observations of periglacial landforms in utopia planitia with the high resolution imaging science experiment hirise 1 the region of western utopia planitia 80 105 e 40 55 n displays several types of landforms similar to earth periglacial features including scallop shaped depressions and networks of polygonal terrains the scalloped depressions have been proposed to originate from thermokarstic processes such as sublimation and or melting of near surface ground ice using hirise imagery we characterize these depressions and several associated distinct polygon networks in unprecedented morphologic and topographic detail and investigate support for an ice based degradation process the scalloped depressions and interior polygons and ridges are found to evolve together mainly influenced by sublimation local proximity of ground ice to the surface and obliquity variations

thermal properties of lobate ejecta in syrtis major mars implications for the mechanisms of formation 1 this paper reports an analysis of the thermal properties of ejecta layers of single and double lobe impact craters on mars first observations of thermal properties were made at low resolution from the phobos 88 mission and did not allow mapping of variations of thermal properties inside the ejecta layer the themis instrument on board the mars odyssey mission provides new high resolution thermal mapping of the surface of mars from these data we observe a systematic temperature increase at night at the edge of the ejecta we evaluate first the possible influences on the surface temperatures at night of postimpact modification processes given the topography of an impact crater and its ejecta we show that the observed thermal signature is more likely related to a particle size distribution inherited immediately after the impact event during the emplacement of ejecta we propose that the kinetic sieving process observed in experimental and natural granular flows like pyroclastic flows is responsible for the accumulation of larger particles at the ejecta flow front and thus is responsible for the temperature increase despite evidence of aeolian activity at syrtis major these craters offer an example of preserved surface physical properties resulting from geological processes which have occurred since the formation of the volcanic shield of syrtis major further studies are underway with the mars express ongoing observations produced by the hrsc and omega instruments in order to explore the interplay between the surface physical properties and the spectroscopic signatures seen at syrtis major

concentric crater fill in utopia planitia history and interaction between glacial brain terrain and periglacial mantle processes abstract at martian mid to high latitudes the surfaces of potentially ice rich features including concentric crater fill lobate debris aprons and lineated valley fill typically display a complex texture known as brain terrain due to its resemblance to the complex patterns on brain surfaces in order to determine the structure and developmental history of concentric crater fill and overlying latitude dependent mantle ldm material brain terrain and polygonally patterned ldm surfaces are analyzed using hirise images from four craters in utopia planitia containing concentric crater fill brain terrain and mantle surface textures are classified based on morphological characteristics 1 closed cell brain terrain 2 open cell brain terrain 3 high center mantle polygons and 4 low center mantle polygons a combined glacial and thermal contraction cracking model is proposed for the formation and modification of the brain terrain texture of concentric crater fill a similar model related to thermal contraction cracking and differential sublimation of underlying ice is proposed for the formation and development of polygonally patterned mantle material both models require atmospheric deposition of ice likely during periods of high obliquity but do not require wet active layer processes crater dating of brain terrain and mantled surfaces suggests a transition at martian mid latitudes from peak glacial conditions occurring within the past 10 100 my to a quiescent period followed by a cold desert periglacial period during the past 1 2 my

formation of double layered ejecta craters on mars a glacial substrate model 1 a class of martian impact craters with particularly unusual ejecta characteristics double layered ejecta dle craters are preferentially located in the midlatitudes in both hemispheres of mars unlike today decameters thick deposits of snow and ice occupied these same latitudes for significant periods during the amazonian period we assess the hypothesis that the unusual double layer morphology could be related to impact into a snow and ice glacial substrate followed by landsliding of ejecta off of the structurally uplifted rim we find that many characteristics of dle craters e g latitudinal distribution lack of secondaries landslide like textures evidence for overthrusting relation to other crater types etc are consistent with such an origin

deep crustal carbonate rocks exposed by meteor impact on mars mars may have once had a co2 rich atmosphere but carbonate rocks that could provide evidence for such conditions are sparse spectral analyses of rocks exposed from deep within an impact crater reveal that carbonate deposits may be extensive on mars but are buried under layers of younger volcanic rocks

emplacement of martian rampart crater deposits 1 we present a basic continuum flow model for the emplacement of the distal rampart crater deposits on mars assuming cylindrical symmetry analytic solutions of the volume and momentum conservation equations yield time dependent flow thickness and velocity profiles the momentum equation has an inertial term and a frictional resistance term that is proportional to the local volumetric flow rate we find that only a few basic physical processes are necessary to form sharp distal ramparts first there must be sufficient material to form a continuum overland flow then for simple choices of boundary conditions at the source of the flow distal ramparts form naturally due to the cylindrical geometry the inertia of the flow and local frictional resistance themis images of rampart deposits show that the ejecta flow velocities were relatively slow being diverted by preexisting obstacles even within 0 2 crater radii from the rim of the parent crater to develop inferences about rampart deposit emplacement we require measurements of the crater radius and flow distance and assumptions about the maximum source flow velocity and depth we measured nine clearly expressed rampart deposits for craters with diameters of 3 4 17 0 km the model provides estimates of the emplacement time the rampart width and the shape of the radial flow depth profiles we find that modest velocities of 27 116 m s 1 maximum source flow depths of 10 40 m and emplacement durations of 12 31 min adequately explain the morphologies of selected rampart craters

concentric crater fill in the northern mid latitudes of mars formation processes and relationships to similar landforms of glacial origin abstract hypotheses accounting for the formation of concentric crater fill ccf on mars range from ice free processes e g aeolian fill to ice assisted talus creep to debris covered glaciers based on analysis of new ctx and hirise data we find that concentric crater fill ccf is a significant component of amazonian aged glacial landsystems on mars we present mapping results documenting the nature and extent of ccf along the martian dichotomy boundary over 30 to 90 e latitude and 20 80 n longitude on the basis of morphological analysis we classify ccf landforms into classic ccf and low definition ccf classic ccf is most typical in the middle latitudes of the analysis area 30 50 n while a range of degradation processes results in the presence of low definition ccf landforms at higher and lower latitudes we evaluate formation mechanisms for ccf on the basis of morphological and topographic analyses and interpret the landforms to be relict debris covered glaciers rather than ice mobilized talus or aeolian units we examine filled crater depth diameter ratios and conclude that in many locations hundreds of meters of ice may still be present under desiccated surficial debris this conclusion is consistent with the abundance of ring mold craters on ccf surfaces that suggest the presence of near surface ice analysis of breached craters and distal glacial deposits suggests that in some locations ccf related ice was once several hundred meters higher than its current level and has sublimated significantly during the most recent amazonian crater counts on ejecta blankets of filled and unfilled craters suggests that ccf formed most recently between 60 and 300 ma consistent with the formation ages of other martian debris covered glacial landforms such as lineated valley fill lvf and lobate debris aprons lda morphological analysis of ccf in the vicinity of lvf and lda suggests that ccf is a part of an integrated lvf lda ccf glacial landsystem instances of morphological continuity between ccf lvf and lda are abundant the presence of formerly more abundant ccf ice coupled with the integration of ccf into lvf and lda suggests the possibility that ccf represents one component of the significant amazonian mid latitude glaciation s on mars

martian impact crater ejecta morphologies as indicators of the distribution of subsurface volatiles 1 fresh martian impact craters display a variety of ejecta blanket morphologies the fluidized appearance of most fresh ejecta types is commonly ascribed to heating and vaporization of subsurface volatiles during crater formation we have conducted a study of the distribution of the three dominant fluidized ejecta morphologies single layer ejecta sle double layer ejecta dle and multiple layer ejecta mle within the 60 latitude zone on mars we have subdivided this region into 5 5 latitude longitude boxes and have computed the following for each box 1 percentage of craters showing any ejecta morphology as a function of total number of craters 2 percentage of sle craters as a function of craters with an ejecta morphology 3 percentage of dle craters as a function of craters with an ejecta morphology and 4 percentage of mle craters as a function of craters with an ejecta morphology we confirm previous reports that the sle morphology is the most common ejecta type within the study area constituting 70 of all ejecta morphologies over most of the study area the dle and mle morphologies are much less common but these morphologies are concentrated in localized regions of the planet using these results we discuss how subsurface volatile reservoirs may be distributed across the planet the regional variations found in this study generally correlate with the proposed locations of near surface h2o reservoirs detected by mars odyssey

three dimensional imaging of active structures using earthquake aftershocks the northridge thrust california abstract aftershocks of the 1994 northridge earthquake m 6 8 allow us to image the structure beneath the san fernando valley in northwestern los angeles in three dimensions we combine aftershocks and geological data to build an image of the three dimensional 3 d geometry of the previously unrecognized north vergent northridge blind thrust to a depth of 21 km the most striking feature of the imaged fault is mega corrugations oriented parallel to the mean aftershock slip vector with most of the 1994 slip confined to west of the largest corrugation we also image the partially overlying south vergent san fernando thrust which broke to the surface in a complex rupture in 1971 m 7 1 both thrusts produce fault related folding because of either fault propagation or fault bends however this deeper folding is masked by overlying complex deformation in the cover which is one reason why the northridge thrust was not identified until it ruptured in 1994 we use trishear fold modeling based on our 3 d fault geometry to evaluate possible folding due to slip on the northridge thrust as well as its interaction with the overlapping san fernando thrust and with shallow structures in the cover this example illustrates the importance of earthquake data to structural geology and the value of its 3 d integration with surface and near surface geological data

dynamically modeling fault step overs using various friction laws it is well known that fault step overs can under some circumstances allow through going rupture and under other circumstances cause rupture to terminate however the effects of different friction law formulations on jumping rupture have not been extensively explored in this study we use the 2 d dynamic finite element method to investigate how different frictional parameterizations affect the ability of rupture to jump a step over in both extensional and compressional settings we compare linear slip weakening friction and three forms of rate and state dependent friction the aging law slip law and slip law with strong rate weakening we have found that for friction parameterizations with the same effective slip weakening distance the functional forms of such friction laws can have a significant effect on maximum jump distance with friction laws scaled to have equivalent fracture energies we find that the functional forms of such friction laws have a second order effect on jumping rupture finally with our specific parameterizations we find that delays in rupture across the step over systems can lead to a previously unseen mode of supershear transition once the rupture renucleates on the secondary fault segment even if the initial stress field precludes such a transition studies using multiple friction laws in complex geometries such as fault step overs can lead to better understanding of the dependence of rupture properties on the type of friction law utilized in models and statistical analysis

atmospheric effects on ejecta emplacement laboratory experiments allow the investigation of complex interactions between impacts and an atmosphere although small in scale they can provide essential first order constraints on the processes affecting late stage ballistic ejecta and styles of ejecta emplacement around much larger craters on planetary surfaces the laboratory experiments involved impacting different fine grained particulate targets under varying atmospheric pressure and density different gas compositions during crater formation ballistic ejecta form the classic cone shaped profile observed under vacuum conditions as atmospheric density increases for a given pressure however the ejecta curtain bulges at the base and pinches above this systematic change in the ejecta curtain reflects the combined effects of deceleration of ejecta smaller than a critical size and entrainment of these ejecta within atmospheric vortices created as the outward moving wall of ejecta displaces the atmosphere additionally a systematic change in emplacement style occurs as a function of atmospheric pressure largely independent of density contiguous ejecta rampart superposing ballistically emplaced deposits 0 06 to 0 3 bar ejecta flow lobes 0 3 to 0 7 bar and radial patterns 0 8 bar underlying processes controlling such systematic changes in emplacement style were revealed by observing the evolution of the ejecta curtain by changing target materials including layered targets and low density particulates by varying atmospheric density by changing impact angle and by comparing the ejecta run out distances with first order models of turbidity flows three distinct ejecta emplacement processes can be characterized ejecta ramparts result from coarser clasts sorted and driven outward by vortical winds behind the outward moving ejecta curtain this style of wind modified emplacement represents minimal ejecta entrainment and is enhanced by a bimodal size distribution in the ejecta such eddy supported flows are observed to increase in run out distance scaled to crater size with increasing atmospheric pressure by analogy with turbidity flows this scaled distance should increase as r1 2 for a given atmospheric pressure and degree of entrainment ejecta flows with much greater run out distances develop as the turbulent power in atmospheric response winds increase such flows overrun and scour the inner ejecta facies thereby producing distinct inner and outer facies the degree of ejecta entrainment depends on the dimensionless ratio of drag to gravity forces acting on individual ejecta and the intensity of the winds created by the outward moving curtain entrainment increases with increasing atmospheric density and ejection velocity crater size but decreases with ejecta density and size the intensity of curtain generated winds increases with ejection velocity crater size the dimensionless drag ratio characterizing the laboratory experiments can be applied to mars since the reduced atmospheric density is offset by the increased ejection velocities for kilometer scale events for a given crater size ejection velocity and atmospheric conditions a wide range of nonballistic ejecta emplacement styles could occur simply by varying ejecta sizes even without the presence of water alternatively the onset crater diameter for nonballistic emplacement styles can reflect the range of ejecta sizes possible from the diverse martian geologic history massive basalts to fine grained aeolian deposits scaling considerations further predict that ejecta run out distances scaled to crater size on mars should increase as r1 2 hence long run out flows dependent on crater diameter need not reflect depth to a buried reservoir of water on venus however the dense atmosphere maximizes entrainment and results in ejecta flow densities approaching a constant fraction of the atmospheric density under such conditions ejecta run out distances should decrease as r 1 2

the three dimensional dynamics of dipping faults recent two dimensional dynamic simulations of dip slip faulting niel sen 1998 oglesby et al 1998 2000 shi et al 1998 have shown that the asym metric geometry of dip slip faults that intersect the free surface can have large effects on the dynamics of earthquake rupture the nonvertical dip angle of such faults leads to larger motion on the footwall than the hanging wall as well as much larger motion from thrust reverse faults than from normal faults with the same geometry and stress magnitudes in the present work we perform full three dimensional simulations of thrust reverse normal and strike slip faults and show that the same effects exist in three dimensions strike slip fault motion is either in between or lower than the motion of both dip slip faults additional three dimensional effects include strong rake rotation at the free surface the results confirm the findings of the previous studies and further elucidate the dynamic effects of the free surface on fault rupture slip and ground motion they are also borne out by early analyses of the 1999 chi chi taiwan thrust earthquake which displayed higher motion on the hanging wall than on the footwall and a strong oblique component of motion at the surface

a grid doubling finite element technique for calculating dynamic three dimensional spontaneous rupture on an earthquake fault summary we present a new finite element technique for calculating dynamic 3 d spontaneous rupture on an earthquake fault which can reduce the required computational resources by a factor of six or more without loss of accuracy the grid doubling technique employs small cells in a thin layer surrounding the fault the remainder of the modelling volume is filled with larger cells typically two or four times as large as the small cells in the resulting non conforming mesh an interpolation method is used to join the thin layer of smaller cells to the volume of larger cells grid doubling is effective because spontaneous rupture calculations typically require higher spatial resolution on and near the fault than elsewhere in the model volume the technique can be applied to non planar faults by morphing or smoothly distorting the entire mesh to produce the desired 3 d fault geometry using our faultmod finite element software we have tested grid doubling with both slip weakening and rate and state friction laws by running the scec usgs 3 d dynamic rupture benchmark problems we have also applied it to a model of the hayward fault northern california which uses realistic fault geometry and rock properties faultmod implements fault slip using common nodes which represent motion common to both sides of the fault and differential nodes which represent motion of one side of the fault relative to the other side we describe how to modify the traction at split nodes method to work with common and differential nodes using an implicit time stepping algorithm

limitations of rupture forecasting exposed by instantaneously triggered earthquake doublet assessments of earthquake risk often assume rupture of a single fault analysis of a 1997 pakistan earthquake reveals that not one but two separate ruptures caused the shaking implying that cascading events should be factored into forecasts

excess ejecta craters record episodic ice rich layers at middle latitudes on mars 1 we infer amazonian climate change events from the presence of fresh craters with excess volumes of ejecta using the mars orbiter laser altimeter data the geometrical properties of 572 fresh impact craters with rim diameters between 2 5 and 102 km were compiled in lowland and highland plains the data reveal a class of fresh craters with anomalously high ejecta volumes preferentially located in utopia planitia these fresh excess ejecta craters have volumes of material above the preimpact surface larger than the crater cavity volumes by factors of 2 5 to 5 8 the excess volume corresponds to an excess thickness of ejecta of about 20 to 100 m averaged over the continuous ejecta blanket the excess material cannot be accommodated by ejecta bulking alone and requires an external process to increase the apparent volume of the ejecta and or the uplifted surface on the basis of the geologic setting ejecta morphology and calculations of increased ice stability with burial we conclude that the most likely origin of the excess ejecta volume is the presence of an ice rich layer tens of meters thick at the time of impact the icy layer or a lag deposit is partially preserved beneath the ejecta blanket today in this scenario the icy layer has since been removed from areas unprotected by ejecta blankets creating an apparent preimpact surface lower than the original elevation the statistical occurrence of excess ejecta craters is consistent with climate model predictions of recent glacial periods on mars

identifying an index of subsurface volatiles on mars through an analysis of impact crater morphometry using principal component analysis layered ejecta craters comprise a significant fraction of the ejecta on mars and may form from the excavation of subsurface volatiles such as ice a recent global catalogue identified extensive numbers of layered ejecta craters and their properties and is examined here in this study over 10 000 single layered and double layered ejecta craters were analyzed by principal component analysis principal component analysis revealed the existence of four significant principal components for single layered ejecta craters and five for double layered ejecta craters which accounted for 73 and 80 of the sample variances respectively the first three pcs were interpreted as indices of impactor energy target volatiles and impactor angle the fourth component for both morphologies was interpreted as a resurfacing index the fifth component for double layered craters was identified as an index of preservation of the impact feature using the putative target volatile index identified through principal component analysis the spatial distribution of potential subsurface volatiles both past and geologically recent is mapped

shattered rock and precarious rock evidence for strong asymmetry in ground motions during thrust faulting recent thrust faulting models both physical and numerical have indicated very high ground motions on the hanging wall and relatively low motions on the footwall of thrust faults in this article recent field evidence supporting this strong asymmetry is described earlier field observations of objects thrown in the air also suggest that ground motions must have exceeded 1 g and 100 cm sec new shattered rock evidence on the hanging wall of thrust faults in southern california supports the occurrence of intense ground motions on the other hand the lack of shattered rock and the presence of precariously balanced rocks on the footwall of two thrust faults in southern california indicate relatively low ground motions thus indicating strong asymmetry in ground motions near the fault trace for thrust faults some current ground motion attenuation curves and hazard maps may give too low values on the hanging wall and too high values on the footwall this could be of critical importance to estimating earthquake hazard from potentially large thrust fault earthquakes in the los angeles basin and elsewhere in the world the new evidence also supports the idea that dynamic inertial detachment of the hanging wall from the footwall occurs in nature in the manner suggested by some recent physical and numerical models if such detachment occurs it could also have important implications for understanding thrust fault rupture mechanics for example the paradox of large overthrusts and the heat flow paradox for thrusts

