atmospheric vortex streets on a radarsat sar image we analyze the sea surface imprint of two atmospheric vortex streets avs s observed on a radarsat a canadian earth observation satellite synthetic aperture radar sar image of the aleutian islands in the western gulf of alaska acquired on may 5 1999 the radarsat sar instrument is operated in c band with hh polarization these avs s are interpreted as the atmosphere analog of classic von karman vortex streets the sar image along with radiosonde data and surface weather charts reveal that the avs lengths are 196 km and 111 km for avs 1 and avs 2 respectively there are five and two pairs of vortices within each avs the vortex shedding period is estimated to be between 35 and 48 minutes the vortex shedding started approximately 4 6 and 2 6 hours prior to the sar imaging time for avs 1 and avs 2 respectively there are seven and three pairs of vortices within the respective avs s the vortex tangential velocity is estimated to be between 1 7 and 2 3 m s and the energy dissipated during the vortex lifetime is estimated to be between 24 9 and 23 6 j m

a linear regression framework for predicting subsurface geometries and displacement rates in deep seated slow moving landslides abstract a new numerical integration linear regression tool is used to investigate kinematic behavior in deep seated sliding surface deeper than 3 m mass movements the technique is developed in the context of real inclinometer records and numerical integration using nine inclinometer case histories from four well documented large landslides carrot river montebestia karya village and pietrapertosa axial metric subsurface geometric deformation rates are predicted and compared for four different case studies from the literature a reactivated composite extremely slow earth slide earthflow a reactivated composite extremely slow debris slide rock fall an active composite very slow earth slide earth flow and a reactivated complex slow earth slide earth spread sensitivity analysis based on sliding surface depth to length d l ratios show that the mobility of these slow moving masses is closely dependent on the mode of sliding the results also show that short term and long term dynamics of slow moving landslides can be captured by geometrical patterns because the parameter determined is a geometric property the technique used in the investigation can be applied in new landslide problems independent of local conditions and triggering mechanisms within the confines of the stipulated boundary conditions hence with this framework also unrelated landslide problems can be analyzed and compared as demonstrated herein additionally this approach is useful for two dimensional reconstructions of subsurface displacement and velocity profiles and thus may act as a precursor to detailed field investigation programs warning systems and mitigation projects at minimal costs

island wakes and headland eddies a comparison between remotely sensed data and laboratory experiments island wakes and headland eddies in coastal waters are identified from spaceborne and airborne remotely sensed imagery in the visible wavelengths the imagery were obtained for the bristol and english channels united kingdom which are characterized by high tidal currents and levels of turbidity suspended matter in the surface waters is used as a passive tracer for the flow features scaling parameters e g the reynolds ekman and rossby numbers obtained from the depth averaged equation of motion are presented based upon information on oceanographic conditions at the times of the overpasses the parameters are compared then with data obtained from laboratory model investigations presented by other experimenters in the published literature the remotely sensed data demonstrate that in coastal waters with nonuniform obstacles and bathymetry for a given ekman number the flow regimes occur at a lower rossby number than might be expected from laboratory experiments in the absence of a method for the accurate determination of the horizontal eddy viscosity hence the reynolds number it is concluded that an island wake parameter wolanski et al 1984a should be adopted to describe such features in coastal waters

island wakes in deep water abstract density stratification and planetary rotation distinguish three dimensional island wakes significantly from a classical fluid dynamical flow around an obstacle a numerical model is used to study the formation and evolution of flow around an idealized island in deep water i e with vertical island sides and surface intensified stratification and upstream flow focusing on wake instability coherent vortex formation and mesoscale and submesoscale eddy activity in a baseline experiment with strong vorticity generation at the island three types of instability are evident centrifugal barotropic and baroclinic sensitivities are shown to three nondimensional parameters the reynolds number re rossby number ro and burger number bu the dependence on re is similar to the classical wake in its transition to turbulence but in contrast the island wake contains coherent eddies no matter how large the re value when re is large enough the shear layer at the island is so narrow that the ver

decalcification and residual shear strength reduction in fuller s earth clay analyses of borehole samples at 1 m intervals through the fuller s earth succession at bath reveal an inverse correlation between calcite content and atterberg limits the calcareous component of t

fault slip distribution of two june 2000 m w 6 5 earthquakes in south iceland estimated from joint inversion of insar and gps measurements abstract we present the first detailed estimates of co seismic slip distribution on faults in the south iceland seismic zone sisz an area of bookshelf tectonics we have estimated source parameters for two m w 6 5 earthquakes in the sisz on june 17 and 21 2000 through a joint inversion of insar and gps measurements our preferred model indicates two simple 15 km long near vertical faults extending from the surface to approximately 10 km depth the geometry is in good agreement with the aftershock distribution the dislocations experienced pure right lateral strike slip reaching maxima of 2 6 m and 2 9 m for the june 17 and 21 events respectively we find that the distribution of slip with depth may be correlated to crustal layering with more than 80 of the total geometric moment release occurring in the uppermost 6 km according to the distributed slip model the middle and upper crust appears to be more apt to generate large displacements than the lower crust the geodetic estimates of seismic moments are 4 4 10 18 nm m w 6 4 and 5 0 10 18 nm m w 6 5 the total moment released by the two events equals that generated by several decades of plate motion in the area but is only a fraction of the moment accumulated in the area since the last major earthquake in 1912

