geologic setting and stratigraphy of the ziegler reservoir fossil site snowmass village colorado the geologic setting of the ziegler reservoir fossil site is somewhat unusual the sediments containing the pleistocene fossils were deposited in a lake on top of a ridge the lake basin was formed near snowmass village colorado usa when a glacier flowing down snowmass creek valley became thick enough to overtop a low point in the eastern valley wall and entered the head of brush creek valley when the glacier retreated at about 155 130 ka near the end of marine oxygen isotope stage 6 the brush creek valley lobe left behind a moraine that impounded a small alpine lake the lake was initially 10 m deep and appears to have been highly productive during most of its existence based on the abundant and exquisitely preserved organic material present in the sediments over time the basin slowly filled with mostly eolian sediment such that by 87 ka it contained a marsh or wetland rather than a true lake open water conditions returned briefly between 77 and 55 ka before the impoundment was finally breached to the east establishing ties with the brush creek drainage system and creating an alpine meadow that persisted until historic times

evidence for the diet and habitat of two late pleistocene mastodons from the midwest usa we analyzed intestinal contents of two late glacial mastodons preserved in lake sediments in ohio burning tree mastodon and michigan heisler mastodon a multi proxy suite of macrofossils and microfossils provided unique insights into what these individuals had eaten just before they died and added significantly to knowledge of mastodon diets we reconstructed the mastodons habitats with similar multi proxy analyses of the embedding lake sediments non pollen palynomorphs especially spores of coprophilous fungi differentiated intestinal and environmental samples the burning tree mastodon gut sample originates from the small intestine the heisler mastodon sample is part of the large intestine to which humans had added clastic material to anchor parts of the carcass under water to cache the meat both carcasses had been dismembered suggesting that the mastodons had been hunted or scavenged in line with other contemporaneous mastodon finds and the timing of early human incursion into the midwest both mastodons lived in mixed coniferous deciduous late glacial forests they browsed tree leaves and twigs especially picea they also ate sedge swamp plants and drank the lake water our multi proxy estimates for a spring summer season of death contrast with autumn estimates derived from prior tusk analyses we document the recovered fossil remains with photographs

effect of melting glaciers on the earth s rotation and gravitational field 1965 1984 summary yearly mass balance data for 85 glaciers in 13 of the 31 mountain glacier systems designated in meier s 1984 paper are averaged for the years 1965 1984 average rates of volume change for the 13 regions are compared to meier s 1984 estimates of glacial melting these data cover regions that account for about 74 per cent of the volume change estimated to have occurred in all the 31 mountain glacier systems from 1900 to 1984 the volume changes in the 13 regions tend to be less than those calculated by using changes in the volume of glaciers between 1900 and 1961 meier 1984 although the reason for this difference is not well known it could result from melting during the first half of the 20th century of ice accumulated during earlier periods or a decrease in the rise in atmospheric temperatures from 1945 to 1980 spatial and temporal empirical orthogonal functional analysis is used to bring out the similarities and differences among the 13 regions and identify those regions contributing most to the variance of the data set these regions are not necessarily those with the greatest average rates of volume change enough spatial variability is present to support the hypothesis that satellites may eventually be able to discern changes in the earth s glaciers through the gravitational field even though the signal from the mass change is small and changes in the gravitational field of the earth are contaminated with gravity signals from other mass changes on the earth s surface and interior zonal coefficients of the spherical harmonic expansion of the gravitational potential are calculated for yearly mass changes for these 13 regions up to i 8 there is little similarity at decadal periods between the polar motion excitation from mountain glacier systems and the observed excitation the majority of observed polar motion excitation could be due to other surface mass changes including continental water storage see for example chao 1988 the amplitude of the interannual excitation due to the glacial signal computed here is less than 10 per cent of the observed excitation and the secular trend of the excitation from melting glaciers in the 13 regions is about one quarter of that of the observed excitation yearly changes in the length of day lod are calculated from the glacial signals and compared to the observed yearly alod excess lod signal the contribution of glaciers to the total excess lod signal is less than one part in 150 of the observed signal as alod is caused mainly by core mantle coupling at decadal periods and atmospheric coupling at shorter periods the contributions to displacement of the centre of mass of the solid earth as seen by a satellite tracked from the earth s surface are calculated for the mountain glaciers and an 80 year record of global sea level for the glaciers the average displacements are as much as 1 mm over 20 years and for sea level the z coordinate of the average displacement is 5mm over its 80 year record interannual signals

high elevation late pleistocene mis 6 5 vertebrate faunas from the ziegler reservoir fossil site snowmass village colorado abstract the vertebrate record at the ziegler reservoir fossil site zrfs near snowmass village colorado ranges from 140 to 77 ka spanning all of marine oxygen isotope stage mis 5 the site contains at least 52 taxa of macro and microvertebrates including one fish three amphibian four reptile ten bird and 34 mammal taxa the most common vertebrate is ambystoma tigrinum tiger salamander which is represented by 22 000 elements representing the entire life cycle the mastodon mammut americanum is the most common mammal and is documented by 1800 skeletal elements making the zrfs one of the largest accumulations of proboscidean remains in north america faunas at the zrfs can be divided into two groups a lake margin group dating to 140 100 ka that is dominated by woodland taxa and a lake center group dating to 87 77 ka characterized by taxa favoring more open conditions the change in faunal assemblages occurred between mis 5c and 5a vertebrates were absent from mis 5b deposits which were times of significant environmental change at the zrfs furthermore the zrfs provides a well dated occurrence of the extinct bison latifrons which has implications for the timing of the rancholabrean mammal age in the region

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

ground rotational motions of the 1999 chi chi taiwan earthquake as inferred from dense array observations 1 large rotational motions excited by the 1999 chi chi taiwan earthquake are inferred from a dense acceleration array near the northern end of the rupture fault where large surface slips along the fault are observed the estimated major frequency content is from 0 1 to 1 0 hz with a peak near 0 2 hz it is found that in the footwall region the observed strong rotational ground motions were most probably excited by the slip of the northern rupture ending segment of the chi chi earthquake fault and that its thrust slips induced a major rock motion in the radial component the analysis here indicates that during the chi chi earthquake significant rotation seismic energy was radiated from the bent northern end of the earthquake fault further analysis of rotational ground motions may provide useful constraints for its rupture mechanisms

the isotopic ecology of late pleistocene mammals in north america part 1 florida abstract mammoths and mastodons are common in pleistocene deposits yet these proboscideans and many other animals disappeared suddenly 10 000 years ago in this study we reconstruct the diets of proboscideans and associated mammals through isotopic analysis of carbonate in tooth enamel apatite in order to test nutritional hypotheses for late pleistocene extinction we analyzed specimens from six sites in florida ranging from full glacial 21 000 bp to late glacial 14 750 to 10 000 bp age the oxygen isotope composition of mammalian apatite covaries with meteoric water composition which in turn varies with climate consequently oxygen isotope analysis can be used to assess the potential for time averaging or mixing of specimens from different geographic regions within fossil assemblages the carbon isotope composition of an herbivore is controlled by the isotopic composition of the plants that it ingests carbon isotope analysis reveals that mastodons ate chiefly c3 plants presumably trees shrubs and herbs whereas mammoths consumed chiefly c4 grass several nutritional hypotheses for late pleistocene extinction entail the assumption that extinct taxa had specialized diets the resource partitioning and focused feeding preferences of florida s proboscideans corroborate this assumption but they do not in themselves prove that nutritional stress was the cause of the late pleistocene extinction

spatio temporal source characteristics of the 26 december 2004 sumatra earthquake as imaged by teleseismic broadband arrays 1 we test the capability of broadband arrays at teleseismic distances to image the spatio temporal characteristics of the seismic energy release during the dec 26 2004 sumatra earthquake at early observation times using a non plane wave array location technique previously reported values for rupture length about 1150 km duration about 480 s and average rupture velocity 2 4 2 7 km s are confirmed three dominant energy releases are identified one near the hypocenter a second at 6 n 94 e about 130 s later and a third one after 300 s at 9 n 92 93 e the spatio temporal distribution of the radiated seismic energy in the source region is calculated from the stacked broadband recordings of two arrays in germany and japan and results in rough estimates of the total seismic energy of 0 55 1018 nm grsn and 1 53 1018 nm fnet respectively changes in the relative ratio of energy as function of spatio temporal location indicate a rotation of the focal mechanism during the rupture process

a high elevation mis 5 hydrologic record using mollusks and ostracodes from snowmass village colorado usa abstract sediments containing terrestrial and aquatic mollusks and ostracodes from the ziegler reservoir fossil site 2705 m elevation near snowmass village colorado span 130 87 ka mis 5e through 5b the southeastern area of the site where taxa were recovered was a relatively fresh shallow well vegetated wetland during mis 5e through 5c time approximately 2 m deep with a total dissolved solids value of 200 1000 mg l 1 the wetland was seasonally or annually variable and groundwater discharged along the margins of the bounding moraine groundwater likely contributed solutes to the system and may have contributed 18 o enriched water based on stable isotopes from ostracode calcite 18 o ost and 13 c ost seasonal evaporation occurred and the dissolved inorganic carbon pool was unexpectedly enriched in 13 c the mollusk and ostracode faunas changed little across the mis 5e 5d 5c boundaries whereas a distinct change in the ostracode fauna occurred between the deposition of unit 11 and unit 13 which corresponds in time to the mis 5c 5b boundary indicating some combination of increased surface and or groundwater flow a decrease in water temperature and a freshening and a possible deepening of the wetland

the chi chi earthquake sequence active out of sequence thrust faulting in taiwan we combined precise focal depths and fault plane solutions of more than 40 events from the 20 september 1999 chi chi earthquake sequence with a synthesis of subsurface geology to show that the dominant structure for generating earthquakes in central taiwan is a moderately dipping 20 to 30 thrust fault away from the deformation front a second subparallel seismic zone lies about 15 kilometers below the main thrust these seismic zones differ from previous models indicating that both the basal decollement and relic normal faults are aseismic

an inversion method to analyze the rupture processes of earthquakes using near field seismograms a new and very practical nonlinear least square inversion method has been developed to investigate the dislocation distribution and the character of rupture propagation on an earthquake fault plane the problem is parameterized using a model in which the fault is composed of subfaults which start rupturing with arbitrary magnitudes at arbitrary times the performance of the method is examined by numerical simulations and the method proves useful for the analysis of source processes of earthquakes including complicated cases such as multiple events the source process of the naganoken seibu earthquake of 1984 has been analyzed using strong motion seismograms the dislocation distribution and the character of rupture propagation have been successfully obtained

identification and dendrochronology of wood found at the ziegler reservoir fossil site colorado usa abstract over 300 wood fossils were collected from the ziegler reservoir fossil site near snowmass village in central colorado usa wood fossils range from fragments of stems and branches only a few centimeters in diameter and length to whole logs 50 cm diameter and 10 m length many of the fossils were collected from a beach horizon where they appear to have been washed up on the side of the interglacial lake and buried the wood is mainly fir abies sp or douglas fir pseudotsuga menziesii with some spruce picea sp pine pinus sp and at least one other unidentified conifer species douglas fir and species of fir spruce and pine are common in the area today dendrochronological analyses compared annual growth rings in fossil wood to similar data from modern trees results suggest that fossil trees from the beach horizon grew under similar environmental conditions and annual climate variability as today three douglas firs and several fir logs also appear to have been alive at the same time based on crossdating of ring widths and other ring characteristics these trees may have died at the same time suggesting a stand mortality event in the surrounding forest that resulted in numerous logs being buried synchronously in the beach horizon

analyses of pseudotachylyte from hole b of taiwan chelungpu fault drilling project tcdp their implications for seismic slip behaviors during the 1999 chi chi earthquake abstract the seismic slip behavior during the 1999 chi chi taiwan earthquake m w 7 6 was contrastive between the northern and southern segments of the activated chelungpu fault large fast and smooth slips with large stress drop in the north while smaller slower and irregular slips with smaller stress drop in the south we analyzed the pseudotachylyte samples recovered from 1194 m 1243 m and 1314 m depths of hole b of taiwan chelungpu fault drilling project tcdp to reveal the spatial difference in friction mechanism all pseudotachylyte layers are thin 0 7 2 8 cm the volume fraction of protoliths is very large more than 63 and the estimated temperature distribution is very heterogeneous from ca 750 1750 c these observations suggest that these pseudotachylyte melts were in the partial melting regime of montgomery montgomery r s 1976 friction and wear at high sliding speeds wear 36 275 298 where friction coefficient is abnormally large similar pseudotachylyte was found already in the core sample from 175 m depth of the nanto borehole penetrating the southern fault since both pseudotachylyte samples from the two boreholes are older than the 1999 chi chi event and have been uplifted from depths farther down dip of their current locations it is likely that recent seismic ruptures also would have encountered these mechanical barriers of viscous melt patches at deeper parts in the north than in the south elastohydrodynamic lubrication of clayey gouge worked effectively at the shallower parts of the northern segment however there is no evidence that it played an important role in the south these differences are the plausible causes of the contrastive local slip behaviors during the chi chi earthquake

linearized inversion for fault rupture behavior application to the 1984 morgan hill california earthquake we present a technique to infer the rupture history of an earthquake from near source records of ground motion unlike most previous studies each point on the fault is assumed to slip only once when the rupture front passes with a spatially variable slip intensity in this parameterization the data are linearly related to slip intensity but nonlinearly related to rupture time we perform a linearized inversion for slip intensity and rupture time by iteratively perturbing an assumed starting model the inverse problem for the model perturbation is solved using a tomographic back projection technique smoothing and inequality constraints are applied to ensure that the resulting solution is stable and feasible asymptotic ray theory is used to calculate theoretical seismograms and partial derivatives with respect to model parameters in test cases with noisy synthetic data sets we found that it is possible to distinguish between rupture models having variable slip amplitude and models having variable rupture velocity provided the station coverage is adequate we apply the technique to recordings of the april 24 1984 morgan hill earthquake the results indicate that slip amplitude on the fault plane was extremely variable and that the rupture front did not propagate uniformly away from the hypocenter in particular rupture was delayed on a 12 km2 section of the fault approximately 14 km to the southeast of the hypocenter the rupture front surrounded the region which subsequently failed with a component of rupture propagation back toward the hypocenter similar behavior has been observed in dynamic rupture models with stress or strength inhomogeneities this segment of the fault ruptured with a large slip amplitude releasing 12 of the total seismic moment from 4 of the total area of the aftershock zone the surface trace of this section of the fault is characterized by a complex left step that could act to increase the normal stress acting across the fault however the distribution of aftershocks suggests that the fault at depth is simpler and that it may bend to the right in either case our rupture model suggests that this segment of the fault represents an asperity which initially resisted rupture but eventually ruptured massively we estimate the shear fracture energy for this earthquake to be 2 106 j m2

characteristics of strong ground motion across a thrust fault tip from the september 21 1999 chi chi taiwan earthquake near fault tip strong motion records from the northern part of the major earthquake mw 7 6 namely the chi chi earthquake on september 21 1999 in central taiwan demonstrated systematic differences on the hanging wall and footwall and simulated by the finite element method the extraordinary ground motion differences on either side of the northern fault tip can be explained by a 2 dimension kinematic source model with fault rupture breaking to surface in this study the earthquake faulting was considered as bilateral from the center of a low angle thrust fault which is 30 km in length with a dip angle of 31 based on waveform modeling the source rupture velocity rise time and dislocation of 2 0 km sec 5 sec and 6 meters respectively are suggested the results of this study show that on the northern part of the chi chi earthquake fault there was lower rupture velocity and longer rise time of the fault slip than that previously reported furthermore the effects of surface breaking from the fault movement contributed large ground deformations near the fault tip and consequently induced extensive damage

a geochronologic framework for the ziegler reservoir fossil site snowmass village colorado abstract the ziegler reservoir fossil site near snowmass village colorado usa provides a unique opportunity to reconstruct high altitude paleoenvironmental conditions in the rocky mountains during the last interglacial period we used four different techniques to establish a chronological framework for the site radiocarbon dating of lake organics bone collagen and shell carbonate and in situ cosmogenic 10 be and 26 al ages on a boulder on the crest of a moraine that impounded the lake suggest that the ages of the sediments that hosted the fossils are between 140 ka and 45 ka uranium series ages of vertebrate remains generally fall within these bounds but extremely low uranium concentrations and evidence of open system behavior limit their utility optically stimulated luminescence osl ages n 18 obtained from fine grained quartz maintain stratigraphic order were replicable and provide reliable ages for the lake sediments analysis of the equivalent dose d e dispersion of the osl samples showed that the sediments were fully bleached prior to deposition and low scatter suggests that eolian processes were likely the dominant transport mechanism for fine grained sediments into the lake the resulting ages show that the fossil bearing sediments span the latest part of marine oxygen isotope stage mis 6 all of mis 5 and mis 4 and the earliest part of mis 3

oxygen isotope variation in the tusks of extinct proboscideans a measure of season of death and seasonality centimetre scale laminae in tusk and molar dentine of late pleistocene mastodonts and mammoths have been interpreted as annual growth bands produced in part by seasonal variation in growth rate to test this interpretation we measured the oxygen isotope composition 18 o of the co 3 fraction of dentinal hydroxyapatite from samples covering consecutive inferred years of growth in tusks in mammals changes in the 18 o value of dental tissues within individuals predominantly reflect variation in the 18 o value of body fluids which is controlled mainly by the isotopic composition of ingested water in northern hemisphere continental regions winter precipitation has substantially lower 18 o values than does precipitation in other seasons if ingested water tracks focal precipitation then seasonal variations in dentinal isotope composition should result the lowest 18 o values representing winter growth we demonstrate that there are substantial variations in the oxygen isotope composition of proboscidean dentinal apatite and that isotopic identifications of winter i e low 18 o values coincide with those based on growth rate i e slow growth zones finally the potential of oxygen isotope analyses of terrestrial mammals for assessing the seasonality of paleoclimates is considered

isotopic reconstruction of past continental environments abstract vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments to interpret these records a greater understanding of isotopic sources as well as fractionations associated with animal physiology soil geochemistry and diagenesis has been essential tooth enamel and fish otoliths yield subannual records of surface environments whereas soil minerals may integrate signals over many thousands of years carbon isotope variations in fossil vertebrates and soils record changes in the structure of vegetation and the isotope composition and concentration of atmospheric co2 oxygen isotope variations may be indirectly related to climate through reconstruction of the oxygen isotope composition of meteoric water or directly related to temperature through application of oxygen isotope paleothermometry to soil minerals or otoliths in africa nitrogen isotope variations show promise as a proxy for rainfall abundance though the gen

stress buildup in the himalaya the seismic cycle on a major fault involves long periods of elastic strain and stress accumulation driven by aseismic ductile deformation at depth ultimately released by sudden fault slip events coseismic slip distributions are generally heterogeneous with most of the energy being released in the rupture of asperities since on the long term the fault s walls generally do not accumulate any significant permanent deformation interseismic deformation might be heterogeneous revealing zones of focused stress buildup the pattern of current deformation along the himalayan arc which is known to produce recurring devastating earthquakes and where several seismic gaps have long been recognized might accordingly show significant lateral variations providing a possible explanation for the uneven microseismic activity along the himalayan arc by contrast the geodetic measurements show a rather uniform pattern of interseismic strain oriented consistently with long term geological deformation as indicated from stretching lineation we show that the geodetic data and seismicity distribution are reconciled from a model in which microseismicity is interpreted as driven by stress buildup increase in the interseismic period the uneven seismicity pattern is shown to reflect the impact of the topography on the stress field indicating low deviatoric stresses 35 mpa and a low friction 0 3 on the main himalayan thrust arc normal thrusting along the himalayan front and east west extension in southern tibet are quantitatively reconciled by the model

global sea level trend in the past century data derived from tide gauge stations throughout the world indicate that the mean sea level rose by about 12 centimeters in the past century the sea level change has a high correlation with the trend of global surface air temperature a large part of the sea level rise can be accounted for in terms of the thermal expansion of the upper layers of the ocean the results also represent weak indirect evidence for a net melting of the continental ice sheets

