quasistatic propagation of a normal fault a fracture mechanics model abstract we have carried out boundary element calculations to simulate quasistatic propagation of a normal fault in the earth s crust under a horizontal tensile loading byerlee s frictional law is employed to describe the mechanical behavior of the fault surface we hypothesize that in order for a normal fault to grow quasistatically the mixed mode effective shear stress intensity factor must exceed a threshold value fracture toughness a crustal material property we suggest that the fault grows in a direction of local maximum shear stress the direction of fault propagation thus depends on the ratio of tensile and shear stress intensity factors a listric normal fault is likely to form in crustal material with a small shear fracture toughness a listric normal fault is also more likely to form in crustal material with a high degree of plasticity the propagation trajectory of an incrementally growing normal fault is examined as the normal fault extends to a greater depth the shear stress intensity factor drops owing to an increase in fault surface friction the equilibrium depth to which a normal fault will grow is controlled by the far field loading and the fracture mechanical property of the crustal material the decrease of shear stress intensity with fault length also stabilizes the fault growth

chloride bearing materials in the southern highlands of mars chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing spectrally distinct surface deposits consistent with chloride bearing materials have been identified and mapped using data from the 2001 mars odyssey thermal emission imaging system these deposits are found throughout regions of low albedo in the southern highlands of mars geomorphologic evidence from orbiting imagery reveals these deposits to be light toned relative to their surroundings and to be polygonally fractured the deposits are small

paleolakes paleofloods and depressions in aurorae and ophir plana mars connectivity of surface and subsurface hydrological systems abstract the plains of aurorae and ophir in the equatorial region of mars display geomorphic evidence indicative of extensive but generally short lived paleohydrological processes elaver vallis in aurorae planum south of ganges chasma is an outflow channel system 180 km long and here inferred to have formed by cataclysmic spillover flooding from a paleolake s contained in the morella crater basin ganges cavus is an enormous 5 km deep depression of probable collapse origin located in the morella basin the fluid responsible for the infilling of the morella basin likely emerged at least partially through ganges cavus or its incipient depression and it may have been supplied also from small scale springs in the basin similar paleohydrological processes are inferred also in ophir planum it is reasonable to assume that water sometimes sediment laden and or mixed with gases was the responsible fluid for these phenomena although some of the observed features could be explained by non aqueous processes such as volcanism water emergence may have occurred as consequences of ground ice melting or breaching of cryosphere to release water from the underlying hydrosphere dike intrusion is considered to be an important cause of formation for the cavi and smaller depressions in aurorae and ophir plana explaining also melting of ground ice or breaching of cryosphere alternatively the depressions and crater basins may have been filled by regional groundwater table rising during the period s when cryosphere was absent or considerably thin the large quantities of water necessary for explaining the paleohydrological processes in aurorae and ophir plana could have been derived through crustal migration from the crust of higher plains in western ophir planum where water existed in confined aquifers or was produced by melting of ground ice due to magmatic heating or climatic shift or from a paleolake in candor chasma further west

eruption history of the elysium volcanic province mars abstract volcanism has played a significant role in shaping the surface of mars volatiles released during eruptions profoundly altered the composition and density of the martian atmosphere in the past quantifying the amounts of volcanic outgassing has been attempted regionally and globally however volume estimates of erupted volcanic material in time are still poorly constrained here we show the first eruption frequency record of a volcanic region the elysium volcanic province which is the second largest volcanic province on mars studied lava flows show model ages ranging from 3 4 ga to 60 ma together with observed resurfacing ages the visible record of volcanic activity extends back to 3 9 ga based on our 190 model ages continuous volcanic activity is apparent with a major peak at 2 2 ga in the last 1 gyr the activity rapidly waned although the majority of volcanic material including volatiles released to the atmosphere erupted within a short time span of less than 200 ma activity continued until the very recent past extrapolating the eruption record it appears likely that this region of mars is still volcanically active today our derivation of the eruption record has profound implications for global thermal and atmospheric modeling indicating sustained heat production melt generation and magma ascent at a single location over most of the planet s geological history

idealized modelling of landfalling cold fronts the effects of land surfaces sea surfaces and coastlines on the dynamics of cold fronts are examined in an idealised two dimensional confluent deformation model of frontogenesis when the deformation field is stationary increasing the surface roughness weakens the fronts while increasing the cross front ageostrophic wind and frontal updraughts the frontogenetic effect of deformation balances the frontolytic effect of turbulent mixing resulting in near steady state fronts in steady state the surface fronts are located near the point at which the cross front flow vanishes this equilibrium point moves towards the warm air as the surface roughness is increased because the cross front ageostophic wind also increases with increasing surface roughness surface sensible heating weakens and slows the fronts during the day whereas surface sensible cooling strengthens and accelerates them at night adding a coastline to the model results in very strong gravity current like fronts in the afternoon with a relative flow of cool air towards their leading edge above the boundary layer the synoptic fronts remain unaffected by the coastline as the turbulent mixing weakens in the late afternoon the coastal fronts surge inland advancing faster than the wind speed in the boundary layer when the deformation field is allowed to translate the fronts advance across the ocean towards land if the fronts reach the coastline between mid morning and late afternoon the daytime heating over the land opposes the onshore advection of cold air retarding the fronts at the coastline if the fronts reach the coastline in the evening or early morning they advance onshore relatively unimpeded hence the fronts arrive onshore preferentially in the late afternoon or evening copyright 2010 royal meteorological society

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

episodes of fluvial and volcanic activity in mangala valles mars a new mapping based study of the 900 km long mangala valles outflow system was motivated by the availability of new high resolution images and continued debates about the roles of water and lava in outflow channels on mars this study uses photogeologic analysis geomorphic surface mapping cratering statistics and relative stratigraphy results show that mangala valles underwent at least two episodes of fluvial activity and at least three episodes of volcanic activity during the late amazonian the occurrence of scoured bedrock at the base of the mapped stratigraphy in addition to evidence provided by crater retention ages suggests that fluvial activity preceded the deposition of two of the volcanic units crater counts performed at 30 locations throughout the area have allowed us to construct the following timeline 1 formation of noachian highlands and possible initial flooding event s before 1 ga 2 emplacement of tharsis lava flows in the valley from 700 to 1000 ma 3 a megaflooding event at 700 800 ma sourced from mangala fossa 4 valley fill by a sequence of lava flows sourced from mangala fossa 400 500 ma 5 another megaflooding event from 400 ma 6 a final phase of volcanism sourced from mangala fossa 300 350 ma and 7 emplacement of eolian sedimentary deposits in the northern portion of the valley 300 ma these results are consistent with alternating episodes of aqueous flooding and volcanism in the valles this pattern of geologic activity is similar to that of other outflow systems such as kasei valles suggesting that there is a recurring and perhaps coupled nature of these processes on mars

novel 3d sequence stratigraphic numerical model for syn rift basins analysing architectural responses to eustasy sedimentation and tectonics syn rift clastic sedimentary systems preserve a complicated stratigraphic architecture that records the interplay of tectonics eustatic sea level and storage and routing of sediments previous conceptual models describe and explain changes in depositional stacking patterns along a fault segment however stacking patterns and the nature of key stratigraphic surfaces is challenging to predict accurately with conventional sequence stratigraphic models that do not consider the three dimensional interplay of subsidence sedimentation and eustasy we present a novel geometric 3d sequence stratigraphic model syn strat which applies temporally and spatially variable fault scale tectonic constraints to stratigraphic forward modelling as well as allowing flexibility in the other controls in time and space syn strat generates a 3d graphical surface that represents accommodation although the model has the capacity to model footwall variation here we present model results from the hangingwall of a normal fault with temporal and spatial dip and strike predictions made of stacking patterns and systems tracts for a given set of controls sensitivity tests are tied to the depositional architecture of field based examples from the loreto basin gulf of california and alkyonides basin gulf of corinth here the relative influence of major sedimentary controls different subsidence histories varying sedimentation distribution including along strike variation in stacking patterns are assessed and demonstrate the potential of syn strat for reducing subsurface uncertainties by resolving multiple scenarios in addition the model demonstrates the nature of diachroneity of key stratigraphic surfaces that can arise in syn rift settings which could be represented by a bypass surface sequence boundary or reservoir seal maximum flooding surface in the rock record enabling a quantitative assessment of these surfaces is critical for prospect analysis in hangingwall half graben fills where these surfaces are heavily relied upon for well correlations that are used for hydrocarbon volume and production rate predictions

implications of selected subsurface data on the structural form and evolution of some basins in the northern basin and range province nevada and utah

geodetic constraints to the kinematics of the kapareli fault reactivated during the 1981 gulf of corinth earthquakes abstract comparison of historical and of post seismic triangulation data is used to model vertical crustal movements in the vicinity of the kapareli fault or the alkynonides earthquakes north fault one of the two antithetic normal faults which reactivated during the 1981 gulf of corinth ms 6 7 earthquakes this fault is characterized by a much smaller geomorphological signature than the south or perachora fault of the same seismic sequence analysis of geodetic data on the basis of polynomial filtering and elastic dislocation modelling as well as analysis of structural and coastal change data permits us to conclude that the upper bound in the uncertainty level of most of the available elevation changes is 20 30 cm usually lower than the corresponding dislocation signal in addition the available geodetic data have a systematic pattern and are consistent with structural data for this reason they permit more precise constraints on the geometry and the role of the kapareli fault or the alkyonides earthquakes north fault its total length is estimated about 17 km about 50 longer than its surface trace about 30 40 cm subsidence of its hanging wall as well as at least 15 cm maximum uplift of its footwall is also inferred this new evidence suggests that although in the long term the kapareli fault may represent a rather secondary antithetic fault to the alkyonides earthquakes south perachora fault during the 1981 earthquakes it probably had a more important structural role