the effect of calcium ions in pore water on the residual shear strength of kaolinite and sodium montmorillonite this paper reviews the literature concerning the effects of pore water chemistry on residual shear strength it presents the results of index limit and residual shear strength testing undertaken on kaolinite and sodium montmorillonite using concentrations of calcium chloride similar to the calcium levels measured in groundwaters obtained from landslipped calcareous mudrock of the fuller s earth formation the residual shear strength of the sodium montmorillonite increased markedly for the sample treated and tested with 80 mg 1 cat compared with that tested with deionized water greater concentra tions of ca2 resulted in only a marginal further increase in the residual shear strength these changes were also reflected in the interpreted parameters or and c the liquid limit of the montmorillonite decreased dramatically when the samples were treated with 80 mg 1 ca2 and this effect persisted and or was slightly enhanced when the concentration of ca2 was increased the residual shear strength

sub mesoscale ocean vortex trains in the luzon strait 1 this study uses the argos satellite tracked surface drifter trajectory data and envisat european satellite asar advanced synthetic aperture radar images to illustrate the ocean vortex trains ovt in the luzon strait two cases that occurred in the northwest of babuyan island are observed the first train of three cyclonic vortices showed up on drifter trajectories from 20 to 20 5 n and from 120 to 121 e and the second consisting of five pairs of cyclonic anticyclonic vortices occurred on the upstream side of the first one from 19 5 to 20 0 n and from 121 0 to 122 0 e and showed up on the asar images acquired on 19 november 2006 the total length of the vortex train axis reaches about 250 km all vortices propagate northwestward 315 tn the mean angular velocity is 2 07 0 18 10 5 s 1 theoretical models of ocean vortex radar image derived from radar imaging theories are used to extract dynamical parameters from asar imagery signatures which include the distance between two consecutive vortices and that between two rows of vortices of 22 6 1 9 km and 8 2 1 2 km respectively the maximum rotational velocity radius as 4 70 km and the vortex rotational angular velocity 3 10 5s 1 dynamical analyses give the mean velocity of the current of 0 65 ms 1 and the propagation velocity of the vortex 0 58 ms 1 the vortex shedding rate is estimated as 2 57 10 5 s 1 the reynolds number is estimated as 50 to 500 for the individual vortex and the vortex train the rossby numbers are o 0 4 and o 0 5 respectively implying that both vortex and vortex train observed in the luzon strait have a sub mesoscale nature this study also reveals a strong current with an average surface current velocity of around 0 7 ms 1 and the direction of around 315 tn flowing directly from the pacific to scs passing through the southern luzon strait the mean flow velocity can be calculated using methods developed in this study and ovt dynamical models this information may provide more insight to the circulation systems in the area including the origin of kuroshio

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

detection of monsoonal phytoplankton blooms in luzon strait with modis data abstract the luzon strait experiences a seasonal surge of phytoplankton based on ocean color data to examine the timing and position of the bloom daily modis chlorophyll data 2002 2005 were acquired and analyzed supporting data such as modis sst and nlw bands quikscat wind data river discharge and bathymetry were also used and processed in order to investigate the possible driving forces behind the bloom occurrence results show that chlorophyll concentration in the luzon strait dramatically increases during ne monsoon reaching to approximately 2 0 mg m 3 highest chlorophyll concentration is observed near the western slope of the luzon strait the monsoonal bloom in the luzon strait is likely due to upwelling and can be possibly associated with the interaction of the northward flowing luzon coastal current with the westward intrusion of kuroshio during ne monsoon the positive wind stress curl also contributes to this occurrence the influence of cagayan river is only limited within few kilometers from the river mouth

a hypothesis for delayed dynamic earthquake triggering 1 it s uncertain whether more near field earthquakes are triggered by static or dynamic stress changes this ratio matters because static earthquake interactions are increasingly incorporated into probabilistic forecasts recent studies were unable to demonstrate all predictions from the static stress change hypothesis particularly seismicity rate reductions however current dynamic stress change hypotheses do not explain delayed earthquake triggering and omori s law here i show numerically that if seismic waves can alter some frictional contacts in neighboring fault zones then dynamic triggering might cause delayed triggering and an omori law response the hypothesis depends on faults following a rate state friction law and on seismic waves changing the mean critical slip distance dc at nucleation zones

foreshocks aftershocks and remote triggering in quasi static fault models 1 we present the results of time space analysis of synthetic catalogs generated using a quasi static discrete fault model that is governed by rate and state dependent friction these analyses reveal that increase in the postmain shock earthquake production rate occurs over an area surrounding the main shock rupture with dimensions that are several times larger than the main shock dimensions we show that the increase in seismicity rate far from the main shock where the static stress changes imposed by the main shock were small is a consequence of multiple stress transfers and that the very distant aftershocks are not directly triggered by the main shock but that instead they are aftershocks of previous aftershocks snapshots of the fault state at progressive times prior to each main shock show that the regions which accelerated toward failure covered areas that were much larger than the final size of the main shock ruptures as a result as time approached the main shock time the seismicity rate in these regions increased while the b value of the earthquake size distribution decreased it has been previously suggested that remote seismicity rate increase could be triggered by the passage of seismic waves remote triggering in a quasi static model indicates that it is not necessary to invoke such a dynamic effect in order to explain distant aftershocks

landslides and residual strength in marl profiles in israel abstract many areas in northern israel show evidence of old landslides in marly profiles and new slides are often activated in these regions such a slide occurred in the town of rechasim near haifa during an exceptionally wet winter in 1992 the present paper analyzes the causes for this slide and suggests that it was due to a combination of downslope flow in the overlying severely cracked chalk limestone layer and mobilization of residual strength at the marl chalk interface the residual strength of israeli marly soils has been studied and it is shown that while many of these consist predominantly of clay sized

evidence of instantaneous dynamic triggering during the seismic sequence of year 2000 in south iceland 1 we analyze the coseismic stress perturbation during the 17 june 2000 south iceland seismic sequence the main shock ms 6 6 was followed by three large events within a few tens of seconds 8 26 and 30 s located within 80 km the aim of this paper is to investigate short term fault interaction and instantaneous triggering this happens when a fault perturbed by a stress change fails before the end of the transient stress perturbation we compute the shear normal and coulomb stress changes as functions of time in a stratified elastic half space by using discrete wave number and reflectivity methods we calculate dynamic stresses caused by the main shock at the hypocenters of these three subsequent events our numerical results show that the onset of the last two events is slightly delayed with respect to the arrival time of the second positive peak of coulomb stress variation while the first event occurred after the first positive stress peak we have also analyzed the response of a spring slider system representing a fault governed by a rate and state dependent friction law perturbed by shear and normal stress variations caused by the main shock the fault response to the computed stress perturbations is always clock advanced we have found suitable constitutive parameters of the modeled fault that allow the instantaneous dynamic triggering of these three earthquakes if the initial sliding velocity is comparable with the tectonic loading velocity we obtained failure times close to the observed origin times for low values of the initial effective normal stress

triggering of earthquake aftershocks by dynamic stresses it is thought that small static stress changes due to permanent fault displacement can alter the likelihood of or trigger earthquakes on nearby faults many studies of triggering in the near field particularly of aftershocks rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault here we report a comparison of the aftershock pattern of the moment magnitude mw 7 3 landers earthquake not only with static stress changes but also with transient oscillatory stress changes transmitted as seismic waves that is dynamic stresses dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone these dynamically weakened faults may fail after the seismic waves have passed by and might even cause earthquakes that would not otherwise have occurred we find similar asymmetries in the aftershock and dynamic stress patterns the latter being due to rupture propagation whereas the static stress changes lack this asymmetry previous studies have shown that dynamic stresses can promote failure at remote distances but here we show that they can also do so nearby

dynamic versus static stress triggering and friction parameters inferences from the november 23 1980 irpinia earthquake this paper concentrates on the problem of fault interaction and earthquake triggering through the 1980 irpinia italy sequence more specifically this paper deals with the problem of the triggering of the second subevent by the mainshock the interaction between the two segments is modeled through a dynamic coulomb failure function the aims of this paper are first to discriminate between the dynamic and the static stress effects on the triggering if these effects exist second to estimate the fault strength relative to the initial state of stress third to determine the parameters of a slip dependent friction law that lead to the observed delay of 20 s numerical simulations show that the critical slip dc may range from 0 03 m up to 1 7 m and that the initial slope of the friction law 0 must be lower than 0 04 m 1 we show that the relative magnitude of the fault strength and the initial state of stress govern the existence and value of a dc lower threshold under which the fault always ruptures before 13 s a close to failure fault is not consistent with a critical slip dc less than 0 8 m whereas small values of dc typically 0 03 m imply a far from failure fault general results concern the effect of a dynamic stress pulse we show that an event can be triggered by a transient stress pulse and that in this case the event can have an initiation duration much longer than the pulse duration we show that it is possible to explain both the triggering and the time delay only with the effect of the transient stress pulse this may explain aftershock triggering even in regions of negative coulomb failure function or long distance triggering of earthquakes by propagating waves

multi sensor satellite and in situ measurements of a warm core ocean eddy south of the brazil malvinas confluence region abstract a warm core eddy was detected south of the brazil malvinas falkland confluence bmc region in satellite images of the southwestern atlantic ocean in late 2002 the structure was also sampled by in situ instruments deployed by a ship in 2 days of november 2002 an analysis of satellite data was performed to account for the lifecycle dimension surface temperature surface chlorophyll concentration surface height anomaly and displacement of the eddy since it was detached from the brazil current in september 2002 satellite data were derived from several sources such as the amsr e modis and radar altimeter the structure lasted 64 days at south of the brazil malvinas confluence region later being re assimilated by the brazil current return flow in situ data collected during 2 days showed that the eddy was about 150 m deep 5 5 c warmer and 1 practical salinity unit saltier than adjacent waters the salt anomaly associated to the eddy was estimated as 1 37 10 12 kg while its heat content was 4 24 10 18 j these are typical estimates for eddies present at the bmc region sea surface temperature sst chlorophyll concentration and sea surface height anomaly time series were analyzed for the eddy s center along its trajectory path throughout its lifetime mean translational velocities for the eddy during its lifetime were computed from visual interpretation and by using an adaptation of the maximum cross correlation mcc method on amsr e sst images the overall deviation between the two methods was 26 this suggests that the mcc method has a potential to be applied in monitoring programs to automatically account for the translational velocities of eddies in the bmc region

detection and classification of mesoscale atmospheric phenomena above sea in sar imagery abstract satellite radar observations above sea are dedicated to small scale and mesoscale phenomena in the ocean and the marine boundary layer what the synthetic aperture radar sar sensors see on the ocean surface is primarily the variation of the bragg resonant waves providing signatures of local wind changes and imprints of atmospheric phenomena and the areas of enhanced wave breaking associated with wave current interaction for oceanographic processes like currents fronts and eddies sar images contain information about the processes in the marine atmosphere boundary layer mabl in particular when variation of wind speed and direction is significant several publications are available in the literature modeling and explaining each phenomenon separately however only a few focus on the identification of each phenomenon in an automatic or semi automatic way the objective of the present paper is to detect and to classify five atmospheric phenomena in sar images low wind areas katabatic wind island wakes atmospheric gravity waves and atmospheric convective cells an object based environment was used to identify the phenomena and fuzzy logic used to classify them several features extracted for each phenomenon were used for feeding the classifier the proposed method used 16 sar images and accuracy was examined in another 16 sar images using 457 object samples the method proved to be successful with an overall accuracy of 80 and kappa index of 0 75 the class of low wind areas negatively affected the overall accuracy due to overlapping feature values with the rest of the categories

kuroshio induced wake in the lee of green island off taiwan 1 the wake of green island was investigated in the alongshore flowing kuroshio east of taiwan where current speeds range from 1 to 1 5 ms 1 vertical profiling with shipboard lowered acoustic doppler current profiler and conductivity temperature depth profiler revealed sizable anomalies in flow and water characteristics in the lee of green island two different stages of wake evolution were observed from two shipboard surveys in the first stage a recirculation developed leeward of the island followed by a wavy wave like tail that resembled a weak vortex street in the second stage a cold eddy probably originating from the leeward side of the island showed up 14 km downstream of the island the wake water was colder saltier higher in chlorophyll a concentration and produced isopycnal doming up to 60 m in the recirculation area the relative vorticity either positive or negative was 10 times of planetary vorticity and the horizontal divergence or convergence was o 10 4 s 1 on average flow divergence and convergence in the wake were expected to form upwelling and downwelling zones producing a vertical circulation that vertically displaces isotherms high inverse richardson number produced by strong vertical shear of horizontal currents was associated with intense overturning events in the wake high vertical shear of horizontal currents drove the mixing the dissipation rate of turbulent kinetic energy in the overturn regions is o 10 7 10 5 w kg 1 the corresponding eddy diffusivity is o 10 3 10 1 m2 s 1 the wake water properties are vertically diffused via upwelling and turbulence and can be delivered downstream through eddy shedding or advection the extent of downstream influence remains to be investigated

deep water seamount wakes on seasat sar image in the gulf stream region 1 a seasat synthetic aperture radar sar image taken over the gulf stream region shows streak like patterns the physics of their generation and interaction with the gulf stream are disputed this study seeks a convincing interpretation for the sar imagery patterns bathymetric maps show that the sea floor area beneath the streaks is the northeast hoyt hills where isolated seamounts with the heights of 20 to 140 m above the background sea floor are distributed all the sar imagery streaks originate from these seamounts and extend downstream thus the sar imagery streaks are interpreted as surface roughness imprints of the seamount wakes hydrostatic flow dynamics of the generation of wakes on the lee side of a solid obstacle is used to explain the generation mechanism and internal structure of the seamount wakes the analysis indicates that boundary conditions and hydrodynamic conditions are favorable for the generation and vertical propagation of the seamount wakes to the upper layer

effectiveness of exceptional rainstorms on a small mediterranean basin abstract a comprehensive investigation of rainstorms and their consequent impacts on landscape evolution is geomorphologically important but only scant information may be available on exceptional events because parameters on synoptic conditions rainstorm landforms and hydrology for such events may be incomparable with previous knowledge we studied an exceptional storm on april 2 2006 in the ramot menashe region israel our investigation of rainfall landslides debris flows and channel suggests the effectiveness of such an event on the development of basin scale morphology the storm caused damage and casualties although it covered relatively narrow strips neither direct rainfall nor runoff measurements exist for the most severely affected area of ramot menashe but the geomorphologic evidence combined with high resolution meteorological radar data provides the basic understanding of the processes and hazardous conditions which prevailed at the time in the storm core based on estimation from meteorological radar data 263 mm of rain fell within 3 h with a maximum intensity of 220 mm h 1 for 10 min triggering both sporadic landslides at the soil bedrock contact on the upper slopes and widespread landslides at the fractured massive bedrock contact on the lower slopes the 1st order channels on the alternation of chalk and marl also underwent erosion and the produced sediment deposited on alluvial fans at the confluence with the main channel the specific peak discharges for catchment size of 0 3 10 km2 were 11 to 73 m3 s 1 km 2 higher than any recorded floods in the mediterranean climatic region of israel the effectiveness of the flood for geomorphic work represented by shear stress and stream power per unit boundary area reached 87 398 n m 2 and 212 2134 w m 2 respectively this kind of analysis can be applied to hazard prediction in other areas under similar geomorphological conditions

phytoplankton bloom during the northeast monsoon in the luzon strait bordering the kuroshio article were discernible for both situations a twin core structure of the bloom was identified the major core lay far offshore in the deep basin to the northwest of luzon with a maximum horizontal scale of 250 km and the other core was nearshore in the babuyan channel with a maximum scale of 100 km variations in cli matological monthly mean aph indicate that the lzs bloom as a whole persists from november to february peaking in december further investigations with satellite altimetry and sea surface temperature suggest that the bloom is primarily associated with the kuroshio and its intrusion which generate various meso scale pro cesses and thus induce enhanced nutrient pumping entrainment from depth when interacting with the topog raphy of the luzon strait and the circulation of the northeastern south china sea i e the luzon gyre meanwhile upwelling at the center of the luzon gyre contributes to the offshore bloom the nearshore bloom is substantially enhanced by nutrient input from the cagayan river

investigation of the island induced ocean vortex train of the kuroshio current using satellite imagery abstract in this study we used satellite imagery to conduct a statistical study of the ocean vortex train induced by the kuroshio current on the leeward side of green island taiwan the spatial scale and characteristics of the ocean vortex train were analyzed using image datasets from five different high resolution satellites including optical imagery from the satellite pour l observation de la terre and the formosat 2 satellites and synthetic aperture radar imagery from the european remote sensing satellite advanced land observing satellite and sentinel 1 satellite altimetry data and a moored acoustic doppler current profiler adcp were used to calculate the velocity of the kuroshio current the adcp data suggest that the velocity increases on the western side of the vortex train when it is formed on the leeward side of green island data from the moderate resolution imaging spectroradiometer modis showed that the sea surface temperature of the recirculation water was over 2 c colder and the chlorophyll a concentration was two times higher than that of the surrounding waters these phenomena suggested upwelling mixing processes and an island mass effect wind forcing had a pronounced effect on the characteristics of the vortex train high resolution satellite images indicate that the averaged aspect ratio of the vortex train is 2 09 and the dimensionless width is 2 02 under southerly winds compared to 1 91 and 2 76 respectively under northerly winds

how islands stir and fertilize the upper ocean 1 large differences between the upstream and lee side flow characteristics of an isolated island in the kuroshio have been identified from a three dimensional velocity survey and from vertical profiles of fine and micro structure in the island wake the relative vorticity is o 10f the horizontal current divergence indicates upwelling of o 0 01 m s 1 and the rate of dissipation of kinetic energy is o 10 4 w kg 1 isopycnal surfaces shoal by 60 m on the lee side and surface nitrate concentration increases seven fold flow blockage by the island and the izu ogasawara ridge on its flanks induces horizontal and vertical flow separation the associated lateral and vertical shear drive the upwelling and the vertical mixing in the wake and produces a very pronounced island mass effect

investigation of kuroshio induced cold core eddy trains in the lee of the izu islands using high resolution satellite images and numerical simulations abstract a series of synthetic aperture radar sar images acquired during the summer of 2006 revealed island wakes in the lee of the izu islands south of japan the wakes were formed of not only meandering disturbances but also a series of eddies with diameters on the order of those of the islands the kuroshio flowed near these islands in the summer of 2006 indicating that the island wakes were induced by a kuroshio island interaction satellite sea surface temperature sst and chlorophyll a chl a images observed during the summer of 2006 revealed low sst and high chl a wakes some of which included low sst eddy trains it is thus inferred that the phenomenon entailed upwelling and mixing processes and biological productivity known as the island mass effect high spatial resolution sst derived by combining a landsat infrared channel and avhrr sst clearly revealed a well defined sst front associated with the island wakes and a 1 km scale low sst wake pattern a numerical simulation was performed to investigate the formation mechanism the simulation qualitatively reproduced the cold eddy pattern with eddy driven mixing developing a mixed layer down to 200 m causing low sst island wakes the shedding frequency and spacing of the model produced eddies were roughly close to those of the karman vortex theory suggesting that karman type cold eddy trains are commonly formed behind the islands when the kuroshio strong flow impinges on them

the transition zone of the canary current upwelling region abstract like all the major upwelling regions the canary current is characterised by intense mesoscale structure in the transition zone between the cool nutrient rich waters of the coastal upwelling regime and the warmer oligotrophic waters of the open ocean the canary island archipelago which straddles the transition introduces a second source of variability by perturbing the general southwestward flow of both ocean currents and trade winds the combined effects of the flow disturbance and the eddying and meandering of the boundary between upwelled and oceanic waters produce a complex pattern of regional variability on the basis of historical data and a series of interdisciplinary field studies the principal features of the region are described these include a prominent upwelling filament originating near 28 n off the african coast cyclonic and anti cyclonic eddies downstream of the archipelago and warm wake regions protected from the trade winds by the high volcanic peaks of the islands the filament is shown to be a recurrent feature apparently arising from the interaction of a topographically trapped cyclonic eddy with the outer edge of the coastal upwelling zone its role in the transport and exchange of biogenic material including fish larvae is considered strong cyclonic eddies observed throughout the year drift slowly southwestward from gran canaria one sampled in late summer was characterised by large vertical isopycnal displacements apparent surface divergence and strong upwelling producing a fourfold increase in chlorophyll concentrations over background values such intense eddies can be responsible for a major contribution to the vertical flux of nitrogen the lee region of gran canaria is shown to be a location of strong pycnocline deformation resulting from ekman pumping on the wind shear boundaries which may contribute to the eddy formation process

lee region of gran canaria the mountainous canary islancls present obstacles to the trade wincls ancl to the canary current flowing equatorwarc past them in situ observations of hydrographic properties ancl surface wincls south of gran canaria together with advancecl very high resolution racliometer ancl synthetic aperture racial images e uring 2 weeks in summer 1995 are analyzecl a cyclonic edcly shecl l rom the west of the islancl c1riftecl southwestwarcl at 5 s j while the southeast coast was approachecl by an upwelling filament originating off nw africa a wincllee region bounclecl by intense horizontal shear lines hacl a weak return islandwarcl wincl in its center the lee formee a triangulai c1iurnally varying war111 water 001 with two sea surface temperature maxima separatecl by lower temperatures below the return wincl shallow temperature stratification occurrecl behincl the islancl in contrast to the l1niform surface mixecllayer in exposecl regions upwelling ancl clownwelling of 10 20 111 were indicatecl on the cyclonic ancl anticyclonic sicles of the lee region in the sar la u lines of strong current shear along a temperature front between the cyclonic eclcly the upwelling filament were iclentifiable i iowever the racial images were clominatecl atmospheric phenomena including mountain lee wave paclcets winclrows and wincl lines estimation of the wincl field l rom the sar backscatter intensity revealed ex structure and intensification on the eclges of the warm lee

an observational study of vortex spacing in island wake vortex streets abstract vortex streets are a frequent occurrence in stratocumulus topped flow downwind of mountainous islands theoretical studies dating back to von karman supported by laboratory and numerical studies have yielded similarity theories for the size and spacing of these vortices behind bluff bodies despite dynamical differences between such two dimensional flows and the three dimensional flow past isolated islands satellite case studies suggest these geometric similarities may also hold for the atmospheric case in this study two of the resulting dimensionless ratios are measured using satellite imagery one is the aspect ratio between cross street and along street spacing of the vortices the second is the ratio of the cross street spacing to the crosswind width of the island a 30 image sample from the aqua and terra moderate resolution imaging spectroradiometer satellites is analyzed to obtain these ratios the resulting set of values for the two dimensionless ratios is tested against the values f

dynamic stress variations due to shear faults in a plane layered medium summary a complete set of expressions is presented for the computation of elastic dynamic stress in plane layered media we use a discrete wavenumber reflectivity method to compute the stress field radiated by arbitrary moment tensor sources the expressions derived here represent an interesting tool for both the observational and theoretical analysis of dynamic stress changes associated with earthquake phenomena dynamic stress changes associated with a strike slip fault having unilateral rupture are shown this modelling which is similar to the 1992 landers california earthquake illustrates the effects of distance directivity and depth on transient stress changes

a small scale oceanic eddy off the coast of west africa studied by multi sensor satellite and surface drifter data a small scale oceanic eddy which was generated in autumn 2011 at the headland of cap vert off the coast of senegal west africa and then propagated westward into the open north atlantic ocean is studied by multi sensor satellite and surface drifter data the eddy was generated after a sudden increase of the trade winds causing an enhanced southward flow and upwelling at the coast of senegal after this wind burst event an extremely nonlinear cyclonic eddy with a radius of about 10 to 20 km evolved downstream of cap vert with rossby number larger than one our analysis suggests that the eddy was generated by flow separation at the headland of cap vert the eddy was tracked on its way into the open north atlantic ocean from satellites over 31 days via its sea surface temperature and chlorophyll a chl signature and by a satellite tracked surface drifter the satellite images show that this small scale eddy transported nutrients from the upwelling region westward into the oligotrophic north atlantic thus giving rise to enhanced chl concentration there maximum chl concentration was encountered few days after vortex generation which is consistent with a delayed plankton growth following nutrient supply into the euphotic zone within the eddy furthermore the eddy was imaged by the synthetic aperture radar sar onboard the envisat satellite it is shown that the radar signatures of cold eddies result from damping of short surface waves by biogenic surface films which arise from surface active material secreted by the biota in the cold eddy as well as by the change of the stability of the air sea interface highlights processes during the onset of coastal upwelling off west africa multi sensor remote sensing and in situ observations highly nonlinear small scale eddy generation at cap vert nrcs reduction in parts of the eddy due to biogenic surface films

transient triggering of near and distant earthquakes we demonstrate qualitatively that frictional instability theory provides a context for understanding how earthquakes may be triggered by transient loads associated with seismic waves from near and distance earthquakes we assume that earthquake triggering is a stick slip process and test two hypotheses about the effect of transients on the timing of instabilities using a simple spring slider model and a rate and state dependent friction constitutive law a critical triggering threshold is implicit in such a model formulation our first hypothesis is that transient loads lead to clock advances i e transients hasten the time of earthquakes that would have happened eventually due to constant background loading alone modeling results demonstrate that transient loads do lead to clock advances and that the triggered instabilities may occur after the transient has ceased i e triggering may be delayed these simple clock advance models predict complex relationships between the triggering delay the clock advance and the transient characteristics the triggering delay and the degree of clock advance both depend nonlinearly on when in the earthquake cycle the transient load is applied this implies that the stress required to bring about failure does not depend linearly on loading time even when the fault is loaded at a constant rate the timing of instability also depends nonlinearly on the transient loading rate faster rates more rapidly hastening instability this implies that higher frequency and or longer duration seismic waves should increase the amount of clock advance these modeling results and simple calculations suggest that near tens of kilometers small moderate earthquakes and remote thousands of kilometers earthquakes with magnitudes 2 to 3 units larger may be equally effective at triggering seismicity our second hypothesis is that some triggered seismicity represents earthquakes that would not have happened without the transient load i e accumulated strain energy would have been relieved via other mechanisms we test this using two new seismicity models that 1 are inherently unstable but slide at steady state conditions under the background load and 2 are conditionally stable such that instability occurs only for sufficiently large perturbations for the new seismicity models very small amplitude transients trigger instability relative to the clock advance models the unstable steady state models predict that the triggering delay depends inversely and nonlinearly on the transient amplitude as in the clock advance models we were unable to generate delayed triggering with conditionally stable models for both new seismicity models the potential for triggering is independent of when the transient load is applied or equivalently of the prestress unlike in the clock advance models in these models a critical triggering threshold appears to be inversely proportional to frequency further advancement of our understanding will require more sophisticated quantitative models and observations that distinguish between our qualitative yet distinctly different model predictions

triggered fault slip on june 17 2000 on the reykjanes peninsula sw iceland captured by radar interferometry 1 dynamically triggered seismicity followed shortly after a ms 6 6 earthquake in iceland on june 17 2000 smaller earthquakes occurred on the reykjanes peninsula up to 100 km from the mainshock rupture using interferometric analysis of synthetic aperture radar images insar we measure crustal deformation associated with three triggered deformation events the largest of these occurred at lake kleifarvatn 85 km west of the mainshock epicenter modeling of the insar data reveals strikeslip on a north striking fault with a geodetic moment of 6 2 1017 nm equivalent to magnitude mw 5 8 earthquake a seismological estimate of the moment is not yet available because the seismic signature of this event is partly hidden by the mainshock waveform the paucity of aftershocks on the triggered rupture plane suggests some aseismic slip there compatible with a thin seismogenic crust high heat flow hydrothermal alteration and the presence of fluids in the area

sea surface signatures of the island mass effect phenomena around madeira island northeast atlantic abstract this is an introductory work that describes the manifestation of the island mass effect phenomena in the atmosphere and at the sea surface for a region of the ocean depleted from oceanographic work the madeira archipelago 33 n 17 w the use of remote sensing tools becomes essential in recognizing some of the sea surface features that characterize the island mass effect phenomena avhrr coastal zone color scanner czcs and seawifs ancillary national center for environmental prediction ncep data together with highly developed processing tools from panorama processing and automatic navigation of real time images allowed the detection of atmospheric von karman vortex streets warm water surface wakes leeward eddies azorean front and localized upwelling results from the remote sensing analysis also helped to promote the reanalysis of historical in situ data for the manifestation of these island effects ipimar cruises carried out between 1979 and 1982 collected temperature salinity density and chlorophyll data which were reinterpolated at the sea surface to study the island mass effect phenomena for the first time results have shown the formation of a warm water wake south of madeira island expanding 400 km offshore the surface signature of the azorean front the so called subtropical front seems to take place within the madeira latitude 33 n north waters were consistently colder than the warm and salty southern waters avhrr data also revealed eddies and fronts being formed in the region leeward eddies were often observed in the flanks of the islands czcs data showed highly productive eddies in the west of madeira island localized cold water with high chlorophyll concentrations was also observed around the island s coast a particularly dynamic area was the underwater ridge that connected madeira and desertas islands future work should continue to sample these regions of interest with the simultaneous use of different satellite sensors vertical characterization of the different phenomena is needed

island wakes in the southern california bight 1 wind and current induced island wakes were investigated using a multiplatform approach of in situ remote sensing and numerical model simulations for the southern california bight scb island wind wakes are a result of sheltering from the wind with weak wind mixing strong heat storage and consequent high sea surface temperature sst wind wakes around santa catalina island are most persistent during spring and summer months current wakes caused by the disruption of the poleward traveling california countercurrent induce eddies to form off the north end of catalina island and these move poleward every 9 12 days current wake eddies induce strong mixing with low sst and high density sea surface signatures whereas wind wakes induce high sea surface temperature signatures associated with the formation of a well defined shallow thermocline current wake eddies vary from 1 to 30 km in diameter from numerical solutions we predicted the frequency of occurrence of current induced wakes off santa catalina island wind wakes were also observed off all the other islands of the scb as seen from the analysis of synthetic aperture radar data time series analysis of the island mass effect phenomenon has shown a concurrence of low sst and high sea surface chlorophyll for santa catalina san nicholas and san clemente islands that might be related to the seasonality of the california current and california countercurrent future oceanographic research in the scb should not ignore the occurrence of wind and current induced island features since they may be important in the transport and or retention of nutrients pollutants and plankton

observations of island wakes at high rossby numbers evolution of submesoscale vortices and free shear layers abstractoceanic vortex evolution on the lee side of taiwan s green island 7 km in diameter where the kuroshio flows at a speed of 1 1 5 m s 1 is observationally examined and compared to theori

a unified model for dynamic and static stress triggering of aftershocks antishocks remote seismicity creep events and multisegmented rupture aftershocks have been thought to be triggered by static stress transfer the 1992 landers and 1999 hector mine california earthquakes have demonstrated the possibility of remote triggering of seismicity highlighting the role of dynamic seismic waves static stress changes and transient deformations have different timescales the mechanisms by which they trigger earthquakes are thought to be different leading to an unwieldy vision of aftershock triggering we propose a model that encompasses both static and dynamic triggering of aftershocks and antishocks as well as the occurrence of stable slip creep events or multisegmented rupture the framework of this model is based on the stability instability transition of faults we propose that dynamic and static stress triggering pertain to the same physical process we study the effect of the complete coulomb failure function we demonstrate the possibility of the triggering of seismicity by a dynamic stress pulse in a stress shadow zone characterized by a negative static stress field the limited time efficiency of dynamic triggering shown by the data is explained by the model we suggest that dynamic waves trigger only the most unstable faults associated with a relatively short characteristic time while the static stress field triggers also faults that are stable associated with a larger characteristic time

glider observations of a mesoscale oceanic island wake abstractin this study a 2 yr time series of velocity profiles to 1000 m from meridional glider surveys is used to characterize the wake in the lee of a large island in the western tropical north p

island wakes in shallow coastal waters rattray island northeast australia is 1 5 km long 300 m wide and lies in well mixed water approximately 25 m deep its long axis is inclined at about 60 into the direction of the dominant semidiurnal tidal current the length of the wake in the lee of the island as documented by aerial photographs and satellite imagery appears to equal that of the wake behind a flat plate in a two dimensional flow at a reynolds number of about 10 however current metering drogues measurements and temperature mapping indicate internal wake velocities much greater than would be consistent with such a simple low reynolds number model further estimates of the turbulent eddy coefficient suggest an effective reynolds number more in the vicinity of 103 to reconcile these observational differences and to explain the observed upwelling in the core of the wake an ekman pumping model is proposed it is postulated that the ekman benthic boundary layer driven by rotation in the wake allows the vertical vorticity introduced into the water at the tip of the island at the point of separation to be negated by the vorticity of opposite sign introduced at the bottom further it is shown that a large fraction of the kinetic energy of the upstream flow facing the island is used to drive the wake eddies leading to the conclusions that the trapping of water in the lee of islands greatly increases head losses on continental shelves with numerous islands coral reefs and rock outcrops

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl