an advanced photogrammetric method to measure surface roughness application to volcanic terrains in the piton de la fournaise reunion island abstract we present a rapid in situ photogrammetric method to characterize surface roughness by taking overlapping photographs of a scene the method uses a single digital camera to create a high resolution digital terrain model pixel size of 1 32 mm by means of a free open source stereovision software it is based on an auto calibration process which calculates the 3d geometry of the images and an efficient multi image correlation algorithm the method is successfully applied to four different volcanic surfaces namely a a lava flows pahoehoe lava flows slabby pahoehoe lava flows and lapilli deposits these surfaces were sampled in the piton de la fournaise volcano reunion island in october 2011 and displayed various terrain roughnesses our in situ measurements allow deriving digital terrain models that reproduce the millimeter scale height variations of the surfaces over about 12 m 2 five parameters characterizing surface topography are derived along unidirectional profiles the root mean square height the correlation length l c the ratio z s 2 l c the tortuosity index and the fractal dimension d anisotropy in the surface roughness has been first investigated using 1 m long profiles circularly arranged around a central point the results show that l c z s and d effectively catch preferential directions in the structure of bare surfaces secondly we studied the variation of these parameters as a function of the profile length by drawing random profiles from 1 to 12 m in length we verified that and l c increase with the profile length and therefore are not appropriate to characterize surface roughness variation we conclude that z s and d are better suited to extract roughness information for multiple eruptive terrains with complex surface texture

formation and spreading of arabian sea high salinity water mass the formation and seasonal spreading of the arabian sea high salinity water ashsw mass were studied based on the monthly mean climatology of temperature and salinity in the arabian sea north of the equator and west of 80 e on a 2 2 grid the ashsw forms in the northern arabian sea during winter and spreads southward along a 24 sigma t surface against the prevailing weak zonal currents the eastern extent of the core is limited by the strong northward coastal current flowing along the west coast of india during the southwest monsoon the northern part of the core shoals under the influence of the findlater jet while the southern part deepens throughout the year the southward extent of the ashsw is inhibited by the equatorial currents the atmospheric forcing that leads to the formation of ashsw was delineated using the monthly mean climatology of heat and freshwater fluxes monsoon winds dominate all the flux fields during summer june september while latent heat release during the relative calm of the winter november february monsoon driven by cool dry continental air from the north results in an increased density of the surface layer thus excess evaporation over precipitation and turbulent heat loss exceeding the radiative heat gain cool the surface waters of the northern arabian sea during winter and drive convective formation of ashsw

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

surface reflectance of mars observed by crism mro 1 multi angle approach for retrieval of surface reflectance from crism observations mars reco 1 this article addresses the correction for aerosol effects in near simultaneous multi angle observations acquired by the compact reconnaissance imaging spectrometer for mars crism aboard the mars reconnaissance orbiter in the targeted mode crism senses the surface of mars using 11 viewing angles which allow it to provide unique information on the scattering properties of surface materials in order to retrieve these data however appropriate strategies must be used to compensate the signal sensed by crism for aerosol contribution this correction is particularly challenging as the photometric curve of these suspended particles is often correlated with the also anisotropic photometric curve of materials at the surface this article puts forward an innovative radiative transfer based method named multi angle approach for retrieval of surface reflectance from crism observations mars reco the proposed method retrieves photometric curves of surface materials in reflectance units after removing aerosol contribution mars reco represents a substantial improvement regarding previous techniques as it takes into consideration the anisotropy of the surface thus providing more realistic surface products furthermore mars reco is fast and provides error bars on the retrieved surface reflectance the validity and accuracy of mars reco is explored in a sensitivity analysis based on realistic synthetic data according to experiments mars reco provides accurate results up to 10 reflectance error under favorable acquisition conditions in the companion article photometric properties of martian materials are retrieved using mars reco and validated using in situ measurements acquired during the mars exploration rovers mission

eddy topography interactions and the fate of the persian gulf outflow the persian gulf feeds a warm and salty outflow in the gulf of oman northern arabian sea the salt climatological distribution is relatively smooth in the gulf of oman and the signature of a slope current carrying salty waters is difficult to distinguish hundreds of kilometers past the strait of hormuz in contrast to other outflows of the world ocean this study focuses on the mechanisms involved in the spreading of persian gulf water pgw in the gulf of oman using a regional primitive equation numerical simulation the authors show that the dispersion of pgw occurs through a regime that is distinct from for example the one responsible for the mediterranean outflow dispersion the background mesoscale eddy field is energetic and participates actively to the spreading of pgw remotely formed eddies propagate into the gulf of oman and interact with the topography leading to submesoscales formation and pgw shedding eddy topography interactions are isolated in idealized simulations and reveal the formation of intense frictional boundary layers generating submesoscale coherent vortices scvs interactions take place at depths encompassing the pgw depth thus scvs trap pgw and contribute to its redistribution from the boundaries to the interior of the gulf of oman the overall efficiency of these processes is confirmed by a strong contribution of eddy salt fluxes in the interior of the basin and is quantified using particle statistics it is found to be a highly dispersive regime with an approximated eddy diffusivity of inline image

non volcanic tremor resulting from the combined effect of earth tides and slow slip events swarms of non volcanic tremor in southeastern japan are associated with slow slip events and tend to occur with a periodicity of 12 or 24 h this periodicity can be reproduced by a combination of stresses due to earth tides and transient stress changes caused by slow slip events non volcanic tremors may therefore be useful for understanding stress relaxation at the subduction zone interface slow slip events1 are accompanied by swarms of non volcanic tremor2 3 along the subduction zone of the philippine sea plate in southwest japan the swarms often occur with a periodicity of about 12 or 24 h refs 4 5 these episodic events are considered to be a manifestation of stress relaxation at the subducting plate interface1 6 7 here we analyse seismic data to record the locations and durations of non volcanic tremor swarms that occurred in may 2005 and february 2006 we evaluate the magnitude of stress changes produced by slow slip events as well as the effective normal stress on the plate interface where slow slip events occur we find that the observed periodicity in tremor occurrence originates from a combined effect of the periodic stress due to earth tides and the transient stress due to slow slip events our calculations show that non volcanic tremor is sensitive to stress change this phenomenon can therefore be effective in monitoring the process of stress relaxation at subducting plate interfaces

resolved hapke parameter maps of the moon we derived spatially resolved near global hapke photometric parameter maps of the moon from 21 months of lunar reconnaissance orbiter camera lroc wide angle camera wac multispectral observations using a novel tile by tile method 1 latitude by 1 longitude bins the derived six parameters w b c bs0 hs and p for each tile were used to normalize the observed reflectance standard angles i g 60 e 0 instead of the traditional angles i g 30 e 0 within each tile resulting in accurate normalization optimized for the local photometric response each pixel in the seven color near global mosaic 70 s to 70 n and 0 e to 360 e was computed by the median of normalized reflectance from large numbers of repeated observations uv 50 and visible 126 on average the derived mosaic exhibits no significant artifacts with latitude or along the tile boundaries demonstrating the quality of the normalization procedure the derived hapke parameter maps reveal regional photometric response variations across the lunar surface the b c henyey greenstein double lobed phase function parameters maps demonstrate decreased backscattering in the maria relative to the highlands except 321 nm band probably due to the higher content of both smfe submicron iron and ilmenite in the interiors of back scattering agglutinates in the maria the hs angular width of shadow hiding opposition effect map exhibits relatively lower values in the maria than the highlands and slightly higher values for immature highland crater ejecta possibly related to the variation in a grain size distribution of regolith

a physical model for predicting bidirectional reflectances over bare soil abstract radiative processes at the earth s surface are affected by the soil optical properties a good understanding of radiative transfer over a bare soil surface is therefore a prerequisite to addressing more complex cases of discontinuous vegetation canopies while most attempts at retrieving surface characteristics are made by fitting empirical functions to the data we have applied an optimization technique to a physically based surface reflectance model initially developed to study planetary surfaces this inversion procedure allows the direct estimation of the following five parameters the single scattering coefficient two parameters describing the hot spot phenomenon and two parameters describing the scattering phase function the approach is validated by testing the inversion procedure against both synthetic data and actual observations the model is able to predict the observed bidirectional reflectances as well as the directional hemispherical reflectances and to build the complete field of radiances over the upward hemisphere the anisotropic behavior of bare soils is investigated and the prospect for inferring other basic soil properties such as the soil porosity is discussed

the dynamics of the southwest monsoon current in 2016 from high resolution in situ observations and models abstractthe strong stratification of the bay of bengal bob causes rapid variations in sea surface temperature sst that influence the development of monsoon rainfall systems this stratification

triggered tremor sweet spots in alaska 1 to better understand what controls fault slip along plate boundaries we have exploited the abundance of seismic and geodetic data available from the richly varied tectonic environments composing alaska a search for tremor triggered by 11 large earthquakes throughout all of seismically monitored alaska reveals two tremor sweet spots regions where large amplitude seismic waves repeatedly triggered tremor between 2006 and 2012 the two sweet spots locate in very different tectonic environments one just trenchward and between the aleutian islands of unalaska and akutan and the other in central mainland alaska the unalaska akutan spot corroborates previous evidence that the region is ripe for tremor perhaps because it is located where plate interface frictional properties transition between stick slip and stably sliding in both the dip direction and laterally the mainland sweet spot coincides with a region of complex and uncertain plate interactions and where no slow slip events or major crustal faults have been noted previously analyses showed that larger triggering wave amplitudes and perhaps lower frequencies 0 03 hz may enhance the probability of triggering tremor however neither the maximum amplitude in the time domain or in a particular frequency band nor the geometric relationship of the wavefield to the tremor source faults alone ensures a high probability of triggering triggered tremor at the two sweet spots also does not occur during slow slip events visually detectable in gps data although slow slip below the detection threshold may have facilitated tremor triggering

surface wave potential for triggering tectonic nonvolcanic tremor corrected abstract source processes commonly posed to explain instances of remote dynamic triggering of tectonic nonvolcanic tremor by surface waves include frictional failure and various modes of fluid activation the relative potential for love and rayleigh wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike slip faults under the coulomb griffith failure criteria as a function of incidence angle are anticorrelated over the 15 to 30 km depth range that hosts tectonic tremor love wave potential is high for strike parallel incidence on low angle reverse faults and null for strike normal incidence the opposite holds for rayleigh waves love wave potential is high for both strike parallel and strike normal incidence on vertical strike slip faults and minimal for 45 incidence angles the opposite holds for rayleigh waves this pattern is consistent with documented instances of tremor triggered by love waves incident on the cascadia megathrust and the san andreas fault saf in central california resulting from shear failure on weak faults apparent friction is 0 2 documented instances of tremor triggered by surface waves with strike parallel incidence along the nankai megathrust beneath shikoku japan however are associated primarily with rayleigh waves this is consistent with the tremor bursts resulting from mixed mode failure crack opening and shear failure facilitated by near lithostatic ambient pore pressure low differential stress with a moderate friction coefficient 0 6 on the nankai subduction interface rayleigh wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process except perhaps for an indirect role on the saf in sustaining tremor into the rayleigh wave coda that was initially triggered by love waves

water mass distributions at intermediate layers off the somali coast during the onset of the southwest monsoon 1979 abstract hydrographic observations at intermediate depth in the somali basin have been made during and after the transition from the northeast monsoon to the southwest monsoon 1979 the data are discussed in relation to measurements of absolute currents during the same time period earlier water mass identification by warren et al 1966 is confirmed and extended by introducing a well defined equatorial water mass the distribution of water masses and its temporal evolution with the changing monsoonal wind field is analyzed on three different spatial scales equatorial and near coastal undercurrents are an important factor in the large scale redistribution of water masses in the intermediate layers cross equatorial exchange of water in particular highly saline red sea water is largely confined to a narrow region off the east african coast no obvious response of these currents to the onset of the southwest monsoon is detected in the mesoscale range anticyclonic subsurface eddies containing equatoria

dynamic stresses coulomb failure and remote triggering dynamic stresses associated with crustal surface waves with 15 30 sec periods and peak amplitudes 5 km the latter is consistent with the observation that extensional or transtensional tectonic regimes are more susceptible to remote triggering by rayleigh wave dynamic stresses than compressional or transpressional regimes locally elevated pore pressures may have a role in the observed prevalence of dynamic triggering in extensional regimes and geothermal volcanic systems

injection of oxygenated persian gulf water into the southern bay of bengal persian gulf water pgw is an oxygenated high salinity water mass that has recently been detected in the bay of bengal bob however little is known about the transport pathways of pgw into the bob ocean glider observations presented here demonstrate the presence of pgw in the southwestern bob output from an ocean reanalysis product shows that this pgw signal is associated with a northward flowing filament of high salinity water particle tracking experiments reveal two pathways one in the eastern arabian sea that takes a minimum of 2 years and another in the western arabian sea that takes a minimum of 3 years the western pathway connects to the bob via equatorial currents the greatest influx of pgw occurs between 82 and 87 e during the southwest monsoon we propose that injection of pgw to the bob oxygen minimum zone omz contributes to keeping oxygen concentrations in the bob above the level at which denitrification occurs

a hycom modeling study of the persian gulf 2 formation and export of persian gulf water 1 the circulation and water mass transformation processes in the persian gulf and the water exchange with the indian ocean through the strait of hormuz are studied using the hybrid coordinate ocean model hycom model results suggest that intruding indian ocean surface water iosw is transformed into hypersaline waters with salinity 41 practical salinity unit by the fresh water loss in the northern end of the gulf and in the southern shallow banks during wintertime intense heat loss from sea to air leads to the formation of cold and saline waters both in the northern gulf and in the southern gulf dense waters formed in the southern gulf have higher salinity and spill into the axial deep trough of the gulf as a sporadic bottom outflow in winter which leads to high salinity pulses in the strait as observed whereas in summer their buoyancy is increased due to heating and they are exported as a warm yet salty intermediate depth flow through the strait dense waters formed in the northern gulf propagate toward the strait along the axial trough throughout the year correspondingly there are two branches of seasonal overturning circulation in density classes the northern branch peaking in august with strength of 0 13 sv and the southern branch peaking in february and december with strength of 0 08 sv these two branches outflow together feed a seasonally varying deep outflow through the strait with an annual mean volume transport of 0 12 sv

dynamics of the indian ocean oxygen minimum zones abstract in the indian ocean mid depth oxygen minimum zones omzs occur in the arabian sea and the bay of bengal the lower part of the arabian sea omz asomz below 400 m intensifies northward across the basin in contrast its upper part above 400 m is located in the central eastern basin well east of the most productive regions along the western boundary the bay of bengal omz bbomz although strong is weaker than the asomz to investigate the processes that maintain the indian ocean omzs we obtain a suite of solutions to a coupled biological physical model its physical component is a variable density 6 1 2 layer model in which each layer corresponds to a distinct dynamical regime or water mass type its biological component has six compartments nutrients phytoplankton zooplankton two size classes of detritus and oxygen because the model grid is non eddy resolving 0 5 the biological model also includes a parameterization of enhanced mixing based on the eddy kinetic energy derived from satellite observations to explore further the impact of local processes on omzs we also obtain analytic solutions to a one dimensional simplified version of the biological model our control run is able to simulate basic features of the oxygen nutrient and phytoplankton fields throughout the indian ocean the model omzs result from a balance or lack thereof between a sink of oxygen by remineralization and subsurface oxygen sources due primarily to northward spreading of oxygenated water from the southern hemisphere with a contribution from persian gulf water in the northern arabian sea the northward intensification of the lower asomz results mostly from horizontal mixing since advection is weak in its depth range the eastward shift of the upper asomz is due primarily to enhanced advection and vertical eddy mixing in the western arabian sea which spread oxygenated waters both horizontally and vertically advection carries small detritus from the western boundary into the central eastern arabian sea where it provides an additional source of remineralization that drives the asomz to suboxic levels the model bbomz is weaker than the asomz because the bay lacks a remote source of detritus from the western boundary although detritus has a prominent annual cycle the model omzs do not because there is not enough time for significant remineralization to occur

retrieving soil surface roughness with the hapke photometric model confrontation with the ground truth abstract surface roughness can be defined as the mean slope angle integrated over all scales from the grain size to the local topography it controls the energy balance of bare soils in particular the angular distribution of scattered and emitted radiation this provides clues to understand the intimate structure and evolution of planetary surfaces over ages in this article we investigate the capacity of the hapke photometric model the most widely used in planetary science to retrieve surface roughness from multiangular reflectance data its performance is still a question at issue and we lack validation experiments comparing model retrievals with ground measurements to address this issue and to show the potentials and limits of the hapke model we compare the mean slope angle determined from very high resolution digital elevation models of volcanic and sedimentary terrains sampled in the asal ghoubbet rift republic of djibouti to the photometric roughness estimated by model inversion on multiangular reflectance data measured on the ground chamelon field goniometer and from space pleiades images the agreement is good on moderately rough surfaces in the domain of validity of the hapke model and poor on others

character and dynamics of the red sea and persian gulf outflows historical hydrographic data and a numerical plume model are used to investigate the initial transformation dynamics and spreading pathways of red sea and persian gulf outflow waters where they enter the indian ocean the annual mean transport of these outflows is relatively small 0 4 sv but they have a major impact on the hydrographic properties of the indian ocean at the thermocline level because of their high salinity they are different from other outflows in that they flow over very shallow sills depth 200 m into a highly stratified upper ocean environment and they are located at relatively low latitudes 12 n and 26 n furthermore the red sea outflow exhibits strong seasonal variability in transport the four main results of this study are as follows first on the basis of observed temperature salinity t s characteristics of the outflow source and product waters we estimate that the red sea and persian gulf outflows are diluted by factors of 2 5 and 4 respectively as they descend from sill depth to their depth of neutral buoyancy the high dilution factor for the persian gulf outflow results from the combined effects of large initial density difference between the outflow source water and oceanic water and low outflow transport second the combination of low latitude and low outflow transport and associated low outflow thickness results in ekman numbers for both outflows that are o 1 this indicates that they should be thought of as frictional density currents modified by rotation rather than geostrophic density currents modified by friction third different mixing histories along the two channels that direct red sea outflow water into the open ocean result in product waters with significantly different densities which probably contributes to the multilayered structure of the red sea product waters in both outflows seasonal variations in source water and oceanic properties have some effect on the t s of the product waters but they have only a minor impact on equilibrium depth fourth product waters from both outflows are advected away from the sill region in narrow boundary currents at least during part of the year at other times the product water appears more in isolated patches

dynamic stresses coulomb failure and remote triggering and to surface wave potential for triggering tectonic nonvolcanic tremor hill 2008 and hill 2010 contain two technical errors 1 a missing factor of 2 for computed love wave amplitudes and 2 a sign error in the off diagonal elements in the euler rotation matrix correction 1 the equations for love wave stresses equation 21 in hill 2008 and equation a8 in hill 2010 are correct a factor of 2 in these equations however was inadvertently omitted in the computational code accordingly the corrected love wave stress amplitudes are double those published in hill 2008 and hill 2010 correction 2 the euler rotation matrix b that was used in hill 2008 and hill

planetary regolith surface analogs optimized determination of hapke parameters using multi angular spectro imaging laboratory data this work presents a method for a determination of the global set of parameters involved in hapke s model for planetary surface analogs when dealing with a set of angular conditions representative of the usual range of observation in planetary exploration for spaceborne optical instruments the present approach is founded on a genetic algorithm the whole set of hapke parameters is treated simultaneously without any a priori assumptions it limits the risk of meeting a local extreme and the stability and repeatability of the determination are improved moreover it requires less computational time than a monte carlo routine as a demonstration using multi angular measurements acquired by a new laboratory wide field multispectral imaging facility parameter values for various grain sizes and material compositions of planetary regolith surface analogs are derived and their potential wavelength dependence is studied the results coherent with the literature validate all the steps in our methodology we focus our interest in the understanding of the physical meaning of hapke s parameters in particular of the parameter of the shadowing function for macroscopic roughness it appears that the features smaller than the centimeter scale contribute predominantly to the photometric effect related to the rocky aspect of planetary soil surfaces the parameter may thus be mainly considered as an integral of the roughness properties in the submillimetric centimetric range indeed the most representative case for describing natural regolith surface lies in texture classes in the millimeter range not involving necessarily a high macroscopic roughness with large surface slopes at hundreds of meters scale these findings strengthen the case that depends on both the grain size and the material geological properties

remote triggering of tremor along the san andreas fault in central california received 30 august 2008 accepted 16 april 2009 published 18 july 2009 1 we perform a systematic survey of triggered tremor along the san andreas fault in central california for the 31 teleseismic earthquakes with mw 7 5 since 2001 we identify 10 teleseismic events associated with clear triggered tremor about 52 of the tremor is concentrated south of parkfield near cholame where ambient tremor has been identified previously and the rest is widely distributed in the creeping section of the san andreas fault north of parkfield tremor is generally initiated and is in phase with the love wave particle velocity however the pattern becomes complicated with the arrival of the rayleigh waves and sometimes tremor continues after the passage of the surface waves we identify two cases in which tremor is triggered during the teleseismic pkp phase these results suggest that while shear stress from the passage of the love waves plays the most important role in triggering tremor in central california other factors such as dilatational stresses from the rayleigh and p waves also contribute we also examine the ambient tremor occurrence rate before and after the teleseismic events and find a transient increase of stacked tremor rate during the passage of the teleseismic surface waves this observation implies that the occurrence time of tremor is temporally advanced by the dynamic stresses of the teleseismic waves the amplitude of the teleseismic waves correlates with the occurrence of triggered tremor and the inferred tremor triggering threshold is 2 3 kpa the relatively low triggering threshold indicates that the effective stress at the tremor source region is very low most likely due to near lithostatic fluid pressure

retrieving photometric properties of desert surfaces in china using the hapke model and misr data abstract the retrieval of photometric properties of desert surfaces is an important first step in the parameterization of land surface components of regional dust emission and global radiation models and in earth system modeling in this study the values of hapke s photometric parameters h b c b0 and were retrieved from the multi angle imaging spectroradiometer misr instrument at locations in china s deserts four pixels represented the typical surface characteristics of the taklimakan desert sand dunes of kumtag desert relatively smooth areas of the kumtag desert and the aeolian sandy soil of loulan in contrast to earlier studies we found that the retrieved parameter values were largely affected by the initial value to combat this problem we used a monte carlo method with physical constraints and a conformity indicator to ensure physically meaningful inversion the results showed that the angular domain of misr observations was sufficiently large to determine confidently the values of hapke s photometric parameters with the exception of the opposition effect width h retrieved values for the single scattering albedo and macroscopic roughness were consistent with qualitative observations about the structure and composition of the surface material and the nature of the dune forms respectively at loulan where the surface was smoother than other sites retrieved values exhibited the strongest backward scattering these results indicated that at the sensor scale a rough surface e g dunes does not necessarily mean more backward scattering than a smooth surface this finding has significant implications for empirical methods e g using the normalized index of backward scattered radiance minus forward scattered radiance as an indicator to indicate surface roughness which should be used carefully for analyzing surface roughness from remote sensing data future research is needed to 1 understand how surface roughness at the sub pixel scale modifies the angular characteristics of reflectance and to 2 find practical methods for rapid whole image processing for mapping the photometric parameters

strong tremor near parkfield ca excited by the 2002 denali fault earthquake 1 we show clear evidence of non volcanic tremor triggered by 2002 mw7 8 denali fault earthquake near parkfield triggered tremor is identified as bursts of high frequency 2 8 hz non impulsive seismic energy whose envelope is coherent among many stations and has the same periodicity as the passing surface waves the tremor originates from at least three hypocenters near the san andreas fault with differing frictional regimes two in the creeping section and the other where the san andreas is transitional between creeping and locked all the sources originate below the seismogenic zone suggesting that transitional frictional properties are necessary conditions for tremor generation tremor is excited by the love waves when the san andreas is sheared in a right lateral sense encouraging slip and is absent when the san andreas is sheared in a left lateral sense consistent with a simple frictional response to the driving stress

dynamic stresses coulomb failure and remote triggering corrected abstract dynamic stresses associated with crustal surface waves with 15 30 s periods and peak amplitudes

testing the hapke photometric model improved inversion and the porosity correction abstract in conjunction with a companion paper shepard m k helfenstein p 2011 icarus submitted for publication we derive test and apply a detailed approach for visualizing the phase angle dependence of light scattering in particulate soils from both whole disk and disk resolved observations to reduce the number of model parameters and provide stronger constraints on model fits we combine hapke s hapke b 2008 icarus 195 918 926 recent correction for effects of porosity with his hapke b 1986 icarus 67 264 280 model of the shadow hiding opposition effect we further develop our method as a tool for least squares fitting of hapke s model to photometric data finally we present an improved method for estimating uncertainties in retrieved values of hapke model parameters we perform a preliminary test of the model on spectrogoniometric measurements from three selected laboratory samples from shepard and helfenstein shepard m k helfenstein p 2007 j geophys res 112 e03001 17 our preliminary suite of test samples is too small and selective to permit the drawing of general conclusions however our results suggest that hapke s porosity correction improves the fidelity of fits to samples composed of low and moderate albedo particles and may allow for more reliable retrieval of porosity estimates in these materials however we find preliminary evidence that in high albedo surfaces the effects of porosity may be difficult to detect

evidence for the existence of persian gulf water and red sea water in the bay of bengal the high salinity water masses that originate in the north indian ocean are arabian sea high salinity water ashsw persian gulf water pgw and red sea water rsw among them only ashsw has been shown to exist in the bay of bengal we use ctd data from recent cruises to show that pgw and rsw also exist in the bay the presence of rsw is marked by a deviation of the salinity vertical profile from a fitted curve at depths ranging from 500 to 1000 m this deviation though small of the order of similar to 0 005 psu and therefore comparable to the ctd accuracy of 0 003 psu is an order of magnitude larger than the similar to 0 0003 psu fluctuations associated with the background turbulence or instrument noise in this depth regime allowing us to infer the existence of rsw throughout the bay pgw is marked by the presence of a salinity maximum at 200 450 m in the southwestern bay pgw can be distinguished from the salinity maximum due to ashsw because of the intervening arabian sea salinity minimum this salinity minimum and the maximum associated with ashsw disappear east and north of the south central bay 85a degrees e 8a degrees n owing to mixing between the fresher surface waters that are native to the bay bay of bengal water or bbw with the high salinity ashsw hence ashsw is not seen as a distinct water mass in the northern and eastern bay and the maximum salinity over most of the bay is associated with pgw the surface water over most of the bay is therefore a mixture of ashsw and the low salinity bbw as a corollary we can also infer that the weak oxygen peak seen within the oxygen minimum zone in the bay at a depth of 250 400 m is associated with pgw the hydrographic data also show that these three high salinity water masses are advected into the bay by the summer monsoon current which is seen to be a deep current extending to 1000 m these deep currents extend into the northern bay as well providing a mechanism for spreading ashsw pgw and rsw throughout the bay

photometric properties of mars soils analogs we have measured the bidirectional reflectance of analogs of dry wet and frozen martian soils over a wide range of phase angles in the visible spectral range all samples were produced from two geologic samples the standard jsc mars 1 soil simulant and hawaiian basaltic sand in a first step experiments were conducted with the dry samples to investigate the effects of surface texture comparisons with results independently obtained by different teams with similar samples showed a satisfying reproducibility of the photometric measurements as well as a noticeable influence of surface textures resulting from different sample preparation procedures in a second step water was introduced to produce wet and frozen samples and their photometry investigated optical microscope images of the samples provided information about their microtexture liquid water even in relatively low amount resulted in the disappearance of the backscattering peak and the appearance of a forward scattering peak whose intensity increases with the amount of water specular reflections only appeared when water was present in an amount large enough to allow water to form a film at the surface of the sample icy samples showed a wide variability of photometric properties depending on the physical properties of the water ice we discuss the implications of these measurements in terms of the expected photometric behavior of the martian surface from equatorial to circum polar regions in particular we propose some simple photometric criteria to improve the identification of wet and or icy soils from multiple observations under different geometries

surface roughness retrieval by inversion of the hapke model a multiscale approach abstract surface roughness is a key property of soils that controls many surface processes and influences the scattering of incident electromagnetic waves at a wide range of scales hapke 2012b designed a photometric model providing an approximate analytical solution of the bidirectional reflectance distribution function brdf of a particulate medium he introduced the effect of surface roughness as a correction factor of the brdf of a smooth surface this photometric roughness is defined as the mean slope angle of the facets composing the surface integrated over all scales from the grain size to the local topography yet its physical meaning is still a question at issue as the scale at which it occurs is not clearly defined this work aims at better understanding the relative influence of roughness scales on soil brdf and to test the ability of the hapke model to retrieve a roughness that depicts effectively the ground truth we apply a wavelet transform on millimeter digital terrain models dtm acquired over volcanic terrains this method allows splitting the frequency band of a signal in several sub bands each corresponding to a spatial scale we demonstrate that sub centimeter surface features dominate both the integrated roughness and the brdf shape we investigate the suitability of the hapke model for surface roughness retrieval by inversion on optical data a global sensitivity analysis of the model shows that soil brdf is very sensitive to surface roughness nearly as much as the single scattering albedo according to the phase angle but also that these two parameters are strongly correlated based on these results a simplified two parameter model depending on surface albedo and roughness is proposed inversion of this model on brdf data simulated by a ray tracing code over natural targets shows a good estimation of surface roughness when the assumptions of the model are verified with a priori knowledge on surface albedo

seasonal spreading of the persian gulf water mass in the arabian sea the characteristics of the subsurface salinity maximum associated with the persian gulf water mass pgw are used to quantify the spreading and mixing of pgw in the thermocline of the arabian sea based on a bimonthly climatology of temperature and salinity examination of the seasonal cycles of heat and freshwater fluxes in the persian gulf region indicates that pgw forms as a result of elevated evaporative cooling in conjunction with reduced insolation during winter maps are presented of the distributions of depth salinity and geostrophic flow on 26 5 which nearly coincides with the core of the pgw after intense mixing in the strait of hormuz the property fields suggest that warm 17 c and high salinity 36 2 psu pgw enters the arabian sea to form a subsurface salinity extremum between 200 and 300 m we have found variability in the distribution of pgw in the arabian sea associated with monsoonal changes in the arabian sea circulation during the winter monsoon there is southward spreading of pgw along the western boundary during summer it is not present lateral mixing with low salinity water from the bay of bengal in the region south of 10 n and along the west coast of india during winter accounts for changes in the characteristics of pgw along these paths associated with the findlater jet during summer the entire thermohaline structure is vertically displaced along the coasts of somalia and arabia ekman convergence in the central arabian sea accounts for deepening of the pgw either lateral or vertical mixing would cause changes in pgw properties in these regions during this time pgw spreads predominantly southward along the central arabian sea as indicated by a tongue of high salinity

spectrogoniometry and modeling of martian and lunar analog samples and apollo soils abstract we present new visible near infrared multispectral reflectance measurements of seven lunar soil simulants two apollo soils and eight martian analog samples as functions of illumination and emission angles using the bloomsburg university goniometer by modeling these data with hapke theory we provide constraints on photometric parameters single scattering albedo phase function parameters macroscopic roughness and opposition effect parameters to provide additional ground truth photometric properties to assist analyses of spacecraft data a wide range of modeled photometric properties were variably related to albedo color grain size and surface texture finer grained samples here have high single scattering albedo values compared to their coarser grained counterparts as well as lower macroscopic roughness values the mars analog samples and apollo soils exhibit slightly lower opposition effect width parameter values than the lunar analogs whereas the opposition effect magnitude is not well constrained by the models the mars analog soils are typically relatively backscattering and consistent with fairly rough particles with a moderate density of internal scatterers similar to the in situ observations of some soils by the mars exploration rover mer spirit some lunar analog soil models result in moderately forward scattering behaviors as do the two apollo soils other fine grained and or glass rich lunar analog samples populate a narrowly forward scattering regime similar to model results from observations of some rover tracks observed by the mer opportunity rover and some dust poor gray rocks by the spirit rover an experiment to mimic the spherule rich soils observed by opportunity demonstrated a large decrease in single scattering albedo compared to spherule free soil surfaces as well as increased surface roughness narrow opposition effects and a significant increase in backscattering similar to some of the opportunity soils phase reddening effects are documented in many soils as an increase in near infrared visible ratios with phase angle some samples exhibit falloffs in these ratio phase curves at phase angles beyond 50 80 that are likely related to an increased importance of surface scattering at high phase angles none of the lunar analog soils perfectly match the modeled photometric parameters of the two apollo soils the phase reddening nature of the mare soil included an upturn in ratio values at phase angles

integrated spectral analysis of mare soils and craters applications to eastern nearside basalts abstract high spatial resolution clementine images are examined to measure the reflectance properties of small and optically immature mare craters that have sampled discrete compositional units the spectral properties of these relatively crystalline mare materials are compared to associated mature soils to determine the effects of space weathering on specific basalt types space weathering is observed to alter the optical properties of distinct lunar basalt units in a systematic manner allowing compositional distinctions to be recognized across maturity states ultraviolet visible reflectance properties of mare basalts are sensitive to titanium content but are relatively independent of maturity state and demonstrate only a slight reddening as regoliths mature to soils other compositional distinctions between basalt types are identified by differences in albedo and band strength of ferrous minerals that are maintained over a full range of maturity states immature deposits within large craters are compared to the spectral properties of well defined mare units to examine the composition of buried materials when craters excavate through the mare highland contamination is readily identified as a mixing relation between mafic and feldspathic lithologies the approach presented here provides new information on the composition and stratigraphy of several nearside mare deposits including the identification of thin low iron and very low titanium basalts in lacus somniorum and more iron rich low titanium basalts in eastern mare frigoris

spectrophotometric properties of materials observed by pancam on the mars exploration rovers 2 opportunity 1 the panoramic camera pancam on the mars exploration rover opportunity acquired visible near infrared multispectral observations of soils and rocks under varying viewing and illumination geometries that were modeled using radiative transfer theory to improve interpretations of the microphysical and surface scattering nature of materials in meridiani planum nearly 25 000 individual measurements were collected of rock and soil units identified by their color and morphologic properties over a wide range of phase angles 0 150 at eagle crater in the surrounding plains in endurance crater and in the plains between endurance and erebus craters through sol 492 corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission disparity maps created from pancam stereo images allowed inclusion of local facet orientation estimates outcrop rocks overall exhibited the highest single scattering albedos 0 9 at 753 nm and most spherule rich soils exhibited the lowest 0 6 at 753 nm macroscopic roughness among outcrop rocks varied but was typically larger than spherule rich soils data sets with sufficient phase angle coverage resulting in well constrained hapke parameters suggested that models using single term and two term henyey greenstein phase functions exhibit a dominantly broad backscattering trend for most undisturbed spherule rich soils rover tracks and other compressed soils exhibited forward scattering while outcrop rocks were intermediate in their scattering behaviors some phase functions exhibited wavelength dependent trends that may result from variations in thin deposits of airfall dust that occurred during the mission

surface reflectance of mars observed by crism mro 2 estimation of surface photometric properties in gusev crater and meridiani planum the present article proposes an approach to analyze the photometric properties of the surface materials from multi angle observations acquired by the compact reconnaissance imaging spectrometer for mars crism on board the mars reconnaissance orbiter we estimate photometric parameters using hapke s model in a bayesian inversion framework this work also represents a validation of the atmospheric correction provided by the multi angle approach for retrieval of surface reflectance from crism observations mars reco proposed in the companion article the latter algorithm retrieves photometric curves of surface materials in reflectance units after removing the aerosol contribution this validation is done by comparing the estimated photometric parameters to those obtained from in situ measurements by panoramic camera instrument at the mars exploration rover mer spirit and mer opportunity landing sites consistent photometric parameters with those from in situ measurements are found demonstrating that mars reco gives access to accurate surface reflectance moreover the assumption of a non lambertian surface as included in mars reco is shown to be significantly more precise to estimate surface photometric properties from space in comparison to methods based on a lambertian surface assumption in the future the presented method will allow us to map from orbit the surface bidirectional reflectance and the related photometric parameters in order to characterize the martian surface

characterization and mapping of surface physical properties of mars from crism multi angular data application to gusev crater and meridiani planum the analysis of particle physical properties grain size shape and internal structure and its organization surface porosity roughness and grain size distribution provides information about the geological processes which formed and modified planetary surfaces crism compact reconnaissance imaging spectrometer for mars multi angular observations varied emission angles allow for the characterization of the surface scattering behavior which depends on the composition and on the material physical properties such as the grain size shape internal structure and the surface roughness after an atmospheric correction compensating mineral aerosol effects by the multi angle approach for retrieval of the surface reflectance from crism observations mars reco the surface reflectances at different geometries were analyzed by inverting the hapke photometric model depending on six parameters single scattering albedo 2 phase function terms macroscopic roughness and 2 opposition effects terms in this work surface photometric maps are created to observe the spatial variations of surface scattering properties as a function of geological units information regarding the single scattering albedo the particle phase function and the macroscopic roughness are provided at the crism spatial resolution 200 m pixel this article describes the application of this methodology to the data covering the mars exploration rover mer landing sites located at gusev crater and meridiani planum where orbital and in situ observations are available complementary orbital observations e g crism spectra thermal emission imaging system themis high resolution imaging science experiment hirise images were used for interpreting the modeled hapke photometric parameters in terms of physical properties which can be used to constrain the geological processes available mer in situ observations were used as ground truth to validate the interpretations of the hapke parameters varied scattering properties were observed within a crism observation 5 10 km suggesting that the surfaces are controlled by local geological processes e g volcanic resurfacing aeolian and impact processes rather than regional or global processes results are consistent with the in situ observations thus validating the approach and the use of photometry for the characterization of martian surface physical properties

a search in strainmeter data for slow slip associated with triggered and ambient tremor near parkfield california 1 we test the hypothesis that as in subduction zones slow slip facilitates triggered and ambient tremor in the transform boundary setting of california our study builds on the study of peng et al 2009 of triggered and ambient tremor near parkfield california during time intervals surrounding 31 potentially triggering m 7 5 teleseismic earthquakes waves from 10 of these triggered tremor and 29 occurred in periods of ambient tremor activity we look for transient slow slip during 3 month windows that include 11 of these triggering and nontriggering teleseisms using continuous strain data recorded on two borehole gladwin tensor strainmeters gtsm located within the distribution of tremor epicenters we model the gtsm data assuming only tidal and drift signals are present and find no detectable slow slip either ongoing when the teleseismic waves passed or triggered by them we infer a conservative detection threshold of about 5 nanostrain for abrupt changes and about twice this for slowly evolving signals this could be lowered slightly by adding analyses of other data types modeled slow slip signals and gtsm data calibration detection of slow slip also depends on the slipping fault s location and size which we describe in terms of equivalent earthquake moment magnitude m in the best case of the gtsm above a very shallow slipping fault detectable slip events must exceed m 2 and if the slow slip is beneath the seismogenic zone below 15 km depth even m 5 events are likely to remain hidden

surface wave potential for triggering tectonic nonvolcanic tremor source processes commonly posed to explain instances of remote dynamic triggering of tectonic nonvolcanic tremor by surface waves include frictional failure and various modes of fluid activation the relative potential for love and rayleigh wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike slip faults under the coulomb griffith failure criteria as a function of incidence angle is anticorrelated over the 15 to 30 km depth range that hosts tectonic tremor love wave potential is high for strike parallel incidence on low angle reverse faults and null for strike normal incidence the opposite holds for rayleigh waves love wave potential is high for both strike parallel and strike normal incidence on vertical strike slip faults and minimal for 45 incidence angles the opposite holds for rayleigh waves this pattern is consistent with documented instances of tremor triggered by love waves incident on the cascadia megathrust and the san andreas fault saf in central california resulting from shear failure on weak faults apparent friction 0 2 however documented instances of tremor triggered by surface waves with strike parallel incidence along the nankai megathrust beneath shikoku japan is associated primarily with rayleigh waves this is consistent with the tremor bursts resulting from mixed mode failure crack opening and shear failure facilitated by near lithostatic ambient pore pressure low differential stress with a moderate friction coefficient 0 6 on the nankai subduction interface rayleigh wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process except perhaps for an indirect role on the saf in sustaining tremor into the rayleigh wave coda that was initially triggered by love waves

the railroad switch effect of seasonally reversing currents on the bay of bengal high salinity core the southwest monsoon current smc flows eastward from the arabian sea into the bay of bengal bob during summer advecting a core of high salinity water this high salinity core has been linked with arabian sea high salinity water that is presumed to enter the bob directly from the arabian sea via the smc here we show that the high salinity core originates primarily from the western equatorial indian ocean reaching the bob via the somali current the equatorial undercurrent and the smc years with anomalously saline high salinity cores are linked with the east africa coastal current and the somali current winter convergence and an anomalously strong equatorial undercurrent seasonal reversals that occur at the somali current and smc junctions act as railroad switches diverting water masses to different basins in the northern indian ocean interannual fluctuations of the equatorial undercurrent are linked to wind stress and el nino