strain analysis of wrench faults and collision tectonics of the arabian nubian shield a conjugate set of regional scale wrench faults produced by collision of converging plate boundaries about 500 700 m y ago extended across the arabian shield five major wrench fault zones distributed across the precambrian continent were subjected to finite strain analysis all were found to have undergone ductile strains in addition to brittle fault displacements four of the zones together enabled a composite strain profile to be constructed east west across the exposed precambrian continental crust that yielded an estimate of a total sinistral displacement of 280 120 km across the najd fault system the strain fields of all the zones deviated from simple shear strain with systematic heterogeneous variations in extensional strain across the zones finite shortening strains increased in intensity eastwards across the continent and were accompanied by a change in deformation mechanism which indicated that the zones in the east formed at higher crustal levels than the zones in the west the conjugate

facies distribution and textural variation in faro drift contourites velocity fluctuation and drift growth abstract detailed study of seismic profiles piston cores and bottom photographs from the faro drift on the southern margin of portugal has led to a better understanding of drift development and its relationship to bottom current circulation data on the contourite facies characteristics and the surface microphysiography have been published elsewhere here we concentrate on sediment distribution and geometry longitudinal trends in facies types mean grain size sedimentary structures and composition can be interpreted in terms of relative intensity of currents over different parts of the drift these are generally more intense in the marginal channels and at the upstream or eastern end of the drift three different scales of vertical variation of facies can be identified at the large scale 300 500 m of sediment has accumulated over 4 6 ma in a regular vertical succession due to the northward progradation of the drift at the medium scale the upper 20 30 m of sediment shows alternating phases of active lateral progradation and uniform vertical accumulation that may correlate with episodes of more and less current activity related to high and low sea level stands respectively over the past 0 3 ma at the small scale the topmost 2 3 m of sediment deposited in approximately 0 03 ma shows three zones of coarser grained sediments separated by finer grained contourites this sequence can also be interpreted in terms of long term fluctuation in bottom current activity although the signal is clearly complex this kind of analysis of sedimentary drifts can lead to more accurate reconstruction of paleocirculation patterns

significance of some geotechnical properties of continental slope and rise sediments off northeast newfoundland shear strength measurements carried out on the 0 20 cm interval of continental slope and continental rise surficial sediments yielded mean values per station that ranged from 3 7 to 8 9 kpa the factors controlling the bathymetric variation of sediment shear strength appear to be sediment texture which is controlled locally by sediment spillover on the upper slope increased deposition of fines silt and clay sized particles from suspension and greater bioturbation activity on the middle slope and bottom current sediment reworking on the base of slope and upper rise sediments deposited on the downslope side of the present presumed location of the western boundary undercurrent wbu axis have comparatively high shear strength gradients that appear to denote the increased proportion of fine sediment deposition during early to middle holocene time when the wbu axis may have been located further upslope than at present

stability of earthquake moment tensor inversions effect of the double couple constraint abstract we show that spurious large non double couple components can be obtained in inversions for the full deviatoric moment tensor for shallow crustal earthquakes due to inaccurate earth models the traditional best double couple solution does not in general provide an optimal estimate of a double couple mechanism and is only reliable when the non double couple component of the full deviatoric solution is small the inverse problem for the moment tensors of the 1998 antarctic plate and 2000 wharton basin strike slip earthquakes is shown in each case to have two well fitting minima in the misfit function of pure double couple solutions such pairs of solutions are most likely to exist for earthquakes which are close either to vertical strike slip or to dip slip on a fault plane dipping at 45 it is shown theoretically that these pairs of solutions arise from the combination of the pure double couple constraint and the instability of two elements of the moment tensor no significant non double couple component is found for the shallow thrusting 1996 biak indonesia earthquake

toward understanding subtle instrumentation effects associated with weak seismic events in the near field abstract broadband observations of small earthquakes at short epicentral distances reveal a mixture of near field effects and instrumental artifacts we investigated these phenomena at a station equipped with an sts 2 and cmg 40t sensor situated almost above shallow m 3 0 to 3 8 events peak ground acceleration 2 10 1 m sec 2 the horizontal components were systematically accompanied by tiltlike disturbances and the tilt obtained from the sts 2 records exceeded more than 10 times the values predicted by the source model we also observed a so far uncommonly recognized type of disturbance whose shape is the first derivative of the tiltlike disturbance the most likely explanation seems to be clipping of high frequency signal peaks within the sensor system a computational model of a broadband feedback velocimeter as a linear dynamic system with saturation proved this interpretation on a qualitative level generally any asymmetry in the transfer of high frequencies in the feedback velocimeter would produce a long period disturbance of this type users of near fault broadband velocigrams may numerically simulate the disturbances without any knowledge of their physical nature and subtract them from the records the decontaminated records still may have a strange bow shaped form related to the near field ramp and the static displacement of the order of 1 10 5 m in this article the effects studied in this article seem to have a general character for apparently any feedback controlled broadband velocimeter

decorrelation in interferometric radar echoes a radar interferometric technique for topographic mapping of surfaces implemented utilizing a single synthetic aperture radar sar system in a nearly repeating orbit is discussed the authors characterize the various sources contributing to the echo correlation statistics and isolate the term which most closely describes surficial change they then examine the application of this approach to topographic mapping of vegetated surfaces which may be expected to possess varying backscatter over time it is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible the authors present such a map of a forested area in oregon which also includes some nearly unvegetated lava flows such a technique could provide a global digital terrain map

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

asperity break after 12 years the mw6 4 2015 lefkada greece earthquake the mw6 4 earthquake sequence of 2015 in western greece is analyzed using seismic data multiple point source modeling nonlinear slip patch and linear slip inversions reveal a coherent rupture image with directivity toward the southwest and several moment release episodes reflected in the complex aftershock distribution the key feature is that the 2015 earthquake ruptured a strong asperity which was left unbroken in between two large subevents of the mw6 2 lefkada doublet in 2003 this finding and the well analyzed cephalonia earthquake sequence of 2014 provide strong evidence of segmentation of the major dextral cephalonia lefkada transform fault ctf being related to extensional duplex transform zones we propose that the duplexes extend farther to the north and that the ctf runs parallel to the western coast of lefkada and cephalonia islands considerably closer to the inhabited islands than previously thought generally this study demonstrates faulting complexity across short time scales earthquake doublets and long time scales seismic gaps

source mechanism of mining induced seismic events resolution of double couple and non double couple models abstract traditional assumption about a seismic source as a double couple dc can represent a serious limitation for describing mechanisms of mining induced seismic events in mining conditions more general process than a shear slip can occur due to stress concentration on mined out areas we assume both non dc components within the dipole description of the source the moment tensor and a single force we processed five seismic events recorded at driefontein gold mine in south africa to demonstrate that waveform modeling is not successful enough due to poor information about the medium inversion of amplitudes of direct p and s waves is more prospective due to their smaller sensitivity to detail of the medium and possibility to correct them for ray bending and shear wave splitting prior to the inversion moreover we are able to estimate the error of the resulting mechanism due to neglect of ray bending all five events processed display non dc mechanisms which are significant at 95 considering the mismodelling of the rock mass by a homogeneous isotropic medium the source mechanisms are in agreement with the underground mining and geological structures one event has a sub vertical pressure single dipole complemented by an implosion which is the body force equivalent of a collapsing horizontal crack or a burst of a pillar supporting the hangingwall of a mined out area two events have mechanisms close to a pressure single couple all three events are located on pillars two out of these three events can be assigned with a downward single force as an alternative mechanism which matches the amplitude data successfully it is the force equivalent of a mined out area collapse when a rock mass falls from the hangingwall to the footwall the events are however rather strong which would require too large rock mass fallen one of the remaining events is a nearly horizontal tensile single couple corresponding to a vertical tensional fault it could be originated by a break of the hangingwall of a mined out area however the hypocenter of this event is deep into the footwall were there is no mining taking place the last event is mostly dc accompanied by a compensated compressive dipole which may be associated to nearly vertical dip slip along a fault in the hangingwall this event is located on the margin of a wide pillar which supports the interpretation

constraints on burial depth and yield of the 25 may 2009 north korean test from hydrodynamic simulations in a granite medium 1 yield depth of burial dob tradeoff curves tocs based on seismic magnitudes of the 25 may 2009 north korean test depend strongly on the choice of empirical cavity radius rc scaling model ambiguities over rc scaling particularly at large scaled dob sdob translate into unacceptably large systematic errors on yield estimates for this test hydrodynamic calculations involving realistic material response models offer a viable alternative to characterize rc scaling for a range of sdob where limited data from past nuclear tests exist results of such calculations are presented for a granite medium with a material response validated by modeling four phenomenological criteria for past nuclear tests in granite free field velocity energy partitioning into the seismic wavefield velocity attenuation and measured rc these results unambiguously favor the rc scaling model of denny and johnson dj91 and the toc based on that model lower bounds on yield and dob of the north korean test are constrained by predictions of an sdob threshold for free surface damage from 2 d simulations since no such reported damage was observed for this test constrained by the hydrodynamic simulations the dj91 model indicates the minimum yield and dob for the 25 may 2009 north korean test is 5 7 kilotons and 375 m

late glacial to recent stratigraphy paleontology and sedimentary processes newfoundland continental slope and rise micropaleontology pollen sediment and 18o studies point to considerable variation in sedimentary processes and water mass characteristics on the northeast newfoundland slope and rise during late glacial and holocene time allochthonous shelf and upper slope foraminiferal species suggestive of turbidity current activity occur relatively frequently in rise sediments during a postglacial interval dated by extrapolation from a probable 9300 year old ash horizon a single late glacial turbidity current deposit involved a much larger volume of sediment than that noted for the earlier events and it appears to have originated primarily on the middle slope in conjunction with a widespread late glacial interval of fecal pellet deposition this larger event suggests an increased flux of material in the form of suspended particulate matter to the continental margin following the late wisconsinan glacial maximum oceanographic conditions during late glacial time appear to have stimulated the productivity of zoop

down canyon evolution of turbidity currents at a late glacial ice margin halibut canyon offshore southeastern canada abstract submarine canyons are the principal conduit for turbidity currents transporting sediment to the deep sea this study examines the interplay between ice margin conditions and the style of turbidity currents during deglaciation from 19 to 11 ka we investigated 7 cores from halibut canyon located seaward of a small ice stream draining the newfoundland ice dome cores were x radiographed for sedimentary structures sediment provenance was assessed from x ray fluorescence geochemistry and age was determined by ams c 14 dating high resolution seismic profiles and cores show three phases of canyon evolution 1 canyon erosion by plunging hyperpycnal meltwater from shelf edge ice at maximum ice extent 2 during deglaciation active deposition of an inner levee by turbidity currents adjacent to an erosional talweg system recorded in cores from the younger dryas 12 ka to before h1 16 5 ka 3 passive canyon fill during the holocene by the alongslope labrador current with only minor down canyon sediment supply in the active canyon depositional phase turbidity currents were of variable size reaching thicknesses 390 m at 40 km down canyon numbers of sand beds and mean grain size decrease down canyon which is inferred to result from rapid entrainment of ambient seawater on the steep gradient and a downflow thinning of the lower part of the current with fine sand in suspension silt becomes increasingly segregated from muds downcanyon as a result of floc break up and re formation the processes inferred from halibut canyon are representative of other canyons on formerly glaciated margins

the rise collapse and compaction of mt mantap from the 3 september 2017 north korean nuclear test surveillance of clandestine nuclear tests relies on a global seismic network but the potential of spaceborne monitoring has been underexploited we used satellite radar imagery to determine the complete surface displacement field of up to 3 5 meters of divergent horizontal motion with 0 5 meters of subsidence associated with north korea s largest underground nuclear test combining insight from geodetic and seismological remote sensing we found that the aftermath of the initial explosive deformation involved subsidence associated with subsurface collapse and aseismic compaction of the damaged rocks of the test site the explosive yield from the nuclear detonation with best fitting source parameters for 450 meter depth was 191 kilotonnes of tnt equivalent our results demonstrate the capability of spaceborne remote sensing to help characterize large underground nuclear tests

the effects of topography on magma chamber deformation models application to mt etna and radar interferometry we have used a three dimensional elastic finite element model to examine the effects of topography on the surface deformation predicted by models of magma chamber deflation we used the topography of mt etna to control the geometry of our model and compared the finite element results to those predicted by an analytical solution for a pressurized sphere in an elastic half space topography has a significant effect on the predicted surface deformation for both displacement profiles and synthetic interferograms not only are the predicted displacement magnitudes significantly different but also the map view patterns of displacement it is possible to match the predicted displacement magnitudes fairly well by adjusting the elevation of a reference surface however the horizontal pattern of deformation is still significantly different thus inversions based on constant elevation reference surfaces may not properly estimate the horizontal position of a magma chamber we have investigated an approach where the elevation of the reference surface varies for each computation point corresponding to topography for vertical displacements and tilts this method provides a good fit to the finite element results and thus may form the basis for an inversion scheme for radial displacements a constant reference elevation provides a better fit to the numerical results

the 9 september 2016 north korean underground nuclear test we characterize the seismic events that occurred in north korea on 9 september 2016 and south korea on 12 september 2016 the 9 september 2016 event was identified as an explosion and the two 12 september 2016 events were identified as natural earthquakes using the p s p and s wave spectral ratios pg lg pn lg and pn sn as discriminants the explosive event was relocated within the north korean nuclear test site using a relative location method and the 2006 north korea underground nuclear test as the master event and the epicenter was identified at 41 2976 degrees n latitude and 129 0804 degrees e longitude from the regional lg and rayleigh waves the body and surface wave magnitudes for the 9 september 2016 event were calculated as m b lg 4 8 0 2 and m s 4 2 0 1 by adopting an empirical magnitude yield relation for the body wave magnitude and assuming that the explosion was fully coupled and detonated at a normally scaled depth we estimated that the seismic yield was similar to 6 kt and the uncertainty range was between 3 and 11 kt if an overburied depth range between 780 and 1200 m was applied then the yield would be increased to 16 22 kt

deep sea sedimentary processes off newfoundland an overview a combination of long range sidescan sonar airgun seismic reflection and high resolution echo sounder data has allowed an overview of the different sedimentary processes along the southeast canad

review of late proterozoic sutures ophiolitic melanges and tectonics of eastern egypt and north east sudan the distribution structural relations and ages of ophiolites and ophiolitic melanges in the eastern deserts of egypt and north east sudan and their relation to arc and post arc magmatism are used to infer the probable positions of sutures and the directions of obduction and subduction the ages of the successive tectonic stages in the terranes decrease northwards by about 100 ma in the region discussed obduction was north westwards the obducted sheets of ophiolite and ophiolitic melange extending about 500 km north from the onib sol flamed suture may all represent a single back arc basin the direction of subduction is still not clearly proved more geochemical evidence of arc magmatic polarity is needed the late tectonic north westward thrusting the nw se stretching lineation the transpressional north south hamisama shear zone and the nw se sinistral najd faults are all attributed to north westward movement present coordinates of terranes towards the older craton west of the nile the najd faults are interpreted as intracontinental transform faults

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

new signatures of underground nuclear tests revealed by satellite radar interferometry 1 new observations of surface displacement caused by past underground nuclear tests at the nevada test site nts are presented using interferometric synthetic aperture radar insar the insar data reveal both coseismic and postseismic subsidence signals that extend one kilometer or more across regardless of whether or not a surface crater was formed from each test while surface craters and other coseismic surface effects ground cracks etc may be detectable using high resolution optical or other remote sensing techniques these broader more subtle subsidence signals one to several centimeters distributed over an area 1 2 kilometers across are not detectable using other methods barker et al 1998 a time series of interferograms reveal that the postseismic signals develop and persist for months to years after the tests and that different rates and styles of deformation occur depending on the geologic and hydrologic setting and conditions of the local test area

labrador current fluctuation during the last glacial cycle abstract records from cores 2011031 059 and 2011031 062 hereafter 59 and 62 have been used to reconstruct changes in the vigor of the labrador current in northern flemish pass during the last glacial cycle grain size proxies for current speed planktonic foramiferal 18o x ray diffraction analysis for dolomite and calcite and abundance of ice rafted detritus ird have been determined an age model back to marine isotope stage mis 5 is based on recognition of seven heinrich events from total dolomite and calcite correlated to the iodp u1302 3 record and confirmed by o isotope stratigraphy and radiocarbon dates a straight line relationship between mean size of sortable silt ss and percent of sortable silt ss and the lack of relationship between ss and ird 500 m indicate well sorted sediments in cores 59 and 62 which can be used to reconstruct the paleocurrent intensity intensified current vigor occurred in mis 5 3 and 1 so that warmer periods show faster currents probably through the irminger current component of the north atlantic subpolar gyre low values of 18o ss and ss correspond to h events suggesting a slowdown in the labrador current followed by a rapid return to strong circulation in some cases current vigor recovery lagged slightly after the h events heinrich events with larger amounts of meltwater show higher current vigor correlation with deep water current vigor records in the iceland basin show a broad correlation on a multi millennial scale with labrador current variations as our study is on a shallow sediment drift formed by the labrador current one of the surface currents of the north atlantic sub polar gyre it provides new evidence for a tight connection between surface current vigor fluctuation and the vigor of the deep thermohaline circulation

new constraints on red sea rifting from correlations of arabian and nubian neoproterozoic outcrops new constraints on the mechanics of red sea opening were obtained by correlating neoproterozoic outcrops of the arabian and nubian shields along two thirds of the red sea coastlines using a mosaic of 23 landsat thematic mapper scenes 5 105 km together with field geochemical and geochronological data we identified and mapped lithologic units mobile belts and terranes within the arabian and nubian shields features best align if arabia is rotated by 6 7 around a pole at latitude 34 6 n longitude 18 1 e implications of our reconstruction include 1 the amount of continental crust underlying the red sea is small because the restored red sea coasts are typically juxtaposed 2 only a single pole is needed implying that the arabian and nubian shields were rigid plates during red sea rifting 3 coastlines reorient to align with preexisting structures suggesting the rift propagated in part along pre existing zones of weakness 4 large sinistral displacements of up to 350 km along the red sea are not supported 5 the pole is inconsistent with the pliocene pleistocene motion along the dead sea transform pole 32 8 n 22 6 e 0 5 joffe and garfunkel 1987 indicating that more than one phase of motion is required to account for the red sea opening however our pole is similar to that for the total motion along the dead sea transform pole 32 7 n 19 8 e 2 joffe and garfunkel 1987 suggesting that the motion between arabia and nubia was parallel to the total motion along the dead sea transform

the role of fracture zones during early red sea rifting structural analysis using space shuttle radar and landsat imagery the structural pattern of the red sea region an area where continental lithosphere is cut by a young oceanic rift was studied by means of satellite and space shuttle radar imagery the space shuttle mission 2 made two passes over the red sea bracketing a region transitional between the southern red sea where true seafloor spreading started about 5 ma bp and the northern red sea where crust is probably continental though thinned and stretched structures on these passes define bands of shearing in the african and arabian margins parallel to the dead sea fracture zone 000 020 combinations of these data with landsat information reveal four shear bands along the margins of the red sea and one oblique to the gulf of suez we have named the northern three red sea shear zones detected on the sir a data the brothers dead sea fracture zone the zabargad fracture zone and the shagara fracture zone two sets of normal faults were also detected trending 330 340 parallel to the northern red sea coastline and 310 320 parallel to the axial deeps in the red sea a map of the 310 320 faults bordering the red sea resembles a v shaped wedge narrowing to the north near the gulf of suez these faults may have formed as a result of the most recent push of seafloor spreading if this is so then there may be a propagating tectonic wedge moving from south to north which thins the continental crust up to distances of 300 km from the axis of spreading following continental deformation oceanic crust may be emplaced in 9hot points9 along the rift axis these 9punctiform9 oceanic spreading centres should propagate in the same direction as continental rifting during this episode palaeo shear zones probably act as barriers 9locked zones9 to the axial propagation one such case is at the zabargad fracture zone where the oblique impact of the propagating rift against the palaeo shear may have placed the red sea9s western side under compression and uplift while the eastern side may have been subject to oblique extension with the formation of pull apart basins the space shuttle imagery allows integration of some of the northern red sea morphotectonic features with structures on the continent

high precision location and yield of north korea s 2013 nuclear test 1 using north korea s 2009 nuclear test as reference and satellite imagery we show that the location and yield of north korea s 2013 nuclear test can be quickly and accurately determined based on seismic data north korea s 2013 nuclear test site is pinpointed by deriving relative location of north korea s 2009 and 2013 nuclear tests and using the previously determined location of the 2009 nuclear test while its yield is estimated based on the relative amplitude ratios of the lg waves recorded for both events the previously determined lg magnitude of 2009 nuclear test and burial depth inferred from satellite imagery north korea s 2013 test site is determined to be located at 41 17 26 88 n 129 4 34 68 e about 345 m south and 453 m west of its 2009 nuclear test site with a geographic precision of 94 m its yield is estimated to be 12 2 3 8 kt

samarium neodymium data on two late proterozoic ophiolites of saudi arabia and implications for crustal and mantle evolution whole rock and mineral samples from the jabal al wask and jabal ess ophiolites northwestern saudi arabia yield sm nd isochron ages of 743 24 ma and 782 38 ma respectively these formation ages which provide maximum limits for possible obduction ages are in broad but not precise agreement with the previously known geologic history of the arabian shield they indicate that the ophiolitic rocks are roughly coeval with nearby volcanic and plutonic rocks supporting a back arc origin for the two ophiolites we suggest that the jabal al wask and jabal ess ophiolites were parts of the same northeast southwest trending ophiolite belt now offset along the najd fault system initial nd values range from 6 6 to 7 6 indicating derivation from a mantle source that has been lil depleted for at least 2 ga reported nd values from the arabian shield that are lower than this suggest the presence of older reworked continental crust

differential response of zircon u pb isotopic systematics to metamorphism across a lithologic boundary an example from the hope valley shear zone southeastern massachusetts usa a detailed morphological chemical and isotopic study of zircons from a single outcrop of two mineralogically and chemically distinct units of the late precambrian ponaganset gneiss was undertaken to investigate the effects of mylonitization and metamorphism on u pb isotopic systematics late paleozoic amphibolite grade approx 600 c mylonitization of the ponaganset gneiss at this locality is associated with movement along the hope valley shear zone the response of zircon to metamorphism in each gneiss unit is distinct zircons in gray augen gneiss are uncorroded and not overgrown whereas zircons from fluorite bearing pink granitic gneiss are variably corroded and over 50 bear opaque overgrowths the zircon overgrowths are chemically distinct from the primary cores and contain high conentrations of hf u hree and th mylonite derived from the gray gneiss contains only a small population of hf u rich metamorphic zircon but zircons in the pink gneiss derived mylonite are dominated by the hf u rich metamorphic component in terms of their u pb isotopic systematics overgrowth free zircons from both units are markedly discordant gray 10 20 pink 35 but overgrown zircons from the pink gneiss are up to 70 discordant zircons from the mylonites yield younger pb pb and u pb ages than those of the protolith gneisses and isotopic data from each gneiss mylonite pair define a linear array on concordia plots upper intercept ages of the gray gneiss 621 27 ma and the pink gneiss 635 50 ma indicate that the crystallization of both units was coeval and the lower intercept ages gray 270 92 ma pink 285 26 ma fall within the range of other published age estimates for alleghanian metamorphism in southeastern new england e g zartman et al 1988 new growth of zircon suggests that zr was mobile during metamorphism the presence of fluorite in the pink gneiss and a discontinuity in log left f text h text 2 text o mathord left vphantom f text h text 2 text o f text hf right kern nulldelimiterspace f text hf right values obtained from biotite across the pink gneiss gray gneiss contact indicates that dissolution and reprecipitation of zircon may be related to local variations in hf fugacity zircon dissolution reprecipitation in the pink gneiss and the lack of similar features in the contiguous gray gneiss suggests that the degree of isotopic perturbation of zircon during metamorphism is related to bulk chemistry fluid chemistry and or the degree of fluid rock interaction

age and chemical characteristics of some pre pan african rocks in the egyptian shield abstract u pb ages on zircons from several types of sialic rocks together with a variety of geochemical data on one sample of early plutonic activity within the egyptian shield are presented the earliest autochthonous granitic rocks in the egyptian shield are probably quartz diorites tonalites emplaced just prior to the main peak of pan african igneous activity 550 650 ma the studied example has an age of 711 ma 7 ma and is characterized by very low initial sr ratio 87sr 86sr 0 7026 and very low abundances of k2o and related large ion lithophile trace elements ree contents are low less than 20 chondritic abundances abundance patterns show only moderate light rare earth enrichment la yb 4 5 these characteristics are inconsistent with any models requiring fractional fusion of pre existing continental crustal material granitic and arkosic cobbles occur in rare conglomerate beds within volcanoclastic and greywacke sedimentary sequences the cobbles show a wide range in ages 1 1 2 3 ga and have no obvious source within the egyptian shield it is suggested that they are not indicative of any sialic plutons in the egyptian shield which might predate deposition of the enclosing immature sediments more probably they were derived from adjacent continental areas such as the uweinat region to the west and were deposited in an evolving arc ocean basin complex

moment tensor resolvability application to southwest iberia abstract we present a method to assess the uncertainty of earthquake focal mechanisms based on the standard theory of linear inverse problems we compute the uncertainty of the moment tensor m then map it into uncertainties of the strike dip and rake the inputs are source and station locations crustal model frequency band of interest and an estimate of data error the output is a six dimensional 6d error ellipsoid which shows the uncertainty of the individual parameters of m we focus on the double couple dc part of m the method is applicable both with and without waveforms the latter is particularly useful for network design as an example we present maps of dc resolvability for earthquakes in southwest europe computed without waveforms we find that the resolvability depends critically on frequency range and source depth shallow dc sources 10 km are theoretically better resolved than deeper sources 40 km and 60 km the dc resolvability of a 40 km deep event improves considerably when the portuguese network is supplemented by stations in spain and morocco the dc resolvability can be further improved by using a few ocean bottom seismometer obs stations or a dense land network a dense land network is able to resolve m well in spite of the large azimuthal gap which spans 200 the theoretical resolution analysis also explains the success of single station inversions when using a broad frequency range as exemplified by an application using waveforms of a m w 6 earthquake offshore iberia

nonisotropic radiation of the 2013 north korean nuclear explosion on 12 february 2013 north korea conducted an underground nuclear test in the northeastern mountainous part of the country the explosion reached magnitude mb 5 1 being recorded at most of seismic stations around the world and becoming one of the best ever recorded nuclear explosions in history similarly as other nuclear explosions buried in nevada kazakhstan or china the 2013 north korean explosion is characterized by a significant nonisotropic radiation this radiation is manifested by distinct sh and love waves in the wave field and is inconsistent with the model of a spherically symmetric source we show that the love waves are not generated by a tectonic earthquake triggered on a nearby fault structures but produced by asymmetry of the explosive source caused by presence of deviatoric stress in the surrounding rock the retrieved moment tensor of the 2013 explosion is characterized by the isotropic component of 57 5 the double couple component of 17 9 and the compensated linear vector dipole component of 24 7 the p t and n axes of the moment tensor are consistent with the principal axes of the regional tectonic stress in the korean peninsula a comparison of waveforms and particle motions of the 2013 explosion and the previous north korean nuclear explosion buried in 2009 indicates that the 2013 explosion was slightly more nonisotropic

origin of the wadi haimur abu swayel gneiss belt south eastern desert egypt petrological and geochronological constraints abstract the wadi haimur abu swayel gneiss belt is composed of biotite gneiss biotite hornblende gneiss and garnet gneiss amphibole and muscovite compositions indicate that these gneisses belong to low to intermediate pressure metamorphic facies temperature values calculated using the hornblende plagioclase geothermometer are in the range of 495 550 c the retrograde part of the metamorphic evolution for these rocks is documented by the presence of epidote and chloritization of biotite the chlorite geothermometer indicates that chloritization occurred around 260 300 c the sedimentary origin of the gneisses is indicated by the high values of normative quartz and corundum it is suggested that the sedimentary protoliths of the wadi haimur abu swayel gneisses evolved in a back arc basin compression of this basin led to intense deformation metamorphism and granite magmatism k ar ages have been determined on hornblende and biotite the hornblende ages 600 ma and the 585 ma of coexisting biotite from the gneisses are interpreted as cooling ages following the peak of metamorphism these ages are within the range of granitic emplacement in the study region 570 675 ma which indicates that the peak of metamorphism could have been contemporaneous with the granitic magmatism in the wadi haimur abu swayel gneisses

interaction of the western boundary undercurrent with the continental margin off newfoundland sedimentation on the newfoundland rise is strongly influenced by the western boundary undercurrent wbu the upper rise 2600 2800 m is swept by a rapid 8 5 cm sec 1 south flowing core of the wbu which has generated a sandy contourite facies characterized by coarse gravelly sandy sediments current induced bedforms such as scour moats lineations and lee drifts ferro manganese stained gravel clasts a high proportion of broken foraminiferal tests and a diagnostic benthic foraminiferal assemblage the overlying nepheloid layer when compared to adjacent waters is thickest 800 m most sediment laden 80 g 1 1 contains the highest proportion of terrigenous sediment and exhibits the best developed bottom mixed layer 15 m thick comparisons with earlier data from the same area imply the dimensions and sediment load of the nepheloid layer vary with time empirical considerations based on near bottom current meter records from labrador and newfoundland suggest the wbu is capable of transporting bedload with threshold friction velocities u of around 0 87 1 14 cm sec 1 for between 1 and 15 of the time the prevailing transport direction is southwards along the rise but this may be punctuated periodically by brief incursions to the north the erosional regime of the upper rise is bordered by a regime of fine grained deposition typified by muddy contourites both the lower slope and lower rise are mantled by bioturbated muds the former zone having terrigenous mud and the latter biogenic calcareous mud the accompanying nepheloid layer is thin biogenic rich and devoid of an identifiable mixed layer

evidence for control of abyssal agglutinated foraminiferal community structure by substrate disturbance results from the hebble area abstract deep sea agglutinated foraminifera have been quantitatively examined from 28 coretop samples from seven box cores collected in june 1983 at the hebble high energy benthic boundary layer experiment site 40 27 n 62 20 w 4815 4825 m depth and hebble shallow site 40 53 n 63 44 w 4185 m depth on the nova scotian continental rise samples from the relatively tranquil hebble shallow site can be distinguished from the hebble site on the basis of their microfauna a q mode varimax factor analysis of species frequency data delineates three major faunal assemblages 1 1 a faunal assemblage from the hebble site dominated by ammobaculties sp cf a americanus this assemblage exhibits lowest species diversity suggesting a disturbed community and strongly associated with box cores containing fine grained laminated sediments 2 2 an assemblage associated with box cores from the hebble meadow dominated by saccammina tubulata psammosphaera sp cf p fusca a coarsely grained species of psammosphaera and reophax sp 1 3 3 a fauna occurring at the hebble shallow site dominated by hormosinella distans with reophax bacillaris and ammobaculites agglutinans unique to the assemblage this fauna displays a higher ratio of calcareous to agglutinated species significantly higher species diversity lower variability and a greater proportion of hormosinids and species utilizing finer grains than samples from the hebble site which is interpreted as reflecting environmental stability marked heterogeneity exists among agglutinated foraminiferal assemblages within box cores at the hebble meadow within box core faunal variability exceeds between box core variability suggesting that environmental factors influencing the distribution of species are patchy on a scale of approximately 40 cm

u pb zircon geochronology and geological evolution of the halaban al amar region of the eastern arabian shield kingdom of saudi arabia u pb zircon model ages for eleven major units from the halaban al amar region of the eastern arabian shield indicate three stages of evolution 1 plate convergence 2 plate collision and 3 post orogenic intracratonic activity convergence occurred between the western afif and eastern ar rayn plates that were separated by oceanic crust remnants of oceanic crust now comprise the ophiolitic complexes of the urd group the oldest plutonic unit in the study is from one of these complexes and gave an age of 694 8 ma detrital zircons from the sedimentary abt formation of the urd group which is intercalated with the ophiolitic rocks were derived from source rocks with a mean age of 710 ma the abt formation may be an accretionary wedge on the western margin of the ar rayn plate plate convergence was terminated by collision of the afif and ar rayn plates during the al amar orogeny which began about 670 ma during collision the urd group rocks were deformed and in part obducted on to one or both plates synorogenic leucogranitoid rocks were intruded from 670 to 640 ma from about 640 to 630 ma widespread unfoliated dioritic plutons were emplaced in the ar rayn block and represent the end of orogenesis related to collision there is no definitive evidence for a significantly older basement beneath the study region

the late proterozoic ophiolite of sol hamed ne sudan abstract the sol hamed complex a sequence from ultramafics through gabbros thin sheeted dykes to pillow lavas is an ophiolite it was obducted tilted nearly to vertical eroded and covered unconformably by the nafirdeib series this is a volcaniclastic series dated at 712 58 ma the lower part of which includes conglomerates with ophiolitic clasts olistostromes one with large oolitic limestone slabs felsitic and dacitic tuffs turbidites and black shales with andesites above some of the structures in the ophiolite are attributed to sub oceanic deformation deformation after the deposition of the nafirdeib series produced folds and cleavage trending about ne sw and more locally a cleavage trending nw in a shear zone where the ophiolite was thrust northeastwards over the nafirdeib series the ophiolite and the nafirdeib series were intruded by the batholithic granite dated elsewhere at ca 669 ma the ophiolite is thought to occur on a suture with the nafirdeib series representing part of an island arc sequence

deep sea records from the southeast labrador sea ocean circulation changes and ice rafting events during the last 160 000 years 1 results from two deep sea cores from northeast of newfoundland at 1251 and 2527 m water depth respectively indicate that during the time period from 160 000 to 10 000 years bp ice rafting events in the labrador sea were accompanied by rapid variations in deep and surface water circulation twelve ice rafting events occurred each coinciding with high concentrations of detrital carbonate and oxygen isotopic depletion of both surface and bottom waters eleven of these can be correlated with the north atlantic heinrich events h1 h11 the remaining very conspicuous ice rafting event took place early in mis substage 5e at a time when the planktic faunal assemblage suggests marked warming of the sea surface in the shallower core benthic delta 13 c values rise from a minimum during the deglaciation to peak substage 5e values following the last ice rafting event indicating that the ventilation of intermediate depths was renewed after the deglaciation was complete and continued throughout substage 5e the benthic foraminifera suggest that this well ventilated water mass was comparable to the modern labrador sea water lsw the benthic faunas suggest that a relatively warm intermediate water mass entered the se labrador sea during heinrich events generally low benthic delta 13 c values indicate that this water mass was poorly ventilated and rich in inorganic nutrients isotope data and benthic faunal distributions indicate that north atlantic deep water nadw formed in the norwegian greenland sea reached the se labrador sea between the heinrich events

quantitative assessment to the impact of insar ionospheric and tropospheric corrections on source parameter modelling application to the 4th nuclear test north korea

advanced seismic analyses of the source characteristics of the 2006 and 2009 north korean nuclear tests in 2006 and 2009 north korea conducted underground nuclear tests at a remote mountainous site in the northeastern part of the country both events were small leading to uncertainties for location yield estimation and discrimination based on seismic observations the objectives of the studies described in this paper have been to more fully exploit data from the international monitoring system ims network and other unclassified sources e g incorporated research institutions for seismology iris japanese national research institute for earth science and disaster prevention nied to analyze these nuclear tests we have used differential waveform interferometry dwif to refine relative locations for the tests and extended the methodology using observations from regional stations to estimate relative emplacement depths which are consistent with explosion source model predictions for broadband regional p wave spectral ratios topographic data from the test site were analyzed to constrain relative locations and depths needed for containment of the two tests based on normal testing practice network averaged teleseismic p wave spectra were inverted using a model based approach and provide explosion yield estimates in the range 0 6 1 0 kt for the 2006 test and 2 0 4 8 kt for the 2009 test depending on assumed emplacement depth detailed spectral analysis of broadband regional p observations are most consistent with theoretical explosion models with yields of 0 9 and 4 6 kt for the 2006 and 2009 tests respectively with associated source depths of 200 and 550 m consistent with previous studies the surface wave m s magnitudes for the 2006 and 2009 tests provide anomalously large m s yield estimates and problematic m s m b identification characteristics finite difference simulations of long period surface wave signals incorporating tensile prestress consistent with the regional tectonics lead to predicted m s values that agree much better with the observed values

the geology and geochemistry of upper proterozoic granitoids from the red sea hills sudan granitoid plutons are common throughout the late proterozoic basement complex of north east sudan frequently accounting for 60 of the outcrop geological petrological and isotopic studies indicate that two distinct types of granitic plutonism can be recognized an older diorite to granodiorite assemblage was emplaced between c 815 and 724 ma and a younger predominantly alkali feldspar granite assemblage consisting of numerous discrete high level intrusions was emplaced between c 717 and 555 ma these granitoids have a calc alkaline character similar to the volcanic rocks of the basement complex to which they are spatially and temporally related the geochemical and isotopic data suggest a destructive plate margin rather than a within plate palaeotectonic association it is suggested that the granitoids represent an evolutionary trend from early diorite to granodiorite intrusions emplaced above a late proterozoic subduction zone to later post tectonic intrusions emplaced during a late stage of volcanic arc development the magmas of the early granitoids were probably mantle derived while the later post tectonic intrusions may have been derived from magmas produced by partial refusion of the volcanic arc protolith

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

seismic patterns of a muddy contourite fan vema channel south brazilian basin and a sandy distal turbidite deep sea fan cap ferret system bay of biscay a comparison abstract the aim of this paper is to discriminate the depositional facies geometries and mechanisms of deposition of contouritic fans from those of turbidite distal fans with a view to provide better resolution of reservoir prediction two examples are analysed the vema contouritic drift in the south brazilian basin and the cap ferret turbiditic fan in the bay of biscaye the vema contourite fan is a neogene mud rich accumulation 200 400 m thick fed by antarctic bottom water bottom currents and located downstream of the rio grande rise it forms one single mound fan shaped body in between two major channels and where the main part of the deep circulation is funnelled into as a result of the morphological and hydrological background the comourite drift progrades mostly downstream the accumulation was built as several depositional units channel levee systems bounded by widespread discontinuities showing erosional patterns this resulted from episodes of strong and or unstable current activity producing the discontinuities alternating with periods of relatively weak and stable currents and major deposition the pliocene quaternary cap ferret distal deep sea fan is a thick 500 m sand rich turbiditic accumulation fed directly by an uplifting mountain range the accumulation is developed downstream of a main turbiditic feeder channel and the volume of sediment involved is much higher than for the vema contourite fan it shows a complex network of shallow channels and low relief levees which merge downstream into thin sandy sheet like deposits several depositional units are stacked vertically each unit is built by the lateral migration of a channel levee system the stacking pattern of the successive units is prograding towards the basin the presence of major discontinuities cutting throughout a whole accumulation and the fairly irregular geometry of the channel levee deposits absence of any obvious migrating trend appear to be the most distinctive features of a contourite fan on the other hand the lateral migration of the channel level geometries and the presence of erosional surfaces of limited extent and restricted to the channels are the main diagnostic features of a distal turbidite fan otherwise the seismo facies are fairly similar in both sedimentary bodies

a multidisciplinary study of the dprk nuclear tests the democratic people republic of korea announced two underground nuclear tests carried out in their territory respectively on october 9th 2006 and may 25th 2009 the scarce information on the precise location and the size of those explosions has stimulated various kinds of studies mostly based on seismological observations by several national agencies concerned with the nuclear test ban treaty verification we analysed the available seismological data collected through a global high quality network for the two tests after picking up the arrival times at the various stations a standard location program has been applied to the observed data if we use all the available data for each single event due to the different magnitude and different number of available stations the locations appear quite different on the contrary if we use only the common stations they happen to be only few km apart from each other and within their respective error ellipses a more accurate relative location has been carried out by the application of algorithms such as double difference joint hypocenter determination ddjhd and waveform alignment the epicentral distance between the two events obtained by these methods is 2 km with the 2006 event shifted to the ese with respect to that of 2009 we then used a dataset of vhr terrasar x satellite images to detect possible surface effects of the underground tests this is the first ever case where these highly performing sar data have been used to such aim we applied insar processing technique to fully exploit the capabilities of sar data to measure very short displacements over large areas two interferograms have been computed one co event and one post event to remove possible residual topographic signals a clear displacement pattern has been highlighted over a mountainous area within the investigated region measuring a maximum displacement of about 45 mm overall the relief hypothesizing that the 2009 nuclear test had been carried out close to the area where the displacement has been observed through the dinsar technique its relation with the epicenter location obtained through seismological processing has been discussed as a possible alternative hypothesis with respect to the preferred solutions reported by the nuclear explosion database nedb the distance of about 10 km between the two places can be considered acceptable in light of the possible systematic location shifts commonly observed in the seismological practice over a global scale the difference between the m b magnitudes of the two tests could reflect differences in geological conditions of the two test sites even if the yield of the two explosions had been the same

source analysis of the memorial day explosion kimchaek north korea 1 a series of source inversions are performed for the 25 may 2009 memorial day north korean seismic event using intermediate period 10 50 s complete waveform modeling an earthquake source is inconsistent with the data and the best fit full seismic moment tensor is dominantly explosive 60 with a moment magnitude mw of 4 5 a pure explosion solution yields a scalar seismic moment of 1 8 1022 dyne cm mw4 1 and fits the data almost as well as the full solution the difference between the full and explosion solutions is the predicted fit to observed tangential displacement which requires some type of non isotropic non explosive radiation possible causes of the tangential displacement are additional tectonic sources tensile failure at depth and anisotropic wave propagation similar displacements may be hidden in the noise of the 2006 event future analyses of this type could be used to identify and characterize non earthquake events such as explosions and mine collapses

arabian shield ophiolites and late proterozoic microplate accretion fragments of late proterozoic ocean crust and mantle ophiolites occur within six major fault zones that mark sutures between crustal blocks microplates that were accreted between about 630 and 715 ma to form the arabian shield we report new u pb zircon ages for ophiolitic gabbro diorite and plagiogranite that range from 840 to 700 ma and establish these complexes among the oldest proven ophiolites by dating the ophiolitic rocks we are able to monitor the magmatic ages of sea floor spreading events during accretion of the arabian shield comparison of the ophiolitic dates with the ages of the adjacent crustal blocks provides a more complete basis for plate tectonics reconstruction of the shield than has previously been possible our new zircon ages confirm earlier sm nd mineral isochrons for ophiolites of the northwestern arabian shield show that the ophiolites are among the oldest oceanic rocks in each terrane support near or within arc tectonic settings for the ophiolites suggest that the bir umq suture extends north along the nabitah mobile belt into the northern shield and suggest that older 1250 ma continental crustal material is locally present in the dominantly oceanic western shield we suggest that indonesia and alaska provide phanerozoic analogues for stages in the accretion history

radar reveals north korea s nuclear test moved a mountain mount mantap shifted by more than 3 metres but no indication of widespread collapse mount mantap shifted by more than 3 metres but no indication of widespread collapse

decorrelation of l band and c band interferometry over vegetated areas in california temporal decorrelation is one of the main limitations for recovering interseismic deformation along the san andreas fault system using interferometric synthetic aperture radar to assess the improved correlation properties of l band with respect to c band we analyzed l band advanced land observation satellite alos interferograms with a range of temporal and spatial baselines over three vegetated areas in california and compared them with corresponding c band european remote sensing satellite ers interferograms over the highly vegetated northern california forests in the coast range area alos remains remarkably well correlated over a 2 year period whereas an ers interferogram with a similar temporal and spatial baseline lost correlation in central california near parkfield we found a similar pattern in decorrelation behavior which enabled the recovery of a fault creep and a local uplifting signal at l band that was not apparent at c band in the imperial valley in southern california both alos and ers have low correlation over farmlands alos has lower correlation over some sandy surfaces than ers probably due to low signal to noise ratio in general l band interferograms with similar seasonal acquisitions have higher correlation than those with dissimilar season for both l and c band correlation over vegetated areas decreases with time for intervals less than 1 year and then remains relatively constant at longer time intervals the decorrelation time for l band is more than 2 years in the forest in california whereas that for c band is less than 6 months overall these results suggest that l band interferograms will reveal near fault interseismic deformation once sufficient data become available

seismic stratigraphy of late cenozoic sediments in the northern labrador sea a history of bottom circulation and glaciation the seismicstratigraphy of the upper 1 km of sediment in the northern labrador sea has been determined from the examination of about 26 000 line kilometres of seismic profiles four key reflectors a to d have been correlated with deep sea drilling project dsdp and ocean drilling program odp holes and range in age from mid pliocene to approximately mid pleistocene ten seismic facies have been distinguished and are interpreted as resulting from slope progradation turbidite deposition in channels and on the basin floor and widespread contourite deposition tertiary sediments are predominantly hemipelagic or contourite but in the mid pliocene turbidite deposition began in the northeast labrador basin which might reflect either greenland glaciation or lowering of sea level at the same time widespread erosion and buildup of drift deposits indicate that there was an intensification of bottom water circulation probably reflecting high latitude cooling this was followed by a return to less dynamic c

m3 spectral analysis of lunar swirls and the link between optical maturation and surface hydroxyl formation at magnetic anomalies 1 we examined the lunar swirls using data from the moon mineralogy mapper m 3 the improved spectral and spatial resolution of m 3 over previous spectral imaging data facilitates distinction of subtle spectral differences and provides new information about the nature of these enigmatic features we characterized spectral features of the swirls interswirl regions dark lanes and surrounding terrain for each of three focus regions reiner gamma gerasimovich and mare ingenii we used principle component analysis to identify spectrally distinct surfaces at each focus region and characterize the spectral features that distinguish them we compared spectra from small recent impact craters with the mature soils into which they penetrated to examine differences in maturation trends on and off swirl fresh on swirl crater spectra are higher albedo exhibit a wider range in albedos and have well preserved mafic absorption features compared with fresh off swirl craters albedoand mafic absorptions are still evident in undisturbed on swirl surface soils suggesting the maturation process is retarded the spectral continuum is more concave compared with off swirl spectra a result of the limited spectral reddening being mostly constrained to wavelengths less than 1500 nm off swirl spectra show very little reddening or change in continuum shape across the entire m 3 spectral range off swirl spectra are dark have attenuated absorption features and the narrow range in off swirl albedos suggests off swirl regions mature rapidly spectral parameter maps depicting the relative oh surface abundance for each of our three swirl focus regions were created using the depth of the hydroxyl absorption feature at 2 82 mm for each of the studied regions the 2 82 mm absorption feature is significantly weaker on swirl than off swirl indicating the swirls are depleted in oh relative to their surroundings the spectral characteristics of the swirls and adjacent terrains from all three focus regions support the hypothesis that the magnetic anomalies deflect solar wind ions away from the swirls and onto off swirl surfaces nanophase iron npfe 0 is largely responsible for the spectral characteristics we attribute to space weathering and maturation and is created by vaporization deposition by micrometeorite impacts and sputtering reduction by solar wind ions on the swirls the decreased proton flux slows the spectral effects of space weathering relative to nonswirl regions by limiting the npfe 0 production mechanism almost exclusively to micrometeoroid impact vaporization deposition immediately adjacent to the swirls maturation is accelerated by the increased flux of protons deflected from the swirls citation kramer g y et al 2011 m 3 spectral analysis of lunar swirls and the link between optical maturation and surface

moment tensor analysis of very shallow sources an issue for moment tensor mt inversion of shallow seismic sources is that some components of the green s functions have vanishing amplitudes at the free surface which can result in bias in the mt solution the effects of the free surface on the stability of the mt method become important as we continue to investigate and improve the capabilities of regional full mt inversion for source type identification and discrimination it is important to understand free surface effects on discriminating shallow explosive sources for nuclear monitoring purposes it may also be important in natural systems that have very shallow seismicity such as volcanic and geothermal systems we examine the effects of the free surface on the mt via synthetic testing and apply the mt based discrimination method to three quarry blasts from the humming albatross experiment these shallow chemical explosions at 10 m depth and recorded up to several kilometers distance represent rather severe source station geometry in terms of free surface effects we show that the method is capable of recovering a predominantly explosive source mechanism and the combined waveform and first motion method enables the unique discrimination of these events recovering the design yield using seismic moment estimates from mt inversion remains challenging but we can begin to put error bounds on our moment estimates using the network sensitivity solution technique ford et al 2010 online material figures showing synthetic tests for a pure explosion and a composite source at local distances and table of moment tensor components

pan african late precambrian tectonic terrains and the reconstruction of the arabian nubian shield the recognition of precambrian ophiolite suites and their dismembered remnants in association with intraoceanic island arc volcanic and plutonic terrains across much of the arabian nubian shield of eastern egypt sudan ethiopia yemen western saudi arabia and sinai has been used by many authors to support the hypothesis of crustal accretion during late proterozoic time 950 550 ma reassembly of the various fragments provides a mosaic of proterozoic microplates in a regular pattern in which at least five oceanic terrains bounded by the remains of ophiolite belts lie between remobilized continental plates to east and west

lightning development associated with two negative gigantic jets 1 we report observations of two negative polarity gigantic jets sufficiently near very high frequency vhf lightning mapping networks that the associated lightning characteristics and charge transfer could be investigated in both cases the gigantic jet producing flash began as ordinary intracloud lightning with upper level channels attempting to exit the cloud and then produced the upward gigantic jet neither flash had developed channels to ground confirming that the major charge transfer during gigantic jets occurred between the cloud and ionosphere the leader progression of one event was detected at altitudes above 20 km demonstrating the possibility of detecting and tracking the propagation of negative jets above the cloud with vhf techniques citation lu g et al 2011 lightning development associated with two negative gigantic jets geophys res lett 38 l12801

late proterozoic evolution of the northern part of the hamisana zone northeast sudan constraints on pan african accretionary tectonics new structural data from the red sea hills northeast sudan add constraints to accretionary tectonic processes that acted in the arabian nubian shield during the late proterozoic geometric constraints provided by field data are used together with landsat thematic mapper imagery to interpret the regional distribution and structural relations of spectrally and lithologically distinctive rock assemblages in contrast to interpretations reported elsewhere these studies indicate that the hamisana zone a prominent structural feature in the northern red sea hills post dated terrane accretion it is characterized by east west crustal shortening and by steep folds and thrust faults calc alkaline magmatism was contemporaneous with and outlasted main phase deformation thus deformation occurred in an intra arc setting thrust faults were reactivated after east west contraction compromising their usefulness in delineating 9sutures9 or as piercing points across older faults pan african accretionary processes may have been analogous to phanerozoic ophiolite and island arc accretion in the western north american cordillera where penetrative deformation occurred in response to periodic intra plate shortening events rather than an ultimate collision of unrelated crustal fragments such an analogy implies a mechanism for crustal thickening by structural as well as igneous processes during evolution of an accretionary belt in a long lived convergent margin setting consistent with the long standing observation that pan african magmatism became more evolved with time this view emphasizes that an interplay of deformation and magmatism resulted in protracted accretion and crustal thickening in contrast to models where crustal shortening results directly from collision of a volcanic arc microcontinent or other buoyant features

age and tectonic setting of granitoid gneisses in the eastern desert of egypt and south west sinai strongly deformed and locally migmatized gneisses occur at several places in the southern eastern desert of egypt and in sinai and have variously been interpreted as a basement to pan african 900 to 600 ma supracrustal and intrusive assemblages a suite of grabbroic to granitic gneisses was investigated in the hafafit area which constitutes an i type calc alkaline intrusive assemblage whose chemistry suggests emplacement along an active continental margin and whose granitoid members can be correlated with the so called older granites of egypt 207pb 206pb single zircon evaporation from three samples of the hafafit gneisses yielded protolith emplacement ages between 677 9 and 700 12 ma and document granitoid activity over a period of about 23 ma a migmatitic granitic gneiss from wadi bitan south west of ras banas has a zircon age of 704 8 ma and its protolith was apparently generated during the same intrusive event as the granitoids at hafafit single zircons from a dioritic gneiss from wadi feiran in south west sinai suggest emplacement of the protolith at 796 6 ma and this is comparable with ages for granitoids in north east sinai and southern israel none of the above gneisses is derived from remelting of older continental crust but they are interpreted as reflecting subduction related calc alkaline magmatism during early pan african magmatic arc formation

the najd fault system saudi arabia and egypt a late precambrian rift related transform system the najd fault system is a complex set of left lateral strike slip faults and ductile shear zones that strike nw se across the precambrian of arabia and egypt this system was developed during the interval 540 620 ma it is up to 400 km wide with an exposed length of 1100 km inferred buried extensions of the najd give it a total length of 2000 km it is the best exposed and may be the largest pre mesozoic zone of transcurrent faulting on earth previous models for the najd fault system suggest it formed as a result of a major late precambrian continent continent collision this model is not preferred here because 1 the lack of evidence for a pre late precambrian continent to the east of the najd fault system 2 the difference between the orientation of the najd fault system and that predicted by slip line theory 3 the younger age of najd movements compared with that of collisional sutures in the arabian shield and 4 lack of evidence for wide spread crustal uplift that would be expected to accompany collision a new model for the origin of the najd fault system accounts for each of these objections the najd fault system formed in response to a broad zone of nw se directed crustal extension that accompanied juvenile continental crustal formation in northernmost afro arabia this model also accounts for the following observations 1 strands of the najd parallel the direction of extension in the north eastern desert of egypt and sinai 2 the timing of the principal rifting movements ca 575 600 ma overlap with those of the najd ca 560 620 ma 3 in spite of observation 2 the najd fault system is not recognized in northernmost afro arabia instead the najd deformation becomes increasingly ductile and these zones are more commonly intruded by sheared and foliated granites as the principal zone of extension is approached the najd fault system thus represents a set of continental transforms developed in response to a major episode of late precambrian extensional continental crust formation in northernmost afro arabia

a late precambrian 710 ma high volcanicity rift in the southern eastern desert of egypt the late precambrian shadli metavolcanics of se egypt constitute a slightly metamorphosed bimodal sequence that has been previously interpreted as manifesting volcanic activity at an island arc we report the first rb sr geochronologic trace element including ree and nd isotopic data for these rocks two types of basalt are recognized the stratigraphically lower suite having compositions like n morb ferrobasalt while the overlying basalt is similar to slightly fractionated e morb the two basalt types were derived from melting of a strongly depleted source most likely within the upper 60 75 km of the upper mantle the origin of the felsic melts is problematic and these could either have fractionated from a mafic melt or resulted from melting of juvenile crust the mafic and felsic lavas yield a rb sr isochron age of 712 24 ma that probably represents the time of volcanic eruption the trace element characteristics of both mafic and felsic members of the shadli metavolcanics show few of the hallmarks of subduction related melts and we reject the hypothesis that these formed at an island arc instead the field and geochemical data are most consistent with the hypothesis that these rocks originated in a magmatic rift where the eruption of large volumes of lava accompanied large scale lithospheric extension this inference suggests that the tectonic setting of the important 700 715 ma crust forming event in ne africa and arabia needs to be critically reexamined

non double couple earthquakes 1 theory historically most quantitative seismological analyses have been based on the assumption that earth quakes are caused by shear faulting for which the equiv alent force system in an isotropic medium is a pair of force couples with no net torque a double couple or dc observations of increasing quality and coverage however now resolve departures from the dc model for many earthquakes and find some earthquakes especially in volcanic and geothermal areas that have strongly non dc mechanisms understanding non dc earth quakes is important both for studying the process of faulting in detail and for identifying nonshear faulting processes that apparently occur in some earthquakes this paper summarizes the theory of moment tensor expansions of equivalent force systems and analyzes many possible physical non dc earthquake processes contrary to long standing assumption sources within the earth can sometimes have net force and torque components described by first rank and asymmetric sec ond rank moment tensors which must be included in analyses of landslides and some volcanic phenomena non dc processes that lead to conventional symmetric second rank moment tensors include geometrically complex shear faulting tensile faulting shear faulting in an anisotropic medium shear faulting in a heteroge neous region e g near an interface and polymorphic phase transformations undoubtedly many non dc earthquake processes remain to be discovered progress will be facilitated by experimental studies that use wave amplitudes amplitude ratios and complete waveforms in addition to wave polarities and thus avoid arbitrary assumptions such as the absence of volume changes or the temporal similarity of different moment tensor com ponents

whole grain evaporation for 207 pb 206 pb age investigations on single zircons using a double filament thermal ion source a technique has been developed and tested to analyse 207pb 206pb apparent ages by thermal evaporation of radiogenic lead directly from untreated whole zircon grains 0 3 mm the evaporation analyses are performed in the double filament arrangement of a thermal ion mass spectrometer thims the method is a powerful tool to distinguish between different lead components occurring in the same grain because differing activation energies of the competing lead components cause their sequential evaporation from the zircons the evaporation of test samples results in 207pb 206pb apparent ages in good agreement with u pb ages known from literature single zircons from a granite of the marble mountains california yield an age of crystallization of 1 410 30 ma ceylon zircons from heavy mineral bearing gravels yield 560 40 ma as age of crystallization of the pegmatitic gravel sources individuals from a heterogeneous zircon population of a diatexite from the southern schwarzwald sw germany indicate metamorphic zircon formation around 500 ma and the existence of middle proterozoic relics 1 95 0 05 ga

u pb isotopic evidence for the accretion of a continental microplate in the zalm region of the saudi arabian shield the area covered by this work includes three of the main tectonic units of the arabian shield the afif continental terrain the nabitah suture with its associated mobile belt and the asir ensimatic arc terrain the geology of the zalm area is well understood and this geochronologic and isotopic study confirms that the southern afif terrain was a continental microplate in the late proterozoic the study also provides a time frame for the crustal evolution of this part of the shield the kabid formation is the oldest in the region and comprises pelitic arkosic and felsic high grade paragneisses u pb zircon data from a pelitic garnet sillimanite gneiss show that this part of the continental basement in the southern afif terrain may be as old as 1770 ma isotopic nalyses indicate that lead from the kabid gneiss resided in the upper continental crust for a long period before 1770 ma and consequently archaean source rocks may be present within the southern afif terrain pb and rb sr isotopic data in the zalm region reveal a change in the nature of the underlying crust from continental basement in the northeast to less radiogenic marginal arc rocks in the southwest this change is coincident with both aeromagnetic data and a facies change within a pre collision marginal basin miogeosynclinal continental shelf facies of the siham group lie unconformably over the kabid formation and are in the area of continental lead signatures eugeosynclinal deep water sediments and volcanics in association with ultramafic rocks occur in the area of marginal arc signatures u pb zircon age determinations show that this 9andean9 continental margin developed before about 720 ma and emplacement of calc alkaline plutonic rocks continued until about 690 ma during the period 685 640 ma the continental afif microplate collided with the asir terrain as part of the nabitah orogeny at approximately 640 ma ago the najd strike slip faulting commenced with a dextral phase that controlled the emplacement of granitic plutons as well as the development of a series of large pull apart grabens some of these grabens were floored by new oceanic crust and were filled with volcanosedimentary rocks of the bani ghayy group subsequently the najd fault system changed to sinistral strike slip motion at about 620 ma ago

seismic source summary for all u s below surface nuclear explosions a summary of information is presented for all u s nuclear tests detonated below the earth s surface the data include explosion times locations yields and depths of burial as well as geophysical information about working point media and for the underground explosions data about surface collapse subsidence phenomena this summary is intended to furnish available and up to date data useful for studies of seismic and hydroacoustic sources as well as for studies of the seismic and hydroacoustic transmission characteristics of the earth manuscript received 2 july 2001

provenance of sediment in the labrador current a record of hinterland glaciation over the past 125 ka the labrador current flows southward along the continental margin off eastern canada and is the principal source of sediment to the outer continental margin areas where ice sheets did not cross the continental shelf we present multi proxy mineralogical and geochemical records based principally on x ray diffraction and x ray fluorescence for core 2011031 059 from northern flemish cap to determine changes in supply and hence to reconstruct provenance evolution during the last glacial cycle the calcite to dolomite ratios in heinrich layers ranged from 2 to 4 suggesting carbonate layers derived from hudson strait as early as marine isotope stage mis 5a d mineral abundance shows three time dependent predominant sediment sources other than in heinrich layers i baffin bay shelves and adjacent land in mis 5 and 1 with high ca sr kaolinite and feldspars and low clay minerals and calcite dolomite ratios ii labrador in mis 3 with low clays and grey color and iii north east newfoundland shelf in mis 2 and 4 with higher concentrations of clay minerals red sandstones and transition elements these results allow a reconstruction of principal ice streams supplying the north west atlantic over the last full glacial cycle

geochronology of the late precambrian hamisana shear zone red sea hills sudan and egypt the hamisana shear zone hsz is a broad zone of deformation approximately 50 km wide and at least 300 km long making it one of the largest basement structures in ne africa it has been interpreted as a precambrian suture as a zone of strike slip displacement or as a zone of crustal shortening the results of new rb sr and u pb zircon geochronological studies indicate that the northern hsz was thermally active during the pan african event until c 550 mg ago initiation of the structure may have begun 40 110 ma earlier all units have low initial 87 sr 86 sr ratios indicating juvenile derivation the timing of activity in the hsz is 50 150 ma younger than collisional suturing and terrane assembly in the arabian nubian shield but is similar to the 655 540 ma najd fault system of egypt and arabia deformation and metamorphism along the hsz clearly post date terrane accretion and probably are closely related to the najd tectonic cycle the most important deformation of the hsz is unrelated to suturing and at least one late precambrian suture must extend west from arabia into the interior of n africa

north korea s 2017 test and its nontectonic aftershock seismology illuminates physical processes occurring during underground explosions not all yet fully understood the thus far strongest north korean test of 3rd september 2017 was followed by a moderate seismic event ml 4 1 after 8 5 minutes here we provide evidence that this aftershock was a non tectonic event which radiated seismic waves as a buried horizontal closing crack this vigorous crack closure occurring shortly after the blast is studied in the north korea test site for the first time the event can be qualitatively explained as rapid destruction of an explosion generated cracked rock chimney due to cavity collapse although other compaction processes cannot be ruled out

extension of the najd shear system from saudi arabia to the central eastern desert of egypt based on integrated field and landsat observations the najd shear system in saudi arabia extends over 1200 km in a nw se direction and has a width of approximately 300 km a digital color mosaic compiled from seven landsat thematic mapper scenes was used to delineate characteristic structural features of the najd system in the midyan region of saudi arabia and to search for similar features in the egyptian eastern desert the digital mosaic was generated using ratios of landsat thematic mapper bands bands 5 4 3 4 5 1 5 7 that are sensitive to the rock content of fe bearing aluminosilicates spectrally opaque phases and hydroxyl bearing or carbonate minerals respectively the mosaic covers approximately 130 000 km of late proterozoic exposures of the arabian nubian shield and has the eastern desert and the midyan region placed in their approximate pre red sea locations the ajjaj shear zone ajz marks the termination of the najd system against the eastern margin of the red sea in the midyan region the ajz aligns with the central eastern desert based on analysis of pre red sea locations analyses of landsat data and field observations show that the ajjaj shear zone and the central eastern desert exhibit the following features in common 1 outcrops that are generally elongate in a nw se direction as a result of folding with fine scale lithologic heterogeneity at the outcrop scale related to deformation associated with faulting 2 nw trending left lateral faults and ductile shear zones 3 subhorizontal nw trending mineral lineations and variably dipping nw trending foliations with local changes in attitude around large competent e g granitic bodies and 4 lithologic contacts that are generally tectonic in nature and related to faulting these features are less common to the north and south of both the ajjaj shear zone and the central eastern desert results are consistent with the najd shear system extending into the eastern desert and dominating the structural patterns within the central part of the eastern desert

a 1 ma record of sediment flux south of the grand banks used to infer the development of glaciation in southeastern canada abstract a 20 m long piston core from a basement ridge on the continental rise off southeastern canada provides a 0 9 ma record of distal continental margin sedimentation sediment sources are distinguished by sand and clay sized mineralogy and detrital palynomorphs they include detritus eroded from a northern canadian shield and lower paleozoic rocks transported southward through the labrador sea b the grand banks and c the gulf of st lawrence and newfoundland isotopic stratigraphy allows correlation of glacial and interglacial stages with changes in sources and flux rates via different transport processes nepheloid layer ice rafting and distal turbidity currents the glacial history of southeastern canada is interpreted from variation in the flux and type of detrital material and correlation with other data from the continental margin from stages 27 to 15 the grand banks formed a forested coastal plain limited local glaciation may have occurred in stages 18 and 16 tertiary regolith and cretaceous clays were stripped from land areas in stages 14 and 12 culminating in the excavation of the laurentian channel late in stage 12 extensive cold based ice sheets are inferred for glacial stages 10 8 and 6 with less severe glaciation in stages 4 and 2 extent of this local appalachian ice correlates poorly with global ice volumes

shingled quaternary debris flow lenses on the north east newfoundland slope debris flow deposits are the principal component of quaternary continental slope sediments between the north east newfoundland shelf and central orphan basin in seismic profiles these deposits occur as shingled elongate acoustically transparent lenses with their long axes orientated downslope deposits of individual flows form positive mounds on the sea floor subsequent flows were diverted by the pre existing topography into bathymetric lows between older debris flow deposits these deposits show a large variation in the area of sea floor covered by individual flows about 60 1000 km2 average thickness of deposits 9 37 m and volume of sediment displaced 1 27 km3 the ratio of average thickness to a measure of deposit diameter termed the aspect ratio has a threefold variation from 0 0006 to 0 0021 very low depositional slopes and low aspect ratios suggest relatively low viscosities probably due to inmixing of water during downslope transport stratified sediments form three distinct horizons and are locally interbedded with the debris flow deposits these are mainly hemipelagic deposits the slope and rise to the west of the orphan basin are constructional in character the apparent absence of upper slope erosional features and the abundance of debris flow deposits on the slope suggest that the supply of sediment to the continental slope occurred predominantly during times of maximum extent of quaternary glacial ice the ice sheet grounding line during several glacial maxima must have been situated at or near the present shelf break supplying vast amounts of sediment directly to the upper slope oversteepening and subsequent slope failures fed material into deeper water

the role of deep water sedimentary processes in shaping a continental margin the northwest atlantic abstract the tectonic history of a margin dictates its general shape however its geomorphology is generally transformed by deep sea sedimentary processes the objective of this study is to show the influences of turbidity currents contour currents and sediment mass failures on the geomorphology of the deep water northwestern atlantic margin nwam between blake ridge and hudson trough spanning about 32 of latitude and the shelf edge to the abyssal plain this assessment is based on new multibeam echosounder data global bathymetric models and sub surface geophysical information the deep water nwam is divided into four broad geomorphologic classifications based on their bathymetric shape graded above grade stepped and out of grade these shapes were created as a function of the balance between sediment accumulation and removal that in turn were related to sedimentary processes and slope accommodation this descriptive method of classifying continental margins while being non interpretative is more informative than the conventional continental shelf slope and rise classification and better facilitates interpretation concerning dominant sedimentary processes areas of the margin dominated by turbidity currents and slope by pass developed graded slopes if sediments did not by pass the slope due to accommodation then an above grade or stepped slope resulted geostrophic currents created sedimentary bodies of a variety of forms and positions along the nwam detached drifts form linear above grade slopes along their crests from the shelf edge to the deep basin plastered drifts formed stepped slope profiles sediment mass failure has had a variety of consequences on the margin morphology large mass failures created out of grade profiles whereas smaller mass failures tended to remain on the slope and formed above grade profiles at trough mouth fans or nearly graded profiles such as offshore cape fear