processing of seismic data in the presence of anisotropy processing techniques for extracting the polarization directions of the fast and slower split shear waves together with their traveltime splitting from vector wavefield data form the basis of prospective procedures for imaging details of the internal structure of subsurface rocks a recently developed technique involving the independent rotation of the source polarization direction and geophone axes provides an effective processing tool for extracting the effects of anisotropy from shear wave data it is theoretically capable of handling nonorthogonal polarization directions of split shear waves it is further developed and its performance examined using vertical seismic profiling vsp shear wave datasets for different anisotropic earth models and computed using full wave modeling the procedure works well for shear waves propagating through an earth model with a uniform crack strike with depth but produces inaccurate estimates of polarization and time delay when the crack strike varies abruptly

alignment of near surface inclusions and appropriate crack geometries for geothermal hot dry rock experiments ubiquitous splitting of seismic shear waves indicates that most rocks in the upper half of the crust are pervaded by stress aligned fluid filled inclusions called eda cracks these inclusions are expected to be aligned perpendicular to the minimum compressional stress by stress relationships similar to those aligning industrial hydraulic fractures at depths where the overburden stress is sufficiently large typically below a few hundred metres this minimum stress is usually horizontal so that the eda cracks and hydraulic fractures are typically aligned vertically striking parallel or subparallel to the direction of maximum compression this is confirmed by the polarizations of the split shear waves along raypaths at depth in the crust at the free surface however the vertical stress is zero or approximately zero and cracks and hydraulic fractures at shallow depths in intact rock tend to be horizontal thus the directions of minimum stress and the orientations of hydraulic fractures are likely to swing through 90 near the surface of the earth since the behaviour of cracks and stress is often crucial to drilling operations the rotation of the crack and stress geometry near surface has important implications particularly for optimizing hydrocarbon production and geothermal reservoir management consequently evidence gained from experiments for example in hot dry rock geothermal heat extraction in inappropriate crack geometries at shallow depths may not be valid when applied to other crack and stress geometries at depth in hot rock

a detailed seismic anisotropy study during the 2011 2012 unrest period in the santorini volcanic complex abstract the santorini volcanic complex svc is an area in the southern aegean greece which has been characterized by low seismicity rates for the last decades especially in the santorini caldera where they have been very low until 2010 this pattern changed completely in february 2011 when intense microseismic activity was initiated within the caldera during the manual analysis of the events the shear wave splitting phenomenon was observed revealing the existence of an anisotropic upper crust in the svc area a detailed anisotropy study has been conducted using 231 events within the shear wave window that fulfilled the selection criteria the polarization direction of the fast shear wave the time delay between the two split shear waves and the source polarization direction were calculated after visual inspection using both the polarigram and the hodogram representations this procedure applied for eight local stations resulted in the determination of 340 splitting parameters the obtained mean anisotropy directions are not homogeneous revealing a complex regime in the activated area nevertheless these results are explained by the ape model related to the stress sensitive behavior of fluid saturated microcracked rocks a detailed analysis of the temporal evolution of both the time delay and anisotropy direction was carried out the time delays measured in the band 1 window exhibit gradual increase and sudden drop that can be related to imminent bursts of seismicity as well as to the major m w 5 1 and 5 2 events which took place about 40 km sw of santorini on 26 and 27 january 2012 respectively on the other hand no significant temporal variations or 90 flips of the s fast polarization direction were observed

integrated use of seismograph and strong motion data to determine soil amplification response of the fraser river delta to the duvall and georgia strait earthquakes we present a new method to estimate site amplification in which re gional seismographic data are used to constrain the input motions to the soil profile the empirical inferred amplification is determined as the ratio of the fourier spec trum of the recorded motion on soil to the spectrum of the inferred input motion at the underlying bedrock interface the method is demonstrated for sites on the fraser river delta british columbia b c that recorded the 1996 m 5 1 duvall wash ington and 1997 m 4 3 georgia strait b c earthquakes regional seismographic recordings on rock sites are used to determine the apparent source spectra of these events these spectra are attenuated to sites in the fraser river delta then input to a specified soil profile we compare the empirical inferred amplification to alternative estimates of the soil amplification based on 1 the quarter wavelength approach and 2 the assumption that the amplification is approximately equal to the observed h v ratio the empirical inferred amplification estimates are grossly consistent with the theoretical amplification estimates but have larger peaks at specific frequencies probably due to resonant effects not accounted for in the quarter wavelength ap proach the h v ratio appears to be a simple and useful first approximation to the site response the fraser river delta amplifies weak motions by factors of three to six over a broad frequency range from 0 2 to 4 hz high frequency motions f 10 hz are attenuated the long period amplifications pose a serious concern in the event of strong earthquake shaking from large earthquakes a useful by product of the analysis is the determination of apparent source spectra for the events the apparent source spectrum of the georgia strait earthquake is in good agreement with the brune point source model with a stress drop of approxi mately 45 bars the apparent source spectrum of the slightly larger duvall earthquake is in reasonable agreement with the brune model with a stress drop of about 70 bars however for the duvall earthquake there is evidence of a sag in spectral amplitudes relative to the brune model at intermediate frequencies 0 3 to 1 hz this inter mediate frequency sag is an expected result of source complexity it is well dem onstrated by the broadband seismic data

interpretation of total wave field data over lost hills field kern county california approximately 5 miles 8 km of total wave field data were acquired by production geophysical services then kim tech inc using the omnipulse multi mode shear wave generator source over the southern end of lost hills field kern county california the quality of the shear wave sections was excellent they represent a significant improvement over conventional p wave sections from the area in that they provide better reflection continuity and imaging of the lost hills anticline a multicomponent vsp which was acquired close to the line provided crucial p wave to s wave correlation as well as fracture information vp vs ratios computed from interval times ranged from 2 79 to 1 63 an anomalously low vp vs ratio of 1 65 in the zone of interest lower reef ridge to mcdonald shale confirmed by multicomponent vsp data corresponds to the producing interval evidence of shear wave splitting due to azimuthal anisotropy was observed so the sv wave and sh wave data sets were rotated into principal compo

estimating paleoatmospheric pco2 during the early eocene climatic optimum from stomatal frequency of ginkgo okanagan highlands british columbia canada abstract estimates of p co 2 for the early paleogene vary widely from near modern day levels to an order of magnitude greater based on various proxy measures resolving the relationship between climate and p co 2 during this globally warm period is a key task in understanding climate dynamics in a warmer world here we use the stomatal frequency of fossil ginkgo adiantoides from the okanagan highlands of british columbia canada to estimate p co 2 during the early eocene climatic optimum eeco the interval of peak warmth in the cenozoic we also examine a dataset of modern ginkgo biloba leaves to critically assess the accuracy and precision of stomatal frequency as a proxy indicator of p co 2 early eocene fossil g adiantoides has significantly lower stomatal frequency than modern g biloba suggesting p co 2 levels 2 modern pre industrial values this result is in contrast to earlier studies using stomatal frequency of ginkgo that indicated near modern day levels of p co 2 in the early paleogene though not including samples from the eeco we also find that levels of p co 2 as indicated by stomatal frequency are correlated with trends in climate mean annual temperature over time at the falkland fossil locality suggesting that climate and p co 2 were coupled during the eeco hyperthermal

high latitude hydrological changes during the eocene thermal maximum 2 abstract the eocene hyperthermals including the paleocene eocene thermal maximum petm and eocene thermal maximum 2 etm2 represent extreme global warming events 56 and 54 million years ago associated with rapid increases in atmospheric greenhouse gas concentrations an initial study on petm characteristics in the arctic region argued for intensification of the hydrological cycle and a substantial increase in poleward moisture transport during global warming based on compound specific carbon and hydrogen isotopic 2h 1h records from sedimentary leaf wax lipids in this study we apply this isotopic and hydrological approach on sediments deposited during etm2 from the lomonosov ridge integrated ocean drilling program expedition 302 our results show similar 2h 1h changes during etm2 as during the petm with a period of 2h enrichment 20 relative to pre event values just prior to the negative carbon isotope shift cie that is often taken as the onset of the hyperthermal and more negative lipid 2h values 15 during peak warming notably lipid 2h enrichment at the base of the event is coeval with colder tex 86 h temperatures if 2h 1h values of leaf waxes primarily reflect the hydrogen isotopic composition of precipitation the observed local relationship between temperature and 2h 1h values for the body of etm2 is precisely the opposite of what would be predicted using a simple rayleigh isotope distillation model assuming a meridional vapor trajectory and a reduction in equator pole temperature gradients overall a negative correlation exists between the average chain length of n alkanes and 2h 1h suggesting that local changes in ecology could have impacted the hydrogen isotopic compositions of leaf waxes the negative correlation falls across three separate intervals the base of the event the initial cie and during the h2 hyperthermal of which the assignment is not fully certain three possible mechanisms potentially explain 2h enriched signals at the base of the event including 1 intense local drying and cooling leading to evaporative 2h enrichment 2 changes in frequency intensity of storm events and its impact on high latitude amount effects and 3 changes in low latitude temperatures evidence for hydrological shifts at the base of both hyperthermals suggests that hydrological change or the factors promoting hydrological change played a role in triggering the release of greenhouse gases generation of similar high resolution isotopic and temperature records at other latitudes is crucial for understanding the causal links between temperature and hydrological changes and may help constrain the source and mechanism of carbon release that triggered the early eocene hyperthermals

nonlinearity liquefaction and velocity variation of soft soil layers in port island kobe during the hyogo ken nanbu earthquake clear nonlinear behavior is analyzed from the acceleration records of the 1995 hyogo ken nanbu earthquake at port island kobe from four triaxial in struments placed at four different depths the surficial effects during strong ground motions were compared with those during weak motions before and after the main shock we used a spectral ratio technique and a nonlinear inversion for velocity structure to analyze the data from the spectral analysis we observed a large variation of the spectral ratios between the surface and different depths during the strong ground motions and during the liquefied state the spectral ratios after the mainshock i e after the liquefied state are different from those before the mainshock the peak frequencies in the spectral ratios after the mainshock are shifted to lower fre quencies with respect to those in the spectral ratios before the mainshock we in verted the s wave velocities using a genetic algorithm technique to determine the velocity structure before during and after the mainshock the s wave velocity struc ture before and after the mainshock was found to be different specifically the s wave velocity of the second layer 5 m to 16 m depth after the mainshock was 20 lower than before our analysis shows that the liquefied state remains at least 3 hr after the mainshock but no more than 24 hr the rigidity of the soil decreased close to zero when liquefaction happened and later increases gradually following a trend that resembles a consolidation curve the strong influence of nonlinearity during the mainshock yielded a big reduction of the horizontal surface ground motions so that the observed horizontal peak acceleration was only about 25 of the peak acceler ation expected from the linear theory however the nonlinear effects in the vertical peak acceleration were not significant

paleoenvironment of the quilchena flora british columbia during the early eocene climatic optimum the quilchena fossil locality is dated 51 5 0 4 ma to the early eocene climatic optimum and this locality is reconstructed as the warmest and wettest of the early eocene upland sites from the okanagan highlands of british columbia and northern washington state mean annual temperature mat is estimated from leaf margin analysis using 55 dicot morphotypes as 16 2 2 1 c 14 6 4 8 c using bioclimatic analysis of 45 nearest living relatives a moist mesothermal climate is indicated mat 12 7 16 6 c cold month mean temperature cmmt 3 5 7 9 c mean annual precipitation map 103 157 cm year leaf size analysis estimates map at 121 39 cm year estimates from the climate leaf analysis multivariate program corroborate these results although with a slightly cooler mat 13 3 2 1 c plants that support an interpretation of warm winters with minimal or no frost include azolla glyptostrobus taxodium keteleeria pseudolarix eucommia dipteronia hovenia ternstroemia and others these ther

eocene paleo physiography and drainage directions southern interior plateau british columbia a map of reconstructed eocene physiography and drainage directions is presented for the southern interior plateau region british columbia south of 53 n eocene landforms are inferred from the distribution and depositional paleoenvironment of eocene rocks and from crosscutting relationships between regional scale geomorphology and bedrock geology of known age eocene drainage directions are inferred from physiography relief and base level elevations of the sub eocene unconformity and the documented distribution provenance and paleocurrents of early cenozoic fluvial sediments the eocene landscape of the southern interior plateau resembled its modern counterpart with highlands plains and deeply incised drainages except regional drainage was to the north an anabranching valley system trending west and northwest from quesnel and shuswap highlands across the cariboo plateau to the fraser river valley contained north flowing streams from eocene to early quaternary time other valleys dating back at least to middle eocene time include the north thompson valley south of clearwater thompson valley from kamloops to spences bridge the valley containing nicola lake bridge river valley and okanagan lake valley during the early cenozoic highlands existed where the coast mountains are today southward drainage along the modern fraser chilcotin and thompson river valleys was established after the late miocene

the range of effects of azimuthal isotropy and eda anisotropy in sedimentary basins summary combinations of bedding or lithology induced azimuthal isotropy with an axis of symmetry perpendicular to the bedding plane and crack induced extensivedilatancy anisotropy eda with a horizontal axis of symmetry are believed to be common in sedimentary basins and cause the widely observed phenomenon of shear wave splitting combinations of two such transversely isotropic forms of anisotropy with orthogonal axes of cylindrical symmetry lead to orthorhombic symmetry this has two major effects 1 the polarizations of the faster split shear waves may no longer be parallel to the strike of the cracks or fractures even for near vertical propagation and 2 such orthorhombic symmetry systems necessarily have a number of directions called shear wave point singularities where shear waves display disturbed or anomalous behaviour again possibly in near vertical directions unless these effects are correctly identified they could be interpreted mistakenly for the effects of structural irregularities or discontinuities in contrast recognition of the 3 d geometry of this behaviour places comparatively tight constraints on possible combinations of anisotropy in the rockmass in order to give some understanding of the geometry of these phenomena this paper presents 3 d patterns of the behaviour of shear wave splitting that have been computed for a range of combinations of crack and bedding induced anisotropy

cenozoic migration of topography in the north american cordillera continental topography is the result of complex interactions among mantle convection continental dynamics and climatic and erosional processes therefore topographic evolution of mountain belts and continental interiors reflects directly upon the coupling between mantle and surface processes it has recently been proposed that the modern topography of western north america is partly controlled by the removal of the subducting farallon plate and replacement of lithospheric mantle by hot asthenosphere creating surface uplift of the colorado plateau the southwestern united states and northern mexico while concomitant subsidence characterizes the central united states how the topography of the cenozoic north american cordillera evolved in the past is largely unknown yet currently debated tectonic models each have a predictable topographic response here we examine cenozoic surface uplift patterns of western north america based on a record of 3000 stable isotope proxy data this data set is consistent with eocene north to south surface uplift in the cordillera culminating in the assembly of an eocene oligocene highland 3 4 km in elevation the diachronous record of surface uplift and associated magmatism further supports tectonic models calling for the convective removal of mantle lithosphere or removal of the farallon slab by buckling along an east west axis the eocene oligocene development of rainout patterns similar to present day patterns along the flanks of the cordilleran orogen is therefore unlikely to be the result of late mesozoic crustal thickening and associated development of an andean style altiplano

geological and industrial implications of extensive dilatancy anisotropy extensive dilatancy anisotropy is the hypothesized distribution of stress aligned fluid filled microcracks pervading most rocks in the earth s crust the geometry of the cracks and the aligning stress field can be monitored by analysing the waveforms of shear waves propagating through the rockmass the ability to estimate some of the parameters of the crack and stress geometry by analysing shear wave particle displacements has widespread implications

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

freshwater molluscan fauna from the florissant formation colorado paleohydrologic reconstruction of a latest eocene lake1 the freshwater molluscan assemblage from the uppermost eocene florissant formation 34 07 0 10 ma colorado usa provides a reliable proxy in reconstructing past ecology and environmental chara

evaluation of anisotropy by shear wave splitting the polarizations of three component shear wavetrains carry unique information about the internal structure of the rock through which they pass specifically commonly observed shear wave splitting may contain information about the orientation of crack distributions this information cannot usually be recovered from shear waves recorded at the free surface because of interference with the interaction of the shear wave with the surface even for nearly vertical incidence however shear wave splitting in synthetic three component vertical seismic profiles in some cases may be interpreted directly in terms of the direction of strike of vertical cracks because the human eye is not skilled at identifying the phase relationships between three component seismograms played out conventionally as parallel time series the polarizations are displayed in orthogonal sections of the particle displacements to facilitate recognition and evaluation of the shear wave splitting estimating the orientations of cracks an

depositional setting fossil flora and paleoenvironment of the early eocene falkland site okanagan highlands british columbia the fossil flora and depositional setting of the early eocene falkland site in the southern interior of british columbia canada is reported in detail for the first time using a census sampling approach the falkland site is part of the series of okanagan highlands fossil localities in british columbia and washington state that represent relatively cool upland environments within the context of the greenhouse world of the early eocene providing microthermal mean annual temperature mat 13 c climatic conditions for the establishment of cool adapted plants geographically adjacent to subtropical elements from lowland floras plant community composition of the falkland flora is most similar to the republic washington and mcabee british columbia floras based on high sorenson similarity coefficients together forming a southern cluster of okanagan highlands sites the site is a lacustrine deposit that formed in a volcanically active landscape paleoclimate reconstructions based on leaf physiognomy

effects of the free surface on shear wavetrains summary the behaviour of shear waves is of great importance in identifying and investigating seismic anisotropy in the earth however shear wavetrains recorded at the earth s surface do not always reflect the motion at depth introducing practical problems of interpretation shear wavetrains incident on the surface of an isotropic half space at angles less than critical about 35 are broadly preserved but at greater angles substantial distortions can occur for stations situated close to the source as in local earthquake studies the local sp phase a radially polarized precursor to s may occur the behaviour at the surface of an anisotropic half space is further complicated by the divergence of phase and energy propagation vectors all of these complications suggest that detailed seismogram modelling is essential to any study of shear wave propagation in the earth and in particular to investigations of anisotropy induced shear wave splitting

biotic processes in the okanagan highlands floras possible evidence of hybridization in plants adapting to a temperate forest hybridization is a key mechanism for increased diversification and speciation among modern plants and is especially important in certain families such as rosaceae and anacardiaceae this mechanism is found to occur most commonly in areas of ecological disturbance distribution and migration resulting hybrid individuals have characteristic intermediate or mosaic patterns that combine those of the two parents in morphologically distinct and identifiable ways the diverse latest early eocene flora of republic washington usa is among the most collected of the okanagan highlands floras this fossil flora includes relatives of modern taxa that are known to hybridize and produce characteristic patterns of leaf morphology and venation rosaceae anacardiaceae in this study we document patterns found in representative fossil leaves that are comparable to those indicative of hybridization in the modern relatives we use the genera sorbus l rosaceae and rhus l anacardiaceae as models to demonstrate pot

regional stratigraphy and structural setting of the kamloops group south central british columbia the kamloops group is redefined as an assemblage of lower to middle eocene volcanic and sedimentary rocks widespread in south central british columbia in the type area west of kamloops the basal

estimating the internal structure of reservoirs with shear wave vsps in the past 10 years vertical seismic profiles vsps have played an increasingly important role in identifying and delineating in situ layers such vsps have usually recorded p wave data three component shear wave trains carry three or four times more information about the source and structure of the rocks along the raypath than the equivalent p wave train so in principle shear wave vsps should be a particularly valuable technique for examining in situ layers

suggestions for a consistent terminology for seismic anisotropy seismic anisotropy is an unfamiliar concept to many geophysicists and the use of misleading and ambiguous terminology has made it more difficult to understand i suggest here a consistent terminology in which simple expressions have specific meanings similar to their colloquial meanings it is hoped that use of such language will help to make the increasing number of papers reporting seismic anisotropy more readily comprehensible to the non specialist this not a manual of anisotropy and it is not intended for theoreticians it is a list of terms which may make anisotropy a little easier to understand for those more familiar with wave propagation in isotropic solids

effects of the internal shear wave window comparison with anisotropy induced splitting in the absence of anisotropy the observed polarizations of shear waves should be those radiated from the source modified only by interaction with internal interfaces and free surface topography it has been suggested that shear wave polarizations may be systematically distorted by internal interfaces which could lead to difficulties in interpreting anisotropy induced shear wave splitting since the literature now reports many investigations of shear wave splitting possible complications caused by internal interfaces would be important and need to be assessed in this paper we investigate the polarization of shear waves in full wave synthetic seismograms incident from a point source at an isotropic to isotropic interface over a range of angles of incidence particle motion due to plane and curved wave fronts has different characteristics internal shear wave windows can be defined analogous to the shear wave window at the free surface within the innermost window the polarizations at subsurface geophones as in vertical seismic profiles are recorded with little distortion but outside this window the waveforms become increasingly distorted for larger angles of incidence this is similar to the behavior of shear waves with respect to the shear wave window at the free surface except that the behavior at internal interfaces is more complicated because of additional critical angles and additional windows we conclude that the interaction of shear waves with internal interfaces is only a serious difficulty when interpretating wide offset vertical seismic profiles wide angle reflections and cross hole data

fossil biotas from the okanagan highlands southern british columbia and northeastern washington state climates and ecosystems across an eocene landscape the late early to early middle eocene okanagan highlands fossil sites spanning 1000 km north south northeastern washington state southern british columbia provide an opportunity to reconstruct biotic communities across a broad upland landscape during the warmest part of the cenozoic plant taxa from these fossil sites are characteristic of the modern eastern north american deciduous forest zone principally the mixed mesophytic forest but also include extinct taxa taxa known only from eastern asian mesothermal forests and a small number of taxa restricted to the present day north american west coast coniferous biome in this preliminary report paleoclimates and forest types are reconstructed using collections from republic in washington state usa and princeton quilchena falkland mcabee hat creek horsefly and driftwood canyon in british columbia canada both leaf margin analysis lma and quantitative bioclimatic analysis of identified nearest living relatives of megaflora indicated uppe

the okanagan highlands eocene biota environments and geological setting southern british columbia canada and northeastern washington usa climate change is a matter of concern to society decision makers and scientists as part of the debate about the science of climate change and in particular the extent to which current climate change is due to human activity or part of the natural variability of the global climate system earth scientists try to understand how climates have changed in the past and how past warming and cooling episodes affected the landscape and the plants and animals that occupied that landscape it is also clear from the fossil record that past climate change has played a role in the evolution of animal and plant lineages as well as plant and animal communities preserved in a series of lake deposits across northeastern washington state usa to smithers in north central british columbia canada the okanagan highlands fossil deposits preserve a record of a time when the world was much warmer than now because of a naturally enhanced greenhouse effect and the poles were ice free and supported great forests these s

paleoclimate and precipitation seasonality of the early eocene mcabee megaflora kamloops group british columbia early eocene fossil floras from british columbia are a rich resource for reconstructing western north american early cenozoic climate the best known of these floras reflect cooler mat 15 c upland forest communities in contrast to coeval mat 18 c forests in lowland western north american sites of particular interest is whether early eocene climates were monsoonal highly seasonal precipitation the mcabee site is a 52 9 0 83 ma 0 5 km outcrop of bedded lacustrine shale interbedded with volcanic ash in this report two historical megaflora collections that were collected independently from different stratigraphic levels and or laterally separated by 100 200 m in the 1980s university of saskatchewan and 2000s brandon university are investigated to i assess whether they represent the same leaf population ii assess whether a combined collection yields more precise climate estimates and iii reconstruct paleoclimate to assess the character of regional early eocene precipitation seas

inversion for subsurface anisotropy using estimates of shear wave splitting summary inversion of the parameters characterizing shear wave splitting polarizations time delays and differential attenuation provides a way of obtaining a good starting model for full wave anisotropic modelling and improves the convergence to a final waveform match this is necessary as the shear waves behave in a highly non linear fashion with respect to anisotropy here we discuss the extent to which polarization and time delay information estimated from split shear waveforms may supply details of this starting model 3 d patterns of these parameters for different anisotropic models are considered to investigate the potential of the inversion scheme guidelines are formed for the best arrangements of sources and geophones to provide optimum resolution of an anisotropic model the study indicates that in most cases different anisotropic models cannot be adequately distinguished using vertical seismic profiles vsps reflection profiles and cross hole surveys in which separate polarization or time delay measurements at one azimuth are made better results are obtained by combining polarization and time delays estimates preferably from more than one azimuth the type of model parameters which can be resolved depends crucially upon the geometry of the acquisition system and to a lesser extent on the background velocity structure individual model parameters are more difficult to extract but some details appear in principle to be resolvable for certain types of survey vsps are most suitable to monitor crack strike and density of parallel vertical aligned cracks and the dip of the fine layering contributing to layer induced anisotropy cross hole experiments are best for measuring the dip of the cracks the resolution of the crack content and aspect ratio are determined principally by the position of line singularities and either an offset vsp or an adapted cross hole survey may be adequate for resolving these properties if the line is shot at an appropriate azimuth with respect to the strike of the cracks the ratio of crack induced anisotropy to matrix anisotropy in sedimentary basins can be evaluated by measuring the positions of the point singularities in recordings of polarization and time delay patterns using a near offset vsp

soil response on the fraser delta to the mw 5 1 duvall washington earthquake strong motion recordings of the 3 may 1996 mw 5 1 duvall washington earthquake made in southwestern british columbia provide the best constraints to date on soil response to seismic shaking on the fraser delta just south of vancouver a total of nine strong motion instruments in southern b c triggered during this earthquake seven of which are on or near the fraser delta these recordings were made at epicentral distances of 140 to 180 km a preliminary analysis of these data clearly shows that for low frequencies 3 hz seismic spectral amplification by a factor of 2 to 7 occurs on the fraser delta relative to nearby bedrock or thin firm soil sites however at higher frequencies moderate attenuation is observed at the fraser delta sites the largest peak ground accelerations recorded generally around 2 to 3 hz were not on the thickest delta sediments but nearer the edge of the delta peak amplification is more pronounced in the horizontal component of ground motion than in the vertical the average sh z ratio for peak values at the fraser delta sites is 4 5 0 9 compared to 1 6 0 6 for the bedrock and firm soil sites in addition to the strong motion records we also utilize five three component broadband recordings of this earthquake made in southern b c epicentral distances of 140 to 520 km and 12 short period vertical component recordings epicentral distances of 130 to 380 km to document attenuation of peak acceleration with distance for this earthquake the observed values are slightly lower than those predicted by the ground motion relations proposed for the year 2000 national building code of canada

systematics and phytogeography of selected eocene okanagan highlands plants the diverse early to middle eocene okanagan highlands floras of south central british columbia and northeastern washington reflect a time of rapid evolution and the early radiation of many dicot families that are currently significant elements of temperate floras recent studies of the republic washington flora klondike mountain formation and related okanagan floras in british columbia have documented both the earliest and sometimes the only known fossil occurrences of genera today many once more widespread taxa are restricted particularly to asian and or eastern north american refugia examples include members of the families betulaceae birch hazelnut rosaceae rose hamamelidaceae witch hazel and the endemic asian family trochodendraceae earliest occurrences are noted for neviusia rosaceae trochodendron trochodendraceae corylus and carpinus both betulaceae the first unequivocal leaf records of corylopsis and fothergilla both hamamelidaceae and two new eocene species of the extinct fruit palaeocarpinus betulaceae are also recognized today trochodendron and corylopsis are restricted to asia whereas neviusia and fothergilla genera with close asian relatives occur only in north america corylus johnsonii from republic is most similar to the extant asian species c heterophylla c wangii and c ferox neviusia leaves from one mile creek near princeton british columbia are more similar to n cliftonii an endemic from mount shasta california than to n alabamensis of southeastern north america a better documentation of the okanagan highlands floras is essential to our understanding of the evolution of north american temperate floras and the nature of asian north american disjunct taxa

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

topographic site effects a comparison of two nonreference methods abstract we present an experimental study of topographic site effects the data we use come from an experiment carried out during the summer of 1989 in epire northern greece ten digital stations recorded a total of 68 small earthquakes a recent article chavez garcia et al 1996 presented a comparison between site effects determined using horizontal to vertical spectral ratios hvsr for this data set and theoretical modeling in this note we compare the topographic site effects determined using hvsr with another independent experimental estimate a generalized inversion scheme gis neither hvsr nor gis depend on the availability of a reference site we obtain a very good agreement between both estimates of topographic site effects for both horizontal components our results support the use of hvsr to determine topographic site effects

inverting shear wave polarizations for anisotropy using three component offset vsps synthetic seismograms summary a numerical algorithm is presented for interpreting shear wave polarization directions from offset vsp data as subsurface anisotropy the technique compares observed synthetic horizontal polarization angles with expected values for a range of physically plausible anisotropic models with different orientations the comparison is implemented in a database inversion scheme the anisotropic models are formed by combining the effective anisotropy of parallel aligned vertical cracks with matrix anisotropy due to thin layering or lithology different models are defined by varying the crack and matrix properties the technique is applied to synthetic offset vsp data for a multilayered anisotropic structure generated by multi azimuth sources analysis of the results indicates that polarization measurements from non zero offsets with at least two and preferably three different azimuths are required in order to reasonably constrain the final inversion solutions the parameters which are resolved depend upon the depth of the subsurface zone of interest crack strike is well resolved in the deeper layers for which directions of propagation are sub vertical whereas other model parameters such as aspect ratio and crack content can only be resolved for wider ranges of incidence angle the key to a successful inversion appears to lie in the selection of propagation paths through the relatively unique patterns of disruption created by singularities

shear wave splitting in cross hole surveys modeling shear wave splitting diagnostic of some form of effective seismic anisotropy is observed along almost all near vertical raypaths through the crust the splitting is caused by propagation through distributions of stress aligned vertical parallel fluid filled cracks microcracks and preferentially oriented pore space that exist in most crustal rocks shear waves have severe interactions with the free surface and may be seriously disturbed by the surface and by near surface layers in principle cross hole surveys chss should be free of much of the near surface interference and could be used for investigating shear waves at higher frequencies and greater resolution along shorter raypaths than is possible with reflection surveys and vsps synthetic seismograms are examined to estimate the effects of vertical cracks on the behavior of shear waves in chs experiments the azimuth of the chs section relative to the strike of the cracks is crucial to the amount of information about seismic anisotropy that can

paleobotanical evidence of eocene and oligocene paleoaltitudes in midlatitude western north america comparisons of the physiognomy of leaves from modern vegetation of known climates with that of eocene and oligocene fossil leaf assemblages from middle latitudes of western north america indicate paleoaltitudes comparable or higher than those at present using canonical correspondence analysis a multivariate statistical approach that includes nonlinear relationships between characters and environmental parameters we relate leaf physiognomy of fossil samples to modern vegetation of known environmental parameters including moist enthalpy of the atmosphere a thermodynamically conserved quantity of the atmosphere that varies with altitude by estimating enthalpy values for both lowland leaf assemblages and coeval interior leaf assemblages altitudes for the interior assemblages can be estimated to 890 m in northeastern washington and southern british columbia the high eocene altitudes indicate subsidence or collapse of an area undergoing crustal extension and may reflect an immediately preceding period of uplift that triggered the extension similarly other areas that have undergone cenozoic crustal extension appear to have been at least as high as they are at present three sites from the rocky mountains also indicate elevations at least as high as at present and therefore suggest subsidence either resulting from cooling of a hot upper mantle or erosion and isostatic compensation of surrounding terrain high altitudes during eocene and oligocene time in western north america appear to have been normal even in areas such as the green river basin and therefore cast doubt on the commonly inferred late cenozoic uplift of that region

