a unified approach to orbital solar and lunar forcing based on the earth s latitudinal insolation temperature gradient widespread empirical evidence suggests that extraterrestrial forcing influences the earth s climate but how this could occur remains unclear here we describe a new approach to this problem that unifies orbital solar and lunar forcing based on their common control of the earth s latitudinal insolation gradient lig the lig influences the climate system through differential solar heating between the tropics and the poles that gives rise to the latitudinal temperature gradient ltg which drives the earth s atmospheric and wind driven ocean circulation we use spectral analysis of recent changes in the earth s ltg to support earlier work on orbital timescales davis and brewer 2009 that suggests the climate system may be unusually sensitive to changes in the lig identification of lig forcing of the ltg is possible because the lig varies according to seasonally specific periodicities based on obliquity in summer 41 kyr orbital and 18 6 yr lunar cycle and precession 21 kyr orbital cycle and total solar irradiance 11 yr solar cycle in winter we analyse changes in the northern hemisphere ltg over the last 120 years and find significant 99 peaks in spectral frequencies corresponding to 11 years in winter and 18 6 years in summer consistent with lig forcing the cross seasonal and multi frequency nature of the lig signal and the diffuse effect of the ltg driver on the climate system may account for the complexity of the response to extraterrestrial forcing as seen throughout the climatic record this hypersensitivity of the ltg to the lig appears poorly reproduced in climate models but would be consistent with the controversial theory that the ltg is finely balanced to maximise entropy c 2011 elsevier ltd all rights reserved

fault reactivation and rift localization northeastern gulf of aden margin 1 the gulf of aden and the sheba spreading ridge gulf of aden forms the southern boundary of the arabian plate its orientation 075 e and its kinematics about 030 e divergence are interpreted as the result of an oblique rifting in this contribution a field study in the northeastern gulf of aden allows us to confirm the oligo miocene synrift directions of extension and to precise the normal fault network geometry the synrift extensions are 020 e and 160 e possibly in this chronological order the normal faults strike 070 e 090 e and 110 e the results show that some characteristics are consistent with oblique rifting analogue models while some others are not especially fault reactivation of mesozoic structures is shown to have occurred significantly at the beginning and during rifting these data are therefore compared to analogue models of oblique reactivation and this comparison demonstrates that fault reactivation played a key role during the early stage of the gulf of aden rifting finally scenarios of the lithospheric evolution during the eastern gulf of aden opening preexisting weaknesses in the lithosphere or not are discussed to better constrain the deformation history of the northern margin especially we show that rift localization processes may imply stress rotations through time

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

influence of hegenshan heihe suture on evolution of late mesozoic extensional structures in wunite depression erlian basin inner mongolia china we integrate previous work on the hegenshan heihe suture with our interpretation of geomagnetic anomaly and seismic reflection data to investigate the role of the hegenshan heihe suture in the evolution of late mesozoic extensional structures in the wunite depression of the erlian basin sags in the wunite depression present as ne50 trending in the western sector n0 ne30 trending in the central sector and ne45 trending in the eastern sector our results highlight the importance of the pre existing hegenshan heihe suture in the evolution of the late mesozoic rift system and reveal the following details 1 the ne50 extent sags in the western sector are controlled by the c ne50 trending suture moreover the extensional deformation of the reactivated suture during early cretaceous time resulted in a further vertical and horizontal extension of major border faults 2 the n0 ne30 extent sags in the central sector are influenced by the c ne75 trending suture the sinistral strike slip component of the reactivated suture during early cretaceous time resulted in a strike rotation of major border faults from nee trending following the suture to nne trending 3 because of strike slip deformation which resulted from the deformation of the reactivated suture accrued in major border faults light dip slip deformation led to less vertical offset 4 the ne45 trending sags in the eastern sector are controlled by the c ne45 trending suture moreover the extensional deformation of the reactivated suture during early cretaceous time facilitated a further vertical and horizontal prolongation of major border faults

the mechanical relationship between strike slip faults and salt diapirs in the zagros fold thrust belt analogue models are used to study the mechanical relationship between basement strike slip faults and salt diapirs displacement along a strike slip fault in 1 g models resulted in extension along pre existing jogs and the formation of oblique extensional faults where reactive diapirs were triggered in some models in the centrifuge models prescribed cuts simulating pre existing structures were reactivated during simple shear deformation of the models resulting in formation of pull apart basins which were intruded by diapirs the models show that because of the low ratio of salt to overburden thickness in the zagros 0 15 0 35 it is unlikely that diapirs have formed solely if at all as a result of movement along basement strike slip faults two mechanisms are suggested first pre kinematic thin overburden and continuous movement along a releasing bend in the cover units may have triggered some of the diapirs in the zagros which were later downbuilt to their current geometry by additional sedimentation second movement along the strike slip faults e g the kazerun and mangarak faults induced oblique movement along nw se zagros structures folds or thrusts resulting in the formation of pull apart basins where diapirs were eventually intruded fault plane solution of shallow earthquakes supports the second scenario which is also in agreement with previous interpretations that some of the salt diapirs associated with basement faults are younger than zagros shortening and young southwestwards

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

evolution of vertical faults at an extensional plate boundary southwest iceland vertical faults having both opening and vertical displacements are common in southwest iceland and hypotheses vary regarding whether they propagated to the surface from below or from the surface downward we address this issue through a study of vertical faults and associated surface fracture zones in regions of both oblique and normal spreading in southwest iceland individual fracture segments are commonly rotated out of the general trend of the fracture zone suggesting oblique motion along subsurface normal faults these faults commonly breach the upper hinge lines of narrow monoclinal folds that flank many fault traces on the hanging wall side based on these field observations and the results of numerical models we propose that 60 758 dipping normal faults in the subsurface propagated to the surface from below vertical fractures formed at the upper tips of the faults at depths of between 250 and 500 m 25 50 of the fault length in response to stress concentrations along the tip line model results indicate that narrow monoclinal folds develop at the surface above these vertical fractures which subsequently breach the monoclines along the upper hinge line forming vertical fault scarps and open fissures at the surface if vertical fractures utilize pre existing cooling joints in basalt to connect directly to the surface the hanging wall is able to pull apart from the footwall without the development of a surface monocline along the fault trace q 2003 elsevier ltd all rights reserved

deep shallow coupling response of the cenozoic bohai bay basin to plate interactions around the eurasian plate abstract the bohai bay basin bbb is a meso cenozoic intracontinental petroliferous basin where four pre existing continental scale fault zones intersect in east china the bbb has experienced complex deformational and evolutionary history that records significant information about how the lithosphere there has responded to the coeval plate interactions around the eurasian plate and or their resulting deep crust mantle processes in the cenozoic now both deep and shallow deformational and evolutionary processes of the bbb have been well studied but many geodynamic mechanisms previously proposed for those processes are too general to explain them well based on various data and principles we first summarized both deep and shallow responses and processes of the bbb in the cenozoic and then matched reasonable geodynamic mechanisms for each of them the results show as follows the cenozoic differential reactivation of pre existing continental scale weak zones controlled the coeval deep shallow differential coupling evolution of the bbb the paleogene extension in the bbb was mainly caused by crust mantle processes triggered by the stagnant izanagi slab the cenozoic strike slip faulting was influenced by various plate interactions in which the oblique subduction and anticlockwise rotation of young pacific plate resulted in the complex pre oligocene strike slip history of the tan lu fault zone to the south of the zhang peng fault zone while the india eurasia collision has caused the intense and synchronous strike slip faulting of various faults there since 35 ma which was then weakened by the oblique subduction and clockwise rotation of young philippine sea plate in the neogene the compression resulting from both the india eurasia collision and the philippine sea plate s subduction contributed to the latest paleogene tectonic inversion in the bbb the arrival of mantle flow triggered by both the india eurasia collision and the stagnant slab of the pacific plate resulted in the tectonic reactivation there in the late neogene

late holocene expansion of istorvet ice cap liverpool land east greenland abstract the greenland ice sheet is undergoing dynamic changes that will have global implications if they continue into the future in this regard an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior small independent ice caps adjacent to the greenland ice sheet hereinafter called local ice caps are sensitive indicators of the response of greenland ice marginal zones to climate change therefore we reconstructed late holocene ice marginal fluctuations of the local istorvet ice cap in east greenland using radiocarbon dates of subfossil plants 10 be dates of surface boulders and analyses of sediment cores from both threshold and control lakes during the last termination the istorvet ice cap had retreated close to its maximum holocene position by 11 730 cal yr bp radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the istorvet cap was smaller than at present from ad 200 to ad 1025 sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its holocene maximum position by ad 1150 thereafter the ice cap remained at or close to this position until at least ad 1660 the timing of this the most extensive of the holocene expansion is similar to that recorded at some glaciers in the alps and in southern alaska however in contrast to these other regions the expansion in east greenland at ad 1150 appears to have been very close to if not at a maximum holocene value comparison of the istorvet ice cap fluctuations with holocene glacier extents in southern hemisphere middle to high latitude locations on the antarctic peninsula and in the andes and the southern alps suggests an out of phase relationship if correct this pattern supports the hypothesis that a bipolar see saw of oceanic and or atmospheric circulation during the holocene produced asynchronous glacier response at some localities in the two polar hemispheres

time scale for adjustment of glaciers to changes in mass balance the length of time tm over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models we show the following tm may in general be estimated by a volume time scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states the factor f in the classical estimate of m l u where i is glacier length and u is terminus velocity has a simple geometrical interpretation ft is the ratio of thickness change averaged over the full length i to the change at the terminus although both u and f relate to dynamic processes local to the terminus zone the ratio f u and therefore tm are insensitive to details of the terminus dynamics in contrast to conclusions derived from some simplified kinematic wave models a more robust estimate of tm independent of terminus dynamics is given by tm h b where h is a thickness scale for the glacier and b is the mass balance rate negative at the terminus we suggest that tm for mountain glaciers can be substantially less than the 1o2 103 years commonly considered to be theoretically expected

structural style in a young flexure induced oblique extensional system north western bonaparte basin australia abstract in the north western bonaparte basin north west shelf of australia neogene to recent flexure induced extension superimposed obliquely over the mesozoic rift structures thus the area offers a good opportunity to investigate the dynamics and architecture of oblique extension fault systems analysis of basin scale 2d and 3d seismic data along the vulcan sub basin shows that neogene deformation produced a new set of extensional en echelon faults at places accompanied by the reactivation of the mesozoic faults the pre existing mesozoic structures strongly control the distribution of the neogene recent deformation both at regional and local scales main controls on the neogene recent fault style density and segmentation linkage include 1 the orientation of the underlying mesozoic structures 2 the obliqueness of the younger extension relative to the rift inherited faults and 3 the proximity to the timor trough three types of vertical relationships have been observed between mesozoic and neogene recent faults hard linkages seems to develop when both fault systems trend parallel therefore increasing risks for trap integrity it is suggested that the orientation of maximum horizontal stress s hmax relative to the mesozoic faults forming hydrocarbon traps is critical for their potential seal leak behaviour stratigraphic growth across the faults indicates that main fault activity occurred during the plio pleistocene which corresponds to the timing of tectonic loading on timor island and the development of lithospheric flexure synchronism of normal faulting with flexural bending suggests that extensional deformation on the descending australian margin accompanied the formation of the timor trough

solar and proxy sensitivity imprints on paleohydrological records for the last millennium in west central europe this paper presents a lake level record established for the last millennium at lake saint point in the french jura mountains a comparison of this lake level record with a solar irradiance record supports the hypothesis of a solar forcing of variations in the hydrological cycle linked to climatic oscillations over the last millennium in west central europe with higher lake levels during the solar minimums of oort around ad 1060 wolf around ad 1320 sporer around ad 1450 maunder around ad 1690 and dalton around ad 1820 further comparisons of the saint point record with the fluctuations of the great aletsch glacier swiss alps and a record of rhone river floods from lake bourget french alps give evidence of possible imprints of proxy sensitivity on reconstructed paleohydrological records in particular the great aletsch record shows an increasing glacier mass from ad 1350 to 1850 suggesting a cumulative effect of the little ice age cooling and or a possible reflection of a millennial scale general cooling until the mid 19th century in the northern hemisphere in contrast the saint point and bourget records show a general trend toward a decrease in lake levels and in flood magnitude anti correlated with generally increasing solar irradiance

kinematic significance of sediment filled fissures in the north mountain basalt fundy rift basin nova scotia canada abstract numerous sediment filled fissures are present near the upper surface of the north mountain basalt 202 ma of the fundy basin which formed during triassic jurassic rifting the fissures are infilled with the same clastic material comprising the basal parts of the overlying earliest jurassic age sedimentary formations which accumulated less than 200 k y after the cooling of the basalt nearly all of the 1368 fissures measured in this study are planar to sub planar and are sub vertical after correcting the basalt flows to paleo horizontal the fissures typically formed along preexisting columnar joints within the basalt northeast striking fissures generally define a preferred orientation and commonly are wider than other fissures the sediment filled fissures therefore indicate earliest jurassic age nw se extension this extension direction is consistent with that indicated by the ne striking shelburne diabase dike the attitude of mesoscopic faults and the geometry of the fundy rift basin thus sediment filled fissures by themselves can serve as useful kinematic indicators and place tight constraints on the relative timing of extension

pattern and forcing of northern hemisphere glacier variations during the last millennium time series depicting mountain glacier fluctuations in the alps display generally similar patterns over the last two centuries as do chronologies of glacier variations for the same interval from elsewhere in the northern hemisphere episodes of glacier advance consistently are associated with intervals of high average volcanic aerosol production as inferred from acidity variations in a greenland ice core advances occur whenever acidity levels rise sharply from background values to reach concentrations 1 2 equiv h kg above background a phase lag of about 10 15 yr equivalent to reported response lags of alpine glacier termini separates the beginning of acidity increases from the beginning of subsequent ice advances a similar relationship but based on limited and less reliable historical data and on lichenometric ages is found for the preceding 2 centuries calibrated radiocarbon dates related to advances of non calving and non surging glaciers during the earlier part of the little ice age display a comparable consistent pattern an interval of reduced acidity values between about 1090 and 1230 a d correlates with a time of inferred glacier contraction during the medieval optimum the observed close relation between noothern hemisphere glacier fluctuations and variations in greenland ice core acidity suggests that sulfur rich aerosols generated by volcanic eruptions are a primary forcing mechanism of glacier fluctuations and therefore of climate on a decadal scale the amount of surface cooling attributable to individual large eruptions or to episodes of eruptions is simlar to the probable average temperature reduction during culminations of little ice age alacier advances ca 0 5 1 2 c as inferred from depression of equilibrium line altitudes

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

k ar illite and apatite fission track constraints on brittle faulting and the evolution of the northern norwegian passive margin abstract determining the timing of post caledonian brittle faulting in northern norway is important for the understanding of the extensional tectonic evolution of the north norwegian continental margin fault gouges from the troms and vesteralen regions of northern norway yield carboniferous to permian and carboniferous to cretaceous k ar illite ages respectively the results show a contrast in fault activity and exhumation between the troms and the vesteralen regions while major faulting in the troms region appears to have ceased after the permian faulting event faulting continued into at least the cretaceous in the vesteralen region the findings highlight the importance of a widespread permian tectonic event followed by a distinct southwestward migration of post permian tectonic activity on the north norwegian passive margin late triassic to early jurassic apatite fission track ages do not show significant age offsets across major fault zones in troms indicating that most or all of fault activity took place prior to the late triassic the thermal history models are consistent and indicate continuous cooling to about 60 c in the late permian triassic

cycles and shifts 1 300 years of multi decadal temperature variability in the gulf of alaska the gulf of alaska goa is highly sensi tive to shifts in north pacific climate variability here we present an extended tree ring record of january september goa coastal surface air temperatures using tree ring width data from coniferous trees growing in the mountain ranges along the goa the reconstruction 1514 1999 based on living trees ex plains 44 of the temperature variance although as the number of chronologies decreases back in time this value decreases to and remains around 30 before 1840 verification of the calibrated models is however robust utilizing sub fossil wood we extend the goa reconstruction back to the early eighth century the goa reconstruction correlates significantly 95 cl with both the pacific decadal oscillation index 0 53 and north pacific index 0 42 and therefore likely yields important information on past climate variability in the north pacific region intervention analysis on the goa reconstruction identifies the known twentieth century climate shifts around the 1940s and 1970s al though the mid 1920s shift is only weakly expressed in the context of the full 1 300 years record the well studied 1976 shift is not unique multi taper method spectral analysis shows that the spectral properties of the living and sub fossil data are similar with both records showing significant 95 cl spectral peaks at 9 11 13 14 and 18 19 years singular spectrum analysis identifies in order of importance significant oscillatory modes at 18 7 50 4 38 0 91 8 24 4 15 3 and 14 1 years the amplitude of these modes varies through time it has been suggested minobe in geo phys res lett 26 855 858 1999 that the regime shifts during the twentieth century can be explained by the interaction between pentadecadal 50 4 years and bi decadal 18 7 years oscillatory modes removal of these two modes of variance from our goa time series does indeed remove the twentieth century shifts but many are still identified prior to the twentieth century our analysis suggests that climate variability of the goa is very complex and that much more work is required to understand the underlying oscillatory behavior that is observed in instrumental and proxy records from the north pacific region

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

structural analysis of fault populations along the oblique ultra slow spreading knipovich ridge north atlantic ocean 74 30 n 77 50 n abstract the knipovich ridge 73 30 78 40 n is an extreme end member of the mid ocean ridge spreading system both in terms of spreading rate fault population characteristics conform to observational and experimental analyses of oblique rifting and spreading systems for the ridge as a whole faults in the axial region are short straight isolated not linked into complex fault zones and exhibit length scaling relationships characteristic of young and active fault systems faults are generally oblique to both the ridge axis and the spreading direction and orientations vary systematically with angle between ridge and spreading direction along axis analysis reveals the influence of axial segmentation on fault population characteristics segment centers are dominated by faults perpendicular and sub perpendicular to plate motion with longer characteristic length and generally lower fracture density conversely segment ends are dominated by faults striking oblique to plate motion with shorter characteristic length and generally higher fracture density we infer that faulting in segment centers is strongly influenced by the mechanical effects of dike intrusion perpendicular to plate motion while faulting in segment ends is controlled by the mechanics of oblique rifting non transform discontinuities and or accommodation zones the contrasts between these distinct structural and mechanical settings along the ridge axis are accentuated by the high obliquity and ultra slow spreading rate of this spreading system

high frequency holocene glacier fluctuations in new zealand differ from the northern signature understanding the timings of interhemispheric climate changes during the holocene along with their causes remains a major problem of climate science here we present a high resolution 10be chronology of glacier fluctuations in new zealand s southern alps over the past 7000 years including at least five events during the last millennium the extents of glacier advances decreased from the middle to the late holocene in contrast with the northern hemisphere pattern several glacier advances occurred in new zealand during classic northern warm periods these findings point to the importance of regional driving and or amplifying mechanisms we suggest that atmospheric circulation changes in the southwest pacific were one important factor in forcing high frequency holocene glacier fluctuations in new zealand

an experimental study of the secondary deformation produced by oblique slip normal faulting we have used scaled clay models to define the secondary deformation produced by oblique slip normal faulting in the models the master fault beneath the clay layer dips 45 degrees and strikes at a 45 degrees angle relative to the heave direction i e the horizontal component of the displacement direction thus the master fault has both normal dip slip and strike slip components of displacement the modeling results show the following 1 the fault patterns produced by oblique slip normal faulting vary significantly with depth secondary faults that strike obliquely to the master fault trend are more abundant near the top of the clay layer whereas secondary faults that are subparallel to the master fault trend are more abundant at depth 2 a single episode of oblique slip normal faulting produces two populations of secondary faults that have different trends and ages secondary faults that strike obliquely to the master fault trend are more abundant during the early stages of the experiments whereas secondary faults that strike subparallel to the master fault trend are more abundant during the later stages of the experiments 3 relay ramps between overlapping secondary synthetic normal faults are wide and temporally persistent in oblique slip models the ramps are cut by numerous small scale normal faults that are subparallel to the ramp bounding faults cross faults are uncommon and begin to develop only during the final stages of the experiments 4 both map and cross section data are necessary to distinguish among the deformation patterns produced by strike slip oblique slip and dip slip faulting the map views of oblique slip models closely resemble those of strike slip models in both models many of the secondary faults strike obliquely to the master fault trend these map views however differ considerably from those of dip slip models in which most of the secondary faults strike subparallel to the master fault trend alternatively the cross sectional views of oblique slip models are similar to those of dip slip models in both models a highly faulted extensional forced fold develops these cross sectional views are dissimilar to those of strike slip models which show no appreciable folding and no change of regional level

volcanic forcing of climate over the past 1500 years an improved ice core based index for climate models 1 understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate we have investigated one of the most important natural causes of climate change volcanic eruptions by using 54 ice core records from both the arctic and antarctica our recently collected suite of ice core data more than double the number of cores ever used before reduces errors inherent in reconstructions based on a single or small number of cores which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects we extracted volcanic deposition signals from each ice core record by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation we then studied the spatial pattern of volcanic sulfate deposition on greenland and antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month latitude and altitude for the past 1500 years we estimated the uncertainties associated with the choice of volcanic signal extraction criteria ice core sulfate deposition to stratospheric loading calibration factor and the season for the eruptions without a recorded month we forced an energy balance climate model with this new volcanic forcing data set together with solar and anthropogenic forcing to simulate the large scale temperature response the results agree well with instrumental observations for the past 150 years and with proxy records for the entire period through better characterization of the natural causes of climate change this new data set will lead to improved prediction of anthropogenic impacts on climate the new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years as a function of latitude altitude and month is available for download in a format suitable for forcing general circulation models of the climate system

late holocene glacial history of the copper river delta coastal south central alaska and controls on valley glacier fluctuations abstract fluctuations of four valley glaciers in coastal south central alaska are reconstructed for the past two millennia tree ring crossdates on 216 glacially killed stumps and logs provide the primary age control and are integrated with glacial stratigraphy ages of living trees on extant landforms and historic forefield photographs to constrain former ice margin positions sheridan glacier shows four distinct phases of advance in the 530s to c 640s in the first millennium a d and the 1240s to 1280s 1510s to 1700s and c 1810s to 1860s during the little ice age lia the latter two lia advances are also recorded on the forefields of nearby scott sherman and saddlebag glaciers comparison of the sheridan record with other two millennia long tree ring constrained valley glacier histories from south central alaska and switzerland shows the same four intervals of advance these expansions were coeval with decreases in insolation supporting solar irradiance as the primary pacemaker for centennial scale fluctuations of mid latitude valley glaciers prior to the 20th century volcanic aerosols coupled atmospheric oceanic systems and local glacier specific effects may be important to glacier fluctuations as supplemental forcing factors for causing decadal scale differences between regions and as a climatic filter affecting the magnitude of advances

wobbly ocean conveyor circulation during the holocene abstract compared to the last glacial period the climate of the holocene has been quite stable however the record does suggest that at high latitudes in the north temperatures have cooled at least since the middle holocene and that this cooling has been modulated by millennial duration fluctuations that culminated in the medieval warm little ice age oscillation in this paper we explore the possibility that these variations were associated with concurrent changes in the strength of the atlantic s conveyor circulation three lines of evidence are considered one involves records that relate directly to ocean operation a second involves the tie between sea ice extent in the northern atlantic and the extent of mountain glaciers in the european alps and in the cordillera of western north america and a third involves evidence for a bipolarity in climate changes in the northern and southern polar regions in addition we look into clues provided by the atlantic multidecadal oscillation amo although at this point no firm conclusion can be drawn the case for ocean involvement is sufficiently strong to merit further attention

transtensional arm of the early mesozoic fundy rift basin penecontemporaneous faulting and sedimentation formed as a major right lateral fault zone during paleozoic collisional orogenies and reactivated as a left oblique system during the early mesozoic the east striking minas fault zone of atlantic canada controlled adjacent sedimentation in the fundy rift basin producing a series of synsedimentary microbasins northeast striking boundary faults of the fundy basin underwent mostly early mesozoic normal slip and are reactivated paleozoic thrusts the adjacent basin has a much thicker section transverse folds and synthetic rider blocks contrasts in structural and stratigraphic styles are a response to local deformation controlled by reactivated fault zones of differing orientation under consistent northwest southeast early mesozoic extension rather than responses to a sequence of changing stress patterns

relation between continental strike slip earthquake segmentation and thickness of the crust 1 high resolution maps of large continental strike slip earthquake surface ruptures show that they are formed of fault segments these segments are bounded by fault bends step overs or combinations of the two the lowest limit in size for such segments may not be relevant in the understanding of earthquake mechanics as it pertains to the granular properties of fault zones the maximum limit in segment length however is important as it is directly relates to the maximum extent of seismic rupture to measure the length of the segments a new quantitative method based on piecewise linear fitting is developed and is used to automatically retrieve segments from earthquake rupture maps next this approach is tested against a set of ten continental strike slip earthquake ruptures derived from similar high quality maps the test suggests that segments have a maximum length of 18 km independent of regional tectonic setting slip inversions for earthquakes based on seismological and or geodetic data most often are not unique and can show some variability even for one particular event some basic characteristics however such as total moment release or general source geometry seem to persist that are relevant to earthquake mechanics measurements of the maximum horizontal extent of individual slip patches derived from seismic source inversion for strike slip ruptures show that their strike dimension does not increase infinitely with magnitude but instead reaches a maximum value of 25 km these two independent lines of observations complemented by earlier data and analog experiments suggest that it is the thickness of the seismogenic crust that controls the structural scaling of the length of seismic segments and that it is independent of the ultimate size of individual earthquakes

3d geometry and kinematics of the lassee flower structure implications for segmentation and seismotectonics of the vienna basin strike slip fault austria abstract the active vienna basin strike slip fault consists of several segments which differ both in their kinematic and seismotectonic properties mapping of industrial 2d seismic geomorphological data and quaternary basin analysis proves that active deformation uses miocene faults this is shown in detail for the negative flower structure of the lassee fault segment which developed during the miocene and was reactivated in the quaternary the flower structure consists of riedel type splay faults which merge in a major branch line at the top of the principle displacement zone pdz in approximately 3 5 5 5 km depth mapping the pdz of the vienna basin strike slip fault in the continuations of the lassee segment reveals several fault segments which differ by the orientation of the pdz ne and nne striking segments with releasing bend geometries are associated with quaternary basins these segments are delimited by fault bends where the strike of the pdz changes by angles of 20 35 and are connected by ene striking segments orientated parallel to the displacement vector among the releasing bends the lassee segment is subject to increased extension due to the high angle ca 35 between the general slip vector and the orientation of the segment resulting extension seems to be accommodated by both the negative flower structure and normal faults which branch off from the pdz south of the lassee releasing bend the significant fault bends of 20 35 delimiting the geometrical fault segments are regarded to act as impediments during dynamic rupture propagation hence fault segment dimensions can be used for constraining the maximum fault surfaces which can break during single earthquakes the data on active kinematics and fault segmentation of the vienna basin strike slip fault system therefore may serve as a basic input for future assessments of maximum credible earthquake estimates

growth and linkage of a complex oblique slip fault zone in the pearl river mouth basin northern south china sea abstract oblique slip faults are ubiquitous in sedimentary basins but have been largely neglected relative to their dip slip counterparts case studies of oblique slip faults are very limited in this study we used 3d seismic data tied to well control to investigate the geometry kinematic characteristics growth and linkage and tempo spatial evolution of a complex oblique slip growth fault zone in the pearl river mouth basin prmb of the northern continental margin south china sea scs the e w oriented 30 5 km long fault zone consists of two superimposed oblique slip fault systems the lower fault system is an integrated zig zag fault consisting of three ene wsw to e w striking right stepping sinistral en echelon fault segments which were hard linked by two nw se trending fault segments while the upper fault system is composed of nine wnw ese striking left stepping dextral en echelon component faults which had overlapping fault tips and were partly hard linked by breaching of the relay zones the lower and upper fault systems were activated in the eocene and the oligocene to pliocene which respectively correspond to the syn rift and post rift stages in the prmb the fault throws up to 288 m and activity rates up to 34 5 m ma of the upper fault system are overall much less than those of its lower counterpart reactivation of the lower syn rift fault system shows clear influence on the development of post rift en echelon fault segments a four stage evolution model of the oblique slip fault zone was presented

effect of block rotation on fault sealing an example in dongpu sag bohai bay basin china abstract pre existing faults or early formed faults may be reactivated or locked in subsequent evolution in a rift basin the reactivation or sealing of a fault affects sedimentation in the related fault block and in turn controls the accumulation of oil and gas based on fault mechanics of reactivation this paper established equations denoting the angle range of the reactivated faults or frictional sliding faults by using mohr stress circles the results were applied to explain the sealing property of pre existing faults or early formed faults in dongpu sag in the dongpu sag reactivation or sealing of the faults in fault blocks is supposed due to the rotation of the fault block which was caused by the activity of high order faults for quantitative calculation of dip range for activated faults the sum of the maximum and minimum principal stresses were determined by acoustic emission experiment based on the kaiser effect of rocks and the cohesion and inner frictional angle of rocks were measured by rock physical experiment the calculations show when the dips of early formed faults are from 87 to 45 the faults will remain activation in the subsequent deformation otherwise the faults will be locked as sealing faults the results of petroleum exploration show that the peak dips of sealing faults are from 36 to 40 and the most of sealing faults are those with dip angles less than 46 50 these results indicate that a shallower fault is of better sealing property in oil and gas reservoirs than a steeper fault in dongpu sag

the three dimensional geometry of relay zones within segmented normal faults abstract individual normal faults are rarely single planar surfaces and often comprise arrays of fault segments arising from the earliest stages of fault propagation current models for the geometry and formation of relay zones between adjacent fault segments have been informed mainly by 2d analysis from either maps or cross sections observed in outcrop and to a lesser extent by the analysis of relay zones from 3d seismic reflection data using high quality 3d seismic reflection datasets from a selection of sedimentary basins we investigate fundamental characteristics of segmentation from the analysis of 67 normal faults with modest displacements

tectonic evolution of the penglai 7 6 structure and its implications for petroleum exploration in a releasing bend of a strike slip fault system tan lu fault zone east china abstract the penglai 7 6 pl7 6 structure is located on the tan lu fault zone a huge fault zone in east asia tectonism of the tan lu fault zone produced complex structural deformation and was an important factor in petroleum accumulation three dimensional seismic data were employed to document the structural geometry and evolutionary process of the pl7 6 structure and implications for petroleum exploration in a releasing bend of a strike slip fault system were discussed systematic analysis of the seismic data indicates that the main fault the bd2 fault of the tan lu fault system slipped right laterally during the cenozoic strike slip movement of the bd2 fault peaked during deposition of e 1 2 k to e 3 d 3 and decreased largely in intensity during e 3 d 1 2 deposition in the neogene and quaternary the bd2 fault was reactivated formation of the bodongnan low uplift is related to the connection between the bodongnan low uplift n and bodongnan low uplift s the bodongnan low uplift n is represented by an anticline produced by strike slip movement of the bd2 fault and the bodongnan low uplift s is represented by the relatively uplifted strata in the vicinity of an extensional fault the bd3 fault the pl7 6 structure developed above a releasing bend formed by the subsequent strike slip movement of the curved bd3 fault orientations of the shallow faults in the pl7 6 structure are not only associated with the lower bd3 fault but also controlled by the basement high unlike traditional releasing bends that are generally disadvantage to petroleum accumulation due to the lower structural elevation in the center the releasing bend in the pl7 6 structure is favorable for petroleum accumulation because of the three reasons 1 adjacent to generative kitchens 2 located on a regional structural high and 3 served by the releasing bend related faults acting as conduits for vertical petroleum migration

fluidization in dry landslides this paper aims at determining the physical properties affecting the distance travelled by landslides with dry particles and elucidating the mechanism of the properties affecting landslide fluidization the procedure is as follows laboratory landslide experiments were conducted to verify the simulation model which was proposed to represent the movement of landslides further sensitivity analysis for some physical properties affecting the travel distance were conducted using this model the simulation model could identify the coordinates velocity and angular velocity for every particle in three dimensional space and the kinetic energy of particles consumed by inelastic and frictional collision with each other in the model the travel distances of landslides simulated by the model were verified by laboratory experiments statistically where the physical properties for the particles and slope angle were changed then sensitivity analysis for the physical properties were conducted using the model to clarify the effect of the properties on the travel distance it was proven that there were no significant differences between the travel distances represented by the simulation model and those found experimentally using statistical analysis i e the simulation model could represent virtual real landslides from the sensitivity analysis using the simulation model the travel distances were positively correlated to volume or number of particles and negative correlated to the slope angle kinetic friction and rolling friction of particles when the initial potential energies were the same the mass of particles of equal size did not affect the distance travelled as the number of particles increased the simulated travel distances tended to be longer compared with theoretical travel distances calculated using the friction between particles and the slope consequently we could determine the distance of the lumped mass model as being critical between fluidized and non fluidized landslides

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

salt diapir reactivation and normal faulting in an oblique extensional system vulcan sub basin nw australia oblique extension and salt diapirism have their own distinct mechanisms that control the geometry and kinematics of structures in this study we document a geological phenomenon from the vulcan sub basin in nw australia that combines these processes a salt diapir reactivated in an oblique extensional system detailed structural analysis of this natural example with a focus on normal fault systems allows characterization of the oblique extensional system and investigation of how the pre existing structural fabrics and salt diapir control deformation and interact with each other under oblique extension after comparison with forward modelling results and using constraints from geological evidence our fault strike analysis indicates that the neogene flexural extension orientation in the oblique extensional system is around 347 revealing a perpendicular relationship between extension direction and fault strikes from the deformation zone the salt diapir reactivated during neogene extension strongly influences local structure in the oblique extensional system by altering fault strikes stepping patterns deformation zone width and fault density indicative of a stress strain concentration effect of the salt diapir owing to its extremely low strength these results provide valuable insights into the understanding of oblique extensional systems the geomechanical role of salt during extension and the neogene tectonic evolution of nw australia supplementary material dominant seismic frequency analysis uninterpreted seismic profiles additional structural and isochron maps a 3d view of fault systems and original measurements of the fault system are available at http doi org 10 6084 m9 figshare c 3148321

experiments on faulting in a two layer cover sequence overlying a reactivated basement fault with oblique slip abstract two series of experiments were undertaken to investigate the development of faults in a cover sequence overlying a reactivated basement fault with oblique slip the experiments represent physical models properly scaled to account for gravitational forces brittle behaviour of the upper cover and ductile behaviour of evaporites in the lower cover models were made with a coulomb layer sand overlying a newtonian ductile layer silicone putty in each series the thickness of the silicone layer was varied from each experiment to the next in all normal wrench experiments a domain of faults appeared in the brittle layer vertical offsets were mostly of normal sense but some reverse faults occurred in experiments with thick silicone layers the thicker the silicone the wider the fault domain the deformation zone was in all cases limited to the faulted domain in the reverse wrench experiments discrete reverse riedel faults appeared without a silicone layer as the silicone layer became thicker the importance of the reverse faults diminished with the thickest layer of silicone 3 cm no faults appeared in the overburden but a monoclinal flexure accommodated the dip slip component in the presence of silicone the deformation zone was not limited to a faulted domain and the strike slip component was accommodated by a bulk shearing of the overburden in the uplifted compartment these experiments demonstrate that in basins deformed in oblique slip mode any deformation that is localized along discrete faults at the basement level becomes distributed over a much wider zone of overburden when this overlies an interval of evaporites

steeply dipping extension fractures in the newark basin new jersey abstract late triassic and early jurassic bedrock in the newark basin is pervasively fractured as a result of mesozoic rifting of the east central north american continental margin tectonic rifting imparted systematic sets of steeply dipping en echelon mode i extension fractures in basin strata including ordinary joints and veins these fractures are arranged in transitional tensional arrays resembling normal dip slip shear zones they contributed to crustal stretching sagging and eventual faulting of basin rift deposits extension fractures display progressive linkage and spatial clustering that probably controlled incipient fault growth they cluster into three prominent strike groups correlated to early intermediate and late stage tectonic events reflecting about 50 60 of counterclockwise rotation of incremental stretching directions finite strain analyses show that extension fractures allowed the stretching of basin strata by a few percent and these fractures impart stratigraphic dips up to a few degrees in directions opposing fracture dips fracture groups display three dimensional spatial variability but consistent geometric relations younger fractures locally cut across and terminate against older fractures having more complex vein cement morphologies and bed normal folds from stratigraphic compaction a fourth youngest group of extension fractures occur sporadically and strike about e w in obliquely inverted crustal blocks a geometric analysis of overlapping fracture sets shows how fracture groups result from incremental rotation of an extending tectonic plate and that old fractures can reactivate with oblique slip components in the contemporary compressive stress regime

tectonic evolution of the fundy rift basin canada evidence of extension and shortening during passive margin development seismic and field data show that the fundy rift basin of southeastern canada experienced two distinct episodes of deformation during mesozoic time the first episode during middle triassic to early jurassic time was extensional rifting associated with nw se extension reactivated ne trending paleozoic compressional structures as normal faults forming the northwestern boundary faults of the fundy basin displacements on the low angle boundary faults locally exceeded 10 km rifting also reactivated east trending paleozoic compressional structures as oblique slip faults with normal and sinistral strike slip components forming the northern boundary faults of the fundy basin several kilometers of sediments and lava flows filled the basin during rifting the second deformational episode occurred during or after early jurassic time and probably before or during early cretaceous time inversion associated with nw se shortening occurred along all faulted margins of the fundy basin the northwestern boundary faults experienced several kilometers of reverse displacement broad anticlines developed within their hanging walls and the fundy basin acquired its synclinal form the northern boundary faults of the fundy basin became oblique slip faults with reverse and dextral strike slip components gentle synclines tight anticlines and faults with reverse separation deformed the synrift strata near the northern margin of the fundy basin neither collision nor subduction zones existed near the fundy basin during mesozoic time hence we believe that tectonic processes associated with seafloor spreading e g incipient ridge push forces continental resistance to plate motion produced the shortening in the fundy basin shortening occurred during the transition from rifting to drifting as north america separated from northern africa and or during the early stages of drifting as the seafloor spreading centers of the north atlantic propagated northward

a double cycle lake basin formed in extensional to transtensional setting the paleogene nanpu sag bohai bay basin china abstract it has been known that both extensional and transtensional tectonics commonly trigger a one cycle evolution of lake sediments but lake cycle development co controlled by extensional and transtensional tectonics still need identification here we report a double cycle of lake sediments formed in extensional to transtensional phases in the paleogene nanpu sag of the bohai bay basin china the sag successively experienced five phases of lake type evolution characterized by 1 overfilled 2 balanced fill 3 overfilled 4 balanced fill and 5 overfilled extensional tectonics was responsible for the opening of the basin and the initial creation of accommodation 1st through 3rd phase next subsidence increased again through transtensional tectonics resulting in the creation of new accommodation 4th 5th phases investigations show this double cycle lake type evolution is also present in other lake basins with similar tectonic settings e g both extensional and transtensional tectonics a different exploration and exploitation strategy should be devoted to the double cycle evolution of lake basins controlled by extensional to transtensional tectonics in comparison to the single cycle evolution in extensional or transtensional lake basins

correlation of late quaternary moraines impact of climate variability glacier response and chronological resolution abstract the last decade has seen a global surge in the number and resolution of well dated geomorphological reconstructions of mountain glacier fluctuations and former ice sheet extents this has been facilitated by the widespread deployment of large samples of terrestrial cosmogenic nuclide dating tcnd allowing more sophisticated probability analyses for reducing the statistical uncertainty of moraine ages and testing of correlations at local regional and hemispheric scales geochronological advances in the field laboratory and on model calibration have taken place in parallel with modelling of palaeoclimate based on glacier reconstructions and of glacier sensitivity to temperature and precipitation forcing in spite of these advances basic conceptual issues remain this review questions whether the technical leap forward in dating has encouraged us to over reach our interpretive limits particularly in terms of the concept and practice of correlation we propose that to enable reliable correlation glacier chronologies should first be examined for their climatic integrity spatial coherence and chronological robustness even with excellent dating interpretive complexity remains due to complex climate signals and glacier response characteristics and to erosion censoring of the landform record all are issues which must be addressed to avoid either spurious lumping correlation or splitting differentiation of glacier chronologies and thus misinterpretation of the climatic significance of reconstructed glacier advances we suggest that the reliability of correlation is no better than the weakest link in the chain of reasoning which connects climatic fluctuations with dated landforms and sediments improved dating means that poor chronological resolution is less likely to be the limiting factor for correlation but shifts the focus onto other less quantifiable sources of uncertainty these conceptual statements are exemplified with reference to holocene glacial chronologies of contrasting mid latitude environments in southern norway iceland and new zealand

holocene and latest pleistocene alpine glacier fluctuations a global perspective abstract alpine glacier fluctuations provide important paleoclimate proxies where other records such as ice cores tree rings and speleothems are not available about 20 years have passed since a special issue of quaternary science reviews was published to review the worldwide evidence for holocene glacier fluctuations since that time numerous sites have been discovered new dating techniques have been developed and refined climatic hypotheses have been proposed that contribute to a better understanding of earth s climate system this special volume includes 12 papers on holocene and latest pleistocene alpine glacier fluctuations that update the seven review papers from 1988 major findings of these 12 papers include the following many but certainly not all alpine areas record glacier advances during the younger dryas cold interval most areas in the northern hemisphere witnessed maximum glacier recession during the early holocene with some glaciers disappearing although a few sites yield possible evidence for advances during the 8 2 ka cooling event in contrast some alpine areas in the southern hemisphere saw glaciers reach their maximum post glacial extents during the early to middle holocene in many parts of the globe glaciers reformed and or advanced during neoglaciation beginning as early as 6 5 ka neoglacial advances commonly occurred with millennial scale oscillations with many alpine glaciers reaching their maximum holocene extents during the little ice age of the last few centuries although the pattern and rhythm of these glacier fluctuations remain uncertain improved spatial coverage coupled with tighter age control for many events will provide a means to assess forcing mechanisms for holocene and latest pleistocene glacial activity and perhaps predict glacier response to future impacts from human induced climate change

holocene glacier fluctuations in alaska abstract this review summarizes forefield and lacustrine records of glacier fluctuations in alaska during the holocene following retreat from latest pleistocene advances valley glaciers with land based termini were in retracted positions during the early to middle holocene neoglaciation began in some areas by 4 0 ka and major advances were underway by 3 0 ka with perhaps two distinct early neoglacial expansions centered respectively on 3 3 2 9 and 2 2 2 0 ka tree ring cross dates of glacially killed trees at two termini in southern alaska show a major advance in the ad 550s 720s the subsequent little ice age lia expansion was underway in the ad 1180s 1320s and culminated with two advance phases respectively in the 1540s 1710s and in the 1810s 1880s the lia advance was the largest holocene expansion in southern alaska although older late holocene moraines are preserved on many forefields in northern and interior alaska tidewater glaciers around the rim of the gulf of alaska have made major advances throughout the holocene expansions were often asynchronous with neighboring termini and spanned both warm and cool intervals suggesting that non climatic factors were important in forcing these advances however climatic warming appears to have initiated most rapid iceberg calving retreats large glaciers terminating on the forelands around the gulf of alaska may have had tidewater termini early in the holocene but have progressively become isolated from the adjacent ocean by the accumulation and subaerial exposure of their own sediments

shear angle and amount of extension calculations for normal faults emanating from a detachment implications on mechanisms to generate rollovers abstract the reconstruction restoration modelling of normal faults both listric and planar emanating from a detachment at depth and their associated rollover folds using the vertical or inclined shear method is widely utilized because its simplicity and the information it can provide however it has a rather serious issue derived from the uncertainty about the shear angle the type of shear and the amount of extension that should be employed in each situation here we describe a new methodology that using easily acquired input data allows estimation of whether the shear was vertical antithetic or synthetic and the values for both the shear dip and the amount of extension these calculations rely on the use of graphs of throw versus heave for different horizons affected by the normal fault and the associated rollover and are checked using an area based method which permits the determination of whether these values are correct these graphs may be used as a predictive tool or as a guide to show how the assumptions deviate such as distinguishing quickly whether other mechanisms apart from vertical inclined shear took place the effects of syn extension sedimentation and reverse fault reactivation on the proposed method are also examined the analysis of experimental and natural examples shows that the initiation of some rollovers with a component of fault propagation and or drag folding and or development of a crestal collapse graben cause the estimated shear dips to be smaller than the actual values and the amounts of extension to be greater in addition these analyses show that the shear dip may increase with increasing extension

evolving efficiency of restraining bends within wet kaolin analog experiments restraining bends along strike slip fault systems evolve by both propagation of new faults and abandonment of fault segments scaled analog modeling using wet kaolin allows for qualitative and quantitative observations of this evolution to explore how bend geometry affects evolution we model bends with a variety of initial angles from 0 for a straight fault to 30 high angle restraining bends 20 overcome initial inefficiencies by abandoning unfavorably oriented restraining segments and propagating multiple new inwardly dipping oblique slip faults that are well oriented to accommodate convergence within the bend restraining bends with 0 15 maintain activity along the restraining bend segment and grow a single new oblique slip fault on one side of the bend in all restraining bends the first new fault propagates at 5 mm of accumulated convergence particle image velocimetry analysis provides a complete velocity field throughout the experiments from these data we quantify the strike slip efficiency of the system as the percentage of applied plate parallel velocity accommodated as slip in the direction of plate motion along faults within the restraining bend bends with small initially have higher strike slip efficiency compared to bends with large although they have different fault geometries all systems with a 5 cm bend width reach a steady strike slip efficiency of 80 after 50 mm of applied plate displacement these experimental restraining bends resemble crustal faults in their asymmetric fault growth asymmetric topographic gradient and strike slip efficiency

new constraints on the timing of flexural deformation along the northern australian margin implications for arc continent collision and the development of the timor trough abstract numerous extensional faults offset the passive margin strata of the northern bonaparte basin this extensional deformation has been attributed to lithospheric flexure of the descending australian plate in an overall convergence setting here we use an extensive 2d and 3d seismic dataset calibrated with well biostratigraphy and strontium sr isotope age data to constrain the timing of deformation along the northern australian margin during the neogene analysis of fault throw and differential thickness variations give new insights on the propagation and slip history of the faults along dip throw profiles exhibit d shape distributions skewed towards the top positive throw gradients above the throw maxima coinciding with intervals of growth strata indicate multiphase fault activity results indicate that post rift extensional deformation initiated during the latest miocene ca 6 ma the development of the modern timor trough as a foreland basin and cartier trough also commenced during this period a second episode of increased tectonic activity occurred around the pliocene quaternary boundary ca 3 ma and the deformation continued intermittently to the present day these new results are in agreement with the timing of initiation of collision between the australian plate and the banda arc and uplift of the timor island recently derived from stratigraphic analysis in timor these regional tectonic events have profoundly affected the paleogeography of the timor sea and may explain major changes in oceanic circulation and climate during the neogene

experimental formation of brittle structural assemblages in oblique divergence abstract a series of experiments is reported in which brittle minor structures are initiated in narrow deformation zones in clay under conditions of kinematically controlled oblique divergent displacement nineteen settings of boundary displacement angle were used from pure wrench to pure divergence under conditions favouring either faults dry experiments or extension fractures wet experiments pure wrench produced the well known assemblage of riedel strike slip faults whereas experiments in pure divergence produced conjugate arrays of normal faults and extension fractures with a dihedral angle of 30 bisected by the direction of the zone as has been described in rift zones experiments with boundary displacements at intermediate settings show a continuum of structural orientations and dihedral angles between these two extremes a boundary between assemblages dominated by strike slip faults and extensional faults was found at a displacement angle of 45 from the deformation zone these results are interpreted kinematically in terms of 1 principal axes of infinitesimal incremental strain 2 material dilatancy control on shear structure dihedral angles and 3 whether the vertical strain in divergent wrench settings is a thickening strike slip assemblage or a thinning normal fault assemblage

how do the properties of a pre existing normal fault population influence fault development during a subsequent phase of extension abstract we use scaled experimental analog models to investigate how the properties of a population of pre existing normal faults influence fault development during a subsequent phase of extension in the models a homogeneous layer of wet clay undergoes two phases of extension whose extension directions differ by 45 to vary the properties of the first phase fault population we vary the magnitude of the first phase extension as the magnitude of the first phase extension increases the number average and maximum length and average and maximum displacement of the first phase normal faults increase for a poorly developed first phase fault population new normal faults which strike perpendicular to the second phase extension direction form during the second phase for a well developed first phase fault population many first phase normal faults are reactivated as oblique slip faults during the second phase new normal faults also form these second phase normal faults are shorter and have displacement maxima adjacent to the reactivated first phase faults they are less likely to cut the pre existing first phase faults than second phase normal faults that form in models with a less developed first phase fault population in all models pre existing faults serve as nucleation sites for new faults in models with a well developed first phase fault population the pre existing faults also act as obstacles to the propagation of the second phase normal faults fault geometries in the models vary considerably parallel zig zag or intersecting fault geometries develop depending on whether the first phase fault population is poorly moderately or well developed respectively

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

the effect of cover composition on extensional faulting above re activated basement faults results from analogue modelling abstract analogue models were used to investigate differences in deformation between sedimentary cover sequences of contrasting composition above reactivated basement faults during extension two types of model arrangements were used the first represented clastic sediments directly overlying faulted basement and the second represented a basal ductile layer in an overburden overlying the same faulted basement the basement configuration consisted of faults both oblique and orthogonal to the bulk extension direction particular attention was paid to the resulting map view fault patterns in experiments without a basal ductile layer in the overburden grabens only developed in areas directly above basement faults in section cover faults above oblique basement faults curved in profile and in places exhibited reverse movement at shallow depth in experiments involving a ductile layer at the base of the overburden faults developed oblique to both the bulk extension direction and the basement faults the resulting fault pattern was influenced by both bulk extension and basement fault reactivation the results indicate that cover sequences that include thick basal ductile layers above reactivated basement faults are more likely to develop faults with strikes perpendicular to the regional extension direction compared to those without faulting in an overburden lacking a basal ductile sequence is more likely to be directly influenced by the underlying reactivated basement faults

variable fault tip propagation rates affected by near surface lithology and implications for fault displacement hazard assessment abstract the fabric of reverse fault zones close to the surface is usually partitioned in between a narrow discrete rupture zone and a more distributed one where folding is predominant this makes quite challenging the adoption of proper setbacks in surface rupture hazard studies for critical facilities or microzoning some of the parameters controlling fault zone fabric are related to mechanics of near surface geology lithology overburden thickness cohesion and water content whose interaction is complex and only partially understood nevertheless these can be seldom measured or derived kinematic models conversely express such an interaction of complex variables as simple synthetic parameters such as the amount of upward propagation of the fault tip for unit of slip usually referred to as the p s ratio propagation on slip here we discuss results on the trishear kinematic inverse modeling of a contractional fault propagation fold at monte netto hill capriano del colle n italy observing a two stage fault and fold growth evolution marked by a significant shift in the p s parameter at this site exceptional sequence of exposures due to ca 10 years of quarry excavations allowed to obtain a series of cross sections across the fault zone we use this detailed high resolution example as a natural analogue for more general large scale surface ruptures involving a thick alluvial cover a very common setting for the siting of critical facilities during the early stage of displacement the fault cut through clast supported fluvial gravels with a high propagation rate p s 7 and a discrete rupture width then during the latest movements of the thrust fault tip propagation slowed down to p s 2 9 as the fault started cutting through several stacked bodies of clays and silty clays pedogenized aeolian silts and overbank deposits causing a pronounced folding of the layers over a wider deformation zone these results strongly suggest that lithological changes in the underlying shallow stratigraphy common in an alluvial plain depositional setting would significantly affect the potential for surface faulting across the same tectonic structure with relevant implications in the fault displacement hazard assessment

neotectonics of the owen fracture zone nw indian ocean structural evolution of an oceanic strike slip plate boundary the owen fracture zone is a 800 km long fault system that accommodates the dextral strike slip motion between india and arabia plates because of slow pelagic sedimentation rates that preserve the seafloor expression of the fault since the early pliocene the fault is clearly observed on bathymetric data it is made up of a series of fault segments separated by releasing and restraining bends including a major pull apart basin at latitude 20 n some distal turbiditic channels from the indus deep sea fan overlap the fault system and are disturbed by its activity thus providing landmarks to date successive stages of fault activity and structural evolution of the owen fracture zone from pliocene to present we determine the durability of relay structures and the timing of their evolution along the principal displacement zone from their inception to their extinction we observe subsidence migration in the 20 n basin and alternate activation of fault splays in the vicinity of the qalhat seamount the present day owen fracture zone is the latest stage of structural evolution of the 20 myr old strike slip fault system buried under indus turbiditic deposits whose activity started at the eastern foot of the owen ridge when the gulf of aden opened the evolution of the owen fracture zone since 3 6 myr reflects a steady state plate motion between arabia and india such as inferred by kinematics for the last 20 myr period the structural evolution of the owen fracture zone since 20 myr including fault segments propagation and migration pull apart basin opening and extinction seems to be characterized by a progressive reorganisation of the fault system and does not require any major kinematics change

three dimensional fault geometries and interactions within experimental models of multiphase extension abstract we use experimental analog models to examine the three dimensional 3 d fault geometries and interactions that develop during two phases of noncoaxial extension in the models a homogeneous layer of wet clay undergoes two phases of extension whose directions differ by 45 the resulting fault pattern varies significantly with depth at shallow levels second phase normal faults accommodate most second phase extension at depth both second phase normal faults and reactivated first phase faults with oblique slip accommodate most second phase extension a variety of interactions occurs between first phase and second phase faults one interaction involves the upward propagation of second phase faults from tips of reactivated blind first phase faults these hybrid faults have deep segments that strike subperpendicular to the first phase extension direction and shallow segments whose strike varies with depth becoming increasingly subperpendicular to the second phase extension direction at shallow levels a second interaction involves the nucleation of second phase normal faults on the surfaces of reactivated first phase faults these splay faults propagate upward and laterally from their nucleation sites into the hanging walls of the first phase faults as they propagate they commonly encounter and link with different first phase faults the resulting composite faults have zigzag geometries in both map and cross sectional views a third interaction involves either the termination of second phase antithetic normal faults against or near first phase faults or the offset of first phase faults by second phase antithetic normal faults the 3 d fault patterns and interactions within our models closely resemble those within the taranaki basin of offshore new zealand and milne point on alaska s north slope

multidisciplinary approach to an extensional syncline model for the mesozoic cameros basin n spain abstract in this paper we explore the possibility of reconstructing the initial geometry of inverted basins using combined geophysical and geological methods seismic reflection profiles paleomagnetism analogue modelling and 3d geometrical analysis these techniques allow for some unknowns in the geometry and evolution of extensional sedimentary basins mainly the normal drag reverse drag geometrical problem to be solved the example chosen for checking these techniques is the cameros basin northern iberian chain formed during the late jurassic early cretaceous and inverted during the tertiary compressional stage according to the reconstruction proposed the cameros basin can be characterised as a lens shaped syncline basin with maximum thickness of deposits of about 8000 m in its depocenter gradually diminishing toward the north and south the extensional geometry of the cameros basin is defined by 1 a large scale growth syncline over the major basement fault with southward dipping beds in the northern basin margin forming a southward opening sedimentary wedge with upward decreasing dip values large scale normal drag geometry 2 roll over anticlines at the contact between the pre rift series against the normal fault limiting the basin smaller scale reverse drag geometry the combined syncline anticline syn extensional structures were characterised by means of paleomagnetic analysis of a remagnetization acquired at the time of extension analogue models indicate that the development of syncline basin geometries in extensional settings as the one interpreted for the cameros basin is closely related to the presence of a detachment level in the pre rift sequence above the main basement faults

oblique rifting at tempe fossae mars this work shows the results of a structural study of the faults observed at the tempe rift northeastern tharsis region mars a new detailed map of faults and fault systems was used to geometrically characterize the fracture architecture of the tempe rift and to measure fault length displacement and spacing data to analyze the spatial distribution of fault centroids and to investigate the fractal nature of fault trace maps a comparison with analog models and the use of conventional techniques of fault population analysis show that the tempe rift was most probably generated under sinistral oblique rifting processes which highlights the importance of the presence of inherited fractures in the tectonic evolution of the noachian crust the angle between the extension direction and the rift axis varies along the tempe rift ranging from 50o 60o at its central southern part to 66o 88o to the southwest fault scaling relationships are similar to those found at midocean ridges on earth with exponential fault length frequency distributions localized inhomogeneous deformation generated weakly interacting faults spanning the entire thickness of the mechanical layer this thickness decreased from southwest to northeast along the rift along with distance from the central part of the tharsis dome

expansion of alpine glaciers in pacific north america in the first millennium a d radiocarbon ages and lichen dated moraines from 17 glaciers in coastal and near coastal british columbia and alaska document a widespread glacier advance during the first millennium a d glaciers at several sites began advancing ca a d 200 300 based on radiocarbon dated overridden forests the advance is centered on a d 400 700 when glaciers along an 2000 km transect of the pacific north american cordillera overrode forests impounded lakes and deposited moraines the synchroneity of this glacier ad vance and inferred cooling over a large area suggest a regional climate forcing and to gether with other proxy evidence for late holocene environmental change during the me dieval warm period and little ice age provide support for millennial scale climate variability in the north pacific region

calendar dated early little ice age glacier advance at robson glacier british columbia canada dendrochronological studies at robson and bennington glaciers have provided the first calendar dating of an early little ice age glacier advance in north america dates derived from in situ stumps indicate that robson glacier began over riding forest between c ad 1142 and 1150 and continued until at least ad 1350 the highest rates of glacier advance c 3 8 m yr 1 occurred between ad 1214 and 1261 based on a series of kill dates from in situ stumps between c ad 1142 1214 and 1261 1350 rates were somewhat lower at c 2 2 5 m yr 1 this glacier advance terminated upvalley of the little ice age maximum position of robson glacier and there is no evidence at this site for glacial events between ad 1350 and 1783 however two smaller glaciers in the robson area and the main tongue of small river glacier have outermost little ice age moraines that date from the first decades of the ad 1700s all glaciers examined in the mount robson area have several well developed moraines dating from the period c

fault patterns associated with extensional fault propagation folding abstract extensional fault propagation drape folds are a common type of structure in rift basins and a number of oil and gas fields produce from these structures the detailed geometry and trap volumes are dependent on the relationship between the basement faults and the overlying folds and associated secondary faults in the sedimentary cover experimental models were used to study the 3 d geometry and secondary fault patterns of drape folds associated with single faults and two or more intersecting faults two layer clay models consisting of stiff and soft clay were used to model the deformation zones in the basement and sedimentary cover respectively extension on single basement faults normal to the direction of extension results in the development of a deformation zone with expanding width in which the fault density initially increases and then remains approximately constant extension on terminating faults results in conical drape folds with faults oblique to the fold axis along the propagating tip basement faults oblique to the direction of extension are characterized by oblique secondary faults along the boundaries of the deformation zone which curve into a direction normal to the extension direction in the center trapdoor fault geometries associated with two or more intersecting faults result in a triangular uplift with maximum relief at the apex the difference in relief between the flanks and the apex is greatest in the case of propagating basement faults en echelon secondary faults initiate on the flanks and extend into the apex area curving into orientations that are closer to normal to the regional direction of extension the width of the fault zone and the total fault length increase with increasing extension the fault density initially increases and then remains approximately constant with increasing extension

influence of preexisting fault fabric on inversion related deformation a case study of the inverted fundy rift basin southeastern canada 1 preexisting zones of weakness significantly influenced the structural development of the fundy basin during rifting and subsequent basin inversion the preexisting fabric consisting of ne striking faults with gentle dips and east striking faults with steeply dipping upper segments and gently dipping lower segments formed during paleozoic and older orogenic activity during mesozoic rifting the preexisting fabric was reactivated creating a border fault system composed of linked ne and east striking extensional fault zones with anomalous dips gentle and steep compared to those of newly formed normal faults during inversion the preexisting fabric was again reactivated as the hanging wall of the composite border fault system moved nne relative to the footwall inversion was highly oblique on the ne striking fault zones producing gentle fault parallel buttress folds and fault perpendicular detachment folds above the low angle fault zones inversion was moderately oblique on the east striking fault zone producing relatively tight fault parallel buttress and detachment folds above the gently dipping lower fault segments and reactivating the steeply dipping upper fault segments as left lateral strike slip faults thus inversion related deformation on the east striking fault zone was partitioned at shallow levels i e partitioned updip our work shows that the geometry of preexisting extensional faults and their obliquity relative to the shortening direction profoundly affect deformation style during basin inversion namely the type of inversion related faults the type and shape of inversion related folds and the distribution of deformation e g updip partitioning depend in part on the geometry of the preexisting extensional faults and the variations in these geometries with depth and along strike

multi segment earthquakes and tsunami potential of the aleutian megathrust abstract large to great earthquakes and related tsunamis generated on the aleutian megathrust produce major hazards for both the area of rupture and heavily populated coastlines around much of the pacific ocean here we use paleoseismic records preserved in coastal sediments to investigate whether segment boundaries control the largest ruptures or whether in some seismic cycles segments combine to produce earthquakes greater than any observed since instrumented records began virtually the entire megathrust has ruptured since ad1900 with four different segments generating earthquakes m8 0 the largest was the m9 2 great alaska earthquake of march 1964 that ruptured 800 km of the eastern segment of the megathrust the tsunami generated caused fatalities in alaska and along the coast as far south as california east of the 1964 zone of deformation the yakutat microplate experienced two m8 0 earthquakes separated by a week in september 1899 for the first time we present evidence that earthquakes 900 and 1500 years ago simultaneously ruptured adjacent segments of the aleutian megathrust and the yakutat microplate with a combined area 15 greater than 1964 giving an earthquake of greater magnitude and increased tsunamigenic potential

experimental models of extensional forced folds we have used single layer and multilayer clay models to study the development of forced folds above normal faults our modeling results show that the deformation patterns associated with extensional forced folding depend on the dip of the underlying normal fault and the presence of layer parallel detachments in single layer clay models extensional forced folds are upward widening monoclines anticlinal axial surfaces dip in the same direction as underlying master normal faults and synclinal axial surfaces dip in the opposite direction of master normal faults most secondary faults are upward steepening normal faults if master normal faults are steeply dipping however many secondary normal faults become high angle reverse faults at shallow depths the propagation and linkage of secondary faults into through going normal faults terminates the development of extensional forced folds more folding occurs prior to fault linkage if the master normal fault is steeply dipping rather than gently dipping most dipping beds and secondary faults are preserved in the hanging walls of the through oing normal faults in multilayer clay models with layer parallel detachments extensional forced folds are also upward widening monoclines slip on the lowest detachment laterally transfers extension induced by normal faulting and forced folding from the master normal fault to the detachment edge slip on overlying detachments accommodates minor thickness changes associated with upward widening of the fold secondary faults include low angle normal faults near the anticlinal axial surface minor thrust faults near the synclinal axial surface and high angle normal faults above the detachment edge the model predicted deformation patterns are similar to those of extensional forced folds from the gulf of suez and offshore norway this similarity suggests that our modeling results apply to extensional forced folds and can provide guidelines for interpreting field well and seismic data

strike slip tectonics and quaternary basin formation along the vienna basin fault system inferred from bouguer gravity derivatives 1 the vienna basin at the transition between the alpine and carpathian belt hosts a number of large pleistocene sub basins forming along an active continental scale strike slip fault vienna basin strike slip fault we utilize first order derivatives from industrial bouguer gravity data to unravel the impacts of pleistocene kinematics on the vienna basin and to compensate for the lack of near surface fault data anomalies have been evaluated by independent geophysical and geological data and were integrated to build up a tectonic model factors influencing the wavelength and the amplitude of anomalies were additionally investigated by 2 d models to better interpret field data subsidence and related accumulation of quaternary sediments in the vienna basin produce significant gravity signals related to the activity of the strike slip fault the constrained fault patterns and structures highlight tight and elongated transtensional pull apart basins with typically associated features like separated depocenters and riedel fractured sidewalls in an en echelon alignment further pleistocene basins are highlighted as tectonic grabens developing along branches of the master fault the vienna basin is additionally affected by minor deformation represented by both subsidence along major miocene sidewalls and nw se faulting resulting in distinct topographic features which manifests kinematics on a regional scale the clear density contrasts between miocene marine and quaternary terrestrial sediments as well as the exceptional database provide a unique framework to demonstrate advantages of incorporating gravity derivatives for near surface fault analysis

terminus behavior and response time of north cascade glaciers washington u s a observation of the terminus behavior of 38 north cascade glaciers washington u s a since 1890 shows three different types of glacier response 1 continuous retreat from the little ice age lia advanced positions from 1890 to approximately 1950 followed by a period of advance from 1950 to 1976 and then retreat since 1976 2 rapid retreat from 1890 to approximately 1950 slow retreat or equilibrium from 1950 to 1976 and moderate to rapid retreat since 1976 3 continuous retreat from 1890 to the present type 1 glaciers are notable for steeper slopes extensive crevassing and higher terminus region velocities type 2 glaciers have intermediate velocities moderate crevassing and intermediate slopes type 3 glaciers have low slopes modest crevassing and low terminus region velocities this indicates that the observed differences in the response time and terminus behavior of north cascade glaciers in reaction to climate change are related to variations in specific characteristics of the glaciers the response time is approximately 20 30 years on type 1 glaciers 40 60 years on type 2 glaciers and a minimum of 60 100 years on type 3 glaciers the high correlation in annual balance between north cascade glaciers indicates that microclimates are not the key to differences in behavior instead it is the physical characteristics slope terminus velocity thickness and accumulation rate of the glacier that determine recent terminus behavior and response time the delay between the onset of a mass balance change and initiation of a noticeable change in terminus behavior has been observed on 21 glaciers to be 4 16 years this initial response time applies to both positive and negative changes in mass balance

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

3d seismic analysis of the structure and evolution of a salt influenced normal fault zone a test of competing fault growth models abstract in this paper we determine the structure and evolution of a normal fault system by applying qualitative and quantitative fault analysis techniques to a 3d seismic reflection dataset from the suez rift egypt our analysis indicates that the october fault zone is composed of two fault systems that are locally decoupled across a salt bearing interval of late miocene messinian age the sub salt system offsets pre rift crystalline basement and was active during the late oligocene early middle miocene it is composed of four planar nw se striking segments that are hard linked by n s striking segments and up to 2 km of displacement occurs at top basement suggesting that this fault system nucleated at or more likely below this structural level the supra salt system was active during the pliocene holocene and is composed of four nw se striking listric fault segments which are soft linked by unbreached relay zones segments in the supra salt fault system nucleated within pliocene strata and have maximum throws of up to 482 m locally the segments of the supra salt fault system breach the messinian salt to hard link downwards with the underlying sub salt fault system thus forming the upper part of a fault zone composed of i a single amalgamated fault system below the salt and ii a fault system composed of multiple soft linked segments above the salt analysis of throw distance t x and throw depth t z plots for the supra salt fault system isopach maps of the associated growth strata and backstripping of intervening relay zones indicates that these faults rapidly established their lengths during the early stages of their slip history the fault tips were then effectively pinned and the faults accumulated displacement via predominantly downward propagation we interpret that the october fault zone had the following evolutionary trend i growth of the sub salt fault system during the oligocene to early middle miocene ii cessation of activity on the sub salt fault system during the middle miocene to early pliocene iii stretching of the sub and supra salt intervals during pliocene regional extension which resulted in mild reactivation of the sub salt fault system and nucleation of the segmented supra salt fault system which at this time was geometrically decoupled from the sub salt fault system and iv pliocene to holocene growth of the supra salt fault system by downwards vertical tip line propagation which resulted in downward breaching of the salt and dip linkage with the sub salt fault system the structure of the october fault zone and the rapid establishment of supra salt fault lengths are compatible with the predictions of the coherent fault model although we note that individual segments in the supra salt array grew in accordance with the isolated fault model our study thereby indicates that both coherent and isolated fault models may be applicable to the growth of kilometre scale basin bounding faults furthermore we highlight the role that fault reactivation and dip linkage in mechanically layered sequences can play in controlling the three dimensional geometry of normal faults

holocene climate inferred from glacier extent lake sediment and tree rings at goat lake kenai mountains alaska usa lake sediment glacier extent and tree rings were used to reconstruct holocene climate changes from goat lake at 550 m asl in the kenai mountains south central alaska radiocarbon dated sediment cores taken at 55 m water depth show glacial lacustrine conditions until about 9500 cal yr bp followed by organic rich sedimentation with an overall increasing trend in organic matter and biogenic silica content leading up to the little ice age lia through most of the holocene the northern outlet of the harding icefield remained below the drainage divide that currently separates it from goat lake a sharp transition from gyttja to inorganic mud about ad 1660 signifies the reappearance of glacier meltwater into goat lake during the lia marking the maximum holocene postglacial extent meltwater continued to discharge into the lake until about ad 1900 a 207 yr tree ring series from 25 mountain hemlocks growing in the goat lake watershed correlates with other regional tree ring series that indicate an average summer temperature reduction of about 1 c during the 19th century compared with the early mid 20th century cirque glaciers around goat lake reached their maximum lia extent in the late 19th century assuming that glacier equilibrium line altitudes ela are controlled solely by summer temperature then the cooling of 1 c combined with the local environmental lapse rate would indicate an ela lowering of 170 m in contrast reconstructed elas of 12 cirque glaciers near goat lake average only 34 18 m lower during the lia the restricted ela lowering can be explained by a reduction in accumulation season precipitation caused by a weakening of the aleutian low pressure system during the late lia copyright 2008 john wiley sons ltd

holocene history of hubbard glacier in yakutat bay and russell fiord southern alaska stratigraphic and geomorphic data defined by radiocarbon ages tree ring dates and historical observations provide evidence of three major holocene expansions of hubbard glacier early in each advance the hubbard glacier margin blocked russell fiord to create russell lake raising base level and causing stream beds and fan deltas throughout the russell drainage basin to aggrade each hubbard glacier expansion continued with an ice lobe advancing through disenchantment and yakutat bays in the west and an eastern lobe advancing into russell fiord the earlier two holocene expansions were respectively under way at 7690 and 5600 calibrated yr b p and each advance culminated more than 1 k y later the late holocene advance was under way by 3100 yr ago and reached 13 km farther south in russell fiord than the preceding two expansions late holocene deglaciation of yakutat and disenchantment bays was complete before a d 1791 nunatak glacier flowing from neves east of russell fiord became the primary ice source to the russell fiord lobe at or before this date ice retreat from the southern end of russell fiord began in the late eighteenth century and the penultimate russell lake drained ca a d 1860 the relatively slow advances and more rapid retreats of hubbard glacier are consistent with the model of the iceberg calving glacier cycle hubbard glacier is currently advancing and will likely reestablish russell lake in the near future affecting local fisheries however glacier lobes are unlikely to reach the area of the town of yakutat built on late holocene glacial deposits in the next 1 k y

geometry and kinematics of extensional structural wedges abstract structural wedges in the compressive environment have been recognized and studied in different locations however extension structural wedges are less well understood based on the normal fault bend folding theory and inclined shear model this paper quantitatively analyses deformations related to extensional structural wedges and builds a series of geometric models for them an extensional structural wedge is a fault block held by two or more normal faults the action of which would fold its overlying strata extensional structural wedges of different shapes will lead to different deformation results for the overlying strata and this paper illustrates both the triangular and quadrangular wedges and their related deformations this paper also discusses differences between the extensional structural wedges and the normal fault bend folding by analysing two seismic sections from langfang gu an sag east china this paper provides two natural examples of the triangular and quadrangular extensional structural wedges where the models can reasonably explain the overlying distinct highs and lows without obvious faults the establishment of a geometric model of extensional structural wedges can provide reference and theoretical bases for future quantitative analysis of deformations in the extensional environment