crustal reworking at nanga parbat pakistan metamorphic consequences of thermal mechanical coupling facilitated by erosion within the syntaxial bends of the india asia collision the himalaya terminate abruptly in a pair of metamorphic massifs nanga parbat in the west and namche barwa in the east are actively deforming antiformal domes which expose quaternary metamorphic rocks and granites the massifs are transected by major himalayan rivers indus and tsangpo and are loci of deep and rapid exhumation on the basis of velocity and attenuation tomography and microseismic magnetotelluric geochronological petrological structural and geomorphic data we have collected at nanga parbat we propose a model in which this intense metamorphic and structural reworking of crustal lithosphere is a consequence of strain focusing caused by significant erosion within deep gorges cut by the indus and tsangpo as these rivers turn sharply toward the foreland and exit their host syntaxes the localization of this phenomenon at the terminations of the himalayan arc owes its origin to both regional and local feedbacks between erosion and tectonics

temporal evolution of decaying summer first year sea ice in the western weddell sea antarctica abstract the evolution of the main physico chemical properties of the unflooded 90 cm thick first year sea ice cover at the ice station polarstern ispol clean site is described ispol was an international experiment of the german research icebreaker r v polarstern the vessel was anchored to an ice floe for an observation period of 5 weeks during the early summer melt onset in the western weddell sea the clean site was specially designed and accessed so as to prevent any trace metal contamination of the sampling area observations were made at 5 day intervals during december 2004 in the central part of the main floe results show the succession of two contrasting phases in the behavior of the brine network brine channels pockets and tubes initially brine salinity was higher than that of sea water leading to brine migration and a decrease in the mean bulk salinity of the ice cover this process is highly favored by the already high bulk porosity 14 which ensures full connectivity of the brine network gravity drainage rather than convection seems to be the dominant brine transfer process half way through the observation period the brine salinity became lower than that of the sea water throughout the ice column the brine network therefore switched to a stratified regime in which exchange with sea water was limited to molecular diffusion strongly stabilizing the bulk mean sea ice salinity during the transition between the two regimes and in areas closer to ridges slush water resulting from a mixture of snow meltwater and sea water accumulated at the snow ice interface penetrated through the growing honeycomb like structure and replaced the downward draining brines this resulted in a slight local replenishment of nutrients as indicated by dissolved silicic acid however as a whole the described decaying regime in this globally unflooded location with limited snow cover should be unfavorable to the development of healthy and active surface and internal microbial communities the switch from gravity to diffusion controlled transport mechanisms within the ice column also should affect the efficiency of gas exchange across the sea ice cover the observed late build up of a continuous impermeable superimposed ice layer should further significantly hamper gas exchange statistical estimates of the evolution of the ice thickness during the observation period and salinity trends of the under ice water salinity down to 30 m corroborate model predictions of a moderate bottom melting 5 10 cm from ocean heat fluxes

contribution of radar interferometry to a two step inversion of the kinematic process of the 1992 landers earthquake we study the rupture process of the 1992 landers earthquake to limit the trade off between slip amplitude and rupture time that affects solutions using only seismological data we adopt a two step approach we first constrain the slip distribution and its uncertainty by independent geodetic data to recover in the second step the temporal details of the rupture propagation the first step consists of an inversion of interferometric data and global positioning system measurements both independently and together to constrain slip distribution on a three segment fault model along both strike and dip direction we use a genetic algorithm to test the uniqueness of the solution and a least squares formulation to find the model which best fits the data we conclude from the results of these geodetic inversions that interferometric data are rich enough to access the slip distribution in the case of the landers earthquake since the surface deformations are more sensitive to shallow slip in our configuration the slip amplitude is better resolved near the surface than at depth the resulting slip distribution is in agreement with geological observations at the surface and confirms the heterogeneous nature of the landers earthquake most of the slip occurs at shallow depths on the homestead valley fault second segment with a maximum value of around 7 m another high slip zone is observed on the johnson valley fault first segment at 8 km depth in the second step we invert strong motion data with the a priori final slip amplitude and its uncertainty deduced from geodetic data to constrain the time history of the rupture process this second step emphasizes a strong variation of the temporal development of the earthquake fast rupture front velocities appear within high slip zones and the rupture slows when it encounters a resistance along the fault on average the rupture front propagates with velocities close to the s wave velocity and terminates about 20 s after initiation the large variations in both slip amplitude and rupture velocity suggest that the rupture process is better described by successively breaking asperities than by a pulse propagating with constant velocity

interseismic strain accumulation on the himalayan crustal ramp nepal the departement of mines and geology has been monitoring the seismicity of the central himalayas of nepal since 1985 intense microseismicity and frequent medium size earthquakes ml 4 tend to cluster beneath the topographic front of the higher himalaya this 10 20km deep seismicity also correlates with a zone of localized uplift that has been evidenced from geodetic data both microseismic and geodetic data indicate strain accumulation on a mid crustal ramp that had been previously inferred from geological and geophysical evidence this ramp connects a flat decollement under the lesser and sub himalaya with a deeper decollement under the higher himalaya and probably acts as a geometric asperity where strain and stress build up during the interseismic period the large himalayan earthquakes could nucleate there and probably activate the whole flat and ramp system up to the blind thrusts of the sub himalaya

deformation due to the 17 august 1999 izmit turkey earthquake measured from spot images the geometry of the ruptured areas and the coseismic slip distribution data are key to highlighting the behavior of seismic faults this information is generally retrieved from field investigations and geodetic measurements or synthetic aperture radar sar interferometry here we show that spot images can also be used to accurately map the fault zone and to determine the slip distribution by subpixel correlation of images acquired before and after an earthquake the measured slip includes the contribution of possible distributed shear that might not be clearly expressed in surface ruptures and smoothes out possible along strike variability due to near surface fault complexities we apply the technique to the m s 7 4 1999 izmit earthquake our results reveal a 100 m wide and very linear fault zone that can be traced for 70 km from golcuk to akyazi along which supershear rupture has been inferred the obtained slip distribution compares well with the field measurements and is consistent with ground deformation measured at some distance from the fault zone using sar images very little deformation was accommodated off the main fault plane maximum slip is observed near sapanca lake at a small fault jog that has probably influenced rupture propagation

focal depths and fault plane solutions of earthquakes and active tectonics of the himalaya synthetic seismograms were compared with long period body waves for nine earthquakes with epicenters in the himalayan arc to determine depths of foci and to improve fault plane solutions focal depths are shallow 10 20 km inferred slip vectors are locally perpendicular to the mountain range they plunge very gently about 10 deg in the eastern sections of the range and more steeply about 25 deg in western sections assuming india to be a rigid plate the radially oriented slip vectors imply that southern tibet extends at about half the rate of underthrusting in the himalaya and therefore probably at about 5 10 mm yr the shallow depths and gentle dips of the fault planes at least for the events in the eastern half of the range are consistent with coherent underthrusting of the indian plate beneath at least the lesser himalaya the steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the greater himalaya

equations for determining the gas and brine volumes in sea ice samples on a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite de salinite et de temperature dans des gammes de temperatures entre 2 c et 30 c inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace on donne aussi des equations qui permettent le calcul du volume de gaz et d eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

rupture history and seismotectonics of the 1991 uttarkashi himalaya earthquake abstract the 19 october 1991 uttarkashi india earthquake occurred in the main thrust zone of the himalaya with a moment magnitude of 6 8 this event is characteristic of the present day motion on the thrust fault system we examine this earthquake using different sets of data in order to understand better the faulting process of a major earthquake in the himalayan region firstly the modeling of the teleseismic records indicates that the mechanism is similar to the published cmt and indicates a shallow between 10 and 15 km depth low angle thrust event in the vicinity of the source the earthquake was recorded by a network of accelerometers run by the university of roorkee six three component accelerometers were triggered within a radius of 60 km two of them were very close to the surface projection of the fault forward modeling of those records shows that the rupture propagated toward the west this forward modeling gives us the possibility to confirm the epicenter location and to evaluate the timing of the accelerograms the accelerogram records are inverted to obtain the distribution of slip on the fault plane the results show a complex rupture process the slip maxima 1 5 m occurred 10 km west and 15 km southwest of the hypocenter the slip source function obtained with near field data is similar to the function obtained from teleseismic records and shows a low moment release at the beginning of the rupture and a maximum rate of moment release 4 seconds after the relation between the slip distribution obtained by inversion isoseimals mapped faults and the aftershocks location is then discussed and we finally propose a seismotectonic interpretation of this earthquake the uttarkashi earthquake probably occurred along the detachment surface which coincides with the upper surface of the subducting indian lithosphere this detachment surface is gently dipping under the lesser himalaya and south of the vaikrita thrust the vaikrita thrust marks the line separating the very shallow dipping detachment along which big earthquakes like the uttarkashi earthquake could occur from the steeper dipping aseismic basement thrust this observation is important for correctly estimating the seismic hazard in the uttarkashi region

displacement field and slip distribution of the 2005 kashmir earthquake from sar imagery 1 the 8th october 2005 kashmir earthquake mw 7 6 involved primarily thrust motion on a ne dipping fault sub pixel correlation of envisat sar images gives the location of the 80 km long fault trace within 300 800 m and a 3d surface displacement field with a sub metric accuracy covering the whole epicentral area the slip distribution inverted using elastic dislocation models indicates that slip occurs mainly in the upper 10 km between the cities of muzaffarabad and balakot the rupture reached the surface in several places in the hanging wall horizontal motions show rotation from pure thrust to oblique right lateral motion that are not observed in the footwall a segmentation of the fault near muzaffarabad is also suggested north of the city of balakot slip decreases dramatically but a diffuse zone of mainly vertical surface displacements which could be post seismic exists further north where most of the aftershocks occur aligned along the nw se indus kohistan seismic zone

horizontal coseismic deformation of the 2003 bam iran earthquake measured from spot 5 thr satellite imagery 1 on 26 december 2003 a destructive mw 6 5 earthquake occurred in kerman province iran killing more than 30 000 people around the ancient city of bam we map the fault zone and determine the slip distribution using sub pixel correlation of images taken by the spot 5 thr sensor before and after the main shock our results show that the surface displacement occurred on a blind fault oriented n174 and located south of bam a 15 km along strike profile depicts a distribution with a maximum displacement of 1 2 0 15 m near the centre of the fault the mean slip that we infer 0 77 0 05 m is much higher than the ground displacement measured in the field 0 2 m we suggest that field measured displacements are underestimated due to slip accommodation within an 500 m wide shear zone furthermore we demonstrate for the first time the relevancy of 2 5 m spot 5 thr images for sub pixel ground displacement measurements

static stress change from the 8 october 2005 m 7 6 kashmir earthquake 1 we calculated static stress changes from the devastating m 7 6 earthquake that shook kashmir on 8 october 2005 we mapped coulomb stress change on target fault planes oriented by assuming a regional compressional stress regime with greatest principal stress directed orthogonally to the mainshock strike we tested calculation sensitivity by varying assumed stress orientations target fault friction and depth our results showed no impact on the active salt range thrust southwest of the rupture active faults north of the main boundary thrust near peshawar fall in a calculated stress decreased zone as does the raikot fault zone to the northeast we calculated increased stress near the rupture where most aftershocks occurred the greatest increase to seismic hazard is in the indus kohistan seismic zone near the indus river northwest of the rupture termination and southeast of the rupture termination near the kashmir basin

surface deformation in the region of the 1905 kangra mw 7 8 earthquake in the period 1846 2001 1 one century after the mw 7 8 kangra earthquake of 4 april 1905 we report weak constraints on its rupture parameters based on the remeasurement of historic triangulation points in the epicentral region the western corner of the 1905 rupture is constrained to within 20 km and its sw edge strikes n135 15w the down dip width of the rupture is inferred from the location of the interseismic locking line to have been less than 55 km scaling laws and revised msk intensities suggest an along arc rupture length of 100 km with uniform slip of 4 m because the earthquake ruptured 60 of the width of the plate boundary and released a fraction of the inferred slip deficit complacency about its re rupture in the distant future is unwarranted the kangra rupture could fail again today in a mw 7 5 earthquake 1 4 m of slip or as part of a much larger earthquake mw 8 6

evidence for an earthquake barrier model from mw 7 8 kokoxili tibet earthquake slip distribution abstract the slip distribution of the mw 7 8 kokoxili tibet 2001 earthquake has been measured at high resolution using optical correlation of satellite images and provides both the parallel and perpendicular components of the horizontal co seismic slip this reveals a variation of the horizontal slip at a scale of 20 km along strike anti correlation of slip parallel and perpendicular to the fault indicates transfer of slip from the horizontal to the vertical component at the ends of segments these features suggest a rupture model with segments separated by strong persistent geometric barriers the unexpected ending of the rupture south of the main fault can be explain by such a structure but bears important implications for the initiation and rupture directivity of the next earthquake

the chemical development of a hypersaline coastal basin in the high arctic we investigated a hypersaline seasonally isolated marine basin simb in the canadian high arctic to elucidate the role of brine rejection tidal forcing and groundwater input over the formation of hypersalinity analyses of physical parameters and seasonal sampling of ionic and isotopic composition were carried out on a coastal basin near shellabear point melville island northwest territories 75 n 113 w observations reveal daily and seasonal variability in the water column due to a seasonal tidal connection during the ice free season which lasts substantially longer than the period of freshwater inflow from the catchment an ice formation model of the volume of brine rejected from surface ice formed from marine water indicates that rapid saline enrichment of the basin due to ice formation is possible from tidally replenished marine water and that the current hypersalinity may have formed in less than a decade modeled isotopic composition of brines are consistent with observations and provide an alternative to freshwater isotopic dilution suggested by other workers a tidal connection is a critical consideration in lake evolution and many hypersaline polar lakes could have developed their current chemical composition before full marine isolation by contrast in some coastal lakes marine stratification caused by ice shelves before isolation provides a setting for minimal brine formation and subsequent meromictic conditions to develop hence the marine setting at the time of isolation represents a key factor in explaining divergent lake chemical evolution in the high arctic

paleoseismic evidence of great surface rupture earthquakes along the indian himalaya 1 toward understanding the relationship between strain accumulation and strain release in the context of the mechanics of the earthquake and mountain building process and quantifying the seismic hazard associated with the globes largest continental thrust system we describe the late quaternary expression and paleoseismic evidence for great surface rupture earthquakes at six sites along the himalayan frontal thrust hft system of india our observations span a distance of 250 km along strike of the hft uplifted and truncated fluvial terrace deposits resulting from the holocene displacements on the hft are preserved along canyons of the ghaggar markanda shajahanpur and kosi rivers dividing the elevation of the bedrock straths at each site by their ages yields estimates of the vertical uplift rate of 4 6 mm yr which when assumed to be the result of slip on an underlying thrust dipping at 20 45 are equivalent to fault slip rates of 6 18 mm yr or shortening rates of 4 16 mm yr trench exposures reveal the hft to fold and break late holocene surface sediments near the cities and villages of chandigarh kala amb rampur ganda lal dhang and ramnagar radiocarbon ages of samples obtained from the displaced sediments indicate surface rupture at each site took place after a d 1200 and before a d 1700 uncertainties attendant to the radiocarbon dating currently do not allow an unambiguous definition of the capping bound on the age of the displacement at each site and hence whether or not the displacements at all sites were contemporaneous trench exposures and vertical separations measured across scarps at rampur ganda lal dhang and ramnagar are interpreted to indicate single event displacements of 11 38 m dividing the observed single event vertical components of displacement by the estimated longer term uplift rates indicates 1330 3250 or more years should be required to accumulate the slip sufficient to produce similar sized displacements surface rupture appears to not have occurred during the historical 1905 kangra mw 7 7 1934 bihar nepal mw 8 1 and 1950 assam mw 8 4 earthquakes which also occurred along the himalayan front yet we observe clear evidence of fault scarps and displacements in young alluvium and progressive and continued offset of fluvial terrace deposits along the hft we suggest on this basis and the size and possible synchroneity of displacements recorded in the trenches that there exists the potential for earthquakes larger than recorded in the historical record and with the potential to rupture lengths of the hft greater than the 250 km we have studied

crustal structure of the himalayan orogen at 90 east longitude from project indepth deep reflection profiles international deep profiling of tibet and the himalaya indepth deep seismic reflection profiles show that the indian lithosphere is underthrusting the central himalaya along a gently north dipping decollement that is traceable northward beneath the tethyan belt to 28 6 n and to a depth of about 45 km the decollement carries in its hanging wall a near crustal thickness slice of internally deformed indian continental basement and cover represented in outcrop by the greater himalayan belt and structurally overlying tethyan belt geometric relationships suggest that the decollement probably ramps downward beneath the northern tethyan belt to near the base of the crust and that the hanging wall crustal slice was detached from indian mantle lithosphere that presently underlies southern tibet to the north the north himalayan anticlinorium kangmar dome appears to be a large duplex ramp anticline in the hanging wall of the decollement the south tibetan detachment appears to have been imaged in two areas in the wagye la area it appears to follow the tethyan belt greater himalayan belt contact northward in the subsurface and to have been folded over the kangmar dome in the zherger la area it appears to have been active relatively recently as a 30 north dipping normal fault that cuts deeply into the greater himalayan belt allochthon palinspastic reconstruction indicates a minimum of about 326 km of shortening of the indian basement across the himalaya since the initiation of the main central thrust hence indian continental lithosphere largely stripped of its overlying crust can extend northward beneath the tibetan plateau to at least 32 n where earthquake seismological observations show that the properties of the upper mantle change markedly e g mcnamara et al 1995 taken together the seismic reflection and earthquake seismological observations lend support for the view that the indian mantle lid mechanically underplates roughly the southern half of the tibetan plateau the indepth reflection data do not show that indian crust attached to this lithosphere extends north of southernmost tibet kangmar dome nor do they negate this possibility similarly the reflection data do not yield direct evidence for or against lower crustal subduction beneath the himalaya

slip history of the 2003 san simeon earthquake constrained by combining 1 hz gps strong motion and teleseismic data 1 the slip history of the 2003 san simeon earthquake is constrained by combining strong motion and teleseismic data along with gps static offsets and 1 hz gps observations comparisons of a 1 hz gps time series and a co located strong motion data are in very good agreement demonstrating a new application of gps the inversion results for this event indicate that the rupture initiated at a depth of 8 5 km and propagated southeastwards with a speed 3 0 km sec with rake vectors forming a fan structure around the hypocenter we obtained a peak slip of 2 8 m and total seismic moment of 6 2 10 18 nm we interpret the slip distribution as indicating that the hanging wall rotates relative to the footwall around the hypocenter in a sense that appears consistent with the shape of the mapped fault trace index terms 1242 geodesy and gravity seismic deformations 7205 7212 seismology earthquake ground motions and engineering 8123 tectonophysics dynamics seismotectonics citation ji c k m larson y tan k w hudnut and k choi 2004 slip history of the 2003 san simeon earthquake constrained by combining 1 hz gps strong motion and teleseismic data geophys res lett 31 l17608 doi 10 1029 2004gl020448

a comparison of physical properties and strength of decaying first year ice in the arctic and sub arctic measurements made on first year ice in the arctic and sub arctic are used to show that ice from both regions decays in a similar manner during the spring summer melt season one notable difference is that melt induced changes in sub arctic labrador occur about 2 months earlier than in the arctic in both regions the temperature and strength of the ice change gradually over the season whereas the bulk salinity and thickness of the ice do not change substantially until later in the season when the ice becomes isothermal at a temperature of 1 88c results show that the seasonal decrease in the strength of first year sea ice and the temperature induced increase in brine volume are correlated once the ice is devoid of salt in late summer the air volume continues to increase but has minimal effect on the ice strength

physical properties of summer sea ice in the fram strait the physical properties of sea ice in the fram strait region of the greenland sea were examined during june and july 1984 in conjunction with the marginal ice zone experiment field program most of the ice sampled within fram strait during this period was multiyear thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years snow cover on the multiyear ice averaged 29 cm while that on first year ice averaged only 8 cm deep this difference may be related to enhanced sublimation of the snow on the thinner first year ice the salinity profiles of first year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores thin section examinations of crystal structure indicate that about 75 of the ice consisted of congelation ice with typically columnar type crystal structure the remaining 25 consisted of granular ice with only a few occurrences of snow ice the granular ice consisted primarily of frazil found in small amounts at the top of floes but mainly observed in multiyear ridges the horizontally oriented crystal c axes showed various degrees of alignment ranging from no alignment to strong alignments in which the alignment direction changed with depth implying a change in floe orientation with respect to the ocean current at the ice water interface during ice growth evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core this retexturing consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet brine layer substructure is attributed to summer warming

the 2005 mw 7 6 kashmir earthquake sub pixel correlation of aster images and seismic waveforms analysis we analyze the m w 7 6 kashmir earthquake of october 8 2005 using sub pixel correlation of aster images to measure ground deformation and modeling seismic waveforms the surface rupture is continuous over a distance of 75 km and cuts across the hazara syntaxis reactivating the tanda and the muzaffarabad faults north of muzaffarabad the surface rupture coincides approximately with the mbt on the southwestern flank of the syntaxis although the two faults have opposite dip angles the rupture terminates abruptly at the hairpin turn of the mbt showing a strong structural control the fault offset is 4 m on average and peaks to 7 m northwest of muzaffarabad the rupture lasted about 25 s and propagated updip and bi laterally 2 km s with a rise time of 2 5 s the shallowness and compactness of the rupture both in time and space provide an explanation for the intensity of destructions this kind of analysis could be achieved as soon as a post earthquake image is available and would provide key information for early assessment of damages the study sheds some light on seismic hazard in the himalaya and raises concern regarding the possibility of a repetition of the 1555 event which presumably ruptured the himalayan front south of the kashmir basin and may have reached a magnitude m w 8

iron mobilization in mineral dust can anthropogenic so2 emissions affect ocean productivity 1 for fe contained in long range transported aeolian dust to act as a micronutrient for oceanic phytoplankton it must be first dissolved or mobilized we propose that fe mobilization can occur in mineral dust from east asia by the incorporation of so2 into the advecting dust plumes and subsequent acidification of the dust through heterogeneous so2 oxidation to test this hypothesis we consider a dust plume that originated from the gobi deserts and advected over the pacific ocean data collected over the yellow sea confirm that this plume contained high concentrations of dust and so2 significant gaseous hno3 concentrations indicate that the dust particles were acidified i e ph 2 at these ph s 1 2 of the fe contained in a deliquescent mineral dust particle would be mobilized within 3 5 days these results suggest a possible link between the rate of c fixation in so called high nitrate low chlorophyll regions of the pacific ocean and so2 emissions from east asia

growth rate and salinity profile of first year sea ice in the high arctic this paper describes the growth of sea ice and the salinity profiles observed in eclipse sound near pond inlet baffin island canada during the winter of 1977 78 a numerical method of calculation has been developed to incorporate the variations in snow conditions and physical properties of ice and snow during the growth season it is shown that the growth rate can be predicted reasonably well it is also shown that the vertical salinity profile in the ice towards the end of the season provides a record of previous climatological conditions a dependence has been shown between the predicted growth rate and the measured salinity

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities