outgassed water on mars constraints from melt inclusions in snc meteorites the snc shergottite nakhlite chassignite meteorites thought to be igneous rocks from mars contain melt inclusions trapped at depth in early formed crystals determination of the pre eruptive water contents of snc parental magmas from calculations of the solidification histories of these amphibole bearing inclusions indicates that martian magmas commonly contained 1 4 percent water by weight when combined with an estimate of the volume of igneous materials on mars this information suggests that the total amount of water outgassed since 3 9 billion years ago corresponds to global depths on the order of 200 meters this value is significantly higher than previous geochemical estimates but lower than estimates based on erosion by floods these results imply a wetter mars interior than has been previously thought and support suggestions of significant outgassing before formation of a stable crust or heterogeneous accretion of a veneer of cometary matter

morphologic stratigraphic and morphometric investigations of valley networks in eastern libya montes mars implications for the noachian hesperian climate change dendritic valley networks and broad longitudinal valleys are widespread within the eastern libya montes region the morphologic characteristics of the studied dendritic valleys especially their occurrence at local summits provide evidence for the initial formation by surface runoff due to atmospheric precipitation whereas the longitudinal valley systems are thought to have been formed and modified by groundwater induced processes our crater counts and model ages show that the dendritic valley networks average age 4 0 ga formed earlier than the longitudinal valley systems average age 3 7 ga both fluvial forms indicate a temporal change of the erosive environment at the noachian hesperian transition at 3 8 ga our results suggest that the fluvial activity within our investigation area lasted for 800 my from 4 1 ga to 3 3 ga the dendritic valleys show valley densities between 0 12 km 1 and 0 57 km 1 indicative of highly mature and integrated valley systems that we interpret to be characteristic of warmer and wetter conditions on mars

recurring and triggered slow slip events near the trench at the nankai trough subduction megathrust the discovery of slow earthquakes has revolutionized the field of earthquake seismology defining the locations of these events and the conditions that favor their occurrence provides important insights into the slip behavior of tectonic faults we report on a family of recurring slow slip events sses on the plate interface immediately seaward of repeated historical moment magnitude mw 8 earthquake rupture areas offshore of japan the sses continue for days to several weeks include both spontaneous and triggered slip recur every 8 to 15 months and are accompanied by swarms of low frequency tremors we can explain the sses with 1 to 4 centimeters of slip along the megathrust centered 25 to 35 kilometers km from the trench 4 to 10 km depth the sses accommodate 30 to 55 of the plate motion indicating frequent release of accumulated strain near the trench

surface displacements in the 1906 san francisco and 1989 loma prieta earthquakes the horizontal displacements accompanying the 1906 san francisco earthquake and the 1989 loma prieta earthquake are computed from geodetic survey measurements the 1906 earthquake displacement field is entirely consistent with right lateral strike slip on the san andreas fault in contrast the 1989 loma prieta earthquake exhibited subequal components of strike slip and reverse faulting this result together with other seismic and geologic data may indicate that the two earthquakes occurred on two different fault planes

geodetic measurement of deformation in the loma prieta california earthquake with very long baseline interferometry following the loma prieta earthquake two mobile very long baseline interferometry vlbi systems operated by the nasa crustal dynamics project and the noaa national geodetic survey were deployed at three previously established vlbi sites in the earthquake area fort ord near monterey the presidio in san francisco and point reyes from repeated vlbi occupations of these sites since 1983 the pre earthquake rates of deformation have been determined with respect to a north american reference frame with 1 formal standard errors of 1 mm yr the vlbi measurements immediately following the earthquake showed that the fort ord site was displaced 49 4 mm at an azimuth of 11 4 and that the presidio site was displaced 12 5 mm at an azimuth of 148 13 no anomalous change was detected at point reyes with 1 uncertainty of 4 mm the estimated displacements at ford ord and the presidio are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the more northern segment of the fault rupture we also give the cartesian positions at epoch 1990 0 of a set of vlbi fiducial stations and the three mobile sites in the vicinity of the earthquake

seismotectonics beneath the tokyo metropolitan area japan effect of slab slab contact and overlap on seismicity 1 we first determine the configuration of the upper surface of the pacific pac slab beneath kanto japan from the distribution of interplate earthquakes relocated by an appropriate 1 d velocity model then traveltime tomography is carried out to estimate three dimensional seismic velocity structures around kanto using 735 520 p wave and 444 049 s wave arrival times from 6508 local earthquakes the obtained results suggest that the philippine sea phs slab is subducting to depths of 130 140 km without a gap even to the northwest of the izu collision zone we subsequently define the lateral extent of the contact zone between the bottom of the phs slab and the upper surface of the pac slab phs pac interface and reveal that the slab contact zone underlies a wider area beneath kanto in harmony with the kanto plain the downdip limit of interplate thrust type earthquakes on the pac slab is deepened by 30 km locally under the slab contact zone this deepening is probably caused by a lower temperature environment in the pac slab resulting from the overlap with the phs slab subducting above and consequent thermal shielding by the phs slab from the hot mantle wedge we detect an extremely low velocity anomaly in the easternmost portion of the phs slab which is probably attributable to serpentinization of mantle peridotite interplate earthquakes are almost absent along the phs pac interface overlain by the serpentinized mantle in the phs slab suggesting that ductile deformation takes place along the interface because of low viscosity of the serpentine

correlation between the geologic record and computed plate motions for central california we have attempted to correlate geologic events in part of central california with computed motions of oceanic plates relative to cratonic north america three composite terranes are considered 1 the sierra nevada 2 the coast ranges northeast of the san andreas fault and 3 the salinian block in the sierra nevada jurassic plutonism ending about 147 m y b p and cretaceous plutonism 120 80 m y b p correlate with deduced farallon north america fa na convergence as does the nevadan orogeny 158 153 m y b p however the gap in plutonism 146 121 m y b p outlasted by far an apparent minimum in convergence 145 135 m y b p magmatism ceased in the sierra and uplift slowed during the laramide orogeny 75 45 m y b p when tectonic activity had moved east to the site of the rockies presumably because of a low angle of subduction but volcanisin resumed in the sierra about 33 m y b p indicating that a steeper angle was reestablished apparently east west compression slackened when the pacific north america pa na transform regime developed basalt was erupted in the southern sierra 12 3 m y b p and during this same time the range started its most rapid rise as a normal fault bounded block the coast ranges north east of the san andreas fault are underlain by the franciscan complex the older parts of the complex were probably assembled in a subduction zone far south of their present location but we believe that the same fa na convergence that was cited for sierran plutonism was responsible despite the disparity in latitude as the farallon plate was probably in contact with most of the western margin of north and south america a perceived strong pulse in convergence 100 85 m y b p evidently produced the coast range thrust which on geologic grounds alone most likely originated between 96 and 88 m y b p some of the northwesterly transport of franciscan rocks relative to north america is ascribed to oblique kula north america ku na convergence 85 43 m y b p during which period the coast range thrust was revived about 60 m y b p the farallon plate again influenced the california margin after the kuia plate had moved northward and fa na convergence caused the accretion of the coastal belt and king range terranes of the neo franciscan the advent of pacific north america pa na interaction was marked by local volcanism which advanced from the southeast toward the northwest in consonance with the passage of the mendocino triple junction dickinson and snyder 1978 in the salinian block plutons 107 82 m y old can be ascribed to the same fa na convergence as the contemporary cretaceous plutons of the sierra nevada although the salinian intrusives originated much farther south paleomagnetic results champion et al 1980 from the salinian related pigeon point formation 75 71 m y in age suggest about 2500 km of poleward essentially coastwise movement this postulated large movement during part or all of the last 75 m y poses the greatest dilemma in our study the kuia is the only known plate whose computed obliquely convergent motion is appropriate for the late cretaceous paleogene part of the migration and even this motion is inadequate for the estimated transport within the most likely time window furthermore the farallon plate seems ideally suited for the laramide orogeny 70 45 m y b p both plates could not have been in contact with the same part of the margin at the same time oblique convergence of the kula plate could possibly have caused large coastwise transport and also the laramide orogeny the coast ranges northeast of the san andreas fault and the salinian block both experienced strike slip faulting and en echelon folding correlative with pa na interaction indicating that they were close together by neogene time faulting and folding have been particularly marked since the inception of spreading in the gulf of california and attachment of westernmost california to the pacific plate about 4 m y b p the rise of individual coastal ranges commencing 3 1 m y b p may possibly have been caused by slight convergence which appears in computed pa na relative motions from 5 m y b p to the present

late neogene motion of the pacific plate oceanic crust between 38 s and 65 s along the pacific antarctic ridge records a complete history of neogene pacific antarctic motion we have modeled magnetic stages corresponding to portions of isochrons 1 2 2a 3 3a 4 and 5 from 17 high quality marine magnetic traverses of the ridge to determine the neogene finite rotation poles for this plate pair we chose to model velocities over time intervals of about 0 5 m y because this greatly increased the number of estimates of pacific antarctic plate velocity our analysis shows that a change in pacific antarctic relative motion occurred between chron 2a 3 40 ma and the beginning of chron 3 time 3 86 ma we used 203 estimates of pacific antarctic spreading velocity to calculate a 0 3 4 ma and 3 86 10 3 ma euler pole combined with tracks of seamounts that record the passage of the pacific plate over mantle plumes our data show that this change in relative motion corresponds to a change in the absolute motion of the pacific plate with respect to the hotspot frame of reference using these euler poles to calculate pacific antarctic africa north america circuit euler poles show that this recent change in pacific plate absolute motion corresponds to a change from strike slip to transpressive motion along the coastal california pacific north america plate boundary interestingly this age of increased tectonism agrees in time with deformation in new zealand and northern japan

que94201 shergottite crystallization of a martian basaltic magma abstract basaltic shergottites are commonly described as having crystallized from magmas that contained entrained or cumulus pyroxenes complexly zoned clinopyroxenes in que94201 a newly recovered antarctic shergottite are similar to those formed during continuous growth in some lunar basaltic melts pyroxene cores have nuclei of magnesian pigeonite mantled by augite in turn rimmed by strongly zoned ferroan pigeonite with outer rims of pyroxferroite fe ti oxide compositions indicate that this meteorite crystallized under relatively reducing conditions more like lunar basalts than other shergottites ree and other trace element abundances in zoned pyroxenes maskelynite and phosphates are consistent with continuous pyroxene crystallization from an evolving magma punctuated by the appearance of new phases on the liquidus the higher proportion of maskelynite in que94201 suggests that its composition may be closer to multiple saturation with pyroxenes plagioclase than other shergottites and all pyroxene zones show negative eu anomalies thus this meteorite may represent the first example of a martian magma unaffected by crystal accumulation the fe fe mg ratio and proportions of incompatible elements reflected in 4 modal whitlockite are high implying that this is a fractionated melt the calculated bulk ree pattern shows extreme lree depletion suggesting either less contamination with enriched crustal materials or a more lree depleted source than other basaltic shergottites

basin evolution during change from convergent to transform continental margin in central california miocene nonmarine and shallow marine strata exposed east of san francisco bay record a change from convergent margin tectonics to transform margin tectonics during the middle miocene the east bay area occupied the oceanward side of a shelved forearc basin that was progressively incorporated in the evolving san andreas strike slip orogene patterns of deposition in the broad forearc basin were relatively simple andesitic arc derived detritus was transported the full width of the forearc basin from the sierras to the east bay area in contrast the wrench tectonic regime produced complex patterns of sedimentation displaying greater local variability on the basis of stratigraphic data we infer that the west facing slope of the forearc basin in the east bay area was reve sed about 13 ma with uplift of the area between the eventual traces of the san andreas and hayward faults on the site of the present bay a fluvial clastic wedge was shed eastward into the east bay area from this uplifted terrane of mesozoic subduction complex and forearc basin rocks initial rupturing along the hayward fault trend followed the uplift at about 10 ma loci of basaltic volcanism 10 7 ma along these fractures interfinger with the clastic wedge a similar pattern of uplift and drainage reversal apparently presaged the onset of wrenching along the nearby calaveras trend from 8 6 ma expansion of the strike slip orogene segmented the outer forearc basin into local basins some characterized by episodic lacustrine deposition and probable internal drainage by the end of the m ocene sierran arc volcanism waned at the latitude of san francisco bay and arc derived volcaniclastics were fully supplanted by recycled coast range derived detritus in the east bay area certain of these coast range sediment sources particularly blueschist bearing franciscan terranes permit an estimate of 7 27 km 4 17 mi of total right slip on the hayward fault

the change of eruption styles of martian volcanoes and estimates of the water content of the martian mantle abstract estimated water contents in the martian mantle range from 36 ppm to more than 1 these values are based on the chemical analyses such as hydrous minerals in snc meteorites and formation models of mars this study evaluates the water content of the martian mantle using the change with time of volcanic eruption style on mars as an observational constraint styles of volcanic activity depend on the volatile content of the magma and the atmospheric pressure because a low atmospheric pressure leads to a more explosive volcanic eruption it has been believed that the volcanism on the current martian environment would be very explosive our calculations however show that under the current martian atmospheric conditions erupted magma cannot entrain the ambient air effectively so the decrease in temperature of the magma during ascent is small consequently the erupted magma may form a lava like deposit when it falls back on the ground this effusive like style of eruption is a counterpart of clastogenic lava on mars on the other hand numerical calculations under a thick co 2 atmosphere which may correspond to an ancient martian atmosphere reveal a rather explosive eruption style geological features of earlier stages of martian history in the noachian and hesperian eras suggest that the volcanic eruptions on mars were explosive then effusive eruptions however became dominant in more recent times it has been widely accepted that mars experienced a major climate change in addition the release factor of volatiles on mars has been suggested to be as small as 0 017 0 112 this may imply that the volatile content has been almost constant throughout martian history consequently we assume that this change in eruption style was caused by the change in atmospheric pressure for a given water content of magma a major climatic change may lead to a transition in eruption style if we know the atmospheric pressure at the time of this transition we can calculate the possible range of the volatile content of the mantle using our numerical simulations if the atmospheric pressure on mars around late hesperian era is about 1 bar the estimated values for a typical martian magma are 0 05 0 25 wt which is within the range of the water content of typical terrestrial basaltic magmas

subnormal geothermal gradients in the great valley forearc basin california during franciscan subduction a fission track study outboard parts of forearcs commonly have subnormal geothermal gradients because relatively cold lithosphere subducts beneath them the strata of the 10 to 15 km thick late jurassic tertiary great valley forearc basin accumulated in the forearc of the franciscan subduction zone of coastal california in this study paleogeothermal gradients in this basin were reconstructed to constrain the tectonic history of the convergent plate margin backstripping was used to reconstruct the burial histories of outcropping basin strata and apatite fission track analysis was used to determine the maximum burial temperatures experienced by 64 rock samples plots of maximum burial temperatures versus maximum burial depths indicate earliest tertiary time of deepest burial forearc basin geothermal gradients of about 9 c km backstripping shows that strata from the lower parts of two sections were deeply buried 6 5 km for the period 90 65 ma without experiencing high temperatures 105 c indicating that gradients were at least moderately subnormal throughout that period the data permit gradients no greater than about 15 c km at 90 ma decreasing to no greater than about 9 c km at 65 ma lower strata in another section were probably deeply buried without experiencing high temperatures from 130 or 120 ma until the latest cretaceous or early tertiary indicating that subnormal gradients probably existed throughout that period k ar ages of franciscan complex blueschists indicate subnormal gradients in the california forearc in the late jurassic and early cretaceous fission track data from the sierra nevada indicate subnormal gradients in the early and middle cenozoic and modern heat flow patterns indicate subnormal gradients in the late cenozoic together these indicators suggest that thermal gradients in the forearc were continuously subnormal from the initiation of franciscan subduction in the late jurassic until the termination of subduction in the late cenozoic gradients in the range that would permit blueschist facies metamorphism in the franciscan complex were thus long lived the broad range of k ar ages noted for franciscan blueschists need not reflect multiple discrete metamorphic events but are also consistent with a continuous extended period of high p t conditions blueschists need not have been uplifted soon after metamorphism to avoid overprinting by normal p t conditions but rather may have remained at depth for extended periods preliminary modeling indicates that an interruption in subduction of longer than 5 20 m y should cause detectable heating of forearc basin strata while a much shorter interruption should heat accretionary wedge rocks since there is no evidence of such heating it appears that convergence at the franciscan trench was essentially continuous if allochthonous terranes traveled northward parallel to the california margin during the late jurassic to late cenozoic period of franciscan subduction they apparently did so during oblique subduction not during extended interludes of pure transform motion

a chemical model for evaporites on early mars possible sedimentary tracers of the early climate and implications for exploration martian geomorphology seems to indicate extensive hydrological activity during the noachian era liquid water at the surface would require a large greenhouse effect that is widely hypothesized to have been caused by a high partial pressure of atmospheric carbon dioxide pco2 a sedimentation model driven by sequential evaporation is used to calculate the evaporite mineral sequence in a closed basin lake subject to high pco2 the initial fluid is derived from weathered igneous rock similar to martian meteorite basalts siderite feco3 is always the first major carbonate to precipitate thus siderite is predicted to be an important fades component in ancient martian sediments along with silica which is also an early precipitate these would form varves in lakes that undergo cycles of evaporation and water recharge after silica and siderite the sequence is magnesian calcite nearly pure hydromagnesite and gypsum followed by highly soluble salts like nacl the presence of siderite sediments generally requires an atmospheric pco2 level in excess of 0 1 bar otherwise iron silicates such as greenalite would form this may be used in exploration as an observational test on the past atmospheric composition of mars subject to consideration of the depositional environment at pco2 of approximately several bar gypsum precipitation could occur before calcite upon evaporation if the initial so42 ca2 ratio is high and there is no water recharge the predicted carbonate sequence upon evaporation is generally consistent with recent hypotheses suggesting traces of evaporite carbonates in some martian meteorites several mechanisms destroy or obscure carbonates at the martian surface consequently in situ analysis of the interior of ejecta from recent impact craters lying within sedimentary basins may offer the most practical approach to future exploration of ancient carbonate sediments

final chemical results from the mars pathfinder alpha proton x ray spectrometer 1 the calibrated pathfinder alpha proton x ray spectrometer apxs instrument is capable of measuring concentrations of all major and minor rock forming elements ranging from carbon through zirconium in atomic number therefore it is capable of constraining the petrology of the measured samples in particular the pathfinder data are the first in situ measurements of martian rocks and may be compared with previous remote sensing measurements as well as with the compositions of snc meteorites pathfinder soil and rock sample abundances from the alpha proton and x ray modes have been quantified the abundances suggest that 1 the rocks are covered with various amounts of soil 2 the soil free rocks on a volatile free basis have some element ratios similar to mars meteorites yet have different bulk chemistry indicative of more evolved rocks with higher silica abundances 3 the carbon and nitrogen contents are below detection limits and 4 the alpha mode oxygen reveals excess amounts of oxygen in some samples which is indicative of sample bound water contained within minerals or glasses in samples

plate convergence and long term crustal deformation in central japan surveys by continuous global positioning system in and around japan revealed that the amurian plate collides with the north american plate in central japan by 2 cm yr long term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short term elastic deformation over the arc here we study the long term deformation field by carefully removing the short term signals inferred from a priori plate convergence vectors and coupling strengths predicted by a thermal model the obtained field shows that the change in velocities occurs along the longitude 135 137 and there exist a relatively rigid block and zones accommodating strains characteristic compressional deformation is found northwest of izu due possibly to the collision of the izu bonin arc with honshu plate convergence rate along the nankai suruga trough is considerably smaller in eastern parts due partly to the transition from the amurian to the north american plate of the landward side and partly to the motion of the izu microplate relative to the philippine sea plate this accounts for longer recurrence intervals of interplate earthquakes in the suruga trough where the tokai earthquake is anticipated to occur

micro raman spectroscopy of amphiboles and pyroxenes in the martian meteorites zagami and lewis cliff 88516 we studied micro raman spectroscopy of amphiboles and pyroxenes in the martian meteorites zagami and lewis cliff lew 88516 the obtained raman spectra of the amphiboles are similar to those of kaersutite reconfirming the previous studies that they are kaersutitic amphiboles enriched in ca al and ti even though actinolite belongs to the same amphibole group calcic amphibole as kaersutite the raman spectra of terrestrial actinolite are distinct from those of kaersutite probably reflecting complex amphibole crystal structures the al ti rich pyroxene observed in the magmatic inclusions within lew 88516 olivine is compositionally similar to kaersutite but shows raman spectra nearly identical to the regular pyroxene rather than amphibole in contrast to amphibole this will be due to relatively simple crystal structures of pyroxene thus the raman spectra of al ti rich phases in the martian meteorites are distinct between kaersutite and al ti rich pyroxene and this study demonstrates that micro raman spectroscopy is one of the best tools to perform mineralogical characterization of mineral phases in martian meteorites

cretaceous metamorphism and plutonism in the santa cruz mountains salinian block california and correlation with the southernmost sierra nevada new data on the ages of plutonism and metamorphism in the northern santa cruz mountains part of the enigmatic salinian block of california clarify the area9s geologic history uranium lead dates on zircon monazite sphene and apatite and initial pb and sr isotopic ratios provide a fingerprint for comparison to the rest of the salinian block and to other terranes the u pb zircon dates of plutonic rocks in the santa cruz mountains fall into three groups emplacement ages of the two younger undeformed groups are 91 ma and between 99 and 103 ma individual zircon analyses range from concordant to significantly discordant but have simple crystallization histories coupled with either inheritance of precambrian zircon or pb loss the older group of plutons includes recrystallized granite to well foliated orthogneisses that share the regional fabric analyses from the older group are slightly discordant and multistage histories that include inheritance pb loss and homogenization of pb complicate interpretation of their age emplacement ages for the older group are early cretaceous greater than about 103 ma and probably less than 130 ma foliated and unfoliated plutons from the older group appear to bracket the age of salinian deformation and metamorphism between about 103 and 130 ma lower intercept ages for detrital zircon from schist and quartzite further support a cretaceous metamorphic age the detrital zircon population contains a component at least 1 6 ga probably close to 1 7 ga uranium lead cooling ages measured on sphene and apatite are 96 to 93 and 93 to 88 ma respectively this cooling history appears to be a response to intrusion and rapid cooling of the youngest plutons common pb and sr initial isotopic ratios are radiogenic compared with ratios of oceanic rocks and the western parts of the cordilleran batholiths but they are the least radiogenic in the salinian block and fit the local geographic gradient of pb and sr initial ratios linear variation of pb isotope ratios between radiogenic wall rock and the least radiogenic rocks and correlation of inherited zircon with elevated pb isotope ratios suggest that plutons assimilated wall rock isotopic data and geologic histories of basement rocks in the northern santa cruz mountains fit the geographic patterns documented in the rest of the salinian block more intriguingly the santa cruz mountains plutons are strikingly similar to parts of the southern sierra nevada batholith ages of plutonism and metamorphism u pb zircon discordance systematics petrography and initial sr isotopes match closely between the santa cruz mountains crystalline rocks and units in the southernmost sierra nevada batholith these data reinforce the long standing view that the salinian block and sierra nevada batholiths were adjacent during their formation prior to right slip of about 310 km on the san andreas fault the probable westward continuation of the low angle rand fault system into the southern sierra nevada and the salinian block appears to have offset these two crystalline suites about 125 km

