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

gravity field of the moon from the gravity recovery and interior laboratory grail mission spacecraft to spacecraft tracking observations from the gravity recovery and interior laboratory grail have been used to construct a gravitational field of the moon to spherical harmonic degree and order 420 the grail field reveals features not previously resolved including tectonic structures volcanic landforms basin rings crater central peaks and numerous simple craters from degrees 80 through 300 over 98 of the gravitational signature is associated with topography a result that reflects the preservation of crater relief in highly fractured crust the remaining 2 represents fine details of subsurface structure not previously resolved grail elucidates the role of impact bombardment in homogenizing the distribution of shallow density anomalies on terrestrial planetary bodies

global distribution of large lunar craters implications for resurfacing and impactor populations by using high resolution altimetric measurements of the moon we produced a catalog of all impact craters 20 kilometers in diameter on the lunar surface and analyzed their distribution and population characteristics the most densely cratered portion of the highlands reached a state of saturation equilibrium large impact events such as orientale basin locally modified the prebasin crater population to 2 basin radii from the basin center basins such as imbrium orientale and nectaris which are important stratigraphic markers in lunar history are temporally distinguishable on the basis of crater statistics the characteristics of pre and postmare crater populations support the hypothesis that there were two populations of impactors in early solar system history and that the transition occurred near the time of the orientale basin event

stress slip and earthquakes in models of complex single fault systems incorporating brittle and creep deformations numerical simulations of slip evolution along a cellular vertical strike slip fault in an elastic half space are performed for several models representing discrete fault systems embedded in three dimensional elastic continua the geometry and imposed boundary conditions correspond approximately to the central san andreas fault the simulations incorporate brittle and creep deformations in series the net fault zone deformation rate is the sum of creep rate and frictional slip rate brittle fault properties are given by various distributions of earthquake stress drops on failing segments numerical cells the assumed distributions represent two idealized situations corresponding to different extreme states along an evolutionary path of a fault 1 a strongly disordered state characterized by a wide range of size scales representing immature fault zones and extended spatial domains and 2 a relatively regular state having a narrow range of size scales representing mature highly slipped faults the assumed creep properties are identical in all cases these are prescribed in terms of coefficients characterizing a power law dependency of creep slip rate on stress the combined brittle creep process and employed parameters lead to an overall pine tree stress depth profile with a brittle ductile transition depth of about 12 5 km and variable stress along strike profiles with brittle creep transition around 65 km nw of the 1857 rupture the spatial patterns of simulated hypocenters are statistically similar to observed data the results indicate that the range of size scales characterizing strong fault zone heterogeneities has important manifestations on the seismic response of a fault system a narrow range of size scales leads to frequency size statistics of earthquakes resembling the characteristic earthquake distribution and quasi periodic temporal distribution of large events as in the seismic gap hypothesis on the other hand a wide range of size scales leads to gutenberg richter power law frequency size statistics and random or clustered temporal distribution of large events the simulations demonstrate that treatment of the various observed forms of frequency size and temporal statistics of earthquakes can be unified through the concept of range of size scales characterizing fault zone heterogeneities this has a clear physical interpretation in terms of structural properties of a given fault zone or broad lithospheric domain and is supported by observed earthquake and fault data in some simulated cases the frequency size statistics of small earthquakes fall sharply below the self similar gutenberg richter line the results indicate that small earthquakes prepare the fault for the occurrence of a large event by smoothing during gradual tectonic loading the long wavelength components of stress on the fault this is done through short wavelength stress roughening associated with the numerous ruptures of the small events the above pattern of smoothing roughening of long short wavelengths of stress on the fault is reversed during large scale ruptures of the big events

the transition from complex craters to multi ring basins on the moon quantitative geometric properties from lunar reconnaissance orbiter lunar orbiter laser altimeter lola data united states national aeronautics and space administration nasa lunar reconnaissance orbiter lunar orbiter laser altimeter lola experiment nnx09am54g

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

pattern recognition applied to seismic signals of the llaima volcano chile an analysis of the events features abstract this paper proposes a computer based classifier to automatically identify four seismic event classes of the llaima volcano one of the most active volcanoes in the southern andes situated in the araucania region of chile a combination of features that provided good recognition performance in our previous papers concerning the llaima and villarica located 100 km south of llaima volcanoes is utilized in order to train the classifiers these features are extracted from the amplitude frequency and phase of the seismic signals unlike the previous works where fixed length windows were used to obtain the seismic signals this paper employs signals of variable lengths that span the entire seismic event the classifiers are implemented using support vector machines a confidence analysis is also included to improve reliability of the classification results indicate that the features used for recognition of the events of villarica volcano also provide good recognition results for the llaima volcano yielding classification exactitude of over 80

