redistribution of dynamic stress during coseismic ruptures evidence for fault interaction and earthquake triggering we investigate the spatiotemporal evolution of dynamic stress outside a rupturing extended fault the dynamic stress variations caused by a coseismic rupture in a half space are computed by using the discrete wavenumber and reflectivity methods after a transient phase the stress time history evolves to the final static stress value we compare the static stress changes resulting from this model with those computed from a static dislocation model we have applied this method to study the interactions between the first two normal faults which ruptured during the 1980 ms 6 9 irpinia earthquake these two subevents are separated in time by nearly 20 s while the third and last subevent occurred 40 s after the rupture onset we compute the dynamic stress changes caused by the rupture of the first subevent our modeling results show that the dynamic stress peak on the second subevent fault plane is reached between 7 s and 8 s after the rupture initiation on the main fault on the average the static stress level on the second subevent 20 s fault plane is reached nearly after 14 s the dynamic rupture did not jump from a rupturing segment to the adjacent one immediately but the triggering of the 20 s subevent is delayed by roughly 10 s with respect to the instant of occurrence of the dynamic stress peak induced by the 0 s event the dynamic stress pulse propagates along the strike direction of the second subevent fault plane at an average velocity of nearly 3 4 km s the delayed triggering of the second subevent can be interpreted in terms of the frictional properties of the faults in particular rate and state dependent frictional law can explain a delayed instability after a sudden change in stress using the estimated values of the subevent triggering delay and the shear stress change we attempt to constrain the parameter a on the 20 s fault the values here inferred agree well with those resulting from previous studies

predictions of changes of glacier mass balance in the nepal himalaya and tibetan plateau a case study of air temperature increase for three glaciers

comparison of geodetic and glaciological mass balance techniques gulkana glacier alaska u s a the net mass balance on gulkana glacier alaska u s a has been measured since 1966 by the glaciological method in which seasonal balances are measured at three index sites and extrapolated over large areas of the glacier systematic errors can accumulate linearly with time in this method therefore the geodetic balance in which errors are less time dependent was calculated for comparison with the glaciological method digital elevation models of the glacier in 1974 1993 and 1999 were prepared using aerial photographs and geodetic balances were computed giving 6 0 0 7 m w e from 1974 to 1993 and 11 8 0 7 m w e from 1974 to 1999 these balances are compared with the glaciological balances over the same intervals which were 5 8 0 9 and 11 2 1 0 m w e respectively both balances show that the thinning rate tripled in the 1990s these cumulative balances differ by 6 for this close agreement the glaciologically measured mass balance of gulkana glacier must be largely free of systematic errors and be based on a time variable area altitude distribution and the photography used in the geodetic method must have enough contrast to enable accurate photogrammetry

retreat of glaciar tyndall patagonia over the last half century we report measurements of ice surface elevation ice thickness and surface area for glaciar tyndall patagonia made in 1999 2002 the measurements together with previously published observations show acceleration over the last few decades of the rates of thinning and retreat of the main calving front the acceleration of shrinkage appears to be driven by a combination of climate and feedback processes the dominant feedback being increased melting associated with lowering of the glacier surface elevation feedback the melting capacity in the main terminus lake is now too small to be a major factor accelerating the retreat the glacier bed has low slope and remains below the elevation of the lake spillway for 14 km upstream from the 2000 calving front indicating the potential for extensive retreat under the influence of strong elevation feedback and increasing interaction with the lake as it enlarges

re visiting the tectonics of the oceanic intraplate earthquake of march 25 1998 m 8 1 in the balleny sea offshore antarctica abstract the antarctic plate earthquake of march 25 1998 m 8 1 and its aftershocks are re visited to evaluate the role of the associated tectonics in stress concentration due to ambient horizontal crustal motion caused by deglaciation in antarctica using a numerical technique called the distinct element method a two dimensional structural model of the epicentral region is developed and tectonically loaded for a year along the inferred direction of the motion a spatial correlation is observed between the resulting locations of relatively high shear stresses and those of the main shock and associated aftershocks in particular seismicity is concentrated at and near the intersections of the main fault carey and gambier fracture zones where the shear stresses are significantly elevated and whose sign duplicate the inferred sense of movement along them the modeling results suggest that stress concentrations near pre existing intersecting fault and fracture zones due to a possible deglaciation induced horizontal crustal force may have been a cause of this enigmatic earthquake

late holocene eolian activity in the mineralogically mature nebraska sand hills abstract the age of sand dunes in the nebraska sand hills has been controversial with some investigators suggesting a full glacial age and others suggesting that they were last active in the late holocene new accelerator mass spectrometry radiocarbon ages of unaltered bison bones and organic rich sediments suggest that eolian sand deposition occurred at least twice in the past 300014c yr b p in three widely separated localities and as many as three times in the past 80014c yr at three other localities these late holocene episodes of eolian activity are probably the result of droughts more intense than the 1930s dust bowl period based on independent great plains climate records from lake sediments and tree rings however new geochemical data indicate that the nebraska sand hills are mineralogically mature eolian sands in nebraska have lower k feldspar and k2o rb and ba contents than most possible source sediments and lower k feldspar contents than dunes of similar age in colorado the most likely explanation for mineralogical maturity is reduction of sand sized k feldspar to silt sized particles via ballistic impacts due to strong winds over many cycles of eolian activity therefore dunes of the nebraska sand hills must have had a long history probably extending over more than one glacial interglacial cycle and the potential for reactivation is high with or without a future greenhouse warming

holocene environments of the central great plains multi proxy evidence from alluvial sequences southeastern nebraska abstract pollen plant macrofossils phytoliths carbon isotopes and alluvial history from sediments exposed along the south fork of the big nemaha river southeastern nebraska usa provide an integrated reconstruction of changes in holocene vegetation climate and fluvial activity from 9000 to 8500 uncalibrated 14 c yr bp climate became more arid and the floodplain and alluvial fans in the main valley aggraded rapidly upland deciduous forest declined and prairie attained its holocene dominance from 8500 to 5800 yr bp upland forest elements disappeared and even riparian trees were sparse under dry climatic conditions alluvial fans continued to aggrade but aggradation in the main valley was interrupted by a stable episode 7000 yr bp from 5800 to 3100 yr bp riparian forests returned to prominence and droughts were intermittent alluviation was slower and punctuated by two major episodes of channel incision and terrace formation in the main valley aggradation on alluvial fans slowed and finally ceased near the end of this period during a short dry interval from 3100 to 2700 yr bp riparian trees except elm disappeared and prairie and weedy species became more abundant this interval is represented by the organic roberts creek member and the alluvial setting was a slightly incised meandering channel belt habitats became similar to presettlement conditions during the last 2700 yr bp weedy taxa dominate modern samples reflecting widespread disturbance alluvial fans and terrace surfaces were stable during the last 2500 years but episodes of floodplain aggradation were punctuated by incision of the main channel

ice elevation changes of glaciar chico southern patagonia using aster dems aerial photographs and gps data hielo patagonico sur hps southern patagonia icefield is the largest temperate ice mass at mid latitudes in the southern hemisphere with few exceptions the glaciers in this region have been retreating during the last 50 years based on field data vertical aerial photographs and satellite images ice elevation changes since 1975 on glaciar chico one of the main tongues of hps are presented a maximum ice thinning of 5 4 0 55 m a 1 was observed at the glacier front between 1975 and 1997 global positioning system gps data were used in the accumulation area of the glacier to infer a thinning rate of 1 9 0 14 m a 1 between 1998 and 2001 this thinning rate is three times higher than the snow accumulation rate estimated for that part of the glacier a mean net glacier mass balance of 0 29 0 097 km 3 w e a 1 was estimated between 1975 and 2001 climate data suggest an increase in temperature and a reduction in precipitation during most of the 20th century in the vicinity of hps although these climate changes are the primary explanation for the observed ice elevation changes of the glacier ice dynamics effects are also believed to play an important role

