an aerodynamic roughness length map derived from extended martian rock abundance data many boundary layer processes simulated within a mars general circulation model mgcm including the description of the processes controlling dust rising from the martian surface are highly sensitive to the aerodynamic roughness length z0 on the basis of rock size frequency distributions inferred from different martian landing sites and earth analog sites we have first established that lognormal modeled rock size frequency distributions are able to reproduce correctly the observed martian rock populations we have validated the hypothesis that the rock abundance of a given area could be estimated at a first order from its thermophysical properties namely its thermal inertia i and its albedo we have demonstrated the possibility of using rock abundance to estimate the roughness density on mars and to retrieve subsequently the aerodynamic roughness length by using semi empirical relationships based on terrestrial wind tunnel and field measurements by combining our methodology with remote sensing measurements of the thermal emission spectrometer aboard mars global surveyor we have derived a global map of the aeolian aerodynamic roughness length with a 1 8 1 8 resolution over the entire martian surface contrary to what is often assumed the martian aeolian aerodynamic roughness length is spatially highly heterogeneous at the fullest resolution the martian aerodynamic roughness length varies from 10 3 cm to 2 33 cm about 84 of the martian surface seems to be characterized by an aeolian aerodynamic roughness length value lower than 1 cm the spatially uniform value that most of the mgcms simulations have assumed recently since the aerodynamic roughness length z0 is a key parameter in deriving the erosion threshold wind velocities we anticipate a significant impact of our findings on the efficiencies for lifting dust in future mgcms

wind erosion on mars and other small terrestrial planets abstract we carried out wind tunnel experiments on parabolic flights with 100 m mojave mars simulant sand the experiments result in shear stress thresholds and erosion rates for varying g levels at 600 pa pressure our data confirm former results on jsc mars 1a simulant where the threshold shear stress is lower under martian gravity than extrapolated from earlier ground based studies which fits observations of martian sand activity the data are consistent with a model by shao and lu 2000 and can also be applied to other small terrestrial exo planets with low pressure atmospheres

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

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

chemistry mineralogy and grain properties at namib and high dunes bagnold dune field gale crater mars a synthesis of curiosity rover observations the mars science laboratory curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active bagnold dune field the bagnold sands are rounded to subrounded very fine to medium sized 45 500 m with 6 distinct grain colors in contrast to sands examined by curiosity in a dust covered inactive bedform called rocknest and soils at other landing sites bagnold sands are darker less red better sorted have fewer silt sized or smaller grains and show no evidence for cohesion nevertheless bagnold mineralogy and rocknest mineralogy are similar with plagioclase olivine and pyroxenes in similar proportions comprising 90 of crystalline phases along with a substantial amorphous component 35 15 yet bagnold and rocknest bulk chemistry differ bagnold sands are si enriched relative to other soils at gale crater and h 2o s and cl are lower relative to all previously measured martian soils and most gale crater rocks mg ni fe and mn are enriched in the coarse sieved fraction of bagnold sands corroborated by visible near infrared spectra that suggest enrichment of olivine collectively patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils 1 amorphous components in the sand sized fraction represented by bagnold that are si enriched hydroxylated alteration products and or h 2o or oh bearing impact or volcanic glasses and 2 amorphous components in the fine fraction 40 m represented by rocknest and other bright soils that are fe s and cl enriched with low si and adsorbed and structural h 2o

