nature of the eastern boundary of the rio grande rift from cocorp surveys in the albuquerque basin new mexico reprocessing and synthetic seismic modeling of cocorp profiles across the eastern margin of the rio grande rift at abo pass new mexico suggest that synthetic and antithetic cenozoic normal faults sole into or are truncated by a northwest dipping listric master fault which bounds the eastern side of the basin and reaches a depth of at least 10 km beneath the southern albuquerque basin this fault appears to project toward the surface position of the los pinos cenozoic normal fault which lies basinward of and trends parallel to a mapped laramide duplex thrust zone the los pinos fault may sole into the older thrust reactivating this preexisting compressional structure at depth a lateral change in reflection amplitude and frequency is conspicuous across the eastern rift margin analysis demonstrates that source coupling is the main cause of a much deteriorated signal below the rift basin although complex ray paths and attenuation by the graben fill may contribute

history of quaternary offset and paleoseismicity along the la jencia fault central rio grande rift new mexico abstract the la jencia fault in the central part of the rio grande rift has a remarkable history of segmented movement during the late pleistocene and holocene after a long period of relative quiescence in the pleistocene movement on the reactivated fault created new scarps along five of its six segments movement occurred at varying intervals of several ka to more than 10 ka and at what appears to be decreasing recurrence intervals from the late pleistocene into the holocene surface rupturing has been in such a manner to fill in intervening unbroken segments of the fault and to produce continuous scarps along 30 km of the fault9s 35 km length many of the segments have scarps that show characteristic and statistically significant relations between their height and their maximum slope angle the holocene and upper pleistocene fault scarps were formed by prehistoric earthquakes having richter magnitudes of 6 8 to 7 1 estimated from two relations of earthquake magnitude to displacement and length of ground rupture and moment magnitudes of 6 6 to 6 7 estimated from one relation of magnitude to area of source rupture the geologic and pedologic evidence derived from trenching demands a minimum of five separate instances of faulting during the past 33 ka although as many as six such events are required if movement along different segments of the fault was not synchronous the average recurrence interval is about 7 5 ka in the former case and about 6 ka in the latter case although earthquakes of richter magnitude 6 or greater have not been felt in the rio grande rift in historic times the abundance of quaternary faults suggests that large earthquakes have been prevalent during the quaternary if these faults have histories of offset and paleoseismicity such as has been documented for the la jencia then the region may have a more significant potential for earthquake hazards than previously considered

ocean tides in the northern north atlantic and adjacent seas from ers 1 altimetry twenty months of ers 1 35 day repeat altimeter data containing 18 repeat cycles have been used to estimate the major diurnal and semidiurnal ocean tide signals in the northern parts of the north atlantic and adjacent seas ers 1 provides valuable information when investigating ocean tides owing to the repeated dense spatial sampling however several tidal constituents are extremely difficult to resolve using conventional harmonic analysis with the chosen sun syncronous orbit instead temporal analysis at each crossover location is applied using a modified form of the orthotide formulation which simultaneously solves for the diurnal and semidiurnal species as well as for the annual signal the use of the response formalism ensures that the sun syncronous component s2 can be resolved although this component is frozen in the orbit maps of the m2 s2 and k1 tidal amplitudes and phases in 0 5 0 5 grids are presented and are seen to compare favorably with measurements at 68 pelagic tide gauges provided by the international association for physical sciences of the ocean the major tidal constituents of the ers 1 derived model are also in close agreement with the improved flather 1981 ocean tide model for the northwest european continental shelf area as well as a numerical model for the arctic and nordic seas by gjevik and straume 1989

spectral analysis of highly aliased sea level signals observing high wavenumber ocean phenomena with a satellite altimeter generally calls for along track analyses of the data measurements along a repeating satellite ground track are analyzed in a point by point fashion as opposed to spatially averaging data over multiple tracks the sea level aliasing problems encountered in such analyses can be especially challenging for topex poseidon all signals with frequency greater than 18 cycles per year cpy including both tidal and subdiurnal signals are folded into the 0 18 cpy band because the tidal bands are wider than 18 cpy residual tidal cusp energy plus any subdiurnal energy is capable of corrupting any low frequency signal of interest the practical consequences of this are explored here by using real sea level measurements from conventional tide gauges for which the true oceanographic spectrum is known and to which a simulated satellite measured spectrum based on coarsely subsampled data may be compared at many locations the spectrum is sufficently red that interannual frequencies remain unaffected intra annual frequencies however must be interpreted with greater caution and even interannual frequencies can be corrupted if the spectrum is flat the results also suggest that whenever tides must be estimated directly from the altimetry response methods of analysis are preferable to harmonic methods even in nonlinear regimes this will remain so for the foreseeable future we concentrate on three example tide gauges two coastal stations on the malay peninsula where the closely aliased k1 and ssa tides are strong and at canton island where trapped equatorial waves are aliased

