validation and joint inversion of teleseismic waveforms for earthquake source models using deep ocean bottom pressure records a case study of the 2006 kuril megathrust earthquake the importance of accurate tsunami simulation has increased since the 2004 sumatra andaman earthquake and the indian ocean tsunami that followed it because it is an important tool for inundation mapping and potentially tsunami warning an important source of uncertainty in tsunami simulations is the source model which is often estimated from some combination of seismic geodetic or geological data a magnitude 8 3 earthquake that occurred in the kuril subduction zone on 15 november 2006 resulted in the first teletsunami to be widely recorded by bottom pressure recorders deployed in the northern pacific ocean because these recordings were unaffected by shallow complicated bathymetry near the coast this provides a unique opportunity to investigate whether seismic rupture models can be inferred from teleseismic waves with sufficient accuracy to be used to forecast teletsunami in this study we estimated the rupture model of the 2006 kuril earthquake by inverting the teleseimic waves and used that to model the tsunami source the tsunami propagation was then calculated by solving the linear long wave equations we found that the simulated 2006 kuril tsunami compared very well to the ocean bottom recordings when simultaneously using p and long period surface waves in the earthquake source process inversion

penetration of atlantic westerly winds into central and east asia abstract the geographical position of the convergence zone where the western atlantic climate system meets the asian winter monsoonal system depends on their relative strength these individual strengths are determined by the intensities of the air pressure gradients over the north atlantic and the siberian high pressure cell respectively since the factors that forced those gradients varied throughout glacial interglacial cycles the location of the convergence zone should have moved accordingly both the grain size characteristics of wind blown sediments and climate modelling prove that the atlantic influence extended remarkably far eastward at times the northeastern tibetan plateau was at the cross road of western and monsoonal influences during the last glacial this region was dominated by an atlantic signal with millennial scale climatic oscillations that are similar to the north atlantic marine and greenland ice core records in contrast that same region was only under monsoonal influence during the last interglacial it implies that the atlantic winds penetrated more vigorously eastward in full glacial conditions than in interglacial conditions

present day structural frame of the santander massif and pamplona wedge the interaction of the northern andes abstract based on regional geology and stress tensor analysis from fault slickensides we propose a structural model to explain the present day configuration of a crystalline core in the northern andes of colombia the santander massif sm the sm has undergone transpressional tectonics in a domino style controlled by longitudinal sinistral strike slip faults as the bucaramanga fault the tectonic style also exhibits ne sw trending transverse inner faults with dextral strike slip kinematics the transpressional regime of the sm differs from the compressive regime that characterizes nearby blocks northern perija range southern floresta massif and eastern pamplona wedge transpressional structures result from a regional w e horizontal compression corresponding to the current stress field as determined here by cross cutting relations mainly observed in the pamplona wedge stress tensors also show maximum horizontal stress shmax in radial pattern towards the wedge deformation front whose influence spreads over the sm western border the w e regional compression also explains the tectonic syntaxes formed by the pamplona wedge to the north and the sierra nevada de guican or el cocuy to the south these two areas are characterized by the opposite outward vergence of their compressive deformation fronts

ray tracing for dispersive tsunamis and source amplitude estimation based on green s law application to the 2015 volcanic tsunami earthquake near torishima south of japan ray tracing which has been widely used for seismic waves was also applied to tsunamis to examine the bathymetry effects during propagation but it was limited to linear shallow water waves green s law which is based on the conservation of energy flux has been used to estimate tsunami amplitude on ray paths in this study we first propose a new ray tracing method extended to dispersive tsunamis by using an iterative algorithm to map two dimensional tsunami velocity fields at different frequencies ray paths at each frequency can be traced we then show that green s law is valid only outside the source region and that extension of green s law is needed for source amplitude estimation as an application example we analyzed tsunami waves generated by an earthquake that occurred at a submarine volcano smith caldera near torishima japan in 2015 the ray tracing results reveal that the ray paths are very dependent on its frequency particularly at deep oceans the validity of our frequency dependent ray tracing is confirmed by the comparison of arrival angles and travel times with those of observed tsunami waveforms at an array of ocean bottom pressure gauges the tsunami amplitude at the source is nearly twice or more of that just outside the source estimated from the array tsunami data by green s law

chronology of cenozoic tectonic events in western venezuela and the leeward antilles based on integration of offshore seismic reflection data and on land geology newly acquired deep penetration broadband onshore offshore lithospheric investigation of venezuela and the antilles arc region seismic reflection data from offshore western venezuela bonaire basin and around the leeward antilles are combined with existing geologic and geophysical data sets to examine the chronology of late cretaceous cenozoic tectonic events in this part of the caribbean south american plate boundary zone these tectonic events have controlled the maturation and structural trapping of known hydrocarbons in the offshore bonaire basin and the adjacent onland falcn basin we infer three tectonic phases that are constrained using these combined data sets 1 the late eocene early oligocene north south opening of the 3 6 km 1 8 3 7 mi thick falcn bonaire basin occurred along east west striking normal fault systems that have locally been inverted by later tectonic phases these paleogene normal faults rifted the upper cretaceous arc crust and paleogene marine depositional sequences within the offshore bonaire basin 2 northwest striking normal faults crosscut the older normal faults of the bonaire basin and leeward antilles and form deep submarine rifts that contain up to 4 km 2 5 mi of sedimentary fill and form deep water channels between islands of the leeward antilles offshore well data and age of onshore sediments in the falcn basin indicate that this second phase of rifting occurred mainly during the late oligocene to early miocene and remains active to the present 3 inversion of the subaerial falcn basin commenced during the middle miocene this inversion phase is reflected in the present day pattern of an east northeast trending fold thrust belt that can be traced over 200 km 124 mi along strike in the falcn basin a second offshore fold thrust belt la vela can be traced over a distance of 175 km 108 mi along strike and parallel to the northeast trending falcn basin coast restoration of imbricate thrusts seen on seismic lines perpendicular to the la vela fold thrust belt indicates a minimum of 7 km 4 3 mi of northeast southwest directed thin skinned shortening geochemical work indicates that source rocks for scattered occurrences of hydrocarbons in the falcn basin and its coastal zone are paleogene and miocene marine shale reservoir rocks are tertiary marine sandstone and shale deposited in paleogene rifts formed during the first tectonic phase in the late eocene to early oligocene structural traps were formed by thrusting during the second tectonic phase in the late oligocene to early miocene

temperature variability over the past millennium inferred from northwestern alaska tree rings we describe a new tree ring width data set of 14 white spruce chronologies for the seward peninsula sp alaska based on living and subfossil wood dating from 1358 to 2001 ad a composite chronology derived from these data correlates positively and significantly with summer temperatures at nome from 1910 to 1970 after which there is some loss of positive temperature response there is inferred cooling during periods within the little ice age lia from the early to middle 1600s and late 1700s to middle 1800s and warming from the middle 1600s to early 1700s we also present a larger composite data set covering 978 2001 ad utilizing the sp ring width data in combination with archaeological wood measurements and other recent collections from northwestern alaska the regional curve standardization rcs method was employed to maximize potential low frequency information in this data set the rcs chronology shows intervals of persistent above average growth around the time of the medieval warm period mwp early in the millennium which are comparable to growth levels in recent centuries there is a more sustained cold interval during the lia inferred from the rcs record as compared to the sp ring width series the chronologies correlate significantly with bering and chukchi sea sea surface temperatures and with the pacific decadal oscillation index these atmosphere ocean linkages probably account for the differences between these records and large scale reconstructions of arctic and northern hemisphere temperatures based largely on continental interior proxy data

thermochronology and tectonics of the merida andes and the santander massif nw south america abstract new apatite u pb and multiphase 40ar 39ar data constrain the high to medium temperature 500 c 300 c thermal histories of igneous and metamorphic rocks exposed in the merida andes of venezuela and new apatite and zircon fission track data constrain the 500 c 60 c thermal histories of pre jurassic igneous and metamorphic rocks of the adjacent santander massif of colombia computed thermal history envelopes using apatite u pb dates and grain size information from an early palaeozoic granodiorite in the merida andes suggest that it cooled from 500 c to the generally accepted timing of amalgamation of pangaea along the ouachita marathon suture pre dates late permian to triassic cooling recorded in basement rocks of the merida andes by 30 ma and its effect on rocks preserved in north western south america is unknown we interpret late permian to triassic cooling in the merida andes to be driven by exhumation previous studies have suggested that a short phase of shortening and anatexis is recorded at 253 ma in the maya block which may have been adjacent to the basement rocks of the merida andes in the late permian the coeval onset of exhumation in the merida andes may be a result of increased coupling in the magmatic arc which was located along the western margin of pangaea triassic extension is documented in the central cordillera of colombia and ecuador between 240 ma and 215 ma although extension at this time has not been clearly identified in the merida andes or the santander massif permian to triassic cooling is not recorded in the structurally isolated caparo block in the southern merida andes suggesting that it may have constituted a distinct fault block in the triassic new fission track data from the santander massif suggest that it started exhuming at 40 ma during a period of accelerated convergence between the nazca farallon plate and the western margin of south america exhumation in the santander massif occurred diachronously since 18 ma in distinct fault blocks at rates of 0 5 1 km ma and may have been driven by east west compression as a result of the indentation of the panama choco terrane to western colombia

a 352 year record of summer temperature reconstruction in the western tianshan mountains china as deduced from tree ring density three robust tree ring density chronologies were developed for the western tianshan mountains of northwestern china the chronologies were significantly correlated and form a regional chronology gld the gld had significant and positive correlations with temperature of warm seasons based on this relationship the mean minimum temperatures of may to august were reconstructed using the gld chronology for the period ad 1657 to 2008 the temperature reconstruction exhibited temperature patterns on interannual to centennial timescales and showed that the end of the 20th century is the warmest period in the past 352 years the reconstructed temperature variation has a teleconnection with large scale atmospheric oceanic variability and captures long and broad scale regional climatic variations

seismic evidence for blind thrusting of the northwestern flank of the venezuelan andes surface geology and seismic and well data from the northwestern flank of the venezuelan andes indicate overthrusting of andean basement rocks toward the adjacent maracaibo basin along a blind thrust fault the frontal monocline is interpreted as the forelimb of a northwestward verging fault related fold deformed over a crustal scale ramp the andean block has been thrust 20 km to the northwest and uplifted 10 km on a ramp that dips about 20o 30 o southeastward the thrust fault ramps up through crystalline basement rocks to a decollement horizon within the shaly units of the cretaceous colon mito juan formations backthrusts in the monocline produce a wedge geometry and reduce the amount of blind slip required on the decollement northwest of the andes the rigid andean uplift was caused by northwest southeast compressive tectonic forces related to the convergence of the caribbean plate the panama volcanic arc and northwestern south america the thick up to 6 km molasse deposits accumulated in the foredeep basin indicate that the venezuelan andes started to rise as early as the early miocene however a late miocene intramolasse unconformity marks the beginning of the formation of the monocline and the greatest uplift the crustal scale fault related fold model may explain structural features seen in other areas of basement involved foreland deformation the regional geologic setting of the area can be described as a mountain front adjacent to a foredeep basin the mountain front represents a precambrian paleozoic igneous metamorphic complex partially covered with sediments of mesozoic and cenozoic ages the foredeep is an asymmetric structural basin that contains up to 12 km of sedimentary section the early miocene to pleistocene molasse deposits up to 6 km in thickness dominate the sedimentary section the oldest sedimentary rocks that crop out in the mountain front are jurassic red beds which are unconformably overlain by a cretaceous sequence up to 2 km in thickness from early cretaceous to middle eocene sediments were deposited in an extensive passive continental margin setting figure 3 coarse clastic sediments of the rio negro formation bioclastic carbonates of the apon formation and siliciclastic sediments of the aguardiente formation were deposited first in the initial stage of the cretaceous transgressive event limestones calcareous shales and black shales of the capacho and la luna formations represent anoxic facies deposited during the maximum marine transgressiolof late cretaceous cenomanian campanian age regression began in the latest cretaceous maestrichtian with marine deposition of the shaly colon formation and the sandier mito juan formation this

annual climate variability in the holocene interpreting the message of ancient trees abstract over vast areas of the world s landmasses where climate beats out a strong seasonal rhythm tree growth keeps unerring time in their rings trees record many climate melodies played in different places and different eras recent years have seen a consolidation and expansion of tree ring sample collections across the traditional research areas of north america and europe and the start of major developments in many new areas of eurasia south america and australasia from such collections are produced networks of precisely dated chronologies records of various aspects of tree growth registered continuously year by year across many centuries their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space with their extensive coverage high temporal resolution and rigid dating control dendroclimatic reconstructions contribute significantly to our knowledge of late holocene climates most importantly on timescales ranging from 1 to 100 years in special areas of the world where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved work building chronologies covering many millennia continues apace very recently trees have provided important new information about major modes of general circulation dynamics linked to the el nino southern oscillation and the north atlantic oscillation and about the effect of large volcanic eruptions as for assessing the significance of 20th century global warming the evidence from dendroclimatology in general supports the notion that the last 100 years have been unusually warm at least within a context of the last two millennia however this evidence should not be considered equivocal the activities of humans may well be impacting on the natural growth of trees in different ways making the task of isolating a clear climate message subtly difficult

effect of variable bathymetry on the amplitude of teleseismic tsunamis a ray tracing experiment we apply surface wave ray tracing techniques to tsunami propagation in an ocean of variable depth because tsunami velocities are proportional to the square root of the depth of the water column the juxtaposition of oceanic plateaux and basins generates strong lateral velocity gradients and bathymetric features can act as lenses focusing or defocusing the tsunami waves we present a reconstruction of the tsunami wave field from the great chilean earthquake of 1960 an order of magnitude computation based on the concept of ray density provides qualitative agreement with observations at several sites in the pacific ocean we also demonstrate the possibility of using reciprocal maps to identify tsunamigenic zones that present particular danger for a given receiving shore

southern oscillation extremes reconstructed from tree rings of the sierra madre occidental and southern great plains abstract the el ninio southern oscillation enso is correlated with climate and tree growth over northern mexico and the southern great plains of the usa warm events favor moist cool conditions from october through march event years 0 and 1 and subsequent tree growth year 1 in the region tends to be above average the opposite climate and tree growth conditions prevail with less consistency during cold events enso sensitive tree ring chronologies from this region were selected to develop two reconstructions of the southern oscillation index soi back to 1699 for the first reconstruction a multiple regression based calibration equation between prewhitened and regionally averaged tree ring data from mexico and oklahoma and a prewhitened winter djf so index during the period 1900 71 were used to estimate the winter soi for each year from 1699 to 1971 the tree ring predictors account for 41 of the winter soi variance from 1900 to 1971 and the reconstructed so indices are significantly correl

revising midlatitude summer temperatures back to a d 600 based on a wood density network annually resolved and millennium long reconstructions of large scale temperature variability are primarily composed of tree ring width trw chronologies changes in ring width however have recently been shown to bias the ratio between low and high frequency signals to overcome limitations in capturing the full spectrum of past temperature variability we present a network of 15 maximum latewood density mxd chronologies distributed across the northern hemisphere extratropics independent subsets of continental scale records consistently reveal high mxd before 1580 and after 1910 with below average values between these periods reconstructed extratropical summer temperatures reflect not only these long term trends but also distinct cooling pulses after large volcanic eruptions in contrast to trw dominated reconstructions this mxd based record indicates a delayed onset of the little ice age by almost two centuries the reduced memory inherent in mxd is likely responsible for the rapid recovery from volcanic induced cooling in the fourteenth century and the continuation of warmer temperatures until 1600

globally scattered 2011 tohoku tsunami waves from a seafloor sensor array in the northeast pacific ocean modeling of tsunami wave propagation for forecasting focuses on the arrival time and amplitude of the earliest tsunami waves reaching coastlines the complex later tsunami wavefield in which scattering is predominant poses additional hazards due to possible constructive interference of coherent packets of wave energy however almost no datasets exist to characterize the geographical sources and temporal evolution of the scattered waves here we show how recordings of the 2011 tohoku tsunami by an array of pressure gauge sensors in the northeastern pacific ocean reveal coherent waves that are produced by scattering from distant coastlines including south america and antarctica as well as multiple seafloor fracture zones ridges and island chains multiple signal classification analysis and backward propagation ray tracing provide tight constraints on the origin of each scattered phase and resolve simultaneous wave arrivals from different scatterers incoming waves from constant back azimuths occur over time durations of several hours revealing the time persistence of specific geographical scatterers the results can advance numerical predictions of tsunami wave impact because they provide direct evidence for the necessity of incorporating both local and distant bathymetry over a range of length scales and for long time durations to account for the azimuthal dependence of scatterer strength

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

tectonic inheritance crustal architecture and contrasting structural styles in the venezuela andes surface and subsurface data image contrasting structural styles for the two flanks of the venezuela andes in the north a flexural basin developed in neogene times between the andes and the lake maracaibo north verging thrusts are mainly detached in the pre cretaceous substratum and form a deeply buried antiformal stack secondary decollement levels occur both in the upper cretaceous and tertiary strata accounting for the passive roof thrust of a conventional frontal triangle zone in the south the barinas basin hardly compares with a flexural basin it is largely dominated by both north and south verging basement involving structures paleogene normal faults are locally inverted and caribbean nappes are frequently reactivated or refolded by younger oblique neogene andean structures seismic profiles in this area also attest to the strong neogene structural inversion of upper jurassic lower cretaceous grabens hercynian or more likely early paleozoic structures account for local preexisting crustal heterogeneities reactivated during both the tethyan rifting and the andean deformations two trans andean regional profiles have been balanced and constrained by an inversion of the gravimetric data they imply a progressive deepening of the northern moho and a south dipping subduction of the infracontinental lithospheric mantle of the maracaibo block the shortening for both sections averages 60 km palinspastic restorations assume a relative cylindricity for the deep crustal architecture of the andes and minimize the possible effects of a progressive right lateral escape of the maracaibo block with respect to stable south america along the bocono fault strain partitioning during neogene oblique convergence induced surficial thrust fronts parallel to the plate boundary strike slip motion in the allochthon along the bocono fault and an asymmetric subduction wedging at depth

the 11 march 2011 tohoku tsunami wavefront mapping across offshore southern california the 11 march 2011 m w 9 0 tohoku tsunami was recorded by a temporary array of seafloor pressure gauges deployed off the coast of southern california demonstrating how dense array data can illustrate and empirically validate predictions of linear tsunami wave propagation characteristics a noise cross correlation method was used to first correct for the pressure gauge instrument phase response phase and group travel times were then measured for the first arrival in the pressure gauge tsunami waveforms filtered in narrow bands around 30 periods between 200 and 3000 s for each period phase velocities were estimated across the pressure gauge array based on the phase travel time gradient using eikonal tomography clear correlation was observed between the phase velocity and long wavelength bathymetry variations where fast and slow velocities occurred for deep and shallow water regions respectively in particular velocity gradients are pronounced at the patton escarpment and near island plateaus due to the abrupt bathymetry change in the deep open ocean area clear phase velocity dispersion is observed comparison with numerically calculated tsunami waveforms validates the approach and provides an independent measure of the finite frequency effect on phase velocities at long periods

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

velocity field across the southern caribbean plate boundary and estimates of caribbean south american plate motion using gps geodesy 1994 2000 global positioning system gps observations between 1994 and 2000 at twenty two sites in the lesser antilles and northern south america indicate that the caribbean plate along its southern boundary slips at a rate of 20 5 2 mm a with an azimuth of n 84 2 e at 65 w relative to the south american plate east of 68 w 80 of the dextral slip is contained within a 80 km wide shear zone centered on the el pilar san sebastian fault system west of 68 w the plate boundary broadens to more than 300 km with dextral shear shared between the northeast trending bocono fault 9 11 mm a in western venezuelan and an offshore system near the northern coast

seismic strain rates and distributed continental deformation in the northern andes and three dimensional seismotectonics of northwestern south america abstract the seismic strain rates and configuration in the northern andes are estimated by summing the components of the centroid moment tensor cmt solutions for earthquakes with mw 5 0 and are compared with those predicted by various models of relative plate motions and gps data moment tensor components are summed linearly in four different regions with similar seismotectonics to infer changes in the regional strain patterns along the northern andes and to retrieve strain rates and relative plate velocities between this region and the stable south american plate the andean seismic strain rates are the result of east southeast directed contraction due to the collision of the nazca and caribbean plates with the south american plate and the collision of the panama block against central colombia with a component of northeast directed motion due to the obliquity of the eastern boundary of the northern andes with respect to the boundary of the nazca and caribbean plates with the south american plate along the colombia trench and the southern caribbean deformation zone respectively where the convergence is normal the present motion of the central andes towards the northeast does not require the plate boundary between the caribbean and south american plates to be along the eastern cordillera of colombia and the bocono fault in venezuela the seismic moment rates for the northern andes are small compared to the total expected seismic strain rates calculated from plate motion models and gps data suggesting that most of the strain is released aseismically and that is accommodated by folding fault creeping rigid block translation or other undetermined processes finally a three dimensional model of the cmt solutions and other seismicity in northwestern south america is presented where major subducting slabs including the peru flat slab and the ecuador and central colombia segments of the nazca and caribbean plates become more evident and easier to interpret the caribbean plate is interpreted to culminate at the location of the bucaramanga nest offering an explanation to this swarm of seismicity in the northern andes