rise and fall of the southern santa cruz mountains california from fission tracks geomorphology and geodesy the santa cruz mountains are closely associated with a left bend along the right lateral san andreas fault the loma prieta area on the northeast side of the san andreas consists of fault bounded blocks that rise along active deeply rooted reverse and oblique slip faults six samples from a transect across this area yield concordant apatite fission track ages averaging 4 6 0 5 ma these ages date the time of cooling below 110 c and suggest that about 3 km of unroofing has occurred over the last 4 6 m y allowing for current elevations of about 1 km this suggests an average uplift rate of the order of 0 8 mm yr over the last 4 6 m y to further define the extent and distribution of this young uplift we used morphometric analyses of the youthful topography of the area steep drainage slopes and high local relief indicate that the area northeast of the san andreas forms a well defined zone of high uplift in contrast the region on the southwest side of the san andreas is characterized by broad upwarping and folding more subdued topography old fission track ages and mean quaternary uplift rates of 0 1 0 4 mm yr geodetic data 1906 san francisco earthquake and subsequent strain transients 20 years of interseismic deformation 1989 loma prieta earthquake and 2 years of post loma prieta earthquake strain show that the southern santa cruz mountains repeatedly rise and subside through a complex sequence of bay area deformation events an additional deformation element that involves reverse slip averaging 2 3 mm yr along the foothills thrust system must occur to explain the longer term uplift pattern in the loma prieta area since the late pliocene the asymmetry in deformation on opposite sides of the san andreas probably reflects the contrasting rock types on opposite sides of the fault the influence of preexisting structures and the interaction with neighboring faults of the san andreas system

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

transitional morphology in west deuteronilus mensae mars implications for modification of the lowland upland boundary abstract west deuteronilus mensae which lies along the lowland upland boundary of mars at 45 latitude 345 longitude exhibits both gradational l a rossbacher 1985 in models in geomorphology woldenberg ed pp 343 372 allen unwin boston and fretted terrain r p sharp 1973 j geophys res 78 4073 4083 boundary types to the west the boundary is gradational and to the east it is defined by fretted terrain the two types of boundaries do not merge with one another within the west deuteronilus mensae region however the gradational boundary materials appear to overlap the fretted terrain by about 500 km contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap the fretted terrain can be identified as much as 300 km north of the gradational boundary in this region lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion changes in the fretted terrain across the gradational boundary from uplands to lowlands include a reduction of canyon wall slopes and depths such that the fretted terrain north of the gradational boundary appears mantled but not obscured there are at least two major classes of processes which might explain the lateral overlap 1 erosion of stratified upland terrain and 2 deposition of plains materials onto the sloping upland margin and fretted terrain erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places of the possible plains emplacement mechanisms eolian deposition would not produce the sharp apparently topographically conformal gradational unit contacts volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain sediment deposition in either a liquid or ice covered sea could produce the draped appearance of the fretted terrain outflow channels along the lowland upland boundary particularly those of the circum chryse and west elysium regions may have flooded the northern lowlands to depths of tens to hundreds of meters the gradational unit contacts may represent the shorelines of such a sea the scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine style wave erosion and redistribution of material along the contacts our limited understanding of the martian paleoclimate and h 2 o inventories allows the possibility of clement periods in the past and other geological evidence e g small valley networks and outflow channels strongly suggests an extensive role of liquid water

complex fault interactions in a restraining bend on the san andreas fault southern santa cruz mountains california the unusual oblique thrust mechanism of the october 18 1989 loma prieta earthquake focused attention on the complex tectonic setting of this segment of the san andreas fault near the mainshock epicenter the san andreas fault curves to the left defining a restraining bend the large thrust component of the mainshock focal mechanism is consistent with the horizontal compression expected across restraining bends however repeated loma prieta type earthquakes cannot exclusively produce the observed topography of the southern santa cruz mountains the highest point of which experienced subsidence during the 1989 earthquake in this paper the authors integrate seismic geomorphic and tectonic data to investigate the possibility that motions on faults adjacent to the san andreas fault play an important role in producing the observed topography the three dimensional geometry of active faults in this region is imaged using the loma prieta preshock and aftershock sequences the most conspicuous features of the fault geometries at depth are 1 the presence of two distinct zones of seismicity corresponding to the san andreas and the sargent berrocal fault zones 2 the concave upward shape of the loma prieta rupture surface 3 the reduction in dip of the deepest portions of the rupture plane asmore the mainshock hypocenter is approached 4 the apparent transfer of shallow slip in some areas from faults in the san andreas fault zone to those in the sargent berrocal fault zone and 5 the presence of a deep northeasterly dipping plane associated with the sargent berrocal fault zone the authors find that a model of fault interactions which involves displacement on faults in both the san andreas and the sargent berrocal fault zones is consistent with loma prieta coseismic displacements preshock and aftershock seismicity and observed topography less

measurements of coseismic deformation in southern california 1972 1982 since 1972 a number of static strain changes have been measured at pinon flat observatory southern california as a result of regional faulting as recorded by a collection of long baselength strainmeters and tiltmeters these signals are in good quantitative agreement with the deformation calculated for a dislocation in an elastic half space in contrast colocated short baselength sensors are found to produce spurious results whose size is much larger than expected theoretically and well correlated with peak site acceleration calculations show that the root mean square rms of the coseismic signals from several different instruments at one site or from several sites at known hypocentral distances provide a good estimate of the seismic moment a result confirmed by the observations static moment estimates for the four largest events in this period are imperial valley 1979 m0 9 0 1018nm mexicali valley 1980 m0 6 1 1018nm westmorland 1981 m0 5 3 1017nm and brawley 1979 m0 2 3 1017 nm these estimated moments generally exceed those determined seismically by about 25 which is as expected since they include some postseismic deformation results from the mexicali valley earthquake are particularly interesting indicating an average fault strike approximately 9 different from the historic fault trace several small to moderate earthquakes ml 3 7 5 2 were also well enough recorded to estimate source parameters for the only other detectable events in the period 1972 1982 a total of three others for which the strain change erms was greater than 0 4 ne high accelerations caused most of the instruments at the site to malfunction no precursory signals were evident for any of the earthquakes recorded at this site

capability of tokai strainmeter network to detect and locate a slow slip first results the tokai strainmeter network tsn a dense network deployed in the tokai region which is the easternmost region of the nankai trough has been designed to monitor slow slips that reflect changes in the coupling state of the plate boundary it is important to evaluate the current capability of tsn to detect and locate slow slips for this purpose the probability based magnitude of completeness developed for seismic networks was modified to be applicable to the evaluation of tsn s performance using 35 slow slips having moment magnitudes m5 1 5 8 recorded by tsn in 2012 2016 this study shows that the probability that tsn detected and located a m5 class slow slip is high 0 9 when considering a region in and around the tsn the probability has been found to depend on the slip duration especially for m5 5 or larger namely the longer the duration the lower the probability a possible use of this method to assess the network s performance for cases where virtual stations are added to the existing network was explored the use of this application when devising a strategic plan of the tsn to extend its coverage westwards is proposed this extension that allows tsn to cover the entire eastern half of the nankai trough is important because the historical records show that the eastern half of this trough tends to rupture first

cooling history of the nw himalaya pakistan fission track and 40ar 39ar cooling ages indicate that the late tertiary cooling history of the himalayan ranges of northern pakistan is largely a function of uplift and erosion interpretation of cooling ages which range from under 0 5 ma to over 80 ma suggests that during the late tertiary long term uplift rates at least doubled from under 0 2 mm yr to in some cases well over 0 5 mm yr uplift rates show strong and systematic regional variations as well which reflect the greater uplift of eastern and northern regions the association of very rapid uplift and erosion with the nanga parbat haramosh massif can be explained by a locally vigorous collision of india with eurasia near a promontory of indian crust the resultant rapid uplift of the nanga parbat haramosh massif reactivated the main mantle thrust melange zone with a reversed sense of motion discontinuities in the coolingage distribution along the main mantle thrust in the southern swat hazara region may be the result of the thermal effects of overthrusting

the long lava flows of elysium planita mars viking orbiter images are used to study the distribution and morphology of 59 lava flows in the elysium planitia region of mars average widths for these flows range from 3 to 16 km and many of the flows exceed 100 km in length the aspect ratio flow length to average width is highly variable 40 1 to 294 km from the summit of elysium mons an unusual attribute of five flows is their segmented nature with up to 13 individual segments on a single flow which each have a surface area from 25 to 250 km2 photoclinometry is used to derive an average thickness of 40 60 m for these flows indicating that individual flow volumes range from 17 7 to 68 1 km3 plausible values for the effusion rate 101 104 m3 s 1 suggest that individual eruptions could have lasted for a few months to several decades and could have injected between 1 36 and 2 04 1012 kg of water vapor into the atmosphere assuming a 1 wt water content for the parental magma a total volume for all 59 flows is estimated to be 817 1226 km3 which would have released 2 04 3 01 1013 kg of water vapor into the atmosphere or 0 2 of the amount previously calculated plescia 1993 as the amount released from the cerberus flows in se elysium planitia

compressional uplift in the central california coast ranges controversy over the relative importance of transverse and compressional deformation surrounds continuing debate over uplift in the california coast ranges a simple model for compressional deformation in the central california coast ranges predicts a significant part of reconstructed post 3 ma surface uplift this result suggests that in addition to passage of the mendocino riple junction and fault interactions in a dominantly strike slip setting late cenozoic surface uplift in the california coast ranges reflects a small compressive component of deformation across the pacific north american plate boundary

geodetic predictions of a strike slip fault model implications for intermediate and short term earthquake prediction mechanical models of faulting during an earthquake cycle now exist that are based on laboratory derived constitutive laws for rock friction such models allow calculation of geodetic changes as a function of depth distance from the fault and time and are useful for gaining insight on the magnitude and timing of geodetic changes that might occur prior to an earthquake we have used the tse and rice 1986 model of a crustal strike slip fault to study the sensitivity of surface deformation to changes in the values of the friction constitutive parameters and the amount of dynamic overshoot during an earthquake models were examined with values of the characteristic decay distance dc in the constitutive law ranging from 5 to 80 mm with near surface values of the steady state velocity dependence a b of 0 0015 and 0 003 and with either zero or 30 dynamic overshoot the time variations of the predicted displacement velocity strain and strain rate distributions are strongly affected by changes in dc and a b and only slightly affected by the amount of dynamic overshoot the larger values of dc and the less negative value of a b i e large ratios of dc to b a produce larger and earlier precursory signals the most useful signals for predicting the model earthquakes are strain changes near the fault because for nearly all model parameters studied the predicted strain changes are considerably larger than the detectability limits of existing borehole strain meters in the presence of earth noise detectable changes occur a few minutes to a month prior to the earthquake depending on parameter values premonitory increases in velocity also occur a pattern of larger velocities at distances a few kilometers away from the fault trace is a diagnostic indication of accelerating slip at depth that would be useful for predictive purposes unfortunately these velocity changes are detectable with creep meters and two color laser electronic distance measuring devices only for the largest ratios of dc to b a in agreement with recent measurements for several earthquakes the predicted amount of preseismic moment release is 0 5 of the earthquake moment for most simulations and the postseismic moment release is a significant fraction of the earthquake moment this two dimensional model suggests that earthquakes of magnitude 6 or greater on strike slip faults that cut the earth s surface could be predicted using existing instrumentation unless the ratio of dc to b a for natural faults is equal to or smaller than the smallest values investigated by tse and rice 1986 study of three dimensional models is needed since premonitory signals will be smaller if along strike variation is considered

