hydrodynamic analysis of storm movement effects on runoff hydrographs and loop rating curves of a v shaped watershed 1 the effects of storm movement on rainfall runoff processes through a v shaped watershed are investigated using a dynamic wave model based on shallow water equations the governing equations are solved by a fourth order accurate finite volume method to obtain accurate computational results once the numerical model is verified a series of rainfall runoff events on a v shaped watershed are simulated to investigate the contribution of each term in the depth averaged momentum equation a scale analysis and quantitative assessment are conducted on the basis of the computational results as a result it is found that the speed and the direction of storm movement can play an important role in determining peak discharge and peak arrival time in addition the storm movement can generate loop in the stage discharge relationship curve finally it is revealed that the rating curve depends on the watershed characteristics rather than the rainfall conditions at least in the idealized v shaped watershed

multidecadal variability of potential temperature salinity and transport in the eastern subpolar north atlantic the extended ellett line eel hydrographic section extends from scotland to iceland crossing the rockall trough hatton rockall basin and iceland basin with 61 full depth stations at a horizontal resolution of 10 to 50 km the eel samples the upper limb of the atlantic meridional overturning circulation flowing across the iceland scotland ridge into the nordic seas the rockall trough has been sampled nearly four times per year from 1975 to 1996 and the full section annually since 1996 the eel is an exceptionally long timeseries of deep ocean temperatures and salinities this study extends prior work in the rockall trough and examines for the first time 18 year records in the iceland and hatton rockall basins we quantify errors in the timeseries from two sources observational errors and aliasing the data quality and annual sampling are suitable for observing interannual to decadal variability because the variability exceeds our error estimates the upper waters of all 3 basins are cooler fresher from 1997 to 2001 warmer more saline 2001 to 2006 and cooler fresher from 2006 to 2014 a reference level for geostrophic shear is developed heuristically and by comparison with sea surface altimetry the mean northward transport in the upper waters is 6 7 3 7 sv and there is a 6 1 2 5 sv southward flow below the thermocline although the magnitude of the iceland basin overturning circulation 4 3 1 9 sv is greater than in the rockall trough 3 0 3 7 sv the variability is greater in the rockall trough we discuss the results in the context of our understanding of drivers of variability this article is protected by copyright all rights reserved

changes in antarctic bottom water properties in the western south atlantic in the late 1980s data collected in 1988 1989 as part of the south atlantic ventilation experiment have been combined with the historical database to study the circulation and water mass variability of the abyssal water in the argentine basin a map of potential temperature at 4000 m used as an indication of geostrophic shear defines a south and western intensified crescent shaped abyssal recirculation within this recirculation and its northward extension to the brazil basin antarctic bottom water aabw properties have undergone two modifications during the 1980s 1 the water mass cooled 0 05 c and freshened 0 008 in salinity ratio on surfaces of constant density 2 the densest layer of aabw was altered to less dense water through mixing or advection out of the study area this water mass change does not appear to have affected the flow pattern data collected in 1983 and 1988 to the north in the brazil basin show penetration of the freshwater mass in the deep western boundary current to between 18 s and 10 s indicating very rapid propagation of the anomaly from the argentine basin into the brazil basin as a deep western boundary current it is suggested that open ocean convective events within the weddell sea contributed to the change in aabw documented here

abyssal connections of antarctic bottom water in a southern ocean state estimate antarctic bottom water aabw is formed in a few locations around the antarctic continent each source with distinct temperature and salinity after formation the different aabw varieties cross the southern ocean and flow into the subtropical abyssal basins it is shown here using the analysis of lagrangian trajectories within the southern ocean state estimate sose model that the pathways of the different sources of aabw have to a large extent amalgamated into one pathway by the time it reaches 31 s in the deep subtropical basins the antarctic circumpolar current appears to play an important role in the amalgamation as 70 of the aabw completes at least one circumpolar loop before reaching the subtropical basins this amalgamation of aabw pathways suggests that on decadal to centennial time scales changes to properties and formation rates in any of the aabw source regions will be conveyed to all three subtropical abyssal basins 2013 american geophysical union all rights reserved

effect of the direction of storm movement on planar flow using kinematic wave equations analytical solutions are derived for flow owing to storms moving up and down a plane by comparing the flow owing to a moving storm with that to an equivalent stationary storm the influence of storm direction is investigated the direction of storm movement exercises a significant influence on the peak flow and time to peak flow as well as the shape of the overland flow hydrograph 1998 john wiley sons ltd

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

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

moment tensor inversions of m 3 earthquakes in the geysers geothermal fields california microearthquakes have come into high public awareness due to being induced by the development and exploitation of enhanced and natural geothermal fields hydrofracturing and co2 sequestration sites characterizing and understanding the faulting process of induced earthquakes which is generally achieved through moment tensor inversion could both help in risk prediction and in reservoir development monitoring however this is a challenging task because of their lower signal to noise ratio at frequencies typically used in earthquake source analyses therefore higher resolution velocity models and modeling of seismic waves at higher frequencies are required in this study we examine both the potentials to obtain moment tensor solutions for small earthquakes and the uncertainty of those solutions we utilize a short period seismic network located in the geysers geothermal field in northern california and limit our study to that which would be achieved by industry in a typical reservoir environment we obtain full moment tensor solutions of m 3 earthquakes using waveform modeling and first motion inversions we find that these two data sets give complimentary but yet different solutions some earthquakes correspond possibly to complex processes in which both shear and tensile failures occur simultaneously or sequentially this illuminates the presence of fluids at depth and their role for the generation of these small magnitude earthquakes finally since first motions are routinely obtained for all magnitude earthquakes our approach could be extended to small earthquakes where noise level and complex green s functions prohibit using waveforms in moment tensor inversions

decadal variability in the outflow from the nordic seas to the deep atlantic ocean the global thermohaline circulation is the oceanic overturning mode which is manifested in the north atlantic ocean as northward flowing surface waters which sink in the nordic greenland iceland and norwegian seas and return southwards after overflowing the greenland scotland ridge as deep water this process has been termed the conveyor belt and is believed to keep europe 5 8 c warmer than it would be if the conveyor were to shut down the variability of today s conveyor belt is therefore an important component of climate regulation the nordic seas are the only northern hemisphere source of deep water and a previous study has revealed no long term variability in the outflow of deep water from the nordic seas to the atlantic ocean here i use flows derived from hydrographic data to show that this outflow has approximately doubled and then returned to previous values over the past four decades i present evidence which suggests that this variability is forced by variability in polar air temperature which in turn may be connected to the recently reported arctic warming

north atlantic climate and deep ocean flow speed changes during the last 230 years variations in the near bottom flow speed of iceland scotland overflow water isow are documented in a 230 year long deep sea sediment record from the eastern flank of reykjanes ridge in the subpolar north atlantic at sub decadal time scales for recent decades the isow palaeocurrent reconstructions show similarities with observational hydrographic data furthermore recent isow flow changes fall mostly within the range of its variability of the past 230 years the record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar north atlantic with the north atlantic oscillation nao index with more less vigorous isow flow during negative positive phases of the nao our results suggest that the changes in isow vigor are largely controlled by the transport and characteristics of labrador sea water rather than variations in the overflow itself with implications for the meridional overturning of the atlantic ocean and climate