crustal thickness variations in venezuela from deep seismic observations abstract the caribbean south america plate boundary zone is a complex zone of plate interactions forming thrust belts and foreland basins in northern venezuela within the framework of the bolivar and geodinos projects the geodynamics of plate interactions is being investigated using interdisciplinary geological and geophysical methods here we focus on the results of the land based active seismic observations done in 2004 along four deep seismic wide angle profiles acquired perpendicular to the caribbean south america plate boundary in northern venezuela between longitudes 63 w and 70 w and ranging from about latitudes 12 n to about 9 n the mostly unreversed profiles provide information on the crustal structure from the oceanic transitional crust on the southern border of the caribbean plate to the continental crust of the caribbean mountain system and their associated foreland basins which are bordered to the south by the guayana shield which corresponds to stable south america plate the derived crustal thickness oscillates around 35 km along the coastline corresponding to the caribbean mountain system and decreases only slightly towards the leeward antilles to the south in the area of the eastern venezuela basin crustal thickness reaches 40 km increasing towards the guayana shield to 45 km nevertheless there are two regions of anomalous crustal thickness proven by arrivals from the lower crust and the moho discontinuity in the eastern part of the eastern venezuela basin crustal thickness reaches up to 50 km with high velocity anomalies within the lower crust which are interpreted as reworked lower crustal and upper mantle material associated to the plate interactions of the south american and the caribbean plates the second anomalous zone is a remarkable crustal thinning from 35 km to 27 km in the falcon basin in western venezuela which extends eastwards into the bonaire basin as documented by pmp reflections derived from land shots and observations of the air gun blasts on the stations of the venezuelan seismological network

tsunami speed variations in density stratified compressible global oceans 1 tsunami speed variations in the deep ocean caused by seawater density stratification is investigated using a newly developed propagator matrix method that is applicable to seawater with depth variable sound speeds and density gradients for a 4 km deep ocean the total tsunami speed reduction is 0 44 compared with incompressible homogeneous seawater two thirds of the reduction is due to elastic energy stored in the water and one third is due to water density stratification mainly by hydrostatic compression tsunami speeds are computed for global ocean density and sound speed profiles and characteristic structures are discussed tsunami speed reductions are proportional to ocean depth with small variations except in warm mediterranean seas the impacts of seawater compressibility and the elasticity effect of the solid earth on tsunami traveltime should be included for precise modeling of transoceanic tsunamis

tectonic implications of tomographic images of subducted lithosphere beneath northwestern south america we used seismic tomography to investigate the complex structure of the upper mantle below northwestern south america images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted caribbean pacific lithosphere beneath the study area beneath western venezuela and colombia we distinguish two slabs a maracaibo and a redefined bucaramanga slab the maracaibo slab coinciding with most of the bucaramanga slab previously defined by w d pennington dips in a direction of 150 at an angle of 17 to a depth of 275 km and correlates to the subducted late cretaceous oceanic plateau of the caribbean plate farther south a second slab dips at an angle of 50 in a direction of 125 to a depth of at least 500 km and correlates to the subducted oceanic crust of the nazca plate and the downdip extension of the panama island arc we refer to this slab as the redefined bucaramanga slab because it is different from the bucaramanga slab segment defined by pennington the area of the south american plate overriding both slabs is characterized by the absence of an active volcanic arc an anomalously wide topographically uplifted and tectonically active area and the northward escape of the maracaibo block along active strike slip faults in support of earlier studies we attribute this to the underthrusting of the caribbean oceanic plateau our shallowly dipping maracaibo slab along the base of the south american lithosphere and to the recent collision of the panama island arc rafted in on more steeply dipping crust of the nazca plate our redefined bucaramanga slab

improving a tree ring reconstruction from west central scandinavia 900 years of warm season temperatures dendroclimatological sampling of scots pine pinus sylvestris l has been made in the province of jamtland in the west central scandinavian mountains since the 1970s the tree ring width trw chronology spans several thousand years and has been used to reconstruct june august temperatures back to 1632 bc a maximum latewood density mxd dataset covering the period ad 1107 1827 with gap 1292 1315 was presented in the 1980s by fritz schweingruber here we combine these historical mxd data with recently collected mxd data covering ad 1292 2006 into a single reconstruction of april september temperatures for the period ad 1107 2006 regional curve standardization rcs provides more low frequency variability than non rcs and stronger correlation with local seasonal temperatures 51 variance explained the mxd chronology shows a stronger relationship with temperatures than the trw data but the two chronologies show similar multi decadal variations back to ad 1500 according to the mxd chronology the period since ad 1930 and around ad 1150 1200 were the warmest during the last 900 years due to large uncertainties in the early part of the combined mxd chronology it is not possible to conclude which period was the warmest more sampling of trees growing near the tree line is needed to further improve the mxd chronology

flexural and gravity modelling of the merida andes and barinas apure basin western venezuela abstract the kinematic evolution of the barinas apure basin and the southern merida andes from lower miocene to the present is numerically modelled using flexural isostatic theory and geophysical and geological data two published regional transects are used to build up a reference section which is then used to constrain important parameters e g shortenings and sedimentary thicknesses for the flexural modelling to control the location of the main fault system in the flexural model earthquake information is also used the estimated flexural elastic thickness of the south american lithosphere beneath the barinas apure basin and the merida andes range is 25 km the value for the final total shortening is 60 km the flexural isostatic model shows that the andean uplift has caused the south american lithosphere subsidence and the development of the barinas apure basin in addition gravity modelling was used to understand deep crustal features that could not be predicted by flexural theory consequently the best fit flexural model is used to build a gravity model across the merida andes and the barinas apure basin preserving the best controlled structural features from the flexural modelling e g basin wavelength and depth and slightly changing the main bodies density values and deep crustal structures the final gravity model is intended to be representative of the major features affecting the gravity field in the study area the predicted morphology in the lower crustal level of the final gravity model favours the hypothesis of a present delamination or megathrust of the maracaibo crust over the south american shield this process would use the conrad discontinuity as a main detachment surface within an incipient nw dipping continental subduction

summer temperature patterns over europe a reconstruction from 1750 a d based on maximum latewood density indices of conifers abstract temperature variations over europe are reconstructed for a 6 month summer season from april to september for the period 1750 1850 using a network of maximum latewood density chronologies of coniferous trees around 44 of the variance of the whole temperature grid was explained in calibration independent verification indicates that over the reconstruction period the explained variance averaged over the whole grid should lie in the range 30 to 35 the reconstructions are better in the north of the region about 50 explained temperature variance based on comparison with independent climate data than in the south below 20 the temperature recontructions indicate cooler summers over europe from 1812 to 1816 and during the 1830s the summers of the 1820s were the warmest reconstructed decadal variations occur on a regional scale but no similar periods of anomalously cooler or warmer summers occurred between 1750 and 1810 throughout europe

microseismicity evidence for subduction of the caribbean plate beneath the south american plate in northwestern venezuela over 1100 microearthquakes with body wave magnitude mb 4 have been located in western venezuela and the southwestern caribbean region since the installation in 1980 of the venezuelan seismological array together with 120 events of mb 4 one of them with surface wave magnitude ms 6 this tectonically complex region is part of the boundary between the caribbean and the south american plates the main seismically active feature inland in western venezuela is the northeast striking 600 km long 100 km wide right lateral strike slip bocono fault zone along the venezuelan andes about 80 of the earthquakes located in the entire region in the period 1980 mid 1995 have occurred on this fault zone at focal depths 20 km microearthquake activity at lower rates also occurs northwest of the venezuelan andes both in the continental and caribbean sea regions part of this activity takes place at depths down to 150 km northwest oriented seismicity depth profiles show the existence of a benioff zone dipping to the southeast beneath northwestern venezuela and northern colombia this indicates the presence of a northeast striking southeast dipping subducted slab of the caribbean plate beneath the south american plate hypocentral locations show that the northeastern end of this subduction occurs northwest of the curacao aruba region in the vicinity of a northwest trending right lateral strike slip fault zone that joins up with the northeastern end of the bocono fault zone this latter place turns out to be the western end of the east west striking san sebastian fault along the venezuelan coast

last millennium climate and its variability in ccsm4 abstractan overview of a simulation referred to as the last millennium lm simulation of the community climate system model version 4 ccsm4 is presented the ccsm4 lm simulation reproduces many large scale climate patterns suggested by historical and proxy data records with northern hemisphere nh and southern hemisphere sh surface temperatures cooling to the early 1800s common era by 0 5 c nh and 0 3 c sh followed by warming to the present high latitudes of both hemispheres show polar amplification of the cooling from the medieval climate anomaly mca to the little ice age lia associated with sea ice increases the lm simulation does not reproduce la nina like cooling in the eastern pacific ocean during the mca relative to the lia as has been suggested by proxy reconstructions still dry medieval conditions over the southwestern and central united states are simulated in agreement with proxy indicators for these regions strong global cooling is associated with large volcanic erup

volcanic forcing of climate over the past 1500 years an improved ice core based index for climate models 1 understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate we have investigated one of the most important natural causes of climate change volcanic eruptions by using 54 ice core records from both the arctic and antarctica our recently collected suite of ice core data more than double the number of cores ever used before reduces errors inherent in reconstructions based on a single or small number of cores which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects we extracted volcanic deposition signals from each ice core record by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation we then studied the spatial pattern of volcanic sulfate deposition on greenland and antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month latitude and altitude for the past 1500 years we estimated the uncertainties associated with the choice of volcanic signal extraction criteria ice core sulfate deposition to stratospheric loading calibration factor and the season for the eruptions without a recorded month we forced an energy balance climate model with this new volcanic forcing data set together with solar and anthropogenic forcing to simulate the large scale temperature response the results agree well with instrumental observations for the past 150 years and with proxy records for the entire period through better characterization of the natural causes of climate change this new data set will lead to improved prediction of anthropogenic impacts on climate the new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years as a function of latitude altitude and month is available for download in a format suitable for forcing general circulation models of the climate system