earthquakes of the holocene geologic studies of earthquakes involve mapping of coseismic surface faulting and secondary deformation from historical events trenching and geomorphic analysis to define the timing and size of past earthquakes and investigations of fault zone structure and geometry in both unconsolidated sediments and bedrock this research is now being referred to as paleoseismology seismic geology and earthquake geology since the mid 1970s it has led to some of the most exciting and important contributions to the understanding of earthquake behavior in space and time hanks 1985 allen 1986 the present report is the first of what is hoped will become a regularly contributed summary of the geologic aspects of the study of earthquakes

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

on the choice of orbits for an altimetric satellite to study ocean circulation and tides the choice of an orbit for satellite altimetric studies of the ocean s circulation and tides requires an understanding of the orbital characteristics that influence the accuracy of the satellite s measurements of sea level and the temporal and spatial distribution of the measurements three orbital parameters determine the temporal and spatial sampling characteristics of the satellite the orbital altitude the inclination of the orbit and the repetition period the eccentricity of the chosen orbit should be less than 0 001 to minimize altimeter errors caused by uncertainty in determining the time of each altimeter measurement and to maintain the rate of height variation over the oceans within the limits of the altimeter tracker the choice of the satellite s orbital altitude is constrained by the influences of atmospheric drag and errors in models of the gravity field which decrease with height and the required complexity of the altimeter e g the power and or antenna size required and the effect on satellite systems of radiation from earth s radiation belts which increase with height the choice of inclination is constrained by a desire to measure sea level over all the ocean by the requirement that the acute angle between intersections of the subsatellite track be as large as possible and by the time phasing of the repeat of the satellite s ground track as a function of inclination which determines the aliased frequencies of the measurements of the oceanic tides the choice of repetition period is constrained by tradeoffs between temporal and spatial coverage and by the aliasing of tidal constituents combining the above constraints leads to a set of orbits in a narrow range of altitude and inclination called here the topex poseidon window this window extends from 1100 to 1500 km altitude and 62 to 66 inclination for a 10 day repeat period and consists of three subwindows following lines of equal orbit plane precession there are four choices of orbits within these subwindows that overfly the planned calibration sites at bermuda and dakar these are at 64 80 and 1335 km 62 01 and 1252 km 65 84 and 1255 km and 62 69 and 1173 km these choices have a minimum separation between the aliased frequencies of the eight largest diurnal and semidiurnal tides of one cycle per 4 71 years one cycle per 4 86 years one cycle per 4 87 years and one cycle per 4 27 years respectively thus there will be less than one cycle separation over the nominal 3 years mission of these four choices the first at 64 8 and 1335 km is preferable because it is less sensitive to error in estimating the upcoming solar cycle which will be a maximum during the mission and because it is more nearly centered in terms of inclination than the other choices for other calibration sites other choices would have to be made additional work beyond the scope of this paper will also be necessary to determine if the topex poseidon mission requires a frozen orbit i e an orbit for which there are no long term variations in the eccentricity and argument of perigee of the orbit if a frozen orbit is required then the first and third choices listed above have frozen orbits with an eccentricity that is acceptable for topex poseidon

multimission empirical ocean tide modeling for shallow waters and polar seas 1 a new global ocean tide model named dtu10 developed at technical university of denmark representing all major diurnal and semidiurnal tidal constituents is proposed based on an empirical correction to the global tide model fes2004 finite element solutions with residual tides determined using the response method the improvements are achieved by introducing 4 years of topex jason 1 interleaved mission into existing 18 years 1993 2010 of primary joint topex jason 1 and jason 2 mission time series hereby the spatial distribution of observations are doubled and satellite altimetry should be able to recover twice the spatial variations of the tidal signal which is particularly important in shallow waters where the spatial scale of the tidal signal is scaled down outside the 66 parallel combined envisat geosat follow on and ers 2 data sets have been included to solve for the tides up to the 82 parallel a new approach to removing the annual sea level variations prior to estimating the residual tides significantly improved tidal determination of diurnal constituents from the sun synchronous satellites e g ers 2 and envisat in the polar seas extensive evaluations with six tide gauge sets show that the new tide model fits the tide gauge measurements favorably to other state of the art global ocean tide models in both the deep and shallow waters especially in the arctic ocean and the southern ocean one example is a comparison with 207 tide gauge data in the east asian marginal seas where the root mean square agreement improved by 35 12 22 61 27 07 and 22 65 m2 s2 k1 and o1 for the dtu10 tide model compared with the fes2004 tide model a similar comparison in the arctic ocean with 151 gauge data improved by 9 93 0 34 7 46 and 9 52 for the m2 s2 k1 and o1 constituents respectively

cenozoic thermal mechanical and tectonic evolution of the rio grande rift careful documentation of the cenozoic geologic history of the rio grande rift in new mexico reveals a complex sequence of events at least two phases of extension have been identified an early phase of extension began in the mid oligocene about 30 ma and may have continued to the early miocene about 18 ma this phase of extension was characterized by local high strain extension events locally 50 100 regionally 30 50 low angle faulting and the development of broad relatively shallow basins all indicating an approximately ne sw 25 extension direction consistent with the regional stress field at that time extension events were not synchronous during early phase extension and were often temporally and spatially associated with major magmatism a late phase of extension occurred primarily in the late miocene 10 5 ma with minor extension continuing to the present it was characterized by apparently synchronous high angle faulting giving large vertical strains with relatively minor lateral strain 5 20 which produced the modern rio grande rift morphology extension direction was approximately e w consistent with the contemporary regional stress field late phase graben or half graben basins cut and often obscure early phase broad basins early phase extensional style and basin formation indicate a ductile lithosphere and this extension occurred during the climax of paleogene magmatic activity in this zone late phase extensional style indicates a more brittle lithosphere and this extension followed a middle miocene lull in volcanism regional uplift of about 1 km appears to have accompanied late phase extension and relatively minor volcanism has continued to the present we have estimated geotherms and calculated lithospheric strength curves for the two phases of extension using geologic data to constrain earlier events and geophysical data to constrain the modern geotherm and crustal structure a high geotherm was deduced for early phase extension resulting in a shallow crustal brittle ductile transition and negligible mantle strength the lithosphere cooled after early phase extension resulting in a deeper crustal brittle ductile transition and perhaps more significantly a considerable zone of mantle strength immediately beneath the moho these results indicate that early phase extensional style was controlled by a crustal decollement near the brittle ductile transition which was prevented during late phase extension by significant strength in the uppermost mantle late cenozoic uplift of the rift zone cannot be explained by crustal thinning during extension and geotherm evolution predicted from simple cooling however this uplift does not appear to be restricted to the rift zone and pliocene to recent volcanism and heat flow data suggest that uplift may be caused by magmatic thickening of the crust perhaps unrelated to rifting the complex interrelationship among regional and local prerifting synrifting and postrifting events in the rio grande rift suggests that rifting at least in this region should not be considered in isolation of other geologic events

a 3 d seismic modeling study of the ladron horst near socorrro new mexico three dimensional seismic modeling demonstrates that the intragraben horst like feature imaged on cocorp s socorro abo pass survey in the albuquerque basin new mexico likely corresponds to the northeast plunging continuation of the ladron uplift this accords with the original interpretation which was expounded with reservations that the feature might be a result of side reflections off a nearby exposed basement uplift this domed feature on socorro line 1a referred to hereafter as the ladron horst cannot be a consequence of side reflections from the nearby ladron mountains three dimensional modeling defines a minimum northeastern extent of the ladron uplift in the subsurface confirms some aspects of previous interpretations and offers a new interpretation of the apparent western boundary of the horst second order discontinuities in the reflections off the horst are modeled as normal faults within the subsurface basement uplift

a census of eddy activities in the south china sea during 1993 2007 1 numerous mesoscale eddies occur each year in the south china sea scs but their statistical characteristics are still not well documented a pacific basin wide three dimensional physical biogeochemical model has been developed and the result in the scs subdomain is used to quantify the eddy activities during the period of 1993 2007 the modeled results are compared with a merged and gridded satellite product of sea level anomaly by using the same eddy identification and tracking method on average there are about 32 9 2 4 eddies predicted by the model and 32 8 3 4 eddies observed by satellite each year and about 52 of them are cyclonic eddies the radius of these eddies ranges from about 46 5 to 223 5 km with a mean value of 87 4 km more than 70 of the eddies have a radius smaller than 100 km the mean area covered by these eddies each year is around 160 170 km2 equivalent to 9 8 of the scs area with water depths greater than 1000 m linear relationships are found between eddy lifetime and eddy magnitude and between eddy vertical extent and eddy magnitude showing that strong eddies usually last longer and penetrate deeper than weak ones interannual variations in eddy numbers and the total eddy occupied area indicate that eddy activities in the scs do not directly correspond to the el nino southern oscillation events the wind stress curls are thought to be an important but not the only mechanism of eddy genesis in the scs

timing of tertiary extension in the railroad valley pioche transect nevada constraints from 40ar 39ar ages of volcanic rocks time space relations of extension and volcanism place critical constraints on models of basin and range extensional processes this paper addresses such relations in a 130 km wide transect in the eastern great basin bounded on the east by the ely springs range and on the west by the grant and quinn canyon ranges stratigraphic and structural data combined with 40ar 39ar isotopic ages of volcanic rocks document a protracted but distinctly episodic extensional history field relations indicate four periods of faulting only one of these periods was synchronous with nearby volcanic activity which implies that volcanism and faulting need not be associated closely in space and time based on published dates and the analyses reported here the periods of extension were 1 prevolcanic pre 32 ma 2 early synvolcanic 30 to 27 ma 3 immediately postvolcanic about 16 to 14 ma and 4 pliocene to quaternary the break between the second and third periods is distinct the minimum gap between the first two periods is 2 ma but the separation may be much larger temporal separation of the last two periods is only suggested by the stratigraphic record and cannot be rigorously demonstrated with present data the three younger periods of faulting apparently occurred across the entire transect the oldest period is recognized only at the eastern end of the transect but appears to correlate about 150 km northward along strike with extension in the northern snake range kern mountains area therefore the oldest period also is regional in extent but affected a different area than that affected by younger periods this relation suggests that distinct extensional structures and master detachment faults were active at different times the correlation of deformation periods of a few million years duration across the railroad valley pioche transect suggests that the scale of active extensional domains in the great basin may be greater than 100 km across strike

tidal littoral offshore shelf deposits lower cambrian gog group southern rocky mountains canada abstract nearly 600 m of shallow marine fine to coarse grained quartzites interbedded with shales of the lower cambrian gog group are exposed at the spiral tunnels section kicking horse pass yoho national park facies are defined and interpreted on the basis of sedimentary structures as follows 1 interbedded shale and sandstone pelagic sediments with interbedded coarse grained bottom current deposits 2 massive to laminated shale pelagic sediments 3 conglomerate storm deposits 4 linsen bedded sandstone in shale bedload deposits with pelagic or suspended sediments 5 planar tabular cross bedded sandstone small scale bedload deposits from two dimensional megaripples large scale sand wave or sand ridge deposits 6 trough cross bedded sandstone three dimensional ripple and megaripple deposits 7 low angle to horizontally stratified standstone shoaling wave deposits and 8 massive sandstone well sorted deposits large scale 1 5 m thick lateral accretion epsilon deposits also occur facies trends are interpreted as reflecting the migration and aggradation of offshore sand ridges larger sand ridge complexes are comprised of amalgamated individual sand ridge accumulations progradation of sand ridge complexes yield coarsening upward sequences whereas retreat of sand ridge complexes yield fining upward trends overall the sequences are poorly defined mainly a consequence of the interaction of sand ridge and inter ridge swales theoretical considerations of the early cambrian configuration of continents earth moon separation and paleoceanographic conditions suggest that storms were not that important in the emplacement of the sand ridge complexes major offshore current systems are interpreted as being tidally driven with perhaps a secondary littoral or geostrophic current influence the thick sequence of the section 500 m along with a consistent trace fossil signature suggests that the gog group was deposited under shallow marine offshore shelf settings of a rapidly subsiding passive continental margin this is consistent with the geophysical model for the proto pacific margin which during the early cambrian was characterized by very rapid thermal subsidence

structural evolution of lake malaŵi africa over 2 000 km of seismic reflection profiles have been collected in lake mala i nyasa the southernmost of the east african rift lakes these studies reported here reveal a severely faulted lake floor bounded by rift structures of pliocene or greater age faults that penetrate the uppermost sedimentary units and numerous earthquakes1 attest to continuing activity in the rift inter basinal differences in fault spacing orientation and sedimentary thicknesses have led to a subdivision of lake mala i into four discrete structural provinces these provinces only now are linked by faults attributed to the most recent episodes of extension an evolutionary sequence of 1 initial block faulting and subsidence 2 fragmentation of fault blocks 3 uplift and 4 renewed subsidence and rotation of fault blocks is proposed for the central part of the mala i rift

limited dynamic earthquake triggering in the socorro magma body region rio grande rift new mexico abstract dynamic earthquake triggering the process through which stresses transmitted through the passage of seismic waves can trigger remote faults to fail has been shown to be fairly common throughout the globe and especially in seismically active areas of high heat flow and geothermal activity we explore the possibility of dynamic earthquake triggering around the socorro magma body a feature within the rio grande rift in new mexico that exhibits high heat flow and heightened seismicity because the area fits the environment type in which triggering preferentially occurs we examine 319 global mainshocks with m w 6 0 for the possibility of increased seismicity rates following the passage of the mainshock waves we examine local event locations and origin times relative to mainshock phase arrivals for patterns distinguishing triggering mainshocks from nontriggering mainshocks we find a small triggering response during the time period analyzed unlike following the 2002 denali fault earthquake dfe this small response corresponds to smaller peak dynamic stresses than are found in other triggering studies m w 7 0 at a regional to small teleseismic distance

tectonic implications of subthrust structures revealed by seismic profiling of appalachian ouachita orogenic belt a growing body of deep seismic reflection profiles across the appalachian ouachita orogenic belt reveals subthrust structures which have been previously interpreted as products of continental rifting of later thrusting or of some combination of rifting and thrusting the subthrust features can be placed into three general categories 1 small normal faults which offset lower plate shelf sequences and basement in the foreland and have been attributed to thrust loading perhaps reactivating earlier rifting faults 2 moderately dipping seismic events which lie entirely below lower plate shelf sediments in the foreland interpreted in part as strata deposited during the earlier rifting and 3 hinterland dipping reflection sequences beneath more interior portions of the mountain belt previously interpreted as thrust faults which imbricate sediments and basement related to the earlier rifted margin these interpretations are evaluated through a comparison of reflection profiles across the orogenic belt to previously interpreted seismic lines across modern extensional and compressional settings the comparisons suggest that although some normal fault offsets of lower plate shelf sequences may be original or reactivated rifting faults the dipping events entirely beneath the shelf sequence are more diagnostic of the rifting process these dipping sequences are therefore consistent with previous interpretations that large portions of the earlier rifted margin are preserved in an undeformed state beneath thrust sheets in the appalachian foreland the comparisons also suggest an alternative to interpretations of the hinterland dipping sequences as thrust related in that the sequences are similar in seismic appearance to that of volcanic wedges commonly observed in the narrow zone separating continental from oceanic basement on modern passive margins the implication of this new interpretation is that the actual continent ocean boundary related to the earlier rifted margin may be preserved on the lower thrust plate beneath interior portions of the appalachians and ouachitas

nloadf a program for computing ocean tide loading the loading of the earth by the ocean tides produces several kinds of signals which can be measured by geodetic technique in order to compute these most accurately a combination of global and local models of the ocean tides may be needed the program nloadf convolves the green functions for loading with ocean tide models using a station centered grid with fixed dimensions making it easy to combine different ocean models without overlap in the convolution the program computes all the quantities of interest gravity displacement tilt and strain and includes the case where measurements are made beneath the surface of the ocean

determination of ocean tides from the first year of topex poseidon altimeter measurements an improved geocentric global ocean tide model has been determined using 1 year of topex poseidon altimeter measurements to provide corrections to the cartwright and ray 1991 model cr91 the corrections were determined on a 3 3 grid using both the harmonic analysis method and the response method the two approaches produce similar solutions the effect on the tide solution of simultaneously adjusting radial orbit correction parameters using altimeter measurements was examined four semidiurnal n2 m2 s2 and k2 four diurnal q1 o1 p1 and k1 and three long period ssa mm and m constituents along with the variation at the annual frequency were included in the harmonic analysis solution the observed annual variation represents the first global measurement describing accurate seasonal changes of the ocean during an el nino year the corrections to the m2 constituent have an rms of 3 6 cm and display a clear banding pattern with regional highs and lows reaching 8 cm the improved tide model reduces the weighted altimeter crossover residual from 9 8 cm rms when the cr91 tide model is used to 8 2 cm rms comparison of the improved model to pelagic tidal constants determined from 80 tide gauges gives rms differences of 2 7 cm for m2 and 1 7 cm for k1 comparable values when the cr91 model is used are 3 9 cm and 2 0 cm respectively examination of topex poseidon sea level anomaly variations using the new tide model further confirms that the tide model has been improved

deep structure of the northern rio grande rift beneath the san luis basin colorado from a seismic reflection survey implications for rift evolution abstract a seismic reflection survey by chevron across the san luis basin northern rio grande rift and san juan volcanic field of southern colorado is reprocessed with extended correlation to search for basement structure the trace of the main bounding fault of the basin a high angle normal fault against the sangre de cristo range can be correlated to a wide zone of dipping reflection fabric and soles out at lower crustal depths 26 28 km the deeper reflection fabric represent either broad extensional strain or pre existing structure such as a laramide thrust system the sangre de cristo bounding fault in san luis basin does not sole out at mid crustal depths but continues into the lower crust with a shallower dip the basin architecture in the northern rio grande rift san luis basin provides little if any evidence that the sangre de cristo bounding fault should flatten in a shallow listric fashion this fault geometry is quite similar to the high angle bounding fault in the espanola basin but contrasts with less deeply rooted faults in the albuquerque basin in the central rio grande rift deeper soling out of the sangre de cristo bounding fault could be due to less extension in the northern rio grande rift and or greater strength of the lithosphere compared to the central rio grande rift unequivocal moho reflections beneath the san luis basin cannot be identified probably due to limited signal penetration or a gradational nature of the moho the majority of rift related movement observed on the sangre de cristo bounding fault is post eocene either the western margin of the basin is marked by a tight monocline or a low angle normal fault

40ar 39ar constraints on the temporal evolution of graciosa island azores portugal lava flows spanning the eruptive record of graciosa island azores archipelago and a gabbro xenolith were dated by 40ar 39ar in order to constrain the pleistocene and holocene volcanic evolution of the island the results range from 1 05 ma to 3 9 ka whereas prior published k ar and 14c ages range from 620 to 2 ka the formation of the serra das fontes shield volcano started at minimum 1 05 ma and the magmatic system was active for ca 600 ky as suggested by the formation of the gabbro xenolith by magmatic differentiation evolved magmas making up the serra das fontes serra branca composite volcano were generated at ca 450 ka after a period of ca 110 ky of volcanic inactivity and erosion of volcanic edifices volcanism was reactivated with the formation of the vitoria unit nw platform later the development of the vulcao central unit started with the formation of monogenetic cones located to the south of the serra das fontes serra branca vitoria unit this volcanism became progressively more evolved and was concentrated in a main eruptive center forming the vulcao central stratovolcano with an age older than 50 ka the caldera related to this stratovolcano is older than 47 ka and was followed by effusion of basaltic magmas into the caldera resulting in the formation of a lava lake which ultimately spilled over the caldera rim at ca 11 ka the most recent eruptions on graciosa formed two small pyroclastic cones within the caldera and the pico do timao cone within the vitoria unit at ca 3 9 ka

ocean tidal solutions in antarctica from grace inter satellite tracking data 1 long wavelength components of the oceanic tides surrounding antarctica are estimated directly from three years of grace satellite to satellite ranging measurements an inversion is performed for the major constituents m2 o1 and s2 with k1 excluded because of inadequate phase sampling the tides are parameterized as localized average mass anomalies over areas approximately 3002 km2 other parameters including satellite state adjustments are estimated simultaneously with the tides qualitative comparison of our solutions with in situ tide measurements shows agreement in spatial pattern clearly indicating regions where our adopted prior model is inadequate to exploit these solutions follow on work must assimilate these long wavelength components into a high resolution numerical tidal model

horst faulting in continental rifts abstract horsts in continental rifts are classified into three types on the basis of their structural characteristics type 1 large horsts bounded by near vertical bifurcating faults at rift termini or structural nodes a subset of this type includes horsts comprising an exceptionally uplifted rift shoulder type 2 generally smaller than type 1 type 2 horsts are commonly associated with graben formed in broad zones of crustal extension and thinning in particular they are a feature of both volcanic and sedimentary basins where they are bounded by listric faults type 3 small horsts occurring close to the margins of rift zones formed in a transtensional regime and bounded by near vertical faults the genesis of type 2 and some type 3 horsts is explained by the vening meinesz isostatic model but type 1 horsts require an additional hydraulic force acting at the base of thick fractured crust small scale convection in the asthenosphere could provide this force

cenozoic normal faulting and the shallow structure of the rio grande rift near socorro new mexico migrated versions of a deep seismic section across the albuquerque basin in the southern rio grande rift cocorp abo pass line 1 and socorro line 1 a are used to develop a detailed interpretation of the shallow structure of the rift our interpretation which is consistent with nearby drill hole and gravity data suggests that listric faulting has been the dominant extensional style of faulting in this part of the rift during the early stages of rifting blocks of paleozoic and mesozoic prerift sedimentary strata overlying precambrian crystalline basement were offset and rotated along listric normal faults rooted in the basement syntectonic deposition of thick sections of mid tertiary sedimentary and volcanic rocks filled the developing fault bounded basins these units were continuously rotated during ongoing listric faulting and subsequently buried by later tertiary and quaternary basin fill present surface fault traces may reflect continued movement on the deeper listric faults or a more recent minor episode of shallow normal faulting in contrast to models of crustal extension proposed for nearby areas in the rio grande rift and basin and range province no clear evidence is seen for two time distinct stages of faulting characterized by early closely spaced faulting with large stratal tilts followed by wide spaced high angle faulting the large listric faults flatten into basement or converge upon an apparent detachment surface at a depth of about 5 km posing intriguing questions about the connection between shallow structure and deeper extension within the crust

evidence from rayleigh wave data for magma in an upper crustal dike in the albuquerque belen basin of the rio grande rift new mexico we have found evidence for a dikelike structure in the middle of the albuquerque belen basin of the rio grande rift from our interpretation of two station rayleigh wave amplitude and phase velocity data two dimensional finite element modeling suggests that the structure is about 200 m thick extends vertically from a depth of about 2 1 2 km to at least 20 km and contains material characterized by a shear wave velocity of about 1 2 km s simple physical arguments suggest that the length of the structure may be at least 28 km long nearby high heat flow values historical swarmlike seismicity recent 0 14 ma volcanism and an extensive sill like magma body at midcrustal depths all suggest that the structure is a magma filled dike source characteristics and seismometer response limit our reliable data to the frequency band of 0 08 hz to 0 250 hz thus we cannot tell whether the dike is solely an upper crustal feature or whether it extends through the crust and in to the upper mantle copyright american geophysical union 1987

dnsc08 mean sea surface and mean dynamic topography models 1 the danish national space center data set dnsc08 mean sea surface mss is a new enhanced mapping of the mean sea surface height of the worlds oceans derived from a combination of 12 years of satellite altimetry from a total of eight different satellites covering the period 1993 2004 it is the first global mss without a polar gap including all of the arctic ocean by including laser altimetry from the icesat mission the mean dynamic topography mdt is the quantity that bridges the geoid and the mean sea surface constraining large scale ocean circulation here we present a new high resolution 1 min global mdt called dnsc08 mdt derived from the slightly smoothed difference between the dnsc08 mss and the egm2008 geoid the derivation and quality control of the new dnsc08 mss and dnsc08 mdt is presented in this paper along with suggestions for time period standardization of the mss and mdt models this way a consistent modeling of the interannual sea level variability is carried out before different mss and mdt models are compared altimetric derived physical mss can be converted into an inverse barometer corrected mss by correcting the altimeter range for the inverse barometer effect of the atmosphere on the sea surface height it is demonstrated that it is important to choose the right version of the mss when comparing with hydrodynamic models and gps measured tide gauges

qualitative comparisons of global ocean tide models by analysis of intersatellite ranging data 1 four global ocean tide models are compared in terms of their contribution to gravity recovery and climate experiment grace satellite to satellite tracking residuals the residuals are computed relative to a comprehensive model of earth s time varying gravity including allowance for mass motions in the atmosphere ocean terrestrial hydrology and mantle in addition to tides for each analyzed tide model 4 years of grace range rate data are processed range and range acceleration residuals are tidally analyzed by geographic location all four global tide models are shown to be error prone in various ways leaving tidally coherent residuals especially in polar regions but also in some lower latitude regions considerable power in the solar semidiurnal s2 tide in low latitudes suggests errors in our adopted model of atmospheric tides which is based on 3 hourly european centre for medium range weather forecasts operational analyses anomalies in the 2 tidal constituent over some shallow seas suggest the presence of unmodeled nonlinear compound tides in this case 2ms2 similarly anomalies in the nonlinear m4 tide are seen if this constituent is omitted from the models errors in assumed seawater density may be contributing to some residuals

structure of the southern keweenawan rift from cocorp surveys across the midcontinent geophysical anomaly in northeastern kansas this is the published version copyright 1984 american geophysical union all rights reserved

shallow water tides in the northwest european shelf region from topex poseidon altimetry during recent years the accurate measurements from the topex poseidon satellite have improved global ocean tide models considerably however these global ocean tide models are still not accurate enough on the continental shelves for detailed oceanographic studies the need for increasing accuracy in shelf regions calls for inclusion of more than just semidiurnal and diurnal constituents in future global ocean tide models this is because a considerable part of the tidal variability on the shelves is caused by shallow water constituents one example is the m4 constituent which exceeds 50 cm at several locations on the northwest european shelf so far topex poseidon has not been considered for resolving these constituents mainly owing to its coarse ground track resolution reliable empirical estimates of several major shallow water constituents can be obtained from topex poseidon by combining along track and crossover observations estimates of the major shallow water constituents for the northwest european shelf m4 m6 and ms4 are presented in this study and compared with tide gauges and existing hydrodynamic models

accuracy assessment of ocean tide models around antarctica 1 accurate ocean tide models for the circum antarctic seas are required to remove unwanted signals from floating ice elevation and space borne time variable gravity measurements e g grace we present accuracy assessments for several global csr4 fes2004 fes99 got00 2 nao 99b tpxo6 2 and antarctic cada00 10 and cats02 01 ocean tide models using coastal and pelagic tide gauges gravimetric data and gps records of ice shelf surface elevation the accuracies of csr4 and nao 99b are poor in the ice shelf regions the optimum model for the entire circum antarctic seas is tpxo6 2 with a root mean square deviation of 5 7 cm 40 lower than the next best model fes2004 the main exception is the filchner ronne ice shelf where cada00 10 and cats02 01 most accurately represent observations from two sites near the rutford ice stream grounding line

multi satellite ocean tide modelling the k1 constituent abstract all major ocean tide constituents are aliased into signals with periods less than 90 days from topex poseidon altimetry except the k 1 constituent the aliased k 1 has a period of 173 days consequently it might be confounded with height variations caused by the semiannual cycle having a period of 183 days the correlation between k 1 and the semiannual signal has been investigated both locally and globally using combinations of t p ers 1 and geosat observations subsequently two empirical methods have been investigated to improve the mapping of k 1 from multiple satellites at high latitudes where the presence of crossing tracks cannot separate k 1 from the semiannual signal from topex poseidon the importance of including ers 1 and geosat observations was demonstrated a comparison with 29 pelagic and coastal tide gauges in the southern ocean south of 50 s gave 5 59 m 2 2 27 s 2 and 5 04 k 1 cm rms agreement for fes95 1 ocean tide model the same comparison for the best empirical estimated constituents based on topex poseidon ers 1 geosat gave 4 32 2 21 and 4 29 cm for m 2 s 2 and k 1 respectively