late cenozoic tectonics of the east ventura basin transverse ranges california the east ventura basin originated in the middle miocene as a rift system bounded on one side by the oak ridge simi hills structural shelf and on the other side by a granitic ridge parallel to the san gabriel fault this fault began accumulating right slip 10 12 m y ago at a rate of 4 5 9 mm yr depending on whether total slip is 45 or 60 km slowing to about 1 mm yr in the quaternary north of the santa clara river rifting ended prior to deposition of the uppermost miocene lower pliocene towsley formation south of the santa clara river the rift axis shifted southwest toward the oak ridge simi hills shelf as the towsley formation accumulated against a normal fault ancestor of the santa susana fault a change to contractile tectonics occurred in the pliocene with depos tion of the fernando formation when the newhall potrero anticline developed as a monocline above a blind reverse fault the pico anticline to the southeast and the temescal and hopper ranch modelo anticlines to the northwest may have a similar origin tectonic inversion and displacement on the southwest verging santa susana fault began about 0 5 ma based on appearance of locally derived clasts in the upper saugus formation and its equivalents and continues today along with the southwest verging san cayetano fault farther west also active are northeast verging backthrusts occurring in the east ventura basin fold belt and a segment of the san gabriel fault which now acts as a northeast dipping oblique slip reverse fault northeast trending discontinuities and structures divide the present deformation zone into four segments in the hopper canyon segment at the west end of the area in the west ventura basin the san cayetano fault places miocene modelo formation over pliocene pleistocene strata more than 5 km thick largely at maximum burial to the southeast the newhall potrero segment is characterized by north vergent backthrusts within the east ventura fold belt and by southward thrusting of the basin sequence tectonic inversion over the structural shelf on the santa susana fault farther southeast the placerita segment is marked by reverse faulting on both the santa susana fault and the san gabriel fault southeast of the basin in the san fernando valley the sylmar segment contains a thick pli cene pleistocene sequence overridden by basement rocks of the san gabriel mountains as well as the south verging mission hills granada hills and northridge hills fault zones

estimation of episodic exfoliation rates of rock sheets on a granite dome in korea from cosmogenic nuclide analysis we have measured concentrations of cosmogenic 10be and 26al produced in situ at bare bedrock surfaces of successive sheets developing on a granite dome in korea and calculated the exfoliation rate of sheeting joints the exfoliation rate was obtained using a simple model in which the sheeting joints experience intermittent denudation i e peeling off along the bedrock face we find that the average exfoliation erosion rate of the episodic peeling off process is 5 6 cm ka 1 the analysis is useful for understanding the evolution of granite sheeting structures on this dome in korea copyright 2006 john wiley sons ltd

inversion of 3 d structural geometry using geological least squares criteria oil exploration requires quantitative determination of structural geometry in sedimentary basins this leads to back and forth use of geological methods e g cross section balancing and geophysical techniques such as tomography and the synthesis becomes tedious especially in three dimensions this suggests that they should be as much as possible quantitatively integrated into a single consistent framework for this integration we propose using inversion techniques i e multicriteria optimization we locally model a geological structure as a geometric foliation the leaves of which represent deposition isochrons we consider a geological structure as a set of foliations joined along faults and unconformities we propose five kinds of geological data to constrain structural geometry quantitatively dip measurements that may be available along wells developability and smoothness of deposition isochrons the directions of fold axes and layer parallelism using concepts of differential geometry we formulate these data in terms of least squares criteria to solve the canonical non uniqueness problem raised by the inversion of parametric representations of geometrical objects such as foliations many parametrizations describe the same object we introduce the additional criterion method which consists of adding an unphysical objective function to the physical objective function so as to make the solution unique assuming well trajectories and borehole correlations to be known we optimize with respect to these criteria several simple structures comprising one foliation including a field example

near surface expression of the eastern part of the san cayetano fault a potentially active thrust fault in the california transverse ranges examined in this study are the near surface geometry late cenozoic geologic history and seismic potential of the eastern part of the san cayetano fault a major north dipping thrust fault of the transverse ranges california the fault generally dips with a low angle close to the surface but the dip increases up to 40 at about 5 km below sea level the fault may become nearly horizontal at depth and root into a midcrustal detachment surface of the transverse ranges the late cenozoic reverse movement along the san cayetano fault may have begun during the deposition of the lower part of the saugus formation the fault has also moved after the deposition of the saugus formation within the last 0 2 m y the san cayetano fault should be considered at least potentially active and may be capable of producing damaging earthquakes this conclusion is based collectively on 1 the presence of several surficial geological features suggestive of recent movement along the fault 2 the presence of microearthquakes on the fault plane and 3 the structural similarity of the fault to seismically active north dipping thrust faults of the region

thin skinned tectonics of the upper ojai valley and sulphur mountain area ventura basin california by integrating surface mapping with subsurface well data and drawing cross sections and subsurface maps the geometry of shallow structures and their geologic history of the upper ojai valley of california can be reconstructed the geometry of shallow structures the geologic history and the location of earthquake foci then offer constraints on the deep structure of this complex area the upper ojai valley is a tectonic depression between opposing reverse faults its northern border is formed by the active north dipping san cayetano fault which has 6 0 km of stratigraphic separation in the silverthread area of the ojai oil field and 2 6 km of stratigraphic separation west of sisar creek the fault dies out farther west in ojai valley where the south vergent shortening is transferred to a blind thrust the southern border of the upper ojai valley is formed by the quaternary lion fault set sisar big canyon and lion faults which dips south and merges into the sisar decollement within the south dipping ductile lower miocene rincon formation folds with north dipping axial planes including the lion mountain anticline and reeves syncline are middle pleistocen or older and are related to movement on an unnamed fault in the footwall block of the san cayetano fault and on the san cayetano fault respectively by the middle pleistocene the sulphur mountain anticlinorium and the big canyon syncline began forming as a fault propagation fold the fault propagation fold is rooted in the sisar decollement a passive backthrust rising from a blind thrust at depth the formation of the sulphur mountain anticlinorium was followed closely by the ramping of the south dipping lion fault set to the surface over the nonmarine upper pleistocene saugus formation to the east the san cayetano fault overrides and folds the lion fault set near the surface area balancing of the deformation shows shortening of 15 5 km and suggests a 17 km depth to the brittle d ctile transition

late wisconsin climate in northeastern usa and southeastern canada reconstructed from fossil beetle assemblages mean july and january temperatures are reconstructed from radiocarbon dated fossil beetle assemblages yielding a synthesis of palaeoclimatic history of the regions south of the laurentide ice sheet in north america from 35 000 to 8500 yr bp mean july temperatures close to the last glacial maximum were 11 12 c colder than present mean january temperatures were possibly 10 19 c colder mutual climatic range analyses of the beetle assemblages show warming of mean summer temperatures as early as 13 7 kyr although ice proximal sites were consistently about 5 c cooler than ice distal sites late glacial mean summer temperatures peaked between 12 and 11 kyr then remained fairly constant through the early holocene mean winter temperatures did not reach modern values until after 10 kyr

three dimensional imaging of active structures using earthquake aftershocks the northridge thrust california abstract aftershocks of the 1994 northridge earthquake m 6 8 allow us to image the structure beneath the san fernando valley in northwestern los angeles in three dimensions we combine aftershocks and geological data to build an image of the three dimensional 3 d geometry of the previously unrecognized north vergent northridge blind thrust to a depth of 21 km the most striking feature of the imaged fault is mega corrugations oriented parallel to the mean aftershock slip vector with most of the 1994 slip confined to west of the largest corrugation we also image the partially overlying south vergent san fernando thrust which broke to the surface in a complex rupture in 1971 m 7 1 both thrusts produce fault related folding because of either fault propagation or fault bends however this deeper folding is masked by overlying complex deformation in the cover which is one reason why the northridge thrust was not identified until it ruptured in 1994 we use trishear fold modeling based on our 3 d fault geometry to evaluate possible folding due to slip on the northridge thrust as well as its interaction with the overlapping san fernando thrust and with shallow structures in the cover this example illustrates the importance of earthquake data to structural geology and the value of its 3 d integration with surface and near surface geological data

constraining recent fault offsets with statistical and geometrical methods example from the jasneuf fault western alps france we propose two new approaches regarding recent fault offset measurements by studying the seismogenic potential of the jasneuf fault the ne trending right lateral strike slip jasneuf fault is the southwestern extension of the belledonne fault system in the vercors massif this fault which is located in an intraplate domain does not show strongly associated seismicity but displays morphological anomalies that are related to recent faulting right lateral offset of late cenozoic cliffs recent talwegs and post ganz scarps the two methods that we use to quantify fault slip are as follows 1 recursive measurements of stream offsets are conducted this analysis reveals that a stream network can display characteristic distances between streams that can be mistakenly interpreted as long term cumulative fault offsets a comparison of the apparent stream offset values and stream spacing values is necessary to identify the true offsets 2 we propose a new method that enables us to determine the fault offset and kinematics by using recursive measurements of topographic apparent offsets to counter the lack of morphologic features that are used to determine piercing points or lines this method enables us to define each possible slip vector for numerous artificial piercing points along a fault the slip vector that is shared by these piercing points is the true slip vector by applying these methodologies we determine that the jasneuf fault has accumulated slip since the messinian which corresponds to an average slip rate of 0 13 0 03 mm year the extension of the fault is poorly constrained nevertheless if we do not consider the potential aseismic creep slip component of the faulting we calculate that this fault could generate mw 5 7 earthquakes every similar to 500 years according to wells and coppersmith s scaling laws and by assuming that the faulting is limited to the sedimentary cover and the vercors plateau c 2016 elsevier b v all rights reserved

late pleistocene and holocene seasonal temperatures reconstructed from fossil beetle assemblages in the rocky mountains abstract mutual climatic range mcr analysis was applied to 20 fossil beetle assemblages from 11 sites dating from 14 500 to 400 yr b p the fossil sites represent a transect of the rocky mountain region from northern montana to central colorado the analyses yielded estimates of mean july and mean january temperatures the oldest assemblage 14 500 yr b p yielded mean july values of 10 11 c colder than present and mean january values 26 30 c colder than present postglacial summer warming was rapid as indicated by an assemblage dating 13 200 yr b p with mean july values only 3 4 c cooler than modern by 10 000 yr b p several assemblages indicate warmer than modern mean summer and winter values by 9000 yr b p mcr reconstructions indicate that both summer and winter temperatures were already declining from an early holocene peak mean july values remained above modern levels and mean january values remained below modern levels until 3000 yr b p a series of small scale oscillations followed

an automatic method for determining three dimensional normal fault geometries we describe a general kinematic method for automatically determining the three dimensional 3 d geometry of normal faults at depth from the 3 d geometry of deformed hanging wall horizons the method should be applicable to normal faults which do not change shape as deformation proceeds it is a generalization of two dimensional models and assumes that the hanging wall deforms by arbitrarily inclined bulk simple shear deformation in three dimensions is parameterized by the three euler angles which describe the horizontal slip vector the rake angle and the inclination of shear planes as in two dimensions differential compaction can be included by assuming that the axis of shortening is parallel to the direction of shear three dimensional fault geometry and the three euler angles can all be automatically determined provided the geometries of two or more hanging wall horizons are known here the method is tested on both synthetic data and on 3 d sand box models synthetic modeling shows that unique solutions can be found and more importantly that the horizontal slip vector can be constrained solutions obtained from sand box models are also encouraging in most cases the method can predict automatically the correct direction of extension and a 3 d fault geometry close to the fault geometry used hence arbitrarily inclined bulk simple shear appears to be a good approximation of hanging wall deformation in three dimensions this general method will allow 3 d palinspastic analysis to be undertaken on 3 d seismic reflection data sets

palaeoecology of postglacial treeline shifts in the northern cascade mountains canada abstract postglacial changes in vegetation and chironomid communities at a subalpine lake in the engelmann spruce subalpine fir zone in the northern cascade mountains british columbia indicate patterns of treeline and climate fluctuation during the holocene in late glacial sediments of cabin lake pollen assemblages representative of alpine vegetation and cold stenothermous chironomids indicate cold conditions prior to the holocene in the early holocene 10 090 to 7000 14 c yr bp co occurrence of spruce fir parkland and a warm adapted chironomid community indicates a warm and probably dry climate in the mid holocene inferred forest closure suggests that precipitation increased and a mixture of warm and cold adapted chironomids indicates temperatures warmer than present but cooler than in the early holocene this period between 7000 and 3200 14 c yr bp represents a transitional climate in which temperature gradually declined culminating in cool neoglacial conditions this transitional interval may correspond with the mesothermic period proposed for lowland sites in southern british columbia palaeobotanical evidence suggests that moist subalpine forest began to establish around 4800 14 c yr bp with minimum temperatures and maximum precipitation between 2435 and ca 1700 14 c yr bp corresponding with neoglacial advances throughout the northern cordillera a cool late holocene 3200 14 c yr bp to present is also supported by a further decline in warm adapted chironomids comparisons with other study sites in the pacific northwest reveal that regional climatic changes were a major factor in driving biotic changes in this area

paleoenvironmental interpretations of holocene insect fossil assemblages from the la poudre pass site northern colorado front range abstract a sequence of peats from the la poudre pass site northern front range colorado rockies yielded abundant insect fossil assemblages studied intervals ranged in age from nearly 10 000 yr b p to about 5400 yr b p seventy named insect taxa were extracted from the peat among these are a mixture of aquatic and terrestrial species several taxa from the lowest 10 cm are indicative of climatic conditions found today in montane forest regions although conifers were probably not present at the site until several centuries after the initiation of peat deposition later insect assemblages contain a mixture of both tundra and forest faunal elements suggesting the close proximity of altitudinal tree limit to the site from about 9500 yr b p through the uppermost level studied 5400 yr b p

active faulting and block rotations in the western transverse ranges california the geometry of faulting slip vectors of major earthquakes and results of very long baseline interferometry vbli are consistent with active clockwise rotation of crustal blocks in the western transverse ranges about vertical axes oblique left lateral thrust faults trending roughly east west across the western transverse ranges apparently separate long east west blocks of upper crust and the large components of lea lateral shear on east striking planes suggest that the blocks rotate with respect to the san andreas fault in the mojave region between the western transverse ranges and the mojave desert paleomagnetic declinations indicate some 35 and possibly 60 of clockwise rotation since about 10 ma and more importantly the relative velocity between the only two frequently measured vbli sites in the western transverse ranges is consistent with a rotation rate of 6 ma 3 ma during a 5 year period in the 1980s azimuths of slip vectors of major earthquakes are essentially orthogonal to the segment of the san andreas fault across the western mojave desert indicating that crustal shortening across the region is absorbed by crustal thickening and not by lateral translation extension of material parallel to that segment of the fault plate motions late quaternary offsets on the san andreas and san jacinto faults and geodetic measurements in the mojave region yield a calculated direction of relative motion between the san gabriel mountains and the pacific plate across the western transverse ranges that also is perpendicular to the san andreas fault in the mojave region rotation rates associated with simple mechanisms for applying essentially normal tractions to the lateral margins of blocks are not consistent with the observed geometry of faulting and with average rotation rates the rotation rate of 2 8 5 3 ma calculated assuming that the long east west blocks rotate in response to a uniform compression of a viscous substratum to the western transverse ranges however overlaps the range of observed average rotation rates thus the hypothesis that blocks of continental crust move as if carried passively by a substratum undergoing continuous deformation passes one test that can be made of it

reconstructing the late holocene history of a subalpine environment charlevoix quebec using fossil insects in southern quebec charlevoix canada reconstructions of the subalpine insect assemblages were made in environments that were transformed by fire during the late holocene since 4500 bp the ecological requirements of beetle species likely to be found as fossils were studied by collecting living beetles in pitfall traps in forest suibalpine and alpine environments the late holocene changes of insect assemblages were reconstructed by recovering fossil insects from 13 peat sections modem beetle assemblages are valuable indicators of tree cover well developed podzol soils under peat as well as numerous spruce charcoal remains overlaying the podzol in all sampling sites suggest that a dense spruce cover was present before the beginning of the accumulation of peat and was eliminated by fire 4570 800 bp ground beetle and bark beetle assemblages at the base of the peat sections contained a mixture of forest and open environment species indicating that the postfire environment was a subalpine one w

the thermal regime of a permafrost body at mont du lac des cygnes quebec a low peat plateau in the alpine forest tundra at mont du lac des cygnes 100 km northeast of quebec city contains a permafrost body 2 m thick at an elevation of 960 m this is the southernmost k

mechanical modeling of compressional basins origin and interaction of faults erosion and subsidence in the ventura basin california using geophysical observations and some basic geological ideas on the present structure of the ventura basin we model its possible mechanical evolution during the last 4 million years we use a two dimensional finite element model with frictional and elastoviscoplastic rheologies that allow strain localization this allows us to study the mechanical origin of the san cayetano thrust fault scf and its interaction with the oak ridge fault orf the results of our modeling indicate that the geometry and activity of a shear zone which mimics the san cayetano fault are conditioned both by the preexistence of the oak ridge fault and by the shape of the brittle ductile transition furthermore the presence of a decollement level is shown to favor the development of the san cayetano fault shear zone as a low angle structure the value of the effective friction on the oak ridge fault is evaluated from this model possible values of the viscosity of the sediments are also estimated it is shown that low sediment viscosity may completely hinder the activity of such a fault at the surface while slip at depth continues the stratigraphic profile of the basin is also shown to depend on the relative strengths of the orf and scf which also provide an explanation for the shortening and rapid subsidence of the basin

compatibility constraints on folded and faulted strata and calculation of total displacement using computational restoration unfold program abstract a balanced surface method is proposed that allows one to test the reliability of the interpretation of the structural geometry of folded and faulted strata it also estimates both the finite total displacement field linked to the folding and faulting processes and the finite displacement field linked to the folding the method describes a thin competent folded and faulted sedimentary layer using rigid triangular elements their sizes depending on the curvature of the surface the elements are laid flat and are automatically fit to form a horizontal surface which represents the initial state of the layer the degree of compatibility given by different indicators tests the reliability of the geometric fitting of the layer if folding and faulting occur without bed stretching or if this change is known and introduced as a parameter in the code a plausible interpretation can be perfectly retrodeformed just as a folded and torn sheet of paper may be smoothed with an iron the method has been applied to two natural examples in oil field regions using three or two dimensional depth migrated seismic data the main results reveal in general that the petroleum company s interpretations of the data were nonoptimal a careful reinterpretation of the seismic data was necessary to obtain balanced folded and faulted surfaces the estimation of the finite displacement fields revealed the compatibility between fold and fault deformation and also the strike slip movement or rotation associated with the deformation

an inverse method for determining three dimensional fault geometry with thread criterion application to strike slip and thrust faults western alps and california abstract in order to draw geological structures such as faults interpolation is generally needed between scattered data the use of an approximation criterion integrating the kinematic properties of the faults helps to document the fault surfaces by adding a compatibility criterion to the data set assuming that two jointed blocks of rocks slipping on each other generate a thread surface an approximation method has been developed which integrates a thread criterion this approximation method is used to solve an inverse problem with least squares criteria including proximity to data points smoothness and thread criteria the aim is to find a smooth surface which is as close as possible to a thread and as close as possible to the observed data set applications to two corrugated fault surfaces with a dense data set located in the western alps france and in the transverse ranges california confirm the validity of the thread assumption despite their difference in mean corrugation wavelength 5 m and 10 km respectively in the type of fault strike slip and thrust fault respectively and in the nature of the faulted rocks limestones and sandstones respectively very similar results are obtained in both cases the observed data fit well with a thread surface and the computed fault displacement fits well with the measured displacement on the fault striae seismic focal mechanism geodetic data restoration the conclusion is that treating a fault as a thread is a valid physical description which gives the slip direction independently of other kinematic indicators the advantage of using a thread criterion in addition to classical proximity and smoothness criteria is that this physical insight allows information from areas where data are relatively dense to help constrain areas where data are relatively sparse these last areas being those that are usually not well constrained by proximity and smoothness criteria

restoration of transpression transtension by generating the three dimensional segmented helical loci of deformed lines across structure contour maps abstract in transpression transtension zones the strain is three dimensional and rotational this causes material to move through the plane of cross section often invalidating balancing and restoration within this plane methods are presented which allow the three dimensional segmented irregular helical locus of an originally straight line to be constructed in any direction on a structure contour map of a folded and faulted surface this construction depends on a knowledge of the kinematics of folding and faulting and can be modified to suit local conditions the ratio of the length of the cylindrical envelope bounding this helical locus to the sum of the lengths of the helical fragments between faults gives the true stretch in the direction of the envelope when the traces of the segmented helices are constructed in different directions on a deformed surface the sectional finite strain ellipse can be found for that surface knowledge of the dimensions of this ellipse and its orientation with respect to the kinematic axes of the transpression zone allows the tensor components to be constrained this permits the three dimensional boundary conditions to be determined and thus restored the methods are applied to the ardross fault zone in central scotland the solutions suggest this fault zone underwent a phase of dextral transpression along a nw zone boundary during hercynian e w compression in the scottish midland valley contemporaneous e w dyke swarms and n s regional flexures support these kinematics

neotectonics of the san cayetano fault transverse ranges california study of late quaternary alluvial deposits cut by the san cayetano reverse fault indicates that the dip slip rate of faulting increases from 1 05 0 2 mm yr at sisar creek near the western end of the fault eastward to 1 35 0 4 mm yr at bear canyon and 2 35 0 55 to 4 15 0 85 mm yr at mud creek at timber canyon near the central part of the fault a minimum slip rate of 3 6 0 4 mm yr is suggested by fanhead segmentation however a higher slip rate of 8 75 1 95 mm yr is suggested by stratigraphic evidence stratigraphic separation of 7 5 km in less than 1 m y across the fault between fillmore and piru indicates a slip rate of at least 7 5 mm yr for the eastern section of the fault recent activity is shown by faulted holocene or latest pleistocene fan alluvium and colluvium at bear canyon and the silverthread oil field respectively and inferred at timber canyon by fanhead deposition active folding of the footwall is demonstrated by tilted and faulted holocene and pleistocene alluvial fans present tilt rates approach 1 10 ka yr and associated bedding plane faulting rates are about 0 5 to 1 5 mm yr the hanging wall however does not appear to be involved in active deformation inasmuch as pleistocene deposits as old as several hundred thousand years are not tilted or affected by bedding plane faulting the only exception is in the silverthread field area where hanging wall deformation is directly relatable to fault geometry not folding of the hanging wall rocks the lack of documented moderate to large magnitude historical earthquakes on this fault is in strong contrast with its demonstrated late quaternary activity based on its length slip rate overall geometry and segmentation into two parts a recurrence interval of between 200 and 600 yr for the western segment and about 230 yr for the eastern segment is suggested

a model for neogene crustal rotations transtension and transpression in southern california two episodes of crustal rotation have occurred in the regions of southern california and the mojave desert since the beginning of miocene time an early miocene episode of clockwise crustal rotation is associated with widespread north south to north northeast south southwest crustal extension throughout southeast california and western arizona this episode is apparently related to changing subduction parameters of the farallon plate a middle miocene and later episode of clockwise rotation in the transverse ranges and bordering areas is related to shear between the pacific and north american plates in both episodes clockwise crustal rotations first occur in a deforming zone which has a component of extension across its trend and shear along its trend the effects of extension are most pronounced in the earlier episode but clear in the later one also the pacific north american deforming zone began contracting in width during pliocene time but clockwise rotations continued and are probably in progress today

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

least squares palinspastic restoration of regions of normal faulting application to the campos basin brazil we have developed an iterative least squares method for palinspastic restoration of regions of normal faulting the method closes the gaps cut off lenses across normal faults on a structure contour map of a given stratigraphie horizon such data are often available for sedimentary basins covered by seismic surveys before restoration we first produce a fault block map where each block is completely surrounded by faults whether real or artificial we then apply an algorithm to minimize d the sum of the squares of the distances across cut off lenses with respect to unknown rigid block translations and rotations minimization results in non linear equations which we solve by an iterative method we deem the solution to have converged when d falls below a given critical level in general restoration not only closes the original gaps but also results in strike slip displacements between blocks thus the deformation need not be a plane strain and displacement vectors need not be parallel we have applied the method to an area of the campos basin on the atlantic margin of brazil where the stratigraphy and structure are well known from seismic surveys and from wells cretaceous and tertiary sediments have glided downslope on a lubricating layer of aptian evaporites producing an uppermost domain of normal faulting the normal faults occupy a strip lying between undisturbed continental crust to the west and relatively unstructured sediments to the east assuming the western boundary to be stationary we have restored an upper oligocene stratigraphie level the marco azul convergence was achieved rapidly and the degree of fit is good according to our restoration the eastern boundary of the area has bowed out seawards since the oligocene block displacement vectors form a fan like pattern with an element of mirror symmetry about a line trending nw se maximum displacements occur in an apical domain bounded by a horseshoe pattern of faults there is a general pattern of block rotations counterclockwise in the northeast clockwise in the southwest some notable exceptions to this general pattern are due to local domino motions we attribute the overall displacement field to divergent gravitational gliding off a local salient in the sea bottom topography because of the three dimensional nature of the displacement field restoration of vertical cross sections alone would yield gross errors this demonstrates the value of palinspastic methods such as ours

mapped plant macrofossil and pollen records of late quaternary vegetation change in eastern north america abstract macrofossil presence absence maps and isopoll maps in 3000 year intervals show how ranges and abundance maxima for 12 eastern north american tree and shrub taxa picea p glauca p mariana larix laricina abies balsamea tsuga canadensis pinus strobus p resinosa p banksiana betula papyrifera b alleghaniensis b series humiles have changed from the last glacial maximum to the present the macrofossil maps corroborate patterns shown by the isopoll maps and provide spatial detail and taxonomic resolution the macrofossils confirm the inference from pollen data that unglaciated southeastern north america was cooler during the last glacial maximum 18 and 15 ka than simulated by the cohmap experiments with the ncar ccm0 general circulation model the geographic distribution of macrofossil occurrences during the late glacial 12 and 9 ka indicate that migration lag of boreal species did not occur at regional to subcontinental scales and that pollen assemblages lacking modern analogs resulted from climate gradients lacking modern analogs early holocene 9 and 6 ka macrofossil maps show rapid northward expansion of tree species ranges into deglaciated regions the data also show modest contractions of northern range limits of temperate species and expansions of southern range limits of boreal species in response to cooling trends during the late holocene 3 and 0 ka comparison of modern macrofossil maps of nine of these taxa with corresponding range maps confirm that the macrofossils record the geographic ranges accurately comparison of the modern macrofossil maps with maps of tree growing stock volume shows that for some taxa abies tsuga macrofossil occurrences were most frequent in regions of maximum tree abundance comparison of modern isopoll maps with the modern range and growing stock volume maps indicate that in contrast to the macrofossil data the pollen data provide poorer resolution of range limits for most taxa but better indications of abundance maxima and minima within the ranges

holocene relict woodlands at the eastern canadian treeline abstract we present direct evidence for the relict nature of lichenspruce woodlands thriving at treeline using 14c dated stands growing in the humid climate of eastern hudson bay in northern quebec black spruce picea mariana mill bsp forms two groups of relict stands a neoglacial group of postfire origin dating between 2000 and 900 yr b p and a pre neoglacial group most likely established between 4500 and 3200 yr b p the latter group shows no evidence of fire absence of charcoal under topsoil organic horizon the stands are exceptional because they probably are the direct lineages of the primeval forests that colonized the land sometime after deglaciation the structure of the relict lichen spruce communities gives strong support to the current thesis that considers lichen spruce woodland as a self perpetuating open forest typical of the subarctic environment

3 d palinspastic restoration of normal faults in the inner moray firth implications for extensional basin development abstract balanced cross section techniques and the construction of a restored section permit 2 dimensional palinspastic restorations to be made in both compressional and extensional terraines in 3 dimensions an equivalent restoration can be made by assuming conservation of bedding plane area and considering the volume of a stratigraphic interval rather than its cross sectional area extensional basins displaying upper crustal listric normal faulting are particularly amenable to this approach computerised 3 d restorations have been made of the inner moray firth basin offshore scotland this basin is not isostatically compensated and was produced by 7 8 post triassic extension of which 2 5 3 is post jurassic above a detachment surface at 20 25 km depth close to the base of the crust limited lower crustal thinning and lithospheric stretching has affected the eastern part of the basin but this can account for no more than half of the measured upper crustal extension some of this shallow extension is probably coupled by low angle faults or shear zones into major zones of lithospheric stretching such as the north sea grabens where it may help account for discrepancies between estimates of lithospheric thinning and upper crustal extension

large scale quaternary detachments in ventura basin southern california the ventura basin is an east north east trending trough in the california transverse ranges which records major quaternary detachment faulting at three levels the earliest thrusting occurred along weak siltstone interbeds in a sequence dominated by competent basin plain turbidite sandstone because sedimentation continued during thrusting the age rate and direction of thrusting can be worked out faulting began 1 3 m y ago and ceased 0 65 m y ago with a maximum slip rate of 2 8 mm yr to the southeast the fault set moved up a 45 ramp and ended as a blind thrust the ramp had topographic expression on the seafloor diverting turbidites around the ramp and preserving ash beds along with other hemipelagic sediments on its crest following the end of deposition 0 2 m y ago the competent basin plain turbidites underwent flexural slip folding over an incompetent miocene sequence dominated by shale underlying competent paleogene strata were not folded the south flank of the ventura avenue anticline tilted at 3 4 rad yr the anticlinal crest rose at a rate of 15 16 mm yr decelerating to 4 3 5 2 mm yr and the anticline and an adjacent syncline shortened at a rate of 20 mm yr the high rate of folding in the ventura avenue oil field resulted in overpressured sandstone reservoirs and oil water interfaces which have not had time to reach gravity equilibrium the red mountain san cayetano and santa susana faults mark the surface expression of a seismically active midcrustal detachment which produced convergence across the ventura basin at rates as high as 23 mm yr total convergence across the eastern san cayetano fault near fillmore is 11 600 2000 m in the last million years

inferring stress from faulting from early concepts to inverse methods abstract we review the evolution of concepts on and methods of estimating the state of stress from fault movements theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip these optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane optimal stress directions for calcite twinning are obtained by a similar construction with the difference that they maximize shear stress force representation of seismic sources independently introduced pressure p and tension t axes at positions that also maximize shear stress on both nodal planes frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre existing faults this suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms early methods relied on geometrical constructions as a substitute for calculations whereas later methods relied on software as these calculations became tractable with the help of computers similar methods were developed for the inversion of stress from crystal twin gliding with non optimal geometry with a different criterion that relies on a threshold of the component of shear stress along the gliding line even though these methods seek a common stress tensor compatible with fault and slip data their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories fault and slip data can also be analyzed to constrain the strain rather than the stress tensor in most cases this involves a summation and yields an average strain for the considered rock volume stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them

recent crustal deformation in southern california deduced from the restoration of folded and faulted strata a rigid element method of restoration unfold is used to restore competent folded and faulted layers of the ventura and los angeles basins to their initial horizontal state comparison of initial undeformed state with present deformed state allows one to estimate both the finite crustal deformation and its associated horizontal displacement field relative to an arbitrary fixed line including data from the santa barbara channel basin the total finite displacement field for the western transverse ranges and vicinity within the pacific plate is inferred from this map restoration and is modeled as a double fan closure this model implies a 10 clockwise rotation of the northeen boundary of the western transverse ranges and a 5 counterclockwise rotation of its northeast boundary lateral variation of the deformation reveals the heterogeneity of the subsurface deformation most of the major thrusts appear to initiate as en echelon structures along the left lateral northern margin and the right lateral northeastern margin of the studied area the resulting deformation and displacement values closely match those derived by other geological methods section balancing techniques or fault slip measurements and by geophysical methods geodetic paleomagnetic and focal mechanism data map restoration thus is a method that can independently quantify both local and regional deformation including folds and faults this method also reveals the zones where problems of compatibility appear with the available geological and geophysical data and thus where the next studies might be focused

a direct method for modeling and unfolding developable surfaces and its application to the ventura basin california n order to draw precise geological structures using scattered data it is relevant to use criteria that integrate the kinematic properties of the structure for example developable folds can be selected by the observation of constant length deformation markers by establishing an accurate drawing of these folds it is possible to precisely determine the geometrical limits of basin we have developed a program developable mesh that integrates these developability criteria this program first builds a 3d mesh using criteria that are based on the geometrical properties of developable surfaces it then slightly modifies the mesh to improve its developability this mesh is finally unfolded this program has been tested on a natural example of the lateral evolution of a thrust system to a fold structure red mountain area in the ventura basin this particular structure has been already balanced by a trial and error method unfold program this test confirms the validity of our approach the developable mesh program builds near perfect developable folded surfaces therefore it is geometrically coherent and can unfold these surfaces in a very short time moreover the program is faster and can construct more complex developable surfaces than other conventional unfolding techniques based on a common interpolator