus surface ranges from old densely cratered terrain to relatively young uncratered plains crossed by grooves and faults tethys has a crater 400 kilometers in diameter whose floor has domed to match tethys surface curvature and a deep trench that extends at least 270 around tethys circumference hyperion is cratered and irregular in shape iapetus bright trailing hemisphere includes several dark floored craters and phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours within saturn s rings the birth of a spoke has been observed and surprising azimuthal and time variability is found in the ringlet structure of the outer b ring these observations lead to speculations about saturn s internal structure and about the collisional and thermal history of the rings and satellites

block models of crustal motion in southern california constrained by gps measurements 1 we estimate slip rates on major active faults in southern california using a block model constrained by global positioning system measurements of interseismic deformation the block model includes the effects of block rotation and elastic strain accumulation consistent with a simple model of the earthquake cycle our estimates of the right lateral strike slip rate on the san andreas fault vary by at least a factor of 5 from a high of 35 9 0 5 mm yr in the carrizo plain to a low of 5 1 1 5 mm yr through the san bernadino segment shortening across the puente hills thrust and left lateral slip on the raymond hill fault are consistent with both thickening and escape tectonics in the los angeles basin discrepancies between geodetic and geologic slip rate estimates along the san andreas and san jacinto faults as well as in the eastern california shear zone may be explained by a temporal change in fault system behavior we find no substantial evidence for long term postseismic relaxation and infer that the viscosity of the lower crust upper mantle may be relatively high 1019 pa s

stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

subduction and volcanism in the iberia north africa collision zone from tomographic images of the upper mantle abstract new tomographic images of the upper mantle beneath the westernmost mediterranean suggest that the evolution of the region experienced two subduction related episodes first subduction of oceanic and or extended continental lithosphere now located mainly beneath the betics at depths greater than 400 km took place on a nw se oriented subduction zone this was followed by a slab tear process that initiated in the east and propagated to the west leading to westward slab rollback and possibly lower crustal delamination the current position of the slab tear is located approximately at 4 w and to the west of this location the subducted lithosphere is still attached to the surface along the gibraltar arc our new p wave velocity model is able to image the attached subducted lithosphere as a narrow high velocity body extending to shallow depths coinciding with the region of maximum curvature of the gibraltar arc the occurrence of intermediate depth earthquakes and anomalously thick crust this thick crust has a large influence in the measured teleseismic travel time residuals and therefore in the obtained p wave tomographic model we show that removing the effects of the thick crust significantly improves the shallow images of the slab and therefore the interpretations based on the seismic structure

incipient mantle delamination active tectonics and crustal thickening in northern morocco insights from gravity data and numerical modeling abstract the betic rif orocline surrounding the alboran sea the westernmost tip of the mediterranean sea accommodates the nw se convergence between the nubia and eurasia plates recent gps observations indicate a 4 mm yr sw motion of the rif mountains relative to stable nubia incompatible with a simple two plate model new gravity data acquired in this study define a pronounced negative bouguer anomaly south of the rif interpreted as a 40 km thick crust in a state of non isostatic equilibrium we study the correlation between these present day kinematic and geodynamic processes using a finite element code to model in 2 d the first order behavior of a lithosphere affected by a downward normal traction representing the pull of a high density body in the upper mantle we show that intermediate viscosities for the lower crust and uppermost mantle 10 21 10 22 pa s allow an efficient coupling between the mantle and the base of the brittle crust thus enabling 1 the conversion of vertical movement resulting from the downward traction to horizontal movement and 2 shortening in the brittle upper crust our results show that incipient delamination of the nubian continental lithosphere linked to slab pull can explain the present day abnormal tectonics contribute to the gravity anomaly observed in northern morocco and give insight into recent tectonics in the western mediterranean region

the control network of rhea abstract a control network of the saturnian satellite rhea has been established photogrammetrically from pictures taken by the two voyager spacecraft coordinates of 288 control points on rhea have been computed and listed some of these are identified on the preliminary u s geological survey map of rhea and many of the control point features have been named pixel measurements of these points were made on 81 voyager 1 and 3 voyager 2 pictures the longitude system on rhea is defined by the crater tore the 340 meridian passes through the center of this crater the mean radius of rhea has been determined as 764 4 km

an integrated geophysical investigation of recent seismicity in the al hoceima region of north morocco abstract data produced by the moroccan national seismological network and marine seismic reflection profiles are used to investigate the most seismically active region in morocco located on the mediterranean coast at the intersection of the rif mountain belt and the submarine alboran ridge this region in the vicinity of the city of al hoceima marks an east west transition in the marine and land deformation styles of the distributed plate boundary between africa and iberia and was the site of an m w 6 0 earthquake on 26 may 1994 the epicenter of the al hoceima earthquake is relocated onshore refining the initial submarine location close to the alboran ridge the spatial distribution of foreshocks and aftershocks shows a ne sw trend that continues partly offshore and is subparallel to the earlier yet still prominent miocene geologic structural trend the predominantly strike slip focal mechanism for the al hoceima event is characteristic of earthquakes in the region marine seismic reflection profiles that intersect the offshore region of seismicity image active high angle faults with possible strike slip components the seismicity trend is not directly related to the submarine alboran ridge or the geomorphologically prominent nekor fault deformation appears to be occurring on a number of subsidiary strike slip faults that together compose a ne sw zone of distributed shear the distributed strike slip and documented normal faulting taking place in the eastern rif mountains although characteristic of the rif region are in contrast to the thrusting style of deformation that occurs farther to the east in the algerian tell atlas this may be related to the reported lateral variations and evolution of the convergent plate boundary in these regions during the neogene and quaternary times

effect of carbon dioxide sequestration on the mechanical properties of deccan basalt carbon dioxide sequestration is considered to be an efficient method of curbing the release of carbon dioxide emissions into the atmosphere and to mitigating corresponding effects on climate change in this regard basaltic rocks are among the potential repositories due to their ability to trap carbon dioxide in form of carbonate minerals a series of laboratory scale saturation experiments was conducted on three types of basalts that were collected from different horizons of the deccan volcanic province dvp india the basalt cores were treated in a saturation chamber for different exposure periods under low pressure and room temperature conditions a set of key mechanical physical and chemical properties of the pre and post treated samples were analyzed to identify saturation related changes the results show that exposure of the basalts to carbon dioxide has a strong effect on their strength however the extent of the effect is different for different types of basalts and is strongly controlled by the exposure time the mineralogical composition and rock texture x ray diffraction and scanning electron microscopy sem show that saturation leads to dissolution of the mafic minerals and precipitation of new carbonate minerals in the cracks and vesicles of the host rock these changes in the mineralogical content and the development of micro cracks in the samples are interpreted as being the primary factors that affect the loss of integrity in the rock

the control networks of tethys and dione control networks of saturnian satellites of tethys and dione have been established photogrammetrically from pictures taken by the two voyager spacecraft during their flybys coordinates of 110 points on tethys and 126 points on dione are listed selected points are identified on u s geological survey maps of the satellites and many are identified by name measurements of these points were made on six pictures from voyager 1 and 21 from voyager 2 for tethys and on 27 pictures from voyager 1 and 1 from voyager 2 for dione the longitude systems on the satellites have been defined by craters on their surfaces the mean radii have been determined as 524 5 km for tethys and 559 5 km for dione

kinematics of the western africa eurasia plate boundary from focal mechanisms and gps data summary the western mediterranean displays a complex pattern of crustal deformation distributed along tectonically active belts developed in the framework of slow oblique plate convergence we used earthquake and global positioning system gps data to study the present day kinematics and tectonics of the africa eurasia plate boundary in this region crustal seismicity and focal mechanisms analysed in terms of seismic moment release and seismic deformation outline the geometry of major seismic belts and characterize their tectonics and kinematics continuous gps data have been analysed to determine euler vectors for the nubian and eurasian plates and to provide the global frame for a new mediterranean gps velocity field obtained by merging continuous and campaign observations collected in the 1991 2005 time span gps velocities and displacements predicted by the nubia eurasia rotation pole provide estimates of the deformation accommodated across the tectonically active belts the rather simple deformation occurring in the atlantic region characterized by extension about perpendicular to the middle atlantic and terceira ridges and right lateral motion along the gloria transform fault turns into a complex pattern of deformation occurring along broader seismic belts where continental lithosphere is involved our analysis reveals a more complex fragmentation of the plate boundary than previously proposed the roughly e w trending mainly compressive segments i e southwestern iberia northern algeria and southern tyrrhenian where plate convergence is largely accomodated across rather localized deformation zones and partially transferred northward to the adjacent domains i e the algero balearic and tyrrhenian basins are interrupted by regions of more distributed deformation i e the rif alboran betics tunisia libya and eastern sicily or limited seismicity i e the strait of sicily which are characterized by less homogeneous tectonics regimes mainly transcurrent to extensional in correspondence of the observed breaks tectonic structures with different orientation interfere and we find belts with only limited deformation i e the high and middle atlas the tunisian atlas and the offshore tunisia libya belt that extends from the plate boundary into the nubian plate along pre existing tectonic lineaments our analysis suggest that the sicilian pelagian domain is moving independently from nubia according to the presence of a right lateral and extensional decoupling zone corresponding to the tunisia libya and strait of sicily deformation zone despite the space variability of active tectonic regimes plate convergence still governs most of the seismotectonic and kinematic setting up to the central aeolian region in general local complexities derive from pre existing structural features inherited from the tectonic evolution of the mediterranean region on the contrary along calabria and the apennines the contribution of the subducted ionian oceanic lithosphere and the occurrence of microplates i e adria appear to substantially modify both tectonics and kinematics finally gps data across the gibraltar arc and the tyrrhenian calabria domain support the hypothesis that slab rollback in these regions is mostly slowed down or stopped

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

co2 permeability of indian bituminous coals implications for carbon sequestration abstract the permeability of coal is one of the most critical parameters in estimating the performance of coal seams as methane reservoirs or carbon dioxide sinks the reservoir behaviour of coal offers many challenges for the long term planning of gas production performance and the drainage of water from reservoirs moreover heterogeneity in coal from basin to basin from seam to seam and within parts of the same seam makes the process more complex reservoir specific understanding is needed for the best possible estimation of its behaviour factors such as shrinkage swelling of coal matrix gas flow and slippage geomechanical changes cleat anisotropy and effective stresses control the flow behaviour of gases in coal studies of these aspects have gathered momentum in recent decades for different basins across the world however no research is available on swelling induced permeability characteristics or the role of effective stresses for gondwana coals in india considering the fairly high co 2 storage potential of indian coals bituminous coals of the barakar formation in jharia basin india were tested using gas phase co 2 under triaxial conditions this paper presents the results of changing effective stresses in terms of confining stresses and pore pressure incorporating the role of coal swelling with time on the flow pattern of gaseous co 2 corresponding to different depths of target coal seams coal was subjected to different confining stresses in a newly developed triaxial cell for each confinement co 2 was injected at different injection pressures to minimize the effects of temperature on the characteristics of the gas phase it was kept constant at 26 c throughout while use of the drained method of testing maintained the downstream pressure equal to one atmosphere the results showed that at low confinement increase in gas injection pressures leads to an initial decrease in permeability of coal which then becomes almost constant however at higher confinements the permeability increases with increasing injection pressure swelling in coal contributes to reduction of permeability the volumetric expansion in coal reduces the permeability with changing gas injection pressure during the initial confinement as the confining pressure is increased coal permeability reduces by one to two orders of magnitude finally an empirical relation accounting for the role of effective stresses and swelling on coal permeability is proposed for indian coals at lower effective stresses the logarithmic decline model is better suited while the exponential decline relationship fits the data better at effective stresses 12 mpa

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

vertical ductile thinning and its contribution to the exhumation of high pressure rocks the cycladic blueschist unit in the aegean the contribution of vertical ductile thinning to the exhumation of high pressure rocks is evaluated by estimating finite strain in 75 exhumed high pressure rocks of the cycladic blueschist unit in the aegean sea greece and western turkey strain data indicate heterogeneous deformation principal stretches are 1 24 5 03 for s x 0 63 2 53 for s y and 0 10 0 81 for s z with a tensor average of s x s y s z 1 52 1 28 0 51 a 1d numerical model which integrates velocity gradients along a vertical flow path with a steady state orogen is used to estimate the contribution of ductile thinning of the overburden of the high pressure rocks to exhumation using a strain rate law that is proportional to depth averaged results show that ductile flow contributed c 20 to exhumation a major implication is that the vertical strain in the exhumed rocks is an overestimate of the contribution that ductile flow makes to the total exhumation a proportional strain rate law that scales linearly with depth implies that material points rising towards the surface move quickly out of the more rapidly deforming part of the orogen therefore very large vertical strains 90 in deeply exhumed rocks are needed for vertical ductile thinning to be a major exhumation process

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

experimental evaluation of in situ co2 water rock reactions during co2 injection in basaltic rocks implications for geological co2 sequestration 1 deep aquifers are potential long term storage sites for anthropogenic co2 emissions the retention time and environmental safety of the injected co2 depend on geologic and physical factors and on the chemical reactions between the co2 the aquifer water and the host rocks the ph buffer capacity of the aquifer water and the acid neutralization potential of the host rocks are important factors for the permanent stabilization of the injected co2 mafic rocks such as basalt which primarily consists of ca mg silicate minerals have a high acid neutralization capacity by providing alkaline earth elements that form stable carbonate minerals the carbonate minerals formed thus sequester co2 in a chemically stable and environmentally benign form in this study we present results from a small scale co2 injection test in mafic and metasedimentary rocks the injection test was conducted using a single well push pull test strategy co2 saturated water ph 3 5 was injected into a hydraulically isolated and permeable aquifer interval to study the acid neutralization capacity of ca mg silicate rocks and to estimate in situ cation release rates release rates for ca mg and na were calculated by use of solute compositions of water samples retrieved after the co2 injection the incubation time of the injected solution within the aquifer and geometric estimates of the reactive surface area of the host rocks our results confirm rapid acid neutralization rates and water rock reactions sufficient for safe and permanent storage of co2 carbonic acid was neutralized within hours of injection into a permeable mafic aquifer by two processes mixing between the injected solution and the aquifer water and water rock reactions calculated cation release rates decrease with increasing ph that is confirmed by laboratory based experiments large differences between release rates obtained from the field and laboratory experiments may be mainly due to uncertainties in the estimation of the reactive surface area in the field experiment and in hydrological and geological factors our results underscore the importance of defining bulk rock dissolution rates under in situ conditions in order to evaluate target formations for permanent mineral sequestration of carbon dioxide

active shallow extension in central and eastern betic cordillera from cgps data abstract the betic cordillera is an alpine belt formed in the western mediterranean by the westward displacement of the alboran domain in between the eurasian and african convergent plates new cgps data from the central and eastern betic cordillera and its foreland obtained mainly from the topo iberia project allowed us to precisely determine the rate of tectonic deformation most of the displacements of the central and eastern betics are westward with a variable southwestward component in relation to the eurasian stable plate while in the iberian foreland the displacements are extremely low some deformation related to low compressional deformation occurs in the easternmost foreland basin and eastern betic cordillera the displacement increases substantially southwards and westwards in relation to present day extensional deformation major active discontinuities correspond to the nw se normal fault zones which dip westwards they are located in almeria tabernas balanegra and western sierra de gador whereas the padul fault zone located west of sierra nevada extends northwards to the granada basin nw se extensional faults are also observed to the north in the baza basin moreover the activity of dextral faults along the sorbas tabernas alpujarras guajares band generally considered as a transfer fault zone is evidenced by the displacement data these results come to demonstrate the low activity or inactivity of the large northern e w oriented folds of the central and eastern internal zone such as the sierra de los filabres antiform they also point to the possible residual activity of the northern part of the ne sw sierra nevada antiform where the maximum relief of the cordillera is found altogether our data support a heterogeneous present day westward extension that affects the upper crust of the betic cordillera and increases towards the thinned continental crust of the alboran sea and towards the west which is compatible with roll back subduction along the gibraltar arc

an evaporite bearing accretionary complex in the northern front of the betic rif orogen the guadalquivir accretionary complex forms a largely oblique prism at the northern edge of the betic rif orogen where miocene sediments plus allochthonous evaporite bearing units were accreted during the displacement of the alboran domain towards the west traditional interpretations end the tectonic structuring of the betic cordillera at the present topographic front beyond which gravitational and or diapiric processes would predominate however this study shows pervasive tectonic deformation in the outer prism with coherent oblique shortening kinematics which is achieved through an alternation of roughly n s arcuate thrust systems connected by e w transfer fault zones these structures accord well with the geophysical models that propose westward rollback subduction the main stage of tectonic activity occurred in the early middle miocene but deformation lasted until the quaternary with the same kinematics evaporite rocks played a leading role in the deformation as evidenced by the suite of ductile structures in gypsum distributed throughout the area s and l gypsum tectonites scaly clay fabrics and brittle fabrics coexist and consistently indicate westward motion top to 290 with subordinate n s contraction almost perpendicular to the transfer zones this work reveals ductile tectonic fabrics in gypsum as a valuable tool to elucidate the structure and deformational history of complex tectonic melanges involving evaporites above the decollement level of accretionary wedges

a new velocity field for africa from combined gps and doris space geodetic solutions contribution to the definition of the african reference frame afref 1 we analyzed 16 years of gps and 17 years of doppler orbitography and radiopositioning integrated by satellite doris data at continuously operating geodetic sites in africa and surroundings to describe the present day kinematics of the nubian and somalian plates and constrain relative motions across the east african rift the resulting velocity field describes horizontal and vertical motion at 133 gps sites and 9 doris sites horizontal velocities at sites located on stable nubia fit a single plate model with a weighted root mean square residual of 0 6 mm yr maximum residual 1 mm yr an upper bound for plate wide motions and for regional scale deformation in the seismically active southern africa and cameroon volcanic line we confirm significant southward motion 1 5 mm yr in morocco with respect to nubia consistent with earlier findings we propose an updated angular velocity for the divergence between nubia and somalia which provides the kinematic boundary conditions to rifting in east africa we update a plate motion model for the east african rift and revise the counterclockwise rotation of the victoria plate and clockwise rotation of the rovuma plate with respect to nubia vertical velocities range from 2 to 2 mm yr close to their uncertainties with no clear geographic pattern this study provides the first continent wide position velocity solution for africa expressed in international terrestrial reference frame itrf2008 a contribution to the upcoming african reference frame afref except for a few regions the african continent remains largely under sampled by continuous space geodetic data efforts are needed to augment the geodetic infrastructure and openly share existing data sets so that the objectives of afref can be fully reached

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

permeability of sub critical carbon dioxide in naturally fractured indian bituminous coal at a range of down hole stress conditions abstract understanding reservoir dynamics from a geotechnical and petrophysical perspective is essential for safe and steady fluid extraction transport or injection in the reservoir the recent approach on storage of anthropogenic greenhouse gases ghg for mitigation of climate change in the deep geologic reservoirs has led to fast paced research on resolving storage related issues a coal seam is one such target reservoir where co 2 may be injected for storage this may be coupled with the enhanced extraction of coalbed methane cbm it is known that the interaction of co 2 with coal induces hydro mechanical changes however detailed investigation is mandatory for site specific operation the lack of such studies on indian coal is the motivation for this research a naturally fractured coal specimen was chosen and the subcritical co 2 flow was maintained by monitoring the injection pressures and ambient temperature the variations in permeability under various scenarios were also investigated the results indicate that initial co 2 injection caused coal matrix swelling which took nearly 5 6 h of flow related sorption for maximum closure of the natural fractures linear variation in flow rate with the pressure gradient across the sample indicated laminar or darcian flow of co 2 through the coal fractures deeper coal seams have high confinements the co 2 permeability results for such in situ conditions indicated an exponential decline in naturally fractured coal due to increasing confining pressures the observed reduction of co 2 permeability with increase in gas inlet pressure is debated and may be attributed fully to matrix swelling or partly to the klinkenberg effect this study is vital for successful ghg sequestration in coal seams and for better understanding of the gas flow behaviour in the seams

comment on deep structure recent deformation and analog modeling of the gulf of cadiz accretionary wedge implications for the 1755 lisbon earthquake by gutscher et al 2009 abstract gutscher et al 2009b address a very interesting and unsolved problem which is the continuation of the azores gibraltar plate boundary to the e of the gorringe bank this comment comprises three parts 1 short introduction to the geologic setting 2 comment on the analogue modelling the relationship of the setup with the prototype and the relationship of the experimental results with the prototype 3 short discussion of proposed subduction to the e

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

goringe alboran tell tectonic zone a transpression system along the africa eurasia plate boundary neotectonic structures distributed from the goringe bank to the tell atlas mountains show that the africa eurasia plate boundary in the western mediterranean corresponds to an east west trending deforming zone goringe alboran tell main pliocene and quaternary tectonic structures of the northern atlas mountains are northeast southwest striking fault related folds similar to that of el asnam and are related to north south to northwest southeast compressional movements active tectonics in agreement with the main seismicity distribution and focal mechanisms also support an oblique plate convergence and the existence of a 50 100 km wide transpression zone from goringe across alboran to the tell atlas mountains a kinematic model shows the interaction between dextral transcurrent faults and left lateral faults with block rotations and no lateral extension pinned model shortening and lateral movement rates during the quaternary are estimated to be 1 0 2 3 mm yr and block rotation rate is estimated as 2 5 3 9 m y the plate boundary may correspond to a transpression zone active thrust faults being controlled by deep seated dextral transcurrent faults

deep structure recent deformation and analog modeling of the gulf of cadiz accretionary wedge implications for the 1755 lisbon earthquake the gulf of cadiz spans the plate boundary between africa and eurasia west of the betic rif mountain belt a narrow east dipping subduction zone descends beneath the gulf of cadiz and the straits of gibraltar the deep crustal structure of the gulf and the adjacent sw iberian and moroccan margins is constrained by numerous multi channel seismic reflection and wide angle seismic surveys a compilation of these existing studies is presented in the form of depth to basement sediment thickness depth to moho and crustal thickness maps these structural maps image an e w trending trough with thin 10 km crust beneath the gulf of cadiz this trough is filled by an eastward thickening wedge of sediments reaching a thickness of 10 15 km in the eastern gulf these sediments are tectonically deformed primarily along a series of westward vergent thrust faults and represent a 200 250 km wide accretionary wedge the northern and especially the southern limits of the accretionary wedge are marked by sharp morphological lineaments showing evidence of recent deformation these tectonic limits are situated in an internal position with respect to the miocene deformation front external betic and rif allocthons which has been abandoned at the western boundary of the accretionary wedge near the adjacent seine and horseshoe abyssal plains an e w trending basement high coral patch ridge can be seen indenting the deformation front in an asymmetric manner analog modeling is performed using granular materials accreted against a semicircular backstop representing the basement of the rif and betic mountain belts the modeling initially produces a symmetric arcuate accretionary wedge the ensuing collision of an oblique rigid indenter retards accretion on one side resulting in an embayment and a locally steeper deformation front the deformation pattern observed in morphology and high resolution seismic profiles suggests the accretionary wedge and underlying subduction system is still active the implications of active subduction for the source region of the 1755 lisbon earthquake and the regional seismic hazard assessment are discussed

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

deep deformation pattern from electrical anisotropy in an arched orogen betic cordillera western mediterranean long period magnetotelluric data acquired in the iberian massif and the betic cordillera arched orogen provide the first evidence of electrical anisotropy in the upper mantle of the mediterranean region strike analysis at different periods reveals preferred structure orientation related to olivine elongation in the mantle and points to a heterogeneous anisotropy pattern at deep levels periods 104 s all the sites show a common north south geoelectrical strike n170 e which may represent a low intensity deformation possibly related to frozen prealpine plate tectonics for periods between 10 and 103 s a north south constant strike n180 e at the betic cordillera sites contrasts with the east west strike n85 e in the iberian massif an increase in the magnitude of the induction arrows from the iberian massif to the inner part of the betic cordillera probably reflects higher deformation toward the axis of the eurasian african plate boundary the integration of electrical anisotropy data with seismic anisotropy allows us to discuss mantle deformation patterns produced by delamination and subduction suggesting that the latter mechanism may be more suitable for the alpine evolution of the western gibraltar arc

numerical simulation of porosity and permeability evolution of mount simon sandstone under geological carbon sequestration conditions abstract a numerical model was developed with the use of reactive transport code crunchflow to estimate porosity permeability and mineral composition changes of mount simon sandstone under typical geological carbon sequestration conditions p 23 8 mpa and t 85 c the model predicted a permeability decrease from 1 60 md to 1 02 md for the mount simon sandstone sample in a static batch reactor after 180 days of exposure to co 2 saturated brine which is consistent with measured permeability results model predicted solution chemistry results were also consistent with laboratory measured solution chemistry data sio 2 am was the primary mineral that causes permeability decrease followed by kaolinite both sio 2 am formation and kaolinite formation were attributed to the dissolution of quartz and feldspar this study shows that the formation of sio 2 am and kaolinite in the pore space of host rock is possible under typical co 2 sequestration conditions sio 2 am and kaolinite precipitation at the co 2 plume extent could reduce the permeability of host rock and improve lateral containment of free phase co 2 contributing to overall security of co 2 storage

apparently deep events in the middle atlas resolved to be shallow implications for lithospheric deformation abstract the occurrence of intermediate depth seismicity in intracontinental settings is rare but it has been postulated with various degrees of certainty in several regions one such region is the middle atlas of morocco since 1960 75 intermediate depth earthquakes have been reported in this region by spain s national geographic institute ign the apparent deep nature of these events is hard to reconcile with well established geophysical evidence of a thin lithosphere under the middle atlas but has been associated with mantle delamination processes we relocate 4 events with ign reported depths 80 km that were recorded by a relatively dense temporary deployment using a recent regional 3d velocity model obtained through teleseismic body and surface wave tomography the relocation procedure uses a grid search approach to minimize the mean normalized misfit where each travel time misfit is normalized by the estimated pick uncertainty we find that our observed arrivals are much better fit by shallow 80 km we propose that these shallow foci earthquakes are the result of regional crustal deformation of this region caused by the present convergence between africa and eurasian plate we infer that if there are any ongoing delamination processes in the area they are aseismic this study is an example of how local earthquake locations in tectonically complex areas can be significantly improved by using a dense local seismic array and a well constrained 3 d velocity model

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

coordinates of features on the galilean satellites control nets of the four galilean satellites have been established photogrammetrically from pictures taken by the two voyager spacecraft during their flybys of jupiter in 1979 coordinates of 504 points on io 112 points on europa 1547 points on ganymede and 439 points on callisto are listed selected points are identified on u s geological survey maps of the satellites measurements of these points were made on 234 pictures of io 115 pictures of europa 282 pictures of ganymede and 200 pictures of callisto the systems of longitude were defined by craters on europa ganymede and callisto preliminary solutions have been found for the directions of the axes of rotation of the galilean satellites new mean radii have been determined as 1815 5 km for io 1569 10 km for europa 2631 10 km for ganymede and 2400 10 km for callisto

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

modern tectonic stress field in the mediterranean region evidence for variation in stress directions at different scales summary a compilation of more than one thousand stress indicators which include in situ stress measurements focal mechanisms microtectonic and other geological data allowed us to reconstruct the modern stress field in the mediterranean region and the surrounding area average stress directions at different scales have been reconstructed by means of a linear interpolation method this method takes into account the distribution scale and quality of stress data the results of the interpolation at plate scale allow us to recognize slightly deformed regions such as the northwestern european platform where average maximum horizontal stress direction is oriented roughly nnw sse subparallel to absolute and relative plate velocity directions other regions such as the caucasus alps and pyrenees where recent tectonic deformation and seismicity are present display important variations of stress directions the reconstruction of the average stress directions at different scales within the french alps pointed out that the average stress field pattern may vary from one scale to another nevertheless variations of stress directions at a given scale are consistent with the kinematics of faults of the same scale

the control networks of mimas and enceladus abstract control networks for mimas and enceladus were computed using a bundle type analytical triangulation program the mimas network encircles the satellite with 110 points measured on 32 voyager 1 pictures the adjustment contained 1356 observation equations and 316 normal equations and gave a standard error of measurement of 13 43 m the enceladus network does not completely encircle the satellite it contains 71 points measured on 22 voyager 2 pictures the adjustment contained 994 observation equations and 208 normal equations and gave a standard error of measurement of 19 19 m many of the control points are identifies on illustrations and by name and their coordinates are given in tables the analytical triangulation program was used to solve for the mean radii and the three principal axes of best fit ellipsoids the mean radius of mimas is 197 3 km and the best fit ellipsoid gives a c 6 3 km the mean radius of enceladus is 251 5 km and the best fit ellipsoid gives a c 8 5 km

crustal resistivity structure of the southwestern transect of the rif cordillera morocco a ne sw magnetotelluric 110 km long profile including 18 sites was acquired across the western rifcordillera along the eurasian african plate boundary allowing to constrain its poorly known deepstructure it extends from the internal zones close to the alboran coast crossing the external zones andup to the gharb foreland basin the periods recorded range from 0 001 s to 1000 s the combination ofmagnetotelluric data with available geological data provides new insight regarding the relationship

modeling global impact effects on middle sized icy bodies applications to saturn s moons disrupted terrains that form as a consequence of giant impacts may help constrain the internal structures of planets asteroids comets and satellites as shock waves and powerful seismic stress waves propagate through a body they interact with the internal structure in ways that may leave a characteristic impression upon the surface variations in peak surface velocity and tensile stress related to landform degradation and surface rupture may be controlled by variations in core size shape and density caloris basin on mercury and imbrium basin on the moon have disturbed terrain at their antipodes where focusing is most intense for an approximately symmetric spheroid although the icy saturnian satellites tethys mimas and rhea possess giant impact structures it is not clear whether these structures have correlated disrupted terrains antipodal or elsewhere in anticipation of high resolution imagery from cassini we investigate antipodal focusing during giant impacts using a 3d sph impact model we first investigate giant impacts into a fiducial 1000 km diameter icy satellite with a variety of core radii and compositions we find that antipodal disruption depends more on core radius than on core density suggesting that core geometry may express a surface signature in global impacts on partially differentiated targets we model tethys mimas and rhea according to their image derived shapes triaxial for tethys and mimas and spherical for rhea varying core radii and densities to give the proper bulk densities tethys shows greater antipodal values of peak surface velocity and peak surface tensile stress indicating more surface damage than either mimas or rhea results for antipodal and global fragmentation and terrain rupture are inconclusive with the hydrocode itself producing global disruption at the limits of model resolution but with peak fracture stresses never exceeding the strength of laboratory ice

active tectonism in the intracontinental middle atlas mountains of morocco synchronous crustal shortening and extension this material has been published in the journal of the geological society of london volume 153 the only definitive repository of the content that has been certified and accepted after peer review copyright and all rights therein are retained by the geological society of london copyright 2006 the geological society of london see also http www geolsoc org uk template cfm name journals jgs home page http atlas geo cornell edu morocco publications gomez1996 htm

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

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

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

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

how much nubia eurasia convergence is accommodated by the ne end of the eastern betic shear zone se spain constraints from gps velocities this research was funded by the spanish ministry of economy and competitiveness research project cgl2011 30153 c02 02 university of alicante research project vigrob053 university of jaen paiuja 2019 2020 ceactierra and rnm282 research group of junta de andalucia