integrated seismic flexural and gravimetric modelling of the coastal cordillera thrust belt and the guarico basin north central region venezuela abstract we constructed two integrated geodynamic transects for the eastern and western areas of the coastal cordillera thrust belt and the guarico basin north central region of venezuela based on information from depth converted reflection seismic cross sections surface geology bouguer anomaly and deep refraction seismic profiling these geodynamic transects were modelled in order to 1 understand the geodynamic processes responsible for the formation of the guarico basin 2 quantitatively determine the contribution of the coastal cordillera thrust sheet loading in the generation of the basin fill i e the effective elastic thickness of the northern part of the south american lithosphere the total shortening of the thrust belt and the maximum subsidence of the basin and 3 characterize the crustal structure and moho depth in north central venezuela we used flexural modelling to obtain important quantitative information related to the total middle eocene to recent shortening of the coastal cordillera the total subsidence observed in the guarico basin and the effective elastic thickness of the south american lithosphere in northern venezuela we conclude that the load of the coastal cordillera on the south american lithosphere is sufficient to generate the subsidence observed in the guarico basin the total shortening and subsidence obtained in the western transect are 44 km and 5 km whereas they are 10 km and 7 km in the eastern transect respectively the effective elastic thickness of the south american lithosphere obtained from the modelling is 25 km the seismically constrained deep structure of north central venezuela indicates that moho reaches a maximum depth of 45 km under the guayana shield and shallows to the north to 35 km beneath the guarico basin according to the gravity models moho is deeper under the coastal cordillera thrust belt than expected from flexural modelling pointing to the existence of a crustal root more than 35 km deep the moho gets shallower 30 km towards the caribbean sea

gpr studies of pyroclastic deposits subsurface information where there are no outcrops we have collected ground penetrating radar gpr data to evaluate its applications and limitations for obtaining subsurface information about pyroclastic deposits where there are no exposures the surveys were conducted mainly in the ubehebe hydro volcanic field death valley national park california u s that is composed of well preserved deposits left by base surges turbulent flows generated by explosive interaction between magma and water base surges have high i e magmatic temperatures and move horizontally on the surface of the ground with hurricane velocity causing extensive damage and loss of life the main vent in this area ubehebe crater is a spectacular feature about 700 800 m in diameter and 235 m deep other much smaller tuff rings are south and west of the main crater

the arcuate shape of the umbria marche sabina apennines central italy abstract the umbria marche belt constitutes the most southern and external portion of the northern apennine arc typically convex to the northeast within this the central part the umbria marche sabina apennines is the most elevated and is characterized by a locally more pronounced curvature the umbria marche belt is a thrust belt built mainly by thrust faults affecting a multilayer sedimentary series characterized by levels with markedly different competence the main thrust the m sibillini thrust produced the tectonic superposition of the umbria marche sabina apennines over the most external units represented by the lazio abruzzi platform to the south and the marche abruzzi domain to the north farther north it joins the thrusts buried under the po plain the most important of the more internal thrusts is that of the valnerina the pronounced local curvature of the umbria marche sabina apennines may be due to accentuation of an original arcuate shape this accentuation is probably caused by differential displacement along the two main thrusts during the initial stage of the evolution of the belt late messinian early pliocene at that time this displacement was more important in the northern part where the thrust fronts show a nw se trend than in the southern portion where they are n s trending on account of the lazio abruzzi carbonate platform which perhaps represented a local obstacle to thrusting as for the initial curvature we think that this is determined by older discontinuities which controlled thrust development the final arcuate shape was not substantially changed during the subsequent compressional history of the belt early pliocene middle pliocene

the monagas fold thrust belt of eastern venezuela part i structural and thermal modeling abstract the eastern venezuelan basin evb contains one of the largest hydrocarbon accumulations in the world main petroleum targets are buried structures of the monagas fold thrust belt mftb which forms the northeastern edge of the evb the objective of this study is to integrate the seismic and well data that has been acquired over the last 10 years across the mftb and evb to create an updated structural model three regional cross sections 60 75 km long are presented across an area of 4000 km2 five structural domains are described amarilis furrial jusepin cotoperi and pirital they are characterized by thrusts and high angle reverse faults structural style changes along strike are related to variations in depth of detachment levels and to the strike slip component of the deformation we have estimated a shortening between 43 and 59 km that increases eastward over a distance of 40 km the evolution of the mftb is divided in four episodes based on stratigraphic structural and thermal maturity evidences 1 oligocene early miocene initial movement of pirital thrust 2 early miocene simultaneous movement on pirital furrial and cotoperi thrusts 3 middle miocene increases in velocity and change in geometry of pirital thrust during an out of sequence period of thrusting 4 late miocene to holocene minor thrust activity this evolution is consistent with the oblique convergence between the caribbean and south american plates and the convergence between north and south america that affected eastern venezuela during the cenozoic by analyzing the along strike variations in structural style new exploratory opportunities have been identified under the orocual and santa barbara fields two untested duplex structures are proposed they were developed during the middle miocene other prospective hydrocarbon traps are associated to oblique transpressive faults that create anticline structures

lateral variations of the upper mantle structure in eurasia from group velocities of surface waves abstract group velocities of both rayleigh and love waves in the 20 70 s period range along paths across asia and the eastern europe are used to obtain group velocity maps of the region for this purpose we developed a method for tomographic inversion on spherical surface which is practically free of a priori assumptions checker board test shows that velocity anomalies of 10 10 size can be resolved the local dispersion curves are inverted to velocity depth curves up to 160 km depth along three profiles 1 tibet the south china platform and the southern part of the japan sea 2 the west siberian platform the tienshan and the pamir 3 the east european platform and the black sea basin lateral s wave velocity variations are presented at the depths of 60 90 and 120 km a low velocity zone in asthenosphere under japan sea is extended under the south china and the north china korean platforms the upper mantle structure of the russian east european and the west siberian platforms is different a low velocity zone at 120 140 km depths is observed under the west siberian platform whereas the velocity under the russian platform increases monotonously with depth a low velocity layer appears under the black sea indicating an oceanic structure of the basin low surface wave velocities in tibet are caused not only by a thick crust but also by low s wave velocities in the upper mantle the precambrian west siberian north indian and north china korean platforms are characterized by high velocities at the depth of 120 km unlike the younger tectonic units

modeling 3d porosity and permeability from gpr data in the ellenburger dolomite central texas three dimensional porosity and permeability were modeled in an ellenburger carbonate reservoir analog from 2d crosshole and 3d surface survey ground penetrating radar gpr data two dimensional gpr crosshole velocity tomography 3d migration of the gpr surface data and porosity and permeability calibration to gpr attributes results in 3d porosity and permeability predictions that provide a consistent model of the paleocave structures and facies distributions picking the maximum instantaneous amplitude of the direct arrival wavelet for velocity tomography reduces uncertainties caused by a low signal to noise ratio uncorrelated noise and the interference between reflections and critical refractions at the earth air interface the gpr velocity is anisotropic with an average vertical to horizontal velocity ratio of 0 93 which is attributed to the dominance of the relatively horizontal orientation of the maximum porosity and permeability porosity and permeability trends are influenced by regional northe

delineation of the north central italian upper mantle anomaly the italian peninsula is the focus of intense deformational tectonic activity it is underlain by mantle material whose inferred relatively anomalous properties1 2 are not inconsistent with the seismic volcanic and thermal activity that is manifested in this region the most effective geophysical tool for mapping the structure of the uppermost 200 300 km of the earth is the observation and analysis of seismic surface wave dispersion on a regional scale here we synthesize the interpretations of rayleigh wave dispersion measurements made by several authors each for different parts of north central italy3 8 to delineate the lateral extent of the upper mantle anomaly in this region

analysis of seismological and geological observations formoderate size earthquakes the colfiorito fault system central apennines italy to contribute to the understanding of the relationships between moderate earthquakes and the faults that are recognisable in the geological record we analysed seismological and geological data related to the 1997 98 umbria marche central italy earthquake swarm the seismological recordings collected by local networks allowed accurate location of about 1000 events whereas the geological field observations provided a picture of the structural features and the ground surface deformations we also re examined and utilised some already published data and results mostly about the fault plane solutions and the geology on the basis of earthquake locations fault plane solutions and geological mapping we explored the possible correlation between the earthquake causative fault planes and the normal faults exposed in the area our results show that the two mainshocks that occurred on september 26 1997 mw 5 7 and mw 6 0 originated on the same structure reactivating at depth the colfiorito normal faults both ruptures did not propagate up to the ground surface but triggered gravitational sliding that occurred along pre existing fault scarps the earthquake that occurred on october 14 1997 mw 5 6 originated on another fault branch at a much shallower depth in spite of the lower magnitude this earthquake produced tectonic ruptures where the fault plane projects to the surface in an area where no faults were previously mapped by comparing the paleostress reconstruction based on slickenside lineations analysis and the focal mechanism solutions we also suggest a possible correlation between the long term early middle pleistocene cumulative effects of the colfiorito fault system and the short term behaviour of the fault planes observed during this earthquake swarm favouring the idea of a seismogenic source producing clustered moderate size earthquakes rather than large events scattered in time our results suggest that the integration of geological and seismological observations can constrain the seismotectonic interpretations in regions of low level seismicity and that this integration can pose a reliable basis in the seismic hazard assessment

traveltime tomography of crosshole ground penetrating radar based on an arctangent functional with compactness constraints abstractregularization has been an effective technique to provide unique and stable solutions for crosshole ground penetrating radar gpr traveltime tomography the traditional form of this method in which a low order differential operator was used commonly yields a smooth solution that may not be appropriate when anomalies occur in block patterns such as voids or irregular objects the minimum support ms functional can be used to improve the resolution of blocky structures however in crosshole gpr traveltime tomography the ms functional is unable to resolve residual artifacts whose departure from an a priori model are smaller than the focusing parameter selected from a trade off curve in addition it would result in severe instability and yield a trade off curve with poorly defined corners when the focusing parameter nears the precision of the apparatus we have developed a new stabilizing functional based on the arctangent at function that effectively removes the artificially small values i

group velocity tomography and regionalization in italy and bordering areas abstract more than 200 group velocity dispersion curves 109 new dispersion data and 101 collected from literature of the fundamental mode of rayleigh waves in the period range from 10 to 35 s have been processed to obtain tomographic maps for the italian peninsula and bordering areas we compute average dispersion relations over a 1 1 grid and since the lateral resolving power of our data set is of about 200 km we group the cells of the grid according to their dispersion curves in this way and without any a priori geological constraints we define seven different regions each characterised by a distinctive mean group velocity dispersion curve the resulting regionalization can be easily correlated with the main tectonic features of the study area and mimics a recently proposed structural sketch average models of the shear wave velocity in the crust and in the upper mantle for a few selected regions are presented the very low s wave velocity values found in the uppermost upper mantle of the southern tyrrhenian basin are consistent with a large percentage of partial melting in agreement with the presence of the vavilov magnaghi and marsili huge volcanic bodies

active tectonics in central italy constraints from surface wave tomography and source moment tensor inversion abstract we investigate the lithosphere asthenosphere structure and active tectonics of central italy with emphasis on the umbria marche area by means of surface wave tomography and seismic moment tensor inversion the data include a large number of short period local and regional group velocity measurements sampling the umbria marche apennines and the adria margin respectively incorporation of published phase velocity measurements sampling italy and surroundings results from deep seismic soundings which go through the umbria marche area the local group velocity maps covering the area reactivated by the 1997 1998 umbria marche earthquake sequence suggest an intimate relationship between the lateral earth structure variations and the distribution of the active fault systems and related sedimentary basins the upper crustal models reveal the importance of inherited compressional tectonics on the recent extensional deformation and associated seismic activity source inversion studies of the main events of the 1997 earthquake sequence show the dominance of normal faulting mechanisms whereas selected aftershocks between the fault segments at the step over reveal that the prevailing deformation is of strike slip faulting type at the regional scale the crust exhibits clear layering and varies in thickness from about 25 km below the tuscan metamorphic complex tmc to about 30 km below the val tiberina extensional thick sedimentary basin and reaches about 35 km below the umbria marche geological domain umd the lithospheric mantle lid is thin about 30 km below tmc while it is about 70 km thick below umd a lithospheric root about 120 km wide between the tmc and umd reaches a depth of at least 130 km a low velocity zone defined mantle wedge vs less than 4 2 km s in the uppermost mantle overlying the high velocity lid is detached this wedge is about 20 km thick and decouples the underlying lid from the crust the retrieved crust and upper mantle structure beneath central italy is in agreement with bouguer anomaly and heat flow data and supports a delamination process the high velocity upper mantle underlying the mantle wedge is inferred to be subcrustal lithospheric material delaminated from the overlying crust

the use of geophysical prospecting for imaging active faults in the roer graben belgium as part of a paleoseismological investigation along the bree fault scarp western border of the roer graben various geophysical methods electrical profiling electromagnetic em profiling refraction seismic tests electrical tomography ground penetrating radar gpr and high resolution reflection seismic profiles were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters these geophysical investigations in parallel with geomorphological and geological analyses helped in the decision to locate trench excavations exposing the fault surfaces the results could then be checked with the observations in four trenches excavated across the scarp geophysical methods pointed out anomalies at all sites of the fault position the contrast of physical properties electrical resistivity and permittivity seismic velocity observed between the two fault blocks is a result of a differences in the lithology of the juxtaposed soil layers and of a change

extensional tectonics in the central iberian peninsula during the variscan to alpine transition abstract the passage from the variscan cycle to the early alpine framework in the central part of the iberian peninsula can be explained in terms of a transitional process involving four clearly differentiated tectonic episodes 1 1 a first variscan compressional stage vi middle devonian to early carboniferous dominated by compressional conditions leading to the building up of the orogenic edifice the stress regime was relevant to what might be called variscan type compression e w oriented this stage was characterized by major himalayan type tectonics with frontal nappes thrusts overturned folds lateral transcurrent ramps and localized anatectic magmatism minor synorogenic extension and plutonism was also recorded during this stage in the tormes granitic dome 2 2 a second variscan stage v2 early to middle carboniferous was characterized by increasing extensional conditions leading to widespread plutonism adamellites granodiorites wanning compressional conditions were restricted to the eastern and southern realms of central iberia the eastern part of the spanish central system and the toledo mountains 3 3 a third stage here defined as late variscan lv developed from middle carboniferous to early permian as a result of n s late orogenic extension this episode is relevant to detachment tectonics and the gravitational collapse of the variscan orogenic edifice under combined simple pure shear conditions plutonism granites and leucogranites was still of major importance early permian andesitic to dacitic volcanism and sedimentary basins developed within the eastern part of the spanish central system 4 4 a fourth stage here defined as early alpine ea early permian to triassic marks the onset of the alpine framework this stage was characterized by what might be called an early alpine type regional stress regime i e e w extension and n s compression within a simple shear model and resulted in the configuration of the iberian peninsula into two contrasted realms a western inherited variscan block and an eastern alpine block subjected to post orogenic extension elements developed during this event include n s high angle normal faults nw se and ne sw conjugate strike slip faulting and asymmetric rifting involving listric low angle detachments

3 d ground penetrating radar applied to fracture imaging in gneiss three dimensional ground penetrating radar georadar techniques suitable for geological engineering applications have been developed and tested initial experiments were conducted on the floor of a quarry in southern switzerland from which ornamental gneissic rock is extracted during a brief two day period constant offset georadar data were recorded over a 650m2 area with a grid cell size of 0 1 m 0 2 m georadar velocities were estimated from the results of expanding spread surveys all georadar data and associated geometry files were recorded automatically in seismic industry formats the experimental georadar data set was processed image enhanced and interpreted using 3 d seismic reflection software operating on a workstation arbitrary vertical sections time slices 3 d images and animated movies in which the observer travels through the entire data volume were constructed from the resultant migrated georadar data semi automatic tracking routines allowed continuous subhorizontal reflectio

tectonostratigraphic evolution of the morichito piggyback basin eastern venezuelan basin abstract the morichito piggyback basin mpb is a sw ne oriented depocenter in the eastern venezuelan foreland basin evfb this piggyback basin formed by overlying the pirital thrust during the middle to late miocene as a result of oblique collision between the caribbean and south american plates the mpb covers an area encompassing approximately 1000 km 2 between the serrania del interior range and the pirital high which is a hanging wall uplift along the pirital thrust that acts as a confining barrier on the southern boundary of the mpb previous studies have tried to address the tectonostratigraphic significance of the mpb but new biostratigraphic information and recently acquired 3d seismic data have allowed us to expand the understanding of this basin the mpb occupies a relatively small area of the evfb however the mpb contains a valuable stratigraphic record that can be used to unveil the timing of the main deformational events that took place in the evfb this work presents the tectonostratigraphic evolution of the mpb by defining four tectonostratigraphic sequences t1 t4 each sequence was defined on the basis of integration of well logs biostratigraphy and seismic geomorphological interpretations t1 24 16 ma late oligocene to middle miocene which was deposited in shallow marine environments extends to the south of the pirital high beyond the boundaries of the mpb t1 is equivalent to the early foredeep stage of the evfb having been formed when structural deformation and uplifting were already occurring to the north on the proto serrania del interior range 24 16 ma and the pirital thrust was active 22 ma t2 16 11 ma middle to late miocene is composed of alluvial fan deposits derived from the proto serrania del interior range the geometry and internal configuration of t2 indicate that during this time the basin was transitioning from an open foreland basin to a confined piggyback basin during deposition of t2 the pirital fault was active as an out of sequence thrusting event 16 11 ma t3 late miocene and t4 early pliocene to recent composed of shallow marine and fluvial deposits were deposited in an already restricted piggyback basin the pirital high was already in place during deposition of t3 11 9 3 ma t3 and t4 represent the final phases of mpb infilling when tectonic activity and subsidence were at their lowest rates mpb sedimentary infilling dates the activity of thrusting events in the proto serrania del interior 24 16 ma timing of maximum deformation associated with the pirital out of sequence thrusting event 16 11 ma timing of final emplacement of the pirital high 11 9 3 ma and the beginning of tectonic quiescence

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

active tectonics in the central apennines and possible implications for seismic hazard analysis in peninsular italy abstract the central apennines fault system cafs of peninsular italy overprints earlier structures of a neogene fold and thrust belt and includes segments characterized by diffuse seismicity distributed within a nnw sse trending zone 50 60 km wide the system has been analysed by means of morphotectonic and structural analysis of exposed active fault segments the resulting fault structure consists of an interconnecting network of roughly n s trending left lateral strike slip segments and mostly nw se oriented transtensional to normal faults evidence for recent activity of cafs structures is provided by faulted middle pleistocene holocene deposits including 30 40 ka old pyroclastites and 40 ka old palustrine sediments fresh scarps in both bedrock and late quaternary continental deposits and decametric lateral offsets locally affecting the post wurmian drainage pattern of the area the regional stress field responsible for the development and evolution of the cafs as inferred from fault slip data is characterized by a nw se compression and by a ne sw extension the cafs pattern and its present day kinematics have been related to left lateral strike slip motion on north south trending crustal faults the existence of deep seated strike slip faults in the central apennines has implications for seismic hazard analysis motion along these structures suggests in fact that coseismic surface faulting is distributed and that cumulative displacements include normal transtensional and strike slip components the seismogenic potential of cafs structures can therefore be best described by multiple rupture models and be better analysed in terms of partial contributions of lower rank features constituting congruent structural associations within the system

eocene paleomagnetic pole for south america northward continental motion in the cenozoic opening of drake passage and caribbean convergence 1 a paleomagnetic study of eocene volcanic rocks in patagonia yields high unblocking temperature and high coercivity magnetizations combining these results with those of a previous study on patagonian eocene basalts yields a high precision high quality pole located at latitude 81s longitude 337 4e a95 5 7 critically this paleopole is indistinguishable from that of the late cretaceous circa 85 65 ma pole position of south america indicating that the plate was essentially motionless with respect to the spin axis for a period of 45 m y the pole position places south america at higher 5 than present day latitudes during the eocene indicating that northward continental motion toward present day latitudes must have been accomplished sometime since the late eocene paleomagnetic and tectonic correlation admits the hypothesis that cenozoic northward drift was associated with oligocene miocene extension in the southern continental edge leading to the opening of the drake passage and it agrees with the timing of foredeep formation and development of fold thrust belts in the northern continental edge this positive correlation between the paleomagnetically predicted drift of a major continent with extension at its trailing edge and convergence at its leading edge during times for which seafloor tectonic fabric and the geological record are particularly well preserved illustrates the utility of paleomagnetism in constraining paleogeographic and tectonic reconstructions for pre cretaceous times

peculiarities of surface wave propagation across central eurasia abstract the recent installation of six broadband digital iris ida seismic stations in the ussr has provided new opportunities for studying surface wave propagation across eurasia group velocities of fundamental rayleigh and love modes between epicenters and these stations were determined for 35 events that occurred since april 1989 to the middle of july 1990 near eurasia differential phase velocities were found for the same arrivals along paths between several pairs of stations group and phase velocities were obtained in the period range from 15 to 300 sec frequency time polarization analysis was used for studying polarization properties of surface waves in some cases significant anomalies in the particle motion for periods up to 100 sec were observed they are attributed to surface wave refraction and scattering due to lateral inhomogeneities at the boundaries and inside the eurasia continent

mapping fractures with gpr a case study from turtle mountain ground penetratingradargprsurveyswereacquiredof rocks on the highly fractured summit of turtle mountain in canada in 1903 a disastrous rock slide occurred at turtle mountain and it still poses a geologic hazard dips shapes and penetration depths of fractures are important parameters inslope stabilityanalysis determinationoffractureorientation at turtle mountain has been based mostly on areal geologic mapping and most recently on data collected from boreholes the purpose of gpr surveys was to test confirm and extend information about fractures and bedding planes data acquisition was complicated by the rough terrain because slopes are steep and uneven this also complicated analysis of the data measurement of in situ velocity an important value for migration was impossible instead data were migrated with different velocities and data results were chosen that were considered to be reasonable analysis and interpretation of the data resulted in confirmation and extension of the a priori information on orientations of fractures and bedding planes at turtle mountain despite the rough terrain and highly fractured rock mass gpr surveys provide reliable information about the shapes and density of fractures informationimportantforslope stabilityevaluation the most reliable migration results obtained for velocities were considerably less than the standard velocities recorded for limestone the dominant lithofacies at turtle mountain we interpret this observation as an indicator of water within the rock however thorough investigation of thisconclusionremainsaprojectforfuturework

global and local controls influencing the deposition of the la luna formation cenomanian campanian western venezuela bulk and molecular geochemical micropalaeontological and carbon isotopic data are used to address the different local and global factors influencing the environment of sedimentation of the la luna formation cenomanian campanian approximate palaeolatitude 15 n in a single section in western venezuela based on the constructed chronostratigraphic framework oxygen depleted bottom water conditions and black shale deposition started in western venezuela well before the widespread occurrence of organic rich sediments in higher palaeolatitude regions such as the tethys and the north atlantic near or at the cenomanian turonian boundary in the la luna formation palaeoenvironmental conditions that allowed the preservation of organic matter mainly of marine origin prevailed until santonian times in a distal platform facies with very low siliciclastic input changes in lithology appear to reflect the local response to eustatic sea level variations and the presence of a migrating upwelling belt affecting the bioproductivity of silica and carbonate a marked 13corg isotopic excursion is recognised in the middle part of the section and is apparently unrelated to local palaeoenvironmental changes in bioproductivity and oxygen depletion biological marker data show no variations in association with the isotopic excursion being mainly controlled by local fluctuations in organic matter input and preservation

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

waveform inversion for point source moment tensor retrieval with variable hypocentral depth and structural model summary in the inversion scheme of high frequency seismograms recorded by a local network we have developed the unconstrained moment tensor description to study weak events which are believed to reflect small scale complexities of the tectonic structure in order to allow the source mechanism to change with time each moment tensor component has its own time history in the inversion the measure of the similarity between the synthetic seismograms and the observed records is obtained by minimizing the norm l2 of their difference the initial synthetic seismograms are constructed by summing a set of time dependent functions named base functions these base functions are computed by normal mode summation for a discrete set of source depths and for two structural models considered to represent acceptable extremes for the region under study in the course of the inversion using a linear interpolation new base functions are computed for intermediate values of the starting depths and structures thereafter new synthetic seismograms are computed and compared with the observed records until the convergence is reached within some pre assigned threshold for the norm l2 the method has been tested by treating as observed records synthetic seismograms both displacement and velocity generated for instantaneous and finite duration sources the observed records have been computed for two structures one belonging to the structural range within which the base functions were computed the other lying outside this range random noise has been superimposed on the records when inverting synthetic records computed for a structure contained within the range of interpolation for the base functions the full moment tensor is retrieved satisfactorily provided that the noise level does not exceed about 20 per cent for records computed for a structure lying outside this range a spurious volumetric part of the moment tensor appears however if the volumetric part of the moment tensor is removed the source time function can be reconstructed satisfactorily and the source mechanism can be determined from the deviatoric part of the moment tensor the procedure has been applied to vertical component seismograms recorded in the friuli ne italy area for the ml 2 9 event of 1987 december 27 the retrieved source mechanism is in agreement with the distribution of the few first arrival polarities available and the source time function indicates a possible multiple rupture process

interpretation of reflection attributes in a 3 d gpr survey at vallee d ossau western pyrenees france to study the attributes of reflected radar waves a 3 d ground penetrating radar gpr data set was recorded processed with promax 3 d seismic processing software and analyzed with stratimagic 3 d seismic interpretation software the zone studied was an old glacial valley vallee d ossau western pyrenees where fluvio glacial deposits 8 10 m thick overlay a karstic limestone bedrock reflections were picked to 250 ns 9 m depth with velocity 0 07 m ns analysis of the isochron map of the bedrock surface reflector showed north south undulations corresponding to the displacement of the old glacier together with sharp discontinuities interpreted as local faults or karstic zones amplitude variations along the reflector were interpreted as being from water saturation and the nearby north south alignment of springs at the surface in the fluvio glacial deposits paths of old channels were also imaged using amplitude analysis the radar wave amplitude attenuation was also characterized within the d

analysis of subsidence in northeastern venezuela as a discriminator of tectonic models for northern south america subsidence analysis of northeastern venezuela9s exposed parautochthonous lower cretaceous miocene sedimentary section reveals an atlantic type passive margin subsidence history for the entire cretaceous middle eocene interval oligocene miocene subsidence was rapid and great and was caused by foredeep formation and emplacement of the fold and thrust belt that now exposes the passive margin sedimentary section our analyses support tectonic models of south america9s northern margin which propose cenozoic eastward migration of a foredeep along northern south america9s late mesozoic passive margin the calculated subsidence is inconsistent with tectonic models that propose middle or late cretaceous subduction or obduction

visualization of active faults using geometric attributes of 3d gpr data an example from the alpine fault zone new zealand three dimensional ground penetrating radar gpr data are routinely acquired for diverse geologic hydrogeologic archeological and civil engineering purposes interpretations of these dataareinvariablybasedonsubjectiveanalysesofreflectionpatterns such analyses are heavily dependent on interpreter expertiseandexperience usingdataacquiredacrossgravelunitsoverlyingthealpinefaultzoneinnewzealand wedemonstratethe utilityofvariousgeometricattributesinreducingthesubjectivity of3dgprdataanalysis weuseacoherence basedtechniqueto compute the coherency azimuth and dip attributes and a graylevel co occurrence matrixglcmmethod to compute the texture basedenergy entropy homogeneity andcontrastattributes a selection of the gpr attribute volumes allows us to highlight key aspects of the fault zone and observe important features not apparent in the standard images this selection also provides information that improves our understanding of gravel deposition andtectonicstructuresatthestudysite anewdepositional structuralmodellargelybasedontheresultsofouranalysisofgprattributes includes four distinct gravel units deposited in three phases and a well defined fault trace this fault trace coincides with a zone of stratal disruption and shearing bound on one side by upward tilted to synclinally folded stratified gravels and on the other side by moderately dipping stratified alluvial fan gravelsthatcouldhavebeenaffectedbylateralfaultdrag whenused in tandem the coherence and texture based attribute volumes can significantly improve the efficiency and quality of 3d gpr interpretation especially for complex data collected across activefaultzones

crustal section based on crop seismic data across the north tyrrhenian northern apennines adriatic sea abstract using deep seismic reflection data from the italian lithospheric exploration project crop in the central mediterranean region a 400 km long section composed of three different profiles crossing the northern tyrrhenian sea crop m 12a profile the northern apennines crop 03 and the adriatic sea crop m 16 is reconstructed and discussed new data allow us to outline a seismically consistent tectono stratigraphic setting for the crust and upper mantle of the northern apennines thrust belt system and its adriatic foreland time space analysis of the deformation of the investigated chain and identification of existing macrostratigraphic crustal intervals and tectonic units allow a reasonably controlled interpretation of the geodynamic evolution and of the main orogenic stages careful seismic reprocessing and application of advanced techniques to key zones of the explored area such as the tuscan archipelago were determinants in obtaining fundamental information for understanding of the complex lithospheric structures and their evolution profile interpretation supports that the northern apennine chain is dominated by a compressive thrust system crustal extension assumed by some authors as the dominating tectonic process for the whole tuscan apennine area represents a subordinate geodynamic event of the last stage tyrrhenian in the early cretaceous late jurassic the paleogeographic framework consisted of the europe and adria plates separated by the alpine tethys ocean during the late cretaceous early eocene adria europe convergence eo alpine stage and subduction beneath the adria plate closed the alpine tethys sea with the tethyan slab being clearly seismically imaged the first apenninic geodynamic stage occurred in the late oligocene early miocene with the opening of the balearic basin which generated a first lithospheric root of the apenninic chain in the tuscan archipelago area this root is represented by adria verging thrust faults that progressively flatten eastward upper parts of the west verging eo alpine thrust blocks were truncated by the east verging thrust faults of the balearic stage a deeper seismic reflector attributed to the top of the asthenosphere forms a mantle high below the elba island from the late miocene to present the corsica basin and western hinterland area were affected by extensional tectonics related to the tyrrhenian opening whereas compressional tectonics continued in the eastern hinterland and mostly on the eastward migrating foreland with development of a second lithospheric root constituted by high angle thrust faults these faults give rise to a huge basement culmination below the main apennines watershed impressive e directed gravity sliding of sedimentary blocks over their sloping basement occur generating the umbria marche shallow seismicity crustal shortening of the apennines system amounts to 170 km 14 km of which are due to the eo alpine stage 71 km to the balearic and 85 km to the tyrrhenian one in the frame of africa europe convergence the tyrrhenian apennines tectonodynamics were mainly conditioned by the mesozoic paleogeography

orogens and slabs vs their direction of subduction abstract subduction zones appear primarily controlled by the polarity of their direction i e w directed or e to nne directed probably due to the westward drift of the lithosphere relative to the asthenosphere the decollement planes behave differently in the two end members in the w directed subduction zone the decollement of the plate to the east is warped and subducted whereas in the e to nne directed it is ramping upward at the surface there are w directed subduction zones that work also in absence of active convergence like the carpathians or the apennines w directed subduction zones have shorter life 30 40 ma than e or ne directed subduction zones even longer than 100 ma the different decollements in the two end members of subduction should control different ptt paths and therefore generate variable metamorphic assemblages in the associated accretionary wedges and orogens these asymmetries also determine different topographic and structural evolutions that are marked by low topography and a fast eastward migrating structural wave along w directed subduction zones whereas the topography and the structure are rapidly growing upward and expanding laterally along the opposite subduction zones the magmatic pair calc alkaline and alkaline tholeiitic volcanic products of the island arc and the back arc basin characterise the w directed subduction zones magmatic rocks associated with e or ne directed subduction zones have higher abundances of incompatible elements and mainly consist of calc alkaline shoshonitic suites with large volumes of batholithic intrusions and porphyry copper ore deposits the subduction zones surrounding the adriatic plate in the central mediterranean confirm the differences among subduction zones as primarily controlled by the geographic polarity of the main direction of the slab the western margin of the adriatic plate contemporaneously overridden and underthrust europe toward the west to generate respectively the alps and the apennines while the eastern margin subducted under the dinarides hellenides these belts confirm the characters of the end members of subduction zones as a function of their geographic polarity similarly to the pacific subduction zones

multiconfiguration gpr measurements for geometric fracture characterization in limestone cliffs alps rock mass fracturing is a key parameter in rock fall hazard assessment however traditional geologic observations can provide information only about discontinuities at the surface in this case study detailed ground penetrating radar gpr measurements with antennas of 50 mhz 100 mhz 200 mhz and 400 mhz were conducted on a test site using different acquisition configurations deployed on vertical cliff faces conventional 2d profile data common midpoint cmp survey data and transmission data were acquired to evaluate the potential use of radar waves to characterize the geometry and properties of the major discontinuities fractures within a mesozoic limestone massif results showed that the continuity and geometry orientation and dip of the major observed fractures which are crucial parameters for assessing rock stability can be obtained by combining vertical and horizontal profiles measured along the cliff we used 100 mhz antennae and reached a maximum penetration of 20 m which limi

the main characteristics of the lithosphere asthenosphere system in italy and surrounding regions we present a summary of the available information on rayleigh wave dispersion data for the italian area the dispersion curves can be grouped into two main families according to their shape one with an almost linear trend in the period range from 40 to 150 sec the other with a relatively flat portion in the period range from 40 to 80 sec the inversion of these data shows that there are strong lateral variation in the lithosphere system a very rapid transition in the lithospheric thickness from about 130 km to about 30 km as well as in the s wave velocity of the lithosphere and asthenosphere

transpression displacement partitioning and exhumation in the eastern caribbean south american plate boundary zone the caribbean south american plate boundary zone in northeastern venezuela is a transpressive orogenic belt consisting from north to south of a nascent subduction zone south caribbean deformed belt a volcanic arc leeward antilles arc a hinterland with high pressure p low temperature t metamorphic rocks cordillera de la costa belt and a southern nonmetamorphic foreland fold and thrust belt serrania del interior the geometry style and orientation of mid cretaceous to tertiary synmetamorphic deformation structures d1 in the hinterland are compatible with formation in a right oblique subduction or collision zone in which displacement partitioning has occurred late oligocene to recent right oblique convergence resulted in the emplacement of the arc and hinterland on the passive south american margin and the formation of the foreland fold and thrust belt d2 the displacements between the caribbean and south american plates are partitioned as well both d1 and d2 deformations are diachronous they are older in the west and younger in the east and related to the eastward passage of the caribbean plate with respect to south america the ascent decompression and exhumation of the high p low t metamorphic rocks occurred in two stages the first in the cretaceous by arc parallel extension d1 and the second in neogene time by thrusting d2 and subsequent erosion

seismotectonic zoning in east central italy deduced from an analysis of the neogene to present deformations and related stress fields this paper concerns the space time evolution of the late miocene to present contractional and extensional deformations within east central italy with an analysis of the pattern and orientation of the related stress field an insight into the cover basement relations and a discussion of the seismotectonic implications the pattern and orientation of the deformation and stress fields have remained unchanged since late miocene time and have been always characterized by the coexistence and parallelism in contiguous areas in a given time of shortening to the east and elongation to the west with time during a multistage deformation history both the contraction and the extension fields have moved eastward basement involved tectonics with a west dipping multiple detachment system would have allowed the progressive eastward shift of crustal slices corresponding at the surface to well defined tectonic domains with consequent crustal thinning in the tuscan zone and crustal thickening beneath the apennine mountain chain by comparing macroseismic epicenters hypocenters and focal mechanisms with crustal structure and independently known active faults it appears evident that the pattern frequency and distribution of the crustal seismicity are tectonically controlled and that a contraction extension pair is active also at the present time in fact along the adriatic coastline contractional deformation prevails with involvement of pleistocene layers whereas beneath the apennine range extensional deformation prevails both t axes in the inner domain and p axes in the outer domain are oriented southwest northeast or west south west east northeast and this coaxiality reflects the situation depicted by the geologic stress field on this basis we have produced a seismotectonic zoning of east central italy with three distinct domains intramountain seismic zone isz foothills seismic zone fsz and coastal seismic zone csz a plausible explanation for the genesis of the active seismic deformations of east central italy is that the locally intense extensional upper crustal seismicity of the intramountain seismic zone is confined to the hanging wall of a major west dipping active extensional discontinuity whereas the less frequent contractional seismic activity of the coastal seismic zone is within the hanging wall of an outer major active west dipping contractional discontinuity an area of overlap between these two zones is represented by the foothills seismic zone where superposed epicentral patterns from different surfaces of weakness at different depths are the predictable result of the asymmetry of the deformation

application of gpr to a site investigation involving shallow faults a series of ground penetrating radar gpr lines were acquired on a proposed multistory building site in fayetteville arkansas because engineering work implied the existence of a shallow fault building a heavy structure in the vicinity of this fault would involve risk due to differential settlement solution cavities and fault reactivation in this case the new radar surveys combined with pre existing borehole data and regional geological knowledge verified and mapped the fault

upper mantle properties of the tuscan tyrrhenian area a framework for its recent tectonic evolution abstract within the alpine mediterranean deformational system several interesting features in the physical properties of the upper mantle have been recognized through the regional analysis of surface wave dispersion a large upper mantle anomaly uma here called the tuscan uma has been identified in the area northeast of corsica which includes part of the northern tyrrhenian sea and part of the north central apennines this anomalous upper mantle area together with the upper mantle characteristics of the tyrrhenian sea located further to the south provides a natural framework for comprehensive interpretation of the large data set of geological and geophysical observations such as land and marine geology volcanism gravity magnetic data seismic data and seismology deep temperatures and surface heat flow

mapping contaminant transport structures in karst bedrock with ground penetrating radar ammonium perchlorate a risk to human health was used formerly to manufacture rocket fuel at the naval weapons industrial reserve plant nwirp mcgregor mclennon county texas perchlorate exists in several groundwater contaminant plumes whose geometries were suspected to be influenced by transmissive bedrock structures to identify these possible contaminant transport pathways a towed array ground penetrating radar gpr system was used to acquire 118 line km of data across 478 hectares of the property the shallow geology consists of bedrock limestone overlain by 0 to 3 m of clay soil for the 50 mhz antennas used the conductive clay limits depth penetration to less than 3 m and yields a 1 4 m wavelength reducing lateral and vertical resolution nevertheless gpr data resolved the top of bedrock in many areas linear discontinuities in bedrock were interpreted as weathered fracture zones and linear areas of signal loss were attributed to deeper clay weathering along fracture zones gpr interprete

moment tensor analysis of the central italy earthquake sequence of september october 1997 the larger earthquakes in the umbria marche central italy seismic sequence of september october 1997 are analyzed using long period seismograms from the mediterranean seismographic network mednet and additional data from the global seismographic network gsn we modify the harvard centroid moment tensor cmt algorithm to allow moment tensor inversion of long period waveforms primarily rayleigh and love waves for small earthquakes at local to regional distances 5 5 in the sequence moment tensors have previously been determined using teleseismic waveforms and standard methods of analysis our results agree well with those of earlier studies we determine additional moment tensors for the largest foreshock and 10 aftershocks with mw 4 2 the earthquakes are characterized by normal faulting mechanisms with a ne sw tension axis and the presumed fault plane dips towards the sw only one of the fourteen events studied has a different faulting geometry indicating instead right lateral strike slip faulting on a plane oriented approximately e w or left lateral faulting on a plane oriented n s the september 26 mainshock 09 40 ut accounts for only approximately 50 of the total moment release in the sequence

tomographic constraints on the geodynamic evolution of the italian region in this paper we present p wave tomographic images of the mantle beneath italy obtained by inverting 6000 teleseismic p and pkp wave arrival times accurately repicked recorded in the time period 1988 1994 by the stations of the national seismic network of the istituto nazionale di geofisica we pay great attention in the data selection and picking procedure of seismic phases to obtain a very high quality data set the data were inverted with the well established aki christofferson husebye tomographic technique different reference models and residuals computation have been tried to verify the stability of the results the high quality of the repicked arrival times allows us to enhance the definition of the deep structures beneath both the alps and the apennines looking for their lateral and vertical continuity down to 800 km depth the main finding of this study is a continuous high velocity body located between 250 and 670 km depth beneath the entire apenninic system dipping toward the tyrrhenian area which continues upward segmented in two main anomalies in the northern apenninic and the calabrian arcs we interpret this high velocity feature as the subducted oceanic lithosphere between the eurasian and african plates dipping down to the upper lower mantle boundary beneath the tyrrhenian sea the retrieved images of the lithosphere subducting beneath apennines are reliable in terms of thickness about 80 90 km and p wave velocity contrast 2 4 higher than the normal mantle furthermore our tomographic images which focus on the deep geometry and continuity of the velocity structures provide new keys to understanding the geodynamic evolution of the italian region the segmentation of the high velocity slab upward suggests a complex evolution of the arc trench system and the initially continuous subduction of the ionian adriatic plate progressively developed in subordinate arcs probably due to lateral heterogeneity of the subducting lithosphere

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

eurid a regionalized 3 d seismological model of europe abstract this paper presents a 3 d regionalized model of the european crust and mantle velocity structure down to depths of approximately 300 km the model is entirely based upon the existing geological and geophysical literature and it incorporates topographic and bathymetric features the resulting model which we call eurid european i data set consists of approximately 6400 1 d vertical structures having an average separation of about 100 km eurid is compared quantitatively with eur s91 a recent s wave velocity tomographic model obtained from body and surface wave waveform inversion zielhuis a nolet g 1994 shear wave velocity variations in the upper mantle beneath central europe geophys j int 117 695 715 it is found that the s wave velocities in eurid and in eur s91 zielhuis and nolet 1994 do not differ by more than about 4 over most of the area to validate eurid surface wave dispersion analysis is performed along some selected paths the fundamental mode group velocity curves obtained using 1 d average models derived from eurid are found in good agreement with those determined from observations broadband waveform synthetics are also calculated along the same paths and compared with the observed time series overall we believe that eurid is representative of our current knowledge of the crust upper mantle structure beneath europe and it can be used to model realistically ground motion for periods above 10 s within structurally homogeneous regions the first digital version of this structure database is available for public use

heavy mineral record of andean uplift and changing sediment sources across the ne margin of south america a case study from trinidad and barbados the heavy mineral compositions of sandstones in trinidad and barbados record the onset of andean related erosion and a reduction of craton derived sediments into ne south america the changing provenance was deduced by comparing heavy mineral assemblages interpreted from ancient sandstones with associations recognized in modern sands that can be reasonably correlated to existing tectonic domains the impact of the andean orogeny across the margin was to introduce a suite of minerals characteristic of low temperature metamorphism that today is prevalent adjacent to the caribbean mountain belt and differs from the zircon rich assemblage produced within cratonic plains twenty one paleocene late pliocene sandstone samples from trinidad revealed systematic changes in mineral diversity and maturity that recorded this provenance transition and suggests andean erosion during deposition of the late oligocene nariva formation similar to palaeogene sandstones of trinidad four eocene scotland formation samples from barbados support craton derivation but with additional evidence of minor andean input probably due to the proximity of the scotland formation delivery systems to an earlier uplift episode by the late miocene most of the sediments delivered into trinidad basins were supplied from the andean orogeny as suggested by the relative abundance of minerals of this affinity the heavy mineral records of trinidad and barbados are similar to that described across northern south america from both modern and ancient environments that collectively mark the uplift of the andean mountain belt with its strong influence on drainage patterns and reservoir provenance along this sector of the continental margin

characterization of a coalesced collapsed paleocave reservoir analog using gpr and well core data the three dimensional architecture spatial complexity and pore type distribution are mapped in a near surface analog of a coalesced collapsed paleocave system in the lower ordovician ellenburger group near the city of marble falls in central texas the surface area of the site has dimensions of about 350 1000 m the data collected include about 12 km of 50 mhz ground penetrating radar gpr data arranged in a grid of orthogonal lines 29 cores of about 15 m length and detailed facies maps of an adjacent quarry face electrical property measurements along with detailed core descriptions were the basis of integrated interpretation of the gpr data three main gpr facies are defined on the basis of degree of brecciation in the corresponding cores undisturbed host rock disturbed host rock and paleocave breccia this gpr facies division defined the major paleocave trends and the distribution of porosity types which correlate with reservoir quality highly brecciated zones are separated by disturbed an

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km