nutrients in an oligotrophic boundary current evidence of a new role for the leeuwin current new observations along the continental shelf of western australia provide a novel explanation for the established 60years relationship between leeuwin current lc strength and greater winter nitrate concentrations at 32 s plus the inter annual variation in the magnitude of the annual shelf scale phytoplankton bloom the potential source of dissolved nitrogen to support the annual shelf scale phytoplankton bloom was identified as thin layers of an unprecedented areal extent nitrate concentration and shallow nature that were observed off the northwest of australia we propose that the dissolved inorganic nitrogen din in these layers enters the lc at depth and then enters the euphotic zone via by three mechanisms instability that results in a warm core eddy cooling that deepens the surface mixed layer and shallowing of the thin layer during the onset of the annual phytoplankton bloom along the west coast of australia from 22 s to 34 s the poleward flowing lc was clearly evident as a surface intensified ocean boundary current transporting warmer lower salinity greater silicate waters in a shallow mixed layer rapidly southward between 24 and 26 s the core of the lc was present as a 50 100m deep layer over one or more thin layers 15 50m thick with high nitrate and low dissolved oxygen do these layers were of lower salinity cooler water with markedly reduced do high nitrate concentrations and distinct nitrate silicate no3 si oh 4 nutrient ratios as the lc flowed south it cooled and deepened thereby entraining the thin layers of high nitrate water into the euphotic zone the lc also formed large greater than 100km diameter warm core eddies with a deep surface mixed layer that also entrained nitrate from these thin layers in some locations as far south as 32 s the lc was still present with the thin layer of high nitrate intact but now within the euphotic zone thus the available evidence suggests the lc arises under conditions that favour rapid and shallow nitrification this nitrification fuels a shelf scale bloom on a downwelling favourable coast depending upon the rate of nitrification the source of the particular organic matter may be local or delivered from the tropics via horizontal advection in a subsurface layer of the lc

applicability of insar to tropical volcanoes insights from central america measuring volcano deformation is key to understanding the behaviour of erupting vol canoes and detecting those in periods of unrest satellite techniques provide the opportunity to do so on a global scale but with some notable exceptions the deformation of volcanoes in the tropics has been understudied relative to those at higher latitudes largely due to technical difficulties in applying interferometric synthetic aperture radar insar we perform a systematic survey of the central american volcanic arc to investigate the appli cability of interferometric synthetic aperture radar insar to volcanoes in the tropics volcano characteristics that may prevent insar measurement include 1 dense vegetation cover 2 per sistent activity and 3 steep slopes measurements of deformation are further inhibited by atmos pheric artefacts associated with 4 large changes in topographical relief we present a systematic method for distinguishing between water vapour artefacts and true deformation our data show a linear relationship c 2 cm km between the magnitudes of water vapour artefacts and volcano edifice height for high relief volcanoes e g fuego guatemala 3763 m a s l above sea level errors are of the order of 4 5 cm across the volcano s edifice but are less than 2 cm for lower relief e g masaya nicaragua 635 m a s l examples such as arenal atitlan and fuego illustrate that satellite acquisition strategies incorporating ascending and descending tracks are particularly important for studying steep sided volcanoes poor coherence is primarily associated with temporal decorrelation which is typically more rapid in southern central america where evergreen broadleaf vegetation dominates land use classification is a better predictorof decorrelation rate thanvegetationindex comparisonof coher ence for different radar wavelengths match expectations high resolution x band radar is best suited to local studies where high resolution digital elevation models dems exist while l bandwavelengths are necessary for regional surveys however this is the first time that relation ships between phase coherence and time perpendicular baseline radar wavelength and land use have been quantified on the scale of a whole volcanic arc

the 1999 mw 7 1 hector mine california earthquake sequence complex conjugate strike slip faulting the 1999 m w 7 1 hector mine mainshock showed right lateral strike slip faulting with an initial strike of n6 w and vertical dip the mainshock was preceded within 20 hours by 18 recorded foreshocks of 1 5 m 3 8 within a few kilometers distance of the mainshock hypocenter the aftershocks delineate how the hector mine earthquake ruptured with strike n6 w to the south for a distance of 15 km and possibly to the north for a distance of several kilometers the two largest aftershocks of m 5 9 and m 5 7 occurred near the north and south ends of the first mainshock rupture segment the second segment of rupture starting 15 km to the south away from the mainshock hypocenter delineated by strike slip and thrust faulting aftershocks extends 10 km farther away with a strike of s140 e along the bullion fault the aftershocks also outline an unusual third rupture segment extending from about 5 km south of the hypocenter with a strike of n30 w to n35 w for a distance of 20 km approximately 10 to 25 km farther to the north and west of the mainshock epicenter several clusters form a complex aftershock distribution three dimensional vp and vp vs models of the region exhibit only small regional changes as is typical for the mojave region nonetheless the mainshock rupture started within a region of rapidly varying vp and at least three regions of low vp vs are imaged within the aftershock zone the rate of decay for the hector mine earthquake sequence has been slightly above the mean for both p values and b values in southern california the focal mechanisms of the aftershocks and the state of stress are consistent with strike slip faulting including a component of normal faulting most prominent to the north the orientation of the regional maximum horizontal stress the variation in orientation of the mainshock fault segments by 30 and scattered distribution of aftershocks suggest that the mainshock and aftershock deformation field exhibit volumetric shear deformation accommodated by complex conjugate sets of strike slip faults

