structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

self driven mode switching of earthquake activity on a fault system theoretical results based on two different modeling approaches indicate that the seismic response of a fault system to steady tectonic loading can exhibit persisting fluctuations in the form of self driven switching of the response back and forth between two distinct modes of activity the first mode is associated with clusters of intense seismic activity including the largest possible earthquakes in the system and frequency size event statistics compatible with the characteristic earthquake distribution the second mode is characterized by relatively low moment release consisting only of small and intermediate size earthquakes and frequency size event statistics following a truncated power law the average duration of each activity mode scales with the time interval of a large earthquake cycle in the system the results are compatible with various long geologic paleoseismic and historical records the mode switching phenomenon may also exist in responses of other systems with many degrees of freedom and nonlinear dynamics 1999 elsevier science b v all rights reserved

a mass failure model for the initial degradation of fault scarps with application to the 1959 scarps at hebgen lake montana abstract calculation of earthquake scarp ages from scarp morphology usually assumes that scarp materials reach their angle of repose immediately after a rupture however observations of the 1959 hebgen lake montana earthquake scarp and similar features worldwide confirm that scarps require a finite period of mass failure to reach the initial conditions for hillslope diffusion so the age of features less than 1000 yr old cannot be accurately estimated with methods based only on the linear diffusion equation we apply a numerical model of this interval of mass failure degradation to vertical initial angle scarps from the 1959 rupture at hebgen lake montana the mass failure rate coefficient r m ranges from 1 0 10 2 to 1 2 10 1 m yr 1 for young scarps at hebgen lake and nine other locations and has little or no dependence on climate conditions such as annual temperature range or average rainfall including an interval of mass failure gives more accurate age estimates where a scarp age is of the same order as the characteristic mass failure relaxation time of 10 1000 yr

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

evolution of terrace risers along the upper rhine graben inferred from morphologic dating methods evidence of climatic and tectonic forcing summary we show that morphologic dating techniques that have been applied successfully in arid and semi arid areas are also suitable for slowly evolving scarps that are usually found in temperate climate environments we have attempted two morphologic approaches based on diffusion to relate the present day shape of an abandoned terrace riser to its age the first assumes a model of scarp degradation based on a diffusive process the d method the second evaluates the state of scarp degradation using the slope distribution the sd method along a topographic profile by using a manmade scarp of known age we have obtained a mass diffusivity close to 1 4 m2 ka 1 when the area experiences a temperate climate characterized by a continuous vegetation cover however this value decreases during glacial episodes probably on account of the permafrost even though the sd method requires an age correction that can be easily computed only this method reveals that at several profiles a later scarp reactivation event has occurred indeed along several profiles the slope distribution was best fitted by two offset gaussian curves suggesting that some scarps have undergone a complex evolution that cannot be modelled with a single diffusive process this scarp reactivation may correspond to a new incisive episode and allows one to estimate the vertical incision rate along the terrace riser applied to a wurmian terrace riser of the upper rhine valley ne france this approach reveals that the vertical incision rate ranges from 0 2 to 0 85 mm yr 1 between 35 and 15 ka and that the terrace bevelling occurred during two episodes related to climatic forcing moreover we can identify a component of tectonic forcing evidenced by an increase to the north of vertical incision rate and rhine stream power another major result is showing that this terrace riser is not isochronous along its strike and that younger portions result from lateral incision of a 30 ka pre existing scarp

the gutenberg richter or characteristic earthquake distribution which is it abstract paleoearthquake and fault slip rate data are combined with the cit usgs catalog for the period 1944 to 1992 to examine the shape of the magnitude frequency distribution along the major strike slip faults of southern california the resulting distributions for the newport inglewood elsinore garlock and san andreas faults are in accord with the characteristic earthquake model of fault behavior the distribution observed along the san jacinto fault satisfies the gutenberg richter relationship if attention is limited to segments of the san jacinto that are marked by the rupture zones of large historical earthquakes or distinct steps in fault trace the observed distribution along each segment is consistent with the characteristic earthquake model the gutenberg richter distribution observed for the entirety of the san jacinto may reflect the sum of seismicity along a number of distinct fault segments each of which displays a characteristic earthquake distribution the limited period of instrumental recording is insufficient to disprove the hypothesis that all faults will display a gutenberg richter distribution when averaged over the course of a complete earthquake cycle but given that 1 the last 5 decades of seismicity are the best indicators of the expected level of small to moderate size earthquakes in the next 50 years and 2 it is generally about this period of time that is of interest in seismic hazard and engineering analysis the answer to the question posed in the title of the article at least when concerned with practical implementation of seismic hazard analysis at sites along these major faults appears to be the characteristic earthquake distribution

analysis of scarp profiles evaluation of errors in morphologic dating morphologic analysis of scarp degradation can be used quantitatively to determine relative ages of different scarps formed in cohesionless materials under the same climatic conditions scarps of tectonic origin as well as wavecut or rivercut terraces can be treated as topographic impulses that are attenuated by surface erosional processes this morphological evolution can be modelled as the convolution of the initial shape with erosion or degradation function whose width increases with time such modeling applies well to scarps less than 10m high formed in unconsolidated fanglomerates to a good approximation the degradation function is gaussian with a variance measuring the degree of rounding of the initial shape this geometric parameter can be called the degradation coefficient a synthetic experiment shows that the degradation coefficient can be obtained by least squares fitting of profiles levelled perpendicular to the scarp gravitational collapse of the free face is accounted for by assuming initial scarp slopes at the angle of repose of the cohesionless materials 30 35 uncertainties in the measured profiles result in an uncertainty in degradation coefficient that can be evaluated graphically because the degradation coefficient is sensitive to the regional slope and to three dimensional processes gullying loess accumulation stream incision etc a reliable and accurate determination of degradation coefficient requires several long profiles across the same scarp the linear diffusion model of scarp degradation is a gaussian model in which the degradation coefficient is proportional to numerical age in that case absolute dating requires only determination of the propotionality constant called the mass diffusivity constant for holocene scarps a few meters high in loose alluvium under arid climatic conditions mass diffusivity constants generally range between 1 and 6 m 2 kyr morphologic analysis is a reliable method to compare ages of different scarps in a given area and it can provide approximate absolute ages of holocene scarplike landforms

daylight imagery of ocean surface waves for wave spectra abstract both surface reflected daylight and upwelling light are modeled to second order to help provide a quantitative and physically interpretable description of daylight imagery of ocean surface waves for wave spectra an image recording of the slope modulated reflected and upwelled radiance can be optically analyzed to provide the surface slope spectrum as a function of wavenumber for a particular patch on the ocean surface sources of error involved in obtaining ocean spectral information from daylight imagery are outlined and methods of alleviating them discussed errors resulting from the nonlinear nature of the transfer function relating wave slope to radiance at the sensor are shown to be minimized using the second order theory in evaluating potential sensor geometries the directional sensitivity of daylight imagery to waves traveling in various directions is also evaluated a modified pierson wave spectrum was used to generate numerically a one dimensional wave slope profile this slope profi

documentation of benchmark photographs that show the effects of the 1983 borah peak earthquake with some considerations for studies of scarp degradation systematic benchmark photography of modern and prehistoric fault scarps provides an accurate and timely method of documenting details of ground breakage related to earthquakes and provides a near permanent record for future quantitative analysis of the degradation of these features during the geologic investigation of surface faulting associated with the 28 october 1983 borah peak earthquake of central idaho i established 14 benchmark stations for repeat photography of selected deformational features about 40 photographs most in stereopairs were made in november 1983 in order to show some of the details of the newly formed fault scarps grabens and an associated landslide one year later october 1984 h e malde and i repeated most of the 1983 photographs and photographed from 14 additional stations this paper provides an account of the location and subject of the photographs that are on file at the u s geological survey photo library in denver hopefully this study will provide the impetus for including systematic benchmark photography in future studies of ground deformation

