relations between jointing and faulting based on fracture spacing ratios and fault slip profiles a new method to estimate strain in layered rocks by using fault slip profiles and fracture spacing ratios fsrs a direct link is established between slip variations across a normal fault zone and anomalous joint densities in adjacent wall rock faulting in bedded chalk near beer sheva israel was impeded by competent cherts requiring the development of subsidiary faults to accommodate unrelieved strain the composite slip profile for the entire normal fault zone is smooth and uniform except for a sharp localized decrease near one bed resulting in a steep slip gradient this bed displays unusually closely spaced joints in the hanging wall fsr 2 2 as opposed to typical joint spacings fsr 1 5 in the footwall the slip deficit may reflect a surplus of elastic strain stored in that bed which was released in the form of additional joints during subsequent jointing this study reveals that joint densities in wall rock can vary as a function of fault geometry and slip distribution and the fsr may be used as an effective tool to estimate strain around local structures

role of vegetation restoration in mitigating hillslope erosion and debris flows abstract after the 2008 wenchuan earthquake a large amount of loose landslide deposits was left in the stricken region a heavy storm in 2010 turned numerous deposits into debris flows after 2010 vegetation gradually recovered on the remnant soil deposits during the wet seasons in 2013 and 2015 the number of debris flows decreased significantly compared with that in 2010 this paper investigates the role of vegetation in mitigating runoff induced hillslope erosion and debris flows the study slope is near the epicentre of the wenchuan earthquake three levels of vegetation restoration are considered bare in 2010 middle level in 2013 and high level in 2015 soil samples were taken from the landslide deposits to determine the root mass density which is used to quantify erosion resistance parameters at different vegetation levels massive erosion is simulated in the 2010 case which in turn develops into hillslope debris flows very little or no erosion is simulated in the 2013 and 2015 cases which is in part attributed to the enhanced resistance to erosion by restored vegetation a parametric study is conducted to further investigate the effectiveness of erosion reduction through revegetation

how well can we simulate complex hydro geomorphic process chains the 2012 multi lake outburst flood in the santa cruz valley cordillera blanca peru changing high mountain environments are characterized by destabilizing ice rock or debris slopes connected to evolving glacial lakes such configurations may lead to potentially devastating sequences of mass movements process chains or cascades computer simulations are supposed to assist in anticipating the possible consequences of such phenomena in order to reduce the losses the present study explores the potential of the novel computational tool r avaflow for simulating complex process chains r avaflow employs an enhanced version of the pudasaini 2012 general two phase mass flow model allowing consideration of the interactions between solid and fluid components of the flow we back calculate an event that occurred in 2012 when a landslide from a moraine slope triggered a multi lake outburst flood in the artizon and santa cruz valleys cordillera blanca peru involving four lakes and a substantial amount of entrained debris along the path the documented and reconstructed flow patterns are reproduced in a largely satisfactory way in the sense of empirical adequacy however small variations in the uncertain parameters can fundamentally influence the behaviour of the process chain through threshold effects and positive feedbacks forward simulations of possible future cascading events will rely on more comprehensive case and parameter studies but particularly on the development of appropriate strategies for decision making based on uncertain simulation results 2017 the authors earth surface processes and landforms published by john wiley sons ltd

the formation and breach of a short lived landslide dam at hsiaolin village taiwan part i post event reconstruction of dam geometry abstract in this paper technologies from multiple disciplines are used to reconstruct the shape of the hsiaolin landslide dam a short lived landslide dam sld that was triggered by typhoon morakot here the formation failure mode and breaching process of this sld are investigated the results indicate that the overtopping time and the debris budget constrained the dam geometry the inferred volume of the hsiaolin landslide dam 15 4 million m3 is much smaller than the actual landslide volume 25 2 million m3 even considering the rock mass dilation and debris entrainment meanwhile a 46 error could be induced if an over simplified equation a function of the dam height length and width is used to calculate the dam volume the saddle of the dam crest which is where overtopping occurred could be used as a reference to measure the dam height and length accordingly the determined dam dimensions of height 44 m length 370 m and width 1500 m are suggested to be the representative geometrical indices that influenced the stability of the hsiaolin landslide dam the flow rate of the dammed river another variable relevant to dam stability was determined from a run off simulation it is suggested that instead of the peak flow before the dam formation the flow rate during the blockage period 2974 m3 s should be used as the training data for building a statistical model for stability predictions finally the low hydraulic gradient at the toe of the dam s surface and the high safety factor of the dam slope indicate that the piping and slope instability were irrelevant to the failure of the hsiaolin short lived landslide dam it is postulated that overtopping about one hour after the blockage dominated the failure process of this heavy rainfall induced landslide dam

hyperconcentrated flow and sediment transport at steep slopes in order to simulate a fine material slurry of a debris flow a clay suspension of various concentrations was recirculated in a steep flume the effect of an increasing fluid density and viscosity on the flow behavior and the bed load transport capacity of the flow was examined viscous effects were found to become important below a limiting particle reynolds number of about 10 above this limiting value density effects cause an increase in the bed load transport rates as compared to similar conditions with clear water as transporting fluid the experimental data in this range can be described with conventional newtonian formulas and is analyzed together with other bed load transport data two different calculation schemes are proposed for the steep slope range is n n 10 where the bed load concentration is significant with respect to the total flow depth below the critical particle reynolds number of 10 the bed load transport rates decreased strongly

laboratory analysis of mudflow properties a rotational viscometer has been designed for laboratory measurements of the rheological properties of natural mudflow deposits in colorado the mudflow matrices comprised of silt and clay particles are sheared under temperature controlled conditions at volumetric sediment concentrations ranging from 0 10 0 45 this study stresses the importance of conducting rheological measurements at low rates of shear because 1 those are the conditions found in natural channels and 2 they avoid the slippage problems observed at large sediment concentrations at low rates of shear the bingham model is fitted to the measured rheograms and both the viscosity and yield stress increase exponentially with the sediment concentration of the fluid matrix both the yield stress and the viscosity increase by three orders of magnitude as the volumetric concentration of sediments in the fluid matrix changes from 10 to 40 the addition of sand particles does not significantly alter the rheological properties of the matrix unless the volumetric concentration of sands exceeds 0 20

entrainment of bed material by earth surface mass flows review and reformulation of depth integrated theory earth surface mass flows such as debris flows rock avalanches and dam break floods can grow greatly in size and destructive potential by entraining bed material they encounter increasing use of depth integrated mass and momentum conservation equations to model these erosive flows motivates a review of the underlying theory our review indicates that many existing models apply depth integrated conservation principles incorrectly leading to spurious inferences about the role of mass and momentum exchanges at flow bed boundaries model discrepancies can be rectified by analyzing conservation of mass and momentum in a two layer system consisting of amoving upper layer and static lower layer our analysis shows that erosion or deposition rates at the interface between layers must in general satisfy three jump conditions these conditions impose constraints on valid erosion formulas and they help determine the correct forms of depth integrated conservation equations two of the three jump conditions are closely analogous to rankine hugoniot conditions that describe the behavior of shocks in compressible gasses and the third jump condition describes shear traction discontinuities that necessarily exist across eroding boundaries grain fluid mixtures commonly behave as compressible materials as they undergo entrainment because changes in bulk density occur as the mixtures mobilize and merge with an overriding flow if no bulk density change occurs then only the shear traction jump condition applies even for this special case however accurate formulation of depth integrated momentum equations requires a clear distinction between boundary shear tractions that exist in the presence or absence of bed erosion

p wave mantle velocity structure beneath northern eurasia from long range recordings along the profile quartz high resolution seismic sounding of the mantle using two peaceful nuclear explosions pnes along the 3950 km long quartz profile in northern eurasia reveal major unexpected vertical and lateral mantle inhomogeneities in contrast to standard seismological earth models such as prem and iasp91 three rather than two mantle discontinuities are found between 400 and 700 km depth they are located at about 420 550 and 670 km depth lateral variations in depths amount to 10 20 km and associated p wave velocities vary by 0 1 km s 1 in the upper mantle the uppermost layer through which pn propagates extends down to about 100 km depth the mantle below this depth but above the 410 km discontinuity is characterized by alternating high and low p wave velocities in the depth range between 100 and 200 km the velocity fluctuates between 8 3 and 8 7 km s 1 and shows variations from shotpoint to shotpoint average velocities are clearly higher than standard seismological reference models this part of the mantle overlies a low velocity zone between about 200 and 300 km depth this channel also displays substantial lateral variation in depth which could be interpreted as a laterally variable asthenosphere beneath the west siberian basin the asthenosphere seems to be well established whereas it is only poorly defined under the uralian belt and the tectonic units to the northwest with the addition of more data from this and other profiles future aims include two dimensional and three dimensional tomographic modelling as well as modelling of petrological composition of the mantle down to 850 km depth beneath northern eurasia

a novel method for measuring the timing of bed erosion during debris flows and floods 1 we describe a novel channel bed erosion sensor and the first results of its usage the sensor is based on a resistance chain built into a column of 5 cm tall cylindrical aluminum elements the timing and change in resistance as elements are removed from the column are logged outside of the channel five sensor columns were placed in the illgraben torrent bed prior to the start of the 2008 flow season before the first debris flow event 0 1 m of sediment was deposited by small flood events during the 16 june 2008 debris flow this layer was eroded and erosion was therefore first measured 44 min after front arrival and took place progressively over the next 12 min the results at the erosion sensors are consistent with measurements over the entire reach using traditional surveying methods and data from the adjacent debris flow monitoring station provide a basis for interpretation the main limitation is that this sensor records only the rate and timing of the maximum bed erosion and cannot be used to determine deposition and subsequent erosion within a given event

particle velocity and concentration profiles in bedload experiments on a steep slope depth profiles of particle streamwise velocity concentration and bedload sediment transport rate were measured in a turbulent and supercritical water flow one size 6 mm diameter spherical glass beads were transported at equilibrium in a two dimensional 10 steep channel with a mobile bed flows were filmed from the side by a high speed camera particle tracking algorithms made it possible to determine the position velocity and trajectory of a very large number of particles approximately half of the sediment transport rate was composed by rolling grains and the other half by saltation this revealed a complex structure with several concentration and flux peaks due to rolling and one peak due to saltation with an increase of the sediment transport rate the depth structure remained the same at the water granular interface with peak value increases but with no shift in elevations the saltation region expanded towards higher elevations with an increase of the particle velocity commensurate to the water velocity the proportion of the sediment transport rate in saltation did not vary significantly the particle streamwise velocity profiles exhibited three segments an exponential decay in the bed a linear increase where rolling and saltation co existed and above this a logarithmic like shape due to saltating particles these results are comparable to profiles measured and modelled in dry granular free surface flows and in more intense bedload such as sheet flows copyright 2014 john wiley sons ltd

flume tests to study the initiation of huge debris flows after the wenchuan earthquake in s w china abstract in the wenchuan area in the southwest of china a huge amount of loose co seismic landslide material was deposited on slopes during the wenchuan earthquake of may 2008 these loose deposits formed the source material for rainfall induced debris flows or shallow landslides in the years after the earthquake on august 13 2010 about 20 large debris flows were triggered by heavy rainfall in the area around the epicenter of the wenchuan earthquake field reconnaissance revealed that the initiation of these post earthquake debris flows was closely related to severe erosion of the loose deposits flume tests were carried out to study the initiation mechanism of these post earthquake debris flows and the related influencing factors the flume was instrumented with ten combination sets of suction and pore pressure sensors these sensors were accompanied by tdr probes to measure the soil water content the flume has a length of 2 5 m and a width of 1 5 m a series of 26 tests was conducted to study the influence of slope gradient and discharge on the initiation mechanism and scale of the debris flows the amount of debris flow discharge was obtained by collecting the washed out deposits every 20 s the experimental results showed that the initiation mechanism of debris flows for gentle slopes and steep slopes was different on steeper slope incision by run off water was very rapid initiating directly the start of a debris flow the debris flow volume increased rapidly by a chain of subsequent cascading processes starting with collapses of the side walls damming and breaching leading to a rapid widening of the erosion channel at gentler slopes less intensive run off incision caused an accumulation of material down slope which after saturation failed as shallow slides transform in a second stage into debris flows it was demonstrated that the slope was the dominant factor in controlling the scale of the debris flows while the effect of discharge on erosion and the size of the debris flows was less clear

coupled cfd dem model for the direct numerical simulation of sediment bed erosion by viscous shear flow abstract debris flows devastate downstream regions with large impulsive forces resulting from the significant increase in volume due to the erosion during their rapid movement as this increase in volume is primarily derived from the sediment bed sediment bed erosion characteristics determine the sediment transport rate and the corresponding severity degree this study presents a coupled model based on computational fluid dynamics cfd and discrete element method dem to simulate sediment bed erosion by viscous shear flow at various shear flow velocities dem is adopted to simulate the granular bed particles and cfd is employed to model the shear flow water and mudflows the numerical model was verified by comparing the erosion formula and critical erosion shear stress with a pre existing laboratory experiment the erosion characteristics of the sediment bed were investigated from macro and micro perspectives a sediment bed can be divided into four layers from top to bottom saltating layer rolling layer creeping layer and static layer the depth profile of the average particle velocity obeyed a linear distribution in the rolling layer and the velocity was approximately zero in the bottom layer dynamic information on the particle loss trajectory velocity and principal stresses was recorded velocity traces demonstrated significant fluctuations with several isolated peaks and the velocity variable displayed gaussian distributions in the streamwise and vertical direction the influence of the shear velocity on the drag force and sediment erosion was more obvious than those of the viscosity coefficient and fluid density the drag force had an effect on the principal stresses and the micromechanical arrangement of the sediment grains the results provide the insights into micro mechanisms of the onset and erosion of sediment grains

experimental study on the triggering mechanisms and kinematic properties of large debris flows in wenjia gully debris flows are typically caused by natural terrain landslides triggered by intense rainfalls if an incoming mountain torrent flows along sloping channels at high velocity huge amounts of sediment from landslide dams and eroded channel beds will be entrained into the flows to form debris flows it is likely that large debris flows are due to the failure of many landslide dams of different scales due to bank slides or collapses bed erosion and solid transport the catastrophic debris flows that occurred in wenjia gully wenchuan earthquake area china on august 13 2010 two years after the mega earthquake were caused by intense rainfall and the serious erosion of sloping channels in the wake of the incident experimental tests were conducted to better understand the process of sediment erosion and entrainment on the channel bed and the formation of debris flows the results show that the bed erosion bank collapses and channel widening caused by erosion accounted for the triggering and scale amplification of downstream debris flows in the wenjia gully event this study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream and how such a complex cascade of geomorphic events failure of landslide dams and erosion of the sloping bed can lead to catastrophic discharges neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in high cost c 2014 elsevier b v all rights reserved

analysis of borehole televiewer measurements in the vorotilov drillhole russia first results abstract in the eurasian part of the world stress map almost the whole region east of the tornquist teisseyre line is terra incognita the closure of this information gap is of fundamental importance to the understanding of the geodynamics of the eurasian continent a detailed analysis of stress induced wellbore breakouts has been performed over a 4 1 km long depth interval in the vorotilov drillhole vgs the borehole is located in the central part of the russian platform right in the center of the vorotilov meteorite impact crater 60 km to the nne of the city of nizni novgorod an ultrasonic borehole televiewer bhtv was used to obtain high resolution acoustical images from the borehole wall with an interactive system for analyzing bhtv data the azimuth and shape of borehole breakouts occurring in the depth range of 1 3 4 8 km were analyzed a statistical analysis of the resulting orientation profile of the breakout azimuths yields an overall direction of the maximum horizontal principal stress s h of n 137 e 15 variations of breakout orientation with depth ranging from a few degrees up to more than 90 are seen on various depth scales the observed stress direction of n 137 e agrees very well with the average s h orientation of n 145 e in central europe if this measurement is taken as representative for the russian platform the stress field in russia is only slightly rotated in comparison to central europe this can possibly be interpreted as indicative for the stress field to be governed by broad scale tectonic forces such as a strong contribution from the forces exerted by the collision zone in the alpine himalayan belt and by the mid atlantic ridge

short scale variations of tectonic regimes in the western european stress province north of the alps and pyrenees the data of the european part of the world stress map wsm are used to study the western european stress province north of the alps and pyrenees the study area is characterised by an almost homogeneous n 145 degrees e orientation of the maximum horizont

low angle detachment origin for the red sea rift system abstract the tectonic and magmatic history of the jizan coastal plain tihama asir southwest arabia suggests a two stage evolution a first stage of extension began during the oligocene and ended with uplift of the arabian graben shoulder which began about 14 ma ago it was followed by a period of approximately 10 ma characterized by magmatic and tectonic quiescence a second stage of extension began roughly contemporaneously with the onset of seafloor spreading in the southern red sea some 4 5 ma ago and is still active today the geometry of faulting in the jizan area supports a wernicke model of simple shear for the development of the southern red sea regional asymmetries of the red sea area such as the distribution of volcanism the marginal topography and asymmetries in the geophysical signatures are consistent with such a model available seismic profiles allow a rough estimate for values of the arabian red sea margin and were used to simulate subsidence history and heat flow of the red sea for classical two layer stretching models neither finite uniform nor finite non uniform stretching models can account for observed subsidence and heat flow data thus two model scenarios of whole lithosphere normal simple shear are presented for the geological history of the southwestern arabian margin of the red sea these models are limited because of the serravallian rearrangement in the kinematics of the red sea

bed scour by debris flows experimental investigation of effects of debris flow composition debris flows can grow greatly in size by entrainment of bed material enhancing their runout and hazardous impact here we experimentally investigate the effects of debris flow composition on the amount and spatial patterns of bed scour and erosion downstream of a fixed to erodible bed transition the experimental debris flows were observed to entrain bed particles both grain by grain and en masse and the majority of entrainment was observed to occur during passage of the flow front the spatial bed scour patterns are highly variable but large scale patterns are largely similar over 22 5 35 channel slopes for debris flows of similar composition scour depth is generally largest slightly downstream of the fixed to erodible bed transition except for clay rich debris flows which cause a relatively uniform scour pattern the spatial variability in the scour depth decreases with increasing water gravel grain size and clay fraction basal scour depth increases with channel slope flow velocity flow depth discharge and shear stress in our experiments whereas there is no correlation with grain collisional stress the strongest correlation is between basal scour and shear stress and discharge there are substantial differences in the scour caused by different types of debris flows in general mean and maximum scour depths become larger with increasing water fraction and grain size and decrease with increasing clay content however the erodibility of coarse grained experimental debris flows gravel fraction 0 64 is similar on a wide range of channel slopes flow depths flow velocities discharges and shear stresses this probably relates to the relatively large influence of grain collisional stress to the total bed stress in these flows 30 50 the relative effect of grain collisional stress is low in the other experimental debris flows 5 causing erosion to be largely controlled by basal shear stress

ray path interpretation of the crustal structure beneath saudi arabia abstract interpretation of a long range seismic refraction line in saudi arabia has shown that beneath the arabian shield velocity generally increases with depth from about 6 km s 1 at the surface to about 7 km s 1 at the top of the crust mantle transition zone the base of this transition zone moho occurs at 37 44 km in depth intracrustal discontinuities can also be recognized the most important being in the 10 20 km depth range and separating the upper from the lower crust laterally the variations in the intracrustal discontinuities and the total crustal thickness can be correlated with previously defined tectonic regions beneath the red sea shelf and coastal plain the crust including 4 km of sediments is only 15 17 5 km thick with the aid of both seismic and gravity data an abrupt steeply dipping transition from the crust of the red sea shelf and coastal plain to that of the arabian shield has been derived with a jump of more than 20 km in moho depth this appears to be the major discontinuity between the red sea depression and the arabian continental shield

observation of high frequency teleseismic p n on the long range quartz profile across northern eurasia short period three component recordings of the seismic wave field of peaceful nuclear explosions pnes on long range profiles are used to determine the fine structure of the mantle lithosphere by analyzing the frequency content of the recorded phases and applying different band pass filters to the data it is possible to divide the wave field into two distinctly different constituents low frequency body waves traveling along fermat paths first arrivals and the high frequency teleseismic or long range pn phase traveling with a group velocity of 8 1 km s and accompanied by a long incoherent coda this high frequency teleseismic pn phase is observable from about 750 km where it separates from the faster first arrival to the maximum recording distance of 3145 km it is recorded from shots at different locations and appears to be almost unaffected by the major tectonic feature along the profile the urals the frequency spectrum of this pn phase contains more high frequency energy up to 12 hz than first arrivals that penetrate deeper into the upper mantle the teleseismic high frequency pn arrival has a remarkable coda which is incoherent between closely spaced stations the coda duration is dependent on the component of motion being shortest on the vertical and longest on the transverse component we propose a velocity model that is characterized by a zone extending from the crust mantle boundary to a depth of about 100 km this zone has randomly distributed spatially anisotropic velocity fluctuations we propose that these velocity heterogeneities are stretched in the horizontal direction this zone forms a scattering waveguide that confines the high frequency teleseismic pn there are indications that below this pn waveguide either the scale of the velocity fluctuations or the q factor changes this is expressed in a separation of the teleseismic pn phase from the phase diving deeper into the mantle lithosphere

pantelleria rift crustal extension in a convergent intraplate setting the pantelleria rift system is a wide zone of post miocene northwest trending grabens and horsts beneath the sicily strait the central grabens host volcanics of predominantly alkalic composition which are exposed on the islands of pantelleria and linosa on the maltese islands along the northeastern shoulder of the rift an oligocene miocene carbonate succession exposed above sea level allows structural analysis and determination of shallow crustal stresses within the otherwise largely submarine rift system an older northeast trending set of normal faults is probably the expression of an oligocene miocene crustal extension event which produced continental rifts in western europe and led to passive margin formation in the western mediterranean younger northwest trending grabens of the pantelleria rift system cut the older faults almost at right angles and define a zone of lithospheric stretching between tunisia and sicily the northwest trending grabens which subsided dramatically since the beginning of pliocene time appear to be connected by east trending dextral and more rarely north trending sinistral transforms displacement along the transforms is probably in the order of a few kilometres in situ stress measurements carried out on the maltese islands show maximum horizontal compression sh parallel to the rift this suggests that in general 1 vertical and 2 horizontal and parallel to the rift are of about the same magnitude both exceed 3 sh which trends northeasterly slight intraplate convergence in a nw se direction seems to be more than balanced by extension in a ne sw direction neotectonics of the region possibly reflects an asthenospheric flow pattern which became established during the messinian salinity crisis the mechanism of recent intraplate deformation of the pelagian shelf has relevance for the understanding of more anciently subsided platforms of the apulian plate

sediment transport formula for steep channels a description is given and results presented of experiments to investigate the sediment capacity of stream flows on flume slopes of up to 20 a comparison of the results with values predicted by the meyer peter mueller equation shows that the latter equation seriously underestimates sediment transport capacity on slopes steeper than 3 mainly because of deficiencies in the form resistance factor a new equation is proposed giving the transport capacity for materials with grain sizes larger than 0 4 mm 0 016 in the equation is calibrated by both the original meyer peter data and new steep flume experiments and modified to incorporate the effect of nonuniform sediment grain size distributions with flow depths calculated by the manning strickler equation the new equation still gives excellent estimates of sediment capacity

crustal structure of the fennoscandian shield a traveltime interpretation of the long range fennolora seismic refraction profile abstract the 1979 fennoscandian long range project fennolora was aimed at the determination of the detailed structure in the earth s mantle down to a depth of about 400 km observation distances reached almost 2000 km within scandinavia between shotpoints off the north cape and the southern coast of sweden to achieve an unbiased regarding the upper mantle structure a careful crustal survey was carried out along the entire profile at the same time beneath the fennoscandian shield i e the central section of the profile the crust is characterized by quite a smooth increase in p wave velocity down to the moho which lies at a depth of about 50 km in the southern half of the shield and at about 45 km further north the mean crustal velocity is 6 6 6 7 km s at the base of the crust the velocity increases gradually from about 7 km s to 8 0 8 4 km s in a 5 10 km thick crust mantle transition zone both in the south and in the north the relatively homogeneous crust of the baltic shield borders on areas with a more differentiated velocity structure first order discontinuities at shallower depth characterize the crust mantle boundary near the southeastern tip of sweden 38 km and under the caledonides in the north 43 km

synopsis sfb 108 stress and stress release in the lithosphere1 abstract stress and stress release in the lithosphere has been studied within a collaborative research centre at karlsruhe university sfb 108 as special contribution from germany to the international lithosphere program ilp this synopsis is an outline of the research results obtained by the sfb 108 as presented in this special volume of tectonophysics it starts with a summary of ideas on stress and stress release in the lithosphere which guided the sfb 108 at its beginning in 1981 it is followed by a review of strategy in cooperative research on rift systems world stress map and the scales of structure of the continental lithosphere from crust to mantle the main observations are then summarized and connections are made between key results from the various disciplines to obtain new views in lithospheric tectonics finally we address open questions and perspectives for future research the research addressed various styles of continental rifting from the afro arabian rift system to the central european rift system with the rhinegraben and the grabens in the french massif central as outstanding features a number of critical parameters such as thickness heat flow rheology composition strength of the crust and of the lithospheric mantle and the influence of active mantle plumes were identified and classified together they strongly influence the style of rifting petrophysical modelling of integrated information on seismic velocities composition and temperature from xenolith analysis density gravity and topography provided essential constraints on plume lithosphere interaction in the french massif central and also in the kenya rift the rhinegraben and its variscan environment offered the opportunity to study different concepts of upper and lower crust including the occurrence of deep crustal earthquakes and the role of an alpine detachment a special concern of the sfb 108 was the distribution of dimensions of heterogeneities in the lithosphere and its relation to the scales of their generating processes the crust mantle boundary was recognized as a major change in scales of heterogeneities by deep seismic sounding dss methods applied to the lower crust and the lithospheric mantle the study of the tectonic stress in western europe revealed that the crust is in frictional equilibrium down to midcrustal levels and is also decoupled from the mantle allowing adjustive motions of blocks and independent subduction in the foreland of the alps this decoupling is achieved in a thin and hot lithosphere driven by mid atlantic ridge push and alpine continent continent collision it is described in a quantitative dynamic model of crust mantle decoupling the sfb 108 has shown that earth scientists have to rediscover the importance of pattern recognition if complex influences are to be recognized

interpretation of a seismic refraction survey across the arabian shield in western saudi arabia abstract in february 1978 seismic refraction profiles were recorded by the u s geological survey along a 1000 km line across the arabian shield in western saudi arabia this report presents a traveltime and relative amplitude study in the form of velocity depth functions for each individual profile assuming horizontally flat layering the corresponding cross section of the lithosphere showing lines of equal velocity reaches to a depth of 60 80 km the crust thickens abruptly from 15 km beneath the red sea rift to about 40 km beneath the arabian shield the upper crust of the western arabian shield yields relatively high velocity material at about 10 km depth underlain by velocity inversions while the upper crust of the eastern shield is relatively uniform the lower crust with a velocity of about 7 km s is underlain by a transitional crust mantle boundary for the lower lithosphere beneath 40 km depth the data indicate the existence of a laterally discontinuous lamellar structure where high velocity zones are intermixed with zones of lower velocities beneath the crust mantle boundary of the red sea rift most probably strong velocity inversions exist here the data do not allow a detailed modelling velocities as low as 6 0 km s seem to be encountered between 25 and 44 km depth

the deep crust of the southern rhine graben reflectivity and seismicity as images of dynamic processes abstract the rhine graben part of the european cenozoic rift system deserves special attention because of its location in the foreland of the alpine orogen the phanerozoic evolution of the lithosphere in this region is defined by a set of major geodynamic events ranging from the variscan orogeny late orogenic crustal re equilibration to the interference of rifting and alpine orogeny in tertiary times the rhine graben is one of the most detailedly studied continental grabens prospecting for hydrocarbons in its sedimentary fill and intensive pre site studies for the continental deep drilling program ktb on its eastern crystalline flank black forest provided a comprehensive set of geoscience data seismic investigations ranging from a deep seismic network of near vertical reflection to concurrent wide angle refraction experiments were accompanied by seismological and geological surveys therefore a direct observational comparison between the two depth definitions of crustal subdivisions elastic vs strength rheological was possible in large parts of western europe deep seismic sounding dss investigation distinguishes between a crystalline upper crust of comparatively low p wave velocities 5 9 6 0 km s with little and discrete reflectivity and a strongly reflective lower crust with higher p wave velocities about 6 4 6 8 km s both are separated by the conrad discontinuity in contrast strength and rheological considerations define a brittle upper crust and a ductile lower crust the boundary between these two realms is usually referred to as the brittle ductile transition zone which in seismically active regions is imaged by the deepest crustal hypocentres the present brittle ductile transition in the rhine graben region as defined by the deepest hypocentres does not necessarily coincide with the structural separation in an upper and lower crust as seen in deep seismic studies this suggests that the laminated lower crust developed during the crustal re equilibration phase at the end of the variscan orogeny the second part of this paper concentrates on evidence of recent tectonic activities related to rifting processes impacting on the variscan lower crust a remarkable concentration of deep crustal earthquakes reaching to the top of an asymmetrical thinned lower crust is observed at or near the eastern border fault of the southern rhine graben and is possibly induced by the young rifting process we suggest that this asymmetry could be a consequence of the uppermost mantle detaching from the upper crust in collision with the alpine orogen this allows us to propose the distinction between the influence of compression extension continental subduction and intra crustal detachment during graben formation the dynamic interference of rifting and foreland compression shown by structural and seismological observations leads to the notion of small scale collisional escape tectonics associated with an intra continental transform fault at the southern end of the rhine graben the rhine sao ne transform zone

crustal thinning in relationship to the evolution of the afro arabian rift system a review of seismic refraction data abstract crustal and upper mantle structure of major units of the afro arabian rift system has been progressively investigated by seismic refraction surveys in the jordan dead sea rift the red sea the afar depression and in the east african rift of kenya the two extreme structures are oceanic crust flooring the axial trough of the southern red sea rift and 30 35 km thick continental crust underneath the jordan dead sea rift and its flanks underlain by a mantle with pn velocities of 8 0 8 2 km s the remainder of the units have a crustal structure of transitional to uncertain nature in the southeastern red sea the change from 15 18 km thick transitional crust to the 40 km thick continental crust of the arabian shield is probably very abrupt and is the major lateral change in structure in this region in the northern afar depression the crust is only 15 20 km thick in the southern afar depression anomalous mantle with 7 2 7 3 km s velocities occurs at depths greater than 25 km also here an abrupt change to a 40 km thick shield crust with a velocity of 8 0 km s is evident from seismic and gravity data crustal thickness of the east african rift system amounts to 30 36 km a recent trial experiment in the eastern rift of kenya indicates a 35 36 km thick crust underlain by a low velocity upper mantle with 7 5 km s at 23 24 km depth a thin high velocity lens of 7 1 km s velocity may be present within the 22 km thick lower crustal layer averaging 6 6 km s velocity investigations of local earthquake body waves in the western rift provide information that the crust here is of continental type with a thickness of about 32 km overlying mantle material of 8 0 km s p velocity and 4 6 km s s velocity in conclusion a model of preferential rifting of continents is applied to the afro arabian rift system where rifting seems to progress into areas with thick continental crust as seen for example in the levant and the east african rift systems instead of using paths in thin crust

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

seismic refraction studies of the afro arabian rift system a brief review abstract the crustal and uppermost mantle structure of major units of the afro arabian rift system has been consecutively investigated by seismic refraction surveys in the jordan dead sea rift the red sea the afar depression and the east african rift of kenya with the exception of the jordan dead sea transform the entire afro arabian rift system is underlain by anomalous mantle with pn velocities less than 8 km s while under the rift flanks the velocity is clearly equal to or above 8 0 km s various styles of rifting have been found oceanic crust floors the axial trough of the southern red sea rift thinned continental crust underlies the margins of the red sea as the afar depression and the northern kenya rift on the other hand 30 35 km thick continental crust is found both under the jordan dead sea rift where strike slip rifting is active and thinning towards the mediterranean occurs and under the central kenya rift where updoming is apparently the controlling feature while the transition from thinned continental to 5 6 km thick oceanic crust in the centre of the red sea appears to be more gradual the transition from rift related structure to undisturbed continental crust of 40 5 km thickness is mostly rather abrupt the seismic data indicate various stages of rifting evidenced by different styles of crustal strucre and they imply the presence of heated uppermost mantle under most parts of the rift system possibly related to plume activity local volcanism may disrupt and or underplate the crust in places altering in particular the structure of the lower crust progressive thickening of the rifted crust away from the oceanized centres in the southern red sea and gulf of aden towards north and south may be viewed as an evolutionary sequence which however may be difficult to explain when viewing the afro arabian rift system as an active rift controlled by plume activity

red sea related history of extension and magmatism in the jizan area southwest saudi arabia indication for simple shear during early red sea rifting the tectonic and magmatic history of the jizan coastal plain of the red sea tihama asir in southwest saudi arabia is dominated by sw ne extension this extension manifests itself by a basic dike swarm and several generations of normal faults that trend roughly nw se the oldest synrift deposits are non marine clastics and bimodal volcanics of the jizan group which were intruded by basic dikes gabbros and granophyres of the tihama asir magmatic complex tamc radiometric ages for the tamc rocks range from 26 to 18 ma rifting in the southern part of the red sea system therefore is certainly older than 26 ma between 26 and 20 ma the southwestern arabian margin was affected by a monoclinal downwarp flexure the oldest extensional features in the jizan area are n s to nnw sse striking dikes and normal faults which were overprinted by other nw se striking extension structures an array of en echelon extensionzones is linked by complex patterns of transfer faults mainly wnw ese striking dextral strike slip or oblique slip faults the observed superposition of dikes and normal faults of different orientations was not necessarily caused by a counterclockwise rotation of the regional stress field but more likely reflects the clockwise rotation of individual faultbounded blocks between the two phases of extension uplift of the graben shoulder east of the jizan coastal plain is probably younger than 14 ma and its development coincides with a major rearrangement of the kinematics along the red sea this new kinematic pattern probably led to the onset of strike slip movement along the aqaba levant transform at the same time extension and volcanism ceased in the jizan area or shifted further to the west after a long hiatus of about 10 ma renewed extension facilitated extrusion of alkali olivine basalts since 2 ma ago