space weathered rims found on the surfaces of the itokawa dust particles on the basis of observations using cs corrected stem we identified three types of surface modification probably formed by space weathering on the surfaces of itokawa particles they are 1 redeposition rims 2 3 nm 2 composite rims 30 60 nm and 3 composite vesicular rims 60 80 nm these rims are characterized by a combination of three zones zone i occupies the outermost part of the surface modification which contains elements that are not included in the unchanged substrate minerals suggesting that this zone is composed of sputter deposits and or impact vapor deposits originating from the surrounding minerals redeposition rims are composed only of zone i and directly attaches to the unchanged minerals zone iii zone i of composite and composite vesicular rims often contains nanophase fe mg s the composite rims and the composite vesicular rims have a two layered structure a combination of zone i and zone ii below which zone iii exists zone ii is the partially amorphized zone zone ii of ferromagnesian silicates contains abundant nanophase fe radiation induced segregation and in situ reduction are the most plausible mechanisms to form nanophase fe in zone ii their lattice fringes indicate that they contain metallic iron which probably causes the reddening of the reflectance spectra of itokawa zone ii of the composite vesicular rims contains vesicles the vesicles in zone ii were probably formed by segregation of solar wind he implanted in this zone the textures strongly suggest that solar wind irradiation damage and implantation are the major causes of surface modification and space weathering on itokawa

propagation of tropospheric gravity waves into the upper atmosphere of mars we study the propagation of gravity waves in the martian atmosphere using a linearized one dimensional full wave model calculations are carried out for atmospheric parameters characteristic of mars orbiter laser altimeter on mars global surveyor mgs observations of apparent gravity waves in high latitude clouds and mgs radio occultation measurements of temperature variations with height suggestive of gravity wave activity waves that reach the thermosphere produce fluctuations in density comparable in amplitude with the density variations detected in mars odyssey aerobraking data gravity waves of modest amplitude are found to deposit momentum and generate significant heating and cooling in the martian atmosphere the largest heating and cooling effects occur in the thermosphere at altitudes between about 130 and 150 km with heating occurring at the lower altitudes and cooling taking place above

seismic investigation of the transition from continental to oceanic subduction along the western hellenic subduction zone 1 the western hellenic subduction zone whsz exhibits well documented along strike variations in lithosphere density i e oceanic versus continental subduction rates and overriding plate extension differences in slab density are believed to drive deformation rates along the whsz however this hypothesis has been difficult to test given the limited seismic constraints on the structure of the whsz particularly beneath northern greece here we present high resolution seismic images across northern and southern greece to constrain the slab composition and mantle wedge geometry along the whsz data from two temporary arrays deployed across greece in a northern line nl and southern line sl are processed using a 2d teleseismic migration algorithm based on the generalized radon transform images of p and s wave velocity perturbations reveal n60e dipping low velocity layers beneath both nl and sl the 8 km thick layer beneath sl is interpreted as subducted oceanic crust while the 20 km thick layer beneath nl is interpreted as subducted continental crust the thickness of subducted continental crust inferred within the upper mantle suggests that 10 km of continental crust has accreted to the overriding plate the relative position of the two subducted crusts implies 70 85 km of additional slab retreat in the south relative to the north overall our seismic images are consistent with the hypothesis that faster sinking of the denser oceanic portion of the slab relative to the continental portion can explain the different rates of slab retreat and deformation in the overriding plate along the whsz

space weathering trends among carbonaceous asteroids abstract we present visible spectroscopic and albedo data of the 2 3 gyr old themis family and the 15 km and small 15 km themis members suggest these phyllosilicate feature and albedo trends result from regolith variations as a function of diameter observations of the beagle asteroids show a small but notable fraction of members with phyllosilicate features the presence of phyllosilicates and the dynamical association of the main belt comet 133p elst pizarro with the beagle family imply the beagle parent body was a heterogenous mixture of ice and aqueously altered minerals

finite frequency rayleigh wave tomography of the western mediterranean mapping its lithospheric structure 1 we present a 3 d shear wave velocity model for the crust and upper mantle of the western mediterranean from rayleigh wave tomography we analyzed the fundamental mode in the 20 167 s period band 6 0 50 0 mhz from earthquakes recorded by a number of temporary and permanent seismograph arrays using the two plane wave method we obtained phase velocity dispersion curves that were inverted for an isotropic vs model that extends from the southern iberian massif across the gibraltar arc and the atlas mountains to the saharan craton the area of the western mediterranean that we have studied has been the site of complex subduction slab rollback and simultaneous compression and extension during african european convergence since the oligocene the shear velocity model shows high velocities beneath the rif from 65 km depth and beneath the granada basin from 70 km depth that extend beneath the alboran domain to more than 250 km depth which we interpret as a near vertical slab dangling from beneath the western alboran sea the slab appears to be attached to the crust beneath the rif and possibly beneath the granada basin and sierra nevada where low shear velocities 3 8 km s are mapped to 55 km depth the attached slab is pulling down the gibraltar arc crust thickening it and removing the continental margin lithospheric mantle beneath both iberia and morocco as it descends into the deeper mantle thin lithosphere is indicated by very low upper mantle velocities beneath the alboran sea above and east of the dangling slab and beneath the cenozoic volcanics

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

gravity wave drag in three dimensional atmospheric models of mars gravity waves are disturbances whose restoring force is buoyancy in the atmosphere they are made possible by the variation of potential temperature with height they can be excited by various mechanisms including flow over orography the momentum carried by these disturbances can exert significant drag forces on the mean flow in the terrestrial mesosphere one parameterization of this effect the lindzen gravity wave drag scheme is inserted into two simplified general circulation models gcms of the martian atmosphere and its effects are described the influence of large amplitude planetary scale topography on wave breaking altitudes is discussed we show that above 60 km in altitude gravity wave drag dominates the momentum balance of the martian atmosphere on the largest scales this indirectly alters the thermal state of the atmosphere through the thermal wind relation model winds at this level are consistent with other simpler studies as well as with earth based spectroscopic observations below 60 km the effects of planetary wave mean flow interaction as well as heating associated with hadley circulation descent are significant in determining the wind strength eddy diffusion coefficients derived from the lindzen parameterization above 50 km are consistent with values implied from chemical modeling of the martian middle atmosphere as well as with simpler models of gravity wave drag

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

observed spectral properties of near earth objects results for population distribution source regions and space weathering processes abstract we present new visible and near infrared spectroscopic measurements for 252 near earth neo and mars crossing mc objects observed from 1994 through 2002 as a complement to the small main belt asteroid spectroscopic survey smass http smass mit edu combined with previously published smass results we have an internally consistent data set of more than 400 of these objects for investigating trends related to size orbits and dynamical history these data also provide the basis for producing a bias corrected estimate for the total neo population stuart and binzel 2004 icarus 170 295 311 we find 25 of the 26 bus 1999 phd thesis taxonomic types are represented with nearly 90 of the objects falling within the broad s q x and c complexes rare a and e types are more common in the mc than neo population about 5 compared to 3 orbits in terms of possible space weathering effects we see a size dependent transition from ordinary chondrite like q type objects to s type asteroids over the size range of 0 1 to 5 km where the transition is effectively complete at 5 km a match between the average surface age of 5 km asteroids and the rate of space weathering could constrain models for both processes however space weathering may proceed at a very rapid rate compared with collisional timescales in this case the presence or absence of a regolith may be the determining factor for whether or not an object appears space weathered thus 0 1 to 5 km appears to be a critical size range for understanding the processes timescales and conditions under which a regolith conducive to space weathering is generated retained and refreshed

deep electrical resistivity structure of the northern gibraltar arc western mediterranean evidence of lithospheric slab break off terra nova 23 179 186 2011 abstract uncertainties about the lithospheric structure of the gibraltar arc have led to the proposal of several contradictory models to explain its geodynamic setting herein we present a novel 3 d model of the lithospheric electrical resistivity distribution beneath the whole betic cordillera obtained by inverting both broad band and long period magnetotelluric data the lithosphere asthenosphere boundary under sw iberia is shown to be deeper than under the alboran basin in addition the sensitivity tests confirm the presence of a n s oriented low resistivity anomaly at lithospheric mantle depths east of the 4 w meridian it coincides with an area of low velocities without earthquake hypocenters and is interpreted as asthenospheric material intruded by the lateral lithospheric tearing and breaking off of the e directed subducting ligurian slab under the alboran domain this scenario suggests that the opening of the alboran basin is related to the westward rollback of this e directed subducting slab

spectral properties of near earth asteroids evidence for sources of ordinary chondrite meteorites although ordinary chondrite oc meteorites dominate observed falls the identification of near earth and main belt asteroid sources has remained elusive telescopic measurements of 35 near earth asteroids 3 kilometers in diameter revealed six that have visible wavelength spectra similar to laboratory spectra of oc meteorites near earth asteroids were found to have spectral properties that span the range between the previously separated domains of oc meteorites and the most common s class asteroids suggesting a link this range of spectral properties could arise through a diversity of mineralogies and regolith particle sizes as well as through a time dependent surface weathering process

the taxonomic distribution of asteroids from multi filter all sky photometric surveys abstract the distribution of asteroids across the main belt has been studied for decades to understand the current compositional distribution and what that tells us about the formation and evolution of our solar system all sky surveys now provide orders of magnitude more data than targeted surveys we present a method to bias correct the asteroid population observed in the sloan digital sky survey sdss according to size distance and albedo we taxonomically classify this dataset consistent with the bus and binzel bus s j binzel r p 2002 icarus 158 146 177 and bus demeo et al demeo f e binzel r p slivan s m bus s j 2009 icarus 202 july 160 180 systems and present the resulting taxonomic distribution the dataset includes asteroids as small as 5 km a factor of three in diameter smaller than in previous work such as by mothe diniz et al mothe diniz t carvano j m a lazzaro d 2003 icarus 162 march 10 21 because of the wide range of sizes in our sample we present the distribution by number surface area volume and mass whereas previous work was exclusively by number while the distribution by number is a useful quantity and has been used for decades these additional quantities provide new insights into the distribution of total material we find evidence for d types in the inner main belt where they are unexpected according to dynamical models of implantation of bodies from the outer solar system into the inner solar system during planetary migration levison h f bottke w f gounelle m morbidelli a nesvorn d tsiganis k 2009 nature 460 july 364 366 we find no evidence of s types or other unexpected classes among trojans and hildas albeit a bias favoring such a detection finally we estimate for the first time the total amount of material of each class in the inner solar system the main belt s most massive classes are c b p v and s in decreasing order excluding the four most massive asteroids 1 ceres 2 pallas 4 vesta and 10 hygiea that heavily skew the values primitive material c p types account for more than half main belt and trojan asteroids by mass most of the remaining mass being in the s types all the other classes are minor contributors to the material between mars and jupiter

slab tears and intermediate depth seismicity 1 active tectonic regions where plate boundaries transition from subduction to strike slip can take several forms such as triple junctions acute and obtuse corners well documented slab tears that are associated with high rates of intermediate depth seismicity are considered here gibraltar arc the southern and northern ends of the lesser antilles arc and the northern end of tonga trench seismicity at each of these locations occurs at times in the form of swarms or clusters and various authors have proposed that each marks an active locus of tear propagation the swarms and clusters start at the top of the slab below the asthenospheric wedge and extend 30 60 km vertically downward within the slab we propose that these swarms and clusters are generated by fluid related embrittlement of mantle rocks focal mechanisms of these swarms generally fit the shear motion that is thought to be associated with the tearing process

abnormal seismological and magmatic processes controlled by the tearing south american flat slabs abstract the influence of flat slab subduction on the formation of intra slab earthquakes volcanic activities and mantle seismic velocity anomalies remains unclear we attempt to better understand these processes by simulating the two flat slabs in peru and chile using data orientated geodynamic models our results successfully reproduce the observed flat slabs as mainly due to two subducting aseismic ridges in contrast to the traditional view of flat slab subduction we find that these slabs are internally torn as is due to the 3d nature of the subducting buoyancy features this broken slab configuration confirmed by regional tomography naturally explains the abnormal distribution of and stress regimes associated with the intermediate depth earthquakes we further show that the slab tearing process could also better explain the formation of adakitic and ore forming magmatism the evolution of the magmatic arc and the enigmatic mantle seismic structures beneath these regions we propose that slab tearing may represent a common result of buoyancy feature subduction and that the resulting mantle processes could affect the long term geodynamic evolution of continents

are subduction zones invading the atlantic evidence from the southwest iberia margin subduction initiation at passive margins plays a central role in the plate tectonics theory however the process by which a passive margin becomes active is not well understood in this paper we use the southwest iberia margin sim in the atlantic ocean to study the process of passive margin reactivation currently there are two tectonic mechanisms operating in the sim migration of the gibraltar arc and africa eurasia convergence based on a new tectonic map we propose that a new subduction zone is forming at the sim as a result of both propagation of compressive stresses from the gibraltar arc and stresses related to the large scale africa eurasia convergence the gibraltar arc and the sim appear to be connected and have the potential to develop into a new eastern atlantic subduction system our work suggests that the formation of new subduction zones in atlantic type oceans may not require the spontaneous foundering of its passive margins instead subduction can be seen as an invasive process that propagates from ocean to ocean

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

space weathering on airless bodies resolving a mystery with lunar samples using new techniques to examine the products of space weathering of lunar soils we demonstrate that nanophase reduced iron npfe0 is produced on the surface of grains by a combination of vapor deposition and irradiation effects the optical properties of soils both measured and modeled are shown to be highly dependent on the cumulative amount of npfe0 which varies with different starting materials and the energetics of different parts of the solar system the measured properties of intermediate albedo asteroids the abundant s type asteroids in particular are shown to directly mimic the effects predicted for small amounts of npfe0 on grains of an ordinary chondrite regolith this measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids

evidence for slab rollback in westernmost mediterranean from improved upper mantle imaging this work is funded by the picasso project nsf grant ear 0808939 the deployment and data processing for spanish stations was funded by consolider ingenio 2010 project topo iberia csd2006 00041 as well as alert es cgl2010 19803 c03 02

global mapping of the degree of space weathering on asteroid 25143 itokawa by hayabusa amica observations we obtained color images of near earth asteroid 25143 itokawa by the hayabusa multiband imaging camera to characterize the regional color properties images were obtained for the whole disk from the gate position gp and home position hp at a spatial resolution of 0 8 3 7 m pixel whole disk spectra are adjusted to the telescopic data obtained by the university of hawaiis 88 inch telescope using the eight color asteroid survey ecas system the disk resolved measurements show large variations in the three visible channels we present a map of an index related to the degree of space weathering which has been newly developed based on laboratory measurements we find large variations in the degree of space weathering on itokawa fresh materials are observed in regions of steep slopes and craters whereas mature materials are ubiquitously distributed this result suggests that pristine ordinary chondrite like materials have been exposed through weathered layers by excavation by also examining close up images obtained during touchdown rehearsal we find that most rocks in itokawas rough terrains are weathered instead of a regolith blanket the surface of this small asteroid is covered with weathered rocks and gravels

identification and tectonic implications of a tear in the south american plate at the southern end of the lesser antilles 1 in the southeast corner of the caribbean westward subduction of atlantic oceanic south america beneath the lesser antilles transitions to east west transform motion between continental south america and the caribbean plate this geometry requires negatively buoyant subducting oceanic south american lithosphere to progressively detach from positively buoyant continental south american lithosphere the most widely accepted model is slab break off with oblique arc continent collision and northwest dipping continental subduction precipitating narrow rifting in the subducting slab in contrast the subduction transform edge propagator step model conceptualizes progressive detachment along a vertical dip slip tear through the lithosphere with stress focused at the edge of the propagating transform boundary we present four types of seismic data to resolve the ongoing lithospheric detachment local seismicity receiver functions wide angle seismic velocity inversion and a regional balanced cross section constrained by petroleum industry data these four data sets image a near vertical tear extending through the entire lithosphere revealing a key mechanism for the structural evolution of venezuela

focal mechanisms for sub crustal earthquakes in the gulf of cadiz from a dense obs deployment 1 an eleven month deployment of 25 ocean bottom seismometers provides an unprecedented opportunity to study low magnitude local earthquakes in the complex transpressive plate boundary setting of the gulf of cadiz known for the 1755 lisbon earthquake and tsunami 36 relocated earthquakes ml 2 2 to 4 8 concentrate at 40 60 km depth near the base of the seismogenic layer in 140 ma old oceanic mantle lithosphere and roughly align along two perpendicular nne ssw and wnw ese striking structures first motion focal mechanisms indicate compressive stress for the cluster close to the northern horseshoe fault termination which trends perpendicular to plate convergence focal mechanisms for the second cluster near the southern termination of the horseshoe fault indicate a strike slip regime providing evidence for present day activity of a dextral shear zone proposed to represent the eurasia africa plate contact we hypothesize that regional tectonics is characterized by slip partitioning

frictional sliding in serpentine at very high pressure abstract using a new four channel system for detecting acoustic emissions in a multianvil apparatus we have assessed the pressure temperature range for such emissions as well as the role of dehydration by deforming samples of extensively serpentinized peridotite we show that in the absence of dehydration and for samples initially faulted at low pressure acoustic emissions occurred well outside the expected pressure temperature field of unassisted brittle failure emissions were also detected during and after dehydration of serpentine microstructures of post run specimens revealed fault slip with offsets up to 500 m regardless of whether or not dehydration took place dehydration appears to effectively stop slip on pre existing faults and create new ones analysis of p wave travel times from the four sensors confirmed that the acoustic emissions originated within the specimen during fault slip these observations suggest that earthquakes can be triggered by slip along an existing fault containing serpentine under significantly higher pressure and temperature conditions than previously thought possible without dehydration

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

thermomechanical modelling of slab detachment abstract slab detachment or breakoff is appreciated as an important geological process as shown by recent tomographic imaging using a 2 d upper mantle model 660 km deep and 2000 km wide we have investigated with a 2 d finite difference and marker in cell numerical technique the multi resolutional character of the thermomechanical phenomena related to this complex geological process our experiments show that this process can be initiated in form of slab necking by a prolonged 8 30 my period of slab weakening due to thermal diffusion 60 c my due to strong positive thermal feedback from shear heating detached slab fragments sink rapidly with a tendency for coherent rotation the influence of temperature and pressure dependent thermal conductivity on the process of thermal weakening of the slab is quite significant this supports the idea that the breakoff process is triggered by thermal diffusion on a time scale linearly dependent on heat conductivity rapid topographic changes and increasing volcanic activities due to the melting of subducted oceanic crust are possible scenarios of this vigorously driven geodynamic process

a narrowly spaced double seismic zone in the subducting nazca plate 1 high precision relocations of intermediate depth earthquakes 80 130 km below the central andes reveal a fine scale double layered wadati benioff zone wbz upper and lower band of seismicity are separated by about 9 km and occur at the top of the oceanic crust and in the uppermost oceanic mantle respectively analysis of focal mechanisms and waveform similarities indicate that fluid processes are causing the events earthquakes in the oceanic crust occur on pre existing normal faults due to hydraulic embrittlement from metamorphic dehydration and on subvertical faults that connect the two layers in a narrow depth range extensional faulting predominates in both layers indicating that slab pull forces are the dominant stress source superseding possible unbending forces in this segment of the nazca plate

intermediate depth earthquake faulting by dehydration embrittlement with negative volume change earthquakes are observed to occur in subduction zones to depths of approximately 680 km even though unassisted brittle failure is inhibited at depths greater than about 50 km owing to the high pressures and temperatures it is thought that such earthquakes particularly those at intermediate depths of 50 300 km may instead be triggered by embrittlement accompanying dehydration of hydrous minerals principally serpentine a problem with failure by serpentine dehydration is that the volume change accompanying dehydration becomes negative at pressures of 2 4 gpa 60 120 km depth above which brittle fracture mechanics predicts that the instability should be quenched here we show that dehydration of antigorite serpentinite under stress results in faults delineated by ultrafine grained solid reaction products formed during dehydration this phenomenon was observed under all conditions tested pressures of 1 6 gpa temperatures of 650 820 degrees c independent of the sign of the volume change of reaction although this result contradicts expectations from fracture mechanics it can be explained by separation of fluid from solid residue before and during faulting a hypothesis supported by our observations these observations confirm that dehydration embrittlement is a viable mechanism for nucleating earthquakes independent of depth as long as there are hydrous minerals breaking down under a differential stress

an extension of the bus asteroid taxonomy into the near infrared the availability of asteroid spectral measurements extending to the near infrared resulting from the development of new telescopic instruments such as spex rayner 2003 provides a new basis for classifying asteroid reflectance spectra we present an asteroid taxonomy classification system based on reflectance spectrum characteristics for 371 asteroids measured over the wavelength range 0 45 to 2 45 microns this system of 24 classes is constructed using principal component analysis following most closely the visible wavelength taxonomy of bus 1999 which itself builds upon the system of tholen 1984 nearly all of the bus taxonomy classes are preserved with one new class sv defined for each class we present boundary definitions spectral descriptions and prototype examples a flow chart method is presented for classifying newly acquired data spanning this wavelength range when data are available only in the near infrared range 0 85 to 2 45 microns classification is also possible in many cases through an alternate flow chart process within our sample several classes remain relatively rare only 6 objects fall into the a class 349 dembowska and 3628 boznemcova reside as the only objects in their respective r and o classes eight q class objects are all near earth asteroids we note 1904 massevitch as an outer main belt v type while 15 other v type objects have inner main belt orbits consistent with an association with vesta

spectral variability on primitive asteroids of the themis and beagle families space weathering effects or parent body heterogeneity themis is an old and statistically robust asteroid family populating the outer main belt and resulting from a catastrophic collision that took place 2 5 1 0 gyr ago within the old themis family a young sub family beagle formed less than 10 myr ago has been identified we present the results of a spectroscopic survey in the visible and near infrared range of 22 themis and 8 beagle families members the themis members investigated exhibit a wide range of spectral behaviors including asteroids with blue neutral and moderately red spectra while the younger beagle family members look spectrally bluer than the themis ones and they have a much smaller spectral slope variability four themis members including 24 themis have absorption bands centered at 0 68 0 73 m indicating the presence of aqueously altered minerals the best meteorite spectral analogues found for both themis and beagle families members are carbonaceous chondrites having experienced different degrees of aqueous alteration prevalently cm2 but also cv3 and ci and some of them are chondrite samples being unusual or heated the presence of aqueous altered materials on the asteroids surfaces and the meteorite matches indicate that the parent body of the themis family experienced mild thermal metamorphism in the past we extended the spectral analysis including the data available in the literature on themis and beagle families members and we looked for correlations between spectral behavior and physical parameters using the albedo and size values derived from the wise data the analysis of this larger sample confirms the spectral diversity within the themis family and that beagle members tend to be bluer and to have an higher albedo the differences between the two families may be partially explained by space weathering processes which act on these primitive surfaces in a similar way than on s type asteroids i e producing reddening and darkening however we see several themis members having albedos and spectral slopes similar to the young beagle members alternative scenarios are proposed including heterogeneity in the parent body having a compositional gradient with depth and or the survival of projectile fragments having a different composition than the parent body

the effect of spatial variations in unresolved topography on gravity wave drag in the martian atmosphere recent three dimensional simulations of the martian atmosphere have shown that gravity wave drag is a large and possibly dominant term in the momentum balance above 50km in previous simulations a constant value was used for the topographic variance on scales smaller than the model grid spatial variations in this quantity are now taken into account and the results described the topographic variance has its highest amplitude in the tharsis and hellas regions correspondingly relatively low breaking levels are found here longitudinal variations in breaking levels and hence accelerations are very large as are zonal asymmetries in zonal wind u these asymmetries are expected to play a role in planetary wave propagation in the martian middle atmosphere momentum balances are found to be dependent on nonlinear coupling terms in the momentum equations due to the high zonal winds and small planetary radius at the equinoxes two regimes exist one is where breaking levels are very low here accelerations and eddy diffusion coefficients resulting from the parameterization of gravity wave breaking in the model are also very low the other regime is where breaking levels are higher and winds are stronger in this region vertical mixing is also very weak these results give further credence to the idea that breaking thermal tides cause the intense vertical diffusion that has been inferred from observations at the martian equinox

seismic evidence for thermal runaway during intermediate depth earthquake rupture 1 intermediate depth earthquakes occur at depths where temperatures and pressures exceed those at which brittle failure is expected there are two leading candidates for the physical mechanism behind these earthquakes dehydration embrittlement and self localizing thermal shear runaway a complete energy budget for a range of earthquake sizes can help constrain whether either of these mechanisms might play a role in intermediate depth earthquake rupture the combination of high stress drop and low radiation efficiency that we observe for mw 4 5 earthquakes in the bucaramanga nest implies a temperature increase of 600 1000 c for a centimeter scale layer during earthquake failure this suggests that substantial shear heating and possibly partial melting occurs during intermediate depth earthquake failure our observations support thermal shear runaway as the mechanism for intermediate depth earthquakes which would help explain differences in their behavior compared to shallow earthquakes

theoretical analysis of shear localization in the lithosphere deformation in the earth is rarely homogeneous and often occurs in narrow regions of concentrated strain referred to as zones of shear localization mylonites found in the continental crust are the manifestation of shear localization white et al 1980 and at the largest scale shear localization is proposed to be crucial for the generation of tectonic plates from a convecting mantle bercovici 1993 1995b bercovici a 1996 1998 bercovici et al 2000 trompert and hansen 1998 tackley 1998 2000a tackley b c d shear localization is apparent in many field of physics including for example metallurgy lemonds and needleman 1986 rock mechanics poirier 1980 jin et al 1998 granular dynamics scott 1996 geminard et al 1999 e g and glaciology yuen and schubert 1979 however basic solid state rheologies such as elasticity visco elasticity viscous flow and even steady state non newtonian viscous flow are insufficient by themselves to generate shear localization this is because in all such rheologies an increase in deformation or rate of deformation results in greater resistance i e stress instead of self weakening and loss of strength shear localization tends to require dynamic feedback mechanisms wherein self weakening is controlled by a macroscopic variable such as temperature or microscopic structure grain size or microcrack density whose evolution and concentration are themselves determined by deformation in this way deformation can induce weakening which subsequently causes deformation to concentrate on the weak zone being most easily deformed causing further weakening and thus more focusing of deformation and so on one of the most fundamental manifestations of such feedback mechanisms arises from the coupling of viscous heating and temperature dependent viscosity wherein the zone of dissipative heating weakens and thus focuses deformation leading to further heating and weakening this mechanism is thought applicable to problems

dynamics of slab detachment 1 we investigate the dynamics of slab detachment around the detachment zone and evaluate the amount of time necessary for slabs to detach the study combines results of two dimensional 2d state of the art thermomechanical numerical simulations and a 1d analytical solution for viscous necking under gravity we show that the dominant deformation mechanism during slab detachment is viscous necking independent of the depth of slab detachment when the slab dip is moderate 35 70 slab detachment is partly affected by localized simple shearing in the colder parts of the slab brittle fracturing breaking plays a minor role during slab detachment our 2d thermomechanical models indicate that the duration of slab detachment quantified from the onset of slab thinning until the actual detachment i e vanishing of slab pull force is relatively short 250 km can occur within a short time interval 1 ma which has implications for geodynamic interpretations using slab detachment as explanation for processes such as melting exhumation or surface uplift the thinning of the slab during detachment observed in 2d simulations agrees well with predictions from a 1d analytical solution indicating that the 1d solution captures the first order features of the detachment process we also evaluate the impact of shear heating on the duration of slab detachment the predictions of a simple semi analytical solution based on dimensionless parameters agree well with our and previously published results

segmented hellenic slab rollback driving aegean deformation and seismicity the ne dipping slab of the hellenic subduction is imaged in unprecedented detail using teleseismic receiver function analysis on a dense 2 d seismic array mapping of slab geometry for over 300 km along strike and down to 100 km depth reveals a segmentation into dipping panels by along dip faults resolved intermediate depth seismicity commonly attributed to dehydration embrittlement is shown to be clustered along these faults large earthquakes occurrence within the upper and lower plate and at the interplate megathrust boundary show a striking correlation with the slab faults suggesting high mechanical coupling between the two plates our results imply that the general slab rollback occurs here in a differential piecewise manner imposing its specific stress and deformation pattern onto the overriding aegean plate

subduction in the southern caribbean images from finite frequency p wave tomography 1 the eastern boundary of the caribbean plate is marked by subduction of the atlantic under the lesser antilles the southeastern plate boundary is characterized by a strike slip margin while different configurations of subduction of the southwest caribbean under south america have been proposed we investigate the slab geometry in the upper mantle using multiple frequency teleseismic p wave tomography waveforms from p and pkpdf phases from 285 mb 5 0 events occurring at epicentral distances from 30 to 90 and greater than 150 were bandpass filtered and cross correlated to obtain up to three sets of delay times for each event the delay times were inverted using approximate first fresnel zone sensitivity kernels our results show the subducting atlantic slab as well as a second slab in the west of the study area that we interpret as a subducting fragment of the caribbean plate both slabs have steep dips where imaged and can be traced to depths greater than 600 km these results are consistent with transition zone boundary topography as determined by receiver function analysis the atlantic slab extends continent ward south of the plate bounding strike slip margin we interpret this extension as continental margin lithospheric mantle that is detaching from beneath south america and subducting along with the oceanic atlantic slab the steep subduction of the caribbean occurs 500 km landward from the trench implying an initial stage of shallow subduction as far to the east as the lake maracaibo merida andes region as has been inferred from intermediate depth seismicity

effects of vertically propagating thermal tides on the mean structure and dynamics of mars lower thermosphere 1 a general circulation model of mars atmosphere is used to elucidate the effects of vertically propagating thermal tides excited near the surface on the zonal mean density temperature and wind structure of mars atmosphere between 90 and 160 km the effects are substantial and amount to order 10 40 10 50 k and 50 160 m s 1 respectively at these altitudes under low dust conditions dust visible optical depth 0 3 these induced changes in the zonal mean structure are dominated by the non migrating tides of particular note are the mean density perturbations which represent an important consideration for modeling of the aerobraking region 100 170 km

solstitial temperature inversions in the martian middle atmosphere observational clues and 2 d modeling abstract the possible existence of stable warming at middle altitudes in the martian atmosphere was first examined by j r barnes j geophys res 95 1401 1990 in one dimensional modeling of the effect of breaking gravity waves on the general circulation this work was motivated by infrared observations of d deming m j mumma f espenak t kostius and d zipoy icarus 66 366 1986 which suggested temperatures far from radiative equilibrium above polar regions at solstice new observational evidence was obtained from heterodyne measurements of the j 2 1 12 co and 13 co transitions made during the 1988 opposition at this date corresponding to southern summer solstice these lines were mapped as a function of the position on the martian disk with the iram 30 m telescope wind velocities near 50 km altitude and vertical thermal profiles were derived from the doppler shift and the line profiles respectively at various locations on mars the northern winter hemisphere profiles indicate the presence of a warm layer in the 40 60 km altitude range with a relative warming of 5 k compared to smoothly decreasing temperature profiles such as those found in the southern hemisphere this may be interpreted in terms of a temperature inversion in the northern middle atmosphere such a phenomenon may be similar to the stable inversion layers observed in the terrestrial mesosphere which are believed to be a response to the gravity wave activity we show that a zonally averaged model of the martian middle atmosphere using the parametrization of gravity waves effects propounded by r s lindzen j geophys res 86 9707 1981 is able to produce both a plausible zonal wind field consistent with the measurements of e lellouch j j goldstein s w bougher g paubert and j rosenqvist astrophys j 383 401 1991 and a thermal field in good agreement with the observations the 2 d modeling further indicates that weak equatorial thermal inversions may occur due to the penetration of the summer hemisphere retrograde jet into the winter hemisphere

generation of intermediate depth earthquakes by self localizing thermal runaway the conditions leading to rock failure during intermediate depth earthquakes in subduction zones are not clear particularly in the absence of free fluid field observations and numerical simulations indicate that thermal weakening due to high temperature shear instabilities may trigger earthquakes under such circumstances intermediate depth 50 300 km earthquakes commonly occur along convergent plate margins but their causes remain unclear in the absence of pore fluid pressures that are sufficiently high to counter the confining pressure in such settings brittle failure is unlikely in such conditions the rocks could fail by the mechanism of progressively self localizing thermal runaway1 whereby ductile deformation in shear zones leads to heating thermal softening and weakening of rock1 2 3 here we test this hypothesis by focusing on fault veins of glassy rock pseudotachylyte formed by fast melting during a seismic event as well as associated ductile shear zones that occur in a precambrian terrane in norway our field observations suggest that the pseudotachylytes as well as shear zones have a single event deformation history and we also document mineralogical evidence for interaction of the rocks with external fluids using fully coupled thermal and viscoelastic models we demonstrate that the simultaneous occurrence of brittle and ductile deformation patterns observed in the field can be explained by self localizing thermal runaway at differential stresses lower than those required for brittle failure our results suggest that by perturbing rock properties weakening by hydration also plays a key role in shear zone formation and seismic failure however thermal runaway enables the rocks to fail in the absence of a free fluid phase

delamination in the betic range deep structure seismicity and gps motion subduction comes to an end when all oceanic lithosphere is consumed and continental or transitional crust with positive buoyancy becomes involved during continental collision the final stage of subduction may be characterized by slab breakoff limited continental subduction and delamination below the fold and thrust belt we report receiver function images constructed from a dense array of seismic broadband stations that reveal the underthrusting of iberia beneath the alboran plate the underthrusted crust is delaminating beneath part of the betic mountain range still connected to the foreland lithosphere on one side and interrupted discontinuously along the other side intermediate deep earthquakes associated with the delamination process do not respond to downdip stresses like subduction earthquakes the gps velocity field and source mechanisms for shallow earthquakes demonstrate ongoing active shortening on top of the hinge of delamination and localized perpendicular extension on top of the edge of delamination introducing independent motion of the overriding crustal block delamination beneath the betic range drives seismicity by inducing fundamental changes in deformation patterns within the collision orogen

active surface deformation and sub lithospheric processes in the western mediterranean constrained by numerical models we present the results of dynamic modeling of the western mediterranean that accounts for observed global positioning system gps surface deformation of the alboran sea and surrounding rif and betic mountains as the result of the combined effects of relative motion of the eurasian and nubian plates low strength in the alboran sea region and sub lithospheric processes occurring beneath the external rif domain assuming that the lithosphere behaves elastically over the short time period of the gps observations an elastic plate model is considered in our study including an area of weak lithosphere factor of 10 centered on the alboran sea and in which lateral boundary conditions consist of the nubia eurasia oblique convergence sub crustal processes are modeled by application of a horizontal traction on a small area patch at the base of the elastic plate our modeling studies demonstrate the need for sub crustal or sub lithospheric southwestward directed forcing to account for observed southwestward motion of the rif and betic domains based on the location orientation and small area of the traction patch we hypothesize that forcing is associated with delamination and rollback of the subducted african continental lithospheric mantle beneath the external rif zone due to the pull of the oceanic part of the western mediterranean slab a dynamic process that may be similar to that where the over riding plate is driven toward the subduction zone during slab rollback

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

new insights from seismic tomography on the complex geodynamic evolution of two adjacent domains gulf of cadiz and alboran sea 1 in this study we present a three dimensional p wave upper mantle tomography model of the southwest iberian margin and alboran sea based on teleseismic arrival times recorded by iberian and moroccan land stations and by a seafloor network deployed for 1 year in the gulf of cadiz area during the european commission integrated observations from near shore sources of tsunamis towards an early warning system ec nearest project the three dimensional model was computed down to 600 km depth the tomographic images exhibit significant velocity contrasts as large as 3 confirming the complex evolution of this plate boundary region prominent high velocity anomalies are found beneath betics alboran sea off shore southwest portugal and north portugal at sublithospheric depths the transition zones between high and low velocity anomalies in southwest and south iberia are associated to the contact of oceanic and continental lithosphere the fast structure below the alboran sea granada area depicts an l shaped body steeply dipping from the uppermost mantle to the transition zone where it becomes less curved this anomaly is consistent with the results of previous tomographic investigations and recent geophysical data such as stress distribution gps measurements of plate motion and anisotropy patterns in the atlantic domain under the horseshoe abyssal plain the main feature is a high velocity zone found at uppermost mantle depths this feature appears laterally separated from the positive anomaly recovered in the alboran domain by the interposition of low velocity zones which characterize the lithosphere beneath the southwest iberian peninsula margin suggesting that there is no continuity between the high velocity anomalies of the two domains west and east of the gibraltar strait

piecewise delamination of moroccan lithosphere from beneath the atlas mountains the elevation of the intracontinental atlas mountains of morocco and surrounding regions requires a mantle component of buoyancy and there is consensus that this buoyancy results from an abnormally thin lithosphere lithospheric delamination under the atlas mountains and thermal erosion caused by upwelling mantle have each been suggested as thinning mechanisms we use seismic tomography to image the upper mantle of morocco our imaging resolves the location and shape of lithospheric cavities and of delaminated lithosphere 400 km beneath the middle atlas we propose discontinuous delamination of an intrinsically unstable atlas lithosphere enabled by the presence of anomalously hot mantle as a mechanism for producing the imaged structures the atlas lithosphere was made unstable by a combination of tectonic shortening and eclogite loading during mesozoic rifting and cenozoic magmatism the presence of hot mantle sourced from regional upwellings in northern africa or the canary islands enhanced the instability of this lithosphere flow around the retreating alboran slab focused upwelling mantle under the middle atlas which we infer to be the site of the most recent delamination the atlas mountains of morocco stand as an example of large scale lithospheric loss in a mildly contractional orogen

slab breakoff insights from 3d thermo mechanical analogue modelling experiments abstract the detachment or breakoff of subducted lithosphere is investigated using scaled three dimensional thermo mechanical analogue experiments in which forces are measured and deformation is monitored using high speed particle imaging velocimetry piv the experiments demonstrate that the convergence rate in a subduction zone determine if and when slab detachment occurs slow subduction experiments with scaled convergence rates 1 cm yr 1 have lower peclet numbers and are characterized by lower tensile strength subducted lithosphere causing detachment to occur when the downward pull force exerted by a relatively short subducted slab is relatively low therefore when continental collision is preceded by slow oceanic subduction the hot and weak subducted lithosphere need not be very long or extremely negatively buoyant to cause detachment under such conditions detachment may occur sooner after the onset of continental subduction than previously predicted in contrast if collision is preceded by rapid subduction 10 cm yr 1 breakoff will be delayed and occur only when the convergence rate has slowed sufficiently to thermally weaken the slab and cause its eventual failure the analogue experiments further confirm that slab detachment occurs diachronously as it propagates along the plate boundary stereoscopic piv reveals a characteristic strain pattern that accompanies the detachment horizontal contraction and subsidence with scaled values up to 1200 m in the trench and forearc area precedes the passage of the detachment and is followed by horizontal extension and uplift up to 900 m high frequency monitoring captures rapid propagation of the detachment along the plate boundary at scaled rates of up to 100 cm yr 1 however this rate is not constant and interaction between the slab and lower mantle or opening of a backarc basin in the upper plate can reduce or stop slab breakoff propagation altogether

high resolution moho topography map beneath iberia and northern morocco from receiver function analysis abstract crustal thickness maps at regional scales are typically compiled using estimations inferred from different geophysical datasets providing a variable coverage of the investigated area consequently spurious effects related to changes in data resolution or artifacts in grid interpolation may affect significant zones of those maps the topoiberia iberarray broad band seismic network covering the iberian peninsula and northern morocco with stations distributed on a regular 60 60 km grid provides a unique opportunity to avoid such technical problems and to obtain a crustal thickness map derived from a same method sampling evenly all the region data from more than 340 stations has been gathered and analyzed using the p to s conversion phases at the moho discontinuity receiver functions the crustal thickness has been inferred applying the classical h stacking technique though in regions of complex crustal structure we have preferred to estimate the thickness directly from the arrival time of the converted phase at some sites the topography of the moho discontinuity is strongly correlated with tectonic processes the investigated area extending from the sahara platform to the bay of biscay has a great geodynamic diversity including north to south crustal imbrication in the pyrenean and cantabrian range a large and relatively undisturbed variscan massif in the center of iberia and areas of complex and still not completely understood geodynamics in the alboran crust domain and the atlas range the crustal thickness map reflects this diversity showing variations reaching 30 km between the thickest and thinnest zones of continental crust the final map has an overall similarity with previous estimations of the crustal thickness using independent data as those coming from more sparse deep seismic sounding profiles but provides further constraints at regional scale

repeating deep earthquakes evidence for fault reactivation at great depth we have identified three groups of deep earthquakes showing nearly identical waveforms in the tonga slab relocation with a cross correlation method shows that each cluster is composed of 10 to 30 earthquakes along a plane 10 to 30 kilometers in length some of the earthquakes are colocated demonstrating repeated rupture of the same fault and one pair of events shows identical rupture complexity suggesting that the temporal and spatial rupture pattern was repeated recurrence intervals show an inverse time distribution indicating a strong temporal control over fault reactivation runaway thermal shear instabilities may explain temporally clustered earthquakes with similar waveforms located along slip zones weakened by shear heating earthquake doublets that occur within a few hours are consistent with events recurring before the thermal energy of the initial rupture can diffuse away

the cm carbonaceous chondrite regolith diepenveen a carbonaceous chondrite was recovered immediately after the fall near the village of diepenveen in the netherlands on october 27 1873 but came to light only in 2012 analysis of sodium and poly aromatic hydrocarbon content suggests little contamination from handling diepenveen is a regolith breccia with an overall petrology consistent with a cm classification unlike most other cm chondrites the bulk oxygen isotopes are extremely 16o rich apparently dominated by the signature of anhydrous minerals distributed on a steep slope pointing to the domain of intrinsic cm water a small subset plots closer to the normal cm regime on a parallel line 2 lower in 17o different lithologies in diepenveen experienced varying levels of aqueous alteration processing being less aqueously altered at places rather than more heated the presence of an agglutinate grain and the properties of methanol soluble organic compounds point to active impact processing of some of the clasts diepenveen belongs to a cm clan with 5 ma cre age longer than most other cm chondrites and has a relatively young k ar resetting age of 1 5 ga as a cm chondrite diepenveen may be representative of samples soon to be returned from the surface of asteroid 162173 ryugu by the hayabusa2 spacecraft

double seismic zone and dehydration embrittlement of the subducting slab 1 dehydration embrittlement of metamorphosed oceanic crust and mantle in the subducting slab may be responsible for the occurrence of intermediate depth earthquakes we explore the possibility that this hypothesis can explain the morphology of the double seismic zones observed in northeast japan southwest japan northeast taiwan northern chile cape mendocino and eastern aleutians we calculate transient temperature structures of slabs based on geologically estimated subduction histories of these regions we then determine dehydration loci of metamorphosed oceanic crust and serpentinized mantle using experimentally derived phase diagrams the depth range of the dehydration loci of metamorphosed oceanic crust and serpentine is dependent on slab age the dehydration loci of serpentine produce a double layered structure because the upper dehydration loci of serpentine are mostly located in the wedge mantle above the slab we regard the upper plane seismicity representing dehydration embrittlement in the oceanic crust and we fix the slab geometry so that the upper plane seismicity is just below the upper surface of the slab we find that the lower plane seismicity is located at the lower dehydration loci of serpentine which indicates that the morphology of the double seismic zones is consistent with the dehydration embrittlement

instability of deformation this chapter addresses the mechanisms by which instabilities can develop in rocks in the nominally ductile regime under conditions that the authors believe are relevant to earth we will not address brittle failure or frictional sliding processes in detail but much of our discussion will be couched in terms of knowledge gained in studies of these processes as a consequence we will begin by discussing why brittle failure and frictional sliding cannot be the mechanism by which rocks become unstable at depth despite the strong evidence that they are the underlying mechanism of earthquakes at shallow depths e g scholz 1990 2002 brittle shear failure in the normal sense is fundamentally a tensile process tensile microcracks must first nucleate and self organize via interaction of the stress concentrations at their tips as a consequence brittle failure and frictional sliding are strongly inhibited by pressure because work must be done against the pressure to open the mode i cracks the inhibition is so strong that the stress required to create a fault or initiate sliding on an existing fault becomes greater than the room temperature flow stress of many rocks at pressures equivalent to only a few tens of kilometers in earth increasing temperature has little effect on brittle processes but in contrast the ductile flow stress of rocks falls exponentially with temperature because both pressure and temperature increase with depth in earth earthquakes by unassisted brittle fracture mechanisms or frictional sliding can only occur at depths less than 30 50 km nevertheless earthquakes occur to depths of almost 700 km in earth and seismological evidence demonstrates unequivocally that they occur by displacement across a surface or narrow zone i e they occur by faulting this conundrum can be explained qualitatively by certain specific types of mineral reactions occurring under certain restricted conditions the

seismic evidence for the presence of jurassic oceanic crust in the central gulf of cadiz sw iberian margin abstract we investigate the crustal structure of the sw iberian margin along a 340 km long refraction and wide angle reflection seismic profile crossing from the central gulf of cadiz to the variscan continental margin in the algarve southern portugal the seismic velocity and crustal geometry model obtained by joint refraction and reflection travel time inversion reveal three distinct crustal domains the 28 30 km thick variscan crust in the north a 60 km wide transition zone offshore where the crust abruptly thins 20 km and finally a 7 km thick and 150 km wide crustal section that appears to be oceanic in nature the oceanic crust is overlain by a 1 3 km thick section of mesozoic to eocene sediments with an additional 3 4 km of low velocity unconsolidated sediments on top belonging to the miocene age gulf of cadiz imbricated wedge the sharp transition between continental and oceanic crust is best explained by an initial rifting setting as a transform margin during the early jurassic that followed the continental break up in the central atlantic the narrow oceanic basin would have formed during an oblique rifting and seafloor spreading episode between iberia and africa that started shortly thereafter bajocian and lasted up to the initiation of oceanic spreading in the north atlantic at the tithonian late jurassic earliest cretaceous the velocity model displays four wide prominent south dipping low velocity anomalies which seem to be related with the presence of crustal scale faults previously identified in the area some of which could well be extensional faults generated during this rifting episode we propose that this oceanic plate segment is the last remnant of an oceanic corridor that once connected the alpine tethys with the atlantic ocean so it is in turn one of the oldest oceanic crustal fragments currently preserved on earth the presence of oceanic crust in the central gulf of cadiz is consistent with geodynamic models suggesting the existence of a narrow westward retreating oceanic slab beneath the gibraltar arc alboran basin system

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

impact of gravity waves on the middle atmosphere of mars a non orographic gravity wave parameterization based on global climate modeling and mcs observations the impact of gravity waves gw on diurnal tides and the global circulation in the middle upper atmosphere of mars is investigated using a general circulation model gcm we have implemented a stochastic parameterization of non orographic gw into the laboratoire de meteorologie dynamique lmd mars gcm lmd mgcm following an innovative approach the source is assumed to be located above typical convective cells urn x wiley jgre media jgre21298 jgre21298 math 0001250 pa and the effect of gw on the circulation and predicted thermal structure above 1 pa urn x wiley jgre media jgre21298 jgre21298 math 000250 km is analyzed we focus on the comparison between model simulations and observations by the mars climate sounder mcs on board mars reconnaissance orbiter during martian year 29 mcs data provide the only systematic measurements of the martian mesosphere up to 80 km to date the primary effect of gw is to damp the thermal tides by reducing the diurnal oscillation of the meridional and zonal winds the gw drag reaches magnitudes of the order of 1 m s sol above 10 urn x wiley jgre media jgre21298 jgre21298 math 0003 pa in the northern hemisphere winter solstice and produces major changes in the zonal wind field from tens to hundreds of m s while the impact on the temperature field is relatively moderate 10 20 k it suggests that gw induced alteration of the meridional flow is the main responsible for the simulated temperature variation the results also show that with the gw scheme included the maximum day night temperature difference due to the diurnal tide is around 10 k and the peak of the tide is shifted toward lower altitudes in better agreement with mcs observations

global and seasonal distribution of gravity wave activity in mars lower atmosphere derived from mgs radio occultation data 1 temperature profiles from mars global surveyor mgs radio occultation measurements reveal vertical wave structures assumed to be atmospheric gravity waves in mars lower atmosphere for each vertical temperature profile derived from a radio occultation measurement wave energy density is calculated and results are locally averaged to derive a global distribution of gravity wave activity global distributions are determined for all values of solar longitude and for solar longitudes corresponding to northern summer and winter to show seasonality and for vertical wavelengths less than 10 km to remove the contribution from thermal tides which dominate in the martian tropics at larger vertical wavelengths the global energy density patterns show significant wave activity over the tropics and the mountainous tharsis region averaged over all seasons and enhanced activity in northern summer compared to winter for the most part the observed data does not correlate well with the orographic forcing schemes used to model gravity waves in general circulation models for mars suggesting that wave sources other than orography play an important role on mars

shear instability in a viscoelastic material as the cause of deep focus earthquakes the mechanism of deep focus earthquakes has been examined by numerical and linear analysis of shear instability in subducting slabs we assume subducting slabs deform such that the spatially averaged strain rate becomes time independent furthermore we assume that rheology depends on temperature in the manner of an activation process using this model we investigate quantitatively the conditions under which shear instability takes place i e the deformation in the material concentrates in a thin layer whose temperature increases explosively until melting occurs first we study instability in a material whose rheological properties are spatially homogeneous shear instability takes place in a homogeneous material when exceeds a certain critical level e c which depends strongly on the stress in the slabs but does not depend on the detail of the creep law the value of the activation energy next we study instability in a material that contains shear zones similar to those often observed by field geologists i e a thin layer made of material with lower vicosity than the surrounding region we find that shear zones trigger shear instability even for the case of provided that g the ratio of characteristic time of thermal diffusion to that of shear heating in shear zones exceeds 1 and that f the ratio of stiffness of elastic deformation in the surrounding region to that of ductile deformation in shear zones becomes lower than 1 applying this condition to subducting slabs with shear zones we find that shear zones trigger shear instability even when the average strain rate is lower than by an order of magnitude from these results and from an estimate of in subducting slabs we conclude that shear instability is a mechanism likely to induce deep focus earthquakes

space weathering of asteroid surfaces abstract visible and near infrared spectra of reflected sunlight from asteroid surfaces exhibit features that hold the promise for identifying surface mineralogy however the very surfaces that are observed by remote sensing are also subject to impingement by micrometeoroids and solar wind particles which are believed to play the dominant role in space weathering which is the time dependent modification of an asteroid s reflectance spectrum such space weathering has confused the interpretations of telescopic spectra of asteroids especially concerning the possible association of common ordinary chondritic meteorites with so called s type asteroids recent spacecraft studies of asteroids especially of eros by near shoemaker have documented aspects of space weathering processes but we still do not understand the physics of space weathering well enough to confidently assay mineralogy of diverse asteroids by remote sensing a review of the intellectual history of this topic reveals the complexity of

space weathering trends on carbonaceous asteroids a possible explanation for bennu s blue slope abstract we compare primitive near earth asteroid spectral properties to the irradiated carbonaceous chondrite samples of lantz et al 2017 in order to assess how space weathering processes might influence taxonomic classification using the same eigenvectors from the asteroid taxonomy by demeo et al 2009 we calculate the principal components for fresh and irradiated meteorites and find that change in spectral slope blueing or reddening causes a corresponding shift in the two first principal components along the same line that the c and x complexes track using a sample of b c x and d type neos with visible and near infrared spectral data we further investigated the correlation between prinicipal components and the spectral curvature for the primitive asteroids we find that space weathering effects are not just slope and albedo but also include spectral curvature we show how through space weathering surfaces having an original c type reflectance can thus turn into a redder p type or a bluer b type and that space weathering can also decrease and disguise the d type population finally we take a look at the case of osiris rex target 101955 bennu and propose an explanation for the blue and possibly red spectra that were previously observed on different locations of its surface parts of bennu s surface could have become blue due to space weathering while fresher areas are redder no clear prediction can be made on hayabusa 2 target 162173 ryugu

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

solar semidiurnal tide in the dusty atmosphere of mars abstract vertical coupling due to the solar semidiurnal tide in mars s atmosphere and effects on zonal mean temperature and wind structures are investigated using a numerical model the model provides self consistent solutions to the coupled zonal mean and tidal equations from the surface to 250 km breaking convective instability of the semidiurnal tide is parameterized using a linear saturation scheme with associated eddy diffusivities thermal forcing in the model gives rise to surface pressure perturbations and middle atmosphere zonal mean winds and temperatures that are consistent with available measurements and general circulation models results presented here primarily focus on globally elevated dust levels during southern hemisphere summer conditions similar to those experienced by the viking 1 and viking 2 landers during the 1977 global dust storms semidiurnal temperature and wind amplitudes maximize in the winter hemisphere and exceed 50 k and 100 m s 1 above 150 km and are typically 10 2

the gibraltar subduction a decade of new geophysical data the gibraltar arc spans a complex portion of the africa eurasia plate boundary marked by slow oblique convergence and intermediate and deep focus seismicity the seemingly contradictory observations of a young extensional marine basin surrounded by an arcuate fold and thrust belt have led to competing geodynamic models delamination and subduction geophysical data acquired in the past decade provide a test for these models and support a narrow east dipping subduction zone seismic refraction studies indicate oceanic crust below the western gulf of cadiz tomography of the upper mantle reveals a steep east dipping high p wave velocity body beneath gibraltar the anisotropic mantle fabric from sks splitting shows arc parallel fast directions consistent with toroidal flow around a narrow westward retreating subducting slab the accompanying wsw advance of the rif betic mountain belt has constructed a thick pile of deformed sediments an accretionary wedge characterized by west vergent thrust anticlines bathymetric swath mapping images an asymmetric embayment at the deformation front where a 2 km high basement ridge has collided subduction has slowed significantly since 5 ma but deformation of recent sediments and abundant mud volcanoes suggest ongoing activity in the accretionary wedge three possible origins for this deformation are discussed gravitational spreading overall nw se convergence between africa and iberia and finally a wsw tectonic push from slow but ongoing roll back subduction in the absence of arc volcanism and shallow dipping thrust type earthquakes evidence in favor of present day subduction can only be indirect and remains the object of debate continued activity of the subduction offers a possible explanation for great m 8 5 earthquakes known to affect the area like the famous 1755 great lisbon earthquake recent gps studies show sw motion of stations in n morocco at velocities of 3 6 mm yr indicating the presence of an independent block a rif betic alboran microplate situated between iberia and africa