3d simulations of multi segment thrust fault rupture thrust faults such as those that underlie the los angeles basin are typically segmented by tear faults that offset the thrust fault segments we perform 3d finite difference simulations of earthquake rupture to evaluate the effectiveness of these offsets in retarding rupture the simulations include orthogonal intersecting faults to model the interaction of the thrust fault segments with the tear fault for reasonable assumptions for fault segment length strength and stress drop rupture can jump offsets of up to 2 km if a tear fault is present consistent with observations of well studied thrust earthquakes absent a tear fault the maximum offset that can be breached is an order of magnitude smaller

comparing landslides to fluidized crater ejecta on mars 1 we use the mars global surveyor and viking data sets to compare and contrast the geomorphology of four large martian landslides located in valles marineris to fluidized ejecta of seven fresh martian craters located in lunae planum both mass movements have flowed over the martian surface and possess characteristics seen in terrestrial mass movements we combine these comparisons with simple flow models to determine how the planar geometry of landslides and the cylindrical geometry of ejecta can generate different topographic expressions for the same input constraints our purpose is to better understand the emplacement processes of both types of mass movements our geomorphic analyses are consistent with previous views that the large martian landslides resemble large terrestrial long run out flows the planar flow model supports this inference martian landslides probably flowed as a basal glide where motion is limited to a narrow interface at the base of the mass movement geomorphic investigations of fresh multilayered ejecta indicate that their inner portions with their subtle rampart probably flowed like their landslide counterparts as a basal glide distal pronounced contiguous ramparts however resemble features akin to terrestrial debris flows the cylindrical flow model shows that differences in geometry can mask the dynamics of flow emplacement this model suggests as expected a basal glide origin for the inner portions of the ejecta surprisingly basal glide also best explains the topography of the distal ejecta ramparts

sinuosity of martian rampart ejecta deposits the sinuosities of 2213 martian rampart ejecta craters are quantified through measurement of the ejecta flow front perimeter and ejecta area this quantity called lobateness was computed for each complete lobe of the 1582 single lobe sl 251 double lobe dl and 380 multiple lobe ml craters included in this study a lobateness value of 1 indicates a circular ejecta blanket whereas more sinuous ejecta perimeters have lobateness values 1 although resolution does have an effect on the absolute values of lobateness the general relationships between lobateness and morphology exist regardless of resolution evaluation of the lobateness values reveals that the outer lobes of dl and ml craters have higher median lobateness values i e are more sinuous than the inner lobes the outermost lobe of ml craters displays higher lobateness values than the outer lobe of dl craters or the single lobe of sl craters previous reports of lobateness diameter lobateness latitude and lobateness terrain relationships for rampart craters are not supported by this study many of the differences between the results of this study and the previous lobateness analyses can be attributed to the inclusion of resolution effects and the distinction between different ejecta morphologies in this study the results of this study taken together with a previous analysis of the distribution and diameter dependence of different ejecta morphologies are most consistent with the theory that martian lobate ejecta morphologies form from impact into subsurface volatiles

standardizing the nomenclature of martian impact crater ejecta morphologies the mars crater morphology consortium recommends the use of a standardized nomenclature system when discussing martian impact crater ejecta morphologies the system utilizes nongenetic descriptors to identify the various ejecta morphologies seen on mars this system is designed to facilitate communication and collaboration between researchers crater morphology databases will be archived through the u s geological survey in flagstaff where a comprehensive catalog of martian crater morphologic information will be maintained

identification of carbonate rich outcrops on mars by the spirit rover decades of speculation about a warmer wetter mars climate in the planet s first billion years postulate a denser co2 rich atmosphere than at present such an atmosphere should have led to the formation of outcrops rich in carbonate minerals for which evidence has been sparse using the mars exploration rover spirit we have now identified outcrops rich in magnesium iron carbonate 16 to 34 weight percent in the columbia hills of gusev crater its composition approximates the average composition of the carbonate globules in martian meteorite alh 84001 the gusev carbonate probably precipitated from carbonate bearing solutions under hydrothermal conditions at near neutral ph in association with volcanic activity during the noachian era

supervolcanoes within an ancient volcanic province in arabia terra mars several irregularly shaped craters located within arabia terra mars represent a new type of highland volcanic construct and together constitute a previously unrecognized martian igneous province similar to terrestrial supervolcanoes these low relief paterae possess a range of geomorphic features related to structural collapse effusive volcanism and explosive eruptions extruded lavas contributed to the formation of enigmatic highland ridged plains in arabia terra outgassed sulphur and erupted fine grained pyroclastics from these calderas probably fed the formation of altered layered sedimentary rocks and fretted terrain found throughout the equatorial region the discovery of a new type of volcanic construct in the arabia volcanic province fundamentally changes the picture of ancient volcanism and climate evolution on mars other eroded topographic basins in the ancient martian highlands that have been dismissed as degraded impact craters should be reconsidered as possible volcanic constructs formed in an early phase of widespread disseminated magmatism on mars several irregularly shaped craters located within arabia terra mars are interpreted as a new type of highland volcanic construct similar to supervolcanoes on earth fundamentally changing the picture of ancient volcanism and climate evolution on mars the geological evolution of mars is largely a story of volcanic activity about 70 of the planet s crust was resurfaced by basaltic volcanism but a significant fraction of that volcanic material is from unknown sources in this issue joseph michalski and jacob bleacher report new results suggesting that supervolcanoes existed in the arabia terra region of mars an area with many deposits of layered rocks of unknown origins that has not previously been considered a volcanic terrain they propose that ancient martian calderas might have been misinterpreted as impact craters that were degraded by erosion if supervolcanoes were common on ancient mars it would have major implications for estimates of volcanic outgassing climate evolution and formation of the planet s layered fragmented upper crust

seismic surveys in the northern red sea asymmetric crustal structure abstract wide angle reflection and refraction seismic warrs surveys at key sections of the northern red sea and adjacent areas enabled a better definition of the crust and upper mantle structure a fundamental asymmetry of the region was revealed by the results of profiles which cover both flanks of the red sea main trough the coastal plains and the bordering precambrian shields this asymmetry is clearly expressed by the presence of different crustal types on both flanks the western flank shows oceanised crust within only 20 km off the african coast while the whole eastern flank is underlain by a continental type of crust likewise the shape of the continent ocean transitions differs significantly on both flanks the arabian margin extends almost into the centre of the red sea and shows considerable stretching and attenuation of the continental crust while the african margin on the other hand even thickens towards the escarpment and appears very abrupt the influence of the red sea opening as reflected by the decrease of seismic velocities and the increase of poisson s ratio in the upper mantle due to partial melting is strictly limited to the area seaward of the egyptian escarpment the asymmetry in the northern red sea is regarded to be the expression of strike slip processes in the initial stages of red sea evolution

the degradation of impact craters in maja valles and arabia mars photoclinometry is being utilized to quantify the degree of degradation suffered by martian impact craters 1 to 5 km diameter range in the arabia and maja valles regions results indicate that present crater depths can vary substantially from crater depths expected for the original fresh craters at all sizes examined localized regions of high moderate and low degradation of the order of 102 km2 have been delineated using the percentage change in crater depth diameter between current and assumed fresh crater morphology regions of low degradation occur randomly across these regions and probably represent recently produced impact craters which have undergone little degradation since their formation aeolian activity including current mantling deposits appears to dominate the processes degrading craters in the arabia region with fluvial and impact processes playing a secondary role in the maja valles region crater degradation is associated primarily with fluvial outflow channel activity with aeolian and impact processes contributing secondary effects to the destruction of impact craters

evidence for amazonian northern mid latitude regional glacial landsystems on mars glacial flow models using gcm driven climate results and comparisons to geological observations a fretted valley system on mars located at the northern mid latitude dichotomy boundary contains lineated valley fill lvf with extensive flow like features interpreted to be glacial in origin we have modeled this deposit using glacial flow models linked to atmospheric general circulation models gcm for conditions consistent with the deposition of snow and ice in amounts sufficient to explain the interpreted glaciation in the first glacial flow model simulation sources were modeled in the alcoves only and were found to be consistent with the alpine valley glaciation interpretation for various environments of flow in the system these results supported the interpretation of the observed lvf deposits as resulting from initial ice accumulation in the alcoves accompanied by debris cover that led to advancing alpine glacial landsystems to the extent observed today with preservation of their flow texture and the underlying ice during downwasting in the waning stages of glaciation in the second glacial flow model simulation the regional accumulation patterns predicted by a gcm linked to simulation of a glacial period were used this glacial flow model simulation produced a much wider region of thick ice accumulation and significant glaciation on the plateaus and in the regional plains surrounding the dichotomy boundary deglaciation produced decreasing ice thicknesses with flow centered on the fretted valleys as plateaus lost ice scarps and cliffs of the valley and dichotomy boundary walls were exposed providing considerable potential for the production of a rock debris cover that could preserve the underlying ice and the surface flow patterns seen today in this model the lineated valley fill and lobate debris aprons were the product of final retreat and downwasting of a much larger regional glacial landsystem rather than representing the maximum extent of an alpine valley glacial landsystem these results favor the interpretation that periods of mid latitude glaciation were characterized by extensive plateau and plains ice cover rather than being restricted to alcoves and adjacent valleys and that the observed lineated valley fill and lobate debris aprons represent debris covered residual remnants of a once more extensive glaciation 2011 elsevier inc

the scaling of complex craters the empirical relation between the transient crater diameter dg and final crater diameter dr of complex craters and basins is estimated using cumulative terrace widths central uplift diameters continuous ejecta radii and transient crater reconstructions determined from lunar and terrestrial impact structures the ratio dg dr is a power law function of dr decreasing uniformly from unity at the diameter of the simple complex crater morphology transition to about 0 5 for large multiring basins like imbrium on the moon the empirical constants in the dg dr relation are interpreted physically to mean that the position of the final rim relative to the transient crater and hence the extent of collapse is controlled or greatly influenced by the properties of the zone of dissociated material produced by the impact shock the continuity of the dg dr relation over the entire spectrum of morphologic types from complex craters to multiring basins implies that the rims of all these structures form in the same tectonic environment despite morphologic differences

explosive volcanism in the tharsis region global evidence in the martian geologic record 1 a global equatorial set of layered deposits on mars has been reexamined with mars global surveyor data the stratigraphy morphology and erosional characteristics of units separated by thousands of kilometers are remarkably similar to each other and consistent with a widespread episodic subaerial source of fine grained material this study is the first to propose a genetic link between many units that have traditionally been considered on a local or regional level including the medusae fossae formation valles marineris interior deposits chaotic terrain terra meridiani and arabia materials mapping relationships suggest that all of these units are post noachian in age and formation may have continued until the recent past thinning of deposits with increasing distance from the tharsis rise suggests that much of these materials may be volcanic ash flows and air fall from explosive eruptions in the tharsis region analogous to those produced by terrestrial plinian eruptions contemporary martian winds would preferentially transport ash from an eruption plume near tharsis east or west along the equator depending on the season erosion has removed much of the original volcanic ash and only isolated layered stacks remain sometimes in topographic depressions that inhibit erosion modeling indicates that widespread dispersion of ash after an eruption is easily attainable in present or past atmospheric conditions consistent with the hypothesis that the far reaching deposits may be composed of ash from past explosive eruptions in the vicinity of tharsis

an instability mechanism in the formation of the martian lobate craters and the implications for the rheology of ejecta 1 lobate craters are an indication of the existence of fluids in the martian megaregolith the emplacement of the ejecta could be similar to debris flow dynamics in this paper we suggest that the lobate ejecta result of an instability mechanism during the surface flow indeed recent experimental studies on injection of heavy viscous fluid in a lighter one show that the wavelength of the instability depends on the viscosity and density contrast between the two fluids an extension of this 2d experiment to a cylindrical geometry has been carried out in that case we demonstrate that a distribution of wavelengths is related to viscosity contrast those results have been applied to 250 single layer craters in lunae planum and sinai planum to measure the variation of viscosity with depth the results are in agreement with a possible 1 km thick volatile rich layer above a less porous one

introducing and discussing a novel diagrammatic representation of impact crater dimensions abstract impact craters on the surface of mars are degraded by erosion and infilling due to combinations of geological processes these result in modifications of relative crater dimensions including diameter increase and reduction of rim floor depths in principle the longer a crater is exposed to geological processes the more pronounced the modifications visualization and analysis of these effects are achieved by plotting the measured depths m of impact craters vs the corresponding theoretical depths predicted p calculated from the crater diameters using depth diameter power laws this type of diagram is referred to as mpd measured depth vs predicted depth diagram the advantage of using the mpd representation consists in the fact that the data plot along linear regressions more easily interpreted than standard depth vs diameter diagrams as an example of application of the method the mpd was used to discriminate different generations of impact craters in terra sabaea into four groups t 0 fresh craters t 1 t 2 and t 3 from younger to older all located on the most ancient geological unit in the area npld other units in the area are hpl 3 and hr impacted only by craters belonging to group t 0 suggesting that these units are stratigraphically correlated the data of 5 craters in superposition relationships with the eastern reaches of evros vallis one of the major valley networks in the area were plotted in the diagram and assigned each to a regression depending on the location of their data points in relation to the prediction bands of the regressions the craters superposed to the valley all belonged to t 0 indicating that evros vallis has the same relative age of units hpl 3 and hr a conceptual discussion of the results demonstrates that mpd statistics a are unaffected by the procedures used to acquire depths and diameters of impact craters and by the power laws used and b can be interpreted irrespective of the sequence or combination of processes leading to modification of the crater morphometric data these properties make the diagram a powerful statistical tool

fault systems of the 1971 san fernando and 1994 northridge earthquakes southern california relocated aftershocks and seismic images from larse ii we have constructed a composite image of the fault systems of the m 6 7 san fernando 1971 and northridge 1994 california earthquakes using industry reflection and oil test well data in the upper few kilometers of the crust relocated aftershocks in the seismogenic crust and larse ii los angeles region seismic experiment phase ii reflection data in the middle and lower crust in this image the san fernando fault system appears to consist of a decollement that extends 50 km northward at a dip of 25 from near the surface at the northridge hills fault in the northern san fernando valley to the san andreas fault in the middle to lower crust it follows a prominent aseismic reflective zone below and northward of the main shock hypocenter interpreted upward splays off this decollement include the mission hills and san gabriel faults and the two main rupture planes of the san fernando earthquake which appear to divide the hanging wall into shingle or wedge like blocks in contrast the fault system for the northridge earthquake appears simple at least east of the larse ii transect consisting of a fault that extends 20 km southward at a dip of 33 from 7 km depth beneath the santa susana mountains where it abuts the interpreted san fernando decollement to 20 km depth beneath the santa monica mountains it follows a weak aseismic reflective zone below and southward of the main shock hypocenter the middle crustal reflective zone along the interpreted san fernando decollement appears similar to a reflective zone imaged beneath the san gabriel mountains along the larse i transect to the east in that it appears to connect major reverse or thrust faults in the los angeles region to the san andreas fault however it differs in having a moderate versus a gentle dip and in containing no mid crustal bright reflections

evidence for extensive denudation of the martian highlands high resolution topographic data from the mars orbiter laser altimeter reveal evidence for widespread denudation from margaritifer sinus to northern arabia terra an area of 1 107 km2 a major resurfacing event is indicated by 1 a heavily degraded landscape hosting numerous inliers 2 truncation or absence of valley networks and 3 a break in slope at the edge of early to middle noachian plateau materials geomorphic mapping was completed on the type locale of denudation 0 30 s 0 30 w superposition relations and crater counts for geomorphic units indicate that large scale resurfacing took place in the late noachian eroding the martian highlands and resulting in transportation and deposition of 4 5 106 km3 of sediment in the northern plains this is equivalent to a 120 m thick uniform layer of sediment on the surface of mars north of 30 n geomorphic mapping and crater counts limit the timing of denudation to the late noachian an interval of 350 500 m y using this limit we estimate a minimum rate of denudation of 2 0 m yr comparable to denudation of typical slopes in a temperate maritime climate on earth the morphology rate of denudation and extensive nature of upland degradation suggest that precipitation fed surface runoff is the most likely geomorphic agent capable of such a process indicative of a warm wet mars during the late noachian epoch

the formation of fluidized ejecta on mars by granular flows a simple granular flow model is used to investigate some of the conditions under which ejecta may flow as a granular media the purpose of this investigation is to provide some bounds as to when either volatiles or an atmosphere are required to explain the fluid like morphology of many martian ejecta deposits we consider the ejecta deposition process from when an ejecta curtain first strikes a target surface via ballistics and possibly flows thereafter a new finding is that either hard smooth surfaces or slightly erodible surfaces allow ejecta to flow readily as a granular medium neither volatiles nor an atmosphere are required to initiate flow a low friction coefficient between ejecta grains can also generate flow and would be analogous to adding volatiles to the ejecta the presence of either a rough or a densely packed erodible surface does not permit easy ejecta flow high friction coefficients between ejecta grain also prevent flow while changes in the coefficient of restitution a measure of how much energy is retained after collisions between particles plays a minor role in the flow dynamics of ejecta a hard smooth or a somewhat erodible surface could be generated by past fluvial activity on mars which can either indurate a surface erode and smooth a surface or generate sedimentary terrains that are fairly easy to erode no ramparts or layered ejecta morphologies are generated by our model but this may be because several simplifying assumptions are used in our model and should not be construed as proof that either volatiles or an atmosphere are required to form fluidized ejecta morphologies

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

scaling of ground motion parameters state of stress and focal depth the ground motion parametersrv and ra where r is hypocentral distance v is peak velocity is density and a is peak acceleration are found observationally to be strong functions of stress state and linearly related to focal depth z if the stress state and focal depth are properly taken into account then the ground motion parameters depend on the seismic moment m0 as expected from basic scaling principles that is rv m01 3 and ra is independent of earthquake size regression lines fitted to observations covering broad ranges in seismic moment and focal depth indicate that for extensional and compressional tectonic regimes corresponding to normal and thrust or reverse faulting earthquakes respectively peak acceleration is given by ra 1 08 mpa 3 06 mpa km z normal and ra 5 65 mpa 8 76 mpa km z thrust and for peak velocity rv m01 3 10 4 m2 s n m 1 3 3 00 0 69 km 1 z normal and rv m01 3 10 4 m2 s n m 1 3 4 63 1 82 km 1 z thrust for strike slip earthquakes the data currently are insufficient to define regression fits but such lines would definitely lie between those for the normal and thrust stress regimes these equations are appropriate for ground motion at small hypocentral distance as recorded in a whole space it follows that for comparable hypocentral depth peak acceleration in a compressional tectonic regime for example much of the eastern united states is a factor of about 3 greater than in an extensional regime such as nevada and for peak velocity a similar comparison yields a factor of 2 difference the similarity in behavior of the peak acceleration parameter to crustal strength estimated from byerlee s law of friction with respect to depth and stress state indicates that crustal strength is probably the factor governing the seismic source processes that give rise to the high frequency peak ground motion analysis of the peak acceleration data in the context of crustal strength suggests bounds on this ground motion parameter as recorded at a typical surface site that depend on stress state specifically a normal 0 5 g and a thrust 1 9 g thus the state of stress as well as the focal depth clearly is an important factor to be taken into account in the prediction of seismic ground motion

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

variations in the onset diameter for martian layered ejecta morphologies and their implications for subsurface volatile reservoirs we investigated regional variations in the onset diameter of craters displaying a single layer ejecta morphology within 30 latitude using viking imagery our results generally agree with those of previous studies which show onset diameters of 5 to 6 km in the equatorial region but we have identified localized regions with unusually small onset diameters the largest region is located in solis and thaumasia planae the 3 5 km onset diameter range in this area indicates a near surface ice rich reservoir depth 110 m this unusual concentration of near surface ice may have resulted from magmatic driven uplifts associated with the tharsis rise which modified parts of a regional aquifer drainage basin system and resulted in the transfer and concentration of subsurface volatiles in this region

evidence for magma carbonate interaction beneath syrtis major mars 1 we used three methods spectral index mapping linear spectral mixture analysis and factor analysis and target transformation to determine if carbonate decomposition products including lime cao periclase mgo portlandite ca oh 2 and brucite mg oh 2 are present on the surface of mars using an expanded spectral library that includes decomposition products of calcite and magnesite we deconvolved a binned emissivity data set from the mars global surveyor thermal emission spectrometer mgs tes the deconvolution model indicates that anhydrous carbonates are not present at kilometer scales above the tes detection limit however carbonate decomposition products may be present at or above the tes detection limit in northeast syrtis major and several other small regions on mars the model results are supported by spectral index mapping and factor analysis and target transformation of tes data in this region the volcanic setting of the detections may indicate the interaction of syrtis major lavas with subsurface carbonates or alternatively the eruption of carbonate bearing lavas that were subsequently devolatilized by impacts or later lava flows

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

a new global database of mars impact craters 1 km 1 database creation properties and parameters 1 impact craters have been used as a standard metric for a plethora of planetary applications for many decades including age dating geologic mapping and stratigraphic relationships as tracers for surface processes and as locations for sampling lower crust and upper mantle material utilizing craters for these and other investigations is significantly aided by a uniform catalog of craters across the surface of interest consequently catalogs of craters have been developed for decades for the moon and other planets we present a new global catalog of martian craters statistically complete to diameters d 1 km it contains 384 343 craters and for each crater it lists detailed positional interior morphologic ejecta morphologic and morphometric data and modification state information if it could be determined in this paper we detail how the database was created the different fields assigned and statistical uncertainties and checks in our companion paper robbins and hynek 2012 we discuss the first broad science applications and results of this work

combinations of processes responsible for martian impact crater layered ejecta structures emplacement 1 we utilized images and stereo derived topographic data acquired by the high resolution stereo camera hrsc and thermal emission imaging system themis images together with other data in order to study the geology of layered ejecta structures associated with relatively pristine martian impact craters the geomorphology and morphometric properties indicate their origin as complex combinations of a variety of impact processes the studied inner layered ejecta structures often exhibit ground hugging characteristics and many of them do not have topographic profiles expected from simple ballistic emplacement such profiles include ones that are plateau shaped or thickening outward we think that water rich fluidized flows driven by the momentum due to the impact and by gravity together with ballistic emplacement and vortex produced by the atmosphere ejecta curtain interaction were essential to the inner layered ejecta structure formation we hypothesize that the thinner outer layered ejecta structures were formed by various combinations of shockwave induced liquefaction of water rich near surface sediments ballistic emplacement of ejecta entraining water and strong winds expanding vapor vortex base surge related to the impact the contribution of each proposed layered ejecta structure formation mechanism should have been variable depending on the condition of the impact

deep impact craters in the isidis and southwestern utopia planitia regions of mars high target material strength as a possible cause using themis moc and mola data we havefound 51 craters in the diameter range 6 11 8 km withinsouthwestern utopia planitia and isidis planitia that aresignificantly deeper than typical fresh craters in the northernlowlands of mars the restricted geographic distribution ofthese craters their simple morphology and data fromimpact and explosion crater studies suggest that unusuallystrong target materials as much as a factor of 2 greater thanaverage materials in the martian lowlands are the cause ofthe excessive crater depth we propose that the greater targetmaterial strength acts to delay gravity dominated collapse tolarger crater sizes furthermore we suggest that a regional olivine rich mafic to untramafic rock unit identified by tesand themis is a reasonable candidate for these strongmaterials the unit is exposed on the southern edge of isidisbasin and in crater ejecta within the basin and forms layersthat dip toward the isidis basin center

ancient oceans in the northern lowlands of mars evidence from impact crater depth diameter relationships 1 we present depth d and diameter d data for 2269 martian impact craters in the diameter range 6 216 km distributed over 11 52 106 km2 of terrain that samples several geologic settings and the full range of latitudes and elevations throughout the northern lowlands of mars our data indicate that there are three major crater types that fall into two major populations those craters that contain vastitis borealis formation vbf and those that do not the deepest type 1 craters comprise a late hesperian early amazonian age population that does not contain vbf type 2 type 3 and subdued type 1 craters comprise a population of hesperian age craters partially buried by the vbf the unique d d distribution of type 3 craters and photogeologic evidence suggest an erosional style for the vbf that requires sublimation processes indicating that the vbf contained a substantial amount of ice type 3 craters occur throughout the northern lowland plains at elevations below 2400 m if the vbf is a sedimentary deposit left by a large body of standing water in the northern lowlands of mars then the northern lowland plains contained a body of water with a volume of 6 107 km3 or the equivalent of a 430 m global ocean during the late hesperian early amazonian this also implies that the vbf contains 4 106 km3 of material in agreement with the estimated amount of material eroded from the outflow channels surrounding chryse basin and washed into the northern lowlands

initiation of run out flows on venus by oblique impacts abstract a hypervelocity oblique impact results in a downrange moving vapor cloud a significant fraction of which is derived from the projectile since the vapor cloud expands to great extent and becomes very tenuous quickly on a planet with a thin or no atmosphere it does not leave a well defined geologic expression the thick atmosphere of venus however is sufficient to contain such a rapidly expanding vapor cloud as a result of atmospheric interactions impact vapor condenses and contributes to run out flows around craters on venus previous results of both laboratory experiments and simple semi analytical calculations indicate that an impact vapor origin can account for the morphology of run out flows on venus most consistently however the detailed dynamics and geologic record of downrange moving impact vapor clouds in venus s atmosphere are not understood quantitatively to approach these problems we carried out two dimensional hydrocode calculations parametric studies of these hydrocode calculations yield simple scaling laws for both the total downrange travel distance and the final temperature of impact vapor clouds under conditions on venus under typical impact conditions impact vapor clouds travel downrange more than a crater radius prior to the completion of crater formation furthermore the scaling law for the total travel distance is compared with observations for the downrange offset of the source regions of run out flows around oblique craters the results of this comparison suggest that energy momentum partitioning processes other than pure shock coupling may play important roles in hypervelocity impact at planetary scales the results of hydrocode calculations also indicate that the terminal temperature of the impact vapor is close to the condensation temperatures of silicates suggesting that two scenarios are possible for expected range of impact conditions 1 impact vapor condenses and forms run out flows 2 impact vapor fails to condense and leaves no run out flows consequently natural variation in impact angle velocity and projectile composition may account for partial occurrence of run out flows around impact craters on venus

firn densification in a late noachian icy highlands mars implications for ice sheet evolution and thermal response abstract recent modeling of a thicker early co2 martian atmosphere and late noachian climate predicts that for pressures beyond a fraction of a bar atmosphere surface thermal coupling occurs resulting in adiabatic cooling of high areas across mars this promotes the transport of water ice from relatively warmer low lying areas to the highlands where deposition and accumulation of water ice result in an icy highlands late noachian mars deposits will remain stable in the highlands under nominal late noachian conditions but the potential exists for punctuated heating by both top down e g impacts volcanism and bottom up e g elevated geothermal heat flux processes important in understanding melt generation from these processes is the state of the accumulated snow and ice through modeling of the firn densification process in the icy highlands framework we assess 1 the nature of snow accumulation and the physical growth and evolution of the predicted ice deposits and 2 the implications for the thermal properties of the ice sheets and the response to heating events analysis of the firn densification process in the icy highlands context indicates that 1 the upper layers of the ice sheet will be more vulnerable to melting from top down heating processes because they are comprised of the least dense and least thermally conductive ice and 2 even with a low thermal conductivity firn layer basal melting is only likely to occur through a combination of top down and bottom up heating this is because at the nominal mean annual surface temperatures and estimated effective thermal conductivities the predicted ice sheet thicknesses do not produce enough basal warming to initiate melting for plausible geothermal heat fluxes variations in spin axis orbital parameters alone are not predicted to cause widespread ablation melting and sublimation of the icy highlands ice sheets

the 1971 san fernando earthquake a double event evidence is presented which suggest that the 1971 san fernando earthquake may have been a double event that occurred on two separate subparallel thrust faults it is postulated that the initial event took place at depth on the sierra madre fault zone which runs along the base of the san gabriel mountains rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km a second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the sierra madre fault zone the surface trace of this fault coincides with the san fernando fault zone which was the principal fault associated with surface rupture it is postulated that rupture propagated from a depth of 8 km to the free surface the moments of the first and second events are approximately 0 7 10 26 dyne cm and 1 0 10 26 dyne cm respectively this model is found to explain the combined data sets of strong ground motions teleseismic p and s waveforms and static offsets better than previous models which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth nevertheless many features of the observed motions remain unexplained and considerable uncertainty still exists regarding the faulting history of the san fernando earthquake

a new global database of mars impact craters 1 km 2 global crater properties and regional variations of the simple to complex transition diameter 1 we have generated a new 384 343 entry global crater database of mars statistically complete for craters with diameters d 1 km in this release the database contains detailed morphologic and morphometric data for craters d 3 km future releases will extend these to smaller diameters with detailed topographic data for the largest crater database to date we analyzed crater depth to diameter ratios for simple and complex morphologies across various terrains and for the planet as a whole and investigated the simple to complex morphology transition our results are similar to those in the published literature but we found a substantial terrain dependence of the simple to complex transition that occurs at 11 km diameter craters at high latitudes this suggests a model that requires melting of volatiles during high latitude crater formation that fill the crater during the modification phase but will still support the simple morphology to larger diameters we also use this database to reexamine previously observed distributions and patterns to show its fidelity and to further explore other global relationships of fresh craters those with central peaks pits and summit pits we present the global distribution of craters with different types of ejecta and morphometric properties overall this database is shown to be comparable to previous databases where there is overlap and to be useful in extending prior work into new regimes

geometric properties of martian impact craters preliminary results from the mars orbiter laser altimeter the mars orbiter laser altimeter mola acquired high spatial and vertical resolution topographic data for 18 tracks across the northern hemisphere of mars during the fall of 1997 it sampled 98 minimally degraded impact craters between the latitudes of 80 n and 12 s the best fitting depth d versus diameter d power law relationship for these craters is d 0 14 d0 90 for simple varieties and d 0 25 d0 49 for complex structures the simple to complex transition diameter is 8 km 0 5 km the cross sectional shape of the crater cavities was determined by fitting a power function to each profile variation in the exponent n suggest the craters flatten with increasing diameter and impact energy the ejecta thickness is skewed suggesting that use of existing empirical expressions for the expected radial decay of ejecta thickness is inappropriate for mars in most cases

outwash plains and thermokarst on mars abstract the spatial distribution of different types of rampart craters on mars suggests a hemispheric asymmetry in the distribution of ground ice the northern plains especially major topographic depressions near the terminations of outflow channels have high percentages of rampart craters two of these basins acidalia and utopia planitiae received extraordinarily large amounts of water and sediment from the chryse and elysium outflow channels in both regions the analysis of high resolution viking pictures 12 m pixel indicates a concentration of kilometer scale depressions that are similar in size and form to thermokarstic features in yakutia siberia and parts of the arctic coastal plain of north america accordingly we infer that 1 utopia planitia and acidalia planitia may contain thick laterally continuous ice rich sedimentary deposits related to outflow channel forming floods and 2 these areas of mars may have experienced thermokarstic processes similar to modern thermokarstic processes in some periglacial regions of earth

martian perched craters and large ejecta volume evidence for episodes of deflation in the northern lowlands the northern lowland plains such as those found in acidalia and utopia planitia have high percentages of impact craters with fluidized ejecta in both regions the analysis of crater geometry from mars orbiter laser altimeter mola data has revealed large ejecta volumes some exceeding the volume of excavation moreover some of the crater cavities and fluidized ejecta blankets of these craters are topographically perched above the surrounding plains these perched craters are concentrated between 40 and 70 n in the northern plains the atypical high volumes of the ejecta and the perched craters suggest that the northern lowlands have experienced one or more episodes of resurfacing that involved deposition and erosion the removal of material most likely caused by the sublimation of ice in the materials and their subsequent erosion and transport by the wind is more rapid on the plains than on the ejecta blankets the thermal inertia difference between the ejecta and the surrounding plains suggests that ejecta characterized by a lower thermal inertia protect the underneath terrain from sublimation this results in a decreased elevation of the plains relative to the ejecta blankets sublimation and eolian erosion can be particularly high during periods of high obliquity

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

seven million years of strike slip and related off fault deformation northeastern marlborough fault system south island new zealand the marlborough fault system mfs south island new zealand is remarkable for the oblique slip nature of its active faulting and can be placed in a framework of pacific australian pac aus plate motions and geodetic strain new zealand illustrates changing degrees of upper plate slip partitioning in an obliquely convergent margin that varies along strike in crustal type and subduction geometry in this paper we focus on the ne part of this transcurrent fault system especially the awatere fault which is the only marlborough fault to offset a major neogene basin strike slip on an ancestral eastern strand of this fault began after 7 4 6 4 ma later vertical axis rotation may have caused it to be abandoned in favor of the currently active strand since 7 ma at least 34 10 km of dextral slip has accrued on the awatere fault 6 km of slip has accrued on two nearby strands and 4 km has accrued on the currently active coastal strand comparison of miocene with late quaternary offsets suggests that rates of strike slip on the fault have been nearly constant or have possibly decelerated we interpret spatial and temporal patterns of strike slip in the mfs to reflect southward migration of transform motion resulting from increased pac aus plate convergence late neogene to present day shortening directions in ne south island are indicative of a partially slip partitioned margin slip partitioning diminishes southward as the underlying subduction interface becomes strongly coupled suggesting a simple mechanical relationship between these processes

orbital identification of carbonate bearing rocks on mars geochemical models for mars predict carbonate formation during aqueous alteration carbonate bearing rocks had not previously been detected on mars surface but mars reconnaissance orbiter mapping reveals a regional rock layer with near infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the nili fossae region the carbonate is closely associated with both phyllosilicate bearing and olivine rich rock units and probably formed during the noachian or early hesperian era from the alteration of olivine by either hydrothermal fluids or near surface water the presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering proposed to be characteristic of hesperian mars did not destroy these carbonates and thus did not dominate all aqueous environments

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

north polar region craterforms on mars geometric characteristics from the mars orbiter laser altimeter abstract this study focuses on topographic characterization of ice associated north polar region impact craters and several enigmatic polar craterforms using new information from the mars orbiter laser altimeter mola an instrument aboard the mars global surveyor mgs orbiter we find that for ice associated craters the topography reveals several surprising results not previously apparent from orbital images alone first geometric properties for several impact craters associated with ice and frost deposits suggest that cavity infill is as high as 80 of reconstructed preerosion levels second craters associated with ice also demonstrate unique cavity geometries relative to their nonpolar counterparts finally in some cases ice associated impact features are anomalously deep on the basis of depths modeled from the best available scaling laws we suggest that burial of these impact features by either episodic advance of the polar cap margin or by continuous deposition at the highest rates previously estimated for the north polar region of mars has occurred subsequent stripping has exhumed the features leaving behind cavity infill deposits and a few of these display topographic levels above the surrounding preimpact surface in at least one case cavity interior deposits show layering with a typical thickness of 10 m suggesting episodic deposition and ablation of materials as in the polar layered terrain in addition to ice associated craters we investigated the topography of several enigmatic polar craterforms in particular a few craterforms within 150 km of the permanent north polar cap appear to resemble simple effusive lava shield volcanoes found on earth their geometric properties cannot be reconciled with previous suggestions that they were manifestations of martian hydromagmatic processes i e maar volcanism mola s initial measurements of impact craters and other craterforms in the north polar latitudes of mars support the concept of a geologically recent surface with evidence of effusive volcanism and enhanced sedimentation in addition the measured impact crater depths for ice associated craters suggest at least a few cases of enhanced excavation and thus a possibly weaker target relative to the typical northern hemisphere plains

latitude dependence of martian pedestal craters evidence for a sublimation driven formation mechanism we report on the results of a survey to document and characterize pedestal craters on mars equatorward of similar to 60 degrees n and 65 degrees s latitude the identification of 2696 pedestal craters reveals a strong latitude dependence with the vast majority found poleward of 33 degrees n and 40 degrees s this latitudinal extent is correlated with many climate indicators consistent with the presence of an ice rich substrate and with climate model predictions of where ice is deposited during periods of higher obliquity in the amazonian we have measured key physical attributes of pedestal craters including the farthest radial extents of the pedestals pedestal heights and the circularity of the pedestal margins in conjunction with the geographic distribution our measurements strongly support a sublimation related formation mechanism this is in contrast to previous hypotheses which have relied on eolian deflation to produce the elevated plateaus the identification of marginal pits on the scarps of some pedestal craters interpreted to be sublimation pits provide direct evidence for the presence of ice rich material underlying the armored surface of pedestal craters on the basis of our findings we propose a formation mechanism whereby projectiles impact into a volatile rich dust snow ice substrate tens to hundreds of meters thick overlying a dominantly fragmental silicate regolith the area surrounding the resulting crater becomes armored pedestals extend to a distance of multiple crater radii farther than typical ejecta deposits necessitating an armoring mechanism that is capable of indurating the surface to a distance greater than the reach of the ejecta return to low obliquity causes sublimation of the volatile rich layer from the intercrater plains lowering the elevation of the regional terrain this yields generally circular pedestal craters elevated above the surrounding plains as a result the armored surfaces of pedestal craters have preserved a significant record of amazonian climate history in the form of ice rich deposits

low angle collision with earth the elliptical impact crater matt wilson northern territory australia nearly all meteorite impact craters on earth are circular however 4 of craters should be formed by impacts at angles lower than 12 from the horizontal which should result in elongated crater structures the crater forming process that produces elliptical shapes is poorly understood we document the first elliptical crater on earth that contains a central uplift and that provides insights into the mechanisms of crater formation at a critical threshold angle of 10 15 the dimensions of the proterozoic matt wilson impact structure northern territory australia are 7 5 by 6 3 km corresponding to an aspect ratio of 1 2 with its long axis trending northeast southwest the exposed crater floor shows a preferred stacking of thrust sheets within the central uplift and in the surrounding syncline indicating northeast southwest shortening and a material transport top to the sw this is consistent with an up range to down range motion of rock caused by remnant horizontal momentum transferred from the impacting projectile to the target this preferential deformation interferes with a radially oriented convergent material flow characteristic for crater collapse the matt wilson crater provides evidence for the usefulness of structural asymmetries as a diagnostic tool to infer impact vectors the new impact crater is confirmed by the presence of planar deformation features planar fractures in quartz grains and its structural inventory

hydrous minerals on mars as seen by the crism and omega imaging spectrometers updated global view 1 the surface of mars has preserved the record of early environments in which its basaltic crust was altered by liquid water these aqueous environments have survived in the form of hydrological morphologies and alteration minerals including clays and hydrated salts because these minerals probe on earth aqueous environments compatible with biotic activity understanding their formation processes on mars is of great exobiological relevance and also offers insight into earth s now erased ancient water environments using remote sensing we conducted a large scale investigation of the distribution composition age and geomorphic settings of hydrous minerals on mars providing a sharpened global view of the early aqueous environments and their evolution with time aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on mars 4 gyr however very diverse aqueous environments have also been found which suggest widespread complex aqueous settings from the surface to kilometric depths and spanning over 1 gyr by building a robust statistical sample of detections the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on mars and provide context for more localized in depth analyses collectively these trends suggest that at least transient conditions have existed on mars which may have been favorable for pre biotic to biotic activity

mosaicking of global planetary image datasets 1 techniques and data processing for thermal emission imaging system themis multi spectral data 1 the mosaicking of global planetary data sets allows for the examination of local regional and global scale processes on all planetary bodies processing techniques that allow us and other users to crate mosaics of tens of thousands of images are documented along with the associated errors introduced by each image processing algorithm these techniques e g non uniformity correction running contrast stretches line and row correlated noise removal and random noise removal were originally developed for the 2001 mars odyssey thermal emission imaging system themis infrared multispectral imager data but can be adapted and applied to other data sets by the alteration of input parameters the techniques for mosaicking planetary image data sets e g image registration blending and normalization are also presented along with the generation of qualitative and quantitative products these techniques are then applied to generate themis daytime and nighttime infrared viking context imager ctx and mars orbiter camera moc visible mosaics using a variety of input and output types at a variety of scales by creating mosaics of the same area using different data sets such as those that illustrate compositional diversity thermophysical properties or small scale morphology it is possible to view the surface of the planet and geologic problems through many different perspectives in addition to the techniques used to create large scale seamless mosaics we also present the themis daytime and nighttime relative temperature global mosaics which are the highest resolution 100m pixel global scale data sets available for mars to date

the slip history of the 1994 northridge california earthquake determined from strong motion teleseismic gps and leveling data we present a rupture model of the northridge earthquake determined from the joint inversion of near source strong ground motion recordings p and sh teleseismic body waves global positioning system gps displacement vectors and permanent uplift measured along leveling lines the fault is defined to strike 122 and dip 40 to the south southwest the average rake vector is determined to be 101 and average slip is 1 3 m the peak slip reaches about 3 m our estimate of the seismic moment is 1 3 0 2 10 26 dyne cm potency of 0 4 km3 the rupture area is small relative to the overall aftershock dimensions and is approximately 15 km along strike nearly 20 km in the dip direction and there is no indication of slip shallower than about 5 to 6 km the up dip strong motion velocity waveforms are dominated by large s wave pulses attributed to source directivity and are comprised of at least 2 to 3 distinct arrivals a few seconds apart stations at southern azimuths indicate two main s wave arrivals separated longer in time about 4 to 5 sec these observations are best modeled with a complex distribution of subevents the initial s wave arrival comes from an asperity that begins at the hypocenter and extends up dip and to the north where a second larger subevent is centered about 12 km away the secondary s arrivals at southern azimuths are best fit with additional energy radiation from another high slip region at a depth of 19 km 8 km west of the hypocenter the resolving power of the individual data sets is examined by predicting the geodetic gps and leveling displacements with the dislocation model determined from the waveform data and vice versa and also by analyzing how well the teleseismic solution predicts the recorded strong motions the general features of the geodetic displacements are not well predicted from the model determined independently from the strong motion data likewise the slip model determined from geodetic data does not adequately reproduce the strong motion characteristics whereas a particularly smooth slip pattern is sufficient to satisfy the geodetic data the strong motion and teleseismic data require a more heterogeneous slip distribution in order to reproduce the velocity amplitudes and frequency content although the teleseismic model can adequately reproduce the overall amplitude and frequency content of the strong motion velocity recordings it does a poor job of predicting the geodetic data consequently a robust representation of the slip history and heterogeneity requires a combined analysis of these data sets

martian low aspect ratio layered ejecta larle craters distribution characteristics and relationship to pedestal craters abstract low aspect ratio layered ejecta larle craters are a unique landform found on mars larle craters are characterized by a crater and normal layered ejecta pattern surrounded by an extensive but thin outer deposit which terminates in a sinuous almost flame like morphology we have conducted a survey to identify all larle craters 1 km diameter within the 75 latitude zone and to determine their morphologic and morphometric characteristics the survey reveals 140 larle craters with the majority 91 located poleward of 40 s and 35 n and all occurring within thick mantles of fine grained deposits which are likely ice rich larle craters range in diameter from the cut off limit of 1 km up to 12 2 km with 83 being smaller than 5 km the radius of the outer larle deposit displays a linear trend with the crater radius and is greatest at higher polar latitudes the larle deposit ranges in length between 2 56 and 14 81 crater radii in average extent with maximum length extending up to 21 4 crater radii the larle layer is very sinuous with lobateness values ranging between 1 45 and 4 35 larle craters display a number of characteristics in common with pedestal craters and we propose that pedestal craters are eroded versions of larle craters the distribution and characteristics of the larle craters lead us to propose that impact excavation into ice rich fine grained deposits produces a dusty base surge cloud like those produced by explosion craters that deposits dust and ice particles to create the larle layers salts emplaced by upward migration of water through the larle deposit produce a surficial duricrust layer which protects the deposit from immediate removal by eolian processes

the effects of water vaporization on rock fragmentation during rapid decompression implications for the formation of fluidized ejecta on mars abstract crater and ejecta morphology provide insight into the composition and structure of the target material fluidized ejecta surrounding martian rampart craters are thought to result from the addition of water to the ejecta during impact into a water rich ice or liquid regolith here we test experimentally an alternate hypothesis we propose that the decompression of a rock water mixture across the water vaporization curve during the excavation stage of impact cratering results in an increased proportion of fines in the ejecta this enables the ejecta to flow with little or no liquid water present to test this hypothesis fragmentation experiments were conducted on sandstone 28 vol open porosity from the northern eldorado mountains nevada using a shock tube apparatus at the lmu munich germany rock samples with 0 92 of their open pore space filled with water were pressurized to 15 mpa at 177 c or 300 c and rapidly decompressed as the water vaporization curve is crossed the water in the pore space rapidly flashes to steam causing together with the expanding gas in the water free pore space the sample to fragment the presence of water has a significant effect on the grain size distribution and grain shape of the fragmented rock samples in comparison with dry control samples samples with water with 15 50 open pore space exhibit much smaller grain sizes the predominant grain shape of dry as well as partially water saturated samples is bladed reflecting fracturing parallel to the decompression front samples with 80 water in open pore space had an increase in fines and larger particles but less intermediate sized particles fragments from experiments with 80 water in open pore space also displayed a more equant grain shape indicating that the decompression of water caused fracturing independent of the orientation of the decompression front these results may provide insight into the morphology of martian rampart craters we propose here that even relatively low water contents in the target 16 may be sufficient to produce a significant increased proportion of fines allowing the ejecta to flow with little or no water present

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

formation of glaciers on mars by atmospheric precipitation at high obliquity surface conditions on mars are currently cold and dry with water ice unstable on the surface except near the poles however geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of mars the ice has been proposed to originate from either a subsurface reservoir or the atmosphere we present high resolution climate simulations performed with a model designed to simulate the present day mars water cycle but assuming a 45 obliquity as experienced by mars a few million years ago the model predicts ice accumulation in regions where glacier landforms are observed on the western flanks of the great volcanoes and in the eastern hellas region this agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on mars

martian impact craters correlations of ejecta and interior morphologies with diameter latitude and terrain abstract the premise of this study is that global analysis of crater morphologies can discriminate between the effects of impact energy atmosphere and subsurface volatiles based on the correlation between morphology and latitude diameter and terrain this study focuses on seven ejecta and nine interior morphologies associated with 3819 craters 8 km in diameter distributed across the entire martian surface this data set is sufficiently large to provide statistically viable results on a global scale the results of the analyses indicate that changes in ejecta and interior morphology correlate with increases in crater diameter excavation depths corresponding to these diameters are calculated from depth diameter relationships and are compared to the theoretical distribution of subsurface volatiles the different ejecta morphologies can be described by impact into material with varying proportions of volatiles and the latidudinal variations seen for rampart crater morphologies correlate well with the proposed latitude depth relationship for ice and brines across the planet many of the interior structres show distributions indicative of terrain dependent influences for example the concentrations of central pit craters around ancient impact basins and on alba patera suggest that volatiles preferentially collect in these areas however central peak and peak ring interior morphologies show little relationship to planetary properties and probably result from changes in impact energy thus many of the unique morphologies associated with martian impact craters result from the presence of subsurface volatiles

rupture and ground motion models on the northern san jacinto fault incorporating realistic complexity we use the 3d finite element method to conduct dynamic models of rupture and resulting ground motion on the claremont casa loma stepover of the northern san jacinto fault we incorporate complex fault geometry from the u s geological survey usgs quaternary faults database see data and resources 1 a realistic velocity structure the southern california earthquake center community velocity model s a realistic regional stress field with an orientation taken from seismicity relocation literature and several stochastic self similar shear stress distributions as we incorporate more types of complexity the specific effects of any individual factor become less apparent within the overall rupture behavior we also find that the distribution of high and low shear stress that arises from combining regional and stochastic stress fields has the strongest control over where the rupture terminates using a regional stress field alone as well as with the combined regional and stochastic stress realization we find that the stepover presents a significant barrier to rupture regardless of our choice of initial nucleation point and that it is difficult for rupture to propagate the full length of either fault segment greater heterogeneity of stresses tends to produce shorter ruptures within this result we find that the claremont strand is more favorable for long ruptures than the casa loma clark strand low frequency ground motion intensity and distribution are controlled largely by the velocity structure rather than by stress heterogeneity the strongest motions produced in these models are in the san bernardino basin although directivity effects do contribute to the low frequency ground motion distribution particularly in the near field they are secondary to the effects of the velocity structure online material figures of ground motions from models used to calibrate the stress conditions for dynamic rupture propagation 1 sec 18

martian subsurface volatile concentrations as a function of time clues from layered ejecta craters 1 martian layered ejecta morphologies are characterized using a new preservation classification system and through measurement of ejecta mobility em ratios em the ratio of ejecta extent to crater radius is believed to provide information about ejecta material fluidity during emplacement this study compares em and preservation classification to determine if subsurface volatile concentrations have changed measurably over time results from both regional and local analyses suggest that concentrations of subsurface volatiles have remained approximately constant at the depths and over the time periods recorded by these craters

on near source earthquake triggering 1 when one earthquake triggers others nearby what connects them two processes are observed static stress change from fault offset and dynamic stress changes from passing seismic waves in the near source region r 50 km for m 5 sources both processes may be operating and since both mechanisms are expected to raise earthquake rates it is difficult to isolate them we thus compare explosions with earthquakes because only earthquakes cause significant static stress changes we find that large explosions at the nevada test site do not trigger earthquakes at rates comparable to similar magnitude earthquakes surface waves are associated with regional and long range dynamic triggering but we note that surface waves with low enough frequency to penetrate to depths where most aftershocks of the 1992 m 5 7 little skull mountain main shock occurred 12 km would not have developed significant amplitude within a 50 km radius we therefore focus on the best candidate phases to cause local dynamic triggering direct waves that pass through observed near source aftershock clusters we examine these phases which arrived at the nearest 200 270 km broadband station before the surface wave train and could thus be isolated for study direct comparison of spectral amplitudes of presurface wave arrivals shows that m 5 explosions and earthquakes deliver the same peak dynamic stresses into the near source crust we conclude that a static stress change model can readily explain observed aftershock patterns whereas it is difficult to attribute near source triggering to a dynamic process because of the dearth of aftershocks near large explosions

rupture dynamics and ground motion from 3 d rough fault simulations 1 we perform three dimensional 3 d numerical calculations of dynamic rupture along non planar faults to study the effects of fault roughness on rupture propagation and resultant ground motion the fault roughness model follows a self similar fractal distribution over length scales spanning three orders of magnitude from 102 to 105 m the fault is governed by a strongly rate weakening friction and the bulk material is subject to drucker prager viscoplasticity fault roughness promotes the development of self healing rupture pulses and a heterogeneous distribution of fault slip at the free surface and at depth the inelastic deformation generated by the large dynamic stress near rupture fronts occurs in a narrow volume around the fault with heterogeneous thickness correlated to local roughness slopes inelastic deformation near the free surface however is induced by the stress waves originated from dynamic rupture at depth and spreads to large distances 10 km away from the fault the present simulations model seismic wave excitation up to 10 hz with rupture lengths of 100 km permitting comparisons with empirical studies of ground motion intensity measures of engineering interest characteristics of site averaged synthetic response spectra including the distance and period dependence of the median values absolute level and intra event standard deviation are comparable to appropriate empirical estimates throughout the period range 0 1 3 0 s this class of model may provide a viable representation of the ground motion excitation process over a wide frequency range in a large spatial domain with potential applications to the numerical prediction of source and path specific effects on earthquake ground motion

preservation of late amazonian mars ice and water related deposits in a unique crater environment in noachis terra age relationships between lobate debris tongues and gullies abstract the amazonian period of mars has been described as static cold and dry recent analysis of high resolution imagery of equatorial and mid latitude regions has revealed an array of young landforms produced in association with ice and liquid water because near surface ice in these regions is currently unstable these ice and water related landforms suggest one or more episodes of martian climate change during the amazonian here we report on the origin and evolution of valley systems within a degraded crater in noachis terra asimov crater the valleys have produced a unique environment in which to study the geomorphic signals of amazonian climate change new high resolution images reveal hesperian aged layered basalt with distinctive columnar jointing capping interior crater fill and providing debris via mass wasting for the surrounding annular valleys the occurrence of steep slopes 20 relatively narrow sheltered valleys and a source of debris have provided favorable conditions for the preservation of shallow ice deposits detailed mapping reveals morphological evidence for viscous ice flow in the form of several lobate debris tongues ldt superimposed on ldt are a series of fresh appearing gullies with typical alcove channel and fan morphologies the shift from ice rich viscous flow formation to gully erosion is best explained as a shift in martian climate from one compatible with excess snowfall and flow of ice rich deposits to one consistent with minor snow and gully formation available dating suggests that the climate transition occurred 8 ma prior to the formation of other small scale ice rich flow features identified elsewhere on mars that have been interpreted to have formed during the most recent phases of high obliquity taken together these older deposits suggest that multiple climatic shifts have occurred over the last tens of millions of years of martian history

impact craters in the northern hemisphere of mars layered ejecta and central pit characteristics mars global surveyor mgs and mars odyssey data are being used to revise the catalog of large martian impact craters analysis of data in the revised catalog provides new details on the distribution and morphologic details of 6795 impact craters in the northern hemisphere of mars this report focuses on the ejecta morphologies and central pit characteristics of these craters the results indicate that single layer ejecta sle morphology is most consistent with impact into an ice rich target double layer ejecta dle and multiple layer ejecta mle craters also likely form in volatile rich materials but the interaction of the ejecta curtain and target produced vapor with the thin martian atmosphere may be responsible for the large runout distances of these ejecta pancake craters appear to be a modified form of double layer craters where the thin outer layer has been destroyed or is unobservable at present resolutions pedestal craters are proposed to form in an ice rich mantle deposited during high obliquity periods from which the ice has subsequently sublimated central pits likely form by the release of vapor produced by impact into ice soil mixed targets therefore results from the present study are consistent with target volatiles playing a dominant role in the formation of crater morphologies found in the martian northern hemisphere

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties

displacement and geometrical characteristics of earthquake surface ruptures issues and implications for seismic hazard analysis and the process of earthquake rupture there now exist about three dozen historical earthquakes for which in vestigators have constructed maps of earthquake rupture traces accompanied by de scriptions of the coseismic slip observed along the fault strike the maps and slip distributions are compiled here to place observational bounds on aspects of seismic hazard analysis and fault mechanics analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults the observations also give support to the ideas that there exists a process zone or volume of about 3 4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes to this may be added the observation that the form of earthquake surface slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike online material maps of surface ruptures digitized values and curve fits to surface slip distributions and notes and references for tables 1 and 2

aftershock triggering by complete coulomb stress changes 1 we examine the correlation between seismicity rate change following the 1992 m7 3 landers california earthquake and characteristics of the complete coulomb failure stress cfs changes cfs t that this earthquake generated at close distances the time varying dynamic portion of the stress change depends on how the rupture develops temporally and spatially and arises from radiated seismic waves and from permanent coseismic fault displacement the permanent static portion cfs depends only on the final coseismic displacement cfs diminishes much more rapidly with distance than the transient dynamic stress changes a common interpretation of the strong correlation between cfs and aftershocks is that load changes can advance or delay failure stress changes may also promote failure by physically altering properties of the fault or its environs because it is transient cfs t can alter the failure rate only by the latter means we calculate both cfs and the maximum positive value of cfs t peak cfs t using a reflectivity program input parameters are constrained by modeling landers displacement seismograms we quantify the correlation between maps of seismicity rate changes and maps of modeled cfs and peak cfs t and find agreement for both models however rupture directivity which does not affect cfs creates larger peak cfs t values northwest of the main shock this asymmetry is also observed in seismicity rate changes but not in cfs this result implies that dynamic stress changes are as effective as static stress changes in triggering aftershocks and may trigger earthquakes long after the waves have passed