on the origin of the warm inflow to the nordic seas abstract warm and saline waters enter the nordic seas from the south as part of the warm to cold water transformation of the thermohaline circulation of the northern north atlantic one explanation for the origin of the nordic seas inflow is a shallow source hypothesis under which the inflow waters are a modification of upper ocean subtropical waters warm waters from the subtropical gyre are carried to the eastern north atlantic by the north atlantic current and branch northwards joined by poleward upper thermocline flow along the upper continental slope to provide the nordic seas inflow along this pathway the upper water column is progressively cooled and freshened by winter convection the subpolar mode water transformation process and this sets the inflow characteristics a deep source hypothesis provides an alternative explanation for the characteristics of the nordic seas inflow and the pathway delivering the waters to the inflow under this hypothesis inflow waters originate from the core of the mediterranean overflow waters in the gulf of cadiz carried northward at mid depth by the eastern boundary undercurrent in the subtropics continuing into the subpolar gyre along the eastern boundary and rising from depths near 1200m in the rockall trough to less than 600m to cross the wyville thomson ridge into the faroe shetland channel and thence to the nordic seas the deep source hypothesis focus is on lower thermocline source waters beneath the sill depth for the nordic seas inflow in contrast to the shallow source hypothesis focus of transformation of upper thermocline waters above the sill depth on the basis of regional water mass distributions geostrophic shear and direct current measurements we reject the deep source hypothesis in favor of the shallow source hypothesis rather than a flow of deep mediterranean overflow water along the eastern boundary rising from depth to feed the nordic seas the inflow is supplied directly by transformed north atlantic current waters from the same depth range as the inflow mediterranean overflow water is a constituent of the inflow but only through its contribution to defining the temperature salinity relationship of the interior of the subtropical gyre from which the north atlantic current draws its water rather than by direct northward advection of mediterranean outflow water via the eastern boundary undercurrent crossing from the subtropics into the subpolar domain instead the eastern boundary undercurrent wholly expels its transport of mediterranean overflow water into the eastern edge of the subtropical gyre creating the mid depth westward extending subtropical salinity plume for the lower thermocline isopycnal range of the core of the mediterranean overflow water measurements show that at the wyville thomson ridge the flow is southward and descending rather than northward and rising representing cold spillover from the faroese channels entraining warm upper ocean waters as the spillover plume descends and warms into the northern rockall trough no evidence is found in rockall trough northward of 54 n porcupine bank for direct advection of mediterranean overflow waters via an eastern boundary undercurrent extension and the very dilute mediterranean overflow waters in the trough reflect the interaction of the wyville thomson ridge plume descending into the trough from the north and lower thermocline waters delivered to the trough from the south

diagnosis of time of increased probability of strong earthquakes in different regions of the world algorithm cn abstract an algorithm for intermediate term earthquake prediction is suggested which allows diagnosis of the times of increased probability of strong earthquakes tips tips are declared for the time period of one year and an area with linear dimensions of a few hundred kilometers and can be extended in time the algorithm is based on the following traits of an earthquake flow level of seismic activity its temporal variation clustering of earthquakes in space and time their concentration in space and their long range interaction the algorithm is normalized so that it can be applied in various regions without readaptation tips diagnosed by the algorithm precede 80 of strong earthquakes and take on average 24 of the total time

localization of intermediate term earthquake prediction relative seismic quiescence within a region which has already been diagnosed as having entered a time of increased probability tip for the occurrence of a strong earthquake can be used to refine the locality in which the earthquake may be expected to occur a simple algorithm with parameters fitted from the data in northern california preceding the 1980 magnitude 7 0 earthquake offshore from eureka depicts relative quiescence within the region of a ttp the procedure was tested without readaptation of parameters on 17 other strong earthquake occurrences in north america japan and eurasia most of which were in regions for which a tip had been previously diagnosed the localization algorithm successfully outlined a region within which the subsequent earthquake occurred for 16 of these 17 strong earthquakes the area of prediction in each case was reduced significantly ranging between 7 and 25 of the total area covered by the tip

prediction of a subsequent large earthquake abstract many large earthquakes come in pairs separated by relatively small times and distances the subsequent earthquake may be a large aftershock of the first one or another main shock the prediction of a subsequent large earthquake is important for reducing the great hazard caused by destabilization of buildings lifelines and other constructions mountain slopes etc after the first large earthquake an algorithm for prediction of a subsequent large earthquake is based on analysis of the aftershock sequence following a first shock and of local seismic activity preceding it the algorithm was found by analysis of 21 large earthquakes in the california nevada region six of them were followed by subsequent large earthquakes in application to these earthquakes the algorithm made one error a failure to predict then this algorithm with all parameters fixed was tested retrospectively on independent data in different regions of the world it was applied to 98 large earthquakes not considered in its development 10 of them were followed by a subsequent large shock there were two failures to predict and four false alarms since 1989 20 advance predictions have been made including the 1991 rachi earthquake in georgia caucasus and three californian earthquakes loma prieta 1989 joshua tree 1992 and northridge 1994 among three mistakes two were false alarms and one was a failure to predict both the advance and retrospective predictions were made by the fixed algorithm previously developed and unambigously defined in publications the statistical significance of advance predictions exceeds 98

near surface transport pathways in the north atlantic ocean looking for throughput from the subtropical to the subpolar gyre abstractmotivated by discrepancies between eulerian transport estimates and the behavior of lagrangian surface drifters near surface transport pathways and processes in the north atlantic are studied using a combination of data altimetric surface heights statistical analysis of trajectories and dynamical systems techniques particular attention is paid to the issue of the subtropical to subpolar intergyre fluid exchange the velocity field used in this study is composed of a steady drifter derived background flow upon which a time dependent altimeter based perturbation is superimposed this analysis suggests that most of the fluid entering the subpolar gyre from the subtropical gyre within two years comes from a narrow region lying inshore of the gulf stream core whereas fluid on the offshore side of the gulf stream is largely prevented from doing so by the gulf stream core which acts as a strong transport barrier in agreement with past studies the transport barrier near the gulf stream core is r

