quaternary deformation and uplift of coral reef terraces produced by oblique subduction and underthrusting of the bahama platform below the northern hispaniola forearc abstract active tectonics linked to the rise of the hispaniola forearc explain the morphological characteristics spatial distribution and u th geochronological ages of the uplifted coral reef terraces of the la isabela formation in both the eastern cordillera septentrional and the samana peninsula of northeastern dominican republic depositional coral reef terraces of mis 5e tii 7e tiii and 9 tiv stages occur respectively at maximum heights of about 25 m 80 m and 120 m above the current sea level the development of heterogeneous brittle deformation structures in the coral limestone at all scales document active tectonics and include small faults shear fractures extensional joints and calcite veins their geometric and kinematic characteristics as well as the stress tensors calculated from fault slip and fracture orientation data are all compatible with ene to ne trending regional shortening and indicate that a left lateral transpressive regime is deforming the forearc during the quaternary along the northern hispaniola coastline the tectonic uplift mimics the distribution of the bathymetric features on the subducting bahamas platform outboard the hispaniola puerto rico trench the highest calculated uplift rates in the eastern cordillera septentrional and samana peninsula correspond to the collision zone of the silver spur and navidad bank 0 4 m ka respectively uplift rates decrease towards the west 0 2 m ka where the oblique collision of carbonate ridges and related forearc deformation would not have been recorded since at least the early pleistocene oblique subduction and underthrusting of the bahamas platform followed by basal erosion at the subduction channel explain the observed time transgressive pattern of uplift and subsidence in the northern hispaniola forearc and the change from accretionary to erosive processes in the convergent margin

an alternative interpretation of the cayman trough evolution from a reidentification of magnetic anomalies magnetic data were collected during the wilkes 1973 and seacarib ii 1987 cruises to the cayman trough a new interpretation of magnetic data is carried out an isochron pattern is drawn up from our anomaly identifications an early eocene age 49 ma ypresian for cayman trough opening is proposed instead of the late oligocene or middle eocene ages suggested by previous studies our plate tectonic reconstruction is simpler and fits the on land geology jamaica and cuba and the tectonics our reconstruction shows a southward propagation of the spreading centre between magnetic anomalies 8 and 6 26 and 20 ma the trough width increases by 30 km in this period the southward propagation of the cayman spreading centre from the middle oligocene to the early miocene induced the development of the restraining bend of the swan islands the formation of a 1 km high scarp on the eastern trace of the cayman trough transform fault walton fault and the formation of a pull apart basin hendrix pull apart magnetic anomalies and magnetization maps give information about the deformation and the rocks the proposed evolutionary model of the cayman trough from the inception of seafloor spreading to the present configuration is presented in relation to the tectonic escape of the northern boundary of the caribbean plate from the maastrichtian to the present

along strike segmentation in the northern caribbean plate boundary zone hispaniola sector tectonic implications abstract the north american noam plate converges with the caribbean carib plate at a rate of 20 0 0 4 mm yr towards 254 1 plate convergence is highly oblique 20 10 resulting in a complex crustal boundary with along strike segmentation strain partitioning and microplate tectonics we study the oblique convergence of the noam and carib plates between southeastern cuba to northern puerto rico using new swath multibeam bathymetry data and 2d multi channel seismic profiles the combined interpretation of marine geophysical data with the seismicity and geodetic data from public databases allow us to perform a regional scale analysis of the shallower structure the seismotectonics and the slab geometry along the plate boundary due to differential rollback between the noam oceanic crust north of puerto rico and the relative thicker bahamas carbonate province crust north of hispaniola a slab tear is created at 68 5 w the northern margin of puerto rico records the oblique high dip subduction and rollback of the noam plate below the island arc those processes have resulted in a forearc transpressive tectonics without strain partitioning controlled by the septentrional oriente fault zone sofz and the bunce fault zone bfz meanwhile in the northern margin of hispaniola the collision of the bahamas carbonate province results in high plate coupling with strain partitioning sofz and northern hispaniola deformed belt nhdb in the northern haitian margin compression is still relevant since seismicity is mostly associated with the deformation front whereas strike slip earthquakes are hardly anecdotal although in hispaniola intermediate depth seismicity should disappear diffuse intermediate depth hypocenter remains evidencing the presence of remnant noam subducted slab below central and western hispaniola results of this study improve our understanding of the active tectonics in the ne caribbean that it is the base for future assessment studies on seismic and tsunamigenic hazard

barotropic tides on the north carolina shelf observations from 18 near bottom pressure sensors and 8 current meter moorings provide a characterization of the barotropic tides over the north carolina continental shelf between chesapeake bay and cape hatteras the largest tidal constituents in this region are the m2 sea level amplitude 47 cm n2 11 cm and s2 10 cm semidiurnal tides and the k1 p1 7 cm and o1 5 cm diurnal tides the barotropic tidal currents are small less than 3 cm s21 except for the m2 current which reaches 10 cm s21 at mid shelf cross shelf currents increase linearly from approximately zero near the coast to a maximum over the mid and outer shelf alongshelf currents are nonzero near the coast and increase to roughly twice the coastal value over the mid and outer shelf while bottom friction is weak over most of the shelf in water depths of less than 10 m bottom friction results in a rapid phase decrease toward the coast in the semidiurnal alongshelf velocities this phase difference is not observed in the k1 p1 alongshelf flow possibly because diurnal wind forcing causes an opposing phase increase toward the coast alongshelf variations in tidal amplitudes and phases near the coast are much larger than expected based on variations along the shelf break inferred from basin scale altimeter estimates the shelf width in this region increases from 25 to 100 km over an alongshelf distance of about 150 km results from an analytic flat bottom two dimensional model indicate that widening of the shelf toward the north causes the observed alongshelf increase in the semidiurnal amplitude and phase but does not explain alongshelf variations in the weaker diurnal constituents

palaeoclimatology formation of precambrian sediment ripples arising from p a allen p f hoffman nature 433 123 127 2005 allen and hoffman reply quantitative estimation of environmental properties using sedimentary structures preserved in rocks is complicated by the fact that some relationships between the fluid flow sediment transport and bed topography are not unique allen and hoffman1 propose that large wave generated sand ripples orbital ripples in precambrian rocks were generated by sustained extreme winds driven by rapid climate change after termination of the marinoan glaciation we show here that these features could equally well have formed under normal storm conditions in tens of metres of water we therefore contend that the ripples do not provide direct evidence for a climatic transit after the break up of a snowball earth s global ice cover

gps estimate of relative motion between the caribbean and south american plates and geologic implications for trinidad and venezuela global positioning system gps data from eight sites on the caribbean plate and five sites on the south american plate were inverted to derive an angular velocity vector describing present day relative plate motion both the caribbean and south american velocity data fit rigid plate models to within 1 2 mm yr the gps velocity uncertainty the caribbean plate moves approximately due east relative to south america at a rate of 20 mm yr along most of the plate boundary significantly faster than the nuvel 1a model prediction but with similar azimuth pure wrenching is concentrated along the approximately east striking seismic el pilar fault in venezuela in contrast transpression occurs along the 068 trending central range warm springs fault in trinidad which is aseismic possibly locked and oblique to local plate motion

plate interaction in the ne caribbean subduction zone from continuous gps observations 1 kinematic similarities between the sumatra and puerto rico trenches highlight the potential for a mega earthquake along the puerto rico trench and the generation of local and trans atlantic tsunamis we used the horizontal components of continuous gps cgps measurements from 10 sites on ne caribbean islands to evaluate strain accumulation along the north american na caribbean ca plate boundary these sites move westward and slightly northward relative to ca interior at rates 2 5 mm y provided this motion originates in the subduction interface the northward motion suggests little or no trench perpendicular thrust accumulation and may in fact indicate divergence north of puerto rico where abnormal subsidence bathymetry and gravity are observed the puerto rico trench thus appears unable to generate mega earthquakes but damaging smaller earthquakes cannot be discounted the westward motion characterized by decreasing rate with distance from the trench is probably due to eastward motion of ca plate impeded at the plate boundary by the bahamas platform two additional cgps sites in mona passage and sw puerto rico move to the sw similar to hispaniola and unlike the other 10 sites that motion relative to the rest of puerto rico may have given rise to seismicity and normal faults in mona rift mona passage and sw puerto rico

on the dynamics of the juan de fuca plate the juan de fuca plate is currently fragmenting along the nootka fault zone in the north while the gorda region in the south shows no evidence of fragmentation this difference is surprising as both the northern and southern regions are young relative to the central juan de fuca plate we develop stress models for the juan de fuca plate to understand this pattern of breakup another objective of our study follows from our hypothesis that small plates are partially driven by larger neighbor plates the transform push force has been proposed to be such a dynamic interaction between the small juan de fuca plate and the pacific plate we aim to establish the relative importance of transform push for juan de fuca dynamics balancing torques from plate tectonic forces like slab pull ridge push and various resistive forces we first derive two groups of force models models which require transform push across the mendocino transform fault and models which do not intraplate stress orientations computed on the basis of the force models are all close to identical orientations of predicted stresses are in agreement with observations stress magnitudes are sensitive to the force model we use but as we have no stress magnitude observations we have no means of discriminating between force models model stresses in the north and the south of the juan de fuca plate are similar breakup along the nootka fault zone and not in the gorda region can be explained if the local strength of a lithosphere column depends on lithospheric age stresses are invariant to whether or not transform push is acting on the mendocino transform fault we therefore conclude that the introduction of this extra plate driving force is not required by observations for the juan de fuca plate fl 2001 elsevier science b v all rights reserved

mid eocene early oligocene sinistral transcurrent faulting in puerto rico associated with formation of the northern caribbean plate boundary zone left lateral transcurrent wrench faulting through the southern puerto rico fault zone sprfz in central southern puerto rico is indicated by fault orientations and motion direction indicators the sprfz is a west northwest trending 3 8 km wide diffuse system of faults and folds that within the study area bounds paleocene and eocene volcaniclastic rocks the eocene belt and is flanked by cretaceous volcanic and volcaniclastic rocks structural data show that much of central southern puerto rico is cut by strike and oblique slip faults whereas locally in the southeastern part of the eocene belt rocks are pervasively thrust northeastward over cretaceous rocks of central puerto rico structural data and the distribution of fault types support two local evolutionary scenarios 1 different structural horizons of the transpressional sprfz i e upper thrust dominated horizon and lower strike slip dominated horizon were juxtaposed along post transpressional normal faults that border the ponce basi

