the ms 7 3 1992 suusamyr kyrgyzstan earthquake in the tien shan 2 aftershock focal mechanisms and surface deformation abstract the m s 7 3 suusamyr earthquake of 19 august 1992 was a large thrust type earthquake in the northern tien shan of kyrgyzstan an intracontinental mountain belt in central asia focal mechanisms of both the mainshock and 13 moderate sized aftershocks are consistent with a seismotectonic setting that is dominated by nnw sse horizontal compression which manifests itself in reverse faulting along roughly east west trending steeply dipping fault planes the earthquake produced surface faulting at two widely separated locations along two different fault segments the total length of which was less than 4 km detailed measurements at one of the locations indicate a net slip of at least 4 2 0 4 m a wide variety of secondary surface effects was observed in the macroseismic zone that extended over an area of 2500 km 2 the lack of extensive surface rupture from such a large event can be explained by a combination of 1 redistribution of the net slip at depth among the secondary splays that branches out from the main fault near the surface and 2 variable surface slip over the fault length the active deformation associated with this event documents a structural style that involves steeply dipping reverse faults extending from mid crustal depths to the surface at nearly uniform dip accommodating crustal shortening in the interior of the tien shan

local scouring at grade control structures in alluvial mountain rivers 1 scour holes below 73 grade control structures check dams and bed sills in six mountain rivers located in the eastern italian alps have been surveyed the most likely formative water discharge is used to evaluate jet thickness at each structure which along with drop height appears to determine scour hole dimensions as shown by the consistent trends observed for nondimensional plots of both maximum scour depth and length versus the respective drop ratio sediment differences regarding size and lithology apparently play a minor role in determining scour hole dimension measured maximum scour depths are well predicted by a semiempirical equation developed through laboratory results showing an average relative error of 0 13 scour hole geometry is described by several ratios that are thought to represent approximately invariant characteristics a new energy based normalization for scour hole dimensions is proposed as the most suited to evaluate the role of jet geometry and aeration upon scouring efficiency it is noteworthy that the ratio between the maximum scour depth and the total energy available at a drop tends toward an asymptotic value around unity for increasing drop heights

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

modelling seismites with a digital shaking table abstract soft sediment deformation structures induced by seismically triggered liquefaction and or fluidization seismites have been reproduced with a digital shaking table we have used natural sediments with variable granulometric ranges clay silt and sand and an earthquake simulator that is able to reproduce real tridimensional seismograms acceleration and pore pressure recording allowed us to follow liquefaction and or fluidization processes in unconsolidated sediments during earthquakes different types of seismites were produced by variations in the tested sedimentary column

local scouring at bed sills in a mountain river plima river italian alps the main characteristics of local scouring below 26 bed sills constituting a sequence of grade control structures in a mountain river plima river italian alps have been surveyed bed sills were built with concrete strengthened boulders and other loose boulders were placed in the river bed to enhance habitat diversity for fish the most likely formative water discharge is used to evaluate specific flow energy at each bed sill measured maximum scour depths are well predicted by an empirical equation developed through laboratory results showing an average relative error of 0 15

late quaternary slip rates across the central tien shan kyrgyzstan central asia 1 slip rates across active faults and folds show that late quaternary faulting is distributed across the central tien shan not concentrated at its margins nearly every intermontane basin contains neogene and quaternary syntectonic strata deformed by holocene north south shortening on thrust or reverse faults in a region that spans two thirds of the north south width of the central tien shan slip rates on eight faults in five basins range from 0 1 to 3 mm yr fault slip rates are derived from faulted and folded river terraces and from trenches radiocarbon optically stimulated luminescence and thermoluminescence ages limit ages of terraces and aid in their regional correlation monte carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95 confidence limits faults in basins appear to merge at relatively shallow depths with crustal scale ramps that underlie mountain ranges composed of pre cenozoic rocks the sum and overall pattern of late quaternary rates of shortening are similar to current rates of north south shortening measured using global positioning system geodesy this similarity suggests that deformation is concentrated along major fault zones near range basin margins such faults separated by rigid blocks accommodate most of the shortening in the upper crust index terms 8107 tectonophysics continental neotectonics 9320 information related to geographic region asia 8010 structural geology fractures and faults

effect of sill spacing and sediment size grading on scouring at grade control structures sequences of arti cial steps are sometimes used to reproduce the natural step pool morphology of high gradient streams the depth length and shape of the scour holes in gravel bed rivers can be predicted reasonably using recently developed formulae however the properties of the scour holes can sometimes be affected by the distance between structures this effect is called geometrical interference and leads to a reduction of the scour hole compared to its potential size geometrical interference may occur in sequences of arti cial steps in high gradient torrents where structures are sometimes built at distances of a few tens of metres apart but may also apply to natural step pool systems in this paper a series of tests have been conducted to determine the effect of bed sill spacing and sediment grading on the potential erosion by jets forming over the sills a new formula is derived applicable to high gradient streams slope 0 04 which can be applied to the special case of scour holes developed by interfering sills sediment size gradation not accounted for in previous formulae is found to have a signi cant effect on the scour dimensions and is included in the new predictive formula copyright 2004 john wiley sons ltd

pool and riffle characteristics in relation to channel gradient abstract the depths of pools relative to the dephts of runs and riffles were correlated with reach scale channel gradient along three rivers in coastal northern california the sample included 122 pools formed in channels with gradients from 0 172 to 0 002 relative pool depth on these rivers and relative distance between pools increase as channel gradient decreases mean pool riffle depth is 2 8 1 at the highest channel gradient and 6 2 1 at the lowest gradient while mean pool riffle length is 1 0 8 at high channel gradient and 1 1 8 at low channel gradient we hypothesize that these trends reflect changes in energy expenditure with decreasing gradient as a result of the flow s ability to erode its channel boundaries channel reaches with high gradients are characterized by resistant channel boundaries coarse material and relatively low discharge and total stream power channel reaches with low gradients have less resistant channel boundaries finger grained bed material and higher values of discharge and total stream power these changes in channel and flow characteristics with decreasing gradient result in flows in high gradient reaches expending a greater proportion of their energy in overcoming boundary and internal resistance with less energy available for channel bed scour and the formation of pools in their relatively resistant channels in contrast with less energy available for channel bed scour the channel bed creating deeper pools because the channel boundaries are less resistant and the proportion of flow energy available for sediment entrainment and transport should be greater

sediment supply and local scouring at bed sills in high gradient streams 1 this paper presents the results of an experimental study about the pattern of local scouring generated at the toe of bed sills which are commonly built in steep gravel bed mountain streams the aim of this study is to evaluate the effect of upstream sediment supply on the scour depth and shape the experiments simulated conditions of a steady upstream sediment supply which had the same grain size composition as the sediment deposit placed on the bed of the flume the geometric characteristics of three scour holes developed under conditions of steady flow discharge and steady upstream sediment supply were measured during 48 different tests this provided a data set containing measurements of 144 scour holes three different sediment feed rates were used and tests were also performed with clear water conditions geometric interference between sills was not observed a natural river gravel with a limited grain size was used the collected data were analyzed using nondimensional groups developed in previous clear water studies it is shown that the imposed sediment transport does not require the introduction of new dimensionless parameters into existing scour depth and length prediction formula the effects of sediment feed are shown to be incorporated in the existing dimensionless parameters the new data set was used to recalibrate existing scour depth formula the influence of jet erosion on scour geometry is also discussed inspection of the data indicates a possible two stage behavior with the threshold between behaviors related to the ratio of the value of the morphological jump created at a scour hole and the flow specific energy at the bed sill