glacier changes in the central and northern tien shan during the last 140 years based on surface and remote sensing data this research presents a precise evaluation of the recession of akshiirak and ala archa glaciers tien shan central asia based on data of geodetic surveys from 1861 69 aerial photographs from 1943 1963 1977 and 1981 1 25 000 scale topographic maps and srtm and aster data from 2000 03 the akshiirak glacierized massif in the central tien shan contains 178 glaciers covering 371 6 km 2 and the ala archa glacier basin in the northern tien shan contains 48 glaciers covering 36 31 km 2 the tien shan glaciers retreated as much as 3 km from the 1860s to 2003 area shrinkage of akshiirak and ala archa was 4 2 and 5 1 respectively from 1943 to 1977 and 8 7 and 10 6 respectively from 1977 to 2003 the volume of the akshiirak glaciers was reduced by 3 566 km 3 from 1943 to 1977 and 6 145 km 3 from 1977 to 2000 the total reduction of the tien shan glaciers is 14 2 during the last 60 years 1943 2003 the northern and central tien shan have not experienced a significant precipitation increase during the last 100 years but they have experienced an increase in summer air temperatures especially observable since the 1970s which accelerated the recession of the tien shan glaciers

changes in static stress on southern california faults after the 1992 landers earthquake the magnitude 7 5 landers earthquake of 28 june 1992 was the largest earthquake to strike california in 40 years the slip that occurs in such an earthquake would be expected to induce large changes in the static stress on neighbouring faults these changes in stress should in turn affect the likelihood of future earthquakes stress changes that load faults towards failure have been cited as the cause of small1 5 moderate6 and large7 earthquakes conversely those that relax neighbouring faults have been related to a decrease in seismicity5 here we use an elastic half space model8 to estimate the stress changes produced by the landers earthquake on selected southern california faults including the san andreas we find that the estimated stress changes are consistent with the triggering of four out of the five aftershocks with magnitude greater than 4 5 and that the largest changes 1 10 bar occurring on part of the san bernardino segment of the san andreas fault may have decreased the time to the next magnitude 8 earthquake by about 14 years

did stress triggering cause the large off fault aftershocks of the 25 march 1998 mw 8 1 antarctic plate earthquake the 1998 antarctic plate earthquake produced clusters of aftershocks mw 6 4 up to 80 km from the fault rupture and up to 100 km beyond the end of the rupture because the mainshock occurred far from the nearest plate boundary and the nearest recorded earthquake it is unusually isolated from the stress perturbations caused by other earthquakes making it a good candidate for stress transfer analysis despite the absence of near field observations we tested whether the off fault aftershocks lie in regions brought closer to coulomb failure by the main rupture we evaluated four published source models for the main rupture in fourteen tests using different aftershocks sets and allowing the rupture sources to be shifted within their uncertainties 6 were significant at 99 confidence 3 at 95 confidence and 5 were not significant 95 level for the 9 successful tests the stress at the site of the aftershocks was typically increased by 1 2 bars 0 1 0 2 mpa thus the antarctic plate event together with the 1992 mw 7 3 landers and its mw 6 5 big bear aftershock 40 km from the main fault supply evidence that small stress changes might indeed trigger large earthquakes far from the main fault rupture

recent volume loss of british columbian glaciers canada 1 we use the shuttle radar topography mission srtm data and digital terrain models from aerial photography to quantify the change of glacier volume in british columbia bc canada for the period 1985 1999 we note substantial elevation bias in the srtm elevations typically on the order of 12 m km 1 the bias corrected thinning rate is 0 78 0 19 m a 1 which yields an annual volume loss of 22 48 5 53 km 3a 1 this rate of glacier volume loss is 65 of the estimate uncorrected for elevation bias 34 7 km 3a 1 and cautions against the use of uncorrected srtm data for glacier change studies glacier recession in bc could account for ca 0 67 0 12 mm of sea level rise over the period 1985 1999 0 05 0 009 mm yr 1 or about 8 3 of the contribution from mountain glaciers and ice caps the recent rate of glacier loss in the coast mountains 17 0 km 3a 1 is approximately double that observed for the previous two decades

loess record of dry climate and aeolian activity in the early to mid holocene central great plains north america thick holocene bignell loess sections provide new evidence for the timing of early to middle holocene aridity in the central great plains the immediate source of loess in these sections was dune fields just upwind based on thickness trends and grain size data thus periods of rapid loess accumulation indicate episodes of extensive dune activity under drier than present climate in typical bignell loess sections a thick zone of coarse textured loess with minimal pedogenic alteration is interpreted as a record of the most rapid sustained holocene loess accumulation optical ages indicate that loess in this zone was deposited beginning about 9000 10000 years ago at five study sites accumulation ended shortly after 6500 years ago at three sites but possibly earlier at the other two in two well dated sections the average rate of loess accumulation between 9000 10000 and 6500 years ago was about 1 6 3 5 times greater than in the late holocene thus we infer that the most extensive sustained holocene

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

stress interactions of three moderate size earthquakes in afyon southwestern turkey abstract we analyze three moderate size earthquakes occurred in the afyon region of southwestern turkey on december 15 2000 m w 6 0 and february 3 2002 m w 6 5 and m w 5 8 this earthquake sequence took place on the sultandag fault having dominantly normal faulting mechanisms with different orientations in an extensional tectonic regime we relocate these mainshocks and their large aftershocks and use the waveform data to determine the rupture dimensions and directivities we carry out both static and dynamic stress analysis to investigate stress interactions and possible earthquake triggering mechanisms in this sequence we show that the 2002 m w 6 5 rupture started at the termination of the 2000 m w 6 0 earthquake where the calculated coulomb stress changes increased more than 0 5 bar thus we conclude that the coseismic stress increase by the 2000 event favored the nucleation and promoted the timing of the 2002 event an intense seismic activity identified as the kizildag aftershock zone developed following both of the large mainshocks where the third largest earthquake m w 5 8 of the sequence occurred 2 h after the 2002 m w 6 5 mainshock the coulomb stress calculations of the 2000 earthquake shows no influence in this zone while the static coulomb stress changes due to the 2002 m w 6 5 mainshock raised the coulomb stresses an additional 0 3 0 7 bar in the kizildag aftershock zone thus we infer that such changes in the coulomb stresses positively influence the occurrence of the aftershocks in this zone since the kizildag aftershock zone takes place in a geothermal area we compute dynamic stress changes imposed by the 2000 and 2002 mainshocks the computed peak dynamic stress levels for both mainshocks are found much higher than the static stress changes calculated within the kizildag aftershock zone thus we propose that transient stress triggering most likely involving elevated fluid pressures in the hydrothermal systems present in this region may have played a major role in the initiation of increased seismicity followed by local multiple elastic stress triggering leading to the further development of aftershocks and the occurrence of the m w 5 8 mainshock