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

the morphology of strike slip faults examples from the san andreas fault california fault zones are seldom straight nor are fractures within them continuous permanent strain fields are imprinted near a fault of complex geometry as a result of continued slip these strain fields may be manifest as vertical deformation near the fault strain fields that increase area result in subsidence and strain fields that reduce area result in uplift although these effects are modified by erosion and deposition the general features of fault zone morphology are a consequence of the geometry and slip distribution along strike graphical views of strain fields associated with simple vertical strike slip faults are derived using boundary element methods if the fault is straight and parallel to the applied shear strain the hills and valleys resulting from finite fault rupture are separated by the fault trace this is rarely observed in nature instead strike slip faults cut through hills and valleys apparently of their own making we show this to be a consequence of segments of the fault being nonparallel to each other and to the overall applied shear strain coseismic strains are large but transient since they are substantially annulled by rupture on contiguous fault segments we test our theory with examples from parts of the san andreas fault system in california the morphologies of the parkfield region and the southern san andreas fault in the coachella valley are shown to be consistent with plausible distributions of slip on mapped surface faults the location of the salton sea appears to be a consequence of a reduction of slip on the san andreas fault toward the brawley seismic zone

the black mountain asperity seismic hazard of the southern san francisco peninsula california black mountain a 860 m high wedge of franciscan formation mostly comprising basic ultrabasic rock sw of palo alto and just ne of the san andreas fault marks an abrupt bend in the fault at the northern end of a 100 km long segment of the fault that strikes 9 more e w than the fault to the north or south it also bounds a marked change in the physiographic setting of the fault which to the north follows a well developed linear fault valley and to the south follows a poorly defined topographic trace that traverses the rugged santa cruz mountains the bend at black mountain had a profound effect on the 1906 rupture the 75 km section to the se of this point slipped only 1 1 4 m as compared to the 2 5 4 m typical of the rupture on the san francisco peninsula to the nw this 75 km long slip deficit region from black mountain to san juan bautista if ruptured in its entirety would produce a ms 6 9 earthquake the conditional probability of this rupturing in the near future is the highest of any section of the san andreas fault except parkfield this earthquake would rupture 30 km farther northwest and be about 3 times larger than that previously proposed by others and this constitutes a greater risk to the southern san francisco peninsula than previously expected

survival of impact induced thermal anomalies in the martian mantle 1 a number of geophysical arguments point out the possibility that global mantle convection could have been extremely sluggish or even absent during a large part of martian history this implies that early mantle thermal anomalies produced during planetary formation might not have been quickly erased by vigorous convection one likely mechanism of early thermal inhomogeneity is large impacts at the end of heavy bombardment we suggest that tharsis province might be related to such an impact induced thermal anomaly rather than a convective plume the shape of the present day geoid for our preferred model is in good agreement with the geoid measured by mars global surveyor mgs

finite element modelling of atmosphere loading effects on strain tilt and displacement at multi sensor stations summary strain and tiltmeter observations are composed of signals of different origin tides are a wellknown phenomenon that can be extracted from the time series by tidal analysis depending on the location of the station residuals however contain contributions of different magnitudes from ocean loading changes in atmospheric or hydrological loading anthropogenic induced signals and tectonics reductions of the residual variations are indispensable for extraction of for example the pure tectonical signal one of the challenges in view of the reductions is to understand transfer mechanisms between loading and local conditions such as topography cavity and geological features which lead to additional or modified deformations in this study systematic numerical modelling using the finite element method with elastic rheology is carried out to estimate these effects barometric pressure changes are used as example for the load to determine the additional deformations strain and tiltmeters are considered as instrumentation having nominal resolutions of 0 2 nstrain and 1 nrad respectively the cavity and the topographic effect are systematically investigated with sophisticated models incorporating typical topographic features such as a plain a hill flank and a valley representative for stations worldwide four observatories in central europe are modelled the geodetic observatory wettzell germany the sopron observatory hungary the geodynamic observatory moxa and the black forest observatory bfo both germany the modelling shows that cavity and topographic effects occur in the same order of magnitude and that both effects interact leading to deformations partly intertwined in a complex way this notwithstanding the results explain observed deformation signals at the observatories the systematic modelling helps to better understand the basic processes from which criteria for the selection of future observation sites are inferred

a search for basaltic to intermediate glasses on mars assessing martian crustal mineralogy multiple datasets have demonstrated that the crust of mars is fundamentally basaltic however spectral libraries used to interrogate thermal infrared spectra of martian dark regions through spectral deconvolution have heretofore lacked mafic glasses despite the importance of amorphous phases or phases with amorphous like spectral signatures in martian mineralogy to establish the presence and importance of basaltic to intermediate glasses in martian lithologies we created five such glasses obtained their thermal infrared spectra and included the spectra in a library used to deconvolve nine regional thermal emission spectrometer spectra from mars we employed the nonnegative least squares nnls deconvolution method which yields deconvolved phase abundances and the uncertainties associated with those abundances the basaltic to intermediate glasses do not appear in the deconvolution solutions indicating they are not globally or regionally important phases because martian igneous or impact processes are capable of basaltic to intermediate glass formation the lack of such glasses in the deconvolved mineralogies suggests either the glasses did not form in detectable quantities or they or their signatures have been removed the masking or replacement of basaltic to intermediate glasses through alteration is supported by the appearance in the deconvolution solutions of amorphous phases e g silica rich glasses opal or phases with amorphous like spectral signatures e g clays zeolites that commonly form through aqueous alteration of mafic glasses the glasses may still be important to local scale thermal infrared studies given the basaltic nature of mars and the variety of local scale lithologies detected by various missions the regional mineralogies derived from the nnls deconvolution analysis divide into five statistically separable groups which provide insight into regional trends in mineralogy

fault zone connectivity slip rates on faults in the san francisco bay area california the slip rate of a fault segment is related to the length of the fault zone of which it is part in turn the slip rate of a fault zone is related to its connectivity with adjoining or contiguous fault zones the observed variation in slip rate on fault segments in the san francisco bay area in california is consistent with connectivity between the hayward calaveras and san andreas fault zones slip rates on the southern hayward fault taper northward from a maximum of more than 10 millimeters per year and are sensitive to the active length of the maacama fault

chassigny petrogenesis melt compositions intensive parameters and water contents of martian magmas abstract the snc meteorites are a class of eight basaltic achondrites that have extremely young crystallization ages 1 3 ga chassigny a unique snc meteorite is a dunite containing fo68 olivines and rare poikilitic ca pyroxenes it is one of the most primitive snc meteorites and thus is most likely to reveal information about the snc basalt source region this study presents a detailed examination of partially crystallized melt inclusions in cumulus olivine grains in chassigny these trapped melts are argued to be representative samples of the melt that existed when chassigny crystallized this melt has been modified however by interaction with the host olivine and by closed system crystallization the phases inside the melt inclusions include hydrous ti rich amphibole kaersutite biotite two pyroxenes and rhyolitic and alkali feldspar glasses all phases have been extensively analyzed with an electron microprobe the new mineralogical information is combined with a complementary experimental study of kaersutite melt equilibria this combined data set can be used to formulate a system of linear equations which can then be solved to determine the composition of the originally trapped melt this calculation reveals that the trapped melt was an feo rich and al2o3 poor basalt the melt composition is shown to be consistent with the crystallization sequence both inside the melt inclusions and in the rock matrix the major element chemistry of this liquid closely resembles terrestrial boninite lavas the new data also allow the intensive conditions temperature total pressure and water fugacity of chassigny crystallization to be estimated two pyroxene geothermometry indicates that equilibration temperatures were 1000 50 c although amphibole does not coexist with melt until t 960 c the trapped liquid initially contained 1 5 wt dissolved water crystallization of anhydrous phases caused water to buildup in the trapped melt prior to kaersutite crystallization the melt must have contained at least 4 wt dissolved water suggesting that a minimum of 1 5 kbar total pressure is required a maximum total pressure cannot be inferred but all available data are consistent with low pressure 5 kbar crystallization finally x h2o in the fluid in the melt inclusion is estimated to have been at least 0 8 in order to stabilize amphibole without plagioclase implying that the water fugacity was 1480 bars the existence of hydrous melts and conditions appropriate for amphibole crystallization suggest that evolved sio2 rich lavas exist on the chassigny parent body mars

magmatic history and parental melt composition of olivine phyric shergottite lar 06319 importance of magmatic degassing and olivine antecrysts in martian magmatism several olivine phyric shergottites contain enough olivine that they could conceivably represent the products of closed system crystallization of primary melts derived from partial melting of the martian mantle larkman nunatak lar 06319 has been suggested to represent a close approach to a martian primary liquid composition based on approximate equilibrium between its olivine and groundmass to better understand the olivine melt relationship and the evolution of this meteorite we report the results of new petrographic and chemical analyses we find that olivine megacryst cores are generally not in equilibrium with the groundmass but rather have been homogenized by diffusion to mg 72 we have identified two unique grain types an olivine glomerocryst and an olivine grain preserving a primary magmatic boundary that constrains the time scale of eruption to be on the order of hours we also report the presence of trace oxide phases and phosphate compositions that suggest that the melt contained approximately 1 1 h2o and lost volatiles during cooling also associated with an increase in oxygen fugacity upon degassing we additionally report in situ rare earth element measurements of the various mineral phases in lar 06319 based on these reported trace element abundances we estimate the oxygen fugacity in the lar 06319 parent melt early in its crystallization sequence i e at the time of crystallization of the low ca and high ca pyroxenes the rare earth element composition of the parent melt and those of melts in equilibrium with later formed phases we suggest that lar 06319 represents the product of closed system crystallization within a shallow magma chamber with additional olivine accumulated from a cumulate pile we infer that the olivine megacrysts are antecrysts derived from a single magma chamber but not directly related to the host magma and suggest that mixing of antecrysts within magma chambers may be a common process in martian magmatic systems

evolution of the northern santa cruz mountains by advection of crust past a san andreas fault bend the late quaternary marine terraces near santa cruz california reflect uplift associated with the nearby restraining bend on the san andreas fault excellent correspondence of the coseismic vertical displacement field caused by the 17 october 1989 magnitude 7 1 loma prieta earthquake and the present elevations of these terraces allows calculation of maximum long term uplift rates 1 to 2 kilometers west of the san andreas fault of 0 8 millimeters per year over several million years this uplift in concert with the right lateral translation of the resulting topography and with continual attack by geomorphic processes can account for the general topography of the northern santa cruz mountains

the rocks of mars from far and near award of the meteoritical society 2001 h y mcsween jr the leonard medal address the rocks of mars from far and near

transpression along the southern san andreas fault durmid hill california transpression is expressed at durmid hill in the development and subsequent rotation of en echelon folds and ongoing vertical uplift the transpression related strain field can be quantified by an analysis of 1 orientation of rotated fold axes which display an angle of about 20 between the san andreas fault and the fold axial traces 2 shortening perpendicular to the fold axes 40 60 3 extension parallel to the fold axes 58 68 measured using a boudinaged ash bed and 4 uplift determined from an antecedent stream 1 1 1 7 mm yr the topographic expression of durmid hill and the exposed stratigraphy the observed deformation may be approximated by a homogeneous transpressional deformation this model suggests that an estimated 9 14 of the total displacement predicted by plate motion models across the san andreas fault has been accommodated by the durmid hill deformation zone adjacent to the fault this off fault deformation is not directly coupled to coseismic or interseismic movement on the fault itself

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

geodetic estimate of coseismic slip during the 1989 loma prieta california earthquake offsets in the relative positions of geodetic stations resulting from the loma prieta earthquake can be explained with a dislocation model that includes buried oblique slip on a rupture surface extending 37 km along the strike of the san andreas fault dipping 70 degree to the sw and extending from a depth of about 5 to 17 5 km assuming uniform slip on a rectangular surface the mean values for a range of reasonable fault geometries are 1 6 plus minus 0 3 m right lateral strike slip and 1 2 plus minus 0 3 m reverse slip slip on an adjacent extension of the rupture to the southeast recorded in the aftershock sequence is not well constrained by the geodetic data the geodetic data clearly preclude rupture extending near the surface

water in the martian interior evidence for terrestrial morb mantle like volatile contents from hydroxyl rich apatite in olivine phyric shergottite nwa 6234 abstract understanding the distribution and behavior of volatiles in martian magmas and the corresponding mantle provides crucial constraints on planetary properties such as mantle melting temperatures and melt production as well as the availability of magmatic fluids for any potential occurrences of life current evaluations of the pre eruptive volatile concentrations of martian magmas are based on analyses of hydrous minerals in martian meteorites such as apatite because they record the volatile content oh f cl and the halogen and water fugacities of their parental magmas estimates for the pre eruptive volatile contents of martian basaltic magmas range from nearly anhydrous to 2 wt h2o however these magmas may have potentially degassed upon eruption and or emplacement losing their magmatic water while retaining some halogens here we report apatite compositional data from the martian meteorite nwa 6234 an intermediate olivine phyric shergottite and calculate f2 cl2 h2o fugacity ratios for its parental magma apatites in nwa 6234 contain the highest observed oh f content among martian meteorites and importantly have volatile fugacity ratios similar to terrestrial basalts this suggests that the actual content of fluorine chlorine and water of the martian mantle parental to snc meteorites are higher than previously thought and are similar to the volatile content of the terrestrial mid ocean ridge basalt source region

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

historic creep rate and potential for seismic slip along the hayward fault california the hayward fault is considered the most likely source of one or more major earthquakes in the san francisco bay area in the next few decades historically at least one and probably two major earthquakes about m 6 8 occurred along the hayward fault one in 1836 and another in 1868 little is known about the 1836 event but the 1868 earthquake was accompanied by a surface rupture that extended as much as 41 km along the southern part of the fault although the amount of surface slip in 1868 is uncertain right slip including afterslip reached at least several centimeters and possibly several decimeters in places this paper documents the spatial variation of creep rate along the hayward fault since the 1868 earthquake creep aseismic fault slip occurs over at least 66 km and may extend over the fault s entire 82 km length of which about 13 km lies underwater creep rate seems nearly constant over decades but short term variations occur we derive creep rate mainly from our own systematic surveying of offset cultural features curbs fences and buildings on each feature we solve directly for accumulated creep by using multiple linear regression creep rate mostly falls in the range of 3 5 6 5 mm yr but systematic variation occurs along strike fault segments with distinctly higher and lower rates generally correspond to parts of the fault most salient from the overall average alinement of the fault most distinctive is a 4 km long section near the south end of the fault that creeps at about 9 mm yr such a high rate has occurred there at least since the 1920s and probably since the 1868 earthquake as indicated by an offset railroad track built in 1869 we suggest that this 9 mm yr slip rate may approach the long term or deep slip rate that controls average recurrence interval between major earthquakes if so assuming an elastic rebound model the potential for slip in large earthquakes below the surficial creeping zone is now 1 1 m in the southern 1868 segment of the fault and 1 4 m in the northern 1836 segment subtracting surface creep rates from a long term slip rate of 9 mm yr gives present potential for surface slip in large earthquakes of up to 0 8 m with an average of 0 6 m in the northern segment and 0 4 m in the southern segment we present a simple hypothesis for rupture potential that is compatible with historic creep rate microseismicity distribution and geodetic data if seismic rupture occurs on segments 41 km long by 10 km deep 7 km fully locked 3 km creeping today s potential for seismic moment release is 1 4 1019 and 1 1 1019 n m for both 1836 and 1868 segments respectively and 2 5 1019 n m for both segments jointly converting moment to magnitude gives ml 6 8 in the northern segment ml 6 7 in the southern segment and ml 7 0 for simultaneous rupture of both

subduction of the philippine sea plate beneath southwestern japan slab geometry and its relationship to arc magmatism 1 we carry out high resolution three dimensional seismic tomography of the crust and upper mantle beneath southwestern sw japan using arrival time data obtained from the nationwide seismograph network the tomographic images provide new insights into the configuration of the philippine sea slab and arc magmatism the results confirm the existence of an aseismic portion of the philippine sea slab at greater depths beyond the seismic portion the philippine sea slab is subducting aseismically down to at least a depth of 200 km in chubu 60 80 km in kinki and 60 km in chugoku and is subducting seismically to depths of 150 200 km in kyushu in the chubu district it is subducting seismically at a shallow dip and then bends downward beneath the volcanic area whereas in the kinki district it is subducting subhorizontally as far as the japan sea the differences in the slab geometry between adjacent regions correlate with the differences in volcanic activity suggesting the importance of the geometry of the philippine sea slab on arc magmatism our tomographic images further imply subduction of the philippine sea slab down to a depth of around 70 km northwest of the izu peninsula the philippine sea slab in that region might have split into western and eastern parts separated by a slab tear and collided with the pacific slab at depths of 150 200 km

zagami product of a two stage magmatic history abstract large specimens of the zagami shergottite show highly varied grain sizes and mineral abundances on a cm scale and preferred alignment of pyroxene laths we document the presence of whitlockite and of melt veins and pockets of shock origin pyroxene crystals have homogeneous mg rich pigeonite and augite cores overgrown by fe rich zoned pyroxene mostly pigeonite rims amphibole bearing magmatic melt inclusions occur exclusively in the cores we conclude that zagami experienced a twostage crystallization history the first stage occurred in a deep seated slowly cooling magma chamber there the homogeneous mg rich cores of the pyroxenes crystallized during relatively slow cooling the deep seated origin of the cores is also indicated by the presence of amphibole within them which requires pressures of formation equivalent to crystallization at depths 7 5 km on mars modest abundance of homogeneous mg rich cores 15 20 indicates that crystal settling did not play a significant role in this part of the magma chamber during the second stage the mg rich pyroxenes were entrained into a magma that either intruded to the near surface and cooled in a relatively thin dike or sill or extruded to the surface and crystallized in a lava flow 10 m thick again without indications for crystal settling this scenario is suggested by estimates of cooling rates of 0 1 0 5 c h based on sizes of the plagioclase maskelynite crystals and of 0 02 c h based on the width of pyroxene exsolution lamellae brearley 1991 irregular shapes of the mg rich cores result from resorption and possible solid state diffusion and the shapes and sizes of the pyroxenes after crystallization of fe rich pigeonite rims onto the cores were strongly controlled by the shapes and sizes of the cores the finer grained areas of the rock inherited smaller and more numerous mg rich pyroxene cores from the first stage than did the coarser grained areas crystallization of both augite and pigeonite cores at depth but mostly pigeonite rims in the nearsurface environment may be the result of a phase boundary shift and expansion of the pigeonite stability field at lower pressures the estimated depth of the magma chamber for zagami of 7 5 km and thickness of the putative lava flow of 10 m are consistent with calculations and observations of volcanic constructs and flows in the tharsis region of mars

three dimensional seismic velocity structure and configuration of the philippine sea slab in southwestern japan estimated by double difference tomography 1 three dimensional seismic velocity structure in and around the philippine sea plate subducting beneath southwestern sw japan is determined by applying double difference tomography method to arrival time data for earthquakes obtained by a dense nationwide seismic network in japan a region of low s wave velocity and high vp vs of several kilometers in thickness is recognized immediately above the region of intraslab seismicity in a wide area from tokai to kyushu this characteristic layer dips shallowly in the direction of slab subduction compared with the upper surface of the philippine sea slab based on seismic reflection and refraction surveys on seven survey lines we interpret that the low vs and high vp vs layer corresponds to the oceanic crust of the philippine sea slab on the basis of the position of the low vs and high vp vs layer and the precisely relocated hypocenter distribution of intraslab earthquakes the upper surface of the philippine sea slab is reliably determined for the entire area of sw japan nonvolcanic deep low frequency earthquakes that occurred associated with the subduction of the philippine sea slab are distributed along the isodepth contour of 30 km in sw japan except for the tokai district where the depth of deep low frequency earthquakes becomes gradually deeper toward northeast

snc meteorites clues to martian petrologic evolution the shergottites nakhlites and chassigny snc meteorites are apparently cumulate mafic and ultramafic rocks that crystallized at shallow levels in the crust of their parent body the mineralogy and chemistry of these meteorites are remarkably like equivalent terrestrial rocks although their ratios of fe fe mg and certain incompatible elements and their oxygen isotopic compositions are distinctive all have crystallization ages of 1 3 b y or younger and formed from magmas produced by partial melting of previously fractionated source regions isotope systematics suggest that the snc parent body had a complex and protracted thermal history spanning most of geologic time some meteorites have been severely shock metamorphosed and all were ejected from their parent body at relatively recent times possibly in several impact events late crystallization ages complex petrogenesis and possible evidence for a large gravitational field suggest that these meteorites are derived from a large planet trapped gases in shergottite shock melts have compositions similar to the composition measured in the martian atmosphere ejection of martian meteorites may have been accomplished by acceleration of near surface spalls or other mechanisms not fully understood if snc meteorites are of martian origin they provide important information on planetary composition and evolution the bulk composition and redox state of the martian mantle as constrained by shergottite phase equilibria must be more earthlike than most current models planetary thermal models should benefit from data on the abundances of radioactive heat sources the melting behavior of the mantle and the timing of planetary differentiation calculated depletion of chalcophile elements in source regions indicates a core dominated by sulfides and paleomagnetic measurements suggest the presence of a weak magnetic field within the last several hundred thousand years concentrations of volatile elements indicate that the snc parent body was not volatile depleted and trapped atmospheric components measured in shock melts may be useful in understanding planetary degassing by providing comparisons for spectral reflectance data and viking soil analyses these meteorites may also constrain surface mineralogy and weathering mechanisms

new lithologies in the zagami meteorite evidence for fractional crystallization of a single magma unit on mars abstract zagami consists of a series of increasingly evolved magmatic lithologies the bulk of the rock is a basaltic lithology dominated by pigeonite fs 28 7 54 3 augite fs 19 5 35 0 and maskelynite ab 42 53 approximately 20 vol of zagami is a basaltic lithology containing feo enriched pyroxene pigeonite fs 27 0 80 8 and mm to cm sized late stage melt pockets the melt pockets are highly enriched in olivine bearing intergrowths mesostases phosphates both whitlockite and water bearing apatite fe ti oxides and sulfides the systematic increases in abundances of late stage phases fs and incompatible element e g y and the rees contents of pigeonite ab contents of maskelynite and feo concentrations of whitlockite all point to a fractional crystallization sequence the crystallization order in zagami and the formation of these various lithologies was controlled by the abundances of iron phosphorus and calcium during fractional crystallization iron and phosphorus enrichment occurred ultimately forcing the crystallization of calcium phosphates and olivine bearing intergrowths the limited amount of calcium in the melt and its partitioning between phosphates and silicates controlled the crystallization of phosphates plagioclase pigeonite and augite the presence of these feo enriched water poor late stage lithologies has important implications discrepancies between experimental and petrologic studies to infer the history of basaltic shergottites may be partially explained by the use of starting compositions which are too feo poor in the experimental studies the water poor nature of the late stage melt pockets suggests crystallization from a very dry magma although whether this magma was always dry or experienced significant near surface degassing remains an open question finally the presence of fractional crystallization products within zagami suggests that this may be a relatively common process on mars

earth and mars water inventories as clues to accretional histories abstract the earth has 2 7 km of water on its surface its mantle contains at least 150 ppm water and probably significantly more depending on the amount of undepleted mantle and subducted crustal water that is present geologic evidence suggests that a few hundred meters of water are close to the martian surface but evidence from snc meteorites indicates that the martian mantle is very dry containing no more than about 35 ppm water part of the difference in water content of the mantles of the two planets is attributed to plate tectonics however the earth s mantle appears to contain at least several times the water content of the martian mantle even accounting for plate tectonics we attribute the difference to two possible causes the first possibility is that melting of the earth s surface during accretion as a result of the development of a steam atmosphere allowed impact devolatized water at the surface to dissolve into the earth s interior in contrast because of mars smaller size and greater distance from the sun the martian surface may not have melted so that the devolatilized water could not dissolve into the surface a second and preferred possibility is that mars like the earth acquired a late volatile rich veneer but it did not get folded into the interior as with the earth but instead remained as a water rich veneer the perception of mars as having a wet surface but a dry interior is consistent with what we know of the geologic history of mars which can be viewed as the progressive intrusion and overplating of a water rich crust by dry mantle derived volcanic rocks

light lithophile elements in martian basalts evaluating the evidence for magmatic water degassing whether water has played a role in the petrogenesis of martian basalts remains a subject of significant debate estimates of pre eruptive water concentrations in martian magmas are impeded by the effects of degassing and shock however zoning trends of light lithophile elements lle in pyroxene have been interpreted as evidence for the degassing of magmatic water on the basis of the soluble behavior of these elements in hydrothermal fluids we provide ion microprobe analyses of lle in pyroxene in the zagami and shergotty martian basalts complemented by detailed electron microprobe analyses and major element x ray maps to independently verify the zoning of lle and its relationship to texture and major element variations our results corroborate previous results specifically that li concentrations are lower in rims than cores of shergotty and zagami pyroxene in contrast we see no evidence for a core to rim decrease in b in the absence of further data we interpret the decrease in li as reflecting either loss after crystallization of pyroxene cores consistent with magmatic degassing or the diffusive preferential loss of li from pyroxene rims possibly as a result of shock because the partitioning behavior of li between hydrous fluid minerals and melt under relevant conditions of pressure temperature and melt composition is unknown the viability of the water degassing hypothesis depends on experiments establishing the compatibility of li in hydrous fluid associated with martian basaltic melt and the incompatibility of li in pyroxene at elevated pressures

mars water abundance an estimate from d h ratio in snc meteorites recent measurements of water composition in snc meteorites have shown a high and variable deuterium to hydrogen d h ratio the highest d h value is nearly equal to the present day value in the mars atmosphere this indicates that between 1 3 billion years gyr ago and 180 million years myr ago the martian atmosphere may have attained the same d h ratio as it has now this also provides evidence for an interaction process involving water operating between atmosphere regolith and rocks in snc meteorites in this paper we have calculated the amount of water at present and at 4 5 ga via the d h fractionation process assuming that water is lost to space as well as to the surface a surface flux smaller than 108 cm 2 s 1 operating over the life history of the planet will not have any influence on the size of the fractionated water reservoir however we find that substantial surface loss of water will be required in case mars exchangeable water inventory has undergone transition from an initial large abundance to a small amount at present our results show that water which is lost to the surface would carry the d h signature of the atmosphere of that period

influence of fo2 and cooling rate on the kinetics and energetics of fe rich basalt crystallization cooling rate and fo2 are each varied over several orders of magnitude in a matrix of 1 atm constant rate cooling experiments using synthetic basalt the modes and compositions of olivine pyroxene and titanomagnetite are sensitive to oxygen fugacity ranging from qfm 4 to qfm 5 log units whereas their textures respond to the degree of undercooling as modulated by cooling rate ranging from 2 8 to 231 c h 1 key results pertain to the trends in mineral composition melt differentiation and

compositional diversity and stratification of the martian crust inferences from crystallization experiments on the picrobasalt humphrey from gusev crater mars 1 phase equilibrium experiments on a liquid composition of the gusev crater rock humphrey with added f and cl with 0 07 wt and 1 67 wt water have revealed the range in compositional diversity of lavas that could arise from fractionation at the base of a thick martian crust humphrey composition melts with 0 07 wt water produce ne normative alkalic residual melts at 9 3 kbar silica progressively decreases with increasing degree of fractionation this decrease in silica is accompanied by fe ti and p enrichment with 1 67 wt bulk water content humphrey like melts instead crystallize to produce residual melts that show progressive silica enrichment al enrichment and fe depletion progressing from mildly alkalic hy normative basalt to trachyandesite coupled with the production of such residual liquids by fractionation is the formation of ultramafic to mafic cumulus lithologies that would remain at the base of the martian crust this process would lead to significant compositional stratigraphy of the crust that contains elements of both trends as early hydrous primary magmas gave way to drier more depleted primary magmas upon dehydration of the magma source regions by repeated episodes of partial melting the possibility of significant contribution of late silica poor fe enriched basalt residual to fractionation at depth to the present martian surface makes it difficult to reliably use surface lithologies to constrain the compositional characteristics of the mantle magmatic source regions and the primary melts produced from them

chronology eruption duration and atmospheric contribution of the martian volcano apollinaris patera geologic mapping thermal inertia measurements and an analysis of the color visual wavelengths of the martian volcano apollinaris patera indicate the existence of two different surface materials comprising an early easily eroded edifice and a more recent competent fan on the southern flank a chronology of six major events that is consistent with the present morphology of the volcano has been identified we propose that large scale explosive activity occurred during the formation of the main edifice and that the distinctive fan on the southern flank appears to have been formed by lavas of low eruptive rate similar to those that form compound pahoehoe flow fields on earth a basal escarpment typically 500 m in relief and morphologically similar to the one surrounding olympus mons was produced between the formation of the main edifice and the fan indicating multistage eruptions over a protracted period of time contact relations between the volcanic units and the adjacent chaotic material indicate that formation of the chaotic material occurred over an extended period of time and may be related to the volcanic activity that formed apollinaris patera stereophotogrammetric measurements permit the volume of the volcano to be estimated at 105 km3 from this volume measurement and an inferred eruption rate 1 5 10 2 km3 yr 1 we estimate the total eruption duration for the main edifice to be 107 yrs plausible estimates of the exsolved volatile content of the parent magma imply that greater than 1015 kg of water vapor was released into the atmosphere as a consequence of this activity this large amount of water vapor as well as other exsolved gases must have had a significant impact on local and possibly global climatic conditions

the role of meteoritics in spaceflight missions and vice versa research on extraterrestrial materials plays a critical role in formulating the science rationale and design for spacecraft missions and conversely spaceflight holds great promise for solving perplexing problems in meteoritics the connections between meteoritics and sample return missions are obvious meteorite research can define sampling strategies the capabilities of sampling devices acceptable levels of chemical contamination and physical alteration of samples and the conditions under which samples are stored prior to and during recovery for their part sample return missions can provide geologic context for meteorites increased sampling diversity including materials not sampled as meteorites such as unconsolidated regolith ices and atmosphere calibration for crater counting chronology and ground truth for remote sensing measurements of meteorite parent bodies meteoritics also relates to spacecraft flyby rendezvous and lander missions that do not necessarily return samples specific illustrations of this mutual relationship based on a selection of recent or planned spacecraft missions include identifying source asteroid classes for ordinary and carbonaceous chondrites and reconstructing their thermal and collisional histories galileo near clementine ii and muses c determining the extent to which cometary dust and interstellar grains are found as interplanetary dust particles and assessing volatile abundances isotopic compositions and molecular species in cometary nuclei stardust and rosetta understanding the compositions of ancient martian crust and the mantle sources for snc meteorites as well as inventorying the planet s volatile reservoirs and interactions mars pathfinder mars global surveyor and mars volatiles and climate surveyor assessing whether lunar meteorites provide a more representative chemical sampling of the highlands crust and of mare volcanism than do apollo samples galileo clementine and lunar prospector spaceflight is the first priority of the space agencies that fund most research on extraterrestrial materials and the continued level of support for such research may be linked in part to its use in exploration by spacecraft

the behavior of li and b in lunar mare basalts during crystallization shock and thermal metamorphism implications for volatile element contents of martian basalts late stage rims of magmatic pyroxenes from some martian basalts show decreases in li and b contents relative to earlier formed pyroxene cores this behavior is different than expected from their documented incompatible element behavior previous workers interpreted such depletions to reflect the loss of several wt magmatic water during basalt crystallization this interpretation has profound implications for the nature of the martian mantle and recent exchange of volatiles between the martian mantle and atmosphere to assess alternative mechanisms that may influence the behavior of li and b in the absence of aqueous fluid activity the effects of changing pyroxene composition during crystallization shock pressure and shock associated thermal metamorphism were studied lithium and b depletions are documented in late stage rims of pyroxenes from anhydrous lunar basalts indicating that mechanisms other than aqueous fluid activity must have influenced li and b partitioning in these pyroxenes depletions of li and b are most likely associated with changing pyroxene composition during crystallization and occur in lunar and martian pyroxenes with late stage fe enrichment it is interesting that pyroxenes without late stage fe enrichment show no concomitant li and b increases lithium loss may occur during breakdown of metastable pyroxferroite additionally changes in cr content may influence the substitution mechanism involved for incorporating li shock does not redistribute li or b but may facilitate subsequent thermally driven diffusion by the introduction of mechanical defects in grains thermally metamorphosed pyroxenes exhibit higher li and lower b contents relative to unheated pyroxenes it is likely therefore that li and b are redistributed through interactions between pyroxenes and surrounding zones of mesostasis during thermal metamorphism

water in snc meteorites evidence for a martian hydrosphere the shergotty nakhla chassigny snc meteorites purportedly of martian origin contain 0 04 to 0 4 percent water by weight oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the snc parent body formed two distinct oxygen isotopic reservoirs if mars was the parent body the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet

rhonite in luna 24 pyroxenes first find from the moon and implications for volatiles in planetary magmas grains ofrhonite have been discovered in magmatic inclusions in augite grains of the lunar regolith from mare crisium returned to earth by the russian luna 24 spacecraft these rhonite grains are up to 8 m long pleochroic from tan to dark brown and associated with ulvospinel and silica rich glass electron microprobe analysis gives a composition near end member ferroan rhonite ca 1 9 mn 0 0 na 0 1 fe 2 4 5 mg 0 1 al 0 3 cr 0 0 ti 1 0 si 4 0 al 2 0 o 20 the raman spectrum of these grains is like those of terrestrial rhonites and distinct from titanian amphiboles compositionally rhonite plus silica plus water or halogens f cl is equivalent to titanian amphibole plus pyroxene so the presence ofrhonite in lunar basaltic rock is consistent with the known low abundance of volatiles in the moon when calibrated mineral reactions involving rhonite and titanian amphibole may provide quantitative constraints on fugacities of water f and cl in basaltic magmas from the moon and other planetary bodies

the parent magma of the nakhlite meteorites clues from melt inclusions abstract several forms of trapped liquid found within nakhlite meteorites have been examined including interstitial melt and magmatic inclusions within the cores of large olivine grains differences in the mineralogy and texture between two types of trapped melt inclusions and between these inclusions and the mesostasis indicate that vitrophyric inclusions are most appropriate for estimating the composition of a nakhlite parental magma in equilibrium with early forming olivine and augite parent liquids were calculated from the mineralogy of large inclusions in nakhla and governador valadares using a system of mass balance equations solved by linear regression methods the chosen parental liquids were cosaturated in olivine and augite and had mg fe values consistent with measured augite liquid kd s these parental magma compositions are similar to other published compositions for nakhla chassigny and shergotty parental melts and may correspond to a significant magma type on mars

combining meteorites and missions to explore mars laboratory studies of meteorites and robotic exploration of mars reveal scant atmosphere no evidence of plate tectonics past evidence for abundant water and a protracted igneous evolution despite indirect hints direct evidence of a martian origin came with the discovery of trapped atmospheric gases in one meteorite since then the study of martian meteorites and findings from missions have been linked although the meteorite source locations are unknown impact ejection modeling and spectral mapping of mars suggest derivation from small craters in terrains of amazonian to hesperian age whereas most martian meteorites are young 4 5 ga and formation of enriched and depleted reservoirs however the history inferred from martian meteorites conflicts with results from recent mars missions calling into doubt whether the igneous histor y inferred from the meteorites is applicable to mars as a whole allan hills 84001 dates to 4 09 ga and contains fluid deposited carbonates accompanying debate about the mechanism and temperature of origin of the carbonates came several features suggestive of past microbial life in the carbonates although highly disputed the suggestion spurred interest in habitable extreme environments on earth and throughout the solar system a flotilla of subsequent spacecraft has redefined mars from a volcanic planet to a hydrologically active planet that may have harbored life understanding the history and habitability of mars depends on understanding the coupling of the atmosphere surface and subsurface sample return that brings back direct evidence from these diverse reservoirs is essential

assessment of shock effects on amphibole water contents and hydrogen isotope compositions 1 amphibolite experiments abstract kaersutitic amphiboles found within a subset of the martian meteorites have low water contents and variably heavy hydrogen isotope compositions in order to assess if impact shock induced devolatilization and hydrogen isotope fractionation were determining factors in these water and isotopic characteristics of the martian kaersutites we conducted impact shock experiments on samples of gore mountain amphibolite in the ames vertical gun range avgr a parallel shock experiment conducted on an anorthosite sample indicated that contamination of shocked samples by the avgr hydrogen propellant was unlikely petrographic study of the experimental amphibolite shock products indicates that only 10 of the shock products experienced levels of damage equivalent to those found in the most highly shocked kaersutite bearing martian meteorites 30 35 gpa ion microprobe studies of highly shocked hornblende from the amphibolite exhibited elevated water contents h 2 o 0 1 wt and enriched hydrogen isotope compositions d 10 relative to unshocked hornblende water and hydrogen isotope analyses of tens of milligrams of unshocked moderately shocked and highly shocked hornblende samples by vacuum extraction uranium reduction and isotope ratio mass spectrometry irms respectively are largely consistent with analyses of single grains from the ion microprobe the mechanisms thought to have produced the excess water in most of the shocked hornblendes are shock induced reduction of hornblende fe and or irreversible adsorption of hydrogen addition of the isotopically enriched martian atmosphere to the martian meteorite kaersutites via these mechanisms could explain their enriched and variable isotopic compositions alternatively regrouping the water extraction and irms analyses on the basis of isotopic composition reveals a small but consistent degree of impact induced devolatilization 0 1 wt h 2 o and h isotope enrichment d 10 extrapolating the shock signature of the regrouped data to grains that experienced martian meteorite like shock pressures suggests that shock induced water losses and hydrogen isotope enrichments could approach 1 wt h 2 o and d 100 respectively if these values are valid then impact shock effects could explain a substantial fraction of the low water contents and variable hydrogen isotope compositions of the martian meteorite kaersutites

late cenozoic uplift of denali and its relation to relative plate motion and fault morphology apatite fission track analysis of samples that cover a 4 kilometer vertical section from the western flank of denali mount mckinley north america9s highest mountain suggests that the mountain massif was formed by rapid uplift 1 kilometer per million years beginning 6 million years ago ma uplift was a result of the morphology of the denali fault and a change in motion of the pacific plate with respect to north america at 5 ma which created opposing tangential vectors of relative movement along the fault and forced the intervening crustal blocks upward

nonlinear strain buildup and the earthquake cycle on the san andreas fault two contrasting models of the earthquake deformation cycle on strike slip faults predict significant temporal declines in shear strain rate near the fault accompanied by a progressive broadening of the zone of deformation adjacent to it in the thin lithosphere model transient deformation results from flow in the asthenosphere due to stress relaxation following faulting through most or all of the lithosphere for an earth model with a thick elastic lithosphere plate thickness depth of seismic slip transient motions are due to postearthquake aseisrnic slip below the coseismic fault plane data from the san andreas fault indicate a long term temporal decrease in strain rate that persists for at least 30 years and may extend through the entire earthquake cycle observations support a cycle long rate decrease and a temporal spreading of the deformation profile only if movement cycles on the northern and southern locked sections of the fault are basically similar if so the usually lower strain rates and broader deformation zone currently observed on the southern san andreas represent a later evolutionary stage of the northern locked section where a great earthquake is a more recent occurrence although the data allow some extreme models to be discarded no sufficiently strong constraints exist to decide between the thin and thick lithosphere models regardless of the appropriate model the geodetic observations themselves indicate that strain buildup is sufficiently nonlinear to cause significant departures from recurrence estimates based on linear strain accumulation and the time predictable model

major quaternary uplift along the northernmost san andreas fault king range northwestern california the king range is a rugged coastal mountain range that parallels the san andreas transform fault system just south of the mendocino triple junction point delgada is a small coastal headland that projects into the pacific ocean just southwest of the king range apatite fission track ages from parts of the king range are remarkably young averaging 1 2 ma indicating that a minimum of 2 5 km of uplift and unroofing have occured in the past 1 2 m y in contrast ages from point delgada are about 12 ma and fission track length data indicate that rocks there have resided at low temperatures le 50 degree c and thus at shallow depths since soon after 12 ma therefore point delgada has experienced relative vertical stability the contrast in uplift histories indicates that the two areas are separated by a major fault with a minimum of approximately 1 km of quaternary vertical offset the fault is probably part of the san andreas system and so may also have undergone major quaternary strike slip offset the uplift in the king range seems too great and too localized to have resulted from isostatic effects accompanying passage of the mendocino triple junction and development of a slab free window rather it is probably amore local response to space problems among the various moving crustal blocks around the triple junction and san andreas fault less

geochemical evidence for magmatic water within mars from pyroxenes in the shergotty meteorite observations of martian surface morphology have been used to argue that an ancient ocean once existed on mars1 it has been thought that significant quantities of such water could have been supplied to the martian surface through volcanic outgassing but this suggestion is contradicted by the low magmatic water content that is generally inferred from chemical analyses of igneous martian meteorites2 here however we report the distributions of trace elements within pyroxenes of the shergotty meteorite a basalt body ejected 175 million years ago from mars3 as well as hydrous and anhydrous crystallization experiments that together imply that water contents of pre eruptive magma on mars could have been up to 1 8 we found that in the shergotty meteorite the inner cores of pyroxene minerals which formed at depth in the martian crust are enriched in soluble trace elements when compared to the outer rims which crystallized on or near to the martian surface this implies that water was present in pyroxenes at depth but was largely lost as pyroxenes were carried to the surface during magma ascent we conclude that ascending magmas possibly delivered significant quantities of water to the martian surface in recent times reconciling geologic and petrologic constraints on the outgassing history of mars

right lateral reverse surface rupture along the san andreas and sargent faults associated with the october 17 1989 loma prieta california earthquake the loma prieta earthquake produced bewildering arrays of surface fractures of all possible modes in the epicentral area preliminary reports of the fracturing though suggested that there was no evidence of right lateral surface slip above the fault as it is defined seismically through detailed mapping of selected localities along the san andreas and sargent faults however we have been able to show that strands of the san andreas and sargent faults ruptured to the surface with right lateral northward thrust components of slip in amounts of 10 to 20 cm

diverse pliocene quaternary tectonics in a transform environment san francisco bay region california the san francisco bay region occupies part of the diffuse transform boundary zone between the pacific and north american plates although dextral strike slip faulting is dominant the plate motion is expressed in a variety of ways some strike slip faults are parallel with the plate boundary but some are slightly oblique the major strike slip faults are zones in which an interplay occurs between strands some of which are en echelon this interplay may be responsible for some apparent pull apart basins and presumed normal faults along the calaveras fault zone in extensive areas between strike slip fault zones there are many compressional structures folds and reverse faults that are pliocene quaternary in age hence largely coeval with the strike slip faults some of the compressional structures are oblique to and others are parallel with the major strike slip faults we have divided the san francisco bay region into domains on the basis of the types orientations and relationships of structures or in one case lack of strong deformation each domain has responded in its own way to the regional northwest southeast dextral shear imposed by the relative plate motion in an attempt to understand the origin of various structures and the interrelationships among them we compared established models with our observations some observed geometric relationships agree quite well with classical coulomb anderson and simple shear models but others require further explanation models based on fault interaction seem to apply to certain cases for example the east bay hills domain which is between the left stepping calaveras and hayward rodgers creek fault zones is under compression resulting from interaction between the two strike slip zones

coseismic deformation and dislocation models of the 1989 loma prieta earthquake derived from global positioning system measurements global positioning system gps surveys were used to determine coseismic displacements within the epicentral region of the 1989 loma prieta earthquake near santa cruz the california highway department caltrans conducted the preearthquake survey in february and march 1989 using single frequency gps receivers in march 1990 we reoccupied eight of the caltrans stations using dual frequency receivers relative displacements were computed by differencing the station coordinates determined from these two surveys displacements were determined relative to sites remote from the earthquake by incorporating gps measurements from loma prieta station lp1 to the very long baseline interferometry vlbi site at fort ord examination of repeated measurements in the single frequency preearthquake survey indicates precision is 10 mm in the horizontal although it may be as low as 40 mm in the weakly connected part of the network the precision in the vertical is generally 30 40 mm in contrast the largest observed coseismic displacement is 410 mm horizontal and 341 mm vertical we use a quasi newton method to estimate the parameters of the uniform rectangular dislocation source that best fits the observed displacements the best fitting dislocation dips 68 southwest extending from 3 to 16 km depth strikes n66 w and has 1 8 m of dip slip and 1 2 m of strike slip the best fitting dislocation overlaps the aftershocks but is rotated 15 counterclockwise from the trend of the afterhock zone we find that the data can be fit nearly as well with a dislocation that is constrained to lie in the plane of the aftershocks in this case the fault extends from 5 to 15 km depth the constrained model explains 96 of the data both models have a moment of m0 2 9 1019 n m we also use the quasi newton method to estimate rectangular dislocation models from the leveling data of marshall et al 1991 and the trilateration and gps data of it lisowski et al 1990 in contrast to the previous studies we find that both of these data sets are independently best fit with dislocations embedded within the aftershock zone

tectonic architecture of the mountain front foreland basin transition south island new zealand assessed by fission track analysis oblique continental convergence across the alpine fault since the mid miocene has loaded the australia plate with the leading edge of the pacific plate and formed a foreland basin the basin occurs mostly offshore beneath the continental shelf but remnants of the marine basin fill overlie ordovician basement in a narrow coastal strip 10 20 km wide in westland between the tasman sea and the alpine fault the results of fission track analyses of apatite and zircon separates from this basement integrated with the regional structure and stratigraphy indicate that the foreland basin formerly extended across the whole of westland and that its succession increased in thickness eastward toward the alpine fault reaching a maximum of about 4 km continuing covergence across the main thrust alpine fault has caused its footwall to thicken by reverse fauting in a transitional zone 10 20 km wide immediately west of the mountain front southern alps consequently the inner margin of the foreland basin has been inverted and the succession almost completely eroded in the southern part of westland upper crustal shortening in the australia plate amounted to about 2 km associated uplift started about 5 m y ago and involved only one major fault bounded block in northern westland upper crustal shortening amounted to about 12 km two major fault bounded blocks were involved and uplift was underway by 10 ma assuming a preuplift geothermal gradient of 25 c km the long term rate of uplift ranged between 0 8 and 2 0 mm yr in southern westland and between 0 4 and 1 2 mm yr in different parts of northern westland

the slip distribution of the 1946 nankai earthquake estimated from tsunami inversion using a new plate model abstract a new model for the shape of the philippine sea plate psp subducting beneath southwest japan was constructed by combining marine seismic survey results and seismicity data this resulted in a plate model that is generally 3 5 km shallower than previous estimates and contains new details of plate boundary structure near the nankai trough axis we estimated the slip distribution of the 1946 nankai earthquake by inverting tsunami waveforms using the new plate boundary model and found that the large slip off cape muroto and seismic moment were reduced by about 10 from the previous estimate of tanioka and satake 2001a however we also found reason to suspect the tide gauge closest to the epicenter at shimotsu and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area we also find that our new rupture model correlates well with features of the subducting plate boundary such as a large subducting seamount off cape muroto kodaira et al 2000a this suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy or both

pliocene change in pacific plate motion the absolute motion of the pacific plate has been nearly constant during the past 15 myr but epp1 recognized that some change took place between 15 myr and the present and tentatively chose 1 myr for the time of the change cox and engebretson2 found a change in pacific absolute motion based on hotspot tracks and a change in pacific antarctic relative motion the pliocene deformation in california and the juan de fuca rotations led them to postulate a 5 myr age for the change the manner and timing of the change are explored more thoroughly here and we put the time for the change in motion of the pacific plate at between 5 and 3 2 myr basing the younger limit on the correlation of computed hotspot tracks with pacific and nazca hotspot traces the change may explain several observations on the neighbouring continental and oceanic plate boundaries including direct adjustments at the pacific spreading ridges a likely mechanism for the change is a large clockwise torque caused by acceleration of the sinking slab beneath the kurile trench where a fossil spreading ridge is inferred to have been subducted

long term seismic potential of the san andreas fault southeast of san francisco california the long term decade or longer seismic potential of the peninsular san andreas fault the 125 km long segment southeast of san francisco has been assessed by comparing the slip accompanying the 1906 mw 7 7 earthquake with the amount of this slip deficit made up since 1906 of particular importance is the longstanding factor of 2 inconsistency between 1906 surface offsets 1 5 m and geodetically determined coseismic slip 2 7 m on the southern 90 km of the peninsular san andreas in reexamining this issue we find that the discrepancy cannot be attributed to either large observational uncertainties in the geodetic data or shortcomings in fault modeling rather the problem lies in the complexity of this 90 km long fault reach where the san andreas trend changes by 6 the zone of recent deformation is 0 5 2 km wide and much of the fault is heavily vegetated and inaccessible farther northwest on the 1906 rupture where the fault geometry is much simpler evidence from deformed fences shows that right lateral coseismic slip was commonly distributed across a zone 20 600 m wide with only about 70 of the total slip occurring at the main fault trace the general importance of distributed coseismic deformation and the evidence for fault zone complexity indicate that the best estimate of 1906 slip on this 90 km fault segment is the geodetically constrained value of 2 6 0 2 m farther northwest on the peninsular san andreas the coseismic slip ranges from 3 4 to 4 4 m and geodetic slip and surface offsets show considerably better agreement following previous work we have assessed the risk posed to the southern peninsular san andreas by two broad classes of earthquakes these appraisals use the geodetic slip distribution apply a long term slip rate of 15 mm yr suggested by geologic and geodetic studies and assume the approximate correctness of the time predictable recurrence model the possibility of an m 6 1 2 earthquake on the 30 km long segment northwest of san juan bautista cannot be completely precluded but the evidence bearing on its likelihood is contradictory in contrast with several previous assessments we find that the risk of an earthquake of m 7 rupturing the southern 90 km of the peninsular san andreas during the next several decades is quite low

temporal variation of crustal deformation during the days preceding a thrust type great earthquake the 1944 tonankai earthquake of magnitude 8 1 japan the temporal variation in precursory ground tilt prior to the 1944 tonankai japan earthquake which is a great thrust type earthquake along the nankai trough is discussed using the analysis of data from repeated surveys along short distance leveling routes sato 1970 pointed out that an anomalous tilt occurred one day before the earthquake at kakegawa near the northern end of the focal region of the earthquake from the analysis of additional leveling data sato s result is re examined and the temporal change in the ground tilt is deduced for the period of about ten days beginning six days before the earthquake a remarkable precursory tilt started two or three days before the earthquake the direction of the precursory tilt was up towards the south uplift on the southern nankai trough side but the coseismic tilt was up towards the southeast perpendicular to the strike of the main thrust fault of the tonankai earthquake the postseismic tilt was probably opposite of the coseismic tilt the preseismic tilt is attributed to precursory slip on part of the main fault if similar precursory deformation occurs before a future earthquake expected to occur in the adjacent tokai region the deformation may help predict the time of the tokai earthquake

heterogeneous distribution of h2o in the martian interior implications for the abundance of h2o in depleted and enriched mantle sources we conducted a petrologic study of apatite within 12 martian meteorites including 11 shergottites and one basaltic regolith breccia these data were combined with previously published data to gain a better understanding of the abundance and distribution of volatiles in the martian interior apatites in individual martian meteorites span a wide range of compositions indicating they did not form by equilibrium crystallization in fact the intrasample variation in apatite is best described by either fractional crystallization or crustal contamination with a cl rich crustal component we determined that most martian meteorites investigated here have been affected by crustal contamination and hence cannot be used to estimate volatile abundances of the martian mantle using the subset of samples that did not exhibit crustal contamination we determined that the enriched shergottite source has 36 73 ppm h2o and the depleted source has 14 23 ppm h2o this result is consistent with other observed geochemical differences between enriched and depleted shergottites and supports the idea that there are at least two geochemically distinct reservoirs in the martian mantle we also estimated the h2o cl and f content of the martian crust using known crust mantle distributions for incompatible lithophile elements we determined that the bulk martian crust has 1410 ppm h2o 450 ppm cl and 106 ppm f and cl and h2o are preferentially distributed toward the martian surface the estimate of crustal h2o results in a global equivalent surface layer gel of 229 m which can account for at least some of the surface features on mars attributed to flowing water and may be sufficient to support the past presence of a shallow sea on mars surface

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr

geomorphic response of coastal streams to low intermediate and high rates of uplift medocino triple junction region northern california analysis of three dimensional morphological properties of 24 coastal drainage basins that have evolved in areas of low 3 m 1 000 yr rates of uplift near the mendocino triple junction mtj coastal northern california identified channel gradients as the best indicator of tectonism in the landscape lower order tributaries best reflect tectonically controlled differences the largest streams examined of third order are able to adjust to most base level change and maintain their profile form whereas lower order streams farther upstream tend to accumulate the effects of net base level fall and have steepest profiles in the areas of highest uplift rates variations in steepness of first order channel gradients indicate that 1 high uplift rates in the wake of the mtj have existed for at least 73 000 yr and 2 differential tilt of the region to the north and south of the current locus of highest uplift rate is occurring in association with regional uplift although first order streams are excellent indicators of areas of both high uplift rates and regional differential tilting they are less useful in distinguishing between areas of low and intermediate uplift rate analysis of the longitudinal profile of the main trunk stream of ten of the 24 drainage basins using the stream gradient index was more useful to categorize broadly the uplift rates and to distinguish between streams in low and intermediate uplift rate areas although the hypotheses tested herein do not identify the exact mechanism off uplift in the mtj region they do indicate that the nature of deformation is most likely regional tilt rather than crustal shortening with localized compressional folding and thrust faulting they also indicate that geomorphic responses trail in the wake of the uplift rate response caused by development of a slab window beneath the north american plate 1 maximum uplift rates occur 9 km south of the northern boundary of the slab window 2 maximum mean first order channel gradient occurs 16 km south of the northern edge of the slab window and 3 maximum drainage basin relief occurs 20 km south of the northern edge of the slab window associated lag times between passage of the southern edge of the subducted gorda plate slab and geomorphic responses are 160 000 yr for maximum uplift rates 290 000 yr for maximum channel gradients and 370 000 yr for maximum relief