analysis of wave induced pore pressure changes recorded during the 1980 mammoth lakes california earthquake sequence abstract acceleration and wave induced pore pressure were recorded in a saturated sand during the 1980 mammoth lakes california earthquake sequence for the largest event recorded the pore pressure was observed to be proportional to vertical surface acceleration during the p wave arrivals and proportional to horizontal surface velocity during the s wave arrivals the results can be quantitatively explained with a linear elastic model of a porous saturated medium such that pore pressure depends on dilatation and is independent of shear strain a slight frequency dependence in the ratio of pore pressure to dilatation indicates local fluid flow on the scale of individual pores the good agreement between observations and theory indicates that the deformation was primarily linear even though maximum shear strains were close to the typical thresholds for liquefaction

seismic evidence for blind thrusting of the northwestern flank of the venezuelan andes surface geology and seismic and well data from the northwestern flank of the venezuelan andes indicate overthrusting of andean basement rocks toward the adjacent maracaibo basin along a blind thrust fault the frontal monocline is interpreted as the forelimb of a northwestward verging fault related fold deformed over a crustal scale ramp the andean block has been thrust 20 km to the northwest and uplifted 10 km on a ramp that dips about 20o 30 o southeastward the thrust fault ramps up through crystalline basement rocks to a decollement horizon within the shaly units of the cretaceous colon mito juan formations backthrusts in the monocline produce a wedge geometry and reduce the amount of blind slip required on the decollement northwest of the andes the rigid andean uplift was caused by northwest southeast compressive tectonic forces related to the convergence of the caribbean plate the panama volcanic arc and northwestern south america the thick up to 6 km molasse deposits accumulated in the foredeep basin indicate that the venezuelan andes started to rise as early as the early miocene however a late miocene intramolasse unconformity marks the beginning of the formation of the monocline and the greatest uplift the crustal scale fault related fold model may explain structural features seen in other areas of basement involved foreland deformation the regional geologic setting of the area can be described as a mountain front adjacent to a foredeep basin the mountain front represents a precambrian paleozoic igneous metamorphic complex partially covered with sediments of mesozoic and cenozoic ages the foredeep is an asymmetric structural basin that contains up to 12 km of sedimentary section the early miocene to pleistocene molasse deposits up to 6 km in thickness dominate the sedimentary section the oldest sedimentary rocks that crop out in the mountain front are jurassic red beds which are unconformably overlain by a cretaceous sequence up to 2 km in thickness from early cretaceous to middle eocene sediments were deposited in an extensive passive continental margin setting figure 3 coarse clastic sediments of the rio negro formation bioclastic carbonates of the apon formation and siliciclastic sediments of the aguardiente formation were deposited first in the initial stage of the cretaceous transgressive event limestones calcareous shales and black shales of the capacho and la luna formations represent anoxic facies deposited during the maximum marine transgressiolof late cretaceous cenomanian campanian age regression began in the latest cretaceous maestrichtian with marine deposition of the shaly colon formation and the sandier mito juan formation this

bed length does not remain constant during deformation recognition and why it matters abstract we apply multiple balancing restoration methods to three examples of fault bend folds exhibiting increasing levels of complexity and uncertainty three methods the chamberlin depth to detachment calculation direct measurement of fault displacement and flexural slip restoration balancing assume that bed lengths and thicknesses blt remain constant during deformation the area depth strain ads method allows bed lengths and thicknesses to vary during deformation for a kinematic model the agreement among methods is exact to within measurement error for an experimental sand model the disagreement among methods is substantial the ads relationship shows that the sand model has significant layer parallel shortening and an area increase of 4 a previously published interpretation of a seismically imaged fault bend fold from the rosario oil field venezuela is nearly line length balanced but the ads relationship indicates small but significant anomalies including an area deficit for the deeper stratigraphic levels a revised interpretation with a more internally consistent ads relationship suggests that much of the footwall uplift is real and not a velocity pull up our comparisons of the results of the various balancing restoration techniques show the resolving power of the ads method to detect sub resolution changes in bed lengths and thicknesses and to identify footwall structures overlooked by the constant blt methods

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

fold evolution matrices and axial surface analysis of fault bend folds application to the medina anticline eastern cordillera colombia the medina anticline is a fault bend fold located in the hanging wall of the aguaclara fault along the southeastern thrust front of the eastern cordillera of colombia a petroleum province with giant fields we employ a modified technique of axial surface analysis using fold evolution matrices which helps define the subsurface geometry and thereby provides important constraints on trap geometry modeling of hydrocarbon migration pathways and prediction of reservoir quality

interpreting the geologic map expression of contractional fault related fold terminations lateral oblique ramps versus displacement gradients abstract fault related folds in contractional settings do not extend indefinitely but rather commonly terminate as plunging anticlines near the tips of the genetically related fault geologists often attribute the formation of such terminations to loss of slip on the underlying fault i e a displacement gradient to changes in fault geometry in which the fault laterally changes stratigraphic position along strike i e a lateral oblique ramp or to some combination of these mechanisms discerning between these formative mechanisms solely through the interpretation of the geologic map expression of the termination can be difficult because of the subjective nature of the criteria used e g lateral oblique ramps often are interpreted at terminations where folds plunge at steep angles where hanging wall cutoff lines trend at high angles to fault strike where stratigraphic contacts trend at high angles to fault strike etc we created pseudo three dimensional model terminations of individual fault related folds using both displacement gradients and lateral oblique ramps to determine if unique characteristics in their map expressions exist we show that map patterns of folds produced by a displacement gradient along a thrust fault of constant geometry are similar to map patterns of folds produced by constant slip on a thrust fault with a lateral oblique ramp specifically our modeling results suggest that 1 simple fault bend folds that plunge less than 20 and simple fault propagation folds that plunge less than 50 at their terminations can be created by both displacement gradients and lateral oblique ramps angles greater than these values suggest that a lateral oblique ramp may be involved in forming the termination 2 hanging wall cutoff lines at terminations that trend at angles less than about 35 to fault strike for simple fault bend and fault propagation folds also may be produced by both displacement gradients and lateral oblique ramps higher angles likely indicate the presence of a lateral oblique ramp at the termination 3 the angle at which stratigraphic contacts trend to the fault strike cannot be used to uniquely identify displacement gradients or lateral oblique ramps for simple fault related folds 4 stratigraphic separation diagrams can indicate the presence of ramps in the thrust sheet but do not uniquely differentiate between frontal ramps with displacement gradients and lateral oblique ramps and 5 actual changes in fault orientation after topographic influences have been taken into account by definition indicate a lateral oblique ramp in reality most natural fault related fold terminations probably share components of both displacement gradients and lateral oblique ramps with each structure possessing contributions from each mechanism

origin of a thrust related fold geometric vs kinematic tests abstract geometric tests to determine the origin of fault related folds are common but as is typical in structural geology more than one fold origin may yield the final natural geometry thus the results of geometric tests are usually non unique in contrast kinematic tests of origin which employ both geometry and data about deformation commonly yield more constrained if not unique results unfortunately the necessary data collection requires much more work than for a geometric test in this study the thrust related barclay anticline is analyzed both geometrically and kinematically to determine which test is more effective geometric tests using angular relationships indicate three possible origins fault bend fault arrest and break thrust for the kinematic test predicted deformations for interlayer and flexural slip flexural flow simple shear and bending strains are compared to micro and mesostructural distributions solution strain and finite strain from the anticline strain measurements indicate that microscale deformation is uniformly distributed through the structure and is lithification dominated the microscale deformation does not match kinematic predictions and did not accommodate fold formation fold growth was achieved primarily through layer parallel slip restricted mostly to the forelimb and absent in the hinge which eliminates fault bend and fault arrest origins that require material transport from forelimb to backlimb the barclay anticline is therefore interpreted to be a break thrust structure interestingly a suite of contraction faults in the forelimb and hinge indicates material transport from forelimb to backlimb such transport has been discounted for break thrust folds the most important result of this study is that a kinematic test was a necessary step for distinguishing fold origin geometric testing alone was insufficient given that the barclay anticline has geometric characteristics typical of many thrust related folds kinematic testing appears necessary to determine their structural origin

hydrogeologic insights for a devil s slide like system tectonically active coastal margins commonly host landslides that are influenced by hydrologic geologic and or anthropogenic perturbations the work reported here is motivated by the hydrologically driven deep seated bedrock slides that intersect the former pacific coast highway in the active landslide zone at devil s slide near pacifica california numerical simulation of subsurface flow is employed to investigate saturated zone fluid pressure scenarios for 3 d devil s slide like systems the four phase concept development effort is comprised of 134 hydrogeologic simulation scenarios which investigate fluid pressure response for complex subsurface conditions and historically based climate forcings recharge heterogeneity and anisotropy are shown to increase fluid pressures in targeted failure prone locations by up to 73 8 10 3 and 1 8 respectively the interaction between fault zone characteristics and topographically driven flow are shown to influence fluid pressures for up to 85 of the approximately 7 0 105 m2 study area simulated fluid pressures support the known slope instability for the devil s slide site a quantitative hypothesis testing discussion explores the likelihood of perched water above the regional water table at the site further understanding of hydrologically driven slope movement in the active landslide zone will require additional data focused on rigorous characterization of the unsaturated zone

fold generated imbricates examples from the caledonides of southern norway abstract the cambro silurian sequence of the oslo region contains fold trains and closely spaced imbricate thrust faults the imbricates could be interpreted as having ramped off the sole detachment and generated fault propagation folds several imbricate thrusts however appear to die out both downwards and upwards into folds this suggests that the thrusts were generated within the cambro silurian sequence and propagated down to the sole thrust rather than propagating upwards from the sole thrust the mechanical stratigraphy is apparently responsible for this style where during folding relatively brittle limestone members faulted in the highly strained fold forelimbs prior to through going faulting developing in the shales understanding the origin of such imbricates is important when choosing a method of section restoration

geometrical modeling of fault related folds a pseudo three dimensional approach abstract area balanced cross sections of ramp anticlines and tip line folds in thin skinned fold thrust belts can be quantitatively constructed using plane strain fault bend and fault propagation fold models cross sections alone however are somewhat inadequate for interpreting along strike changes in thrust related fold geometry complex interplay between along strike changes in fault slip and fault shape determines a range of geometric configurations which are difficult to visualize without the aid of quantitative three dimensional models we extend conventional two dimensional folding theories into the third dimension by allowing for continuous variations in fault slip and fault shape along strike geometric equations relating map view angles between fold axial surface traces are derived for a case assuming a uniform fault geometry and an along strike displacement gradient the resulting folds possess no unique fold axis but rather are characterized by multiple fold hingelines each corresponding to bends in the fault for typical displacement gradients observed in the field analysis of the models suggests that discernible differences exist between map patterns of fault bend folds and fault propagation folds whereas little difference exists between map patterns of similar and parallel fault bend folds map view angles between axial surface traces for parallel fault bend folds and fault propagation folds are a function of both ramp cutoff angle and fault slip whereas these same angles for similar fault bend folds are solely a manifestation of fault slip examples assuming uniform shortening and continuously varying fault geometry along strike are also presented fault geometry is varied along strike to simulate oblique and lateral ramps depending upon model type and fault shape parameter modified resulting folds exhibit either cylindrical or non cylindrical fold geometries closure is generated by a decrease in fold amplitude where there is a decrease in ramp cutoff angle along strike or where a fault laterally cuts up section in either instance closure develops without varying shortening along strike model map patterns resemble actual thrust related fold geometries and can be compared to maps of real structures to help predict subsurface geology

within plate deformations in the maracaibo and east zulia basins western venezuela abstract subsurface data help in understanding the complex geometry of major structures of the maracaibo basin and surrounding areas during extensional and compressional phases decoupling levels were activated in the upper cretaceous black shales and the paleogene flysch sequences thus inducing frequent disharmony between a rigid basement and thin skinned cover structures two main extensional episodes are widespread across the maracaibo basin the first episode late jurassic in age accounts for the development of north northeast trending basement horsts and asymmetrical grabens the second episode more probably a transtensive one occurred during paleogene times it reactivated older north and northwest trending basement involving faults i e the ceuta and pueblo viejo faults but also generated listric normal faults and negative flower structures in the sedimentary cover by contrast compressional deformations are localized and reactivate older basement faults inducing the frequent inversion of former jurassic or lower to middle eocene grabens shortcuts in the basement and coeval wedging or fishtails in the sedimentary cover thus the major inversion episode in the maracaibo basin is upper eocene in age and probably relates to the emplacement of the caribbean nappes further to the northeast it was followed by an episode of tectonic quiescence and erosion during the oligocene neogene deformations have a limited extent beneath lake maracaibo but become widespread in the west towards the perija foothills or in the southeast near the north andean thrust front where they account for the development of frontal triangle zones east of the lake the east zulia basin is characterized by extremely thick paleogene flysch and a post middle eocene continental molasse superimposed on late jurassic or early paleogene troughs and normal vertical offsets of the basement the upper eocene to oligocene basin fill is largely detached from its substratum along a regional detachment in the eocene mud pile thus these thin skinned extensional structures display a piggyback attitude with progressive migration of depocenters overtime and gentle gliding of the sedimentary cover over underlying basement blocks the faulted borders of these late eocene oligocene basins were subsequently reactivated transpressively during late neogene times accounting for the frequent inversion of former oligocene depocenters

alternative model of thrust fault propagation a widely accepted explanation for the geometry of thrust faults is that initial failures occur on deeply buried planes of weak rock and that thrust faults propagate toward the surface along a staircase trajectory we propose an alternative model that applies gretener s beam failure mechanism to a multilayered sequence invoking compatibility conditions which demand that a thrust propagate both upsection and downsection we suggest that ramps form first at shallow levels and are subsequently connected by flat faults this hypothesis also explains the formation of many minor structures associated with thrusts such as backthrusts wedge structures pop ups and duplexes and provides a unified conceptual framework in which to evaluate field observations

low amplitude evolution of break thrust folding abstract this paper proposes a mechanistic explanation for fault related flexural slip folds that form predominantly by fixed hinge folding i e break thrust folds it also presents a stepwise evolutionary history for these folds which contrasts with the model suggested for self similar migrating hinge fault propagation fold models both mechanical folding theory and rock fabric evidence suggest that folding in advance of a growing thrust fault can evolve in a five step process 1 initial sinusoidal buckling instability

seismic expression and kinematics of a fault related fold termination rosario structure maracaibo basin venezuela abstract fold terminations are primary features of deformed belts and are critical elements in understanding the 3 d kinematics of fault related folds typically such terminations form due to loss of displacement on the genetically related thrust fault and or to along strike change in fault attitude forming a lateral or oblique ramp to unambiguously determine the mechanism responsible for a given fault related fold termination footwall cutoffs and along strike displacement variation must be constrained reflection seismic data can provide the detail necessary to uniquely describe these features the rosario structure in the maracaibo basin venezuela is an example of a natural fault related fold that possesses a southern termination whose fold fault geometry and along strike displacement variation are constrained by industry reflection seismic and well data we interpret that the fold plunge near the southern termination is due to an along strike decrease in displacement the fault geometry associated with the southern termination changes from a flat ramp flat at the crest of the structure where displacement is greatest to simply a ramp near the lateral fault tip without forming a lateral or oblique ramp we combine these observations regarding displacement and fault geometry with the assumption that along strike spatial variations reflect temporal variations during development of a fault related fold to propose a kinematic model for the rosario structure specifically we suggest that the structure first initiated as an isolated fault ramp within the stiff carbonate and clastic units with increased shortening the fault grew to link with upper and lower detachments in the weaker shale units to create a hybridized fault bend fold our model suggests a possible explanation for the evolution of the rosario structure and also provides an alternative to existing pseudo three dimensional models for fault related fold growth that relaxes the rigidity in the assumption of along strike self similarity

the kinematics of break thrust folds abstract the kinematics of asymmetric open to close often overturned thrust related folds are commonly explained with fault propagation or detachment fold models field observations of thrust related folds exposed in tennessee virginia wyoming and montana that exhibit this geometry indicate that models of fault propagation and detachment folds do not adequately describe the kinematics of these structures existing models of fault propagation and detachment folding employ migrating kink shaped hinges and relate fold geometry entirely to fault geometry slip and to the thickness of the basal detachment layers the models exclude the relation between fold shape and amplitude and they do not predict a correlation between competent layer thickness and fold wavelength as expected from buckling theory thrust related folds examined in this study exhibit unique distributions of fabrics in the hinges and forelimbs which demonstrate a lack of hinge migration furthermore the ratios of dominant member thickness to fold wavelenght agree with those expected for folds controlled by a single layer and they are within the expected range for folds with multiple evenly spaced harmonically deforming layers our analyses suggest these folds evolved from an initial brief stage of sinusoidal buckling to a later stage of fixed hinge kinking and thrusting thrust related folds which exhibit a geometry and mesofabric distribution suggesting this type of evolution are defined as break thrust folds

structural trend analysis by axial surface mapping we present a new method of structural trend analysis in which axial surfaces fold hinges are mapped through grids of seismic reflection profiles and balanced forward models axial surface maps 1 define fold trends lateral terminations and closure in structure 2 constrain underlying fault geometry and slip and 3 highlight and connect regions that can be interpreted by a series of balanced models or cross sections maps of folds in southern california and northeastern pennsylvania are compared with forward model solutions and used to construct balanced three dimensional structural interpretations using fault bend fold theory axial surface maps generated from balanced fault bend fold models define theoretical relationships between map patterns and structural geo etry and fault slip kink band widths between paired axial surfaces in map view are related to underlying fault slip lateral variations in fault slip which can be identified on axial surface maps may cause fold plunge and provide lateral closure lateral changes in subsurface fault geometry which include lateral and oblique ramps are also reflected by terminations bends or offsets of axial surfaces in map view based on these relationships between folding and faulting we develop map view interpretations and balanced cross sections across structures that are consistent with the geology along trend

the behavior of shape preferred orientations in metamorphic rocks amphiboles and jadeites from the monte mucrone area sesia lanzo zone italian western alps abstract in the eclogitic micaschists of the monte mucrone area sesia lanzo zone italian western alps we have measured in detail the eclogitic lineation at several outcrops we present observations at the markers scale this scale allowing the whole range of progressive deformations to be described populations of glaucophanes and jadeites show different statistical features which must be at least for a part produced by the distinct mechanical behavior for these markers during the alpine history the glaucophanes show a positive correlation between the intensity of preferred orientation and their aspect ratio due to a mainly rigid behavior the observed differences in shape and orientation of jadeites also show different behavior related to different retromorphic overprints we briefly discuss the implications of these observations on the significance of metamorphic lineations

estimation of regional material yield from coastal landslides based on historical digital terrain modelling high resolution historical 1942 and recent 1994 digital terrain models were derived from aerial photographs along the big sur coastline in central california to measure the long term volume of material that enters the nearshore environment during the 52 year measurement time period an average of 21 000 3100 m3 km 1 a 1 of material was eroded from nine study sections distributed along the coast with a low yield of 1000 240 m3 km 1 a 1 and a high of 46 700 7300 m3 km 1 a 1 the results compare well with known volumes from several deep seated landslides in the area and suggest that the processes by which material is delivered to the coast are episodic in nature in addition a number of parameters are investigated to determine what influences the substantial variation in yield along the coast it is found that the magnitude of regional coastal landslide sediment yield is primarily related to the physical strength of the slope forming material coastal highway 1 runs along the lower portion of the slope along this stretch of coastline and winter storms frequently damage the highway the california department of transportation is responsible for maintaining this scenic highway while minimizing the impacts to the coastal ecosystems that are part of the monterey bay national marine sanctuary this study provides environmental managers with critical background data on the volumes of material that historically enter the nearshore from landslides as well as demonstrating the application of deriving historical digital terrain data to model landscape evolution published in 2005 by john wiley sons ltd

jurassic la quinta formation in the sierra de perija northwestern venezuela geology and tectonic environment of red beds and volcanic rocks

differential transport and continuity of thrust sheets abstract structural geologists long have strived to establish basic tenets describing the interaction between thrust displacement and lateral extent of thrust sheets individual non metamorphic thrust sheets can be partitioned into segments that exhibit linear variations in displacement along strike the differential transport between endpoints of each segment define an along strike bulk shear angle which describes the spatial rate of change in displacement along the length of the fault empirical measurements of differential transport angles for continuous thrust sheets from different north american fold thrust belts yield bulk shear angles that do not exceed 35 40 without formation of tear faults these values might thus be considered a limit for coherent behavior of continuous non metamorphic thrust sheets thereby providing constraints on three dimensional interpretations of fold thrust belts

predicting the orientation of joints from fold shape results of pseudo three dimensional modeling and curvature analysis we treat layers of sedimentary rock as elastic plates and predict the orientations of joints by assuming that they open parallel to the maximum instantaneous stretch of a layer because the direction of maximum instantaneous stretch is parallel to the maximum curvature of a surface we hypothesize that joints will trend parallel to the minimum curvature of an elastically deformed layer after constructing pseudo three dimensional trishear models of laramide style uplifts that grow self similarly we calculated the direction of minimum curvature axes during the evolution of the fold our analysis of minimum curvature axes in evolving folds suggests several important characteristics for fold related joint sets 1 joints that are neither parallel nor perpendicular to the fold axis may be induced by local fold related strains 2 at any time during folding joint orientations may vary according to the structural position on a fold 3 at any location on a fold joint orientation may depend on when a joint forms during the evolution of the fold and 4 joint patterns in trishear folds may vary with stratigraphic position natural folds that evolve along simple geometric pathways may develop fold related joint sets the orientation dominance abutting relationships spacing and continuity of which will vary systematically throughout the structure this variation in joint system architecture may reflect the history of fold growth

fluid pressure responses for a devil s slide like system problem formulation and simulation this study employs a hydrogeologic simulation approach to investigate subsurface fluid pressures for a landslide prone section of the central california usa coast known as devil s slide understanding the relative changes in subsurface fluid pressures is important for systems such as devil s slide where slope creep can be interrupted by episodic slip events surface mapping exploratory core tunnel excavation records and dip meter data were leveraged to conceptualize the parameter space for three dimensional 3d devil s slide like simulations field observations i e seepage meter water retention and infiltration experiments well records and piezometric data and groundwater flow simulation i e one dimensional vertical transient and variably saturated were used to design the boundary conditions for 3d devil s slide like problems twenty four simulations of steady state saturated subsurface flow were conducted in a concept development mode recharge heterogeneity and anisotropy are shown to increase fluid pressures for failure prone locations by up to 18 1 4 5 and 1 8 respectively previous estimates of slope stability driven by simple water balances are significantly improved upon with the fluid pressures reported here the results for a devil s slide like system provide a foundation for future investigations copyright 2014 john wiley sons ltd

fault displacement gradient folds and the structure at lost hills california u s a abstract geometric models of fault propagation folds require that the underlying fault tip propagate upward across layering however related folds can be generated if the tip remains stationary or even moves back along the ramp as a pre existing fault is reactivated fault propagation folds detachment folds as well as those produced when there is no propagation are generated by a displacement gradient along the underlying fault and as a general class can be called fault displacement gradient folds new geometric equations are derived which relate fold shape to displacement gradient and fault propagation folds are a special case of these more general equations growth sequences associated with these structures have been used to distinguish fault propagation folds from fault bend folds when the underlying structure is obscured a displacement gradient fold in which the fault tip retreats back down the ramp generates a growth sequence that in some cases could be confused with that of a fault bend fold the structure at lost hills in the san joaquin valley of california u s a has been interpreted as a fault bend fold but it may be a displacement gradient fold which formed as a pre existing fault was reactivated during a pliocene change in plate motion