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

mars aerosol studies with the mgs tes emission phase function observations optical depths particle sizes and ice cloud types versus latitude and solar longitude 1 emission phase function epf observations taken in 1999 2001 by mars global surveyor thermal emission spectrometer mgs tes support the broadest study of martian aerosol properties to date tes solar band and infrared ir spectral epf sequences are analyzed to obtain first time seasonal latitudinal distributions of visible optical depths particle sizes and single scattering phase functions this combined angular and wavelength coverage enables identification of two distinct ice cloud types over 45 s 45 n type 1 ice clouds exhibit small particle sizes reff 1 2 m and a distinctive backscattering increase they are most prevalent in the southern hemisphere during aphelion but also appear more widely distributed in season and latitude as topographic and high altitude 20 km ice hazes type 2 ice clouds exhibit larger particle sizes reff 3 4 m a distinct side scattering minimum at 90 100 phase angles characteristic of a change in particle shape relative to the type 1 and appear most prominently in the northern subtropical aphelion cloud belt the majority of retrieved dust visible to ir optical depth ratios are indicative of reff 1 5 0 1 m consistent with pathfinder and viking mariner 9 reanalyses however increased ratios 2 7 versus 1 7 appear frequently in the northern hemisphere over ls 50 200 indicating substantially smaller dust particles sizes reff 1 0 0 2 m at this time in addition larger reff 1 8 2 5 m dust particles were observed locally in the southern hemisphere during the peak of the 2001 global dust storm detailed spectral modeling of the tes visible band pass indicates agreement of epf derived dust single scattering albedos 0 92 0 94 with the spectrally resolved results from pathfinder observations

orbital change experiments with a mars general circulation model abstract we use a mars general circulation model to examine the effect of orbital changes on the planet s general circulation and climate system experiments are performed for obliquities ranging from 0 to 60 for two different longitudes of perihelion each experiment simulates a full mars year assuming a fixed atmospheric dust distribution and fixed amount of co 2 in the atmosphere cap system we find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps the seasonal co 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices the most significant feature of the high obliquity solstice circulations is the development of an intense low level jet associated with the return branch of the hadley circulation model surface stresses are used to map regions of preferred dust lifting which are defined in terms of an annual deflation potential for the present obliquity the model predicted regions of high deflation potential are in good agreement with cantor et al s 2001 j geophys res 106 23653 23688 observations which gives us some confidence in the model s ability to predict where lifting might occur when mars orbit parameters are different than they are today in general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice over an obliquity cycle the model global annual deflation potential ranges from several tenths of a millimeter at 0 obliquity to almost 15 mm at 60 obliquity much higher values are possible when the atmosphere is very dusty we find a strong correlation between the deflation potential and surface thermal inertia regions of high deflation potential correspond to regions of high thermal inertia high rock abundance and regions of low deflation potential correspond to regions of low thermal inertia high dust sand abundance furthermore while the regions of preferred lifting high deflation potential expand somewhat with increasing obliquity and dust loading the central parts of tharsis arabia and elysium show no tendency for significant lifting at any obliquity or longitude of perihelion these regions may therefore be very old and represent net long term sinks for atmospheric dust it is the topography of the planet through its influence on surface pressure and wind systems which ultimately determines where dust accumulates finally as was found by fenton and richardson 2001 j geophys res 106 32885 32909 we find no tendency for the development of east southeasterly winds at the pathfinder site for any of our orbital change experiments this suggests that the ancient wind regime discussed by greeley et al 2000 j geophys res 105 1829 1840 was produced by other factors such as polar wander

spectral and petrologic analyses of basaltic sands in ka u desert hawaii implications for the dark dunes on mars dark aeolian bedforms on mars are thought to consist of volcanic materials due to their mineral assemblages which are common to basalts however the sediment source is still debated and needs further affirmation basaltic dunes on earth are rare and can only be found in a few places including new zealand iceland the western usa peru and hawaii these dunes composed of volcaniclastic sediments are promising analogues for providing further insights into the assumed basaltic sand dunes on mars in our study we use basaltic dunes sands collected in hawaii s ka u desert which are especially interesting for addressing the source of martian dunes because of the co occurrence of active volcanic processes and dune development for these dunes we could prove that their material has been derived from airfall ashes from phreatomagmatic eruptions of kilaulea and reworked lava basaltic dunes sand from arizona builds a second set of terrestrial analogue samples in our study these sands have been collected from aeolian bedforms that are composed of reworked volcanic ash erupted from nearby sinter cones spectral analyses of the terrestrial samples show that the dune sands are enriched in pyroxene and olivine a basaltic composition similar to that of the martian dark dunes microprobe analyses show that the terrestrial sands are dominated by olivine pyroxene plagioclase and glasses resulting from the volcanic source of these aeolian sediments this result is consistent with modal mineralogy modeling of martian dunes sands these correlations prove the hypothesis of a similar origin of the martian and terrestrial dune sands consistent with reworked volcanic ash and lava

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

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

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

eolianite grain size distributions as a proxy for large changes in planetary atmospheric density a digitized version of the ahlbrandt 1979 global dune dataset and data for distributions in figure are available at https github com erikgoosmann aeoliandata

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

active dust devils in gusev crater mars observations from the mars exploration rover spirit 1 a full dust devil season was observed from spirit from 10 march 2005 sol 421 first active dust devil observed to 12 december 2005 sol 691 last dust devil seen this corresponds to the period ls 173 2 to 339 5 or the southern spring and summer on mars thermal emission spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in gusev and that spirit landed in the waning stages of a dust devil season as temperatures decreased 533 active dust devils were observed enabling new characterizations they ranged in diameter from 2 to 276 m with most in the range of 10 20 m in diameter and occurred from about 0930 to 1630 hours local true solar time with the maximum forming around 1300 hours and a peak occurrence in southern late spring ls 250 horizontal speeds of the dust devils ranged from 1 to 21 m s while vertical wind speeds within the dust devils ranged from 0 2 to 8 8 m s these data when combined with estimates of the dust content within the dust devils yield dust fluxes of 3 95 10 9 to 4 59 4 kg m2 s analysis of the dust devil frequency distribution over the inferred dust devil zone within gusev crater yields 50 active dust devils km2 sol suggesting a dust loading into the atmosphere of 19 kg km2 sol this value is less than one tenth the estimates by cantor et al 2001 for regional dust storms on mars

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

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

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

saltation under martian gravity and its influence on the global dust distribution abstract dust and sand motion are a common sight on mars understanding the interaction of atmosphere and martian soil is fundamental to describe the planet s weather climate and surface morphology we set up a wind tunnel to study the lift of a mixture between very fine sand and dust in a mars simulant soil the experiments were carried out under martian gravity in a parabolic flight the reduced gravity was provided by a centrifuge under external microgravity the onset of saltation was measured for a fluid threshold shear velocity of 0 82 0 04 m s this is considerably lower than found under earth gravity in addition to a reduction in weight this low threshold can be attributed to gravity dependent cohesive forces within the sand bed which drop by 2 3 under martian gravity the new threshold for saltation leads to a simulation of the annual dust cycle with a mars gcm that is in agreement with observations

giant saltation on mars saltation the motion of sand grains in a sequence of ballistic trajectories close to the ground is a major factor for surface erosion dune formation and triggering of dust storms on mars although this mode of sand transport has been matter of research for decades through both simulations and wind tunnel experiments under earth and mars conditions it has not been possible to provide accurate measurements of particle trajectories in fully developed turbulent flow here we calculate the motion of saltating grains by directly solving the turbulent wind field and its interaction with the particles our calculations show that the minimal wind velocity required to sustain saltation on mars may be surprisingly lower than the aerodynamic minimal threshold measurable in wind tunnels indeed mars grains saltate in 100 times higher and longer trajectories and reach 5 10 times higher velocities than earth grains do on the basis of our results we arrive at general expressions that can be applied to calculate the length and height of saltation trajectories and the flux of grains in saltation under various physical conditions when the wind velocity is close to the minimal threshold for saltation

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

observations of the initiation and evolution of the 2001 mars global dust storm 1 a global dust storm occurred on mars between june and october 2001 the storm began near hellas just before southern spring equinox ls 177 local storms likely forced by a combination of slope flow and ice cap thermal contrasts were observed to propagate along the northwestern rim of hellas apparently triggering the global storm cap edge storm activity for much of late southern winter was similar in 2001 to one mars year earlier however a very large storm propagated into the basin just after ls 177 subsequently the total area of storm activity in 2001 was roughly double that of the previous year for about 10 days dust lifting was limited to the hellas region as additional storms propagated into hellas activity built and extended northward into syrtis and eastward into hesperia it is not clear whether transport or spreading of lifting were of greatest importance for expansion at ls 185 the storm began to spread rapidly to the east along a line from the southern pole to the northern tropics essentially no storm propagation to the west occurred yielding strong zonal asymmetry of expansion as the dust storm reached the western edge of tharsis secondary dust lifting centers developed in daedalia and solis southeastern tharsis subsequently the storm rapidly encompassed the planet by ls 193 once fully global the syria solis daedalia lifting center appeared to dominate on the basis of cloud top morphology with hellas quiescent by ls 212 lifting could no longer be discerned thereafter dust haze appeared uniform and diffuse and decay appeared to have set in

planet wide sand motion on mars prior to mars reconnaissance orbiter data images of mars showed no direct evidence for dune and ripple motion this was consistent with climate models and lander measurements indicating that winds of sufficient intensity to mobilize sand were rare in the low density atmosphere we show that many sand ripples and dunes across mars exhibit movement of as much as a few meters per year demonstrating that martian sand migrates under current conditions in diverse areas of the planet most motion is probably driven by wind gusts that are not resolved in global circulation models a past climate with a thicker atmosphere is only required to move large ripples that contain coarse grains

results of the mars pathfinder atmospheric structure investigation we report on a thorough analysis of the mars pathfinder atmospheric structure investigation asi accelerometer data spanning the altitude range 161 8 9 km entry descent and landing occurred within 850 km of the viking 1 lander and somewhat later in northern summer the early morning entry 0300 hours provided the first opportunity to study mars nighttime atmospheric structure the close proximity to the viking 1 site has permitted a search for changes in atmospheric structure during the 21 years between the landings our results confirm and refine the major features of the atmospheric structure discovered in the initial analysis of the asi results reported by schofield et al 1997 the current analysis has yielded a much better definition of the temperature structure above 90 km altitude pathfinder measured a thermospheric peak temperature of 153 k at 134 km which is 30 k colder than the value found by viking 1 between 110 and 88 km pathfinder found a broad nearly isothermal plateau at 127 k which correlates very well with a similar structure evident in viking 1 data at the same pressures although the pathfinder layer is 25 k colder at levels above 88 km wavelike oscillations with a wavelength 5 km and amplitudes of 2 3 k are evident possibly reflecting gravity or planetary wave activity between 90 and 60 km the average temperature is 20 30 k cooler than viking 1 values large amplitude 10 20 k long wavelength 20 40 km oscillations which show a remarkable correspondence to equivalent structures found in the viking 1 profile at the same pressures occur in this region and are likely due to a diurnal tidal mode between 85 and 77 km a minimum of one oscillation results in temperatures up to 7 k below the saturation temperature of co2 well outside the uncertainties in the measurements and the vapor pressure curve and comparable to observed supersaturations of water in earth s mesosphere between 55 and 16 km temperatures are close to or warmer than viking 1 values superposed long wavelength oscillations correspond well with similar structures observed by viking 1 between 16 and 9 9 km the temperature profile shows an unexpected strong thermal inversion which may reflect radiative cooling due to a water cloud at the base of the inversion temperatures begin to increase abruptly until the last measurement at 8 9 km the viking like temperatures in the lower atmosphere are consistent with the viking like dust optical depths observed by the mars pathfinder imager the cool temperatures in the middle and upper atmosphere may be indicative of significant nighttime cooling at these levels although other interpretations are possible

