dynamic earthquake rupture modelled with an unstructured 3 d spectral element method applied to the 2011 m9 tohoku earthquake an important goal of computational seismology is to simulate dynamic earthquake rupture and strong ground motion in realistic models that include crustal heterogeneities and complex fault geometries to accomplish this we incorporate dynamic rupture modelling capabilities in a spectral element solver on unstructured meshes the 3 d open source code specfem3d and employ state of the art software for the generation of unstructured meshes of hexahedral elements these tools provide high flexibility in representing fault systems with complex geometries including faults with branches and non planar faults the domain size is extended with progressive mesh coarsening to maintain an accurate resolution of the static field our implementation of dynamic rupture does not affect the parallel scalability of the code we verify our implementation by comparing our results to those of two finite element codes on benchmark problems including branched faults finally we present a preliminary dynamic rupture model of the 2011 m w 9 0 tohoku earthquake including a non planar plate interface with heterogeneous frictional properties and initial stresses our simulation reproduces qualitatively the depth dependent frequency content of the source and the large slip close to the trench observed for this earthquake

small intermediate fault segments can either aid or hinder rupture propagation at stepovers 1 large scale geometrical complexities along faults are known to be likely endpoints for coseismic rupture as suggested by analysis of historic ruptures and corroborated by models of rupture on bent or discontinuous faults however natural faults also include smaller scale complexities we use the 3d finite element method to model dynamic ruptures on strike slip fault stepovers with a smaller intermediate fault between the main strands we find that such small faults can have a controlling effect on rupture behavior and ground motion intensity and distribution in particular the intermediate fault can either aid or prevent rupture propagation across the stepover depending on its length and basal depth the results have important implications for hazard assessment of faults with large and small scale geometrical complexities and also suggest that more site specific modeling studies may be necessary to develop realistic rupture scenarios for individual complex fault systems

postglacial vegetation fire and climate dynamics at central chilean patagonia lake shaman 44 s a 19 cal ka bp pollen and charcoal record from lake shaman 44 s 71 w chile was analyzed to establish vegetation fire and climate dynamics of the forest steppe ecotone in central chilean patagonia lake shaman record indicates that the upper rio cisnes valley was free of ice at around 19 cal ka bp from this date and until 14 8 cal ka bp a grass steppe with high proportions of shrubs associated to colder and drier conditions than present developed in this area a continuous increase of nothofagus accompanied by a decline in the steppe shrubs and sudden dominance of paludal over aquatic plants from 11 cal ka bp was associated to effective moisture increase but still under modern values the replacement of the cold dry grass shrub steppe by a similar than present forest steppe ecotone suggests an increase in temperature indicating the onset of the holocene at the same time moderate fire activity suggested by the charcoal record could be related to major fuel availability as consequence of nothofagus forest expansion between 8 and 3 cal ka bp the record indicates the easternmost position of the forest steppe ecotone suggesting the highest effective moisture with the establishment of seasonality between 5 and 3 cal ka bp from 3 cal ka bp the record indicates a retraction of the forest steppe ecotone accompanied by a high pollen record variability and an increased fire activity these late changes suggest decreased effective moisture associated with a high climatic variability at regional and extra regional scale climatic changes at lake shaman s record are mostly associated to changes latitudinal shifts and or strengthening weakening of past southern westerlies that were previously recorded along patagonia from the lateglacial to the mid holocene during the late holocene a regional pattern characterized by high record variability emerges throughout central chilean patagonia this variability would be related to 1 low magnitude southern westerlies changes probably associated to enso and or sam or 2 the complex relationships between vegetation fire and human occupations during the last 3 cal ka

long term monitoring of creep rate along the hayward fault and evidence for a lasting creep response to 1989 loma prieta earthquake we present results from over 30 yr of precise surveys of creep along the hayward fault along most of the fault spatial variability in long term creep rates is well determined by these data and can help constrain 3d models of the depth of the creeping zone however creep at the south end of the fault stopped completely for more than 6 years after the m7 1989 loma prieta earthquake lpeq perhaps delayed by stress drop imposed by this event with a decade of detailed data before lpeq and a decade after it we report that creep response to that event does indeed indicate the expected deficit in creep

dynamically modeling fault step overs using various friction laws it is well known that fault step overs can under some circumstances allow through going rupture and under other circumstances cause rupture to terminate however the effects of different friction law formulations on jumping rupture have not been extensively explored in this study we use the 2 d dynamic finite element method to investigate how different frictional parameterizations affect the ability of rupture to jump a step over in both extensional and compressional settings we compare linear slip weakening friction and three forms of rate and state dependent friction the aging law slip law and slip law with strong rate weakening we have found that for friction parameterizations with the same effective slip weakening distance the functional forms of such friction laws can have a significant effect on maximum jump distance with friction laws scaled to have equivalent fracture energies we find that the functional forms of such friction laws have a second order effect on jumping rupture finally with our specific parameterizations we find that delays in rupture across the step over systems can lead to a previously unseen mode of supershear transition once the rupture renucleates on the secondary fault segment even if the initial stress field precludes such a transition studies using multiple friction laws in complex geometries such as fault step overs can lead to better understanding of the dependence of rupture properties on the type of friction law utilized in models and statistical analysis

dynamic models of an earthquake and tsunami offshore ventura california the ventura basin in southern california includes coastal dip slip faults that can likely produce earthquakes of magnitude 7 or greater and significant local tsunamis we construct a 3 d dynamic rupture model of an earthquake on the pitas point and lower red mountain faults to model low frequency ground motion and the resulting tsunami with a goal of elucidating the seismic and tsunami hazard in this area our model results in an average stress drop of 6 mpa an average fault slip of 7 4 m and a moment magnitude of 7 7 consistent with regional paleoseismic data our corresponding tsunami model uses final seafloor displacement from the rupture model as initial conditions to compute local propagation and inundation resulting in large peak tsunami amplitudes northward and eastward due to site and path effects modeled inundation in the ventura area is significantly greater than that indicated by state of california s current reference inundation line

