geophysical investigation of the denali fault and alaska range orogen within the aftershock zone of the october november 2002 m 7 9 denali fault earthquake the aftershock zone of the 3 november 2002 m 7 9 earthquake that ruptured along the right slip denali fault in south central alaska has been investigated by using gravity and magnetic magnetotelluric and deep crustal seismic reflection data as well as outcrop geology and earthquake seismology strong seismic reflections from within the alaska range orogen north of the denali fault dip as steeply as 25 n and extend to depths as great as 20 km these reflections outline a relict crustal architecture that in the past 20 yr has produced little seismicity the denali fault is nonreflective probably because this fault dips steeply to vertical the most intriguing finding from geophysical data is that earthquake aftershocks occurred above a rock body with low electrical resistivity 10 m that is at depths below 10 km aftershocks of the denali fault earthquake have mainly occurred shallower than 10 km a high geothermal gradient may cause the shallow seismicity another possibility is that the low resistivity results from fluids which could have played a role in locating the aftershock zone by reducing rock friction within the middle and lower crust

kinematics of shot geophone migration recent analysis and synthetic examples have shown that many prestack depth migration methods produce nonflat image gathers containing spurious events even when provided with a kinematically correct migration velocity field if this velocityfieldishighlyrefractive thispathologyoccursinall migration methods that produce partial images as independent migrations of data bins shot geophone prestack depth migration is an exception to this pattern each point in the prestack image volume depends explicitly on all traces within the migration aperture using a ray theoretical analysis we have found that shot geophone migration produces focusedsubsurface offsetdomainorflatscattering angledomain image gathers provided there is a curvilinear coordinate system defining pseudodepth with respect to which the rays carrying significant energy do not turn and that the acquisitioncoverageissufficienttodetermineallsuchrays although the analysis is theoretical and idealized a synthetic example suggests that its implications remain valid for practical implementations and that shot geophone prestack depth migration could be a particularly appropriate tool for velocityanalysisinacomplexstructure

first observations of polar mesosphere summer echoes in antarctica a 25 kw peak power 50 mhz radar was installed at the peruvian base on king george island antarctica 62 s in early 1993 a search for polar mesospheric summer echoes pmses was made during late january and early february of the first year of operation with negative results these results have been reported in the literature balsley et al 1993 1995 we report here results obtained during the austral summer of the second year 1994 of operation observations during the second year were begun earlier i e closer to the austral summer solstice pmses were observed during this period albeit the echoes were much weaker than what one would expect based on earlier poker flat radar results at a comparable latitude 65 n in the northern hemisphere a large and measurable asymmetry in pmse strength in the two hemispheres therefore exists we explain this asymmetry by postulating a difference in summer mesopause temperatures between the two hemispheres of 7 5 k this difference has been estimated using an empirical relationship between the variations of the poker flat pmse power as a function of temperature given by the mass spectrometer incoherent scatter extended msise 90 model

seismic velocity models for the denali fault zone along the richardson highway alaska crustal scale seismic velocity models across the denali fault zone along the richardson highway show a 50 km thick crust a near vertical fault trace and a 5 km wide damage zone associated with the fault near trans alaska pipeline pump station 10 which provided the closest strong ground motion recordings of the 2002 denali fault earthquake we compare models derived from seismic reflection and refraction surveys acquired in 1986 and 1987 to laboratory measurements of seismic velocities for typical metamorphic rocks exposed along the profiles our model for the 1986 seismic reflection profile indicates a 5 km wide low velocity zone in the upper 1 km of the denali fault zone which we interpret as fault gouge deeper refractions from our 1987 line image a 40 km wide 5 km deep low velocity zone along the denali fault and nearby associated fault strands which we attribute to a composite damage zone along several strands of the denali fault zone and to the obliquity of the seismic line to the fault zone our velocity model and other geophysical data indicate a nearly vertical denali fault zone to a depth of 30 km aftershocks of the 2002 denali fault earthquake and our velocity model provide evidence for a flower structure along the fault zone consisting of faults dipping toward and truncated by the denali fault wide angle reflections indicate that the crustal thickness beneath the denali fault is transitional between the 60 km thick crust beneath the alaska range to the south and the extended 30 km thick crust of the yukon tanana terrane to the north online material tables of locations for the tact 1986 and tact 1987 lines

point spread functions for interferometric imaging interferometric redatuming is a data driven method to transform seismic responses with sources at one level and receivers at a deeper level into virtual reflection data with both sources and receivers at the deeper level although this method has traditionally been applied by cross correlation accurate redatuming through a heterogeneous overburden requires solving a multidimensional deconvolution problem input data can be obtained either by direct observation for instance in a horizontal borehole by modelling or by a novel iterative scheme that is currently being developed the output of interferometric redatuming can be used for imaging below the redatuming level resulting in a so called interferometric image internal multiples from above the redatuming level are eliminated during this process in the past we introduced point spread functions for interferometric redatuming by cross correlation these point spread functions quantify distortions in the redatumed data caused by internal multiple reflections in the overburden in this paper we define point spread functions for interferometric imaging to quantify these distortions in the image domain these point spread functions are similar to conventional resolution functions for seismic migration but they contain additional information on the internal multiples in the overburden and they are partly data driven we show how these point spread functions can be visualized to diagnose image defocusing and artefacts finally we illustrate how point spread functions can also be defined for interferometric imaging with passive noise sources in the subsurface or with simultaneous source acquisition at the surface

acquisition geometry analysis in complex 3d media increasingly we must deal with complex subsurface structures in seismic exploration often resulting in poor illumination and therefore poor image quality consequently it is desirable to take into consideration the effects of wave propagation in the subsurface structure when designing an acquisition geometry we developed a new model based implementation of the previously introduced focal beam analysis method the method s objective is to provide quantitative insight into the combined influence of acquisition geometry overburden structure and migration operators on image resolution and angle dependent amplitude accuracy this is achieved by simulation of migrated grid point responses using focal beams note that the seismic response of any subsurface can be composed of a linear sum of grid point responses the focal beams have been chosen because any migration process represents double focusing in addition the focal source beam and focal detector beam relate migration quality to illumination properties of the source geometry and sensing properties of the detector geometry respectively wave equation modeling ensures that frequency dependent effects in the seismic frequency range are incorporated we tested our method by application to a 3d salt model in the gulf of mexico investigation of well sampled all azimuth long offset acquisition geometries revealed fundamental illumination and sensing limitations further results exposed the shortcomings of narrow azimuth data acquisition the method also demonstrates how acquisition related amplitude errors affect seismic inversion results

