self similarity of the largest scale segmentation of the faults implications for earthquake behavior article i nfo article history earthquakes are sensitive to the along strike segmentation of the faults they break especially in their initiation propagation and arrest we examine that segmentation and search whether it shows any specific properties we focus on the largest scale fault segmentation which controls the largest earthquakes it is well established that major segments within faults markedly shape their surface cumulative slip length profiles segments appear as large slip bumps separated by narrow pronounced slip troughs inter segments we use that property to examine the distribution location number length of the major segments in 927 active normal faults in afar east africa of various lengths 0 3 65 km cumulative slips 1 1300 m slip rates 0 5 5 mm yr and ages 10 4 10 6 yr this is the largest fault population ever analyzed to identify the major bumps in the slip profiles and determine their number location and length we analyze the profiles using both the classical fourier transform and a space frequency representation of the profiles the s transform which is well adapted for characterizing local spectral properties our work reveals the fol lowing results irrespective of their length 70 of the slip profiles have a triangular envelope shape in conflict with the elastic crack concept irrespective of their length the majority of the faults at least 50 70 have a limited number of major segments between 2 and 5 and more commonly equal to 3 5 the largest scale segmentation of the faults is thus self similar and likely to be controlled by the fault mechanics the slip deficits at the major inter segment slip troughs tend to smooth as the faults accumulate more slip resulting in increased connection of the major segments the faults having accumulated more slip therefore generally appear as un segmented 10 30 our observations therefore show that whatever the fault on which they initiate large earthquakes face the same number of major segments to potentially break the number of segments that they eventually break seems to depend on the slip history structural maturity of the fault

soil aggregate stability within morphologically diverse areas abstract knowledge of spatial distribution of soil aggregate stability as an indicator of soil degradation vulnerability and its possible prediction are required for many scientific and practical environmental studies the goal of our study was to provide a model for predicting soil aggregate stability within morphologically diverse areas where soil properties have been affected by soil material redistribution due to erosion the study was performed on a study site 6 ha area in the loess region of southern moravia czech republic haplic chernozem which is an original dominant soil unit has been transformed into different soil units eroded phases of chernozem regosol colluvial chernozem and colluvial soil 36 sampling spots were selected in order to represent diverse soils the following soil properties were measured oxidable organic carbon content cox caco3 content phh2o phkcl soil particle density s bulk density d porosity p actual field soil water content field content of iron and manganese in ammonium oxalate extract feo and mno and dithionite citrate extract fed and mnd and mass specific magnetic susceptibility lf and hf the aggregate stability was assessed using various tests to study different disruption mechanisms terrain attributes were derived from a digital elevation model in general the lowest soil aggregate stability was observed on steep slopes which were highly impacted by soil erosion the highest aggregate stability was measured on soils sampled at relatively flat upper parts which were less influenced by erosion processes higher stability was also obtained on toe slopes where the sedimentation of previously eroded soil material occurred the simple correlations revealed that characteristics resulting from the tests studying aggregate slaking due to the compression of the entrapped air water stable aggregate index and coefficient of vulnerability from fast wetting test were positively impacted by the cox p feo mno fed mnd lf and hf values and negatively by the d value the soil aggregate stability was also negatively influenced by the plan and total terrain curvatures i e larger aggregate stability was measured at concave parts in comparison with that at convex parts almost no statistically significant relationships were found in the case of the tests evaluating either aggregate disintegration caused by the micro cracking due to the different swelling or by the physico chemical dispersion due to the osmotic stress or the mechanical aggregate breakdown the multiple linear regressions resulted in the model for estimating the wsa index using the cox content total terrain curvature and actual field soil water content field in this model the cox content positively and the total terrain curvature and field value negatively influenced the value of the wsa index since cox was positively related with iron content and thus also with the magnetic susceptibility the alternative model was proposed for less costly and time consuming wsa estimation the wsa index may be predicted by combining the mass specific magnetic susceptibility lf and hf total terrain curvature and actual field soil water content field

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

3d geometry of range front blind ramp and its effects on structural segmentation of the southern longmen shan front eastern tibet abstract a 3d fault morphology model has been constructed from seismic profiles covering the piedmont of the southern longmen shan lms eastern margin of the tibetan plateau it reveals a spatial correlation between an 3 5 km high geometrical bump on the range front blind ramp rfbr and the gap between the 2008 m w 7 9 wenchuan and 2013 m w 6 6 lushan earthquakes sandbox modeling is then used to probe the effects of the geometrical irregularity of the rfbr on fault behaviors and the lms range front deformation sand wedges are designed to thrust over artificial blind ramps analogous to the thrusting of the lms orogenic wedge toward the sichuan basin through the rfbr the experiments reproduce the first order deformation features presented in the southern lms range front confirming that along strike geometrical variations of the rfbr have induced the segmentation of both fault motion and the range front deformation their results also suggest that the gap between the wenchuan and lushan earthquakes is located directly within the structural transition zone originating from the geometrical bump on the rfbr additionally there is a duplex structure occurring in the hanging wall of the geometrical bump which localizes significant shear strain with progressive shortening and represents a fracture zone corresponding to the observed geophysical anomaly low seismic velocity underneath the seismic gap it is likely that this fractured body protected the gap from the ruptures of the wenchuan and lushan earthquakes

accounting for uncertain fault geometry in earthquake source inversions i theory and simplified application the ill posed nature of earthquake source estimation derives from several factors including the quality and quantity of available observations and the fidelity of our forward theory observational errors are usually accounted for in the inversion process epistemic errors which stem from our simplified description of the forward problem are rarely dealt with despite their potential to bias the estimate of a source model in this study we explore the impact of uncertainties related to the choice of a fault geometry in source inversion problems the geometry of a fault structure is generally reduced to a set of parameters such as position strike and dip for one or a few planar fault segments while some of these parameters can be solved for more often they are fixed to an uncertain value we propose a practical framework to address this limitation by following a previously implemented method exploring the impact of uncertainties on the elastic properties of our models we develop a sensitivity analysis to small perturbations of fault dip and position the uncertainties of our fixed fault geometry are included in the inverse problem under the formulation of the misfit covariance matrix that combines both prediction and observation uncertainties we validate this approach with the simplified case of a fault that extends infinitely along strike using both bayesian and optimization formulations of a static slip inversion if epistemic errors are ignored predictions are overconfident in the data and slip parameters are not reliably estimated in contrast inclusion of uncertainties in fault geometry allows us to infer a robust posterior slip model epistemic uncertainties can be many orders of magnitude larger than observational errors for great earthquakes mw 8 not accounting for uncertainties in fault geometry may partly explain observed shallow slip deficits for continental earthquakes similarly ignoring the impact of epistemic errors can also bias estimates of near surface slip and predictions of tsunamis induced by megathrust earthquakes

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies a review of magnetic methods and challenges abstract magnetic iron oxide minerals principally magnetite maghemite hematite and goethite are formed in well drained soils in response to a suite of physical chemical and biological factors despite a wide range of complexity in the pedogenic processes that lead to magnetic mineral formation dissolution and transformation there are well documented empirical relationships between various magnetic mineral assemblages in soils with environmental and climatic conditions recently there has been an increase in the number of quantitative magnetic paleoprecipitation proxies that have been developed and there is great potential for magnetic methods to be used in the geologic record to develop reconstructions of past climates magnetic paleoprecipitation proxies have been widely utilized in quaternary or younger loess paleosol systems however they have yet to be utilized in the pre quaternary fossil record future studies of magnetic mineralogy of soils and paleosols should aim to explore non loessic modern soils and pre quaternary paleosols with more focus on understanding the interaction between magnetic mineral assemblages and soil moisture applications of existing and novel magnetic paleoprecipitation proxies in the fossil record should prove to be a valuable resource for paleoclimatologists

frequency dependence of magnetic susceptibility as a proxy for fine grained iron minerals and aggregate stability of south chilean volcanic ash soils aggregate stability as is an important property controlling erodibility of volcanic ash soils and is known to be strongly affected by fine grained iron fe and aluminum al minerals assuming that frequency dependence of magnetic susceptibility ms is related to the amount of fine grained fe minerals and considering that formation of fine grained fe and al minerals is closely coupled in volcanic ash soils we hypothesized that the measurement of ms can be used to evaluate as of these soils to verify this we investigated volcanic ash soils along a 120 km transect in southern chile reaching from the andean southern volcanic zone svz to the pacific coastal range stability of 1 cm macroaggregates from topsoil 0 5 cm and subsoil 20 25 cm was determined by wet sieving combining long term water immersion and subsequent ultrasonic treatment ms was measured at 465 and 4650 khz to calculate its frequency dependence we found an increasing amount of organic matter fine grained fe and al minerals and clay and decreasing bulk density with increasing distance from the svz indicating progressing soil development along the transect likewise as increased with increasing distance from the svz and was found to be controlled primarily by soil organic matter and fine grained fe and al minerals while ms itself showed only slight variation its frequency dependence continuously increased with increasing distance from the svz indicating an increasing fraction of fine grained ferrimagnetic particles accordingly frequency dependence of ms was found to be linearly related to the amount of fine grained fe minerals as quantified by dithionite extraction and moreover due to the close linear relationship between fine grained fe and al phases it revealed to be suitable for estimating the total amount of both fine grained fe and al minerals analysis of underlying material 60 65 cm indicated that the increase in frequency dependence of ms with increasing distance from the svz was caused by fine grained ferrimagnetic particles of pedogenic and lithogenic origin although overall organic matter content turned out to be more closely related to the stability of the investigated aggregates we conclude that frequency dependence of ms can be used as an easily obtainable proxy for assessing the contribution of fine grained fe and al minerals to as

new aspects of rhomb structures abstract the acute angles of 48 rhombic trapezoidal and triangular grabens horsts and upthrusts throughout the world were determined the results indicate an angular spread of 7 73 in most structures the two acute angles differ considerably most rhomb structures are grabens which show affinities to seismic faults and only a few are horsts and upthrusts in this connection modes of static crustal fracture propagation are compared to dynamic propagation rhomb structures occur along strike slip faults and in rifts these results question the universality of the pull apart model as a mechanism for rhomb structure development the two mechanisms that can lead to the formation of rhomb structures are 1 interaction of en echelon or non coplanar fractures by shear and extensional modes and 2 fracture bifurcation in an extensional mode the two mechanisms may result in faults of different shapes characterized by curved and straight boundaries respectively the grabens and horsts in extensional regions are the consequence of early fracture and later vertical displacements

the sou hills a barrier to faulting in the central nevada seismic belt bedrock zones transverse to regional structures may indicate barriers at depth that inhibit the propagation of fault ruptures in the basin and range province the tertiary bedrock of the sou hills separates dixie and pleasant valleys and is transverse to the trends of physiography and historic surface faulting in central nevada four lines of evidence indicate that the sou hills are a barrier to faulting in the seismic belt first total late cenozoic vertical displacement on range bounding faults decreases toward the sou hills second analyses of landforms that reflect rates of relative uplift show that quaternary uplift decreases where range bounding faults meet the sou hills third the most recent prehistoric faulting south of the transverse zone is several thousand years younger than faulting to the north fourth patterns of late quaternary fault scarps in the sou hills are similar to rupture patterns observed at the termination of faults elsewhere

geometry of cenozoic extensional faulting dixie valley nevada precise definition of geometric relationships between individual basins and ranges may help to reveal the mechanical processes of basin and range cenozoic extensional faulting at depth previous studies have attempted to identify simple horsts and grabens tilted crustal blocks with planar faulting or tilted crustal blocks with listric faulting in the shallow crust normal faults defining these crustal blocks may root 1 individually in the ductile lower crust 2 in regional or local low angle detachment faults or 3 in igneous intrusions or decoupling surfaces produced by the intrusions the present study in dixie valley west central nevada makes use of a seismic reflection survey gravity models seismograms from earthquakes occurring on december 16 1954 and geometrical block models these data show a structurally asymmetric basin bounded by a single zone of faulting on the northwest and by a downbowed and step faulted floor to the southeast the northwest bounding fault is moderately dipping 50 and planar to a depth of 3 km the southeast boundary is step faulted and altogether the faults indicate an extension of 20 across the valley at the rate of 0 38 mm y for the last 8 my synthetic earthquake seismograms confirm a focal depth of 15 km and fault dip of 62 for the fairview peak earthquake and suggest that the focal depth of the dixie valley earthquake was also 15 km instead of the previously reported 40 km local microearthquakes cluster around 10 15 km the geometrical block models indicate that crustal horst graben faulting and planar high angle normal faults rooted in a low angle detachment surface do not readily account for development of the subsidiary step faults found in dixie valley extension of the crust by intrusion may develop high angle faults and with further intrusion may develop the subsidiary faults and produce a complex sagged asymmetric graben like dixie valley

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

land use change and erosional history in a lake catchment system on the canadian prairies abstract the introduction of agriculture in the late 1800s and early 1900s brought about many changes in the natural prairie landscape of western canada the objective of this research project is to evaluate landscape response to land use change by relating observed changes in the sedimentary record of a lake drainage basin to documented land use change that has occurred since the onset of settlement a 52 cm lake sediment core was sectioned into 1 cm layers the sediment was separated into allogenic and authigenic fractions using a wet chemical extraction technique close interval 210pb dating enabled the calculation of sediment and elemental influx rates prior to european settlement erosion rates were low

research on the geometry of shear fracture zones the geometry of brittle shear fracture zones has been studied by the examination of some strike slip faults and shear joints in china pinnate and en echelon deformational patterns are two fundamental arrangements of fractures within brittle shear fracture zones the pinnate angle is usually less than 25 and the en echelon is more than 25 the deformation in the rock bridge the area between two secondary fractures depends on the arrangements of secondary fractures and the sense of shear some tensile ruptures are formed at the terminations of both primary shear fracture zones and secondary fractures the direction of a tensile rupture is commonly parallel to the orientation of the principal compression along the direction of propagation of the shear fracture the horizontal displacement is large and the attenuation of displacements is slow the maximum horizontal displacement of the shear zone may be located in the region of the initial fracture under certain conditions the shear fracture zones may possess pivotal movement this type of movement may be expressed by the behavior of the fault or by the geomorphology of the fault zone

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

patterns and timing of late quaternary faulting in the great basin province and relation to some regional tectonic features large scale surface faulting events each tens of kilometers long and involving more than a meter of displacement of late quaternary age have not been uniformly distributed but have been concentrated in subprovincial and smaller belts and areas within the great basin province furthermore faulting apparently has not been uniformly distributed over time the average recurrence interval of large scale faulting events on individual faults in the province is measured in thousands or tens of thousands of years in contrast to such long recurrence intervals in the central nevada and eastern california seismic belts large scale faulting events have occurred during the last 111 years in an apparently coherent sequential belt filling pulse of activity in which events were separated by only a few years or a few decades the questions are where are other pulses of large scale faulting likely to occur and what controls the localization of such belts and areas characterized by higher rates of faulting two examples of tectonic subprovinces that may play a role in delimiting smaller zones of faulting are the black rock carson sink zone of extension and the central nevada downwarp the central nevada seismic belt lies along the dividing line between these two subprovinces and the northwest margin of the black rock carson sink zone of extension coincides with the margin of a fingerlike belt of dense faulting in northwestern nevada

particle size and analytical considerations in the mineral magnetic interpretation of soil loss from cultivated landscapes abstract prior research has highlighted the potential for using soil magnetism as a rapid estimator of total cumulative soil loss on cultivated land in this study the influences of particle size choice of magnetic measurement and initial conditions on a proposed model linking surface soil magnetism and soil loss are described and evaluated output model curves are generated for several parameter sets corresponding to different model assumptions and physical scenarios output is also compared to a new high resolution surfacial magnetism data set from a cultivated site gilbert farm in northwestern alabama usa to further evaluate the model magnetic susceptibility values at gilbert farm range from 150 to 220 10 8 m 3 kg 1 in a control soil profile the original model output ranges from 180 to 192 10 8 m 3 kg 1 and many magnetism values in the cultivated area fall outside this range introduction of a particle size sorting correction factor decreases the range of output values and results in even greater numbers of out of range observations however there is evidence suggesting that particle size distributions in the upper soil at this site are not strongly affected by differences in water erosion mechanism lower tillage depths cause magnetic susceptibility values to come in range but may be unrealistic and create a twin value problem for complex magnetic profiles use of the remanence sirm volume susceptibility lf ratio profile with values ranging from 35 to 120 ma m 1 10 5 si instead of magnetic susceptibility as used in the original model was found to eliminate out of range and twin value anomalous magnetism values were identifiable and treatable on the high resolution magnetism maps but other types of natural spatial variation remain at issue

the role of coseismic coulomb stress changes in shaping the hard link between normal fault segments the mechanism and evolution of fault linkage is important in the growth and development of large faults here we investigate the role of coseismic stress changes in shaping the hard links between parallel normal fault segments or faults by comparing numerical models of the coulomb stress change from simulated earthquakes on two en echelon fault segments to natural observations of hard linked fault geometry we consider three simplified linking fault geometries 1 fault bend 2 breached relay ramp and 3 strike slip transform fault we consider scenarios where either one or both segments rupture and vary the distance between segment tips fault bends and breached relay ramps are favoured where segments underlap or when the strike perpendicular distance between overlapping segments is less than 20 of their total length matching all documented examples transform fault linkage geometries are preferred when overlapping segments are laterally offset at larger distances few transform faults exist in continental extensional settings and our model suggests that propagating faults or fault segments may first link through fault bends or breached ramps before reaching sufficient overlap for a transform fault to develop our results suggest that coulomb stresses arising from multi segment ruptures or repeated earthquakes are consistent with natural observations of the geometry of hard links between parallel normal fault segments

simple equations to represent the volume area depth relations of shallow wetlands in small topographic depressions abstract small topographic depressions have important functions in hydrology and ecology because they store water in the form of shallow lakes wetlands or ephemeral ponds the relations between the area a the volume v and the depth h of water in depressions are important for evaluating water and dissolved mass balances of the system the a h and v h relations are usually determined from fine resolution elevation maps based on detailed survey data simple equations are presented in this paper which can be used to 1 interpolate a h and v h data points obtained by a detailed survey 2 approximate unknown a h and v h relations of a depression from a minimal set of field data without a time consuming elevation survey and 3 serve as a geometric model of depressions in simulation studies the equations are simple power functions having two constants the first constant s is related to the size of the depression and the second constant p is related to the geometry of the depression the power functions adequately represent a h and v h relations of all 27 wetlands and ephemeral ponds examined in this paper which are situated in the northern prairie region of north america assuming that the power functions are applicable for other similar topographic depressions an observer only needs to measure a and h twice to determine the two constants in the equation the equations will be useful in field studies requiring approximate a h and v h relations and in theoretical and modeling studies

interaction and linkage of extension fractures and normal faults examples from the rift zone of iceland abstract field and photogeological studies were made of 90 zones of interacting fracture segments along the rift zone of iceland each zone consists of a pair of extension fractures or a pair of normal faults with lengths from metres to kilometres these zones evolve from an underlapping stage through an overlapping stage the most common configuration and finally to a linkage stage of all the zones only 7 are underlapping whereas 93 are overlapping with hook shaped fracture pairs the length width ratios of the overlapping zones have a mean value of 3 5 the preferred geometry of the overlapping zones depends upon the initial configuration of the interacting fractures length overstep and the development of the interaction in the overlapping zones most fracture pairs show moderate shear strike slip components related to local variations in the extension opening directions vertical displacements on normal faults decrease as the overstep and length of overlapping zones increase both in turn are proportional to the total lengths of the faults forming the pair the geometrical and kinematic features of overlapping spreading centres at mid ocean ridges show close similarities to those reported here these similarities indicate that the architecture and evolution of overlapping zones are scale independent

using magnetic susceptibility to assess soil degradation in the eastern rif morocco 25 pag 4 tabl 7 fig the definitive version is available at http www3 interscience wiley com journal 2388 home

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

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

mapping units based on spatial uncertainty of magnetic susceptibility and clay content abstract this study aimed to use spatial uncertainty of magnetic susceptibility ms and clay content to improve soil mapping units in an experimental area of 870 ha a regular sampling grid containing 371 points was set in which ms and clay content were assessed at a depth range of 0 0 25 m using a digital elevation model and field observations a 4440 m transect was established on the study area from hilltop to the foothill toward the gentlest slope standard deviation maps based on 200 realizations of the sequential gaussian simulation measured spatial estimate uncertainties to limit transition zones along the transect uncertainty isolines representative of the transition between soil mapping units were selected both attributes presented peaks of uncertainties near the change of mapping units previously known uncertainty zones previously delineated ranged from 45 to 210 m and from 60 to 170 m for ms and clay content respectively however after extrapolating the uncertainties to the side of the transect amplitude changes of the uncertainty zones were observed especially in the transition regions between landscape shape and geology delineation of mapping units which incorporated the uncertainties of ms and clay content was similar however due to lower cost and promptness ms becomes the most feasible alternative knowing spatial uncertainties enables readjusting limits in maps of soil mapping units and may support identification of most favorable regions for determining modal pedon representative of each unit

use of mineral magnetic measurements to investigate soil erosion and sediment delivery in a small agricultural catchment in limestone terrain abstract understanding sediment delivery at the hillslope scale requires information on the spatial distributions and magnitudes of erosion and deposition empirical models such as the rusle may be useful for predicting erosion but are poorly suited for quantifying deposition cesium 137 cs 137 is useful for quantifying both erosion and deposition but is costly to inventory over a large area and directly gauges soil redistribution only for recent decades the use of rapidly acquired magnetic measurements represents a relatively new potential means of mapping and measuring soil redistribution in this study variations in surface magnetism are analyzed to determine patterns of erosion and sedimentation in a small agricultural catchment in northwestern alabama usa magnetic indicators of erosion are combined with published soil morphology cs 137 and short term suspended sediment data from this former experimental watershed to evaluate long term sediment delivery all magnetic parameters measured could be related to soil erosion although their patterns in space are not identical magnetic evidence suggests approximately 30 cm of soil loss on the steepest mid slope portions of the catchment distributing soil loss across space according to magnetic patterns gives average long term values lower than a prior estimate based on cs 137 data long term sediment delivery calculated using soil morphology to determine depositional volume ranges up to 45 depending on the magnetic parameter used to index soil loss and assumptions regarding deposit geometry these results suggest the need for continued refinement of magnetic techniques for purposes of erosion model validation and general sediment tracing applications

surface faulting accompanying the borah peak earthquake and segmentation of the lost river fault central idaho on the morning of 28 october 1983 the ms 7 3 borah peak earthquake struck central idaho and formed a y shaped zone of surface faults that is divided into a southern a western and a northern section the total length of the surface faults is 36 4 3 1 km and the maximum net throw is 2 5 to 2 7 m the near surface net slip direction determined from the rakes of striations in colluvium averaged 0 17 m of sinistral slip for 1 00 m of dip slip the 20 8 km long southern section is the main zone of surface faulting and coincides with the thousand springs segment of the lost river fault it has the largest amount of net throw most complex rupture patterns and best evidence of sinistral slip the surface faults include zones of ground breakage as much as 140 m wide en echelon scarps with synthetic and antithetic displacements and individual scarps that are nearly 5 m high the 14 2 km long western section diverges away from the lost river fault near the northern end of the southern section the net throw on this section is generally less than 0 5 m but locally is as much as 1 6 m the new ruptures are poorly developed across the crest and north flank of the willow creek hills they are mostly downhill facing arcuate scars perhaps incipient landslides that may overlie a deeper zone of tectonic movement the northern section at least 7 9 km long is on the warm spring segment of the lost river fault and has a maximum net throw of about 1 m the pattern of surface faulting on this section is simple compared to the other sections a 4 7 km long gap in 1983 surface faults separates the northern and southern sections but contains an older scarp of late pleistocene age geologic seismologic and geodetic data from the earthquake suggest that barriers confined the primary coseismic rupture to the thousand springs segment of the fault the rupture propagated unilaterally to the northwest from a hypocenter near the southeastern end of the segment the southeastern boundary of the segment is marked by an abrupt bend in the range front a 4 km long gap in late quaternary scarps and transverse faults of eocene age that intersect the lost river fault the northwestern boundary of the thousand springs segment is at the junction of the willow creek hills and the lost river fault here the southern and western sections of surface faults diverge and there is a gap in the 1983 scarps during the first few weeks after the main shock the large magnitude and large stress drop aftershocks clustered near this barrier later aftershocks were mainly northwest of the barrier on the warm spring and challis segments and showed that strain adjustments eventually affected the entire northern part of the lost river fault fault scarp morphology and the bedrock geology suggest that the boundary between the thousand springs and warm spring segments has probably ruptured less frequently and had less net slip during much of the late cenozoic than the interior of the adjacent segments the 1983 faulting shows that although segment boundaries can stop or deflect primary ruptures secondary surface faulting can occur on adjacent segments of the main fault a late pleistocene scarp in the 1983 gap suggests that infrequent earthquakes perhaps larger than the 1983 event might break through a segment boundary and thus release strain on two adjacent segments

active fold deformation and crustal shortening rates of the qilian shan foreland thrust belt ne tibet since the late pleistocene abstract quantification of crustal shortening rates across foreland fold and thrust belts is essential for evaluating how convergence is accommodated throughout the orogenic belt and analyzing seismic hazard in neighboring cities in this study we focused on active fold along the western portion of the qilian shan foreland thrust belt in ne tibet the shortening rate across the hujiatai anticline ha along the eastern segment of the fodongmiao hongyazi fault fhf is 0 8 0 2 mm a based on terrestrial cosmogenic nuclide tcn dating of deformed late pleistocene fluvial terrace when this rate is combined with the shortening rates of 1 1 1 4 mm a and 0 7 1 2 mm a along the western and central segments obtained by previous studies it is apparent that crustal shortening rates along the fhf gradually decrease to the east this eastward decrease in fault activity may be a result of the northward propagation of the fhf or partitioning of strain off to nearby faults or folds furthermore tectonic geomorphology and trenching suggest that several thrust faults around the ha ruptured during the historical 1609 earthquake combining the shortening rate of 0 6 0 8 mm a across the north side of the jiudong basin with our rate we suggest that the total crustal shortening rate across the basin is about 1 3 2 2 mm a assuming little internal deformation which accounts for roughly 20 40 of the amount of crustal shortening deformation across the qilian block these results demonstrate that the qilian shan foreland basin plays an important role in accommodating the crustal deformation of northeastern tibet

surface faulting of the 1954 fairview peak ms 7 2 and dixie valley ms 6 8 earthquakes central nevada abstract the 1954 fairview peak earthquake was followed 4 min and 20 sec later by the dixie valley earthquake surface ruptures were distributed among six different faults that define a complex north trending zone 100 km long and over 15 km wide the rupture sequence progressed from south to north the initial event produced a 32 km rupture of right oblique slip along the east dipping fairview fault where the components of right lateral offset and vertical separation reached 2 9 and 3 8 m respectively the northernmost ruptures occurred during the subsequent event along a 46 km portion of the east dipping dixie valley fault where the sense of slip was normal and reached a maximum vertical separation of 2 8 m average surface offset for both events is about 1 2 m the west dipping west gate louderback mountains and gold king faults also ruptured during the earthquake sequence these faults form a complex structural linkage within a 15 km left step that separates the surface traces of the fairview and dixie valley faults the west dipping faults likely played an important role in the redistribution of static stress from the fairview peak earthquake and subsequent triggering of the dixie valley earthquake right lateral offsets of more than a meter occurred along both the west gate and louder back mountains faults slip was limited to normal motion of 1 m or less along the gold king fault the change from right oblique motion along the fairview fault to pure normal motion on the dixie valley fault may reflect the transition from principally northwest extension in the south to more westerly extension in the north alternatively slip at the latitude of the dixie valley fault may be partitioned between pure normal slip along the dixie valley fault and strike slip motion on faults immediately to the west observations of fault dip provide insight to the complex three dimensional geometry of the rupture sequence of particular note a significant section of the dixie valley fault appears to be characterized by dip angles as low as 25 at the surface slip variation or earthquake endpoints do not generally appear to have been influenced by changes in bedrock type we do not observe systematic relations between slip variation and aspects of fault trace geometry such as salients and reentrants yet the relative competence of footwall bedrock appears to have influenced the long term development of large salients and reentrants along both the dixie valley and the fairview faults as well as the style of rupture along the southern portion of the dixie valley fault

late quaternary history of the stillwater seismic gap nevada abstract fault scarps that formed during the 1915 and 1954 earthquakes in central nevada are roughly aligned but are separated by a gap of 40 km the gap contains no historical scarps and has been termed the stillwater seismic gap the abundance size and distribution of prehistorical fault scarps is similar in the stillwater seismic gap and the 1915 and 1954 earthquake areas and overall height and long term uplift rates of range blocks are similar throughout the area studied thus the faults in the gap do not appear to be locked or appreciably more or less active on a long term basis than those in areas of the 1915 and 1954 earthquakes none of the scarps in the gap is likely younger than about 300 yr so that no major earthquake occurred in that period the stillwater seismic gap is part of the central nevada eastern california seismic belt where large scale surface faulting events have occurred at intervals of a few years to a few decades in a pattern that suggests incremental filling of the belt if that pattern of belt filling continues the stillwater gap is a likely site for future major faulting but the low level of seismicity in the gap area suggests that the next major earthquake there is not imminent

the use of magnetic susceptibility to measure long term soil redistribution abstract several studies have documented the severity of recent soil erosion on the canadian prairies where cultivation started about a century ago little quantitative information is available on erosion before 1960 this study attempts to quantify post and pre 1960 soil erosion in a small cultivated basin near saskatoon saskatchewan canada by measuring 137cs and magnetic susceptibility distribution with depth soil cores were collected along six transects three across closed depressions and three across the drainage channel in the cultivated field and one transect across an uncultivated depression the cores were sliced into 3 cm layers and the soil analyzed for 137cs and organic and inorganic c high variability in with depth in eroding areas as indicated by 137cs made it impossible to use to quantify past soil losses in these locations however these eroding upper and middle slope positions have a much higher than lower slope areas where soil deposition occurs and where the variability in with depth could be used to estimate soil deposition estimating soil deposition from the vs depth profiles was more successful in the closed depressions than in the drainage channel where the profiles may reflect the variable source areas of the materials rather than the pedological conditions the data indicated that soil deposition since 1960 has been about 30 to 50 of that prior to 1960 this suggests that soil deposition rates and by implication soil erosion rates have been relatively steady since cultivation of these soils started although there are clear indications that the spatial pattern of deposition has varied

fault geometries and structures associated with the rupture endpoints of the 2008 mw 7 9 wenchuan earthquake eastern tibet plateau china

aftershocks of the coyote lake california earthquake of august 6 1979 a detailed study aftershock hypocenters and focal mechanism solutions for the coyote lake california earthquake reveal a geometrically complex fault structure consisting of multiple slip surfaces the faulting surface principally consists of two right stepping en echelon northwest trending partially overlapping nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 parkfield california earthquake the overlap occurs near a prominent bend in the surface trace of the calaveras fault at san felipe lake slip during the main rupture as inferred from the distribution of early aftershocks appears to have been confined to a 14 km portion of the northeastern sheet between 4 and 10 km depth focal mechanisms and the hypocentral distribution of aftershocks suggest that the main rupture surface itself is geometrically complex with left stepping imbricate structure seismic shear displacement on the southwestern slip surface commenced some 5 hours after the mainshock aftershocks in this zone define a single vertical plane 8 km long between 3 and 7 km depth within the overlap zone between the two main slip surfaces the average strike of aftershock nodal planes is significantly rotated clockwise relative to the strike of the fault zone in close agreement with the stress perturbations predicted by crack interaction models aftershock activity in the overlap zone is not associated with a simple dislocation surface space and time clustering within the entire aftershock set suggest an alternation of seismic displacement between the component parts of the fault zone this alternation is consistent with local stress perturbations predicted by crack interaction models we conclude that the fault structure is geometrically complex and that the displacements that occur on its component surfaces during the aftershock process dynamically interact by generating perturbations in the local stress field which in turn control the displacements table 5 is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 006 1 00 payment must accompany order

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

timing of late quaternary faulting in the 1954 dixie valley earthquake area central nevada the 1954 dixie valley earthquake m 6 9 in central nevada produced about 3 m of total vertical displacement distributed across two principal fault zones along the east flank of the stillwater range most of the 1954 displacement was along the range front fault with minor amounts on the piedmont fault zone in contrast to an earlier holocene displacement that was restricted to the piedmont fault detailed chronostratigraphic exploratory drilling and trenching studies indicate that faulting events have migrated back and forth between the range front and piedmont fault zones in the late quaternary prior to the 1954 earthquake the range front fault last ruptured in the late pleistocene during a large magnitude event here called the ixl event the northern half of the piedmont fault zone last ruptured between 1 5 and 6 8 ka during a large magnitude event here called the bend event on the basis of 6 m total slip since the deposition of shoreline gravels at approximately 12 ka the estimated holocene vertical slip rate is 0 5 mm yr for the dixie valley rupture zone overlapping and migratory patterns of late quaternary faulting indicate that the dixie valley zone does not fit a simple segmentation model

pattern and rates of faulting in the central nevada seismic belt and paleoseismic evidence for prior beltlike behavior the central nevada seismic belt cnsb is a concentration of historical 1915 1932 1954 surface faulting in the western basin and range province forming a linear nearly continuous 300 km long rupture zone previous results are integrated in this study with new paleoseismic and exploratory trenching data from the historical zones to look for evidence of older similar beltlike patterns or elevated slip rates that could indicate whether the cnsb is a zone of focused long term crustal strain the data show that the continuous rupture belt produced by the seven earthquakes occurring between 1915 and 1954 is unique in the available paleoseismic record at the 1954 fairview peak fault the lack of prehistorical faulting in deposits containing the wilson creek bed 19 tephra eliminates the possibility of an identical seismic belt in the past 35 4 ka our studies also show that the faults have net slip rates ranging from a low of 0 09 mm yr on the fairview peak fault to a high of 0 7 mm yr on the 1932 cedar mountain fault these are considered moderate to low rates that are similar to most late quaternary faults in the western basin and range province a space time comparison shows that the paleoseismic histories for these multiple rupture zones are diverse and the number and timing of events in each of the zones indicate that there is little evidence for older contemporaneous ruptures of these same faults based on these results we reach several conclusions regarding the longer term holocene behavior of the cnsb although paleoseismic data preclude an older identical rupture belt among the historical zones consideration of associated holocene faults within the greater cnsb region indicates that several similar but not identical beltlike rupture patterns are plausible during the past 13 ka although each requires seismic gaps in the along strike pattern although long term strain represented by density of young faults does appear to increase from east to west into the cnsb the slip rate data demonstrate that the cnsb is not a belt of concentrated or elevated crustal strain compared with areas that extend west to the sierra nevada the increase in the distribution of holocene fault activity from east to west into the cnsb is consistent with a marked increase in the 1992 2002 gps velocity field at the latitude of the 1954 rupture sequence however a comparison of the geologic rates across the belt at this same latitude indicates that the extension rates 0 59 1 37 mm yr are systematically lower than both the campaign and continuous gps rates 2 20 3 13 mm yr by factors of 2 5 these discrepancies may be due to postseismic strain or to some form of off fault deformation we conclude that the results of our study of fault behavior in the cnsb best support the belt migration model proposed by wallace 1987 for the western basin and range province in which temporal tectonic pulses are believed to migrate regionally activating different beltlike combinations of late quaternary faults in an as yet unknown pattern of migration

mineral precipitation as a mechanism of fault core growth abstract faults vary in structural style from simple planes to complex systems composed of fault cores and damage zones increased fault complexity results from the interaction of mechanical and chemical processes including fracture growth shear and linkage and mineral dissolution and precipitation although water rock interaction is traditionally associated with fault rock weakening and shear localization we investigate processes of fault core widening by water rock interactions that resulted in quartz precipitation we combine field and petrographic observations with prior mechanical characterization to assess the impact of alteration and cementation on fault architecture at the dixie comstock epithermal gold deposit nevada usa mineralized portions of the fault contain strong thick silicified fault cores and wide weak damage zones with evidence for widening of the core through entrainment of damage zone material and repeated cycles of embrittlement dilation and cementation we present a model of fault zone evolution in which the hydrothermal regimes favoring either alteration weakening or precipitation strengthening result in distinct fault zone architecture and mechanical and flow properties of fault systems alteration weakening favors localization of the fault into thinner clay rich low permeability fault cores precipitation strengthening promotes thick strong and low permeability fault cores with mineralization embrittlement enhancing transient permeability following coseismic failure

rupture segmentation and process of the 2001 mw 7 8 central kunlun china earthquake field investigations allow us to constrain the coseismic surface rupture zone of 400 km with a strike slip up to 16 3 m associated with the 2001 m w 7 8 central kunlun earthquake that occurred along one of the western segments of the kunlun fault northern tibet the rupture zone may be divided into four segments based on the geological structures tectonic landform features spatial displacement distributions obtained from field observations and analysis of teleseismic waveforms the deformational characteristics of the surface ruptures and focal mechanism solutions reveal that the earthquake had a nearly pure strike slip mechanism the inversion results from seismic data show that the rupture started from the west near the epicentral area bilaterally and rapidly extended to the east in an unilateral manner for 380 km and that the largest slip region was limited in the subsegment 150 280 km east of the epicenter consistent with field observations the average stress drop is estimated to be 7 mpa in the area where the largest displacements occurred a value typical of intraplate earthquakes the geologic evidence and the inversion results from seismic data clearly show that temporal and spatial displacement distributions and the rupture process are restricted by the pre existing geological structures of the kunlun fault

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

impacts of data sampling on the interpretation of normal fault propagation and segment linkage abstract throw distance t d and throw depth t z plots are widely used by researchers and industry to examine the growth of normal faults this study uses high quality three dimensional 3d seismic and outcrop information to review the effect of data sampling on the interpretation of normal fault growth the results show that the accuracy of t d and t z data and of resulting fault slip tendency and leakage factor analyses are dependent on the sampling strategy followed by interpreters and field geologists i e on a sampling interval fault length ratio for discrete structures in particular this work demonstrates that significant geometric changes in t d plots occur when a module error ei for the ratio is larger than 6 9 for faults of all scales and growth histories this implies that a minimum number of measurements should be gathered on discrete faults to produce accurate t d and t z plots and that the number of measurements is dependent on fault length with no prior knowledge of fault segmentation a value of 0 05 should be applied when interpreting faults to fulfil the pre requisite of a i

comparing mineral magnetic properties of sediments in two reservoirs in strongly and mildly eroded regions on the guizhou plateau southwest china a tool for inferring differences in sediment sources and soil erosion shibanqiao reservoir 0 24 km 2 and xiaohe reservoir 0 28 km 2 have catchments of 6 00 km 2 and 22 69 km 2 respectively they essentially represent strongly eroded shibanqiao and mildly eroded xiaohe regions in guizhou plateau southwestern china sediment cores were retrieved from the two reservoirs and soils were also sampled from their catchments mineral magnetic measurements were performed on the sediments and soils and the particle size analysis of selected sediment cores and soil profiles were also made sirm versus chi if was used to compare sediment and soil samples in addition correlations between percentages of different particle size fractions and magnetic parameters ratios of sediment samples were also checked these results revealed differences in sediment sources and soil erosion in these two representative catchments the sediments in shibanqiao reservoir are derived from both the topsoil and subsoil when erosion is relatively weak it is limited to the topsoil and preferentially transports the relatively finer magnetic grains into the reservoir which may imply rain splash and or sheet erosion in this relatively steep catchment stronger erosional forces are capable of not only moving relatively coarser ferrimagnetic grains from the topsoil but also incising the subsoil and moving anti ferromagnetic minerals into the reservoir which seems to hint at not only sheet wash but also rill and gully erosion as there are no stable streams nor channel networks developed in this mountainous catchment contributions from river bank erosion to sediment yield are almost negligible the sediments in xiaohe reservoir which has a lower relief are predominately derived from topsoil erosion here erosion is concentrated to the topsoil and preferentially transports the relatively fine magnetic grains into the reservoir when erosional forces are weak however even when erosional forces increase in this relatively flat catchment erosion is still restricted to the topsoil thus relatively coarser ferrimagnetic grains from the topsoil are transported to the reservoir but the subsoil remains undisturbed and there are no significant changes in the proportion of anti ferromagnetic minerals in the sediments consequently only sheet washing occurs even when erosion is intensifying in this hilly plain catchment in general the more effective erosion in the shibanqiao catchment is probably due to its steeper topography than xiaohe catchment although higher and more seasonal rainfalls and lower percentages of woodlands may also contribute to the differences in susceptibility to erosional forces c 2011 elsevier b v all rights reserved less

fault scarp features and cascading rupture model for the mw 7 9 wenchuan earthquake eastern tibetan plateau china on 12 may 2008 the m w 7 9 wenchuan earthquake ruptured two northeast striking imbricated reverse faults and one northwest striking reverse fault along the middle longmen shan thrust belt at the eastern margin of the tibetan plateau the morphology of the coseismic scarp varies drastically along strike we distinguish eight different categories 1 simple thrust scarp 2 hanging wall collapse scarp 3 simple pressure ridge 4 dextral pressure ridge 5 fault related fold scarp 6 backthrust pressure ridge 7 local normal fault scarp and 8 pavement suprathrust scarp the coseismic surface ruptures confirm that the wenchuan earthquake is dominated by reverse faulting with some right lateral component that varies from site to site the surface rupture can be divided into two parts the yingxiu segment and the beichuan segment when the earthquake is split into two subevents accordingly they correspond to an m w 7 8 event and an m w 7 6 event respectively these two segments can in turn be divided into four second order subsegments which are equivalent to four subevents of m w 7 5 m w 7 7 m w 7 0 and m w 7 5 respectively the segmentation of the rupture is consistent with a cascading rupture pattern responsible for the total 110 s of the earthquake rupture in addition to surface ruptures the focal mechanisms determined for the aftershocks recorded by the local seismic network are used to constrain the fault geometry of the subsegments they show that the dip of the fault responsible for the earthquake varies along strike and the fault tends to flatten at depth in addition the fault plane gets steeper northward enabling the fault to accommodate a larger strike slip component along a lateral ramp this major earthquake confirms that crustal shortening could be the main driving force for the growth of high topography along the eastern margin of the tibetan plateau and that lower crustal flow is not required

extensional aspects of earthquake induced ruptures determined by an analysis of fracture bifurcation abstract numerical and experimental investigation of symmetric fracture bifurcation kalthoff 1972 has shown that for forks with small branch angles c where c is approximately 14 the propagation of the branches tends to enlarge the angle for forks with larger branch angles c the propagation of the branches tends to diminish the angle forks with the critical angle c will propagate in their original direction kalthoff theorized that the branch angle changes as a function of k i k ii where k i and k ii are the stress intensity factors for tensile and shear sliding modes respectively and k i is considerably larger than k ii in this study i test the hypothesis that this fracture mechanic theory applies to the analysis of fault bifurcation in the crust particularly in cases of rapid fracture fractures produced during the 1968 earthquake at the coyote creek fault in california are intensively branched and an example of rapid rupture the angular behaviour of the branching ruptures in eight forks follows kalthoffs theory unusually well this implies that fracture at the surface was dominated by the tensile mode additional observations that support this implication are series of prominent ruptures which show openings of 20 30 mm per rupture the symmetrical and bilateral forking the high intensity and angular shapes of individual branches the opening of grabens associated with several bifurcations lack of bifurcation in the southern break of the coyote creek fault and the patterns of en echelon fractures which reflect mixed mode surfacial rupture hence contrary to previous interpretations according to field evidence and fracture mechanic theory the fault bifurcation and opening along the coyote creek fault are not compatible with local tension caused by the primary shear fracture probably occurred by different mechanical modes at depth and at the surface while faulting may have originated by shear at depth rupture at the surface was dominated by far field tension associated with ne sw extension in south california the present model predicts the directions of fracture propagation along the fault

rupture terminations and size of segment boundaries from historical earthquake ruptures in the basin and range province abstract the fault segmentation method is commonly used to estimate the potential earthquake size segment boundaries play an important role in arresting earthquake ruptures from event to event in the basin and range province earthquake rupture terminations are commonly associated with structural discontinuities but not all structural discontinuities have the capability to terminate an earthquake rupture the size of structural discontinuities with respect to the rupture length and displacement may play an important role in controlling rupture termination studies of the geometric pattern of seven well documented historical earthquake ruptures in the basin and range province reveal three important relationships between rupture termination and the size of structural discontinuities firstly terminations of normal faulting earthquakes are often associated with structural discontinuities at least for the five historical ruptures studied in this paper secondly the sizes of structural discontinuities at the end of earthquake rupture zones are generally the largest among the structural discontinuities within the rupture zone thirdly there appears to be a trend that larger earthquake ruptures are stopped by larger structural discontinuities the size of structural discontinuities that stopped the earthquake seems to scale with the length and displacement of earthquake surface rupture

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

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

characteristics geometry and segmentation of the surface rupture associated with the 14 april 2010 yushu earthquake eastern tibet china on the morning of 14 april 2010 the m s 7 1 yushu earthquake struck the eastern tibet plateau and an m s 6 3 aftershock followed west southwest of the mainshock epicenter one and a half hours later the yushu earthquake occurred on the northwestern continuation of the ganzi xianshuihe fault zone and reactivated two segments of the fault ruptures associated with yushu earthquake span a zone 70 km long extending from south of jielong in the west to south of gyegu yushu in the east detailed mapping of the surface rupture zone shows that it consists of two strike slip segments the western and eastern segments separated by the longbao lake step over pull apart basin our analysis suggests that the 18 km long western segment of the surface rupture south of the longbao lake basin may have been associated with the m s 6 3 aftershock the eastern rupture segment which is inferred to be associated with the mainshock is 32 km long the main surface rupture can also be divided into two sections with a 2 km long gap between them the surface rupture exhibits left lateral slip and is localized in a zone about 50 m wide along the present day trace of the yushu fault a single break without splays or branching traces characterizes most of the surface rupture zone the observed magnitudes of surface displacement are typically 0 5 1 m with a maximum slip of 2 m both field observations and seismic inversion results suggest rupture of m s 7 1 yushu earthquake nucleated near the longbao lake step over basin in the west propagated unilaterally eastward and terminated within the east segment margin of the yushu fault

tracing movements of topsoil by magnetic measurements two case studies an array of magnetic measurements is used to trace the occurrence of magnetically enhanced topsoil in two different environmental settings the first is a cultivated slope section where the results confirm that movements of topsoil have occurred but that identification of specific erosional processes is problematic the second is a lake catchment system where measurements on soils and sediments allow a partial reconstruction of soil movements from different sources over the last 200 y the study highlights both the need to analyse the magnetic mineralogies of different particle size fractions and the difficulties that may be encountered in trying to discriminate between topsoil and subsoil material on the basis of demagnetization parameters alone

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

tracer techniques in aeolian research approaches applications and challenges abstract aeolian processes the entrainment transport and deposition of sediments by wind impacts climate biogeochemical cycles food security environmental quality and human health considering the multitude of interactions between aeolian processes and all the major components of the earth system there is a growing interest in the scientific community to quantify the wind related sediment movement process and redistribution rates at different spatial and temporal scales however this quantification is rather challenging due to the complexities of physical mechanisms involved in aeolian processes and the inherent fundamental differences from the rather well studied processes controlling fluvial erosion traditional techniques such as erosion plots and surveying methods for monitoring wind erosion are capable of quantifying sediment movement on small scales but they have a number of limitations in terms of the representativeness of the data obtained spatial and temporal resolution and the patterns over extended areas and the costs involved the demand for alternative methods of soil loss and sediment redistribution assessment in order to complement and enhance the existing methods has directed attention to use tracing approaches for monitoring rates and spatial patterns of sediment redistribution at various scales a comprehensive synthesis of available information from different scientific disciplines on aeolian tracer techniques their applications and limitations are important in understanding the role of aeolian processes and their interactions with the earths systems in changing climate and management scenarios the objective of this paper is to provide a scientific review of the current tracer approaches in aeolian studies including fallout radionuclides rare earth elements sediment finger printing and soil magnetism as well as giving an introduction of the potential tracers that are in development

segmentation and holocene surface faulting on the median tectonic line southwest japan the median tectonic line mtl active fault system is a 300 km long arc parallel right lateral strike slip fault related to oblique subduction of the philippine sea plate beneath the eurasian plate at the nankai trough southwest japan the fault on shikoku island has a slip rate of 5 10 mm yr one of the highest in onshore japan we identified 12 geometric segments along the mtl separated by discontinuities such as en echelon steps bends changes in strike and gaps in the surface trace a chronology of latest holocene surface faulting on the mtl was constructed based on previously published and new work including trenching geomorphic mapping and acoustic profiling and piston coring of the submarine extension of the fault zone the mtl probably does not rupture along its entire length in a single earthquake but instead consists of multiple earthquake segments that rupture independently of one another the recurrence interval and surficial offset for surface rupturing earthquakes at four individual sites on the mtl in shikoku island are 1000 3000 years and 5 8 m respectively the relatively long recurrence interval and large surficial offset per earthquake suggest large seismic moment release during surface rupturing earthquakes on the mtl as commonly observed for japanese moderate to large intraplate earthquakes because the predicted rupture lengths based on empirical relations between surface displacement and rupture length are considerably larger than those of individual segments large earthquakes on the mtl probably rupture multiple geometrically defined segments the fault was previously thought to be unruptured at least in the past 1000 years based on the absence of historical evidence for destructive earthquakes however trench excavations show that part of the mtl ruptured most recently during or after the 16th century a d with at least 6 9 0 7 m of slip along the main fault trace this rupture may be correlated to the 1596 keicho kinki earthquake but further geological and historical investigations are needed to confirm this hypothesis

terrain controls on depressional soil distribution in a hummocky morainal landscape in hummocky morainal landscapes soil distribution in well drained landscape positions tends to follow a consistent pattern soils in depressions however are more difficult to predict reliably this study had two objectives 1 to determine the parent material and landscape properties controlling the formation of the different depressional soils and 2 to use these controls to identify quantitative terrain based predictors of soil type in depressions only two terrain attributes specific dispersal area sda and elevation relative to open water bodies were required to distinguish three main soil groups gley recharge non gley recharge and discharge soils specific dispersal area is the downslope area draining flow from a given grid cell gley recharge soils occur primarily at points with sda of less than 2 m2 m 1 regardless of elevation within a given site because most of the runoff flowing to a point with very low sda values will pond or infiltrate vertically rather than flow downslope non gley recharge soils and discharge soils both occur at points with sda of greater than 2 m2 m 1 the majority of the non gley recharge soils occur above 5 m elevation relative to an open water body and the majority of the discharge soils occur below 5 m elevation relative to an open water body reflecting the importance of solute cycling in the development of discharge conditions buried and depositional soils could not be predicted from current terrain attributes because their profile characteristics were derived from the paleosurface

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

speculations on the geometry of the initiation and termination processes of earthquake rupture and its relation to morphology and geological structure earthquake initiation and termination processes are commonly described in terms of barriers and asperities barriers fall into two classes geometric barriers are associated with places where the orientation of a failure surface changes and relaxation barriers where stress is low because aseismic creep processes outpace tectonic loading geometric barriers fall into conservative and nonconservative subgroups according to whether finite fault motion can proceed without the creation of new structures or whether it demands the creation of new faulting or void space the multiple faulting or fragmentation associated with some nonconservative barriers can disrupt fault planes and form asperities by means of selected examples it is shown that a description in terms of these barriers can help one to visualise the processes of earthquake rupture and its relation to the geological environment

controlling factors for the spatial variability of soil magnetic susceptibility across england and wales abstract we review the nature and importance of soil factors implicated in the formation of secondary ferrimagnetic minerals in soils and palaeosols worldwide the findings are examined with respect to temperate regions through a comprehensive analysis of over 5000 samples of surface soil from england and wales taken from a 5 5 km grid over 30 soil and environmental attributes are considered for each sample as proxies for soil forming factors measurements of low field magnetic susceptibility mass specific and frequency dependent susceptibility mass specific and percentage on each sample provide estimates of the concentration and grain size of ferrimagnetic minerals maps of soil magnetism across england and wales show non random distributions and clusters one subset of data is clearly linked to contamination from atmospheric pollution and excluded from subsequent analyses the concentration of ferrimagnetic minerals in the non polluted set is broadly proportional to the concentration of minerals falling into the viscous superparamagnetic domain size range 15 25 nm this set shows clusters of high magnetic concentrations particularly over specific parent materials such as schists and slates mudstones and limestones bivariate analyses and linear multiple regression models show that the main controlling factors are parent material and drainage the latter represented by soil drainage classes and particle size together these two factors account for 30 of the magnetic variability in the complete dataset a second group of factors including climate mean annual rainfall relief slope and altitude and organisms land use organic carbon and ph have subordinate control climate as represented by mean annual temperature and also pedogenic time are deemed not relevant at these spatio temporal scales the findings are consistent with a largely abiotic system where the role of iron reducing bacteria appears minor at coarse spatial and temporal scales secondary ferrimagnetic mineral formation is controlled by the weathering capacity to supply fe to the surface soil at finer scales soluble fe precipitates as ferrihydrite before transformation in response to periodically anaerobic conditions into other minerals including nanoscale magnetite

geomorphological and structural characterization of the southern weihe graben central china implications for fault segmentation abstract the cenozoic graben systems around the tectonically stable ordos block central china have been considered as ideal places for investigating active deformation within continental rifts such as the weihe graben at the southern margin with high historical seismicity e g 1556 m 8 5 huaxian great earthquake however previous investigations have mostly focused on the active structures in the eastern and northern parts of this graben by contrast in the southwest tectonic activity along the northern margin of the qinling mountains has not been systematically investigated yet in this study based on digital elevation models dems we carried out geomorphological analysis to evaluate the relative tectonic activity along the whole south border fault sbf on the basis of field observations high resolution dems acquired by small unmanned aerial vehicles suva using structure for motion techniques radiocarbon 14c age dating we demonstrate that 1 tectonic activity along the sbf changes along strike being higher in the eastern sector 2 seven major segment boundaries have been assigned where the fault changes its strike and has lower tectonic activity 3 the fault segment between the cities of huaxian and huayin characterized by almost pure normal slip has been active during the holocene we suggest that these findings would provide a basis for further investigating on the seismic risk in densely populated weihe graben

sedimentary basins investigation using teleseismic p wave time delays abstract passive seismic methods have been proven successful in recent years at retrieving information about the large scale structure of a sedimentary basin these methods are based on ambient noise recordings and local and distant teleseismic earthquake data in particular it has been previously observed that the arrival time of teleseismic p waves recorded inside a sedimentary basin shows time delays and polarization that both strongly depend on the basin properties and structure in this paper we present a new methodology for determining seismic p wave velocity in a sedimentary basin based on the time delay of a teleseismic p wave travelling through the low velocity basin infill with respect to a teleseismic wave recorded outside the basin the new methodology is developed in a bayesian framework and thus it includes estimates of the uncertainties of the p wave velocities for this study we exploit synchronous recordings of teleseismic p wave arrivals at a dense linear array of broadband seismic stations using data from two teleseismic events coming from two different incoming angles the results obtained by the new proposed methodology are successfully compared to classical cross correlation measurements and are used to infer properties of a sedimentary basin such as the basin bounding fault s geometry and the average p wave velocity of the sedimentary basin fill

paleoseismology and neotectonics of the shivwits section of the hurricane fault northwestern arizona the shivwits section of the hurricane fault in northwestern arizona has been largely ignored in evaluating the seismic hazard posed to the rapidly growing populations of southwestern utah to assess this hazard we conducted studies along the shivwits section using field observations and geomorphic modeling to understand the quaternary tectonism of this portion of the hurricane fault we have found evidence that it ruptured with up to 2 to 3 m of vertical displacement per event and likely produced m 7 earthquakes our results suggest that the slip rate along the southern hurricane fault has not decreased during the quaternary the moriah knoll basalt offset 150 to 200 m along the hurricane fault yielded a maximum long term slip rate of 0 15 to 0 25 mm yr estimated using a new 40ar 39ar age of 0 85 0 06 ma the late quaternary slip rates on alluvial fan surfaces offset 2 to 7 4 m were estimated using pedogenic carbonate rind thickness as a calibrated proxy for age these observations yielded slip rates of 0 05 to 0 3 mm yr paleoseismic trench investigations showed that two surface rupturing events occurred in the past 15 78 k y a radiocarbon sample from a most recent event mre fissure yielded a calibrated age of 8900 10 400 years b p the penultimate event was likely 10 k y before the most recent event slip rate estimates using the moriah knoll basalt 0 15 0 24 mm yr 850 ka surface offset 0 05 0 3 mm yr 100 ka morphologic modeling 0 06 0 21 mm yr 100 ka and observations from the trench 0 06 0 34 mm yr 15 75 ka suggest that there has been no detectable change in slip rate in the past 1 million years or so this implies a constant deformation rate for this portion of the colorado plateau margin therefore basin and range extension is actively encroaching manuscript received 24 november 2003

land use change soil erosion and alluvial dynamic in the lower doubs valley over the 1st millenium ad neublans jura france abstract geochemical and particle size analyses surface scanning magnetic susceptibility microscopic charcoal counting and pollen analysis have been carried out on two cores from the lower doubs valley in order to reconstruct the land use history the interpretation of anthropogenic pollen indicators and micro charcoal deposits is discussed in relation to the lithological variation of sedimentary accumulation and evolution of the settlement the environmental changes which occurred during the 1st and the 6th century ad reflect the impact of human activities on the landscape in the immediate surroundings of the site multiproxy indicators indicate that soil erosion as a consequence of agricultural activities including fire practices a reactivation of hydrologic flow of the river recorded in the sedimentary sequences attests to a larger environmental perturbation between 1st 3rd and 7th 8th century ad

fractal analysis applied to characteristic segments of the san andreas fault fractal theory is applied in a quantitative analysis of the san andreas fault saf geometry the method which directly measures the increase in total fault length with a decrease in ruler size gives the fractal dimension d and scaling properties for the chosen length band 0 5 1000 km a physical interpretation of d is that it measures the irregularity of the fault trace in the selected band the fault is subdivided into six segments of distinctive seismic behavior a main fault trace which shows either maximum coseismic slip or creeping was selected for analysis with three alternative branches examined for the saf system south of san bernardino branches of the fault trace are not considered in this work fractal dimensions calculated for the different segments range from 1 0008 to 1 0191 and are different from 1 0 to the 95 confidence interval these small changes reflect the overall smoothness of the main fault trace significant variations in d among segments indicate heterogeneities in the fault smoothness along strike d also changes significantly from the short length band to the long length band where the demarcation point ranges from 1 to 2 km the short length band has larger d values a slight correlation is obtained between the fractal dimension of the main trace and the extent of subparallel faulting this indicates some correspondence between the main fault trace irregularity and the complexity of subsidiary fault traces in plan view

a rock magnetic record of pleistocene rainfall variations at the palaeolithic site of attirampakkam southeastern india abstract attirampakkam an open air stratified palaeolithic site in southeastern india is the focus of ongoing studies to investigate the nature of lower and middle palaeolithic occupation in relation to changing pleistocene environments the paucity of faunal or palaeobotanical remains at the site required the use of rock magnetic properties lf fd fd arm sirm arm sirm sirm lf arm lf arm fd s ratio hirm and hirm irm 300mt as proxies for deciphering the palaeoenvironments and palaeoclimates of the region rock magnetic data from stratified deposits within excavated trenches show that the bulk of the sedimentation was intermittent with no subaerial exposure of sediments for long periods and points to fluctuating wetter and drier climates associated with the acheulian to late middle palaeolithic levels there is a general trend towards a wetter climate from layer 5 upwards layer 7 offers evidence of bacterial magnetite arm lf 40 and arm fd 1000 suggesting the onset of micro anaerobic environments as a result of floods greigite is indicated in layer 5 sirm lf 30 10 3 a m 1 which indicates a reducing environment layer 2 represents an arid climate higher proportion of haematite and a coarser magnetic grain size layer 1a again is indicative of an arid climate presence of calcrete magnetically hard minerals and coarser magnetic grain size results indicate that the southeast coast of india experienced a mostly dry tropical climate during the pleistocene the detected occurrence of a few notably more arid intervals did not disrupt occupation of the site by successive groups of hominins

magnetic susceptibility of soils in different slope positions in saskatchewan canada abstract the magnetic susceptibility of soils varies with the slope position due to some factors such as texture and drainage class this study attempts to link to soil profile characteristics soil horizon type organic and inorganic c sand and oxalate feo and dithionite fed extractable iron measured on soil cores collected from the three uncultivated soil catenas in saskatchewan the parent material at all sites consisted of medium textured hummocky glacial till the waitville catena gray luvisol was developed under trees the weyburn catena dark brown chernozem under grass and the oxbow catena black chernozem had trees on the lower slope and grass in the center of the depression and on the upper and middle slopes in all the three catenas a downslope decrease in was correlated with increasing feo fed ratios and decreasing sand content lower slope gleyed profiles in the two chernozemic catenas had high feo fed ratios and low the impact of gleying was most evident in the solum and tended to increase in the c horizons of these profiles the of the sand and silt fractions was positively correlated with that of the bulk soil whereas the of the clay fraction did not vary with the of the bulk soil stable sand sized magnetite grains are believed to be rare in these soils

the gubbio normal fault central italy geometry displacement distribution and tectonic evolution abstract normal faults within orogenic belts can be pre syn or post orogenic features we studied the gubbio normal fault central italy which is an example of a pre orogenic fault reactivated in a post orogenic stage the gubbio fault is a 22 km long fault bordering a quaternary basin and part of an active faults system in the umbria marche region central italy the interpretation of a set of seismic profiles enables us to reconstruct the fault geometry in detail and to measure displacement and throw distributions along the fault strike seismic data indicate that the gubbio fault represents an example of multiple reactivation at least a portion of the fault was active in the miocene and only a part of the total displacement was achieved in the quaternary the reconstruction of the fault geometry at depth shows that the fault is characterised by listric geometry the fault is also characterised by a bend along strike and structure contours show that this geometry is maintained at depth as the fault is commonly addressed as presently active the maximum fault dimensions are correlated to the maximum expected earthquake and the presence of the fault bend is discussed as a possible barrier to seismic ruptures propagation