a grid doubling finite element technique for calculating dynamic three dimensional spontaneous rupture on an earthquake fault summary we present a new finite element technique for calculating dynamic 3 d spontaneous rupture on an earthquake fault which can reduce the required computational resources by a factor of six or more without loss of accuracy the grid doubling technique employs small cells in a thin layer surrounding the fault the remainder of the modelling volume is filled with larger cells typically two or four times as large as the small cells in the resulting non conforming mesh an interpolation method is used to join the thin layer of smaller cells to the volume of larger cells grid doubling is effective because spontaneous rupture calculations typically require higher spatial resolution on and near the fault than elsewhere in the model volume the technique can be applied to non planar faults by morphing or smoothly distorting the entire mesh to produce the desired 3 d fault geometry using our faultmod finite element software we have tested grid doubling with both slip weakening and rate and state friction laws by running the scec usgs 3 d dynamic rupture benchmark problems we have also applied it to a model of the hayward fault northern california which uses realistic fault geometry and rock properties faultmod implements fault slip using common nodes which represent motion common to both sides of the fault and differential nodes which represent motion of one side of the fault relative to the other side we describe how to modify the traction at split nodes method to work with common and differential nodes using an implicit time stepping algorithm

the effects of fault stepovers on ground motion abstract using 3d dynamic models we investigate the effect of fault stepovers on near source ground motion we use the finite element method to model the rupture slip and ground motion of two parallel strike slip faults with an unlinked overlapping stepover of variable width we model this system as both an extensional and a compressional stepover and compare the results to those of single planar faults we find that overall the presence of a stepover along the fault trace reduces the maximum ground motion when compared to the long planar fault whether the compressional or extensional stepover exhibits higher ground motion overall depends on the width of the separation between the faults there is a region of reduced ground motion at the end of the first fault segment when the faults are embedded in a homogeneous material we also experiment with stress fields leading to supershear and subshear rupture velocities and with different stress drops within those conditions we find that subshear rupture produces stronger motions than supershear rupture but supershear ruptures produce that maximum over a larger area than subshear areas even though the overall area that experiences any shaking at all is not drastically different between the two cases lastly we experiment with placing realistic materials along and around the faults such as a sedimentary basin in an extensional stepover a damage zone around the fault and a soft rock layer on top of bedrock through the entire model area these configurations alter the pattern of ground motion from the homogeneous case the peaks in ground motion for the bimaterial cases depend on the materials in question the results may have implications for ground motion prediction in future earthquakes on geometrically complex faults online material mpeg 4 movies of models of dynamic rupture of fault stepovers embedded in heterogeneous material settings

ensemble water isotope enabled coupled general circulation modeling insights into the 8 2 ka event 1 freshwater forcing has long been postulated as a catalyst for abrupt climate change because of its potential to interfere with thermohaline circulation thc the most recent example may have occurred about 8 2 ka ago with the sudden drainage of glacial lakes agassiz and ojibway into the hudson bay we perform an ensemble of simulations for this freshwater release using the fully coupled atmosphere ocean general circulation model goddard institute for space studies modele r in all cases simulated effects include reduced ocean heat transport and enhanced atmospheric heat transport in the atlantic increased surface albedo through greater low cloud and sea ice cover and local cooling of up to 3 c our suite of ensemble experiments allows us to examine the importance of the initial ocean state in particular the presence or absence of labrador sea water in controlling the magnitude and length of the climate response water isotope tracers included in this model provide an improved means for direct comparisons of the modeled tracer response to water isotope based climate proxy data comparison of model simulations to data implies that there was an abrupt approximate halving of atlantic thc hence providing strong support for the hypothesis that the 8 2 ka event was caused by an abrupt release of fresh water into the north atlantic

three dimensional geologic map of the hayward fault northern california correlation of rock units with variations in seismicity creep rate and fault dip in order to better understand mechanisms of active faults we studied relationships between fault behavior and rock units along the hayward fault using a three dimensional geologic map the three dimensional map constructed from hypocenters potential field data and surface map data provided a geologic map of each fault surface showing rock units on either side of the fault truncated by the fault the two fault surface maps were superimposed to create a rock rock juxtaposition map the three maps were compared with seismicity including aseismic patches surface creep and fault dip along the fault by using visualization software to explore three dimensional relationships fault behavior appears to be correlated to the fault surface maps but not to the rock rock juxtaposition map suggesting that properties of individual wall rock units including rock strength play an important role in fault behavior although preliminary these results suggest that any attempt to understand the detailed distribution of earthquakes or creep along a fault should include consideration of the rock types that abut the fault surface including the incorporation of observations of physical properties of the rock bodies that intersect the fault at depth

results of the sea ice model intercomparison project evaluation of sea ice rheology schemes for use in climate simulations a hierarchy of sea ice rheologies is evaluated on the basis of a comprehensive set of observational data the investigations are part of the sea ice model intercomparison project simip four different sea ice rheology schemes are compared a viscous plastic rheology a cavitating fluid model a compressible newtonian fluid and a simple free drift approach with velocity correction the same grid land boundaries and forcing fields are applied to all models as verification data there are 1 ice thickness data from upward looking sonars uls 2 ice concentration data from the passive microwave radiometers smmr and ssm i 3 daily buoy drift data obtained by the international arctic buoy program iabp and 4 satellite derived ice drift fields based on the 85 ghz channel of ssm i all models are optimized individually with respect to mean drift speed and daily drift speed statistics the impact of ice strength on the ice cover is best revealed by the spatial pattern of ice thickness ice drift on different timescales daily drift speed statistics and the drift velocities in fram strait overall the viscous plastic rheology yields the most realistic simulation in contrast the results of the very simple free drift model with velocity correction clearly show large errors in simulated ice drift as well as in ice thicknesses and ice export through fram strait compared to observation the compressible newtonian fluid cannot prevent excessive ice thickness buildup in the central arctic and overestimates the internal forces in fram strait because of the lack of shear strength the cavitating fluid model shows marked differences to the statistics of observed ice drift and the observed spatial pattern of ice thickness comparison of required computer resources demonstrates that the additional cost for the viscous plastic sea ice rheology is minor compared with the atmospheric and oceanic model components in global climate simulations

controls on timing and amount of right lateral offset on the east bay fault system san francisco bay region california the distribution of offset correlated rock units relative position of northward younging volcanic rocks and distribution of units not offset together reveal the history of strike slip deformation along the east bay fault system the system accumulated 175 km of right lateral offset since 12 ma but of this amount only 25 km was accumulated between 12 and 10 ma and only 75 km between 12 and 6 ma the westernmost hayward fault zone is responsible for more than half 100 km of the total and it too has undergone more offset 60 km after 6 ma than before the activity on any single fault zone in the system has been sporadic and alternating periods of activity and inactivity have been recorded on at least some of the fault zones

numerical simulations of large earthquakes dynamic rupture propagation on heterogeneous faults our current conceptions of earthquake rupture dynamics especially for large earthquakes require knowledge of the geometry of the faults involved in the rupture the material properties of the rocks surrounding the faults the initial state of stress on the faults and a constitutive formulation that determines when the faults can slip in numerical simulations each of these factors appears to play a significant role in rupture propagation at the kilometer length scale observational evidence of the earth indicates that at least the first three of the elements geometry material and stress can vary over many scale dimensions future research on earthquake rupture dynamics needs to consider at which length scales these features are significant in affecting rupture propagation

interseismic coupling and refined earthquake potential on the hayward calaveras fault zone interseismic strain accumulation and fault creep is usually estimated from gps and alignment arrays data which provide precise but spatially sparse measurements here we use interferometric synthetic aperture radar to resolve the interseismic deformation associated with the hayward and calaveras faults hf and cf in the east san francisco bay area the large 1992 2011 sar data set permits evaluation of short and long wavelength deformation larger than 2 mm yr without alignment of the velocity field to a gps based model our time series approach in which the interferogram selection is based on the spatial coherence enables deformation mapping in vegetated areas and leads to refined estimates of along fault surface creep rates creep rates vary from 0 2 mm yr on the northern cf to 14 2 mm yr on the central cf south of the hf surface junction we estimate the long term slip rates by inverting the long wavelength deformation and the distribution of shallow slip due to creep by inverting the remaining velocity field this distribution of slip reveals the locations of locked and slowly creeping patches with potential for a m6 8 0 3 on the hf near san leandro a m6 6 0 2 on the northern cf near dublin a m6 5 0 1 on the hf south of fremont and a m6 2 0 2 on the central cf near morgan hill with cascading multisegment ruptures the hf rupturing from berkeley to the cf junction could produce a m6 9 0 1 the northern cf a m6 6 0 1 the central cf a m6 9 0 2 from the junction to gilroy and a joint rupture of the hf and central cf could produce a m7 1 0 1

deducing paleoearthquake timing and recurrence from paleoseismic data part ii analysis of paleoseismic excavation data and earthquake behavior along the central and southern san andreas fault we present an analysis of paleoseismic data along the central and southern san andreas fault that seeks to establish the timing recurrence and along fault correlation of paleoearthquakes we use bayesian methods to compute a series of probability density functions pdfs that cast paleoearthquake timing in the context of yearly probabilities to quantify the uncertainties present in the paleoseismic dataset based on stratigraphic interpretations we use a scenario based approach in which different viable stratigraphic interpretations are used to infer paleoearthquake timing using these pdfs we attempt to correlate earthquakes along the fault through time to image a time series of past fault ruptures we find that site to site correlation is often difficult due to significant uncertainties nonetheless some ruptures could be correlated from site to site assuming the paleoseismic record is complete these inferences may indicate that ruptures begin and terminate more or less randomly in space the results of our analysis may prove beneficial to future probabalistic seismic hazard assessments of this area and may serve as inputs to studies that seek to quantitatively test rupture models against data in the paleoseismic record

dynamic rupture modeling of the m7 2 2010 el mayor cucapah earthquake comparison with a geodetic model author s kyriakopoulos c oglesby dd funning gj ryan kj abstract 2017 american geophysical union all rights reserved the 2010 mw 7 2 el mayor cucapah earthquake is the largest event recorded in the broader southern california baja california region in the last 18nyears here we try to analyze primary features of this type of event by using dynamic rupture simulations based on a multifault interface and later compare our results with space geodetic models our results show that starting from homogeneous prestress conditions slip heterogeneity can be achieved as a result of variable dip angle along strike and the modulation imposed by step over segments we also considered effects from a topographic free surface and find that although this does not produce significant first order effects for this earthquake even a low topographic dome such as the cucapah range can affect the rupture front pattern and fault slip rate finally we inverted available interferometric synthetic aperture radar data using the same geometry as the dynamic rupture model and retrieved the space geodetic slip distribution that serves to constrain the dynamic rupture models the one to one comparison of the final fault slip pattern generated with dynamic rupture models and the space geodetic inversion show good agreement our results lead us to the following conclusion in a possible multifault rupture scenario and if we have first order geometry constraints dynamic rupture models can be very efficient in predicting large scale slip heterogeneities that are important for the correct assessment of seismic hazard and the magnitude of future events our work contributes to understanding the complex nature of multifault systems

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

sea ice response to wind forcing from amip models abstract the arctic surface circulation simulated by atmospheric general circulation models is assessed in the context of driving sea ice motion a sea ice model is forced by geostrophic winds from eight models participating in the first atmospheric model intercomparison project amip1 and the results are compared to simulations with the sea ice model forced by observed winds the mean sea level pressure in the amip models is generally too high over the arctic ocean except in the beaufort and chukchi seas where it is too low this pattern creates anomalous winds that tend to transport too much ice away from the coast of greenland and the canadian archipalego and into the east siberian sea producing a pattern of ice thickness in the arctic that is rotated by roughly 180 relative to what is expected based on observations amip winds also drive too little ice transport through fram strait and too much transport east of svalbard by way of the barents sea these errors in ice thickness and transport inf

modeling thermodynamic ice ocean interactions at the base of an ice shelf abstract models of ocean circulation beneath ice shelves are driven primarily by the heat and freshwater fluxes that are associated with phase changes at the ice ocean boundary their behavior is therefore closely linked to the mathematical description of the interaction between ice and ocean that is included in the code an hierarchy of formulations that could be used to describe this interaction is presented the main difference between them is the treatment of turbulent transfer within the oceanic boundary layer the computed response to various levels of thermal driving and turbulent agitation in the mixed layer is discussed as is the effect of various treatments of the conductive heat flux into the ice shelf the performance of the different formulations that have been used in models of sub ice shelf circulation is assessed in comparison with observations of the turbulent heat flux beneath sea ice formulations that include an explicit parameterization of the oceanic boundary layer give results that

sea ice transport a highly variable link between arctic and north atlantic the variability of the ice volume flux into the northeast atlantic is investigated with an optimized dynamic thermodynamic sea ice model using 40 years 1958 1997 of atmospheric forcing fields derived from the ncep ncar reanalysis project the simulated sea ice export from the arctic exhibits considerable interannual to decadal variability and is primarily a linear response to sea level pressure anomalies over greenland and over the barents and kara seas our model results suggest that ice export anomalies such as in 1968 which supposedly caused the so called great salinity anomaly in the northern north atlantic are not unique but rather frequent events as part of the variability of the arctic climate system

dynamic rupture models of earthquakes on the bartlett springs fault northern california the bartlett springs fault bsf the easternmost branch of the northern san andreas fault system creeps along much of its length geodetic data for the bsf are sparse and surface creep rates are generally poorly constrained the two existing geodetic slip rate inversions resolve at least one locked patch within the creeping zones we use the 3 d finite element code faultmod to conduct dynamic rupture models based on both geodetic inversions in order to determine the ability of rupture to propagate into the creeping regions as well as to assess possible magnitudes for bsf ruptures for both sets of models we find that the distribution of aseismic creep limits the extent of coseismic rupture due to the contrast in frictional properties between the locked and creeping regions

three dimensional space dependent mesoscale diffusivity derivation and implications abstractrecently we presented a parameterization of an arbitrary tracer 3d mesoscale flux that describes both diabatic and adiabatic regimes without using arbitrary tapering functions however we

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

removal of ambiguity of two dimensional power spectra obtained by processing ship radar images of ocean waves the usual spatial power spectra of ocean wave images taken from ppi of a ship radar show an ambiguity in the wave propagation direction a simple numerical procedure is suggested and realized to remove this ambiguity it makes use of the data from two consecutive turns of the radar antenna as well as of the wave dispersion law the results obtained show a good agreement with the ground truth

sea ice and polar climate in the ncar csm the climate system model csm consists of atmosphere ocean land and sea ice components linked by a flux coupler which computes fluxes of energy and momentum between components the sea ice component consists of a thermodynamic formulation for ice snow and leads within the ice pack and ice dynamics using the cavitating fluid ice rheology which allows for the compressive strength of ice but ignores shear viscosity the results of a 300 yr climate simulation are presented with the focus on sea ice and the atmospheric forcing over sea ice in the polar regions the atmospheric model results are compared to analyses from the european centre for medium range weather forecasts and other observational sources the sea ice concentrations and velocities are compared to satellite observational data the atmospheric sea level pressure slp in csm exhibits a high in the central arctic displaced poleward from the observed beaufort high the southern hemisphere slp over sea ice is generally 5 mb lower than observed air temperatures over sea ice in both hemispheres exhibit cold biases of 2 4 k the precipitationminus evaporation fields in both hemispheres are greatly improved over those from earlier versions of the atmospheric gcm the simulated ice covered area is close to observations in the southern hemisphere but too large in the northern hemisphere the ice concentration fields show that the ice cover is too extensive in the north pacific and subarctic north atlantic oceans the interannual variability of the ice area is similar to observations in both hemispheres the ice thickness pattern in the antarctic is realistic but generally too thin away from the continent the maximum thickness in the arctic occurs against the bering strait not against the canadian archipelago as observed the ice velocities are stronger than observed in both hemispheres with a consistently greater turning angle to the left in the southern hemisphere they produce a northward ice transport in the southern hemisphere that is 3 4 times the satellite derived value sensitivity tests with the sea ice component show that both the pattern of wind forcing in csm and the air ice drag parameter used contribute to the biases in thickness drift speeds and transport plans for further development of the ice model to incorporate a viscousplastic ice rheology are presented in spite of the biases of the sea ice simulation the 300 yr climate simulation exhibits only a small degree of drift in the surface climate without the use of flux adjustment this suggests a robust stability in the simulated climate in the presence of significant variability

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

sensitivity of sea ice to physical parameterizations in the giss global climate model 1 the giss coupled model is used to investigate the sensitivity of sea ice to each of the following parameterizations 1 two sea ice dynamics cf cavitating fluid vp viscous plastic 2 the specification of oceanic isopycnal mixing coefficients in the gent and mcwillams isopyncal mixing gm and 3 the wajsowicz viscosity diffusion wv the large scale sea ice properties are highly sensitive to sea ice dynamics with the inclusion of resistance to shear stress vp captures the major observed sea ice drift features and improves the simulations of sea ice concentrations thickness and export through fram strait relative to cf gm significantly improves the simulation of vertical temperature distributions in the southern ocean although it leads to a dramatic reduction of antarctic sea ice cover the reduced oceanic isopycnal mixing coefficients lead to arctic sea ice that tends to be less and thinner in almost the entire arctic except in the north pacific and labrador sea while antarctic sea ice that extends more equatorward throughout the circumpolar regions the responses of sea ice to wv show an enlargement and thickening of sea ice in the arctic within the ice packs around the antarctic and a reduction and thinning of sea ice in the northern weddell and ross seas on the basis of these experiments two composite experiments with the best parameterizations are investigated the atmospheric responses associated with sea ice changes are discussed while improvements are seen there are still many unrealistic aspects that will require further improvements to sea ice and ocean components

modeling the thermodynamics of a sea ice thickness distribution 1 sensitivity to ice thickness resolution a one dimensional ice thickness distribution model is presented to determine the minimum number of ice thicknesses necessary to resolve the area averaged annual cycles of ice thickness and turbulent fluxes the baseline case includes 40 ice thickness categories ice thickness and area meltwater ponds ice salinity and age snow cover and surface albedo evolve independently for each ice category a ridging and ice export parameterization and a coupled one dimensional ocean mixed layer model are also included sensitivity studies indicate that 16 ice thickness categories can accurately resolve the baseline annual cycles of area averaged ice thickness and the summertime turbulent fluxes in this model provided that one third of the thickness categories represent ice thinner than 0 8 m resolving the distribution of ice in this thickness range is important in simulating the area averaged ice characteristics wintertime values of the turbulent fluxes differ from the baseline by up to 1 w m 2 for fewer than 40 ice thickness categories the large difference in turbulent fluxes between open water and ice thicker than 1 6 m makes the area averaged value sensitive to the number of ice thickness categories since this number can affect the categories that are merged the categories that melt completely ice that is ridged and the resolution of the ice thickness distribution this makes an accurate simulation of the baseline wintertime turbulent fluxes difficult model simulations with fewer than 40 categories provide a reasonable estimate of the baseline response to a surface longwave heat flux perturbation of greater than 5 w m 2 the annually area averaged ice thickness is within 10 cm the model response to a heat flux perturbation of less than 5 w m 2 is similar for a wide range of ice thickness categories since the thickness distribution of ice thinner than 1 m is not affected

determination of ocean wave propagation direction by split look processing using jers 1 sar data the purpose of the present article is to show that the jers 1 synthetic aperture radar sar primarily designed for global land observation can be applied to deriving ocean wave spectra and determining the wave propagation direction split look multilook processing is used to produce a sequence of individual sub images of ocean waves this processing technique has an inherent property that the successive sub images are formed at different discretely delayed times wave propagation direction can therefore be determined from a pair of wave images in different looks the l band jers 1 sar despite its low signal to noise ratio has an advantage over c band spaceborne sars for having a longer integration time suitable for the wave analysis using split look processing several different methods are applied to the wave data collected near the coasts of japan including the methods of look sum taking the standard fourier spectrum of look summed image spectral sum spectral phase shift and cross correlation function of sub images

future of the arctic sea ice cover implications of an antarctic analog recent observations reveal a significant change in the upper ocean characteristics of the eastern arctic in 1995 the change is manifested through the loss of a near surface layer known as the cold halocline layer chl without the chl the arctic water column looks and behaves like the antarctic water column the expected local impact is the appearance of significant winter ocean heat fluxes 15 20 w m and reduction of winter ice growth by 70 80 relative to years in which the chl was present preliminary results suggest a partial recovery of the chl in the late 1990 s tracking the weakening of the arctic oscillation

resolution of the ocean wave propagation direction in sar imagery there is an inherent 180 degrees ambiguity in the derived wave propagation direction when using conventional spectral analysis techniques on standard synthetic aperture radar sar image products three different techniques are successfully used to resolve this ambiguity in propagation direction using a single pass of airborne sar data the fact that the sar is characterized by a large time bandwidth product is used to advantage a sequence of individual looks extracted from the doppler spectrum represents images of the scene collected at a sequence of discretely delayed intervals of time the techniques utilized include cross correlation based motion analysis of a pair of looks phase weighting based upon a pair of looks and the ocean wave dispersion relation and a three dimensional spectral analysis the phase weighting technique is also demonstrated for a seasat sar scene

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

ground motion modeling of hayward fault scenario earthquakes part i construction of the suite of scenarios abstract we construct kinematic earthquake rupture models for a suite of 39 m w 6 6 7 2 scenario earthquakes involving the hayward calaveras and rodgers creek faults we use these rupture models in 3d ground motion simulations as discussed in part ii aagaard et al 2010 to provide detailed estimates of the shaking for each scenario we employ both geophysical constraints and empirical relations to provide realistic variation in the rupture dimensions slip heterogeneity hypocenters rupture speeds and rise times the five rupture lengths include portions of the hayward fault as well as combined rupture of the hayward and rodgers creek faults and the hayward and calaveras faults we vary rupture directivity using multiple hypocenters typically three per rupture length yielding north to south rupture bilateral rupture and south to north rupture for each rupture length and hypocenter we consider multiple random distributions of slip we use two approaches to account for how aseismic creep might reduce coseismic slip for one subset of scenarios we follow the slip predictable approach and reduce the nominal slip in creeping regions according to the creep rate and time since the most recent earthquake whereas for another subset of scenarios we apply a vertical gradient to the nominal slip in creeping regions the rupture models include local variations in rupture speed and use a ray tracing algorithm to propagate the rupture front although we are not attempting to simulate the 1868 hayward fault earthquake in detail a few of the scenarios are designed to have source parameters that might be similar to this historical event