where does dense water sink a subpolar gyre example it is proposed that a dominant component of the downwelling limb of the thermohaline circulation takes place in regions where convective mixing is found adjacent to steep topography a simple theoretical estimate of the overturning forced by such boundary convection is derived that depends only on the properties of the oceanic mixed layer along the boundary scaling estimates indicate that sinking forced by boundary convection is an order of magnitude greater than sinking in the open ocean resulting from large scale dynamics or baroclinic instability of deep convective sites recent hydrographic observations in the labrador sea are used to estimate the downwelling due to these different mechanisms and support the notion that boundary sinking dominates the theory compares well with the overturning rates diagnosed in a noneddy resolving general circulation model over a wide range of parameters as a direct consequence of these dynamics the high latitude hydrography and overturning circulation in the model are very sensitive to the presence of cyclonic rim currents lateral density advection by the rim currents in the subpolar gyre increases the stratification and limits the mixing near the boundaries thus reducing the maximum downwelling as a result most of the high latitude meridional heat transport is carried by the horizontal circulation instead of the overturning circulation such rim currents are found in different configurations of the model including 1 a continental slope and standard diffusion parameters and 2 zero horizontal diffusion and a flat bottom

error estimation and optimization of gravity surveys1 abstract gravity data are often acquired over long periods of time using different instruments and various survey techniques resulting in data sets of non uniform accuracy as station locations are inhomogeneously distributed gravity values are interpolated on to a regular grid to allow further processing such as computing horizontal or vertical gradients some interpolation techniques can estimate the interpolation error although estimation of the error due to interpolation is of importance it is more useful to estimate the maximum gravity anomaly that may have gone undetected by a survey this is equivalent to the determination of the maximum mass whose gravity anomaly will be undetected at any station location given the data accuracy at each station assuming that the maximum density contrast present in the survey area is known or can be reasonably assumed from a knowledge of the geology the proposed procedure is as follows at every grid node the maximum mass whose gravity anomaly does not disturb any of the surrounding observed gravity values by more than their accuracies is determined a finite vertical cylinder is used as the mass model in the computations the resulting map gives the maximum detection error and as such it is a worst case scenario moreover the map can be used to optimize future gravity surveys new stations should be located at or near map maxima the technique is applied to a set of gravity observations obtained from different surveys made over a period of more than 40 years in the abitibi greenstone belt in eastern canada

interpretation of seismic and potential field data from western new york state and lake ontario abstract lithoprobe and industry seismic profiles have furnished evidence of major zones of easterly dipping grenville deformed crust extending southwest from exposed grenville rocks north of lake ontario additional constraints on subsurface structure limited to the postulated clarendon linden fault system south of lake ontario are provided by five east west reflection lines recorded in 1976 spatial correlations between seismic structure and magnetic anomalies are described from both lake ontario and the newly reprocessed new york lines in the paleozoic to precambrian upper crust the new york seismic sections show 1 an easterly thickening wedge of subhorizontal paleozoic strata unconformably overlying a precambrian basement whose surface has an apparent regional easterly dip of 1 2 minor apparent normal offsets possibly on the order of tens of meters occur within the paleozoic section the generally poorly reflective unconformity may be locally characterized by topographic relief on the order of 100 m 2 apparent local displacement on the order of 90 m at the level of the black river group diminishes upward to little or no apparent offset of queenston shale 3 within the limited seismic sections there appears to be no evidence that the complete upper crustal section is vertically or subvertically offset 4 dipping structure in the paleozoic strata 15 to 35 resembles some underlying precambrian basement elements 5 the surface continuity of inferred faults constituting the clarendon linden system is not strongly supported by the seismic data beneath the paleozoic strata the seismic sections show both linear and arcuate reflector geometry with easterly apparent dips of 15 to 35 similar to the deep structures imaged on seismic lines from nearby lake ontario and on lithoprobe lines to the north the similarity supports an extension of easterly dipping central metasedimentary belt structures of the grenville orogen from southern ontario to beneath western new york state from a comparison of the magnetic and gravity fields with the new york seismic sections we suggest 1 the largely nonmagnetic paleozoic strata appear to contribute negligibly to magnetic anomalies seismically imaged fractures in the new york paleozoic strata appear to lie mainly west of a positive gravity anomaly the relationship between magnetic and gravity anomalies and the changes in the geometry of interpreted precambrian structures remains enigmatic 2 north to northeast trending curvilinear magnetic and gravity anomalies parallel but are not restricted to the principal trend of the postulated clarendon linden fault system paleozoic fractures of the clarendon linden system may partly overlie a southward extension of the composite arc belt boundary zone

premonitory patterns of seismicity months before a large earthquake five case histories in southern california this article explores the problem of short term earthquake prediction based on spatio temporal variations of seismicity previous approaches to this problem have used precursory seismicity patterns that precede large earthquakes with intermediate lead times of years examples include increases of earthquake correlation range and increases of seismic activity here we look for a renormalization of these patterns that would reduce the predictive lead time from years to months we demonstrate a combination of renormalized patterns that preceded within 1 7 months five large m 6 4 strike slip earthquakes in southeastern california since 1960 an algorithm for short term prediction is formulated the algorithm is self adapting to the level of seismicity it can be transferred without readaptation from earthquake to earthquake and from area to area exhaustive retrospective tests show that the algorithm is stable to variations of its adjustable elements this finding encourages further tests in other regions the final test as always should be advance prediction the suggested algorithm has a simple qualitative interpretation in terms of deformations around a soon to break fault the blocks surrounding that fault began to move as a whole a more general interpretation comes from the phenomenon of self similarity since our premonitory patterns retain their predictive power after renormalization to smaller spatial and temporal scales the suggested algorithm is designed to provide a short term approximation to an intermediate term prediction it remains unclear whether it could be used independently it seems worthwhile to explore similar renormalizations for other premonitory seismicity patterns

geometric incompatibility in a fault system abstract interdependence between geometry of a fault system its kinematics and seismicity is investigated quantitative measure is introduced for inconsistency between a fixed configuration of faults and the slip rates on each fault this measure named geometric incompatibility g depicts summarily the instability near the fault junctions their divergence or convergence unlocking or locking up and accumulation of stress and deformations accordingly the changes in g are connected with dynamics of seismicity apart from geometric incompatibility we consider deviation k from well known saint venant condition of kinematic compatibility this deviation depicts summarily unaccounted stress and strain accumulation in the region and or internal inconsistencies in a reconstruction of block and fault system its geometry and movements the estimates of g and k provide a useful tool for bringing together the data on different types of movement in a fault system an analog of stokes formula is found that allows determination of the total values of g and k in a region from the data on its boundary the phenomenon of geometric incompatibility implies that nucleation of strong earthquakes is to large extent controlled by processes near fault junctions the junctions that have been locked up may act as transient asperities and unlocked junctions may act as transient weakest links tentative estimates of k and g are made for each end of the big bend of the san andreas fault system in southern california recent strong earthquakes landers 1992 m 7 3 and northridge 1994 m 6 7 both reduced k but had opposite impact on g landers unlocked the area whereas northridge locked it up again

reverse tracing of short term earthquake precursors abstract we introduce a new approach to short term earthquake prediction named reverse tracing of precursors rtp since it considers precursors in reverse order of their appearance first we detect the candidates for the short term precursors in our case these are newly introduced chains of earthquakes reflecting the rise of an earthquake correlation range then we consider each chain one by one checking whether it was preceded by an intermediate term precursor in its vicinity if yes we regard this chain as a precursor in prediction it would start a short term alarm the chain indicates the narrow area of possibly complex shape where an intermediate term precursor should be looked for this makes possible to detect precursors undetectable by the direct analysis rtp can best be described on an example of its application we describe retrospective prediction of two prominent californian earthquakes landers 1992 m 7 6 and hector mine 1999 m 7 3 and suggest a hypothetical prediction algorithm this paper descripes the rtp methodology which has potentially important applications to many other data and to prediction of other critical phenomena besides earthquakes in particular it might vindicate some short term precursors previously rejected as giving too many false alarms validation of the algorithm per se requires its application in different regions with a substantial number of strong earthquakes first and positive retrospective results are obtained for 21 more strong earthquakes in california m 6 4 japan m 7 0 and the eastern mediterranean m 6 5 these results are described elsewhere the final validation requires as always prediction in advance for which this study sets up a base we have the first case of a precursory chain reported in advance of a subsequent strong earthquake tokachi oki japan 25 september 2003 m 8 1 possible mechanisms underlying rtp are outlined

gold bearing fault zones related to late archean orogenic folding of upper and middle crust in the abitibi granite greenstone belt ontario abstract this work investigates the structures of the abitibi granite greenstone belt ontario with a focus on regional scale folds and on regional scale auriferous fault zones the folds and the fault zones resulted from late archean orogenesis the analysis is based on studies of surface geology and on modelling of the gravity field amphibolite grade orthogneiss was involved in the regional folding that also deformed the overlying greenstones folding resulted in uplift of the orthogneiss that preserves the metamorphic mineral assemblage ferropargasite garnet biotite andesine quartz geothermobarometric calculations indicate recrystallization of a metatonalite sample under peak paleopressures of 7 0 1 2 to 7 9 1 1 kb providing evidence that folding involved crust to depths of at least 18 25 km the regional bouger anomaly map reveals previously unrecognized first order folds interpretation of the bouger anomaly map also confirms that granitic batholiths are hosted by anticlines a wavelet based inversion method was used to determine the locations orientations and continuations at depth of the maxima of density contrasts the maximum density contrasts correspond to steeply dipping geological contacts on the limbs of the open to tight regional scale folds regional scale fault zones only have prominent gravity signatures where they correspond to sheared rocks on the limbs of folds modelled gravity profiles were used to produce profiles that visualize the shapes of batholiths and greenstone bodies within the present day upper crust the granitic batholiths have tabular shapes which are locally folded with preserved main body thicknesses of 1 3 km the greenstones form keels corresponding to synclines some of which reach 5 6 km depth the results of this study confirm that the principal deformational response of the abitibi granite greenstone belt to late archean collisional tectonics was large half wavelength 10 40 km folding of the upper and middle crust our results and interpretations also strongly suggest the regional scale fault zones which are loci for orogenic gold deposits are fold related structures they represent quasi continuous lineaments of shearing and faulting on the limbs of regional folds and locally in the cores of detachment anticlines as shown in a previous paper

cooling spirals and recirculation in the subtropical gyre abstract the influence of cooling in a western boundary current on the recirculation of parcels in the subtropical gyre and their eventual transfer into the subpolar gyre is investigated it is shown that heat loss to the atmosphere and the resulting vertical convection of dense water in the gulf stream of a general circulation primitive equation model forces a counterclockwise spiral of the velocity vector with depth a cooling spiral parcels that pass through this region of cooling are forced to cross under the upper level trajectories from south to north in opposite sense to the beta spiral experienced in the interior of the subtropical gyre this crossing of trajectories is an important consequence of the cooling in the western boundary current as it influences both scale and structure of the subtropical gyre recirculation a simple expression is derived that relates the spatial scale of the recirculation to the cooling rate in the western boundary current and the wind forcing in the subtropical gyre

risk and return evaluating reverse tracing of precursors earthquake predictions summary in 2003 the reverse tracing of precursors rtp algorithm attracted the attention of seismologists and international news agencies when researchers claimed two successful predictions of large earthquakes these researchers had begun applying rtp to seismicity in japan california the eastern mediterranean and italy they have since applied it to seismicity in the northern pacific oregon and nevada rtp is a pattern recognition algorithm that uses earthquake catalogue data to declare alarms and these alarms indicate that rtp expects a moderate to large earthquake in the following months the spatial extent of alarms is highly variable and each alarm typically lasts 9 months although the algorithm may extend alarms in time and space we examined the record of alarms and outcomes since the prospective application of rtp began and in this paper we report on the performance of rtp to date to analyse these predictions we used a recently developed approach based on a gambling score and we used a simple reference model to estimate the prior probability of target earthquakes for each alarm formally we believe that rtp investigators did not rigorously specify the first two successful predictions in advance of the relevant earthquakes because this issue is contentious we consider analyses with and without these alarms when we included contentious alarms rtp predictions demonstrate statistically significant skill under a stricter interpretation the predictions are marginally unsuccessful

a lagrangian method to isolate the impacts of mixed layer subduction on the meridional overturning circulation in a numerical model large differences in the atlantic meridional overturning circulation amoc exhibited between the available ocean models pose problems as to how they can be interpreted for climate policy a novel lagrangian methodology has been developed for use with ocean models that enables a decomposition of the amoc according to its source waters of subduction from the mixed layer of different geographical regions the method is described here and used to decompose the amoc of the centre national de recherches meteorologiques cnrm ocean model which is approximately 4 5 sv 1 sv 106 m3 s 1 too weak at 26 n compared to observations contributions from mixed layer subduction to the peak amoc at 26 n in the model are dominated by the labrador sea which contributes 7 51 sv but contributions from the nordic seas the irminger sea and the rockall basin are also important these waters mostly originate where deep mixed layers border the topographic slopes of the subpolar gyre and nordic seas the too weak model amoc can be explained by weak model representations of the overflow and of irminger sea subduction these are offset by the large labrador sea component which is likely to be too strong as a result of unrealistically distributed and too deep mixed layers near the shelf

premonitory spreading of seismicity over the faults network in southern california precursor accord 1 we establish a connection between geometry of the faults network in a region and seismicity preceding the strong earthquakes in the intermediate term timescale of years previous studies of observed and computer simulated seismicity demonstrated that strong earthquakes are preceded in that timescale by the rise of seismic activity in a lower magnitude range here we explore a complementary phenomenon spreading of activity over the fault network this phenomenon is depicted by the seismicity pattern accord defined as a simultaneous rise of seismicity in a sufficiently large number of fault zones hence its name pattern accord has been found recently in synthetic seismicity generated by the colliding cascades cc model the present study demonstrates this pattern in observed seismicity of southern california we applied to observations a prediction algorithm based on the pattern accord scaled to the target magnitude 7 5 the pattern accord emerges within a few years before each of the three largest earthquakes in southern california kern county 1952 landers 1992 and hector mine 1999 and at no other time scaled to the target magnitude interval from 6 5 to 7 4 the pattern accord precedes six out of nine earthquakes the duration of alarms in both cases is about 30 of the time considered we repeated prediction with different combinations of adjustable numerical parameters of the algorithm summing up the success and error scores on an error diagram this numerical experiment shows that the prediction results are stable under moderate variations of adjustable parameters the final test would be as always an advance prediction the pattern accord has a simple physical explanation connected with equilibrium of the crustal blocks system under the impact of tectonic driving forces at the same time accord is a manifestation of a broader phenomenon premonitory increase of earthquakes correlation range the latter phenomenon was found for the first time in the cc model although it was hypothesized by one of the authors much earlier

interpretation of the gravity anomaly field in the noranda val d or region abitibi greenstone belt canadian shield gravity data from the noranda val d or region have been reprocessed the bouguer anomaly map the first vertical derivative map and an apparent density map have been used for geological interpretation of the gravity field in this region it is found that variations in the bouguer anomaly can be mainly explained by density structures located within the uppermost 5 km of the crust the vertical derivative map helps to better locate some geological contacts and the apparent density map allows the easy distinction between thin and thick batholiths generalized inversion was used to calculate density cross sections from the bouguer anomaly values and measured surface formation densities were used as constraints analysis of a detailed profile in the rouyn noranda area shows that steep north dipping reflectors observed in a seismic reflection survey are associated with a north dipping density structure

increased correlation range of seismicity before large events manifested by earthquake chains earthquake chains are clusters of moderate size earthquakes which extend over large distances and are formed by statistically rare pairs of events that are close in space and time neighbors earthquake chains are supposed to be precursors of large earthquakes with lead times of a few months here we substantiate this hypothesis by mass testing it using a random earthquake catalog also we study stability under variation of parameters and some properties of the chains we found two invariant parameters they characterize the spatial and energy scales of earthquake correlation both parameters of the chains show good correlation with the magnitudes of the earthquakes they precede earthquake chains are known as the first stage of the earthquake prediction algorithm reverse tracing of precursors rtp now tested in forward prediction a discussion of the complete rtp algorithm is outside the scope of this paper but the results presented here are important to substantiate the rtp approach

premonitory raise of the earthquakes correlation range lesser antilles abstract we apply to the observed seismicity of lesser antilles a short term earthquake precursor which has been recently found by analysis of synthetic seismicity the latter was generated by a lattice type colliding cascades model of interacting elements precursor named roc depicted premonitory increase of the earthquakes correlation range here this precursor is used as a second approximation to the intermediate term prediction as a first approximation we use the alarms determined in the previous publication by the algorithm seismic reversal sr it depicts premonitory reversal of territorial distribution of seismicity we consider combined performance of both algorithms in prediction of earthquakes with magnitude 5 5 or above four such earthquakes occurred in the territory considered during 1984 1998 the alarms occupy 0 5 of the total time space three alarms happened to be correct two alarms were false and one earthquake was missed by prediction the alarms are very stable to variation of adjustable parameters of prediction method in view of this stability such a prediction is unusually good even for retrospective analysis we present this prediction method as a hypothesis to be tested on advance prediction

constraints in 3d gravity inversion a three dimensional 3d inversion program is developed to interpret gravity data using a selection of constraints this selection includes minimum distance flatness smoothness and compactness constraints which can be combined using a lagrangian formulation a multigrid technique is also implemented to resolve separately large and short gravity wavelengths the subsurface in the survey area is divided into rectangular prismatic blocks and the problem is solved by calculating the model parameters i e the densities of each block weights are given to each block depending on depth a priori information on density and the density range allowed for the region under investigation the present computer code is tested on modelled data for a dipping dike and multiple bodies results combining different constraints and a weight depending on depth are shown for the dipping dike the advantages and behaviour of each method are compared in the 3d reconstruction recovery of geometry depth size and density distribution of the original model is dependent on the set of constraints used from experimentation the best combination of constraints for multiple bodies seems to be flatness and a minimum volume for the multiple bodies the inversion method is tested on real gravity data from the rouyn noranda quebec mining camp the 3d inversion model for the first 10 km is in agreement with the known major lithological contacts at the surface it enables the determination of the geometry of plutons and intrusive rocks at depth

geostrophic closure of the zonally averaged atlantic meridional overturning circulation it is typically assumed that the meridional density gradient in the north atlantic is well and positively correlated with the atlantic meridional overturning circulation amoc in numerical water hosing experiments for example imposing an anomalous freshwater flux in the northern hemisphere leads to a slowdown of the amoc however on planetary scale the first order dynamics are linked to the geostrophic balance relating the north south pressure gradient to the zonal circulation in this study these two approaches are reconciled at steady state and under geostrophic dynamics an analytical expression is derived to relate the zonal and meridional pressure gradient this solution is only valid where the meridional density gradient length scale is shorter than earth s curvature length scale that is north of 35 n this theoretical expression links the north south density gradient to the amoc and can be used as a closure for zonally averaged ocean models assumptions and shortcomings of the approach are presented implications of these results for paleoclimate problems such as amoc collapse and asymmetry in the meridional overturning circulation of the atlantic and of the pacific are discussed

a diagnostic study of the wind and buoyancy driven north atlantic circulation a two moving layer diagnostic model with a variable depth mixed layer on top is applied to the annual mean climatology of the north atlantic estimates of the annual mean mass flux from the mixed layer into the upper thermocline called mixed layer pumping and subsurface heating rates are obtained on the basin scale from hydrographic data alone no independent measures of wind stress or other surface forcings are required in addition it is shown that the nonlinear terms in the vorticity equation are critical to balance the subsurface heat flux in the gulf stream and over most of the subtropical gyre evidence is presented for the existence of interior southeastern northeastern and recirculation regimes in the north atlantic these regimes are distinguished by the behavior of the characteristic trajectories of the system and by whether the flow is a direct cell interfacial flux and vertical velocity have the same sign or indirect cell interfacial flux and vertical velocity have the opposite sign it is demonstrated here that one can make use of analytic approaches in the analysis of historical data sets to yield relatively simple solutions that give a direct link between theory and observations

phenomenon of local seismic reversal before strong earthquakes abstract we explore here the following hypothetical phenomenon the territorial distribution of low magnitude seismicity is reversed within several months prior to a strong earthquake in the area surrounding its source the diameter of this area is on the order of 100 km this phenomenon is investigated for the lesser antilles and southern california on that basis we suggest a hypothetical earthquake prediction algorithm to be tested by advance prediction retrospective application of the algorithm and the first three years of advance prediction in lesser antilles give encouraging results in comparison with well known intermediate term prediction algorithms m8 cn and mendocino scenario the sr algorithm gives smaller time space areas of the alarm it has a serious disadvantage however the catalogue should be complete for a longer period of time and for smaller magnitudes than are required in cn and m8

understanding the structure of the subtropical thermocline closing a gyre with a western boundary current imposes a constraint on its vertical structure that requires there to be no net vertical flux of potential vorticity through any closed pressure contour in steady state this constraint resembles the traditional similarity balance for the internal thermocline with additional terms representing friction in the western boundary current and convection in the mixed layer the terms in the integral constraint are diagnosed in a planetary geostrophic ocean model and are used to understand the coexistence of ventilated and internal thermoclines within the subtropical gyre

patterns of seismic release in the southern california region southern california experiences earthquakes on the san andreas system of vertical right lateral predominantly strike slip faults and on a second system of faults that includes thrusts oblique slip left lateral and other faults pattern recognition and cluster analysis are used to analyze the catalog of earthquakes with magnitudes 5 5 from 1915 to 1994 we use pattern recognition to find a suite of traits that would characterize each of these two systems and distinguish them from each other both pattern recognition and cluster analysis show that epochs of seismic release occur in which one or the other system is the predominant form of earthquake activity for the past 2 decades the second system has been the active one small changes in the direction of plate movements could account for this phenomenon seismic release on the san andreas system is preceded by episodes of activity in the great basin or in the gulf of california presumably these episodes would represent extension in the former region and spreading and slip on transform faults in the latter

hierarchical model of defect development and seismicity abstract the multiscale model of defect development kinetics is studied some critical effects have been found simulation produces phenomena which allow one to predict the time of appearance of large defects

colliding cascades model for earthquake prediction a wide set of premonitory seismicity patterns is reproduced on a numerical model of seismicity and their performance in the prediction of major model earthquakes is evaluated seismicity is generated by the colliding cascades model recently developed by the authors the model has a hierarchical structure it describes the interaction of two cascades a direct cascade of loading which is applied to the top largest element and transfers down the hierarchy and an inverse cascade of failures which goes up the hierarchy from the smaller to the larger elements these cascades collide and interact loading leads to failures while failures release and redistribute the loading three basic types of earthquake precursors are considered i the clustering of earthquakes in space and time ii the intensity of earthquake sequences and iii the correlation distance between earthquakes patterns of the first two types are used in intermediate term earthquake prediction algorithms patterns of the third type are found in the colliding cascades model although they were hypothesized previously they have not been validated by observations for each precursor we explore what is called an error diagram showing the total duration of alarms the rate of failures to predict and the rate of false alarms

transient triggering of near and distant earthquakes we demonstrate qualitatively that frictional instability theory provides a context for understanding how earthquakes may be triggered by transient loads associated with seismic waves from near and distance earthquakes we assume that earthquake triggering is a stick slip process and test two hypotheses about the effect of transients on the timing of instabilities using a simple spring slider model and a rate and state dependent friction constitutive law a critical triggering threshold is implicit in such a model formulation our first hypothesis is that transient loads lead to clock advances i e transients hasten the time of earthquakes that would have happened eventually due to constant background loading alone modeling results demonstrate that transient loads do lead to clock advances and that the triggered instabilities may occur after the transient has ceased i e triggering may be delayed these simple clock advance models predict complex relationships between the triggering delay the clock advance and the transient characteristics the triggering delay and the degree of clock advance both depend nonlinearly on when in the earthquake cycle the transient load is applied this implies that the stress required to bring about failure does not depend linearly on loading time even when the fault is loaded at a constant rate the timing of instability also depends nonlinearly on the transient loading rate faster rates more rapidly hastening instability this implies that higher frequency and or longer duration seismic waves should increase the amount of clock advance these modeling results and simple calculations suggest that near tens of kilometers small moderate earthquakes and remote thousands of kilometers earthquakes with magnitudes 2 to 3 units larger may be equally effective at triggering seismicity our second hypothesis is that some triggered seismicity represents earthquakes that would not have happened without the transient load i e accumulated strain energy would have been relieved via other mechanisms we test this using two new seismicity models that 1 are inherently unstable but slide at steady state conditions under the background load and 2 are conditionally stable such that instability occurs only for sufficiently large perturbations for the new seismicity models very small amplitude transients trigger instability relative to the clock advance models the unstable steady state models predict that the triggering delay depends inversely and nonlinearly on the transient amplitude as in the clock advance models we were unable to generate delayed triggering with conditionally stable models for both new seismicity models the potential for triggering is independent of when the transient load is applied or equivalently of the prestress unlike in the clock advance models in these models a critical triggering threshold appears to be inversely proportional to frequency further advancement of our understanding will require more sophisticated quantitative models and observations that distinguish between our qualitative yet distinctly different model predictions

global scale analysis of seismic activity prior to 2004 sumatra andaman mega earthquake abstract following our experience in intermediate term monitoring of seismicity before large earthquakes worldwide and in some regions we apply a similar approach to the analysis of seismicity on global scale several decades before the december 26 2004 sumatra andaman mega earthquake the earth lithosphere is being considered as a single whole representing the ultimate level of the complex earth s hierarchy the study brings up the following questions are there any anomalies of the global seismicity behaviour observed in advance of the mega earthquake do these anomalies correspond to the global scale seismic patterns similar to those detected on the regional scale before great major and strong events in other words does the earth lithosphere considered as a single whole show up an approach of the mega earthquake in the way typical for events on the smaller levels of hierarchy the results of our investigation favour the positive answer to the questions specifically we found that during the decade before the sumatra andaman mega earthquake the earth lithosphere reveals at least in intermediate term scale classical symptoms of instability which can be depicted by known precursory seismic patterns these are i transformation of frequency magnitude distribution ii change in the rate of seismic activity and iii depth redistribution of activity moreover changes of dependencies between magnitudes of different types are detected at the same time the observed global scale patterns of collective behaviour of seismicity may indicate the state of criticality of the earth lithosphere before the sumatra andaman mega earthquake

local overturn of active and non active seismic zones as a precursor of large earthquakes in the lesser antillean arc abstract the effect of short term activation of locally less active seismic zones simultaneously with relative quiescence of locally more active zones before strong earthquakes has been studied in the region of the lesser antillean arc this precursory pattern has been found earlier in southern california it takes place in the epicentral area several months before strong earthquakes on the basis of this effect a new preliminary prediction algorithm has been developed the algorithm determines regions of 100 km 100 km approximately in which the probability of the occurrence of strong earthquakes is increased for the period of 1 year in the present work the algorithm is improved a new version of the algorithm is applied retrospectively in the lesser antillean arc the results for the period 1984 june 1995 are as follows of the seven earthquakes with m 5 five have occurred in time space areas of increased probability tsip for strong earthquakes the time space volume of tsips is 8 of the total considered volume two tsips are false alarms the precursory pattern can be explained by the break up of asperities which is reflected in activation of less active areas corresponding to the asperities on the background of the larger scale quiescence

seismic reversal pattern for the 1999 chi chi taiwan mw 7 6 earthquake we in this study have calculated the standard normal deviate z value to investigate the variations in seismicity patterns in the taiwan region before and after the chi chi earthquake we have found that the areas with relatively high seismicity in the eastern taiwan became abnormally quiet before the chi chi earthquake while the area in the central taiwan with relatively low seismicity showed unusually active such a spatially changing pattern in seismicity strikingly demonstrates the phenomenon of seismic reversal and we here thus present a complete representative cycle of seismic reversal embedding in the changes of seismicity patterns before and after the chi chi earthquake

crustal models of the eastern superior province quebec derived from new gravity data new gravity data were collected in the nemiscau and la grande subprovinces of the superior province this 350 km gravity profile follows the matagami radisson road and extends northward the gravity transect along the 260 km long lithoprobe seismic line 48 across the northern abitibi and opatica subprovinces for the abitibi opatica segment the interpretation is consistent with the lithoprobe seismic profile it calls for crustal thickening near the boundary between the abitibi and opatica belts where the moho is 5 km deeper than in the abitibi subprovince and 8 km deeper than in the northern opatica subprovince the gravity model complements the seismic reflection data and provides information on the uppermost supracrustal sequences poorly imaged in the seismic profile most of the intrusive rocks in the opatica belt appear as thin 5 km bodies across the nemiscau and la grande subprovinces the bouguer anomalies are of short wavelengths and their sources lie in the upper crust the crustal thickness is constant from the northern opatica belt throughout the southern part of the nemiscau subprovince den sity measurements indicate that the upper crustal density is higher in the nemiscau and la grande subprovinces than in the abitibi and opatica belts there is some crustal thickening beneath the la grande subprovince and a gravity high at the northern end of the subprovince is related to the occurrence of mafic supracrustal sequences the gravity anomaly signature associated with the lateral density variation and field evidence indicate that the main tectonic bound aries dip to the north

earthquake aftereffects and triggered seismic phenomena the physical basis for delayed aftereffects of large crustal earthquakes is analyzed these effects apparently range in scale from typical aftershocks near the source region of a prior earthquake to the triggering of groundwater and deformation related anomalies possibly including other large earthquakes at locations as much as a few hundred kilometers from the source of a great earthquake observational reports of such aftereffects are reviewed and possible mechanisms for their occurrence are discussed

seismicity of oceanic and continental rifts a geodynamic approach abstract two major kinds of divergent structures oceanic and intracontinental rifts were compared in principal seismic and tectonic characteristics first the role of main components of the mid oceanic ridges mor was estimated for the whole earth we considered two levels of the mor segmentation the first order structures are the segments of mor between triple junctions and the second order structures are a transform faults and rift parts of mor the seismic catalogues neic and cmt were used to assess the seismic moment release the seismic moment release was calculated another way using the global plate tectonic model nuvel 1 and brune s formulae comparison of these two values shows that the seismic coupling coefficient varies from 1 to 10 for most of mor and is always higher for transform faults most of the deformation therefore is aseismic slip most seismicity of mor is confined to transform faults the energy contribution of transform faults is one to two orders magnitude higher than that of the rift and increases with the spreading rate there is a strong correlation between the seismic moment release of strike slip faults and their total lengths the correlation shows that the seismic moment release depends on the total transform area and confirms the simple thermal model of transform seismicity that was given by burr and solomon the seismic moment release and the spreading rate have opposite patterns for the rifts there is an inverse correlation between the seismic moment of normal faults and spreading velocity while it seems for transforms that these parameters are independent finally these results show that the seismicity of transforms and rifts depends first of all on the thermal structure of oceanic lithosphere in the case of continental rifts one can distinguish in the degree of seismic activity depending on the stage of rifting hence analysis of the continental seismicity requires the consideration of factors of a geological evolution that play practically no role in the case of oceanic lithosphere the comparison of geological and seismic data for the east african region has allowed us to outline the regular changes of the seismic regime during development of the rift zone from the stage of incipient rift to mature oceanic rift in the evolutionary series intracontinental incipient rift intracontinental mature rift intercontinental rift oceanic slow spreading rift oceanic fast spreading rift there is a gradual decrease of the role of rifts sensu stricto as tension structures and increase of the role of strike slip faults epicenters concentrate along major faults as well the level of seismic energy becomes lower although the rate of deformation increases

short term earthquake prediction by reverse analysis of lithosphere dynamics abstract short term earthquake prediction months in advance is an elusive goal of earth sciences of great importance for fundamental science and for disaster preparedness here we describe a methodology for short term prediction named rtp reverse tracing of precursors using this methodology the san simeon earthquake in central california magnitude 6 5 dec 22 2003 and the tokachi oki earthquake in northern japan magnitude 8 1 sept 25 2003 were predicted 6 and 7 months in advance respectively the physical basis of rtp can be summed up as follows an earthquake is generated by two interacting processes in a fault network an accumulation of energy that the earthquake will release and a rise of instability triggering this release energy is carried by the stress field instability is carried by the difference between the stress and strength fields both processes can be detected and characterized by premonitory patterns of seismicity or other relevant fields here we consider an ensemble of premonitory seismicity patterns rtp methodology is able to reconstruct these patterns by tracing their sequence backwards in time the principles of rtp are not specific to earthquakes and may be applicable to critical transitions in a wide class of hierarchical non linear systems

a perspective on the future of physical oceanography the ocean flows because it is forced by winds tides and exchanges of heat and freshwater with the overlying atmosphere and cryosphere to achieve a state where the defining properties of the ocean such as its energy and momentum do not continuously increase some form of dissipation or damping is required to balance the forcing the ocean circulation is thought to be forced primarily at the large scales characteristic of ocean basins yet to be damped at much smaller scales down to those of centimetre sized turbulence for decades physical oceanographers have sought to comprehend the fundamentals of this fractal puzzle how the ocean circulation is driven how it is damped and how ocean dynamics connects the very different scales of forcing and dissipation while in the last two decades significant advances have taken place on all these three fronts the thrust of progress has been in understanding the driving mechanisms of ocean circulation and the ocean s ensuing dynamical response with issues surrounding dissipation receiving comparatively little attention this choice of research priorities stems not only from logistical and technological difficulties in observing and modelling the physical processes responsible for damping the circulation but also from the untested assumption that the evolution of the ocean s state over time scales of concern to humankind is largely independent of dissipative processes in this article i illustrate some of the key advances in our understanding of ocean circulation that have been achieved in the last 20 years and based on a range of evidence contend that the field will soon reach a stage in which uncertainties surrounding the arrest of ocean circulation will pose the main challenge to further progress it is argued that the role of the circulation in the coupled climate system will stand as a further focal point of major advances in understanding within the next two decades supported by the drive of physical oceanography towards a more operational enterprise by contextual factors the basic elements that a strategy for the future must have to foster progress in these two areas are discussed with an overarching emphasis on the promotion of curiosity driven fundamental research against opposing external pressures and on the importance of upholding fundamental research as the apex of education in the field

scoring annual earthquake predictions in china abstract the annual consultation meeting on earthquake tendency in china is held by the china earthquake administration cea in order to provide one year earthquake predictions over most china in these predictions regions of concern are denoted together with the corresponding magnitude range of the largest earthquake expected during the next year evaluating the performance of these earthquake predictions is rather difficult especially for regions that are of no concern because they are made on arbitrary regions with flexible magnitude ranges in the present study the gambling score is used to evaluate the performance of these earthquake predictions based on a reference model this scoring method rewards successful predictions and penalizes failures according to the risk probability of being failure that the predictors have taken using the poisson model which is spatially inhomogeneous and temporally stationary with the gutenberg richter law for earthquake magnitudes as the reference model we evaluate the cea predictions based on 1 a partial score for evaluating whether issuing the alarmed regions is based on information that differs from the reference model knowledge of average seismicity level and 2 a complete score that evaluates whether the overall performance of the prediction is better than the reference model the predictions made by the annual consultation meetings on earthquake tendency from 1990 to 2003 are found to include significant precursory information but the overall performance is close to that of the reference model

testing earthquake prediction algorithms statistically significant advance prediction of the largest earthquakes in the circum pacific 1992 1997 abstract algorithms m8 and msc i e the mendocino scenario were used in a real time intermediate term research prediction of the strongest earthquakes in the circum pacific seismic belt predictions are made by m8 first then the areas of alarm are reduced by msc at the cost that some earthquakes are missed in the second approximation of prediction in 1992 1997 five earthquakes of magnitude 8 and above occurred in the test area all of them were predicted by m8 and msc identified correctly the locations of four of them the space time volume of the alarms is 36 and 18 correspondingly when estimated with a normalized product measure of empirical distribution of epicenters and uniform time the statistical significance of the achieved results is beyond 99 both for m8 and msc for magnitude 7 5 10 out of 19 earthquakes were predicted by m8 in 40 and five were predicted by m8 msc in 13 of the total volume considered this implies a significance level of 81 for m8 and 92 for m8 msc the lower significance levels might result from a global change in seismic regime in 1993 1996 when the rate of the largest events has doubled and all of them become exclusively normal or reversed faults the predictions are fully reproducible the algorithms m8 and msc in complete formal definitions were published before we started our experiment keilis borok v i kossobokov v g 1990 premonitory activation of seismic flow algorithm m8 phys earth and planet inter 61 73 83 kossobokov v g keilis borok v i smith s w 1990 localization of intermediate term earthquake prediction j geophys res 95 19763 19772 healy j h kossobokov v g dewey j w 1992 a test to evaluate the earthquake prediction algorithm m8 u s geol surv ofr 92 401 m8 is available from the iaspei software library healy j h keilis borok v i lee w h k eds 1997 algorithms for earthquake statistics and prediction vol 6 iaspei software library

the eastern subtropical pacific origin of the equatorial cold bias in climate models a lagrangian perspective abstractglobal climate models frequently exhibit cold biases in tropical sea surface temperature sst in the central and eastern equatorial pacific here lagrangian particle back trajectories are used to investigate the source regions of the water that upwells along the equator in the ipsl climate model to test and confirm the hypothesis that the sst biases are caused by remote biases advected in from the extratropics and to identify the dominant source regions water in the model is found to be sourced primarily from localized regions along the western and eastern flanks of the subtropical gyres however while the model sst bias is especially large in the northwestern subtropical pacific about 5 c it is found that the eastern subtropics contribute to the equatorial bias the most this is due to two distinct subsurface pathways connecting these regions to the equator the first pathway originating in the northwestern subtropical pacific has relatively long advection time scales close to or exceed

crustal velocity models for the archean abitibi greenstone belt from seismic refraction data we present velocity models for two seismic wide angle refraction profiles across the archean abitibi greenstone belt and the pontiac subprovince the seismic profiles are 210 and 220 km long traveltime inversion and amplitude forward modelling were used to obtain two dimensional velocity structure and interface geometry the main features of the velocity models include 1 three crustal layers 2 variable velocities 5 6 6 4 km s in the upper crust 0 12 km with the higher velocities generally associated with mafic metavolcanics and the lower velocities with metasediments and granitic plutons 3 a relatively uniform middle crust 12 30 km with velocities ranging from 6 4 to 6 6 km s 4 a velocity increase of 0 3 km s across the middle crust lower crust boundary 5 a lower crust 30 40 km with velocities increasing from 6 9 km s at the top to 7 3 km s at the base 6 an average upper mantle velocity of 8 15 km s 7 depth to moho of about 40 km in the north central abitibi belt decreasi