mid to late holocene mediterranean climate variability contribution of multi proxy and multi sequence comparison using wavelet analysis in the northwestern mediterranean basin abstract forcings and mechanisms underlying holocene climate variability still remain poorly this work review already published paleoclimatic time series and proposes an alternative way to compare them using spectral analysis such an approach may emphasize joint features between different signals and lead us closer to the causes of climate changes ten paleoclimatic proxy records from 5 sequences from the gulf of lions and surrounding areas were compiled these paleoclimate time series were supplemented with proxies of the north atlantic oscillations nao el nino southern oscillations enso and the intertropical convergence zone itcz variability a comparison of their frequency content is proposed using wavelet analysis for unevenly sampled time series a new algorithm is used in order to propagate the age model errors within wavelet power spectra three main groups of shared features specific to the mid and late holocene after 7000 yrs cal bp can be defined on the basis of the results of these analyses an atlantic cyclic period solar cyclic periods and tropical cyclic periods the atlantic cyclic period is probably related to fluctuations of the atlantic thermohaline circulation which would induce changes in the storm track extension and position thereby impacting upon precipitation and storminess over a millennial scale the centennial scale solar variability might induce a nao like variability of the atmospheric circulation thereby influencing storminess in western europe and mediterranean finally tropical cyclic periods are possibly registered in of the gulf of lions and atlantic climate proxies potentially highlighting the influence of enso variability over the western mediterranean

dual influence of atlantic and pacific sst anomalies on the north atlantic europe winter climate clustering analyses are used in both ncep reanalyses and model simulations to identify relationships between the low frequency variability of the zonal wind jet at 200hpa u200 over the north atlantic europe domain and the geographical distribution of the sea surface temperature sst anomalies for winter months over the 1959 1998 period the u200 signature of the two phases of the north atlantic oscillation nao is captured from ncep in a cluster pair associated with the north atlantic sst tripole the classification also extracts a la nina mode related to a strong ridge off europe and reduced jet over the azores model results confirm this dual oceanic association while exaggerating the enso influence the role of the atlantic ssts is confirmed in model experiments where climatological ssts are prescribed in the other basins tropical anomalies dominate the atlantic sst signals and are linked to fluctuations of the jet consistently with the nao phase

magmatic record of neoarchean arc polarity reversal from the dengfeng segment of the central orogenic belt north china craton abstract the dengfeng segment of the archean central orogenic belt in the north china craton ncc includes circa 2 66 2 5 ga metavolcanics metasedimentary and plutonic rocks all units are intruded by 2 5 2 4 ga mafic dykes and a suite of coeval circa 2 5 2 45 ga potassic granites and leucogranitic veins mafic dykes are characterized by mixed alkaline and calc alkaline affinities enriched lree and negative nb and zr anomalies indicating a lithospheric mantle source region potassic granitic dykes exhibit highly fractionated lree patterns and negative hfse anomalies and positive zircon ehf t values which are similar to those of ttg gneisses in the area leucogranitic veins cutting across the diorites are characterized by high contents of sio2 and k2o lree enriched patterns positive eu and sr anomalies negative nb and ti anomalies we suggest that the granitic dykes and leucogranitic veins were derived from partial melting of thickened older crusts combined with other reported 2 5 ga mafic dykes and potassic granites from the ncc we propose that they demonstrate an ancient example of arc polarity reversal and provide a record of the formation of a new plate boundary in the archean the underplating of the mafic dyke source beneath the newly accreted eastern block may have generated the widespread 2 5 2 47 ht lp metamorphism with anticlockwise p t paths in the eastern block

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

circum pacific mid cretaceous deformation and uplift a superplume related event evidence of short lived episodes of mid cretaceous deformation metamorphism uplift and hiatus in sedimentation is widespread in the lower cretaceous rocks that bordered the cretaceous pacific basin i present a model in which these coeval but widely spaced events are linked to increased ridge push force at subduction zones triggered by large scale upwelling of mantle associated with the mid cretaceous superplume this model can account for mid cretaceous terrane accretion and ophiolite obduction events and can explain brief compressional phases in predominantly extensional orogenies as recognized in alaska british columbia california western south america and west antarctica

moment magnitude relations based on strong motion records in greece in this work the variation of the local magnitude mlsm derived from strong motion records at short distances is examined in terms of moment magnitude m w strong motion data from greek earthquakes are used to determine the strong motion local magnitude mlsm by performing an integration of the equation of mo tion of the wood anderson wa seismograph subjected to an input acceleration the most reliable strong motion data are utilized for earthquakes with seismic mo ments log m 0 22 0 dynecm and calculated local magnitudes mls m 3 7 the correlation between the seismic moments log m0 and the calculated local magni tudes mlsm using strong motion records is given by log m 0 1 5 mcsu 16 07 which is very similar to that proposed by hanks and kanamori 1979 moreover it is shown that mls m is equal to moment magnitude mw for a large mls m range 3 9 to 6 6 comparison of the strong motion local magnitude and the me magnitude estimated in greece ml n and surrounding area shows a systematic bias of 0 4 to 0 5 similar to the difference that has been found between m w and mlgr for the same area the contribution of the local site effects in the calculation of the local magni tude mlsm is also considered by taking into account two indices of soil classification namely rock and alluvium or the shear wave velocity vs30 of the first 30 m based on nehrp 1994 and ubc 1997 an increase of mls m by 0 16 is observed for alluvium sites alternative relations showing the mls m variation with v 3 are also presented finally examination of the wa amplitude attenuation log a0 with distance shows that the jennings and kanamori 1983 relation for a 100 km is appropriate for greece the same results confirm earlier suggestions that the 0 4 to 0 5 bias between mlgr and mw also mlsa4 should be attributed to a low static magnification 800 of the athens wa instrument on which all other m l relations in greece have been calibrated

effect of distance on local magnitudes found from strong motion records values of local magnitude m l are calculated from 56 strong motion accelerograms recorded in the imperial valley earthquake of 15 october 1979 according to procedures developed earlier kanamori and jennings 1978 these data plus similar data from the san fernando earthquake of 9 february 1971 and additional less numerous data from several other california earthquakes are used to investigate the use of different measures of distance in near field determinations of m l this investigation has relevance for similar uses of distances in determining seismic design criteria in addition the consistency of the values of m l found from the strong motion data is examined from the viewpoint of assessing the need for any correction in the standard attenuation curve log 10 a 0 it was found that the most consistent values of m l result when distance is measured to the closest point on the surface trace of the fault if a site lies within a circle with diameter equal to the extent of faulting and centered on the center of faulting center of energy release outside this circle the distance measured to the center of the circle is recommended a consistent trend in the values of m l found from strong motion records is seen in the data the values start at zero distance at essentially the far field value and then decrease to 1 4 unit at about 20 km then they rise to 1 4 unit at 50 to 60 km a smooth revision to the standard attenuation curve is presented which removes this systematic trend

effect of unbalanced topography and overloading on coulomb wedge kinematics insights from sandbox modeling 1 this study addresses the effect of variable unbalanced topography and overload on the kinematics of a fold and thrust belt developed within a collisional belt that underwent a subduction polarity reversal event this was done by physical modeling of doubly vergent coulomb wedges using sand as an analogue material during the experimental procedure a preexisting topography was generated by a first phase of subduction in one direction a second phase of subduction was then initiated in the opposite direction simulating a subduction flip an anomalous strong frontal growth for the wedge during the second phase was experimentally shown to be dependent upon surface slope breaks and the critical asymmetrical architecture achieved by the wedge at mature stages of deformation the latter is suggested to be the rule for doubly vergent orogens at steady state even after a subduction flip during the experiments surface processes like syntectonic erosion and sedimentation markedly altered mass transfer within the wedge in particular lowering the surface slope by syntectonic erosion favored cycling between accretion and underthrusting modes by contrast a sudden syntectonic sediment load in the prowedge region promoted prolonged phases of underthrusting retarding accretion of new imbricates at the prowedge toe however at later stages of deformation the prowedge was forced to regain its characteristic minimum critical taper as predicted by theory and did so by the sudden nucleation of long flat thrust units rapidly rebalancing the asymmetry between prowedge and retrowedge regions the experiments suggest that given a fixed critical taper related to time invariant frictional properties along the wedge bounding surfaces deformation does vary within the wedge according to time varying location of normal stress surpluses and unbalanced topography acting on potential failure surfaces these in turn alter the equilibrium between prowedge and retrowedge basal detachments that is here considered to be a major factor controlling the self regulating dynamics of collisional orogens

a damped decadal oscillation in the north atlantic climate system a simple stochastic atmosphere model is coupled to a realistic model of the north atlantic ocean a north south sst dipole with its zero line centered along the subpolar front influences the atmosphere model which in turn forces the ocean model by surface fluxes related to the north atlantic oscillation the coupled system exhibits a damped decadal oscillation associated with the adjustment through the ocean model to the changing surface forcing the oscillation consists of a fast wind driven positive feedback of the ocean and a delayed negative feedback orchestrated by overturning circulation anomalies the positive feedback turns out to be necessary to distinguish the coupled oscillation from that in a model without any influence from the ocean to the atmosphere using a novel diagnosing technique it is possible to rule out the importance of baroclinic wave processes for determining the period of the oscillation and to show the important role played by anomalous geostrophic advection in sustaining the oscillation

storm track response to oceanic eddies in idealized atmospheric simulations abstractlarge scale oceanic fronts such as in western boundary currents have been shown to play an important role in the dynamics of atmospheric storm tracks little is known about the influence

the ml scale in southern california measurements 9 941 of peak amplitudes on wood anderson instruments or simulated wood anderson instruments in the southern california seismographic network for 972 earthquakes primarily located in southern california were studied with the aim of determining a new distance correction curve for use in determining the local magnitude m l events in the mammoth lakes area were found to give an unusual attenuation pattern and were excluded from the analysis as were readings from any one earthquake at distances beyond the first occurrence of amplitudes less than 0 3 mm the remaining 7 355 amplitudes from 814 earthquakes yielded the following equation for m l distance correction log a 0 log a 0 1 110log r 100 0 00189 r 100 3 0 where r is hypocentral distance in kilometers a new set of station corrections was also determined from the analysis the standard deviation of the m l residuals obtained by using this curve and the station corrections was 0 21 the data used to derive the equation came from earthquakes with hypocentral distances ranging from about 10 to 700 km and focal depths down to 20 km with most depths less than 10 km the log a 0 values from this equation are similar to the standard values listed in richter 1958 for 50 200 km the effect at close distances is consistent with that found in several other studies and is simply due to a difference in the observed 1 r geometrical spreading for body waves and the 1 r 2 spreading assumed by gutenberg and richter in the construction of the log a 0 table m l s computed from our curve and those reported in the caltech catalog show a systematic dependence on magnitude small earthquakes have larger magnitudes than in the catalog and large earthquakes have smaller magnitudes by as much as 0 6 units to a large extent these systematic differences are due to the nonuniform distribution of data in magnitude distance space small earthquakes are preferentially recorded at close distances relative to large earthquakes for large earthquakes however the difference in the two magnitudes is not solely due to the new correction for attenuation magnitudes computed using richter s log a 0 curve are also low relative to the catalog values the differences in that case may be due to subjective judgment on the part of those determining the catalog magnitudes the use of data other than the caltech wood anderson seismographs the use of different station corrections or the use of teleseismic magnitude determinations whatever their cause the departures at large magnitude may explain a 1 0 0 7 proportionality found by luco 1982 between m l s determined from real wood anderson records and those from records synthesized from strong motion instruments if it were not for the biases in reported magnitudes luco s finding would imply a magnitude dependent shape in the attenuation curves we studied residuals in three magnitude classes 2 0 m l 3 5 3 5 m l 5 5 and 5 5 m l 7 0 and found no support for such a magnitude dependence based on our results we propose that local magnitude scales be defined such that m l 3 correspond to 10 mm of motion on a wood anderson instrument at 17 km hypocentral distance rather than 1 mm of motion at 100 km this is consistent with the original definition of magnitude in southern california and will allow more meaningful comparison of earthquakes in regions having very different attenuation of waves within the first 100 km

local magnitude determinations for intermountain seismic belt earthquakes from broadband digital data the university of utah seismograph stations uuss earthquake catalogs for the utah and yellowstone national park regions contain two types of size measurements local magnitude m l and coda magnitude m c which is calibrated against m l from 1962 through 1993 uuss calculated m l values for southern and central intermountain seismic belt earthquakes using maximum peak to peak p p amplitudes on paper records from one to five wood anderson w a seismographs in utah for m l determinations of earthquakes since 1994 uuss has utilized synthetic w a seismograms from u s national seismic network and uuss broadband digital telemetry stations in the region which numbered 23 by the end of our study period on 30 june 2002 this change has greatly increased the percentage of earthquakes for which m l can be determined it is now possible to determine m l for all m 3 earthquakes in the utah and yellowstone regions and earthquakes as small as m to maintain continuity in the magnitudes in the uuss earthquake catalogs we determined empirical m l station corrections that minimize differences between m l s calculated from paper and synthetic w a records application of these station corrections in combination with distance corrections from richter 1958 which have been in use at uuss since 1962 produces m l values that do not show any significant distance dependence m l determinations for the utah and yellowstone regions for 1981 2002 using our station corrections and richter s distance corrections have provided a reliable data set for recalibrating the m c scales for these regions our revised m l values are consistent with available moment magnitude determinations for intermountain seismic belt earthquakes to facilitate automatic m l measurements we analyzed the distribution of the times of maximum p p amplitudes in synthetic w a records a 30 sec time window for maximum amplitudes beginning 5 sec before the predicted sg time encompasses 95 of the maximum p p amplitudes in our judgment this time window represents a good compromise between maximizing the chances of capturing the maximum amplitude and minimizing the risk of including other seismic events

recycling in the subduction factory archaean to permian zircons in the oceanic cretaceous caribbean island arc hispaniola abstract little mineralogical evidence is left of the recycling of continental and oceanic crust into the mantle at subduction zones zircon because of its exceptional robustness is probably the only surviving phase and the best mineral tracer of this global scale process this article combines new in situ u pb dating and o and hf isotope analyses on cretaceous co magmatic and pre cretaceous inherited zircons separated from albian aptian arc related igneous rocks from the dominican republic the o and hf systematics of cretaceous zircons reflect derivation from predominantly juvenile sources and variable mixing with evolved melts as expected for an oceanic island arc inherited zircons yield u pb ages between 256 and 2923 ma n 219 most studied inherited zircons are permian carboniferous peaking at ca 300 ma and formed in continental crust to judge from mineral inclusions including quartz orthoclase muscovite and apatite 18o 6 16 to 12 67 and ehf t 11 9 to 1 12 values ordovician to proterozoic zircons yield 18o between 4 93 and 9 21 and ehf t between 19 9 and 8 5 and hence crystallized in equilibrium with either mantle derived juvenile magmas or magmas derived from melting of supracrustal rocks for archean zircons 18o between 6 98 and 7 94 and ehf t between 18 5 and 1 6 might reflect contribution of supracrustal materials in the parent magmas we suggest that arc magmas picked up the inherited zircon cargo from their mantle sources accounting paleogeographic and paleo tectonic constraints mexican and colombian terranes are identified as the potential primary magmatic and secondary sedimentary sources for the studied inherited zircons we envisage that inherited zircons were transported downward to the mantle beneath the caribbean plate as detrital grains on top of the subducting proto caribbean and or pacific slabs

critical metals ree sc pge in ni laterites from cuba and the dominican republic ni laterites are considered worthy targets for critical metals cm exploration as rare earth elements ree sc and platinum group elements pge can be concentrated during weathering as a result

episodicity of mesozoic terrane accretion along the pacific margin of gondwana implications for superplume plate interactions a review of evidence for deformation and terrane accretion on the late triassic early jurassic margins of pangea and the mid cretaceous margins of the palaeo pacific ocean shows that deformation was global and synchronous with probable superplume events late triassic early jurassic deformation appears to be concentrated in the period 202 197 ma and was coeval with eruption of the central atlantic magmatic province onset of pangaea break up a period of extended normal magnetic polarity and a major mass extinction event all possible expressions of a superplume event mid cretaceous deformation occurred in two brief periods the first from approximately 116 to 110 ma in the west palaeo pacific and the second from roughly 105 to 99 ma in the east palaeo pacific with both events possibly represented in northeast siberia this deformation was coeval with eruption of major oceanic plateaus core complex formation and rifting of new zealand from gondwana the cretaceous normal polarity epoch and a major radiation of flowering plants and several animal groups all linked with the mid cretaceous superplume event a simple unifying mechanism is presented suggesting that large continental or oceanic plates when impacted by a superplume tend to break up reorganize associated with gravitational spreading away from a broad thermally generated topographic high and with a resulting short lived pulse of plate marginal deformation and terrane accretion

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

the modeled atmospheric response to midlatitude sst anomalies and its dependence on background circulation states abstract the atmospheric response to a midlatitude sst anomaly in the north pacific and its dependence on background flow are examined in a gcm experiments are conducted using the same warm sst anomalies but two different model states perpetual january and perpetual february the atmospheric responses to the sst anomalies are statistically significant in both january and february but are completely different the anomalous circulation in january is characterized by a trough decaying with height immediately downstream of the sst anomalies in february the anomalous circulation is dominated by a downstream ridge growing with height the patterns of the anomalous heights in the two months are nearly orthogonal vorticity and thermodynamic budgets are diagnosed to illustrate how the anomalous circulations are maintained over the sst anomalies low level convergence and ascent are observed in both months in january the anomalous convergence is balanced by a residual due primarily to the forcing by submont

impacts of different types of el nino and la nina on northern tropical atlantic sea surface temperature the present study investigates the dependence of the northern tropical atlantic nta sea surface temperature sst response to el nino and la nina events on the decay time and amplitude of tropical pacific sst anomalies it is found that the nta sst response to la nina events displays a notable difference between late and early decaying events similar to that in response to el nino events but with a weaker signal latent heat flux is a dominant term in the nta sst change in preceding winter early spring in both el nino and la nina events and in the difference of the nta sst anomaly between late and early decaying el nino and la nina events the zonal and meridional advections have an opposite effect on the nta sst warming in late decaying el nino events although the warming in the nta region is similar in late decaying moderate and strong el nino events the distribution of the sst anomalies in the mid latitude north atlantic ocean shows a notable difference between the two types of late decaying el nino events the sst anomalies also display difference in the early decaying weak and moderate el nino events surface heat flux differences are largely attributed to wind differences

the influence of atlantic sea surface temperature anomalies on the north atlantic oscillation abstract the influence of atlantic sea surface temperature sst anomalies on the atmospheric circulation over the north atlantic sector during winter is investigated by performing experiments with an atmospheric general circulation model these consist of a 30 yr run with observed sst anomalies for the period 1961 90 confined geographically to the atlantic ocean and of a control run with climatological ssts prescribed globally a third 30 yr integration with observed ssts confined to the south atlantic is made to confirm present findings the simulated interannual variance of 500 hpa wintertime geopotential heights over the north atlantic attains much more realistic values when observed atlantic ssts are prescribed circulation patterns that resemble the positive phase of the north atlantic oscillation nao become more pronounced in terms of the leading eof of winter means and a cluster analysis of daily fields the variance of an interannual nao index increases by fivefold over its control value atl

pliocene lower pleistocene shallow water mixed siliciclastics and carbonates yanigua and los haitises formations in eastern hispaniola dominican republic the virtually unfolded sedimentary cover of the cordilleras central and oriental in the eastern dominican republic eastern hispaniola tropical north atlantic largely consists of pliocene to early pleistocene mixed siliciclastics and carbonates these deposits have been grouped into two laterally interfingering mapping units the yanigua and los haitises formations the former mainly siliciclastics comprises marl marly limestone and minor conglomerate sandstone lignite and carbonaceous clay and crops out closest to the basement the los haitises formation mainly consists of limestone and intercalating beds of marly limestone and marl lithological mapping at the 1 50 000 scale and facies analysis of twelve measured sections and of additional fourteen outcrops suggest that these deposits mainly formed on a shallow water marine platform fringing the precursor reliefs of the cordillera oriental and the southeastern end of the cordillera central only a limited proportion of sediment formed in floodplains and marshes marl and marly limestone dominated the inner platform sediments terrigenous mud decreased away from the emergent basement and carbonate sedimentation dominated the more external platform corals molluscs echinoids foraminifers bryozoans coralline algae and halimeda are the main components with varying amounts of carbonate mud the platform was generally a low energy environment with seagrass patches in the inner platform corals grew as isolated colonies or as small patch reefs dominated by porites in marly and bioclastic substrates branching corals stylophora and acropora grew in extensive carpets in more distal areas at least in the last stage of its development early pleistocene the platform was rimmed by a reef barrier similar to the holocene caribbean barrier reefs with acropora gr palmata a cervicornis porites montastrea siderastrea and diploria as the main reef builders

spectral analysis and earthquake scaling of the petatlan earthquake m s 7 6 aftershocks recorded at stations along the pacific coast and between the coast and mexico city spectral parameters have been estimated for 214 petatlan aftershocks recorded at stations between petatlan and mexico city and between petatlan and acapulco the spectral parameters were used to obtain empirical relations for the estimation of seismic moment from coda length and fromm l stress drops using brune s model were calculated for these aftershocks six events with large stress drop are located within a previously suggested asperity and seven more suggest a boundary zone at the intersection of the petatlan and zihuatanejo aftershock rupture volumes stress drops increase with increasing seismic moment up to 1020 dyne cm but appear to be constant at greater moment values the peak horizontal velocity times distance of aftershocks recorded near the coast and between the coast and mexico city 30 to 270 km away scales linearly with seismic moment and predicts well the peak horizontal values of large m s 7 0 coastal thrust events recorded on rock sites at mexico city peak horizontal velocity is a straightforward measurement thus this relation allows us to evaluate expected ground motion between the pacific coast and mexico city from the seismic moment of subduction related earthquakes along the coast

cretaceous paleogene thrust emplacement of serpentinite in southwestern puerto rico serpentinite emplacement mechanisms along convergent plate boundaries are complex and not well understood this investigation combined structural and stratigraphic data from serpentinite in puerto rico to suggest an emplacement mechanism along the north american caribbean plate boundary northward dipping thrust faults and foliations along the southern margins of the monte del estado and rio guanajibo serpentinite bodies in southwestern puerto rico indicate southwestward thrust movement of serpentinite structural analysis of faults folds and foliation recorded within the serpentinite bodies and analysis of contact relationships with volcano sedimentary rocks lead to the interpretation that thrust movements record contractional deformations occurring during the maastrichtian paleocene and late eocene early oligocene intervals the conclusion that serpentinite has been most recently emplaced above thrust faults during transpression between the caribbean north america plates is in contrast to the earlier hypothesis that serpentinite was emplaced in response to diapirism late eocene transpression reactivated older faults and also displaced the serpentinite although the timing of the serpentinite emplacement in southwestern puerto rico is similar to emplacement events in cuba and hispaniola there are differences in the origin mechanism and direction of emplacement of the serpentinite masses the heterogeneity in the serpentinite emplacement mechanism and transport direction evokes reconsideration of the deformation history along the caribbean north american plate boundary

surface temperature patterns associated with the southern oscillation abstract the typical global and large scale regional temperature patterns associated with the low warm and high cold phases of the southern oscillation so are investigated a total of 12 separate regions were found to have consistent temperature patterns associated with low phase of the so while 11 areas were found to have temperature patterns associated with the high phase of these areas 9 have expected temperature patterns during both phases of the so in the tropics temperature anomalies are of the same sign as the so related sea surface temperature sst anomaly in all land regions except for one area in the west pacific three extratropical responses to the low phase of the so are found over north america and one is found in japan high so temperature patterns were found in the extratropies for japan western europe and northwestern north america the identified temperature responses are more consistent in tropical regions than in the extratropies the so can influence the estimation of

modes of climate variability synthesis and review of proxy based reconstructions through the holocene abstract modes of climate variability affect global and regional climates on different spatio temporal scales and they have important impacts on human activities and ecosystems as these modes are a useful tool for simplifying the understanding of the climate system it is crucial that we gain improved knowledge of their long term past evolution and interactions over time to contextualise their present and future behaviour we review the literature focused on proxy based reconstructions of modes of climate variability during the holocene i e the last 11 7 thousand years with a special emphasis on i proxy based reconstruction methods ii available proxy based reconstructions of the main modes of variability i e el nino southern oscillation pacific decadal variability atlantic multidecadal variability the north atlantic oscillation the southern annular mode and the indian ocean dipole iii major interactions between these modes and iv external forcing mechanisms related to the evolution of these modes this review shows that modes of variability can be reconstructed using proxy based records from a wide range of natural archives but these reconstructions are scarce beyond the last millennium partly due to the lack of robust chronologies with reduced dating uncertainties technical issues related to proxy calibration and difficulty elucidating their stationary impact or not on regional climates over time while for each mode the available reconstructions tend to agree at mutidecadal timescales they show notable disagreement on shorter timescales beyond the instrumental period the reviewed evidence suggests that the intrinsic variability of modes can be modulated by external forcing such as orbital solar volcanic and anthropogenic forcing the review also highlights some modes experience higher variability over the instrumental period which is partly ascribed to anthropogenic forcing these features stress the paramount importance of further studying their past variations using long climate proxy records for the progress of climate science

40ar 39ar dating of alunite from the pueblo viejo gold silver district dominican republic new 40 ar 39 ar ages for alunite from the moore and monte negro deposits in the pueblo viejo district as well as from a newly discovered alunite bearing zone on loma la cuaba west of the known deposits are reported here the ages range from about 80 to 40 ma with closely adjacent samples exhibiting very different ages interpretation of these results in the context of estimated closure temperatures for alunite and the geologic and tectonic evolution of hispaniola does not lead to a simple conclusion about the age of mineralization the simplest interpretation that mineralization was caused by a buried late cretaceous 80 ma intrusion is complicated by lack of intrusions of this age in the area and absence of alteration in overlying limestone the alternative interpretation that mineralization was formed during early cretaceous 110 ma magmatism and that the 40 ar 39 ar ages were completely reset by late cretaceous thrusting is complicated by a lack of information on the timing and thermal effects of thrusting in central hispaniola alunite studies have yielded similar unclear results in other pre cenozoic ore systems notably those of the lachlan fold belt in australia

was the laramide orogeny related to subduction of an oceanic plateau numerous models have been presented to explain the late cretaceous early cenozoic laramide orogeny which affected the foreland region of the western cordillera within the us1 the most attractive models invoke low angle subduction2 4 which can develop for various reasons5 6 evidence from south america indicates that one such reason may be the subduction of buoyant ocean floor we here extend the low angle subduction models by attributing the shallowing of the subduction angle during the laramide orogeny to subduction of a large oceanic plateau of anomalously thick and buoyant oceanic crust pacific plate history indicates that a twin to the hess rise may represent the oceanic plateau that triggered laramide events

garnierites and garnierites textures mineralogy and geochemistry of garnierites in the falcondo ni laterite deposit dominican republic abstract garnierites ni mg bearing phyllosilicates are significant ore minerals in ni laterites of the hydrous silicate type in the falcondo ni laterite deposit dominican republic garnierites are found within the saprolite horizon mainly as fracture fillings and thin coatings on joints field observations indicate an important role of active brittle tectonics during garnierite precipitation different greenish colours and textures can be distinguished which correspond to different mineral phases defined according to x ray diffraction xrd and electron microprobe emp analyses a talc like 10 a type b serpentine like 7 a type c a mixture of talc and serpentine like and d sepiolite like types compositional data indicate continuous mg ni solid solution along the joins lizardite nepouite serpentine like kerolite pimelite talc like and sepiolite falcondoite sepiolite like in general talc like garnierite is dominant in falcondo ni laterite and displays higher ni contents than serpentine like garnierites emp analyses showing deviations from the stoichiometric mg ni solid solutions of serpentine and talc are best explained by talc and serpentine like mixing at the nanoscale a detailed textural study by means of quantified x ray element imaging provides a wealth of new information about the relationships between textural position sequence of crystallization and mineral composition of the studied garnierite samples these results indicate several stages of growth with variable ni content pointing to recurrent changes in the physical chemical conditions during garnierite precipitation in addition our detailed mineralogical study of the falcondo garnierites revealed that the different types identified have characteristic h 2 o content and sio 2 mgo ratios which play important roles during the pyrometallurgy process

timing of deformational events in the rio san juan complex implications for the tectonic controls on the exhumation of high p rocks in the northern caribbean subduction accretionary prism abstract an integrated structural petrological and geochronological study was undertaken to constrain the tectonic history and controls on the exhumation of the high p rocks of the rio san juan complex in the northern caribbean subduction accretionary wedge in the main structural units of the complex microtextural analyses were performed to identify the fabrics formed at peak of metamorphism in eclogite facies conditions and during the main retrogressive event toward the low p amphibolite or blueschist greenschist facies conditions u pb shrimp dating on zircon rims 71 3 0 7 ma coupled with 40 ar 39 ar analyses on phengite 70 69 ma in felsic sills placed temporal constraints on the exhumation of the jagua clara serpentinite matrix melange during the blueschist facies stage at the early maastrichtian in the cuaba unit u pb tims zircon ages of 89 7 0 1 ma and 90 1 0 2 ma obtained for the crystallization of tonalitic trondhjemitic melts in the lower guaconejo and upper jobito subunits respectively are similar these ages coupled with a u pb shrimp zircon age of 87 1 8 ma obtained in a garnet amphibolite and a group of older 40 ar 39 ar cooling ages on calcic amphibole constrain the exhumation of the guaconejo subunit from the high p stage to the low p stage at the 90 83 ma time interval further the age data collectively supports a genetic relationship between the distributed extensional ductile shearing the related decompression and the local partial anatexis in the subunit at least from the turonian coniacian boundary to the early campanian a group of younger 40 ar 39 ar ages obtained in the mylonitized amphibolites of the basal jobito detachment zone indicates late ductile deformation and exhumation cooling in the late campanian to maastrichtian 75 70 ma therefore structural and age data established deformation partitioning and reworking of retrograde fabrics during 20 ma in the cuaba unit the different exhumation rates obtained for the jagua clara melange can be explained by uplift in two contrasting tectonic settings a first stage of slow exhumation 1 4 mm yr in the subduction channel largely lower than plate velocities and a second stage of relatively fast exhumation 7 6 mm yr up to the surface therefore the exhumation was temporally discontinuous and the velocity increase at 70 ma probably was triggered in response to the entrance of buoyant material in the subduction zone such as a caribeana continental ribbon or the distal part of yucatan bahamas continental margin in contrast the exhumation path of the guaconejo subunit is composed of a first segment from the baric peak to the low p amphibolite stage at 84 83 ma with an exhumation rate of 7 2 mm yr a second segment around the closure temperature of calcic amphibole at 82 70 ma with a rate of 0 4 mm yr and a third segment to the surface exposure at 60 ma with a rate of 1 8 mm yr these velocity differences can be correlated with the p t path proposed for the exhumation of the subunit with an initial isothermal decompression from the peak in the high p amphibolite to the eclogite facies produced by distributed extensional shearing followed by a relatively slow cooling at low p in the newly acquired structural position and the final tectonics mainly partitioned in the late jobito detachment zone the initial fast exhumation can be related to a major modification in the convergence conditions across the intra oceanic subduction zone as a jump of the basal subduction thrust beyond a previously accreted arc terrane

local coupled equatorial variability versus remote enso forcing in an intermediate coupled model of the tropical atlantic the relative roles played by the remote el nino southern oscillation enso forcing and the local air sea interactions in the tropical atlantic are investigated using an intermediate coupled model icm of the tropical atlantic the oceanic component of the icm consists of a six baroclinic mode ocean model and a simple mixed layer model that has been validated from observations the atmospheric component is a global atmospheric general circulation model developed at the university of california los angeles ucla in a forced context the icm realistically simulates both the sea surface temperature anomaly ssta variability in the equatorial band and the relaxation of the atlantic northeast trade winds and the intensification of the equatorial westerlies in boreal spring that usually follows an el nino event the results of coupled experiments with or without pacific enso forcing and with or without explicit air sea interactions in the equatorial atlantic indicate that the background energy in the equatorial atlantic is provided by enso however the time scale of the variability and the magnitude of some peculiar events cannot be explained solely by enso remote forcing it is demonstrated that the peak of ssta variability in the 1 3 yr band as observed in the equatorial atlantic is due to the local air sea interactions and is not a linear response to enso seasonal phase locking in boreal summer is also the result of the local coupling the analysis of the intrinsic sustainable modes indicates that the atlantic el nino is qualitatively a noisedriven stable system such a system can produce coherent interdecadal variability that is not forced by the pacific or extraequatorial variability it is shown that when a simple slab mixed layer model is embedded into the system to simulate the northern tropical atlantic nta sst variability the warming over nta following el nino events have characteristics location and peak phase that depend on air sea interaction in the equatorial atlantic in the model the interaction between the equatorial mode and nta can produce a dipolelike structure of the ssta variability that evolves at a decadal time scale the results herein illustrate the complexity of the tropical atlantic ocean atmosphere system whose predictability jointly depends on enso and the connections between the atlantic modes of variability

discovery of ni smectite rich saprolite at loma ortega falcondo mining district dominican republic geochemistry and mineralogy of an unusual case of hybrid hydrous mg silicate clay silicate type ni laterite hydrous mg silicate type ni laterite deposits like those in the falcondo district dominican republic are dominated by ni enriched serpentine and garnierite recently abundant ni smectite in the saprolite zone have been discovered in loma ortega one of the nine ni laterite deposits in falcondo a first detailed study on these ni smectites has been performed xrd sem epma in addition to a geochemical and mineralogical characterisation of the loma ortega profile xrf icp ms xrd unlike other smectite occurrences in laterite profiles worldwide the loma ortega smectites are trioctahedral and exhibit high ni contents never reported before these ni smectites may be formed from weathering of pyroxene and olivine and their composition can be explained by the mineralogy and the composition of the al depleted olivine rich parent ultramafic rock our study shows that ni laterites are mineralogically complex and that a hydrous mg silicate ore and a clay silicate ore can be confined to the same horizon in the weathering profile which has significant implications from a recovery perspective in accordance the classification of hybrid hydrous mg silicate clay silicate type ni laterite deposit for loma ortega would be more appropriate

rotational atmospheric circulation during north atlantic european winter the influence of enso the dominant variability modes of the north atlantic european rotational flow are examined by applying a principal component analysis pca eof to the 200 hpa streamfunction mid winter anomalies jan feb monthly means the results reveal that when this norm is used the leading mode eof1 does not correspond to the traditional north atlantic oscillation nao which appears in our analysis as the second leading mode eof2 but is the local manifestation of the leading hemispheric streamfunction eof the regression of this regional mode onto the global sst field exhibits a clear el nino signature with no signal over the atlantic while the associated upper height anomalies resemble the tropical northern hemisphere tnh pattern east of north america this tnh like wavetrain produces a meridional dipole like pattern at lower levels although in some ways this pattern resembles the nao eof2 the dynamics of these two modes are very different in that only eof2 is associated with a latitudinal shift of the north atlantic stormtrack thus the choice of the streamfunction norm in the eof analysis allows the separation of two different phenomena that can produce similar dipolar surface pressure anomalies over the north atlantic but that have different impact on european climate these two modes also differ on their contribution to variability at lower levels while nao eof2 is mostly confined to the north atlantic tnh eof1 has a more annular global character at upper levels nao eof2 also produces a global pattern but with no annular structure reminiscent of the circumglobal teleconnection

age of the los ranchos formation dominican republic timing and tectonic setting of primitive island arc volcanism in the caribbean region this study reports u pb ages for zircons from the los ranchos formation which is part of the primitive island arc sequence the oldest volcanic rocks in the greater antilles zircons were analyzed from three samples quartz porphyry quartz keratophyre from the lower part of the formation quita sueno member fragmental quartz porphyry from the upper part of the formation pueblo viejo member and the cotui quartz diorite stock that intrudes the lower part of the formation the lower part of the los ranchos formation represented by the quita sueno sample formed at either 113 9 0 8 or 118 6 0 5 ma depending on interpretation of the data whereas the upper part represented by the pueblo viejo sample formed ca 110 9 0 8 ma the cotui stock rd 73 601 was emplaced ca 111 8 0 6 ma or 112 9 0 9 ma depending on whether eight grains reflect subtle inheritance these results show that the los ranchos formation was emplaced during the aptian albian transition that the cotui stock could have supplied magma to the volcanic sequence and fluids to the pueblo viejo gold silver deposit in the upper part of the formation and that carbonaceous sediments in the upper part of the formation formed at the same time as ocean anoxic event 1b paquier caribbean plate tectonic models involving invasion of anomalous pacific crust into the caribbean region appear to agree best with this age because they provide a mechanism for the change from primitive island arc pia to calcalkaline magmatism and account for the restricted ocean circulation necessary to generate regional anoxic conditions

a local magnitude scale for crustal earthquakes in italy abstract in this study a new local magnitude m l scale is derived for the italian region from the analysis of seismic signals recorded by a dense broadband network between 2003 and 2009 the m l computation is performed by measuring peak amplitudes of synthetic wood anderson seismograms based on the original definition by richter 1935 these amplitudes are inverted for earthquake magnitudes site corrections and the distance dependent term that corrects amplitudes for geometrical spreading and scattering anelastic attenuation the latter is expressed as a function of r hypocentral distance and log r by means of a two parameter linear form and is constrained at the distance of 100 km in accordance with richter s definition using the newly derived distance dependent term and site corrections magnitudes are consistently estimated for the stations recording each earthquake within an overall root mean square residual of 0 18 no anomalous trend with distance is appreciable in the magnitude residuals for the italian region as a whole or for smaller areas along the italian peninsula the only exception is represented by northeastern italy where increasingly negative residuals are observed for distances decreasing below 100 km the spatial pattern of site corrections reveals contrasting attenuation properties of the crust between the tyrrhenian side of the italian peninsula high attenuation west of the apennines and the adriatic side low attenuation east of the apennines as previously found in other studies finally the magnitudes computed with the new m l scale are compared with global estimates of body wave magnitude m b and with local and regional estimates of moment magnitude m w they display a satisfactory agreement in most of the magnitude range considered roughly from 3 to 5 5 online material tables of station parameters maximum amplitudes and magnitude

the 4 september 1981 santa barbara island california earthquake interpretation of strong motion data abstract seven timed strong motion accelerograms were recorded between the distances of 45 and 80 km from the santa barbara island earthquake from the accelerograms the average estimate for m l is 6 0 compared to an average of m l 5 5 from more distant recordings when m l is estimated from accelerograph data using the distance correction to the m l scale proposed by luco 1982 an average of 5 3 is obtained this suggests that the correction slightly overcompensates in this magnitude and distance range in which luco lacked data at least for this earthquake s wave spectra from three accelerograms which recorded the complete s wave imply a seismic moment of 1 5 10 24 dyne cm and by the method of brune 1970 a source radius of 2 km and a stress drop of 90 bars if the displacement spectrum is assumed to be approximated by two asymptotes f 0 at frequencies less than the corner frequency and f 2 at frequencies greater than the corner frequency the level of the f 2 asymptote can be constrained by rms acceleration hanks 1979 this leads to a smaller estimated source radius and a higher stress drop in the process of matching these spectra an average value of q can be inferred to be consistent with the spectra at high frequencies this value is between 300 and 500 for the assumed spectral shapes one accelerograph located on a ridge recorded an anomalously high amplitude ringing at 2 hz on the transverse component only subsurface geological structure is the most likely cause of the amplification

geochemical characteristics of the rio verde complex central hispaniola implications for the paleotectonic reconstruction of the lower cretaceous caribbean island arc abstract new geochronological trace element and sr nd isotope data for metabasalts dolerites and amphibolites from the rio verde complex central hispaniola are integrated with existing geochemical data for mafic volcanic rocks and metamorphic derivatives from the los ranchos amina and maimon formations giving new insights into magma petrogenesis and paleotectonic reconstruction of the lower cretaceous caribbean island arc back arc system u pb and 40ar 39ar age data show that the rio verde complex protoliths were in part coeval with volcanic rocks of the los ranchos formation upper aptian to lower albian the geochemical data establish the existence of gradients in trace element parameters nb yb th yb zr yb zr ba and normalized ti sm y and yb abundances and nd isotope compositions from throughout hispaniola which reflect differences in the degree of mantle wedge depletion and contributions from the subducting slab the rio verde complex mafic rocks and some mafic sills and dykes intruding in the loma caribe peridotite have a transitional iat to n morb geochemistry and a weak subduction related signature and are interpreted to form in a rifted arc or evolving back arc basin setting the los ranchos amina and maimon formations volcanic rocks have arc like characteristics and represent magmatism in the volcanic front trace element and nd isotope modeling reproduce observed data trends from arc to back arc and suggest that the variations in several geochemical parameters observed in a sw direction across the caribbean subduction system can be explained from the progressively lower subduction flux into a progressively less depleted mantle source the low nb contents and high end i values in both arc and back arc mafic rocks imply however the absence of a significant lower cretaceous plume enriched component in order to explain these observations a model of proto caribbean oceanic lithosphere subducting to the sw at least in the 120 110 ma interval is proposed to cause the observed magmatic variations in the lower cretaceous caribbean island arc back arc system in this context arc rifting and initial sea floor spreading to form the rio verde complex protoliths occurred in the back arc setting of this primitive island arc built on the ne edge of the caribbean plate

late jurassic oceanic crust and upper cretaceous caribbean plateau picritic basalts exposed in the duarte igneous complex hispaniola abstract four distinct rock units have been recognized near el aguacate in the janico juncalito la vega area of the duarte complex dominican republic 1 serpentinites crosscut by numerous diabasic dikes 2 basalts interbedded with late jurassic ribbon cherts 3 picrites and ankaramites relatively enriched in incompatible trace elements and 4 amphibolites and gneissic amphibolites chemically similar to oceanic plateau basalts similar ar ar ages of late magmatic amphibole from a picrite and hornblende from an amphibolite documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty decl

differential preservation in the geologic record of intraoceanic arc sedimentary and tectonic processes abstract records of ancient intraoceanic arc activity now preserved in continental suture zones are commonly used to reconstruct paleogeography and plate motion and to understand how continental crust is formed recycled and maintained through time however interpreting tectonic and sedimentary records from ancient terranes after arc continent collision is complicated by preferential preservation of evidence for some arc processes and loss of evidence for others in this synthesis we examine what is lost and what is preserved in the translation from modern processes to the ancient record of intraoceanic arcs composition of accreted arc terranes differs as a function of arc continent collision geometry forward facing collision can accrete an oceanic arc on to either a passive or an active continental margin with the arc facing the continent and colliding trench and forearc side first in a backward facing collision involving two subduction zones with similar polarity the arc collides backarc first with an active continental margin the preservation of evidence for contemporary sedimentary and tectonic arc processes in the geologic record depends greatly on how well the various parts of the arc survive collision and orogeny in each case preservation of arc terranes likely is biased towards those that were in a state of tectonic accretion for tens of millions of years before collision rather than tectonic erosion the prevalence of tectonic erosion in modern intraoceanic arcs implies that valuable records of arc processes are commonly destroyed even before the arc collides with a continent arc systems are most likely to undergo tectonic accretion shortly before forward facing collision with a continent and thus most forearc and accretionary prism material in ancient arc terranes likely is temporally biased toward the final stages of arc activity when sediment flux to the trench was greatest and tectonic accretion prevailed collision geometry and tectonic erosion vs accretion are important controls on the ultimate survival of material from the trench forearc arc massif intra arc basins and backarc basins and thus on how well an ancient arc terrane preserves evidence for tectonic processes such as subduction of aseismic ridges and seamounts oblique plate convergence and arc rifting forward facing collision involves substantial recycling melting and fractionation of continent derived material during and after collision and so produces melts rich in silica and incompatible trace elements as a result forward facing collision can drive the composition of accreted arc crust toward that of average continental crust

platinum group minerals pgm in the falcondo ni laterite deposit loma caribe peridotite dominican republic two ni laterite profiles from the loma caribe peridotite dominican republic have been investigated for their platinum group element pge geochemistry and mineralogy one profile loma peguera i

fluctuations in northern hemisphere 700 mb height field associated with the southern oscillation abstract variations in the mid troposphere circulation associated with the southern oscillation so are investigated and documented using mean monthly 700 mb height data for the period 1951 79 the so was defined by a southern oscillation index soi consisting of the difference in normalized mean monthly sea level pressures at tahiti and darwin results for all four seasons are presented in the form of lagged as well as contemporaneous correlations and composites of height anomalies obtained separately for high and low soi values different so teleconnection patterns are observed for each season strongest so signals appear in the winter with soi leading the height field by one to two seasons the time lead may he useful in prognostic applications the correlation in the summer is negligible the winter teleconnection pattern over the north pacific north america north atlantic sector is similar to that shown by bjerknes and others patterns for other seasons are also presented the statistical signifi

an interdecadal change in the influence of the central pacific enso on the subsequent north tropical atlantic spring sst variability around the mid 1980s north tropical atlantic nta spring sea surface temperature sst tends to be warmer cooler than normal in central pacific cp el nino decaying years during 1960s to mid 1980s however the relationship between the nta spring sst and cp el nino southern oscillation enso is weakened after mid 1980s this study presents this interdecadal change and investigates possible causes before the mid 1980s above normal nta sst peaks in post el nino spring the cp el nino can affect nta spring sst by inducing a negative phase of north atlantic oscillation nao anomaly over north atlantic from winter to spring this negative nao circulation weakens the azores high and causes weaker than normal trade wind as a result less heat loses from the nta ocean and above normal sst anomalies generated in contrast after the middle 1980s the connection between cp enso and nao like anomaly has been disrupted this leads to a weakening of cp enso influences on the nta spring sst the observed change in the relationship between nta spring sst and cp enso is likely related to the state of the polar vortex before the middle 1980s the polar vortex is weak this favors the propagation of enso related wave flux the rossby wave trains spread to the stratosphere during el nino conditions and cause weaker than normal polar vortex resulting in a negative nao in the low levels and the subtropical jet is enhanced and elongated which provides a potential waveguide for wave activity propagating to the atlantic through a tropospheric way however the polar vortex is strong after mid 1980s preventing the propagation of the enso related wave trains through the stratosphere or the troposphere

role of preexisting topography and overburden on strain partitioning of oblique doubly vergent convergent wedges 1 scaled sandbox modeling was used to analyze the three dimensional aspects of strain partitioning along obliquely convergent margins that underwent a subduction polarity reversal event in the experiments the first phase of shortening produced a preexisting topography that affected wedge kinematics during the second phase increasing degrees of obliquity during the first shortening phase produced different amounts of inherited topography and overburden giving way to different effects on wedge response during the second phase of shortening during the second phase the models with an inherited heavy overburden show an anomalous orientation for riedel shears predating the development of a margin parallel strike slip fault these shears are oriented at an angle that is higher than kinematically predicted with respect to the subduction slot suggesting a transient rotation of the stress applied by the obliquity of subduction in contrast experiments with a lighter overburden do not show this inconsistency in addition all the models displayed an unexpectedly high accretion rate during the second phase of shortening which we interpret to be dependent on topographical slope breaks inherited after the first phase of shortening and the critical asymmetrical architecture of doubly vergent wedges

pueblo viejo high sulfidation epithermal gold silver deposit dominican republic a new model of formation beneath barren limestone cover a discussion sillitoe et al 2006 suggest that the pueblo viejo au ag deposit is younger than its early cretaceous los ranchos formation host rocks this interpretation contrasts with our earlier observations that the mineralization is coeval with the los ranchos formation although a younger age would allow pueblo viejo to be conveniently grouped with many other high sulfidation deposits in a subaerial calc alkaline setting evidence for it conflicts with geologic observations in and around the deposit the new interpretation of the age of mineralization depends largely on the contention that the hatillo limestone which overlies the los ranchos formation was replaced along its basal contact by silica and magnetite that are coeval with pueblo viejo mineralization in their figure 2 p 1429 sillitoe et al show two silicified and iron oxide bearing zones along the poorly exposed base of the hatillo limestone outliers one of these zones is along the southern edge of the pueblo viejo mine where mine workings and exploration drill holes immediately south of the contact provide good exposures in this area the contact which is tectonized locally ranges from a basal conglomerate with silicified cobbles to calcareous sandstone siltstone mudstone with abundant marine fossils silicified cobbles require that silicification preceded deposition of the hatillo limestone similarly carbonaceous sediments containing silicified boulders and cobbles and underlying fragmental rocks with clasts exhibiting different alteration assemblages are widespread in the mine area russell and kesler 1991 fig 3 sillitoe et al 2006 do cite one outcrop containing veinlets of iron oxide limonite with marginal silicification russell and kesler 1991 p 210 211 as evidence of silicification and iron oxides in the basal few meters of the hatillo limestone they acknowledge however that we interpreted these features as paleo supergene which they clearly are furthermore they are

a neoarchean subduction polarity reversal event in the north china craton abstract subduction polarity reversal events following arc continent arc arc or continent continent collisions have been well documented from cenozoic mesozoic and paleozoic orogens but not from the archean we here document a neoarchean subduction reversal event after an arc continent collision between the eastern block of the north china craton ncc and the fuping arc using field geochemical and geochronological data we focus our work on the wangjiazhuang granite in the zanhuang massif located along the eastern margin of the central orogenic belt cob of the ncc and a regional tectonic comparison with other granitic rocks with similar ages geochemical and petrogenetic characteristics the ca 2 5 ga a type wangjiazhuang granite intrudes the neoarchean zanhuang melange belt and contains mafic and felsic inclusions it has positive end t values 0 12 to 1 13 and tdm2 ages between 2784 ma and 2869 ma this work shows clearly from field structural relationships geochemistry and geochronology that the wangjiazhuang granite formed after an arc continent collision between the eastern block which is defined as a continental block and the fuping arc after a subduction polarity reversal event placed a new slab beneath the collisionally modified margin of the eastern block and converted it to an andean type margin the subduction polarity reversal event at ca 2 5 ga resulted in melting of the enriched mantle meanwhile the rising magma induced partial melting of the old and thickened ttg crust leading to the intrusion of ca 2 5 ga wangjiazhuang granite into the neoarchean zanhuang melange there are other granitic rocks with similar ages and geochemical and petrogenetic features in the central orogenic belt and eastern block of the north china craton suggesting that they formed in a similar tectonic setting as the circa 2 5 ga granites across the eastern block the neoarchean subduction polarity reversal event and prior arc continent collision provide strong evidence that plate tectonics was operating by the end of the neoarchean

impacts of sst anomalies on the north atlantic atmospheric circulation a case study for the northern winter 1995 1996 the present paper selects the northern winter of december 1995 february 1996 for a case study on the impact of sea surface temperature sst anomalies on the atmospheric circulation over the north atlantic and western europe in the atlantic the selected winter was characterized by positive sst anomalies over the northern subtropics and east of newfoundland and negative anomalies along the us coast a weak la nina event developed in the pacific the north atlantic oscillation nao index was low precipitation over the iberian peninsula and northern africa was anomalously high and precipitation over northern europe was anomalously low the method of study consists of assessing the sensitivity of ensemble simulations by the ucla atmospheric general circulation model ucla agcm to sst anomalies from the observation which are prescribed either in the world oceans the atlantic ocean only or the subtropical north atlantic only the results obtained are compared with a control run that uses global time varying climatological sst the ensemble simulations with global and atlantic only sst anomalies both produce results that resemble the observations over the north atlantic and western europe it is suggested that the anomalous behavior of the atmosphere in the selected winter over those regions therefore was primarily determined by conditions within the atlantic basin the simulated fields in the tropical north atlantic show anomalous upward motion and lower upper level convergence divergence in the atmosphere overlying the positive sst anomalies consistently the subtropical jet intensifies and its core moves equatorward and precipitation increases over northern africa and southern europe the results also suggest that the sst anomalies in the tropical north atlantic only do not suffice to produce the atmospheric anomalies observed in the basin during the selected winter the extratropical sst anomalies would provide a key contribution through increased transient eddy activity which causes an extension of the subtropical jet eastward from the coast of north america

ammonite radiolarian assemblage tobago volcanic group tobago west indies implications for the evolution of the great arc of the caribbean an unusually fossiliferous sedimentary sequence is exposed near scarborough tobago west indies it occurs within the tobago volcanic group above an undifferentiated sequence of volcaniclastic breccia and lava and includes volcanogenic sedimentary rocks at the base of the bacolet formation an ammonite radiolarian assemblage has been recovered from this sedimentary interval in the tobago volcanic group ammonites from the spring gardens quarry are moderately evolute and have unbranched ribs they are probably juveniles of mojsisoviczia of middle albian age another ammonite from a stratigraphically higher locality i e volcanogenic sedimentary rocks at the base of the bacolet formation is identified as manuaniceras decsernae young of early late albian age radiolarian assemblages from intercalations of black siliceous argillite of the tobago volcanic group are characterized by abundant a rchaeospongoprunum spp and the common occurrence of pseudodictyomitra pentacolaensis dictyomitra montisserei thanarla brouweri and pantanellium ventosum also present in lesser abundances are other members of the family archaeodictyomitridae xitus napora durhami and sciadiocapsa speciosa this assemblage correlates with the romanus subzone of o dogherty 1994 1 and kozurium zingulai zone of pessagno 1977 2 both of which are dated as early to middle albian these newly reported fossils indicate an albian age for deposition of the tobago volcanic group earlier published 40ar 39ar radiometric ages from the group are consistent with the stratigraphic age assignment of the fossils and thereby suggest that volcanism associated with the tobago volcanic group began ca 105 ma possible correlative accreted fragments of the mesozoic oceanic arc of the southern caribbean include the curacao lava formation the lower part of the washikemba formation bonaire the tiara formation of north central venezuela and possibly the subsurface mejillones complex of the carupano basin the mesozoic rocks of tobago consist of two distinct oceanic arc rock sequences the older north coast schist 120 ma exhibits polyphase deformation and lower greenschist facies metamorphism the structurally overlying tobago volcanic group is not penetratively deformed or folded it has undergone prehnite pumpellyite facies metamorphic conditions and has been tilted to moderate dips by various brittle faults we interpret the hiatus that separates these oceanic arc rock sequences as representing a significant event in the evolution of the great arc of the caribbean consequently we propose that the commonly postulated reversal in subduction zone polarity of the great arc occurred prior to deposition of the tobago volcanic group ca 105 ma and that older more highly deformed and metamorphosed oceanic arc sequences e g north coast schist served as a basement for younger sequences or as wall rock for intrusive elements of younger magmatic suites of the great arc 1 ref 23 2 ref 26

kinematic analysis of serpentinite structures and the manifestation of transpression in southwestern puerto rico abstract faults and shear zones recorded in the monte del estado and rio guanajibo serpentinite masses in southwestern puerto rico show previously unrecognized southwestward tectonic transport the orientations of planar and linear structures and the sense of slip along faults and shear zones determined by offset rock layers drag folds in foliations and steps in slickensided surfaces and or s c fabrics from 1846 shear planes studied at more than 300 stations reveal two predominant groups of faults 1 northwesterly striking thrust faults and easterly striking left lateral faults and 2 northwesterly striking right lateral faults and easterly striking thrust faults shortening and extension p and t axes calculated for geographic domains within the serpentinite reveal early north trending shortening followed by southwestward directed movement during which older structures were re activated the sw directed shortening is attributed to transpression that accompanied late eocene left lateral shearing of the serpentinite a third younger group comprising fewer faults consists of northwesterly striking left lateral faults and north directed thrusts that also may be related to the latest transpressional deformation within puerto rico deformational events in puerto rico correlate to tectonic events along the caribbean north american plate boundary

chronology of the pueblo viejo epithermal gold silver deposit dominican republic formation in an early cretaceous intra oceanic island arc and burial under ophiolite the pueblo viejo deposit production to 1996 166 t au 760 t ag is located in the dominican republic on the caribbean island of hispaniola and ranks as one of the largest high sulfidation acid sulfate epithermal deposits reserves in 2007 635 t au 3 648 t ag one of the advanced argillic ore bodies is cut by an inter mineral andesite porphyry dike which is altered to a retrograde chlorite illite assemblage but overprinted by late stage quartz pyrite sphalerite veins and associated low grade au ag zn cd hg in as se and te mineralization the precise tims u pb age 109 6 0 6 ma of the youngest zircon population in this dike confirms that the deposit is part of the early cretaceous los ranchos intra oceanic island arc intrusion related gold sulfide mineralization took place during late andesite dacite volcanism within a thick pile 200 m of carbonaceous sand and siltstones deposited in a restricted marine basin the high level deposit was shielded from erosion after burial under a late albian 109 100 ma ophiolite complex 8 km thick which was in turn covered by the volcano sedimentary successions 4 km of a late cretaceous early tertiary calc akaline magmatic arc estimates of stratigraphic thickness and published alunite illite and feldspar k ar ages and closure temperatures alunite 270 20 c illite 260 30 c k feldspar 150 c indicate a burial depth of about 12 km at 80 ma during peak burial metamorphism 300 c and 300 mpa the alteration assemblage kaolinite quartz in the deposit dehydrated to pyrophyllite temperature time relations imply that the los ranchos terrane then cooled at a rate of 3 4 c ma during slow uplift and erosion

multiscale variabilities in global sea surface temperatures and their relationships with tropospheric climate patterns el nino southern oscillation enso is a global phenomenon with significant phase propagation within and between basins this is captured and described in the first mode of a complex empirical orthogonal function ceof analysis of sea surface temperature anomaly ssta from the midnineteenth century through 1991 the global enso from the ssta data plus a linear trend everywhere are subsequently removed in order to consider other global modes of variability uncontaminated by the intra and interbasin effects of enso an ordinary eof analysis of the ssta residuals reveals three non enso modes of low frequency variability that are related to slow oceanic and climate signals described in the literature the first two modes have decadal to multidecadal timescales with high loadings in the pacific they bear some spatial similarities to the enso pattern but are broader more intense at high latitudes and differ in the time domain a ceof analysis confirms that they are not merely the phase related components of a single mode and that all three modes are without significant phase propagation the third mode is a multidecadal signal with maximal realization in the extratropical north atlantic southeast of greenland it is consistent with studies that have documented connections between north atlantic ssta and the tropospheric north atlantic oscillation nao all three ssta modes have midtropospheric associations related to previously classified northern hemisphere teleconnection patterns the relationships between ssta modes and tropospheric patterns are consistent with the ocean atmosphere interactions discussed in previous studies to explain low frequency climate oscillations in the north pacific and north atlantic sectors the first three leading modes of non enso ssta are most related to the tropospheric patterns of the pacific north american the north pacific and the arctic oscillations ao respectively the 500 hpa pattern associated with the third ssta mode also bears similarities to the nao in its atlantic sector this north atlantic mode has a region of high positive ssta loadings in the gulf of alaska which appear to be connected to the north atlantic ssta by a tropospheric bridge effect in the ao

modification of an oceanic plateau aruba dutch caribbean implications for the generation of continental crust the generation of the continental crust may be connected to mantle plume activity however the nature of this link and the processes involved are not well constrained an obstacle to understanding relationships between plume related mafic material and associated silicic rocks is that later tectonic movements are liable to obscure the original relationships particularly in ancient greenstone belts studies of younger analogous regions may help to clarify these relationships on the island of aruba in the southern caribbean a sequence of partly deformed mafic volcanic rocks intruded by a predominantly tonalitic batholith is exposed the mafic lavas show geochemical and isotopic affinities with other basaltic picritic and komatiitic rocks that crop out elsewhere in the caribbean these are well documented as belonging to an 88 91 ma plume related oceanic plateau which is allochthonous with respect to the americas and is thought to have been formed in the pacific region the 85 to 82 ma tonalitic rocks share some geochemical characteristics high sr and ba low nb and y with archaean tonalite trondhjemite granodiorite ttg suites field relationships suggest that deformation of the plateau sequence possibly related to collision with a subduction zone was synchronous with intrusion of the aruba batholith new incremental heating 40ar 39ar dates combined with existing palaeontological evidence show that cooling of the batholith occurred shortly after eruption of the plateau basalt sequence sr nd isotopic data for both rock suites are uniform 87sr 86sri 0 7035 endi 7 whereas pb isotopes are more variable plateau sequence 206pb 204pb 18 6 19 1 207pb 204pb 15 54 15 60 208pb 204pb 38 3 38 75 aruba batholith 206pb 204pb 18 4 18 9 207pb 204pb 15 51 15 56 208pb 204pb 38 0 38 5 this suggests that there has been a minor sedimentary input into the source region of the batholith however the limited time interval between basaltic and tonalitic magmatism makes a normal subduction related origin for the tonalites improbable instead models involving derivation of tonalite from partial melting of the plateau sequence or alternatively genesis in an unusual subduction zone environment are investigated

decay of aftershock density with distance does not indicate triggering by dynamic stress the most predictable earthquakes are aftershocks which invariably follow mainshocks so what triggers aftershocks it was recently argued controversially that the decay of aftershocks with distance from the main earthquake could only be explained by dynamic triggering keith richards dinger and colleagues have tested this hypothesis and conclude that the observed decay can be better explained by static triggering resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard it has recently been argued that the decay of aftershocks with distance from the main earthquake could be explained only by dynamic triggering this hypothesis has now been tested the conclusion being that the observed decay can be better explained by static triggering resolving whether static1 2 3 or dynamic4 5 6 7 8 stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard9 felzer and brodsky10 examined the distance distribution of earthquakes occurring in the first five minutes after 2 m 3 and 3 m 4 mainshocks and found that their magnitude m 2 aftershocks showed a uniform power law decay with slope 1 35 out to 50 km from the mainshocks from this they argued that the distance decay could be explained only by dynamic triggering here we propose an alternative explanation for the decay and subject their hypothesis to a series of tests none of which it passes at distances more than 300 m from the 2 m 3 mainshocks the seismicity decay 5 min before the mainshocks is indistinguishable from the decay five minutes afterwards indicating that the mainshocks have no effect at distances outside their static triggering range omori temporal decay the fundamental signature of aftershocks is absent at distances exceeding 10 km from the mainshocks finally the distance decay is found among aftershocks that occur before the arrival of the seismic wave front from the mainshock which violates causality we argue that felzer and brodsky10 implicitly assume that the first of two independent aftershocks along a fault rupture triggers the second and that the first of two shocks in a creep or intrusion driven swarm triggers the second when this need not be the case

weathering profile of the cerro de maimon vms deposit dominican republic textures mineralogy gossan evolution and mobility of gold and silver abstract cerro de maimon in the central dominican republic is currently the only vms deposit under production in the caribbean region it is hosted in the maimon formation of early cretaceous age which is part of the oldest and chemically most primitive island arc in the caribbean from bottom to top this deposit can be divided into i a primary sulfide zone ii a supergene enrichment zone and iii an oxidized zone this study reports new data on the textural and mineralogical characteristics of the oxidized zone gossan leached capping zone with emphasis in the au ag bearing phases the mineral paragenesis of the oxidized zone is essentially composed of goethite hematite quartz and barite botryoidal cellular and brecciated textures can be distinguished botryoidal and brecciated textures dominate in the upper parts of the oxidized zone whereas cellular textures are more common in the intermediate and lower parts however the weathering profile is very heterogeneous the leached capping profile shows evidence of both transported and indigenous gossans gold in the oxide paragenesis is extremely pure 99 au suggesting that chemical refining took place silver occurs mainly as iodargyrite agi and minor agbr agcl in botryoidal aggregates particles of au ag alloy in the primary mineralization exposed to a weathering environment can be leached and transported by various agents chemical and biochemical that may exist simultaneously in the presence of halides gold and silver can be leached and transported in a wide range of ph eh conditions especially if iodine is present silver is leached more rapidly and over a broader range of ph eh conditions and is preferentially transported as iodine complexes than other halides the presence of iodargyrite in the cerro de maimon gossan fully developed under tropical conditions suggests that this mineral cannot be considered an indicator of extremely arid environments as typically claimed by many authors iodargyrite occurrence would rather point to the presence of saline halide rich groundwater in oxide deposits

the richter scale its development and use for determining earthquake source parameters abstract the m l scale introduced by richter in 1935 is the antecedent of every magnitude scale in use today the scale is defined such that a magnitude 3 earthquake recorded on a wood anderson torsion seismometer at a distance of 100 km would write a record with a peak excursion of 1 mm to be useful some means are needed to correct recordings to the standard distance of 100 km richter provides a table of correction values which he terms log a o the latest of which is contained in his 1958 textbook a new analysis of over 9000 readings from almost 1000 earthquakes in the southern california region was recently completed to redetermine the log a o values although some systematic differences were found between this analysis and richter s values such that using richter s values would lead to underand overestimates of m l at distances less than 40 km and greater than 200 km respectively the accuracy of his values is remarkable in view of the small number of data used in their determination richter s corrections for the distance attenuation of the peak amplitudes on wood anderson seismographs apply only to the southern california region of course and should not be used in other areas without first checking to make sure that they are applicable often in the past this has not been done but recently a number of papers have been published determining the corrections for other areas if there are significant differences in the attenuation within 100 km between regions then the definition of the magnitude at 100 km could lead to difficulty in comparing the sizes of earthquakes in various parts of the world to alleviate this it is proposed that the scale be defined such that a magnitude 3 corresponds to 10 mm of motion at 17 km this is consistent both with richter s definition of m l at 100 km and with the newly determined distance corrections in the southern california region aside from the obvious and original use as a means of cataloguing earthquakes according to size m l has been used in predictions of ground shaking as a function of distance and magnitude it has also been used in estimating energy and seismic moment there is a good correlation of peak ground velocity and the peak motion on a wood anderson instrument at the same location as well as an observationally defined and theoretically predicted nonlinear relation between m l and seismic moment an important byproduct of the establishment of the m l scale is the continuous operation of the network of wood anderson seismographs on which the scale is based the records from these instruments can be used to make relative comparisons of amplitudes and waveforms of recent and historic earthquakes furthermore because of the moderate gain the instruments can write onscale records from great earthquakes at teleseismic distances and thus can provide important information about the energy radiated from such earthquakes at frequencies where many instruments have saturated

oscillatory zoning in eclogitic garnet and amphibole northern serpentinite melange cuba a record of tectonic instability during subduction exotic blocks of eclogite from distant localities along the northern serpentinite melange of cuba have comparable p t histories that include high pressure prograde sections 450 600 c 15 kbar associ ated with subduction of oceanic lithosphere and retrograde sections within the albite epidote amphibolite facies 500 c 10 kbar related to melange uplift 40 ar 39 ar and rb sr cooling ages 118 103 ma of one of the blocks indicate pre aptian subduction and aptian albian uplift detailed x ray imaging and profiling further reveals that minerals in these eclogite blocks notably garnet and amphibole display subtle but well defined oscillatory zoning that developed along the prograde trajectory of the rocks previous to attainment of peak eclogitic conditions the chemistry e g coupled changes of mg and mn in garnet and of si ti al and na in amphibole and geometry euhedral to anhedral shapes of the oscillations can be interpreted in terms of subtle fluctuations in p t during the general prograde subduction related metamorphic path a near equilibrium model is presented for the formation of oscillations at near peak conditions by means of recurrent dissolution growth reaction processes this model for near peak conditions and the chemical signatures of earlier oscillations notably in amphibole suggest that episodes of retrogression upward movement affected parts of the subducting slab it is proposed that these retrograde episodes record the tectonic rupture of the subducting slab and probably of the upper plate mantle either due to the intrinsic dynamic behaviour of subduction systems or to the effects of the plate tectonic rearrangement of the caribbean region during the early cretaceous

the changing relationship between interannual variations of the north atlantic oscillation and northern tropical atlantic sst abstractthe relationship between interannual variations of boreal winter north atlantic oscillation nao and northern tropical atlantic nta sea surface temperature sst experienced obvious interdecadal changes during 1870 2012 similar interdecadal changes are observed in the amplitude of nta sst anomalies the mean nta sst change may be a plausible reason for several changes in the nao nta sst connection under a higher mean nta sst nta sst anomalies induce larger wind anomalies over the north atlantic that produce a tripole sst anomaly pattern and amplify nta sst anomalies comparison of the evolution of anomalies between 1970 86 and 1996 2012 unravels changing roles of el nino southern oscillation enso and extratropical atmospheric disturbances in the formation of nta sst anomalies during 1970 86 enso events play a key role in initiating nta sst anomalies in the preceding spring through atmospheric circulation changes with the decay of enso sst anomalies in the midlatitude north atlantic wea

multiproxy evidence of holocene climate variability from estuarine sediments eastern north america water temperature estimated from ostracode mg ca ratios the results indicate a much drier early holocene in which mean paleosalinity was 28 ppt in the northern bay falling 25 to 20 ppt during the late holocene early holocene mg ca derived temperatures varied in a relatively narrow range of 13 to 16 c with a mean temperature of 14 2 c and excursions above 16 c the late holocene was on average cooler mean temperature of 12 8 c in addition to the large contrast between early and late holocene regional climate conditions multidecadal 20 40 years salinity and temperature variability is an inherent part of the region s climate during both the early and late holocene including the medieval warm period and little ice age these patterns are similar to those observed during the twentieth century caused by nao related processes comparison of the midlatitude chesapeake bay salinity record with tropical climate records of intertropical convergence zone fluctuations inferred from the cariaco basin titanium record suggests an anticorrelation between precipitation in the two regions at both millennial and centennial timescales

from intra oceanic subduction to arc accretion and arc continent collision insights from the structural evolution of the rio san juan metamorphic complex northern hispaniola the rio san juan metamorphic complex exposes a segment of a high pressure subduction accretionary complex built during caribbean island arc north america continental margin convergence it is composed of accreted arc and oceanic derived metaigneous rocks serpentinized peridotites and minor metasediments forming a structural pile combined detailed mapping structural and metamorphic analysis and geochronology show that the deformation can be divided into five main events d1 d5 an early subduction related d1 deformation and m1 metamorphism produced greenschist mafic rocks of the gaspar hernandez peridotite tectonite blueschist and eclogite metamafic blocks in the jagua clara melange high p epidote amphibolite and eclogite cuaba unit and lower blueschist and greenschist facies conditions morrito unit this was followed by m2 decompression and cooling in the blueschist greenschist and low p amphibolite facies conditions the shape of the retrograde p t path the age of the exhumation related d2 structures and the tectonic significance of d2 deformation are different in each structural unit published u pb and 40ar 39ar plateau ages and t t p t estimations reveal diachronic turonian coniacian to maastrichtian retrograde m2 metamorphism in the different structural units of the complex during a consistent d2 top to the ne ene tectonic transport regionally a similar top to the ene tectonic transport also took place in the metasedimentary nappes of the samana complex during the eocene to earliest miocene this kinematic compatibility indicates a general northeastward progradation of deformation in the northern caribbean convergent margin as the successive tectonic incorporation of arc oceanic and continental derived terrains to the developing caribbean subduction accretionary complex took place d3 d5 deformations are discontinuous and much less penetrative recording the evolution from ductile to brittle conditions of deformation in the complex the d3 event substantially modified the nappe stack and produced open folds with amplitudes up to kilometer scale the late paleocene eocene d4 structures are ductile to ductile brittle thrusts and inverse shear bands d5 is a tertiary entirely brittle deformation that had considerable influence in the geometry of the whole complex from the miocene to the present it has been cut and laterally displaced by a d5 sinistral strike slip fault system associated with the septentrional fault zone

some aspects of source characteristics of the 19 september 1985 michoacan earthquake and ground motion amplification in and near mexico city from strong motion data abstract the fourier amplitude ratio of the 19 september m s 8 1 to the 21 september 1985 m s 7 6 michoacan earthquakes obtained from data in and near mexico city increases from about 3 5 at 0 5 hz to about 10 at 0 2 hz this increase is neither seen in the coastal data nor in the teleseismic broadband gdsn p wave spectra it is also not predicted by 2 or gusev9s scaling laws we tentatively attribute the increase at frequencies of less than 0 5 hz to a special path and or a depth of energy release effect for the 19 september earthquake the damage to mexico city is mostly related to 0 5 hz energy since at f 0 5 hz the fourier amplitude ratios in and near mexico city along the coast and at teleseismic distances are nearly equal we attribute this energy to the source characteristics of the 19 september earthquake the evidence suggests that the 19 september was about twice more energetic at f 0 5 hz than expected from scaling laws and from spectral regression of coastal earthquakes recorded in mexico city the analysis of strong motion data recorded in mexico city shows that the ground motions in the lake bed zone are amplified by 8 to 50 times with respect to a hill zone site in ciudad universitaria the frequency at which the maximum relative amplification occurs varies from site to site and lies between 0 2 and 0 7 hz the data suggest that f o 4 h where f o frequency at which maximum relative amplitude occurs and and h are the shear wave velocity and the thickness of the clay layer respectively relatively small if any nonlinear behavior of the clay is found at strains of about 0 2 per cent during the great 19 september earthquake for a given lake bed site maximum relative amplitude and f o are roughly constant independent of magnitude depth and azimuth of sources located more than about 200 km ground motion at lake bed sites in mexico city with f o 0 5 hz appear to be amplified 75 times with respect to hard rock coastal sites at equal distances from the source this is also confirmed by m l calculation of the 19 and 21 september earthquakes for the 19 and 21 september earthquakes the average values of m l at hard rock coastal sites 100 distance 250 km are 7 4 and 6 7 whereas they are 8 7 and 8 4 in the lake bed zone distance 300 km respectively

a local magnitude scale for the western great basin eastern sierra nevada from synthetic wood anderson seismograms abstract we have computed synthetic wood anderson seismograms for over 1100 arrivals at 10 three component broadband digital stations in the unr western great basin eastern sierra nevada network these represent all the available records from local earthquakes over magnitude 3 5 between 1990 and june of 1993 plus selected events of smaller magnitude there were 77 events ranging in magnitude from 2 2 to 5 9 including four events over magnitude 5 the distances considered ranged from 15 to 600 km with the best represented range being from 30 to 450 km we invert these measurements to determine distance and station corrections appropriate for a local magnitude scale constrained by richter9s original definition that an earthquake of m l 3 will cause a 1 mm zero to peak deflection of the wood anderson seismogram at 100 km from the epicenter the results between 30 and 450 km were essentially independent of choice of curve fitting parameters in the 30 to 500 km distance region the smooth distance correction curves were very similar to that determined by richter 1958 which is still used for southern california earthquakes we propose to use richter9s distance correction curve in reporting amplitude magnitudes from our digital network

thrust emplacement of the hispaniola peridotite belt orogenic expression of the mid cretaceous caribbean arc polarity reversal articulo sobre el emplazamiento fallero en la zona de peridotitas de la hispaniola republica dominicana estudiando si es la expresion orogenica de la polaridad reversa en la zona del caribe en el cretacico medio

the 1978 tabas iran earthquake an interpretation of the strong motion records the 1978 tabas iran earthquake ms 7 4 was registered on 11 accelerograph stations with source distances ranging from 3 to 350 km and corresponding recorded peak accelerations ranging from 0 95 down to 0 01 g respectively at least four subevents are recognized at dayhook the station nearest the epicenter at the southern limit of the fault the rupture propagated to the northwest with a rupture velocity of 2 7 km sec the subevents occurred along the fault as the rupture proceeded curves which describe the distance dependence of peak values of acceleration velocity and band passed acceleration are constructed for this earthquake although attenuation of seismic waves is similar in iran and the western united states the prediction curves based on peak strong motion acceleration data from the western united states systematically underestimate the peak values of the tabas earthquake and the similar 1952 kern county earthquake prediction curves based on peak velocity in the western united states overestimate peak velocity for distances less than about 60 km site effects are recognized at some recording stations the various estimates for stress operating during the earthquake range from 25 to 90 bars the radiated energy of the main event estimated from accelerograms by two methods is about 2 3 1023 ergs larger than the energy calculated by gutenberg and richter energy formula with ms 7 4 each of the four subevents released approximately the same amount of energy corresponding to ms 7 teleseismic energy estimates for this earthquake are one to two orders of magnitude smaller indicating large systematic errors exist in one or both of the energy estimation procedures