highland contamination in lunar mare soils improved mapping with multiple end member spectral mixture analysis mesma 1 multiple end member spectral mixture analysis mesma was applied to the clementine uvvis global 1 km multispectral data set and the resulting highland material fraction image was used to investigate highland contamination of mare surfaces by impact cratering mesma decomposes each pixel with the number of end members fewer than the number of the spectral bands of clementine uvvis data this allows the use of variable end member combinations to accommodate global spectral variance a 13 end member set of lunar soil components that spans the lunar spectral diversity was selected from the uvvis data and included 1 mature and 4 fresh highland soils 4 mature and 2 fresh mare soils and 2 soils of dark mantling materials this set was applied to the lunar data through mesma and an aggregated global highland abundance was derived comparison of the highland fraction results from mesma and traditional spectral mixture analysis sma demonstrated that mesma better accommodates the compositional variation of mare soils resulting in a greater accuracy in the measurement of highland with the derived products we investigated highland contamination in mare nectaris mare fecunditatis and mare crisium these mare surfaces are proximal to the large craters theophilus taruntius langrenus and proclus and provided an opportunity to investigate highland contamination by large impacts the analyses indicated that theophilus impact resulted in highland contamination of 20 80 on most of mare nectaris while taruntius and langrenus impacts caused 5 40 contamination of mare fecunditatis the trend of minimal highland abundance in mare fecunditatis correlates poorly with basalt thickness suggesting an efficient lateral mixing due to the large craters taruntius and langrenus additionally proclus combining with other craters was responsible for highland contamination in most of the mare crisium surface and some basalt classification in this mare reflects highland contamination of the spectral properties mesma significantly reduces uncertainty in calculating global composition variations due to mixing and these analyses demonstrate that large impacts played a dominant role in delivering highland materials onto three mare surfaces

a processing system to monitor greenland outlet glacier velocity variations at decadal and seasonal time scales utilizing the landsat imagery abstract in this paper we present a monitoring system for area wide flow velocity fields of the outlet glaciers of the greenland ice sheet gris utilizing the freely available landsat archive in order to process this large amount of satellite images an almost automatic monitoring system was developed with the global digital elevation map v2 gdem v2 of the advanced spaceborne thermal emission and reflection radiometer aster an improved orthorectification was applied which in combination with a destriping correction of the landsat 7 products with scan line corrector slc failure leads to more precise flow velocity information in addition outliers were removed using an adaptive recursive filter approach for the time span 1972 2012 more than 100 000 flow velocity fields were derived from over 16 000 optical multi sensoral landsat scenes landsat 1 to landsat 7 allowing the determination of the long term flow velocity trend moreover the high temporal resolution facilitates the analysis of seasonal flow velocity variations of numerous outlet glaciers for many of the major outlet glaciers the results show an acceleration pattern that is consistent with most of the previously published analyses however the flow velocity changes do not have a uniform pattern in their temporal and spatial distribution this study provides both a high temporal densification and an extension of existing flow velocity information of the gris margin finally this processing chain in its generality allows for the determination of various types of surface displacements and can be applied to other glacier regions

the nature of crater rays the copernicus example crater rays are formed during a cratering event as target material is ballistically ejected to distances of many crater radii forming narrow generally high albedo approximately linear features extending outward from the crater the nature of crater rays was examined for the lunar crater copernicus using new information on the composition of surface material from near ir reflectance measurements surface roughness from radar backscatter measurements and photogeologic data from available images part of the data analysis included use of mixing models to quantify the mixing systematics observed between primary ejecta and local substrate of the ray on the basis of compositional parameters from reflectance spectra primary material from copernicus can be detected in the surface material of rays in decreasing amounts with increasing radial distance e g 20 25 primary ejecta at six crater radii for distances greater than three crater radii the proportion of local material to primary ejecta observed from these compositional reflectance data is approximately equal to that predicted by previous laboratory and ballistic studies of craters within three crater radii the compositional data indicate a higher proportion of primary ejecta than predicted for extended areas along the ray that do not contain large secondary craters the primary ejecta is intimately mixed on the granular scale with local material throughout the regolith the relatively high albedo of the rays of copernicus is due to the feldspathic composition highland of the primary ejecta in rays emplaced on a mare substrate immature local substrate is only observed in copernicus s ray at large unmantied secondary craters or other areas with sufficient topographic slope to prevent the accumulation of mature soils crater rays are filamentous generally high albedo features that emanate nearly radially from young impact structures rays are narrow in relation to the crater radius extend distally for many crater radii and constitute a distinctive albedo feature around some of the largest and freshest lunar craters visible from earth synoptic views of ray systems figure la give the strong impression that the rays comprise bright material that has been excavated from the crater cavity and been emplaced beyond the continuous ejecta deposit if this visual impression is correct then the process that forms crater rays represents a significant mechanism for the lateral transport of primary material to great distances from its point of origin and particularly for craters larger than a let tens of kilometers in diameter constitutes a fundamental process for the regional mixing of crustal materials earth based telescopic images of the moon allowed the first studies and descriptions of rays and ray systems shoemaker 1962 described the arcuate and loop shaped streaks of the copernicus ray systems and showed that these patterns could be locally resolved into individual en echelon feather shaped elements 15 20 km in length with their long axes oriented approximately radially to the crater he noted the presence of elongate depressions or gouges in the ray system ranking in diameter from 8 km down to the limits of resolution and generally located at the proximal ends of the individual ray elements shoemaker observed that some of the gouges were

remote sensing and geologic studies of the schiller schickard region of the moon near infrared reflectance spectra multispectral images and photogeologic data for the schiller schickard ss region were obtained and analyzed in order to determine the composition and origin of a variety of geologic units these include light plains deposits orientale related deposits mare units and dark haloed impact craters dhcs spectral data indicate that the pre orientale highland surface was dominated by noritic anorthosite near ir spectra show that dhcs in the region have excavated ancient 3 8 ga mare basalts from beneath highland bearing material emplaced by the orientale impact ancient mare basalts were widespread in the ss region prior to the orientale event and their distribution appears to have been controlled by the presence of several old impact basins including the schiller zucchius basin and a basin previously unrecognized both near ir spectra and multispectral images indicate that light plains and other orientale related units in the ss region contain major amounts of local pre orientale mare basalt the amounts of local material in these deposits approach but seldom exceed the maximum values predicted by the local mixing hypothesis of oberbeck and co workers

dynamic modeling of the 2004 mw 6 0 parkfield california earthquake 1 we present two spontaneous rupture models of the 2004 mw 6 0 parkfield earthquake constrained by near source ground motions we start with a stress drop distribution calculated from a kinematic slip distribution using a linear slip weakening friction law we utilize trial and error to obtain both the stress conditions and frictional parameters on the fault that produce synthetics consistent with records the material contrast across the san andreas fault is incorporated using different one dimensional velocity structures on each side of the fault an approximately constant s parameter of 0 3 and a uniform slip weakening distance of 0 15 m are used in the dynamic models in our preferred dynamic model consistent with the ground motion and gps the slip is bounded by seismicity streaks at 5 and 10 km depths confirming a locked zone at depth the stress drop is approximately 10 mpa in the hypocentral region and about 2 mpa elsewhere the material contrast across the fault causes significant normal stress variations 1 mpa leading to a larger strength drop to the southeast than to the northwest the main rupture front propagates at nearly a constant subshear rupture velocity 3 km s in both directions the total radiated energy determined from the preferred dynamic model is 1 1 1013 j seismic moment is 1 0 1018 nm and fracture energy is 3 0 1013 j the limited number of aftershocks in the slipped area suggests the important role of stress on the distribution of seismicity in the locked zone

effective normal stress alteration due to pore pressure changes induced by dynamic slip propagation on a plane between dissimilar materials 1 recent detailed examinations of fault zones show that walls of faults are often bordered by materials that are different from each other and from the more uniform material farther away in addition they show that the ultracataclastic core of mature fault zones where slip is concentrated is less permeable to flow across it than the adjoining material of the damage zone inhomogeneous slip at the interface between materials with different poroelastic properties and permeabilities causes a change in pore pressure there because slip causes compression on one side of the fault wall and extension on the other the pore pressure on the fault increases substantially when the compressed side is significantly more permeable and decreases when instead the extended side is more permeable this change in pore pressure alters the effective normal stress on the slip plane in a way that is analogous to the normal stress alteration in sliding between elastically dissimilar solids the magnitude of the effect due to induced pore pressure can be comparable to or larger than that induced by sliding between elastic solids with a dissimilarity of properties consistent with seismic observations the induced pore pressure effect is increased by increasing contrast in permeability but the normal stress alteration due to elastic contrast increases rapidly as the rupture velocity approaches the generalized rayleigh velocity because the alteration in effective normal stress due to either effect can be positive or negative depending on the contrast in properties the two effects can augment or offset each other

pulse like crack like and supershear earthquake ruptures with shear strain localization 1 we incorporate shear strain localization into spontaneous elastodynamic rupture simulations using a shear transformation zone stz friction law in the stz model plastic strain in the granular fault gouge occurs in local regions called stzs the number density of stzs is governed by an effective disorder temperature and regions with elevated effective temperature have an increased strain rate stz theory resolves the dynamic evolution of the effective temperature across the width of the fault zone shear bands spontaneously form in the model due to feedbacks amplifying heterogeneities in the initial effective temperature in dynamic earthquake simulations strain localization is a mechanism for dynamic fault weakening a shear band dynamically forms reduces the sliding stress and decreases the frictional energy dissipation on the fault we investigate the effect of the dynamic weakening due to localization in generating pulse like crack like and supershear rupture our results illustrate that the additional weakening and reduction of on fault energy dissipation due to localization have a significant impact on the initial shear stress required for supershear or pulse like rupture to propagate on a fault

a constitutive model for fault gouge deformation in dynamic rupture simulations 1 in the context of numerical simulations of elastodynamic ruptures we compare friction laws including the linear slip weakening sw law the dieterich ruina dr law and the free volume fv law the fv law is based on microscopic physics incorporating shear transformation zone stz theory which describes local nonaffine rearrangements within the granular fault gouge a dynamic state variable models dilation and compaction of the gouge and accounts for weakening and restrengthening in the fv law the principal difference between the fv law and the dr law is associated with the characteristic length scale l in the fv law lfv grows with increasing slip rate while in the dr law ldr is independent of slip rate the length scale for friction is observed to vary with slip velocity in laboratory experiments with simulated fault gouge suggesting that the fv law captures an essential feature of gouge filled faults in simulations of spontaneous elastodynamic rupture for equal energy dissipation the fv law produces ruptures with smaller nucleation lengths lower peak slip velocities and increased slip required for friction to fully weaken to steady sliding when compared to ruptures governed by the sw or dr laws we also examine generalizations of the dr and fv laws that incorporate rapid velocity weakening the rapid weakening laws produce self healing slip pulse ruptures for low initial shear loads for parameters which produce identical net slip in the pulses of each rapid weakening friction law the fv law exhibits a much shorter nucleation length a larger slip weakening distance and less frictional energy dissipation than corresponding ruptures obtained using the dr law

lunar dark haloed impact craters origin and implications for early mare volcanism remote sensing and photogeologic data were used to determine the composition and origin of lunar dark haloed craters near infrared reflectance spectra were obtained for numerous dark haloed impact craters located on either the ejecta blankets of large impact craters or imbrian and nectarian age light plains deposits spectral thermal radar and photogeologic data conclusively demonstrate that copernicus h and other dark haloed craters on the ejecta blanket of copernicus excavated mare basalts from beneath lighter surface deposits rich in highlands material analyses of reflectance spectra of dark haloed craters on light plains indicate that in every instance these craters exposed mare basalt which had previously been covered by varying thicknesses of highlands debris in the schiller schickard region a relatively thick highlands unit was emplaced as a result of the orientale impact event on the interior of balmer basin marelike basalt has been excavated from beneath much thinner highlands deposits emplaced by nearby craters mafic orbital geochemical anomalies are commonly associated with regions with abundant light plains deposits which exhibit dark haloed impact craters apparently some mare material has been incorporated into the regolith either by local mixing during the emplacement of the highlands debris or by subsequent vertical mixing the results of recent remote sensing photogeologic and lunar sample studies strongly indicate that mare volcanism was a significant process during much of the pre imbrian and may have been initiated as early as 4 2 4 3 ga these very early volcanic episodes contributed materials to the lunar surface which were incorporated into the upper portion of the highlands crust by subsequent impact mixing models concerning the extent and duration of mare volcanism as well as those involving the composition and thermal evolution of the lunar interior will have to be revised

the effect of the subglacial water pressure on the sliding velocity of a glacier in an idealized numerical model in order to interpret observed short term variations of the sliding velocity of a glacier the effect of a variable subglacial water pressure on the sliding velocity has been studied using an idealized numerical model in particular the transient stages of growing or shrinking water filled cavities at the ice bedrock interface were analysed it was found that the sliding velocity was larger when cavities were growing than when they had reached the steady state size for a given water pressure the smallest sliding velocities occurred while cavities were shrinking when cavitation is substantial a small drop of water pressure below the steady state value e g by 0 5 bar can temporarily cause backward sliding a limiting water pressure at which sliding becomes unstable is derived the consequences of more realistic assumptions than those of the model are discussed

the clementine mission to the moon scientific overview in the course of 71 days in lunar orbit from 19 february to 3 may 1994 the clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths these data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side in addition laser ranging measurements provided the first view of the global topographic figure of the moon the topography of many ancient impact basins has been measured and a global map of the thickness of the lunar crust has been derived from the topography and gravity

evaluating the compatibility of dynamic rupture based synthetic ground motion with empirical ground motion prediction equation we performed an assessment of a database of synthetic ground motion generated by a suite of dynamic rupture simulations to verify compatibility of the peak ground amplitudes with respect to empirical ground motion prediction equations gmpes the dynamic rupture model database developed by dalguer and mai 2011 is composed of 360 earthquake scenarios with moment magnitudes in the range of 5 5 7 for three mechanisms of faulting reverse normal and strike slip and for both buried faults and surface rupturing faults having depth and non depth dependent normal stresses initial shear stress distribution follows a von karman stochastic distribution overall we show quantitatively that the upper frequency limit of the suite of simulations is 1 0 hz up to this frequency the synthetic data are compatible with the empirical model which means that the residuals defined as the differences between observed and predicted ground motions fall in the range of of the empirical gmpe characteristics of the mean values along distance 10 45 km and period t 1 0 s including standard deviation of the synthetic response spectra and peak ground velocity are comparable to their counterpart empirical gmpe at very near source 1 2 km synthetics show supersaturation of the mean peak values which is different from the saturation features predicted by the gmpes the effect of source parameters such as stress drop peak slip velocity and rupture speed and of surface and buried rupture as well as hanging wall and footwall are highly sensitive to ground motion suggesting that these effects contribute to the variability of ground motion near the source and that inclusion of them in the source terms may contribute to reducing uncertainties in gmpes

terashake2 spontaneous rupture simulations of mw 7 7 earthquakes on the southern san andreas fault abstract previous numerical simulations terashake1 of large m w 7 7 southern san andreas fault earthquakes predicted localized areas of strong amplification in the los angeles area associated with directivity and wave guide effects from northwestward propagating rupture scenarios the terashake1 source was derived from inversions of the 2002 m w 7 9 denali alaska earthquake that source was relatively smooth in its slip distribution and rupture characteristics owing both to resolution limits of the inversions and simplifications imposed by the kinematic parameterization new simulations terashake2 with a more complex source derived from spontaneous rupture modeling with small scale stress drop heterogeneity predict a similar spatial pattern of peak ground velocity pgv but with the pgv extremes decreased by factors of 2 3 relative to terashake1 the terashake2 source excites a less coherent wave field with reduced along strike directivity accompanied by streaks of elevated ground motion extending away from the fault trace the source complexity entails abrupt changes in the direction and speed of rupture correlated to changes in slip velocity amplitude and waveform features that might prove challenging to capture in a purely kinematic parameterization despite the reduced pgv extremes northwest rupturing terashake2 simulations still predict entrainment by basin structure of a strong directivity pulse with pgvs in los angeles and san gabriel basins that are much higher than predicted by empirical methods significant areas of those basins have predicted pgv above the 2 probability of exceedance poe level relative to current attenuation relationships even when the latter includes a site term to account for local sediment depth and wave guide focusing produces localized areas with pgv at roughly 0 1 0 2 poe about a factor of 4 5 above the median in contrast at rock sites in the 0 100 km distance range the median terashake2 pgvs are in very close agreement with the median empirical prediction and extremes nowhere reach the 2 poe level the rock site agreement lends credibility to some of our source modeling assumptions including overall stress drop level and the manner in which we assigned dynamic parameters to represent the mechanical weakness of near surface material future efforts should focus on validating and refining these findings assessing their probabilities of occurrence relative to alternative rupture scenarios for the southern san andreas fault and incorporating them into seismic hazard estimation for southern california

remote sensing studies of the lomonosov fleming region of the moon 1 lomonosov fleming is a 620 km pre nectarian impact basin centered at 19 n 105 e clementine multispectral images and a variety of spacecraft photographs were used to investigate the composition and origin of geologic units in the region mare basalt deposits in the lomonosov fleming region are small and exhibit varying degrees of highlands contamination four previously unrecognized dark mantle deposits of probable pyroclastic origin were identified and mapped a major expanse of cryptomare was mapped in and around the lomonosov fleming basin spectral and chemical data obtained for dark haloed craters dhc established that these impact craters excavated mare basalt from beneath higher albedo highlands rich surface units the buried basalts exposed by dhcs in the region exhibit a variety of compositions which range from very low titanium basalt to intermediate tio2 mare basalt nectarian aged units with subjacent cryptomare are much more extensive than imbrian aged deposits with underlying basalt at least some of the buried mare basalts in the region may have been emplaced during pre nectarian time while both impact basins and craters played a role in cryptomare formation by transporting highlands material to mare surfaces the evidence indicates that most of the cryptomare inside the basin are of the distal basin ejecta type the enhanced feo and tio2 abundances exhibited by these cryptomare surfaces usually light plains units demonstrate that ballistic erosion and sedimentation played an important role in their formation

from sub rayleigh to supershear ruptures during stick slip experiments on crustal rocks supershear earthquake ruptures propagate faster than the shear wave velocity although there is evidence that this occurs in nature it has not been experimentally demonstrated with the use of crustal rocks we performed stick slip experiments with westerly granite under controlled upper crustal stress conditions supershear ruptures systematically occur when the normal stress exceeds 43 megapascals mpa with resulting stress drops on the order of 3 to 25 mpa comparable to the stress drops inferred by seismology for crustal earthquakes in our experiments the sub rayleigh to supershear transition length is a few centimeters at most suggesting that the rupture of asperities along a fault may propagate locally at supershear velocities in turn these sudden accelerations and decelerations could play an important role in the generation of high frequency radiation and the overall rupture energy budget

supershear mach waves expose the fault breakdown slip abstract mikumo et al 2003 showed that it is possible to estimate the breakdown slip dc as the slip at the time of the peak slip rate for rupture propagation with subshear speeds cruz atienza et al 2009 later attempted to extend this method to extract information about dc as the displacement at the time of the peak particle velocity from seismic strong motion records however a reasonably accurate estimate of dc was only possible in a narrow zone adjacent to the fault typically on the order of hundreds of meters due to the fast decay with distance from the fault of the seismic energy related to the stress breakdown process when the rupture propagates with supershear speeds on the other hand this energy is carried much farther away from the fault by mach waves in particular rayleigh mach waves when rupture reaches the earth s surface dunham and bhat 2008 here we present a new approach to estimate dc from strong motion records containing mach waves first we show that the method by mikumo et al is valid for supershear rupture propagation this method is then used to estimate dc via an asymptotic approximation of the slip and slip rate time histories from the mach waves using spontaneous rupture simulations we demonstrate that for a visco elastic half space model dc can be estimated within an error of 40 from mach waves that have propagated a distance of at least 3 km from the fault the method is applied to estimate dc for the 2002 mw7 9 denali alaska earthquake 1 5 m and for the 1999 mw7 6 izmit turkey earthquake 1 7 m

attenuation of radiated ground motion and stresses from three dimensional supershear ruptures 1 radiating shear and rayleigh waves from supershear ruptures form mach waves that transmit large amplitude ground motion and stresses to locations far from the fault we simulate bilateral ruptures on a finite width vertical strike slip fault of width w and half length l with l w breaking the surface of an elastic half space and focus on the wavefield out to distances comparable to l at distances much smaller than w two dimensional plane strain slip pulse models i e models in which the lateral extent of the slip zone is unbounded accurately predict the subsurface wavefield amplitudes in the shear mach wedge of those models are undiminished with distance from the fault when viewed from distances far greater than w rupture is accurately modeled as a moving point source that produces a shear mach cone and on the free surface rayleigh wave mach fronts geometrical spreading of the shear mach cone occurs radially and amplitudes there decrease with the inverse square root of distance the transition between these two asymptotic limits occurs at distances comparable to w similar considerations suggest that rayleigh mach waves suffer no attenuation in the ideally elastic medium studied here the rate at which fault strength weakens at the rupture front exerts a strong influence on the off fault fields only in the immediate vicinity of the fault for both sub rayleigh and supershear ruptures and at the mach fronts of supershear ruptures more rapid weakening generates larger amplitudes at the mach fronts

coherence of mach fronts during heterogeneous supershear earthquake rupture propagation simulations and comparison with observations 1 we study how heterogeneous rupture propagation affects the coherence of shear and rayleigh mach wavefronts radiated by supershear earthquakes we address this question using numerical simulations of ruptures on a planar vertical strike slip fault embedded in a three dimensional homogeneous linear elastic half space ruptures propagate spontaneously in accordance with a linear slip weakening friction law through both homogeneous and heterogeneous initial shear stress fields in the 3 d homogeneous case rupture fronts are curved owing to interactions with the free surface and the finite fault width however this curvature does not greatly diminish the coherence of mach fronts relative to cases in which the rupture front is constrained to be straight as studied by dunham and bhat 2008a introducing heterogeneity in the initial shear stress distribution causes ruptures to propagate at speeds that locally fluctuate above and below the shear wave speed calculations of the fourier amplitude spectra fas of ground velocity time histories corroborate the kinematic results of bizzarri and spudich 2008a 1 the ground motion of a supershear rupture is richer in high frequency with respect to a subshear one 2 when a mach pulse is present its high frequency content overwhelms that arising from stress heterogeneity present numerical experiments indicate that a mach pulse causes approximately an 1 7 high frequency falloff in the fas of ground displacement moreover within the context of the employed representation of heterogeneities and over the range of parameter space that is accessible with current computational resources our simulations suggest that while heterogeneities reduce peak ground velocity and diminish the coherence of the mach fronts ground motion at stations experiencing mach pulses should be richer in high frequencies compared to stations without mach pulses in contrast to the foregoing theoretical results we find no average elevation of 5 damped absolute response spectral accelerations sa in the period band 0 05 0 4 s observed at stations that presumably experienced mach pulses during the 1979 imperial valley 1999 kocaeli and 2002 denali fault earthquakes compared to sa observed at non mach pulse stations in the same earthquakes a 20 amplification of short period sa is seen only at a few of the imperial valley stations closest to the fault this lack of elevated sa suggests that either mach pulses in real earthquakes are even more incoherent that in our simulations or that mach pulses are vulnerable to attenuation through nonlinear soil response in any case this result might imply that current engineering models of high frequency earthquake ground motions do not need to be modified by more than 20 close to the fault to account for mach pulses provided that the existing data are adequately representative of ground motions from supershear earthquakes

does a damaged fault zone mitigate the near field impact of supershear earthquakes application to the 2018 7 5 palu indonesia earthquake the impact of earthquakes can be severely aggravated by cascading secondary hazards the 2018 m w 7 5 palu indonesia earthquake led to devastating tsunamis and landslides while triggered submarine landslides possibly contributed substantially to generate the tsunami the rupture was supershear over most of its length but its speed was unexpectedly slow for a supershear event between the wave velocity v s and eshelby s speed 2v s an unstable speed range in conventional theory here we investigate whether dynamic rupture models including a low velocity fault zone can reproduce such a steady supershear rupture with a relatively low speed we then examine numerically how this peculiar feature of the palu earthquake could have affected the near field ground motion and thus the secondary hazards our findings suggest that the presence of a low velocity fault zone can explain the unexpected rupture speed and may have mitigated the near field ground motion and the induced landslides in palu

on the deterministic description of earthquakes 1 the quantitative estimate of earthquake damage due to ground shaking is of pivotal importance in geosciences and its knowledge should hopefully lead to the formulation of improved strategies for seismic hazard assessment numerical models of the processes occurring during seismogenic faulting represent a powerful tool to explore realistic scenarios that are often far from being fully reproduced in laboratory experiments because of intrinsic technical limitations in this paper we discuss the prominent role of the fault governing model which describes the behavior of the fault traction during a dynamic slip failure and accounts for the different and potentially competing chemical and physical dissipative mechanisms we show in a comprehensive sketch the large number of constitutive models adopted in dynamic modeling of seismic events and we emphasize their prominent features limitations and specific advantages in a quantitative comparison we show through numerical simulations that spontaneous dynamic ruptures obeying the idealized linear slip weakening sw equation and a more elaborated rate and state dependent friction law produce very similar results in terms of rupture times peaks slip velocity developed slip and stress drops provided that the frictional parameters are adequately comparable and more importantly that the fracture energy density is the same our numerical experiments also illustrate that the different models predict fault slip velocity time histories characterized by a similar frequency content a feeble predominance of high frequencies in the sw case emerges in the frequency ranges 0 3 1 and 11 50 hz these simulations clearly indicate that even forgiving the frequency band limitation it would be very difficult virtually impossible to discriminate between two different but energetically identical constitutive models on the basis of the seismograms recorded after a natural earthquake

estimation of the breakdown slip from strong motion seismograms insights from numerical experiments fukuyama and mikumo 2007 presented a method to extract informa tion about the friction controlling earthquake rupture directly from near field seismo grams recorded out to several kilometers from a fault this method computes a parameter d 00 approximating the breakdown slip dc from the rake parallel dis placement at the time of the peak particle velocity the validation of the method was based on simple 2d steady state green s functions an approach lacking sufficient physics of the rupture process to support their conclusions here we use 3d simula tions of subshear strike slip spontaneous rupture propagation to demonstrate that d 00 is almost always controlled by rupture and wave propagation effects rather than the fault friction process only if rupture reaches the earth s surface and within a short distance from the fault rc is it possible to extract information about dc from strong motion data due to the fast decay with distance from the fault of the seismic energy related to the stress breakdown process beyond rc d 00 is controlled by the dynamic stress drop from the earthquake rupture without information about dc rc is comparable to the length of the fault cohesive zone where the breakdown process takes place during rupture and approximately equal to 80 of the wavelength associated with the break down frequency defined as the reciprocal of the time span required by the stress to drop to the dynamic level our findings suggest that the dc estimate by fukuyama and mikumo 2007 for the 2000 mw 6 6 tottori earthquake is unrelated to the breakdown slip moreover the very narrow widths for rc obtained from our simulations are in agreement with previous studies challenging the resolution of bandlimited strong motion data to estimate dc from kinematic rupture models guatteri and spudich 2000 spudich and guatteri 2004

space weathering from mercury to the asteroid belt the variety of evidence bearing on the nature of space weathering is reviewed the effects of space weathering include spectral darkening reddening and subdued absorption bands and the distinctive magnetic electron spin resonance caused by single domain metallic iron particles ever since the apollo missions two paradigms have dominated the thinking of the planetary science community concerning space weathering 1 the optical effects are caused by impact vitrified glass in agglutinates and 2 the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind however studies carried out since the apollo program showed that both of these paradigms are invalid a hypothesis first suggested by the author and his colleagues 26 years ago but not generally accepted at that time now appears to be essentially correct both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor deposited coatings on soil particle surfaces and inside agglutinates the vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith the iron is reduced by a physical process the selective loss of oxygen that occurs during deposition of the vapor and does not require heating melting or a reducing environment a mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the moon mercury and an s asteroid

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

estimation of the high frequency radiation of the 2000 tottori japan earthquake based on a dynamic model of fault rupture application to the strong ground motion simulation abstract in the present study we investigate the high frequency hf radiation mechanism of the 2000 tottori earthquake in japan based on a 3d spontaneous fault rupture dynamic model we generalize the model of hf radiation of a suddenly stopping circular crack madariaga 1977 boatwright 1982 to the radiation from a general 3d rupture in a planar fault where hf is radiated during gradual changes of rupture velocity at the rupture front local rupture velocity changes are expressed as the divergence of local rupture velocity vectors that are derived from gradients of rupture times from the dynamic model our numerical model of the tottori earthquake indicates that rupture velocity changes are largely induced by barriers locally stronger fault sections across the fault plane and that hf radiation mainly originates within asperities large stress drop regions in areas where the product of dynamic stress drop and rupture velocity changes is maximum we develop a strong ground motion simulation methodology that incorporates hf radiation inferred from a dynamic fault rupture model using this methodology we investigate the hf radiation of the tottori earthquake by inverting observed near source acceleration envelopes of the earthquake our inversion results corroborate that hf radiation originates within asperities and show that significant hf radiation represents no more than a 20 of the total asperity area our results show that the incorporation of a directivity factor on the basis of a well defined physical rupture model to the radiation pattern leads to a significant improvement in fitting of observed ground motions our simulated near source strong ground motions of the tottori earthquake are also able to reproduce the 2 radiation theoretically predicted in 2d dynamic fault rupture models

rupture to the trench dynamic rupture simulations of the 11 march 2011 tohoku earthquake there is strong evidence that the 11 march 2011 tohoku earthquake rupture reached the seafloor this is surprising because the shallow portion of the plate interface in subduction zones is thought to be frictionally stable leading to the widely held view that coseismic rupture would stop several tens of kilometers downdip of the seafloor various explanations have been proposed to reconcile this seeming inconsistency including dynamic weakening e g thermal pressurization and extreme stress release around shallow subducted seamounts we offer a simpler explanation supported by 2d dynamic rupture simulations of the tohoku earthquake our models account for depth dependent material properties and the complex geometry of the fault seafloor and material interfaces based on seismic surveys of the japan trench the fault obeys rate and state friction with standard logarithmic dependence of shear strength on slip velocity in steady state in our preferred model the uppermost section of the fault is velocity strengthening rupture nucleates on a deeper velocity weakening section waves released by deep slip reflect off the seafloor transmitting large stress changes to the upper section of the fault driving the rupture through the velocity strengthening region to the trench we validate the model against seafloor deformation and 1 hz global positioning system gps data the seafloor displacements constrain the seismogenic depth and overall amount of slip particularly near the trench our simulations reproduce many features in the gps data thereby providing insight into the rupture process and seismic wave field sensitivity to parameters is explored through an extensive suite of simulations neither static seafloor deformation nor onshore 1 hz gps data can uniquely determine near trench frictional properties due to trade offs with average stress drop while conducted specifically for the japan trench region our simulations suggest that rupture to the trench in megathrust events is quite possible even if velocity strengthening properties extend tens of kilometers landward from the trench online material mp4 movies of particle velocities

remote sensing studies of the dionysius region of the moon 1 the dionysius region is located near the western edge of mare tranquillitatis and is centered on dionysius crater which exhibits a well developed dark ray system proposed origins for these dark rays included impact melt deposits and dark primary ejecta the region also contains extensive deposits of cayley type light plains clementine multispectral images and a variety of spacecraft photography were utilized to investigate the composition and origin of geologic units in the dionysius region the portions of the dark rays for which spectral and chemical data were obtained are composed of mare debris contaminated with minor amounts of highland material both five point spectra and values of the optical maturity omat parameter indicate that the dark rays are dominated by mare basalts not glassy impact melts the high albedo rays associated with dionysius exhibit feo and tio2 values that are lower than those of the adjacent dark ray surfaces and omat values that indicate that bright ray surfaces are not fully mature the high albedo rays are bright largely because of the contrast in albedo between ray material containing highlands rich ejecta and the adjacent mare rich surfaces the mafic debris ejected by dionysius was derived from a dark iron rich unit exposed high on the inner wall of the crater this layer probably represents a mare deposit that was present at the surface of the preimpact target site with one possible exception there is no evidence for buried mare basalts associated with cayley plains in the region

mineralogy of the lunar crust results from clementine received 1997 december 5 accepted in revised form 1998 september 15 abstract the central peaks of 109 impact craters across the moon are examined with clementine ultraviolet visible uvvis camera multispectral data the craters range in diameter from 40 to 180 km and are believed to have exhumed material from 5 30 km beneath the surface to form the peaks including both upper and lower crustal rocks depending on whether craters have impacted into highlands or basins representative five color spectra from spectrally and spatially distinct areas within the peaks are classified using spectral parameters including key ratio which is related to mafic mineral abundance and spectral curvature linked to absorption band shape which distinguishes between low and high ca pyroxene and olivine the spectral parameters are correlated to mineralogical abundances related in turn to highland plutonic rock compositions the derived rock compositions for the various central peaks are presented in a global map from these results it is evident that the lunar crust is compositionally diverse both globally and at local 100 m scales found within individual sets of central peaks although the central peaks compositions imply a crust that is generally consistent with previous models of crustal structure they also indicate a more anorthositic crust than generally assumed with a bulk plagioclase content of 8 1 evolving from pure anorthosite near the surface towards more mafic low ca pyroxene rich compositions with depth comparable to anorthositic norite evidence for mafic plutons occurs in both highlands and basins and represent all mafic highland rock types however the lower crust is more compositionally diverse than the highlands with both a greater range of rock types and more diversity within individual sets of central peaks

identifying the unique ground motion signatures of supershear earthquakes theory and experiments the near field ground motion signatures associated with sub rayleigh and supershear ruptures are investigated using the laboratory earthquake experiment originally developed by rosakis and co workers xia et al 2004 2005a lu et al 2007 rosakis et al 2007 heterodyne laser interferometers enable continuous high bandwidth measurements of fault normal fn fault parallel fp and vertical v particle velocity ground motion records at discrete locations on the surface of a homalite 100 test specimen as a sub rayleigh or a supershear rupture sweeps along the frictional fault photoelastic interference fringes acquired using high speed digital photography provide a synchronized spatially resolved whole field view of the advancing rupture tip and surrounding maximum shear stress field the first phase of experimental investigations examine and verify the ground motion signatures of supershear ruptures experimental results demonstrate that a shear mach front produced by a stable supershear rupture is characterized by a dominant fp velocity component the situation is shown to reverse in the sub rayleigh rupture speed regime whereby the fn particle velocity component dominates the ground motion record additional distinguishing particle velocity signatures consistent with theoretical and numerical predictions and repeatedly observed in experimental records are 1 a pronounced peak in the fp velocity record induced by the leading dilatational field which sweeps the measurement station in advance of the shear mach front and 2 a pronounced velocity swing in the fn record associated with the arrival of a trailing rayleigh sub rayleigh secondary rupture which follows the arrival of the shear mach front analysis of the particle velocity records also confirms 2d steady state theoretical predictions pertaining to the separation attenuation and radiation partitioning of the shear and dilatational portions of the rupture velocity field components the second phase of our experimental investigations re examine the 2002 mw7 9 denali fault earthquake and the remarkable set of near source ground motion records obtained at ps10 located approximately 85 km east of the epicenter and just 3 km north of the fault along the alaska pipeline motivated by the analysis and interpretation of these records by ellsworth et al 2004 dunham and archuleta 2004 2005 we attempt to mimic the denali strike slip rupture scenario and replicate the ps10 ground motion signatures using a laboratory earthquake experiment the experiments feature a left to right west to east propagating right lateral rupture within a homalite 100 test specimen with particle velocity data collected at a near field station situated just above north of the fault both sub rayleigh and supershear laboratory earthquake experiments are conducted using the denali ps10 configuration in order to compare and contrast the resulting particle velocity signatures supershear laboratory records capture all of the prominent features displayed within the ps10 ground motion records noted velocity signatures are correlated to the location of the rupture fronts and their noted arrival times in the synchronized photoelastic image sequence scaling relationships are also presented which transform the laboratory records through six orders of magnitude in time to match the scale of the ps10 ground motion records the strong correlation between the scaled experimental records and the actual ps10 ground motion records support the hypothesis that the denali strike slip fault exhibited a supershear burst finally we present a 2d steady state stress velocity formulation that relates the fp and fn particle velocity records measured close to the fault to the evolution of the stress tensor at the same location a locally steady state condition is assumed within a restricted time interval in order to invoke these relationships and estimate the dynamic stresses xx t and t at the near fault station dynamic stress measurements enable a new class of friction investigations using the laboratory earthquake configuration experimental findings are presented which capture the temporal and spatial distributions of xx and evolution of the dynamic friction coefficient and velocity weakening behavior of a supershear slip pulse

mechanics of 3 d shear cracks between rayleigh and shear wave rupture speeds abstract though mode ii shear fractures primarily strike slip earthquakes can not only exceed the shear wave speed of the medium but can even reach the compressional wave speed steady state calculations showed that speeds between the rayleigh and shear wave speeds were not possible thus defining a forbidden zone for more than 30 years it was believed that this result in which the rupture jumps over the forbidden zone also holds for 3 d ruptures in which mode ii and mode iii mainly dip slip faulting are mixed using unprecedentedly fine spatial and temporal grids we show that even in the simple configuration of homogeneous fault properties and linear slip weakening friction law a realistic 3 d rupture which starts from rest and accelerates to some higher velocity actually does pass smoothly through this forbidden zone but very fast the energy flux from the rupture tip is always positive even within the so called forbidden zone contrary to the 2 d case finally our results show that the width of the cohesive zone initially decreases then increases as the rupture exceeds the shear wave speed and finally again decreases as the rupture accelerates to a speed of 90 of the compressional wave speed

effects of supershear rupture speed on the high frequency content of s waves investigated using spontaneous dynamic rupture models and isochrone theory 1 in this paper we achieve three goals 1 we demonstrate that crack tips governed by friction laws including slip weakening rate and state dependent laws and thermal pressurization of pore fluids propagating at supershear speed have slip velocity functions with reduced high frequency content compared to crack tips traveling at subshear speeds this is demonstrated using a fully dynamic spontaneous three dimensional earthquake model in which we calculate fault slip velocity at nine points locations distributed along a quarter circle on the fault where the rupture is traveling at supershear speed in the in plane direction and subshear speed in the antiplane direction this holds for a fault governed by the linear slip weakening constitutive equation by slip weakening with thermal pressurization of pore fluid and by rate and state dependent laws with thermal pressurization the same is also true even assuming a highly heterogeneous initial shear stress field on the fault 2 using isochrone theory we derive a general expression for the spectral characteristics and geometric spreading of two pulses arising from supershear rupture the well known mach wave and a second lesser known pulse caused by rupture acceleration 3 we demonstrate that the mach cone amplification of high frequencies overwhelms the de amplification of high frequency content in the slip velocity functions in supershear ruptures consequently when earthquake ruptures travel at supershear speed a net enhancement of high frequency radiation is expected and the alleged low peak accelerations observed for the 2002 denali and other large earthquakes are probably not caused by diminished high frequency content in the slip velocity function as has been speculated

rupture dynamics and ground motions from earthquakes in 2 d heterogeneous media we perform 2 d simulations of earthquakes on rough faults in media with random heterogeneities with von karman distribution to study the effects of geometric and material heterogeneity on the rupture process and resulting high frequency ground motions in the near fault region out to 20 km variations in slip and rupture velocity can arise from material heterogeneity alone but are dominantly controlled by fault roughness scattering effects become appreciable beyond 3 km from the fault near fault scattering extends the duration of incoherent high frequency ground motions and at least in our 2 d simulations elevates root mean square accelerations i e arias intensity with negligible reduction in peak velocities we also demonstrate that near fault scattering typically occurs in the power law tail of the power spectral density function quantified by the hurst exponent and another parameter combining standard deviation and correlation length

subglacial drainage evolution modulates seasonal ice flow variability of three tidewater glaciers in southwest greenland b j d was funded in the form of a phd studentship provided by the scottish association for geosciences environment and society sages and the university of st andrews uk j m l is supported by a ukri future leaders fellowship grant no mr s017232 1 d f would like to acknowledge the support of this work through the epsrc and esrc centre for doctoral training on quantification and management of risk and uncertainty in complex systems environments grant no ep l015927 1

imaging of lunar surface maturity the physical evolution of the lunar surface with exposure to the space environment is termed maturation and maturity is the degree to which a particular lunar soil possesses quantitative characteristics consistent with that exposure several quantitative measures or indices of maturity have been proposed and employed including the abundance of solar wind gas abundance of various types of agglutinates various measures of grain size and is feo among the changes attendant with space exposure are striking changes in the optical characteristics of soils mature lunar soils are dark red and exhibit reduced spectral contrast relative to immature soils this paper presents an optical maturity index that quantifies the spectral effects of maturation we show that this optical maturity index correlates with other maturity indices about as well as the accepted maturity indices correlate among themselves and is only weakly coupled to composition the modest correlations among maturity indices suggest important controls on individual maturity indices other than age uncorrelated variations in the rates of accumulation of individual indicators or variations in depths over which indicators are emplaced in addition to mixing these effects conspire to reduce the equivalence of maturity and duration of surface exposure optical maturity illustrates some of these effects showing that ejecta of large and small craters mature at different rates and that the interiors and ejecta of large craters exhibit systematically different optical maturities the same or analogous effects are likely to influence other maturity indices

near source ground motion from steady state dynamic rupture pulses 1 ground motion from two dimensional steady state dynamic ruptures is examined for both subshear and supershear rupture velocities synthetic seismograms demonstrate that coherent high frequency information about the source process rapidly attenuates with distance from the fault for subshear ruptures such records provide almost no resolution of the spatial extent of the stress breakdown zone at supershear speeds s waves radiate away from the fault preserving the full source spectrum and carrying an exact history of the slip velocity on both the fault parallel and fault normal components of motion whose amplitudes are given by a function of rupture speed that vanishes at times the s wave speed the energy liberated from the strain field by the passage of a supershear rupture is partitioned into fracture energy dissipated within the fault zone and far field s wave radiation the partition depends on both the rupture velocity and the size of the breakdown zone

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

clementine uvvis multispectral data and the apollo 17 landing site what can we tell and how well multispectral data obtained by the clementine mission are correlated to compositional and petrographic information for individual sample stations at the apollo 17 landing site the soils contain a variety of fe2 bearing phases in different proportions including low and high ca pyroxene olivine ilmenite and glass in the mare soils ilmenite carries a substantial proportion of the fe2 and in all soils glasses particularly agglutinates carry nearly as much or more fe2 as the silicates using an empirical calibration concentrations of feo and tio2 estimated from the ultraviolet visible uvvis data correlate well with measured compositions of surface soils yielding correlation coefficients of 0 94 and 0 95 respectively the ferrous absorption however is weak in the mostly submature to mature apollo 17 soils thus spectral curvature is useful only for investigating the mafic silicate mineralogy around fresh craters and deposits the effects of local topography cause significant variations in feo and tio2 derived from clementine uvvis data but do not impair first order geologic interpretations parameters derived from the uvvis data allow quantification of the composition and nature of the soils and by inference underlying rock formations and are consistent with the known geologic character of the landing site the highland regions along this part of the serenitatis rim are relatively feo rich partly as a result of abundant mafic impact melt breccia and partly from the addition of basaltic material in the form of impact debris and pyroclastic deposits at high elevations massif soils are rich in a mafic melt breccia component although slopes and areas mixed by small craters reveal a mixture of melt breccia and older highland material of anorthositic norite composition soils developed on hummocky deposits that postdate the massifs such as the sculptured hills have a similar range of compositions as the massifs elevated plains northeast of the sculptured hills are more mafic than the known impact melt breccias suggesting that they may also contain an older volcanic component sources of low ti basalt or very low ti basalt though not present in the immediate vicinity of the landing site occur east and northeast of taurus littrow valley and are readily identified using the uvvis data

experimental investigation of strong ground motion due to thrust fault earthquakes thrust fault earthquakes are studied in a laboratory earthquake setup previously used to investigate analog strike slip seismic events dynamic mode ii ruptures are generated along preexisting faults in an analog material homalite h 100 and their interaction with the free surface is studied for both sub rayleigh and supershear rupture speeds high speed digital photography and laser velocimeter diagnostics are used synergistically to identify and study the ground velocity signatures caused by the various features of the generated ruptures the obtained surface normal motions of both sub rayleigh and supershear ruptures show substantial asymmetry between the hanging and footwall with the hanging wall experiencing much larger velocity amplitudes the main features of the surface velocity traces at various stations can be explained by the calculated arrivals of various waves and fronts mach cones pand s waves and sub rayleigh features in both the sub rayleigh and supershear cases the arrival of the rupture tip generates a prominent rayleigh wave traveling along the simulated earth s surface supershear events feature larger amplitudes of ground shaking profiles all signatures in the surface motion records attenuate and broaden with increasing distance from the fault trace the signatures corresponding to the arrival of the mach fronts attenuate with distance at a slower rate than those from sub rayleigh ruptures the arrival of the updip supershear rupture at the free surface creates a downdip propagating slip feature with its own mach cone these additional mach fronts further amplify ground shaking on the hanging and footwalls

igneous activity in the southern highlands of the moon 1 detailed investigations of both endogenic and exogenic dark haloed craters can provide critical information concerning the geology composition and evolution of portions of the lunar surface several dark haloed and dark rayed craters have been identified in the maurolycus region in the southeastern nearside highlands clementine and galileo multispectral imagery as well as earth based remote sensing data were used to investigate the composition and origin of dark haloed craters in the region a striking albedo anomaly is associated with buch b crater which exhibits both a dark halo and dark rays the result of a morphologic analysis clearly indicated that buch b is an impact structure not a volcanic vent the optical maturity image shows that the buch b ejecta deposits are immature and the radar and thermal data indicate a high abundance of fresh rocks and fragments in the 1 50 cm size range feo and tio2 data as well as five point spectra extracted from clementine uv vis images indicate that the dark ejecta is composed of immature mare like material and may contain minor amounts of highland debris buch b excavated either an isolated cryptomare or more likely a mafic intrusion one or more dikes of basaltic composition are possible candidates minor low albedo anomalies have been identified around three other impact craters maurolycus a and b and barocius m in the region while small feo enhancements are seen in portions of the ejecta deposits associated with these craters they do not approach the feo values 12 14 wt exhibited by the dark deposits of buch b and they do fall within the range of feo abundances 5 9 wt exhibited by highland terrain in the maurolycus region hence the presence of a basaltic component is not required and it cannot be concluded that either cryptomare or mafic intrusions were present in the target sites of these craters

supershear transition due to a free surface in 3 d simulations of spontaneous dynamic rupture on vertical strike slip faults supershear rupture propagation has been inferred from seismic observations for natural faults and observed in laboratory experiments we study the effect of the free surface on the transition of earthquake rupture from subshear to supershear speeds using simulations of spontaneous dynamic rupture on vertical strike slip faults we find that locally supershear rupture near the free surface can occur due to i the generalized burridge andrews mechanism that is a supershear loading field between p and sv wave arrivals generated by the main rupture front at depths and ii the phase conversion of sv to p diffracted waves at the free surface weaker supershear slip due to the generalized burridge andrews mechanism is caused by the low strength at shallow portions of the fault relative to deeper ones dominant supershear rupture is supported by the additional supershear loading field produced by phase conversion locally supershear propagation at the free surface occurs regardless of the level of prestress and can cause transition to supershear propagation over the entire seismogenic depth such global supershear transition which depends on prestress can occur under prestress levels lower than the theoretical estimates for models with no free surface although the effectiveness of supershear transition due to the free surface can be diminished by several potentially important factors it may play an important role on natural faults at least in those strike slip earthquakes that accumulate significant surface slip

mare tranquillitatis basalt emplacement history and relation to lunar samples galileo and clementine multispectral data of the mare tranquillitatis region have been analyzed to investigate the stratigraphy of basaltic units and the effects of lateral and vertical mixing processes within the mare the distribution of compositionally distinct mare units is observed to be correlated with previous uv vis ratio images although estimates of soil titanium contents are low in some areas as a result of mixing of local basalts with nonmare feldspathic materials basalt units identified by their spectral properties and spectral mixture analysis are compared with groups of apollo 11 samples defined by previous workers on the basis of age and chemistry spectral studies presented here indicate that the apollo 11 site lies at the edge of a localized western mare unit which includes the youngest and most titanium rich basalts in tranquillitatis apollo 11 high k high ti samples in southern tranquillitatis these basalts have been contaminated by a large degree of mixing with nonmare feldspathic materials nonmare materials near the apollo 11 site are attributed largely to crater rays from theophilus 100 km in diameter which is located approximately 300 km to the south a more extensive and stratigraphically older unit exposed near apollo 11 is related to the low k high ti apollo 11 samples and appears to extend as a coherent surface unit as far north as the apollo 17 site in southern serenitatis the distribution of this spectrally identified basalt unit supports petrologic and geochemical evidence for the grouping of the high ti low k apollo 11 and 17 basalt samples into the same regional volcanic events multispectral analysis of tranquillitatis deposits also identify low titanium basalts in the northeastern and southeastern portions of the basin that are older than the high ti basalts and are believed to be unsampled by apollo 11 several lines of evidence suggest that the cayley formation along the western tranquillitatis margin may indeed lie on top of an ancient mare deposit buried by imbrium basin ejecta e g a cryptomare deposit the distribution of vertically excavated feldspathic premare material within the mare provides information on the depth of the mare units and the proximity of the underlying basin topography compositional stratigraphy observed in both sets of multispectral data supports an asymmetric premare fill basin topography containing thicker basalts in the northwestern portion of the basin than previously predicted by crater flooding data

dynamic rupture modelling of the 1999 duzce turkey earthquake the dynamic rupture process and near source ground motion of the 1999 mw 7 1 duzce earthquake are simulated the fault rupture is governed by the slip weakening friction model coupled to a three dimensional viscoelastic wave equation the problem is solved numerically by a 3 d dynamic rupture code that uses a generalized finite difference method initial parameterization of stress drop delta tau and strength excess s text e for dynamic rupture calculations is obtained from the slip velocity distribution of a kinematic waveform inversion ki model by solving the elastodynamic equation with the kinematic slip as a boundary condition using the kinematic slip distribution and observed ground motion as constraints a trial and error procedure was followed to define the stress parameterization preferred model describes the source in terms of stress with three asperities located respectively at the deep middle and shallow and strong barriers between asperities s text e is as high as 19 mpa at barriers between the three asperities and delta tau is maximum about 40 mpa at the deepest asperity this heterogeneity in stress distribution produces abrupt jumps in rupture velocity exhibiting locally apparent rupture speed exceeding the p wave velocity at the borders between barriers and asperities due to sharp changes of fault strength and stress drop at those areas overall consistent with other studies the rupture propagation is dominated by supershear speed toward the eastern asperities and at shallow surface simulated surface rupture at the eastern fault is consistent with other studies nevertheless the western shallower parts did not rupture during the simulation suggesting that those regions may have already broken during the 1999 kocaeli event which occurred three months earlier ground motion simulation catches the major characteristics of the observed waveforms distribution of simulated peak ground velocity pgv in low frequency 0 1 0 5 hz inside the study area reveals the propagation pattern on the field with pgv reaching to 1 2 and 2 2 m s in the ns and ew components respectively

reproducing the supershear portion of the 2002 denali earthquake rupture in laboratory article history an otable feature of the 2002mw 7 9d enali alaska earthquake was that au nique set of near f ield seismic ground motion records at pump station 10 ps10 captured the passage of a supershear rupture followed by what was surmised to be a secondary slip pulse trailing rayleigh pulse dunham and archuleta 2004 mello et al 2010 motivated by the unique features contained in these near field ground motion records which were obtained only 3 km away from the fault a series of scaled laboratory earthquake experiments was conducted in an attempt to replicate the dominant features of the ps10 ground motion signatures particle velocity records bearing a striking similarity to the denali ground motion records are presented and discussed the success of the comparison opens up the possibility of routinely generating near source ground motion records in a scaled and controlled laboratory setting that could be of great societal interest towards assessing seismic hazard from large and potentially devastating earthquakes

spatiotemporal properties of sub rayleigh and supershear ruptures inferred from full field dynamic imaging of laboratory experiments many earthquakes propagate at sub rayleigh speeds earthquakes propagating at supershear speeds though less common are by far more destructive hence it is important to quantify the motion characteristics associated with both types of earthquake ruptures here we report on the spatiotemporal properties of dynamic ruptures measured in our laboratory experiments using the dynamic digital image correlation technique earthquakes are mimicked by the frictional rupture propagating along the interface of two homalite plates digital images of the propagating ruptures are captured by an ultrahigh speed camera and processed with digital image correlation in order to produce sequences of evolving displacement and velocity maps our measurements reveal the full field structure of the velocity components bridge the gap between previous spatially sparse velocimeter measurements available only at two to three locations and enable us to quantify the attenuation patterns away from the interface

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

why did the most severe seismic hazard occur in the beichuan area in the 2008 wenchuan earthquake china insight from finite element modelling abstract the beichuan area suffered the most serious seismic damage in the 2008 wenchuan earthquake although the beichuan is over 100 km away from the instrumental epicenter of the mainshock the mechanism for this peculiar phenomenon remains unclear even though 10 years has passed since the wenchuan event for this purpose we construct a spontaneous rupture model in which gaochuan right bend grb is included in the middle of yingxiu beichuan fault a major seismogenic fault for the wenchuan event the simulated results show that the complex geometry of the grb played a controlling role in the rupture propagation once the rupture was initiated at the epicenter of the wenchuan mainshock it propagated spontaneously and the rupture speed on the first segment of the fault is 2 79 km s slower than the shear wave speed of local medium when the rupture front spread near the end of the yingxiu gaochuan fault a new rupture was re nucleated at the curve section of the gaochuan bend and propagated in the northeast direction with the speed of 5 02 km s greater than the s wave velocity in addition this rupture speed transition from subshear to supershear does not need any time delay much distinct from the case of fault stepover in which delay is needed in supershear transition the result also demonstrates that the relation between the high values of peak ground acceleration pga and the supershear rupture is strong the large area with high values of pga distributed in the beichuan directly led to grave seismic catastrophe there therefore this work may give some insight into why the most serious seismic damage occurred in the beichuan area and may have important implications for understanding earthquake dynamics and assessing seismic hazards

remote sensing and geological studies of the hadley apennine region of the moon we have used data from the clementine and lunar prospector spacecraft in conjunction with reflectance spectra collected with earth based telescopes to study the geology of the hadley apennine portion of the lunar imbrium basin the apennine mountains and the imbrium backslope are composed of imbrium basin ejecta with a noritic or anorthositic norite composition we find that the two major facies of imbrium ejecta the apenninus material and the alpes formation differ in iron and titanium content pure anorthosite has tentatively been identified in the ejecta of the crater conon based on low iron content a difference in th and rare earth element ree abundance between the northeast apennine mountains lower and the southwest apennines higher is noted pyroclastic deposits are common in the region and are dominated by mare basalt material probably plug rock ejected in vulcanian eruptions the apennine bench formation which is likely to be a deposit of non mare volcanic material has an fe ti and th composition consistent with that of apollo 15 kreep basalt samples thought to be fragments of the bench aristillus crater is a th and ree hot spot and the stratigraphy of the impact target site has been reconstructed from knowledge of the composition of the crater interior and exterior deposits we infer that the target consisted of highland basement kreep plutonics and volcanics and both high and low ti mare basalt

physical limits on ground motion at yucca mountain abstract physical limits on possible maximum ground motion at yucca mountain nevada the designated site of a high level radioactive waste repository are set by the shear stress available in the seismogenic depth of the crust and by limits on stress change that can propagate through the medium we find in dynamic deterministic 2d calculations that maximum possible horizontal peak ground velocity pgv at the underground repository site is 3 6 m sec which is smaller than the mean pgv predicted by the probabilistic seismic hazard analysis psha at annual exceedance probabilities less than 10 6 per year the physical limit on vertical pgv 5 7 m sec arises from supershear rupture and is larger than that from the psha down to 10 8 per year in addition to these physical limits we also calculate the maximum ground motion subject to the constraint of known fault slip at the surface as inferred from paleoseismic studies using a published probabilistic fault displacement hazard curve these calculations provide a probabilistic hazard curve for horizontal pgv that is lower than that from the psha in all cases the maximum ground motion at the repository site is found by maximizing constructive interference of signals from the rupture front for physically realizable rupture velocity from all parts of the fault vertical pgv is maximized for ruptures propagating near the p wave speed and horizontal pgv is maximized for ruptures propagating near the rayleigh wave speed yielding in shear with a mohr coulomb yield condition reduces ground motion only a modest amount in events with supershear rupture velocity because ground motion consists primarily of p waves in that case the possibility of compaction of the porous unsaturated tuffs at the higher ground motion levels is another attenuating mechanism that needs to be investigated

compositional gradients across mare highland contacts importance and geological implication of lateral transport observations of mixing across mare highland contacts using high resolution clementine data allow a new assessment of the relative importance of vertical versus lateral mass transport on the moon at least at mare highland contact we analyze mare highland contacts in the grimaldi orientale and fecunditatis basins and tsiolkovsky crater through image based nonlinear spectral mixture modeling of clementine ultraviolet visible uv vis light spectrometer multi spectral data the mare in these regions differ in ages but they are characterized by having simple geological contacts the symmetric distribution of mare and highland soil constituents across their geological contact indicates that lateral transport is more efficient than deep vertical transport during the formation of the observed mixing zones observations across the lunar limb with the clementine uv vis filters show that there is a stray light component of scattered light across high contrast albedo boundaries however the magnitude and spatial properties of scattered light do not significantly affect the nature of compositional boundaries determined here since repetitive meteorite bombardment governs lateral transport across the geological contacts and is a random process a stochastic model is developed to describe this lateral transport analysis of the power decay law for crater ejecta thickness indicates that the high velocity ejecta travels long distances and follows a 3 power decay law this results in an infinite variance which requires an anomalous diffusion model since a classical diffusion model would be invalid mathematical modeling supports this result where it is shown that classical diffusion produces a relatively poor fit to profiles of material abundance while the anomalous diffusion model fits the profiles adequately these results indicate that high velocity ejecta dominates the formation of the observed compositional gradients while the ejecta near the crater rim is relatively less important on the basis of these ejecta distributions and the assumption of random impact cratering we derive a relationship that can be used as an index for relative age dating of geological contacts as well as for investigating cratering rates

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

off fault damage patterns due to supershear ruptures with application to the 2001 mw 8 1 kokoxili kunlun tibet earthquake 1 we extend a model of a two dimensional self healing slip pulse propagating dynamically in steady state with slip weakening failure criterion to the supershear regime in order to study the off fault stressing induced by such a slip pulse and investigate features unique to the supershear range specifically we show that there exists a nonattenuating stress field behind the mach front that radiates high stresses arbitrarily far from the fault practically this would be limited to distances comparable to the depth of the seismogenic zone thus being capable of creating fresh damage or inducing coulomb failure in known structures at large distances away from the main fault we allow for both strike slip and dip slip failure induced by such a slip pulse we show that off fault damage is controlled by the speed of the slip pulse scaled stress drop and principal stress orientation of the prestress field we apply this model to study damage features induced during the 2001 kokoxili kunlun event in tibet for which it has been suggested that much of the rupture was supershear we argue that an interval of simultaneous induced normal faulting is more likely due to a slip partitioning mechanism suggested previously than to the special features of supershear rupture however those features do provide an explanation for otherwise anomalous ground cracking at several kilometers from the main fault we also make some estimates of fracture energy which for a given net slip and dynamic stress drop is lower than for a sub rayleigh slip pulse because part of the energy fed by the far field stress is radiated back along the mach fronts

clementine images of the lunar sample return stations refinement of feo and tio2 mapping techniques clementine uvvis images of the lunar sample return sites have been processed and used to produce refined calibrations for the iron and titanium determination algorithms of lucey et al 1995 1996 the high spatial resolution of the clementine data permits individual sampling stations to be resolved at the apollo 15 16 and 17 landing sites we find an excellent linear correlation between the spectral fe and ti parameters and the average feo and tio 2 contents of soils sampled at each site or station this correlation demonstrates that these techniques can confidently be applied to other areas of the moon the luna 24 site does not fit the ti relation found for other sites suggesting that either its sample is nonrepresentative or the reported landing coordinates are incorrect

ground motion signatures of supershear ruptures in the burridge andrews and free surface induced mechanisms abstract we analyze the ground motions of supershear ruptures in the burridge andrews bam and free surface induced fsi mechanisms bam supershear ruptures require higher initial shear stress than fsi supershear ruptures thus cause faster rupture speed the supershear slip pulse initiates at the free surface or upper boundary of a fault for fsi and at the hypocenter depth in the in plane direction for bam in homogeneous models both bam and fsi supershear ruptures can generate mach waves and the rayleigh wave field the bam and the faster fsi supershear ruptures can make stronger shear mach waves the shear mach waves show a larger amplitude of negative component for a faster fsi supershear rupture the fsi supershear ruptures make the strongest dilatational wave next to the fault while it is at a distance away from the fault for the bam supershear ruptures the different shapes of supershear rupture front locations of supershear triggered and the rupture speeds contribute to these contrasts and we find that the bam and the faster fsi supershear ruptures can trigger more high frequency radiation due to the sharper and stronger shear mach waves finally the comparisons between the simulated seismograms and the records of ps10 indicate that the 2002 denali earthquake may represent a supershear one with the fsi mechanism and a slow supershear rupture speed

dependency of supershear transition and ground motion on the autocorrelation of initial stress abstract theoretical and observational studies show that earthquakes on strike slip faults can have rupture speeds exceeding the shear wave speed due to the close relationship between the rupture velocity and the radiated wave field it is important to understand the conditions leading to supershear ruptures and their effect on the resulting ground motion we compute dynamic strike slip ruptures in a 3d elastic half space using heterogeneous frictional properties on faults that are 60 km long we use a grid spacing of 60 m allowing us to compute ground motion for frequencies from 0 to 5 hz we analyze the resulting ground motion using isochrones to explain phenomena we observe we model the amplitudes of the initial shear stress as a self similar random field with cauchy distributed amplitudes the wavenumber amplitude spectrum of initial stress decays as a power law with exponent that controls the decay and the spatial correlation of the initial stress the faster the decay corresponding to larger value of the more correlated is the stress on the fault i e the stress field appears spatially smoother the strength on the fault is computed under the assumption of a constant s factor where s is the ratio of strength excess over stress drop on a fault with uniform strength and stress drop the s factor has to be less than a critical value for the supershear transition to occur for models with heterogeneous initial stress we find that both the s factor and the value of the spectral decay constant affect the occurrence of supershear rupture we observe that for a given but small enough s factor a smooth model 2 can run at supershear speed while a rough model 1 will rupture at subshear speeds for the same s factor based on the theory of fracture a non dimensional number was introduced to quantify the condition when a transition to supershear rupture velocity can occur during an earthquake transition will occur when exceeds a critical value we introduce a modified dimensionless parameter ac that is based on the original parameter the parameter ac incorporates a length scale w ac that reflects the degree of the autocorrelation of the stress field we compute ac for a large number of available dynamic ruptures that propagate at subshear and supershear speeds and find i there is a critical value ac c below which all ruptures propagate subshear ii for values larger than ac c there is only a finite probability that the rupture goes supershear i e it is a necessary but not a sufficient condition for the occurrence of supershear rupture propagation

the origin of lunar crater rays abstract lunar rays are filamentous high albedo deposits occurring radial or subradial to impact craters the nature and origin of lunar rays have long been the subjects of major controversies we have determined the origin of selected lunar ray segments utilizing earth based spectral and radar data as well as feo tio 2 and optical maturity maps produced from clementine uvvis images these include rays associated with tycho olbers a lichtenberg and the messier crater complex it was found that lunar rays are bright because of compositional contrast with the surrounding terrain the presence of immature material or some combination of the two mature compositional rays such as those exhibited by lichtenberg crater are due entirely to the contrast in albedo between ray material containing highlands rich primary ejecta and the adjacent dark mare surfaces immaturity rays are bright due to the presence of fresh high albedo material this fresh debris was produced by one or more of the following 1 the emplacement of immature primary ejecta 2 the deposition of immature local material from secondary craters 3 the action of debris surges downrange of secondary clusters and 4 the presence of immature interior walls of secondary impact craters both composition and state of maturity play a role in producing a third combination class of lunar rays the working distinction between the eratosthenian and copernican systems is that copernican craters still have visible rays whereas eratosthenian aged craters do not compositional rays can persist far longer than 1 1 ga the currently accepted age of the copernican eratosthenian boundary hence the mere presence of rays is not a reliable indication of crater age the optical maturity parameter should be used to define the copernican eratosthenian boundary the time required for an immature surface to reach the optical maturity index saturation point could be defined as the copernican period

evidence for a supershear transient during the 2002 denali fault earthquake elastodynamic considerations suggest that the acceleration of ruptures to supershear velocities is accompanied by the release of rayleigh waves along the fault from the stress breakdown zone these waves generate a secondary slip pulse trailing the rupture front but manifest almost entirely in ground motion perpendicular to the fault in the near source region we construct a spontaneously propagating rupture model exhibiting these features and use it to explain ground motions recorded during the 2002 denali fault earthquake at pump station 10 located 3 km from the fault we show that the initial pulses on both the fault normal and fault parallel components are due to the supershear stress release on the fault whereas the later arriving fault normal pulses result from the trailing subshear slip pulse on the fault online material mpeg movies of rupture history and ground motion

seismic characteristics of supershear and sub rayleigh earthquakes implication from simple cases numerous investigations of supershear earthquakes make a conclusion that a supershear earthquake produces a seismic shock wave on the ground that may increase the resulting destruction we investigate a supershear rupture promoted by the free surface and find out that although the seismic energy of a supershear earthquake can be transmitted further with large amplitudes the peak slip velocity on a fault near the free surface is smaller than that caused by a subshear rupture earthquake our results show that the free surface induced supershear rupture mitigates the amplitudes of ground motions near the fault plane compared with the subshear rupture the coulomb failure change derived from dynamic modeling further suggests that this free surface induced supershear reduces aftershock potential compared to a subshear rupture both ground motion at near fault and aftershock possibility show low risk for the free surface induced supershear rupture earthquake than subshear earthquake contrary to the traditional concept