three dimensional tomographic velocity structure of upper crust coaxial segment juan de fuca ridge implications for on axis evolution and hydrothermal circulation three dimensional models of compressional velocity and azimuthal anisotropy from tomographic inversions using 23 564 ocean bottom seismometer p wave arrivals define systematic lateral variations in seismic structure of the coaxial segment of the juan de fuca ridge jdfr over much of the segment the across axis structure is roughly axisymmetric characterized by a progressive increase in dike velocities moving away from the ridge axis this trend is most apparent in the basal dikes where on axis velocities are about 800 m s slower than those measured elsewhere within the rift valley the on axis sheeted dikes also exhibit ridge oriented azimuthal anisotropy with a peak to peak amplitude of about 600 m s outboard of the rift valley beneath ridge flanks with fault scarps velocities in the upper 1500 m of crust are reduced the maximum amplitude of this anomaly is about 700 m s located near the top of the sheeted dikes variations in the three dimensional velocity model are believed to reflect changes in crustal porosity from which we infer an axisymmetric porosity model for seismic layer 2 of the coaxial segment as the crust ages the evolution of layer 2 porosity could occur in the following way 1 the porosity of zero age on axis dikes is set at formation by the contraction of molten material 2 hydrothermal alteration fills pore spaces as the dikes move away from the center of the axial valley and 3 normal faulting on the ridge flank scarps opens fractures and increases porosity of the upper dikes as they move off axis at the north end of the segment dike velocities are several hundred meters per second slower on average and the across axis structure is lost the transition from a coherent aligned seismic structure to a less distinct pattern with reduced velocities may represent a shift from magmatic to amagmatic extension moving away from the cobb hotspot on the ridge axis the porosity structure we have derived for the coaxial segment suggests an alternative to the usual hydrothermal circulation model of cross axis convection cells a circulation model with along axis convection cells located entirely within the axial valley appears to be more compatible with our data

a comparison of terrasar x radarsat 2 and alos palsar interferometry for monitoring permafrost environments case study from herschel island canada abstract interferometric synthetic aperture radar insar data sets from terrasar x radarsat 2 and alos palsar are compared for their ability to detect ground movement over the continuous permafrost site of herschel island yukon territory canada all three sensors maintain good coherence within a summer season and can be used to create summer displacement products stacking is advantageous for the terrasar x and radarsat 2 data sets although mottling possibly an interaction of the sar with vegetation or residual tropospheric noise is visible reducing the reliability of the results radarsat 2 and alos palsar provide the most promising results with the ability to form one year interval interferograms palsar can also form two and three year interval interferograms long interval data sets spanning 2007 to 2010 identify a band of movement of 20 to 30 cm year along the north east coast and a region of movement of up to 5 cm year near the northern tip of the island the ability to form long interval displacement products holds the most promise for permafrost monitoring since long term trends are of greater interest for permafrost stability than short term seasonal changes terrasar x data have the disadvantage that year to year interferograms cannot be formed insar is not the ideal monitoring technique for the large thaw slumps of herschel island although general areas of instability can be identified specific slump detection is limited by radar look direction and the large and abrupt slump movement often accompanied by disintegration and collapse of slump sections causes loss of coherence in the insar data thaw slumps may require a different interferometric approach such as slump extent mapping from coherence loss or the installation of corner reflectors and point target techniques the frequent revisit and high spatial resolution of terrasar x provide the best chance of maintaining coherence over thaw slumps in general insar is more successful at identifying broad areas of subtle subsidence in gentle relief areas of terrain instability possibly due to permafrost thaw or ground ice melt and the removal of water volume and prior to significant slumping

the challenging retrieval of the displacement field from insar data for andesitic stratovolcanoes case study of popocatepetl and colima volcano mexico abstract despite the ability of synthetic aperture radar sar interferometry to measure ground motion with high resolution application of this remote sensing technique to monitor andesitic stratovolcanoes remains limited specific acquisition conditions characterizing andesitic stratovolcanoes mainly vegetated areas with large elevation ranges induce low signal coherence as well as strong tropospheric artefacts that result in small signal to noise ratio we propose here a way to mitigate these difficulties and improve the sar measurements we derive ground motions for two of the most active mexican stratovolcanoes popocatepetl and colima volcano from the time series of sar data acquired from december 2002 to august 2006 the sar data are processed using a method that combines both persistent scatterers and small baseline approaches stratified tropospheric delays are estimated for each interferogram using inputs from the global atmospheric model narr up to a maximum of 10 rad km these delays are validated using spectrometer data as well as the correlation between the wrapped phase and the elevation the tropospheric effect is removed from the wrapped phase in order to improve the unwrapping process on popocatepetl we observe no significant deformation the colima summit area exhibits a constant subsidence rate of more than 1 cm year centered on the summit but enhanced reaching more than 2 cm year around the 1998 lava flow we model this subsidence considering both a deflating magma source at depth and the effect of the eruptive deposits load

along strike variations of the partitioning of convergence across the haiyuan fault system detected by insar oblique convergence across tibet leads to slip partitioning with the coexistence of strike slip normal and thrust motion on major fault systems a key point is to understand and model how faults interact and accumulate strain at depth here we extract ground deformation across the haiyuan fault restraining bend at the northeastern boundary of the tibetan plateau from envisat radar data spanning the 2001 textendash2011 period we show that the complexity of the surface displacement field can be explained by the partitioning of a uniform deep seated convergence mountains and sand dunes in the study area make the radar data processing challenging and require the latest developments in processing procedures for synthetic aperture radar interferometry the processing strategy is based on a small baseline approach before unwrapping we correct for atmospheric phase delays from global atmospheric models and digital elevation model errors a series of filtering steps is applied to improve the signal to noise ratio across high ranges of the tibetan plateau and the phase unwrapping capability across the fault required for reliable estimate of fault movement we then jointly invert our insar time series together with published gps displacements to test a proposed long term slip partitioning model between the haiyuan and gulang left lateral faults and the qilian shan thrusts we explore the geometry of the fault system at depth and associated slip rates using a bayesian approach and test the consistency of present day geodetic surface displacements with a long term tectonic model we determine a uniform convergence rate of 10 8 6 textendash11 5 mm yr 1 with an n89 81 textendash97 e across the whole fault system with a variable partitioning west and east of a major extensional fault jog the tianzhu pull apart basin our 2 d model of two profiles perpendicular to the fault system gives a quantitative understanding of how crustal deformation is accommodated by the various branches of this thrust strike slip fault system and demonstrates how the geometry of the haiyuan fault system controls the partitioning of the deep secular motion

new constraints on the active tectonic deformation of the aegean 1 site velocities from six separate global positioning system gps networks comprising 374 stations have been referred to a single common eurasia fixed reference frame to map the velocity distribution over the entire aegean we use the gps velocity field to identify deforming regions rigid elements and potential microplate boundaries and build upon previous work by others to initially specify rigid elements in central greece the south aegean anatolia and the sea of marmara we apply an iterative approach tentatively defining microplate boundaries determining best fit rigid rotations examining misfit patterns and revising the boundaries to achieve a better match between model and data short term seismic cycle effects are minor contaminants of the data that we remove when necessary to isolate the long term kinematics we find that present day aegean deformation is due to the relative motions of four microplates and straining in several isolated zones internal to them the rms misfit of model to data is about 2 sigma very good when compared to the typical match between coseismic fault models and gps data the simplicity of the microplate description of the deformation and its good fit to the gps data are surprising and were not anticipated by previous work which had suggested either many rigid elements or broad deforming zones that comprise much of the aegean region the isolated deforming zones are also unexpected and cannot be explained by the kinematics of the microplate motions strain rates within internally deforming zones are extensional and range from 30 to 50 nanostrain year nstrain year 10 9 year 1 to 2 orders of magnitude lower than rates observed across the major microplate boundaries lower strain rates may exist elsewhere within the microplates but are only resolved in anatolia where extension of 13 4 nstrain year is required by the data our results suggest that despite the detailed complexity of active continental deformation revealed by seismicity active faulting fault geomorphology and earthquake fault plane solutions continental tectonics at least in the aegean is to first order very similar to global plate tectonics and obeys the same simple kinematic rules although the widespread distribution of aegean seismicity and active faulting might suggest a rather spatially homogeneous seismic hazard the focusing of deformation near microplate boundaries implies the highest hazard is comparably localized

deepening of the axial magma chamber on the southern east pacific rise toward the garrett fracture zone a wide aperture profile along the ridge axis from 14 29 s to 13 39 s 120 km to 30 km south of the garrett fracture zone is analyzed to constrain the thickness of layer 2a and the depth to the axial magma chamber reflector five areas along the 90 km line are examined in detail with several consecutive gathers being analyzed for each area to establish the degree of consistency within each area a genetic algorithm code is used to find a best fit model from a comparison of the data and wkbj synthetic seismograms one hundred starting models are generated using a predefined set of velocity nodes with a fixed window of allowable depth variations between nodes an evolutionary process favors the better fitting models in each generation and a satisfactory misfit is usually obtained within 40 generations within individual areas the models were in good agreement with the depth of a given velocity node generally varying by not more than 20 m the depth discretization interval for the models a consistent deepening trend of the axial magma chamber amc is observed across the five areas as the garrett fracture zone is approached the depth varies from 0 99 km at area 1 which is approximately 100 km south of the garrett to 1 23 km at area 5 which is approximately 40 km south of the garrett the depth to the axial magma chamber is highly sensitive to any ship wander off axis since layer 2a thickens rapidly off axis with age for the areas examined here layer 2a is observed to be relatively constant in thickness along the axis although it is about 40 m thicker over area 5 where the axial magma chamber is deepest this variation is within the scatter of previously detailed layer 2a measurements at 13 n on the east pacific rise where an effectively constant thickness is observed this implies that layer 2a thickening is not a significant factor along this profile and that the amc deepening is real rather than apparent theoretical modeling suggests that the depth to the lid of the axial magma chamber is related to the rate of heat supply at a given location thus the gradual consistent deepening of the axial magma chamber can be taken as an indication of a slightly reduced magma supply toward the garrett fracture zone which marks a major interruption of hundreds of kilometers of continuous ridge axis the deepening may also be interpreted as a downward limb from a central injection point however there is no indication of a similar downward trend in the other southern direction furthermore there is no accompanying systematic variation in axial depth or axial volume both of which are proposed to be indicators of central injection and along axis flow

three dimensional shallow crustal emplacement at the 9 03 n overlapping spreading center on the east pacific rise correlations between magnetization and tomographic images we report a three dimensional 3 d seismic reflection and tomographic survey conducted at the 9 03 n overlapping spreading center osc on the east pacific rise to understand crustal accretion at this feature inversions of travel time data from 19 ocean bottom hydrophones provide a 3 d image of the shallow velocity structure beneath the nontransform offset and associated discordance zone seismic analysis indicates that layer 2a thickness varies between 100 and 900 m and averages 430 m throughout the study area the heterogeneous upper crustal structure at the osc region contrasts with the simpler symmetric structure flanking the midsegments of the east pacific rise the crust affected by the osc migration carries evidence for the complex accretion at the axial discontinuity where the overlap basin may act as a lava pond an area of thick layer 2a covers the southern half of the overlap basin and the propagating ridge tip and shows good correlation with a high magnetization region comparison of the magnetic field anomaly derived from the seismic structure model with the observed sea surface magnetic anomaly suggests that a significant portion of the high magnetization can be related to magnetic source thickness variation rather than solely to the geochemistry of the volcanic rocks

the accretion of oceanic crust by episodic sill intrusion seismic refraction data from mature oceanic regions show remarkable consistency in crustal thickness between sites yet the characteristics of different spreading centers show great variation this leads to the paradox that the similarity in mature oceanic crust suggests that the igneous processes in crustal accretion are the same across a range of spreading rates but that the differences in the spreading centers themselves imply the opposite we have developed a simple two dimensional model for crustal accretion at oceanic spreading centers by the episodic addition of sills at a high level within the crust as implied by recent geophysical studies of spreading centers using our model we have calculated velocity and temperature fields in the crust including the effects of hydrothermal cooling we show that oscillations in the temperature field due to episodicities of 200 20000 years have an effect localized to the region within 50 500 m of the intrusion by assuming that all latent heat and excess specific heat introduced by the injection of sills is convected away by hydrothermal circulation we estimate that the maximum heat transfer associated with hydrothermal cooling in the upper crust is of the order of 10 times greater than the conductive flux we have calculated seismic velocities associated with the model temperature field in the crust and we show that these are consistent with results from both seismic refraction and reflection experiments the model may be applied to both fast and slow spreading ridges and it accounts for the apparent increases in both the mean crustal temperature and the frequency of presence of melt with increasing spreading rate hence resolving the paradox we also show that the implications of this model are consistent with geological observations of layering in ophiolites

slip distribution of the 2003 boumerdes zemmouri earthquake algeria from teleseismic gps and coastal uplift data 1 using a joint inversion of seismological waveforms and ground displacement observations we estimate several parameters of the fault geometry and rupture process of the mw 6 9 may 21 2003 boumerdes zemmouri earthquake the relocated epicenter is considered as a known parameter total rupture length rupture duration and maximum slip are 55 km from 3 4 e to 4 0 e 12 s and 3 m the modeled south dipping reverse fault oriented ene wsw outcrops a few km offshore which is consistent with the absence of observed surface rupture inland two shallow and relatively localized slip zones are found on both sides of the hypocenter to the sw between boumerdes and zemmouri slip is concentrated between 11 and 2 km depth to the ne between zemmouri and dellys slip is concentrated between 6 km depth and the sea floor various resolution tests indicate that our model is well constrained by the available data and help understanding which data constrains each parameter of the model

interferogram formation in the presence of complex and large deformation 1 sierra negra volcano in isabela island galapagos erupted from october 22 to october 30 in 2005 during the 8 days of eruption the center of sierra negra s caldera subsided about 5 4 meters three hours prior to the onset of the eruption an earthquake mw 5 4 occurred near the caldera because of the large and complex phase gradient due to the huge subsidence and the earthquake it is difficult to form an interferogram inside the caldera that spans the eruption the deformation is so large and spatially variable that the approximations used in existing insar software roi roi pac doris gamma cannot properly coregister sar image pairs spanning the eruption we have developed here a two step algorithm that can form intra caldera interferograms from these data the first step involves a rubber sheeting sar image coregistration in the second step we use range offset estimates to mitigate the steep phase gradient using this new algorithm we retrieve an interferogram with the best coverage to date inside the caldera of sierra negra

east pacific rise 8 10 30 n evolution of ridge segments and discontinuities from seamarc ii and three dimensional magnetic studies magnetic bathymetric and seamarc ii side scan sonar data from the ridge flanks adjoining the overlapping spreading center osc at 9 03 n on the east pacific rise epr are used to establish the evolution of this ridge axis discontinuity and adjacent ridge segments within the past 2 4 m y a three dimensional inversion for magnetization shows the discontinuity evolved from one of small offset 2 km to an 8 km offset osc within the past approximately 1 0 m y the osc has left a v shaped discordant zone indicating an average southward migration of 42 km m y since the beginning of anomaly 2 time 1 8 m y the west flank discordant zone consists of discrete abandoned overlap basins bounded by highly magnetized ridge tips with anomalous lineations while the east flank discordant zone is a broad swath of high magnetization anomalous lineations and greater depths kinematic modelling indicates that southward migration has not been steady but has been accomplished by a series of episodic propagation events with rates ranging from 500 mm yr ridge tips have been abandoned at intervals of approximately 50 000 100 000 years both by linkage of neighboring ridge segments and by self decapitation magnetic modelling suggests rotations of overlap basins of 25 consistent with predictions of kinematic modelling orientation of magnetic isochrons indicate a 3 6 counterclockwise change in pacifie cocos plate motion within the past 1 m y assuming orthogonal spreading throughout this time although the discontinuity currently located at 9 03 n existed prior to this change in plate motion its growth into a right stepping 8 km offset osc may be causally related to this change the current configuration of intratransform spreading within the siqueiros has developed since onset of the brunhes anomaly 0 73 m y possibly in response to this recent counterclockwise change in plate motion in addition to the osc there is evidence for several small discontinuities offsetting the ridge during anomaly 2 time which have since migrated along the ridge and vanished an axial magnetization high is observed along the crest of the epr change in the magnitude of the axial magnetization high or shifts in its location relative to the bathymetric axis coincide with several devals within the area magnetization maxima are found at ridge transform intersections and the osc these highs may reflect presence of highly fractionated feti basalts erupted from magma chambers with restricted supply located adjacent to both large and short offset ridge axis discontinuities discrete magnetization highs are found off axis adjacent to clipperton and siqueiros fracture zones indicating that production of feti basalts at ridge transform intersections is episodic magnetizations are higher north of clipperton than south of it possibly reflecting a long lived starvation in magma supply north of clipperton and more abundant supply to the south most seamounts within the area have the same magnetization polarity as surrounding seafloor indicating that seamount formation occurs near the ridge axis the exceptions lie near magnetic reversal boundaries and are consistent with seamount formation as close as 10 km from the ridge axis few pronounced magnetization highs are associated with seamounts indicating that the magnetized source layer is no thicker beneath them than surrounding seafloor or that seamount basalts are substantially less magnetic than normal mid ocean ridge basalts

neotectonics and morphotectonics of the southern almeria region betic cordillera spain kinematic implications most previous studies related to the recent tectonic development of southeastern betic cordillera and in particular the south of almeria agree with the kinematic variety that can be observed in the post miocene structures at different scales this variety is difficult to explain if we consider only the regional stress field related to the convergence of the eurasian and african plates that remained relatively steady over the last 9 ma this work proposes a block tectonics with horizontal and vertical relative movements driven by strike slip movements of major faults to explain the variety of kinematics observed in the area from middle miocene to present the combined activity of the alpujarras fault zone dextral strike slip and the carboneras fault zone sinistral strike slip induces within the major block bounded by them the squeezing of minor pre existing fault bounded crustal blocks this process generates traction areas inside the escaping block which are linked with the existence of gradients of westward movement rate this tectonics can explain some of the structures related with the extensional tectonics predominant in the south of almeria province and the development of the minor and major morphostructures driven by faults with different kinematics the tectonics of blocks proposed is useful to give a coherent interpretation of apparently incoherent local structural data into a regional and homogeneous compressional stress field

morphology and genesis of slow spreading ridges seabed scattering and seismic imaging within the oceanic crust a grid of 32 across axis and five axis parallel multichannel seismic mcs reflection profiles were acquired at an axial volcanic ridge avr segment at 57 45 n 32 35 w on the slow spreading reykjanes ridge mid atlantic ridge to determine the along axis variation and geometry of the axial magmatic system and to investigate the relationship between magma chamber structure the along axis continuity and segmentation of melt supply to the crust the development of faulting and the thickness of oceanic layer 2a seismic reflection profiles acquired at mid ocean ridges are prone to being swamped by high amplitude seabed scattered noise which can either mask or be mistaken for intracrustal reflection events in this paper we present the results of two approaches to this problem which simulate seabed scatter and which can either be used to remove or simply predict events within processed mcs profiles the 37 mcs profiles show clear intracrustal seismic events which are related to the structure of oceanic layer 2 to the axial magmatic system and to the faults which dismember each avr as it ages through its tectono magmatic life cycle and which form the median valley walls the layer 2a event can be mapped around the entirety of the survey area between 0 1 and 0 5 s two way traveltime below the seabed being thickest at avr centres and thinning both off axis and along axis towards avr tips both avr parallel and ridge parallel trends are observed with the pattern of on axis layer 2a thickness variation preserved beneath relict avrs which are rafted off axis largely intact each active avr is underlain by a mid crustal melt lens reflection extending almost along its entire length similar reflection events are observed beneath the offset basins between adjacent avrs these are interpreted as new avrs at the start of their life cycle developing centrally within the median valley the east west spacings of relict avrs and offset basins is 5 7 km corresponding to a life span of the order of 0 5 0 7 myr during which avrs appear to undergo multiple 20 60 kyr tectono magmatic cycles

discrete plumbing systems and heterogeneous magma sources of a 24 km3 off axis lava field on the western flank of east pacific rise 14 s the largest known mid ocean ridge off axis lava flow field occurs slightly off axis near 14 s along the east pacific rise epr it comprises at least four volcanologically discrete units we collected lava samples from 24 sites within the off axis lava field and 7 sites on the adjacent ridge crest using the shinkai 6500 submersible the lava field comprises at least three distinct morb compositions all of which are different from the lavas collected from the nearby ridge axis the east and west cones and the northern lobe of the lava field consist of normal morb n morb lavas with a low concentration of incompatible elements and low lile hfse and lree hree ratios by contrast the samples from the west plain of the field have a higher concentration of incompatible elements and higher lile hfse and lree hree ratios indicating t morb character the lava samples collected from the summit of the east cone show the highest concentration of lile elements and lrees among the lava field emorb lava the n morb of the off axis lava field are more depleted in incompatible elements than the adjacent epr axis lavas possibly reflecting the re melting of the residual mantle in the off axis region the e morb lava was probably derived from fertile mantle that did not undergo melting beneath the spreading center t morb which occupies the main part of the 14 s lava field is the product of magma mixing between n morb and e morb magmas 2007 elsevier b v all rights reserved

insar measurements of surface deformation over permafrost on the north slope of alaska 1 ground based measurements of active layer thickness provide useful data for validating calibrating remote sensing and modeling results however these in situ measurements are usually site specific with limited spatial coverage here we apply interferometric synthetic aperture radar insar to measure surface deformation over permafrost on the north slope of alaska during the 1992 2000 thawing seasons we find significantly systematic differences in surface deformation between floodplain areas and the tundra covered areas away from the rivers using floodplain areas as the reference for insar s relative deformation measurements we find seasonally varying vertical displacements of 1 4 cm with subsidence occurring during the thawing season and a secular subsidence of 1 4 cm decade we hypothesize that the seasonal subsidence is caused by thaw settlement of the active layer and that the secular subsidence is probably due to thawing of ice rich permafrost near the permafrost table these mechanisms could explain why in situ measurements on alaskan north slope reveal negligible trends in active layer thickness during the 1990s despite the fact that atmospheric and permafrost temperatures in this region increased during that time this study demonstrates that surface deformation measurements from insar are complementary to more traditional in situ measurements of active layer thickness and can provide new insights into the dynamics of permafrost systems and changes in permafrost conditions

significance of widespread low effusion rate eruptions over the past two million years for delivery of magma to the overlapping spreading centers at 9 n east pacific rise abstract ever since the discovery that the mid ocean ridge axis deepens at most axial discontinuities there has been vigorous debate about whether ridge axis depth and shape reflect magma supply here we report evidence from one of the most thoroughly studied ridge discontinuities on a fast spreading mid ocean ridge that volcanic eruption effusion rates have been low relative to nearby segment centers throughout its two million year history this pattern of low volcanic effusion rates is inferred from the fields of constructional volcanic mounds on the seafloor which are much more abundant in the off axis discordant zone of the east pacific rise epr 9 n overlapping spreading centers osc than on typical epr seafloor detailed seafloor mapping in 2007 shows that these mound fields consist of concentrations of large pillow mounds that formed within the current osc basin and ridge tips rather than off axis pillow lava erupted at approximately an order of magnitude lower effusion rate than lobate or sheet flows primarily builds mounds on the seafloor crustal thickness a proxy for long term magma supply does not decrease in spite of the decreased lava effusion rates implied by widespread pillow eruptions to resolve the problem of achieving the same magma emplacement rate with lower effusion rates without violating our observations by requiring drastically increased eruption frequency or unreasonably long eruption durations we propose that eruptions occur across the entire osc basin the current configuration of mid crustal melt sills within the osc as resolved by multichannel seismic reflection surveys have neither the correct location nor appropriate size to deliver magma to these eruptive vents in the osc basin via vertically propagating dikes instead we propose that magma delivery to eruptions occurs via laterally propagating dikes from robust mid crustal melt sills outside of the overlap zone

influence of enhanced melt supply on upper crustal structure at a mid ocean ridge discontinuity a three dimensional seismic tomographic study of 9 n east pacific rise we present a three dimensional upper crustal model of the 9degrees03 n overlapping spreading center osc on the east pacific rise that assists in understanding the relationship between melt sills and upper crustal structure at a ridge discontinuity with enhanced melt supply at crustal levels our p wave velocity model obtained from tomographic inversion of similar to 70 000 crustal first arrival travel times suggests that the geometry of extrusive emplacement are significantly different beneath the overlapping spreading limbs extrusive volcanic rocks above the western melt sill are inferred to be thin similar to 250 m more extensive accumulation of extrusives is inferred to the west than to the east of the western melt sill the extrusive layer inferred above the eastern melt sill thickens from similar to 350 at the neovolcanic axis to 550 m to the west of the melt sill volcanic construction is likely to be significant in the formation of ridge crest morphology at the osc particularly at the tip of the eastern limb on the basis of our interpretation of the velocity model we propose that enhanced magma supply at crustal levels at the osc may provide an effective mechanism for the migration of ridge discontinuities this dynamic magma supply model may explain the commonly observed nonsteady migration pattern of ridge discontinuities by attributing this to the temporal fluctuations in melt availability to the overlapping spreading limbs

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

east pacific rise from siqueiros to orozco fracture zones along strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers we have used the sea beam multibeam echo sounding system to survey the east pacific rise epr from 8 20 n to 18 30 n obtaining complete coverage of the epr axial neovolcanic zone and all intervening transform faults here we focus on the epr neovolcanic zone and the definition of overlapping spreading centers ocs s between the orozco and siqueiros transform faults the neovolcanic zone is narrow 0 5 2 0 km and continuous along strike and occurs within and near a strike continuous axial summit graben the neovolcanic zone and summit graben reside along the crest of a volcanic axial high which is 2 10 km wide and which continues uninterrupted along strike for 40 140 km within 20 50 km of an intersection with a transform fault the axial neovolcanic zone narrows and deepens and within only 3 6 km of the intersection the neovolcanic zone turns sharply into the transform valley at seven locations between the siqueiros and orozco transform faults the axial neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast with a classic ridge transform ridge plate boundary however offset rise terminations overlap each other by a distance approximately 3 times greater than their offset they curve toward each other and often one merges into the other along strike separating the osc s is an elliptical overlap basin up to 600 m deep whose long axis is subparallel to the adjacent spreading centers the overlap basin is characterized by volcanic constructional edifices a key difference between these offsets and small transform faults in the atlantic is that there are no transform fault structures in the overlap basin which link the offset rise axes a continuous axial depth profile reveals a long wavelength 20 60 km undulation of the rise axis which may be associated with variations in the magmatic budget along strike the lowest points in the axial depth profile occur near transform faults and at osc s suggesting that these features are associated with along strike minima in the magmatic budget we suggest that major phases of volcanic activity propagate episodically along the axis away from centers of magmatic inflation and that osc s develop where magmatic pulses fail to meet due to misalignment of fracture systems sinuous bends in the rise axis or other heterogeneities transform faults fail to develop on fast spreading centers where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate ridge transform fault pattern the osc geometry is unstable and evolves rapidly and the overlapping rises may propagate at rates faster than the local spreading rate one of the two osc s prevails while the other is abandoned while the locations of osc s may not be fixed relative to the rise axis they may tend to recur near the same place creating scars in older lithosphere which resemble fracture zones but whose fine scale structure is quite different there is excellent agreement between the observed structure of osc s and laboratory studies of osc s using wax models photoelastic studies of overlapping cracks and boundary element modeling of overlapping cracks seismic refraction and reflection near two osc s suggests that large offset osc s have separate magma chambers beneath the offset rise axes while small offset osc s may share a single axial magma chamber three dimensional inversion of magnetic anomalies suggests that significant petrologic anomalies may occur near some osc tips waxing and waning of overlapping magma chambers may give rise to the eruption of highly fractionated feti basalts and associated magnetic anomalies

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

a multichannel seismic investigation of upper crustal structure at 9 n on the east pacific rise implications for crustal accretion reprocessed multichannel seismic profiles from the 9 n segment of the east pacific rise reveal prominent shallow subbasement events these events are identified as wide angle reflections from the base of seismic layer 2a based upon modeling of expanding spread profile data and velocity functions the layer 2a reflections typically increase from 0 15 s after the seafloor reflection at the rise axis to 0 3 0 45 s within 1 2 km of the axis corresponding to an increase in layer thickness of 200 600 m no further systematic increase in layer thickness is observed although lateral variability of the order of a few hundred meters in thickness is observed at greater offsets from the rise axis however the intermittent character of the imaged layer 2a reflection is attributed to focusing and defocusing of energy by the seafloor bathymetry rather than necessarily to intrinsic lateral variability at the base of the layer the base of layer 2a is interpreted as corresponding to the transition between the extrusive section pillow basalts and sheet flows and a sheeted dike complex the rapid thickening of the layer near the rise axis is attributed to successive lava flows burying the initially shallow top of the sheeted dike complex as the layer passes through the neovolcanic zone lateral variability of layer 2a can significantly affect the imaging of the underlying axial magma chambers as average velocities within layer 2a are approximately half that of layer 2b for an along axis profile apparent along axis variability in the depth of the axial magma chamber is traced to variability in the thickness of layer 2a caused by wandering of the profile relative to axis within the resolution of the data the time delay of the magma chamber reflection relative to the base of layer 2a is constant

short and long term deformation patterns in the aegean anatolian systems insights from space geodetic data gps geodetic measurements gps in the eastern mediterranean suggest higher rates of motion of about 10 mm yr in the aegean western anatolian zone with respect to those in the central eastern anatolia in this work we explore the plausibility of the hypothesis that the observed kinematics may be significantly influenced by post seismic relaxation processes induced by the seismic activation of the north anatolian fault since 1939 the major implications of this hypothesis are tentatively quantified by a simplified model constituted by an elastic lithosphere 100 km thick coupled with a viscous asthenosphere 250 km thick with a viscosity of 10 19 pas the predicted perturbation of the displacement and stress fields is consistent with geodetic velocities and could also account for the major features of seismic activity in the period considered