event discrimination using regional moment tensors with teleseismic p constraints determining whether a seismic event is an earthquake explosion collapse or something more complex can be done using regional 10 s full waveform moment tensors down to low magnitudes m 3 5 the moment tensor results can be improved for sparse station configurations when teleseismic 30 array based short period t 1 s p constraints are added the inclusion of teleseismic p aids in event discrimination because it samples the lower region of the focal sphere a region where intermediate period waveforms recorded at the surface have low sensitivity for shallow event depths the teleseismic p constraint is particularly useful in reducing the trade off between a shallow explosion and a shallow volume compensated linear vector dipole with a vertical axis in compression this trade off can complicate discrimination the teleseismic p constraint is applied to the source type analysis of the announced nuclear test of the democratic people s republic of korea on 25 may 2009 resulting in greater confidence in a dominantly explosive solution

accurate source depths and focal mechanisms of shallow earthquakes in western south america and in the new hebrides island arc synthetic seismograms are matched to long period p waveforms in order to obtain accurate depths of shallow earthquakes with known focal mechanisms accurate depths are obtained for a large sample of moderate sized 6 ms 7 events which produced relatively simple p waveforms and do not require intensive analysis the estimated error in the determination of depth is about 5 km or less for most of the events considered the procedure is applied to two suites of events one in south america 83 events and one in the new hebrides 61 events in these two areas of contrasting styles of subduction the accurate depths provide new information on the bending of descending plates near trenches the seismicity and tectonics of the upper plate and the geometry and structure of the zone of contact between the upper and descending plates depths of suboceanic earthquakes which occurred near the trench and which have either tensional and compressional horizontal stress axes agree well with chapple and forsyth s 1979 preferred model of a bending elastic perfectly plastic plate however an unusually deep event occurred beneath the fiji plateau in an area of young ocean floor supposed to have been formed by sea floor spreading processes only since late miocene time the calculated depth of the event 48 km places it below the lithosphere asthenosphere boundary derived from thermal models vertical cross sections through the shallow parts of the subduction zones show that most of the earthquakes with thrust faulting focal mechanisms can be interpreted to be interplate events located in a thin 10 km thick curved zone of contact dipping arcward or landward from the trench axis however a few events with focal mechanisms similar to the interplate events do not fit on the inferred thin zone of contact these events would be accommodated by an interplate zone 15 km thick in both subduction zones interplate events occur at depths between about 15 and 50 km however the downdip width of the south american interplate zone is 2 to 3 times larger than that in the new hebrides most of the intraplate events near the interplate boundary are located in the descending plate in the upper plate seismicity is more pronounced in the back arc regions of the two subduction zones thus our results support the generality of a relatively aseismic zone in the upper plate located trenchward of the magmatic arc depths of shallow earthquakes in the eastern andes and sub andean regions of south america range between about 9 and 36 km indicating that both the upper and middle crust are seismically active about 75 of the events occurred in the upper 25 km furthermore the focal mechanisms indicate that from ecuador to argentina the crust of the eastern side of the andean cordilleran is in a state of east west compression oriented nearly parallel to the direction of convergence between the nazca and south american plates the depths the orientations of the earthquake nodal planes and the close relationships to quaternary tectonics imply basement involved crustal shortening in much of the eastern andes and sub andean zones of peru and argentina

inversion for parameters of tensile earthquakes the tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane the proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic iso compensated linear vector dipole clvd and double couple dc components in seismic moment tensors the most significant parameters inverted are the ratio at the fault denoted as the parameter and the inclination of the slip vector from the fault the parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes the inclination can be accurately determined from the dc component in the moment tensor because the dc component rapidly decreases with increasing for example the inclination of 20 causes dc being 50 60 only the inversion is applied to earthquakes which occurred in january 1997 in west bohemia czech republic it is shown that some of these earthquakes display tensile faulting the parameter is 0 1 the inclination of the slip from the fault attains values of up to 20 this inclination is a result of tensile traction and reduced shear traction along the fault and high fluid pressure in the region

a quantitative comparison between 1d and 3d source inversion methodologies application to the middle east we present a quantitative comparison between seismic moment tensor mt inversion solutions using 1d and 3d synthetic seismograms at two frequency bands for events in the middle east to assess the effects of 3d models on source studies complex geology associated with the active continental convergent margin leads to a scarcity of reliable available data necessitating a thorough examination of solution stability and robustness to assure an accurate description of sources with well characterized source parameters solutions were calculated for 195 events m w 5 5 using a full waveform mt inversion matching both phase and amplitude seismic data processed at two frequency bands compares short and long period performance for 1d and 3d synthetic seismograms an improvement in fit between data and synthetics is seen using 3d over 1d synthetic seismograms especially for complex body wave propagation and surface wave dispersion at short periods 3d synthetics provide a more robust solution compared with 1d showing a reduction in error of the source mechanism the percentage of double couple components increases with the addition of 3d structure and suggests the percentage of non double couple components is a result of poorly constrained earth structure event solutions contained in the catalog graphic 1 table s1 in the electronic supplement to this paper have an average cross correlation value of 0 87 with good amplitude ratios and are improved i e increased variance reduction yet consistent with longer period solutions from the global centroid moment tensor cmt catalog online material table of 184 event solutions from 3d moment tensor inversion 1 embed inline graphic 1 gif

similarity in catchment response 2 moving rainstorms the influence of storm motion on runoff is explored with a focus on dimensionless hydrologic similarity parameters one and two dimensional physically based runoff models are subjected to moving rainstorms a dimensionless storm speed parameterute lp where u is the storm speed te is the runoff plane kinematic time to equilibrium and lp is the length of the runoff plane is identified as a similarity condition storm motion effects on the peak discharge are greatest when the storm is traversing a one dimensional runoff plane in the downslope direction at a dimensionless speed of ute lp 0 5 this conclusion holds for all values of the dimensionless storm sizes ls lp where ls is the length of the storm in the direction of motion simulations with a two dimensional rainfall runoff model confirm the applicability of this similarity parameter on natural watershed topography results indicate that the detailed simulation of storm motion is necessary when the storm is moving near the velocity of maximum effect which is considerably slower than typical storm velocities

diapiric ascent of silicic magma beneath the bolivian altiplano 1 the vertical transport of large volumes of silicic magma which drives volcanic eruptions and the long term compositional evolution of the continental crust is a highly debated problem in recent years dyking has been favored as the main ascent mechanism but the structural connection between a distributed configuration of melt filled pores in the source region and shallow magma reservoirs remains unsolved in the central andes inversion of a new high resolution bouguer anomaly data over the altiplano puna magma body apmb reveals 15 km wide vertically elongated low density 3d structures rooted at the top of the apmb at 20 km depth we integrate our gravity inversion with the available geophysical geological and petrological observations and in agreement with petrological mechanical considerations propose that in this region of the andes partially molten granitic bodies ascend diapirically through the hot ductile mid upper crust

sombrero uplift above the altiplano puna magma body evidence of a ballooning mid crustal diapir the altiplano puna ultralow velocity zone in the central andes south america is the largest active magma body in earth s continental crust space geodetic observations reported an uplift in the altiplano puna proper at a rate of 10 mm year however the nature of the inferred inflation source has been uncertain we present data showing that the uplift has persisted at a nearly constant rate over the past two decades and is surrounded by a broad zone of subsidence we show that the ongoing uplift and peripheral subsidence may result from a large mid crustal diapir fed by partial melt from the altiplano puna magma body

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

dem based modelling of surface runoff using diffusion wave equation a digital elevation model dem based overland flow routing model was developed for computation of surface runoff for isolated storm events the model operates on a grid or cell basis and routes the rainfall excess generated over the cells following the dem derived drainage paths to the catchment outlet the rainfall excess for each cell of the catchment was computed using the philip two term infiltration model utilizing the physical properties of the cell the overland flow was described by a finite volume based numerical solution of the diffusion wave approximation of the st venant equations the cell physical properties such as topographic characteristics land use soil etc were extracted from published maps for discretized cells of the catchment using a geographic information system the results of model application indicate that the model satisfactorily predicted the runoff hydrograph the cell based structure of the model allowed for generation of spatially distributed catchment information in terms of the model computed variables such as the depth of flow and discharge

microseismic moment tensors a path to understanding frac growth microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracture treatments determination of event locations and magnitudes leads to estimations of the geometry of the fracture zone and certain dynamics of the fracturing process with sufficient resolution the hypocenters may even reveal failure planes or other underlying structures controlling the distribution of events and of interest to petroleum engineers to test various hypotheses on fracture growth

beyond the dots in the box microseismicity constrained fracture models for reservoir simulation summary monitoring of induced microseismic events usually results in locations for these events and a geometrical interpretation of these dots in the box in this study we show how additional information obtained from observed microseismic events namely the source mechanisms were used to generate a discrete fracture network using the wide aperture of a surface star like array fracstar allows inversion for both shear and non shear source mechanisms both volumetric and shear only source mechanism inversion was carried out on microseismic events from the treatment of a shale gas reservoir in the continental us during the same hydraulic fracture stimulation treatment both dip slip and reverse faulting sources were active in this reservoir the source mechanisms revealed fracture orientations more accurately than could be inferred from microseismic event locations alone the activity associated with different mechanisms is interpreted as indicating reactivation of existing fractures in the rock as well as suggesting generation of new fractures failure analysis using source mechanisms on individual events allows an integrated understanding of the complex fracture interactions taking place in the reservoir and also provides a more complete understanding of the stress conditions in the reservoir during the treatment fracture orientations locations and failure mechanisms are translated into discrete fracture network dfn models that can be used to verify the extent and character of the fractures created or reactivated during the fracture treatment and may ultimately be used to generate fracture flow properties for reservoir simulation

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

on the total input of antarctic waters to the deep ocean a preliminary estimate from chlorofluorocarbon measurements 1 deep ocean inventories of dissolved chlorofluorocarbon 11 cfc 11 along representative sections off antarctica provide the first estimate of the overall strength of all dense water sources in the southern ocean their formation rates are reported for three density layers that span the main water masses involved in the lower limb of the thermohaline circulation thc the bottom layer is supplied via sinking of antarctic bottom water aabw produced at a few continental shelves the middle layer receives the offshore injection of ventilated modified circumpolar deep water mcdw produced along much of the lengthy antarctic slope front the top layer is ventilated by northward export of antarctic surface water into the upper circumpolar deep water of the antarctic circumpolar current average southern ocean inputs to the upper two layers of the deep ocean for the 1970 1990 period are derived on the basis of the cfc 11 distributions along meridional sections the mean cfc 11 saturations of all water mass ingredients and the inferred mixing leading to production of dense source waters about 5 4 1 7 sv 1 sv 10 6 m 3 s 1 of near freezing shelf water ventilate the bottom layer and 4 7 1 7 sv and 3 6 1 3 sv of cold antarctic surface water ventilate the middle and top layers therefore the total contribution of ventilated southern ocean waters to the lower limb of the global thc is about 14 sv this is close to the about 17 sv estimated for north atlantic near surface sources from cfc 11 inventories their entrainment of 7 4 2 4 sv of cfc poor subsurface lower circumpolar deep water during the formation and sinking of aabw and mcdw raises the total southern ocean input to the deep ocean to about 21 sv

eulerian and lagrangian correlation structures of convective rainstorms the eulerian and lagrangian correlation structures of 13 convective rainstorms were investigated using rainfall data from the 1987 convective initiation downburst experiment in denver colorado one minute rainfall data were available for two superposed raingage networks 46 raingages on the portable automated mesonet pam network at a mean spacing of 10 6 km and 31 additional raingages on the federal aviation administration lincoln laboratory operational weather studies flows network at a mean spacing of 2 4 km eulerian correlation coefficients are low and often negative for high resolution 1 min rainfall data correlation increases with time averaging beyond 10 15 min for single rain cells on the flows network and small mesoscale rainstorms on the pam network the average speed of rain cells and small mesoscale rainstorms was found to be 76 5 and 56 4 km hr 1 respectively storm kinematic is identified as the cause of data scatter and low eulerian correlations convective rainstorms are essentially uncorrelated in the eulerian reference frame at a typical raingage spacing of 2 3 km for rain cells and 10 15 km for small mesoscale rainstorms a spatial cross correlation analysis in a lagrangian reference frame moving with the center of mass of the storm separates the kinematic component from the structural component of a rainfall field the spatial cross correlations in the lagrangian rainfall field show considerable improvement over the eulerian spatial correlation plots and data scatter is greatly reduced the increase in correlation coefficients from eulerian to lagrangian reference frames typically ranged from 0 5 to 1 1

source mechanism of a lower crust earthquake beneath the himalayas and its possible relation to metamorphism abstract the nature of deep crustal intermediate and deep focus earthquakes and their relation to metamorphic reactions is a topic of debate here we seek to better understand a possible link between the earthquake process and metamorphism by analyzing the mechanism of ongoing deep crustal earthquakes we focus on a region in the himalayas with observed seismicity at depths expected to experience active eclogite facies metamorphism and dehydration reactions there are few permanent seismic stations in the region therefore we use waveform data from a temporary seismic array deployment we find two earthquakes with magnitude and station coverage adequate for moment tensor inversion for a given earthquake we estimate its seismic full moment tensors and magnitude together with uncertainties using all available waveforms for the largest earthquake mw 3 7 we obtain a best fitting moment tensor and uncertainties that show a double couple with a tensional crack component in the context of geological records that document similar processes and of laboratory experiments conducted at spatial scales that are 5 6 orders of magnitude smaller this mechanism may be related to dehydration driven stress changes triggering slight crack opening and ambient stresses favoring slip along a fault

seismic discrimination of controlled explosions and earthquakes near mount st helens using p s ratios explosions and earthquakes are effectively discriminated by p s amplitude ratios for moderate magnitude events m 4 observed at regional to teleseismic distances 200 km it is less clear if p s

trends in the deep southern ocean 1958 2010 implications for antarctic bottom water properties and volume export 1 regional formation of deep and bottom water masses around the antarctic continental shelf is one of the most important processes contributing to variability of the global meridional overturning circulation deep cell southern ocean hydrographic data collected during the years 1958 2010 indicate that dense shelf waters cooled and freshened during that period in the surrounding open ocean antarctic bottom water aabw warmed with no evidence of salinity change as a result of source water property changes aabw exported from the southern ocean to the deep world ocean became lighter over the period analyzed the average rate of density change within the areas that experienced statistically significant change was 0 0019 kg m 3 yr 1 for the last 20 years of the analysis a negative aabw volume anomaly relative to the half century average 1958 2010 was indicated possibly due to production of a lighter aabw variety or to changes in formation rates over the entire five decades the upper isopycnal of the aabw layer deepened at a rate of 8 1 m yr 1 changes in fundamental hydrographic properties such as these can have important implications for long term global ocean circulation and climate

ventilation of the deep western boundary current and abyssal western north atlantic estimates from tritium and 3he distributions abstract the tritium and excess 3he data from the 1981 tto nas program are used to study the time scales for the ventilation of the deep western basin by recently formed north atlantic deep water nadw the large scale distributions of tritium and 3he in the deep north atlantic are presented and tracer inventories are computed for individual deep water basins the bulk of the bomb tritium and thus new nadw resided in 1981 in the deep labrador sea and western subpolar gyre with a slightly smaller amount in the deep western subtropical gyre the maximum excess 3he values were located south of the overflows in the labrador sea the result of competition between ventilation and in situ tritium decay the subpolar gyre was also the site of the strongest increase in decay corrected tritium 120 and excess 3he 100 between the 1972 geosecs survey and the 1981 tto nas program the observed deep water tritium inventory is in reasonable agreement with model tracer inputs computed for the combined overflow

seismic moment tensor resolution on a local scale simulated rockburst and mine induced seismic events in the kopanang gold mine south africa seismic records contain information about the effect of the source as well as the effect of wave propagation through the rock mass the effect of wave propagation is usually not well known as only simplified models of geological structures are available therefore the information about the source retrieved by inverting seismograms may include errors due to incomplete knowledge of the rock mass along the propagation path which in turn cause a distortion in the calculated moment tensor mt the distortion of the mt on a local scale was observed by inverting records of a simulated rockburst conducted at the kopanang gold mine in south africa a dominant isotropic component of the explosive characteristics was found from the inversion the deviatoric components retrieved from the blast are spurious a test of their stability indicated that they are not significant assuming an uncertainty above 5 for velocities and 10 for attenuation within the homogeneous model available for the mine thus the retrieval of the mt from records of local networks in mines using a homogeneous model of the rock mass seems to be feasible however the homogeneous model of the rock mass can only be applied to close stations within a few kilometers of the source the seismic records from distant stations were too complex to be modelled by a homogeneous rock mass records of six mine induced seismic events recorded at the kopanang gold mine were also inverted a vertical linear dipole along the pressure p axis was found for three of the events suggesting a pillar burst the mechanism of two events contains an isotropic implosion together with a nearly vertical dip slip and seems to indicate a combination of a cavity collapse with a down dip slip along a nearly vertical fault one event corresponds to a dipole along the tensional t axis however it is vertical thus its association with tensile faulting of the hangingwall is uncertain

variability of labrador sea water transported through flemish pass during 1993 2013 flemish pass located at the western subpolar margin is a passage sill depth 1200 m that is constrained by the grand banks and the underwater plateau flemish cap in addition to the deep western boundary current dwbc pathway offshore of flemish cap flemish pass represents another southward transport pathway for two modes of labrador sea water lsw the lightest component of north atlantic deep water carried with the dwbc this pathway avoids potential stirring regions east of flemish cap and deflection into the interior north atlantic ship based velocity measurements between 2009 and 2013 at 47 n in flemish pass and in the dwbc east of flemish cap revealed a considerable southward transport of upper lsw through flemish pass 15 27 1 0 to 1 5 sv about 98 of the denser deep lsw were carried around flemish cap as flemish pass is too shallow for considerable transport of deep lsw hydrographic time series from ship based measurements show a significant warming of 0 3 c decade and a salinification of 0 03 decade of the upper lsw in flemish pass between 1993 and 2013 almost identical trends were found for the evolution in the labrador sea and in the dwbc east of flemish cap this indicates that the long term hydrographic variability of upper lsw in flemish pass as well as in the dwbc at 47 n is dominated by changes in the labrador sea which are advected southward fifty years of numerical ocean model simulations in flemish pass suggest that these trends are part of a multidecadal cycle

source water distribution and quantification of north atlantic deep water and antarctic bottom water in the atlantic ocean abstract the distribution and quantification of the source waters of the north atlantic deep water nadw and the antarctic bottom water aabw in the atlantic ocean were investigated using 40 years of climatology data 1973 2014 constructed from the dataset available in the 2013 world ocean database the quasi interdecadal variability of nadw and aabw source waters spanned the late 1980s until early 2010 in the analysis of three world ocean circulation experiment sections woce a05 a10 and a16 the study was performed by applying optimum multiparameter analysis to quantify the mixture of six nadw and aabw source waters four for nadw and two for aabw the nadw source waters decrease their contributions from north to south except for the region between 30 s and 45 s where the labrador sea water lsw contribution suggests an upper nadw deepening in addition iceland scotland overflow water isow and lsw contribute to the southernmost boundary of nadw in the southern ocean the aabw source waters were observed as far as 45 n with a 15 contribution with significant recirculation in equatorial regions and higher contributions in argentine and brazil basins the denmark strait overflow water dsow and isow showed the highest temporal variability 20 not only near their formation region but also in the south atlantic the aabw source waters did not present high temporal variability although temporal changes were found near their formation region based on their spatial distribution the argentine and brazil basins were noted as the main locations to use for investigating this issue the results provide new insights into the mixing inside the deep atlantic ocean and the global circulation cell the results also specify the source water masses that present higher temporal variability and the suitable locations to observe these changes

effects of storm direction and duration on infiltrating planar flow with partial coverage using kinematic wave equations analytical solutions are derived for flow resulting from a storm moving either up or down an infiltrating plane but not fully covering it by comparing the flow resulting from this storm with that from a stationary storm of the same duration the influence of storm duration direction and velocity is investigated it is found that the direction of storm movement duration and velocity of storms as well as basin infiltration have a pronounced effect on the discharge hydrograph copyright 2004 john wiley sons ltd

moment tensors of the january 1997 earthquake swarm in nw bohemia czech republic double couple vs non double couple events abstract we investigated moment tensors mts of 70 events of the earthquake swarm which occurred in january 1997 in nw bohemia a refined location using the master event procedure shows that all the foci clustered in a volume of less than 0 5 km3 comprising two compact clusters the southern and northern ones the results of single source absolute moment tensor inversion of the p and sh peak amplitudes reveal two types of the source mechanisms a and b in our denotation which dominated in the swarm type a implies an oblique normal faulting with a nearly pure double couple dc source for the b type an oblique thrust faulting and a combined source double couple combined with the isotropic iso and compensated linear vector dipole clvd components are typical magnitudes of the non double couple components of mt appear unrelated to the ml magnitude of the event the proximity of hypocentres of a and b events guarantees the non double couple source mechanisms of the b events not to be an artefact of a mismodelling of the medium to exclude finiteness of the focus or station site effects as possible causes of spurious non double couple components of mts of the b events the residuals of the peak amplitudes across the set of the b events were analysed and the jack knife test was applied the a and b events separate in time and space consequently three major phases of swarm activity can be distinguished in the first only the southern cluster was active and a events prevailed while b events dominated in the northern cluster in the third phase both a and b events occurred the former in the southern cluster the latter in the northern one during the second phase the initiation of the b events in the northern cluster are reflected in a pronounced increase in the non double couple components of the mts which points to tensile source mechanisms as a consequence of a hypothesised fluid injection

effect of the duration and direction of storm movement on infiltrating planar flow with full areal coverage using kinematic wave equations analytical solutions are derived for flow due to a storm moving up or down an infiltrating plane and covering it completely the storm duration is assumed in two ways first the plane is covered everywhere for the same duration by the storm second the plane is covered in a linearly decreasing manner from the beginning of its coverage of the plane to the other end of the plane by comparing the flow due to this storm with that due to a stationary storm of the same duration the influence of storm duration direction and velocity on flow hydrograph is investigated it is found that storm movement has a pronounced effect on runoff hydrograph copyright 2002 john wiley sons ltd

dense bottom layers in the scotia sea southern ocean creation lifespan and destruction the lower limb of the atlantic overturning circulation is renewed by dense waters from the southern ocean a substantial portion of which flow through the scotia sea we report dense bottom layers here with gradients in temperature and salinity comparable to those seen near the surface of the southern ocean these are overlain by layers with much weaker stratification and are caused by episodic overflows of dense waters across the south scotia ridge and topographic trapping within deep trenches one such layer was found to be at least 3 4 years older than the water immediately above the estimated vertical diffusivity to which this layer was subject is substantially less than the strong basin average deep mixing reported previously we conjecture that a vertical mixing in the scotia sea is strongly spatially inhomogeneous and b the flushing of these layers like their formation is related to overflow events and hence also strongly episodic

structure transports and transformations of the water masses in the atlantic subpolar gyre we discuss the distributions and transports of the main water masses in the north atlantic subpolar gyre naspg for the mean of the period 2002 2010 ovide sections 2002 2010 every other year as well as the inter annual variability of the water mass structure from 1997 4x and meteor sections to 2010 the water mass structure of the naspg quantitatively assessed by means of an optimum multiparameter analysis with 14 water masses was combined with the velocity fields resulting from previous studies using inverse models to obtain the water mass volume transports we also evaluate the relative contribution to the atlantic meridional overturning circulation amoc of the main water masses characterizing the naspg identifying the water masses that contribute to the amoc variability the reduction of the magnitude of the upper limb of the amoc between 1997 and the 2000s is associated with the reduction in the northward transport of the central waters this reduction of the northward flow of the amoc is partially compensated by the reduction of the southward flow of the lower limb of the amoc associated with the decrease in the transports of polar intermediate water and subpolar mode water spmw in the irminger basin we also decompose the flow over the reykjanes ridge from the east north atlantic basin to the irminger basin 9 4 4 7 sv into the contributions of the central waters 2 1 1 8 sv labrador sea water lsw 2 4 2 0 sv subarctic intermediate water saiw 4 0 0 5 sv and iceland scotland overflow water isow 0 9 0 9 sv once lsw and isow cross over the reykjanes ridge favoured by the strong mixing around it they leave the irminger basin through the deep to bottom levels the results also give insights into the water mass transformations within the naspg such as the contribution of the central waters and saiw to the formation of the different varieties of spmw due to air sea interaction

effect of the duration and direction of storm movement on planar flow with full and partial areal coverage using kinematic wave equations analytical solutions are derived for flow resulting from storms moving either up or down the plane and covering it fully or partially by comparing the flow resulting from a moving storm with that from a stationary storm of the same duration and areal coverage the influence of storm duration direction and areal coverage is investigated it is found that the direction duration and areal coverage of storm movement have a pronounced effect on the discharge hydrograph the runoff hydrographs resulting from storms moving downstream are quite different from those from storms moving upstream likewise the areal coverage of the storm has a pronounced effect on the runoff hydrograph copyright 2002 john wiley sons ltd

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

coincident anomalies of seismic attenuation and electrical resistivity beneath the southern bolivian altiplano plateau 1 reassessment of local earthquake data from the ancorp seismological network allowed the calculation of 3d attenuation qp tomographic images of crust and upper mantle beneath the southern bolivian altiplano around 21 s the images reveal a low qp middle and lower crust and a moderate qp upper mantle beneath the southern altiplano beneath the recent magmatic arc qp is not significantly decreased at this latitude the distribution of crustal qp coincides with the variation of electrical resistivity thus limiting the possible mechanisms causing the anomalies our findings support the hypothesis that partial melts in middle and lower crust beneath the altiplano are present on a large scale we see no evidence for a shallow asthenosphere beneath the southern altiplano

depths and focal mechanisms of crustal earthquakes in the central andes determined from teleseismic waveform analysis and insar 1 we investigate the depths of crustal earthquakes mw 5 5 earthquakes from the global cmt catalog and previous work spanning 1944 2007 for 38 well recorded events we use teleseismic p and sh waveforms to model the strike dip rake focal depth and source time function we use insar observations of surface deformation from 9 earthquakes to compare inferred fault parameters with the waveform inversions and global catalogs to assess their accuracies while the depths from the insar and waveform analyses generally agree within error horizontal and depth errors in global catalogs are 10 to 50 km as found elsewhere as noted in previous work the majority of crustal earthquakes occur in the eastern cordillera and foreland regions of the central andes although a few normal and strike slip earthquakes occur beneath the altiplano plateau and in the forearc in southern peru and northernmost chile we propose a new interpretation of one of the basement thrusts shira mountain peru as a pop up block on the basis of our new earthquake depths we confirm that earthquakes in the flat slab areas of peru and argentina are within the sometimes aseismic lower crust lower crustal earthquakes are globally found in all types of tectonic settings only when the thermal lithosphere is more than 80 km thick and the amount of recent shortening extension is 30

uturuncu volcano bolivia volcanic unrest due to mid crustal magma intrusion uturuncu volcano sw bolivia is a dormant stratovolcano 85 km3 dominated by dacitic lava domes and flows 39ar 40ar ages show that the volcano was active between 890 ka and 271 ka with the lavas becoming younger and less extensive at higher elevations there are current signs of unrest between 1992 and 2006 geodetic satellite measurements record an ongoing 70 km deformation field with a central uplift rate of 1 to 2 cm yr deformation indicates volume changes of 400 x 108 m3 over 14 years an average of 1 m3 s 10 2 km3 yr the deformation is attributed to magma intrusion into the altiplano puna regional crustal magma body deformation models indicate a source at depths of 17 to 30 km beneath current local relief in a reconnaissance survey persistent seismic activity mean of 2 6 earthquakes per hour with a maximum of 14 per hour was recorded at about 4 km depth below the center of the uplift 4 km sw of the volcano s summit the seismic events have a normal b value 1 04 and activity is attributed to brittle deformation in the elastic crust above the active deep magma intrusion the porphyritic dacite lavas 64 68 sio2 have a plagioclase orthopyroxene biotite magnetite ilmenite assemblage and commonly contain juvenile silicic andesite inclusions cognate norite nodules and crustal xenoliths temperature estimates are in the range 805 to 872 c for the dacites and about 980 c for the silicic andesites the dacite magmas formed by fractional crystallization of andesite forming norite cumulates and involving partial melting of crust compositions and zoning patterns of orthopyroxene and plagioclase phenocrysts indicate that compositional variation in the dacites is caused by magma mixing with the silicic andesite reversely zoned orthopyroxene phenocrysts in the andesitic end member are explained by changing oxidation states during crystallization fe3 fe2 ratios from orthopyroxene crystals and fe3 in plagioclase provide evidence for a relatively reduced melt that subsequently ascended degassed and became more oxidized as a consequence of degassing the geophysical and petrological observations suggest that dacite magma is being intruded into the altiplano puna regional crustal magma body at 17 km or more depth consistent with deformation models in the late pleistocene dacitic and andesitic magmas ascended from the regional crustal magma body to a shallow magma system at a few kilometers depth where they crystallized and mingled together the current unrest together with geophysical anomalies and 270 ka of dormancy indicate that the magmatic system is in a prolonged period of intrusion such circumstances might eventually lead to eruption of large volumes of intruded magma with potential for caldera formation

finite moment tensor of the 3 september 2002 yorba linda earthquake we have developed procedures for inverting broadband waveforms for the finite moment tensors fmts of regional earthquakes the fmt is defined in terms of second order polynomial moments of the source space time function it removes the fault plane ambiguity of the centroid moment tensor cmt and yields several additional parameters of seismological interest the characteristic length lc width wc and duration tc of the faulting as well as the directivity vector v d of the fault slip following mcguire et al 2001 we represent the observed waveform relative to the synthetic in terms of two frequency dependent differential times a phase delay p and an amplitude reduction time q which we measure using the generalized seismological data functional gsdf method gee and jordan 1992 we numerically calculate the fmt partial derivatives which allows us to use synthetics computed by using any forward modeling tools we have tested our methodology on southern california seismic network scsn recordings of the 03 september 2002 yorba linda earthquake m w 4 3 using 1d synthetic green s functions we determined the cmt and resolved fault plane ambiguity to resolve the details of source finiteness we employed a joint inversion technique that recovers the cmt parameters of the aftershocks and the cmt and fmt parameters of the mainshock the joint system of equations relating the data to the source parameters of the mainshock aftershock cluster is denuisanced for path anomalies in both observables this projection operation effectively corrects the mainshock data for path related anomalies in a way similar to but more flexible than empirical green s function egf techniques our results indicate that the yorba linda rupture occurred as left lateral slip on a fault patch conjugate to the nearby right lateral whittier fault we obtained source dimensions of lc 0 7 0 1 km wc 0 4 0 1 km and tc 0 2 0 05 sec implying a stress drop of about 3 2 mpa and we found a directivity of 0 8 0 2 oriented up and to the northeast the inferred fault plane is consistent with the mainshock aftershock distribution relocated by hauksson et al 2002

focal mechanisms of deep low frequency earthquakes in eastern shimane in western japan 1 deep low frequency earthquakes lfes are small earthquakes m 2 that occur at depths of 10 45 km with seismic wave radiation mainly in the frequency range of 2 8 hz lfes in western japan are categorized into tectonic lfes in the nankai subduction zone volcanic lfes beneath active volcanoes and semi volcanic lfes that occur far from active volcanoes but are otherwise similar to volcanic lfes while tectonic lfes are considered to reflect shear slip on a plate boundary the mechanisms of volcanic and semi volcanic lfes remain unclear we have determined the mechanisms of 38 semi volcanic lfes in eastern shimane which is the site of the most frequent semi volcanic lfe activity in japan for each event velocity seismograms at five stations were inverted into a focal mechanism and moment rate function by a combined grid search and linear inversion analysis synthetic waveforms were calculated for a one dimensional structure and the local site amplification effects were corrected using body waves from deep earthquakes the estimated moment rate function was found to often oscillate between positive and negative values which are unlike those of regular earthquakes the focal mechanisms for many lfes are dominated by a compensated linear vector dipole with symmetry axes parallel to the lineation formed by the hypocenter distribution and the direction of the minimum principal axis of regional stress

spectral element moment tensor inversions for earthquakes in southern california we have developed and implemented an automated moment tensor inversion procedure to determine source parameters for southern california earthquakes the method is based upon spectral element simulations of regional seismic wave propagation in an integrated 3d southern california velocity model sensitivity to source parameters is determined by numerically calculating the frechet derivatives required for the moment tensor inversion we minimize a waveform misfit function and allow limited time shifts between data and corresponding synthetics to accommodate additional 3d heterogeneity not included in our model the technique is applied to three recent southern california earthquakes the 9 september 2001 m l 4 2 hollywood event the 22 february 2003 m l 5 4 big bear event and the 14 december 2001 m l 4 0 diamond bar event using about half of the available three component data at periods of 6 sec and longer we obtain focal mechanisms depths and moment magnitudes that are generally in good agreement with estimates based upon traditional body wave and surface wave inversions

determination and uncertainty of moment tensors for microearthquakes at okmok volcano alaska summary efforts to determine general moment tensors mts for microearthquakes in volcanic areas are often hampered by small seismic networks which can lead to poorly constrained hypocentres and inadequate modelling of seismic velocity heterogeneity in addition noisy seismic signals can make it difficult to identify phase arrivals correctly for small magnitude events however small volcanic earthquakes can have source mechanisms that deviate from brittle double couple shear failure due to magmatic and or hydrothermal processes thus determining reliable mts in such conditions is a challenging but potentially rewarding pursuit we pursued such a goal at okmok volcano alaska which erupted recently in 1997 and in 2008 the alaska volcano observatory operates a seismic network of 12 stations at okmok and routinely catalogues recorded seismicity using these data we have determined general mts for seven microearthquakes recorded between 2004 and 2007 by inverting peak amplitude measurements of p and s phases we computed green s functions using precisely relocated hypocentres and a 3 d velocity model we thoroughly assessed the quality of the solutions by computing formal uncertainty estimates conducting a variety of synthetic and sensitivity tests and by comparing the mts to solutions obtained using alternative methods the results show that mts are sensitive to station distribution and errors in the data velocity model and hypocentral parameters although each of the seven mts contains a significant non shear component we judge several of the solutions to be unreliable however several reliable mts are obtained for a group of previously identified repeating events and are interpreted as compensated linear vector dipole events

evidence for near horizontal tensile faulting at the base of gornergletscher a swiss alpine glacier abstract using 3d green s functions we determine full and constrained moment tensor solutions of icequakes near the base of gornergletscher switzerland the seismic events were recorded in the summer of 2004 using a high density seismometer array the seismic velocity model used in the generation of green s functions is based on radio echo soundings to approximate the basal topography which beneath the study site exhibits a strong inclination as the basal conditions are not well known we try moment tensor inversions with seismic velocity profiles consisting of two and three media the former case consists of homogeneous ice resting on bedrock whereas the latter case includes a thin basal layer with slow seismic velocities representing eroded material or highly fractured ice effects of errors in green s functions are estimated by sensitivity studies in which we invert 1d and 3d synthetics using green s functions of wrong velocity models the results show that calculations of source types and fault plane orientations of tensile cracks are rather robust with respect to errors in green s functions however the quality of the waveform fits depends on strike and dip of the synthetic source when inverting seismograms green s functions of the seismic model that includes the basal slow velocity layer are found to give the most realistic source types as well as the best waveform fits the fault mechanisms derived from constrained moment tensor inversions are near horizontal tensile cracks which suggest a complex time dependent basal stress field

magnetotelluric images of magma distribution beneath volcan uturuncu bolivia implications for magma dynamics the altiplano puna volcanic complex in the central andes records a history of major caldera forming eruptions over the past 10 m y geophysical and geodetic data indicate that magma is still present and perhaps mobile in the crust broadband magnetotelluric data were used to generate two dimensional and three dimensional electrical resistivity models of the altiplano puna magma body apmb with a focus on the zone of inflation around volcan uturuncu in southern bolivia low electrical resistivities 20 the upper surface of the apmb is shallowest beneath uturuncu and the geometry is consistent with geodynamic models that require the upward movement of a melt layer at this location the shallower resistivity structure is characterized by discrete electrically conductive bodies oriented east west near sea level depth of 5 km which are interpreted as a combination of partial melt and fluids

the central andean altiplano puna magma body receiver function analysis of 14 teleseismic events recorded by 6 temporary passcal broadband stations within the altiplano puna volcanic complex apvc shows a consistent 2 s negative polarity p to s conversion for all stations for all available azimuths forward modeling of the largest amplitudes suggests that this conversion is produced by the top of a very low velocity zone at a depth of 19 km with a vs 0 5 km s and a thickness of 750 810 m we interpret the characteristics of the low velocity zone low vs areal extent and flatness to be consistent with a sill like magma body on the basis of additional data from the german ancorp experiment the altiplano puna magma body appears to underlie much of the apvc and it may therefore be the largest known active continental crustal magma body

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

non double couple mechanisms of microearthquakes induced by hydraulic fracturing 1 we have inverted polarity and amplitude information of representative microearthquakes to investigate source mechanisms of seismicity induced by hydraulic fracturing in the carthage cotton valley east texas gas field with vertical arrays of four and eight three component geophones in two monitoring wells respectively we were able to reliably determine source mechanisms of the strongest events with the best signal to noise ratio our analysis indicates predominantly non double couple source mechanisms with positive volumetric component consistent with opening cracks oriented close to expected hydraulic fracture orientation our observations suggest the induced events are directly the result of opening cracks by fluid injection in contrast to many previous studies where the seismicity is interpreted to be primarily shearing caused by pore pressure diffusion into the surrounding rock or associated with shear stresses created at the hydraulic fracture tip

anomalous crust of the bolivian altiplano central andes constraints from broadband regional seismic waveforms a one year deployment of broadband seismographs in the bolivian altiplano recorded numerous intermediate depth earthquakes at near regional distances we modeled the associated broadband waveforms of two earthquakes to estimate an average crustal structure for the altiplano the resulting model is characterized by an anomalously low mean p velocity of 6 0 km s a low poisson s ratio of 0 25 and a crustal thickness of 65 km the combination of the low mean velocity and low poisson s ratio can be explained only by a predominantly quartz rich felsic bulk composition this constraint precludes significant volumes of magmatic addition from the mantle contributing to the great thickness of the altiplano crust but is consistent with thickening by compressive shortening concentrated in a weak felsic layer

crustal earthquakes in the cook inlet and susitna region of southern alaska abstract several large m 6 earthquakes have occurred in the vicinity of anchorage alaska within the past century the presence of the underlying subducting pacific plate makes it difficult to determine the origin of these older earthquakes as either crustal slab or the subduction plate interface we perform a seismological study of historical and modern earthquakes within the cook inlet and susitna region west of anchorage we first estimate hypocenters for historical large earthquakes in order to assess their likelihood of origin as crustal slab or plate interface we then examine modern crustal seismicity to better understand the style of faulting and the location of active structures including within and beneath the cook inlet and susitna basins we perform double couple moment tensor inversions using high frequency body waves 1 10 hz for small to moderate m 2 5 crustal earthquakes depth 30 km occurring from 2007 to 2017 our misfit function combines both waveforms differences as well as first motion polarities in order to obtain reliable moment tensor solutions the three focus regions beluga upper cook inlet and susitna exhibit predominantly thrust mechanisms for crustal earthquakes indicating an overall compressive regime within the crust that is approximately consistent with the direction of plate convergence mechanisms within upper cook inlet have strike directions aligned with active anticlines previously identified in cook inlet from active source seismic data our catalog of moment tensors is helpful for identifying and characterizing subsurface faults from seismic lineaments and from faults inferred from subsurface images from active source seismic data

hydrographic changes in the labrador sea 1960 2005 abstract the labrador sea has exhibited significant temperature and salinity variations over the past five decades the whole basin was extremely warm and salty between the mid 1960s and early 1970s and fresh and cold between the late 1980s and mid 1990s the full column salinity change observed between these periods is equivalent to mixing a 6 m thick freshwater layer into the water column of the early 1970s the freshening and cooling trends reversed in 1994 starting a new phase of heat and salt accumulation in the labrador sea sustained throughout the subsequent years it took only a decade for the whole water column to lose most of its excessive freshwater reinstate stratification and accumulate enough salt and heat to approach its record high salt and heat contents observed between the late 1960s and the early 1970s if the recent tendencies persist the basin s storages of salt and heat will fairly soon likely by 2008 exceed their historic highs the main process responsible for the net cooling and freshening of the labrador sea between 1987 and 1994 was deep winter convection which during this period progressively developed to its record depths it was caused by the recurrence of severe winters during these years and in its turn produced the deepest densest and most voluminous labrador sea water lsw1987 1994 ever observed the estimated annual production of this water during the period of 1987 1994 is equivalent to the average volume flux of about 4 5 sv with some individual annual rates exceeding 7 0 sv once winter convection had lost its strength in the winter of 1994 1995 the deep lsw1987 1994 layer lost communication with the mixed layer above consequently losing its volume while gaining heat and salt from the intermediate waters outside the labrador sea while the 1000 2000 m layer was steadily becoming warmer and saltier between 1994 and 2005 the upper 1000 m layer experienced another episode of cooling caused by an abrupt increase in the air sea heat fluxes in the winter of 1999 2000 this change in the atmospheric forcing resulted in fairly intense convective mixing sufficient to produce a new prominent lsw class lsw2000 penetrating deeper than 1300 m this layer was steadily sinking or deepening over the years following its production and is presently overlain by even warmer and apparently less dense water mass implying that lsw2000 is likely to follow the fate of its deeper precursor lsw1987 1994 the increasing stratification of the intermediate layer implies intensification in the baroclinic component of the boundary currents around the mid depth perimeter of the labrador sea the near bottom waters originating from the denmark strait overflow exhibit strong interannual variability featuring distinct short term basin scale events or pulses of anomalously cold and fresh water separated by warm and salty overflow modifications regardless of their sign these anomalies pass through the abyss of the labrador sea first appearing at the greenland side and then about a year later at the labrador side and in the central labrador basin the northeast atlantic deep water 2500 3200 m originating from the iceland scotland overflow water reached its historically freshest state in the 2000 2001 period and has been steadily becoming saltier since then it is argued that lsw1987 1994 significantly contributed to the freshening density decrease and volume loss experienced by this water mass between the late 1960s and the mid 1990s via the increased entrainment of freshening lsw the hydrostatic adjustment to expanding lsw or both

crustal anisotropy and state of stress at uturuncu volcano bolivia from shear wave splitting measurements and magnitude frequency distributions in seismicity abstract the physical signatures of unrest in large silicic magma systems are commonly observed in geophysical surveys yet the interactions between magmatic processes and crustal stresses are often left unconstrained stresses in the mid and upper crust exert a strong control on the propagation and stalling of magma and magma ascent can in turn change the magnitude and orientation of these stresses including those associated with hydrothermal systems this study assesses the state of stress at the restless uturuncu volcano in the bolivian andes with space depth and time using observations of seismic anisotropy and the magnitude frequency distributions of local earthquakes shear wave splitting measurements are made for 677 events in the upper crust 1 25 km below sea level between june 1 2009 and march 10 2012 and b values are calculated using the aki maximum likelihood method for a range of catalog subsets in the entire crust 5 to 65 km below sea level the b value of the crustal events is unusually low b 0 66 0 09 indicating that the seismogenic region features strong material with high stresses that are released with limited influence from hydrothermal fluids the 410 good quality shear wave splitting results have an average delay time of 0 06 0 002 s and an average percent anisotropy ranging from 0 25 0 04 to 6 2 0 94 with a mean of 1 70 0 32 fast shear wave polarization directions are highly variable and appear to reflect a combination of tectonic and magmatic stresses that overprint the regional e w compressive stress associated with the convergence of the nazca and south american plates the shear wave splitting results and b values suggest that the upper crust beneath uturuncu 0 7 km below the summit is characterized by a weak and localized hydrothermal system in a poorly developed fracture network we conclude that stresses imposed by crustal flexure due to magmatic unrest above the altiplano puna magma body activate crack opening on a pre existing fault beneath the volcano generating seismicity and a spatially variable 1 10 anisotropy above the brittle ductile transition zone these results suggest that strong stresses in relatively unfractured upper crustal rocks may locally inhibit fluid migration in large silicic magma systems leading to pluton emplacement and effusive volcanism rather than explosive eruptions

three dimensional seismic structure and moment tensors of non double couple earthquakes at the hengill grensdalur volcanic complex iceland summary the volcanic and geothermal areas of iceland are rich sources of non double couple non dc earthquakes a state of the art digital seismometer network deployed at the hengill grensdalur volcanic complex in 1991 recorded 4000 small earthquakes we used the best recorded of these to determine 3 d v p and v p v s structure tomographically and accurate earthquake moment tensors the v p field is dominated by high seismic wave speed bodies interpreted as solidified intrusions a widespread negative 4 per cent v p v s anomaly in the upper 4 km correlates with the geothermal field but is too strong to be caused solely by the evect of temperature upon liquid water or the presence of vapour and requires in addition mineralogical or lithological diverences between the geothermal reservoir and its surroundings these may be caused by geothermal alteration well constrained moment tensors were obtained for 70 of the best recorded events by applying linear programming methods to p and s wave polarities and amplitude ratios about 25 per cent of the mechanisms are within observational error consistent with dc mechanisms consistent with shear faulting the other 75 per cent have significantly non dc mechanisms many have substantial explosive components one has a substantial implosive component and the deviatoric component of many is strongly non dc many of the non dc mechanisms are consistent within observational error with simultaneous tensile and shear faulting however the mechanisms occupy a continuum in source type parameter space and probably at least one additional source process is occurring this may be fluid flow into newly formed cracks causing partial compensation of the volumetric component studying non shear earthquakes such as these has great potential for improving our understanding of geothermal processes and earthquake source processes in general

recent changes in the freshwater composition east of greenland results from three hydrographic surveys across the east greenland current between 2011 and 2013 are presented with focus on the freshwater sources end member analysis using salinity 18o and nutrient data shows that while meteoric water dominated the freshwater content a significant amount of pacific freshwater was present near denmark strait with a maximum in august 2013 while in 2011 and 2012 the net sea ice melt was dominated by brine in 2013 it became close to zero the amount of pacific freshwater observed near denmark strait in 2013 is as large as the previous maximum in 1998 this together with the decrease in meteoric water and brine suggests a larger contribution from the canadian basin we hypothesize that the increase of pacific freshwater is the result of enhanced flux through bering strait and a shorter pathway of pacific water through the interior arctic to fram strait

imaging hydraulic fractures in a geothermal reservoir 1 an injection experiment at the coso geothermal field in eastern california in march 2005 caused a swarm of microearthquakes that was recorded by a local network of three component digital seismometers high resolution relative hypocenter locations propagated upward and northward on a 700 600 m plane striking n 20 e and dipping 75 to the wnw this plane is a pre existing fault whose surface projection coincides with an active scarp the earthquakes have similar non double couple mechanisms that involve volume increases and the fault plane bisects their dilatational fields implying a process dominated by tensile failure the source types require the additional involvement of subsidiary shear faulting however events before and after the swarm have variable orientations and volume changes of both signs similar tensile shear failure is observed in some natural microearthquake swarms for example at long valley caldera california its occurrence under low fluid pressure may imply a heterogeneous stress field or the induction of thermal stresses by introduction of cold fluid

resolution of non double couple components in the seismic moment tensor using regional networks ii application to aftershocks of the 1999 mw 7 4 izmit earthquake summary we study potential non double couple non dc components in aftershocks of the 1999 izmit earthquake the izmit earthquake ruptured a 140 km long segment of the north anatolian fault zone in northwestern turkey and was followed by the mw 7 1 d uzce earthquake that extended the rupture further to the east focal mechanisms of izmit aftershocks clearly indicate a segmentation of the rupture into several segments one of which is the akyazi plain a pull apart structure where significant non dc components might be observed the analysedearthquakecataloguecontainswaveformsofmorethan4000accuratelylocatedevents observedat35three componentshort periodseismicstations toensurehigh qualitydatawith good focal coverage we apply strict quality criteria to the aftershock catalogue reducing the number of events to only 33 aftershocks for which stable moment tensors were calculated using p and s wave amplitudes the moment tensors of the 33 analysed aftershocks display significant differences in the percentage of the non dc components for the three distinct fault segments the izmit sapanca karadere d uzce and the akyazi segments events located in the izmit sapanca and karadere d uzce segments exhibit only small percentages of the non dc components and if existent they are mainly positive this correlates well with the predominant strike slip stress regime along these segment and also with the main shock rupture being rightlateral strike slip in contrary we found a substantial percentage of non dc components for events below the akyazi plain where the sapanca fault splits into the mudurnu and karadere faults there the observed non dc components are entirely positive indicating a tensional regime and ranging from 20 to 48 percent clearly exceeding the defined error bounds found in a synthetic study this observation is in accordance with the post seismic setting following the izmit main shock that left a remarkable slip deficit of 3 5 m below the akyazi bend

shallow seismicity triggered seismicity and ambient noise tomography at the long dormant uturuncu volcano bolivia using a network of 15 seismometers around the inflating uturuncu volcano from april 2009 to 2010 we find an average rate of about three local volcano tectonic earthquakes per day and swarms of 5 60 events a few times per month with local magnitudes ranging from 1 2 to 3 7 the earthquake depths are near sea level more than 10 km above the geodetically inferred inflation source and the altiplano puna magma body the mw 8 8 maule earthquake on 27 february 2010 triggered hundreds of earthquakes at uturuncu with the onset of the love and rayleigh waves and again with the passage of the x2 x3 overtone phases of rayleigh waves this is one of the first incidences in which triggering has been observed from multiple surface wave trains the earthquakes are oriented nw se similar to the regional faults and lineaments the b value of the catalog is 0 49 consistent with a tectonic origin of the earthquakes we perform ambient noise tomography using love wave cross correlations to image a low velocity zone at 1 9 to 3 9 km depth below the surface centered slightly north of the summit the low velocities are perhaps related to the hydrothermal system and the low velocity zone is spatially correlated with earthquake locations the earthquake rate appears to vary with time a seismic deployment from 1996 to 1997 reveals 1 5 earthquakes per day whereas 60 events day were seen during 5 days using one seismometer in 2003 however differences in analysis methods and magnitudes of completeness do not allow direct comparison of these seismicity rates the rate of seismic activity at uturuncu is higher than at other well monitored inflating volcanoes during periods of repose the frequent swarms and triggered earthquakes suggest the hydrothermal system is metastable