evidence for perchlorates and the origin of chlorinated hydrocarbons detected by sam at the rocknest aeolian deposit in gale crater 1 a single scoop of the rocknest aeolian deposit was sieved 150 m and four separate sample portions each with a mass of 50mg were delivered to individual cups inside the sample analysis at mars sam instrument by the mars science laboratory rover ss ample acquisition system the samples were analyzed separately by the sam pyrolysis evolved gas and gas chromatograph mass spectrometer analysis modes several chlorinated hydrocarbons including chloromethane dichloromethane trichloromethane a chloromethylpropene and chlorobenzene were identified by sam above background levels with abundances of 0 01 to 2 3nmol the evolution of the chloromethanes observed during pyrolysis is coincident with the increase in o2 released from the rocknest sample and the decomposition of a product of n methyl n tert butyldimethylsilyl trifluoroacetamide mtbstfa a chemical whose vapors were released from a derivatization cup inside sam the best candidate for the oxychlorine compounds in rocknest is a hydrated calcium perchlorate ca clo4 2 nh2o based on the temperature release of o2 that correlates with the release of the chlorinated hydrocarbons measured by sam although other chlorine bearing phases are being considered laboratory analog experiments suggest that the reaction of martian chlorine from perchlorate decomposition with terrestrial organic carbon from mtbstfa during pyrolysis can explain the presence of three chloromethanes and a chloromethylpropene detected by sam chlorobenzene may be attributed to reactionsofmartian chlorine released during pyrolysiswith terrestrial benzene or toluene derived from 2 6 diphenylphenylene oxide tenax on the sam hydrocarbon trap at this time we do not have definitive evidence to support a nonterrestrial carbon source for these chlorinated hydrocarbons nor do we exclude the possibility that future sam analyses will reveal the presence of organic compounds native to the martian regolith

the new athena alpha particle x ray spectrometer for the mars exploration rovers 1 the new alpha particle x ray spectrometer apxs is part of the athena payload of the two mars exploration rovers mer the apxs sensor head is attached to the turret of the instrument deployment device idd of the rover the apxs is a very light weight instrument for determining the major and minor elemental composition of martian soils rocks and other geological materials at the mer landing sites the sensor head has simply to be docked by the idd on the surface of the selected sample x ray radiation excited by alpha particles and x rays of the radioactive sources is recorded by a high resolution x ray detector the x ray spectra show elements starting from sodium up to yttrium depending on their concentrations the backscattered alpha spectra measured by a ring of detectors provide additional data on carbon and oxygen by means of a proper calibration the elemental concentrations are derived together with data from the two other athena instruments mounted on the idd the samples under investigation can be fully characterized key apxs objectives are the determination of the chemistry of crustal rocks and soils and the examination of water related deposits sediments or evaporates using the rock abrasion tool attached to the idd issues of weathering can be addressed by measuring natural and abraded surfaces of rocks

constraints on the martian lithosphere from gravity and topography data localized spectral admittances of the large martian volcanoes are modeled by assuming that surface and subsurface loads are elastically supported by the lithosphere in order to model the case where the load density differs from that of the crust a new method for calculating gravity anomalies and lithospheric deflections is developed the modeled gravity anomalies depend upon the elastic thickness crustal thickness load density and crustal density and these parameters were exhaustively sampled in order to determine their effect on the misfit between the observed and modeled admittance function we find that the densities of the martian volcanoes are generally well constrained with values of 3200 100 kg m 3 which is considerably greater than those reported previously these higher densities are consistent with those of the martian basaltic meteorites which are believed to originate from the tharsis and elysium volcanic provinces the crustal density is constrained only beneath the elysium rise to be 3270 150 kg m 3 if this value is representative of the northern lowlands then pratt compensation is likely responsible for the approximately 6 km elevation difference between the northern and southern hemispheres the elastic thicknesses of the major martian volcanoes when subsurface loads are ignored are found to be the following elysium rise 56 20 km olympus mons 93 40 km alba patera 66 20 km and ascraeus mons 105 40 km we have also investigated the effects of subsurface loads allowing the bottom load to be located either in the crust as dense intrusive material or in the mantle as less dense material we found that all volcanoes except pavonis are better modeled with the presence of less dense material in the upper mantle which is indicative of either a mantle plume or a depleted mantle composition an active plume beneath the major volcanoes is consistent with recent analyses of cratering statistics on olympus mons and the elysium rise which indicate that some lava flows are as young as 10 30 myr as well as with the crystallization ages of the shergottites of which some are as young as 180 myr

alteration of hawaiian basalts under sulfur rich conditions applications to understanding surface atmosphere interactions on mars and venus a suite of hawaiian basalts that were variably altered in the presence of so 2 rich gases during the current summit eruptive episode at halemaumau crater kilauea were studied to determine their alteration phase assemblage and reactive pathways using electron microscopy mossbauer spectroscopy and x ray diffraction the alteration conditions represent an acid fog environment alteration rinds on the basalts vary in thickness from tens of micrometers to the entirety of the rock and are composed of amorphous silica rims 85 95 wt sio 2 overlain by sulfates sulfate mineralogy consisted of gypsum anhydrite and natroalunite jarosite no phyllosilicates were observed in any alteration assemblages phenocrysts and glass were both observed to be extensively reacted during alteration the halemaumau samples may provide good analogs for basalt alteration on other rocky planetary bodies i e mars venus and mercury where s is ubiquitous and low fluid rock ratios are common

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

shumagin seismic gap alaska peninsula history of great earthquakes tectonic setting and evidence for high seismic potential the shumagin seismic gap a segment of the plate boundary along the eastern aleutian arc has not ruptured during a great earthquake since at least 1899 1903 because at least 77 years have elapsed since the shumagin gap last ruptured in a great earthquake and repeat times for the 1938 rupture zone and part of the shumagin gap are estimated to be 50 to 90 years a high probability exists for a great earthquake to occur within the shumagin gap during the next one to two decades reconsideration of the rupture zones of the aleutian earthquakes of 1938 1946 and 1948 suggests that those events did not break the interplate boundary beneath the shumagin islands thus the shumagin seismic gap extends from the western end of the 1938 rupture zone to the eastern end of that of 1946 these boundaries also coincide with transverse structural features at least the eastern half of the shumagin gap broke in great earthquakes in 1788 and 1847 and possibly in 1898 1903 the shumagin gap is probably not the result of aseismic slip rather plate motion is accommodated there seismically and episodically and can be expected to produce large earthquakes in the future although there is no definitive evidence of long term precursors of a possible future earthquake several observations suggest that the shumagin gap is in an advanced stage of the earthquake cycle both teleseismic and local network data indicate a near absence of seismic activity m 2 above a depth of 30 km along the main thrust zone within the gap this is in strong contrast to adjacent portions of the arc where seismic activity is scattered across most of the main thrust zone two earthquakes with high stress drops 600 900 bars which occurred at the base of the main thrust zone may indicate the accumulation of a considerable amount of strain energy within the gap a possible seismic gap at the eastern end of the aftershock zone of the aleutian earthquake of 1957 has been identified near unalaska island an earthquake that nucleates in the shumagin gap could also rupture the possible unalaska gap to the west the 1938 aftershock zone to the east or both with resultant magnitude up to mw 9 0 alternatively the shumagin gap alone or in one of the above combinations could rupture in a series of very large earthquakes instead of a single great shock past alaska aleutian earthquakes including those of 1788 1938 1946 1957 1964 and 1965 have generated very large tsunamis future large earthquakes in the shumagin islands region could generate wave heights of several tens of meters along shorelines near the rupture areas the shumagin gap is one of two major gaps along the united states portion of the alaska aleutian plate boundary and is one of the few areas in the united states where processes leading to a great earthquake are likely to be observed within a reasonable span of time

seismic rupture and arc segmentation within the shumagin islands seismic gap alaska the locations of teleseismically well recorded earthquakes suggest that up to 80 of the shumagin gap has ruptured seismically during the last 90 years an earthquake in 1917 ms 7 9 nucleated near the gap s eastern edge and appears to have ruptured as much as a 200 km long section of the gap and an event in 1948 ms 7 5 appears to have ruptured the deepest portion of the main thrust zone 30 km in the central section of the gap the rupture extents of these earthquakes suggest that the gap can be divided into two or three smaller arc segments these observations do not preclude the possibility of failure of the entire region in a single great earthquake mw 8 5 in the near future the two historically documented recurrence intervals for the eastern portion of the gap are 59 and 70 years if the average recurrence interval for large earthquakes near the shumagin islands is 65 years the conditional probability of a large earthquake rupturing this portion of the arc in the next 20 years is between 62 and 96

