slab induced waveform effects as revealed by the taiger seismic array evidence of slab beneath central taiwan here we tackle a tectonically important question the upper mantle velocity structure beneath central taiwan with seismically interesting observations receiver side slab waveform effects we use teleseismic p waveforms of the ns broadband array deployed by the taiger project to examine patterns of variation in arrival time pulse width and amplitude measuring the first two by gaussian fitting and contrast measurements of earthquakes to the southeast se earthquakes with those of one sumatra earthquake in order to focus on upper mantle heterogeneities overall variation patterns as a function of earthquake are compatible with ray tracing predictions relative reduced arrival times and amplitudes at central taiwan stations suggest the existence of a deep aseismic slab below from simulations of 2 d wave propagation we conclude that lateral heterogeneity of crust and uppermost mantle primarily contributes to variations in arrival time and only secondarily to variations in amplitude and pulse width furthermore discrepancies between source side and receiver side waveform effects where the latter are not always amplitude reduced are explained by constructive interference between the fast and slow phase thus the use of full waveform information can provide independent constraints to complement results of previous studies a future extension will be to incorporate s waves and apply waveform inversion to yield quantitative constraints

active shoreline of ontario lacus titan a morphological study of the lake and its surroundings of more than 400 filled lakes now identified on titan the first and largest reported in the southern latitudes is ontario lacus which is dark in both infrared and microwave here we describe recent observations including synthetic aperture radar sar images by cassini s radar instrument 2 cm and show morphological evidence for active material transport and erosion ontario lacus lies in a shallow depression with greater relief on the southwestern shore and a gently sloping possibly wave generated beach to the northeast the lake has a closed internal drainage system fed by earth like rivers deltas and alluvial fans evidence for active shoreline processes including the wave modified lakefront and deltaic deposition indicates that ontario is a dynamic feature undergoing typical terrestrial forms of littoral modification

active continental subduction and crustal exhumation the taiwan orogeny a tectonic model of active continental subduction followed by crustal exhumation is proposed to explain the orogeny in taiwan the subducted crust is represented by a low velocity zone dipping eastwards beneath the major part of taiwan while the exhumed crust is marked by a high velocity bulge high heat flow and absence of seismicity beneath the eastern central range the boundary between the subducted and exhumed crust has been identified from surface geology and analyses of thermal history across the central range the dynamic force that has been driving the exhumed crust is identified by results from focal mechanisms structural geology and geodetic survey in the eastern central range such a tectonic model may provide a good explanation for the evolution of the taiwan orogeny as well as an active case for studying other long extinct systems of continental subduction and exhumation

bathymetry and absorptivity of titan s ontario lacus ontario lacus is the largest and best characterized lake in titan s south polar region in june and july 2009 the cassini radar acquired its first synthetic aperture radar sar images of the area together with closest approach altimetry acquired in december 2008 these observations provide a unique opportunity to study the lake s nearshore bathymetry and complex refractive properties average radar backscatter is observed to decrease exponentially with distance from the local shoreline this behavior is consistent with attenuation through a deepening layer of liquid and if local topography is known can be used to derive absorptive dielectric properties accordingly we estimate nearshore topography from a radar altimetry profile that intersects the shoreline on the east and west sides of the lake we then analyze sar backscatter in these regions to determine the imaginary component of the liquid s complex index of refraction the derived value 6 1 1 3 1 7 10 4 corresponds to a loss tangent of tan 9 2 2 0 2 5 10 4 and is consistent with a composition dominated by liquid hydrocarbons this value can be used to test compositional models once the microwave optical properties of candidate materials have been measured in areas that do not intersect altimetry profiles relative slopes can be calculated assuming the index of refraction is constant throughout the liquid accordingly we construct a coarse bathymetry map for the nearshore region by measuring bathymetric slopes for eleven additional areas around the lake these slopes vary by a factor of 5 and correlate well with observed shoreline morphologies

elasticity of magnesite and dolomite from a genetic algorithm for inverting brillouin spectroscopy measurements a hybrid numerical scheme that simultaneously retrieves single crystal elastic constants cij and wave normal directions is applied to determine the elasticity of natural samples of both magnesite and dolomite as measured by brillouin spectroscopy at ambient conditions the scheme incorporates the genetic algorithm ga as a global searching tool and a final local linearization to overcome the intrinsic difficulty of fitting non linear christoffel s equation to compensate for the stochastic nature of ga especially when the misfit function of the problem manifests highly rugged topography in the model space the procedure was repeated for multi runs this is to assure that the best solution is captured by examining the statistics among the runs that yield the fittest solutions the resultant elastic constants c11 c12 c13 c14 c33 and c44 are respectively 260 3 2 6 82 9 4 5 59 6 3 1 20 1 1 3 153 7 4 1 and 59 7 1 4 gpa for magnesite for dolomite c11 c12 c13 c14 c15 c33 and c44 are respectively 204 1 2 2 68 5 3 4 45 8 4 4 20 6 1 3 6 7 1 5 97 4 5 3 and 39 1 1 5 gpa unfortunately the results for dolomite are statistically non unique in the numerical calculation the above data were adopted because the cleavage plane of dolomite was used in the experiment the results for both magnesite and dolomite are compatible with those determined earlier by ultrasonic methods it is anticipated that the new method developed in the present study should be applicable to less symmetric crystals since there are no particular assumptions on the crystal symmetry embedded within the scheme 2005 elsevier b v all rights reserved

anisotropy beneath an active collision orogen of taiwan results from across islands array observations 1 we examined shear wave splitting in sks phases from a large event recorded by a temporary array across southern taiwan the span extends from the western plain to the east coast we applied particle motion and cross correlation methods to estimate its polarization directions and delay times analysis shows clear evidence of splitting except stations on the east coast the fast split shear wave along this transect are approximately parallel to the strike of the mountain belt ne sw the delay times show a short wavelength variation and are well correlated to the surface geology the largest split time is about 1 6 sec located at eastern central mountain range and indicates its possible mantle origin implications suggest that anisotropy is related to the collision tectonics which built the taiwan islands and that this tectonic compression involved the lithosphere and is characterized by a strong coherent deformation of the upper mantle and the crust

quantitative geomorphic modeling of martian bedrock shorelines 1 multiple researchers have identified shoreline features such as scarps on mars these features occur in both paleocrater lake basins and the northern hemispheric basin here we use a simple numerical model to investigate the viability of forming martian bedrock scarps via wind wave action we use the pierson moskowitz equation modified for martian gravity to generate wave fields under a variety of wind speeds and use those wave fields to drive a terrestrial bedrock shore erosion model modified for martian conditions our results indicate that even with conservative assumptions for the key parameters of wind speed slope and substrate it is difficult to form shoreline features of sufficient magnitude to be captured by spacecraft imaging under many combinations of reasonable initial conditions no shoreline features are formed in cases where shoreline features do develop the largest equilibrium scarp height is 5 m and the shorelines require nearly 2000 model years to form in light of these results and the difficulty of maintaining warm wet climates on mars it seems unlikely that the putative shoreline features identified in images are a result of water wave erosion and alternative hypotheses such as ice cover should be entertained

the growth of wind waves in titan s hydrocarbon seas abstract ocean wave growth on titan is considered the classic sverdrup munk theory for terrestrial wave growth is applied to titan and is compared with a simple energy balance model that exposes the effect of titan s environmental parameters air density gravity and fluid density these approaches are compared with the only previously published semi empirical model ghafoor n a l zarnecki j c challenor p srokosz m a 2000 j geophys res 105 12 077 12 091 hereafter g2k and allow the impact of various parameters such as atmospheric density to be transparently explored our model like g2k suggests fully developed significant wave heights on titan h s 0 2 u 2 where u is the windspeed si units in dimensionless terms this is rather close to h s 0 2 u 2 g a rule of thumb previously noted for terrestrial waves we find various datasets where the prefactor varies by 2 it is noted that liquid and air densities affect the growth rate of waves but not their fully developed height for 1 m s winds wave amplitude reaches 0 15 m 75 of fully developed with a fetch of only 1 km rather faster than predicted by g2k liquid viscosity has no major effect on gravity wave growth but does influence the threshold windspeed at which gravity capillary waves form in the first place the model is used to develop predicted ranges for wave height to guide the design of the titan mare explorer time a proposed discovery class mission to float a capsule on ligeia mare in 2023 for the expected maximum 1 m s winds a significant wave height of 0 2 m and wavelength of 4 m can be expected assuming that wave heights follow rayleigh statistics as they do on earth then given the wave period of 4 s individual waves of 0 6 m might be encountered over a 3 month period for predicted titan winds at kraken mare significant wave heights may reach 0 6 m in the peak of summer but do not exceed the tidal amplitude at its northern end consistent with the area around mayda insula being a tidal flat while elsewhere on kraken and ligeia and at ontario lacus shorelines may be wave or tidally dominated depending on the specific location

cassini radar data estimation of titan s lake features by means of a bayesian inversion algorithm the analysis derived from the cassini sar imagery reflects the complex titan s surface morphology with a wide range of backscattering coefficients and peculiar features such as periodic structures and lakelike features which were observed on july 22 2006 when polar areas were first imaged and are considered good candidates to be filled with liquid hydrocarbons in this paper the modeling description of lakes is addressed by means of a double layer model which considers an upper liquid hydrocarbon layer and a lower layer compatible with the radar response of the neighboring areas this model is introduced into a bayesian framework for the purpose of inferring the likely ranges of some parameters and in particular of the optical thickness of the hypothesized liquid hydrocarbon layer and of the wind speed the main idea is to use the information contained in the parameter probability density function which describes how probability is distributed among the different values of parameters according to the various scenarios considered the analysis carried out on lakes and surrounding areas on flybys t16 and t19 determines optical thickness values from 0 2 to 6 for t25 flyby the inferred values of optical thickness indicate that a limit value of optical thickness may be 9 considering that beyond these values the signal from the bottom layer is completely attenuated information on the wind speed on the upper layer can be inferred the found mean values of wind speed are around 0 2 0 3 m s according to different hypotheses on the upper layer dielectric constant

wind driven surface waves on titan the surface of titan represents the largest surface area in the solar system essentially unexplored although recent observations from hubble space telescope and ground based telescopes using adaptive optics have given perhaps the first low resolution indications of its nature whilst early models citing global oceans have been all but abandoned substantial bodies of liquid up to several hundred kilometers in extent are not precluded if such reservoirs do exist then in the presence of any surface winds it is expected that wind driven surface waves will be generated as on earth gravity remains the dominant controlling factor for such waves with surface tension and viscous effects only becoming significant below wavelengths of several centimeters empirical models used for terrestrial wind driven sea waves are adapted to investigate the properties of such waves on titan using predicted parameters for titan s liquids significant wave height peak period wavelength phase speed and wave steepness are predicted as a function of wind speed and liquid body extent it is found that waves will grow to a limiting height limiting wavelength and limiting period which are all inversely proportional to gravity the limiting significant wave height under the action of a 1 m s 1 titan wind over 50 km for example is predicted to be 0 2 m compared to 0 02 m on earth under similar circumstances more interesting however is the wave growth prior to this limiting value a useful visualization is that surface waves on a titan sea arising from surface wind speeds of 0 3 and 1 m s 1 will resemble in scale waves on earth generated by terrestrial winds of 1 and 3 m s 1 respectively these particular titan waves will have nearly 3 times the period and travel almost 3 times slower than the terrestrial waves however the wave parameters predicted in this work have potential surface mission implications for the european space agency s huygens probe which will land on titan in 2004 conversely their measurement by instruments on board huygens and nasa s cassini spacecraft could yield important planetological information

a radar map of titan seas tidal dissipation and ocean mixing through the throat of kraken abstract we present a radar map of the titan s seas with bathymetry estimated as proportional to distance from the nearest shore this naive analytic bathymetry scaled to a recent radar sounding of ligeia mare suggests a total liquid volume of 32 000 km 3 at the low end of estimates made in 2008 when mapping coverage was incomplete we note that kraken mare has two principal basins separated by a narrow 17 km wide 40 km long strait we refer to as the throat tidal currents in this strait may be dramatic 0 5 m s generating observable effects such as dynamic topography whirlpools and acoustic noise much like tidal races on earth such as the corryvreckan off scotland if tidal flow through this strait is the dominant mixing process the two basins take 20 earth years to exchange their liquid inventory thus compositional differences over seasonal timescales may exist but the composition of solutes and thus evaporites over croll milankovich timescales should be homogenized

sediments of the lomonosov ridge and makarov basin a pleistocene stratigraphy for the north pole sediments of 16 short cores taken as part of the lomonosov ridge experiment lorex can be organized into the first pleistocene stratigraphy for the north polar region this stratigraphy can be correlated with stratigraphic units described from the alpha chukchi areas 300 km distant the lorex cores include at least 12 sedimentary subunits differentiated by texture color and carbonate content the units are silty and arenaceous lutites and are principally glacial marine benthic and planktonic foraminifera degree of bioturbation and fe mn micro nodule abundance generally are positively correlated foraminifera in core b 8 from 3 956 m in the makarov basin may have been affected by ccd fluctuations that did not affect fossils in core b 24 from 1 600 m on the crest of the lomonosov ridge the 12 stratigraphic units were deposited during the late pleistocene and represent the same major sedimentary events as those of stratigraphic units k l and m of the amerasian basin this correlation is excellent evidence for the remarkable and widespread uniform depositional style of glacial marine sediment times of major glacial ice transport reflect deglaciation events in the central arctic ocean surface currents during deglaciation transport glacial ice in a more or less uniform pattern over at least 50 of the arctic ocean even thin sedimentary units deposited during relatively long time intervals are correlated over 500 000 km 2

smoothness of titan s ontario lacus constraints from cassini radar specular reflection data 1 cassini radar altimetry data collected on the 49th flyby of titan 2008 december 21 over ontario lacus in titan s south polar region provides strong evidence for an extremely smooth surface with less than 3 mm rms surface height variation over the 100m wide fresnel zone histograms of the raw radar echoes imply a mirror like specular reflection of the transmitted signal such an echo is possible only if the surface is extremely flat relative to our 2 2 cm wavelength the 3 mm upper bound follows from analyzing the strength of the specular return which declines exponentially with increasing surface height variance in this experiment the strength of the echo was larger than expected severely saturating the receiver we developed a method to partially correct the echoes for the distortion incurred while the implied mm scale smoothness is not proof that the surface is liquid it is unlikely that a solid surface is so smooth

the lakes of titan the surface of saturn s haze shrouded moon titan has long been proposed to have oceans or lakes on the basis of the stability of liquid methane at the surface1 2 initial visible3 and radar4 5 imaging failed to find any evidence of an ocean although abundant evidence was found that flowing liquids have existed on the surface5 6 here we provide definitive evidence for the presence of lakes on the surface of titan obtained during the cassini radar flyby of titan on 22 july 2006 t16 the radar imaging polewards of 70 north shows more than 75 circular to irregular radar dark patches in a region where liquid methane and ethane are expected to be abundant and stable on the surface2 7 the radar dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes including associated channels and location in topographic depressions some of the lakes do not completely fill the depressions in which they lie and apparently dry depressions are present we interpret this to indicate that lakes are present in a number of states including partly dry and liquid filled these northern hemisphere lakes constitute the strongest evidence yet that a condensable liquid hydrological cycle is active in titan s surface and atmosphere in which the lakes are filled through rainfall and or intersection with the subsurface liquid methane table

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

upper mantle seismic velocity anomaly beneath southern taiwan as revealed by teleseismic relative arrival times article i nfo probing the lateral heterogeneity of the upper mantle seismic velocity structure beneath southern and central taiwan is critical to understanding the local tectonics and orogeny a linear broadband array that transects southern taiwan together with carefully selected teleseismic sources with the right azimuth provides useful constraints they are capable of differentiating the lateral heterogeneity along the profile with systematic coverage of ray paths we implement a scheme based on the genetic algorithm to simultaneously determine the relative delayed times of the teleseismic first arrivals of array data the resulting patterns of the delayed times systematically vary as a function of the incident angle ray tracing attributes the observed variations to a high velocity anomaly dipping east in the mantle beneath the southeast of taiwan combining the ray tracing analysis and a pseudo spectral method to solve the 2 d wave propagations we determine the extent of the anomaly that best fits the observations via the forward grid search the east dipping fast anomaly in the upper mantle beneath the southeast of taiwan agrees with the results from several previous studies and indicates that the nature of the local ongoing arc continent collision is likely characterized by the thin skinned style

wind driven circulation in titan s seas circulation in titan s seas forced by wind is simulated by an ocean circulation model using surface wind data predicted by a global circulation model wind driven circulation is insignificant throughout much of the annual cycle but becomes significant from late spring to late summer when the wind stress becomes strong the large scale circulation in summer is predominantly southward near the sea surface and northward near the sea bottom the sea surface current can get as fast as 5 cms 1 in some areas titan s rotation affects the vertical structure of sea currents in the form of an ekman spiral if the wind is strong the maximum wind setup at the shores is of the same order of magnitude as the tidal range wind stirring may reduce thermal stratification in summer but may be unable to destroy stratification of methane rich liquids on top of ethane rich liquids that can result from imbalances between evaporation and precipitation

classification of sedimentary furrows and a model for furrow initiation and evolution sedimentary furrows are longitudinal bed forms which form in fine grained cohesive sediments of the deep sea floor as well as in similar sediments in estuaries and in large lakes deep sea furrows have been observed where bottom currents often flow in one direction at 5 to 20 cm sec currents are much stronger greater than 50 cm sec in furrowed estuarine environments but sediment accumulation rates are higher a review of furrows studied in a variety of locations and environments suggests that these bed forms fall into two broad morphological classes those developed in muddy cohesive sediments tend to have steep walls and flat floors while those developed in carbonate rich cohesive sediments are broad and have gently sloping walls at abyssal depths furrows can often be detected by their distinctive echo patterns on 3 5 khz echo sounders a series of similar evenly spaced hyperbolic echoes which often have their apices tangent to the sea floor however different furrow cross sections may generate distinctive hyperbolic echo patterns a model for furrow initiation and development in muddy cohesive sediments suggests that furrows develop in depositional environments swept by recurring directionally stable and episodically strong currents furrows are initiated when secondary circulations in the boundary layer align coarse generally light debris in sand ribbon like bed forms as the coarse light sediments move along the sea floor they abrade small longitudinal troughs into the muds the grooves may fill in during intervals between strong current events if sedimentation rates are too high once a furrow is established on the sea floor further development may be controlled by the balance between sediment deposition and erosion where deposition occurs continuously and erosion occurs only episodically during brief periods of increased current strength narrow furrows width 1 5 to 1 15 of spacing appear to develop where deposition exceeds erosion whereas wide furrows width 1 2 of spacing develop where erosion exceeds or equals deposition dissolution may play an important role in the formation and evolution of furrows in carbonate rich cohesive sediments secondary circulation patterns over established furrows may be strongly controlled by bed form topography

high resolution seismo stratigraphy and sedimentological properties of late and postglacial sediments in lac guillaume delisle estuary and nastapoka sound eastern hudson bay lac guillaume delisle estuary and nastapoka sound are two sedimentary basins that recorded the late quaternary deglaciation on the eastern coast of hudson bay acoustic profiles reveal an average sediments thickness of 15 m in the estuary and 6 m in the sound these sediments reach 70 m thick in deep glacial troughs within the studied basins four seismo stratigraphic units overlying the acoustic basement were recognized unit 1 subaqueous ice contact and draped glaciomarine deposits associated with the quebec labrador ice sector qlis of the laurentide ice sheet lis and the tyrrell sea records the presence of a short ice marginal stillstand during glacial retreat unit 2 paraglacial and postglacial fluvial deltaic deposits and unit 3 postglacial silty deposits result from erosion of emerged sediments and redeposition in response to changes in relative sea level rsl finally unit 4 is composed of deformed deposits associated with a mass wasting event the stratigraphic sequence and the spatia

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

overconsolidated section on the yermak plateau arctic ocean ice sheet grounding prior to ca 660 ka the sediment sequence at ocean drilling program odp site 910 556 m water depth on the yermak plateau in the arctic ocean features a remarkable overconsolidated section from 19 to 70 95 m below sea floor m bsf marked by large increases in bulk density and sediment strength the odp leg 151 shipboard scientific party interpreted the overconsolidated section to be caused by 1 grounding of a marine based ice sheet derived from svalbard and perhaps the barents sea ice sheet and or 2 coarser grained glacial sedimentation which allowed increased compaction here i present planktonic foraminiferal 18 o data based on neogloboquadrina pachyderma sinistrally coiling that date the termination of overconsolidation near the boundary between isotope stages 16 and 17 ca 660 ka no evidence is found for coarser grained sedimentation because lithic fragments 150 m exhibit similar mean concentrations throughout the upper 24 5 m bsf the overconsolidated section may reflect more extensive ice sheet grounding prior to ca 660 ka suggesting a major change in state of the svalbard ice sheets during the mid quaternary furthermore continuous sedimentation since that time argues against a pervasive arctic ice shelf impinged on the yermak plateau during the past 660 k y these findings suggest that svalbard ice sheet history was largely independent of circum arctic ice sheet history during the middle to late quaternary

high frequency waves guided by the subducted plates underneath taiwan and their association with seismic intensity anomalies 1 energy from seismic events traveling up a subduction zone is frequently associated with significant large amplitude high frequency signals with sustained long coda such seismic waves guided by the subducted plate with high wave velocity and high q can cause surprisingly large seismic intensity in the fore arc area in this study we characterize the guiding behavior of the subducted philippine sea plate psp underneath taiwan and investigate their relationship with anomalous peak ground acceleration pga patterns obliquesubductionof philippine seaplatebeneathnortheast taiwan complicatestheguiding phenomena seismic waves from events deeper than 60km offshore northern taiwan reveal wave guide behavior large sustained high frequency 3 10hz signalinpandswavetrains with increasing depth a low frequency 1hz first arrival becomes more significant especially for events deeper than 100km the time separation between the low frequency onset and the later high frequency arrival slightly increases with depth while the value varies with station due to different travel distances in the shallow crust the depth dependent high frequency content confirms the association with a waveguide effect in the subducting slab rather than localized site amplification effects we attempt here to obtain a practicable quantification scheme to determine the duration of higher frequency energy which can be regarded as an indicator of the guiding effect of the philippine sea plate

evidence of a slab of subducted lithosphere beneath central taiwan from seismic waveforms and travel times abstract knowing whether there is a slab of subducted lithosphere beneath central taiwan is important for our understanding of the regional tectonic evolution in this study we aim at resolving this issue by investigating the seismic effects of a potential near receiver slab using data from a local broadband array rays from deep and intermediate depth earthquakes in the tonga kermadec subduction zone to central taiwan stations exhibit reduced amplitudes and travel times relative to kmnb in the 0 1 0 4 hz band with a correlation between the degree of reduction and earthquake latitudes the overall amplitude reduction observed at central taiwan stations is not observed for earthquakes from the hindu kush our analysis suggests that the observations are not caused by crustal structure but by receiver side heterogeneous mantle or more specifically an eastern dipping aseismic slab beneath central taiwan the extent of the slab is determined by jointly modeling amplitude and travel time observations at sslb and tpub using a 2 d pseudospectral method

surface roughness of titan s hydrocarbon seas abstract we derive fields of solutions for the surface properties roughness and permittivity of the liquid hydrocarbon bodies ligeia kraken and punga mare on titan by applying the radar statistical reconnaissance rsr technique to the cassini radar observations in altimeter mode during the northern early summer at the time of observation kraken and ligeia were confined within root mean square heights of 1 5 2 5 mm similar to wave heights of 6 10 mm correlation lengths of 45 115 mm and corresponding to effective slopes of 1 1 2 4 the latter extends up to 3 6 4 9 if the rougher punga is included the lower bound of those ranges has to be considered if the composition of the seas is methane dominant these are the first measurements to simultaneously constrain both the vertical and horizontal roughness parameters of titan s seas from the same observations our results are representative for the global properties of the sea scaled portion of the studied tracks and suggest that quiet surfaces are a dominant trend over the seas during the northern early summer fields of rougher textures if existent might develop mainly over local patches and or might not be sustained over significant periods of time

pleistocene calcite lysocline and paleocurrents of the central arctic ocean and their paleoclimatic significance most previous references to the depth of the arctic ocean calcite lysocline have been based on comparison with the known north atlantic carbonate compensation depth foraminifera from cores taken at depths ranging from 2316 to 3956 m provide the first firm calcite lysocline constraints for the central arctic ocean these data suggest progressive lowering of the calcite lysocline to at least 3956 m during the past 1 5 m y interrupted by 300 m rises of the lysocline level that apparently correspond with interglacial and early glacial climate conditions most cores from less than 2450 m indicate variable foraminifera abundance but continual presence of foraminifera for the past 1 5 m y low abundances commonly occur in coarse textured sediment and are interpreted to represent low productivity during major deglaciations within certain equivalent lithostratigraphic units representing the past 1 5 m y there is an absence of foraminifera in cores from depths greater than 2450 m this absence of foraminifera is interpreted to be due to dissolution dissolution intervals are associated with fine grain sediments interpreted to represent interglacial and early glacial climate conditions the interpretation of a rise in the lysocline level during interglacials is in apparent disagreement with studies reported from lower latitudes in the atlantic ocean but is complementary with the hypothesis that formation of norwegian greenland sea deep water ngdw and cold canada basin deep water occurs during interglacials paleocurrent data from the lomonosov ridge and the adjacent makarov basin are interpreted to indicate that during periods of increased glacial ice influx into the arctic ocean system there was reduced current activity in the bottom and intermediate water masses relative to periods when little glacial ice was present this is in accord with the idea that ngdw affects intermediate and deep water circulation in the central arctic ocean and hence the calcite lysocline level

global seismicity of 2003 centroid moment tensor solutions for 1087 earthquakes abstract centroid moment tensor cmt solutions are presented for 1087 earthquakes that occurred during 2003 the solutions are obtained using the method of dziewonski et al dziewonski a m chou t a woodward j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 and applying corrections for aspherical earth structure as represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging vol 19 plenum press new york pp 785 797 the model of inelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of inelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms the focal mechanisms of the largest or otherwise significant earthquakes of 2003 are reviewed

surface of ligeia mare titan from cassini altimeter and radiometer analysis cassini radar observations of the surface of ligeia mare collected during the 23 may 2013 t91 cassini fly by show that it is extremely smooth likely to be mostly methane in composition and exhibits no surface wave activity the radar parameters were tuned for nadir looking geometry of liquid surfaces using experience from cassini s only comparable observation of ontario lacus on 21 december 2008 t49 and also include coincident radiometric observations radar echoes from both passes show very strong specular radar reflections and limit surface height variations to 1 mm rms the surface physical temperature at 80 n is 92 0 5 k if the sea is liquid hydrocarbon and the land is solid hydrocarbon essentially the same as cassini cirs measurements furthermore radiometry measurements over the surrounding terrain suggest dielectric constants from 2 2 2 4 arguing against significant surface water ice unless it is extremely porous

threshold of wave generation on titan s lakes and seas effect of viscosity and implications for cassini observations motivated by radar and near infrared data indicating that titan s polar lakes are extremely smooth we consider the conditions under which a lake surface will be ruffled by wind to form capillary waves we evaluate laboratory data on wind generation and derive without scaling for surface tension effects a threshold for pure methane ethane of 0 5 1 m s however we compute the physical properties of predicted titan lake compositions using the national institute for standards technology nist code and note that dissolved amounts of c3 and c4 compounds are likely to make titan lakes much more viscous than pure ethane or methane even without allowing for suspended particulates which would increase the viscosity further wind tunnel experiments show a strong dependence of capillary wave growth on liquid viscosity and this effect may explain the apparent absence so far of waves contrary to prior expectations that generation of gravity waves by wind should be easy on titan on the other hand we note that winds over titan lakes predicted with the titanwrf global circulation model indicate radar observations so far have in any case been when winds have been low 0 5 0 7 m s possibly below the wave generation threshold while peak winds during summer may reach 1 2 m s thus observations of titan s northern lakes during the coming years by the cassini solstice mission offer the highest probability of observing wind roughening of lake surfaces while observations of ontario lacus in the south will likely continue to show it to be flat and smooth

physical oceanography near the north pole as part of lorex 79 observations of current conductivity temperature and depth were made for 40 days from an ice floe which drifted in the area within 1 5 of the north pole daily profiles were taken to a maximum depth of 1400 m observations were analyzed to give profiles of s t and t and of water speed and true direction the water column was stable at all stations density increased with depth observations of the under ice mixed layer showed it to become both thinner and warmer during northward drift of the floe downward motion and cooling of atlantic water advected southward were observed near the middle of the drift period the surface salinity dropped abruptly by 1 indicating passage into a different water mass a rough calculation showed only small water transport over the lomonosov ridge where the drift track crossed it

deep pleistocene iceberg plowmarks on the yermak plateau sidescan and 3 5 khz evidence for thick calving ice fronts and a possible marine ice sheet in the arctic ocean the southern yermak plateau northwest of spitsbergen was investigated with 11 12 khz sidescan sonar and 3 5 khz profiler to test whether thick pleistocene ice streams ever calved into the arctic ocean and or whether a continuous arctic ice sheet existed in either case the ice would have grounded on the plateau crest on its way out of the arctic several distinct sets of relict iceberg plowmarks were discovered at present water depths from less than 450 m to at least 850 m perhaps recording the deepest iceberg keels known the plateau crest 510 530 m is nearly bare of plowmarks perhaps because of beveling by an ice rise formed of grounding shelf ice this implies continuous 400 600 m thick grounded ice consistent with but not proving the postulated existence of an arctic ice sheet most plowmarks are probably late pleistocene products of the calving of barents kara ice sheets into the arctic ocean plowmarks in 450 850 m deep water require unusually deep ice sheet grounding lines e g svyataya anna trough and or drat increasing capsizing events even if sea levels were 100 50 m lower than today at water depths of 800 to 1800 m the sidescan texture and topography suggest bottom currents descending the northeast slope of the plateau

wave constraints for titan s jingpo lacus and kraken mare from vims specular reflection lightcurves abstract stephan et al stephan k et al 2010 geophys res lett 37 7104 first saw the glint of sunlight specularly reflected off of titan s lakes we develop a quantitative model for analyzing the photometric lightcurve generated during a flyby in which the specularly reflected light flux depends on the fraction of the solar specular footprint that is covered by liquid we allow for surface waves that spread out the geographic specular intensity distribution applying the model to the vims t58 observations shows that the waves on jingpo lacus must have slopes of no greater than 0 15 two orders of magnitude flatter than waves on earth s oceans combining the model with theoretical estimates of the intensity of the specular reflection allows a tighter constraint on the waves 0 05 residual specular signal while the specular point lies on land implies that either the land is wetted the wave slope distribution is non gaussian or that 5 of the land off the southwest edge of jingpo lacus is covered in puddles another specular sequence off of kraken mare acquired during cassini s t59 flyby shows rapid flux changes that the static model cannot reproduce points just 1 min apart vary in flux by more than a factor of two the present dataset does not uniquely determine the mechanism causing these rapid changes we suggest that changing wind conditions kilometer wavelength waves or moving clouds could account for the variability future specular observations should be designed with a fast cadence at least 6 points per minute in order to differentiate between these hypotheses such new data will further constrain the nature of titan s lakes and their interactions with titan s atmosphere

significant contribution of the shallow crust to seismic pkp travel time residuals and implications an example from taiwan and nearby islands abstract array observations indicate that the relative pkp travel time residuals in the taiwan region vary from 2 5 to 2 0 s a range greater than the largest known teleseismic travel time residuals from deep earth pkp waves are generally employed to probe structures of the deep earth however the contribution of shallow geological structures to pkp waves is generally undefined and the implications of such a contribution have rarely been discussed current travel time tomographic models of taiwan are able to predict less than 40 of the observed pkp residuals and the pkp residuals are consistent with the pattern of station corrections used in determining local earthquakes detailed island wide gravity measurements indicate that the distribution of bouguer anomalies which were previously proposed to be induced by thick sedimentary deposits in large tectonic basins is consistent with the pattern of pkp travel time residuals in conclusion the observed pkp residuals are strongly affected by shallow sediments therefore the contribution of residuals from shallow crustal structures should be carefully considered when employing pkp observations for imaging structures of the deep earth or the deep crust and upper mantle

stable isotope stratigraphy sedimentation rates and salinity changes in the latest pleistocene to holocene eastern central arctic ocean a high resolution study including oxygen and carbon stable isotopes as well as carbonate and total organic carbon contents has been performed on undisturbed near surface 0 40 cm sediment sequences taken in the eastern arctic ocean during the international arctic 91 expedition based on the oxygen stable isotope records measured on neogloboquadrina pachyderma sin and ams 14c dating the upper 10 to 20 cm of the sediment sequences represent isotope stage 1 and the base of termination i 15 7 ka can be identified very well stage 1 sedimentation rates vary between 0 4 and 2 0 cm kyr in general glacial stage 2 sedimentation rates are probably lower and vary between 0 4 and 0 7 cm kyr the glacial interglacial shifts in 18o values of n pachyderma sin may reach values of 1 3 to 2 5 indicating 1 that in addition to the glacial interglacial global ice volume signal changes in surface water salinity have effected the isotope records and 2 that these salinity changes have varied laterally glacial interglacial differences in salinity were small in the lomonosov ridge area 0 0 4 and relatively high in the morris jesup rise area up to 1 4 this implies that the supply of low saline waters onto the eurasian shelves and its further transport into the central arctic ocean via the transpolar drift should have continued during the last glacial and should have significantly influenced the surface water characteristics in parts of the central arctic on the morris jesup rise on the other hand the glacial low saline water signal at that time was strongly reduced in comparison to the modern situation at the glacial interglacial stage 12 boundary a strong meltwater signal is recorded in a sharp depletion in 18o as well as 13c this central arctic ocean meltwater event can be correlated from the makarov basin through the lomonosov ridge and amundsen basin to the eastern gakkel ridge the beginning of this event is ams 14c dated at 15 7 ka i e significantly older than the major decrease in the global ice volume signal which occurs between 9 and 13 5 ka large amounts of freshwater meltwater were probably supplied from the eurasian continent due to the decay of the barents sea ice sheet causing this distinct early meltwater anomaly in the central arctic ocean the extension of a well oxygenated surface near water mass in the arctic ocean and at least seasonal open ice conditions and some increased bioproductivity were probably established at the end of termination i as indicated by the increase in 13c to modern values as well as increased carbonate i e foraminifers coccoliths ostracodes and total organic carbon contents

compelling evidence of an aseismic slab beneath central taiwan from a dense linear seismic array abstract from a dense linear seismic array consisting of 15 short period seismic stations deployed across the suture zone an aseismic slab subducted beneath central taiwan was clearly detected in addition to the direct p waves the identification of the mantle refracted phases generated by an intermediate depth earthquake m l 5 8 in southeastern taiwan and recorded by the linear array as well as some seismic stations cwbsn along the eastern central range shows that a subducted crust with a low velocity exists down at the depth of at least 89 km this strongly suggests that the subduction of the eurasian plate in southern taiwan most likely extends to central taiwan where there has been an absence of mantle earthquakes in the wadati benioff zone what the subduction slab without mantle earthquakes could very well be attributed to is the subducted continental crust where the rock strength is totally different from that of the oceanic crust

first high resolution chirp sonar profiles from the central arctic ocean reveal erosion of lomonosov ridge sediments the swedish arctic ocean 96 expedition to the central arctic ocean with the icebreaker oden carried out a geological geophysical program focused mainly on lomonosov ridge sediments approximately 195 km of high resolution seismic data from the ridge crest and slope were collected with a chirp sonar system providing new insights into the sediment stratigraphy and the accompanying depositional history these data reveal evidence of substantial erosion that acted in laterally limited areas on shallow parts of the investigated ridge segment more than 50 m of sediment stratigraphy is missing in the most eroded parts moreover the chirp sonar records indicate that below the erosional surface the ridge crest and slope is characterized by a low energy sedimentary environment the termination of the erosional phase is indicated by a prominent reflector the subsequent depositional phase resulted in an approximately 3 m thick stratigraphic unit the cause of the erosion is attributed to either ice grounding or current erosion furthermore oden echo sounding data has been used together with data from the us navy scicex program in order to update existing bathymetric charts in the arctic ocean 96 working area the update shows a narrower ridge crest with a different outline than in previously published charts with a minimum depth of 607 m which is the shallowest depth of the lomonosov ridge recorded in the public domain in the central arctic ocean 1999 elsevier science b v all rights reserved

structure of the upper mantle and transition zone beneath southeast asia from traveltime tomography 1 tomographic images of the mantle beneath east asia were obtained from the inversion of traveltime data from global and regional seismograph networks and from temporary arrays on and around the tibetan plateau our results are consistent with previous studies but the unprecedented resolution of mantle heterogeneity provides new insight into the large scale tectonic framework of the continental india asia collision in the western part of the study region and subduction of the oceanic lithosphere in the east in the realm of continental collision west of 100 e a relatively slow p wave speed characterizes the upper mantle beneath much of the tibetan plateau but the wave speed is high beneath cratonic india the southern and western part of the tibetan plateau hindu kush and the tian shan in the subduction realm east of 110 e the main structures are i pronounced low wave speed anomalies at a depth of between 100 and 400 km beneath asia s southeastern seaboard and the back arc regions of ongoing subduction ii narrow fast anomalies in the upper mantle beneath major subduction zones and iii widespread fast anomalies at a depth of 500 700 km beneath the sea of japan the northern part of the philippine sea plate and southeastern china if the latter anomalies represent stagnant slabs their fragmented nature and large lateral extent suggest that they are produced by different episodes of subduction beneath western pacific island arcs along the old se margin of asia or during the mesozoic collision of cratonic units in southeast asia attribution to ancient subduction systems implies that slab fragments can reside in the transition zone for at least several tens of millions of years shallow slow anomalies beneath the red river fault region connect to deep anomalies beneath the south china fold belt and south china sea suggesting a causal relationship between the evolution of the continental lithosphere of sw china and deeper mantle processes between the collision and the subduction realms tomography reveals high wave speed continental roots beneath the western part of the north china craton ordos block and the south china or yangtze craton sichuan basin to a depth of 300 km

chirp subbottom profiler for quantitative sediment analysis a wide band frequency modulated subbottom profiling system the chirp sonar can remotely determine the acoustic attenuation of ocean sediments and produce artifact free sediment profiles in real time the chirp sonar is controlled by a minicomputer which performs analog to digital and digital to analog conversion correlation processing and attenuation estimation in real time the minicomputer generates an fm pulse that is phase and amplitude compensated to correct for the sonar system response such precise waveform control helps suppress correlation noise and source ringing the chirp sonar which has an effective bandwidth of 5 khz can generate chirp klauder wavelets with a tuning thickness rayleigh s criterion for resolution of approximately 0 1 ms after each return is correlated a computationally fast algorithm estimates the attenuation of subbottom reflections by waveform matching with a theoretically attenuated waveform this algorithm obtains an attenuation estimate by minimizing the m