faulting of rocks in three dimensional strain fields i failure of rocks in polyaxial servo control experiments abstract the dependence of the number of sets of faults and their orientation on the intermediate strain axis is investigated through polyaxial tests reported here and theoretical analysis reported in an accompanying paper in the experiments cubic samples of berea sandstone sierra white and westerly granites and candoro and solnhofen limestones were loaded on their three pairs of faces by three independent mutually perpendicular presses at room temperature two of the presses were servo controlled and applied constant displacement rates throughout the experiment most samples display three or four sets of faults in orthorhombic symmetry these faults form in several yielding events that follow a stage of elastic deformation in many experiments the maximum and the intermediate compressive stresses interchange orientations during the yielding events where the corresponding strains are constant the final stage of most experiments is characterized by slip along the faults

relay zone geometry and displacement transfer between normal faults recorded in coal mine plans abstract overlap lengths separations and throw gradients were measured on 132 relay zones recorded on coal mine plans throws on the relay bounding fault traces are usually 2 m and individual structures are recorded on only one seam throw gradients associated with relay zones are not always higher than on single faults but asymmetry of throw profiles is diagnostic of relay zones bed geometries around larger faults in opencast mines are used to assess the displacement accommodated by shear in the vertical plane normal to the faults and displacement transfer accommodated by shear in the fault parallel plane three dimensional structure is defined for two relay zones each recorded on five seam plans these relay zones are effectively holes through the fault surfaces and overlap occurs between salients or lobes of the parent fault surfaces lobes initially terminated at tip lines but as the faults grew gradually rejoined the main fault surfaces along branch lines this type of relay zone originates by bifurcation of a single fault surface at a locally retarded tip line and is an almost inevitable result of a tip line irregularity

late pliocene pleistocene stress field in the teruel and jiloca grabens eastern spain contribution of a new method of stress inversion samples of non striated fracture surfaces within clastic materials of late pliocene pleistocene age from the teruel grabens eastern spain have been analysed using a stress inversion method based on observations of slip sense the results obtained at 21 sites are compared with late miocene early pliocene extensional stress tensors previously inferred from striated faults in the same area the similarity between both sets of stress states suggests that the extensional miocene pliocene stress field essentially continues with minor changes into pliocene pleistocene times the main changes involve a the dominant trend of 3 trajectories which evolve from ese to ene b the waning of the compressional component caused by europe iberia africa convergence and c the progressive trend towards a multidirectional extension regime stress deflection caused by large scale extensional faults as well as switching of 2 and 3 axes induced by fracture development are common within this stress field they produce groups of local stress ellipsoids with 3 axes orthogonal to each other and either orthogonal or parallel to the faults bounding the grabens the regional consistency of the new results gives support to the new inversion method and demonstrates its utility in research on young sedimentary rocks where gaps in palaeostress records may exist due to absence of striated faults

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

stress evolution and structural inheritance controlling an intracontinental extensional basin the central northern sector of the neogene teruel basin abstract the teruel basin is a nne ssw trending intracontinental extensional basin located in central eastern iberia it is asymmetrically bounded to the east by a major fault zone but intrabasinal faults with diverse orientation nne ssw to ne sw e w or nw se also appear offsets of the successive sedimentary units and of two planation surfaces reveal that tectonic activity initiated at the border faults while intrabasinal ones mainly developed in a later stage fractures on a map scale show a prevailing n s strike in neogene synrift rocks while a dense network made of four main fracture sets ne sw e w to ese wnw n s and nnw sse likely inherited from mesozoic rifting stages is observed in pre rift units the results of palaeostress analyses indicate an overall predominance of 3 directions around e w although two stress episodes have been distinguished during the late miocene pleistocene i triaxial extension with 3 e w ii almost radial extension 1 vertical 2 3 with a somehow prevailing 3 ene wsw a scenario in which the evolving extensional stress field was able to gradually activate major basement structures with different orientation inherited from previous tectonic events is proposed as responsible for the evolution and overall pattern of both the eastern active margin and central parts of the central northern sector of the teruel basin

seismites from a well core of palustrine deposits as a tool for reconstructing the palaeoseismic history of a fault abstract the concud fault is located at the junction between the jiloca and teruel grabens central eastern iberian chain spain the late pleistocene activity of this fault has been well logged from structural and palaeoseismological trench studies but only scattered data of the late pliocene seismic activity exist the late pliocene early pleistocene syn tectonic infill consists of an endorheic continental succession in which a 75 m long continuous well was drilled near the concud fault along the entire well core several types of soft sediment deformation structures with variable morphology size and frequency have occurred including clastic dykes load structures and slumps the rigorous analysis of the deformation structures their relationships with the involved sedimentary facies and the discrimination of possible deformation mechanisms and trigger processes allow us to interpret part of them as seismically induced structures the recognition of 21 deformed beds seismites allow the late pliocene early pleistocene seismic history of the concud fault to be reconstructed therefore 21 seismic events with m 5 and an apparent recurrence period of about 45 ka have been inferred

slip partitioning by elastoplastic propagation of oblique slip at depth oblique motion along tectonic boundaries is commonly partitioned into slip on faults with different senses of motion the origin of slip partitioning is important to structural geology tectonophysics and earthquake mechanics partitioning can be explained by the upward elastoplastic propagation of oblique slip from a fault or shear zone at depth the strain field ahead of the propagating fault separates into zones of predominantly normal reverse and strike slip faulting the model successfully predicts the distribution of fault types along parts of the san andreas and haiyuan faults

formation of listric normal faults by extensional duplexing a case study from the active langshan piedmont fault nw china abstract the development of normal faults is controlled by many factors among which mechanical layers or pre existing fabrics play an important role in the growth of normal faults it is widely accepted that normal faults are rarely continuous surfaces but are zones composed of fault segments heterogeneously distributed fault rocks of various compositions slip bands blocks and other deformation elements listric normal faults particularly those developed in metamorphic crystalline rocks or preexisting fabric developed basements may be composed of subparallel faults in cross sections linked by extensional duplex structures here we choose a listric rift bounding fault rooted in foliation developed basements the langshan normal fault in the northwest corner of the ordos block to conduct an outcrop analysis of fault geometry and linkage behavior from cross sectional views the langshan normal fault zone is composed of mixed regions of high and low angle segments linked by duplex structures at various scales mylonitic foliations play a significant role in the formation of fault segments and the evolution of the listric fault zones lines of evidence show that small en echelon faults initiated from preexisting foliations local stress perturbation between overstepping faults results in the formation of duplex structures and displays a high fracture density which serve to the coalesce of fault segments consequently the progressive localization of strain onto a large listric fault is achieved by progressive development of extensional duplexing among fault segments in cross sections these extensional duplexes imply a scale invariant property based on which we can extrapolate this pattern occurs on larger scales and is verified by seismic data the case of langshan piedmont fault demonstrates the possibility of a listric fault being formed by subparallel planner faults and highlights the effects of preexisting fabrics on the evolution of listric faults especially in basement fabrics developed regions along the fault

regional state of stress and characteristic fault kinematics instabilities shown by aftershock sequences the aftershock sequences of the 1978 thessaloniki greece and 1980 campania lucania italia earthquakes as examples abstract usual analysis of fault kinematics in terms of stress supposes that the slip occurs in the direction of the shear stress resolved on the fault plane due to an homogeneous state of stress however as a block moves this yields perturbations of the static stress conditions the resulting displacement may produce interactions of blocks and may induce complex fault motions such as those demonstrated by the aftershock sequences of the thessaloniki and campania lucania earthquakes each of which shows a main group of focal mechanisms whose normal fault motions are modelled using a stress deviator tm in agreement both with the motion of the main seismic fault and with the regional stress pattern deduced from quarternary and recent faults it is therefore considered as representative of the mean state of stress acting in the epicentral area but two other families of fault motions are also demonstrated one shows reverse motions explained by a compressional stress deviator tc the other involving normal motions is explained by a tensional stress deviator te these deviators are not representative of the mean regional state of stress the compressional 1 axis of tc and the tensional 3 axis of te are roughly orthogonal to the 3 axis of the mean state of stress tm these tc and te deviators may be deduced from the mean state of stress tm by adding respectively td1 and td2 deviators to this latter this means that on each fault plane having a reverse c or a normal e motion this motion may be deduced from the normal kinematics m it should have occurred in the mean regional state of stress tm by adding local pushes d1 and d2 respectively the deviator td2 being nearly axisymmetric around a vertical 3 axis the local reverse pushes d1 are nearly dip slip and td2 having a high angle dipping 2 axis the local pushes d2 are essentially strike slip approximated solutions of these td1 and td2 deviators have been calculated by taking tm td1 tc and tm td2 te the mean state of stress tm being divided into two parts tv and ts which respectively produce the dip slip and essentially strike slip components of the stress resolved on the fault plane a first approximation of the data shows that td1 kv tv and td2 ks ts with kv and ks equal to 2 this approximation supposes that tm tc and te are coaxial and that td1 and td2 are respectively axisymmetric around the vertical 3 axis and planar in the horizontal plane actually the data give kv 2 and ks in the order of 4 5 it is suggested that the local reverse and strike slip pushes are induced by the reaction of the rocky body surrounding small blocks moving as a consequence of a motion on a major fault particularly as there are incompatibilities of motion of adjacent small blocks however data are not sufficient to demonstrate the mechanical and geometric conditions which control the observed different behaviors of the small seismic faults numerical simulations or experiments could probably precise these conditions whatever under certain conditions the stable solution m is replaced by kinematics instabilities e and c however it is usually observed that faults studied in the field in a simple way often yield a single stress deviator this is probably due to the nature of the measured striations which are often growth fibers and oblique stylolithes resulting from creep fault motions in this case incompatibilities of block motions are probably accommodated by a pressure dissolution phenomena therefore it is suggested that the bifurcation parameter which controls the occurrence of the characteristic instabilities possibly depends on a ratio of the deformation rate versus the pressure dissolution rate of the material a question remains unanswered are these instabilities scale invariant or is there a changeover in the behavior between minor and major faults

