structural characterization of natural loess and remolded loess under triaxial tests this paper characterizes the microstructural evolution of saturated natural loess from a site in jingyang china during triaxial test along two stress paths for comparison the same soil in remolded state is also characterized mercury intrusion porosimetry mip scanning electron microscopy sem and environmental scanning electron microscopy esem were used for the microstructure investigation results show that the microstructure of natural loess is similar to that of remolded loess before the consolidated undrained cu triaxial tests including conventional triaxial compression ctc test and reduced triaxial compression rtc test on the contrary their microstructures are different after the tests deeper examination shows that loading led to a significant change of inter aggregate pores without modifying the intra aggregate pores in addition the volume of inter aggregate pores after the rtc test is greater than that after the ctc test under the same consolidation stress the microstructure features of natural and remolded loess after the tests are further used to analyze the macro mechanical behavior for better understanding the relationship between them the results show that it is the cementation bonds of which breakage is influenced by stress path and confining pressure that play important roles in the strength and deformation behavior

evidences for cessation of indian plate subduction in the burmese arc region the issue of whether subduction is still active in the india burma plate boundary zone has been rather controversial while the presence of an eastward dipping indian lithospheric slab is undisputed different opinions have been voiced regarding the continuance of subduction at present analysis of the harvard cmt data in comparison with major subduction zones of the world demonstrates that the burmese arc is a unique region where there is a subducted slab but the direction of plate motion is nearly perpendicular to the down dip direction we propose a major right lateral shearing of the indian plate along with its subducted slab past the burmese plate in the nne direction

a seismotectonic study of the burma and andaman arc regions using centroid moment tensor data abstract the concept of a mean slip angle is introduced this enables a classification of focal mechanisms in any region into predominantly strike slip thrust and normal categories based on this concept the harvard centroid moment tensor cmt data in the burma and andaman arc regions from 1977 to 1992 comprising 167 focal mechanism solutions are examined and categorized distinct trends on the surface and in depth sections emerge on examination of these categories for instance in the burmese arc there is a clear segregation along the slab between strike slip type mechanisms down to a depth of about 90 km and thrust events which occur exclusively below this depth in addition a study of p and t axis orientations indicates that the stress pattern in the subducted slab is different from that farther east whereas the p axes of the thrust and strike slip mechanisms in the slab show a predominantly nne trend commensurate with the direction of motion of the indian plate with respect to the eurasian plate those in the region to the east show interestingly an average e w oriented compressive regime the northern and southern parts of the andaman are region exhibit distinct tectonic patterns whereas in the southern part the disposition of focal mechanisms along the slab and the p and t axis orientations indicate active subduction the mechanisms in the northern part exhibit a peculiar segregation into clusters of thrust normal and strike slip types without conforming to the local trend of the arc a similar study in the western aleutian trench region indicates a much simpler subduction pattern

idealized modelling of landfalling cold fronts the effects of land surfaces sea surfaces and coastlines on the dynamics of cold fronts are examined in an idealised two dimensional confluent deformation model of frontogenesis when the deformation field is stationary increasing the surface roughness weakens the fronts while increasing the cross front ageostrophic wind and frontal updraughts the frontogenetic effect of deformation balances the frontolytic effect of turbulent mixing resulting in near steady state fronts in steady state the surface fronts are located near the point at which the cross front flow vanishes this equilibrium point moves towards the warm air as the surface roughness is increased because the cross front ageostophic wind also increases with increasing surface roughness surface sensible heating weakens and slows the fronts during the day whereas surface sensible cooling strengthens and accelerates them at night adding a coastline to the model results in very strong gravity current like fronts in the afternoon with a relative flow of cool air towards their leading edge above the boundary layer the synoptic fronts remain unaffected by the coastline as the turbulent mixing weakens in the late afternoon the coastal fronts surge inland advancing faster than the wind speed in the boundary layer when the deformation field is allowed to translate the fronts advance across the ocean towards land if the fronts reach the coastline between mid morning and late afternoon the daytime heating over the land opposes the onshore advection of cold air retarding the fronts at the coastline if the fronts reach the coastline in the evening or early morning they advance onshore relatively unimpeded hence the fronts arrive onshore preferentially in the late afternoon or evening copyright 2010 royal meteorological society

role of the kopili fault in deformation tectonics of the indo burmese arc inferred from the rupture process of the 3 january 2016 mw 6 7 imphal earthquake the burmese arc is a peculiar plate boundary where there exists an eastward subducted indian slab but the current tectonics of the region are predominantly governed by a northward strike slip motion of the indian plate past the burmese plate as evidenced by seismic and global positioning system data the shallower portion of the dipping indian slab is characterized mostly by earthquakes with strike slip type focal mechanisms with roughly northwest and northeast trending fault planes although there is no clear evidence for the choice of rupture planes in the present study we use teleseismic broadband waveforms to model the rupture propagation of an m w 6 7 strike slip earthquake of 3 january 2016 that occurred in the indian city of imphal and infer the fault plane orientation the result indicates a right lateral strike slip motion along a n21 w plane which is confirmed by both waveform fitting and distribution of aftershocks interestingly this earthquake occurred at the intersection of three major faults in this region the churachandpur mao fault bounding the india and burma plates the dauki fault south of the shillong plateau and the kopili fault separating the shillong plateau from the brahmaputra valley this raises various possibilities for interpreting this event however based on the finite fault inversion we infer that this earthquake occurred on the kopili fault running northwest southeast from bhutan himalaya down to the burmese arc and manifested as a right lateral strike slip motion in response to the northward motion of the indian plate and a counterclockwise rotation of the brahmaputra valley we further interpret that the overall deformation in the burmese arc region is accommodated by northward slivering of the eastward subducted indian lithospheric slab along a series of northwest to north south trending right lateral strike slip faults from west to east as the indian plate moves northward past the burma and sunda blocks

seismotectonics in northeast india a stress analysis of focal mechanism solutions of earthquakes and its kinematic implications summary in northeast india three major plates interact along two convergent boundaries the himalayas and the indo burma ranges which meet at the assam syntaxis to clarify this tectonic interaction and the underlying dynamics we determine the regional seismotectonic stress from the stress inversion of 285 double couple focal mechanism solutions of earthquakes with an average magnitude of 5 we then compare the reconstructed stress regimes with the available information about geodetically determined relative displacements north south compression in a direction consistent with india eurasia convergence prevails in the whole area from the eastern himalayas to the bengal basin through the shillong mikir massif and the upper assam valley e w extension in tibet is related to this n s india eurasia convergence not only does the major n s compression affect the outer segments of the indo burma ranges it also extends into the descending slab of indian lithosphere below these ranges although stresses at depth are controlled by bending of the slab beneath the burmese arc the existence of widespread n s compression in the bengal basin far away from the himalayan front is compatible with the previously proposed convergence between a shillong mikir assam valley block and the indian craton e w compression inside this block supports the hypothesis of a component of eastward extrusion stress inversion of focal mechanism solutions in the indo burma ranges reveals a complex stress pattern the burmese arc and its underlying lithosphere experience nearly arcperpendicular extension with ese wnw trends in the northernmost ne trending segment and ene wsw trends in the main n s arc segment such extensional stress documented from many arcs is likely a response to pull from and bending of the subducting plate at the same time the indo burma ranges are under compression as a result of oblique convergence between the sunda and indian plates the maximum compressive stress rotates from ne sw across the inner and northern arc to e w near the bengal basin this rotation is consistent with the deformation partitioning reflected in the rotation of relative displacement vectors from a ssw directed sunda burma motion to a wsw directed burma india motion as a consequence of this partitioning the major belt parallel fault zones show a variety of movements across the main n s arc segment from right lateral slip in the inner ranges to oblique reverse dextral slip in the outer ranges and pure thrusting in the westernmost foreland belt

influence of structure on the behavior of a saturated clayey loess an intensive experimental investigation by means of triaxial and oedometer tests was performed on a clayey loess that was retrieved from two depths at a location on the southern chinese loess plate

drained residual shear strength at effective normal stresses relevant to soil slope stability analyses abstract an extensive torsional ring shear testing program has been conducted to measure the drained residual shear strength of soils at the wide range of effective normal stress 10 to 700 kpa usually mobilized in reactivated and first time landslides soils mudstones and shales of different plasticity and gradation were tested in the program the effects of the change in nonlinearity of shear strength envelope over the utilized normal stress ranges on slope stability analyses were investigated using this data new empirical residual shear strength correlations were developed as a function of soil index parameters and wide range of effective normal stresses in essence the correlations are presented as revised versions of those previously developed for a limited number of normal stresses utilizing the same soil index parameters comparisons were made with a considerable amount of back calculated shear strength data reported in the literature for reactivated landslides as well as results predicted from existing shear strength correlations to verify the increased suitability of the new correlations for use in slope stability analyses a numerical expression was also introduced to express the residual shear strength correlations for direct incorporation in slope stability software

transcurrent movements in the burma andaman sea region the drag produced by the northward movement of the indian plate has caused the indoburman ranges an accretionary prism to decouple from the burma plate along the kabaw fault and the burma plate itself has decoupled from the eastern highlands of burma along the sagaing fault the indoburman ranges have probably been dragged north slightly ahead of the burma plate although at times the two plates may have locked together to move as one unit it is suggested that the double arc formed by the indoburman ranges and the andaman nicobar sumatra islands was formerly one large single arc northward translation of this larger single arcuate structure has caused the tail end of the arc i e the andaman nicobar sumatra section to rotate into the burma plate causing a bending of the arc to form the present double arc and compression within the burma plate to form the pegu yoma folding northward movement of the burma plate has also resulted in offset by over 400 km of the irrawaddy river from its former connection through the channel of what is now the chindwin river

loess paleosol sequences at the northern european loess belt in germany distribution geomorphology and stratigraphy abstract pleistocene loess and loess derivates are distributed along the mountain front of the central european mountain belt in northern and central germany examples from two regions the lower rhine embayment lre and the northern foreland of the harz mountains fhm show that the distribution of loess and the development of loess paleosol sequences lps are controlled by relief climate tectonics the distance to large river systems the distance to the scandinavian ice sheet and the distance to the shelf of the north sea in the oceanic lre higher humidity enhanced the periglacial processes which increased erosion but also led to preservation in accumulative positions in contrast in the more continental fhm the sediments were affected by less intensive periglacial processes and no solifluction can be detected new loess distribution maps are presented for both key areas and key sections especially for the last glacial cycle are compared and summarized both study regions are located in the west east trending loess belt north of the central european mountain belt in front of the rhenish shield ardennes eifel and harz mountains finally a synthesis of typical sediment sequences for both regions is given as an example of paleoenvironmental landscape development in northern central europe

deep structure and tectonics of the burmese arc constraints from earthquake and gravity data abstract active subduction of the indian plate is currently occurring beneath the burmese arc along an east dipping benioff zone which extends to a depth of about 180 km the overriding burma plate has an appearance of an inland seismic slab that is deflected downwards in the vicinity of the benioff zone a crustal seismic zone some 60 80 km east of the benioff zone correlates to backarc activity a triangular aseismic wedge in the top part of the crust outlines the central belt molasse basin east of the burmese foldbdt fault plane solutions show that the burmese benioff zone is characterized by shallow angle thrusting at its upper edge whereas down tip tensional events dominate its lower edge most of the backarc seismicity is accounted for by the sagaing transform or by the activity of the shan scarp normal fault zone at the margin of the asian plate a gravity anomaly pair with amplitude of 175 mgal coincides with the 1100 km long burmese arc lying in a north south direction the gravity anomalies along a profile in central burma and in adjacent areas of the bengal basin are interpreted in terms of plate subduction as well as near surface mass anomalies this suggests that sediments below the central belt may have an average thickness of the order of 10 km but may be as thick as 15 km at the subduction zone the oceanic crust underlying deeper parts of the bengal basin experiences phase transition at about 30 km depth in a benioff zone environment east of the burmese foldbelt several thrust planes are present within the folded and deformed cretaceous tertiary sediments of the fold belt these are often associated with ophiolites and basic to ultrabasic rocks a low density zone at least 60 km wide underlies the andesitic volcanic axis in the overriding plate

effects of overconsolidation ratios on the shear strength of remoulded slip surface soils in ring shear the drained shear strength of clay soils is independent of stress history though there have been instances in the geotechnical literature of studies that have suggested some dependence of stress history on the drained shear strength accordingly the effect of artificial overconsolidation ratios ocr on the drained shear behaviour and shear strength of a high plasticity clay soil and a loess soil has been discussed from an experimental point of view the slip surface materials of two landslides were remoulded and consolidated from slurry and were subjected to drained shear tests four overconsolidation ratios ocr 1 ocr 2 ocr 4 and ocr 6 were tested under constant effective normal stress in a ring shear apparatus the overconsolidated specimens achieved peak friction coefficients at relatively lesser shear displacements in contrast to the normally consolidated specimens in the kamenose soil the fully softened friction coefficient and the residual friction coefficient showed stress dependency in the ocr 1 bloc of both soils however between the two soils although dissimilar patterns of variation of these two shear strength parameters in the overconsolidated state compared to the normally consolidated state was evident significant differences in the residual friction coefficient attributable to overconsolidation were not found

a comparison between frontogenesis in the two dimensional eady model of baroclinic instability and summertime cold fronts in the australian region a two dimensional anelastic numerical model with a simple turbulence parametrization is integrated with eady s linear normal mode solution for an unstable baroclinic wave as initial condition the structure of the surface front which develops after five days of model integration is compared with data on summertime cold fronts or cool changes in south eastern australia obtained during recent field experiments of the australian cold fronts research programme it is shown that the ridge trough structure of an amplifying baroclinic wave and its attendant surface front captures many of the important features of cool changes together with the broad scale flow in which they develop indeed it is argued that the model provides a useful theoretical framework in which the dynamics of the australian summertime cool change may be understood

a review of cold fronts with prefrontal troughs and wind shifts the conceptual model of a classical surface based cold front consists of a sharp temperature decrease coincident with a pressure trough and a distinct wind shift at the surface many cold fronts however do not conform to this model time series at a single surface station may possess a pressure trough and wind shift in the warm air preceding the cold front hereafter called a prefrontal trough and prefrontal wind shift respectively although many authors have recognized these prefrontal features previously a review of the responsible mechanisms has not been performed to date this paper presents such a review ten disparate mechanisms with different frontal structures have been identified from the previous literature these mechanisms include those external to the front i e those not directly associated with the cold front itself synoptic scale forcing interaction with lee troughs drylines interaction with fronts in the mid and upper troposphere and frontogenesis associated with inhomogeneities in the prefrontal air mechanisms internal to the front i e those directly associated with the structure and dynamics of the front include the following surface friction frontogenesis acting on alongfront temperature gradients moist processes descent of air ascent of air at the front and generation of prefrontal bores gravity waves given the gaps in our knowledge of the structure evolution and dynamics of surface cold fronts this paper closes with an admonition for improving the links between theory observations and modeling to advance understanding and develop better conceptual models of cold fronts with the goal of improving both scientific understanding and operational forecasting

the role of forcing in cell morphology and evolution within midlatitude squall lines abstract this study assesses the role of mesoscale forcing on cell morphology and early evolution of midlatitude squall lines the forcing chosen was a cold front simulated to frontal collapse to produce a specific set of thermodynamic profiles at the leading edge of the front use of a realistic balanced and persistent forced state allowed a unique evaluation of its importance in thunderstorm evolution compared with a traditional homogeneous environment without forcing three dimensional squall lines were modeled with and without the front present in low and high bulk richardson number environments the forced convection evolved in significantly different ways than their isolated unforced counterparts in low shear conditions the line of isolated convective cells split with the adjacent split cells interfering destructively with neighboring cells in the line with forcing present differences in anticyclonic cell intensity and propagation prevented this interaction from occurring leading to longe

accurate relative earthquake hypocenters reveal structure of the burma subduction zone the burma arc links the himalaya to the andaman sumatra trench and comprehension of the geological features in the region is vital to understand the active tectonic processes in the area subduction on the sumatra trench produced the devastating 2004 sumatra earthquake m w 9 0 but the mechanisms accommodating relative india sundaland motion in burma are still unknown previous seismological studies of the area use only earthquake catalog hypocenters so structural details of subducted material remain poorly understood here accurate relative hypocenters for 81 earthquakes are estimated using first arrivals picked from regional and teleseismic recordings depth determination is improved using measured travel time differences between p onsets and depth phases pp and sp the results clearly illustrate a slab 21 25 n dipping 25 at 40 80 km deep 40 at 80 120 km deep and 60 at 120 160 km deep and its strike follows the indo burman ranges at latitudes 25 n earthquakes become more shallow and a diffuse picture of hypocenters with an east west lateral discontinuity at depth is observed indicating lateral deformation of the slab previous studies suggest there is a transition at 90 km deep from shallower strike slip earthquakes to deeper thrust type events here accurate depth estimates combined with confirmation of two global centroid moment tensor solutions using body wave modeling shows that thrust and strike slip earthquakes both occur deeper than 100 km in the burma arc

shear zone structures and stress fluctuations in large ring shear tests abstract large ring shear tests are carried out in order to investigate the naturally drained shear behavior of slip zone soils of three giant landslides in the three gorges project area twenty seven specimens are sheared at three shearing rates 0 1 1 and 10 mm s shear zone structure and stress fluctuation at residual state are examined with reference to sample properties and test conditions it is observed that a shear stress continues to increase at large displacements presumably due to slow dissipation of pore pressure within the shear zone b the presence of coarse particles impedes development of a slickensided shear surface c increasing shearing rate tends to positively influence residual shear stress by allowing rougher shear surfaces but this effect is dimmed by increasing coarse fraction and density d the amplitude and wavelength of the most dominant first order component of complex shear stress fluctuation pattern are measures of roughness of shear surfaces and turbulence within the zones and e these fundamental sinusoidal wave parameters correlate well with atterberg limits particle shape and shearing rate increasing atterberg limits ip and ll and or decreasing particle elongation lead to larger wavelength and smaller amplitude favoring relatively smooth shear surface whereas increasing shearing rate produces a decrease in both amplitude and wavelength

seismicity gravity anomalies and lithospheric structure of the andaman arc ne indian ocean abstract the andaman arc in the northeastern indian ocean defines nearly 1100 km long active plate margin between the india and burma plates where an oblique benioff zone develops down to 200 km depth several east trending seismologic sections taken across the andaman benioff zone abz are presented here to detail the subduction zone geometry in a 3 d perspective the slab gravity anomaly computed from the 3 d abz configuration is a smooth long wavelength and symmetric gravity high of 85 mgal amplitude centering to the immediate east of the nicobar island where a prominent gravity high follows the nicobar deep the slab residual gravity anomaly srga and mantle bouguer anomaly mba maps prepared for the andaman plate margin bring out a double peaked srga low in the range of 150 to 240 mgal and a wider cum larger mba low having the amplitude of 280 to 315 mgal demarcating the andaman arc trench system the gravity models provide evidences for structural control in propagating the rupture within the lithosphere the plate margin configuration below the andaman arc is sliced by the west andaman fault waf as well as by a set of sympathetic faults of various proportions often cutting across the fore arc sediment package some of these fore arc thrust faults clearly give rise to considerably high post seismic activity but the seismic incidence along the waf further east is comparatively much less particularly in the north although the lack of depth resolution for many of the events prohibits tracing the downward continuity of these faults tectonic correlation of the gravity derived models presented here tends to favour the presence of oceanic crust below the andaman nicobar outer arc ridge

detailed description of deformation induced semi geostrophic frontogenesis examen dans la limite de la semi geostrophie d une variante du probleme classique de la frontogenese de surface induite par la deformation le systeme particulier d ecoulement considere constitue la reponse a un champ de deformation donne d une atmosphere barocline semi infinie stratifiee et a vorticite potentielle uniforme resultats obtention d une classe de solutions analytiques simples dans l espace geostrophique obtention d une solution explicite de l equation de sawyer eliassen relative a la circulation ageostrophique obtention d une equation autonome non lineaire dans l espace reel relative au developpement a la surface de la composante du vent alignee le long du front application aux divers aspects frontogenes a savoir l echelle temporelle du developpement du front la co occurrence des differents types frontaux la pente et le mouvement des figures frontales la structure et la force de la circulation ageostrophique et le degre de validite de l approximation semi geostrophique

influence of structure on shear characteristics of the unsaturated loess in lanzhou china abstract loess is typically a kind of soil with metastable structure which makes loess sensitive to collapse and sliding upon wetting such structure has thus profound influence on loess s mechanical behavior however there have been arguments about how the metastable structure influences on loess s mechanical behavior and what the mechanism behind is in this study the influence of structure on shear characteristics of the unsaturated loess in lanzhou city of china was investigated with comparison of variation of shear strength and its parameters between six pairs of the undisturbed and remolded samples it is found that the peak shear strength and strength parameters of the loess significantly reduced once its structure was destroyed while shear behavior of the loess showed little change strength parameter c was much more sensitive to structure of the loess than shear strength reduction of the loess due to change of structure should be largely attributed to breaking up of cementation bonds between particles evidenced by the difference in pore size distribution and microstructure of soil fabrics between the undisturbed and remolded samples the bonds provided by clays and carbonates contributed the most to structure of the loess with minor by soluble salts while matric suction played little role in structure of the loess

a review of shear and tensile strengths of the malan loess in china abstract loess deposits cover about 640 000 km 2 of china equivalent to about 6 7 of the total area of the country the loess plateau alone covers approximately 317 000 km 2 making it the largest bulk accumulation of loess on the earth land instability hazards in the loess plateau are frequent and varied among which the cracking sliding beng hua in chinese failure is a typical mode cracking sliding failures commonly occur in the malan loess at volumes of the order of 100 m 3 and cause more than 100 deaths per year as the tension in the upper part of the failure plane and shearing sliding along the lower part mobilize cracking sliding failures this failure mode demands an investigation into the tensile and shear strengths this paper presents a review of these properties based on a large collection of literature both tensile and shear strengths of the malan loess decrease with water content and increase with dry density resulting in close multi regression correlations large differences between undisturbed and disturbed tensile strengths of the loess indicate the significance of its structure shear strength of the loess is direction dependent indicating strong anisotropy of the loess structure test method sample size and loading rate all influence the measured tensile strength

surface deformation of the barren island volcano andaman sea 2007 2017 constrained by insar measurements evidence for shallow magma reservoir and lava field subsidence abstract barren island situated in the andaman sea is the northernmost active volcano of the sunda arc the oldest known eruption of the volcano was during the period 1787 1832 after about 150 years of quiescence volcanic activity resumed in 1991 and continues since then the magmatic plumbing system of this volcano is largely unknown due to lack of geophysical experiments owing to its remote location we report for the first time time series surface deformation measurements of barren island volcano from interferometric synthetic aperture radar insar during epochs 2007 2011 and 2015 2017 line of sight los deformation of 50 mm yr during 2007 2011 at the cinder cone is interpreted as the co eruptive pressure changes associated with the 2008 2010 eruptions bayesian inversion suggests a shallow magma reservoir at a depth of 578 100 300 m below the summit the depth of the magma reservoir is shallower than that of other volcanoes of the sunda arc probably due to the extensional stress regime imposed by the oblique subduction based on the present studies and previous works we propose a plausible source model for barren island volcano we also discuss potential biases in the present source parameter estimation due to the lack of high quality insar data from both ascending and descending directions significant deformation 15 to 150 mm yr observed along the lava delta of barren island volcano for both the epochs are interpreted as post emplacement subsidence of the lava flow further we characterise the lava flow including volcanic deposits by mapping its spatial extent and elevation changes during 1979 2000 and 2000 2017 periods using geodetic measurements

cyclic variability in microstructure and physio mechanical properties of the xiashu loess palaeosol sequence in nanjing china abstract for the xiashu loess palaeosol sequence in nanjing china further to our work on the cyclic variability in its chemical composition and swelling shrinkage properties xia j huang g l liu z t chen x m 2007 cyclic variability in chemical composition and swelling shrinkage properties of the xiashu loess stratum near nanjing china pedosphere 17 5 666 672 this paper studies the cyclic variability in its microstructure and physico mechanical properties and the corresponding influence on its engineering behaviour for geotechnical and geological practices in addition the cyclic variability in the soil s grain size distribution and geochemical characteristics is compared with that of the loess palaeosol sequences at two other sites in china indicating a geographical pattern of cyclic variation of the sequences

aftershocks and seismotectonic implications of the 13 september 2002 earthquake mw 6 5 in the andaman sea basin a medium size earthquake mainshock m w 6 5 occurred on 13 september 2002 22 h 28 m 31 s utc in the andaman sea about 20 km offshore diglipur north andaman island the epicenter at 13 087 n and 93 112 e and centroid depth at 31 km were estimated by the u s geological survey usgs the main shock was a reverse faulting event four digital seismograph stations were established in the andaman islands to monitor aftershocks about 200 aftershocks m d 1 0 were recorded during a period from 19 september to 7 october 2002 the epicenter map shows a northwest southeast trending aftershock cluster in an area of about 140 70 km2 which reflects the rupture area of the mainshock the aftershocks occurred mostly at a depth range of 5 20 km except one at 38 km the moment tensor solutions usgs of the mainshock and the largest aftershock m w 5 8 which occurred 22 hr after the mainshock revealed consistent reverse faulting the northeast dipping northwest southeast trending nodal plane which is comparable with the aftershock trend is inferred to be the fault plane the northeast southwest compressional stress p axis obtained by the fault plane solutions is compatible with the north northeast movement of the indian plate the mainshock and the two well located largest aftershocks located by the usgs occurred within the subducted plate one composite fault plane solution is obtained for the shallower aftershocks recorded by the temporary network the solution shows normal faulting with a northeast southwest tensional t axis these aftershocks occurred off the subducted plate at a much shallower depth 10 km and are due to local tension in the overriding plate

an experimental study to characterize the initiation of the seismic induced tsaoling rock avalanche abstract the tsaoling rock avalanche which had a sliding volume of 120 million m3 and a maximum thickness of 170 m was triggered by the chi chi earthquake in 1999 however the initiation mechanism has not been well understood because different friction models have been proposed to describe the triggering process using the newmark sliding model and numerical simulations in this study a new dynamic ring shear test with a maximum normal stress higher than 3400 kpa is applied as an alternative approach to investigate the initiation of the seismic induced rock avalanche along the wet sliding surface at the interface of the cholan sandstone and consolidated remold shale experimental results verify that the seismic stresses at the wet sliding surface touch the failure surface and generate significant cumulative shear displacements additionally the shear surface should have non linear failure criteria rather than the well known linear mohr coulomb failure criteria with a constant friction angle furthermore the initiation time of the tsaoling rock avalanche obtained from the dynamic ring shear test is strongly correlated with the available seismic signal interpretations and the interviews of witnesses who travelled with the sliding mass this is the first experiment clarifying the co seismic behavior of the sliding surface and the initiation of the tsaoling landslide during the chi chi earthquake additionally from the development of the ring shear test the integrations of high normal stress the wet sandstone shale interface and the dynamic test with seismic loadings greatly extend the use of ring shear tests to rock avalanches

controlling factors of loess landslides in western china based on detailed field data from recent geo hazards surveys in the loess plateau region of western china this study analyzes the key factors that control loess landslides the evolution phase of river valleys the geological structure of slopes and the geometry of slopes are all found to play a role in determining the occurrence distribution and other characteristics of loess landslides groundwater and vegetation also contribute to their formation a combination of human engineering activities and precipitation events are the principal triggering factors for the instability of loess slopes

state of tectonic stress in northeast india and adjoining south asia region an appraisal an attempt is made to map the spatial variation of the tectonic stress pattern in northeast india and its adjoining south asia region using stress tensor inversion of some 516 fault plane solutions the bhutan himalaya and the arunachal himalaya are mapped with north south to north northwest south southeast compression the eastern himalaya syntaxis zone on the other hand shows a clockwise rotation a north northeast compression is dominant to the south in the intraplate part of the region the shillong plateau assam valley bengal basin bangladesh and tripura fold belt exhibit north northwest to north northeast compression orthogonal horizontal extension is dominant in southern tibet bhutan and partly in the syntaxis zone and the same is also observed in the shillong plateau and assam valley area of the intraplate region the indo burma ranges and the sagaing fault in the myanmar region show a northeast southwest compression an orthogonal horizontal northwest southeast extension is also observed in the sagaing fault zone a depth variation of the tectonic stress is observed below the indo burma ranges it changes from north south to northeast southwest in the southern part and from northeast southwest to north northeast south southwest in the northern part in the deeper seismogenic zone the stress inversion results of clusters of events in individual zones though mostly conformable with the average observations indicate a variation in the shillong plateau due to heterogeneity and tectonic complexity

research on loess paleosol engineering geology features from the borehole cores of a typical section in baoji area shaanxi province china despite the vast amount of research regarding loess paleosol engineering geology features on the loess plateau in northwest china a completely systematic study from holocene series q4 to lower pleistocene series q1 is absent investigation into this yet unexplored problem was done firstly by sampling undisturbed cores in a typical loess paleosol section at jiacun terrace in baoji area shaanxi province china then physical mechanical parameters and material formation of the cores were systematically tested in the office the results show that there is an inversely proportional correlation between density and void ratio and a directionally proportional correlation between liquid limit and plastic index the results also show an inversely proportional correlation between compression modulus and compressible factor and an inverse relationship between internal cohesion and internal friction angle the depth of collapsible soils in the borehole is about 7 8 m which is more accurate than published data the analysis on grain sizes and carbonate content shows that there is a directionally proportional correlation between 0 075 0 010 mm grain content and carbonate content both of which have inversely proportional correlations with internal cohesion and are directly proportional to internal friction angle testing on major clay minerals has proven that there are directly proportional relationships between 0 002 mm colloid grain content with major clay minerals and internal cohesion as well as an inversely proportional relationship with internal friction angle in addition testing also shows that the dominant clay minerals in loess paleosol series are the mixed layer illite montmorillonite i s and are not single illite or montmorillonite or kaolinite this testing and analyzing of undisturbed core samples from a typical loess paleosol section is important to the exploration of landslide triggering mechanisms and engineering construction safety

shear strength of soils containing amorphous clay size materials in a slow moving landslide abstract the shear behavior of soils rich in amorphous clay size materials was not well reported in the literature this study analyzed the direct shear and ring shear test data of soil samples containing 55 74 amorphous materials in the clay fraction from a slow moving landslide in eastern honolulu hi the direct shear test results showed that the undisturbed soil samples when not sheared internally had peak cohesion c of about 50 kpa and internal friction angle o of about 10 this implies that the amorphous clay size materials provided strong interparticle bonds for the soils breaking of the bonds during the softening process and redistribution of the amorphous clay size materials were primarily responsible for the drop from the peak strength to the residual strength c 0 o 10 from back calculation with slope w and c 0 o 5 7 from the ring shear test the drained residual failure envelope is stress dependent due to the interaction of the gel like amorphous clay size materials with crystalline silt and sand sized particles the amorphous clay size materials act as the contact between crystalline particles the contact increases with increasing consolidation stress resulting in a decrease in the shear strength and the residual friction angle

shear band formation observed in ring shear tests on sandy soils shear band formation is an important factor in understanding failures in soil in this paper shear localization and shear band formation and evolution are examined using ring shear tests performed on three sands prepared by air pluviation a transparent outer confining ring was used to visualize formation and evolution of the entire shear band by comparing the ring shear stress paths with visual observations made during shearing the writers show that the specimen shears uniformly over its entire height prior to shear localization bifurcation under constant volume and drained conditions occurs as the soil fully mobilizes its effective friction angle and subsequent shear displacements occur only within the shear band consistent with previous studies the final thickness of the observed shear band ranged from 10 to 14 times the median particle diameter substantial particle damage occurred within the shear band after large displacements particularly for dilative specimens causing additional strain softening in contractive specimens and a second phase transformation and considerable strain softening in dilative specimens

tectonic segmentation of the burmese indonesian arc abstract several lines of evidences which include change in trend and offset in arcs bathymetry and sedimentation faulting in the region change in composition and trend of the line of volcanoes spatial distribution of earthquakes and change in dip of the benioff zone suggest a tectonic segmentation of the burmese indonesian arc two transverse boundary zones viz the north andaman boundary zone and the sunda boundary zone separating segments of the arc are identified larger than usual thickness of the oceanic crust beneath the ninetyeast ridge reduces the average density of the lithosphere carrying the ridge the buoyancy effect caused by the reduced average density inhibits the subduction of an approximately triangular shaped lithosphere between the burmese indonesian arc and the ninetyeast ridge which in turn causes tectonic segmentation along the arc the model predicts and some available focal mechanism solutions confirm left lateral northeast faulting within the sunda boundary zone

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

seismotectonics of subduction and back arc rifting under the andaman sea abstract active underthrusting of the indian plate below the burma plate produces seismic activity under the andaman and burmese arcs it is suggested that significant differences exist in the configuration of the benioff zone underlying the two arcs several parallel and linearly extensive fault zones are outlined by epicentral distribution in the andaman arc the andaman back arc spreading ridge is defined by a relatively narrow shallow seismic zone that orients nne to sse in north and south parts of the andaman sea respectively the spreading ridge is offset by active transform faults on the far north the spreading ridge appears to connect to a major transform fault in burma across the burmese coast focal mechanism study provides evidence for tensional stress near the inner wall of the andaman trench dominant compressive deviatoric stress within the overriding burma plate and tensional stress under the back arc spreading ridge

significant trends related to the slab seismicity and tectonics in the burmese arc region from harvard cmt solutions abstract a careful examination of 50 centroid moment tensor cmt earthquake focal mechanisms in an east west depth section in the burmese arc region reveals some interesting trends the p axis azimuths of most of the mechanisms in the region of the east dipping indian lithospheric slab are on average oriented nne this indicates that the principal compressive stress direction in the burmese arc region is commensurate with the direction of convergence of the indian plate with respect to the eurasian plate rather than with respect to the burmese plate another interesting observation is that the strike slip and thrust type focal mechanisms along the slab do not coexist but are distinctly segregated the predominantly strike slip type occurring in the upper half of the slab down to a depth of about 90 km and the thrust type in the lower hair below that depth level the former possibly indicates shearing of the indian plate past the burmese plate along the zone of contact which is inferred down to a depth of 90 km the latter is suggestive of a nne directed stress on the lower portion of the subducted slab as it is dragged against the asthenosphere by the indian plate

the australian summertime cool change part ii mesoscale aspects abstract observations of four cold frontal systems traversing the coastal region of southeast australia in late spring and early summer are described in terms of process occurring on the mesoscale a conceptual model is presented which summarizes the main results of the data analysis features found in common with other studies of cold fronts include i the multiple line nature of the frontal transition zone ftz ii concentration of cyclonic relative vorticity at a height z 1 to 1 5 km in the rear of the ftz and iii the existence of a prefrontal jet at z 1 5 km northerly in our case southerly in the northern hemisphere the change lines within the ftz and at the leading edge if there is no sea breeze are most probably convective instability lines whose alignment and movement depend on the large scale cloud layer winds the lines are evident as mesoscale cloud bands from satellite imagery and as rainbands from radar at least one of these develops into a vigorous squall line whose cold outflo

the diurnal evolution of cold fronts in the australian subtropics the effect of the diurnal cycle on the evolution of cold fronts in the australian subtropics is investigated in two high resolution numerical simulations the simulations are made using the pennsylvania state university national center for atmospheric research mesoscale model mm5 with the initial and boundary conditions taken from the operational analyses of the european centre for medium range weather forecasts these simulations are compared with the observations of two cold fronts taken during the central australian fronts experiment in 1991 the simulations show a number of features that have been suspected but never confirmed or quantified i although the wind field in the boundary layer is frontogenetic daytime turbulent mixing is strongly frontolytic which accounts for the weakening and deceleration of the fronts during the late morning and afternoon when convective mixing in the boundary layer is most vigorous ii when the mixing subsides in the early evening the low level winds increase along with the deformation and convergence leading to a strengthening and acceleration of the fronts iii bore like disturbances are generated during the early hours of the morning as the nocturnal inversion strengthens these bores propagate ahead of the front developing a series of large amplitude waves at their leading edge copyright c 2009 royal meteorological society

structure of the cold front observed in sesame ave iii and its comparison with the hoskins bretherton frontogenesis model abstract a cold front which passed through the dense network of the sesame ave severe environmental storms and mesoscale experiment atmospheric variability experiment on 25 26 april 1979 was investigated rawinsonde data collected from 23 special stations and 19 national weather service stations at three hour intervals for a 24 hour period were used along with hourly surface data radar summary charts and goes east satellite images severe storms formed along the surface front during this period the analysis focused on the vertical circulation across the frontal surface at low levels the major features of the cold frontal system that emerged from an analysis of this unique data set include a familiar direct vertical circulation with moist warm air ascending just above the surface front however the upgliding motion was intercepted by a secondary circulation at middle levels the analysis result was compared with model predictions of hoskins and bretherton 1972 as calculated by blumen 1980 sever

active faulting and tectonics of burma and surrounding regions this study of the active tectonics of burma and surrounding regions is based mostly on an interpretation of landsat imagery and on fault plane solutions for shallow and intermediate earthquakes fold axes in the indoburman ranges and an east dipping inclined zone of intermediate depth earthquakes suggest that a slab of oceanic lithosphere was recently subducted to the east under the indoburman ranges fault plane solutions of shallow earthquakes however do not show underthrusting at the present time instead p axes are oriented roughly north south parallel not perpendicular to the fold axes in the ranges p axes for fault plane solutions of intermediate shocks also trend north south parallel to the strike of the subducted slab and may indicate that the hanging slab is being dragged north by india through the surrounding asthenosphere the sagaing fault probably accommodates most of the right lateral slip of india past indochina but india s northward movement also causes internal deformation within burma thailand and yunnan differences between the tectonic fabric seen on the landsat images and the tectonic regime compatible with the fault plane solutions throughout the region imply major changes in the directions of relative motion in the orientations of strain and in the style of deformation in the late cenozoic presumably these changes reflect the transition from subduction to collision and strike slip motion as india penetrated into eurasia past burma large parts of burma and thailand may have rotated several tens of degrees clockwise in this process

three dimensional baroclinic instability and summertime frontogenesis in the australian region the structure of a mature three dimensional baroclinic wave and its attendant cold front is examined using an idealized numerical model with a simple parametrization of dry buoyant convection resulting from diurnal heating relative flow isentropic analyses of the numerical solution and of an observed australian summertime frontal system are compared it is shown that the model well represents the typical synoptic environment accompanying frontogenesis in the australian region a diagnosis of the three dimensional vertical circulation is obtained using a technique involving a vector streamfunction the circulation in a cross sectional plane parallel with the low level temperature gradient is found to be highly two dimensional with geostrophic confluence constituting the principal frontogenetical forcing at low levels while at upper levels the frontogentical forcing is dominated by geostrophic horizontal shear in a second cross section taken zonally the frontogenetic forcing is found to consist almost solely of geostrophic horizontal shear throughout the entire troposphere however in this case the circulation in the plane of cross section is found to be only qualitatively two dimensional as a significant proportion of the low level postfrontal subsidence is associated with circulation normal to the cross section it is shown that the frontal structure analysed is sensitive to the location of the chosen cross sectional plane and that this in turn provides an explanation for the observed relative shallowness of australian summertime fronts the effects of diurnal heating are important but confined to the surface based mixed layer with the addition of diurnal heating the prefrontal updraught amplifies almost threefold and the frontal temperature contrast over the heated region approximately doubles the diabatic forcing term in the well known sawyer eliassen equation is shown to be negligible this suggests that the increased low level convergence is a reflection of the model s enhanced response to frontogenetic forcing in the presence of low static stability in the surface based well mixed layer finally the numerical model solution is compared with a simpler two dimensional model specifically developed to study australian summertime fronts

accretionary tectonics of burma and the three dimensional geometry of the burma subduction zone the geometry of the burma wadati benioff zone wbz has been determined by fitting a trend surface parameterized with eight effective degrees of freedom to 184 well located hypocenters the dip of this surface which passes through the middle of the wbz varies from about 50 in the north near the eastern himalayan syntaxis to about 30 in the bay of bengal area the eastern edge of the indo burman ranges closely follows the map projection of the 60 km depth contour of the wbz the curvature of the indo burman ranges is controlled by the geometry of the interface between the more steeply dipping part of the indian plate and the leading edge of the overriding burma platelet shallow earthquakes beneath the indo burman ranges are primarily confined to the underthrusting indian plate their focal mechanisms indicate strike slip faulting and north south shortening parallel to the eastern margin of the indian plate

rossby waves extreme fronts and wildfires in southeastern australia the most catastrophic fires in recent history in southern australia have been associated with extreme cold fronts here an extreme cold front is defined as one for which the maximum temperature at 2 m is at least 17 c lower on the day following the front an anticyclone which precedes the cold front directs very dry northerlies or northwesterlies from the interior of the continent across the region the passage of the cold front is followed by strong southerlies or southwesterlies european centre for medium range weather forecasts era interim reanalyses show that this regional synoptic pattern common to all strong cold fronts and hence severe fire conditions is a consequence of propagating rossby waves which grow to large amplitude and eventually irreversibly overturn the process of overturning produces the low level anticyclone and dry conditions over southern australia while simultaneously producing an upper level trough and often precipitation in northeastern australia

a new ring shear device for testing rocks under high normal stress and dynamic conditions abstract a new ring shear device was developed to investigate the sliding mechanism of earthquake triggered large rock avalanches the loading capacity of the new device is adequate to apply dynamic normal force and torque to a rock specimen to simulate the dynamic stress path of the sliding surface in an earthquake a rock sample taken from cholan formation at the tsaoling landslide site which was triggered by the 1999 chi chi earthquake was the primary test material investigated the failure conditions of the sliding surface and the effect of seismic inertial force on the sliding blocks are considered as the terms of this test the experimental results reveal that different cumulative shear displacements under different initial normal stresses the accumulated shear displacements with and without seismic inertial forces are 38 7 mm and 2 mm respectively the negative accumulated shear displacement indicates an abnormal sliding orientation that moved toward the top of the slope therefore the new ring shear device is a useful tool in realizing the dynamic behavior and shear mechanics of the sliding surface of an earthquake triggered large rock avalanche

distribution of stress axes orientation in the andaman nicobar island region a possible stress model and its significance for extensional tectonics of the andaman sea abstract composite plots of pressure and tension axes of the available focal mechanism solutions of earthquakes are used to investigate the nature and process of the stress system and their bearing on tectonics in the andaman nicobar island region the composite plots show that the andaman nicobar island arc and the andaman sea are subjected to ssw nne directed compressive force in response to the ne drifting motion and or oblique subduction of the indian plate beneath the andaman nicobar island arc stress study also reveals that the andaman sea at the same time is experiencing an ese wnw tensile stress analogous to active back arc opening extension based on this stress pattern a strain ellipse model is proposed to explain the extensional tectonics of the andaman sea it is suggested that the oblique subduction of the indian plate invokes ne sw directed compression as well as north south directed shear stress these combined stresses are transmitted to or act on the andaman sea plate and result in stretching of the andaman sea plate in a nw se least stress direction on the strain ellipse this stretching leads to ne sw directed fracture zones normal to stretching where ascending magmas are emplaced to form active mid oceanic spreading ridges and thus active back arc extension or opening of the marginal basin takes place nearly n s dominated fracture zones which form ridge ridge type transform faults by offsetting the spreading ridges are thought to originate chiefly along the plane of maximum shear of the strain ellipse that makes an angle of 45 5 with the greatest horizontal stress component 1 and both have a close resemblance

aftershock investigation in the andaman nicobar islands of india and its seismotectonic implications six three component short period digital seismograph four reftek and two kinemetrics stations were established in different parts of the andaman nicobar islands following the 26 december 2004 devastating sumatra andaman mainshock m w 9 3 here we analyze about 18 000 aftershocks m 3 0 recorded from 6 january to 16 march 2005 to better understand the seismotectonics of the region a sudden burst of aftershock activity with irregular trend in the month of january 2005 was observed at almost all seismograph stations the estimate of p value 0 9532 from aftershocks m 4 5 is near to normal value of 1 0 which suggests a slow decay sequence of aftershock with complex and nonuniform stress change in a fault system creep effects and history dependent stress changes the frequency magnitude relation of the aftershocks followed the power law with average b value of 0 7723 and it varies from 0 49 to 1 03 indicating the compressive stress state of the region and its heterogeneous structure with possible variations in frictional conditions along the fault the distribution of the located aftershocks by a multistation method shows a north south trending aftershock cluster in an area of about 800 300 km 2 which reflects an approximate rupture dimension of the mainshock beneath the andaman nicobar islands most of aftershocks occurred in a depth range of 5 65 km the determination of composite fault plane solutions of the best located aftershock clusters at three different depth ranges 0 15 16 30 and 31 km in the ten blocks of the region suggests that the mainshock rupture propagated through normal reverse and strike slip earthquakes the areas in the vicinity of barren and narcondum volcanic zones show a dominantly normal fault mechanism due to predominant tensional forces suggesting the facilitation of brittle failure in the weakened crust by the process of underheating the zone near baratang mud volcano is associated predominantly with thrust fault at depth of 0 30 km suggesting a high compressive force beneath the baratang that ejected a huge amount of mud and slurry materials to the surface after the 26 december 2004 sumatra andaman earthquake m w 9 3 here we propose that the relocation of our large aftershock dataset using converted sp depth phase technique for precise depth control is needed and its sharing with global earthquake data can render more information on the subduction dynamics and geodynamical processes of the region

paleosols in loess deposits of the argentine pampas abstract paleosol studies are in their first stages in argentina as far as we know the soil and paleosols correspond to buried alfisols and mollisols with hydromorphic and carbonatic features the paleosol sequences on loess are made up of a succession of b or c horizons which furthermore are polygenetic as a result of encroachment of each pedogenesis on the underlying loess mantle differences in mineral composition are scarce with the exception of increases in glass shards and phytoliths in some loess mantles the b fabric is mostly stipple speckled or mosaic speckled and microlaminated clay coatings are very common there are also amorphous features related to voids or to the soil matrix evidences of biological activity are present as an excremental fabric on which a fissure microstructure is superimposed the paleosol sequences consist of several loessoid mantles each corresponding to a depositional pulse followed by a quiescent pulse during which pedogenesis took place truncation is considered to be due to eolian fluviatile erosion also there probably are a horizons masked by alteration and pedogenesis a pedogenetic origin of the calcretes with redeposition in the buried paleosols is assumed

distribution and characteristics of landslide in loess plateau a case study in shaanxi province abstract every year about one third of the geohazards in china occur in the loess plateau causing human loss damaging gas and oil pipelines destroying highways railways and degrading farmland field investigation and monitoring in situ tests and laboratory experiments were performed to improve our understanding of the factors effecting the distribution characteristics and causes of loess landslides first we find that 79 of the landslides are shallower than10m 85 have a volume of less than 100 000 m3 second landslides on the loess plateau occur primarily on concave slope profiles that have slope angles of 20 35 and that face south east third the equivalent coefficient of friction of loess landslides is very low resulting in long run out with a low angle sliding surface loess landslides generally transform into mud flows resulting in an increase in volume in transit and forming a geohazard chain antecedent rainfall plays an important role in triggering loess landslides finally clusters of landslides in the loess plateau occur because the loess easily disintegrates under high pressure due to its loose and highly porous structure there is a sharp decrease in cohesive strength with increase in deformation and water content and thus landslides tend to undergo static liquefaction during sliding

undrained shear behavior of loess saturated with different concentrations of sodium chloride solution abstract a series of ring shear tests was conducted on saturated loess to investigate the effects of nacl concentration in pore water and desalinization on the shear behavior under undrained conditions the loess samples were taken from the ground surface of a frequently active landslide in china were saturated by de aired distilled water with different concentrations of nacl and then were sheared undrained after that the samples were retrieved remolded re set into the shear box and re saturated by passing through de aired distilled water such that the samples were desalinized and then were sheared undrained again through comparing the undrained shear behavior the effects of nacl in the pore water and desalinization on the undrained shear behavior of loess were examined the results showed that the variation of nacl concentration in pore water can strongly affect the shear behavior of saturated loess both the peak shear strength and steady state strength increased with increase of nacl concentration until a certain value after which they decreased with further increase of nacl concentration meanwhile the peak shear strength and steady state strength of the desalinized samples recovered to those of the original sample hence the effects of salinization are reversible these findings may be of practical importance to better understand the repeated occurrence of some irrigation induced loess landslides in china

experimental study on the shear behavior of loess and paleosol based on ring shear tests abstract landslide hazards frequently occur in the chinese loess plateau every year causing devastating casualties damage to engineering structures and reduction in land resources this work presents an experimental investigation of four samples retrieved from jingyang in the southeast of the chinese loess plateau using ring shear tests and microscopic observation in an attempt to explore the shear behavior of loess and paleosol under the larger deformations that are involved in landslide hazards the results of ring shear tests reveal that the loess and paleosol samples exhibited different strength characteristics the residual strength envelopes could be assumed to be a straight line and the overconsolidated state had negligible influence on the residual shear strength after the shear experiment shear bands were studied from both macroscopic and microscopic perspectives macroscopic observation and mechanical analysis indicate that all samples developed a main horizontal failure plane related to the maximum shear stress while loess samples also developed en echelon failure planes tilting from the horizontal at angles of 14 18 which are interpreted as coulomb slip planes scanning electron microscopy reveals that the particles inside shear bands tend to be re oriented particle crushing occurred in the shear process which was also verified by particle size distribution analysis

the effect of the continental boundary layer on the dynamics of fronts in a 2d model of baroclinic instability ii surface heating and cooling the effect of surface heating and cooling on the structure and evolution of the surface front that develops in the finite amplitude eady wave is investigated spatially uniform short wave radiative heating of the surface is weakly frontolytic although it appears this result may be sensitive to the way in which the boundary layer turbulence is parametrized the cross front potential temperature gradient is weakened principally by the differential heating produced by horizontal variations in the depth of the mixed layer and to a smaller extent by horizontal variations in the surface sensible heat flux the direct effect of enhanced daytime turbulent stresses is to retard the winds in the boundary layer reducing the convergence in the cross front plane while the indirect effect is to produce a strong cross isobaric flow towards the trough thereby increasing the convergence the net effect is to reduce the rate of frontogenesis near the surface front during the day the front is oriented vertically in the boundary layer because of the strong mixing nocturnal cooling through long wave radiative emission from the surface is strongly frontogenetic at night as the turbulence decays in the trough ahead of the surface front air parcels accelerate down the pressure gradient towards the centre of the trough producing low level cross front surges on both sides of the trough axis this enhanced nocturnal convergence rapidly strengthens the cross front potential temperature gradient and tilts the front westward with height such nocturnal frontogenesis is especially intense when it follows strong daytime turbulent mixing copyright 2005 royal meteorological society

3 d seismic tomography of the lithosphere and its geodynamic implications beneath the northeast india region we have evolved 3 d seismic velocity structures in northeast india region and its adjoining areas to understand the geodynamic processes of indian lithosphere that gently underthrusts under the himalayas and steeply subducts below the indo burma ranges the region is tectonically buttressed between the himalayan arc to the north and the indo burmese arc to the east the tomographic image shows heterogeneous structure of lithosphere depicting different tectonic blocks though our results are limited to shallower depth 0 90 km it matches well with the deeper continuation of lithospheric structure obtained in an earlier study koulakov 2011 we observe low velocity structure all along the eastern himalayas down to 70 km depth which may be attributed to deeper roots thicker crust developed by underthrusting of indian plate parallel to this low velocity zone lies a high velocity zone in foredeep region represents the indian lithosphere the underthrusting indian lithosphere under the himalayas as well as below the indo burma ranges is well reflected as a high velocity dipping structure the buckled up part of bending indian plate in study region the shillong plateau mikir hills tectonic block is marked as a high velocity structure at shallower depth the eastern himalayan syntaxis tectonic block where the two arcs meet is identified as a high velocity structure the bengal basin tectonic block to the south of shillong plateau shows low velocity due to its thicker sediments based on the tomographic image a schematic model is presented to elucidate the structure and geodynamics of indian lithosphere in study region

seismicity and tectonic stress field of a part of the burma andaman nicobar arc abstract the nature of instrumentally recorded seismicity for a part of the burma andaman nicobar arc bounded by latitudes 2 and 24 n and longitudes 91 and 99 e was investigated based on the spatial distribution of the earthquakes and their focal mechanism solutions four tectonic units were identified from the south going northward these are the sumatra trench region characterized by strike slip and thrust faulting the andaman spreading ridge characterized by normal and a few strike slip faults the andaman nicobar ranges where faulting is mostly thrust type and the indo burman ranges region dominated by thrust faulting the stress orientations in these segments and their changes with depth were studied in relation to the tectonics of the region the direction of maximum compression in the burma andaman nicobar region is ne sw to n s compatible with the postulated motion of the indian plate changes in stress orientations are attributable to local tectonics

micromorphology and genesis of paleosols in the luochuan loess section china pedostratigraphic and environmental implications the loess paleosol sequence in the well known potou section near luochuan covers the entire pleistocene back to 2 5 ma in a much more complete sequence than any known from europe or north america to deduce a record of the pleistocene climatic history an understanding of the genesis of the paleosols is important main diagnostic features normally observable in surface soils have disappeared in the case of fossil soils therefore micromorphology is of outstanding importance because it enables the reconstruction of original properties and polygenetic soil development especially in pedocomplexes the upper part of the loess paleosol sequence can well be compared with the 18o record shown in the specmap curve of the brunhes epoch although the sequence of paleosols shows partly an even more detailed record of cold and warm stages and allows more specific informations regarding the paleoclimate of the interglacial periods cf fig 2 the last four paleosols represented by the s1 pedocomplex the upper part of the s2 and the s3 are genetically well comparable with the natural holocene soil indicating a similar climate with a tall grass steppe vegetation the s6 is a steppe soil also whereas the five soils of the s4 the s5 complex and the s7 are forest soils indicating more moist and partly warmer interglaciations than the holocene the loess paleosol sequence of the matuyama epoch seems to give more paleoclimatic informations than the deep sea cores known so far the lishi loess below the b m boundary down to 84 m in the section contains two more soils s11 and s13 which are developed under steppe vegetation in interglaciations similar to the present one and four forest soils the s8 complex the upper soil of the s9 and the s10 indicating again more moist interglaciations than the holocene most of the numerous soils in the wusheng loess are probably formed synsedimentarily as alternation of soil formation and addition of loess the red clay at the basis consists of four intensively developed but truncated paleosols the parent material of at least the lower part must be regarded as pliocene loess