caribbean intra plate deformation paleomagnetic evidence from st barthelemy island for post oligocene rotation in the lesser antilles forearc abstract as subduction zones and their related processes are often studied in 2d or cylindrical 3d sections the dynamic effects of trench curvature and its evolution through time remain under explored whereas temporal variations in trench trend may be estimated through restoring upper plate deformation we investigate the forearc deformation history of the strongly curved northern lesser antilles trench connecting the near orthogonal lesser antilles subduction zone with the motagua cayman transform plate boundary our new paleomagnetic dataset consists of 310 cores from eo oligocene magmatic rocks and limestones from st barthelemy island the limestones yielded a post folding magnetization containing a similar magnetic direction to those stored in magmatic rocks that intrude the folded carbonates both indicating a post oligocene 15 and perhaps up to 25 counterclockwise rotation of the island our results highlight that the present day trench curvature formed progressively during the cenozoic allowing us to discuss different tectonic scenarios explaining ne caribbean plate deformation and to identify key targets for future research on tectonic architecture and the potential present day activity of intra plate deformation that may pose seismic hazards

momentum balances on the north carolina inner shelf four months of moored current pressure temperature conductivity wave and wind observations on the north carolina shelf indicate three dynamically distinct regions the surf zone the inner shelf between the surf zone and the 13 m isobath and the midshelf in the surf zone the along shelf momentum balance is between the cross shelf gradient of the wave radiation stress and the bottom stress the linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone on the inner shelf the along shelf momentum balance is also frictional the along shelf wind stress and pressure gradient are balanced by bottom stress in the cross shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the coriolis force geostrophy and wave setdown from shoaling unbroken surface gravity waves at midshelf the along shelf momentum balance is less frictional and hence flow accelerations are important the cross shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown the cross shelf density gradient is in thermal wind balance with the vertical shear in the along shelf flow in depths as shallow as 10 m the dominant along shelf momentum balances provide a simple estimate of the depth averaged along shelf current in terms of the measured forcing i e wind stress wave radiation stress divergence and along shelf pressure gradient that reproduces accurately the observed cross shelf variation of the depth averaged along shelf current between the surf zone and midshelf

interseismic plate coupling and strain partitioning in the northeastern caribbean summary the northeastern caribbean provides a natural laboratory to investigate strain partitioning its causes and its consequences on the stress regime and tectonic evolution of a subduction plate boundary here we use gps and earthquake slip vector data to produce a present day kinematic model that accounts for secular block rotation and elastic strain accumulation with variable interplate coupling on active faults we confirm that the oblique convergence between caribbean and north america in hispaniola is partitioned between plate boundary parallel motion on the septentrional and enriquillo faults in the overriding plate and plateboundary normal motion at the plate interface on the northern hispaniola fault to the east the caribbean north america plate motion is accommodated by oblique slip on the faults bounding the puerto rico block to the north puerto rico subduction and to the south muertos thrust with no evidence for partitioning the spatial correlation between interplate coupling strain partitioning and the subduction of buoyant oceanic asperities suggests that the latter enhance the transfer of interplate shear stresses to the overriding plate facilitating strike slip faulting in the overriding plate the model slip rate deficit together with the dates of large historical earthquakes indicates the potential for a large m w7 5 or greater earthquake on the septentrional fault in the dominican republic similarly the enriquillo fault in haiti is currently capable of a m w7 2 earthquake if the entire elastic strain accumulated since the last major earthquake was released in a single event today the model results show that the puerto rico lesser antilles subduction thrust is only partially coupled meaning that the plate interface is accumulating elastic strain at rates slower than the total plate motion this does not preclude the existence of isolated locked patches accumulating elastic strain to be released in future earthquakes but whose location and geometry are not resolvable with the present data distribution slip deficit on faults from this study are used in a companion paper to calculate interseismic stress loading and together with stress changes due to historical earthquakes derive the recent stress evolution in the ne caribbean

geometry prediction for wave generated bedforms published data on wave generated bedform geometry from field and laboratory measurements are re evaluated in terms of relative fluid orbit diameter at the bed and a wave period parameter d 8t2 laboratory bedform data shows a strong dependence on these parameters however for very small values of the period parameter typically field data there is evidence that bedform length depends only on sediment grain size the disappearance of sediment bedforms at high fluid velocities apparently occurs through a decrease in bedform height improved methods for the prediction of bedform geometry under waves are provided in graphical form and computer code

grain size variability on a rip channeled beach abstract grain size is an important variable when predicting beach morphodynamics beaches to the eye seem relatively uniform in grain size and morphodynamic modeling efforts usually assume a single mean grain size for an entire beach environment therefore estimating grain size is traditionally done by collecting only a few samples and averaging to characterize the mean grain size of the whole beach however some studies have shown that even small variations in grain size can have a significant effect on model results when predicting beach morphology changes here a mobile digital imaging system dis has been developed for surveying spatial and temporal variation in grain size across a beach following the ideas of rubin 2004 using an off the shelf camera and underwater housing macro photographs are taken of sand across a beach which produce estimates of mean grain size that are highly correlated with estimates from sieves r2 0 92 high resolution maps of mean surface grain size are produced using the dis with 1000 images over a 300 500 m area which suggest that large variations in grain size exist 0 2 0 7 mm over tens of meters with accuracies of 0 03 mm and that there is a correlation between spatial grain size variations and morphological variability

the polyphased tectonic evolution of the anegada passage in the northern lesser antilles subduction zone the influence of the highly oblique plate convergence at the northern lesser antilles onto the margin strain partitioning and deformation pattern although frequently invoked has never been clearly imaged the anegada passage is a set of basins and deep valleys regularly related to the southern boundary of the puerto rico virgin islands prvi microplate despite the publications of various tectonic models mostly based on bathymetric data the tectonic origin and deformation of this passage remains unconstrained in the absence of deep structure imaging during cruises antithesis 1 and 3 2013 2016 we recorded the first deep multichannel seismic images and new multibeam data in the northern lesser antilles margin segment in order to shed a new light on the structure and tectonic pattern of the anegada passage we image the northeastern extent of the anegada passage from the sombrero basin to the lesser antilles margin front our results reveal that this northeastern segment is an ew trending left stepping en echelon strike slip system that consists of the sombrero and malliwana pull apart basins the malliwana and anguilla left lateral faults and the ne sw compressional restraining bend at the malliwana hill reviewing the structure of the anegada passage from the south of puerto rico to the lesser antilles margin front reveals a polyphased tectonic history the anegada passage is formed by a nw se extension possibly related to the rotation or escape of prvi block due to collision of the bahamas bank currently it is deformed by an active wnw ese strike slip deformation associated to the shear component of the strain partitioning resulting from the subduction obliquity

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

sand transport on an estuarine submarine dune field abstract by means of surveys carried out with a phase measuring bathymetric system and current profiles obtained through an adcp of the internal area of the bahia blanca estuary a field of large dunes was analysed there are two different and well defined zones characterized by particular dune morphology and differing hydrodynamics the reduction in the channel cross section by a geological control leads to the increase in tidal current velocity which together with the available sediment leads to the formation of very large dunes h 4 m and l 100 m with the typical morphology of a limited amount of sediment overlying a rigid substrate the migration rate of these dunes between 65 and 130 m year 1 decreases as the bedform height increases differing sediment transport rates across the channel result in a non uniform migration rate which is responsible for the formation of dunes with linear crests oblique to the tidal current direction this fact indicates that determination of the sediment transport direction by using only large bedform orientation may be subject to a significant error

segmentation and kinematics of the north america caribbean plate boundary offshore hispaniola we explored the submarine portions of the enriquillo plantain garden fault zone epgfz and the septentrional oriente fault zone sofz along the northern caribbean plate boundary using high resolution multi beam echo sounding and shallow seismic reflection the bathymetric data shed light on poorly documented or previously unknown submarine fault zones running over 200 km between haiti and jamaica epgfz and 300 km between the dominican republic and cuba sofz the primary plate boundary structures are a series of strike slip fault segments associated with pressure ridges restraining bends step overs and dogleg offsets indicating very active tectonics several distinct segments 50 to 100 km long cut across pre existing structures inherited from former tectonic regimes or bypass recent morphologies formed under the current strike slip regime along the most recent trace of the sofz we measured a strike slip offset of 16 5 km which indicates steady activity for the past 1 8 ma if its current gps derived motion of 9 8 2 mm yr has remained stable during the entire quaternary

seamarc ii mapping of transform faults in the cayman trough caribbean sea seamarc ii maps of the southern wall of the cayman trough between honduras and jamaica show zones of continuous well defined fault lineaments adjacent and parallel to the wall both to the east and west of the cayman spreading axis these lineaments mark the present active traces of transform faults which intersect the southern end of the spreading axis at a triple junction the swan islands transform fault to the west is dominated by two major lineaments that overlap with right stepping sense across a large push up ridge beneath the swan islands the fault zone to the east of the axis named the walton fault is more complex containing multiple fault strands and a large pull apart structure the walton fault links the spreading axis to jamaican and hispaniolan strike slip faults and it defines the southern boundary of a microplate composed of the eastern cayman trough and western hispaniola the presence of this microplate raises questions about the veracity of caribbean plate velocities based primarily on cayman trough opening rates

experiments on bed configurations in fine sands under bidirectional purely oscillatory flow and the origin of hummocky cross stratification abstract we made experiments on bed configurations in bidirectional purely oscillatory flows at a wide range of oscillation periods t and maximum orbital velocities um in two closed flow ducts 0 1 m and 0 4 m wide the motivation was that understanding of bed configurations in oscillatory flows with long periods and high velocities during storm induced deposition in the shallow ocean is needed for interpreting the stratification in such deposits the ripples produced were classified geometrically as two dimensional 2d or three dimensional 3d in plan view geometry and dynamically as oscillatory current ripples dependent upon the patterns of flow and sediment transport specific to the existence of the oscillation itself and reversing current ripples dependent on he existence of the current in one direction or the other during the oscillation runs in the small duct with effectively 0 19 mm and 0 30 mm sand showed the familiar small 2d oscillatory current ripples at short t and low um passing into much larger ripples with spacing up to 2 m at periods of 6 20 s and velocities up to 1 m s with no apparent limit on size with increasing t and um even in such a narrow duct there was some evidence of 3d geometry of the large ripples runs in the large duct with effectively 0 11 mm sand at a single period of about 9 5 s showed a progression from small 2d oscillatory current ripples through small 3d reversing current ripples to large round crested 3d oscillatory current ripples with prominent superimposed 3d to 2d reversing current ripples the large 3d ripples which increased in spacing to 1 3 m at the h ghest attainable um of 1 m s shifted in position and changed in size with time seemingly at random causing substantial local and temporary erosion and deposition at a given point on the bed there was no net aggradation during the runs but a deposit was synthesized by taking a time series of sidewall bed profiles during a run in which large 3d ripples developed from an initially plane bed and changed irregularly in size and position as they grew toward equilibrium and then plotting the profiles one above the previous with a constant upward increment the resulting stratification is strikingly similar to much hummocky cross stratification in ancient sandstones this suggests that some hummocky cross stratification is generated during sediment fallout from strong purely oscillatory flows at moderate to long oscillation periods as large 3d oscillatory current bed forms develop from a planar bed during strong but waning flow

muertos trough subduction microplate tectonics in the northern caribbean the relative plate motion between the north american and caribbean plates has been commonly assumed to take place in the form of oblique subduction along the puerto rico trench1 west of hispaniola this plate boundary becomes pure strike slip nevertheless it has been suggested that this boundary is more diffuse with part of the plate motion taken up by subduction along the muertos trough mt south of hispaniola2 5 fig 1 but there has been no direct seismological evidence of subduction to confirm this here we present the results of a study of the 24 june 1984 earthquake beneath mt the focal mechanism shows thrusting at a depth of 32 km which together with reports of a great earthquake in 1751 confirms that mt is an active plate boundary this implies that plate motion is accommodated by several tectonic boundaries delineating microplates caught between the caribbean and north american plates fig 4

swell transformation across the continental shelf part i attenuation and directional broadening abstract extensive wave measurements were collected on the north carolina virginia continental shelf in the autumn of 1999 comparisons of observations and spectral refraction computations reveal strong cross shelf decay of energetic remotely generated swell with for one particular event a maximum reduction in wave energy of 93 near the virginia coastline where the shelf is widest these dramatic energy losses were observed in light wind conditions when dissipation in the surface boundary layer caused by wave breaking whitecaps was weak and wave propagation directions were onshore with little directional spreading these observations suggest that strong dissipation of wave energy takes place in the bottom boundary layer the inferred dissipation is weaker for smaller amplitude swells for the three swell events described here observations are reproduced well by numerical model hindcasts using a parameterization of wave friction over a movable sandy bed directional spectra that are narrow off the s

tectonic evolution and mantle structure of the caribbean we investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic p wave velocity structure under the caribbean region in the upper mantle positive seismic anomalies are imaged under the lesser antilles and puerto rico these anomalies are interpreted as remnants of atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the lesser antilles island arc during the past 45 myr the imaged lesser antilles slab consists of a northern and southern anomaly separated by a low velocity anomaly across most of the upper mantle which we interpret as the subducted north america south america plate boundary the southern edge of the imaged lesser antilles slab agrees with vertical tearing of south america lithosphere the northern lesser antilles slab is continuous with the puerto rico slab along the northeastern plate boundary this results in an amphitheater shaped slab and it is interpreted as westward subducting north america lithosphere that remained attached to the surface along the northeastern boundary of the caribbean plate at the muertos trough however material is imaged until a depth of only 100 km suggesting a small amount of subduction the location and length of the imaged south caribbean slab agrees with proposed subduction of caribbean lithosphere under the northern south america plate an anomaly related to proposed oligocene subduction at the nicaragua rise is absent in the tomographic model beneath panama a subduction window exists across the upper mantle which is related to the cessation of subduction of the nazca plate under panama since 9 5 ma and possibly the preceding subduction of the extinct cocos nazca spreading center in the lower mantle two large anomaly patterns are imaged the westernmost anomaly agrees with the subduction of farallon lithosphere the second lower mantle anomaly is found east of the farallon anomaly and is interpreted as a remnant of the late mesozoic subduction of north and south america oceanic lithosphere at the greater antilles aves ridge and leeward antilles the imaged mantle structure does not allow us to discriminate between an intra americas origin and a pacific origin of the caribbean plate key points tectonic reconstructions for the caribbean validated by seismic tomography cenozoic lesser antilles and mesozoic greater antilles subduction confirmed tomography gives insight into geodynamics of lesser antilles

intrawave observations of sediment entrainment processes above sand ripples under irregular waves 1 measurements of intrawave sediment entrainment processes are reported above ripples under irregular waves generated in a large scale flume facility the data consist of substantive observations of small scale processes collected at high spatial and temporal resolution under irregular wave forcing typical of coastal environments acoustic measurements were made of water velocities bed forms and suspended sediment concentration over plane and rippled beds during each rippled bed experiment measurements were taken over the crests of steep sided ripples above which flow separation was considered likely to occur above the ripple crests a strong intrawave variation in the near bed suspended sediment indicative of vortex formation and shedding was observed to dominate wave half cycles where the orbital diameter was greater than 1 2 times the ripple wavelength l the irregular waves were parameterized with a significant wave height hs and a significant orbital diameter d0s thus during irregular wave conditions and over steep ripples where d0s l 1 2 vortex shedding was deemed as the dominant sediment entrainment process furthermore the percentage of wave half cycles where vortex shedding was observed was found to scale as 26 d0s l these results demonstrate for under irregular waves the existence of a clear suspended sediment structure consistent with vortex shedding previously observed under regular waves citation o hara murray r b p d thorne and d m hodgson 2011 intrawave observations of sediment entrainment processes above sand ripples under irregular waves j geophys res 116 c01001 doi 10 1029 2010jc006216

indentation induced tearing of a subducting continent evidence from the tan lu fault zone east china abstract vertical tearing of oceanic slabs has been well documented at subduction zones it remains unclear whether a subducting continent can tear vertically origin of the continental scale tan lu fault zone tlfz in east china provides an example of the vertical tearing of the subducting continent at the convergent stage the dabie and sulu orogens between the north china plate ncp and the yangtze plate yzp are left laterally offset about 400 km along the ne striking tlfz but the fault zone terminates abruptly at the southeastern corner of the dabie orogen suggesting unique origin of the fault zone we present structural evidence to show that the tlfz initiated as a sinistral fault zone that is exposed in ductile shear belts just to the east of the dabie orogen our muscovite 40ar 39ar dating results coupled with existing age data indicate that the tlfz formed at 240 230 ma middle triassic when the yzp continental crust was subducted beneath the ncp along both the dabie and sulu sutures we also show that se directed extrusion of the subducted crust in the dabie orogen occurred during 230 209 ma late triassic and overprinted contractional deformation in the tlfz to the southeast of the dabie orogen syn collisional folds and thrusts in the yzp to the east of the tlfz exhibit evidence for large scale dragging by the sinistral fault zone whereas those in the ncp to the west are perpendicular to the tlfz without obvious evidence for drag combining these lines of evidence with published data on the tectonic evolution of the two orogenic belts we propose an indentation induced continent tearing model for the origin of the tlfz we suggest that the present southern boundary of the ncp represents its original shape with a promontory in front of the dabie orogen at the oceanic subduction stage the overriding ncp promontory led to vertical tearing of the subducting oceanic plate along the tlfz which formed the eastern boundary of the promontory once the rigid ncp indenter collided with the passive yzp along the dabie orogen the oceanic slab tear propagated into the yzp lithosphere resulting in long distance low angle subduction of the yzp underneath the ncp indenter and nne ward horizontal motion of the torn yzp east of the tlfz until the final collision at the sulu orogen thus the indentation induced the vertical tearing of the subducting yzp along the tlfz

wind waves and moveable bed bottom friction abstract effects of moveable bed bottom friction for wave observations and wave modeling are investigated using a state of the art bottom friction model this model combines the hydrodynamic friction model of madsen et al with a moveable bed roughness model based on grant and madsen analyzing the present model for idealized swell cases it is shown that swell might result in wave generated sand ripples the large change of roughness corresponding to initial ripple formation results in a preferred wave height for swell related to bathymetric scales as generally occur in shelf seas away from the coast the corresponding wave generated bottom roughness is not defined by the local wave conditions but is related to the overall energy balance of the wave field sediment data thus is imperative for the interpretation of observed decay rates and friction factors for swell for idealized depth limited wind seas near bottom wave motion is expected to generate partially washed out ripples and moderate sheet flo

tectonics of the virgin islands basin north eastern caribbean the tectonics of the virgin islands basin are controlled by the plate boundary between the puerto rico virgin islands microplate and the stable part of the caribbean plate several contradicting theories about the formation and development of this basin have previously been proposed as part of the danish galathea 3 expedition extensive marine geological investigations of the basin were carried out in march 2007 including sediment coring and acquisition of multi beam and two dimensional seismic data this paper represents a summary of the key observations from the multi beam and the seismic data set the interpretation of these observations leads to the proposition of a tectonic model for the virgin islands basin the model consists of n s to nw se directed extension combined with e w trending sinistral strike slip and the new structural evidence from the virgin islands basin is entirely consistent with the most recently published gps data

fish tooth δ18o revising late cretaceous meridional upper ocean water temperature gradients the oxygen isotope composition of fossil fi sh teeth a paleo upper ocean temperature proxy exceptionally resistant to diagenetic alteration provides new insight on the evolution of the low to middlelatitude thermal gradient between the middle cretaceous climatic optimum and the cooler latest cretaceous period the new middle cretaceous low to middle latitude thermal gradient agrees with that previously inferred from planktonic foraminifera 18o recovered from deep sea drilling project and ocean drilling program drilling sites although the isotopic temperatures derived from 18o of fish teeth are uniformly higher by 3 4 c in contrast our new latest cretaceous thermal gradient is markedly steeper than those previously published for this period fish tooth 18o data demonstrate that low to middle latitude thermal gradients of the middle cretaceous climatic optimum and of the cooler latest cretaceous are similar to the modern one despite a cooling of 7 c between the two periods our new results imply that no drastic changes in meridional heat transport are required to explain the late cretaceous climate based on climate models such a cooling without any change in the low to middle latitude thermal gradient supports an atmospheric co2 decrease as the primary driver of the climatic evolution recorded during the late cretaceous

initial motion and pivoting characteristics of sand particles in uniform and heterogeneous beds experiments and modelling experiments are described in which the threshold conditions for sediment entrainment are measured for uniform and mixed sand beds beneath both steady and combined steady oscillatory flows derived critical shear stresses are compared with the mixed bed entrainment model of wiberg smith 1987 as predicted by the model coarser grains within a sand mixture are entrained at lower bed shear stresses than progressively finer grains entrainment occurs generally at lower shear stresses than predicted by the model especially under unidirectional flows this may be the result of grains resting in unusually unstable positions during the experiments because the beds are unworked at the start of the experiments the model of wiberg and smith predicts threshold conditions more accurately for the mixed beds if the bed pivoting angle is correctly defined the pivoting angles of the beds used here are measured using a new technique designed specifically for comparison with the threshold data the measured angles repeat the finding that the coarse grains are more mobile than the finer fractions of a mixture the results are poorly described by the pivoting angle model presented by wiberg smith 1987 and are better represented by a model of the form d di d50 after li komar 1986 where and are empirical constants the threshold model is found to be more effective using the improved pivoting relationship the entrainment of grains is found to be easier beneath unidirectional flows than combined flows in accordance with previous authors findings a suggestion that this result is caused by a change in the erosion mechanism beneath wave flows is made wave boundary layers may act as an extended laminar sublayer over bed grains and reduce the erosive efficiency of the overlying current flow the results of the experiment have implications for the natural sorting mechanisms of sediment beds being deposited in near threshold flows

modeling of vortex ripple morphodynamics 1 a new morphology module has been developed in order to perform simulations of the bed form evolution under hydrodynamic forcing this module has been implemented into the numerical model dune2d which solves the reynolds averaged navier stokes rans equations in the boundary layer and resolves sediment transport over moving sand beds the morphology module is composed of a modified central scheme and a routine that simulates avalanches and has been successfully applied to the study of orbital ripples evolution ripple growth from a quasiflat bed have been simulated and the growth behavior has been compared to previous experimental measurements the simulated ripples reach an equilibrium state where energy damping processes avalanches compensate energy production processes flux of sediment these processes have been analyzed during ripple creation growth merging and annihilation furthermore sandy bed evolutions have been simulated with random initial bed forms in order to examine the influence of the bed history on the final solution and the wave energy dissipated during these evolutions

transpressional rupture of an unmapped fault during the 2010 haiti earthquake the enriquillo plantain garden strike slip fault accommodates the relative motion between the north american and caribbean plates and was thought to have ruptured during the 2010 haiti earthquake satellite data instead indicate that a blind thrust fault possibly related to the haitian fold thrust belt was responsible and caused some contractional deformation on 12 january 2010 a mw 7 0 earthquake struck the port au prince region of haiti the disaster killed more than 200 000 people and caused an estimated 8 billion in damages about 100 of the country s gross domestic product1 the earthquake was initially thought to have ruptured the enriquillo plantain garden fault of the southern peninsula of haiti which is one of two main strike slip faults inferred to accommodate the 2 cm yr 1 relative motion between the caribbean and north american plates2 3 here we use global positioning system and radar interferometry measurements of ground motion to show that the earthquake involved a combination of horizontal and contractional slip causing transpressional motion this result is consistent with the long term pattern of strain accumulation in hispaniola the unexpected contractional deformation caused by the earthquake and by the pattern of strain accumulation indicates present activity on faults other than the enriquillo plantain garden fault we show that the earthquake instead ruptured an unmapped north dipping fault called the leog ne fault the leog ne fault lies subparallel to but is different from the enriquillo plantain garden fault we suggest that the 2010 earthquake may have activated the southernmost front of the haitian fold and thrust belt4 as it abuts against the enriquillo plantain garden fault as the enriquillo plantain garden fault did not release any significant accumulated elastic strain it remains a significant seismic threat for haiti and for port au prince in particular

sand ripples under sea waves part 2 finite amplitude development in the present paper the authors formulate a theory to predict the time development of sand ripples characterised by small but finite amplitude under the action of surface gravity waves the theory is based on a weakly nonlinear stability analysis of a flat sandy bottom subject to viscous oscillatory flow the parameters of the problem namely the reynolds number of the flow and the reynolds and froude numbers of sediments are assumed to fall within a neighbourhood of the critical conditions determined in blondeaux 1990 the analysis can predict the actual ripple height wavelength and profile when flow separation is absent i e for the case of rolling grain ripples assuming sleath s 1984 criterion for separation the values of the relevant parameters at which transition from rolling grain ripples to vortex ripples occurs are predicted a comparison between theoretical findings and experimental data supports the validity of the present theory

how deep was the early himalayan foredeep abstract the himalayan foredeep is a good archive of the events that occurred during different stages of the basin evolution the early part of this archive is used here to interpret depositional environments and paleobathymetry based on facies associations sedimentary structures and larger foraminifera three facies associations are recognized in the early himalayan foreland basin sequences facies association i containing chert breccia bauxite quartzose sandstone coal and black shale was deposited in short lived ephemeral streams swamps and inner parts of lagoons the limestones and shales of the facies association ii were deposited in a barrier lagoonal system where the former represent barrier and the latter represent lagoon deposits the limestone beds containing hummocks and wavy ripples were deposited under the influence of oscillatory storms and represent tempestites siltstone beds containing hummocky cross stratification and ripple cross laminae were deposited in the shoreface or foreshore zone where storm activities were dominant facies association iii comprises marl laminites and purple shale deposited in intertidal and supratidal zones of a tidal flat larger foraminifera such as nummulites and assilina flourished in the tropical climatic belt and accumulated in the coastal zone as a result of their transportation by waves and tides in general the sedimentation took place on a ramp similar to the present day persian gulf with a paleobathymetry of 55 m in strike continuity in pakistan the coeval sequences were deposited on shelves with a paleobathymetry

slip rate and earthquake recurrence along the central septentrional fault north american caribbean plate boundary dominican republic 1 the septentrional fault zone sfz is the major north american caribbean strike slip plate boundary fault at the longitude of eastern hispaniola the sfz traverses the densely populated cibao valley of the dominican republic forming a prominent scarp in alluvium our studies at four sites along the central sfz are aimed at quantifying the late quaternary behavior of this structure to better understand the seismic hazard it represents for the northeastern caribbean our investigations of excavations at sites near rio cenovi show that the most recent ground rupturing earthquake along this fault in the north central dominican republic occurred between a d 1040 and a d 1230 and involved a minimum of 4 m of left lateral slip and 2 3 m of normal dip slip at that site our studies of offset stream terraces at two locations rio juan lopez and rio licey provide late holocene slip rate estimates of 6 9 mm yr and a maximum of 11 12 mm yr respectively across the septentrional fault combining these results gives a best estimate of 6 12 mm yr for the slip rate across the sfz three excavations two near tenares and one at the rio licey site yielded evidence for the occurrence of earlier prehistoric earthquakes dates of strata associated with the penultimate event suggest that it occurred post a d 30 giving a recurrence interval of 800 1200 years these studies indicate that the sfz has likely accumulated elastic strain sufficient to generate a major earthquake during the more than 800 years since it last slipped and should be considered likely to produce a destructive future earthquake

the caribbean plate pulled pushed or dragged 1 mechanical coupling between the lithosphere and the asthenosphere remains a controversial topic in the geosciences beneath the caribbean plate shear wave splitting measurements indicate ew strain in the asthenosphere which can be interpreted as mantle flow driving or resisting motion of the overlying lithosphere here we constrain the average shear traction on the base of the caribbean plate by balancing all torques these torques result from body forces that act on the caribbean slab pull ridge push lateral density variations from plate boundary friction and from basal shear tractions we obtain a range of physically realistic torque solutions which we examine further by computing the corresponding stresses and rotations within the caribbean plate for comparison with observations the deformation field for the caribbean is particularly sensitive to the amount of friction on intraplate faults representative models have a good fit with observations and are characterized by 1 a near zero basal shear traction 0 3 mpa 2 lithosphere averaged plate boundary friction 10 mpa 3 local forces due to indenters and trench pull 4 a net pull by the caribbean slab and 5 intraplate fault shear stresses on the order of tens of megapascals we conclude that the mechanical coupling of the caribbean plate to the underlying asthenosphere is small

is there a northern lesser antilles forearc block 1 a systematic discrepancy exists between slip vectors of thrust fault earthquakes at the lesser antilles trench lat and the predicted direction of north american caribbean convergence a possibility has been that the discrepancy resulted because neither was well constrained estimating caribbean motion has been challenging owing to the limited data along the plate s complex boundaries similarly earlier studies had few slip vectors because interplate thrust events are infrequent to address these difficulties we estimate a new caribbean north america euler vector using recently available gps data from sites in the presumably stable interior of the caribbean and compare the predicted velocities to a larger set of slip vectors the discrepancy persists suggesting the northern lesser antilles forearc nlaf moves as a distinct entity from both the caribbean and north america for simplicity we treat its motion as a coherent block but because gps sites are not within the nlaf distributed deformation is also possible although there is no geologic evidence for the boundaries of the presumed nlaf block gps data show that the motions of martinique barbados and trinidad are similar to that of the caribbean suggesting that none are on the nlaf block and the southern lat is weakly coupled

morphology structure and tectonic evolution of the mona canyon northern mona passage from multibeam bathymetry side scan sonar and seismic reflection profiles 1 the submarine mona canyon is a rift between puerto rico and hispaniola of the greater antilles an integrated marine geophysical data set including multibeam bathymetry side scan sonar imagery single channel and multichannel seismic reflection profiles is used to evaluate the morphology structure and tectonic evolution of the mona canyon a structural restoration of the central mona canyon indicates that extension in the rift initiated in the middle oligocene approximately 30 ma a minimum total extension of 6 1 km and a minimum longitudinal strain of 11 4 across the central mona canyon are calculated the overall extension is proposed to have occurred over two phases phase i occurred from the middle oligocene to late miocene and was a slow 0 09 mm yr stage of at least 1 7 km of opening phase ii was most likely controlled by the impact of the subducted southeast portion of the bahamas platform beneath the northeastern caribbean plate margin phase ii was a more rapid 0 4 mm yr stage of extension of at least 4 4 km that occurred from the late pliocene to the recent as the se bahamas collision warped the middle and upper slope of the northern puerto rico margin along its advancing path and slowed the eastward movement of hispaniola relative to puerto rico the upper reaches of the mona canyon form the trailing edge of the puerto rico virgin islands block as it pulls away from a pinned hispaniola the mona reentrant marks the trailing edge of a northern hispaniola forearc sliver that forms due to increased coupling between the subducting north america plate and the overriding plate

on the plate boundary forces that drive and resist baja california motion the driving forces of microplate transport remain one of the major unknowns in plate tectonics our hypothesis postulates that the baja california microplate is transported along the north america pacific plate boundary by partial coupling to the pacific plate and low coupling to the north america plate to test this idea we use numerical modeling to examine the interplate coupling on a multiple earthquake cycle time scale along the baja california pacific plate boundary and compare the modeled velocity field with the observed geodetic motion of the baja california microplate we find that when the strain can localize along a weak structure surrounding microplate faults high interplate coupling produced by frictional tectonic stresses can reproduce the observed kinematics of the baja california microplate as seen from geodetic rigid plate motions we also find that the northward motion of baja california can influence the fault slip partitioning of the major faults in the north america pacific plate boundary region north of baja california

bragg scattering of random surface gravity waves by irregular seabed topography the bragg scattering of random non stationary surface gravity waves by random topography on a gently sloping bottom is investigated a correction is given of previously published expressions for the triad wave wave bottom interaction source term in the spectral energy balance equation and the result is reconciled with deterministic theories for the reflection of waves from sinusoidal seabed undulations for both normal and oblique incidence the stochastic and deterministic theories are equivalent in the limit of long propagation distances even for relatively short distances for example two bottom undulations the reflected energy predicted by the stochastic source term formulation is generally within 15 of values predicted by deterministic theories the detuning of bragg resonance by refraction and shoaling is discussed suggesting practical validity conditions for the stochastic theory the effect of bottom scattering on swell propagation is illustrated with numerical model computations for the north carolina continental shelf using high resolution bathymetry and an efficient semi implicit scheme to evaluate the bottom scattering source term and integrate the energy balance equation model results demonstrate the importance of forward scattering of waves that propagate at large oblique angles over bottom features with typical scales of one to several surface wavelengths this process contributes significantly to the directional spread of swell on the continental shelf by diffusing energy in the spectrum around the mean wave direction back scattering caused by bottom features with crests parallel to those of the surface waves and wavelengths close to half the surface wavelength is weak owing to the sharp roll off of the bottom elevation spectrum at high wavenumbers model predictions are consistent with field measurements

submarine morpho structure and active processes along the north american caribbean plate boundary dominican republic sector abstract the northern margin of hispaniola records the oblique collision underthrusting of the bahamas carbonate province with the island arc due to the collision northern hispaniola has suffered several natural disasters caused by major earthquakes and tsunamis such as the historic earthquake of 1842 the tsunami caused by earthquake driven slumping in 1918 in the mona passage the seismic crisis of 1943 1953 with five events of m 7 0 or the seismic crisis of 2003 with a main shock of m6 3 and a large aftershock of m5 3 using new swath multibeam bathymetry data and vintage single and multi channel seismic profiles we have performed a regional scale analysis and interpretation of the shallow morpho structure and active processes along the northern margin of the dominican republic we have identified three morphostructural provinces a the bahamas carbonate province b the hispaniola trench and c the insular margin which are divided into two tectonic domains the collision domain and underthrusting domain the southern slope of the bahamas carbonate province shows a very irregular morphology produced by active erosive processes and normal dip slip faulting evidence of an extensional tectonic regime and margin collapse this collapse is of major extent in the oblique collision domain where there are erosive and fault escarpments with higher dip slip fault throws the hispaniola trench is formed by the caicos and hispaniola basins in the underthrusting domain and by the santisima trinidad and navidad basins in the oblique collision domain they have a flat seafloor with a sedimentary filling of variable thickness consisting of horizontal or sub horizontal turbiditic levels the turbiditic fill mostly proceeds from the island arc through wide channels and canyons which transports sediment from the shelf and upper slope the insular margin comprises the insular shelf and the insular slope the active processes are generated on the insular slope where the northern hispaniola deformed belt is developed this deformed belt shows a very irregular morphology with a wnw ese trending n verging imbricate thrust and fold system this system is the result of the adjustment of the oblique collision underthrusting between the north american plate and the caribbean plate in the oblique underthrusting domain the along strike development of the imbricate system is highly variable forming salients and recesses this variability is due to along strike changes in the sediment thickness of the hispaniola trench as well as to the variable topography of the underthrusting bahamas carbonate province in the oblique collision domain the morphology of the insular slope and the development of the deformed belt deeply change the imbricate system is barely inferred and lies upslope these changes are due to the active collision of bahamas carbonate province with the insular margin where the spurs are indented against the insular margin throughout the entire area studied gravitational instabilities have been observed especially on the insular margin and to a lesser extent on the southern slope of the bahamas carbonate province these instabilities are a direct consequence of the active underthrusting collision process we have mapped large individual slumps north of puerto plata in the oblique underthrusting domain and zones of major slumps in the oblique collision domain these evidences of active processes must be considered as near field sources in future studies on the assessment of tsunami hazards in the region

measurements of the evolution of ocean wave spectra due to bottom friction data from a field experiment in which seven wave measurement instruments were placed in a linear transect across the great australian bight are analyzed to determine the spectral decay which can be attributed to bottom friction since other processes such as atmospheric input nonlinear interactions whitecap dissipation refraction and shoaling will also be active the spectral wave model wam is used as an analysis tool explicitly taking these additional processes into account in the analysis the data show marked spectral decay across the shelf analysis reveals that the bottom friction coefficient c is not constant as often assumed in operational wave models the bottom friction coefficient varies approximately inversely with the wave induced bed velocity consistent with the predictions of previous laboratory data and eddy viscosity models it is possible that percolation may also be important in the region but the available data do not allow the relative contributions of bottom friction and percolation to be determined

possible atmospheric co2 extremes of the middle cretaceous late albian turonian 1 atmospheric carbon dioxide co2 estimates for the middle cretaceous mk have a range of 4000 ppm which presents considerable uncertainty in understanding the possible causes of warmth for this interval this paper examines the problem of mk greenhouse forcing from an inverse perspective we estimate upper ocean water temperatures from oxygen isotope measurements of well preserved late albian turonian planktonic foraminifera and compare these against temperatures predicted by general circulation model gcm experiments with co2 concentrations of 500 7500 ppm at least 4500 ppm co2 is required to match maximum temperatures inferred from well preserved planktonic foraminifera approximately 900 ppm co2 produces a good match between the model and the minimum temperature estimates for the mk an ocean model forced by these two extremes in surface conditions brackets nearly all available bottom water temperature estimates for this interval the climate model results support nearly the entire range of mk co2 estimates from proxy data the ocean model suggests possible mk oceanographic changes from deep water formation in the high latitude region of one hemisphere to the other hemisphere in response to changes in atmospheric temperatures and hydrologic cycle strength we suggest that rather than contradicting one another the various proxy co2 techniques especially those with high temporal resolution may capture true variability in co2 concentrations and that mk co2 could have varied by several thousand ppm through this interval

ephemeral crustal thickening at a triple junction the mendocino crustal conveyor as the north american crust interacts with the migrating mendocino triple junction the crust is first significantly thickened and then equivalently thinned over a distance of a few hundred kilometers within a time frame of 5 m y or less this process of ephemeral crustal thickening is proposed to result from viscous coupling between the northward migrating gorda slab and the base of north america south of the triple junction a time dependent thermal mechanical finite element model is developed to test this hypothesis of plate boundary tectonics results of the numerical simulations show patterns of crustal deformation consistent with the mapped sequence of folding and faulting in the area the observed crustal structure and triple junction regional seismicity and localized regions of crustal extension coincident with the position of a hypothesized lower crustal melt zone

paleomagnetic evidence for late miocene counterclockwise rotation of north coast carbonate sequence puerto rico a paleomagnetic study of the essentially undeformed middle tertiary carbonate sequence along the north coast of puerto rico reveals statistically significant pre pliocene discordance of characteristic component directions against those expected from cratonic north america for much of the section despite generally weak to moderately weak magnetic intensities confirmation of the magnetization as primary in origin comes from the presence of two distinct components of magnetization intrasite bipolarity and or the reproducibility of measurements the mean geographic direction for the upper oligocene to middle miocene strata is 335 2 degree 32 9 degree and the corrected mean paleomagnetic pole is 207 6 degree 66 5 degree n 3 alpha 95 4 3 degree this suggests a counter clockwise ccw block rotation of puerto rico and its microplate of 24 5 degrees plus minus 5 8 degrees during the late miocene using a width of 250 km for the northern caribbean plate boundary zone ncpbz between the north american plate and caribbean plate the mean left lateral displacement implied is 1 8 to 2 4 cm yr which agrees fairly well with published relative motion rates for the two plates average rotation rate for 50 ma to 20 ma was 0 7 degree my but perhaps as great as 4 degree my in the miocene resolution of mean paleolatitude indicates northward motion of a degree or lessmore during the period of rotation causes of this short lived rotation may include 1 tectonic escape from the inhibiting presence of the bahama banks and beata ridge during eastward motion of puerto rico along the sinistral transpressive puerto rico trench and muertos trough fault systems or 2 changes in relative plate motions of the caribbean and north american plate during the late miocene less

propagation of swell across a wide continental shelf the transformation of ocean swell across a wide shallow nominal depths 25 50 m continental shelf is examined with data from a 100 km long transect of bottom pressure recorders extending from the shelf break to the beach at duck north carolina the analysis is restricted to periods with light winds when surface boundary layer processes e g wave generation by wind and wave breaking in the form of whitecaps are expected to be relatively unimportant the majority of the observations with low energy incident swell conditions significant wave heights 1 m shows weak variations in swell energy across the shelf in qualitative agreement with predictions of a spectral refraction model although the predicted ray trajectories of waves propagating over the irregular shelf bathymetry are quite sensitive to the deep water incident wave directions the predicted spatial energy variations for broadbanded wave fields are small and relatively insensitive to incident wave conditions consistent with the observations whereas swell dissipation on the shelf appears to be insignificant in low energy conditions strong attenuation of swell energy levels a factor 4 between the shelf break and nearshore sites was observed in high energy conditions significant wave height 2 5 m this decay not predicted by the energy conserving refraction model indicates that dissipative bottom boundary layer processes can play an important role in the transformation of swell across wide continental shelves

sand ripples under sea waves part 1 ripple formation in the present paper we formulate a predictive theory of the formation of sand ripples under sea waves the theory is based on a linear stability analysis of a flat sandy bottom subject to a viscous oscillatory flow the conditions for decay or amplification of a bottom perturbation are determined along with the wavelength of the most unstable component as a function of the reynolds number of the flow and of the froude and reynolds numbers of the sediments a comparison between theoretical findings and experimental data supports the validity of the present theory an analytical solution for viscous oscillatory flow over a small amplitude wavy bottom is determined for arbitrary values of the ratio r between the amplitude of fluid displacement and the wavelength of bottom waviness previous works by lyne 1971 and sleath 1976 who considered small or large values of r are thus extended

oblique collision in the northeastern caribbean from gps measurements and geological observations 1 previous caribbean gps studies have shown that the rigid interior of the caribbean plate is moving east northeastward 070 at a rate of 18 20 3 mm yr relative to north america this direction implies maximum oblique convergence between the island of hispaniola on the caribbean plate and the 22 27 km thick crust of the bahama carbonate platform on the adjacent north america plate we present a tectonic interpretation of a 15 site gps network which spans the hispaniola bahama oblique collision zone and includes stable plate interior sites on both the north america and caribbean plates measurements span the time period of 1994 1999 in a north america reference frame gps velocities in puerto rico st croix and the lesser antilles indicate that these areas move as a single block in an east northeast direction 070 at a rate of 19 20 mm yr consistent with the movement of the rigid interior of the caribbean plate gps velocities at six sites in central and eastern hispaniola dominican republic show drastically different behavior with more eastwardly strikes 080 and much slower rates 4 17 mm yr than areas of the stable caribbean plate the boundary between the relatively slower moving hispaniola collisional zone and the relatively faster moving uncollided puerto rico virgin islands area is the mona passage where late neogene rifting occurs in a broad zone elastic modeling favors strain partitioning with oblique slip on the outer low angle submarine thrust faults north hispaniola muertos and strike slip on the inner subvertical subaerial strike slip faults septentrional enriquillo

constraints from finite element modeling on the active tectonics of northern central america and the middle america trench 1 we have developed an elastic finite element model in order to study the role of the different forces acting on the northwestern part of the central american volcanic arc and the chortis block we present synthetic focal mechanisms maps of tectonic regime and strain crosses to analyze the results the models show that to achieve the observed state of stress on the volcanic arc the arc must be modeled as a lithospheric weak zone also the forces related to the eastward drift of the caribbean plate must be higher than those related to the subduction of the cocos plate the coupling on the subduction interface must be low with or without slip partitioning due to the obliquity of the subduction at the trench at guatemala the western edge of the chortis block is pinned against north america even with low trench normal forces making the triple junction between the cocos north american and caribbean plates a zone of diffuse deformation the extension in the western part of the chortis block from guatemala to the honduras depression is explained by the geometry of the north american caribbean plate boundary and the direction of motion of the caribbean plate with respect to north america the direction of extension in the chortis block is always e w regardless of the magnitude of the applied forces and the main part of the deformation is absorbed between the ipala graben and the honduras depression both features being consistent with our models

mechanics of graben formation in crustal rocks a finite element analysis small 1 10 km wide grabens are ubiquitous tectonic structures that have been observed on the surfaces of all the terrestrial planets and satellites in spite of their frequent occurrence there is no fundamental understanding of how they form other than that they are characteristic of extensional terranes this paper examines the mechanics of the initial stages of graben formation and demonstrates that the configuration of a pair of antithetically dipping normal faults a graben is the energetically most favorable fault configuration in elastic brittle rocks subjected to pure extension a corollary to this hypothesis is that the occurrence of synthetic normal faults is indicative of a stress field other than purely extensional or of nonhomogeneous characteristics of the rock the analysis proceeds by computing the stress field in the vicinity of a single initial normal fault using a two dimensional finite element model it is shown that slip on this fault substantially lowers the proximity to failure of the surrounding rocks except for two small regions one near the surface of the downthrown block and the other near the fault tip the region on the downthrown block is located a horizontal distance from the initial fault slightly less than the fault s depth the proximity to failure actually increases here and a secondary fault develops an antithetic secondary fault would link this region with the other failure zone near the fault tip to demonstrate the preference for antithetic secondary faults more rigorously we show that this fault configuration results in a smaller total strain energy than the synthetic configuration in addition a two layer model is used to show that the graben s width is only weakly dependent upon the presence of mechanically distinct layers in the crust both weak over strong and strong over weak configurations are investigated the depth of the initial fault and the thickness of the top layer are varied and the width of the resulting graben is evaluated by computing the distance between the initial fault and the region of highest proximity to failure near the surface this analysis indicates that the depth of the initial fault is the major factor controlling graben width

deformation of jamaica and motion of the gonâve microplate from gps and seismic data summary we use velocities from 20 gps sites on the island of jamaica and seismic data from the jamaican seismic network to quantify motion of the proposed gonave microplate and study deformation and earthquake hazard in jamaica all 20 jamaican gps sites move significantly relative to both the caribbean and north american plates thereby confirming the existence of the gonave microplate in a caribbean plate reference frame the fastest site velocities in jamaica are 8 1m m yr 1 representing a minimum estimate for the rate of gonave caribbean plate motion we estimate a firm upper limit of 13 1m m yr 1 for gonave caribbean plate motion assuming that additional elastic or permanent deformation occurs north of jamaica beyond the reach of our gps network the range of estimates for gonave caribbean plate motion exceeds the 3 7m m yr 1 range of geologically derived rates for post 10 ma fault slip in jamaica suggesting that motion has either increased relative to the long term deformation rate or that estimates of the long term deformation rate are too slow minimum and maximum rates for gonave north america plate motion are 6 1m m yr 1 and 11 1m m yr 1 based on the differences between the estimated gonave caribbean rates and a recent gps based estimate of 19 3 1m m yr 1 of caribbean north american plate motion in jamaica these are slower than 15 20 mm yr 1 published estimates of the long term seafloor spreading rate across the cayman spreading centre which records gonave north american plate motion our observations are thus consistent with a model in which gonave caribbean plate motion has increased through time while gonave north america plate motion has decreased possibly reflecting a progressive transfer of slip from plate boundary structures that accommodate gonave north america motion to faults that carry gonave caribbean plate motion in jamaica gps site directions in both the caribbean and north american plate reference frames are parallel to the caribbean north america plate slip direction and are only 10 20 different from the azimuths of the island s major strike slip faults the mean p and t axes for 48 earthquakes since 1941 have near horizontal plunges and are oriented 45 from the predicted plate slip direction the kinematic and seismic data thus indicate that deformation on the island is dominated by left lateral shear along largely e w trending strike slip faults relative to the caribbean plate the jamaican gps velocities exhibit a nearly monotonic increase in site velocities from south to north along a transect orthogonal to the island s major e w faults this velocity gradient likely reflects the accumulation of elastic strain due to frictional locking of the major e w faults velocities however also increase monotonically from the wsw to ene along a transect orthogonal to the island s numerous nnw striking faults consistent with the accumulation of significant elastic shortening along those faults and supportive of an interpretation of those faults as restraining bends seismic hazard assessment based on the gps derived deformation budget likely maximum fault rupture lengths and the historical seismic record suggests approximate repeat times of one to several centuries for earthquakes of maximum magnitudes of m w 7 0 7 3 the strain that has accumulated since the destructive 1692 earthquake near the capital city of kingston is presently sufficient to release a m w 7 2 earthquake in eastern jamaica

accretionary margin of north western hispaniola morphology structure and development of part of the northern caribbean plate boundary abstract broad range side scan sonar gloria images and single and multi channel seismic reflection profiles demonstrate that the margin of north western hispaniola has experienced compression as a consequence of oblique north american caribbean plate convergence two principal morphological or structural types of accretionary wedges are observed along this margin the first type is characterized by a gently sloping 4 sea floor and generally margin parallel linear sets of sea floor ridges that gradually deepen towards the flat hispaniola basin floor to the north the ridges are caused by an internal structure consisting of broad anticlines bounded by thrust faults that dip southwards beneath hispaniola anticlines form at the base of the slope and are eventually sheared and underthrust beneath the slope in contrast the second type of accretionary wedge exhibits a steeper 6 16 sea floor slope characterized by local slumping and a more abrupt morphological transition to the adjacent basin the internal structure appears chaotic on seismic reflection profiles and probably consists of tight folds and closely spaced faults we suggest that changes in sea floor declivity and internal structure may result from variations in the dip or frictional resistance of the decollement or possibly from changes in the cohesive strength of the wedge sediments the observed pattern of thickening of hispaniola basin turbidites towards the insular margin suggests differential southwards tilting of the hispaniola basin strata probably in response to north america caribbean plate interactions since the early tertiary based upon indirect age control from adjacent parts of the northern caribbean plate boundary we infer a late eocene to early miocene episode of transcurrent motion i e little or no tilting an early miocene to late pliocene period of oblique convergence i e increased tilt during which the accretionary wedge began to be constructed and a late pliocene to recent episode of increased convergence i e twice the miocene to pliocene tilt which has led to rapid uplift and erosion of sediment sources on the margin and on hispaniola generating a submarine fan at the base of the insular slope

strain partitioning and fault slip rates in the northeastern caribbean from gps measurements 1 gps data collected in the dominican republic from 1994 to 2001 show that oblique convergence between the north american and caribbean plates is partitioned between 5 2 2 mm yr 1 of dip slip reverse motion on the north hispaniola thrust approximately n s and 12 8 2 5 mm yr 1 and 9 0 9 0 mm yr 1 of approximately e w left lateral strike slip motion on the septentrional and enriquillo faults 95 confidence the agreement between gps and paleoseimological slip rates on the septentrional fault together with the 770 960 years since the last major earthquake and the 800 1200 years maximum repeat time of major earthquakes may indicate that the septentrional fault is currently in the late phase of its rupture cycle

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

coulomb stress evolution in northeastern caribbean over the past 250 years due to coseismic postseismic and interseismic deformation summary the northeastern caribbean region accommodates 20 mm yr 1 of oblique convergence between the north american and caribbean plates which is distributed between the subduction interface and major strike slip faults within the overriding plate as a result this heavily populated region has experienced eleven large m 7 0 earthquakes over the past 250 yr in an effort to improve our understanding of the location and timing of these earthquakes with an eye to understand where current seismic hazards may be greatest we calculate the evolution of coulomb stress on the major faults since 1751 due to coseismic postseismic and interseismic deformation our results quantify how earthquakes serve to relieve stress accumulated due to interseismic loading and how fault systems communicate with each other serving both to advance or retard subsequent events we find that the observed progressive westwards propagation of earthquakes on the septentrional and enriquillo strike slip faults and along the megathrust was encouraged by coseismic stress changes associated with prior earthquakes for the strike slip faults the loading of adjacent segments was further amplified by postseismic relaxation of a viscoelastic mantle in the decades following each event furthermore earthquakes on the septentrional fault relieve a small level of coulomb stress on the parallel enriquillo fault to the south and vice versa perhaps explaining anticorrelated timing of events on these respective fault systems the greatest net build up of coulomb stress changes over the past 250 yr occurs along the central and eastern segment of the septentrional and the bowin strike slip faults 65 71 w as no recent earthquake has relieved stress in these regions for oblique thrust faults net stress build up over the past 250 yr is the largest on the north american caribbean megathrust west of 70 5 w high coulomb stress has also developed east of 65 5 w where no historic events have been inferred to have relieved stress though uncertainties in fault slip rates from our block model associated with a lack of gps observations in this region may have led to an over estimation of stress changes

seismic evidence for a slab tear at the puerto rico trench 1 the fore arc region of the northeast caribbean plate north of puerto rico and the virgin islands has been the site of numerous seismic swarms since at least 1976 a 6 month deployment of five ocean bottom seismographs recorded two such tightly clustered swarms along with additional events joint analyses of the ocean bottom seismographs and land based seismic data reveal that the swarms are located at depths of 50 150 km focal mechanism solutions found by jointly fitting p wave first motion polarities and s p amplitude ratios indicate that the broadly distributed events outside the swarm generally have strike and dip slip mechanisms at depths of 50 100 km while events at depths of 100 150 km have oblique mechanisms a stress inversion reveals two distinct stress regimes the slab segment east of 65 w longitude is dominated by trench normal tensile stresses at shallower depths 50 100 km and by trench parallel tensile stresses at deeper depths 100 150 km whereas the slab segment west of 65 w longitude has tensile stresses that are consistently trench normal throughout the depth range at which events were observed 50 100 km the simple stress pattern in the western segment implies relatively straightforward subduction of an unimpeded slab while the stress pattern observed in the eastern segment shallow trench normal tension and deeper trench normal compression is consistent with flexure of the slab due to rollback these results support the hypothesis that the subducting north american plate is tearing at or near these swarms the 35 year record of seismic swarms at this location and the recent increase in seismicity suggest that the tear is still propagating

development of subaqueous barchanoid shaped dunes due to lateral grain size variability in a tidal inlet channel of the danish wadden sea 1 high resolution bathymetry at centimeter scale accuracy acquired with a multibeam echo sounder system revealed the existence of barchanoid shaped large i e length 10 100 m to very large i e length 100 m dunes in the gradyb tidal inlet channel in the danish wadden sea the development of these dunes is due to an increase in dune celerity from 12 m yr in the center of the channel to around 30 m yr at the sides this increase in dune celerity can be explained by the fact that dune heights decrease from 3 1 m in the center of the channel to 1 4 m at the sides as a smaller sediment volume has to be moved per unit time for equal dune celerity water depth is uniform across the channel likewise high resolution acoustic doppler current profiler measurements across the channel showed a uniform distribution of both ebb and flood flow thus no correlation between dune dimensions and water depth or flow velocity was established instead high accuracy bed sampling along the crests of the dunes showed a decrease in mean grain size from 0 63 mm in the center to 0 36 mm at the sides of the channel the decrease in dune height is ascribed to this decrease in grain size given that flow depth and flow velocity are uniform across the channel the lateral decrease in grain size is suggested to result from sorting effects by secondary currents directed from the center toward the sides of the channel in the trough lee side region of the barchanoid shaped dunes

unifying large and small wave generated ripples 1 frequently in field and laboratory studies of wave generated bed forms on beds of sandy sediments both large and small wave generated ripples lwrs and swrs are observed and in some situations may be superimposed upon one another the present paper examines relationships between measured wave conditions and the geometry of lwrs and swrs and shows that existing empirical equations used to predict the dimensions of swrs perform badly for lwrs to address this problem relationships found between ripple geometry and the wave reynolds number are used as the basis for new expressions for prediction of ripple height wavelength and steepness that improve the accuracy of existing approaches for both lwrs and swrs the present results indicate strongly that swrs and lwrs are related and their superposition in certain conditions reflects the time lag between the response of the bed to changing hydrodynamic conditions they must be considered therefore when estimating the total bed roughness in a range of practical engineering and numerical modeling applications

absolute plate motions and regional subduction evolution we investigate the influence of absolute plate motion on regional 3 d evolution of subduction using numerical thermomechanical modeling building on our previous work we explore the potential impact of four different absolute plate motion frames on subduction evolution in the western mediterranean region during the last 35 my one frame is data based and derived from the global moving hotspot reference frame gmhrf of doubrovine et al 2012 and three are invented frames a motion frame in which the african plate motion is twice that in the gmhrf and two frames in which either the african plate or the iberian continent is assumed fixed to the mantle the relative africa iberia convergence is the same in all frames all motion frames result in distinctly different 3 d subduction evolution showing a critical dependence of slab morphology evolution on absolute plate motion we attribute this to slab dragging through the mantle forced by the absolute motion of the subducting plate which causes additional viscous resistance affecting subduction evolution we observed a strong correlation between increase in northward africa motion and decrease in the speed of westward slab rollback along the african margin we relate this to increased mantle resistance against slab dragging providing new insight into propagation and dynamics of subduction transform edge propagator step faults our results demonstrate a large sensitivity of 3 d slab evolution to the absolute motion of the subducting plate which inversely suggests that detailed modeling of natural subduction may provide novel constraints on absolute plate motions

development of subaqueous barchanoid shaped dunes due to lateral grain size variability in a tidal inlet channel of the danish wadden sea development of barchanoid shaped dunes

movable bed roughness in unsteady oscillatory flow a model to predict the roughness in unsteady oscillatory flows over movable noncohesive beds is presented the roughness over movable beds is shown to be a function of the boundary shear stress rather than a fixed geometrical scale as is the case for fully rough turbulent boundary shear flows over immobile beds the model partitions the roughness into two distinct contributions these two contributions are due to the form drag around individual bed forms and to the near bed sediment transport the form drag over the bed forms is treated explicitly as a function of the boundary geometry and shear stress the ripples are predicted as a function of the local skin friction and a semiempirical expression is derived using standard law of the wall arguments which gives the ripple or form roughness as a function of the boundary geometry the ripple roughness is found to be proportional to the product of the ripple steepness and height favorable comparison of the form drag model with the results of bagnold s 1946 fixed ripple study is found the value of z0 associated with intense sediment transport in oscillatory flow over a flat bed is determined from carstens et al s 1969 experiments this value is found to be 7 or 8 grain diameters an expression is derived for the roughness associated with the maximum thickness of a near bottom sediment transporting layer consistent with owen s 1964 roughness hypothesis for saltation of uniform grains in air at large values of the boundary shear stress relative to the critical value for initial sediment motion the derived expression is similar to the results of smith and mclean s 1977 unidirectional flow approach modified for oscillatory flow the total roughness model is found to compare favorably with carstens et al s 1969 data in contrast to smith and mclean s 1977 steady flow findings the results here show that when ripples are present they account for a significant portion of the boundary roughness

observations of wave generated vortex ripples on the north carolina continental shelf 1 sand ripples with wavelengths between 0 5 and 3 m were observed on the bottom across the u s east coast continental shelf off north carolina during three side scan sonar surveys in september and december 1999 ripples were present in about 75 of the survey images in particular in regions with coarser sediments analysis of surficial sediment samples shows that median grain diameters range from 0 1 to 4 7 mm with large variations on the inner shelf over distances 1 km the observed ripple properties are consistent with wave generated vortex ripples analysis of concurrent wave observations indicates that the ripple crests were aligned perpendicular to the average direction of near bottom wave induced motions during preceding events that were sufficiently energetic to mobilize surficial sediments furthermore the ripple wavelengths proportionality to near bottom wave orbital excursions is consistent with wave formed vortex ripples these findings support the hypothesis that the observed strong attenuation of waves across the shelf resulted from form drag over large vortex ripples

megaripple migration in a natural surf zone migrating megaripples are bedforms that appear in the surf zone of sandy coasts1 with heights of 0 1 0 5 m and wavelengths of 1 5 m they are similar in size and shape to small dunes large ripples or sand waves such sedimentary bedforms have been studied in subaerial2 steady flow3 and intertidal4 environments as well as in laboratory flume experiments5 they affect overlying currents by introducing hydraulic roughness4 6 and may provide a mechanism for sediment transport7 8 as well as forming sedimentary structures in preserved facies9 10 the formation orientation and migration of such bedforms is not understood well11 12 dunes for example can be aligned with their crests perpendicular to steady unidirectional winds13 but in more complex wind fields their orientation becomes difficult to predict14 15 16 17 similarly it is not known how sea floor megaripples become aligned and migrate in the complex flows of the surf zone here we present observations in the surf zone of a natural beach which indicate that megaripples do not migrate in the direction of the vector sum of the currents but are aligned so that the sediment transport normal to the bedform crest is maximized17 this may need to be taken into account in modelling morphology change and interpreting existing and fossil morphologic patterns

kinematic reconstruction of the caribbean region since the early jurassic abstract the caribbean oceanic crust was formed west of the north and south american continents probably from late jurassic through early cretaceous time its subsequent evolution has resulted from a complex tectonic history governed by the interplay of the north american south american and paleo pacific plates during its entire tectonic evolution the caribbean plate was largely surrounded by subduction and transform boundaries and the oceanic crust has been overlain by the caribbean large igneous province clip since 90 ma the consequent absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into the global circuit of plate motions here we present an updated quantitatively described kinematic reconstruction of the caribbean region back to 200 ma integrated into the global plate circuit and implemented with gplates free software our reconstruction includes description of the tectonic units in terms of euler poles and finite rotation angles our analysis of caribbean tectonic evolution incorporates an extensive literature review to constrain the caribbean plate motion between the american continents we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input and uses regionally extensive metamorphic and magmatic phenomena such as the great arc of the caribbean the clip and the caribbean high pressure belt as correlation markers the resulting model restores the caribbean plate back along the cayman trough and major strike slip faults in guatemala offshore nicaragua offshore belize and along the northern andes towards its position of origin west of the north and south american continents in early cretaceous time we provide the paleomagnetic reference frame for the caribbean region by rotating the global apparent polar wander path into coordinates of the caribbean plate interior cuba and the chortis block we conclude that formation of the caribbean plate west of the north and south americas as a result of panthalassa pacific spreading leads to a much simpler plate kinematic scenario than proto caribbean atlantic spreading placing our reconstruction in the most recent mantle reference frames shows that the clip originated 2000 3000 km east of the modern galapagos hotspot and may not have been derived from the corresponding mantle plume finally our reconstruction suggests that most if not all modern subduction zones surrounding the caribbean plate initiated at transform faults two of these along the southern mexican and nw south american margins evolved diachronously as a result of migrating trench trench transform triple junctions

a hybrid eulerian lagrangian model for spectral wave evolution with application to bottom friction on the continental shelf abstract a hybrid eulerian lagrangian wave model is presented that solves the spectral energy balance equation for surface gravity waves in varying depth the energy of each spectral component is advected along lagrangian ray trajectories the source terms in the energy balance equation e g interactions between wave components and nonconservative processes are computed on a fixed eulerian grid and interpolated onto the ray trajectories the source terms are integrated in time along the rays this integration is performed in parallel over the entire model domain the main advantage of this new model named crest coupled rays with eulerian source terms is that refraction of waves by subgrid scale depth variations is evaluated accurately using precomputed rays and thus the model can be applied with relatively coarse source term grids to large coastal areas hindcasts of swell evolution across the north carolina continental shelf are presented for a source term restricted to energy dissipation in th

observations of wave orbital scale ripples and a nonequilibrium time dependent model 1 measurements of seafloor ripples under wave dominated conditions from the leo15 site and the martha s vineyard coastal observatory were used to develop a time dependent model for ripple geometry the measurements consisted of backscatter imagery from rotary side scan sonars centimeter resolution bathymetric maps from a two axis rotary pencil beam sonar and forcing hydrodynamics during moderate energy conditions the ripple wavelength typically scaled with wave orbital diameter in more energetic conditions the ripples reached a maximum wavelength of 0 8 to 1 2 m and did not continue to increase in wavelength or decrease in height the observations showed that the relict ripples left after storms typically had wavelengths close to the maximum wavelength the time dependent model is based on an equilibrium model that allows the ripples to maintain wavelength proportional to wave orbital diameter until a suspension threshold determined by wave velocity and grain size is reached the time dependent model allows the ripple spectra to follow the equilibrium solution with a temporal delay that is based on the ratio of the ripple cross sectional area to the sediment transport rate the data was compared to the equilibrium model a simplified version of the time dependent model where the ripples were assumed to follow the equilibrium model only when the bed stress was sufficient to move sediment and the complete time dependent model it was found that only the complete time dependent model was able to correctly predict the long wavelength relict ripples and that the other approaches underpredicted relict ripple wavelengths

what drives microplate motion and deformation in the northeastern caribbean plate boundary region the north caribbean plate boundary zone is a broad deformation zone with several fault systems and tectonic blocks that move with different velocities the indentation by the bahamas platform the bahamas collision is generally invoked as a cause of this fragmentation we propose that a second driver of deformation is the western edge of the south dipping puerto rico slab moving sideways with the north america plate the westward motion of the slab edge results in a push on the caribbean plate farther west we refer to this second mechanism for deformation as slab edge push the motion of the north america plate relative to the caribbean plate causes both drivers to migrate from east to west the bahamas collision and slab edge push have been operating simultaneously since the miocene the question is the relative importance of the two mechanisms we use mechanical finite element models that represent the two mechanisms from the late oligocene 30 ma to the present for the present both models successfully reproduce observed deformation implying that both models are viable back in time the slab edge push mechanism better reproduces observations neither mechanism successfully reproduces the observed miocene counterclockwise rotation of puerto rico we use this rotation to tune a final model that includes fractional contributions of both mechanisms we find that the slab edge push was the dominant driver of deformation in the north caribbean plate boundary zone since 30 ma

neotectonics of puerto rico and the virgin islands northeastern caribbean from gps geodesy the boundary between the north american and caribbean plates is characterized primarily by left lateral motion along predominantly east west striking faults seismicity and marine geophysical survey data are consistent with at least two and possibly three microplates in the diffuse boundary zone in the northeastern caribbean 1 the gonave 2 the hispaniola and 3 the puerto rico northern virgin islands prvi we discuss results from gps geodetic measurements acquired since 1994 to test the microplate hypothesis define prvi translation and rotation within the boundary zone and constrain prvi neotectonics gps derived velocities are analyzed with respect to both north american and caribbean plate reference frames integrated displacements across prvi are limited to a few millimeters per year consistent with a rigid prvi and permitting calculation of an average velocity for prvi the motions of prvi relative to north america and the caribbean are 16 9 1 1 mm yr toward n68 e 3 1 and 2 4 1 4 mm yr toward s79 w 26 1 respectively in contrast with some recent models ongoing rotation of prvi about a nearby 25 distant vertical axis is not supported by the geodetic data in addition we argue against eastward tectonic escape of prvi and favor a simple progressive increase in velocity across the plate boundary zone requiring that the summed magnitude of strike slip fault slip rates will equal the total plate motion rate between the caribbean and north america gps data are consistent with components of left lateral strike slip faulting along the muertos trough south of puerto rico and shortening across the puerto rico trench comparison of gps velocities for prvi with respect to north america with total north america caribbean relative motion suggests up to 85 of north american caribbean plate motion is accommodated by the puerto rico trench and offshore faults north of puerto rico differences in gps derived velocities from hispaniola and prvi yield east west extension across the n s trending mona rift of a few millimeters per year when estimated elastic strain accumulation effects along the north hispaniola deformed belt and the septentrional fault zone are considered the opening rate implies an age of the mona rift of 2 3 million years agreeing with marine geophysical data that support a young age for the structure

video based observations of nearshore sand ripples and ripple migration 1 observations of o 1 m length and o 0 1 m height sand ripples at waimea bay a steep slope 0 05 pocket beach on the north shore of oahu hawaii are presented time series of ripple patterns over a 900 m2 section of the nearshore in depths of 1 2 m are obtained using time averaged video images from an argus station overlooking the bay ripples are detected during weak wave conditions in the summer or between winter swell events the ripple field exhibits narrow band wave number structure with ripple crests oriented parallel to the shoreline the ripple wavelengths vary with wave orbital displacements but they are shorter than predicted by orbital vortex ripple scaling relationships a new suspension limited model smith and wiberg 2006 traykovski 2006 in which the suborbital ripple wavelengths vary with wave period appears to describe well the observed ripple wavelength scaling lagged correlations between sequential argus images reveal area average ripple migration rates ranging from 3 3 m day 1 offshore to 4 5 m day 1 the corresponding estimated sediment transport ranges from 0 3 m3 m 1 day 1 to 0 5 m3 m 1 day 1 similar to previous estimates of cross shore transport based on observed volume changes at the subaerial beach this suggests that the recovery of beach sand following major swell driven erosion events may be accomplished in part by the shoreward migration of seabed ripples

north american plate dynamics deformation within the north american plate in response to various tectonic processes is modeled using an elastic finite element analysis a coarse grid contains 328 elements and 190 nodes while a fine grid contains 718 elements and 396 nodes for a spatial resolution of 2 3 abundant information about the present day state of intraplate stress constrains the modeling the dominant pattern that must be fit by all acceptable models is an ene trend for the maximum compressive stress for most of the plate east of the rocky mountains the tectonic processes considered in the modeling include ridge forces associated with the normal thermal evolution of oceanic lithosphere shear and normal stresses transmitted across transforms normal stresses transmitted across convergent boundaries stresses due to horizontal density contrasts within the continent and shear tractions applied along the base of the plate model stresses are calculated with respect to a lithostatic reference stress state distributed ridge forces of magnitude 2 1012 n m predict deviatoric stresses of the order of 20 40 mpa that are capable of accounting for the dominant observed ene stress trend driving drag models also fit the trend but are not preferred because of a predicted tenfold increase in compressive stress magnitudes from east to west across the plate assuming that ridge forces account for the dominant ene stress trend bounds may be placed on other possible forces for example shear stresses transmitted across transform boundaries along the san andreas and caribbean are small of the order of 5 10 mpa also compressive stresses of the order of 5 10 mpa transmitted across the major transforms improve the fit to the data compressive stresses across convergent margins along the aleutians and the middle america trench are important

the neotectonic setting of puerto rico the island of puerto rico in the northeast caribbean lies within a broad deformation zone between the caribbean and north american plates the simplest model for the tectonic setting of puerto rico has major strike slip movement on nearly east west lines in the vicinity of the puerto rico trench coupled to a small counterclockwise rotation of a puerto rico block within the broader plate boundary zone this simple model is attractive because it predicts the tectonic regime south of puerto rico and provides an explanation for a possible component of extension across the puerto rico trench west of 65 5 w gloria long range sidescan sonar data and seismic reflection profiles have been used to test this model by mapping the major tectonic features across the plate boundary north and south of puerto rico to the north the new data help to resolve between conflicting models of underthrusting or strike slip motion at the puerto rico trench no direct evidence of compression is seen although evidence for normal and strike slip movement is abundant this combined with regional considerations leads us to conclude that the main east west trending part of the puerto rico trench between 65 5 w and 68 w lies within a strike slip regime although oblique convergence occurs both to the east and west where the plate boundary trends east southeast to the south of puerto rico underthrusting of the caribbean plate beneath the island decreases from west to east and it is ultimately replaced by extension in the virgin islands basin east of 65 w