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

tilt and seismicity changes in the shumagin seismic gap changes in the ground surface tilt and in the rate of seismicity indicate that an aseismic deformation event may have occurred between 1978 and 1980 along the plate boundary in the eastern aleutians alaska within the shumagin seismic gap pavlof volcano was unusually quiescent during this period the proposed event would cause an increase of stress on the shallow locked portion of the plate boundary bringing it closer to rupture in a great earthquake

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

refined data of alpha proton x ray spectrometer analyses of soils and rocks at the mars pathfinder site implications for surface chemistry 1 an extensive recalibration of the alpha proton x ray spectrometer apxs was performed to improve the data evaluation of the mars pathfinder mpf rock and soil in situ measurements many samples and geostandards were measured with an mpf identical spare apxs under simulated martian atmospheric pressure and low night temperature conditions precise calibration curves for major and minor elements were obtained using an improved spectral evaluation method for the original mpf spectra refined and new elemental compositions of the mpf rocks and soils were derived however all initial conclusions about soils and rocks remained valid the mpf soil composition revealed the mafic nature of the surface as inferred from the results of viking 1 and 2 data however the mpf rocks reflect a felsic composition for all samples linear correlations of sulphur with all other elements were noticed reflecting the fact that the rocks were covered with varying degrees of soil which compared to the rocks is rich in sulphur extrapolating to low sulphur abundance 0 3 the composition of a soil free rock was calculated the mpf rock composition is high in si and k and low in mg and fe compared to the soil using elemental data from mpf and martian meteorites a global estimation of the martian crust composition was derived the crust is of basaltic nature with a high abundance of incompatible elements k rb nd u th and volatile elements s cl while carbonates are lower or absent

spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of mars mineral abundances derived from the analysis of remotely sensed thermal emission data from mars have been interpreted to indicate that the surface is composed of basalt surface type 1 and andesite surface type 2 1 the global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient heavily cratered crust in the southern hemisphere basalt from younger lowland plains in the north andesite 1 but the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of mars here we reinterpret martian surface rock lithologies using mineral abundances from previous work1 and new mineralogies derived from a spectral end member set representing minerals common in unaltered and low temperature aqueously altered basalts our results continue to indicate the dominance of unaltered basalt in the southern highlands but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite the coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre

constraints on the maximum crustal density from gravity topography modeling applications to the southern highlands of mars abstract gravimetric methods commonly used to constrain crustal parameters such as the mean crustal thickness and density are ambiguous with a noted trade off between these parameters however combining two different methods the geoid topography ratio and bouguer inversion in regions that are homogeneous with respect to lateral density variations and compensation state can help to constrain a maximum density of the crust for the martian noachian southern highlands a combination of these methods gives us a maximum crustal density of 3020 70 kg m 3 assuming a single layer crustal structure we also test various two layer crustal structures to check how they influence the results we find a possibility to fit the observed data with a crust having a dense uniformly thick lower crust but in these models the upper crustal density was also limited to 3000 kg m 3 the obtained results together with the findings on crustal densities and composition of other regions on mars are consistent with various scenarios of crustal evolution a temporal increase in the crustal density or a large scale density variation that has been already manifested in the early evolution during the formation of the crustal dichotomy

petrological constraints on the density of the martian crust new insights into the chemistry of the martian crust have been made available since the derivation of crustal thickness maps from mars global surveyor gravity and topography data that used a conservative range of density values 2700 3100 kg m3 a new range of crustal density values is calculated from the major element chemistry of martian meteorites 3100 3700 kg m3 igneous rocks at gusev crater 3100 3600 kg m3 and from the surface concentration of fe al ca si and k measured by the gamma ray spectrometer on board mars odyssey 3250 3450 kg m3 in addition the density of mineral assemblages resulting from low pressure crystallization of primary melts of the primitive mantle are estimated for plausible conditions of partial melting corresponding to the noachian to amazonian periods 3100 3300 kg m3 despite the differences between these approaches the results are all consistent with an average density above 3100 kg m3 for those materials that are close to the surface the density may be compatible with the measured mass of mars and the moment of inertia factor but only if the average crustal thickness is thicker than previously thought approaching 100 km a thicker crust implies that crustal delamination and recycling could be possible and may even control its thickness globally or locally alternatively and considering that geoid to topography ratios argue against such a thick crust for the highlands our results suggest the existence of a buried felsic or anorthositic component in the southern hemisphere of mars

determination of the chemical composition of martian soil and rocks the alpha proton x ray spectrometer the alpha proton x ray spectrometer apxs for the mars pathfinder mission is designed to provide a complete and detailed analysis of chemical elements in martian soil and rocks near the landing site the apxs instrument is carried on the pathfinder microrover which will provide transportation to places of interest on the martian surface it consists of a complex sensor head mounted on a simple but sophisticated apxs deployment mechanism adm outside the warm electronics box web of the microrover and the instrument electronics mounted inside the web the adm permits the instrument sensor head to be placed against soil and rock samples in arbitrary positions ranging from horizontal to vertical in order to perform in situ analysis the possibility to transport the apxs to an arbitrary location preselected on earth and to perform in situ analysis there constitutes one of the most exciting aspects of the pathfinder mission the principle of the apxs technique is based on three interactions of alpha particles from a radioisotope source with matter simple rutherford backscattering production of protons from p reactions on light elements and generation of characteristic x rays upon recombination of atomic shell vacancies created by a bombardment measurement of the intensities and energy distributions of these three components yields information on the abundance of chemical elements in the sample in terms of sensitivity and selectivity data are partly redundant and partly complementary alpha backscattering is superior for light elements c o while proton emission is mainly sensitive to na mg al si s and x ray emission is more sensitive to heavier elements na to fe and beyond a combination of all three measurements enables determination of all elements with the exception of h and he present at concentration levels above typically a fraction of 1

internal structure and early thermal evolution of mars from mars global surveyor topography and gravity topography and gravity measured by the mars global surveyor have enabled determination of the global crust and upper mantle structure of mars the planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy a region of crust that thins progressively from south to north and encompasses much of the southern highlands and tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and arabia terra the strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history the thickness of the elastic lithosphere increases with time of loading in the northern plains and tharsis the northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing

investigation of the near infrared spectral character of putative martian chloride deposits 1 putative chloride salt deposits observed throughout the southern highlands of mars by the compact reconnaissance imaging spectrometer for mars crism display featureless red slopes in near infrared ratio spectra it is hypothesized that the admixture of anhydrous chlorides or unoxidized sulfides with silicate rocks or minerals could imitate this spectral behavior three different sets of spectra were collected 1 simple mixtures of halite with labradorite and flood basalt at multiple concentrations 2 halite crusts formed on both labradorite and flood basalt and 3 simple mixtures of 25 and 50 wt acid washed pyrite with labradorite and flood basalt in all three instances multiple grain sizes were used to evaluate the effect of particle size on spectral results spectra of the mixtures and crusts were divided by pure labradorite and flood basalt spectra of the same grain size to produce ratio spectra comparable to the crism ratio spectra our study rules out pyrite as a possible component of these deposits whereas flood basalt mixtures with halite reproduced the observed red slope under some conditions this allows us to place some broad constraints on halite proportions and the effective grain sizes of these deposits

