thermohaline variability the effects of horizontal resolution and diffusion abstract an idealized coupled ocean atmosphere model is utilized to study the influence of horizontal resolution and parameterized eddy processes on the thermohaline circulation a series of experiments ranging from 4 to 0 25 resolution with appropriate horizontal viscosities and diffusivities in each case is performed for both coupled and ocean only models spontaneous internal variability primarily on the decadal timescale is found to exist in the higher resolution cases with the exception of one of the restoring experiments the decadal oscillation whose period varies slightly between cases is described as an advective convective mechanism that is thermally driven and linked to the value of the horizontal diffusivity utilized in the model increasing the diffusivity in the high resolution cases presented in this paper is enough to destroy the variability whereas decreasing the diffusivity in the moderately coarse resolution cases is capable of inducing decadal scale variability as the resol

reconciling the stommel box model with the stommel arons model a possible role for southern hemisphere wind forcing abstract in the stommel box model the strength of the overturning circulation is parameterized in terms of the density and hence the pressure difference between the two boxes straub has pointed out that this parameterization is not consistent with the stommel arons model for the abyssal circulation in particular the zonally averaged density field implied by the stommel arons model is unrelated to the strength or the direction of the meridional overturning circulation here the inconsistency is examined using the abyssal circulation model of kawase and a variant to include the effect of southern hemisphere wind forcing the important parameter is r the ratio of two timescales the timescale for a perturbation to the density field to propagate by either wave or advective processes from a high latitude source to the equator and the timescale for the dissipation of a perturbation to the density field by diapycnal mixing if the model is forced only by a deep water source in the northern basin it is

stress slip and earthquakes in models of complex single fault systems incorporating brittle and creep deformations numerical simulations of slip evolution along a cellular vertical strike slip fault in an elastic half space are performed for several models representing discrete fault systems embedded in three dimensional elastic continua the geometry and imposed boundary conditions correspond approximately to the central san andreas fault the simulations incorporate brittle and creep deformations in series the net fault zone deformation rate is the sum of creep rate and frictional slip rate brittle fault properties are given by various distributions of earthquake stress drops on failing segments numerical cells the assumed distributions represent two idealized situations corresponding to different extreme states along an evolutionary path of a fault 1 a strongly disordered state characterized by a wide range of size scales representing immature fault zones and extended spatial domains and 2 a relatively regular state having a narrow range of size scales representing mature highly slipped faults the assumed creep properties are identical in all cases these are prescribed in terms of coefficients characterizing a power law dependency of creep slip rate on stress the combined brittle creep process and employed parameters lead to an overall pine tree stress depth profile with a brittle ductile transition depth of about 12 5 km and variable stress along strike profiles with brittle creep transition around 65 km nw of the 1857 rupture the spatial patterns of simulated hypocenters are statistically similar to observed data the results indicate that the range of size scales characterizing strong fault zone heterogeneities has important manifestations on the seismic response of a fault system a narrow range of size scales leads to frequency size statistics of earthquakes resembling the characteristic earthquake distribution and quasi periodic temporal distribution of large events as in the seismic gap hypothesis on the other hand a wide range of size scales leads to gutenberg richter power law frequency size statistics and random or clustered temporal distribution of large events the simulations demonstrate that treatment of the various observed forms of frequency size and temporal statistics of earthquakes can be unified through the concept of range of size scales characterizing fault zone heterogeneities this has a clear physical interpretation in terms of structural properties of a given fault zone or broad lithospheric domain and is supported by observed earthquake and fault data in some simulated cases the frequency size statistics of small earthquakes fall sharply below the self similar gutenberg richter line the results indicate that small earthquakes prepare the fault for the occurrence of a large event by smoothing during gradual tectonic loading the long wavelength components of stress on the fault this is done through short wavelength stress roughening associated with the numerous ruptures of the small events the above pattern of smoothing roughening of long short wavelengths of stress on the fault is reversed during large scale ruptures of the big events

the response of an idealized ocean basin to variable buoyancy forcing the response of an idealized ocean basin to variable buoyancy forcing is examined a general circulation model that employs a gent mcwilliams mixing parameterization is forced by a zonally constant restoring surface temperature profile which varies with latitude and time over a period p in each experiment 17 different values of p are studied ranging from 6 months to 32 000 yr the model s meridional overturning circulation moc exhibits a very strong response on all time scales greater than 15 yr up to and including the longest forcing time scales examined the peak to peak values of the moc oscillations reach up to 125 of the steady state maximum moc and exhibit resonance like behavior with a maximum at centennial to millennial forcing periods depending on the vertical diffusivity this resonance like behavior stems from the existence of two adjustment time scales one of which is set by the vertical diffusion and the other of which is set by the basin width furthermore the linearity of the response as well as its lag with the forcing varies with the forcing period the considerable deviation from the quasi equilibrium response at all time scales above 15 yr is surprising and suggests a potentially important role of the ocean circulation for climate even at milankovich time scales

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

dynamic stress drop of recent earthquakes variations within subduction zones stress drop is a fundamental parameter of earthquakes but it is difficult to obtain reliable stress drop estimates for most earthquakes static stress drop estimates require knowledge of the seismic moment and fault area dynamic stress drop estimates are based entirely upon the observed source time functions based on analytical formulas that i derive for the crack and slip pulse rupture models the amplitude and time of the initial peak in source time functions can be inverted for dynamic stress drop for multiple event earthquakes this method only gives the dynamic stress drop of the first event the michigan stf catalog provides a uniform data base for all large earthquakes that have occurred in the past four years dynamic stress drops are calculated for the nearly 200 events in this catalog and the resultant estimates scatter between 0 1 and 100 mpa there is some coherent tectonic signal within this scatter in the sanriku japan and mexico subduction zones underthrusting earthquakes that occur at the up dip and down dip edges of the seismogenic zone have correspondingly low and high values of stress drop a speculative picture of the stress state of subduction zones emerges from these results a previous study found that the absolute value of shear stress linearly increases down the seismogenic interface to a value of about 50 mpa at the down dip edge in this study the dynamic stress drop of earthquakes at the up dip edge is about 0 2 mpa while large earthquakes at the down dip edge of the seismogenic plate interface have dynamic stress drops of up to 5 mpa these results imply that 1 large earthquakes only reduce the shear stress on the plate interface by a small fraction of the absolute level and thus 2 most of the earthquake energy is partitioned into friction at the plate interface

interdecadal variability in an ocean model driven by a small zonal redistribution of the surface buoyancy flux abstract an idealized three dimensional model of size comparable to the atlantic is used to study interdecadal variability of the thermohaline circulation thc in most of the model experiments salinity is kept uniform and constant the model being driven by surface heat flux only when the model is driven by the surface heat flux diagnosed from a restoring spinup experiment no oscillations occur driving the model by a time independent surface heat flux obtained by applying a small zonal redistribution to the diagnosed flux leads to strong interdecadal oscillations small means that the modification to the diagnosed flux is within the error bars on estimates of surface heat flux based on observations the model sea surface temperature sst anomalies are similar to the observed pattern of sst anomalies in the north atlantic and to the sst anomalies associated with the interdecadal oscillation in the gfdl fully coupled ocean atmosphere model for redistributions that weaken the east west varia

interdecadal variability of the thermohaline circulation in box ocean models forced by fixed surface fluxes intrinsic modes of decadal variability are analyzed using box geometry ocean models forced by constant surface fluxes an extensive parameter sensitivity analysis of the oscillatory behavior is carried out with respect to the spherical cartesian geometry the b effect the coriolis parameter the parameterization of momentum dissipation and associated boundary conditions the vertical and horizontal diffusivities the convective adjustment algorithm the horizontal and vertical model resolution the forcing amplitude and the basin width the oscillations stand out as a robust geostrophic feature whose amplitude is mainly controlled by the horizontal diffusivity unsuccessful attempts to reproduce the variability in zonally averaged 2d models suggest that the 3d adjustment processes are necessary however the b effect is not necessary for decadal variability to occur and therefore classical rossby waves play no fundamental role in the mechanism various experiments with different geometry and forcing are conducted and do not support the necessity of viscous numerical boundary waves or any boundary in sustaining the oscillations the models show two types of oscillatory behavior 1 temperature anomalies propagating geostrophically westward in the eastward jet northern part of the basin and inducing an opposite anomaly in their wake and 2 stationary temperature anomalies in the northwest quarter that respond to the western boundary current transport changes and reinforce geostrophically this change until the opposite temperature anomaly built on the east finally reverses the meridional overturning anomaly the analysis of the transition from steady to oscillatory states using heat fluxes diagnosed at the equilibrium under restoring boundary conditions and the comparison of the variability under various forcing fields suggest that the oscillations are triggered in the regions of strongest surface cooling finally a simple box model analogy is proposed that captures the crucial phase shift between meridional overturning and north south density gradient anomalies on these decadal timescales

a damped decadal oscillation in the north atlantic climate system a simple stochastic atmosphere model is coupled to a realistic model of the north atlantic ocean a north south sst dipole with its zero line centered along the subpolar front influences the atmosphere model which in turn forces the ocean model by surface fluxes related to the north atlantic oscillation the coupled system exhibits a damped decadal oscillation associated with the adjustment through the ocean model to the changing surface forcing the oscillation consists of a fast wind driven positive feedback of the ocean and a delayed negative feedback orchestrated by overturning circulation anomalies the positive feedback turns out to be necessary to distinguish the coupled oscillation from that in a model without any influence from the ocean to the atmosphere using a novel diagnosing technique it is possible to rule out the importance of baroclinic wave processes for determining the period of the oscillation and to show the important role played by anomalous geostrophic advection in sustaining the oscillation

adjustment of the ocean under buoyancy forces part i the role of kelvin waves abstract the early stages of the adjustment of an ocean toward equilibrium is examined using an ocean general circulation model the initial state is one with uniform meridional potential temperature gradients yielding density gradients representative of those observed in the north atlantic the main adjustment in the time examined here the first few months is by coastal kelvin waves the first baroclinic mode dominates so the behavior proves to be very similar to that in a shallow water model also the dynamics is locally close to that for an f plane but account must be taken of the way f varies with latitude the essential result of the coastal adjustment is to reduce the temperature gradients around the perimeter of the basin especially at the level where the first mode has the maximum effect this study also examines the way this adjustment process is distorted in models due to the constraints imposed by computer limitations namely in a model with too coarse a horizontal resolution and an artif

the role of horizontal boundaries in parameter sensitivity and decadal scale variability of coarse resolution ocean general circulation models abstract coarse resolution f plane and plane frictional geostrophic models are used to study the response to restored surface buoyancies and fixed surface buoyancy fluxes with restored surface buoyancies it is found that the overturning and meridional buoyancy transport generally follow the scaling from thermal wind and vertical advective diffusive balance when maximum midbasin rather than maximum overall streamfunction is used as the metric the sensitivity of overturning magnitude to vertical diffusivity agrees quite closely with that of a two dimensional rayleigh frictional model that follows an analogous scaling this measure of meridional overturning as well as the meridional buoyancy transport also roughly follow the predicted f 1 3 scaling and are relatively insensitive to variations in and horizontal viscosity the sensitivity experiments indicate that the coarse resolution model overturning and thermodynamic structure are well characterized by the adjustment of a uniformly rotating viscous

interseismic strain accumulation measured by gps in the seismic gap between constitucion and concepcion in chile the concepcion constitucion area 35 37 s in south central chile is very likely a mature seismic gap since no large subduction earthquake has occurred there since 1835 three campaigns of global positioning system gps measurements were carried out in this area in 1996 1999 and 2002 we observed a network of about 40 sites including two east west transects ranging from the coastal area to the argentina border and one north south profile along the coast our measurements are consistent with the nazca south america relative angular velocity 55 9 n 95 2 w 0 610 ma discussed by vigny et al 2008 this issue which predicts a convergence of 68 mm year oriented 79 n at the chilean trench near

oceanic kelvin waves and tropical atlantic intraseasonal variability 1 kelvin wave characterization 1 oceanic kelvin waves from the equator to the west african coast are investigated in the framework of tropical atlantic intraseasonal variability in order to better highlight the wave propagations a 25 95 day band pass filter was applied to the sea surface height ssh product derived from the topex poseidon altimeter and an ocean general circulation model simulation for the 1993 2000 period in addition to equatorial eastward propagations our analysis reveals recurrent and continuous propagations distinguishable over thousands of kilometers poleward along the coasts as far as about 10 15 latitude a novel result with altimeter data the variance of the filtered ssh signal goes from 1 cm at the equator to 2 cm at the african coast estimates of the phase speed range from 1 5 to 2 1 m s along the equator and the west african coastline such values are very close to those of equatorial kelvin wave propagations likely dominated by the first two baroclinic modes supporting the fact that the coastal propagations are coastally trapped kelvin waves in order to simplify the description of these kelvin waves we present an intraseasonal climatology which reveals regular boreal autumn winter equator to coast propagations an improved description is achieved thanks to the computation of an extended empirical orthogonal function for the boreal autumn winter propagations lag correlation of ssh signals allows for a twofold quantification the phase speed and the importance of remote forcing along the coast the remote forcing effect of intraseasonal kelvin waves is clearly evidenced over coastal upwelling regions as far as 10 15 latitude the physical mechanism associated with the forcing of the kelvin waves and its impacts will be investigated in a future paper