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

bed stability variations after check dam construction in torrential channels south east spain the effects of check dams on the bed stability of torrential channels have been analysed in several tributary basins of the segura and guadalentin rivers south east spain in order to illustrate the large variability in channel bed forms and bed sediment sizes along the stream 52 reaches of 150 m in length were surveyed this variability is due to the behaviour of check dams which depends on bedrock control bed slope channel roughness lateral sediment input and a highly variable sediment transport capacity though the purpose of check dams is to diminish the boundary shear stress reducing the longitudinal slope and to stabilize the channel bed downstream they reduce the volume of channel stored material favouring local scour processes and upstream they can destabilize the sidewalls the results enable us to evaluate the impact of every check dam on the bed morphology distinguishing the structures installed in limy marl areas e g catchment of the carcavo rambla cieza and in schist and slate terrains e g catchment of the torrecilla rambla close to lorca in the first type bedrock and moderately thick granular beds predominate downstream from the check dams so that the length of bedrock reaches and increase of roughness due to scour processes are the best indicators to verify its geomorphological effectiveness on the other hand the metamorphic areas drained by ramblas and gullies produce great quantities of gravel that are retained by check dams creating more uniform and permeable beds where the balance between sedimentation and scouring and the ratio c84 0 rbs appear to be the parameters most frequently adopted to estimate the bed stability analysis of slope adjustments and the application of other indices to estimate the bed substrate stability lrbs sri and the structural influence of the dams sibs corroborate the differences in bed stability found in the corrected reaches in each catchment copyright 2007 john wiley sons ltd

cenozoic tectonic and geodynamic evolution of the kyrgyz tien shan mountains a review of geological thermochronological and geophysical data abstract the complex crustal structure of the tien shan has a strong impact on the distribution of strain induced by the india eurasia collision with intracontinental deformation in eurasia s interior as a distant effect the northward propagation of the india eurasia deformation front is suggested by the rejuvenation of mountain ranges and intermittent intramontane basins the tien shan basement is formed by the rigid heterogeneous precambrian blocks microcontinents of tarim issyk kul or central tien shan and aktyuz boordin surrounded by a soft matrix of paleozoic accretion collision belts the kyrgyz tien shan mountains are situated between the active structures of the tarim plate and the pamir indenter south and the stable kazakhstan shield north underplating by the tarim plate and thrusting by the pamirs are responsible for the building of the cenozoic tien shan the reactivation of its inherited structural fabric and the tectonic layering of the upper lithosphere underlying the area large earthquakes m 6 delineate the northern and southern margins of the issyk kul microcontinent indicating that crustal heterogeneity influenced the location of active structures in the northern kyrgyz tien shan

late pleistocene seismites from lake issyk kul the tien shan range kyrghyzstan abstract the aim of the study is to record the occurrence of sediment deformation structures in one of the tectonically most active areas on the globe the tien shan range in central asia and to examine the significance of the deformations as indicators of palaeoseismicity soft sediment deformation structures in form of balls and pseudo nodules are exposed in the issyk kul basin within interfingering beds of shallow lacustrine beach and fluviatile origin additional deformation structures that were encountered are a complex and chaotic folded structure giant balls and a pillar structure which has not been previously reported where marl intrudes down into coarse pebbley sand and forms pillar morphology liquefaction features and bedforms related to storm and breaking waves were not encountered neither was there evidence of turbidites seven field criteria for relating soft sediment deformation to palaeoseismic triggering provide strong evidence for a seismic origin of the deformation structures empirical relationships between magnitude and the maximum distance from an epicenter to liquefaction sites make the active epicentral zone north of lake issyk kul with its frequent high magnitude events the most favorable source for the deformation structures luminescence dating of the sediments gives a time window of 26 2 1 to 10 5 0 7 ka bp indicating latest pleistocene seismic activity

kinematics topography shortening and extrusion in the india eurasia collision we examine the problem of partitioning between shortening and extrusion in the india asia collision since 45 ma we compute the amount of shortening expected from the kinematics of india s motion with respect to eurasia using the reconstruction at collision time to put bounds on the possible amounts of surface loss within greater india and within eurasia we then compute the amounts of surface loss corresponding to the thickened crust of tibet and of the himalayas assuming conservation of continental crust the spatial distribution of the topography reveals a large systematic deficit of crustal thickening distributed rather uniformly west of the eastern syntaxis but an excess of shortening east of it this distribution indicates an important eastward crustal mass transfer however the excess mass east of the eastern syntaxis does not account for more than one third to one half of the deficit west of the eastern syntaxis the deficit may be accounted either by loss of lower crust into the mantle for example through massive eclogitization or by lateral extrusion of nonthickened crust a mass budget of the crust of the himalayas indicates that lower crust has not been conserved there but the deficit is so large that local loss in the mantle is unlikely to be the unique cause of the deficit alternatively following zhao and morgan 1985 lower crust may have been transferred below the tibetan crust we conclude that a combination of possible transfer of lower crust to the mantle by eclogitization and lateral extrusion has to account for a minimum of one third and a maximum of one half of the total amount of shortening between india and asia since 45 ma this conclusion leaves open the possibility that the partitioning between extrusion and loss of lower crust into the mantle on the one hand and shortening on the other hand has significantly changed during the 45 m y history of the collision

mesozoic and cenozoic tectonic history of the central chinese tian shan reactivated tectonic structures and active deformation 1 the present day topography of the tian shan range is considered to result from crustal shortening related to the ongoing india asia collision that started in the early tertiary in this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event apatite fission track analysis and u th he dating on apatite and zircon indicate that inherited paleozoic structures were reactivated in the late paleozoic early mesozoic during a cimmerian orogenic episode and also in the late cretaceous paleogene around 65 60 ma these reactivations could have resulted from the accretion of the kohistan dras arc or lithospheric extension in the siberia mongolia zone activity resumed in the late mesozoic prior to the major tertiary orogenic phase finally the ongoing deformation which again reactivates inherited tectonic structures tends to propagate inside the endoreic basins that were preserved in the range leading to their progressive closure this study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas

cenozoic deformation and exhumation history of the central kyrgyz tien shan new low temperature thermochronological data from 80 samples in eastern kyrgyzstan are combined with previously published data from 61 samples to constrain exhumation in a number of mountain ranges in the central kyrgyz tien shan all sampled ranges are found to have a broadly consistent cenozoic exhumation history characterized by initially low cooling rates 1 c myr followed by a series of increases in exhumation that occurred diachronously across the region in the late cenozoic that are interpreted to record the onset of deformation in different mountain ranges combined with geological estimates for the onset of proximal deformation our data suggest that the central kyrgyz tien shan started deforming in the late oligocene early miocene leading to the development of several widely spaced mountain ranges separated by large intermontane basins subsequently more ranges have been constructed in response to significant shortening increases across the central kyrgyz tien shan notably in the late miocene the order of range construction is interpreted to reflect variations in the susceptibility of inherited structures to reactivation reactivated structures are also shown to have significance along strike variations in fault vergence and displacement which have influenced the development and growth of individual mountain ranges moreover the timing of deformation allows the former extent of many intermontane basins that have since been partitioned to be inferred this can be linked to the highly time transgressive onset of late cenozoic coarse clastic sedimentation

exhumation of basement cored uplifts example of the kyrgyz range quantified with apatite fission track thermochronology 1 the kyrgyz range the northernmost portion of the kyrgyzstan tien shan displays topographic evidence for lateral propagation of surface uplift and exhumation the highest most deeply dissected segment lies in the center of the range to the east topography and relief decrease and preserved remnants of a cretaceous regional erosion surface imply minimal amounts of bedrock exhumation the timing of exhumation of range segments defines the lateral propagation rate of the range bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology new multicompositional apatite fission track aft data from three transects from the eastern kyrgyz range combined with published aft data demonstrate that the range has propagated over 110 km eastward over the last 7 11 myr on the basis of the thermal and topographic evolutionary history we present a model for a time varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift easily eroded cenozoic sedimentary rocks overlying resistant basement control early rapid exhumation and exhibit slow surface uplift rates as increasing amounts of resistant basement are exposed exhumation rates decrease while surface uplift rates are sustained or increase thereby growing topography as the range becomes high enough to cause ice accumulation and to develop steep river valleys fluvial and glacial erosion becomes more powerful and exhumation rates once again increase independently determined range normal shortening rates also varied over time suggesting a feedback between erosional efficiency and shortening rate

squeezing river catchments through tectonics shortening and erosion across the indus valley nw himalaya tectonic displacement of drainage divides and the consequent deformation of river networks during crustal shortening have been proposed for a number of mountain ranges but never tested in order to preserve crustal strain in surface topography surface displacements across thrust faults must be retained without being recovered by consequent erosion quantification of these competing processes and the implications for catchment topography have not previously been demonstrated here we use structural mapping combined with dating of terrace sediments to measure quaternary shortening across the indus river valley in ladakh nw himalaya we demonstrate 0 21 m k y 1 of horizontal displacement since ca 45 ka on the stok thrust in ladakh which defines the southwestern margin of the indus valley catchment and is the major back thrust to the tethyan himalaya in this region we use normalized river channel gradients of the tributaries that drain into the indus river to show that the lateral continuation of the stok thrust was active for at least 70 km along strike shortening rates combined with fault geometries yield vertical displacement rates that are compared to time equivalent erosion rates in the hanging wall derived from published detrital 10be analyses the results demonstrate that vertical displacement rates across the stok thrust were approximately twice that of the time equivalent erosion rates implying a net horizontal displacement of the surface topography and hence narrowing of the indus valley at 0 1 m k y 1 a fill terrace records debris flow emplacement linked to thrust activity resulting in damming of the valley and extensive lake development conglomerates beneath some of the modern alluvial fans indicate a northeastward shift of the indus river channel since ca 45 ka to its present course against the opposite side of the valley from the stok thrust the integration of structural topographic erosional and sedimentological data provides the first demonstration of the tectonic convergence of drainage divides in a mountain range and yields a model of the surface processes involved

seismic moments of major earthquakes and the rate of shortening across the tien shan three twentieth century earthquakes that richter assigned m 8 and two of comparable magnitude in the nineteenth century imply rapid deformation within the tien shan seismic moment tensors of major earthquakes in this century suggest an average shortening rate of 7 2 mm yr 1 across the tien shan in the western part however where three of the five largest earthquakes occurred the calculated rate is consistent with the value of 20 mm yr 1 measured using gps in that area by abdrakhmatov et al as avouac et al suggested the high rate in the western part apparently is a manifestation of counter clockwise rotation of the tarim basin relative to eurasia about an axis near the east end of the tien shan

earthquakes and deformational structures seismites in holocene sediments from the himalayan andaman arc india soft sediment deformational structures from the himalayan arc caused by episodic earthquake recurrences during the holocene recent are produced by the ongoing tectonic processes these small scale subtle structures occur along some major thrusts in the garhwal himalaya and vary from normal faults in the lower zone to compressional structures in the middle zone along the main central thrust in the tons valley the latter includes isoclinal angular kink and disharmonic folds with discrete displacements along their axial surfaces thrusts with decollement listric and overstep thrusts in duplex style and load slumping the upper zone is marked by very low angle thrusts with left lateral displacement and associated displacement shears d riedel shears r and thrust shears p as well as small scale sporadic kinks three zones reveal changing tectonic character from gravity tectonics in the lower zone to compression in both the middle and upper zones with the maximum principal stress 1 oriented n60 to n110 respectively along the tons thrust post depositional structures include drag along normal fault zone characterized by d r and p shears and conjugate fractures that provide localized orientation of stresses 1 at 75 n60 2 at 12 n280 and 3 at 12 n290 earthquake induced liquefaction and subtle variations in physiomechanical properties of soft sediments have primarily controlled the deformational pattern due to localized tectonic stresses ground and sediment deformations during two earthquakes in the himalayan andaman arc provide additional support for the seismogenic origin of such structures preserved in loose or consolidated sediments

cretaceous paleogene basaltic rocks of the tuyon basin nw china and the kyrgyz tian shan the trace of a small plume abstract the tuyon basin nw china and the central portion of the kyrgyz tian shan preserve a volumetrically small series of basaltic extrusive and intrusive units emplaced primarily in mesozoic paleogene sedimentary rocks four units from the tuyon basin yield 40 ar 39 ar ages of 67 59 46 and between 110 and 120 ma major and trace element analysis combined with sr nd and pb isotopic data suggest that these units were derived from apparently ocean island basalts oib like mantle melts which have characteristics close to asthenospheric prema mixed with an enriched component in the continental mantle lithosphere or emplaced with some crustal contamination two basalts from kyrgyzstan were also dated by 40 ar 39 ar as 54 ma these results agree with previous k ar analysis which show that most kyrgyz basalts were emplaced during the eocene major element data from the kyrgyz basalts knauf et al 1980 fortuna et al 1994 show strong similarities with the tuyon data suggesting that the more extensive tuyon data can be taken as representative of the entire basaltic suite there is little geological data to support either late cretaceous paleogene rifting or the presence of a large plume beneath the region instead these magmas point to the presence of a small thermally anomalous region in the mantle beneath the central tian shan which might best be described as a small plume which probably rooted at a shallow level in the asthenosphere

building the northern tien shan integrated thermal structural and topographic constraints abstract paired apatite fission track and u th he dates provide the first late cenozoic cooling ages for the northern tien shan these data clearly argue for pulsed deformation since the late miocene with early 10 11 ma and late 0 3 ma intervals of rapid exhumation separated by an extended interval of much slower rates by integrating these bedrock cooling rates with shortening estimates derived from a balanced section detrital cooling ages and geomorphological estimates of conditions before deformation we reconstruct a four stage history of range growth and exhumation following 100 m yr of tectonic quiescence abruptly accelerated rock uplift exhumation and cooling in the kyrgyz range commenced at 11 ma with rates exceeding 1 km m yr during the subsequent 7 m yr deformation and cooling rates decreased three to sixfold before accelerating by comparable amounts during the past 3 m yr since mid miocene times the surface elevation of the kyrgyz range has increased 2 km consistent with

the ms 7 3 1992 suusamyr kyrgyzstan earthquake 1 constraints on fault geometry and source parameters based on aftershocks and body wave modeling we investigated the suusamyr kyrgyzstan earthquake of 19 august 1992 using aftershock data teleseismic body wave modeling and field observations aftershocks were recorded by the iris kyrgyzstan broadband network a temporary six station aftershock network and a regional network operated by the kyrgyz institute of seismology the aftershocks which range in depth from the surface to 18 km defined a 50 10 km long rupture zone that dips 50 13 to the south and strikes roughly east west the base of the eastern end of the aftershock zone shallowed to the east along strike and may represent a lateral ramp the surface ruptures also had an east west strike and dipped south but the total length less than 4 km was much shorter than the aftershock zone a teleseismic body wave inversion using a point source and a directivity correction yields a focal mechanism with a strike of 221 dip of 46 and a slip of 43 we obtained a moment of 4 1 1019 n m with a centroid depth between 5 and 21 km the rupture propagated along an azimuth of 330 60 which matches the relative location of the mainshock with respect to the aftershock zone the results of the aftershock study and teleseismic inversion yield a clear picture of the fault geometry of a large thrust earthquake

erosional processes as a control on the structural evolution of an actively deforming fold and thrust belt an example from the pamir tien shan region central asia the foreland of the pamir mountains displays an unusual orogenic topography in which an active north vergent thin skinned fold and thrust belt shows no topographic foredeep in advance of the thrust sheets instead the thrusts are impinging on a topographic barrier formed by the southern edge of the tien shan the deformation front of this thrust belt is coincident with a deeply incised river valley occupied by a large river the surkhob we suggest that this river played a key role in the evolution of this orogenic system by acting as a lateral conveyor belt for the transport of mass delivered to the deformation front by thrusting on the basis of reconnaissance geologic mapping it is clear that the present system developed in the late miocene or pliocene when the tien shan were uplifted within an existing foreland basin as the tien shan highland developed a longitudinal river within the foreland basin was trapped between the north directed thrusts and the tien shan highland with continued deformation the river was squeezed into a narrow canyon and since that time the system has been in an unusual equilibrium where thrusting acts to push the deformation front northward toward the tien shan but fluvial erosion and transport act to keep it in a constant position geologic relationships indicate that the vakhsh thrust the frontal thrust of the north directed system is now emerging on an erosion surface beneath a thin quaternary cover throughout the canyon suggesting that the river has been unable to keep pace with the tectonic mass flux and the thrust front as well as the river have been pushed northward across the beveled edge of what was originally the southern edge of the tien shan we suggest that the original deformation front of the tien shan now lies 10 km south of the present day topographic front of the tien shan beneath the north vergent vakhsh thrust as indicated by 1 a near vertical zone of intense basement seismicity the petrovsky seismic zone 2 an en echelon array of backthrusts along the south flank of the peter the first range and 3 footwall cutoff relationships of the vakhsh thrust system order of magnitude mass balance considerations based on sediment budgets support this conclusion but suggest that the mass imbalance may be small thus large volumes of material may have passed through the thrust fron and been carried out of the system by erosion a relationship that may account for the narrow 30 50 km wide band of deformed sedimentary rock between the pamir salient and the tien shan the present near equilibrium is maintained by long term tectonic transport rates and fluvial transport rates the latter closely linked to climate particularly precipitation thus although there is apparently a mass pile up within this system other systems of this type might show grossly different structural and stratigraphic relationships depending on the amount of rainfall and corresponding variations in rates of fluvial sediment transport similar settings can be recognized in the active thick skinned thrust systems of the tien shan and ancient systems like the laramide belt of western north america

seismites as an indicator for determination of earthquake recurrence interval a case study from ercis fault eastern anatolia turkey abstract the southern part of the eastern anatolian plateau is a key region for understanding the tectonic activity and related deformation patterns of the arabian eurasian collision zone the geological record of seismic events collected from lacustrine deposits of lake van basin is a critical requirement for seismic hazard assessment and seismic risk reduction our paleoseismic investigations revealed well preserved seismites at five locations in late pleistocene lacustrine deposits the seismites were dated using an optically stimulated luminescence dating method and were arranged according to their ages their type such as convolute dish and pillar flame and ball and pillow structures as well as their locations ages and stratigraphic distribution enable us to identify the responsible fault and the earthquake recurrence interval on the basis of these properties the ercis fault has been recognized as the structure responsible for creating the seismites the time span between the seismites indicates an apparent earthquake recurrence interval of 125 250 years for large earthquakes m 5 related to the ercis fault the method applied here enriches our knowledge on the seismic hazards present in the northern lake van region

timing and process of river and lake terrace formation in the kyrgyz tien shan abstract well preserved flights of river and lake terraces traverse an actively deforming rangefront and form a link between glaciated mountains and a large intermontane lake in the issyk kul basin of the kyrgyz tien shan we investigated the history and geometry of these lake and river terraces using geologic mapping surveying and radiocarbon and terrestrial cosmogenic nuclide dating a prominent late pleistocene highstand of the lake occurred over at least the period of 43 25 ka followed by a period of deep regression and subsequent rise of the lake to the modern sill level in the late holocene major aggradation of the most prominent latest quaternary river terrace along the ak terek and barskaun rivers likely started at 70 60 ka coincident to the local last glacial maximum in this region in contrast to some models of aggradation and incision the rivers appear to have stayed near the top of the fill for 20 ka incising subtly below the top of this fill by 37 ka locally deep incision likely did not occur until the peak deglaciation in the latest pleistocene older dated terrace surfaces are consistent with one major terrace forming event per glacial constant deformation and incision rates and typical fluvial gradients lower than the modern incising streams the dating confirms regional terrace correlations for the most prominent late quaternary terraces but correlating higher terraces is complicated by spatially varying uplift rates and preferential terrace preservation between basins in the tien shan

channel morphology gradient profiles and bed stresses during flood in a step pool channel abstract the stability of a step pool channel is investigated on the basis of measurements during a median annual flood the study reaches range in gradient from 5 to 10 and the flow was 3 m3 s 1 in an 8 m wide channel the estimated shear stress based on the channel gradient was 102 pa which implies that the channel ought to move half meter class boulders calculations of the shear stress using flow resistance equations yield values of about 30 pa these figures imply that the largest boulders in the channel could be moved in fact the channel is stable the effective stress remains well below the threshold to move the large structure forming boulders the steps are stable structures that result from interlocking of the larger stones they are semi randomly located depending on the location of keystones that are deposited in the channel by debris flows or fall out of the banks the high variation in step pool wavelength step height residual pool depth and pool length is indicative of the random nature of step location and structure along a reach there is no convincing evidence that special conditions govern their formation

morphological response to quaternary deformation at an intermontane basin piedmont the northern tien shan kyrghyzstan abstract the tien shan is a most active intracontinental mountain building range with abundant quaternary fault related folding in order to improve our understanding of quaternary intermontane basin deformation we investigated the intermontane issyk kul lake area an anticline that was up warped through the piedmont cover causing partitioning of the alluvial fan veneer to follow the morphological scenario during the warping process we relied on surface exposed and trenched structures and on alluvial fans and bajadas as reference surfaces we used air photos and satellite images to analyze the spatial temporal morphological record and determined the age of near surface sediments by luminescence dating we demonstrate that the up warped ak teke hills are a thrust generated subdued anticline with strong morphological asymmetry which results from the coupling of the competing processes of up warp and erosional feedback the active creeks across the up warped anticline indicate that the antecedent drainage system kept pace with the rate of uplift the rivers which once sourced the piedmont like the toru aygyr kultor and the dyuresu became deeply entrenched and gradually transformed the study area into an abandoned morphological surface the up warp caused local lateral drainage diversion in front of the northern backlimb and triggered the formation of a dendritic drainage pattern upfan luminescence dating suggest that the period of up warp and antecedent entrenchment started after 157 ka the morphologically mature study area demonstrates the response of fluvial systems to growing folds on piedmont areas induced by a propagating frontal fold at a thrust belt edge following shortening

basin evolution in a folding lithosphere altai sayan and tien shan belts in central asia abstract central asia is a classical example for continental lithospheric folding in particular the altay sayan belt in south siberia and the kyrgyz tien shan display a special mode of lithospheric deformation involving decoupled lithospheric mantle folding and upper crustal folding and faulting both areas have a heterogenous crust with a long history of accretion collision subsequently reactivated as a far field effect of the indian eurasian collision thanks to the youthfulness of the tectonic deformation in this region peak deformation in late pliocene early pleistocene the surface expression of lithospheric deformation is well documented by the surface topography and superficial tectonic structures a review of the paleostress data and tectono stratigraphic evolution of the kurai chuya basin in siberian altai zaisan basin in kazakh south altai and issyk kul basin in kyrgyz tien shan suggests that they were initiated in an extensional context and inverted by a combination of fault controlled deformation and flexural folding in these basins fault controlled deformation alone appears largely insufficient to explain their architecture lithospheric buckling inducing surface tilting uplift and subsidence also played an important role they form typical basins in a folding lithosphere flb their characteristic basin fill and symmetry inner structure folding wavelength and amplitude thermal regime time frame are examined in relation to basement structure stress field strain rate timing of deformation and compared to existing modelling results

great earthquakes in low strain rate continental interiors an example from se kazakhstan the lepsy fault of the northern tien shan se kazakhstan extends e w 120 km from the high mountains of the dzhungarian ala tau a subrange of the northern tien shan into the low lying kazakh platform it is an example of an active structure that connects a more rapidly deforming mountain region with an apparently stable continental region and follows a known palaeozoic structure field based and satellite observations reveal an 10 m vertical offset exceptionally preserved along the entire length of the fault geomorphic analysis and age control from radiocarbon and optically stimulated luminescence dating methods indicate that the scarp formed in the holocene and was generated by at least two substantial earthquakes the most recent event dated to sometime after 400 years b p is likely to have ruptured the entire 120 km fault length in a m w 7 5 8 2 earthquake the lepsy fault kinematics were characterized using digital elevation models and high resolution satellite imagery which indicate that the predominant sense of motion is reverse right lateral with a fault strike dip and slip vector azimuth of 110 50 s and 317 343 respectively which is consistent with predominant n s shortening related to the india eurasia collision in light of these observations and because the activity of the lepsy fault would have been hard to ascertain if it had not ruptured in the recent past we note that the absence of known active faults within low relief and low strain rate continental interiors does not always imply an absence of seismic hazard

experimental soft sediment deformation structures formed by the liquefaction of unconsolidated sands and some ancient examples the effects of liquefaction in saturated sand bodies under a variety of driving forces are described from shaking table experiments and structures from the geological record are presented which are analogous to the experimental structures the collapse of sloping heaps of cross bedded sand under a gravitational body force generates low angle essentially uncontorted stratification a basal zone of shearing may be present with steepened and folded foresets stretching of foresets may be accommodated on normal faults and bottomsets may be contorted into inclined folds in natural systems the substrate may also liquefy causing deformation driven by an unevenly distributed confining load stratification in the surface bedform is flattened and stratification in the substratum contorted experiments failed to produce relative displacement at the interface between stacked sand bodies liquefaction of gravitationally unstable systems in sands generates load structures comparable to those from sand mud systems recumbent folded deformed cross bedding is formed by current shear over a liquefied bed as has been inferred from field and theoretical analyses shear of nonliquefied sand forms angular folds other deformation mechanisms such as fluidization or seepage may generate structures similar to all of these local water escape structures driven by fluidization occur in the upper parts of some liquefied sand bodies they include cusps sand volcanoes and clastic dykes transient cavities formed in some experiments and seemed to be preserved as breached cusps although the experiments tried to isolate individual driving forces driving forces may operate together and there may be a continuum between deformation driven by water escape and deformation driven by loading different structures from those described here may form where liquefaction develops in a buried layer as opposed to at the sediment surface

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

seismogenically induced fluidization of jurassic erg sands south central utah large bodies of fluidized sandstone occur in the jurassic entrada carmel page and navajo formations at several locations in south central utah they are most abundant in the entrada sandstone where they commonly occur in clusters have a cylindrical form and have a sharp contact with their cross bedded host rock these clastic pipes are as wide as 75 m and have exposed heights of as much as 100 m some of the entrada pipes extend well into the underlying carmel redbeds other clastic pipes in the entrada sandstone are less deformed and display various degrees of brittle to hydroplastic deformation and liquefaction clastic pipes in the page and navajo sandstones are less common but are similar in size and form to those in the entrada and carmel and probably have a similar origin some massive sandstone bodies are irregular in form and have tongue like projections into the host rock implying forcible injection of fluidized sand several pipe host contacts in the entrada sandstone display small scale ring faults where relative displacement can be clearly demonstrated pipe sandstones are invariably down faulted locally as much as 5 m at two sites carmel host rock is upwarped around the entrada pipes stratified and cross bedded breccia blocks occur in many entrada pipes and preliminary petrographic analysis indicates that at least some of these breccia blocks are derived from the host rock homogeneous pipe sandstones are also petrographically similar to their entrada host rock suggesting that some pipes originate through fluidization of the fine grained entrada fluidization of the entrada must have occurred in a water saturated environment during early diagenesis but before complete lithification most probably under considerable porewater pressure although there are no known modern analogues to these huge masses of structureless sandstone they may have a small scale modern counterpart in earthquake induced sandblows these features were most probably caused by large magnitude seismic events during the middle jurassic although other possibilities cannot be ruled out at this point

classification of geomorphological effects downstream of dams abstract the effects of dams on downstream geomorphology are reviewed and a typology is devised consisting of nine cases the classification can be seen as a further development of lane s balance between water discharge sediment load grain size and river slope depending on changes in released water flow and changes in released sediment load relative to the transport capacity of the flow it is possible to estimate resulting cross sectional geomorphology the longitudinal extent of changes and their variability with time and the tributary response to altered mainstream cross section changes are also discussed

inherited strike slip faults as an origin for basement cored uplifts example of the kungey and zailiskey ranges northern tian shan 1 basement cored uplifts bounded by steeply dipping reverse faults are mechanically difficult to explain reactivation of strike slip faults that aid the formation of new high angle reverse faults in the surrounding crust may provide one origin for these structures this hypothesis is explored by examining the late miocene to quaternary evolution of the kungey and zailiskey ranges in the northern tian shan these ranges are cored by the kemin chilik fault kcf an inherited paleozoic structure with sinistral separation of basement terranes range growth in response to northward propagation of the tian shan has taken place along a network of steeply dipping reverse and oblique slip faults surrounding the kcf deformation of a low relief unconformity separating neogene strata from paleozoic basement records structural growth in response to fault slip deformed river terraces surrounding the ranges are correlated to a well preserved chronosequence in the southern kungey range cosmogenic10be dating of this chronosequence combined with offset measurements yields slip rates ranging from 0 07 to 0 37 mm yr for dip slip faults and 1 1 to 1 5 mm yr for strike slip faults late quaternary activity in the kungey zailiskey ranges is consistent with the longer term outward stepping pattern of range growth based on cross sections constrained from the folded unconformity surface deformed neogene strata and quaternary terraces faults building the kungey range are inferred to steepen at depth and emanate from a shear zone co located with the reactivated kcf this geometry is consistent with a slip partitioned system developed by an obliquely slipping reactivated fault at depth

large ancient earthquakes in the western issyk kul basin kyrgyzstan northern tien shan abstract new paleoseismological and archaeoseismological data from the western issyk kul basin of kyrgyzstan northern tien shan provide new insights on active fault in the actively deforming basement involved thrust system of central asia newly discovered fault scarps follow south and north dipping thrust faults which delineate the kyrgyz and kungey ranges bordering the issyk kul basin motion on these faults generated earthquakes with magnitudes 6 2 7 6 and msk 64 shaking intensities viii xi deformation observed in the zone of the toguz bulak fault results from two holocene earthquakes and another event that occurred about 8000 yr bp two more events at 13 000 and 3000 yr bp deformed the northeastern periphery of the kyzyl ompul uplift archaeoseismological research in the northern sary bulun settlement in the western periphery of the boz barmak uplift revealed traces of another earthquake of msk 64 shaking intensity i viii dating back to the 12th century the obtained data correlates well with results of previous paleoseismological and archeoseismological studies they show that in the northern tien shan there were clusters of strong earthquakes with ages of 14 13 8 4 3 ka ago and in the 11 12th centuries ad divided by periods of 4 5 ka we infer that coseismic slip on these faults may have formed a tectonic dam at the edge of the basin through growth of the boz barmak uplift and this dam ultimately deflected the chu river into its modern channel which bypasses the lake lacustrine sediments in the northeastern periclinal segment of the boz barmak uplift bear signatures of soft sediment deformation structures seismites corresponding to seven m 5 5 5 i vi vii earthquakes timed at about 20 000 yr bp

reconstruction of the main parameters of old large earthquakes in soviet central asia using the paleoseismogeological method abstract the paleoseismogeological method has been improved on the basis of the frequent occurrence of recent seismogenic dislocations in soviet central asia the possibilities are studied and methods for reconstructing epicentral zones and determining the magnitude and age of large earthquakes in the past are proposed worldwide and regional scales of magnitude determination by dislocations are compared on the basis of concrete data new methods of age determination are cited examples are given in which parameters of previously unknown large paleoearthquakes at the pamirs tien shan boundary zone are studied the first for soviet central asia experience in map making for paleoseismodislocations and paleoearthquakes in one of the seismically active and dangerous areas in soviet central asia is described the existing limitations of the method are analysed

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

response of a channel with alternate bars to a decrease in supply of mixed size bed load a flume experiment the response of a channel with a topography and modeled bed material size typical of gravel bed rivers to reductions in sediment supply was investigated in a laboratory flume filled and fed with a sand gravel mixture after a series of quasi stationary alternate bars were formed under equilibrium sediment transport feed rate was reduced in two steps to one third and one tenth the initial rate as discharge was held constant the primary response following both reductions was an increase in bed surface particle size as a corridor of intensive bed load transport contracted and local transport rates decreased after the first feed rate reduction the channel incised by twice the mean water depth on average and caused distal bar surfaces to emerge as terracelike features bar roughness decreased and mean boundary shear stress exerted on bed surface particles increased little incision occurred after the second feed rate reduction

pliocene pleistocene initiation style and sequencing of deformation in the central tien shan in response to the indo asian collision deformation of the tien shan initiated at 25 ma along the northwestern margin of the tarim basin 300 km north the kyrgyz range began deforming 15 ma later although multiple intervening structures across the tien shan are currently active the sequencing of initial deformation across the orogen s entire width remains poorly known to determine whether deformation migrated sequentially northward or developed less predictably we documented deformation patterns within the naryn basin in south central kyrgyzstan detailed mapping and a published balanced cross section across the naryn basin suggest that deep seated relatively steeply dipping thrust faults have disrupted the basin during late cenozoic deformation dating of deformed fluvial terraces with ages between 10 and 250 ka constrains the rate of deformation across relatively young structures in the tien shan interior based on geodetic surveys of dated terraces local rates of relative rock uplift span from 0 3 to 3 5 mm yr folding rates and patterns are temporally persistent at a given site moreover they mimic modern geodetic rates measured from interferometric synthetic aperture radar extrapolating these rates into the past suggests that structures within the interior of the naryn basin formed in the last 1 myr whereas the ranges surrounding the basin initiated at least 1 4 myr earlier hence within the naryn basin itself deformation has migrated from margins to interior similarly these new chronologies indicate that at least some deformation in the interior of the tien shan initiated millions of years later than along either orogenic margin 2014 american geophysical union all rights reserved

seismites an attempt at critical analysis and classification abstract the main types of seismites are reviewed following the proposed classification and are illustrated by our own case studies the large variety of seismites depends on the sedimentologic hydrodynamic and diagenetic characters of the deposits subject to seismic shocks on a given site generally different types of seismites cane be related to the same seismic event these peculiar but widespread sedimentary structures are not always univocal and may often be related to different causes therefore the structures discussed must necessarily be placed in a detailed geological context

early jurassic extensional basin formation in the daqing shan segment of the yinshan belt northern north china block inner mongolia abstract structural and stratigraphic studies of the western daqing shan segment of the yinshan belt have recognized an early jurassic extensional episode supported by several lines of evidence first normal faults cut the lowermost jurassic sequence and are overlapped by younger lower jurassic rocks second lower jurassic rocks include growth strata in small scale graben at the base of the jurassic basin third rapid lateral facies changes are mapped from boulder conglomerates along the basin bounding faults to lacustrine and meandering fluvial rocks in the basin center fourth paleodrainage systems provided sediment input from three sides of the basin two transverse and one axial finally there is a strongly asymmetric distribution of coarse proximal and fine distal facies within the basin the early jurassic extensional episode was responsible for formation of an east trending half graben basin in the western daqing shan in which at least 1800 m of syn extensional nonmarine sediments accumulated and are preserved previous studies in the triassic and jurassic of other parts of northwest and north central china have concluded that the early mesozoic was a time of continental amalgamation and contractile deformation the recognition of an early jurassic extensional episode along the northern margin of the north china block is problematic in this context at least superficially we propose two possible explanations for the early jurassic extension transtension associated with strike slip tectonics or gravitational collapse of a pre existing late paleozoic early mesozoic contractile orogenic belt the first possibility transtensional deformation is problematic because specific strike slip faults have not been identified that could control extension in the western daqing shan however several lines of evidence allow the possibility of such a driving mechanism including documented early jurassic transtensional systems in the southwestern north china block several candidate strike slip faults along the china mongolia border region structural discontinuity between the daqing shan and southern mongolia and along strike changes in structural style within the yinshan belt the second possibility orogenic collapse is similarly difficult to establish because of the limited amount of data concerning the regional distribution and orientation of pre jurassic contractile structures and early jurassic extensional structures however documented late paleozoic triassic contractile deformation as well as the close temporal and spatial association and parallelism between early jurassic extensional structures and older contractile structures in the western daqing shan requires consideration of gravitational collapse as a driving mechanism for early jurassic extension in the yinshan belt

thermo tectonic history of the issyk kul basement kyrgyz northern tien shan central asia abstract lake issyk kul occupies a large late mesozoic cenozoic intramontane basin between the mountain ranges of the northern kyrgyz tien shan these ranges are often composed of granitoid basement that forms part of a complex mosaic assemblage of microcontinents and volcanic arcs several granites from the terskey kungey trans ili and zhetyzhol ranges were dated with the zircon u pb method shrimp la icp ms and yield concordant late ordovician silurian 456 420 ma emplacement ages these constrain the caledonian accretion history of the northern kyrgyz tien shan in the amalgamated palaeo kazakhstan continent the ancestral tien shan orogen assembled in the early permian when final closure of the turkestan ocean ensued collision of palaeo kazakhstan and tarim a late palaeozoic structural basement fabric formed and middle late permian post collisional magmatism added to crustal growth of the tien shan permo triassic cooling 300 220 ma of the ancestral tien shan was unraveled using 40 ar 39 ar k feldspar and titanite fission track ft thermochronology on the issyk kul granitoids apatite thermochronology ft and u th sm he applied to the broader issyk kul region elucidates the meso cenozoic thermo tectonic evolution and constrains several tectonic reactivation episodes in the jurassic cretaceous and cenozoic exhumation of the studied units occurred during a protracted period of intracontinental orogenesis linked to far field effects of late jurassic cretaceous accretion of peri gondwanan blocks from the tethyan realm to eurasian following a subsequent period of stability and peneplanation incipient building of the modern tien shan orogen in northern kyrgyzstan started in the oligocene according to our data intense basement cooling in distinct reactivated and fault controlled sections of the trans ili and terskey ranges finally pinpoint important miocene pliocene 22 5 ma exhumation of the issyk kul basement late cenozoic formation of the tien shan is associated with ongoing indentation of india into eurasia and is a quintessential driving force for the reactivation of the entire central asian orogenic belt

tectonic and gravity induced deformation along the active talas fergana fault tien shan kyrgyzstan abstract this paper shows by field palaeoseismological data the holocene activity of the central segment of the intracontinental talas fergana fault tff and the relevance of possible future seismic shaking on slope stability around a large water reservoir the fault striking nw se is marked by a continuous series of scarps deflected streams and water divides and prehistoric earthquakes that offset substrate and holocene deposits fault movements are characterised by right lateral strike slip kinematics with a subordinate component of uplift of the ne block structural geological and geomorphological field data indicate that shallow and deep landslides are aligned along the tff and some of them are active where the tff runs close to the reservoir the fault trace is obscured by a series of landslides affecting rock and soil materials and ranging in size from small slope instabilities to deep seated gravity induced slope deformations dgsds the largest of these which does not show clear evidence of present day activity involves a volume of about 1 km3 and is associated with smaller but active landslides in its lower part with volumes in the order of 2 5 104 m3 to 1 106 m3 based on the spatial and temporal relations between landslides and faults we argue that at least some of these slope failures may have a coseismic character stability analyses by means of limit equilibrium methods lems and stress strain analysis by finite difference numerical modelling fdm were carried out to evaluate different hazard scenarios linked to these slope instabilities the results indicate concern for the different threats posed ranging from the possible disruption of the m 41 highway the main transportation route in central asia to the possible collapse of huge rock masses into the reservoir possibly generating a tsunami

soft sediment deformation structures in late albian to cenomanian deposits sao luis basin northern brazil evidence for palaeoseismicity soft sediment deformation structures from the alc ntara formation late albian to cenomanian sao luis basin northern brazil consist of 1 contorted structures which include convolute folds ball and pillow structures concave up paths with consolidation lamination recumbently folded cross stratification and irregular convolute stratification that grades into massive beds 2 intruded structures which include pillars dykes cusps and subsidence lobes and 3 brittle structures represented by fractures and faults displaying planes with a delicate ragged morphology and sharp peaks these structures result from a complex combination of processes mostly including reverse density gradients fluidization and liquefaction reverse density gradients promoted by differential liquefaction associated with different degrees of sediment compaction led to the genesis of convolute folds more intense deformation promoted the development of ball and pillow structures subsidence lobes and sand rolls which are attributed to denser and thus more compacted less liquefied portions that sank down into less dense more liquefied sediments irregular convolute stratification that grades into massive beds would have formed at periods of maximum deformation the subsidence of beds was accompanied by lateral current drag and fluid escape from water saturated sands in addition the fractures and faults record brittle deformation penecontemporaneous with sediment deposition all these mechanisms were triggered by a seismic agent as suggested by a combination of criteria including 1 the position of the study area at the edge of a major strike slip fault zone that was reactivated several times from the albian to the holocene 2 a relative increase in the degree of deformation in sites located closer to the fault zone 3 continuity of the deformed beds over large distances several kilometres 4 restriction of soft sediment deformation structures to single stratigraphic intervals bounded by entirely undeformed strata 5 recurrence through time and 6 similarities to many other earthquake induced deformational structures

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

soft sediment deformation structures interpreted as seismites in lacustrine sediments of the prebetic zone se spain and their potential use as indicators of earthquake magnitudes during the late miocene lacustrine formations of late miocene age in the prebetic area se spain show several types of deformational structures that are interpreted as seismites they are present in both marginal and deep lacustrine facies seismites formed in marginal lake environments comprise sand dikes pillows and intruded and fractured gravels in deep lacustrine facies the seismites are represented by pseudonodules mushroom like silts protruding into laminites mixed layers disturbed varved lamination and loop bedding the measured orientations of these structures are consistent with the orientations of the main faults limiting the basins showing that their origin is clearly related to the tectonic stress field that prevailed in the region during the late miocene the magnitudes of the earthquakes that deformed the sediments have been estimated after published data from both ancient and recent lake deposits accumulated in tectonic active regions elsewhere a rank of earthquake magnitudes with two end members i e the lowest magnitudes recorded by loop bedding in laminites and the highest magnitudes represented by intruded and fractured gravels is proposed

local scouring and morphological adjustments in steep channels with check dam sequences this paper describes bed profile and grain size distribution adjustments in a mountain river maso di spinelle river italian alps stabilized by a sequence of boulder check dams the control works were originally designed to simulate the geometry of natural step pool channels where tumbling flow is the dominant hydraulic regime local scouring downstream of 29 drop structures is analysed through the use of nondimensional parameters where maximum scour depth and scour length are normalised to the drop height prior laboratory data reveal a pattern similar to field scours where complex interactions occur between drop height critical flow depth and step spacing the linkage between scour length and depth is also discussed there seems to be a maximum step height for impinging jets that is approximately twice the drop height this maximum may explain the upper limit of the steepness factor found in high gradient step pool streams if such a maximum upper limit is confirmed by further studies this may aid designs of foundation heights for transverse control works in steep channels

earthquake induced soft sediment deformation structures in late pleistocene lacustrine deposits of issyk kul lake kyrgyzstan abstract this paper discusses the composition and distribution of soft sediment deformation structures induced by liquefaction in late pleistocene lacustrine terrace deposits on the southern shore of issyk kul lake in the northern tien shan mountains of kyrgyzstan the section contains seven deformed beds grouped in two intervals five deformed beds in the upper interval contain load structures load casts and flame structures convolute lamination ball and pillow structures folds and slumps deformation patterns indicate that a seismic trigger generated a multiple slump on a gentle slope the dating of overlying subaerial deposits suggests correlation between the deformation features and strong earthquakes in the late pleistocene

morphological effects of local scouring in step pool streams step pool morphology characterizes many high gradient streams in a variety of natural settings but formative processes and evolutionary dynamics are still poorly understood in this paper natural step pool geometry is compared with steep alluvial channels where grade control structures such as check dams and bed sills make the stream profile resemble a natural stepped stream along these channels local scouring due to falling jets forms plunge pools under each structure analogous to natural steps determining the formation of pools in order to test the hypothesis that natural pools are analogous to pools formed below grade control works with respect to their dimensions shape and formative dynamics 37 natural pools and 73 artificial pools were surveyed in 10 mountain streams of the eastern italian alps pools below grade control works featured a transitional zone between the scour hole and the downstream sloping bed marked by a depositional berm when geometric parameters such as maximum pool depth length and step berm distances are normalized to the jet virtual energy no statistically significant differences were detected between natural and artificial systems these results lend support to an upstream forced cascade model for step pool formation where the energy of falling jets controls the geometry of the pools and is therefore regarded as the most important scaling independent variable copyright 2005 john wiley sons ltd