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

double averaging turbulence characteristics in seeping rough bed streams 1 results of an experimental study on the effects of bed injection upward seepage from the permeable bed and suction downward seepage on the double averaged da turbulent flow characteristics over and within the interface of flow gravel beds are presented the da reynolds shear stress within the interfacial sublayer undergoes a higher damping with suction and a lesser damping with injection as compared to that with no seepage the form induced stress within the interfacial sublayer has a decelerating effect with no seepage and suction and an accelerating effect with injection the quadrant analysis suggests that within the interfacial sublayer the sweep events in flows with injection and the ejection events with suction are the primary contributors toward the reynolds shear stress production while both the events in flows with no seepage are equally prevalent in the roughness sublayer form induced and interfacial sublayers together the mean duration of bursting increases with suction and decreases with injection but the bursting events become less frequent with suction and more frequent with injection the analysis of da higher order moments confirms that the seepage affects the reynolds normal stress flux the turbulent kinetic energy tke flux and the tke budget a downward upstream flux of tke is developed within the roughness sublayer with injection while an upward downstream flux of tke is prevalent over the entire flow depth with suction the significance of this study lies on the hydrodynamic process in such a physical system that may result in modifying the flow resistance sediment entrainment and morphological characteristics of a streambed

velocity distribution of turbulent open channel flow with bed suction this study investigates theoretically and experimentally the velocity distributions of turbulent open channel flow with bed suction a velocity profile with a slip velocity at the bed surface and an origin displacement under the bed surface is proposed and discussed based on this assumption a modified logarithmic law is derived the measured experimental velocity distribution verifies the accuracy of the theoretically derived profile the data show a significant increase in the near bed velocity and a velocity reduction near the water surface resulting in the formation of a more uniform velocity distribution the values of the origin displacement slip velocity and shear velocity are found to increase with increasing relative suction the measured data show the occurrence of two flow regions in the suction zone a transitional region in which the velocity readjusts rapidly and an equilibrium region

glacier changes in southeast alaska and northwest british columbia and contribution to sea level rise 1 the digital elevation model dem from the 2000 shuttle radar topography mission srtm was differenced from a composite dem based on air photos dating from 1948 to 1987 to determine glacier volume changes in southeast alaska and adjoining canada srtm accuracy was assessed at 5 m through comparison with airborne laser altimetry and control locations measured with gps glacier surface elevations lowered over 95 of the 14 580 km2 glacier covered area analyzed with some glaciers thinning as much as 640 m a combination of factors have contributed to this wastage including calving retreats of tidewater and lacustrine glaciers and climate change many glaciers in this region are particularly sensitive to climate change as they have large areas at low elevations however several tidewater glaciers that had historically undergone calving retreats are now expanding and appear to be in the advancing stage of the tidewater glacier cycle the net average rate of ice loss is estimated at 16 7 4 4 km3 yr equivalent to a global sea level rise contribution of 0 04 0 01 mm yr

geologic evaluation of plate kinematic models for the north american caribbean plate boundary zone heubeck ch and mann p 1991 geologic evaluation of plate kinematic models for the north american caribbean plate boundary zone tectonophysics 191 l 26 four published plate kinematic models for the present day north american caribbean plate boundary predict significantly different fault behavior along this dominantly strike slip plate boundary zone pbz using a computer graphics system we compare the deformational pattern predicted by the four kinematic models with geologic and seismic observations along the entire length of the pbz from central america to the northern lesser antilles our results indicate that none of the kinematic models predict all the geologic and seismic observations across the entire pbz however all four models predict mapped fault character and observed earthquake focal mechanisms along certain segments of the pbz we conclude that the present day deformation within the north american caribbean plate boundary zone cannot be described by rotation about a single pole instead the caribbean plate appears to be segmented into at least three major sub plates or blocks each of which requires an individual pole of rotation to describe its motion relative to the north american plate sub plate boundaries correspond to two poorly studied zones of diffuse deformation within the caribbean plate honduras depression of central america and beata ridge of the caribbean sea

bed suction effects on structure of turbulent open channel flow the effects of bed suction on the structure of turbulent open channel flow are studied numerically by solving the reynolds averaged navier stokes equations two low r turbulence models of the k e type are used for closing the system of equations the models of nagano and hishida and of launder and sharma give similar predictions for suction rates up to 9 against experimental measurements performed by maclean the bed suction effects on the mean flow characteristics are found to be significant within the suction region the near bed velocities are increased with increasing suction rate as well as the bed shear stress the law of the wall with suction developed by stevenson is found to be applicable for low rates of bed suction up to o 3ty the excess bed shear stress resulting from suction is calculated in the order of three to eight times the respective one with no suction the turbulence levels are greatly reduced with increasing suction rate and a new normalization of the turbulence characteristics is satisfactory for suction rates up to 0 3

vertical dimensions and age of the wicklow mountains ice dome eastern ireland and implications for the extent of the last irish ice sheet abstract patterns of erratic distribution show that the wicklow mountains formerly supported an independent ice cap or ice dome geomorphological mapping of the upper limits of evidence for glaciation ice scoured and moulded bedrock perched boulders and the distribution of features indicative of prolonged periglacial conditions tors frost shattered rock blockfields indicates that along the main axis of high ground erosive warm based ice buried all but the highest 725 m summits and over ran adjacent lower peaks and cols the presence of gibbsite in soil samples from above the inferred upper limit of glacial erosion and its absence in all samples from below this limit is consistent with the geomorphological evidence and implies removal of gibbsitic soils below 725 m by glacial erosion during the last glacial stage cosmogenic 10 be exposure ages for rock outcrops above the inferred upper limit of glacial erosion yield pre last glacial maximum lgm ages of 46 9 3 0 ka to 95 9 6 1 ka whereas rock outcrops on summits over ridden by warm based ice give post lgm ages of 18 2 1 2 to 19 1 1 2 ka all geomorphological and dating evidence thus indicates an lgm age for the ice dome the thickness of the ice dome and limited lateral dispersal of erratics indicate that at the lgm the wicklow ice was encircled by and confluent with thick powerful ice streams moving se from the irish midlands and southwards down the irish sea basin this conclusion is irreconcilable with the traditional view that the last irish ice sheet terminated at the south ireland end moraine but consistent with recent proposals that the last ice sheet was much more extensive than previously believed and over ran the south coast of ireland

current block motions and strain accumulation on active faults in the caribbean the caribbean plate and its boundaries with north and south america marked by subduction and large intra arc strike slip faults are a natural laboratory for the study of strain partitioning and interseismic plate coupling in relation to large earthquakes here we use most of the available campaign and continuous gps measurements in the caribbean to derive a regional velocity field expressed in a consistent reference frame we use this velocity field as input to a kinematic model where surface velocities results from the rotation of rigid blocks bounded by locked faults accumulating interseismic strain while allowing for partial locking along the lesser antilles puerto rico and hispaniola subduction we test various block geometries guided by previous regional kinematic models and geological information on active faults our findings refine a number of previously established results in particular slip rates on the strike slip faults systems bounding the caribbean plate to the north and south and the kinematics of the gonave microplate our much improved gps velocity field in the lesser antilles compared to previous studies does not require the existence of a distinct northern lesser antilles block and excludes more than 3 mm yr of strain accumulation on the lesser antilles puerto rico subduction plate interface which appears essentially uncoupled the transition from a coupled to an uncoupled subduction coincides with a transition in the long term geological behavior of the caribbean plate margin from compressional hispaniola to extensional puerto rico and lesser antilles a characteristics shared with several other subduction systems

gps estimates of microplate motions northern caribbean evidence for a hispaniola microplate and implications for earthquake hazard summary we use elastic block modelling of 126 gps site velocities from jamaica hispaniola puerto rico and other islands in the northern caribbean to test for the existence of a hispaniola microplate and estimate angular velocities for the gonave hispaniola puerto rico virgin islands and two smaller microplates relative to each other and the caribbean and north america plates a model in which the gonave microplate spans the whole plate boundary between the cayman spreading centre and mona passage west of puerto rico is rejected at a high confidence level the data instead require an independently moving hispaniola microplate between the mona passage and a likely diffuse boundary within or offshore from western hispaniola our updated angular velocities predict 6 8 1 0 mm yr 1 of left lateral slip along the seismically hazardous enriquillo plantain garden fault zone of southwest hispaniola 9 8 2 0 mm yr 1 of slip along the septentrional fault of northern hispaniola and 14 15 mm yr 1 of left lateral slip along the oriente fault south of cuba they also predict 5 7 1 mm yr 1 of fault normal motion in the vicinity of the enriquillo plantain garden fault zone faster than previously estimated and possibly accommodated by folds and faults in the enriquillo plantain garden fault zone borderlands our new and a previous estimate of gonave caribbean plate motion suggest that enough elastic strain accumulates to generate one to two mw 7 earthquakes per century along the enriquillo plantain garden and nearby faults of southwest hispaniola that the 2010 m 7 0 haiti earthquake ended a 240 yr long period of seismic quiescence in this region raises concerns that it could mark the onset of a new earthquake sequence that will relieve elastic strain that has accumulated since the late 18th century

actively evolving microplate formation by oblique collision and sideways motion along strike slip faults an example from the northeastern caribbean plate margin abstract the pattern of folding faulting and late quaternary coral reef uplift rates in western and central hispaniola haiti and dominican republic suggest that the elongate gonave microplate a 190 000 km2 area of the northeastern caribbean plate is in the process of shearing off the caribbean plate and accreting to the north american plate late cenozoic transpression between the southeastern bahama platform and the caribbean plate in hispaniola has inhibited the eastward motion of the northeastern corner of the plate transpression is manifested in western and central hispaniola by the formation of regional scale folds that correspond to present day anticlinal topographic mountain chains continuous with offshore anticlinal ridges areas of most rapid quaternary uplift determined from onland coral reefs 125 ka and younger coincide with the axial traces of these folds offshore data suggest recent folding and faulting of the seafloor onshore reef data do not conclusively require late quaternary folding but demonstrate that tectonic uplift rates of the axial areas of the anticlines decrease from the northwest peninsula of haiti 0 37 mm yr to to the central part of the coast of western haiti 0 19 mm yr to the south central part of western haiti 0 mm yr formation of the 1200 km long enriquillo plantain garden walton fault zone as a bypass strike slip fault has isolated the southern edge of the gonave microplate and is allowing continued unimpeded eastward motion of a smaller caribbean plate past the zone of late neogene convergence and quaternary uplift of coral reefs in hispaniola offshore seismic reflection data from the jamaica passage the marine strait separating jamaica and haiti show that the enriquillo plantain garden fault zone forms a narrow but deep active fault bounded trough beneath the passage the active fault is continuous with active faults mapped onshore in western haiti and eastern jamaica the bathymetric deep is present because the jamaica passage fault segment represents a 50 km wide transtensional left step of the fault trace between haiti and jamaica onshore satellite imagery and field observations suggest that the enriquillo plantain garden fault forms a continuous trace extending from central hispaniola east of lake enriquillo dominican republic to the westernmost end of the southern peninsula of haiti the regional lineament corresponds to a recent fault scarp in quaternary alluvium of the clonard pull apart basin in the central part of the southern peninsula of haiti and suggests that at least this part of the lineament has undergone recent slip calmus 1983 has suggested a total offset of 30 50 km of the enriquillo plantain garden fault zone in the southern peninsula of haiti using the apparent offset of lithologic units seismic reflection data from lake enriquillo document recent deformation of quaternary lake sediments where the lineament crosses the lake leveling of the crest of a late holocene coral reef and associated algal tufa around lake enriquillo demonstrate late holocene vertical movement and tilting in a 1500 m wide zone parallel to the fault trend lateral offset is difficult to show in the enriquillo valley area because of rapid recent sedimentation into the valley the pattern of inactive strike slip faults and fold belts of cenozoic age in cuba and the yucatan basin suggest that two elongate microplates were sheared off the proto caribbean plate and accreted to the north american plate by a similar process in paleocene and eocene times age of terminal deformation in western central and eastern cuba is consistent with southeastward younging and migration of arc collision the similarity of the size and sequence of events in cuba suggests that the process of oblique collision and sideways motion of the plate along a new strike slip fault towards a free face may be an important process of microplate formation and interplate transfer in other areas

young rift kinematics in the tadjoura rift western gulf of aden republic of djibouti the tadjoura rift forms the westernmost edge of the westerly propagating sheba ridge between arabia a nd somalia as it enters into the afar depression fro m structural and remote sensing dataset the tadjou ra rift is interpreted as an asymmetrical south facing half gr aben about 40 km wide dominated by a large boundary fault zone to the north it is partially filled up by the 1 3 ma old gulf basalts which onlapped the older s omali basalts along its shallower southern flexural margin the m ajor and trace element analysis of 78 young onshore lavas allows us to distinguish and map four distinct basa ltic types namely the gulf somali goumarre and h ayyabley basalts these results together with radiometric a ge data lead us to propose a revised volcano strat igraphic sketch of the two exposed tadjoura rift margins an d to discriminate and date several distinct fault n etworks of this oblique rift morphological and statistical an alyses of onshore extensional fault populations sho w marked changes in structural styles along strike in a dir ection parallel to the rift axis these major fault disturbances are assigned to the arrest of axial fault tip propagati on against pre existing discontinuities in the ns o riented arta transverse zone according to our model the sinist ral jump of rifting into the asal ghoubbet rift seg ment results from structural inheritance in contrast with the en echelon or transform mechanism of propagation that prevail ed along the entire length of the gulf of aden extensi onal system

seismic hazard of the enriquillo plantain garden fault in haiti inferred from palaeoseismology the enriquillo plantain garden fault zone is the primary plate bounding fault system in haiti and was initially thought to be responsible for the 2010 earthquake palaeoseismic analyses of the fault system indicate that it ruptured during a large earthquake in either 1750 or 1770 but did not rupture during the 2010 earthquake the enriquillo plantain garden fault zone is recognized as one of the primary plate bounding fault systems in haiti1 2 the strike slip fault runs adjacent to the city of port au prince and was initially thought to be the source of the 12 january 2010 mw 7 0 earthquake haiti experienced significant earthquakes in 1751 and 1770 refs 3 4 5 but the role of the enriquillo plantain garden fault zone in these earthquakes is poorly known we use satellite imagery aerial photography light detection and ranging lidar and field investigations to document quaternary activity on the enriquillo plantain garden fault we report late quaternary left lateral offsets of up to 160 m and a set of small offsets ranging from 1 3 to 3 3 m that we associate with one of the eighteenth century earthquakes the size of the small offsets implies that the historical earthquake was larger than mw 7 0 but probably smaller than mw 7 6 we found no significant surface rupture associated with the 2010 earthquake the lack of surface rupture coupled with other seismologic geologic and geodetic observations6 7 suggests that little if any accumulated strain was released on the enriquillo plantain garden fault in the 2010 earthquake these results confirm that the enriquillo plantain garden fault remains a significant seismic hazard

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

channel hydrodynamics of submerged flexible vegetation with seepage abstractthe presence of aquatic vegetation changes the flow characteristics in a channel the impact of the presence of submerged flexible vegetation in a channel with an additional parameter such as downward seepage is analyzed in the present work two patterns staggered and uniform and two different vegetation spacing 15 and 10 cm center center were adopted experiments were conducted for the case of no seepage 10 seepage and 15 seepage velocity profiles show the presence of an inflection point near the top of the vegetation where maximum reynolds stress is achieved the velocity profiles measured in the unobstructed region of uniform pattern are higher compared to the velocity measured in line with the vegetation stems downward seepage increases the velocity reynolds stress and turbulent intensities in the average range of 10 15 as compared to the no seepage case higher order turbulent statistics such as moment analysis quadrant analysis and turbulent kinetic budget are derived through

turbulent characteristics and evolution of sheet flow in an alluvial channel with downward seepage abstract experimental investigation of the flow hydrodynamics and temporal changes in the cross sectional profile of an alluvial channel has been studied in the present work experiments were carried out in a curvilinear cross sectional shaped channel with no seepage and with a downward seepage condition to ascertain seepage effects on channel geometry and turbulent characteristics of flow measures of turbulent characteristics such as time averaged near bed velocities and reynolds stresses were found to increase with the application of downward seepage stream power and the value of shields parameter are increased under the action of downward seepage causing bed particles to move in the form of a sheet layer integral scales of flow suggest that the size of eddies increases with the application of downward seepage which is linked to the evolution of the sheet layer sheet development causes reduction in flow depth and rapid channel widening cross sectional parabolic shape of the threshold channel is transformed into a trapezoidal shape with the presence of the sheet layer with the passage of time 11 h the channel attains another equilibrium geometrical state with the value of shields stress around 0 074 from the no seepage value of 0 0399 an empirical equation for sheet flow rate is derived with the consideration of seepage in the downward direction

the 2010 haiti earthquake a complex fault pattern constrained by seismologic and tectonic observations after the january 12 2010 haiti earthquake we deployed a mainly offshore temporary network of seismologic stations around the damaged area the distribution of the recorded aftershocks together with morphotectonic observations and mainshock analysis allow us to constrain a complex fault pattern in the area almost all of the aftershocks have a n s compressive mechanism and not the expected left lateral strike slip mechanism a first order slip model of the mainshock shows a n264 e north dipping plane with a major left lateral component and a strong reverse component as the aftershock distribution is sub parallel and close to the enriquillo fault we assume that although the cause of the catastrophe was not a rupture along the enriquillo fault this fault had an important role as a mechanical boundary the azimuth of the focal planes of the aftershocks are parallel to the north dipping faults of the transhaitian belt which suggests a triggering of failure on these discontinuities in the western part the aftershock distribution reflects the triggering of slip on similar faults and or alternatively of the south dipping faults such the trois baies submarine fault these observations are in agreement with a model of an oblique collision of an indenter of the oceanic crust of the southern peninsula and the sedimentary wedge of the transhaitian belt the rupture occurred on a wrench fault at the rheologic boundary on top of the under thrusting rigid oceanic block whereas the aftershocks were the result of the relaxation on the hanging wall along pre existing discontinuities in the frontal part of the transhaitian belt

migration of neogene marine environments southwestern dominican republic the azua basin contains a 4000 m thick regressive neogene sedimentary sequence that records the effects of neotectonic activity along the northern bounary of the caribbean plate shifts of benthic foraminiferal depth zone boundaries between stratigraphic sections demonstrate a southeastward migration of paleoenvironments in the miocene and early pliocene which suggest that the hispaniola restraining bend was activated near the beginning of the late miocene in the morthwestern part of the azua basin the boundary between the middle and upper bathyal biofacies is in the uppermost miocene globorotalia humerosa zone the bathyal neritic boundary is near the top of the same zone in contrast toward the southeastern i e seaward end of the basin the middle bathyal upper bathyal boundary is just above the base of the lower pliocene globorotalia margaritae margaritae subzone and the bathyal neritic transition falls within the upper part of the same zone or in the overlying globorotalia margaritae evoluta subzone the diachroneity of biofacies boundaries spans a time interval of ca 1 m y the foraminiferal trends are corroborated by the disposition of time transgressive lithofacies

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

north caribbean neotectonic events the trans haitian fault system tertiary record of an oblique transcurrent shear zone uplifted in hispaniola abstract the left lateral relative motion between the caribbean and the north american plates has previously been inferred as occurring along a fault zone located north of hispaniola east of the northern dominican republic a relatively linear fracture zone the septentrional fault zone sfz extends into the puerto rico subduction zone similarly south of haiti the trace of the inactive enriquillo plantain garden fault zone epgfz extends into the muertos trench and may represent a major fault along the plate boundary between these two major strike slip fault systems the central part of haiti shows a diffuse fracture zone that trends n130 the chronology of deformation involves an initial paleocene to eocene suturing of allochthonous terranes a late miocene development of a strong spaced cleavage within the late paleocene to late miocene strata that overlap the terrane suture and diffuse pliocene to pleistocene strike slip faulting along traces that reactivate the older spaced cleavage planes during the pleistocene basalts ranging in age from 0 4 to 1 3 ma were extruded in pull apart basins associated with n130 trending faults antithetic features of the sfz and n30 normal faults antecedent synthetic features of the sfz this event is coeval with the compression recorded at the muertos beata collision front in the southwestern dominican republic the most recent phase of tectonism involves strong uplifts and broad open folding along nw striking axes which is consistent with the regional maximum deformation pattern predicted for e w left lateral shear along the north america caribbean plate boundary

significant earthquakes on the enriquillo fault system hispaniola 1500 2010 implications for seismic hazard abstract historical records indicate frequent seismic activity along the north east caribbean plate boundary over the past 500 years particularly on the island of hispaniola we use accounts of historical earthquakes to assign intensities and the intensity assignments for the 2010 haiti earthquakes to derive an intensity attenuation relation for hispaniola the intensity assignments and the attenuation relation are used in a grid search to find source locations and magnitudes that best fit the intensity assignments here we describe a sequence of devastating earthquakes on the enriquillo fault system in the eighteenth century an intensity magnitude m i 6 6 earthquake in 1701 occurred near the location of the 2010 haiti earthquake and the accounts of the shaking in the 1701 earthquake are similar to those of the 2010 earthquake a series of large earthquakes migrating from east to west started with the 18 october 1751 m i 7 4 7 5 earthquake probably located near the eastern end of the fault in the dominican republic followed by the 21 november 1751 m i 6 6 earthquake near port au prince haiti and the 3 june 1770 m i 7 5 earthquake west of the 2010 earthquake rupture the 2010 haiti earthquake may mark the beginning of a new cycle of large earthquakes on the enriquillo fault system after 240 years of seismic quiescence the entire enriquillo fault system appears to be seismically active haiti and the dominican republic should prepare for future devastating earthquakes online material table listing small earthquakes and figures of intensity assignments and intensity magnitude estimates

complex rupture during the 12 january 2010 haiti earthquake initially the devastating mw 7 0 12 january 2010 haiti earthquake seemed to involve straightforward accommodation of oblique relative motion between the caribbean and north american plates along the enriquillo plantain garden fault zone here we combine seismological observations geologic field data and space geodetic measurements to show that instead the rupture process involved slip on multiple faults primary surface deformation was driven by rupture on blind thrust faults with only minor deep lateral slip along or near the main enriquillo plantain garden fault zone thus the event only partially relieved centuries of accumulated left lateral strain on a small part of the plate boundary system together with the predominance of shallow off fault thrusting the lack of surface deformation implies that remaining shallow shear strain will be released in future surface rupturing earthquakes on the enriquillo plantain garden fault zone as occurred in inferred holocene and probable historic events we suggest that the geological signature of this earthquake broad warping and coastal deformation rather than surface rupture along the main fault zone will not be easily recognized by standard palaeoseismic studies we conclude that similarly complex earthquakes in tectonic environments that accommodate both translation and convergence such as the san andreas fault through the transverse ranges of california may be missing from the prehistoric earthquake record

seismotectonics of southern haiti a new faulting model for the 12 january 2010 m7 0 earthquake the prevailing consensus is that the 2010 mw7 0 haiti earthquake left the enriquillo plantain garden strike slip fault epgf unruptured but broke unmapped blind north dipping thrusts using high resolution topography aerial images bathymetry and geology we identified previously unrecognized south dipping nw se striking active thrusts in southern haiti one of them lamentin thrust lt cuts across the crowded city of carrefour extends offshore into port au prince bay and connects at depth with the epgf we propose that both faults broke in 2010 the rupture likely initiated on the thrust and propagated further along the epgf due to unclamping this scenario is consistent with geodetic seismological and field data the 2010 earthquake increased the stress toward failure on the unruptured segments of the epgf and on neighboring thrusts significantly increasing the seismic hazard in the port au prince urban area the numerous active thrusts recognized in that area must be considered for future evaluation of the seismic hazard

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

eocene paleomagnetic pole for south america northward continental motion in the cenozoic opening of drake passage and caribbean convergence 1 a paleomagnetic study of eocene volcanic rocks in patagonia yields high unblocking temperature and high coercivity magnetizations combining these results with those of a previous study on patagonian eocene basalts yields a high precision high quality pole located at latitude 81s longitude 337 4e a95 5 7 critically this paleopole is indistinguishable from that of the late cretaceous circa 85 65 ma pole position of south america indicating that the plate was essentially motionless with respect to the spin axis for a period of 45 m y the pole position places south america at higher 5 than present day latitudes during the eocene indicating that northward continental motion toward present day latitudes must have been accomplished sometime since the late eocene paleomagnetic and tectonic correlation admits the hypothesis that cenozoic northward drift was associated with oligocene miocene extension in the southern continental edge leading to the opening of the drake passage and it agrees with the timing of foredeep formation and development of fold thrust belts in the northern continental edge this positive correlation between the paleomagnetically predicted drift of a major continent with extension at its trailing edge and convergence at its leading edge during times for which seafloor tectonic fabric and the geological record are particularly well preserved illustrates the utility of paleomagnetism in constraining paleogeographic and tectonic reconstructions for pre cretaceous times

energy and heat fluxes due to vertically propagating yanai waves observed in the equatorial indian ocean shipboard current measurements in the equatorial indian ocean in october and november of 2011 revealed oscillations in the meridional velocity with amplitude 0 10m s these were clearest in a layer extending from 300 to 600 m depth and had periods near 3 weeks phase propagation was upward measurements from two sequential time series at the equator four meridional transects and one zonal transect are used to identify the oscillation as a yanai wave packet and to establish its dominant frequency and vertical wavelength the doppler shift is accounted for so that measured wave properties are translated into the reference frame of the mean zonal flow we take advantage of the fact that in the depth range where the wave signal was clearest the time averaged current and buoyancy frequency were nearly uniform with depth allowing application of the classical theoretical representation of vertically propagating plane waves using the theory we estimate wave properties that are not directly measured such as the group velocity and the zonal wavelength and phase speed the theory predicts a vertical energy flux that is comparable to that carried by midlatitude near inertial waves we also quantify the wave driven meridional heat flux and the stokes drift

neotectonics of the caribbean a compilation of earthquake focal mechanism solutions together with the interpretation of inclined intermediate depth seismic zones neogene strike slip faults fault controlled basins and volcanism is used to test three existing models for the neotectonic i e neogene or post oligocene development of the caribbean the current models although based on different hypotheses using different data sets are similar and suggest varying degrees of convergence between the caribbean and either north or south american plates or convergence between the caribbean plate and continental fragments of the northwestern corner of south america using model 1 previous workers have interpreted the disposition of fracture zones and magnetic anomalies in the central and south atlantic as indicating that the caribbean plate is being compressed by north south convergence between the americas with the result that it is being driven eastward relative to the americas along strike slip faults while producing east west trending subductionlike convergent zones along northern and southern plate margins using model 2 previous workers have interpreted the azimuths of active strike slip faults and focal mechanism solutions and closure of three plate velocity circuits as indicating that the south american plate converges in a west northwesterly direction on the southern margin of the caribbean plate and has produced compressional features while strike slip motion dominates along the northern boundary using model 3 previous workers have interpreted focal mechanism solutions and the pattern of strike faulting and basin development in northwestern south america to suggest right lateral displacement of the northwestern corner of south america relative to the craton with convergence and compression in the south central caribbean our integration of geologic information on faults basins and volcanism considerably extends the limited record of plate interactions known from historical reports of the past few hundred years and recorded earthquakes and suggests that 1 relative motion between the north american and caribbean plates is dominantly east west strike slip motion although areas of complex internal deformation associated with restraining bend or compressional strike slip fault segments have been identified in jamaica hispaniola and central america 2 relative motion between the south american and caribbean plates is dominantly east west strike slip motion although an area of restraining bend deformation has been identified in the araya peninsula of venezuela 3 relative motion between a triangular continental fragment of northwestern south america the maracaibo block ranges from northwest to northeast along the south central margin of the caribbean and appears to be driven mostly by the late miocene pliocene collision of the panama arc although additional driving forces may include the collision of the carnegie ridge and or oblique subduction to the northeast in ecuador and 4 relative motion internal deformation may be occurring at a very slow rate between fault bounded blocks within the caribbean plate as a result of the convergence of the maracaibo block and or eastward motion of the caribbean plate relative to a continental promontory of north america in northern central america because the caribbean margins are composed mainly of anisotropic easily deformed continental and arc lithosphere plate boundaries are zones of diffuse deformation and it is difficult to assess the degree of convergence between the americas although data from the caribbean itself suggest that it may be smaller than the amount inferred by some workers using model 1 fracture zone and magnetic anomalies in the atlantic some of the compressional features cited as evidence for the relative convergence of the americas may be instead related to the convergence between the maracaibo block relative to the southern margin of the caribbean many aspects of caribbean neotectonics remain less than completely understood but more integration of seismic and geologic studies particularly exploratory fault trenching of onshore faults and seismic profiling of offshore faults should lead to rapid advances

polyphase tectonic history of the southern peninsula haiti from folding and thrusting to transpressive strike slip abstract the southern peninsula of haiti is a seismically active east west trending transpressive mountain range with elevations over 2 km present day deformation is mainly partitioned along the left lateral enriquillo plantain garden fault zone epgfz and associated oblique reverse faults and or folds the configuration of these faults their respective timing and the role of structural heritage on their development is poorly understood to address these questions we present the results of extensive field campaigns combined with satellite imagery interpretation and published data which allows us to constrain the cenozoic evolution of the southern peninsula our results show a polyphase tectonic history consisting of three major tectonic events 1 maastrichtian to early paleocene crustal scale folding that developed coevally with predominantly north to northeast dipping thrusts resulting in uplift and erosion of the cretaceous sedimentary cover in large parts of the southern peninsula 2 early miocene uplift and erosion which was strongest in the southwestern part of the peninsula and decreased eastwards did not affect the massif de la selle uplift is most likely unrelated to strike slip activity but resulted from folding in response to ne sw shortening that possibly reactivated older predominantly n to ne dipping thrusts 3 late miocene to present day deformation and uplift spatially distributed strike slip started during the late miocene and became progressively focused along the epgfz in the latest miocene oblique and thrust faults locally post date strike slip activity from the pliocene onward increase in compressional deformation from west to east is reflected by a change in structural style with predominantly strike slip faults in the west and transpressional faults in the east the latter possibly rooted on the epgfz at depth paleo stresses associated with a strike slip regime are at a significantly high angle to the trace of the epgfz indicating that the epgfz is a mechanically weak fault

experimental study of bore driven swash hydrodynamics on impermeable rough slopes abstract a detailed experimental investigation of the hydrodynamics of large scale bore driven swash on impermeable rough beach slopes is described the experiments were carried out on 1 10 impermeable rough slopes with three different surface roughnesses based on 1 3 mm sand 5 4 mm gravel and 8 4 mm gravel the large scale discrete swash event was produced by the collapse of a dambreak generated bore on the beach simultaneous depths and velocities were measured using lif laser induced fluorescence and piv particle image velocimetry respectively yielding better resolution of the hydrodynamics than previous studies depth time series instantaneous velocity profiles depth averaged velocities instantaneous turbulent kinetic energy profiles depth averaged turbulent kinetic energy reynolds stress profiles and bed shear stresses are presented for five cross shore measurement locations in the swash the measurements resolve the backwash shoreline position and the late backwash period when depths are shallow and velocities are high the detailed data can be used to test and develop advanced numerical models for bore driven waves on rough slopes

a plate tectonic model for the mesozoic and early cenozoic history of the caribbean plate abstract we present a model in which the caribbean plate is an intra american feature formed along the caribbean spreading center as opposed to the current model that considers the caribbean plate as a far travelled crustal segment that formed in the pacific region paleomagnetic data which cover an age range from jurassic through paleocene indicate the ophiolite complexes in costa rica and panama formed in an equatorial position the ophiolites did not fundamentally change their position relative to south america since their origin basaltic rocks of the lower part of the ophiolites are of mid ocean ridge type suggesting formation at a spreading center they are interpreted to have formed as part of the proto caribbean crust at a spreading axis in an intra american position during jurassic and early cretaceous times the upper part of the ophiolites is mainly built up by island arc and intraplate basalts the island arc basalts evolved at the central american landbridge which started in the middle cretaceous the intraplate basalts are related to the caribbean plateau basalt which thickened and stiffened the caribbean crust in middle cretaceous to probably campanian times changes in relative plate motions along the middle american convergent plate margin are reflected by orientations and time sequences of paleostress tensors calculated from fault slip data in southern mexico and costa rica kinematic indicators from mylonite zones display sinistral movement along secondary shear zones within the southern mexican crustal complexes and along the northern boundary of the chortis block in the motagua polochic fault system this reflects the eastward drift of the chortis block since the beginning of the cenozoic at this time the chortis block became part of the caribbean plate which moved more than 1000 km towards the east relative to the north and south american plates during the cenozoic

coseismic slip distribution of the 2010 m 7 0 haiti earthquake and resulting stress changes on regional faults the 12 january 2010 mw 7 0 haiti earthquake ruptured the previously unmapped leog ne fault a secondary transpressional structure located close to the enriquillo fault the major fault system assumed to be the primary source of seismic hazard for southern haiti in the absence of a precise aftershock catalog previous estimations of coseismic slip had to infer the rupture geometry from geodetic and or seismological data here we use a catalog of precisely relocated aftershocks begin ning one month after the event and covering the following 5 months to constrain the rupture geometry estimate a slip distribution from an inversion of global positional systems gps interferometric synthetic aperture radar insar and coastal uplift data and calculate the resulting changes of coulomb failure stress on neighboring faults the relocated aftershocks confirm a north dipping structure consistent with the leog ne fault as inferred from previous slip inversions but with two subfaults each corresponding to a major slip patch the rupture increased coulomb stresses on the shallow enriquillo fault parallel to the leog ne rupture surface and to the west mirago ne area and east port au prince results show that the cluster of reverse faulting earthquakes observed further to the west coincident with the offshore trois baies fault are triggered by an increase in coulomb stress other major regional faults did not experience a significant change in stress the increase of stress on faults such as the enriquillo are a concern as this could advance the timing of future events on this fault still capable of magnitude 7 or greater earthquakes online material figures showing observed and calculated insar ranges for

structural geology invisible faults under shaky ground the haiti earthquake ruptured one or more buried faults generated tsunamis and caused extensive structural damage in port au prince investigations in the epicentral region quantify seismic hazards but offer no clear views of haiti s seismic future

impacts tsunamis and the haitian cretaceous tertiary boundary layer the marker bed at the cretaceous tertiary boundary of the beloc formation southern haiti contains abundant coarse grained microtektites and minor amounts of shocked quartz grains in the basal part the upper part is composed of medium grained marl with amalgamated microtektite lenses and finer grained marl lenses disseminated throughout field and petrographic observations and the distribution of planktonic foraminifera suggest that the bed formed from a complex sequence of events a bolide impact nearby produced microtektites that sett1led to form a nearly pure layer at the base vaporized materials with anomalously high extraterrestrial components settled last along with carbonate sediments the entire bed became sparsely consolidated subsequently another major disruptive event perhaps a giant tsunami partly reworked the initial deposit cohesive fragments of the original marker bed mixed with exotic materials were redeposited as lenticular bodies this process also may have caused further mixing of cretaceous and tertiary microfossils as observed at beloc and elsewhere

bed shear stress and scour over bed type river intake laboratory experiments are carried out to determine the increase in bed shear stress and local scour over the zone of suction associated with a bed type river intake in a channel with a mobile bed bed shear stress is estimated first by observing the movement of indicator grains whose threshold shear stress in uniform flow was already known and second by observing the rate at which local scour takes place evaluation of the two sets of results indicates that at the onset of scour when particles are lifted from the bed by increased bed shear stress they do not strike the bed again until they are clear of the scour zone the final scour depth is found to be directly proportional to the difference between the initial bed shear stress because of suction and the threshold bed shear stress for the bed grains in the presence of suction

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

suction effects on bridge pier scour under clear water conditions abstractthe experimental study investigates how the application of point suction at different bed locations affects local scour around a cylindrical bridge pier under clear water conditions the results show that suction has a profound effect on pier scour development and the extent of the influence is related to the location of the suction source when the suction source is located at or upstream of the pier the equilibrium scour depth is reduced by up to 50 with qs qo 2 where qs and qo suction flow rate and undisturbed approach flow rate respectively the data also show that for the suction source that is located downstream of the pier the equilibrium scour depth is reduced by up to 30 with the same suction flow rate the extent of pier scour depth reduction at different locations from the suction source is closely associated with changes to the local effective shear and critical shear velocity results of this study show that bed suction may be used as an effective pier scour countermeasure

late cretaceous miocene diachronous onset of back thrusting along the south caribbean deformed belt and its importance for understanding processes of arc collision and crustal growth 1 the venezuelan basin is obliquely subducted to the east southeast beneath the continental south american plate at the east west trending south caribbean deformed belt scdb a 50 100 km wide wedge of accreted sedimentary rocks derived both from offscraping of the 0 5 to 1 km thick sedimentary cover of the subducting venezuelan basin and from incorporation of clastic sediments derived from the continental margin of south america in this paper we describe the structure and sequence stratigraphy of five late cretaceous to recent sedimentary sequences overlying a 230 000 km2 area of the southern venezuelan basin and beata ridge the data set includes 5900 km of 2d seismic reflection data that are tied to lithologic and age data taken from dsdp sites 146 149 and 150 in the central part of the venezuelan basin we use observed patterns of wedging in mapped and dated sedimentary sequences adjacent to the scdb to determine the age of the diachronous west to east initiation of thrusting and subduction at the scdb the onset of subduction in the scdb corresponds with the cessation of thrusting from west to east along the zone of collision between the intraoceanic caribbean arc and the south american continent this correlation in the age of deformation indicates that collision between the caribbean arc and the south american continent led to subduction polarity reversal a process that is commonly observed at various stages of tectonic evolution in other areas of active arc continent collision including japan and sunda

an alternative model for the growth of faults conventional growth models suggest that faults become larger due to systematic increases in both maximum displacement and length we propose an alternative growth model where fault lengths are near constant from an early stage and growth is achieved mainly by increase in cumulative displacement the model reconciles the scaling properties of faults and earthquakes and predicts a progressive increase in fault displacement to length ratios as a fault system matures this growth scheme is directly applicable to reactivated fault systems in which fault lengths were inherited from underlying structure and established rapidly the model may also apply to some non reactivated fault systems near constant fault lengths during subsequent growth are attributed to retardation of lateral propagation by interaction between fault tips the model is validated using kinematic constraints from growth strata which are displaced by a system of reactivated normal faults in the timor sea nw australia

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

plate boundary readjustment in oblique convergence example of the neogene of hispaniola greater antilles the haitian fold and thrust belt is the major mountain belt of haiti western part of hispaniola greater antilles and resembles a compressive restraining bend between the two major faults which have driven the opening of the cayman basin since the eocene during the rifting stage from the middle to the late eocene this area underwent an extensional evolution with fissural volcanic activity along ne sw tilted blocks the haitian fold and thrust belt was constructed from the early miocene until the present by stacking sedimentary units into a collisional wedge perpendicular to the tilted blocks which was propagating to the southwest during the construction of the wedge piggyback basins were formed and progressively uplifted during the late neogene convergence is localized in the cul de sac enriquillo trough where the active front proceeds southward onto the beata ridge in this area miocene to quaternary wrench structures of the lower plate like the southern peninsula and the enriquillo plantain garden faults are reactivated as normal faults owing to the loading of the fold and thrust belt

abrupt onset of the little ice age triggered by volcanism and sustained by sea ice ocean feedbacks 1 northern hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes however the causes of superposed century scale cold summer anomalies of which the little ice age lia is the most extreme remain debated largely because the natural forcings are either weak or in the case of volcanism short lived here we present precisely dated records of ice cap growth from arctic canada and iceland showing that lia summer cold and ice growth began abruptly between 1275 and 1300 ad followed by a substantial intensification 1430 1455 ad intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium a transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times and that cold summers can be maintained by sea ice ocean feedbacks long after volcanic aerosols are removed our results suggest that the onset of the lia can be linked to an unusual 50 year long episode with four large sulfur rich explosive eruptions each with global sulfate loading 60 tg the persistence of cold summers is best explained by consequent sea ice ocean feedbacks during a hemispheric summer insolation minimum large changes in solar irradiance are not required

coupled 3 d stream flow and hyporheic flow model under varying stream and ambient groundwater flow conditions in a pool riffle system 1 exchange of water and solutes across the stream sediment interface is an important control for biogeochemical transformations in the hyporheic zone hz in this paper we investigate the interplay between turbulent stream flow and hz flow in pool riffle streams under various ambient groundwater flow conditions streambed pressures derived from a computational fluid dynamics cfd model are assigned at the top of the groundwater model and fluxes at the bottom of the groundwater model domain represent losing and gaining conditions simulations for different reynolds numbers re and pool riffle morphologies are performed results show increasing hyporheic exchange flows m3 d for larger re and a concurrent decrease in residence time rt losing and gaining conditions were found to significantly affect the hyporheic flow field and diminish its spatial extent as well as rates of hyporheic exchange flow the fraction of stream water circulating through the hyporheic zone is in the range of 1 10 5 to 1 10 6 per meter stream length decreasing with increasing discharge complex distributions of pressure across the streambed cause significant lateral hyporheic flow components with a mean lateral travel distance of 20 of the longitudinal flow paths length we found that the relationship between pool riffle height and hyporheic exchange flow is characterized by a threshold in pool riffle amplitude beyond which hyporheic exchange flow becomes independent of riffle height hyporheic residence time distributions rtd are log normally distributed with medians ranging between 0 7 and 19 h

seismic stratigraphy and structure of the caribbean igneous province multichannel seismic reflection profiles reveal the tectonic and stratigraphic complexity of the caribbean province a smooth reflector b forms the top of widespread cretaceous volcanic flows drilled during dsdp leg 15 and odp leg 165 in addition we also show other seismic evidence of volcanism sills and dipping horizons the southern parts of the venezuela and colombia basins are underlain by rough basement that shows many characteristics of oceanic crust several thick volcanic plateaus separated by deep basins with thin crust comprise the caribbean volcanic province in the venezuela basin only normal oceanic crust is present but in other basins this crust is underlain by underplated volcanic material the crust of the venezuela basin is less than 5 km thick and was probably formed in the pacific during the jurassic refraction data indicate that a thin layer 2v is formed by original oceanic crust overlain by a thin volcanic layer an intra basement reflection sub b marks the top of original oceanic crust that is sandwiched between an upper volcanic layer and lower underplated material this underplated layer forms a very thick layer 3v beneath the beata and nicaragua volcanic plateaus the upper part of layer 3v is gabbroic and outcrops on the beata ridge the thickening occurs mainly in the high velocity lower part of layer 3v and is attributed to the presence of magnesian rocks picrites or ultramafic cumulates a highly reflective horizon r is located at the top of this layer we present a model where the galapagos plume is 2500 km wide but has narrow heads that formed the caribbean volcanic plateaus separated by deep basins the caribbean igneous province is compared to similar volcanic features in the indian ocean kerguelen plateau and in the western pacific ocean ontong java plateau nauru and pigafetta basins the thick plateaus of the caribbean province resemble the kerguelen and ontong java plateaus whereas the deep basins present some similarities with the nauru and pigafetta basins the caribbean igneous province is younger 90 75 ma than the indian and pacific plateaus 110 130 ma however several geological evidences from land and geophysical offshore observations indicate that the onset of volcanic activity in the caribbean province could be as old as 115 ma