tomographic images of the el asnam fault zone and the evolution of a seismogenic thrust related fold the p wave velocity structure of the upper 9 km of the el asnam algeria fault zone the site of the ms7 3 earthquake october 10 1980 is obtained by inverting arrival times from 310 selected aftershocks computed crustal structure and relocation of aftershocks yield new insight on the structural geology of the area and help to clarify the evolution of fault related folding and the complexity of the rupture episodes during the el asnam earthquake the correlation between tomograms and geologic structures observed at the surface and inferred at depth delineates local heterogeneities of the upper crust there is evidence for distinct large scale structural trends consisting of two main thrusts with antithetic reverse faults seismic tomography provides reasonable constraints on the el asnam fault related fold geometry pointing out a complex preexisting structure along which the rupture evolution is controlled by the heterogeneous crust we propose that the main shock originated along an inverted normal fault bordering the pre neogene basement lateral lithologic heterogeneities obtained by seismic tomography reflect the fault segmentation and geometrical discontinuities along strike in agreement with the tectonic pattern

shallow subduction beneath italy three dimensional images of the adriatic european tyrrhenian lithosphere system based on high quality p wave arrival times 1 this paper presents a velocity model of the italian central mediterranean lithosphere in unprecedented detail the model is derived by inverting a set of 166 000 pg and pn seismic wave arrival times restricted to the highest quality data available the tomographic images reveal the geometry of the subduction collision system between the european adriatic and tyrrhenian plates over a larger volume and with finer resolution than previous studies we find two arcs of low vp anomalies running along the alps and the apennines describing the collision zones of underthrusting continental lithospheres our results suggest that in the apennines a significant portion of the crust has been subducted below the mountain belt from the velocity model we can also infer thermal softening of the crustal wedge above the subducting adriatic plate in the tyrrhenian back arc region strong and extensive low vp anomalies depict upwelling asthenospheric material the tomographic images also allow us to trace the boundary between the adriatic and the tyrrhenian plates at moho depth revealing some tears in the adriatic ionian subducting lithosphere the complex lithospheric structure described by this study is the result of a long evolution the heterogeneities of continental margins lithospheric underthrusting and plate indentation have led to subduction variations slab tears and asthenospheric upwelling at the present day the high resolution model provided here greatly improves our understanding of the central mediterranean s structural puzzle the results of this study can also shed light on the evolution of other regions experiencing both oceanic and continental subduction

small fluctuations in the density and thickness of a dry firn column it is of practical importance to have a description on time scales of 1 100 years of the relationship between the mass imbalance of an ice sheet and its rate of change of thickness in this paper a linearized treatment off the relationship is described closed form expressions are derived that relate the time variant density in an isothermal firn layer to the fluctuations in accumulation rate and density that occur at the surface these expressions are used to provide a spectral description of the contribution of surface accumulation and surface density fluctuations to the rate of change of thickness of an ice sheet using these the contribution of firn densification to the variability of ice sheet thickness is examined as a function of the time interval over which the ice sheet is observed this contribution is illustrated for sites in antarctica and greenland it is concluded that it is important to give greater attention than hitherto to the spatial scale of accumulation fluctuations if satellite observations of ice sheet elevation change are to be used to estimate ice sheet imbalance over short time intervals

african easterly wave variability and its relationship to atlantic tropical cyclone activity abstract automatic tracking of vorticity centers in european centre for medium range weather forecasts analyses has been used to develop a 20 yr climatology of african easterly wave activity the tracking statistics at 600 and 850 mb confirm the complicated easterly wave structures present over the african continent the rainy zone equatorward of 15 n is dominated by 600 mb activity and the much drier saharan region poleward of 15 n is more dominated by 850 mb activity over the atlantic ocean there is just one storm track with the 600 and 850 mb wave activity collocated based on growth decay and genesis statistics it appears that the 850 mb waves poleward of 15 n over land generally do not get involved with the equatorward storm track over the ocean instead there appears to be significant development of 850 mb activity at the west african coast in the rainy zone around 10 n 10 w which it is proposed is associated with latent heat release based on the tracking statistics it has been shown th

relationship between tropical easterly waves and precipitation during the north american monsoon abstract relationships between tropical easterly waves tews and precipitation over mexico and the united states are examined during the north american monsoon nam the national centers for environmental prediction national center for atmospheric research reanalysis data are used to identify 137 tews that cross mexico north of 20 n after monsoon onset over a 31 yr period from 1975 to 2005 mean precipitation anomalies over two day periods both before and after tew passage are determined using climate prediction center daily precipitation analyses results indicate that positive precipitation anomalies occur along the west coast of mexico and extending into the west central united states in association with tew passage negative precipitation anomalies are found in the south central united states these precipitation anomaly patterns share many similarities to precipitation anomaly patterns previously defined in association with gulf surge events on longer time scales correlations between the total nu

recent seismicity and tomographic modeling of the mount etna plumbing system the monitoring of seismic activity in eastern sicily southern italy has been recently improved in the framework of the poseidon project to investigate both tectonics and volcanic processes of mount etna this effort has produced a homogeneous and complete data set which we use to image the deep structure of the volcano and to define the space and time distribution of the recent seismicity encompassing the 1995 eruption diffuse eruptions between 1995 and 1997 a further magma intrusion started in 1997 and an increase of volcanic activity in july 1998 we inverted p wave arrival times from 307 selected local earthquakes to obtain a three dimensional velocity model of the volcano with a simultaneous inversion for hypocenters and velocity parameters the new tomographic images permit us to define the structure beneath the volcano from the surface down to 18 km depth the main structural feature revealed by our inversion is a high velocity body located beneath the central craters whose lateral extent increases from 6 km between 18 and 9 km depth to 12 km between 9 and 3 km depth near the surface the fast anomaly branches in two separate high vp regions which are located below the summit craters and the eastern flank valle del bove respectively the high velocity features are interpreted as high density cumulates of solidified magma that intruded the shallow crust we hypothesize that magma ascends the crust within the relatively small high velocity conduit below 9 km depth and is stored at depth shallower than 9 km within the broad high velocity region as also suggested by petrological data a sharp increase of seismicity in 1997 with earthquakes occurring at the border of the high velocity body suggests that mount etna sustained recent episodes of intrusions which possibly herald future eruptions no large low velocity anomaly interpretable as a melted magma chamber is imaged in the upper 18 km of the crust while a broad low velocity anomaly in the uppermost mantle revealed by regional seismic data possibly indicates the magma source region at depth earthquake occurrence from the deep source to the shallow intrusive area helps to trace the magma migration and the feeding of the volcanic system

an analysis of the landfall of hurricane nora 1997 abstract the changes to the motion and structure of the eastern pacific tropical cyclone nora 1997 during landfall are investigated nora developed south of the mexican coast intensified into a hurricane and made landfall over northwestern mexico and the southwestern united states in this study the authors document the evolution of the structure of nora from a variety of sources observations derived from satellite imagery show the approach of the hurricane to the baja california peninsula and the development of a localized area of mesoscale convection that intensified while moving over the gulf of california the propagation of this convective system became the dominant feature of the landfall and provided heavy precipitation over a region confined to western arizona numerical simulations with the pennsylvania state university national center for atmospheric research mesoscale model version 5 are used to examine the details of the evolution of the observed area of convection over the gulf simulat

crustal structure of northern latium central italy from receiver functions analysis new evidences of a post collisional back arc margin evolution abstract the crustal velocity structure in a region of central apennines of italy at the hinge between the highly stretched portion of the monte argentario promontory and the magmatic province of the tolfa domes complex northern latium is discussed in this study s wave velocities at depth have been constrained by the modeling of p wave receiver functions rf from both temporary and permanent broadband seismic stations the computer 3d vs models show a thin crust 19 25 km made of a shallow and thin sedimentary cover a very high velocity and anisotropic layer related to a metamorphic basement and a low vs anisotropic layer in the middle lower crust above a shallow moho discontinuity modeled at about 20 km depth the volcano tectonic evolution of this portion of tyrrhenian back arc margin has been strongly influenced by its peculiar crustal architecture the low vs layer acted as a shear zone in the middle lower crust during the tyrrhenian extension also helping the development of plio quaternary magmatism our findings potentially give new constraints on the evolution of the area and to the general comprehension of back arc development in collisional regions