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

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

late albian paleoceanography of the western subtropical north atlantic a late albian early cenomanian record 103 3 to 99 0 ma including organic rich deposits and a 13c increase associated with oceanic anoxic event 1d oae 1d is described from ocean drilling program sites 1050 and 1052 in the subtropical atlantic foraminifera are well preserved at these sites paleotemperatures estimated from benthic 18o values average 14 c for middle bathyal site 1050 and 17 c for upper bathyal site 1052 whereas surface temperatures are estimated to have ranged from 26 c to 31 c at both sites among planktonic foraminifera there is a steady balance of speciation and extinction with no discrete time of major faunal turnover oae 1d is recognized on the basis of a 1 2 13c increase 100 0 99 6 ma which is similar in age and magnitude to 13c excursions documented in the north atlantic and western tethys organic rich black shales are present throughout the studied interval at both sites however deposition of individual black shale beds was not synchronous between sites and most of the black shale was deposited before the oae 1d 13c increase a similar pattern is observed at the other sites where oae 1d has been recognized indicating that the site s of excess organic carbon burial that could have caused the 13c increase has have yet to be found our findings add weight to the view that oaes should be chemostratigraphically 13c rather than lithostratigraphically defined

winds measured by the rover environmental monitoring station rems during the mars science laboratory msl rover s bagnold dunes campaign and comparison with numerical modeling using marswrf abstract a high density of rems wind measurements were collected in three science investigations during msl s bagnold dunes campaign which took place over 80 sols around southern winter solstice ls 90 and constituted the first in situ analysis of the environmental conditions morphology structure and composition of an active dune field on mars the wind characterization investigation was designed to fully characterize the near surface wind field just outside the dunes and confirmed the primarily upslope downslope flow expected from theory and modeling of the circulation on the slopes of aeolis mons in this season the basic pattern of winds is upslope from the northwest heading up aeolis mons during the daytime 09 00 17 00 or 18 00 and downslope from the southeast heading down aeolis mons at night 20 00 to some time before 08 00 between these times the wind rotates largely clockwise giving generally westerly winds mid morning and easterly winds in the early evening the timings of these direction changes are relatively consistent from sol to sol however the wind direction and speed at any given time shows considerable intersol variability this pattern and timing is similar to predictions from the marswrf numerical model run at a resolution of 490 m in this region although the model predicts the upslope winds to have a stronger component from the e than the w misses a wind speed peak at 09 00 and under predicts the strength of daytime wind speeds by 2 4 m s the namib dune lee investigation reveals blocking of northerly winds by the dune leaving primarily a westerly component to the daytime winds and also shows a broadening of the 1 hz wind speed distribution likely associated with lee turbulence the namib dune side investigation measured primarily daytime winds at the side of the same dune in support of aeolian change detection experiments designed to put limits on the saltation threshold and also appears to show the influence of the dune body on the local flow though less clearly than in the lee using a vertical grid with lower resolution near the surface reduces the relative strength of nighttime winds predicted by marswrf and produces a peak in wind speed at 09 00 improving the match to the observed diurnal variation of wind speed albeit with an offset in magnitude the annual wind field predicted using this grid also provides a far better match to observations of aeolian dune morphology and motion in the bagnold dunes however the lower overall wind speeds than observed and disagreement with the observed wind direction at 09 00 suggest that the problem has not been solved and that alternative boundary layer mixing schemes should be explored which may result in more mixing of momentum down to the near surface from higher layers these results demonstrate a strong need for in situ wind data to constrain the setup and assumptions used in numerical models so that they may be used with more confidence to predict the circulation at other times and locations on mars

determination of the wind induced detachment threshold for granular material on mars using wind tunnel simulations experimental results are presented of wind induced grain detachment under mars simulation conditions a simple force balance equation is applied to quantify the wind shear stress required for removal of glass spheres from a sand bed the transport of fine grained martian dust is simulated by the detachment of hollow glass spheres which resemble low mass density dust aggregates observed to form during simulations when using mars analogue material the results agree well with observations of dust removal and wind speed measurements made by the nasa viking landers at the martian surface this work supports the suggestion that dust aggregate fragmentation allows wind induced dust entrainment at substantially lower wind shear than that of solid sand grains and has direct application to the study of global dust transport and martian climatology

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

unsteady saltation on mars abstract saltation is an important process on mars as it contributes to dust raising bedform dynamics and aeolian abrasion lander measurements and mesoscale meteorological models suggest that winds in the martian atmosphere rarely exceed the fluid threshold value that is necessary to aerodynamically initiate saltation a fact in stark contrast to the existence of dunes and ripples on the planet many of which are in an active state of migration in an attempt to reconcile these observations we perform an unsteady simulation with a simple turbulence model to calculate the saltation transport rate sinusoidal wind variations are imposed on the saltation layer the numerical simulations verify that gusty transport is one of the main manifestations of martian sediment transport events a formula for the saltation transport rate is reported q m u u it p where u and u it are the friction velocity and impact threshold friction velocity the power p varies in the range of 0 7 1 8 on mars and 1 5 on earth depending on the period and amplitude of the gusty inflow wind our results show that the law of martian and terrestrial transport rate are not universal and hence one should be cautious when trying to extrapolate existing terrestrial results to mars

the particle size of martian aeolian dunes the effective particle size of unconsolidated materials on the martian surface can be determined from thermal inertia due to a pore size dependence of thermal conductivity at martian atmospheric pressures because dunes consist of a narrow range of well sorted unconsolidated particles they provide for a test of the relationship between particle size and thermal inertia calculated from midinfrared emission data for the martian surface we use two independent approaches first thermal inertia data indicate that martian dunes have an average particle size of about 500 100 m or medium to coarse sand second we determine expected dune particle sizes from grain trajectory calculations and the particle size transition from suspension to saltation on earth the transition occurs for a grain when the ratio of the terminal fall velocity to the wind friction speed u t is near unity for grains at u t this occurs at about 52 m terrestrial dune sands have a mean of 250 m and are composed entirely of grains 52 m the corresponding martian transition grain size is about 210 m suggesting that martian dunes should be significantly coarser than terrestrial dunes grain saltation path length as a function of particle size also shows that under martian conditions larger grains than on earth will become suspended both approaches indicate that martian dune sand should be coarser than terrestrial dune sand thus while terrestrial dune grains are in the fine to medium sand range the average martian dune sediments are probably medium to coarse sands these results closely match the grain sizes determined from thermal inertia models providing the first direct test of the validity of these models for actual martian surface materials

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

a scaling law for aeolian dunes on mars venus earth and for subaqueous ripples abstract the linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength at which the bed destabilises to form dunes should scale with the drag length l drag s f d this scaling law is tested using existing and new measurements performed in water subaqueous ripples in air aeolian dunes and fresh snow dunes in a high pressure co2 wind tunnel reproducing conditions close to venus atmosphere and in the low pressure co2 martian atmosphere martian dunes the difficulty is to determine the diameter of saltating grains on mars a first estimate comes from photographs of aeolian ripples taken by the rovers opportunity and spirit showing grains whose diameters are smaller than on earth dunes in addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds it confirms that the small grains visualised by the rovers should be grains experiencing saltation finally we show that within error bars the scaling of with ldrag holds over almost five decades we conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on mars

spatial grain size sorting in eolian ripples and estimation of wind conditions on planetary surfaces application to meridiani planum mars the landscape seen by the mars exploration rover mer opportunity at meridiani planum is dominated by eolian wind blown ripples with concentrated surface lags of hematitic spherules and fragments these ripples exhibit profound spatial grain size sorting with well sorted coarse grained crests and poorly sorted generally finer grained troughs these ripples were the most common bed form encountered by opportunity in its traverse from eagle crater to endurance crater field measurements from white sands national monument new mexico show that such coarse grained ripples form by the different transport modes of coarse and fine grain fractions on the basis of our field study and simple theoretical and experimental considerations we show how surface deposits of coarse grained ripples can be used to place tight constraints on formative wind conditions on planetary surfaces activation of meridiani planum coarse grained ripples requires a wind velocity of 70 m s at a reference elevation of 1 m above the bed from images by the mars orbiter camera moc of reversing dust streaks we estimate that modern surface winds reach a velocity of at least 40 m s and hence may occasionally activate these ripples the presence of hematite at meridiani planum is ultimately related to formation of concretions during aqueous diagenesis in groundwater environments however the eolian concentration of these durable particles may have led to the recognition from orbit of this environmentally significant landing site

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

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