a decade of shear wave splitting in the earth s crust what does it mean what use can we make of it and what should we do next it is 10 years since shear wave splitting throught to be diagnostic of some form of seismic anisotropy was first positively identified in the earth s crust from the beginning it was argued that the splitting was probably associated with the presence of stress aligned cracks inclusions in the crust and that this would provide the opportunity for monitoring the in situ geometry of cracks and stress in a variety of different circumstances and in a variety of different applications

characteristics of nonlinear response of deep saturated soil deposits abstract recent epri seismic design guidelines call for dynamic soil properties shear modulus ratio and damping and liquefaction strength curves to be characterized as a function of the effective vertical stress or depth a modified version of the desra2 constitutive model for saturated soil has been applied to study the nonlinear seismic response including liquefaction of medium dense soil deposits of various thicknesses the results of the stress dependent soil properties model show lower deamplification and higher first mode resonant frequency than that of the stress independent soil properties model by using the stress dependent model with impulse base excitation the nonlinear behavior of various soil deposits has been investigated under a variety of conditions the results show that 1 the saturated soil deposit has a smaller surface amplitude and significantly lower resonant frequency than the unsaturated soil deposit of the same thickness 2 for the saturated soil conditions the larger the base excitation the lower the surface amplification and the resonant frequency 3 the deep soil deposits show lower surface amplification and resonant frequency compared to the response of shallow deposits 4 when shallow and deep deposits are compared the shallow deposits develop much higher residual pore water pressure and 5 the amplification and residual pore water pressure response of deposits deeper than 100 m or so are very similar the application of the method has also been illustrated using a strong synthetic base excitation applied to the base at a site near reno the results in general are consistent with those computed using the impulse loading the study reveals that the response predicted from the conventionally used stress independent soil properties model is unconservative for deep deposit

basin structure effects on long period strong motions in the san fernando valley and the los angeles basin from the 1994 northridge earthquake and an aftershock the strong ground motions recorded within the san fernando valley and in the los angeles basin during the 17 january 1994 northridge earthquake show complex waveforms and complicated patterns of peak acceleration and veloc ity this complexity persists even at long periods 1 to 10 sec we investigate basin structure effects on long period wave propagation in the san fernando valley and in the los angeles basin by the two dimensional finite difference modeling of the mainshock and one selected aftershock with m 4 1 the aftershock ground motion records in the san fernando valley and in the los angeles basin can be explained by basin structure effects assuming a simple point source model the structural effects and a source model composed of two subevents can explain the most prominent characteristics of the strong motion waveforms ob served during the mainshock at sites south of the epicenter while such a combination is not enough to explain the large strong motions observed in the north this result suggests that the rupture propagation effects significantly amplified the ground mo tions at sites north of the epicenter

nonlinear soil amplification its corroboration in taiwan nonlinear ground response at two strong motion arrays in taiwan is studied using the spectral ratio technique at the smart1 array we calculate the frequency dependent soil amplification functions as a ratio of the spectra at alluvium to rock sites and study their dependence on the excitation level hor izontal components of shear waves are considered we compare 1 the average spectral ratios on weak and strong motions 2 the ratios for the mainshocks and aftershocks and 3 the ratios for the strong shear waves and their coda at the smart1 array weak motions have a peak horizontal acceleration pha less than 30 gal strong motions are in the range of 100 to 267 gal comparison of the average weak and strong motion spectral ratios shows a significant deamplification of strong motion between 2 and 9 hz exceeding the error margin estimated by the standard deviations the maximum deamplifi cation occurs at approximately 6 5 hz where the average weak motion ampli fication is 2 9 versus 0 40 in the strong motion a similar pattern is exhibited by the ratios calculated for the mainshocks and the aftershocks as well as for the shear waves and their coda the spectral ratio calculated from a single re alization of coda is identical to the average ratio obtained from many small earthquakes at the smart2 we analyze spectral ratios between the stations on pleistocene terrace deposits and recent alluvium which characterize the rel ative response at these two types of sediments weak motion is pha less than 13 gal while strong motion extends from 100 to 295 gal strong motion spec tral ratios between terrace and alluvial sites are consistently reduced in the fre quency range from 1 to 10 hz compared with the weak motion this effect is insensitive to the variation in distance between stations from 7 9 to 11 4 km as well as the azimuthal change of up to 80 in the station pair strike we attribute the observed discrepancies between weak and strong motion ampli fications to the differential nonlinear response occurring at terrace and alluvial sites our results document a significant nonlinear ground response at both ar rays

life at the top of the greenhouse eocene world a review of the eocene flora and vertebrate fauna from canada s high arctic early middle eocene ca 53 38 ma sediments of the eureka sound group in canada s arctic archipelago preserve evidence of lush mixed conifer broadleaf rain forests inhabited at times by alligators turtles and diverse mammals including primates tapirs brontotheres and hippo like coryphodon this biota reflects a greenhouse world offering a climatic and ecologic deep time analog of a mild ice free arctic that may be our best means to predict what is in store for the future arctic if current climate change goes unchecked in our review of the early middle eocene arctic flora and vertebrate fauna we place the arctic fossil localities in historic geographic and stratigraphic context and we provide an integrated synthesis and discussion of the paleobiology and paleoecology of these eocene arctic forests and their vertebrate inhabitants the abundance and diversity of tapirs and plagiomenids both rare elements in midlatitude faunas and the absence of artiodactyls early horses and the hyopsodontid condylarth hyopsodus well represented at midlatitude localities are peculiar to the eocene arctic the eocene arctic macrofloras reveal a forested landscape analogous to the swamp cypress and broadleaf floodplain forests of the modern southeastern united states multiple climate proxies indicate a mild temperate early middle eocene arctic with winter temperatures at or just above freezing and summer temperatures of 20 c or higher and high precipitation at times this high precipitation resulted in freshwater discharge into a nearly enclosed arctic ocean basin sufficient to cause surface freshening of the arctic ocean supporting mats of the floating fern azolla fluctuating arctic ocean sea level due to freshwater inputs as well as tectonics produced temporary land bridges allowing land plants and animals to disperse between north america and both europe and asia

earthquake ground motion and 3d georgia basin amplification in southwest british columbia shallow blind thrust scenario earthquakes abstract finite difference modeling of 3d long period 2 s ground motions for large m w 6 8 scenario earthquakes is conducted to investigate the effects of the georgia basin structure on ground shaking in greater vancouver british columbia canada scenario earthquakes include shallow blind thrust north america na plate earthquakes simulated in locations congruent with linear clusters of shallow seismicity that is potential active faults a slip distribution model of the m w 6 7 northridge california blind thrust earthquake with the hypocenter modified to 5 km depth is used to characterize the source rupture process two sets of simulations are performed for a given scenario earthquake using models with and without georgia basin sediments the ratio of predicted peak ground velocity pgv for the two simulations is applied here as a quantitative measure of amplification due to 3d basin structure a total of eight shallow blind thrust na plate scenario earthquakes are simulated within 100 km of greater vancouver overall predicted ground motions are higher in the down dip direction of each epicenter due to the source radiation pattern hence scenario earthquakes located south of vancouver produce the highest motions in the city the average maximum pgv at stiff soil sites across greater vancouver considering all eight scenario earthquakes is 17 8 cm s modified mercalli intensity vii the average increase in peak motion due to the presence of georgia basin sediments is a factor of 4 1 the effective duration of moderate level 3 4 cm s shaking within greater vancouver is an average of 22 s longer when georgia basin sediments are included in the 3d structure model online material snapshots and videos of wave propagation and peak ground velocity maps

site response for urban los angeles using aftershocks of the northridge earthquake ground motion records from aftershocks of the 1994 northridge earthquake are used to estimate site response in the urban los angeles area over 1300 shear wave records from 61 sources and 90 sites are used in a linear inversion for source and site response spectra the methodology makes no assumptions about the shape of the source spectrum to obtain a stable unique inverse a q model and geometrical spreading factor are assumed in addition the site response at a hard rock site is constrained to be approximately 1 0 with a kappa of 0 02 the site response spectra compare favorably with the results of previous and on going investigations in los angeles a couple of first order effects are lower site response in the surrounding mountains dominated by mesozoic and tertiary rocks and higher values in the san fernando and los angeles basins containing surficial pleistocene and holocene alluvial deposits results show good correlation of high site response spectral values with localized areas of severe damage interstate 10 collapse sherman oaks northridge interstate 5 14 collapse however widespread trends in site response across the sedimentary basins are not obvious the data suggest that site responses are lower near the southern margin of the san fernando valley for sources to the north due to north dipping sedimentary structures but the general pattern of site response is characterized by high variability on length scales less than a kilometer variations of a factor of 2 in site response are observed over the length scale of 200 m and for the same surficial geologic unit for some of the alluvial basin sites surface wave generation is a significant contributor to elevated site response at lower frequencies below 2 hz the total damage pattern for the northridge earthquake is influenced by strong source directivity to the north and strong local site effects the correlation of weak motion site response estimates with areas of significant damage demonstrates the value of these field measurements in future urban planning and in the reduction of seismic risk in urban areas

effects of point singularities on shear wave propagation in sedimentary basins summary in most directions of propagation in anisotropic solids seismic shear waves split in regular and predictable ways that in principle can be directly related to the degree of anisotropy and the anisotropic symmetry of the rockmass in all anisotropic solids however there are directions of propagation known as shear wave singularities where the split shear waves have the same phase velocities for directions of propagation near the commonest type of singularity the point singularity the relationship between the phase and group velocities may undergo rapid variations for small changes in direction this results in shear waves along rays propagating at the grozq velocity behaving anomalously with irregular polarizations and amplitude changes as if they were propagating near cusps although the degree of anisotropy may be too small to cause conventional cusps on the group velocity wave surfaces the effects of propagation near such point singularities have been identified in sedimentary basins where they are features of the well established phenomenon of azimuthal isotropy transverse isotropy with a vertical axis of symmetry caused by horizontal lithology or by fine layering ptl anisotropy combining with the more recently recognized azimuthal anisotropy caused by distributions of near parallel near vertical fluid filled inclusions eda anisotropy this paper demonstrates these irregular effects by calculating synthetic shear waves in directions near a point singularity in a material simulating a possible sedimentary basin such anomalies may be important in exploration seismology as point singularities can occur along nearly vertical ray paths in sedimentary basins if not identified correctly the effects of such point singularities could be mistakenly attributed to structural irregularities and if correctly identified the directions of such singularities can place tight constraints on possible combinations of ptl and eda anisotropy in sedimentary basins

localized amplification of seismic waves and correlation with damage due to the northridge earthquake evidence for focusing in santa monica abstract the analysis of seismograms from 32 aftershocks recorded by 98 seismic stations installed after the northridge earthquake in the san fernando valley the santa monica mountains and santa monica california indicates that the enhanced damage in santa monica is explained in the main by focusing due to a lens structure at a depth of several kilometers beneath the surface and having a finite lateral extent the diagnosis was made from the observation of late arriving s phases with large amplitudes localized in the zones of large damage the azimuths and angles of incidence of the seismic rays that give rise to the greatest focusing effects correspond to radiation that would have emerged from the lower part of the rupture surface of the mainshock thus the focusing and hence the large damage in santa monica were highly dependent on the location of the northridge event and an earthquake of similar size located as little as one source dimension away would not be likely to repeat this pattern we show from coda wave analysis that the influence of surface geology as well as site effects on damage in santa monica is significantly smaller than are the focusing effects

was the arctic eocene rainforest monsoonal estimates of seasonal precipitation from early eocene megafloras from ellesmere island nunavut abstract the early eocene was the warmest interval of the cenozoic and included within it were several hyperthermal events with the paleocene eocene thermal maximum petm the most pronounced of these these globally warm climates extended into the arctic and substantive paleobotanical evidence for high arctic precipitation map 150 cm yr is indicative of an arctic rainforest which contradicts some climate models that show low arctic precipitation prior studies of arctic early eocene wood stable isotope chemistry however have shown a summer peak in precipitation which suggests modern analogs are best sought on the summer wet east coast of the asia e g china japan south korea not the winter wet west coasts of the pacific northwest of north america furthermore some prior modeling data suggest that highly seasonal monsoon type summer wet precipitation regimes i e summer map 55 characterized certain mid and lower latitude regions in the early to mid eocene presented here is a new analysis using leaf physiognomy of 3 leaf megafloras split lake stenkul fiord and strathcona fiord and palynofloral bioclimatic analysis from the margaret formation from ellesmere island placed stratigraphically as early eocene possibly occurring during or following one of the early eocene hyperthermals these new data indicate high summer precipitation in the arctic during the early eocene which in part corroborates the results from eocene wood chemistry nevertheless in contradiction to the wood analysis monsoonal conditions are not indicated by our analysis consistent with current modeling studies high summer light season and winter dark season precipitation in the eocene arctic during hyperthermals would have contributed to regional warmth

paris basin vsps case history establishing combinations of fine layer or lithologic anisotropy and crack anisotropy from modelling shear wavefields near point singularities summary this paper examines shear wave splitting in multi offset vsps at a borehole site in the paris basin and demonstrates that the sedimentary structure must have at least orthorhombic anisotropic symmetry it is suggested that the most likely cause for such an orthorhombic symmetry is the combination of fine layer or lithologic anisotropy and crack anisotropy transition zones close to shear wave singularities where there are rapid changes of shear wave polarizations and delays can account for the anomalous observed waveforms observations of large variations in shear wave polarizations in propagation directions close to point singularities are probably the first positive identification of the effects of singularities in sedimentary basins

eocene paleontology and geology of western north america western north america preserves a rich record of eocene life and environments under globally warm climates and represents an interval where significant coal and other minerals were deposited the eocene is of interest to biologists and paleontologists for its record of the appearance and rise to dominance of many plant insect and mammal groups now typical of the temperate forests of north america admixed with groups now well represented in tropical areas or restricted to eastern asia this record is also of interest for its potential contribution to our understanding of interactions between climate the biota and the ecosystems they occupied under atmospheric carbon dioxide levels much higher than today documentation of the eocene in western north america offers insights into the effects of future greenhouse climates a special symposium held at the 2014 annual meeting of the geological society of america in vancouver british columbia brought together geologists paleontologists and biologists w

nonlinear soil response a reality geotechnical models consistently indicate that the stress strain relationship of soils is nonlinear and hysteretic especially at shear strains larger than 10 5 to 10 4 nonlinear effects such as an increase in damping and reduction in shear wave velocity as excitation strength increases are commonly recognized in the dynamic loading of soils on the other hand these effects are usually ignored in seismological models of ground motion prediction because of the lack of compelling corroborative evidence from strong motion observations the situation is being changed by recently obtained data explicit evidence of strong motion deamplification accompanied by changes in resonant frequencies are found in the data from the 1985 michoacan mexico and the 1989 loma prieta california earthquakes the events recorded by the vertical and surface accelerograph arrays in taiwan as well as a number of other events throughout the world evidence of nonlinear behavior becomes apparent beyond a threshold acceleration of 100 to 200 gal nonlinearity is considerable in cohesionless soil but may be negligible in stiff soils the findings of recent years indicate that nonlinear site effects are more common than previously recognized in strong motion seismology

a comparative ground response study near los angeles using recordings of nevada nuclear tests and the 1971 san fernando earthquake a comparative ground response study at sites in the los angeles region is based on the extensive strong motion data set recorded in the 1971 san fernando earthquake and 159 three component recordings of distant nuclear tests in nevada amplitude spectral ratios computed for the nuclear test data over those frequency bands for which there is an adequate signal to noise ratio provide statistically stable estimates of the local ground response related to the type of local geologic conditions comparison of the strong motion data recorded from the 1971 san fernando earthquake with that recorded at 28 of the same sites for the nuclear tests show that the corresponding amplitude spectral ratios are statistically equivalent for most sites provided reference stations are chosen to minimize effects on the earthquake data of azimuthal source variations and crustal propagation path statistical equivalence of the spectral ratios for the two types of data sources suggests that amplitude spectral ratios computed with respect to the appropriate reference station provide a first order estimate of local ground response

comparison of signal processing techniques for estimating the effects of anisotropy1 three component recordings of shear waves in exploration surveys provide an opportunity to measure crustal anisotropy which may be important in estimating the geometrical and physical parameters of reservoir rocks vsps are particularly important for this purpose as they are less subject to the complex interactions of the shear wavefield with the free surface the first stage in characterizing the subsurface anisotropy requires that the distinctive phenomenon of shear wave splitting must be examined for every arrival at each geo phone this effect may be defined by two parameters the polarization of the leading shear wave and the time delay between corresponding split shear waves a variety of techniques have been designed to estimate these parameters of shear wave splitting here we classify the published techniques into four main categories and review their properties representative procedures from each group are applied to a common synthetic data set contaminated with signal generated noise the results allow some general statements to be made about the utility of these methods for processing shear waves in vsp data

what is a reference site many methods for estimating site response compare ground motions at sites of interest to a nearby rock site that is considered a reference motion the critical assumption in these methods is that the surface rock site record reference is equivalent to the input motion at the base of the soil layers data collected in this study show that surface rock sites can have a site response of their own which could lead to an underestimation of the seismic hazard when these sites are used as reference sites data were collected from local and regional earthquakes on digital recorders both at the surface and in boreholes at two rock sites and one basin site in the san jacinto mountains southern california the two rock sites keenwild and pinon flat are located on granitic bedrock of the southern california peninsular ranges batholith the basin site garner valley is an ancestral lake bed with watersaturated sediments on top of a section of decomposed granite which overlies the competent bedrock ground motion is recorded simultaneously at the surface and in the bedrock at all three sites when the surface rock sites are used as the reference site i e the surface rock motion is used as the input to the basin the computed amplification underestimates the actual amplification at the basin site for frequencies above 2 to 5 hz this underestimation by a factor of 2 to 4 depending on frequency and site results from the rock sites having a site response of their own above the 2 to 5 hz frequencies the near surface weathering and cracking of the bedrock affects the recorded ground motions at frequencies of engineering interest even at sites that appear to be located on competent crystalline rock the bedrock borehole ground motion can be used as the reference motion but the effect of the downgoing wave field and the resulting destructive interference must be considered this destructive interference may produce pseudo resonances in the spectral amplification estimates if one is careful the bedrock borehole ground motion can be considered a good reference site for seismic hazard analysis even at distances as large as 20 km from the soil site

the slip history of the 1994 northridge california earthquake determined from strong motion teleseismic gps and leveling data we present a rupture model of the northridge earthquake determined from the joint inversion of near source strong ground motion recordings p and sh teleseismic body waves global positioning system gps displacement vectors and permanent uplift measured along leveling lines the fault is defined to strike 122 and dip 40 to the south southwest the average rake vector is determined to be 101 and average slip is 1 3 m the peak slip reaches about 3 m our estimate of the seismic moment is 1 3 0 2 10 26 dyne cm potency of 0 4 km3 the rupture area is small relative to the overall aftershock dimensions and is approximately 15 km along strike nearly 20 km in the dip direction and there is no indication of slip shallower than about 5 to 6 km the up dip strong motion velocity waveforms are dominated by large s wave pulses attributed to source directivity and are comprised of at least 2 to 3 distinct arrivals a few seconds apart stations at southern azimuths indicate two main s wave arrivals separated longer in time about 4 to 5 sec these observations are best modeled with a complex distribution of subevents the initial s wave arrival comes from an asperity that begins at the hypocenter and extends up dip and to the north where a second larger subevent is centered about 12 km away the secondary s arrivals at southern azimuths are best fit with additional energy radiation from another high slip region at a depth of 19 km 8 km west of the hypocenter the resolving power of the individual data sets is examined by predicting the geodetic gps and leveling displacements with the dislocation model determined from the waveform data and vice versa and also by analyzing how well the teleseismic solution predicts the recorded strong motions the general features of the geodetic displacements are not well predicted from the model determined independently from the strong motion data likewise the slip model determined from geodetic data does not adequately reproduce the strong motion characteristics whereas a particularly smooth slip pattern is sufficient to satisfy the geodetic data the strong motion and teleseismic data require a more heterogeneous slip distribution in order to reproduce the velocity amplitudes and frequency content although the teleseismic model can adequately reproduce the overall amplitude and frequency content of the strong motion velocity recordings it does a poor job of predicting the geodetic data consequently a robust representation of the slip history and heterogeneity requires a combined analysis of these data sets

characterization of active faulting beneath the strait of georgia british columbia southwestern british columbia and northwestern washington state are subject to megathrust earthquakes deep intraslab events and earthquakes in the continental crust of the three types of earthquakes the most poorly understood are the crustal events despite a high level of seismicity there is no obvious correlation between the historical crustal earthquakes and the mapped surface faults of the region on 24 june 1997 a m l 4 6 earthquake occurred 3 4 km beneath the strait of georgia 30 km to the west of vancouver british columbia this well recorded earthquake was preceded by 11 days by a felt foreshock m l 3 4 and was followed by numerous small aftershocks this earthquake sequence occurred in one of the few regions of persistent shallow seismic activity in southwestern british columbia thus providing an ideal opportunity to attempt to characterize an active near surface fault we have computed focal mechanisms and utilized a waveform cross correlation and joint hypocentral determination routine to obtain accurate relative hypocenters of the mainshock foreshock and 53 small aftershocks in an attempt to image the active fault and the extent of rupture associated with this earthquake sequence both p nodal and cmt focal mechanisms show thrust faulting for the mainshock and the foreshock the relocated hypocenters delineate a north dipping plane at 2 4 km depth dipping at 53 in good agreement with the focal mechanism nodal plane dipping to the north at 47 the rupture area is estimated to be a 1 3 km diameter circular area comparable to that estimated using a brune rupture model with the estimated seismic moment of 3 17 10 15 n m and the stress drop of 45 bars the temporal sequence indicates a downdip migration of the seismicity along the fault plane the results of this study provide the first unambiguous evidence for the orientation and sense of motion for active faulting in the georgia strait area of british columbia

spectral amplification in a sediment filled valley exhibiting clear basin edge induced waves various site response estimates are presented for a linear array deployed in the coachella valley california during the 1992 landers big bear aftershock sequence this systematic comparison is unique in that the response of the site is clearly dominated by basin edge induced waves average sediment to bedrock spectral ratios for long s wave windows which include the basin edge induced waves exhibit amplification factors as high as 18 below 7 hz the deep basin structure which gives rise to the obvious multi dimensional effects produces a fundamental resonant peak that shifts between basin sites from 0 23 to 0 48 hz as the depth to bedrock changes above 0 6 hz where the largest amplifications occur the response is remarkably similar between sites and appears to be dominated by a near surface layer that is relatively uniform across the valley the apparent fundamental resonant frequency of this layer is between 0 8 and 1 hz sediment to bedrock spectral ratios computed using shorter windows that exclude the basin edge induced waves imply that the multi dimensional effects are significant only below 4 hz where they increase amplifications by an approximate factor of 2 spectral ratios computed using coda windows taken at twice the s wave travel time exhibit amplifications that are an average factor of 1 7 greater between 1 and 4 hz than those of the s wave estimates this discrepancy does not improve by taking coda windows later at four times the s wave travel time horizontal to vertical component s wave spectral ratios do not agree with the sediment to bedrock ratios however they do exhibit a clear peak at the fundamental resonant frequency of the deep basin structure sediment to bedrock spectral ratios of ambient seismic noise are also inconsistent with the s wave estimates however horizontal to vertical noise ratios exhibit clear peaks near the fundamental resonant frequencies of both the deep basin structure below 0 6 hz and the suspected near surface layer between 0 8 and 1 hz therefore ambient noise data appear to provide valuable constraints on the basin structure ongoing efforts involve multi dimensional modeling of the observed basin edge induced phases and resonant frequencies

an eocene brontothere and tillodonts mammalia from british columbia and their paleoenvironments we describe eocene fossils of the tillodont trogosus from the allenby formation in princeton british columbia b c as well as teeth of brontotheriina from the lower australian creek formation near quesnel b c these fossils represent the only occurrence of tillodontia and brontotheriidae in b c further the presence of the largest species of trogosus t latidens as well as a smaller species identified only as trogosus sp supports a late early early middle eocene bridgerian age for the vermilion bluffs shale of the allenby formation based on their morphology and large size the teeth referred here to brontotheriina represent one of the larger more derived brontothere genera and suggest a uintan chadronian middle late eocene age range for the lower australian creek formation that is consistent with radiometric ages of underlying volcanic rocks paleobotanical data from sediments correlative to those that produced these eocene mammal fossils suggest they inhabited forested landscapes inte

a window into mid latitudinal early eocene environmental variability a high resolution palynological analysis of the falkland site okanagan highlands british columbia canada a series of eocene lake shale deposits from british columbia coined the okanagan highlands are dated from associated volcanic ash as mostly from the early eocene climatic optimum eeco the longest persisting of the early paleogene hyperthermals in this report we focus on high resolution palynological sampling of short sequences for the falkland site to determine if they record centennial or millennial scale vegetation change during the eeco the falkland shales consist of alternating dark and light coloured irregular laminae along with interleaved tephras from volcanic eruptions at this site it is apparent that deposition occurred over several millennia pollen grains were counted under light microscopy using a standard transect method with clustering analysis determining whether the data show any long term trends in plant representation and abundance our data show that regional vegetation was impacted by millennial to centennial scale climatic variability as well as the effects of volcanic e

eocene bird tracks from the chuckanut formation northwest washington early tertiary nonmarine sediments occur as a discontinuous series of outcrops that extends throughout large areas of northwest washington and southwestern british columbia these fluvial and deltaic deposits contain abundant plant fossils but faunal remains are rare the recent discovery of an outcrop of chuckanut formation arkose containing nine fossil bird tracks provides the first clear evidence of terrestrial vertebrate life in the extensive coastal wetland zone that existed prior to the uplift of the cascade range

inversion for seismic anisotropy using genetic algorithms1 a general inversion scheme based on a genetic algorithm is developed to invert seismic observations for anisotropic parameters the technique is applied to the inversion of shear wave observations from two azimuthal vsp data sets from the conoco test site in oklahoma horizontal polarizations and time delays are inverted for hexagonal and orthorhombic symmetries the model solutions are consistent with previous studies using trial and error matching of full waveform synthetics the shear wave splitting observations suggest the presence of a shear wave line singularity and are consistent with a dipping fracture system which is known to exist at the test site application of the inversion scheme prior to full waveform modelling demonstrates that a considerable saving in time is possible whilst retaining the same degree of accuracy

variation of reflection and transmission coefficients with crack strike and crack density in anisotropic media1 recent observations show that the differential amplitudes between the faster and slower split shear waves in reflection surveys contain information about lateral variations of crack density in cracked reservoirs however the variation of amplitude with crack geometry when the crack strike changes with depth has not been reported previously in this paper we derive expressions for reflection and transmission coefficients of plane split shear waves at vertical incidence at an interface separating two cracked anisotropic media with different crack strikes we examine the effects on these coefficients as crack strike and crack density vary for interfaces with large velocity contrasts the reflection coefficients carry little information about crack geometry and the effects of crack strike varying with depth are negligible in such cases the polarization and time delay of the split shear waves are the only features which reliably diagnose anisotropy and contain information about the variation of crack strike and density however for interfaces with small velocity contrasts the effects of any variation of crack strike with depth cannot be neglected in such cases in addition to the polarization and time delays of split shear waves both the differential amplitude of faster and slower shear waves and the amplitude ratio of the two off diagonal elements in the reflected data matrix after separation of split shear waves contain information about the variation of crack strike and crack density in contrast effects of crack strike changing with depth on transmitted waves are more sensitive regardless of the velocity contrast and the degree of anisotropy

seismic site response in the greater vancouver british columbia area spectral ratios from moderate earthquakes three component digital recordings of two recent moderate earthquakes provide valuable new insight into the response to seismic shaking in the greater vancouver area particularly on the fraser ri

determining the paleoclimate and elevation of the late eocene florissant flora support from the coexistence approach published estimates on the paleoclimate of the florissant fossil beds site of colorado 34 1 ma have led to extremely different estimates of paleoelevation the purpose of this paper is to review the paleoclimate methods used and to add the coexistence approach ca method to estimate paleotemperature for the florissant site the basis of the ca method is the dependence on overlapping climatic requirements for different taxa in the flora and their nearest living relatives these relationships tie the fossil identities to the actual plant habitats and climatic requirements of close relatives based on the ca method we conclude that the mean annual temperature ranged between 14 3 and 18 2 c these results support the conclusions offered by several other studies that the florissant was a warm temperate to subtropical flora and they are consistent with recent conclusions by structural geologists as well as other studies indicating that the florissant site was deposited at a relatively low elevation prob

directional topographic site response at tarzana observed in aftershocks of the 1994 northridge california earthquake implications for mainshock motions abstract the northridge earthquake caused 1 78 g acceleration in the east west direction at a site in tarzana california located about 6 km south of the mainshock epicenter the accelerograph was located atop a hill about 15 m high 500 m long and 130 m wide striking about n78 e during the aftershock sequence a temporary array of 21 three component geophones was deployed in six radial lines centered on the accelerograph with an average sensor spacing of 35 m station c00 was located about 2 m from the accelerograph we inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion we identified a 3 2 hz resonance that is a transverse oscillation of the hill a directional topographic effect the top base amplification ratio at 3 2 hz is about 4 5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill this resonance is seen most strongly within 50 m of c00 other resonant frequencies were also observed a strong lateral variation in attenuation probably associated with a fault caused substantially lower motion at frequencies above 6 hz at the east end of the hill there may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill causing particle motions not spectral ratios at the top of the hill to be rotated about 20 away from the direction transverse to the hill the resonant frequency but not the amplitude of our observed topographic resonance agrees well with theory even for such a low hill comparisons of our observations with theoretical results indicate that the 3d shape of the hill and its internal structure are important factors affecting its response the strong transverse resonance of the hill does not account for the large east west mainshock motions assuming linear soil response mainshock east west motions at the tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill probable variations in surficial shear wave velocity do not account for the observed differences among mainshock acceleration observed at tarzana and at two different sites within 2 km of tarzana

preservation of mandibular zinc in a beetle from the eocene kishenehn formation of montana usa fossil insects of the 46 million year old coal creek member of the kishenehn formation exhibit exceptional preservation as evidenced by the preservation of color and the blood derived pigment heme in a blood engorged mosquito in the present study analysis of a fossil rove beetle coleoptera staphylinidae from the kishenehn formation document preservation of zinc a metal often used to harden the cutting surfaces of mandibles in extant insects localized to the mandibles of the fossil insect scanning electron microscopy and energy dispersive x ray spectroscopy demonstrate that the carbonaceous bodies of preserved insects are physically homogeneous composed primarily of carbon and are distinct from the adjacent microbial mat within which the insects are thought to have been preserved the microbial mat that covered the fossil insects is shown to consist of in part well consolidated silicates this thin layer while completely transparent when wet obscures the fossil when dry the in situ preservat

the effect of the aspect ratio on crack induced anisotropy1 media containing aligned cracks show anisotropy with respect to elastic wave propagation there are several models describing the wave propagation in cracked media most of them only valid for cracks with small aspect ratios one of these models crampin s model is compared with a model valid for all aspect ratios nishizawa s model the elastic constants and the group velocities are compared for both dry and liquid filled inclusions with aspect ratios ranging from 0 0001 flat cracks up to 1 spheres the difference between both models is small for small aspect ratios but becomes larger for increasing aspect ratios at a crack density of 0 05 both models give within an error of 5 the same results for aspect ratios up to 0 3 therefore crampin s model can be applied to a large range of cracked media even if the aspect ratio of the inclusions is not small the variation of the anisotropy as a function of the aspect ratio can be studied using thomsen s dimensionless parameters e and y they show how inclusions with large aspect ratios result in elliptical anisotropy