the gravina sequence remnants of a mid mesozoic oceanic arc in southern southeast alaska fragments of upper jurassic to lower cretaceous volcanic and basinal strata constitute the gravina belt in southeast alaska in the ketchikan area the gravina belt is made up of two lithotectonic units the lower unit consists of coarse marine pyroclastic and volcaniclastic strata mafic flows breccia and fine grained tuff which are locally intruded by hypabyssal bodies of diorite and quartz diorite the volcanic rocks are characterized by tholeiitic arc basalts lack felsic volcanic strata and overlie upper triassic and older strata of the alexander terrane augite and or hornblende bearing porphyritic rocks are common and locally intrude the alexander terrane basement where they are thought to represent the intrusive equivalents of lavas within the section age constraints for the volcanic unit based on structural and stratigraphic relations with adjacent units are late middle to late jurassic the gravina belt upper unit consists of fine to coarse grained turbidites and related conglomeratic channel fill deposits the basinal rocks unconformably overlie permian and triassic rocks of the taku terrane and remnants of the lower volcanic part of the gravina sequence which overlie the alexander terrane the conglomerate units contain mostly volcanic and plutonic lithic clasts some of which yield pb u zircon ages of 154 158 ma the predominance of pyroclastic deposits interbedded with massive flows tuff breccia and argillaceous turbidites and the lithologic and chemical composition of the volcanic rocks indicate a submarine volcanic arc setting for the gravina sequence the basinal pyroclastic rocks are inferred to have been shed from submarine stratovolcanos during the late jurassic epiclastic rocks were deposited as submarine fans derived in part from erosion of a magmatic arc the presence of fine grained tuffaceous turbidites implies ongoing but distant volcanism the pyroclastic and volcaniclastic rocks represent remnants of a late jurassic oceanic arc constructed on a composite basement consisting of the alexander and taku terranes the strata accumulated in an intra arc basin on the eastern edge of the alexander terrane the volcanic and basinal rocks were deformed during a major mid cretaceous intra arc contractional event in conjunction with the emplacement of a distinctly younger arc related plutonic suite

velocity model building from seismic reflection data by full waveform inversion full waveform inversion is re emerging as a powerful data fitting procedure for quantitative seismic imaging of the subsurface from wide azimuth seismic data this method is suitable to build high resolution velocity models provided that the targeted area is sampled by both diving waves and reflected waves however the conventional formulation of full waveform inversion prevents the reconstruction of the small wavenumber components of the velocity model when the subsurface is sampled by reflected waves only this typically occurs as the depth becomes significant with respect to the length of the receiver array this study first aims to highlight the limits of the conventional form of full waveform inversion when applied to seismic reflection data through a simple canonical example of seismic imaging and to propose a new inversion workflow that overcomes these limitations the governing idea is to decompose the subsurface model as a background part which we seek to update and a singular part that corresponds to some prior knowledge of the reflectivity forcing this scale uncoupling in the full waveform inversion formalism brings out the transmitted wavepaths that connect the sources and receivers to the reflectors in the sensitivity kernel of the full waveform inversion which is otherwise dominated by the migration impulse responses formed by the correlation of the downgoing direct wavefields coming from the shot and receiver positions this transmission regime makes full waveform inversion amenable to the update of the long to intermediate wavelengths of the background model from the wide scattering angle information however we show that this prior knowledge of the reflectivity does not prevent the use of a suitable misfit measurement based on cross correlation to avoid cycleskipping issues as well as a suitable inversion domain as the pseudo depth domain that allows us to preserve the invariant property of the zero offset time this latter feature is useful to avoid updating the reflectivity information at each non linear iteration of the full waveform inversion hence considerably reducing the computational cost of the entire workflow prior information of the reflectivity in the full waveform inversion formalism a robust misfit function that prevents cycle skipping issues and a suitable inversion domain that preserves the seismic invariant are the three key ingredients that should ensure well posedness and computational efficiency of fullwaveform inversion algorithms for seismic reflection data

estimating the elastic parameters of anisotropic media using a joint inversion of p wave and sv wave traveltime error a method is presented to estimate the elastic parameters and thickness of media that are locally laterally homogeneous using p wave and vertically polarized shear wave sv wave data this method is a layer stripping technique and it uses many aspects of common focal point cfp technology for each layer a focusing operator is computed using a model of the elastic parameters with which a cfp gather can be constructed using the seismic data assuming local homogeneity the resulting differential time shifts dtss represent error in the model due to anisotropy and error in thickness in the r p domain dtss are traveltimes that connect error in layer thickness z vertical slowness q and ray parameter p series expansion is used to linearize with respect to error in the elastic parameters and thickness and least squares inversion is used to update the model for stability joint inversion of p and sv data is employed and as pure sv data are relatively rare the use of mode converted psv data to represent sv in the joint inversion is proposed analytic and synthetic examples are used to demonstrate the utility and practicality of this inversion

the metallogeny of late triassic rifting of the alexander terrane in southeastern alaska and northwestern british columbia a belt of unusual volcanogenic massive sulfide vms occurrences is located along the eastern margin of the alexander terrane throughout southeastern alaska and northwestern british columbia and exhibits a range of characteristics consistent with a variety of syngenetic to epigenetic deposit types deposits within this belt include greens creek and windy craggy the economically most significant vms deposit in alaska and the largest in north america respectively the occurrences are hosted by a discontinuously exposed 800 km long belt of rocks that consist of a 200 to 800 m thick sequence of conglomerate limestone marine clastic sedimentary rocks and tuff intercalated with and overlain by a distinctive unit of mafic pyroclastic rocks and pillowed flows faunal data bracket the age of the host rocks between anisian middle triassic and late norian late late triassic this metallogenic belt is herein referred to as the alexander triassic metallogenic belt the vms occurrences show systematic differences in degree of structural control chemistry and stratigraphic setting along the alexander triassic metallogenic belt that suggest important spatial or temporal changes in the tectonic environment of formation at the southern end of the belt felsic volcanic rocks overlain by shallow water limestones characterize the lower part of the sequence in the southern and middle portion of the belt a distinctive pebble conglomerate marks the base of the section and is indicative of high energy deposition in a near slope or basin margin setting at the northern end of the belt the conglomerates limestones and felsic volcanic rocks are absent and the belt is composed of deep water sedimentary and mafic volcanic rocks this northward change in depositional environment and lithofacies is accompanied by a northward transition from epithermal like structurally controlled discontinuous vein and pod shaped pb zn agba cu occurrences with relatively simple mineralogy to sulfosalt enriched vms occurrences exhibiting characteristics of vein diagenetic replacement and exhalative styles of mineralization and finally to cu zn co au occurrences with larger and more clearly stratiform orebody morphologies occurrences in the middle of the belt are transitional in nature between structurally controlled types of mineralization that formed in a shallow water near arc setting to those having a more stratiform appearance formed in a deeper water rift basin setting the geologic setting in the south is consistent with shallow subaqueous emplacement on the flanks of the alexander terrane northward the setting changes to an increasingly deeper back or intra arc rift basin igneous activity in the alexander triassic metallogenic belt is characterized by a bimodal suite of volcanic rocks and a previously unrecognized association with mafic ultramafic hypabyssal intrusions immobile trace and rare earth element ree geochemical data indicate that felsic rocks in the southern portion of the belt are typical calc alkaline rhyolites which give way in the middle of the belt to peralkaline rhyolites rhyolites are largely absent in the northern part of the belt throughout the belt the capping basaltic rocks have transitional geochemical signatures radiogenic isotope data for these rocks are also transitional basalts and gabbros end 4 9 and 87sr 86sr initial at 215 ma 0 7037 0 7074 together these data are interpreted to reflect variable assimilation of mature island arc crust by more primitive melts having the characteristics of either mid ocean ridge morb or intraplate within plate basalts wpb the ore and host rock geochemistry and the sulfosalt rich mineralogy of the deposits are strikingly similar to recent descriptions of active sea floor hydrothermal white smoker systems in back arcs of the southwest pacific ocean these data in concert with existing faunal ages record the formation of a belt of vms deposits and occurrences in a propagating intra to back arc rift tectonic setting during the late triassic a modern analogue having similar tectonic and metallogenic features is the southward projection of the lau basin from the active sea floor hydrothermal vents of the valu fa ridge to the taupo volcanic zone of the north island new zealand

southern hemisphere pmse where are they we report a surprising absence of pmse polar mesospheric summer echoes in vhf radar observations of the southern summer high latitude mesosphere our observations cover about twenty days during january february 1993 from king george island antarctica

extending illumination using all multiples application to 3d acquisition geometry analysis recent advances in survey design have led to conventional common midpoint based analysis being replaced by subsurface based seismic acquisition analysis with emphasis on advanced techniques of illumination analysis among them is the so called focal beam method which is a wave equation based seismic illumination analysis method the objective of the focal beam method is to provide a quantitative insight into the combined influence of acquisition geometry overburden structure and migration operators on the resolution and angle dependent amplitude fidelity of the image the method distinguishes between illumination and sensing capability of a particular acquisition geometry by computing the focal source beam and the focal detector beam respectively sensing is related to the detection properties of a detector configuration whereas illumination is related to the emission properties of a source configuration the focal source beam analyses the incident wavefield at a specific subsurface grid point from all available sources whereas the focal detector beam analyses the sensing wavefield reaching at the detector locations from the same subsurface grid point in the past this method could only address illumination by primary reflections in this paper we will extend the concept of the focal beam method to incorporate the illumination due to the surface and internal multiples this in fact complies with the trend of including multiples in the imaging process multiple reflections can illuminate a target location from other angles compared with primary reflections resulting in a higher resolution and an improved illumination we demonstrate how an acquisition related footprint can be corrected using both the surface and the internal multiples

evidence of gravity wave saturation and local turbulence production in the summer mesosphere and lower thermosphere during the state experiment this study utilizes the unique data set obtained during the structure and atmospheric turbulence environment state experiment conducted during june 1983 at poker flat alaska to examine the structure and characteristics of the wave field near the summer mesopause it is shown that the rocket and radar data together permit a much more detailed specification of wave parameters than would be possible using either data set alone the results of this analysis suggest that the wave field near the summer mesopause is composed in general of a superposition of wave motions which act collectively to produce regions in which the wave field is convectively or dynamically unstable these regions are found to correlate well with zones of enhanced turbulence and small scale wave activity suggesting the processes and effects of wave field saturation

vhf echoes from the high latitude mesosphere and lower thermosphere observations and interpretations abstract recently published data ecklund and balsley describing vhf radar echo characteristics from the arctic mesosphere and lower thermosphere show a remarkable seasonal dependence of both the echo height and echo intensity during the three month period around the summer solstice intense and nearly continuous echoes are returned from a narrow 2 km half power region centered at 86 km during the remainder of the year however the echoes are much weaker more sporadic and occur at a much lower altitude 70 km 9 km in this paper we present additional data that suggest that the summer echoes are primarily the result of shear instability of low frequency tidal motions in the region of high stratification above the arctic summer mesopause while the winter echoes arise from the nonlinear breakup of upward propagating gravity waves

observations of mean winds and tides in the upper mesosphere during 1980 1984 using the poker flat alaska mst radar as a meteor radar a postprocessing selection algorithm is used to determine the meteor echoes detected on the poker flat alaska mst radar 65 n 147 w from a composite data base consisting of meteor and turbulence echoes the echo distributions depend on the geometry of the antenna beams the presence of strong turbulence echoes average power transmitted and the number of coherent averages used in the signal processing winds are derived from the meteor echoes and are used to compute monthly mean winds and tides in the upper mesosphere these results are consistent with previous high latitude observations tidal amplitudes are largest in summer and weakest in winter the tides exhibit large month to month variability although the seasonal averages in 1983 are in agreement with those of 1984 the semidiurnal tide exhibits a dramatic phase shift of approximately 180 from october to november in both years results suggest future enhancement of the mst wind data can be achieved with real time meteor echo detection

reinterpretation of lower mesozoic rocks on the chilkat peninsula alaska as a displaced fragment of wrangellia the southern chilkat peninsula is underlain by low grade metamorphic rocks consisting of a thick unit of greenstone in part of carnian age that is locally overlain by an attenuated section of calcareous sedimentary rocks and chart of latest carnian to late norian age and a thick flysch unit of jurassic and or cretaceous age the triassic part of this sequence has previously been inferred to be part of the taku terrane however its lithology age fossils and regional distribution indicate that it is probably a sliver of wrangellia that was offset from the eastern alaska range to its present position by at least 350 km dextral displacement on the denali fault

marine seismic surveys with enhanced azimuth coverage lessons in survey design and acquisition the azimuth from the source to the receiver in a marine seismic survey acquired with towed streamers is by nature usually close to the sail line direction deviations in this recording azimuth such as those caused by ocean currents diminish the quality of the survey results so a substantial effort is made to minimize the damage conventional streamer surveys are now called narrow azimuth or naz even though the same thing was formerly called wide azimuth and the quality of a constant offset minimal data set from such a survey has been debated padhi and holley 1997 there recently have been several surveys designed to increase the multiplicity of azimuths by sailing in multiple directions called multi azimuth or maz hegna and gaus 2002 by deploying sources on multiple vessels to widen the effective receiver array which is known as wide azimuth or waz sukup 2002 and by using a combination of both maz and waz which is rich azimuth or raz howard 2004 in 2006 westerngeco acquired a r

mesozoic evolution of exotic terranes and marginal seas western north america abstract regional terrane analysis has been combined with a global evaluation of plate kinematics to produce a new tectonic model for the mesozoic evolution of western north america and its associated marginal seas the model employs a two tiered data reliability ranking system to resolve conflicts within data sets the lower tier of the ranking system involves the assignment of a numerical rank to paleomagnetic and or paleobiogeographic data based on each data set s reliability the upper tier of the ranking system places the paleomagnetic and paleobiogeographic data in perspective by assigning a relative order of importance to different types of data the most reliable data are considered to be departure rift and arrival collision times that are tightly constrained by independent data sets evidence of subduction and or strike slip motion also ranks high in the master ranking system paleomagnetic and vertebrate paleobiogeographic data come next in the hierarchy followed by invertebrate and floral paleobiogeographic data application of this approach to a case study the baja british columbia controversy has resulted in a coherent model for the entire region results derived from the application of this modelling approach to the problem of the mesozoic assembly of western north america suggest that its evolution may be modeled using a minimum of 57 large terranes oblique convergence may have been the dominant tectonic process along the western north american margin during the mesozoic causing large scale latitudinal transport of many exotic terranes the motions of the terranes produced a number of marginal seas yukonia etc that were short lived but important components of western margin tectonics a combination of collision events side swiping episodes and changes in plate kinematics led to the initiation of several regional tectonic upheavals including the nevadan and sevier orogenies

angle dependent reflectivity by means of prestack migration most present day seismic migration schemes determine only the zero offset reflection coefficient for each grid point depth point in the subsurface in matrix notation the zero offset reflection coefficient is found on the diagonal of a reflectivity matrix operator that transforms the illuminating source wave field into a reflected wave field however angle dependent reflectivity information is contained in the full reflectivity matrix our objective is to obtain angle dependent reflection coefficients from seismic data by means of prestack migration multisource multioffset after downward extrapolation of source and reflected wave fields to one depth level the rows of the reflectivity matrix representing angle dependent reflectivity information for each grid point at that depth level are recovered by deconvolving the reflected wave fields with the related source wave fields this process is carried out in the space frequency domain in order to preserve the angle dependent reflectivity in the im

the effect of el chichon on wind variability in the troposphere stratosphere and mesosphere over alaska data from the poker flat alaska mst radar combined with standard nws balloon observations at fairbanks alaska show that low frequency 3 11 day wind fluctuations within the troposphere and lower stratosphere for the period january march 1983 were noticeably weaker than those for other similar periods between 1979 1984 similar effects can be detected in the higher frequency 1 6 hr and 8 48 hr wind fluctuations obtained from the radar data alone in contrast to these decreases in the troposphere and lower stratosphere wind variations the magnitude of the tidal period 8 48 hr atmospheric wind fluctuations observed by radar in the mesosphere during june july were significantly increased in 1983 relative to surrounding years all of these variations appear to be reasonably well associated with the presence of enhanced aerosol concentrations in the lower stratosphere following the explosion of el chichon volcano in april 1982

a review of gravity wave saturation processes effects and variability in the middle atmosphere this paper provides a review of our current understanding of the processes responsible for gravity wave saturation as well as the principal effects and variability of saturation in the lower and middle atmosphere we discuss the theoretical and observational evidence for linear and nonlinear saturation processes and examine the consequences of saturation for wave amplitude limits momentum and energy fluxes the diffusion of heat and constituents and the establishment of a near universal vertical wavenumber spectrum recent studies of gravity wave variability are reviewed and are seen to provide insights into the significant causes of wave variability throughout the atmosphere

full wavefield migration of vertical seismic profiling data using all multiples to extend the illumination area vertical seismic profiling data can provide a high resolution reservoir image because the receivers are located close to the reservoir and hence the wavefield encounters less distortion in the overburden compared to surface seismic data however conventional migration of vertical seismic profiling data using only upgoing primary wavefields often suffers from poor illumination imaging artefacts and low image reliability especially at image locations away from the well we propose full wavefield migration to image vertical seismic profiling data using the primaries and all orders of surface multiples and internal multiples the downgoing internal or surface multiples are treated as an additional source of illumination in full wavefield migration we aim to estimate a high resolution reflectivity image of the subsurface with this extended illumination the algorithm is recursive in depth like conventional wavefield extrapolation based migration however it incorporates the non linear transmission and scattering effects at each depth level further full wavefield migration is posed as a constrained least squares inversion problem that could be solved using a conjugate gradient method we propose an iterative full wavefield forward modelling engine as the backbone of this inversion scheme the parameter used in the modelling is subsurface reflectivity full wavefield modelling iteratively incorporates the non linearity of the wavefield due to multiple scattering where every iteration utilizes one higher order of scattered wavefields to estimate the subsurface reflectivity in addition the constrained inversion helps in reducing the extrapolation artefacts and provides a high resolution image of the reservoir in this paper we discuss the concept of full wavefield migration and demonstrate its potential as an imaging tool for vertical seismic profiling data using synthetic examples key words vertical seismic profiling true amplitude migration inversion modelling illumination

rocket vapor trail releases revisited turbulence and the scale of gravity waves implications for the imaging doppler interferometry incoherent scatter radar controversy the rate of diffusion of a trimethyl aluminum trail released by a skylark rocket over woomera australia 31 s 137 e in 1969 is interpreted in terms of molecular and turbulent diffusion and is related to the scale of internal atmospheric gravity wave winds implications for disagreement between imaging doppler interferometry and incoherent scatter radar winds are explored

simultaneous na lidar and hf radar observations of vertical velocities in the mesosphere above urbana illinois the first simultaneous na lidar and medium frequency 2 66 mhz doppler radar observations of vertical winds in the mesosphere 79 5 100 km above urbana illinois are reported the lidar and radar systems were operated simultaneously for a 24 h period during january 1989 the lidar measured na density profiles and the radar measured the vertical component of velocity the na density data was used to derive the vertical velocity using the continuity equation this data set provides a unique opportunity to check the consistency of parameters measured by the two very different experimental techniques excellent agreement is found between the radar velocities and the velocities inferred from the na density on the bottomside of the na layer significant differences are found between the velocities obtained with the two techniques on the top side of the na layer possible reasons for this discrepancy are discussed

uplift and denudation of the central alaska range a case study in the use of apatite fission track thermochronology to determine absolute uplift parameters apatite fission track thermochronology aftt on granitic samples collected in the central alaska range in conjunction with geologic constraints from basins to the north nenana basin and south cook inlet of the range is used to constrain the timing amount rate and pattern of surface uplift rock uplift and denudation since the late miocene the conversion from a thermal frame of reference apatite fission track data to an absolute frame of reference with respect to mean sea level which requires constraining the paleoland surface elevation the paleomean annual temperature and the paleogeothermal gradient is evaluated and shown to be viable in the context of an exhumed apatite partial annealing zone paz apatite ages at denali mount mckinley range from 16 ma near the summit 6 km elevation to 4 ma at 2 km elevation a distinctive break in slope in the apatite age profile at an elevation of 4 5 km also marked by a change in confined track length distributions marks the base of an exhumed apatite paz rock uplift and denudation are greatest at denali decreasing southward away from the mckinley strand of the denali fault system as shown by progressively older apatite ages 7 35 ma from a suite of samples along the kahiltna glacier a correlative decrease in topography occurs southward from the fault the central alaska range lies within an arc defined by the denali fault with the highest peaks including denali concentrated at the arc apex patterns of rock uplift and denudation within the central alaska range mimic topography between early and late miocene and possibly earlier the central alaska range was most likely an area of relative tectonic and thermal stability rock uplift denudation and mean surface uplift of the denali region began by the late miocene 5 6 ma being 8 5 km 5 7 km and 2 8 km respectively at average rates of 1 5 km m y 1 km m y and 0 5 km m y the amount of rock uplift denudation and surface uplift decreases to 3 km 2 km and 1 km at little switzerland some 45 km south of the denali fault we conclude that the topographic and rock uplift patterns of the central alaska range the shape and proximity of the mckinley strand of the denali fault to these patterns the timing of the onset of rock uplift and denudation at 5 6 ma and a significant change in relative plate motion between north america and the pacific plates circa 5 6 ma are all inherently related

protolith relations of the gravina belt and yukon tanana terrane in central southeastern alaska metamorphic rocks west of the coast mountains batholith in central southeastern alaska are divided into the gravina belt taku terrane and newly defined ruth assemblage the ruth assemblage comprises metapelite quartzose metaclastic strata quartzite marble felsic metatuff mafic metavolcanic rocks and orthogneiss depositional and emplacement ages of 367 pm 10 ma and 345 pm 13 ma inferred from discordant u pb zircon analyses on felsic metatuff and granodioritic orthogneiss respectively require that at least portions of the ruth assemblage be late devonian and early mississippian in age the assemblage is similar in age and protolith to and thus correlated with the yukon tanana terrane the gravina belt is characterized by upper jurassic and lower cretaceous mafic volcanic rocks and tuffaceous turbiditic clastic strata that unconformably overlie the alexander terrane metamorphic rocks that structurally underlie the taku terrane and ruth assemblage are included in this assemblage trace

nd and sr isotopic characterization of the wrangellia terrane and implications for crustal growth of the canadian cordillera nd and sr isotopic data are reported from samples of most of the major lithologic units of the wrangellia terrane exposed on vancouver island and the queen charlotte islands initial epsilon nd values range from 1 0 to 7 3 and initial 87 sr 86 sr ratios range from 0 70323 to 0 70481 these ratios are similar to those of modern island arcs and demonstrate the unevolved juvenile nature of this terrane these data indicate that wrangellia probably resided in an intra oceanic environment until its accretion to north america nd crustal residence ages for clastic sedimentary rocks of wrangellia mean t cr 0 77 pm 0 33 ga t dm 0 57 pm 0 35 ga are much closer to their stratigraphic ages than is the case for the ages of many other phanerozoic sedimentary rocks thus providing strong evidence for phanerozoic crustal addition to north america early proterozoic crustal components cannot comprise more than about 6 of wrangellia therefore the terrane consists of 94 new mantle d

polarization based wave equation migration velocity analysis in acoustic media abstractthe source extrapolation step in wave equation prestack reverse time migration gives wavefield polarization information which can be used to generate angle domain common image gathers adcigs from seismic reflection data from acoustic media concatenation of p wave polarization segments gives wavefield propagation paths wavepaths which are similar to the raypaths in ray based velocity tomography the adcigs provide residual depth moveout rmo information from which a system of linear equations is constructed for tomography to solve for the velocity ratio used for velocity updating an empirical relation between the rmo data and the velocity ratio updates reduces the amount of computation and is stabilized by the feedback provided by the iterative loop through prestack migration to rmo to velocity update to prestack migration correcting the rmos to flatten the adgigs is the convergence condition synthetic data for a layered model with a fault successfully illustrates the method

first vhf radar measurements of mesopause summer echoes at mid latitudes observations of the summer mesosphere using the stationary sousy vhf 53 5 mhz radar located in the harz mountains of germany 52 n 10 e indicate the presence of very strong radar returns from heights near 85 86 km on some occasions these echoes occur in the form of a layer with a full power half width of less than about 1 km and exhibit an aspect sensitivity of about 1 db deg 1 these features are very similar to those of the so called polar mesopause summer echo pmse known to occur at high latitudes and suggest a common production mechanism

analysis of long period waves using the mesosphere stratosphere troposphere radar at poker flat alaska using the mesosphere stratosphere troposphere radar at poker flat alaska the long period waves greater than 1 5 but less than 36 days in the troposphere lower stratosphere and mesosphere were analyzed for the first 340 days of 1984 a 16 day wave was significant the whole year in all regions resolved by the radar and had maxima in the winter lower stratosphere consistent with the 1 3 rossby normal mode contrary to the theory of the 1 3 normal mode the observed 16 day wave had a maximum in the summer mesosphere two possible explanations are given 1 the 16 day wave was generated in the winter hemisphere then propagated vertically and toward the summer pole following the westerly mean winds and 2 gravity waves from the summer troposphere modulated by the 16 day tropospheric wave propagated vertically into the mesosphere where the resulting momentum deposition varied in a 16 day cycle the period of the 16 day wave varied from 12 to 19 days in the summer mesosphere the quasi 2 day period in the high summer mesosphere migrated from about 51 to 47 hours over midsummer to midautumn

a middle jurassic to early tertiary andean sierran arc model for the coast belt of british columbia regional tectonic features of the western canadian cordillera can be interpreted in terms of middle jurassic accretion of a single composite superterrane stikinia wrangellia alexander to ancestral north america closure of the intervening cache creek bridge river ocean moved the continental edge to a new position west of the accreted superterrane the coast belt is primarily a succession of superimposed middle jurassic to early tertiary magmatic arcs related to prolonged subduction of pacific ocean lithosphere beneath the new north american margin discrete magmatic pulses separated by lulls or periods of relative quiescence successively overprinted the new margin the insular and intermontane superterranes previously viewed as widely separate entities prior to mid cretaceous time were already amalgamated before an initial middle jurassic overprint produced an ancestral coast belt late jurassic to early cretaceous rift related marine basins mid to late cretaceous compressional structures and early tertiary extensional features coincident with the coast belt are subsidiary intraplate attributes that reflect external adjustments in plate motions within a primary subduction related andean magmatic arc

offset and angle domain common image point gathers for shot profile migration prestack depth migration of shot profiles by downward continuation is a practical imaging algorithm that is especially cost effective for sparse shot wide azimuth geometries the interpretation of offset as the displacement between the downward propagating shot wavefield and upward propagating receiver wavefield enables us to extract offset domain common image point cip gathers during shot profile migration the offset domain gathers can then be transformed to the angle domain with a radial trace mapping originally introduced for shot geophone migration the computational implications of this procedure include both the additional cost of multioffset imaging and an implicit transformation from shot geophone to midpoint offset coordinates although this algorithm provides a mechanism for imaging angle dependent reflectivity via shot profile migration for sparse shot geometries the fundamental problem of shot aliasing may severely impact the quality of cip gathers

scattering and dip angle decomposition based on subsurface offset extended wave equation migration abstractan angle dependent reflection coefficient is recovered by seismic migration in the angle domain we have developed a postmigration technique for computing scattering and dip angle common image gathers cigs from seismic images extended by the subsurface offset based on wave equation migration methods our methodology suggests a system of radon transform operators by introducing local transform relations between the subsurface offset image and the angle domain components in addition to the commonly used decomposition of the scattering angle the methodology associates the wave equation migration with dip domain images as well the same postmigration subsurface offset image is used to decompose scattering and dip angle cigs individually or to decompose a multiangle cig by showing simultaneously both angles on the gather s axis we show that the dip angle response of seismic reflections is a spot like signature focused at the specular dip of the subsurface reflector it differs from the well stu

geology of the western flank of the coast mountains between cape fanshaw and taku inlet southeastern alaska the western flank of the coast mountains batholith between cape fanshaw and taku inlet is underlain primarily by jura cretaceous strata of the gravina belt pre permian permian and triassic strata of the taku terrane and mid proterozoic to upper paleozoic rocks of continental margin affinity the continental margin rocks include mid proterozoic to lower paleozoic quartzite and marble of the tracy arm assemblage mid paleozoic metavolcanic and subordinate metasedimentary rocks of the endicott arm assemblage and upper paleozoic quartz rich metaturbidites and metaconglomerate of the port houghton assemblage we suggest that these three assemblages are correlative with components of the yukon tanana terrane which underlies a large region of yukon and eastern alaska rocks of the gravina belt taku terrane and yukon tanana terrane are juxtaposed along west vergent thrust faults of mid cretaceous age and are internally deformed and disrupted along latest cretaceous to early eocene dip slip and possibly strike slip shear zones these rocks and structures together with mid cretaceous to eocene plutons of the coast mountains batholith separate rocks of the alexander wrangellia terrane to the west from rocks of the stikine terrane to the east mid cretaceous thrust faults in the area belong to a system of thrusts that form the inboard margin of the alexander wrangellia terrane from central alaska to northwestern washington the continental margin rocks in the northern coast mountains may be part of the in situ north american margin that has been overthrust by the stikine and adjacent terranes alternatively these rocks may have 1 rifted from and then returned to the north american margin 2 moved 800 km along left lateral or right lateral faults from elsewhere along the north american margin or 3 originated near a continent other than north america

3d angle gathers with plane wave reverse time migration angle domain common image gathers adcigs from reverse time migration rtm provide new tools for imaging complex geologic structures such as salt flank or subsalt areas characterized by multiarrivals compared with common image gathers from kirchoff or beam migration the adcigs from rtm have the advantage of relying on wave propagation providing a more reliable input for tomography or amplitude analysis in practice however most current wide azimuth surveys e g deep water regions of the gulf of mexico are acquired with coarsely sampled shot and receiver locations on the surface which leads to severe angular undersampling this phenomenon is frequently observed on shallow seismic events in high resolution 3d adcigs from common shot rtm in addition because small offsets are frequently not recorded seismic events are missing at small incidence angles in angle gathers we have made a detailed study of the angular sampling issue in 3d angle gathers we then used plane wave rtm to generate 3d angle gathers plane wave rtm with its low cost and automatic angular interpolation is a promising solution for improving the quality of 3d angle gathers

decomposition of multicomponent seismic data into primary p and s wave responses1 inversion of multicomponent seismic data can be subdivided in three main processes 1 surface related preprocessing decomposition of the multicomponent data into primary p and s wave responses 2 prestack migration of the primary p and s wave responses yielding the angle dependent p p p s s p and s s reflectivity of the subsurface 3 target related post processing transformation of the reflectivity into the rock and pore parameters in the target this paper deals with the theoretical aspects of surface related preprocessing which consists of two steps 1 decomposition of the multicomponent data pseudo p and s wave responses into true p and s wave responses 2 elimination of the surface related multiple reflections and conversions

target enclosed seismic imaging seismic reflection data can be redatumed to a specified boundary in the subsurface by solving an inverse or multidimensional deconvolution problem the redatumed data can be interpreted as an extended image of the subsurface at the redatuming boundary depending on the subsurface offset and time we retrieve targetenclosed extended images by using two redatuming boundaries which are selected above and below a specified target volume as input we require the upgoing and downgoing wavefields at both redatuming boundaries due to impulsive sources at the earth s surface these wavefields can be obtained from actual measurements in the subsurface they can be numerically modeled or they can be retrieved by solving a multidimensional marchenko equation as output we retrieved virtual reflection and transmission responses as if sources and receivers were located at the two target enclosing boundaries these data contain all orders of reflections inside the target volume but exclude all interactions with the part of the medium outside this volume the retrieved reflection responses can be used to image the target volume from above or from below we found that the images from above and below are similar given that the marchenko equation is used for wavefield retrieval if a model with sharp boundaries in the target volume is available the redatumed data can also be used for two sided imaging where the retrieved reflection and transmission responses are exploited because multiple reflections are used by this strategy seismic resolution can be improved significantly because target enclosed extended images are independent on the part of the medium outside the target volume our methodology is also beneficial to reduce the computational burden of localized inversion which can now be applied inside the target volume only without suffering from interactions with other parts of the medium

modulation of tropospheric ozone by a propagating gravity wave the modulation of tropospheric ozone by a propagating gravity wave is inferred from the analysis of more than 200 lidar profiles obtained over a 14 hour period during september 3 4 1993 near rollinsville colorado 39 9 n 105 3 w 2 68 km msl periodic fluctuations of up to 30 in the ozone mixing ratios are attributed to a nearly monochromatic gravity wave with a downward phase velocity of 0 08 0 01 m s 1 a mean vertical wavelength of 3 0 0 5 km and an apparent frequency of 1 7 0 4 10 4 s 1 wind profiles from nearby radar soundings suggest that these fluctuations are induced by a gravity wave that propagates from the nw to se with a horizontal wavelength of 180 km these results imply that gravity waves may contribute significantly to the short term 1 day variability of ozone and other trace gases in the troposphere

3d angle domain common image gathers for migration velocity analysis angle domain common image gathers adcigs are an essential tool for migration velocity analysis mva we present a method for computing adcigs in 3d from the results of wavefield continuation migration the proposed methodology can be applied before or after the imaging step in a migration procedure when computed before imaging 3d adcigs are functions of the offset ray parameters we derive the geometric relationship that links the offset ray parameters to the aperture angle and the reflection azimuth when computed after imaging 3d adcigs are directly produced as functions of and the mapping of the offset ray parameters into the angles depends on both the local dips and the local interval velocity therefore the transformation of adcigs computed before imaging into adcigs that are functions of the actual angles is difficult in complex structure by contrast the computation of adcigs after imaging is efficient and accurate even in the presence of complex structure and a heterogeneous velocity function on the other hand the estimation of the offset ray parameters is less sensitive to velocity errors than the estimation of the angles when adcigs that are functions of the offset ray parameters are adequate for the application of interest e g ray based tomography the computation of adcigs before imaging might be preferable errors in the migration velocity cause the image point in the angle domain to shift along the normal to the apparent geological dip by assuming stationary rays i e small velocity errors we derive a quantitative relationship between this normal shift and the traveltime perturbation caused by velocity errors this relationship can be directly used in an mva procedure to invert depth errors measured from adcigs into migration velocity updates in this paper we use it to derive an approximate 3d residual moveout rmo function for measuring inconsistencies between the migrated images at different and we tested the accuracy of our kinematic analysis on a 3d synthetic data set with steeply dipping reflectors and a vertically varying propagation velocity the tests confirm the accuracy of our analysis and illustrate the limitations of the straight ray approximation underlying our derivation of the 3d rmo function

vhf radar measurements of the aspect sensitivity of the summer polar mesopause echoes over andenes 69 n 16 e norway the mobile sousy vhf 53 5 mhz radar located near andenes on the island of andoya in northern norway has been used to measure the aspect sensitivity of the very strong radar returns obtained from near the summer polar mesopause this so called polar mesopause summer echo pmse exhibits substantial aspect sensitivity with angular polar diagrams of the backscatter of 2 10 half width for a two day average during one three hour period in which the power received in the antenna vertical beam was particularly intense the grating lobes of the antenna polar diagram were utilized as additional beams and the power returned at angles of 35 and 38 off zenith was obtained these measurements provide an estimate of the ratio of the specular to the turbulent contributions to the backscatter

multibeam radar observations of winds in the mesosphere we present the results of a statistical analysis of mesospheric wind fluctuations with periods in the range 5 min to 8 hours the data were collected with the sousy vhf radar by observing line of sight doppler velocities sequentially in three directions the temporal spectrum is computed for the vertical fluctuations as well as for line of sight fluctuations on two oblique beams at 3 6 zenith angle separated by 90 in azimuth the observed spectra are shown to be mutually consistent if interpreted in terms of a field of propagating gravity waves using the three beam data the temporal spectrum for the underlying gravity waves is obtained the height dependence of the line of sight component of the mean square wave amplitudes is also studied

use of rtm full 3d subsurface angle gathers for subsalt velocity update and image optimization case study at shenzi field various reverse time migration rtm angle gather generation techniques have been developed to address poor subsalt data quality and multiarrival induced problems in gathers from kirchhoff migration but these techniques introduce new problems such as inaccuracies in 2d subsurface angle gathers and edge diffraction artifacts in 3d subsurface angle gathers the unique rich azimuth data set acquired over the shenzi field in the gulf of mexico enabled the generally artifact free generation of 3d subsurface angle gathers using this data set we carried out suprasalt tomography and salt model building steps and then produced 3d angle gathers to update the subsalt velocity we used tilted transverse isotropy rtm with extended image condition to generate full 3d subsurface offset domain common image gathers which were subsequently converted to 3d angle gathers the angle gathers were substacked along the subsurface azimuth axis into azimuth sectors residual moveout analysis was carried out and ray based tom

3 d shallow water seismic survey evaluation and design using the focal beam method a case study offshore abu dhabi for 3 d shallow water seismic surveys offshore abu dhabi imaging the target reflectors requires high resolution characterization and monitoring of hydrocarbon reservoirs by seismic amplitude versus offset techniques demands high pre stack amplitude fidelity in this region however it still was not clear how the survey parameters should be chosen to satisfy the required data quality to answer this question we applied the focal beam method to survey evaluation and design this subsurfaceand target oriented approach enables quantitative analysis of attributes such as the best achievable resolution and pre stack amplitude fidelity at a fixed grid point in the subsurface for a given acquisition geometry at the surface this method offers an efficient way to optimize the acquisition geometry for maximum resolution and minimum amplitude versus offset imprint we applied it to several acquisition geometries in order to understand the effects of survey parameters such as the four spatial sampling intervals and apertures of the template geometry the results led to a good understanding of the relationship between the survey parameters and the resulting data quality and identification of the survey parameters for reflection imaging and amplitude versus offset applications

climatology of low latitude mesospheric echo characteristics observed by indian mesosphere stratosphere and troposphere radar 1 low latitude mesospheric echo characteristics are investigated using data collected during june 1994 to july 2005 11 years by the indian mesosphere stratosphere and troposphere radar located at gadanki 13 5 n 79 2 e mesospheric echoes are frequently observed during 1000 1530 hrs local time in the height range of 68 78 km and are found to be highly intermittent in both space and time consistent with those reported elsewhere although echoes are observed throughout the year strong seasonal dependence has been observed in both echo occurrence and signal to noise ratio snr percentage occurrence po of mesospheric echoes shows two maxima one during late march equinox and early summer and another during september however corresponding snr suggests that strong echoes occur in both equinoxes with a minimum during winter a clear semiannual variation is observed in po of echoes with a peak occurring during the months of may and october similar variation is observed in snr with peaks in march and september november these features are quite different from those observed at midlatitudes and high latitudes annual oscillation seems to fit well above 78 km and below 68 km although on many occasions occurrence of echo is poor at these heights the ratio of vertical to off vertical beam snr which could be taken as a measure of aspect sensitivity was close to unity at these heights indicating that scattering is due to turbulence generated refractive index fluctuations a positive correlation r 0 37 between po and solar activity is observed whereas a negative correlation r 0 55 is found between snr and solar activity the echo characteristics observed have been compared in detail with those reported from midlatitudes and high latitudes the mechanisms behind the observed features are discussed in the light of mesospheric temperature inversions mtis which are often noticed at this location and wave breaking at these altitudes

a northern cordilleran ocean continent transect sitka sound alaska to atlin lake british columbia the 155 km wide 310 km long sitka sound atlin lake continent ocean transect includes almost all the geologic geophysical and geotectonic elements of the canadian cordillera it crosses the chugach wrangellia alexander stikine and cache creek terranes the gravina and laberge overlap assemblages intrusive and metamorphic belts and neotectonic faults that bound major blocks linear belts of magnetic highs are associated with jurassic and cretaceous granitic belts in wrangellia and the western and central parts of the alexander terrane and with the granitic rocks of the coast plutonic metamorphic complex cpmc the border ranges fault may be expressed at depth on either side of the peril strait fault an enigmatic northeast trending gradient in the cpmc and adjacent rocks separates a regional magnetic low to the northwest from a 300 nt high field to the southeast the bouguer gravity field decreases in broad steps from pacific crust high values to lows at the international boundary with pronounc

vhf radar observations of the dynamics of the summer polar mesopause region observations of the dynamics of the mesopause region over the norwegian island of andoya 69 n 16 e made during 2 days in summer 1987 using the mobile sousy vhf 53 5 mhz doppler radar are reported measurements of the three mean wind components and the 12 and 24 hour horizontal tidal components as well as preliminary estimates of the component of the total upward flux of density normalized horizontal momentum in the sw ne plane and the anisotropy of the horizontal wind are presented for the 83 to 90 km height interval values of the component of the density normalized flux in the sw ne plane for the 10 min to 48 hour period range after the 12 and 24 hour tidal components have been removed vary from 1 m2 s 2 near 84 km to 16 m2 s 2 near 89 km the major contribution is from the 10 min to 12 hour period range the corresponding mean flow acceleration takes a mean value of 136 m s 1 d 1over the 83 90 km height interval the anisotropy is considerable and may suggest the presence of standing waves

vhf radar echoes observed in the summer and winter polar mesosphere over andoya norway the mobile sousy vhf 53 5 mhz radar has been operated on a campaign basis on the island of andoya in northern norway 69 17 n 16 01 e with the aim of investigating the backseattering structures and dynamics of the polar middle atmosphere since november 1983 during winter the occurrence of mesospheric echoes at altitudes from 50 to 90 km is strongly correlated with radio wave absorption events measured with a riometer on 32 5 mhz individual structures are observed for up to 8 hours and in general appear as thin layers separated by 3 5 km with typical maximum signal to noise ratios snrs of 5 25 db many of these are related to variations in the background wind produced by long period gravity waves and tidal period motions and in as much are similar to mesospheric layers at middle and low latitudes in summer the echo region is largely restricted to a height interval from 75 to 95 km with 80 of the echoes occurring in the 80 to 93 km height range and on average it has a distinct maximum in snr near 86 km in the 83 to 91 km height region echoes are detected almost continuously with a minimum occurrence rate of 85 there is a low correlation 0 26 between echo strength and absorption many of the weaker echoing regions those with snrs up to 30 db are related to the background wind shear spectral analysis of time series of both snr and zonal velocity for a period of 9 days reveals 54 24 12 and 8 hour components with the 12 hour component dominating strong bursts in backscattered power tend to occur in the late afternoon and early morning hours so they coincide with the time of maximum westward velocity of the semidiurnal tide this suggests that the bursts are due to an increase in the turbulent intensity produced by dynamical instability of this mode layers consistent with dynamically unstable upward propagating inertio gravity waves are also often observed to move down through the 93 to 80 km height range thus dynamical instability of the semidiurnal tide and long period gravity waves appears to play a major role in determining much of the structure observed in the backscatter region however the strongest summer polar mesopause echoes those with peak snrs greater than 30 db while showing modulation due to the background winds often show no clear relation to the background wind shear this supports the view that the production mechanism of the very strong snrs associated with this layer is different in character from that of winter echoes observed in the polar mesosphere by vhf radars and to those mesospheric layers observed at mid latitudes using the same technique

vhf echoes from the midlatitude mesosphere and the thermal structure observed by lidar observations with a 46 5 mhz radar system at aberystwyth wales 52 n 4 w over the period february 1990 to may 1994 have shown a pronounced seasonal variation in the height range of mesospheric echoes these were observed over the range 64 84 km in all seasons but those at still greater heights were confined to summer months coordinated radar and lidar observations at the same site during 1993 have shown that these intense echoes in summer analogous to polar mesosphere summer echoes pmse are associated with low mesopause temperatures the weaker echoes observed in winter seem to be associated with regions of superadiabatic lapse rates and echoes are observed both above and below the maxima in temperature inversions commonly observed below the mesopause the types of instability implied in these associations of echo height and temperature structure are considered

lower crustal deformation during terrane dispersion along strike slip faults abstract after accretion terranes caught between obliquely converging plates are often displaced several hundreds of kilometers how this motion is accommodated at depth is not well known spurred by our trans alaskan crustal transect tact seismic studies of the yukon tanana terrane alaska i propose that the lower crust responds ductilely to accommodate differential movement between upper crust and upper mantle during margin parallel translation the locations of these ductile regions are dependent on temperature composition and strain rate for geotherms based on moderate surface heat flow 60 90 mwm 2 and reasonable geological strain rates 100 in 3 ma typical lower crustal rocks can deform ductilely the resultant subhorizontal layered fabric should be detectable with seismic techniques two terranes that have experienced hundreds of kilometers of margin parallel translation the yukon tanana terrane sampled by our seismic refraction wide angle reflection profiles and the salinian block california sampled by both seismic refraction and reflection have reflective lower crust both of these terranes have moderate to high surface heat flows have relatively thin crust and are interpreted seismically to be underlain by a quartzo feldspathic lower crust conditions favorable for ductile deformation in the lower crust interpretations of lower crustal layering for these two terranes is based on an increase in lower crustal reflectivity this layering is attributed to tectonic banding consistent with ductile deformation

tectonic framework of the upper paleozoic and lower mesozoic alava sequence a revised view of the polygenetic taku terrane in southern southeast alaska fragments of upper paleozoic and lower mesozoic metavolcanic and metasedimentary sequences of the taku terrane are exposed discontinuously along a narrow belt in southeast alaska and form a distinct lithostratigraphic package in the ketchikan area called the alava sequence crinoidal and argillaceous marble carbonaceous phyllite argillite mafic flows pillow breccia pyroclastic tuff and quartzite characterize the sequence these strata are unconformably overlain by upper jurassic to lower cretaceous fine to coarse grained epiclastic rocks of the gravina sequence the upper paleozoic part of the alava sequence may be correlative with the yukon tanana terrane whereas the middle and upper triassic portion of the alava sequence may represent a metamorphic vestige of the stikine terrane both parts are now exposed on the western flank of the coast plutonic complex in contrast with their correlatives to the east these relations suggest that the stikine and alexander terranes were juxtaposed prior to deposition of the gravina sequence the western boundary between rocks of north american affinity and allochthonous ensimatic crustal fragments of the alexander and wrangellian terranes lies west of the coast plutonic complex

detrital zircon geochronology of the taku terrane southeast alaska u pb geochronologic studies have been conducted on 60 detrital zircon grains from permian and triassic metasandstones of the taku terrane in central southeast alaska the resulting ages are mainly in the range 349 387 ma with five additional grains that yield probable ages ranging from 906 to 2643 ma these ages are similar to the ages of detrital zircons in carboniferous and older rocks of the yukon tanana terrane which lies directly east of the taku terrane in contrast these ages are different from the ages of detrital zircon grains in the alexander terrane to the west the data are accordingly consistent with models in which the taku terrane is a western component of the stikine and yukon tanana terranes and that this crustal fragment is separated by a fundamental tectonic boundary from rocks of the alexander and wrangellia terranes to the west

seismic reflection refraction mapping of faulting and regional dips in the eastern alaska range we present the results of a trans alaska crustal transect tact investigation of the upper 2 5 km of the eastern alaska range in the vicinity of the denali fault based on seismic reflection refraction data laboratory measurements of rock velocities and structural mapping the denali fault is a major dextral slip structure mappable for more than 2000 km separating the wrangellia and adjacent terranes to the south from the yukon tanana and adjacent terranes to the north geologic mapping suggests over 400 km of dextral slip has occurred on the fault yet within the upper 1 5 km of the crust along the tact corridor basement rocks juxtaposed along the denali fault reveal no significant seismic velocity differences although the fault zone itself is associated with a minor lowering of velocity the lack of seismic velocity contrast adjacent to the fault is in agreement with laboratory measurements of elastic wave velocities of samples from terranes bordering the fault laboratory measurements of elastic wave velocities of the metasedimentary mica quartz schists comprising the yukon tanana basement are highly anisotropic because of preferred orientation of mica and predict significant variations in velocity accompanying variations in foliation dip although other interpretations are possible the northward shallowing of foliation dip of basement rocks in the yukon tanana terrane combined with the strong anisotropy associated with these highly foliated rocks can explain an observed northward increase in seismic velocity within this terrane seismic reflections from basement rocks within the yukon tanana terrane may originate from variations in anisotropy with depth and or changes in composition reflecting different proportions of sandstone and shale in the protolith

on the lack of southern hemisphere polar mesosphere summer echoes we report vhf radar observations of the southern high latitude mesopause region using wind profilers that were installed recently on king george island antarctica and ushuaia argentina briefly our observations which were made during january and february 1993 show almost no evidence of so called polar mesosphere summer echoes or pmse since these echoes are a predominant feature of the northern high latitude mesosphere in summer their absence in the southern hemisphere is both surprising and intriguing in this paper we present evidence demonstrating the virtual absence of the echoes and demonstrate that our systems were capable of detecting them had they been present we also outline some of the consequences of this intriguing result which are supported by observed hemispheric differences in polar mesospheric clouds mesospheric temperatures upper atmospheric gravity wave activity and mean circulation patterns

book reviewseismic migration imaging of acoustic energy by wavefield extrapolation a theoretical aspects a j berkhout developments in solid earth geophysics 14a elsevier amsterdam 1982 2nd revised

nd isotopic characterization of metamorphic rocks in the coast mountains alaskan and canadian cordillera ancient crust bounded by juvenile terranes nd isotopic data are reported for 52 samples from the crustal region between the alexander wrangellia terrane and the stikine terrane of the alaskan and canadian cordillera this region is composed of the gravina belt a jurassic cretaceous assemblage of volcanic and clastic sedimentary rocks the taku terrane a terrane of probable early permian to late triassic age and four assemblages of metamorphic rocks that occur to the west of and within the coast mountains batholith the gravina belt has end t values that range from 1 1 to 8 3 similar to values of the underlying alexander terrane and consistent with the interpretation that it is a juvenile belt that formed in a back arc or intra arc basin within the alexander terrane mid cretaceous plutons that were emplaced into the gravina belt have end t values of 4 4 to 5 7 and were probably produced by mantle derived melts that incorporated some alexander terrane crust the taku terrane has end 0 values that range from 5 5 to 3 3 with corresponding depleted mantle model tdm ages of 440 to 1430 ma a mid cretaceous pluton intruding the taku terrane has an end t value of 5 1 a value indistinguishable from those determined for cretaceous plutons intruding the gravina belt metamorphic rocks east of and structurally overlying the taku terrane are divided into the tracy arm assemblage end 0 26 to 0 tdm 800 2450 ma the endicott arm assemblage end 0 10 to 1 3 tdm 950 1500 ma the port houghton assemblage end 0 9 4 to 1 1 tdm 550 1500 ma and the ruth assemblage end 0 9 4 to 2 0 tdm 650 1300 ma these isotopic signatures indicate that a substantial component of each metamorphic assemblage was derived from precambrian continental crust the metamorphic rocks from these assemblages are lithologically very similar to rocks of the yukon tanana ytt terrane of eastern alaska and yukon territory and have such similar u pb detrital zircon ages and nd isotopic compositions to ytt rocks that they are considered part of that terrane possible tectonic scenarios that can explain the present geometry of the ytt with respect to the alexander wrangellia and stikine terranes include 1 the ytt is the upturned stratigraphic basement of the stikine terrane 2 part of the ytt was structurally emplaced beside the stikine terrane in a transpressive tectonic regime 3 the stikine terrane and other inboard terranes are huge sheets that were thrust over the margin of the ytt before the final accretion of the alexander wrangellia terrane