constraints from gps measurements on the dynamics of the zone of convergence between arabia and eurasia we investigate the dynamics of deformation in the zone of convergence between the arabian and eurasian plates using a physical model that treats the lithosphere as a thin fluid sheet deforming in response to lateral variations in gravitational potential energy gpe this model has two free material parameters the power law exponent n of the vertically averaged rheology of the lithosphere and the argand number ar which expresses the relative importance of gpe and stresses required to deform the lithosphere with boundary conditions described by three free parameters the model fits the observed deformation as measured by 367 gps velocities with a root mean square residual of 2 4 mm yr we find negligible improvement when variations in material properties are introduced that represent increases or decreases in the lithospheric strength of the central iranian and turkish iranian plateaux and the zagros mountains effective viscosity of the lithosphere ranges from 5 1022 pa s at 10 nanostrain yr to 1022 pa s at 100 nanostrain yr as well as matching the decadal timescale predominantly interseismic strain rates determined from gps the computed distribution of strain rates is also consistent with the distribution and types of earthquake focal mechanism significant historical earthquake activity is seen in regions with strain rates lower than 20 nanostrain yr implying that it is prudent to base assessments of seismic hazard on regional strain rates

tectonics of the central zagros iran deduced from microearthquake seismicity summary microearthquakes in central zagros recorded for 7 weeks in 1997 lie in a 6 8 km zone that is likely located beneath 11 km of sediments they are not located on an active decollement between the sediments and the crystalline crust but rather define a pattern of nnw sse trending lineaments parallel to the fold axes observed at the surface the spacing between the seismic lineaments is 15 20 km and therefore different from that between the folds 10 15 km which suggests that there is not a simple relationship between the two focal mechanisms and precise relative locations are consistent with nw se striking reverse faulting connected by nnw sse striking right lateral strike slip faults the dip of the reverse faults is not certain but is likely ne for the northernmost faults the strain pattern deduced from the p axes is remarkably similar to the shortening deduced from gps based geodesy suggesting that microearthquakes are the response of the prefractured brittle crust to strain rather than localized on single active faults

neotectonic deformation in central eurasia a geodynamic model approach funding was granted by the spanish government through the project mite cgl2014 59516 p and alpimed piecsic 201530e082

effects of tectonic deformation and sea level on river path selection theory and application to the ganges brahmaputra meghna river delta the set of active rivers of the ganges brahmaputra meghna gbm delta in bangladesh overlies an active plate boundary that continually modifies the landscape of the delta by deformation the response of rivers to spatially variable subsidence from tectonic tilting or other causes has been thought to include preferred occupation of regions of higher subsidence in this paper we develop further the theoretical framework for analysis of the interplay of tectonics and river dynamics and apply this model to conditions in the gbm delta first we examine the overall competition between variable subsidence and channel dynamics and find that tilting in bangladesh should be strong enough to influence river path selection we then present new theory for the effect of subsidence that is spatially not temporally variable we find a constant residence timescale on different parts of the delta and differing frequencies of avulsion to these locations and describe the effects of incision or floodplain deposition on these quantities we present estimates of the channel residence timescale of the jamuna brahmaputra river reconstructed from the lithology provenance and dating of sediment cores we apply our framework to a map of regional subsidence to predict the effects on avulsion for the jamuna river comparison between our predicted 2150 years and our stratigraphically based estimates of avulsion timescale 1800 years shows encouraging consistency

microseismicity and seismotectonics of the south caspian lowlands ne iran this paper is concerned with the microseismicity and seismotectonics of the eastern south caspian sea region where the east alborz mountains descend to meet the south caspian lowlands of ne iran to better understand the present day tectonics and seismicity of this region which includes the cities of gorgan and gonbad e qabus combined population 500 000 we installed a temporary local seismic network across the area for 6 months between 2009 and 2010 we analysed the seismicity and focal mechanisms together with data from the permanent networks of the institute of geophysics university of tehran igut and the international institute of earthquake engineering and seismology iiees based in tehran microseismicity is focused primarily on the shahrud fault system which bounds the east alborz range to the south relatively few earthquakes are associated with the khazar thrust fault which bounds the north side of the range a cluster of shallow microseismicity 15 km depth occurs 40 km north of the khazar fault within the south caspian lowlands scl an area typically thought to be non deforming this area coincides with the location of three relatively deep thrust earthquakes m w 5 3 5 5 which occurred in 1999 2004 and 2005 inversion of teleseismic body waveforms allows us to constrain the depth of these earthquakes at 26 29 km although significant sedimentation throughout the scl obscures any expression of recent fault activity at the surface focal mechanisms of well located events from the shallow cluster of micro seismicity show a significant component of left lateral strike slip motion assuming slip occurs on ne sw fault planes typical of active faults in the region as well as a small normal component inversion of traveltimes for well located events in our network yields a velocity structure for the region and a moho depth of 41 km the pattern of deep thrust and shallow normal seismicity could be explained by bending of the rigid south caspian crust as it underthrusts the east alborz mountains and central iran late quaternary reorganization of drainage systems in the scl may be the result of shallow normal fault activity within the scl

the continuation of the kazerun fault system across the sanandaj sirjan zone iran abstract the kazerun or kazerun qatar fault system is a north trending dextral strike slip fault zone in the zagros mountain belt of iran it probably originated as a structure in the panafrican basement this fault system played an important role in the sedimentation and deformation of the phanerozoic cover sequence and is still seismically active no previous studies have reported the continuation of this important and ancient fault system northward across the sanandaj sirjan zone the isfahan fault system is a north trending dextral strike slip fault across the sanandaj sirjan zone that passes west of isfahan city and is here recognized for the first time this important fault system is about 220 km long and is seismically active in the basement as well as the sedimentary cover sequence this fault system terminates to the south near the main zagros thrust and to the north at the southern boundary of the urumieh dokhtar zone the isfahan fault system is the boundary between the northern and southern parts of sanandaj sirjan zone which have fundamentally different stratigraphy petrology geomorphology and geodynamic histories similarities in the orientations kinematics and geologic histories of the isfahan and kazerun faults and the way they affect the magnetic basement suggest that they are related in fact the isfahan fault is a continuation of the kazerun fault across the sanandaj sirjan zone that has been offset by about 50 km of dextral strike slip displacement along the main zagros thrust

lithospheric structure beneath the south eastern zagros mountains iran recent slab break off integrated lithospheric modelling based on the combined interpretation of gravity geoid and topography data sets highlights a previously undocumented lithospheric thinning beneath the zagros collisional belt iran which we propose to relate to recent slab break off at the continent ocean transitional lithosphere recent published data on the distribution of seismicity at depth support this interpretation in agreement with other published models for the zagros mountains the overlying crust exhibits by contrast a noticeable thickening reaching a maximum of 52 km the consequent thermal uplift expected from slab break off is suggested to have modified the zagros wedge taper and triggered the recently documented switch from thin skinned to thick skinned deformation in the zagros fold thrust belt

competition between uplift and transverse sedimentation in an experimental delta mass is commonly injected into alluvial systems either laterally by transport from source regions or vertically from below via local uplift we report results on the competition between these two fundamental processes using an experimental basin with a deformable substrate the lateral supply is via two alluvial fans on orthogonal walls of the basin the uplifting region is downstream of one of the fans axial and opposite to the other transverse we show that the presence of a transverse sediment input increases the erosion rate of the uplifting region by pushing the mixing zone between the two alluvial sources against the uplifting mass however increase in sediment delivery to the transverse fan does not cause a proportional increase in erosion rate of the uplifting region instead the system reaches a steady state balance between uplift and erosion induced by the transverse fan such that there is no change in the total mass above the active alluvial surface a lateral analog of the classical steady state between vertical erosion and uplift we also show that the mixing zone is instrumental in limiting upstream aggradation and funneling sediments to the shore resulting in limited river lateral mobility and increased shoreline progradation hence the interaction between alluvial sources buffers river erosion and leads to consistent deviations from predictions of the area of influence of each fan based on simple mass balance arguments in the ganges brahmaputra meghna delta we suggest that similar dynamics help stabilize the brahmaputra river course in the jamuna valley during holocene time

depositional environments of campanian maastrichtian successions in the kirthar fold belt southwest pakistan tectonic influences on late cretaceous sedimentation across the indian passive margin abstract the creation of a complex submarine morphology on the passive margin of the indo pakistan continental plate during later stages of its northward drift just prior to collision with eurasia is clearly demonstrated by the nature architecture and regional distribution of sandstone bodies within the campanian maastrichtian successions mughal kot and pab formations exposed within the north south trending kirthar fold belt of southwest pakistan these successions range in thickness from 7 m to more than 500 m and are dominated by fine to coarse sometimes pebbly thin to thick bedded sandstones with subordinate mudstones and marls all of which were deposited on the north facing passive margin of the indo pakistan plate twelve facies have been identified in these sequences and these have been grouped into nine facies associations which were formed within two broadly coeval depositional systems that occupied the contiguous southern kirthar and central kirthar sub basins it is argued here that these sub basins and their fill sequences developed mainly in response to major tectonically induced changes in both the morphology of this sector of the palaeo margin and in the sediment supply systems the more proximal sequences in the east and southeast sectors of the southern kirthar sub basin are dominated by fluviodeltaic deposits while more distal areas to the northwest are characterized by turbidite sandstone bodies formed in channel levee and lobe complexes within slope and basin floor settings of a relatively confined deep marine trough in this southern kirthar sub basin the mughal kot formation comprises basin floor lobes submarine channel fill sand bodies and base of slope mud rich lobes whereas the succeeding pab formation reflects overall progradation of the system being dominated by submarine slope fan lobes channels and levee deposits the central kirthar sub basin displays a broadly east to west transition from shoreface inner shelf through shelfal delta lobes middle shelf and deeper shelf ramp outer shelf facies associations all formed on a gently inclined storm and flood dominated clastic ramp synsedimentary normal faults observed in this study were controlled the depositional architecture and creation of closed deep marine southern kirthar sub basin during late cretaceous

testing morphodynamic controls on the location and frequency of river avulsions on fans versus deltas huanghe yellow river china a mechanistic understanding of river avulsion location and frequency is needed to predict the growth of alluvial fans and deltas the huanghe china provides a rare opportunity to test emerging theories because its high sediment load produces regular avulsions at two distinct nodes where the river debouches from the loess plateau avulsions occur at an abrupt decrease in bed slope and reoccur at a time interval 607 yrs consistent with a channel filling timescale set by the superelevation height of the levees downstream natural deltaic avulsions reoccur at a timescale that is fast 7 yrs compared to channel filling timescale due to large stage height variability during floods unlike the upstream node deltaic avulsions cluster at a location influenced by backwater hydrodynamics and show evidence for episodic downstream migration in concert with progradation of the shoreline providing new expectations for the interplay between avulsion location frequency shoreline rugosity and delta morphology

contributions of a strengthened early holocene monsoon and sediment loading to present day subsidence of the ganges brahmaputra delta the contribution of subsidence to relative sea level rise in the ganges brahmaputra delta gbd is largely unknown and may considerably enhance exposure of the bengal basin populations to sea level rise and storm surges this paper focuses on estimating the present day subsidence induced by holocene sediment in the bengal basin and by oceanic loading due to eustatic sea level rise over the past 18 kyr using a viscoelastic earth model and sediment deposition history based on in situ measurements results suggest that massive sediment influx initiated in the early holocene under a strengthened south asian monsoon may have contributed significantly to the present day subsidence of the gbd we estimate that the holocene loading generates up to 1 6 mm yr of the present day subsidence along the gbd coast depending on the rheological model of the earth this rate is close to the twentieth century global mean sea level rise 1 1 1 7 mm yr thus past climate change by way of enhanced sedimentation is impacting vulnerability of the gbd populations

accelerated river avulsion frequency on lowland deltas due to sea level rise sea level rise subsidence and reduced fluvial sediment supply are causing river deltas to drown worldwide affecting ecosystems and billions of people abrupt changes in river course called avulsions naturally nourish sinking land with sediment however they also create catastrophic flood hazards existing observations and models conflict on whether the occurrence of avulsions will change due to relative sea level rise hampering the ability to forecast delta response to global climate change here we combined theory numerical modeling and field observations to develop a mechanistic framework to predict avulsion frequency on deltas with multiple self formed lobes that scale with backwater hydrodynamics results show that avulsion frequency is controlled by the competition between relative sea level rise and sediment supply that drives lobe progradation we find that most large deltas are experiencing sufficiently low progradation rates such that relative sea level rise enhances aggradation rates accelerating avulsion frequency and associated hazards compared to preindustrial conditions some deltas may face even greater risk if relative sea level rise significantly outpaces sediment supply then avulsion frequency is maximized delta plains drown and avulsion locations shift inland posing new hazards to upstream communities results indicate that managed deltas can support more frequent engineered avulsions to recover sinking land however there is a threshold beyond which coastal land will be lost and mitigation efforts should shift upstream

slip rate of the kazerun fault and main recent fault zagros iran from 3d mechanical modeling abstract the aim of this work is using gps velocities and 3d mechanical modeling including preexisting faults with frictional properties that obey coulomb failure process to explore the long term slip rates of the mrf fault and kazerun faults in the zagros mountain of iran a model was constructed using spatially varying crustal thickness geothermal gradient and two major faults structural boundaries are derived from the several deep seismic soundings carried out in the area far field gps velocities and late quaternary fault slip rates are used to compare the model results rheological tests show that effective fault friction lower than 0 05 leads to high slip rates that fit with geologically and geodetically determined slip rates of mrf and kazerun fault these results suggest that mrf and kazerun fault are weak faults like san andreas and north anatolian fault

predicting delta avulsions implications for coastal wetland restoration river deltas create new wetlands through a continuous cycle of delta lobe extension avulsion and abandonment but the mechanics and timing of this cycle are poorly understood here we use physical experiments to quantitatively define one type of cycle for river dominated deltas the cycle begins as a distributary channel and its river mouth bar prograde basinward eventually the mouth bar reaches a critical size and stops prograding the stagnated mouth bar triggers a wave of bed aggradation that moves upstream and increases overbank flows and bed shear stresses on the levees an avulsion occurs as a time dependent failure of the levee where the largest average bed shear stress has been applied for the longest time r 2 0 93 these results provide a guide for predicting the growth of intradelta lobes which can be used to engineer the creation of new wetlands within the delta channel network and improve stratigraphic models of deltas

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

floodplain processes in the bengal basin and the storage of ganges brahmaputra river sediment an accretion study using 137cs and 210pb geochronology floodplain deposits are recognized as potentially large sinks for fluvial sediments yet spatial and temporal patterns of accumulation are not known for many river systems in the tectonically active bengal basin the ganges and brahmaputra rivers coalesce and have formed a large floodplain delta complex where widespread overbank flooding may deposit a significant portion of the river s estimated sediment discharge to investigate the magnitude and distribution of this process accumulation rates were determined by 137cs and 210pb radioisotope geochronology at 60 sites located in three regions of the bengal basin differing in age physiography and river influence these geochronological methods have been applied to floodplain environments in only a few recent studies and the present research offers a revised approach for heterogeneous systems patterns of sediment deposition in the bengal basin reveal three dominant controls on floodplain accretion channel processes overbank flooding and surface runoff accretion is most rapid in the river braidbelt and adjacent floodplain decreasing rapidly with distance from the main channel accumulation rates increase again in low lying distal basins where several meters of annual precipitation and associated runoff rework surrounding floodplain surfaces and transport remobilized sediments to local catchments the extent and magnitude of this process indicate its comparable importance with overbank deposition for floodplain accumulation a sediment budget for the study area reveals that at least 15 of the estimated 1 billion tonnes of fluvial sediment discharge is stored annually and not reaching the oceans as previously assumed extrapolated to the remaining 60 000 km2 of floodplain not covered in this project the sequestered load could rise to 30 of annual sediment discharge

piecing together the ganges brahmaputra meghna river delta use of sediment provenance to reconstruct the history and interaction of multiple fluvial systems during holocene delta evolution three main rivers the ganges brahmaputra and meghna coalesce in the bengal basin to form the world s largest delta system which serves as filter and gateway between the himalayan collision and vast bengal fan repository new insights into the holocene construction of the ganges brahmaputra meghna delta with a focus on river sedimentation channel migration and avulsion history are presented here using the sr geochemistry of bulk sediments as a provenance tracer the sediment load of each river transmits a distinct sr signature owing to differences in source rocks from the himalaya tibet and local regions allowing for effective tracking of river channels and stratigraphic development within the delta in the early holocene vigorous delta aggradation occurred under rapid sea level rise and high river discharge and supported the construction of sand dominated stratigraphy by laterally mobile braided stream channels however the vertically i e temporally uniform but geographically distinct sr signatures from these deposits indicate that the ganges brahmaputra and meghna fluvial systems remained isolated from one another and apparently constrained within their lowstand valleys by the mid holocene though delta stratigraphy records spatially and temporally nonuniform sr signatures that hallmark the onset of avulsions and unconstrained channel migration like those that characterize the modern ganges and brahmaputra fluvial systems such mobility developed in the mid holocene despite declining discharge and sea level rise suggesting that earlier channel behavior had been strongly influenced by antecedent topography of the lowstand valleys it is only after the delta had aggraded above the valley margins that the fluvial systems were able to avulse freely resulting in numerous channel reorganizations from mid holocene to present these channel system behaviors and their role in delta evolution remain coarsely defined based only on this initial application of sr based provenance tools but the approach is promising and suggests that a more complete understanding can be achieved with continued study

scale dependent compensational stacking an estimate of autogenic time scales in channelized sedimentary deposits recent studies show that paleoenvironmental allogenic signals preserved in the stratigraphic record may be contaminated or overprinted by internally generated autogenic sedimentation this is problematic but it is unclear over what temporal and spatial scales autogenic patterns are most prevalent we propose that scale breaks in basin fi lling trends can be used to identify the transition between allogenic and autogenic stratigraphy using data from numerical and physical experiments and an ancient outcrop we explore how compensation the tendency for sediment transport systems to preferentially fi ll topographic lows varies with stratigraphic scale object based models demonstrate the temporal scales at which stratigraphy changes from being partially infl uenced by autogenic processes to being completely determined by allo genic forcings and suggest that this transition occurs at a time scale set by the maximum scale of surface roughness in a transport system divided by the long term aggradation rate this hypothesis is validated in a physical experiment where delta topography was monitored along fl ow perpendicular transects at a high temporal resolution relative to channel kine matics the strength of compensation in the experiment changes at the predicted time scale where the maxi mum surface roughness is equal to the depth of the experimental channels above this compensation time scale deposits stack purely compensationally but below this time scale deposits stack somewhere between randomly and deterministically similar scale dependent stacking is also observed in the ferris formation cretaceous paleogene hanna basin wyoming united states this study demonstrates that scale dependent compensational stack ing may be useful for isolating allogenic and autogenic stratigraphy in sedimentary basins

autogenic erosional surfaces in fluvio deltaic stratigraphy from floods avulsions and backwater hydrodynamics erosional surfaces set the architecture of fluvio deltaic stratigraphy and they have classically been interpreted in terms of changes in boundary conditions such as climate tectonics and base level allogenic forces intrinsic dynamics of sedimentary systems autogenic dynamics can also create a rich stratigraphic architecture and a major knowledge gap exists in parsing the relative roles of autogenic versus allogenic processes emerging theoretical and experimental work suggests that backwater hydrodynamics play an important role in driving transient channel incision in river deltas even those experiencing net aggradation here we identify and quantify two autogenic mechanisms that produce broad erosional surfaces in fluvio deltaic stratigraphy namely floods and avulsions using a simple mass balance model for single threaded delta channel systems we show that flood induced scours begin near the shoreline and avulsion induced scours begin at the avulsion site and both propagate upstream over a distance that scales with the backwater length bed slope and bed grain size we also develop scaling relationships for the maximum scour depths arising from these mechanisms which are functions of characteristic flow depth and formative flood variability we test our theoretical predictions using a flume experiment of river delta evolution governed by persistent backwater hydrodynamics under constant relative sea level results indicate that autogenic dynamics of backwater mediated deltas under conditions of constant base level can result in stratigraphic surfaces and shoreline trajectories similar to those often interpreted to represent multiple sea level cycles our work provides a quantitative framework to decouple autogenic and allogenic controls on erosional surfaces preserved in fluvio deltaic stratigraphy

structural evidence for superposition of transtension on transpression in the zagros collision zone main recent fault piranshahr area nw iran abstract the main recent fault of the zagros orogen is an active major dextral strike slip fault along the zagros collision zone generated by oblique continent continent collision of the arabian plate with iranian micro continent two different fault styles are observed along the piranshahr fault segment of the main recent fault in nw iran the first style is a sw dipping oblique reverse fault with dextral strike slip displacement and the second style consists of cross cutting ne dipping oblique normal fault dipping to the ne with the same dextral strike slip displacement a fault propagation anticline is generated sw of the oblique reverse fault an active pull apart basin has been produced to the ne of the piranshahr oblique normal fault and is associated with other sub parallel ne dipping normal faults cutting the reverse oblique fault another cross cutting set of ne sw trending normal faults are also exist in the pull apart area we conclude that the ne verging major dextral oblique reverse fault initiated as a sw verging thrust system due to dextral transpression tectonic of the zagros collision zone and later it has been overprinted by the ne dipping oblique normal fault producing dextral strike slip displacement reflecting progressive change of transpression into transtension in the collision zone the active piranshahr pull apart basin has been generated due to a releasing damage zone along the nw segment of the main recent fault in this area at an overlap of piranshahr oblique normal fault segment of the main recent fault and the serow fault the continuation of the main recent fault to the n

sedimentation and tectonics of the sylhet trough bangladesh the sylhet trough a sub basin of the bengal basin in northeastern bangladesh contains a thick fill 12 to 16 km of late mesozoic and cenozoic strata that record its tectonic evolution stratigraphic sedimentologic and petrographic data collected from outcrops cores well logs and seismic lines are here used to reconstruct the history of this trough the sylhet trough occupied a slope basinal setting on a passive continental margin from late mesozoic through eocene time subsidence may have increased slightly in oligocene time when the trough was located in the distal part of a foreland basin paired to the indo burman ranges oligocene fluvial deltaic strata barail formation were derived from incipient uplifts in the eastern himalayas subsidence increased markedly in the miocene epoch in response to western encroachment of the indo burman ranges miocene to earliest pliocene sediments of the surma group were deposited in a large mud rich delta system that may have drained a significant proportion of the eastern himalayas subsidence rates in the sylhet trough increased dramatically 3 8 times from miocene to pliocene pleistocene time when the fluvial tipam sandstone and dupi tila formation were deposited this dramatic subsidence change is attributed to south directed overthrusting of the shillong plateau on the dauki fault for the following reasons 1 pliocene and pleistocene strata thin markedly away from the shillong plateau consistent with a crustal load emplaced on the northern basin margin 2 the shillong plateau is draped by mesozoic to miocene rocks but pliocene and younger strata are not represented suggesting that the massif was an uplifted block at this time 3 south directed overthrusting of the shillong plateau is consistent with gravity data and with recent seismotectonic observations sandstone in the tioam has a marked increase in sedimentary lithic fragments compared to older rocks reflecting uplift and erosion of the sedimentary cover of the shillong plateau if the dauki fault has a dip similar to that of other himalayan overthrusts then a few tens of kilometers of horizontal tectonic transport would be required to carry the shillong plateau to its present elevation uplift of the shillong plateau probably generated a major 300 km westward shift in the course of the brahmaputra river

variation of structural style and basin evolution in the central zagros izeh zone and dezful embayment iran abstract structural style and its relationship to sedimentary facies and the evolution of sedimentary depocenters since late cretaceous times have been studied on the basis of one regional balanced transect and several updated isopach maps in the izeh zone and the dezful embayment central zagros this study relies on fieldwork data existing geological maps seismic data and well information a new structural classification for part of the zagros sedimentary cover is presented to highlight the different mechanical behavior of the formations in the stratigraphic column it shows the existence of several local decollement levels activated during folding these decollement levels separate lithotectonic units which accommodate shortening in different ways the lower paleozoic is the basal decollement level throughout the studied area triassic evaporites albian shales eocene marls and miocene evaporites can act as intermediate decollement levels and present variable facies in the central zagros lateral facies and thickness variations the sedimentary overburden and the close relationship with inherited fault patterns influenced the wavelength amplitude and style of folding in the study area furthermore surface structures do not necessarily coincide with deeper objectives where these disharmonic levels are involved in folding the evolution of sedimentary depocenters from the late cretaceous obduction episode until early miocene collision is described based on updated isopach maps and tectonic subsidence curves this analysis shows continuous compression and movements along n s and nw se trending faults in the zagros basement which predate the neogene zagros folding and influence sedimentation history it also indicates a southwestward migration of the depocenters through time in addition to the basement involvement below some folds during the zagros orogeny

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

difference in the gps deformation pattern of north and central zagros iran summary measurements on either side of the kazerun fault system in the zagros mountain belt iran show that the accommodation of the convergence of the arabian and eurasian plates differs across the region in northwest zagros the deformation is partitioned as 3 6 mm yr 1 of shortening perpendicular to the axis of the mountain belt and 4 6 mm yr 1 of dextral strikeslip motion on northwest southeast trending faults no individual strike slip fault seems to slip at a rate higher than 2m m yr 1 in southeast zagros the deformation is pure shortening of 8 2m m yr 1 occurring perpendicular to the simple folded belt and restricted to the persian gulf shore the fact that most of the deformation is located in front of the simple folded belt close to the persian gulf while seismicity is more widely spread across the mountain belt confirms the decoupling of the surface sedimentary layers from the seismogenic basement a comparison with the folding and topography corroborates a southwestward propagation of the surface deformation the difference in deformation between the two regions suggests that right lateral shear cumulates on the north south trending kazerun strike slip fault system to 6 2m m yr 1

distribution of the right lateral strike slip motion from the main recent fault to the kazerun fault system zagros iran evidence from present day gps velocities article i nfo gps measurements across the kazerun fault system in the zagros mountain belt provide first instantaneous velocities on the different segments these results are closely consistent with the geological fault slip rates over 150 ka implying stable velocities over a longer period the present day strike slip motion is distributed from the main recent fault to the n trending kazerun fault system along a preferential en echelon fault zone included in a more distributed fan shape fault pattern the hormuz salt decoupling layer cannot be the only cause of a sedimentary spreading because seismicity attests these faults are rooted in the basement the dena fault 3 7 mm yr transfers the mrf fault slip mainly to the kazerun 3 6 mm yr and slightly to the high zagros and sabz pushan faults 1 5 mm yr and the kazerun fault further to the kareh bas fault 3 4 mm yr total geological horizontal offsets associated with gps slip rates help inferring precise fault slip onset ages the successive onsets deduced by this approach imply that the right lateral strike slip activity of the mrf has propagated in time southeastward to the dena segment and then to the kazerun segment and to the kareh bas fault

importance of flood plain sedimentation for river sediment budgets and terrigenous input to the oceans insights from the brahmaputra jamuna river recent authors have suggested that a significant proportion of the worldwide terrigenous sediment budget is trapped landward of the river ocean boundary in high load tectonically active basins to test this idea modern flood plain sediment accumulation rates were determined along a 110 km reach of the brahmaputra locally jamuna river using 137cs geochronology of sediment cores and geographic information system gis extrapolation to adjacent areas 137cs accumulation rates decrease exponentially away from the channel from 4 cm yr on the natural levees to 1 cm yr within a few tens of kilometers basinward important controls on sedimentation in this area include proximity to distributary channels local topography and interannual variability of the flood pulse model results indicate that an average of 23 m t yr of sediment are sequestered in this section of the flood plain extrapolated basinwide as much as 39 71 of the river sediment budget may be trapped landward of the ganges brahmaputra mouth

how much subsidence is enough to change the morphology of river deltas understanding the effect of subsidence on fluviodeltaic morphology is important not only to maintain sustainable coastal cities and habitats but also to interpret the information contained in the stratigraphic record while tectonic steering in alluvial environments has been investigated similar studies in fluviodeltaic environments are limited to physical experiments and field observations we perform numerical experiments with a parcel based cellular model to analyze the deltaic surface and subsurface responses to regional subsidence we quantify model results using robust metrics and show that while sediment partitioning and shoreline pattern vary gradually with increasing subsidence rate channel mobility and stratigraphic connectivity of channel deposits show a threshold transition conditions for this transition are captured with a dimensionless filling index defined as the ratio between the rates of accommodation creation and sediment supply a channel locking mechanism activates when exceeds 0 6 and is responsible for the threshold transition

seismic versus aseismic deformation in iran inferred from earthquakes and geodetic data summary a combined analysis of the geodetic strain rate field and the strain rate field deduced from the seismicity allows us to define the style of deformation and to distinguish seismic from aseismic deformation we perform this analysis in iran where the present day tectonics results from the north south convergence between the plates of arabia to the south and eurasia to the north the data consist of velocities measured with a gps network of 28 benchmarks and of instrumental and historical earthquake catalogues the axes of the seismic strain rate tensor have similar orientations to those deduced from the gps velocity field this indicates that the seismicity can be used to improve gps information on the style and the orientation of the deformation comparison of seismic and geodetic strain rates indicates that highly strained zones experience mainly aseismic deformation in southern iran and seismic deformation in northern iran a large contrast is observed between the zagros less than 5 per cent seismic deformation and the alborz kopet dag regions more than 30 100 per cent seismic deformation the distribution of the seismic geodetic ratio correlates with the distribution of large earthquakes intensive low magnitude seismicity is observed in the zagros whereas the largest earthquakes occur in northern iran the contrast of seismic deformation between the zagros and peri caspian mountains is confirmed considering 300 or 1000 yr of seismicity rather than 100 or 200 yr

autogenic sedimentation in clastic stratigraphy internally generated or autogenic terrestrial and marine sediment transport dynamics can produce depositional patterns similar to those associated with climatic tectonic or sea level changes a central challenge in accurately interpreting the sedimentary archive is determining what scales and types of deposits reflect autogenic controls on sedimentation in different environments autogenic sediment transport dynamics commonly result from intermittent sediment storage in transient landforms which produces episodic spatially discontinuous sedimentation across a basin the transition from localized variable sedimentation to even basin wide sedimentation marks the shift from stochastic landscape dynamics to deterministic deposition responding to the long term balance between sediment supply and the creation of space to accommodate sediment this threshold can be measured in a wide variety of stratigraphic successions and has important bearing on whether climatic tectonic or sea level signals can be

the present day deformation of the central zagros from gps measurements 1 in 1997 and in 2000 we measured the distances between 14 geodetic benchmarks across the central zagros mountain belt the results show that about 10 mm yr of shortening in the central zagros is distributed across the mountain belt this shortening corresponds to roughly 50 of the total convergence between arabia and eurasia and is consistent in direction the persian gulf does not deform significantly the main zagros reverse fault is not an active kinematic boundary the internal deformation of the folded belt is rather homogeneous at the scale of our survey which does not allow us to detect any individual active blind fault however the strain pattern suggests that n s dextral strike slip faults may accommodate part of the deformation

controls on gravel termination in seven distributary channels of the selenga river delta baikal rift basin russia the selenga river delta lake baikal russia is 600 km2 in size and contains multiple distributary channels that receive varying amounts of water and sediment discharge the delta is positioned along the deep water 1600 m margin of lake baikal a half graben styled rift basin qualifying it as a modern analogue of a shelf edge delta system this study provides a detailed field survey of channel bed sediment composition channel geometry and water discharge the data and analyses presented here indicate that the selenga delta exhibits downstream sediment fining over tens of kilometers ranging from predominantly gravel coarse pebble and sand near its apex to silt and sand at the delta lake interface we developed an analytical framework to evaluate the downstream elimination of gravel within the multiple distributary channels the findings include the following 1 the selenga river delta consists of at least eight orders of distributary channels 2 with increasing channel order downstream channel cross sectional area width depth ratio water discharge boundary shear stress and sediment flux systematically decrease 3 the downstream elimination of gravel in distributary channels is caused by declining boundary shear stress as a result of water discharge partitioning among the bifurcating channels 4 over longer time scales gravel is contained on the delta topset due to frequent and discrete seismic events that produce subsidence and accommodation so that coarse sediment cannot be transported to the axis of the baikal rift basin the distribution of sediment grain size in deltaic channels as related to hydrodynamics and sediment transport plays a critical role in influencing stratigraphy because the sustained tectonism leads to high preservation potential of the delta topset sedimentary deposits therefore the selenga river delta provides an opportunity to explore the interactions between modern deltaic sedimentation processes and tectonics that affect the production of basin stratigraphy

plateau pop up in the great 1897 assam earthquake the great assam earthquake of 12 june 1897 reduced to rubble all masonry buildings within a region of northeastern india roughly the size of england and was felt over an area exceeding that of the great 1755 lisbon earthquake1 hitherto it was believed that rupture occurred on a north dipping himalayan thrust fault propagating south of bhutan2 3 4 5 but here we show that the northern edge of the shillong plateau rose violently by at least 11 m during the assam earthquake and that this was due to the rupture of a buried reverse fault approximately 110 km in length and dipping steeply away from the himalaya the stress drop implied by the rupture geometry and the prodigious fault slip of 18 7 m explains epicentral accelerations observed to exceed 1g vertically and surface velocities exceeding 3 m s 1 ref 1 this quantitative observation of active deformation of a pop up structure confirms that faults bounding such structures can penetrate the whole crust plateau uplift in the past 2 5 million years has caused the indian plate to contract locally by 4 2 mm yr 1 reducing seismic risk in bhutan but increasing the risk in northern bangladesh

flume experiments on the horizontal stream offset by strike slip faults flume experiments in which the middle section of an erosion channel is displaced horizontally have been conducted to assess the response of streams to horizontal displacement by a strike slip fault the experimental erosion channel was developed in a mixture of sand and clay which provided relatively stable banks with its cohesiveness horizontal displacement of a strike slip fault perpendicular to the channel is expected to add a flat section to its longitudinal profile along the fault line the experimental stream eliminated this flat section with downstream degradation upstream aggradation and lateral channel shift as a result a roughly continuous longitudinal profile was maintained this maintenance of a continuous longitudinal profile along channel is considered to be the principle of stream response to horizontal displacement by a strikeslip fault downstream degradation was the dominant process of this stream response in the overall tendency of erosion without sand supply when the rate of fault displacement was low long recurrence interval the experimental stream eroded the fault surface jutting laterally into the channel like a scarp and deflected the channel within the recurrence interval this lateral channel shift gave some gradient to the reach created by fault displacement offset reach and the downstream degradation occurred as much as completing the remaining longitudinal profile adjustment when the rate of fault displacement was high short recurrence interval the lateral erosion on the first fault surface was interrupted by the next fault displacement the displacement was then added incrementally to the existing channel offset making channel shift by lateral erosion increasingly difficult the channel offset with sharp bends persisted without much modification and downstream degradation and upstream aggradation became evident with the effect of the offset channel course which worked like a dam in this case a slight local convexity which was incidentally formed by downstream degradation and upstream aggradation tended to remain in the roughly continuous longitudinal profile as long as the horizontal channel offset persisted in either case once the experimental stream obtained a roughly continuous gradient further channel adjustment seemed to halt horizontal channel offset remained to a greater or lesser extent at the end of each run long after the last fault displacement copyright 2004 john wiley sons ltd

coupling mass extraction and downstream fining with fluvial facies changes across the sylhet basin of the ganges brahmaputra meghna delta

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

holocene and modern sediment budgets for the ganges brahmaputra river system evidence for highstand dispersal to flood plain shelf and deep sea depocenters the partitioning of fluvial sediment load across continental margins is an important control on strata formation and sequence development however few quantitative sediment budgets that encompass entire dispersal systems exist for the ganges brahmaputra river system sediment discharge is estimated to be 10 9 t yr at gauging stations 300 km inland of the coast but little has been known of the downstream fate of this material geochronological geophysical and stratigraphic investigations of the lowland flood plain delta plain and shelf help to delineate the extent of holocene fill and allow calculation of a first order sediment budget results reveal that 1500 10 9 m 3 of sediment fill has been sequestered within the flood plain and delta plain since ca 7000 yr b p or about one third of the annual discharge the remaining load appears to be apportioned between the prograding subaqueous delta 1970 10 9 m 3 and transport to the deep sea bengal fan via a nearshore canyon modern 100 yr budget estimates based on short term accretion rates indicate a similar dispersal pattern and show that contemporaneous deposition continues within these disparate depocenters the roughly equal partitioning of sediment among flood plain shelf and deep sea settings reflects the respective influence of an inland tectonic basin a wide shelf and a deeply incised canyon system the findings also support new sequence stratigraphic models for these settings and indicate the important insight that modern river deltas can provide for ancient margin systems furthermore results affirm that values of riverine sediment flux to the oceans may be considerably overestimated by not accounting for loss to the flood plains downstream of the gauging stations

flood variability determines the location of lobe scale avulsions on deltas madagascar river deltas grow through repeated lobe scale avulsions which often occur at a location that correlates with the backwater lengthscale competing hypotheses attribute the avulsion node origin to either the morphodynamic feedbacks caused by natural flood discharge variability backwater hypothesis or to the prograding delta lobe geometry geometric hypothesis here using theory historical flood records and remotely sensed elevation data we analyzed five lobe scale delta avulsions in madagascar captured by landsat imagery avulsion lengths were 5 55 km distances significantly longer than the backwater lengthscale and inconsistent with the geometric hypothesis we show that the steep silt bedded rivers of madagascar have flood induced bed scour driven by backwater hydrodynamics that propagates farther upstream than the backwater lengthscale the avulsion lengths are 3 1 1 5 times the predicted flood scour lengths similar to low gradient deltas and consistent with backwater hypothesis results demonstrate that erosion initiated by nonuniform flows in the backwater zone is a primary control on delta avulsion locations

integrating geochronologic and instrumental approaches across the bengal basin constraining time is of critical importance to evaluating the rates and relative contributions of processes driving landscape change in sedimentary basins the geomorphic character of the field setting guides the application of geochronologic or instrumental tools to this problem because the viability of methods can be highly influenced by geomorphic attributes for example sediment yield and the linked potential for organic preservation may govern the usefulness of radiocarbon dating similarly the rate of sediment transport from source to sink may determine the maturity and or light exposure of mineral grains arriving in the delta and thus the feasibility of luminescence dating here we explore the viability and quirks of dating and instrumental methods that have been applied in the bengal basin and review the records that they have yielded this immense dynamic and spatially variable system hosts the world s most inhabited delta outlining a framework for successful chronologic applications is thus of value to managing water and sediment resources for humans here and in other populated deltas worldwide our review covers radiocarbon dating luminescence dating archaeological records and historical maps short lived radioisotopes horizon markers and rod surface elevation tables geodetic observations and surface instrumentation combined these tools can be used to reconstruct the history of the bengal basin from late pleistocene to present day the growing variety and scope of bengal basin geochronology and instrumentation opens doors for research integrating basin processes across spatial and temporal scales

a re assessment of focal depth distributions in southern iran the tien shan and northern india do earthquakes really occur in the continental mantle summary we investigate the depth distribution of earthquakes within the continental lithosphere of southern iran the tien shan and northern india by using synthetic seismograms to analyse p and sh body waveforms in the zagros mountains of southern iran earthquakes are apparently restricted to the upper crust depths of 20 km whereas in the tien shan and northern india they occur throughout the thickness of the continental crust to depths of 40 45 km we find no convincing evidence for earthquakes in the continental mantle of these regions in spite of previous suggestions to the contrary and question whether seismicity in the continental mantle is important in any part of the world in some regions such as iran the aegean tibet and california seismicity is virtually restricted to the upper continental crust whereas in others including parts of east africa the tien shan and northern india the lower crust is also seismically active although usually less so than the upper crust such variations cannot reliably be demonstrated from published catalogue or bulletin locations even from ones in which depth resolution is generally improved in contrast to the oceanic mantle lithosphere in which earthquakes certainly occur the continental mantle lithosphere is we suggest virtually aseismic and may not be significantly stronger than the lower continental crust these variations in continental seismogenic thickness are broadly correlated with variations in effective elastic thickness suggesting that the strength of the continental lithosphere resides in the crust and require some modification to prevalent views of lithosphere rheology

first quantitative test of alluvial stratigraphic models southern rio grande rift new mexico since 1978 the results of computational architectural models have been widely used to aid interpretation of ancient alluvial successions here we present the first quantitative test of such models we parameterize variables from field and magnetostratigraphic data collected from the well exposed pliocene pleistocene camp rice and palomas formations of the rio grande rift in south central new mexico computational runs establish that the lab leeder allen and bridge model correctly predicts the gross architectural patterns of ancestral axial rio grande half grabens and full grabens convergence of tectonic subsidence rate and mean sedimentation rate over the studied interval suggests that the dynamic basis of the models is correct i e it is the tectonic drawdown of axially supplied sediment that controls the net preservation potential of alluvial successions

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

experimental alluvial fan evolution channel dynamics slope controls and shoreline growth 1 river deltas and alluvial fans have channelization and deposition dynamics that are not entirely understood but which dictate the evolution of landscapes of great social economic and ecologic value our lack of a process based understanding of fan dynamics hampers our ability to construct accurate prediction and hazard models leaving these regions vulnerable here we describe the growth of a series of experimental alluvial fans composed of a noncohesive grain mixture bimodal in size and density we impose conditions that simulate a gravel sand fan prograding into a static basin with constant water and sediment influx and the resulting fans display realistic channelization and avulsion dynamics we find that we can describe the dynamics of our fans in terms of a few processes 1 an avulsion sequence with a timescale dictated by mass conservation between incoming flux and deposit volume 2 a tendency for flow to reoccupy former channel paths and 3 bistable slopes corresponding to separate entrainment and deposition conditions for grains several important observations related to these processes are an avulsion timescale that increases with time and decreases with sediment feed rate fan lobes that grow in a self similar quasi radial pattern and channel geometry that is adjusted to the threshold entrainment stress we propose that the formation of well defined channels in noncohesive fans is a transient phenomenon resulting from incision following avulsion and can be directly described with dual transport thresholds we present a fairly complete process based description of the mechanics of avulsion and its resulting timescale on our fans because the relevant dynamics depend only on threshold transport conditions and conservation of mass we show how results may be directly applied to field scale systems

one dimensional modeling of a recent ganga avulsion assessing the potential effect of tectonic subsidence on a large river abstract river avulsion as studied in small sized and medium sized rivers is partly explained by the water surface gradient advantage of a new channel course over the old course caused by spatial differences in aggradation and compaction recently the effect of meandering upstream of the avulsion node or bifurcation was shown to have an equally large effect on avulsion duration as gradient advantage these effects remain poorly understood for the largest rivers on earth where gradients are very small subtle gradient advantages are affected by tectonics and often several anabranches remain active simultaneously our objective was to assess the relative importance of these factors in the river ganga in determining the pacing of an avulsion we used a combination of historical data remote sensing and one dimensional modeling the course of the ganga in historical times was through the present ganga bhagirathi system but then there was either a gradual or sudden shift to the present ganga padma system historical evidence and remnant paleochannels as observed in satellite sensor data corroborate the changing pattern of the ganga river system but the exact causes of the shifting and of the short avulsion duration remain unclear based on generalized data using a one dimensional model we ran idealized scenarios bracketing different tectonic subsidence estimates for long term morphodynamic evolution of the upstream channel and the two downstream bifurcates the model predicts flow and sediment partitioning at the bifurcation node and includes the effect of migrating meanders at the bifurcation and width adjustment of the bifurcates our modeling demonstrates that the old and the new branches can remain open and morphologically active for a long time because of the large backwater effect and the high mobility of the sediment the bifurcation stabilizes at an asymmetrical flow and sediment division which in smaller rivers such as the river rhine would be followed by residual channel filling but in the much larger ganges results in morphologically active anabranches the model results reveal that neither a gradient advantage nor a bend upstream of the bifurcation leads to an avulsion within centuries as has been observed in some large rivers in tectonically inactive regions on the other hand a realistic tectonic uplift of the old branch or subsidence of the new branch may force an avulsion to take place quickly and historical data show that the study area is seismically active the combination of these factors leads to a realistic modeled avulsion duration of less than three centuries historical data indicate that these general conclusions might also apply to other large rivers in this region e g the brahmaputra and the teesta we conclude that large rivers may avulse quickly in response to tectonics but attain an anabranching pattern because of the large dimension of the residual channel and backwater effects

14c deformation chronologies in coastal iran greece and jordan shoreline chronologies calibrated by 14 c dating can help to disentangle the history of continental deformation holocene uplift rates in the se zagros of iran may be explained by serial folding which is partly aseismic and currently in abeyance the geometry and age of raised beach platforms in the western makran are consistent with structural models which postulate imbricate thrusting powered by low angle subduction the late quaternary fossil beaches bordering the eastern gulf of corinth indicate repeated shifts in the locus of seismic activity and owe their present elevation to uplift of the footwalls of major normal faults on the gulf of aqaba coastal emergence during the last 30 000 years appears to represent the early stages of spreading on the red sea axis coastal sequences thus contribute to structural analysis by revealing changes in the pattern as well as the rate of deformation over the last 50 000 years

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

microearthquake seismicity at the intersection between the kazerun fault and the main recent fault zagros iran summary seismicity and fault plane solutions of earthquakes at the intersection between the main recent fault a right lateral strike slip fault that bounds the zagros to the ne and the kazerun fault system another right lateral zone that crosses the zagros show slip to be partitioned into nearly pure strike slip at shallow depths and nearly pure thrust slip below 12 km such slip partitioning is commonly observed where oblique convergence occurs but in general faults of different styles lie adjacent to one another not at different depths with one below the other we provide evidence for this partitioning in a microearthquake study in which we deployed a temporary network of 29 seismographs for 7 weeks we located no activity north of the main zagros reverse fault mzrf which separates the zagros fold belt from central iran most earthquakes occurred between the northern termination of the kazerun fault and the mzrf but not near to known major faults activity is limited to the upper crust between 2 and 16 km most of the focal mechanisms show strike slip faulting dextral if the ns striking plane is the active plane but a few for the deepest events show reverse faulting distributed between the kazerun fault and the mzrf with p axis trending consistently ns this partitioning of the deformation with depth suggests that the brittle upper crust deforms by slip on pre existing faults that strike obliquely but that the lower crust accommodates the shortening by reverse faulting we infer that the deformation in the upper part of the crust reflects a stiffer medium in which pre existing faults localize the deformation the largest event recorded during this experiment located at the same place as the destructive 1977 naghan earthquake mw 5 9 348 victims shows reverse faulting likely related to the dopolan high zagros fault the crustal thickness deduced from receiver function analysis does not show a marked difference across the kazerun fault which suggests a pure strike slip motion on the fault

the bengal fan external controls on the holocene active channel turbidite activity the eastern levee of the active channel in the bengal fan has been investigated in order to better understand the history of turbidite activity in this channel during the holocene in the context of

gps constraints on africa nubia and arabia plate motions summary we use continuously recording gps cgps and survey mode gps sgps observations to determine euler vectors for relative motion of the african nubian arabian and eurasian plates we present a well constrained eurasia nubia euler vector derived from 23 igs sites in europe and four cgps and three sgps sites on the nubian plate 0 95 4 8 n 21 8 4 3 e 0 06 0 005 myr 1 we see no significant 1m m yr 1 internal deformation of the nubian plate the gps nubian eurasian euler vector differs significantly from nuvel 1a 21 0 4 2 n 20 6 0 6 e 0 12 0 015 myr 1 implying more westward motion of africa relative to eurasia and slower convergence in the eastern mediterranean the arabia eurasia and arabia nubia gps euler vectors are less well determined based on only one cgps and three sgps sites on the arabian plate the preliminary arabia eurasia and arabia nubia euler vectors are 27 4 1 0 n 18 4 2 5 e 0 40 0 04 myr 1 and 30 5 1 0 n 25 7 2 3 e 0 37 0 04 myr 1 respectively the gps arabia nubia euler vector differs significantly from nuvel 1a 24 1 1 7 n 24 0 3 5 e 0 40 0 05 myr 1 but is statistically consistent at the 95 per cent confidence level with the revised euler vector reported by chu gordon based on a re evaluation of magnetic anomalies in the red sea 31 5 1 2 n 23 0 2 7 e 0 40 0 05 myr 1 the motion implied in the gulf of aqaba and on the dead sea fault dsf by the new gps nubia arabia euler vector i e ignoring possible sinai block motion and possible internal plate deformation grades from pure left lateral strike slip in the gulf and on the southern dsf with increasing compression on the central and northern dsf with relative motion increasing from 5 6 to 7 5 mm yr 1 1m m yr 1 from south to north along the northern dsf i e north of the lebanon restraining bend motion is partitioned between 6 1m m yr 1 left lateral motion parallel to the fault trace and 4 1m m yr 1 faultnormal compression relative motions on other plate boundaries including the anatolian and aegean microplates derived from the gps euler vectors agree qualitatively with the sense of motion indicated by focal mechanisms for large crustal earthquakes m 6 where data are available on fault slip rates on plate bounding faults north anatolian fault east anatolian fault dead sea fault red sea rift they are generally lower than but not significantly different from the full plate motion estimates suggesting that the majority of relative plate motion is accommodated on these structures

the paleogene record of himalayan erosion bengal basin bangladesh a knowledge of himalayan erosion history is critical to understanding crustal deformation processes and the proposed link between the orogen s erosion and changes in both global climate and ocean geochemistry the most commonly quoted age of india asia collision is 50 ma yet the record of paleogene himalayan erosion is scant either absent or of low age resolution we apply biostratigraphic petrographic geochemical isotopic and seismic techniques to paleogene rocks of the bengal basin bangladesh of previously disputed age and provenance our data show that the first major input of sands into the basin in the 1 km thick deltaic barail formation occurred at 38 ma our biostratigraphic and isotopic mineral ages date the barail formation as spanning late eocene to early miocene and the provenance data are consistent with its derivation from the himalaya but inconsistent with indian cratonic or burman margin sources detrital mineral lag times show that exhumation of the orogen was rapid by 38 ma the identification of sediments shed from the rapidly exhuming southern flanks of the eastern central himalaya at 38 ma provides a well dated accessible sediment record 17 myr older than the previously described 21 ma sediments in the foreland basin in nepal discovery of himalayan detritus in the bengal basin from 38 ma 1 resolves the puzzling discrepancy between the lack of erosional evidence for paleogene crustal thickening that is recorded in the hinterland 2 invalidates those previously proposed evidences of diachronous collision which were based on the tenet that himalayan derived sediments were deposited earlier in the west than the east 3 enables models of himalayan exhumation e g by mid crustal channel flow to be revised to reflect vigorous erosion and rapid exhumation by 38 ma and 4 provides evidence that rapid erosion in the himalaya was coincident with the marked rise in marine 87sr 86sr values since 40 ma whether 38 ma represents the actual initial onset of vigorous erosion from the southern flanks of the east central himalaya or whether older material was deposited elsewhere remains an open question

tectonic control on sedimentary facies pattern and sediment accumulation rates in the miocene foreland basin of the southern alborz mountains northern iran 1 the southern alborz mountains of northern iran are an integral part of the arabia eurasia collision zone a magnetostratigraphic and rock magnetic investigation of the eyvanekey stratigraphic section in the southern alborz mountains reveals the spatiotemporal character of sedimentary facies migration in the alborz foreland basin the section constitutes three coarsening upward units units 1 2 and 3 comprising the upper red and hezardarreh formations our data reveal that the upper red formation was deposited between 17 5 and 7 5 ma while the depositional age of the top of the hezardarreh formation can be extrapolated to 6 2 ma slow sediment accumulation rates correlate with sedimentary facies comprising prograding coarsening upward units this is likely the result of intraforeland uplift units 1 and 2 and basin inversion probably associated with a growth syncline located in the proximal foreland unit 3 in contrast fine grained strata at the bottom of each cycle are associated with faster sediment accumulation rates testifying to enhanced flexural basin subsidence in the course of thrust loading progradation of coarse grained facies also occurred during relatively fast sediment accumulation top of unit 2 suggesting that the influx of coarse grained sediment outpaced the storage capacity of the proximal foreland thus despite an overall southward propagation of deformation into the southern alborz foreland the locus of active deformation must have migrated back and forth on a time scale of circa 0 7 to 2 ma

a base level stratigraphic approach to determining holocene subsidence of the ganges meghna brahmaputra delta plain abstract relative sea level history which is the result of the combined effects of land subsidence sediment supply and absolute sea level history may be reconstructed from preserved sediment thicknesses however variations in the preserved sediment thicknesses between different sedimentary environments strongly limit the accuracy of this type of geological approach particularly in fluvial channelized systems such as delta plains to address this we apply three different and independent stratigraphic approaches to the case of the ganges brahmaputra meghna delta gbmd our approach has been made possible by a broad dataset of geological archives we have collected which includes more than 400 hand drilled stratigraphic wells 198 radiocarbon ages and river seismic reflection data 255 km of high resolution multichannel seismic images the seaward gradient of accommodation and the limit of the subsiding delta plain are estimated assuming that the delta is near or at the base level which is considered to be the relative sea level first a statistical analysis of the variability of preserved sediment thicknesses is used to derive the average pattern of accommodation from the holocene isopach secondly the preserved sediment thicknesses are analyzed by geomorphotectonic domains to estimate an average pattern of accommodation thirdly the burial history of the seismically imaged last glacial incision of the brahmaputra river is reconstructed results suggest that the variability of preserved sediment thicknesses can be up to 35 in a delta plain between river channel and flood plain deposits for the same relative sea level history taking this variability into consideration the holocene relative sea level history of the gbmd and the most likely pattern of subsidence are determined results provide evidence of moderate holocene subsidence over the delta gently increasing seaward from

late cenozoic partitioning of oblique plate convergence in the zagros fold and thrust belt iran the nw trending zagros fold and thrust belt is affected by two major dextral faults 1 the nw trending main recent fault that accommodates partitioning of oblique convergence at the rear of the western zagros and 2 the north trending kazerun fault located in the central zagros combined structural and fault kinematics studies and spot images analysis have shown a pliocene kinematic change accompanied by a fault pattern reorganization which has led to a modification in the accommodation of oblique convergence since the late pliocene the distributed transpressional deformation operating at the rear of the belt has become partitioned along the newly formed main recent fault this fault cuts through early pliocene nappes and transpressional structures by right laterally reactivating high angle thrusts the southeastern termination of the main recent fault connects to the northern termination of kazerun fault that consists of three fault zones that end in bent orogen parallel splay thrust faults the kazerun fault together with a series of north to nnw trending inherited basement strike slip faults define an orogen scale fan shaped fault pattern pointing toward the main recent fault kazerun fault junction this structural pattern allows slip from along the main recent fault to become distributed by transfer to the longitudinal thrust faults and folds of the zagros belt with the fan shaped fault pattern acting as a horse tail termination of the main recent fault

controls on facies distribution and stratigraphic preservation in the ganges brahmaputra delta sequence abundant sediment supply and accommodation space in the bengal basin have led to the development of a major late quaternary delta sequence this sequence has formed in a tectonically active setting and represents an important example of a high energy marine and fluvial high yield continental margin deposit recent studies have detailed the delta s stratigraphy and development noting that tectonics and sediment supply control the ganges brahmaputra more significantly than in many other delta systems these ideas are developed here through a discussion of the effects that spatial and temporal variations in tectonics and sediment supply have had on deltaic processes and sequence character unique and differing stratigraphies are found within thedeltasystem suchthatfine grainedsedimentpreservationisfavoredinareasofactivetectonicprocessessuchasfolding block faulting and subsidence coarse grained deposits dominate the stratigraphy under the control of high energy fluvial processes and mixed fine coarse stratigraphies are found in areas dominantly influenced by eustatic sea level change overlaid upon these spatially varying stratigraphic patterns are temporal patterns related to episodic events e g earthquakes and rivers avulsions and long termchangesinclimate andsediment supply modelingisalsousedtoinvestigatethe influenceofavariable sedimentsupply on sequence character results show that the timing and magnitude of sediment input relative to sea level rise is a significant control on the subaerial extent of the delta and the relative dominance of alluvial and marine facies within the sequence d 2002 elsevier science b v all rights reserved

estimation of sediment compaction and its relationship with river channel distributions in the yellow river delta china abstract the geomechanical properties of the stratigraphic sequences strongly influence the land surface subsidence as the latter can be caused by the sediment compaction depositional units of transitional environments such as coastal plain and deltas are characterized by a high lithological variability due to the history and complexity of the sedimentary processes therefore detailed modeling of the stratigraphic architecture is necessary to better understand the land surface subsidence process and accurately estimate its rates the frequent avulsion and rearrangement of the channel network in the modern yellow river delta since 1855 has led to the rapid accumulation and deposition of large amounts of sediment in the delta plain the compaction of the substratum sediment due to the new sediment load and the consolidation of younger deposits caused land surface subsidence we used 108 sediment core data covering the delta and obtained detailed stratigraphic structural information a detailed distribution of clay and soft clayey soils which are the primary contributors to land subsidence was identified furthermore the compaction rates and the consolidation at time of the subaerial area and neritic area for the entire modern yellow river delta were estimated we also analyzed the characteristics of present land subsidence by combining a ground movement dataset obtained by high resolution topographic surveys with synthetic aperture radar sar interferometry insar of satellite images the results show that during the early stages of the development of the active deltaic lobe the compaction of neritic sediments was the primary contributor to initial subsidence furthermore combined with the relevant sedimentary age and environment determined by previous studies we found that the spatial variation in compaction induced subsidence in the subaerial deltaic area over time is closely related to the historical distributions of the river channels in the modern yellow river delta our findings providing a better characterization of the spatial and time heterogeneity of the land surface subsidence of both subaerial and submarine areas significantly improved the previous knowledge on land subsidence of the yellow river delta our results also demonstrate that the subaerial delta becomes increasingly stable over time with the gradual decrease in the average subsidence rate of each deltaic lobe

collision of the ganges brahmaputra delta with the burma arc implications for earthquake hazard abstract we take a fresh look at the topography structure and seismicity of the ganges brahmaputra delta gbd burma arc collision zone in order to reevaluate the nature of the accretionary prism and its seismic potential the gbd the world s largest delta has been built from sediments eroded from the himalayan collision these sediments prograded the continental margin of the indian subcontinent by 400 km forming a huge sediment pile that is now entering the burma arc subduction zone subduction of oceanic lithosphere with 20 km sediment thickness is fueling the growth of an active accretionary prism exposed on land the prism starts at an apex south of the gbd shelf edge at 18 n and widens northwards to form a broad triangle that may be up to 300 km wide at its northern limit the front of the prism is blind buried by the gbd sediments thus the deformation front extends 100 km west of the surface fold belt beneath the comilla tract which is uplifted by 3 4 m relative to the delta this accretionary prism has the lowest surface slope of any active subduction zone the gradient of the prism is only 0 1 rising to 0 5 in the forearc region to the east this low slope is consistent with the high level of overpressure found in the subsurface and indicates a very weak detachment since its onset the collision of the gbd and burma arc has expanded westward at 2 cm yr and propagated southwards at 5 cm yr seismic hazard in the gbd is largely unknown intermediate size earthquakes are associated with surface ruptures and fold growth in the external part of the prism however the possibility of large subduction ruptures has not been accounted for and may be higher than generally believed although sediment clogged systems are thought to not be able to sustain the stresses and strain weakening behavior required for great earthquakes some of the largest known earthquakes have occurred in heavily sedimented subduction zones a large earthquake in 1762 ruptured 250 km of the southern part of the gbd suggesting large earthquakes are possible there a large but poorly documented earthquake in 1548 damaged population centers at the northern and southern ends of the onshore prism and is the only known candidate for a rupture of the plate boundary along the subaerial part of the gbd burma arc collision zone

influence of steady base level rise on channel mobility shoreline migration and scaling properties of a cohesive experimental delta 1 here we describe results from an alluvial delta physical experiment with and without steady base level rise using a unique cohesive sediment mixture that promotes the development of persistent channels and a rugose shoreline we quantitatively characterize channel network properties as a function of base level rise in a distributary system that reproduces many aspects of the geometry of natural deltas analysis of the experimental data shows clear dynamical differences between the predominantly progadational and aggradational phases of the experiment the experiment was conducted in two phases a first in which the delta prograded into standing water of constant depth in the absence of base level rise and a second during which steady base level rise was imposed on the system forcing a twofold increase in topset aggradation due to greater sediment retention in the fluvial reach the shift in sediment mass balance to enhanced fluvial deposition in the second phase caused channel network mobility to increase reducing the autogenic channel time scale from 23 5 to 12 5 h and supporting a positive correlation between deposition and channel avulsion frequency an independent shoreline time scale that characterizes the dominant time over which shoreline regression is persistent closely correlates with measurements of the channel network 28 3 h during fan progradation and 9 5 h during fan aggradation these metrics suggest a strong coupling between channel network and shoreline kinematics and a more active fluvial surface during fan aggradation by a factor of 2 to 3 similar to the increase in aggradation rate spatial scaling of shoreline roughness reveals that maximum shoreline variability is set by the scale of distributary lobes strong coupling exists between delta growth and shoreline geometry during progradation during aggradation however shoreline variability is not solely due to distributary lobe growth but is also set by shoreline transgression over inactive portions of the delta illustrating a decoupling between fan kinematics and fan geometry this decoupling together with the matched increase in channel network mobility and fluvial aggradation suggest the stratigraphic architecture may not be a strong geometric signal of different fluvial surface conditions either

backwater controls of avulsion location on deltas river delta complexes are built in part through repeated river channel avulsions which often occur about a persistent spatial node creating delta lobes that form a fan like morphology predicting the location of avulsions is poorly understood but it is essential for wetland restoration hazard mitigation reservoir characterization and delta morphodynamics following previous work we show that the upstream distance from the river mouth where avulsions occur is coincident with the backwater length i e the upstream extent of river flow that is affected by hydrodynamic processes in the receiving basin to explain this observation we formulate a fluvial morphodynamic model that is coupled to an offshore spreading river plume and subject it to a range of river discharges results show that avulsion is less likely in the downstream portion of the backwater zone because during high flow events the water surface is drawn down near the river mouth to match that of the offshore plume resulting in river bed scour and a reduced likelihood of overbank flow furthermore during low discharge events flow deceleration near the upstream extent of backwater causes enhanced deposition locally and a reduced channel fill timescale there both mechanisms favor preferential avulsion in the upstream part of the backwater zone these dynamics are fundamentally due to variable river discharges and a coupled offshore river plume with implications for predicting delta response to climate and sea level change and fluvio deltaic stratigraphy

offset on the main recent fault of nw iran and implications for the late cenozoic tectonics of the arabia eurasia collision zone summary we use drainage patterns geological markers and geomorphological features to determine a right lateral offset of 50 km and possibly as much as 70 km on the main recent fault in nw iran this fault trends nw se and forms the ne border of the zagros mountains it accommodates the strike slip component of the n s convergence between arabia and eurasia with the ne sw shortening component being accommodated in the zagros fold belt its 50 km strike slip offset implies a shortening of 50 km in the fold belt and 70 km total n s convergence accommodated in the nw zagros this is a substantial fraction of the 85 140 km overall arabia eurasia convergence expected over the last 3 5 ma if the main recent fault initiated at that time as seems likely from geological arguments it has a horizontal slip rate of at least 10 17 mm yr 1 and should be the source of frequent earthquakes of ms 6 7 as has been seen in the 20th century and the earlier historical record the similarity of the offsets and probable ages of the north anatolian and main recent faults suggests that they have been active as an almost continuous zone of right lateral shear on the north edge of the arabian and anatolian plates since the early pliocene

present day crustal deformation and plate kinematics in the middle east constrained by gps measurements in iran and northern oman summary a network of 27 gps sites was implemented in iran and northern oman to measure displacements in this part of the alpine himalayan mountain belt we present and interpret the results of two surveys performed in 1999 september and 2001 october gps sites in oman show northward motion of the arabian plate relative to eurasia slower than the nuvel 1a estimates e g 22 2m m yr 1 at n8 5 e instead of 30 5 mm yr 1 at n6 e at bahrain longitude we define a gps arabia eurasia euler vector of 27 9 0 5 n 19 5 1 4 e 0 41 0 1 myr 1 the arabia eurasia convergence is accommodated differently in eastern and western iran east of 58 e most of the shortening is accommodated by the makran subduction zone 19 5 2m m yr 1 and less by the kopet dag 6 5 2m m yr 1 west of 58 e the deformation is distributed in separate fold and thrust belts at the longitude of tehran the zagros and the alborz mountain ranges accommodate 6 5 2m m yr 1 and 8 2m m yr 1 respectively the right lateral displacement along the main recent fault in the northern zagros is about 3 2m m yr 1 smaller than what was generally expected by contrast large rightlateral displacement takes place in northwestern iran up to 8 mm yr 1 the central iranian block is characterized by coherent plate motion internal deformation 2m m yr 1 sites east of 61 e show very low displacements relative to eurasia the kinematic contrast between eastern and western iran is accommodated by strike slip motions along the lut block to the south the transition zone between zagros and makran is under transpression with right lateral displacements of 11 2m m yr 1

the southern zagros collisional orogen new insights from transdimensional trees inversion of seismic noise the natural environmental research council nerc grant ne r013500 1 and from the european union s horizon 2020 research and innovation program under marie sklodowska curie grant agreement 790203

the planform mobility of river channel confluences insights from analysis of remotely sensed imagery river channel confluences are widely acknowledged as important geomorphological nodes that control the downstream routing of water and sediment and which are locations for the preservation of thick fluvial deposits overlying a basal scour despite their importance there has been little study of the stratigraphic characteristics of river junctions or the role of confluence morphodynamics in influencing stratigraphic character and preservation potential as a result although it is known that confluences can migrate through time models of confluence geomorphology and sedimentology are usually presented from the perspective that the confluence remains at a fixed location this is problematic for a number of reasons not least of which is the continuing debate over whether it is possible to discriminate between scour that has been generated by autocyclic processes such as confluence scour and that driven by allocyclic controls such as sea level change this paper investigates the spatial mobility of river confluences by using the 40 year record of landsat imagery to elucidate the styles rates of change and areal extent over which large river confluence scours may migrate on the basis of these observations a new classification of the types of confluence scour is proposed and applied to the amazon and ganges brahmaputra meghna gbm basins this analysis demonstrates that the drivers of confluence mobility are broadly the same as those that drive channel change more generally thus in the gbm basin a high sediment supply large variability in monsoonal driven discharge and easily erodible bank materials result in a catchment where over 80 of large confluences are mobile over this 40 year window conversely this figure is 40 for the amazon basin these results highlight that i the potential areal extent of confluence scours is much greater than previously assumed with the location of some confluences on the jamuna brahmaputra river migrating over a distance of 20 times the tributary channel width ii extensive migration in the confluence location is more common than currently assumed and iii confluence mobility is often tied to the lithological and hydrological characteristics of the drainage basins that determine sediment yield

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

experimental steep braided flow application to flooding risk on fans flooding processes occurring on alluvial fans are considerably different from those occurring along single thread rivers with well defined floodplains active erosion rapid sedimentation and the uncertainty in flow path make the prediction of flood evolution and extent difficult based on a large scale experiment this study investigates the long term evolution of the flow on a steep noncohesive sediment surface resembling a complex of merged alluvial fans the results are pertinent to the assessment of flooding hazard on alluvial fans at any given time the average flow occupancy was 21 of the surface however the flow was characterized by active channel switching and overflow processes the percentage of the surface remaining dry was found to decay harmonically with time a reworking time was defined as the time at which half of the surface that was initially dry remained dry whereas the other half was inundated at least once an empirical expression was developed in which reworking time is proportional to the average cross sectional area of flow and inversely proportional to the sediment supply

experimental investigation of sediment dominated vs tectonics dominated sediment transport systems in subsiding basins abstract models of stratigraphic architecture make testable predictions regarding the subsurface spatial density and connectivity of channel sandstone bodies in subsiding basins here we test one of these predictions that lateral gradients of subsidence rate in alluvial basins tend to draw channels to local subsidence maxima and thus increase the subsurface stacking density of channel sand bodies in the vicinity of subsidence maxima here we define channel steering as any change in channel course due to lateral gradients in subsidence focusing on the attraction of channels to regions of high subsidence we examine the hypothesis that steering is controlled by the tilting ratio the ratio of the rate of lateral tilting to that of lateral channel mobility with steering effects expected to increase as the tilting ratio increases we present measurements of channel steering from experiments in which we varied the tilting ratio over four stages the experiments used a relay ramp geometry with laterally variable uplift and subsidence initially with a small value of the tilting ratio we did not detect noticeable channel steering through reductions in input sediment discharge qs and water discharge qw we decreased channel mobility in later stages while keeping the subsidence regime the same this resulted in systematic increases in the tilting ratio and in observable steering towards regions of high subsidence interestingly the increase in tilting rate relative to channel mobility also resulted in a preference for channel occupation over uplift regions as channels were trapped by incision into the rising surface we also develop theory to predict when the strength and duration of pulsed tilting events are sufficient to steer channels as with the theory for steady subsidence the new theory suggests that pulsed events must be strong enough and long lived enough to produce comparable cross basin to down basin transport slopes an experimental stage with pulsed tectonics supports this theory finally we document autogenic shoreline transgressions in the relay zone during deformation these transgressions produce downstream to upstream facies translation of the sand coal boundary in the preserved stratigraphy and illustrate a mechanism by which transgressions can develop without external cause

progressive unconformities within an evolving foreland fold thrust belt zagros mountains a major angular unconformity between the bakhtyari conglomerates and the underlying agha jari formation has long been interpreted as indicating that orogeny in the zagros simply folded zone took place in plio pleistocene times this study uses field evidence of unconformities between older units in conjunction with geological maps and cross sections to argue that the front of the zagros simply folded zone has propagated in time and space these unconformities indicate that deformation started as early as end eocene in the northeast of the simply folded zone and propagated progressively to the southwest where unconformable contacts are only seen between younger units as shortening continued the southwest migration of the deformation front drove the foreland basin in front of it to its present position along the persian gulf and mesopotamia the climax of orogeny took place at end pliocene time when the most extensive unconformity in the zagros simply folded zone developed between the upper bakhtyari formation and older units active seismicity and documented present uplift imply that the simply folded zone is still propagating southwestward

an overview of the sedimentary geology of the bengal basin in relation to the regional tectonic framework and basin fill history abstract the bengal basin in the northeastern part of indian subcontinent between the indian shield and indo burman ranges comprises three geo tectonic provinces 1 the stable shelf 2 the central deep basin extending from the sylhet trough in the northeast towards the hatia trough in the south and 3 the chittagong tripura fold belt due to location of the basin at the juncture of three interacting plates viz the indian burma and tibetan eurasian plates the basin fill history of these geo tectonic provinces varied considerably precambrian metasediments and permian carboniferous rocks have been encountered only in drill holes in the stable shelf province after precambrian peneplanation of the indian shield sedimentation in the bengal basin started in isolated graben controlled basins on the basement with the breakup of gondwanaland in the jurassic and cretaceous and northward movement of the indian plate the basin started downwarping in the early cretaceous and sedimentation started on the stable shelf and deep basin and since then sedimentation has been continuous for most of the basin subsidence of the basin can be attributed to differential adjustments of the crust collision with the various elements of south asia and uplift of the eastern himalayas and the indo burman ranges movements along several well established faults were initiated following the breakup of gondwanaland and during downwarping in the cretaceous by eocene because of a major marine transgression the stable shelf came under a carbonate regime whereas the deep basinal area was dominated by deep water sedimentation a major switch in sedimentation pattern over the bengal basin occurred during the middle eocene to early miocene as a result of collision of india with the burma and tibetan blocks the influx of clastic sediment into the basin from the himalayas to the north and the indo burman ranges to the east rapidly increased at this time and this was followed by an increase in the rate of subsidence of the basin at this stage deep marine sedimentation dominated in the deep basinal part while deep to shallow marine conditions prevailed in the eastern part of the basin by middle miocene with continuing collision events between the plates and uplift in the himalayas and indo burman ranges a huge influx of clastic sediments came into the basin from the northeast and east throughout the miocene the depositional settings continued to vary from deep marine in the basin to shallow and coastal marine in the marginal parts of the basin from pliocene onwards large amounts of sediment were filling the bengal basin from the west and northwest and major delta building processes continued to develop the present day delta morphology since the cretaceous architecture of the bengal basin has been changing due to the collision pattern and movements of the major plates in the region however three notable changes in basin configuration can be recognized that occurred during early eocene middle miocene and plio pleistocene times when both the paleogeographic settings and source areas changed the present basin configuration with the ganges brahmaputra delta system on the north and the bengal deep sea fan on the south was established during the later part of pliocene and pleistocene and delta progradation since then has been strongly affected by orogeny in the eastern himalayas pleistocene glacial activities in the north accompanied sea level changes in the bay of bengal

experimental test of tectonic controls on three dimensional alluvial facies architecture abstract in an extended series of papers by m leeder j r l allen j s bridge j alexander and others the depositional stacking patterns of channel belt deposits were related to tectonic and other external controls we refer to these models collectively as lab models these models established a basic connection between subsidence channel avulsion and the mesoscale channel belt architecture of an alluvial deposit two fundamental predictions resulted from this work 1 channel belt stacking density and hence connectedness is inversely correlated to temporal vertical changes in sedimentation rate and 2 channel belt stacking density and hence connectedness is directly correlated to lateral changes in sedimentation rate in this paper we make use of the experimental earthscape xes facility at the st anthony falls laboratory to examine the effects of temporally and laterally variable subsidence rates on mesoscale alluvial architecture we then compare the experimental results with the main predictions of the early lab models regarding the predictions of the lab models under conditions of high sediment supply and a highly active alluvial system lateral and downstream variation in subsidence geometry and rate have little effect on the details of alluvial architecture we found that the principal architectural signature of changes in subsidence geometry i e laterally variable subsidence rate is stratal tilting and that channel belts are not attracted to the subsidence maximum we hypothesize that the effect of variable subsidence geometry is felt by the fluvial system only if subsidence proceeds faster than the river can adjust to the formation of a topographic low via the deposition of overbank material in the form of splays and sheet sands our results lend impetus to the development of more complete three dimensional numerical models of mesoscale alluvial architecture that couple architecture to broader allogenic forcing mechanisms

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

the geology of the kuh e dalneshin area of southern iran and its bearing on the evolution of southern tethys the kuh e dalneshin area lay close to the northern margin of the arabian continent during mesozoic and palaeogene times recent mapping has shown that except perhaps in the late cretaceous it was inactive until it collided with central iran in the miocene the collision represented by a neogene melange zone in the ne resulted in the zagros orogeny and is expressed in the shelf sediments by folding parallel faulting and a possible arcuate sinistral shear in the late cretaceous a localized deepening of the shelf dates from the cenomanian a narrow trough in the w subsided to abyssal depths in the turonian following a period of faulting a more wide spread subsidence affected the shelf in the coniacian and santonian autochthonous cherts and associated sediments accumulated basaltic volcanics were erupted in the ne part of this basin and permian to cenomanian neritic exotic blocks were derived presumably from an uplift at the shelf edge the rocks from the outer edge of this basin slid westwards over their autochthonous counterparts probably in the campanian accompanied by further gliding of masses of earlier mesozoic cherts which had previously been emplaced on the continental margin a sheet of mantle peridotite partly serpentinized and enclosing neritic and metamorphic exotics in turn slid into the basin shelf sedimentation was renewed in the late campanian or maestrichtian but the transgression did not reach the area until the eocene the derivation and emplacement of the allochthonous rocks in the late cretaceous are still imperfectly understood alternative models are discussed one involving gliding from an aborted spreading ridge along the continental margin the other more conventionally based on subduction processes a preference is expressed for the former

the significance of large sediment supply active tectonism and eustasy on margin sequence development late quaternary stratigraphy and evolution of the ganges brahmaputra delta abstract borehole data from the ganges brahmaputra delta system unveil an intriguing late quaternary history controlled by immense sediment discharge tectonics and eustasy sea level first intersected a major portion of the lowstand surface 10 000 11 000 cal yr bp marking the onset of sediment trapping and delta growth despite rapid sea level rise 1 cm yr sediment load was sufficient to maintain relative shoreline stability during this time by 7000 cal yr bp accommodation was quickly infilled with slowed sea level rise leading to upstream channel migration and widespread dispersal of sands this forced coastal progradation along the western delta front where the ganges was situated and much of the river s fine grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf concurrently brahmaputra sediments were sequestered to an inland tectonic basin thus starving the adjacent shoreline and leading to transgression along the eastern delta by 5000 cal yr bp the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river mouth estuary present delta configuration appears to have developed by 3000 cal yr bp evolution of the tectonically active ganges brahmaputra g b system reveals important similarities and differences with other deltas overall facies succession follows that of basic models progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain however the timing thickness and controls of these deposits differ immense sediment discharge from the ganges and brahmaputra rivers allowed initial delta growth 2000 3000 yr earlier than the global average despite debouching onto a canyon incised high energy margin subsequently a thick 50 m transgressive systems tract was formed during the early holocene phase of delta aggradation contrasting with extensive shoreline retreat documented along most margins highstand progradation of coastal and shelf sequences ensued by the middle holocene but subsiding inland basins also favored accumulation of a thick to 40 m highstand sequence in the lower floodplains unlike many other delta systems subsidence in the subaerial g b delta is not dominated by compaction but rather by plate driven tectonic processes that generate rates up to 4 mm year overall the huge sediment load tectonic subsidence major seismic events and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta shelf and deep sea bengal fan throughout the late quaternary

the accommodation of arabia eurasia plate convergence in iran continental convergence between arabia and eurasia is taken up by distributed deformation in iran at wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field the only quantitative source of information on the spatial distribution of strain rates within iran is the record of earthquakes we find that we can reproduce the style of deformation observed in the seismicity by simply minimizing the rate of work in a continuous viscous medium that has to accommodate the arabia eurasia plate motion between the defined shapes of iran s rigid borders when in addition we specify central iran azerbaijan and the southern caspian basin to be relatively rigid blocks within the deforming zone then the fit to the style of the observed strain rate distribution is even better we conclude that much of the pattern of deformation in iran is predetermined by the shape of its rigid borders and by the disposition of relatively rigid blocks within it this is likely also to have been a common occurrence in older orogenic belts we confirm earlier suggestions that earthquakes between 1909 and 1992 can account for only a small part 10 20 of the total deformation required by the convergence between the arabia and eurasia plates we then show that the whole plate motion can be accommodated by a velocity field with the same orientations and relative magnitudes of principal strain rates seen in the earthquakes but with larger absolute magnitudes there is therefore no requirement that the large proportion of aseismic deformation in iran is substantially different in style orientation or distribution from that released seismically in the earthquakes

late quaternary sedimentary record and holocene channel avulsions of the jamuna and old brahmaputra river valleys in the upper bengal delta plain abstract the first holocene stratigraphic record of river channel occupation and switching between the brahmaputra jamuna and old brahmaputra paleovalleys is presented here motivated by the brahmaputra river s historic avulsion from the old brahmaputra channel to its present day jamuna course we have obtained sediment and radiocarbon samples from 41 boreholes along a 120 km transect crossing these two braided river valleys the stratigraphy along this transect reveals sand dominated holocene channel systems each bound by remnant mud capped pleistocene stratigraphy using sediment lithology and bulk strontium concentration as a provenance indicator we define the geometry and channel occupation history of each paleovalley the western brahmaputra jamuna valley is broad and somewhat deeper compared with the old brahmaputra valley the latter actually comprising a composite of two narrower sub valleys bifurcated by an antecedent topographic remnant the gently sloped valley margins slope 0 002 to 0 007 and high width to thickness ratio w t 1000 of the brahmaputra jamuna valley suggest that it was filled primarily through lateral channel migration and the reworking of braidbelt and overbank deposits conversely the two old brahmaputra sub valleys have comparatively steeper valley margins slope 0 007 to 0 022 and lower width to thickness ratios w t 125 and 250 indicating that these were filled primarily through vertical aggradation of channel sands we attribute this disparity in valley geometry and fill processes to the different occupation histories for each valley in this case the much larger brahmaputra jamuna valley represents the principal if not singular river course during the last lowstand of sea level with a prominent gravel lag underlying the valley in contrast the smaller old brahmaputra valleys do not appear to have been present or at least well developed at the last lowstand rather these courses were first occupied during the early holocene transgression and we infer that the river had been previously excluded from this region by the relatively higher elevation between the madhupur terrace and the shillong massif we also demonstrate that the brahmaputra river experienced 3 4 major avulsions during the holocene with considerably longer occupation times within the principal brahmaputra jamuna valley together these observations indicate that occupation history and antecedent topography have been important controls on river course mobility and avulsion behavior

earthquakes on the kazerun line in the zagros mountains of iran strike slip faulting within a fold and thrust belt summary the kazerun line is a transverse valley of about 200 km long that obliquely crosses the regular anticlines of the zagros fold belt in sw iran at its northern end it is a clear fault which can be mapped on the surface anticline axes die out or bend towards this valley but do not cross it six moderate sized earthquakes that occurred close the the kazerun line and within a 25 km area involved right lateral strike slip motion parallel to the strike of the valley they indicate that the kazerun line is the surface expression of a buried strike slip fault slip vectors in these strike slip earthquakes are different from those of neighbouring reverse fault earthquakes suggesting that the kazerun line accommodates some of the shortening between arabia and central iran by an elongation of the zagros mountains parallel to strike the centroid depths and the source dimensions of these earthquakes combined with the lack of seismogenic surface faulting in the zagros suggest to us that all these earthquakes involve faulting in the metamorphic basement beneath the sedimentary cover the sedimentary cover is almost certainly decoupled from the basement by several thick evaporite horizons the seismicity of the kazerun line thus demonstrates how lateral interruptions to the regularity of a fold belt can arise from faulting in the basement and not just from lateral ramps between the thrust sheets that deform the sedimentary cover

spatial variation in the frequency magnitude distribution of earthquakes under the tectonic framework in the middle east abstract spatial variations of seismic energy released and b value over the middle east region are investigated based on a seismicity catalog from 1995 to 2007 the goal is to use these seismic parameters and based on other geodetic and geophysical observations such as gps measurements strain rate model fault distribution focal mechanism crustal model q model and gravity measurements etc to uncover spatial patterns that seem anomalous areas of high energy released cumulative seem to correspond to the areas of relatively high b values areas of high energy released and high b values seem to correspond very well with the location of continental collision where earthquake activities are high the divergent boundary between arabia and african plates and subduction zone at makran seem to correspond to low to moderate energy release northern pamir azerbaijan caucasus the lower part of zagros mountains eastern turkey owen fracture zone strait of bob el mandeb and south of the sulaiman shear zone seem to correspond to high cumulative energy released high strain rate high b values and high fault density while the central and eastern iran southern zagros northern pakistan gulf of aden alborz southwest of the caspian sea western caucasus and kopeh dagh seem to correspond with lower b values the cross section map for hindu kush shows general decreasing of the b values with depth however a region of high b value is observed underneath pamir at depths from 170 to 230 km this anomaly region can be due to dehydration of pamir crustal slab at depth

the 2006 march 25 fin earthquakes iran insights into the vertical extents of faulting in the zagros simply folded belt summary we investigate the depth of faulting and its connection with surface folding in the zagros simply folded belt of iran our focus is a sequence of earthquakes mw 5 7 5 5 5 2 5 0 4 9 that struck the fin region in the south eastern simply folded belt on 2006 march 25 modelling ground displacements measured with radar interferometry we find that either n or s dipping model reverse faults can reproduce the observed fringe patterns despite the uncertainty in fault orientation we can constrain the vertical extents of rupture to between a top depth of 5 6 km and a bottom depth of 9 10 km consistent with the 8 km centroid depth of the largest earthquake we suggest that the faulting ruptured the thick competent group of paleozoic and mesozoic conglomerates and platform carbonates which makes up the lower part of the sedimentary cover the rupture probably terminated within the precambrian hormuz salt at its base and the cretaceous gurpi marls at its top these mechanically weak layers act as barriers to rupture separating faulting within the competent group from deformation in the layers above and below the pattern of coseismic surface uplift is centred on the common limb of the fin syncline and guniz anticline but is oblique by 20 to the trend of these open symmetric whaleback folds and also overlaps a section of the fin syncline axis these observations suggest that locally surface folding is decoupled from the underlying reverse faulting although the fin syncline and guniz anticline are symmetric structures some other nearby folds show a strong asymmetry with steep or overturned southern limbs consistent with growth above n dipping reverse faults this suggests that the simply folded belt contains a combination of forced folds and detachment folds we also investigate the distribution of locally recorded aftershocks in the weeks following the main earthquakes most of these occurred at depths of 10 30 km with a particularly high concentration of events at 20 25 km these aftershocks therefore lie within the crystalline basement rather than the sedimentary cover and are vertically separated from the main rupture this study confirms earlier suggestions that earthquakes of mw 5 6 are capable of being generated within the thick competent group of paleozoic and mesozoic sediments as well as in the basement below the hormuz salt formation