hypocentre determination offshore of eastern taiwan using the maximum intersection method summary the maximum intersection maxi method which derives from the master station method msm determines within a 3 d velocity model the absolute hypocentral location based on observed arrival times first the spatial node that better satisfies the arrival time differences computed at all station pairs plus or minus an error tolerance value in seconds is defined as the preliminary hypocentral solution pred second because pred depends neither on the estimate of origin time nor on the residual root mean square rms residual outliers are objectively detected and cleaned out from the original data set without any iterative process or weighting third a statistical minimization residual rms is conducted in a small domain around the pred node which results in a unique final solution the maxi method is applied to the determination of earthquake hypocentres with the proper station correction terms in the southernmost extremity of the ryukyu subduction zone where several dense seismic clusters occur near the seismogenic plate interface the location of earthquakes recorded at both the taiwanese and japanese networks is obtained for about a thousand events between 1992 and 1997 the process uses a detailed 3 d velocity model based on multiple geophysical data sources obtained in the junction area between subduction and collision east of taiwan the earthquake clustering and the significant drop in residual statistics 1 20 0 80 and 0 35 s for taiwanese catalogue msm and maxim solutions respectively indicate the accuracy of the method which can be used to routinely determine absolute hypocentre location based on observed arrival times

a new data reduction approach for the clementine nir data set application to aristillus aristarchus and kepler the clementine spacecraft launched in january 1994 has performed a nearly global surface mapping of the moon in eleven broad spectral bands at a resolution of 200 m the uv visible uv vis camera performed observations in five bands ranging from 0 415 to 1 0 m while the near infrared camera nir acquired data in six spectral bands ranging from 1 1 to 2 78 m uv vis images are calibrated to 4 the calibrated nir data set is yet to be finalized due to instrumental problems independently of the calibration effort for the full data set which is under the responsibility of the pi team we present here the first results of a heuristic approach to extract mineralogical information from raw images in regions of particular interest we processed images of craters aristillus aristarchus and kepler we computed band ratios using 0 75 0 9 0 95 1 0 1 1 1 25 1 5 and 2 0 m images to map the compositional heterogeneity and to discriminate between pyroxene olivine or feldspar rich areas absolute reflectance spectra have been derived using telescopic spectra as ground truth high orthopyroxene and clinopyroxene contents have been detected and spatially mapped on aristillus our results are in good agreement with previous studies in the case of aristarchus and show additional details due to the improved registration two regions exhibit spectra consistent with a high proportion of olivine with 25 pyroxene the rim of kepler exhibits a strong feature at 2 m correlated with the 1 m feature suggesting either a high orthopyroxene content or a very immature soil our method could be of interest for further investigations of the lunar surface using clementine nir data

seismicity and active tectonic processes in the ultra slow spreading lena trough arctic ocean summary with its remote location in the ice covered fram strait lena trough is a poorly known segment of the global mid ocean ridge system it is a prominent member of the ultra slow spreading mid ocean ridges but its spreading mechanisms are not well understood we relocalized teleseismically recorded earthquakes from the past five decades to identify tectonic processes in lena trough and the adjacent spitsbergen fracture zone fz during two cruises with rv polarstern in 2008 and 2009 we deployed seismic arrays on ice floes to record the local seismicity of lena trough we could identify and localize microseismic events which we assume to be present in the entire rift valley in contrast our relocalization of teleseismically recorded earthquakes shows an asymmetric epicentre distribution along lena trough with earthquakes occurring predominately along the western valley flanks of lena trough in 2009 february march several high magnitude earthquakes peaking in an mb 6 6 event occurred in an outside corner setting of the spitsbergen fz this is the strongest earthquake which has ever been recorded in fram strait and its location at the outside corner high of the ultra slow spreading ridge is exceptional comparing the seismicity with the magnetic anomalies and high resolution multibeam bathymetry we divide lena trough in a symmetrically spreading northern part and an asymmetrically spreading southern part south of the south lena fz we propose that a complex interaction between the former de geer megashear zone which separated greenland from svalbard starting at late mesozoic early cenozoic times and the developing rift in the southern lena trough resulted an increasing eastward dislocation towards the spitsbergen fz between older spreading axes and the recent active spreading axis which we believe to be located west of the bathymetric rift valley flanks in a wide extensional plain

terrestrial mantle siderophiles and the lunar impact record a simple analytical fit to the lunar cratering record scaled from final to transient crater diameters then to impactor masses implies a total mass 1 0 1020kg incident on the moon subsequent to the solidification of the lunar crust 4 4 gyr ago about half this mass would be retained and a comparable lunar mass would be eroded these results are in good agreement with geochemical estimates of the meteoritic component mixed into the lunar crust which give 0 4 1 5 1020 kg gravitationally scaling to earth and taking account of the statistical probability that the largest impactors incident on earth were more massive than the largest incident on the moon gives an estimate of 1 5 1022 kg of material accumulated by earth subsequent to 4 4 gyr ago this result is in excellent accord with geochemical estimates of post core formation meteoritic input these estimates based on abundances of highly siderophile elements in the terrestrial mantle lie in the range 1 4 1022 kg the significant result is the approximate agreement of the lunar cratering record scaling with both lunar and terrestrial geochemical constraints numerous uncertainties render exact comparisons pointless nevertheless the close agreement suggests the model developed here may credibly be used to estimate exogenous volatile and prebiotic organic delivery

lithological mapping of central part of mare moscoviense using chandrayaan 1 hyperspectral imager hysi data abstract we conducted spectral analysis of central region of the mare moscoviense area on the far side of the moon using the hyperspectral imager hysi data from the chandrayaan 1 mission in an effort to identify and map the major lithological units present in the area various spectral band parameters namely band curvature band tilt and band strength have been used for lithological discrimination based on the nature of the spectral profile these band parameters essentially measure the shape position and strength of the absorption feature near 1000 nm arising due to electronic transition of fe 2 in crystallographic sites of major rock forming silicates spectral band parameters have been used for generating rock type composite image based on spectral studies and rock type composite image as obtained using band parameters five major compositional units have been identified highland basin soils ancient mature mare highland contaminated mare buried unit with abundant low ca pyroxene lcp and youngest mare unit in the present study a multispectral approach in the form of spectral band parameters has been adopted for analysing the hysi hyperspectral data from chandrayaan 1 mission present study clearly shows that the spectral band parameters obtained using selected hysi channels could efficiently be used to discriminate and delineate the major litho units present across the central part of mare moscoviense and the same approach can thus be used for lithological mapping of other parts of lunar surface using hysi data

teleseismic earthquake swarms at ultraslow spreading ridges indicator for dyke intrusions earthquakes at mid ocean ridges reflect the active magmatic and tectonic processes that form new oceanic crust studies of large earthquakes observed on land and smaller earthquakes observed locally or regionally by ocean bottom seismometers or autonomous underwater hydrophones have greatly contributed to our understanding of the structure and active spreading processes at the mid ocean ridges of the atlantic and pacific ocean opening with velocities in excess of 25 mm yr 1 at spreading rates below 20 mm yr 1 full rate the appearance and the accretion processes of mid ocean ridges undergo fundamental changes as the melt supply is drastically reduced the active spreading processes at these so called ultraslow spreading ridges are still poorly known as the main representatives the arctic ridge system and the southwest indian ridge are poorly accessible and neither autonomous underwater hydrophone nor ocean bottom seismometer records of local seismicity are available in an attempt to compare on a large scale the accretion style of ultraslow spreading ridge sections i analyse the teleseismically recorded seismicity in 11 sections of the arctic ridge system and the southwest indian ridge spanning altogether 7200 km epicentres located within 30 35 km of the rift axis were extracted from the catalogue of the international seismological centre for a time period of 35 yr on the basis of a single link cluster analysis i identified 27 swarms with eight or more events these swarms occur almost exclusively at centres of focussed magmatism suggesting that the swarms are probably initiated by magmatism normal faults along several tens of kilometres surrounding the volcanic centres react in large earthquakes m 5 to dyke emplacement the routine generation of large earthquakes in the cold brittle lithosphere of ultraslow spreading ridges makes the teleseismic record a valuable means to study ultraslow accretion processes and to provide a global framework for the interpretation of the limited local and regional seismicity studies

the june july 1993 seismo acoustic event at coaxial segment juan de fuca ridge evidence for a lateral dike injection the coaxial segment juan de fuca ridge was the site of an intense swarm of earthquakes that began at 21 43 gmt on june 26 1993 julian day 177 the swarm started near 46 15 n and migrated northward over the next 40 hours to 46 36 n where the majority of 676 events occurred during the following 3 weeks of activity the earthquakes propagated nne at a velocity of 0 3 0 1 m s 1 from the southern to northern swarm sites the activity went undetected by land based seismic networks along the oregon and washington coasts suggesting that the earthquakes were all m 4 0 the character of this earthquake swarm is very similar to dike injections observed at krafla and kilauea volcanoes the earthquake activity and subsequent migration probably represent a lateral dike injection into faults and fissures comprising the coaxial segment the reservoir acting as the dike s source likely resides beneath or to the south of the initial southern swarm of earthquakes the large magma supply at axial volcano cannot be ruled out as the source for the coaxial dike even though axial volcano exhibited no earthquake activity related to the coaxial swarm the t wave earthquake swarm reported here is the first deep ocean observation of volcanic seismicity associated with what most likely was a mid ocean ridge dike injection event