a zonally averaged ocean model for the thermohaline circulation part i model development and flow dynamics abstract a two dimensional latitude depth ocean model is developed on the basis of the zonally averaged balance equations of mass momentum heat and salt its purpose is to investigate the dynamics and variability of the buoyancy forced thermohaline circulation for the time scales of interest an annually averaged model is selected and the momentum balance is taken to be diagnostic the east west pressure gradient which arises upon zonally averaging the momentum equations is parameterized in terms of the meridional pressure gradient the thermohaline circulation is driven by mixed surface boundary conditions i e temperatures are relaxed to prescribed values while the salt flux is held constant the dynamics of the flow is investigated in hemispheric and global geometries for both short and long time integrations the latter extending over many thousands of years as has been noted by previous investigators it is possible to perturb a steady state such that a diffusively dominated regime results

joint determination of slip and stress drop in a bayesian inversion approach a case study for the 2010 m8 8 maule earthquake stress drop is a key factor in earthquake mechanics and engineering seismology however stress drop calculations based on fault slip can be significantly biased particularly due to subjectively determined smoothing conditions in the traditional least square slip inversion in this study we introduce a mechanically constrained bayesian approach to simultaneously invert for fault slip and stress drop based on geodetic measurements a gaussian distribution for stress drop is implemented in the inversion as a prior we have done several synthetic tests to evaluate the stability and reliability of the inversion approach considering different fault discretization fault geometries utilized datasets and variability of the slip direction respectively we finally apply the approach to the 2010 m8 8 maule earthquake and invert for the coseismic slip and stress drop simultaneously two fault geometries from the literature are tested our results indicate that the derived slip models based on both fault geometries are similar showing major slip north of the hypocenter and relatively weak slip in the south as indicated in the slip models of other studies the derived mean stress drop is 5 6 mpa which is close to the stress drop of 7 mpa that was independently determined according to force balance in this region luttrell et al j geophys res 2011 these findings indicate that stress drop values can be consistently extracted from geodetic data

multi and quasi decadal variations of sea surface temperature in the north atlantic abstract the multi and quasi decadal variabilities of the sea surface temperature sst anomaly over the north atlantic are investigated by means of two dimensional propagating ceof forty six years of the coads sst dataset from 1947 to 1992 are used after removing the monthly climatology and four year low pass filtering the sst anomaly is submitted to ceof the total variance of the three largest modes accounts for 87 0 of the total variance mode 1 is a very slow oscillation with an approximate 42 yr period and has basinwide spatial evolution with alternate warm and cold anomalies appearing off newfoundland and migrating northward until they disappear south of greenland the center of action of the anomalies both occur in the vicinity of the labrador sea newfoundland and south of greenland where deep water formation takes place mode 2 3 is a quasi decadal fluctuation with an approximate 14 yr period mode 2 3 contains quasi decadal timescales with alternating warm and cold anomalies propagati

interdecadal variability in a zonally averaged ocean model an adjustment oscillator abstract a meridional plane hemispherical ocean model is developed to study interdecadal variability of the thermohaline circulation thc the model differs from previous formulations of zonally averaged ocean models by using a prognostic equation to calculate the meridional velocity this allows the incorporation of an adjustment timescale comparable to the advective timescale of the meridional overturning an interdecadal oscillation is documented for an idealized ocean of homogeneous salinity forced by a time independent surface heat flux the governing equations are linearized about a basic state in order to isolate the effect of parameter changes on the oscillation an eigenvalue analysis reveals that the frequency of the oscillation is independent of the advective timescale instead the interdecadal timescale of the oscillation is set by the slow adjustment of the overturning intensity to a meridional pressure gradient anomaly the oscillatory instability on the other hand is dependent on both

oceanic responses to gradual transitions of equator to pole temperature gradients summary responses of an ocean model to gradual transitions of equator to pole gradients show that several quasiequilibrium states within the thermally driven regime are generated under identical forcing conditions these different states are associated with different patterns the location and the penetration depth of oceanic convection small changes in the thermal forcing conditions can push the system into an oscillatory regime once in this regime oscillations appear to proceed as internal processes one important implication of these results is that the presentday ocean climate may not recover fully if the atmospheric coz level after doubling is lowered to the present day level

a spatial random field model to characterize complexity in earthquake slip 1 finite fault source inversions reveal the spatial complexity of earthquake slip over the fault plane we develop a stochastic characterization of earthquake slip complexity based on published finite source rupture models in which we model the distribution of slip as a spatial random field the model most consistent with the data follows a von karman autocorrelation function acf for which the correlation lengths a increase with source dimension for earthquakes with large fault aspect ratios we observe substantial differences of the correlation length in the along strike a x and downdip a z directions increasing correlation length with increasing magnitude can be understood using concepts of dynamic rupture propagation the power spectrum of the slip distribution can also be well described with a power law decay i e a fractal distribution in which the fractal dimension d remains scale invariant with a median value d 2 29 0 23 while the comer wave number k c which is inversely proportional to source size decreases with earthquake magnitude accounting for larger slip patches for large magnitude events our stochastic slip model can be used to generate realizations of scenario earthquakes for near source ground motion simulations

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

toward understanding tectonic control on the mw 8 8 2010 maule chile earthquake the maule earthquake of 27th february 2010 m w 8 8 affected similar to 500 km of the nazca south america plate boundary in south central chile producing spectacular crustal deformation here we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous gps both in near and far field regions earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published gps insar and land level changes data using green s functions generated by a spherical finite element model with realistic subduction zone geometry the combination of the data sets provided a good resolution indicating that most of the slip was well resolved coseismic slip was concentrated north of the epicenter with up to 16 m of slip whereas to the south it reached over 10 m within two minor patches a comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap slip deficit distribution shows an apparent local overshoot that highlight cycle to cycle variability which has to be taken into account when anticipating future events from interseismic observations rupture propagation was obviously not affected by bathymetric features of the incoming plate instead splay faults in the upper plate seem to have limited rupture propagation in the updip and along strike directions additionally we found that along strike gradients in slip are spatially correlated with geometrical inflections of the megathrust our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts c 2012 elsevier b v all rights reserved

stress field associated with the rupture of the 1992 landers california earthquake and its implications concerning the fault strength at the onset of the earthquake we investigate the space and time history of the shear stress produced on the fault during the 1992 landers earthquake the stress is directly calculated from the tomographic image of slip on the fault derived from near source strong motion data the results obtained shed some light on why the earthquake rupture cascaded along a series of previously distinct fault segments to produce the largest earthquake in california in over 40 years rupture on the 30 km long northernmost segment of the fault was triggered by a large dynamic increase of the stress field of the order of 20 to 30 mpa produced by the rupturing of the adjacent fault segments such a large increase was necessary to overcome the static friction on this strand of the fault unfavorably oriented in today s tectonic stress field this misorientation eventually led to the arrest of rupture the same mechanism explains why rupture broke only a small portion of the johnson valley fault on which the earthquake originally started before jumping to an adjacent fault more favorably oriented we conclude from these results that the dynamic stress field could not sustain and drive the rupture along the strongly misoriented nw se strands of the preexisting fault system instead the dynamic stress field produced new fractures favorably oriented in a n s direction and connecting parts of the old fault system

a two level wind and buoyancy driven thermocline model abstract a simple two level model is designed to simulate the thermocline equations applicable for large scale steady oceanic flow the model serves two functions first it replaces problems with the interpretation of slablike dynamics e g luyten et al 1983 by using continuously horizontally varying buoyancy but at the cost of reducing the vertical resolution drastically the equations used are geostrophy plus a small linear drag to close a stommel like western boundary layer mass conservation and buoyancy conservation with a small but necessary horizontal diffusion inclusion of vertical diffusion has little effect the ocean is driven by an ekman layer whose functions are to provide a given surface input of mass through ekman pumping and buoyancy through a specified buoyancy in the ekman layer i e to maintain the same boundary conditions as in classical thermocline studies sidewall conditions are not well understood and are almost certainly over specified in this formulation s

active faulting and heterogeneous deformation across a megathrust segment boundary from gps data south central chile 36 39 s 1 this study focuses on the present day deformation mechanisms of the south central chile margin at the transition zone between two megathrust earthquake segments defined from historical data the valdivia and concepcion sectors new gps data and finite element models with complex geometries constrained by geophysical data are presented to gain insight into forearc kinematics and to address the role of upper plate faults on contemporary deformation gps vectors are heterogeneously distributed in two domains that follow these two earthquake segments we find that models which simulate only interseismic locking on the plate interface fail to reproduce surface deformation in the entire study area in the concepcion domain models that include a crustal scale fault in the upper plate better reproduce the gps observations in the valdivia domain gps data show regional scale vertical axis rotations which could reflect postseismic deformation processes at the edge of the mw 9 5 earthquake that ruptured in 1960 and or activity of another crustal fault related to motion of a forearc sliver our study suggests that upper plate faults in addition to earthquake cycle transients may exert an important control on the surface velocity of subduction zone forearcs

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

teleseismic inversion for rupture process of the 27 february 2010 chile mw 8 8 earthquake the 27 february 2010 chile m w 8 8 earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation the faulting geometry slip distribution seismic moment and moment rate function are estimated from broadband teleseismic p sh and rayleigh wave signals we explore some of the trade offs in the rupture process estimation due to model parameterizations limited teleseismic sampling of seismic phase velocities and uncertainty in fault geometry the average slip over the 81 500 km 2 rupture area is about 5 m with slip concentrations down dip up dip and southwest and up dip and north of the hypocenter relatively little slip occurred up dip offshore of the hypocenter the average rupture velocity is 2 0 2 5 km s

baroclinic instability an oceanic wavemaker for interdecadal variability numerical simulations of coarse resolution idealized ocean basins under constant surface heat flux are analyzed to show that the interdecadal oscillations that emerge naturally in such configurations are driven by baroclinic instability of the mean state and damped by horizontal diffusion when the surface heat fluxes are diagnosed from a spinup in which surface temperatures are strongly restored to apparent atmospheric temperatures the most unstable regions diagnosed by large downgradient eddy heat fluxes are located in the basin northwest corner where the surface heat losses are largest the long wave limit of the baroclinic instability of idealized mean flows in a three layer model with vertical shears as observed in the gcms demonstrates that growth rates of order one cycle per year can be produced locally large enough to amplify thermal anomalies in the face of lateral diffusion the proposed instability mechanism that favors surface intensified perturbations also explains the lack of oscillations if the restoring to a surface climatology is too strong to assess whether this instability process of oceanic origin is robust enough to cause interdecadal variability of coupled ocean atmosphere models a four box ocean atmosphere model is constructed given the large heat capacity of the ocean as compared to the atmosphere the dynamical system that governs the model evolution is reduced to only two degrees of freedom the oceanic overturning thermohaline circulation and the interior north south temperature gradient the authors show that when the baroclinic instability growth rate exceeds the overall dissipation caused by turbulent eddy diffusion in the atmosphere and ocean and infrared back radiation the dynamical system undergoes a hopf bifurcation and interdecadal oscillations emerge through a limit cycle

a two level model of a thermally forced ocean basin abstract some simple solutions mostly analytic are presented for the large scale baroclinic response to thermal forcing on a mid latitude beta plane surface heat flux is parameterized as ta tt tau with atmospheric temperature ta prescribed as a function of latitude varying ocean surface temperature tt and equilibration time for long times decades benthic forcing is included using a similar representation the model allows horizontal density variations at each level when there are no meridional boundaries there is only a local response to the forcing a geostrophic baroclinic zonal flow is driven by the north south temperature gradient but it has no associated advection or divergence effects this picture is greatly changed when east and or west coasts are added kelvin waves pass information rapidly about 200 km day 1 along coasts and rossby waves travel slowly offshore most effectively from the cut with speed c 1 km day 1 for spin up problems e g the response to a change in for

coseismic slip distribution of the february 27 2010 mw 8 8 maule chile earthquake 1 static offsets produced by the february 27 2010 mw 8 8 maule chile earthquake as measured by gps and insar constrain coseismic slip along a section of the andean megathrust of dimensions 650 km in length 180 km in width gps data have been collected from both campaign and continuous sites sampling both the near field and far field alos palsar data from several ascending and descending tracks constrain the near field crustal deformation inversions of the geodetic data for distributed slip on the megathrust reveal a pronounced slip maximum of order 15 m at 15 25 km depth on the megathrust offshore lloca indicating that seismic slip was greatest north of the epicenter of the bilaterally propagating rupture a secondary slip maximum appears at depth 25 km on the megathrust just west of concepcion coseismic slip is negligible below 35 km depth estimates of the seismic moment based on different datasets and modeling approaches vary from 1 8 to 2 6 1022 n m our study is the first to model the static displacement field using a layered spherical earth model allowing us to incorporate both near field and far field static displacements in a consistent manner the obtained seismic moment of 1 97 1022 n m corresponding to a moment magnitude of 8 8 is similar to that obtained by previous seismic and geodetic inversions

oceanic wave dynamics and interdecadal variability in a climate system model western boundary disturbances detected in the first multicentury integration of the national center for atmospheric research climate system model are analyzed and the role they play in the model interdecadal variability is investigated the boundary signals propagate southwestward along the coast of north america at depth they reach the equator and propagate along the equator but with decreasing amplitude away from the western boundary their southwestward propagation is associated with the evolution of the western boundary current system the gulf stream system in the upper part of the water column and the deep western boundary current at depth from weaker than average to stronger than average conditions thus the boundary disturbances seem to play an important role in the model thermohaline circulation variability at interdecadal timescales they show similarities with the boundary waves found in ocean only models exhibiting interdecadal variability and their role in the model s response to changes in the rate of sinking appears to be in agreement with the theory of the spin up of the deep ocean circulation the main result of this study is that the similarities with ocean only results and theories support the idea that interdecadal timescales of variability originate from the ocean dynamics