vertical distribution of hydrogen at high northern latitudes on mars the mars odyssey neutron spectrometer 1 neutron leakage currents measured using the mars odyssey neutron spectrometer are used to develop a two layer model of the distribution of hydrogen here parameterized as water equivalent hydrogen weh at high northern latitudes the weh abundance in the upper layer wup was found to range between 1 and about 5 the maximum value of the apparent thickness d of this upper layer peaks at about 60 latitude giving the appearance of zonal bands of enhanced d in both hemispheres this maximum is consistent with an expected transition from weh contained solely in hydrous minerals at lower latitudes to weh contained both in the forms of water ice and water of hydration at high latitudes a strong anti correlation between the weh concentration in the lower layer and apparent depth d at high latitudes is observed and may provide clues to the origin of these deposits

martian surface heat production and crustal heat flow from mars odyssey gamma ray spectrometry 1 martian thermal state and evolution depend principally on the radiogenic heat producing element hpe distributions in the planet s crust and mantle the gamma ray spectrometer grs on the 2001 mars odyssey spacecraft has mapped the surface abundances of hpes across mars from these data we produce the first models of global and regional surface heat production and crustal heat flow as previous studies have suggested that the crust is a repository for approximately 50 of the radiogenic elements on mars these models provide important directly measurable constraints on martian heat generation our calculations show considerable geographic and temporal variations in crustal heat flow and demonstrate the existence of anomalous heat flow provinces we calculate a present day average surface heat production of 4 9 0 3 10 11 w kg 1 we also calculate the average crustal component of heat flow of 6 4 0 4 mw m 2 the crustal component of radiogenically produced heat flow ranges from 1 mw m 2 in the hellas basin and utopia planitia regions to 13 mw m 2 in the sirenum fossae region these heat production and crustal heat flow values from geochemical measurements support previous heat flow estimates produced by different methodologies

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

gradual unlocking of plate boundary controlled initiation of the 2014 iquique earthquake a long foreshock series unlocked the south american plate boundary until eventually initiating the m 8 1 iquique chile earthquake two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure on 1 april 2014 northern chile was struck by a magnitude 8 1 earthquake following a protracted series of foreshocks the integrated plate boundary observatory chile monitored the entire sequence of events providing unprecedented resolution of the build up to the main event and its rupture evolution here we show that the iquique earthquake broke a central fraction of the so called northern chile seismic gap the last major segment of the south american plate boundary that had not ruptured in the past century1 2 since july 2013 three seismic clusters each lasting a few weeks hit this part of the plate boundary with earthquakes of increasing peak magnitudes starting with the second cluster geodetic observations show surface displacements that can be associated with slip on the plate interface these seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion leading up to this earthquake the b value of the foreshocks gradually decreased during the years before the earthquake reversing its trend a few days before the iquique earthquake the mainshock finally nucleated at the northern end of the foreshock area which skirted a locked patch and ruptured mainly downdip towards higher locking peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch we conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure distinguishing the iquique earthquake from most great earthquakes finally only one third of the gap was broken and the remaining locked segments now pose a significant increased seismic hazard with the potential to host an earthquake with a magnitude of 8 5

decade scale decrease inb value prior to the m9 class 2011 tohoku and 2004 sumatra quakes 1 the gutenberg richter frequency magnitude distribution of earthquakes has become well established in seismology the slope of the relation between frequency and magnitude b value is typically 1 but it often shows variations around 1 based on an analysis of seismicity prior to the 2011 tohoku and 2004 sumatra earthquakes both in magnitude m 9 class we show that the pronounced decade scale decrease inbvalue was a common precursor to both mega quakes around their hypocenters this is the first report onm9 class quakes to confirm a change inb value which has been predicted based on the results of laboratory experiments we propose that the b value is an important indicator of an impending great earthquake and has great potential in terms of predicting a future large quake off the pacific coast of hokkaido japan

evidence for and implications of a bering plate based on geodetic measurements from the aleutians and western alaska 1 global positioning system gps measurements are used to examine the hypothesis of a clockwise rotating bering plate originally proposed on the basis of seismicity the bering plate encompasses the bering sea western alaska and the aleutian islands gps measurements from the bering plate s interior show south to southwest motions of 3 5 mm a where a is years we construct elastic dislocation models to determine the spatial distribution and intensity of locked patches on the aleutian subduction interface we use these to remove interseismic strain from the gps observation and determine an arc translation velocity for each region of the aleutians revealing south and southwest motions of 4 8 mm a we combine the arc translation rates with measurements from the bering plate s interior sites and estimate the euler pole for the bering plate relative to north america to be located at 42 5 n 121 3 e with an angular speed of 6 0 ma the clockwise rotation of the bering plate may cause left lateral faulting in interior alaska the bering plate s interaction with south central alaska may be responsible for the decreased slip rate on the western denali fault and for contraction across the central alaska range we analyze slip partitioning along the aleutian arc on the basis of both gps measurements and slip azimuths of thrust earthquakes and find a systematic discrepancy between plate convergence direction and slip azimuths we conclude that slip partitioning in the back arc only develops west of amchitka pass whereas slip partitioning in the fore arc is present throughout the arc

chemical composition of martian soil and rocks complex mixing and sedimentary transport chemical compositions of martian soil and rocks indicate complex mixing relationships mixing of rock and soil clearly takes place and explains some of the chemical variation because sulfur chlorine magnesium and perhaps iron are positively correlated due to their control from a secondary sedimentary mineralogy e g mg and possibly fesulfate fe oxides that is present within the soils certain deviations from simple soil rock mixing are consistent with mineralogical fractionation of detrital iron and titanium oxides during sedimentary transport

apxs derived chemistry of the bagnold dune sands comparisons with gale crater soils and the global martian average we present apxs data for the active bagnold dune field within the gale impact crater msl mission we derive an apxs based average basaltic soil abs composition for mars based on past and recent data from the msl and mer missions this represents an update to the taylor and mclennan 2009 average martian soil and facilitates comparison across martian datasets the active bagnold dune field is compositionally distinct from the abs with elevated mg ni and fe suggesting mafic mineral enrichment and uniformly low levels of s cl and zn indicating only a minimal dust component a relationship between decreasing grain size and increasing felsic content is revealed the bagnold sands possess the lowest s cl of all martian unconsolidated materials gale soils exhibit relatively uniform major element compositions similar to meridiani planum and gusev crater basaltic soils mer missions however they show minor enrichments in k cr mn and fe which may signify a local contribution the lithified eolian stimson formation within the gale impact crater is compositionally similar to the abs and bagnold sands which provide a modern analogue for these ancient eolian deposits compilation of apxs derived soil data reveals a generally homogenous global composition for martian soils but one that can be locally modified due to past or extant geologic processes that are limited in both space and time

earth science microseismicity data forecast rupture area on 28 september 2004 there was an earthquake of magnitude 6 0 at parkfield california here we show that the size distribution of the micro earthquakes recorded in the decades before the main shock occurred allowed an accurate forecast of its eventual rupture area applying this approach to other well monitored faults should improve earthquake hazard assessment in future

bounce rock a shergottite like basalt encountered at meridiani planum mars additional co authors thanasis economou steven p gorevan brian c hahn gostar klingelhofer timothy j mccoy harry y mcsween jr douglas w ming richard v morris daniel s rodionov steven w squyres heinrich wanke shawn p wright michael b wyatt albert s yen