three dimensional tomographic inversion of combined reflection and refraction seismic traveltime data summary a tomographic inversion method is presented for the determination of 3 d velocity and interface structure from a wide range of body wave seismic traveltime data types it is applicable to refraction wide angle reflection normal incidence and multichannel seismic data and is best suited to a combination of these that provides good independent constraints on seismic velocities and interface depths the inversion process seeks a layer interface minimum structure model that is able to explain the given data satisfactorily by inverting to minimize data misfit and model roughness norms simultaneously this regularized inversion and the use of smooth functions to describe velocities and depths allows the highly non linear tomographic problem to be approximated as a series of linear steps the inversion process begins by optimizing the fit to the data of a highly smoothed initial model in each subsequent step structure is allowed to develop in the model with successively greater detail evolving until a satisfactory fit to the data is obtained parameter uncertainties for the final model are then estimated using an a posteriori covariance matrix analysis smooth layer interface models are parametrized using regular grids of velocity and depth nodes from which spline interpolated interface surfaces and velocity fields are defined forward modelling is achieved using ray perturbation theory and a two point ray tracing method that is optimized for a large number of closely spaced shot or receiver points the method may be used to generate 1 and 2 d models from for example vertical seismic profile data or 2 d surveys in which the 3 d geometry of a survey is correctly accounted for the ability of the method to resolve typical target structures is tested in a synthetic salt dome inversion from a set of noisy traveltime data the model converges quickly to a well resolved final model from different starting models the application of this method to real data is demonstrated with a combined 3 d inversion of refraction and reflection data which provide p wave velocity constraints on the methane hydrate stability zone in the cascadia margin offshore vancouver island

tomographic imaging of the shallow crustal structure of the east pacific rise at 9 30 n compressional wave travel times from a seismic tomography experiment at 9 30 n on the east pacific rise are analyzed by a new tomographic method to determine the three dimensional seismic velocity structure of the upper 2 5 km of oceanic crust within a 20 18 km2 area centered on the rise axis the data comprise the travel times and associated uncertainties of 1459 compressional waves that have propagated above the axial magma chamber a careful analysis of source and receiver parameters in conjunction with an automated method of picking p wave onsets and assigning uncertainties constrains the prior uncertainty in the data to 5 to 20 ms the new tomographic method employs graph theory to estimate ray paths and travel times through strongly heterogeneous and densely parameterized seismic velocity models the nonlinear inverse method uses a jumping strategy to minimize a functional that includes the penalty function horizontal and vertical smoothing constraints and prior model assumptions all constraints applied to model perturbations are normalized to remove bias we use the tomographic method to reject the null hypothesis that the axial seismic structure is two dimensional three dimensional models reveal a seismic structure that correlates well with cross and along axis variations in seafloor morphology the location of the axial summit caldera and the distribution of seafloor hydrothermal activity the along axis segmentation of the seismic structure above the axial magma chamber is consistent with the hypothesis that mantle derived melt is preferentially injected midway along a locally linear segment of the rise and that the architecture of the crustal section is characterized by an en echelon series of elongate axial volcanoes approximately 10 km in length the seismic data are compatible with a 300 to 500 m thick thermal anomaly above a midcrustal melt lens such an interpretation suggests that hydrothermal fluids may not have penetrated this region in the last 103 years asymmetries in the seismic structure across the rise support the inferences that the thickness of seismic layer 2 and the average midcrustal temperature increase to the west of the rise axis these anomalies may be the result of off axis magmatism alternatively the asymmetric thermal anomaly may be the consequence of differences in the depth extent of hydrothermal cooling

using persistent scatterer interferometry to map and quantify permafrost thaw subsidence a case study of eboling mountain on the qinghai tibet plateau

two dimensional finite difference model of seafloor compliance summary seafloor compliance is the measure of seafloor deformation under a pressure signal our new 2 d finite difference compliance modelling algorithm presents several advantages over the existing compliance models including the ability to handle any gridded subsurface structure with no limitations on the gradients of the material properties as well as significantly improved performance applying this method to some of the problems inaccessible to previously existing methods demonstrates that lateral variations in subsurface structure must be accounted for to adequately interpret compliance data in areas with significant lateral variations the utilization of 1 d modelling and inversion is likely to result in high interpretation errors even when additional subsurface structure information is available we find that flattened pure melt bodies have a significantly higher compliance than cylindrical melt bodies with the same cross sectional area the compliance created by such bodies often has side peaks over their edges which are as strong as or stronger than the central peak requiring a series of measurements to best constrain their size and shear velocity finally we find that the compliance data are far and away most sensitive to the broad thick lower crustal partial melt zone our simple data fitting model for the compliance measurements on the east pacific rise at 9 48 n required shear velocities as low as 700 m s 1 in the centre of this zone far below the values previously estimated using 1 d model based inversions suggesting higher melt percentages than those previously estimated while small melt bodies in the upper part of the crust were found to have little or no effect on the measured compliance

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

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

p wave tomographic images in the central betics alboran sea south spain using local earthquakes contribution for a continental collision to investigate the relationship between shallow and intermediate depth earthquakes and the crust and upper mantle structure beneath the betic cordillera and alboran sea region we have applied seismic tomography to 2569 p wave arrival times from 367 microearthquakes recorded by both permanent and temporary seismic stations deployed in the region these earthquakes occurred in the depth range of 0 to 110 km beneath the central betic cordilleras and alboran sea our results have revealed significant structural heterogeneities in the crust and upper mantle beneath the study area in the upper crust there is a high velocity anomaly at sierra gorda western boundary of the granada basin penetrating to 15 km depth which is in good agreement with the aeromagnetic anomaly in the granada basin a low velocity anomaly is located in the middle crust which coincides with a previously detected greater cutoff depth of seismicity and are considered to be associated with a highly fractured zone generated by an intracrustal detachment the northern boundary of the alboran sea malaga coast is well imaged as low velocities from 50 to 90 km depths this low velocity zone in the upper mantle is associated with the intermediate depth seismicity which outline a section of continental crust related to the collision subduction beneath the northern part of the alboran sea southern part of the central betics

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

effects of tectonism and magmatism on crack structure in oceanic crust a seismic anisotropy study we analyzed 25 675 traveltime residuals from a three dimensional seismic tomographic inversion to investigate crack induced seismic anisotropy in the upper oceanic crust the study covered two regions with contrasting levels of magmatic activity on the western limb of the 9 n overlapping spreading center on the east pacific rise the level of anisotropy gradually decreases with depth in the magmatically and hydrothermally active ridge region in contrast we observed a highly variable anisotropic structure in the magmatically and hydrothermally less active tip region at the end of the dying ridge segment a weakly anisotropic layer beneath strongly anisotropic extrusive volcanic rocks is likely to be the result of relatively shallow cracks closed by hydrothermal precipitation strongly anisotropic dikes with inferred narrow and water saturated cracks provide important along axis pathways for the circulation of hydrothermal fluids beneath the shallow cracks in the less magmatically active regions furthermore a significant clockwise rotation 20 30 of fast directions occurs in both regions with increasing depth such a rotation provides evidence that the geometry of the underlying crack structure of the western limb is significantly different from that defined by the bathymetric ridge crest

tectonic reconstruction of the clipperton and siqueiros fracture zones evidence and consequences of plate motion change for the last 3 myr bathymetry side looking sonar and magnetics data from the northern east pacific rise have been analyzed to determine the tectonic history of the clipperton fracture zone cfz and the siqueiros fracture zone sfz over the last 2 3 m y results of tectonic reconstructions indicate a series of counterclockwise changes in spreading direction at 2 5 ma 1 2 1 5 ma 1 2 and 0 5 ma 4 5 along the right stepping clipperton transform the most recent change in spreading direction has resulted in fracture zone normal compression which we propose has created a median ridge and transform parallel troughs along the active transform fault volcanic intersection highs located near the ridge transform intersections rti of the cfz are interpreted to be the result of fracture zone normal extension that has created pathways for magma emplacement into onto the older lithosphere across from the rti along the left stepping sfz we propose the changes in spreading direction have generated extension across the transform and have resulted in the formation of intratransform spreading centers and flexural transverse ridges tectonic reconstructions indicate a single euler pole is unable to describe the motion of the pacific cocos plate boundary between the cfz and sfz during periods of spreading direction change since 3 ma transtensional transforms will adjust to a new spreading direction almost immediately while transpressional transforms will experience compression for a period of time comparable to half the age offset of the compressional transform

interseismic and postseismic shallow creep of the north qaidam thrust faults detected with a multitemporal insar analysis understanding the mechanisms by which earthquake cycles produce folding and accommodate shortening is essential to quantify the seismic potential of active faults and integrate aseismic slip within our understanding of the physical mechanisms of the long term deformation however measuring such small deformation signals in mountainous areas is challenging with current space geodesy techniques due to the low rates of motion relative to the amplitude of the noise here we successfully carry out a multitemporal interferometric synthetic aperture radar analysis over the north qaidam fold thrust system in ne tibet where eight mw 5 2 earthquakes occurred between 2003 and 2009 we report various cases of aseismic slip uplifting the thickened crust at short wavelengths we provide a rare example of a steep shallow 13 km long and 6 km wide afterslip signal that coincides spatially with an anticline and that continues into 2011 in response to a mw 6 3 event in 2003 we suggest that a buried seismic slip during the 2003 earthquake has triggered both plastic an elastic folding and aseismic slip on the shallow thrusts we produce a first order two dimensional model of the postseismic surface displacements due to the 2003 earthquake and highlight a segmented slip on three fault patches that steepen approaching the surface this study emphasizes the fundamental role of shallow aseismic slip in the long term and permanent deformation of thrusts and folds and the potential of interferometric synthetic aperture radar for detecting and characterizing the spatiotemporal behavior of aseismic slip over large mountainous regions

