correlation scales objective mapping and absolute geostrophic flow in the california current the spatial covariances of the time dependent density and geostrophic velocity fields off southern california are determined from a unique set of repeated hydrographic observations 44 cruises made by the california cooperative oceanic fisheries investigations from 1984 to 1994 the covariances and objective analysis are used to combine direct velocity observations from shipboard acoustic doppler current profiler adcp measurements made on a recent survey october 1993 with hydrographic observations the analysis reduces ageostrophic noise in the adcp velocities by smoothing and enforcing horizontal nondivergence additionally the velocities are mapped over scales that are dynamically consistent with the hydrography maximum surface geostrophic flow in the california current in october 1993 is about 35 cm s 1 50 larger than that estimated assuming a 500 m level of no motion absolute flow at 500 m is o 10 cm s 1 and indicates that the surface eddy field penetrates through the thermocline uncertainty in the geostrophic reference calculated from the adcp measurements is of o 4 cm s 1 the velocity residual objectively analyzed minus raw adcp estimates exhibits smaller correlation scales than the geostrophic flow

topographically induced baroclinic eddies near a coastline with application to he northeast pacific abstract a mathematical model is developed to describe the interaction between variable bottom topography and a steady horizontally sheared baroclinic coastal current the topography modeled in this study consists of an offshore seamount and a seaward protrusion of the continental slope the fluid motions are assumed to conserve potential vorticity on the f plane and expressions for the pressure density velocity and mass transport fields are obtained using a normal mode analysis and the appropriate green s function for the horizontal problem the theory is applied to the northeast pacific ocean in an attempt to model the anticyclonic eddy which has been observed by tabata west of sitka alaska the numerical calculations of the model and the observed location dimensions velocities and transports of the sitka eddy are in good agreement the axial velocities and dimensions of the calculated eddy field are largest for upstream surface and bottom currents of approximately 5 7 and 1 2 cm s 1 respectivel

an empirical orthogonal function analysis of remotely sensed sea surface temperature variability and its relation to interior oceanic processes off baja california abstract empirical orthogonal function eof analysis was applied to a 4 6 year sequence of avhrr images off baja california centered near punta eugenia to examine large and mesoscale processes in this region of the california current system ccs the mean structure found in the image sequence describes the seasonal cycle in sea surface temperature sst and the large scale north south oceanic sst gradient of the region the first eof amplitude pair also describes the seasonal cycle in sst both results are consistent with long term large scale mean shipboard data for the region the second eof amplitude pair defines two distinct regions paralleling the coast the inshore region coincides with the coastal zone of lynn and simpson 1987 and the adjacent region farther offshore is identical to their transition zone the third through fifth eof amplitude pairs primarily represent meandering of the california current and anticyclonic mesoscale eddy occurrences in the region these results also are consonant with a large number of shipboard observations the eof results provide independent satellite derived evidence for the existence of a transition zone off baja california which is similar to that found off central and southern california moreover the agreement between the satellite based results and the shipboard observations indicates that satellite data can be used successfully to study other current systems e g peru current where in situ observations ships buoys are less abundant

a double vortex along the california coast a double vortex was observed at the entrance to the santa barbara channel california with sequential ir imagery from the noaa 7 satellite during may 1984 while the wind blew strongly to the southeast the double vortex moved westward with a velocity greater than that estimated for the mutual interaction of two idealized vortices the effect of the double vortex on incoming pacific swell is calculated by numerical integration of the ray equations this calculation shows areas of focusing of the rays near the entrance to the channel which suggests elevated wave energy there with reduced wave energy nearby the pattern of wave refraction by mesoscale features such as a double vortex can help detect them and estimate their velocity distribution from remotely sensed surface wave imagery the similarities and differences between refraction patterns produced by double vortices and by eddies is outlined the double vortex and its generation by an episodic or tidal flow is investigated using kashiwai s 1984 approach an example of the related generation of a single vortex in the alboran sea by tidal flow in the strait of gibraltar is briefly discussed

an offshore eddy in the california current system part iii chemical structure abstract from january 9 to 17 1981 detailed physical chemical and biological measurements were made through the historical surface signature berstein breaker and whritner 1977 burkov and pavlova 1980 simpson 1982 of a warm core eddy in the california current system the data show a three layer system surface layer to 75 m intermediate cold core region to about 200 m and the physically dominant subsurface warm core eddy to about 1400 m the chemical structure simultaneously possesses characteristics of both warm and cold core eddies this structure results from a complex interplay among non local eddy generation processes at the time the three layer system was formed and a continuous set of interactions within the three layer system both inshore cold and offshore warm waters of the california current and coastal and local biological processes e g this california current system eddy is not an isolated structure like some gulf stream rings the dominant biological chemical process in the euphotic zone is phytoplankton photosynthesis photosynthetic alteration of the chemical structure below 100 m is much reduced the effects of heterotrophic activity on the deeper lying chemical structure however are not as significant as those of autotrophs on the chemical structure of the euphotic zone hence below 100 m the distribution and structure of chemical properties is controlled primarily by physical processes the continuous set of interactions of the three layer system with coastal and oceanic waters of the california current make this offshore eddy in the california current system fundamentally different chemically and biologically from cold core gulf stream rings and rather similar to some of the warm core eddies found in the east australian current

reflection polarity of the midcrustal surrency bright spot beneath southeastern georgia testing the fluid hypothesis a small reflection seismic experiment with an explosive source was conducted in southeastern georgia to determine the polarity of an unusually strong midcrustal reflector the surrency bright spot sbs which was found at a depth of approximately 16 km during earlier cocorp profiling in the region in addition to being very bright the sbs is notable for being unusually flat and horizontal for about half of its 4 km length as these characteristics are similar to those of fluid caused reflections at shallow depths it has been suggested that the sbs may be caused by in situ midcrustal fluids if caused by fluid enclosed in fracture porosity in solid rock the reflection would be expected to exhibit a negative polarity from the top of the porous zone the vibroseis data however gave ambiguous results with regard to polarity due to the limited bandwidth and inherent uncertainties about the phase of the source signal the new experiment consisted of four dynamite shots each recorded at three receiver stations by seismic group recorders sgr borrowed from amoco production company comparison of the dynamite records with geophone polarity tests indicate that the sbs is characterized by a positive reflection coefficient at its top this result itself does not negate the fluid hypothesis a fluid fluid interface could cause the positive reflection as well as the flat spot nature of the reflector waveform modeling shows that the sbs is caused by two or more thinly spaced reflectors a relatively high impedance layer about 120 m thick provided a good match to the observed dynamite data but requires a lower boundary having a slightly smaller reflection coefficient than the upper boundary 0 7 versus 1 0 a 150 m thick porous zone model also provided a relatively good fit to the observed dynamite data but in this model the polarity test requires that the initial sbs reflection of positive polarity be caused by a fluid fluid interface within the porous zone and that the top of the porous zone be relatively non reflective though these observations do not preclude the fluid hypothesis they certainly make the high impedance model the simpler of the two alternatives presented here the additional constraints imposed by the modeling also suggest that the sbs is more complex than these simple two interface models in either of these cases wavelet tuning contributes in part to the unusually large amplitude of the sbs reflection

direct hydrocarbon detection using comparative p wave and s wave seismic sections two field experiments in the sacramento basin and one in the green river basin demonstrate that comparative p wave and s wave cdp seismic sections can be used to detect gas directly in sandstone reservoirs the lines in the sacramento basin were shot over producing gas fields known to correlate with amplitude anomalies on p wave sections reflections of comparable strength are present on the p wave and s wave sections at lithologic boundaries but gas saturated zones correlating with p wave bright spots show no equivalent s wave amplitude anomalies the responses are consistent with laboratory observations that p wave velocity is more sensitive to the introduction of gas into liquid saturated pore space than s wave velocity the line in the green river basin was shot over a relatively deep gas field producing from an overpressured reservoir not associated with a conventional p wave bright spot the p wave reflection strength of the reservoir is about 50 percent greater than the s wave reflection strength

mesoscale eddies in the northeastern pacific tropical subtropical transition zone statistical characterization from satellite altimetry 1 mesoscale eddies in the northeastern pacific tropical subtropical transition zone 16 n 30 n 130 w 102 w are analyzed using nearly 18 years of satellite altimetry and an automated eddy identification algorithm eddies that lasted more than 10 weeks are described based on the analysis of 465 anticyclonic and 529 cyclonic eddy trajectories we found three near coastal eddy prolific areas 1 punta eugenia 2 cabo san lucas and 3 cabo corrientes these three areas are located in places where the coastal morphology changes abruptly and strong surface current intensification occurs at some phase of the seasonal cycle although mesoscale eddies in these areas have been previously reported this study provides their first statistically supported characterization punta eugenia showed the highest eddy production with more cyclones generated followed by cabo corrientes also with more cyclones and cabo san lucas with more anticyclones cabo corrientes eddies showed the highest mean values in propagation speed swirling speed and eddy kinetic energy whereas punta eugenia eddies showed the lowest values cyclonic eddies increased their distance traveled and duration from south to north in contrast anticyclonic eddies increased from north to south in average anticyclones tend to travel faster than cyclones in all the subregions these long lived eddies were mainly nonlinear and therefore can redistribute coastal waters relatively far into the open ocean the peaks in the seasonal signal of eddy generation can be associated with the peaks in the strength of the offshore currents and or in the coastal upwelling index no clear relationship could be established between el nino events and eddy generation

an offshore eddy in the california current system part ii surface manifestation abstract ship and satellite observations taken over the last thirty years show that mesoscale patterns of sea surface temperature sst in the california current system are consistently found throughout the year and usually occur in approximately the same geographical locations typically these patterns are more pronounced in fall winter than in spring summer the temporal and spatial characteristics of these persistent feature were examined with satellite infrared ir measurements during winter 1980 1981 in january 1981 a ship surveyed the vertical structure of several physical chemical and biological parameters beneath one of these sst features centered near 32 n 124 w the surface ir pattern had a length scale of 200 km and a time scale of about 100 days it disintegrated following the first two storms of the winter season motion studies of the pattern in late october indicated an anticyclonic rotation with maximum velocities of 50 cm s 1 at 50 km from the axis of rotation as a unit the pattern advected southward with an average speed of 1 cm s 1 thermal fronts determined from the satellite imagery were strongest 0 4 c km 1 along the rim of the pattern and were advected anticyclonically with the pattern their length scales were 20 30 km in the along front direction and less than 10 km wide the hydrographic data revealed a three layer structure beneath the surface pattern a 75 m deep surface layer a cold core region from 75 to 200 m depth and a warm core eddy extending from 250 to 1450 m the anticyclonic motion of the surface layer was caused by a geostrophic adjustment to the surface dynamic height anomaly produced by the subsurface warm core eddy the ir pattern observed from space reflects the horizontal structure of the surface layer and is consistent with a theoretical model of a mean horizontal sst gradient perturbed by a subsurface density anomaly ship of opportunity sst observations collected by the national marine fisheries are shown to resolve mesoscale patterns for december 1980 the sst pattern near 32 n 124 w represented a 2 c warm anomaly compared with the 20 year mean monthly sst pattern

vertical structure of mesoscale eddies in the eastern south pacific ocean a composite analysis from altimetry and argo profiling floats 1 the mean vertical structure of mesoscale eddies in the peru chile current system is investigated by combining the historical records of argo float profiles and satellite altimetry data a composite average of 420 526 profiles acquired by argo floats that surfaced into cyclonic anticyclonic mesoscale eddies allowed constructing the mean three dimensional eddy structure of the eastern south pacific ocean key differences in their thermohaline vertical structure were revealed the core of cyclonic eddies ces is centered at 150 m depth within the 25 2 26 0 kg m 3 potential density layer corresponding to the thermocline in contrast the core of the anticyclonic eddies aes is located below the thermocline at 400 m depth impacting the 26 0 26 8 kg m 3 density layer this difference was attributed to the mechanisms involved in the eddy formation while intrathermocline ces would be formed by instabilities of the surface equatorward coastal currents the subthermocline aes are likely to be shed by the subsurface poleward peru chile undercurrent in the eddy core maximum temperature and salinity anomalies are of 1 c and 0 1 with positive negative values for aes ces this study also provides new insight into the potential impact of mesoscale eddies for the cross shore transport of heat and salt in the eastern south pacific considering only the fraction of the water column associated with the fluid trapped within the eddies each ce and ae has a typical volume anomaly flux of 0 1 sv and yields to a heat and salt transport anomaly of 1 3 1011 w and 3 8 103 kg s 1 respectively

fluid geochemical transect in the northern apennines central northern italy fluid genesis and migration and tectonic implications chemical and isotopic characteristics of natural gas and thermal water discharges from the western back arc tyrrhenian sea across the apennine thrust belt to the po valley and adriatic coast foredeep basins in the northern apennines central northern italy reveal a large scale fluid motion in the upper crust both vertically and horizontally on the basis of gas compositions two different domains of rising fluids have been distinguished 1 co2 rich he poor 3he 4he high domain in the western peri tyrrhenian extensional sector 2 ch4 rich he rich 3he 4he low domain in the eastern adriatic compressional sector such gases rising from various depths are crossed by a huge lateral n2 rich water flow in the peri tyrrhenian sector of ca so4 hco3 meteoric derived waters that move in a regional wide aquifer hosted in a quite thick mesozoic carbonate series morphologically the co2 vents consist of mud basins with high gas rate emission where the rising fluids move upwards through diatremes on the other hand ch4 emissions seep out from typical mud volcanoes with a reduced gas flow rate where the fluid motion is likely related to saline diapir extrusions and the methane is mostly carried to the surface by the associated mud the two rising mechanisms described locate southwest and northeast of the apennine watershed respectively from a seismic point of view the ch4 domain in the thrust belt and foredeep areas is characterized by a large number of earthquakes indirectly pointing to a different rheological behavior of the terrains with respect to the more internal peri tyrrhenian area owing to the quite high thermal gradient of the latter the boundary of the brittle ductile crust in the peri tyrrhenian sector can be located at a 10 km shallow depth although the presence of several post orogenic basins would suggest widespread extensional tectonics in all areas west of the apennine watershed those located in the easternmost part display gas vents with typical crustal 3he 4he ratios as this ratio is very sensitive to deep fluids rising from the mantle we hypothesize that such basins at the foot of the apennines are not due to tensive stress as suggested by their morphological shape they are piggy back thrust top basins developed and evolved in a still acting compressive tectonic regime

recent tectonic evolution and present stress in the northern apennines italy the present day stress field and its recent tectonic evolution in the northern apennines are reconstructed from borehole breakout analysis and focal mechanisms of crustal earthquakes and through the comparison with paleostress data we have considered 86 wells for breakout analysis with depths down to 6 7 km 125 fault plane solutions of crustal earthquakes with m 5 that occurred between 1988 and 1995 in the northern and central apennines and data of stronger earthquakes m 6 reported in other studies the tyrrhenian coastal region and the apenninic belt are characterized by shmin direction mainly trending ne sw with predominantly normal fault plane solutions along the outer front of the belt and the adriatic offshore shmin is oriented nw se and focal solutions are thrust or strike slip with maximum compression around ne sw conversely south of 43 n breakouts evidence an orthogonal direction of horizontal compression nw se following the southern apennine trend where a widespread ne sw extension was recognized by previous investigations comparing these results to the recent tectonic evolution inferred from structural geology we argue that the extension compression pair characteristic of the post tortonian evolution of the mountain belt has been migrating in time from late miocene to present only in the northern sector of the arc whereas the southern sector underwent a generalized extension at least since middle pleistocene the striking correspondence between the active compression front and the region with evidence of a remnant subducted slab suggests that the migrating extension compression pair has been controlled by progressive retreat of the slab

equatorial pacific 13 c water eddies in the eastern subtropical south pacific ocean abstract argo float profile data are used to analyze warm salty weakly stratified subthermocline eddies of tropical origin in the eastern subtropical south pacific ocean these eddies contain anomalous signatures of the equatorial pacific 13 c water that is carried poleward within the peru chile undercurrent pcu as it flows along the west coast of south america from their source along the chilean coast between 29 and 39 s the eddies spread westward and slightly northward likely at least partly advected by the subtropical gyre the eddy water properties contrast strongly with the colder fresher more strongly stratified waters of subantarctic origin being carried northward then westward by the gyre near the eddy source about 6 of argo profiles sample eddies that are above selected thresholds for both salinity and potential vorticity anomalies relative to maps of the mean distributions of these properties on and around the core isopycnal for the eddies the proportion of such profiles dimini

global observations of submesoscale coherent vortices in the ocean abstract subsurface intensified anticyclones are ubiquitous in the ocean yet their impact on the large scale transport of heat salt and chemical tracers is poorly understood these submesoscale coherent vortices scvs can trap and advect waters thousands of kilometers away from the formation region providing a transport pathway that is unresolved by low resolution earth system models however knowledge of the importance of these eddies for the large scale circulation is hindered by the lack of systematic observations here we take advantage of the global network of argo floats to identify occurrences of these eddies which appear as weakly stratified anomalous water masses with gaussian shaped vertical structures we develop a general algorithm to detect subsurface eddies that have propagated away from their source region and apply it to the database of argo float profiles resulting in roughly 4000 detections from more than 20 years of observations we further group detections into regional populations to identify hot spots of generation and mechanisms of formation analysis of regional scv statistics reveals important sites of scv generation in eastern boundary upwelling systems marginal sea overflows and mode water formation regions along major open ocean fronts because of the heat and salt anomaly contained within their cores scv could leave a significant imprint on the hydrographic properties of water masses in regions of high scv density

semiannual variability of the california undercurrent along the southern california current system a tropical generated phenomenon we used a high resolution numerical model implementation to analyze the california undercurrent cu dynamics along the southern california current system in agreement with reported observations the modeled cu was stronger during june july and december january when it flowed continuously along baja california and southern california reaching long term averages up to 6 cm s 1 previous research has associated the biannual cu intensification to the local dynamics off southern california our results evidenced however that the passage of remote semiannual coastal trapped waves sctw primarily explained the semiannual cu variability the cu was stronger 2 3 months after the passage of the upwelling sctw phase when the offshore propagation of rossby waves brought about by the sctw transit induced an energetic cross shore pressure gradient that strengthened the subsurface poleward circulation along the continental slope the sctw were independent of the local wind they corresponded to the northward extension of semiannual equatorial kelvin waves that have been observed along the northeastern tropical pacific

possible seismogenic shallow dipping normal faults in the woodlark d entrecasteaux extensional province papua new guinea active normal faults dipping less than 30 have not been documented in the seismic record but they are commonly observed in geologic structures one interpretation is that seismogenic low angle faulting is physically impossible and that the geologic structures do not form at shallow dips to better examine this problem teleseismic body waves were inverted to determine source parameters for five large earthquakes in the woodlark d9entrecasteaux region a rare example of active continental extension associated with pliocene quaternary metamorphic core complexes the inversions show that at least two and possibly four events are consistent with normal dip slip on shallow dipping faults the largest earthquake m w 6 8 is located near the mapped core complexes the shallow dipping plane for this event determined to dip between 10 and 25 is nearly coplanar to the faults bounding the core complexes and may represent slip on these or other parallel low angle structures although slip on the conjugate high angle plane cannot be ruled out observations of quaternary uplift and the similarity to the adjacent core complex bounding structures favor motion on the low angle plane similar earthquake mechanisms have not yet been documented in most other extensional provinces perhaps because instances of active core complex exhumation are rare

image masking using polygon fills and morphological transformations abstract for the vast majority of oceanographic applications advanced very high resolution radiometer avhrr data must be preprocessed prior to meaningful analysis e g empirical orthogonal function analysis frontal analysis some of these preprocessing steps include but are not limited to land masking and coastline correction polygon fill operations and morphological transformations can be effective computational tools for land masking and coastline correction collectively these tools can be used in conjunction with cloud screening techniques to isolate the oceanographically relevant portions of a satellite scene prior to analysis these masking operations also can be used on other oceanographically useful satellite data coastal zone color scanner czcs geostationary earth observing satellite goes and landsat data finally the sensitivity of the methods to regional variations in atmospheric conditions and land ocean temperature gradients is assessed using satellite data representative of tropical mid and high latitude regions these results indicate that polygon fill operations and morphological transformations can be used successfully in many global studies

temperature plant pigment optical relations in a recurrent offshore mesoscale eddy near point conception california the temperature plant pigment optical structure of a mesoscale anticyclonic eddy consistently found in shipboard surveys and satellite sensed data several hundred kilometers southwest of point conception california is described on three different time scales 100 day mesoscale annual and several year the satellite coastal zone color scanner czcs ocean color imagery detected the near surface chlorophyll structure of the eddy but in situ optical and plant pigment data suggest that such imagery does not provide a good estimate of the integrated chlorophyll field of the eddy the temperature and plant pigment boundaries of the eddy as determined from two dimensional gradients of advanced very high resolution radiometer avhrr and czcs imagery do not coincide spatially this and in situ temperature plant pigment and optical structure provide additional evidence that some eddy systems in the california current are not isolated vortex systems but rather continuously entrain waters of nonlocal origin laterally into their upper layers within the california current a ratio of avhrr czcs data is useful for separating inshore from oceanic water masses and following their surface entrainment by offshore vortices the historical 28 year california cooperative oceanic fisheries investigations data for the point conception region of the california current and remotely sensed data over this region show that the point conception eddy is a recurrent feature in the offshore california current moreover the available data provide evidence that a large number of warm core mesoscale eddies occur simultaneously in a transition zone between coastal and oceanic regimes that these features recur at preferred locations within the transition zone and that this family of eddies should impose a significant offshore boundary condition on the flow of the california current

multiple dipole eddies in the alaska coastal current detected with landsat thematic mapper data seventeen dipole eddies including five large well formed ones three second generation eddies and two double eddies were observed in the alaska coastal current near kayak island in one single scene of the landsat thematic mapper tm on april 22 1985 the digital landsat tm satellite data were computer analyzed to extract details in the near coastal circulation in the northern gulf of alaska enhancement techniques were applied to the visible and thermal ir bands the features are evident only in the visible bands because of the ability of these bands to detect the distribution of sediments in the near surface these eddies did not have a significant thermal signature the sources of these sediments are the glacial streams found throughout the gulf of alaska coast eddies of this configuration and frequency have never been observed here previously however the oceanographic and meteorological conditions are typical for this time of year these eddies should be important to the cross shelf mixing processes in the alaska coastal current and are an indicator that the flow here can be unstable at certain times of the year

recurrent patterns in surface thermal fronts associated with cold filaments along the west coast of north america abstract previous studies indicate that cold filaments off northern california have sharp southern s type and diffuse northern d type thermal boundaries in this study 44 avhrr satellite images taken from three coastal regions in the california current system northern central and baja california over a period of 10 years were used to examine the regional variation in surface frontal structure associated with cold filaments the images were specifically chose from months where past mean wind conditions indicated upwelling occurred because cold filaments appear to be more abundant during the upwelling season the images also were chosen to provide independent realizations of filament structure distributions of average gradient magnitude as a function of gradient angle were used to provide a more compact representation of the frontal information contained in each image an analysis of these distributions shows that the sharp diffuse boundary structure associated with cold filaments observed in shipboard data dominates the total surface frontal structure found in satellite data for two of the three regions studied the recurrent ubiquitous patterns found in the satellite determined frontal structure are discussed in terms of their potential effects on acoustic propagation and regional implications on ecological community structure in the california current system

a mesoscale eddy dipole in the offshore california current there is a transition zone in the california current system between inshore coastal and offshore oceanic flow this transition zone is associated with the main core of the california current and is populated with offshore mesoscale eddies the structure of isolated eddies and dipole eddy pairs found within the transition zone is examined using water mass analysis spiciness and dissolved oxygen the analyses show that these offshore mesoscale eddies have cores which contain california undercurrent water these observations and independent observations of the sitka eddy near sitka alaska support the conclusion that a bathymetrically induced instability of the california undercurrent is a likely generation mechanism for the offshore eddies this conclusion also is consistent with mathematical models of eddy generation in a subsurface poleward baroclinic current the similarity between long term mean conditions caicofi conditions observed during january 1981 and july 1985 and those of the sitka eddy coupled with the bathymetric effects provides a plausible explanation for the recurrence of offshore mesoscale eddies at preferred locations within the transition zone

the katla volcanic system imaged using local earthquakes recorded with a temporary seismic network katla is one of the most active subglacial volcanoes in iceland a temporary seismic network was operated on and around katla for 2 5 years a subset of similar to 800 analyzed local earthquakes cl

a low angle normal fault in the umbria region central italy a mechanical model for the related microseismicity abstract in the northern apennines the upper crust is thinned by a set of east dipping low angle normal faults lanfs the easternmost and more recent of these lanfs is the altotiberina fault atf located in northern umbria the geometry of the atf has been reconstructed matching surface geology with seismic reflection profiles and borehole data the fault whose average dip is 20 borders the upper pliocene quaternary tiber basin and has a displacement of about 8 km the deeper portion of the atf is located below the axial zone of the northern apennines where the strongest instrumental and historical seismicity is recorded the microseismicity of the region m 1 to evaluate the boundary conditions for the brittle activity of the atf the fault can be reactivated for low values of differential stress 1 3 t 10 mpa and tensile fluid overpressure p f 3 e g v 0 93 in the peculiar situation of the northern apennines the deep emissions of large amounts of co 2 documented in the area can be entrapped in their ascent by structural seals e g atf favouring localised fluid overpressures the impossibility of sustaining p f 3 for wide fault portions counteracted by hydraulic fracturing increased permeability under low effective stress and load weakening behaviour for normal faulting would prevent the nucleation of moderate ruptures along the fault the short lived attainment of p f 3 along small fault portions can account for the microseismic activity located along the atf which occurs on rupture surfaces in the range of 10 1 10 3 km 2

an offshore eddy in the california current system part i interior dynamics abstract from january 9 to 17 1981 detailed observations of the horizontal and vertical structure beneath one of the quasi permanent semi stationary mesoscale offshore eddy signatures in the california current system ccs discussed by bernstein breaker and whritner 1977 burkov and pavlova 1980 and simpson 1982 were made the vertical sections of temperature and density show the presence of three layer system a subsurface warm core eddy whose diameter is about 150 km at the 7 c isotherm is the dominant feature a warm surface layer which extends to a depth of 75 m lies over the eddy between the warm surface layer and the subsurface warm core eddy there is a cold core region which extends to a depth of about 200 m there is a high degree of symmetry about the vertical axis of rotation vertical sections of salinity and dissolved oxygen are entirely different from sections of temperature and density diagrams of water mass characteristics confirm that the core of the eddy found between 250 600 m consists of inshore water from the california undercurrent cu below about 700 m local waters from the deep poleward flow dpf have been incorporated into the eddy the observed distributions of properties t s o 2 are inconsistent with a single local generation process for the eddy system radial distributions of angular velocity normalized gradient velocity and relative vorticity support the use of a gaussian radial height field as an initial condition in eddy models possible reasons why ccs eddies may differ dynamically from gulf stream rings are given in the text at the time the observations were made the system as a whole was in near geostrophic balance local geostrophic balance however cannot explain the observed distribution of properties and structure the observed symmetry in the structure of the eddy system chemical evidence simpson 1984 biological distributions haury 1984 and satellite images of the cc koblinsky simpson and dickey 1984 suggest that lateral entrainment of warm oceanic and cold coastal water into the upper two layers of the three layer system by the subsurface eddy is a likely generation mechanism for the cold core region the coastal origin of the frontal structure along the northeastern quadrant and the oceanic origin of the frontal structure along the southwestern quadrant of the eddy system further support lateral entrainment as a generation mechanism for the cold core this entrainment makes the ccs eddy system different from cold core rings in the gulf stream and rather similar to some warm core eddies found in the east australian current the presence of cu water in the core of this eddy raises the question of how cu water was transported from the continental slope eddy generation mechanisms other than baroclinic instability of the cc may be required to explain the distribution persistence and core composition of offshore mesoscale eddies in the ccs there is evidence that barotropic in addition to baroclinic processes may be important

modulus decomposition of compressional and shear velocities in sand bodies the advent of borehole shear slowness measurements in sonically slow formations has lead to breakthroughs in the subsurface profiling of geological bodies in sand bodies compressional and shear velocities depend predictably on porosity mineralogy grain contacts and fluid saturation an interpretation is best performed by decomposing the velocities into moduli that are intrinsic measures of the rock frame and pore fluid compressibilities careful experiments on pure materials i e pure quartz sandstones demonstrate two simplifying constitutive relationships first the bulk and shear frame moduli are simple functions of the porosity a comparison of the measured shear frame modulus to the prediction for the pure material distinguishes sand from shale second the ratio of the bulk and shear frame moduli is a constant 0 9 independent of the porosity the measured velocities are directly inverted to yield the bulk modulus of the pore fluid the fluid saturation effects are so dramatic at high porosit

eddy properties in the california current system 1 eddy detection and tracking algorithms are applied to both satellite altimetry and a high resolution dx 5 km climatological model solution of the u s west coast to study the properties of surface and undercurrent eddies in the california current system eddy properties show remarkable similarity in space and time and even somewhat in polarity summer and fall are the most active seasons for undercurrent eddy generation while there is less seasonal variation at surface most of the eddies have radii in the range of 25 100 km sea level anomaly amplitudes of 1 4 cm and vorticity normalized by f amplitudes of 0 025 0 2 many of the eddies formed near the coast travel considerable distance westward with speeds about 2 km day consistent with the effect anticyclones and cyclones show equatorward and poleward displacements respectively long lived surface eddies show a cyclonic dominance the subsurface california undercurrent generates more long lived anticyclones than cyclones through instabilities and topographic coastline effects in contrast surface eddies and subsurface cyclones have much more widely distributed birth sites the majority of the identified eddies have lifetimes less than a season eddies extend to 800 1500 m depth and have distinctive vertical structures for cyclones and anticyclones eddies show high nonlinearity rotation speed higher than propagation speed and hence can be efficient in transporting materials offshore

the relationship between downward irradiance and upper ocean structure abstract the relationship between downward irradiance and upper ocean structure has been studied using a numerical model two general classes of irradiance parameterizations were utilized the first case i employed a single attenuation length while the second cast ii involved two attenuation lengths the latter formulation provided for enhanced absorbance in the upper few meters wind speeds of 0 1 2 3 4 5 10 and 20 m s 1 were used for the simulations in order to characterize heat versus wind dominated regimes a one dimensional second moment turbulent closure model was selected for the study so that heat could be treated differentially with depth the case ii results indicated warmer surface temperatures shallower mixed layers and more intense thermoclines than case i for wind speeds 10 m s 1 results converged for higher wind speeds there was considerably greater sensitivity to wind speed for case ii when compared with case i mean horizontal velocity as well as thermal structure was sensi

an offshore eddy in the california current system part iv plankton distributions abstract the distribution of plankton across a warm core eddy system in the california current 400 km off point conception california was studied in january 1981 the eddy system about 150 km in diameter at the 7 c isotherm was made up of a 75 m thick surface layer a cold core region extending from 75 m to about 200 m and a warm core eddy below 200 m extending to at least 1450 m casts for the vertical distribution of chlorophyll phaeophytin and integrating zooplankton net tows were taken at 37 stations located about 20 km apart on two orthogonal transects across the eddy system vertical distributions of microplankton were determined on one section from the eddy center to beyond the eastern edge integrated chlorophyll phaeophytin values were highest to the north and east of the eddy system across the system itself there was only a small increase of values near the center asymmetrical distributions of maximum concen current water was being entrained into the center of the eddy system from the northeast dinoflagellates were numerically the most important member of the microplankton especially in the deep chlorophyll maximum zooplankton distributions indicated the intermingling of warm and cool water species throughout at least the upper 200 m of the eddy system some cold water species were as abundant inside the system as outside to the north and east their numbers were much reduced in a band surrounding the system where warm water species were most abundant the presence of species characteristic of different water types throughout the region of the eddy system provides an indication of the mixing that had occurred since the system originally formed the biological data together with the physical and chemical results indicate the importance of frontal boundary processes and lateral entrainment of surrounding water into the eddy system in determining the character and productivity of such systems

seasonal renewal of the california current the spring transition off california 1 a pair of high resolution oceanographic surveys in march and april 1995 revealed a large and rapid transition from late winter to spring conditions in the coastal zone off central and southern california these data are unique in capturing the detailed three dimensional physical structure of and biological response to the spring transition in the southern california current system ccs changes associated with the transition included a strong tilting of isopycnals which lifted by up to 60 m near the coast and dropped 20 40 m offshore a subsequent increase in cross shore density gradients the development of a strong nearshore equatorward jet and an increase in net equatorward transport from the shelf break out to 300 km offshore the most dramatic physical changes were confined to the shoreward 150 km and extended at least to the depth of the core of the california undercurrent 300 m in response to these physical changes there was an apparent strong increase in primary productivity as indicated by changes in nearshore vertically integrated fluorescence and beam attenuation coefficient atmospheric and oceanic conditions in the ccs were near seasonal norms in the winter and spring of 1995 implying that a transition of the magnitude and rapidity observed here may be an annual event furthermore the development of the coastal upwelling jet was independent of the winter manifestation of the main core of the california current which was maintained well off shore this suggests that the california current is regenerated seasonally through the development and offshore evolution of the coastal upwelling jet it is not known whether the new jet joins and strengthens or replaces the offshore core of the previous winter

subthermocline eddies in the western equatorial pacific as shown by an eddy resolving ogcm abstractsporadic in situ observations have shown evidence that subthermocline eddies exist off the mindanao coast these subthermocline eddies are believed to play an important role in the heat freshwater and other ocean property transports of the region but their characteristics and in particular their pathway and source of energy are poorly explored because of the lack of long term observations analysis of results from an eddy resolving general ocean circulation model has revealed that most subthermocline eddies off the mindanao coast originate from the equatorial south pacific ocean to the west of the ninigo group these eddies propagate northward along the new guinea coast cross the equator in the far western pacific and reach the mindanao coast at a typical propagation speed of 0 12 m s 1 the dominant time scales of these eddies range between 50 and 60 days

earthquakes as a coupled shear stress high pore pressure dynamical system the migration coalescence and localization of slip seismicity and zones of high pore pressure are modeled using a porosity reduction mechanism to drive pore pressure within a fault zone in excess of hydrostatic increased pore pressure in discrete cells creates zones of low effective stress which induces slip that may propagate to surrounding cells depending on the local state of stress at slip stress is transferred using the solution for a rectangular dislocation in an elastic half space and pore pressures are redistributed by conserving fluid mass using simple assumptions about fault rheology and permeability it is shown that the interaction between shear stress and effective stress evolves to a state of earthquake clustering with repeated events locked zones and large variations in fault strength the model evolves from a uniform shear stress state on a strong fault to a heterogeneous shear stress state on a weak fault

effects of mesoscale processes on phytoplankton chlorophyll off baja california 1 using satellite sea surface height ssh and chlorophyll chl the year 2000 is analyzed to characterize the effects of mesoscale circulation patterns on phytoplankton spatial variability in the california current cc off baja california satellite data are combined with and compared to in situ field measurements chlorophyll a and hydrographic variables along vertical alongshore sections located 130 km offshore between 24 5 33 n monthly average maps of ssh and surface geostrophic velocities depict the characteristics of mesoscale meanders and eddies which correspond well with the subsurface hydrographic and velocity fields satellite derived pigment chl represent in situ fields in the upper 0 20 m overall r 0 53 p 0 05 but their representation of peak values in deep chlorophyll maxima dcm at 50 m depth are inaccurate dcm are traced in all three seasons january july descending from near the surface north of 31 n to 50 m over a large extent of the transect to the south approximately following the 24 7 25 1 isopycnals as they and the isotherms deepen to the south in january phytoplankton chlorophyll concentrations in the dcm are relatively uniform originating during upwelling events that occur farther north then following the equatorward flow of the cc during april and july the discrete maxima in the dcm occur at the centers of cyclonic meanders and the chlorophyll concentrations inside these maxima are enhanced as a result of local coastal upwelling off baja california phytoplankton blooms created by coastal upwelling spread offshore and subduct along the 24 7 25 1 isopycnals creating the dcm along the inner part of the meandering jet

main eddy vertical structures observed in the four major eastern boundary upwelling systems in the four major eastern boundary upwelling systems ebus mesoscale eddies are known to modulate the biological productivity and transport near coastal seawater properties toward the offshore ocean however little is known about their main characteristics and vertical structure this study combines 10 years of satellite altimetry data and argo float profiles of temperature and salinity and our main goals are i to describe the main surface characteristics of long lived eddies formed in each ebus and their evolution and ii to depict the main vertical structure of the eddy types that coexist in these regions a clustering analysis of the argo profiles surfacing within the long lived eddies of each ebus allows us to determine the proportion of surface and subsurface intensified eddies in each region and to describe their vertical structure in terms of temperature salinity and dynamic height anomalies in the peru chile upwelling system 55 of the sampled anticyclonic eddies aes have subsurface intensified maximum temperature and salinity anomalies below the seasonal pycnocline whereas 88 of the cyclonic eddies ces are surface intensified in the california upwelling system only 30 of the aes are subsurface intensified and all of the ces show maximum anomalies above the pycnocline in the canary upwelling system 40 of the aes and 60 of the ces are subsurface intensified with maximum anomalies extending down to 800 m depth finally the benguela upwelling system tends to generate 40 50 of weak surface intensified eddies and 50 60 of much stronger subsurface intensified eddies with a clear geographical distribution the mechanisms involved in the observed eddy vertical shapes are discussed

3d effects of sedimentary wedges and subsurface canyons ground motion amplification in the israeli coastal plain abstract we study the propagation of seismic waves the resulting ground motions and their amplification atop sedimentary structures underlying continental passive margins we employ a set of generic models with increasing complexity within a framework of a 3d numerical scheme the basic geological structure and velocity model were derived from the subsurface of the israeli coastal plain where soft sediments form a wedge over the stiffer bedrock and fill subsurface canyons that incise deep into the bedrock ground motions were modeled for both seaside and landside seismic sources we show that for a landside source peak ground velocities pgvs atop a sedimentary wedge are amplified by a maximum factor of 2 6 and on average by a factor of 1 6 relative to a reference model this amplification is mainly due to the ellipticity of rayleigh waves in the soft sediment layer spatial distribution of amplification factors shows that sedimentary wedges do not exhibit a prominent edge effect atop sediment filled canyons and landside source pgv are amplified by a maximum factor of 3 3 relative to a reference model along the exposed part of the canyon the pgv amplification factor in the canyon relative to adjacent hard rock site is up to 2 4 pgv amplification atop the sediment filled canyons is mainly due to the geometrical focusing of sh waves based on our findings we present a simplified ground motion amplification map for the israeli coastal plain electronic supplement animations of the three components of the ground motion models

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

three dimensional analytical model for the mixed layer depth we have recently developed a three dimensional semi analytical mixed layer remote sensing model which includes the horizontal advection and diffusion processes in our previous one dimensional model yan et al 1991a the three dimensional 3 d model can be used as a supplement to the one dimensional 1 d model in the area where advection is important and for a finer resolution grid prediction the 3 d thermal inertia model is based on the 3 d thermal energy conservation equation using sine transformation and inverse sine transformation methods we obtained the solution for mixed layer thermal inertia which in turn can be used to calculate mixed layer depth using a similar method to that of yan et al 1991a in the solution the thermal inertia which is proportional to the mixed layer depth is expressed as functions of sea surface temperature changes sst heat flux q and surface layer velocity u v and w the vertical entrainment and wind effects are accounted for in the model by eddy diffusivity while changes of sst result from entrainment e g if vertical entrainment is larger sst will be smaller and vice versa the advantages of this model are that it can be easily forced by remotely sensed data and that it is much simpler to compute than numerical 3 d mixed layer turbulence closure models the model was tested using the data from the advanced very high resolution radiometer multichannel sea surface temperature data set and the cooperative ocean atmosphere data set for the north pacific ocean the model predicted mixed layer depths compared favorably with the mixed layer depths calculated from 14 years of volunteer observing ship expendable bathythermograph observation data the model data comparison also exhibited a number of mesoscale features of seasonal changes and anomalies of the mixed layer depth

mesoscale distribution of clupeoid larvae in an upwelling filament trapped by a quasi permanent cyclonic eddy off northwest africa abstract the distribution of fish larvae in relation to a filament shed from the northwest african coastal upwelling was studied in february 2001 during the cruise the filament was located between 27 n and 28 n extending from the african coastal upwelling zone to the south of fuerteventura island canary islands this filament was trapped and remained over the quasi permanent cyclonic eddy observed in previous studies almost all sardina pilchardus engraulis encrasicolus and sardinella aurita larvae caught during the cruise were associated with upwelled waters and filament structures the sampled larval fish assemblage was composed by 12 6 of clupeoid larvae these were distributed as follows 73 9 were s pilchardus 20 7 were e encrasicolus and 5 4 were s aurita their distribution suggested that the coastal upwelling filament is a mechanism of transport from the upwelling area to oceanic waters but its junction with the generated cyclonic eddy may not always work as a retention structure for those transported larvae as described in previous studies physiological studies based on gut fluorescence and ets activity of clupeoid larvae as proxies for grazing and respiration respectively denoted a switch from pigmented food near the upwelling zone to unpigmented food toward the ocean this pattern agrees with observed mesozooplankton feeding along an upwelling filament in previous studies therefore this work confirms the close relationship between clupeoids distribution and mesoscale circulation as well as constitutes the first assessment of the metabolic activity of those larvae in the region

looping rafos floats in the california current system abstract looping motions of rafos floats deployed off the central california coast between 1992 and 2010 are described most floats were deployed in the california undercurrent floats at 300 m were observed to loop 26 of the time with anticyclonic rotation observed about twice as often as cyclonic rotation characteristics of anticyclonic rotation at 300 m included median swirl speeds of 14 cm s for diameters of 59 km and 14 day periods long lived 70 days and at least 8 consecutive loops anticyclonic loopers are identified as california undercurrent eddies or cuddies one cuddy was observed to move southwestward 1650 km over a period of 520 days before observations ended kinematically cuddies are similar to mediterranean water eddies meddies in the iberian basin except that meddies are somewhat stronger larger and deeper over the slope most cuddies were formed between either pt sur and pt reyes or cape mendocino and cape blanco the region north of cape mendocino is estimated to generate six cuddies each year these eddies form from waters on the inshore side of the california undercurrent as they move past cape mendocino topographic drag is the most likely formation mechanism two of eight deep floats were observed to loop one anticyclonically 1545 m for 279 days and the other cyclonically 1167 m for 192 days looping for these floats ended near taney seamounts

rapid water transport by long lasting modon eddy pairs in the southern midlatitude oceans water in the ocean is generally carried with the mean flow mixed by eddies or transported westward by coherent eddies at speeds close to the long baroclinic rossby wave speed modons dipole eddy pairs are a theoretically predicted exception to this behaviour which can carry water to the east or west at speeds much larger than the rossby wave speed leading to unusual transports of heat nutrients and carbon we provide the first observational evidence of such rapidly moving modons propagating over large distances these modons are found in the midlatitude oceans around australia with one also seen in the south atlantic west of the agulhas region they can travel at more than ten times the rossby wave speed of 1 2 cm s 1 and typically persist for about six months carrying their unusual water mass properties with them before splitting into individual vortices which can persist for many months longer

developments in exploration geophysics 1975 1980 advances in exploration geophysics have continued apace during the last six years we have entered a new era of exploration maturity which will be characterized by the extension of our technologies to their ultimate limits of precision in gravity and magnetics new inertial navigation systems permit the very rapid helicopter supported land acquisition of precise surface gravity data which is cost effective in regions of severe topography considerable effort is being expended to obtain airborne gravity data via helicopter which is of exploration quality significant progress has also been made in processing and interpreting potential field data the goal of deriving the maximum amount of accurate subsurface information from seismic data has led to much more densely sampled and precise 2 and 3 d land data acquisition techniques land surveying accuracy has been greatly improved the number of individually recorded detector channels has been increased dramatically up to 1024 in order to approximate much

stress state and fluid pressure level along the whipple detachment fault california brittle structures in the upper 200 m of the footwall of the whipple detachment fault are used to characterize the state of stress under which the detachment slipped they are younger than or coeval with chloride brecciation and those that record shear typically are either moderately northeast dipping normal structures or steep northwest striking southwest down structures that we interpret as conjugate shears from this we infer that the maximum principal stress was oriented 55 80 from the detachment while they were active the angle between the conjugate faults averages about 30 indicating failure in the transtensional regime during conjugate faulting the effective least principal stress was nearly equal to the tensile strength the whipple fault probably had a normal coefficient of static friction and it slipped under hydrostatic to only moderately elevated fluid pressure rapid mineralization in the surroundings of major fault zones allows transtensional failure there and permits differential stress to be higher than if cohesionless friction limits strength this causes resolved shear stress sufficient for slip on faults severely misoriented relative to the maximum principal stress

subthermocline eddies over the washington continental slope as observed by seagliders 2003 09 abstractin the california current system subthermocline lenslike anticyclonic eddies generated within the california undercurrent cu are one mechanism for lateral transport of the warm saline waters of the cu garfield et al established the name cuddies for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of cu water this study presents observations of subthermocline eddies collected from a time series of seaglider surveys in the northern california current system gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5 5 yr close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones water properties at the core of anticyclonic eddies were similar to those in the core of the cu over the continental slope these anticyclones are examples of cuddies anticyclonic cyclonic eddies had average radii of 20 4 20 6 km peak azimuthal current speeds of 0 25 0 23

crustal shortening and duplication of the moho in the northern apennines a view from seismic refraction data abstract a reappraisal of the dss refraction seismic campaigns of 1978 and 1974 in the northern apennines and the northern tyrrhenian sea after digitization of the original analog data and a new interpretation of crustal structures are presented in this paper the layering of the adria crust consists of a low velocity lower crust topped by a 6 7 km s horizon and an upper crust again formed by a low velocity layer capped by a faster one in the tuscany sector the crust mantle boundary and lower crust show attenuated velocities and a reduced thickness with respect to the adriatic counterpart these differences are due to the extensional tectonics restricted to tuscany and occurred in a high heat flow regime related to an uplifting astenosphere it has been confirmed that a deep thrust is responsible for moho doubling in correspondence with the zero bouguer anomaly line the tuscan moho overlaps the umbro marchean one for a length of about 30 km it is hypothesized that another shallower thrust involves upper crust in the mid tuscany range mt cetona and perugia massifs had their roots in the mantle and that subsequent extensional tectonics obliterated every trace of thrusting in lower crust and mantle rocks no conclusive proof of the existence of a european moho below a tuscan one in the area underneath elba has yet been found revision of dss data excludes the presence of a refractor reflector 60 km deep the same data however are compatible with the existence of a crust mantle boundary at 30 35 km depth

intrathermocline eddies in the coastal transition zone off central chile 31 41 s 1 the three dimensional structure and the origin of mesoscale anticyclonic intrathermocline eddies ites in the coastal transition zone ctz off central chile 31 41 s were analyzed through the combination of data from oceanographic cruises and satellite altimetry and the application of an eddy resolving primitive equation ocean model coupled with a numerical experiment using a passive tracer in this region ites are represented by subsurface lenses 100 km diameter 500 m thickness or vertical extension of nearly homogeneous salinity 34 5 and oxygen deficient 1 0 ml l 1 waters properties which are linked to the equatorial subsurface water mass essw transported poleward by the peru chile undercurrent pcuc in the coastal band at least five to seven ites were observed simultaneously in the area between 31 and 38 s during winter cruises in 1997 and 2009 satellite data indicated that the ites identified from in situ data moved westward each at a mean speed of 2 km d 1 and transported a total volume of 1 106 m3 s 1 1 sv the lifespan of each ite ranged from a few months to 1 year model results indicate that ites become detached from the pcuc under summer upwelling conditions in the coastal zone

the flow of the undercurrent over the continental borderland off southern california 1 iniroduction 2 background the bottom topography off southern california has been the cc a slow had equatornard flow is the eastern limb of termed a continental borderland to distinguish it from the ordinary the large scale anticyclonic gyre of the temperate north pacific shelf slope morphology found along most continental margins ocean the cc carries relatively cool low salinity waters of shepard and emuy 19411 islands shallow banks basins and subarctic origin to lower latitudes on average the core of the cc troughs form a complex bathymetric region extending from the has velocities of 0 10 to 0 15 m s and traces a path roughly coast to 200 lon offshore the southern california coastline has a parallel to the california baja california coastline localized concave curvature between the headland at point conception to measurements of flow can exceed 0 5 m s davis 19851 an the u s mexican border as a whole this region is referred to as instantaneous realization of the cc includes a tangle of meanders the california bight the geographic bathymetric dguration eddies and narrow jetlike flows and counterllows the cc lies at of the bight exm a pronounced influence upon the local circula varying distances off the coast and at the latitude of the tion patterns and heme upon the distributions of physical e u s mexican border there is a strong shoreward component to sverdrup and fleming 19411 and biological quantities e g the flow in most seasons especially summa the flow splits one allen 1945 owen 19801 during 1985 we conducted an oceano branch turns and flows northward into the california bight graphic survey off southern california the sampling grid was becoming the eastern limb of a cyclonic eddy centered about the designed to reveal the mumce of the geographic bathymetric offshore banks seasonally fall and winter a weak inshore features upon the circulation of the california current system countercurrent ic develops at the surface along various portion6 ccs especially the flow of the california undercurrent cu of the coastline reid et d 19581 at depth the cu cdes the survey grid also includes station lines mss the core of the waters of subtropical origin poleward along the continental slope california current cc and transects an offshore dipole eddy these waters are relatively warm and saline and have low mm simpson and lym this issue the station grid of this study trations of dissolved oxygen the cu also demonstrates a welldiffers considerably from that used by the california cooperative defined seasonality and at times opposes the overlying dace oceanic fisheries investigations calcofi surveys in both its flow maps and sections of the long term seasonal means of relaspatial resolution and depth of sampling the objectives of thic tive geostrophic velocity and distributions of ocean characteristics report are 1 to examine the spatial continuity of the cu through for the ccs are available in calcofi atlas 30 lym et d 19821 the complex bathymeny of the bight 2 to trace the poleward for a comprehensive review of the long term seasonal large scale paths and offshore spread of waters of southern origin transported description of the ccs the readex is referred to recent papas by by the cu 3 to contrast this subsurface flow with the surface hickey 1979 chelton 19841 and lynn andslnpsm 19871 and flow and 4 to compare these results with the long term calcofi to important references of pioneering work given therein mean conditions

marked along strike variations in dip of normal faults the lokichar fault n kenya rift a possible cause for metamorphic core complexes abstract the lokichar fault is a major boundary fault in the northern kenya rift mapped from seismic reflection data the fault is a mixture of high 45 60 low 20 45 and very low 12 20 angle segments the areas of least displacement up to a maximum 10 km heave are the very low angle fault segments 12 20 the southern higher angle fault segment has a maximum estimated heave of about 20 km initiation of normal faults at a low angle cannot be easily explained by rock mechanics theory common explanations for such faults include 1 rotation of higher angle faults by the domino faulting model 2 rotation of large displacement faults by isostatic instability created by the faulting rolling hinge models and 3 reactivation of low angle pre existing fabrics the lokichar fault geometry is inconsistent with any of the above explanations the very low angle segments coincide with regions of intense igneous intrusive activity re orientation of the stress axes from the simple andersonian condition could permit normal faults to form at a lower angle this may happen around intrusive complexes or by setting up a basal shear stress between flowing and static crust if faults associated with metamorphic core complexes were associated with marked along strike changes in fault angle the resulting variations in footwall uplift could give rise to the antiformal metamorphic core complex geometry

spatial and temporal characteristics of the mesoscale circulation of the california current from eddy resolving moored and shipboard measurements moored observations of currents and temperatures made in the upper 600 rn on eddy resolving scales over a 2 year period are used to examine the spatial and temporal characteristics of the california current mesoscale circulation the observations were made at three principal longitudes 124ow 126ow and 128ow in the vicinity of point arena they bracket the 600 km wide band of high mesoscale variability found along the eastern boundary of the north pacific at all locations the mesoscale variability was larger than the mean flow and the spatial modes of variability as determined from empirical orthogonal function analysis consisted of an alongshore mode a cross shore mode and a rotational mode observations made near the continental slope 124ow were dominated by the poleward flowing california undercurrent with mesoscale eddies and meanders superposed the nearshore eddy kinetic energy peaked in a band centered around 60 days observations made at 128ow near the offshore boundary between the energetic mesoscale band and the eddy desert of the northeast pacific were characterized by small means fewer eddy events and a peak in eddy kinetic energy at 120 180 days the good horizontal resolution of the current meter arrays allowed us to estimate the relative vorticity horizontal divergence and rossby number and therefore to evaluate the relative strength and occurrence of anticyclones and cyclones we found the mesoscale eddy field to be strongly nonlinear with rossby numbers ranging from 0 1 to 0 5 all of the eddies observed at the offshore site were nonlinear deep warm anticyclones shipboard hydrography revealed the origin of one of these anticyclones to be the california undercurrent and this eddy retained its strong anomalies after several months and several hundred kilometers of propagation despite the lower incidence of eddies as one moves west from the coast the eddies that we observed offshore provide evidence for propagation and transport of properties from the coast to the central north pacific across the california current system

seasonal dynamics of the surface circulation in the southern california current system abstract the seasonal dynamics of the southern california current scc is investigated using a primitive equation ocean model with real coastlines and topography the model is tested with different wind forcing and the resulting flow fields are compared to the mean and seasonal circulation inferred from long term in situ observations california cooperative oceanic fisheries investigation calcofi the model integration forced with the output winds of a regional atmospheric model rsm best captures the statistics of the observed circulation with a 0 9 correlation coefficient for the streamlines and 0 5 for the velocity fields the model integrations reveal a pronounced linear response of the flow field to changes in winds on the shelf region a dynamical feature inferred from calcofi hydrography also suggested in topex ers maps is an annually recurrent westward propagation of ssh anomalies originated in the southern california bight scb during the upwelling season the rsm integration is the only one to capture the correct timing and spatial evolution of this process we therefore use this model integration for guidance in constructing a dynamical framework to interpret the observed circulation and its variability during the upwelling season in spring there is an upward tilt of the isopycnals along the coast directly forced by the winds in the bight as the spring transitions to the summer the upwelling winds relax in the bight but are still strong in the region offshore approximately in correspondence of the continental slope positive wind stress curl condition anomalous denser waters in the location of the southern california eddy are maintained and reinforced by the combined interaction of the coastal islands geometry and the wind stress curl through ekman dynamics the adjustment process to the denser water initiates a westward propagation of ocean density anomaly through rossby waves and reinforces the cyclonic gyre like circulation of the sce increasing positive vorticity surface poleward flow maintained by the positive wind stress curl is also reinforced in proximity of point conception as a consequence of the adjustment during the summer the cyclonic gyre becomes increasingly unstable as the core of the ocean anomalies crosses the continental slope instability processes within the cyclonic region characterized by a sharp increase in eke shed eddies that leave the region either drifting to the west or interacting with existing eddies in the region offshore the eke reaches a seasonal maximum at the end the summer in the cyclonic region and in late fall further offshore where the eddies are fully developed the shedding of eddies cannot be directly seen in the calcofi observations because of the sampling aliasing for this point we rely on the strong suggestion of the model which we assume is able to capture the leading order dynamics additional integrations with a linearized version of the model are also presented to reinforce our interpretation of the westward propagation of the isopycnal anomalous displacement associated with rossby wave dynamics

crustal structure and deep reflector properties wide angle shear and compressional wave studies of the midcrustal surrency bright spot beneath southeastern georgia three component p sh and sv expanding spread profiles esp common midpoint profiles and sparse three dimensional p wave data were collected over an unusually strong midcrustal reflector the surrency bright spot sbs in southeastern georgia shear wave reflections from the sbs at 10 9 s 16 km depth and possibly from the lower crust at 18 3 s 29 km depth were recorded but required substantial source effort stacking and were too weak for reliable reflectivity measurements reflections on the esps delineate a 1 5 km thick atlantic coastal plain section whose seismic properties vp 2 53 km s vs 1 51 km s vp vs 1 67 are consistent with quartz rich sandstones and siltstones sitting atop a 15 km thick upper crust vp 6 38 km s vs 3 25 km s vp vs 1 96 which in turn overlies a 15 km thick lower crust of slower material vp 6 02 km s vs 3 26 km s vp vs 1 84 the velocity inversion may result from underthrusting of upper crustal rocks during suturing of florida to north america amplitude versus offset analyses combined with an earlier reflection polarity test and waveform modeling indicate that the sbs originates from a thin 80 120 m high impedance layer most likely a mafic dike or tectonically emplaced ultramafic body

dip range for intracontinental reverse fault ruptures truth not stranger than friction abstract histograms of fault dips have been compiled for moderate to large m 5 5 reverse slip intracontinental earthquakes with the slip vector raking 90 30 in the fault plane the principal data set is restricted to earthquakes where the fault plane in the focal mechanism can be unambiguously distinguished from the auxilliary plane the reverse fault dips are bracketed within the range 12 1 the observed dip range is consistent with reactivation of faults possessing rock friction coefficients within byerlee9s 1978 range 0 85 s 0 6 undergoing frictional lockup at dips approaching 60 the broad 25 to 35 peak may arise from progressive domino steepening of imbricate reverse faults above the optimal dip for reactivation in regions undergoing bulk shortening paucity of very low angle thrusts implies that it is generally the steeper ramps within ramp flat assemblages that fail in moderate to large earthquakes the subsidiary peak at 45 to 55 likely results from compressional reactivation of former normal faults in areas undergoing tectonic inversion requiring some degree of fluid overpressuring the results are consistent with previous studies on the dip range for active normal faults that again demonstrate frictional lockup at reactivation angles approaching 60 together these analyses suggest that byerlee friction coefficients apply to faults with displacements of up to a few kilometers

seasonal variability of alongshore geostrophic velocity off central california seasonal variability of alongshore geostrophic velocity relative to 500 dbar is examined from 23 years of hydrographic data along two sections off central california one off point sur and the other off point conception the seasonal cycles are determined by least square fits of the gappy data records to harmonics with annual and semiannual periods attention is focused on variability over the outer continental slope geostrophic flow in the upper 100 m along both sections is coherent and predominantly annual with equatorward flow from february to september and poleward flow from october to january the flow deeper than 100 m is distinctly different along the two sections the nearshore deep flow is predominantly semiannual off point conception notably different from surface flow and poleward all year with maxima in december and june this semiannual variability at depth is a prevalent feature of the california current system the nearshore deep flow off point sur is unusual in that it is predominantly annual with maximum poleward flow in december and weak equatorward flow from march to may the seasonal variations over the continental slope compare favorably with existing models of eastern boundary current systems in two respects 1 the surface flow leads the predominantly annual wind forcing in this region by about one month and 2 the deep poleward counterflow is coherent with the local poleward barotropic pressure gradient at both locations with a phase lag of approximately 2 months however contrary to the results of existing dynamical models the semiannual poleward pressure gradient and undercurrent off point conception appear to be unrelated to the wind forcing which is predominantly annual in this region these semiannual variations are highly coupled to the semiannual flow throughout the water column inside the southern california bight suggesting that they may be topographically generated

the anticyclonic baroclinic eddy off sitka alaska in the northeast pacific ocean abstract among the many mesoscale eddies found in the northeast pacific ocean is a well developed anticyclonic baroclinic eddy situated within a few hundred kilometers of sitka alaska 57 n 138 w it has definitely been observed during spring and summer 1958 summer 1960 and summer 1961 observations made at other times show some evidence of its occurrence also the trajectories of three norpax drifting buoys for april may 1977 also indicated the probable presence of an eddy there the eddy whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m recurs at the same location the center of the eddy is characterized by the following features the surface water is less saline and only somewhat warmer than at its periphery at depths within and below the halocline it is warmer less saline and contains more dissolved oxygen than at the periphery and a warm core is situated within the halocline the halocline is usually depressed by less than 100 m but

a subsurface warm eddy off northern baja california in july 2004 1 upper ocean eddies are commonly observed from remote sensing but submerged eddies are more difficult to detect during july 2004 a 21 day hydrographic survey in the southern region of the california current was carried out to investigate the mesoscale variability we observed for the first time a subsurface anticyclonic eddy off northern baja california with the same water mass characteristics as the california undercurrent the core of the eddy was quasi circular with radii of 35 km and thickness of 250 m the maximum swirl velocity was 3 cms 1 the water mass of the core of the eddy was characterized by potential temperature of 11 c salinity of 34 5 and dissolved oxygen of 1 4 mll 1 the eddy propagated westward the subsurface warm eddy could transport relatively saline water into the north pacific subtropical gyre

rate of diffuse carbon dioxide earth degassing estimated from carbon balance of regional aquifers the case of central apennine italy central italy is characterized by an anomalous flux of deeply derived co2 in the western tyrrhenian sector of central italy co2 degassing occurs mainly from focused emissions vents and strong diffuse degassing and thermal springs whereas in the eastern apennine area deep co2 is dissolved in cold groundwaters of regional aquifers hosted by mesozoic carbonate evaporite formations influx of deep co2 into 12 carbonate aquifers 12 500 km2 of the central apennine is computed through a carbon mass balance that couples aquifer geochemistry with isotopic and hydrogeological data mass balance calculations estimate that 6 5 1010 mol yr 1 of inorganic carbon are dissolved in the studied aquifers approximately 23 of this amount derives from biological sources active during the infiltration of the recharge waters 36 comes from carbonate dissolution while 41 is representative of deep carbon sources characterized by a common isotopic signature 13c 3 the calculated deep co2 influx rate ranges from 105 to 107 mol yr 1 km 2 increasing regionally from east to west in the study area

shear wave reflectivity anisotropies poisson s ratios and densities of a southern appalachian paleozoic sedimentary sequence abstract the physical properties of a sequence of paleozoic sedimentary rocks have been examined in detail with an emphasis on laboratory measurements of density shear wave velocity shear wave splitting and vp vs ratios seismic properties of 147 cores from 49 rock samples collected from the thorn hill sedimentary sequence of eastern tennessee are examined in terms of implications for future seismic studies in the southern appalachians the shear wave velocities of these rocks are strongly influenced by the relatively high shear wave velocity of quartz shear wave velocity anisotropy is present in most of the lithologic groups it is highest in the shales while being almost insignificant in the dolostones the related phenomenon of shear wave splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation splitting due to preferred mineral orientation is most prominent in the shales but also is significant in some of the carbonates compressional to shear velocity vp vs ratios of approximately 1 82 dolostones and 1 95 limestones effectively characterize the carbonates while other lithologies display wider ranges of vp vs primarily due to the influence of accessory minerals such as quartz densities of the sample suite range from 2 34 g cm3 shale to 2 86 g cm3 dolostone using average data for each lithologic group to calculate normal incidence reflection coefficients significant differences in the shear and compressional reflectivity of hypothetical interfaces are found normal incidence shear and compressional wave synthetic seismograms approximating the subsurface reflectivity of the entire thorn hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3327 m thick sequence overall the shear and compressional synthetics are similar in appearance differences are seen at some interfaces in the mississippian devonian interval which are more reflective to shear waves and in the ordovician martinsburg formation which appears more reflective to compressional waves

the subarctic and northern subtropical fronts in the eastern north pacific ocean in spring abstract the subarctic and subtropical frontal zones of the eastern north pacific ocean were surveyed in june for five consecutive years starting in 1972 these surveys from the basis for a description of the complex frontal distributions and their year to year differences the fronts appear as surface outcroppings of haloclines the subarctic halocline where salinity increases with depth and the subtropical halocline where the opposite prevails between the fronts lies a transition zone where strong vertical gradients of salinity are generally absent an examination of the northern boundary of subtropical waters in this new dataset reveals the presence of two major fronts in the subtropical frontal zone in addition to the front commonly identified as the subtropical front 18 c and 34 8 is a northern subtropical front that forms the northern boundary of the subtropical halocline in the eastern north pacific it falls some 2 to 3 of latitude north of the subtropical front and is the same front observ

seismic source theory in stratified anisotropic media we extend seismic source theory to general anisotropic media for the numerical evaluation of spectral amplitudes of point sources in multilayered anisotropic crustal models first we obtain an explicit representation of the spectral elastodynamic green s tensor in general homogeneous anisotropic media as a sum of three integrals over the corresponding three slowness surfaces the multidimensional stationary phase principle is then applied to derive an asymptotic approximation at the far field in the case of azimuthally isotropic media we offer an alternative representation of the green s tensor and its ensuing displacements fields in the form of an exact hankel transform over the horizontal wave number variable the total field is specified here in terms of two potentials an sh potential and a mixed quasi transverse quasi longitudinal potential both of which assume the role of two scalar green s functions the availability of the green s tensor in analytical form enables one to obtain readily numerical solutions for a wide selection of media and sources it is shown that the radiation field of an explosion has the following new features 1 quasi transverse waves are created with four and eight lobe patterns 2 quasi longitudinal waves are generated for the collatitudinal displacement with four lobe patterns 3 the energy ratio sv p may reach the value of 20 for more than 50 of the azimuths in crustal structures such as tuff and shales and 4 radiation patterns for vertical shear waves are created which are indistinguishable from corresponding waves produced by earthquake faults our formalism allows us to establish a haskell type matrix algorithm for a multilayered azimuthally isotropic half space which enables us to calculate body waves and surface waves in real earth crustal models

the inertial chimney the near inertial energy drainage from the ocean surface to the deep layer a three dimensional primitive equation numerical model is used to study the behavior of near inertial waves generated by surface wind stress on an plane the model is fixed depth with a rigid lid on the surface and is horizontally periodic this study shows the behaviors of the wind generated near inertial waves for four different eddies 1 a subtropical cold core eddy 2 a subtropical warm core eddy 3 a california subsurface warm core eddy and 4 the gulf stream warm core ring the mean secondary circulation generated by the wind eddy interaction has magnitude to comparable to that of the ekman current and its characteristics are determined by the relative angle between wind and current the propagation characteristics of near inertial waves are quite different depending upon the sign of the relative vorticity in a cyclonic eddy near inertial wave propagation is outward from the core of the eddy the propagation direction in an anticyclonic eddy is downward and toward the core vertically propagating waves inside the eddy are trapped above a critical layer and slowly dissipated by parameterized viscous effects the model shows that anticyclones efficiently drain near inertial energy from the surface to the deep layer below the thermocline

comparison of model and observational ocean circulation climatologies for the new zealand region 1 primitive equation three dimensional regional models driven by global models can be used to generate climatologies of the ocean circulation with 1 12 resolution these model climatologies begin to resolve the coastal circulation and it is appropriate to ask whether they are adequate to replace observational climatologies we compare circulation climatologies derived from a z coordinate 36 vertical layer model run with three different diffusivities with an observational climatology csiro atlas of regional seas cars and with surface velocities derived from lagrangian drifters deployed under the global drifter program gdp all the climatologies capture the major features in the mean circulation south of the chatham rise and east of new zealand the model climatologies agree better with gdp than does cars north of the chatham rise the models overestimate the strength of the east cape eddy wave number spectra from the models suggest that instability processes which are important in the mean are captured with diffusion less than 25 m2 s 1 the model with lowest diffusion may be providing the best estimate of the mean circulation but at the expense of numerical instability

the origin of large local uplift in extensional regions large localized uplift is commonly observed in continental regions undergoing extension these observations can be modelled by planar high angle normal faulting of an elastic upper crust overlying an inviscid lower crust isostasy provides the necessary driving force the model quantifies the role of flexural rigidity density variations in the crust and erosion and deposition of sediment

centrifugal instability and mixing in the california undercurrent abstracta regional numerical study of the california current system near monterey bay california is conducted using both hydrostatic and nonhydrostatic models frequent sighting of strong anticyclones cuddies have occurred in the area and previous studies have identified monterey bay as an apparent region of strong unbalanced flow generation here by means of a downscaling exercise a domain just downstream of point sur is analyzed and argued to be a preferred site of diapycnal mixing the scenario suggested by the simulations involves the generation of negative relative vorticity in a bottom boundary layer of the california undercurrent on the continental shelf break at point sur the current separates from the coast and moves into deep waters where it rapidly develops finite amplitude instabilities these manifest as isopycnal overturnings but in contrast to the normal kelvin helmholtz paradigm for mixing this study argues that the instability is primarily centrifugal the evidence for this com

a separating coastal upwelling jet at cape blanco oregon and its connection to the california current system the coastal upwelling region near cape blanco oregon 433n o the west coast of the united states was studied using a towed ctd on seasoar a shipboard acoustic doppler current pro ler adcp satellite sea surface temperature maps and surface drifters during august 1995 the equatorward upwelling jet was inshore of the shelfbreak north of cape blanco meandered gently o shore around the cape and then veered sharply o shore just to the south of the cape analysis of vertical sections of density velocity and spicinessa con rmed the separation of an upwelling jet and front the jet was followed from over the shelfbreak north of the cape to 100 km o shore downstream of the cape the separating jet originates from the coastal upwelling jet leaving the shelf but is augmented by an o shore branching of the poleward undercurrent by combining information from adcp streamfunction maps with analysis of hydrographic data including distributions of the tracer like quantity spicinessa a conceptual model of the three dimensional circulation near the cape emerges a mid shelf upwelling jet encounters a coastal promontory then turns o shore stretching and deepening as it crosses the continental margin the jet then turns back shoreward cyclonically where the deepened equatorward ow encounters the top of the poleward undercurrent owing along the continental slope this causes a portion of the undercurrent to turn o shore to join and strengthen the equatorward transport in the separated jet throughout the separation process the coastal upwelling front and jet are continuous robust features separation of a coastal upwelling jet is an important mechanism for cross shelf transport from the coast to the deep ocean cape blanco appears to be the northernmost point where an equatorward jet regularly separates from the coast to become an oceanic jet and thus serves as the northern boundary of the region where an intense meandering current characteristic of the california current system