the formation of lunar mascon basins from impact to contemporary form positive free air gravity anomalies associated with large lunar impact basins represent a superisostatic mass concentration or mascon high resolution lunar gravity data from the gravity recovery and interior laboratory spacecraft reveal that these mascons are part of a bulls eye pattern in which the central positive anomaly is surrounded by an annulus of negative anomalies which in turn is surrounded by an outer annulus of positive anomalies to understand the origin of this gravity pattern we modeled numerically the entire evolution of basin formation from impact to contemporary form with a hydrocode we simulated impact excavation and collapse and show that during the major basin forming era the preimpact crust and mantle were sufficiently weak to enable a crustal cap to flow back over and cover the mantle exposed by the impact within hours with hydrocode results as initial conditions we simulated subsequent cooling and viscoelastic relaxation of topography using a finite element model focusing on the mare free freundlich sharonov and mare infilled humorum basins by constraining these models with measured free air and bouguer gravity anomalies as well as surface topography we show that lunar basins evolve by isostatic adjustment from an initially subisostatic state following the collapse stage the key to the development of a superisostatic inner basin center is its mechanical coupling to the outer basin that rises in response to subisostatic stresses enabling the inner basin to rise above isostatic equilibrium our calculations relate basin size to impactor diameter and velocity and they constrain the preimpact lunar thermal structure crustal thickness viscoelastic rheology and for the humorum basin the thickness of its postimpact mare fill

investigating the onset of multi ring impact basin formation multi ring basins represent some of the largest oldest rarest and therefore least understood impact crater structures various theories have been put forward to explain their formation there is currently however no consensus here numerical modeling is used to investigate the onset of multi ring basin formation on the moon using two thermal profiles suitable for the lunar basin forming epoch various multi ring basin formation hypotheses are discussed compared and evaluated against target deformation and strain distribution in the models as well as geological and geophysical observations the mechanism that most closely resembles the numerical models in terms of basin formation and structure as well as observations appears to be the ring tectonic theory whereby ring formation is dependent on transient cavities penetrating entirely through the moon s lithosphere into the asthenosphere below the numerical models suggest that all lunar basins larger than schrodinger 320 km diameter should be capable of forming multiple rings as their transient cavities penetrate into the asthenosphere for both thermal profiles additionally the models demonstrate that the target s thermal profile starts to influence basin formation and structure when impact energy exceeds that of the schrodinger event

grail gravity observations of the transition from complex crater to peak ring basin on the moon implications for crustal structure and impact basin formation abstract high resolution gravity data from the gravity recovery and interior laboratory grail mission provide the opportunity to analyze the detailed gravity and crustal structure of impact features in the morphological transition from complex craters to peak ring basins on the moon we calculate average radial profiles of free air anomalies and bouguer anomalies for peak ring basins protobasins and the largest complex craters complex craters and protobasins have free air anomalies that are positively correlated with surface topography unlike the prominent lunar mascons positive free air anomalies in areas of low elevation associated with large basins the bouguer gravity anomaly profiles of complex craters are highly irregular with central positive anomalies that are generally absent or not clearly tied to interior morphology in contrast gravity profiles for peak ring basins 200 km to 580 km are much more regular and are highly correlated with surface morphology a central positive bouguer anomaly is confined within the peak ring and a negative bouguer anomaly annulus extends from the edge of the positive anomaly outward to about the rim crest a number of degraded basins lacking interior peak rings have diameters and gravity patterns similar to those of well preserved peak ring basins if these structures represent degraded peak ring basins the number of peak ring basins on the moon would increase by more than a factor of two to 34 the gravity anomalies within basins are interpreted to be due to uplift of the mantle confined within the peak ring and an annulus of thickened crust between the peak ring and rim crest we hypothesize that mantle uplift is influenced by interaction between the transient cavity and the mantle further mascon formation is generally disconnected from the number of basin rings formed and occurs over a wide range of basin sizes these observations have important implications for models of basin and mascon formation on the moon and other planetary bodies

the constitution and structure of the lunar interior the current state of understanding of the lunar interior is the sum of nearly four decades of work and a range of exploration programs spanning that same time period missions of the 1960s including the rangers surveyors and lunar orbiters as well as earth based telescopic studies laid the groundwork for the apollo program and provided a basic understanding of the surface its stratigraphy and chronology through a combination of remote sensing surface exploration and sample return the apollo missions provided a general picture of the lunar interior and spawned the concept of the lunar magma ocean in particular the discovery of anorthite clasts in the returned samples led to the view that a large portion of the moon was initially molten and that crystallization of this magma ocean gave rise to mafic cumulates that make up the mantle and plagioclase flotation cumulates that make up the crust smith et al 1970 wood et al 1970 this model is now generally accepted and is the framework that unifies our knowledge of the structure and composition of the moon the intention of this chapter is to review the major advances that have been made over the past decade regarding the constitution of the moon s interior much of this new knowledge is a direct result of data acquired from the successful clementine and lunar prospector missions as well as the analysis of new lunar meteorites as will be seen results from these studies have led to many fundamental amendments to the magma ocean model much of what we know from sample analyses has been previously summarized elsewhere and only their most important aspects will be discussed in this chapter the reader is referred to the relevant chapters in the books basaltic volcanism on the terrestrial planets basaltic volcanism study project 1981 the

the fractured moon production and saturation of porosity in the lunar highlands from impact cratering we have analyzed the bouguer anomaly ba of 1200 complex craters in the lunar highlands from gravity recovery and interior laboratory observations the ba of these craters is generally negative though positive ba values are observed particularly for smaller craters crater ba values scale inversely with crater diameter quantifying how larger impacts produce more extensive fracturing and dilatant bulking the bouguer anomaly of craters larger than 93 47 19 km in diameter is independent of crater size indicating that there is a limiting depth to impact generated porosity presumably from pore collapse associated with either overburden pressure or viscous flow impact generated porosity of the bulk lunar crust is likely in a state of equilibrium for craters smaller than 30km in diameter consistent with an 8km thick lunar megaregolith whereas the gravity signature of larger craters is still preserved and provides new insight into the cratering record of even the oldest lunar surfaces

mantle deformation beneath the chicxulub impact crater abstract the surface expression of impact craters is well known from visual images of the moon venus and other planets and planetary bodies but constraints on deep structure of these craters is largely limited to interpretations of gravity data although the gravity models are non unique they do suggest that large impact craters are associated with structure at the base of the crust we use seismic data to map moho crust mantle interface topography beneath the chicxulub crater the youngest and best preserved of the three largest known terrestrial impact craters the moho is upwarped by 1 5 2 km near the center of the chicxulub crater and depressed by 0 5 1 0 km at a distance of 30 55 km from the crater center a comparison with numerical modeling results reveal that immediately following impact a transient crater reached a maximum depth of at least 30 km prior to collapse and that subsequent collapse of the transient crater uplifted target material from deep below the crater floor these results demonstrate that deformation from large terrestrial impacts can extend to the base of the continental crust a similar moho topography is also modeled for some large lunar and martian craters which suggests that mantle deformation may play a prominent role in large crater formation

effect of grain scale alignment on seismic anisotropy and reflectivity of shales the elastic properties and anisotropy of shales are strongly influenced by the degree of alignment of the grain scale texture in general an orientation distribution function odf can be used to describe this alignment which in practice can be characterized by two legendre coefficients we discuss various statistical odfs that define the alignment by spreading from a mean value in particular the gaussian fisher and bingham distributions we compare the statistical models with an odf resulting from pure vertical compaction no shear strain of a sediment the compaction odf may be used to estimate how the elastic properties and anisotropy evolve due to burial of clayey sediments our study shows that the three statistical odfs produce almost identical correspondence between the two legendre coefficients as a function of the spreading parameter so that the spreading parameter of one odf can be converted to the spreading parameter of another odf in most cases it is then sufficient to apply the spreading parameter for the odf instead of the two legendre coefficients the effect of compaction on the odf gives a slightly different correspondence between the two legendre coefficients from that for the other models in principle this opens up the possibility of distinguishing anisotropy effects due to compaction from those due to other processes we also study reflection amplitudes versus angle of incidence ava for all wave modes where shales having various odfs overlie an isotropic medium the ava responses are modelled using both exact and approximation formulae and their intercepts and gradients are compared the modelling shows that the s wave velocity is sensitive to any perturbation in the spreading parameter while the p wave velocity becomes increasingly sensitive to a perturbation of a less ordered system similar observations are found for the ava of the p p and p sv waves modelling indicates that a combined use of the amplitude versus offset of p p and p sv reflected waves may reveal certain grain scale alignment properties of shale like rocks

wavelet analysis for geophysical applications wavelet transforms originated in geophysics in the early 1980s for the analysis of seismic signals since then significant mathematical advances in wavelet theory have enabled a suite of applications in diverse fields in geophysics the power of wavelets for analysis of nonstationary processes that contain multiscale features detection of singularities analysis of transient phenom ena fractal and multifractal processes and signal com pression is now being exploited for the study of several processes including space time precipitation remotely sensed hydrologic fluxes atmospheric turbulence can opy cover land surface topography seafloor bathymetry and ocean wind waves it is anticipated that in the near future significant further advances in understanding and modeling geophysical processes will result from the use of wavelet analysis in this paper we review the basic properties of wavelets that make them such an attractive and powerful tool for geophysical applications we dis cuss continuous discrete orthogonal wavelets and wavelet packets and present applications to geophysical processes

estimating transient crater size using the crustal annular bulge insights from numerical modeling of lunar basin scale impacts 1 the transient crater is an important impact cratering concept its volume and diameter can be used to predict impact energy and momentum impact melt volume and maximum depth and volume of ejected material transient crater sizes are often estimated using scaling laws based on final crater rim diameters however crater rim estimates especially for lunar basins can be controversial here we use numerical modeling of lunar basin scale impacts to produce a new alternative method for estimating transient crater radius using the annular bulge of crust observed beneath most lunar basins using target thermal conditions appropriate for the lunar imbrian and nectarian periods we find this relationship to be dependent on lunar crust and upper mantle temperatures this result is potentially important when analyzing lunar basin subsurface structures inferred from the grail mission

differential melt scaling for oblique impacts on terrestrial planets abstract analytical estimates of melt volumes produced by a given projectile and contained in a given impact crater are derived as a function of impact velocity impact angle planetary gravity target and projectile densities and specific internal energy of melting applications to impact events and impact craters on the earth moon and mars are demonstrated and discussed the most probable oblique impact 45 produces 1 6 times less melt volume than a vertical impact and 1 6 and 3 7 times more melt volume than impacts with 30 and 15 trajectories respectively the melt volume for a particular crater diameter increases with planetary gravity so a crater on earth should have more melt than similar size craters on mars and the moon the melt volume for a particular projectile diameter does not depend on gravity but has a strong dependence on impact velocity so the melt generated by a given projectile on the moon is significantly larger than on mars higher surface temperatures and geothermal gradients increase melt production as do lower energies of melting collectively the results imply thinner central melt sheets and a smaller proportion of melt particles in impact breccias on the moon and mars than on earth these effects are illustrated in a comparison of the chicxulub crater on earth linked to the cretaceous tertiary mass extinction gusev crater on mars where the mars exploration rover spirit landed and tsiolkovsky crater on the moon the results are comparable to those obtained from field and spacecraft observations other analytical expressions and hydrocode simulations

on the origin of mascon basins on the moon and beyond 1 mascon basins on the moon are large craters that display significant positive free air and bouguer gravity anomalies an important question is why is not every large crater a mascon as less than half have been previously determined to be we detrend the free air topographic and bouguer gravity anomalies and find that most large basins 28 of 41 display mascon characteristics e g strong positive bouguer anomalies narrower than the surface rims negative free air gravity annuli surrounding the central highs generally are absent in the bouguer gravity implicating surface topography we propose that beneath a forming large basin the relatively narrow transient crater drives mantle uplift while upward and inward collapse forms the surface topography furthermore the nonmascon basins are all ancient and heavily degraded indicating a postimpact evolutionary process our results suggest that mascon formation is the standard for large impacts on the moon and by extension on other terrestrial planets

full waveform tomographic images of the peak ring at the chicxulub impact crater peak rings are a feature of large impact craters on the terrestrial planets and are generally believed to be formed from deeply buried rocks that are uplifted during crater formation the precise lithology and kinematics of peak ring formation however remains unclear previous work has revealed a suite of bright inward dipping reflectors beneath the peak ring at the chicxulub impact crater and that the peak ring was formed from rocks with a relatively low seismic velocity new two dimensional full waveform tomographic velocity images show that the uppermost lithology of the peak ring is formed from a thin 100 200 m thick layer of low velocity 3000 3200 m s rocks this low velocity layer is most likely composed of highly porous allogenic impact breccias our models also show that the change in velocity between lithologies within and outside the peak ring is more abrupt than previously realized and occurs close to the location of the dipping reflectors across the peak ring velocity appears to correlate well with predicted shock pressures from a dynamic model of crater formation where the rocks that form the peak ring originate from an uplifted basement that has been subjected to high shock pressures 10 50 gpa and lie above downthrown sedimentary rocks that have been subjected to shock pressures of 5 gpa these observations suggest that low velocities within the peak ring may be related to shock effects and that the dipping reflectors underneath the peak ring might represent the boundary between highly shocked basement and weakly shocked sediments

three dimensional simulation of a magnitude 7 75 earthquake on the san andreas fault simulation of 2 minutes of long period ground motion in the los angeles area with the use of a three dimensional finite difference method on a parallel supercomputer provides an estimate of the seismic hazard from a magnitude 7 75 earthquake along the 170 kilometer section of the san andreas fault between tejon pass and san bernardino maximum ground velocities are predicted to occur near the fault 2 5 meters per second and in the los angeles basin 1 4 meters per second where large amplitude surface waves prolong shaking for more than 60 seconds simulated spectral amplitudes for some regions within the los angeles basin are up to 10 times larger than those at sites outside the basin at similar distances from the san andreas fault

capabilities of 3 d wavelet transforms to detect plume like structures from seismic tomography the wavelet transform methods have been applied to viewing 3 d seismic tomography by casting the transformed quantities into two proxy distributions e max the maximum of the magnitude of the local spectra about a local point and the associated local wavenumber k max using a stochastic background noise we test the capability of this procedure in picking up the coherent structures of upper mantle plumes plumes with a gaussian shape and a characteristic width up to 2250 km have been tested for various amounts of the signal to noise ratios snr we have found that plumes can be picked out for snr as low as 0 08 db and that the optimal plume width for detection is around 1500 km for plume width ranging between 700 km and 2000 km the snr can be lower than 1 db this length scale falls within the range for plume detection based on the signal to noise levels associated with the current global tomographical models

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

a wavelet toolkit for visualization and analysis of large data sets in earthquake research wavelets have a wide range of useful functions that permit them to effectively treat problems such as data compression scale localization analysis feature extraction visualization statistics numerical simulation and communication we discuss their features and their use in an integrated manner to handle large scale problems in earthquake physics and other nonlinear problems in the solid earth geosciences

scaling of melt production in hypervelocity impacts from high resolution numerical simulations the volume of melt produced in hypervelocity planetary impacts and the size and shape of the melted region are key to understanding the impact histories of solid planetary bodies and the geological effects of impacts on their surfaces and interiors prior work of pierazzo et al pierazzo e vickery a m melosh h j 1997 icarus 127 408 423 gave the first estimates of impact melt production in geological materials using a modern hydrocode and equation of state however computational limits at the time forced use of low resolution which may have resulted in low melt volumes our simulations with 50 times higher resolution provide independent confirmation of the pierazzo et al pierazzo e vickery a m melosh h j 1997 icarus 127 408 423 melt volumes in aluminum iron dunite and granite impacts at velocities between 20 and 80 km s in ice ice impacts we find that melt volumes depend on target temperature and are lower than predicted by pierazzo et al pierazzo e vickery a m melosh h j 1997 icarus 127 408 423 our melt volumes are directly proportional to impact energy for all materials over a wide range of impact velocity we also report new data for melt volume scalings for ice dunite and iron dunite impacts and the size and shape of melted region valuable for interpretation of cratering records and studies of impact induced differentiation

measurement and analysis of lunar basin depths from clementine altimetry altimetric profiles from the clementine lidar are used to calculate the depths of 29 large craters and basins on the moon plotting the depths of the best preserved structures together with values for simple and complex craters measured in pre clementine studies reveals an inflection in the depth diameter d d curve in addition to the one revealed by pre clementine data this inflection occurs in the diameter range that corresponds to the morphologic transition from complex crater to basin the best empirical power law fit for basin depths is log10 d 0 41 log10 d 0 57 this relationship is characterized by a lower slope than that for complex craters demonstrating that this morphologic transition corresponds to a further decrease in the depth of an impact structure relative to its diameter with increasing size qualitative consideration of possible causes for the second inflection leads to the conclusion that it is most likely a consequence of a short term modification mechanism that influences fundamental crater morphology such as the increasing influence of gravity with diameter thicknesses of maria in the major basins are calculated by assuming that their unfilled depths would follow thed drelation results are compared with previous estimates and yield thicknesses that are generally greater than those determined by studies of flooded craters and less than those obtained from analysis of gravity

discriminating seismic events of the llaima volcano chile based on spectrogram cross correlations abstract the surveillance of active volcanoes around the world has become a critical security issue for many countries requiring a continuous monitoring of seismic signals by analyzing such signals we intend to understand volcanic activities e g explosions eruptions and depressurization and take decisions to reduce the effects and damages to the economy and society of nearby regions active volcanoes constantly produce signals which may then be characterized as data streams making impractical the presence of specialists to monitor and label every activity to overcome this drawback we present a new and straightforward approach to discriminate volcano seismic signals using spectrogram cross correlations spcc in conjunction with the k nearest neighbors algorithm a supervised machine learning strategy experiments were performed on signals collected from the llaima volcano chile and results confirmed the ability of our approach to discriminate events with a sensitivity over 95 for three out of the five classes considered

the origin of lunar mascon basins high resolution gravity data from the gravity recovery and interior laboratory spacecraft have clarified the origin of lunar mass concentrations mascons free air gravity anomalies over lunar impact basins display bull s eye patterns consisting of a central positive mascon anomaly a surrounding negative collar and a positive outer annulus we show that this pattern results from impact basin excavation and collapse followed by isostatic adjustment and cooling and contraction of a voluminous melt pool we used a hydrocode to simulate the impact and a self consistent finite element model to simulate the subsequent viscoelastic relaxation and cooling the primary parameters controlling the modeled gravity signatures of mascon basins are the impactor energy the lunar thermal gradient at the time of impact the crustal thickness and the extent of volcanic fill

impact ejecta emplacement on terrestrial planets abstract impact cratering is one of the most fundamental processes responsible for shaping the surfaces of solid planetary bodies one of the principal characteristics of impact events is the formation and emplacement of ejecta deposits an understanding of which is critical for planetary exploration current models of ejecta emplacement however do not account for several important observations of ejecta deposits on the terrestrial planets in particular the presence of more than one layer of ejecta furthermore there is also no universal model for the origin and emplacement of ejecta on different planetary bodies we present a unifying working hypothesis for the origin and emplacement of ejecta on the terrestrial planets in which the ejecta are emplaced in a multi stage process the generation of the continuous ejecta blanket occurs during the excavation stage of cratering via the conventional ballistic sedimentation and radial flow model this is followed by the emplacement of more melt rich ground hugging flows the surface melt flow phase during the terminal stages of crater excavation and the modification stage of crater formation minor fallback occurs during the final stages of crater formation several factors will affect the final morphology and character of ejecta deposits the volatile content and cohesiveness of the uppermost target rocks will significantly affect the runout distance of the ballistically emplaced continuous ejecta blanket with impact angle also influencing the overall geometry of the deposits e g the production of the characteristic butterfly pattern seen in very oblique impacts ejecta deposited during the surface melt flow stage is influenced by several factors most importantly planetary gravity surface temperature and the physical properties of the target rocks topography and angle of impact play important roles in determining the final distribution of surface melt flow ejecta deposits with respect to the source crater this working hypothesis of ballistic sedimentation and surface melt flow provides a framework in which observations of ejecta at impact craters can be compared and placed in the context of the respective terrestrial planets

lunar multiring basins and the cratering process abstract numerous studies of the lunar gravity field have concluded that the lunar moho is substantially uplifted beneath the young multiring basins this uplift is presumably due to the excavation of large quantities of crustal material during the cratering process and subsequent rebound of the impact basin floor using a new dual layered crustal thickness model of the moon the excavation cavities of some nearside multiring basins grimaldi and larger and younger than tranquillitatis were reconstructed by restoring the uplifted moho to its preimpact location the farside south pole aitken spa basin was also considered due to its importance in deciphering lunar evolution restoring the moho to its preimpact position beneath these basins resulted in a roughly parabolic depression from which the depth and diameter of the excavation cavity could be determined using these reconstructed excavation cavities the basin forming process was investigated excavation cavity diameters were generally found to be on the small side of most previous estimates for orientale the modeled excavation cavity lies within the inner rook ring additionally with the exception of the three largest basins serenitatis imbrium and south pole aitken the depth diameter ratios of the excavation cavities were found to be 0 115 0 005 a value consistent with theoretical and experimental results for impact craters orders of magnitude smaller in size the three largest basins however appear to have significantly shallower depths of excavation compared to this trend it is possible that this may reflect a different physical process of crater formation e g nonproportional scaling special impact conditions or postimpact modification processes the crustal thickness model also shows that each basin is surrounded by an annulus of thickened crust we interpret this thickened crust as representing thick basin ejecta deposits and we show that the radial variation in the thickness of these deposits is consistent with scaling laws obtained from small scale experimental studies if multiring basins ever possessed a terraced main crater rim this terraced zone may be presently unrecognizable at the surface due to the emplacement of ejecta deposits that exceed a few kilometers in thickness exterior to the excavation cavity rim we also show that the interiors of many basins were superisostatic before mare volcanism commenced those basins that were closest to approaching a premare isostatic state lie close to or within an anomalous geochemical province rich in heat producing elements

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

understanding oblique impacts from experiments observations and modeling natural impacts in which the projectile strikes the target vertically are virtually nonexistent nevertheless our inherent drive to simplify nature often causes us to suppose most impacts are nearly vertical recent theoretical observational and experimental work is improving this situation but even with the current wealth of studies on impact cratering the effect of impact angle on the final crater is not well understood although craters rims may appear circular down to low impact angles the distribution of ejecta around the crater is more sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts experimental studies established that crater dimensions depend only on the vertical component of the impact velocity the shock wave generated by the impact weakens with decreasing impact angle as a result melting and vaporization depend on impact angle however these processes do not seem to depend on the vertical component of the velocity alone finally obliquity influences the fate of the projectile in particular the amount and velocity of ricochet are a strong function of impact angle

farside gravity field of the moon from four way doppler measurements of selene kaguya the farside gravity field of the moon is improved from the tracking data of the selenological and engineering explorer selene via a relay subsatellite the new gravity field model reveals that the farside has negative anomaly rings unlike positive anomalies on the nearside several basins have large central gravity highs likely due to super isostatic dynamic uplift of the mantle other basins with highs are associated with mare fill implying basalt eruption facilitated by developed faults basin topography and mantle uplift on the farside are supported by a rigid lithosphere whereas basins on the nearside deformed substantially with eruption variable styles of compensation on the near and farsides suggest that reheating and weakening of the lithosphere on the nearside was more extensive than previously considered

anomalous moscoviense basin single oblique impact or double impact origin 1 the moscoviense basin is the most prominent mare basalt filled impact basin on the farside highlands of the moon the moscoviense basin has been studied extensively because of its characteristic geological and mineralogical context and distinct mare volcanism the success of kaguya s direct farside gravity recovery and global laser altimetry revealed that the moscoviense basin shows unique characteristics not only for geological and mineralogical but also for the geophysical contexts we measured geomorphological features of the moscoviense basin and the asymmetry suggests an oblique impact formation process moho undulation beneath the moscoviense basin however can hardly be explained by a single oblique impact formation process we propose an alternative hypothesis for the moscoviense basin formation which is called double impact scenario this scenario simultaneously accounts for the anomalously large mantle plug asymmetric surface geo morphology and excavation of olivine rich material originally located beneath the thickest crust on the moon on the basis of a set of monte carlo simulations we statistically examine the occurrence of a small spatial separation of two nearby basins the probability of double impact as seen on the moscoviense basin where the two impacts occurred 80 km apart is estimated to be about 50

numerical modeling of the formation and structure of the orientale impact basin 1 the orientale impact basin is the youngest and best preserved lunar multi ring basin and has thus been the focus of studies investigating basin forming processes and final structures a consensus about how multi ring basins form however remains elusive here we numerically model the orientale basin forming impact with the aim of resolving some of the uncertainties associated with this basin by using two thermal profiles estimating lunar conditions at the time of orientale s formation and constraining the numerical models with crustal structures inferred from gravity data we provide estimates for orientale s impact energy 2 9 1025 j impactor size 50 80 km diameter transient crater size 320 480 km excavation depth 40 55 km and impact melt volume 106 km3 we also analyze the distribution and deformation of target material and compare our model results and orientale observations with the chicxulub crater to investigate similarities between these two impact structures

the lunar crust global structure and signature of major basins new lunar gravity and topography data from the clementine mission provide a global bouguer anomaly map corrected for the gravitational attraction of mare fill in mascon basins most of the gravity signal remaining after corrections for the attraction of topography and mare fill can be attributed to variations in depth to the lunar moho and therefore crustal thickness the large range of global crustal thickness 20 120 km is indicative of major spatial variations in melting of the lunar exterior and or significant impact related redistribution the 61 km average crustal thickness constrained by a depth to moho measured during the apollo 12 and 14 missions is preferentially distributed toward the farside accounting for much of the offset in center of figure from the center of mass while the average farside thickness is 12 km greater than the nearside the distribution is nonuniform with dramatic thinning beneath the farside south pole aitken basin with the global crustal thickness map as a constraint regional inversions of gravity and topography resolve the crustal structure of major mascon basins to half wavelengths of 150 km in order to yield crustal thickness maps with the maximum horizontal resolution permitted by the data the downward continuation of the bouguer gravity is stabilized by a three dimensional minimum slope and curvature algorithm both mare and non mare basins are characterized by a central upwarped moho that is surrounded by rings of thickened crust lying mainly within the basin rims the inferred relief at this density interface suggests a deep structural component to the surficial features of multiring lunar impact basins for large 300 km diameter basins moho relief appears uncorrelated with diameter but is negatively correlated with basin age in several cases it appears that the multiring structures were out of isostatic equilibrium prior to mare emplacement suggesting that the lithosphere was strong enough to maintain their state of stress to the present

the transition from complex crater to peak ring basin on the moon new observations from the lunar orbiter laser altimeter lola instrument impact craters on planetary bodies transition with increasing size from simple to complex to peak ring basins and finally to multi ring basins important to understanding the relationship between complex craters with central peaks and multi ring basins is the analysis of protobasins exhibiting a rim crest and interior ring plus a central peak and peak ring basins exhibiting a rim crest and an interior ring new data have permitted improved portrayal and classification of these transitional features on the moon we used new 128 pixel degree gridded topographic data from the lunar orbiter laser altimeter lola instrument onboard the lunar reconnaissance orbiter combined with image mosaics to conduct a survey of craters 50 km in diameter on the moon and to update the existing catalogs of lunar peak ring basins and protobasins our updated catalog includes 17 peak ring basins rim crest diameters range from 207 km to 582 km geometric mean 343 km and 3 protobasins 137 170 km geometric mean 157 km several basins inferred to be multi ring basins in prior studies apollo moscoviense grimaldi freundlich sharonov coulomb sarton and korolev are now classified as peak ring basins due to their similarities with lunar peak ring basin morphologies and absence of definitive topographic ring structures greater than two in number we also include in our catalog 23 craters exhibiting small ring like clusters of peaks 50 205 km geometric mean 81 km one humboldt exhibits a rim crest diameter and an interior morphology that may be uniquely transitional to the process of forming peak rings a power law fit to ring diameters d ring and rim crest diameters dr of peak ring basins on the

properties of near surface marine sediments from wavelet correlation analysis 1 we present the first results from applying the wavelet correlation analysis to study physical properties of near top marine sediments this technique applied to the synthetic and field data yields well resolved group velocity dispersion curves for the first two shear modes and surface waves this method can be potentially useful for detecting of different seismic modes at frequencies masked by other neighboring modes this novel technique is superior to traditional cross correlation and fourier analysis for inferring the physical properties of near surface marine sediments such as density porosity variations in depth and distance under diverse field conditions

geology of the moscoviense basin 1 the moscoviense basin on the northern portion of the lunar farside displays topography with a partial peak ring in addition to rings that are offset to the southeast these rings do not follow the typical concentric ring spacing that is recognized with other basins suggesting that they may have formed as a result of an oblique impact or perhaps multiple impacts in addition to the unusual ring spacing present the moscoviense basin contains diverse mare basalt units covering the basin floor and a few highland mafic exposures within its rings new analysis of previously mapped mare units suggests that the oldest mare unit is the remnant of the impact melt sheet the moscoviense basin provides a glimpse into the lunar highlands terrain and an opportunity to explore the geologic context of initial lunar crustal development and modification

the origin of the non mare mascon gravity anomalies in lunar basins abstract many lunar basins are characterized by prominent positive gravity anomalies over the basin interiors referred to as mass concentrations or mascons while a significant fraction of some near side mascon anomalies can be explained as a result of the flexural support of the mare basalts within the basins a number of basins including orientale exhibit mascons in excess of those that can be plausibly ascribed to the mare some basins exhibit mascons but lack mare altogether lunar gravity and topography data are used to map the isostatic anomaly or the height of the surface above or below its isostatic level orientale is representative of the majority of lunar basins in which the super isostatic basin center is surrounded by a sub isostatic annulus of comparable magnitude but greater area the basin structure as a whole is found to be strongly sub isostatic high resolution crustal thickness models of orientale confirm that it is surrounded by an annulus of thickened but sub isostatic crust it is proposed that the flexural uplift of the annulus causes the uplift and positive gravity anomalies within the basin center finite element models are used to examine the flexural uplift of the sub isostatic annulus and the basin center for a range of lithosphere thicknesses both outside the basin and in the basin interior the uplift of the basin center can exceed 2 km increasing the central gravity anomaly by 200 mgal this annular uplift explains a significant fraction of the orientale mascon and is likely a dominant cause of non mare mascons globally

transition from complex craters to multi ringed basins on terrestrial planetary bodies scale dependent role of the expanding melt cavity and progressive interaction with the displaced zone 1 the observed differences between complex craters and multi ringed basins are described and a combined transient cavity displaced zone melt cavity model is explored to account for the observations in this nested melt cavity model the increasing influence of the percentage of the target undergoing impact melting at the sub impact point with increasing size the differential melt scaling of cintala and grieve 1998 causes fundamental changes in the nature of the transient cavity its relationship to the displaced zone and its short term collapse behavior the transition from complex craters to two ring basins involves expansion of the melting front into the displaced zone formation of a two component excavation cavity and a concomitant radial expansion outward of the zone of maximum elastic rebound the short term modification stage is then dominated by the strength differences between the fluid melt in the inner cavity and rocks of the displaced zone the highly shocked rocks at the outer margin of the expanded parabolic melting front rebound to form the expanded peak ring moving upward and laterally inward easily displacing fluid melt filling the inner depression at larger sizes differential melt scaling causes the peak ring diameter to expand relatively more rapidly than the basin rim and upon collapse the increased volume of melt ponds in the rebounded melt cavity inside the expanding peak ring as the transient melt cavity further increases proportionally in size it penetrates through the base of the displaced zone with significant consequences the resulting modification stage now incorporates into the collapse process inward and upward movement along the base of the displaced zone listric failure occurs inward into the fluid melt cavity beginning at the edge of the melt cavity and extending out along the base of the displaced zone up to the base of the rim structural uplift at 1 5 crater radii this forms an additional outer ring and a resulting megaterrace modifying the radial ejecta on the collapsed rim to form a domical facies at multi ring basin scales the significantly deeper penetration that occurs in the expanding melt cavity accounts for the maximum crustal thickness decrease that occurs inside the peak ring in the final basin early onset and higher density of peak ring basins on mercury is predicted by higher mean impact velocity and differential melt scaling