widespread fault creep in the northern san francisco bay area revealed by multistation cluster detection of repeating earthquakes we search for repeating earthquakes res in the northern san francisco bay area in 1984 2016 by comparing over 670 000 waveforms from 75 000 events we identify candidate clusters of events whos

dynamic triggering and earthquake swarms on east pacific rise transform faults while dynamic earthquake triggering has been reported in several continental settings offshore observations are rare oceanic transform faults share properties with continental geothermal areas known for dynamic triggering high geothermal gradients high seismicity rates and frequent swarms we study dynamic triggering along the east pacific rise by analyzing 1 year of seismicity recorded by ocean bottom seismographs by comparing the response to teleseismic waves from global earthquakes we find triggering to be most sensitive to changes in normal stress and to preferentially occur above 0 25 kpa the clearest example of triggering occurs on the quebrada and gofar faults after the mw8 0 wenchuan earthquake on gofar triggered seismicity occurs between the rupture areas of large earthquakes within a zone characterized by aseismic slip abundant microseismicity frequent swarms and low vp we infer that lithological properties inhibiting rupture propagation such as high porosity and fluid content also favor dynamic triggering

lunar fast neutron leakage flux calculation and its elemental abundance dependence a numerical code has been developed to simulate fast neutron leakage flux from planetary surfaces these neutrons are produced in copious number by interactions between galactic cosmic rays and the nuclei of surface material their leakage flux spectrum depends on the composition of the upper layers of planetary bodies measurement of these neutrons allows the mapping of major compositional units this technique is successfully used on lunar prospector data to obtain global geochemical maps of the lunar surface with the help of simulations relations between soil composition and neutron fluxes in the fast energy range 500 kev 10 mev are established the numerical code reproduces correctly the measurements of fast neutrons over the moon variation in the neutron flux between highland and mare soils is calculated a simple formula is suggested to estimate quickly the integrated fast neutron leakage flux for a given soil composition

comparison of seismic moment release rates along different types of plate boundaries summary this is a global survey of seismic moment release rates scalar moment length time along five categories of plate boundaries for shallow earthquakes we evaluate divergent transcurrent and convergent boundaries for deep earthquakes we consider separately boundaries where the deepest seismicity is intermediate 300 km or deep focus 500 600 km the objective is to evaluate the typical range of rates observed and present the results in a form where it is straightforward to compare factors that affect rates in the different environments for earthquakes occurring 1977 2005 the data are scalar moments from the global centroid moment tensor catalogue for earthquakes 1900 1976 we use a standard formula to obtain moment

groundwater chemistry of al under dutch sandy soils effects of land use and depth aluminium has received great attention in the second half of the 20th century mainly in the context of the acid rain problem mostly in forest soils in this research the effect of land use and depth of the groundwater on al ph and doc concentration in groundwater under dutch sandy soils has been studied both ph and doc concentration play a major role in the speciation of al in solution furthermore the equilibrium with mineral phases like gibbsite amorphous al oh 3 and imogolite has been considered agricultural and natural land use were expected to have different effects on the ph and doc concentration which in turn could influence the total al concentration and the speciation of al in groundwater at different depths phreatic shallow and deep an extensive dataset n 2181 from the national and some provincial monitoring networks on soil and groundwater quality was used land use type and groundwater depth did influence the ph and al and doc concentrations in groundwater samples the al concentration ranged from 7 to 1941 mol l 1 at ph 4 highest al concentrations were found for natural phreatic groundwater the doc concentration decreased and the median ph increased with depth of the groundwater natural phreatic groundwater showed lower ph than the agricultural phreatic groundwater highest doc concentrations were found for the agricultural phreatic groundwater induced by the application of organic fertilizers besides inorganic complexation the nica donnan model was used to calculate al3 concentrations for complexation with doc below ph 4 5 groundwater samples were mainly in disequilibrium with a mineral phase this disequilibrium is considered to be the result of kinetic constraints or equilibrium with organic matter log k values were derived by linear regression and were close to theoretical values for al oh 3 minerals e g gibbsite or amorphous al oh 3 except for natural phreatic groundwater for which lower log k values were found complexation of al with doc is shown to be an important factor for the al concentrations especially at high doc concentrations as was found for agricultural phreatic groundwater 2007 elsevier ltd all rights reserved

systematic survey of high resolution b value imaging along californian faults inference on asperities understanding and forecasting earthquake occurrences is presumably linked to understanding the stress distribution in the earth s crust this cannot be measured instrumentally with useful coverage however the size distribution of earthquakes quantified by the gutenberg richter b value is possibly a proxy to differential stress conditions and could therewith act as a crude stress meter wherever seismicity is observed in this study we improve the methodology of b value imaging for application to a high resolution 3 d analysis of a complex fault network in particular we develop a distance dependent sampling algorithm and introduce a linearity measure to restrict our output to those regions where the magnitude distribution strictly follows a power law we assess the catalog completeness along the fault traces using the bayesian magnitude of completeness method and systematically image b values for 243 major fault segments in california we identify and report b value structures revisiting previously published features e g the parkfield asperity and documenting additional anomalies e g along the san andreas and northridge faults combining local b values with local earthquake productivity rates we derive probability maps for the annual potential of one or more m6 events as indicated by the microseismicity of the last three decades we present a physical concept of how different stressing conditions along a fault surface may lead to b value variation and explain nonlinear frequency magnitude distributions detailed spatial b value information and its physical interpretation can advance our understanding of earthquake occurrence and ideally lead to improved forecasting ability

coulomb stress interactions among m 5 9 earthquakes in the gorda deformation zone and on the mendocino fault zone cascadia subduction zone and northern san andreas fault 1 the gorda deformation zone a 50 000 km2 area of diffuse shear and rotation offshore northernmost california has been the site of 20 m 5 9 earthquakes on four different fault orientations since 1976 including four m 7 shocks this is the highest rate of large earthquakes in the contiguous united states we calculate that the source faults of six recent m 5 9 earthquakes had experienced 0 6 bar coulomb stress increases imparted by earthquakes that struck less than 9 months beforehand control tests indicate that 0 6 bar coulomb stress interactions between m 5 9 earthquakes separated by 9 months are unlikely to occur by random chance suggesting that the multiple short term stress interactions observed among the recent gorda zone earthquakes are not an apparent effect in all well constrained 0 2 bar coulomb stress interactions between earthquakes that occurred within 4 years of each other the second earthquake is promoted on longer timescales calculated stress changes imparted by the 1980 mw 7 3 trinidad earthquake are consistent with the locations of m 5 9 earthquakes in the gorda zone until at least 1995 as well as earthquakes on the mendocino fault zone in 1994 and 2000 coulomb stress changes imparted by the 1980 earthquake are also consistent with its distinct elbow shaped aftershock pattern from these observations we derive generalized static stress interactions among right lateral left lateral and thrust faults near triple junctions

feo and tio2 concentrations in the south pole aitken basin implications for mantle composition and basin formation we use newly developed spectroscopic methods for determining feo and tio2 abundances to study the huge 2500 km diameter south pole aitken basin the floor of this basin shows iron and titanium values which are weakly correlated and largely range from 7 to 14 wt feo and from 0 5 to 1 5 wt tio2 this composition is consistent with an approximate 1 1 mixture of lower crustal material like that found elsewhere on the moon and mantle rock containing 10 16 wt feo and 0 1 wt tio2 although mantle rock appears to compose about 50 of the floor deposits models of the formation of large impact basins predict that virtually all the floor materials ought to be derived from the mantle

new results and implications for lunar crustal iron distribution using sensor data fusion techniques remote measurements of the moon have provided iron maps and thus essential constraints for models of lunar crustal formation and mare basalt petrogenesis a bulk crustal iron map was produced for the equatorial region from apollo gamma ray agr spectrometer measurements and a global iron variation map from recent clementine spectral reflectance csr measurements both iron maps show bimodal distribution but have significantly different peak values and variations in this paper csr data have been recalibrated to pyroxene in lunar landing site soils a residual iron map is derived from the difference between agr bulk and recalibrated csr pyroxene iron abundances the most likely interpretation is that the residual represents ferrous iron in olivine this residual iron is anticorrelated to basin age with older basins containing less olivine suggesting segregation of basin basalt sources from a progressively fractionating underlying source region at the time of basin formation results presented here provide a quantitative basis for 1 establishing the relationship between direct geochemical gamma ray x ray and mineralogical near ir remote sensing data sets using sensor data fusion techniques to allow 2 simultaneous determination of elemental and mineralogical component distribution on remote targets and 3 meaningful interpretation of orbital and ground based spectral reflectance measurements when calibrated data from the lunar prospector mission are available mapping of bulk crustal iron and iron bearing soil components will be possible for the entire moon similar analyses for data from the near earth asteroid rendezvous near mission to asteroid 433 eros will constrain models of asteroid formation

mineralogy of the mafic anomaly in the south pole aitken basin implications for excavation of the lunar mantle the mineralogy of south pole aitken basin spa the largest confirmed impact basin on the moon is evaluated using five color images from clementine although olivine rich material as well as basalts rich in clinopyroxene are readily identified elsewhere on the farside the dominant rock type observed across the interior of spa is of a very noritic composition this mineralogy suggests that lower crust rather than the mantle is the dominant source of the mafic component at spa the lack of variation in observed noritic composition is probably due to basin formation processes during which extensive melting and mixing of target materials are likely to occur

viscoelastic cycle model of interseismic deformation in the northwestern united states summary we apply a viscoelastic cycle model to a compilation of gps velocity fields in order to address the kinematics of deformation in the northwestern united states a viscoelastic cycle model accounts for time dependent deformation following large crustal earthquakes and is an alternative to block models for explaining the interseismic crustal velocity field building on the approach taken in pollitz et al we construct a deformation model for the entire western united states based on combined fault slip and distributed deformation and focus on the implications for the mendocino triple junction mtj cascadia megathrust and western washington we find significant partitioning between strike slip and dip slip motion near the mtj as the tectonic environment shifts from northwest directed shear along the san andreas fault system to east west convergence along the juan de fuca plate by better accounting for the budget of aseismic and seismic slip along the cascadia subduction interface in conjunction with an assumed rheology we revise a previous model of slip for the m 9 1700 cascadia earthquake in western washington we infer slip rates on a number of strike slip and dip slip faults that accommodate northward convergence of the oregon coast block and northwestward convergence of the juan de fuca plate lateral variations in first order mechanical properties e g mantle viscosity vertically averaged rigidity explain to a large extent crustal strain that cannot be rationalized with cyclic deformation on a laterally homogeneous viscoelastic structure our analysis also shows that present crustal deformation measurements particularly with the addition of the plate boundary observatory can constrain such lateral variations

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

active deformation of the gorda plate constraining deformation models with new geophysical data the gorda plate the southernmost fragment of the larger juan de fuca plate system is an example of a nonrigidly deforming tectonic accommodation zone or buffer plate absorbing deformation and allowing the surrounding larger plates to act in a more rigid fashion here we present a new structural analysis of the plate based on full plate bathy metric coverage augmented by seismic reflection data and earthquake moment tensors and locations we interpret internal deformation of the gorda plate as an asymmetrical flexural slip buckle with a vertical axis utilizing reactivation of spreading ridge fabric normal faults as strike slip faults newly formed second generation faults crosscutting the structural grain overprint the reactivated structures the spreading fabric faults finally begin a second phase of extension as the plate approaches the subduction zone this model based on fault constraints has allowed investigation of ridge plate subduction interac tions and suggests that spreading rate variations along the gorda ridge may be con trolled by internal deformation of the plate rather than the reverse as previously hypothesized

concentrations of radioactive elements in lunar materials as an aid to interpreting data obtained remotely on the distribution of radioactive elements on the lunar surface average concentrations of k u and th as well as al fe and ti in different types of lunar rocks and soils are tabulated the u th ratio in representative samples of lunar rocks and regolith is constant at 0 27 k th ratios are more variable because k and th are carried by different mineral phases in nonmare regoliths at the apollo sites the main carriers of radioactive elements are mafic i e 6 8 fe impact melt breccias created at the time of basin formation and products derived therefrom

space weathering on airless bodies resolving a mystery with lunar samples using new techniques to examine the products of space weathering of lunar soils we demonstrate that nanophase reduced iron npfe0 is produced on the surface of grains by a combination of vapor deposition and irradiation effects the optical properties of soils both measured and modeled are shown to be highly dependent on the cumulative amount of npfe0 which varies with different starting materials and the energetics of different parts of the solar system the measured properties of intermediate albedo asteroids the abundant s type asteroids in particular are shown to directly mimic the effects predicted for small amounts of npfe0 on grains of an ordinary chondrite regolith this measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids

ancient multiring basins on the moon revealed by clementine laser altimetry analysis of laser altimetry data from clementine has confirmed and extended our knowledge of nearly obliterated multiring basins on the moon these basins were formed during the early bombardment phase of lunar history have been filled to varying degrees by mare lavas and regional ejecta blankets and have been degraded by the superposition of large impact craters the mendel rydberg basin a degraded three ring feature over 600 kilometers in diameter on the lunar western limb is about 6 kilometers deep from rim to floor only slightly less deep than the nearby younger and much better preserved orientale basin 8 kilometers deep the south pole aitken basin the oldest discernible impact feature on the moon is revealed as a basin 2500 kilometers in diameter with an average depth of more than 13 kilometers rim crest to floor this feature is the largest deepest impact crater yet discovered in the solar system several additional depressions seen in the data may represent previously unmapped ancient impact basins

fluxes of fast and epithermal neutrons from lunar prospector evidence for water ice at the lunar poles maps of epithermal and fast neutron fluxes measured by lunar prospector were used to search for deposits enriched in hydrogen at both lunar poles depressions in epithermal fluxes were observed close to permanently shaded areas at both poles the peak depression at the north pole is 4 6 percent below the average epithermal flux intensity at lower latitudes and that at the south pole is 3 0 percent below the low latitude average no measurable depression in fast neutrons is seen at either pole these data are consistent with deposits of hydrogen in the form of water ice that are covered by as much as 40 centimeters of desiccated regolith within permanently shaded craters near both poles

model near infrared optical constants of olivine and pyroxene as a function of iron content the imaginary coefficients of the complex index of refraction of olivine low ca orthopyroxene and high ca clinopyroxene are derived as a function of iron content and wavelength over the spectral region 0 4 to 2 5 m from reflectance spectra of powders and hapke radiative transfer theory reflectance spectra as a function of composition and grain size are computed and compared i find that while spectral effects of variations in these parameters are similar they are distinguishable variations in iron content do not explain all the observed spectral variations in the spectra of the samples investigated

aseismic transform fault slip at the mendocino triple junction from characteristically repeating earthquakes author s materna k taira t burgmann r abstract 2018 american geophysical union all rights reserved the mendocino triple junction mtj at the northern terminus of the san andreas fault system is an actively deforming plate boundary region with poorly constrained estimates of seismic coupling on most offshore fault surfaces characteristically repeating earthquakes provide spatial and temporal descriptions of aseismic creep at the mtj including on the oceanic transform mendocino fault zone mfz as it subducts beneath north america using a dataset of earthquakes from 2008 to 2017 we find that the easternmost segment of the mfz displays creep during this period at about 65 of the long term slip rate we also find creep at slower rates on the shallower strike slip interface between the pacific plate and the north american accretionary wedge as well as on a fault that accommodates gorda subplate internal deformation after a nearby m5 7 earthquake in 2015 we observe a possible decrease in aseismic slip on the near shore mfz that lasts from 2015 to at least early 2017

the cape mendocino california earthquakes of april 1992 subduction at the triple junction the 25 april 1992 magnitude 7 1 cape mendocino thrust earthquake demonstrated that the north america gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the cascadia region the shock occurred just north of the mendocino triple junction and caused strong ground motion and moderate damage in the immediate area rupture initiated onshore at a depth of 10 5 kilometers and propagated up dip and seaward slip on steep faults in the gorda plate generated two magnitude 6 6 aftershocks on 26 april the main shock did not produce surface rupture on land but caused coastal uplift and a tsunami the emerging picture of seismicity and faulting at the triple junction suggests that the region is likely to continue experiencing significant seismicity

measuring earthquake source parameters in the mendocino triple junction region using a dense obs array implications for fault strength variations abstract subduction zones produce earthquakes on a set of faults that operate under a wide variety of conditions resulting from considerable variations in depth temperature rock type and fluid pressure these variations likely lead to variation in the stress levels that drives particular earthquakes and that in turn effects the magnitude of seismic shaking they produce in the mendocino triple junction mtj region intraplate faults within the mantle of the subducting plate fail regularly in energetic earthquakes while the adjacent thrust interface of the cascadia subduction zone remains seismically quiet despite the likelihood that it operates at much lower levels of stress and strength in 2012 as part of the cascadia initiative community experiment an ocean bottom seismometer obs array was deployed in the mtj area providing unusually dense data covering both the inter and intra plate earthquakes combining these data with onshore networks we detect and relocate 1137 earthquakes with a three dimensional velocity model we perform detailed spectral and time domain analysis to study variations in earthquake source properties between the different types of faults we observe a wide variability of stress drops and systematic lateral and depth variations in the earthquake source spectra resulting from the different types of tectonic fault systems in this region intraplate faults within the subducted oceanic mantle the mendocino transform plate boundary fault and the thrust interface of the cascadia subduction zone some of the depth variability of source spectra can be explained by the expected increase in rupture velocity with depth however the overall variation in stress drop estimates is consistent with the highest stress drop earthquakes occurring in the depth range predicted by strength envelopes moreover the earthquakes in the vicinity of the thrust interface likely including some within the subducted oceanic crust show clearly lower stress drops and depletion of high frequency radiation for their size compared to events in the oceanic mantle and along the transform fault at a given depth our results suggest that the variability in earthquake source spectra that can be expected in the cascadia subduction zone is systematic and that the thrust interface operates at a lower stress level than the core of the subducted plate a few kilometers away

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

towards a universal rule on the recurrence interval scaling of repeating earthquakes 1 a recent analysis of recurrence properties of small repeating earthquakes on a creeping oblique thrust fault in eastern taiwan reveals a weak variation in recurrence interval tr with seismic moment mo compared to the scaling of tr with mo from repeating earthquake data near parkfield in california the repeating data from eastern taiwan has recurrence intervals that are 2 times shorter also in northeastern japan tr of repeating quakes are 4 times shorter than those expected from the parkfield scaling law when adjusted to account for differences in the geodetically derived slip rates for the three fault zones however the tr mo scaling is remarkably consistent among the three regions it suggests that the tectonic loading rate is likely the most important factor that controls the repeat time it also suggests that there seems to exist a universal rule on recurrence interval scaling of repeating earthquakes in diverse tectonic settings

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

do earthquakes talk to each other triggering and interaction of repeating sequences at parkfield 1 knowledge of what governs the timing of earthquakes is essential to understanding the nature of the earthquake cycle and to determining earthquake hazard yet the variability and controls of earthquake recurrences are not well established the large population of small characteristically repeating earthquakes at parkfield provides a unique opportunity to study how the interaction of earthquakes affects their recurrence properties we analyze 112 m 0 4 3 0 repeating earthquake sequences ress to examine the triggering effect from nearby microseismicity we find that the repeating events with a smaller number of neighboring earthquakes in their immediate vicinity tend to recur in a more periodic manner i e the coefficient of variation in recurrence intervals is less than 0 3 the total static stress perturbation from close by earthquakes however does not seem to strongly influence res regularity the uneven distribution of stress changes in time has a modest but significant impact on recurrence intervals a significant reduction of recurrence intervals occurs in the case of very high stress changes from neighboring events close by events influence res timing in a matter of several days or less by short term triggering events that occurred within less than 1 day of an res often imposed or experienced high stress changes a static stress increment of 30 kpa can be enough to produce such short term triggering we find that the triggered repeating events are often near the end of their average earthquake cycle but some events occur following a substantially shortened interval when comparing the accelerated occurrence at the time of res events following neighboring events with varying magnitudes we find that the distance of short term triggering increases from 1 km to 4 km for m1 to m4 events

structure and seismotectonics of the mendocino triple junction california 1 we analyze and interpret two marine multichannel seismic reflection onshore offshore ocean bottom seismometer obs seismic profiles that cross in the region of the mendocino triple junction over the fault plane of the 1992 petrolia california ms 7 1 earthquake from the offshore reflection data and the wide angle constraints provided by the onshore offshore and obs data we have determined a rough three dimensional view of crustal and uppermost mantle structure beneath the triple junction region this structure is also consistent with gravity data the upper and mid crust has seismic velocities and densities consistent with accretionary complex rocks of the franciscan terrane a ubiquitous lower crustal layer with velocities of 6 5 7 1 km s 1 is 5 7 km thick throughout most of the region over an area extending at least 25 km to the south and 60 km to the west of the triple junction the lower crustal layer is up to 12 km thick this area is overlain by undisturbed pre 11 ma sediments indicating little deformation since that date the thick lower crust extends beneath the coast suggesting that the deep boundary between pacific and north american terranes lies onshore the northeastern edge of the thick lower crustal layer is marked by concentrated seismicity with the hypocenter of the 1992 petrolia earthquake lying close to the ne corner we speculate that at depth the pacific lower crust acts an asperity acting to concentrate stress from which the petrolia earthquake ruptured

dual megathrust slip behaviors of the 2014 iquique earthquake sequence the transition between seismic rupture and aseismic creep is of central interest to better understand the mechanics of subduction processes a mw 8 2 earthquake occurred on april 1st 2014 in the iquique seismic gap of northern chile this event was preceded by a long foreshock sequence including a 2 week long migration of seismicity initiated by a mw 6 7 earthquake repeating earthquakes were found among the foreshock sequence that migrated towards the mainshock hypocenter suggesting a large scale slow slip event on the megathrust preceding the mainshock the variations of the recurrence times of the repeating earthquakes highlight the diverse seismic and aseismic slip behaviors on different megathrust segments the repeaters that were active only before the mainshock recurred more often and were distributed in areas of substantial coseismic slip while repeaters that occurred both before and after the mainshock were in the area complementary to the mainshock rupture the spatiotemporal distribution of the repeating earthquakes illustrates the essential role of propagating aseismic slip leading up to the mainshock and illuminates the distribution of postseismic afterslip various finite fault models indicate that the largest coseismic slip generally occurred down dip from the foreshock activity and the mainshock hypocenter source imaging by teleseismic back projection indicates an initial down dip propagation stage followed by a rupture expansion stage in the first stage the finite fault models show an emergent onset of moment rate at low frequency 0 5 hz 0 5 hz this indicates frequency dependent manifestations of seismic radiation in the low stress foreshock region in the second stage the rupture expands in rich bursts along the rim of a semi elliptical region with episodes of re ruptures suggesting delayed failure of asperities the high frequency rupture remains within an area of local high trench parallel gravity anomaly tpga suggesting the presence of subducting seamounts that promote high frequency generation our results highlight the complexity of the interactions between large scale aseismic slow slip and dynamic ruptures of megathrust earthquakes

chemical information content of lunar thermal and epithermal neutrons simulations of equilibrium thermal and epithermal neutron flux spectra for the moon have been studied to determine their chemical information content most of this information resides in a single parameter the ratio of macroscopic absorption to energy loss cross sections although this parameter cannot specify the chemistry of lunar soils uniquely it provides an index that can be used to quantitatively separate anorthositic from mafic chemistries hydrogen abundances can best be derived from measurements of the epithermal neutron flux which is strongly related to its macroscopic energy loss cross section the ratio of thermal to epithermal neutron flux measured by lunar prospector is shown to agree quantitatively with simulations this agreement is used to show that the highlands terrane on the farside of the moon is anorthositic containing high percentages of plagioclase and possibly a range of mg suite minerals with a high mg mg fe atomic ratio our best estimate of the abundance of feo is 2 with an upper limit of 5

the magma ocean concept and lunar evolution the model of lunar evolution in which the anorthositic plagioclase rich oldest crust of the moon is formed over a period of 300 myr or less by crystallization as it floats on a global ocean of magma tens or hundreds of km thick is examined in a review of petrological and theoretical studies consideration is given to the classification of lunar rocks the evidence for primordial deep global differentiation constraints on the depth of the molten zone the effects of pressure on mineral stability relationships mainly liquid vs mainly magmifer ocean models and the evidence for multiple ancient differentiation episodes a synthesis of the model of primordial differentiation and its aftereffects is presented and the generalization of the model to the earth and to mars mercury venus and the asteroids is discussed

crustal structure of the northwestern vizcaino block and gorda escarpment offshore northern california and implications for postsubduction deformation of a paleoaccretionary margin the vizcaino block is an anomalously shallow region of the western u s continental margin located southwest of the mendocino triple junction it originated as part of the accretionary prism of the north america plate and was transferred to the pacific plate in the miocene as the pacific north america plate boundary migrated 130 km eastward forming the gorda escarpment at its northern boundary we present hybrid crustal models for the northwestern part of the vizcaino block derived from marine seismic and gravity data the velocity and density structure of the northwestern vizcaino block are compatible with paleoaccretionary complex material similar to san simeon patton terrane overlying oceanic crust or a mafic layer the most significant result of our modeling is an abrupt increase in moho dip from 5 to 20 30 beneath the western edge of the oconostota ridge along the northwestern margin of the vizcaino block this moho dip is steeper than observed anywhere along the cascadia subduction zone indicating postsubduction deformation we suggest that the paleotrench was deformed by compression which reactivated preexisting thrust faults in the upper crust and thickened the crust within this apparent weak zone at least part of the deformation predates late pliocene pacific north america plate convergence and may result mainly from north south compression between the pacific juan de fuca plates across the mendocino transform fault north south compression continues today and may dynamically support the uplifted northern margin of the vizcaino block although the primary locus of deformation shifted to the relatively weak gorda plate sometime prior to 3 ma

internal deformation of the southern gorda plate fragmentation of a weak plate near the mendocino triple junction north south compression across the gorda pacific plate boundary caused by the northward migrating mendocino triple junction appears to reactivate gorda plate normal faults originally formed at the spreading ridge as left lateral strike slip faults both seismically imaged faults and magnetic anomalies fan eastward from n208e near the gorda ridge to n758e near the triple junction near the triple junction the gorda plate is faulted pervasively and appears to be extending east southeast as it subducts beneath north america continuation of northeast southwest oriented deformation in the southern gorda plate beneath the continental margin contrasts with the northwest southeast trending structures in the overlying accretionary prism suggesting partial gorda north american plate decoupling southeast of the triple junction a slabless window is generated by removal of the subducting gorda plate southwest of the triple junction the pacific plate acts as a rigid barrier forcing southern gorda crust to rotate clockwise fragment and flow into the slabless window net clockwise rotation of the southern gorda crust forms a boundary with the nonrotating northern gorda plate which is observed as a bend in the magnetic anomalies this boundary which is compressional on the western end and extensional to the east may separate the stress regime of the southern gorda plate from the remainder of the cascadia subduction zone

the long recurrence intervals of small repeating earthquakes may be due to the slow slip rates of small fault strands observations since 1998 have revealed that repeating earthquakes and particularly small repeating earthquakes occur less often than expected given their seismically derived slip and the regional fault slip rate here we test the hypothesis that small repeaters occur infrequently because they occur on fault segments or strands with low slip rates we analyze the recurrence interval moment scaling of earthquake sequences near parkfield california we find that closely spaced sequences which likely occur on the same fault strand and respond to the same slip rate follow a scaling consistent with seismic slip rates while widely spaced sequences which likely occur on different strands follow a scaling consistent with the previous counter intuitive observations these results suggest that spatially varying slip rates could create the recurrence interval scaling though we cannot exclude other explanations

influence of the mendocino triple junction on the tectonics of coastal california abstract the migration of the mendocino triple junction through central and northern california over the past 25 30 million years has led to a profound change in plate interactions along coastal california the tectonic consequences of the abrupt change from subduction plate interactions north of the triple junction to the development of the san andreas transform system south of the triple junction can be seen in the geologic record and geophysical observations the primary driver of this tectonism is a coupling among the subducting juan de fuca gorda north american and pacific plates that migrates with the triple junction this coupling leads to ephemeral thickening of the overlying north american crust associated uplift and subsequent subsidence and a distinctive sequence of fault development and volcanism

mapping the feo and tio2 content of the lunar surface with multispectral imagery the derivation of quantitative elemental concentrations from multispectral imaging of the moon has long been a goal of lunar remote sensing concentration maps at the spatial resolutions available from the recent clementine mission would provide a revolutionary new tool for understanding the origin and evolution of the lunar crust lucey et al 1995 presented a method for extracting the concentration of fe from multispectral imaging of the moon this paper examines and quantifies important aspects ofthat technique left unexamined by lucey et al which had the potential to severely limit its utility these aspects include the effects of maturity grain size mineralogy shading due to topography and the presence of glass we also present a new algorithm for derivation of tio2 from multispectral imaging of both mare and highland units we find that both techniques are only weakly sensitive to maturity and that they have about 1 wt accuracy based on examination of the spectral properties and compositions of resolved lunar sampling stations presented by blewett et al 1997 we also discuss these findings in the context of two contrasting views of the effect of composition on lunar spectral properties presented by pieters and coworkers and hapke and coworkers we find the view of hapke and coworkers to be more consistent with our observations using a global mosaic of clementine multispectral data and these element derivation algorithms we find that the global modal abundance of feo is 4 5 wt 1 wt and the global modal abundance of tio2 is 0 45 wt 1 wt

feldspar weathering as the key to understanding soil acidification monitoring data a study of acid sandy soils in the netherlands abstract monitoring activities pose special demands on the type of survey results needed in the early 1990s a soil acidification monitoring methodology was adopted in the netherlands that leaned heavily on methods developed in more fundamental research most notably the use of proton budgets consequently various controversies still not resolved in the scientific debate reflect on the current practice of soil acidity monitoring and complicate interpretation of the monitoring results in a pilot study we address the most pressing issues capacity versus intensity parameters choice of monitoring objective and natural variation in the compartment to be monitored focus is on the major source of buffering the possible usefulness of the historic approach and the regional patterns present in the sandy soils of the netherlands in a field campaign 92 locations in sandy regions all over the country were sampled at two depths the solid phase the displaced soil solution and solid phase extractions with 0 01 m cacl2 and 0 43 m hno3 for the 184 samples were analyzed by a variety of methods aluminum release is the major source of buffering and is shown to contribute substantially to acid buffering already under natural conditions the predominant al bearing phases in dutch sandy soils are feldspars and secondary al minerals feldspars are found to be the determinative phase in acid buffering application of the historic approach using the subsoil as a proxy for the initial composition of the topsoil proved feasible for this regional dataset the average depletion of the anc s of 230 mmolc kg 1 in the topsoil matches well with estimates of the total proton load since the last ice age with the anthropogenic contribution being between 20 and 50 fuzzy c means cluster analyses of the solid phase and soil solution data show a distinct regionality that was also reflected in the parameters generally used to indicate the acidity status of soils anc s and al bc ratios a combined insight into both solid phase and soil solution based on a comprehensive set of parameters proves essential for interpreting soil acidity monitoring data

global elemental maps of the moon the lunar prospector gamma ray spectrometer lunar prospector gamma ray spectrometer spectra along with counting rate maps of thorium potassium and iron delineate large compositional variations over the lunar surface thorium and potassium are highly concentrated in and around the nearside western maria and less so in the south pole aitken basin counting rate maps of iron gamma rays show a surface iron distribution that is in general agreement with other measurements from clementine and the lunar prospector neutron detectors

central cascadia subduction zone creep central cascadia between 43 n and 46 n has reduced interseismic uplift observed in geodetic data and coseismic subsidence seen in multiple thrust earthquakes suggesting elevated persistent fault creep in this section of the subduction zone we estimate subduction thrust decade scale locking and crustal block rotations from three component continuous global positioning system gps time series from 1997 to 2013 as well as 80 year tide gauge and leveling derived uplift rates geodetic observations indicate coastal central oregon is rising at a slower rate than coastal washington southern oregon and northern california modeled locking distributions suggest a wide locking transition zone that extends inland under central oregon paleoseismic records of multiple great earthquakes along cascadia indicate less subsidence in central oregon the cascade thrust under central oregon may be partially creeping for at least 6500 years the length of the paleoseismic record reducing interseismic uplift and resulting in reduced coseismic subsidence large accretions of eocene age basalt siletzia terrane between 43 n and 46 n may be less permeable compared to surrounding terranes potentially increasing pore fluid pressures along the fault interface resulting in a wide zone of persistent fault creep in a separate inversion three component gps time series from 1 july 2005 to 1 january 2011 are used to estimate upper plate deformation locking between slow slip events sses slip from 16 sses and an earthquake mechanism cumulative sses and tectonic tremor are weakest between 43 n and 46 n where partial fault creep is increased and siletzia terrane is thick suggesting that surrounding rock properties may influence the mode of slip

topography of the moon from the clementine lidar range measurements from the lidar instrument carried aboard the clementine spacecraft have been used to produce an accurate global topographic model of the moon this paper discusses the function of the lidar the acquisition processing and filtering of observations to produce a global topographic model and the determination of parameters that define the fundamental shape of the moon our topographic model a 72nd degree and order spherical harmonic expansion of lunar radii is designated goddard lunar topography model 2 gltm 2 this topographic field has an absolute vertical accuracy of approximately 100 m and a spatial resolution of 2 5 the field shows that the moon can be described as a sphere with maximum positive and negative deviations of 8 km both occurring on the farside in the areas of the korolev and south pole aitken s p aitken basins the amplitude spectrum of the topography shows more power at longer wavelengths as compared to previous models owing to more complete sampling of the surface particularly the farside a comparison of elevations derived from the clementine lidar to control point elevations from the apollo laser altimeters indicates that measured relative topographic heights generally agree to within 200 m over the maria while the major axis of the lunar gravity field is aligned in the earth moon direction the major axis of topography is displaced from this line by approximately 10 to the east and intersects the farside 24 north of the equator the magnitude of impact basin topography is greater than the lunar flattening 2 km and equatorial ellipticity 800 m which imposes a significant challenge to interpreting the lunar figure the floors of mare basins are shown to lie close to an equipotential surface while the floors of unflooded large basins except for s p aitken lie above this equipotential the radii of basin floors are thus consistent with a hydrostatic mechanism for the absence of significant farside maria except for s p aitken whose depth and lack of mare require significant internal compositional and or thermal heterogeneity a macroscale surface roughness map shows that roughness at length scales of 10 1 10 2 km correlates with elevation and surface age

periodic pulsing of characteristic microearthquakes on the san andreas fault deep fault slip information from characteristically repeating microearthquakes reveals previously unrecognized patterns of extensive large amplitude long duration quasiperiodic repetition of aseismic events along much of a 175 kilometer segment of the central san andreas fault pulsing occurs both in conjunction with and independent of transient slip from larger earthquakes it extends to depths of 10 to 11 kilometers but may be deeper and it may be related to similar phenomena occurring in subduction zones over much of the study area pulse onset periods also show a higher probability of larger earthquakes which may provide useful information for earthquake forecasting

lunar fe and ti abundances comparison of lunar prospector and clementine data the lunar prospector neutron spectrometer data correlate well with iron and titanium abundances obtained through analysis of clementine spectral reflectance data with the iron and titanium dependence removed the neutron spectrometer data also reveal regions with enhanced amounts of gadolinium and samarium incompatible rare earth elements that are enriched in the final phases of magma crystallization these regions are found mainly around the ramparts of the imbrium impact basin but not around the other basins including the much larger and deeper south pole aitken basin this result confirms the compositional uniqueness of the surface and interior of the imbrium region

acid groundwater in an anoxic aquifer reactive transport modelling of buffering processes abstract the acidification of groundwater due to acid rain was investigated in a quaternary sandy aquifer in the fuhrberger feld near hannover germany the groundwater recharged through an area covered by a coniferous forest had a ph in the range 4 5 down to a depth of 5 m the evolution in groundwater chemistry along the flow path was investigated in a transect of multisamplers a 2d groundwater flow model was established delineating the groundwater flow field and a groundwater flow velocity of around 80 m a along the flow path was derived speciation calculations showed the groundwater to be close to equilibrium with the mineral jurbanite alohso4 over the ph range 4 0 6 5 this suggests an accumulation of acid rain derived so 4 2 in the aquifer sediment during the decades with high atmospheric s deposition the groundwater has a ph of around 4 5 in the upstream part of the flow path increasing to near 6 further downstream 1d reactive transport modelling using phreeqc was used to analyze different combinations of buffering processes the first model contains ion exchange in combination with jurbanite dissolution at the ion exchange front al3 is adsorbed leading to the dissolution of jurbanite and an increase in ph comparison with field data showed that the simulated increases in ph and alkalinity are much lower than observed in the field the second model includes organic matter degradation in addition to ion exchange and jurbanite dissolution the model included the reduction of so 4 2 and fe oxides as well as the precipitation of fe sulfide this model matches the field data well and illustrates the importance of redox processes for ph buffering in the fuhrberg aquifer the current progress of the acidification front is about 4 m a this corresponds to an average value of 150 a of acid input which covers large historical variations remediation is expected to take the same time span because it requires desorption and neutralization of adsorbed al3 from the aquifer sediment

double seismic zone and dehydration embrittlement of the subducting slab 1 dehydration embrittlement of metamorphosed oceanic crust and mantle in the subducting slab may be responsible for the occurrence of intermediate depth earthquakes we explore the possibility that this hypothesis can explain the morphology of the double seismic zones observed in northeast japan southwest japan northeast taiwan northern chile cape mendocino and eastern aleutians we calculate transient temperature structures of slabs based on geologically estimated subduction histories of these regions we then determine dehydration loci of metamorphosed oceanic crust and serpentinized mantle using experimentally derived phase diagrams the depth range of the dehydration loci of metamorphosed oceanic crust and serpentine is dependent on slab age the dehydration loci of serpentine produce a double layered structure because the upper dehydration loci of serpentine are mostly located in the wedge mantle above the slab we regard the upper plane seismicity representing dehydration embrittlement in the oceanic crust and we fix the slab geometry so that the upper plane seismicity is just below the upper surface of the slab we find that the lower plane seismicity is located at the lower dehydration loci of serpentine which indicates that the morphology of the double seismic zones is consistent with the dehydration embrittlement

a kinematic model for the gorda deformation zone as a diffuse southern boundary of the juan de fuca plate several lines of evidence indicate that the space problem caused by southeastward motion of the juan de fuca plate toward the east west mendocino transform is resolved by distributed deformation of the oceanic crust north of the transform a kinematic model for this deformation based on the assumption of nondivergent flow conservation of area within the area known as the gorda plate and on the assumption of no subduction along the mendocino transform successfully matches the isochron pattern inferred from magnetic anomalies the model assumes strain rate decreasing to zero approaching the rigid juan de fuca plate with no sharp boundary or separate rigid area that would imply a discrete gorda plate this interpretation allows magnetic anomalies from south of the blanco fracture zone to be used to constrain the kinematics of the juan de fuca plate these anomalies imply a substantial change in the distance to the rotation pole at roughly 3 ma in addition to the clockwise shift in motion direction at 5 ma

beginning and end of lunar mare volcanism mare volcanism on the moon is commonly attributed to an important but relatively short lived epoch of internal heating after 3 900 myr bp but before about 2 500 myr bp refs 1 2 although some studies suggested that mare volcanism had started earlier3 5 than times indicated by dated lunar samples only recently have photogeological spectral and geochemical data6 8 documented the importance of a pre 4 000 myr bp epoch similarly early earth based geological mapping revealed a bright rayed crater lichtenberg superposed by mare units9 thereby indicating that mare volcanism must have extended to times significantly more recent than 3 100 myr bp lunar orbital photography confirmed this inferred strati graphical relationship10 but crater statistics indicated that the youngest units were at least twice the age of copernicus or between 1 700 and 2 000 myr bp refs 11 13 we present here the inferred distribution and style of the early phases of mare volcanism based on current evidence and conclude that certain regions of the moon underwent two distinct pulses of igneous activity we then examine crater statistics for the post lichtenberg mare unit and other selected units and conclude that mare volcanism extended to a time comparable with that of the copernicus impact or 1 myr bp these reassessments of the oldest and youngest maria provide new constraints on geophysical models of the internal thermal history of the moon