the seismic sequence of 30 th may 9 th june 2016 in the geothermal site of torre alfina central italy and related variations in soil gas emissions abstract in the framework of a medium enthalpy geothermal exploitation project seismicity and soil gas emissions have been monitored in the area of castel giorgio torre alfina central italy since 2014 a dedicated local seismic network called remota allows deepening of the knowledge of the natural local seismicity in terms of source mechanisms high quality event localization and magnitude estimation from november 2014 to may 2016 remota recorded 846 seismic events with a magnitude range from md 0 1 to ml 2 8 and with hypocentres between 4 and 8 km depth most of these events occurred in six short lasting clusters on the 30th may 2016 a mw 4 3 earthquake occurred near castel giorgio followed by almost 1700 aftershocks the moment tensor solution for the main shock depicts a wnw ese oriented normal fault with small right lateral strike component an overview of the epicentral distribution of the different clusters recorded since 2014 highlights that the active tectonic structures are orientated principally along the ne sw and wnw ese directions the relocation of the 1957 me 4 9 earthquake suggests that this event occurred in the same fault system as of the 2016 seismic sequence in the study area there is only one natural emergence solfanare emitting a co2 dominated gas having the same chemical and isotopic composition of the gas contained in a cap at the summit of the geothermal reservoir apart from small perturbations no significant compositional variations were recorded during the 2016 seismic sequence in the gas of the solfanare vents that was analyzed continuously by an automatic gas chromatographic station the diffuse soil co2 flux is monitored since 2013 in six target areas located around the future production and reinjection wells in order to assess the level of background natural degassing in all target areas the maximum value of soil co2 flux has been recorded during the 2016 seismic sequence however values remained relatively low maximum 112 g m 2 d 1 and the values of 13c of the emitted co2 25 25 to 24 22 vs pdb indicated a shallow biological origin of the gas by soil respiration only at solfanare high values of diffuse soil co2 flux were recorded up to a maximum of 20125 g m 2 d 1 all the seismicity of the may june 2016 sequence is located above the ml4 1 main event and is distributed on small distinct faults such as at san lorenzo nuovo and acquapendente and triggered by the main shock the source mechanism provided by the full moment tensor indicates that rupture processes at depth probably deviate from a pure normal fault the significant contribution of clvd and isotropic components suggest a possible opening of fluid cracks below the geothermal reservoir hosted in fractured mesozoic limestones in spite of the increase of the co2 flux no significant changes have been observed in the chemical and isotopic composition of the solfanare gas the seismo tectonic scenario indicates that the solfanare fault was not activated kinematics and orientation of the activated faults suggest a relationship with the bolsena caldera collapse

principal component analysis of the summertime winds over the gulf of california a gulf surge index a principal component analysis of the summertime near surface quick scatterometer quikscat winds is used to identify the leading mode of synoptic scale variability of the low level flow along the gulf of california during the north american monsoon season a gulf surge mode emerges from this analysis as the leading eof with the corresponding principal component time series interpretable as an objective index for gulf surge occurrence this index is used as a reference time series for regression analysis and compositing meteorological fields of interest to explore the relationship between gulf surges and precipitation over the core and marginal regions of the monsoon as well as the manifestation of these transient events in the large scale circulation it is found that although seemingly mesoscale features confined over the gulf of california gulf surges are intimately linked to patterns of large scale variability of the eastern pacific itcz and greatly contribute to the definition of the northward extent of the monsoonal rains

upscale effects of deep convection during the north american monsoon abstractthe ability of deep monsoon convection to influence the larger scale circulation over north america is investigated for a 6 day long case study during the 2006 north american monsoon results from rossby wave ray tracing and numerical simulations using the advanced research weather research and forecasting model indicate that north american monsoon convection provides a source region for stationary rossby waves two wave trains are seen in the numerical model simulations with behaviors that agree well with expectations from theory and ray tracing the shorter and faster moving wave train moves eastward from the source region in mexico and reaches the western atlantic within 4 days the longer and slower moving wave train travels northeastward and reaches the coastal new england region within 6 days an upstream tail of anticyclonic vorticity extends westward from the source region into the central pacific ocean the monsoon convection appears to help cut off the low level anticyclonic flow by deve

analysis of local ice crystal growth in snow the structural evolution of snow under metamorphism is one of the key challenges in snow modeling the main driving forces for metamorphism are curvature differences and temperature gradients inducing water vapor transport and corresponding crystal growth which is detectable by the motion of the ice air interface to provide quantitative means for a microscopic validation of metamorphism models a vtk based image analysis method is developed to track the ice air interface in time lapse ct experiments to measure local interface velocities under both isothermal and temperature gradient conditions using estimates of local temperatures from microstructure based finite element simulations a quantitative comparison of measured interface velocities with theoretical expressions is facilitated for isothermal metamorphism the data are compared with a kinetics and a diffusion limited growth law in both cases the data are largely scattered but consistently show a mean curvature dependency of the interface velocity for temperature gradient metamorphism we confirm that the main contribution stems from the temperature gradient induced vapor flux accompanied by effects of mean curvature as a secondary process the scatter and uncertainties are discussed in view of the present theoretical understanding the experimental setup and complications such as mechanical deformations

early formation of preferential flow in a homogeneous snowpack observed by micro ct we performed x ray microtomographic observations of wet snow metamorphism during controlled continuous melting and melt freeze events in the laboratory three blocks of snow were sieved into boxes and subjected to cyclic superficial heating or heating cooling to reproduce vertical water infiltration patterns in snow similarly to natural conditions periodically samples were taken at different heights and scanned results suggest that wet snow metamorphism dynamics are highly heterogeneous even in an initially homogeneous snowpack consistent with previous work we observed an increase with time in the thickness of the ice structure which is a measure of grain size however this was coupled with large temporal scatter between consecutive measurements of the specific surface area and of the statistical moments of grain thickness distributions because of marked differences in the right tail grain thickness distributions did not show shape invariance with time contrary to previous analyses in our experiments wet snow metamorphism showed two strikingly different patterns homogeneous coarsening superimposed by faster heterogeneous coarsening in areas that were affected by preferential percolation of water liquid water movement in snow and fast structural evolution may be thus intrinsically coupled by early formation of preferential flow at local scale these observations suggest that further experiments are highly needed to fully understand wet snow metamorphism and infiltration patterns in a natural snowpack

velocity structure of the vulsinian volcanic complex latium italy from seismic refraction data and three dimensional inversion of travel times we have interpreted three reversed seismic refraction profiles and three related fans in the monti vulsini volcanic complex modelling travel times and amplitudes calculated using the asymptotic ray theory the interpretation of the refraction lines revealed complex structure in the shallow crust 0 7 km characterized by strong lateral heterogeneities the three layer seismic model of the volcanic area is characterized by relatively high p wave velocities generally ranging from 4 0 4 5 km s in the uppermost layer to 6 7 7 1 km s at a depth of about 7 km the upper layer 0 5 2 7 km thick corresponds to the volcanic cover and the upper part of the flysch sequence the depth to the top of the middle layer corresponding to the lower part of the flysch unit and to the meso cenozoic carbonate sequence is very irregular and is strongly controlled by the tectonic evolution of the area the thickness of this layer ranges between 2 2 and 5 0 km the third layer extends beneath the whole vulsinian region and is characterized by high p velocity 6 7 7 1 km s at relatively shallow depth 5 7 km we interpret the high velocity observed in the third layer as being caused by mafic intrusive rocks such as gabbros or by high grade metamorphic rocks such as schists granulates or metatuffs the results of the refraction modelling have been compared with a three dimensional 3 d p velocity model calculated by inverting travel time residuals from explosions and local earthquakes generally close agreement is observed between refraction and inversion models the fan profiles as well as three unreversed refraction profiles and 3 d inversion showed a velocity decrease as low as 5 within the deepest layer in the central part of the volcanic complex the low velocity zone in the central region could be related either to high temperatures and or partial melt in the intrusive or metamorphic body or to the deepening of the top of the third layer

the relationship between tropical easterly waves and surges over the gulf of california during the north american monsoon abstract coastally trapped disturbances which occur over the gulf of california and are commonly referred to as gulf surges are an important mechanism in the transport of low level moisture into the southwestern united states to determine whether or not gulf surges develop in association with the passage of tropical easterly waves as hypothesized in previous studies standard surface observations and european centre for medium range weather forecasts reanalysis data during the months of july and august over a 14 yr period are examined results indicate that tropical easterly wave troughs often cross western mexico 1 3 days prior to surge onset at yuma arizona indicating a strong correlation between these two events this analysis documents yet another mechanism by which the tropics influences convection in the midlatitudes

case study of an intense african easterly wave abstract the life cycle of an intense african easterly wave aew over the african continent is examined using european centre for medium range weather forecasts ecmwf operational analyses meteosat satellite images and synoptic observations this system the strongest aew of 2000 can be tracked from central north africa into the eastern atlantic ocean where it is associated with the genesis of hurricane alberto synoptic analysis of the kinematic and thermodynamic fields is supplemented by analysis of potential vorticity pv allowing exploration at the role of multiple scales in the evolution of this aew the authors analysis promotes the division of the aew life cycle into three distinctive phases i initiation the aew development is preceded by a large convective event composed of several mesoscale convective systems over elevated terrain in sudan this convection provides a forcing on the baroclinically and barotropically unstable state that exists over tropical north africa ii baroclini

on the anatomy of magma chamber and caldera collapse the example of trachy phonolitic explosive eruptions of the roman province central italy abstract textural and compositional features of pyroclastic products erupted during caldera forming events often reveal the tapping of different portions of variably zoned magma chambers due to changing geometries of the conduit vent systems here we report on ultrapotassic trachytic phonolitic explosive eruptions of the roman province central italy which show remarkable changes of textural features and glass compositions in the juvenile material even if the bulk chemical composition is essentially constant in each example the lower eruption sequence contains whitish crystal poor leucite free highly vesicular pumice emplaced by early plinian fallout and or pyroclastic currents upsection the eruption sequence contains black low porphyritic sanidine leucite bearing moderately vesicular scoria or spatter emplaced by major pyroclastic flows red tuff with black scoria and associated co ignimbrite coarse lithic rich breccias this suggests a shift from a central feeder conduit tapping the central part of the magma chamber to a ring fracture vent system tapping the peripheral portions of the magma chamber during caldera collapse key features of these evacuating magma chambers are the thermal and volatile concentration xvol gradients that produce the observed textural and compositional spectrum of trachy phonolitic rock types in particular the degrees of freedom during the crystallization of these ultrapotassic magmas are increased by the variation of the leucite stability field at different ph2o conditions both leucite free and leucite bearing differentiated ultrapotassic rock types can be produced in the course of individual eruptions as a result of pre eruptive conditions in the feeder magma with no need to invoke different differentiation suites related to mantle source heterogeneities of parental magmas

diurnal variation and horizontal extent of the low level jet over the northern gulf of california abstract this note describes aspects of the diurnal variation and geographical location of the summertime low level jet over the gulf of california based on wind soundings made at two sites near the northern end of the gulf during a two week summer field program in 1995 the low level wind observations from puerto penasco a site along the northern shore of the gulf showed a strong diurnal cycle decreasing in amplitude to near 0 by the 1800 m altitude a weaker but deeper diurnal cycle was observed at mexicali an inland site some 200 km west northwest of puerto penasco the strongest winds were observed at the coastal site the observations suggest that the strongest southerly winds in the northern gulf lie closer to the eastern shore of the gulf

upper crustal tomographic images of the amiata vulsini geothermal region central italy we computed the three dimensional p wave velocity structure of the upper crust beneath the adjacent amiata and vulsini quaternary volcanoes central italy inverting local earthquake arrival times we used 676 selected earthquakes out of more than 3000 in the m range 1 5 4 0 located between 1977 and 1992 by two contiguous microseismic networks operated by ente nazionale energia elettrica to monitor three geothermal areas namely latera torre alfina and mount amiata the resolving capability of the data set has been verified both with a priori synthetic tests and an a posteriori analysis of the resolution matrix we find a 40 25 7 h km3 crustal volume where we can resolve details as small as 2 to 4 km our analysis is favored by numerous geological and geophysical data collected for geothermal exploration these independent data give us specific constraints for both choosing a starting model and interpreting tomographic results we find high velocity anomalies in the upper 3 km of the crust beneath latera torre alfina and mount amiata geothermal fields related to uplifted limestone units the lateral extension of limestone units is defined by the three dimensional velocity pattern a negative anomaly clearly identifies the radicofani graben a plio quaternary depression filled with low velocity clayey sediments between 1 and 3 km depth a sharp gradient between high velocities 6 9 km s in the northern region and lower velocities in the southern one is recovered at 7 km depth this feature may indicate the transition between the tuscan province uplifted metamorphic crust and thickened carbonate series of the latium province

crustal and uppermost mantle structure in italy from the inversion of p wave arrival times geodynamic implications summary in this paper we present a 3 d image of the p wave velocity structure in the crust and uppermost mantle beneath italy obtained by inverting p wave arrival times of crustal earthquakes we used about 48000 arrival times at stations close to the epicentres within 200 km to mitigate the eiects of both reading errors and intrinsic complexity for long distance ray paths due to the scale of heterogeneities in the earth structure beneath italy whereas two of the inverted layers located in the lower crust and beneath the moho are well resolved by the data the upper crustal layer has regions of relatively poor resolution beneath the central apennines due to the sparse station spacing we made several attempts varying the moho geometry to obtain reliable and stable results without introducing too complex and unconstrained ap rioriinformation one of the most important results is the discovery of low velocity anomalies at 38 km depth beneath the northern apenninic and calabrian arcs which we interpret as subducted crustal material of the adriatic and ionian lithospheres in the lower crust beneath the entire apennines a pronounced low velocitybelt is present suggesting high temperatures in front of the bent adriatic lithosphere based on our results and on those previously obtained from seismic tomography we propose amodel for the geodynamic evolution of the apenninic system in which the present day scenario re ects lateral heterogeneities in the subducting ionian oceanic and adriatic continental lithosphere

earthquake relocation and three dimensional vp and vp vs models along the low angle alto tiberina fault central italy evidence for fluid overpressure summary the active extension in the central portion of the northern apennines is believed to be accommodated by an ene dipping low angle normal fault cutting the upper crust called alto tiberina fault atf the physical properties and mechanics of such a severely misoriented fault are still unknown and debated in this study we constrain the deep geometry of the atf and investigate the material properties of the fault system by using microseismicity recorded by a dense local seismic network the inversion of local earthquake p and s wave arrival times yields high resolution v p and v p v s images of the fault system we find positive v p anomalies that define the eastward verging thrust and fold belt developed in the sedimentary cover which inner bulk consists of triassic evaporites remains of the older compression microseismicity reveals the 20 ne dipping atf nearly planar from 3 to 14 km depth no sharp velocity contrasts are observed across the fault but only a gentle warping of the velocity anomalies and the dislocation of the triassic evaporites top at shallow depth on the fault hangingwall normal v p and strong high v p v s indicate the presence of a fractured high fluid pressure volume within which steep normal fault segments are located this evidence suggests that fluid pressure plays a dominant role in triggering the shallow background seismicity along the atf low v p v s anomalies are observed suggesting a different level of cracking and pore saturation and that the fault acts as impermeable barrier we speculate that the microseismic activity on the atf is favoured by the entrapped and locally overpressured co2 testified by the low v p v s volumes

characteristics of african easterly waves depicted by ecmwf reanalyses for 1991 2000 abstract several interesting characteristics of african easterly waves aews were observed and investigated by previous studies two separate propagation paths genesis mechanisms restriction of vertical development and the interaction with the african easterly jet aej however some aspects of these characteristics have been neglected the contrast of the aew population along the two propagation paths the aew genesis mechanism over the saharan thermal low and the role played by the low level north african circulation in this mechanism the dynamical mechanism restricting the vertical development of aews and the synoptic relationship and interaction between the aej and the aews along the two propagation paths the ecmwf reanalyses for the 1991 2000 period supplemented with those of 1979 were analyzed to explore these aew features major findings of this effort are the following the population of aews along the propagation path north of the aej aewn is approximately 2 5 times of that along the pr

snow replica method for three dimensional x ray microtomographic imaging visualization and quantification of snow structures at a scale of a few millimetres is important in understanding the mechanical thermal and electromagnetic properties of snow surface sections and to an even greater degree three dimensional 3 d reconstructions of cast snow samples are difficult to prepare and automatic image processing is notoriously difficult and often requires manual evaluation here we present a new method to measure the 3 d structure of cast snow samples snow samples cast with diethyl phthalate dep and frozen are cut to a sample size a few centimetres in diameter and up to 10 cm in height the ice of these samples is then sublimated in high vacuum and the remaining negative structure replica is imaged using x ray microtomography micro ct the accuracy of the method is demonstrated by comparing micro ct scans of the original snow structure and the replica the method described here allows easy transportation of samples requires little manual interaction has a very high spatial resolution of up to 10 m and is environmentally friendly

crustal models of the geothermal areas of southern tuscany italy abstract geological and geophysical data gathered in the geothermal areas of southern tuscany located in the inner part of the northern apennines indicate the presence of granite intrusions the most relevant data are 1 regional asthenospheric ascent to a depth of 40 50 km 2 granitic dykes as old as 3 8 2 9 ma and a widespread contact aureole found in several deep geothermal wells 3 very high heat flow values interpreted as the result of convective circulation of hot fluids above shallow magmatic bodies 4 the presence of low density bodies inferred from low gravity values often correlated with positive heat flow anomalies 5 the occurrence of a highly reflective horizon named k in a depth range of 3 12 km in the geothermal areas as shown by seismic reflection data 6 a 30 40 km wide low velocity body below the k horizon whose existence is supported by local earthquake tomography and teleseismic studies 7 the presence of a conductive body which correlates well with the anomalous tomographic and teleseismic body as revealed by magnetotelluric surveys the goal of the paper is to test different alternative crustal models by using these data the models are 1 granite intrusion 2 geopressurized fluids below impervious layers 3 contact metamorphic aureole 4 mylonite layers at the upper lower crust transition and 5 some combination of the four the occurrence of shallow intrusive bodies still partially molten and associated with saline brines is considered the most tenable model

magnetic interpretation related to geo magnetic provinces the italian case history abstract a comparison of the results obtained from the geophysical interpretation with the available information regarding the italian geological situation permitted us to establish our so called geo magnetic provinces the relationship between the magnetic characteristics and the tectonic evolution permitted the identification of each of the four following provinces that exist inside the global tectonic confines 1 1 the sardo corso block which represents the eastern boundary of stable europe this province is characterized by medium wavelength low amplitude anomalies that originate in an outcropping basement hercynian granites s l 2 2 the orogenic belt which constitutes the double alps apennines system from a magnetic standpoint this system is characterized by short wavelength low amplitude anomalies that are due to a paleozoic outcropping and or buried acid crystalline basement these anomalies are found to overlie long wavelength medium amplitude regional anomalies that are related to a deep apenninic basement central northern apennines 3 3 the foreland area which occurs from sicily hyblean plateau and apulia northwards to ancona and the po plain this area is characterized by a crystalline basement which is typically differentiated from the standpoint of basicity 4 4 the rifting zone which is represented by the part of the tyrrhenian sea lying south of the 41st parallel discontinuity the ionian abyssal plain and the pantelleria and linosa troughs in the sicily channel the main characteristic of this province is its extreme basicity differentiation in the crystalline basement which is induced by the geochemical processes connected with the deep geodynamic events these phenomena do not permit the correlation of the semioceanic basement of the rifting zone with the continental basement by means of interactive modeling a structural tectonic picture of the basement of the various italian geo magnetic provinces has been obtained the main result was found to be that the orogenic belt basement is undergoing intense tectonic compression and overlies the structural highs of the foreland area which mainly show tensive events

three dimensional velocity structure and earthquake relocation in the alban hills volcano central italy abstract the alban hills is a quaternary volcano located along the tyrrhenian margin of the apennines central italy which has erupted from 0 7 to 0 027 ma the high density of population around the volcano as well as the proximity to rome 20 km spurred us to investigate the three dimensional 3d crustal structure beneath the volcano with particular emphasis to the identification of volcano related phenomena hydrothermal circulation and frequent seismic activity characterize the present state of the volcano a seismic swarm from april 1989 to march 1990 consisted of shallow seismicity depths less than 6 km located beneath the western side of the volcano where the phreatomagmatic eruptions 0 03 ma occurred in this paper we present new results obtained from seismic tomography using the recorded local earthquakes we imaged the earthquake distribution jointly with the 3d velocity structure by inverting 1314 p and 1185 s arrival times from 163 selected events using the method developed by thurber 1983 we progressively focused toward the well sampled crustal volume decreasing the model gridspacing in subsequent inversion detailed resolution analysis and comparison with results of a synthetic test ensure that the computed models are reliable at least in the volume where the ray coverage is sufficient the calculated model improves the hypocentral locations of the 1989 1990 earthquakes allowing us to visualize the structures that generated the seismic swarm the relocated earthquakes are confined between 3 and 6 km in depth and they surround a body with anomalously high p wave velocity that is probably uplifted and metamorphosed carbonate rocks

an index of interannual precipitation variability in the core of the north american monsoon region abstract seasonal precipitation anomalies associated with the continental north american monsoon system are characterized using a land based dataset derived from in situ observations across the southwestern united states and northwestern mexico coherent regions of interannual continental precipitation variability are derived from principal component analysis after defining separate early and late summer monsoon seasons the gravest mode of late season interannual variability captures precipitation anomalies in the core of the continental monsoon domain a simple spatial average is developed as an index of this core variability the seasonal separation allows examination of persistence of precipitation anomalies as an indicator of practical late season predictability possible influences of large scale oceanic interannual fluctuations enso and pacific decadal oscillation pdo on core index precipitation anomalies are also considered the core precipitation index exhibits considerably more early to

the low level circulation of the north american monsoon as revealed by quikscat five years 1999 2003 of near surface quikscat ocean winds over the gulf of california and northeast pacific ocean are used to characterize the changes in the low level circulation associated with the north american monsoon our analysis shows that the onset of the summer season is accompanied by a seasonal reversal of the flow along the gulf of california with the establishment of a time mean southerly wind throughout the gulf this reversal not evident in the global reanalysis products occurs in late spring and precedes the onset of the monsoonal rains in the core of the monsoon the time mean flow is found to be modulated by transient events namely gulf surges detected in the near surface wind field as periods of enhanced southerly flow which typically originate at the southern end of the gulf and propagate northward the histogram of the summertime along shore winds identifies these surges as a distinct population of events readily distinguishable from the background flow

surges over the gulf of california during the mexican monsoon abstract northward surges of relatively cool moist maritime air from the tropical pacific into the southwestern united states occur via the gulf of california every summer during the mexican monsoon season these surges advect large amounts of moisture northward and promote increased convective activity in arizona mesoscale model output from 32 successive 24 h simulations are used to examine both the large scale and mesoscale features associated with surge events model data are compared to high resolution aircraft measurements on two days showing clearly that the model is capable of reproducing many of the detailed structures found in the observations results from a large scale analysis indicate that strong surges are produced in the model when a midlatitude trough is in the proper phase relationship with a tropical easterly wave weak surges occur when this relationship is missing

firn model intercomparison experiment firnmice evolution of cold dry snow and firn plays important roles in glaciology however the physical formulation of a densification law is still an active research topic we forced eight firn densification models and one seasonal snow model in six different experiments by imposing step changes in temperature and accumulation rate boundary conditions all of the boundary conditions were chosen to simulate firn densification in cold dry environments while the intended application of the participating models varies they are describing the same physical system and should in principle yield the same solutions the firn models all produce plausible depth density profiles but the model outputs in both steady state and transient modes differ for quantities that are of interest in ice core and altimetry research these differences demonstrate that firn densification models are incorrectly or incompletely representing physical processes we quantitatively characterize the differences among the results from the various models for example we find depth integrated porosity is unlikely to be inferred with confidence from a firn model to better than 2 m in steady state at a specific site with known accumulation rate and temperature firn model intercomparison experiment can provide a benchmark of results for future models provide a basis to quantify model uncertainties and guide future directions of firn densification modeling

faults strengthening and seismicity induced by geothermal exploitation on a spreading volcano mt amiata italia abstract seismogenic structures such as faults play a primary role in geothermal system generation recharge and output they are also the most susceptible to release seismic energy over fluid injection extraction operations during anthropic exploitation we describe the microseismic activity recorded in 2000 2001 in the piancastagnaio geothermal field on the se flank of mt amiata volcano southern tuscany italy from our field observations we find that a relatively high percentage i e about 5 of the recorded events are of hydro fracturing origin and have a distinct waveform seismic signature when compared to the recorded events of tectonic shear fracturing origin while hydrofracturing events are mostly concentrated around the geothermal fields the spatial distribution of hypocenters shows a deepening and a density increase of the micro seismic activity from the volcanic axis toward the exploited geothermal reservoir suggesting that volcanic spreading at amiata is still active the study of different data sets from different time periods together with the knowledge from terzaghi s law that production of large quantity of pore fluid with the associated fluid pressure reduction could augment the stress normal to faults surfaces and thus their resistance to slip make us argue that the process of volcanic spreading affecting the edifice of amiata may allow augmented accumulation of stresses on faults eventually leading to the release of higher stress drops once ruptures occur the gutenberg richter magnitude frequency distribution shows that the strongest events on record have a local magnitude in the 5 5 5 m l range for 100 year recurrence time in conclusions we infer that geothermal exploitation at mt amiata should be closely monitored in order to understand how fluid injection production is responsible for the hydrofracturing seismic activity and affects stress accumulation on and rupture of faults within and in the neighborhood of the geothermal fields this understanding may allow a geothermal field management that will hopefully reduce the risk for inducing larger seismic events in the area

a climatological perspective of transient synoptic features during name 2004 abstract this note provides a first look at a recently developed long term climatology of transient synoptic features in northern mexico key features investigated include inverted troughs cutoff lows cold fronts and open troughs westerly short waves this 35 yr analysis of transient systems crossing northern mexico 1967 2001 was developed to help place the summer climatology of the 2004 north american monsoon experiment name into a broader perspective inverted troughs are found to be the most commonly occurring transient synoptic feature during the monsoon with a mean frequency of occurrence of 55 days per summer season june september inverted troughs are found to contribute from 20 to 25 of the average summer rainfall observed in northern mexico rainfall doubles during inverted trough days compared to days without transient systems being present in 2004 the monsoon season was greatly shortened due to a poorly developed subtropical high compared to long term means inverted troughs cont

caldera structure amount of collapse and erupted volumes the case of bolsena caldera italy calderas are common on volcanoes but their structure is seldom visible the 19 km wide bolsena caldera italy formed between 0 6 and 0 2 ma the largely preserved structural rim and subsurface data make bolsena ideal to investigate caldera structure in relation to the subsidence and erupted volume in this paper we use remote sensing field analysis and available subsurface data at the surface the caldera passes from a downsag south rim to a narrow and densely faulted area north rim with outer normal and inner reverse faults the caldera structure on the widely faulted east rim appears to be scale dependent with a staircase like fault zone larger scale horst and graben like structures intermediate scale and domino like structures smaller scale subsurface data indicate asymmetric collapse with a northward increase in subsidence ranging from diffuse to the south to focused to the north deformation at the surface the collapse rate constant between ca 490 and 175 ka was more than magma output between ca 330 and 130 ka highlighting significant 200 m and prolonged 200 ka posteruptive subsidence as the nearby latera caldera west rim of bolsena was mostly active between ca 265 and 160 ka much of the subsidence at bolsena may be related to this activity suggesting a common magmatic reservoir the subsidence related structural variations along the caldera rim and the significant posteruptive subsidence found at bolsena have not been found in other calderas

mapping of a magma reservoir beneath nikko shirane volcano in northern kanto japan from travel time and seismogram shape anomalies since ray paths of direct p and s waves are largely distorted in a magma body a seismic shadow zone is created however scattered or diffracted waves with very small amplitudes can arrive in the shadow zone because their ray paths are different from those of the direct waves they become the first arrival in the shadow zone more than 100 seismologists from many institutions in japan joined together to perform an intensified seismic study in the nikko ashio area northern kanto japan it was suggested that there is a magma body beneath mount nikko shirane an active volcano that causes a seismic shadow zone because p waves recorded by the joint observation are anomalously attenuated in cases when they propagate through a zone beneath the eastern part of the volcano we developed a new method to estimate the shape of the anomalous attenuation zone by proposing the use of a new parameter the energy ratio between directp or s waves and their coda waves to discriminate whether or not each observation station is located inside or outside the shadow zone we estimated the shape of the anomalous attenuation zone by dividing the study area into blocks with dimensions of 2 km 2 km 1 km and using the energy ratio data of p waves for local events the obtained result shows the existence of an anomalous attenuation zone in the area east of nikko shirane volcano with a diameter of about 10 km at depths greater than 3 km it was also found from plots of deep event seismograms recorded by the same observation that travel times are delayed by about 0 7 s for ray paths crossing the anomalous attenuation zone obtained by the energy ratio data this value requires the p wave velocity in the anomalous zone to be less than that of the surrounding crustal material by at least about 30 suggesting the existence of a huge magma reservoir in this area

analysis of the 13 14 july gulf surge event during the 2004 north american monsoon experiment abstract gulf surges are disturbances that move northward along the gulf of california goc frequently advecting cool moist air from the goc or eastern tropical pacific ocean into the deserts of the southwest united states and northwest mexico during the north american monsoon nam little attention has been given to the dynamics of these disturbances because of the lack of reliable high resolution data across the nam region high temporal and spatial observations collected during the 2004 north american monsoon experiment are used to investigate the structure and dynamical mechanisms of a significant gulf surge on 13 14 july 2004 integrated sounding systems deployed along the east coast of the goc and an enhanced network of rawinsonde sites across the nam region are used in this study observations show that the 13 14 july gulf surge occurred in two primary stages the first stage was preceded by anomalous low level warming along the northern goc on 13 july sharp cooling moistening and increased

structural features of the shallow plumbing system of vulcano island italy in this study we integrate information gathered from surface geology and tectonics with the results of a shallow 0 2 km b s l seismic tomography of vulcano island italy obtained from the analysis of local earthquakes the observed low vp regions correspond to caldera filling products mainly consisting of pyroclastics tuffs lava flows and hyaloclastites high velocity anomalies represent intrusive bodies the striking correspondence between the stratigraphy from deep wells and the calculated velocity structure allows us to reconstruct the geometry and distribution of a main intrusion and to recognize some intra caldera depressions the shape and location of the high and low vp anomalies are consistent with nw se and n s strikes eruptive centres younger than 42 kyr as well as the structural depressions of vulcano and of the neighbour lipari island align along a n s direction the combined interpretation of the available structural data and of the results from the tomography suggests that magmatic reservoirs of vulcano at shallow depth 0 5 km align along a nw se strike but their shape is controlled by n s striking normal faults and or cracks that accommodate the right lateral movements of the nw se strike slip fault system

the use of laboratory velocity data for estimating temperature and partial melt fraction in the low velocity zone comparison with heat flow and electrical conductivity studies peridotite is widely considered to be the dominant component of the upper most mantle seismic velocities of a dry peridotite determined in the laboratory at high pressure and hypersolidus temperature show a rapid decrease with increasing temperature the strong temperature dependence of velocities can be used to estimate temperature and melt fraction in the low velocity zone of the earth the laboratory results show that the pressure dependence of both velocity and melt fraction appears to be well accounted for by the pressure dependence of the solidus temperature of the peridotite i e homologous temperature dependence this observation allows us to extrapolate laboratory results to higher pressures greater depths with some confidence requiring only a knowledge of the solidus as a function of pressure using the ratios of lithospheric to asthenospheric velocities temperature and melt fraction in the asthenosphere the low velocity zone can be determined from laboratory velocity data examples of thermal structures of the upper mantle beneath oceanic plates are presented we choose three locations of geophysical interest iceland plateau pacific ocean and philippine sea where reliable seismic velocities have been determined in the upper mantle from surface wave studies a large amount of partial melt 5 vol and a higher temperature than the dry peridotite solidus are inferred in 0 5 m y asthenosphere under the iceland plateau and the active marginal basin of the east philippine sea the partial melt zone appears to extend deeper 100 km and to greater ages 20 m y in the pacific ocean region than under the slowly spreading iceland plateau partial melting is not expected in the asthenosphere older than 5 m y under the iceland plateau even though the volume fraction of partial melt is not so large 3 vol beneath the pacific plate the melting zone may extend to a distance of above 2000 km from the ridge many seamounts observed in the pacific ocean may result from this vast region of melting under the plate we suggest a linear relation between the width of melting zone and the plate velocity the laboratory results are also applied to other low velocity zones it is suggested that a velocity drop up to about 6 in the asthenosphere does not necessarily require the existence of partial melt but can be explained by high subsolidus temperature this implies that partial melt may not exist generally but only in limited areas in the low velocity zone comparison of seismic results with theoretical models may overestimate the temperature and melt fraction if the velocity drop at subsolidus temperature is neglected temperature and melt fraction obtained in this study are discussed together with results from heat flow and electrical studies almost the same temperatures as inferred from seismic velocity and a dry peridotite solidus are calculated from heat flow data indicating that the upper mantle under mid ocean ridges may be fairly dry even a water or co2 undersaturated solidus 0 1 wt does not give a temperature consistent with the lithospheric geotherm and laboratory velocity results it is noted that electrical conductivity studies generally yield lower temperatures and larger melt fractions than this study unknown pressure frequency and impurity effects on laboratory conductivities of partially molten mantle rocks are suggested as possible reasons for this discrepancy

growth of a pleistocene giant carbonate vein and nearby thermogene travertine deposits at semproniano southern tuscany italy estimate of co2 leakage abstract a giant carbonate vein 50 m thick fissure ridge travertines and nearby travertine plateaus in the semproniano area mt amiata geothermal field southern tuscany italy are investigated through a multidisciplinary approach including field and laboratory geochemical analyses u th geochronology c nd o and sr isotope systematics ree abundances and fluid inclusion microthermometry the main aim of this work is to understand 1 modes and rates for the growth of the giant vein and nearby travertine deposits within a quaternary volcano tectonic domain 2 implications in terms of the co 2 leakage and 3 possible relationships with quaternary paleoclimate and hydrological oscillations results show that the giant vein was the inner portion of a large fissure ridge travertine and grew asymmetrically and ataxially through repeated shallow fluid injections between 650 and 85 ka with growth rates in the 10 2 10 3 mm a order the giant vein developed mainly during warm humid interglacial periods partially overlapping with the growth of nearby travertine plateaus estimated values of co 2 leakage connected with the vein precipitation are between about 5 10 6 and 3 10 7 mol a 1 km 2 approximately representing one millionth of the present global co 2 leakage from volcanic areas temperature estimates obtained from o isotopes and fluid inclusion microthermometry indicate epithermal conditions 90 50 c for the circulating fluid during the giant vein growth with only slight evidence of cooling with time geochemical and isotope data document that the travertine deposits formed mainly during pleistocene warm humid periods within a tectonically controlled convective fluid circuit fed by meteoric infiltration and maintained by the regional geothermal anomaly hosted by the carbonate reservoir of the mt amiata field

high resolution seismic tomography of compressional wave velocity structure at newberry volcano oregon cascade range compressional wave velocity structure is determined for the upper crust beneath newberry volcano central oregon using a high resolution active source seismic tomography method newberry volcano is a bimodal shield volcano east of the axis of the cascade range it is associated both with the cascade range and with northwest migrating silicic volcanism in southeast oregon high frequency 7 hz crustal phases nominally pg and a midcrustal reflected phase travel upward through a target volume beneath newberry volcano to a dense array of 120 seismographs this arrangement is limited by station spacing to 1 to 2 km resolution in the upper 5 to 6 km of the crust beneath the volcano s summit caldera the experiment tests the hypothesis that cascade range volcanoes are underlain only by small magma chambers a small low velocity anomaly delineated about 3 km below the summit caldera supports this hypothesis for newberry volcano and is interpreted as a possible magma chamber of a few to a few tens of km3 in volume a ring shaped high velocity anomaly nearer the surface coincides with the inner mapped ring fractures of the caldera it also coincides with a circular gravity high and we interpret it as largely subsolidus silicic cone sheets the presence of this anomaly and of silicic vents along the ring fractures suggests that the fractures are a likely eruption path between the small magma chamber and the surface

the low level structure of african easterly waves in 1995 abstract the existence of african easterly waves aews north of the african easterly jet aej core with maximum amplitude at low levels has been confirmed and clarified using radiosonde data and the u k meteorological office global model analysis from the hurricane season of 1995 at bamako 12 5 n 8 0 w the aews were characterized mainly by maximum amplitudes at the level of the aej around 700 mb whereas at dakar 14 7 n 17 5 w the waves were characterized by maxima between 850 and 950 mb the low level waves to the north of the aej arise in association with baroclinic interactions between the negative meridional potential vorticity pv gradients in the jet core and the positive low level gradient of potential temperature enhanced by the presence of low static stability air north of the aej these waves follow the positive meridional gradients over northern africa in contrast to the jet level aews that follow the meridional pv gradients at the level of the aej cross correlation analysis

structural control on fault geometry example of the grevena ms 6 6 normal faulting earthquake in this paper we present a three dimensional velocity structure of the kozani grevena region a relatively low seismicity area of the western margin of the internal hellenides which was struck by a ms 6 6 earthquake on may 13 1995 p wave arrival times from 656 aftershocks are inverted to resolve the velocity structure of the upper 12 km of the crust the 1995 ruptured fault dheskati fault lies at the southeastern end of a 35 km long normal fault the servia fault the crustal heterogeneities identified by tomography help to constrain the geometry and structure of the 1995 fault and the rupture evolution during the mainshock the aftershocks and the velocity structure define a fault dipping 35 toward nw which from 5 km depth splays upward into two nearly parallel shallow faults the slip during the mainshock and the aftershocks all were concentrated along the deeper portion of the fault while the limited slip observed at the surface occurred on the northern of the two shallower splays the paleochori fault it appears that the lithological heterogeneities of the shallow crust are responsible for the splaying of the main fault upward our work stresses the importance of crustal structure in determining fault geometry and segmentation and rupture evolution

interfacial and structural relaxations of snow under isothermal conditions we investigated the morphological evolution of laboratory snow under isothermal conditions at 3 9a nd 19 c using x ray tomography we employed a two point density correlation function to measure spatial fluctuations of the density of the bicontinuous ice vapor system at different length scales length scales were derived from the correlation function to distinguish between interfacial coarsening due to the minimization of surface energy on the smallest scales and anisotropic structural re arrangements due to gravity on larger scales on the smallest scales our data suggest a crossover between t 9a nd 19 c from evaporation condensation to surface diffusion as the dominant transport mechanism anomalous growth was found for the slope of the correlation function at the origin and it was similar to those reported for the coarsening of fractal clusters this is consistent with the observed persistence of dendritic structures throughout an entire year the dynamics of large scale morphology was characterized by the first zero crossing of the correlation function which displays a nonmonotonic evolution with a pronounced anisotropy between the direction of gravity and horizontal directions since the correlation function naturally emerges in problems of scattering of radiation in snow our results appear to be important for optical and remote sensing methods

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

atlantic tropical systems of 1994 and 1995 a comparison of a quiet season to a near record breaking one abstract totals of 70 and 63 tropical waves also known as african or easterly waves were counted in the atlantic basin during the 1994 and 1995 hurricane seasons these waves led to the formation of 9 of the 12 total number of tropical cyclones in 1994 and 19 of the 21 total number of tropical cyclones in 1995 tropical waves contributed to the formation of 75 of the eastern pacific tropical cyclones in 1994 and 73 in 1995 upper and lower level prevailing wind patterns observed during the below normal season of 1994 and the very active one of 1995 are discussed tropical wave characteristics between the two years are compared

triaxial tests on snow at low strain rate part ii constitutive behaviour fine grained dry snow with a density range of 190 435 kg m 3 was tested in triaxial compression at 12 c with confining pressures varying between 0 and 40 kpa the tests were strain rate controlled with strain rates ranging between 7 4 x 10 7 s 1 and 6 6 10 5 s 1 the analysis of the test results revealed that the relationship between yield stress and viscous strain rate is best given by a power law similar to polycrystalline ice however the power law exponent n is a function of density and varies between 1 8 low density snow p 320 kg in 3 the tests also showed that lower density snow displays a significant non linear stress strain response before yielding two further aspects of the constitutive behaviour of snow were identified 1 the strain rate independence of the post yield work hardening behaviour in compression and 2 the independence of the axial yield stress in relation to the confining pressure the experimental observations are discussed with respect to the mechanical properties of polycrystalline ice which is the constituent material of the load bearing ice skeleton

mean state and wave disturbances during phases i ii and iii of gate based on era 40 abstract using ecmwf s second generation reanalysis era 40 the large scale mean state and synoptic scale features associated with african easterly wave disturbances aews are examined over west africa and the adjacent eastern atlantic ocean during the three 21 day observing periods of the global atmospheric research program garp atlantic tropical experiment gate in 1974 phase i 26 june 16 july phase ii 28 july 17 august phase iii 30 august 19 september results are partitioned into four geographical boxes in order to highlight differences among the aew vortices as they propagate westward along two tracks northern and southern over west africa land and the adjacent eastern atlantic ocean water this marks the first time that a detailed diagnosis of the northerly track aews has been conducted results are also compared to previous gate studies and a 30 yr climatology is extracted from era 40 in general the subjectively analyzed wind fields presented in earlier studies compare favorabl

three dimensional velocity structure in northern california coast ranges from inversion of local earthquake arrival times abstract the three dimensional p wave velocity structure in the upper crust in the northern california coast ranges from santa rosa to ukiah is obtained by simultaneous inversion of local earthquake and refraction travel time data for velocity and hypocentral parameters in this region where there are lateral heterogeneities the three dimensional inversion provides important results not found in two dimensional refraction studies the medium is parameterized with velocities at the intersections gridpoints of a nonuniform three dimensional grid travel times are calculated with approximate ray tracing along arcuate paths which are reasonable for lateral distances less than 45 km inversions with 5 to 10 and 2 to 3 km gridspacing achieved 80 per cent decreases in data variance the inversion with 2 to 3 km gridspacing reduced the rms residual level to approximately the level of timing error anomalously low velocities to at least 6 km depth are found along the maacama and healdsburg rodgers creek hrc fault zones the low velocity region is widest at the en echelon junction of the maacama and hrc fault zones low velocities are associated with the clear lake basin where there is a thick sequence of volcanics interbedded with sedimentary deposits there is a high velocity body located southeast of the geysers between the maacama and collayomi fault zones which may be associated with igneous intrusives or high grade metamorphism related to an underlying inferred partial melt body modeled in previous teleseismic travel time studies there is some indication in the vapor dominated geothermal reservoir of lower velocities relative to surrounding water saturated rock as has been shown in some laboratory experiments hypocenter locations obtained in the inversion show little variation from hypocenters obtained through inversion for one dimensional velocity model and station corrections for the inversion with 2 to 3 km gridspacing however some groups of events become more tightly clustered

tomographic inversion of local earthquake data from the hengill grensdalur central volcano complex iceland parameters is generally low however a quantitative analysis of resolution provides an unambiguous assessment of well resolved volumes within the better resolved regions of the model the averaging volumes are 1 2 km and 2 4 km in vertical and horizontal extent respectively results of tomographic inversion image three distinct bodies of anomalously high velocity two of these extend from near the surface to a depth of about 3 km these high velocity volumes are located directly beneath the surface expressions of the extinct grensdalur volcano and the extinct husmuli basalt shield the third high velocity structure occurs in the depth range of 3 4 km but does not extend to the surface these three high velocity bodies are interpreted to be solidified magmatic intrusions relatively low velocities underlay limited portions of the trace of the present accretionary axis and a low velocity body is imaged in the roots of the active hengill volcano the volume of lower velocities located beneath the surface expression of the hengill volcano is interpreted to be a region of partial melt

tomographic models and seismotectonics of the reggio emilia region italy the aim of this study is to define the vp and vp vs structure of the fault zone ruptured by the ml 5 1 earthquake of october 15 1996 which occurred near reggio emilia central northern italy a 1 month long seismic sequence followed the mainshock and occurred in a small region along the outer border of the northern apenninic belt at depth ranging between 10 and 17 km p and s wave arrival times from 304 aftershocks recorded by two local dense seismic arrays installed in the epicentral region have been inverted to obtain one and three dimensional velocity models by using state of the art local earthquake tomographic techniques velocity models and aftershock relocation help us to infer the seismotectonic of the region earthquakes originated along a nw dipping backthrust of a ne trending main thrust composing the western part of the broad ferrara arc a main high vp and high vp vs region delineates a pop up structure in the center of the area the high vp vs within the pop up structure supports the presence of a zone with increased pore pressure the hypocentral depth of both mainshock and aftershocks is greater than those usually found for the main seismogenic regions of the apenninic belt p wave velocity values in the seismogenic area obtained by tomography are compatible with rocks of the mesozoic cover and suggest that seismicity occurred within the mesozoic units stack at present by compressional tectonics

travitonics using travertines in active fault studies abstract late quaternary travertines deposited from hot springs can reveal much about the neotectonic attributes and histories of structures on the basis of field studies in the aegean region turkey and greece the northern apennines italy and the basin and range province usa we conclude that the following relationships are of predictive value i travertine deposits are preferentially located along fracture traces either immediately above extensional fissures or in the hanging walls of normal faults ii the locations of many travertine fissure ridge deposits coincide with step over zones relay ramps between fault segments networks of intersecting tensional fissures reflecting the complex strains experienced in such settings are probably responsible for enhancing hydrothermal flow iii the morphology of travertine deposits overlying extensional fissures is controlled by the rheology of the underlying materials tufa cones towers pinnacles form on former and present lake floors where fissures underlie unconsolidated sediments whereas fissure ridges develop where fissures cut bedrocks at the surface iv fissure ridges comprise outwardly dipping bedded travertine flanking a central tensional fissure filled by vertically banded travertines fissures can be used to infer local stretching directions v where there are travertines datable by the u series method it is possible to calculate time averaged dilation and lateral propagation rates for individual fissures vi most fissures cutting fissure ridges comprise self similar angular segments with fractal dimensions in the range 1 00 1 12 the properties of bedded travertine combined with stress perturbations at fissure tips probably being responsible for such similar fractal dimensions being inferred from such a wide range of locations fissures gradually increasing in width with depth are products of continuous fracture dilation in contrast to those that form during episodic dilation which display stepped increases of width with depth vii travertine deposited from springs along fault zones accumulate in terraced mounds sited down slope of the spring line viii many post depositional fractures cutting travertine deposits are locally oriented at right angles to deposit margins and ix systematic joints in travertines are restricted to those parts of eroded sheet deposits that have been exhumed

an energy and mass model of snow cover suitable for operational avalanche forecasting a numerical model has been developed to simulate energy and mass evolution of snow cover at a given location as a function of meteorological conditions precipitation air temperature humidity wind velocity and incoming short wave and long wave radiation this model named crocus was first tested on a well instrumented field during a whole winter showing its ability to simulate the important phenomena affecting the evolution of the snow layers high temperature gradients wetting compaction and melting freezing cycles a second test was conducted at two locations in the french network used for operational avalanche forecasting though the weather observations are made there only twice daily the snow profiles calculated by the model were very close to those obtained once a week by a pit observation crocus proved itself sufficient to be considered now as a useful objective tool for operational avalanche forecasting

upper crustal structure of the benevento area southern italy fault heterogeneities and potential for large earthquakes summary the benevento region is part of the southern apennines seismogenic belt which experienced large destructive seismic events both in historical and in recent times the study area lies at the northern end of the irpinia fault which ruptured in 1980 with a ms 6 9 normal faulting event which caused about 3000 casualties the aims of this paper are to image lateral heterogeneities in the upper crust of the benevento region and to try to identify the fault segments that are expected to generate such large earthquakes this work is motivated by the recognition that lithological heterogeneities along major fault zones inferred from velocity anomalies reflect the presence of fault patches that behave differently during large rupture episodes in this paper we define the crustal structure of the benevento region by using the background seismicity recorded during 1991 and 1992 by a local seismic array these data offer a unique opportunity to investigate the presence of structural discontinuities of a major seismogenic zone before the occurrence of the next large earthquake the main result that we obtained is the delineation of two nw trending high velocity zones hvzs in the upper crust beneath the matese limestone massif these high velocities are interpreted as high strength regions that extend for 30 40 km down to at least 12 km depth the correspondence of these hvzs with the maximum intensity regions of historical earthquakes 1688 ad 1805 ad suggests that these anomalies delineate the extent of two fault segments of the southern apenninic belt capable of generating m 6 5 7 earthquakes the lateral offset observed between the two segments from tomographic results and isoseismal areas is possibly related to transverse right lateral faults

three dimensional p velocity structure in the region of the ms 6 9 irpinia italy normal faulting earthquake abstract we have calculated the three dimensional velocity structure in the epicentral region of the 1980 irpinia southern italy earthquake using thurber s inversion technique for hypocenter and velocity parameters particular care was given to the evaluation of the resolution of the models because of the poor reading accuracy of the analog stations operating at that time we analyzed the averaging vector for each node of the model in order to estimate the degree of smearing within the final tomographic image this approach is suitable for determining the best parametrization to use i e the minimum grid spacing and for evaluating the region where the computed velocities are meaningful the results show that the main rupture occurred along a sharp nw se trending velocity contrast which probably reflects a crustal discontinuity the velocity variations along the fault probably due to lithological heterogeneities account for the complex character of this earthquake based on the velocity distribution at depth the secondary rupture that started about 40 s after the mainshock is interpreted to be the result of reactivation of an old thrust as a normal fault

evidence for sub lacustrine volcanic activity in lake bolsena central italy revealed by high resolution seismic data sets abstract the bolsena caldera that formed between 0 6 and 0 2 ma has a well preserved structural rim which makes it an ideal site to study the tectonic and volcanic evolution of calderas however the main area is covered by a 150 m deep lake which makes it rather difficult to investigate the subsurface structure directly to overcome this problem new high resolution hydro acoustic surveys using a multichannel reflection seismic system and a sediment echo sounder system were conducted in september 2012 as space was limited we used a rowing boat towed by a rubber boat to handle a 36 m long and 24 channel streamer to receive seismic reflections produced using a mini gi gun 0 25 l the subsurface structure of lake bolsena was imaged up to a sediment depth of 190 m which is estimated to have filled over a period of 333 kyrs however massive pyroclastic flow deposits found in the deeper parts of the basin indicate an initial infill of volcanic deposits from two adjacent younger calderas the latera w and montefiascone se calderas our data suggest that the caldera has a long history of active volcanism because the lacustrine sediments show post sedimentary influences of geothermal fluids we mapped several mound structures at various stratigraphic depths two volcanic structures outcrop at the modern lake surface implying recent activity one of these structures is hardly covered by sediments and has a crater like feature in its summit the other structure shows a pockmark like depression on top another observable feature is a partially sediment filled crater located in the western part of the lake which further implies the existence of a magma chamber located beneath the bolsena caldera since the late pleistocene and holocene the sedimentation was mainly hemipelagic evidenced by a sediment drape of up to 10 m thick sediment drape on the uppermost sediments beneath the drape we found evidence for a distal tephra layer likely related to an explosive eruption from the campanian volcanic province occurring as the neapolitan yellow tuff our new geophysical data set is a valuable record with a potential to constrain the sedimentary and volcanic evolution of the vulsini volcanic district in areas that have not been assessed previously due to logistical challenges of conducting surveys in water filled settings

vp and vp vs images in the mw 6 0 colfiorito fault region central italy a contribution to the understanding of seismotectonic and seismogenic processes 1 in 1997 the umbria marche apennines central italy was struck by a series of moderate magnitude normal faulting earthquakes accompanied by a prolonged sequence of aftershocks seismological analysis revealed a 40 km long nw trending structure composed by several low angle normal fault segments in this paper we present the three dimensional 3 d vp and vp vs structure of the fault zone determined by the inversion of p and s wave arrival times from 1982 aftershocks the high resolution tomographic images reveal strong heterogeneity along and across the fault zone and allow us along with the 3 d location of earthquakes to define the fault geometry at depth and to improve our understanding on the seismotectonics of this part of the northern apennines thrust and fold belt the relocated aftershocks suggest that the main ruptures occurred on planes slightly steeper than previously hypothesized and at depths shallower than those evidenced by 1 d locations we find that the preexisting structure which developed during the neogene compressional tectonics plays an important role in the earthquake generation and rupture evolution of the normal faulting events we propose that the main shocks whose hypocenters are all located at 6 km depth originated along a shallow decollement of the meso cenozoic cover thrust over the metamorphic basement geometrical discontinuities and lateral steps along the inherited structures control the lateral fault extent and determine fault segmentation this study offers a good example of how lithological heterogeneities and the complexity of the upper crust structure strongly affect the faulting process

climate simulations of african easterly waves the three dimensional structure and propagation characteristics of african easterly waves for the 1986 94 period are studied with june august european centre for medium range weather forecasts ecmwf operational analyses national centers for environmental prediction ncep reanalyses and canadian centre for climate modelling and analysis gcm output specific consideration is given to the differences in the timemean circulation synoptic scale variance covariance and principal oscillation patterns the african easterly waves derived from the ecmwf and ncep analyses are very similar with both providing a reasonably realistic depiction of african easterly waves given the agreement with one another earlier station data studies and theory where significant differences exist between the results from the two data assimilation systems they expectably do so over the tropical atlantic and in fields that are not directly observed such as vertical velocity the situation with the gcm is not as favorable but there are some encouraging areas of agreement despite the gcm s relatively coarse resolution and absence of observed data to constrain it selected points of agreement and disagreement between the gcm and the analyses include the following i the gcm african easterly wave energetics are comparable with the analyses in terms of the sign and magnitude of the energy transfers from the time mean state to the waves ii the northern track of easterly waves seen in the analyses terminates prematurely in the gcm at the african coast iii the southerly track of moist easterly waves seen in the analyses near the seasonal rainband is absent in the gcm possible reasons for the deficiencies are discussed the sensitivity of the gcm simulated african easterly waves to co2 doubling is investigated together with significant mean warming and moistening over the northern sahara the level of simulated african easterly wave activity increases with co 2 doubling

evidence of incremental growth in the vulsinian calderas central italy abstract a comparative work on the vulsini calderas has been carried out fundamentally from volcanological field study drilling and gravity anomalies data on the basis of a detailed stratigraphy four volcanic complexes have been recognized in the vulsini volcanic district from the oldest to the youngest paleo bolsena bolsena montefiascone and latera the latter two complexes having a contemporaneous evolution in their activity each complex gave rise to several little calderas caused by piecemeal collapses due to moderate size explosive eruptions or coherent subsidence of a superficial piston like block nevertheless the extensional volcano tectonic regime affecting this area could have accounted for as much of the total subsidence as the caldera forming eruptions bolsena and latera calderas respectively 16 km and 8 km in average diameter represent the main depressions of the vulsini district and their topographic features are still well preserved several collapses forming the main poligenetic calderas of bolsena and latera are masked at present by the bolsena lake the younger volcanic covering the lacustrine deposits and erosion in a minor amount only the little montefiascone and vepe calderas which represent the youngest collapses of the vulsini area have not been masked bolsena caldera could be considered a depression caused mostly by a subsidence hinged to the southwest by down sagging and by collapses which occurred after the most important explosive eruptions of the paleo bolsena bolsena and montefiascone volcanic complexes meanwhile latera caldera is mostly due to a piecemeal collapse linked to several moderate size ignimbrite units which were emplaced throughout the explosive activity of the latera complex therefore the vulsinian calderas did not form by catastrophic eruptions because several and frequent moderate size eruptions downsagging and tectonic hinged subsidence concur indicating an incremental growth

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

velocity and attenuation tomography of the umbria marche 1997 fault system evidence of a fluid governed seismic sequence abstract the 1997 umbria marche is probably the best ever monitored normal faulting seismic sequence seismicity migration and multiple main shocks characterize the activation of a 40 km long system of contiguous fault segments as documented by seismological data many authors as indicative of fault weakening by fluids migration have interpreted this behaviour in this study we create a new catalogue of high quality p and s wave arrival times merging data recorded by permanent and temporary stations to improve the resolution of velocity and attenuation models and earthquake locations we show that the relocated earthquakes and the joint interpretation of p and s wave velocity and attenuation models help in understanding the faulting processes revealing new details of the geometry of the main faults and physical state of fluids within the crustal volume we observe that large aftershocks occur on the top and within the triassic evaporitic layer a rock volume locally characterised by fluid over pressured as evidenced by high vp vs and low qp qs anomalies velocity and attenuation heterogeneities are evidence that the migration of fluid pressure along the fault system is the driving mechanism of the prolonged earthquake sequence