patterns and timing of late quaternary faulting in the great basin province and relation to some regional tectonic features large scale surface faulting events each tens of kilometers long and involving more than a meter of displacement of late quaternary age have not been uniformly distributed but have been concentrated in subprovincial and smaller belts and areas within the great basin province furthermore faulting apparently has not been uniformly distributed over time the average recurrence interval of large scale faulting events on individual faults in the province is measured in thousands or tens of thousands of years in contrast to such long recurrence intervals in the central nevada and eastern california seismic belts large scale faulting events have occurred during the last 111 years in an apparently coherent sequential belt filling pulse of activity in which events were separated by only a few years or a few decades the questions are where are other pulses of large scale faulting likely to occur and what controls the localization of such belts and areas characterized by higher rates of faulting two examples of tectonic subprovinces that may play a role in delimiting smaller zones of faulting are the black rock carson sink zone of extension and the central nevada downwarp the central nevada seismic belt lies along the dividing line between these two subprovinces and the northwest margin of the black rock carson sink zone of extension coincides with the margin of a fingerlike belt of dense faulting in northwestern nevada

geometry of cenozoic extensional faulting dixie valley nevada precise definition of geometric relationships between individual basins and ranges may help to reveal the mechanical processes of basin and range cenozoic extensional faulting at depth previous studies have attempted to identify simple horsts and grabens tilted crustal blocks with planar faulting or tilted crustal blocks with listric faulting in the shallow crust normal faults defining these crustal blocks may root 1 individually in the ductile lower crust 2 in regional or local low angle detachment faults or 3 in igneous intrusions or decoupling surfaces produced by the intrusions the present study in dixie valley west central nevada makes use of a seismic reflection survey gravity models seismograms from earthquakes occurring on december 16 1954 and geometrical block models these data show a structurally asymmetric basin bounded by a single zone of faulting on the northwest and by a downbowed and step faulted floor to the southeast the northwest bounding fault is moderately dipping 50 and planar to a depth of 3 km the southeast boundary is step faulted and altogether the faults indicate an extension of 20 across the valley at the rate of 0 38 mm y for the last 8 my synthetic earthquake seismograms confirm a focal depth of 15 km and fault dip of 62 for the fairview peak earthquake and suggest that the focal depth of the dixie valley earthquake was also 15 km instead of the previously reported 40 km local microearthquakes cluster around 10 15 km the geometrical block models indicate that crustal horst graben faulting and planar high angle normal faults rooted in a low angle detachment surface do not readily account for development of the subsidiary step faults found in dixie valley extension of the crust by intrusion may develop high angle faults and with further intrusion may develop the subsidiary faults and produce a complex sagged asymmetric graben like dixie valley

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

role of rift structural inheritance in orogeny highlighted by the western pyrenees case study abstract it is commonly accepted that many orogens form by contractional reactivation of earlier continental rifts or rifted margins therefore to better understand orogenesis it is important to also understand how rift domains and their associated structures are incorporated into orogens we investigate the role of rift structural inheritance during orogeny using the western pyrenees as a case study to achieve our aim we use a kinematic forward lithosphere deformation model rifter to produce flexural isostatically compensated as well as balanced cross sections showing the structural and stratigraphic development of both the rift and orogenic stages of the western pyrenees the cross section produced extends from the northern to the southern foreland basins and crosses the mauleon arzacq basin our modelling results show how rift domains and their faults are sequentially reactivated and incorporated into the present day western pyrenees architecture based on the results from our case study we identify a sequence of tectonic stages separated by critical events that record the transition between different tectonic styles by which lithosphere is deformed the pre orogenic extensional stage is characterized by a hyper extended rift system that eventually led to exhumed mantle this constitutes the pre orogenic template the subsequent contractional tectonics consists of two stages i the inversion of the hyper extended rift system reactivating extensional structures and ii the crustal shortening of the southern proximal rift domain results of the western pyrenees case study may be used to understand the development of other alpine type collisional systems involving the sequential reactivation and inversion of former hyper extended rift systems

tectonic history of the tharsis region mars the faults of the tharsis region of mars have been mapped and delineated on the basis of age the orientation of each group of faults was analyzed to determine if they were radial to a point the results indicate that there are at least four discrete centers of faulting within the tharsis area which are of significantly different age the four centers proposed are from oldest to youngest 1 in the thaumasia highlands 2 in northern syria planum and finally 3 and 4 near pavonis mons while episodes 3 and 4 occupy the same geographic position they are separated in time by the development of the tharsis lava plains and shields each episode of tectonism was separated from the next by a period of major basaltic volcanism the tectonic features of the tharsis area are thus viewed as being the cumulative result of the superposition of several discrete episodes of faulting rather than the result of one episode about a single point

a review of cold fronts with prefrontal troughs and wind shifts the conceptual model of a classical surface based cold front consists of a sharp temperature decrease coincident with a pressure trough and a distinct wind shift at the surface many cold fronts however do not conform to this model time series at a single surface station may possess a pressure trough and wind shift in the warm air preceding the cold front hereafter called a prefrontal trough and prefrontal wind shift respectively although many authors have recognized these prefrontal features previously a review of the responsible mechanisms has not been performed to date this paper presents such a review ten disparate mechanisms with different frontal structures have been identified from the previous literature these mechanisms include those external to the front i e those not directly associated with the cold front itself synoptic scale forcing interaction with lee troughs drylines interaction with fronts in the mid and upper troposphere and frontogenesis associated with inhomogeneities in the prefrontal air mechanisms internal to the front i e those directly associated with the structure and dynamics of the front include the following surface friction frontogenesis acting on alongfront temperature gradients moist processes descent of air ascent of air at the front and generation of prefrontal bores gravity waves given the gaps in our knowledge of the structure evolution and dynamics of surface cold fronts this paper closes with an admonition for improving the links between theory observations and modeling to advance understanding and develop better conceptual models of cold fronts with the goal of improving both scientific understanding and operational forecasting

what sets topographic relief in extensional footwalls we use three large normal fault arrays in the northeastern basin and range province western united states to document catchment development and relief production during fault growth fault slip and slip rates increase systematically along strike from zero at the fault tips catchment relief and across strike range width both increase as slip accumulates but reach maximum values at a distance of 15 km from the fault tips and remain uniform along strike over much of the footwalls catchment outlet spacing also increases away from the fault tips but does not reach a uniform value and may vary by a factor of 5 6 along strike we infer that catchments first elongate in the across strike direction as slip accumulates and the range half width increases once the half width reaches its maximum value continued catchment growth is possible only by along strike capture which increases outlet spacing but not relief the close correspondence between catchment relief and range half width suggests that geomorphically limited hillslope and channel gradients are achieved within the 15 km tip zone thus the limiting factor in footwall development is the width of the range which is controlled by two external agents the geometry and spacing of the major faults and the elevations of base level on both flanks

new evidence for a magmatic influence on the origin of valles marineris mars in this paper we show that the complex geological evolution of valles marineris mars has been highly influenced by the manifestation of magmatism e g possible plume activity this is based on a diversity of evidence reported here for the central part melas chasma and nearby regions including uplift loss of huge volumes of material flexure volcanism and possible hydrothermal and endogenic induced outflow channel activity observations include 1 the identification of a new 50 km diameter caldera vent like feature on the southwest flank of melas which is spatially associated with a previously identified center of tectonic activity using viking data 2 a prominent topographic rise at the central part of valles marineris which includes melas chasma interpreted to mark an uplift consistent with faults that are radial and concentric about it 3 hirise identified landforms along the floor of the southeast part of melas chasma that are interpreted to reveal a volcanic field 4 crism identification of sulfate rich outcrops which could be indicative of hydrothermal deposits 5 grs k th signature interpreted as water magma interactions and or variations in rock composition and 6 geophysical evidence that may indicate partial compensation of the canyon and or higher density intrusives beneath it long term magma tectonic and water interactions late noachian into the amazonian albeit intermittent point to an elevated life potential and thus valles marineris is considered a prime target for future life detection missions

surface faulting accompanying the borah peak earthquake central idaho the ms 7 3 borah peak earthquake that struck central idaho on october 28 1983 was one of the strongest historic earthquakes in the intermountain seismic belt much of the 34 km long northwest trending zone of fault scarps and surface ruptures that formed during the earthquake follows holocene and upper pleistocene scarps of the lost river fault throw along the new fault scarps averages 0 8 m exceeds 1 0 m along 43 of their length and attains a maximum of 2 7 m along the broad and complex zone of deformation in the southern section the net slip was normal sinistral averaging 17 cm lateral slip for 100 cm of dip slip the preferred nodal plane from the focal mechanism strikes n22 w dips 59 sw and suggests a much larger component of strike slip than do the geologic data

zumba crater daedalia planum mars geologic investigation of a young rayed impact crater and its secondary field abstract zumba is a 2 9 km diameter rayed crater on mars located on extensive lava plains in daedalia planum to the southwest of arsia mons it is a well preserved young crater with large ejecta rays that extend for hundreds of kilometers from the impact site the rays are thermally distinct from the background lava flows in themis daytime and nighttime thermal infrared data a unique characteristic among martian rayed craters concentrated within the rays are solitary or dense clusters of secondary craters with associated diffuse dark toned deposits along with fewer secondary craters lacking dark toned deposits using ctx images we have mapped secondary craters with dark toned deposits collectively termed secondary fields to investigate their distribution as a function of distance from the impact site the mapped secondary field was then used to investigate various aspects of the crater forming event such as the surface angle and direction of the projectile the effect of secondary craters on surface age estimates and the number of secondary craters produced by the impact event from our mapping a total of 13 064 secondary fields were documented out to a 200 km radial distance beyond a 15 km wide non secondary zone around zumba crater results show that the highest areal coverage of secondary fields occurs within 100 km of zumba and within its rays decreasing radially with distance to a background scattering of small secondary fields that are 2 in size 91 9 of the total population the strong east west asymmetry of crater rays and low areal coverage of fields to the south of zumba correlate well with studies of zumba impact melt deposits indicating a moderately oblique impact projectile coming from the south using primary craters in a 101 km 2 sample region and all craters primaries and secondaries from 43 select secondary fields in two map sectors in the study area we obtain ages of 580 100 ma and 650 70 ma respectively for the lava flows into which zumba impacted these ages are consistent with and intermediate to 0 1 1 ga volcanic flow units within and near daedalia planum for craters within the secondary fields a log differential plot of the data shows a pronounced downward deflection of the binned points for craters 100 m we estimate that 352 000 secondary craters were produced by the zumba impact event

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

topographic amplification of tectonic displacement implications for geodetic measurement of strain changes correlations of level changes with topography demand an assessment of the effect of an irregular free boundary on surface deformation this is examined through a plane strain elastic model with topography of small slope subjected to a change in the far field horizontal stress to leading order vertical surface displacements due to the topographic perturbation are proportional to the local relief elevationdependent uplift results from a compressional change and downdrop results from a tensional change the model further predicts that the ratio of elevation change to elevation is proportional to and of the same order of magnitude as the regional strain horizontal strains are locally perturbed by topography as well with the magnitude scaling with the local slope the predicted localization of level changes is very small in aseismic regions and cannot contribute significantly to measured correlations a test case in southern california bears this out with strains of order 10 6 accompanied by elevation change to elevation ratios of order 10 4 releveling following the nankaido tonankai earthquakes which induced large coseismic and postseismic strains reveals scattered examples of elevation dependent level changes however when compared to modeled strains the correlations are again at least an order of magnitude larger than the localization effect predicted by the elastic model although the topographic perturbation of vertical displacements appears to be unmeasurably small local variations in horizontal strain or borehole dilatation across steep relief may be discernible with current technology

teleseismic estimates of the energy radiated by shallow earthquakes the energy flux contained in the p wave groups p pp sp or the s wave groups s ps ss radiated by a shallow earthquake is modeled assuming that the energy flux in the direct and depth phases adds incoherently by defining generalized radiation patterns which incorporate this neutral interference the wave groups are analyzed as though they were comprised of a single phase measurements of the energy flux in the wave groups are corrected in the frequency domain for both the body wave attenuation and the frequency band of the recording the corrected measurements are then used to estimate the seismic energy radiated by the earthquake this analysis is applied to digital recordings of the teleseismic wave groups radiated by the may 2 1983 coalinga california earthquake and the october 28 1983 borah peak idaho earthquake for the coalinga earthquake an estimate of es 1 6 0 4 1021 dyn cm was determined from six p wave groups while the sh wave group recorded at station col returned an estimate of es 1 2 1021 dyn cm for the borah peak earthquake an estimate ofes 3 2 0 5 1021 dyn cm was determined from seven p wave groups the distribution of the isoseismals for the borah peak earthquake indicate that the energy radiated by this event was focussed to the northwest in the direction of rupture propagation correcting the teleseismic estimate for this focussing gives es 3 6 0 5 1021 dyn cm combining these estimates of the radiated energy with broad band estimates of the seismic moment yields estimates of the apparent stress of 17 and 7 bars for the coalinga and the borah peak earthquakes respectively

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

vertical deformation associated with normal fault systems evolved over coseismic postseismic and multiseismic periods vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways sparse but robust geodetic seismic and geologic observations in the basin and range province of the western united states indicate that immediately after an earthquake vertical change primarily occurs as subsidence of the normal fault hanging wall a few decades later a 100 km wide zone is symmetrically uplifted the preserved topography of long term rifting shows bent and tilted footwall flanks rising high above deep basins we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting we replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust a 60 dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width 10 km which is predicted to take place within 1 2 decades after each large earthquake thus the best preserved topographic signature of rifting is expected to occur early in the postseismic period the relatively stronger lower crust in our models is necessary to replicate broader postseismic uplift that is observed geodetically in subsequent decades

diagnosis of frontal instabilities over the southern ocean the development of three fronts over the southern ocean is described using seawinds on quikscat scatterometer surface winds and an attribution technique to partition the wind field in three components nondivergent and irrotational components at the scale of the front and the remaining harmonic component or environmental flow induced by the synoptic scale flow the front and the environment in which the front is embedded are analyzed separately a frontal wave is shown to develop out of the first front when the large scale alongfront stretching decreases the environmental flow becomes frontolytic and a connection with the upper levels is established in the second case the stretching remains relatively strong and no frontal wave develops the third front exhibits a developing wave but is not in a favorable configuration with the upper levels the frontal wave does not deepen significantly

surface dynamics of observed maritime fronts abstract the problem of establishing the important mechanisms and processes in surface fronts is examined it is shown that boundary layer processes may modify the details of frontal dynamics near the surface and that at the same time fronts may alter boundary layer solutions a similarity model that assumes a horizontally homogeneous steady state planetary boundary layer is used to test the effects of baroclinity and stratification on the ageostrophic vorticity model response to baroclinity and stratification is tested a boundary layer positive feedback mechanism that stems from the variation in stratification and thermal advection across a front and favors the creation of stronger temperature gradients in cold fronts is proposed a compatible model that includes the effects of horizontal inhomogeneity is derived and used in conjunction with scatterometer data to observe the behavior of five surface fronts observations are compared to results of numerical models by several authors and it is concluded

onset timing and slip history of the teton fault wyoming a multidisciplinary reevaluation the dramatic relief of the teton range in northwestern wyoming results from motion along the teton normal fault new apatite u th he ahe and fission track aft ages of samples collected in the footwall yield fundamental constraints on contrasting models of teton fault activity and consequent relative footwall uplift low elevation samples in the immediate footwall of the fault range from 12 5 to 6 5 ma ahe ages of samples from subvertical transects range from 57 8 to 6 5 ma rendezvous 54 0 to 6 8 ma grand and 20 5 to 7 1 ma moran with all three transects yielding an expected trend of decreasing age with decreasing elevation aft ages obtained from the three transects range from 55 4 to 45 7 ma rendezvous 43 2 to 13 3 ma grand and 38 0 to 11 7 ma moran inverse thermal history modeling indicates that the onset of relatively rapid cooling as a proxy for relative footwall uplift initiated first in the northern part of the range 15 13 ma and then migrated south as fault displacement continued 7 ma to present at rendezvous thus this work suggests that although the teton fault likely initiated due to basin and range extension this structure remains active normal fault displacement models also suggest a minimum of 6 km displacement for footwall uplift of 2 km if evaluated in the context of established normal fault length displacement relationships this yields a length of 180 km substantially longer than current estimates of teton fault length and putting the northern end of the fault well into and potentially beyond the bounds of yellowstone national park

morphologic and thermophysical characteristics of lava flows southwest of arsia mons mars abstract the morphologic and thermophysical characteristics of part of the extensive lava flow fields southwest of arsia mons 22 5 27 5 s 120 130 w have been examined using a combination of orbital vnir and tir datasets themis images provide context for the regional geology and record diurnal temperature variability that is diverse and unusual for flow surfaces in such close proximity ctx images were used to distinguish dominant flow types and assess local age relationships between individual lava flows ctx and hirise images provide detailed information on flow surface textures and document aeolian effects as they reveal fine grained deposits in many low lying areas of the flow surfaces as well as small patches of transverse aeolian ridges although this region is generally dust covered and has a lower overall thermal inertia the themis data indicate subtle spectral variations within the population of lava flows studied these variations could be due to compositional differences among the flows or related to mixing of flow and aeolian materials specific results regarding flow morphology include a two main lava flow types bright rugged and dark smooth as observed in ctx images dominate the southwest arsia mons ne daedalia planum region b the bright rugged flows have knobby ridged and or platy surface textures commonly have medial channel levee systems and may have broad distal lobes c the dark smooth flows extend from distributary systems that consist of combinations of lava channels lava tubes and or sinuous ridges and plateaus and d steep sided terraced margins digitate breakout lobes and smooth surfaced plateaus along lava channel tube systems are interpreted as signatures of flow inflation within the dark smooth flow type these flows exhibit smoother upper surfaces are thinner and have more numerous smaller lobes which along with their the channel tube fed nature indicate a lower viscosity lava than for the bright rugged flows flow patterns and local interfingering and overlapping relationships are delineated in ctx images and allow reconstruction of the complex flow field surfaces darker channel tube fed flows are generally younger than adjacent thicker bright rugged flows however the diversity and complexity of temporal relationships observed along with the thermophysical variability suggests that lava sources with different eruptive styles and magnitudes and or lavas that experienced different local emplacement conditions were active contemporaneously

spectral analysis of topography and gravity in the basin and range province abstract a two dimensional spectral analysis has been carried out for the topography and the bouguer gravity anomaly of the basin and range province in western north america the aim was to investigate the possible presence of dominant wavelengths in the deformation pattern at the surface and at the depth of compensation the results suggest that a 200 km wavelength in the deep compensating mass distribution has been inherited from an early tectonic phase of extension at an azimuth n65 e the corresponding surface topography exhibits prominent overtones at wavelength of 100 75 and possibly 45 km it is argued that these characterize the non linear rheology of the upper crust the short wavelengths in the topography reflect the present phase of deformation mixed with the results of the older deformations these results point to a need to extend the physical models of lithospheric stretching beyond the presently available one phase scenario however they show that the boudinage instability concept is consistent with the data

spatial and temporal distribution of deformation at the front of the andean orogenic wedge in southern bolivia new observations from an active orogenic wedge help link the seismotectonic behavior of individual faults to wedge deformation rates and patterns over multiple timescales we provide the first detailed constraints on the distribution and timing of deformation at the front of the andean orogenic wedge in southern bolivia where a recent study suggests that great mw 8 earthquakes could rupture the master fault underlying the wedge we use stratigraphic relationships across fault related folds and elastic dislocation modeling of seismic reflection horizons to obtain probabilistic estimates of wedge front fault ages and slip rates our analyses reveal that at least half of the previously determined gps based wedge loading and quaternary whole wedge shortening rates are absorbed across a 20 40 km wide wedge front zone consisting of 1 4 en echelon and partially to fully overlapping faults and folds associated with blind thrust faults the difference between our slip rates and the geodetic geologic observations combined with evidence for activity across internal wedge structures supports the notion that nonsteady state mass balance conditions coupled with elevated erosional efficiency result in distributed wedge deformation the orogenic wedge in southern bolivia behaves in a similar fashion to the taiwanese and himalayan ranges slip accumulates at downdip locations along the master fault and is released incrementally by earthquakes that rupture the wedge front fault zone the faults and folds comprising this zone pose a major source of seismic hazard accumulating slip is also released in the wedge interior and older internal wedge faults must be considered in any future assessment of regional earthquake risk

geometry and slip distribution in normal fault systems implications for mechanics and fault related hazards normal faults are important sources of large destructive earthquakes in continental rift provinces we investigate the mechanical characteristics of multiple linked master and subsidiary faults using two dimensional boundary element models the master fault system is a coulomb frictional fault that dips 50 from the surface to a depth of 15 km where it is linked to a subjacent shear zone that creeps under low resolved shear stress we consider two basic configurations one in which the shear zone and master fault are coplanar and the other in which the shear zone dips 20 forming a bent or crudely listric fault system antithetic and splay faults are added to the master fault system in each case to model failure of multiple fault systems that are typical of half grabens we focus on the mechanical interactions between the various faults in order to identify points of initial failure spatial variations in the amount of fault slip and the patterns of surface deformation that may precede catastrophic failure of the master fault system in all cases failure on the master frictional fault initiates at the base where it joins the creeping shear zone and at the earth s surface during the same stress increment the listric fault system fails at lower regional differential stress than the planar fault system failure of a large antithetic fault that dips at 70 from the surface to the base of the frictional master fault initiates at lower regional differential stress for the listric than for the planar case several repeated failure episodes may be required to cause surface offset on the antithetic fault if the master fault system is planar but antithetic surface faulting may occur during each master fault failure episode in the listric case modeled splay faults dip from the surface at either greater 70 or lower 50 angles than the frictional master fault to a depth of 5 km where they intersect the master fault in both cases surface slip is greater on the master fault and lesser on the splay fault surface deformation prior to catastrophic failure of the frictional master fault is generated by creep on the deep seated shear zone and during the initial stages of master fault rupture footwall uplift is predicted above a steeply dipping locked coulomb fault and creeping shear zone but the footwall uplift is absent in the listric fault shear zone case a localized zone of increased extensional strain is centered on the surface trace of the master fault as the result of near surface extensional and shear fracturing during the initial stages of fault slip these geodetic anomalies are of interest because they are a near surface phenomenon which may also alter fluid flow and gas flux and be detectable by hydrologic and geochemical instrumentation as well as geodetic measurements

a large sedimentary basin in the terra sirenum region of the southern highlands of mars abstract different lines of evidence point to hydrological cycling in the martian past the extent duration and magnitude of this cycling remains unclear as well as the magnitude of aqueous processes on the surface here we provide geomorphic and mineralogic evidence of a large inter crater sedimentary basin located in the terra sirenum region which was once covered by a body of liquid water with an areal extent of at least 30 000 km 2 and a depth of approximately 200 m the topographic basin which is modified by a number of large impact craters is partly controlled by ancient impact and tectonic structures as a result of evaporation of the large body of water salt flats formed in the lowest topographic reaches of the basin hydrated phyllosilicates occur in close proximity to the salt flats and in the ejecta and rim materials of small impact craters with stratigraphic relations that suggest that they underlie the evaporite deposits crater statistics place the maximum age of aqueous activity during the late noachian epoch the relatively pristine mineral deposits in the basin have a high potential to yield information of the geochemistry and water activity during the ancient noachian period when conditions were seemingly more conducive to life

geometry of continental normal faults seismological constraints teleseismic body waves from large earthquakes are used to study the downdip geometry of continental normal faults in the aegean waveform modeling techniques together with rigorous statistical tests are applied to put firm bounds on the amount of downdip curvature of these faults and the role of coseismic slip on a basal detachment synthetic modeling shows that good azimuthal station coverage and inclusion of sh waves are necessary to resolve fault curvature the data indicate ruptures of the aegean events occurred on planar faults extending across the entire brittle portion of the crust no seismogenic low angle detachment faulting at the base of the upper crust was detected for these events decoupling of the brittle upper crust from the plastic lower crust probably occurs aseismically in a ductile fashion

space and time aliasing structure in monthly mean polar orbiting satellite data monthly mean wind fields from the european remote sensing satellite ers1 scatterometer are presented a banded structure which resembles the satellite subtrack is clearly and consistently apparent in the isotachs as well as the u and v components of the rou tinely produced fields the structure also appears in the means of data from other polar orbit ing satellites and instruments an experiment is designed to trace the cause of the banded structure the european centre for medium range weather forecasts gridded surface wind analyses are used as a control set these analyses are also sampled with the ers1 temporal spatial sampling pattern to form a simulated scatterometer wind set both sets are used to cre ate monthly averages the banded structures appear in the monthly mean simulated data but do not appear in the control set it is concluded that the source of the banded structure lies in the spatial and temporal sampling of the polar orbiting satellite which results in undersam pling the problem involves multiple timescales and space scales oversampling and under sampling in space aliasing in the time and space domains and preferentially sampled variability it is shown that commonly used spatial smoothers or filters while producing visually pleasing results also significantly bias the true mean a three dimensional spatial temporal interpolator is designed and used to determine the mean field it is found to produce satisfactory monthly means from both simulated and real ers1 data the implications to cli mate studies involving polar orbiting satellite data are discussed

the formation of tharsis on mars what the line of sight gravity is telling us line of sight los spacecraft acceleration profiles from the radio science experiment and topography from the mars orbiter laser altimeter mola instrument of the mars global surveyor mgs are analyzed to estimate the effective elastic thickness te for various regions of tharsis we identify a buried basin flanking the thaumasia highlands at the southeastern margin of tharsis assuming that this basin results from lithospheric flexure from surface loading by the thaumasia highlands we fit los profiles across the feature with a thin shell elastic flexure model and find the mountain belt to reflect a value of te 20 km consistent with a noachian formation age we also determine admittances from los profiles for five regions across tharsis and fit them with theoretical admittances calculated using the flexural model crater density surface density and predominant surface age are found to vary systematically across tharsis while te does not the highest surface density and lowest te values are obtained for the western portion of tharsis where crater densities are lowest our results imply the majority of the topographic rise was emplaced within the noachian irrespective of the surface ages topographic loading and resurfacing i e volcanic activity persisted into the amazonian while becoming increasingly confined to the western margin where the youngest surface ages are found and the eruptive style transitioned from effusive volcanism to shield forming volcanism as te increased

mars high resolution gravity fields from mro mars seasonal gravity and other dynamical parameters abstract with 2 years of tracking data collection from the mro spacecraft there is noticeable improvement in the high frequency portion of the spherical harmonic mars gravity field the new jpl mars gravity fields mro110b and mro110b2 show resolution near degree 90 additional years of mgs and mars odyssey tracking data result in improvement for the seasonal j 3 gravity changes which compares well to global circulation models and odyssey neutron data and mars rotation and precession 7594 10 mas year once atmospheric dust is accounted for in the spacecraft solar pressure model solutions for mars solar tide are consistent between data sets and show slightly larger values k2 0 164 0 009 after correction for atmospheric tide compared to previous results further constraining core models an additional 4 years of mars range data improves the mars ephemeris determines 21 asteroid masses and bounds solar mass loss dgmsun dt

a scheme for improving scatterometer surface wind fields a method is presented for improving quikscat surface wind fields the university of washington planetary boundary layer model is used to retrieve a surface pressure field from any swath of quikscat surface wind vectors an alternate set of surface wind vectors is computed from the newly calculated pressure field the latter can be smoothed and the process can be iterated new surface wind vectors can be calculated where ambiguity removal fails and where measurements are missing the present methodology preserves boundary layer dynamics and is an improvement over a statistical filter

airborne observations of a front near a col during fastex abstract an analysis of an oceanic front situated near a col defined by the surface pressure field is presented there have been few observational examples of this type of front presented in the literature the primary source of information for this study was data recorded by an aircraft equipped with a doppler radar the front was approximately two dimensional and the cross frontal scale at low levels was 30 40 km a prefrontal low level jet was identified in the high resolution analyses and was shown to be supergeostrophic surface pressure measurements and the horizontal temperature gradients were used to calculate the geostrophic wind and the thermal wind imbalance twi in the alongfront direction large negative values of twi the vertical shear is less than predicted for the given horizontal temperature gradient were located near a region of frontogenesis the strong ageostrophic component of the wind parallel to the front suggests that the alongfrontal component of the wind may not have been in g

unraveling the geologic and tectonic history of the memnonia sirenum region of mars implications on the early formation of the tharsis rise abstract the geologic and tectonic history of the memnonia sirenum region of mars has been reconstructed on the basis of geologic mapping and relative age dating of rock units and structures using crater counts and superposition relations comparisons between the ages of rock unit formation and the orientations of the earliest structures associated with tharsis demonstrate a strong interplay among tectonic magmatic and aqueous activity in the memnonia sirenum region early noachian geologic activity identified within this region includes the formation of large northeast trending extensional basins stratigraphic and tectonic evidence suggests that these basins formed concurrently with the early formation of tharsis when the dynamo and associated magnetosphere were still in operation in addition to the ancient basins later tharsis influenced activity includes prominent tectonic fault systems associated with the formation of tharsis and arsia mons detailed mapping of the faults indicates that structures associated with memnonia and sirenum fossae resulted from the formation of tharsis during the middle to late noachian late stage amazonian activity also identified within this region includes valley networks and collapse depressions that are linked and or occur among tharsis centered faults that cut features throughout this region including mangala valles

the formation of valles marineris 2 stress focusing along the buried dichotomy boundary 1 although valles marineris is widely regarded as an extensional tectonic feature the source of stress responsible for its formation remains unknown this study argues that the tensile stresses that triggered valles marineris tectonism are a result of its location south of and subparallel to the buried crustal dichotomy boundary beneath tharsis the emplacement of the tharsis volcanic load straddling the pre existing topographic step of the crustal dichotomy boundary would have resulted in an abrupt change in the thickness of the load causing differential subsidence and extension across the boundary thin shell flexural models predict a narrow belt of focused tensile stresses south of the buried dichotomy boundary coinciding with the location of present day valles marineris the interaction of these boundary generated stresses with the competing stress fields associated with tharsis loading can explain the formation of noctis labyrinthus in the west and the deflection of the valles marineris troughs away from the buried boundary toward the east finite element models demonstrate that the magnitudes and vertical variations of stress at valles marineris are sensitive to the timing of loading and flexure in tharsis the incremental loading and flexure expected for a large volcanic rise results in the maximum tensile stress at valles marineris occurring at depth with tensile stresses through the majority of the lithospheric column dikes forming within this tensile stress belt would propagate through the full vertical extent of the lithosphere due to the stress release associated with the dilation of the dikes playing a crucial role in the formation of the valles marineris troughs

thrust fault vergence directions on mars a foundation for investigating global scale tharsis driven tectonics 1 insight into the mechanical and thermal structure of the martian lithosphere and the character of tharsis driven tectonics is gained from detailed mapping of the global distribution of thrust fault vergence directions with respect to the center of the tharsis tectono volcanic province our results reveal sub equal frequencies of thrust faults that verge away from and toward tharsis based on the observed distribution of thrust fault vergence directions we conclude that the base of the tharsis load was effectively welded by frictional and cohesive strength to the subjacent noachian crust throughout its periods of sustained volcanism and faulting during the late noachian to early hesperian rather than being detached along a ductile layer at its base

the formation of the south tharsis ridge belt basin and range style extension on early mars the south tharsis ridge belt strb is located along the northeastern edge of terra sirenum and partially surrounds the southwestern part of tharsis in an arc it consists of 29 large ridges separated by distances 130 to 260 km with average relief of 1 5 km above the surrounding plains because the strb is among the oldest tectonic features associated both spatially and developmentally with tharsis it may provide key information on the early evolution of tharsis and possibly pre tharsis processes earlier studies concluded that the ridges formed through compressional tectonism however the shape size and separation of the ridges support the interpretation that the strb resembles the extensional basin and range province on earth both regions are characterized by series of parallel mountain ranges separated by broad valleys in this study we evaluate both extensional and compressional hypotheses for the origin of the ridges using evidence from topography deformed craters crustal thickness models and strain modeling though neither interpretation explains all aspects of the ridges the topography of the ridges and crustal thinning associated with the western part of the ridge belt support an extensional origin strain models predict that basin and range style wide rifting would be expected for early martian conditions this extension may have been initiated by plume induced uplift in the early stages of tharsis formation but the large amount of extensional strain inferred in the western strb must have been accommodated by compression elsewhere possibly in the heavily deformed craters of western terra sirenum

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

quaternary uplift and tilting of amorgos island southern aegean and the 1956 earthquake uplifted pleistocene marine sediments submerged ancient ruins and raised beaches confirm earlier views that the asymmetry of the relief of amorgos island southern aegean testifies to a fault bounded block uplifted and tilted along a sw ne trending horizontal axis the uplifted coast corresponds to a high gradient slope controlled by an oblique master normal fault furthermore geomorphic and biological evidence radiometric data and comparison of aerial photographs indicates that the 1956 earthquake ms 7 4 uplifted the footwall of this normal fault by about 30 cm

cenozoic and mesozoic structure of the eastern basin and range province utah from cocorp seismic reflection data cocorp seismic reflection data collected from the eastern basin and range in west central utah provide information on cenozoic extensional tectonics mesozoic thrusting and their interrelationships those data show a series of remarkably continuous low angle reflectors that extend more than 120 km perpendicular to strike and can be traced as deep as 15 20 km over that distance none of these events are significantly cut by any high angle normal faults a major detachment beneath the sevier desert can be traced from a surface zone of normal faulting to a depth of 12 15 km with a regional apparent westward dip of 12 tentative correlation of upper and lower plate events suggests 30 60 km of extensional displacement on this detachment whether this structure is a reactivated mesozoic thrust is uncertain west steepening splays off the end of the detachment reach depths of 20 km and may represent a major mesozoic ramp or zones of distributed ductile shearing during extension some events are interpreted to be mesozoic thrusts of which at least one beneath the house range has been reactivated during the cenozoic the snake range decollement dips gently east and has a sense of cenozoic displacement opposite to that of other cenozoic detachments farther east deep events are most numerous beneath the east side of the sevier desert where they occur to depths of 30 km at the top of or perhaps partly within the anomalously low velocity upper mantle

reverse drag revisited why footwall deformation may be the key to inferring listric fault geometry abstract although reverse drag the down warping of hanging wall strata toward a normal fault is widely accepted as an indicator of listric fault geometry previous studies have shown that similar folding may form in response to slip on faults of finite vertical extent with listric or planar geometry in this study we therefore seek more general criteria for inferring subsurface fault geometry from observations of near surface deformation by directly comparing patterns of displacement stress and strain around planar and listric faults as predicted by elastic boundary element models in agreement with previous work we find that models with finite planar planar detached and listric detached faults all develop hanging wall reverse drag folds all of these model geometries also predict a region of tension and elevated maximum coulomb stress in the hanging wall suggesting that the distribution and orientation of near surface joints and secondary faults may also be of limited utility in predicting subsurface fault geometry the most notable difference between the three models however is the magnitude of footwall uplift footwall uplift decreases slightly with introduction of a detachment and more significantly with the addition of a listric fault shape a parametric investigation of faults with constant slip ranging from nearly planar to strongly listric over depths from 1 to 15 km reveals that footwall fold width is sensitive to fault geometry while hanging wall fold width largely reflects fault depth application of a graphical approach based on these results as well as more complete inverse modeling illustrates how patterns of combined hanging wall and footwall deformation may be used to constrain subsurface fault geometry

redefinition of the crater density and absolute age boundaries for the chronostratigraphic system of mars abstract for the boundaries of each chronostratigraphic epoch on mars we present systematically derived crater size frequencies based on crater counts of geologic referent surfaces and three proposed standard crater size frequency production distributions as defined by a a simple 2 power law b neukum and ivanov c hartmann in turn these crater count values are converted to model absolute ages based on the inferred cratering rate histories we present a new boundary definition for the late hesperian early amazonian transition our fitting of crater size frequency distributions to the chronostratigraphic record of mars permits the assignment of cumulative counts of craters down to 100 m 1 km 2 km 5 km and 16 km diameters to martian epochs due to differences in the standard crater size frequency production distributions a generalized crater density based definition to the chronostratigraphic system cannot be provided for the diameter range used for the boundary definitions the resulting model absolute age fits vary within 1 5 for a given set of production function and chronology model ages crater distributions translated to absolute ages utilizing different curve descriptions can result in absolute age differences exceeding 10

episodic flood inundations of the northern plains of mars throughout the recorded history of mars liquid water has distinctly shaped its landscape including the prominent circum chryse and the northwestern slope valleys outflow channel systems and the extremely flat northern plains topography at the distal reaches of these outflow channel systems paleotopographic reconstructions of the tharsis magmatic complex reveal the existence of an europe sized noachian drainage basin and subsequent aquifer system in eastern tharsis this basin is proposed to have sourced outburst floodwaters that sculpted the outflow channels and ponded to form various hypothesized oceans seas and lakes episodically through time these floodwaters decreased in volume with time due to inadequate groundwater recharge of the tharsis aquifer system martian topography as observed from the mars orbiter laser altimeter corresponds well to these ancient flood inundations including the approximated shorelines that have been proposed for the northern plains stratigraphy geomorphology and topography record at least one great noachian early hesperian northern plains ocean a late hesperian sea inset within the margin of the high water marks of the previous ocean and a number of widely distributed minor lakes that may represent a reduced late hesperian sea or ponded waters in the deepest reaches of the northern plains related to minor tharsis and elysium induced amazonian flooding

distribution and formation of chlorides and phyllosilicates in terra sirenum mars 1 the terra sirenum region of mars located in the noachian southern highlands is mineralogically diverse providing unique insight into ancient aqueous processes analyses of remote sensing data over the region indicate the presence of both fe or mg rich phyllosilicates and a spectrally unique deposit interpreted to be rich in chloride salts the stratigraphic relationships indicate that the phyllosilicates are part of the ancient highland crust and that the salts were deposited at a later time in some instances there is clear morphological evidence that salts were mobilized and deposited by near surface waters

coseismic and postseismic subsurface displacements and strains for a dip slip normal fault in a three layer elastic gravitational medium a three layer elastic gravitational fault displacement model has been developed using elastic dislocation and employed to examine the effects of rigidity layering gravity and stress relaxation on surface and subsurface displacements fields for a dip slip normal fault within our three layer model layer 1 represents the upper crust layer 2 the lower crust and layer 3 the upper mantle the fault is embedded in the upper crust horizontal as well as vertical displacement components have been determined displacement field changes due to postseismic stress relaxation have been calculated using both the correspondence principle and relaxed rigidity moduli and results are in close agreement the relaxed rigidity method provides an accurate and computationally efficient method of examining postseismic relaxation postseismic relaxation within the lower two layers only gives surface uplift increasing footwall uplift and decreasing hangingwall subsidence and also increases the wavelength of surface vertical displacement postseismic stress relaxation within all three layers i e uniform half space produces a shorter wavelength of surface vertical deformation with respect to the coseismic response moho topography created during coseismic deformation is initially amplified during postseismic relaxation the relaxed moho topography is dependent on the strength of the upper crust as well as the strength of the lower crust and mantle gravity has a significant influence on displacements only at the postseismic stage when the effective rigidity of the lower layers is small coseismic and postseismic normal strains associated with dip slip normal faulting have been examined for a large normal basement fault intersecting the free surface the coseismic horizontal surface strain perpendicular to fault strike is compressive adjacent to the fault and in the footwall and tensile in the hangingwall away from the fault coseismic stress redistribution may generate significant tensile brittle failure of the upper crust adjacent to large basement faults

igneous dikes on mars revealed by mars orbiter laser altimeter topography the origin of martian grabens has remained controversial for decades given the nonuniqueness of graben morphology and conflicting interpretations of dike induced or faultingbased formation processes we use measurements from the mars orbiter laser altimeter to identify the characteristic topographic signature at the surface of an igneous dike beneath a martian graben our results suggest that this subtle but diagnostic signature can be used to test competing interpretations of the formation of grabens and associated fissures and collapse depressions

martian plate tectonics the northern lowlands of mars may have been produced by plate tectonics preexisting old thick highland crust was subducted while seafloor spreading produced thin lowland crust during late noachian and early hesperian time in the preferred reconstruction a breakup margin extended north of cimmeria terra between daedalia planum and isidis planitia where the highland lowland transition is relatively simple south dipping subduction occurred beneath arabia terra and east dipping subduction beneath thatsis montes and tempe terra lineations associated with gordii dotsum are attributed to ridge parallel structures while phelegra montes and scandia colles are interpreted as transform parallel structures or ridge fault fault triple junction tracks other than for these few features there is little topographic roughness in the lowlands seafloor spreading if it occurred must have been relatively rapid quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower c 0 4 g gravity of mars the absence of vertical scarps from age differences across fracture zones and the smooth axial topography to the first order the height of vertical scarps across fracture zones does not involve gravity crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity thus the velocity of the rough smooth transition for axial topography also scales inversely with gravity plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age possible plate reorganizations for example the end of spreading through alba patera occur when the ridge axis is far from the trench that is rapid plate motions are inferred to have placed young oceanic crust far from the ridge axis the preferred full spreading rate 900 from the plate pole is 80 mm yr 1 plate tectonics if it occurred dominated the thermal and stress history of the planet a geochemical implication is that the lower gravity of mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the earth age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses about mars plate tectonics

lithospheric scale buckling and thrust structures on mars the coprates rise and south tharsis ridge belt detailed photogeologic mapping documents for the first time the deformation sequence of the coprates rise materials of middle noachian through perhaps early hesperian age were involved in the horizontal shortening of crustal and lithospheric rocks that produced uplift and asymmetric east vergent folding of these layers during the late noachian and perhaps early hesperian previous suggestions of normal faulting as the deforming mechanism are not supported by the new mapping or by dislocation models of rise topography the most likely mechanism for producing the coprates rise is folding due to buckling instability and perhaps thrust faulting an extensive ridge belt concentric to south tharsis is defined by a newly recognized system of approximately coeval long wavelength topographic ridges and swales that include the coprates rise horizontal shortening of crust and lithosphere is manifested by periodically spaced structures at two different scales wrinkle ridges spaced tens of kilometers apart and the south tharsis system of ridges spaced hundreds of kilometers apart both types of structures may be associated with early volcanotectonic activity and crustal thickening in south tharsis these and other large ridges indicate that lithospheric buckling and thrust faulting may have been common on early mars

relocated aftershocks of the march 10 1988 trinidad earthquake normal faulting slab detachment and extension at upper mantle depths abstract we relocated aftershocks of the march 10 1988 earthquake off the east coast of trinidad in order to determine the fault plane for the main shock and to understand this anomalous earthquake series the march 10 main shock m w 6 6 was the first significant instrumentally recorded earthquake to occur in the epicentral region east of trinidad the reported depth of the main shock 53 km by the international seismological centre isc is unusual but is consistent with observations of pp p times the main shock harvard centroid moment tensor cmt solution nearly pure normal faulting on nodal planes striking ene is also unusual given the depths of the seisms and the rarity of extensional faulting at these depths using p arrival times tabulated by the isc we relocated the aftershocks using the joint hypocentral determination method to find new locations relative to the main shock in map view the relocated epicenters form a tight elliptical cluster with major axis trending wnw ese and minor axis nne ssw virtually all the seisms in the earthquake series occurred at depths ranging from 30 to 60 km deeper than normal crustal earthquakes in an area previously not considered a locus of subducting lithosphere the aftershocks define a distinct plane dipping 34 nw this dip is consistent with the harvard cmt focal mechanism of the main shock one cmt nodal plane dips 38 n and strikes ene very close to our estimate of the active fault plane thus the march 10 aftershocks are consistent with slip on the north dipping plane of the main shock because the earthquake series occurred 100 km se of oceanic south american slab subducting beneath the caribbean plate at a depth generally inconsistent with shallow normal faulting outside of slabs we interpret the main shock as having occurred deep 50 km in south american lithosphere currently moving nw into the subduction zone the occurrence of this earthquake indicates an extensional stress applied to the lithosphere of the south american plate likely related to a combination of slab pull to the nw as the slab subducts beneath the caribbean plate and to detachment of the subducting lithosphere from buoyant continental south america

the pocatello valley idaho utah border earthquake sequence of march to april 1975 abstract an earthquake sequence during march and april 1975 which included a main shock of magnitude m l 6 0 on 28 march was centered in pocatello valley on the idaho utah border a foreshock of magnitude m l 4 2 preceded the main shock by 22 hr and was followed by at least 156 microearthquakes that behaved as aftershocks of the first event accurate locations of 587 aftershocks that occurred during the first 20 days after the main shock define irregular zones of concentrated activity beneath the south central western and northern parts of pocatello valley the main shock is interpreted to have involved nonuniform dipslip rupture without surface faulting on a previously unrecognized normal fault that dips nw obliquely transecting the north trending pocatello valley graben the speace time pattern of aftershocks and composite focal mechanisms indicate subsidiary faulting and the interaction of diverse fracture trends resulting in a mixture of normal strike slip and oblique faulting details of the earthquake sequence imply a complex episode of basin and range graben subsidence that may typify similar source regions elsewhere in utah9s wasatch front area

volcanic rifting at martian grabens 1 a large fraction of surface extension on mars occurred at segmented grabens having width length ratios akin to oceanic rifts on earth association with volcanic landforms such as pit craters clearly suggests interconnection between tectonic and magmatic processes a martian rift evolution model is proposed on the basis of new geomorphological and structural interpretations of imagery high resolution digital elevation models dems scaled experimental modeling and three dimensional boundary element modeling of magmatic and tectonic processes and a comparison with terrestrial rifts the dems were obtained from mars observer laser altimeter viking orbiter stereo images or a combination of both comparison of terrestrial rifts included afar iceland and the east pacific rise the ambient extensional stress field induced by regional body forces is combined at depth with decompression melting and mantle plume thermal anomaly resulting in emplacement of elongated magma reservoirs along the grabens injection of dikes above the reservoirs and flood basalt eruption result in a reservoir underpressurization of up to hundreds of mpa and induces surface collapse each collapse event is associated with an eruption of volcanic volumes akin to those of individual flow eruptions in large terrestrial igneous provinces the geometry and mechanisms of graben formation and surface collapse are described and used to infer reservoir depth and width we conclude from this study that giant dike swarms akin to typical giant terrestrial dike swarms are unlikely to underlie the volcanic martian grabens on the basis one graben one dike rather every volcanic graben segment appears to own a local dike swarm perhaps analogous to the dike swarms in the icelandic fissure zones index terms 5475 planetology solid surface planets tectonics 8149 5480 planetology solid surface planets volcanism 8450 6225 planetology solar system objects mars 8121 tectonophysics dynamics convection currents and mantle plumes 8010 structural geology fractures and faults keywords rifting graben pit crater magma chamber dyke

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

source parameters of the 28 october 1983 borah peak idaho earthquake from body wave analysis modeling of long period body waves of the m s 7 3 borah peak idaho earthquake suggests that the earthquake was a simple rupture that nucleated at a depth of about 16 km and propagated unilaterally northwestward toward the surface the seismic moment tensor obtained from the inversion of teleseismic body wave amplitude data agrees well with the fault plane solution obtained from short period first motion data strike 138 3 dip 45 3 rake 60 5 and the observed surface faulting the scalar double couple moment of 2 1 10 26 dyne cm obtained from the inversion is comparable to a moment of 1 4 10 26 dyne cm estimated from the observed surface faulting estimates of stress drop based on these values for the moment are 17 to 12 bars respectively

tectonic history of the syria planum province of mars we attribute most of the development of extensive fractures in the tharsis region to discrete tectonic provinces within the region rather than to tharsis as a single entity one of these provinces is in syria planum faults and collapse structures in the syria planum tectonic province on mars are grouped into 13 sets based on relative age areal distribution and morphology according to superposition and fault crosscutting relations and crater counts we designate six distinct episodes of tectonic activity in the following chronologic order stage i is an early to late noachian deformation forming mostly east west structures fault set ia some large volcanoes also formed faults were produced possibly by flexural uplift also arcuate north trending grabens set ib indicate that faulting is transitional to the next stage stage ii is late noachian to early hesperian radial faulting centered in syria planum possibly due to isostatic uplift in late noachian set iia to early hesperian set iib time stage iii is early to late hesperian faulting tangential to syria planum that was related to local centers of uplift sets iii1 iii3 on the periphery of syria planum stage iv is a late hesperian graben formation that was circumferential to syria planum set iva caused either by collapse associated with eruption of magma or by flexure of the lithosphere due to volcanic loading in association with volcanism minor faulting occurred producing an oval pattern of faults in southwest syria planum set ivbl and a radial pattern south of the planum set ivb2 that apparently rejuvenated buried stage ii faults stage v is a late hesperian to early amazonian development of grabens and troughs of noctis labyrinthus and western valles marineris set v that was probably instigated by local uplift exposure of groundwater or ground ice zones may have produced further collapse and trough enlargement stage vi is early amazonian northwest trending faulting in noctis fossae set vil perhaps due to tharsis monies centered tectonism and north northwest normal faulting along the eastern side of the claritas rise set vi2 that was due to tectonic subsidence the duration of tectonic activity in the syria planum province was perhaps 2 3 b y photoclinometric topographic profiles across 132 grabens and fault scarps show that syria planum grabens have widths average of 2 5 km and most range from 1 to 6 km similar to lunar grabens but the martian grabens have slightly higher side walls average about 132 m and gentler wall slopes average of 9 and range of 2 25 than lunar grabens 93 m high and 18 slopes scarp degradation on mars has progressed through quakes impact shaking and dry slope processes the lower slopes may be due to mars higher gravity estimates of the amount of extension for individual grabens range from 20 to 350 m most estimates of the thickness of the faulted layer range from 0 5 to 4 5 km average is 1 5 km this thickness range corresponds closely to the 0 8 to 3 6 km range in depth for pits troughs and canyons in noctis labyrinthus and along the walls of valles marineris we propose that the predominant 1 to 1 5 km values obtained for both the thickness of the faulted layer and the depths of the pits troughs and theater heads of the canyons reflect the initial depth to the water table in this region as governed by the depth to the base of ground ice maximum depths for these features may indicate lowered groundwater table depths and the base of ejecta material

geological and hydrological histories of the argyre province mars the geologic history of the multi ringed argyre impact basin and surroundings has been reconstructed on the basis of geologic mapping and relative age dating of rock materials and structures the impact formed a primary basin rim materials and a complex basement structural fabric including faults and valleys that are radial and concentric about the primary basin as well as structurally controlled local basins since its formation the basin has been a regional catchment for volatiles and sedimentary materials as well as a dominant influence on the flow of surface ice debris flows and groundwater through and over its basement structures the basin is interpreted to have been occupied by lakes including a possible mediterranean sized sea that formed in the aftermath of the argyre impact event the hypothesized lakes froze and diminished through time though liquid water may have remained beneath the ice cover and sedimentation may have continued for some time at its deepest the main argyre lake may have taken more than a hundred thousand years to freeze to the bottom even absent any heat source besides the sun but with impact induced hydrothermal heat geothermal heat flow due to long lived radioactivities in early martian history and concentration of solutes in sub ice brine liquid water may have persisted beneath thick ice for many millions of years existence of an ice covered sea perhaps was long enough for life to originate and evolve with gradually colder and more hypersaline conditions the argyre rock materials diverse in origin and emplacement mechanisms have been modified by impact magmatic eolian fluvial lacustrine glacial periglacial alluvial colluvial and tectonic processes post impact adjustment of part of the impact generated basement structural fabric such as concentric faults is apparent distinct basin stratigraphic units are interpreted to be linked to large scale geologic activity far from the basin including growth of the tharsis magmatic tectonic complex and the growth into southern middle latitudes of south polar ice sheets along with the migration of surface and sub surface volatiles towards the central part of the primary basin the substantial difference in elevation with respect to the surrounding highlands and tharsis and the thaumasia highlands result in the trapping of atmospheric volatiles within the basin in the form of fog and regional or local precipitation even today in addition the impact event caused long term millions of years hydrothermal activity as well as deep seated basement structures that have tapped the internal heat of mars as conduits for far greater time possibly even today this possibility is raised by the observation of putative open system pingos and nearby gullies that occur in linear depressions with accompanying systems of faults and fractures long term water and heat energy enrichment complemented by the interaction of the nutrient enriched primordial crustal and mantle materials favorable to life excavated to the surface and near surface environs through the argyre impact event has not only resulted in distinct geomorphology but also makes the argyre basin a potential site of exceptional astrobiological significance

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

tectonic histories between alba patera and syria planum mars syria planum and alba patera are two of the most prominent features of magmatic driven activity identified for the tharsis region and perhaps for all of mars in this study we have performed a geographic information system based comparative investigation of their tectonic histories using published geologic map information and mars orbiter laser altimetry mola data our primary objective is to assess their evolutional histories by focusing on their extent of deformation in space and time through stratigraphic paleotectonic topographic and geomorphologic analyses though there are similarities among the two prominent features there are several distinct differences including timing deformational extent and tectonic intensity of formation whereas alba patera displays a major pulse of activity during the late hesperian early amazonian syria planum is a long lived center that displays a more uniform distribution of simple graben densities ranging from the noachian to the amazonian many of which occur at greater distances away from the primary center of activity the histories of the two features presented here are representative of the complex long lived evolutional history of tharsis

response of unconfined turbidity current to normal fault topography turbidity currents descending the slopes of deep water extensional basins or passive continental margins commonly encounter normal fault escarpments but such large magnitude phenomena are hydraulically difficult to replicate at small scale in the laboratory this study uses advanced computational fluid dynamics numerical simulations to monitor the response of large natural scale unconfined turbidity currents 100 m thick and 2000 m wide at the inlet gate to normal fault topography with a maximum relief of nearly 300 m for comparative purposes the turbidity current is first released on a non faulted pristine slope of 1 5 simulation model 1 the expanding and waxing flow bypasses the slope without recognizable deposition within the vertical resolution limit of 2 m similar flow is then released towards the tip model 2 and towards the centre model 3 of a normal fault escarpment in both of these latter models the sand carried by flow tends to be entrapped in four distinct depozones an upslope near gate zone of flow abrupt expansion and self regulation a flow transverse zone at the fault footwall edge a flow transverse zone at the immediate hangingwall and a similar transverse zone near the crest of the hangingwall counter slope where some of the deposited sand also tends to be reshuffled to the previous zone by a secondary reverse underflow the near bottom reverse flow appears to be generated on a counter slope of 1 1 increased to 2 by deposition the kelvin helmholtz interface instability plays an important role by causing three dimensional fluctuations in the flow velocity magnitude and sediment concentration the thick deposits of large single surge flows may thus show hydraulic fluctuations resembling those widely ascribed to hyperpycnal flows the study indicates further that the turbiditic slope fans formed on such fault topographies are likely to be patchy and hence may differ considerably from the existing slope fan conceptual models when it comes to the spatial prediction of main sand depozones this article is protected by copyright all rights reserved

constraints on early events in martian history as derived from the cratering record the shapes and densities of crater size frequency distribution curves are used to constrain two major events early in martian history termination of high obliteration rates and viability of the multiple impact origin of the crustal dichotomy distribution curves of fresh craters superposed on uplands intercrater plains and ridged plains display shapes and densities indicative of formation prior to the end of heavy bombardment this observation correlates with other geologic evidence suggesting a major change in the erosional regime following the last major basin size impact i e argrye in addition the multisloped nature of the curves supports the idea that the downturn in the crater size frequency distribution curves reflects the size frequency distribution of the impactors rather than being the result of erosion the crustal dichotomy formed prior to the heavy bombardment intermediate epoch based on distribution curves of knobby terrain if the dichotomy resulted from a single gigantic impact this observation places constraints on when this event happened an alternate theory for dichotomy formation the multiple impact basin idea is questioned since distribution curves of large basins as well as heavy bombardment era units are not represented by a 3 differential power law function this study finds fewer basins missing on mars compare to the moon and mercury than previously reported the area covered by these missing basins is less than that covered the northern plains

thermal evolution of the martian core implications for an early dynamo mars is thought to have possessed a dynamo that ceased 0 5 b y after the formation of the planet a possible but ad hoc explanation is an early episode of plate tectonics which drove core convection by rapid cooling of the mantle we present an alternative explanation that the martian core was initially hotter than the mantle after core formation providing an initial high heat flux out of the core a core initially 150 k hotter than the mantle can explain the early dynamo without requiring plate tectonics recent experimental results suggest that potassium is likely to partition into the martian core potentially providing an extra source of energy to power a dynamo we find that the radioactive decay of 40 k cannot explain the inferred dynamo history without the presence of a hot core our results also suggest that core solidification is unlikely to have occurred because this process would have generated a long lived 1 b y dynamo if as we conclude the core is entirely liquid it must contain at least 5 wt sulfur an initially hot core is consistent with geochemical evidence for rapid core formation and incomplete thermal equilibration with the mantle thus the early history of planetary dynamos provides constraints on the processes of accretion and differentiation

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

active normal faulting along the seerteng shan north china geometry and kinematics abstract although rotation of fault blocks during seismic and long term periods has long been recognized in extensional tectonic regimes the geometry and kinematic behaviors of normal faults at outcrop scale have scarcely been investigated in sufficient detail in this study combining with the analysis of high resolution topography acquired by small unmanned aerial vehicle suav using the structure from motion sfm technique we present the results of our field observations on the structural characteristics of the seertengshan piedmont fault spf a major active normal fault bounding the northern margin of the hetao graben north china although previous studies have reported the recent tectonic activity of this fault including timing of most recent earthquake average slip rate and repeat time of paleo earthquakes few of them have focused on geometric patterns of the outcropping fault zones which provide excellent outcrop scale examples to investigating geometry and kinematics of active normal faults besides the observed prominent fault scarps indicative of recent tectonic activity along the spf outcrop observations indicate that in some cases both planar and curved normal faults are developed forming complex fault zones sequential development of normal faults may have rotated the early formed fault blocks resulting in shallowly dipping faults and highly tilted strata collectively structural similarities probably exit among normal faults at multiple spatial scales we suggest that the results of this study are also helpful for a better understanding of structural development and evolution in other actively extending areas

a new crustal fault formed the modern corinth rift abstract this review shows how collective analysis of morphotectonic elements on uplifting rift margins can constrain the mechanical behaviour of continents during early rifting this is shown for the modern corinth rift one of the fastest extending and most seismically active continental regions worldwide we reconstruct the growth of the normal fault system that accommodates most of the rift strain and the uplift of the rift margin it bounds from onset to present and at rift scale our approach allows first order inferences on the mechanics and evolution of the rift and can be used in other areas of early continental rifting we review and re assess known geologic evidence in the corinth rift and compile morphotectonic elements into a new map we analyse the rift topo bathymetry and the footwall relief river catchments and tectonic knickpoints in its uplifting margin we also review studies that constrain the growth of normal faults using morphotectonic elements in their footwall and propose a novel theoretical framework to reconstruct fault time evolution during early rifting we couple known and new data to derive fault displacement profiles in time and use the theoretical framework to infer the history of growth and linkage of rift border faults in turn constraining rift growth mechanics and evolution our rift scale morphotectonic investigation shows that the current rift bounding faults are kinematically coherent at depth and constitute a fault 80 km in length this composite master fault grew along strike from the rift centre linking and integrating individual fault segments that developed co linearly at earlier times the observed fault elastic flexure footwall relief wavelength and high uplift and slip rates throughout the rift margin suggest the border fault is steep and highly localized in strain and transects the entire seismogenic layer growing in a long term strong elastic lithosphere integration of previous and our new findings suggest the corinth rift evolved in two distinct extensional phases these extensional phases are delimited by the fast overwriting growth of the new rift forming fault that switched rift mechanics in a 300 kyr timespan and controls rift evolution thereafter the new rift forming fault enlarges the modern rift as an asymmetric half graben along and across strike superimposed onto the preceding 4 my distributed extension

quaternary tectonic setting of the 1983 borah peak earthquake central idaho the 1983 borah peak earthquake was accompanied by extensive surface faulting along a part of the lost river fault that has abundant evidence of latest quaternary last 15 000 yr offset this fault and two similar range front normal faults along the lemhi range and beaverhead mountains lie in an area of basinand range structure in central idaho that is part of a roughly v shaped belt of latest quaternary surface faulting that extends from the wasatch fault through the yellowstone area to the lost river fault the position of this belt may be related to the outward migration of a thermal front associated with the northeastward progression of late cenozoic silicic volcanism along the yellowstonesnake river plain axis the central segments of the lost river lemhi and beaverhead faults have been active more recently and probably more active throughout quaternary time than the southern and northern segments the main 1983 surface faulting occurred in an area of high structural relief along a central segment of the lost river fault that has ruptured in latest quaternary time which suggests that comparable areas along other range fronts in the area should be regarded as likely sites of future surface faulting other perspective of fault behavior suggest additional possible sites and all segments of the range front faults are regarded as capable of surface faulting

comparison of various inversion techniques as applied to the determination of a geophysical deformation model for the 1983 borah peak earthquake abstract a number of techniques are employed to overcome nonuniqueness and instability inherent in linear inverse problems to test the factors that enter into the selection of an inversion technique for fault slip distribution we used a penalty function with smoothness pf s a damped least squares method dls damped least squares method with a positivity constraint dls p and a penalty function with smoothness and a positivity constraint pf s p for inverting the elevation changes for slip associated with the 1983 borah peak earthquake unlike solving an ill posed inverse problem using a gradient technique ward and barrientos 1986 we have restored the well posed character between the elevation changes and normal slip distribution studies showed that the constraints based on sound understanding of the physical nature of the problem are crucial in the derivation of a meaningful solution and dictates primarily the selection of a particular inversion technique all available geological and geophysical information were used to determine a geophysical deformation model for the earthquake it is suggested that the pf s p solution for a fault length of 75 km is the preferred model the long wavelength features in the estimated slip distribution are similar to those obtained by ward and barrientos 1986 whereas the shorter wavelength features differ between two solutions the fault dips 49 to the southwest the slipped zones deepen from the surface at the northwest to about 20 km downdip depth at the southeast the fault extends to the southeast beyond the epicenter of the mainshock it is also shown that only the long wavelength features of the slip distribution are well resolved the resolution is better at shallower levels than at deeper levels the resolution deteriorates when the deformation sources are away from the leveling lines smoothness constraints provide better resolution than damping does at depth the addition of a positivity constraint significantly improves the model resolution

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

planetary surface dating from crater size frequency distribution measurements multiple resurfacing episodes and differential isochron fitting abstract the analysis of crater size frequency distributions and absolute densities forms the basis of current approaches for estimating the absolute and relative ages of planetary surfaces users of the neukum system of crater dating have conventionally used a cumulative presentation of the data but because of the recent proliferation of interest in identifying resurfacing ages it is worth emphasising the utility of the differential presentation of crater data in identifying resurfacing events and particularly in distinguishing the signature of short lived events such as volcanic flows from long acting processes such as aeolian erosion the work describes some additional considerations for making isochron fits to differentially plotted crater populations with respect to the removal of a binning bias for incrementally differentially plotted data the hartmann approach has not typically employed the fitting of isochrons but differential fitting would be a natural choice for this system and is implemented in the craterstats software a revised calculation of the martian epoch boundary times in both chronology systems is provided

relationship of late quaternary fault scarps to subjacent faults eastern great basin utah high resolution seismic reflection profiles in the sevier desert basin in western utah help clarify the relationship between some late quaternary fault scarps and subjacent faults a profile crossing the clear lake fault confirms that holocene displacement has occurred on a high angle normal fault that is directly connected to the sevier desert detachment if detachment faults can act as seismogenic source zones then the young movement on the normal fault suggests that the sevier desert detachment may be unstable and perhaps the source of future earthquakes a swarm of late quaternary scarps near the drum mountains overlies a network of steep faults in competent rock that have had recurrent movement many subsurface faults are not associated with scarps suggesting that selected faults ruptured during the last episode of surface faulting

topography of closed depressions scarps and grabens in the north tharsis region of mars implications for shallow crustal discontinuities and graben formation abstract using viking orbiter images detailed photoclinometric profiles were obtained across 10 irregular depressions 32 fretted fractures 49 troughs and pits 124 solitary scarps and 370 simple grabens in the north tharsis region of mars these data allow inferences to be made on the shallow crustal structure of this region the frequency modes of measured scarp heights correspond with previous general thickness estimates of the heavily cratered and ridged plains units the depths of the flat floored irregular depressions 55 175 m fretted fractures 85 890 m and troughs and pits 60 1620 m are also similar to scarp heights thicknesses of the geologic units in which these depressions occur which suggests that the depths of these flat floored features were controlled by erosional base levels created by lithologic contacts although the features have a similar age both their depths and their observed local structural control increase in the order listed above which suggests that the more advanced stages of associated fracturing facilitated the development of these depressions by increasing permeability if a ground ice zone is a factor in development of these features as has been suggested our observation that the depths of these features decrease with increasing latitude suggests that either the thickness of the ground ice zone does not increase poleward or the depths of the depressions were controlled by the top of the ground ice zone whose depth may decrease with latitude deeper discontinuities are inferred from fault intersection depths of 370 simple grabens assuming 60 dipping faults that initiate at a mechanical discontinuity in tempe terra and alba patera and from the depths of the large flat floored troughs in tempe terra the frequency distributions of these fault intersection and large trough depths show a concentration at 1 0 1 6 km depth similar to data obtained for syria sinai and lunae plana the consistency of these depth data over such a large region of western mars suggests that a discontinuity or a process that transcends local and regional geology is responsible for the formation of these features if this discontinuity is represented by the base of the cryosphere its uniform depth over 55 of latitude suggests that the cryosphere did not thicken poleward alternatively the concentration of depths at 1 0 1 6 km may represent the upper level of noneruptive dike ascent lateral dike propagation of mars which is controlled by gravity and atmospheric pressure and magma and country rock characteristics and was probably controlled in part by ground ice fault intersection depths in the north tharsis region locally extend down to a depth of 5 7 km the depth data between 2 and 3 km are attributed to the discontinuity at the interface of megaregolith and basement or to the upper limit of noneruptive dike ascent of magma with a high volatile content intersection depths greater than 3 km which were found at alba patera may be due to the megaregolith basement discontinuity which was buried and depressed by volcanic loading or to the upper level of noneruptive dike ascent of magma with a low volatile content the near absence of narrow simple grabens with fault initiation depths less than 0 6 1 0 km in this study area as well as in most of western mars suggests that this depth represents the minimum depth that normal faults can initiate at shallower depths tension cracks or joints would form instead this hypothesis is supported by the application of the griffith failure criterion to this minimum depth of normal fault initiation which suggests that shallow crustal materials have a tensile strength of 2 4 mpa throughout most of western mars in close agreement with previous estimates of tensile strength of martian basaltic rock

claritas rise mars pre tharsis magmatism claritas rise is a prominent ancient noachian center of tectonism identified through investigation of comprehensive paleotectonic information of the western hemisphere of mars this center is interpreted to be the result of magmatic driven activity including uplift and associated tectonism as well as possible hydrothermal activity coupled with its ancient stratigraphy high density of impact craters and complex structure a possible magnetic signature may indicate that it formed during an ancient period of mars evolution such as when the dynamo was in operation as tharsis lacks magnetic signatures claritas rise may pre date the development of tharsis or mark incipient development since some of the crustal materials underlying tharsis and older parts of the magmatic complex respectively could have been highly resurfaced destroying any remanent magnetism here we detail the significant characteristics of the claritas rise and present a case for why it should be targeted by the mars odyssey mars reconnaissance orbiter and mars express spacecrafts as well as be considered as a prime target for future tier scalable robotic reconnaissance