high elevation paleoenvironmental change during mis 6 4 in the central rockies of colorado as determined from pollen analysis abstract paleoecological studies from rocky mountain usa high elevations encompassing the previous interglacial mis 5e are rare the 10 m composite profile from the ziegler reservoir fossil site 2705 m asl of central colorado allows us to determine paleoenvironments from marine oxygen isotope stages mis 6 4 using pollen zones that are approximately equivalent to marine oxygen isotope stages during pollen zone pz 6 time pollen assemblages dominated by artemisia sagebrush suggest that alpine tundra or steppe occurred nearby the transition to pz 5e was characterized by a rapid increase in tree pollen initially picea spruce and pinus pine but also quercus oak and pseudotsuga menziesii douglas fir non arboreal pollen nap types increased during pz 5d while abies fir and juniperus juniper increased during pz 5c pollen evidence suggests that temperatures during pz 5b were as cold as during pz 6 with the site again surrounded by alpine tundra picea dominated during pz 5a before the onset of cooler conditions during pz 4 the mis 6 mis 5e transition here was similar to the mis 2 mis 1 transition at other rocky mountain sites however the ziegler reservoir pollen record contains evidence suggesting unexpected climatic trends at this site including a warmer than expected mis 5d and cooler than expected mis 5b

deterministic frequency wavenumber methods and direct measurements of rupture propagation during earthquakes using a dense array data analysis data recorded by the smart 1 array in taiwan are used to make the first direct measurements of two dimensional earthquake rupture propagation using frequency wavenumber techniques and ray theory we obtain estimates of the spatial extent duration and directions of rupture propagation during two earthquakes located offshore taiwan our estimates include uncertainties due to errors in fault plane location and orientation velocity structure and slowness ray parameter measured at the array we find that the january 29 1981 ml 6 3 taiwan earthquake ruptured unilaterally updip and toward the west on a 60 dipping 109 striking reverse fault using p waves we find its fault length and duration to be 25 18 km and 7 4 3 4 s respectively s waves indicate a fault length and duration of 27 15 km and 9 4 3 6 s respectively we suggest that the november 14 1986 ml 7 0 hualien taiwan earthquake was triggered by a shallow h 14 km foreshock ml 5 4 which occurred on a subparallel or splay fault approximately 5 s before the mainshock based on p waves rupture propagation during the foreshock is unilateral towards the northeast and slightly downdip on a 58 dipping 38 striking reverse fault its spatial extent and duration are approximately 23 km and 5 4 s the mainshock initiated at greater depth h 34 km than the foreshock with its primary direction of rupture unilateral toward the northeast and slightly updip on a 57 dipping 43 striking reverse fault using p waves we found a spatial extent and duration of 68 15 km and 12 4 2 2 s s waves indicate a similar extent duration and direction of propagation for the mainshock however we found it difficult to distinguish the foreshock and mainshock 5 waves we show by example that these results represent an improvement over what can be obtained using long period t 5 s teleseismic methods comparison of our results with those obtained using teleseismic data suggests either a short duration slip time function or that most slip occurs near the rupture front our results indicate that much of the complexity in the seismograms recorded during these events by the smart 1 array is due to spatial and temporal variations of the source this suggests that at least in some cases predictions of both the phase and amplitude of strong ground motion as a function of time would require a priori knowledge of source properties finally we recommend siting small 10 station dense arrays on land above offshore subduction zones which are considered seismic gaps because they can provide more detailed measurements of rupture propagation than is presently possible

source process of the 1995 kobe earthquake determination of spatio temporal slip distribution by bayesian modeling the kobe hyogo ken nanbu earthquake ms 6 8 occurred on 16 january 1995 in western japan bringing about a tremendous disaster we constructed its source model by determining a spatio temporal slip distribution using strong motion seismograms recorded at a number of stations near the hypocenter the source area is expressed using both a rough and a detailed subfault discretization system and a source time function expanded with a finite number of basis functions at each subfault is determined to perform stable inversions with many parameters we construct a bayesian model with unknown hyperparameters incorporating prior constraints on the smoothness of spatio temporal slip distribution in the observation equation using akaike s bayesian information criterion abic the optimal set of hyperparameters are objectively determined from observed data which enables us to uniquely determine a spatio temporal slip distribution after rough analysis in which the actual rupture area is estimated as 45 20 km we carried out a detailed analysis with a finer subfault discretization system 5 5 km in our final source model most of the slip exists beneath awaji island and the rupture below the city of kobe where the damage was most serious is relatively smaller the large slips of about 2 m in the shallowest subfaults located southwest of the hypocenter correspond to the surface offsets observed along the nojima fault the overall focal mechanism of the source is right lateral strike slip with a small thrust component while total seismic moment is 2 0 1019 nm the source time functions at shallow subfaults show a longer duration than those at deeper ones being hypothesized to represent a possible combined effect of low rupture propagation velocity and varying friction behavior in shallow regions of crust

taxonomic overview and tusk growth analyses of ziegler reservoir proboscideans abstract at an altitude of 2705 m in the colorado rockies usa the ziegler reservoir fossil site gives a rare look at a high elevation ecosystem from the late pleistocene especially mis 5 of north america remains of more than four mammoths and about 35 mastodons dominate the macrofossil assemblage mammoth remains are attributed to mammuthus columbi and mastodon remains are referred to the well known continent wide mammut americanum mastodon remains occur within and between several lake margin slump deposits their deposition must therefore have occurred as events that were to some degree separate in time we treat the mastodon assemblage in each stratigraphic unit as a source of information on environmental conditions during the lives of these individuals mastodon mandibular tusks are abundant at the site and represent both males and females from calves to full grown adults this study presents the first attempt to use microct thin section and isotope records from mandibular tusks to reconstruct features of life history we recognize an up section trend in 18o profiles toward higher values suggestive of warmer temperatures throughout this sequence mastodon growth histories show low mean sensitivities suggestive of low levels of environmental stress this work helps frame expectations for assessing environmental pressures on terminal pleistocene populations

evidence for azimuthal and temporal variations of the rupture propagation of the 1999 chi chi taiwan earthquake from dense seismic array observations data recorded by the smart 2 array and its nearby accelerometers in eastern taiwan were used to make direct measurements of the rupture propagation of the 1999 mw 7 6 chi chi taiwan earthquake the n th root stack method was employed to window and stack seismic waveforms and it revealed that coherent seismic energy showed clear temporal changes with regard to azimuth the results of this study elicited unambiguous observations as to rupture propagation direction rupture duration time and spatial distribution of the major asperities on the fault plane the rupture propagation of the chi chi earthquake was reconstructed and demonstrated that the source of the early arrived coherent energy was close to the epicenter and that the subsequent major energy moved southward twelve seconds after the initial rupture clear arrival energy was resolved and then propagated northward the horizontal apparent rupture velocity is estimated at 2 1 km sec for its northward propagation the largest source of radiated energy was identified and its location was near the northern end of the earthquake fault the strong shaking was continuous for about 24 seconds the analysed results of this study provide direct observations of the rupture properties of this earthquake these properties may serve as valuable constraints for other chi chi earthquake rupture propagation studies based on other indirect measurement methods

coseismic displacement bilateral rupture and structural characteristics at the southern end of the 1999 chi chi earthquake rupture central taiwan 1 the 1999 chi chi earthquake mw 7 6 was due to slip along the chelungpu fault a major n striking thrust fault in the fold thrust belt of western taiwan the surface rupture extends over 100 km in a n s trend with nw trending horizontal displacement increasing from 2 to 10 m from south to north the central segment of the chelungpu fault is characterized by bedding slip along the pliocene chinshui shale which has resulted in the development of a monoclinal structure on the hanging wall at the southern end of the chi chi earthquake rupture however the chelungpu fault connects with the ne striking tachienshan fault and cuts into miocene strata with complex structures on the hanging wall in this study we use digital cadastral data to calculate coseismic horizontal displacement around the chushan area results show the amount and direction of horizontal displacement to be ca 1 2 to 2 6 m and ca 220 to 260 respectively on the hanging wall and ca 1 4 m and 105 respectively on the footwall coseismic displacement and seismological data pertaining to the hanging wall at the southern end of the chi chi earthquake rupture indicate the existence of three distinct blocks horizontal displacement indicates the chushan block s movement trended sw this result reflects the chushiang and luliao faults being reactivated with different faulting mechanisms and slip azimuths this study considers a complex coseismic displacement field resulting from a bilateral rupture process whereby a southward rupture with sw trending movement results in right lateral strike slip faulting of the tachienshan fault and thrusting with a right lateral component on the ns strike of the chelungpu fault the northward rupture is associated with nw trending movement that results in activation of the luliao and chushiang faults

the use of oxygen isotope variation in shells of estuarine mollusks as a quantitative record of seasonal and annual colorado river discharge abstract we describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river water seawater mixing zone of the colorado river estuary sclerochronological techniques are used to identify tidally induced fortnight scale bundles of daily growth increments within shell cross sections these fortnightly markers are used to establish a chronology for samples taken for 18 o analysis a composite seasonal 18 o profile derived from five shells that grew in the absence of river water flow is used as a baseline against which profiles of river influenced shells are compared because this comparison is between matched fortnights within a year the temperature of shell growth is likely to be very similar the difference in 18 o between the river influenced shell and the no flow composite shell therefore represents the change in the 18 o of the water due to the presence of river water in the mixing zone the river water end member is also determined within a fortnightly context so that the change in the 18 o of mixing zone water can be used to calculate the relative proportions of seawater and fresh water the fresh water end member is calculated from the 18 o of bivalves alive prior to the emplacement of dams and water diversions on the colorado river the marine end member is based on direct measurements of the 18 o of northern gulf of california water during times of no colorado river flow the system has been calibrated to absolute flow amounts using recent releases of known volume and rate