deep tow studies of the overlapping spreading centers at 9 03 n on the east pacific rise the deeply towed instrument package of the scripps institution of oceanography was used to study for the first time the fine scale structure of an overlapping spreading center osc system the 9 03 n osc on the east pacific rise epr the eastern and western limbs of this osc system which are 8 km apart and overlap by 27 km show marked differences away from the tips the spreading centers are highly tectonized and differ greatly from the ridge tips the western ridge tip exhibits a few fissures but no sign of recent volcanic activity whereas the eastern ridge tip is highly fissured and has experienced more recent volcanic episodes which are confined to a narrow zone within this highly fissured area in both cases the ridge tip fissures are 10 15 oblique to the strike of the faults that occur on the flanks of the adjacent portion of the opposite spreading axis indicating a recent change in the direction of deviatoric tension and suggesting that the eastern and western spreading centers have been propagating southward and northward respectively the eastern ridge tip fissures are transecting the flank of the western spreading axis suggesting that the eastern spreading center is about to become the through going trace of the east pacific rise in contrast the western spreading center disappears into abyssal hill terrain that was presumably created at the eastern ridge axis some of the very few tectonic features observed in the overlap basin may reflect the existence of a short lived shear couple due to the interaction of the two overlapping spreading centers sediment cover over the whole area and especially in the overlap basin is relatively thick supporting the idea of a time averaged deficit in the magmatic budget at this osc we suggest that the 9 03 n osc developed where two magmatic pulses independent in space and time and propagating along the strike of the east pacific rise away from the loci of melt emplacement failed to meet misalignment of the magmatic conduits resulted in the propagation of the two spreading centers past each other and the development of the ensuing osc geometry independent lines of evidence derived from the three dimensional inversion of the magnetic field at the 9 03 n osc sempere et al 1984 from numerical modelling of the growth of two en echelon elastic cracks in a tensile stress field sempere and macdonald 1986 and from geochemical data langmuir et al 1986 support our interpretation of the deep tow data we suggest that deviations from axial linearity of the spreading centers devals langmuir et al 1986 and small nonoverlapping offsets snoos batiza and margolis 1986 are simply local lows or saddle points along the axial depth profile that arise when two magmatic pulses propagating toward one another meet head on oscs and some saddle points i e devals snoos are all small rapidly evolving ridge axis discontinuities which may represent the surficial expression of the distal ends of small scale longitudinal convection cells beneath the east pacific rise

landscape response to strike slip faulting linked to collisional settings quaternary tectonics and basin formation in the eastern betics southeastern spain abstract neotectonic behaviour of the eastern betics southeastern spain has been controlled by the presence of a large left lateral shear zone this is an intraplate transcurrent zone probably decoupled by a mid crustal detachment horizon the morphological expression of this crustal structure is a sigmoidal corridor in which the main quaternary basins are located three types of morphostructural domains can be distinguished in the sigmoidal corridor the central segment and the northern and southern terminal splays the central segment is characterized by wrench tectonics whilst the southern and northern terminal splays are controlled by transtensional and transpressional tectonics respectively the quaternary morphostructural pattern is only the more recent picture of the tectonic processes that have controlled the late orogenic evolution of the eastern betics the indentation of the aguilas arc accompanied by thin skinned thrusting and tectonic escape in its easternmost sector and extensional collapse accompanied by thin skinned stretching in its westernmost sector

propagation and linkage of oceanic ridge segments we have investigated the propagation of spreading ridges and the development of structures that link ridge segments using an analogy between ridges and cracks in elastic plates the ridge propagation force and a path factor that controls propagation direction were calculated for echelon ridge segments propagating toward each other the ridge propagation force increases as ridge ends approach but then declines sharply as the ends pass so ridge segments may overlap somewhat the sign of the path factor changes as ridge ends approach and pass so the overlapping ridge ends may diverge and then converge following a hook shaped path the magnitudes of shear stresses in the plane of the plate and orientations of maximum shear planes between adjacent ridge segments were calculated to study transform faulting for different loading conditions simulating ridge push plate pull and ridge suction we identify a zone of intense mechanical interaction between adjacent ridge ends in which stresses are concentrated for all conditions the shear stress in the interaction zone increases as ends approach and remains large as the ends overlap thus crust in this zone may fracture and weaken in preparation for the formation of a through going transform fault the calculated shear planes rotate toward an orientation about 90 from the strike of ridges as the ends pass thus favoring the orthogonal arrangement of ridges and transforms the magnitudes of mean stresses in the plane of the plate and orientations of principal stress planes were also calculated the mean stress is tensile in the interaction zone so basins may form there except in the case of ridge push loading the planes across which the maximum tension acts are oblique to ridges thus favoring obliquely oriented normal faults bounding the transform valley

seismic sources on the iberia african plate boundary and their tectonic implications the plate boundary between iberia and africa has been studied using data on seismicity and focal mechanisms the region has been divided into three areas a the gulf of cadiz b the betics alboran sea and northern morocco and c algeria seismicity shows a complex behavior large shallow earthquakes h 30 km occur in areas a and c and moderate shocks in area b intermediate depth activity 30 h 150 km is located in area b the depth earthquakes h 650 km are located to the south of granada moment rate slip velocity andhvalues have been estimated for shallow shocks and show similar characteristics for the gulf of cadiz and algeria and quite different ones for the central region focal mechanisms of 80 selected shallow earthquakes 8 mb 4 show thrust faulting in the gulf of cadiz and algeria with horizontal nnw sse compression and normal faulting in the alboran sea with e w extension focal mechanisms of 26 intermediate depth earthquakes in the alboran sea display vertical motions with a predominant plane trending e w solutions for very deep shocks correspond to vertical dip slip along n s trends frohlich diagrams and seismic moment tensors show different behavior in the gulf of cadiz betic alboran sea and northern morocco and northern algeria for shallow events the stress pattern of intermediate depth and very deep earthquakes has different directions vertical extension in the nw se direction for intermediate depth earthquakes and tension and pressure axes dipping about 45 o for very deep earthquakes regional stress pattern may result from the collision between the african plate and iberia with extension and subduction of lithospheric material in the alboran sea at intermediate depth the very deep seismicity may be correlated with older subduction processes

post wildfire surface deformation near batagay eastern siberia detected by l band and c band insar thawing of ice rich permafrost and subsequent ground subsidence can form characteristic landforms and the resulting topography they create are collectively called thermokarst the impact of wild

tectonic evolution of ridge axis discontinuities by the meeting linking or self decapitation of neighboring ridge segments recent deep tow sea beam and seamarc ii studies indicate that ridge axis discontinuities along the east pacific rise evolve in several different ways where magmatic pulses along the spreading center happen to meet head on a low point or saddle point occurs along the axial depth profile of the spreading center where the magmatic pulses misalign overlapping spreading centers develop and two distinct evolutionary paths are possible one spreading center tip may cut through to and link with the adjacent en echelon ridge chopping off the opposing ridge tip as proposed by macdonald and fox 1983 in addition either spreading center may cut inside or outside of itself repeatedly decapitating its own ridge tip crack propagation studies show that the crack propagation force g drops significantly when the ratio of crack overlap to crack offset l w exceeds 3 applying this relation to spreading centers we suggest that propagation of the individual spreading center tips may stall when l w is greater than 3 if linkage has not yet occurred then the next magmatic pulse that propagates along the ridge may be deflected away from the path of the existing ridge tip decapitating the ridge tip in a process we call self decapitation subsequent magmatic pulses may be deflected or derailed from the existing path of the ridge because freezing of the axial magma chamber near ridge axis discontinuities creates a core of coherent unfaulted gabbroic rock along the spreading axis which is strong relative to the intensely faulted lithosphere on either side of the frozen magma chamber in addition the local stress field rotates near the discontinuity so that subsequent magma pulses and associated cracking fronts will tend to deflect away from the preexisting path of the ridge for propagating rifts which represent first order changes in plate boundary geometry l w remains 1 5 so that g is maintained near its maximum value and episodes of continued propagation in the same direction are enhanced

sentinel 1 insar measurements of deformation over discontinuous permafrost terrain northern quebec canada abstract differential synthetic aperture radar interferometry d insar has been applied in permafrost environments to detect surface deformation caused by freeze thaw processes in the active layer and underlying permafrost the effectiveness of sentinel 1 insar in monitoring ground surface deformation over continuous permafrost terrain above the treeline has been proven the heterogeneous landscape and developed vegetation cover increase the difficulty of applying d insar in sub arctic discontinuous permafrost terrain the potential of sentinel 1 insar in such an environment has not been fully explored in this study we explore the capabilities and limitations of applying sentinel 1 time series data for monitoring surface deformation over discontinuous permafrost terrain the interferometric coherence time series from september 2016 to april 2018 were analyzed over typical landscapes in discontinuous permafrost environments and their thaw subsidence curves are revealed by the small baseline subset sbas insar technique the seasonal thaw subsidence in the summer of 2017 was in the range of 15 80 mm in the study area the land cover types with thaw subsidence magnitudes from low to high are exposed land peatland lichen low shrub lichen dominated and wetland low vegetation the difference in displacement pattern between lichen dominated and wetland low vegetation dominated permafrost terrains is especially clear at the end of the thawing stage in september and october the differences in thaw subsidence magnitude and pattern reveal the influence of the soil water content in the active layer and permafrost properties on the thaw subsidence patterns we also compared the sentinel 1 retrieved cumulative displacement with the x band terrasar x and l band alos palsar results the difference of retrieved deformation magnitude using the three sensors is amplified when shrubs are more developed the findings indicate that sentinel 1 time series with a 6 day or 12 day span work well over discontinuous permafrost terrain above the tree line i e tundra tundra wetlands and less developed shrub tundra environments during the thawed season but the results and accuracy are not promising over developed shrub tundra and especially forest tundra environments

evidence for an active sinistral shear zone in the westeren alboran region a compilation of gravity seismicity neotectonics geology tomography and topography data from the alboran region reveals distinctive differences between the eastern and western part of the alboran region and betic cordillera calculated profiles of integrated crustal strength reveal that lateral differences in mechanical behaviour are caused by marked inherited differences in crustal make up the two domains with different tectonic behaviour are separated by a n025 trending lineament in the western alboran and central betic cordillera this lineament can be interpreted as an upper mantle lower crustal sinistral shear zone accommodating a large part of the convergence between africa and iberia

independent component analysis and parametric approach for source separation in insar time series at regional scale application to the 2017 2018 slow slip event in guerrero mexico

systematic insar tropospheric phase delay corrections from global meteorological reanalysis data 1 despite remarkable successes achieved by differential insar estimations of low tectonic strain rates remain challenging in areas where deformation and topography are correlated mainly because of the topography related atmospheric phase screen aps in areas of high relief empirical removal of the stratified component of the aps may lead to biased estimations of tectonic deformation rates here we describe a method to correct interferograms from the effects of the spatial and temporal variations in tropospheric stratification by computing tropospheric delay maps coincident with sar acquisitions using the era interim global meteorological model the modeled phase delay is integrated along vertical profiles at the era i grid nodes and interpolated at the spatial sampling of the interferograms above the elevation of each image pixel this approach is validated on unwrapped interferograms we show that the removal of the atmospheric signal before phase unwrapping reduces the risk of unwrapping errors in areas of rough topography

a new method for measuring deformation on volcanoes and other natural terrains using insar persistent scatterers 1 we present here a new insar persistent scatterer ps method for analyzing episodic crustal deformation in non urban environments with application to volcanic settings our method for identifying ps pixels in a series of interferograms is based primarily on phase characteristics and finds low amplitude pixels with phase stability that are not identified by the existing amplitude based algorithm our method also uses the spatial correlation of the phases rather than a well defined phase history so that we can observe temporally variable processes e g volcanic deformation the algorithm involves removing the residual topographic component of flattened interferogram phase for each ps then unwrapping the ps phases both spatially and temporally our method finds scatterers with stable phase characteristics independent of amplitudes associated with man made objects and is applicable to areas where conventional insar fails due to complete decorrelation of the majority of scatterers yet a few stable scatterers are present

seafloor photo geology and sonar terrain modeling at the 9 n overlapping spreading center east pacific rise 1 a fundamental goal in the study of mid ocean ridges is to understand the relationship between the distribution of melt at depth and seafloor features building on geophysical information on subsurface melt at the 9 n overlapping spreading center on the east pacific rise we use terrain modeling dsl 120a side scan and bathymetry photo geology jason ii and whoi towcam and geochemical data to explore this relationship terrain modeling identified four distinct geomorphic provinces with common seafloor characteristics that correspond well to changes in subsurface melt distribution visual observations were used to interpret terrain modeling results and to establish a relative seafloor age scale calibrated with radiometric age dates to identify areas of recent volcanism on the east limb recent eruptions in the north are localized over the margins of the 4 km wide asymmetric melt sill forming a prominent off axis pillow ridge along the southern east limb recent eruptions occur along a neovolcanic ridge that hugs the overlap basin and lies several kilometers west of the plunging melt sill our results suggest that long term southward migration of the east limb occurs through a series of diking events with a net southward propagation direction examining sites of recent eruptions in the context of geophysical data on melt distribution in the crust and upper mantle suggests melt may follow complex paths from depth to the surface overall our findings emphasize the value of integrating information obtained from photo geology terrain modeling lava geochemistry and petrography and geophysics to constrain the nature of melt delivery at mid ocean ridges

mechanical decoupling and thermal structure at the east pacific rise axis 9 n constraints from axial magma chamber geometry and seafloor structures abstract we study the relationships between the seafloor structures and the axial magma chamber geometry in the 9 n overlapping spreading center osc area on the fast spreading east pacific rise epr our observations are based on a new high resolution bathymetric map of the 9 n osc area derived from picks of the seafloor arrival on 3d seismic data and on previously published data that constrain the presence and distribution of melt below the 9 n osc differences in the orientation of structures between the seafloor and the magma chamber indicate a sharp change in principal stress directions with depth suggesting that the brittle crust above the melt sill is decoupled from the melt sill itself and the ductile crust underlying it the stress field within the brittle upper crust results from a local interaction of the two overlapping spreading centers whereas the stress field in the crust below the melt sill corresponds to the regional stress field imposed by plate separation given this mechanical structure of the crust the melt sill shape and location appear to be controlled by the following factors the location of the deep melt source below the melt sill the ambient stress field at the depth of the melt sill and the stress field in the brittle upper crust above the melt sill which thermally shapes the roof of the melt sill through repeated eruptions

a spatially varying scaling method for insar tropospheric corrections using a high resolution weather model variation in tropospheric delay is a major limiting factor on the accuracy of interferometric synthetic aperture radar insar measurements this is particularly the case when deformation and topography are correlated to address limitations of previous insar tropospheric correction methods here we present a new approach that combines the use of both external weather model data and the interferometric phase we assume that vertical refractivity profiles calculated from a high resolution weather model data can generally describe the form of the relationship between tropospheric delay and height but that the magnitude can be incorrect we estimate a magnitude correction by scaling the original delays to best match the interferometric phase we validated our new method using simulated data and demonstrate that both coseismic and interseismic signals can be separated from strong tropospheric delays we also applied our algorithm to the central portion of the altyn tagh fault in northern tibet where deformation correlates strongly with topographic relief of 6 000 m and show that the derived velocity field is more internally consistent and agrees better with independent global positioning system measurements

magmatic and tectonic segmentation of the intermediate spreading costa rica rift a fine balance between magma supply rate faulting and hydrothermal circulation 3 d tomographic modelling of wide angle seismic data recorded at the intermediate spreading costa rica rift has revealed a p wave seismic velocity anomaly low located beneath a small overlapping spreading centre that forms a non transform discontinuity at the ridge axis this low velocity zone displays a maximum velocity anomaly relative to the background ridge axis crustal structure of 0 5 km s 1 has lateral dimensions of 10 5 km and extends to depths 2 5 km below the seabed placing it within layer 2 of the oceanic crust we interpret these observations as representing increased fracturing under enhanced tectonic stress associated with the opening of the overlapping spreading centre that results in higher upper crustal bulk porosity and permeability evidence for ongoing magmatic accretion at the costa rica rift ridge axis takes the form of an axial magma lens beneath the western ridge segment and observations of hydrothermal plume activity and microearthquakes support the presence of an active fluid circulation system we propose that fracture pathways associated with the low velocity zone may provide the system through which hydrothermal fluids circulate these fluids cause rapid cooling of the adjacent ridge axis and any magma accumulations which may be present the costa rica rift exists at a tipping point between episodic phases of magmatic and tectonically enhanced spreading the characteristics inherited from each spreading mode have been preserved in the crustal morphology off axis for the past 7 myr using potential field data we contextualize our seismic observations of the axial ridge structure at the whole segment scale and find that the proposed balance between magmatic and tectonically dominated spreading processes observed off axis may also be apparent along axis and that the current larger scale magma supply system at the costa rica rift may be relatively weak based on all available geophysical observations we suggest a model for the inter relationships between magmatism faulting and fluid circulation at the costa rica rift across a range of scales which may also be influenced by large lithosphere scale structural and or thermal heterogeneity

long term growth of the himalaya inferred from interseismic insar measurement the rise and support of the 5000 m topographic scarp at the front of indian eurasian collision in the himalaya involves long term uplift above a mid crustal ramp within the main himalayan thrust mht system locking of the shallower portion of the flat ramp flat during the interseismic period also produces transient uplift above the transition zone however spatial and temporal relationships between permanent and transient vertical deformation in the himalaya are poorly constrained leading to an unresolved causal relationship between the two here we use interferometric synthetic aperture radar insar to measure interseismic uplift on a transect crossing the whole himalaya in central nepal the uplift velocity of 7 mm yr at the front of the annapurna mountain range is explained by an 18 21 mm yr slip rate on the deep shallow dipping portion of the mht with full locking of the mid crustal ramp underlying the high himalaya the transient uplift peak observed by insar matches spatially with the long term uplift peak deduced from the study of trans himalayan river incision although models of the seismic cycle involving thrusting over a ramp of fixed geometry predict an 20 km separation between the two peaks we argue that this coincidence indicates that today s mid crustal ramp in central nepal is located southward with respect to its average long term location suggesting that mountain growth proceeds by frontward migration of the ramp driven by underplating of material from the indian plate under the himalaya

reconciling geochemical and geophysical observations of magma supply and melt distribution at the 9 n overlapping spreading center east pacific rise 1 early studies of mid ocean ridge discontinuities such as transform faults and overlapping spreading centers suggested a lower magma supply compared to ridge segment centers this is reflected in bathymetrically deeper ridge axes decreased hydrothermal activity and the eruption of more evolved lava compositions while many signatures of lower magma supply are observed at the 9 n overlapping spreading center on the east pacific rise geophysical studies indicate extensive sub surface melt in the region suggesting that the present magmatic system is not diminished here major and trace element concentrations of erupted lavas are used to better understand magma supply at a large second order ridge discontinuity we show that the wide range of lava compositions erupted at the 9 n overlapping spreading center is generally consistent with early petrologic models of ridge propagation and require variable degrees of fractional crystallization extensive magma mixing and in some instances crustal assimilation moderately evolved ferrobasalts and feti basalts erupted at the osc indicate that crustal residence times are long enough for significant crystallization of all magmas within the region but the presence of dacitic lavas reflects periods of even lower magma supply where melt replenishment is subordinate to cooling and crystallization the geophysical observations of extensive melt within the shallow crust are reconciled with the geochemistry of the lavas if melts are supplied intermittently to the propagating ridge over relatively short timescales

microseismicity and tectonics in the granada basin spain a microseismic experiment carried out in 1994 in the granada basin spain permitted the precise recording of more than 80 local earthquakes the dense distribution of the local network with 40 to 50 instrumental records for each event enabled us to have well controlled hypocenters and also 10 reliable focal mechanisms the above observations are interpreted together with topographic data neotectonics and sub surface information microtectonic observations in sierra elvira padul and zafarraya gave a set of fault planes and striae which were interpreted in terms of the recent regional stress tensor the actual stress tensor obtained from the microseismic campaign data gives a regime in radial extension with r1 vertical and r3 oriented ns to nne microtectonic information is coherent with these orientations but closer to 3 axial extension a set of 64 mechanisms obtained from the permanent andalusian network favors a ns orientation for r3 this results are interpreted in terms of the general model implying the lateral ejection of the betic ranges towards the atlantic d 2002 elsevier science b v all rights reserved

asymmetric melt sills and upper crustal construction beneath overlapping ridge segments implications for the development of melt sills and ridge crests a new three dimensional tomographic velocity model and depth converted reflection images of the melt sills beneath the 9 03 n overlapping spreading center on the east pacific rise show that the upper crustal construction at this ridge discontinuity is highly asymmetric with reference to the bathymetric ridge crests of the overlapping limbs despite the similarly curved ridge crests the asymmetries are markedly different under the two limbs and appear to be related to the contrasting evolutionary history of the limbs the overlap basin is closely related to the propagating eastern limb in terms of its seismic structure by contrast the western limb forms a distinct morphologic region that displays little structural relationship to the adjacent overlap basin and other relict basins as the overlapping spreading center is migrating southward the differential development of melt sills and ridge crests may be inferred from the results of this study ridge propagation appears to involve two major processes the advancement of the melt sill at the ridge tip and the development of ridge crest morphology and the neovolcanic axis to the north of the overlap basin region near the existing propagating limb the latter process may result in the abandonment of the current neovolcanic axis leading to the self decapitation of the propagating limb by contrast the self decapitation of the western limb is related to the receding melt sill which lags behind the anticlockwise rotational motion of the ridge crest

