the location and source parameters of the lompoc california earthquake of 4 november 1927 in this paper we address the relocation magnitudes and the style of faulting of the lompoc earthquake from a sparse assortment of teleseismic and regional seismograms the highest quality teleseismic waveform data come from a station at de bilt netherlands that remains in operation thus recordings of numerous modern events in central coastal california i e the 1969 santa lucia banks 1983 coalinga 1978 santa barbara and 1989 loma prieta earthquakes have been used for comparison with the 1927 records location constraints for the lompoc event were established from the de bilt recording by comparing s p and sss s waveform matches against the above master events to avoid the effect of unknown clock errors on locations that use absolute times these same seismograms were modeled to estimate the depth faulting parameters and source strength a similar approach using observational comparisons and numerical modeling was applied to the regional waveform data obtained from the stations at berkeley tucson and pasadena our results indicate a north northwesterly striking reverse event located about 40 km west of point conception which is in excellent agreement with the recent tsunami modeling results by satake and somerville 1992 this location is 25 km south of that proposed by hanks 1979 and well within his error bars we obtain a body wave moment of 1 10 26 dyne cm a trapezoidal time history of 2 2 2 sec and a source depth of 10 km the weak beginning of the pnl wavetrain at berkeley indicates some source complexity which is characteristic of many large events the fault parameters are strike n20 w dip 66 ne and rake 95 most seismicity catalogs report a m s 7 3 for this event after gutenberg and richter 1956 but this was a long period body wave magnitude and not a surface wave result their original worksheets indicate a smaller ms 7 0 the body waves of the loma prieta event m s 7 1 appear distinctly larger than those of the lompoc event at de bilt in agreement with our lower estimate of source strength

estimating locations and magnitudes of earthquakes in southern california from modified mercalli intensities modified mercalli intensity mmi assignments instrumental moment magnitudes m and epicenter locations of thirteen 5 6 m 7 1 training set events in southern california were used to obtain the attenuation relation mmi 1 64 1 41 m 0 00526 h 2 63 log h where h is the hypocentral distance in kilometers and m is moment magnitude intensity magnitudes m i and locations for five 5 9 m 7 3 independent test events were consistent with the instrumental source parameters fourteen historical earthquakes between 1890 and 1927 were then analyzed of particular interest are the m i 7 2 9 february 1890 and m i 6 6 28 may 1892 earthquakes which were previously assumed to have occurred near the southern san jacinto fault a more likely location is in the eastern california shear zone ecsz these events and the 1992 m 7 3 landers and 1999 m 7 1 hector mine events suggest that the ecsz has been seismically active since at least the end of the nineteenth century the earthquake catalog completeness level in the ecsz is m 6 5 at least until the early twentieth century online material figures and table of empirical mmi site corrections

a modeling study of the climatological current field and the trajectories of upwelled particles in the east australian current the climatological current field off the coast of new south wales australia is investigated using results from a field experiment and a diagnostic numerical modeling study in particular the flow dynamics are examined near smoky cape 308559s in the vicinity of the east australian current separation point modeled velocity fields compare favorably with observed velocity measurements that were obtained in this region during november 1998 an investigation of the role of advection in the alongshore momentum equation reveals that uvx and vvy change sign about the separation point representing a shift in the flow regime from onshore advection and southward acceleration north of the separation to seaward advection and weaker southward currents south of the separation bottom stress increases on the continental shelf downstream of the separation point coincident with high horizontal divergence throughout the region south of smoky cape the near bottom flow is characterized by a low burger number coincident with a subcritical richardson number these characteristics imply that the timescale in which bottom boundary layer shutdown occurs will be lengthened enabling a persistent flow of potentially nutrient rich water into the coastal region a series of lagrangian particle tracking experiments designed to investigate the fate of the upwelled water are presented motivated by an observed chlorophyll a maximum along the 25 25 su isopycnal water of this density is used as a proxy for nutrient enriched water it is found that upwelled water originates at depth to the north of smoky cape and at times well offshore south of smoky cape coastal recirculations are evident suggesting that upwelled water could be trapped in eddy fields adjacent to the coast and thus explaining why phytoplankton blooms are prevalent in the region south of smoky cape

characterizing frontal eddies along the east australian current from hf radar observations the east australian current eac dominates the ocean circulation along south eastern australia however little is known about the submesoscale frontal instabilities associated with this western boundary current one year of surface current measurements from hf radars in conjunction with mooring and satellite observations highlight the occurrence and propagation of meanders and frontal eddies along the inshore edge of the eac eddies were systematically identified using the geometry of the high spatial resolution 1 5 km surface currents and tracked every hour cyclonic eddies were observed irregularly on average every 7 days with inshore radius 10 km among various forms of structures frontal eddies associated with eac meanders were characterized by poleward advection speeds of 0 3 0 4 m s migrating as far as 500 km south based on satellite imagery flow field kinematics show that cyclonic eddies have high rossby numbers 0 6 1 9 and enhance particle dispersion patches of intensified surface divergence at the leading edge of the structures are expected to generate vertical uplift this is confirmed by subsurface measurements showing temperature uplift of up to 55 m over 24 h and rough estimates of vertical velocities of 10s of meters per day while frontal eddies propagate through the radar domain independently of local wind stress upfront wind can influence their stalling and growth and can also generate large cold core eddies through intense shear such coherent structures are a major mechanism for the transport and entrainment of nutrient rich coastal or deep waters influencing physical and biological dynamics and connectivity over large distances