volcanism on mercury evidence from the first messenger flyby for extrusive and explosive activity and the volcanic origin of plains the first messenger flyby of mercury obtained images of 21 of the surface not seen by mariner 10 including the center and western half of the caloris basin and regions near the terminator that show details of the nature of smooth and intercrater plains these new data have helped to address and resolve a series of longstanding questions on the existence and nature of volcanism on mercury and the distribution of volcanic materials data from the mercury dual imaging system mdis on the messenger spacecraft have shown the following 1 numerous volcanic vents in the form of irregularly shaped rimless depressions are concentrated around the interior edge of the caloris basin 2 these vents appear to be sources for effusive volcanism that in one case built a shield in excess of 100 km in diameter and in some cases formed bright haloes around the vents that are interpreted to represent pyroclastic eruptions 3 lobate margins of plains units seen previously in mariner 10 data are documented in messenger images with more clarity and are often distinctive in morphology and color properties supporting the interpretation that these features are the edges of lava flow units 4 the interior of the caloris basin is filled with plains units spectrally distinctive from the rim deposits and comparison with the lunar imbrium basin and superposed impact crater stratigraphy provide evidence that these units are volcanic in origin detailed differences in the mineralogy of lava flow units so prominent in imbrium are not seen in the caloris interior 5 some of the smooth plains surrounding the exterior of the caloris basin show distinct differences in color and morphological properties supporting a volcanic origin 6 some smooth and intercrater plains units distant from the caloris basin show evidence of flooding and embayment relations unrelated to caloris ejecta emplacement local and regional geological and color relationships support a volcanic origin for these plains 7 large impact craters show a sequence of embayment of interior floor and exterior ejecta deposits that supports a volcanic origin for the embayment and filling processes 8 crater embayment and flooding relationships in selected areas suggest volcanic plains thicknesses of many hundreds of meters and local thicknesses inside impact craters of up to several kilometers 9 impact crater size frequency distributions for caloris exterior deposits including the facies of the caloris group and relatively high and low albedo smooth plains show that they are younger than plains interior to caloris and thus must be dominantly the product of post caloris volcanism these new data provide evidence that supports and confirms earlier hypotheses from mariner 10 data that volcanism was important in shaping the surface of mercury the emerging picture of the volcanic style of mercury is similar to that of the moon the other small one plate planetary body there are no major shield volcanoes e g comparable to tharsis montes on mars shallow magma reservoirs are rare and there is little evidence for surface deformation or long lived volcanic sources related to sites of upwelling mantle the close association of volcanic plains and surface deformation features suggests that future observations and analyses can help document the relation between the volcanic flux and the evolving state and magnitude of stress in the lithosphere of mercury

the manicouagan impact structure an analysis of its original dimensions and form manicouagan quebec 51 23 n 68 42 w is the most intensively studied large complex terrestrial impact structure in a predominantly crystalline target the ground truth data available from manicouagan have considerable potential for interpreting the subsurface characteristics of lunar impact structures of comparable morphology and size two contrasting hypotheses however exist for the preerosional form of manicouagan 1 a multi ring basin with a final diameter of 75 km and a transient cavity diameter of 30 45 km floran and dence 1976 and 2 an endogenically modified peak ring basin with a final diameter of 100 km and a transient cavity diameter of 80 km orphal and schultz 1978 both hypotheses are based largely on topographic data and interpret the prominent 65 km diameter annular moat as a graben like feature formed either 1 by collapse of the outer slope of the transient cavity rim or 2 by uplift of the final crater floor through post impact intrusive activity the present analysis suggests that this annular moat is primarily an erosional feature and that the original form of the impact structure cannot be determined unequivocally on the basis of present topography if all the available topographic geologic and geophysical data are considered however then an internally consistent interpretation of original dimensions is possible the distribution of shock deformation effects in the basement rocks of the present crater floor suggests an original transient cavity diameter of 60 km the 55 km diameter impact melt covered inner plateau provides a minimum estimate for the diameter of the final floor of the crater and the annular moat with its outliers of downdropped ordovician limestone is interpreted as marking the contact between the floor and the innermost slump blocks of the final rim there is no compelling evidence to regard the annular moat as a graben by analogy with fresh lunar and mercurian structures a floor width of 55 km suggests a final rim diameter of 86 95 km this is consistent with the topographic data from outside the annular moat and with the residual peripheral gravity low which suggests a final rim diameter of 85 95 km due to erosion it is difficult to assign manicouagan to a particular morphological class of impact structure but on the basis of the available data it is most likely that the preerosional form was that of a central peak crater or possibly a peak ring basin at the time of its formation manicouagan may have been dimensionally and possibly morphologically similar to the 96 km diameter lunar crater copernicus

assessment of earthquake locations in 3 d deterministic velocity models a case study from the altotiberina near fault observatory italy the accuracy of earthquake locations and their correspondence with subsurface geology depends strongly on the accuracy of the available seismic velocity model most modern methods to construct a velocity model for earthquake location are based on the inversion of passive source seismological data another approach is the integration of high resolution geological and geophysical data to construct deterministic velocity models in which earthquake locations can be directly correlated to the geological structures such models have to be kinematically consistent with independent seismological data in order to provide precise hypocenter solutions we present the altotiberina at seismic model a three dimensional velocity model for the upper tiber valley region northern apennines italy constructed by combining 300 km of seismic reflection profiles 6 deep boreholes down to 5 km depth detailed data from geological surveys and direct measurements of p and s wave velocities performed in situ and in laboratory we assess the robustness of the at seismic model by locating 11 713 earthquakes with a non linear global search inversion method and comparing the probabilistic hypocenter solutions to those calculated in three previously published velocity models constructed by inverting passive seismological data only our results demonstrate that the at seismic model is able to provide higher quality hypocenter locations than the previous velocity models earthquake locations are consistent with the subsurface geological structures and show a high degree of spatial correlation with specific lithostratigraphic units suggesting a lithological control on the seismic activity evolution

mapping of spectral variations on the surface of mars from high spectral resolution telescopic images abstract we analyze a high spectral resolution r 200 visible and near infrared 0 44 1 02 m telescopic spectral image of mars to explore surface material variations across the observed face of the planet which is centered on sinus meridiani two independent analysis methods are employed linear mixture modeling and supervised spectral pattern classification with an artificial neural network four endmember type regions are identified with linear mixing further refinement is achieved with the nonlinear neural network classification algorithm separating eight units of geological significance differences in spectral features among the mapped units are characterized among the medium to high albedo units northern lowlands typified by chryse planitia show far less evidence of bulk crystalline hematite than western arabia or any other highland regions the relationship of these bright units to the globally distributed aeolian dust is not yet clear within our image low albedo regions with the most pronounced crystalline hematite signature primarily correlate with the classic dark regions with the exception of acidalia planitia spectral evidence for pyroxenes also correlates well with most of the classic low albedo regions but again acidalia planitia is the major exception significant spectral anomaly is also found in an equatorial region deucalionis regio a companion paper in this issue discusses the soil properties of deucalionis our data and analysis support a compositional trend that is consistent with the global geologic crustal dichotomy of mars namely that the younger northern lowlands contain less bulk crystalline hematite than southern highlands

hypocenter determination in strongly heterogeneous earth models using the shortest path method the shortest path method moser 1991 for the calculation of seismic ray paths and travel times along them can be applied directly in the hypocenter location method proposed by tarantola and valette 1982 it uses the analogy between seismic rays in the earth and shortest paths in networks to construct first arrival times from one point to all other points of a three dimensional grid simultaneously in a fast robust way in earth models of arbitrary complexity doing this for all stations of a seismic array one can find the hypocenter location by minimizing the difference between the observed and the calculated travel times at the stations over the three dimensional grid the concept of probability density functions allows then for a fully nonlinear examination of the uncertainties in the hypocenter location due to uncertainties in the travel time data numerical errors in the calculated travel times and to a limited extent incomplete knowledge about the earth model the result is a three dimensional contour map of regions of equal confidence for the earthquake location the method becomes especially attractive when more than one event recorded by the same array is studied because the calculation of the travel times which is relatively the most time consuming operation has to be done only once the method is applied on the location of an event that occurred on january 18 1989 in israel

local and regional lunar regolith characteristics at reiner gamma formation optical and spectroscopic properties from clementine and earth based data a detailed remote sensing survey of the reiner gamma formation rgf region by means of earth based telescopic and clementine multispectral imaging has been made in the uv visible near infrared domain the spectral mixture analysis reveals the existence of three basic end members relevant for modeling the observed spectral variations in the rgf vicinity these are mb mare background sws southwest swirl and rgs reiner gamma soil the first two components exhibit spectral characteristics consistent with a prevailing contribution of mature mare soils for the surroundings mb and of immature mare crater like soils rgs at rgf the third intermediate albedo component sws has general characteristics of a mature mare soil but with a redder continuum slope the reported observation can be modeled by a mechanism which would remove the finest fraction in the soil particle diameter 45 m at rgf and redistribute it in the vicinity with a laterally variable proportion and local accumulations such as at sws site according to the available set of in situ data documenting variations in the chemical composition in the distribution of particle sizes and in the degree of maturity with depth in the mare regolith the characteristics depicted at rgf are those of a subsurface soil layer from a depth of the order of 0 3 0 8 m in our view the simplest way to account for the whole body of information available from the present work lies in the proposition that in the area of rgf the uppermost layer of the regolith has been optically and mechanically modified by a process involving the fall of fragments of a low density cometary nucleus previously disrupted by tidal interaction in the earth moon system we recognize however that in the present state of knowledge one cannot rule out the hypothesized existence of a zone of seismically modified terrain peripheral to the imbrium or orientale basins just beneath the mare surface that would be the actual source of the rgf magnetic anomaly

evidence of a recent magma dike intrusion at the slow spreading lucky strike segment mid atlantic ridge 1 mid ocean ridge volcanic activity is the fundamental process for creation of ocean crust yet the dynamics of magma emplacement along the slow spreading mid atlantic ridge mar are largely unknown we present acoustical seismological and biological evidence of a magmatic dike intrusion at the lucky strike segment the first detected from the deeper sections 1500 m of the mar the dike caused the largest teleseismic earthquake swarm recorded at lucky strike in 20 years of seismic monitoring and one of the largest ever recorded on the northern mar hydrophone records indicate that the rate of earthquake activity decays in a nontectonic manner and that the onset of the swarm was accompanied by 30 min of broadband 3 hz intrusion tremor suggesting a volcanic origin two submersible investigations of high temperature vents located at the summit of lucky strike seamount 3 months and 1 year after the swarm showed a significant increase in microbial activity and diffuse venting this magmatic episode may represent one form of volcanism along the mar where highly focused pockets of magma are intruded sporadically into the shallow ocean crust beneath long lived discrete volcanic structures recharging preexisting seafloor hydrothermal vents and ecosystems index terms 3035 marine geology and geophysics midocean ridge processes 7280 seismology volcano seismology 8419 8149 tectonophysics planetary tectonics 5475 4259 oceanography general ocean acoustics 9325 information related to geographic region atlantic ocean keywords mid atlantic ridge earthquake hydroacoustic

earthquake location in strongly heterogeneous media traveltime computation methods for strongly heterogeneous 3 d media developed during recent years are well suited for earthquake location we present here a new method based on the traveltime algorithm of podvin lecomte related to the inverse problem formulation of tarantola valette the podvin lecomte method based on the huygens principle is very robust and allows arbitrary surface topography and station placement even for borehole instruments first arrival traveltimes are computed for each of the recording stations using a fine 3 d velocity mesh up to 106 cells on a workstation the traveltime grid allows the use of the tarantola valette formulation which enables a full non linear approach the solution is given as a 3 d probability density function of hypocentre coordinates which accounts for the arrival time measurements as well as a priori information for the location the accuracy of both the arrival time readings and the computation of the theoretical traveltimes this powerful method called 3dgridloc gives the location of the induced seismicity of the gas field of lacq france using 443 520 cells of a 3 d velocity mesh and the observations from nine recording stations one of which is located at the bottom of a 3880 m deep borehole location of synthetic foci as well as more than 500 actual earthquakes shows the real advantages of this new method versus the classical hypo71 a new insight into the induced seismicity is now possible induced seismicity may occur as far away as 10 km from the gas reservoir and involve a much greater volume of rock than expected using earlier locations

anomalous earthquakes associated with nyiragongo volcano observations and potential mechanisms abstract a series of five unusual earthquakes 4 6 m 5 3 has been recently located near nyiragongo volcano d r congo in the western rift valley of the east african rift despite their moderate size these earthquakes do not appear in global seismicity catalogs but were located using long period surface waves primarily recorded on the global seismographic network three of the events occurred in the week following the january 2002 eruption of nyiragongo while the final two occurred in 2003 and 2005 respectively and are not linked to a major eruption at nyiragongo or its neighboring volcano nyamuragira several common techniques were used to investigate the characteristics of these seismic sources in the context of the volcanic activity of the region the frequency content of the five anomalous earthquakes was compared to that from local events found in global catalogs and the newly detected earthquakes were shown to be slow events being greatly depleted in frequencies above 0 1 hz each of the newly detected earthquakes was modeled by a series of forces and by a centroid moment tensor a deviatoric moment tensor was shown to provide a better fit to the data the newly detected earthquakes are highly non double couple in nature each having a large compensated linear vector dipole component of the moment tensor drawing on models based on similar observations from other active volcanoes we propose that the earthquakes are caused by slip on non planar faults beneath the volcano we suggest a mechanism in which these newly detected earthquakes are generated by the collapse of the roof of a shallow magma chamber along an inward dipping cone shaped ring fault diking events which result in magma evacuation from shallow magma chambers could trigger such earthquakes our results provide new constraints on the dynamics of the poorly understood magma system beneath nyiragongo an active volcano that is a significant threat to life and property

microearthquake activity lithospheric structure and deformation modes at an amagmatic ultraslow spreading southwest indian ridge segment while nascent oceanic lithosphere at slow to fast spreading mid ocean ridges mor is relatively well studied much less is known about the lithospheric structure and properties at ultraslow mors here we present microearthquake data from a 1 year ocean bottom seismometer deployment at the amagmatic oblique supersegment of the ultraslow spreading southwest indian ridge a refraction seismic experiment was performed to constrain upper lithosphere p velocities and results were used to construct a 1d velocity model for earthquake location earthquake foci were located individually and subsequently relocated relative to each other to sharpen the image of seismically active structures frequent earthquake activity extends to 31 km beneath the seafloor indicating an exceptionally thick brittle lithosphere and an undulating brittle ductile transition that implies significant variations in the along axis thermal structure of the lithosphere we observe a strong relation between petrology microseismicity distribution and topography along the ridge axis peridotite dominated areas associate with deepest hypocenters vast volumes of lithosphere that deforms aseismically as a consequence of alteration and the deepest axial rift valley areas of basalt exposure correspond to shallower hypocenters shallower and more rugged axial seafloor focal mechanisms deviate from pure extension and are spatially variable earthquakes form an undulating band of background seismicity and do not delineate discrete detachment faults as common on slow spreading ridges instead the seismicity band sharply terminates to the south immediately beneath the rift boundary considering the deep alteration large steep boundary faults might be present but are entirely aseismic

seismic character of volcanic activity at the ultraslow spreading gakkel ridge never before has a volcanic eruption on a slow or ultraslow spreading mid ocean ridge been both observed seismically and confirmed on the seafloor during the first half of 1999 a long lived volcanic spreading event occurred on the ultraslow spreading gakkel ridge in the arctic ocean the seismicity associated with this event was unprecedented in duration and magnitude for a seafloor eruption sonar images from the u s s hawkbill which passed over the area within four months of the start of activity are consistent with the presence of a large recently erupted flow and a volcanic peak directly in the area of seismic activity seismic activity began in mid january and continued vigorously for three months a reduced rate of activity persisted for an additional four months or more in total 252 events were large enough to be recorded on global seismic networks although a limited number of volcanic spreading events have been observed globally the duration and magnitude of the gakkel ridge swarm when compared with volcanic seismicity at ridges spreading at intermediate and fast spreading rates suggest that a negative power law relationship may exist between these parameters and spreading rate fault activation in response to magmatic emplacement appears to have occurred over a broad region suggesting that magma may have been tapped from mantle depths the slow migration of the largest magnitude events along the axis of the rift valley suggests multiple magmatic pulses at depth in combination with bathymetric setting and sidescan sonar confirmation the seismic data for this event have provided a unique look at the scale and character of eruption processes at ultraslow spreading rates

fissure swarms and fracture systems within the western volcanic zone iceland effects of spreading rates abstract the western volcanic zone wvz in iceland is 120 km long and 40 km wide it offers an opportunity to study rift zones in a local ultra slow spreading area close to a hotspot fractures were mapped from aerial photographs and digital elevation models most surface fractures are located in the southern part of the wvz the majority of the fractures have a north northeasterly orientation some deviations occur from this especially in the north part of the wvz fracture orientations are therefore quite uniform in the southern faster spreading part of the wvz but more irregular in the slower spreading northern part this suggests different stress fields in the north part which could be due to the influence of the hreppar microplate and possibly also due to stress fields induced by crustal deformation because of changes in glacial load in the area such glacially induced stress fields may have similar or even more influence than crustal spreading in the slower spreading northern part of the wvz lower fracture density towards the north within the wvz suggests lower frequency of rifting events in the north part in accordance with less spreading in the north as measured by gps geodetic measurements

lunar ferroan anorthosites and mare basalt sources the mixed connection global overturn of a hot gravitationally unstable lunar mantle immediately following the solidification of a magma ocean and essentially complete by 4 4 ga explains several characteristics of lunar petrology lunar mare basalt sources are inferred to be depleted in europium and alumina these depletions are consensually attributed to complementary plagioclase floating from a magma ocean however the connection cannot be so simple and direct in contrast to the mare basalt source parent magma the ferroan anorthosite parent magma was more evolved by virtue of its lower mg fe ratio and ni abundances although less evolved in its poverty of clinopyroxene constituents flat rare earth pattern and lower incompatible element abundances the europium anomaly in mare sources is inferred to be present at 400 km depth too deep to have been directly influenced by plagioclase crystallization massive overturning of the post magma ocean mantle would have carried down clinopyroxene ilmenite and phases containing fractionated rare earths europium anomalies and some heat producing radionuclides these phases contributed to deep mare basalt sources upward moving phases would have been magnesian mafic minerals their immediate melting on pressure release contributed the magnesian suite of plutonic norites and troctolites that post date the anorthosites in the highlands crust

a deep earthquake aftershock sequence and implications for the rupture mechanism of deep earthquakes a distinguishing characteristic of deep earthquakes has been the absence of observable aftershock sequences1 2 here we report the first extensive deep earthquake aftershock sequence to be observed it was recorded by an array of eight broadband seismographs following the 9 march 1994 deep tonga earthquake the aftershocks show a power law decay with time following the main shock as is typical of shallow events most of the well located aftershocks are concentrated along a steeply dipping plane consistent with one of the nodal planes of the main shock mechanism and the mechanisms of three large aftershocks assuming these aftershocks denote the main shock rupture area they define a 50 65 km fault plane extending across the entire width of the active seismic zone and into the surrounding aseismic region the width of the aftershock zone is wider than the expected width of the metastable olivine wedge demonstrating that either the width of the metastable olivine material exceeds previous estimates or the aftershocks are not confined in such a wedge

seismicity within a propagating ice shelf rift the relationship between icequake locations and ice shelf structure iceberg calving is a dominant mass loss mechanism for antarctic ice shelves second only to basal melting an important process involved in calving is the initiation and propagation of through penetrating fractures called rifts however the mechanisms controlling rift propagation remain poorly understood to investigate the mechanics of ice shelf rifting we analyzed seismicity associated with a propagating rift tip on the amery ice shelf using data collected during the austral summers of 2004 2007 we apply a suite of passive seismological techniques including icequake locations back projection and moment tensor inversion we confirm previous results that show ice shelf rifting is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of 1 to 3 h even during periods of quiescence we find significant deformation around the rift tip moment tensors calculated for a subset of the largest icequakes mw 2 0 located near the rift tip show steeply dipping fault planes horizontal or shallowly plunging stress orientations and often have a significant volumetric component they also reveal that much of the observed seismicity is limited to the upper 50 m of the ice shelf this suggests a complex system of deformation that involves the propagating rift the region behind the rift tip and a system of rift transverse crevasses small scale variations in the mechanical structure of the ice shelf especially rift transverse crevasses and accreted marine ice play an important role in modulating the rate and location of seismicity associated with the propagating ice shelf rifts

integration of the clementine uv vis spectral reflectance data and the lunar prospector gamma ray spectrometer data a global scale multielement analysis of the lunar surface using iron titanium and thorium abundances 1 we present a statistical analysis based on a systematic clustering method of a data set integrating the global abundances maps of iron titanium and thorium derived from clementine and lunar prospector homogeneous geological units are compositionally characterized and spatially defined in relation to the major rock types sampled on the moon with the lowest abundances in fe ti and th found on the moon the lunar highlands terrains are quite homogeneous with two major large feldspathic units one being slightly more mafic than the other two distinct regions with unique compositions are unambiguously identified the procellarum kreep terrane pkt and the south pole aitken spa the pkt which includes all the units with th abundances higher than 3 5 ppm kreep rich materials is delimited by an almost continuous ring like unit in particular it includes the western nearside maria except for mare humorum within the pkt a th rich unit corresponding to the highest th concentrations found on the moon may represent kreep volcanic deposits excavated from relatively shallow depth with concentrations in fe ti and th enhanced relative to the surrounding highlands the south pole aitken basin floor represents a large mafic anomaly on the farside suggesting wide deposits of lower crust and possible mantle materials however due to indirect residual latitude effects in the clementine spectral reflectance measurements iron abundances might have been overestimated in spa thus implying that crustal materials rather than mantle materials might represent the dominant contributor to the mafic component exposed on the basin floor

teleseismic location techniques and their application to earthquake clusters in the south central pacific abstract improved methods for single and multiple event hypocenter determinations are developed and applied to the problem of locating earthquake clusters in the south central pacific ocean bayesian statistical methods are used to incorporate a priori information about arrival time variance into the derivation of hypocenter confidence ellipsoids permitting a more realistic calculation of critical parameters in the case where the number of stations is small the diagonal elements of certain projection operators called data importances by minster et al 1974 are used to evaluate network balance the hypocentroid of an event cluster is defined to be the average location of events within the cluster and the deviations of individual hypocenters from the hypocentroid are called cluster vectors the problem of estimating the cluster vectors can be decoupled from the problem of estimating the hypocentroid by a simple but fundamental mathematical result here termed the hypocentroidal decomposition theorem the algorithm based on this analysis appears to have many advantages over other published methods for multiple event location both in its efficient use of available information and its computational speed the application of this method to three clusters of shallow intraplate seismicity in the south central pacific designated regions a b and c demonstrates that the seismicity within each cluster is very localized the rms lengths of the cluster vectors for each group of epicenters are estimated to be only 9 6 and 12 km respectively estimates of the epicentroids are

the distribution of olivine in the crater copernicus we employed multispectral imaging in the visible and near ir at four wavelengths 0 73 0 96 1 45 and 1 99 m of copernicus crater in order to map the distribution of olivine rich pyroxene poor material known previously to occur in the central peak complex we identified three additional portions of the crater to exhibit spectral characteristics similar to those of the central peaks strongly suggesting the presence of material similar to that exposed in the central peaks these areas are a scarp forming a portion of the northern rim of copernicus and two slump blocks in the north wall which may have been derived from the same portion of the ejecta now exposed in the rim scarp these occurrences decrease the minimum allowable depth for this unusual material in the copernicus target site though still represent some of the deepest material exposed by copernicus

analysis and modeling of hydrothermal plume data acquired from the 85 e segment of the gakkel ridge 1 we use data from a ctd plume mapping campaign conducted during the arctic gakkel vents agave expedition in 2007 to constrain the nature of hydrothermal processes on the gakkel ridge at 85 e thermal and redox potential eh anomalies were detected in two discrete depth intervals 2400 2800 m interval 1 and 3000 3800 m interval 2 the spatial and temporal patterns of the signals indicate that the interval 1 anomalies were most likely generated by a single large high temperature t 100 c vent field located on the fault terraces that form the ne axial valley wall in contrast the interval 2 anomalies appear to have been generated by up to 7 spatially distinct vent fields associated with constructional volcanic features on the floor of the axial valley many of which may be sites of diffuse low temperature t 10 c discharge numerical simulations of turbulent plumes rising in a weakly stratified arctic ocean water column indicate that the high temperature field on the axial valley wall has a thermal power of 1 8 gw similar to the trans atlantic geotraverse and rainbow fields in the atlantic ocean whereas the sites on the axial valley floor have values ranging from 5 to 110 mw

spectral analysis of the cerean geological unit crater central peak material as an indicator of subsurface mineral composition abstract the dwarf planet ceres is a heavily cratered rocky body and complex craters with a central peak are widely observed on its surface these types of craters form when a large body impacts the surface generating extreme temperatures and pressures during the impact event a large volume of rock is raised from the subsurface and a central uplift is formed the material composing the central uplift is called crater central peak material ccp and the spectral analysis of such geologic areas can provide information about the composition of ceres subsurface reflectance spectra of 32 ccps acquired by the vir spectrometer on board the nasa dawn spacecraft were analyzed and shows absorption bands located at about 2 7 3 1 3 4 and 4 0 m which are also common on the cerean surface these absorptions are related respectively to mg phyllosilicates nh 4 phyllosilicates and mg ca carbonates the spectral parameters considered in this work are spectral slopes estimated between 1 2 m and 1 9 m band depths at 2 7 3 1 3 4 and 4 0 m and band centers near 4 0 m the ccps spectral parameters were analyzed in conjunction with other cerean parameters such as the estimated depth of excavation of the material composing the central peak in order to search for correlations and information about ceres subsurface central peak material located polewards show stronger 2 7 and 3 1 m band depths with respect to those at the equatorial region suggesting that subsurface deposits closer to poles are probably richer in mg and nh 4 phyllosilicates the 3 4 m spectral feature is also deeper in ccps located at poleward latitudes similar to the phyllosilicates conversely the 4 0 m band does not show this trend with latitude an increase in both 3 1 and 3 4 m band depths with the estimated depth of excavation indicates that the spectral feature at 3 4 m is the result of different contributions from carbonates and nh 4 phyllosilicates as expected however depending on their relative influence the shape of the 3 4 m spectral feature can vary phyllosilicates and carbonates are the resulting products of aqueous alteration of chondritic material and given the increasing abundance of such minerals in particular ammoniated phyllosilicates with depth of excavation it is likely that our investigation involved subsurface layers nearby the boundary between the volatile rich crust and the silicate rich mantle na carbonate is found in the crater central peak material of ernutet haulani and ikapati characterized by an estimated depth of excavation of about 6 9 km where deposits of sodium carbonates could be locally present

evidence of recent volcanic activity on the ultraslow spreading gakkel ridge seafloor spreading is accommodated by volcanic and tectonic processes along the global mid ocean ridge system as spreading rate decreases the influence of volcanism also decreases and it is unknown whether significant volcanism occurs at all at ultraslow spreading rates 1 5 cm yr 1 here we present three dimensional sonar maps of the gakkel ridge earth s slowest spreading mid ocean ridge located in the arctic basin under the arctic ocean ice canopy we acquired this data using hull mounted sonars attached to a nuclear powered submarine the uss hawkbill sidescan data for the ultraslow spreading approximately 1 0 cm yr 1 eastern gakkel ridge depict two young volcanoes covering approximately 720 km2 of an otherwise heavily sedimented axial valley the western volcano coincides with the average location of epicentres for more than 250 teleseismic events detected in 1999 suggesting that an axial eruption was imaged shortly after its occurrence these findings demonstrate that eruptions along the ultraslow spreading gakkel ridge are focused at discrete locations and appear to be more voluminous and occur more frequently than was previously thought

large mineralogically distinct impact melt feature at copernicus crater evidence for retention of compositional heterogeneity 1 despite several lines of evidence for efficient mixing of impact melt in complex craters we document mineralogical heterogeneity in impact melt deposit on a scale of tens of kilometers on the moon in the 96 km diameter copernicus crater this heterogeneity is in the form of a large sinuous impact melt feature on the floor and northern wall that is spectrally distinct from melt in its immediate vicinity this melt feature spanning 30 km in length and 0 5 5 km in width has relatively short wavelength narrow ferrous absorption bands near 900 nm and 2000 nm indicating a more mg rich pyroxene composition as compared to impact melt deposit in the vicinity which is relatively rich in fe ca pyroxenes this distinction provides evidence for the preservation of compositional heterogeneity in impact melt in complex craters on the moon and documents an example of inefficient mixing of melt during the cratering process

hyposat an enhanced routine to locate seismic events a program package called hyposat has been under development that attempts to use the maximum information possible to estimate the hypocenter of a seismic source the standard input parameters can be used arrival times of first and later onsets with backazimuths and ray parameters or apparent velocities in addition travel time differences between different phases observed at the same station can be optionally used the observed standard deviations are used to weight all input parameters and the inversion is done with a generalized matrix inversion code

possible mantle origin of olivine around lunar impact basins detected by selene the composition structure and evolution of the moon s mantle is poorly constrained a global survey of the moon s surface using the spectral profiler onboard the lunar explorer selene kaguya identifies a number of exposures of olivine in concentric regions around lunar craters with a possible mantle origin

seismicity and structure of the 85 e volcanic complex at the ultraslow spreading gakkel ridge from local earthquake tomography accretion mechanisms at ultraslow spreading ridges are still only poorly understood due to difficult survey conditions for seismic experiments at these ridges melts gets focused in distinct magmatic centres with thin crust in between at the 85 e 85 n volcanic complex at gakkel ridge arctic ocean where a recent spreading episode has been observed perennial sea ice cover challenges traditional investigations of seismic structure and microseismicity we used an unusual survey set up to gather seismological data during 16 days in july 2007 using seismometer arrays mounted on ice floes despite only 12 stations the drift of the ice floes over the survey area resulted in a multitude of crossing rays in the rift valley the data included 303 microearthquakes of which 248 events could be confidently located we compiled a 1d velocity model by localizing a subset of these earthquakes with a suite of randomly created velocity models in this model the moho is placed at 7 km depth below seafloor inferring a thick basaltic crust using 124 events which were recorded by at least two arrays we inverted for p wave velocity structure in a local earthquake tomography resolution tests indicate reliable results in the central rift valley illuminating the thermal structure underneath the asgard volcanic chain in the aftermath of its most recent spreading episode our results show microearthquake activity down to 16 km beneath seafloor inferring a cold lithosphere most hypocentres cluster at the centre of the rift valley at the site the asgard volcanic chain this may mean that existing thermal models for this class of ridges have to be refined an area of decreased seismic velocities crosses the rift valley at this location and microearthquake activity is located at its eastern fringe where the velocity gradient is highest we therefore speculate that the reduced velocities may be caused by warm intruded material and that the observed seismicity predominatly reflects the relaxation of thermal stresses following recent intrusion

probabilistic earthquake location in complex three dimensional velocity models application to switzerland 1 we present a new approach to determine precise and reliable hypocenter locations in the tectonically complex region of switzerland a three dimensional 3 d p wave velocity model to be used for earthquake relocation is obtained by simultaneously inverting arrival times of local earthquakes for hypocenter locations and 3 d p wave velocity structure a 3 d p wave velocity model derived from controlled source seismology css is used as an initial reference model the final 3 d model thus combines all available information from both css and local earthquake data the probabilistic nonlinear formulation of the earthquake location problem includes a complete description of location uncertainties and can be used with any kind of velocity model in particular the combination of nonlinear global search algorithms such as the oct tree importance sampling with probabilistic earthquake location provides a fast and reliable tool for earthquake location the comparison of hypocenter locations obtained routinely by the swiss seismological service sed to those relocated in the new 3 d velocity model using a probabilistic approach reveals no systematic shifts but does exhibit large individual shifts in some epicenter locations and focal depths we can attribute these large shifts in part to large uncertainties in the hypocenter location events with a low number of observations 8 and no observation within the critical focal depth distance typically show large location uncertainties improved hypocentral locations particularly for mine blasts and earthquakes whose routine hypocenter locations had been questionable confirm that improved velocity model and probabilistic earthquake location yield more precise and reliable hypocenter locations and associated location uncertainties for switzerland

the distribution of olivine in the crater aristarchus inferred from clementine nir data clementine imaged the moon entirely at eleven wavelengths this paper presents new results obtained on the crater aristarchus using a heuristic method for the calibration of the near infrared nir data set we computed band ratios and we extracted spectra using a telescopic spectrum as reference a new 4 10 km olivine rich area has been identified on the southeastern rim of the crater in addition to a smaller olivine rich area previously reported the olivine to pyroxene ratio exceeds 6 in this new zone this demonstrates the uniqueness of the clementine nir data set in discriminating olivine from pyroxene on the lunar surface with implications for magmatic processes in the lunar mantle and crust

compositional heterogeneity of impact melt rocks at the haughton impact structure canada implications for planetary processes and remote sensing connecting the surface expression of impact crater related lithologies to planetary or regional subsurface compositions requires an understanding of material transport during crater formation here we use imaging spectroscopy of 6 clast rich impact melt rock outcrops within the well preserved 23 5 ma 23 km diameter haughton impact structure canada to determine melt rock composition and spatial heterogeneity we compare results from outcrop to outcrop using clasts groundmass and integrated clast groundmass compositions as tracers of transport during crater fill melt rock formation and cooling supporting laboratory imaging spectroscopy analyses of 91 melt bearing breccia and clast samples and microscopic x ray fluorescence elemental mapping of cut samples paired with spectroscopy of identical surfaces validate outcrop scale lithological determinations results show different clast rich impact melt rock compositions at three sites kilometers apart and an inverse correlation between silica rich sandstone gneiss and phyllosilicate rich shales and gypsum rich rocks that suggests differences in source depth with location in the target stratigraphy gypsum is primarily sourced from 1 km depth while gneiss is from 1 8 km depth sandstone from 1 3 km and shales from 1 6 1 7 km observed heterogeneities likely result from different excavation depths coupled with rapid quenching of the melt due to high content of cool clasts results provide quantitative constraints for numerical models of impact structure formation and give new details on melt rock heterogeneity important in interpreting mission data and planning sample return of impactites particularly for bodies with impacts into sedimentary and volatile bearing targets e g mars and ceres

spectral identification of geological units on the surface of mars related to the presence of silicates from earth based near infrared telescopic charge coupled device imaging during the september 1988 mars opposition the authors obtained new high spatial 100 150 km and spectral delta lambda lambda 1 resolution near ir telescopic charge coupled device images of mars from pic du midi observatory these images allow the association of spectral units with morphologic surface units on mars especially within the dark regions which exhibit much greater variability than the bright regions mineralogical interpretation of the data leads to a global description of the surface state of alteration consistent with the spatial distribution of bright and dark regions with the bright regions being more altered than the dark within the less altered regions fe sup 2 crystal field absorption bands are detected indicative of the presence of mafic minerals opx cpx o1 in agreement with a likely crustal basaltic composition the most conspicuous fe sup 2 absorption features are clearly related to the volcanic regions of the syrtis major shield and hesperia planum unit the strongest observed absorptions due to olivine and clinopyroxene are spatially associated with the restricted central caldera complex of nili meroe paterae within syrtis major and the tyrrhena patera unit within hesperia planum and indicate an ultramafic composition

bulk mineralogy of lunar crater central peaks via thermal infrared spectra from the diviner lunar radiometer a study of the moon s crustal composition at depth 1 the central peaks of lunar impact craters are thought to be composed of uplifted material originating from varying depths of the crustal column the interpreted crystallization sequence of the early lunar magma ocean resulted in an anorthositic upper crust that may become progressively more mafic as it approaches the olivine rich mantle emissivity spectra from the lunar reconnaissance orbiter lro diviner radiometer are used to derive the wavelength location of the christiansen feature cf which is sensitive to bulk silicate mineralogy here a survey of cf values has been performed for the central peaks of 135 complex craters providing global and regional observations of the heterogeneity of crustal compositions crustal thickness models give context to the preimpact depth of the central peak material and its proximity to the crust mantle boundary this study has identified six craters with potentially ultramafic compositions within their central peaks more common occurrences of mafic material found in a wide variety of crater central peaks show a silicate composition roughly similar to mare basalt or an olivine bearing gabbro the range of central peak cf values is similar to that of the rest of the lunar surface bulk mineralogy of the central peak material does not appear to be correlated with its crustal depth of origin suggesting both lateral and vertical heterogeneity in crustal composition rather than a gradual transition from felsic to mafic composition it is likely that the moon s extensive cratering history has continually overturned the original crust erasing any original systematic dependence of composition on depth or proximity to the mantle

characteristics of tectonomagmatic earthquake swarms at the southwest indian ridge between 16 e and 25 e summary the ultraslow spreading southwest indian ridge swir is a prominent end member of the global mid ocean ridge system it spreads with a full rate of 14 16 mm y 1 and shows several segments of various obliquities the western swir consists of the oblique and orthogonal supersegments lying at an epicentral distance of 21 to the vna2 seismic array operated by the german neumayer station in east antarctica the array monitors backazimuth apparent velocity and signal to noise ratio of arriving waves and provides a data set of seismicity from the western swir over several years compared to the global seismological network its detection threshold for earthquakes occurring at the western swir is more than 0 5 mb lower enabling a more comprehensive study of mid ocean ridge processes than the teleseismic earthquake catalogues we identified a total number of 743 earthquakes occurring at the western part of the swir and calculated the body wave magnitudes mb from p wave amplitude picks on the vna2 broad band sensor obtaining a magnitude range from mb 3 18 to mb 5 34 in the years of 2001 2004 2005 and 2008 significantly increased event rates indicated four earthquake swarms with up to 164 events lasting for several days all swarms had strong events registered in the international seismological centre catalogue the relocalization of these events confirmed that all swarms occurred in the same region on the orthogonal supersegment we analysed event and moment release rate histories b values and aftershock decay rates modified omori law finding that the swarms of 2001 2004 and 2005 have similarities in the temporal distribution of seismic moment and event numbers the swarm of 2008 is smaller with high magnitude events at the swarm s onset which represent shear failure on normal faults the application of the modified omori law and the b value show that the earthquakes of the swarms do not follow the classical main shock aftershock pattern of purely tectonic earthquake sequences at the orthogonal supersegment a continuous positive magnetic anomaly along the rift axis a negative mantle bouguer anomaly basalts at the seafloor and potentially volcanic edifices indicate robust magmatic crustal accretion the high resolution bathymetry shows ubiquitous rift parallel ridges with steep flanks towards the rift axis indicating high angle normal faults the high magnitude earthquakes detected teleseismically during the swarms are generated there we interpret that the swarms are caused by magmatic accretion episodes at a suggested volcanic centre of the orthogonal supersegment and that possible magma injection activates the steeply dipping fault planes

global seismicity of 2003 centroid moment tensor solutions for 1087 earthquakes abstract centroid moment tensor cmt solutions are presented for 1087 earthquakes that occurred during 2003 the solutions are obtained using the method of dziewonski et al dziewonski a m chou t a woodward j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 and applying corrections for aspherical earth structure as represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging vol 19 plenum press new york pp 785 797 the model of inelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of inelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms the focal mechanisms of the largest or otherwise significant earthquakes of 2003 are reviewed

copernicus a regional probe of the lunar interior earth based telescopic spectral imaging techniques were used to document the spatial distribution of crater materials within the large lunar crater copernicus at the subkilometer scale on the basis of spectral ultraviolet visible near infrared characteristics the proposed spectral mixing analysis leads to a first order mapping of the impact melt material within the crater olivine was detected not only within the three central peaks but also along a significant portion of the crater rim consideration of an olivine bearing end member in the mixing model emphasizes the overall morphological pattern of the rim and wall terraces in the associated fraction image the identification of widely exposed olivine units supports the idea that the lower crust and possibly the lunar mantle itself are regionally at shallow depth

