release fault a variety of cross fault in linked extensional fault systems in the sergipe alagoas basin ne brazil abstract two types of cross faults are herein recognized transfer faults and the newly termed release faults transfer faults form where cross faults connect distinct normal faults and horizontal displacements predominate over vertical ones in contrast release faults form where cross faults associated with individual normal faults die out within the hangingwall before connecting to other normal faults and have predominantly vertical displacements release faults are geometrically required to accommodate variable displacements along the strike of a normal fault thus they form to release the bending stresses in the hangingwall and do not cut normal fault planes nor detachment surfaces at depth release faults have maximum throws adjacent to normal faults and may be nearly perpendicular or obliquely oriented to the strike of the latter such geometry appears not to depend upon pre existing weaknesses but such variable orientation to normal faults is an inherent property of release faults release faults commonly appear as simple normal faults in seismic sections without implying extension along the strike of rift and basins three dimensional strain deformation occurs in the hangingwall only between the terminations of an individual normal fault but regionally release faulting is associated with plane strain deformation in linked extensional fault systems

evaluating sand and clay models do rheological differences matter abstract dry sand and wet clay are the most frequently used materials for physical modeling of brittle deformation we present a series of experiments that shows when the two materials can be used interchangeably document the differences in deformation patterns and discuss how best to evaluate and apply results of physical models extension and shortening produce similar large scale deformation patterns in dry sand and wet clay models indicating that the two materials can be used interchangeably for analysis of gross deformation geometries there are subtle deformation features that are significantly different 1 fault propagation and fault linkage 2 fault width spacing and displacement 3 extent of deformation zone and 4 amount of folding vs faulting these differences are primarily due to the lower cohesion of sand and its larger grain size if these features are of interest the best practice would be to repeat the experiments with more than one material to ensure that rheological differences are not biasing results dry sand and wet clay produce very different results in inversion models almost all faults are reactivated in wet clay and few if any are significantly reactivated in sand models fault reactivation is attributed to high fluid pressure along the fault zone in the wet clay a situation that may be analogous to many rocks sand inversion models may be best applied to areas where most faults experience little to no reactivation while clay models best fit areas where most pre existing normal faults are reactivated

fault trends on the seaward slope of the aleutian trench implications for a laterally changing stress field tied to a westward increase in oblique convergence 1 normal faults along the seaward trench slope sts commonly strike parallel to the trench in response to bending of the oceanic plate into the subduction zone this is not the circumstance for the aleutian trench where the direction of convergence gradually changes westward from normal to transform motion gloria side scan sonar images document that the aleutian sts is dominated by faults striking oblique to the trench west of 179 e and east of 172 w these images also show a pattern of east west trending seafloor faults that are aligned parallel to the spreading fabric defined by magnetic anomalies the stress strain field along the sts is divided into two domains west and east respectively of 179 e over the western domain sts faults and nodal planes of earthquakes are oriented oblique 9 46 to the trench axis and 69 90 to the magnetic fabric west of 179 e sts fault strikes change by 36 from the e w trend of sts where the trench parallel slip gets larger than its orthogonal component of convergence this rotation indicates that horizontal stresses along the western domain of the sts are deflected by the increasing obliquity in convergence an analytical model supports the idea that strikes of sts faults result from a superposition of stresses associated with the dextral shear couple of the oblique convergence and stresses caused by plate bending for the eastern domain most nodal planes of earthquakes strike parallel to the outer rise indicating bending as the prevailing mechanism causing normal faulting east of 172 w sts faults strike parallel to the magnetic fabric but oblique 10 26 to the axis of the trench on the basis of a coulomb failure criterion the trench oblique strikes probably result from reactivation of crustal faults generated by spreading

influence of rift obliquity on fault population systematics results of experimental clay models abstract we use clay models to simulate how fault population systematics vary as a function of rift obliquity rift obliquity is related to the acute angle between the rift trend and the displacement direction so that the value of is inverse to the degree of obliquity the range of azimuths in a fault population increases as rift obliquity increases i e as decreases the length of the longest faults the sum of fault lengths and the width of the deformed zone all increase as rift obliquity decreases i e as increases the majority of faults in our models are segmented and have highly tortuous traces tortuosity is maximum when 30 as segments of widely varying azimuth link during fault growth significant changes occur in the fault patterns between 30 and 45 at 30 two fault populations of equal importance develop in the center of the rift zone one approximately rift parallel and the other displacement normal between 30 and 45 the number of faults more than doubles and between 45 and 60 summed fault length more than doubles fault patterns for all models are fractal with fractal dimensions that increase with increasing and that are comparable to those found in the field fault populations are not multi fractal because the cumulative frequency distributions of fault lengths do not generally follow a power law relationship an exponential distribution best describes the data for whole faults with the characteristic length increasing with increasing segment lengths also follow an exponential distribution with characteristic length varying very little with the fault patterns in our models resemble the spatial pattern of brittle deformation observed at oblique mid ocean ridge segments and are similar in geometry to those in oblique continental rift basins at the rift margins tensional stresses are modulated and reoriented by a secondary stress field related to a change in boundary conditions resulting in the formation of two distinct sub populations of faults during oblique rifting

normal fault development during two phases of non coaxial extension an experimental study we use scaled experimental analog models to study the effect of a pre existing fault fabric on fault development during extension in our models a homogeneous layer of wet clay undergoes two noncoaxial phases of extension whose directions differ by up to 45 the normal faults that develop during the first phase create a pronounced fault fabric that influences normal fault development during the second phase in all models the pre existing faults are reactivated during the second phase of extension their sense of slip depends on the angle between the first and second phase extension directions specifically the component of dip slip relative to strike slip decreases as the angle between the first and second phase extension directions increases new normal faults also form during the second phase of extension in all models the number of new fault segments increases as the angle between the first and second phase extension directions increases the orientations of the new normal fault segments are both orthogonal and oblique to the second phase extension direction indicating that both the secondphase extension direction and the pre existing fault fabric control the orientation of new fault segments some of the new normal faults cut and offset the pre existing faults whereas others terminate against them producing complex fault patterns and interactions the modeling results explain fault interactions observed in the jeanne d arc rift basin of offshore newfoundland canada and the reactivation of abyssal hill normal faults at outer highs near subduction zones

tropical sea surface temperatures for the past four centuries reconstructed from coral archives most annually resolved climate reconstructions of the common era are based on terrestrial data making it a challenge to independently assess how recent climate changes have affected the oceans here as part of the past global changes ocean2k project we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives validation exercises suggest that our reconstructions are interpretable for much of the past 400 years depending on the availability of paleoclimate data within and the reconstruction validation statistics for each target region analysis of the trends in the data suggests that the indian western pacific and western atlantic ocean regions were cooling until modern warming began around the 1830s the early 1800s were an exceptionally cool period in the indo pacific region likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century decadal scale variability is a quasi persistent feature of all basins twentieth century warming associated with greenhouse gas emissions is apparent in the indian west pacific and western atlantic oceans but we find no evidence that either natural or anthropogenic forcings have altered el nino southern oscillation related variance in tropical sea surface temperatures our marine based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change

the evolution of illite to muscovite an example of the behaviour of isotopes in low grade metamorphic terrains abstract a review of the possibilities and limitations of the use of radiogenic isotopes in low grade terrains i e in the temperature range below the blocking temperature of potassic white mica is discussed using a background of a data base of over 500 isotope analyses on more than 250 illitic muscovitic samples published in various papers special stress is laid on the main problems 1 distinction between detrital and neoformed minerals 2 the slow evolution of minerals without pronounced breaks and 3 retention problems of radiogenic daughter products a brief description of low grade metamorphism is given and criteria enabling a subdivision into low to very low grade metamorphism are discussed comprising illite crystallinity mineralogy fluid inclusions and coal rank measurements the useful type of lithologies for this kind of work ranges from shales slates through volcaniclastic tuffs with high primary glass contents and limestone dolomites marbles to mylonites it can be concluded that carefully selected illitic muscovites yield geologically meaningful ages provided that more than one isotopic method is applied