a composite rupture model for the great 1950 assam earthquake across the cusp of the east himalayan syntaxis abstract although the m w 8 7 1950 assam earthquake endures as the largest continental earthquake ever recorded its exact source and mechanism remain contentious in this paper we jointly analyze the spatial distributions of reappraised aftershocks and landslides and provide new field evidence for its hitherto unknown surface rupture extent along the mishmi and abor hills within both mountain fronts relocated aftershocks and fresh landslide scars spread over an area of 330 km by 100 km the former are more abundant in the abor hills while the later mostly affect the front of the mishmi hills we found steep seismic scarps cutting across fluvial deposits and bounding recently uplifted terraces some of which less than two thousand years or even a couple centuries old at several sites along both mountain fronts they likely attest to a minimum 200 km long 1950 surface rupture on both the mishmi and main himalayan frontal thrusts mt and mft respectively crossing the east himalayan syntaxis at two key sites wakro and pasighat co seismic surface throw appears to have been over twice as large on the mt as on the mft 7 6 0 2 m vs 2 6 0 1 m in keeping with the relative average mountain heights 3200 m vs 1400 m mapped landslide scar numbers 182 vs 96 and average thrust dips 25 28 vs 13 15 consistent with relocated aftershocks depths corresponding average slip amounts at depth would have been 17 and 11 m on the mt and mft respectively while surface slip at wakro might have reached 34 m note that this amount of superficial slip would be out of reach using classic paleo seismological trenching to reconstruct paleo earthquake history most of the 1950 first arrivals fit with a composite focal mechanism co involving the two shallow dipping thrust planes their intersection lies roughly beneath the dibang valley implying forced slip parallel to gps vectors across the east himalayan syntaxis successive near identical terrace uplifts at wakro suggest near characteristic slip during the last two surface rupturing earthquakes while terrace boulder ages may be taken to imply bi millennial return time for 1950 size events as in nepal east himalayan mega quakes are not blind and release most of the elastic interseismic shortening that accumulates across the range

rapid late quaternary slip repeated prehistoric earthquake rupture and widespread landsliding associated with the karakudzhur thrust central kyrgyz tien shan field studies have shown that active faulting in the sw tien shan is distributed across a series of e w reverse faults along the range fronts and within basin interiors with summed shortening rates that are consistent with gps measurements in contrast few field studies have been undertaken to determine the distribution and the average slip rates of faults in the central and eastern parts of the tien shan in this paper we use remote and field based observations to characterize the active faulting and tectonic geomorphology of the karakudzhur basin in the central tien shan of kyrgyzstan we use radiocarbon luminescence and uranium series dating to provide ages on three fluvial terraces that are vertically displaced across the basin bounding reverse fault and estimate fault slip rates using a 20 s dipping fault exposure we find that the fault has a slip rate of 2 4 5 9 mm year averaged over the holocene indicating that it accommodates a major part of the shortening measured by gps in contrast to the relatively uniform distribution of n s shortening in the sw tien shan significant shortening may instead be concentrated at present on a few active faults in the northern part of the central tien shan the fresh geomorphic expression of the karakudzhur fault suggests that it has ruptured in recent prehistory in a large magnitude mw 7 earthquake from palaeoseismic trenching we show that two significant surface rupturing earthquakes have occurred since 2 4 ka the most recent earthquake was potentially accompanied by widespread landsliding and faulting in the surrounding highlands

morphologic dating of slowly evolving scarps using a diffusive analogue morphologic dating techniques that have been applied successfully in arid and semi arid areas are also suitable for slowly evolving scarps that are usually found in temperate climate environments two approaches based on diffusion to relate the present day shape of a scarp to its age are used here the first assumes a model of scarp degradation based on a diffusive process d method the second evaluates the state of scarp degradation using the slope distribution along a topographic profile sd method based on an anthropic scarp of known age we have obtained a mass diffusivity close to 1 5 m ka a reasonable value for areas characterized by a continuous vegetation cover and a temperate climate we show that the sd method requires an age correction since it does not take into account the earliest stage for which the mid height point is not yet affected by erosion however only the sd method reveals that at several profiles a later scarp reactivation event has occurred such information can be important when trying to identity the recent geological or environmental events that have affected a region

the armenian earthquake of 1988 december 7 faulting and folding neotectonics and palaeoseismicity summary the spitak earthquake of 1988 december 7 is the first well documented event directly associated with surface breaks in the transcaucasian regions of the ussr the earthquake was located within the ese wnw oriented pambak sevan thrust and fold zone corresponding to the southern front of the lesser caucasus the mechanism of the earthquake is consistent with the nearly ns compressive tectonics due to the active continental collision between the arabian block and the russian platform the rupture is composed by several branches two of which reach the surface the first branch oriented n140 begins near the village of alavar has a length of 11 km and disappears at about 4 km se of spitak it consists of a right lateral en echelon system of strike slip faults with a maximum offset of 50 cm the second branch is the main one and breaks for about 8 km between spitak and gekhasar with a general orientation n120 showing reverse faulting dipping to the north with a right lateral component surface ruptures between gekhasar and spitak show either a narrow band of pressure ridges in alluvial deposits and soil or a fault scarp in the bed rocks when soil is absent maximum displacements observed between spitak and gekhasar attain 160 cm of vertical motion and 90 cm of horizontal dextral offset the displacement also varies within this branch showing finer segmentation few secondary deformations are observed some normal faults near gekhasar correspond to the collapse of the uplifted block an anticline fold oriented parallel to the fault scarp and situated along its northwestern prolongation emphasizes the regional compressive tectonics landslides were activated on its flanks a 200 m long reverse fault break observed along the hinge of a secondary fold suggests the occurrence of a blind thrust at depth and that the hidden branches which continue the main central segment towards the nw are associated to surface folding therefore the total length of the fault and fold zone is about 40 km in agreement with the rupture length and seismic moment obtained on the basis of surface wave modelling well developed uplifted terraces in the northern block and subsiding valleys in the southern block indicate past quaternary activity in the fault region palaeoseismological evidence of ancient earthquakes has been recognized in trenches across the spitak fault one old event occurred between 17 000 years bp and the beginning of the formation of present day soil

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

late pleistocene to holocene slip rates for the gurvan bulag thrust fault gobi altay mongolia estimated with 10be dates 1 we surveyed morphotectonic markers along the central part of the gurvan bulag thrust a fault that ruptured with the bogd fault during the gobi altay earthquake 1957 m 8 3 to document climatic and tectonic processes along the fault for the late pleistoceneholocene period the markers were dated using 10 be produced in situ two major periods of alluviation ended at 131 20 and 16 4 8 ka these appear to be contemporaneous with global climatic changes at the terminations of marine isotope stages mis 6 and 2 the vertical slip rates determined from offset measurements and surfaces ages are 0 14 0 03 mm yr over the late pleistocene holocene and between 0 44 0 11 and 1 05 0 25 mm yr since the end of the late pleistocene the higher of these slip rates for the last 16 kyr is consistent with paleoseismic investigations along the fault prentice et al 2002 and suggests that at the end of late pleistocene the fault evolved from quiescence to having recurrence intervals of 4 0 1 2 kyr for surface ruptures with 4 m vertical offset similar to that of 1957 the inferred recurrence interval is comparable to that of the bogd fault 3 7 1 3 kyr suggesting that the two faults may have ruptured together also earlier during the last 16 kyr index terms 7221 seismology paleoseismology 1208 geodesy and gravity crustal movements intraplate 8110 1824 hydrology geomorphology 1625 7230 seismology seismicity and seismotectonics 8107 tectonophysics continental neotectonics keywords late pleistocene holocene thrust fault slip rate 10be dating mongolia

morphological dating of cumulative reverse fault scarps examples from the gurvan bogd fault system mongolia summary we relate reverse fault scarp morphology formed by several earthquake dislocations to the average deformation rate using a morphological dating model based on a diffusion analogue of erosion our scarp degradation model includes diffusive erosion during the interseismic period the gravitational collapse of the coseismic fault scarp just after formation and the variation of the surface rupture location interactions between thrusting and geomorphic processes acting on scarp morphology are analysed along the gurvan bogd range in mongolia four main processes acting on scarp morphology were distinguished i gravitational collapse of the frontal scarp resetting the diffusive scarp if fault offsets are big and faulting is localized 2 progressive erosion of the fault scarp during the interseismic period 3 folding associated with the frontal thrust and backthrusts 4 competing alluvial deposition on mountain piedmont slopes and abrasion of the fault scarp by wash processes the growth of cumulative reverse fault scarps is suppressed when they are located in the outwash of major drainage basins they can grow higher in distance from major catchment discharges the modelling suggests that the morphology of the scarp and its apparent degradation stage depend on the parameters controlling the amount of frontal collapse the magnitude of coseismic offsets the dip of the fault near the surface and the step distance between faults folding associated with thrusting creates a convexity on the upper part of the scarp and increases its height the comparison of different scarp profiles suggests that folding leads to an overestimate of the morphological age we estimate a diffusion coefficient at 3 3 1 7 m 2 ka l morphological ages calculated with our model confirm that slip rate along reverse faults of the gurvan bogd range has not been constant over the last 100 ka