what controls interplate coupling evidence for abrupt change in coupling across a border between two overlying plates in the ne japan subduction zone article i nfo interplate coupling in the southernmost extent of the northeast japan subduction zone east off kanto japan is investigated in detail using a large data set of small repeating earthquakes in this region of the trench trench trench type triple junction the subducting pacific plate is in contact with two different overlying plates the north american and philippine sea plates the border between the two overlying plates extending northwestward from the triple junction is identified along the upper surface of the pacific plate based on the slip vectors of many interplate events including small repeating earthquakes the interplate coupling coefficient estimated from the cumulative slip of small repeating earthquakes for the period from 1993 to 2007 reveals a distinct change from south ca 0 3 to north ca 0 7 across the border this border also corresponds to the southern limit of the source areas of mn7 interplate earthquakes in the last 80 years along the japan trench again indicating the stronger coupling to the north we also investigate hypocenter distribution and seismic velocity structure along the plate boundary from a large number of travel time data obtained from the nationwide seismograph network the results reveal a distinct low velocity zone just above the pacific plate and low seismicity along the plate boundary in the region overlain by the philippine sea plate whereas there are no low velocity zones and the seismicity is high in the region overlain by the north american plate these observations imply that the geological difference of overlying plate controls large scale coupling at the plate interface

pre and postseismic slow slip surrounding the 2011 tohoku oki earthquake rupture abstract slow aseismic slip that accommodates part of the long term plate motion on subduction megathrusts is thought to be strongly related to the occurrence of large earthquakes on the same fault zone however the temporal evolution and spatial distribution of the aseismic slip before major earthquakes and of accelerated postseismic afterslip are largely unconstrained we estimate cumulative offsets of small repeating earthquakes that are interpreted to reflect the in situ aseismic slip history on the subduction zone offshore northeastern japan these data reveal contrasting aseismic slip patterns between the coseismic rupture area of the mw 9 0 tohoku oki earthquake and surrounding portions of the subduction thrust the rupture area is characterised by low and variable slip rates before 2008 and the slip stopped almost completely after the earthquake the region surrounding the rupture area exhibited higher aseismic fault slip rates before the earthquake and clear postseismic slip of up to 1 6 m within 9 months following the main shock the frictional fault properties and complete relief of ambient stress in the central rupture zone of the main shock probably control the observed distribution the postseismic slip shows a more abrupt increase in the region closer to the source suggesting outwards propagation of afterslip small but distinct increases in the slip rate in the 3 yr before the earthquake near the area of large coseismic slip suggests preseismic unfastening of the locked area in the last stage of the earthquake cycle

detailed spatiotemporal evolution of microseismicity and repeating earthquakes following the 2012 mw 7 6 nicoya earthquake we apply a waveform matching technique to obtain a detailed earthquake catalog around the rupture zone of the 5 september 2012 moment magnitude 7 6 nicoya earthquake with emphasis on its aftershock sequence starting from a preliminary catalog we relocate 7900 events using tomodd to better quantify their spatiotemporal behavior relocated aftershocks are mostly clustered in two groups the first is immediately above the major coseismic slip patch partially overlapping with shallow afterslip the second one is 50 km se to the main shock nucleation point and near the terminus of coseismic rupture in a zone that exhibited little resolvable afterslip using the relocated events as templates we scan through the continuous recording from 29 june 2012 to 30 december 2012 detecting approximately 17 times more than template events we find 190 aftershocks in the first half hour following the main shock mostly along the plate interface later events become more scattered in location showing moderate expansion in both along trench and downdip directions from the detected catalog we identify 53 repeating aftershock clusters with mean cross correlation values larger than 0 9 and indistinguishably intracluster event locations suggesting slip on the same fault patch most repeating clusters occurred within the first major aftershock group very few repeating clusters were found in the aftershock grouping along the southern edge of the peninsula which is not associated with substantial afterslip our observations suggest that loading from nearby afterslip along the plate interface drives spatiotemporal evolution of aftershocks just above the main shock rupture patch while aftershocks in the se group are to the se of the observed updip afterslip and poorly constrained

lunar rare earth element distribution and ramifications for feo and tio2 lunar prospector neutron spectrometer observations lunar prospector neutron spectrometer data have been used to map the global surface distribution of the incompatible rare earth elements gadolinium and samarium from the low altitude 30 15 km mapping orbit these results afford improved surface resolution and detailed views of the potassium rare earth elements and phosphorus kreep distribution within and around mare imbrium and elsewhere the gd and sm results serve as a complementary and independent check of the distribution of kreep on the moon in contrast with the lunar prospector gamma ray spectrometer results for thorium the neutron spectrometer observations reflect the presence of fe and ti as well as gd and sm the contributions of fe and ti are removed using high spatial resolution clementine spectral reflectance determinations of feo and tio2 abundances overall the resulting gd and sm abundance map agrees with the th abundance map determined using the lunar prospector gamma ray spectrometer in general the detailed features of the procellarum imbrium kreep terrane are found in both for example distinct highs in gd sm and th abundances are resolved over the craters mairan aristarchus kepler reinhold lalande and aristillus over the apennine bench and fra mauro regions and over the montes jura and montes carpatus indicating an enhanced abundance of kreep in these locations the neutron observations also provide constraints on feo and tio2 abundances for some high ti locales there is a significant disagreement with tio2 abundances inferred from clementine spectral reflectance

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

abundance and distribution of iron on the moon the abundance and distribution of iron on the moon is derived from a near global data set from clementine the determined iron content of the lunar highlands crust 3 percent iron by weight supports the hypothesis that much of the lunar crust was derived from a magma ocean the iron content of lower crustal material exposed by the south pole aitken impact basin on the lunar farside is higher 7 to 8 percent by weight and consistent with a basaltic composition this composition supports earlier evidence that the lunar crust becomes more mafic with depth the data also suggest that the bulk composition of the moon differs from that of the earth9s mantle this difference excludes models for lunar origin that require the earth and moon to have the same compositions such as fission and coaccretion and favors giant impact and capture

seimological studies at parkfield v characteristic microearthquake sequences as fault zone drilling targets studies at very high resolution of microearthquakes at parkfield california since 1987 reveal a systematic organization in space and time dominated by clustering of nearly identical regularly occurring microearthquakes characteristic events on 10 to 20 m wide patches within the fault zone more than half of the 4000 events in our 1987 to 1996 catalog exhibit this trait in general recurrence intervals 0 5 to 2 yr scale with the magnitude of the repeating events for the on scale range mw 0 2 to 1 3 in this study the similar waveforms superimposed locations quasi periodic recurrence and uniform size of these characteristic events permit relative hypocenter location accuracy of meters and predictable occurrence times within windows of a few months clustered characteristic events occur at depths as shallow as about 3 km and these are feasible targets for deep scientific drilling and observation at the focus of a subsequent small earthquake within an active plate boundary fault zone at parkfield the achievable location accuracy to which a hypocenter can be specified as well as the predictability of its occurrence time appear to be uniquely favorable for in situ fault zone measurements

from geodetic imaging of seismic and aseismic fault slip to dynamic modeling of the seismic cycle understanding the partitioning of seismic and aseismic fault slip is central to seismotectonics as it ultimately determines the seismic potential of faults thanks to advances in tectonic geodesy it is now possible to develop kinematic models of the spatiotemporal evolution of slip over the seismic cycle and to determine the budget of seismic and aseismic slip studies of subduction zones and continental faults have shown that aseismic creep is common and sometimes prevalent within the seismogenic depth range interseismic coupling is generally observed to be spatially heterogeneous defining locked patches of stress accumulation to be released in future earthquakes or aseismic transients surrounded by creeping areas clay rich tectonites high temperature and elevated pore fluid pressure seem to be key factors promoting aseismic creep the generally logarithmic time evolution of afterslip is a distinctive feature of creeping faults that suggests a logarithmic dependency of fault friction on slip rate

deformation of the so called gorda plate a new compilation of magnetic anomaly identifications recent side scan sonar data and other data provide constraints on the mechanism of deformation of the area commonly known as the gorda plate a sharp boundary between the rigid juan de fuca plate and deformed material trends southeast from the northern part of the gorda ridge in material older than 2 3 ma the boundary is gradational and trends more to the east previous observations that the anomalies east of the ridge are shorter than their counterparts on the pacific plate are confirmed there is no evidence for subduction or obduction along the mendocino transform adjacent to the ridge the deformation is interpreted to be distributed nw se right lateral simple shear possibly controlled by ductile deformation of the lower crust deformation of this sense is capable of producing the observed shortening the anomalies away from the ridge apparently in crust of age 2 3 ma there must be a transition to deformation on observed ne sw left lateral faults parallel to the original spreading fabric

earthquake scaling relations for mid ocean ridge transform faults 1 a mid ocean ridge transform fault rtf of length l slip rate v and moment release rate can be characterized by a seismic coupling coefficient ae at where ae v is an effective seismic area and at l3 2v 1 2 is the area above an isotherm tref a global set of 65 rtfs with a combined length of 16 410 km is well described by a linear scaling relation 1 ae at which yields 0 15 0 05 for tref 600 c therefore about 85 of the slip above the 600 c isotherm must be accommodated by subseismic mechanisms and this slip partitioning does not depend systematically on either v or l rtf seismicity can be fit by a truncated gutenberg richter distribution with a slope 2 3 in which the cumulative number of events n0 and the upper cutoff moment mc dcac depend on at data for the largest events are consistent with a self similar slip scaling dc ac1 2 and a square root areal scaling 2 ac at1 2 if relations 1 and 2 apply then moment balance requires that the dimensionless seismic productivity 0 0 atv should scale as 0 at 1 4 which we confirm using small events hence the frequencies of both small and large earthquakes adjust with at to maintain constant coupling rtf scaling relations appear to violate the single mode hypothesis which states that a fault patch is either fully seismic or fully aseismic and thus implies ac ae the heterogeneities in the stress distribution and fault structure responsible for relation 2 may arise from a thermally regulated dynamic balance between the growth and coalescence of fault segments within a rapidly evolving fault zone

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

millimeter level precision in a seafloor geodesy experiment at the discovery transform fault east pacific rise 1 direct path acoustic ranging is a promising seafloor geodetic technique for continuous high resolution monitoring of geodynamical process such as fault slip and magma intrusion here we report on a yearlong acoustic ranging experiment conducted across the discovery transform fault at 4 s on the east pacific rise the ranging instruments utilized a novel acoustic signal designed to enhance precision we find that after correcting for variations in sound speed at the path end points the ranging measurements have a precision of 1 mm over baselines approaching 1 km in length the primary difficulty in this particular experiment was with the physical stability of the benchmarks which were deployed free fall from a ship despite the stability issues it appears that the portion of the transform fault that the array covered was locked during the year of our survey the primary obstacle to continuous high sample rate high precision geodetic monitoring of oceanic ridges and transform faults is now limited to the construction of geodetic monuments that are well anchored into bedrock

spatial temporal distribution of early aftershocks following the 2016 ms 6 4 menyuan qinghai china earthquake abstract the lenglongling fault located in the north qilian fold zone along the northeastern margin of the tibetan plateau plays an important role in accommodating the tectonic deformation between the tibetan plateau and the alxa block on 21 january 2016 the ms 6 4 menyuan earthquake occurred near the lenglongling fault in this study we utilize the waveform matched filter technique and double difference earthquake location algorithm to examine the spatial temporal evolution of aftershocks following the menyuan mainshock events from both china earthquake networks center cenc routine catalog and relocated catalog are used as templates to scan through the continuous waveform data 21 january 2016 to 31 december 2016 we identify three and eleven times more events than listed in cenc routine catalog and relocated catalog respectively we find that the earliest aftershocks e g in the first 10 min or so mostly illuminated a steeply dipping plane while aftershocks at later times outlined a near vertical dipping plane with mostly strike slip focal mechanisms the relocated aftershocks also suggest that the menyuan mainshock occurred in a secondary fault rather than the major lenglongling fault which is consistent with geodetic and geological observations moreover we find that aftershocks systematically expand with time along the fault strike and 16 repeating earthquake clusters occur in the rupture zone which are likely driven by afterslip of the mainshock

rock types of south pole aitken basin and extent of basaltic volcanism the enormous pre nectarian south pole aitken spa basin represents a geophysically and compositionally unique region on the moon we present and analyze the mineralogical diversity across this basin and discuss the implications for basin evolution rock types are derived from clementine multispectral data based on diagnostic characteristics of ferrous absorptions in fresh materials individual areas are characterized as noritic dominated by low ca pyroxene gabbroic basaltic dominated by high ca pyroxene feldspathic 3 6 feo and olivine gabbro dominated by high ca pyroxene and olivine the anorthositic crust has effectively been removed from the interior of the basin the style of volcanism within the basin extends over several 100 myr and includes mare basalt and pyroclastic deposits several areas of ancient pre orientale volcanism or cryptomaria have also been identified the nonmare mafic lithology that occurs across the basin is shown to be noritic in composition and is pervasive laterally and vertically we interpret this to represent impact melt breccia deposits derived from the lower crust a few localized areas are identified within the basin that contain more diverse lithologies gabbro olivine gabbro some of which may represent material from the deepest part of the lower crust and perhaps uppermost mantle involved in the spa event

juan de fuca slab geometry and its relation to wadati benioff zone seismicity 1 a new model of the subducted juan de fuca plate beneath western north america allows first order correlations between the occurrence of wadati benioff zone earthquakes and slab geometry temperature and hydration state the geo referenced 3d model constructed from weighted control points integrates depth information from earthquake locations and regional seismic velocity studies we use the model to separate earthquakes that occur in the cascadia forearc from those that occur within the underlying juan de fuca plate and thereby reveal previously obscured details regarding the spatial distribution of earthquakes seismicity within the slab is most prevalent where the slab is warped beneath northwestern california and western washington suggesting that slab flexure in addition to expected metamorphic dehydration processes promotes earthquake occurrence within the subducted oceanic plate earthquake patterns beneath western vancouver island are consistent with slab dehydration processes conversely the lack of slab earthquakes beneath western oregon is consistent with an anhydrous slab double differenced relocated seismicity resolves a double seismic zone within the slab beneath northwestern california that strongly constrains the location of the plate interface and delineates a cluster of seismicity 10 km above the surface that includes the 1992 m7 1 mendocino earthquake we infer that this earthquake ruptured a surface within the cascadia accretionary margin above the juan de fuca plate we further speculate that this earthquake is associated with a detached fragment of former farallon plate other subsurface tectonic elements within the forearc may have the potential to generate similar damaging earthquakes

impact of acid effluent from kawah ijen crater lake on irrigated agricultural soils soil chemical processes and plant uptake abstract volcanogenic contamination of irrigation water caused by effluent from the hyperacid ijen crater lake has severely affected the properties of agricultural soils in east java indonesia from a comparison of acidified topsoil with subsoil and with top and subsoil in a reference area we identified processes responsible for changes in soil and soil solution chemistry induced by acid irrigation water with emphasis on the nutrients ca mg fe and mn and on al which may become phytotoxic under acid conditions in soils compositional data for bulk soil composition and selective extractions with 1 m kcl and 0 2 m acid ammonium oxalate are used in a mass balance approach to specify element fluxes including uptake by rice plants the results show that input via irrigation water has produced an increase in the total aluminum content in the affected topsoil which is of the same order of magnitude as the increase in labile al high bioavailability of al as reflected by concentrations in kcl extracts is consistent with elevated concentrations observed in rice plants in contrast and despite the high input via irrigation water ca and mg concentrations have decreased in all measured soil fractions through dissolution of amorphous phases and minerals and through competition of al for adsorption sites on the exchange complex and plant roots strong leaching is also evident for fe and especially mn in terms of the overall mass balance of the topsoil plant uptake of al ca fe mg and mn is negligible if the use of acid irrigation would be stopped and the soil ph were to increase to values above 4 5 the observed phytotoxicity of al will be halted however crops may then become fully dependent on the input from irrigation water or fertilizer for essential elements due to the previous removal from the topsoil through leaching

lunar iron and titanium abundance algorithms based on final processing of clementine ultraviolet visible images the clementine mission to the moon returned global imaging data collected by the ultraviolet visible uvvis camera this data set is now in a final state of calibration and a five band multispectral digital image model dim of the lunar surface will soon be available to the science community we have used observations of the lunar sample return sites and stations extracted from the final dim in conjunction with compositional information for returned lunar soils to revise our previously published algorithms for the spectral determination of the feo and tio2 content of the lunar surface the algorithms successfully normalize the effects of space weathering so that composition may be determined without regard to a surface s state of maturity these algorithms permit anyone with access to the standard archived dim to construct high spatial resolution maps of feo and tio2 abundance such maps will be of great utility in a variety of lunar geologic studies

large scale relocation of two decades of northern california seismicity using cross correlation and double difference methods 1 we simultaneously reanalyzed two decades 1984 2003 of the digital seismic archive of northern california using waveform cross correlation cc and double difference dd methods to improve the resolution in hypocenter locations in the existing earthquake catalog generated at the northern california seismic network ncsn by up to three orders of magnitude we used a combination of 3 billion cc differential times measured from all correlated pairs of events that are separated by less than 5 km and 7 million p wave arrival time picks listed in the ncsn bulletin data were inverted for precise relative locations of 311 273 events using the dd method the relocated catalog is able to image the fine scale structure of seismicity associated with active faults and revealed characteristic spatiotemporal structures such as streaks and repeating earthquakes we found that 90 of the earthquakes have correlated p wave and s wave trains at common stations and that 12 are colocated repeating events an analysis of the repeating events indicates that uncertainties at the 95 confidence level in the existing network locations are on average 0 7 km laterally and 2 km vertically correlation characteristics and relative location improvement are remarkably similar across most of northern california implying the general applicability of these techniques to image high resolution seismicity caused by a variety of plate tectonic and anthropogenic processes we show that consistent long term seismic monitoring and data archiving practices are key to increase resolution in existing hypocenter catalogs and to estimate the precise location of future events on a routine basis

repeating earthquakes and interplate coupling along the western part of the north anatolian fault abstract the sea of marmara accommodates segments of the north anatolian fault naf in turkey and remains the only part of the western naf that has not ruptured during the last century at its nearest the segment is 20 km from istanbul the largest city in turkey thus it is important to understand the locking state of the fault since it illuminates the strain accumulation rate along the fault segments which in turn is an important input parameter in seismic hazard studies to infer the interplate locking state we used repeating earthquakes that indicate fault creep in the surrounding area using long term april 2005 to may 2013 seismic observations at 12 broadband seismic stations operated by bogazici university kandilli observatory and earthquake research institute we defined repeating earthquakes from waveform coherences that were 0 95 for 40 second long waveforms of the vertical component using the selection procedure we found 21 repeating earthquakes with magnitude 2 3 to 3 2 that are grouped into 9 sequences they are distributed along the main naf comprising three groups of activity one group in the sea of marmara and a group either side to the east and west the three groups are located near the boundary of previous large earthquake ruptures suggesting relatively weak coupling there we also estimated the fault creep rate from the cumulative slip of the repeating earthquakes using a scaling relationship between repeating earthquakes moment and slip the slip rate for these three groups are similar 3 4 cm yr and comparable to albeit slightly higher than those expected from global plate models 2 4 cm yr this suggests relatively weak locking around the groups the relocation results of the repeating earthquake hypocenters in the sea of marmara suggest the creep is occurring at 10 to 20 km depth these results suggest heterogeneous coupling in the segment

an explanation for the double seismic layers north of the mendocino triple junction we propose that the gently eastward dipping double planed seismic zone observed at 15 25 km depths in the southern cascadia subduction zone just north of the mendocino triple junction is a direct consequence of the thermally controlled rheology as the oceanic lithosphere subducts to a depth of about 15 km the temperature regime causes a brittle plastic transition to occur within the oceanic crust thus a ductile layer forms in the lower oceanic crust sandwiched between the brittle upper crust and brittle upper mantle the very high strain rates near the triple junction caused by the northward push of the pacific plate on the gorda plate increase the seismicity and thus accentuate the double seismic zone in this region this model explains the focal mechanisms observed in the seismic zone and their spatial change the double seismic layers clearly define the position of the subducting gorda plate previously uncertain in the cape mendocino region

large earthquakes and creeping faults faults are ubiquitous throughout the earth s crust the majority are silent for decades to centuries until they suddenly rupture and produce earthquakes with a focus on shallow continental active tectonic regions this paper reviews a subset of faults that have a different behavior these unusual faults slowly creep for long periods of time and produce many small earthquakes the presence of fault creep and the related microseismicity helps illuminate faults that might not otherwise be located in fine detail but there is also the question of how creeping faults contribute to seismic hazard it appears that well recorded creeping fault earthquakes of up to magnitude 6 6 that have occurred in shallow continental regions produce similar fault surface rupture areas and similar peak ground shaking as their locked fault counterparts of the same earthquake magnitude the behavior of much larger earthquakes on shallow creeping continental faults is less well known because there is a dearth of comprehensive observations computational simulations provide an opportunity to fill the gaps in our understanding particularly of the dynamic processes that occur during large earthquake rupture and arrest

behavior of repeating earthquake sequences in central california and the implications for subsurface fault creep repeating earthquakes res are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth we investigate the occurrence of these res along faults in central california to determine which faults exhibit creep and the spatiotemporal distribution of this creep at the juncture of the san andreas and southern calaveras paicines faults both faults as well as a smaller secondary fault the quien sabe fault are observed to produce res over the observation period of march 1984 through may 2005 res in this area reflect a heterogeneous creep distribution along the fault plane with significant variations in time cumulative slip over the observation period at individual sequence locations is determined to range from 5 5 58 2 cm on the san andreas fault from 4 8 14 1 cm on the southern calaveras paicines fault and from 4 9 24 8 cm on the quien sabe fault creep at depth appears to mimic the behaviors seen for creep on the surface in that evidence of steady slip triggered slip and episodic slip phenomena are also observed in the re sequences for comparison we investigate the occurrence of res west of the san andreas fault within the southern coast range events within these re sequences occurred only minutes to weeks apart from each other and then did not repeat again over the observation period suggesting that res in this area are not produced by steady aseismic creep of the surrounding fault surface

iron abundances on the lunar surface as measured by the lunar prospector gamma ray and neutron spectrometers i global measurements of iron abundances on the lunar surface are presented using data from the lunar prospector lp gamma ray spectrometer grs and neutron spectrometer ns in this study we derive relative iron abundances from the low altitude high spatial resolution 45 km 2 lp data using the 7 6 mev neutron capture gamma ray doublet as part of the lp grs analysis we demonstrate the importance of accounting for variations in neutron number density across the lunar surface by measuring neutron fluxes using lp ns data in a first step of comparing the lp grs data with previously published iron abundances inferred from clementine spectral reflectance csr data we show that the existing csr feo data are nonlinear with respect to the lp relative iron abundances we use the lp data to linearize the relationship between the csr and the relative iron values then recalibrate the csr data to iron abundance using returned soil abundances we then correlate the csr data except for major anomalies with the lp relative iron measurements to convert the lp data to absolute iron abundances when we compare the lp grs and revised csr data sets we find a very good correspondence there are two locations mare tranquillitatis and south pole aitken spa basin that show major discrepancies suggesting that the csr data are locally overestimating iron abundances in both these regions the discrepancies identified by the lp grs csr comparison are possibly explained by mineralogical differences that are not accounted for in the csr to feo calibration in regards to our understanding of the moon the lp data have found the following i there exist large expanses of mare basalt in the western mare regions that have very high iron abundances 22 23 wt feo that are underrepresented but not absent from the returned sample collection and are highly unusual for mare soils which typically contain a significant amount of highlands contamination 2 the low iron abundances in the lunar highlands 5 feo wt are consistent with a previous analysis using thermal and epithermal neutrons and with the idea that the lunar crust formed by a relatively simple magma ocean process 3 the comparison of lp and csr derived iron abundances suggests that the material within spa basin is similar to a norite type rock without an enriched mantle feo signature 4 a comparison of lp and csr data at tycho crater shows a large discrepancy such that the csr data show moderate iron abundances of 8 9 wt feo while the lp data show very low iron abundances of 3 4 wt feo this discrepancy cannot yet be easily explained by any known process