asperities and barriers on the seismogenic zone in north chile state of the art after the 2007 mw 7 7 tocopilla earthquake inferred by gps and insar data the mw 7 7 2007 november 14 earthquake had an epicentre located close to the city of tocopilla at the southern end of a known seismic gap in north chile through modelling of global positioning system gps and radar interferometry insar data we show that this event ruptured the deeper part of the seismogenic interface 30 50 km and did not reach the surface the earthquake initiated at the hypocentre and was arrested 150 km south beneath the mejillones peninsula an area already identified as an important structural barrier between two segments of the peru chile subduction zone our preferred models for the tocopilla main shock show slip concentrated in two main asperities consistent with previous inversions of seismological data slip appears to have propagated towards relatively shallow depths at its southern extremity under the mejillones peninsula our analysis of post seismic deformation suggests that small but still significant post seismic slip occurred within the first 10 d after the main shock and that it was mostly concentrated at the southern end of the rupture the post seismic deformation occurring in this period represents 12 19 per cent of the coseismic deformation of which 30 55 per cent has been released aseismically post seismic slip appears to concentrate within regions that exhibit low coseismic slip suggesting that the afterslip distribution during the first month of the post seismic interval complements the coseismic slip the 2007 tocopilla earthquake released only 2 5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500 km long north chile seismic gap

coseismic displacements from the hector mine california earthquake results from survey mode global positioning system measurements we describe the collection and processing of global positioning system gps data from 77 locations around the hector mine earthquake which we use to estimate coseismic displacements related to this shock the existence of pre event gps data some collected to monitor postseismic displacements from the 1992 landers earthquake and some to establish survey control in the meizoseismal area provided a relatively dense coverage close to the rupture zone the data available were collected mostly within the 2 years prior to the 1999 earthquake we reobserved many points within a few days after the shock and all within 6 months after we include corrections for interseismic motion to provide the best value possible for coseismic motion caused by this earthquake the displacements in general display the pattern expected for a strike slip fault though a few show significant vertical motion the maximum horizontal displacement observed was 2 m one station between fault ruptures showed little horizontal motion but significant uplift

contribution of radar interferometry to a two step inversion of the kinematic process of the 1992 landers earthquake we study the rupture process of the 1992 landers earthquake to limit the trade off between slip amplitude and rupture time that affects solutions using only seismological data we adopt a two step approach we first constrain the slip distribution and its uncertainty by independent geodetic data to recover in the second step the temporal details of the rupture propagation the first step consists of an inversion of interferometric data and global positioning system measurements both independently and together to constrain slip distribution on a three segment fault model along both strike and dip direction we use a genetic algorithm to test the uniqueness of the solution and a least squares formulation to find the model which best fits the data we conclude from the results of these geodetic inversions that interferometric data are rich enough to access the slip distribution in the case of the landers earthquake since the surface deformations are more sensitive to shallow slip in our configuration the slip amplitude is better resolved near the surface than at depth the resulting slip distribution is in agreement with geological observations at the surface and confirms the heterogeneous nature of the landers earthquake most of the slip occurs at shallow depths on the homestead valley fault second segment with a maximum value of around 7 m another high slip zone is observed on the johnson valley fault first segment at 8 km depth in the second step we invert strong motion data with the a priori final slip amplitude and its uncertainty deduced from geodetic data to constrain the time history of the rupture process this second step emphasizes a strong variation of the temporal development of the earthquake fast rupture front velocities appear within high slip zones and the rupture slows when it encounters a resistance along the fault on average the rupture front propagates with velocities close to the s wave velocity and terminates about 20 s after initiation the large variations in both slip amplitude and rupture velocity suggest that the rupture process is better described by successively breaking asperities than by a pulse propagating with constant velocity

seismic remote sensing for the earthquake source process and near source strong shaking a case study of the october 16 1999 hector mine earthquake a new methodology to automatically determine the earthquake source process and near source strong ground motions using regional and local distance data was used to study the october 16 1999 hector mine earthquake mw7 1 broadband displacement data were inverted for the seismic moment tensor and to resolve the fault plane ambiguity independent of aftershock location and surface faulting information the identified nnw striking fault plane was used to invert for the distribution of fault slip over a planar surface the slip model was used to predict near fault peak ground velocity which was found to agree well with the trinet shakemap and also with near fault observations that were not available at the time of the initial analysis our method if automated is capable of providing near source strong ground motion information within 30 minutes of the earthquake origin time even in cases where there are few near fault recording instruments

diurnal sea breezes force near inertial waves along rottnest continental shelf southwestern australia abstractobservations of upper ocean dynamics close to the critical latitude ratio of the local inertial to diurnal frequency is 0 94 from a range of platforms surface currents using hf radar moored instruments and satellite remote sensing data off southwest australia indicated the presence of energetic near inertial waves generated through the diurnal inertial resonance during the austral summer when southerly winds and land sea breeze lsb system dominated the wind regime strong counterclockwise diurnal motions amplitudes surpassing 0 3 m s 1 penetrated to 300 m depth with diurnal vertical isotherm fluctuations up to 60 m the upward phase propagation speed of 140 m day 1 deep penetration of diurnal currents below the mixed layer and the 180 phase difference between the upper and lower water column suggested that the local lsb system caused the resonant diurnal motions relative vorticity fluctuations along two cross shore transects indicated changes to the local effective coriolis freq

inflation model of uzon caldera kamchatka constrained by satellite radar interferometry observations 1 we analyzed radarsat 1 synthetic aperture radar sar data to compute interferometric sar insar images of surface deformation at uzon caldera kamchatka russia from 2000 to 2003 approximately 0 15 m of inflation occurred at uzon caldera extending beneath adjacent kikhpinych volcano this contrasts with insar data showing no significant deformation during either the 1999 to 2000 or 2003 to 2004 time periods we performed three sets of numerical source inversions to fit insar data from three different swaths spanning 2000 to 2003 the preferred source model is an irregularly shaped pressurized crack dipping 20 to the nw 4 km below the surface the geometry of this solution is similar to the upper boundary of the geologically inferred magma chamber extension of the surface deformation and source to adjacent kikhpinych volcano without an eruption suggests that the deformation is more likely of hydrothermal origin possibly driven by recharge of the magma chamber

evidence of nonlinear elasticity of the crust from the mw7 6 manyi tibet earthquake satellite synthetic aperture radar sar interferometry shows that the magnitude 7 6 manyi earthquake of 8 november 1997 produced a 170 kilometer long surface break with up to 7 meters of left lateral slip reactivating a n76 e quaternary fault in western tibet the radar interferometric map reveals asymmetric along strike displacement profiles between the two sides of the surface rupture a pattern that cannot be explained with linear elastic theory this observation suggests that the elastic moduli of the crust in tension and in compression are different because of the presence of cracks in the crust at shallow depth a model indicates that a ratio of 2 between compressive and tensile elastic moduli can account for the observed asymmetry a ratio that is consistent with laboratory and borehole measurements

characteristics of two counter rotating eddies in the leeuwin current system off the western australian coast abstract a multi disciplinary r v southern surveyor cruise was conducted in october 2003 to quantify upper ocean productivity within two adjacent counter rotating mesoscale eddies an eddy pair off the coast of western australia wa in the southeast indian ocean in this study a combination of satellite data altimeter sea surface temperature and chlorophyll a and shipboard measurements acoustic doppler current profiler adcp and conductivity temperature depth ctd were used to characterize the temporal evolution and spatial structures of the eddy pair satellite data show that the eddy pair evolved from meander structures of the poleward flowing leeuwin current lc in may 2003 and fully detached from the current in late august early september gaussian fits to the adcp velocities show that the anticyclonic eddy had a maximum azimuthal velocity of 65 cm s 1 at 63 km from the eddy centre the apparent radius and the cyclonic eddy had a maximum azimuthal velocity of 60 cm s 1 at the apparent radius of 49 km the mixed layer temperature and salinity properties in the cores of the eddy pair were quite stable over the period of the cruise temperature salinity diagrams indicate that the mixed layer water in the core of the anticyclonic eddy was composed mainly of lc water while in the core of the cyclonic eddy the mixed layer water was similar to surrounding open ocean water the total volume of the lc water retained in the anticyclonic eddy was 5 6 1012 m3 equivalent to 19 days annual mean transport of the lc the chlorophyll a concentration in the surface layer of the anticyclonic eddy lc water was higher than in the cyclonic eddy open ocean water which was likely a result of the entrainment of the productive water from the continental shelf during the eddy formation stage the offshore transport of the chlorophyll a biomass may be important for the pelagic ecosystem off the coast of wa

an improvement of the performance of multiple aperture sar interferometry mai multiple aperture synthetic aperture radar sar interferometry mai enables the measurement of along track surface deformations by means of split beam sar processing this paper examines the effects of flat earth and topographic phases on the mai phase and derives formulas to correct them detailed mai processing steps are introduced and discussed with particular consideration given to coherence improvement as well as to computational efficiency forward and backward looking mai pairs have different perpendicular baselines which play a key role in phase distortion consequently an orbital deviation of only a few centimeters could result in a significant flat earth phase a second order polynomial model was used to estimate the perpendicular baseline difference european remote sensing 2 satellite sar data sets of the hector mine earthquake event in 1999 were used for performance evaluation the proposed processing with the flat earth and topographic phase corrections achieved precision of along track deformation ranging from 10 2 to 13 1 cm two coseismic pairs were compared and the standard deviation of the difference between the two independent measurements was 7 0 cm with a mean difference of 0 24 cm thus the measurement accuracy of mai was improved using flat earth correction and coherence enhancement

slip distribution of the 2015 lefkada earthquake and its implications for fault segmentation this work was partially supported by the uk natural environmental research council nerc through ne k011006 1 ne p008828 1 and the centre for the observation and modelling of earthquakes volcanoes and tectonics comet ga 13 m 031 http comet nerc ac uk

measuring ground displacements from sar amplitude images application to the landers earthquake ers sar amplitude images are utilized to map ground displacements from a sub pixel correlation method it yields a ground two dimensional displacement field with independent measurements about every 128m in azimuth and 250m in range the accuracy depends on the characteristics of the images for the landers test case the 1 uncertainty is 0 8m in range and 0 4m in azimuth we show that this measurement provides a map of major surface fault ruptures accurate to better than 1km and information on coseismic deformation comparable to the 92 gps measurements available although less accurate this technique is more robust than sar interferometry and provides complementary information since interferograms are only sensitive to the displacement in range

physical and chemical signatures of a developing anticyclonic eddy in the leeuwin current eastern indian ocean a multidisciplinary cruise aboard the r v southern surveyor was conducted in may 2006 to sample a developing anticyclonic eddy of the leeuwin current off western australia the eddy formed from a meander of the leeuwin current in mid april 2006 and remained attached to the current until mid august in this study a combination of satellite data altimeter sea surface temperature and chlorophyll a and shipboard measurements acoustic doppler current profiler and conductivity temperature depth were used to characterize the physical and chemical signatures of the eddy the temperature salinity properties of the mixed layer waters within the anticyclonic eddy and on the shelf were both connected to that of the leeuwin current indicating the water mass in the eddy is mainly derived from the leeuwin current and the modified leeuwin current water on the shelf above the salinity maximum near the eddy center there was a regionally significant concentration of nitrate 0 9 mol l 1 and the maximum 2 mol l 1 was at 150 in depth below the photic zone nitrification within the eddy and or local upwelling due to the forming eddy could be responsible for this high concentration of nitrate near the eddy center which potentially makes the eddy a relatively productive feature in the leeuwin current

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

estimating source parameters from deformation data with an application to the march 1997 earthquake swarm off the izu peninsula japan we have applied two monte carlo optimization techniques simulated annealing and random cost to the inversion of deformation data for fault and magma chamber geometry these techniques involve an element of randomness that permits them to escape local minima and ultimately converge to the global minimum of misfit space we have tested the monte carlo algorithms on two synthetic data sets we have also compared them to one another in terms of their efficiency and reliability we have applied the bootstrap method to estimate confidence intervals for the source parameters including the correlations inherent in the data additionally we present methods that use the information from the bootstrapping procedure to visualize the correlations between the different model parameters we have applied these techniques to gps tilt and leveling data from the march 1997 earthquake swarm off of the izu peninsula japan using the two monte carlo algorithms we have inferred two sources a dike and a fault that fit the deformation data and the patterns of seismicity and that are consistent with the regional stress field

thrust faulting and 3d ground deformation of the 3 july 2015 mw 6 4 pishan china earthquake from sentinel 1a radar interferometry abstract boosted by the launch of sentinel 1a radar satellite from the european space agency esa we now have the opportunity of fast full and multiple coverage of the land based deformation field of earthquakes here we use the data to investigate a strong earthquake struck pishan western china on july 3 2015 the earthquake fault is blind and no ground break features are found on site thus synthetic aperture radar sar data give full play to its technical advantage for the recovery of coseismic deformation field by using the sentinel 1a radar data in the interferometric wide swath mode we obtain 3 tracks of insar data over the struck region and resolve the 3d ground deformation generated by the earthquake then the line of sight los insar data are inverted for the slip distribution of the seismogenic fault the final model shows that the earthquake is completely blind with pure thrust motion the maximum slip is 0 48 m at a depth of 7 km consistent with the depth estimate from seismic reflection data in particular the inverted model is also compatible with a south dipping fault ramp among a group of fault interfaces detected by the seismic reflection profile over the region the seismic moment obtained equals to a mw 6 4 earthquake the pishan earthquake ruptured the frontal part of the thrust ramps under the slik anticline and unloaded the coulomb stress of them however it may have loaded stress to the back thrust above the thrust ramps by 1 4 bar and promoted it for future failure moreover the stress loading on the west side of the earthquake fault is much larger than that on the east side indicating a higher risk for failure to the west of the zepu fault

coseismic deformation of the 2001 mw 7 8 kokoxili earthquake in tibet measured by synthetic aperture radar interferometry the 14 november 2001 m w 7 8 kokoxili earthquake ruptured more than 400 km of the westernmost stretch of the left lateral kunlun fault in northern tibet interferometric synthetic aperture radar data from descending orbits along four adjacent tracks covering almost the entire rupture and 1 m pixel ikonos satellite images are used to map the rupture geometry and the surface displacements produced by the event interferograms are then inverted to solve for coseismic slip on the fault at depth the radar data show that the rupture connected the heituo fault where the earthquake initiated to the main kunlun fault cutting across a pull apart trough in between the two strike slip faults the fault model includes two vertical sections extending to a depth of 20 km and discretized into 5 km 5 km patches using a nonnegative least squares method that includes an appropriate degree of smoothing we solve for the left lateral slip on each fault patch our solution shows that the largest slip occurred at depths between 0 and 5 km reaching 8 m in two areas 200 and 250 km east of the earthquake epicenter significant slip took place below 10 km at both ends of the rupture slip appears to have been highly variable along the fault defining six sections of major moment release these sections correspond to six subsegments of the kunlun fault system defined from the surface morphology of the fault this suggests that fault geometry exerted a predominant influence on controlling the rupture propagation

delayed triggering of the 1999 hector mine earthquake by viscoelastic stress transfer stress changes in the crust due to an earthquake can hasten the failure of neighbouring faults and induce earthquake sequences in some cases1 2 3 4 5 the 1999 hector mine earthquake in southern california magnitude 7 1 occurred only 20 km from and 7 years after the 1992 landers earthquake magnitude 7 3 this suggests that the hector mine earthquake was triggered in some fashion by the earlier event but uncertainties in the slip distribution and rock friction properties associated with the landers earthquake have led to widely varying estimates of both the magnitude and sign of the resulting stress change that would be induced at the location of the hector mine hypocentre with estimates varying from 1 4 bar ref 6 to 0 5 bar ref 7 more importantly coseismic stress changes alone cannot satisfactorily explain the delay of 7 years between the two events here we present the results of a three dimensional viscoelastic model that simulates stress transfer from the ductile lower crust and upper mantle to the brittle upper crust in the 7 years following the landers earthquake using viscoelastic parameters that can reproduce the observed horizontal surface deformation following the landers earthquake our calculations suggest that lower crustal or upper mantle flow can lead to postseismic stress increases of up to 1 2 bar at the location of the hector mine hypocentre during this time period contributing to the eventual occurrence of the 1999 hector mine earthquake these results attest to the importance of considering viscoelastic processes in the assessment of seismic hazard8 9 10 11

postseismic rebound in fault step overs caused by pore fluid flow near field strain induced by large crustal earthquakes results in changes in pore fluid pressure that dissipate with time and produce surface deformation synthetic aperture radar sar interferometry revealed several centimeters of postseismic uplift in pull apart structures and subsidence in a compressive jog along the landers california 1992 earthquake surface rupture with a relaxation time of 270 45 days such a postseismic rebound may be explained by the transition of the poisson s ratio of the deformed volumes of rock from undrained to drained conditions as pore fluid flow allows pore pressure to return to hydrostatic equilibrium

viscoelastic flow in the lower crust after the 1992 landers california earthquake space geodesy showed that broad scale postseismic deformation occurred after the 1992 landers earthquake three dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation whereas viscoelastic flow can explain the horizontal and near vertical displacements the viscosity of a weak about 10 km thick layer in the lower crust beneath the rupture zone that controls the rebound is about 10 18 pascal seconds the viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the basin and range province and it may be used for the analysis of earthquake hazard

viscoelastic stress triggering of the 1999 hector mine earthquake by the 1992 landers earthquake the 1999 mw 7 1 hector mine earthquake occurred only 20 km from the 1992 mw 7 3 landers earthquake fault the close spacing between the two earthquakes suggests that the landers earthquake trigger the hector mine event based on an elastic half space model scientists from the usgs scec and cdmg 2000 have found a negative coulomb stress change at the hector mine hypocenter due to landers this negative stress change is inconsistent with the hypothesis of static stress triggering in this paper i show evidence of stress triggering of the hector mine earthquake by landers due to a process governed by viscoelastic flow in the lower crust this visoelastic flow has produced broad scale postseismic rebound observed by gps and insar measurements the result of this study is that viscoelastic flow has significantly modified the regional stress field in the mojave desert after the landers earthquake the evolving stress field including viscoelastic flow has gradually moved the coulomb stress change at the hector mine hypocenter to a positive level the increase in coulomb stress exceeded 1 bar right before the hector mine earthquake bringing the hector mine ruptures to the proximity of catastrophic failure

nutrients plankton and productivity in a warm core ring in the western gulf of mexico argos drift buoy trajectory data showed that a region of anticyclonic circulation about 100 km in diameter was present over the upper continental slope of the nw corner of the gulf of mexico in september october 1988 guided by these data texas am however a maximum of only 36 54 psu at t 25 5 in contrast to as much as 36 88 psu at this density surface in a fresh ring indicated that this feature had spent many months in the western gulf since its separation from the loop current biologically the warm core ring was oligotrophic its surface waters were generally depleted in nitrate to depths of more than 100 m and chlorophyll standing stocks 20 mg m 2 primary productivity 0 4 mg c m 3 h 1 and zooplankton biomass only 4 ml 100 m 3 day and 6 ml 100 m 3 night in the upper 200 m were all extremely low deployments of floating sediment traps within the feature on two consecutive days intercepted fluxes of only 10 20 mg dry weight m 2 d 1 at 50 m and at 100 m by comparison at ring periphery where there was measurable nitrate at 100 m 0 2 1 g at l 1 chlorophyll standing stocks and primary production in the surface mixed layer were 1 5 2 times higher

an active ring fault detected at tendurek volcano by using insar 1 although ring faults are present at many ancient deeply eroded volcanoes they have been detected at only very few modern volcanic centers at the so far little studied tendurek volcano in eastern turkey we generated an ascending and a descending insar time series of its surface displacement field for the period from 2003 to 2010 we detected a large 105 km2 region that underwent subsidence at the rate of 1 cm yr during this period source modeling results show that the observed signal fits best to simulations of a near horizontal contracting sill located at around 4 5 km below the volcano summit intriguingly the residual displacement velocity field contains a steep gradient that systematically follows a system of arcuate fractures visible on the volcano s midflanks rapideye satellite optical images show that this fracture system has deflected holocene lava flows thus indicating its presence for at least several millennia we interpret the arcuate fracture system as the surface expression of an inherited ring fault that has been slowly reactivated during the detected recent subsidence these results show that volcano ring faults may not only slip rapidly during eruptive or intrusive phases but also slowly during dormant phases

the 1994 sefidabeh eastern iran earthquakes revisited new evidence from satellite radar interferometry and carbonate dating about the growth of an active fold above a blind thrust fault in 1994 three shallow earthquakes of mw 6 occurred close together on blind thrusts near sefidabeh in eastern iran in an earlier study of the teleseismic waveforms the geomorphology and the faulting in the epicentral region it was suggested that these earthquakes were associated with the growth of a ridge above a blind thrust fault system whose activity could be detected by its effect on the surface drainage in this study we present a sar interferogram that precisely determines the location and amount of coseismic surface displacements showing that the earthquakes in the sefidabeh sequence probably occurred on en echelon fault segments associated with three stepping ridges we also present u th dates of 100 ka for lake deposits uplifted by the growing ridge from the cumulative dated uplift and knowledge of the surface displacements due to an earthquake sequence we estimate that 120 such events have occurred in the past 100 ka with an average recurrence interval of 830 yr and an average convergence rate of 1 5 mm yr 1 on the sefidabeh thrust each estimate has an uncertainty of a factor of two either way we argue that the sefidabeh fault originally formed by coalescence of many small fault segments and has grown in length at about 2 cm yr 1 in the past 100 ka though the coseismic surface deformation observed in the sar interferogram closely resembles folding the overall topography does not because of inherited topography associated with earlier geological deformation in spite of this the activity of the buried thrust fault can easily be detected by its effect on the surface drainage a significant lesson when interpreting landscapes that are not entirely due to the present day deformation

the coseismic geodetic signature of the 1999 hector mine earthquake the m 7 1 hector mine earthquake ruptured the lavic lake fault near twentynine palms ca at 09 46 utc october 16 1999 because it occurred near the eastern edge of the southern california integrated gps network scign a network of permanent continuously recording gps receivers for measuring the crustal deformation field around los angeles ca it was possible to determine the deformation associated with the earthquake with unprecedented speed and reliability thirty four stations recorded displacements over the 3 sigma level the displacements measured with gps can be modeled by a fault 46 2 2 6 km long 8 2 1 0 km wide striking 330 dipping 84 east with 301 36 cm right lateral strike slip and 145 36 cm of east up dip slip yielding a potency of 1 3 km and geodetic moment of 3 8 1026 dyne cm the trace and dip of the model fault is consistent with the observed ground rupture and seismic focal mechanisms

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

environmental controls at multiple scales for the western pacific an okinawan case study in this study the principal controls on the coastal environment around the pacific island of okinawa typical of the many mountainous islands of the sub tropical and tropical northwest pacific in the arc from melanesia to the ryukyu islands are investigated two principal satellite remote sensing data products were used to observe properties at regional scale and in the okinawan coastal zone 1 avhrr sea surface temperature sst for 1985 2006 and 2 a seawifs ocean colour variable to estimate combined sediment and chlorophyll a loadings for 1998 2006 along with direct observations e g climatological data river discharge suspended sediment and typhoon tracks analysis suggested that coastal sst is strongly influenced by the outer ocean sst indicating a regional control however the local winds with associated summer rainfall and copious sediment laden run off had a significant secondary impact typhoons are also an important factor leading to ocean colour variation along the western coastal zone of okinawa the winter east asian monsoon causes significant upwelling and seafloor sediment removal while terrestrial impact is a significant secondary control in summer on ocean colour variability via sediment laden river run off previously noted changes in the magnitude of extreme rainfall events in the area suggest that sediment delivery to the coastal zones of islands in the region has been increasing in recent decades providing a combined climate and terrestrial impact on the coastal environment although typhoons and heavy rainfall are episodic events appropriate land management on the many hilly and mountainous islands of the sub tropical northwestern pacific is needed if such events are not to lead to deterioration and decrease of resilience of coastal ecosystems

adaptive regularization of earthquake slip distribution inversion abstract regularization is a routine approach used in earthquake slip distribution inversion to avoid numerically abnormal solutions to date most slip inversion studies have imposed uniform regularization on all the fault patches however adaptive regularization where each retrieved parameter is regularized differently has exhibited better performances in other research fields such as image restoration in this paper we implement an investigation into adaptive regularization for earthquake slip distribution inversion it is found that adaptive regularization can achieve a significantly smaller mean square error mse than uniform regularization if it is set properly we propose an adaptive regularization method based on weighted total least squares wtls this approach assumes that errors exist in both the regularization matrix and observation and an iterative algorithm is used to solve the solution a weight coefficient is used to balance the regularization matrix residual and the observation residual an experiment using four slip patterns was carried out to validate the proposed method the results show that the proposed regularization method can derive a smaller mse than uniform regularization and resolution based adaptive regularization and the improvement in mse is more significant for slip patterns with low resolution slip patches in this paper we apply the proposed regularization method to study the slip distribution of the 2011 mw 9 0 tohoku earthquake the retrieved slip distribution is less smooth and more detailed than the one retrieved with the uniform regularization method and is closer to the existing slip model from joint inversion of the geodetic and seismic data

measuring near field coseismic displacements from sar images application to the landers earthquake we describe a procedure to compute sar interferograms based on the compensation of the images mis registrations due to the ground deformation and on a specific adaptive filtering to improve the snr in the measurement where displacement gradients are large applied to the landers earthquake case the registration reduces the phase noise by 20 rms near the fault and the interferogram reveals fringes that would not show out otherwise the interferogram is validated by comparison in the far field with a gps edm based model the inferred displacement field shows discontinuities that follow the fault within few hundred meters close to the fault the measured displacements differ significantly from that predicted by elastic modeling of the far field data interferometry and measurements derived from the images amplitude offsets appear to be complementary techniques providing original measurements that may help to reconcile seismological and geodetic models of coseismic deformation with measurements of fault slip at the surface

evolution movement and decay of warm core leeuwin current eddies abstract characteristics of eddies originating in the leeuwin current lc have been investigated using 10 day sea level anomaly maps of combined topex poseidon and ers altimeter data for the period 1995 2000 during these 6 years 37 long lived anticyclonic eddies were tracked from the west coast of australian to 90 e between three and nine eddies were spawned each year and their trajectories are described in detail most long lived eddies are generated in may june when the lc is most intense and at three preferred locations 20 21 5 s 24 25 s and 28 31 s the temporal evolution and latitudinal variations of the sea level anomalies and their radius and drift speed are discussed topography plays an important role in the evolution and structure of the eddies interactions with topography can induce splitting or merging of eddies which further affects the eddy decay

the combined inversion of seismic and geodetic data for the source process of the 16 october 1999 mw 7 1 hector mine california earthquake we investigate the source process of the m w 7 1 hector mine earthquake by inverting broadband regional and local seismic displacement waveforms com bined with global positioning system gps and synthetic aperture radar interfer ometry insar geodetic measurements we find that the three data sets individually produce remarkably similar slip distributions over a multisegment fault a simulta neous inversion of the three data sets is presented and the sensitivity of the combined inversion to the weighting of the three independent data sets is examined the results indicate that the overall length of the fault that slipped is 42 km with a peak slip of 5 50 m and total scalar seismic moment of 6 8 10 19 n m the majority of slip is located on the western branch of the lavic lake fault to the northwest of the hypo center although the overall rupture is bilateral with appreciable slip on the bullion fault to the southeast some slip is located on an eastern branch of the lavic lake fault an apparent bifurcation which is also evident from aftershock locations the average slip and stress drops are 2 70 1 62 1 60 m and 78 36 and 55 bars for the western lavic lake the eastern lavic lake and bullion faults respectively the results also indicate that the overall rupture process is relatively slow which is char acterized by a several second delay before the onset of significant slip a 1 8 km sec rupture velocity of the primary asperity and long spatially variable dislocation rise times

time dependent model of creep on the hayward fault from joint inversion of 18 years of insar and surface creep data 1 spatial and temporal variations of aseismic fault creep influence the size and timing of large earthquakes along partially coupled faults to solve for a time dependent model of creep on the hayward fault we invert 18 years of surface deformation data 1992 2010 obtained by interferometric processing of 52 and 50 sar images acquired by the ers1 2 and envisat satellites respectively and surface creep data obtained at 19 alinement and 4 creepmeter stations for multi temporal analysis of the sar data we developed a method for identifying stable pixels using wavelet multi resolution analysis we also implement a variety of wavelet based filters for reducing the effects of environmental artifacts using a reweighted least squares approach we inverted the interferometric data to generate a time series of surface deformation over the san francisco bay area with a precision of better than a few millimeters to jointly invert the insar displacement time series and the surface creep data for a time dependent model of fault creep we use a robust inversion approach combined with a kalman filter the time dependent model constrains a zone of high slip deficit that may represent the locked rupture asperity of past and future m 7 earthquakes we identify several additional temporal variations in creep rate along the hayward fault the most important one being a zone of accelerating slip just northwest of the major locked zone we estimate that a slip rate deficit equivalent to mw 6 3 6 8 has accumulated on the fault since the last event in 1868

on the derivation of coseismic displacement fields using differential radar interferometry the landers earthquake we present a map of the coseismic displacement field resulting from the landers california june 28 1992 earthquake derived using data acquired from an orbiting high resolution radar system we achieve results more accurate than previous space studies and similar in accuracy to those obtained by conventional field survey techniques data from the ers 1 synthetic aperture radar instrument acquired in april july and august 1992 are used to generate a high resolution wide area map of the displacements the data represent the motion in the direction of the radar line of sight to centimeter level precision of each 30 m resolution element in a 113 km by 90 km image our coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake fine structure observed as displacement tiling in regions several kilometers from the fault appears to be the result of local surface fracturing comparison of these data with global positioning system and electronic distance measurement survey data yield a correlation of 0 96 thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format the technique we use is 1 more automatic 2 more precise and 3 better validated than previous similar applications of differential radar interferometry since we require only remotely sensed satellite data with no additional requirements for ancillary information the technique is well suited for global seismic monitoring and analysis

subsidence derived volumetric strain models for mapping extensional fissures and constraining rock mechanical properties in the san joaquin valley california large scale subsidence due to aquifer overdraft is an ongoing hazard in the san joaquin valley subsidence continues to cause damage to infrastructure and increases the risk of extensional fissures here we use insar derived vertical land motion vlm to model the volumetric strain rate due to groundwater storage change during the 2007 2010 drought in the san joaquin valley central valley california we then use this volumetric strain rate model to calculate surface tensile stress in order to predict regions that are at the highest risk for hazardous tensile surface fissures we find a maximum volumetric strain rate of 232 microstrain yr at a depth of 0 to 200 m in tulare and kings county california the highest risk of tensile fissure development occurs at the periphery of the largest subsiding zones particularly in tulare county and merced county finally we assume that subsidence is likely due to aquifer pressure change which is calculated using groundwater level changes observed at 300 wells during this drought we combine pressure data from selected wells with our volumetric strain maps to estimate the quasi static bulk modulus k a poroelastic parameter applicable when pressure change within the aquifer is inducing volumetric strain this parameter is reflective of a slow deformation process and is one to two orders of magnitude lower than typical values for the bulk modulus found using seismic velocity data the results of this study highlight the importance of large scale high resolution vlm measurements in evaluating aquifer system dynamics hazards associated with overdraft and in estimating important poroelastic parameters

static stress impact of the 1992 landers earthquake sequence on nucleation and slip at the site of the 1999 m 7 1 hector mine earthquake southern california the proximity in time 7 years and space 20 km between the 1992 m 7 3 landers earthquake and the 1999 m 7 1 hector mine event suggests a possible link between the quakes we thus calculated the static stress changes following the 1992 joshua tree landers big bear earthquake sequence on the 1999 m 7 1 hector mine rupture plane in southern california resolving the stress tensor into rake parallel and fault normal components and comparing with changes in the post landers seismicity rate allows us to estimate a coefficient of friction on the hector mine plane seismicity following the 1992 sequence increased at hector mine where the fault was unclamped this increase occurred despite a calculated reduction in right lateral shear stress the dependence of seismicity change primarily on normal stress change implies a high coefficient of static friction 0 8 we calculated the coulomb stress change using 0 8 and found that the hector mine hypocenter was mildly encouraged 0 5 bars by the 1992 earthquake sequence in addition the region of peak slip during the hector mine quake occurred where coulomb stress is calculated to have increased by 0 5 1 5 bars in general slip was more limited where coulomb stress was reduced though there was some slip where the strongest stress decrease was calculated interestingly many smaller earthquakes nucleated at or near the 1999 hector mine hypocenter after 1992 but only in 1999 did an event spread to become a m 7 1 earthquake

a non linear geodetic data inversion using abic for slip distribution on a fault with an unknown dip angle summary we have developed a method of geodetic data inversion for slip distribution on a fault with an unknown dip angle a common strategy for obtaining slip distribution in previous studies is to first determine the fault geometry by minimizing the square misfit under the assumption of a uniform slip on a rectangular fault and then apply the usual linear inversion technique to estimate a slip distribution on the determined fault it is not guaranteed however that the fault determined under the assumption of a uniform slip gives the best fault geometry for a spatially variable slip distribution the inverse problem is non linear for cases with unknown fault geometries but the non linearity of the problems is actually weak when we can assume the fault surface to be a flat plane in particular when a clear trace of coseismic faults is observed on the earth s surface only the dip angle is an unknown parameter to determine the fault geometry then we regarded the dip angle as an hyperparameter that prescribed the structure of parametric models and obtained the best estimate of the dip angle using akaike s bayesian information criterion abic with the best estimate of the dip angle we can obtain the slip distribution on the fault based on the maximum likelihood principle we applied the method to the insar data of the 1995 dinar turkey earthquake and obtained a much lower dip angle than the previous analyses

linking synoptic forcing and local mesoscale processes with biological dynamics off ningaloo reef 1 a hydrographic survey offshore ningaloo reef north west australia in austral autumn 2010 revealed relatively stable subsurface water masses in the region despite the influence of interannual variability of the leeuwin current lc the surface water mass seems slightly more variable at seasonal time scale probably due to various contributions of the geographically distinct source waters of the lc a subsurface nitrate maximum 110 230 m a prominent feature of the ningaloo area during autumn was consistently observed within different water masses tightly coupled variations of subsurface nitrate and oxygen at small vertical scale suggest it is due to local in situ remineralization of organic matter likely to accumulate along sharp physical interfaces and possibly favored by injections of oxygenated subsurface waters offshore enhanced levels of surface chlorophyll a within the downwelling favorable lc are associated with deeper mixed layer depth eroding the shallow source of nutrients close to the continental shelf these nutrients are observed to be efficiently uplifted within the core of quasi persistent topographically trapped submesoscale cyclonic eddies dominated by nonlinear effects a wind driven coastal upwelling event occurred in autumn and was characterized by a relatively deep source 100 150 m coinciding with the subsurface maximum of nutrients thus promoting coastal productivity locally and farther north by alongshore advection within the ningaloo current

insight into the 2016 menyuan m w 5 9 earthquake with insar a blind reverse event promoted by historical earthquakes in 2016 the mw 5 9 menyuan earthquake occurred at the western end of the tianzhu seismic gap in the middle segment of the left lateral strike slip haiyuan fault system studying the focal mechanism of the menyuan earthquake and its correlation with historical seismicity is of great significance in understanding the tectonic style of the haiyuan fault system and assessing the tianzhu gap seismic risk using sentinel 1a radar imagery we obtain the coseismic deformation field of the menyuan earthquake in the los direction and invert the deformation field slip distribution model based on the interseismic deformation field reflected by gps data and the relocated results of aftershocks provided by previous studies we then analyze the seismogenic nodal plane of the menyuan earthquake and consider the west dipping model to be the most likely seismogenic solution the west dipping model indicates that the average slip of the menyuan earthquake is 0 41 m and the average rake angle is 68 with a magnitude of mw 5 905 considering the historical strong earthquakes and viscoelastic layered crust the results from coulomb failure stress modeling indicate that the coulomb stress loading caused by the historical strong events promoted the occurrence of the 2016 menyuan earthquake both the low seismicity within the tianzhu gap and the cluster phenomenon of medium earthquakes on the lao hu shan lhs and leng long ling lll faults have strong correlations with the stress change distribution resulting from the historical strong earthquakes a series of medium events occurring on the north side of the lll fault represented by the 2016 menyuan earthquake would raise the seismic risk on the western end of the tianzhu gap

fault geometry and slip distribution of the 2013 mw 6 6 lushan earthquake in china constrained by gps insar leveling and strong motion data

the 2006 march 25 fin earthquakes iran insights into the vertical extents of faulting in the zagros simply folded belt summary we investigate the depth of faulting and its connection with surface folding in the zagros simply folded belt of iran our focus is a sequence of earthquakes mw 5 7 5 5 5 2 5 0 4 9 that struck the fin region in the south eastern simply folded belt on 2006 march 25 modelling ground displacements measured with radar interferometry we find that either n or s dipping model reverse faults can reproduce the observed fringe patterns despite the uncertainty in fault orientation we can constrain the vertical extents of rupture to between a top depth of 5 6 km and a bottom depth of 9 10 km consistent with the 8 km centroid depth of the largest earthquake we suggest that the faulting ruptured the thick competent group of paleozoic and mesozoic conglomerates and platform carbonates which makes up the lower part of the sedimentary cover the rupture probably terminated within the precambrian hormuz salt at its base and the cretaceous gurpi marls at its top these mechanically weak layers act as barriers to rupture separating faulting within the competent group from deformation in the layers above and below the pattern of coseismic surface uplift is centred on the common limb of the fin syncline and guniz anticline but is oblique by 20 to the trend of these open symmetric whaleback folds and also overlaps a section of the fin syncline axis these observations suggest that locally surface folding is decoupled from the underlying reverse faulting although the fin syncline and guniz anticline are symmetric structures some other nearby folds show a strong asymmetry with steep or overturned southern limbs consistent with growth above n dipping reverse faults this suggests that the simply folded belt contains a combination of forced folds and detachment folds we also investigate the distribution of locally recorded aftershocks in the weeks following the main earthquakes most of these occurred at depths of 10 30 km with a particularly high concentration of events at 20 25 km these aftershocks therefore lie within the crystalline basement rather than the sedimentary cover and are vertically separated from the main rupture this study confirms earlier suggestions that earthquakes of mw 5 6 are capable of being generated within the thick competent group of paleozoic and mesozoic sediments as well as in the basement below the hormuz salt formation