morphologic dating of scarps formed by repeated slip events along the san andreas fault carrizo plain california morphologic dating of fault scarps determines late cenozoic fault activity by comparing observed topographic profiles with those determined using a calibrated hillslope development model we postulate that the material transport rate along the profile is a function only of local slope and is transport limited morphologic dating of hillslopes bounded by continuously dropping boundaries or cut by continuously slipping faults is used to determine the material transport rate constant the time since the downdrop was initiated or the fault began to slip we calibrated the hillslope development model on the southwest facing scarp southeast of wallace creek along the san andreas fault saf in the carrizo plain california the scarp has been exposed by right lateral offset of a southeast sloping shutter ridge located on the southwest side of the saf and by vertical offset related to secondary deformation we assume that all the observed offset occurs after initial exposure of the scarp by passage of the shutter ridge forward modeling of profile development yielded a mass diffusivity of 8 6 0 8 m2 kyr 1 normal fault slip rates were determined for two graben bounding faults in the northern elkhorn hills in the southeastern carrizo plain by applying the calibrated to the degradation of the scarps to determine the scarp age one fault scarp began to form about 12 kyr ago and the other about 63 kyr ago those ages and estimates of the dip slip along the faults result in slip rates of 1 2 mm yr 1

morphologic dating of fluvial terrace scarps and fault scarps near west yellowstone montana analysis of fault and fluvial terrace scarps in the west yellowstone basin south of hebgen lake montana indicates that during degradation the gradient of the scarp face and the curvatures of the basal concavity and crestal convexity of the scarp face decrease become more rounded with time the pattern of degradation is identical with that predicted by a simple analytical model for degradation by creep in which the change in elevation at a point on a hillslope is proportional to the curvature of the profile at that point the model therefore provides the basis for morphologic dating a technique for determining the age of a scarp by the extent to which its initial morphology has been degraded in order to date a scarp the coefficient of proportionality c must be known the technique is probably not suitable for use on hillslopes degraded by processes other than creep both the potential and the limitations of morphologic dating are demonstrated via measurements of a sequence of terrace scarps along the madison river the calculated relative ages are in agreement with the known relative ages despite the fact that the gradient of the youngest scarp is significantly less than that of the older scarps to calculate an absolute morphologic age c must be derived from analysis of a scarp of known age having the same aspect must be underlain by the same material and must be within the same climatic zone as the scarp to be dated in the west yellowstone basin a value of c 2 00 0 38 10 3 m 2 yr was calculated from a minimum date of 7100 50 yr b p determined by radiocarbon dating for one of the terrace scarps scarps formed by normal faulting in the west yellowstone basin are much more difficult to date than are terrace scarps because of the possible complexity of their initial morphology fault scarps formed during the 1959 yellowstone earthquake commonly consist of an assemblage of two or more smaller scarps or are superimposed on preexisting scarps formed by one or more previous faulting events by using a selective sampling procedure however one can screen out these fault scarps in this way it was possible to determine an age of 2 800 1 100 yr for a pre 1959 fault scarp in the west yellowstone basin because the fault and terrace scarps in the west yellowstone area do not vary significantly in height the morphologic dating technique proposed earlier by nash 1980a cannot be applied to them the substantially modified procedure developed for the present study does not require a wide range of heights for each scarp to be dated it can be performed using a relatively small number of scarp profiles if c is known it is easy to use and when used with considerable care it is reasonably accurate 36 59 in this study it is potentially applicable to scarps in other areas

temporal clustering of paleoseismic events on the oued fodda fault algeria paleoseismic investigations of the oued fodda fault which underwent surface fault rupture during the algeria earthquake of october 10 1980 m s 7 3 indicate that the average recurrence interval based on the long term geologic slip rate past 100 ka is at least an order of magnitude longer than the intervals between recent surface faulting events which are determined by radiocarbon dating of faulted colluvial deposits exposed in trenches across the fault evidence from trenches excavated across the 1980 surface rupture indicates that there have been at least three and possibly four surface faulting events on the oued fodda fault during the past 1 5 ka including the 1980 earthquake the ages of the three most recent events are well constrained the most recent event occurred in 1980 a surface faulting event occurred before 320 220 c 14 yr b p radiocarbon years before 1950 and after 875 240 yr b p and another event occurred just prior to deposition of a layer containing charcoal dated at 875 250 yr b p i e about 900 yr ago the average interval between the three most recent surface faulting events on the oued fodda fault was about 450 yr the cumulative slip on the oued fodda fault was produced by relatively short episodes characterized by frequent displacements surface faulting events every few hundred years separated by long periods of quiescence lasting several thousands to tens of thousands of years

quaternary climate change and the formation of river terraces across growing anticlines on the north flank of the tien shan china nested stream terraces warped upward over actively growing anticlines along the north flank of the tien shan in western china appear to record alternating phases of valley widening and incision differences of relative heights between remnants of four separate strath terraces along one river and between two such terraces along another reach 100 to 120 m over the crests of the anticlines we infer that this spacing is due to alternating stages of valley widening and rapid incision associated with climate changes with a periodicity of 100 kyr the crests of the anticlines appear to emerge from the aggrading flanks of the anticlines at an average rate of about 1 mm a the maximum heights of 25 and 35 10 m for the lowest terraces above their projected initial profiles imply ages of roughly 25 kyr and 35 kyr 10 kyr hence they suggest that flood plains which were abandoned to form the terraces developed adjacent to active stream beds during the last glacial period when climates were relatively

trench investigations through the trace of the 1980 el asnam thrust fault evidence for paleoseismicity during the ei asnam earthquake of 10 october 1980 ms 7 3 a clear active thrust fault with left lateral offset was observed three trenches have been excavated across this fault in order to determine slip rate and recurrence intervals between large earthquakes and thus reconstruct its past activity exposure i was excavated in the flood area created in 1980 by a pressure ridge across the cheliff and fodda rivers six flood deposits silty sandy and muddy horizons alternating with paleosoils appear in this exposure they are affected by normal faults associated with the main thrust fault assuming that every flood deposit results from a tectonic event of magnitude greater than 7 we can correlate previous flood deposits with these events exposures ii and iii display thrust faults displacing different paleosoils we propose a sequence of reconstructions based on the thickness of the various deposits and the dip slip of each tectonic event the late holocene slip rate is 0 65 mm yr for the dip slip and 0 46 mm yr for each of the horizontal and the vertical movements radiocarbon dates of coseismic movements indicate a rather irregular seismic activity during the past 7000 yr two sequences of large earthquakes around 4000 yr b p and around the modern age are separated with a period of quiescence the average late holocene recurrence interval of large earthquakes is 1061 yr however during the active faulting episodes the recurrence time varies from approximately 300 to 500 yr

slip rates along active faults estimated with cosmic ray exposure dates application to the bogd fault gobi altai mongolia dating morphological features displaced along active faults presents a major difficulty in evaluation of slip rates we used in situ produced 10 be to calculate minimum ages for alluvial surfaces misaligned by movement along a major active fault in the gobi altai western mongolia the maximum slip rate of 1 2 mm yr suggested by this method contrasts strongly with rates of 20 mm yr that we estimated by correlation of alluvial deposition with warm humid periods associated with the last glacial termination estimated to have occurred about 12 ka in western tibet the 10 be based slip rate indicates that strong earthquakes can occur along faults with low slip rates and demonstrates the contribution of cosmic ray exposure dating in quaternary tectonic analyses

prehistoric ruptures of the gurvan bulag fault gobi altay mongolia 1 the 1957 gobi altay m8 3 earthquake in southern mongolia was associated with the simultaneous rupture of several faults including the gurvan bulag reverse fault which is located about 25 km south of the main strike slip bogd fault our study of paleoseismic excavations across the gurvan bulag fault suggests that the penultimate surface rupture occurred after 6 0 ka most likely between 2 6 and 4 4 ka and a possible earlier rupture occurred after 7 3 ka our interpretation of the stratigraphic relations in one of the exposures suggests that at least five earthquakes have generated surface rupture of the gurvan bulag fault since the abandonment of an ancient alluvial fan surface luminescence dating of sediment associated with this surface indicates that it formed either 26 6 2 1 ka or 16 1 2 0 ka these data imply that the recurrence intervals for surface faulting on the gurvan bulag and bogd faults are similar on the order of several thousands of years but that the penultimate surface ruptures of the two faults did not occur during the same earthquake

experimental modelling of tectonics erosion sedimentation interactions in compressional extensional and strike slip settings tectonically controlled landforms develop morphologic features that provide useful markers to investigate crustal deformation and relief growth dynamics in this paper we present results of morphotectonic experiments obtained with an innovative approach combining tectonic and surface processes erosion transport and sedimentation coupled with accurate model monitoring techniques this approach allows for a qualitative and quantitative analysis of landscape evolution in response to active deformation in the three end member geological settings compression extension and strike slip experimental results outline first that experimental morphologies evolve significantly at a short time scale numerous morphologic markers form continuously but their lifetime is generally short because erosion and sedimentation processes tend to destroy or bury them for the compressional setting the formation of terraces above an active thrust appears mainly controlled by narrowing and incision of the main channel through the uplifting hanging wall and by avulsion of deposits on fan like bodies terrace formation is irregular even under steady tectonic rates and erosional conditions terrace deformation analysis allows retrieving the growth history of the structure and the fault slip rate evolution for the extensional setting the dynamics of hanging wall sedimentary filling appears to control the position of the base level which in turn controls footwall erosion two phases of relief evolution can be evidenced the first is a phase of relief growth and the second is a phase of upstream propagation of topographic equilibrium that is reached first in the sedimentary basin during the phase of relief growth the formation of triangular facets occurs by degradation of the fault scarp and their geometry height becomes stationary during the phase of upstream propagation of the topographic equilibrium for the strike slip setting the complex morphology of the wrench zone composed of several interacting fault segments enhances the interactions with the drainage network because of the widening of the main fault zone toward the surface a significant amount of distributed deformation is observed along the wrench zone locally where two terminations of fault segments interact less than a quarter of the far field displacement can remain measurable using fault offsets leading to a systematic underestimation of the real fault slip rate these different experimental examples illustrate the great potential of the approach coupling deformation mechanisms and erosion transport sedimentation processes to investigate qualitatively and quantitatively the morphotectonic evolution of tectonically controlled landscapes

faulting and folding in quaternary deposits of tehran s piedmont iran abstract tehran lies on the southern flank of the central alborz an active mountain belt characterized by many historical earthquakes some of which have affected tehran itself the border between the alborz mountain and the tehran s piedmont northern part of tehran city is marked by the north tehran fault ntf dividing the eocene rock formation from the alluvial units of different ages early pleistocene to the recent alluvium a detail mapping of the piedmont combined with structural study reveal that two active thrust faults situated south of the ntf are of importance for hazard assessment of the city the geomorphological evidences along the ntf are not in agreement with an active fault indicating that the fault activity may have been shifted southward furthermore differentiation of newly recognized alluvial units and their inferred ages together with the mapped fault pattern permit us to characterize the quaternary deformation the late pleistocene alluvial deposits consist of three alluvial fans among them the youngest one together with the modern alluvial fan defines the holocene deposit the present deformation in the piedmont is accommodated along vertically left lateral strike slip faults and low angle thrust faults trending in range from n070 to n110e

do river profiles record along stream variations of low uplift rate environments 1m m yr 1 where climate changes may have erased tectonic features we evaluate the respective contribution of low uplift rate 0 1 mm yr 1 and pleistocene climate oscillations on gradient variations of two comparable river profiles crossing different uplift zones in the southern upper rhine graben we compare the observed points of discontinuity in river profile knickpoints and convex portions knickzones with those predicted by a detachment limited model that includes stochastic short term and cyclic long term variations in climate a bedrock detachment threshold and rock uplift the detachment limited model is chosen as it predicts the development of persistent knickpoints differing values of the shear stress exponent erosion threshold climate variability and uplift pattern have been checked our modeling suggests that climate changes had no significant effects on profiles and that anomalies are more likely due to anticline growth this surprising result arises from the combination of a very low regional uplift rate and the detachment limited assumption the detachment limited model implies an upstream propagation of knickpoints and knickzones generated by uplift at the outlet during dry climate periods of low erosion the greater the uplift rate the larger the variations in river bed elevation thus for high uplift rate knickpoints and knickzones generated by climate oscillations are more likely to hide tectonic features this result seems counterintuitive because it suggests that tectonic knickzones will be better preserved in low uplift rate environments provided that the lithology is homogeneous

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

the growth of geological structures by repeated earthquakes 2 field examples of continental dip slip faults a strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault bounded geological structures such as basins and ranges which are built by repeated cycles of deformation along strike slip faults the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign resulting in little permanent deformation except for the fault offset for dip slip faults portions of the crust are lifted and dropped and so buoyancy forces are exerted the seismic and interseismic deformations do not balance and structures grow and become subject to erosion and deposition we consider three examples for which the structure and fault geometry are well known the white wolf reverse fault in california site of the 1952 kern county m 7 3 earthquake the lost river normal fault in idaho site of the 1983 borah peak m 7 0 earthquake and the cricket mountain normal fault in utah site of quaternary slip events basin stratigraphy and seismic reflection records are used to profile the structure and coseismic deformation measured by leveling surveys is used to estimate the fault geometry to reproduce these structures we add the deformation associated with the earthquake cycle the coseismic slip and postseismic relaxation to the flexure caused by the observed sediment load treating the crust as a thin elastic plate overlying a fluid substrate the cumulative deformation is principally dependent on the elastic plate thickness modestly sensitive to the sediment substrate density difference and insensitive to the fluid viscosity for the 4 to 8 ma structures we deduce a longterm flexural rigidity of 2 15 1019 nm this is equivalent to an elastic plate thickness of 2 4 km for a young s modulus of 2 5 1010 nm 2 this value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km but where coseismic fault slip extends to a depth of 10 15 km thus much of the seismogenic crust must weaken substantially during the life of active faults causing the fault bounded basins to narrow over time

timing of formation of forebergs in the northeastern gobi altai mongolia implications for estimating mountain uplift rates and earthquake recurrence intervals bedrock and quaternary alluvial fans in the forelands of the northern gobi altai have been faulted and warped by foreland propagating thrust faults to form elongate hills known as forebergs forebergs near bogd town north of arsta bogd and at ih hetsuu north of baga bogd were mapped and their formation constrained using luminescence dating of lacustrine and fanglomerates sediments to give localized uplift rates of c 0 05 m ka 1 and between c 1 6 and 4 1 m ka 1 respectively comparisons between vertical surface rupture during the 1957 gobi altai earthquake with the age and amount of uplift of lacustrine sediments provide a tentative estimate of between 1288 382 to 497 120 years for the average recurrence interval of great earthquakes in the baga bogd region these localized uplifts rates support the view that the gobi altai mountains probably took between 50 and 25 million years to form and were therefore coeval with the uplift of the himalayas and the tibetan plateau

relic permafrost structures in the gobi of mongolia age and significance relict permafrost structures ice wedge casts and cryoturbation structures are present in the gobi of southern mongolia luminescence dates of sediments are presented to constrain the age of formation of permafrost structures these data show that there was a phase of permafrost development during the latter part of the last glacial after about 22 to 15 ka that resulted in cryoturbated sediments and ice wedge casts furthermore permafrost degradation occurred during late pleistocene times 13 10 ka and was absent during the early holocene these permafrost structures mark the southernmost evidence of permafrost in northern asia during late quaternary times and indicate that the mean annual air temperature was below approximately 6 c during their formation 1998 john wiley sons ltd

estimating the ages of fault scarps in the arava israel abstract systematic age estimations for the numerous fault scarps that rupture the alluvial fans in the southern arava valley israel are rare or nonexistent here we estimate the morphologic ages of several of these faults by the fault scarp degradation method and show that the ages agree well with ages estimated by the independent earlier soil geomorphic studies the values we use for the coefficient of diffusion for the fault scarp degradation process are calibrated by a few numerical ages these ages were determined by the infrared stimulated luminescence irsl method on one of the fault scarps and are the only numerical ages in the region the morphologic ages are all in a correct stratigraphic order and in agreement with field stratigraphic relationships determined by earlier studies they indicate that the studied fault scarps range in age from the latest pleistocene to very recent times the most recent fault scarps which were analyzed are less than 2000 years old and perhaps much younger they indicate that at least two earthquakes with magnitude 6 5 have affected southern israel and jordan during that period it is emphasized that so far we have studied only a limited number of fault scarps and therefore the number of large earthquakes during the last one to two millennia is a minimum

large earthquake nucleation associated with stress exchange between middle and upper crust earthquake nucleation and propagation can be explained using two basic concepts crustal strength and fault rheology despite numerous experimental and modeling studies the way in which a faulted crust generates a seismic cycle under loading is still controversial we discuss earthquake generation using a 2 d finite element model which includes relevant features of geodynamical problems such as rheological layering dynamic coulomb faulting and relative plate velocity the occurrence of a deep nucleation is explained by the strong viscosity drop at the base of the seismogenic layer without any transition of frictional properties of the fault rather viscosity contrast causes a stress transfer around the fault that reloads the fault plane during the postseismic phase we argue that this mechanism may explain the seismic cycle for large faults in the continental crust

the global continent ocean magnetization contrast abstract a schematic global model for the distribution of magnetization in the lithosphere is devised this model is characterized by a uniform stepwise change of radially integrated susceptibility at continent ocean boundaries and an axial dipolar inducing field a spherical harmonic expansion of the magnetic field produced by this source distribution is computed then the standard method of truncation at degree n 13 is used to determine the respective contribution of this field to the main field and to the lithospheric anomaly field the latter is shown to display significant anomalies near continental margins as well as within continents and oceanic basins the energy density spectrum of this field is shown to be very similar to the spectrum of the magsat derived lithospheric anomaly field furthermore several features of this field are shown to account for unexplained anomalies of the magsat field this supports the hypothesis that such an abrupt magnetization variation may occur at several continental margins and contribute to the signal in the magsat derived long wavelength anomaly maps this hypothesis provides an order of magnitude estimate for the magnetization difference between oceanic and continental lithospheres finally it is argued that the synthetic anomaly field produced by this model provides an upper bound to the energy density spectrum of the lithospheric field at low harmonic degrees and concluded that the lithospheric field does not contribute significantly to the earth s field below degree 13

the role of bed parallel slip in the formation of blind thrust faults abstract a finite element code is used to model the mechanical behaviour of elastoplastic sedimentary layers that are deformed by the movement of a faulted deformable basement the propagation of the blind thrust fault is analysed in terms of the evolution of strain localization in the elastoplastic layers of strain softening and strain hardening materials the role of layer thickness bedding parallel slip and fault dip are also studied we found that if no interlayer slip is allowed blind thrusts tend to propagate with constant dip regardless of the rheological properties of the sediment layers however if bedding parallel slip is present a mechanical decoupling appears between layers allowing stress transfers along large distances and favouring the formation of backthrusts fault dip also has significant influence on the qualitative behaviour when interlayer slip is possible a steep fault will tend to split

coseismic elastic models of folds above blind thrusts in the betic cordilleras spain and evaluation of seismic hazard abstract although it is generally considered that near surface earthquakes result from movements along faults that cut through the surface several recent large earthquakes have been partly attributed to blind thrusts movements along blind thrusts lead to the formation of surface folds which are highly dependent upon fault geometry at depth and often not considered in seismic hazard evaluation several authors have studied the relationship between surface folding and thrusting for geological situations in which fault geometries are quite simple however active fault geometries can be quite complex e g segmented thrust faults associated with strike slip faults the aim of this contribution is to reconstruct the fault kinematics at depth for a relatively complex geological structure located in the eastern betic cordilleras orihuela guardamar torrevieja region using the patterns of kilometre scale folds observed in the field in order to model surface deformation the assumption is made that surface km scale folds have been created by coseismic deformation associated with movement along blind thrusts by means of a coseismic deformation model movements at depth have been calculated for three possible hypotheses hypothesis 1 assumes that each superficial fold is created by an independent fault hypotheses 2 and 3 assume that a sequence of two superficial folds can be created by movement along a single fault displaying a flat and ramp geometry in hypothesis 2 the flat is a superficial decollement level between the sedimentary cover and the betic basement in hypothesis 3 it is a deeper decollement level within the betic basement knowing the approximate age of surface deformation rough estimates of fault slip rates and recurrence periods for two possible earthquake magnitudes 7 ms and 6 7 ms have been made from calculated dislocations at depth slip rates and recurrence periods for flat and ramp fault geometries are in the range of 0 75 1 mm yr and 1000 2000 yr respectively these values are close to those calculated by direct methods in similar seismotectonic contexts

hillslope development in areas of active tectonics tectonic and geomorphic displacements of the earth s surface control topographic profile development therefore their analysis should be combined in the model presented here transient finite difference solutions to the continuity equation for material transport determine geomorphic displacements the material transport rate is a function of distance from the divide to the power m local slope to the power n and a rate constant values of m and n may be adjusted to simulate processes varying from rainsplash and soil creep i e diffusive m 0 n 1 to slope wash and river flow m 0 n 0 the actual geomorphic displacements may be transport or weathering limited depending on soil profile development superimposed edge dislocations in an elastic half plane are used to model tectonic displacements slip along a normal or reverse fault of any dip depth and down dip length may be incremental earthquake or continuous aseismic creep considering climate and material properties constant the ratio of the transport capacity rate constant to the fault slip rate roughly determines form this model extends existing morphologic diffusion erosion analyses to include other geomorphic conditions and processes transport or weathering limited conditions material flux boundary conditions and the development of gullies and knickpoints and more heterogeneous spatial and temporal distributions of tectonic displacement such as those due to slip along buried thrust faults we advocate calibration of these parameters and processes to provide a quantitative approach to modeling landform development determining deformation rates and inferring earthquake hazards

cosmogenic ages for earthquake recurrence intervals and debris flow fan deposition owens valley california model exposure ages beryllium 10 aluminum 26 of boulders on an offset debris flow fan yield an earthquake recurrence interval between 5800 and 8000 10be 26al years for a strand of the owens valley fault in california which last ruptured in an earthquake of moment magnitude 7 5 in 1872 cosmogenic age estimates for this and several nearby fan surfaces flanking the eastern sierra nevada are consistent with stratigraphic relations and suggest that these surfaces were abandoned after 1000 8000 and 21 000 10be 26al years ago the wide scatter and nonconcordance of 10be 26al ages on an older fan surface suggest that boulder erosion and lowering of the fan surface there have influenced apparent exposure ages

1957 gobi altay mongolia earthquake as a prototype for southern california s most devastating earthquake the 1957 gobi altay earthquake was associated with both strike slip and thrust faulting processes similar to those along the san andreas fault and the faults bounding the san gabriel mountains just north of los angeles california clearly a major rupture either on the san andreas fault north of los angeles or on the thrust faults bounding the los angeles basin poses a serious hazard to inhabitants of that area by analogy with the gobi altay earthquake we suggest that simultaneous rupturing of both the san andreas fault and the thrust faults nearer los angeles is a real possibility that amplifies the hazard posed by ruptures on either fault system separately

transpressional tectonics and stream terraces of the gobi altay mongolia we studied the patterns rates and evolution of fluvial terraces and fault system during the building process of an intracontinental transpressional mountain in the gobi altay mongolia by analyzing incisions and offsets of fluvial terraces and alluvial fans we show that the massif has grown by outward migration of thrust faults through time on the northern flank the present bounding thrust fault began its activity 600 ka ago while a more internal sub parallel fault was still active until 200 100 ka vertical offset of an alluvial fan abandoned 100 ka ago allows an estimate of 0 1 mm yr upper pleistocene holocene uplift rate the morphology of the catchment piedmont system strongly suggests a periodical formation of the alluvial surfaces controlled by the climatic pulses at the beginning of the wet interglacial periods the abandonment of the alluvial terraces lags by several thousand years the abandonment of the alluvial fans showing a diachronous incision propagating upstream the incision rate deduced from the different elevations of straths exceeds of one order of magnitude the rock uplift rate this excess is mostly due to ongoing drainage network growth at the core of the massif and incision due to alluvial apron entrenchment near the outlet this implies that fluvial response is mainly controlled by drainage growth interaction with piedmont and cyclic climatic variations rather than by rock uplift

the egiin davaa prehistoric rupture central mongolia a large magnitude normal faulting earthquake on a reactivated fault with little cumulative slip located in a slowly deforming intraplate setting the prehistoric egiin davaa earthquake rupture is well preserved in late quaternary deposits within the hangay mountains of central mongolia the rupture is expressed by a semicontinuous 80 km long topographic scarp geomorphological reconstructions reveal a relatively constant scarp height of 4 4 5 m and a nw directed slip vector previous researchers have suggested that the scarp s exceptional geomorphological preservation indicates that it may correspond to an earthquake that occurred in the region c 500 years ago however we constrain the last rupture to have been at least 4 ka ago from morphological dating and 7 4 ka ago based on radiocarbon dating from one of two palaeoseismic trenches our study shows that discrete earthquake ruptures along with details such as the locations of partially infilled fissures can be preserved for periods well in excess of 1000 years in the interior of asia providing an archive of fault movements that can be directly read from the earth s surface over a timescale appropriate for the study of slowly deforming continental interiors the egiin davaa rupture involved c 8 m of slip which along with the observations that it is largely unsegmented along its length and that the ratio of cumulative slip c 250 m to fault length c 80 km is small suggests relatively recent reactivation of a pre existing geological structure

control of geomorphic processes on 10be concentrations in individual clasts complexity of the exposure history in gobi altay range mongolia the dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre deposition inheritance from the post deposition history of the clasts in the studied marker moreover estimating catchment scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local regional relationships between rock exhumation and transport through space and time this is still poorly known for timescales of tens of thousand years in order to document the evolution of clast exhumation and transport rates through time we analyze in situ 10be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in gobi altay mongolia strongly affected by global climatic changes during the pleistocene holocene period samples were collected on bedrock abandoned alluvial deposits active colluvia and alluvia our results show a large 10be scattering in the active river bed consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision on the contrary pre exposure signal within abandoned terraces is much more homogeneous consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport these results show that exhumation transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations the occurrence of abrupt climatic changes during short periods of time recorded by 10be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers on the other hand strong and short erosion events limit and homogenize the pre exposure 10be signal in associated deposits like debris flows making them particularly suitable markers for dating in active tectonic and paleoclimatic studies

active tectonics in southern xinjiang china analysis of terrace riser and normal fault scarp degradation along the hotan qira fault system the northern piedmont of the western kunlun mountains xinjiang china is marked at its easternmost extremity south of the hotan qira oases by a set of normal faults trending n50e for nearly 70 km conspicuous on landsat and spot images these faults follow the southeastern border of a deep flexural basin and may be related to the subsidence of the tarim platform loaded by the western kunlun northward overthrust the hotan qira normal fault system vertically offsets the piedmont slope by 70 m highest fault scarps reach 20 m and often display evidence for recent reactivations about 2 m high successive stream entrenchments in uplifted footwalls have formed inset terraces we have leveled topographic profiles across fault scarps and transverse abandoned terrace risers the state of degradation of each terrace edge has been characterized by a degradation coefficient derived by comparison with analytical erosion models edges of highest abandoned terraces yield a degradation coefficient of 33 4 m 2 profiles of cumulative fault scarps have been analyzed in a similar way using synthetic profiles generated with a simple incremental fault scarp model the analysis shows that 1 rate of fault slip remained essentially constant since the aggradation of the piedmont surface and 2 the occurrence of inset terraces was synchronous at all studied sites suggesting a climate driven terrace formation observation of glacial and periglacial geomorphic features along the northern front of the western kunlun range indicates that the qira glaciofluvial fan emplaced after the last glacial maximum during the retreat of the kunlun glaciers 12 22 ka the age of the most developed inset terrace in uplifted valleys is inferred to be 10 3 ka coeval with humid climate pulses of the last deglaciation the mass diffusivity constant k t being time b p in the hotan region is determined to be 3 3 1 4 m 2 10 3 years consistent with other estimates in similar climatic and geologic environments of western china these results imply a minimum rate for the tarim subsidence of 3 5 2 mm yr if western kunlun overthrusts the tarim platform on a crustal ramp dipping 40 45 to the south it would absorb at least 4 5 3 mm yr of convergence between western tibet and tarim

repeated large magnitude earthquakes in a tectonically active low strain continental interior the northern tien shan kyrgyzstan the northern tien shan of kyrgyzstan and kazakhstan has been affected by a series of major earthquakes in the late 19th and early 20th centuries to assess the significance of such a pulse of strain release in a continental interior it is important to analyze and quantify strain release over multiple time scales we have undertaken paleoseismological investigations at two geomorphically distinct sites panfilovkoe and rot front near the kyrgyz capital bishkek although located near the historic epicenters both sites were not affected by these earthquakes trenching was accompanied by dating stratigraphy and offset surfaces using luminescence radiocarbon and 10be terrestrial cosmogenic nuclide methods at rot front trenching of a small scarp did not reveal evidence for surface rupture during the last 5000 years the scarp rather resembles an extensive debris flow lobe at panfilovkoe we estimate a late pleistocene minimum slip rate of 0 2 0 1 mm a averaged over at least two probably three earthquake cycles dip slip reverse motion along segmented moderately steep faults resulted in hanging wall collapse scarps during different events the most recent earthquake occurred around 3 6 1 3 kyr ago 1 with dip slip offsets between 1 2 and 1 4 m we calculate a probabilistic paleomagnitude to be between 6 7 and 7 2 which is in agreement with regional data from the kyrgyz range the morphotectonic signals in the northern tien shan are a prime example of deformation in a tectonically active intracontinental mountain belt and as such can help understand the longer term coevolution of topography and seismogenic processes in similar structural settings worldwide

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

fault trace complexity cumulative slip and the shape of the magnitude frequency distribution for strike slip faults a global survey summary we examine whether the shape of the magnitude frequency distribution for strike slip faults is described by the gutenburg richter relationship log n a bm or by the characteristic earthquake model by analysing a data set of faults from california mexico japan new zealand china and turkey for faults within regional seismic networks curves of the form log n yrpl a bm where n yr is the number of events per year equal to magnitude m are fit to the instrumental record of seismicity and geological data are used to estimate independently the size and recurrence rate of the largest expected earthquakes that would rupture the total length of the fault extrapolation of instrumentally derived curves to larger magnitudes agrees with geological estimates of the recurrence rate of the largest earthquakes for only four of the 22 faults if uncertainties in curve slope are considered and significantly underestimates the geological recurrence rates in the remaining cases also if we predict the seismicity of the faults as a function of fault length and slip rate and the predicted seismicity is distributed in accord with the gutenburg richter relationship we find the predicted recurrence rate to be greater than the observed recurrence rates of smaller earthquakes along most faults if individual fault zones satisfy the gutenburg richter relationship over the long term our observations imply that during the recurrence interval of the largest expected earthquakes the recurrence of lesser sized events is not steady but rather strongly clustered in time however if the instrumental records provide an estimate of the long term rate of small to moderate earthquakes along the faults our observations imply that the faults generally exhibit a magnitude frequency distribution consistent with the characteristic earthquake model also we observe that the geometrical complexity of strike slip faults is a decreasing function of cumulative strike slip offset the four faults we observe to be consistent with the gutenburgrichter relationship are among those characterized by the least amount of cumulative slip and greatest fault trace complexity we therefore suggest that the ratio of the recurrence rate of small to large earthquakes along a fault zone may decrease as slip accumulates and the fault becomes smoother

a creeping intracontinental thrust fault past and present slip rates on the northern edge of the tien shan kazakhstan we demonstrate that a continental interior reverse fault is deforming by aseismic creep presently and likely also in the long term the karkara rangefront fault part of the larger main terskey front forms the northern boundary of the high terskey tien shan in southeastern kazakhstan and is a mature structure with evidence for high slip rates throughout the late cenozoic combining field studies with a satellite stereo image derived digital elevation model 2 m resolution we map a series of fluvial terraces along the rangefront which are uplifted by up to 300 m above the present river level radiocarbon ages from one catchment constrain the ages of the lowermost two terraces to be 4 5 ka and 10 15 ka consistent with prominent regionally extensive terraces observed elsewhere in the tien shan based on conservative estimates for the fault dip under the displaced terraces we estimate a slip rate along the fault plane of 3 5 1 7 0 4 mm yr 1 on the karkara rangefront fault and a further 0 8 mm yr 1 on a fold structure in the kegen basin that we infer is driven by a detachment from the main rangefront we therefore estimate a minimum shortening rate across the rangefront of 1 1 3 3 mm yr 1 elastic modelling of the regional gps velocity field suggests that the fault is presently creeping at 3 mm yr 1 horizontal shortening consistent with the upper limit of our late quaternary slip rate estimate this is the fastest known slip rate in the northern tien shan and the only individual structure resolved in the regional velocity field at present the fault is accumulating minimal strain and there is evidence in the geomorphology that this creep is sustained in the long term but whether or not it is also capable of generating earthquakes requires further study

quaternary geology of willow creek and some age constraints on prehistoric faulting lost river range east central idaho new data on the geochronology of upper quaternary units in the willow creek drainage bear on the timing of the last prehistoric surface faulting event along the thousand springs segment of the lost river fault surficial effects of this event were paralleled by the 1983 ms 7 3 borah peak earthquake radiocarbon dated till 8 470 160 b p at doublespring pass can be traced to the geomorphically youngest alluvial surface cut by the fault the alluvial surface is related to deglaciation and thus postdates 8 470 b p the faulting also postdates this time aeolian sheetwash sediments draped over the fault scarp are 14c dated as 530 80 b p providing an upper age bracket for faulting geomorphological analysis of presence absence relations of regionally widespread mt mazama tephra 6 850 14c yr b p suggests that the faulting event may postdate this tephra fall and thus lies in the age range 6 850 to 530 b p based on the amount of pre 1983 offset 2 1 to 2 6 m and a maximum of 6 850 yr between events minimum short term slip rates range from 0 3 to 0 4 m 1 000 yr along this segment

dating faulted alluvial fans with cosmogenic 10be in the gurvan bogd mountain range gobi altay mongolia climatic and tectonic implications the gurvan bogd mountain range is a fault system characterized by strong earthquakes m 8 separated by long periods of quiescence further to the previous works in the area our study provides new data concerning the tectonic and climatic processes in the gobi altay to quantify the slip rates along the faults we dated offset alluvial fans analysing the in situ produced 10 be along profiles at depth the slip rates along the bogd strike slip fault and its associated thrust faults over the upper pleistocene holocene period are 0 95 0 29 mm yr 1 and comprised between 0 12 0 02 and 0 13 0 02 mm yr 1 respectively the surfaces ages account for a cyclic formation of the fans over the past 360 ka in correlation with the terminations of the marine isotope stages 2 6 8 and 10

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

influence of lithology on hillslope morphology and response to tectonic forcing in the northern sierra nevada of california 1 many geomorphic studies assume that bedrock geology is not a first order control on landscape form in order to isolate drivers of geomorphic change e g climate or tectonics yet underlying geology may influence the efficacy of soil production and sediment transport on hillslopes we performed quantitative analysis of lidar digital terrain models to examine the topographic form of hillslopes in two distinct lithologies in the feather river catchment in northern california a granodiorite pluton and metamorphosed volcanics the two sites separated by 2 km and spanning similar elevations were assumed to have similar climatic histories and are experiencing a transience in landscape evolution characterized by a propagating incision wave in response to accelerated surface uplift c 5 ma responding to increased incision rates hillslopes in granodiorite tend to have morphology similar to model predictions for steady state hillslopes suggesting that they adjust rapidly to keep pace with the incision wave by contrast hillslopes in metavolcanics exhibit high gradients but lower hilltop curvature indicative of ongoing transient adjustment to incision we used existing erosion rate data and the curvature of hilltops proximal to the main channels where hillslopes have most likely adjusted to accelerated erosion rates to demonstrate that the sediment transport coefficient is higher in granodiorite 8 8 m2 ka 1 than in metavolcanics 4 8 m2 ka 1 hillslopes in both lithologies get shorter i e drainage density increases with increasing erosion rates

cosmogenic dating ranging from 20 to 700 ka of a series of alluvial fan surfaces affected by the el tigre fault argentina it is crucial to date continental landforms to quantify processes involved in terrestrial surface evolution especially in regions affected by active tectonics andean quaternary alluvial fan surfaces affected by the el tigre strike slip fault have been studied using combined geomorphic and 10 be exposure age approaches field observations and spot french acronym for satellite for observation of the earth image analysis enable the identification of six alluvial fan units measurements of in situ produced cosmogenic 10 be concentrations in quartzite boulders exposed on the top of fan surfaces show that the depositional periods ended during successive major interglacial stages the calculated minimum exposure ages date the abandonments of the alluvial fan surface from 41 000 8500 yr for the youngest to 670 000 140 000 yr for the oldest unit when linked to the measured maximum cumulative right lateral displacement of stream channels the exposure ages yield a horizontal slip rate of about 1 mm yr on the el tigre fault this study shows that for arid regions where fan surface erosion is minimal in situ produced 10 be can be used to constrain the age of stratigraphically separate alluvial fan surfaces these fan surface exposure ages can be further used to calculate slip rates on active faults and infer depositional periods correlative with climatic events

slip rate and slip magnitudes of past earthquakes along the bogd left lateral strike slip fault mongolia we carried out morphotectonic studies along the left lateral strike slip bogd fault the principal structure involved in the gobi altay earthquake of 1957 december 4 published magnitudes range from 7 8 to 8 3 the bogd fault is 260 km long and can be subdivided into five main geometric segments based on variation in strike direction west to east these segments are respectively the west ih bogd wib the north ih bogd nib the west ih bogd wib the west baga bogd wbb and the east baga bogd ebb segments morphological analysis of offset streams ridges and alluvial fans particularly well preserved in the arid environment of the gobi region allows evaluation of late quaternary slip rates along the different faults segments in this paper we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the bogd fault our results show that the left lateral slip rate is similar to 1 mm yr 1 along the wib and eib segments and similar to 0 5 mm yr 1 along the nib segment these variations are consistent with the restraining bend geometry of the bogd fault our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the bogd rupture complementing previously published studies we show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5 2 m in the west to 2 0 m in the east reflecting the progressive change of kinematic style from pure left lateral strike slip faulting to left lateral reverse faulting along the three western segments we measure cumulative displacements that are multiples of the 1957 coseismic offset which may be consistent with a characteristic slip moreover using these data we re estimate the moment magnitude of the gobi altay earthquake at m w 7 78 7 95 combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of similar to 2500 5200 yr for past earthquakes along the different segments of the western bogd fault this suggests that the three western segments of the bogd fault and the gurvan bulag thrust fault a reverse fault bounding the southern side of the ih bogd range that ruptured during the 1957 earthquake have similar average recurrence times and therefore may have ruptured together in previous earthquakes as they did in 1957 these results suggest that the western part of the bogd fault system including the gurvan bulag thrust fault usually behaves in a characteristic earthquake mode

scarp degraded by linear diffusion inverse solution for age under the assumption that landforms unaffected by drainage channels are degraded according to the linear diffusion equation a procedure is developed to invert a scarp profile to find its diffusion age diffusion age having dimension length 2 is the product of diffusivity times chronological age the second moment of scarp slope grows linearly with age this fact together with an assumption about initial scarp shape allows the inverse determination of diffusion age age found assuming a vertical initial scarp is termed apparent age any nonvertical initial scarp profile has a nonzero initial apparent age true diffusion age differs from apparent age by a fraction of scarp offset squared the inverse procedure applied to synthetic data yields the following rules of thumb evidence of initial scarp shape has been lost when apparent age reaches twice its initial value if a scarp is formed by two events the inversion gives their offset weighted mean age with an error that is a fraction of offset squared a scarp that appears to have been formed by one event may have been formed by two with an interval between them as large as apparent age after scarps of two fault traces have diffused to appear as one the error in inferred age may be as large as half the apparent age variation of apparent age along strike would indicate multiple fault traces the simplicity of scarp profile measurement and this inversion makes profile analysis attractive if linearity of the flow law time for a free face to be reduced to the angle of repose and variation of diffusivity with climate and material could be established profile analysis would become a reliable dating technique

an indication of time dependent seismic behavior an assessment of paleoseismic evidence from the arava fault israel abstract we discuss the implications of 56 kyr of paleoseismic data from a fault on the southern segment of the arava fault system in israel at least nine events are evident beginning 37 ka we study in detail the frequency magnitude relation for the fault and develop a bayesian analysis to compare the characteristic earthquake ce model and the gutenberg richter gr model our analysis leads to the conclusion that there was a change in seismic behavior at about 14 ka from 37 ka to 14 ka the seismic activity is best described by the ce model from 14 ka to the present there is no strong indication favoring one model over the other the earthquake record is somewhat more consistent with the classical gr equation than with the ce model if one does assume that the ce model is appropriate for the younger episode then there is evidence of a change in the characteristic magnitude thus there is evidence of a change in earthquake behavior on the fault segment 14 ka

horizontal surface slip distribution through several seismic cycles the eastern bogd fault gobi altai mongolia abstract the 1957 mw 8 1 gobi altai earthquake southern mongolia produced a 360 km long surface rupture along the eastern bogd fault cumulative offsets of geomorphic features suggest that the eastern bogd fault might produce characteristic slip over the last seismic cycles using orthophotographs derived from a dataset of historical aerial photographs acquired in 1958 we measured horizontal offsets along two thirds 170 km of the 1957 left lateral strike slip surface rupture we propose a new empirical methodology to extract the average slip for each past earthquake that could be recognized along successive fault segments to determine the slip distribution associated with successive past earthquakes our results suggest that the horizontal slip distribution of the 1957 gobi altai earthquake is fairly flat with an average offset of 3 5 m 1 3 m a combination of our lateral measurements with vertical displacements derived from the literature allows us to re assess the magnitude of the gobi altai earthquake to be between mw 7 8 and mw 8 2 depending on the depth of the rupture and related value of the shear modulus when comparing this magnitude to magnitudes derived from seismic data it suggests that the rupture may have extended deeper than the 15 km to 20 km usually considered for the seismogenic crust we observe that some fault segments are more likely than others to record seismic deformation through several seismic cycles depending on the local rupture complexity and geomorphology additionally our results allow us to model the horizontal slip function for the 1957 gobi altai earthquake and for three previous paleoseismic events along 70 of the studied area along about 50 of the fault sections where we could recognize three past earthquakes our results suggest that the slip per event was similar for each earthquake

high resolution spatial rupture pattern of a multiphase flower structure rex hills nevada new insights on scarp evolution in complex topography based on 3 d laser scanning fault scarps represent the most obvious expression of tectonic activity at the earth9s surface studies on scarp morphology place constraints on fault kinematics and scarp degradation processes and were often based on geomorphic dating techniques fault scarps exposed in areas of simple topography facilitate data acquisition and interpretation whereas little work had been done where fault scarps are superimposed on complex dissected topography fault scarps developed in complex topography are commonly observed along flower structures and at tips of strike slip faults such structures are important elements for evaluating the evolution and linking of strike slip fault systems and appear to be scale independent from several meters to hundreds of kilometers we examined the detailed meter to hundred meter scale structure and surface expression of a flank of one fault scarp bounded pressure ridge rex hills flower structure by combining field mapping with high resolution digital elevation model dem analysis based on terrestrial laser scanning we generated a detailed dem and extracted high resolution topographic cross sections which enabled us to identify fault scarps and to determine their relative ages and geometry our study site is located on the transpressional left bend between the pahrump and amargosa segments of the dextral stateline fault system the topography is characterized by alternating valleys and ridges each 100 m long relief of 4 m we observed the following the southern rex hills slope exhibits three fault scarps related to three reverse fault branches the basal scarp scarp 1 is most continuous and exhibits five segments the upper two scarps scarps 2 and 3 are less continuous furthermore fault scarps exposed on ridge crests are more numerous up to four to five scarps and smaller 5 m high valleys often exhibit single large 10 m high smoothed scarps to easily detect differences between the scarps we evaluated the height and slope angle of the scarps using topographic cross sections our analysis indicates that scarp shape is influenced by fault dip lithology and degradation processes resulting in large scatter and broad overlap in scarp height slope angle space the analysis further indicates that scarp degradation is stronger in the valleys and that the preservation potential of small individual fault scarps is therefore greater on the ridge crests we compared our fault scarp data with published calibrated data yielding an age of 2 ka for the rex hills scarps consistent with an earlier finding this suggests that the scarp shape mainly reflects progressive degradation since the most recent surface rupture our approach of analyzing high resolution topographic data of closely spaced fault scarps is promising especially when combined with subsurface data as well as geochronological and paleoseismic data and it provides a basic scheme for analyzing scarp populations in a complex topographic region despite the absence of subsurface data our approach allowed the study of complex high resolution fault scarp morphologies across a flower structure for the first time

morphologic dating of the pre 1983 fault scarp on the lost river fault at doublespring pass road custer county idaho abstract the focus of this study is the age of the earthquake antecedent to the 1983 borah peak earthquake in the vicinity of doublespring pass road where the faulting signature of both events has been studied in detail through trenching operations in 1976 and again in 1984 we sample the morphologic expression of the pre 1983 event with six profiles along a 100 m segment of the fault scarps adjacent to and just north of the trench site where both the 1983 and pre 1983 scarps are remarkably linear and regular diffusion equation modeling of the profiles suggest that the age of the pre 1983 event is 6000 to 8000 yr before present exclusive of the uncertainties in applying the lakes bonneville and lahontan mass diffusivity to this central idaho setting

forebergs flower structures and the development of large intra continental strike slip faults the gurvan bogd fault system in mongolia the gurvan bogd mountains of the gobi altay mongolia contain a system of strike slip faults with a reverse component part of which moved in a large earthquake mw 8 0 in 1957 adjacent and sub parallel to the main ranges are numerous thrust related folds thrust faults and elongated low ridges forebergs all of which result from the shortening component on the fault zone the appearance of these thrust related structures is varied depending on their stage of development preservation and exposure evidence from geomorphology and surface ruptures suggests that they may all serve a common function which is to broaden the deforming zone by creating new structures that are able to accommodate both the strike slip and the shortening components of motion the geomorphology further suggests that these new structures then evolve by lateral propagation and increase in amplitude to eventually merge and form through going new faults subparallel to the old in their early stages the new faults and related structures appear to be influenced by the underlying sediments adjacent to the main range which may include weak layers such as lake beds that can ultimately cause the collapse of foreberg ridges in landslides the migration of faulting away from the main range is likely to be driven by stresses associated with topography which in turn is a consequence of the shortening component the evolution described here is thus peculiar to strike slip faults with a reverse component and can form many of the features of the flower structures that are often described in such oblique shortening zones although the shortening component is often localized in restraining bends its origin may ultimately be related to rotations about vertical axes which are common in deforming continental regions

field examples of strike slip fault terminations in mongolia and their tectonic significance deformation at the ends of large intracontinental strike slip faults that do not simply link other major structures often involves rotations about a vertical axis we use earthquake slip vectors surface rupture in earthquakes and geomorphology to examine the ends of three major strike slip faults in mongolia in these places a simple pattern is seen consisting of a thrust fault on one side with a displacement that decreases away from the strike slip fault consistent with local rotational deformation strike slip faults that terminate in this way allow the style of faulting to change spatially within a deforming area for example from dominantly strike slip to dominantly dip slip while still accommodating the overall deformation required by larger scale regional motions such a change in fault style should also be accompanied by a change in the rotation rate about a vertical axis which may be detected paleomagnetically the kind of strike slip fault termination described here may have consequences for how large strike slip fxaults evolve and grow and for the variation in displacement along their length

in situ10be 26al exposure ages at meteor crater arizona a new method of dating the surface exposure of rocks from in situ production of 10be and 26al has been applied to determine the age of meteor crater arizona a lower bound on the crater age of 49 200 1 700 years has been obtained by this method

investigating paleoseismicity using fault scarp morphology of the dushanzi reverse fault in the northern tian shan china abstract this study uses the morphology of fault scarps to study the paleoseismic history of the dushanzi reverse fault drf in the northern tian shan region china using high resolution lidar dems to create a large number of scarp profiles we detected slope breaks in the fault scarp morphology to quantify the number of paleoearthquakes that occurred on the scarps and obtained the along strike scarp height distribution to determine the cumulative and single event vertical displacements our results revealed four surface rupturing events with similar co seismic vertical displacements of 1 4 m via the statistical analysis of displacement datasets and slope breaks which were in agreement with the findings from paleoseismic trenching we then assessed the paleomagnitudes using the empirical scaling relationships between moment magnitude and rupture parameters and the recurrence interval for surface rupturing events using the formation ages of the displaced terrace surfaces the results indicate that the possible magnitudes range from mw 6 5 to 6 7 even reaching mw 7 2 in the case of a multi fault rupture of the entire anticline fault belt with an average recurrence interval of 2 4 3 0 ka this study also demonstrates the importance of using high resolution topographic data in paleoseismic investigations which enables the determination of fine scale tectono geomorphic interpretations and detailed offset measurements over large regions along the fault

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient