laboratory earthquakes the sub rayleigh to supershear rupture transition we report on the experimental observation of spontaneously nucleated supershear rupture and on the visualization of sub rayleigh to supershear rupture transitions in frictionally held interfaces the laboratory experiments mimic natural earthquakes the results suggest that under certain conditions supershear rupture propagation can be facilitated during large earthquake events

three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

a supershear transition mechanism for cracks seismic data indicate that fault ruptures follow complicated paths with variable velocity because of inhomogeneities in initial stress or fracture energy we report a phenomenon unique to three dimensional cracks locally stronger fault sections rather than slowing ruptures drive them forward at velocities exceeding the shear wave speed this supershear mechanism differentiates barrier and asperity models of fault heterogeneity which previously have been regarded as indistinguishable high strength barriers concentrate energy producing potentially destructive pulses of strong ground motion

the 5 september 2012 nicoya costa rica mw 7 6 earthquake rupture process from joint inversion of high rate gps strong motion and teleseismic p wave data and its relationship to adjacent plate boundary interface properties 1 on 5 september 2012 a large thrust earthquake mw 7 6 ruptured a densely instrumented seismic gap on the shallow dipping plate boundary beneath the nicoya peninsula costa rica ground motion recordings directly above the rupture zone provide a unique opportunity to study the detailed source process of a large shallow megathrust earthquake using very nearby land observations hypocenter relocation using local seismic network data indicates that the event initiated with small emergent seismic waves from a hypocenter 10 km offshore 13 km deep on the megathrust a joint finite fault inversion using high rate gps strong motion ground velocity recordings gps static offsets and teleseismic p waves reveals that the primary slip zone slip 1 m is located beneath the peninsula the rupture propagated downdip from the hypocenter with a rupture velocity of 3 0 km s the primary slip zone extends 70 km along strike and 30 km along dip with an average slip of 2 m the associated static stress drop is 3 mpa the seismic moment is 3 5 1020 nm giving mw 7 6 the coseismic large slip patch directly overlaps an onshore interseismic locked region indicated by geodetic observations and extends downdip to the intersection with the upper plate moho at deeper depths below the upper plate moho seismic tremor and low frequency earthquakes have been observed most tremor locates in adjacent areas of the megathrust that have little coseismic slip a region of prior slow slip deformation to the southeast also has no significant coseismic slip or aftershocks an offshore locked patch indicated by geodetic observations does not appear to have experienced coseismic slip and aftershocks do not overlap this region allowing the potential for a comparable size rupture offshore in the future

laboratory earthquakes along inhomogeneous faults directionality and supershear we report on the experimental observation of spontaneously nucleated ruptures occurring on frictionally held bimaterial interfaces with small amounts of wave speed mismatch rupture is always found to be asymmetric bilateral in one direction rupture always propagates at the generalized rayleigh wave speed whereas in the opposite direction it is subshear or it transitions to supershear the lack of a preferred rupture direction and the conditions leading to supershear are discussed in relation to existing theory and to the earthquake sequence in parkfield california and in north anatolia

germanium isotopic variations in igneous rocks and marine sediments a new technique for the precise and accurate determination of ge stable isotope compositions has been developed and applied to silicate rocks and biogenic opal the analyses were performed using a continuous flow hydride generation system coupled to a mc icpms samples have been purified through anion and cation exchange resins to separate ge from matrix elements and eliminate potential isobaric interferences variations of 74ge 70ge ratios are expressed as 74ge values relative to our internal standard and the long term external reproducibility of the data is better than 0 2 for sample size as low as 15 ng of ge data are presented for igneous and sedimentary rocks and the overall variation is 2 4 in 74ge representing 12 times the uncertainty of the measurements and demonstrating that the terrestrial isotopic composition of ge is not unique co variations of 74ge 70ge 73ge 70ge and 72ge 70ge ratios follow a mass dependent behaviour and imply natural isotopic fractionation of ge by physicochemical processes the range of 74ge in igneous rocks is only 0 25 without systematic differences among continental crust oceanic crust or mantle material on this basis a bulk silicate earth reservoir with a 74ge of 1 3 0 2 can be defined in contrast modern biogenic opal such as marine sponges and authigenic glauconite displayed higher 74ge values between 2 0 and 3 0 this suggests that biogenic opal may be significantly enriched in light isotopes with respect to seawater and places a lower bound on the 74ge of the seawater to 3 0 this suggests that seawater is isotopically heavy relative to bulk silicate earth and that biogenic opal may be significantly fractionated with respect to seawater deep sea sediments are within the range of the bulk silicate earth while mesozoic deep sea cherts opal and quartz have 74ge values ranging from 0 7 to 2 0 the variable values of the cherts cannot be explained by binary mixing between a biogenic component and a detrital component and are suggestive of enrichment in the light isotope of diagenetic quartz further work is now required to determine ge isotope fractionation by siliceous organisms and to investigate the effect of diagenetic processes during chert lithification

hydrological and solute budgets of lake qinghai the largest lake on the tibetan plateau abstract water level and chemistry of lake qinghai are sensitive to climate changes and are important for paleoclimatic implications an accurate understanding of hydrological and chemical budgets is crucial for quantifying geochemical proxies and carbon cycle published results of water budget are firstly reviewed in this paper chemical budget and residence time of major dissolved constituents in the lake are estimated using reliable water budget and newly obtained data for seasonal water chemistry the results indicate that carbonate weathering is the most important riverine process resulting in dominance of ca2 and dic for river waters and groundwater groundwater contribution to major dissolved constituents is relatively small 4 2 0 5 wet atmospheric deposition contributes annually 7 4 44 0 soluble flux to the lake resulting from eolian dust throughout the seasons estimates of chemical budget further suggest that 1 the buha type water dominates the chemical components of the lake water 2 na cl mg2 and k in lake water are enriched owing to their conservative behaviors and 3 precipitation of authigenic carbonates low mg calcite aragonite and dolomite transits quickly dissolved ca2 into the bottom sediments of the lake resulting in very low ca2 in the lake water therefore authigenic carbonates in the sediments hold potential information on the relative contribution of different solute inputs to the lake and the lake chemistry in the past

late pliocene quaternary evolution of redox conditions in the western qaidam paleolake ne tibetan plateau deduced from mn geochemistry in the drilling core sg 1 abstract manganese mn in lake sediments reacts strongly to changes of redox conditions this study analyzed mn concentrations in oxides carbonates and bulk phases of the calcareous lacustrine sediments of a 938 5 m long core sg 1 taken from the western qaidam basin well dated from 2 77 ma to 0 1 ma comparisons of extractions from diluted hydrochloric acid acetic acid and citrate bicarbonate dithionite demonstrate that variations of mn concentrations from acetic acid leaching mnhoac are mostly responsible for mn ii fluctuations in the carbonate phase taking into account the relevant processes during weathering transportation deposition and post deposition of mn bearing rocks we conclude that mn input from catchment weathering and paleolake redox condition provide the primary controls on variations in the mn records of carbonate and oxide phases we propose mnhoac as a new sensitive indicator of paleolake redox evolution and catchment scale climate change the mnhoac variations show a long term upward decreasing trend indicating a long term decrease of mn input from catchment weathering associated with increasing oxygen content in the paleolake bottom water the great similarities of the mnhoac record with other regional and global records suggest that paleolake redox changes and climatic drying in the qaidam basin may be largely related to global cooling

rupture model of the 1999 duzce turkey earthquake deduced from high and low frequency strong motion data 1 we investigated the rupture process of the 1999 duzce earthquake by applying the multi time window linear waveform inversion method to low frequency ground motions 0 5 hz in the near source area then we performed theforwardmodellingofhigherfrequencyground motions 0 3 10 0 hz by the empirical green s function egf method to image the strong motion generation area smga we also examined the source model to check whether the supershear phenomenon occurred inside the asperities or not slip distribution model from the inversion suggests 2 asperities the maximum slip is obtained as 5 m near the hypocenter the high first time window front propagation velocity ftwfpv and consequently high apparent rupture velocity found from the investigation of rupture progression indicated that eastern propagation partially showed supershear behaviour the egf simulation which identifies an average rupture velocity vr in smga supports this finding index terms 7212 seismology earthquake ground motions and engineering 7215 seismology earthquake parameters 7223 seismology seismic hazard assessment and prediction citation birgoren g h sekiguchi and k irikura 2004 rupture model of the 1999 duzce turkey earthquake deduced from high and low frequency strong motion data geophys res lett 31 l05610 doi 10 1029 2003gl019194

sources and flux of trace elements in river water collected from the lake qinghai catchment ne tibetan plateau river waters play a significant role in supplying naturally and anthropogenically derived materials to lake qinghai northeastern tibetan plateau to define the sources and controlling processes for river water chemistry within the lake qinghai catchment high precision icp ms trace element concentrations were measured in water samples collected from the buha river weekly in 2007 and from other major rivers in the post monsoon late october 2006 and monsoon late july 2007 seasons the distributions of trace elements vary in time and space with distinct seasonal patterns the primary flux in the buha river is higher tds and dissolved al b cr li mo rb sr and u during springtime than those during other seasons and is attributed to the inputs derived from both rock weathering and atmospheric processes among these elements the fluxes of dissolved cr b and rb are strongly influenced by eolian dust input the fluxes of dissolved li mo sr and u are also influenced by weathering processes reflecting the sensitivity of chemical weathering to monsoon conditions the anthropogenic sources appear to be the dominant contribution to potentially harmful metals ni cu co zn and pb with high fluxes at onset of the main discharge pulses due at least partially to a runoff washout effect for other major rivers except for ba concentrations of trace elements are higher in the monsoon than in the post monsoon season a total of 38 5 3 1 tons of potentially harmful elements are transported into the lake annually despite human activities within the catchment being limited nearly all river water samples contain dissolved trace elements below the world health organization guidelines for drinking water with the exception of as and b in the daotang river water samples collected in late july probably mobilized from underlying lacustrine sediments

en echelon and orthogonal fault ruptures of the 11 april 2012 great intraplate earthquakes the magnitude 8 7 earthquake that occurred off the coast of the sumatra subduction zone on 11 april 2012 is shown to have had an extraordinarily complex four fault rupture these great ruptures represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates on 11 april 2012 two of the largest strike slip earthquakes ever recorded at magnitudes of 8 7 and 8 2 occurred in the northeastern indian ocean a few hundred kilometres off the coast of sumatra three groups now report the analysis of seismic data from the days and months before and after these events as well as the events themselves matthias delescluse and co authors show that these earthquakes are part of the ongoing boost of intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes they conclude that the australian plate driven by slab pull forces at the sunda trench is gradually detaching from the indian plate han yue and colleagues show that the 11 april event involved a complex four fault rupture lasting several minutes followed two hours later by a magnitude 8 2 aftershock these great ruptures on a lattice of strike slip faults that extends through the crust and into the upper mantle represent large lithospheric deformation that may eventually create a localized boundary between the indian and australian plates fred pollitz and colleagues show that in the six days following 11 april the global rate of remote earthquakes with magnitudes greater than 5 5 increased nearly fivefold and events up to magnitude 7 seem to have been triggered the unprecedented delayed triggering power of this earthquake may arise from its strike slip source geometry or because it struck at a time of an unusually low global earthquake rate and increased the number of nucleation sites that were very close to failure the indo australian plate is undergoing distributed internal deformation caused by the lateral transition along its northern boundary from an environment of continental collision to an island arc subduction zone1 2 on 11 april 2012 one of the largest strike slip earthquakes ever recorded seismic moment magnitude mw 8 7 occurred about 100 200 kilometres southwest of the sumatra subduction zone occurrence of great intraplate strike slip faulting located seaward of a subduction zone is unusual it results from northwest southeast compression within the plate caused by the india eurasia continental collision to the northwest together with northeast southwest extension associated with slab pull stresses as the plate underthrusts sumatra to the northeast here we use seismic wave analyses to reveal that the 11 april 2012 event had an extraordinarily complex four fault rupture lasting about 160 seconds and was followed approximately two hours later by a great mw 8 2 aftershock the mainshock rupture initially expanded bilaterally with large slip 20 30 metres on a right lateral strike slip fault trending west northwest to east southeast wnw ese and then bilateral rupture was triggered on an orthogonal left lateral strike slip fault trending north northeast to south southwest nne ssw that crosses the first fault this was followed by westward rupture on a second wnw ese strike slip fault offset about 150 kilometres towards the southwest from the first fault finally rupture was triggered on another en echelon wnw ese fault about 330 kilometres west of the epicentre crossing the ninetyeast ridge the great aftershock with an epicentre located 185 kilometres to the ssw of the mainshock epicentre ruptured bilaterally on a nne ssw fault the complex faulting limits our resolution of the slip distribution these great ruptures on a lattice of strike slip faults that extend through the crust and a further 30 40 kilometres into the upper mantle represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates

influence of the rupture initiation on the intersonic transition crack like versus pulse like modes we numerically investigate the supershear transition of inplane rupture under slip weakening friction and tectonic loading using a non smooth spectral element method nucleation of the rupture in the vicinity of an initial stress concentration is consistently solved together with the dynamic propagation nucleation is shown to influence the transition to the supershear propagation and depending upon the initiation process and the level of the stress out of the nucleating asperity crack like or pulse like solutions can be selected in the intersonic regime pulses are triggered by dynamic unloading of the traction ahead of the rayleigh wave and tend to become metastable the asymptotic numerical solution is always a crack propagating close to p wave speed the rupture front and the arrest velocities are numerically characterized we argue that the nucleation phase introduces a trade off with the state of the stress in determining the distance at which supershear appears

source complexity of the 1988 armenian earthquake evidence for a slow after slip event we analyzed teleseismic p and s waves using a multiple event deconvolution method to investigate the source process of the spitak armenia earthquake of december 7 1988 teleseismic long period body waves exhibit complex waveforms significantly more complex than those normally seen for an event of this size we identified two groups of subevents one is a group of strike slip events during the first 20 s the other is a dip slip event initiating at about 30 s after the initial rupture the tensor sum of all the subevents is essentially strike slip strike 302 dip 59 rake 143 with a scalar moment of 1 47 10 19 n m the seismic moment of the dip slip event strike 89 dip 60 rake 88 is 5 6 10 18 n m nearly 40 of the total and the moment release rate is slower than the other subevents with a strike slip mechanism we call this event a slow after slip event the mechanism of the after sup event is consistent with the present day deformation pattern in the caucasus where north south compression is predominant due to the continental collision between the arabian plate and the russian platform this result suggests that in a region where both strike slip motion and crustal shortening are taking place like southern california a large strike slip event may accompany large thrust events and vice versa in order to determine the total coseismic deformation pattern it is essential to resolve these multiple events in time space and mechanism

direct observation of rupture propagation during the 1979 imperial valley earthquake using a short baseline accelerometer array abstract the 1979 imperial valley california earthquake m s 6 9 was recorded on the el centro differential array a 213 m long linear array of 5 three component digital accelerometers 5 6 km from the nearest tectonic surface rupture although absolute time was not recorded on the array elements a relative time base was established using the main shock hypocentral p wave and the p and s waves from a later aftershock a cross correlation technique was used to measure the difference in arrival times of individual seismic waves in a moving 0 6 to 1 2 sec window at each array element which would then be converted into the wave9s slowness 1 velocity along the array when applied to the main shock vertical and horizontal accelerograms results from both components of motion indicated that the early arriving energy came from a source to the south of the array and the source of the energy moved rapidly to the north of the array during the strong shaking the ground motions at the array elements were well correlated for about the first 11 sec of motion these observations suggest that we have observed the initiation of rupture south of the array and its subsequent propagation along the fault to a position north of the array in about 10 sec and that the energy was radiated from a fairly compact region around the rupture front if the observed vertical and horizontal ground motions are assumed to be caused by p and s waves respectively then the observed slownesses show irregularities which can be interpreted as implying that the observed high frequency ground motions originated at irregularly distributed regions on the fault surface or that the rupture velocity was variable or both one possible interpretation of the data suggests that the rupture proceeded at near p wave velocity over a 7 km long section of fault average rupture velocities of about 2 7 to 3 2 km sec at 8 km depth are consistent with the data and 2 8 km sec is weakly preferred under the assumption that rupture propagates at a fixed fraction of the shear velocity the large vertical pulse which had a peak acceleration of 1 7 g at e06 was emitted from the portion of the fault extending 25 to 30 km northwest of the hypocenter near meloland overpass and not from the point on the fault closest to the differential array nothing can be said about fault behavior southeast of the hypocenter

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

geochemistry and solute sources of surface waters of the tarim river basin in the extreme arid region nw tibetan plateau abstract major ion concentrations of river lake and snow waters were measured to better understand the water quality hydrochemical processes and solute sources of surface waters within the tarim river basin in the extreme arid region surface waters are slightly alkaline and are characterized by high total dissolved solids tds tds values varies over two orders of magnitude from fresh 76 to brackish 24 with a mean value of 1000 mg l higher than the global river average and river waters draining the himalayas and the southeastern tibetan plateau most of the samples were ca2 mg2 hco 3 type and suited for drinking and irrigation water quality of aksu river ak hotan river ht and northern rivers nr is better than the others rock weathering ion exchange and precipitation are the major hydrogeochemical processes responsible for the solutes in rivers waters anthropogenic input to the water chemistry is minor and human activities accelerate increase of river tds the quantitative solute sources are first calculated using a forward model in this area the results show that evaporite dissolution carbonate weathering atmospheric input and silicate weathering contributed 58 3 25 7 8 7 and 8 2 of the total dissolved cations for the whole basin evaporite dissolution dominated in lake waters lw ht yarkant river yk tarim river tr and southern rivers sr contributing 73 5 53 4 56 7 77 and 74 2 of the total dissolved cations respectively carbonate weathering dominated in ak and nr contributing 48 and 44 4 of the total dissolved cations respectively the tds flux of ht tr ak yk was 66 0 118 6 134 9 and 170 4 t km2 yr respectively higher than most of the rivers in the world knowledge of our research can promote effective management of water resources in this desert environment and add new data to global river database

lake qinghai sediment geochemistry linked to hydroclimate variability since the last glacial abstract geochemistry of basin sediments from semi arid regions is valuable to understand past hydroclimatic changes here we investigate the links of sedimentary geochemistry rb sr ca zr toc and caco 3 carbonate mineralogy and ostracod shell 18 o of lake qinghai a basin proximal to major dust production centers at mid latitudes of the northern hemisphere to changes in depositional conditions and hydroclimate during the past 32 ka surface lacustrine sediments are characterized by low rb high sr low rb sr high caco 3 and high ca zr values in contrast to the chemical compositions of eolian loess high rb low sr high rb sr low caco 3 and low ca zr a direct comparison of soluble ca and sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in lake qinghai are dominated by authigenic aragonite formed under ca 2 limited water conditions and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons late may to september our high resolution down core records show that sediments during the last glacial 32 19 8 ka had high rb low sr low caco 3 and low ca zr indicating eolian dust loess accumulation in a desiccated basin under dry glacial conditions further supported by grain size and pollen results this type of sedimentation was maintained during the last deglacial 19 8 11 5 ka but interrupted by episodic lacustrine precipitates with high sr high caco 3 high ca zr and low rb at 11 5 ka sedimentary rb sr ca zr caco 3 and toc show dramatic and permanent changes implying an abrupt shift in the atmospheric circulation at the onset of the holocene in the lake qinghai region lacustrine precipitates have persisted throughout the holocene with a maximum during the early to mid holocene 10 5 8 0 ka since 8 0 ka the gradual and significant decreases in aragonite and sr accumulations in tandem with increasing dust deposit and more positive ostracod 18 o may be linked to a weakening of asian summer monsoons during the mid to late holocene overall our records appear to show a high sensitivity of sediment development and geochemistry in lake qinghai to the regional hydroclimate changes since the last glacial

toward a geochemical mass balance of major elements in lake qinghai ne tibetan plateau a significant role of atmospheric deposition abstract sediments in lake qinghai archive important information about past environmental changes in order to faithfully interpret the sediment records and constrain the elemental cycles it is critical to trace various sources of sediments in the lake the results show that the elemental input output budgets are imbalanced for most major elements between riverine fluxes and mass accumulation rate mar of lake qinghai sediments a realistic model must include contributions of dry wet atmospheric deposition that allow the major element mass balance for the lake to be defined the budget estimation is based on mass balances of si and al which are relatively immobile and carried to the lake via particulate forms estimated annual budget of dry atmospheric deposition is 1 3 0 3 103 kt a accounting for 65 of the total inputs to the lake sediments assuming local loess within the catchment as a candidate for dry atmospheric deposition to the lake the resultant flux of 300 45 g m2 a falls within the flux average of the desert area 400 g m2 a and the loess plateau 250 g m2 a consistent with the geographical setting of lake qinghai the role of atmospheric deposition would be more significant if wet deposition via rainfall and snow were taken into account this highlights the potential importance of dust as a significant source for sediment preservation flux for other catchments worldwide the results also indicate that nearly all ca input was preserved in the lake sediments under modern conditions consistent with ca2 supersaturation of the lake water

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

runoff processes in the qinghai lake basin northeast qinghai tibet plateau china insights from stable isotope and hydrochemistry abstract qinghai lake is one of china s national nature reserves and supports the ecological security of the ne qinghai tibet plateau more than half of the rivers flowing into qinghai lake are currently dry due to climate change and human activity this study was designed to learn more about the causes of environmental problems in the basin using stable isotopes and hydrochemistry of qinghai lake basin river water to explore runoff processes and their relationship with climate change results indicated that the river water was mainly fed by precipitation in the basin which has undergone weak evaporation river discharges were generated mainly from the middle and upper basin due to high precipitation low evapotranspiration and alpine swamp land use cover in those areas river water in tributaries would experience relatively stronger evaporation than in the main stream main hydrochemical types of river waters were ca2 mg2 hc o 3 and river water chemistry was mainly controlled by carbonate weathering in the qinghai lake basin the effects of human activity on water chemistry were relatively mild in the basin the interaction between water and rocks was slighter in the river water than in the groundwater river runoff was more sensitive to precipitation than to temperature lake level rises were closely related to increases in river runoff and precipitation conversely lake level declines were closely related to declines in river runoff and precipitation lake level could rise due to increasing precipitation and runoff in the future

evaluation of lacustrine groundwater discharge and associated nutrients trace elements and dic loadings into qinghai lake in qinghai tibetan plateau using radium isotopes and hydrological methods abstract qinghai lake the largest lake in china with a surface area of 4260 km2 lies in the northeastern qinghai tibet plateau qtp at a mean altitude of 3194 m above sea level the lake has a water volume of 71 6 109 m3 a salinity ranges of 4 18 0 14 ppt to 12 3 0 14 ppt during sampling period which is about a half of typical seawater the aquifer systems at the lake shoreline have obvious saline water and freshwater mixing zones with similar hydrogeological and biogeochemical settings to coastal aquifers this study aims to estimate lacustrine groundwater discharge lgd and the associated chemical loadings to western qinghai lake naturally occurring radium isotopes 223ra 224ra 226ra and 228ra nutrients heavy metals and dissolved inorganic carbon dic were systematically investigated in different water endmembers of western qinghai lake lgd was estimated with radium inventory model and radium eddy diffusion model leading to a lgd estimate of 7 67 106 m3 d 1 and 8 52 106 m3 d 1 respectively the fresh groundwater discharge obtained based on regional water budget is about 5 97 106 m3 d 1 during sampling period accounting for 73 74 ranging from 53 22 to 80 43 of total lgd this study reveals that the fresh groundwater component is dominant in lgd of qinghai lake which is quite different from most coastal scenarios furthermore the chemical loadings derived from fresh lgd and recirculated lgd are evaluated the preliminary results indicate that fresh lgd is an important source of nutrient barium strontium uranium and dic to the lake and may significantly impact biogeochemical and ecological processes in the lake this study presents the first lgd estimate in the largest qtp saline lake in china and would be instructive to further similar studies in saline lakes in qtp and elsewhere in the world

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

solute geochemistry and its sources of the groundwaters in the qinghai lake catchment nw china major ion compositions were analyzed in 65 groundwater samples to decipher water quality solute geochemistry and sources of groundwater within the qinghai lake catchment ne tibetan plateau groundwaters were slightly alkaline with ph varying from 7 2 to 8 7 the total dissolved solids tds varied over two orders of magnitude from fresh 88 to brackish 12 with a mean value of 672 mg l higher than river waters within the qinghai lake catchment and river waters draining the himalayas and the southeastern tibetan plateau most of the samples approximately 80 were the ca 2 mg 2 hco 3 type and suitable for drinking and irrigation some of the lakeside the buha and the qinghai lake water were cl type and not suitable for drinking and irrigation water quality of hargai and shaliu samples was better than the others rock weathering ion exchange and precipitation are the major geochemical processes responsible for the solutes in the groundwater within the qinghai lake catchment anthropogenic input to the groundwater is minor the forward models on the input of groundwaters from various sources showed that the contributions were 40 1 for carbonate weathering 29 0 for evaporite dissolution 16 8 for atmospheric input and 14 1 for silicate weathering of the total dissolved cations for the whole catchment evaporite dissolution was dominating in the lakeside the buha and the daotang samples contributing 15 3 45 9 20 4 61 1 and 21 3 63 9 of the total dissolved cations respectively carbonate weathering was dominated in the shaliu and the hargai samples contributing 23 9 71 7 and 31 8 95 4 of the total dissolved cations respectively the result also demonstrated that carbonate weathering had higher contribution to the groundwaters than silicate weathering

supershear rupture of the 5 january 2013 craig alaska mw 7 5 earthquake supershear rupture in which a fracture s crack tip expansion velocity exceeds the elastic shear wave velocity has been extensively investigated theoretically and experimentally and previously inferred from seismic wave observations for six continental strike slip earthquakes we find extensive evidence of supershear rupture expansion of an oceanic interplate earthquake the 5 january 2013 mw 7 5 craig alaska earthquake this asymmetric bilateral strike slip rupture occurred on the queen charlotte fault offshore of southeastern alaska observations of first arriving sn and sg shear waves originating from positions on the fault closer than the hypocenter for several regional seismic stations with path calibrations provided by an empirical green s function approach indicate a supershear rupture process several waveform inversion and modeling techniques were further applied to determine the rupture velocity and space time distribution of slip using regional seismic and geodetic observations both theoretical and empirical green s functions were used in the analyses with all results being consistent with a rupture velocity of 5 5 to 6 km s exceeding the crustal and upper mantle s wave velocity and approaching the crustal p wave velocity supershear rupture occurred along 100 km of the northern portion of the rupture zone but not along the shorter southern rupture extension the direction in which supershear rupture developed may be related to the strong material contrast across the continental oceanic plate boundary as predicted theoretically and experimentally the shear and surface wave mach waves involve strongly enhanced ground motions at azimuths oblique to the rupture direction emphasizing the enhanced hazard posed by supershear rupture of large strike slip earthquakes

supershear rupture on multiple faults for the mw 8 6 off northern sumatra indonesia earthquake of april 11 2012 1 we perform a back projection method to image the rupture propagation and short period energy release of the 2012 off northern sumatra earthquake mw8 6 using hi net data recorded in japan the results show a complex pattern of four conjugate faults over about 180 sec there is a striking correspondence between the lengths and orientations of our rupture pattern with the distribution of aftershocks each of the first three stages of the rupture corresponds to a clear lineation in the aftershocks with lengths of 200 to 400 km rupture speeds for several of the fault segments were very high about 5 km s and exceed the local s wave velocity this is the first example of an oceanic earthquake with supershear rupture speed

the october 28 2012 mw 7 8 haida gwaii underthrusting earthquake and tsunami slip partitioning along the queen charlotte fault transpressional plate boundary the pacific north american plate boundary is undergoing predominantly right lateral strike slip motion along the queen charlotte and fairweather transform faults the queen charlotte fault qcf hosted the largest historical earthquake in canada the 1949 m s 8 1 strike slip earthquake which ruptured from offshore northern haida gwaii several hundred kilometers northwestward on january 5 2013 an m w 7 5 strike slip faulting event occurred near the northern end of the 1949 rupture zone along central and southern haida gwaii the relative plate motion has 20 oblique convergence across the left stepping plate boundary there had been uncertainty in how the compressional component of plate motion is accommodated the october 28 2012 m w 7 8 haida gwaii earthquake involved slightly 20 oblique thrust faulting on a shallow 18 5 northeast dipping fault plane with strike 320 parallel to the qcf consistent with prior inferences of pacific plate underthrusting beneath haida gwaii the rupture extended to shallow depth offshore of moresby island beneath a 25 30 km wide terrace of sediments that has accumulated in a wedge seaward of the qcf the shallow thrusting caused seafloor uplift that generated substantial localized tsunami run up and a modest far field tsunami that spread across the northern pacific prompting a tsunami warning beach closure and coastal evacuation in hawaii although ultimately tide gauges showed less than 0 8 m of water level increase the mainshock rupture appears to have spread with a 2 3 km s rupture velocity over a length of 150 km with slip averaging 3 3 m concentrated beneath the sedimentary wedge the event was followed by a substantial aftershock sequence in which almost all of the larger events involve distributed intraplate normal faulting extending 50 km oceanward from the qcf the highly oblique slip partitioning in southern haida gwaii is distinctive in that the local plate boundary parallel motion on the qcf may be accommodated either by infrequent large strike slip ruptures or by aseismic creep as seems to be the case for deeper oblique relative plate motion beneath haida gwaii while the sedimentary terrace accumulates plate boundary perpendicular compressional strain that releases in almost pure thrust faulting earthquakes seaward of the qcf

the manifestation of the younger dryas event in the east asian summer monsoon margin new evidence from carbonate geochemistry of the dali lake sediments in northern china the processes and mechanisms of the younger dryas yd event in the modern northern margin of the east asian summer monsoon easm are still heatedly debated this study presents new high resolutio

late cenozoic climate changes in china s western interior a review of research on lake qinghai and comparison with other records abstract we review late cenozoic climate and environment changes in the western interior of china with an emphasis on lacustrine records from lake qinghai widespread deposition of red clay in the marginal basins of the tibetan plateau indicates that the asian monsoon system was initially established by 8 ma when the plateau reached a threshold altitude subsequent strengthening of the winter monsoon along with the establishment of the northern hemisphere ice sheets reflects a long term trend of global cooling the few cores from the tibetan plateau that reach back a million years suggest that they record the mid pleistocene transition from glacial cycles dominated by 41 ka cycles to those dominated by 100 ka cycles during terminations i and ii strengthening of the summer monsoon in china s interior was delayed compared with sea level and insolation records and it did not reach the western tibetan plateau and the tarim basin lacustrine carbonate 18 o records reveal no climatic anomaly during mis3 so that high terraces interpreted as evidence for extremely high lake levels during mis3 remain an enigma following the last glacial maximum lsm several lines of evidence from lake qinghai and elsewhere point to an initial warming of regional climate about 14 500 cal yr bp which was followed by a brief cold reversal possibly corresponding to the younger dryas event in the north atlantic region maximum warming occurred about 10 000 cal yr bp accompanied by increased monsoon precipitation in the eastern tibetan plateau superimposed on this general pattern are small amplitude centennial scale oscillations during the holocene warmer than present climate conditions terminated about 4000 cal yr bp progressive lowering of the water level in lake qinghai during the last half century is mainly a result of negative precipitation evaporation balance within the context of global warming

otolith microchemistry of modern versus well dated ancient naked carp gymnocypris przewalskii implication for water evolution of lake qinghai there is ongoing debate over how the water level and composition of the water in lake qinghai changed in the past and might change in future this study of the microchemistry of otoliths from ancient naked carp explores the chemistry of a relict lake isolated from lake qinghai during the little ice age lia a close correlation between the ages measured on fish bone and otoliths by ams 14c and by optically stimulated luminescence on overlying sediments confirms a high water level in lake qinghai before 680 300 years ago the contrasting compositions of the ancient otoliths relative to modern otoliths and waters indicate that the relict lake became enriched in 18o mg li b and to a lesser extent ba but depleted in 13c owing to strong evaporation authigenic carbonates precipitation micro organism activity and less fresh water input after it was isolated if there were long term fresh water input however a reverse trend might occur the most important observation is that because the waters have been supersaturated with respect to carbonates authigenic carbonate precipitation would result in low but consistent sr ca ratios in the lakes as recorded by both the ancient and modern otoliths the geochemical records of ancient versus modern biogenic carbonates provide insights into the long term hydroclimatic evolution processes of an inland water body

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

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

geochemical evolution of closed basin lakes general model and application to lakes qinghai and turkana in contrast to most previous models for the evolution of closed basin lakes we present an integrated model which considers various water budget patterns clay regradation so4 reduction and subbottom leakage in addition to the classical equilibrium approach of mineral precipitation the model was applied to lakes qinghai and turkana which significantly differ in the lithologies of their drainage areas but are representative of the carbonate rich sedimentary rock province of the tibet qinghai plateau and the silicate rock province of eastern africa both lakes are now topographically closed but to some degree hydrologically open subbottom leakage major results of the mode calculations show that the lithology controls the ultimate brine which is of na k cl type for qinghai lake and of na hco3 cl type for lake turkana so4 reduction delays the onset of sulfatic mineral precipitation and favours the formation of na carbonates such as trona at the expense of calcite clay mineral regradation plays an important role before the saturation of sulfatic or chlorine minerals is reached in particular magnesite formation may be in competition with mg bearing clay minerals finally simulations with various hydrological scenarios have shown that the modern hydrochemistry of both lakes cannot be reproduced by simply evaporating inflow water but reflects long term accumulation and evolution of solutes by continuous inflow over several thousand years the diversity of lake water composition within a uniform lithological province can thus be largely ascribed to varying hydrological conditions

holocene moisture and east asian summer monsoon evolution in the northeastern tibetan plateau recorded by lake qinghai and its environs a review of conflicting proxies abstract climatic and environmental changes in the northeastern tibetan plateau are controlled by the asian summer monsoon asm and the westerlies two key circulation components of the global climate system which directly affect a large human population and associated ecosystems in eastern asia during the past few decades a series of holocene palaeoclimatic records have been obtained from sediment cores from lake qinghai and from various other geological archives in the surrounding area of the northeastern tibetan plateau however because of uncertainties regarding the sediment chronologies and the climatic significance of the proxies used the nature of holocene climatic changes in the region remains unclear and even controversial here we review all major classes of the published data from drilled cores from lake qinghai as well as other evidence from lakes and aeolian deposits from surrounding areas in order to reconstruct changes in moisture patterns and possible summer monsoon evolution in the area during the holocene combining the results of moisture and precipitation proxies such as vegetation history pollen based precipitation reconstruction aeolian activity lake water depth lake level changes salinity and sediment redness we conclude that moisture and precipitation began to increase in the early holocene reached their maximum during the middle holocene and decreased during the late holocene similar to the pattern of the east asian summer monsoon easm in northern china it is clear that the region experienced a relatively dry climate and weak easm during the early holocene as indicated by relatively low tree pollen percentages and fluctuating pollen concentrations generally low lake levels of lake qinghai and the adjacent lake hurleg and lake toson in the qaidam basin and widely distributed aeolian sand deposition in the lake qinghai basin and the nearby gonghe basin to the south and in the eastern qaidam basin to the west we argue that the ostracod 18o record which is widely used as a proxy of effective moisture and summer monsoon intensity in lake sediments at least in lake qinghai and which exhibits light values in the early holocene and heavier values thereafter cannot be used to reflect the strength of the easm or the intensity of monsoon precipitation as is also the case for leaf wax 2h records rather we argue that as is the case of the chinese speleothem 18o record which also is often interpreted as an easm proxy it reflects variation in the 18o of precipitation overall we suggest that the easm significantly affected precipitation in the northeastern tibetan plateau during the holocene and that it increased in strength during the early holocene reached a maximum during the middle holocene and decreased during the late holocene

water depth affecting thaumarchaeol production in lake qinghai northeastern qinghai tibetan plateau implications for paleo lake levels and paleoclimate abstract archaeal glycerol dialkyl glycerol tetraethers gdgts are increasingly popular and versatile tool for palaeolimnology studies but their applications in paleohydrology are scarce especially for thaumarchaeol which is specific for the newly proposed phylum thaumarchaeota after investigating our published gdgt data of lake qinghai we found that both the concentration of thaumarchaeol and the relative abundance of thaumarchaeol to total archaeal gdgts thaum in core top sediments increased significantly with increasing water depth r 0 88 and 0 95 respectively with lower concentrations of 5 5 ng g in shallow areas water depth 10 m this is likely because that the producers of thaumarchaeol thaumarchaeota prefer living in the relative deeper zone in lacustrine systems where probably both competition of ammonium the substrate from other microbes and light intensity are low therefore we proposed that thaumarchaeol was mainly produced in situ and changes in thaum might reflect water depth variations in this closed basin lake the application of thaum as a water depth indicator in a holocene sediment sequence of core qh 2011 provided a high resolution relative lake level history of lake qinghai which resembles that inferred from the 13corg value obtained in the same core this supports the use of thaum as an indicator of lake water depth in paleohydrology studies especially for medium lakes moreover the records of the two independent proxies in core qh 2011 confirmed a shallow lake qinghai in the early holocene and a late holocene highstand highlighting the importance of local temperature and evaporation loss in controlling effective moisture in the arid semi arid region

chemical and isotopic o h c composition of surface waters in the catchment of lake donggi cona nw china and implications for paleoenvironmental reconstructions abstract the oxygen hydrogen and carbon isotope ratios and major and trace element concentrations of surface waters are reported for the catchment of lake donggi cona qinghai province china the chemistry of the surface waters in the southeastern catchment is reflecting the dissolution of carbonate rocks whereas thermal waters add sodium and chlorine to the waters in the northern catchment the dongqu river draining the southeast catchment contributes 87 to 94 to the water budget of the lake thermal waters and waters from the northern catchment add 6 to 13 the combination of hydrogen and oxygen isotopes provides evidence that only small amounts of recycled lake water contribute to the precipitation in the catchment most of the moisture may be transported by the east asian summer monsoon or an eastern branch of the south asian monsoon into the donggi cona region from oxygen isotope ratios it is calculated that about 45 of the lake water input is evaporated and 55 leaves the lake through a channeled outflow the carbon isotope ratios identifies microbial respiration of organic matter probably in soils and sediments of the catchment as the major source of dissolved inorganic carbon in most surface waters and the lake an isotope effect from biological processes in the lake is minor and can be neglected in order to explain isotope ratios of inorganic carbon in lake water the results imply that oxygen isotope ratios in the lake sediment archives mainly mirror the relation between precipitation and evaporation p e which may be controlled by changes in the global water cycle like monsoon intensity or by tectonically driven local changes affecting the outflow flux a comparison between lake archives based on ostracod shells and the modern system indicates similar 18o values for the lake water since 4 3 ka but different 13cdic values this discrepancy between carbon isotope ratios in ostracod shells and modern lake water samples may be due to thermal waters with high 13cdic emerging near the coring site it is suggested that carbon isotopes of ostracods from a sediment drill core reflect the activity of a local thermal spring at the lake bottom whereas oxygen isotopes provide evidence for an open lake system since about 11 ka and that the climate and environment of the donggi cona region changed very little over the last 4300 years

faulting characteristics of supershear earthquakes article i nfo recent observations of large continental strike slip earthquakes show that different fault segments may rupture at different speeds and that rupture may propagate faster than the shear wave velocity of surrounding rocks we report that all the documented occurrences of supershear rupture are associated with faults which have simple geometry the surface trace of these faults is described in the field or seen on satellite images as remarkably linear continuous and narrow segmentation features along these segments are small or absent and the deformation is highly localized as theoretically predicted supershear is clearly associated with mode ii rupture

the aftershock signature of supershear earthquakes recent studies show that earthquake faults may rupture at speeds exceeding the shear wave velocity of rocks this supershear rupture produces in the ground a seismic shock wave similar to the sonic boom produced by a supersonic airplane this shock wave may increase the destruction caused by the earthquake we report that supershear earthquakes are characterized by a specific pattern of aftershocks the fault plane itself is remarkably quiet whereas aftershocks cluster off the fault on secondary structures that are activated by the supershear rupture the post earthquake quiescence of the fault shows that friction is relatively uniform over supershear segments whereas the activation of off fault structures is explained by the shock wave radiation which produces high stresses over a wide zone surrounding the fault

carbonate composition and its impact on fluvial geochemistry in the ne tibetan plateau region using co variations of sr ca and mg ca we examined the carbonate compositions of various bedrocks silicate and carbonate rocks and sediments eolian and fluvial sediments sand and topsoil found in the ne tibetan plateau tp region a combined carbonate composition dataset based on our results and other reported data shows that bedrock carbonate composition on the ne tp displays a much broader range of sr ca and mg ca ratios than restricted source carbonate endmembers reported upon in previous studies this has clear implications for modern weathering studies in addition to paleo reconstructions in this tectonically active and climatically variable area during the late cenozoic bedrock carbonate compositions are characterized by disseminated carbonates with higher sr ca and mg ca ratios and sedimentary carbonates mostly marine with lower sr ca but variable mg ca ratios the mostly authigenic carbonates found in sediments show similar trends with a gradient 0 97 1 00 in a plot of log sr ca versus log mg ca suggesting that calcite precipitation processes i e the sources of the dissolved cations in the water control their chemistry based on observations and modeling we conclude that the mixing of authigenic and bedrock carbonate endmembers plus the incongruent dissolution of bedrock carbonates accounts for the bulk carbonate composition of sediments e g loess sand and topsoil a comparison of bedrock and sedimentary carbonate composition with reported fluvial water data in the ne tp suggests that weathering of carbonates in terrigenous sediments rather than in bedrock is mostly responsible for the changes in fluvial sr mg and ca compositions our study suggests that interactions between carbonates and water occur widely during the exposure transport and deposition of sediments significantly modifying regional carbonate compositions and fluvial geochemistry

wide angle seismic imaging across accreted terranes southeastern alaska and western british columbia abstract this study addresses the question of crustal moho and uppermost mantle structure across an accreted terrane continental arc and fold and thrust belt in southeastern alaska and western british columbia the 186 km long portland canal line of the accrete wide angle seismic dataset across the coast mountains is analyzed using a combination of travel time analysis techniques including delay time tomography turning ray tomography reciprocal time analysis intercept time inversion and forward ray tracing additional constraints on the model are obtained from a coincident vertical incidence seismic section and from correlation with the mapping of geologic structures plunging into the seismic section the study reveals moderately high crustal velocities low velocity gradient in the middle crust and decreasing average crustal velocity and a north deepening moho termination of crustal reflectivity across a vertical zone the coast shear zone csz indicates that the csz is most likely a strike slip fault associated with a transpressive tectonic regime a mid cretaceous thrust system mapped on the surface to the west of the csz is imaged by several groups of mid to lower crustal reflectors extending close to the moho indicating it was a thick skinned thrust system ne dipping fabric imaged within the coast mountains batholith cmb is associated with a ductile deformation during early eocene crustal extension the crustal section under the cmb which has an average velocity of 6 55 km s and shallower than average crustal thickness of 31 km can be considered as corresponding to the lower two thirds of an average crustal section which has been inflated by intrusions of high velocity tonalite to gabbro sills

source of nile sediments in the floodplain at saqqara inferred from mineralogical geochemical and pollen data and their palaeoclimatic and geoarchaeological significance abstract we present results of mineralogical light heavy and clay minerals geochemical and palynological investigations of floodplain sediments at saqqara our investigations provide new insights into our understanding of the source of the holocene nile sediments local palaeoclimate and palaeoenvironment of the floodplain at saqqara as well as the holocene palaeoclimatic variations at the nile headwaters we also investigate the relationship between nile floods and global climate changes and the impact of changing flood conditions on episodes of societal and central governmental collapse at the end of the egyptian old kingdom the holocene sequences recorded in two shallow drill cores saqa 21 and 22 were investigated and subdivided into six sedimentary units from underlying late pleistocene sand and gravels unit i to overlying modern soil unit viii early holocene sediments were essentially missing in the studied cores probably due to intensive erosion during the well known 8 2 kyr cal bp arid event middle holocene sediments are represented by unit ii which reflect high nile floods of equatorial african origin with less contribution from ethiopian sources the old kingdom sediments unit iii seems to be mainly of white nile sources with frequent contributions from the blue nile late holocene sediments unit iv vii show an increased contribution from blue nile river sources low nile flow episodes were recorded at 5 2 between units ii and iii 4 2 between units iii and iv 3 5 within unit iv and 2 7 kyr cal bp between units v and vi the second event corresponds to the first intermediate period fip and the third probably coincides with the second intermediate period 2nd ip periods of disorder in egypt

ground water control of evaporite deposition topographically closed basins may be hydrologically open as a result of seepage losses to underlying or surrounding ground water systems in such cases these losses can have a substantial control over the suite and the thicknesses of evaporite minerals formed in the basin the ratio of ground water outflow to inflow flux ratio in hydrologically open basins is as important in determining the mineralogy and thicknesses of evaporite deposits as the solute composition of the inflow water attainment of steady state flux ratios permits large thicknesses of two or three minerals to form rather than thin veneers of many minerals the presence or absence of glauberite mirabilite halite bloedite polyhalite and hexahydrite caused by subtle changes in the ground water seepage is illustrated using an example from the southern high plains of texas and new mexico however the model is general and is applicable with any solute composition including that of seawater and the use of surface rather than ground water an analytical lumped parameter solute mass balance model is developed to define the concept of a ground water flux ratio as it applies to topographically closed basins in which evaporation exceeds precipitation diffusion advection and density driven flow are proposed as mechanisms by which solutes can escape to the ground water from these closed basins the geochemical reaction computer program phrqpitz is used to document the effects of various flux ratios on the mineralogy and thickness of deposits solute analyses used in conjunction with the model can be used to screen prospective basins as well as to provide insights for exploratory drilling program

the mw 7 8 2001 kunlunshan earthquake extreme rupture speed variability and effect of fault geometry 1 by analyzing body wave seismograms we show that the rupture speed on the main kunlun fault during the mw 7 8 2001 kunlunshan tibet earthquake was highly variable and the rupture process consisted of three stages in the first stage the rupture accelerated from rest to an average speed of 3 3 km s over a distance of 120 km the rupture then propagated for another 150 km at an apparent rupture speed exceeding the p wave speed in the final stage the earthquake fault bifurcates and the rupture front slowed down the region of highest rupture velocity is found to coincide with the region of highest fault slip has the longest slip duration and is where off fault ground cracking is observed in the field stress drops are found to be higher in regions of higher rupture speeds the greatest concentration of aftershocks is located near the fault bifurcation zone and hence coincides with the region of highest fault slip highest stress drop and highest rupture velocity the fault width is no more than 10 km in most places and is about 20 km in the region of highest slip this narrow fault width is attributed to the fact that crust below this depth is sufficiently warm not to permit brittle failure to occur the remarkable similarity of this earthquake with the 1906 california earthquake in spite of occurring in very different tectonic regimes is discussed

observation of far field mach waves generated by the 2001 kokoxili supershear earthquake regional surface wave observations offer a powerful tool for determining source properties of large earthquakes especially rupture velocity supershear ruptures being faster than surface wave phase velocities create far field surface wave mach cones along which waves from all sections of the fault arrive simultaneously and over a sufficiently narrow frequency band in phase we present the first observation of far field mach waves from the major kokoxili earthquake tibet 2001 11 14 mw7 9 and confirm that ground motion amplitudes are indeed enhanced on the mach cone theory predicts that on the mach cone bandpassed surface wave seismograms from a large supershear rupture will be identical to those from much smaller events with similar focal mechanisms with an amplitude ratio equal to the ratio of the seismic moments of the two events cross correlation of 15 25 s love waves from the kokoxili event with those from a much smaller mw5 foreshock indicates a high degree of similarity correlation coefficients ranging from 0 8 to 0 95 in waveforms recorded at stations near the far field mach cone this similarity vanishes away from the mach cone these observations provide further evidence for supershear propagation of the kokoxili rupture and demonstrate how this simple waveform correlation procedure can be used to identify supershear ruptures

illuminating the near sonic rupture velocities of the intracontinental kokoxili mw 7 8 and denali fault mw 7 9 strike slip earthquakes with global p wave back projection imaging 1 the denali and kokoxili strike slip earthquakes are two of the longest recent intracontinental ruptures previous studies report a range of rupture velocities here we image these earthquakes by reverse time migration of the intermediate frequency p wave train recorded by global broadband seismometers this technique permits a relatively direct measure of rupture velocity speed and direction as constrained by the radiated seismic energy free from restrictive assumptions or rupture speed bounds placed on the solution we compare our results with published seismic gps displacement and surface slip inversion results both ruptures were initially subshear and transitioned over a distance no longer than 40 km to supershear speeds close to the p wave speed of 5 6 km s we investigate the accuracy of our results with synthetic data and experiment with using different imaging parameters and seismic subnetworks these tests allow us to rule out the possibility of subshear speeds along the supershear segments although we cannot exclude supershear speeds of 4 5 6 5 km s our most reliable rupture velocities of 5 6 km s are close to the local p wave speeds we hypothesize that these intracontinental faults have weak shear strengths or high breakdown slips or crustal rigidities and experience at least moderate slip or slip rate weakening our observations and previous published results lead us to speculate that very long surface extending faults with general homogeneity in prestress and fault strength together with smaller adjacent fault segments to provide triggering may be necessary ingredients for the sub rayleigh to supershear rupture speed transition in strike slip earthquakes

hydrogen isotopic compositions of long chain leaf wax n alkanes in lake qinghai sediments record palaeohydrological variations during the past 12 ka abstract lake qinghai the largest saltwater lake in china is located on the northeastern qinghai tibetan plateau the lake sediments record the climatic variation and response to global climate change on the plateau numerous studies of the lake have been conducted but various opinions remain regarding the palaeoclimatic conditions for the lake since the last glacial maximum especially the palaeohydrological conditions for the northeastern plateau in the early holocene here we discuss the hydrogen isotopic composition d of long chain leaf wax n alkanes for studying the hydrological changes in the lake since the holocene the results show that on the northeastern qinghai tibetan plateau c 31 d values were quite negative avg 202 4 in the early holocene 8 12 ka indicating a strong monsoon and greater precipitation during that period during 8 4 ka c 31 d values gradually became more positive indicating that the monsoon gradually weakened and precipitation gradually decreased the c 31 d values were more positive in the late holocene with a mean value of 186 3 showing that the regional monsoon weakened and the amount of precipitation was low in addition c 31 d values indicated large amounts of precipitation in the early holocene but the c 29 d values during the same period were significantly more positive than c 31 due to a large contribution from aquatic plants therefore the water level of the lake was low in this period which could be related to strong evaporation of the lake water because of the high temperature in the early holocene our study clarifies the changes in the monsoon and precipitation in the northeastern qinghai tibetan plateau and it provides a new estimate of the water level variation in lake qinghai in the early holocene

seasonal and long term vertical deformation in the nepal himalaya constrained by gps and grace measurements 1 we analyze continuous gps measurements in nepal southern side of the himalaya and compare gps results with grace observations in this area we find both gps and grace show significant seasonal variations further comparison indicates that the observed seasonal gps height variation and grace derived seasonal vertical displacement due to the changing hydrologic load exhibit very consistent results for both amplitude and phase for continuous gps stations whose observation time span are longer than 3 years the average wrms reduction is 45 when we subtract grace derived vertical displacements from gps observed time series the comparison for annual amplitudes between gps observed and grace derived seasonal displacements also shows consistent correlation the good seasonal correlation between gps and grace is due to the improved gps processing strategies and also because of the strong seasonal hydrological variations in nepal besides the seasonal signal grace also indicates a long term mass loss in the himalaya region assuming no gia effect this mass loss therefore will lead to crustal uplift since the earth behaves as an elastic body we model this effect and remove it from gps observed vertical rates with a 2d dislocation model most gps vertical rates especially in the central part of nepal can be interpreted by interseismic strain from the main himalayan thrust and several exceptions may indicate the complexity of vertical motion in this region and some potential local effects

rupture imaging of the mw 7 9 12 may 2008 wenchuan earthquake from back projection of teleseismic p waves 1 the mw 7 9 wenchuan earthquake of 12 may 2008 was the most destructive chinese earthquake since the 1976 tangshan event tens of thousands of people were killed hundreds of thousands were injured and millions were left homeless here we infer the detailed rupture process of the wenchuan earthquake by back projecting teleseismic p energy from several arrays of seismometers this technique has only recently become feasible and is potentially faster than traditional finite fault inversion of teleseismic body waves therefore it may reduce the notification time to emergency response agencies using the iris dmc we collected 255 vertical component broadband p waves at 30 95 from the epicenter we found that at periods of 5 s and greater nearly all of these p waves were coherent enough to be used in a global array we applied a simple down sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function arf we also considered three regional subarrays of seismometers in alaska australia and europe that had apertures less than 30 and p waves that were coherent to periods as short as 1 s individual arfs for these subarrays were skewed toward the subarrays however the linear sum of the regional subarray beams at 1 s produced a symmetric arf similar to that of the groomed global subarray at 5 s for both configurations we obtained the same rupture direction rupture length and rupture time we found that the wenchuan earthquake had three distinct pulses of high beam power at 0 23 and 57 s after the origin time with the pulse at 23 s being highest and that it ruptured unilaterally to the northeast for about 300 km and 110 s with an average speed of 2 8 km s it is possible that similar results can be determined for future large dip slip earthquakes within 20 30 min of the origin time using relatively sparse global networks of seismometers such as those the usgs uses to locate earthquakes in near real time