plate motions in the north andean region repeated geodetic measurements with the global positioning system gps provide direct measurements of displacements due to plate motions and active crustal deformation in central america and northern south america an area of complex interaction of the nazca cocos caribbean and south american plates the displacement rates for the period 1988 1991 obtained from the results of the first three central and south america casa gps campaigns are in general agreement with the predictions of the nuvel 1 plate motion model but there are differences in detail between the observations and the model the nazca north andes convergence rate vector measured by gps is different from the nuvel 1 vector at 95 confidence the difference implies that the north andes are moving northward relative to south america the measured convergence between the caribbean plate and the north andes suggests that the southern margin of the caribbean plate is located in the south caribbean deformed belt the april 1991 costa rica earthquake and the cocos caribbean convergence rate determined by gps suggest the possibility of significant ongoing deformation between central america and the stable interior of the caribbean plate our gps results are consistent with deformation of the overriding plates at the convergent margins of central and south america and confirm that active convergence is occurring around much of the southern margin of the caribbean plate from colombia west to costa rica costa rica and panama are not part of the stable caribbean plate instead the south caribbean deformed belt and the north panama fold belt probably represent the southern margin of the caribbean plate

subduction of the caribbean plate and basement uplifts in the overriding south american plate the new tectonic interpretations presented in this paper are based on geologic field mapping and gravity data supplemented by well logs seismic profiles and radiometric and earthquake data the present caribbean south american plate boundary is the south caribbean marginal fault where subduction is indicated by folding and thrusting in the deformed belt and a seismic zone that dips 30 to the southeast and terminates 200 km below the maracaibo basin the caribbean south american convergence rate is estimated as 1 9 0 3 cm yr on the basis of the 390 km length of the seismic zone and a thermal equilibration time of 10 m y the caribbean south american convergence has produced a northwest southeast maximum principal stress direction 1 in the overriding south american plate the mean 1 direction for the maracaibo santa marta block is 310 10 based on earthquake focal mechanism determinations and structural and gravity data on the overriding south american plate basement blocks have been uplifted 7 12 km in the last 10 m y to form the venezuelan andes sierra de perija and the colombian santa marta massif crystalline basement of the venezuelan andes has been thrust to the northwest over tertiary sediments on a fault dipping about 25 and extending to the mantle in the sierra de perija mesozoic sediments have been thrust 16 26 km to the northwest over tertiary sandstones along the cerrejon fault a thrust fault dipping 15 10 to the southeast is consistent with field mapping and gravity and density data the santa marta massif has been uplifted 12 km in the last 10 m y by northwest thrusting over sediments the basement block overthrusts of the perijas venezuelan andes and the santa marta massif are pliocene pleistocene analogs for laramide orogenic structures in the middle and southern rocky mountains of the united states the nonmagmatic basement block uplifts along low angle thrust faults reveal horizontal compression in the overriding plate over 500 km from the convergent margin present day east northeast west southwest 080 compression is indicated by earthquake focal mechanisms and strike slip motion on the bocono fault these earthquakes are intraplate deformation associated with east west 080 nazca south american convergence

climate response to the samalas volcanic eruption in 1257 revealed by proxy records the eruption of samalas in indonesia in 1257 ranks among the largest sulfur rich eruptions of the common era with sulfur deposition in ice cores reaching twice the volume of the tambora eruption in 1815 sedimentological analyses of deposits confirm the exceptional size of the event which had both an eruption magnitude and a volcanic explosivity index of 7 during the samalas eruption more than 40 km 3 of dense magma was expelled and the eruption column is estimated to have reached altitudes of 43 km however the climatic response to the samalas event is debated since climate model simulations generally predict a stronger and more prolonged surface air cooling of northern hemisphere summers than inferred from tree ring based temperature reconstructions here we draw on historical archives ice core data and tree ring records to reconstruct the spatial and temporal climate response to the samalas eruption we find that 1258 and 1259 experienced some of the coldest northern hemisphere summers of the past millennium however cooling across the northern hemisphere was spatially heterogeneous western europe siberia and japan experienced strong cooling coinciding with warmer than average conditions over alaska and northern canada we suggest that in north america volcanic radiative forcing was modulated by a positive phase of the el nino southern oscillation contemporary records attest to severe famines in england and japan but these began prior to the eruption we conclude that the samalas eruption aggravated existing crises but did not trigger the famines

european summer temperature response to annually dated volcanic eruptions over the past nine centuries the drop in temperature following large volcanic eruptions has been identified as an important component of natural climate variability however due to the limited number of large eruptions that occurred during the period of instrumen tal observations the precise amplitude of post volcanic cooling is not well constrained here we present new evidence on summer temperature cooling over europe in years following volcanic eruptions we compile and analyze an updated net work of tree ring maximum latewood density chronologies spanning the past nine centuries and compare cooling sig natures in this network with exceptionally long instru mental station records and state of the art general circu lation models results indicate post volcanic june august cooling is strongest in northern europe 2 years after an eruption 0 52 0 05 c whereas in central europe the temperature response is smaller and occurs 1 year after an eruption 0 18 0 07 c we validate these estimates by comparisonwith the shorter instrumental network and evaluate the statistical significance of post volcanic summer tempera ture cooling in the context of natural climate variability over the past nine centuries finding no significant post volcanic temperature cooling lasting longer than 2 years our results question the ability of large eruptions to initiate long term temperature changes through feedback mechanisms in the climate system we discuss the implications of these findings with respect to the response seen in general circulation models and emphasize the importance of considering well documented annually dated eruptions when assessing the

tornetrask tree ring width and density ad 500 2004 a test of climatic sensitivity and a new 1500 year reconstruction of north fennoscandian summers this paper presents updated tree ring width trw and maximum density mxd from tornetrask in northern sweden now covering the period ad 500 2004 by including data from relatively young trees for the most recent period a previously noted decline in recent mxd is eliminated non climatological growth trends in the data are removed using regional curve standardization rcs thus producing trw and mxd chronologies with preserved low frequency variability the chronologies are calibrated using local and regional instrumental climate records a bootstrapped response function analysis using regional climate data shows that tree growth is forced by april august temperatures and that the regression weights for mxd are much stronger than for trw the robustness of the reconstruction equation is verified by independent temperature data and shows that 63 64 of the instrumental inter annual variation is captured by the tree ring data this is a significant improvement compared to previously published reconstructions based on tree ring data from tornetrask a divergence phenomenon around ad 1800 expressed as an increase in trw that is not paralleled by temperature and mxd is most likely an effect of major changes in the density of the pine population at this northern tree line site the bias introduced by this trw phenomenon is assessed by producing a summer temperature reconstruction based on mxd exclusively the new data show generally higher temperature estimates than previous reconstructions based on tornetrask tree ring data the late twentieth century however is not exceptionally warm in the new record on decadal to centennial timescales periods around ad 750 1000 1400 and 1750 were equally warm or warmer the 200 year long warm period centered on ad 1000 was significantly warmer than the late twentieth century p 0 05 and is supported by other local and regional paleoclimate data the new tree ring evidence from tornetrask suggests that this medieval warm period in northern fennoscandia was much warmer than previously recognized

deep structure of the merida andes and sierra de perija mountain fronts maracaibo basin venezuela the maracaibo basin is a 50 000 km2 19 305 mi2 topographic depression bounded to the east and south by the mrida andes of venezuela and to the west by the sierra de perij of venezuela and colombia both uplifted mountain blocks expose paleozoic basement rocks and mesozoic cenozoic carbonate and clastic rocks that were mainly folded and thrusted by regional shortening in the paleogene and late neogene using geologic maps seismic reflection data and wells from the steep mountain front areas we test different structural models of how late paleogene neogene convergence is accommodated along subsurface faults and folds at the mountain fronts seismic imaging of the deep 5 km 3 1 mi structure of both maracaibo mountain fronts shows basinward dipping monoclines with stratal dips ranging from 20 to overturned and an almost complete lack of faulting in the basin edge monocline or in adjacent horizontally bedded strata of the maracaibo basin seismic data reveal the presence of one or more triangle zones at depth along both the mrida andes and sierra de perij that exhibit characteristic thrust wedge geometries the lower part of the wedge is defined by imbricate thrust faults dipping beneath the mountain block and involving the paleozoic basement the upper part of the wedge is defined by a basinward dipping thrust associated with fault propagation folds at the surface and an overlain basin edge monocline the creation of the steep to overturned dips of the monocline is attributed to the effects of 6 10 km 3 7 6 2 mi of shortening along the lower zone of imbricated thrust faults this 6 10 km 3 7 6 2 mi of shortening calculated from triangle zones of both the sierra de prija and mrida andes is significantly less than regional estimates from 12 to 60 km 7 4 to 37 mi of shortening inferred by previous workers from regional balanced cross sections that assume low angle thrust type geometries we propose that a pop up style of deformation related to the inversion of jurassic rift features may be a more realistic interpretation of the convergent fault systems that have controlled uplift of the mrida andes and sierra de perij inversion of relatively steep basement normal faults at the edges of and within both ranges may explain lesser amounts of observed shortening

fennoscandian summers from ad 500 temperature changes on short and long timescales quantitative estimates of 1480 years of summer temperatures in northern fennoscandia have previously been derived from continuous treering records from northern sweden here we show the results of spectral analyses of these data only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub periods relatively timestable peaks are apparent at periods of 2 1 2 5 3 1 3 6 4 8 32 33 and for a range between 55 100 years these results offer no strong evidence for solar related forcing of summer temperatures in these regions our previously published reconstruction was limited in its ability to represent long timescale temperature change because of the method used to standardize the original tree ring data here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales considerable variance is now reconstructed on timescales of several centuries in comparison with modern normals 1951 70 generally extended periods when cool conditions prevailed prior to the start of the instrumental record include 500 700 790 870 1110 1150 1190 1360 1570 1750 a d with the most significant cold troughs centred on about 660 800 1140 1580 1620 and 1640 predominantly warm conditions occurred in 720 790 870 1110 and 1360 1570 with peaks of warmth around 750 930 990 1060 1090 1160 1410 1430 1760 and 1820

