from transtension to transpression along the northern caribbean plate boundary off cuba implications for the recent motion of the caribbean plate abstract marine geophysical surveys using seabeam single channel seismic reflection gravimetric and magnetic measurements have been conducted along a segment of the northern caribbean transcurrent plate boundary seacarib ii cruise the data allow a better definition of the geometry and the tectonic regime of this major strike slip area they support the following results 1 1 along the southern cuban margin the oriente fault displays a discontinuous trace mainly composed of dextral offset en echelon segments some pull apart basins are located between fault segments cabo cruz basin chivirico and baitiquiri basins in the windward passage area the plate boundary enters into the tortue channel and is not connected with the subduction front off northern hispaniola 2 2 the eastern part of the oriente deep and the santiago promontory are characterised by active compressional tectonics they form the santiago deformed belt described here for the first time this deformed belt can be divided longitudinally into three main segments each one characterised by a particular tectonic style its development is related to a transpressional mechanism along the left lateral oriente strike slip fault our observations suggest that a tectonic and kinematic reorganisation occurred recently in this area probably in the late pliocene which may be compared with the recent geological events recorded on land in the northern caribbean domain the precise knowledge of both geometry and structures along the oriente strike slip fault south of cuba provides new constraints for the recent kinematic evolution along the northern caribbean transcurrent plate boundary it leads us to infer the existence of a convergence component associated with the slip component along the oriente transform fault

tectonic and kinematic regime along the northern caribbean plate boundary new insights from broad band modeling of the may 25 1992 m s 6 9 cabo cruz cuba earthquake on may 25th 1992 an m s 6 9 earthquake occurred off the southwestern tip of cuba along the boundary between the caribbean and north american plates this earthquake was the largest to strike southern cuba since 1917 and the largest ever recorded in that region by global seismic networks it is therefore a key element for our understanding of the tectonic and kinematic regime along the northern caribbean plate boundary in order to test the previously proposed source parameters of the cabo cruz earthquake and to better constrain its focal mechanism we derived a new set of source parameters from unfiltered broad band teleseismic records we used a hybrid ray tracing method that allows us to take into account propagation effects of seismic waves in a realistic crustal model around the source our solution is consistent with the long period focal mechanism solution of virieux et al 1992 our solution also models the higher frequency crustal and water layer phases the primarily strike slip focal mechanism has a small thrust component its shows an east west trending nodal plane dipping 55 to the north that we interpret as the rupture plane since it corresponds to the geometry of the major active fault in that area the displacement on this plane is a left lateral strike slip combined with a small amount of southward thrust the result is in good agreement with the active tectonic structures observed along the oriente fault south of cuba the small thrust component demonstrates that contrary to prior belief the transpressive regime extends along this whole segment of the caribbean north american plate boundary together with historical seismicity it suggests that most of the stress accumulated by the caribbean north american plate motion is released seismically along the southern cuban margin during relatively few but large earthquakes

seismotectonics of jamaica summary this is the first seismological investigation of the stress regime in the jamaican crust the fault plane solutions of 32 well recorded local earthquakes were determined and used as inputs for determining stress directions the results consistently show that a strike slip fault regime sh sv sh e xists in three homogeneous crustal areas namely the blue mountain wagwater restraining bend of eastern jamaica the rio minho crawle river rmcr fault of central jamaica and the montpelier newmarket belt mnb of western jamaica however for the island as a whole a thrust faulting regime sh sh sv w as found but inhomogeneity is implied by the higher level of misfit obtained these results are in keeping with results of other recent studies in the jamaica cuba region and with the strike slip regime of the gonave microplate boundaries

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

the tectonics and active faulting of haiti from seismicity and tomography oblique convergence of the caribbean and north american plates has partitioned strain across a major transpressional fault system that bisects the island of hispaniola the devastating mw 7 0 2010 earthquake that struck southern haiti rupturing an unknown fault highlighted our limited understanding of regional fault segmentation and its link to plate boundary deformation here we assess seismic activity and fault structures across haiti using data from 33 broadband seismic stations deployed for 16 months we use travel time tomography to obtain relocated hypocenters and models of vp and vp vs crustal structure earthquake locations reveal two clusters of seismic activity the first corresponds to aftershocks of the 2010 earthquake and delineates faults associated with that rupture the second cluster shows shallow activity north of lake enriquillo dominican republic interpreted to have occurred on a north dipping thrust fault crustal seismic velocities show a narrow low velocity region with an increased vp vs ratio 1 80 1 85 dipping underneath the massif de la selle which coincides with a southward dipping zone of hypocenters to a depth of 20 km beneath southern haiti our observations of seismicity and crustal structure in southern haiti suggests a transition in the enriquillo fault system from a near vertical strike slip fault along the southern peninsula to a southward dipping oblique slip fault along the southern border of the cul de sac enriquillo basin this result consistent with recent geodetic results but at odds with the classical seismotectonic interpretation of the enriquillo fault system is an important constraint in our understanding of regional seismic hazard

crustal velocity model along the southern cuban margin implications for the tectonic regime at an active plate boundary summary a new 1 d velocity model along the southern cuban margin has been determined using local earthquake data which are the result of the merged cuban and jamaican catalogues simultaneous inversion using joint hypocentre determination was applied to solve the coupled hypocentre velocity model problem we obtained a seven layer model with an average moho interface at 20 km the average velocity was found to be 7 6 km s 1 on the top of the crust mantle transition zone and 6 9 km s 1 in the basaltic layer of the crust the improvement in the earthquake locations allowed us for the first time to use local seismicity to characterize the activity on local faults and the stress regime in the area for this purpose 34 earthquake focal mechanisms were determined along the eastern segments of the oriente fault these solutions are consistent with the known left lateral strike slip motion along this major structure as well as with the stress regime of two local structures 1 the cabo cruz basin and 2 the santiago deformed belt the first structure is dominated by normal faults with minor strikeslip components and the second by reverse faults the shallow seismicity in the cabo cruz basin is associated with fault planes trending n55 58 e and dipping 38 45 to the north the santiago deformed belt on the other hand exhibits diverse fault plane orientations these local structures account for most of the earthquake activity along the southern cuban margin deep seismicity observed in the santiago deformed belt supported by focal mechanisms suggests underthrusting of the gonave microplate beneath the cuban block in this area the principal stress orientations obtained from stress inversion of earthquake focal mechanisms suggest a thrust faulting regime along the southern cuban margin we obtained a nearly horizontal 1 and nearly vertical 3 which indicates active compressional deformation along the major oriente transcurrent fault in agreement with the dominant structural trend associated with the santiago deformed belt

carbonate platforms along the southeast bahamas hispaniola collision zone the southeast bahama banks have been colliding with the island of hispaniola along a restraining bend within the northern caribbean plate boundary zone since the late miocene a seamarc ii seismic reflection investigation was conducted along the deep water flanks of mouchoir bank and navidad bank to evaluate the response of these carbonate platforms to active plate tectonic collision overall our data provide evidence of large scale platform margin retreat which contrasts sharply with the prograding platform margins in the tectonically passive northwest bahamas north of silver bank there is a large 5 000 km2 deep water 3 000 4 000 m plateau that records the drowning and step back 50 km of an early cretaceous carbonate platform margin intact uneroded segments of this cretaceou platform margin may occur along the seaward edge of the deep water plateau bahama escarpment separated by large 20 km across erosional reentrants a coalescing system of broad up to 10 km shallow 200 m relief canyons akin to mountainous avalanche chutes funnel debris into the reentrants from the flank of silver bank the reentrants are interpreted as zones of structural weakness produced by passage of the atlantic spreading center along a transform plate boundary during the late jurassic early cretaceous drowning and step back appear to be part of a global response of carbonate platforms to a mid cretaceous tectonic pulse of ocean crust formation and relative sea level rise the southern margin of mouchoir bank has also been drowned and has stepped back by about 30 km this event occurred during the late tertiary prior to the mid pliocene and is attributed to tectonic tilting and subsidence resulting from oblique underthrusting of the southeast bahamas beneath hispaniola the southern margin of mouchoir bank is also characterized by large 20 km across amphitheater shaped scallops that expose tertiary shallow water limestones along their deep water flanks seaward of one scallop is a large 25 km wide 50 km long mass movement with flow lines preserved on the seafloor we interpret these scallops as catastrophic collapse structures triggered by large earthquakes generated along the collision zone since the late tertiary south of navidad and silver banks is a very complex seafloor morphology resulting in part from the accretion of a portion of the bahamas onto hispaniola there is also a series of e w oriented down to basin normal faults that have caused the platform margin to retreat extensional stress along this predominantly transpressive plate boundary may be a consequence of rotation of the nearby puerto rico block or lithospheric bending during oblique subduction this study provides an initial framework within which to view the actualistic response of carbonate platforms to plate tectonic collision

role of strike slip faulting in the evolution of allochthonous terranes in the philippines concepts of allochthonous terrane transport and emplacement are dominated by the assumption that most terranes originate on the subducting plate collide with the upper plate and are emplaced there movement of terranes along the convergent margin is recognized but is generally attributed to postcollision slip in the northern philippines allochthonous terranes originate primarily within the arc system have been translated along it by strike slip faults and were emplaced by cessation of that slip the authors suggest that in the philippines some originally vertical strike slip boundaries may have evolved into shallow dipping sutures marked by fold and thrust systems this mode of terrane evolution may be more common than generally appreciated particularly in orogenic belts developed in response to oblique convergence

crustal structure of western hispaniola haiti from a teleseismic receiver function study haiti located at the northern caribbean plate boundary records a geological history of terrane accretion from cretaceous island arc formations to the eocene to recent oblique collision with the bahamas platform little is presently known about the underlying crustal structure of the island we analyze p waveforms arriving at 27 temporary broadband seismic stations deployed over a distance of 200 km across the major terrane boundaries in haiti to determine the crustal structure of western hispaniola we compute teleseismic receiver functions using the extended time multi taper method and determine crustal thickness and bulk composition vp vs using the h stacking method three distinctive and fault bounded crustal domains defined by their characteristic moho depth distributions and bulk crustal vp vs are imaged across haiti we relate these domains to three crustal terranes that have been accreted along the plate boundary during the northeastwards displacement of the caribbean plate and are presently being deformed in a localized fold and thrust belt in the northern domain made up of volcanic arc facies the crust has a thickness of 23 km and vp vs of 1 75 0 1 typical of average continental crust the crust in the southern domain is part of the caribbean large igneous province caribbean lip and is 22 km thick with vp vs of 1 80 0 03 consistent with plume related rocks of late cretaceous age significantly thicker the crust in central haiti has values of moho depths averaging 41 km and with vp vs of 1 80 0 05 we propose that the central domain is likely constructed of an island arc upper crust with fragments of dense material originating from mafic lavas or lip material we produce a crustal profile along a n s transect across haiti accounting for the surface geology shallow structural history and new seismological constraints provided by variations of crustal thickness and bulk composition

relative motion between the caribbean and north american plates and related boundary zone deformation from a decade of gps observations global positioning system gps measurements in 1986 1994 and 1995 at sites in dominican republic puerto rico cuba and grand turk define the velocity of the caribbean plate relative to north america the data show eastward motion of the caribbean plate at a rate of 21 1 mm yr 1 standard error in the vicinity of southern dominican republic a factor of 2 higher than the nuvel 1a plate motion model prediction of 11 3 mm yr independent measurements on san andres island and an euler vector derived from these data also suggest a rate that is much higher than the nuvel 1a model available data combined with simple elastic strain models give the following slip rate estimates for major left lateral faults in hispaniola 1 the north hispaniola fault offshore the north coast of hispaniola 4 3 mm yr 2 the septentrional fault in northern dominican republic 8 3 mm yr and 3 the enriquillo fault in southern dominican republic and haiti 8 4 mm yr the relatively high plate motion rate and fault slip rates suggested by our study combined with evidence for strain accumulation and historical seismicity imply that seismic risk in the region may be higher than previous estimates based on low plate rate low fault slip rate models and the relatively low rate of seismicity over the last century

lithospheric structure below seismic stations in cuba from the joint inversion of rayleigh surface waves dispersion and receiver functions summary the joint inversion of rayleigh wave group velocity dispersion and receiver functions has been used to study the crust and upper mantle structure at eight seismic stations in cuba receiver functions have been computed from teleseismic recordings of earthquakes at epicentral angular distances in the range from 30 to 90 and rayleigh wave group velocity dispersion relations have been taken from earlier surface wave tomographic studies in the caribbean area the thickest crust 30 km below cuban stations is found at cascorro ccc and maisi mas whereas the thinnest crust 18 km is found at stations rio carpintero rcc and guantanamo bay gtby in the southeastern part of cuba this result is in agreement with the southward gradual thinning of the crust revealed by previous studies in the crystalline crust the s wave velocity varies between 2 8 and 3 9 km s 1 and at the crust mantle transition zone the shear wave velocity varies from 4 0 and 4 3 km s 1 the lithospheric thickness varies from 65 km in the youngest lithosphere to 150 km in the northeastern part of the cuban island below maisi mas and moa moa stations evidence of a subducted slab possibly belonging to the caribbean plate is present below the stations las mercedes lmg rcc and gtby whereas earlier subducted slabs could explain the results obtained below the soroa sor manicaragua mgv and cascorro ccc station

seismic hazard maps for cuba and surrounding areas a seismic hazard assessment for cuba and the surrounding areas has been performed in response to a possible revision of the national building code the hazard assessment has been done according to the standard methodology adopted by the global seismic hazard assessment program and by introducing some computational techniques used for the seismic hazard map of italy problems of earthquake catalog treatment attenuation of peak ground acceleration and macroseismic intensity as well as seismic source definition have been rigorously analyzed thirty six seismogenic zones have been identified and characterized from a seismicity point of view the present study offers a picture of the seismic hazard on cuban territory based on historical seismicity and the benefits drawn from the most recent international investigations on the subject such as the logic tree approach used to represent the inevitable uncertainties encountered through the choice of attenuation relation the final results are maps of the expected shaking with a 475 year return period in terms of peak ground acceleration and macroseismic intensity which point out the high hazard along the southern coast of cuba where the expected ground motion without the aleatoric uncertainty in the attenuation relations is between 0 20 g and 0 30 g the rest of the island is characterized by values representing less severe shaking

faulting processes of historic 1917 1962 m 6 0 earthquakes along the north central caribbean margin the plate boundary along the north central caribbean margin is geologically complex our understanding of this complexity is hampered by the fact that plate motions are relatively slow 1 to 2 cm yr so that recent seismicity often does not provide a complete picture of tectonic deformation studies of the faulting processes of instrumentally recorded earthquakes occurring prior to 1962 thus provide important information regarding the nature and rate of seismic deformation within the region and are essential for a comprehensive assessment of seismic hazard we have conducted body waveform modeling studies of eight earthquakes which occurred along the north central caribbean plate margin extending from southeastern cuba to the swan island fracture zone 75 to 83 w none of these earthquakes has been previously studied and several occurred in regions where no recent post 1962 seismicity has been recorded the plate margin in the western portion of our study area is characterized by a transform fault spreading center system in the central and eastern portions of our study area the plate margin is a complex diffuse region of deformation that couples transform motion in the cayman trough to subduction along the lesser antilles arc our results show that the western portion of the study area has only experienced large strike slip earthquakes off southeastern cuba two earthquakes appear to have occurred on high angle northward dipping reverse faults with south to southeastward directed slip vectors an earthquake in northern jamaica in 1957 shows pure strike slip faulting most likely along an east west trending fault finally an unusual sequence of events located in the pedro bank region 70 km southwest of jamaica has a mainshock with a reverse oblique mechanism suggesting continuity of the plate interface stress field well south of the northern caribbean margin

variation of palaeostress patterns along the oriente transform wrench corridor cuba significance for neogene quaternary tectonics of the caribbean realm abstract in this study we address the late miocene to recent tectonic evolution of the north caribbean oriente transform wrench corridor in the southern sierra maestra mountain range se cuba the region has been affected by historical earthquakes and shows many features of brittle deformation in late miocene to pleistocene reef and other shallow water deposits as well as in pre neogene late cretaceous to eocene basement rocks these late miocene to quaternary rocks are faulted fractured and contain calcite and karst filled extension gashes type and orientation of the principal normal palaeostress vary along strike in accordance with observations of large scale submarine structures at the south eastern cuban margin initial n s extension is correlated with a transtensional regime associated with the fault later reactivated by sinistral and or dextral shear mainly along e w oriented strike slip faults sinistral shear predominated and recorded similar kinematics as historical earthquakes in the santiago region we correlate palaeostress changes with the kinematic evolution along the boundary between the north american and caribbean plates three different tectonic regimes were distinguished for the oriente transform wrench corridor otwc compression from late eocene oligocene transtension from late oligocene to miocene d1 and transpression from pliocene to present d2 d4 when this fault became a transform system furthermore present day structures vary along strike of the oriente transform wrench corridor otwc on the south eastern cuban coast with dominantly transpressional compressional and strike slip structures in the east and transtension in the west the focal mechanisms of historical earthquakes are in agreement with the dominant ene wsw transpressional structures found on land

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

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

s wave velocities of the lithosphere asthenosphere system in the caribbean region an overview of the s wave velocity v s structural model of the caribbean with a resolution of 2 2 is presented new tomographic maps of rayleigh wave group velocity dispersion at periods ranging from 10 to 40 s were obtained as a result of the frequency time analysis of seismic signals of more than 400 ray paths in the region for each cell of 2 2 group velocity dispersion curves were determined and extended to 150 s by adding data from a larger scale tomographic study vdovin et al geophys j int 136 324 340 1999 using as independent a priori information the available geological and geophysical data of the region each dispersion curve has been inverted by the hedgehog non linear procedure valyus determining seismic profiles from a set of observations in russian vychislitielnaya seismologiya 4 3 14 english translation computational seismology v i keylis borok ed 4 114 118 1968 in order to compute a set of v s versus depth models up to 300 km of depth because of the non uniqueness of the solutions for each cell a local smoothness optimization has been applied to the whole region in order to choose a three dimensional model of v s satisfying this way the occam s razor concept several known and some new main features of the caribbean lithosphere and asthenosphere are shown on these models such as the west directed subduction zone of the eastern caribbean region with a clear mantle wedge between the caribbean lithosphere and the subducted slab the complex and asymmetric behavior of the crustal and lithospheric thickness in the cayman ridge the predominant oceanic crust in the region the presence of continental type crust in central america and the south and north america plates as well as the fact that the bottom of the upper asthenosphere gets shallower going from west to east

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

crust and upper mantle structure in the caribbean region by group velocity tomography and regionalization an overview of the crust and upper mantle structure of central america and the caribbean region is presented as a result of the processing of more than 200 seismograms recorded by digital broadband stations from sssn and gsn seismic networks group velocity dispersion curves are obtained in the period range from 10s to 40s by ftan analysis of the fundamental mode of the rayleigh waves the error of these measurements varies from 0 06 and 0 09 km s from the dispersion curve seven tomographic maps at different periods and with average spatial resolution of 500 km are obtained using the logical combinatorial classification techniques eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions each one characterized by one kind of dispersion curves are identified the average dispersion curves obtained for each region are extended to 150s by adding data from a larger scale tomographic study vdovin et al 1999 and inverted using a nonlinear procedure a set of models of the s wave velocity vs depth in the crust and upper mantle is found as a result of the inversion process in six regions we identify a typically oceanic crust and upper mantle structure while in the other two the models are consistent with the presence of a continental structure two regions located over the major geological zones of the accretionary crust of the caribbean region are characterized by a peculiar crust and upper mantle structure indicating the presence of lithospheric roots reaching at least about 200 km of depth

reconciling down core anticorrelation of diatom carbon and nitrogen isotopic ratios from the southern ocean 1 oceanic nutrient cycling in the southern ocean is supposed to have an important impact on glacial interglacial atmospheric co2 changes and global climate in order to characterize such nutrient cycling over the last two climatic cycles we investigated carbon and nitrogen isotopic ratios of diatom bound organic matter 13cdiat and 15ndiat respectively in two cores retrieved form the atlantic and indian sectors of the antarctic ocean the two cores show the same isotopic patterns the 13cdiat values are depleted during glacial periods and enriched during interglacial periods indicating lower productivity during cold times the 15ndiat values are enriched during glacial periods and depleted during interglacial periods arguing for greater nitrate utilization during cold times taken at face value this apparent contradiction leads to opposite conclusions on the role of the southern ocean biological pump on the atmospheric co2 changes however the two sets of data can be reconciled by a sea ice plus mixing rate scenario that calls upon a balance between the effect of cutting off gas transfer at the ocean atmosphere boundary and the effect of reducing vertical transport of nutrients through the pycnocline