evidence of nonlinear dynamics in the eastward shift of the nao 1 hilmer and jung 2000 have identified an eastward shift in the sea level pressure slp pattern associated with interannual variability of the north atlantic oscillation nao that took place around 1980 we investigate the nature of the eastward shift using a primitive equation dry atmospheric model driven by diabatic forcing diagnosed from observations the model results reveal the nonlinear dependence of the spatial pattern of the nao on the nao index the pattern being shifted to the east west for high low nao index general agreement is found between the model and observations we suggest that the eastward shift noted by hilmer and jung 2000 is a consequence of the trend towards higher nao index during the last several decades of the 20th century

the link between the north atlantic oscillation and arctic sea ice export through fram strait abstract recently hilmer and jung have shown that the wintertime link between the north atlantic oscillation nao and the sea ice export through fram strait changed from zero correlation 1958 77 to about 0 7 1978 97 during the last four decades in the current study the authors focus on the question of how the two phenomena are linked in a long term context during wintertime december march this is done on a statistical basis using data from a century scale control integration of the coupled general circulation model echam4 opyc3 along with historical sea level pressure data for the period 1908 97 from the results of this study there is less indication that a significant link on interannual and decadal timescales between the nao and the sea ice export through fram strait is a characteristic property of the climate system at least under present day climate conditions this missing link can be explained by a vanishing net impact of the nao on sea ice thickness as well as sea ice drift near fram st

geodetic detection of active faults in s california a new analysis of velocities of geodetic mark ers straddling the san andreas fault system in southern california reveals that interseismic deformation is localized along a dozen sub parallel narrow belts of high shear strain rate that correlate well with active geologic fault segments andlocallywithconcentratedzonesofmicroseismicity high shearstrainrates 0 3 0 95strain year areobservednorth ward and southward of the san andreas fault s big bend whereas the big bend itself is characterized by a diuse low magnitudeshearstrainrate dilatationaldeformationisdif fuse and of relatively low magnitude 0 2 strain year with the highest contraction rates occurring in the ventura andlos angeles basins because no prior assumptions were made regarding the geology tectonics or seismicity of the region ouranalysisdemonstratesthatgeodeticobservations alone can be used to detect active fault segments

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

spatial pattern and zonal shift of the north atlantic oscillation part ii numerical experiments abstract in this part the spatial evolution of an initial dipole anomaly in a prescribed jet is at first investigated by numerically solving linear and nonlinear models without forcing in order to examine how the spatial pattern of a dipole anomaly depends on the meridional distribution of a specified jet it is shown that in a linear experiment an initial symmetric dipole anomaly in the meridional direction can evolve into a northeast southwest ne sw or northwest southeast nw se tilted dipole structure if the core of this jet is in higher latitudes the north or in lower latitudes the south this is in agreement with the result predicted by the linear rossby wave theory in slowly varying media the conclusion also holds for the nonlinear and unforced experiment north atlantic oscillation nao events are then reproduced in a fully nonlinear barotropic model with a wavemaker that mimics the atlantic storm track eddy activity in the absence of topography the spatial tilting of the eddy driven nao

viscoelastic coupling model of the san andreas fault along the big bend southern california the big bend segment of the san andreas fault is the 300 km long segment in southern california that strikes about n65 w roughly 25 counterclockwise from the local tangent to the small circle about the pacific north america pole of rotation the broad distribution of deformation of trilateration networks along this segment implies a locking depth of at least 25 km as interpreted by the conventional model of strain accumulation continuous slip on the fault below the locking depth at the rate of relative plate motion whereas the observed seismicity and laboratory data on fault strength suggest that the locking depth should be no greater than 10 to 15 km the discrepancy is explained by the viscoelastic coupling model which accounts for the viscoelastic response of the lower crust thus the broad distribution of deformation observed across the big bend segment can be largely associated with the san andreas fault itself not subsidiary faults distributed throughout the region the working group on california earthquake probabilities 1995 in using geodetic data to estimate the seismic risk in southern california has assumed that strain accumulated off the san andreas fault is released by earthquakes located off the san andreas fault thus they count the san andreas contribution to total seismic moment accumulation more than once leading to an overestimate of the seismicity for magnitude 6 and greater earthquakes in their type c zones

variable rates of late quaternary strike slip on the san jacinto fault zone southern california three strike slip displacements of strata with known approximate ages have been measured at two locations on the san jacinto fault zone minimum horizontal offset between 5 7 and 8 6 km in no more than 0 73 m y northeast of anza indicates 8 12 mm yr average slip rate since late pleistocene time two measures of more recent displacement are based on trenching studies of stratigraphic offsets on the coyote creek fault in western imperial valley horizontal slip of 1 7 m has been calculated for the youngest sediment of lake cahuilla since its deposition 275 510 yr b p the corresponding slip rate is 2 8 5 0 mm yr right lateral offset of 10 9 m measured on a buried stream channel older than 5060 yr b p but younger than 6820 yr b p yields average slip rates for the intermediate time periods 400 to 6000 yr b p of 1 2 mm yr the average rates of slip for these three time intervals suggest a relatively quiescent period for the san jacinto fault zone from about 4000 b c to about 1600 a d to the extent that long term variations in seismic activity of major strike slip faults elsewhere are known fluctuations in slip rate for the san jacinto fault would not appear to be abnormal if the san jacinto and adjacent segments of the san andreas fault alternately assume dominant roles in absorbing motion between the pacific and american plates perhaps even more recently than 400 yr ago the san andreas fault south of the transverse ranges expressed most of the motion but has since become relatively inactive

tropospheric rossby wave breaking and the nao nam objective analysis of several hundred thousand anticyclonic and cyclonic breaking rossby waves is performed for the northern hemisphere nh winters of 1958 2006 a winter climatology of both anticyclonic and cyclonic rossby wave breaking rwb frequency and size zonal extent is presented for the 350 k isentropic surface over the nh and the spatial distribution of rwb is shown to agree with theoretical ideas of rwb in shear flow composites of the two types of rwb reveal their characteristic sea level pressure anomalies upper and lower tropospheric velocity fields and forcing of the upper tropospheric zonal flow it is shown how these signatures project onto the centers of action and force the velocity patterns associated with the north atlantic oscillation nao and northern hemisphere annular mode nam previous studies have presented evidence that anticyclonic cyclonic breaking leads to the positive negative polarity of the nao and this relationship is confirmed for rwb over the midlatitudes centered near 50 n however an opposite and statistically significant relationship in which cyclonic rwb forces the positive nao and anticyclonic rwb forces the negative nao is shown over regions 20 to the north and south centered at 70 and 30 n respectively on a winter mean basis the frequency of rwb over objectively defined regions covering 12 of the area of the nh accounts for 95 of the nao index and 92 of the nam index a 6 hourly analysis of all the winters indicates that rwb over the objectively defined regions affects the nao nam without a time lag details of the objective wave breaking analysis method are provided in the appendix

comparison of geodetic and geologic data from the wasatch region utah and implications for the spectral character of earth deformation at periods of 10 to 10 million years the wasatch fault and adjacent fault zones provide an opportunity to compare present day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows ranging from the last millennium up to 10 myr the three easternmost gps sites of the basin and range geodetic network bargen at this latitude define a 130 km wide region spanning three major normal faults extending east west at a total rate of 2 7 0 4 mm yr with an average regional strain rate estimated to be 21 4 nstrain yr about twice the basin and range average on the wasatch fault the vertical component of the geologic displacement rate is 1 7 0 5 mm yr since 6 ka 0 6 mm yr since 130 ka and 0 5 0 7 mm yr since 10 ma however it appears likely that at the longest timescale rates slowed over time from 1 0 to 1 4 mm yr between 10 and 6 ma to 0 2 to 0 3 mm yr since 6 ma the cumulative vertical displacement record across all three faults also shows time variable strain release ranging from 2 to 4 mm yr since 10 ka to 1 mm yr averaged over the past 130 kyr conventional earthquake recurrence models reid type behavior would require an accordingly large variation in strain accumulation or loading rate on a 10 kyr timescale for which there appears to be no obvious geophysical explanation alternatively seismic strain release given a wide range of plausible constitutive behaviors for frictional sliding may be clustered on the 10 kyr timescale resulting in the high holocene rates with comparatively low uniform strain accumulation rates on the 100 kyr timescale wallace type behavior the latter alternative combined with observations at the million year timescale and the likelihood of a significant contribution of postseismic transients implies maxima of spectral amplitude in the velocity field at periods of 10 myr variations in tectonic loading 10 kyr clustered strain release and of 100 years postseismic transients if so measurements of strain accumulation and strain release may be strongly timescale dependent for any given fault system

late quaternary rate of slip along the san jacinto fault zone near anza southern california the anza section of the san jacinto fault southern california has not experienced a groundbreaking earthquake since at least 1918 and probably since before 1899 leading previous workers to designate this 20 km long fault segment as a seismic gap study of displaced pleistocene and holocene alluvial fan and fluvial deposits across the san jacinto fault near anza california dated using 14c and soil development age control indicates a minimum right lateral slip rate of 9 2 2 mm yr since 9 5 ka and a slip rate of 11 9 5 mm yr since 14 ka 12 9 5 mm yr since 17 ka and 13 10 6 mm yr since 50 ka these estimates agree with a previously determined 700 ka to present minimum slip rate of 10 2 mm yr based on an estimated average slip rate of 12 mm yr from the longer term slip rate estimates about 0 8 m of potential slip has accumulated if the 1918 earthquake broke the anza segment over 1 1 m of potential slip has accumulated if the last earthquake occurred prior to 1899 these data attest to the potential for an earthquake m6 5 for this section of the fault

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

the motion of crustal blocks driven by flow of the lower lithosphere and implications for slip rates of continental strike slip faults geodetic measurements in actively deforming areas of the continents reveal the pattern of deformation in the lithosphere if the dominant forces acting on crustal blocks are tractions at their bases then the long term motion of each block will be given by the average velocity of the underlying lithosphere slip rates between blocks estimated in this way from recent geodetic measurements across fault zones in the south island of new zealand and southern california are in good agreement with slip rates estimated geologically

an elusive blind thrust fault beneath metropolitan los angeles seismic reflection profiles petroleum wells and relocated earthquakes reveal the presence of an active blind thrust fault beneath metropolitan los angeles a segment of this fault likely caused the 1987 whittier narrows magnitude 6 0 earthquake mapped sizes of other fault segments suggest that the system is capable of much larger magnitude 6 5 to 7 and more destructive earthquakes

viscoelastic flow in the lower crust after the 1992 landers california earthquake space geodesy showed that broad scale postseismic deformation occurred after the 1992 landers earthquake three dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation whereas viscoelastic flow can explain the horizontal and near vertical displacements the viscosity of a weak about 10 km thick layer in the lower crust beneath the rupture zone that controls the rebound is about 10 18 pascal seconds the viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the basin and range province and it may be used for the analysis of earthquake hazard

present day kinematics of the eastern california shear zone from a geodetically constrained block model we use global positioning system gps data from 1993 2000 to determine horizontal velocities of 65 stations in eastern california and western nevada between 35 and 37 n we relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km the velocity of the sierra nevada block with respect to nevada is 11 1 0 3 mm yr with slip partitioned across the death valley 2 8 0 5 mm yr panamint valley 2 5 0 8 mm yr and airport lake owens valley 5 3 0 7 4 6 0 5 mm yr faults the western mojave block rotates at 2 1 0 8 my clockwise with 3 7 0 7 mm yr of left lateral motion across the western garlock fault we infer 11 2 mm yr of right lateral motion across the mojave region of the eastern california shear zone

coulomb stress accumulation along the san andreas fault system 1 stress accumulation rates along the primary segments of the san andreas fault system are computed using a three dimensional 3 d elastic half space model with realistic fault geometry the model is developed in the fourier domain by solving for the response of an elastic half space due to a point vector body force and analytically integrating the force from a locking depth to infinite depth this approach is then applied to the san andreas fault system using published slip rates along 18 major fault strands of the fault zone gps derived horizontal velocity measurements spanning the entire 1700 200 km region are then used to solve for apparent locking depth along each primary fault segment this simple model fits remarkably well 2 43 mm yr rms misfit although some discrepancies occur in the eastern california shear zone the model also predicts vertical uplift and subsidence rates that are in agreement with independent geologic and geodetic estimates in addition shear and normal stresses along the major fault strands are used to compute coulomb stress accumulation rate as a result we find earthquake recurrence intervals along the san andreas fault system to be inversely proportional to coulomb stress accumulation rate in agreement with typical coseismic stress drops of 1 10 mpa this 3 d deformation model can ultimately be extended to include both time dependent forcing and viscoelastic response

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

how rossby wave breaking over the pacific forces the north atlantic oscillation 1 anticyclonic rossby wave breaking rwb over a well defined limited area region of the east pacific leads to the positive polarity of the north atlantic oscillation nao by locally piling up wave activity where it may be advected downstream resulting in increased wave activity flux and anticyclonic rwb over the subtropical atlantic a composite time series shows that pacific rwb occurs several days prior to the atlantic rwb and the peak of the nao index following pacific rwb a channel of increased pseudomomentum flux extends from the pacific wave breaking region northeastward toward midlatitudes of eastern north america where pseudomomentum density accumulates for several days prior to moving eastward and leading to anticyclonic rwb over the atlantic

the relationship between the north atlantic jet and tropical convection over the indian and western pacific oceans abstractboreal winter jet variability over the north atlantic is investigated using 40 yr european centre for medium range weather forecasts re analysis era 40 data where the variability is defined by the first eof of the zonal wind on seven vertical levels the principal component time series of this eof is referred to as the jet index a pattern correlation analysis indicates that the jet index more accurately describes intraseasonal north atlantic zonal wind variability than does the north atlantic oscillation nao a series of composite calculations of the jet index based on events of intraseasonal convective precipitation over the tropical indian and western pacific oceans reveals the following statistically significant relationships 1 negative jet events lead enhanced indian ocean precipitation 2 positive jet events lag enhanced indian ocean precipitation 3 positive jet events lead enhanced western pacific ocean precipitation and 4 negative jet events lag enhanced western pacific ocean p

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

the dynamics of nao teleconnection pattern growth and decay this investigation performs both diagnostic analyses with ncep ncar re analysis data and forced barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the north atlantic oscillation nao teleconnection pattern the diagnostic calculations include projection and composite analyses of each term in the stream function tendency equation the results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks the positive nao phase is found to develop after anomalous wavetrain propagation across the north pacific to the east coast of north america this contrasts with the negative nao phase which appeared to develop in situ both high frequency period 10 days transient eddy fluxes drive the nao growth after the nao anomaly attains its maximum amplitude the high frequency transient eddy fluxes continue to drive the nao anomaly in a manner that is consistent with a positive feedback process the decay of the nao occurs through both the divergence term and the low frequency transient eddy fluxes the temporal and spatial properties of the divergence term are found to be consistent with ekman pumping these results illustrate many important differences between the nao and pacific north american pna teleconnection patterns perhaps most striking being that the nao life cycle is dominated by nonlinear processes whereas the pna evolution is primarily linear in addition the relation between the nao and the zonal index is discussed copyright 2003 royal meteorological society

characteristics of the recent eastward shift of interannual nao variability recent observational studies have shown that the centers of action of interannual variability of the north atlantic oscillation nao were located farther eastward during winters of the period 1978 97 compared to previous decades of the twentieth century in this study which focuses on the winter season december march new diagnostics characterizing this shift are presented further the importance of this shift for nao related interannual climate variability in the north atlantic region is discussed it is shown that an nao related eastward shift in variability can be found for a wide range of different parameters like the number of deep cyclones near surface air temperature and turbulent surface heat flux throughout the north atlantic region by using a near surface air temperature dataset that is homogenous with respect to the kind of observations used it is shown that the eastward shift is not an artifact of changes in observational practices that took place around the late 1970s finally an eof based monte carlo test is developed to quantify the probability of changes in the spatial structure of interannual nao variability for a relatively short 20 yr time series given multivariate white noise it is estimated that the likelihood for differences in the spatial structure of the nao between two independent 20 yr periods which are similar as measured by the angle and pattern correlation between two nao patterns to the observed differences to occur just by chance is about 18 from the above results it is argued that care has to be taken when conclusions about long term properties of nao related climate variability are being drawn from relatively short recent observational data e g 1978 97

the shift of the northern node of the nao and cyclonic rossby wave breaking abstractseveral studies have found an eastward shift in the northern node of the north atlantic oscillation nao during the winters of 1978 97 compared to 1958 77 this study focuses on the connection between this shift of the northern node of the nao and rossby wave breaking rwb for the period 1958 97 it is found that the region of frequent cyclonic rwb underwent a northeastward shift at high latitudes in the latter 20 yr period on a year to year basis the cyclonic rwb region moves along a southwest northeast sw ne directed axis both latitude and longitude of the winter maximum frequency of cyclonic rwb occurrence are positively correlated with the nao index to investigate the role of location of cyclonic rwb in influencing the nao pattern the geographical location of frequent cyclonic rwb is divided into two subdomains located along the sw ne axis to the south sw domain and east ne domain of greenland two composites are assembled as one cyclonic rwb occurrence is detected in one of the t

the continuum of northern hemisphere teleconnection patterns and a description of the nao shift with the use of self organizing maps abstract in this study the method of self organizing maps soms is used with ncep ncar reanalysis data to advance the continuum perspective of northern hemisphere teleconnection patterns and to shed light on the secular eastward shift of the north atlantic oscillation nao that began in the late 1970s a 20 pattern som analysis of daily wintertime northern hemisphere sea level pressure reveals a continuum of patterns that correspond closely with well known teleconnection patterns this analysis also reveals that interdecadal variability of the hemispheric sea level pressure field may be understood in terms of changes in the frequency distribution within the continuum of sea level pressure patterns described by the som based on the continuum perspective illustrated with the som the above secular shift of the nao may be understood as a change in dominance from westward displaced negative nao like patterns to eastward displaced positive nao like patterns though westward and eastward displaced nao

how regularly do earthquakes recur a synthetic seismicity model for the san andreas fault we have been attempting to improve estimates of long term earthquake recurrence probabilities along the san andreas fault by means of synthetic seismicity calculations the calculations are based on the concept of fault segmentation and incorporate the physics of static dislocation theory forecasts constructed from synthetic seismicity are robust in that they embody regional seismicity information over several units of magnitude they tie together in a physical manner a spectrum of fault segment features such as length strength characteristic magnitude mean repeat time and slip rate they can reasonably account for fault segment interactions and they are formulated from a catalog which can be extended as long as needed to be statistically significant we contend earthquake recurrence is more aperiodic than previously thought and as a result probabilities of major san andreas earthquakes should be revised downward

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

a new rossby wave breaking interpretation of the north atlantic oscillation this paper proposes the hypothesis that the low frequency variability of the north atlantic oscillation nao arises as a result of variations in the occurrence of upper level rossby wave breaking events over the north atlantic these events lead to synoptic situations similar to midlatitude blocking that are referred to as high latitude blocking episodes a positive nao is envisaged as being a description of periods in which these episodes are infrequent and can be considered as a basic unblocked situation a negative nao is a description of periods in which episodes occur frequently a similar but weaker relationship exists between wave breaking over the pacific and the west pacific pattern evidence is given to support this hypothesis by using a two dimensional potential vorticity based index to identify wave breaking at various latitudes this is applied to northern hemisphere winter data from the 40 yr ecmwf re analysis era 40 and the events identified are then related to the nao certain dynamical precursors are identified that appear to increase the likelihood of wave breaking these suggest mechanisms by which variability in the tropical pacific and in the stratosphere could affect the nao

dynamics of the pacific north american plate boundary in the western united states the vertically averaged deviatoric stress tensor field within the western united states was determined with topographic data geoid data recent global positioning system observations and strain rate magnitudes and styles from quaternary faults gravitational potential energy differences control the large fault normal compression on the california coast deformation in the basin and range is driven in part by gravitational potential energy differences but extension directions there are modified by plate interaction stresses the california shear zone has relatively low vertically averaged viscosity of about 1021 pascal seconds whereas the basin and range has a higher vertically averaged viscosity of 1022pascal seconds

tropospheric rossby wave breaking and the sam an objective analysis of tropospheric anticyclonic and cyclonic breaking rossby waves is performed for the southern hemisphere in austral summer december february of 1979 2009 the climatology of both anticyclonicandcyclonic rossbywavebreaking rwb frequencyispresented thefrequencyofanticyclonic rwb is highest in an extended region of theeastern hemisphere on the anticyclonic side of the jet whilethat of cyclonic rwb is highest on the cyclonic side of the jet a composite analysis of anticyclonic and cyclonic rwb shows howtheycontributetoapositiveandnegativesouthernannualmode sam index respectively thetimeseries of austral summer anticyclonic rwb occurrence has a trend that closely matches the trend in the sam index regions of rwb that are significantly correlated with the sam index are objectively determined even thoughseveralsuchregionsareidentified onlytworegions anticyclonicandcyclonic covering17 ofthearea of the hemisphere are required in a linear regression model of the sam index the anticyclonic rwb region is zonally extended at 458s and explains 78 of the variability of the summer mean sam index the cyclonic region is located at high latitudes somewhat decoupled from the jet in the longitudinal sector of the indian ocean on synoptic time scales transitions of the sam index respond to rwb without time lag ensocyclespresentaninterestingzonalasymmetrytothedistributionofsouthernhemisphericrwbinthe

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

the effect of loading rate on static friction and the rate of fault healing during the earthquake cycle the seismic cycle requires that faults strengthen heal between earthquakes and the rate of this healing process plays a key role in determining earthquake stress drop1 2 3 4 rupture characteristics5 6 and seismic scaling relations2 3 4 7 frictional healing as evidenced by increasing static friction during quasi stationary contact between two surfaces1 8 9 10 11 12 is considered the mechanism most likely to be responsible for fault strengthening2 3 13 14 previous studies however have shown a large discrepancy between laboratory and seismic field estimates of the healing rate2 3 4 14 15 in the laboratory rock friction changes by only a few per cent per order of magnitude change in slip rate whereas seismic stress drop increases by a factor of 2 to 5 per order of magnitude increase in earthquake recurrence interval but in such comparisons it is assumed that healing and static friction are independent of loading rate here i summarize laboratory measurements showing that static friction and healing vary with loading rate and time as expected from friction theory16 17 18 applying these results to seismic faulting and accounting for differences in laboratory seismic and tectonic slip rates i demonstrate that post seismic healing is expected to be retardedfor a period of several hundred days following an earthquake in agreement with recent findings from repeating earthquakes13 14 19 20

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

tectonic geomorphology of the san andreas fault zone in the southern indio hills coachella valley california geomorphic investigation of the san andreas fault zone in the indio hills indicates many tectonically produced landforms including beheaded streams right lateral deflected and offset streams sags shutter ridges pressure ridges and fault scarps near biskra palms an alluvial fan pediment complex has an apparent cumulative offset of about 0 7 km along the mission creek fault zone north branch san andreas fault many of the tectonic landforms as well as the fracture pattern that has developed during the pleistocene are explainable by simple shear or uplift associated with a small left bend in the main trace of the mission creek fault the ratio of vertical to horizontal displacement in the vicinity of the bend is about 0 04 exposed in pushawalla canyon 5 km northwest of the alluvial fan pediment complex are 1 a sequence of stream terraces 2 folded plio pleistocene fanglomerates and 3 an example of stream capture following a right lateral deflection or offset of several hundred metres a left step of the mission creek fault in pushawalla canyon is a probably cause of folds and sporadic uplift that produced the stream terraces possible cause of recent stream capture are 1 juxtaposition of pushawalla canyon with a relict canyon moving northwestward along the mission creek fault or 2 right lateral deflection or offset of pushawalla canyon along the fault with simultaneous headward erosion of a shorter steep stream flowing toward the coachella valley estimation of a slip rate and identification of paleoseismicity for the san andreas fault in the indio hills is difficult however degree of topographic dissection formation and preservation of desert pavement and relative soil profile development suggest that the age of the offset fan may be as old as 70 000 yr but that most likely it is on the order of 20 000 to 30 000 yr these age estimates for the offset fan indicate a minimum slip rate for the san andreas fault of 10 to 35 mm yr with about 23 to 35 mm yr the most likely the pattern of observed offset drainages is complex but suggests that during the past few thousand years creep events or moderately large earthquakes have periodically produced several metres of right lateral displacement

foraminiferal oxygen and carbon isotopes during the last 34 kyr off northern japan northwestern pacific abstract oxygen and carbon isotopes of foraminifera were analyzed in core pc4 water depth 1366 m off northern japan near the east side of the tsugaru strait 130 m depth between the open northwestern pacific ocean and the japan sea at present the site is at the confluence of the tsugaru warm current which flows eastwards out of the sea of japan through the tsugaru strait the subarctic oyashio current and the subtropic kuroshio current during the last glacial maximum lgm the oyashio current penetrated further to the south and outflow from the japan sea was restricted by glacio eustatic sea level lowering the isotopic values of the planktic foraminifer neogloboquadrina pachyderma sinistral and the benthic foraminifer uvigerina akitaensis reflect rapid millennial scale paleoceanographic changes between 34 and 6 ka hydrographic changes during deglaciation were related to events at high northern latitudes but holocene hydrographic changes were dominated by local effects such as the development of the outflow of the tsugaru warm current high values of planktic 18 o during the lgm reflect the southward advance of the oyashio current these values decreased by 0 3 from 19 4 to 18 9 ka then increased by 0 5 at 18 ka with highest values between 17 5 and 15 ka the 18 o oscillations between 19 4 and 15 ka may reflect millennial scale warm cold oscillations during heinrich event 1 planktic microfossil data indicate that cold oyashio waters flowed from the northwestern pacific into the japan sea via the tsugaru strait between 17 and 16 ka consistent with the occurrence of the highest planktic 18 o values in core pc4 planktic 18 o values rapidly decreased by 0 9 at 15 ka possibly reflecting the effects of both a rapid increase in fresh water flux and rising temperatures in the subarctic north pacific during the younger dryas cold event planktic 18 o values increased by 0 5 followed by a gradual decrease by 1 from the early to middle holocene reflecting a gradual increase in eastward outflow via the tsugaru strait with sea level rise both planktic and benthic foraminiferal 13 c values oscillated between 34 and 10 ka at relatively large amplitudes about 0 5 then remained relatively stable during the last 10 kyr several negative planktic and benthic 0 7 13 c excursions were present in sediment dated between the precipitation of secondary carbonates during episodic methane release possibly associated with methane release from continental margin sediments

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake

effect of latitudinal variations in low level baroclinicity on eddy life cycles and upper tropospheric wave breaking processes abstract an analysis of the potential vorticity gradient and the refractive index in quasigeostrophic qg flows on the sphere reveals that the absolute vorticity and the stretching parts have two contradictory effects on the horizontal shape of the baroclinic waves when the full variations of the coriolis parameter are taken into account in each term the absolute vorticity effect favors the anticyclonic southwest northeast tilt and anticyclonic wave breaking awb and is stronger in the upper troposphere in contrast the stretching effect promotes the cyclonic northwest southeast tilt and cyclonic wave breaking cwb and is more efficient at lower levels a positive eddy feedback acting on the latitudinal variations of the zonal winds is deduced because the absolute vorticity and the stretching effects are respectively more and less efficient with increasing latitude a more northward southward jet renders awb more less probable and cwb less more probable the jet is pushed or maintained mor

characteristics of the atlantic storm track eddy activity and its relation with the north atlantic oscillation abstract this study focuses on feedbacks of the high frequency eddy activity onto the quasi stationary circulation particularly with regard to the north atlantic oscillation nao the methodology consists of analyzing ncep ncar reanalysis data and sensitivity runs from a high resolution nonhydrostatic regional model consistent with recent studies results show that the jet displacement characteristic of the nao phenomenon depends strongly on the dynamics of the synoptic scale waves and the way they break positive and negative phases of the nao are closely related to anticyclonic and cyclonic wave breaking respectively indeed the high frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the nao index over the atlantic the peak of the momentum flux signal precedes that of the nao by a few days suggesting that wave breaking is triggering nao events two examples illustrate the significant impact of single storms in particular those occurring in the e