continental collision and slab break off a comparison of 3 d numerical models with observations abstract conditions and dynamics of subduction collision and subsequent 3 d slab break off and slab tear propagation are quantified for the first time using fully dynamic numerical models model results indicate that collision after the subduction of old strong subducting oceanic slab leads to slab break off at 20 25 myr after the onset of continental collision and subsequently a slab tear migrates more or less horizontally through the slab with a propagation speed of 100 150 mm yr in contrast young weak oceanic slabs show the first break off already 10 myr after continental collision and can experience tear migration rates up to 800 mm yr slab strength plays a more important role in the timing of slab break off and the speed of a propagating slab tear than negative slab buoyancy does slab break off is viable even for slabs that are supported by the viscosity jump and phase change between the upper and lower mantle the density of the oceanic slab and the subducting continental block is important for the amount of continental subduction and the depth of slab break off a 40 km thick continental crust can be buried to depths greater than 200 km although this maximum depth is significantly less for younger or very weak slabs or thicker continental crust slab break off typically starts at a depth of 300 km mostly independent of mantle rheology but like continental crustal burial can be shallower for young or buoyant plates our 3 d models illustrate how due to the difference in necking in 2 d and 3 d break off has an intrinsic small preference to start as a slab window within the slab s interior rather than as a slab tear at the slab edge however any significant asymmetry in the collision setting e g earlier collision at one end of the subduction zone would override this and leads to slab tearing starting near one edge of the slab these results put important new constraints on the dynamics of the collision and subsequent slab break off for modern collision belts for a proposed timing of the initial arabia eurasia collision at 35 ma break off of the 200 myr old neo tethys slab is unlikely to have occurred before 15 10 ma furthermore our results illustrate that shallow early break off of weak slabs provides a viable explanation for the absence of blueschists and ultra high pressure metamorphism in the precambrian geological record

tectonic denudation and topographic development in the spanish sierra nevada 1 the denudation history of the rapidly uplifting western part of the spanish sierra nevada was assessed using apatite fission track aft ages and 10be analyses of bedrock and fluvial sediments major contrasts in the denudation history are recorded within the 27 km2 rio torrente catchment upland areas are characterized by low relief low slope angles and locally the preservation of shallow marine sediments which have experienced 2 km of denudation since circa 4 ma the minimum denudation rates of 0 4 mm yr 1 derived from aft also contrast with the slow medium term 104 years erosion rates 0 044 0 015 mm yr 1 estimated from 10be measurements at high elevations the local medium long term contrasts in denudation rates within the high sierra nevada indicate that much of the unroofing occurs by tectonic denudation on flat lying detachments in lower elevation parts of the catchment rapid river incision coupled to rock uplift has produced 1 6 km of relief implying that the rivers and adjacent hillslopes close to the edge of the orogen are sensitive to normal fault driven changes in base level however these changes are not transmitted into the low relief slowly eroding upland areas thus the core of the mountain range continues to increase in elevation until the limits of crustal strength are reached and denudation is initiated along planes of structural weakness we propose that this form of tectonic denudation provides an effective limit to relief in young orogens

high resolution teleseismic body wave tomography beneath se romania ii imaging of a slab detachment scenario summary non linear teleseismic bodywave tomography with data of the 1999 calixto field experiment carpathian arc lithosphere x tomography in romania provides high resolution imaging of the upper mantle structure in this paper we present the relative p wave velocity distribution of the lithosphere asthenosphere system smearing from strong crustal velocity anomalies into the upper mantle is successfully suppressed by traveltime corrections with an a priori 3 d regional crustal velocity model see martin et al 2005 herein referenced as paper 1 our high resolution image shows a high velocity body beneath vrancea and the moesian platform with a ne sw orientation between 70 and 200 km depth beneath 200 km a change in the orientation from ne sw to n s can be observed the body reaches a maximum depth of about 350 370 km the velocity perturbation is maximal between 110 and 150 km depth 5 2 5 8 per cent and almost constant for depths beneath 200 km 3 2 3 8 per cent as most authors of previous studies agree on miocene subduction along the arc followed by soft continental collision we interpret the high velocity body as the subducted yet not fully detached slab the ne part of the slab appears to be mechanically coupled to the moesian lithosphere and hosts the intermediate depth seismicity in contrast the aseismic sw part is interpreted as decoupled from the overlying lithosphere and torn off from the underlying lithospheric material beneath 200 km depth low velocity anomalies nw of the slab above 110 km depth are interpreted as a shallow asthenospheric upwelling further low velocity anomalies are in agreement with a lithosphere asthenosphere boundary at 110 150 km depth below the moesian platform and deeper than 200 km under the east european platform eep the tomographic images support models proposing slab rollback during subduction collision followed by slab steepening and lithospheric delamination the different degrees of mechanical coupling of the slab to the overlying lithosphere allow to understand the loci of seismicity as volumes of stress concentration independent on the specifics of data interpretation our high resolution image is a novel contribution to understand the process of ongoing lithospheric detachment associated with strong intermediate depth seismicity in se romania

spectral slope variations for osiris rex target asteroid 101955 bennu possible evidence for a fine grained regolith equatorial ridge ongoing spectroscopic reconnaissance of the osiris rex target asteroid 101955 bennu was performed in july 2011 and may 2012 near infrared spectra taken during these apparitions display slightly more positive redder spectral slopes than most previously reported measurements while observational systematic effects can produce such slope changes and these effects cannot be ruled out we entertain the hypothesis that the measurements are correct under this assumption we present laboratory measurements investigating a plausible explanation that positive spectral slopes indicate a finer grain size for the most directly observed sub earth region on the asteroid in all cases the positive spectral slopes correspond to sub earth latitudes nearest to the equatorial ridge of bennu if confirmed by osiris rex in situ observations one possible physical implication is that if the equatorial ridge is created by regolith migration during episodes of rapid rotation that migration is most strongly dominated by finer grain material alternatively after formation of the ridge by regolith of any size distribution larger sized equatorial material may be more subject to loss due to centrifugal acceleration relative to finer grain material where cohesive forces can preferentially retain the finest fraction rozitis b maclennan e emery j p 2014 nature 512 174 176

slab breakoff a model for syncollisional magmatism and tectonics in the alps slab breakoff is the buoyancy driven detachment of subducted oceanic lithosphere from the light continental lithosphere that follows it during continental collision in a recent paper davies and von blanckenburg 1994 have assessed the physical conditions leading to breakoff by quantitative thermomechanical modeling and have predicted various consequences in the evolution of mountain belts breakoff will lead to heating of the overriding lithospheric mantle by upwelling asthenosphere melting of its enriched layers and thus to bimodal magmatism breakoff will also lead to thermal weakening of the subducted crustal lithosphere thereby allowing buoyant rise of released crustal slices from mantle depths in this paper we present a test of this model in the tertiary evolution of the european alps in the alps both basaltic and granitoid magmatism occur between 42 and 25 ma following the closure of oceanic basins by subduction and continental collision the granitoids are now well established to result from mixing of basalt with assimilated continental crust to identify the tectonically crucial origin of the partial mantle melts we have compiled all published geochemical and isotopic data of numerous mafic dykes occurring throughout the whole alpine arc their trace element and isotopic composition suggests that they have been formed by low degree melting of the mechanically stable lithospheric mantle we see no evidence for melting of asthenospheric mantle it was thus not decompressed to depths shallower than 50 km once initiated rapid lateral migration of slab breakoff will result in a linear trace of magmatism in locally thermal weakened crust this explains why all alpine magmatic rocks intruded almost synchronously along a strike slip fault the periadriatic lineament a compilation of ages from penninic high pressure rocks subducted to depths of up to 100 km shows that subduction took place at circa 55 40 ma followed by uplift at 40 35 ma from the short time interval between their uplift and the onset of magmatism we infer that both processes have been induced by the breakoff the slab breakoff model fulfills its predictions in the case of the alps and therefore supports the assumptions made in the theoretical model on a geological basis we believe that the characteristic association of magmatic activity with the return of high pressure rocks to the surface allows the identification of this process in the earth s mountain belts

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

winter polar warmings and the meridional transport on mars simulated with a general circulation model abstract winter polar warmings in the middle atmosphere of mars occur due to the adiabatic heating associated with the downward branch of the cross equatorial meridional circulation thus they are the manifestation of the global meridional transport rather than of local radiative effects we report on a series of numerical experiments with a recently developed general circulation model of the martian atmosphere to examine the relative roles of the mechanical and thermal forcing in the meridional transport the experiments were focused on answering the question of whether the martian circulation is consistent with the thermally driven nearly inviscid hadley cell as was pointed out by some previous studies or it is forced mainly by zonally asymmetric eddies it is demonstrated that under realistic conditions in the middle atmosphere the meridional transport is maintained primarily by dissipating large scale planetary waves and solar tides this mechanism is similar to the extratropical pump in the middle atmosphere on earth only in the run with artificially weak zonal disturbances was the circulation reminiscent of thermally induced hadley cells in the experiment with an imposed dust storm the modified atmospheric refraction changes the vertical propagation of the eddies as the result the eliassen palm fluxes convergence increases in high winter latitudes of the middle atmosphere the meridional transport gets stronger and the polar temperature rises additional numerical experiments demonstrated that insufficient model resolution increased numerical dissipation and especially neglect of non lte effects for the 15 m co2 band could weaken the meridional transport and the magnitude of polar warmings in gcms

mean and gravity wave structures and variability in the mars upper atmosphere inferred from mars global surveyor and mars odyssey aerobraking densities 1 we have used density measurements obtained during aerobraking ab on mars global surveyor and mars odyssey to examine mean densities and the characteristics and variability of gravity waves gws in the upper atmosphere of mars mean densities exhibit variability with latitude and season and in response to variable forcing and filtering from below these data also reveal significant variability of gws both spatially and temporally in general gw amplitudes increase while apparent horizontal scales remain the same with increasing altitude the dominant spatial scales at the lower ab altitudes are typically 20 200 km and density fluctuations vary from 5 to 50 though even larger values are occasionally observed gw amplitudes also vary significantly with season being generally larger in winter and at middle and high latitudes and apparently reflecting mean source and filtering conditions amplitudes also appear to vary with longitude and time and may provide clues to variability of and interactions with larger scale motions

representing anisotropic subduction zones with isotropic velocity models a characterization of the problem and some steps on a possible path forward despite the widely known fact that mantle flow in and around subduction zones produces the development of considerable seismic anisotropy most p wave tomography efforts still rely on the assumption of isotropy in this study we explore the potential effects of erroneous assumption on tomographic images and explore an alternative approach we conduct a series of synthetic tomography tests based on a geodynamic simulation of subduction and rollback the simulation results provide a self consistent distribution of isotropic thermal anomalies and seismic anisotropy which we use to calculate synthetic delay times for a number of realistic and hypothetical event distributions we find that anisotropy induced artifacts are abundant and significant for teleseismic local and mixed event distributions the occurrence of artifacts is not reduced and indeed can be exacerbated by increasing richness in ray path azimuths and incidence angles the artifacts that we observe are in all cases important enough to significantly impact the interpretation of the images we test an approach based on prescribing the anisotropy field as an a priori constraint and find that even coarse approximations to the true anisotropy field produce useful results using approximate anisotropy fields can result in reduced rms misfit to the travel time delays and reduced abundance and severity of imaging artifacts we propose that the use of anisotropy fields derived from geodynamic modeling and constrained by seismic observables may constitute a viable alternative to isotropic tomography that does not require the inversion for anisotropy parameters in each node of the model

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

wind measurements in mars middle atmosphere iram plateau de bure interferometric co observations the iram plateau de bure interferometer has been used to map the co 1 0 rotational line in mars middle atmosphere absolute winds and thermal profiles were retrieved during the 1999 2001 2003 and 2005 planet s oppositions the observations sampled various seasons l 143 196 262 317 and 322 and different dust situations clear global storm regional storm the absolute winds were derived by measuring directly the doppler lineshifts the main zonal circulation near 50 km is dominated by strong retrograde winds with typical velocities of 70 170 m s strongly varying seasonally latitudinally and longitudinally in particular between morning and evening comparison of the retrieved temperature with a general circulation model indicates that the model often underestimates the temperatures in the middle 20 50 km atmosphere and overestimates them above 50 km

estimates of gravity wave drag on mars indication of a possible lower thermospheric wind reversal spectral gravity wave parameterization suitable for planetary thermospheres applied to wind and temperature from mars climate database reveals enormously strong drag incompatible with the wind distribution it points out to a possible wind reversal in the 110 140 km layer similar to the one in the earth s lower thermosphere

magmatic evolution of the alboran region the role of subduction in forming the western mediterranean and causing the messinian salinity crisis the magmatic evolution of the alboran region westernmost mediterranean contains important clues for improving our understanding of the origin of mediterranean style back arc basins and the desiccation of the mediterranean sea in the messinian we use new laser 40ar 39ar age and geochemical major and trace element and o sr nd pb isotope data from igneous rocks from southern spain the alboran sea and northern morocco to reconstruct the magmatic evolution of the westernmost mediterranean since the eocene lower oligocene dikes near malaga 33 6 0 6 ma and middle to upper miocene volcanic rocks from the alboran sea area 6 57 0 04 to 11 8 0 4 ma can be subdivided into two groups 1 lree depleted relative to n morb primarily tholeiitic series and 2 lree enriched primarily calc alkaline series volcanic rocks both groups are generally enriched in fluid mobile elements e g rb th u k and pb relative to fluid immobile elements e g nb ta lree the lree depleted group has 143nd 144nd 0 5128 0 5130 isotope ratios similar to atlantic morb but higher 87sr 86sr 0 7046 0 7100 in contrast the lree enriched group has less radiogenic nd 0 5121 0 5126 and tend to more radiogenic sr 0 7066 0 7205 isotopic composition pb isotope ratios are surprisingly uniform and have compositions similar to marine sediments analyses of mineral separates show that mafic melts with relatively low 18o 5 6 7 2 had high 87sr 86sr 0 7048 0 7088 7 4 10 6 14 1 and 8 4 40 0 49 3 modeling of the trace elements and sr nd pb o isotopic compositions provides compelling evidence for the contamination of the mantle source with hydrous fluids melts which can be explained through subduction of oceanic lithosphere beneath the alboran basin but not through detachment delamination of lithospheric mantle we present a geodynamic model that reconstructs the late eocene to quaternary evolution of the western mediterranean through westward roll back of subducted tethys oceanic lithosphere slab roll back resulted in a large scale reorganization of the western mediterranean paleogeography causing the closure of marine gateways linking the atlantic ocean to the mediterranean sea isolation of the mediterranean sea led to its desiccation causing the messinian salinity crisis

density variability at scales typical of gravity waves observed in mars thermosphere by the mgs accelerometer 1 examination of the small scale density perturbations in mars thermosphere inferred from mars global surveyor mgs accelerometer data reveals wave like structures consistent with gravity waves the structures are interpreted to be horizontal with dominant wavelengths of 100 300 km observed along the orbital path density perturbations are significantly stronger in winter versus spring summer suggesting that the zonal mean winds play a major role in filtering these waves there is also evidence of possible modulation by the mean winds due to local time differences no correlation is found with the underlying topography a source region on earth for gravity waves in fact density perturbations in the northern hemisphere are observed to be greater than those in the southern hemisphere which has a higher orographic variance over the martian tropics an observed source region for gravity waves density perturbations are again not elevated leaving questions on how gravity waves observed in the lower atmosphere are related to those observed in the thermosphere

dehydration of lawsonite could directly trigger earthquakes in subducting oceanic crust intermediate depth earthquakes in cold subduction zones are observed within the subducting oceanic crust as well as the mantle in contrast intermediate depth earthquakes in hot subduction zones predominantly occur just below the mohorovicic discontinuity these observations have stimulated interest in relationships between blueschist facies metamorphism and seismicity particularly through dehydration reactions involving the mineral lawsonite here we conducted deformation experiments on lawsonite while monitoring acoustic emissions in a griggs type deformation apparatus the temperature was increased above the thermal stability of lawsonite while the sample was deforming to test whether the lawsonite dehydration reaction induces unstable fault slip in contrast to similar tests on antigorite unstable fault slip that is stick slip occurred during dehydration reactions in the lawsonite and acoustic emission signals were continuously observed microstructural observations indicate that strain is highly localized along the fault r1 and b shears and that the fault surface develops slickensides very smooth fault surfaces polished by frictional sliding the unloading slope during the unstable slip follows the stiffness of the apparatus at all experimental conditions regardless of the strain rate and temperature ramping rate a thermomechanical scaling factor for the experiments is within the range estimated for natural subduction zones indicating the potential for unstable frictional sliding within natural lawsonite layers

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

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

global prevalence of double benioff zones double benioff zones provide opportunities for insight into seismogenesis because the underlying mechanism must explain two layers of deep earthquakes and the separation between them we characterize layer separation inside subducting plates with a coordinate rotation to calculate the slab normal distribution of earthquakes benchmark tests on well established examples confirm that layer separation is accurately quantified with global seismicity catalogs alone global analysis reveals double benioff zones in 30 segments including all 16 subduction zones investigated with varying subducting plate ages and stress orientations which implies that they are inherent in subducting plates layer separation increases with age and is more consistent with dehydration of antigorite than chlorite

convective instability in the martian middle atmosphere dry convective instabilities in mars s middle atmosphere are detected and mapped using temperature retrievals from mars climate sounder observations spanning 1 5 martian years the instabilities are moderately frequent in the winter extratropics the frequency and strength of middle atmospheric convective instability in the northern extratropics is significantly higher in my 28 than in my 29 this may have coupled with changes to the northern hemisphere mid latitude and tropical middle atmospheric temperatures and contributed to the development of the 2007 global dust storm we interpret these instabilities to be the result of gravity waves saturating within regions of low stability created by the thermal tides gravity wave saturation in the winter extratropics has been proposed to provide the momentum lacking in general circulation models to produce the strong dynamically maintained temperature maximum at 1 2 pa over the winter pole so these observations could be a partial control on modeling experiments