a sharper view of impact craters from clementine data the ultraviolet visible camera on the clementine spacecraft obtained high spatial resolution images of the moon in five spectral channels impact craters mapped with these multispectral images show a scale of lithologic diversity that varies with crater size and target stratigraphy prominent lithologic variations feldspathic versus basaltic occur within the south wall of copernicus 93 kilometers in diameter on the scale of 1 to 2 kilometers lithologic diversity at tycho 85 kilometers in diameter is less apparent at this scale although the impact melt of these two large craters is remarkably similar in this spectral range the lunar surface within and around the smaller crater giordano bruno 22 kilometers in diameter is largely dominated by the mixing of freshly excavated material with surrounding older soils derived from a generally similar feldspathic lithology

implosive earthquakes at the active accretionary plate boundary in northern iceland non double couple earthquake focal mechanisms imply a mode of seismic failure other than simple shear and movements perpendicular to the fault plane reports of such events are rare and it is controversial whether such failure can occur at depth in the earth following reports of such earthquakes from the hengill and reykjanes volcanic systems on the accretionary plate boundary in iceland1 3 a seismological survey was conducted in the krafla system iceland to explore whether such earthquakes occur elsewhere along the boundary here we report the observation of a mixed suite of focal mechanisms at krafla including shear events explosive tensile crack events such as were observed at hengill and reykjanes and implosive events these last represent cavity collapse and constitute an entirely new class of earthquake the krafla system had undergone a crustal spreading episode4 10 during the decade before the observations were made and our results indicate that immediately after such an episode the accretionary plate boundary is characterized by a heterogeneous stress regime with shear extensional and compressional sources in close juxtaposition

paleomagnetic secular variation at vulcano aeolian islands during the last 135 kyr abstract paleosecular variation psv of the earth s magnetic field during the last 135 kyr has been investigated in lavas scoriae and pyroclastic rocks of vulcano aeolian islands about 1000 samples have been collected at 77 sites from 25 distinct volcanic units whose age is either known from published isotopical data or constrained on the grounds of statigraphical relationships magnetic mineralogy investigation shows that ti magnetite is the main ferromagnetic mineral at most sites secondary magnetization components are either absent or easily removed by stepwise thermal or alternating field demagnetization the mean site direction of the characteristic remanent magnetization is usually well defined since the semi angle of confidence is greater than 5 at only four sites the mean paleomagnetic direction over the last 135 kyr d 9 4 i 53 2 95 3 5 differs from the geocentric axial dipole gad at vulcano d 0 i 57 8 and might be interpreted as the effect of a long term non axial dipolar component the psv record from vulcano agrees well with those from the lacustrine sediments of lago grande di monticchio 100 kyr bp and lago di mezzano 30 kyr bp located in the italian peninsula brandt et al quat sci rev 18 1999 961 976 the inclination anomaly i found at vulcano corresponds to about half of the shallowing observed in the sediments of the two lakes and the declination anomaly d may be used to tie the declination values derived from azimuthally unoriented cores to the geographical reference system in order to find the optimum site to be used as reference for psv studies in italy the angular values of the earth s magnetic field measured at the 113 repeat stations of the italian geomagnetic network coticchia et al boll geod sci aff 40 2001 277 291 have been analyzed with the relocation via pole method noel and batt geophys j int 102 1990 753 756 the viterbo station lat 42 27 n long 12 02 e proved the best since the mean error is 0 3 for both declination and inclination wherever the original psv site is located in italy a preliminary composite psv curve for the last 30 kyr bp is thus proposed merging and relocating to viterbo the data from vulcano and the curve from lago di mezzano corrected for the gad deviation found at vulcano

fracturing and earthquake activity within the prestahnukur fissure swarm in the western volcanic rift zone of iceland the prestahnukur fissure swarm is located within the ultraslowly spreading western volcanic zone in iceland the fissure swarm is characterized by normal faults open fractures and evidence of subglacial fissure eruptions tindars in this study fractures and faults within the prestahnukur fissure swarm were mapped in detail from aerial photographs to determine the extent and activity of the fissure swarm earthquakes during the last 23 years were relocated to map the subsurface fault planes that they delineate the prestahnukur fissure swarm is 40 80 km long and up to 20 km wide most of the areas of the fissure swarm have been glacially eroded although a part of it is covered by postglacial lava flows the fissure swarm includes numerous faults with tens of meters vertical offset within the older glacially eroded part whereas open fractures are found within postglacial lava flows comparison of relocated earthquakes and surface fractures indicates that some of the surface fractures have been activated at depth during the last 23 years although no dike intrusions have been ongoing the existence of tindars nevertheless indicates that dike intrusions and rifting events do occur within the prestahnukur fissure swarm the low fracture density within postglacial lava flows and low density of postglacial eruptive fissures indicate that rifting episodes occur less often than in the faster spreading northern volcanic zone

effusive and explosive volcanism on the ultraslow spreading gakkel ridge 85 e 1 we use high definition seafloor digital imagery and multibeam bathymetric data acquired during the 2007 arctic gakkel vents expedition agave to evaluate the volcanic characteristics of the 85 e segment of the ultraslow spreading gakkel ridge 9 mm yr 1full rate our seafloor imagery reveals that the axial valley is covered by numerous small volume order 1000 m3 lava flows displaying a range of ages and morphologies as well as unconsolidated volcaniclastic deposits with thicknesses up to 10 cm the valley floor contains two prominent volcanic lineaments made up of axis parallel ridges and small cratered volcanic cones the lava flows appear to have erupted from a number of distinct source vents within the 12 15 km wide axial valley only a few of these flows are fresh enough to have potentially erupted during the 1999 seismic swarm at this site and these are associated with the oden and loke volcanic cones we model the widespread volcaniclastic deposits we observed on the seafloor as having been generated by the explosive discharge of co2 that accumulated in possibly deep crustal melt reservoirs the energy released during explosive discharge combined with the buoyant rise of hot fluid lofted fragmented clasts of rapidly cooling magma into the water column and they subsequently settled onto the seafloor as fall deposits surrounding the source vent

locations of mid oceanic earthquakes constrained by seafloor bathymetry 1 earthquakes associated with the creation of new oceanic crust are difficult to locate precisely because they normally occur far away from seismic stations we assume that epicenters of these events can be constrained by seafloor topography and use the harvard centroid moment tensor cmt focal mechanism of an interplate earthquake to relate the event to either a transform fault a parallel in a coordinate system defined by the pole of rotation between two plates or a mid oceanic ridge a meridian using arrival times from the international seismological center isc bulletin we have relocated about 1500 globally distributed events for the time period 1976 1998 the isc locations can be as much as 70 km away from appropriate topographic features our new locations support that large interplate earthquakes occur on or very close to the primary bathymetric features for earthquakes with unknown mechanism or magnitude below the cmt threshold or predate the cmt catalog we use a simultaneous joint hypocenter determination procedure with respect to the already relocated master events jhdme we invert for earthquakes first for the romanche fracture zone rfz and then for a region extending from 30 n to 30 s seismicity agrees well with the main active ridge or transform however a small number of events might be related to the secondary bathymetry features the improved locations for mid oceanic earthquakes based on bathymetry could help improve our understanding of the oceanic crustal and deep earth structure seismic slip and budget constraint along plate boundaries and dynamics of plate tectonics

gruithuisen domes region a candidate for an extended nonmare volcanism unit on the moon small lunar areas known as red spots are thought to represent good candidates for nonmare volcanic units predating or contemporaneous with the period of mare volcanism in this study we present imaging telescopic and orbital clementine multispectral surveys of the gruithuisen region located in the northwestern border of mare imbrium which contains imbrian age domical features of likely viscous volcanic origin with spectral characteristics of red spot areas a rather spectrally homogeneous unit having typical characteristics of red spots is found to coincide with the material within the morphological boundaries of the gruithuisen delta gamma and northwest domes an extended dome like unit is identified spectrally and surrounds and extends to the west and the north of the domes this unit shows spectral characteristics close to those of the domes suggesting the presence of a significant amount of dome material extending many kilometers away from the domes themselves both the spectral characteristics of the dome and the dome like unit are clearly different from those of highlands and the surrounding mare basalts the spectral identification of a widespread dome like unit suggests that the specific style of eruption that is inferred for the formation of the domes i e viscous flows of possible more silicic composition might have occurred on a regional scale in this part of the moon prior to the iridum event about 3 8 gyr ago this volcanic style appears to be more widespread in the early part of lunar history than previously thought

discrimination between maturity and composition of lunar soils from integrated clementine uv visible near infrared data application to the aristarchus plateau the reflectance spectrum of a lunar soil is mainly dominated by the composition and the degree of exposure to space weathering processes such as micrometeorite bombardment and solar wind implantation the spectral alteration effects of space weathering should be removed for accurately investigating the composition of the lunar surface using remote sensing data in this paper we show that the integration of the clementine uv visible uvvis and near infrared nir channels provides an improved evaluation of the spectral alteration the depth of the mafic absorption feature at 0 95 m is also better defined by combining the uvvis and nir data laboratory spectra of lunar soil samples indicate that the continuum slope derived from the 1500 750 nm ratio is closely related to the concentration of fine grained submicroscopic iron is the continuum slope therefore provides an evaluation of the spectral alteration of the surface which can be subtracted from the 1 or 2 m absorption band depths to retrieve compositional information this method has been applied to the aristarchus plateau which exhibits a broad range of mineralogical composition and maturity a nine channel multispectral mosaic of 680 clementine images of the aristarchus plateau has been processed eight telescopic spectra have been used to check the validity of the reduction process for the near infrared bands the 1 m absorption band once corrected for spectral alteration provides an evaluation of the initial feo content in mafic silicates mafic iron lunar soil samples show that it is possible to quantitatively map mafic iron with this technique our results are in good agreement with those obtained using the algorithm of lucey et al 1995 1998a which is based on uvvis bands alone the mafic iron content and total iron content which can be derived from the combined uvvis and nir data sets are less sensitive to local slopes than that derived from lucey et al s method this new method could therefore be useful for investigating areas at middle to high latitudes removing spectral alteration from the 2000 1500 nm ratio also makes possible a better discrimination between olivine and pyroxene within identified mare basalts on the aristarchus plateau

rapid three dimensional hypocentral determination using a master station method a master station ms method is presented in this paper to rapidly determine hypocenters in three dimensional 3 d heterogeneous velocities an equal differential time edt surface is defined as the collection of all spatial points that satisfy the time difference between two arrivals which can be two picks at two stations or two different phase picks at one station the edt surface is independent of the origin time and will contain the hypocenter for an event with j arrivals there are j 1 independent edt surfaces the ms method determines the hypocenter that satisfies two types of constraints to be traversed by most edt surfaces and to yield minimum travel time residual statistics the statistics include both the residual variance and the amplitude of the origin time error the combined use of the edt surfaces and residual statistics allows for a unique determination of the hypocenter and origin time using different types of phase arrivals in principle only three arrivals are minimally required to constrain a unique solution if three different stations are used for a 3 d velocity model the edt surfaces and the residual statistics can be computed efficiently using a reference file created by moser s 1991 ray tracing method an illustration of the ms method is given for 27 small events that occurred in southern california using a p wave velocity model modified from that of magistrale et al 1992 the average misfit between the bulletin hypocenters and the new solutions is 3 8 km if a 3 d velocity model is accurate the ms method can be a viable means of hypocenter determination

discovery of abundant hydrothermal venting on the ultraslow spreading gakkel ridge in the arctic ocean submarine hydrothermal venting along mid ocean ridges is an important contributor to ridge thermal structure and the global distribution of such vents has implications for heat and mass fluxes from the earth s crust and mantle and for the biogeography of vent endemic organisms previous studies have predicted that the incidence of hydrothermal venting would be extremely low on ultraslow spreading ridges ridges with full spreading rates 2 cm yr 1 which make up 25 per cent of the global ridge length and that such vent systems would be hosted in ultramafic in addition to volcanic rocks here we present evidence for active hydrothermal venting on the gakkel ridge which is the slowest spreading 0 6 1 3 cm yr 1 and least explored mid ocean ridge on the basis of water column profiles of light scattering temperature and manganese concentration along 1 100 km of the rift valley we identify hydrothermal plumes dispersing from at least nine to twelve discrete vent sites our discovery of such abundant venting and its apparent localization near volcanic centres requires a reassessment of the geologic conditions that control hydrothermal circulation on ultraslow spreading ridges

thermal and near infrared analyses of central peaks of martian impact craters evidence for a heterogeneous martian crust central peaks of impact craters contain materials exhumed from depth and therefore investigation of these materials provides clues to subsurface geology and mineralogy a global spectral survey of central peaks of martian impact craters between 10 and 200 km diameter was completed using mars odyssey thermal emission imaging system themis data twenty six central peaks with distinctive spectral signatures from surrounding plains were identified and characterized with thermal infrared and visible near infrared data the distribution of spectrally distinct central peaks sdcps shows some degree of regional clustering with most craters found in western noachis terra tyrrhena terra within the northern rim of hellas basin and fewer in the northern lowlands with the exception of four craters in western noachis terra sdcps contain only one spectrally distinct unit at themis resolution 100 m pixel the maximum number of spectrally distinct units observed was three in jones and ostrov craters the western noachis terra sdcps may expose crustal stratigraphies of multiple igneous compositions or impact materials from argyre in the highlands most sdcp units are consistent with enrichments in olivine or pyroxene relative to surrounding plains suggesting olivine and pyroxene basaltic lithologies few are olivine and pyroxene poor no spatial trend in spectrally derived compositions of sdcps was observed three sdcps contain themis signatures consistent with high abundances of phyllosilicates which may contain the most phyllosilicate rich lithologies found in central peak associated materials globally

melt supply variations to a magma poor ultra slow spreading ridge southwest indian ridge 61 to 69 e the southwest indian ridge swir to the east of the melville fracture zone receives anomalously low volumes of melt on average however a small number of ridge segments appear to receive more melt than this regional average we use off axis bathymetry gravity and magnetic data to show that this melt distribution pattern quite distinct from what is observed at the mid atlantic ridge mar has been a characteristic of the easternmost swir for at least the past 10 myr we also show that segments of the easternmost swir are substantially shorter lived than most segments of the mar melt distribution in our swir study area is therefore both more focused and more variable in time than at the mar we tentatively propose a mechanism by which strong and transient melt focusing events could be initiated by a localized increase in the volume of melt supplied by the melting mantle to the base of the axial lithosphere causing thermal thinning of this lithosphere and along axis melt migration these two processes may combine to effectively focus larger volumes of melt toward the center of future thick crust segments rapid melt extraction by dikes that feed large volcanic constructions on the seafloor followed by tectonic disruption of these volcanic constructions by deep reaching faults may then cool the axial lithosphere back to its original thickness and end the melt focusing events the easternmost swir is also characterized by a common departure from isostatic compensation of seafloor topography and by a pronounced asymmetry of crustal thickness and seafloor relief between the two ridge flanks at the faster spreading mar similar characteristics are found near the ends of ridge segments we propose that spreading at the ultra slow swir during periods when the melt supply is low i e most of the time for the easternmost swir is dominated by large offset asymmetric normal faulting with significant flexural uplift of the footwalls faults face either north or south and changes in fault polarity are frequent both along axis and along flow lines i e with time producing large faults and maintaining high uncompensated reliefs require the axial lithosphere to be thick a predictable characteristic for this ultra slow ridge which has an anomalously low regionally averaged melt supply

lunar impact basins and crustal heterogeneity new western limb and far side data from galileo multispectral images of the lunar western limb and far side obtained from galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution the data reveal that the ejecta from the orientale impact basin 900 kilometers in diameter lying outside the cordillera mountains was excavated from the crust not the mantle and covers pre orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts the inside of the far side south pole aitken basin 2000 kilometers in diameter has low albedo red color and a relatively high abundance of iron and magnesium rich materials these features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta

variation with spreading rate of oceanic crustal thickness and geochemistry abstract away from the influence of fracture zones hotspots and marginal basins oceanic crust exhibits remarkably uniform crustal thickness rare earth element concentrations and bulk composition at all but the most slowly spreading ridges at full spreading rates below 15 mm a however all these observed parameters show marked and abrupt changes the seismically determined crustal thicknesses decrease sharply from their average of 7 1 km as do melt thicknesses inferred from rare earth element inversions of basalts bulk element compositions of basalts show an increase in the percentage of na2o and decreases in the feo content and cao al2o3 ratio as the full spreading rate drops below 15 mm a we present a model of the melting beneath oceanic spreading centres which reproduces the observed variations with spreading rate of crustal thickness and the main geochemical changes observed in basalts changes in the volume and composition of melt generated at very slow spreading rates are caused by conductive heat loss from the mantle welling up beneath rifts we model the observed behaviour with normal mantle potential temperatures of 1300 20 c greater crustal thicknesses are generated at the north atlantic spreading centre adjacent to the iceland mantle plume suggesting mantle temperatures about 80 c hotter than normal in this area

comparison of location procedures the kara sea event of 16 august 1997 various location procedures and velocity models are compared for the ml 3 3 kara sea event of 16 august 1997 this event has been the subject of considerable discussion because of its geographical position and the difficulty in obtaining a reliable focal depth estimate a comprehensive data set was extracted by re reading the records from all available stations these readings have then been used in a sequence of location experiments to examine the effect of using different velocity models to describe the travel times of the phases and also to compare the use of a fully nonlinear scheme shakena sambridge and kennett 2001 and a linearized location algorithm hyposat schweitzer 2001 2002 a standard least squares misfit criterion has been used for direct comparisons between the two methods the results confirm both the importance of s wave information in assessing the depth of regional events and the need to apply a reliable velocity model to place the strongest constraints on the location of the event even with only a limited data set but an adequate velocity model it is possible to find the position of the kara sea event close to the most probable locations however there is then no depth resolution reported error ellipses from standard data centers tend to have relatively small error ellipses with the commonly made assumption that the reading errors and the a posteriori residuals have an unbiased normal distribution such inversion results may indicate an unreasonably high resolution and accuracy of the solution the epicenter estimates for the whole data set using the range of different tech niques agree quite well with some overlap of the estimated confidence regions the observed seismic source was most likely an earthquake in the middle or lower crust at about 10 30 km depth

near infrared spectroscopy of probable impact melt from three large lunar highland craters abstract the composition of small areas within three large lunar highland craters are compared using near infrared earth based telescopic data spectra from many areas in the walls and central peaks of the craters indicate the presence of crystalline components which include olivine two types of pyroxene and sometimes fe bearing feldspar spectra from other regions suspected of being impact melt deposits located on the floors and walls of the three craters have remarkably similar yet anomalous features these features are interpreted to indicate the presence of pyroxene fe bearing glass and fe bearing feldspar pyroxene and feldspar are believed to occur primarily in the form of lithic clasts and rapidly recrystallized impact melt the fe bearing glass is interpreted as impact melt glass

seismoacoustic evidence for volcanic activity on the ultraslow spreading gakkel ridge arctic ocean 1 in 1999 a swarm of earthquakes and a lava flow signaled a volcanic eruption at the eastern end of gakkel ridge the slowest spreading ridge worldwide in summer 2001 the multidisciplinary arctic mid ocean ridge expedition studied these ridge processes which are unusual at ultraslow spreading rates as part of these studies we examined the microearthquake activity of the ridge with seismological arrays on ice floes near the volcanic center 85 40 n 85 e active in 1999 we recorded a remarkable swarm of 200 acoustic events the signals consist of two to four explosive phases representing the direct water wave and multiple reflections we localized the acoustic source at the northern rim of the lava flow of 1999 by comparison with similar signals produced at the ocean entry of the kilauea lava we postulate that we made an exceptional observation of the sounds of active submarine volcanism

performance of localization algorithms for teleseismic mid ocean ridge earthquakes the 1999 gakkel ridge earthquake swarm and its geological interpretation in 1999 an unusual earthquake swarm at the 85 e 85 n volcanic centre on the ultraslow spreading gakkel ridge arctic ocean was detected teleseismically the swarm lasted over 9 months and counted 252 events with mb 3 1 it represents the strongest and largest ever recorded mid ocean ridge earthquake swarm and it occurred at a site where spreading rates are only about 10 mm yr 1 we relocated the earthquake swarm comparing the performance of three different localization algorithms 1 the absolute least squares routine hyposat 2 the absolute probabilistic routine nonlinloc and 3 the relative least squares routine mlocate the epicentres as calculated by each algorithm mostly did not agree within their error ellipses thus the choice of location algorithm proved more critical than for example the choice of a local velocity model we compiled a set of well localized events which closely agree in at least two routines mostly mlocate and nonlinloc we conclude that the earthquake swarm of 1999 was related to a spreading episode and shows a complex interplay of tectonic and magmatic events our geological interpretation revealed three phases in swarm activity in the first phase from january 17 up to february 1 fracturing of the crust took place either as a result of or enabling magmatic intrusion seismicity in the second phase from february 2 to april 6 expanded along and across axis it showed signs of magmatic interaction but a clear dyke migration pattern is absent at the beginning of the third phase a distinct break in the event rate suggested a change in the physical process either an adjustment of the stress field to the new regime or a transition to an effusive stage

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

an in depth look at the lunar crater copernicus exposed mineralogy by high resolution near infrared spectroscopy abstract newly acquired sequentially spaced high resolution near infrared spectra across the central section of crater copernicus interior have been analyzed using a range of complementary techniques and indexes we have developed a new interpretative method based on a multiple stage normalization process that appears to both confirm and expand on previous mineralogical estimations and mapping in broad terms the interpreted distribution of the principle mafic species suggests an overall composition of surface materials dominated by calcium poor pyroxenes and minor olivine but with notable exceptions the southern rim displays strong ca rich pyroxene absorption features and five other locations the uppermost northern crater wall opposite rim sections facing the crater floor and the central peak pk1 and at the foot of pk3 show instead strong olivine signatures we also propose impact glass an alternative interpretation to the source of the weak but widespread olivine like spectral signature found in low reflectance samples since it probably represents a major regolith constituent and component in large craters such as copernicus the high quality and performance of the sir 2 data allows for the detection of diagnostic key mineral species even when investigating spectral samples with very subdued absorption features confirming the intrinsic high quality value of the returned data

composition of the lunar highland crust from near infrared spectroscopy near infrared reflectance spectra of the lunar highlands are synthesized to obtain global information about the composition of the lunar near side crust immature exposed surfaces from small fresh craters mountains and massifs and large craters with central peaks are included in a survey of rock types across the lunar near side compositions recognized in these data include anorthosite noritic gabbric and troctolitic mineral assemblages three quarters of the areas studied that represent samples from the upper 1 2 km of lunar crust exhibit noritic compositions with different amounts of pyroxene and or brecciation alteration norites are ubiquitous across the near side and show no spatial clustering associated with any of the major basins in contrast to this noritic megaregolith of the upper crust material representing stratigraphically deeper zones 5 15 km of the lunar crust is dominated by gabbros anorthosites and troctolites with less than a quarter of the areas studied exhibiting a noritic composition the origin of the noritic megaregolith and its relation to deeper crustal material is thus somewhat of an enigma the current limited statistics for areas identified as anorthosites and troctolites are insufficient to derive global spatial distributions gabbroic areas however are notably concentrated in the western hemisphere although incomplete for a global assessment of crustal materials these data demonstrate that the lunar near side crust is clearly mineralogically heterogeneous both laterally and vertically and not well mixed below 1 2 km

location and source mechanism of sound signals at gakkel ridge arctic ocean submarine strombolian activity in the 1999 2001 volcanic episode 1 gakkel ridge is the slowest spreading mid ocean ridge with full spreading rates 10 mm yr in 1999 a teleseismic earthquake swarm signaled the onset of an eruptive episode at 85 e the arctic mid ocean ridge expedition in 2001 detected a hydrothermal event plume and explosive seismoacoustic signals in 2007 the arctic gakkel vents expedition found direct evidence for recent submarine explosive activity on the seafloor at 4000 m the newest data motivated a reassessment of the seismoacoustic events of 2001 we undertake 2 d finite difference wavefield modeling to relocate the source of the signals and investigate the possible source mechanism the explosion sounds likely result from submarine strombolian eruptions with bursting gas bubbles rising from a magma reservoir along a major fault at the southern rift valley wall

nonlinear spectral mixture modeling of lunar multispectral data implications for lateral transport linear and nonlinear spectral mixture models applied to clementine multispectral images of the moon result in roughly similar spatial distributions of end member abundances however there are important differences in the absolute values of the predicted abundances the magnitude of these differences and the implications for understanding geological processes are investigated across a geologic contact between mare and highland in the grimaldi basin on the western nearside of the moon vertical and lateral mass transport due to impact cratering has redistributed mare and highland materials across the contract creating a gradient in composition solutions to linear and nonlinear spectral mixture models for identical spectral end members of mature mare mature highland and fresh crater materials are compared across this simple geologic contact in the grimaldi basin formal estimates of uncertainty in the calculated fractions of the end members are 1 profiles of mare abundance across the contact are extracted and compared quantitatively profiles from the linear mixture models indicate that the geologic contact has an average mare abundance of 60 and the compositional boundary is asymmetric with more mare transported onto the highland side of the contact than highland onto the mare side of the contact in contrast the nonlinear abundance profiles indicate that the geologic contact has an average mare abundance of 50 and the compositional boundary is remarkably symmetric given the expectation that materials will be intimately mixed on the surface of the moon and that the asymmetries implied by the linear model are not consistent with our understanding of lunar surface processes the non linear spectral mixture model is preferred and should be applied whenever quantitative abundance information is required the remarkable symmetry in the compositional gradients across this contact indicates that lateral mass transport dominates over vertical transport at this boundary

bullialdus strengthening the case for lunar plutons although many craters expose material of a composition different from that of the local surroundings bullialdus has excavated material representing three distinct stratigraphic zones that occur in the upper 6 km of crust the top two of which are gabbroic and the deepest of which is noritic this three component stratigraphy at bullialdus provides strong evidence that the lunar crust includes pockets of compositionally layered material reminiscent of mafic layered plutons when combined with previous information on the compositional diversity at other large craters these remote analyses obtained in a geologic context substantially stretigthen the hypothesis suggested from lunar samples that plutons play an integral role in lunar crustal evolution years after the origin of the moon about 4 5 billion years ago once formed this primordial crust appears to have been altered largely by the cumulative flux of large and small bodies impacting the surface at high velocity creating craters basins and a suite of impact debris e g see taylor 1982 wilhelms 1987 an unknown amount of endogenous or reprocessed material was also involved in lunar crustal evolution during the first billion and a half years the most readily recognized of which are the dark mare basalts that fill lowlands dominantly on the near side and account for approximately 17 of the lunar surface head 1976 a growing number of pristine rock fragments thought to represent original crustal material have been identified in the sample collection e g see warren 1985 compositional and petrographic relations among these samples suggest that not only did a major differentiation event occur soon after formation of the moon the magma ocean but that unmapped plutonic activity contributed significantly to early crustal evolution the focus of the following discussion is on related implications of compositional variations of the crust with depth that are inferred from remote compositional analyses obtained in a geologic context although the stratigraphy of the lunar crust has not been sampled directly large impact craters can be used as probes to the interior from a combination of laboratory experiments and studies of terrestrial impact craters it is known that during an impact event material derived from different stratigraphic depths are deposited in a regular pattern around the crater and the depth of material excavated by a crater scales with the diameter of the crater maximum excavation depth is roughly 1 10 the crater diameter and central peaks formed by dynamic rebound represent material from the greatest depth e g see melosh 1989 discussed here are compositional analyses of

olivine rich exposures in the south pole aitken basin abstract the distribution and the geological context of the olivine rich exposures in the south pole aitken spa basin on the moon were investigated based on the spectral data obtained from the spectral profiler sp and multiband imager mi onboard the japanese lunar explorer kaguya selene the olivine rich exposures are found only in the peak rings or central peaks of the schrodinger basin and zeeman crater which are located in the outer region of the spa basin and not in the center region on a localized scale the olivine rich materials are exposed on landslide features on the crater walls or sloped wall of the central peaks or the peak rings another observational finding is the co existence of olivine rich and plagioclase rich materials on a kilometer scale spanning most of the olivine rich sites in the schrodinger basin pyroxene rich materials are found in fresh craters outside the peak rings or the central peaks with olivine rich materials based on these results the following scenario are proposed 1 the impact to form the spa basin melted a large amount of the lunar upper mantle and crust and distributed the melted materials to the outer region 2 local differentiation of melted materials hid the olivine rich materials in the center region of the spa basin 3 later impacts that formed the schrodinger and zeeman craters excavated and exposed the olivine rich materials to the surface again and 4 space weathering and regolith gardening obscured the olivine rich spectra at the exposure sites but recent small scale impacts or landslides on the sloped wall exposed fresh olivine rich materials allowing the identification of the olivine rich exposures by spectral remote sensing this suggests that several different scale events play an important role in forming the surface distributions of originally deep seated materials on the moon as well as on other planetary bodies

copernicus crater central peak lunar mountain of unique composition olivine is identified as the major mafic mineral in a central peak of copernicus crater information on the mineral assemblages of such unsampled lunar surface material is provided by near infrared reflectance spectra 0 7 to 2 5 micrometers obtained with earth based telescopes the composition of the deep seated material comprising the copernicus central peak is unique among measured areas other lunar terra areas and the wall of copernicus exhibit spectral characteristics of mineral assemblages comparable to the feldspathic breccias returned by the apollo missions with low calcium orthopyroxene being the major mafic mineral