relation between mainshock rupture process and omori s law for aftershock moment release rate summary we compare the source time functions i e moment release rates of three large california mainshocks with the seismic moment release rates during their aftershock sequences aftershock moment release rates computed by summing aftershock moments in time intervals follow a power law time dependence similar to omori s law from minutes to months after the mainshock furthermore in contrast to the previously observed saturation in numbers of aftershocks shortly after the mainshock rupture no such saturation is seen in the aftershock moment release rates which are dominated by the largest aftershocks we argue that the observed saturation in aftershock numbers described by the time offset parameter c in omori s law is likely an artefact due to the underreporting of small aftershocks which is related to the difficulty of detecting large numbers of small aftershocks in the mainshock coda we further propose that it is more natural for c to be negative i e singularity follows the onset of mainshock rupture than positive singularity precedes onset of rupture to make a more general comparison of mainshock rupture process and aftershock moment rates we then scale mainshock time functions to equalize the effects of the varied seismic moments for the three california mainshocks we compare the scaled time functions with similarly scaled aftershock moment rates finally we compare global averages of scaled time functions of many shallow events to the average scaled aftershock moment release rate for six california mainshocks in each of these comparisons the extrapolation using omori s law of the aftershock moment rates back in time to the onset of the mainshock rupture indicates that the temporal intensity of the aftershock moment release is about 1 5 orders of magnitude less than the maximum reached by the mainshock rupture this may be due to the differing amplitudes and relative importance of static and dynamic stresses in aftershock initiation compared to mainshock rupture propagation

pollen diagram from the nebraska sandhills and the age of the dunes abstract radiocarbon dates of organic alluvium beneath as much as 40 m of dune sand along the dismal river have led to the suggestion that the nebraska sandhills date from the holocene rather than the last glacial period on the other hand the basal layers of lake and marsh deposits in interdune depressions at three localities date in the range of 9000 to 12 000 yr b p implying a pre holocene age for the sand dunes a pollen diagram for one of these sites swan lake indicates prairie vegetation throughout the last 9000 yr with no suggestion that the landscape was barren enough to permit the shaping of the massive dunes characterizing the area sand was not transported across the site during the holocene either during the marsh phase which lasted until 3700 yr b p or during the subsequent lake phase the sand that buries the alluvium along the dismal river may represent only local eolian activity or it may indicate that the younger of the two main dune series identified by h t u smith 1965 journal of geology 73 557 578 is holocene in age and the older one late wisconsin in age

triggering of earthquake aftershocks by dynamic stresses it is thought that small static stress changes due to permanent fault displacement can alter the likelihood of or trigger earthquakes on nearby faults many studies of triggering in the near field particularly of aftershocks rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault here we report a comparison of the aftershock pattern of the moment magnitude mw 7 3 landers earthquake not only with static stress changes but also with transient oscillatory stress changes transmitted as seismic waves that is dynamic stresses dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone these dynamically weakened faults may fail after the seismic waves have passed by and might even cause earthquakes that would not otherwise have occurred we find similar asymmetries in the aftershock and dynamic stress patterns the latter being due to rupture propagation whereas the static stress changes lack this asymmetry previous studies have shown that dynamic stresses can promote failure at remote distances but here we show that they can also do so nearby

evidence of instantaneous dynamic triggering during the seismic sequence of year 2000 in south iceland 1 we analyze the coseismic stress perturbation during the 17 june 2000 south iceland seismic sequence the main shock ms 6 6 was followed by three large events within a few tens of seconds 8 26 and 30 s located within 80 km the aim of this paper is to investigate short term fault interaction and instantaneous triggering this happens when a fault perturbed by a stress change fails before the end of the transient stress perturbation we compute the shear normal and coulomb stress changes as functions of time in a stratified elastic half space by using discrete wave number and reflectivity methods we calculate dynamic stresses caused by the main shock at the hypocenters of these three subsequent events our numerical results show that the onset of the last two events is slightly delayed with respect to the arrival time of the second positive peak of coulomb stress variation while the first event occurred after the first positive stress peak we have also analyzed the response of a spring slider system representing a fault governed by a rate and state dependent friction law perturbed by shear and normal stress variations caused by the main shock the fault response to the computed stress perturbations is always clock advanced we have found suitable constitutive parameters of the modeled fault that allow the instantaneous dynamic triggering of these three earthquakes if the initial sliding velocity is comparable with the tectonic loading velocity we obtained failure times close to the observed origin times for low values of the initial effective normal stress

rupture propagation beyond fault discontinuities significance of fault strike and location summary earthquake rupture sometimes occurs on several faults and often decelerates or terminates at fault stepovers factors that control the rupture processes across stepovers are important for an understanding of earthquake growth and termination in this study we investigate such factors by calculating the spontaneous rupture processes of two non coplanar faults in a 3 d model dealing with two extreme models in which two strike slip faults are either parallel or perpendicular we show that the rupture processes beyond fault discontinuities are drastically different for the two models we find three factors influencing rupture processes beyond fault discontinuities depth of the upper edge of the two faults location of the edge of the first fault and geometry of the two faults these factors determine the time and location of rupture jumps to the second fault for rupture propagation to the second fault it is essential for rupture on the first fault to arrive at the edge of the fault in particular whether rupture on the first fault reaches the earth s surface or not controls the difficulty of rupture jumps and the locations where the rupture is triggered which is also related to the step direction of the two faults this is because the stress perturbation at the fault edge is affected by the earth s free surface

thermoluminescence and new 14c age estimates for late quaternary loesses in southwestern nebraska abstract loess of late quaternary age mantles most of nebraska south of the platte river valley at least five late quaternary loesses are recognized from oldest to youngest one or more undifferentiated pre illinoian loesses the loveland loess the gilman canyon loess which exhibits a well developed soil and rests unconformably on the sangamon soil the peoria loess capped by the brady soil and the bignell loess which is distributed discontinuously previous research shows that the loveland loess is illinoian the gilman canyon loess and peoria loess are wisconsin and the bignell loess is holocene we present here the first thermoluminescence tl age estimates and new 14 c ages for these late quaternary loesses at two key sections in southwestern nebraska the eustis ash pit and the bignell hill road cut tl age estimates from all samples collected from eustis ash pit and bignell hill were internally consistent tl and 14 c age estimates from these two sections generally agree and support previous age determinations the tl age estimate on loveland loess indicates deposition at 163 ka tl and radiocarbon age estimates indicate that gilman canyon loess believed to be deposited during the farmdale interstade first began to accumulate at about 40 ka the lower part of the gilman canyon loess is 36 ka at eustis and the middle of the unit is 30 ka at bignell hill the lower and upper parts of the peoria loess give age estimates of 24 ka and 17 ka respectively tl age estimates for deposition of the bignell loess are 9 ka near the base in agreement with radiocarbon age estimates and 6 ka immediately below the modern soil substantiating its holocene age comparisons of tl age estimates with 18 o and insolation curves which show loess deposition during interglacial and interstadial as well as glacial periods indicate that loess deposition on the great plains can occur under a variety of climatic conditions

earthquake triggering by static and dynamic stress changes 1 in this study we aim to understand the effect of static and dynamic stress changes in promoting earthquake failures on secondary faults toward this goal we solve the equation of motion of a spring slider dynamic system including inertia and using rate and state dependent constitutive laws we separately investigate the dynamic response of this fault analog system to a sudden stress change represented either as a stress step or as a stress pulse which are used to model permanent static and transient dynamic stress perturbations the induced earthquake failure does not occur immediately at the application of the coseismic stress change but it is delayed in time we define this time interval as the triggering delay for a given stress perturbation we analyze the dependence of triggering delays on different system conditions and constitutive parameters our results clearly show that the effects of static and dynamic stress changes are quite different while a static stress change is able to advance as well as to delay an induced instability depending on its sign a dynamic stress pulse is only able to promote a nearly instantaneous failure provided its amplitude is positive and large enough with respect to the direct effect of friction in other words dynamic stress changes can only cause nearly instantaneous failures without any relevant triggering delay these results should be considered in interpreting the seismicity rate changes caused by large earthquakes at least as long as seismic events are interpreted as sliding instabilities obeying rate and state dependent friction laws

dynamic versus static stress triggering and friction parameters inferences from the november 23 1980 irpinia earthquake this paper concentrates on the problem of fault interaction and earthquake triggering through the 1980 irpinia italy sequence more specifically this paper deals with the problem of the triggering of the second subevent by the mainshock the interaction between the two segments is modeled through a dynamic coulomb failure function the aims of this paper are first to discriminate between the dynamic and the static stress effects on the triggering if these effects exist second to estimate the fault strength relative to the initial state of stress third to determine the parameters of a slip dependent friction law that lead to the observed delay of 20 s numerical simulations show that the critical slip dc may range from 0 03 m up to 1 7 m and that the initial slope of the friction law 0 must be lower than 0 04 m 1 we show that the relative magnitude of the fault strength and the initial state of stress govern the existence and value of a dc lower threshold under which the fault always ruptures before 13 s a close to failure fault is not consistent with a critical slip dc less than 0 8 m whereas small values of dc typically 0 03 m imply a far from failure fault general results concern the effect of a dynamic stress pulse we show that an event can be triggered by a transient stress pulse and that in this case the event can have an initiation duration much longer than the pulse duration we show that it is possible to explain both the triggering and the time delay only with the effect of the transient stress pulse this may explain aftershock triggering even in regions of negative coulomb failure function or long distance triggering of earthquakes by propagating waves

scaling relations of earthquake source parameter estimates with special focus on subduction environment abstract earthquake rupture length and width estimates are in demand in many seismological applications earthquake magnitude estimates are often available whereas the geometrical extensions of the rupture fault mostly are lacking therefore scaling relations are needed to derive length and width from magnitude most frequently used are the relationships of wells and coppersmith 1994 derived on the basis of a large dataset including all slip types with the exception of thrust faulting events in subduction environments however there are many applications dealing with earthquakes in subduction zones because of their high seismic and tsunamigenic potential there are no well established scaling relations for moment magnitude and length width for subduction events within this study we compiled a large database of source parameter estimates of 283 earthquakes all focal mechanisms are represented but special focus is set on large subduction zone events in particular scaling relations were fitted with linear least square as well as orthogonal regression and analyzed regarding the difference between continental and subduction zone oceanic relationships additionally the effect of technical progress in earthquake parameter estimation on scaling relations was tested as well as the influence of different fault mechanisms for a given moment magnitude we found shorter but wider rupture areas of thrust events compared to wells and coppersmith 1994 the thrust event relationships for pure continental and pure subduction zone rupture areas were found to be almost identical the scaling relations differ significantly for slip types the exclusion of events prior to 1964 when the worldwide standard seismic network was established resulted in a remarkable effect on strike slip scaling relations the data do not show any saturation of rupture width of strike slip earthquakes generally rupture area seems to scale with mean slip independent of magnitude the aspect ratio l w however depends on moment and differs for each slip type

estimating volume change of mountain glaciers using srtm and map based topographic data this paper describes a method for estimating the volume change of mountain glaciers using the shuttle radar topography mission srtm c band data 2000 and a digital elevation model dem generated from topographic maps this approach was developed with srtm data and topographic maps of 1 25 000 scale 1977 from the akshiirak glaciers tien shan central asia the dem for 1977 was generated using 10 m contour lines from 18 map sheets covering the akshiirak massif and surrounding area the nominal vertical accuracy of the maps is 3 3 m the standard deviation of the differences between the map derived dem and the srtm data on glacier free areas of less than 25deg is 6 3 m a single localized region in the western periphery of the study area with systematic error in the srtm data from 20 to 12 m on a 30 km spatial scale was found and excluded from the error analysis assuming a 10 m map error on the upper snow covered glacier areas the estimated root mean square error of the glacier surface change is 8 2 m from 1977 to 1999 the average glacier surface thinning is 15 1 m and the estimated volume loss is 6 15 km3 the rate of the akshiirak glacier volume loss has increased by 2 7 times compared with historical data from 1943 to 1977 the srtm data show an opportunity for quantifying climatic and dynamic surface elevation changes in mountain glaciers ice cloud and land elevation satellite icesat laser altimetry and srtm data could also be used for the estimation of short term surface changes of mountain glaciers

multi decadal ice velocity and elevation changes of a monsoonal maritime glacier hailuogou glacier china digital elevation models dems of the ablation area of hailuogou glacier china produced from advanced spaceborne thermal emission and reflection radiometer aster data obtained in 2009 differential gps dgps data surveyed in 2008 and aerial photographs acquired in 1966 and 1989 are differenced to estimate long and short term glacier surface elevation change dh dt the mean dh dt of the ablation area over 43 years 1966 2009 is 1 1 0 4 m a 1 since 1989 the thinning has accelerated significantly ice velocities measured by dgps at 28 fixed stakes implanted in the ablation area increase with distance from the glacier terminus ranging from 41 0 m a 1 approaching the glacier terminus to a maximum of 205 0 m a 1 at the base of an icefall our results reveal that the overall average ice velocity in the ablation area has undergone significant temporal variability over the past several decades changes in glacier surface elevation in the ablation area result from the combined effects of climate change and glacier dynamics which are driven by different factors for different regions and periods

glacier change 1958 1998 in the north cascades national park complex washington usa the spatial characteristics for all glaciers in the north cascades national park complex usa were estimated in 1958 and again in 1998 the total glacier area in 1958 was 117 3 1 1 km 2 by 1998 the glacier area had decreased to 109 1 1 1 km 2 a reduction of 8 2 0 1 km 2 7 estimated volume loss during the 40 year period was 0 8 0 1 km 3 of ice this volume loss contributes up to 6 of the august september stream flow and equals 16 of the august september precipitation no significant correlations were found between magnitude of glacier shrinkage and topographic characteristics of elevation aspect or slope however the smaller glaciers lost proportionally more area than the larger glaciers and had a greater variability in fractional change than larger glaciers most of the well studied alpine glaciers are much larger than the population median so global estimates of glacier shrinkage based on these well studied glaciers probably underestimate the true magnitude of regional glacier change

modelling dynamic stress changes caused by an extended rupture in an elastic stratified half space summary we model the time histories of coseismic stress changes produced by an earthquake rupture on an extended fault in a layered elastic half space we compute the stress perturbations caused by earthquakes using the discrete wavenumber and the reflectivity methods we investigate the influence on the computed coulomb stress changes of the adopted crustal velocity model the rupture history and slip duration as well as the poro elastic model assumed to calculate the pore pressure changes the comparison between the spatio temporal evolution of the induced stress field calculated for different crustal models and rupture histories allows us to assess the depth and frequency dependence of the induced stress perturbation and the relative weight of dynamic and static stress changes our results show that the rise time and the rupture directivity are more important for characterizing the simulated stress time histories than the details of the rupture history the adopted poro elastic model affects the static stress changes more than the transient stress perturbations the results of this study should be taken into account to model fault interaction through elastic stress transfer

spatial and morphological change on eliot glacier mount hood oregon usa eliot glacier is a small 1 6 km 2 glacier on mount hood oregon usa and its ablation zone is largely covered with rock debris we examine the interrelated processes of ablation rates ice thickness and surface velocities to understand the retreat rate of this glacier since measurements began in 1901 the glacier has retreated 680 m lost 19 of its area and thinned by about 50 m at the lower glacier profile before the terminus retreated past that point the upper profile 800 m up glacier has shown thinning and thickening due to a kinematic wave resulting from a cool period during the 1940s 70s and is currently about the same thickness as in 1940 overall the glacier has retreated at a slower rate than other glaciers on mount hood we hypothesize that the rock debris covering the ablation zone reduces eliot glacier s sensitivity to global warming and slows its retreat rate compared to other glaciers on mount hood spatial variations in debris thickness are the primary factor in controlling spatial variations in melt a continuity model of debris thickness shows the rate of debris thickening down glacier is roughly constant and is a result of the compensating effects of strain thickening and debris melt out from the ice

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

early holocene change in atmospheric circulation in the northern great plains an upstream view of the 8 2 ka cold event elk lake in northwestern minnesota contains numerous proxy records of climatic and environmental change contained in varved sediments with annual resolution for the last 10 000 years these proxies show that about 8200 calendar years ago 8 2 cal ka 7300 radiocarbon years elk lake went froma well stratified lake that was wind protected in a boreal forest to a wellmixed lake in open prairie savanna receiving northwesterly wind blown dust probably from the dry floor of lake agassiz this change in climate marks the initiation of the widely recognized mid holocene altithermal in central north america the coincidence of this change with the so called 8 2 cal ka cold event recognized in ice core and other records fromthe circum north atlantic and thought by some to be caused by catastrophic discharge of freshwater from proglacial lakes agassiz and ojibway suggests that the two events might be related our interpretation of the elk lake proxy records and of other records from less accurately dated sites suggests that change in climate over north america was the result of a fundamental change in atmospheric circulation in response to marked changes in the relative proportions of land water and especially glacial ice in north america during the early holocene this change in circulation probably post dates the final drainage of proglacial lakes along the southern margin of the laurentide ice sheet and may have produced a minor perturbation in climate over greenland that resulted in a brief cold pulse detected in ice cores r 2002 elsevier science ltd all rights reserved

climatic and hydrologic changes in the tien shan central asia abstract the authors analyze climatic and hydrologic data from 110 sites collected from the middle of the twentieth century to the present in the tien shan one of the largest mountain systems of central asia in spite of a few confounding interregional variations in the temporal changes of surface air temperature precipitation runoff glacier mass and snow thickness in the tien shan it has been possible to establish statistically significant long term trends in these key hydroclimatic variables the average rise in air temperature was 0 01 c yr 1 over the range with slightly lower values below 2000 m elevation the precipitation in the tien shan increased 1 2 mm yr 1 over the past half century the precipitation increase is larger at low altitudes in the northern and western regions than at altitudes above 2000 m a decrease in snow resources occurred almost everywhere in the tien shan the maximum snow thickness and snow duration have decreased on average 10 cm and 9 days respectively the annual

quantifying the effects of climate and surface change on glacier mass balance when a mass balance is computed using an outdated map that computation does not reveal the actual mass change but older maps often must be used for practical reasons we present a method by which with a few additional measurements each year a mass balance computed with an outdated map can be transformed into an actual mass change this is done by taking into account the influence of changes in areal extent and changes in the surface elevation of the glacier since the map was made this method is applied to south cascade glacier washington u s a as an example the computed cumulative mass balance from 1970 to 1997 would have been 16 too negative if the 1970 map had not been updated while the actual volume change of a glacier is relevant to hydrological studies the change that would have occurred on a constant or static surface is more relevant to certain glacier dynamics problems and most climate problems we term this the reference surface balance and propose that such a balance which deliberately omits the influence of changes in area and surface elevation is better correlated to climatic variations than the conventional one which incorporates those influences

responses of two branches of glacier no 1 to climate change from 1993 to 2005 tianshan china abstract clear understanding of how alpine glaciers respond to climate change is critical to accurately evaluate water resources and to retrieve climate information from the alpine glaciers however different glaciers may have different responses to climate change this study focuses on two branches of glacier no 1 at the head of urumqi river tianshan china these two branches west branch wb and east branch eb have experienced the same pattern of climate warming since their separation in 1993 however these glaciers have responded differently as observed by fieldwork and analysis of their annual mass balances lengths areas equilibrium line altitudes elas to illustrate the different responses of climate change increase in both temperature and precipitation the glacier length response time t rl and climate sensitivity c are calculated for the two branches the length response time and climate sensitivity are 1 89 y and 8 81 for the eb and 1 63 y and 5 92 for wb the different responses are interpreted to be controlled by glacial topographical features with larger slopes and smaller areas making the wb more sensitive to the recent climate warming

effect of summer accumulation on glacier mass balance on the tibetan plateau revealed by mass balance model the characteristics and sensitivities of a cold based glacier on the tibetan plateau where the summer monsoon provides most of the mass input to glaciers are discussed using an energy balance model incorporating the process of water refreezing the model accurately represents the observational results related to the mass balance of xiao dongkemadi glacier on the central plateau during 1992 93 our data revealed that the mass balance of cold glaciers cannot simply be described by the surface mass heat balances because about 20 of infiltrated water is refrozen and thus does not run off from the glacier model calculations demonstrate that glaciers in an arid environment can maintain their mass since the monsoon provides precipitation during the melting season snowfall in summer keeps surface albedo high and largely restrains ablation nevertheless the calculations also make clear that glaciers on the plateau are more vulnerable than those of other regions because of summer accumulation in the monsoon climate warming would cause not only a decrease in accumulation but also a drastic increase in ablation in combination with surface albedo lowering therefore although glaciers on and around the plateau can be sustained by summer accumulation they are more vulnerable to warming than winter accumulation type glaciers

hydrogen isotope values in lacustrine kerogen abstract kerogen derived from plankton and sedge cattail that accumulated in sediment during two distinct phases of swan lake s development was extracted from segments of radiocarbon dated cores carbon c hydrogen h and nitrogen n amounts and the d values of kerogen extracts were determined kerogen extracts younger than 3900 ybp contained higher average h c and n c atom ratios than older kerogen 5000 to 3900 ybp the more recent kerogen extracts were derived primarily from plankton in open water sediment and are characterized by significantly higher lipid and protein fractions than those from the sedge cattail that formed the marsh layer plankton derived kerogen was more depleted in d averaging 20 per mil lighter than that from older extracts 5000 to 3900 ybp which according to pollen analysis were dominated by sedge cattail derived kerogen in the sediment profiles differences in the d values appear more related to kerogen source than to postdepositional hydrogen loss or temperature

new geochemical evidence for the origin of north america s largest dune field the nebraska sand hills central great plains usa abstract the nebraska sand hills region is the largest dune field in north america and has diverse aeolian landforms it has been active during both the late pleistocene and late holocene despite decades of study the source of sediment for this large sand sea is still controversial here we report new trace element compositions of aeolian sand that are compared to four hypothesized sediment sources tertiary rocks of the arikaree group and ogallala group unconsolidated sands of pliocene age and platte river system sands all four potential sources have a mineralogy that is similar to the nebraska sand hills k rb k ba sc th la eu eu lan ybn as sb and fe sc values show however that pliocene sediments and sands from the platte river system are not likely sources the arikaree group could be a minor contributor but sands from the ogallala group appear to have the best compositional fit to the nebraska sand hills although past studies have proposed the ogallala group as an important sand source the hypothesis has been questioned because the unit is well cemented by calcrete in its upper part however examination of the landscape upwind of the nebraska sand hills shows that the ogallala group where it occurs at the land surface is highly dissected in much of this region which makes sand sized particles available for aeolian entrainment whenever drought conditions diminish a protective vegetation cover

the great march 25 1998 antarctic plate earthquake moment tensor and rupture history we use broadband body and mantle wave data to study the 1998 antarctic intraplate earthquake the centroid moment tensor cmt has a large non double couple component there exist two pure double couple constrained solutions that fit the data almost equally well the frequent practice of taking the best double couple gives a far from optimal solution we use p and sh body waves to determine the rupture parameters of the first and larger of the two observed subevents the best rupture plane with strike 96 dip 69 and rake 18 is compatible with only one of the two cmt solutions strike 96 dip 64 rake 23 centroid location 63 1 s 148 4 e 10 km depth centroid time 0313 02 ut and m0 1 3 1021 n m mw 8 0 the first subevent is a simple primarily westward propagating 140 km rupture of 45 s duration with average velocity 3 km s 1 it has a seismic moment of 1 2 1021 n m mw 8 0 with 75 of its moment released between 10 and 27 s and a stress drop of 240 bars the rupture is physically bounded by two fracture zones at 147 5 e and 150 e the second subevent lasted from 70 to 90 s on a fault extending from 210 to 270 km west of the epicenter with a moment of 0 3 0 6 1021 n m mw 7 6 7 8 this is a spectacular example of dynamic stress triggering over a 100 km separation distance with a time delay of 40 s the complex pattern of aftershocks is primarily controlled by preexisting fracture zones on the ocean floor

mass balance of glaciers and ice caps consensus estimates for 1961 2004 1 working with comprehensive collections of directly measured data on the annual mass balance of glaciers other than the two ice sheets we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960 mass balance was slightly below zero around 1970 and has been growing more negative since then excluding peripheral ice bodies in greenland and antarctica global average specific balance for 1961 1990 was 219 112 kg m 2 a 1 representing 0 33 0 17 mm sle sea level equivalent a 1 for 2001 2004 the figures are 510 101 kg m 2 a 1 and 0 77 0 15 mm sle a 1 including the smaller greenland and antarctic glaciers global total balance becomes 0 38 0 19 mm sle a 1 for 1961 1990 and 0 98 0 19 mm sle a 1 for 2001 2004 for 1991 2004 the glacier contribution 0 77 0 26 mm sle a 1 is 20 30 of a recent estimate of 3 2 0 4 mm a 1 of total sea level rise for 1993 2005 while our error estimates are not rigorous we believe them to be liberal as far as they go but we also discuss several unquantified biases of which any may prove to be significant

the march 25 1998 antarctic plate earthquake the march 25 1998 antarctic plate earthquake mw 8 1 occurred 250 km from the nearest plate boundary in oceanic lithosphere with an age of 35 55 my analysis of aftershock patterns shows that the earthquake ruptured a fault or series of strike slip fault segments nearly 300 km long the strike of the fault s is nearly perpendicular to the north south trending fossil fracture zones which are the most marked bathymetric features of this region moment release during the mainshock was concentrated in two large subevents clearly visible in the teleseismic body wave waveforms modeling of these body waves using a finite fault source places the first of the two subevents near the point of rupture initiation on the eastern end of the fault with the second large subevent occurring 220 280 km to the west the two pulses of moment release are found to be separated in time by 65 s comparison of the relative s wave amplitudes of the first and second pulses suggests that a rotation of the focal mechanism by 10 occurred between the two subevents

hurd peninsula glaciers livingston island antarctica as indicators of regional warming ice volume changes during the period 1956 2000 johnsons and hurd glaciers are the two main glacier units of hurd peninsula ice cap livingston island south shetland islands antarctica they presently cover an area of about 10 km 2 johnsons is a tidewater glacier while hurd glacier ends on emerged land in this paper we estimate the changes in ice volume during the period 1956 2000 and compare them with the regional meteorological records the volume change estimates are based on the comparison of digital terrain models for the glacier surface constructed from aerial photographs taken by the british antarctic survey in 1956 and from our geodetic measurements in 1999 2000 the total volume estimates are based on an ice thickness map constructed from radio echo sounding profiles 18 25 mhz done in 1999 2001 showing maximum ice thickness of about 200 m we estimate the changes in ice volume during the period 1956 2000 to be 0 108 0 048 km 3 which represents a 10 0 4 5 decrease from the 1956 total volume of 1 076 0 055 km 3 and is equivalent to an average annual mass balance of 0 23 0 10 m w e during 1956 2000 ice thickness changes range from 40 to 20 m averaging 5 5 4 4 m most areas show ice thinning the thickening is limited to a small area within johnsons glacier all glacier fronts except johnsons calving front show retreat these changes are consistent with the regional meteorological records for mean summer temperature which show a trend of 0 023 0 0058 ca 1 during the period 1956 2000

middle and late holocene dune reactivation in the nebraska sand hills usa a combination of optical dating of aeolian sand and radiocarbon dating of palaeosols and interdune sediments has allowed some refinements to the chronostratigraphy of the nebraska sand hills our results directly confirm previous inferences that multiple phases of aeolian deposition including megabarchan dune reactivation occurred within the sand hills during the middle and late holocene optical dates on stratified aeolian barchan dune sediments from two localities provide ages ranging from c 6 ka to 300 years ago weakly developed palaeosols intercalated within the dune sediments and other forms of post depositional modification indicate periods of relative stability and reduced dune mobilization optical dates on the upper 12 15 m of two dune exposures indicate repeated possibly regionally correlative reactivations which occurred between c 400 500 and 200 300 years ago comparison of late holocene aeolian activity with local and regional palaeoclimatic proxy records suggests that dune reacti

dynamic stress variations due to shear faults in a plane layered medium summary a complete set of expressions is presented for the computation of elastic dynamic stress in plane layered media we use a discrete wavenumber reflectivity method to compute the stress field radiated by arbitrary moment tensor sources the expressions derived here represent an interesting tool for both the observational and theoretical analysis of dynamic stress changes associated with earthquake phenomena dynamic stress changes associated with a strike slip fault having unilateral rupture are shown this modelling which is similar to the 1992 landers california earthquake illustrates the effects of distance directivity and depth on transient stress changes

transient triggering of near and distant earthquakes we demonstrate qualitatively that frictional instability theory provides a context for understanding how earthquakes may be triggered by transient loads associated with seismic waves from near and distance earthquakes we assume that earthquake triggering is a stick slip process and test two hypotheses about the effect of transients on the timing of instabilities using a simple spring slider model and a rate and state dependent friction constitutive law a critical triggering threshold is implicit in such a model formulation our first hypothesis is that transient loads lead to clock advances i e transients hasten the time of earthquakes that would have happened eventually due to constant background loading alone modeling results demonstrate that transient loads do lead to clock advances and that the triggered instabilities may occur after the transient has ceased i e triggering may be delayed these simple clock advance models predict complex relationships between the triggering delay the clock advance and the transient characteristics the triggering delay and the degree of clock advance both depend nonlinearly on when in the earthquake cycle the transient load is applied this implies that the stress required to bring about failure does not depend linearly on loading time even when the fault is loaded at a constant rate the timing of instability also depends nonlinearly on the transient loading rate faster rates more rapidly hastening instability this implies that higher frequency and or longer duration seismic waves should increase the amount of clock advance these modeling results and simple calculations suggest that near tens of kilometers small moderate earthquakes and remote thousands of kilometers earthquakes with magnitudes 2 to 3 units larger may be equally effective at triggering seismicity our second hypothesis is that some triggered seismicity represents earthquakes that would not have happened without the transient load i e accumulated strain energy would have been relieved via other mechanisms we test this using two new seismicity models that 1 are inherently unstable but slide at steady state conditions under the background load and 2 are conditionally stable such that instability occurs only for sufficiently large perturbations for the new seismicity models very small amplitude transients trigger instability relative to the clock advance models the unstable steady state models predict that the triggering delay depends inversely and nonlinearly on the transient amplitude as in the clock advance models we were unable to generate delayed triggering with conditionally stable models for both new seismicity models the potential for triggering is independent of when the transient load is applied or equivalently of the prestress unlike in the clock advance models in these models a critical triggering threshold appears to be inversely proportional to frequency further advancement of our understanding will require more sophisticated quantitative models and observations that distinguish between our qualitative yet distinctly different model predictions

patterns of hydroclimatic change in the rocky mountains and surrounding regions since the last glacial maximum abstract the paleohydrologic record of western north america since the last glacial maximum reveals a wide range of hydroclimatic variability in time and space to improve the understanding of abrupt hydroclimatic shifts and millennial scale hydrologic changes in the central rocky mountains we reconstruct the lake level histories of two small lakes in the beartooth and bighorn mountains in northern wyoming over the past 17 ka to do so we use ground penetrating radar gpr and sediment cores to track the elevations of shoreline sediments within the lakes through time we compare the stratigraphies with those from four other lakes in wyoming and colorado and find widespread evidence for a terminal pleistocene drought from 15 to 11 ka an early holocene humid period from 11 to 8 ka and mid holocene aridity from 8 to 5 5 ka the northern wyoming lakes also provide evidence of high levels in the pleistocene possibly before ca 15 ka and rapid hydroclimatic changes that may have correlated with heinrich event 1 ca 16 8 ka we place the changes in a broad context by summarizing and mapping water level changes from 107 additional previously studied lakes important patterns include 1 extensive drying across the western u s after 15 ka 2 sub regional differences during the pleistocene holocene transition 3 a north south contrast from 9 to 6 ka consistent with a northward shift in storm tracks as the influence of the laurentide ice sheet diminished and 4 rapid increases in effective moisture across much of western north america from 6 to 4 ka

dynamic stress triggering during the great 25 march 1998 antarctic plate earthquake we investigate the coseismic stress redistribution during the 25 march 1998 great antarctic plate mw 8 1 earthquake in which the mainshock consisted of two distinct subevents separated in time by several tens of seconds we compute the dynamic stress time histories for the fault geometry and the rupture and slip history determined by henry et al 2000 using the discrete wavenumber and re flectivity method of cotton and coutant 1997 both for a homogeneous and a strat ified half space we first image the coseismic stress evolution caused by the first subevent on the fault plane of the second one for both the velocity models we compute both shear and normal stress changes and a time dependent coulomb failure function cff our results show that the shear stress changes have larger amplitudes than the other stress components and hence are the primary control on the evolution of the cff the dynamic stress amplitudes are larger than the static stress pertur bations with the largest positive dynamic stress peak on the second subevent fault plane reaching slightly less than 0 2 mpa at 60 sec and 65 sec after the nucleation for the layered and the homogeneous crustal models respectively we suggest that the dynamic stress changes caused by the first subevent promoted a nearly instan taneous failure on the second subevent fault

compound rupture of the great 1998 antarctic plate earthquake the march 25 1998 antarctic plate earthquake ruptured a portion of the antarctic plate more than 200 km west of its boundary with the australian plate the harvard centroid moment tensor solution indicates that the earthquake was primarily a strike slip event but the large non double couple component of the moment tensor suggests considerable complexity in the rupture process we use a finite fault inversion method to determine details of the rupture process from teleseismic body waves recorded by the global seismic network the p waves are poorly fit by one or more subevents having only a strike slip mechanism we find that the presence of a large oblique normal faulting subevent located to the east of the hypocenter is necessary to improve the fit this subevent combines with a larger strike slip subevent to the west to comprise the main moment release in the earthquake and is the cause of the large non double couple component in the long period focal mechanism the earthquake exhibited very high slip and high stress drop compared with most interplate strike slip events and the rupture was largely confined to the upper 15 20 km of the lithosphere both constituent focal mechanisms indicate that this part of the antarctic plate is under nw se oriented tension although the origin of these stresses is unknown

late pleistocene dune activity in the central great plains usa abstract stabilized dunes of the central great plains especially the megabarchans and large barchanoid ridges of the nebraska sand hills provide dramatic evidence of late quaternary environmental change episodic holocene dune activity in this region is now well documented but late pleistocene dune mobility has remained poorly documented despite early interpretations of the sand hills dunes as pleistocene relicts new optically stimulated luminescence osl ages from drill cores and outcrops provide evidence of late pleistocene dune activity at sites distributed across the central great plains in addition late pleistocene eolian sands deposited at 20 25 ka are interbedded with loess south of the sand hills several of the large dunes sampled in the sand hills clearly contain a substantial core of late pleistocene sand thus they had developed by the late pleistocene and were fully mobile at that time although substantial sand deposition and extensive longitudinal dune construction occurred during the holocene many of the late pleistocene osl ages fall between 17 and 14 ka but it is likely that these ages represent only the later part of a longer period of dune construction and migration at several sites significant late pleistocene or holocene large dune migration also probably occurred after the time represented by the pleistocene osl ages sedimentary structures in late pleistocene eolian sand and the forms of large dunes potentially constructed in the late pleistocene both indicate sand transport dominated by northerly to westerly winds consistent with late pleistocene loess transport directions numerical modeling of the climate of the last glacial maximum has often yielded mean monthly surface winds southwest of the laurentide ice sheet that are consistent with this geologic evidence despite strengthened anticyclonic circulation over the ice sheet mobility of large dunes during the late pleistocene on the central great plains may have been the result of cold short growing seasons with relatively low precipitation and low atmospheric co 2 that increased plant moisture stress limiting the ability of vegetation to stabilize active dune sand the apparent coexistence of large mobile dunes with boreal forest taxa suggests a late pleistocene environment with few modern analogs

changes of climate glaciers and runoff in china s monsoonal temperate glacier region during the last several decades changes of climate glaciers and runoff during the last several decades in china s monsoonal temperate glacier region have been studied temperature has increased in a fluctuating manner during the last several decades and temperature rise has accelerated since the 1980s net accumulation of dasuopu ice core has consistently declined and the precipitation decrease was also obvious from the end of 1970s through the middle 1980s and particularly after the 1990s in china s monsoonal temperate glacier region as a response to climate change eight monsoonal temperate glaciers were stationary or advancing between the 1900s 1930s and the 1960s 1980s and were in retreat from the 1930s to the 1960s and from the 1980s to the present ablation is heavy in the glacier tongue areas and the mean ablation water equivalent in hailuogou glacier during 1990 91 1997 98 was 876 mm more than that in 1982 83 ablation depth on the exposed ice area increased by 1 4 m a 1 over the period 1983 84 1990 91 mass balance records also show that glaciers suffered a constant mass loss of snow and ice and the accumulated mass balance in hailuogou basin and baishui glacier no 1 was 10 83 m water equivalent in the past 45 years and 11 38 m in the past 52 years as glaciers become shorter narrower and thinner under the background of climate warming changes of internal and upper surface morphology also occurred providing evidence of the response to climatic warming in recent years local hydrological and climatic data demonstrated that in yanggong basin during 1979 2003 and hailuogou basin during 1988 2004 runoff from the glacier areas has been increasing both seasonally and annually overall it is clear that china s monsoonal temperate glaciers are losing mass and are retreating under the background of climate warming c 2009 elsevier ltd and inqua all rights reserved

ancient and modern cold climate aeolian sand deposition a review although partly active aeolian sand sheets and dunes cover large areas in the zones of dis continuous permafrost little precise information is available about the influence of cold climate conditions on modern aeolian processes this means that palaeoenvironmental reconstructions in the stabilised mainly late pleistocene dune fields and cover sand regions in the sand belts of the european lowlands and the northern great plains of the usa and canada are necessarily still based on ancient evidence cold climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains glacial outwash plains till plains and lake shores the common parabolic and transverse dune forms resemble those observed in temperate regions although a variety of periglacial features has been identified in late pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces the nature of annual sedimentation cycles and the processes by which strata were deposited and or contorted but surprisingly little is known about the role of vegetation in the process of sand accumulation dunes are most informative with respect to reconstructions of past wind regimes which offer important data for verification of palaeoclimatic simulations

glacial changes of five southwest british columbia icefields canada mid 1980s to 1999 this study adjusts and compares digital elevation models dems created from photogrammetric and interferometric synthetic aperture radar techniques to determine volume and surface elevation changes of five icefields in a remote region of southwest british columbia canada between the mid 1980s and 1999 preliminary differences between the dems in ice free and vegetation free areas indicated variable elevation offsets with increasing altitude 11 m km 1 and with increasing slope 2 7 m 108 1 results indicate a surface elevation change of 6 0 2 7 m 0 5 0 2 m a 1 and a total volume loss of 19 4 8 8 km 3 1 5 0 7 km 3 a 1 which represents a potential sea level rise contribution of 0 004 0 002 mm a 1 temperature and snowfall data from four nearby meteorological stations indicate that increased temperatures and decreased snowfall throughout the late 1980s and 1990s are a likely cause of the thinning glacier terminus positions were compared between a historical map 1927 and satellite images 1974 1990 91 and 2000 01 all observed glaciers were in retreat between 1927 and 1974 as well as between 1990 91 and 2000 01 but many glaciers advanced or significantly slowed in their retreat between 1974 and 1990 91

a unified model for dynamic and static stress triggering of aftershocks antishocks remote seismicity creep events and multisegmented rupture aftershocks have been thought to be triggered by static stress transfer the 1992 landers and 1999 hector mine california earthquakes have demonstrated the possibility of remote triggering of seismicity highlighting the role of dynamic seismic waves static stress changes and transient deformations have different timescales the mechanisms by which they trigger earthquakes are thought to be different leading to an unwieldy vision of aftershock triggering we propose a model that encompasses both static and dynamic triggering of aftershocks and antishocks as well as the occurrence of stable slip creep events or multisegmented rupture the framework of this model is based on the stability instability transition of faults we propose that dynamic and static stress triggering pertain to the same physical process we study the effect of the complete coulomb failure function we demonstrate the possibility of the triggering of seismicity by a dynamic stress pulse in a stress shadow zone characterized by a negative static stress field the limited time efficiency of dynamic triggering shown by the data is explained by the model we suggest that dynamic waves trigger only the most unstable faults associated with a relatively short characteristic time while the static stress field triggers also faults that are stable associated with a larger characteristic time

late holocene alluvial chronology and climate change in the central great plains abstract alluvium in one reach of the republican river valley south central nebraska dates to the holocene radiocarbon dating of fills underlying the two terraces in the valley reveals that entrenchment between 4500 and 3700 yr b p formed the high terrace subsequently alternating aggradation and stability occurred until sometime between 1800 and 1100 yr b p following another period of alluviation channel incision formed the low terrace general synchrony between this chronology and other late holocene fluvial chronologies of the central great plains suggests climatic control of fluvial activity the episodes of incision are tentatively correlated with different climate regimes illustrating the difficulty of attributing a given fluvial response to a particular direction of climatic change

origin of the late quaternary dune fields of northeastern colorado stabilized eolian deposits mostly parabolic dunes and sand sheets cover much of the landscape of northeastern colorado and adjacent parts of southwestern nebraska in four geographically distinct dune fields stratigraphic and soil geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka possibly between 11 ka and 4 ka and within the past 1 5 ka thus eolian sand deposition took place under both glacial and interglacial climatic conditions in the youngest episodes of eolian sand movement holocene parabolic dunes partially buried pleistocene sand sheet deposits late holocene sands in the fort morgan and wray dune fields to the south of the south platte river have trace element ratios that are indistinguishable from modern south platte river sands but different from ogallala formation bedrock which has previously been cited as the main source of dune sand on the great plains sands in the greeley dune field to the north of the south platte river have trace element concentrations that indicate a probable laramie formation source measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields in good agreement with resultant drift directions calculated for nearby weather stations thus paleowinds were probably not significantly different from present day winds and are consistent with a south platte river source for the fort morgan and wray dune fields and a laramie formation source for the greeley dune field sand accumulated downwind of the south platte river to form the fort morgan duen field in addition sand was also transported farther downwind over the upland formed by the calcrete caprock of the ogallala formation and deposited in the lee of the upland on the southeast side because of high wind energy the upland itself served as a zone of sand transport but little or no sand accumulation took place on this surface these studies which demonstrate the importance of fluvial source sediments for dune fields in colorado may be applicable to other dune fields in north america because modern drift potentials in northeastern colorado are among the highest in the world the present stability of dunes in the region may be in part a function of the dunes being supply limited rather than solely transport limited extensive 7700 km2 late holocene dunes document that eolian sand in northeastern colorado is very sensitive to small changes in climate or fluvial source conditions

glacier no 4 of sigong river over mt bogda of eastern tianshan central asia thinning and retreat during the period 1962 2009 rtk gps data aerial photographs and aster images were used to quantify volume surface elevation terminus position and area changes of glacier no 4 of sigong river over mt bogda tianshan during the period from 1962 to 2009 glacier surface elevation of the tongue area decreased by 15 8 m 0 32 0 17 m a 1 and ice volume loss reached 0 014 0 008 km3 0 013 0 007 km3 w e the glacier terminus retreated at a rate of 8 0 m a 1 and the area decreased by about 0 53 km2 accounting for 15 8 of the glacier area in 1962 3 33 km2 the changes can be primarily attributed to the significant increase in temperature in this region a comparison with glacier changes by field measurements in other regions of eastern tianshan showed obvious spatial differences in the magnitude of the changes owing to a combination of regional climate change and topographical factors

integrated monitoring of mountain glaciers as key indicators of global climate change the european alps the internationally recommended multi level strategy for monitoring mountain glaciers is illustrated using the example of the european alps where especially dense information has been available through historical times this strategy combines in situ measurements mass balance length change with remote sensing inventories and numerical modelling it helps to bridge the gap between detailed local process oriented studies and global coverage since the 1980s mass balances have become increasingly negative with values close to 1 m w e a 1 during the first 5 years of the 21st century the hot dry summer of 2003 alone caused a record mean loss of 2 45 m w e roughly 50 above the previous record loss in 1998 more than three times the average between 1980 and 2000 and an order of magnitude more than characteristic long term averages since the end of the little ice age and other extended periods of glacier shrinkage during the past 2000 years it can be estimated that glaciers in the european alps lost about half their total volume roughly 0 5 a 1 between 1850 and around 1975 another 25 or 1 a 1 of the remaining amount between 1975 and 2000 and an additional 10 15 or 2 3 a 1 in the first 5 years of this century

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

sensitivity of mass balance of five swiss glaciers to temperature changes assessed by tuning a degree day model a degree day model is used to assess the sensitivity of the mass balance of five swiss glaciers to temperature changes the model uses temperature data extrapolated from nearby climate stations and is tuned by varying precipitation to make the model fit the observed distribution of mass balance with altitude once the model is tuned the effect of temperature change is simulated by recalculating the mass balance with the same parameters as before but with a temperature increase of 1 c throughout the year the largest mass balance changes involving increased ablation of 1 m w e a 1 c 1 occur at the snout with a progressively smaller increase with altitude the area averaged sensitivities for the five glaciers are 0 7 to 0 9 m w e a 1 c 1 if annual precipitation also increased by 20 it would partly offset the effect of the 1 c higher temperatures but could not compensate for it