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

overview of the mars pathfinder mission launch through landing surface operations data sets and science results mars pathfinder successfully landed at ares vallis on july 4 1997 deployed and navigated a small rover about 100 m clockwise around the lander and collected data from three science instruments and ten technology experiments the mission operated for three months and returned 2 3 gbits of data including over 16 500 lander and 550 rover images 16 chemical analyses of rocks and soil and 8 5 million individual temperature pressure and wind measurements path finder is the best known location on mars having been clearly identified with respect to other features on the surface by correlating five prominent horizon features and two small craters in lander images with those in high resolution orbiter images and in inertial space from two way ranging and doppler tracking tracking of the lander has fixed the spin pole of mars determined the precession rate since viking 20 years ago and indicates a polar moment of inertia which constrains a central metallic core to be between 1300 and 2000 km in radius dark rocks appear to be high in silica and geochemically similar to anorogenic andesites lighter rocks are richer in sulfur and lower in silica consistent with being coated with various amounts of dust rover and lander images show rocks with a variety of morphologies fabrics and textures suggesting a variety of rock types are present rounded pebbles and cobbles on the surface as well as rounded bumps and pits on some rocks indicate these rocks may be conglomerates although other explanations are also possible which almost definitely require liquid water to form and a warmer and wetter past air borne dust is composed of composite silicate particles with a small fraction of a highly magnetic mineral interpreted to be most likely maghemite explanations suggest iron was dissolved from crustal materials during an active hydrologic cycle with maghemite freeze dried onto silicate dust grains remote sensing data at a scale of a kilometer or greater and an earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catstrophic floods which are relatively dust free the surface appears to have changed little since it formed billions of years ago with the exception that eolian activity may have deflated the surface by 3 7 cm sculpted wind tails collected sand into dunes and eroded ventifacts fluted and grooved rocks pathfinder found a dusty lower atmosphere early morning water ice clouds and morning near surface air temperatures that changed abruptly with time and height small scale vortices interpreted to be dust devils were observed repeatedly in the afternoon by the meteorology instruments and have been imaged

geochemistry of martian soil and bedrock in mantled and less mantled terrains with gamma ray data from mars odyssey 1 surficial materials including soil and dust are abundant in the upper tens of centimeters of the martian surface sensed by the mars odyssey gamma ray spectrometer grs seven large areas 14 of the martian surface that represent possible compositional end members were selected including three regions heavily mantled with surficial materials the selection process included mapping the ratio of exposed rocky terrain to surficial materials using high resolution imagery grs data for h cl fe si k and th were obtained for each area the areas are chemically homogeneous within each area given the spatial resolution and analytical uncertainty of the grs data however substantial chemical differences exist among the areas including the different mantled terrains contrary to earlier assumptions that surficial materials are globally homogeneous due to aeolian mixing the observed chemical differences among the areas may be due to variations in the protolith compositions extent of alteration of the protolith regions or post soil formation processes the abundances of cl k and th in rockier but still soil rich areas such as syrtis major planum can be explained by mixing between a soil with higher concentrations of cl k and th similar to the abundances in the mantled terrains and some of the landing sites and crustal rocks containing lower abundances of these elements similar to martian meteorites

deep low frequency earthquakes in tectonic tremor along the alaska aleutian subduction zone 1 we characterize and locate tremor not associated with volcanoes along the alaska aleutian subduction zone using continuous seismic data recorded by the alaska volcano observatory and the alaska earthquake information center from 2005 to present visual inspection of waveform spectra and time series reveal dozens of 10 to 20 min bursts of tremor along the length of the alaska aleutian subduction zone we use autocorrelation to demonstrate that these tremor signals are composed of hundreds of repeating low frequency earthquakes lfes the tremor activity we characterize is localized in four segments from east to west kodiak island shumagin gap unalaska and andreanof islands although the geometry age thermal structure frictional and other relevant properties of the alaska aleutian subduction zone are poorly known these characteristics are likely to differ systematically from east to west locations near kodiak island are the most reliable because station coverage is more complete lfe hypocenters in this region are located on the plate interface near the down dip limit of the 1964 mw 9 2 alaska earthquake rupture area lfe hypocenters in the remaining areas along the arc are also located down dip of the most recent mw 8 megathrust earthquakes although these locations are less well constrained our results support the hypothesis that tremor activity marks the down dip rupture limit for great megathrust earthquakes in this subduction zone lastly there is no correlation between the presence of tremor and particular aspects of over riding or subducting plate geology or coupling it appears that lfes are a fundamental characteristic of the alaska aleutian subduction zone

body wave and surface wave analysis of large and great earthquakes along the eastern aleutian arc 1923 1993 implications for future events the 500 km long alaska peninsula and shumagin islands segments of the aleutian arc have a moderate to high probability of rupturing in one or more large or great earthquakes in the next few decades to understand the likely modes of rupture in the next sequence of large and great events and to delineate the current geometry of the plate interface we determine focal mechanisms depths and source time functions from seismic records for the largest events since 1917 the great earthquake of november 10 1938 and seven events with surface wave magnitude ms of 6 9 to 7 5 teleseismic body waves and surface waves are used to estimate the seismic moment and gross rupture characteristics of the great earthquake of november 10 1938 along the alaska peninsula body wave inversion of five p and four sh waves gives a duration of about 110 s in which moment was released in two episodes each of about 50 s duration with the second being larger than the first the first source was located in the general vicinity of the epicenter of the mainshock and the second which occurred about 60 s later was centered about 180 km to the northeast the body wave derived seismic moment is 3 7 1021 n m mw 8 3 we corroborate the body wave results by calculating surface waves by normal mode summation and comparing them with data at periods greater than 50 s an adequate fit to observed seismograms is obtained for either a single point source or two point sources with one located about 180 km northeast of the mainshock epicenter rupture in 1938 appears to have been confined to the alaska peninsula segment uniform rupture into the shumagin region is not supported by the data the ms 6 9 earthquake of may 13 1993 ruptured a small portion of the shumagin gap the earthquake of may 14 1948 ms 7 5 occurred on a shallow dipping thrust fault with a depth of about 31 km not 60 km as originally suggested five ms 7 events in the 1938 rupture zone have locations depths and mechanisms that define a shallow dipping 16 19 plate interface which shallows to 8 under kodiak island subduction of seamounts of the gulf of alaska seamount province may explain the location moment focal mechanism and depth of the five ms 7 events the plate interface dips nearly uniformly between the alaska peninsula and shumagin segments indicating that segmentation if any is not controlled by the orientation of the plate interface a slight warp of the plate interface may form the boundary between rupture zones of great earthquakes along the kodiak and alaska peninsula segments of the arc and may explain why rupture zones of large to great earthquakes rarely cross this tectonic boundary

the gravitational signature of martian volcanoes by modeling the elastic flexure of the martian lithosphere under imposed loads we provide a systematic study of the old and low relief volcanoes 3 2 ga 0 5 to 7 4 km and the younger and larger prominent constructs within the tharsis and elysium provinces 3 2 ga 0 5 to 7 4 km and the younger and larger constructs clustered in the tharsis and elysium provinces 3 ga 5 8 to 21 9 km the observed topography is used to define the load and to derive a simulated gravity field that is compared to the observed gravity the bulk density of the lava that composes all volcanoes is found to be 3 200 kg m 3 which is representative of iron rich basalts as sampled by the martian basaltic meteorites the elastic part of the lithosphere that is the part maintaining loads over geologic time is found to have been thin when the small old volcanoes formed which implies that the lithosphere was hot early in geologic history conversely larger volcanoes are found to have been emplaced on a cold and thicker elastic lithosphere

remote laser induced breakdown spectroscopy analyses of dar al gani 476 and zagami martian meteorites 1 laser induced breakdown spectroscopy libs was recently selected to provide active remote sensing compositional information on the mars science laboratory msl rover the ability of libs to remotely determine differences between basaltic rock types on mars is investigated by analyzing two martian basaltic shergottite meteorites whose compositions differ slightly and which also differ slightly in texture using 14 analysis spots of 400 m diameter on dar al gani dag 476 and 9 analysis spots on zagami the libs technique at a 5 4 m standoff distance clearly distinguished the olivine phyric dag 476 from the basaltic zagami shergottite on the basis of mgo and cao mean elemental abundances agreed with literature values for these meteorites to within 12 for most of the major elements the ability of libs to remotely distinguish between basaltic and andesitic compositions in a martian environment was also investigated by analyzing a known andesite standard and comparing its spectra to the martian basaltic shergottite spectra yielding agreement with the literature andesite composition within 9 the data presented here demonstrate the ability of libs to provide reasonable estimates of whole rock composition as well as determine relatively subtle differences in rock types from a distance

soils of eagle crater and meridiani planum at the opportunity rover landing site the soils at the opportunity site are fine grained basaltic sands mixed with dust and sulfate rich outcrop debris hematite is concentrated in spherules eroded from the strata ongoing saltation exhumes the spherules and their fragments concentrating them at the surface spherules emerge from soils coated perhaps from subsurface cementation by salts two types of vesicular clasts may represent basaltic sand sources eolian ripples armored by well sorted hematite rich grains pervade meridiani planum the thickness of the soil on the plain is estimated to be about a meter the flatness and thin cover suggest that the plain may represent the original sedimentary surface

chemical composition of martian fines of the 21 samples acquired for the viking x ray fluorescence spectrometer 17 were analyzed to high precision compared to typical terrestrial continental soils and lunar mare fines the martian fines are lower in al higher in fe and much higher in s and cl concentrations protected fines at the two lander sites are almost indistinguishable but concentration of the element s is somewhat higher at utopia duricrust fragments successfully acquired only at the chryse site invariably contained about 50 higher s than fines no elements correlate positively with s except cl and possibly mg a sympathetic variation is found among the triad si al ca positive correlation occurs between ti and fe sample variabilities are as great within a few meters as between lander locations 4500 km apart implying the existence of a universal martian regolith component of constant average composition the nature of the source materials for the regolith fines must be mafic to ultramafic

geophysical constraints on the composition and structure of the martian interior 1 most recent martian interior structure models are based on the planet s polar moment of inertia c although the mean moment of inertia i is required for constructing spherically symmetric models of planetary interiors using the improved value of c mprp2 recently obtained from a combined reanalysis of the entire set of radio science data collected during the last three decades and accounting for the rotationally and topographically induced shape of the planet s gravitational field we find a mean moment of inertia factor of i mprp2 0 3635 0 0012 the new lower value suggests a core radius several tens of kilometers larger if other parameters like core density crust density and crust thickness are fixed it further implies that the martian crust is several tens of kilometers thicker than previously thought if crust and mantle densities and core size are given moreover the martian mantle may be less dense about several tens of kg m 3 with a smaller iron content than previously thought if crust thickness and core size are specified the mantle density of mars is relatively well determined by the planet s moment of inertia factor if crust thickness and density are specified

chemical compositions at mars landing sites subject to mars odyssey gamma ray spectrometer constraints 1 the mars odyssey gamma ray spectrometer grs is the first instrument suite to return elemental abundances throughout the midlatitudes of mars concentrations of cl fe h k si and th have been determined to tens of centimeter depths as mass fractions with reasonable confidence comparing such data with or normalizing them to in situ compositional data is difficult due to issues such as dramatic differences in spatial resolution difficulties in convolving densities abundances and compositions of different regolith components and a limited number of elements observed in common we address these concerns in the context of the grs using si at pathfinder to normalize remote data in addition we determine representative in situ compositions for spirit both with and without columbia hills rocks opportunity and viking 1 landing sites using grs derived h content to hydrate the soil component our estimate of the si mass fraction at pathfinder with 13 areal fraction of rocks is 21 the composition of major elements such as si and fe is similar across the four landing sites while minor elements show significant variability areal dominance of soil at all four landing sites causes representative compositions to be driven by the soil component while proportionally large uncertainties of bulk densities dominate the net uncertainties grs compositional determinations compare favorably with the in situ estimates for cl and k and for si by virtue of the normalization however the grs determined fe content at each landing site is consistently higher than the in situ value

constraints on the petrogenesis of martian meteorites from the rb sr and sm nd isotopic systematics of the lherzolitic shergottites alh77005 and lew88516 abstract detailed rb sr and sm nd isotopic analyses have been completed on the lherzolitic shergottites alh77005 and lew88516 alh77005 yields a rb sr age of 185 11 ma and a sm nd age of 173 6 ma whereas the rb sr and sm nd ages of lew88516 are 183 10 and 166 16 ma respectively the initial sr isotopic composition of alh77005 is 0 71026 4 and the initial end value is 11 1 0 2 these values are distinct from those of lew88516 which has an initial sr isotopic composition of 0 71052 4 and an initial end value of 8 2 0 6 several of the mineral and whole rock leachates lie off the rb sr and sm nd isochrons indicating that the isotopic systematics of the meteorites have been disturbed the sm nd isotopic compositions of the leachates appear to be mixtures of primary igneous phosphates and an alteration component with a low 143nd 144nd ratio that was probably added to the meteorites on mars tie lines between leachate residue pairs from lew88516 mineral fractions and whole rocks have nearly identical slopes that correspond to rb sr ages of 90 1 ma this age may record a major shock event that fractionated rb sr from lattice sites located on mineral grain boundaries on the other hand the leachates could contain secondary alteration products and the parallel slopes of the tie lines could be coincidental nearly identical mineral modes compositions and ages suggest that these meteorites are very closely related nevertheless their initial sr and nd isotopic compositions differ outside analytical uncertainty requiring derivation from unique sources assimilation fractional crystallization models indicate that these two lherzolitic meteorites can only be related to a common parental magma if the assimilant has a sr nd ratio near 1 and a radiogenic sr isotopic composition further constraints placed on the evolved component by the geochemical and isotopic systematics of the shergottite meteorite suite suggest that it a formed at 4 5 ga b has a high la yb ratio c is an oxidant and d is basaltic in composition or is strongly enriched in incompatible elements the composition and isotopic systematics of the evolved component are unlike any evolved lunar or terrestrial igneous rocks its unusual geochemical and isotopic characteristics could reflect hydrous alteration of an evolved martian crustal component or hydrous metasomatism within the martian mantle

evidence for montmorillonite or its compositional equivalent in columbia hills mars 1 during its exploration of the columbia hills the mars exploration rover spirit encountered several similar samples that are distinctly different from martian meteorites and known gusev crater soils rocks and sediments occurring in a variety of contexts and locations these independence class samples are rough textured iron poor equivalent feo 4 wt have high al si ratios and often contain unexpectedly high concentrations of one or more minor or trace elements including cr ni cu sr and y apart from accessory minerals the major component common to these samples has a compositional profile of major and minor elements which is similar to the smectite montmorillonite implicating this mineral or its compositional equivalent infrared thermal emission spectra do not indicate the presence of crystalline smectite one of these samples was found spatially associated with a ferric sulfate enriched soil horizon possibly indicating a genetic relationship between these disparate types of materials compared to the nearby wishstone and watchtower class rocks major aqueous alteration involving mineral dissolution and mobilization with consequent depletions of certain elements is implied for this setting and may be undetectable by remote sensing from orbit because of the small scale of the occurrences and obscuration by mantling with soil and dust

basaltic rocks analyzed by the spirit rover in gusev crater the spirit landing site in gusev crater on mars contains dark fine grained vesicular rocks interpreted as lavas pancam and mini thermal emission spectrometer mini tes spectra suggest that all of these rocks are similar but have variable coatings and dust mantles magnified images of brushed and abraded rock surfaces show alteration rinds and veins rock interiors contain 25 megacrysts chemical analyses of rocks by the alpha particle x ray spectrometer are consistent with picritic basalts containing normative olivine pyroxenes plagioclase and accessory feti oxides mossbauer pancam and mini tes spectra confirm the presence of olivine magnetite and probably pyroxene these basalts extend the known range of rock compositions composing the martian crust

estimates of martian crustal thickness from viscous relaxation of topography isostatically compensated crustal thickness variations and associated topographic contrasts at the surface of a planet result in lateral pressure gradients which may cause the lower crust to flow and reduce the relief areas of thicker crust are generally associated with more rapid relaxation of topography on mars topographic features such as impact basins and the hemispheric dichotomy have survived for 4 gyr we use a finite difference representation of depth dependent non newtonian lower crustal flow to investigate how topography decays with time for a dry diabase rheology total radiogenic concentrations 80 of terrestrial values and crustal radiogenic concentrations similar to terrestrial basalts we find that an upper bound on the mean planetary crustal thickness is 100 km in the probably unrealistic case where all the radiogenic elements are in the crust this maximum crustal thickness can be increased to 115 km the main uncertainty in these results is the total radiogenic abundances on mars comparing our results with the observed shape of the crustal dichotomy provides no evidence that this slope is primarily the result of lower crustal flow both hellas and the dichotomy are isostatically compensated if the mechanism is airy isostasy then the lower bound on mean crustal thickness is 30 km crustal thicknesses of 30 100 km on mars can be produced by mid ocean ridge spreading at potential temperatures of 1350 1600 c however for such crustal thicknesses the lithosphere is likely to be positively buoyant making subduction difficult

geochemical components in martian soil abstract trends in element compositional variation among samples at the viking lander sites on mars provide evidence for multiple geochemical components in the soils a simple two component model can explain all pair wise trends of eight elements analyzed component a contains si and most or all the al ca ti and fe component b which is 16 3 by weight of the total contains s and most or all the cl and mg these results constrain several models of martian soil mineralogy but are consistent with a mixture of silicates and salts

rupture extent of the 1938 alaskan earthquake as inferred from tsunami waveforms using tsunami waveforms we estimate the source parameters of the 10 november 1938 alaskan earthquake the earthquake ruptured a 300 kin long segment of the alaskan arc which corresponds to the aftershock area the seismic moment is approximately 20x102o nm or mw 8 2 and the moment release was concentrated in the eastern end of the aftershock zone the tsunami and seismic evidence strongly suggest that the 1938 earthquake did not rupture into the shumagin islands gap

experimental study of the effect of excavation on existing loaded piles abstractexcavation beneath an existing building to add a new basement is an effective mean to expand underground space that caters to the increased need of space in urban areas because piles serve

sulfur bearing phases detected by evolved gas analysis of the rocknest aeolian deposit gale crater mars the sample analysis at mars sam instrument suite detected so2 h2s ocs and cs2 from 450 to 800 c during evolved gas analysis ega of materials from the rocknest aeolian deposit in gale crater mars this was the first detection of evolved sulfur species from a martian surface sample during in situ ega so2 3 22 mol is consistent with the thermal decomposition of fe sulfates or ca sulfites or evolution desorption from sulfur bearing amorphous phases reactions between reduced sulfur phases such as sulfides and evolved o2 or h2o in the sam oven are another candidate so2 source h2s 41 109 nmol is consistent with interactions of h2o h2 and or hcl with reduced sulfur phases and or so2 in the sam oven ocs 1 5 nmol and cs2 0 2 1 nmol are likely derived from reactions between carbon bearing compounds and reduced sulfur sulfates and sulfites indicate some aqueous interactions although not necessarily at the rocknest site fe sulfates imply interaction with acid solutions whereas ca sulfites can form from acidic to near neutral solutions sulfides in the rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source the presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering the possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage understanding the sulfur mineralogy in rocknest materials which exhibit chemical similarities to basaltic fines analyzed elsewhere on mars can provide insight in to the origin and alteration history of martian surface materials

mars odyssey gamma ray spectrometer elemental abundances and apparent relative surface age implications for martian crustal evolution 1 quantifying secular variations in the chemical composition of the martian crust provides unique insights into the processes that have guided the evolution of the martian crust mantle system using global abundances for a suite of elements determined by the gamma ray spectrometer grs on board the mars odyssey spacecraft and global mapping of apparent surface age adapted from existing geologic maps in the usgs martian geologic investigation series we report the average abundance of k th fe cl h and si for the major martian geologic epochs noachian hesperian and amazonian average grs determined k and th abundances generally decrease by 9 and 7 respectively between the hesperian and the amazonian possibly implying evolving magma chemistry throughout major resurfacing events although the effects of surficial alteration processes cannot be entirely discounted grs determined fe and cl averages increase by 12 and 19 respectively with younger apparent relative surface age suggesting the possible mobilization and transport of these elements through aqueous processes although an igneous origin for the variation in fe also cannot be excluded while h abundance does vary with surface age the relationship is likely not governed by geologic processes no statistically reliable apparent surface age relation was found for si

common dependence on stress for the two fundamental laws of statistical seismology the gutenberg richter relation and the omori utsu law both power laws are two of the long standing relationships of statistical seismology here aftershock sequences are described according to the faulting style of their main shocks showing that the time delay before the onset of the power law aftershock decay rate is on average shorter for thrust main shocks than for normal fault earthquakes these similar dependences on the faulting style indicate that both the fundamental power laws are governed by the state of stress

little late holocene strain accumulation and release on the aleutian megathrust below the shumagin islands alaska can a predominantly creeping segment of a subduction zone generate a great m 8 earthquake despite russian accounts of strong shaking and high tsunamis in 1788 geodetic observations above the aleutian megathrust indicate creeping subduction across the shumagin islands segment a well known seismic gap seeking evidence for prehistoric great earthquakes we investigated simeonof island the archipelago s easternmost island and found no evidence for uplifted marine terraces or subsided shorelines instead we found freshwater peat blanketing lowlands and organic rich silt and tephra draping higher glacially smoothed bedrock basal peat ages place glacier retreat prior to 10 4 ka and imply slowly rising 0 2 m ka relative sea level since 3 4 ka storms rather than tsunamis probably deposited thin discontinuous deposits in coastal sites if rupture of the megathrust beneath simeonof island produced great earthquakes in the late holocene then coseismic uplift or subsidence was too small 0 3 m to perturb the onshore geologic record

chemical multispectral and textural constraints on the composition and origin of rocks at the mars pathfinder landing site rocks at the mars pathfinder site are probably locally derived textures on rock surfaces may indicate volcanic sedimentary or impact generated rocks but aeolian abration and dust coatings prevent unambiguous interpretation multispectral imaging has resolved four spectral classes of rocks gray and red which occur on different surfaces of the same rocks pink which is probably soil crusts and maroon which occurs as large boulders mostly in the far field rocks are assigned to two spectral trends based on the position of peak reflectance the primary spectral trend contains gray red and pink rocks maroon rocks constitute the secondary spectral trend the spatial pattern of spectral variations observed is oriented along the prevailing wind direction the primary spectral trend arises from thin ferric coatings of aeolian dust on darker rocks the secondary spectral trend is apparently due to coating by a different mineral probably maghemite or ferrihydrite a chronology based on rock spectra suggests that rounded maroon boulders constitute the oldest petrologic unit a flood deposit succeeded by smaller cobbles possibly deposited by impact and followed by aeolian erosion and deposition nearly linear chemical trends in alpha proton x ray spectrometer rock compositions are interpreted as mixing lines between rock and adhering dust a conclusion supported by a correlation between sulfur abundance and red blue spectral ratio extrapolations of regression lines to zero sulfur give the composition of a presumed igneous rock the chemistry and normative mineralogy of the sulfur free rock resemble common terrestrial volcanic rocks and its classification corresponds to andesite igneous rocks of this composition may occur with clastic sedimentary rocks or impact melts and breccias however the spectral mottling expected on conglomerates or breccias is not observed in any apxs analyzed rocks interpretation of the rocks as andesites is complicated by absence of a 1 m pyroxene absorption band plausible explanations include impact glass band masking by magnetite or presence of calcium and iron rich pyroxenes and olivine which push the absorption band minimum past the imager s spectral range the inferred andesitic composition is most similar to terrestrial anorogenic icelandites formed by fractionation of tholeiitic basaltic magmas early melting of a relatively primitive martian mantle could produce an appropriate parent magma supporting the ancient age of pathfinder rocks inferred from their incorporation in hesperian flood deposits although rocks of andesitic composition at the pathfinder site may represent samples of ancient martian crust inferences drawn about a necessary role for water or plate tectonics in their petrogenesis are probably unwarranted

equatorial and midlatitude distribution of chlorine measured by mars odyssey grs 1 the 2001 mars odyssey gamma ray spectrometer grs has made the first measurement of the equatorial and midlatitude distribution of cl at the near surface of mars a mean concentration value of 0 49 wt cl has been determined from a grand sum of grs spectra collected over the planet excluding high latitude regions cl is significantly enriched within the upper few tens of centimeters of the surface relative to the martian meteorites and estimates for the bulk composition of the planet however cl is not homogeneously distributed and varies by a factor of 4 even after smoothing of data with a 10 arc radius filter several contiguous geographically large 20 regions of high and low cl concentrations are present in particular a region centered over the medusae fossae formation west of tharsis shows significantly elevated cl a large region north of syrtis major extending into utopia planitia in the northern hemisphere shows the lowest cl concentrations on the basis of hierarchical multivariate correlations cl is positively associated with h while negatively associated with si and thermal inertia we discuss four possible geologic mechanisms aeolian volcanic aqueous and hydrothermal that may have affected the cl distribution seen by grs while some of the distribution may be due to cl rich dust deposits transported by aeolian processes this mechanism does not appear to account for all of the observed variability we propose that reactions with volcanic exhalations may have been important for enriching cl in medusae fossae formation material

crustal heat production and the thermal evolution of mars the chemical composition of soils and rocks from the pathfinder site and phobos 2 orbital gamma ray spectroscopy indicate that the martian crust has a bulk composition equivalent to large ion lithophile lil and heat producing element k th u enriched basalt with a potassium content of about 0 5 a variety of radiogenic isotope data also suggest that separation of lil enriched crust and depleted mantle reservoirs took place very early in martian history 4 0 ga accordingly if the enriched martian crust is 30 km thick it is likely that a large fraction up to at least 50 of the heat producing elements in mars was transferred into the crust very early in the planet s history this would greatly diminish the possibility of early widespread melting of the martian mantle

geochemical diversity in first rocks examined by the curiosity rover in gale crater evidence for and significance of an alkali and volatile rich igneous source the first four rocks examined by the mars science laboratory alpha particle x ray spectrometer indicate that curiosity landed in a lithologically diverse region of mars these rocks collectively dubbed the bradbury assemblage were studied along an eastward traverse sols 46 102 compositions range from na and al rich mugearite jake matijevic to fe mg and zn rich alkali rich basalt hawaiite bathurst inlet and span nearly the entire range in feo and mno of the data sets from previous martian missions and martian meteorites the bradbury assemblage is also enriched in k and moderately volatile metals zn and ge these elements do not correlate with cl or s suggesting that they are associated with the rocks themselves and not with salt rich coatings three out of the four bradbury rocks plot along a line in elemental variation diagrams suggesting mixing between al rich and fe rich components chemcam analyses give insight to their degree of chemical heterogeneity and grain size variations in trace elements detected by chemcam suggest chemical weathering li and concentration in mineral phases e g rb and sr in feldspars we interpret the bradbury assemblage to be broadly volcanic and or volcaniclastic derived either from near the gale crater rim and transported by the peace vallis fan network or from a local volcanic source within gale crater high fe and fe mn in et then likely reflect secondary precipitation of fe 3 oxides as a cement or rind the k rich signature of the bradbury assemblage if igneous in origin may have formed by small degrees of partial melting of metasomatized mantle

a review of the handheld x ray fluorescence spectrometer as a tool for field geologic investigations on earth and in planetary surface exploration x ray fluorescence xrf spectroscopy is a well established and commonly used technique in obtaining diagnostic compositional data on geological samples recently developments in x ray tube and detector technologies have resulted in miniaturized field portable instruments that enable new applications both in and out of standard laboratory settings these applications however have not been extensively applied to geologic field campaigns this study investigates the feasibility of using developing handheld xrf hxrf technology to enhance terrestrial field geology with potential applications in planetary surface exploration missions we demonstrate that the hxrf is quite stable providing reliable and accurate data continuously over a several year period additionally sample preparation is proved to have a marked effect on the strategy for collecting and assimilating hxrf data while the hxrf is capable of obtaining data that are comparable to laboratory xrf analysis for several geologically important elements such as si ca ti and k the instrument is unable to detect other elements such as mg and na reliably while this limits the use of the hxrf especially when compared to laboratory xrf techniques the hxrf is still capable of providing the field user with significantly improved contextual awareness of a field site and more work is needed to fully evaluate the potential of this instrument in more complex geologic environments

petrogenesis of high phosphorous wishstone class rocks in gusev crater mars 1 the spirit rover has analyzed a wide variety of alkaline volcanic rocks in gusev crater among them are wishstone class tephrites with unusually high p2o5 5 wt abundances to obtain the chemical compositions of rock interiors we extrapolated a trend defined by brushed and abraded surface compositions the extrapolation analysis suggests the high p2o5 tephrite signature is not attributable to secondary aqueous alteration but represents an igneous rock composition assessment of the compositional trend also suggests that merrillite is the phosphate mineral in wishstone class modified cipw norm calculations using merrillite instead of apatite show that wishstone class rocks are silica saturated hypersthene olivine normative and alkaline the high p2o5 whole rock compositions plot above solubility curves of merrillite in a diagram of p2o5 versus aluminosity suggesting that mechanical admixture of merrillite is required a source supplying merrillite cannot be a common silicate magma instead it could be a carbonatitic melt or a highly fractionated residual melt jotunite after anorthosite crystallization comparison with earth analogs suggests that the wishstone class is akin to alkaline basalts in the eastern snake river plain with regard to its chemistry texture and geologic context these alkaline basalts are interpreted to originate from mantle metasomatized by co2 fluids and highly alkaline melts in the wake of the yellowstone hot spot thus we propose that the wishstone class represents a silica saturated alkaline suite that has mechanically mixed xenocrystic merrillites probably during explosive volcanic eruption the merrillites crystallized from carbonate rich magma produced by melting of a co2 bearing martian mantle

absence of strain accumulation in the western shumagin segment of the alaska subduction zone gps measurements in the western shumagin segment of the alaska subduction zone show no significant strain the elastic dislocation model that best fits the data has the entire plate interface slipping freely the simplest explanation is that steady slip at the plate convergence rate is occurring on the entire plate interface although we cannot rule out the existence of a shallow locked patch close to the trench large enough to generate a m 7 earthquake the 99 confidence upper bound on the down dip width of the locked patch is 55 km assuming the trench is the the updip limit of the locked zone unless there is significant temporal variability in the locking of the plate interface or viscoelastic effects from a past earthquake the shumagin segment cannot by itself release enough moment to generate a great m 8 earthquake

evidence for perchlorates and the origin of chlorinated hydrocarbons detected by sam at the rocknest aeolian deposit in gale crater evidence for perchlorates at rocknest

strain accumulation in the shumagin seismic gap alaska strain accumulation in the shumagin seismic gap was estimated from repeated trilateration surveys made between 1980 and 1985 the measured rate of shear strain accumulation 0 01 0 03 rad a was an order of magnitude less than the rate 0 18 rad a predicted for seismic subduction the absence of measurable shear strain accumulation in the shumagin islands suggests that the main thrust zone there may not be locked but rather may slip stably if this is indeed the case the probability of a great shallow thrust earthquake in the shumagin gap is greatly diminished a moderate earthquake mb 6 0 occurred at the seaward end of the trilateration network 4 months after the most recent survey however no significant anomalies that could be interpreted as precursors were detected in that survey

incipient hydrothermal alteration of basalts and the origin of martian soil the martian soil is a fine grained regolith that is chemically basaltic in character with evidence for both gains and losses of volatile and mobile elements compared to martian basalt compositions these chemical fractionations provide clues to geochemical processes on the surface of mars geochemical processes contributing to the soil proposed in the past include the chemical and mechanical breakdown of rocks under surface conditions the addition of volcanic aerosols containing s and cl compounds and the alteration of basaltic glass to palagonite our studies of terrestrial analogs suggest that hydrothermal alteration processes involving impact craters and volcanism could also contribute to the major element trends observed in martian soil data from viking pathfinder and the current mer missions consistently show that relative to basaltic martian meteorite compositions the major element compositions of the soils are 1 depleted in the fluid mobile element calcium 2 generally similar or somewhat enriched in iron oxide and magnesium but mgo depleted compared to gusev rocks 3 locally variable in potassium 4 possibly poorer in aluminum and 6 very enriched in chlorine and sulfur the major element trends aside from the cl and s enrichment could be explained by the formation or addition of palagonite according to mcsween and keil 2000 but the missing cao remains a problem the chlorine and sulfur are probably derived from other processes such as volcanic aerosols and hydrothermal fluids mcsween and keil 2000 also argued that hydrothermal alteration of basalts produce alteration trends that are inconsistent with the mars soil but this study concludes otherwise we have used quantitative mass balance mixing models to investigate possible models involving mixtures of basaltic compositions with different types of alteration materials including palagonite we show that the mars soil composition can be matched with a combination of unweathered basaltic martian meteorites with basaltic feo rich cao poor alteration products palagonite is a possible but not a necessary component of successful model mixtures the hydrothermal alteration materials that form successful model mixtures are formed in low temperature low water rock ratio environments and they can reproduce the required geochemical trends because they are poorer in cao but not in feo compared to their respective protoliths these results argue that material altered by hydrothermal processes could be a plausible component of the soil and that removal of cao from the soil into some undiscovered reservoir after its formation is not required the current soil on mars therefore did not have to undergo an episode of in situ aqueous alteration but could represent a sink for materials that experienced aqueous processes in a different setting before erosion to form the soil the soil can also represent a sink for mobile elements e g s cl and br derived from other sources such as volcanic aerosols and hydrothermal fluids

radar subsurface mapping of the polar layered deposits on mars 1 determining the three dimensional 3 d structure of the martian polar caps is fundamental to understanding their hydrologic history dynamic behavior past climatic changes and the underlying lithosphere and radar sounding is the most promising technique to do so we model the dielectric profile of the martian polar layered deposits pld apply it to a 1 d electromagnetic plane wave propagation model and calculate the relative strength of radar reflections produced by layering within these deposits variations in dust fraction with depth derive from albedo profiles of a northern polar trough and a radiative transfer model detection of the fine scale layering present in the polar deposits with sharad is likely under a wide range of possible dielectric properties of the ice and silicate inclusions as long as minimum inclusion volumetric fractions are larger than 10 3 our models indicate also that stratigraphic mapping of the pld is feasible with a vertical resolution of 20 m under ideal conditions penetration depths depend greatly on the dielectric properties of silicate inclusions reaching at least 250 m for ice rich in highly conductive altered basaltic dust to at least 2 km for weakly conducting silicate inclusions because of the wide parameter space and unconstrained composition interpretation of polar radar data will be best accomplished in conjunction with updated thermal models and other data sets such as the recently published results from orbital infrared remote sensing that impose limits on ice grain size and dust

the composition and thickness of the crust of mars estimated from rare earth elements and neodymium isotopic compositions of martian meteorites isotopic and trace element compositions of martian meteorites show that early differentiation of mars produced complementary crustal and mantle reservoirs that were sampled by later magmatic events this paper describes a mass balance model that estimates the rare earth element ree content and thickness of the crust of mars from the compositions of shergottites the diverse ree and nd isotopic compositions of shergottites are most easily explained by variable addition of light rare earth element lree enriched crust to basaltic magmas derived from lree depleted mantle source regions antarctic shergottites eet 79001 alh 77005 lew 88516 and que 94201 all have strongly lree depleted patterns and positive initial 143nd isotopic compositions which is consistent with the generation of these magmas from depleted mantle sources and little or no interaction with enriched crust in contrast shergotty and zagami have negative initial 143nd isotopic compositions and less pronounced depletions of the lree which have been explained by incorporation of enriched crustal components into mantle derived magmas jones 1989 longhi 1991 borg et al 1997 the mass balance model presented here derives the ree composition of the crustal component in shergotty by assuming it represents a mixture between a mantle derived magma similar in composition to eet 79001a and a lree enriched crustal component the amount of crust in shergotty is constrained by mixing relations based on nd isotopic compositions which allows the ree pattern of the crustal component to be calculated by mass balance the effectiveness of this model is demonstrated by the successful recovery of important characteristics of the earth s continental crust from terrestrial columbia river basalts self consistent results for nd isotopic compositions and ree abundances are obtained if shergotty contains 10 30 of lree enriched crust with 10 ppm nd this crustal component would have moderately enriched lree sm nd 0 25 0 27 147sm 144nd 0 15 0 17 la yb 2 7 3 8 relatively unfractionated heavy rare earth elements hree and no eu anomaly crust with these characteristics can be produced from a primitive lherzolitic martian mantle by modest amounts 2 8 of partial melting and it would have a globally averaged thickness of 45 km which is consistent with geophysical estimates mars may serve as a laboratory to investigate planetary differentiation by extraction of a primary basaltic crust

slip history and dynamic implications of the 1999 chi chi taiwan earthquake we investigate the rupture process of the 1999 chi chi taiwan earthquake using extensive near source observations including three component velocity waveforms at 36 strong motion stations and 119 gps measurements a three plane fault geometry derived from our previous inversion using only static data ji et al 2001 is applied the slip amplitude rake angle rupture initiation time and risetime function are inverted simultaneously with a recently developed finite fault inverse method that combines a wavelet transform approach with a simulated annealing algorithm ji et al 2002b the inversion results are validated by the forward prediction of an independent data set the teleseismic p and sh ground velocities with notable agreement the results show that the total seismic moment release of this earthquake is 2 7 10 20 n m and that most of the slip occurred in a triangular shaped asperity involving two fault segments which is consistent with our previous static inversion the rupture front propagates with an average rupture velocity of 2 0 km s 1 and the average slip duration risetime is 7 2 s several interesting observations related to the temporal evolution of the chi chi earthquake are also investigated including 1 the strong effect of the sinuous fault plane of the chelungpu fault on spatial and temporal variations in slip history 2 the intersection of fault 1 and fault 2 not being a strong impediment to the rupture propagation and 3 the observation that the peak slip velocity near the surface is in general higher than on the deeper portion of the fault plane as predicted by dynamic modeling