a simple multicloud parameterization for convectively coupled tropical waves part i linear analysis abstract recent observational analysis reveals the central role of three multicloud types congestus stratiform and deep convective cumulus clouds in the dynamics of large scale convectively coupled kelvin waves westward propagating two day waves and the madden julian oscillation a systematic model convective parameterization highlighting the dynamic role of the three cloud types is developed here through two baroclinic modes of vertical structure a deep convective heating mode and a second mode with low level heating and cooling corresponding respectively to congestus and stratiform clouds a systematic moisture equation is developed where the lower troposphere moisture increases through detrainment of shallow cumulus clouds evaporation of stratiform rain and moisture convergence and decreases through deep convective precipitation a nonlinear switch is developed that favors either deep or congestus convection depending on the relative dryness of the troposphere in particular a dry troposphere

propagation and the vertical structure of the madden julian oscillation abstract the madden julian oscillation mjo dominates tropical variability on time scales of 30 70 days during the boreal winter spring it is manifested as an eastward propagating disturbance with a strong convective signature over the eastern hemisphere the space time structure of the mjo is described using the national centers for environmental prediction national center for atmospheric research reanalysis advanced very high resolution radiometer outgoing longwave radiation observed sea surface temperature and the climate prediction center merged analysis of precipitation empirical orthogonal function analysis is used to identify the convective signature of the mjo and regression is used to identify key relationships with the convection compared to analyzing successive years of data the selection of years of strong mjo activity results in a more robust lead lag structure and an increase in explained variance the mjo exhibits a rich vertical structure with low level moisture convergence bein

planetary scale selection of the madden julian oscillation in an air sea coupled dynamic moisture model the authors present an air sea coupled dynamic moisture asdm model to explore the mechanism of preferred planetary scale of the madden julian oscillation mjo this asdm model extended from the original frictionally coupled dynamic moisture model and a mixed layer model can present a good simulation of planetary scale characteristics of the mjo including a slow eastward propagation of 5 m s 1 coupled rossby kelvin wave like structure and phase leading of convective center by warm sea surface temperature sst it is interesting that the planetary scale selection in terms of instability is only found in the nonlinear asdm model with the assumption of positive only heating such a scale selection however cannot be found in the asdm model with linear heating or in an uncoupled atmosphere model the essential mechanism for the scale selection is nonlinear positive only heating and the air sea interaction primarily provides an instability source to support this scale selection this scale selection is attributed to different phase speeds of coupled moist rossby kelvin waves and dry kelvin waves from short wave initial perturbations the easterly wind anomalies of eastward propagating dry kelvin waves from a stronger wave component will catch up with other weaker moist components and suppress their westerly wind anomalies resulting in weak sst gradient as well as reduced moisture convergence and precipitation for these suppressed components as a result the wavenumber one structure is selected the warm pool like mean state will select the stronger component among the initial short wave perturbations and accelerate this scale selection process these results provide new insight into mjo mechanism in terms of air sea interaction

a multiscale model for tropical intraseasonal oscillations the tropical intraseasonal 40 to 50 day oscillation tio is the dominant component of variability in the tropical atmosphere with remarkable planetary scale circulation generated as envelopes of complex multiscale processes a new multiscale model is developed here that clearly demonstrates the fashion in which planetary scale circulations sharing many features in common with the observational record for the tio are generated on intraseasonal time scales through the upscale transfer of kinetic and thermal energy generated by wave trains of organized synoptic scale circulations having features in common with observed superclusters the appeal of the multiscale models developed below is their firm mathematical underpinnings simplicity and analytic tractability while remaining self consistent with key features of the observational record the results below demonstrate in a transparent fashion the central role of organized vertically tilted synoptic scale circulations in generating a planetary circulation resembling the tio

interaction of deep and shallow convection is key to madden julian oscillation simulation 1 this study investigates the role of the interaction between deep and shallow convection in mjo simulation using the ncar cam3 two simulations were performed one using a revised zhang mcfarlane convection scheme for deep convection and the hack scheme for shallow convection and the other disallowing shallow convection below 700 mb in the tropical belt the two simulations produce dramatically different mjo characteristics while the control simulation produces realistic mjos the simulation without shallow convection has very weak mjo signals in the indian ocean and western pacific composite analysis finds that shallow convection serves to precondition the lower troposphere by moistening it ahead of deep convection it also produces enhanced low level mass convergence below 850 mb ahead of deep convection this work together with previous studies suggests that a correct simulation of the interaction between deep and shallow convection is key to mjo simulation in global climate models

pre columbian agriculture in the bolivian lowlands construction history and management of raised fields in bermeo abstract recent archaeological research suggests that some parts of the amazon basin were significantly modified by pre columbian populations one of the most impressive examples of such transformations is the raised fields of south western amazonia in the llanos de moxos in the bolivian lowlands despite a growing interest in raised field agriculture due to the important role it seems to have played in the development of pre columbian complex societies very few field based investigations have been performed in the amazon basin as a result there is limited knowledge of how these fields were constructed managed and within which time frame they were in use this study provides a new interpretation of how pre columbian raised fields were managed and a chronological sequence of their utilisation and eventual abandonment fieldwork was carried out in the indigenous community of bermeo in the vicinity of san ignacio de moxos where some of the best preserved fields in the llanos moxos are found magnetic susceptibility and the geochemistry of the sediments combined with radiocarbon and optically stimulated luminescence dating show that the raised fields were in intermittent use since as early as ad 570 770 the original surface on which the fields were built and distinct periods of construction and use have been identified the data suggests that raised fields were built during a few separate construction events probably linked to periods of more frequent and severe floods the study challenges the most widely accepted theory that suggests that pre columbians were able to cultivate these fields on a continuous basis by transferring nutrient rich sediments from the canals to the fields we conclude that pre columbians built raised fields to overcome periods of increased flooding with the main objective of improving drainage

role of the boundary layer moisture asymmetry in causing the eastward propagation of the madden julian oscillation the moisture budget associated with the eastward propagating madden julian oscillation mjo was diagnosed using 1979 2001 40 yr ecmwf re analysis era 40 data a marked zonal asymmetry of the moisture relative to the mjo convection appears in the planetary boundary layer pbl below 700 hpa creatingapotentiallymoreunstablestratificationtotheeastofthemjoconvectionandfavoringtheeastward propagation of mjo the pbl integrated moisture budget diagnosis indicates that the vertical advection of moisture dominates the low level moistening ahead of the convection a further diagnosis indicates that the leading term in the vertical moisture advection is the advection of the background moisture by the mjo ascending flow associated with pbl convergence the cause of the zonally asymmetric pbl convergence is further examined it is found that heating induced free atmospheric wave dynamics account for 75 90 of the total pbl convergence while the warm sst anomaly induced by air sea interaction contributes 10 25 of the total pbl convergence the horizontal moisture advection also plays a role in contributing to the pbl moistening ahead of the mjo convection the leadingterm in the moistureadvectionis the advectionacross the backgroundmoisture gradient by the mjo flow in the western indian ocean maritime continent and western pacific the meridional moisture advection by the mjo northerly flow dominates while in the eastern indian ocean the zonal moisture advection is greater the contribution of the moisture advection by synoptic eddies is in generalsmall ithas a negativeeffect overthetropicalindianoceanand westernpacificandbecomespositive in the maritime continent region

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

the dynamics of back arc extension an experimental approach to the opening of the tyrrhenian sea the e w opening tyrrhenian sea developed after the cretaceous palaeogene alpine collision nearly perpendicular to the motion of the african plate as a back arc of the adria ionian westward subduction three driving mechanisms have been proposed to explain the dynamic evolution of the tyrrhenian apennine system 1 the northward indentation of the african plate 2 the retreating subduction of the adria ionian lithosphere and 3 the gravitational collapse of the alpine post collisional wedge in order to define the relative contribution of each of these mechanisms in the neogene dynamic of the tyrrhenian apennine system we performed 3 d laboratory experiments in which we simulated a retreating subduction process in a compressional regime oriented perpendicularly to the direction of subduction in this framework we also tested the influence of the gravitational collapse of the overriding plate experiments were constructed using dry sand and silicone putties to simulate brittle upper crust and ductile lower crust upper mantle respectively these layers floated on a high density low viscosity glucose syrup which simulated the asthenosphere the main conclusion of our experiments is that large scale continental extension similar to that observed in the tyrrhenian area could be reproduced perpendicular to the shortening direction induced by the indentation of the african plate in this framework extensional processes are indeed possible if the trench retreat velocity is higher than the rate of shortening induced by the advancing african plate our experimental results indicate that this high trench retreat velocity could be explained by the coexistence of the gravitational collapse of the post alpine wedge with a slab pull process linked to the retreating subduction of the adria ionian plate while the first mechanism is predominant in the northern tyrrhenian area the second one seems to be important in the latest stage of extension and oceanic accretion of the southern tyrrhenian area

horizontal crustal motion in the central and eastern mediterranean inferred from satellite laser ranging measurements four campaigns to acquire satellite laser ranging slr measurements at sites in the mediterranean region have been completed these measurements to the lageos satellite made largely by mobile systems cover a time span beginning in november 1985 and ending in june 1993 the range data from 18 sites in the central and eastern mediterranean have been simultaneously analyzed with data acquired by the remainder of the global laser tracking network estimates of horizontal motion were placed into a regional northern europe fixed kinematic reference frame uncertainties are on the order of 5 mm yr for sites having at least four occupations by mobile systems and approach 1 mm yr for permanently located sites with long histories of tracking the resulting relative motion between sites in the aegean exhibit characteristics of broadly distributed pattern of radial extension but at rates that are about 50 larger than those implied from studies of seismic strain rates based on seismicity of magnitude 6 or greater or across the region the motion estimated for sites in turkey exhibit velocity components associated with the westward motion of the anatolian block relative to eurasia these results provide a present day snapshot of ongoing deformational processes as experienced by the locations occupiedmore by slr systems less

three dimensional modelling of crustal motions caused by subduction and continental convergence in the central mediterranean summary crustal deformation in the central mediterranean is modelled by means of 3 d finite element models assuming a viscoelastic rheology the tectonic mechanisms under investigation are subduction of the ionian oceanic lithosphere beneath the calabrian arc and continental convergence between the african and eurasian blocks very long baseline interferometry vlbi data at the station noto in sicily and the results from global models of plate motions are taken as representative of the motion of the african plate with respect to eurasia while vlbi solutions at matera and medicina in the southern and northern parts of the italian peninsula are geodetic observations that must be compared with modelling results vertical deformation rates are taken from geological and tide gauge records the model that best fits the observations includes the effects of subduction in the southern tyrrhenian and convergence between africa and europe the overthrusting of the tyrrhenian domain onto the adriatic domain results in an eastward component of the velocity at the eastern border of the tyrrhenian domain in agreement with vlbi data from the matera and medicina stations and gps data from northeastern sicily and the eolian islands the highest subsidence rates are obtainedinthe southern tyrrhenian and are of the order of 1 2 1 4 mm yr 1 along the whole adriatic coast of the italian peninsula subsidence in the foredeeps is of the order of 0 2 0 5 mm yr 1 the apenninic chain is rising with rates of the order of 0 2 0 4 mm yr 1 subduction beneath the calabrian arc is responsible for a roll back velocity higher than in the northern areas 2 d models built for the geological past indicate the possibility of roll back velocities of several centimetres per year in particular active rifting in the tyrrhenian and softening of the crust in the back arc basin result in a trench retreat velocity in agreement with geological estimates our results show that numerical modelling can be used to estimate present day deformation rates and the contribution of active tectonics to sea level changes along coastal areas

a simple multicloud parameterization for convectively coupled tropical waves part ii nonlinear simulations observations in the tropics point to the important role of three cloud types congestus stratiform and deep convective clouds besides ubiquitous shallow boundary layer clouds for both the climatology and large scale organized anomalies such as convectively coupled kelvin waves two day waves and the madden julian oscillation recently the authors have developed a systematic model convective parameterization highlighting the dynamic role of the three cloud types through two baroclinic modes of vertical structure a deep convective heating mode and a second mode with lower troposphere heating and cooling corresponding respectively to congestus and stratiform clouds the model includes both a systematic moisture equation where the lower troposphere moisture increases through detrainment of shallow cumulus clouds evaporation of stratiform rain and moisture convergence and decreases through deep convective precipitation and also a nonlinear switch that favors either deep or congestus convection depending on whether the lower middle troposphere is moist or dry here these model convective parameterizations are applied to a 40 000 km periodic equatorial ring without rotation with a background sea surface temperature sst gradient and realistic radiative cooling mimicking a tropical warm pool both the emerging walker cell climatology and the convectively coupled wave fluctuations are analyzed here while various parameters in the model are varied the model exhibits weak congestus moisture coupled waves outside the warm pool in a turbulent bath that intermittently amplify in the warm pool generating convectively coupled moist gravity wave trains propagating at speeds ranging from 15 to 20 m s 1 over the warm pool while retaining a classical walker cell in the mean climatology the envelope of the deep convective events in these convectively coupled wave trains often exhibits large scale organization with a slower propagation speed of 3 5 m s 1 over the warm pool and adjacent region occasional much rarer intermittent deep convection also occurs outside the warm pool the realistic parameter regimes in the multicloud model are identified as those with linearized growth rates for large scale instabilities roughly in the range of 0 5 k day 1

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

dynamic models of subduction geophysical and geological evidence in the tyrrhenian sea summary predictions based on a 2 d finite element model for subduction underneath the calabrian arc in southern italy are compared with a variety of geophysical and geological data such as the present day stress pattern within the slab uplift from the elevation of marine terraces in calabria and subsidence in the tyrrhenian marsili basin from odp leg 107 we model the behaviour of the slab driven by slab pull in agreement with the present tectonic style in this part of the mediterranean as suggested by several investigators the model accounts for the crustal lithospheric and mantle structures in a vertical cross section perpendicular to the calabrian subduction zone the shape of the slab is constrained on the basis of new tomographic images in the southern tyrrhenian sea which were obtained from the regional seismic stations of the istituto nazionale di geofisica while the rheological properties of the mantle are taken from global dynamic models density contrasts between the subducted slab and the surrounding mantle based on petrological models drive the flow in our viscoelastic model stress values displacements and vertical velocities at the surface are sampled at different times after loading until dynamic equilibrium is reached our estimates are appropriate for a time window of 100 kyr the validity of our comparison with the geological record is based on the assumption that the tectonic configuration in the past was not substantially different from that of the present day two families of models with unlocked and locked subduction faults are considered the unlocked models allow for roll back of the trench of about 20 mm yr in agreement with some geological estimates the same family of models predicts uplift of the calabrian arc of about 1 mm yr l and subsidence in the marsili basin of 1 2 mm yr in agreement with geological surveys the deviatoric stress obtained from the unlocked model is consistent with the continuous distribution of deep seismicity in the southern tyrrhenian sea with minor concentration within the lithospheric wedge locked models fail to reproduce these geophysical and geological observations predictions derived from a detached slab model are not consistent with the continuous hypocentral distribution of deep seismicity in the southern tyrrhenian sea deformation at the surface and the stress patterns at depth for a detached slab differ substantially from those of a continuous plate dynamic topography and horizontal motions are reduced when compared with the continuous plate with deviatoric stresses concentrated within the relict slab our results indicate that subduction is a major tectonic process in the southern tyrrhenian sea

subduction related intermediate depth and deep seismicity in italy insights from thermal and rheological modelling geological data suggest that after a period of oceanic lithosphere subduction about 170 km of continental lithosphere were subducted under the northern apennines since about 23 myear at rates of ca 1 cm year whereas more than 700 km of mesozoic oceanic lithosphere ionian lithosphere have been subducted under the calabrian arc at rates of about 3 cm year however a well developed wadati benioff zone can be only recognised below the calabrian arc down to depths of 450 500 km whereas intermediate depth seismicity reaches maximum depths of about 90 km under the northern apennines we model the thermal state of these two subduction zones and apply temperature dependent non linear rheological laws to evaluate the down dip extent of brittle regions in the two subduction zones we show that differences in subduction rate and in slab composition continental vs oceanic produce a far deeper down to 290 380 km brittle field in the colder calabrian slab than in the warmer northern apenninic slab 70 120 km thus explaining differences in the maximum depth of seismicity in both regions concerning deep earthquakes in the calabrian subduction zone models predict that metastable olivine persists down to depths of 430 km this could possibly explain the maximum depth of earthquakes in the area the small extent of the metastable olivine wedge produces a small density anomaly that cannot explain the pervasive down dip compression observed in the ionian slab 2004 elsevier b v all rights reserved

the role of surface friction in tropical intraseasonal oscillation abstract the role of surface friction in the tropical intraseasonal oscillation or the madden julian oscillation mjo is investigated by comparing two 4 yr integrations with the goddard atmospheric general circulation model one with the original model design with one added feature to enhance the intensity of the mjo and the other is identical but with surface friction in the tropics replaced by its zonal mean value this comparison indicates that in the second experiment the mjo not only still exists but also exists with similar intensity the oft cited frictional wave cisk fwc interpretation for the origin of the mjo which emphasizes the role of frictionally induced convergence in the surface layer is reassessed in light of these experiments the possibility of the mjo in the second experiment being forced by the middle latitudes is excluded by a third experiment these experiments do not support one of the central ideas in fwc that surface friction plays an instability enhancing role

an idealized semi empirical framework for modeling the madden julian oscillation abstractthe authors present a simple semi empirical model to explore the hypothesis that the madden julian oscillation can be represented as a moisture mode destabilized by surface flux and cloud radiative feedbacks the model is one dimensional in longitude the vertical and meridional structure is entirely implicit the only prognostic variable is column water vapor w the zonal wind field is an instantaneous diagnostic function of the precipitation field the linearized version of the model has only westward propagating relative to the mean flow unstable modes because wind induced surface latent heat flux anomalies occur to the west of precipitation anomalies the maximum growth rate occurs at the wavelength at which the correlation between precipitation and surface latent heat flux is maximized this wavelength lies in the synoptic to planetary scale range and is proportional to the horizontal scale associated with the assumed diagnostic wind response to precipitation anomalies the nonlinear version

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

the importance of subduction for the modern stress field in the tyrrhenian area the tyrrhenian sea was formed by lithospheric extension in a context of continental convergence between africa and eurasia at present a compilation of strain and stress indicators in this region by rebai et al 1992 shows that an extensive regime is still predominant in the tyrrhenian sea while northern italy and southern sicily are undergoing compression this tectonic configuration is the result of two major contributions which act on a very heterogeneous lithosphere the africa eurasia collision on the one hand and the subduction along the calabrian arc on the other the latter is expected to create a trench suction force on the overriding tyrrhenian plate the objective of this paper is to investigate the relative importance of these contributions using a numerical model developed by p bird 1989 based on an improved version of the thin plate approach which models lithospheric deformation in an horizontal plane the results of this model demonstrate the necessity of considering the forces related to subduction to understand the modern stress and strain field an extrusion mechanism alone cannot explain present day observations the salient features of the current tectonic regime are reproduced by the model which however predicts more limited extension than expected further work will be needed to find a better tuning of the parameters and ascertain the quality of available data

asymmetric intraseasonal events in the stochastic skeleton mjo model with seasonal cycle the stochastic skeleton model is a simplified model for the madden julian oscillation mjo and intraseasonal planetary variability in general involving coupling of planetary scale dry dynamics moisture and a stochastic parametrization for the unresolved details of synoptic scale activity the model captures the fundamental features of the mjo such as the intermittent growth and demise of mjo wave trains the mjo propagation speed peculiar dispersion relation quadrupole vortex structure etc we analyze here the solutions of a stochastic skeleton model with an idealized seasonal cycle namely a background warm pool state of heating moistening displacing meridionally during the year the present model considers both equatorial and off equatorial components of the envelope of synoptic scale convective activity which allows for a large diversity of meridionally symmetric and asymmetric intraseasonal events found in nature these include examples of symmetric events with mjo quadrupole vortex structure half quadrupole events with off equatorial convective heating structure as well as tilted events with convective heating structure oriented north westward and associated northward propagation that is reminiscent of the summer monsoon intraseasonal oscillation the model also reproduces qualitatively the meridional migration of intraseasonal variability during the year that approximatively follows the meridional migration of the background warm pool

stresses and plate boundary forces associated with subduction plate margins primary tectonic stress in the lithosphere is predominantly caused by lateral density variations within the earth and associated topographical loading when such a stress system caused by major sublithospheric density anomalies is intersected by a weak zone which cuts across the lithosphere plate boundary forces develop and modify the plate interior stresses in this paper unite element analysis is used to model the stresses and plate boundary forces associated with subduction plate boundaries with dipping and vertical slabs extending to about 270 and 400 km depths having the subduction fault both locked and unlocked in such regions several types of horizontal deviatoric stress may occur including 1 local compression in the trench arc region caused by the dense sinking slab and the associated surface downflexure 2 plate interior tension which occurs when this compression is intersected by a weak subduction fault 3 local tension associated with thickening of the crust at the arc and elsewhere 4 local tension in the back arc region produced by the underlying low density upper mantle and 5 downbending stresses in the subducting slab thermal stresses and transmitted ridge push which are not included in the modelling here a gradient from compression in the forearc to tension in the back arc can be modelled in terms of these stresses when the fault is partially locked it is however the intersection of the local compression 1 by an unlocked or partially locked subduction fault that modifies the plate interior stresses and gives rise to the slab pull and trench suction plate boundary forces the state of stress in the interior of the overriding plate is also crucially influenced by back arc spreading where this occurs plate boundary forces have been evaluated for each of the models it is shown that slab pull and trench suction may be of comparable magnitude

modeling tropical convergence based on the moist static energy budget abstract the vertically integrated moist static energy equation provides a convenient starting point for the construction of simple models of the time mean low level convergence in the tropics a vertically integrated measure of the moist static stability the gross moist stability proves to be of central importance minima in this quantity mark the positions of the tropical convergence zones we argue that the positions of these minima are determined by the time mean moisture field which is in turn closely tied to the time mean surface temperature

plio quaternary vertical motion of the northern apennines insights from dynamic modeling we test the effects of different geodynamic mechanisms on the pliocene to present day dynamics and in particular on the vertical motions of the northern apennines system by means of two dimensional finite element models we show that the pliocene features of the northern apennines exhumation of deep rocks in western italy and fast subsidence rates in the adriatic foredeep can be adequately reproduced by a model slab characterized by the passive sinking of a negatively buoyant adriatic slab and by the upwelling of buoyant asthenosphere beneath western italy model slab is however not able to account for the quaternary and present day pattern of vertical motion of eastern italy and of the adriatic basin a deep configuration of the system characterized by a detached slab model detach may explain the vertical motions of these areas constrained by uplift of the eastern portions of the apenninic chain by an eastward shift of the foredeep depocenter and by lower subsidence rates in the adriatic basin the tectonic and stratigraphic data showing major differences between the tertiary and the quaternary evolution of the northern apennines are discussed

propagating versus nonpropagating madden julian oscillation events abstractbasinwide convective anomalies over the indian ocean io associated with the madden julian oscillation mjo sometimes propagate eastward and reach the west pacific wp but sometimes do not long term observations and reanalysis products are used to investigate the difference between the propagating and nonpropagating mjo events io convection onset events associated with the mjo are grouped into three categories based on the strengths of the simultaneous dry anomalies over the eastern maritime continent and wp the io convection anomaly preferentially makes eastward propagation and reaches the wp when the dry anomaly is stronger analysis of the column integrated moist static energy mse budget shows that horizontal advection moistens the atmosphere to the east of the positive mse anomaly associated with the active convection over the io and is of sufficient magnitude to explain the eastward propagation of the positive mse anomaly interpretation is complicated however by lack of closure in

modern tectonic regime in the tyrrhenian area observations and models summary the rapid opening since 10 ma of the tyrrhenian sea in a context of convergence between eurasia and africa remains a puzzling geodynamic problem one of the most plausible scenarios proposed by malinverno ryan 1986 attributes extension to southward and eastward migration of the trench resulting from subduction of the african adriatic lithosphere below the european lithosphere at present subduction only continues along the calabrian arc a compilation of recent strain and stress indicators by rebai philip taboada 1992 indicates that an extensional regime still prevails in the tyrrhenian sea whereas compression dominates north and south of this area in an earlier paper bassi sabadini 1994 used a numerical model to demonstrate the necessity of a trench suction force acting along the subduction trench to produce the present extension in the tyrrhenian domain this study however did not discuss in detail the tectonic regime in the different areas composing the domain nor the match between the observations and the model in this paper we first review the constraints provided by the observations compiled by rebaiet al 1992 and by more recent measurements we then investigate how much of the observed tectonic regime can be understood in terms of plate interaction forces using thin plate models bird 1989 the geometry and heterogeneous lithospheric properties of the models are constrained by observations the best constrained boundary conditions are held constant the remaining are regarded as parameters that we tune in order to fit the observations our results indicate that the present day tectonic regime in the tyrrhenian area can be explained as a consequence of trench retreat associated with the subduction of ionian oceanic lithosphere under the calabrian arc combined with a rotation of the apennines possibly related to a rotation of the adriatic microplate this study supports therefore the model of malinverno ryan 1986 and suggests moreover that rotation of the apennines is an ongoing process which is supported by seismological and geodetic data but remains to be understood in terms of geodynamics a discrepancy between observations and models is observed in western sicily which can be attributed to modelling limitations the weak extensional activity of the corsica sardinia block however is not explained by this model

thermo mechanical modeling of the tyrrhenian sea lithospheric necking and kinematics of rifting we present the results of quantitative forward modeling of the sardinian rifted margin of the tyrrhenian sea the purpose of this study is to investigate the thermo mechanical structure that affects the thinning of the lithosphere across the margin the role of lithospheric necking during basin formation constrained by basement topography moho depth and gravity anomalies is modeled for different compensation models independent constraints are obtained from the analysis of the predicted thermal structure a deep level of necking 25 km is required to explain the observed crustal geometries and gravity anomaly signature the model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning prerift lithospheric conditions strain rate and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the tyrrhenian sea a forward model for basin stratigraphy is presented for the polyphase history of the tyrrhenian rifting this model provides quantitative estimates of time space dependent crustal thinning and rates of extension

phase transformations in a harzburgite composition to 26 gpa implications for dynamical behaviour of the subducting slab abstract the mineralogy adopted by a depleted harzburgite composition has been studied over the pressure interval 5 26 gpa at temperatures of 1300 1400 c the pyroxene garnet component of the harzburgite composition harzburgite minus 82 wt olivine transforms to majorite garnet by 18 19 gpa and further disproportionates to the assemblage of garnet stishovite mg 2 sio 4 spinel above 20 gpa at still higher pressures first ilmenite 22 24 gpa and then perovskite mgsio 3 24 26 gpa are found to coexist with garnet garnet disappears at 26 gpa and almost complete transition to perovskite is achieved at this pressure the mineral proportions and density profiles in the subducting oceanic lithosphere modelled by a combination of 80 harzburgite 20 primitive morb compositions are calculated as a function of depth under conditions isothermal with surrounding pyrolite mantle and also for a temperature distribution in which the slab is substantially cooler than surrounding mantle to below 700 km under isothermal conditions the slab has a density similar to surrounding mantle to a depth of 600 km however between 600 and 700 km the slab is up to 0 08 g cm 3 denser than surrounding mantle this is caused primarily by the higher alumina content in pyrolite as compared to harzburgite which causes the transition to perovskite in pyrolite to occur at substantially higher pressures than in harzburgite the presence of alumina also smears out the garnet perovskite transition in pyrolite over a depth interval of 50 km whereas this transformation is much sharper in the harzburgite composition calculations based on the observed phase equilibria also show that a subducted cool slab remains much denser by 0 1 0 3 g cm 3 than surrounding mantle to a depth of 700 km but possesses a density similar to surrounding mantle below this depth these results have important implications for the dynamical behaviour of slabs possessing different thermal regimes when they encounter the 670 km discontinuity and also for the nature of this discontinuity

free surface formulation of mantle convection ii implication for subduction zone observables summary viscous and viscoelastic models for a subduction zone with a faulted lithosphere and internal buoyancy can self consistently and simultaneously predict long wavelength geoid highs over slabs short wavelength gravity lows over trenches trench forebulge morphology and explain the high apparent strength of oceanic lithosphere in trench environments the models use two different free surface formulations of buoyancydriven flows see for example part i lagrangian viscoelastic and pseudo free surface viscous formulations the lower mantle must be stronger than the upper in order to obtain geoid highs at long wavelengths trenches are a simple consequence of the negative buoyancy of slabs and a large thrust fault decoupling the overriding from underthrusting plates the lower oceanic lithosphere must have a viscosity of less than pa s in order to be consistent with the flexural wavelength of forebulges forebulges are dynamically maintained by viscous flow in the lower lithosphere and mantle and give rise to apparently stiffer oceanic lithosphere at trenches with purely viscous models using a pseudo free surface formulation we find that viscous relaxation of oceanic lithosphere in the presence of rapid trench rollback leads to wider and shallower back arc basins when compared to cases without viscous relaxation moreover in agreement with earlier studies the stresses necessary to generate forebulges are small 100 bars compared to the unrealistically high stresses needed in classic thin elastic plate models

excitation of true polar wander by subduction true polar wander the global motion of the mantle relative to the earth s rotation axis is known from the analysis of palaeomagnetic data hotspot tracks and plate motions to have occurred at velocities of up to 0 5 myr 1 since the late cretaceous period1 4 we address here the longstanding question of how fast episodes of true polar wander tpw can be excited5 by analysing the impact of the distribution and activity of subduction zones on polar motion using nonlinear liouville equations which allow us to treat large excursions of the polar axis we show that unrealistically fast tpw is excited by subduction episodes unless the lower mantle has a viscosity at least 10 times that of the upper mantle this need for a viscosity increase with depth in the mantle reinforces the conclusions of previous studies on post glacial rebound and geoid anomalies theoretical creep laws and some preliminary results on tpw induced by density anomalies embedded in the mantle6 10 the lower viscosity in the upper mantle means that upper mantle density anomalies are most effective in exciting tpw changes in the pattern of subduction through time may be responsible for both episodes of fast tpw and times of quiescence in polar motion

fundamental causes of propagating and nonpropagating mjos in mjotf gass models abstractthis study investigates the fundamental causes of differences in the madden julian oscillation mjo eastward propagation among models that participated in a recent model intercomparison project these models are categorized into good and poor groups characterized by prominent eastward propagation and nonpropagation respectively column integrated moist static energy mse budgets are diagnosed for the good and the poor models it is found that a zonal asymmetry in the mse tendency characteristic of eastward mjo propagation occurs in the good group whereas such an asymmetry does not exist in the poor group the difference arises mainly from anomalous vertical and horizontal mse advection the former is attributed to the zonal asymmetry of upper midtropospheric vertical velocity anomalies acting on background mse vertical gradient the latter is mainly attributed to the asymmetric zonal distribution of low tropospheric meridional wind anomalies advecting background mse and moisture fields base

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

spatial variation of present day stress field and tectonic regime in tunisia and surroundings from formal inversion of focal mechanisms geodynamic implications for central mediterranean we compiled 123 focal mechanisms from various sources for tunisia and adjacent regions up to sicily to image the current stress field in the maghrebides chain from tunisia to sicily and its foreland stress inversion of all the available data provides a first order stress field with a n150 e horizontal compression shmax and a transpressional tectonic regime but the obtained stress tensor poorly fit to the data set we separated them into regional subsets boxes in function of their geographical proximity kinematic regime homogeneity of kinematic orientations and tectonic setting their respective inversion evidences second and third order spatial variations in tectonic regime and horizontal stress directions the stress field gradually changes from compression in the maghrebides thrust belt to transpression and strike slip in the atlassic and pelagian foreland respectively where preexisting nw se to e w deep faults system are reactivated this spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data the major slab transfer edge propagator faults i e north south axis hammamet relay and malte escarpment which laterally delimit the subducting slabs play an active role in second and third order lateral variations of the tectonic regime and stress field orientations over the tunisian sicilian domain the past and current tectonic deformations and kinematics of the central mediterranean are subordinately guided by the plate convergence i e africa eurasia controlled or influenced by lateral slab migration segmentation and by deep dynamics such as lithosphere mantle interaction

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

a coupled moisture dynamics model of the madden julian oscillation convection interaction with first and second baroclinic modes and planetary boundary layer a theoretical model with a single prognostic variable column integrated moist static energy mse was constructed to understand the dynamics of mjo eastward propagation and planetary scale selection a key process in the model is the interaction of mse dependent convection with free atmospheric first second baroclinic modes and planetary boundary layer under a realistic parameter regime the model reproduces the most unstable mode at zonal wavenumber 1 with a slow eastward phase speed of about 5 ms 1 the slow eastward phase speed in the model arises from the competition of eastward moving mse tendencies caused by horizontal mse advection vertical mse advection and boundary layer moistening with westward moving tendencies contributed by surface latent heat flux and atmospheric longwave radiative heating the planetary scale selection is primarily attributed to the phase lag of longwave radiative heating associated with upper level stratiform clouds that occur in the rear of mjo deep convection

seismic strain and seismogenic stress regimes in the crust of the southern tyrrhenian region abstract an investigation has been performed to identify and characterize the seismic deformation zones active over the last decades in the region of italy that has experienced the strongest seismicity during the last centuries the study is based on the estimate of hypocenter locations fault plane solutions seismogenic stress and seismic strain tensor orientations carried out using the entire dataset of the national and local seismic networks and the recently improved three dimensional 3d crustal velocity model of the study area a series of simulation tests have been performed to evaluate the significance of the earthquake space distribution obtained and whether it was influenced by network geometry problems related to the sea and the lack of ocean bottom seismometers in the sectors where hypocentral location was synthetically proved to be reliable space distributions of earthquakes located with epicenter and focal depth errors less than 3 and 4 km respectively have been compared with local geology in order to identify seismogenic faults the dataset of 32 fault plane solutions estimated with fault parameter errors less than 20 has been used to investigate space variations of seismogenic stress and seismic strain orientations over the study area stress was found to be uniform in the messina strait and southern calabria where inversion of the available set of 11 fault plane solutions showed clear evidence of an extensional regime the different orientations of the minimum compressive stress and strain found in this sector together with the information available on local geology and tectonics lead us to propose that the seismicity occurring over the last decades in the messina strait and southern calabria was not in general produced at the main faults but at minor faults activated by the main tectonic stress field acting in the area to the west in the sector including western etna the nebrodi chain and the western aeolian islands analysis of the available set of 16 fault plane solutions revealed a certain degree of stress heterogeneity with an apparent prevalence of north south compression this east to west change of stress strain regimes is evaluated in the light of current hypotheses regarding the geodynamics of the study region

when did sardinia stop rotating new palaeomagnetic results previous palaeomagnetic results from tertiary volcanic rocks of sardinia suggest that the island underwent a quick counterclockwise rotation between 20 5 and 19 ma in order to test this hypothesis a new palaeomagnetic study was carried out on sediments and volcanic rocks with well controlled biostratigraphic or radiometric ages younger than the suggested age for the end of the rotation unrotated palaeomagnetic directions obtained from the upper ignimbrites radiometric age 18 5 19 7 myr and the aquitanian tuffs collected in the anglona region n sardinia would suggest that the rotation ended earlier than 20 5 myr the directions found in the volcanics are perhaps the result of secular variation rather than differential rotation of the anglona region with respect to surrounding regions two sites belonging to the upper ignimbritic unit si2 in the monte traessu monte rispisu area logudoro region exhibited a large amount of rotation d 320 4 i 60 which may be age related radiometric age 19 9 myr four dikes radiometric age 18 3 16 7 myr in the arcuentu volcanic complex arburese region yield results d 348 4 i 33 8 that indicate a further amount of rotation after their emplacement stable end point directions were successfully isolated from three upper burdigalian langhian sedimentary sites biostratigraphic age 18 15ma from the marmilla and logudoro regions consistent paleomagnetic directions obtained from these sites d 352 i 49 indicate that a small amount of rotation was still to be completed in the langhian time this result is consistent with the history of sardinian volcanism which did not end until 13 ma

macro anisotropy of the electrical conductivity of the crust a magnetotelluric study of the german continental deep drilling site ktb summary the interpretation of magnetotelluric mt data collected in the vicinity of the german continental drilling project ktb has revealed two major structures in the earth s crust first a large scale mid crustal layer of enhanced conductivity is required to fit the regional observations of the anomalous vertical magnetic field second the mt impedances of the area close to the ktb namely the crustal unit of the zone erbendorf vohenstraus zev support a model with a highly anisotropic upper to middle crust the extremely high values of anisotropy derived from the mt measurements exceed the values of anisotropy observed on rock samples in the laboratory by an order of magnitude and therefore exclude intrinsic features as a source for the observed anisotropy the regional mid crustal conductor is in agreement with central europe wide observations of high conductivity layers in the crust while the proposed model of well conducting subvertical dykes within a resistive host rock explains the mt observations and agrees with the steeply dipping seismic reflectors the downhole and core observations from the drilling and the model of the tectonic development of this area however the superposition of both structures leaves some unanswered questions

modern tectonic stress field in the mediterranean region evidence for variation in stress directions at different scales summary a compilation of more than one thousand stress indicators which include in situ stress measurements focal mechanisms microtectonic and other geological data allowed us to reconstruct the modern stress field in the mediterranean region and the surrounding area average stress directions at different scales have been reconstructed by means of a linear interpolation method this method takes into account the distribution scale and quality of stress data the results of the interpolation at plate scale allow us to recognize slightly deformed regions such as the northwestern european platform where average maximum horizontal stress direction is oriented roughly nnw sse subparallel to absolute and relative plate velocity directions other regions such as the caucasus alps and pyrenees where recent tectonic deformation and seismicity are present display important variations of stress directions the reconstruction of the average stress directions at different scales within the french alps pointed out that the average stress field pattern may vary from one scale to another nevertheless variations of stress directions at a given scale are consistent with the kinematics of faults of the same scale

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

the structure and propagation of intraseasonal oscillations appearing in a gfdl general circulation model abstract the three dimensional structure and temporal evolution of quasi periodic planetary scale tropospheric oscillations simulated by a 15 wavenurnber gcm are investigated by applying cross spectral eigenvector composite and temporal correlation techniques to 12 years of model output evident from this diagnostic study is the presence in the model tropics of well defined eastward traveling features with spatial scales of zonal wavenumbers 1 and 2 and with temporal scales of 25 40 and 15 20 days respectively the flow pattern associated with the oscillations of both spatial scales is characterized by circulation cells oriented along the equatorial zonal plane with the zonal wind and geopotential height fluctuations near the sea level being negatively correlated with the corresponding fluctuations in the upper troposphere the movement of these zonal circulation cells along the equatorial bell is accompanied by systematic migration of the global scale horizontal divergence field and by dipole like

impact of rossby and kelvin wave components on mjo eastward propagation abstractthere are contrasting views concerning the impact of rossby wave component of mjo flow on its eastward propagation one view called drag effect argues that because rossby waves propagat

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

seismic deformation in the mediterranean area estimated by moment tensor summation summary theoretical relationships allow the distributed deformation due to seismic activity to be quantified on the basis of the analysis of moment tensors we apply this method to a data set consisting of seismic events that have occurred in the past 85 yr 1908 1992 along the most important seismogenic zones of the mediterranean region we use the centroid moment tensor cmt catalog prepared at harvard university covering the last 16yr and older data from jackson mckenzie 1988 we determine the seismic deformation and compare it to estimates of the overall deformation as obtained from global plate motion and geological studies we generally find that the geometry of seismic deformation is similar to tectonic predictions even though spanning a shorter time interval the cmt catalog often gives a better estimate of deformation geometry than the whole data set 85yr seismic deformation generally ranges from less than 10 per cent to more than 90 per cent of the total deformation uncertainties arise because data sets may not be representative of the long term seismic behaviour of each zone more reliable estimates for comparison with geodynamic processes should result from analysis of a longer time period for which no instrumental data are available the similarity of the deformation geometry using cmt data with tectonic expectations suggests for several zones the possibility of using historical data to infer longer term deformation rates based on current deformation geometry

seismicity and p wave velocity image of the southern tyrrhenian subduction zone summary this paper focuses on the deep earth structure and earthquake distribution within the southern tyrrhenian subduction zone we discuss seismological observations which provide insight into the mechanics of subduction processes for an unusual compressional margin the motivation for this work derives from the recognition that little is known about one of the most intriguing geodynamic features of the italian peninsula and the fact that a large amount of information can be extracted from data collected by the istituto nazionale di geofisica national seismic network we show that the hypocentres of intermediate and deep earthquakes that have occurred since 1988 image a nw dipping plane continuous from the ionian sea to the tyrrhenian down to 450 km depth we also present a 3 d model of the deep structure beneath southern italy derived using deep earthquake seismic tomography tomographic images reveal a high velocity body dipping from the apulian and iblean forelands towards the tyrrhenian basin in the crust and upper mantle at least down to 320 km depth this high velocity body may be related to the cold subducted ionian lithosphere earthquake hypocentres are confined within the high velocity body delineating the subduction beneath the calabrian arc

the role of subduction on the horizontal motions in the tyrrhenian basin a numerical model the horizontal motions in the tyrrhenian basin and surrounding chains induced by subduction along the calabrian arc and northern apennines are analyzed by means of numerical models based on finite element techniques the driving mechanism in 2 dimensional vertical cross sections perpendicular to the trench is the slab pull due to the negative buoyancy of a stratified viscoelastic plate that models the ionic oceanic lithosphere or adriatic plate sinking in the upper mantle for the modern tectonic setting of the area we test the sensitivity of extension in the back arc and of roll back of the overriding plate to variations in the viscosity structure and in the geometry of subduction our results are compared with extensional velocities inferred from geology and slr vlbi data

interplay between subduction and continental convergence a three dimensional dynamic model for the central mediterranean summary the mediterranean region is attracting considerable attention due to the complexities of its tectonic setting which is considered worldwide a unique natural laboratory for studying the occurrence of extensional tectonics in a general context of continental convergence the tyrrhenian apennine system is controlled by the west dipping subduction of the adria ionian lithosphere and by the near north south convergence between the african and eurasian plates we provide the first 3 d dynamic model of the central mediterranean that quantifies the effects of subduction and convergence on surface deformation in simplified geometry the axis of the model extends from sicily to the alps along the subduction hinge line a convergence rate of 1 cm yr 1parallel to the subduction hinge has been applied to the tyrrhenian block in agreement with global plate motion models density contrasts within the slab cause the gravitational sinking and roll back of the slab in the southern tyrrhenian domain modelling results show a gradual decrease of hinge retreat from south to north with values ranging between 8 and 2 mm yr 1 indicating that the arculate geometry of the hinge line along the italian peninsula is ultimately controlled by the interplay between subduction and convergence the pattern of vertical velocity along directions perpendicular to the hinge with subsidence in the foredeeps and uplift at the eastern border of the tyrrhenian domain is maintained along the whole italian peninsula with higher values in the southern areas

subcrustal earthquakes in the northern apennines italy evidence for a still active subduction previously unreported subcrustal earthquakes have been located up to 90 km depth beneath the northern apennines italy these earthquakes occur beneath a zone of abundant upper crustal seismicity mostly confined to the upper 20 km of the crust although there are relatively few well located subcrustal earthquakes there appears to be a general southwestward deepening of the hypocenters from the adriatic to the tyrrhenian sea consistent with other geophysical data which suggest that the adriatic lithosphere is presently subducting beneath the northern apennines

constraints on the seismotectonics of the central mediterranean from very long baseline interferometry summary very long baseline interferometry vlbi determined site velocities from seven stations in western europe reveal a stable continental platform north of the alps deformations between sweden germany and spain can not exceed 2 mm yr south of the alps significant motions are occurring with respect to stable europe two sites east of the apennine mountains on peninsular italy have north easttrending velocities which increase from 2 mm yr l in the north at medicina to 6 mm yr l in the south at matera in contrast the vlbi site in the south eastern corner of sicily is moving 7 mm yr i to the north north west these velocities are largely explained if southern sicily is attached to a north westerly moving african plate and the eastern portion of the italian peninsula forms part of a hypothesized adriatic sea crustal block which is rotating counter clockwise with respect to europe about a pole near the alps such an explanation is consistent with the styles of the larger historical earthquakes of the region which show ne sw extension across the apennines north south convergence across the alps and ne sw compression in coastal yugoslavia the adria plate model generates 1 5 2 2 x 10l8 nm yr l of potential earthquake moment along the northern and central apennines historical records suggest that 30 60 per cent of this moment is released seismically based on a direct strain rate measurement recurrence intervals for italian earthquakes south of medicina are estimated to be 12 46 yr for m6 5 quakes and 35 143 years for m7 0 quakes

shear wave attenuation in the lithosphere beneath italy and surrounding regions tectonic implications more than 700 waveforms produced by 51 shallow earthquakes and recorded at regional distances 250 1400 km by the italian seismic network have been analyzed to characterize the amplitude and frequency contents of the crustal and uppermost mantle shear waves lg and sn respectively the crustal phase lg efficiently propagates through the relatively stable adriatic continental crust while it is not observed along propagation paths crossing major physiographic features like the apennine chain and the basinal domain of the tyrrhenian and ionian seas similar to lg efficient sn propagation is observed in the uppermost mantle beneath the po plain and the adriatic sea efficient sn transmission is also observed across the northern ionian sea and sicily and in the area between sardinia and the northern coasts of africa sn are efficiently transmitted across the sicily channel and rather efficient sn propagate beneath the ligurian sea on the contrary inefficient sn transmission characterizes the uppermost mantle beneath the apennines the western margin of the italian peninsula and the southern tyrrhenian sea shear wave attenuation suggests the presence of asthenospheric material in the uppermost mantle probably related to the present day extension along the apennine chain and in the tyrrhenian basin this interpretation is consistent with the presence of extensive neogene and quaternary volcanic activity in these areas and related high heat flow proposed lithospheric delaminatioh processes beneath the apennines and subduction beneath the tyrrhenian sea can reasonably explain the observed high attenuation zones in the uppermost mantle in contrast a high strength mantle lid is inferred to underlay the po plain the adriatic sea and the northern ionian sea the available waveforms also indicate that a continuous mantle lid is present beneath sicily and the extensional domain of the sicily channel as well as in the marine area south of sardinia

the influence of sea surface temperature on the tropical intraseasonal oscillation a numerical study abstract the development and movement of the tropical intraseasonal system tis exhibit remarkable annual variations it was hypothesized that spatial and temporal variation in sea surface temperature sst is one of the primary climatic factors that are responsible for the annual variation of tiss this paper examines possible influences of sst on the tis through numerical experiments with a 2 5 layer atmospheric model on an equatorial plane in which sst affects atmospheric heating via control of the horizontal distribution of moist static energy and the degree of convective instability the gradient of the antisymmetric with respect to the equator component of sst causes a southward propagation of the model tis toward northern australia in boreal winter and a northward propagation over the indian and western pacific oceans in boreal summer the phase speed of the meridional propagation increases with the magnitude of antisymmetric sst gradients the poleward propagation of the equatorial disturba

palaeomagnetic study of cretaceous red beds from the eastern hindukush ranges northern pakistan palaeoreconstruction of the kohistan karakoram composite unit before the india asia collision we report palaeomagnetic results obtained from cretaceous red bed samples collected from the eastern hindukush mountains northern pakistan rock magnetic studies revealed specular haematite as the dominant remanence carrier while pigmentary haematite magnetite and goethite are responsible for the acquisition of secondary magnetizations thermal treatment generally revealed three components of magnetization the most unstable component a was removed between 200 c and 500 c which corresponds to the local present field direction the intermediate component b was generally separated between 200 c and 660 c the omnipresence of this complex secondary component across the northern suture zone suggests that movement of chemically active orogenic fluids at or slightly before the time of the india asia collision was probably responsible for the authigenic remagnetization processes the characteristic component c was generally unblocked between 600 c and 685 c the characteristic directions from 12 sites fall into two groups the sites from the purit formation give a tilt corrected mean direction of d 311 2 i 4 4 k 12 4 95 17 8 indicating a counter clockwise rotation of about 66 and 15 relative to eurasia and india respectively the tilt corrected mean direction for the reshun and drosh formations is d 263 0 i 2 2 k 52 7 95 10 6 which indicates that the sampling area experienced a counter clockwise rotation of about 114 and 63 with respect to eurasia and india respectively in both cases the palaeomagnetic rotation is consistent with the regional superstructure of the hindukush pamir karakoram syntaxial bend the difference in rotation between these two groups is probably due to local tectonic movement caused by the net rotation of thrust sheets along the northern suture zone the palaeolatitudes calculated for purit and reshun drosh formations are 2 2 s and 1 1 n respectively this indicates that about 4000 km of convergence has taken place since the mid cretaceous of which about 90 per cent post dates the india asia collision the late cretaceous inclination values across the northern suture zone are almost identical which indicates that suturing had been completed at the time of chrm acquisition