trace element geochemistry of martian iddingsite in the lafayette meteorite the lafayette meteorite contains abundant iddingsite a fine grained intergrowth of smectite clay ferrihydrite and ionic salt minerals both the meteorite and iddingsite formed on mars samples of iddingsite olivine and augite pyroxene were extracted from lafayette and analyzed for trace elements by instrumental neutron activation our results are comparable to independent analyses by electron and ion microbeam methods abundances of most elements in the iddingsite do not covary significantly the iddingsite is extremely rich in hg which is probably terrestrial contamination for the elements si ai fe mn ni co and zn the composition of the iddingsite is close to a mixture of 50 lafayette olivine 40 lafayette siliceous glass 10 water concordant behavior among these elements is not compatible with element fractionations between smectite and water but the hydrous nature and petrographic setting of the iddingsite clearly suggest an aqueous origin these inferences are both consistent however with deposition of the iddingsite originally as a silicate gel which then crystallized neoformed nearly isochemically the iddingsite contains significantly more magnesium than implied by the model which may suggest that the altering solutions were rich in mg 2

broadband waveform inversion of moderate earthquakes in the messina straits southern italy abstract we report the first application of the cut and paste cap method to compute earthquake focal mechanisms in the messina straits area by waveform inversion of pnl and surface wave segments this application of cap has furnished new knowledge about low magnitude earthquake mechanics that will be useful for improved understanding of the local geodynamics this is possible because the cap inversion technique can be applied to small earthquakes for which traditional moment tensor inversion methods are not appropriate and p onset focal mechanisms in the study area fail because of a lack of sufficient observations we estimate the focal mechanisms of 23 earthquakes with local magnitudes in the range of 3 4 occurring in the 2004 2008 time period and recorded by the broadband stations of the italian national seismic network and the mediterranean very broadband seismographic network mednet run by the istituto nazionale di geofisica e vulcanologia ingv the solutions show that normal faulting is the prevailing style of seismic deformation in the northern part of the study area while co existence of normal faulting and strike slip has been detected in the southern part in the whole area of investigation the t axes of focal mechanisms display a preferential northwest southeast direction of extension combined with the findings of previous investigations this improved database of focal mechanisms allows us to better detail the transitional area between the extensional domain related to subduction trench retreat southern calabria and the compressional one associated with continental collision western central sicily the observed spatial change of seismic deformation regime offers new data to current seismotectonic and seismic hazard investigations in the area of messina straits where a magnitude 7 2 earthquake caused more than 60 000 casualties on 28 december 1908

recycling of iodine in fore arc areas evidence from the iodine brines in chiba japan the distribution of iodine in the earth s crust is dominated by its accumulation in marine sediments if fluxes between terrestrial and marine compartments are considered however a significant imbalance exists between known sources and sinks of iodine we present here evidence from the fore arc area near chiba japan the world s largest brine iodine producing area that iodine is mobilized from marine sediments during the early stages of subduction based on detailed chemical analyses of 22 brines and 129i dating of 13 of these samples collected from the kazusa formation we show that iodine in these fluids is derived from organic rich marine sediments with a minimum age of 50 myr geochemical characteristics of the brines and the age of the iodine indicate that the iodine enrichment is caused by mobilization from subducting marine sediments and not by derivation from the host formation age 1 2 myr the direct return of iodine from marine sediments into the oceans during the subduction of oceanic plates could provide the missing link in the iodine cycle and be an important pathway also in the marine cycle of carbon

samarium neodymium and rubidium strontium systematics of nakhlite governador valadares abstract the sm nd systematics of whole rock and mineral separate samples from nakhlite governador valadares define a good 147sm 143nd mineral isochron age of 1 37 0 02 ga this age is in excellent agreement with the 39ar 40ar and rb sr ages obtained previously for this meteorite however the rb sr isotopic data for our sample show that the isotopic system is disturbed the lack of isotopic equilibrium is probably caused by the weathering of the sample as indicated by the presence of secondary alteration phases the whole rock and acid washed mineral data yield a rb sr age of 1 20 0 05 ga which probably represents a lower limit to the crystallization age of the rock the petrographic evidence indicates that this meteorite is a clinopyroxene cumulate that probably crystallized in a subsurface sill mcsween 1994 thus the sm nd isotopic age probably represents the age of such a magmatic event the initial e143nd value determined for the rock at 1 37 ga is 17 1 indicating that the parent magma of the rock came from a light rare earth element depleted source of 147sm 144nd 0 237 based on a simple two stage evolution model results of the same model calculation for the initial 87sr 86sr ratio of the rock suggest that its source material was depleted in 87rb 86sr by 50 relative to the estimated martian value at 1 37 ga both the high sm nd and low rb sr values support a clinopyroxene rich cumulate source for the genesis of the nakhlite governador valadares furthermore our sm nd age and e143nd data and the previously published e142nd datum for the rock harper et al 1995 are consistent with early differentiation of the parent planet formation of cumulate sources 4 56 ga ago and late melting of the sources and formation of the rock 1 37 ga ago the good agreement of isotopic ages and petrographic features among governador valadares nakhla and lafayette strongly suggests that all three nakhlites have undergone similar evolutionary histories the nakhlite age data suggest that isotopic heterogeneity in the martian mantle sources existed up to 1 37 ga ago and early mantle structures probably have not been disturbed for a significant portion of martian history

39ar 40ar ages of martian nakhlites abstract we report 39ar 40ar ages of whole rock wr and plagioclase and pyroxene mineral separates of nakhlites mil 03346 and y 000593 and of wr samples of nakhlites nwa 998 and nakhla all age spectra are complex and indicate variable degrees of 39ar recoil and variable amounts of trapped 40ar in the samples thus we examine possible ar ar ages in several ways from consideration of both limited plateau ages and isochron ages we prefer ar ar ages of nwa 998 1334 11 ma mil 03346 1368 83 ma mesostasis and 1334 54 ma pyroxene y 000593 1367 7 ma and nakhla 1357 11 ma 2 errors for nwa 998 and mil 03346 the ar ar ages are within uncertainties of preliminary rb sr isochron ages reported in the literature these ar ar ages for y 000593 and nakhla are several ma older than sm nd ages reported in the literature we conclude that the major factor in producing ar ar ages slightly too old is the presence of small amounts of trapped martian or terrestrial 40ar on weathered grain surfaces that was degassed along with the first several percent of 39ar a total k 40ar isochron for wr and mineral data from five nakhlites analyzed by us plus lafayette data in the literature gives an isochron age of 1325 18 ma 2 we emphasize the precision of this isochron over the value of the isochron age our ar ar data are consistent with a common formation age for nakhlites the cosmic ray exposure cre age for nwa 998 of 12 ma is also similar to cre ages for other nakhlites

hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument phyllosilicates a class of hydrous mineral first definitively identified on mars by the omega observatoire pour la mineralogie l eau les glaces et l activitie instrument preserve a record of the interaction of water with rocks on mars global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy fe mg and al smectite clays this was interpreted to indicate that phyllosilicate formation occurred during the noachian the earliest geological era of mars and that the conditions necessary for phyllosilicate formation moderate to high ph and high water activity were specific to surface environments during the earliest era of mars s history here we report results from the compact reconnaissance imaging spectrometer for mars crism of phyllosilicate rich regions we expand the diversity of phyllosilicate mineralogy with the identification of kaolinite chlorite and illite or muscovite and a new class of hydrated silicate hydrated silica we observe diverse fe mg oh phyllosilicates and find that smectites such as nontronite and saponite are the most common but chlorites are also present in some locations stratigraphic relationships in the nili fossae region show olivine rich materials overlying phyllosilicate bearing units indicating the cessation of aqueous alteration before emplacement of the olivine bearing unit hundreds of detections of fe mg phyllosilicate in rims ejecta and central peaks of craters in the southern highland noachian cratered terrain indicate excavation of altered crust from depth we also find phyllosilicate in sedimentary deposits clearly laid by water these results point to a rich diversity of noachian environments conducive to habitability

crustal velocity structure in italy from analysis of regional seismic waveforms abstract in this article we use regional seismic waveforms recorded by the recently installed istituto nazionale di geofisica e vulcanologia ingv national network and the mediterranean very broadband seismographic network mednet stations to develop 1d crustal velocity models for the italian peninsula about 55 000 p wave and 35 000 s wave arrival times from 4727 events are used to derive average seismic parameters in the crust and uppermost mantle we define four regions according to geological constraints and recent travel time tomography results based on the average seismic parameters we combine broadband seismic waveforms and travel times of regional phases to model crustal structures for the four regions by applying the genetic algorithm our results indicate smooth velocity gradients with a depth beneath the apennines and a deep moho beneath the central alps green s functions from the regionalized 1d velocity models are used to determine source depths and focal mechanisms for 37 events with a magnitude larger than 3 5 by a grid search technique our results show that normal and strike slip faulting source mechanisms dominate the apenninic belt and that most thrust faulting events occur in the adriatic sea and the outer margin of the northern apennines

the nature of martian fluids based on mobile element studies in salt assemblages from martian meteorites the s cl and br abundances determined in salt assemblages in nakhla and lafayette olivine fracture fillings and in gas rich impact melt grim glasses from shergotty and eet79001 lithologies a b using empa eds aps x ray microprobe techniques are compared with the s and cl abundances determined by gooding and coworkers in similar samples using quadrupole mass spectrometric techniques all the analytical methods yield relatively high cl and low so sub 3 abundances in nakhla indicating a so sub 3 cl ratio of approx 0 2 the same ratio in lafayette secondary salts seems to be approx 2 in the case of grim glasses from shergotty and eet79001 lith a lith b the so sub 3 abundance is found to be high whereas the cl abundance is low yielding a so sub 3 cl ratio of approx 5 300 large errors are associated with these ratios because of low cl signals the salts found in nakhla fracturefillings are inferred to have formed from cl rich fluids high ph near nakhlite source region on mars whereas the secondary minerals found in shergottite grim glasses seem to be associated with so sub 3 rich fluids low ph near shergottite source region on mars the cl rich fluids seem to have infiltrated into the nakhlite source region approx 600 ma ago more whereas the so sub 3 rich fluids likely percolated into the shergottite source region at approx 180 ma or less suggesting the possible existence of two types of fluid sources on mars less

disentangling xenon components in nakhla martian atmosphere spallation and martian interior abstract a powdered sample of nakhla was separated into 3 subsamples one was left otherwise untreated one was washed in water and one etched with hno3 removing 6 of the original mass we report results of isotopic analysis of xenon released by laser step heating on aliquots of each of these subsamples some aliquots were neutron irradiated before isotopic analysis to allow determination of i ba and u as daughter xenon isotopes and some were not there is evidence that water soluble phases contain both martian atmospheric xenon and a component with low 129xe 132xe either martian interior xenon or terrestrial atmosphere higher temperature data from unirradiated aliquots of the water and acid treated samples reveal two component mixing one is a trapped xenon component with 129xe 132xe 2 350 0 026 isotopically identical to the martian atmosphere as measured in shock glass from shergottites it is associated with leachable iodine suggesting it is trapped close to grain boundaries it may be a result of shock incorporation of adsorbed atmospheric gas the second component is best explained as an intimate mixture of martian interior xenon and spallation xenon the martian interior component is present at a concentration of 10 12 cm3 stp g 1 132xe around 40 times lower than that observed in chassigny its association with spallation xenon produced from ba and light rare earth elements suggests it is in the feldspathic mesostasis we propose that it was trapped during crystallisation and reflects the mantle source of the parental magma

halogen and cl isotopic systematics in martian phosphates implications for the cl cycle and surface halogen reservoirs on mars abstract the cl isotopic compositions and halogen cl f br and i abundances in phosphates from eight martian meteorites spanning most rock types and ages currently available have been measured in situ by secondary ion mass spectrometry sims likewise the distribution of halogens has been documented by x ray mapping halogen concentrations range over several orders of magnitude up to some of the largest concentrations yet measured in martian samples or on the martian surface and the inter element ratios are highly variable similarly cl isotope compositions exhibit a larger range than all pristine terrestrial igneous rocks phosphates in ancient 4 ga meteorites orthopyroxenite alh 84001 and breccia nwa 7533 have positive 37 cl anomalies 1 1 to 2 5 these samples also exhibit explicit whole rock and grain scale evidence for hydrothermal or aqueous activity in contrast the phosphates in the younger basaltic shergottite meteorites 37 cl anomalies 0 2 to 5 6 phosphates with the largest negative 37 cl anomalies display zonation in which the rims of the grains are enriched in all halogens and have significantly more negative 37 cl anomalies suggestive of interaction with the surface of mars during the latest stages of basalt crystallization the phosphates with no textural major element or halogen enrichment evidence for mixing with this surface reservoir have an average 37 cl of 0 6 supporting a similar initial cl isotope composition for mars the earth and the moon oxidation and reduction of chlorine are the only processes known to strongly fractionate cl isotopes both positively and negatively and perchlorate has been detected in weight percent concentrations on the martian surface the age range and obvious mixing history of the phosphates studied here suggest perchlorate formation and halogen cycling via brines which have been documented on the martian surface has been active throughout martian history

locating seismic events in the ctbt context the verification of the comprehensive nuclear test ban treaty ctbt requires the determination of accurate location of seismic events from a fixed network of seismic stations across the globe the requirements of possible on site inspections mean that the goal is to place the location estimate in a zone smaller than 1000 km2that includes the true location because a defined set of stations will be used corrections can be refined to represent the influence of departures from the global reference model iaspei91 the primary stations in the international monitoring scheme ims are mostly seismic arrays and therefore the present location scheme is based on minimisation of a misfit function built from arrival time azimuth and array slowness residuals the effective network will change markedly with the magnitude of the event and as a result regional information has to be integrated into the location process

seismic location calibration of the european arctic a crustal velocity model has been developed for fennoscandia the baltic shield and adjacent areas this model represents a simplified average of various models developed for parts of this region we show that p wave travel times calculated with this model provide an excellent fit to observations at the fennoscandian krsc and iris station networks for a set of seismic events with known or very well constrained locations the station event paths cover large parts of western russia and the barents sea thus indicating that this model which we denote the barents model is appropriate for this entire region we show by examples that significant improvements in event location precision can be achieved compared to using the 1aspei model we finally use the barents model to calculate locations of recent small seismic events in the novaya zemlya region of interest in a ctbt monitoring context

rapid source mechanism determination of large mw 5 earthquakes in the western united states inversion of complete long period ground motions is used for rapid determination of source mechanisms of mw 5 earthquakes in the western united states the first few minutes of ground motions on local and regional distance waveforms are inverted for point source centroid moment tensors waveforms recorded at regional distances 300 1500 km can be adequately modeled at periods longer than 50 s using the laterally homogeneous prem model dziewonski and anderson 1981 at closer distances 300 km waves with periods as short as 35 s can be analyzed using prem best double couple focal mechanisms for 18 recent large western u s earthquakes compare very well with those obtained by other methods our procedure interfaced with automated data retrieval and source location methods is a viable tool for reliable determination of seismic moment and fault mechanism within 30 minutes after an earthquake

new oxygen isotope evidence for long term cretaceous climatic change in the southern hemisphere a new composite 18 o record generated from calcareous fine fraction and bulk sediments from the exmouth plateau details long term cretaceous climatic change at mid latitudes in the southern hemisphere assessment of new and previously published 18 o data indicates that a mid cretaceous global climatic optimum was achieved sometime between the time of the cenomanian turonian boundary and the middle turonian when surface ocean paleotemperatures were the highest of the past 115 m y periods of cooling and warming that reversed the general patterns were superimposed on long term aptian turonian warming and turonian maastrichtian cooling trends respectively extrapolation of southern hemisphere paleotemperature trends to maastrichtian paleotemperature data from a low latitude pacific guyot implies that maximum mid cretaceous low latitude paleotemperatures could have been in excess of 33 c

noble gases in iddingsite from the lafayette meteorite evidence for liquid water on mars in the last few hundred million years we analyzed noble gases from 18 samples of weathering products iddingsite from the lafayette meteorite potassium argon ages of 12 samples range from near zero to 670 91 ma these ages confirm the martian origin of the iddingsite but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric 40ar in any case because iddingsite formation requires liquid water this data requires the presence of liquid water near the surface of mars at least as recently as 1300 ma ago and probably as recently as 650 ma ago krypton and xe analysis of a single 34 g sample indicates the presence of fractionated martian atmosphere within the iddingsite this also confirms the martian origin of the iddingsite the mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas our strongest conclusion is that the iddingsite in lafayette formed on mars in agreement with the microstratigraphic arguments of gooding et al 1991 and treiman et al 1993 a preterrestrial origin of the iddingsite is required both by the many non zero k ar ages and by the presence of xe that is isotopically distinct from any terrestrial xe the xe is accompanied by kr but the kr and xe have been fractionated if they are derived from the present martian atmosphere this is presumably the result of either incorporation via interaction with liquid water drake et al 1994 bogard and garrison 1998 or by adsorption from the martian atmosphere perhaps accompanied by shock see also gilmour et al 1998 1999 although the iddingsite is enriched in kr and xe compared to whole rock analyses it is not clear whether iddingsite is the dominant carrier of the atmospheric derived gas drake et al 1994 or merely a minor carrier gilmour et al 1999 our 40ar 39ar experiment was disappointing in that it mostly served to confirm that the iddingsite which contains fine grained clays is susceptible to recoil loss of 39ar during irradiation only one sample of five gave a clear signal of radiogenic or extraterrestrial 40ar and that was only by 3 potassium argon ages of the second set of samples were more successful ranging from near 0 to 670 91 ma it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration the fact that a rb sr experiment shih et al 1998 gave an apparent age for iddingsite of 679 66 ma 2a suggests that perhaps formation of iddingsite occurred or began 650 ma ago and that some samples either formed or were thermally altered later the ages could be even younger than 650 ma if the samples have incorporated martian atmospheric 40ar this means that liquid water was certainly present on mars in the last 1300 ma the formation age of lafayette and probably within the last 650 ma

oceans on mars an assessment of the observational evidence and possible fate the edges of the northern plains and interpreted to be shorelines remaining from these former standing bodies of water we examine the elevations and geologic relations along these contacts in detail and find little support for their interpretation as shorelines some contacts are clearly of volcanic origin and all have significant variations in elevation better support for the former presence of water over large parts of the northern plains is provided by the vastitas borealis formation vbf most of the post noachian fill within the northern basin is ridged plains of lower hesperian age interpreted to be volcanic in origin overlying the ridged plains is the vbf a thin veneer of material of upper hesperian age the vbf may have been deposited from large floods support for this interpretation is the similarity in age between the outflow channels and the vbf the presence of the vbf at the lower ends of the outflow channels and identification of numerous features in the outcrop areas of the vbf that are suggestive of basal melting of an ice sheet to cover all the area over which the vbf is exposed would require 2 3 10 7 km 3 of water spread over the entire surface of mars this volume is equal to a global layer global equivalent layer or gel 156 m deep we find no support for the larger estimates of ocean volumes that range up to 3 10 8 km 3 and which imply comparable amounts of water per unit area as are currently present on the surface of the earth under present climatic conditions on mars an ocean would freeze in a geologically short time period 10 4 years then would sublimate away at rates strongly dependent on the presence or absence of debris on the ice surface the present vbf is interpreted as a sublimation residue from the ponded outflow channel effluents the fate of a volume of water thought to have been emplaced by the outflow channels 2 3 10 7 km 3 is largely accounted for by the presence of other existing reservoirs on the planet an approximately 20 30 m gel of water is estimated to be in the present polar caps and a 50 m gel may have escaped to space since the hesperian leaving 80 m gel unaccounted for this amount may be partly trapped in other volatile rich deposits on the surface and a significant amount could have reentered the groundwater system by south polar basal melting and been progressively cold trapped at the base of a growing cryosphere on the basis of our assessment of the hesperian aged deposits we predict that testing of the clifford and parker 2001 hypothesis that a noachian aged ocean covered up to one third of the surface of mars will be made very difficult by the enhanced degradation rates in the noachian and subsequent geological events in the northern lowlands index terms 6225 planetology solar system objects mars 4267 oceanography general paleoceanography 5407 planetary sciences atmospheres evolution 5470 planetary sciences surface materials and properties 1635 global change oceans 4203 keywords mars oceans channels shorelines hesperian