on the east australian current variability encroachment and upwelling 1 observations from an intensive oceanographic field program which took place in 1998 1999 about the separation point of the east australian current eac show significant spatial and temporal variability of the eac upstream of the separation point southward flowing currents are strong with subinertial velocities of up to 130 cm s 1 in the near surface waters whereas downstream currents are highly variable in both strength 1 70 cm s 1 and direction upwelling is observed to occur through both wind driven and current driven processes with wind effects playing a lesser role by contrast the encroachment of the eac upon the coast has a profound effect on the coastal waters accelerating the southward alongshore currents and decreasing the temperature in the bottom boundary layer bbl by up to 5 degreesc as the axis of the jet moves onshore negative vorticity increases in association with an increase in nonlinear acceleration during this time bottom friction is increased the burger number is reduced and the bbl shut down time lengthens the observed upwelling is attributed to enhanced onshore ekman pumping through the bbl resulting from increased bottom stress as the southerly flow accelerates when the eac encroaches across the continental shelf

sedimentology and development of parabolic dunes grande prairie dune field alberta the grande prairie dune field in northwest central alberta is composed of parabolic and dome dunes presently inactive but which had developed under westerly winds two parabolic dune types are rec

high resolution mapping of two large scale transpressional fault zones in the california continental borderland santa cruz catalina ridge and ferrelo faults new mapping of two active transpressional fault zones in the california continental borderland the santa cruz catalina ridge fault and the ferrelo fault was carried out to characterize their geometries using over 4500 line km of new multibeam bathymetry data collected in 2010 combined with existing data faults identified from seafloor morphology were verified in the subsurface using existing seismic reflection data including single channel and multichannel seismic profiles compiled over the past three decades the two fault systems are parallel and are capable of large lateral offsets and reverse slip during earthquakes the geometry of the fault systems shows evidence of multiple segments that could experience throughgoing rupture over distances exceeding 100 km published earthquake hypocenters from regional seismicity studies further define the lateral and depth extent of the historic fault ruptures historical and recent focal mechanisms obtained from first motion and moment tensor studies confirm regional strain partitioning dominated by right slip on major throughgoing faults with reverse oblique mechanisms on adjacent structures transpression on west and northwest trending structures persists as far as 270 km south of the transverse ranges extension persists in the southern borderland a logjam model describes the tectonic evolution of crustal blocks bounded by strike slip and reverse faults which are restrained from northwest displacement by the transverse ranges and the southern san andreas fault big bend because of their potential for dip slip rupture the faults may also be capable of generating local tsunamis that would impact southern california coastlines including populated regions in the channel islands

modes of mesoscale sea surface height and temperature variability in the east australian current 1 mesoscale variability where the east australian current eac separates from the coast is studied using sea surface temperature and surface velocity streamfunction observed by satellite and a regional numerical model the mean circulation simulated by the model the regional ocean modeling system roms is compared to a high resolution regional climatology and the realism of the simulated mesoscale variability is tested by comparison to statistical analyses of the satellite data both roms and data show spectral peaks in the mesoscale energy band at periods between 90 and 180 days complex empirical orthogonal function eof analysis identifies two significant modes of mesoscale variability in the data an eddy mode for which the variability propagates southwestward along the coast and a wave mode for which phase propagation is predominantly onshore the regional model open boundary conditions include only annual and semiannual harmonics of variability so remote mesoscale forcing is absent the eddy mode is represented well in the model indicating this aspect of the circulation results from local instabilities of the flow and that its underlying dynamical process is simulated well while the observed and modeled wave modes have some similarities their differences suggest the model is deficient in representing westward propagation of mesoscale period variability in the region whatever the source of this energy the orthogonality property of the eof analysis indicates the wave mode does not interact significantly with eddy processes in the eac separation

comments on the lompoc california earthquake november 4 1927 m 7 3 and its aftershocks by thomas c hanks

momentum balances on the north carolina inner shelf four months of moored current pressure temperature conductivity wave and wind observations on the north carolina shelf indicate three dynamically distinct regions the surf zone the inner shelf between the surf zone and the 13 m isobath and the midshelf in the surf zone the along shelf momentum balance is between the cross shelf gradient of the wave radiation stress and the bottom stress the linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone on the inner shelf the along shelf momentum balance is also frictional the along shelf wind stress and pressure gradient are balanced by bottom stress in the cross shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the coriolis force geostrophy and wave setdown from shoaling unbroken surface gravity waves at midshelf the along shelf momentum balance is less frictional and hence flow accelerations are important the cross shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown the cross shelf density gradient is in thermal wind balance with the vertical shear in the along shelf flow in depths as shallow as 10 m the dominant along shelf momentum balances provide a simple estimate of the depth averaged along shelf current in terms of the measured forcing i e wind stress wave radiation stress divergence and along shelf pressure gradient that reproduces accurately the observed cross shelf variation of the depth averaged along shelf current between the surf zone and midshelf

variation in sea temperature and the east australian current in the solitary islands region between 2001 2008 abstract improved understanding of the east australian current eac and sea temperature patterns within the solitary islands region of northern new south wales an area where tropical and temperate faunas overlap is an essential step in explaining cross shelf gradients in biotic patterns sea temperature at 10 m was logged using thermistors at seven stations every 30 minutes between january 2001 and december 2008 stations were replicated in three distance from shore categories 6 km from the coast corresponding with predominant assemblage patterns of reef fish daily monthly seasonal and yearly sea temperature patterns were compared between and within stations and distance from shore categories sst images were examined to determine the role of the eac in producing short period 2 to 4 days temperature anomalies sea temperatures ranged between 16 6 27 5 c and were highest offshore and lowest inshore offshore sites experienced average temperatures 1 c higher than nearshore sites over the 8 year study there was considerable variation in sea temperature between years with 2002 and 2006 being the warmest and 2007 the coolest these patterns correspond with strong inter annual variability of the eac at the scale of the solitary islands region the eac influenced shelf waters most strongly during late spring summer when temperatures were also most variable over the smallest temporal scales hours days short period anomalies between and within stations could largely be explained by variable encroachment of the eac across the shelf and or colder intrusions of water forming adjacent to the coastline previous assumptions that the eac strongly influences gradients in the distribution of tropical species in this nearshore region are strongly supported

inversion of tsunami waveforms for the estimation of heterogeneous fault motion of large submarine earthquakes the 1968 tokachi oki and 1983 japan sea earthquakes waveform inversion of tsunami data provides independent and reliable information on earthquake source processes the propagation effects of tsunamis are accounted for by computing green s functions using a finite difference method and using the known bathymetry which is much better constrained than the seismic velocity structure the observed tsunami waveforms are corrected for the response of the tide gage system by using the results of in situ measurements using green s functions computed from bathymetric data on a 2 5 km grid and the observed waveforms digitized at 1 min intervals the spatial resolution of the faulting heterogeneity by the present method is as small as 30 km this method is applied to the 1968 tokachi oki and 1983 japan sea earthquakes the slip is concentrated at the northwestern part of the fault plane for the 1968 event for the 1983 event the slip on the fault just north of the epicenter is twice that of the other parts these asperity distributions are similar to those inferred from seismic wave analysis however the recovered total seismic moments are smaller the present method is shown to be a useful technique for estimating heterogeneous fault motion especially for historical events with no or poor seismic records and tsunami earthquakes in which the excitations of seismic and tsunami waves are different

intrusive upwelling in the central great barrier reef in the central great barrier reef the outer continental shelf has an open reef matrix that facilitates the exchange of waters with the coral sea during austral summer cool water intrudes onto the shelf along the seafloor temperature observations reveal cool bottom intrusions during a 6 year period from the queensland integrated marine observing system s palm passage mooring a metric is used to identify 64 intrusion events these intrusions predominantly occur from october to march including the wet season during an event the outer shelf s near bottom temperature decreases by 1 3 c typically over 1 week the near bottom salinity tends to increase while near surface changes do not reflect these tendencies intrusion events occur predominantly with either weakening equatorward winds or poleward wind bursts a regional hydrodynamic model for the great barrier reef captures the timing and amplitude of these intrusions during intrusion events isotherms tend to uplift over the continental slope and onto the shelf and the east australian current intensifies poleward over the shelf a bottom intensified onshore current coincides with bottom cooling for numerous events the model diagnostics reveal that the cross shelf flow is dominated by the geostrophic contribution a vertical circulation tilts the isopycnals upward on the southern side of the passage causing an along shelf density gradient and geostrophic onshore flow with depth while wind fluctuations play a major role in controlling the along shelf currents model results indicate that a concurrent topographically induced circulation can assist the onshore spread of cool water

quantitative mapping of the east australian current encroachment using time series himawari 8 sea surface temperature data the east australian current eac is a highly dynamic western boundary current that exerts significant influences on the marine ecosystem off south east margin of australia for the first time a quantitative mapping of the eac system was conducted using himawari 8 sea surface temperature data and a topographic position index tpi based image processing technique the validation using bluelink reanalysis data suggested good reliability of our mapping results subsequent quantitative examination provides new insights into the eac s cross shelf movement which is a driving force of adjacent slope shelf circulations along the coast of new south wales nsw large scale and high frequency eac encroachment was observed being every 60 80 days upstream 30 32 s and every 90 100 days downstream 33 35 s which is associated with the eac s intrinsic oscillation and eddy shedding downstream the eac encroachment exhibits a 20 day longer period and a double amplitude such dephasing is most likely due to the abrupt change of regime at the eac separation point 32 33 s upstream the eac encroachment also exhibits seasonality being 10 15 km closer to the coast in austral summer which is due to the seasonal eac broadening higher frequency 16 32 days and smaller magnitude eac intrusion was observed along the entire nsw coast 28 37 s which is possibly associated with eac s meanders and frontal eddies in the extension zone 37 30 44 s we observed maximum eac encroachment in summer which is an expression of the seasonal boundary flow off eastern tasmania a dataset of eac encroachment 2015 2017 is available see data availability

the fraser gyre a cyclonic eddy off the coast of eastern australia this paper examines the on shelf circulation of the eastern australian continental shelf for a region off southeast queensland we identify a characteristic seasonally reoccurring wind driven cyclonic flow it influences the cross shelf exchange with the east australian current eac which is the western boundary current of the south pacific ocean we refer to this cyclonic circulation as the fraser gyre it is located south of fraser island between about 25 s and 27 s the region is adjacent to the intensification zone of the eac where the current accelerates and establishes a swift albeit seasonally variable southward boundary flow through the analysis of several data sets including remotely sensed sea surface temperature and sea surface height anomaly satellite tracked surface drifters ocean and atmospheric reanalysis data as well as geostrophic currents from altimetry we find that the on shelf fraser gyre develops during the southern hemisphere autumn and winter months the gyre is associated with a longshore near coast northward flow maximum northward on shelf depth averaged velocities are estimated with about 0 15 0 26 ms 1 the flow turns eastward just to the south of fraser island and joins the persistent southward eac flow along the shelf break the annual mean net cross shelf outward and inward flow associated with the gyre is about 1 17 0 23 sv in the north and 0 23 0 13 sv 1 sv 106 m3s 1 in the south mean seasonal water renewal time scales of the continental shelf are longest during austral winter with an average of about 3 3 days due to the fraser gyre retaining water over the shelf however monthly estimates range from 2 to 8 days with the longer timescale during the austral autumn and winter the southerly wind during austral autumn and winter is identified as controlling the on shelf circulation and is the principal driver of the seasonally appearing fraser gyre the conceptual model of the fraser gyre is consistent with general physical principals of the coastal shelf circulation a southerly wind is associated with surface layer flow toward the coast a near coast positive ssha with a current in the direction of the wind down welling and export of shelf water the fraser gyre influenced cross shelf exchanges are possibly facilitating the offshore transport of fish larvae sediments nutrients river discharges and other properties across the shelf break and into the southward flowing eac during the austral autumn and winter

an avenue of eddies quantifying the biophysical properties of mesoscale eddies in the tasman sea 1 the tasman sea is unique characterised by a strong seasonal western boundary current that breaks down into a complicated field of mesoscale eddies almost immediately after separating from the coast through a 16 year analysis of tasman sea eddies we identify a region along the southeast australian coast which we name eddy avenue where eddies have higher sea level anomalies faster rotation and greater sea surface temperature and chlorophyll a anomalies the density of cyclonic and anticyclonic eddies within eddy avenue is 23 and 16 higher respectively than the broader tasman sea we find that eddy avenue cyclonic and anticyclonic eddies have more strongly differentiated biological properties than those of the broader tasmansea as a result of larger anticyclonic eddies formed from coral sea water depressing chl a concentrations and for coastal cyclonic eddies due to the entrainment of nutrient rich shelf waters cyclonic eddies within eddy avenue have almost double the chlorophyll a 0 35 mg m 3 of anticyclonic eddies 0 18 mg m 3 the average chlorophyll a concentration for cyclonic eddies is 16 higher in eddy avenue and 28 lower for anticyclonic eddies when compared to the tasman sea with a strengthening east australian current the propagation of these eddies will have significant implications for heat transport and the entrainment and connectivity of plankton and larval fish populations citation everett j d m e baird p r oke and i m suthers 2012 an avenue of eddies quantifying the biophysical properties of mesoscale eddies in the tasman sea geophys res lett 39 l16608 doi 10 1029 2012gl053091

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

eddy shedding and energy conversions in the east australian current 1 mesoscale variability and eddy shedding in the tasman sea particularly of the east australian current eac is studied through the analysis of remotely sensed observations and outputs from a global ocean model previous observations of the western boundary current separation from the coast showed strong variability at periods ranging between 90 and 140 days we show from satellite altimetric observations that rapid northward migration of the separation point of the eac follows the formation of large eddies at periods of 100 days after an eddy separation event the normally southward flowing current swiftly assumes a more zonal configuration near the separation latitude with a cyclonic circulation developing inshore the formation of large separation eddies is preceded by the southward propagation of sea level anomalies along the east australian continental slope from 25 s sea level anomalies grow as they travel south eventually being pinched off in the form of large anticyclones at 32 s in the current retroflection area energy conversion terms in a global ocean model and in altimetric data suggest both barotropic and baroclinic instability may account for the growth of these anomalies as they propagate south east of the main eac jet there is evidence that eddies may be feeding potential energy back to the mean flow

cyclonic entrainment of preconditioned shelf waters into a frontal eddy the volume transport of nutrient rich continental shelf water into a cyclonic frontal eddy entrainment was examined from satellite observations a slocum glider and numerical simulation outputs within the frontal eddy parcels of water with temperature salinity signatures of the continental shelf 18 19 c and 35 5 respectively were recorded the distribution of patches of shelf water observed within the eddy was consistent with the spiral pattern shown within the numerical simulations a numerical dye tracer experiment showed that the surface waters 50 m depth of the frontal eddy are almost entirely 95 shelf waters particle tracking experiments showed that water was drawn into the eddy from over 4 of latitude 30 34 5 s consistent with the glider observations the modeled particles entrained into the eddy sunk relative to their initial position particles released south of 33 s where the waters are cooler and denser sunk 34 m deeper than their release position distance to the shelf was a critical factor in determining the volume of shelf water entrained into the eddy entrainment reduced to 0 23 sv when the eddy was furthest from the shelf compared to 0 61 sv when the eddy was within 10 km of the shelf from a biological perspective quantifying the entrainment of shelf water into frontal eddies is important as it is thought to play a significant role in providing an offshore nursery habitat for coastally spawned larval fish

baroclinic response of sydney shelf waters to local wind and deep ocean forcing a study of the forcing processes responsible for upwelling events in the coastal ocean of sydney australia has been performed using data collected over the summer of 1994 from a shore normal aligned mooring array and a numerical model analyses of the data show that vertical displacements of fluid in the nearshore zone responded principally to the local wind stress during the experimental period however intrusions of mesoscale east australian current features are shown to significantly influence the vertical structure of the water column over the middle and outer shelf regions numerical simulations are performed to investigate the internal processes occurring during strong steady intrusion events of the east australian current onto the sydney shelf these simulations suggest that ekman transport in the bottom boundary layer underlying an intrusion event is not an efficient mechanism for advecting colder water into the nearshore zone on the sydney shelf preconditioning of shelf waters by the east australian current and concurrent forcing by local winds is suggested as an efficient process by which upwelling states may be achieved in the sydney coastal ocean

on the dynamics of an observed thermal front off central eastern australia in the alongshore currents are measured by a mooring array over the inner shelf with use of avhrr images adcp and ctd surveys it is reasoned that these events correspond to the periodic advection of a thermal front past the inshore moorings the front involves a temperature change of 1 2 c with a southward jet of greater than 0 5 ms 1 over a width of 1 2 km in 25 m of water the dynamical balances of the momentum equations are examined it is demonstrated that at the onset of each event the local tendency of alongshore velocity is balanced by across shore advection additionally a quasi balance between the surface and bottom stress terms is noted throughout the experiment demonstrating the prominence of mixing over the inner shelf index terms 4528 oceanography physical fronts and jets 4512 oceanography physical currents 4576 oceanography physical western boundary currents keywords fronts upwelling momentum balance coastal circulation inner shelf circulation

agulhas current meanders facilitate shelf slope exchange on the eastern agulhas bank large solitary meanders are arguably the dominant mode of variability in the agulhas current observational studies have shown that these large meanders are associated with strong upwelling velocities and affect the shelf circulation for over 100 days per year here 10 year time series from two ocean general circulation models are used to create a composite picture of the agulhas current and its interactions with the shelf circulation in meandering and nonmeandering modes both models show good agreement with the size propagation speed and frequency of observed meanders these composite meanders are then used to examine the response of shelf waters to the onset of large meanders with the use of model output enabling the dynamics at depth to be explored results show a composite mean warming of up to 3 c of depth averaged temperature along the shelf edge associated with an intrusion of the current jet onto the shelf driven by an intensification of the flow along the leading edge of large meanders however this intensification of flow results in cooling of bottom waters driving cold events at the shelf break of 10 c at 100 m thus the intensification of the current jet associated with large meander events appears to drive strong up and downwelling events across the inshore front of the agulhas current facilitating shelf slope exchange

influence of a western boundary current on shelf dynamics and upwelling from repeat glider deployments the separation zone of a dynamically important western boundary current wbc is resolved through a series of sustained glider deployments along the coastal edge of the jet the comprehensive data set from 23 missions 2008 2014 provides a new high resolution hydrographic climatology which is exploited to understand the spatial extent of dense water uplift and the depth averaged momentum balances across the east australian current eac separation zone the predominantly geostrophic shelf circulation and temperature fields are least most variable upstream downstream where encroachment separation dominates for the first time we resolve the nonlinear advection terms which are considerable in the along shelf momentum balance near bottom water masses indicate dense water uplift as a result of the eac encroachment and separation the data provide both new insight into and a climatology of separation induced uplift and demonstrate a successful model for repeat glider missions in a dynamic wbc environment

reply to w gawthrop s comments on the lompoc california earthquake november 4 1927 m 7 3 and its aftershocks

observed bottom boundary layer transport and uplift on the continental shelf adjacent to a western boundary current western boundary currents strongly influence the dynamics on the adjacent continental shelf and in particular the cross shelf transport and uplift through the bottom boundary layer four years of moored in situ observations on the narrow southeastern australian shelf in water depths of between 65 and 140 m were used to investigate bottom cross shelf transport both upstream 30 s and downstream 34 s of the separation zone of the east australian current eac bottom transport was estimated and assessed against ekman theory showing consistent results for a number of different formulations of the boundary layer thickness net bottom cross shelf transport was onshore at all locations ekman theory indicates that up to 64 of the transport variability is driven by the along shelf bottom stress onshore transport in the bottom boundary layer was more intense and frequent upstream than downstream occurring 64 of the time at 30 s wind driven surface ekman transport estimates did not balance the bottom cross shelf flow at both locations strong variability was found in bottom water transport at periods of approximately 90 100 days this corresponds with periodicity in eac fluctuations and eddy shedding as evidenced from altimeter observations highlighting the eac as a driver of variability in the continental shelf waters ocean glider and hf radar observations were used to identify the bio physical response to an eac encroachment event resulting in a strong onshore bottom flow the uplift of cold slope water and elevated coastal chlorophyll concentrations

lagrangian and eulerian characterization of two counter rotating submesoscale eddies in a western boundary current in recent decades high spatial resolution ocean radar and satellite imagery measurements have revealed a complex tangle of submesoscale filaments and eddies in the surface velocity temperature and chlorophyll a fields we use a suite of high resolution data to characterize two counter rotating short lived eddies formed at the front between the warm east australian current eac and temperate coastal waters 308s eastern australia in this region submesoscale filaments and short lived eddies are dynamically generated and decay at time scales of hours to days dominant cyclonic filaments of o 1 rossby number formed along frontal jets and eddy boundaries generating localized ageostrophic circulations at the submesoscale measurements of over ocean wind direction and surface currents from high frequency radars reveal the influence of the short term small scale wind forcing on the surface circulation enhancement of the horizontal shear frontal jet destabilization and the generation and decay of the cyclonic eddy by contrast the anticyclonic eddy formation was most likely associated with eac mesoscale instability and anticyclonic vorticity lagrangian tracks show that surface particles can be temporarily trapped in the eddies and frontal convergent zones limiting their transport mixing between eac derived and coastal waters was increased along the frontal regions and particles starting at the divergent regions around the eddies experienced significant dispersion at submesoscales the cyclonic cold core eddy entrained high chlorophyll a shelf waters on its convergent side suggesting spiral eddy cyclogenesis

cross shelf dynamics in a western boundary current regime implications for upwelling abstractthe cross shelf dynamics up and downstream of the separation of the south pacific ocean s western boundary current wbc are studied using two years of high resolution velocity and temperature measurements from mooring arrays the shelf circulation is dominated by the east australian current eac and its eddy field with mean poleward depth integrated magnitudes on the shelf break of 0 35 and 0 15 m s 1 up and downstream of the separation point respectively the high cross shelf variability is analyzed though a momentum budget showing a dominant geostrophic balance at both locations among the secondary midshelf terms the bottom stress influence is higher upstream of the separation point while the wind stress is dominant downstream this study investigates the response of the velocity and temperature cross shelf structure to both wind and eac intrusions despite the deep water up to 140 m the response to a dominant along shelf wind stress forcing is a classic two layer ekman structure du

on the variability of the east australian current jet structure meandering and influence on shelf circulation given the importance of western boundary currents over a wide range of scales in the ocean it is crucial that we understand their dynamics to accurately predict future changes for this we need detailed knowledge of their structure and variability here we investigate the jet structure of the east australian current eac using observations from hf radars and moorings deployed at 30 s 31 s meandering core velocity width and eddy kinetic energy eke are quantified from 4 years of hourly 1 5 km resolution surface current maps 2012 2016 to obtain the most detailed representation of the surface eac jet to date the eac flows predominantly over the 1 500 m isobath 50 km offshore but makes large amplitude displacements eastward every 65 100 days the time scale associated with mesoscale eddy shedding at the eac separation smaller amplitude higher frequency meanders occur every 20 45 days using a coordinate frame that follows the jet we show core velocity and eke exhibit seasonality in both magnitude and variance being maximum in summer 1 55 m s 1 mean core velocity minimum in winter 0 8 m s 1 however it is the eddy shedding time scale that dominates jet variability as the eac moves shoreward shelf temperature and along stream velocity vary linearly with jet movement within 35 km of the core the eac is within this range 75 of the time demonstrating its importance to the shelf circulation temperature and velocity fluctuations at the 70 m 100 m isobath are more influenced by wind eac encroachment with the strongest response occurring when wind and eac act constructively

the separation of the east australian current a lagrangian approach to potential vorticity and upstream control the east australian current eac is the western boundary current flowing along the east coast of australia separating from the coast at approximately 34 s after the separation two main pathways can be distinguished the eastward flowing tasman front and the extension of the eac flowing southward the area south of the separation latitude is eddy rich and the separation latitude of the eac is variable little is known of the properties of the water masses that separate at the bifurcation of the eac this paper presents new insights from the lagrangian perspective where the water masses that veer east and those that continue south are tracked in an eddy permitting numerical model the transport along the two pathways is computed and a 1 3 ratio between transport in the eac extension and transport in the tasman front is found the results show that the fate of the particles is to first order already determined by the particle distribution within the eac current upstream of the separation latitude where 85 of the particles following the eac extension originate from below 460 m and 90 of the particles following the tasman front originate from the top 460 m depth at 28 s the separation and pathways are controlled by the structure of the isopycnals in this region analysis of anomalies in potential vorticity show that in the region where the two water masses overlap the fate of the water depends on the presence of anticyclonic eddies that push isopycnals down and therefore enable particles to travel further south

mesoscale structure of the mean east australian current system and its relationship with topography abstract we document the mean circulation of the east australian current eac system which is the major western boundary current in the southwest pacific ocean a new high resolution climatology of the region csiro atlas of regional seas cars is used to produce regional fields of steric height and sections of geostrophic velocity the realism of these fields has been enhanced by the high spatial resolution allowance for bathymetric control and the influence of land barriers the increased detail in the maps and sections reveal the major influence that the complex regional topography has on the circulation the results also provide the appropriate resolution for comparison with recent model studies of the region we have been able to both resolve well known features with greater detail and identify previously unrecognized aspects of the circulation important results include 1 the zonal inflow north of 30 s breaks into a series of individual jets after flowing through the island chains as suggested by recent model results 2 the interaction of the zonal inflow with the local topography as it undergoes bifurcation is documented 3 a detailed picture of the evolution of the eac at the western boundary is presented including surface currents and transports 4 separation and recirculation of the eac within the tasman abyssal basin are shown to occur as a double cell structure constrained by bathymetry 5 the eac outflow is resolved as a series of eastward and northeastward currents 6 the path of the tasman front is defined as it interacts with the tasman ridge systems 7 a quasi permanent eddy is identified for the first time adjacent to the norfolk ridge northwest of new zealand

transport and retention in an upwelling region the role of across shelf structure abstract the paradox of upwelling is the relationship between strong wind forcing nutrient enrichment and shelf productivity here we investigate how across shelf structure in velocity and hydrography plays a role in the retention inshore and export offshore of particles such as nutrients plankton and larvae we examine the spatial structure of the coastal currents during wind driven upwelling and relaxation on the northern californian shelf the field work was conducted as part of the wind events and shelf transport west project a 5 year nsf coop funded study of the role of wind driven transport in shelf productivity off bodega bay northern california from 2000 to 2003 we combine shipboard velocity profiles adcp and water properties from hydrographic surveys during the upwelling season to examine the mean across shelf structure of the hydrography and velocity fields during three contrasting upwelling seasons and throughout the upwelling relaxation cycle we also present results from two winter seasons that serve as contrast to the upwelling seasons during all three upwelling seasons clear spatial structure is evident in velocity and hydrography across the shelf exemplified by current reversals inshore and the presence of a persistent upwelling jet at the shelf break this jet feature changes in structure and distance from the coast under different wind forcing regimes the jet also changes from the north of our region where it is a single narrow jet adjacent to the coast and to the south of our region where it broadens and at times two jets become evident we present observations of the california under current which was observed at the outer edge of our domain during all three upwelling seasons the observed across shelf structure could aid both in the retention of plankton inshore during periods of upwelling followed by relaxation and in the export of plankton offshore in the upwelling jet

the cold core eddy and strong upwelling off the coast of new south wales in early 2007 abstract during the austral summer of 2006 07 a series of extreme oceanic events occurred in the tasman sea following a series of strong wind driven upwelling events an intense cold core eddy developed off sydney australia a data assimilating eddy resolving ocean model is used to create a three dimensional time varying reanalysis of these events the reanalysis indicates that the cold anomalies associated with the upwellings were in excess of 5 c near the coast where sea level decreased by as much as 0 2 m the reanalysed three dimensional structure of the cold core eddy shows the eddy leaning to the west north west in towards the continental shelf the diameter of the eddy is about 100 km and the sea level anomaly at the eddy centre peaks at around 1 m with an associated sub surface temperature anomaly in excess of 8 c at 200 m depth corresponding to an upward isotherm excursion of 600 m the circulation around the cyclonic eddy is ageostrophic with upwelling in the southern sector of the eddy where flow is onshore and climbing the continental slope and downwelling in the northern sector where flow is descending off the slope three dimensional trajectories of water parcels around the eddy involve 50 100 m vertical excursions based on the reanalysed circulation and composite satellite images of chlorophyll a we hypothesise that the circulation around the eddy led to significant nutrient enrichment in the euphotic zone around the perimeter of the eddy

location and size of the 1927 lompoc california earthquake from tsunami data abstract the lompoc earthquake of 4 november 1927 m s 7 0 was one of the largest offshore events in california and the associated tsunami was recorded in hawaii as well as on the california coast the epicenter of this event has long been debated one location is offshore where the ocean is about 1000 m deep whereas another location is very near shore beneath a water depth of less than 100 m we analyzed the tsunami records from this event from tsunami travel times the source location was estimated to be well offshore at about 34 2 n 120 75 w consistent with recent seismic waveform analysis waveform modeling of the tsunami also supports an outer continental shelf location the seismic moment is estimated to be 3 10 26 dyne cm corresponding to a moment magnitude of 7 0 the tsunami computation reproduced the large tsunami in hawaii indicating that the observed large tsunami was due to bathymetry effects particularly near hilo bay the tsunami magnitude of 7 6 obtained from the hawaiian recordings by abe thus appears to be an overestimate

topographically induced upwelling off eastern australia abstract a high resolution numerical study of an idealized western boundary current flow over variable topography is presented with application to the east australian current eac the results indicate that alongshelf topographic variations off australia s east coast cause the eac to accelerate over the narrowing continental shelf near cape byron this acceleration is sufficient to hinder the geostrophic adjustment in the bottom boundary layer bbl which would usually cause the eac driven bbl to shut down consequently a region of persistent high bottom stress was established off cape byron which was responsible for driving an upwelling bbl it is shown that the enhanced vertical mixing associated with a low richardson number flow beneath the eac reduced the local stratification consequently the burger number is decreased resulting in a long shutdown timescale of the bbl which enables a nearshore thermal to be established and maintained such fronts are commonly observed in the region as a p

the oroville earthquakes a study of source characteristics and site effects half space modeling in the time domain of broadband seismic records from the oroville aftershock sequence demonstrates that these events have simple sources systematic scaling between the far field source duration and seismic moment for the aftershocks studied here and other california earthquakes confirms brune s 1970 source model and shows that the stress drops for california earthquakes range between 10 and 100 bars these events also show no trend in stress drop as a function of size for 3 0 or m sub l or 6 4 analysis of the static deformation associated with the main shock shows that the slip occurred on a fault 81 km sup 2 in area corresponding to the zone defined by the first 3 days of aftershocks teleseismic studies indicate that the seismic source area was 50 km sup 2 corresponding to a zone completely free of aftershocks in the middle of the aftershock zone both results imply a stress drop of 29 39 bars and seismic moment between 5 7 and 8 7 x 10 sup 24 dyn cm the evidence suggests that faulting occurred seismically on the central portion of the fault and propagated out slowly enlarging the fault plane complicated waveforms recorded for the same events at nearby sites on alluvium indicatemore the critical role that propagation through complex structure plays in determining the character of the observed seismic signal at close in stations modeling of these records show that dipping structure may account for the observed waveform complexities less

seasonality of sporadic physical processes driving temperature and nutrient high frequency variability in the coastal ocean off southeast australia physical processes forced by alongshore winds and currents are known to strongly influence the biogeochemistry of coastal waters combining in situ observations moored platforms hydrographic surveys and satellite data sea surface wind and sea surface height we investigate the transient occurrence of wind driven upwelling downwelling and current driven upwelling events off southeast australia remote sensed indices are developed and calibrated with multiannual time series of in situ temperature and current measurements at two shelf locations based on archives up to 10 years long climatological analyses of these indices reveal various latitudinal regimes with respect to seasonality magnitude duration of events and their driving mechanisms wind or current generally downwelling favorable winds prevail in this region however we demonstrate that up to 10 wind driven upwelling days per month occur during spring summer at 28 33 5 degrees s and up to 5 days in summer further south current driven upwelling upstream of the east australian current separation zone approximate to 32 degrees s occurs twice as often as downstream using independent in situ data sets we show that the response of the coastal ocean is consistent with our climatology of shelf processes upwelling leads to a large range of temperatures and elevated nutrient concentrations on the shelf maximized in the wind driven case while downwelling results in destratified nutrient poor waters the combination of these sporadic wind and current driven processes may drive an important part of the high frequency variability of coastal temperature and nutrient content our results suggest that localized nutrient enrichment events of variable magnitude are favored at specific latitudes and seasons potentially impacting coastal ecosystems key points multisensor analysis of shelf processes combining in situ and satellite data spatio temporal variability of transient wind and current driven up downwelling cold nutrient rich water intrusions favoured at specific locations seasons

m 6 earthquakes in southern california during the twentieth century no evidence for a seismicity or moment deficit abstract a broadly based report on seismic hazards in southern california wgcep 1995 concluded that the predicted seismicity exceeds that observed since 1850 a subsequent independent analysis argued that infrequent huge m 8 earthquakes are needed to explain the low rate of large earthquakes jackson 1996 frequency magnitude relationships and earthquake reporting suggest that the 1903 to 1997 catalog we present here with a b value of 1 0 and a rate of m 6 shocks of 0 42 to 0 49 yr 1 is nearly complete in contrast the 1850 to 1994 catalog used by wgcep is incomplete before the turn of the century and thus its reported seismicity rate of 0 32 m 6 shocks yr 1 is too low principally because the wgcep 1995 model results in b values of up to 4 0 for regions of lesser and blind faults the rate of m 6 shocks off the san andreas system predicted by the wgcep 1995 model is three times greater than that observed in this century because they obtained b 0 4 for m b 2 2 for m 7 3 on major faults their expected rate of m 7 san andreas shocks is twice as high as observed thus part of the seismicity and moment discrepancy identified by wgcep was caused by use of an incomplete catalog and part was caused by inappropriate b values we obtain a southern california moment release rate of 8 to 12 10 18 n m yr 1 which cannot be distinguished from the moment release estimated by fault slip or the moment accumulation inferred from plate motions or geodetically measured shear strain we thus find no evidence for a moment deficit significant aseismic moment release or for rare m 8 earthquakes off the san andreas fault system finally the number of m 6 earthquakes per decade does not depart significantly from a poisson process during this century and thus we find no evidence that the rate of seismicity is increasing now or at any other time since 1900

tsunamis within the eastern santa barbara channel several locally generated tsunamis have been reported in southern california during the past 200 years yet the hazard from locally generated tsunamis has received considerably little attention we consider here tsunamis generated by coseismic displacements on the channel islands thrust cit system as well as waves generated by slope failures along the walls of the santa barbara channel we find that purely tectonic sources could generate regional tsunamis with 2m runup whereas combinations of tectonic sources and submarine mass movements could generate local runup as large as 15m