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

the neogene structure of the eastern iberian margin structural constraints on the crustal evolution of the valencia trough western mediterranean abstract the presence of a thinned crust beneath the valencia trough has been recognized for a long time however to date no attempt to link this thinning inferred from geophysical data with the superficial structures has been made a quantification of the neogene extensional processes in the crustal evolution of the valencia trough is presented as a consequence of the complexity of the betic balearic domain the analysis has been done for the catalan valencian domain northwestern areas of the trough crustal and superficial data in this area show that neogene extension was accommodated by a listric normal fault system detached in a deep upper crustal level 13 15 km in the marginal zone of the domain quantitative analysis of the neogene structure shows the incoherence between the upper crustal thinning inferred from the geometric analysis of the superficial structures factor 1 4 1 5 and from geophysical data 1 8 although the latter value agrees with that deduced from the analysis of neogene subsidence this incoherence suggests that the present thinned crust would be partially inherited from the mesozoic extension in this way mesozoic subsidence analysts and the recognized mesozoic structure show that the mesozoic extension was almost as important as the neogene one

analysis of non striated faults in a recent extensional setting the plio pleistocene concud fault jiloca graben eastern spain the integration of palaeostress results obtained from the analysis of non striated faults and joints affecting plio pleistocene deposits near the concud fault southern jiloca graben eastern spain yields a multidirectional tension stress field vertical s1 s2zs3 where the primary s3 trajectories trend ene the results also show strong deflections of stress trajectories with many local s3 axes being either orthogonal or parallel to the trace of the concud fault the stress field persisted throughout the period of activity of the fault i e late pliocene and pleistocene the agreement between the present results and the regional picture gives support to the stress inversion method and shows its usefulness in palaeostress analysis of young poorly lithified rocks

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

triggering effect of m 4 5 earthquakes on the earthquake cycle of repeating events at parkfield california stress perturbations influence earthquake recurrence and are of funda mental importance to understanding the earthquake cycle and determining earthquake hazard the large population of repeating earthquakes on the san andreas fault at parkfield california provides a unique opportunity to examine the response of the repeating events to the occurrence of moderate earthquakes using 187 m 0 4 to 1 7 repeating earthquake sequences from the high resolution seismic network cat alog we find that the time to recurrence of repeating events subsequent to nearby m 4 5 earthquakes is shortened suggesting triggering by major events the triggering effect is found to be most evident within a distance of 5 km corresponding to static coseismic stress changes of 0 6 26 6 kpa and decays with distance we also find coherently reduced recurrence intervals from 1993 to 1998 this enduring recurrence acceleration over several years reflects accelerated fault slip and thus loading rates during the early 1990s online material figures of event chronologies of res estimates of dt and coseismic static stress changes

role of transverse structures in paleoseismicity and drainage rearrangement in rift systems the case of the valdecebro fault zone teruel graben eastern spain the e w trending nearly pure extensional valdecebro fault zone is a transverse structure at the central sector of the n s teruel graben it was activated by the late ruscinian early pliocene ca 3 7 ma giving rise to structural rearrangement of the graben margin until the late pleistocene it has accommodated a net slip ca 205 m with slip rate of 0 055 mm a paleoseismicity has been analysed in a 29 m long 5 m deep trench excavated through a fault branch that offsets a pleistocene pediment surface the paleoseismic succession includes a minimum of 6 7 events occurred since ca 142 ka bp although a model with 12 events could be more realistic the following paleoseismic parameters have been inferred assuming a minimum of 6 and a maximum of 12 events average coseismic slip 58 117 cm recurrence period 8 4 28 4 ka potential moment magnitude mw 5 8 5 9 the recorded displacement since ca 142 ka bp totalizes 7 0 m with slip rate of 0 05 0 07 mm a slip on the transverse valdecebro fault zone has critically contributed to bulk deformation under a prevailing multidirectional extensional regime drainage patterns have been rearranged recurrently switching between westward and southward directions as a consequence of diverse slip episodes at the valdecebro fault zone e w and the neighbouring la hita n s and concud nw se faults the ultimate westward drainage of the valdecebro depression incised and dismantled a southward sloping pleistocene pediment sourced at the valdecebro mountain front representing a capture by the alfambra river occurred between 124 and 22 ka bp

continental deposits magnetostratigraphy and vertebrate paleontology late neogene of eastern spain abstract eleven sections have been sampled for magnetostratigraphy in the fossil mammal productive late neogene basins of eastern spain the characteristic direction of magnetization was determined through progressive thermal and alternating field demagnetization it was possible to correlate the magnetozones from the various sections to the gpts as well as to the fossil mn zones within the sediment the mn zone boundaries based on this correlation are as follows mn 11 12 8 1 my mn 12 13 6 my mn 13 14 4 9 my mn 14 15 4 18 my mn 15 16 3 58 my new fossil lists are presented for the fuente del viso and loma del castillo faunas in the cabriel basin

neotectonics and late holocene paleoseismic evidence in the plio quaternary daroca half graben iberian chain ne spain implications for fault source characterization this work has been supported by project cgl2017 85045 p ministerio de economia industria y competitividad gobierno de espana

lapse time dependent coda wave depth sensitivity to local velocity perturbations in 3 d heterogeneous elastic media in the context of seismic monitoring recent studies made successful use of seismic coda waves to locate medium changes on the horizontal plane locating the depth of the changes however remains a challenge in this paper we use 3 d wavefield simulations to address two problems first we evaluate the contribution of surface and body wave sensitivity to a change at depth we introduce a thin layer with a perturbed velocity at different depths and measure the apparent relative velocity changes due to this layer at different times in the coda and for different degrees of heterogeneity of the model we show that the depth sensitivity can be modelled as a linear combination of body and surface wave sensitivity the lapse time dependent sensitivity ratio of body waves and surface waves can be used to build 3 d sensitivity kernels for imaging purposes second we compare the lapse time behaviour in the presence of a perturbation in horizontal and vertical slabs to address for instance the origin of the velocity changes detected after large earthquakes

segmentation and increasing activity in the neogene quaternary teruel basin rift spain revealed by morphotectonic approach abstract the nnw sse trending teruel basin rift is the largest late miocene quaternary extensional intracontinental structure located within the central eastern iberian chain spain the structural and morphotectonic study carried out in the central northern part of this half graben basin north of teruel city has allowed us to analyse rift segmentation deformation partitioning and rift evolution results are based on vertical displacement calculations fault throw and bending of the main border and intrabasin fault zones we use two geomorfological stratigraphical markers the intramiocene erosion surface ies 11 2 ma and the fundamental erosion surface fes 3 5 ma while the first marker reveals rift initiation under an e w extension the late marker records vertical displacements associated to a second late pliocene quaternary rifting stage characterized by a nearly multidirectional extension regime with prevailing ene wsw trending o3 despite the along axis rift segmentation into three structural domains northern central and southern and the distribution of deformation among border and intrabasin faults in the central and southern domains a consistent average slip rate post ies of 0 09 mm a has been calculated on distinct transects across the basin suggesting a homogeneous crustal scale extension process in the region the results also reveal that slip rates during the late pliocene quaternary 0 12 0 16 mm a are higher than the late miocene early pliocene 0 05 0 07 mm a slip rate increase is caused by i a westward propagation of deformation from the valencia through and ii a change in the regional stress field both enhanced by crustal doming affecting central eastern iberia as well as progressive fault linkage throw vs distance graphs suggest that the main faults are in a transient stage towards coalescence less advanced within the southern domain regional late pliocene quaternary uplift concomitant with increasing slip rates in the teruel basin rift has caused the basin to rise so that synrift sedimentation only took place in rapidly subsiding residual basins until the region became exorheic and the basin was incised by the present day fluvial network

assessing interaction of active extensional faults from structural and paleoseismological analysis the teruel and concud faults eastern spain abstract the relationship of independence interaction or linkage between two neighbouring intraplate active extensional faults the teruel and concud faults are investigated from structural and paleoseismological data and the results are discussed to improve seismic hazard assessment for the region this paper provides the structural and paleoseismological characterization of the almost unknown teruel fault from detailed mapping and trench analysis and discusses its kinematic and dynamic relationships with the concud fault four individual events occurred between 76 0 ka and 9 2 ka bp have been recorded at two branches of the teruel fault unfortunately these only represent a small fraction of its overall activity during such time lapse and their time constraints do not allow correlating them with those at the concud fault the teruel and concud faults are independent structures from the geometric and kinematic point of view as evinced by their distinct i transport directions n275 e and n220 e respectively and ii average coseismic displacements 0 5 m and 1 9 m respectively these displacements are consistent with their respective lengths 9 0 km and 14 2 km and significantly smaller than those expected for a hypothetically joint concud teruel 23 km long fault however their displacement gradients close to the relay zone indicate that both faults undergo dynamic interaction thus suggesting a transient stage from independence to linkage we hypothesize that slip on both structures occurred at the scale of the seismic cycle in a broadly alternating manner which induced strain partitioning between them and allowed accommodating bulk biaxial extension in the region such deformation pattern would have increased the earthquake frequency with respect to the scenario of a hypothetically linked concud teruel fault but diminished the potential seismic magnitude

magnitude versus faults surface parameters quantitative relationships from the aegean region historical and seismotectonic data from the broader aegean region have been collected and all possible information relative to ground deformation associated to earthquakes that hit the area have been re evaluated all events associated to co seismic surface faulting have been selected and further investigated while geomorphologic and geological criteria have been used to recognise and characterise the seismogenic faults associated to these morphogenic earthquakes sensu bull inqua 16 1993 24 in particular in order to perform seismic hazard analyses we compiled a list of all earthquakes where the surface rupture length srl the maximum vertical displacement mvd or the average displacement ad is available we thus obtained reliable values of these source parameters for 36 earthquakes of which 26 occurred during the 20th century 6 in the 19th century and the 3 remaining earlier magnitude versus srl and mvd has been compiled for estimating empirical relationships the calculated regression equations are ms 0 90 log srl 5 48 and ms 0 5 9log mvd 6 75 showing good correlation coefficients equal to 0 84 and 0 82 respectively co seismic fault rupture lengths and especially maximum displacements in the aegean region have systematically lower values than the same parameters worldwide but are similar to those of the eastern mediterranean middle east region the envelopes of our diagrams are also calculated and discussed for estimating the worst case scenario furthermore for all investigated seismogenic structures based on several geological criteria we measured the geological fault length gfl which is the total length of the neotectonic faults showing cumulative recent activity we then compared srl with gfl and their ratio shows a clear bimodal distribution with a major peak at 0 8 1 0 indicating that about 50 of the investigated earthquakes ruptured almost the entire fault length while a second peak around the value of 0 5 is clearly related to a segmentation process of longer neotectonic structures further implications of this distribution are also discussed eventually from the distribution of gfl versus magnitude we also infer an important geological threshold for the occurrence of morphogenic earthquakes at about 5 5 degrees

fault relay zones evolving through distributed longitudinal fractures the case of the teruel graben system iberian chain spain abstract a new type of fault relay zone in extensional contexts dominated by distributed along strike or longitudinal fractures is defined it contrasts with the classical models reported in the literature in which transverse connecting faults controlled by the own relay kinematics prevail the new model is based on structural features of the teruel graben system as well as on analogue modelling relay zones between the nw se to nnw sse striking faults that delimit the eastern boundary of the jiloca graben calamocha sierra palomera and concud faults together with the teruel fault have been studied all of these relay faults show recent neogene quaternary ruptures at different scales mostly parallel to the macrostructural trend and to the maximum horizontal stress shmax trajectories i e orthogonal to the ene wsw regional extension direction that characterises the nearly biaxial or radial stress regime active during upper pliocene quaternary times transverse ruptures are almost absent with the exception of the northern relay zone calamocha sierra palomera where an incipient ne sw striking connecting fault does exist analogue models have been run under a biaxial extension regime similar to the regional one they allowed analysing the main factors controlling fracture propagation depending on the ratio of extension velocities and the orientation of the master faults relative to extension directions laboratory fracture patterns as in the natural studied examples are mostly controlled by the inherited anisotropies and in a greater extent by the imposed extension trajectories which results in a clear prevalence of longitudinal fractures such external controls usually disregarded in numerical and analogue modelling tend to induce fault coalescence through along strike parallel or at very low angle propagation resulting in a final braided fault pattern

facies architecture of asymmetrical branching distributary channels cretaceous ferron sandstone utah usa distributary channel systems are an important component of deltaic systems but details of their branching pattern stream order internal variability and relation with adjacent levee bay and bayhead delta are rather poorly documented in ancient examples photomosaic and measured sections collected along a gooseneck shaped canyon in southern utah allow direct mapping of the branching pattern of an ancient distributary system the main channel belt is ca 250 m wide and narrows to ca 200 m downstream of the branching point a subordinate channel belt ca 80 m wide branches off of the main channel forming a distinctly asymmetrical branching pattern water discharge in the main channel is estimated to be 85 to 170 m3 sec 1 comparison with palaeodischarge estimates of trunk rivers mapped in previous studies suggests that the branching documented in this study probably is a fourth order split the distributary channels are characterized by a u shaped geometry filled with medium grained cross bedded sandstone and are dominated by lateral accretion suggesting limited lateral migration and moderate sinuosity tidally influenced facies and limited trace fossils indicate direct marine influence the distributary channels erode into adjacent levee and underlying heterolithic bay fill deposits and the marine influence suggests that they were deposited on a lower delta plain rather than on a non marine floodplain the subordinate channel fed a bayhead delta suggesting that it was formed by a partial avulsion rather than bifurcation around a mouth bar as is more characteristic of terminal distributary channels channel floor drapes bar accretion drapes and abandoned channel fills within the sandstone channel belts represent the most important heterogeneity from the perspective of reservoir characterization

scaling relationships and evolution of distributary networks on wave influenced deltas 1 no genetic model can explain the variability in distributary network pattern on modern deltas here we derive scaling relationships for two processes known to create distributary channels and with these laws construct a simple model for distributary network evolution the first process is mouth bar deposition at the shoreline and subsequent channel bifurcation the second is avulsion the wholesale abandonment of a channel in favor of a new path the former creates relatively small networks with power law distributions of channel length the latter generates relatively few backwater scale distributaries frequency magnitude plots of channel length on natural deltas agree with theoretical predictions and show a clear separation in scale that reflects these processes mouth bar distributary lengths scale with the width of the parent channel and avulsive distributary lengths scale with the backwater length intermediate channel lengths are relatively rare wave energy controls network topology by suppressing mouth bar development thereby preferentially eliminating smaller scale distributaries

stress variability and brittle tectonic structures the problem of stress variability both in space and time during brittle deformation of rocks is faced in this note several possible causes of the temporal and spatial variations of the stress tensor are reviewed and discussed a genetic partitioning of the stress tensor is proposed showing that any stress field within a crustal volume can be seen as the sum of relatively simple stress tensors associated to specific genetic components the genetic components discussed in this note are the gravitational the tectonic the fluid the thermal and the diagenetic one each genetic component is a function of several parameters but for all of them the possible important role played by the variable time is emphasised according to numerous researches based on theoretical and experimental grounds brittle deformation in a rock mass occurs when some critical conditions are reached starting from initial equilibrium conditions and leading to even different stress conditions as a consequence of failure field examples are presented and data from literature are discussed to exhibit evidences from complex tectonic structures and to argue about small and large scale spatial variations as well as about short and long term temporal variations of the stress trajectories and of the stress magnitudes that continuously occur during a brittle deformational event the relationships between local and temporal stress variations and what is commonly defined the regional stress field are discussed adding recommendations for future researches

plio quaternary extensional seismotectonics and drainage network development in the central sector of the iberian chain ne spain abstract westward propagation of postorogenic rifting in the central sector of the iberian chain generated the teruel and calatayud mio pliocene grabens and the jiloca daroca and munebrega plio quaternary half grabens partially superimposed on the western margins of the pre existing basins the progressive capture and transformation from endorheic aggradational to exorheic incisional drainage of the active grabens resulted in the development of a drainage network dominated by axial streams controlled by neotectonic activity and the distribution of basin fill lithofacies this paper reviews the geomorphic and stratigraphic evidence of plio quaternary extensional tectonics and provides new chronological data radiocarbon and osl dating on offset deposits and the associated paleoseismic record the daroca fault offsets mantled pediment deposits dated at 113 119 ka based on a radiocarbon age of the colluvial sequence 43 ka affected by the rubielos de la cerida fault a vertical slip rate of 0 05 0 07 mm yr has been estimated for this fault four paleoearthquakes subsequent to 72 ka have been inferred from the classic exposure of the concud fault indicating a recurrence interval of less than 18 ka a gravitational origin related to the dissolution of subjacent evaporites is attributed to two faults affecting an upper pleistocene terrace 15 ka in the alfambra valley close to the concud fault these structures have recently been interpreted as evidence of coseismic deformation on the concud fault although the faults have a low slip rate and a long seismic cycle their length

displacement and geometrical characteristics of earthquake surface ruptures issues and implications for seismic hazard analysis and the process of earthquake rupture there now exist about three dozen historical earthquakes for which in vestigators have constructed maps of earthquake rupture traces accompanied by de scriptions of the coseismic slip observed along the fault strike the maps and slip distributions are compiled here to place observational bounds on aspects of seismic hazard analysis and fault mechanics analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults the observations also give support to the ideas that there exists a process zone or volume of about 3 4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes to this may be added the observation that the form of earthquake surface slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike online material maps of surface ruptures digitized values and curve fits to surface slip distributions and notes and references for tables 1 and 2

magnitude distribution of linear morphogenic earthquakes in the mediterranean region insights from palaeoseismological and historical data we analyse the earthquake magnitude distribution of linear morphogenic earthquakes that reactivated dip slip normal faults within the mediterranean region information on past events is obtained following two distinct methodological approaches the geological one morphotectonic investigations and palaeoseismological excavations and the historical one contemporaneous descriptions and surveys of coseismic ruptures in order to homogenize the different data sets and therefore enabling a comparison we calculate moment magnitudes m w starting from seismic moments m 0 estimates the cumulative distributions thus obtained for the two data sets show differences that a series of non parametric tests suggests to be statistically significant coseismic displacements are systematically overestimated for strong m w 6 5 historically based earthquakes and for moderate 5 0 6 0 palaeoseismologically observed events also concerning the rupture length the geological information generally provides larger values for moderate earthquakes the possible causes of this discrepancy and the consequences in using the two data sets for seismic hazard assessment analyses are also discussed

spatial and temporal variation of palaeoseismic activity at an intraplate historically quiescent structure the concud fault iberian chain spain abstract several faults in the teruel and jiloca grabens iberian chain ne spain particularly the targeted concud fault show evidences of recent continuous activity despite their scarce instrumental and historic seismic record three trenches are studied in two locations central and southeastern sectors of the concud fault respectively after comparing with previous works we reconstruct a palaeoseismic succession with nine events distributed along a maximum time lapse bracketed between 81 6 and 14 0 ka this succession involves an average recurrence interval of 7 4 2 8 ka with individual interseismic periods between 4 and 11 ka the calculated coseismic displacements range from 0 6 to 2 7 m with an average value of 1 9 m that results in a slip rate of 0 26 mm a due to the incomplete sedimentary record for holocene times we cannot affirm that the youngest event detected was actually the last one we conjecture that some other events may have occurred during the period between 15 0 and 3 4 ka temporal and spatial variations have been detected in palaeoseismic activity specifically in the distribution of coseismic displacements first a non steady slip rate is evidenced during plio pleistocene times a long term tendency towards increasing slip rate is modulated in detail by the occurrence of minor cycles as the sequence of increasing decreasing activity recorded within the studied time window suggests secondly an asymmetric distribution of coseismic slip along the fault trace is observed paralleling the distribution of total fault throw which shows an absolute maximum close to the southeastern tip a combination of factors is proposed to explain this branching of the main fault dominant remote stress driven slip towards n 220 e on the nw se fault segment guided movement on the passive nnw sse segment giving rise to an oblique roll over monocline and decoupling of the hanging wall block owing to the transverse los mansuetos valdecebro fault zone

paleoseismological analysis of an intraplate extensional structure the concud fault iberian chain eastern spain the concud fault is a 13 5 km long nw se striking normal fault at the eastern iberian chain its recent late pleistocene slip history is characterized from mapping and trench analysis and discussed in the context of the accretion incision history of the alfambra river the fault has been active since late pliocene times with slip rates ranging from 0 07 to 0 33 mm year that are consistent with its present day geomorphologic expression the most likely empirical correlation suggests that the associated paleoseisms have potential magnitudes close to 6 8 coseismic displacements of 2 0 m and recurrence intervals from 6 1 to 28 9 ka at least six paleoseismic events have been identified between 113 and 32 ka the first three events u to w involved displacement along the major fault plane the last three events x to z encompassed downthrow and hanging wall synthetic bending prompting fissure opening this change is accompanied by a decrease in slip rate from 0 63 to 0 08 0 17 mm year and has been attributed to activation of a synthetic blind fault at the hanging wall the average coseismic displacement 1 9 2 0 m and recurrence period 6 7 7 9 ka inferred from this paleoseismic succession are within the ranges predicted from empirical correlation such paleoseismic activity contrasts with the moderate present day seismicity of the area maximum instrumental mb 4 4 which can be explained by the long recurrence interval that characterizes intraplate regions

stress drop slip type earthquake magnitude and seismic hazard care must be taken to provide reliable antiseismic protection in earthquake prone areas where the impact of a large earthquake in megacities with industrial facilities as well as in ordinary buildings is liable to cause massive loss of human life and to cripple the nation s economy this protection needs to take into account not only vibratory ground motion but also permanent ground failure and notably surface faulting hazard a fact tragically illustrated during the recent events of turkey and taiwan the purpose of this contribution is to conduct a survey of our current state of knowledge concerning theoretical relationships between earthquake source parameters such as moment magnitude m m w surface wave magnitude m s seismic moment m o stress drop rupture length l and displacement on the fault d a relationship is proposed that links m s to l and m s 2 log l 1 33 log 1 66 using a simple rupture model earthquake data from all over the world for which the parameters of rupture length fault width w fault displacement and surface wave magnitude are available have enabled stress drop values to be computed for each event using both geological observation 1 and the previously proposed equation 2 the results obtained tend to indicate that stress drop values increase versus fault width depth up to approximately 15 km corresponding perhaps to the brittle ductile boundary this increase is more pronounced in the case of reverse faults than it is for those with strike slip or normal mechanisms an equation of the type kw n has been used to fit the data and preliminary values for k and n have been supplied for the three slip types for depths in excess of 15 km the data do not display significant variation 100 bars these results are in agreement with certain laboratory models of the continental lithosphere although more data particularly in the large magnitude range are needed to ascertain whether it is the w or the l model that better describes earthquake scaling laws stress drop does not appear to be fault length dependent thus being supportive of the l model the risk of surface faulting is dependent on the dynamic environment of the fault that is the stress drop the rupture length and the fault width although statistics show that surface faulting appears in most instances at magnitudes of at least 6 1 data from certain regions indicate that seismicity at superficial depths is under certain conditions accompanied by significant surface faulting even for magnitudes as small as 5 5 suggesting a change in scaling law the threshold magnitude for surface faulting is accordingly seen to depend on the rheology of materials in the fault area and on the stress environment manuscript received 31 may 2000

empirical relationships between aftershock area dimensions and magnitude for earthquakes in the mediterranean sea region fault dimension estimates derived from the aftershock area extent of 36 shallow depth v31 km earthquakes that occurred in the mediterranean sea region have been used in order to establish empirical relationships between length width area and surface wave moment magnitude this dataset consists of events whose aftershock sequence was recorded by a dense local or regional network and the reported location errors did not exceed on average 3 5 km surface wave magnitudes for these events were obtained from the neic database and or published reports while moment magnitudes as well as focal mechanisms were available from the harvard usgs catalogues contrary to the results of some previously published studies we found no evidence in our dataset that faulting type may have an effect on the fault dimension estimates and therefore we derived relationships for the whole of the dataset comparisons by means of statistical f tests of our relationships with other previously published regional and global relationships were performed in order to check possible similarities or differences most such comparisons showed relatively low significance levels b95 since the differences in source dimension estimates were large mainly for magnitudes lower than 6 5 becoming smaller with increasing magnitude some degree of similarity however could be observed between our fault length relationship and the one derived from aftershock area lengths of events in greece while a difference was found between our regional and global fault length relationships a calculation of the ratio defined as the fault length derived from our relationships to the length estimated from regional empirical relationships involving surface ruptures showed that it can take a maximum value of about 7 for small magnitudes while it approaches unity at ms 7 2 when calculating the same ratio using instead global empirical relationships we see the maximum value not exceeding 1 8 while unity is reached at mw 7 8 indicating the existence of a strong regional variation in the fault lengths of earthquakes occurring in the mediterranean sea region also a relationship between the logarithms of the rupture area and seismic moment is established and it is inferred that there is some variation of stress drop as a function of seismic moment in particular it is observed that for magnitudes

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

neogene quaternary tectonic stratigraphy of the eastern southern alps ne italy abstract in order to reconstruct the neogene quaternary tectonic stratigraphy of the eastern southern alps the late tortonian lower pleistocene foredeep clastic sequences cropping out in the veneto and friuli piedmont areas have been extensively investigated focusing on the contractional features observed in the frequent conglomerate layers pitted pebbles the eastern southern alps is the result of a typical polyphase tectonic activity initiated in late oligocene characterised by the occurrence of several non coaxial stress regimes based on careful analyses of the pebbles surfaces shape and orientation of the indented features and following a systematic and statistical approach the mean orientation of the maximum compressive stress axis 1 has been obtained for more than 30 sites of measurements along the ca 120 km long investigated piedmont area the affected lithostratigraphic units and the orientation pre versus post tilting of the stereonets density peaks make it possible to recognize four distinct deformational events and characterize them in terms of mean 1 direction and timing late tortonian 1 313 00 late messinian early pliocene 338 04 late pliocene 314 03 and early middle pleistocene 160 03 the tectonic stratigraphy of the eastern southern alps during the last ca 10 ma shows the occurrence of several variations of the stress field characterized by a repeated oscillation of the 1 axis between an nnw sse and nw se directions twist tectonics taking also into account literature data about older deformational events chattian burdigalian and serravallian tortonian we analyse the neogene quaternary tectonic evolution in the frame of the central mediterranean realm and compare it with the convergence direction between the adria africa and europe lithospheric plates we show that compressional directions within the eastern southern alps are basically governed by the remote plate convergence though since late messinian the approaching northern apennines started to play a crucial role within the investigated area alternating short lived phases 1 2 ma of coupling and decoupling along the basal detachment of the apennines accretionary wedge probably caused temporary perturbations of the local stress field and complex accommodation structures in this region of ongoing crustal collision

the recent upper miocene to quaternary and present tectonic stress distributions in the iberian peninsula a general synthesis of the recent and present stress situation and evolution in the iberian peninsula was obtained from microstructural and seismological analysis the stress evolution was deduced from 1 fault population analysis fpa from 409 sites distributed throughout the iberian peninsula 2 paleostress indicators given by 324 stations taken from the bibliography and 3 seismic data corresponding to 161 focal mechanisms evenly spread in the studied region the application of fpa together with the determination of stress tensors and focal mechanisms for the whole iberian microplate has provided two main results 1 the iberian peninsula is undergoing a nw se oriented compression except for the northeastern part pyrenees ebro basin and iberian chain where it is n s to ne sw and the gulf of cadiz where it seems to be e w and 2 the main trends of the stress field have remained almost constant since the upper miocene the analysis performed by zones suggests the presence of local heterogeneities in the stress field

comparison of earthquake scaling relations derived from data of the instrumental and preinstrumental era estimates of surface rupture displacement and magnitude for crustal earthquakes from the preinstrumental era pre 1900 tend to be greater than the corresponding estimates derived from modern scaling relations we investigate this tendency using an expanded and updated version of the earthquake dataset of wells and coppersmith 1994 to fit regression relations of moment magnitude on surface rupture length and rupture area and average surface displacement on surface rupture length separate relations are fitted to preinstrumental and instrumental data and the results compared to the equivalent relations of wells and coppersmith we find that our relations for instrumental data remove some but not all of the differences between the preinstrumental data and the relations of wells and coppersmith we attribute the remaining differences largely to natural censoring of surface displacements less than about 1 m and surface rupture lengths less than about 5 km from the dataset for the preinstrumental era because regressions constructed from similarly censored instrumental data are indistinguishable from the preinstrumental regressions since the regressions for our censored instrumental data i e restricted to moderate to large earthquakes are different from regressions for our complete dataset of instrumental earthquakes and from the regressions of wells and coppersmith both with a larger proportion of small to moderate earthquakes the results may indicate that large earthquakes have different scaling relationships from those of smaller earthquakes

late cenozoic stress field and fracturing in the iberian chain and ebro basin spain detailed study of mesoscopic faults and joints affecting neogene and pleistocene deposits in the iberian chain and the ebro basin involving statistical study of fracture directions and palaeostress analysis from striated fault planes together with analysis of macrostructures suggest a complex late cenozoic stress field in which both primary and secondary stress systems are superposed 1 regional n s compression was caused by convergence between the iberian and african plates 2 multidirectional extension was caused by crustal doming in the iberian chain 3 stress trajectories were deflected near major faults 4 small scale swapping of the horizontal tension axes 2 and 3 was caused by development of fractures at right angles to either the primary or the deflected 3 axis

revisiting the slip rate of quaternary faults in the iberian chain ne spain geomorphic and seismic hazard implications abstract the seismogenic potential of active faults for seismic hazard analyses are typically constrained using slip rates these parameters derived from numerically dated quaternary deposits and landforms have a critical impact on seismic hazard estimates with relevant societal and economic implications recently published geomorphological and paleoseismic investigations on active normal faults in the intraplate iberian chain spain based on osl ages from a now closed commercial laboratory indicate anomalously high slip rates and paleoearthquake frequencies and extremely high fluvial incision rates parameters derived from those numerical ages have been used for seismic hazard assessments at critical facilities this work revisits the chronology of quaternary deposits associated with several faults applying various geochronological methods electro spin resonance esr ams radiocarbon optically stimulated luminescence osl and u series dating the totality of the new numerical ages is markedly different from the previously published osl ages the thirteen new esr osl and u series ages are systematically between three and six times older than the previous osl ages these data strongly suggest that previous ages overestimate the activity of the faults and seismic hazard in the region the lack of validity of the revisited osl analyses is attributed to inadequate dating procedures slip rates calculated with the new numerical ages are consistent with the slip rates estimated using pliocene markers in the iberian chain and the slip rates published for other normal faults in eastern spain the new geochronological data also indicate reasonable fluvial incision rates comparable with those estimated in nearby regions the findings presented in this work have also implications for other quaternary geomorphological studies in spain based on potentially non valid osl ages