slow slip hidden in the noise the intermittence of tectonic release referred to as slow slip events the transient aseismic slip that occurs along plate boundaries can be indirectly characterized through colocated seismicity such as tectonic tremor and low frequency earthquakes lfes using the timing of cataloged lfe and tremor activity in guerrero mexico and northern cascadia i decompose the inter aseismic gps displacement defined as the surface deformation between previously detected slow slip events into separate regimes of tectonic loading and release in such a way previously undetected slow slip events that produce less than a millimeter of surface deformation are extracted from the geodetic noise these new observations demonstrate that the inter aseismic period is not quiescent and that slow slip occurs much more often than previously thought this suggests that the plate interface where slow slip and tremor occur is in fact strongly coupled and that slow aseismic release occurs over a wide spectrum of time scales

major ion geochemistry of shallow groundwater in the qinghai lake catchment ne qinghai tibet plateau conventional hydrochemical techniques and statistical analyses were applied to better understand the solute geochemistry and the hydrochemical process of shallow groundwater in the qinghai lake catchment shallow groundwater in the qinghai lake catchment is slightly alkaline and is characterized by a high ion concentrations and low water temperature the total dissolved solids tds in most of the samples are 1 000 mg l i e fresh water and depend mainly on the concentration of so42 cl and na groundwater table is influenced directly by the residents groundwater consumption most of the groundwaters in the qinghai lake catchment belong to the ca2 na hco3 type while the qinghai lake part of the buha bhr and the lake side ls samples belong to the na cl type the groundwater is oversaturated with respect to aragonite calcite and dolomite but not to magnesite and gypsum solutes are mainly derived from strong evaporite dissolution in daotang bhr and ls samples and from strong carbonate weathering in hargai and shaliu samples carbonate weathering is stronger than evaporite dissolution with weak silicate weathering in the qinghai lake catchment carbonate weathering ion exchange reaction and precipitation are the major hydrogeochemical processes responsible for the solutes in the groundwater in the qinghai lake catchment most of the shallow groundwaters are suitable for drinking more attention should be paid to the potential pollution of nitrate chloride and sulfide in shallow groundwater in the future

the seismic structure across an active oceanic continental transform fault zone a seismic structural section across the southern queen charlotte transform fault zone which separates the oceanic pacific plate from the continental america plate off western canada has been determined from an offshore onshore refraction experiment two explosion profiles one parallel and one perpendicular to the fault strike were recorded on three ocean bottom seismographs obs and seven land based seismographs lbs assuming lateral homogeneity along the parallel profile recorded over oceanic crust at one obs one dimensional amplitude modeling produced a velocity model with the characteristics of standard ocean crust the partially reversed perpendicular profile recorded at two obs s and one good quality lbs extended across the fault zone which in bathymetric cross section shows two linear fault escarpments separated by a flat terrace an initial velocity structure provided by time term analysis of the complete data set was modified by ray tracing until the travel time data for the three stations were satisfied by one seismic structural section this model shows three distinctive crustal blocks the oceanic terrace and continental blocks separated by two major crustally pervasive faults the outer and inner queen charlotte faults the rock units composing the terrace block have lower velocities at equivalent depths than those of the blocks on either side this may have resulted from deformation associated with oblique convergence and or the effects of a jump in the position of the active queen charlotte fault from its outer to inner positions about 1 0 5 ma ago depth to the base of the crustal section increases from 12 to 18 km below sea level across the terrace transition zone representing an eastward dip of about 20 the seismic model after conversion to a density model agrees well with the gravity anomaly along the profile the interpreted structural section is consistent with recent tectonic models that require a component of convergence along the transform fault zone

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

influence of super shear earthquake rupture models on simulated near source ground motion from the 1999 izmit turkey earthquake we numerically simulate seismic wave propagation from the 1999 mw 7 4 earthquake in izmit turkey using a 3d finite difference method based on published finite source models obtained by waveform inversions this earthquake has been reported based on observations at the near fault station skr as an example of supershear rupture propagation toward the east although the modeled ground motion does show a characteristic mach wave from the fault plane it is difficult to identify any particular effects in terms of peak ground velocity pgv an important parameter in earthquake engineering this is because the fault s spatial heterogeneity is strong enough to mask the properties of supershear rupture which has been reported through several numerical simulations mostly based on homogeneous fault conditions this article demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite fault source models

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

characteristics of stable isotopes and hydrochemistry of river water in the qinghai lake basin northeast qinghai tibet plateau china the integrated use of isotopic and hydrochemical tracers is an effective way to investigate hydrological processes on a range of spatial and temporal scales this study investigated stable isotopes and hydrochemistry of the river water in the qinghai lake basin and discussed relationships between runoff and variations of air temperature and precipitation results indicated that all of the river water points lie close to the local meteoric water line lmwl and the slope of local evaporation line of river water samples 6 82 was smaller than that of the lmwl 7 98 indicating that the river water mainly originated from the precipitation in the catchments which underwent weak evaporation the river water in the tributaries would undergo relatively stronger evaporation than that in the main stream the hydrochemical type of river water was ca mg hco3 and the river water chemistry was mainly controlled by carbonate dissolution in the qinghai lake basin the river discharge was generated mainly from the middle and upper catchment the runoff depths of buha river catchment and shaliu river catchment were 91 0 mm and 283 4 mm respectively and the runoff coefficients were 0 164 and 0 531 respectively because of a relatively longer channel larger drainage area and smaller gradient the surface water flowed more slowly and infiltrated more in the large river catchment therefore the runoff coefficient in the large river catchment was smaller than that in the relatively smaller catchment the river runoff in the qinghai lake basin was primarily influenced by precipitation this study provides insights into the hydrological and geochemical processes of cold and alpine rivers along with water resource management options in the qinghai lake basin and northeast qinghai tibet plateau

geochemical and isotopic characteristics of shallow groundwater within the lake qinghai catchment ne tibetan plateau abstract major ions isotopic ratios of strontium 87 sr 86 sr hydrogen d and oxygen 18 o of groundwater samples were analyzed to decipher spatial variation controlling factors solute sources and the recharge source of shallow groundwaters within the lake qinghai catchment shallow groundwaters in this area are slightly alkaline with 97 being fresh water of good quality though there are high concentrations of nitrate and sulfide in buha and lakeside groundwaters most of the shallow groundwaters are of the ca 2 hco 3 type whereas part of groundwaters surrounding the lake ls belongs to the na cl type as lake water qhl groundwater geochemistry is controlled by regional lithological association ion exchange and mineral precipitation the dissolved sr concentrations and 87 sr 86 sr ratios vary from 1 0 to 15 6 mol l and from 0 709859 to 0 715779 respectively the first quantitative calculation in groundwater using a forward model shows that 40 of dissolved sr is from carbonate weathering 33 from evaporite dissolution 17 from silicate weathering and the remainder from atmospheric input for the whole catchment carbonate weathering dominates groundwater geochemistry in shaliu sl hargai hg and buha bh samples while evaporite dissolution dominates ls and daotang dt samples d and 18 o data show that rain water is the major recharge source of both river water and shallow groundwater within the lake qinghai catchment qinghai lake water is characterized by buha type water but its sr geochemistry is different from the shallow groundwater due to carbonate precipitation although shallow groundwater contributes 5 of the dissolved sr to the qhl groundwater must be taken into account when the chemistry and budget of lake water are characterized