estimation of the rupture velocity and fault length of the 2004 sumatra andaman earthquake using a dense broadband seismic array in taiwan abstract the rupture process of the disastrous sumatra andaman earthquake of 26 december 2004 was analyzed by array processes for teleseismic p waves recorded by a dense broadband seismic array in taiwan with epicentral distances of close to 31 the azimuthal variation from the bats array center to both ends of the rupture fault is approximately 21 which is larger than that reported previously for seismic arrays used to image the rupture process of this earthquake thereby providing a high spatial resolution in studying the source rupture behavior two array processing methods were used to analyze teleseismic p wave trains both analyses were based on data recorded by a broadband network covering a region of 200 400 km with the aim of evaluating the rupture behavior of the earthquake consistent results from both analyses indicate that the earthquake had a rupture duration exceeding 500 s with major asperities encountered at 80 260 and 330 s after the initiation of rupturing we traced the ruptured fault for more than 1200 km from the point of initial rupture the average rupture velocity was approximately 3 0 km s and the major northward rupture propagation began at 80 s after the initiation of rupturing

estimation of rupture processes of the 2008 wenchuan earthquake from joint analyses of two regional seismic arrays article i nfo article history we estimated the source rupture of the 2008 wenchuan earthquake ms 8 china based on a back projection of seismic waves to their source plane using data from regional broadband arrays in taiwan and northern vietnam observations from these arrays located at different azimuths were processed to eval uate the spatio temporal rupture behavior of the fault the seismic energy spot converted from windowed array waveforms was back projected to the rupture plane of the earthquake to image the instantaneous slip on the fault plane rupture processes were reconstructed based on the imaged time dependent seismic energy radiating from the earthquake fault plane the high station density of both arrays enabled a detailed examination of the rupture processes the results indicate that the 2008 wenchuan earthquake had a rupture duration of approximately 100 s with major asperities radiating energy at 50 s after the initiation of rupture the location of asperities is in good agreement with sections of the earthquake fault along which major dam age occurred such as along the yingxiu beichuan fault the radiated seismic energy shows a complex spatial distribution on the fault plane our analysis indicates that the rupture initiated at the epicenter and extended to the northeast for approximately 280 km the average rupture velocity of this earthquake was approxi mately 2 8 km s

revealing coseismic displacements and the deformation zones of the 1999 chi chi earthquake in the tsaotung area central taiwan using digital cadastral data 1 the 1999 chi chi taiwan earthquake mw 7 6 was the largest earthquake to strike taiwan in the twentieth century this earthquake is associated with a 100 km long surface rupture in order to reveal the details of displacement near the surface rupture we use a digital cadastral system to calculate coseismic displacement around the tsaotung area central taiwan the digital cadastral system was originally conceived to survey land and building boundaries in the tsaotung area taiwan authorities have taken digital cadastral measurements before and after the chi chi earthquake the cadastral system affords high density control points that reach 1421 points km2 a system denser than that of the gps accuracy is to within 11 cm a level that is higher than spot imaging and one that allows us to study surface deformation in detail coseismic displacement is 4 3 4 6 m at distance from the surface rupture and decreases to 3 4 m near the surface rupture the azimuth of horizontal displacements is 310 315 and rotates to 280 305 near the surface rupture this produced a compression left lateral deformation zone with 10 3 compression strain near the surface rupture coseismic displacement of the footwall is 1 1 2 m in 110 which is similar to that from using gps data in the tsaotung thrust slice we observed that the azimuth of horizontal displacement rotates from a nw trend to a south trend as a result of slip partitioning and gravity slide effect

variability of marine climate on the north icelandic shelf in a 1357 year proxy archive based on growth increments in the bivalve arctica islandica a multicentennial and absolutely dated shell based chronology for the marine environment of the north icelandic shelf has been constructed using annual growth increments in the shell of the long lived bivalve clam arctica islandica the region from which the shells were collected is close to the north atlantic polar front and is highly sensitive to the varying influences of atlantic and arctic water masses a strong common environmental signal is apparent in the increment widths and although the correlations between the growth increment indices and regional sea surface temperatures are significant at the 95 confidence level they are low r 0 2 indicating that a more complex combination of environmental forcings is driving growth remarkable longevities of individual animals are apparent in the increment width series used in the chronology with several animals having lifetimes in excess of 300 years and one at 507 years being the longest lived non colonial animal so far reported whose age at death can be accurately determined the sample depth is at least three shells after ad 1175 and the time series has been extended back to ad 649 with a sample depth of one or two by the addition of two further series thus providing a 1357 year archive of dated shell material the statistical and spectral characteristics of the chronology are investigated by using two different methods of removing the age related trend in shell growth comparison with other proxy archives from the same region reveals several similarities in variability on multidecadal timescales particularly during the period surrounding the transition from the medieval climate anomaly to the little ice age

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

tusk pairs in the ziegler reservoir mastodon mammut americanum assemblage implications for site taphonomy and stratigraphy abstract the ziegler reservoir zr mastodon assemblage consists of remains from dozens of individuals that represent one or more populations living in a high elevation region of the colorado rocky mountains during marine isotope stage mis 5 several left right pairs of mastodon mandibular tusks were discovered in different stratigraphic units challenging previous assumptions that depositional units preserving mastodon remains sample a comparable succession of regional populations through time it is now recognized as likely that at least some of the specimens contained in these layers were transported from original deposits located on the lake margin and that successive slumps transported parts of the same skeleton on different occasions depositing them in different stratigraphic units assigning both tusks of a pair to the lowest depositional unit in which either occurs alters the temporal pattern in season of death for zr mastodons and somewhat modifies a census of individuals but does not significantly affect the secular trend previously detected in average oxygen isotope values two tusks with matching isotope profiles were previously treated as potential evidence of a catastrophic death event that had been proposed to explain the assemblage of remains but these are now considered to be from the same individual newly paired records highlight the importance of careful taphonomic studies for any synthetic analysis of paleoecological history

tracking the rupture of the mw 9 3 sumatra earthquake over 1 150 km at teleseismic distance on 26 december 2004 a moment magnitude mw 9 3 earthquake occurred along northern sumatra the nicobar and andaman islands resulting in a devastating tsunami in the indian ocean region the rapid and accurate estimation of the rupture length and direction of such tsunami generating earthquakes is crucial for constraining both tsunami wave height models as well as the seismic moment of the events compressional seismic waves generated at the hypocentre of the sumatra earthquake arrived after about 12 min at the broadband seismic stations of the german regional seismic network grsn located approximately 9 000 km from the event here we present a modification of a standard array seismological approach and show that it is possible to track the propagating rupture front of the sumatra earthquake over a total rupture length of 1 150 km we estimate the average rupture speed to be 2 3 2 7 km s 1 and the total duration of rupture to be at least 430 s and probably between 480 and 500 s

summary of the snowmastodon project special volume a high elevation multi proxy biotic and environmental record of mis 6 4 from the ziegler reservoir fossil site snowmass village colorado usa abstract in north america terrestrial records of biodiversity and climate change that span marine oxygen isotope stage mis 5 are rare where found they provide insight into how the coupling of the ocean atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change in 2010 2011 construction at ziegler reservoir near snowmass village colorado usa revealed a nearly continuous lacustrine wetland sedimentary sequence that preserved evidence of past plant communities between 140 and 55 ka including all of mis 5 at an elevation of 2705 m the ziegler reservoir fossil site also contained thousands of well preserved bones of late pleistocene megafauna including mastodons mammoths ground sloths horses camels deer bison black bear coyotes and bighorn sheep in addition the site contained more than 26 000 bones from at least 30 species of small animals including salamanders otters muskrats minks rabbits beavers frogs lizards snakes fish and birds the combination of macro and micro vertebrates invertebrates terrestrial and aquatic plant macrofossils a detailed pollen record and a robust directly dated stratigraphic framework shows that high elevation ecosystems in the rocky mountains of colorado are climatically sensitive and varied dramatically throughout mis 5

a review of quaternary proboscideans from alberta canada here we present a summary of the largest museum collection of quaternary proboscideans known from alberta housed at the royal alberta museum the 378 specimens reported here come from localities across the province highlighting the broad distribution of proboscideans in southwestern canada during the late pleistocene despite the isolated nature of most individual specimen records the cumulative record provides a broad sense of the chronologic distribution of late pleistocene proboscideans in a large portion of southwestern canada new and summary radiocarbon data indicate that the sparse record of pre lgm mastodon mammut americanum is limited to 40 700 3000 yr bp suggesting a pattern of pre lgm extirpation previously observed at more northern latitudes mammoths mammuthus spp occur in greater numbers and have a more lengthy late pleistocene record characterized by a temporal gap related to the last glacial maximum lgm

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

on the temperature correlation of δ18o in modern precipitation reevaluation of modern precipitation temperature and isotope data permits reconciliation of previous disparate values for the correlation between 18o of modern precipitation and surface temperature past analysis has used the mean surface temperature over the time interval of sample collection e g mean weekly monthly or annual temperature to calculate temperature coefficients and different approaches at mid latitudes yield different temperature coefficients 18o t spatial correlations among geographically distinct sites yield 0 55 k seasonal variations at single sites yield 0 2 0 4 k and 12 month running averages yield 0 5 1 k however there are systematic differences in temperature during precipitation events vs time averaged surface temperature means correction for this bias using hourly weather and monthly isotope data from u s sites yields a single value of 0 55 k for all three approaches revised temperature coefficients based on surface observations are also commensurate with coefficients obtained using cloud base temperatures and with theoretical distillation models 0 5 0 7 k these coefficients provide a consistent basis for validation of general circulation models that incorporate stable isotopes of precipitation and for comparison to independent estimators of the isotopic response to climate change

two dimensional reconstruction of the surface ground motions of an earthquake the september 21 1999 chi chi taiwan earthquake the observed time history and spatial dependence of the surface ground motions of the september 21 1999 chi chi taiwan earthquake over the entire island are presented for the first time this report presents an analysis of time dependent spatial ground motions at both near source and local distances using strong motion records the two dimensional ground motions of the chi chi earthquake were reconstructed from more than 400 free field strong motion records after being corrected for absolute times the reconstructed seismic wavefields can be considered as a new type of observed data named 3 d seismograms here results of this study offer some insight into the study of earthquake source and wave propagation based on 3 d numerical modelling and greatly compliment our ability to distinguish wave generations due to sources and or structures