active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

bed by bed fold growth by kink band migration sant llorenc de morunys eastern pyrenees ahstract rowth strata deposited over and against the flank of the sant llorenc de morunys fold during its final stages of deformation have been mapped at high resolution as the basis for unraveling the kinematics of fold growth we use restoration techniques based on normal balancing assumptions to decipher the detailed kinematic history of folding the progressive restorations as well as balanced forward modeling show that the last few hundred meters of fold growth were dominated by kink band migration of a sort that is typical of much faultrelated folding the kink band migration has produced complex anticlinal hinge zone geometry including segmented fold hinges linked by disconformities and unconformities which has direct and detailed explanation in terms of fluctuations in deposition rate relative to curved hinge kink band migration rate large fluctuations in the convolution of non steady sedimentation and deformation are demonstrated although the absolute fluctuations in deformation and sedimentation are unknown at a length scale of 100 m kink band migration with little or no deposition is interspersed with sedimentation with little or no deformation at the length scale of 500 m deposition ranges from 200 to 50 of uplift 0 1997 elsevier science ltd all rights reserved

tectonic variation in the dniepr donets basin from automated modelling of backstripped subsidence curves abstract the multiphase rift evolution of the dniepr donets dd basin is analysed by 1d backstripping and tectonic modelling of 66 stratigraphic sections mostly from well data distributed throughout the basin the backstripping results illustrate strong temporal and lateral variations in tectonic subsidence it is minor during an inceptive pre rift phase givetian early frasnian 380 8 370 ma and does not show clear spatial correlations within the dd basin framework the main rift phase frasnian famennian 370 362 5 ma corresponds to an acceleration in subsidence rates with tectonic subsidence up to 1500 m along the basin axis displaying a slight increase from the northwest to the southeast strong lateral variations perpendicular to the basin axis reflect the effects of major basin border faults a rift phase in the visean 345 340 ma is characterised by relatively minor subsidence up to about 500 m except for some wells in the southeast following a stage of extremely low rates of deposition in the earliest carboniferous the end of this rift phase can be taken to mark the onset of convex subsidence patterns in the later carboniferous and permian typical in shape of post rift thermal subsidence but significantly increasing in magnitude from northwest to southeast in the basin this trend shows no one to one relationship with late devonian syn rift subsidence the tectonic subsidence curves have been modelled using lithospheric stretching assumptions allowing different stretching factors for the crustal and sub crustal lithosphere and the incorporation of finite and multiple stretching phases a numerical technique was developed that automatically finds best fit stretching parameters for part or all of the tectonic subsidence data given the specification of onset and duration of the various rifting events maps of the 1d modelling results display intrabasinal variations in terms of timing and magnitude of rifting the results indicate that the observed spatial and temporal variations of tectonic subsidence in the dd basin specifically the increasing ratio of carboniferous to late devonian subsidence from northwest to southeast cannot be explained by either a uniform or depth dependent stretching model adopting only a single frasnian famennian rift phase a two phase model in which a significant part of carboniferous tectonic subsidence is related to visean rift activity strongly dominated by sub crustal lithospheric attenuation provides a satisfactory fit to the data although the tectonic implications of such a model are not easily reconcilable by independent constraints a semi quantitative investigation of the possible role of withdrawal of underlying devonian salt during the carboniferous to produce additional post devonian rift phase sediment accommodation space suggests that the effects of such a mechanism could be significant but that they are unlikely to preclude the necessity of the visean rifting event to explain the carboniferous basin evolution

fault slip rates in the modern new madrid seismic zone structural and geomorphic analysis of late holocene sediments in the lake county region of the new madrid seismic zone indicates that they are deformed by fault related folding above the blind reelfoot thrust fault the widths of narrow kink bands exposed in trenches were used to model the reelfoot scarp as a forelimb on a fault bend fold this coupled with the age of folded sediment yields a slip rate on the blind thrust of 6 1 0 7 mm year for the past 2300 100 years an alternative method used structural relief across the scarp and the estimated dip of the underlying blind thrust to calculate a slip rate of 4 8 0 2 mm year geometric relations suggest that the right lateral slip rate on the new madrid seismic zone is 1 8 to 2 0 mm year

shallow seismic imaging of folds above the puente hills blind thrust fault los angeles california 1 high resolution seismic reflection profiles image discrete folds in the shallow subsurface 600 m above two segments of the puente hills blind thrust fault system los angeles basin california the profiles demonstrate late quaternary activity at the fault tip precisely locate the axial surfaces of folds within the upper 100 m and constrain the geometry and kinematics of recent folding the santa fe springs segment of the puente hills fault zone shows an upward narrowing kink band with an active anticlinal axial surface consistent with fault bend folding above an active thrust ramp the coyote hills segment shows an active synclinal axial surface that coincides with the base of a 9 m high scarp consistent with tip line folding or the presence of a backthrust the seismic profiles pinpoint targets for future geologic work to constrain slip rates and ages of past events on this important fault system

recurring variations of probable solar origin in the atmospheric δ14c time record after removal of the 11 000 year geomagnetic contribution to a relatively high precision atmospheric 14c record covering the past 7200 years residual variations exhibit a 2200 2600 year quasi periodicity that has been recognized in earlier studies we find here that century scale variations in the most recent cycle are positively correlated with similar short term variations in each of the two previous cycles thus the quasi periodicity consists of both a long term variation of the mean and a superposed approximately recurring pattern of century scale variations the strongest of these latter variations occur near successive maxima of the 2400 year cycles during the last millennium the largest century scale variations occurring near the most recent 2400 year maximum are known to be mainly a consequence of the pronounced maunder sporer and wolf solar activity minima therefore the recurrence of large amplitude 14c variations at 2400 year intervals is most directly explained as due to solar forcing at both the 2400 year and century scale periods a fully terrestrial 2400 year modulation of an independent century scale solar forcing function is disfavored by the joint occurrence of relatively strong 14c maxima and solar activity minima during the current millennium according to independent proxy records the probable existence of a 2400 year solar quasi cycle has implications for the predictability of future pronounced solar activity minima and for the interpretation of certain minor holocene climatic variations

an elusive blind thrust fault beneath metropolitan los angeles seismic reflection profiles petroleum wells and relocated earthquakes reveal the presence of an active blind thrust fault beneath metropolitan los angeles a segment of this fault likely caused the 1987 whittier narrows magnitude 6 0 earthquake mapped sizes of other fault segments suggest that the system is capable of much larger magnitude 6 5 to 7 and more destructive earthquakes

discrete element modelling of contractional fault propagation folding above rigid basement fault blocks many studies have shown that discrete blind faults at depth are commonly linked to more distributed deformation in particular folding at higher levels one category of fault related folds forced folds is common where there is a distinct mechanical contrast between faulted basement and sedimentary cover outcrop numerical and analogue modelling studies indicate that such folds form as upward widening zones of distributed deformation monoclines above discrete faults at depth with increasing displacement the folds are often cut by faults as they propagate upwards into the cover while the trishear kinematic model of fault propagation folding appears to approximately represent the geometric development of such structures comparatively little is known of the mechanical controls on their development here we present a 2d discrete element model of sedimentary cover deformation above a contractional fault in rigid basement the elements consist of a series of soft spheres that obey newton s equations of motion and initially interact with elastic forces under the influence of gravity particles are bonded until the separation between them exceeds a defined breaking strain at which time the bond breaks simulated by the transition from repulsive attractive forces to solely repulsive forces the model is used to investigate the influence of basement fault dip and sedimentary cover strength on the geometry of the folds developed and the rate of fault propagation in all cases an upward widening monocline occurs above the basement fault we find that shallow basement fault dips produce homogenous thickening of the monocline limb while steeper dips produce contemporaneous thinning and thickening within the monocline thinning and thickening within the monocline are accommodated by a combination of small scale faulting and folding with decreasing cover strength the zone of deformation becomes wider localization does not occur on a single fault and fold geometries resemble trishear fold profiles with low propagation to slip ratios p s 1 in contrast a stronger cover produces a narrower zone of deformation localization on a single fault and more rapid fault propagation similar to trishear fold profiles where p s 2 3 the fault propagates into the cover at approximately the same angle as the basement fault the model reproduces well many of the features observed in analogue modelling and reported from outcrop and seismic studies