coral microatolls from the central pacific record late holocene el nino microatolls are discoid corals that have grown laterally because vertical growth is constrained by exposure at lowest tides we demonstrate that a modern reef flat porites microatoll from christmas kiritimati island preserves an oxygen isotope record of substantial sea surface temperature variations related to el nino southern oscillation enso we also show that a late holocene fossil microatoll from the centre of the island contains interannual oxygen isotope variations over an approximate 20 year period three pronounced negative isotope anomalies attributed to warm el nino events are superimposed on an annual cycle el nino events similar to those seen in recent decades appear to have been a feature of mid pacific climate in the late holocene analysis of further microatolls offers a source of pre instrumental el nino tropical climate data it may be possible to extend the nino c proxy to indicate intensity and frequency of enso over the past three millennia

reconstruction of historical sea surface temperatures using empirical orthogonal functions abstract studies of climate variability often rely on high quality sea surface temperature sst anomalies although the high resolution national centers for environmental prediction formerly the national meteorological center optimum interpolation oi sst analysis is satisfactory for these studies the oi resolution cannot be maintained before november 1931 due to the lack of satellite data longer periods of ssts have come from traditional analyses of in situ ship and buoy sst observations alone a new interpolation method is developed using spatial patterns from empirical orthogonal functions e0fs that is a principal component analysis to improve analyses of sst anomalies from 1950 to 1981 the method uses the more accurate oi analyses from 1982 to 1993 to produce the spatial eofs the dominant eof modes which correspond to the largest variance are used as basis functions and are fit in a least squares sense to the in situ data to determine the time dependence of each mode a complete field

mid late holocene el nino variability in the equatorial pacific from coral microatolls 1 oxygen isotope ratios in porites microatolls from christmas island in the central pacific provide high resolution proxy records of el nino southern oscillation enso variability since 3 8 thousand years ago ka compared with modern microatolls reconstructions from fossil microatolls imply that interannual variations in enso sea surface temperature and precipitation were less intense 3 8 2 8 ka but more pronounced at 1 7 ka amplification of enso at 2 ka is consistent with precessional changes in insolation seasonality but exceeds model predictions and may reflect stronger rainfall teleconnections through enhanced interaction between the southern oscillation and the pacific intertropical convergence zone

pacific sea surface temperature field reconstruction from coral δ18o data using reduced space objective analysis 1 a systematic methodology for the reconstruction of climate fields from sparse observational networks of proxy data employing the technique of reduced space objective analysis is applied to the reconstruction of gridded pacific ocean basin sea surface temperature sst from coral stable isotope 18o data for the period 1607 1990 in this approach we seek to reconstruct only the leading modes of large scale variability which are both observed in the modern climate and resolved in the proxy data we find that the coral data verifiably resolve two spatial patterns of sst variability the first and dominant pattern is that of the el nino southern oscillation enso a second pattern reflects uniform changes over most of the pacific basin calibration and verification tests for 1856 1990 show that root mean square variance is small 0 5 c rms and reconstruction errors are large 0 6 c rms limiting interpretation to the tropical region periods of enhanced enso activity similar to those observed in the past two decades are evident in the reconstruction for the early nineteenth century the changing frequency of enso warm phase events appears to coincide with warming of the pacific mean state inferred from similar reconstruction efforts using tree ring indicators over the last two centuries

monsoon tropical ocean interaction in a network of coral records spanning the 20th century abstract the 20th century evolution of basin wide gradients in surface ocean properties provides one essential test for recent models of the interaction between the asian monsoon and the tropical ocean because various feedback mechanisms should result in characteristic regional patterns of variability although the instrumental record of climate variability in the tropics is essentially limited to the last few decades the stable isotopic composition of living corals provides an effective means for extending the instrumental observations here we present two coral isotopic records from the indonesian maritime continent and we use these records with other previously published records to describe i the relationship between western pacific and central pacific climate variability over the past century with special emphasis on the biennial band and ii the strength of the west east indian ocean dipole we find that the amplitude of the biennial cycle in the pacific did not vary inversely with the strength of enso el nino southern oscillation as might be expected from some models of monsoonal feedback on the central pacific instead the biennial variability was modulated on decadal timescales throughout much of the pacific we also show that the zonal oxygen isotopic gradient in the indian ocean coral records was significantly correlated with central pacific sea surface temperature on a variety of timescales thus it is likely that this coral dipole was a product of strong enso like teleconnections over the indian ocean as opposed to being the result of unique indian ocean or monsoonal dynamics

strain migration during multiphase extension observations from the northern north sea many rifts develop through multiphase extension it can be difficult however to determine how strain is distributed during reactivation because structural and stratigraphic evidence associated with earlier rifting is often deeply buried using 2 d and 3 d seismic reflection and borehole data from the northern north sea we examine the style magnitude and timing of reactivation of a preexisting permian triassic rift phase 1 fault array during a subsequent period of middle jurassic to early cretaceous rift phase 2 extension we show that rift phase 2 led to the formation of new n s striking faults close to the north viking graben but did not initially reactivate preexisting rift phase 1 structures on the horda platform we suggest that at the beginning of rift phase 2 strain was focused in a zone of thermally weakened lithosphere associated with the middle jurassic north sea thermal dome rather than reactivating extant faults diachronous reactivation of the permian triassic fault network eventually occurred with those faults located closer to the middle jurassic to early cretaceous rift axis reactivating earlier than those toward the eastern margin this diachroneity may have been related to flexural down bending as strain became focused within the north viking graben and or the shifting of the locus of rifting from the north sea to the proto north atlantic our study shows that the geometry and evolution of multiphase rifts is not only controlled by the orientation of the underlying fault network but also by the thermal and rheological evolution of the lithosphere and variations in the regional stress field

interaction between the enso and the asian monsoon in a coral record of tropical climate the oxygen isotopic composition of a banded coral from the western equatorial indian ocean provides a 150 year long history of the relation between the el nino southern oscillation enso phenomenon and the asian monsoon interannual cycles in the coral time series were found to correlate with pacific coral and instrumental climate records suggesting a consistent linkage across ocean basins despite the changing frequency and amplitude of the enso however decadal variability that is characteristic of the monsoon system also dominates the coral record which implies important interactions between tropical and midlatitude climate variability one prominent manifestation of this interaction is the strong amplitude modulation of the quasi biennial cycle

extensional tectonics and stratigraphy of hibernia oil field grand banks newfoundland the tectonic evolution of the grand banks involved several episodes of rifting and sequential development of the continental margin the dominant period of rifting and basin formation in the central grand banks was late callovian to aptian extensional failure of the central grand banks crust probably occurred along a shear zone that dipped gently to the west listric normal basin forming faults merge at depth with this detachment system the listric murre fault soles at 26 km 16 mi creating the very deep jeanne d arc basin cross basin transfer faults accommodated different amounts and rates of extension and resulted in the conspicuous offset pattern and funnel shaped geometry of the jeanne d arc basin the hibernia oil field is associated with one of these structural salients the stratigraphy of the jeanne d arc basin and the hibernia oil field is a direct response to this tectonic and structural framework large scale unconformity bounded sequences correspond to major plate reorganizations and zipper type opening of the atlantic ocean smaller scale adjustments to episodic extension are expressed in multiple stacking of depositional sequences the broad scale evolution of the synrift succession involved the early deposition of limestones and oil prone shales about 10 12 m y later rifting climaxed resulting in floods of coarse terrestrial material from the rift shoulders the characteristics of these depositional systems reflect a pervasive structural control affecting the distribution of facies tracts dip slip movement on basin bounding faults and c oss basin transfer fault trends were equally important a profound structural modification of the hibernia structure occurred in late barremian time when a major detachment developed within the basin fill this structural modification and associated antithetic and synthetic faulting in the hanging wall largely controlled reservoir distribution and the maturation migration and trapping of hydrocarbons

a review of modern coral δ18o and δ14c proxy records abstract this paper is a review of published modern coral 18 o and 14 c isotopic records that are at least 30 and 20 years long respectively the data are presented to show basin scale trends in both of these proxy records on decadal to centennial timescales the goal was to qualitatively integrate the general inter annual to centennial timescale variability revealed in these data as well as the statistical and modeling output results that have been produced using these coral records while many review papers typically include a representative subset of the data available this review aims to include as much of the available data as possible in general coral 18 o records show a long term warming and or freshening throughout the tropical oceans and agree with the noaa extended reconstruction sea surface temperature 2 ersst on decadal timescales in the western pacific it is most likely a freshening of the seawater 18 o that dominates the signal el nino southern oscillation enso variability dominates most 18 o records either by varying local seawater temperature or salinity depending on the regional oceanography climatology outside of the pacific enso affects seawater temperature and salinity via atmospheric or oceanic teleconnections post bomb coral 14 c records collectively show that the uptake of 14 c has been greatest in gyre water fed sites followed in descending order by western boundary current areas equatorial upwelling regions and eastern tropical pacific upwelling sites these surface water 14 c values indicate the proportion of surface water and or the residence time of water at the surface at a given location and can be used to model water mass mixing rates such models have only begun to be run and show that the amount of eastern pacific water entering the central south pacific increases during el ninos and that the indonesian throughflow is supplied year round by the north pacific comparing ocean circulation models with coral 14 c modelled circulation enables researchers to explore the mechanisms that drive seawater 14 c variability and fine tune their models in addition our comparison between the rate of coral 14 c increase between 1960 and 1970 and total anthropogenic co 2 uptake rates show general agreement demonstrating the value of coral records in understanding past carbon fluxes overall coral 18 o and 14 c proxy records represent natural archives of seawater conditions and are critical for studying the natural variability in local and regional patterns within and teleconnection patterns between the tropics extra tropics temperate and polar regions on intra annual to centennial timescales

a 170 year sr ca and ba ca coral record from the western pacific warm pool 1 what can we learn from an unusual coral record 1 a long lived porites coral from new ireland 2 5 s 150 5 e papua new guinea has been analyzed for sr ca and ba ca by laser ablation inductively coupled plasma mass spectrometry la icpms the top 50 years of the core are examined here and compared with instrumental sea surface temperatures ssts for the small range of sst in the warm pool sr ca shows an unusually large response the best estimate for the slope of a temperature calibration is 0 23 0 03 mmol mol per c this strong slope is partly a result of the high resolution sampling but is also due to additional biological mediation of the sr ca ratios which appears to be associated with seasonal changes of calcification rate and limits the prediction skills of this proxy thermometer high density bands synchronous with high sr ca ratios suggest that calcification may be enhanced by beneficial small amounts of nutrients available during el nino transient ba enrichment synchronous with colder than average sst is also observed during el nino and attributed to the shoaling of the new ireland coastal undercurrent the high level of enrichment in particular during upwelling triggered by westerly wind bursts suggests an origin from both dissolved seawater and marine biological barium

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

timing coral based climatic histories using 13c enrichments driven by synchronized spawning high resolution measurements of the skeletal 13c 12c ratios of massive porites corals from the great barrier reef and eastern indian ocean reveal 13c enrichments culminating sharply at the time of the annual coral spawning event these 13c skeletal enrichments appear to be driven by the rapid sequestering of 12c required to build the reproductive tissue prior to spawning coral spawning is commonly synchronized with the lunar phase and in this case is predictable to within 3 days the results suggest that reproductive modulation of 13c 12c can be exploited as an accurate built in time marker for constructing realistic time series with proxy climate data extracted from corals recognition of the 13c 12c response to reproduction also facilitates the separation of physiological and environmental influences and should expand the utility of stable carbon isotopes in paleoceanography

analogue modelling of orthogonal and oblique rifting abstract the three dimensional progressive development of orthogonal and oblique rift systems has been simulated using scaled analogue sandbox models the orientation of the zone of rifting where angle between the rift axis and the extension direction was varied systematically from 90 orthogonal rifting to 75 60 and 45 oblique rifting completed models were impregnated and sectioned both vertically and horizontally orthogonal rift models are characterized by long straight rift border faults and intra rift faults perpendicular to the extension direction oblique rift models are characterized by shorter segmented rift border faults and intrarift faults in the oblique models the rift border faults formed en echelon arrays parallel to the inderlying zone of basement stretching whereas the intra rift faults formed at a high angle to the extension vector increased extension in the moderately oblique and oblique rift systems 60 and 45 caused the intra rift faults to rotate towards parallelism with the rift border faults no strike slip or oblique slip transfer faults were found in any experiments rift border faults and intra rift faults in the models are segmented along strike with relay ramp structures formed between overlapping fault tips along the strike of the rift variations in half graben polarities and offsets of depocentres are accomplished by accommodation zones formed by interlocking conjugate fault arrays the experimental fault patterns compare well with the fault architectures found in those modern or relatively young rift systems where well defined basement controlled strike slip or oblique slip transfer faults are absent an accommodation zone model consisting of interlocking conjugate extension faults is proposed for the along strike switching of half graben asymmetries and offsetting of depocentres in rift systems the fault geometries in the analogue models can be used as templates for recognition of fault styles in both orthogonal and in oblique rift environments

high resolution isotopic records from corals using ocean temperature and mass spawning chronometers abstract we present a 6 year long 1978 1984 18 o and 13 c record from a great barrier reef pandora reef porites lutea coral based on near weekly sample intervals a sampling technique was designed to minimise any smoothing or distortion of the isotopic record due to complex coral growth calyx architecture and calcification at depth within the tissue layer the arrival time of the mid winter minimum sea surface temperature is very consistent 2 weeks near pandora reef and provides an annual time marker offering more precision than the traditional density band chronometer the improved chronology and high resolution record demonstrate that signal distortion in porites due to calcification within the tissue layer and variable intra annual coral extension is generally negligible also confirmed is that the arrival time of monsoonal floods is precisely preserved 1 week within the skeleton of porites the sensitivity of weekly sampling allows the detection of a subtle warm to cool sea surface temperature anomaly which preceded by more than one year a similar temperature anomaly associated with the 1982 83 el nin o in the east pacific sharply higher 13 c values coincide with the time of the annual coral mass spawning event in the great barrier reef recognition of this mass spawning signal should simplify the interpretation of coral 13 c records and provides an additional precise time marker with which to adjust chronologies when intra annual coral extension is not constant

el nino southern oscillation enso and decadal scale climate variability at 10 n in the eastern pacific from 1893 to 1994 a coral based reconstruction from clipperton atoll we have developed a 101 year 1893 1994 subseasonal oxygen 18o and carbon 13c isotopic time series from clipperton atoll in the eastern pacific using the coral porites lobata in agreement with linsley et al 1999 we find that seasonal and interannual coral 18o variability at clipperton results from variability in both water temperature and salinity three new coral time series demonstrate the reproducibility of a secular coral 18o trend of 0 35 since 1910 but show varying 13c trends strong decadal scale variability in the 18o record appears related to the pacific decadal oscillation pdo through postulated changes in the strengths of the equatorial counter current and north equatorial current interannual variability in this coral 18o record is directly related to the el nino southern oscillation enso and isolation of this frequency band indicates reduced enso variability in the eastern equatorial pacific in the period 1925 to 1940 in agreement with instrumental and other pacific coral records

fault superimposition and linkage resulting from stress changes during rifting examples from 3d seismic data phitsanulok basin thailand abstract the phitsanulok basin thailand provides examples of changing fault displacement patterns with time associated with faults of different orientations in the northern phitsanulok basin three main stress states have been identified associated with late oligocene recent fault development 1 late oligocene late miocene approximately e w extension n s shmax main rift stage 2 late miocene pliocene transtension to tranpression e w to ne sw shmax late rift stage and 3 pliocene recent very minor faulting e w extension n s shmax post rift stage syn rift faults tend to strike n s but also follow ne sw and nw se trends and are basement involved the late miocene deformation produced a distinctly different type of fault population from the main rift fault set characterized by numerous small displacement tens of metres faults striking predominantly ne sw most of these faults are convergent conjugate sets aligned in discrete zones and nucleated within the sedimentary basin reactivation of main rift faults trends during the late rift stage favoured strike directions between 350 and 50 the displacement characteristics of three large faults within the basin show variations depending upon fault orientation the low angle 23 30 dip western boundary fault 7 km throw displays little discernible difference in the distribution of displacement on fault zone during the different stress states other than increases and decreases in displacement amount smaller faults exhibit a more selective reactivation history than the western boundary fault and are more informative about fault response to a varying stress field activation of the oblique ne sw striking ntm 1 initially produced a fault divided into three segments splaying into n s trends stress reorientation during the late rift stage finally linked ne sw striking segments the partial linkage of the fault zone at the time of oil migration resulted in the southwestern part of the ntm 1 fault sealing hydrocarbon bearing reservoirs whilst late linkage areas along the northeastern part failed to seal hydrocarbons the n s striking pto 1 fault shows early isolated fault segments linkage during syn rift motion then a more patchy distribution of displacement late in the fault history perhaps due to non optimal orientation of the fault to the regional stress field when compared with the ntm 1 fault the fault characteristics described indicate that where strong pre existing fabrics are present and varying stress regimes have occurred fault population characteristics and evolution of fault displacement can depart considerably from extensional fault populations associated with a single phase of extension

quantifying errors in coral based enso estimates toward improved forward modeling of δ18o 1 the oxygen isotopic ratio 18o in tropical pacific coral skeletons reflects past el nino southern oscillation enso variability but the 18o enso relationship is poorly quantified uncertainties arise when constructing 18o data sets combining records from different sites and converting between 18o and sea surface temperature sst and salinity sss here we use seasonally resolved 18o from 1958 to 1985 at 15 tropical pacific sites to estimate these errors and evaluate possible improvements observational uncertainties from kiritimati new caledonia and rarotonga are 0 12 0 14 leading to errors of 8 25 on the typical 18o variance multicoral syntheses using five to seven sites capture the principal components pcs well but site selection dramatically influences enso spatial structure using sites in the eastern pacific western pacific warm pool and south pacific convergence zone spcz captures eastern pacific type variability while central pacific type events are best observed by combining sites in the warm pool and spcz the major obstacle to quantitative enso estimation is the 18o climate conversion demonstrated by the large errors on both 18o variance and the amplitude of the first principal component resulting from the use of commonly employed bivariate formulae to relate sst and sss to 18o errors likely arise from either the instrumental data used for pseudoproxy calibration or influences from other processes 18o advection atmospheric fractionation etc at some sites modeling seasonal changes to these influences reduces conversion errors by up to 20 this indicates that understanding of past enso dynamics using coral 18o could be greatly advanced by improving 18o forward models

eastern pacific sea surface temperature since 1600 a d the δ18o record of climate variability in galapagos corals we measured stable oxygen isotope ratios and skeletal growth rates in the massive corals pavona clavus and p gigantea from the west coast of isabela island galapagos to assess interannual to decadal climate variability in the eastern pacific comparisons of instrumental data sets show that sea surface temperatures sst in the galapagos region are representative of a broad portion of the eastern equatorial pacific the site is especially well suited for long term studies of the el nino southern oscillation enso phenomenon as it lies within the eastern pacific center of action for thermal anomalies associated with enso the p gigantea isotope record is nearly monthly in resolution spans the period 1961 1982 and shows strong correlation with a galapagos instrumental sst record r 0 90 for annual averages cross spectral analysis shows that sst can explain greater than 80 of the variance in 18o at both the annual cycle and within the high frequency portion of the enso band 3 5 years the p clavus record is annual in resolution extends from 1587 to 1953 a d and was obtained from a 10 m diameter colony preserved within the urvina bay uplift because seawater 18o variations in the region are very small we interpret the urvina bay coral 18o record in terms of annual average sst the isotopic record appears to be a very good but not perfect indicator of enso events and shows good correspondence with the historical enso reconstruction of quinn et al 1987 a number of low 18o excursions that we observe during the 17th and 18th centuries very likely represent enso events that are missing from the historical tabulations most interannual 18o variations between 1607 and 1953 a d represent annual average temperature excursions of 1 to 2 5 c during the little ice age the annual 18o series correlates well with many north american tree ring records and shows low temperatures during the early 1600s and early 1800s and relatively warmer conditions during the 1700s unlike most northern hemisphere tree ring and instrumental records we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling 28 of the total variance the main enso mode is centered at 4 6 years and accounts for 12 of the total variance additional significant oscillations occur at periods of 3 3 6 8 11 17 22 and 34 years both annual growth rate and 18o show variance at periods equivalent to the solar and solar magnetic periods e g 11 and 22 years respectively in addition the amplitude of the 11 year 18o cycle generally varies with the amplitude of the solar cycle supporting previous suggestions that the solar cycle may modulate interannual to decadal climate variability in the tropics the dominant oscillatory modes both within the enso and interdecadal frequency bands shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s this may reflect major reorganizations within the tropical ocean atmosphere system and suggests that tropical pacific climate variability is linked across timescales ranging from years to decades

calibrations of bermuda corals against large scale sea surface temperature and sea level pressure pattern time series and implications for climate reconstructions 1 proxy records from stony reef corals are established tools for reconstructing climate features however validation procedures for proving the calibrations are often insufficient or even lacking we address this problem by the establishment and validation of statistical regression models for the reconstruction of large scale climate patterns from local coral records upscaling we apply the upscaling technique to the annual growth rates of two coral species from bermuda representing a period of about 140 years the coral records are related to reanalyzed sea surface temperature sst and sea level pressure slp fields in the western north atlantic the correlation maps between the ssts and the single coral records and their leading principal component show similar structures on the basis of regression patterns for limited areas upscaling models are established validation of such models for the sst yields an explained variance of 30 of the low pass filtered data using the first principal component of both corals for the detrended slp time series representing an almost hemispheric slp pattern 21 of the interannual variability is explained by means of only one coral thus different corals from neighboring sites represent similar climate signals however to slightly varying degrees leading to different reconstruction skills problems remain in reconstructing long term trends we conclude that reconstructions from multiple corals are not a priori predominant to those from single corals a calibration to what extent a single coral represents a climate parameter should be the first step before combining multiple corals as the basis for a reconstruction

evolution of the enso signal over the indo pacific domain abstract the evolution of the el nino southern oscillation enso in the indian and western pacific oceans is investigated observations of sea surface temperature sst heat storage in the upper 400 m hs zonal surface wind stress zsws and meridional surface wind stress msws are mapped monthly onto a 2 latitude longitude grid over as much of the indian and western pacific oceans i e 40 s 50 n 40 e 180 as possible for a 13 year period 1979 91 this grid resolution allows upper ocean temperature variability to be resolved in the eastern indian ocean i e timor sea and the western pacific ocean i e philippine sea time sequences of these variables at each grid node are band passed filtered to yield the enso period scales of 3 to 6 years extended empirical orthogonal functions analysis is applied to the filtered time sequences yielding an animation of the enso development in indian and western pacific oceans for the first modes of the four variables sst hs zsws and msws peak a

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

influence of fault reactivation during multiphase rifting the oseberg area northern north sea rift abstract multiphase rifts tend to produce fault populations that evolve by the formation of new faults and reactivation of earlier faults the resulting fault patterns tend to be complex and difficult to decipher in this work we use seismic reflection data to examine the evolution of a normal fault network in the oseberg fault block in the northern north sea rift system a rift system that experienced permian early triassic and middle jurassic early cretaceous rifting and exhibits n s nw se and ne sw oriented faults both n s and nw se striking faults were established during the permian early triassic rifting as indicated by triassic growth packages in their hanging walls in contrast the ne sw striking faults are younger as they show no evidence of permian early triassic growth and offset several n s and nw se striking faults structural analysis show that a new population of nw se striking faults formed in the lower middle jurassic inter rift period together with reactivation of n s striking permian early triassic faults indicating a ne sw inter rift extension direction during the middle jurassic early cretaceous rifting faults of all orientations n s nw se and ne sw were active however faults initiated during the middle jurassic early cretaceous rifting show mainly n s orientation indicating e w extension during this phase these observations suggest a reorientation of the stress field from e w during the permian early triassic rift phase to ne sw during inter rift fault growth and back to e w during the middle jurassic early cretaceous rift phase in the oseberg area hence the current study demonstrates that rift activity between established rift phases can locally develop faults with new orientations that add to the geometric and kinematic complexity of the final fault population

successive orthogonal and oblique extension episodes in a rift zone laboratory experiments with application to the ethiopian rift small scale modeling was performed to examine the effects of the superposition of two successive extensional phases from orthogonal to oblique type 1 and from oblique to orthogonal type 2 in both the type 1 and type 2 models faults produced during the first stage strongly control fault development during the second stage in type 1 models the oblique faults developed during the second oblique phase are confined within a first phase graben whereas in type 2 models the oblique faults produced during the first phase continue to develop during orthogonal extension and connect with each other to give sigmoidal fault blocks type 1 models are compared with the structural setting of the ethiopian rift the evolution of the rift is related to a recent extensional event whose principal direction of stretching trends at around 50 to preexisting major normal faults type 1 laboratory models are fairly comparable to the northern sector of the ethiopian rift referred to here as mer they account for both the development of the en echelon oblique faults of the wonji fault belt and the sinistral shear gradient running parallel to the eastern border of the mer which formed during an oblique rifting extension the statistical analysis of the whole ethiopian rift fault pattern by reference to the experimental data allows the determination of a n100 n110 mean direction of stretching

characterizing seawater oxygen isotopic variability in a regional ocean modeling framework implications for coral proxy records reconstructions of the el nino southern oscillation enso are often created using the oxygen isotopic ratio in tropical coral skeletons 18o however coral 18o can be difficult to interpret quantitatively as it reflects changes in both temperature and the 18o value of seawater small scale 10 100 km processes affecting local temperature and seawater 18o are also poorly quantified and contribute an unknown amount to intercoral 18o offsets a new version of the regional ocean modeling system capable of directly simulating seawater 18o isoroms is therefore presented to address these issues the model is used to simulate 18o variations over the 1979 2009 period throughout the pacific at coarse o 50 km resolution in addition to 10 km downscaling experiments covering the central equatorial pacific line islands a preferred site for paleo enso reconstruction from corals a major impact of downscaling at the line islands is the ability to resolve fronts associated with tropical instability waves tiws which generate large excursions in both temperature and seawater 18o at palmyra atoll 5 9 n 162 1 w tiw related sea surface temperature gradients are smaller at neighboring christmas island 1 9 n 157 5 w but the interaction of mesoscale features with the steep island topography nonetheless generates cross island temperature differences of up to 1 c these nonlinear processes alter the slope of the salinity seawater 18o relationship at palmyra and christmas as well as affect the relation between coral 18o and indices of enso variability consideration of the full physical oceanographic context of reef environments is therefore crucial for improving 18o based enso reconstructions

geometric and experimental models of extensional fault bend folds the geometric models ranged from simple models of listric normal faults with continuous hanging wall deposition to complex models of normal faults with ramps and flats and footwall deposition and or erosion the inclined shear angle i e the angle between the horizontal and the shear direction was 70 in all models withjack and peterson 1993 describe the modeling technique in the experimental models a 4 cm thick layer of either wet clay or dry sand covered a flat metal base consisting of overlapping plates or precut blocks movement of the plates or blocks produced a listric normal fault in the overlying clay or sand layer we added growth layers after every centimeter of displacement withjack and callaway 2000 describe the properties of the wet clay and dry sand

the growth of non colinear normal fault systems what can we learn from 3d seismic reflection data abstract many rift zones exhibit a range of fault orientations rather than simple colinear faults that strike orthogonal to the inferred least principal stress the formation of non colinear fault sets has implications for assessing rift zone kinematics as well as determining palaeo stress state in extensional basins using 3d seismic reflection data we deduce the likely mechanisms responsible for the formation of a population of non colinear faults in the maloy slope area of the northern north sea three basement displacing fault populations exist on the maloy slope i large 1 km throw n s striking faults ii smaller

intercomparison of coral oxygen isotope data and historical sea surface temperature sst potential for coral based sst field reconstructions we examine the extent to which the large scale features of the sea surface temperature sst anomaly field are represented by a sparse observational network of coral oxygen isotope 18o time series regression of annually averaged 18o data against gridded estimates of local sst anomaly within the period 1856 1990 confirm the literature regression of 18o anomaly on sst anomaly for indo pacific corals however while interannual sst variability is generally well represented by individual coral time series observed decadal and secular variability does not always display a linear relationship to local sst anomaly instead many records appear to better recover nonlocal large scale phenomena which in turn are related to either the coral local sst or sst covariant changes in seawater 18o we employ empirical orthogonal function eof analysis to identify common patterns of variability in the coral data we find two significant patterns which are interpretable as the oceanographic signature of the el nino southern oscillation enso and as a near global warming in which the eastern equatorial pacific cools a third pattern weakly resembles the pacific decadal oscillation these modes are seen more clearly in a singular vector decomposition svd of the covariance between the coral data and the dominant patterns of large scale historical sst variability the results are consistent with those found in eof and svd analyses of sst data from the coral locations as additional coral based proxy estimates become available they will improve the resolution of the patterns recovered these results suggest that a sparse network of coral data may be used to reconstruct interannual secular and decadal sst variability for preinstrumental periods albeit with large uncertainty

structural analysis and miocene to present tectonic evolution of a lithospheric scale transcurrent lineament the sciacca fault sicilian channel central mediterranean sea abstract seismo stratigraphic and structural analysis of a large number of multichannel seismic reflection profiles acquired in the northern part of the sicilian channel allowed a 3 d reconstruction of a regional ns trending transfer zone which displays a transcurrent tectonic regime and that is of broad relevance for its seismotectonic and geodynamic implications it is constituted of two major transcurrent faults delimiting a 30 km wide mostly undeformed basin the western fault capo granitola does not show clear evidence of present day tectonic activity and toward the south it is connected with the volcanic area of the graham bank the eastern fault sciacca is structurally more complex showing active deformation at the sea floor particularly evident along the nerita bank the sciacca fault is constituted of a master and splay faults compatible with a right lateral kinematics sciacca fault is superimposed on an inherited weakness zone a mesozoic carbonate ramp which borders to the east a 2 5 km thick plio quaternary basin and that was reactivated during the pliocene a set of scaled claybox analogue models was carried out in order to better understand the tectonic processes that led to the structural setting displayed by seismic data tectonic structures and uplift subsidence patterns generated by the models are compatible with the 3 d model obtained from seismic reflection profiles the best fit between the tectonic setting deriving from the interpretation of seismic profiles and the analogue models was obtained considering a right lateral movement for the sciacca fault nevertheless the stress field in the study area derived from gps measurements does not support the present day modelled right lateral kinematics along the sciacca fault moreover seismic events along this fault show focal mechanisms with a left lateral component we ascribe the slip change along the sciacca fault from a right lateral transcurrent regime to the present day left lateral kinematics to a change of principal horizontal stress direction starting from late pliocene

the thermal oceanographic signal of el nino reconstructed from a kiritimati island coral central equatorial pacific sea surface temperature sst anomaly is a critical predictor of basin wide oceanographic and atmospheric effects of the el nino southern oscillation enso phenomenon we employ two geochemical thermometers measured on coralline aragonite to reconstruct an independent proxy based measure of central equatorial pacific sea surface temperature anomaly in addition we assess the observational error associated with extraction of large scale sst anomalies from 18o and sr ca measurements on the basis of paired data for the 1981 1987 period rms error for the estimation of sst from kiritimati coral 18o is about 0 4 c assuming no seawater 18o influence for sr ca the observational error is about 0 5 c singular spectrum analysis of the 18o time series suggests that 1 3 of the variance is explained by sst anomaly and that this variance may be separated from other signals in the frequency domain the interannual component of the 18o record shares 70 variance with the interannual component of local sst anomaly estimates 0 84 and correlates as highly with nino3 region 150 w 90 w 5 n 5 s sst anomaly estimates comparison of annual averages of the 18o data with analyzed sst for 55 years suggests that the error in deriving annually averaged sst anomalies at kiritimati is about 0 4 c a global sst correlation analysis suggests significant correlation with the rest of the pacific basin and the tropical indian and atlantic sectors the ocean wide level of correlation achieved using the coral data is indistinguishable from that achieved using the nino3 sst anomaly index and suggests that a few well located coral reconstructions with low observational error may be sufficient to reconstruct the global sst anomaly field associated with enso activity

sequence stratigraphic response to aptian albian rifting in conjugate margin basins a comparison of the jeanne d arc basin offshore newfoundland and the porcupine basin offshore ireland

using stress deflections to identify slip events in fault systems abstract a new approach for identifying past slip events in strike slip fault systems without geological markers is presented a 2 d distinct element modeling code is used to simulate the stress distribution around a strike slip fault zone after a major slip event mature and immature fault zones are investigated slip on the fault is responsible for stress rotations near the active fault strand series of experiments reveal that the stress deflections are qualitatively the same whatever the fault strike fault friction and far field differential stresses for a left lateral fault stresses are rotated clockwise in the two compressive quadrants near the fault tips and counterclockwise in the two extensive quadrants the stress field signature of a slip event thus highlights the extent of the active fault strand conversely the reconstruction of paleostress fields through inversion of minor striated faults that commonly follow slip on the master fault and the analysis of their deflections allow recognition of the fault strands that slipped in a close or remote past application to the left lateral pontarlier fault zone in the jura fold and thrust belt france late cenozoic in age shows that the fault activity has migrated northward in agreement with the in sequence development of the mountain belt

analogue modelling of multiphase rift systems abstract analogue models of multiphase rift systems show that structures produced by the first phase of extension exertsignificant control on the geometries of the later phase extensional faults two experimental series series 1 and series 2 used different modelling media subjected to two phases of extension series 1 models used a simple homogeneous sandpack whereas series 2 models used a sand polymer multilayer in each series kinematic scenarios included orthogonal extension followed by oblique extension or vice versa extension directions for oblique rift kinematics varied from 75 to 30 to the axis of rifting in all models where oblique rifting superseded earlier orthogonal rift structures the second deformation phase produced segmented fault systems and reorientation of fault tips into high angles with respect to the extension vector higher angles of obliquity resulted in increased fault segmentation orthogonal extension superposed on earlier oblique rifting leads to coalescence of segmented faults although remnants of the inherited initial rift structure remained even for low angles of obliquity the sand polymer multilayer models produced more complex fault patterns than those in the simple homogeneous sandpack showing the possible complexities that can be generated during polyphase rifting persistent first phase rift faults caused boundary fault segmentation and salients and embayments along the boundary faults during the second deformation phase the natural occurrence of similar structural styles particularly in map view may indicate that previously unrecognised multiphase rifting has occurred in these natural examples

global climate variations connected with sea surface temperature anomalies in the eastern equatorial pacific ocean for the 1958 73 period abstract the sea surface temperature anomalies in the eastern equatorial pacific ocean are shown to demarcate a key region new 130 w for observed variations in the global general circulation various techniques are used to describe global conditions during warm and cold sea surface conditions in the key region based on a global 15 year set of surface and upper air analyses earlier work is confirmed that during warm episodes 1 the westerly jets in both hemispheres are strengthened and 2 some of the semi permanent circulation features such as the intertropical convergence zone the subtropical high over the western and central pacific and the aleutian low increase in strength and vice versa for cold episodes the time series of monthly mean atmospheric temperature averaged over the entire man of the northern hemisphere is found to be highly correlated with the sea surface temperature anomalies in the key region the highest correlation of r 0 65 is found when the atmosphere lags the ocean by 6 m

sea surface temperature and salinity reconstruction from coral geochemical tracers massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers corals present several advantages for palaeoclimate research they grow continuously and can live up to 1000 years they are easy to date and they can be sampled at high resolution weekly to monthly resolution both live and fossil corals can be collected in the field in the past two decades significant efforts have been made to identify robust tracers of sea surface temperature sst and salinity sss in corals to date sr ca and 18o are considered to be the most reliable sst tracers although changes in seawater 18o can significantly alter sst reconstructed from coralline 18o because these variations in seawater 18o can be linked to sss changes this initial problem can in fact be turned into an advantage and provide us with an sss tracer the sst component in the coral 18o signal can either be evaluated through sr ca measurements or in some case simply filtered out however there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton the effects of growth rate light intensity feeding habits ph and water chemistry are still poorly documented a review of the strength and weaknesses of sr ca and 18o is presented together with some examples of sst and sss reconstructions other potential sst tracers are also reviewed it is expected that the ability to grow corals in aquarium under controlled conditions and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite

two hundred fifty years of reconstructed and modeled tropical temperatures 1 recent large scale palaeoclimate reconstructions of past temperature have been essentially biased to the extratropics owing to a paucity of proxy data in tropical regions herein we describe the first coral based reconstruction of sea surface temperatures ssts for the whole of the tropics 30 n 30 s it was developed from 14 disparate coral records located in the indian and pacific oceans over the most replicated period the reconstruction explains 57 of the tropical sst variance however the strength of this signal weakens markedly as the number of coral records decreases the reconstruction is robust between 1850 and 1993 but some fidelity is indicated back as far as the mid 18th century these results suggest that ambiguities in the low frequency domain of 18o measurements can be partially overcome by pooling together multiple time series from different locations around the tropics agreement with simulations from two general circulation models indicates that the late 20th century is likely the warmest period in the tropics for the last 250 years and that this recent warming can only be explained by anthropogenic forcing the high frequency variability is dominated by the el nino southern oscillation the reconstruction owing to the small number of coral records is unfortunately restricted both in time and space therefore we hope that this study will spur the palaeoclimate community to develop new and longer proxy series to improve the current meager data base of temperature sensitive series in the tropics

nonlinear variability of the climatic system from singular and power spectra of late quaternary records stable isotope records from seven marine cores and one ice core provide invaluable information on the intricate behavior of the climatic system over time scales of 104 to 105 years these records in conjunction with a simple coupled climate model help us understand major mechanisms of paleoclimatic variability the time intervals covered by the records include the last glacial interglacial cycle in spite of the difference in the nature of the records common features are revealed by advanced spectral analysis tools the dominant features are the presence of orbital frequencies on the one hand and a low number of internal degrees of freedom on the other the climatic system appears therefore to act on the quaternary time scales considered as a forced nonlinear oscillator the internal mechanisms giving rise to the aperiodic oscillations include ice albedo feedback precipitation temperature feedback and interactions between the ice sheets and the bedrock

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

shear test results for cohesion and friction coefficients for different granular materials scaling implications for their usage in analogue modelling abstract laboratory tests have been carried out on dry granular materials such as quartz sand glass microspheres and sugar with different grain size rounding and sphericity the measurements have been made with a simple shear test machine for different values of normal stress 50 900 pa shear stress has been plotted against normal stress in order to determine the cohesion and coefficient of internal friction for the investigated materials resulting values of cohesion and coefficient of internal friction are mainly dependent on rounding and sphericity while grain size has a less significant influence further the behaviour of the materials for very small normal stresses 0 400 pa is more complex than previously assumed the fracture envelopes for all materials investigated are convex outward for this small range and converge towards a straight failure envelope with increasing normal stress finally in extensional faulting experiments there is no significant change in fault dip with increasing depth therefore the non linear behaviour for small normal stresses is best described as a dependence of the cohesion on the normal stress and not as a dependence of the coefficient of internal friction on the normal stress values for cohesion increase from 0 pa 15 pa at zero normal stress to 137 247 pa 15 pa for normal stresses greater than 250 400 pa the results show that well rounded spherical material is better suited to model brittle behaviour of rocks in crustal and lithospheric scale analogue models than less well rounded material since it has a smaller cohesion and a coefficient of internal friction which is closer to values of natural rocks

characterization of stress perturbations near major fault zones insights from 2 d distinct element numerical modelling and field studies jura mountains abstract we consider and discuss the presence of discontinuities in the crust as a major source of stress perturbations based on 2 d distinct element modelling we reconstruct the local stress field around a vertical discontinuity in various geological contexts the resulting stress distribution reveals that major directional stress changes occur near the tips of the discontinuity so that stress deviations can reach values as large as 50 we establish simple relationships controlling stress changes around a pre existing fault zone as a function of 1 the remote differential stress magnitude 1 3 2 the friction coefficient on the discontinuity and 3 the strike of the discontinuity relative to the far field stress as a geological example we present the morez fault zone in the internal jura paleostress reconstruction in forty two sites indicates that the trends of the mio pliocene compression are n110 on average near the fault whereas they are n130 in the surrounding areas a comparison between the results of the tectonic study and those of theoretical modelling suggests that the 20 counterclockwise deviation is directly related to the reactivation of this large weak zone we thus evaluate the role of mechanical decoupling along pre existing zones of weakness especially with consideration to the accommodation of the alpine deformation in the jura belt

salt flow and diapirism related to extension at crustal scale abstract the analysis of the structure and history of salt diapirs in large ancient evaporitic basins such as the southeastern north sea basin suggests that diapirism is controlled by crustal scale extension laboratory experiments on small scale models designed to simulate configurations comparable to the southeastern north sea basin show that diapirs which grow in a sedimentary cover during basement extension can develop close to basement normal faults or at a significant distance from them if the displacement on the basement faults is transfered horizontally along the salt layer for given values of salt viscosity strain rate and friction coefficient in brittle rocks the pattern of salt diapirism in a particular area depends on the ratio of cover thickness to salt thickness as well as the absolute thicknesses of cover and salt layers the experiments give criteria for identifying different types of diapirs and provide models of horizontal flow in a salt layer undergoing extension and diapir development some dynamic implications of the experiments are applied to the southeastern north sea basin

a strategy to improve the contribution of coral data to high resolution paleoclimatology abstract various geochemical tracers measured in massive coral skeletons have the potential to compliment other sources of high resolution proxy climate information e g tree rings ice cores by providing paleoclimatic data from shallow water tropical ocean regions twenty previously published coral records 19 18o and one sr ca series between 54 and 346 years in length were examined for their local and larger scale relationships el nino southern oscillation with climate series were examined in a consistent manner over the same time periods and relationships were tested for stability through time the results demonstrate a spectrum of climatic interpretation ranging from 1 no significant relationship of the coral record with either local or larger scale climate variables 2 significant relationship of the coral record with climate but the relationship is not stable through time and 3 the coral record shows a significant and temporally stable relationship with climate which explains a significant and useful proportion of climate variance it is concluded that reliance to date on analyzing only one long coral core from a site has prevented identification of coral records or parts of coral records where non climatic factors are dominating the geochemical signal various factors may cause these non climatic signals to dominate more process studies into how corals of particular species with various growth rates and from various environmental settings incorporate geochemical tracers into their skeleton are required to understand exactly what is being measured in addition it is recommended that some level of replication ideally three separate corals of geochemical tracers will ensure accurate dating of the record identification of periods when non climatic factors dominate and thus enhance the reliability of the paleoclimatic record such an approach will allow the rich archive of environmental information contained in massive coral skeletons to make a significant contribution to high resolution paleoclimatology and improve our understanding of the nature and causes of past climate variability

the structural evolution of the northern viking graben and its bearing upon extensional modes of basin formation recent advances in the understanding of rift basin formation coupled with the increasing public availability of seismic and well data across the northern viking graben 60 61 n have enabled a detailed analysis of its development two rifting episodes can be recognized late permian early triassic and bathonian ryazanian major regional unconformities thought to be primarily tectonic rather than eustatic in origin separate and subdivide the rifting episodes the earlier episode involved extension about a n s axis ensuing triassic mid jurassic thermal subsidence was accommodated on steep faults during the later episode a new ne sw fault trend was superimposed on pre existing patterns major block rotation marking active rifting ceased at the end of the ryazanian during the second post rift episode there was a progressive migration of active faulting towards the basin margins and as a result a widening with time of the area undergoing subsidence asymmetric subsidence of the central part of the basin was hinged at the western margin of the horda platform and accommodated to the nw on major faults within the tampen spur factors for the second rifting episode were calculated both by relating subsidence to extension and by measuring observed extension values calculated by both methods increase consistently towards the basin axis for both rifting and thermal subsidence phases but are greater for the latter phase subsidence patterns are similar for both rifting and thermal subsidence episodes so that there is vertical stacking of relatively thick sequences in the axis of the northern viking graben these factors preclude the application of models involving uniform and non uniform stretching and also preclude oblique extension depth dependent stretching is preferred

intraseasonal oscillations in the global atmosphere i northern hemisphere and tropics abstract we have examined systematically oscillatory modes in the northern hemisphere and in the tropics the 700 mb heights were used to analyze extratropical oscillations and the outgoing longwave radiation to study tropical oscillations in convection all datasets were band pass filtered to focus on the intraseasonal is band of 10 120 days leading spatial patterns of variability were obtained by applying eof analysis to these is data the leading principal components pcs were subjected to singular spectrum analysis ssa ssa is a statistical technique related to eof analysis but in the time domain rather than the spatial domain it helps identify nonlinear oscillations in short and noisy time series in the northern hemisphere there are two important modes of oscillation with periods near 48 and 23 days respectively the 48 day mode is the most important of the two it has both traveling and standing components and is dominated by a zonal wavenumber two the 23 day mode has the spatial stru

the temperature relationship in coralline aragonite influence of variability in and skeletal growth parameters this paper provides an evaluation of two of the most likely pitfalls of sr ca thermometry i e the effect of biogenic cycling of sr vs ca in the surface ocean and the effect of variable extension rate on sr incorporation in coralline aragonite the authors also report calibration of the sr ca temperature relationship for three coral species porites lobata pocillopora eydouxi and pavona clavus collected for the hawaiian and galapagos islands analyses of seawater samples show significant spatial and depth variability in the sr ca ratio the uncertainty introduced by this effect is estimated to be 0 2 degrees c for corals located in tropical oligotrophic waters and potentially larger for corals located in upwelling areas sr ca along two different growth axes of a galapagos pavona clavus with annual extension rates of approximately 6 and 12 mm y respectively indicate an offset of 1 2 degrees c with higher sr ca values associated with slower extension rates the offset observed between the two growth axes may be the result of variations in extension and or calcification rate these results are important in determining past sea surface temperatures for reconstruction of paleoclimates

lithium in the aragonite skeletons of massive porites corals a new tool to reconstruct tropical sea surface temperatures previous studies have demonstrated the potential for the li content of coral aragonite to record information about environmental conditions but no detailed study of tropical corals exists here we present the li and mg to ca ratios at a bimonthly to monthly resolution over 25 years in two modern porites corals the genus most often used for paleoclimate reconstructions in the tropical indo pacific a strong relationship exists between coral li ca and locally measured sst indicating that coral li ca can be used to reconstruct tropical sst variations however li ca ratios of the skeleton deposited during 1979 1980 do not track local sst well and are anomalously high in places the mg ca ratios of this interval are also anomalously high and we suggest li ca can be used to reconstruct tropical sst only when mg ca data are used to carefully screen for relatively rare biological effects mg li or li mg ratios provide little advantage over li ca ratios except that the slope of the li mg temperature relationship is more similar between the two corals the mg li temperature relationship for the coral that experienced a large temperature range is similar to that found for cold water corals and aragonitic benthic foraminifera in previous studies the comparison with data from other biogenic aragonites suggests the relationship between li mg and water temperature can be described by a single exponential relationship despite this hint at an overarching control it is clear that biological processes strongly influence coral li ca and more calibration work is required before widely applying the proxy

a high resolution sr ca and δ18o coral record from the great barrier reef australia and the 1982 1983 el nino abstract a high resolution near weekly sr ca and oxygen isotopic record is presented for a coral from the pandora reef in the great barrier reef gbr of australia during the period 1978 to 1984 the records are well correlated except for periods of high rainfall when river runoff has significantly modified the 18o value of seawater using the sr ca temperature calibration of de villiers et al 1994 the sr ca records exhibit seasonally controlled cyclical sst sea surface temperature variations of from 21 to 28 c during the very strong el nino of 1982 1983 the sr ca systematics indicate a sharp drop in the winter sst to 18 5 c this represents a temperature anomaly of 3 c which is approximately twice that given by the 18o variations suggesting an 2 amplification of the anomaly by the sr ca system possibly due to the increasing dominance of inorganically controlled aragoniteseawater fractionation the oxygen isotopic systematics show the combined effects of both temperature and changing seawater 18o values the latter reflecting the influx of 18o depleted runoff during periods of high rainfall due to the extremely low 10 3 sr and ca contents of river run off relative to seawater it is possible to use the sr ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the 18o value of seawater using this approach it is possible to quantitatively reproduce the volume of runoff from the burdekin river during the periods of major flooding that occurred in early 1979 and 1981 the results of this study demonstrate that the combined use of high resolution sr ca and 18o systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate

systematic enso driven nutrient variability recorded by central equatorial pacific corals 1 variations in ocean productivity are driven largely by nutrient supply to the photic zone but temporal records of nutrient variability are sparse here we show scleractinian coral p ca proxy records of variations in phosphate concentrations during el nino southern oscillation enso cycles in the central equatorial pacific covarying p ca records in porites corals from christmas and fanning islands show a regional 40 decrease during the upwelling relaxation of the 1997 1998 el nino consistent with less frequent nutrient measurements from this area similar 35 45 skeletal p ca decreases occur during the 1982 1983 and 1986 1987 el nino events which predate satellite color and regional nutrient measurements after each el nino event nutrient increases lag temperature recovery by 4 12 months likely reflecting uptake by massive phytoplankton blooms that followed resumption of upwelling the results support the utility of coral p ca to probe the mechanisms linking enso equatorial upwelling and carbon cycling in the past

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

bathymetric gradients of lineated abyssal hills inferring seafloor spreading vectors and a new model for hills formed at ultra fast rates abstract abyssal hill morphology provides a preliminary measure of the direction and rate of seafloor spreading however additional information e g magnetic anomaly data or a nearby mid ocean ridge is usually required to verify these estimates previous attempts to identify a unique spreading rate proxy from abyssal hill dimensions e g height length width have largely failed due to the relatively large scatter of data or the non linear character of spreading rate trends we present a new stand alone method of determining both spreading rate and spreading direction using the distribution of azimuths for slopes facing toward and away from the ridge axis the spreading rate is determined with the peak height parameter defined as the difference in the height maximum frequency of the two dominant modes observed in the azimuthal histograms this parameter exhibits a clear nearly linear spreading rate trend and allows half spreading rates to be estimated to within 10 20 km myr the spreading direction is determined with the peak width parameter which compares the average width of the two dominant modes in the azimuthal histograms the wider distribution of slope azimuths is oriented away form the paleo ridge axis for all spreading rates and thus spreading direction can be determined the trends in the peak height and width parameters are used to constrain a new model of abyssal hill formation at ultra fast spreading rates which require greater off axis extensional faulting resulting in a few large throw faults on the outward facing hillsides and many smaller throw faults on the inward facing hillsides

trench triple junction off central japan preliminary results of french japanese 1984 kaiko cruise leg 2 abstract leg 2 of the french japanese 1984 kaiko cruise has surveyed the trench triple junction off central japan where the japan izu bonin and sagami trenches intersect the izu bonin trench is deeper than the japan trench and filled by a thick turbiditic series its anomalous depth is explained by the westward retreat of the edge of the northwestward moving philippine sea plate on the contrary to what happens in the japan trench horst and graben structures of the pacific plate obliquely enters the izu bonin trench suggesting that the actual boundary between these two trenches is located to the north of the triple junction the inner wall of the izu bonin trench is characterized in the triple junction area by a series of slope basins whose occurrence is related to the dynamics of this area the northernmost basin is overthrust by the edge of the fore arc area of the northeast japan plate the plate boundary is hardly discernible further east which makes it impossible to locate precisely the triple junction itself these features suggest that large intra plate deformation occurs there due to the interaction of the plates involved in the triple junction and the weak mechanical strength of the wedge shaped margin of the overriding plates

environmental control of the oxygen isotope composition of porites coral microatolls abstract understanding the influence of climatic and non climatic factors on geochemical signals in corals is critical for assessing coral derived records of tropical climate variability porites microatolls form large disk shaped colonies constrained in their upward growth by exposure at or close to mean spring low water level and occur on indo pacific reefs microatolls appear suitable for paleoclimate reconstruction however the systematics of the microatoll chemistry climate relationship are yet to be characterized in this study the 18o signal in porites microatolls from well flushed reef flats on kiritimati christmas island central pacific was investigated for intra coral growth aspect and extension rate effects and between coral effects and to explore the climate signal contained within their skeletons samples for 18o analysis were taken from six individual transects from different positions within porites microatoll xm22 the results show that 1 the average standard deviation for the mean 18o values of transects that represent the same time periods is 0 03 and is within measurement error for a single analysis 0 04 2 the average standard deviation for time equivalent near monthly samples along the transects within the same microatoll is 0 07 and 3 comparison of the average 18o values of records for different microatolls from across kiritimati island show only a small between coral differences of 0 04 and 0 11 for different time periods these differences in mean 18o are within the range for intra and inter colony differences in seasonal and interannual 18o reported for dome shaped porites based on these results a stacked microatoll 18o record was constructed for the period 1978 2007 for comparison with published coral 18o records for nearby dome shaped porites there is a systematic offset between the two types of records which is probably due to variations in 18o seawater across kiritimati island despite the offset all records show similar amplitudes for the seasonal cycle of 18o and there is a strong correlation r 0 71 between microatoll 18o and local sea surface temperature sst the 18o sst slope relationship for microatolls is 0 15 c very similar to that reported for fast growing domed corals 0 18 to 0 22 c statistical analysis of the stacked microatoll 18o record shows that it is correlated with both local and large scale climate variables primarily sst at semiannual annual and interannual timescales our results show that the signal reproducibility and fidelity of skeletal 18o in coral microatolls is comparable to that observed for more conventional coral growth forms longer lived and fossil porites microatolls where they have grown in suitably flushed environments are likely to contain 18o signals that can significantly extend instrumental records of tropical climate variability

active normal faulting beneath a salt layer an experimental study of deformation patterns in the cover sequence scaled experimental models show that the presence of a viscous layer such as salt facilitates the development of extensional forced folds above active normal faults the geometries of the extensional forced folds and their associated secondary fault patterns depend on the thickness and viscosity of the viscous layer the thickness of the cover sequence the strength and ductility of the cover sequence and the magnitude and rate of displacement on the underlying master normal fault increasing the thickness of the viscous layer and the cohesive strength and ductility of the overburden enhances the decoupling between the deep and shallow deformation alternatively increasing the viscosity of the viscous layer the thickness of the overburden and the magnitude and rate of displacement on the master normal fault reduces the decoupling between the deep and shallow deformation enhanced decoupling facilitates the formation of broad extensional forced folds and the development of detached secondary faults both near and far from the master normal faults the model predicted deformation patterns closely resemble those observed in the gulf of suez the haltenbanken area of offshore norway and the jeanne d arc basin of the grand banks offshore southeastern canada

determination of fault friction from reactivation of abyssal hill faults in subduction zones abyssal hill faults are reactivated on the outer slope of trenches when they strike within 25 from trench parallel otherwise new faults form parallel to the trench we use the observed transition angle 25 and a three dimensional failure analysis to determine the coeffi cient of friction on reactivated abyssal hill faults the stress state in the outer slope is modeled as the superposition of the overburden stress and bending induced plane strain deformation if new trench parallel faults fail according to a linear failure relationship with no cohesion then determination of the coeffi cient of sliding friction s on reactivated faults is independent of the absolute value of the principal stresses and depends only on the poisson ratio of the crust and the slope of the failure law for new faults f we fi nd that reactivated faults dipping at 45 are 30 weaker than surrounding crust e g s 0 6 for f 0 85 these results suggest that the variation in the strength of oceanic crust due to the seafl oor spreading fabric is small and that the coeffi cient of sliding friction on oceanic faults is consistent with that observed in the laboratory