proximity of the present day thermohaline circulation to an instability threshold the relation between the mean state of the thermohaline circulation thc and its stability is examined using a realistic geometry primitive equation coupled ocean atmosphere ice global general circulation model the main finding is that a thermohaline circulation that is 25 weaker and less dominated by thermal forcing than that of today s ocean is unstable within this coupled gcm unstable initial ocean climates lead in the coupled model to an increase of the thc to strong oscillations or to a thc collapse the existence of an unstable range of weak states of the thc provides a natural explanation for largeamplitude thc variability seen in the paleo record prior to the past 10 000 years a weakening of the thc due to an external forcing e g ice melting and freshening of the north atlantic may push it into the unstable regime once in this regime the thc strongly oscillates due to the inherent instability of a weak thc hence the strong thc variability in this scenario does not result from switches between two or more quasi stable steady states

the damping effect of bottom topography on internal decadal scale oscillations of the thermohaline circulation by comparing the response of flat and bowl shaped basins to fixed heat fluxes of various magnitudes it is determined that coastal topography has a considerable damping influence upon internal decadal oscillations of the thermohaline circulation it is proposed that this is because the adjustment of baroclinic currents to the no normal flow boundary condition at weakly stratified coasts is aided in the topography case by the generation of substantial barotropic flow

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

adjustment of the ocean under buoyancy forces part ii the role of planetary waves abstract a numerical ocean general circulation model is used to investigate the early stages in the adjustment to equilibrium of an ocean initially at rest with imposed uniform meridional potential temperature gradients which yield density gradients representative of those observed in the north atlantic the main feature of the adjustment during the early stages the first year is the formation and decay of a subtropical warm core and a subpolar cold core density gyre the gyres are formed by the irreversible winding up of the initially zonal isotherms by first baroclinic mode coastally trapped dissipative kelvin waves this phase and the north south asymmetry arising from the variation in viscous diffusive kelvin wave properties with latitude were discussed in part i of this series within a month effects become significant especially in the evolution of the southern gyre which develops a distinct east west asymmetry through western intensification and long planetary wave propagation of b

middle miocene to earliest pliocene sedimentological and geochemical records of climate change in the western qaidam basin on the ne tibetan plateau global cooling tibetan plateau uplift and the retreat of the para tethys sea have long been thought to be the key controls of the cenozoic climate change in the asian inland however due to the scarcity of long term palaeoclimate records it is not entirely clear which of these factors plays the major role here we present new sedimentological and geochemical proxy records toc carbonate so42 and cl from a 1040 m late cenozoic sedimentary sequence ca 17 to 5 0 ma from the western part of the qaidam basin the largest inland basin on the ne tibetan plateau geochemical records reveal an evident two stage change from ca 17 ma to 11 1 ma phase i the proxies show an upward decrease of carbonate content and toc concentration and a persistent increase in the concentration of the soluble anions so42 and cl even though superimposed high frequency fluctuations are evident from ca 11 1 ma to 5 0 ma phase ii the average concentrations of so42 and cl are higher than those from phase i and a sharp decrease in the carbonate content occurred the sedimentological and geochemical proxy records demonstrate that the qaidam basin has experienced increased aridity since ca 11 1 ma we suggest that the miocene global cooling exerted a significant influence on the drying of the qaidam basin by decreasing evaporation rates and water vapour concentrations in the atmosphere the mio pliocene episodic and persistent uplift of the ne tibetan plateau exerted an important influence superimposed upon this driving force while during ca 11 1 to 8 ma the rapid uplift of the altun shan might have played a key role in climate change of the qaidam basin c 2013 elsevier b v all rights reserved

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

constraining earthquake source inversions with gps data 1 resolution based removal of artifacts 1 we present a resolution analysis of an inversion of gps data from the 2004 mw 6 0 parkfield earthquake this earthquake was recorded at thirteen 1 hz gps receivers which provides for a truly coseismic data set that can be used to infer the static slip field we find that the resolution of our inverted slip model is poor at depth and near the edges of the modeled fault plane that are far from gps receivers the spatial heterogeneity of the model resolution in the static field inversion leads to artifacts in poorly resolved areas of the fault plane these artifacts look qualitatively similar to asperities commonly seen in the final slip models of earthquake source inversions but in this inversion they are caused by a surplus of free parameters the location of the artifacts depends on the station geometry and the assumed velocity structure we demonstrate that a nonuniform gridding of model parameters on the fault can remove these artifacts from the inversion we generate a nonuniform grid with a grid spacing that matches the local resolution length on the fault and show that it outperforms uniform grids which either generate spurious structure in poorly resolved regions or lose recoverable information in well resolved areas of the fault in a synthetic test the nonuniform grid correctly averages slip in poorly resolved areas of the fault while recovering small scale structure near the surface finally we present an inversion of the parkfield gps data set on the nonuniform grid and analyze the errors in the final model

anomalies of meridional overturning mechanisms in the north atlantic abstract optimal observations are used to investigate the overturning streamfunction in the north atlantic at 30 n and 900 m depth those observations are designed to impact the meridional overturning circulation moc in numerical models maximally when assimilated and therefore establish the most efficient observation network for studying changes in the moc they are also ideally suited for studying the related physical mechanisms in a general circulation model optimal observations are evaluated here in the framework of a global 1 model over a 10 yr period hydrographic observations useful to monitor the moc are primarily located along the western boundary north of 30 n and along the eastern boundary south of 30 n additional locations are in the labrador irminger and iberian seas on time scales of less than a year variations in moc are mainly wind driven and are made up through changes in ekman transport and coastal up and downwelling only a small fraction is buoyancy driven and constitutes a sl

bayesian imaging of the 2000 western tottori japan earthquake through fitting of strong motion and gps data summary we image the rupture process of the 2000 western tottori earthquake m w 6 6 through fitting of strong motion and gps data we consider an observational network consisting of 18 strong motion and 16 gps stations located within three fault lengths from the epicentre we assume a planar fault and compute green s functions for a 1 d velocity model the earthquake rupture is described as a shear dislocation parameterized in terms of peak slip velocity rake angle rupture time and rise time defined on a regular grid of nodes on the fault surface and derived at inner points through bilinear interpolation our inversion procedure is based on a bayesian approach the solution of the inverse problem is stated in terms of a posterior probability density function pdf representing the conjunction of prior information with information contained in the data and in the physical law relating model parameters with data inferences on model parameters are thus expressed in terms of posterior marginal pdfs due to the non linearity of the problem we use a markov chain monte carlo mcmc method based on the metropolis algorithm to compute posterior marginals except for a few cases posterior marginals do not show a gaussian like distribution this prevents us from providing a mean model and from characterizing uncertainties in terms of standard deviations only resolution on each single parameter is analysed by looking at the difference between prior and posterior marginal pdfs posterior marginals indicate that the best resolved feature is a major slip patch peak value of 311 140 cm located between the hypocentre and the top edge of the fault centered at a depth of 4 5 km this shallow slip patch is triggered about 3 s after the earthquake nucleated and required about 4 s to reach its final slip value the presence of this shallow slip patch is common to all previous studies in contrast to some previous studies we do not identify any significant slip 1 m at the bottom of the fault we also compare inferences from both strong motion and gps data with inferences derived from strong motion data only in both cases the shallow slip patch is identified at other locations the main effect of the gps data is in reducing the probability associated with high values of slip gps data reduce the presence of spurious fault slip and therefore strongly influence the resulting final seismic moment

constraints on fault slip rates of the southern california plate boundary from gps velocity and stress inversions summary we use global positioning system gps velocities and stress orientations inferred from seismicity to invert for the distribution of slip on faults in the southern california plate boundary region of particular interest is how long term slip rates are partitioned between the indio segment of the san andreas fault saf the san jacinto fault sjf and the san bernardino segment of the saf we use two new sets of constraints to address this problem the first is geodetic velocities from the southern california earthquake center s scec crustal motion map version 3 by shen et al which includes significantly more data than previous models the second is a regional model of stress field orientations at seismogenic depths as determined from earthquake focal mechanisms while gps data have been used in similar studies before this is the first application of stress field observations to this problem we construct a simplified model of the southern california fault system and estimate the interseismic surface velocities using a backslip approach with purely elastic strain accumulation following meade et al in addition we model the stress orientations at seismogenic depths assuming that crustal stress results from the loading of active faults the geodetically derived stressing rates are found to be aligned with the stress orientations from seismicity we therefore proceed to invert simultaneously gps and stress observations for slip rates of the faults in our network we find that the regional patterns of crustal deformation as imaged by both data sets can be explained by our model and that joint inversions lead to better constrained slip rates in our preferred model the sjf accommodates 15 mm yr 1 and the indio segment of the saf 23 mm yr 1 of right lateral motion accompanied by a low slip rate on the san bernardino segment of the saf anomalous fault segments such as around the 1992 m w 7 3 landers surface rupture can be detected there observed stresses deviate strongly from the long term loading as predicted by our simple model evaluation of model misfits together with information from palaeoseismology may provide further insights into the time dependence of strain accumulation along the san andreas system

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

interdecadal variability and oceanic thermohaline adjustment changes in the strength of the thermohaline overturning circulation are associated by geostrophy with changes in the east west pressure difference across an ocean basin the tropical polar density contrast and the east west pressure difference are connected by an adjustment process in flat bottomed ocean models the adjustment is associated with viscous baroclinic kelvin wave propagation weak high latitude stratification leads to the adjustment having an interdecadal timescale we reexamine model interdecadal oscillations in the context of the adjustment process for both constant flux and mixed surface boundary conditions under constant surface flux interdecadal oscillations are associated with the passage of a viscous kelvin wave around the model domain we carry out experiments suppressing wave propagation along each of the model boundaries suppressing wave propagation along either the tropical or eastern boundary does not eliminate the oscillation but increases both its period and amplitude suppressing wave propagation along either the polar or the western boundary eliminates the oscillation our results suggest the oscillations can be self sustained by perturbations to the western boundary current arising from the southward boundary wave propagation mixed boundary condition oscillations are characterized by the eastward cross basin movement of salinity dominated density anomalies and the westward return of these anomalies along the northern boundary we suggest the latter is associated with viscous kelvin wave propagation under both types of boundary conditions the strength of the thermohaline overturning and the tropical polar density contrast vary out of phase we show how the phase relationship is related to the boundary wave propagation box models and zonally averaged models assume that the east west and north south pressure gradients vary in phase and are proportional to one another we suggest this assumption is valid only on timescales long compared to the adjustment timescale the importance of boundary regions indicates an urgent need to examine the robustness of interdecadal variability in models as the resolution is increased and as the representation of the coastal shelf slope wave guide is improved

signal propagation related to the north atlantic overturning 1 changes of the meridional overturning circulation moc due to surface heat flux variability related to the north atlantic oscillation nao are analyzed in various ocean models i e eddying and non eddying cases a prime signature of the forcing is variability of the winter time convection in the labrador sea the associated changes in the strength of the moc near the subpolar front 45 n are closely related to the nao index leading moc anomalies by about 2 3 years in both the eddying and non eddying simulation further south the speed of the meridional signal propagation depends on model resolution with lower resolution non eddying case 4 3 resolution the moc signal propagates equatorward with a mean speed of about 0 6 cm s similar as spreading rates of passive tracer anomalies eddy permitting experiments 1 3 show a significantly faster propagation with speeds corresponding to boundary waves thus leading to an almost in phase variation of the moc transport over the subtropical to subpolar north atlantic

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

mechanical constraints on inversion of coseismic geodetic data for fault slip and geometry example from insar observation of the 6 october 2008 mw 6 3 dangxiong yangyi tibet earthquake 1 modern geodetic techniques such as the global positioning system gps and interferometric synthetic aperture radar insar provide high precision deformation measurements of earthquakes through elastic models and mathematical optimization methods the observations can be related to a slip distribution model the classic linear kinematic and static slip inversion problem requires specification of a smoothing norm of slip parameters and a residual norm of the data and a choice about the relative weight between the two norms inversions for unknown fault geometry are nonlinear and therefore the fault geometry is often assumed to be known for the slip inversion problem we present a new method to invert simultaneously for fault slip and fault geometry assuming a uniform stress drop over the slipping area of the fault the method uses a full bayesian inference method as an engine to estimate the posterior probability distribution of stress drop fault geometry parameters and fault slip we validate the method with a synthetic data set and apply the method to insar observations of a moderate sized normal faulting event the 6 october 2008 mw 6 3 dangxiong yangyi tibet earthquake the results show a 45 0 0 2 west dipping fault with a maximum net slip of 1 13 m and the static stress drop and rake angle are estimated as 5 43 mpa and 92 5 respectively the stress drop estimate falls within the typical range of earthquake stress drops known from previous studies

assessment of stress coupling among the inter co and post seismic phases related to the 2004 m6 parkfield earthquake due to large uncertainties and non uniqueness in fault slip inversion the investigation of stress coupling based on the direct comparison of independent slip inversions for example between the coseismic slip distribution and the interseismic slip deficit may lead to ambiguous conclusions in this study we therefore adopt the stress constrained joint inversion in the bayesian approach of wang et al and implement the physical hypothesis of stress coupling as a prior we test the hypothesis that interseismic locking is coupled with the coseismic rupture and the early post seismic deformation is a stress relaxation process in response to the coseismic stress perturbation we characterize the role of stress coupling in the seismic cycle by evaluating the efficiency of the model to explain the available data taking the 2004 m6 parkfield earthquake as a study case we find that the stress coupling hypothesis is in agreement with the data the coseismic rupture zone is found to be strongly locked during the interseismic phase and the post seismic slip zone is indicated to be weakly creeping the post seismic deformation plays an important role to rebuild stress in the coseismic rupture zone based on our results for the stress accumulation during both inter and post seismic phase in the coseismic rupture zone together with the coseismic stress drop we estimate a recurrence time of m6 earthquake in parkfield around 23 41 yr suggesting that the duration of 38 yr between the two recent m6 events in parkfield is not a surprise

a thermal oscillation under a restorative forcing summary the authors report an interdecadal oscillation in a wind and thermally driven ocean general circulation model ogcm the oscillation is tantalizing in that it occursunder a relatively strong thermal damping 26 3 w m 2k examinations involving a two dimensional ogcm a simple thermal flip flop model and a three dimensional ogcm with and without the nonlinear effect of temperature in the state equation of sea water demonstrate that the oscillation is not driven by mechanisms such as the so called convective oscillator or the advective overshooting oscillator instead the oscillation is associated with the propagation of modelled long rossby waves with westward phase velocity it is found that the north south basin extent of the ogcm is an important factor a larger northsouth basin extent is conducive to the generation of thermal wind flows crucial for initiating the propagation of disturbances the geophysical relevance of these results is discussed

flow properties in rotating stratified hydraulics abstract this paper discusses three distinct features of rotating stratified hydraulics using a reduced gravity configuration first a new upstream condition is derived corresponding to a wide almost motionless basin and this is applied to flow across a rectangular sill and compared with the case of a zero potential vorticity upstream condition for this geometry it is shown that unidirectional flow permits more water to pass through the sill than bidirectional flow second the general problem is considered of flow from any upstream configuration that passes through sills that vary slowly in depth cross sill and so are effectively many deformation radii wide only two flow configurations permit any realistic amount of flux across the sill either the fluid occupies a narrow region within the sill with a small flux or the fluid occupies a wide region with sluggish geostrophic flow except for at boundary layers at each side in the latter case hydraulic control is not likely to occur the zero

global teleconnections of meridional overturning circulation anomalies there is a wide range of evidence from both models and palaeoclimatic data that indicates the possibility of abrupt changes in the oceanic meridional overturning circulation moc however much of our dynamical understanding of the moc comes from steady state models that rely upon the assumption of thermodynamic equilibrium and are therefore only valid on millennial time scales here a dynamical model for the global teleconnections of moc anomalies on annual to multidecadal time scales is developed it is based on a linear theory for the propagation of zonally integrated meridional transport anomalies in a reduced gravity ocean and allows for multiple ocean basins connected by a circumpolar channel to the south the theory demonstrates that the equator acts as a low pass filter to moc anomalies as a consequence moc anomalies on decadal and shorter time scales are confined to the hemispheric basin in which they are generated and have little impact on the remainder of the global ocean the linear theory is compared with the results of a global nonlinear numerical integration which it reproduces to a good approximation

slip distribution of the february 27 2010 mw 8 8 maule earthquake central chile from static and high rate gps insar and broadband teleseismic data 1 the shallow depth underthrust earthquake of february 27 2010 mw 8 8 ruptured the subduction plate interface in central chile between 34 s and 38 s we retrieve the spatial and temporal distribution of slip during this mega earthquake through a joint inversion of teleseismic records insar and high rate gps hrgps data additionally our model is shown to agree with broadband surface waves rupture initiated at about 32 km depth and propagated bilaterally resulting in two main slip zones located ssw and nne of the hypocenter nucleation did not take place within or at the edge of one of these main asperities but in between during the first 30s slip propagated predominantly southwards later on the rupture evolved more slowly and more symmetrically eventually the northern asperity became predominant with maximum slip reaching about 20 m most of the seismic moment was released within 110s a relatively short time explained by the bilateral propagation the overall average rupture velocity is 2 6 km s but propagation occurred initially faster towards the south 3 2 km s large slip did not reach the trench a result consistent with the moderate size of the tsunami down dip rupture stopped at about 50 km depth in agreement with the lower limit of the locked zone inferred by ruegg et al 2009 from pre seismic gps data

spatial and temporal stress drop variations in small earthquakes near parkfield california 1 we estimate source parameters from spectra of 42367 earthquakes between 1984 and 2005 that occurred in the parkfield segment of the san andreas fault in central california we use a method that isolates the source term of the displacement spectra based on a convolutional model and correct the observed p wave source spectra with a spatially varying empirical green s function egf our brune type stress drop estimates vary from 0 1 to over 100 mpa with a median value of 6 75 mpa which is nearly constant with moment implying self similarity over the ml 0 5 to 3 0 range of our data the corner frequency decreases for earthquakes at shallower depths consistent with slower rupture velocities and reduced shear wave velocities in local velocity models the estimated median stress drops show significant lateral variations we find lower stress drops in the middle mountain asperity and along the creeping fault section and higher stress drops in the hypocentral region of the 2004 m6 0 parkfield earthquake the main shock did not alter the overall pattern of high and low stress drop regions however a statistical test reveals areas with significant changes in computed stress drops after the main shock which we compare to estimated absolute shear stress changes from a main shock slip model by calculating t from the spectral egf ratio we also identify areas with increased attenuation after the main shock and we are able to distinguish source effects and near source attenuation effects in the spectral analysis these results are confirmed independently from spectral ratios of repeating microearthquake clusters

estimates of stress drop and crustal tectonic stress from the 27 february 2010 maule chile earthquake implications for fault strength 1 the great 27 february 2010 mw 8 8 earthquake off the coast of southern chile ruptured a 600 km length of subduction zone in this paper we make two independent estimates of shear stress in the crust in the region of the chile earthquake first we use a coseismic slip model constrained by geodetic observations from interferometric synthetic aperture radar insar and gps to derive a spatially variable estimate of the change in static shear stress along the ruptured fault second we use a static force balance model to constrain the crustal shear stress required to simultaneously support observed fore arc topography and the stress orientation indicated by the earthquake focal mechanism this includes the derivation of a semianalytic solution for the stress field exerted by surface and moho topography loading the crust we find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid with a poisson ratio of 0 5 and is independent of young s modulus this places a strict lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography we estimate the coseismic shear stress change from the maule event ranged from 6 mpa stress increase to 17 mpa stress drop with a maximum depth averaged crustal shear stress drop of 4 mpa we separately estimate that the plate driving forces acting in the region regardless of their exact mechanism must contribute at least 27 mpa trench perpendicular compression and 15 mpa trench parallel compression this corresponds to a depth averaged shear stress of at least 7 mpa the comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the maule earthquake is weak with the seismic cycle relieving much of the total sustained shear stress in the crust

limited overlap between the seismic gap and coseismic slip of the great 2010 chile earthquake the mw 8 8 chile earthquake on 27 february 2010 occurred in a broad region where tectonic loading has been accumulating since the great 1835 earthquake a joint inversion of tsunami and geodetic data suggests that the 2010 earthquake rupture only partly overlapped with the zone of preseismic locking

signature of the atlantic meridional overturning circulation in sea level along the east coast of north america in this letter we examine the relationship between the north atlantic meridional overturning circulation moc and sea level sl along the east coast of north america in the eddy permitting ocean model occam we find a distinctive topography following pattern of sl variability in the western north atlantic that is closely linked with the changing strength of the moc with a 2 cm drop in sl along the us east coast corresponding to a 1sv increase in the moc we find a similar pattern of sl variability in the altimetry record and show that this meridionally coherent sl mode dominates interannual sl variability at tide gauges along the north american east coast between 40 50n hence we conclude that north american coastal sea level may indeed be a useful indicator of moc variability on interannual timescales allowing an observationally based estimate of the likely range of interannual moc fluctuations to be determined citation bingham r j and c w hughes 2009 signature of the atlantic meridional overturning circulation in sea level along the east coast of north america geophys res lett 36 l02603 doi 10 1029 2008gl036215

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

stress and aftershock constrained joint inversions for coseismic and postseismic slip applied to the 2004 m6 0 parkfield earthquake 1 both aftershocks and geodetically measured postseismic displacements are important markers of the stress relaxation process following large earthquakes postseismic displacements can be related to creep like relaxation in the vicinity of the coseismic rupture by means of inversion methods however the results of slip inversions are typically non unique and subject to large uncertainties therefore we explore the possibility to improve inversions by mechanical constraints in particular we take into account the physical understanding that postseismic deformation is stress driven and occurs in the coseismically stressed zone we do joint inversions for coseismic and postseismic slip in a bayesian framework in the case of the 2004 m6 0 parkfield earthquake we perform a number of inversions with different constraints and calculate their statistical significance according to information criteria the best result is preferably related to a physically reasonable model constrained by the stress condition namely postseismic creep is driven by coseismic stress and the condition that coseismic slip and large aftershocks are disjunct this model explains 97 of the coseismic displacements and 91 of the postseismic displacements during day 1 5 following the parkfield event respectively it indicates that the major postseismic deformation can be generally explained by a stress relaxation process for the parkfield case this result also indicates that the data to constrain the coseismic slip model could be enriched postseismically for the 2004 parkfield event we additionally observe asymmetric relaxation process at the two sides of the fault which can be explained by material contrast ratio across the fault of 1 15 in seismic velocity

identification of the mechanism of interdecadal variability in the north atlantic ocean the aim of this paper is to identify the physical mechanism of interdecadal variability in simulations of the north atlantic ocean circulation with the modular ocean model of the geophysical fluid dynamics laboratory to that end a hierarchy of increasingly complex model configurations is used the variability in the simplest case that of viscous purely thermally driven flows in a flat bottom ocean basin with a box shaped geometry is shown to be caused by an internal interdecadal mode the westward propagation of temperature anomalies and the phase difference between the anomalous zonal and meridional overturning that characterize the interdecadal mode are used as fingerprints of the physical mechanism of the variability in this way the variability can be followed toward a less viscous regime in which the effects of continental geometry and bottom topography are also included it is shown that although quantitative aspects of the variability like period and spatial pattern are changing the physical mechanism of the interdecadal variability in the more complex simulations can be attributed to the same processes as in the simplest model configuration

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

on the influence of dsow in a numerical model of the north atlantic general circulation abstract two numerical experiments regarding the north atlantic circulation are compared the two experiments are initialized with climatological temperatures and salinities and are integrated for ten years with different surface boundary conditions in the lceland sea one case climatological wind stress sst and surface salinity to force the model it reproduces the atlantic circulation found in similar studies a change in surface boundary values in the iceland sea in order to improve the denmark strait overflow water properties in the second case results in major changes in circulation and hydrography the meridional overturning more than doubles and horizontal gyres are intensified recirculation cells occur north and south of the gulf stream the gulf stream separates from the north american coast in a more realistic manner and its further course is in better agreement with observations than in the reference run the subsurface temperature distribution differs by several kelvin in the subpolar and

on the robustness of the interdecadal modes of the thermohaline circulation ocean models in box geometry forced by constant surface fluxes of density have been found to spontaneously generate interdecadal oscillations of the thermohaline circulation this paper analyzes the sensitivity of these oscillations to various physical effects including the presence of mesoscale turbulence various thermal surface boundary conditions and the presence of wind forcing or bottom topography the role of unstable long baroclinic waves is also reexamined in an attempt to understand the oscillation period in idealized geometry it is found that the low frequency variability of the thermohaline circulation under quasi constant surface fluxes is a robust feature of the large scale circulation it is not strongly affected by energetic mesoscale turbulence the oscillation period is relatively invariant with respect to varying resolution and momentum and tracer horizontal mixing coefficients although it loses some regularity as shorter and longer periods of variability emerge when the mesoscale activity increases in strength with smaller mixing coefficients the oscillations are also retained as the ocean model is coupled to an interactive atmospheric energy balance model the thermohaline modes are robust to a range of exchange coefficients that widens with the amplitude of the mean circulation the presence of an additional wind forced component generally weakens the oscillation and depending on the relative strength of thermodynamic and dynamic forcings the oscillation may be completely killed a simple interpretation is given highlighting the role of upward ekman pumping in damping density anomalies finally the interaction of these baroclinic modes with bottom topography depends strongly on the relative directions of the mean topographic features and the mean currents and baroclinic waves but usually results in a damping influence

response of circulation and heat transport in the north atlantic to changes in thermohaline forcing in northern latitudes a model study to avoid an explicit simulation of the overflows across the greenland scotland ridge many models of the large scale ocean circulation seek to include the net effect of the inflowing dense water masses by restoring temperature and salinity near the ridge to observed conditions in this paper the authors examine the effect of different datasets for the northern restoring condition in two versions eddy resolving and non eddy resolving of the model of the north and equatorial atlantic that has been developed in recent years as a community modeling effort for woce it is shown that the use of smoothed climatological fields of temperature and salinity south of the denmark strait leads to strong deficiencies in the simulation of the deep flow field in the basin a switch to actual hydrographic data from the denmark strait ignites a rapid dynamic response throughout the north atlantic affecting the transport and vertical structure of the deep western boundary current and by virtue of the jebar efffect the transport of the horizontal gyres meridional overturning and northward heat transport too weak in the cases with climatological boundary conditions increase to more realistic levels in the subtropical north atlantic the initial response to switches in the high latitude thermohaline forcing is mediated by fast waves along the westurn boundary leading to changes in the deep western boundary current in low latitudes after about two years in the non eddy resolving cast the initial timescale depends on the horizontal grid spacing of the model in the high resolution case the first signal reaches the equator in a few months the adjustment to a new dynamic quasi equilibrium involves kelvin waves along the equator and rossby wave in the interior and is attained in less than two decades throughout the north atlantic it is suggested that these fast dynamic adjustment processes could play an important role in possible fluctuations of the thermohaline circulation or transitions between different equilibrium states of the coupled ocean atmosphere system and may have determined the timescale of the observed climatic transitions before and during the last deglaciation