regional geologic and tectonic setting of the maracaibo supergiant basin western venezuela this special issue contains eight topical studies on the structure stratigraphy and petroleum system of the maracaibo basin a supergiant basin in western venezuela most of the work reported in this special issue is the product of thesis related research by master s and doctoral level students at the jackson school of geosciences of the university of texas at austin during a collaborative relationship with the venezuelan national oil company petrleos de venezuela s a that was initiated in the late 1980s this introductory article presents a regional overview of the tectonic setting and geology of the maracaibo basin with a cumulative oil production of more than 30 billion bbl since the first production well was drilled in 1914 and estimated ultimate oil reserves of more than 44 billion bbl the maracaibo basin is the most prolific hydrocarbon basin in the western hemisphere unlike the more extensive gulf of mexico giant hydrocarbon provinces the relatively small size 50 000 km2 19 305 mi2 relative simplicity in its structure and stratigraphy and wealth of surface and subsurface data make the maracaibo basin an attractive target for basinwide synthesis the objective of this article is to present a regional compilation of two dimensional 2 d and three dimensional 3 d seismic data wells and outcrop data at a basinwide scale to reveal the basin s 3 d structure and stratigraphy moreover we show regional tectonic reconstructions regional geologic maps and basin subsidence history to better constrain four major tectonic events that affected the basin and that are critical for understanding the timing and distribution of major unconformities and clastic wedges the distribution of the reservoir rocks the reactivation of older fault trends and the timing of maturation for underlying source rocks many of these topics are discussed in greater detail in the other eight articles in this special issue

introduction to global tsunami science past and future volume ii twenty two papers on the study of tsunamis are included in volume ii of the pageoph topical issue global tsunami science past and future volume i of this topical issue was published as pageoph vol 173 no 12 2016 eds e l geist h m fritz a b rabinovich and y tanioka three papers in volume ii focus on details of the 2011 and 2016 tsunami generating earthquakes offshore of tohoku japan the next six papers describe important case studies and observations of recent and historical events four papers related to tsunami hazard assessment are followed by three papers on tsunami hydrodynamics and numerical modelling three papers discuss problems of tsunami warning and real time forecasting the final set of three papers importantly investigates tsunamis generated by non seismic sources volcanic explosions landslides and meteorological disturbances collectively this volume highlights contemporary trends in global tsunami research both fundamental and applied toward hazard assessment and mitigation

conjugate margins of canada and europe results from deep reflection profiling deep seismic reflection profiles have been collected across the conjugate margins of the north atlantic ocean the eastern north atlantic margin is traversed in the goban spur region and the western north atlantic margin is crossed in the vicinity of flemish cap in the grand banks region these seismic profiles allow us to examine the deep structures and mode of extension in crust that was once contiguous the flemish cap and goban spur margins have different structural styles thick and relatively unfaulted crust is present on the flemish cap margin west of the continent ocean boundary whereas the goban spur margin exhibits a zone of extensional faulting and thinned continental crust the restored rift zone displays overall symmetry in which a bridge of thin crust 15 km thick about 60 km wide joins the two crustal blocks of normal continental thickness 28 km the configuration of the moho the geometry and distribution of the lower crustal reflections and the overall symmetry of the rift zone favor pure shear stretching in the lower lithosphere although either pure or simple shear could accommodate crustal extension

jurassic la quinta formation in the sierra de perija northwestern venezuela geology and tectonic environment of red beds and volcanic rocks

reassessing the evidence for tree growth and inferred temperature change during the common era in yamalia northwest siberia the development of research into the history of tree growth and inferred summer temperature changes in yamalia spanning the last 2000 years is reviewed one focus is the evolving production of tree ring width trw and tree ring maximum latewood density mxd larch larix sibirica chronologies incorporating different applications of regional curve standardisation rcs another focus is the comparison of independent data representing past tree growth in adjacent yamalia areas yamal and polar urals and the examination of the evidence for common growth behaviour at different timescales the sample data we use are far more numerous and cover a longer time span at yamal compared to the polar urals but yamal has only trw while there are both trw and mxd for the polar urals we use more data sub fossil and from living trees than in previous dendroclimatic studies in this region we develop a new trw chronology for yamal more than 2000 years long and running up to 2005 for the polar urals we develop new trw and mxd chronologies that show good agreement at short 15 years and medium 15e100 years timescales demonstrating the validity of attempts to reconcile the evidence of longer timescale information that they provide we use a conservative application of the rcs approach two curve signal free rcs guarding against the possibility of modern sample bias a possible inflation of recent chronology values arising out of inadvertent selection of mostly relatively fast growing trees in recent centuries we also transform tree indices to have a normal distribution to remove the positive chronology skew often apparent in rcs trw chronologies this also reduces the apparent magnitude of 20th century tree growth levels thereis generallygoodagreement between all chronologies as regardsthe major featuresof the decadal to centennial variability low tree growth periods for which the inferred summer temperatures are approximately 2 5 c below the 1961e90 reference are apparent in the 15 year smoothed reconstructions

earthquake geology of the last millennium along the bocono fault venezuela abstract the holocene tectonic activity of latin american countries is poorly constrained because of the short time span of the instrumental record and the lack of any seismic calendar during pre colonization times therefore some areas with low and diffused seismicity have been catalogued as a seismic gap it has been suggested that the northernmost segment of the bocono fault in venezuela is one of these areas although a recent mw 7 4 event that occurred in 1812 has been well documented by a historical investigation in this study we mapped the historical events triggered by the bocono fault using a paleoseismological investigation a geological interpretation of high resolution satellite images field mapping as well as ground penetrating radar gpr profiles at selected trench sites our results suggest that at least three seismic events had produced surface ruptures in the trench site based on the exposed trench stratigraphy as well as the results of radiocarbon dating and age models i a latest event e3 that occurred between 1545 and 1825 ce ii a previous event e2 that occurred between 1483 and 1743 ce and iii an older event e1 before 1456 1636 ce the e3 event might correspond to the 1812 major earthquake these results further support the fact that the 1812 event was triggered by the bocono fault and that the rupture reached the surface the potential slip deficit along the studied segment ranges from 1 7 to 2 3 m and corresponds to mw 7 assuming that the 1812 ce earthquake released all of the strain stored earlier as the time span between events e2 and e3 is short

structure of the merida andes venezuela relations with the south america caribbean geodynamic interaction for over 50 years several models based on diverse geologic concepts and variable quality of data have been proposed to explain the major structure and history of the merida andes ma in western venezuela lately this chain growth and associated flexural basins deepening have been related to incipient type a subductions of either polarity accounting for the across chain asymmetry however these recent models have not well integrated the present tectonically active setting driven by neighboring major plate interactions at present this chain exhibits ongoing strain partitioning where cumulative right lateral slip along chain axis is as much as half of or about the same as the transverse shortening since late miocene thus implying that the nne directed maracaibo block extrusion with respect to the south america sa plate is not a secondary feature consequently this paper discusses some limitations exhibited by the se directed continental subduction models maracaibo crust underthrusting the merida andes in the light of available geological and geophysical data besides it is herein proposed that the merida andes structuration is related to a nw directed gently dipping incipient type a subduction where chain growth and evolution are similar to those of a sedimentary accretionary wedge i e barbados but at crustal scale and with ongoing strain partitioning this continental subduction is the se portion of a major orogenic float that also comprises the perija range and the santa marta block d 2002 elsevier science b v all rights reserved

orogenic float of the venezuelan andes abstract the venezuelan or merida andes are a ne trending intracontinental orogen that started to rise from the middle miocene due to the e w far field convergence between the maracaibo block to the northwest and the guyana shield to the southeast oblique convergence is responsible for strain partitioning with thrusting along both foreland basins and right lateral strike slip faulting along the ne sw bocono fault cutting the venezuelan andes along strike the central part of the belt is also cut by the n s left lateral strike slip valera fault that connects the bocono fault both faults bounding the trujillo block that escapes towards the nne even though the regional geology of belt is well known its structure at depth remains a matter of debate our work based on the integration of geological and geophysical data aims to better constrain the deep geometry of faults and the tectonic evolution of the mountain belt we used the orogenic float model to construct two nw se trans andean crustal scale balanced sections the late neogene quaternary shortening varies from 40 km in the south to 30 km in the north across the trujillo block indicating that a quarter of the deformation seems to be absorbed by the tectonic escape process more importantly a major reorganization in the crust took place in the early pliocene it is characterized by the imbrication of the maracaibo crust into the guyana crust this resulted in the subduction of the guyana lower crust and the formation of a nw vergent basement thrust propagating upwards and surfacing along the las virtudes thrust rapid uplift of the northern flank of the belt subsequently occurred together with massive deposition of the plio quaternary coarse grained betijoque formation in the northwestern foreland basin

the crustal structure of the guayana shield venezuela from seismic refraction and gravity data abstract we present results from a seismic refraction experiment on the northern margin of the guayana shield performed during june 1998 along nine profiles of up to 320 km length using the daily blasts of the cerro bolivar mines as energy source as well as from gravimetric measurements clear moho arrivals can be observed on the main e w profile on the shield whereas the profiles entering the oriental basin to the north are more noisy the crustal thickness of the shield is unusually high with up to 46 km on the archean segment in the west and 43 km on the proterozoic segment in the east a 20 km thick upper crust with p wave velocities between 6 0 and 6 3 km s can be separated from a lower crust with velocities ranging from 6 5 to 7 2 km s a lower crustal low velocity zone with a velocity reduction to 6 3 km s is observed between 25 and 25 km depth the average crustal velocity is 6 5 km s the changes in the bouguer anomaly positive 30 mgal in the west and negative 20 mgal in the east cannot be explained by the observed seismic crustal features alone lateral variations in the crust or in the upper mantle must be responsible for these observations

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

low frequency temperature variations from a northern tree ring density network we describe new reconstructions of northern extratropical summer temperatures for nine subcontinental scale regions and a composite series representing quasi northern hemisphere temperature change over the last 600 years these series are based on tree ring density data that have been processed using a novel statistical technique age band decomposition designed to preserve greater long timescale variability than in previous analyses we provide time dependent and timescale dependent uncertainty estimates for all of the reconstructions the new regional estimates are generally cooler in almost all precalibration periods compared to estimates obtained using earlier processing methods particularly during the 17th century one exception is the reconstruction for northern siberia where 15th century summers are now estimated to be warmer than those observed in the 20th century in producing a new northern hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data and the reliability of each regional series begins to decrease we compare our new hemisphere series to other published large regional temperature histories most of which lie within the 1 confidence band of our estimates over most of the last 600 years the 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period

did a submarine landslide contribute to the 2011 tohoku tsunami many studies have modeled the tohoku tsunami of march 11 2011 as being due entirely to slip on an earthquake fault but the following discrepancies suggest that further research is warranted 1 published models of tsunami propagation and coastal impact underpredict the observed runup heights of up to 40 m measured along the coast of the sanriku district in the northeast part of honshu island 2 published models cannot reproduce the timing and high frequency content of tsunami waves recorded at three nearshore buoys off sanriku nor the timing and dispersion properties of the waveforms at offshore dart buoy 21418 3 the rupture centroids obtained by tsunami inversions are biased about 60 km nne of that obtained by the global cmt project based on an analysis of seismic and geodetic data together with recorded tsunami waveforms we propose that while the primary source of the tsunami was the vertical displacement of the seafloor due to the earthquake an additional tsunami source is also required we infer the location of the proposed additional source based on an analysis of the travel times of higher frequency tsunami waves observed at nearshore buoys we further propose that the most likely additional tsunami source was a submarine mass failure smf i e a submarine landslide a comparison of pre and post tsunami bathymetric surveys reveals tens of meters of vertical seafloor movement at the proposed smf location and a slope stability analysis confirms that the horizontal acceleration from the earthquake was sufficient to trigger an smf forward modeling of the tsunami generated by a combination of the earthquake and the smf reproduces the recorded on near and offshore tsunami observations well particularly the high frequency component of the tsunami waves off sanriku which were not well simulated by previous models the conclusion that a significant part of the 2011 tohoku tsunami was generated by an smf source has important implications for estimates of tsunami hazard in the tohoku region as well as in other tectonically similar regions

last millennium northern hemisphere summer temperatures from tree rings part i the long term context abstract large scale millennial length northern hemisphere nh temperature reconstructions have been progressively improved over the last 20 years as new datasets have been developed this paper and its companion part ii anchukaitis et al in prep details the latest tree ring tr based nh land air temperature reconstruction from a temporal and spatial perspective this work is the first product of a consortium called n trend n orthern hemisphere tre e ring n etwork d evelopment which brings together dendroclimatologists to identify a collective strategy for improving large scale summer temperature reconstructions the new reconstruction n trend2015 utilises 54 records a significant expansion compared with previous tr studies and yields an improved reconstruction with stronger statistical calibration metrics n trend2015 is relatively insensitive to the compositing method and spatial weighting used and validation metrics indicate that the new record portrays reasonable coherence with large scale summer temperatures and is robust at all time scales from 918 to 2004 where at least 3 tr records exist from each major continental mass n trend2015 indicates a longer and warmer medieval period 900 1170 than portrayed by previous tr nh reconstructions and by the cmip5 model ensemble but with better overall agreement between records for the last 600 years future dendroclimatic projects should focus on developing new long records from data sparse regions such as north america and eastern eurasia as well as ensuring the measurement of parameters related to latewood density to complement ring width records which can improve local based calibration substantially

paleoseismicity studies on the oca ancon fault system northwestern venezuela abstract the e w trending right lateral oca ancon fault system extends eastward for 650 km from the colombian caribbean coast near the city of santa marta to the town of boca de aroa located on the eastern coast of falcon state northwestern venezuela across the goajira peninsula the outlet of lake maracaibo the coastal plains of buchivacoa and the central falcon range this system is very conspicuous west of the city of maracaibo where its single trace sharply truncates the northern ends of the santa marta block and the perija range fault related landforms along the system trace e g displaced beach strandlines at sinamaica and fault scarplets in the buchivacoa plains suggest that it may have been active during holocene times a first trenching attempt carried out north of maracaibo at sinamaica in 1969 only confirmed its holocene tectonic activity on the western coastal plains of falcon state and east of lake maracaibo the system is less simple as it is composed of two parallel fault strands but they are clearly evidenced by holocene paleoseismic scarplets recently this system has been paleoseismically evaluated by means of two trenches placed across each of the two parallel branches known as the oca and the ancon faults dimensions of these bulldozer dug trenches are 80 m long and 8 m deep various lines of evidence obtained from these exploratory trenches indicate that a three surface rupture events dated slightly prior to 7755 320 6240 39 and 1945 630 yr b p have occurred along the oca fault b one surface rupture event has occurred within the past 3125 185 yr on the ancon fault c the holocene slip rate of the system is close to 2 mm yr and d either of the faults can generate a maximum event of magnitude 7 4 7 5 recurrence of such earthquakes on the ancon fault is close to 1900 years while it is about 4300 years on the oca fault

three dimensional structural architecture and evolution of the eocene pull apart basin central maracaibo basin venezuela abstract three dimensional seismic mapping of interpretative sub surface time slice sections incorporating age data and detailed structural observations places constraints on the structural architecture and stratigraphic evolution of the icotea pull apart basin in the central maracaibo basin venezuela all four fault bounded sides of the icotea basin its 3 km thick eocene basin fill of clastic sediments and faults pre dating the opening of the basin can be mapped in three dimensions the development of the icotea basin provides an excellent observational basis for understanding the structural history of three sets of regionally extensive faults and testing two models for the formation of pull apart basins in general three main fault trends produced at different periods in the formation of the cretaceous recent maracaibo basin are mapped using 3d seismic data in the central part of the basin 1 n ne striking normal faults including the icotea fault these faults formed originally during late jurassic early cretaceous rifting and reactivated as left lateral strike slip faults during late paleocene eocene convergent deformation between the caribbean and south american plates 2 nw striking faults formed by late paleocene eocene overthrusting of the caribbean plate and downward flexure of the south american plate to create a major foreland basin depocenter and 3 ne striking normal faults of pre cretaceous age were reactivated during late paleocene eocene plate convergence three dimensional architecture of the icotea basin interpreted from five time slices through the basin and its flank areas supports the simple pull apart model for the eocene opening of the icotea basin the amount of extension across the suite of normal faults ranges between 0 8 and 2 25 km this range of offset is consistent with some previous estimates of minor left lateral displacement along the icotea fault but is inconsistent with either low angle or high angle thrusting during eocene time as inferred from previous interpretations of widely spaced two dimensional seismic lines the normal faults that formed the pull apart basin reactivated pre existing faults due to plate flexure

current states of stress in the northern andes as indicated by focal mechanisms of earthquakes abstract systematic inversion of double couple focal mechanisms of shallow earthquakes in the northern andes reveals relatively homogeneous patterns of crustal stress in three main regions the first region presently under the influence of the caribbean plate includes the northern segment of the eastern cordillera of colombia and the western flank of the central cordillera north of 4 n it is characterized by wnw ese compression of dominantly reverse type that deflects to nw se in the merida andes of venezuela where it becomes mainly strike slip in type a major bend of the eastern thrust front of the eastern cordillera near its junction with the merida andes coincides with a local deflection of the stress regime sw ne compression suggesting local accommodation of the thrust belt to a rigid indenter in this area the second region includes the sw pacific coast of colombia and ecuador currently under the influence of the nazca plate in this area approximately e w compression is mainly reverse in type it deflects to wsw ene in the northern andes south of 4 n where it is accommodated by right lateral displacement of the romeral fault complex and the eastern front of the northern andes the third and most complex region is the area of the triple junction between the south american nazca and caribbean plates it reveals two major stress regimes both mainly strike slip in type the first regime involves sw ne compression related to the interaction between the nazca and caribbean plates and the panama micro plate typically accommodated in an e w left lateral shear zone the second regime involves nw se compression mainly related to the interaction between the caribbean plate and the north andes block which induces left lateral displacement on the uramita and romeral faults north of 4 n deep seismicity about 150 170 km concentrates in the bucaramanga nest and cauca valley areas the inversion reveals a rather homogeneous attitude of the minimum stress axis which dips towards the e this extension is consistent with the present plunge of the nazca and caribbean slabs suggesting that a broken slab may be torn under gravitational stresses in the bucaramanga nest this model is compatible with current blocking of the subduction in the western northern andes inhibiting the eastward displacement of slabs which are forced to break and sink in to the asthenosphere under their own weight

tsunami waveform inversion including dispersive waves the 2004 earthquake off kii peninsula japan 1 long waves are often assumed to model tsunamis but the wavelength of the initial water height distribution produced by a large submarine earthquake particularly in the direction perpendicular to the fault strike is sometimes not much greater than the water depth the resulting tsunami may have a dispersive character that cannot be simulated based on a conventional long wave approximation the 2004 earthquake off kii peninsula m 7 4 on the southern coast of japan indeed produced a dispersive tsunami that was recorded at two stations located off shikoku for the foreshock m 7 1 on the contrary a dominant dispersive tsunami was not recognized at these stations because dispersive waves show strong directional dependence with respect to the fault strike the above difference indicates that the strikes of the main shock and the foreshock were different we conducted a tsunami waveform inversion analysis based on the dispersive tsunami equations to estimate the initial water height distribution of the main shock the estimated initial water height distribution overlapped with the aftershock region suggesting that the fault strike was perpendicular to the trough axis and the total displaced water volume was 1 7 2 0 109 m3 when we used the conventional long wave approximation the estimated initial water height distribution extended considerably from the aftershock area because artificial sources were needed outside the aftershock area to reproduce the observed dispersive waves

on the long term context for late twentieth century warming 1 previous tree ring based northern hemisphere temperature reconstructions portray a varying amplitude range between the medieval warm period mwp little ice age lia and present we describe a new reconstruction developed using largely different methodologies and additional new data compared to previous efforts unlike earlier studies we quantify differences between more traditional std and regional curve standardization rcs methodologies concluding that rcs is superior for retention of low frequency trends continental north american versus eurasian rcs series developed prior to merging to the hemispheric scale cohere surprisingly well suggesting common forcing although there are notable deviations e g fifteenth to sixteenth century results indicate clear mwp warm lia cool and recent warm episodes direct interpretation of the rcs reconstruction suggests that mwp temperatures were nearly 0 7c cooler than in the late twentieth century with an amplitude difference of 1 14c from the coldest 1600 1609 to warmest 1937 1946 decades however we advise caution with this analysis although we conclude as found elsewhere that recent warming has been substantial relative to natural fluctuations of the past millennium we also note that owing to the spatially heterogeneous nature of the mwp and its different timing within different regions present palaeoclimatic methodologies will likely flatten out estimates for this period relative to twentieth century warming which expresses a more homogenous global fingerprint therefore we stress that presently available paleoclimatic reconstructions are inadequate for making specific inferences at hemispheric scales about mwp warmth relative to the present anthropogenic period and that such comparisons can only still be made at the local regional scale

cretaceous to holocene structural and stratigraphic development in south lake maracaibo venezuela inferred from well and three dimensional seismic data the subsurface of the southern part of the maracaibo basin has been studied in much less detail than the central and northern basin because hydrocarbon rich rocks of cretaceous and paleogene age are deeply buried to a depth of 4 5 km 2 7 mi by a thick neogene clastic section eroded off of surrounding mountain ranges in this article we describe the results of the interpretation of 1600 km2 617 mi2 three dimensional 3 d seismic reflection data centered on this horizontal to monoclinally southwestward dipping middle cretaceous to holocene section adjacent to a zone of northwestward overthrusting along the mountain front of the mrida andes to establish the structural and stratigraphic history of the 3 d seismic study area a series of time slices were constructed at key horizons through the 3 d seismic volume the ages of units in these time slices were correlated to stratigraphic formations known from outcrops at the basin edges well data from the 3 d seismic study area and subsurface correlation with better studied areas in the northern basin the type and orientations of structures along each time horizon were mapped to constrain the successive structural and stratigraphic events that affected the different tectonosequences in the southern maracaibo basin the main tectonic events recorded both by structures and unconformity bound tectonosequences include the following events from youngest to oldest 1 pliocene holocene shortening produced by the uplift of the mrida andes and overthrusting at the mountain front has produced an approximately 6 km 3 7 mi deep localized foredeep basin the axial traces of these folds trend northeast southwest and parallel the strike of a set of normal faults all structural features are consistent with regional northwest southeast shortening a low angle thrust fault responsible for the formation of the main northeast southwest fold is inferred to continue downdip as a flat lying thrust that may be continuous with low angle thrust faults observed along the northern mrida andes mountain front the level of thrust detachment occurs at the cretaceous coln shale and accommodates a negligible amount of shortening 500 m 1640 ft 2 late miocene pliocene shortening caused by uplift of the sierra de perij and the mrida andes produced an inversion of north south striking normal faults and folds in a parallel orientation the axial traces of these folds and the trend of inverted structures coincide with the trends of the most prolific eocene sandstone reservoirs in the central and northern lake maracaibo areas 3 late paleocene middle eocene formation of a foreland basin is related to the southward overthrusting at the northeastern margin of the basin normal faults with an average trend of s37e record flexure of the basin during this event faults also include the southern splayed termination of the left lateral icotea strike slip fault 4 the termination of the icotea fault in the south lake area is consistent with the small amount of left lateral strike slip displacement previously inferred from the geometry of the eocene icotea pull apart basin in central lake maracaibo

trench investigation on the main strand of the bocono fault in its central section at mesa del caballo merida andes venezuela the mesa del caballo trench assessment confirms the holocene activity of the main strand of the bocono fault at the apartaderos pull apart basin fifteen earthquakes of which fourteen have been radiocarbon dated have been recognized spanning the last 20 500 yr recurrence intervals of these 7 magnitude events are variable the dominant mode of recurrence is 400 450 yr and the second one is 900 yr eventually some events are 1400 1800 yr apart we suspect that our seismic record may be incomplete this could be easily justified by several conditions most of the earthquake recognitions is based on open crack filling and they superpose spatially eventually masking or destroying older fills trenching may miss some events because the fault is made of en echelon riedel shears and a short return period may lead to faint differences between paleosoils few hundreds years of age apart this trench also images an older activity of the fault as evidenced by plentiful earthquake triggered liquefaction features as well as slumping and rotational sliding by comparing paleoseismic results between the morro de los hoyos and mesa del caballo trenches it appears that both fault strands bounding the apartaderos pull apart basin move simultaneously besides the main strand also coseismically slips twice in between those common events in other words the seismic scenario could be that the northern strand recurs every 1200 1350 yr while the southern does every 400 450 yr this is also in agreement with a respective slip share of 25 and 75 of the 9 10 mm yr average slip of the bocono fault in the merida andes central sector

summer temperatures in the canadian rockies during the last millennium a revised record we present a significant update to a millennial summer temperature reconstruction 1073 1983 that was originally published in 1997 utilising new tree ring data predominantly picea engelmannii the reconstruction is not only better replicated but has been extended 950 1994 and is now more regionally representative calibration and verification statistics were improved with the new model explaining 53 of may august maximum temperature variation compared to the original 39 of april august mean temperatures the maximum latewood density data which are weighted more strongly in the regression model than ringwidth were processed using regional curve standardisation to capture potential centennial to millennial scale variability the reconstruction shows warm intervals comparable to twentieth century values for the first half of the eleventh century the late 1300s and early 1400s the bulk of the record however is below the 1901 1980 normals with prolonged cool periods from 1200 to 1350 and from 1450 to the late 19th century the most extreme cool period is observed to be in the 1690s these reconstructed cool periods compare well with known regional records of glacier advances between 1150 and the 1300s possibly in the early 1500s early 1700s and 1800s evidence is also presented of the influence of solar activity and volcanic events on summer temperature in the canadian rockies over the last 1 000 years although this reconstruction is regional in scope it compares well at multi decadal to centennial scales with northern hemisphere temperature proxies and at millennial scales with reconstructions that were also processed to capture longer timescale variability this coherence suggests that this series is globally important for the assessment of natural temperature variability over the last 1 000 years

assessment of three temperature reconstruction methods in the virtual reality of a climate simulation the performance of statistical climate reconstruction methods in the pre instrumental period is uncertain as they are calibrated in a short instrumental period but applied to much longer reconstructions time spans here the virtual reality created by a climate simulation of the past millennium with the model echo g is used as a test bed of three methods to reconstruct the annual northern hemisphere temperature the methods are composite plus scaling the inverse regression method of mann et al nature 392 779 787 1998 and a direct principal components regression method the testing methodology is based on the construction of pseudo proxies derived from the climate model output the application of each of these methods to pseudo proxy timeseries and the comparison of their result with the simulated mean temperature different structures of the noise have been used to construct pseudo proxies ranging from the simulated grid point precipitation also one sparse and one denser pseudo proxy network co located with two real networks have been considered all three methods underestimate the simulated variations of the northern hemisphere temperature but the composite plus scaling method clearly displays a better performance and is robust against the different noise models and network size the most relevant factor determining the skill of the reconstruction appears to be the network size whereas the different noise models tend to yield similar results

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

asynchronous miocene pliocene exhumation of the central venezuelan andes constraining the uplift and exhumation history of the venezuelan andes is critical for understanding the complex geodynamic evolution of northern south america we present new apatite fission track aft data from the sierra nevada de merida in the central venezuelan andes and compare the results with previously published aft data for the sierra la culata el carmen block to the north the aft data are combined with three dimensional thermal modeling to constrain the exhumation and relief history of both blocks which show significant differences the sierra nevada indicates exhumation rates of 1 7 km m y from ca 10 ma until 4 ma decreasing to 0 4 km m y from 4 ma to present the el carmen block in contrast underwent much more rapid recent exhumation with rates of 1 4 km m y since 4 ma the data suggest 4 km of relative rock uplift of the sierra la culata with respect to the sierra nevada since 4 ma and support significant uplift of basement blocks along major preexisting discontinuities during transpression in the northern andes linked to accretion of the panama arc and indentation of the maracaibo block rapid middle late miocene exhumation in the sierra nevada resulted from surface uplift that caused the late miocene deflection of the orinoco river inferred from the neogene sedimentary record

volcanic cooling signal in tree ring temperature records for the past millennium the authors acknowledge the national science foundation for funding much of the research presented herein rw s scottish work is currently funded through the uk leverhulme trust and natural environment research council nerc projects relic reconstructing 8000 years of environmental and landscape change in the cairngorms f 00 268 bg and scot2k reconstructing 2000 years of scottish climate from tree rings ne k003097 1

effects of bathymetry on tsunami propagation application of ray tracing to tsunamis ray tracing of seismic surface waves is applied to tsunami propagation to examine bathymetric effect along its propagation path computations are made for trans pacific tsunamis and for near field tsunamis in the japan sea for tsunamis across the pacific ocean the comparison to a uniform ocean shows that focusing and defocusing due to bathymetry are significant for some combinations of source and receiver for example the refraction of rays is predominant at the east pacific rise for the tsunami from chile the tsunamis in the japan sea are strongly affected by the shallow yamato rise the predicted arrival time and amplitude distribution generally agree with the observations from an actual tsunami since the computation can be made very quickly the method is useful for preliminary analysis of tsunami propagation such as in an operational warning system or in the determination of computational area for finite difference computation

geodynamics of the northern andes subductions and intracontinental deformation colombia new regional seismological data acquired in colombia during 1993 to 1996 and tectonic field data from the eastern cordillera ec permit a reexamination of the complex geodynamics of northwestern south america the effect of the accretion of the baudo panama oceanic arc which began 12 myr ago is highlighted in connection with mountain building in the ec the istmina and ibague faults in the south and the santa marta bucaramanga fault to the northeast limit an e se moving continental wedge progressive indentation of the wedge is absorbed along reverse faults located in the foothills of the cordilleras northward of 5 n and transpressive deformation in the santander massif crustal seismicity in colombia is accurately correlated with active faults showing neotectonic morphological evidences intermediate seismicity allows to identify a n ne trending subduction segment beneath the ec which plunges toward the e se this subduction is interpreted as a remnant of the paleo caribbean plateau pcp as suggested by geological and tomographic profiles the pcp shows a low angle subduction northward of 5 2 n and is limited southward by a major e w transpressive shear zone normal oceanic subduction of the nazca plate np ends abruptly at the southern limit of the baudo range northward the np subducts beneath the choco block overlapping the southern part of the pcp cenozoic shortening in the ec estimated from a balanced section is 120 km stress analysis of fault slip data in the ec northward of 4 n indicates an e se orientation of 1 in agreement with the pcp subduction direction northward near bucaramanga two stress solutions were observed 1 a late andean n80 e compression and 2 an early andean nw se compression

summer temperature variations in the european alps a d 755 2004 abstract annually resolved summer temperatures for the european alps are described the reconstruction covers the a d 755 2004 period and is based on 180 recent and historic larch larix decidua mill density series the regional curve standardization method was applied to preserve interannual to multicentennial variations in this high elevation proxy dataset instrumental measurements from high low elevation grid boxes back to 1818 1760 reveal strongest growth response to current year june september mean temperatures the reconstruction correlates at 0 7 with high elevation temperatures back to 1818 with a greater signal in the higher frequency domain r 0 8 low elevation instrumental data back to 1760 agree with the reconstruction s interannual variation although a decoupling between warmer instrumental and cooler proxy data before 1840 is noted this offset is larger than during any period of overlap with more recent high elevation instrumental data even though the proxy time series

