late carboniferous to permian sedimentation in inner mongolia china and tectonic relationships between north china and siberia a belt of deformed permo carboniferous sedimentary rocks in inner mongolia represents an orogenic zone between the north china and siberian blocks the belt apparently contains accretionary terranes thrust onto the margins of both blocks with scattered ophiolite blueschist suites indicating the consumption of oceanic crust at least slightly older than the age of deformation upper carboniferous to lower permian strata in central inner mongolia show both sedimentological and paleontological differences from middle and upper permian rocks in comparison with pre middle permian rocks younger permian strata 1 contain less laterally extensive limestone and more lensoidal carbonate in clastic sections 2 contain a higher percentage of coarse clastic material 3 grade upward from marine to terrestrial deposits 4 contain fauna indicating more restricted circulation particularly toward the western part of the belt and 5 contain fauna that are consistent with but do not require northward movement

boundary fault linkage and its effect on upper jurassic to lower cretaceous sedimentation in the gudian half graben songliao basin northeastern china abstract the songliao basin northeastern china is one of the few ultra large petroleum basins in the world fault superposition linkage and stratigraphic architecture have produced a complicated basin evolutionary history in this study we report the boundary fault linkage and associated upper jurassic and lower cretaceous stratigraphic record using 3d seismic reflection data and well data our results show that the geometry of the boundary gudian fault was originally controlled by six shorter fault segments which grew and were linked during a syn rift stage then frictionally weakened and inverted in a post rift stage this boundary fault has variably controlled coeval syn rift sedimentation fault segments in the middle section controlled the development of the limited but thickest huoshiling and the first member of shahezi formations in the early syn rift stage ca 150 133 9 ma later that control gradually weakened and vanished on succeeding the second member of shahezi and yingcheng formations in the late syn rift stage ca 133 9 105 ma the processes and the diverse syn rift sedimentation response to gudian fault growth and linkage have further implications for graben evolution and can guide hydrocarbon exploration in the songliao basin this study will help elucidate the different controls of boundary fault linkage on associated sedimentation as well as rift basins development in eastern china and similar areas throughout the world

proterozoic depletion of the lithosphere recorded in mantle xenoliths from inner mongolia mantle xenoliths entrained in alkali basalt provide direct samples from a cross section of the lithosphere in most cases the chemistry and isotope systematics of these objects have suggested a complex history of chemical change by processes such as metasomatism and partial melting see for example ref 1 here however we present evidence from a suite of xenoliths from alkali basalts in the chinese province of inner mongolia suggesting that the lithosphere in this region has remained stable and closed to chemical modification since experiencing partial melting in the proterozoic clinopyroxene separates from these xenoliths yield an approximate isochron in the 143nd 144nd versus 147sm 144nd diagram suggesting an episode of depletion 1 6 gyr ago although other explanations for this correlation such as mixing cannot be ruled out definitively further evidence for the long term undisturbed nature of the lithosphere in this region comes from neodymium model ages of the clinopyroxenes in particular one highly depleted sample with very high 147sm 144nd provides a model age of 1 6 gyr consistent with the isochron result

transient landscapes at fault tips 1 fault growth produces patterns of displacement and slip rate that are highly variable in both space and time this transience is most pronounced near fault tips where along strike displacement gradients vary in time as the fault array lengthens we use a set of statistical and field observations to quantify the response of catchments and their associated fans in three large normal fault arrays to transient patterns of displacement and slip rate catchments near the fault tips show distinct scaling of channel slope with drainage area compared with catchments near the strike center this scaling becomes uniform beyond about 10 km from the fault tips and is therefore like footwall relief largely decoupled from the fault displacement profile the estimated catchment response times to a change in slip rate also vary between fault tips and strike center the response times for tip catchments are much longer than the inferred time since fault activity began indicating that they are unlikely to be in equilibrium with the current fault displacement field this disequilibrium combined with the decoupling of slope area scaling from displacement indicates that landscapes are most sensitive to fault activity near fault tips active faults characterized by along strike variation in slip rate thus provide excellent opportunities to explore the transient response of landscapes to tectonic forcing

deposition of harmattan dust and its influence on base saturation of soils in northern ghana ferruginous soils formed from volta shale deposits in northern ghana are highly weathered have high iron and aluminium oxide contents and a mineralogy dominated by quartz and low activity clays with low effective cec despite their advanced weathering state base saturation values of top soils are generally above 80 and deficiencies of basic cations are uncommon we postulated that the annual deposition of dust from the sahara carried by the harmattan weather system may be responsible for the high base saturation therefore we collected dust material for two entire dry seasons at nyankpala surrounded by highly weathered volta shale deposits and during several events of harmattan and local dust storms at bolgatanga surrounded by a variety of parent materials long distance harmattan dust had a clearly finer particle size distribution than dust collected during local storms but angularity and evidence of weathering on dust particles did not distinguish dust from different sources in bolgatanga soils contained unweathered minerals derived from local parent materials and both local storm and harmattan dust contained large amounts of bases significant amounts of micas and feldspars and k contents up to 3 in the dust collected at nyankpala showed harmattan dust to be the source of k and other bases found on volta shale soils short distance dust in nyankpala was mostly quartz and vegetation ashes dust deposition during one harmattan season at nyankpala amounted to about 15 g m 2 and carried a total of 140 400 300 and 60 mg m 2 of mg ca k and na respectively these amounts could account for the high base saturation of the low cec in volta shale soils

the rudbār mw 7 3 earthquake of 1990 june 20 seismotectonics coseismic and geomorphic displacements and historic earthquakes of the western high alborz iran summary the rudb r earthquake of 1990 june 20 the first large magnitude earthquake with 80 km left lateral strike slip motion in the western high alborz fold thrust mountain belt was one of the largest and most destructive earthquakes to have occurred in iran during the instrumental period we bring together new and existing data on macroseismic effects the rupture characteristics of the mainshock field data and the distribution of aftershocks to provide a better description of the earthquake source its surface ruptures and active tectonic characteristics of the western high alborz the rudb r earthquake is one of three large magnitude events to have occurred in this part of the alborz during recorded history the damage distribution of the 1485 august 15 upper polrud earthquake suggests the east west kelishom left lateral fault which is situated east of the rudb r earthquake fault as a possible source the 1608 april 20 alamutrud earthquake may have occurred on the alamutrud fault farther east analysis of satellite imagery suggests that total left lateral displacements on the rudb r fault are a maximum of 1 km apparent left lateral river displacements of 200 m on the kashach l fault and up to 1 5 km of the kelishom fault which are situated at the eastern end of the rudb r earthquake fault also appear to indicate rather small cumulative displacements given the relatively small displacements the presently active left lateral strike slip faults of the western high alborz fold thrust belt may be younger than onset of deformation within the alborz mountains as a whole

synchronous opening of the rio grande rift along its entire length at 25 10 ma supported by apatite u th he and fission track thermochronology and evaluation of possible driving mechanisms one hundred and forty seven new apatite u th he ahe ages are presented from 32 sample locations along the flanks of the rio grande rift in new mexico and colorado these data are combined with apatite fission track aft analyses of the same rocks and modeled together to create well constrained cooling histories for rio grande rift flank shoulders the data indicate rapid cooling due to extension from ca 28 to 5 ma in the sawatch range ca 28 ma to quaternary in the sangre de cristo mountains ca 25 to 5 ma in the albuquerque basin and ca 25 to 10 ma in the southern rio grande rift in southern new mexico rapid cooling of rift flanks followed the oligocene ignimbrite flare up and the northern section of the rio grande rift in colorado exhibits semicontinuous cooling since the oligocene overall however rift flank cooling along the length of the rift was out of phase with high volume magmatism and hence is inferred to have been driven mainly by exhumation due to faulting although each location preserves a unique cooling history when combined with existing ahe data from the gore range in northern colorado and the sandia mountains in new mexico together these data indicate that extension and exhumation of rift shoulders were synchronous along 850 km of the length of the rio grande rift from 25 to 10 ma these time space constraints provide an important new data set with which to develop geodynamic models for initiation and evolution of continental rifting models involving northward propagation of rifting and colorado plateau rotation are not favored as primary mechanisms driving extension instead a geodynamic model is proposed that involves upper mantle dynamics during multistage foundering and rollback of a segment of the farallon plate near the laramide hinge region that extended between the wyoming and se new mexico high velocity mantle domains the first stage of flat slab removal accompanied ca 40 20 ma volcanism in the san juan and mogollon datil ignimbrite centers which initiated asthenospheric upwelling and circulation a second stage involved a ca 30 25 ma detachment of remaining fragments of the farallon slab intensifying asthenospheric upwelling and focusing it along a n s trend beneath colorado and new mexico by 25 ma the north american lithosphere had become weakened critically along this narrow zone so that extension was accelerated resulting in the observed 25 10 ma cooling indicated by the thermochronologic data this developed a central graben with increased fault related high strain rates and resulted in maximum sediment accumulation in the rio grande rift our geodynamic model thus involves oligocene removal of parts of the farallon slab beneath the ignimbrite centers followed by a major oligocene miocene slab break that instigated the discrete n s rio grande rift through focused upper mantle convection beneath the southern rocky mountain rio grande rift region

seismic imaging of the crust and upper mantle under beijing and surrounding regions abstract we determined a high resolution 3d p wave velocity model of the crust and upper mantle under beijing and surrounding regions in north china by jointly inverting 48 750 arrival times from 2973 local events and 12 249 relative residuals from 234 teleseismic events recorded by the newly built capital seismic network our results show considerable differences in the lithospheric structure down to about 200 km depth between the north china basin the taihangshan uplift and the yanshan uplift which are the three main tectonic units in the study area at depths of 50 150 km a pronounced low velocity anomaly exists under north china basin and bohai bay and right beneath it a high velocity anomaly extends down to about 200 300 km depth suggesting that this area has experienced large scale lithospheric thinning and lithospheric detachment has occurred the taihangshan front fault and the zhangjiakou penglai fault zone may have cut through the crust to lithosphere and they become flimsy tectonic boundaries and the asthenospheric materials may upwell from the two channels we consider that the deep and shallow structures beneath this region are closely related to dynamic processes that result from the deep subduction of the pacific slab and its stagnancy in the mantle transition zone under east asia

moment tensor solutions of the 1994 to 1996 double spring flat nevada earthquake sequence and implications for local tectonic models abstract the 12 september 1994 m w 5 8 double spring flat nevada earthquake initiated at the intersection of a northeast and northwest striking set of conjugate faults within an overlapping zone between the genoa and antelope valley fault zones of the eastern sierra nevadan range frontal fault system the mainshock ruptured on the northeast striking fault plane eight days after the mainshock the aftershock activity migrated from the mainshock fault plane to the northwest striking conjugate fault over the next 2 years aftershocks migrated southward onto another set of conjugate faults and then onto the antelope valley fault zone the focal mechanisms of 17 m 4 aftershocks were estimated from a time domain moment tensor inversion using regional broadband data the t axis minimum stress direction is oriented east west n80 e to n100 e for the m 4 events as is commonly observed along the eastern sierra nevadan range front in northwestern nevada from these results we make some general points that can be considered in seismic hazard assessment the maximum magnitude in overlapping normal fault zone is limited to the size of the overlapping zone this makes small to moderate size m m 7 earthquakes the seismicity within this overlapping zone may indicate interseismic strain accumulation from east west extension mainly through strike slip deformation the apparent scarcity of modern normal faulting earthquakes along the sierran range front faults suggests a characteristic model while a gutenberg and richter model for the recurrence behavior of earthquakes applies to the overlap zones between the normal faults the pattern of seismicity and principle stress directions from the aftershock fault plane solutions suggest a tectonic model of changing fault geometry for the overlapping zone between the genoa and antelope valley fault zones two plausible long term tectonic outcomes may develop with this model a normal fault growth model where the overlapping segments of the genoa and antelope valley faults eventually become hard linked form a throughgoing fault or a normal fault growth model where the overlapping segment of the genoa fault system grows southward while the antelope valley fault is isolated in the formation of new basins and ranges

what sets topographic relief in extensional footwalls we use three large normal fault arrays in the northeastern basin and range province western united states to document catchment development and relief production during fault growth fault slip and slip rates increase systematically along strike from zero at the fault tips catchment relief and across strike range width both increase as slip accumulates but reach maximum values at a distance of 15 km from the fault tips and remain uniform along strike over much of the footwalls catchment outlet spacing also increases away from the fault tips but does not reach a uniform value and may vary by a factor of 5 6 along strike we infer that catchments first elongate in the across strike direction as slip accumulates and the range half width increases once the half width reaches its maximum value continued catchment growth is possible only by along strike capture which increases outlet spacing but not relief the close correspondence between catchment relief and range half width suggests that geomorphically limited hillslope and channel gradients are achieved within the 15 km tip zone thus the limiting factor in footwall development is the width of the range which is controlled by two external agents the geometry and spacing of the major faults and the elevations of base level on both flanks

relay ramp forms and normal fault linkages canyonlands national park utah fieldwork within a series of mesoscale grabens in southeast utah has revealed a particularly well exposed system of interlinked extensional faults a series of down faulted grabens are developed within a 460 m thick brittle layer of upper paleozoic sandstone and shale which overlies a ductile layer with a high gypsum content all the major grabens consist of two or more overlapping elements which are composed of fault segments these segments may be hard linked fault surfaces are joined or soft linked fault surfaces are isolated but linked by ductile strain of the rock volume between them in map view relay structures are defined as zones connecting the footwalls and hanging walls of overlapping fault segments representing soft linkage of fault segments in the canyonlands grabens the transfer of displacement between soft linked fault segments is characterized by well de fined dipping relay ramps commonly rotated and extended to accommodate the ductile strain between the overlapping fault segments relay ramps develop as ephemeral structures eventually becoming breached by hard linkage of the fault segments breakdown of ramps by breaching is part of the process of fault growth by segment linkage within the canyonlands graben system four orders of segmentation are present this may be a consequence of different scales of mechanical heterogeneity but evidence from the canyonlands grabens and elsewhere points to a fundamental process of discontinuous fault growth by segment linkage

displacement geometry in the volume containing a single normal fault fault displacements measured in coal mines and from seismic data are used to develop a model describing the near field displacements associated with an ideal single normal fault displacement on a fault surface ranges from a maximum at the center of the fault to zero at the edge or tip line the tip line is elliptical with the shorter axis of the ellipse parallel to the displacement direction contours of equal displacement form concentric ellipses centered on the point of maximum displacement displacement gradients vary with fault size and with mechanical properties of host rock fault radius to maximum displacement ratios range from 5 to 500 plotting of displacement contour diagrams and knowledge of displacement gradients are useful in interpreting seismic reflectio data both for quality control of interpretations and for quantitative extrapolation of limited data displacements associated with faulting decrease systematically with increasing distance along the normal to the fault surface this decrease is seen as reverse drag in both hanging wall and footwall hanging wall rollover and tilting of the reflectors cannot be used to distinguish listric from planar normal faults even where fault block rotation can be demonstrated neither listric fault geometry nor a flat detachment surface is geometrically necessary because faulting is accommodated by ductile deformation rigid fault bounded blocks cannot exist except in some special circumstances related to a free surface the displacements within the rock volume affected by a single fault are not simply related to regional extension apparent horizontal extension by faulting varies from one layer to another and a significant proportion of the extension in a basin may be due to ductile deformation

structural geology and 4d evolution of a half graben new digital outcrop modelling techniques applied to the nukhul half graben suez rift egypt abstract lidar based digital outcrop mapping in conjunction with a new surface modelling approach specifically designed to deal with outcrop datasets is used to examine the evolution of a half graben scale normal fault array in the suez rift syn rift deposition in the nukhul half graben was controlled by the graben bounding nukhul fault the fault can be divided into four segments based on the strike of the fault the morphology of hangingwall strata and the variation in throw along strike the segments of the fault became geometrically linked within the first 2 5 m y of rifting as evidenced by the presence of early syn rift abu zenima formation strata at the segment linkage points fault perpendicular folds in the hangingwall related to along strike variations in throw associated with precursor fault segments persist for a further 1 8 m y after linkage of the segments suggesting that the fault remains kinematically segmented we suggest this occurs because of sudden changes in fault strike at the segment linkage points that inhibit earthquake rupture propagation or because displacement is geometrically inhibited at fault linkage points where the orientation of the intersection line of the segments is significantly different from the orientation of the slip vector on the fault system length throw plots and throw contour patterns for minor faults show that some faults initiated in pre rift strata whereas late east striking faults initiated in the syn rift basin fill the late initiating faults are spatially associated with the east striking baba markha fault which was active throughout the rift history but developed as a transfer fault between major block bounding fault systems around 6 7 ma after rift initiation

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

the growth of fault bounded tilt blocks a series of uniformly tilted fault bounded blocks is a common feature in actively extending regions such as the basin and range province if the tilted blocks were produced by rigid domino style rotation one would predict large voids at either end of a series of these blocks using tilt data and a simple flexural calculation we suggest that much of the apparent rigid behavior could also be produced by internal block deformation in our model of normal fault growth isostatic elastic uplift of the footwall is coupled with hanging wall downdrop within the region between faults resulting in the appearance of a tilted rigid block we present tilt data sampled at varying distances from several block defining faults within the northeast basin and range province tilt measurements between a series of 30 km spaced block defining faults are found to be uniform while tilts between more widely spaced faults exhibit a pattern of tilt that diminishes to zero in less than 30 km using a simple flexural calculation for internal block deformation we show that for this region the patterns of tilt are consistent with a flexural length scale of 8 12 km and deflections of 2 4 km these estimates are compatible with both the lower limit to seismicity and basin depth determined from earthquake and seismic reflection studies

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

evidence for high frequency cyclic fault activity from high resolution seismic reflection survey rukwa rift tanzania a high resolution seismic survey of the rukwa rift has imaged the upper 300 m of the pliocene holocene section the sediments are characterized by aggradational deposition in shallow lacustrine conditions that episodically dried out overall the reflection package expands northeastwards towards the lupa fault half graben bounding fault isopach maps for nine intervals 6 m to 65 m thick show four periods of marked expansion of the section towards the lupa fault interpreted to represent times of fault activity or infilling of fault created topography during the early stage of fault quiescence there are three periods of little or much reduced expansion interpreted to represent infilling of the accommodation space between the lake floor and the lake surface during periods of fault inactivity cyclicity of such high frequency has not been widely reported for faults which penetrate the crust the periods of activity show remarkably similar displacement patterns with no lateral migration of the main depocentre implying that seismic and aseismic slip has persistently clustered in the same parts of the fault identification of high frequency fault cyclicity has implications for sequence stratigraphy in tectonically active areas since there is a tendency to assume faults do not have cyclic effects on the scale of tens of thousands of years

drainage systems and the development of normal faults an example from pleasant valley nevada abstract drainage systems in regions of active extension contain information about fault zone structure and development and particularly about the lateral growth of individual fault segments that is difficult to obtain by more conventional means such as the dating of sedimentary material we investigate drainage fault interaction in pleasant valley nevada where a large normal faulting earthquake occurred in 1915 we find geomorphological evidence for a propagation increase in length of several km at both ends of one of the 1915 fault segments at one end we estimate the propagation rate to be about 50 m per earthquake this estimate is uncertain but is within the range predicted by theoretical models of fault growth drainage along the axes of half graben in this region may be influenced by the spacing of tilted fault blocks the highest valleys are also the narrowest whether the axial streams succeed in reaching lower neighbouring sinks depends on whether sedimentation rates are able to keep basins filled to the levels of the basement highs that separate half graben of opposite polarity a knowledge of modern drainage fault interactions may help predict drainage systems and the position of potential syn rift reservoir sediments in older extensional terrains where fault configurations but not facies distributions are known from seismic reflection surveys

dem based morphometry of range front escarpments in attica central greece and its relation to fault slip rates in this paper we apply current geological knowledge on faulting processes to digital processing of digital elevation models dem in order to pinpoint locations of active faults the analysis is based on semiautomatic interpretation of 20 and 60 m dem and their products slope shaded relief in northern eastern attica five normal fault segments were recognized on the 20 m dem all faults strike wnw ese the faults are from west to east thriassion thfs fili fifs afidnai affs avlon avfs and pendeli pefs and range in length from 10 to 20 km all of them show geomorphic evidence for recent activity such as prominent range front escarpments v shaped valleys triangular facets and tilted footwall areas however escarpment morphometry and footwall geometry reveal systematic differences between the bexternalq segments pefs thfs and avfs and the binternalq segments affs and fifs which may be due to mechanical interaction among segments and or preexisting topography in addition transects across all five escarpments show mean scarp slope angles of 22 18f0 78 for both carbonate and metamorphic bedrock the slope angle equation for the external segments shows asymptotic behaviour with increasing height we make an empirical suggestion that slope angle is a function of the long term fault slip rate which ranges between 0 13 and 0 3 mm yr the identified faults may rupture up to magnitude 6 4 6 6 earthquakes the analysis of the 60 m dem shows a difference in fault patterns between western and northern attica which is related to crustal rheology variations d 2004 elsevier b v all rights reserved

origin damping and pattern of development of faults in granite observations of brittle fractures in the granite of the massif de la borne as well as in other rocks allow us to discuss the different hypotheses regarding the origin of faults it seems that all faults originate by shear along a preexisting plane which can be an important fracture joint former fault or a microflaw pore grain boundary the shear on the plane gives rise to an array of en echelon cracks that makes the rock less resistant and permits the lengthening of the fault we also found an arrangement of horsetail fractures damping the movements on the faults we then propose a pattern for the development of the faults they originate on preexisting plane and propagate by initiating en echelon cracks the movements are damped by horsetails which permit by faults connection in relays the creation of larger faults

the dinevar transtensional pull apart basin nw zagros mountains iran a geological study and comparison to 2d finite element elastic models the dinevar transtensional pull apart basin is a nw se trending basin located in the northwest part of the zagros mountains sanandaj sirjan tectonic zone iran this basin was formed by oblique extension in a strike slip fault system which was controlled by the pre existing sahneh and the mianrahan faults in addition to a field study we constructed a 2d finite element elastic model based on the major fault segments according to the field study various geological structures are formed around the pre existing fault segments including pencil structures with 13 aspect ratio 19 tight to open asymmetric folds oblique normal faults synthetic and antithetic faults normal and reverse fault drags and negative and hybrid type flower structure fe model results show that around the fault step is a zone of displacement gradient that indicates extension transtension within the overlapping zone consequently subsidence is predicted over the releasing fault step the modelled stress distributions within the fault step and around the fault segment tips are asymmetric elastic modelling shows that the mean normal stress within the step is tensional which would impede plastic yield while the region outside the step is characterised by compressive mean normal stress the mean normal stress pattern is characterised by a regional minimum localised inside the extensional step transtension zone and two local maximum and minimum couples formed at the advancing and retreating sides respectively in the fault segment tips the results show that two main subsidence regions depocentres or sub basins form along and in the proximity of the fault segment tips the imposed relative motion is entirely accommodated by creep on the faults which causes plastic strain to accumulate outside the faults mostly localised within the fault step this localised strain between fault segments could initiate connecting faults or reactivate earlier faults generally at high angles relative to the master fault segments as suggested by the stress and strain patterns the rotation and magnitude variation in the stress and strain trajectories reflects heterogeneous deformation in general the dinevar transtensional pull apart basin is characterised by an elongate rhomboidal to trapezoidal shaped geometry the modelled stress distribution and strain localisations within the basin are in general agreement with the locations of fault segments within the dinevar transtensional pull apart basin

fault growth and propagation during incipient continental rifting insights from a combined aeromagnetic and shuttle radar topography mission digital elevation model investigation of the okavango rift zone northwest botswana 1 digital elevation models dem extracted from the shuttle radar topography mission srtm data and high resolution aeromagnetic data are used to characterize the growth and propagation of faults associated with the early stages of continental extension in the okavango rift zone orz northwest botswana significant differences in the height of fault scarps and the throws across the faults in the basement indicate extended fault histories accompanied by sediment accumulation within the rift graben faults in the center of the rift either lack topographic expressions or are interpreted to have become inactive or have large throws and small scarp heights indicating waning activity faults on the outer margins of the rift exhibit either 1 large throws or significant scarp heights and are considered older and active or 2 throws and scarp heights that are in closer agreement and are considered young and active fault linkages between major fault systems through a process of fault piracy have combined to establish an immature border fault for the orz thus in addition to growing in length by along axis linkage of segments the rift is also growing in width by transferring motion to younger faults along the outer margins while abandoning older faults in the middle finally utilization of preexisting zones of weakness allowed the development of very long faults 100 km at a very early stage of continental rifting explaining the apparent paradox between the fault length versus throw for this young rift this study clearly demonstrates that the integration of the srtm dem and aeromagnetic data provides a 3 d view of the faults and fault systems providing new insight into fault growth and propagation during the nascent stages of continental rifting

mesozoic crust mantle interaction beneath the north china craton a consequence of the dispersal of gondwanaland and accretion of asia we present evidence from zircons entrained within lower crustal xenoliths in the cenozoic hannuoba basalt of multiple melting events beneath the north china craton in the late mesozoic peak activity was between 180 and 80 ma the upper crustal signature of which was the generation of voluminous granitoids and related volcanic rocks emplacement of dioritic and lamprophyric dikes and widespread gold mineralization the process involved partial loss of mantle lithosphere accompanied by wholesale rising of asthenospheric mantle beneath eastern china we correlate these events with lithospheric thinning resulting from the breakup and dispersal of gondwanaland accompanied by a major mantle overturn fueled by the destruction of oceanic lithosphere and triggered by its sinking into the lower mantle during the subsequent accretion of asia

active simultaneous uplift and margin normal extension in a forearc high crete greece abstract the island of crete occupies a forearc high in the central hellenic subduction zone and is characterized by sustained exhumation surface uplift and extension the processes governing orogenesis and topographic development here remain poorly understood dramatic topographic relief 2 6 km astride the southern coastline of crete is associated with large margin parallel faults responsible for deep bathymetric depressions known as the hellenic troughs these structures have been interpreted as both active and inactive with either contractional strike slip or extensional movement histories distinguishing between these different structural styles and kinematic histories here allows us to explore more general models for improving our global understanding of the tectonic and geodynamic processes of syn convergent extension we present new observations from the south central coastline of crete that clarifies the role of these faults in the late cenozoic evolution of the central hellenic margin and the processes controlling quaternary surface uplift pleistocene marine terraces are used in conjunction with optically stimulated luminesce dating and correlation to the quaternary eustatic curve to document coastal uplift and identify active faults two south dipping normal faults are observed which extend offshore offset these marine terrace deposits and indicate active n s margin normal extension further marine terraces preserved in the footwall and hanging wall of both faults demonstrate that regional net uplift of crete is occurring despite active extension field mapping and geometric reconstructions of an active onshore normal fault reveal that the subaqueous range front fault of south central crete is synthetic to the south dipping normal faults on shore these findings are inconsistent with models of active horizontal shortening in the upper crust of the hellenic forearc rather they are consistent with topographic growth of the forearc in a viscous orogenic wedge where crustal thickening and uplift are a result of basal underplating of material that is accompanied by extension in the upper portions of the wedge within this framework a new conceptual model is presented for the late cenozoic vertical tectonics of the hellenic forearc

tracing tectonic deformation using the sedimentary record an overview tectonic activity on a range of scales is a fundamental control on sedimentary activity the range of structural deformation within a region extends from the plate tectonic scale governing for example rift initiation to the basin scale with the formation of basin bounding faults internal basin configuration is also strongly influenced by tectonic activity however the relationship between tectonic activity and sedimentation is a complex one given the many additional factors which can also influence sedimentary activity including erosion sediment transport source area lithology groundwater chemistry range of depositional environments climate eustasy and the relative location of an area and its distality to marine influences in this paper we provide a selective overview of the issues associated with the interlinked themes of tectonics and sedimentation examining the main basin types forming in both extensional and compressional plate settings we then review the various models of sedimentation in the selected basins both on a local and a basinal scale finally we look to the future providing a series of possible research areas almost exclusively multidisciplinary which would help to improve existing models of interlinked sediment tectonics systems

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

magnetostratigraphic dating of the late miocene baogeda ula formation and associated fauna in central inner mongolia northern china abstract detailed understanding to the evolution of neogene land mammals in east asia and its intercontinental correlation has been impeded by the absence of an integrated biochronological system of this region the numerous and diverse records of neogene vertebrate fossils preserved in inner mongolia of northern china play a key role in the establishment of an independent biochronological framework in east asia however most of these faunas are poorly constrained by independent chronological controls due to the scattered distribution of fossil localities and insufficient exposure of the fossiliferous strata additionally age estimates by mammalian evolution and correlation often have uncertainties greater than 1 2 million years here we present new magnetostratigraphic results of the baogeda ula fauna which was generally assigned an early baodean age late miocene or equivalent to the european mn12 zone middle turolian hipparion remains and associated vertebrate fossils were excavated from the upper part of the fluvio lacustrine baogeda ula formation near abaga banner central inner mongolia of northern china at least two layers of basalt sheet flows can be observed on top of the baogeda ula formation our magnetostratigraphy aided by published biochronology data and k ar ages of the lower basalt layer suggests that the baogeda ula fauna consisting of three fossiliferous horizons can be placed within chron c4n 1n with an age range of 7 642 7 528 ma thus the baogeda ula fauna becomes the first and only baodean assemblage that is constrained by both magnetostratigraphy and radiometric ages offering an anchoring point for future biochronological correlations

early tertiary sinistral transpression and fault reactivation in the western voring basin norwegian sea implications for hydrocarbon exploration and pre breakup deformation in ocean margin basins the nyk high is an approximately northeast trending late cretaceous to early tertiary structural high situated in the western voring basin offshore norway it is defined by a thick sequence of upper cretaceous to lower tertiary sediments that dip toward the southeast and are cut by normal faults with throws up to 1500 m 4921 ft across fault sediment thickness variations and stratigraphic onlap relationships show that these faults were active during campanian to early paleocene extension prior to the separation of norway from greenland ca 55 ma sediments preserved in the hanging walls of these rift related normal faults are deformed by two populations of folds one set is oriented clockwise of the fault strike the other is oriented parallel to the fault strike stratigraphic relationships show that both sets of folds formed subsequent to rifting during the latest paleocene to the earliest eocene we interpret these folds as having developed during minor sinistral transpression which was partitioned between the northeast southwest sinistral strike slip reactivation of the normal faults and the northwest southeast coaxial shortening folding within the fault hanging walls the nyk high is oriented counterclockwise to the inferred line of the continental breakup we speculate that transpression was driven by north northwest forces arising from the differential topography along the incipient plate boundary and the presence of hot buoyant material beneath this elevated axial region such deformation will not necessarily impact significantly on source rock maturity or the distribution of reservoir sands but can give rise to unusual structural trap geometries it is also likely to increase the connectivity of trap bounding faults

pattern of shallow ground water flow at mount princeton hot springs colorado using geoelectrical methods abstract in geothermal fields open faults and fractures often act as high permeability pathways bringing hydrothermal fluids to the surface from deep reservoirs the mount princeton area in south central colorado is an area that has an active geothermal system related to faulting and is therefore a suitable natural laboratory to test geophysical methods the sawatch range front normal fault bordering the half graben of the upper arkansas valley is characterized by a right lateral offset at mount princeton hot springs this offset is associated with the chalk cliffs of hydrothermally altered quartz monzonite because fault identification in this area is complicated by quaternary deposits including glacial and fluvial deposits we use dc electrical resistivity tomography and self potential mapping to identify preferential fluid flow pathways the geophysical data over 5600 resistivity and 2700 self potential measurements provide evidence of the existence of a dextral strike slip fault zone fault b responsible for the offset of the sawatch fault a segment of this dextral strike slip fault termed u1 is acting as the dominant vertical flow path bringing thermal waters to a shallow unconfined aquifer upwelling of the thermal waters is also observed at two zones u2 and u3 of an open fracture called fault a this fault is located at the tip of the sawatch fault and is likely associated with an extensional strain regime in this area self potential measurements are used to estimate the flux of upwelling thermal water the upflow estimate 4 1 10 3 m 3 day for the open segment of the fault b and 2 1 10 3 m 3 day for fault a from the geophysical data is remarkably consistent with the downstream mt princeton hot water production 4 3 4 9 10 3 m 3 day at approximately 60 86 c a temperature map indicates that a third upwelling zone termed u4 may exist at the southern tip of the sawatch fault

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

meteorological causes of harmattan dust in west africa we investigated the temporal dynamics of dust entrainment in the bodele depression central sahara to better understand the intra annual variability of aerosol emission in the world s largest dust source the linkages between dust entrainment and large scale meteorological factors were examined by correlating several meteorological variables in the mediterranean and africa north of the equator with the aerosol concentrations in the bodele depression separately for winter and summer the methodological tools applied are ncep ncar reanalysis data and the aerosol index of the total ozone mapping spectrometer toms ai available for 15 years from 1978 to 1993 we found that dust mobilisation during the harmattan season is highly dependent on air pressure variability in the mediterranean area high pressure to the north of the bodele intensifies the ne trade winds leading to an increased entrainment of dust in the bodele depression in summer dust mobilization cannot be explained by the large scale meteorological conditions this highlights the importance of local to regional wind systems linked to the northernmost position of the intertropical convection zone itcz during this time

postglacial slip rate increase on the teton normal fault northern basin and range province caused by melting of the yellowstone ice cap and deglaciation of the teton range along the eastern front of the teton range wyoming prominent fault scarps offset pinedale deposits by up to 30 m and document that multiple earthquakes ruptured the range bounding teton normal fault after the last glacial period paleoseismological data suggest that 70 of the postglacial slip on the southern teton fault accumulated during or shortly after deglaciation before 8 ka here we use a three dimensional fi nite element model to show that melting of the yellowstone ice cap and the valley glaciers in the teton range may have caused the postglacial slip rate increase on the teton fault during deglaciation slip on our model fault accelerates by a factor of 6 with respect to the long term rate our model further shows that the impact of the melting yellowstone ice cap on fault slip increases along strike of the fault from south to north and is everywhere larger than the effect of the former valley glaciers in the teton range the results demonstrate that postglacial slip on faults in glaciated regions may not have been uniform through time rather a signifi cant fraction of slip may have accumulated within a few thousand years after the last glaciation we hypothesize that the rebound caused by the yellowstone ice cap has also triggered clusters of earthquakes on other normal faults in the surrounding basin and range province

structural and geomorphological constraints on active normal faulting and landscape evolution in calabria italy calabria is one of the fastest uplifting and most seismically active regions in the mediterranean yet the time averaged c 10 6 years rates of normal faulting remain poorly constrained here we use digital elevation model analysis geological cross sections and a compilation of published data to quantify systematically along strike the fault throws and time averaged throw rates of the serre cittanova armo east crati and west crati faults we show that regional uplift has uplifted both their hanging wall and footwall blocks by c 200 400 m and the aspromonte massif by up to c 1150 1300 m we find that these faults have throws between c 640 and 1430 m and throw rates between c 0 6 and 1 4 mm a 1 their footwall ranges have variable proportions of inherited relief up to c 300 800 m the channels draining these ranges reflect the active normal faulting and relief in their steepness indices becoming c 5 8 m 0 9 steeper for each 0 1 mm a 1 throw rate increment and each 100 m relief increase finally the presence of knickpoints suggests that these channels are transiently responding to changes in relative base level which could be due to fault linkage or regional strain rate increases for the southern calabrian faults and to regional uplift acceleration in the case of the crati faults supplementary material topographic profiles of the marine terraces and long profiles of rivers are available at https doi org 10 6084 m9 figshare c 3689464

is lithostatic loading important for the slip behavior and evolution of normal faults in the earth s crust normal faults growing in the earth s crust are subject to the effects of an increasing frictional resistance to slip caused by the increasing lithostatic load with depth we use three dimensional 3 d boundary element method numerical models to evaluate these effects on planar normal faults with variable elliptical tip line shapes in an elastic solid as a result of increasing friction with depth normal fault slip maxima for a single slip event are skewed away from the fault center toward the upper fault tip there is a correspondingly greater propagation tendency at the upper tip however the tall faults that would result from such a propagation tendency are generally not observed in nature we show how mechanical interaction between laterally stepping fault segments significantly competes with the lithostatic loading effect in the evolution of a normal fault system promoting lateral propagation and possibly segment linkage resultant composite faults are wider than they are tall resembling both 3 d seismic data interpretations and previously documented characteristics of normal fault systems however this effect may be greatly complemented by the influence of a heterogeneous stratigraphy which can control fault nucleation depth and inhibit fault propagation across the mechanical layering our models demonstrate that although lithostatic loading may be an important control on fault evolution in relatively homogeneous rocks the contribution of lithologic influences and mechanical interaction between closely spaced laterally stepping faults may predominate in determining the slip behavior and propagation tendency of normal faults in the earth s crust

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

modelling of bed contours and cross sections adjacent to planar normal faults the geometry of beds in the volume surrounding a single blind planar fault depends on i the axial ratio of the fault surface ellipse ii the ratio between the maximum displacement and the maximum dimension of the fault surface iii the displacement distribution on the fault surface from the point of maximum displacement to zero displacement at the tip line loop fault surface displacement profile and iv the rate at which the displacement decreases to zero along a normal to the fault surface reverse drag displacement profile these relationships which are either known or can be estimated are incorporated in a computer model which generates structural contours on horizons intersected by a planar fault structural contour patterns also vary with the pre faulting dip and strike of beds the dip and strike of the fault and the level at which a bed intersects the fault surface when the boundary conditions are relaxed to include synsedimentary faults the ratio of hangingwall to footwall displacement varies systematically with fault dip a synthetic structural contour map is matched with that of an actual fault model isopachs based on simple depositional models are generated for synsedimentary units cross sections are generated for synsedimentary faults by sequential fault growth and sedimentary deposition and show features similar to actual cross sections the soft domino model is applicable primarily to dip slip tectonic faults with maximum displacements of up to about 5 km listric faults are not considered

investigating topographic metrics to decipher structural model and morphotectonic evolution of the frontal siwalik ranges central himalaya nepal abstract the fold and thrust belt in the himalayan front is marked by the upliftment of the frontal outermost siwalik hills along the main frontal thrust mft these frontal ranges display distinct morphology with prominent curved stair stepped and overlapping segments in the central himalaya in this study we analyse the structural framework morphology growth and relative uplift rates of the frontal ranges in the central himalaya using various topographic metrics the results suggest that the frontal ranges are folds developed along six mft segments that have interacted to form the present day topography these segments are also overlapping in some areas thus resulting in stress partitioning we also identify a nw se trending pre existing tear fault in the region that forms barrier to the growth and propagation of the mft segments and the frontal ranges along it the uplift rates are generally lower on relatively older fault segments due to initiation of the younger overlapping faults it is supported by the results of the morphometric indices as the older and less active mft segments yield high mountain front sinuosity ratio 1 3 2 2 and valley floor width to height ratio 3 3 14 6 and low values of steepness index 0 2 0 8 and hypsometric integral 0 4 0 5 growing folds along the mft segments have resulted in the deflection of the narayani and the east rapti rivers we establish a model for the initiation and growth of various structural segments in the study area and the resultant drainage reorganisation

role of tectonic denudation in warping and uplift of low angle normal faults large displacement on a low angle normal fault results in isostatic uplift of the lower plate in response to tectonic denudation simple models of the denudation process predict warping of the lower plate into a broad antiform or antiform synform pair with axes perpendicular to the direction of extension the amount of warping is strongly influenced by initial fault geometry surface topography the amount of extension and the distribution of extension within the upper plate late stage processes that augment antiform growth include one sided denudation of the antiform reverse faulting due to concave upward flexure and wholesale detachment and reverse drag folding of the antiform antiformal uplifts now exhumed by erosion form mountain ranges in the southwestern united states where conditions were favorable for warping during mid tertiary crustal extension four major structural domains are apparent in transects across these uplifts and adjacent areas 1 unextended area 2 synformal upper plate 3 antiformal uplift and 4 wedge shaped upper plate each domain is separated from adjacent domains by the traces of a master low angle normal fault

magmatism and extension the thermal and mechanical effects of the yellowstone hotspot currently there is a parabolic shaped pattern of seismicity and latest quaternary faulting which centers on the axis of the eastern snake river plain srp and has its apex at the yellowstone plateau the pattern of activity surrounds a region of aseismicity that includes the eastern srp geologic evidence suggests that this pattern has migrated in tandem with rhyolitic volcanism induced by the yellowstone hotspot during its 16 m y trek across western north america similarly there is a migration in the onset of basaltic lava flows and the emplacement of up to 12 km of midcrustal mafic intrusions that follows the track of rhyolitic volcanism these observations suggest that the intrusion of magmas has a significant influence on the pattern of seismicity and faulting we present a one dimensional finite difference thermomechanical model that accounts for the observed pattern of increased faulting followed by fault quiescence within the circum eastern srp in this model mafic magmas are intruded into a lithosphere that is already extending the intrusions heat the surrounding rocks resulting in locally increased strain rates as the intruded magmas solidify the length of time required to return strain rates to their pre intrusion level is then determined the model assumes constant horizontal tectonic forces and maps strain rate as a function of yield strength and time since intrusion we vary model parameters such as crustal thickness initial geothermal gradient and amount of magma intruded in order to assess how they affect turnaround time for strain rates the amount and timing of intruded material allowed by the model are constrained by seismic refraction data as well as by regional geochronologic and petrologic studies we assume intruded rock rheology to be a maryland diabase mantle rheology we base on dry olivine we represent the crust by both dry granite and dry anorthosite rheologies our results suggest that 2 to 3 m y appears to be a reasonable length of time for strain rates to return to levels present before a midcrustal mafic intrusion equivalent in magnitude to the yellowstone intrusion this corresponds closely to the length of time between the onset of along axis accelerated faulting and subsequent fault quiescence assuming a hotspot velocity of 3 5 to 4 0 cm yr relative to the north american plate

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

initiation conditions for debris flows generated by runoff at chalk cliffs central colorado abstract we have monitored initiation conditions for six debris flows between may 2004 and july 2006 in a 0 3 km 2 drainage basin at chalk cliffs a band of hydrothermally altered quartz monzonite in central colorado debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14 to 45 the availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes rainfall exceeding i 6 61 d 0 77 where i is rainfall intensity mm h and d is duration h was required for the initiation of debris flows in the drainage basin the approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0 15 m 3 s colluvium in the basin was unsaturated immediately prior to antecedent and during debris flows antecedent volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4 9 and 4 7 respectively during debris flows peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10 20 and 4 12 respectively channel sediment at a depth of 45 cm was unsaturated before and during debris flows antecedent moisture ranged from 20 22 and peak moisture ranged from 24 38 although we have no measurements from shallow rill or channel sediment we infer that it was unsaturated before debris flows and saturated by surface water runoff during debris flows our results allow us to make the following general statements with regard to debris flows generated by runoff in semi arid to arid mountainous regions 1 high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff 2 locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows and 3 rainfall and simulated surface water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment

geochemical tracers of mantle processes the mantle can be sampled directly only very rarely geochemists have thus come to rely heavily on mantle derived magmas to study the composition and evolution of the mantle only those compositional features that are unaffected by magmatic processes are useful as tracers of mantle processes these include radiogenic isotope ratios such as those of he sr hf and os stable isotope ratios and ratios of highly incompatible elements or elements of similar incompatibility such as ba nb or pb ce the term incompatible denotes a preference of the element for a melt over mantle minerals highly incompatible elements will partition entirely into the melt under most circumstances so that the ratio of two such elements in a basalt will be virtually identical to that ratio in its source this is also true to a lesser degree of ratios such as la sm and zr nb as zr and sm are not highly incompatible elements

structural and stratigraphic development of the newark extensional basin eastern north america evidence for the growth of the basin and its bounding structures the newark basin is a half graben bounded on its northwestern margin by a system of mostly normal slip faults many of which are reactivated paleozoic thrust faults and were active at least sporadically during the deposition of the entire basin fill as a result of along strike variations in displacement on the border fault system subsidence increased from the lateral edges toward the center of the basin and from the hinged margin toward the border fault system some intrabasinal faults also formed during the deposition of units currently preserved in their hanging walls along strike variations in the density of intrabasinal faults probably reflect changes in the dip angle of the border fault system variations in the amount of extension accommodated on these intrabasinal faults resulted in the formation of a transfer fault along strike variations in fault displacement probably produced the transverse folds in the hanging walls immediately adjacent to border faults and major intrabasinal normal faults some folds formed syndepositionally progressively younger strata onlap basement rocks along the hinged margin of the basin and younger splays of the border fault system propagated into the footwall the basin therefore grew deeper wider and longer through time

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

evidence for spreading rate dependence in the displacement length ratios of abyssal hill faults at mid ocean ridges new data from the eastern flank of the mid atlantic ridge 25 27 n show that slow spreading abyssal hill faults maintain maximum displacement length ratios that are systematically greater than those reported on the fast spreading east pacific rise lower displacement length ratios in the fast spreading environment may reflect the importance of fault linkage rather than lateral propagation in determining the lengths of abyssal hill faults and the limited ability of fault systems that evolve within an extremely thin lithosphere to acquire additional displacement during or following linkage

integrating 3 d seismic data field analogs and mechanical models in the analysis of segmented normal faults in the wytch farm oil field southern england united kingdom we propose a methodology for the analysis of normal fault geometries in three dimensional 3 d seismic data sets to provide insights into the evolution of segmented normal fault systems and to improve recovery efforts in fault controlled oil fields limited seismic resolution can obscure subtle fault characteristics such as segmentation and gaps in fault continuity that are significant for oil migration and thus accurate reservoir characterization detailed seismic data analyses that incorporate principles of normal fault mechanics however can reveal evidence of fault segmentation we integrate seismic attribute analyses outcrop analog observations and numerical models of fault slip and displacement fields to augment the use of 3 d seismic data for fault interpretation we applied these techniques to the wytch farm oil field in southern england resulting in the recognition of significant lateral and to a lesser extent vertical segmentation of reservoir scale faults slip maxima on fault surfaces indicate two unambiguous segment nucleation depths controlled by the lithological heterogeneity of the faulted section faults initiated preferentially in brittle sandstone and limestone units subsequent growth and linkage of segments predominantly in the lateral direction resulted in composite fault surfaces that have long lateral dimensions and multiple slip maxima reservoir compartmentalization is greatest at the level of prevalent segment linkages which corresponds at wytch farm with the predominant hydrocarbon producing unit the sherwood sandstone at relatively shallower depths fault segments are younger and less evolved resulting in a greater degree of segmentation with intact relay zones

sediment entrainment by debris flows in situ measurements from the headwaters of a steep catchment 1 debris flows can dramatically increase their volume and hence their destructive potential by entraining sediment yet quantitative constraints on rates and mechanics of sediment entrainment by debris flows are limited using an in situ sensor network in the headwaters of a natural catchment we measured flow and bed properties during six erosive debris flow events despite similar flow properties and thicknesses of bed sediment entrained across all events time averaged entrainment rates were significantly faster for bed sediment that was saturated prior to flow arrival compared with rates for sediment that was dry bed sediment was entrained from the sediment surface downward in a progressive fashion and occurred during passage of dense granular fronts as well as water rich inter surge flow en massefailure of bed sediment along the sediment bedrock interface was never observed large magnitude high frequency fluctuations in total normal basal stress were dissipated within the upper 5 cm of bed sediment within this near surface layer concomitant fluctuations in coulomb frictional resistance are expected irrespective of the influence of pore fluid pressure or fluctuations in shear stress if the near surface sediment was wet as it was overridden by a flow additional large magnitude high frequency pore pressure fluctuations were measured in the near surface bed sediment these pore pressure fluctuations propagated to depth at subsonic rates and in a diffusive manner the depth to which large excess pore pressures propagated was typically less than 10 cm but scaled as d fi 0 5 in which d is the hydraulic diffusivity and fiis the frequency of a particular pore pressure fluctuation shallow penetration depths of granular normal stress fluctuations and excess pore pressures demonstrate that only near surface bed sediment experiences the full dynamic range of effective stress fluctuations and as a result can be more easily entrained than deeper sediment these data provide robust tests for mechanical models of entrainment and demonstrate that a debris flow over wet bed sediment will be larger than the same flow over dry bed sediment

active breaching of a geometric segment boundary in the sawatch range normal fault colorado usa abstract the northwest trending sawatch range normal fault system is the principal range bounding fault of the northern rio grande rift of central colorado it displays a geometric segment boundary in the form of a prominent en echelon step at the chalk cliffs a zone of highly fractured and hydrothermally altered quartz monzonite there the modern fault geometry suggests that the sawatch range fault is presently breaching the boundary immediately north of the chalk cliffs the range front fault is active whereas immediately south the range front fault is inactive instead it is replaced by a north trending break that transects much of the boundary the chalk cliffs also display a four stage history of faulting and alteration mineralization that appears to track the boundary s evolution first stage chlorite filled faults and second stage laumontite filled faults affect the entire boundary and likely pre date the breach they record a change of fluid chemistry during oblique extension associated with the boundary s early history third stage calcite filled fractures are generally restricted to the eastern half of the boundary between the breaching fault s projection into the chalk cliffs and the active range front fault these fractures probably coincide with initiation of the breach modern fourth stage hydrothermal activity occurs at and slightly beyond the eastern edge this coincidence of hydrothermal events with changes in large scale fault geometry illustrates how normal fault zones through breaching can simplify their geometries and localize associated deformation and hydrothermal activity

dip domain method applied to the mesozoic connecticut valley rift basins this paper presents a new approach to structural analysis of u s east coast mesozoic basins a contoured compilation of numerical values of dip data for the connecticut valley rift basins reveals distinct domains related to their broader tectonic development additional more standard geologic constraints are then used to interpret the dip domain patterns most of the tilt deformation involved and hence postdated early jurassic basaltic flow units and overlying jurassic thick alluvial deposits normal drag characterizes the attitude of mesozoic strata along the western border fault of the main hartford basin whereas reverse drag is common along its larger listric eastern border fault strata within the basin mostly along its eastern margin include several subgrabens and or strongly tilted zones associated with early subbasins marked by local changes in strike of the early border fault the meriden cross graben may be a similar structure that extended much farther southwestward across the basin within the hartford basin linear domains of steeper dips are interpreted as surface expressions of the edges of a 5 to 15 km wide late stage central graben that trends n15 e diagonally across the basin possibly a reflection of very late strike slip stress systems

scales of structural heterogeneity within neotectonic normal fault zones in the aegean region abstract structural heterogeneities within neotectonic normal fault zones in the aegean region are important controls on the geomorphic expression of their uplifted footwall blocks contrasting fault rocks and slip plane phenomena corrugations comb fractures slip parallel fractures and pluck holes are responsible for mesoscopic inhomogeneities within fault scarps along strike disruptions in the continuity of fault scarps step over zones step up zones step down zones footwall cross faults and hangingwall cross faults are products of perturbations in slip plane geometry or intersections with transverse faults large scale variations in range front morphology reflect contrasting patterns of deformation within fault zones some major fault zones and many minor fault zones are characterized by a migration of the active slip plane towards the hangingwall resulting in a distributed network of high angle faults and a range front which is stepped in profile the presence of a localized mass of uneroded bedrock hangingwall salients protruding from the hangingwall of some major fault zones results in intense deformation along a principal slip plane and a range front which is ramp like in profile as a consequence of structural heterogeneities within neotectonic normal fault zones fault scarps and range fronts in the aegean region are subject to a temporally and spatially variable pattern of degradation

the geometry kinematics and rates of deformation within an en echelon normal fault segment boundary central italy abstract the geometry kinematics and rates of deformation have been investigated within an en echelon fault segment boundary between two left stepping major normal faults in the central apennines italy examination of faulted post glacial sediments and geomorphic features attributed to glacial retreat 18 ka reveals that the two major faults dominate the recent slip with rates that are 5 10 times greater than the other faults at the centres of the major faults slip is parallel to the regional extension direction ne sw defined by focal mechanisms and borehole breakouts slip vector azimuths defined by striations on faults in the stepover zone indicate ne sw extension on nw se faults sub parallel to the regional extension direction together with significant and contemporaneous nw se extension along the strike of the apennines on ese wnw and ene wsw faults thus distributed three dimensional strain occurs in the stepover between the two major bounding faults extension rates summed across the stepover are 0 68 mm y parallel to the regional extension compared to 2 mm y at the centre of one of the major faults extension rates along strike of the fault zone are 0 14 mm y within the stepover and zero at the centres of the two major bounding faults the above information is used to discuss how extension is partitioned between different structures during the growth and linkage of normal faults

growth of a normal fault system observations from the lake malawi basin of the east african rift abstract we have studied the growth history of the usisya normal fault system which bounds the west side of the lake malawi basin one of the largest rift basins in the east african rift system the lake malawi rift basin is a complex of intrabasins and intrabasin highs formed by three major fault segments each about 100 km in length the basin has been actively subsiding since the late miocene and has a maximum depth of about 3 km unlike the majority of previous studies of fault systems we are able to define the temporal evolution of this fault system using the patterns of sediment infill this is due almost exclusively to the availability of a high density seismic reflection network in combination with several clearly identifiable temporal marker beds an analysis of the seismic reflection data reveals that growth of the basin bounding faults occurred in the following sequence 1 in the early stages of rifting starting about 8 6 ma the northern fault was the most active 2 then extension shifted to the southernmost fault segment and lasted until about 2 5 ma 3 during the interval between about 2 3 ma and 1 6 ma the central segment was most active prior to the last interval the central segment accrued the least total displacement of the three segments this contradicts the common notion that the location of maximum displacement remains at a fixed location from fault inception or that the largest fault in any population of faults always maintained the highest displacement rate consistent with observations on smaller faults there is a marked increase in the displacement gradient on individual faults in the regions of overlapping segments although there is an observable asymmetry in individual segment displacement profiles there is a clear evolution toward a flattened bell shaped total displacement profile for the fault system that is consistent with the shape and scaling relationships of displacement vs length that are observed on a wide range of individual normal faults this suggests that the irregularities in the shape and scaling relationships observed in complex fault systems will eventually smooth out moreover the observed growth pattern suggests that the profile of the fault system will progress toward that of isolated faults provided the system is allowed sufficient time to evolve this in turn describes a process for maintaining a self similar scaling observed in large populations of faults which span several orders of magnitude in fault length

crustal velocity structure across the eastern snake river plain and the yellowstone swell teleseismic receiver functions are used to estimate the crustal structure beneath a 36 station 500 km long nw oriented linear array centered on the eastern snake river plain and crossing the yellowstone hotspot swell 250 km sw of yellowstone structure derived previously for this region from wide angle reflection data is used as an initial model and this structure explains most features observed in our receiver functions based on a combination of forward and inverse modeling our data require several modifications to the initial structure 1 moho depth is 42 km beneath most of the snake river plain shallows to 37 km to either side and thickens abruptly to 47 km beneath sw wyoming 2 a midcrustal layer interpreted previously as a 9 km thick gabbroic sill is flat topped across the entire 90 km width of the snake river plain and 3 a low velocity layer is found beneath and southeast of the snake river plain which probably is partially molten lower most crust using the seismic structure of the crust to estimate the crustal load upon the mantle and assuming local isostasy we calculate that mantle beneath the yellowstone swell is approximately uniformly as buoyant as 12 million year old ocean mantle and more buoyant than the adjacent wyoming mantle by an amount equivalent of 1 5 km of elevation the transition between these regions of greatly different mantle occurs across a major paleozoic boundary that now separates the basin and range from the rocky mountains

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

geometric pattern rupture termination and fault segmentation of the dixie valley pleasant valley active normal fault system nevada u s a abstract active fault systems of both interplate and intraplate settings clearly show patterns of segmentation fault segmentation therefore is very important for understanding fault behavior and assessing seismic hazard the complexity of geometric patterns along fault systems has a strong influence on the propagation of earthquake ruptures because it can form structural heterogeneities that tend to inhibit rupture propagation this implies that there should be relations between fault segmentation and the complexity of fault geometry the active normal faults of the dixie valley pleasant valley system provide an excellent example to study such relations and to establish the geometric method of normal fault segmentation in the basin and range province studies of fault segmentation in the dixie valley pleasant valley fault system indicate that there are changes of both geometric pattern and geomorphic character in the area of the segment boundary the characteristics of segment boundaries on normal faults of the dixie valley pleasant valley system can be explained in terms of the nature of rupture propagation and termination these changes may be helpful criteria for distinguishing normal fault segmentation at least in the basin and range province

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

the nature and origin of the aeolian mantles of central northern nigeria abstract evidence is presented here to show that the upland soils of central northern nigeria are formed in aeolian mantles deposited by two aeolian processes aeolian suspension or dust deposition and aeolian saltation or dune sand deposition the soils to the south and west of kano are largely the product of harmattan dust deposition whereas the northern soils appear to originate from dune sand migration from the quaternary dune fields to the east of the study area the spatial pattern of particle size populations or quanta and quartz grain roundness characteristics within the mantles and dune sands indicates that considerable mixing of dune sands and dust has occurred in the formation of these mantles

fractal characteristics of active normal faults an example of the eastern gulf of corinth greece abstract we present a model proposing the evolution of segmented normal faults in a currently extended area allowing an explanation of strong earthquakes hosted by short faults active normal faults accommodating the current extension in the gulf of corinth result from the linkage of smaller component faults well exposed fault zones in the sofiko range are arranged as pairs of graben bounding faults and thus our structural analysis has implications for the evolution of active normal faults as well as graben evolution a basal strip of fresh bedrock at the base of fault scarps suggests continuous seismic or aseismic creep thus the structural analysis of component faults that show a power law length distribution describes an evolved fault zone of particular interest is that faulting in this region is self similar between limits distribution is characterized by a fractal dimension of d 1 and the limits in our study are between 10 m mapping resolution and double the maximum displacement of each fault zone component segments of any compartmentalized fault show a length to maximum displacement ratio of two basin architecture and structural analysis suggest that the nucleation points of faults are detectable over the entire evolution of the fault zone all analyzed faults evolved by an independent nucleation model morphotectonic and kinematic data as well as fractal dimension of trace length population plots all suggest that fault zones defining north and south dipping conjugates are active at least over the late stages of basin evolution although this study was focused on a relatively small area this pattern of fault growth appears to be applicable to the entire fault population in the gulf of corinth and is thus an important model for normal faults

influence of the inter tropical discontinuity on harmattan dust deposition in ghana the harmattan is a dry dust laden continental wind and in the boreal winter harmattan dust plumes affects many west african countries including ghana when the harmattan is strongest the southern part of ghana is affected by the inter tropical discontinuity itd in this study we investigate if the itd functions as a barrier preventing long transported harmattan dust to settle south of and below it this is done by analyzing a harmattan dust outbreak mapped using earth observation eo data from the spinning enhanced visible and infrared imager seviri onboard the meteosat second generation msg platform coupled with data from west african aeronet stations and comparing these observations with wind data from noaa s air resources laboratory arl program and the mineral suite of samples from seasonal dust deposits in north and south ghana in northern ghana traces of minerals indicate a weak influence of particles from an arid environment which is found consistent with the mapped dust plumes and ne wind directions in southern ghana the mineral composition show no sediments of an arid origin the mapped dust plumes is less intense and the surface wind directions and wind mass trajectories are more varying with lower wind speeds based on the results of this study it is concluded that dust deposited or measured near ground in the harmattan period under the itd and south of it does not contain material from the chad basin due to the local winds conditions less

a model of rift basin evolution constrained by first order stratigraphic observations the stratigraphy of many nonmarine rift basins records a common sedimentological history consisting of a relatively abrupt increase of water depth followed by a slower shoaling upward trend we explore in this paper the origin of these sequences through a three dimensional physical model that incorporates the affects of fault growth flexure erosion sedimentation and isostasy fault growth is assumed to occur in a self similar manner and is treated as dislocations inducing flexure in a thin elastic plate topography generated by faulting and flexure is allowed to undergo diffusion to simulate erosive and sedimentary processes isostatic response to the redistribution of mass results in additional flexure of the thin plate the model is tested using two models of fault growth and we compare the numerical results with the stratigraphy observed in nonmarine rifts basins generated using a constant lengthening rate mode of fault growth fail to reproduce the stratigraphy of continental rift basins we find that the commonly observed stratigraphic succession of lacustrine to fluvial conditions requires the displacement rate of the bounding fault to decrease with time consistent with opening at a relatively constant areal extension rate

overlapping faults intrabasin highs and the growth of normal faults normal fault systems bounding extensional basins are typically adjoined by a series of subbasins separated by intrabasin highs the strata within these basins form syndepositional anticlines and synclines whose axes are transverse to the strike of the main bounding fault one possible explanation for these intrabasin highs is that they result from persistent along strike deficits in fault displacement such deficits are incompatible with scaling relationships observed between fault displacement and length based on large populations of faults we present data from active normal faults within the basin and range province and from inactive normal faults of the newark basin of eastern north america demonstrating a clear correlation between the along strike position of overlapping splay faults and the location of intrabasin highs as well as syndepositional transverse folds summed displacements for all faults within an intrabasin high are comparable to the displacements on faults bounding flanking subbasins o

relay zones between mesoscopic thrust faults in layered sedimentary sequences abstract we examine the geometry formation and destruction of relay zones in well bedded sedimentary sequences containing thrust fault segments with maximum observed displacements of 0 64 8 m contractional extensional and neutral relay zones are distinguished based on the stepping sense of the interacting fault segments and the orientation of the associated fault slip vectors large displacement gradients 0 17 1 0 in relay zones are mainly accommodated by folding with aggregate displacements maintained across segment boundaries and a significant component of the fault slip converted to fold related shortening folds in contractional relay zones verge in the direction of hanging wall motion with the steeper limb defining a parallelogram shaped zone between thrusts fault segment lengths are established after minimal displacement and folds in relay zones grow between segments as displacement accrues on the thrusts with increasing displacement upper and lower thrust tip lines in contractional and extensional relay zones are fixed at stratigraphic boundaries while the lateral thrust tip lines may propagate in a strike parallel direction upper and lower tip lines may eventually propagate to bypass relay zones that formed early in the fault growth history contractional relay zones remain intact at higher displacements than extensional relay zones

the role of fault interaction and linkage in controlling synrift stratigraphic sequences late jurassic statfjord east area northern north sea examination of well constrained three dimensional seismic data demonstrates the role of fault interaction and linkage in controlling the nature of synrift sequences on the hanging wall of the statfjord east fault a typical late jurassic structure in the northern north sea brent province al though now a single fault the statfjord east fault originally consisted of several en echelon segments each of which defined individual subbasins structural and stratigraphic evidence both along and across fault strike indicates that the fault resulted from segment propagation interaction and linkage facies architecture thickness variations and the internal character of synrift formations are temporally and spatially related to the subbasin geometry variations in displacement along the fault segments exhibit characteristics of interacting en echelon faults including anomalous displacement gradients in regions of segment overlap we attribute the observed shifts in depocenters to local enhancement of displacement rates resulting from the interaction of neighboring fault segments the results have far reaching consequences for synrift plays in the northern north sea because they imply that only from the perspective of fault growth and linkage can the late jurassic structure and stratigraphy be fully understood

a new crustal fault formed the modern corinth rift abstract this review shows how collective analysis of morphotectonic elements on uplifting rift margins can constrain the mechanical behaviour of continents during early rifting this is shown for the modern corinth rift one of the fastest extending and most seismically active continental regions worldwide we reconstruct the growth of the normal fault system that accommodates most of the rift strain and the uplift of the rift margin it bounds from onset to present and at rift scale our approach allows first order inferences on the mechanics and evolution of the rift and can be used in other areas of early continental rifting we review and re assess known geologic evidence in the corinth rift and compile morphotectonic elements into a new map we analyse the rift topo bathymetry and the footwall relief river catchments and tectonic knickpoints in its uplifting margin we also review studies that constrain the growth of normal faults using morphotectonic elements in their footwall and propose a novel theoretical framework to reconstruct fault time evolution during early rifting we couple known and new data to derive fault displacement profiles in time and use the theoretical framework to infer the history of growth and linkage of rift border faults in turn constraining rift growth mechanics and evolution our rift scale morphotectonic investigation shows that the current rift bounding faults are kinematically coherent at depth and constitute a fault 80 km in length this composite master fault grew along strike from the rift centre linking and integrating individual fault segments that developed co linearly at earlier times the observed fault elastic flexure footwall relief wavelength and high uplift and slip rates throughout the rift margin suggest the border fault is steep and highly localized in strain and transects the entire seismogenic layer growing in a long term strong elastic lithosphere integration of previous and our new findings suggest the corinth rift evolved in two distinct extensional phases these extensional phases are delimited by the fast overwriting growth of the new rift forming fault that switched rift mechanics in a 300 kyr timespan and controls rift evolution thereafter the new rift forming fault enlarges the modern rift as an asymmetric half graben along and across strike superimposed onto the preceding 4 my distributed extension

provenance of present day eolian dust collected off nw africa 1 atmospheric dust samples collected along a transect off the west african coast have been investigated for their physical grain size distribution mineralogical and chemical major elements composition on the basis of these data the samples were grouped into sets of samples that most likely originated from the same source area in addition shipboard collected atmospheric meteorological data modeled 4 day back trajectories for each sampling day and location and total ozone mapping spectrometer aerosol index data for the time period of dust collection february march 1998 were combined and used to reconstruct the sources of the groups of dust samples on the basis of these data we were able to determine the provenance of the various dust samples it appears that the bulk of the wind blown sediments that are deposited in the proximal equatorial atlantic ocean are transported in the lower level 900 hpa ne trade wind layer which is a very dominant feature north of the intertropical convergence zone itcz however south of the surface expression of the itcz down to 5 s where surface winds are southwesterly we still collected sediments that originated from the north and east carried there by the ne trade wind layer as well as by easterly winds from higher altitudes the fact that the size of the wind blown dust depends not only on the wind strength of the transporting agent but also on the distance to the source hampers a direct comparison of the dust s size distributions and measured wind strengths however a comparison between eolian dust and terrigenous sediments collected in three submarine sediment traps off the west coast of nw africa shows that knowledge of the composition of eolian dust is a prerequisite for the interpretation of paleorecords obtained from sediment cores in the equatorial atlantic

the early mesozoic birdsboro central atlantic margin basin in the mid atlantic region eastern united states discussion faill 2003 1 provides an important contribution to our understanding of the geology and evolution of the triassic jurassic basins of the central atlantic margin that formed during the breakup of pangea e g olsen 1997 2 in particular faill draws attention to the importance of fluvial

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays

the depositional evolution of diapir and fault bounded rift basins examples from the lusitanian basin of west iberia new data on the evolution of rift basins is presented after analysing the late jurassic stratigraphy of the central lusitanian basin west iberia well outcrop and regional 2d seismic reflection profiles are used to investigate the differences in stratigraphic signature between diapir and fault bounded sub basins during the late jurassic syn rift phase surface rupturing in fault bounded sub basins resulted in the formation of tectonic scarps from which footwall derived gravity flows were sourced in contrast the diapir bounded bombarral alcobaca sub basin evolved as a distal bowl shaped depocentre with an axis located up to 10 km away from its basin margins low gradient marginal slopes developed in the bombarral alcobaca sub basin during the late jurassic rifting while growing salt pillows limited the vertical propagation of basement normal faults differences in tectonic evolution basin physiography and sediment input are the main factors responsible for the distinct sedimentary evolutions recorded in the study area 1 transverse footwall derived sediment fans predominant in fault bounded regions give place to axial southwards prograding fluvial to shallow marine units in the diapir bounded sub basins 2 growing salt pillows absent in the fault bounded sub basins formed barriers to and limited the development of transverse drainage systems