seismic velocity structure and seismotectonics of the eastern san francisco bay region california the hayward fault system is considered the most likely fault system in the san francisco bay area california to produce a major earthquake in the next 30 years to better understand this fault system we use microseismicity to study its structure and kinematics we present a new 3d seismic velocity model for the eastern san francisco bay region using microseismicity and controlled sources which reveals a 10 velocity contrast across the hayward fault in the upper 10 km with higher velocity in the franciscan complex to the west relative to the great valley sequence to the east this contrast is imaged more sharply in our localized model than in previous regional scale models thick cenozoic sedimentary basins such as the livermore basin which may experience particularly strong shaking during an earthquake are imaged in the model the accurate earthquake locations and focal mechanisms obtained by using the 3d model allow us to study fault complexity and its implications for seismic hazard the relocated hypocenters along the hayward fault in general are consistent with a near vertical or steeply east dipping fault zone the southern hayward fault merges smoothly with the calaveras fault at depth suggesting that large earthquakes may rupture across both faults the use of the 3d velocity model reveals that most earthquakes along the hayward fault have near vertical strike slip focal mechanisms consistent with the large scale orientation and sense of slip of the fault with no evidence for zones of complex fracturing acting as barriers to earthquake rupture online material velocity model validation experiments and additional seismicity plots

continental scale river flow in climate models abstract the hydrologic cycle is a major part of the global climate system there is an atmospheric flux of water from the ocean surface to the continents the cycle is closed by return flow in rivers in this paper a river routing model is developed to use with grid box climate models for the whole earth the routing model needs an algorithm for the river mass flow and a river direction file which has been compiled for 4 5 and 20 2 5 resolutions river basins are defined by the direction files the river flow leaving each grid box depends on river and lake mass downstream distance and an effective flow speed that depends on topography as input the routing model uses monthly land source runoff from a 5 yr simulation of the nasa giss atmospheric climate model hansen et al the land source runoff from the 4 5 resolution model is quartered onto a 2 2 5 grid and the effect of grid resolution is examined monthly flow at the mouth of the world s major rivers is compared with observations and a

sea ice feedback and cenozoic evolution of antarctic climate and ice sheets 1 the extent and thickness of antarctic sea ice have important climatic effects on radiation balance energy transfer between the atmosphere and ocean and moisture availability this paper explores the role of sea ice and related feedbacks in the cenozoic evolution of antarctic climate and ice sheets using a numerical climate model with explicit dynamical representations of sea ice and continental ice sheets in a scenario of decreasing cenozoic greenhouse gas concentrations our model initiates continental glaciation before any significant sea ice forms around the continent once variable ice sheets are established seasonal sea ice distribution is highly sensitive to orbital forcing and ice sheet geometry via the ice sheet s control on regional temperature and low level winds although the expansion of sea ice has significant climatic effects near the coast it has only minimal effects in the continental interior and on the size of the ice sheet therefore the cenozoic appearance of antarctic sea ice was primarily a response to the growth of grounded ice sheets and was not a critical factor in episodes of paleogene and neogene glaciation the influence of the east antarctic ice sheet on sea ice southern ocean surface temperatures and winds has important implications for ocean circulation the marine carbon cycle and the development of the west antarctic ice sheet the sensitivity of sea ice to grounded ice sheets implies reconstructions of sea ice based on marine diatoms are good indicators of glacial conditions in the continental interior and may provide insight into the long term stability of antarctic ice sheets

fault structure and mechanics of the hayward fault california from double difference earthquake locations 1 the relationship between small magnitude seismicity and large scale crustal faulting along the hayward fault california is investigated using a double difference dd earthquake location algorithm we used the dd method to determine high resolution hypocenter locations of the seismicity that occurred between 1967 and 1998 the dd technique incorporates catalog travel time data and relative p and s wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events the relocated seismicity reveals a narrow near vertical fault zone at most locations this zone follows the hayward fault along its northern half and then diverges from it to the east near san leandro forming the mission trend the relocated seismicity is consistent with the idea that slip from the calaveras fault is transferred over the mission trend onto the northern hayward fault the mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the calaveras fault at calaveras reservoir in some locations discrete structures adjacent to the main trace are seen features that were previously hidden in the uncertainty of the network locations the fine structure of the seismicity suggests that the fault surface on the northern hayward fault is curved or that the events occur on several substructures near san leandro where the more westerly striking trend of the mission seismicity intersects with the surface trace of the aseismic southern hayward fault the seismicity remains diffuse after relocation with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation the seismicity is highly organized in space especially on the northern hayward fault where it forms horizontal slip parallel streaks of hypocenters of only a few tens of meters width bounded by areas almost absent of seismic activity during the interval from 1984 to 1998 when digital waveforms are available we find that fewer than 6 5 of the earthquakes can be classified as repeating earthquakes events that rupture the same fault patch more than one time these most commonly are located in the shallow creeping part of the fault or within the streaks at greater depth the slow repeat rate of 2 3 times within the 15 year observation period for events with magnitudes around m 1 5 is indicative of a low slip rate or a high stress drop the absence of microearthquakes over large contiguous areas of the northern hayward fault plane in the depth interval from 5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large magnitude earthquakes

dynamics and thermodynamics of the ice upper ocean system in the marginal ice zone of the greenland sea measurements were made of the ice upper ocean system in the marginal ice zone of the greenland sea during a 4 day storm in which wind blew the ice south across a frontal region coinciding with the ice edge that had existed when the storm began in response to wind stress of about 0 2 pa a turbulent boundary layer developed under the ice that exhibited marked ekman rotation in both mean velocity average surface speed about 0 17 m s 1 deflection angle about 33 and turbulent stress profiles typical reynolds stress about 0 1 pa ablation of the ice undersurface increased rapidly after crossing the surface temperature front and the observed melt rate corresponded with direct heat flux measurements in the oceanic boundary layer with maximum upward heat flux of about 200 w m 2 we discuss overall momentum and energy balances interpret observed boundary layer measurements with a numerical model and show that molecular effects are important for heat and mass transport at the hydraulically rough ice ocean interface we also develop a simple model for predicting ice melt from interfacial stress and temperature and salinity of the mixed layer

preconditioning of antarctic maximum sea ice extent by upper ocean stratification on a seasonal timescale this study uses an observationally constrained and dynamically consistent ocean and sea ice state estimate the author presents a remarkable agreement between the location of the edge of antarctic maximum sea ice extent reached in september and the narrow transition band for the upper ocean 0 100 m depths stratification as early as april to june to the south of this edge the upper ocean has high stratification which forbids convective fluxes to cross through consequently the ocean heat loss to the atmosphere is an efficient way to cool the surface ocean to the freezing point during april to september to the north the upper ocean has low stratification such that the ocean heat loss to the atmosphere is not efficient to cool the upper ocean the upper ocean is instead cooled mainly through mixing with the colder inflow carried by northward ekman transport but cannot reach the freezing point due to the nature of mixing therefore upper ocean stratification dominated by salinity here provides an important constraint on the northward expansion of antarctic sea ice to its maximum

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

rupture and ground motion models on the northern san jacinto fault incorporating realistic complexity we use the 3d finite element method to conduct dynamic models of rupture and resulting ground motion on the claremont casa loma stepover of the northern san jacinto fault we incorporate complex fault geometry from the u s geological survey usgs quaternary faults database see data and resources 1 a realistic velocity structure the southern california earthquake center community velocity model s a realistic regional stress field with an orientation taken from seismicity relocation literature and several stochastic self similar shear stress distributions as we incorporate more types of complexity the specific effects of any individual factor become less apparent within the overall rupture behavior we also find that the distribution of high and low shear stress that arises from combining regional and stochastic stress fields has the strongest control over where the rupture terminates using a regional stress field alone as well as with the combined regional and stochastic stress realization we find that the stepover presents a significant barrier to rupture regardless of our choice of initial nucleation point and that it is difficult for rupture to propagate the full length of either fault segment greater heterogeneity of stresses tends to produce shorter ruptures within this result we find that the claremont strand is more favorable for long ruptures than the casa loma clark strand low frequency ground motion intensity and distribution are controlled largely by the velocity structure rather than by stress heterogeneity the strongest motions produced in these models are in the san bernardino basin although directivity effects do contribute to the low frequency ground motion distribution particularly in the near field they are secondary to the effects of the velocity structure online material figures of ground motions from models used to calibrate the stress conditions for dynamic rupture propagation 1 sec 18

acc subduction by mesoscales abstractthe mesoscale contribution to subduction in the southern ocean was studied by sallee and rintoul in 2011 sr11 using the following mesoscale model the adiabatic a regime was modeled wit

gravity and magnetic expression of the san leandro gabbro with implications for the geometry and evolution of the hayward fault zone northern california the hayward fault one of the most hazardous faults in northern california trends north northwest and extends for about 90 km along the eastern san francisco bay region at numerous locations along its length distinct and elongate gravity and magnetic anomalies correlate with mapped mafic and ultramafic rocks the most prominent of these anomalies reflects the 16 km long san leandro gabbroic block inversion of magnetic and gravity data constrained with physical property measurements is used to define the subsurface extent of the san leandro gabbro body and to speculate on its origin and relationship to the hayward fault zone modeling indicates that the san leandro gabbro body is about 3 km wide dips about 75 80 northeast and extends to a depth of at least 6 km one of the most striking results of the modeling which was performed independently of seismicity data is that accurately relocated seismicity is concentrated along the western edge or stratigraphically lower bounding surface of the san leandro gabbro the western boundary of the san leandro gabbro block is the base of an incomplete ophiolite sequence and represented at one time a low angle roof thrust related to the tectonic wedging of the franciscan complex after repeated episodes of extension and attenuation the roof thrust of this tectonic wedge was rotated to near vertical and in places the strike slip hayward fault probably reactivated or preferentially followed this preexisting feature because earthquakes concentrate near the edge of the san leandro gabbro but tend to avoid its interior we qualitatively explore mechanical models to explain how this massive igneous block may influence the distribution of stress the microseismicity cluster along the western flank of the san leandro gabbro leads us to suggest that this stressed volume may be the site of future moderate to large earthquakes improved understanding of the three dimensional geometry and physical properties along the hayward fault will provide additional constraints on seismic hazard probability earthquake modeling and fault interactions that are applicable to other major strike slip faults around the world manuscript received 11 january 2002

compressional and shear wave velocity versus depth relations for common rock types in northern california abstract this article presents new empirical compressional and shear wave velocity vp and vs versus depth relationships for the most common rock types in northern california vp versus depth relations were developed from borehole laboratory seismic refraction and tomography and density measurements and were converted to vs versus depth relations using new empirical relations between vp and vs the relations proposed here account for increasing overburden pressure but not for variations in other factors that can influence velocity over short distance scales such as lithology consolidation induration porosity and stratigraphic age standard deviations of the misfits predicted by these relations thus provide a measure of the importance of the variability in vp and vs caused by these other factors because gabbros greenstones basalts and other mafic rocks have a different vp and vs relationship than sedimentary and granitic rocks the differences in vs between these rock types at depths below 6 or 7 km are generally small the new relations were used to derive the 2005 u s geological survey seismic velocity model for northern california employed in the broadband strong motion simulations of the 1989 loma prieta and 1906 san francisco earthquakes initial tests of the model indicate that the vp model generally compares favorably to regional seismic tomography models but that the vp and vs values proposed for the franciscan complex may be about 5 too high

sensitivity of seawater oxygen isotopes to climatic and tectonic boundary conditions in an early paleogene simulation with giss modele r 1 an isotope enabled ocean atmosphere general circulation model giss modele r is used to estimate the spatial gradients of the oxygen isotopic composition of seawater 18osw where is the deviation from a known reference material in per mil during the early paleogene 45 65 ma understanding the response of 18osw to changes in climatic and tectonic boundary conditions is important because records of carbonate 18o document changes in hydrology as well as changes in temperature and global ice volume we present results from an early paleogene configuration of modele r which indicate that spatial gradients of surface ocean 18osw during this period could have been significantly different to those in the modern ocean the differences inferred from modele r are sufficient to change early paleogene sea surface temperature estimates derived from primary carbonate 18o signatures by more than 2 c in large areas of the ocean in the north atlantic indian and southern oceans the differences in 18osw inferred from our simulation with modele r are in direct contrast with those from another 18o tracing model study which used different but equally plausible early paleogene boundary conditions the large differences in 18osw between preindustrial and early paleogene simulations and between models emphasizes the sensitivity of 18osw to climatic and tectonic boundary conditions for this reason absolute estimates of eocene paleocene temperature derived from carbonate 18o alone are likely to have larger uncertainties than are usually assumed

airborne sar observations of ocean surface waves penetrating floating ice the results are presented for a new and improved procedure for estimating the synthetic aperture radar sar image spectrum of ocean waves this procedure the spectral sum method involves summing individual image spectra derived from each of the looks of a multilook set an automatic registration of the per look spectral information is achieved accounting for subimage look misregistration due to the wave propagation between looks spectral sum processing is compared with traditional look sum processing as a function of the radar slant range spectral sum processing is applied to sar imagery of waves penetrating the marginal ice zone

parameterization of mixed layer and deep ocean mesoscales including nonlinearity abstractin 2011 chelton et al carried out a comprehensive census of mesoscales using altimetry data and reached the following conclusions essentially all of the observed mesoscale features are nonlinear and mesoscales do not move with the mean velocity but with their own drift velocity which is the most germane of all the nonlinear metrics accounting for these results in a mesoscale parameterization presents conceptual and practical challenges since linear analysis is no longer usable and one needs a model of nonlinearity a mesoscale parameterization is presented that has the following features 1 it is based on the solutions of the nonlinear mesoscale dynamical equations 2 it describes arbitrary tracers 3 it includes adiabatic a and diabatic d regimes 4 the eddy induced velocity is the sum of a gent and mcwilliams gm term plus a new term representing the difference between drift and mean velocities 5 the new term lowers the transfer of mean potential energy to mesoscales 6 th

evolution of the southern ocean winter mixed layer and sea ice open ocean deepwater formation and ventilation an analytical model has been developed to describe the nature of the winter ocean sea ice interaction in the southern ocean to determine the principal processes responsible for maintaining stability in this marginally stable region and to predict the response to changes in the external forcing and initial conditions the model accurately describes the sparse winter observations and the general temporal evolution of the ice mixed layer depth and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth a scale analysis and sensitivity study reveal the system parameter dependence this indicates that the magnitude of entrainment is proportional to fst h0 s where fs is the external salt flux h0 the depth of the winter mixed layer and s the salinity gradient through the pycnocline thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads a strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere this limits the amount of ice growth possible and plays the principal role in maintaining the system stability since the ice growth is required for destabilization through haline rejection during the growth process the system is also sensitive to the large ratio of heat to salt in the pycnocline this introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere this moderates the ability to grow ice and drive further entrainment the absolute strength of the salinity gradient on the other hand dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment the effectiveness with which changes in these parameters as well as several other external parameters can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis

holocene slip rate of the hayward fault at union city california measured offsets of well dated alluvial fan deposits near the masonic home in union city constrain holocene slip rate of the hayward fault between 7 and 9 mm yr our best minimum geologic slip rate over the past 8 27 0 08 kyr i e 8270 years is 8 0 0 7 mm yr a steep stream its channel cut into bedrock flows southwest out of the east bay hills crosses the fault and deposits its load on an alluvial fan we cut two 5 m deep fault parallel trenches 20 30 m southwest of the main fault through the crest of the fan walls of the trenches reveal a series of nested distributary channel fills these channels had cut into old surfaces that are indicated by paleosols developed on flood silts we distinguished many channel fills by their shape clast size flow direction elevation and relation to paleosols enabling us to correlate them between both trenches two distinct episodes of fan deposition occurred during the holocene reconstructing the apex positions of these fan units indicates that about 42 6 m and 66 6 m of fault slip has occurred since their inceptions at about 4 58 0 05 ka and 8 27 0 05 ka respectively we lowered the age and age uncertainty of the younger unit from earlier reports based on new multiple radiocarbon dates the 4 58 ka slip rate of 9 2 1 3 mm yr is not significantly different at 95 confidence from the 8 27 ka slip rate of 8 0 0 7 mm yr because current regional strain rates are fully consistent with neogene plate tectonic rates lisowski et al 1991 and the historic surface rate of creep in union city is only 4 7 0 1 mm yr galehouse 1994 the larger 8 mm yr holocene slip rate implies that strain is now accumulating on a locked zone at depth the 8 mm yr rate is probably minimal because earlier trenching evidence nearby implies that some unknown additional amount of fault deformation occurs outside of the narrow fault zone assumed in measuring slip lienkaemper et al 1991 suggest that the fast creep rate of 9 mm yr measured near the southern end of the hayward fault may underestimate the deep slip rate because 1868 surface slip occurred there in addition to the continuing fast creep if the historic deep slip rate equals the long term rate then the 9 mm yr creep rate reflects the minimum seismic loading rate of the hayward fault better than the 8 mm yr holocene rates do