estimating 1992 2000 average active layer thickness on the alaskan north slope from remotely sensed surface subsidence 1 the measurement of temporal changes in active layer thickness alt is crucial to monitoring permafrost degradation in the arctic we develop a retrieval algorithm to estimate long term average alt using thaw season surface subsidence derived from spaceborne interferometric synthetic aperture radar insar measurements our algorithm uses a model of vertical distribution of water content within the active layer accounting for soil texture organic matter and moisture we determine the 1992 2000 average alt for an 80 100 km study area of continuous permafrost on the north slope of alaska near prudhoe bay we obtain an alt of 30 50 cm over moist tundra areas and a larger alt of 50 80 cm over wet tundra areas our estimated alt values match in situ measurements at circumpolar active layer monitoring calm sites within uncertainties our results demonstrate that insar can provide alt estimates over large areas at high spatial resolution

kinematics of overlapping rift propagation with cyclic rift failure existing kinematic models for propagation of oceanic spreading ridges that incorporate overlap between ridge segments fail to describe detailed observations of the failed segments i present a new model which discards the assumption of steady state behavior of the failing rift permitting inward curvature of both rift tips in the overlap region the shape of an inward curving failing rift must continuously change but is assumed to cyclically return to its original shape by discrete inward ridge jumps other assumptions of symmetric spreading and uniform simple shear deformation between the overlapping rift tips are retained from previous models inward curvature of failed rift structures provides much better agreement with observations and is consistent with tensile fracture theory if the offset between ridge segments is small enough the inward jumps of the failing rift will cut across deformed structures originally formed at the propagating tip possibly generating seafloor fabrics that crosscut each other at nearly right angles observations of such structures near the gorda ridge can be explained by a model incorporating variable cyclieity of the failing rift chrons curve inward toward the ridge faithfully recording the shape of the propagating tip in an undeformed part of the plate isochrons also curve toward the ridge along the inner pseudofault but in the original formulation of the rules of plate tectonics transform faults were assumed to be fixed relative to each other and the ridge segments they offset the propagating rift model 1 which discards this assumption has been very successful in describing oblique offsets in magnetic anomalies as a result of the lengthening of a ridge segment through time at the expense of the adjacent segment detailed observations of active propagating rifts suggest that the assumption that ridges are necessarily offset by discrete transform faults should also be discarded with the segments instead offset by zones of distributed shear with widths of 10 or more km 2 3

seismic structure and indicators of magma budget along the southern east pacific rise in this paper we re examine the relationship between seismically constrained variations in crustal structure along the southern east pacific rise sepr and the segment scale variations in axial depth morphology basalt geochemistry and hydrothermal activity that have often been attributed to along axis differences in the supply of magma to the mid ocean ridge along 800 km of the fast spreading sepr good correlations exist between axial depth ridge cross sectional area mantle bouguer anomaly and the mgo weight percent of basalts recovered from the rise axis these correlations indicate along axis changes in crustal thickness and temperature consistent with variations in magma supply on time scales of 100 000 years in contrast we show that the depth and width of the midcrustal magma sill the thickness of seismic layer 2a and the intensity of hydrothermal venting are poorly correlated with regional variations in ridge depth and cross sectional area we suggest that the emplacement geometry width of the intrusion zone and flow lengths not magma supply controls extrusive layer seismic layer 2a thickness we hypothesize that magma lens properties and hydrothermal activity are closely linked to spreading events dike intrusion eruptions faulting which occur on much shorter timescales 10 100 years than the longer term variations in magma supply reflected in along axis changes in the shape and depth of the ridge axis

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

lithospheric folding in iberia integration of stress indicator data gravity data crustal kinematics data and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large scale alpine to recent intraplate deformation in iberia the inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of iberia patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present day intraplate compression in iberia inferred from structural analysis of stress indicator data and focal mechanism solutions these findings suggest the presence of lithospheric folds with wavelengths compatible with theoretical predictions of folding wavelengths of variscan lithosphere stress induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present day deep mantle lithosphere interactions inferred from seismic tomography

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

evidence for a post 3 16 ma change in nubia eurasia north america plate motions we combine updated gps velocities from the nubian nu eurasian eu and north american na plates with 500 new 3 16 myr average seafloor spreading rates and nine transform fault azimuths from the northern atlantic and arctic basin seafloor spreading centers to estimate and test for changes in the relative motion between these plates the numerous new seafloor spreading rates and gps velocities improve our ability to detect recent changes in the relative motions of these plates the angular velocity vector that best fits the eu na gps velocities lies significantly north of the 3 ma average pole in accord with previously published geologic evidence that the eu na pole has migrated northward since v3 ma although we also find evidence for a significant post 3 ma change in nu na motion it is less compelling because the nubian plate gps velocity field is sparse and nu na seafloor spreading rates appear to have remained steady within the 1 mm yr 31 uncertainties if we systematically decrease the seafloor spreading rates to correct for outward displacement of seafloor spreading magnetic lineations the nu eu pole derived from gps site velocities lies more than 30 angular degrees south of the tightly constrained 3 ma average estimate and predicts significantly slower and more oblique present day nu eu convergence in the mediterranean both models for nu eu motion pass a key test for their accuracy namely they correctly predict strike slip motion along the well mapped gloria fault east of the azores the change to more oblique nu eu motion may reflect increasing difficulty in maintaining margin normal convergence within this continent continent collision zone 8 2003 published by elsevier b v

classification of slope processes based on multitemporal dinsar analyses in the himalaya of nw bhutan abstract slope deformation in mountainous terrain can be driven by different processes the nature of which is either gravitational and irreversible or seasonal and reversible the latter induced by permafrost variations or by hydromechanical or thermomechanical effects the importance of identifying such deformations is not only related to the hazard they can pose but also to the understanding of changes that permafrost or local hydrological conditions undergo here we carry out a multi temporal insar analysis over a mountainous area 8000 km2 large straddling north western bhutan and southern tibet we propose a methodology to separate locally deforming areas from the effects of long wavelength signals through the analysis of the spatio temporal behaviour of 4 years long time series of surface displacements we present the mapping of hundreds of small scale features that appear to be actively deforming as well as several examples of reversible deformation rarely detected at this scale in such a challenging and vast region the analysis of the multi annual trend of ground deformation shows a relatively small number of irreversible gravitational movements clearly related to rock slides which attests a low level of recent activity of large rock slope instabilities in the region in the southernmost lower elevation parts of the study area we quantify reversible surface displacements with amplitudes ranging between 5 and 17 mm and showing maximum displacements towards the satellite in summer months thus compatible with hydro mechanical effects related to groundwater table variations in addition the ground movement induced by the active layer s response to thawing and freezing over the gentler slopes and high elevation permafrost regions of bhutan and southern tibet is on average around 10 mm with maxima up to 28 mm the localised displacements appear to be largely associated to braided stream plains glacier outwash plains or low angle fine sediment covered slopes

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

seismic signature of intracrustal magmatic intrusions in the eastern betics internal zone se iberia 1 receiver functions at three broad band stations located in the most easterly inner betics have been analyzed to investigate the structure of its underlying crust and uppermost mantle these stations are located within a geologically distinctive block bounded by the palomares alhama de murcia faults which is characterized by high heat flow values widespread strike slip faulting and neogene volcanism our analysis shows that a low velocity zone pervades the uppermost mantle beneath the stations and that the overlying crust has a high vp vs ratio and a prominent intracrustal low velocity zone i between the palomares and alhama de murcia faults and ii east of murcia perhaps thermally perturbing the upper crust north and east of cartagena independent studies show that the seismic velocities of the intervening mantle lid are normal beneath the stations and we suggest that our observations result from rapidly ascending magma diapirs ponding at intracrustal levels within the distinctive block

the adriatic region an independent microplate within the africa eurasia collision zone 1 we use gps measurements and block modeling to investigate the present day deformation of the adriatic region whose kinematics within the nubia eurasia plate boundary zone is not well constrained and remains controversial block modeling allows us to compute rigid plate angular velocities while accounting for elastic strain accumulation along block bounding faults results suggest that the adriatic is a microplate adria and that the southern boundary with the nubia plate and the aegean domain may be located along the apulia escarpment and the kefallinia fault geodetic data alone cannot discriminate between a single block ap or a two blocks gdap description of adria but the gdap model predicts boundary slip rates that are in better agreement with observations from previous studies

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

a one million year history of the 11 45 n east pacific rise discontinuity bathymetric magnetic and side scan sonar data from a june 1987 seamarc ii cruise aboard the r v moana wave have been combined with additional data in an area 140 km by 154 km centered on the overlapping spreading center pair osc located at 11 45 n on the east pacific rise epr the purpose of this study is to correlate and interpret these data sets in order to determine the recent 1 m y history of this osc the data sets include gridded bathymetry and magnetic field anomalies a side scan sonar mosaic and a fault map the bathymetry and anomaly grids were used as inputs in a three dimensional fourier inversion resulting in a crustal rock magnetization distribution solution the most prominent feature of all five maps is a roughly v shaped anomalous zone centered on the osc the zone is characterized by a positive depth anomaly a negative magnetic field anomaly within the central positive anomaly and a zone of high magnetization in the inversion solution a hummock y texture and sparse curved faults mark the zone in the side scan mosaic and fault map the shape of this zone indicates a short period of northward migration of the discontinuity 0 72 0 6 ma at approximately 75 mm yr followed by slow less than 30 mm yr and then fast 140 200 mm yr southward migration for the past 0 6 m y the anomalous zone is not well defined beyond the edge of the central anomaly which is straight and continuous indicating that if this discontinuity of the epr existed 0 72 ma its offset was negligible the present day axis has an orientation of 349 the edge of the central anomaly has an orientation of 353 and jaramillo age crust to the east of the epr has an orientation of 353 355 this variation in magnetic linealion directions suggests a 4 to 6 counter clockwise change in the direction of spreading in the past 1 m y which seems to have been accommodated by asymmetric spreading variations in mean fault trend with age are consistent with a counter clockwise change in the direction of spreading for the same time period

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

ice loss in the northeastern tibetan plateau permafrost as seen by 16 yr of esa sar missions abstract insar time series of surface deformation from 16 yr of envisat 2003 2011 and sentinel 1 2014 2019 esa satellite radar measurements have been constructed to characterise spatial and temporal dynamics of ground deformation over an 80 000 km2 area in the permafrost of the northeastern tibetan plateau the regional deformation maps encompass various types of periglacial landforms and show that seasonal thaw effects are controlled by the sediment type and local topography high seasonal ground movements are concentrated on shallow slopes and poor drainage areas in unconsolidated frost susceptible and fine grained sediments within glacier outwash plains braided stream plains alluvial deposits or floodplains fast subsidence due to thaw settlement takes place during june july while frost heave is intense during december january when two sided freezing of pore water under pressure causes prolonged ice segregation near the permafrost table the analysis reveals pervasive subsidence of the ground of up to 2 cm yr and increasing by a factor of 2 to 5 from 2003 to today in high relief and well drained areas the findings suggest that seasonal thaw increasingly affects ice rich layers at the permafrost table as well as high rates of widespread mass movements of non consolidated sediments the latter amplified by an increase of effects from frost heave thaw settlement

insar measurement of the deformation around siling co lake inferences on the lower crust viscosity in central tibet the siling co lake is the largest endorheic lake in central tibet altimetric measures combined with lake contours show that in 1972 1999 its water level remained stable while it increased by about 1 0 m yr in the period 2000 2006 the increased rate gradually stepped down to 0 2 m yr in 2007 2011 the ground motion associated with the water load increase is studied by interferometric synthetic aperture radar insar using 107 ers and envisat sar images during the period 1992 2011 the deformation amplitude closely follows the lake level temporal evolution except that subsidence continues in 2008 2011 while the lake level stagnated this temporal evolution suggests a non elastic relaxation process taking place at a decade timescale phase delay maps are used to constrain possible layered viscoelastic rheological models an elastic model could partly explain the observed subsidence rate if elastic moduli are about twice lower than those extracted from vp vs profiles the surface deformation pattern is also extracted by projecting the phase delay maps against the best fit model temporal behavior it shows that deep relaxation in the asthenosphere is negligible at the decade timescale and favors the existence of a ductile channel in the deep crust above a more rigid mantle overall the best fit model includes a ductile lower crust with a viscosity of 1 3 1018 pa s between 25 and 35 km and the moho at 65 km overlying a rigid mantle

large scale insar monitoring of permafrost freeze thaw cycles on the tibetan plateau multitemporal interferometric synthetic aperture radar insar observations are used to characterize spatial variations of the permafrost active layer and its temporal evolution in northwestern tibet we develop a method to enhance insar performances for such difficult terrain conditions and construct an 8 year timeline of the surface deformation over a 60 000 km2 area the ground movement induced by the active layer s response to climate forcing is limited to cenozoic sedimentary basins and is spatially variable in both its seasonal amplitude 2 5 12 mm and multiannual trend 2 to 3 mm yr a degree day integrated model adjusted to the data indicates that subsidence occurs when the surface temperature exceeds zero may to october over areas where seasonal movements are large 8 mm the period of subsidence is delayed by 1 2 months over areas where smaller seasonal movements are observed suggesting an unsaturated soil where water occurs in the deeper part of the active layer

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

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

lake water and glacier mass gains in the northwestern tibetan plateau observed from multi sensor remote sensing data implication of an enhanced hydrological cycle abstract lakes and glaciers are widely distributed in the northwestern tibetan plateau a synchronized examination of lake and glacier mass variations there has not previously been conducted which has limited the understanding of the lake water balance and the hydrologic cycle in the region in this study we comprehensively examine lake area and volume and glacier mass changes using multi sensor satellite data we find that lake expansion in the northwestern tibetan plateau was more robust from 1976 to 2018 when compared to other regions of the plateau especially for the glacier fed and endorheic lakes lake volume changes show that most of the lakes had an increase in water volume particularly in 2000 2018 with a total water storage gain of 28 6 gt by using high resolution kh 9 and tandem x data we observe that the glacier surface elevation of the western kunlun mountains had a slight thinning rate of 0 07 0 16 m yr in 1973 2000 but a positive rate of 0 002 0 003 m yr in 2000 2018 the heterogeneous pattern of glacier elevation changes between the north n and south s slopes are revealed i e 0 02 0 01 m yr n against 0 12 0 03 m yr s in 1973 2000 and 0 05 0 02 m yr n against 0 06 0 02 m yr s in 2000 2018 overall the glaciers trend to a stable state 0 05 m yr in both the south slope of the western kunlun mountains and aru co regions between 2000 and 2018 similar patterns are also found for basin wide examinations of lake storage changes mass gains and glacier mass budgets positive or close to stable the seasonal snow cover area changes derived from cloud free modis snow cover products present a variable and insignificant trend between 2003 and 2017 snow depth derived from passive microwave remote sensing data exhibits a decreasing trend between 1979 and 2015 but the water equivalent could contribute only an insignificant amount to the observed lake changes the lake water gains and almost positive glacier mass balance imply that the hydrological cycle in the northwestern tibetan plateau has become enhanced

seasonal dynamics of a permafrost landscape adventdalen svalbard investigated by insar abstract nordenskiold land in central spitsbergen svalbard is characterized as a high latitude high relief periglacial landscape with permafrost occurring both in mountains and lowlands freezing and thawing of the active layer causes seasonal frost heave and thaw subsidence while permafrost related mass wasting processes induce downslope ground displacements on valley sides displacement rate varies spatially and temporally depending on environmental factors in our study we apply satellite synthetic aperture radar interferometry insar to investigate the magnitude spatial distribution and timing of seasonal ground displacements in and around adventdalen using terrasar x stripmap mode 2009 2017 and sentinel 1 interferometric wide swath mode 2015 2017 sar images first we show that insar results from both sensors highlight consistent patterns and provide a comprehensive overview of the distribution of displacement rates secondly two dimensional 2d terrasar x insar results from combined ascending and descending geometries document the spatial variability of the vertical and east west horizontal displacement rates for an average of nine thawing seasons the remote sensing results are compared to a simplified geomorphological map enabling the identification of specific magnitudes and orientations of displacements for 14 selected geomorphological units finally june to december 2017 6 day sampling interval sentinel 1 time series was retrieved and compared to active layer ground temperatures from two boreholes the timing of the subsidence and heave detected by insar matches the thawing and freeze back periods measured by in situ sensors our results highlight the value of insar to obtain landscape scale knowledge about the seasonal dynamics of complex periglacial environments

remote sensing measurements of thermokarst subsidence using insar thawing of ice rich permafrost followed by surface subsidence results in irregular depressed landforms known as thermokarst many remote sensing studies have identified thermokarst landforms and mapped their changes however the intrinsic dynamic thermokarst process of surface subsidence remains a challenge to quantify and is seldom examined using remote sensing methods in this study we used spaceborne interferometric synthetic aperture radar insar data to map surface subsidence trends at a thermokarst landform located near deadhorse on the north slope of alaska a pipeline access road constructed in the 1970s triggered the thawing of the permafrost causing subsequent expansion of the thermokarst landform using phased array type l band synthetic aperture radar images acquired by the advanced land observing satellite 1 our insar analysis reveals localized thermokarst subsidence of 2 8 cm yr between 2006 and 2010 equivalent to an ice volume loss of about 1 2 107 m3 yr comparisons between insar subsidence trends and lidar microtopography suggest a characteristic time of 8 years of thermokarst development we also quantitatively explain the difficulty uncertainties and possible biases in separating thermokarst induced irreversible subsidence from cyclic seasonal deformation our study illustrates that insar is an effective tool for mapping and studying active thermokarst processes and quantifying ice loss

distribution of magma beneath the east pacific rise near the 9 03 n overlapping spreading center from forward modeling of common depth point data we have reprocessed six cross axis and three along axis common depth point cdp profiles near the 9 03 n overlapping spreading center osc to understand the relationship between axial magma chamber amc width and seafloor morphology travel time modeling of the amc reflector reveals an asymmetric distribution of melt across the 9 03 n osc the variation of modeled amc width beneath either osc limb is minimal but the width increases nearly fourfold across the offset attaining an estimated maximum width of 4 15 km near the 9 17 n ridge axis discontinuity additionally melt distribution underlying the eastern rise limb is not symmetric with respect to the rise axis neovolcanic zone but is displaced toward the western rise flank depth migration based on a continuum velocity model consistent with postcritical reflections from the base of layer 2a places the skewed amc reflector beneath a nearly constant thickness sheeted dike section which dips 10 away from the rise axis to confirm amc continuity beneath the western rise flank we use the maslov synthetic seismogram method to show that amplitude enhancement of the amc reflector is consistent with a continuous melt body underlying a thickening extrusive layer analysis of along strike cdp profiles indicates an amc which is neither overlapping nor discontinuous when projected onto the along strike plane identifying intracrustal events on along axis cdp lines however requires extreme caution we have modeled out of plane scattering using a kirchhoff formulation and we show that a coherent event identified beneath the overlap basin results from diffraction off the amc which lies nearly 3 km to the west of the profile we attribute the asymmetric pattern of melt to a decoupling of melt supply from preexisting weaknesses in the brittle upper crust in this model melt ascends upward buoyancy forces until deflected by the impermeable sheeted dike complex melt then migrates updip beneath the base of the sheeted dikes toward the neovplcanic zone where fissuring produces a temporary conduit for emplacement discrete jumps in modeled amc width toward the overlap basin represent a further displacement defocusing of melt supply western amc edge relative to the neovolcanic zone eastern amc edge the asymmetric pattern of melt therefore represents a gradual en echelon accommodation of melt supply across the 9 km of ridge axis offset at 9 03 n thus for asymmetric configurations amc width may not correlate solely with magmatic robustness but may signify the amount of decoupling which exists between melt supply and extrusive emplacement within the neovolcanic zone here we present a new model for osc development which invokes a significant component of cross axis melt migration moreover abrupt changes in amc width near ridge axis discontinuities e g 9 17 n deviation in axial linearity suggest that any along axis melt migration is confined to subsegments of the ridge and seem to preclude the segment length migration of melt proposed in some current models the transition of melt supply beneath the overlap basin might favor a continuous low velocity zone underlying this feature if true basin development may be related to the subsidence of a mechanically weak crustal lid the proposed model for osc development therefore views ridge axis discontinuities as the surficial response of misalignment and or defocusing of melt supply in the uppermost mantle