investigation of growth fault bend folding using discrete element modeling implications for signatures of active folding above blind thrust faults 1 using the discrete element modeling method we examine the two dimensional nature of fold development above an anticlinal bend in a blind thrust fault our models were composed of numerical disks bonded together to form pregrowth strata overlying a fixed fault surface this pregrowth package was then driven along the fault surface at a fixed velocity using a vertical backstop additionally new particles were generated and deposited onto the pregrowth strata at a fixed rate to produce sequential growth layers models with and without mechanical layering were used and the process of folding was analyzed in comparison with fold geometries predicted by kinematic fault bend folding as well as those observed in natural settings our results show that parallel fault bend folding behavior holds to first order in these models however a significant decrease in limb dip is noted for younger growth layers in all models on the basis of comparisons to natural examples we believe this deviation from kinematic fault bend folding to be a realistic feature of fold development resulting from an axial zone of finite width produced by materials with inherent mechanical strength these results have important implications for how growth fold structures are used to constrain slip and paleoearthquake ages above blind thrust faults most notably deformation localized about axial surfaces and structural relief across the fold limb seem to be the most robust observations that can readily constrain fault activity and slip in contrast fold limb width and shallow growth layer dips appear more variable and dependent on mechanical properties of the strata

earthquake by earthquake fold growth above the puente hills blind thrust fault los angeles california implications for fold kinematics and seismic hazard 1 boreholes and high resolution seismic reflection data collected across the forelimb growth triangle above the central segment of the puente hills thrust fault pht beneath los angeles california provide a detailed record of incremental fold growth during large earthquakes on this major blind thrust fault these data document fold growth within a discrete kink band that narrows upward from 460 m at the base of the quaternary section 200 250 m depth to 82 at 250 m depth folding and uplift occur within discrete kink bands thereby enabling us to develop a paleoseismic history of the underlying blind thrust fault the borehole data reveal that the youngest part of the growth triangle in the uppermost 20 m comprises three stratigraphically discrete growth intervals marked by southward thickening sedimentary strata that are separated by intervals in which sediments do not change thickness across the site we interpret the intervals of growth as occurring after the formation of now buried paleofold scarps during three large pht earthquakes in the past 8 kyr the intervening intervals of no growth record periods of structural quiescence and deposition at the regional near horizontal stream gradient at the study site minimum uplift in each of the scarp forming events which occurred at 0 2 2 2 ka event y 3 0 6 3 ka event x and 6 6 8 1 ka event w ranged from 1 1 to 1 6 m indicating minimum thrust displacements of 2 5 to 4 5 m such large displacements are consistent with the occurrence of large magnitude earthquakes mw 7 cumulative minimum uplift in the past three events was 3 3 to 4 7 m suggesting cumulative thrust displacement of 7 to 10 5 m these values yield a minimum holocene slip rate for the pht of 0 9 to 1 6 mm yr the borehole and seismic reflection data demonstrate that dip within the kink band is acquired incrementally such that older strata that have been deformed by more earthquakes dip more steeply than younger strata specifically strata dip 0 4 at 4 m depth 0 7 at 20 m depth 8 at 90 m 16 at 110 m and 17 at 200 m moreover structural restorations of the borehole data show that the locus of active folding the anticlinal active axial surface does not extend to the surface in exactly the same location from earthquake to earthquake rather that the axial surfaces migrate from earthquake to earthquake reflecting a component of fold growth by kink band migration the incremental acquisition of bed dip in the growth triangle may reflect some combination of fold growth by limb rotation in addition to kink band migration possibly through a component of trishear or shear fault bend folding alternatively the component of limb rotation may result from curved hinge fault bend folding and or the mechanical response of loosely consolidated granular sediments in the shallow subsurface to folding at depth

geometries of frontal fold and thrust belts insights from discrete element simulations abstract this study investigated the evolution of frontal structures of fold and thrust belts with 2d numerical simulations using the discrete element method dem of specific interest is the occurrence of triangle zones and how mechanical stratigraphy affects the formation of the triangle zones in our simulations we varied the strength of a two unit stratigraphy as well as the decollement horizons to determine the controlling parameters of different types of frontal structures for models with homogenous stratigraphy deformation was concentrated along forethrusts which involved both the upper and lower units with the addition of a mechanically weak upper unit deformation along forethrusts and popup structures largely occurred in the upper unit with relatively little deformation of the lower unit with thicker decollement surfaces and strong upper and lower units decoupling was enhanced and allowed for the formation of triangle zones in front of the deforming wedge the triangle zones were uplifted along lower forethrusts until a new frontal triangle zone formed results compared favorably with triangle zones found in the canadian cordillera in southern alberta

puente hills blind thrust system los angeles california we describe the three dimensional geometry and quaternary slip history of the puente hills blind thrust system pht using seismic reflection profiles petroleum well data and precisely located seismicity the pht generated the 1987 whittier narrows moment magnitude m w 6 0 earthquake and extends for more than 40 km along strike beneath the northern los angeles basin the pht comprises three north dipping ramp segments that are overlain by contractional fault related folds based on an analysis of these folds we produce quaternary slip profiles along each ramp segment the fault geometry and slip patterns indicate that segments of the pht are related by soft linkage boundaries where the fault ramps are en echelon and displacements are gradually transferred from one segment to the next average quaternary slip rates on the ramp segments range from 0 44 to 1 7 mm yr with preferred rates between 0 62 and 1 28 mm yr using empirical relations among rupture area magnitude and coseismic displacement we estimate the magnitude and frequency of single m w 6 5 6 6 and multisegment m w 7 1 rupture scenarios for the pht manuscript received 16 november 2001

influence of mobile shale on thrust faults insights from discrete element simulations we study the effects of sedimentary loading of a mobile shale substrate using two dimensional discrete element modeling we develop an updip extensional zone connected at depth to a downdip contractional zone allowing us to study the formation of gravity driven fold and thrust belts and the evolution of decollements within this system we compare our models to the niger delta type locale for shale tectonics in general most seismic interpretations of the niger delta include decollement s at the top of the mobile shale unit but exact locations vary depending on area of investigation our models particularly ones with mobile shale thicker than 2 km 1 2 mi show more diffuse decollements spanning the width of the mobile shale unit which propagate out in front of the syntectonic sediment wedge and connect normal faults in the extensional zone with toe thrusts in the contractional zone we also look at the distributions of stress and strain within our models plotting the distributions of maximum principal stress and relating that to the vergence of thrust faults developed in our models we quantify the amount of strain in different sections of the models showing that extension is much greater than compression in the fold and thrust belt s alone and that compression is distributed throughout the model including in front of the fold and thrust belt

recognition of paleoearthquakes on the puente hills blind thrust fault california borehole data from young sediments folded above the puente hills blind thrust fault beneath los angeles reveal that the folding extends to the surface as a discrete zone 145 meters wide buried fold scarps within an upward narrowing zone of deformation which extends from the upward termination of the thrust ramp at 3 kilometers depth to the surface document the occurrence of at least four large moment magnitude 7 2 to 7 5 earthquakes on this fault during the past 11 000 years future events of this type pose a seismic hazard to metropolitan los angeles moreover the methods developed in this study can be used to refine seismic hazard assessments of blind thrusts in other metropolitan regions