graben inversion in nature and experiments the inversion of crustal scale basement grabens is studied here through laboratory experiments on small scale models and available oil industry seismic lines from the southern north sea two basic configurations are considered first both the basement and the sedimentary cover are brittle and inversion does not involve any potential decollement between them second the basement and sedimentary cover are separated by a weak ductile layer e g salt which can allow decollement of the cover during both extension and later compression and inversion the second configuration is more complicated and can lead to a large variety of geological structures laboratory experiments were carried out on brittle ductile models built with sand to represent brittle layers basement and sedimentary cover and silicone putty to simulate the decollement layer between basement and cover a mechanically based classification of inversion structures is proposed the effects of some crucial parameters are investigated including obliquity between the direction of shortening and normal faults as well as strength profiles and the presence or absence of salt diapirs the experimental investigation leads to the following conclusions 1 the inversion of the graben by reactivation of normal faults implies that the angle between the direction of compression and the graben is less than 45 2 if there is a superficial decollement e g basement cover interface inversion initiates low dipping thrust faults in the cover localized at graben borders 3 salt diapirs or salt walls localized along the graben borders in the cover are preferential sites for the development of thrust faults and 4 when the cover is decoupled from the basement by a decollement layer inversion induced deformation in the cover which is partitioned between thrust faults along the graben borders and strike slip faults within the graben trending oblique to the graben borders experimental results are compared with field examples in particular from the southern north sea

spatial and temporal relationships between compression strike slip and extension in the central venezuelan andes clues for plio quaternary tectonic escape abstract the geometry of tectonic structures attributed to the neogene quaternary time interval is described in the active setting of the venezuelan andes our methodology is based on the analysis of radar satellite and digital elevation model imagery complemented by structural fieldwork and the compilation of seismotectonic data to make a structural analysis on a regional scale radar images provide first class data for morphostructural analysis in areas of dense vegetation and frequent cloud covering like the venezuelan andes we focused our analysis in the burbusay rio momboy and bocono faults corner located in the central part of the belt we have described three stages of deformation during the neogene quaternary the first one mio pliocene in age is a nw se compression responsible for the uplift of the venezuelan andes the second tectonic stage corresponds to a strike slip regime of deformation marked by shearing along the bocono burbusay and valera faults which separates two triangular wedges in the larger trujillo block this strike slip faulting dominated compressional extensional tectonic regime allowed the trujillo crustal block to move towards the ne wrenching has therefore started at some point between the pliocene and the quaternary these two tectonic events are consistent with ongoing strain partitioning in the venezuelan andes the third stage corresponds to extensional deformation limited to the trujillo block and is still active today extension is associated with the motion of crustal blocks moving relative to each other probably above the upper lower crust boundary such extensional deformation can be understood considering that the crust extends and stretches at the same time as it moves towards the ne the combination of both horizontal lateral motion and extension is characteristic of a tectonic escape process the northeastward escape of the trujillo block which belongs to the larger north andes block occurs as a result of the combination of the nw se intracontinental convergence between the south american plate and the maracaibo block and the presence to the north of the caribbean oceanic plate considered as a free boundary we have showed that the kinematics of the caribbean plate offers not only a favorable environment but may also be considered as the driving force of the tectonic escape of the north andes block

paleomagnetism and magnetic fabric of the eastern cordillera of colombia evidence for oblique convergence and nonrotational reactivation of a mesozoic intracontinental rift we report the paleomagnetic and magnetic fabric results of 58 sites from cretaceous miocene marine and continental strata from the eastern cordillera ec and the cucuta zone at the junction between the santander massif and the merida andes of colombia the ec is an intracontinental doubly vergent range inverting a triassic to early cretaceous rift zone twenty three sites reveal nonsystematic tectonic rotations including unrotated areas of the ec range with respect to stable south america our data show that the ec inverted a nne oriented rift zone and that the orientation of the mesozoic rift and the mountain chain roughly correspond interestingly magnetic lineations from anisotropy of magnetic susceptibility analysis do not trend parallel to the chain but rather are oblique to the main orogenic trend by also considering gps evidence of a 1 cm yr ene displacement of central western colombia accommodated by the ec we suggest that the miocene recent deformation event of this belt arises from ene oblique convergence reactivating a nne oriented rift zone oblique shortening was likely partitioned into pure dip slip shear characterizing thick skinned frontal thrust sheets well known along both chain fronts and by range parallel right lateral strike slip faults which have not been identified yet but likely exist in the axial part of the ec finally the 35 9 clockwise rotation observed in four post miocene magnetically overprinted sites from the cucuta zone reflects late cenozoic and ongoing right lateral strike slip displacement occurring along faults parallel to the bocono fault system possibly connected with the right lateral faults inferred to exist along the axial part of the ec

tsunami waveform inversion for sea surface displacement following the 2011 tohoku earthquake importance of dispersion and source kinematics this paper considers the importance of model parameterization including dispersion source kinematics and source discretization in tsunami source inversion we implement single and multiple time window methods for dispersive and nondispersive wave propagation to estimate source models for the tsunami generated by the 2011 tohoku oki earthquake our source model is described by sea surface displacement instead of fault slip since sea surface displacement accounts for various tsunami generation mechanisms in addition to fault slip the results show that tsunami source models can strongly depend on such model choices particularly when high quality open ocean tsunami waveform data are available we carry out several synthetic inversion tests to validate the method and assess the impact of parameterization including dispersion and variable rupture velocity in data predictions on the inversion results although each of these effects has been considered separately in previous studies we show that it is important to consider them together in order to obtain more meaningful inversion results our results suggest that the discretization of the source the use of dispersive waves and accounting for source kinematics are all important factors in tsunami source inversion of large events such as the tohoku oki earthquake particularly when an extensive set of high quality tsunami waveform recordings are available for the tohoku event a dispersive model with variable rupture velocity results in a profound improvement in waveform fits that justify the higher source complexity and provide a more realistic source model

plio quaternary extension in the venezuelan andes mapping from sar jers imagery abstract the geometry of extensional structures is described for the first time in the active setting of the venezuelan andes using remote sensing imagery we favored the use of a mosaic of synthetic aperture radar sar scenes of the japanese earth resources satellite 1 jers 1 assisted by complementary remote sensing devices landsat tm digital elevation models and field observations to make a structural analysis at regional scale radar images are particularly efficient in the venezuelan andes where dense vegetation and frequent cloud covering earlier lent difficulties to remote sensing studies we focused our analysis in the valera rio momboy and bocono faults corner and in the mucujun area we show that in an area where ongoing compression and strike slip deformations occur brittle extension can be detected independently from previous knowledge extensional structures correspond to elongated tilted blocks with dimension less than 10 km in width blocks are bounded by curved faults in plan view the concavity being turned towards the axial part of the belt the geometry and kinematics of such structures suggest that syn orogenic extension started together with initiation of right lateral strike slip motion along the bocono fault in the plio quaternary

pleistocene slip rates on the bocono fault along the north andean block plate boundary venezuela the bocono fault is a strike slip fault lying between the north andean block and the south american plate which has triggered at least five mw 7 historical earthquakes in venezuela the north andean block is moving toward nne with respect to a stable south american plate this relative displacement at 12 mm yr 1 in venezuela within the maracaibo block was measured by geodesy but until now the distribution and rates of quaternary deformation have remained partially unclear we used two alluvial fans offset by the bocono fault yaracuy valley to quantify slip rates by combining 10be cosmogenic dating with measurements of tectonic displacements on high resolution satellite images pleiades based upon a fan dated at 79 ka and offset by 1350 1580 m and a second fan dated at 120 273 ka and offset by 1236 1500 m we obtained two pleistocene rates of 5 0 11 2 and 20 0 mm yr 1 consistent with the regional geodesy this indicates that the bocono fault in the yaracuy valley accommodates 40 to 100 of the deformation between the south american plate and the maracaibo block as no aseismic deformation was shown by insar analysis we can assume that the fault is locked since the 1812 event this implies that there is a slip deficit in the yaracuy valley since the last earthquake ranging from 1 to 4 m corresponding to a mw 7 7 6 earthquake this magnitude is comparable to the 1812 earthquake and to other historical events along the bocono fault

quaternary fault kinematics and stress tensors along the southern caribbean from fault slip data and focal mechanism solutions deformation along the southern caribbean coast as confirmed by the compilation of stress tensors derived from fault plane kinematic indicators microtectonics and further supported by focal mechanism solutions herein presented results from a compressive strike slip transpressional senso lato regime characterized by a nnw sse maximum horizontal stress 1h 11 and or an ene wsw minimum 1h 13 or 12 horizontal stress which is responsible for present activity and kinematics of six sets of brittle features east west right lateral faults nw se right lateral faults synthetic riedel shears ene wsw to east west dextral faults p shears nnw sse normal faults almost north south left lateral faults antithetic riedel shears and ene wsw reverse faults sub parallel to fold axes and mostly in the subsurface the latter ones being associated to ene wsw trending folding in this particular region the brittle deformation obeys the simple shear model although not all the deformation can be accounted for it since partitioning is also taking place regional folding and thrusting is essentially due to the normal to structure component of the partitioned maximum horizontal stress conversely the maximum horizontal stress on

a matter of divergence tracking recent warming at hemispheric scales using tree ring data 1 no current tree ring tr based reconstruction of extratropical northern hemisphere enh temperatures that extends into the 1990s captures the full range of late 20th century warming observed in the instrumental record over recent decades a divergence between cooler reconstructed and warmer instrumental large scale temperatures is observed we hypothesize that this problem is partly related to the fact that some of the constituent chronologies used for previous reconstructions show divergence against local temperatures in the recent period in this study we compiled tr data and published local regional reconstructions that show no divergence against local temperatures these data have not been included in other large scale temperature reconstructions utilizing this data set we developed a new completely independent reconstruction of enh annual temperatures 1750 2000 this record is not meant to replace existing reconstructions but allows some degree of independent validation of these earlier studies as well as demonstrating that tr data can better model recent warming at large scales when careful selection of constituent chronologies is made at the local scale although the new series tracks the increase in enh annual temperatures over the last few decades better than any existing reconstruction it still slightly under predicts values in the post 1988 period we finally discuss possible reasons why it is so difficult to model post mid 1980s warming provide some possible alternative approaches with regards to the instrumental target and detail several recommendations that should be followed in future large scale reconstruction attempts that may result in more robust temperature estimates

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget