structure of the north indian continental margin in the ladakh zanskar himalayas implications for the timing of obduction of the spontang ophiolite india asia collision and deformation events in the himalaya the collision of india and asia can be defined as a process that started with the closing of the tethyan ocean that during mesozoic and early tertiary times separated the two continental plates following initial contact of indian and asian continental crust the indian plate continued its northward drift into asia a process which continues to this day in the ladakh zanskar himalaya the youngest marine sediments both in the indus suture zone and along the northern continental margin of india are lowermost eocene nummulitic limestones dated at similar 54 ma along the north indian shelf margin southwest facing folded palaeocene lower eocene shallow marine limestones unconformably overlie highly deformed mesozoic shelf carbonates and allochthonous upper cretaceous shales indicating an initial deformation event during the latest cretaceous early palaeocene corresponding with the timing of obduction of the spontang ophiolite onto the indian margin it is suggested here that all the ophiolites from oman along western pakistan bela muslim bagh zhob and waziristan to the spontang and amlang la ophiolites in the himalaya were obducted during the late cretaceous and earliest palaeocene prior to the closing of tethys

local atmospheric forcing during the coastal ocean dynamics experiment 1 a description of the marine boundary layer and atmospheric conditions over a northern california upwelling region as part of the coastal ocean dynamics experiment code meteorological instruments were deployed on buoys and at coastal stations and instrumented aircraft flights and coastal soundings were made to study the three dimensional structure of the marine boundary layer over the continental shelf off northern california during the 1981 and 1982 upwelling seasons these measurements show that after the atmospheric spring transition the airflow in the marine layer is dominated by the north pacific high and the surface wind field over the shelf is characterized by periods of strong 7 15 m s upwelling favorable alongshelf winds lasting for up to 30 days interrupted by shorter periods of much weaker winds directed either equatorward or poleward these periods of weak or reversed winds typically last several days and are called wind relaxations even though they are primarily associated with coastally trapped perturbations of the marine layer along the central and northern california coast and not with a large scale weakening of the north pacific high the atmospheric boundary layer measurements made in code suggest a simple conceptual model which can explain much of the physiology or structure of the marine layer and associated surface wind field during periods of persistent upwelling favorable winds during these periods which represent the quasi steady state regime during the upwelling season the inversion base of the marine layer drops eastward toward the coast until it intersects the coastal mountain range at a height of several hundred meters and the associated thermal wind produces an alongshelf wind jet which has a maximum speed just below the inversion base turbulent mixing tends to homogenize any stratification in the marine layer beneath the jet and couple the jet to the ocean surface producing strong upwelling favorable winds over the shelf day night heating cooling over the narrow coastal strip beneath the marine layer generates a weak cross coast secondary circulation which causes the core of the alongshelf jet to drop in elevation and shift onshore this diurnal change in the marine layer structure explains both the daytime acceleration of the surface winds observed over and near the coast and its offshore decay and the associated offshore increase in the subdiurnal alongshelf wind thus the quasi steady component of the wind stress has a significant curl over the inner shelf during periods of active upwelling this mean summer atmospheric boundary layer regime is occasionally interrupted by synoptic and or mesoscale events or anomalous conditions analysis of the code observations suggests five types of events two primarily synoptic scale conditions which lead to stronger than normal upwelling favorable winds over the shelf and three primarily mesoscale events which lead to wind relaxation about half of the wind relaxation events observed in 1981 and 1982 are believed to be associated with either coastal trapped gravity currents or internal kelvin waves which propagate north ward in the marine layer along the central and northern california coastal mountain range

erosional control on the geometry and kinematics of thrust belt development in the central andes long term erosion rates in the central andes may have influenced not only mean elevation and relief but also the regional geometry and kinematic history of the orogenic belt a drastic along strike erosional gradient exists in the modern central andes from a high erosion region directly north of the 17 5 s bend in the andes to a low erosion region south of the bend this gradient has existed since 10 15 ma based on fission track analyses of middle miocene to holocene denudation and qualitative evaluations of the preservation potential of middle late tertiary volcanic edifices and synorogenic sediment global positioning system velocity data indicate conflicting patterns of active surface shortening north and south of the 17 5 s bend whereas present day shortening in the thrust belt north of the bend is distributed over much of the width of the belt south of the bend it is concentrated near the eastern frontal margin structural data suggest a similar kinematic situation during late miocene to holocene shortening an out of sequence chronology of thrusting in the narrow 200 km wide thrust belt to the north versus a forward breaking sequence of thrusting in the relatively wide 350 km wide thrust belt to the south the long term internal deformation and limited width of the thrust belt north of the bend are attributed to prolonged subcritical thrust wedge conditions induced by rapid erosion rates since 10 15 ma such conditions inhibit thrust front advance and favor distributed deformation within the thrust belt interior in the thrust belt south of the bend a progressive eastward migration of thrusting is interpreted to be the result of long term critical thrust wedge conditions promoted by extremely low rates of denudation since middle miocene time

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

observations of large wind shear above the marine boundary layer near point buchon california abstractparticularly strong winds along the coast of southern california on 24 may 2012 were measured by the wyoming king air research aircraft during the precision atmospheric marine boundary layer experiment preamble the fast flow is bounded laterally by the coastal topography and vertically by a pronounced temperature inversion separating the cool moist air in the marine boundary layer mbl from the warm dry air aloft many studies have investigated the response of this two layer flow to changes in the coastline by invoking hydraulic theory which explains the essential characteristics including changes in mbl depth and the attendant wind processes occurring just above the mbl are important to the low level thermodynamic and kinematic structure observations on this day demonstrate how the large shear above the mbl can impact the lower atmosphere a typical two layer system was observed north of point buchon which was supercritical around point buchon the depth of the mbl decreased and wind i

jurassic and cretaceous paleomagnetic data from the southern alps italy jurassic and cretaceous paleomagnetic data from 46 sites in the venetian alps trento plateau and se lombardian basin have been compiled nine of these site mean directions have been previously published the sites can be divided into four age groups senonian hauterivian barremian kimmeridgian tithonian and callovian oxfordian for three of the age groups positive regional fold tests indicate at the 99 confidence level that the characteristic magnetization components predate the deformation structural mapping in the venetian alps allowed us to assign sites to individual thrust sheets and we observe no significant relative rotation of thrust sheets in the nappe pile indeed we observe remarkable consistency in mean direction throughout the entire sampling area for each of the four age groups the senonian and hauterivian barremian pole positions lie close to coeval poles on african apparent polar wander paths apwps this result is consistent with previous analyses of middle and late cretaceous data from the venetian alps the new jurassic poles deviate significantly from recently published african apwps reflecting either the poor definition of the african apwp in the late jurassic or about 20 anticlockwise rotation of the southern alps relative to africa during early cretaceous time the former of the two possibilities is favored by a new late jurassic early cretaceous pole from north america and by early permian paleomagnetic data from the southern alps which are consistent with coeval african data implying that the movement of the southern alps was similar to that of africa since early permian

the catalina eddy and its effect on pollution over southern california abstract a case study of a catalina eddy during project basin is presented there appears to he a topographic influence in the generation of this eddy detailed surface and upper air data over los angeles illustrate the effect of the eddy on the boundary layer and on the transport of ozone out of the basin isentropic analyses are consistent with visual satellite images of the phenomena the catalina eddy was shown to extend throughout the entire depth of the strong temperature inversion that exist over los angeles with maximum wind speeds within the inversion surface ozone levels downwind of the eddy are shown to vary depending on the local circulations

an active margin across the adriatic sea central mediterranean sea abstract new seismological and structural data from the central adriatic gargano promontory area demonstrate that the current models of an aseismic and slightly deformed adriatic block have to be revised a seismically active deformational belt is mapped along two main fault systems the tremiti islands and mattinata faults moreover geologic and geophysical evidence suggests that a more extensive lithospheric boundary may cut across the central italian peninsula to the tyrrhenian basin

paleomagnetic evidence for a pleistocene counterclockwise rotation of the sant arcangelo basin southern italy new paleomagnetic results from 182 cores sampled at 15 sites in pliocene and pleistocene clayey units in the sant arcangelo basin southern italy and its surroundings are presented they indicate that this area underwent a counterclockwise rotation of 22 after the deposition of the lower pleistocene clays

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

mesoscale simulation of supercritical subcritical and transcritical flow along coastal topography abstract a mesoscale atmospheric model is used to address the characteristics of stratified flow bounded by a side wall along a varying coastline initial froude number values are varied through alteration of marine inversion strength permitting examination of supercritical subcritical and transcritical flow regimes encountering several coastal configurations consistent with shallow water models sharp drops in boundary layer depth and flow acceleration occur in flow rounding convex bends however significant flow response occurs in the stratified layer aloft which is unexplained by conventional shallow water theory the strongest flow acceleration occurs in the transcritical case while regardless of inversion strength the deformation of the isentropes aloft shows general structural similarity advection of horizontal momentum is an important component of the horizontal force balance a simulation having several coastline bends exhibits a detached oblique hydraulic jump upwind of a concave bend t

paleomagnetic study of sicily consequences for the deformation of italian and african margins over the last 100 million years abstract paleomagnetic analysis of cenozoic sediments from the iblean platform 12 sites 100 samples has provided four new poles these data are combined with those available from volcanic series to yield a new apparent polar wander path for stable sicily since the upper cretaceous this curve when compared to a revised curve for africa using a selection of available data points demonstrates a 15 rotation of sicily with respect to africa during the plio pleistocene this rotation accounts for the extensional tectonic regime that prevails in the pelagian sea and which is evidenced by en relais rifts malta pantelleria linosa associated with alkaline volcanism of pliocene and quaternary age paleomagnetic directions from various areas of the italian peninsula also indicate anticlockwise rotations with diverse amplitudes the chronology of these rotations is consistent with a deformation of the western italian margin during progressive suturation from north to south of the corsican sardinian block since the end of the oligocene

palaeomagnetism of some cenozoic sediments cairo fayum area egypt abstract the palaeomagnetic and rock magnetic characteristics of some cenozoic rocks from the cairo fayum area have been investigated a total number of 259 oriented core samples were collected at 32 sites located in rocks of eocene 13 sites oligocene 11 sites and pliocene 9 sites ages most of these rocks carry a weak but stable remanent magnetisation that is principally carried by hematite goethite and magnetite are also found in some samples as subordinate constituents careful thermal demagnetisation successfully enabled the isolation of the characteristic remanent magnetisation normal and reversed polarities that passed a reversal test have been recorded in the three age groups this magnetisation is probably of primary origin and reflects the ages of the rocks the resultant palaeomagnetic poles are considered reliable and represent a good contribution to the african palaeomagnetic database and should help in further refining of the cenozoic apwp for africa

paleomagnetism of jurassic sediments as evidence for oroclinal bending of the inner west carpathians abstract the jurassic carbonates from the krizna nappe contain a pre tectonic characteristic component of remanence the declinations for individual nappe fragments differ and form a fan like pattern they are close to the tectonic vergencies measured in the field which suggests that the arcuate structure of the inner carpathians results from an oroclinal bending of an originally straight belt

tectonics of the akamas and mamonia ophiolites western cyprus magnetic petrofabrics and paleomagnetism abstract the akamas ophiolite is shown to be a distal off axis extension of the main outcrop of cretaceous ophiolite in the troodos complex of cyprus mantle sequence harzburgites of both ophiolites share similarly oriented mantle flow fabrics and the same tertiary magnetizations acquired during exhumation however compared with the troodos mantle sequence rocks the akamas ferromagnetic mineralogy is more oxidized and remanences with lower blocking temperatures were acquired chemically paleopoles calculated from published vectors and our own new data define an apparent polar wander path apwp for the troodos microplate the apwp shows that between 88 and 50 ma the troodos microplate was equatorial and the vertical axis for its 60 anticlockwise rotation was located within the microplate subsequently the microplate drifted northward to 34 n with minor anticlockwise rotation at a reduced rate that requires microplate rotation about a vertical axis located to the west of cyprus in the last 50 ma the allochthonous triassic mamonia terrane docked with the cretaceous troodos terrane in sw cyprus within it disrupted tectonized ophiolite has been regarded as part of a triassic ocean floor or as sheared fragments of cretaceous troodos ophiolite incorporated into the mamonia terrane when it docked with the troodos terrane whatever their provenance their paleomagnetic signals postdate their penetrative deformation and metamorphism and their paleopoles may still be used to track their post strain motion our calculations of paleopoles from published vectors for the mamonia terrane smear along an extension of the apwp for the troodos microplate that is moreover concentric with the troodos microplate this suggests that the paleopole dispersion of the triassic mamonia rocks and their post magnetization disruption occurred during their accretion onto the anticlockwise spinning troodos microplate

a palaeomagnetic study of the upper mesozoic succession in northern tunisia summary the upper mesozoic section from northern tunisia provided an upper jurassic palaeomagnetic pole of 65 2 s 20 3 e ag5 6 1 calculated from the means of normal and reversely magnetized samples from the uppermost callovian oxfordian kimmeridgian and portlandian rocks in general the only cretaceous rocks to yield acceptable results were the few samples collected from fresh outcrops a polarity sequence can be established for the upper jurassic which can be correlated with the oceanic keathley anomaly sequence one consequence of the proposed correlation of the oceanic anomaly with the terrestrial palaeomagnetic sequence is to suggest a slightly different age for the oxfordiankimmeridgian boundary one interpretation of the frequent intermediate directions of magnetization in the cretaceous sequence is that there may be a number of unrecognized short period reversals within the cretaceous and more particularly during the so called cretaceous normal period

coastal jet adjustment near point conception california with opposing wind in the bight abstracttypical spring and summer conditions offshore of california consist of strong northerly low level wind contained within the cool well mixed marine boundary layer mbl that is separated from the warm and dry free troposphere by a sharp temperature inversion this system is often represented by two layers constrained by a lateral boundary aircraft measurements near point conception california on 3 june 2012 during the precision atmospheric mbl experiment preamble captured small scale features associated with northerly flow approaching the point with the added complexity of encountering opposing wind in the santa barbara channel an extremely sharp cloud edge extends south southwest of point conception and the flight strategy consisted of a spoke pattern to map the features across the cloud edge lidar and in situ measurements reveal a nearly vertical jump in the mbl from 500 to 100 m close to the coast and a sharp edge at least 70 km away from the coast in this case it is hypothesized that

evidence of kelvin waves in california s marine layer and related eddy generation abstract evidence suggests that an internal solitary kelvin wave exists in the marine layer along california the marine layer is lifted over the central coast by a weak cyclonic circulation this bump initially 850 m high moves to the north along the coast at 6 m s 1 the undisturbed layer depth is 100 200 m thick the crest height of the wave decreases to 500 m farther north winds under the raised marine layer are southerly the leading edge of the wave is easily followed by satellite as the thickened marine layer is marked by overcast stratus a greatly curved offshore leading edge indicates that nonlinear effects are important offshore scale in the overcast is about 300 km in the south and 50 km in the north surface pressure gradient alongshore is closely related to the marine layer depth the surface wind shifts when the leading and trailing edge of the wave passes northerly wave progression ceases at the sharp bend formed by cape mendocino at this time a vortex is formed in the marine laye

paleomagnetism and the adriatic promontory a reappraisal the geodynamic evolution of the western mediterranean area was influenced strongly by the adriatic promontory of the african plate which can be outlined at present by current seismicity and by facies and ophiolite distributions paleomagnetic results from different parts of the promontory contribute useful information about its past history the evaluation of these data is made difficult by the lack of a well defined apparent polar wander path for africa this has resulted in occasional overinterpretation of some paleomagnetic studies results from umbria and the southern alps cover a long enough period of time to define part of an apw path and support the idea that the promontory moved as an adjunct to the african plate during the late mesozoic and early cenozoic a conservative evaluation of cretaceous paleomagnetic data the most abundant for the promontory as a whole shows no strong evidence for previously proposed counterclockwise rotations of sicily or the southern alps relative to the african plate paleomagnetic data however suggest about 17 degrees counterclockwise rotation of autochthonous gargano and istria and about 25 degrees counterclockwise rotation of allochthonous umbria tectonic rotation of the middle part of the promontory appears to have occurred without significant rotation of its northern and southern extremities

paleomagnetic evidence for rotation of the iberian peninsula and the external betic cordillera southern spain abstract paleomagnetic investigations of jurassic cretaceous and tertiary sites in the external betic cordillera indicate that while the observed remanence vectors have inclinations which are conformable with the expected inclinations for stable iberia declinations deviate significantly these results indicate that 1 the mesozoic limestones of the penibetic have been rotated clockwise with respect to stable iberia and 2 there is a differential rotation between the cretaceous sites dec 61 11 and the jurassic sites dec 38 8 the differential rotation of 23 between the late jurassic and late cretaceous is consistent with the cretaceous anticlockwise rotation of the iberian peninsula with respect to eurasia it follows that during this time period this part of the betic mobile belt waspart of the continental margin of the iberian peninsula a study which was confined to a single unbroken stratigraphic section west of ronda indicates that most of the anticlockwise rotation 20 probably occurred between the cenomanian and the campanian the anticlockwise rotation of these rocks must have been followed by a clockwise rotation of at least 60 to account for the observed clockwise declination anomalies

the marine atmospheric boundary layer jet in the coastal ocean dynamics experiment the vertical and horizontal structure of the atmospheric boundary layer near the northern california coast was investigated during spring upwelling conditions as part of the 1981 coastal ocean dynamics experiment two daytime aircraft flights were devised to measure mean and turbulent quantities for 25 km tracks along and across the continental shelf from 30 to 1200 m altitude the pacific high offshore and an inland thermal low characterized the synoptic situations and equatorward winds resulted which produced intense ocean upwelling the wind profile was found to be jet shaped maximum wind speeds were 25 m s 1 and 16 m s 1 at 400 and 100 m respectively in the two flights above and below the heights of the jet speed maxima the wind speed decreased rapidly sharp density inversions existed at the levels of the peak wind speeds in one flight the inversion also sloped down toward the coast turbulence was effectively confined below the inversions strong zonal temperature gradients above the inversion between the hot land and cool marine air caused a thermal wind for which the wind speed decreased with height below the inversion turbulent stress divergence was large and effective in transferring the horizontal momentum of the wind to the sea slowing the wind there was also a small thermal wind below the inversion but opposite to the one above owing to the well mixed air temperature following the sea surface temperature which was cold at the coast and relatively warmer offshore owing to the upwelling these effects explain the jet shaped wind profile the mean momentum equations show that an acceleration toward the coast can balance the pressure gradient coriolis and turbulent stress divergence forces and there were some observations to support this complete balance was not obtained for the turbulent kinetic energy budget inferred dissipation rates were too large

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

response of the summer marine layer flow to an extreme california coastal bend abstract a summer wind speed maximum extending more than 200 km occurs over water around point conception california the most extreme bend along the u s west coast the following several causes were investigated for this wind speed maximum 1 synoptic conditions 2 marine layer hydraulic flow effects 3 diurnal variations 4 mountain leeside downslope flow 5 sea surface temperature structure and 6 island influence synoptic conditions set the general wind speed around point conception and these winds are classified as strong moderate or weak the strong wind condition extends about point conception reaching well offshore toward the southwest and the highest speeds are within 20 km to the south moderate wind cases do not extend as far offshore and they have a moderate maximum wind speed that occurs over a smaller area in the western mouth of the santa barbara channel the weak wind speed case consists of light and variable winds about point conception each category occurs about one third

a case study of the interaction of the summertime coastal jet with the california topography coast parallel low level jets are commonplace in the marine boundary layer off the west coast of the united states during summer a field study was conducted in early summer of 1997 to document the forcing of boundary layer winds in the near coastal environment off california on 8 june 1997 the wyoming king air collected data along a 350 km stretch of coastal margin from cape mendocino to san francisco in order to examine the interaction between the coastal topography and the low level jet during the course of the flight 32 soundings were conducted the maximum speed of the coastal jet was found near the top of the marine boundary layer at altitudes from 200 to 600 m analysis of the data revealed a westward increase in the height of the marine boundary layer and maximum jet wind speeds strongest jet winds were observed southwest of cape mendocino with a maximum speed of 28 m s21 the coastal jet was characterized by a broad horizontal extent wind maxima were found at distances approximately 30 km to more than 100 km offshore hydraulic features such as jumps and expansion fans have previously been observed downwind of coastal capes and points along the california coast the flow upwind of cape mendocino and point arena was found to be supercritical but the king air data showed that accelerations associated with possible expansion fan phenomena were minimal it is proposed that the sloping inversion at the top of the marine boundary layer and attendant coastal jet are fundamentally the result of a geostrophic adjustment process arising because of the horizontal temperature contrast between the cool ocean and warm continent this view emphasizes that the coastal jet is a ubiquitous large scale feature of the summertime coastal environment terrain induced wind speed variations associated with expansion fans and hydraulic jumps only modulate the primary jet structure

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

the summertime low level jet and marine boundary layer structure along the california coast abstract this paper examines the strong summertime northerly low level jet llj that frequently exists along the california coast the persistent synoptic scale pressure distribution north pacific high to the west thermal low to the east and baroclinity created by the juxtaposition of the heated continent and the cool marine layer produce the mean structure of this llj strong diurnal thermal forcing coupled with topographic influences on the flow modulate the jet structure position and intensity a mesoscale model is used to examine many of the complex facets of the llj flow dynamics several sensitivity studies in addition to a control experiment aid in this investigation principal findings of this study include the following the pronounced east west slope of the marine planetary boundary layer mpbl is not due primarily to colder sst values along the coast dynamically forced low level coastal divergence coupled with synoptic scale divergence appears to be dominant in determining mpbl i

supercritical flow interaction within the cape blanco cape mendocino orographic complex abstract supercritical flow interaction occurring in the marine boundary layer between closely spaced coastal capes is investigated with a mesoscale numerical prediction model as an extension of previous work the u s navy s coupled ocean atmosphere mesoscale prediction system coamps is used to perform idealized model simulations with marine layers of varying upstream froude number to elucidate the different flow responses for a single convex bend the impact upon the supercritical flow of introducing a series of closely spaced coastal bends is then investigated the expansion fan is significantly reduced in magnitude and size by the formation of a compression wave at a blocking concave bend approximately 150 km downstream building upon the idealized marine layer response real data forecasts are then examined for several time periods of supercritical flow interaction between cape blanco oregon and cape mendocino california observations from the coastal waves 1996 cw96 field program were colle

palaeopoles on an expanding earth a comparison between synthetic and real data sets abstract using an ad absurdum reasoning applied to synthetic plates and associated palaeopoles it is possible to prove that if the earth s radius during the early cambrian had been half its present size palaeopoles of the continents or of their particular sub sets should show typical patterns these effects due to the variable curvature of the earth s surface suggest possible tests on the real situation using the available palaeomagnetic data if such effects could be detected on the real earth they could constitute a new clue favouring the hypothesis of an expanding earth the results of applying palaeopoles and ocean floor magnetic anomaly boundary conditions to palaeogeographical reconstructions for a variable radius earth are presented taking into consideration the real continental shapes

possible origins of permian remagnetizations in devonian and carboniferous limestones from the moroccan anti atlas tafilalet and meseta abstract permian overprints have been recognized for several years in different regions of the hercynian chain this process seems to affect not only large internal parts but also external zones of the chain devonian limestones sampled in the tafilalet and maider massifs near erfoud and msissi reveal a strong permian component carried mainly by magnetite scanning electron microscope sem and x ray investigations were performed in order to unravel the origin of this magnetite permian remagnetizations are also present in visean limestones from the meseta isothermal remanent magnetization studies and sem analysis of magnetic separates show that this magnetization is carried mainly by pyrrhotite which could be a result of oxidation of pre existing pyrite

the tibetan side of the india eurasia collision results are reported from the 1980 joint french chinese field expedition in tibet the area covered was from the high himalaya in the south to the region of nagqu 250 km north of yangbajain ophiolites in the zangbo valley represent remnants of the crust of an ocean basin which lay adjacent to the gangdise granodiorite belt in the late mesozoic the ophiolites were thrust to the south onto the cretaceous melange and triassic flysch but the age of this event is unclear in the tertiary sediments of the indian margin and the xigaze basin were folded with steeply dipping cleavage which indicates some north south shortening of the crust however the tertiary volcanic sequence on the lhasa block and further north shows comparatively little folding and thrusting in the quaternary deformation of tibet was characterized by east west extension

deformation of leucogranites of the crystalline main central sheet in southern tibet china abstract towards the top of the main central sheet in southern tibet china leucogranites intrude metamorphic rocks related to rocks of the main central thrust in the himalayas our study shows that the leucogranites suffered a northward shear deformation the significance of this event is discussed in terms of gravity driven decollement of the 10 000 m thick tethyan sedimentary pile over its crystalline basement

synthesis of observations from the precision atmospheric marine boundary layer experiment preamble abstractresearch flights during the precision atmospheric marine boundary layer experiment preamble in southern california during may june 2012 focused on three main features found in the nearshore marine boundary layer mbl the coastal jet 10 flights the catalina eddy 3 flights and the initiation of a southerly surge 1 flight several topics were examined with case studies but results from individual events may not represent typical conditions although these flights do not constitute a long term set of data observations from preamble are used to find common features two main topics are addressed the mbl collapse into the expansion fan and the subsequent transition into the santa barbara channel sbc the midmorning to late afternoon flights occur during moderate to strong northerly wind slope of the mbl in the expansion fan varies and wave perturbations can be embedded within the expansion fan as the cool mbl flow turns into the sbc it moves underneath a deeper and warmer mbl that o

paleomagnetic evidence for no tectonic rotation of the central italy tyrrhenian margin since upper pliocene we present paleomagnetic results from 141 samples collected at 12 sites from plio pleistocene clayey units in the extensional central italy tyrrhenian margin all samples were subjected to stepwise alternating field and or thermal demagnetization positive fold and reversal tests indicate that the results refer to a primary component of magnetization paleomagnetic mean direction declination 358 0 inclination 55 2 95 4 1 reflects the expected geocentric axial dipole field for the locality thus indicating that this sector of the tyrrhenian margin did not undergo any tectonic rotation during the past 4 million years

the marine layer off northern california an example of supercritical channel flow abstract during the spring and summer northerly winds driven by the north pacific high pressure system are prevalent over the northern california continental shelf only interrupted for periods of a few days when weak or southerly winds occur in the course of the coastal ocean dynamics experiment code fixed station and observations were made to describe the temporal and spatial structure of the lower atmosphere and their relation to the strong upwelling of coastal waters in a region extending up to 40 km offshore and 100 km along the coast these observations suggest that atmospheric conditions during the spring and summer usually fall into one of three categories the surface wind can be everywhere weak pattern 1 it can blow at large speeds in a uniform pattern pattern 2 or finally the structure of the northerly surface wind can be complex with large changes in the wind speed and corresponding changes in the surface pressure over short spatial scales pattern 3 the latter pattern which o

age of the plio pleistocene boundary in the vrica section southern italy new palaeomagnetic data from the proposed plio pleistocene boundary stratotype section vrica section southern italy are presented here in order to improve the correlation of these sediments to the magnetic polarity time scale if the interpretation preferred here is correct the boundary falls above the olduvai normal subchron at approximately 1 6 myr

adjustment of the summer marine boundary layer around point sur california an instrumented c 130 aircraft flew over water around point sur california on 17 june 1996 under strong northwest wind conditions and a strong marine inversion patterns were flown from 30 to 1200 m elevation and up to 120 km offshore nearshore marine air accelerated past point sur reaching a surface maximum of 17 ms 21 in the lee winds measured over water in and above the marine layer were alongshore with no significant cross shore flow sea level pressure 10 m air temperature and air temperature inversion base generally decreased toward the coast and were an absolute minimum just downcoast of the wind speed maximum the sea surface temperature also decreased toward the coast but was an absolute minimum directly off point sur the nearcoast air temperature inversion base height was 400 m north of point sur decreased to a minimum of 50 m in the lee of point sur then increased farther to the south wind speeds were at a maximum centered along the air temperature inversion base the fastest was 27 m s 21 in the lee of point sur using a froude number calculation that includes the lower half of the capping layer the marine layer in the area is determined to have been supercritical most of the marine layer had froude numbers between 1 0 and 2 0 with the extreme range of 0 8 2 8 temperatures in the air temperature inversion in the lee were substantially greater than elsewhere modifying the surface pressure gradient the overall structure was a hydraulic supercritical expansion fan in the lee of point sur under the influence of rotation and surface friction the naval research laboratory nonhydrostatic coupled ocean atmosphere mesoscale prediction system coamps indicated a broad supercritical marine boundary layer moving to the south along central california and point sur during the aircraft flight the marine boundary layer thinned and accelerated into the lee of point sur which was the site of the fastest sea level wind speed along central california isotherms dip and speeds decreased in the lee of point sur in the capping inversion well above the marine layer coamps forecasted a compression shock wave initiating off the upwind side of the topography behind point sur and other coastal points to the north evidence from the model and the aircraft supports the existence of an oblique hydraulic jump on the north side of point sur

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

the structure and variability of the marine atmosphere around the santa barbara channel the santa barbara channel is a region characterized by coupled interaction between the lower level atmosphere the underlying ocean and the elevated topography of the coastline the nature of these interactions and the resulting weather patterns vary between summer and winter during summer synoptic winds are largely controlled by the combined effect of the north pacific anticyclone and the thermal low located over the southwestern united states resulting in persistent northwesterly winds a well defined marine atmospheric boundary layer mabl with properties distinct from the free atmosphere above is a conspicuous feature during the summer the wind has different characteristics in each of three zones maximum winds occur in the area extending south and east from pt conception zone 1 where they initially increase as they turn to follow the coast then decrease farther east winds are usually weak in zone 2 located in the easternmost part of the channel offshore from the oxnard plain winds are also weak in zone 3 sometimes reversing to easterly at night in a narrow band located along the mainland coast summer air temperature at the surface follows the sst closely and varies significantly with location summer sea level pressure gradients are large with the lowest pressure occurring on the northeast end of the santa barbara channel diurnal variations are strongest in summer although the modulation is weakest in zone 1 the diurnal variation is parallel to the coast in all of zone 3 but the oxnard plain where it is perpendicular to the coast the height of the marine layer varies between 300 m in late afternoon and 350 m in late morning in winter synoptic conditions are driven by traveling cyclones and sometimes accompanied by fronts these are usually preceded by strong southeast winds and followed by strong northwest winds atmospheric parameters are distributed more uniformly than in summer and diurnal variations are greatly reduced sea level air temperature and pressure are more spatially uniform than in the summer spatial variations in the observed fields in the summer are consistent with a hydraulic model of the mabl as a transcritical expansion fan the summertime situation is governed by a coupled interaction between the atmosphere and the underlying water the ocean influences the density of the mabl to the extent that it behaves distinctly from the free atmosphere above resulting in strong winds polarized in the direction parallel to the coast in turn these winds provoke an upwelling response in the coastal ocean which in part determines the surface properties of the water

aircraft observations and numerical simulations of the developing stage of a southerly surge near southern california abstractsummertime low level winds in the marine boundary layer off the california coast are predominantly from the north this pattern is interrupted periodically by southerly winds and low stratus that can propagate for hundreds of kilometers northward along the coast these events have been termed coastally trapped disturbances coastally trapped wind reversals and southerly surges their forcing has been the subject of extensive study and debate southerly surges remain difficult to forecast yet have a significant impact on coastal activities the beginning stage of a southerly surge on 16 june 2012 was explored during the precision atmospheric marine boundary layer experiment measurements of the horizontal wind and pressure field in the marine layer offshore from cape arguello hours prior to the onset of the surge were made using the university of wyoming king air research aircraft airborne measurements show that a horizontal pressure field is established with higher pressure to the south just pri

airborne measurements of coastal jet transition around point conception california low level winds along the californian coast during spring and early summer are typically strong and contained within the cool well mixed marine boundary layer mbl a temperature inversion separates the mbl from the warmer free troposphere this setup is often represented by a two layer shallow water system with a lateral boundary near a prominent point such as point conception california the fast moving mbl flow is supercritical and can exhibit distinct features including a compression bulge and an expansion fan measurements from the university of wyoming king air research aircraft on 19 may 2012 during the precision atmospheric mbl experiment preamble captured wind in excess of 14ms 21 off of point conception under clear skies and wind 2ms 21 east of san miguel in the california bight a compression bulge was identified upwind of point conception when the flow rounds the point the mbl undergoes a near collapse and there is a spike in mbl height embedded in the general decrease of mbl height with greater turbulence just downwind that is associated with greater mixing through the inversion layer lidar and in situ measurements reveal that transport of continental aerosol is present near the pronounced mbl height change and that there is a complex vertical structure within the santa barbara channel horizontal pressure gradients are obtained by measuring the slope of an isobaric surface observations of wind and pressure perturbations are able to be linked through a simple bernoulli relationship variation of mbl depth explains most but not all of the variation of the isobaric surface

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

nonconventional pangea reconstructions new evidence for an expanding earth abstract new tectonic maps of the globe were examined to determine lineaments which could be important for the reconstruction of the stages in continental displacement but which had not been used in previous reconstructions the use of these data and knowledge of the configuration of the continental plates together with a newly developed more accurate computer programme of lambert s oblique azimuthal equal area projection offer a new insight into the sequence of continental displacement the basis for the reconstructions is best provided by the large crustal fracture identified as the tonga kermadec new zealand macquarie geosyncline from this basis and using tectonic lineament and geological match data reconstructions using the new programme were made with earth radii less than its present value in order to match the data the classic pangea reconstruction and its problems are discussed in the light of this computerized cartographic experiment

supercritical marine layer flow along a smoothly varying coastline abstract a model for hydraulically supercritical atmospheric marine layer flow along a smoothly varying coastline is formulated and solved numerically the model is motivated by a recent comparison of code observations to a simple hydraulic theory which suggested the presence of an expansion fan and a compression jump downstream of topographic features the marine layer is modeled as a homogeneous rotating fluid layer decelerated by surface friction and forced by imposed upper level pressure gradients the equations are solved by a characteristic based gridpoint scheme the results indicate that the expansion fan is a robust feature that persists under most conditions in the present more realistic model but is dramatically altered in structure by the presence of friction while the jump may weaken rapidly offshore due mainly to offshore variations of the layer height upstream of the jump the agreement between observations and model predictions is good enough to suggest that a first order description of

steady state erosion of critical coulomb wedges with applications to taiwan and the himalaya 1 orogenic structure appears to be partially controlled by the addition to and removal of material from the mountain belt by tectonic accretion and geomorphic erosion respectively we developed a coupled erosion deformation model for orogenic wedges that are in erosional steady state and deform at their coulomb failure limit erosional steady state is reached when all material introduced into the wedge is removed by erosion that is limited by the rate at which rivers erode through bedrock we found that the ultimate form of a wedge is controlled by the wedge mechanical properties sole out depth of the basal decollement erosional exponents basin geometry and the ratio of the added material flux to the erosional constant as this latter ratio is increased wedge width and surface slopes increase we applied these models to the taiwan and himalayan orogenic wedges and found that despite a higher flux of material entering the former the inferred ratio was larger for the latter calculated values for the erodibility of each wedge showed at least an order of magnitude lower value for the himalaya relative to taiwan these values are consistent with the lower precipitation regime in the himalaya relative to taiwan and the exposure of crystalline rocks within the himalayan orogenic wedge independently determined rock erodibility estimates are consistent with the accretionary wedge sediments and metasediments and the crystalline and high grade metamorphic rocks exposed within taiwan and the himalaya respectively therefore differences in rock type and climate apparently lead to key differences in the erosion and hence orogenic structure of these two mountain belts

growth and erosion of fold and thrust belts with an application to the aconcagua fold and thrust belt argentina 1 the development of topography within and erosional removal of material from an orogen exerts a primary control on its structure we develop a model that describes the temporal development of a frontally accreting critically growing coulomb wedge whose topography is largely limited by bedrock fluvial incision we present general results for arbitrary initial critical wedge geometries and investigate the temporal development of a critical wedge with no initial topography increasing rock erodibility and or precipitation decreasing mass flux accreting to the wedge front increasing wedge sole out depth decreasing wedge and basal decollement overpressure and increasing basal decollement friction lead to narrow wedges large power law exponent values cause the wedge geometry to quickly reach a condition in which all material accreted to the front of the wedge is removed by erosion we apply our model to the aconcagua fold and thrust belt in the central andes of argentina where wedge development over time is well constrained we solve for the erosional coefficient k that is required to recreate the field constrained wedge growth history and these values are within the range of independently determined values in analogous rock types using qualitative observations of rock erodibilities within the wedge we speculate that power law exponents of 1 3 m 0 4 and 2 3 n 1 characterize the erosional growth of the aconcagua fold and thrust belt this general model may be used to understand the development of mountain belts where orogenic wedges grow as they deform at their coulomb failure limit

airborne observations of a catalina eddy summertime low level winds over the ocean adjacent to the california coast are typically from the north roughly parallel to the coastline past point conception the flow often turns eastward thereby generating cyclonic vorticity in the california bight clouds are frequently present when the cyclonic motion is well developed and at such times the circulation is referred to as a catalina eddy onshore flow south of the california bight associated with the eddy circulation can result in a thickening of the low level marine stratus adjacent to the coast during nighttime hours the marine stratus typically expands over a larger area and moves northward along the coast with the cyclonic circulation a catalina eddy was captured during the precisionatmosphericmarineboundarylayerexperimentinjuneof2012 measurementsweremadeofthe cloud structure in the marine layer and the horizontal pressure field associated with the cyclonic circulation using the university of wyoming king air research aircraft airborne measurements show that the coastal mountains to the south of los angeles block the flow resulting in enhanced marine stratus heights and a local pressure maximum near the coast the horizontal pressure field also supports a south north movement of marine stratus little evidence of leeside troughing south of santa barbara california was observed for this case implying that the horizontal pressure field is forced primarily through topographic blocking by the coastal terrain south of los angeles california and the ambient large scale circulation associated with the mean flow

subduction of asian lithospheric mantle beneath tibet inferred from models of continental collision the relative northward motion of the indian subcontinent that followed the onset of continental collision with asia has produced extensive deformation of the earth s crust giving rise to the world s highest mountains in the himalayan chain and the world s largest high elevation region the tibetan plateau the formation of the broad mountain belt implies that contrary to the original tenets of plate tectonics the lithospheric plates have experienced widespread deformation far from the plate boundary1 several models have been proposed2 6 to explain the manner in which this post collisional deformation is distributed within the continental lithosphere of the indian and asian plates here we propose an alternative model in which subduction of the asian lithospheric mantle develops following the collision of india our model is supported by numerical calculations of crustal deformation and thickening and is consistent with available geological and geophysical data7 9 this picture suggests that lithospheric mantle is not deformed along with the crust and would imply that continental collision zones are more analogous to oceanic subduction zones than was previously believed

paleomagnetism of middle tertiary volcanic rocks from the western cascade series northern california the western cascade series wcs is a 3 5 km thick crudely homoclinal east dipping calcalkaline volcanic sequence of mid oligocene to early miocene age that crops out near the southern tip of the cascade range in northern california the mean direction of remanent magnetization in the wcs is d 4 9 i 57 6 n 53 k 14 4 95 5 3 when compared to a reference direction for the north american craton the wcs direction indicates that the southern cascade range has rotated 14 0 9 0 since the wcs accumulated a difference in mean direction between the lower and upper halves of the wcs suggests that much of this rotation occurred during the late oligocene six other paleomagnetic studies of rock units of an age roughly comparable to the wcs also are available from western oregon northwestern california and southwestern washington all show statistically significant clockwise rotation inclinations of all but one are concordant comparison of directions indicates that the pacific northwest did not rotate as a rigid body but neither did it behave as a collection of small independently rotating domains the amount of rotation found throughout the area increases to the west or northwest suggesting a driving force for rotation operating at the continental margin