mixed hydrothermal fluids and the origin of the martian soil the martian soil consists mainly of weathered basaltic rock and a salt component enriched in volatile and mobile elements primarily sulfur chlorine sodium and potassium since the discovery of this mobile element component by the viking x ray fluorescence spectrometer volcanic aerosols have been considered a likely source for these enrichments alternative sources of the mobile element component are fluids supplied to the surface by hydrothermal processes related to impact craters and volcanism we show that a mixed hydrothermal fluid model can successfully explain the composition of the mobile element component of the soil this model is constructed using terrestrial analogs constrained by the viking and pathfinder measurements of the martian soil chemistry the potential hydrothermal fluid contributions to the soil are tightly constrained because the relative abundances of the mobile elements in hydrothermal fluids are nearly constant the two end member types of hydrothermal fluids considered in the model are the neutral chloride and the acid sulfate type the neutral chloride fluids have high cl and na contents and a significant amount of k but their s abundance relative to cl s cl ratio is too low to match the martian soil however acid sulfate hydrothermal systems characterized by substantial vapor transport and high s cl ratios are likely on mars due to the low abundance of water indeed as the availability of water declines in a hydrothermal system the neutral chloride system can evolve to a vapor dominated acid sulfate system a combination of the two types of fluids can quantitatively explain the s and cl abundance in the soil and provide reasonable abundances of other mobile elements including na k and br without predicting an excess of any element measured in the soil however the hydrothermal fluids are unlikely to be involved in the formation of the magnetic minerals in the soil because the fe contents of the fluids are too low although the acid sulfate fluids have fe concentrations a factor of 100 larger than the neutral chloride fluids the acid sulfate fluids would contribute less than 1 of the total fe in the soil the volcanic aerosol models are poorly constrained in contrast to the hydrothermal fluid models because in volcanic aerosols the relative abundances of the mobile elements are highly variable therefore while volcanic aerosols can explain the mobile element component of the soil significant contributions from other sources cannot be excluded determining the relative contributions of hydrothermal components compared to volcanic aerosols will require measurements in the martian soil of trace elements that provide signatures of the hydrothermal fluids such as high lithium contents that are associated with neutral chloride fluids

shergottites dhofar 019 sau 005 shergotty and zagami 40ar 39ar chronology and trapped martian atmospheric and interior argon we report a high resolution 40ar 39ar study of mineral separates and whole rock samples of olivine phyric dhofar 019 sayh al uhaymir sau 005 and basaltic shergotty zagami shergottites excess argon is present in all samples the highest 40ar 36ar trapped ratios are found for argon in pyroxene melt inclusions 1500 maskelynite 1200 impact glass 1800 of shergotty and impact glass of sau 005 1200 a high 40ar 36ar trapped componentusually uniquely ascribed to martian atmosphere can also originate from the martian interior indicating a heterogeneous martian mantle composition as additional explanation of variable high 40ar 36ar trapped ratios in shocked shergottites we suggest argon implantation from a transient atmosphere during impact induced degassing the best 40ar 39ar age estimate for dhofar 019 is 642 72 ma maskelynite sau 005 samples are between 700900 ma old relatively high 40ar 39ar ages of melt inclusions within dhofar 019 1086 252 ma and sau 005 olivine 885 66 ma could date entrapment of a magmatic liquid during early olivine crystallization or reflect unrecognized excess 40ar components the youngest 40ar 39ar age of shergotty separates maskelynite is 370 ma that of zagami is 200 ma the 40ar 39ar chronology of dhofar 019 and sau 005 indicate 1 ga ages apparent ages uncorrected for trapped e g martian atmosphere mantle argon components approach 4 5 ga but are not caused by inherited 40ar because excess 40ar is supported by 36artrapped young ages obtained by 40ar 39ar and other chronometers argue for primary rather than secondary events the cosmic ray exposure ages calculated from cosmogenic argon are 15 7 0 7 ma dhofar 019 1 0 1 6 ma sau 005 2 1 2 5 ma shergotty and 2 2 3 0 ma zagami

lunar and martian meteorite delivery services launch mechanisms for lunar and martian meteorites have been investigated by integrating physical modeling constraints geochemical cosmic ray exposure cre constraints and petrologic constraints the potential source region for lunar meteorites is remarkably small compared to the final crater volume cre constraints indicate that most launches start at depths of 3 2 m and cratering theory implies derivation of suitably accelerated objects from a subvolume with diameter only about 0 3 the final crater diameter the shallow depth provenance is probably related to shock wave interference enhanced by the lunar regolith s extremely low compressional wave velocity cre constraints alone imply that four to five separate launch events are represented among the eight well studied lunar meteorites most of the lunar meteorites are regolith breccias which tend to show only limited compositional diversity within any kilometer scale region of the moon several others are polymict breccias which also show relatively subdued compositional diversity compared to igneous rocks the observed diversity among these samples in terms of abundances of mare basalt and kreep and in mg mg fe ratio implies that among eight well studied lunar meteorites only two potential source crater pairings are plausible between asuka 881757 y 793169 most probable and between y 793274 eet875721 altogether these eight lunar meteorites apparently represent at least six separate source craters including three in the past 105 years and five in the past 106 years cre constraints imply that snc meteorites are launched from systematically greater depths than lunar meteorites sncs are also systematically bigger and all nine well studied sncs are uncommonly young by martian standards mafic igneous rocks comparison between viking and apollo results reveals that rocks the size of common meteorites are remarkably scarce in the martian regolith probably due to pervasive weathering a plausible explanation for these trends is that most old small and shallow rocks on mars have been weakened by a two stage process of brecciation followed by pervasive weathering to the point where they seldom survive the stresses of spallation off the planet the scarcity of source crater pairing among the lunar meteorites implies that these objects can be launched from craters much smaller than previously estimated and tends to support the suggestion of rabinowitz 1993 astrophys j 407 412 427 that present day cratering rates for the earth moon region may be higher than previously estimated

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

refined insight into 40ar 39ar progressive crushing technique from k cl ar correlations in fluid inclusions abstract hydrothermal fluid activity associated with geological processes can now be dated by 40ar 39ar progressive crushing of minerals thanks to recent advances in high precision mass spectrometry however methods of data analysis and interpretation for these high resolution measurements still need to be refined in this study we report further insights into using k cl ar diagrams as tools for interpreting ages of secondary and primary fluids from 40ar 39ar stepwise crushing experiments three paragenetic mineral pairs of muscovite and wolframites from a southern china tungsten deposit were investigated using the 40ar 39ar technique through laser incremental heating and progressive crushing of single minerals incremental heating analyses of muscovites yielded flat age spectra defining plateau ages of 156 153 ma progressive crushing experiments of wolframites yielded anomalously old apparent ages due to excess 40ar however the apparent ages decline quickly after the initial steps and stabilize to form age plateaus of 156 153 ma without excess 40ar the plateau age steps interpreted as ages of gases derived from primary fluid inclusions pfis yield well defined isochrons with ages ranging from 157 to 153 ma and initial 40ar 36ar values that are indistinguishable from the modern atmospheric value digitally created 2d and 3d diagrams of k cl ar correlations can easily reveal distribution trends and correlation planes from the crushing steps interpretations of these diagrams further reveal the ages of secondary fluid inclusions sfis 87 to 83 ma and primary fluid inclusions pfis 159 to 150 ma raw data from sfis degassed during the initial crushing steps form scatters on inverse isochron plots however 2d and 3d k cl ar diagrams yield sfi ages that agree with 40ar 39ar ages of k feldspar veins cutting the tungsten ore bodies

constraints on the age and halogen composition of mantle fluids in siberian coated diamonds extension of the ar ar stepped heating technique has been used to characterise the ar halogen cl br i ca and k components in seven coated diamonds from the aikhal kimberlite siberia at least three components have been identified with different ar isotope compositions the major component is characterised by high 40ar 36ar 11 000 and constant 40ar cl 527 22 10 6 br cl 1 74 0 18 10 3 and i cl 22 0 3 4 10 6 indicative of a mantle fluid phase this component is widespread in coated diamonds having been previously reported in samples from africa and canada estimates of halogen abundances in the sub continental mantle based on data from african and siberian coated diamonds are 3 ppm cl 11 ppb br and 0 4 ppb i these low abundances which are in good agreement with values derived for the depleted asthenospheric mantle derived from morb data imply that the upper mantle is 90 degassed of its halogens a second ar component in coated stones is most simply understood by in situ decay of 40k and is consistent with the coat forming event occurring close to the time of host kimberlite eruption 350 380 ma ago a third ar component has a low 40ar 36ar ratio 300 is unassociated with release of k or halogens and is most likely to be atmospheric blank

40ar 39ar studies of whole rock nakhlites evidence for the timing of formation and aqueous alteration on mars 20 25 mg whole rock samples of the nakhlites lafayette and nakhla have been analyzed via the 40ar 39ar technique in part to verify their formation ages but primarily in an attempt to determine the timing of aqueous alteration in these martian meteorites as in previous studies plateaus in apparent age are observed at about 1300 ma 1322 10 for lafayette 1332 10 and 1323 11 for nakhla presumably corresponding to crystallization ages the plateaus are not entirely flat perhaps reflecting the effects of recoil during creation of 39ar in the nuclear irradiation the first 5 20 of the k derived ar released from all three samples give apparent ages 1300 ma coupled with the fact that chronometric isotopic studies of nakhlites typically show some disturbance we believe the low temperature pattern represents more recent than 1300 ma formation of martian aqueous alteration products such as iddingsite no low temperature plateaus are observed this is consistent with petrographic evidence for multiple formation events although the lack of low temperature plateaus is far from conclusive on the other hand if there was a single time of alteration we believe that it will be difficult if not impossible to determine it using the k ar system

alpha particle x ray spectrometer apxs results from gusev crater and calibration report 1 the chemical composition of rocks and soils on mars analyzed during the mars exploration rover spirit mission was determined by x ray analyses with the alpha particle x ray spectrometer apxs details of the data analysis method and the instrument calibration are presented measurements performed on mars to address geometry effects and background contributions are shown cross calibration measurements among several instrument sensors and sources are discussed an unintentional swap of the two flight instruments is evaluated new concentration data acquired during the first 470 sols of rover spirit in gusev crater are presented there are two geological regions the gusev plains and the columbia hills the plains contain soils that are very similar to previous landing sites on mars a meteoritic component in the soil is identified rocks in the plains revealed thin weathering rinds the underlying abraded rock was classified as primitive basalt one of these rocks contained significant br that is probably associated with vein filling material of different composition one of the trenches showed large subsurface enrichments of mg s and br disturbed soils and rocks in the columbia hills revealed different elemental compositions these rocks are significantly weathered and enriched in mobile elements such as p s cl or br even abraded rock surfaces have high br concentrations thus in contrast to the rocks and soils in the gusev plains the columbia hills material shows more significant evidence of ancient aqueous alteration

seismicity of central tibet from project indepth iii seismic recordings as part of project international deep profiling of tibet and the himalaya iii a 400 km long densely spaced array of 57 broadband and short period seismic stations was deployed in central tibet from august 1998 through may 1999 although originally designed to image the lithosphere with teleseismic events the array also recorded numerous local and regional seismic events more than 900 local and regional events were detected on at least 10 stations during the 1 year deployment and we were able to locate 267 local earthquakes a substantial number of the events were found to cluster in or near large grabens and along known strike slip faults while other events show no obvious correlation with known structures in addition to spatial clustering at least one of the large clusters also exhibits temporal clustering that may be associated with magmatic or geothermal activity in the upper crust the average v p and v s are estimated to be 5 85 and 3 35 km sec for the upper crust and 7 0 and 3 9 km sec for the lower crust respectively the 50 focal mechanisms computed from this set of events are consistent with north south shortening and east west extension there are no clear indications of significant local perturbations in the regional stress field induced by the collision between india and eurasia the majority of the focal mechanisms indicate normal and strike slip faulting at least six of the newly computed focal mechanisms however indicate thrust faulting which is a phenomenon not well documented previously ninety nine percent of the local earthquakes have focal depths shallower than 25 km and the locations of the few deeper events are poorly constrained the shallow earthquake focal depths are consistent with high temperatures and proposed ductile or aseismic behavior in the middle to lower crust of central tibet figure 6 1 figure 6 a earthquake locations computed from this study shown on shaded topographic data triangles are indepth iii seismic stations circles are events and are scaled by magnitude graphic 2 a color version of this figure is available online at the ssa web site b earthquake locations shown with major geologic structures from taylor et al 2003 3 reproduced with permission m h taylor personal comm 2002 triangles are indepth iii seismic stations geologic structures are as in figure 2 4 1 pending yes 2 f1 embed inline graphic 1 gif 3 ref 46 4 f3

clues to martian brines based on halogens in salts from nakhlites and mer samples 1 chlorine and br abundances in fracture filling secondary salts in nakhla veins determined in this study by synchrotron x ray microprobe br and electron microprobe cl techniques compare well to the halogens determined recently by apxs instruments in soils and rock rinds at the gusev and meridiani sites the salts in these mars rocks arise from martian brines that have undergone evaporative or freezing concentration the halogen abundances in these salts are corrected for dilution effect because of mixing with halogen poor phases to obtain their true abundances which seem to be close to the halogen abundances in terrestrial sea brines consistent with the petrographic evidence for evaporative salt deposition sequence of carbonate sulfate halite in nakhlite meteorites nakhla veins yield high br 250 ppm and low cl br ratios 10 50 suggesting possible salt deposition from concentrated brines whereas lafayette iddingsite with low br 11 ppm and high cl br ratios 250 300 indicates salt deposition from dilute brines on mars the low cl br ratios 20 to 80 in salts from gusev and meridiani rock rinds indicate that they presumably originate from concentrated subsurface martian brines the high cl br ratio 270 in salts deposited by dilute solutions in lafayette and adirondack is similar to the chondritic cl br ratio which seems to characterize the dilute brines on mars prior to halite precipitation including early mars waters noachian or earlier our results seem to be consistent with the burt knauth model involving density stratification during evaporation freezing of brine solutions in martian regolith

volatile composition of microinclusions in diamonds from the panda kimberlite canada implications for chemical and isotopic heterogeneity in the mantle abstract in order to better investigate the compositions and the origins of fluids associated with diamond growth we have carried out combined noble gas he and ar c and n isotope k ca and halogen cl br i determinations on fragments of individual microinclusion bearing diamonds from the panda kimberlite north west territories canada the fluid concentrations of halogens and noble gases in panda diamonds are enriched by several orders of magnitude over typical upper mantle abundances however noble gas c and n isotopic ratios 3he 4he 4 6 ra 40ar 36ar 20 000 30 000 13c 4 5 to 6 9 and 15n 1 2 to 8 8 are within the worldwide range determined for fibrous diamonds and similar to the mid ocean ridge basalt morb source value the high 36ar content of the diamonds 1 10 9 cm3 g is at least an order of magnitude higher than any previously reported mantle sample and enables the 36ar content of the subcontinental lithospheric mantle to be estimated at 0 6 10 12 cm3 g again similar to estimates for the morb source three fluid types distinguished on the basis of ca k cl compositions are consistent with carbonatitic silicic and saline end members identified in previous studies of diamonds from worldwide sources these fluid end members also have distinct halogen ratios br cl and i cl the role of subducted seawater derived halogens originally invoked to explain some of the halogen ratio variations in diamonds is not considered an essential component in the formation of the fluids in contrast it is considered that large halogen fractionation of a primitive mantle ratio occurs during fluid melt partitioning in forming silicic fluids and during separation of an immiscible saline fluid

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

formation of a martian pyroxenite a comparative study of the nakhlite meteorites and theo s flow the unusual composition of the nakhlites a group of pyroxenitic martian meteorites with young ages presents an opportunity to learn about nonbasaltic magmatic activity on another planet however the limited number of these meteorites makes unraveling their history difficult a promising terrestrial analog for the formation of the nakhlites is theo s flow in ontario canada this atypical 120 m thick flow differentiated in place forming distinct layered lithologies of peridotite pyroxenite and gabbro theo s pyroxenite and the nakhlites share strikingly similar petrographies with concentrated euhedral to subhedral augite grains set in a plagioclase rich matrix these two suites of rocks also share specific petrologic features mineral and whole rock compositional features and size and spatial distributions of cumulus grains the numerous similarities suggest that the nakhlites formed by a similar mechanism in a surface lava flow or shallow intrusion their formation could have involved settling of crystals in a phenocryst laden flow or in situ nucleation and growth of pyroxenes in an ultramafic lava flow the latter case is more likely and requires steady state nucleation and growth of clusters of pyroxene grains and olivine in the nakhlites circulating in a strongly convecting melt pool followed by settling and continued growth in a thickening cumulate pile trapped pockets of intercumulus liquid in the pile gradually evolved finally growing fe enriched rims on cumulus grains with sufficient evolution the melt reached plagioclase supersaturation causing rapid growth of plagioclase sprays and late stage mesostasis growth

argon 39 argon 40 ages and trapped argon in martian shergottites chassigny and allan hills 84001 abstract argon isotopic abundances were measured in neutron irradiated samples of martian meteorites chassigny allan hills alh 84001 alh 77005 elephant moraine eet 79001 yamato y 793605 shergotty zagami and queen alexandra range que 94201 and in unirradiated samples of alh 77005 chassigny gives a 39ar 40ar age of 1 32 0 07 ga which is similar to radiometric ages of the nakhlites argon 39 argon 40 data for alh 84001 indicate ages between 3 9 and 4 3 ga a more precise definition of this age requires detailed characterization of the multiple trapped ar components in alh 84001 and of 39ar recoil distribution all six shergottite samples show apparent 39ar 40ar ages substantially older than the 165 200 ma range in ages given by other isotope dating techniques shergottites appear to contain ubiquitous ar components acquired from the martian atmosphere the martian mantle and commonly terrestrial atmospheric contamination zagami feldspar also suggests inherited radiogenic 40ar these data analyses indicate that the recent martian atmospheric component trapped in shergottites has a 40ar 36ar ratio possibly as low as 1750 and no greater than 1900 these ratios are less than the value of 3000 500 reported by viking the 40ar 36ar ratio for the martian mantle component is probably 500 but is poorly constrained the correlation between trapped 40ar 36ar and 129xe 132xe ratios in shergottite impact glasses and unirradiated samples of alh 77005 shows considerable scatter and suggests that the 36ar 132xe ratio in the martian components may vary resolution of martian atmospheric 40ar 36ar ratio at different time periods i e at 4 0 and 0 2 ga is also difficult without an understanding of the composition of various trapped components

ancient impact and aqueous processes at endeavour crater mars the rover opportunity has investigated the rim of endeavour crater a large ancient impact crater on mars basaltic breccias produced by the impact form the rim deposits with stratigraphy similar to that observed at similar sized craters on earth highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits gypsum rich veins cut sedimentary rocks adjacent to the crater rim the gypsum was precipitated from low temperature aqueous fluids flowing upward from the ancient materials of the rim leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate rich sandstones of the meridiani region

teleseismic slowness azimuth station corrections for the international monitoring system seismic network abstract the prototype international data center pidc in arlington virginia has been developing and testing software and procedures for use in the verification of the comprehensive test ban treaty after three years of operation with a global network of array and three component stations it has been possible to characterize various systematic biases of those stations that are designated in the treaty as part of the international monitoring system ims these biases include deviations of azimuth and slowness measurements from predicted values caused largely by lateral heterogeneity for events recorded by few stations azimuth and slowness are used in addition to arrival time data for location by the pidc corrections to teleseismic azimuth and slowness observations have been empirically determined for most ims stations providing data to the pidc application of these corrections is shown to improve signal association and event location at some stations an overall systematic bias can be ascribed to local crustal structure or to unreported instrumental problems the corrections have been applied in routine operation of the pidc since february 1998

passcal instrument performance during the tibetan plateau passive seismic experiment summary the passcal instrumentation performed very well in the tibetan plateau seismic experiment this experiment has demonstrated the viability of recording high quality broadband data at temporary sites in extreme environments it also highlights some areas where further development is needed primarily more effort is needed to develop more versatile triggering options for the passcal instruments such developments could both increase the instrument9s success at recording low magnitude teleseismic events for travel time studies and save disk space when recording local events thus further increasing the feasibility of long deployments in remote regions although the use of the passcal instrument9s calibration circuitry for sensor recentering is a valuable technique more experience is needed in the construction of sensor pads to minimize tilt problems that require site visits to relevel the seismometer such as we experienced at a few sites in the winter this may also lead to improved low frequency noise levels although signals with periods greater than 200 sec can be recovered from these sites the most exciting aspect of the data we have collected is its broad frequency content and spatial density we anticipate that this type of experiment will be increasingly useful in the study of lithospheric interactions as well as deep earth structure this data was delivered to the iris data management center in early september 1993 and is available to the community two other broadband passive seismic experiments the baikal rift experiment gao et al 1992 and the rocky mountain front experiment sheehan et al 1992 should be delivered to the iris dmc in the fall of 1993 as well temporary broadband seismic experiments represent an extension of the permanent global seismic network gsn we encourage the seismological community to incorporate these data into any research using gsn data in order to maximize the potential utility of this new mode of seismic recording

40ar 39ar and cosmic ray exposure ages of nakhlites nakhla lafayette governador valadares and chassigny we present 40ar 39ar dating results of handpicked mineral separates and wholerock samples of nakhla lafayette and chassigny our data on nakhla and lafayette and recently reported ages for some nakhlites and chassigny misawa et al 2006 park et al 2009 point to formation ages of approximately 1 4 ga rather than 1 3 ga that is consistent with previous suggestions of close in time formation of nakhlites and chassigny in lafayette mesostasis we detected a secondary degassing event at approximately 1 1 ga which is not related to iddingsite formation it may have been caused by a medium grade thermal event resetting the mesostasis age but not influencing the k ar system of magmatic inclusions and the original igneous texture of this rock cosmic ray exposure ages for these meteorites and for governador valadares were calculated from bulk rock concentrations of cosmogenic nuclides 3he 21ne and 38ar individual results are similar to literature data the considerable scatter of t3 t21 and t38 ages is due to systematic uncertainties related to bulk rock and target element chemistry production rates and shielding effects this hampers efforts to better constrain the hypothesis of a single ejection event for all nakhlites and chassigny from a confined martian surface terrain eugster 2003 garrison and bogard 2005 cosmic ray exposure ages from stepwise release age spectra using 38ar and neutron induced 37ar from ca in irradiated samples can eliminate errors induced by bulk chemistry on production rates although not from shielding conditions

the parent magma of the nakhla snc meteorite inferred from magmatic inclusions abstract the nakhla meteorite one of the snc group of putative martian origin is an igneous rock a cumulate of augite and olivine that does not represent a magma composition samples of its parent magma were trapped as magmatic inclusions in its cumulus olivine crystals the inclusions range from 10 350 m in diameter and consist of augite rich in ti and al silica rich glass iron oxides ilmenite apatite and rare amphibole each inclusion has a rind of augite and chromite against its host olivine and a core of radiating sprays of augite set in glass and feldspar these textures are consistent with an origin as trapped silicate liquid twenty four inclusions were analyzed by electron microprobe by averaging series of rastered beam analyses on average the analyses are independent of the size of the inclusion most clearly for inclusions larger than 70 m diameter and variations among analyses are consistent with small differences in the proportions of augite glass and iron oxides exposed on thin section surfaces the average inclusion analysis is calculated to represent 28 host olivine and 72 inclusion composition the inclusion rinds are calculated to be 13 of the inclusion composition for which a small correction is made the inclusion composition is then corrected for mg fe exchange with the host olivine to chemical equilibrium with the cumulus augite cores and crystallization of 13 olivine onto the host crystal to yield a magma composition with the proper mgo feo ratio and with olivine and augite on its liquidus this composition nk93 is an estimate of nakhla s parent magma originally trapped in the inclusions nk93 is basaltic rich in iron and poor in aluminum compared to terrestrial basalts its abundances of al ti and na are consistent with the geochemistry of the snc meteorites as a whole nk93 is similar to the parent magmas proposed in an independent study of magmatic inclusions in nakhla but unlike other proposed compositions one proposed parent magma based on mass balance and the assumption that nakhla was a closed system after crystal accumulation is inconsistent with the magmatic inclusion studies and nakhla s petrography this suggests that nakhla was not a closed system but was infiltrated by post cumulus basaltic magmas another suggested parent magma was derived from element distribution between augite and basaltic magma but that calculation relied on an incorrect augite composition using a correct augite composition in that calculation yields a parent magma much closer in composition to nk93 thus three independent approaches converge in requiring that nakhla originally formed from a low al low mgo feo basalt like nk93

calibration of the tibetan plateau using regional seismic waveforms we use the recordings from 51 earthquakes produced by a passcal deployment in tibet to develop a two layer crustal model for the region starting with their isc locations we iteratively fit the p arrival times to relocate the earthquakes and estimate mantle and crustal seismic parameters an average crustal p velocity of 6 2 6 3 km s is obtained for a crustal thickness of 65 km while the p velocity of the uppermost mantle is 8 1 km s the upper layer of the model is further fine tuned by obtaining the best synthetic sh waveform match to an observed waveform for a well located event green s functions from this model are then used to estimate the source parameters for those events using a grid search procedure average event relocation relative to the isc locations excluding two poorly located earthquakes is 16 km all but one earthquake are determined by the waveform inversion to be at depths between 5 and 15 km this is 15 km shallower on average than depths reported by the isc the shallow seismicity cut off depth and low crustal velocities suggest high temperatures in the lower crust thrust faulting source mechanisms dominate at the margins of the plateau within the plateau at locations with surface elevations less than 5 km source mechanisms are a mixture of strike slip and thrust most events occurring in the high plateau where elevations are above 5 km show normal faulting this indicates that a large portion of the plateau is under ew extension

terrestrial and martian weathering signatures of xenon components in shergottite mineral separates abstract xenon isotopic ratios step heating release patterns and gas concentrations of mineral separates from martian shergottites roberts massif rbt 04262 dar al gani dag 489 shergotty and elephant moraine eet 79001 lithology b are reported concentrations of martian atmospheric xenon are similar in mineral separates from all meteorites but more weathered samples contain more terrestrial atmospheric xenon the distributions of xenon from the martian and terrestrial atmospheres among minerals in any one sample are similar suggesting similarities in the processes by which they were acquired however in opaque and maskelynite fractions martian atmospheric xenon is released at higher temperatures than terrestrial atmospheric xenon it is suggested that both martian and terrestrial atmospheric xenon were initially introduced by weathering low temperature alteration processes however the martian component was redistributed by shock accounting for its current residence in more retentive sites the presence or absence of detectable 129xe from the martian atmosphere in mafic minerals may correspond to the extent of crustal contamination of the rock s parent melt variable contents of excess 129xe contrast with previously reported consistent concentrations of excess 40ar suggesting distinct sources contributed these gases to the parent magma

geological and geochemical legacy of a cold early mars 1 we consider the hypothesis that mars never experienced an early warm wet period and the implications of a continuously cold martian climate for the hydrology and geochemistry of the planet geomorphic evidence previously interpreted to indicate a more temperate early climate can be explained by cold climate processes and the transient flow of liquid water at the surface rather than a terrestrial like hydrological cycle in this scenario freezing and confinement of crustal aquifers lead to the eruption of water or brines to the surface hesperian events formed massive ice sheets and triggered floods that carved the outflow channels while smaller present day aqueous eruptions are responsible for the seepage and gully like landforms identified in high resolution imaging this process may have fluxed a significant volume of groundwater to the surface and the polar caps a primordial source of groundwater reconciles the present d h isotopic ratio of the atmosphere with fractionating atmospheric escape and a primordial martian d h inferred from hydrous phases of snc meteorites a cold early climate and a thin co2 atmosphere are consistent with the ubiquity of primary igneous minerals and the apparent absence of secondary minerals and copious carbonates on the surface aqueous eruptions introduced soluble chloride and sulfate salts into martian soils leaving clays and carbonates within the crust if the martian crust hosts a deep biosphere aqueous eruptions can bring organisms or their chemical signature to the surface the biotic component of any recent eruptions may be preserved in transient ice in cold traps on the surface

joint inversion for earthquake depths using local waveforms and amplitude spectra of rayleigh waves reliable earthquake depth is fundamental to many seismological problems in this paper we present a method to jointly invert for centroid depths with local distance 5 seismic waveforms and regional distance of 5 15 rayleigh wave amplitude spectra on sparse networks we use earthquake focal mechanisms and magnitudes retrieved with the cut and paste cap method to compute synthetic amplitude spectra of fundamental mode rayleigh wave for a range of depths then we grid search to find the optimal depth that minimizes the joint misfit of amplitude spectra and local waveforms as case studies we apply this method to the 2008 wells nevada mw6 0 earthquake and a mw5 6 outer rise earthquake to the east of japan trench in 2013 uncertainties estimated with a bootstrap re sampling approach show that this joint inversion approach constrains centroid depths well which are also verified by independent teleseismic depth phase data

halogen contamination in antarctic h5 and h6 chondrites and relation to sites of recovery abstract the distribution of the elements f cl br and i was analysed in layers removed stepwise from antarctic h5 and h6 chondrites all meteorites show higher concentrations of these elements on their surfaces than in their interiors the degree of halogen enrichment cannot be correlated with the degree of visual weathering and is proportional to the time the meteorites were residing on the surface of the antarctic ice during this period aerosols salts and gaseous components are deposited on the surfaces of the meteorites and diffuse into their interior the observed contamination level of the meteorites is influenced by leaching properties and diffusion behaviour of the individual halogens the major contamination source for f cl and probably br is air borne seaspray for i it is the gaseous compound methyl iodide ch3i produced by biological processes in the sea methyl iodide and its oxidation products formed in the antarctic atmosphere e g i2 can be transported over longer distances to the interior of antarctica than air borne seaspray therefore the ratio of the halogen contamination is related to the collection site of the meteorites all meteorites that were found in the antarctic interior are contaminated to a lesser degree by f cl and br relative to i than those found near the coast the measured enrichment ratio of i f is a function of the distance between the collection site and the open sea and increases from the allan hills to the thiel mountains by revealing the degree of contamination of a meteorite it is possible to determine its maximum surface residence time on the antarctic ice

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

cl br and i analyses of metamorphic and sedimentary rocks by isotope dilution mass spectrometry isotope dilution mass spectrometry with negative thermal ions was applied to determine cl br and i in rocks which in part contained less than 100 ppb of br and i two sets of samples have been investigated a a series of al rich metapelites of increasing metamorphic grade from the damara orogen namibia and b fresh and hydrothermally altered greywackes from the pb zn deposit bad grund in germany it was found that regional metamorphism of al rich metapelites causes no strong fractionation of the halides the br cl ratios in the metapelites are similar to those of sea water the i cl and i br ratios however are 500 times higher the i depleted in the ocean most probably is associated with organic matter stored in sediments the unaltered greywackes from near the pb zn vein have about the same concentrations of halides as the metamorphic al rich pelites by contrast the hydrothemally altered greywackes contain about twice as much cl and i and about 2 5 times as much br as the unaltered samples the element ratios however are similar for all three categories of rocks thereby indicating that sea water played no role in the hydrothermal system

noble gases in mineral separates from three shergottites shergotty zagami and eeta79001 this study provides a complete data set of all five noble gases for bulk samples and mineral separates from three martian shergottites shergotty bulk pyroxene maskelynite zagami bulk pyroxene maskelynite and elephant moraine eet a79001 lithology a bulk pyroxene we also give a compilation of all noble gas and nitrogen studies performed on these meteorites our mean values for cosmic ray exposure ages from 3he 21ne and 38ar are 2 48 myr for shergotty 2 73 myr for zagami and 0 65 myr for eeta79001 lith a serious loss of radiogenic 4he due to shock is observed cosmogenic neon results for bulk samples from 13 martian meteorites new data and literature data are used in addition to the mineral separates of this study in a new approach to explore evidence of solar cosmic ray effects while a contribution of this low energy irradiation is strongly indicated for all of the shergottites spallation ne in chassigny allan hills alh 84001 and the nakhlites is fully explained by galactic cosmic ray spallation implanted martian atmospheric gases are present in all mineral separates and the thermal release indicates a near surface siting we derive an estimate for the 40ar 36ar ratio of the martian interior component by subtracting from measured ar in the k poor pyroxenes the small radiogenic component as well as the implanted atmospheric component as indicated from 129xe excesses unless compromised by the presence of additional components a high ratio of 2000 is indicated for martian interior argon similar to that in the martian atmosphere since much lower ratios have been inferred for chassigny and alh 84001 the result may indicate spatial and or temporal variations of 40ar 36ar in the martian mantle

locating and modeling regional earthquakes with two stations 1 we developed a new technique caploc to retrieve full source parameters of small seismic events from regional seismograms which include origin time epicenter location depth focal mechanism and moment magnitude despite rather complicated propagation effects at short periods a simple localized one dimensional model can well explain signals of periods 3 10 s if we break the three component records into different segments and allow differential time shifts among them these differential time shifts once established from a calibration process or a well determined tomographic map can be used together with p wave travel times to refine an event s location in this study we tested whether our new method could produce satisfactory results with as few as two stations so that we can improve source estimates of poorly monitored events with sparse waveform data we conducted the test on 28 events in the tibetan plateau the focal mechanisms and locations determined from only two stations agree well with those determined from a whole passcal array in particular our new method produces better locations than international seismological centre with the average mislocation error reduced from 16 to 5 km we also tested whether an event s depth and mechanism can be determined separately from its epicenter relocation in a two step approach we find that the two step approach does not always give the correct solution but the reliability of a solution can be evaluated using a reduced chi square value

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

origin and evolution of the nakhla meteorite inferred from the sm nd and u pb systematics and ree ba sr rb and k abundances analyses of sm nd and u th pb systematics ree ba sr rb and k concentrations were carried out for whole rock and mineral separates from the nakhla meteorite the 1 26 07 b y sm nd age obtained in this work is in good agreement with those previously obtained by the rb sr and ar ar methods the high initial nd value of 16 suggests that nakhla was derived from a light ree depleted old planetary mantle source u th pb data after correction for pre analytical terrestrial pb contamination assuming an age of 1 26 b y suggest that the age of the nakhla source is 4 33 b y the agreement in the age determined by three independent radiometric methods and the high initial nd value strongly suggest that the 1 3 b y age dates one thorough igneous event in the parent body which not only reset these isotopic systems but also established the chemical and petrologic characteristics observed for the nakhla meteorite using a three stage sm nd evolution model in combination with lil element data and estimated partition coefficients we have tested partial melting and fractional crystallization models to estimate lil element abundances in a possible nakhla source our model calculations suggest that partial melting of the light ree depleted source followed by extensive fractional crystallization 50 of the partial melt could account for the ree abundances in the nakhla constituent minerals the estimated source is depleted in the light ree ba rb and k and therefore may resemble the morb source in the earth s upper mantle or the upper 60 300 km of the moon the significantly younger age of nakhla than the youngest lunar rock the young differentiation age inferred from the u th pb data and the estimated lil element abundances including those of k u and th in the source suggest that the nakhla meteorite may have been derived from a relatively large well differentiated planetary body such as mars

5hz gps seismology of the el mayor cucapah earthquake estimating the earthquake focal mechanism summary high rate 5hz gps records observed in the near field following the magnitude 7 2 el mayor cucapah earthquake that occurred in northern mexico on 2010 april 4 are compared with broad band seismograms the high rate gps displacement records are consistent with the twice integrated strong motion seismic records in the near field where broad band seismograms are clipped due to strong shaking agreement degrades at distances greater than about 150 km from the epicentre where displacement amplitudes approach the noise level of gps seismograms using high rate gps data the focal mechanism of the main shock is estimated and is shown to be consistent with teleseismic estimates the result is seen as confirmation that high rate gps observed at near field stations can be applied together with teleseismic seismometers to yield better information about earthquake rupture properties and parameters

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

source specific station corrections for regional phases at fennoscandian stations the iaspei91 global travel time curves are used as the default for event location at the prototype international data center pidc in order to improve event location a 1 d baltic travel time model was implemented at the pidc in 1997 for locating events using regional phases from fennoscandian stations where a single model is insufficient for characterizing the regional geology path dependent corrections or source specific station corrections ssscs are more appropriate for event locations we have developed ssscs for regional phases at the fennoscandian stations by interpolating travel times through different 1 d models ssscs for stations nris and spits are also derived given the fact that paths from both stations to high latitude events are within the fennoscandia regionalization as baltic

hydrothermal fluid origins in mississippi valley type ore districts combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the illinois kentucky fluorspar district viburnum trend and tri state districts midcontinent united states samples were selected from three of the classic mississippi valley type districts in the midcontinent area of north america the illinois kentucky fluorspar district belongs to the fluoritic subtype of mississippi valleytype districts and the ozark districts of the viburnum trend and tri state are representative of the pb rich and more typical zn rich subtypes of mississippi valley type mineralization respectively noble gas ar kr and halogen cl br i data have been obtained simultaneously by noble gas mass spectrometry of inclusion fluids released by in vacuo crushing of irradiated fluorite quartz carbonate and sphalerite samples additionally he analyses have been obtained from nonirradiated fluorite from the illinois kentucky fluorspar district fluorite from the illinois kentucky fluorspar district has a maximum 3 he 4 he ratio of 0 35 ra where ra atmospheric 3 he 4 he ratio of 1 4 10 6 higher than values typical of crustal fluids and confirming the presence of a minor mantle component equal to less than 6 percent of the total he in the fluids of the illinois kentucky fluorspar district the br cl mol ratios of all the deposits are with one exception higher than the value of seawater 1 54 10 3 ranging from 1 69 to 3 70 10 3 and indicating acquisition of salinity by the evaporation of seawater beyond the point of halite saturation late quartz from the tri state district contains a very minor component of halite dissolution water and has a br cl mol ratio of 1 46 10 3 the i cl mol ratios are typical of oil field brines and are ubiquitously higher than what is attainable by the evaporation of seawater alone i cl mol ratios are in the range of 6 to 270 10 6 indicating that the fluids have interacted with i rich organic matter present in sedimentary rocks in the ozark districts 40 ar 36 ar ratios vary between 320 and 345 in the tri state and between 350 and 420 in the viburnum trend in the illinois kentucky fluorspar district 40 ar 36 ar ratios reach values of 1 200 the corresponding concentrations of 40 arexcess 40 ar not attributable to radiogenic decay of 40 k or an atmospheric source are similarly elevated in the main stage fluorite mineralization of the illinois kentucky fluorspar district 6 8 18 2 10 4 cm 3 cm 3 h2o relative to the viburnum trend and tri state districts mostly 1 3 3 3 10 4 cm 3 cm 3 h2o and 0 3 1 4 10 4 cm 3 cm 3 h2o respectively together the noble gas and halogen data indicate the existence of three brine provinces 1 a regional tristate brine present throughout the ozark region 2 a viburnum trend brine and 3 an illinois kentucky brine furthermore in the viburnum trend the halogen composition of main stage dolomite is distinct from that of the main stage sphalerite but identical to the regional hydrothermal dolomite seen in the tri state district the data imply that mixing relationships in the viburnum trend are highly complex but are compatible with regional models in which the tri state brine present throughout the ozark region was sourced in the arkoma basin

martian fluid and martian weathering signatures identified in nakhla nwa 998 and mil 03346 by halogen and noble gas analysis we report argon ar noble gas ar ar ages and halogen abundances cl br i of martian nakhlites nakhla nwa 998 and mil 03346 to determine the presence of martian hydrous fluids and weathering products neutron irradiated samples were either crushed and step heated nakhla only or simply step heated using a laser or furnace and analysed for noble gases using an extension of the 40 ar 39 ar technique to determine halogen abundances the data obtained provide the first isotopic evidence for a trapped fluid that is cl rich has a strong correlation with 40 ar xs 40 ar xs 40 ar measured 40 ar radiogenic and displays 40 ar xs 36 ar of 1000 consistent with the martian atmosphere this component was released predominantly in the low temperature and crush experiments which may suggest a fluid inclusion host for the halogens we observe similar br cl and i cl ratios between the nakhlites and terrestrial reservoirs which is surprising given the absence of crustal recycling organic matter and frequent fluid activity on mars in particular br cl ratios in our nakhla samples especially olivine are consistent with previously analysed martian weathering products and both low temperature and crush analyses show a similar trend to the evaporation of seawater this may indicate that surface brines play an important role on mars and on halogen assemblages within martian meteorites and rocks elevated i cl ratios in the low temperature nwa 998 and mil 03346 releases may relate to in situ terrestrial contamination though we are unable to distinguish between low temperature terrestrial or martian components whilst estimates of the amount of water present based on the 36 ar concentrations are too high to be explained by a fluid component alone they are consistent with a mixed phase inclusion gas and fluid or with shock implanted martian atmospheric argon the observed fluid is dilute low salinity but high br cl and i cl ratios contains a martian atmospheric component and may represent a mixture of a shallow fluid with one derived from fluid circulation within the nakhlite cumulate pile with heat for fluid circulation supplied by either the igneous intrusion or by an impact event

seismogenic stress field estimation in the calabrian arc region south italy from a bayesian approach a new high quality waveform inversion focal mechanism database of the calabrian arc region has been compiled by integrating 292 mechanisms selected from literature and catalogs with 146 newly computed solutions the new database has then been used for computation of posterior density distributions of stress tensor components by a bayesian method never applied in south italy before the present study the application of this method to the enhanced database has allowed us to provide a detailed picture of seismotectonic stress regimes in this very complex area where lithospheric unit configuration and geodynamic engines are still strongly debated our results well constrain the extensional domain of calabrian arc and the compressional one of the southernmost tyrrhenian sea in addition previously undetected transcurrent regimes have been identified in the ionian offshore the new information released here will furnish useful tools and constraints for future geodynamic investigations

the formation environment of potassic chloro hastingsite in the nakhlites mil 03346 and pairs and nwa 5790 insights from terrestrial chloro amphibole potassic chloro hastingsite has been found in melt inclusions in mil 03346 its paired stones and nwa 5790 it is some of the most chlorine rich amphibole ever analyzed in this article we evaluate what crystal chemistry terrestrial analogs and experiments have shown about how chlorine dominant amphibole chloro amphibole forms and apply these insights to the nakhlites chloro amphibole is rare with about a dozen identified localities on earth it is always rich in potassium and iron and poor in titanium in terrestrial settings its presence has been interpreted to result from medium to high grade alteration 400 c of a protolith by an alkali and or iron chloride rich aqueous fluid ferrous chloride fluids exsolved from mafic magmas can cause such alteration as can crustal fluids that have reacted with rock and lost h2o in preference to chloride resulting in concentrated alkali chloride fluids in the case of the nakhlites an aqueous alkali ferrous chloride fluid was exsolved from the parental melt as it crystallized this aqueous chloride fluid itself likely unmixed into chloride dominant and water dominant fluids chloride dominant fluid was trapped in some melt inclusions and reacted with the silicate contents of the inclusion to form potassic chloro hastingsite

the determination of source parameters for small earthquakes from a single very broadband seismic station the installation of very broadband seismic stations makes it possible to recover the source parameters of small earthquakes 2 5 ml 5 0 which occur at local and regional distances if the gross crustal structure along the travel path is known it is possible to use the p sv and sh displacement waveforms from a single station to determine the seismic moment tensor although the details of the crustal structure strongly affect the body waveforms at regional distances the signature of the seismic source orientation on the waveform is robust at frequencies less than 1 3 hz we explore the trade offs between crustal model hypocentral depth and filtering for a linear moment tensor inversion procedure the procedure is tested on two small earthquakes which occurred in the rio grande rift and were recorded at the iris usgs station anmo the agreement between the single station moment tensor inversion fault plane parameters and those determined from local first motions is excellent

earthquake centroid locations using calibration from ambient seismic noise earthquakes occur in complex geology making it difficult to determine their source parameters and locations because of uncertainty in path effects we can avoid some of these problems by applying the cut and paste cap method which allows for timing shifts between phases assuming a 1d model and determines source parameters if the travel times or lags of the phases due to path effects are known relative to a reference model we can locate the events centroid with surface waves without knowledge of the 3d velocity structure here we use ambient seismic noise for such a calibration we cross correlate the seismic stations near the earthquake with stations 100 300 km away to obtain the 10 100 s surface wave green s functions the new method is tested in southern california to locate the 2008 chino hills earthquake which proves consistent with the epicenter location from p waves it appears possible to use the location offset between the high frequency p wave onset relative to the centroid to provide a fast estimate of directivity

path dependent regional phase travel time corrections for the international monitoring system in north america the software developed for the comprehensive nuclear test ban treaty ctbt international data centre idc in vienna austria uses the iaspei91 seismic travel time tables as default however in reality travel times as a function of source location are different for each station especially at regional distances this is not modeled by a global one dimensional model such as iaspei91 the software therefore allows the application of a suite of travel time corrections for improved travel time prediction and consequently more accurate hypocentral locations to account for path dependency we have developed gridded source specific station corrections ssscs for pn sn pg and lg phases for 22 international monitoring system ims stations in north america in deriving the ssscs and associated modeling errors we used a methodology that had been successfully applied previously for fennoscandia we first compiled regionalized one dimensional travel times for north america then we assigned travel times as weighted sums of the travel times in each region to calculate ssscs validation testing of the ssscs was conducted using two separate sets of north american ground truth gt events with location accuracies within 10 km gt0 gt10 these events were recorded at ims stations between 1995 and 1999 and distributed throughout north america test event location results with ssscs applied show reductions in both mislocations and error ellipses for gt events with location accuracies better than 2 km the median change in location was a 5 km improvement and the median area of the 90th percentile error ellipses was reduced from 2550 km 2 to 910 km 2 using ssscs for both data sets the median improvement is less than 5 km the testing emphasized that gt events with accuracies 5 km or better are crucial for validating ssscs using ssscs for all 51 gt0 gt10 events used in the validation testing the median area of the error ellipses was reduced to less than 1000 km 2 and the error ellipse reductions were achieved without significant degradation of coverage the modeling errors used in this study may be somewhat underestimated however leaving the target goal of error ellipses less than 1000 km 2 still somewhat in question we expect the ssscs event locations and uncertainties can be improved by future refinement of travel times and modeling errors these corrections were implemented in the operational prototype idc system located in arlington virginia in march 2000 and have been delivered to the vienna idc in january 2001

moment tensor inversions for local earthquakes using surface waves recorded at terrascope we have developed a method to determine moment tensors for local earthquakes using short period 10 to 50 sec surface waves recorded at terrascope stations to correct for the substantial lateral variations in crustal structure we applied phase corrections to the data using a regionalized phase velocity model we have determined moment tensors for over 180 events in the last 3 yr in southern california for magnitudes as small as 3 2 and as large as 6 5 the results are consistent with those obtained from first motion data as well as other waveform inversions when continuous data telemetry from the stations becomes available this method can yield moment tensors for earthquakes in southern california and adjacent regions within minutes after the occurrence of an event our results confirm the relation log m o seismic moment 1 5m l local magnitude obtained by an earlier study

monitoring of strain release in central and northern california using broadband data systematic cataloguing of seismic moment depth and mechanism of regional earthquakes down to magnitude m 4 can now be achieved in close to real time using data from sparse networks of digital broadband stations the procedure we have developed relies on 3 independent methods for the determination of moment tensor providing confidence limits on the results we show the results of application to the seismicity in central and northern california for a one year period starting in march 1992 and illustrate how patterns of stress and strain release can now be monitored systematically and reliably in a timely fashion

best practice in earthquake location using broadband three component seismic waveform data we present an earthquake location algorithm the broadband waveform regional earthquake location program bw relp which utilizes phase onset times and wave azimuths recorded by three component broadband seismic stations and an adaptive migrating grid search algorithm to find the global minimum in an arbitrary normed misfit parameter the performance ofbw relpis demonstrated using regional 300 800 km distant broadband recordings to locate events in the 1995 ridgecrest california earthquake sequence the purpose of this study is to introduce thebw relpalgorithm in detail and to expand on the previous paper by dregeret al bssa 88 1353 1362 1998 using one berkeley digital seismic network bdsn station ybh and two usnsn stations elk and mnv which span 300 800 km in distance and 55 degrees in azimuth to further investigate the capability of a sparse broadband network of three component stations at monitoring a region located outside of the network as will be the case in the monitoring of the comprehensive test ban treaty ctbt for low magnitude seismic events we assess the capability of this sparse three station broadband network and we compare locations estimated from phase onset time and wave azimuth measurements to a ground truth catalog of high quality earthquake locations derived from data recorded by the southern california seismic network scsn the results indicate that in the regional distance range it is possible when an appropriate calibration event is available to obtain absolute event locations to within 18 km as is prescribed by the ctbt

application of 3 d crustal and upper mantle velocity model of north america for location of regional seismic events seismic event locations based on regional 1 d velocity depth sections can have bias errors caused by travel time variations within different tectonic provinces and due to ray paths crossing boundaries between tectonic provinces with different crustal and upper mantle velocity structures seismic event locations based on 3 d velocity models have the potential to overcome these limitations this paper summarizes preliminary results for calibration of ims for north america using 3 d velocity model a 3 d modeling software was used to compute source station specific corrections ssscs 3 d for pn travel times utilizing 3 d crustal and upper mantle velocity model for the region this research was performed within the framework of the united states russian federation joint program of seismic calibration of the international monitoring system ims in northern eurasia and north america an initial 3 d velocity model for north america was derived by combining and interpolating 1 d velocity depth sections for different tectonic units in areas where no information on 1 d velocity depth sections was available tectonic regionalization was used to extrapolate or interpolate a moho depth map was integrated this approach combines the information obtained from refraction profiles with information derived from local and regional network data the initial 3 d velocity model was tested against maps of pn travel time residuals for eight calibration explosions corrections to the 3 d model were made to fit the observed residuals our goal was to find a 3 d crustal and upper mantle velocity model capable predicting pn travel times with an accuracy of 1 0 1 5 seconds r m s the 3 d velocity model for north america that gave the best fit to the observed travel times was used to produce maps of ssscs 3 d for seismic stations the computed ssscs 3 d vary approximately from 5 seconds to 5 seconds for the western usa and the pre cambrian platform respectively these ssscs 3 d along with estimated modeling and measurement errors were used to relocate using regional data an independent set of large chemical explosions with known locations and origin times detonated within various tectonic provinces of north america utilization of the 3 d velocity model through application of the computed ssscs 3 d resulted in a substantial improvement in seismic event location accuracy and in a significant decrease of error ellipse area for all events analyzed in comparison both with locations based on the iaspei91 travel times and locations based on 1 d regional velocity models

one minute after strong motion map effective epicenter and effective magnitude abstract this article reports the recent progress on real time seismic monitoring in taiwan particularly the real time strong motion monitoring by the taiwan central weather bureau9s telemetered seismic network cwbsn which is presently aiming at rapid reporting immediately after a large earthquake occurrence if rapid reporting can be achieved before the arrival of the strong shaking earthquake early warning will become possible cwbsn has achieved the generation of the intensity map epicenter and magnitude within 1 min of the occurrence of a large earthquake both rapid reporting and early warning are principally applied to large m 5 events the requirement of on scale waveform recording prompted cwbsn in 1995 to integrate strong motion sensors e g force balance accelerometers into its telemetered seismic monitoring system time domain recursive processing is applied to the multi channel incoming seismic signals by a group of networked personal computers to generate the intensity map from the isoseismal contours an effective epicenter is immediately identified that resides in the middle of the largest usually the 100 gal contour curve of the intensity map an effective magnitude is also defined that can be derived immediately from the surface area covered by the largest usually the 100 gal contour curve for a large event with a finite rupture surface the epicenter and magnitude so derived are more adequate estimates of the source location and of the strength of destruction the effective epicenter gives the center of the damage area it stands in contrast with the conventional epicenter location which only gives the initial point of rupture nucleation the effective magnitude reflects more closely the earthquake damage potential instead of the classical magnitude definition that emphasizes the total energy release the cwbsn has achieved in obtaining the above crucial source information well within 1 min this time can further be reduced to better than 30 sec as illustrated by the example in this article showing that earthquake early warning is indeed an achievable goal the rapid reporting and early warning information is electronically transmitted to users to allow rapid response actions with or without further human intervention

the source and significance of argon isotopes in fluid inclusions from areas of mineralization argon isotopes in fluid inclusions in quartz veins associated with granite hosted tungsten mineralization in the southwest and north of england have been investigated in detail by the40ar 39ar technique the natural argon is present as a number of discrete components which can be identified through correlations with39ar 38ar and 37ar induced by neutron bombardment of potassium chlorine and calcium the potassium correlated component arises principally from in situ decay of potassium in solid phases in the inclusions in the case of the hemerdon tungsten deposit of southwest england the phases responsible are small 25 m captive authigenic micas which are shown to have been deposited from a fluid 268 20 ma ago shortly after the emplacement of the host granite the chlorine correlated component is present in the brines which constitute the fluid phase of the inclusions the argon in these hydrothermal fluids is made up in part of parentless or excess 40ar leached from surrounding crustal rocks and in part of dissolved ancient atmospheric argon absolute concentrations of both atmospheric and excess components in the brine can be estimated from 40arcl ratios and independent determinations of the salinity of the inclusions the absolute concentrations of the atmospheric argon are close to those found in modern meteoric water while those of the excess component can be interpreted in terms of the degree of interaction betwen the circulating fluids and country rock a calcium correlated component with a much higher ratio of excess to atmospheric argon than that in the brine was found to be a dominant phase in one sample from the hemerdon deposit indicating the presence of a solid phase probably a caso4 daughter mineral inclusions of this composition represent fluids which have had a more prolonged interaction with crustal rocks the results obtained from this study provide a systematization and a framework for future multi component argon studies of fluid inclusions together with an indication of the wide range of information which can be inferred

ejection times of martian meteorites noble gas isotopic analyses were made for four meteorites whose origin is mars basaltic shergottites queen alexandra range 94201 zagami the iherzolite lew88516 and orthopyroxenite allan hills 84001 the latter one was separated into orthopyroxene chromite and maskelynite fractions ejection times were calculated for all martian meteorites using cosmic ray exposure ages based on 3he 21ne and 38ar concentrations and literature data on the terrestrial ages we discuss the arguments for a scenario in which they were ejected from mars by asteroidal or cometary impact as small meteoroids and were delivered to earth within and up to 15 million years the basaltic shergottites que94201 shergotty and zagami show an ejection age cluster at 2 76 ma the fourth basaltic shergottite eet79001 being younger 0 82 ma lherzolites lew88516 and alh77005 were ejected by a later event 3 84 ma ago all nakhlites nakhla governador valadares and lafayette originate from an event 11 0 ma ago although chassigny is chemically distinct from the nakhlites its ejection age is 11 6 ma whether this is a separate event cannot be decided from the available data finally orthopyroxenite alh84001 was launched from mars 14 4 ma ago the distribution of the delivery times for martian meteorites to earth reflect individual impact events onto five or six different source terrains this result is significant in the context of a comprehensive knowledge of the martian crust composition finally we derived the k 40ar gas retention age of alh84001 mineral fractions adopting two different models assuming a component of martian atmospheric ar with 40ar36ar 1790 trapped by this meteorite we obtained an age of 3390 ma on the other hand assuming no contribution of martian atmospheric ar the resulting k 40ar age is about 4100 ma that is roughly 500 ma younger than the reported sm nd crystallization age

petrology of martian meteorite northwest africa 998 nakhlite northwest africa nwa 998 is an augite rich cumulate igneous rock with mineral compositions and oxygen isotopic composition consistent with an origin on mars this 456 gram partially fusion crusted meteorite consists of by volume 75 augite core composition wo39en39fs22 9 olivine fo35 7 plagioclase ab61an35 as anhedra among augite and olivine 3 5 low calcium pyroxenes pigeonite and orthopyroxene replacing or forming overgrowths on olivine and augite 1 titanomagnetite and other phases including potassium feldspar apatite pyrrhotite chalcopyrite ilmenite and fine grained mesostasis material minor secondary alteration materials include iddingsite associated with olivine probably martian calcite crack fillings and iron oxide hydroxide staining both probably terrestrial shock effects are limited to minor cataclasis and twinning in augite in comparison to other nakhlites nwa 998 contains more low calcium pyroxenes and its plagioclase crystals are blockier the large size of the intercumulus feldspars and the chemical homogeneity of the olivine imply relatively slow cooling and chemical equilibration in the late and post igneous history of this specimen and mineral thermometers give subsolidus temperatures near 730 c oxidation state was near that of the qfm buffer from about qfm 2 in earliest crystallization to near qfm in late crystallization and to about qfm 1 5 in some magmatic inclusions the replacement or overgrowth of olivine by pigeonite and orthopyroxene with or without titanomagnetite and the marginal replacement of augite by pigeonite are interpreted to result from late stage reactions with residual melts consistent with experimental phase equilibrium relationships apatite is concentrated in planar zones separating apatite free domains which suggests that residual magma rich in p and ree was concentrated in planar fracture zones and possibly migrated through them loss of late magma through these zones is consistent with the low bulk ree content of nwa 998 compared with the calculated ree content of its parent magma

a focused look at the alpine fault new zealand seismicity focal mechanisms and stress observations the alpine fault is the pacific australian plate boundary in the south island of new zealand this study analyzes 195 earthquakes recorded during the 6 month duration of the southern alps passive seismic experiment sapse in 1995 1996 and two mr 5 0 earthquakes and aftershocks in 1997 which occurred close to the central part of the alpine fault precise earthquake locations are derived by simultaneous inversion for hypocenter parameters a one dimensional velocity model and station corrections together with focal mechanisms calculated using a first motion and amplitude ratio method these results provide a picture of the seismotectonics in the central south island over a 6 month period moment tensor inversions of three earthquakes provide an independent means of comparison to the focal mechanisms derived using the amplitude first motion method to validate our observations over time we compare the sapse seismicity with the seismicity recorded by the new zealand national seismic network nznsn and a local network at lake pukaki east of the southern alps 6 months versus 8 years our study indicates that the alpine fault releases elastic strain seismically from the surface down to 10 12 km depth between milford sound in the south and the hope fault in the north the seismicity rate of the alpine fault is low but comparable to locked sections of the san andreas fault with large earthquakes expected seismicity decreases north of bruce bay at the alpine fault and within a triangular region along the alpine fault located between the hope and porters pass fault zones we interpret this as the result of deformation distributed on the alpine fault and the hope and porters pass fault zones the base of the seismogenic zone is fairly uniform at 12 km 2km over large parts of the south island the high alps region has a shallower base of the seismogenic zone indicating localized elevated temperatures east of the alpine fault most of the study region deforms under a uniform stress field with a maximum principal horizontal shortening direction of 110o 120 o similar to geodetic observations and plate motions this confirms that the region is not undergoing strain partitioning the earthquake data show that the deformation away from the alpine fault is distributed on mainly nne trending thrust faults and strike slip transfer faults with a maximum seismogenic depth of 12km

martian magmas contained abundant chlorine but little water the martian water cycle a key for the habitability of mars largely relies on the abundance of water in martian magmas and their mantle sources yet martian snc shergottite nakhlite and chassigny classes meteorites contain minimal water however some experimental studies have suggested that martian parental magmas contained as much as 2 h2o here we integrate mineral chemical experimental and cosmochemical constraints to show that martian magmas contained little water but abundant chlorine apatite and amphibole in martian meteorites are chlorine rich and water poor this constrains the chlorine contents in their parental magmas to 0 3 wt and water contents to 0 3 wt our experimental work has shown that large amounts of water are not needed to explain the mineralogy of the martian meteorites because chlorine has effects similar to those of water on crystallization such chlorine rich water poor martian magmas are consistent with mars being chlorine rich 2 5 compared with the earth furthermore the bulk cl composition of martian meteorites shows that they have not preferentially lost cl by degassing of an h2o rich vapor together these results show that chlorine not water was the dominant volatile species in martian basalts and that these basalts contributed little h2o to mars surface environment