growth stratal records of instantaneous and progressive limb rotation in the precordillera thrust belt and bermejo basin argentina analysis of synorogenic deposits preserved near the thrust front zone of the precordillera fold and thrust belt and in the bermejo foreland basin in central argentina documents the evolution of deformation during the last 5 myr as well as the thrust system kinematics seismic lines across the area display examples of progressive and instantaneous limb rotations the easternmost thrust plate of the central precordillera the niquivil thrust experienced episodic motion in two main stages a first thrust movement as a fault propagation fold and a second movement as a high angle anticlinal breakthrough fault after a period of quiescence growth strata deposited in the la pareja intermontane basin and the las salinas and bermejo anticline recorded continuous growth of eastern precordilleran structures beginning at 2 7 ma with uplift rates of 0 3 mm yr for the niquivil anticline 1 08 mm yr for the las salinas anticline and between 0 6 and 0 38 mm yr during the last 2 myr for the bermejo anticline once the eastern precordillera began to grow the propagation of the niquivil thrust stopped restricting the deformation to the young vallecito out of sequence thrust the complex geometry of growth strata deposited on the back limb of the las salinas anticline can be explained by using a model of a two step fault propagation fold with constant layer thickness the bermejo anticline of the eastern precordillera is formed by the simultaneous propagation of a shallow fault responsible for the fold shape and a deep fault that produced vertical uplift a growth triangle that documents instantaneous forelimb rotation for a fault propagation fold is recorded for the first time in a published seismic line

mechanisms of active folding of the landscape southern tian shan china 1 we explore the kinematic mechanisms of active large scale folding based on analysis of two adjacent major anticlines in tian shan central asia that share an acceleration of shortening rate leading to topographic emergence and folded geomorphic surfaces their folding mechanisms are fundamentally different yakeng anticline is a gentle pure shear detachment fold with 1200 m of shortening and a well constrained history of growth beginning at 5 5 ma with an order of magnitude increase in shortening rate from 0 16 to 1 2 1 6 mm yr at 0 16 0 21 ma the shape of the deformed topographic surface and of subsurface horizons deposited during deformation is a linearly proportional image at reduced amplitude of the deeper structure which shows that instantaneous uplift rates have been pointwise linearly proportional to the current finite fold amplitude in contrast quilitak anticline is a complex fault bend fold with uplift rates proportional to the sine of the fault dip showing discontinuities in uplift rate across active axial surfaces the 10 to 20 km wide anticline is topographically emergent only in a central 5 to 7 km wide mountainous uplift the abrupt southern edge of which is marked by 600 to 700 m high triangular facets that result from active folding of a pediment across an active axial surface the giant facets are shown to form by kink band migration and record postemergence deformation since an order of magnitude acceleration in shortening rate from 0 6 to 4 5 mm yr apparently contemporaneous with yakeng sections logged across the active 115 m wide hinge zone show that recent strata provide a bed by bed record of fold scarp growth which is quantitatively deciphered by fitting bed shapes to a finite width kink band migration model

discrete element modelling of the influence of cover strength on basement involved fault propagation folding abstract a discrete element model is used to investigate the influence of sedimentary cover strength on the development of basement involved fault propagation folds we find that uniformly weak cover best promotes the development of classical trishear like fault related folds showing marked anticlinal thinning and synclinal thickening with cover dips increasing downwards towards the fault tip uniformly strong cover results in more rounded fold forms with only minor hinge thickening thinning and significant basement fault propagation into the sedimentary cover heterogeneous layered cover sequences with marked differences in strength promote the development of more complex and variable fold forms with a close juxtaposition of brittle and macroscopically ductile features which diverge from the predictions of simple kinematic models in these structures the upper layers are often poor indicators of deeper structure in addition we find that in layered cover sequences fault propagation into the cover is a complex process and is strongly buffered by the weaker cover units

discrete element simulations of gravitational volcanic deformation 2 mechanical analysis 1 particle dynamics simulations of granular piles constructed upon planar substrates with different shear strengths model the gravitational deformation of natural volcanoes results reveal direct correlations among pile morphology layer stratigraphy deformation structures and stress field dependent upon the shear strength along the base of the pile piles constructed above a strong cohesive substrate that prevents basal slip develop outward dipping layers through particle avalanching down angle of repose slopes in the absence of basal cohesion slip occurs along a basal decollement if the topographically induced shear stresses exceed the basal shear strength for friction coefficients decreasing from 0 3 to 0 1 fault planes migrate progressively inward defining a transition in deformation mode from shallow slumping to deep seated landsliding and finally to full gravitational spreading the variations in deformation mode reflect the dependence of internal fault geometry on basal strength in accordance with critical coulomb wedge theory in order for slip to occur both internal and basal failure criteria must be met simultaneously topographically induced shear stresses increase outward along the base of the pile enabling decollement sliding once the basal failure criterion is met normal faults arise from the inside edge of the slipping decollement accommodating downward and outward displacements of the flanks surface slopes evolve to maintain equilibrium between gravitational driving and basal resisting stresses this simple mechanical understanding of gravitational deformation of granular piles provides insight into the controls on modes of volcanic deformation providing a predictive tool for understanding volcanic evolution and hazards in many settings

earthquake hazards of active blind thrust faults under the central los angeles basin california we document several blind thrust faults under the los angeles basin that if active and seismogenic are capable of generating large earthquakes m 6 3 to 7 3 pliocene to quaternary growth folds imaged in seismic reflection profiles record the existence size and slip rates of these blind faults the growth structures have shapes characteristic of fault bend folds above blind thrusts as demonstrated by balanced kinematic models geologic cross sections and axial surface maps we interpret the compton los alamitos trend as a growth fold above the compton ramp which extends along strike from west los angeles to at least the santa ana river the compton thrust is part of a larger fault system including a decollement and ramps beneath the elysian park and palos verdes trends the cienegas and coyote hills growth folds overlie additional blind thrusts in the elysian park trend that are not closely linked to the compton ramp analysis of folded pliocene to quaternary strata yields slip rates of 1 4 0 4 mm yr on the compton thrust and 1 7 0 4 mm yr on a ramp beneath the elysian park trend assuming that slip is released in large earthquakes we estimate magnitudes of 6 3 to 6 8 for earthquakes on individual ramp segments based on geometric segment sizes derived from axial surface maps multiple segment ruptures could yield larger earthquakes m 6 9 to 7 3 relations among magnitude coseismic displacement and slip rate yield an average recurrence interval of 380 years for single segment earthquakes and a range of 400 to 1300 years for multiple segment events if these newly documented blind thrust faults are active they will contribute substantially to the seismic hazards in los angeles because of their locations directly beneath the metropolitan area

out of plane motion of a thrust sheet during along strike propagation of a thrust ramp a distinct element approach abstract using a 3d distinct element mechanical modeling program we examined the nature and magnitude of out of plane motion during along strike propagation of a simple thrust ramp and attendant fault related folding our numerical model was composed of about 83 000 spherical elastic particles that were bonded together to create an initial solid numerical rock mass capable of macroscopic fracture and faulting in response to displacement loading the algorithim is fully dynamic and as such allowed for the storage and sudden release of elastic strain energy in the form of seismic events we induced progressive along strike fault growth and attendant non cylindrical fold development by varying the along strike friction within a seeded planar zone of weakness within the aggregate a zone that was to become the fault the result was a well developed plunging ramp anticline that grew in amplitude and along strike length as the macroscopic fault propagated from lower to higher friction regions lateral fault propagation was relatively rapid compared with shortening with a ratio of thrust displacement to propagation length k of 6 5 incremental motion of the particles reflected episodic slip at both the laterally propagating fault tip and along the existing fault these episodes were characterized by local clusters of outward radiating velocity vectors that propagated at seismic velocities marking the model equivalents of earthquakes the finite displacement vectors in the hanging wall were approximately parallel to the far field transport direction with a strike parallel component that ranged from one to two orders of magnitude less than the strike perpendicular component furthermore about two thirds of the particles had strike parallel motion in the direction of fault propagation and fold plunge because the far field shortening boundary conditions were uniformly perpendicular to fault strike this component of motion in the plunge direction was apparently due to a topographically induced plunge parallel shear stress the along strike motion involved slip on the main fault as well as transient strike slip on minor vertical sometimes conjugate zones apparently induced by the increased topographic load

active faulting and growth folding in the eastern santa barbara channel california we develop new methods to identify blind thrust fault systems determine fault slip rates and estimate potential earthquake magnitudes and recurrence intervals in active fold and thrust belts these methods are applied to compressive folds along the offshore oak ridge and blue bottle trends which overlie active blind thrust faults in the eastern santa barbara channel these folds and their causative faults are interpreted using fault bend fold theory and are represented in balanced models and cross sections that integrate surface and subsurface data the structures are mapped using a new technique of axial surface mapping in seismic reflection grids which defines three dimensional structural geometries and shows changes in slip and subsurface fault geometry along strike analysis of syntectonic growth sediments yields pliocene and quaternary fault slip rates of 1 3 mm yr on a deep thrust 16 km and 1 3 mm yr on shallower faults 2 5 km the combined 2 6 mm yr slip rate represents only part of the 6 mm yr of shortening measured by geodesy across the channel and estimated from relative pacific north american plate motions across the transverse ranges additional shortening is probably accommodated on other active thrusts in the western transverse ranges and in the northern channel along the santa barbara coast deformed seafloor sediments and a swarm of axial surface seismicity along the fold trends indicate that the underlying thrusts are active and may pose significant earthquake hazards to coastal southern california unsegmented fault surfaces are used through empirical relationships between fault surface area and rupture magnitude to estimate the sizes of potential earthquakes this analysis suggests that a ramp in the channel islands fault beneath the offshore oak ridge trend is capable of rupturing in a m s 7 2 earthquake earthquakes of this magnitude may release 2 m of slip which when combined with the estimated slip rate 1 3 mm yr yields an earthquake recurrence interval of 1500 yr for this channel islands fault ramp

discrete element simulations of gravitational volcanic deformation 1 deformation structures and geometries 1 we have carried out two dimensional particle dynamics simulations of granular piles subject to frictional coulomb failure criteria to gain a first order understanding of different modes of gravitational deformation within volcanoes under uniform basal and internal strength conditions granular piles grow self similarly developing distinctive stratigraphies morphologies and structures piles constructed upon cohesive substrates exhibit particle avalanching forming outward dipping strata and angle of repose slopes systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults and slip along a basal decollement landslide forms grade from shallow slumps to deep seated landslide and finally to axial subsidence and outward flank displacements or volcanic spreading surface slopes decrease and develop concave up morphologies with decreasing decollement strength depositional layers tilt progressively inward spatial variations in basal strength cause lateral transitions in pile structure stratigraphy and morphology this approximation of volcanoes as coulomb granular piles reproduces the richness of deformational structures and surface morphologies in many volcanic settings the gentle slopes of hawaiian volcanoes and olympus mons on mars suggest weak basal decollements that enable volcanic spreading high angle normal faults favored above weak decollements are interpreted in both settings and may explain catastrophic sector collapse in hawaii and broad aureole deposits surrounding olympus mons in contrast steeper slopes and shallow detachment faults predominate in the canary islands thought to lack a weak decollement favoring smaller more frequent slope failures than predicted for hawaii the numerical results provide a useful predictive tool for interpreting dynamic behavior and associated geologic hazards of active volcanoes