geology and petrology of enormous volumes of impact melt on the moon a case study of the orientale basin impact melt sea abstract lunar basin forming impacts produce enormous volumes 10 5 km 3 of impact melt all known basin forming impacts combined may produce 10 8 km 3 of impact melt 1 20th the volume of the lunar crust despite their volumetric importance the geology and petrology of massive deposits of impact melt on the moon have been little studied in part because most basin impact melt deposits are old and have been obscured or buried by subsequent impact cratering and mare infill we investigate the geology and model the petrology of fresh massive impact melt deposits in the relatively young 930 km diameter orientale basin models of impact melt production combined with geologic analyses based on new lola topographic data suggest that most of the impact melt 2 3 produced by the orientale forming impact occurs in a 15 km thick impact melt sheet better described as an impact melt sea 350 km in diameter with a volume of 10 6 km 3 we anticipate that the orientale melt sea has undergone large scale igneous differentiation since terrestrial impact melt sheets such as manicouagan sudbury and morokweng less than a tenth of the thickness and a hundredth of the volume of the orientale melt sea have differentiated we develop a model for the cumulate stratigraphy of the solidified orientale impact melt sea a modeled cumulate stratigraphy occurring below a quench crust and anorthositic fallback breccia with an 8 km thick layer of norite overlying a 4 km layer of pyroxenite and a basal 2 km thick layer of dunite produced by equilibrium crystallization of a homogenized melt sea consistent with vigorous convection in that melt sea is supported by remotely sensed norite excavated by the central peak of maunder crater from 4 km depth generally we predict that very large basin forming impacts including the south pole aitken spa basin forming impact produce melt seas with a cumulate stratigraphy similar to that of the orientale melt sea impact melt differentiation may explain apparently anomalous lithologies excavated in the spa basin interior we note that impact melt differentiates are slow cooled the orientale melt sea took on the order of 10 5 years to solidify and if meteoritic siderophiles fractionate into metal or sulfide layers may not be siderophile enriched therefore impact melt differentiates may pass for pristine highland plutonic rocks in the lunar sample suite these predictions can be tested with current and future mission data

planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

composition and structure of the central aleutian island arc from arc parallel wide angle seismic data new results from wide angle seismic data collected parallel to the central aleutian island arc require an intermediate to mafic composition for the middle crust and a mafic to ultramafic composition for the lower crust and yield lateral velocity variations that correspond to arc segmentation and trends in major element geochemistry the 3 d ray tracing 2 5 d inversion of this sparse wide angle data set which incorporates independent phase interpretations and new constraints on shallow velocity structure produces a faster and smoother result than a previously published velocity model middle crustal velocities of 6 5 7 3 km s over depths of 10 20 km indicate an andesitic to basaltic composition high lower crustal velocities of 7 3 7 7 km s over depths of 20 35 km are interpreted as ultramafic mafic cumulates and or garnet granulites the total crustal thickness is 35 37 km this result indicates that the aleutian island arc has higher velocities and thus more mafic compositions than average continental crust implying that significant modifications would be required for this arc to be a suitable building block for continental crust lateral variations in average crustal velocity below 10 km roughly correspond to trends in major element geochemistry of primitive mg 0 6 lavas the highest lower crustal velocities and presumably most mafic material are detected in the center of an arc segment between unmak and unalaska islands implying that arc segmentation exerts control over crustal composition

erosional modification and gully formation at meteor crater arizona insights into crater degradation processes on mars hydrogeological modification of meteor crater produced a spectacular set of gullies throughout the interior wall in response to rainwater precipitation snow melting and possible groundwater discharge the crater wall has an exceptionally well developed centripetal drainage pattern consisting of individual alcoves channels and fans some of the gullies originate from the rim crest and others from the middle crater wall where a lithologic transition occurs broad gullies occur along the crater corner radial faults deeply incised alcoves are well developed on the soft coconino sandstone exposed on the middle crater wall beneath overlying dolomite in general the gully locations are along crater wall radial fractures and faults which are favorable locales of erosion due to preferential rock breakup from faulting and groundwater flow discharge these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow causing erosion and crater degradation channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor caves exposed on the lower crater level point to percolation of surface runoff and selective discharge through fractures on the crater wall in addition lake sediments on the crater floor provide significant evidence of a past pluvial climate when the water table was higher and groundwater may have seeped from springs on the crater wall although these hydrological processes continue at meteor crater today conditions at the crater are much more arid than they were soon after impact reflecting a climatic shift this climate shift and the hydrological modifications observed at meteor crater provide insights for landscape sculpturing on mars during various parts of its history

the long lived and recent seismicity at the lunar orientale basin evidence from morphology and formation ages of boulder avalanches tectonics and seismic ground motion

50 ma initiation of hawaiian emperor bend records major change in pacific plate motion the hawaiian emperor bend has played a prominent yet controversial role in deciphering past pacific plate motions and the tempo of plate motion change new ages for volcanoes of the central and southern emperor chain define large changes in volcanic migration rate with little associated change in the chain s trend which suggests that the bend did not form by slowing of the hawaiian hot spot initiation of the bend near kimmei seamount about 50 million years ago ma was coincident with realignment of pacific spreading centers and early magmatism in western pacific arcs consistent with formation of the bend by changed pacific plate motion

normal faulting origin for the cordillera and outer rook rings of orientale basin the moon 1 orientale basin is the youngest and best preserved large impact basin on the moon with at least four topographic rings contained within the topographic rim marked by the cordillera ring diameter 930 km its well exposed interior makes this basin a prime location to study basin formation processes forward mechanical modeling of basin ring topography shows that the outermost rings the cordillera ring cr and outer rook ring orr are large scale normal faults with displacements d of 0 8 to 5 2 km fault dip angles of 54 to 80 and vertical depth of faulting t between 19 and 37 km with most faults having t 30 5 km these faults and the distribution of maria inside the basin suggest that the transient crater important for determining many impact related characteristics such as projectile size was contained entirely within the orr and likely had a diameter between 500 and 550 km the difference in crustal thickness between the western and eastern sides of the basin is not a result of the basin forming event which indicates the formation of the hemispheric crustal thickness asymmetry was likely before the formation of orientale basin 3 68 to 3 85 ga

crustal structure and evolution of the mariana intra oceanic island arc a new high resolution velocity model of the mariana arc backarc system obtained from active source seismic profiling demonstrates velocity variations within the arc middle and lower crusts of intermediate to felsic and mafic compositions the characteristics of the oceanic island arc crust are a middle crust with velocity of 6 km s laterally heterogeneous lower crust with velocities of 7 km s and unusually low mantle velocities petrologic modeling suggests that the volume of the lower crust composed of restites and olivine cumulates after the extraction of the middle crust should be significantly larger than is observed suggesting that a part of the lower crust especially the cumulates is seismically a part of the mantle

lunar orientale impact basin secondary craters spatial distribution size frequency distribution and estimation of fragment size secondary impact craters features created by projectiles ejected from a primary impact contain important information about the primary cratering event and the nature and distribution of its ejecta the orientale impact basin d similar to 930km is the youngest and the least degraded large impact basin on the moon and has the most recognizable secondary impact craters we identified and mapped 2 728 secondary craters in the investigated area of similar to 1 66x10 7 km 2 covering an area from the rim of orientale to six radii secondary crater diameters range from similar to 2 to 27km and the median diameter decreases as distance increases secondary craters are concentrated predominantly in the northwest and southwest the ejecta deposit pattern inferred from secondary crater distribution suggests that the orientale basin was formed by an oblique impact in which the downrange direction was 240 degrees 265 degrees in azimuth and the incidence angle was steeper than 20 degrees the cumulative size frequency distribution of mapped secondary craters steepens as diameter increases and is very well approximated with a weibull distribution with an exponent 1 32 a widely used crater scaling relationship predicts that the fragments that produced the secondary craters were predominantly in similar to 0 5 2 km diameter range over the investigated area the diameter of the largest fragment however decreases with increasing distance from orientale on the basis of the diameter of the largest secondary crater of orientale and other craters and basins the largest secondary crater of the south pole aitken basin is estimated to be similar to 40km in diameter we explore the implications of these findings for the evolution of the megaregolith and future sample return missions

recent shallow moonquake and impact triggered boulder falls on the moon new insights from the schrodinger basin shallow moonquakes are thought to be of tectonic origin however the geologic structures responsible for these moonquakes are unknown here we report sites where moonquakes possibly occurred along young lobate scarps in the schrodinger basin our analysis of lunar reconnaissance orbiter and chandrayaan 1 images revealed four lobate scarps in different parts of the schrodinger basin the scarps crosscut small fresh impact craters 1500 boulders associated with trails and bouncing marks their origins are largely controlled by recent impact events ejecta rays and secondary crater chains from a 14 km diameter impact crater traversed schrodinger and triggered significant boulder falls about 17 ma therefore a combination of recent shallow moonquakes and impact events triggered the boulder falls in the schrodinger basin

grabens basin tectonics and the maximum total expansion of the moon the presence of grabens and wrinkle ridges indicates that stresses sufficient to deform or fault crustal rocks have existed for at least part of lunar history these structures have been explained as due to global expansion and contraction basin subsidence or both even if the extension implied by all lunar grabens were due to global expansion the total radius increase permissible after terminal bombardment would be much less than that predicted by the most conservative models of lunar thermal evolution the obvious areal association of most grabens and wrinkle ridges with impact basins suggests that a genetic relationship exists also but it is necessary to develop either kinematic or dynamic models to determine if basin subsidence alone can account for these structures kinematic models are the most useful because fewer assumptions regarding material properties are needed than for dynamic models for both types the grabens and wrinkle ridges provide the data that must be predicted by the models considerations of geometry kinematics and mechanics suggest that the simple grabens on the moon are reliable indicators of crustal extension two end member kinematic models of postimpact basin modification are derived one assuming that subsidence is accomplished entirely by an increase in radius of curvature of the basin floor the other assuming that subsidence is accomplished without any change in radius of curvature of the basin floor any combination of the two also would be possible both models predict enough extension to account completely for basin related grabens and thus they indicate that virtually all of the extension implied by lunar grabens can be provided by modest amounts of basin subsidence in addition both models also predict total radial and hoop shortening of the basin floor of about the correct magnitude to explain wrinkle ridges if these features are structures resulting from compression consequently almost all extension and shortening of the lunar crust implied by grabens and wrinkle ridges can be explained by basin subsidence alone significant global expansion after 3 9 b y is unlikely and significant global contraction is unnecessary

new morphological mapping and interpretation of ejecta deposits from orientale basin on the moon abstract orientale basin is one of the youngest and best preserved multi ring impact basins in the solar system the structure is 950 km across and is located on the western edge of the nearside of the moon the interior of the basin which possesses three distinct rings and a post impact mare fill has been studied extensively using modern high resolution datasets exterior to these rings orientale has an extensive ejecta blanket that extends out radially for at least 800 km from the basin rim in all directions and covers portions of both the nearside and farside of the moon these deposits known as the hevelius formation were first mapped using photographic data from the lunar orbiter iv probe in this study we map in detail the morphology of each distinct facies observed within the orientale ejecta blanket using high resolution lunar reconnaissance orbiter lro wide angle camera wac and narrow angle camera nac images and lunar orbiter laser altimeter lola elevation data we identified 5 unique facies within the ejecta blanket facies a is identified as a region of hummocky plains located in a low lying topographic region between the outer rook and cordillera rings this facies is interpreted to be a mix of crater derived impact melt and km scale blocks of ballistic ejecta and host rock broken up during the modification stage and formation of the cordillera ring facies b is an inner facies marked by radial grooves extending outward from the direction of the basin center this facies is interpreted as the continuous ballistic ejecta blanket facies c consists of inner and outer groupings of flat smooth surfaced deposits isolated in local topographic lows facies d displays characteristic sinuous ridges and lobate extensions facies c and d are interpreted to be impact melt rich materials which manifest as flows and ponds our observations suggest that these facies were emplaced subsequent to the ballistic ejecta blanket most likely during the modification stage of crater formation and flowed and ponded in topographically low lying regions facies e consists of distinct crater chains emanating radially from the basin center and extending from 700 to 1000 km from the center of orientale this facies is considered to be chains of secondary craters formed from large blocks of ballistic ejecta our mapping effort shows that the individual ejecta facies were influenced and controlled to varying degrees by pre existing slopes and topography at the basin scale the overall downslope direction toward the lunar lowlands to the east and southeast of the basin center resulted in large impact melt flows 100 s of kilometers in length while the regional upslope trends in the west and northwest inhibited the development of extensive impact melt flows on a smaller scale it can be observed that ground hugging ejecta collected behind and flowed around high topographic obstacles while diverting into topographic low regions e g around uplifted pre existing crater rims but down into pre existing crater floors the dispersion of the various ejecta facies mapped here also indicates both a direction and an angle for the impact event that formed orientale basin the bilateral distribution of both ballistic and impact melt rich ejecta deposits across a line running northeast southwest suggests the impact occurred from the northeast toward the southwest careful mapping of the secondary impact crater chains facies e shows the development of a forbidden zone lacking these impacts to the northeast as well as a concentration of the longest secondary crater chains to the northwest and southeast perpendicular to the aforementioned line of bilateral ejecta distribution this distribution of secondary impact craters contrasts with the circularity of the basin and suggests that orientale basin was formed by 25 45 impact from the northeast

global thrust faulting on the moon and the influence of tidal stresses lunar reconnaissance orbiter camera images reveal a vast globally distributed network of over 3200 lobate thrust fault scarps making them the most common tectonic landform on the moon based on their small scale and crisp appearance crosscutting relations with small diameter impact craters and rates of infilling of associated small shallow graben these fault scarps are estimated to be younger than 50 ma and may be actively forming today the non random distribution of the scarp orientations is inconsistent with isotropic stresses from late stage global contraction as the sole source of stress we propose that tidal stresses contribute significantly to the current stress state of the lunar crust orbital recession stresses superimposed on stresses from global contraction with the addition of diurnal tidal stresses result in non isotropic compressional stress and thrust faults consistent with lobate scarp orientations the addition of diurnal tidal stresses at apogee result in peak stresses that may help trigger coseismic slip events on currently active thrust faults on the moon

formation of the orientale lunar multiring basin multiring basins large impact craters characterized by multiple concentric topographic rings dominate the stratigraphy tectonics and crustal structure of the moon using a hydrocode we simulated the formation of the orientale multiring basin producing a subsurface structure consistent with high resolution gravity data from the gravity recovery and interior laboratory grail spacecraft the simulated impact produced a transient crater 390 kilometers in diameter that was not maintained because of subsequent gravitational collapse our simulations indicate that the flow of warm weak material at depth was crucial to the formation of the basin s outer rings which are large normal faults that formed at different times during the collapse stage the key parameters controlling ring location and spacing are impactor diameter and lunar thermal gradients

large impact basins on mercury global distribution characteristics and modification history from messenger orbital data 1 the formation of large impact basins diameter d 300 km was an important process in the early geological evolution of mercury and influenced the planet s topography stratigraphy and crustal structure we catalog and characterize this basin population on mercury from global observations by the messenger spacecraft and we use the new data to evaluate basins suggested on the basis of the mariner 10 flybys forty six certain or probable impact basins are recognized a few additional basins that may have been degraded to the point of ambiguity are plausible on the basis of new data but are classified as uncertain the spatial density of large basins d 500 km on mercury is lower than that on the moon morphological characteristics of basins on mercury suggest that on average they are more degraded than lunar basins these observations are consistent with more efficient modification degradation and obliteration of the largest basins on mercury than on the moon this distinction may be a result of differences in the basin formation process producing fewer rings relaxation of topography after basin formation subduing relief or rates of volcanism burying basin rings and interiors during the period of heavy bombardment on mercury from those on the moon

ring faults and ring dikes around the orientale basin on the moon the orientale basin is the youngest and best preserved multiring impact basin on the moon having experienced only modest modification by subsequent impacts and volcanism orientale is often treated as the type example of a multiring basin with three prominent rings outside of the inner depression the inner rook montes the outer rook montes and the cordillera here we use gravity data from nasa s gravity recovery and interior laboratory grail mission to reveal the subsurface structure of orientale and its ring system gradients of the gravity data reveal a continuous ring dike intruded into the outer rook along the plane of the fault associated with the ring scarp the volume of this ring dike is 18 times greater than the volume of all extrusive mare deposits associated with the basin the gravity gradient signature of the cordillera ring indicates an offset along the fault across a shallow density interface interpreted to be the base of the low density ejecta blanket both gravity gradients and crustal thickness models indicate that the edge of the central cavity is shifted inward relative to the equivalent inner rook ring at the surface models of the deep basin structure show inflections along the crust mantle interface at both the outer rook and cordillera rings indicating that the basin ring faults extend from the surface to at least the base of the crust fault dips range from 13 22 for the cordillera fault in the northeastern quadrant to 90 for the outer rook in the northwestern quadrant the fault dips for both outer rings are lowest in the northeast possibly due to the effects of either the direction of projectile motion or regional gradients in pre impact crustal thickness similar ring dikes and ring faults are observed around the majority of lunar basins

shallow seismic activity and young thrust faults on the moon the discovery of young thrust faults on the moon is evidence of recent tectonic activity but how recent is unknown seismometers at four apollo landing sites recorded 28 shallow moonquakes between 1969 and 1977 some of these shallow quakes could be associated with activity on the young faults however the epicentre locations of these quakes are poorly constrained here we present more accurate estimates of the epicentre locations based on an algorithm for sparse seismic networks we found that the epicentres of eight near surface quakes fall within 30 km of a fault scarp the distance of the expected strong ground shaking from an analysis of the timing of these eight events we found that six occurred when the moon was less than 15 000 km from the apogee distance analytical modelling of tidal forces that contribute to the current lunar stress state indicates that seven near apogee events within 60 km of a fault scarp occur at or near the time of peak compressional stresses when fault slip events are most likely we conclude that the proximity of moonquakes to the young thrust faults together with evidence of regolith disturbance and boulder movements on and near the fault scarps strongly suggest the moon is tectonically active shallow moonquakes detected at four apollo landing sites between 1969 and 1977 occurred during maximum stress and in close proximity to young faults suggesting that the moon is tectonically active according to reanalyses of the seismic data and tidal force modelling

gravity field of the orientale basin from the gravity recovery and interior laboratory mission the orientale basin is the youngest and best preserved major impact structure on the moon we used the gravity recovery and interior laboratory grail spacecraft to investigate the gravitational field of orientale at 3 to 5 kilometer km horizontal resolution a volume of at least 3 4 0 2 106 km3 of crustal material was removed and redistributed during basin formation there is no preserved evidence of the transient crater that would reveal the basin s maximum volume but its diameter may now be inferred to be between 320 and 460 km the gravity field resolves distinctive structures of orientale s three rings and suggests the presence of faults associated with the outer two that penetrate to the mantle the crustal structure of orientale provides constraints on the formation of multiring basins

impact fragmentation of lonar crater india implications for impact cratering processes in basalt impact fragmentation is an energetic process that has affected all planetary bodies to understand its effects in basalt we studied lonar crater which is a rare terrestrial simple impact crater in basalt and analogues to kilometer scale simple craters on mars the lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder the cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges suggesting simple and complex fragmentation the general shape of the fragments is compact platy bladed and elongated with an average edge angle of 100 the size distribution of cobble to boulder sized fragments is similar to the fracture spacing distribution in the upper crater wall indicating the provenance of those large fragments its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target whereas the small fragments from deeper level the petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments the presence of fe mg phyllosilicates smectites both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration the seismic images reveal a thickness variation in the ejecta blanket segregation of boulders fractures and faults in the bedrock beneath the crater rim the fracturing fragmentation and fluvial degradation of lonar crater have important implications for mars

the distribution and purity of anorthosite across the orientale basin new perspectives from moon mineralogy mapper data 1 the orientale basin is a multiring impact structure on the western limb of the moon that provides a clear view of the primary lunar crust exposed during basin formation previously near infrared reflectance spectra suggested that orientale s inner rook ring irr is very poor in mafic minerals and may represent anorthosite excavated from the moon s upper crust however detailed assessment of the mineralogy of these anorthosites was prohibited because the available spectroscopic data sets did not identify the diagnostic plagioclase absorption feature near 1250 nm recently however this absorption has been identified in several spectroscopic data sets including the moon mineralogy mapper m3 enabling the unique identification of a plagioclase dominated lithology at orientale for the first time here we present the first in depth characterization of the orientale anorthosites based on direct measurement of their plagioclase component in addition detailed geologic context of the exposures is discussed based on analysis of lunar reconnaissance orbiter narrow angle camera images for selected anorthosite identifications the results confirm that anorthosite is overwhelmingly concentrated in the irr comparison with nonlinear spectral mixing models suggests that the anorthosite is exceedingly pure containing 95 vol plagioclase in most areas and commonly 99 100 vol these new data place important constraints on magma ocean crystallization scenarios which must produce a zone of highly pure anorthosite spanning the entire lateral extent of the 430 km diameter irr

the steepest slopes on the moon from lunar orbiter laser altimeter lola data spatial distribution and correlation with geologic features abstract we calculated topographic gradients over the surface of the moon at a 25 m baseline using data obtained by the lunar orbiter laser altimeter lola instrument onboard the lunar reconnaissance orbiter lro spacecraft the relative spatial distribution of steep slopes can be reliably obtained although some technical characteristics of the lola dataset preclude statistical studies of slope orientation the derived slope frequency distribution revealed a steep rollover for slopes close to the angle of repose slopes significantly steeper than the angle of repose are almost absent on the moon due to 1 the general absence of cohesion strength of the fractured and fragmented megaregolith of the lunar highlands and 2 the absence of geological processes producing steep slopes in the recent geological past the majority of slopes steeper than 32 35 are associated with relatively young large impact craters we demonstrate that these impact craters progressively lose their steepest slopes we also found that features of early imbrian and older ages have almost no slopes steeper than 35 we interpret this to be due to removal of all steep slopes by the latest basin forming impact orientale probably by global seismic shaking the global spatial distribution of the steepest slopes correlates moderately well with the predicted spatial distribution of impact rate however a significant paucity of steep slopes in the southern farside remains unexplained

granular avalanches on the moon mass wasting conditions processes and features seven lunar crater sites of granular avalanches are studied utilizing high resolution images 0 42 1 3 m pixel from the lunar reconnaissance orbiter camera one in kepler crater is examined in detail all the sites are slopes of debris extensively aggraded by frictional freezing at their dynamic angle of repose four in craters formed in basaltic mare and three in the anorthositic highlands diverse styles of mass wasting occur and three types of dry debris flow deposit are recognized 1 multiple channel and lobe type with coarse grained levees and lobate terminations that impound finer debris 2 single surge polylobate type with sub parallel arrays of lobes and fingers with segregated coarse grained margins and 3 multiple ribbon type with tracks reflecting reworked substrate minor levees and no coarse terminations the latter type results from propagation of granular erosion deposition waves down slopes dominantly of fine regolith and it is the first recognized natural example dimensions architectures and granular segregation styles of the two coarse grained deposit types are like those formed in natural and experimental avalanches on earth although the timescale of motion differs due to the reduced gravity influences of reduced gravity and fine grained regolith on dynamics of granular flow and deposition appear slight but we distinguish for the first time extensive remobilization of coarse talus by inundation with finer debris the few sites show no clear difference attributable to the contrasting mare basalt and highland megaregolith host rocks and their fragmentation this lunar study offers a benchmarking of deposit types that can be attributed to formation without influence of liquid or gas

recent seismicity in valles marineris mars insights from young faults landslides boulder falls and possible mud volcanoes abstract current seismicity of mars is poorly known geodynamic models and analysis of surface faults indicate that mars could be seismically active globally particularly within the tharsis region however published geologic constraints on such activity are sparse in this study we use geomorphologic observations and crater size frequency age determinations gleaned from high resolution orbiter data to demonstrate that the valles marineris region is recently seismo tectonically active the chasmata shows evidence of reactivated dip slip faults that cross cut the chasmata walls and floors and indicates up to 1 2 km total vertical displacement along the trough bounding faults more than 16000 boulder fall occurrences with pristine trails are observed throughout the chasmata wall with an average slope of 25 degrees the boulder falls are interpreted to have been triggered by recent seismic shaking from the shallow marsquakes occurring along the chasmata faults possibly in the last thousands of years synthetic ground motion models indicate several m w 4 6 marsquakes at shallow depths 1 6 km are required to produce these canyon wide boulder falls in addition the presence of many young landslides 22 790 ma proximal to the reactivated trough bounding faults and formation of thousands of possible mud volcanic cones throughout the chasmata floor all suggest marsquake triggered shaking in the past tens to hundreds of million years corresponding to late to middle amazonian epochs we estimate formation of 20 m to 1 3 km diameter fresh impact craters around the chasmata had negligible contribution to the recent seismicity therefore valles marineris tectonism is an important source of marsquakes that may be readily detectable by the upcoming insight seismometers

the seismically active lobate scarps and coseismic lunar boulder avalanches triggered by 3 january 1975 mw 4 1 shallow moonquake

a trapped philippine sea plate origin for morb from the inner slope of the izu bonin trench basement outcrops sampled by submersible and dredge from the inner slope of the izu bonin trench at 32 n and 6200 6700 m water depth have a distinct mid ocean ridge basalt morb chemistry unlike any other rocks previously sampled in the izu bonin arc they are low k tholeiites with moderate tio2 0 7 1 8 wt extremely low ba 1 5 7 parts per million low ba la 1 2 3 and are depleted in light rare earth elements these samples could represent either an accreted piece of subducting pacific plate or a trapped remnant of philippine sea plate on which the izu bonin arc was built although their major and trace element chemistry do not help to distinguish their source the sr nd and pb isotopes clearly support a philippine sea plate origin the isotopic signature of the inner trench slope samples matches that of philippine sea plate lavas with 87 sr 86 sr 0 70321 0 70373 143 nd 144 nd 0 513057 0 513077 and 206 pb 204 pb 18 2 18 5 the samples have elevated 207 pb 204 pb 15 3 15 5 and 208 pb 204 pb 38 0 38 2 values compared to the northern hemisphere reference line nhrl and their isotopic signature is distinct from the mesozoic pacific morb being subducted these are the first samples of trapped philippine sea oceanic crust discovered in the izu bonin mariana arc they require that models for the formation of intra oceanic arc crust account for pre existing oceanic crust and that estimates of arc magma production rates are lowered accordingly fl 1999 elsevier science b v all rights reserved

initial results from the insight mission on mars nasa s insight interior exploration using seismic investigations geodesy and heat transport mission landed in elysium planitia on mars on 26 november 2018 it aims to determine the interior structure composition and thermal state of mars as well as constrain present day seismicity and impact cratering rates such information is key to understanding the differentiation and subsequent thermal evolution of mars and thus the forces that shape the planet s surface geology and volatile processes here we report an overview of the first ten months of geophysical observations by insight as of 30 september 2019 174 seismic events have been recorded by the lander s seismometer including over 20 events of moment magnitude mw 3 4 the detections thus far are consistent with tectonic origins with no impact induced seismicity yet observed and indicate a seismically active planet an assessment of these detections suggests that the frequency of global seismic events below approximately mw 3 is similar to that of terrestrial intraplate seismic activity but there are fewer larger quakes no quakes exceeding mw 4 have been observed the lander s other instruments two cameras atmospheric pressure temperature and wind sensors a magnetometer and a radiometer have yielded much more than the intended supporting data for seismometer noise characterization magnetic field measurements indicate a local magnetic field that is ten times stronger than orbital estimates and meteorological measurements reveal a more dynamic atmosphere than expected hosting baroclinic and gravity waves and convective vortices with the mission due to last for an entire martian year or longer these results will be built on by further measurements by the insight lander geophysical and meteorological measurements by nasa s insight lander on mars reveal a planet that is seismically active and provide information about the interior surface and atmospheric workings of mars

galapagos hot spot spreading center system 1 spatial petrological and geochemical variations 83 w 101 w we report on the petrology and geochemistry of basalts dredged at 40 50 km intervals along the galapagos spreading center between 83 sup 0 w and 101 sup 0 w 40 stations emphasis is on spatial variations of whole rock major elements rare earths trace metals of the first transition series and the nature of phenocryst assemblages and their abundances these results provide new constraints on the nature and scale of mantle source heterogeneities melting conditions thermal field and dynamics of crustal formation of the region we suggest that ridge segments outside the high magnetic amplitude zone are at a steady state as a result of passive seafloor spreading basalts from these segments are apparently derived from an asthenosphere relatively uniformally depleted in incompatible elements which appears of worldwide extent we reject vogt and deboer s 1976 model invoking damming at fracture zones of subaxial asthenosphere flow of crystal slushes and increasing fractional crystallization down the flow line because this model would not explain the gradients in ree observed about the galapagos platform our preferred model combines the mantle plume binary mixing model of schilling 1973 with the concept of recurring rift propagation proposed by hey 1977a we further propose that pulsating mantle plume flux perhaps inmore the form of a chain of blobs may initiate the development of new rifts and their propagation the present position of the tips of such new propagating rifts locate the wave fronts of such pulsating mantle plume flow a two million year period is suggested for the last 4 m y from wilson and hey s 1979 information rigorous testing of our preferred model is possible less

evidence for ring faults around the orientale basin on the moon from gravity abstract the orientale basin is the best preserved multi ring impact basin on the moon spanning 900 km in diameter at its outermost ring it consists of three concentric ring structures known as the inner rook outer rook and cordillera based on geologic and topographic evidence the cordillera ring has been interpreted as forming through listric normal faulting from the inward collapse of the interior basin a similar mechanism may have been responsible for the formation of the outer rook though it has also been interpreted as the rim corresponding to the collapsed excavation cavity this study uses gravity and topography data to examine the subsurface structure of the orientale rings a markov chain monte carlo approach was implemented to find the best fit fault dip and displacement as well as the depth to an intra crustal density interface and the density contrast across that interface we find that the data supports the presence of a low angle normal fault beneath the cordillera ring that offsets a shallow interface separating a lower density upper crust from a higher density lower crust the best fit solution for the case of faults at both the cordillera and outer rook has a vertical component of fault displacement of 7 8 km a fault dip of 28 an intra crustal interface depth of 10 8 km and a density contrast of 350 kg m 3 between the upper and lower crust however models with faults only at the cordillera or with faults that do not cross the crust mantle interface also provide adequate fits to the data this analysis presents quantitative evidence for the existence of faults beneath the rings of orientale and for density stratification of the crust beneath the basin based on gravity data

geology and composition of the orientale basin impact melt sheet 1 the orientale basin is one of the largest 930 km diameter and youngest 3 8 ga impact craters on the moon as the basin is only partly flooded by mare lava its floor materials expose a major portion of the basin impact melt sheet which some previous work has suggested might have undergone igneous differentiation to test this idea we remapped the geology of the orientale basin using images and topography from the lunar reconnaissance orbiter mineralogical information from the chandrayaan 1 moon mineralogy mapper and elemental concentration maps from clementine multispectral imaging and lunar prospector gamma ray data the maunder formation impact melt sheet of the basin is uniform in chemical composition equivalent to anorthositic norite in at least the upper 2 km of the deposit the deepest sampling of the basin melt sheet maximum depths of 3 5 km by the crater maunder 55 km in diameter shows a variety of lithologies but these rock types anorthosite anorthositic norite melt rocks mare basalt and gabbro are not those predicted by the differentiation model we conclude that no differentiation of the orientale basin melt sheet has occurred and that such a process is not evident from new remote sensing data for the moon or in the apollo lunar samples

a new lunar digital elevation model from the lunar orbiter laser altimeter and selene terrain camera abstract we present an improved lunar digital elevation model dem covering latitudes within 60 at a horizontal resolution of 512 pixels per degree 60 m at the equator and a typical vertical accuracy 3 to 4 m this dem is constructed from 4 5 10 9 geodetically accurate topographic heights from the lunar orbiter laser altimeter lola onboard the lunar reconnaissance orbiter to which we co registered 43 200 stereo derived dems each 1 1 from the selene terrain camera tc 1010 pixels total after co registration approximately 90 of the tc dems show root mean square vertical residuals with the lola data of

how old are lunar lobate scarps 1 seismic resetting of crater size frequency distributions abstract previous studies have estimated the ages of lunar lobate scarps some of the youngest tectonic landforms on the moon based on the estimated life times of their fresh morphologies and associated small graben using crater degradation ages or via buffered and traditional crater size frequency distribution csfd measurements here we reexamine five scarps previously dated by binder and gunga 1985 with crater degradation ages to benchmark the evaluation of both the buffered and traditional csfd approaches for determination of absolute model ages amas at scarps both csfd methods yield similar ages for each individual scarp indicating that fault activity not only can be measured on the scarp itself but also in the surrounding terrain an indication that tectonic activity causes surface renewal both adjacent to and even kilometers distant from scarps size frequency variations in the regions surrounding the scarps are thus useful for studying the extent and severity of the ground motion caused by coseismic slip events during scarp formation all age determination approaches continue to indicate that lunar lobate scarps were active in the late copernican with some scarps possibly experiencing activity within the last 100 ma

quantifying crater production and regolith overturn on the moon with temporal imaging random bombardment by comets asteroids and associated fragments form and alter the lunar regolith and other rocky surfaces the accumulation of impact craters over time is of fundamental use in evaluating the relative ages of geologic units crater counts and radiometric ages from returned samples provide constraints with which to derive absolute model ages for unsampled units on the moon and other solar system objects however although studies of existing craters and returned samples offer insight into the process of crater formation and the past cratering rate questions still remain about the present rate of crater production the effect of early stage jetting during impacts and the influence that distal ejecta have on the regolith here we use lunar reconnaissance orbiter camera lroc narrow angle camera nac temporal before and after image pairs to quantify the contemporary rate of crater production on the moon to reveal previously unknown details of impact induced jetting and to identify a secondary impact process that is rapidly churning the regolith from this temporal dataset we detected 222 new impact craters and found 33 per cent more craters with diameters of at least ten metres than predicted by the standard neukum production and chronology functions for the moon we identified broad reflectance zones associated with the new craters that we interpret as evidence of a surface bound jetting process we also observe a secondary cratering process that we estimate churns the top two centimetres of regolith on a timescale of 81 000 years more than a hundred times faster than previous models estimated from meteoritic impacts ten million years

the origin of neotectonics on the lunar nearside new observations of wrinkle ridges on the nearside maria of the moon display signs of ongoing ridge modification in association with the wrinkle ridges we observed an absence of superposed craters narrow 30 m lobate scarps and graben and thermal anomalies related to exposures of meter size blocks many of these active wrinkle ridge systems are well beyond the influence of mascon basins and unrelated to any global tectonic pattern nevertheless they spatially correlate with ancient deep seated dike intrusions on the lunar nearside revealed by gravity data analysis we propose that this active nearside tectonic system ants reflects ongoing reactivation of an ancient system related to offset antipodal effects from the south pole aitken basin

seismic imaging of a possible paleoarc in the izu bonin intraoceanic arc and its implications for arc evolution processes crustal evolution processes in intraoceanic arcs including crustal accretion and rifting have been long discussed to examine crustal evolution in the izu bonin intraoceanic island arc we conducted an active source wide angle seismic study along a north south profile 500 km long within a possible paleoarc in the rear arc i e the nishi shichito ridge about 150 km west of the present day volcanic front in this study the seismic velocity and reflectivity images are obtained using the wide angle seismic data for the seismic velocity imaging we applied refraction tomography in which 93 535 picks were used the overall root mean square rms misfit calculated from the initial model of the refraction tomography was 483 1 ms and those calculated from the final model were reduced to 66 7 ms the resultant seismic image shows marked variations of crustal thickness along the seismic profile thin crust 10 15 km thick in the northern part three discrete thick crustal segments 20 25 km thick in the central part and a moderately thick crust 15 km thick in the southern part these variations are mainly attributed to thickness variations of the middle crust having seismic velocity of 6 0 6 8 km s this variation of crustal thickness does not correlate with seafloor topography which is characterized by post miocene across arc seamount chains it does correlate well with crustal variations observed along the present day volcanic front of the izu bonin arc these findings suggest that the magmatic activity that created the across arc seamount chains had little effect on the rear arc crust and that the main part of the rear arc crust was created before the rear arc separated from the volcanic front by correlating the structural variations along the rear arc i e the variation of the average seismic velocity as well as the thickness of the middle crust and those along the present day volcanic front we found that the direction of rifting to separate the rear arc paleoarc from the present day volcanic front was north northeast

nonlinear refraction and reflection travel time tomography we develop a rapid nonlinear travel time tomography method that simultaneously inverts refraction and reflection travel times on a regular velocity grid for travel time and ray path calculations we apply a wave front method employing graph theory the first arrival refraction travel times are calculated on the basis of cell velocities and the later refraction and reflection travel times are computed using both cell velocities and given interfaces we solve a regularized nonlinear inverse problem a laplacian operator is applied to regularize the model parameters cell slownesses and reflector geometry so that the inverse problem is valid for a continuum the travel times are also regularized such that we invert travel time curves rather than travel time points a conjugate gradient method is applied to minimize the nonlinear objective function after obtaining a solution we perform nonlinear monte carlo inversions for uncertainty analysis and compute the posterior model covariance in numerical experiments we demonstrate that combining the first arrival refraction travel times with later reflection travel times can better reconstruct the velocity field as well as the reflector geometry this combination is particularly important for modeling crustal structures where large velocity variations occur in the upper crust we apply this approach to model the crustal structure of the california borderland using ocean bottom seismometer and land data collected during the los angeles region seismic experiment along two marine survey lines details of our image include a high velocity zone under the catalina ridge but a smooth gradient zone between catalina ridge and san clemente ridge the moho depth is about 22 km with lateral variations

structural variations of arc crusts and rifted margins in the southern izu ogasawara arc back arc system 1 we carried out a reflection refraction seismic survey across the southern izu ogasawara arc back arc system covering three arcs with different crustal ages the oldest eocene arc has middle and lower crust with high velocities of 6 4 6 6 and 6 8 7 4 km s respectively suggesting denser crustal materials the current volcanic arc has middle and lower crust with lower velocities of 5 7 6 5 and 6 7 7 1 km s suggesting advanced crustal differentiation the crust mantle transition layer with a velocity of 7 5 8 0 km s is distributed beneath the current volcanic arc and the rear arc suggesting a pool of dense materials emanating from the crust through the crustal growth these structural differences between the eocene arc and current arc indicate a difference of crustal growth based on basaltic and andesitic magmas according to known petrologic studies commonly rifted crusts have lower crusts with high velocities of over 7 0 km s and the arc back arc transition zone also has a thinner more reflective crust that may have been affected by postrifting magmatism

amplitude modeling of the seismic reflectors in the crust mantle transition layer beneath the volcanic front along the northern izu bonin island arc the izu bonin island arc is a typical oceanic island arc formed by subduction of the pacific plate beneath the philippine sea plate although some crustal structures of this island arc have been identified detailed information about the region between the deeper crust and uppermost mantle especially the crust mantle transition layer has been inadequate to elucidate a crustal growth model comparison of the observed and synthetic waveforms of wide angle seismic data yielded velocity contrast values of the top and bottom of this transition layer beneath the volcanic front along the northern izu bonin island arc using those data we clarify the nature of the crust mantle transition layer the top of the crust mantle transition layer has a velocity contrast value of about 0 4 km s in the southern area extending from kurose hall to tori shima along the northern izu bonin island arc except for the northern area extending from nii jima to kurose hall 0 25 km s the velocity contrast value at the bottom of this transition layer is large 0 4 km s between nii jima and kurose hall and small 0 2 km s from kurose hall southward these results and the average p wave velocity in the crust mantle transition layer indicate that this transition layer beneath the volcanic front along the northern izu bonin island arc is a mixture of mafic residues and olivine cumulates formed during crustal growth furthermore the variation of the velocity contrast at the top and bottom of this transition layer and the average p wave velocity in this layer along this arc imply that this layer in the southern area extending from kurose hall southward has a larger ratio of mantle materials olivine cumulates to mafic residues than that in the northern area extending from nii jima to kurose hall the moho along the volcanic front in the oceanic island arc probably has a complex signature as suggested by the crust mantle transition layer comprising a mixture of mafic residues and olivine cumulates

impact spallation processes on the moon a case study from the size and shape analysis of ejecta boulders and secondary craters of censorinus crater abstract impact spallation is a fundamental process responsible for formation of ejecta boulders from impact craters although theoretical spallation models were developed about three decades ago only limited geological observations have been made so far to test these models the 3 8 km censorinus crater on the moon provides an excellent opportunity for studying the impact spallation processes associated with a fresh simple crater formed by oblique impact using the lunar reconnaissance orbiter narrow angle camera images we prepared the ejecta boulder distribution map of censorinus crater and measured the boulder sizes and shapes mapping of about 242 000 ejecta boulders enabled us to document the size distribution of boulders both radial and concentric to the impact crater larger size boulders dominate the crater rim areas while they become smaller away from the crater the boulder distribution exhibits a radial asymmetry suggesting censorinus is a oblique impact in which the uprange ejecta have smaller ranges with larger concentration of boulders near the southwestern crater rim while the downrange ejecta are in general characterized by smaller boulders with high spatial dispersion the cumulative size frequency distribution csfd of boulders shows a highly variable fragmentation history in which the uprange boulders suffered more complex fragmentation the ejecta boulders also exhibit a variety of shapes that are gleaned from their axial ratios and edge angle characteristics there is a general decrease of axial ratios away from the crater rim rectangular boulders dominate the crater rim and they become more equant away from the crater in addition to the boulder sizes the boulder shape distribution also exhibits a mild asymmetry in response to the oblique impact small size fresh impact craters 84 000 craters are abundant on the censorinus ejecta and post date censorinus these craters are found in two morphologic types in which a large majority of craters have subdued ejecta rayless craters while some possess bright rayed ejecta bright rayed craters the csfd of rayless craters show a steep power law slope with a b value of 4 0 similar to the secondary craters produced by the impact of ejecta from primary craters we therefore interpret the rayless craters as the secondary craters of censorinus on the other hand the csfd of bright rayed craters have smaller power law slope b value 2 7 which is a characteristic of primary craters and thus provide 3 ma age for censorinus crater when the characteristics of censorinus boulders are compared with the theoretical spallation models that are sensitive to the petrophysical properties of the target lunar highland the models generally agree with the censorinus boulders however the observed shape and size characteristics of the censorinus boulders are found to be more complex than the theoretical spallation models the ejecta boulders suffered more complex fragmentation and asymmetric distribution in response to the oblique impact the spallation models accounting oblique impacts have not yet been developed therefore our censorinus boulder observations can be used to develop and validate the new theoretical spallation models for the effects of oblique impacts

structural effects of meteorite impact on basalt evidence from lonar crater india received 31 january 2005 revised 17 august 2005 accepted 26 august 2005 published 8 december 2005 1 lonar crater is a simple bowl shaped near circular impact crater in the 65 myr old deccan volcanic province in india as lonar crater is a rare terrestrial crater formed entirely in basalt it provides an excellent opportunity to study the impact deformation in target basalt which is common on the surfaces of other terrestrial planets and their satellites the present study aims at documenting the impact deformational structures in the massive basalt well exposed on the upper crater wall where the basalt shows upward turning of the flow sequence resulting in a circular deformation pattern three fracture systems radial concentric and conical fractures are exposed on the inner crater wall on the fracture planes plumose structures are common uplift and tilting of the basalt sequence and formation of the fractures inside the crater are clearly related to the impact event and are different from the preimpact structures such as cooling related columnar joints and fractures of possible tectonic origin which are observed outside the crater slumping is common throughout the inner wall and listric faulting displaces the flows in the northeastern inner wall the impact structures of lonar crater are broadly similar to those at other simple terrestrial craters in granites and clastic sedimentary rocks and even small scale experimental craters formed in gabbro targets as lonar crater is similar to the strength controlled laboratory craters impact parameters could be modeled for this crater provided maximum depth of fracture formation would be known citation kumar p s 2005 structural effects of meteorite impact on basalt evidence from lonar crater india j geophys res 110 b12402 doi 10 1029 2005jb003662

initial observations from the lunar orbiter laser altimeter lola as of june 19 2010 the lunar orbiter laser altimeter an instrument on the lunar reconnaissance orbiter has collected over 2 0 10 9 measurements of elevation that collectively represent the highest resolution global model of lunar topography yet produced these altimetric observations have been used to improve the lunar geodetic grid to 10 m radial and 100 m spatial accuracy with respect to the moon s center of mass lola has also provided the highest resolution global maps yet produced of slopes roughness and the 1064 nm reflectance of the lunar surface regional topography of the lunar polar regions allows precise characterization of present and past illumination conditions lola s initial global data sets as well as the first high resolution digital elevation models dems of polar topography are described herein

numerical modeling of the ejecta distribution and formation of the orientale basin on the moon the formation and structure of the orientale basin on the moon has been extensively studied in the past however estimates of its transient crater size excavated volume and depth and ejecta distribution remain uncertain here we present a new numerical model to reinvestigate the formation and structure of orientale basin and better constrain impact parameters such as impactor size and velocity unlike previous models the observed ejecta distribution and ejecta thickness were used as the primary constraints to estimate transient crater size the best measure of impact energy models were also compared to basin morphology and morphometry and subsurface structures derived from high resolution remote sensing observations and gravity data respectively the best fit model suggests a 100 km diameter impactor with a velocity of 12 km s 1 formed the orientale basin on a relatively cold moon in this impact scenario the transient crater diameter is 400 km or 460 km depending on whether the crater is defined using the diameter of the excavation zone or the diameter of the growing cavity at the time of maximum crater volume respectively the volume of ejecta material is 4 70 106 km3 in agreement with recent estimates of the orientale ejecta blanket thickness from remote sensing studies the model also confirms the remote sensing spectroscopic observations that no mantle material was excavated and deposited at orientale s rim

new seismological constraints on growth of continental crust in the izu bonin intra oceanic arc the process by which continental crust has formed is not well understood though such crust mostly forms at convergent plate margins today it is thus imperative to study modern intra oceanic arcs such as those common in the western pacific ocean new seismic studies along the representative izu bonin intra oceanic arc provide unique along strike images of arc crust and uppermost mantle to complement earlier cross arc lithospheric profiles these reveal two scales 1000 10 km scale of variations one at the scale of the izu versus bonin thick versus thin arc crust the other at the intervolcano 50 km scale these images show that 1 the bulk composition of the izu bonin arc crust is more mafic than typical continental crust 2 the middle crust with seismic velocities similar to continental crust is predominantly beneath basaltic arc volcanoes 3 the bulk composition beneath basaltic volcanoes changes little at thick and thin arc segments and 4 a process to return lower crustal components to the mantle such as delamination is required for an arc crust to evolve into continental crust continued thickening of the izu bonin crust accompanied by delamination of lowermost crust can yield velocity structure of typical continental crust

strong ground motion estimation during the kutch india earthquake in the absence of strong motion records ground motion during the 26th january 2001 kutch india earthquake has been estimated by analytical methods a contour map of peak ground acceleration pga values in the near source region is provided these results are validated by comparing them with spectral response recorder data and field observations it is found that very near the epicenter pga would have exceeded 0 6 g a set of three aftershock records have been used as empirical green s functions to simulate ground acceleration time history and 5 damped response spectrum at bhuj city it is found that at bhuj pga would have been 0 31 g 0 37 g it is demonstrated that source mechanism models can be effectively used to understand spatial variability of large scale ground movements near urban areas due to the rupture of active faults

mass wasting features on the moon how active is the lunar surface abstract mass wasting features have long been noticed on the moon but there has been no systematic studies for their morphological geometrical or distribution characteristics the effect of mass wasting on topographic evolution and surface erosion on the moon is not fully understood using high resolution image and topography data obtained from the lunar reconnaissance orbiter spacecraft we found that mass wasting has been globally and continuously occurring on the moon meteor impacts and moonquakes are the two major triggering mechanisms in forming lunar mass wasting features we selected over 300 examples of lunar mass wasting features and classified them as falls flows slides slumps and creeps after studying their morphology potential mode of emplacement and sizes of displaced materials the slope and age distributions for their host terrains are studied to estimate the topographic evolutionary sequence of the lunar surface under the effect of mass wasting due to continuous reshaping by mass wasting surface topographies on the moon tend to become smoother with time with fewer mass wasting events occurring on older surfaces pre nectarian surfaces may represent the final stage of surface topographic evolution on slope angles regarding the effect of mass wasting crater densities on lunar surfaces vary with slope angles because the surface erosion rate and regolith production rate on slopes are larger than those on flat areas

influence of the madden julian oscillation on upper tropospheric humidity 1 variations of upper tropospheric humidity uth and cold cloud in the tropics reveal coherent changes that propagate eastward from the indian ocean into the pacific the coherence of uth is high at periods of 30 90 days along the equator near the tropical tropopause uth coherence is large over the equator in the indian ocean and over the subtropics in the central pacific a composite life cycle shows that enhanced uth in the subtropics coincides with two anticyclonic gyres they straddle anomalous cold cloud over the equator as it propagates eastward the enhancement of uth is consistent with anomalously cold temperature which mirrors the anticyclonic gyres those temperature anomalies cancel the height anomaly of the gyres overhead the complex of anomalous uth cold cloud and anticyclonic motion marches eastward across the western pacific until reaching the dateline anomalous convection over the equator then collapses along with the subtropical gyres and enhanced uth accompanying it index terms 3374 meteorology and atmospheric dynamics tropical meteorology 3399 meteorology and atmospheric dynamics general or miscellaneous 3319 meteorology and atmospheric dynamics general circulation 3314 meteorology and atmospheric dynamics convective processes keywords madden julian oscillation upper tropospheric humidity tropical convection

lunar mare deposits associated with the orientale impact basin new insights into mineralogy history mode of emplacement and relation to orientale basin evolution from moon mineralogy mapper m3 data from chandrayaan 1 1 moon mineralogy mapper m3 image and spectral reflectance data are combined to analyze mare basalt units in and adjacent to the orientale multiring impact basin models are assessed for the relationships between basin formation and mare basalt emplacement mare basalt emplacement on the western nearside limb began prior to the orientale event as evidenced by the presence of cryptomaria the earliest post orientale event mare basalt emplacement occurred in the center of the basin mare orientale and postdated the formation of the orientale basin by about 60 100 ma over the next several hundred million years basalt patches were emplaced first along the base of the outer rook ring lacus veris and then along the base of the cordillera ring lacus autumni with some overlap in ages the latest basalt patches are as young as some of the youngest basalt deposits on the lunar nearside m3 data show several previously undetected mare patches on the southwestern margins of the basin interior regardless the previously documented increase in mare abundance from the southwest toward the northeast is still prominent we attribute this to crustal and lithospheric trends moving from the farside to the nearside with correspondingly shallower density and thermal barriers to basaltic magma ascent and eruption toward the nearside the wide range of model ages for orientale mare deposits 3 70 1 66 ga mirrors the range of nearside mare ages indicating that the small amount of mare fill in orientale is not due to early cessation of mare emplacement but rather to limited volumes of extrusion for each phase during the entire period of nearside mare basalt volcanism this suggests that nearside and farside source regions may be similar but that other factors such as thermal and crustal thickness barriers to magma ascent and eruption may be determining the abundance of surface deposits on the limbs and farside the sequence timing and elevation of mare basalt deposits suggest that regional basin related stresses exerted control on their distribution our analysis clearly shows that orientale serves as an excellent example of the early stages of the filling of impact basins with mare basalt

physical properties of basalt ejecta boulders at lonar crater india insights into the target heterogeneity and impact spallation processes in basalt with application to mars

gullies and landslides on the moon evidence for dry granular flows 1 high resolution images from chandrayaan 1 terrain mapping camera and lunar reconnaissance orbiter camera reveal landslides and gully formation on the interior wall of a 7 km diameter simple crater emplaced in schrodinger basin on the farside of the moon these features occur on the steep upper crater wall where the slope is 35 the gullies show a typical alcove channel fan morphology some gullies incise bedrock where impact related faults are present slope failure along the concentric faults also led to formation of landslides dark slope streaks are abundant at the bright gully regions especially near the fan and channel deposits spectral characteristics inferred from data obtained by hyperspectral imager and moon mineralogy mapper on board chandrayaan 1 show that the gullies and landslides are characterized by high optical immaturity and devoid of prominent spectral absorption features related to water or hydroxyl molecules suggesting youthful dry granular flows mass movements on the crater wall led to the formation of arcuate ridges and ponding of fine grained sediments on the crater floor runout flows from small impact craters on the slopes indicate that impact induced seismic shaking was responsible for the downslope mass movements crater size frequency distributions suggest a minimum age of 18 2 ma for the gullies and 2 ma for the landslides while age of the host crater ejecta was inferred to be about 175 ma the gullies and landslides also occur on the interior wall of other impact craters elsewhere on the moon and probably formed by similar processes

impact fracturing and structural modification of sedimentary rocks at meteor crater arizona 1 meteor crater provides a rare opportunity to study impact deformation of sedimentary target rocks and isolate those features from preexisting tectonic deformation and impact generated reactivation of preexisting tectonic features this study reports over 2500 new measurements of orientations of bedding faults and fractures in crater walls and in surrounding bedrock target rocks are characterized by horizontal bedding planes that are cut by at least three prominent sets of preimpact tectonic fracture systems the crater rim is also cut by three distinct groups of fractures radial concentric and conical fractures when the crater rim is restored to preimpact condition the radial and concentric fractures resemble preimpact fracture populations indicating that crater wall deformation and rim uplift were partly accommodated by activation of preexisting fractures in contrast the conical fractures are dissimilar to the preimpact fractures and apparently formed as a direct result of impact deformation some of the preimpact fractures were transformed into tear faults during the impact event and motion along those faults appears to have controlled the geometry of the impact deformational features the crater rim is thus square in plan view rather than circular faults occurring in the crater diagonals are prominent ones allowing greater vertical displacement the deformation pattern of meteor crater is different from that at lonar crater which was excavated in basalt with fewer preimpact fractures the differences between deformation at meteor crater and lonar crater may reflect the same disparities seen in simple craters produced in different target lithologies on mars and other planetary surfaces

unusually high stress drops associated with shallow moonquakes new estimates of stress drops and energy release associated with shallow moonquakes believed to represent the only lunar seismic events of tectonic origin have been made taking into account 1 properties of source spectra 2 radiation pattern of foci 3 anelastic attenuation of seismic waves 4 response of the seismometer and 5 intense scattering of seismic signals the results indicate that the three largest events show body wave magnitudes of mb 5 5 and stress drops of 100 mpa the values for stress drops are high compared with those generally associated with most terrestrial events but they are compatible with results predicted from thermoelastic models of the moon presence of high stresses in the lunar crust may indicate that at the beginning of its history the moon was originally molten not only in the outer surface region but throughout its whole volume