the simud tiu valles hydrologic system a multidisciplinary study of a possible site for future mars on site exploration abstract when looking for traces of past life on mars we have to look primarily for places where water was present possibly for long time intervals the simud and tiu valles are two large outflow channels connected to the north with the chryse basin oxia palus quadrangle the area carved by water during the noachian early hesperian is characterized by a complex geological evolution the geomorphological analysis shows the presence of fluvial and alluvial structures interpreted as fluvial channels and terraces debris flow fronts and short lasting small water flows coexisting with maar diatremes and mud volcanoes several morphological features indicate a change in water flux direction after the main erosive phase during this period water originated from the masursky crater and flown southwards into the hydraotes chaos this phenomenon caused the studied area to become a depocenter where fine grained material deposition took place possibly in association with ponding water this setting is potentially quite valuable as traces of life may have been preserved the presence of water at various times over a period of about 1 ga in the area is corroborated by mineralogical analyses of different areas that indicate the possible presence of hydrated minerals mixtures such as sulfate bearing deposits given the uniqueness of the evolution of this region the long term interactions between fluvial volcanic and tectonic processes and its extremely favorable landing parameters elevation slope roughness rock distribution thermal inertia albedo etc we decided to propose this location as a possible landing site for the esa exomars 2018 the nasa mars 2020 and future on site missions

broad band deconvolution of gdsn data summary advances in the theory of wave propagation and source mechanism have coincided with the recent deployment of a global network of digitally recording seismographs the gdsn global digital seismograph network we demonstrate that broad band records of body wave ground displacement and velocity with spectral information from several hertz to tens of seconds can be obtained by the simultaneous deconvolution of the long and short period components of the gdsn seismographs frequency dependent effects in body waves that may arise from source complexity or from propagation through the earth are much more apparent and measurable in the broad band records than in the original seismograms

evolution and depositional environments of the eberswalde fan delta mars the eberswalde crater and its contributing basins have been analyzed in detail in order to reconstruct the geological evolution of the water related landforms with particular focus on the eberswalde delta like feature based on a complex strata organization characterized by a topset foreset bottomset geometry typical of delta progradation on earth we interpret the eberswalde feature to be a fan delta associated with a lacustrine system depositional sub environments have been recognized and mapped and the sedimentary processes discussed a sequence stratigraphy approach has been used to evaluate the system which we interpret to result from three depositional sequences these sequences suggest relative water level fluctuations and a longer trend over time towards decreasing water content inside the basin

complex evolution of paleolacustrine systems on mars an example from the holden crater 1 the 150 km wide holden crater lies in an area characterized by high density of valley networks implying conditions conducive to forming of water related environments we undertook geological mapping and a stratigraphic survey in order to probe the evolution of water related landforms and their paleoenvironmental implications our investigations lead us to propose that the holden area was subjected to a wet lacustrine phase of hesperian age and an icy phase during the amazonian deltaic coastal and lacustrine environments occurred during the wet phase some displaying a cyclic depositional pattern presumably related to autogenic processes water was delivered to the basin by the uzboi vallis and by surface runoff channels from a series of drainage basins along the crater walls fan delta geometries and coastal onlap enabled estimation of major water levels two levels of major stand of the water have been recognized possibly reflecting allogenic controls geologic units related to this wet lacustrine phase were subsequently eroded by glacial abrasion and plucking and were disconformably overlain by glacial deposits of amazonian age defining an icy phase these features are consistent with a warm based glacier entering the holden crater through the wide uzboi vallis to form a proglacial lake in the central part of the crater changes in sedimentary units reflect changes of depositional environments probably connected with climatic variation

geometry and mechanism of faulting of the 1980 el asnam algeria earthquake from inversion of teleseismic body waves and comparison with field observations the el asnam earthquake of october 10 1980 ms 7 3 provided a wealth of geological and seismological data and is an ideal event for comparing geologically and seismologically derived models the event produced extensive surface faulting in addition to the main tectonic deformation which is clearly a thrust widespread secondary normal faulting was observed at the surface in the southwest region the surface break of a thrust fault could be traced for 24 km in the northeast part of the fault zone normal faults with throws of several meters were observed although no clear thrust type surface breaks were observed in this region geodetic measurements and aftershocks indicate that thrusting was nonetheless the main tectonic mode of deformation in this paper the rupture process of the el asnam earthquake is investigated by inversion of teleseismic p and sh waves the effort is concentrated on the late part of the waveforms which carries information about the faulting in the least understood north eastern segment of the fault zone during the earthquake rupture initiated at the southern terminus of the southwestern fault segment and propagated northward as indicated by the epicentral location and the observable azimuthal directivity of the body wave shapes and amplitudes the seismogenic faulting in the southwestern segment has a thrust mechanism with the following average parameters seismic moment 3 9 1019 n m depth 6 km strike 220 dip 46 and rake 72 the duration of rupture on this fault segment was approximately 10 s which together with the observed fault length of 24 km indicates a rupture velocity of 2 4 km s unconstrained inversions suggest normal faulting in the northeast part of the source region that began immediately following the arrival of the rupture to the northeast region the normal faulting mechanism is in agreement with that observed for the large surface fault scarps in this region guided by the evidence from aftershocks and geodetic measurements a solution with a thrust type mechanism was also sought using a priori constraints based on the field observations the observed strike and slip angle we obtain the following thrust source mechanism for the northeast segment seismic moment 3 6 1019 n m depth 6 km strike 230 dip 20 and rake 91 this solution requires that the thrusting in the northeast be initiated 10 s after the arrival of the rupture from the southwest suggesting that some time is required to overcome the geometric barrier marked by the abrupt change in the dip and azimuth inversions are nonunique with respect to the seismic moment associated with normal faulting the ambiguity being caused by the limited bandwidth of the observed body waves the moment estimated from the surface waves at periods about 300 s however favors thrust faulting to be dominant in the northeast region

spade a rock crushing and sample handling system developed for mars missions 1 a novel system has been developed to access and analyze the interior of rocks on mars by crushing rocks a miniature rock crusher has been prototyped along with a method for distribution of the fines and fragments produced by the rock crusher to inspection and analysis instruments the science goals and advantages of this approach are substantial with respect to understanding the geologic and climate history of mars via the investigation of its mineralogy and petrology the system is described in detail and results of various performance metrics are reported engineering considerations constraints on functionality fault tolerance and its previously planned deployment on the 2009 mars science laboratory mission are described

nature and hydrological relevance of the shalbatana complex underground cavernous system 1 the geomorphology of the north east trending long fractured depression between the ganges chasma and the shalbatana vallis headwater source region is examined and interpreted to be the result of collapse of part of an extensive underground cavernous system we propose that this cavernous system undermines at least a valley which extends from the vicinities of the ganges chasma and terminates in the shalbatana vallis headwater source region and the aromatum chaos we believe that the origin of this cavernous system was related to the formation and interconnection of discrete cavernous bodies and propose a hypothesis which involves the interaction of permafrost and intrusive magmatism to explain their formation the shalbatana vallis headwater source is interpreted as produced by a noachian impact crater and surface collapse over part of the underground cavernous system finally we propose that the water sources which were involved in the excavation of the shalbatana and ravis outflow channels might have included water segregated from the permafrost through interaction of intrusive magmatism and permafrost water drained from a paleolake in the ganges chasma and water released from the catastrophic evacuation of confined aquifers

positive identification of lake strandlines in shalbatana vallis mars 1 remote sensing studies of possible martian paleolakes have hinted at the presence of paleoshorelines on mars although have never been unequivocally identified recently acquired sub meter scale high resolution imaging science experiment hirise images of shalbatana vallis reveal the first direct evidence of strandlines along a delta formed within an intravalley lake during the hesperian epoch 3 4 ga hirise images show where water from a 57 km long valley built a delta flowed over its subaerial plain and finally debouched into a more than 450 m deep lake forming chutes in the subaqueous part of the deposit at present the studied system contains some of the most pristine distinctive and recent lacustrine evidence among all the candidate martian paleolakes the associated sedimentary deposits provide a valuable target for future in situ analyses aimed at the characterization of the hydrology climate and biological potential of ancient mars

post jurassic tectonic evolution of papua new guinea abstract synthesis of available geologic and geophysical data for papua new guinea yields a series of kinematically constrained tectonic reconstructions these reconstructions document the post jurassic evolution of the northern margin of the australian plate from a rifted passive continental margin to one composed of accreted tectonostratigraphic terranes undergoing sinistral oblique transpression the allochthonous terranes represent marginal basins and fringing island arcs which began docking to the australian plate in the miocene at present assemblage forms a diffuse suture zone between the australian and pacific plates structurally responding in a complex fashion to the regional oblique compression

a steep fan at coprates catena valles marineris mars as seen by hrsc data 1 we investigate a steep fan like deposit in the coprates catena region using the new high resolution stereo camera hrsc data and other martian data sets water flowing in a 45 km long sapping valley entered a deep trough and formed a stepped fan 1100 m high above the trough floor with a mean slope of 7 4 the origin of the fan is uncertain however we favor an alluvial sheetflood dominated deposition for the sedimentary feature though there is weak evidence for a possible stationary water level 500 m above the floor and a fan delta origin regional morphotectonics and previous geological mapping suggest that groundwater related aqueous sedimentation could have been active from hesperian to early amazonian implying favorable climatic conditions for the flow and possible ponding of water during that period

depth determination for shallow teleseismic earthquakes methods and results the depths of moderate sized shallow earthquakes can be routinely determined to an accuracy of several kilometers using teleseismic data alone making it possible to determine the vertical positions of earthquakes within the lithosphere this capability provides a valuable tool for plate tectonic studies since earthquake depths can be used to constrain lithospheric thermal and mechanical structure at plate boundaries and in intraplate regions two basic techniques are used for depth analyses surface wave spectra can be used to determine focal depths as mode excitation reflects the behavior of the eigenfunctions with depth the primary limitation on such studies stems from lateral heterogeneity of velocity structure the waveforms of body waves are also diagnostic of focal depth which controls the time separation between the direct arrival and near source surface reflections these studies can be limited by a partial trade off between depth and source time function duration the reliability of the body wave modeling approach now in general use is shown by excellent agreement between depths determined by different investigators using different algorithms the depth determination is robust to typical uncertainties in focal mechanism and near source structure the trade off with source time function duration generally does not produce major difficulties for small events ms 6 5 for larger events the trade off can be resolved using a approach in which for a given depth the time function yielding the best fit to a suite of seismograms is found by deconvolution deconvolution at a series of depths yields a misfit function whose minimum indicates the focal depth tests with synthetic data show that the deconvolution process yields reliable depth estimates even given uncertainties in focal mechanism and near source structure it successfully handles multiple sources moderate sized finite sources and horizontally propagating ruptures good results are obtained for vertically propagating ruptures until the fault area becomes so large that waveforms differ significantly from the point source approximation a number of important tectonic results have emerged from studies using these depth determination methods the maximum depth of oceanic intraplate seismicity increases with lithospheric age and is approximately bounded by the 750 c isotherm this depth roughly equals the flexural thickness of the lithosphere but is much less than the depth to the low velocity zone indicated by surface wave dispersion the maximum depth of continental intraplate seismicity is also temperature limited but by a lower temperature these observations are consistent with the rapid weakening of the appropriate rocks with depth predicted by standard temperature dependent rheologies the maximum depth of oceanic transform seismicity corresponds to an isotherm of about 400 c this temperature is lower than would be predicted from the intraplate results and may indicate that transforms are either hotter or weaker than expected the depths of ridge crest earthquakes large enough for teleseismic analysis are extremely shallow 0 8 km the depth distribution of seismicity in continental normal faulting regions provides constraints on the nature of the extension process at subduction zones precise depth determinations can resolve the upper and lower flexural regions in the bending downgoing plate precisely locate the plate interface and map the vertical extent and position of faulting in large earthquakes

timescales of fluvial activity and intermittency in milna crater mars milna crater mars 23 4s 12 3w exhibits signs of fluvial modification early in mars history including a large multi lobed fan deposit cut by several sinuous valleys we describe the past hydrologic conditions in milna and the surrounding area including a potential lake with a volume of 50 km 3 we also introduce new methods i to calculate the timescale of sediment deposition by considering fluvial sediment input into the entire crater while accounting for non fluvial input and ii to place improved constraints on the channel dimensions through which sediment was delivered to milna by comparing to the dimensions of inner channels found in valleys in the region surrounding milna by calculating the flux of fluid and sediment into the crater we find that the crater cavity was flooded for at least months and that the time of active fluvial sediment transport without hiatus is on the order of decades to centuries with a preferred timescale of centuries we also calculate the total amount of water required to transport the volume of sediment we measure in milna and conclude that impacts alone are likely insufficient to deliver enough water to milna to allow the sedimentary fill we see combining the timescales of fluvial activity in the adjacent parana valles with estimates for global noachian erosion rates we calculate an intermittency factor for fluvial activity of 0 01 0 1 during 10 5 10 6 yr near the noachian hesperian boundary in the parana valles region these values are comparable to arid climates on earth where the majority of fluvial sedimentary transport takes place during floods with multi year to decadal recurrence intervals our calculations of intermittency help to quantitatively reconcile the divergent estimates of the short and long timescales of fluvial activity on mars reported in the literature

alternating seismic uplift and subsidence in the late holocene at madang papua new guinea evidence from raised reefs well preserved mid late holocene coral reefs are exposed in low coastal cliffs in the vicinity of the madang lagoon on the north coast of papua new guinea results from u th and 14 c dating of corals surveying and field mapping indicate several major changes in relative sea level over this period specifically there is evidence for a relative sea level fall of 4 5 m about 3000 calendar years b p followed by relative sea level rises of 1 5 m about 2400 calendar years b p and 0 5 m about 1200 calendar years b p and a subsequent relative sea level fall of 3 m some time in the past 1000 years since regional eustatic sea levels are believed to have been dropping gradually over this time frame these observed changes in relative sea level are interpreted as reflecting alternating tectonic uplift and subsidence furthermore the detailed structure and age relationships of the coral deposits indicate that both uplift and subsidence occurred rapidly most probably as coseismic events with vertical displacements of 0 5 to 4 5 m these events may be related to rupture on nw se trending reverse faults which have been mapped in the nearby adelbert range and possibly on ne trending cross faults which have been inferred from seismicity this interpretation implies a much greater degree of tectonic instability and potential seismic hazard in the region than previously recognized although the inferred coseismic vertical displacements are shown to be consistent with present day local seismicity in a broader context the study illustrates how detailed analysis of vertical changes in coral reef structure and assemblages may be used as a sensitive indicator of changing relative sea level capable of resolving century timescale events and reversals

hydraulic modeling of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle we present a steady state hydraulic model of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle between 167 0 0 w and 167 30 0 w longitude and between 9 25 0 s and 9 45 0 s latitude the mars express high resolution stereo camera hrsc digital elevation model h31850000da4 with a spatial resolution of 75 m is used to describe the geometrical features of the hydraulic system a steady state hydraulic model through a monte carlo procedure is adopted to investigate the assumption that the tributary lake outlet hydraulic system was acting simultaneously during its last water related evolutionary phase through our analysis we infer the roughness coefficient and the discharge of both the tributary and the outlet channels geomorphic evidence such as river terraces were used to constrain the water discharge and the manning s roughness coefficient thereby obtaining estimates of the water level in the lake during the last evolutionary phase of the system our analysis of the outlet reveals a median paleodischarge of 7135 m3 s 1 and a median manning s roughness coefficient of 0 067 m 1 3 s tributary analysis provides a median flow and a median roughness coefficient of 6405 m3 s 1 and 0 123 m 1 3 s respectively moreover the hydraulic analysis suggests that the paleolake water surface level was 1397 m median value hrsc elevation which is consistent with the observed paleoshoreline the results imply that the tributary the lake and the outlet were hydraulically synchronized therefore confirming the presence of a connected water system this study demonstrates that hydraulic analysis can provide valuable information regarding ancient martian water fluxes

geology of xanthe terra outflow channels and the mars pathfinder landing site the mars pathfinder landing site mpls was selected for its location at the mouths of ares and tiu valles outflow channels on mars where sediments from a variety of geologic units could have accumulated in a lacustrine environment recent geologic mapping at 1 2 m scale of the xanthe terra channels and chryse planitia near mpls reveals a progression of fluvial erosion and deposition throughout the hesperian period from the geology the watersheds of the channels were inferred and a sequence of paleogeologic maps was produced three outflow episodes are recognized 1 broad sheetwash during the early hesperian emanating from eastern valles marineris and equatorial chaos regions with initial erosion into highland plateau basement 2 early channel formation and 3 subsequent flooding which deepened the channels to their current morphologies the most recent flooding issued from simud and tiu valles during the late hesperian indicated by stratigraphic superposition striations along the floor of the channel and the orientation of streamlined islands in the flood direction this suggests that surface sediments deposited at mpls are most likely to have come from these channels and to a lesser extent from ares vallis a ranking scheme was developed to assess the potential origins for the sediments found at mpls the most abundant materials are inferred to have come from the noachian and hesperian highland plains and reworked sediments from previous floods underlying materials from earlier floods could also be found at mpls as ejecta from nearby impact craters

fore arc deformation at the transition between collision and subduction insights from 3 d thermomechanical laboratory experiments 1 three dimensional thermomechanical laboratory experiments of arc continent collision investigate the deformation of the fore arc at the transition between collision and subduction the deformation of the plates in the collision area propagates into the subduction collision transition zone via along strike coupling of the neighboring segments of the plate boundary in our experiments the largest along strike gradient of trench perpendicular compression does not produce sufficiently localized shear strain in the transition zone to form a strike slip system because of the fast propagation of arc lithosphere failure deformation is continuous along strike but the deformation mechanism is three dimensional progressive along strike structural variations arise because coupling between neighboring segments induces either advanced or delayed failure of the arc lithosphere and passive margin the modeling results suggest that orogenic belts should experience deeper subduction of continental crust and hence higher pressure metamorphism where the two plates first collided than elsewhere along the plate boundary where collision subsequently propagated furthermore during the initial stage of collision the accretionary wedge is partially subducted which leads to lubrication of the interplate zone and a reduction of shear traction therefore a large convergence obliquity angle does not produce a migrating fore arc sliver rather the pressure force generated by subduction of the buoyant continental crust causes fore arc motion it follows that convergence obliquity during collision does not yield trench parallel deformation of the fore arc and its influence on the collision process is limited however convergence obliquity may control the geometry of the active margin during the oceanic subduction stage prior to collision and inherited structures may influence the propagation mechanism

a very broad band inversion method for the recovery of earthquake source parameters abstract waveform studies of the earthquake source have traditionally been performed in narrow bands of the seismic spectrum waveform matching of p and sh waves emphasizes frequencies near and above the corner frequency normal mode and surface wave analyses on the other hand are performed on data which contain information only below the corner frequency a new method is presented which formally includes the result of a long period centroid moment tensor analysis in an inversion of broad band body wave phases a parametrized source model is used which allows for the recovery of a detailed source time function as well as the direction and magnitude of rupture propagation the technical details and the performance of the method are demonstrated in an analysis of the october 28 1983 borah peak idaho earthquake in particular it is shown how the combination of the long period and broad band data sets in the inversion improves the resolution of both the focal mechanism and the scalar moment the very broad band method is applied in an analysis of the september 19 1985 michoacan m w 8 0 earthquake two concentrations of moment release are identified in the source time function separated by 25 30 s in time the spatial distribution of moment is well explained both by a model of unilateral rupture towards the east with a propagation velocity of 2 4 km s 1 and by two point sources separated by 95 km it is shown that the p wave data are largely insensitive to the scalar moment and that source time functions obtained without consideration of the total moment release exaggerate the heterogeneity of slip on the fault plane source time functions which do contain the total moment show that a large fraction of the moment was released smoothly over the whole duration 80 s of the event the results suggest that the fault plane was characterized by two regions of high stress drop but that a large portion of slip occurred on surrounding weak portions of the plane

regional gravity anomalies depth of the foreland basin and isostatic compensation of the new guinea highlands the new guinea highlands form an active thrust belt advancing southward over the australian continental margin surface geology indicates thin skinned deformation of sediments and continental basement building mountains 2 4 km in average elevation the depth of the adjacent foreland basin is no more than 1500 m in papua new guinea and in many places only 100 200 m indicating little deflection of the australian lithosphere beneath the load of the mountains calculations of elastic loading in which the topographic load of the entire mountain range is supported by australian lithosphere of uniform flexural rigidity d predict a basin 2 10 times deeper than observed in eastern new guinea for a wide range of flexural rigidities 1021 1025 nm bouguer gravity anomalies in the eastern highlands between 143 e and 144 e are consistent with local airy compensation of the mountains and preclude a continuous plate with d 1022 nm underlying any significant portion of the mountains in contrast the observed broad foredeep flexure in central new guinea near 141 142 e requires a strong lithosphere d 1024 1025 nm and limited gravity and sediment thickness observations farther west indicate similar flexural rigidities bouguer gravity measurements and observed foreland basin depths throughout new guinea can be explained by a strong and continuous lithosphere beneath the foreland basin extending no more than 20 60 km north of the range front implying that the plate has weakened beneath the thrust belt collateral evidence for plate weakening beneath the highlands may be found in earthquakes at 10 25 km depth with high angle thrust mechanisms and in widespread quaternary volcanism throughout the eastern thrust belt a 50 mgal positive residual anomaly over the northern 100 km of the eastern highlands cannot be explained by local compensation or mechanical support from the south indicating either a large excess mass at depth or some additional form of support for the northeastern highlands the gravity observations in eastern new guinea require 10 15 km of crustal thickening but observed sediment thicknesses can only account for 0 5 km necessitating 5 15 km of thickening in the basement

terraces and gilbert type deltas in crater lakes in ismenius lacus and memnonia mars paleolacustrine environments have been widely recognized from landform associations on the surface of mars in contrast to paleolakes in more open areas putative crater lakes commonly display well developed sedimentary landforms especially wave formed terraces and gilbert type deltas this study focuses on terraces and deltas of western memnonia and ismenius lacus as on earth these landforms provide important indications of water dynamics and sedimentary processes the putative martian paleolakes must have been active for thousands of years to have permitted the water movement and wave formation necessary to form one or more terraces fan shaped landforms at the mouths of channels entering crater lake areas may indicate various channel water interaction of these gilbert type deltas are particularly informative their presence indicates multiple flooding events whereby the inlet channels conveyed coarse grained sediment to the crater lake both terraces and deltaic progradation indicate that the crater lakes of memnonia and ismenius lacus were active for long time periods at least for thousands of years during the post heavy bombardment period of the later martian history the unequivocal presence of standing bodies of water of relatively long durations indicates that climatic settings very different from those prevailing today must have occurred at least locally and temporarily during parts of the martian planetary history

deep structure of an arc continent collision earthquake relocation and inversion for upper mantle p and s wave velocities beneath papua new guinea we examine mechanisms of lithospheric growth and modes accommodating subcrustal convergence following the cessation of subduction by analyzing the seismicity and upper mantle velocities in the new guinea arc continent collision earthquakes in the papua new guinea png region from 1967 to 1984 have been relocated in a joint inversion with seismic velocities using p and s wave arrival times recorded by seismographs in png a total of 957 well recorded earthquakes were chosen for use in three dimensional velocity inversions from an initial catalog of 12 960 events based on the stability of initial hypocenter relocations constant velocity blocks were defined as irregular polyhedra to give fine detail in heavily sampled areas without introducing a large number of poorly controlled parameters and to exploit a priori knowledge of the geometry of velocity anomalies spherical geometry was used to accurately calculate long ray paths up to 1500 km in length most of the 700 best located hypocenters from the png data set are in the upper mantle beneath the finisterre huon fh ranges the newly accreted island arc terrane beneath the papuan peninsula and in the new britain seismic zone an oceanic subduction system these hypocenters show a well defined seismic zone dipping vertically or steeply to the north beneath the northern fh ranges from 125 to 250 km depth continuous along strike with the new britain seismic zone to the east which shows earthquakes to 600 km depth the steeply dipping intermediate depth seismicity flattens near 100 km depth beneath the fh ranges and forms a subhorizontal seismic zone beneath the fh ranges by contrast seismicity continues upward to the surface beneath new britain where the arc has not yet collided with new guinea the 100 km deep flat zone does not continue south of the fh ranges but appears to be truncated below the eastern and southern boundaries of the island arc terrane and no clear evidence for a south dipping seismic zone could be found the relationship of the flat part of the slab 100 km beneath the fh ranges and surface faulting is difficult to discern the apparent surface suture bounding the south side of the fh ranges is 100 km directly above the southern termination of intermediate depth seismicity nowhere in png could clear evidence for arc polarity reversal be found from seismicity all of the well located subcrustal earthquakes beneath the papuan peninsula lie in a narrow horizontal line between 125 and 175 km depth that follows the center of the peninsula and are distinctly separated from the fh seismic zone to the north these events do not require a southward subducting plate beneath the papuan peninsula an alternate and reasonable explanation for these events is that they are a result of unstable thickening of the lithosphere information on lateral heterogeneity in the mantle is limited because large variations in crustal velocities dominate the observed pattern of travel time residuals allowing for only crustal heterogeneity reduces travel time residual variances by 40 from a simple one dimensional structure while allowing for additional mantle heterogeneity results in 10 further reduction for the various parameterization s attempted here inversions with several different block geometries show low velocities at 35 to 171 km km depth beneath the bismarck sea back arc basin and high velocities just south of the intermediate depth fh seismic zone the pattern of lateral heterogeneity supports the inference from seismicity of north dipping slabs beneath both northeast new guinea and new britain

shallow seismicity of arc continent collision near lae papua new guinea abstract in northeastern new guinea the narrow ramu markham valley rmv separates island arc rocks to the north from those of continental origin to the south and appears to be the western onland extension of the new britain trench to explore the tectonic processes at the leading edge of the island arc during collision we operated a portable seismic network for six weeks near the city of lae at the eastern end of the rmv we observed a narrow near vertical belt of seismicity between 10 and 30 km depth that we call the lae seismic zone lsz starting at the rmv in the southwest and trending northeasterly cutting across surface geologic structure the truncation of the lsz along a steep plane by the ramu markham fault zone rmfz and earthquake first motions suggest that the earthquakes occur in the hanging wall of a steep n dipping fault that crops out at the rmfz we also consider that the lsz is within the lower plate of a gently dipping thrust below 20 km depth the microearthquake zone is truncated by a gently ne dipping plane coinciding in depth and dip with nodal planes of recent large mb 5 6 and 6 0 thrust earthquakes we suggest that the huon peninsula is being emplaced onto the australian plate along a gently 25 dipping thrust fault that is 20 km deep beneath lae the rmfz may be a steeply dipping thrust fault that connects with this gently n dipping thrust but accommodates little convergence at present the lsz trends nearly perpendicular to an anticlinal range which appears to be sheared in a left lateral sense p wave first motions for earthquakes in the lsz with steep 70 to 90 dip nodal planes that strike parallel to the lsz suggest a component of south side up displacement also hence the crustal block south of the lsz may be rising relative to the huon peninsula and the rapid quaternary uplift rates estimated for the lae coastal region may be higher than the uplift rate of the huon peninsula as a whole we suggest that the lsz reveals a tear of small offset in the huon terrane but may be similar to a structure that produced a magnitude 7 earthquake near madang in 1970

constraints on the structure of the himalaya from an analysis of gravity anomalies and a flexural model of the lithosphere the intracontinental subduction of india beneath the himalaya presents several similarities to that occurring at island arcs we study one of those similarities by analyzing gravity anomalies across the himalaya assuming that the topography is supported by the indian elastic plate flexed under the weight of both the overthrust mountains and the sediments in the ganga basin we first examine in detail the effects of each of the following parameters on the configuration of the elastic plate and on the gravity anomalies the flexural rigidity the position of the northern end of the elastic plate the amount of underthrusting of such a plate beneath the range and the density contrasts between the crust and mantle and between the sediments and the crust a plate with a constant flexural rigidity of about 0 7 1025 n m between 0 2 and 2 0 1025 n m allows a good fit to the data from the lesser himalaya and the ganga basin such a plate however cannot underthrust the entire himalaya instead the gravity anomalies show that the moho steepens from only about 3 beneath the lesser himalaya to about 15 beneath the greater himalaya this implies a smaller flexural rigidity beneath the greater himalaya 0 1 to 1 0 1023 n m than beneath the ganga basin and the lesser himalaya even with a thin weak plate beneath the greater himalaya the weight of the mountains depresses the plate too much unless an additional force or moment is applied to the plate the application of a bending moment unit length to the end of the plate of about 0 6 1018 n m is adequate to elevate the indian plate and to bring the calculated gravity anomalies in agreement with those observed both the smaller flexural rigidity and the bending moment can be understood if we assume that part or all of the indian crust has been detached from the lower lithosphere that underthrusts the greater himalaya we study the tectonic implications of these results by means of a series of idealized balanced cross sections from the collision to the present that reproduce several important features of the geology of the himalaya and predict an amount of eroded material comparable to that in the ganga basin and the bay of bengal these cross sections include high grade metamorphic rocks near the main central thrust and a steeper dip of it there than in the lesser himalaya they predict rapid uplift only in the greater himalaya and at the foot of the lesser himalaya

a case for ancient evaporite basins on mars observations indicate that a martian analog to the earth s salt pans and saline lakes of arid regions may have existed in crater basins during mars early noachian epoch terraced and channelized crater basins point to ponding of surface water as well as possible prolonged and evolving base levels in addition supportive evaporite basin analogs are offered for three other morphologic features of martian crater basins an evaporite basin model for crater basins on mars has major implications for the mechanical chemical and even biological processes that potentially have operated in mars past and represent a spectrum of potential mineral resources

late quaternary coseismic uplift events on the huon peninsula papua new guinea deduced from coral terrace data up to six regressive terraces occur on the holocene raised reef tract and up to 15 occur on late pleistocene raised reef tracts along 40 km of coastline at huon peninsula papua new guinea we suggest that the regressive terraces represent repeated episodic uplift caused by great earthquakes ages of holocene coseismic uplift events are established by radiocarbon dating the late pleistocene events are bracketed by u series ages of the raised reef tracts on which they occur the mean recurrence interval of great earthquakes that caused the uplift events is 970 to 1165 years in the holocene and probably the same in the late pleistocene the interval ranged from about 200 to 1900 years the uplift rate increases parallel to the coast from northwest to southeast and the amplitude of coseismic uplifts generally increases similarly although some events produced uplift with little shore parallel tilting the mean amplitude of coseismic uplifts throughout the study area is 3 m in for both holocene and late pleistocene sequences large late quaternary landslides are numerous and some probably were triggered by the great earthquakes that caused coseismic uplift there appears to be no continuum between historical large earthquakes at huon peninsula of magnitudes 7 that produced no or only minor uplift and the great earthquakes represented by meter scale coseismic uplifts and very large landslides two tectonic subregions are recognized which were uplifted together by some holocene events but not by others there is no surface trace of holocene faulting between the subregions and a buried fault is thought to separate them

outflow channels with deltaic deposits in ismenius lacus mars abstract a connected series of outflow channels in the ismenius lacus quadrangle are identified for the first time and characterized using high resolution stereo camera images of mars express the context camera images of mars reconnaissance orbiter and the topography of the mars observer laser altimeter these channels named okavango valles which stretch over 400 km south to north and join the northern plains were identified from braided channels scour groove marks poorly sinuous valleys and depositional landforms discharge rates were estimated to 0 1 5 10 6 m 3 s 1 from analysis of the topography of scour marks pathways of channels segments were extracted from topography showing a unique source at a breached crater rim suggesting overflow from ponded depressions a series of delta fans are observed inside depressions along the channel pathways the presence of these deltas formed in former bodies of water is a compelling argument for formation of this outflow channel system by fluvial flows the similarity of these flows with other outflow channels on mars proves that volcanically related outflows cannot explain all such features in addition this study also shows that catastrophic floods are able to create fan deltas in transient lakes this example has to be taken into account in the interpretation of late stage fans associated with poorly branched valleys and single channels

recent and episodic volcanic and glacial activity on mars revealed by the high resolution stereo camera the large area coverage at a resolution of 10 20 metres per pixel in colour and three dimensions with the high resolution stereo camera experiment on the european space agency mars express mission has made it possible to study the time stratigraphic relationships of volcanic and glacial structures in unprecedented detail and give insight into the geological evolution of mars here we show that calderas on five major volcanoes on mars have undergone repeated activation and resurfacing during the last 20 per cent of martian history with phases of activity as young as two million years suggesting that the volcanoes are potentially still active today glacial deposits at the base of the olympus mons escarpment show evidence for repeated phases of activity as recently as about four million years ago morphological evidence is found that snow and ice deposition on the olympus construct at elevations of more than 7 000 metres led to episodes of glacial activity at this height even now water ice protected by an insulating layer of dust may be present at high altitudes on olympus mons

martian fan deposits insights on depositional processes and origin from mass balance survey abstract fan deposits located at the mouths of martian valleys have been interpreted as indicators of wet conditions during mars history however the processes time and amount of water needed to carve the valleys and form the fans are still debated here we present a detailed morphometric and mass balance analysis of valleys and fan shaped deposits using high resolution topography which provides new insights into past depositional environments based on morphometric and volumetric measurements we found that several martian fans previously interpreted as deltas can be categorized into two main types type i fans are more numerous relatively well preserved are associated with smaller and less mature drainage networks and were deposited on steeper gradients the balance between eroded and deposited materials indicates that this set of fans might have been formed mainly in subaerial settings by depositional processes other than typical deltaic sedimentation e g alluvial glacial mass wasting in general since a significant loss of sediment during deposition did not occur we obtained a volume ratio of eroded vs deposited materials of approximately 1 therefore we propose that the identified type i fans were not deposited in prevailing subaqueous deltaic settings but mainly in subaerial conditions with perhaps sporadic presence of ephemeral bodies of standing water within the basins in contrast type ii fans are less abundant highly eroded were deposited on flatter areas and formed downstream of more mature drainage networks with longer deeper and wider valleys the mass balance for this set of fans clearly shows that considerable amounts of sediment were not retained in the fans implying large offshore transport of sediment during their formation eroded vs deposited volume ratios between 3 and 10 are probable this evidence supports a fluvio deltaic origin for this class of fans indicating the existence of paleolakes over substantial periods of time based on the collected morphometric measurements and mass balance modeling we conclude that only a small percentage of the fans type ii fans correspond to 1 3 of the sampled areas are consistent with the occurrence of favorable and durable conditions for life i e long lived integrated fluvial deltaic and lacustrine environments whereas the majority of fans might have been formed in subaerial settings with significant contributions of alternative processes besides fluvial transport and deposition thus not necessarily requiring the occurrence of extended epochs of clement climatic conditions

the central new britain earthquake of may 10 1985 tensional stresses in the frontal arc abstract aftershocks of the ms 7 1 central new britain earthquake show a shallow fault 0 to 20 km in depth dipping steeply 75 85 toward the south and extending for about 50 km in an east west direction this is consistent with the focal mechanism which can be interpreted as left lateral motion on a nodal plane oriented n100 e and dipping 80 to the south southwest the orientation of the principal stress axes indicates that this frontal arc region is under tensional stresses

evidence for paleolakes in erythraea fossa mars implications for an ancient hydrological cycle there is now widespread agreement that the surface of mars underwent some degree of fluvial modification but there is not yet full understanding of its surface hydrological cycle and the nature of standing bodies of water rivers and precipitation that affected its surface in this paper we explore erythraea fossa 31 5 w 27 3 s a graben adjacent to holden crater which exhibits strong evidence that it once housed a chain of three lakes had overland water flow and was subject to precipitation the inlet valley outlet valley and fan morphologies in the paleolakes are used to qualitatively discern the hydrologic history of the paleolakes based on topography constraints the three basins combined once held 56 km 3 of water depositional features within the basins that change with drainage area and nearby valleys that start near drainage divides indicate that the paleolakes may have been fed by precipitation driven runoff this suggests the presence of an atmosphere at least locally that was capable of supporting a hydrological cycle

winds waves and shorelines from ancient martian seas we consider under what environmental conditions water waves and thus eventually shorelines should be expected to be produced on hypothetical ancient martian seas and lakes for winds and atmospheric pressures that are too small no waves should be expected and thus no shorelines if the winds and atmospheric pressure are above some threshold then waves can be formed and shorelines are possible we establish these criteria separating conditions under which waves will or will not form on an ancient martian open body of water we consider not only atmospheric pressure and wind but also temperature and salinity but find these latter effects to be secondary the normal criterion for the onset of water waves under terrestrial conditions is extended to recognize the greater atmospheric viscous boundary layer depth for low atmospheric pressures we used terrestrial wave models to predict the wave environment expected for reasonable ranges of atmospheric pressure and wind for end member cases of ocean salinity these models were modified only to reflect the different fluids considered at mars the different martian surface gravity and the varying atmospheric pressure wind and fetch the models were favorably validated against one another and also against experiments conducted in a wave tank in a pressure controlled wind tunnel nasa ames marswit we conclude that if wave cut shorelines can be confirmed on mars this can constrain the range of possible atmospheric pressures and wind speeds that could have existed when the open water was present on mars

convergent margin extension associated with arc continent collision the finsch deep papua new guinea the finsch deep is an asymmetric rhomboidal basin with a maximum depth of 5400 m situated to the north of the solomon sea triple junction papua new guinea anomalous slip vector azimuths regional plate velocities earthquake hypocenters and bathymetric depth relative to surrounding terranes all indicate that the finsch deep is not a passive feature developed behind the subduction front our interpretation of all available data including seismological studies detailed bathymetry side scan character and seismic sections suggests that the finsch deep has developed due to n s extension in the transition zone from continental collision west of the solomon sea triple junction to oceanic subduction to the east the key mechanisms thought to drive convergent margin extension within the new guinea collision are slab pull and oblique subduction researchers studying other convergent margins have recognized underplating and tectonic erosion as driving mechanisms for extension though we have no evidence to either support or discount their presence within the new guinea collision

evidence for ponding and catastrophic floods in central valles marineris mars abstract the valles marineris canyon system of mars is closely related to large flood channels some of which emerge full born from chaotic terrain in canyon floors coprates chasma one of the largest valles marineris canyons is connected at its west end to melas chasma and on its east end to chaotic terrain filled capri and eos chasmata the area from central melas to eos chasmata contains a 1500 km long and about 1 km deep depression in its floor despite the large volumes of groundwater that likely discharged from chaotic terrain in this depression no evidence of related fluvial activity has thus far been reported we present an analysis of the regional topography which together with photogeologic interpretation of available imagery suggests that ponding due to late hesperian discharge of water possibly produced a lake mean depth 842 m spanning parts of the valles marineris depression vmd overflow of this lake at its eastern end resulted in delivery of water to downstream chaos regions and outflow channels our ponding hypothesis is motivated primarily by the identification of scarp and terrace features which despite a lateral spread of about 1500 km have similar elevations furthermore these elevations correspond to the maximum ponding elevation of the region 3560 m simulated ponding in the vmd yields an overflow point at its eastern extremity in eos chasma the neighborhood of this overflow point contains clear indicators of fluvial erosion in a consistent east west orientation

martian layered fluvial deposits implications for noachian climate scenarios 1 fluvial deposits in a basin north of holden crater exhibiting a sinuous anabranching pattern are of deltaic or fan origin channel width and meander wavelength indicate persistent flow magnitudes of about 700 m3 s if these flows were produced by quasi periodic climate episodes involving typical terrestrial style precipitation the deposit required thousands to millions of years to accumulate however a scenario of deposition during a few short episodes of constant heavy precipitation resulting from large impacts cannot be excluded

shallow dips of normal faults during rapid extension earthquakes in the woodlark d entrecasteaux rift system papua new guinea earthquakes in the woodlark d entrecasteaux rift system reveal changes in fault geometry along strike as extension progresses from continental to oceanic modes in one segment evidence is found for earthquakes on shallow dipping normal faults to examine these trends locations of 147 earthquakes are redetermined and focal mechanisms for 21 events are derived from waveform inversion where seafloor spreading occurs east of 152 e most earthquakes illuminate a ne sw strike slip fault north of the oceanic rift system along the woodlark rise elsewhere earthquakes occur along a well defined rift zone and focal mechanisms reveal normal faulting with north south t axes and depths less than 10 km most normal faulting earthquakes show high angle fault planes dips 40 50 but several are consistent with slip on moderately low angle planes dipping 15 35 these low angle nodal planes are only found in a region between 150 5 e and 152 5 e where the transition occurs from seafloor spreading to continental rifting a seismic reflection profile near 151 e reveals a major normal fault that dips to the north at 25 35 just landward of the oceanic rift tip that fault and parallel structures are excellent candidates for the fault that slipped in at least two of the earthquakes studied hence normal faults dipping 30 are likely to be seismically active in at least one part of this rift system in this region just landward from the rift tip the highest extension rates are expected 40 mm yr and strain appears localized on a single system of normal faults because shallow dips for normal faults are seen near the rift tip but not elsewhere along strike high strain rates may be an important factor in allowing normal faults to slip at unusually shallow dips perhaps high shear traction at the base of the upper crust localized by nearby spreading sufficiently alters the local stress regime

evidence for late hesperian lacustrine activity in shalbatana vallis mars 1 an intravalley paleolake more than 400 m deep was detected along the course of shalbatana vallis from the evidence of shorelines and the occurrence of a few fan delta deposits including a gilbert type delta the fronts of all the sedimentary deposits strikingly match the same topographic contours 2800 and 3000 m below the martian datum indicating the paleolake water levels under which they formed also the corresponding shorelines are visible along the shalbatana vallis walls the peculiar settings of the lake suggest that shalbatana vallis was impounded during its final hydrological activity and that ponding of water lasted enough time to allow the formation and evolution of the lacustrine system water source is uncertain but a composite sapping mechanism is hypothesized in order to take into account the amount of water required to excavate transport and deposit the materials found in the deposits previous works and new crater counting computations indicate that the paleolake was active during the hesperian epoch therefore at that time surface conditions were different from those of modern mars and supportive of flow and ponding of water it is unclear whether the hydrological activity was sustained entirely by a favorable climatic regime and secondary regional factors like volcanism impact cratering and tectonism could have also triggered accelerated the local groundwater activity implying that the system could have evolved relatively independent from climatic conditions the latter eventuality and the regional importance of this research advised against an extrapolation of its results to the overall debate about martian climatic geomorphological evolution

active arc continent collision earthquakes gravity anomalies and fault kinematics in the huon finisterre collision zone papua new guinea the huon finisterre island arc terrane is actively colliding with the north edge of the australian continent the collision provides a rare opportunity to study continental accretion while it occurs we examine the geometry and kinematics of the collision by comparing earthquake source parameters to surface fault geometries and plate motions and we constrain the forces active in the collision by comparing topographic loads to gravity anomalies waveform inversion is used to constrain focal mechanisms for 21 shallow earthquakes that occurred between 1966 and 1992 seismic moment 1017 to 3 1020 n m twelve earthquakes show thrust faulting at 22 37 km depth the largest thrust events are on the north side of the huon peninsula and are consistent with slip on the ramu markham thrust fault zone the northeast dipping thrust fault system that bounds the huon finisterre terrane thus much of the terrane s crust but little of its mantle is presently being added to the australian continent the large thrust earthquakes also reveal a plausible mechanism for the uplift of pleistocene coral terraces on the north side of the huon peninsula bouguer gravity anomalies are too negative to allow simple regional compensation of topography and require large additional downward forces to depress the lower plate beneath the huon peninsula with such forces plate configurations are found that are consistent with observed gravity and basin geometry other earthquakes give evidence of deformation above and below the ramu markham thrust system four thrust events 22 27 km depth directly below the ramu markham fault outcrop are too deep to be part of a planar ramu markham thrust system and may connect to the north dipping highlands thrust system farther south two large strike slip faulting earthquakes and their aftershocks in 1970 and 1987 show faulting within the upper plate of the thrust system the inferred fault planes show slip vectors parallel to those on nearby thrust faults and may represent small offsets in the overriding plate these faults along with small normal faulting earthquakes beneath the huon finisterre ranges and a 25 along strike rotation of slip vectors demonstrate the presence of along strike extension of the accreting terrane and along strike compression of the lower plate

fluvial sedimentary deposits on mars ancient deltas in a crater lake in the nili fossae region 1 new spacecraft observations in the nili fossae region of mars reveal two valley networks 80 and 200 km long that each formed distributary fans as they entered an ancient 40 km diameter impact crater an outlet channel on the eastern crater rim lying at an elevation above the fans suggests these fans formed as subaqueous deltas in a crater lake water flowing in the valley networks entered the crater and deposited the fans and ponded to a maximum depth of about 450 m the lake then overtopped and breached the crater rim incising it and dropping the lake level by 100 m geological evidence combined with the volume of water necessary to fill the crater suggests the duration of flow through this system was prolonged the existence of the deposits described here implies that the early martian environment supported overland flow and ponding of water for an extended period of time

parallel thrust and normal faulting in peru and constraints on the state of stress abstract we present evidence for recent normal faulting in the cordillera blanca of peru along planes trending approximately n40 w parallel to the chain this type of faulting suggests that there is an important component of extension perpendicular to the chain and contrasts markedly with the underthrusting of the nazca plate on the west side of peru and with the folding and thrusting observed in the sub andes on the eastern flank of the chain these contrasting styles of deformation and associated stress fields can be explained by buoyancy forces due to the high mountains and crustal roots in so far as this explanation is correct the difference in elevation between zones of normal and thrust faulting can be used to place an upper bound of 500 bars on the average stress difference in the crust

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

seismotectonics of new guinea a model for arc reversal following arc continent collision the structure and evolution of the northern new guinea collision zone is deduced from international seismological center isc seismicity 1964 1985 new and previously published focal mechanisms and a reexamination of pertinent geological data a tectonic model for the new guinea margin is derived which illustrates the sequential stages in the collision and suturing of the bewani toricelli adelbert finisterre huon new britain arc to central new guinea followed by subduction polarity reversal in the west east of 149 e the solomon plate is being subducted both to the north and south bringing the new britain and trobriand forearcs toward collision west of 149 e the forearcs have collided and together they override a fold in the doubly subducted solomon plate lithosphere which has an axis that is parallel to the strike of the ramu markham suture and that plunges westward at an angle of 5 beneath the coast ranges of northern new guinea active volcanism off the north coast of new guinea is related to subduction of the solomon plate beneath the bismarck plate active volcanism of the papuan peninsula and quaternary volcanism of the new guinea highlands are related to slow subduction of the solomon plate beneath the indo australian plate along the trobriand trough and the trough s former extension to the west respectively from 144 148 e seismicity and focal mechanisms reveal that convergence between the sutured bismarck and indo australian plates is accommodated by thrusting within the finisterre and adelbert ranges and compression of the new guinea orogenic belt together with basement involved foreland folding and thrusting to the south the finisterre block overthrusts the new guinea orogenic belt whereas the adelbert block is sutured to new guinea and overthrusts the oceanic lithosphere of the bismarck sea along the new guinea trench west of 144 e seismicity defines a southward dipping wadati benioif zone and focal mechanisms indicate oblique subduction only this oldest westernmost portion of the collision has progressed past suturing to a full reversal in subduction polarity

a seismological study of the eastern new guinea and the western solomon sea regions and its tectonic implications summary we use new and pre existing seismological data to study the neotectonics and the state of stress in the seismic zones of eastern papua new guinea and the western solomon sea regions earthquake hypocentres for the period 1964 90 were relocated using the joint hypocentre determination jhd technique we show that the t axes of earthquakes in the 100 250km depth range beneath eastern papua new guinea are aligned parallel to the seismic zone with no seismicity below 250 km this intermediate depth seismic zone forms an inverted u shaped zone with limbs dipping to the north and south and is interpreted to be seismicity along the subducted solomon sea plate the northern and southern limbs of the seismic zone are connected by a flattened zone of seismicity which is marked by predominantly strike slip and a few normal fault mechanisms we suggest that the solomon sea plate at depth beneath the finisterre mountains is no longer influenced by the tectonic forces acting at the surface but breaking up and sinking under its own gravitational forces a significant north dipping seismic zone is imaged above the deeper seismic zone this feature characterized by thrust mechanisms extrapolates to the surface along the ramu markham valley and is attributed to the ramu markham fault rmf the rmf has an average dip of about 40 to the north east but its detailed geometry would appear to be complex the rmf is interpreted to ramp steeply in the uppermost 10 20 km flattening out sharply to a dip of 15 at a depth of about 20km the rmf marks the suture between the finisterre terrane and the australia new guinea plate and may extend to a depth of 90km beneath the western limit of the finisterre mountains there is a clear gap in seismicity between the rmf and the deeper solomon sea plate seismic zone beneath the finisterre mountains which together with the alignment of the t axes of earthquakes along the seismic zone at depths 100km indicates that these are indeed two distinct features the seismicity in the depth range 50 80 km along the new britain arc follows the trend of the 2000m bathymetric contour of the new britain trench and the finsch deep far more closely than it does the trend of the surface plate boundary indicating that the increase in the distance between the solomon sea south bismarck plate boundary and the active volcanos along the new britain arc west of 6 83 150 o e is only a shallow phenomenon and does not reflect the geometry of the solomon sea plate at depths greater than 50 km

the opening of the woodlark basin subduction of the woodlark spreading system and the evolution of northern melanesia since mid pliocene time abstract magnetic anomaly and seismological data define segments of active seafloor spreading and associated magnetic lineations trending ene in the woodlark basin the total opening rate has been approximately 6 cm yr for the last 1 m y spreading rates diminish by over 10 from east to west along the woodlark spreading system implying a pole of current opening 15 20 to the west commencement of seafloor spreading in the basin has apparently been time transgressive beginning prior to 3 5 m y in the east and at successively later times to the west earthquake focal mechanisms and geological evidence suggest that the land areas bounding the western end of the woodlark basin are undergoing tensional deformation we believe that eventually the woodlark basin plate boundary will propagate westward through the d entrecasteaux islands into the papuan peninsula hitherto unreported shallow seismicity associated with the northern margin of the ne trending section of the woodlark rise probably reflects partial decoupling of the woodlark and solomon basins possibly due to mechanical difficulties in subducting the young woodlark lithosphere analysis of the relative motions between the solomon indo australian and pacific plates shows that the woodlark spreading system has been subducted at high rates 10 cm yr beneath the solomon islands during the opening of the woodlark basin several tectonic and geological features limited to the region of interaction of the woodlark basin with the solomon trench and arc may be symptomatic of ridge subduction these features include high heat flow in the solomon trench which shoals to 4 km low levels of seismicity and only shallow hypocenters and voluminous eruptions of high k 2 o tio 2 olivine basalts and basaltic andesites extremely close to the trench axis this close association in space and time of an unusual volcanic suite with ridge subduction implies a strong dependence of the petrogenesis on the tectonic regime a combination of this study of the woodlark basin and the previous study of the bismarck basin taylor 1979 provides a reconstruction of the positions of the continents ocean basins and island chains in northern melanesia for mid pliocene time in accepting the existence of a solomon plate we can explain the trench like structure off the trobriand margin of new guinea the occurrence of late cenozoic calc alkaline volcanism along the papuan peninsula and the presence of intermediate depth seismicity beneath the north papuan peninsula the rapid changes in relative motions along or across the new ireland solomons chain over the past 3 5 m y may explain the spatial and temporal changes in igneous activity observed on these islands

potential desiccation cracks on mars a synthesis from modeling analogue field studies and global observations potential desiccation polygons pdps are polygonal surface patterns that are a common feature in noachian to hesperian aged phyllosilicate and chloride bearing terrains and have been observed with size scales that range from cm wide by current rovers to 10s of meters wide the global distribution of pdps shows that they share certain traits in terms of morphology and geologic setting that can aid identification and distinction from fracturing patterns caused by other processes they are mostly associated with sedimentary deposits that display spectral evidence for the presence of fe mg smectites al rich smectites or less commonly kaolinites carbonates and sulfates in addition pdps may indicate paleolacustrine environments which are of high interest for planetary exploration and their presence implies that the fractured units are rich in smectite minerals that may have been deposited in a standing body of water a collective synthesis with new data particularly from the hirise camera suggests that desiccation cracks may be more common on the surface of mars than previously thought a review of terrestrial research on desiccation processes with emphasis on the theoretical background field studies and modeling constraints is presented here as well and shown to be consistent with and relevant to certain polygonal patterns on mars

evidence for persistent flow and aqueous sedimentation on early mars landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in mars global surveyor mars orbiter camera and mars odyssey thermal emission imaging system images evidence of distributary channelized flow in particular flow that lasted long enough to foster meandering and the resulting deposition of a fan shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial and potentially lacustrine environments

partial breaking of a mature seismic gap the 1987 earthquakes in new britain to better understand the mechanics of subduction and the process of breaking a mature seismic gap we study seismic activity along the western new britain subduction segment 147 e 151 e 4 s 8 s through earthquakes with m b 5 0 in the outer rise the upper area of subducting slab and at intermediate depths to 250 km from january 1964 to december 1990 the segment last broke fully in large earthquakes of december 28 1945 m s 7 9 and may 6 1947 m s 7 7 and its higher seismic potential has been recognized by mccann et al 1979 recently the segment broke partially in two smaller events of february 8 1987 m s 7 4 and october 16 1987 m s 7 4 leaving still unbroken areas

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

impact crater lakes on mars the robotic search for life on mars centers on identifying accessible environments where the biological catalyst water has existed the formation of large impact craters on mars 65 km diameter may have resulted in the creation of ice covered impact crater lakes which would not freeze for thousands of years even under present climatic conditions water could be supplied from deep confined aquifers penetrated by the impact craters without the need for surface melt water freezing of the lakes is postponed owing to heat from impact generated melt bearing deposits from impact related uplift of hotter rocks from depth and from the latent heat of freezing of a deep crater lake abundant morphologic evidence for ancient crater lakes has not been found in viking images except for craters associated with outflow channels however ice covered crater lakes could have formed and further searches for evidence of these lakes are warranted the lake deposits from dissected impact craters may represent one of the best targets for future surface exobiology investigations or sample return missions from mars

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

collision propagation in papua new guinea and the solomon sea the mountain system in papua new guinea png is growing by accretion of australian margin strata to the front of the papuan fold and thrust belt in the south and by accretion of exotic terranes along its ne margin presently the finisterre terrane is being accreted along the ne margin of png and the collision point is migrating eastward within the solomon sea east of the collision point the new britain trench marks the tectonic front between the solomon sea and south bismarck sea plates whereas to the west the tectonic front lies in the southern part of the papuan fold and thrust belt present day sedimentary environments within the western solomon sea are inferred from interpretation of seismic reflection data similar facies are observed accreted to the front of the finisterre terrane in the markham valley the frontal leron formation is largely fluvial and shallow marine and the erap complex contains elements of turbidites and pelagic deposits there appears to be a smaller volume of coarse proximal marine strata accreted to the front of the finisterre terrane than is expected from interpretation of reflection profiles in the western solomon sea this difference may be attributed to a combination of submarine erosion in the markham canyon partial incorporation of these deposits into the erap complex and a difference in depositional rates and products carried to the solomon sea in the past relative to what is observed today based on plate motions alternative collision geometries and the youngest dates available for the erap complex we determine a rate of progression of the collision point of about 212 km m y during the past 1 m y

sedimentary history and mass flow structures of chryse and acidalia planitiae mars geologic mapping and crater counting in chryse and acidalia planitiae cap reveal five major sedimentary deposits of hesperian to early amazonian age including 1 a mass flow deposited during the early hesperian near deuteronilus mensae northeast of the map region that may have resulted from the carving of kasei valles 3000 km southwest of the exposed part of the deposit 2 knobby plains material consisting of channel likely from simud and tiu valles and possibly ares and shalbatana valles and mass wasting deposits in central and eastern cap 3 material largely from maja and ares valles emplaced in at least western and southern cap outcrops in southern chryse planitia developed thermokarst 4 a thin mass flow covering much of southern chryse planitia that emanated from simud and tiu valles and 5 a thick extensive perhaps 3500 km across mass flow deposit in central and northern cap derived from accumulation and backflow of the preceding thin mass flow or perhaps melting of polar deposits other possible deposits may not be recognizable owing to burial by younger materials or a lack of morphologic signature various associated landforms appear to be consistent with the mass flow interpretations including lobate and linear scarps along deposit edges fractures related to desiccation of thick sediments troughs and ridges near the edges of the deposit indicative of secondary mass movement and deformation pitted domes and fissure fed flows possibly formed by sedimentary mud eruptions and longitudinal channel grooves perhaps formed by roller vortices no convincing evidence for paleoshorelines or stagnant ice sheets is found in cap these findings suggest that mass flow and hyperconcentrated flooding may have been the predominant processes of outflow channel dissection in cap elsewhere in the northern plains similar landforms are prevalent the mass flow interpretation does not require either multiple episodes of extraordinarily high water discharge rates achieved by freeing huge volumes of water from the crust repetitive recycling of immense volumes of water into highland aquifers at the heads of chryse channels or profound climate change mars pathfinder will most likely land on and inspect the surface of the thin mass flow that originated from the canyons of simud and tiu valles

orogeny in arc continent collision the banda arc and western new guinea eastern indonesia contains a modern continent island arc collision that demonstrates how a complex juxtaposition of continental and oceanic elements can occur in an orogenic belt shallow earthquakes show that strike slip faulting transports large crustal blocks into out of and along the collision zone while crustal shortening and thickening occur by steep angle thrust faulting near the strike slip faulting whereas strike slip faulting is paramount in positioning australian continental rocks so as to enclose the oceanic and island arc rocks of eastern indonesia its role may be overshadowed by the contemporaneous thrusting and may confuse geologic interpretations of the resulting orogenic belt

ma adim vallis revisited through new topographic data evidence for an ancient intravalley lake abstract based on a comprehensive study of the recent topographic map usgs mc 23 se i 2119 usgs 1991 topographical map of aeolis plus geomorphic and digital elevation we have constructed a geometric model of ma adim vallis the sedimentary history of the valley was determined by the damming of the valley by two impact craters one by the southern crater over gusev rim and the second located 120 km upstream the presence of an intravalley lake system is inferred from independent sedimentary analysis and from geomorphic evidence for valley benches peripheral and parallel topographic contour intervals of the putative intravalley lake shores suggest that the lake was covered by a thick ice sheet the longitudinal profile of the valley floor shows a peculiar reverse slope located 300 km upstream from the southern gusev crater rim we conclude that this is an accumulation of sedimentary deposits adjacent to the crater rampart which defined the northern boundary of the lake when the water level reached the lowest point of the west bank which is 0 4 km below the top of the rim of gusev crater it began to floor the surrounding plateau as the intravalley lake level raised its ice cover formed a wide lateral bench later this ponded water was funneled into gusev crater through the breaching of the southern gusev rampart by an impact crater the paleolacustrine sediments transported by the lake water that channeled through the rampart debris slope mantled the floor of gusev crater the sublacustrine sediments are promising targets for future missions and of high priority in the search for past life

a new method for determining the long period component of the source time function of large earthquakes inversions of seismic body waves indicate that most large earthquakes involve spatial and temporal heterogeneity of the moment release but seismic body waves usually lack sufficient bandwidth to constrain the long period component of the radiation analysis of long period surface waves and free oscillations can constrain the overall source duration and moment however most procedures assume simple trapezoidal or boxcar source time histories inconsistent with the body wave complexity the authors find that source time function complexity can affect long period surface waves sufficiently to impact estimates of the source moment tensor rupture duration and centroid depth they present a procedure to objectively determine the long period component of complex source time functions in which they directly utilize results from body wave analysis the method is applied to two great normal fault events of june 22 1977 tonga m sub w 8 2 and august 19 1977 indonesia m sub w 8 5 standard long period analysis procedures underestimate the total slip duration in both cases the overall source process times of both earthquakes are longer than 120 s

the seismic reflection moho beneath the united kingdom and adjacent areas abstract onshore and offshore deep seismic reflection data have been integrated to produce two way travel time and depth maps of the seismic reflection moho beneath the uk moho travel times are mostly in the range 9 5 11 5 s showing only weak correlation with specific upper crustal structural features but decreasing generally northwestward towards the atlantic margin moho depths show a much stronger correlation with upper crustal structure than do travel times there is pronounced crustal thinning moho depths 32 km are found generally beneath basement massifs particularly onshore short wavelength topographic features on the moho are quite rare and are generally restricted to ancient zones of continental collision and or subduction some of these ancient collision and or subduction zones are spatially associated with a highly reflective moho this is particularly evident where low angle shear zones in the lower crust or uppermost mantle converge with or intersect the moho it is suggested that development of a moho detachment surface can tectonically smooth the moho and thereby markedly increase its reflectivity a tendency in certain areas for the moho to remain at roughly constant two way travel time though not constant depth beneath both sedimentary basins and intervening basement massifs is interpreted as indicating that structural features on the scale of several tens of kilometres are in regional isostatic equilibrium conversely travel time perturbations beneath smaller features 10 km across indicate that these are at least partially uncompensated the uk crust is therefore weak but not sufficiently weak to attain local airy isostasy basement massifs west of scotland show systematically smaller moho two way travel times than similar structures farther south within the constraints of regional isostasy this can be interpreted in two main ways greater rigidity and strength of lewisian rocks within the west scottish massifs manifest as higher seismic velocity relative to density could be a cause of the observed travel time differences alternatively low density material beneath the crust could buoy up the western scottish massifs if this buoyancy were the consequence of igneous underplating then any underplated material would have to lie beneath the seismic reflection moho

hydrogeologic processes in saline systems playas sabkhas and saline lakes abstract pans playas sabkhas salinas saline lakes and salt flats are hydrologically similar varying only in their boundary conditions thus in evaluating geochemical processes in these systems a generic water and solute mass balance approach can be utilized a conceptual model of a coastal sabkha near the arabian gulf is used as an example to illustrate the various water and solute fluxes analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha but contribute only a small volume of the water local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge to rainfall ratio of more than 50 the contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha because of a short residence time of water steady state flow is expected within a short time 50 000 years the solute composition of the brine in a closed saline system depends largely on the original composition of the input water the high total ion content in the brine limits the efficiency of water rock interaction and absorption because most natural systems are hydrologically open the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation thus during the hot dry season months minerals exhibit retrograde solubility so that gypsum anhydrite and calcite precipitate evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone e g halite and carnallite provided that the relative humidity of the atmosphere is less than the activity of water the slope of the fresh brine water interface in saline lake systems is shallower than in fresh seawater interface because of the greater density difference between the fresh brine water bodies the interface between sabkha brines and seawater slopes seaward unlike normal marine fresh water systems that slope landward moreover the brine seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha s brine

estimation of current plate motions in papua new guinea from global positioning system observations plate tectonic motions have been estimated in papua new guinea from a 20 station network of global positioning system sites that has been observed over five campaigns from 1990 to 1996 the present velocities of the sites are consistent with geological models in which the south bismarck woodlark and solomon sea plates form the principal tectonic elements between the pacific and australian plates in this region active spreading is observed on the woodlark basin spreading centre but at a rate that is about half the rate determined from magnetic reversals the other major motions observed are subduction on the new britain trench seafloor spreading across the bismarck sea seismic lineation convergence across the ramu markham fault and left lateral strike slip across the papuan peninsula these motions are consistent with a 8 2 myr 1 clockwise rotation of the south bismarck plate about a pole in the huon gulf and a rotation of the woodlark plate away from the australian plate second order deformation may also be occurring in particular manus island and northern new ireland may be moving northward relative to the pacific plate at 5 8 mm yr 1 significant at the 95 but not at the 99 confidence level which may suggest the existence of a north bismarck plate

active tectonics of the eastern sunda and banda arcs the tectonics of the eastern sunda and banda arcs of eastern indonesia are inferred from the centroid depths seismic moments and fault plane solutions of 63 large earthquakes that occurred between 1962 and 1984 source parameters are estimated by inverting long period teleseismic p and sh waves earthquakes show that the collision of the australian continent with the banda arc shortens the upper plate beneath the forearc and back arc basin over the broad area between the timor and seram troughs along the eastern end of the sunda arc and along the southern banda arc earthquakes reveal that the arc and forearc respond to collision by shortening in the direction of convergence by elongating in the direction perpendicular to convergence and by thrusting over the back arc basin shallow thrust and strike slip earthquakes beneath the banda basin the back arc basin demonstrate that deformation within the back arc accommodates some of the northward motion of the australian continent the rate of north south shortening of the entire upper plate at the longitude of timor calculated from the seismic moments of the earthquakes over the 22 year period is roughly 20 of the predicted convergence rate between australia and southeast asia strike slip faulting within the banda basin results also in eastward motion of the banda arc with respect to western indonesia and australia eastward extrusion of the banda arc results in thrusting at the aru trough earthquakes due to thrusting of the back arc basin beneath the volcanic arc are too shallow to corroborate that the arc s polarity has reversed although the wetar back arc thrust zone at present has a high seismic slip rate earthquakes and their mechanisms provide evidence that the lithosphere of the weber basin a 7500 m deep forearc basin rests on the subducting lithosphere without intervening asthenosphere so that the weber basin subsides in response to sinking of the subducting lithosphere closure of the banda basin is geometrically incompatible with the australian plate subducting simultaneously beneath both the timor and seram troughs instead the bird s head which subducts beneath seram is decoupled from the australian plate in western new guinea and probably moves west or southwest with respect to australia in the eastern indonesian example strike slip faulting plays a major role in the evolution of the collision zone and clearly demonstrates the complexity in three dimensions of continental accretion and mountain building by arc continent collision

active deformation in the new guinea fold and thrust belt seismological evidence for strike slip faulting and basement involved thrusting the new guinea fold and thrust belt forms a 1000 km long mountain chain running the length of new guinea but its trend is oblique to the predicted convergence direction a large component of left lateral shear across the mountain belt is expected but geological evidence for such motion is ambiguous surface structures in the fold and thrust belt show mountain building by folding and thrusting supposedly thin skinned of pre pliocene continental shelf sediments although some evidence indicates that active faulting penetrates the basement we examine the active deformation of this mountain belt by using teleseismic long period p and sh waveforms short period p waveforms and p wave first motions to determine reliable focal mechanisms and source depths for the 18 largest earthquakes in the new guinea fold and thrust belt since 1964 eight thrust events with seismic moments m0 between 1017 and 2 1018 n m are distributed throughout the thrust belt at depths ranging from 0 5 to 45 km and have steeply dipping fault planes that strike parallel to surface structural trends six of the eight events are between 11 and 25 km deep the steep dips of nodal planes the depths of these earthquakes and the known thicknesses of the sedimentary section show that thrust faulting is not exclusively thin skinned i e confined above a shallow detachment surface but penetrates the crystalline basement at high angles most earthquakes in the western half of the thrust belt including the three largest earthquakes examined m0 5 1018 n m show strike slip faulting with the probable fault plane oriented east west so that displacement is left lateral the nine strike slip earthquakes account for almost 90 of the observed seismic moment in the period 1964 1985 and indicate a seismic slip rate of 5 25 mm a all but one of these strike slip earthquakes are shallower than the thrust earthquakes suggesting that east northeast convergence across the fold and thrust belt is accommodated by a decoupled system of strike slip and dip slip faults while the great height of the mountain belt is an obvious indication that crustal thickening is an important consequence of plate motion in new guinea seismological evidence suggests that translation by strike slip faulting may play a much greater role than previously recognized by analogy in older collisional orogens whose motions can be inferred only from remnant structures and not from seismicity strike slip faulting may have been equally important in accommodating convergence we estimate from seismic moments of earthquakes and from the volume of the mountains that deformation of the new guinea highlands may account for 5 20 of the total convergence between the pacific plate and australia in new guinea

geological evolution of the tyras vallis paleolacustrine system mars 1 using the new high resolution stereo camera hrsc data and other martian data sets we reconstructed the hydrological history of an unnamed complex crater in the xanthe terra region the crater hosted a lacustrine basin fed by a dense and centripetal drainage system developed along its inner rim and by the tyras vallis channel where the tyras vallis opens into the crater a prominent delta like feature is visible characterized by a central terrace and two small longitudinal scarps this deposit has been used as sedimentary recorder of the crater lake history and allowed assessment of the overall hydrological evolution two major stands of the water level have been inferred at 700 and 550 m above the crater floor based on the correlation between the morphology and topography of the fan and the crater floor deposits our reconstruction reveals a complex sedimentary evolution of the fan which underwent deltaic and alluvial sedimentation as a result of the different lake water levels and tyras vallis supplies a dominant erosional evolution of the fan delta was determined by the interaction between the fluvial characteristics and basin wave regime wave height analysis and morphological comparison with terrestrial analogues support this hypothesis the lacustrine activity could be chronologically placed between the late noachian and the hesperian the climatic conditions could have allowed the recharge of the regional groundwater system by precipitation and episodic fluvial activity however also heating effects of cratering could have affected the system rejuvenating or accelerating the recharge of the local aquifer

active thrust front of the greater caucasus the april 29 1991 racha earthquake sequence and its tectonic implications although fault bounded thrust sheest are common in the geological record seismic evidence for their motion is sparse the april 29 1991 racha earthquake m s 7 0 the largest instrumentally recorded earthquake in the greater caucasus is one of the largest recent earthquakes in continental thrust belts and provides evidence on mechanisms of thrust sheet motion using data from a deployment of program for array seismic studies of the continental lithosphere passcal digital seismographs and various other instrumental we locate 1952 aftershocks occurring between may 7 and june 30 1991 the aftershocks form a zone 70 km long and 10 25 km wide striking e w following the racha ridge at the southern boundary of the greater caucasus thrust system teleseismic body waves are inverted for source parameters of the mainshock and the two largest aftershocks the solutions show thrust faulting with centroid depths of 3 10 km comparable to depths of locally recorded aftershocks 2 12 km the shallow dipping nodal plane the aftershock distribution and surface geology demonstrate that the main event was caused by faulting on a thrust system dipping nne at 20 o 31 o bounding the southern slope of the greater caucasus this fault system thrusts the greater caucasus structures south over the dzhirula basement massif the inferred fault geometry suggests that the active fault is either a detachment between sediments and dzhirula basement or cuts through the basement at shallow depths the 1500 m high racha ridge overlies the aftershock zone and is a likely consequence of repeated similar earthquakes hence the 1991 earthquake sequence shows that the western greater caucasus is accommodating plate convergence at a rate possibly comparable to the eastern greater caucasus a few millimeters per year along strike geological discontinuities above and below the thrust surface correspond to the eastern end of the mainshock rupture area no strong evidence for transfer structures could be found along strike suggesting that differences in collisional style between the western and eastern greater caucasus may reflect differences in mechanical properties rather than differences in convergence rate a june 15 1991 event and its aftershocks southeast of the primary aftershock zone along strike show fault planes and slip vectors rotated 41 o clockwise from the mainshock this rotation is consistent with an along strike change in direction of the thrust front near 44 o e longitude and demonstrates strong local structural or topographic control on slip direction the rotation requires along strike shortening within the greater caucasus thrust system at a rate comparable to the rate of thrusting

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve