time resolved seismic tomography detects magma intrusions at mount etna the continuous volcanic and seismic activity at mount etna makes this volcano an important laboratory for seismological and geophysical studies we used repeated three dimensional tomography to detect variations in elastic parameters during different volcanic cycles before and during the october 2002 january 2003 flank eruption well defined anomalous low p to s wave velocity ratio volumes were revealed absent during the pre eruptive period the anomalies trace the intrusion of volatile rich 4 weight percent basaltic magma most of which rose up only a few months before the onset of eruption the observed time changes of velocity anomalies suggest that four dimensional tomography provides a basis for more efficient volcano monitoring and short and midterm eruption forecasting of explosive activity

fission track analysis reveals character of collisional tectonics in new zealand during the late cenozoic the pacific plate has been obliquely converging with the australia plate in south island new zealand this has resulted in westward obduction of continental crust of the pacific plate and consequently a major mountain range the southern alps has formed east of the alpine fault and within the leading edge of the pacific plate we have applied the apatite and zircon fission track dating technique to a suite of outcrop samples from three transects across the southern alps starting at the alpine fault to better understand the uplift age and structure of the continental collision the results show the following 1 uplift was underway at 7 ma in the south at haast pass and by 5 ma in the north at arthur s pass 2 profiles of the total amount of late cenozoic uplift show an exponential increase toward the alpine fault adjacent to the alpine fault there has been 14 5 to 21 5 km of uplift in the vicinity of haast pass 14 5 to 21 km near mt cook and 12 5 to 15 5 km in the arthur s pass transect adjacent to the alpine fault in the mount cook region the average uplift rate from 5 5 ma to 1 ma was 2 3 to 2 5 mm yr between 1 ma and the present it has averaged 6 2 mm yr the strongly asymmetric uplift pattern is responsible for the exposure of a 13 25 km wide belt of greenschist to midamphibolite facies rocks immediately east of the alpine fault known as the alpine schists 3 late cenozoic uplift of torlesse greywackes and alpine schists was preceeded during the jurassic early cretaceous by 5 8 km of uplift the otago schist belt to the south was uplifted much more during this interval and in addition western parts of the otago schists were uplifted 5 6 km during the late cretaceous 4 the fission track data do not support the notion of significant late cenozoic shear heating about the alpine fault as previously suggested from spatial variations in k ar ages of the otago and alpine schists

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

evolution of volcanism around the eastern sector of mt etna inland and offshore in the structural framework of eastern sicily abstract the authors highlight a new perspective to understanding the volcanism in the mt etna eastern sector inland and offshore based on original studies of the sea floor off the ionian coast of etna by means of various direct surveying methods underwater explorations and indirect ones bathymetric reconstructions using echosounders they also propose a new interpretation of geophysical geochemical and structural surveys carried out over the last two decades results show that eastern etnean sector s volcanism extends as far as the ionian sea to a maximum distance from the coast of probably about 20 km in their opinion the absence of outcropping apparatuses in the lower eastern flank of etna is due to these apparatuses being buried by a large detritic formation chiancone due to the dismantling of the ancient alkaline centres aac localised to the west the authors consider the structures highlighted by the study of the digital elevation model dem of the ionian sea floor and by the multibeam analysis marani et al 2004 from seafloor to deep mantle architecture of the tyrrhenian backarc basin vol 44 mem descr carta geol ital pp 1 2 to be of a volcanic nature this hypothesis opens up a new field of study within the evolution of the eastern etnean edge s volcanism inland and offshore in the last 500 ky and would further confirm the eruptive axes migration from east to west

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

age relations among oslo rift magmatic rocks implications for tectonic and magmatic modelling abstract this paper presents a compilation of 67 published and unpublished radiometric age determinations by the rb sr method on magmatic rocks in the continental oslo rift in southeast norway the data include most major rock types and structural units in the subaerial part of the rift the implications of these data with respect to the tectonomagmatic evolution of the rift and processes in the mantle and crust are discussed the oslo rift was active for about 60 million years the earliest recorded magmatic activity was the intrusion of basaltic and syenitic sills in the pre rift lower paleozoic sediments at about 300 ma extrusion of plateau lavas of basaltic and intermediate composition rhomb porphyries started about 295 ma and lasted to about 275 ma with largest magma volumes and highest extrusion rate from 295 to 285 ma in the vestfold graben segment gs one flow per 250 000 years and 0 30 km3 per 103 years the main faulting activity and graben formation occurred during this period the plateau volcanism was succeeded by a stage of bimodal central volcanoes most of which later underwent caldera collapses ring dykes and central intrusions in these calderas give ages in the range 268 266 ma in the vestfold and 266 243 ma in the akershus gs large composite intrusive complexes were emplaced in the periods 27 268 and 273 241 ma in the vestfold and akershus gs respectively a rate of propagation of the rift from ssw towards the nne has been estimated to 1 2 cm y 1 on the basis of 87 sr 86 sr initial ratios and type of magmatic products we estimate magmas to have been emplaced into the crust only during the first 20 25 ma of the magmatic period some of the magmatism appears to be initiated by movement along precambrian fault zones which were reactivated during the oslo rifting event

influence of hegenshan heihe suture on evolution of late mesozoic extensional structures in wunite depression erlian basin inner mongolia china we integrate previous work on the hegenshan heihe suture with our interpretation of geomagnetic anomaly and seismic reflection data to investigate the role of the hegenshan heihe suture in the evolution of late mesozoic extensional structures in the wunite depression of the erlian basin sags in the wunite depression present as ne50 trending in the western sector n0 ne30 trending in the central sector and ne45 trending in the eastern sector our results highlight the importance of the pre existing hegenshan heihe suture in the evolution of the late mesozoic rift system and reveal the following details 1 the ne50 extent sags in the western sector are controlled by the c ne50 trending suture moreover the extensional deformation of the reactivated suture during early cretaceous time resulted in a further vertical and horizontal extension of major border faults 2 the n0 ne30 extent sags in the central sector are influenced by the c ne75 trending suture the sinistral strike slip component of the reactivated suture during early cretaceous time resulted in a strike rotation of major border faults from nee trending following the suture to nne trending 3 because of strike slip deformation which resulted from the deformation of the reactivated suture accrued in major border faults light dip slip deformation led to less vertical offset 4 the ne45 trending sags in the eastern sector are controlled by the c ne45 trending suture moreover the extensional deformation of the reactivated suture during early cretaceous time facilitated a further vertical and horizontal prolongation of major border faults

finite duration extension and decompression melting abstract decompression melting of the upwelling mantle during extension of continental lithosphere provides a viable mechanism for the magmatism observed in many rifted sedimentary basins and passive volcanic margins a model has been developed in which in addition to the adiabatic temperature decrease syntectonic conductive cooling melt transport and emplacement at crustal levels are accounted for the heat equation including latent heat is solved numerically and the incremental melt fraction is traced to simulate dynamic melting the emplaced magma is considered an integral part of the continental crust we find that relative to an instantaneous rifting model with only adiabatic cooling there is a more than 10 decrease in the melt thickness even when the duration of rifting is as short as 1 m y whether extension takes place with constant horizontal velocity or strain rate has important implications for the amount of melt produced consequently pressure release melting does not only depend on the amount of stretching and duration of the rift episode but also on how extension develops through time

asthenospheric structure beneath a neogene basin in southeast hungary abstract beneath one of the subbasins of the pannonian basin formed between the alps carpathians and dinarides the bekes basin in southeast hungary a typical structure of the lithosphere and an upwelling of the asthenosphere can be inferred from seismic reflection geothermal geomagnetic gravity and magnetotelluric investigations in the bekes basin the thickness of neogene sediments reaches 6 7 km i e the basement of the neogene basin sinks 3 4 km over the basin area in the reflection section of the pannonian geotraverse that ends in the bekes basin the crust mantle boundary rises by 5 6 km up to a depth of 22 km in the course of performing and processing seismic reflection measurements particular care was given to the preservation of low frequency 2 10 hz information this explains that data were successfully received even from the upper mantle amplitude distribution of reflection arrivals and the dipping of reflecting surfaces permit to infer an uplift by 15 20 km in the lithosphere asthenosphere boundary which thus is assumed to be at a depth of 40 45 km beneath the bekes basin in geothermal investigations the model was established with seismic results being accounted for assuming an upwelling in the lithosphere asthenosphere boundary the superficial heat flow density corrected for the cooling effect of sediments was in good agreement with the values of model calculations the latest magnetotelluric results support the upwelling position of the lithosphere asthenosphere boundary the geomagnetic anomaly determined over the area of the bekes basin can be explained by the uplifted position of the lower crust the gravity anomaly can be attributed to the combined effect of this and the upwelling in the crust mantle boundary it is hoped that the integrated interpretation of results obtained by various geophysical methods confirms the assumption that said methods permit to investigate the structure of the whole lithosphere and thus the disclosed results may contribute to the completion and precision of basin models studied so far

crustal evolution of the rhinegraben area 1 exploring the lower crust in the rhinegraben rift by unified geophysical experiments abstract unified geophysical investigations of the lithosphere in the rhinegraben rift system have revealed new details of the lower crust and its role in the rifting process the new findings allow an assessment of the compatibility of four different geophysical notions and properties of the lower crust 1 1 the lower crust as the layer beneath the conrad discontinuity with a p wave velocity of about 6 5 km s or greater refraction seismics 2 2 the laminated band of reflections as seen in the near vertical reflection seismic experiments in many parts of the continents 3 3 the ductile part of the crust below the brittle ductile transition devoid of earthquakes in seismically active regions 4 4 the electrical conductivity of the lower crust indicative of dry or wet conditions or still unknown conduction phenomena in the rhinegraben area the lamination of the lower crust serves as an outstanding marker of deep tectonic activity during the rifting process in which the crust of the rhinegraben rift system has been subjected to three different natural dynamic processes 1 uplift by 2 to 3 km with subsequent erosion of the rhinegraben shoulders black forest and vosges mountains caused decompression possibly leading to the formation of a low velocity high electrical conductivity zone right on top of the laminated lower crust beneath the elevated shoulders of the black forest 2 the brittle crystalline wedge of the graben proper subsided nearly undeformed into the lower crust which became about 5 to 7 km thinner below the graben than below the shoulders 3 the deepest hypocentres in the black forest dinkelberg area if projected onto the neighbouring reflection profile would be located 7 to 8 km within the laminated lower crust beneath the southern black forest indicating a discrepancy between the top of the lower crust as defined by the brittle ductile transition as seen by the deepest earthquakes and by the top of the laminated reflection band the rhinegraben rift system reveals the properties and behaviour of the lower crust under a wide variety of tectonic situations

footwall geometry and the rheology of thrust sheets abstract the inter relationships between the exact footwall geometry and the rheology of thrust sheets are investigated deviations in the thrust fault surface from an ideal plane will induce a local heterogeneous deformation the resulting deformation processes depend upon the rate of thrust sheet displacement the geometry of the feature causing heterogeneous flow the deformation conditions and the lithologies involved two classes of features are particularly important in causing heterogeneous deformation in thrust sheets the first features are small perturbations on bedding planes which may be inherited sedimentary structures or produced during layer parallel shortening the second class of features are ramps where the thrust sheet climbs up the stratigraphic section displacement over these features causes repeated cyclic straining in the hanging wall during movement the strain rates associated with deformation at perturbations ramps of different geometries and different displacement rates are estimated and used to discuss the influence of footwall geometry on the structural evolution of a thrust sheet particular attention is given to the range of fault rocks and deformation microstructures preserved after movement over a footwall with a complex geometry perturbations are suggested to be important in the localization of ramps either because they create sticking points near the fault tip during propagation or because they induce eventual failure in the hanging wall after the movement over a number of these features raises the accumulated damage to a critical level analysis of the influence of the exact geometry of ramps on deformation processes during displacement leads to two important conclusions firstly the exact geometry of ramps i e the maximum dip angle and the straining distance from a flat to this maximum angle may be used to estimate a maximum displacement rate of the thrust sheet secondly the listric geometry of ramps may be an equilibrium shape adjusted to the displacement rate and the rheology of the hanging wall adjustments towards the final geometry may involve the generation of shortcuts on either hanging or footwall which reduce the imposed deformation rate in the hanging wall during displacement

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

fractal dimension of fault systems in japan fractal structure in rock fracture geometry at various scales based on fault maps whether or not the fracture geometry of rocks is self similar was examined by using a box counting algorithm the statistical self similarity fractal structure of the fault fracture systems holds well at the scale of about 2 to 20 km the fractal dimension in japan varied from 1 05 to 1 60 the fractal dimension is about 1 5 1 6 at the central part of the japan arc and decreases with distance from the center at a smaller scale the fractal structure also holds well in the rock fracture geometry the fractal dimension of the north izu peninsula fault system branching faults is 1 49 at the scale of 0 625 to 10 km the fractal dimension of rock fracture geometry at the scale order of 10 1 to 10 2 meters is about 1 49 1 61 the upper limit of the fractal dimension of rock fracture geometry is about 1 6 judging from the estimation of fractal dimension on actual fracture geometry of rocks this value may impose a restraint on modeling of faulting and the fracture process of rocks

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

introduction to special issue on integrated basin studies ibs a european commission dgxii project this issue contains papers issued from the integrated basin studies project ibs which is part of a larger program of the european commission dgxii entitled geosciences ii the ibs project ec contract jou2 ct92 0110 originated in geosciences consultation meetings the first of them being held in strasbourg in june 1989 under the auspices of mr hubert curien former french minister for research and technology and the subsequent meeting being held in brussels these consultation meetings have resulted in the conclusion that a main axis of future research in geosciences should be the study of sedimentary basins upstream of industrial activities mainly the oil and gas industry but also water resources management the mining industry the storage of undesirable products and coastal engineering they also resulted in the conclusion that future research on sedimentary basins should fulfill two requirements integration of disciplines and modelling such a conclusion may now seem trivial but was not so generally accepted at that time in this spirit the ibs project was designed to provide the oil and gas industry with a new generation of models for basin formation basin evolution and basin fill architecture from basin scale to reservoir scale its main objectives are the linkage of crust thermomechanical behaviour to basin formation and deformation mechanics and the corresponding modelling the quantification of tectonic control on the sedimentary record and the analysis of compaction and mass and heat transfer the ibs strategy is to link subsurface data to field data and an important part of the project is devoted to thematic field studies in european sedimentary basins of different tectonic styles taken as natural laboratories basin research has gone through a rapid evolution during the last decade in particular through the development of new acquisition and processing methods for seismic data and advances in drilling technology modelling provides an important tool to analyse different aspects of basin formation processes and find their tectonic expression in the basin fill the need for 3 d modelling techniques and models capable of linking processes operating on basinwide to subbasin scales is increasingly recognized and a significant effort has been made in the ibs project to develop a new generation of basin formation models coping with these needs see also cloetingh et al 1993a van wees and cloetingh 1994 as many data required to test these models reside in industrial companies ibs has promoted a closer link between academic research and basin studies carried out by industry the participation of the petroleum industry has been vital in this project and ibs has been able to establish a well functioning system of cooperation that not only facilitated data access but most important guaranteed the suitability of the end products of the project this has led to an intensive exchange of modelling concepts and data sets between industry and academia the ibs project has also used extensively the international lithosphere program task force origin of sedimentary basins see cloetingh sassi and task force team 1994 cloetingh et al 1993a b 1994 to implement planning and to discuss preliminary results it also builds partly on joint research through the european commission tempus and peco programs on pannonian basin studies horvath 1993 van balen and cloetingh 1995 van balen et al 1995 horvath and cloetingh 1995 a stimulating aspect of the activity of the ibs group is the creation of a research network in the corresponding field of knowledge which comprises now 30 teams belonging to eight european countries england france germany hungary norway spain switzerland and the netherlands this demonstrates the capacity of the procedures used by the dgxii of the european community to formulate a really european research space phd students and young researchers form an important component of the research groups

two dimensional p t t modelling and the dynamics of extension and inversion in the betic zone se spain abstract the internal zone of the betic cordilleras offers a unique opportunity to study the dynamics of lithospheric processes at mid crustal levels which controlled the formation and evolution of the southeastern margin of iberia in this paper we present the result of two dimensional numerical modelling of p t t paths related to latest oligocene and early miocene extension and inversion in the betic zone the ages of p t t loops are constrained by an extensive data set of geothermo barometric and geochronological data including 40 ar 39 ar laser probe data we investigate the thermo mechanical evolution of the betic zone using numerical models for simple shear pure shear and combined shear the wernicke simple shear model fails to explain the observed temperatures in excess of 500 c and is not consistent with the occurrence of intrusions of ultramafic rocks in the western betics however the delaminated simple shear model with low angle faults located only at lower crustal levels is found to be consistent with the p t t data after a heating phase associated with a finite extension of 80 km rapid cooling occurred reflecting inversion of the extensional structure by nw se to n s directed compression palaeo rheological models for the latest oligocene early miocene times demonstrate the important role of the detachments produced during crustal extension for the dynamics of the subsequent inversion phase the modelling strongly suggest that inversion locked after 60 km of finite convergence after locking of the inversion overthrusting in a northward direction occurred which is compensated by pure shear deformation in the lower crust in the southeastern part of the betic zone

ground and marine magnetic surveys of the lower eastern flank of etna volcano italy abstract in 1996 and 1997 two high resolution magnetic surveys one on land and the other at sea were carried out on the lower eastern flank of mount etna the magnetic surveys covering an area of about 400 km2 aimed to elucidate the relationships between the main tectonic and morphologic features of this flank of mount etna major features include widespread nnw and nne trending active faults and the valle del bove a depression considered to be the source area of the chiancone deposit the largest etnean volcaniclastic sequence magnetic surveys show anomalies that roughly follow the trend of active main structures although few magnetization measurements are available for the most representative outcrops of the lower eastern side of mount etna interpretation of the anomalies defines the underground geometry of the chiancone deposit and its relationship with volcano stratigraphic units and the underlying sedimentary rocks in particular a volume of about 14 km3 was ascribed to the chiancone deposit such a large amount of material was likely produced by a catastrophic event and deposited at different periods at the exit of the valle del bove in an area produced by the interaction on a regional scale of the main tectonic structures affecting this flank of the volcano

seismic reflection coefficients from mantle fault zones summary several bright reflections from structures within the mantle can be seen on birps deep seismic reflection profiles we have calculated apparent reflection coefficients for the brightest of these events and obtain values around 0 1 it is not possible to produce such large reflections by either compositional layering or seismic anisotropy if olivine and pyroxene are the only significant minerals in the mantle these large reflections can be produced by a mafic layer or a partially hydrated layer within normal peridotite the brightest reflections seem to be best explained as major faults or shear zones within the mantle

the origin of sedimentary basins a status report from the task force of the international lithosphere program abstract better insights into the mechanisms of basin formation have a direct bearing on the predictive power of forward models for basin fill models that link flexure normal faulting and thrusting on a subbasin scale provide important constraints on the tectonic control of the sedimentary record enabling a quantitative comparsion with eustatic contributions to the basin architecture thus of special importance is the need to link processes with different spatial and temporal scales involved in the evolution of extensional and compressional basins by numerical modelling a new generation of basin modelling concepts and techniques is one of the main objectives of the task force origin of sedimentary basins of the international lithosphere program the focus of this work is on the quantification of the effects of the thermomechanical structure of the lithosphere and its interplay with regional and local stress changes other important developments include the step towards three dimensional modelling and the full integration of rapidly expanding fission track and other data sets to constrain vertical motions in basins as natural laboratories for the interactive testing and development of new basin modelling techniques a number of basins with high quality data from industry government and academia have been selected on the basis of specific testable problems

origin of cratonic basins tectonic subsidence curves show that the illinois michigan and williston basins formed by initial fault controlled mechanical subsidence during rifting and by subsequent thermal subsidence thermal subsidence began around 525 ma in the illinois basin 520 460 ma in the michigan basin and 530 500 ma in the williston basin in the illinois basin a second subsidence episode middle mississippian through early permian was caused by flexural foreland subsidence in response to the alleghanian hercynian orogeny resurgent permian rifting in the illinois basin is inferred because of intrusion of well dated permian alnoites such intrusive rocks are normally associated with rifting processes the process of formation of these cratonic basins remains controversial past workers have suggested mantle phase changes at the base of the crust mechanical subsidence in response to isostatically uncompensated excess mass following igneous intrusions intrusion of mantle plumes into the crust or regional thermal metamorphic events as causes of basin initiation cratonic basins of north america europe africa and south america share common ages of formation around 550 to 500 ma histories of sediment accumulation temporal volume changes of sediment fills and common dates of interregional unconformities their common date of formation suggests initiation of cratonic basins in response to breakup of a late precambrian super continent this supercontinent acted as a heat lens that caused partial melting of the lower crust and upper mantle followed by emplacement of anorogenic granites during extensional tectonics in response to supercontinent breakup intrusion of anorogenic granites and other partially melted intrusive rocks weakened continental lithosphere thus providing a zone of localized regional stretching and permitting formation of cratonic basins almost simultaneously over sites of intrusion of these anorogenic granites and other partially melted intrusive rocks

lithosphere rheology and sedimentary basins introduction the dynamics of sedimentary basins is re flected in the wide range of observational scales inside sedimentary basins the advent of high qu ality data sets have significantly improved the resolution of the record of near surface tectonic processes crustal thinning mechanical and thermal sub sidence sediment filling are involved in exten sional basin evolution and controlled by complex interactions between ductile and brittle modes of deformation of the whole lithosphere the rate of loading extension and sediment filling and the thermal evolution are among the most important controlling parameters these nonlinear interac tions do possess a memory of the evolution his tory and loading quantitative understanding of basin subsidence and the offlap onlap strati graphic patterns of a specific basin obviously benefits from progress in understanding the geo dynamical context horvlth 1993 this issue in compressional settings foreland basins re sult from the flexural lithospheric response to loading most of the models proposed so far have considered the lithosphere as a rheological unit and have been based on classical elastic and viscoelastic plate theory the wavelength and am plitude of the flexural response is not an intrinsic property of the lithosphere but result from the history of the competitive interactions between rate of loading and rate of viscous dissipation thermally activated a clear physical description of this flexural mode has not yet been proposed even though some recent results on the mecha nisms of uplift shoulder formation during rifting evolution may be considered bassi 1991 chery et al 1992 the geodynamical context of those basins is complex and the relationship between the transition of extensional and compressional domains is a topic of vigorous research current models for extensional and compressional basins are strongly based on a bulk rheological descrip tion of the whole lithosphere and on a kinematic description of the deformation mechanisms sawyer 1985 houseman and england 1986 quinlan et al 1993 this issue the basin record does reveal to some extend the memory of the deformation history starting from the construction of the internal structure of the basins i e from the processes leading to the formation of rocks sedimentation diagenesis compaction including possible buildup of fluid overpressures and the pattern of the large de formations by faulting or folding to enhance the understanding of the formation and evolution of sedimentary basins it is important to fully address the physical mechanisms operating at different scale in the continental lithosphere for example faulting forms a most important expression at least at the surface of large scale deformation in the basins how those basins are related to the faulting process and the fault interactions is an unsolved question pull apart basins are certainly

interplay of extensional and compression in basin formation this volume contains a collection of papers on the interplay of extension and compression in basin dynamics presented at the 4th annual workshop of the international lithosphere project task force origin of sedimentary basins in benevento italy 25 september l october 1993 previous workshops of the ilp task force have been held in rueil malmaison france 19901 in matrahaza hungary 1991 on the rim of the pannonian basin and in sundvollen in the oslo rift 1992 meeting reports have been published in a number of special volumes and papers cloetingh et al 1993a b 1994 cloetingh sassi and task force team 1994 the 5th task force meeting focusing on basin extension and strike slip tectonics was held in the dead sea rift israel 29 september 5 october 1994 a selection of papers presented at the 5th task force workshop will be published in a forthcoming special volume of tectonophysics the 1995 workshop has taken place in the southern pyrenean foreland basin to examine the relationships between tectonics and eustasy in foreland fold and thrust belts the emphasis of the benevento workshop was on

the role of rheology in extensional basin formation modelling the rheology of the lithosphere determines its deformation under given initial and boundary conditions this paper presents a critical discussion on how rheological properties are taken into account in extensional basin modelling since strength envelopes are often used in models we review the uncertainties in temperature and rheological parameters and assumptions in type of rheology and mode of deformation involved in their construction models of extensional basins are classified into three groups kinematic kinematic with rheological constraints and dynamic rheology enters kinematic models only implicitly in the assumption of an isostatic compensation mechanism we show that there is a critical level of necking that reconciles local isostasy with the finite strength of the lithosphere which requires a flexural response kinematic models with rheological constraints make use of strength envelopes to assess the initial lateral variations of lithospheric strength and its evolution with time at the site of extension dynamic models are the only ones to explicitly introduce rheological constitutive equations usually in plane strain or plane stress they usually however require the presence of an initial perturbation thickness variations pre existing faults thermal inhomogeneities rheological inhomogeneities the mechanical boundary conditions kinematic and dynamic and the thermal boundary conditions constant temperature or constant heat flux at the lower boundary of the lithosphere may result in negative positive feedbacks leading to cessation acceleration of extension we conclude that while kinematic models with rheological constraints if possible are very successful in accounting for the observed characteristics of sedimentary basins dynamic models are necessary to gain insight into the physical processes underlying basin formation and evolution

structural assessment of mount etna volcano from permanent scatterers analysis a study of the deformation pattern of mount etna volcano based on the results from the permanent scatterers ps technique is reported ground motion data provided by the interferometric synthetic aperture radar insar ps technique from 1995 to 2000 are compared and validated by gps data an analysis of the ascending and descending line of sight los components of ground velocities has yielded detailed ground deformation maps and cross sections this analysis allows detection and constraint of discontinuities in the surface velocity field los velocities have then been combined to calculate the vertical and horizontal e w ground velocities a wide inflation of the edifice has been detected on the western and northern flanks over an area of about 350 km2 a seaward motion of the eastern and southern flanks has also been measured ps data allows the geometry and kinematics of the several blocks composing the unstable flanks to be defined even in the highly urbanized areas and their displacement rates have been measured with millimeter precision this analysis reveals the extension of some features beyond their field evidences and defines new important features the results of this work depict a new comprehensive kinematic model of the volcano highlighting the gravitational reorganization of the unbuttressed volcanic pile on its slippery clay basement on the southern flank but an additional drag force due to a strong subsidence of the continental margin facing the etna volcano is necessary to explain the ps velocity field observed on the eastern flank

relationship between deeper lithospheric processes and near surface tectonics of sedimentary basins interactions between upper lithosphere deformation as manifested in the structure and evolution of sedimentary basins and lower lithospheric deformation presumably reflect large scale regional or global tectonic events we review the current state of knowledge regarding these interactions and suggest areas of research which may lead to an improvement in this knowledge understanding the development of sedimentary basins requires insight into the processes responsible both for basin subsidence and also for distribution and preservation of sediments within the basins while some classes of basins are better understood than others there remain significant gaps both in our ability to account for available data and also in the data available to test current models and develop new ones subsidence in some classes of basins can be related to lithospheric scale processes occurring as part of the overall plate tectonic paradigm for example it is widely accepted that passive margin basins subside as a result of lithospheric extension mckenzie 1978 and that foreland basins are flexural consequences of collision between a continent and outboard terranes beaumont 1981 on the other hand models for the origin of intracratonic forearc and trans tensional basins are essentially still at cartoon level involving processes that are difficult to quantify and evaluate in the following we review a number of fundamental questions of vital interest for understanding of the relationship between deeper lithospheric processes and near surface tectonics

malta escarpment fault zone offshore eastern sicily pliocene quaternary tectonic evolution based on new multichannel seismic data 1 the malta escarpment represents the dominant morphological feature offshore eastern sicily linking the deep ionian basin to the east with the hyblean carbonate platform to the west interpretation of purposely acquired multichannel seismic data allows division of the malta escarpment into two portions characterized by different tectonic structures along the segment south of siracusa the malta escarpment is not affected by recent faulting and appears as a steep surface that flattens out toward the ionian basin a recent deformation characterized by a broad area of uplift occurs 20 30 km east from the slope along a nnw sse trend the segment of the malta escarpment extending north of siracusa on the other hand is characterized by the presence of nnw sse east dipping recent extensional faults and related sedimentary basins the observed structural features support the occurrence of a lithospheric tear between the ionian oceanic basin and the hyblean plateau

crust and upper mantle structure along the dss baltic profile in se finland summary the 430 km long dss baltic profile in se finland runs through the rapakivi intrusion the svecokarelian geosynclinal complex including the ladoga bothnian bay zone and the archean basement complex a brief description of field operations in 1982 is presented record sections of p and s waves were used for the interpretations a starting model was constructed by inverse methods and improved by dynamic ray tracing modelling three blocks are indentified on the cross section from sw to ne these are the southern associated with the rapakivi massif depth to moho m about 40 km the central ladoga bothnian bay zone with m of approximately 55 60 km and the northern archean crystalline basement with m about 40 45 km the average crustal velocity is 6 6 6 7 kms the crustal structure along the baltic profile is compared with the surrounding dss profiles finnish sveka and soviet kern tulos and ladoga profiles the eastern border of the ladoga bothnian bay zone was located and specific features of the crust and uppermost mantle along the profile area are discussed

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

how preexisting weaknesses control the style of continental breakup continental breakup is a highly variable process differences occur in the relative timing and extent of volcanism uplift and graben formation as well as in the mode and amount of continental extension before breakup we propose a model which reconciles this variability with the previously recognized tendency for breakup to occur along preexisting weak trends continental lithosphere is viewed as a composite material composed of two strong layers one in the upper mantle and one in the middle crust finite element simulation indicates that extensional failure at weaknesses in the mantle causes concentrated extension in the mantle and diffuse extension in the crust this leads to early melt segregation and volcanism margin uplift during the late stages of the extension process and relatively narrow symmetrical extended margins in contrast failure at weaknesses in the crustal strong zone causes focused extension in the crust and diffuse extension in the mantle this produces initial graben formation cooling in the lower crust and upper mantle and broad asymmetrical extended margins volcanism only occurs late in the process failure at laterally offset weaknesses within both strong layers leads to a deformation pattern dominated simple shear thus differences in the prerift configuration of the continental lithosphere can control the overall style of continental breakup

a synthetic stratigraphic model of foreland basin development the processes of erosion and deposition must be included in foreland basin models to predict correctly basin geometry and stratigraphy we present a synthetic stratigraphic model of the development of nonmarine foreland basins that predicts progressive geometry topography and facies patterns in the model steady crustal shortening occurs according to a wedgethickening model erosion and deposition follow a diffusive process and the lithosphere is compensated elastically erosion and deposition are controlled by the transport coefficients r of the diffusion equation for a range of thrust velocities and lithospheric rigidities transport coefficients are of order 102 103 m yr in the mountain belt these values are much higher than those derived from the study of scarp degradation in the sedimentary basin transport coefficients of order 104 m2 yr are appropriate and are compatible with previous studies of fluvial and deltaic deposition rapid thrusting results in a narrow underfilled basin while slow thrusting results in a wide overfilled basin in addition by varying the erosional and depositional transport coefficients while holding other parameters constant we generate both overfilled and underfilled basins these results suggest that changes in the rate of thrust loading the climate or the source rock lithology can create stratigraphic signatures that have been interpreted to record viscoelastic relaxation of the lithosphere clearly to understand either the long term behavior of the lithosphere or to interpret orogenic history from preserved foreland strata the manner in which a basin was filled must be considered we apply the model to the evolution of the modern sub andean foreland and find that an erosional transport coefficient of 3000 m2 yr and a depositional transport coefficient of 20 000 m2 yr successfully predict the observed basin geometry

extensional basins of the former soviet union structure basin formation mechanisms and subsidence history abstract we review the structure and evolution of a number of riphean phanerozoic rifts and extensional basins within the territory of the former soviet union fsu horst and graben formation in strong crustal and subcrustal lithosphere layers can explain the multi trough character of rift systems observed in the russian platform the vilyuy rift the west siberian rift system the pechora kolva rift system and the laptev sea rift many features in the evolution of these rifted basins are incompatible with predictions of classical stretching models basin subsidence often occurs in the absence of any noticeable stretching and over time scales much longer than predicted by models of thermal subsidence other observations include a time gap between rifting and the onset of post rift basin subsidence of tens to hundreds ma and a correlation in timing of subsidence phases of rifted basins and platforms with opening and closure events of adjacent ocean basins these observations point to an important role for mechanisms such as ecologite formation within or beneath the lithosphere as well as intraplate compression and stress induced lithospheric deflection

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

iapetus suture located beneath the north sea by birps deep seismic reflection profiling the iapetus suture one of the more fundamental geologic boundaries of the british isles has been located beneath the north sea by deep seismic reflection profiling carried out by the british institutions reflection profiling syndicate birps reflection profiling and magnetotelluric sounding have previously been used to infer the position of the iapetus suture beneath the irish sea and the southern uplands but the present study provides the first direct evidence for the location of the iapetus suture east of britain a comparison of the seismic reflection profiles over the iapetus suture east and west of britain shows variations in the dip of the suture which steepens to the northeast beneath the north sea the comparison also reveals unexpected changes in lower crustal reflectivity along the strike of the suture and suggests that there may be no straightforward relation in this area between the crustal reflectivity and the crustal age

structural controls on sedimentary basin evolution introduction this volume contains a collection of papers on structural controls on sedimentary basin evolution presented at the sixth annual workshop of the international lithosphere program task force origin of sedimentary basins in sitges at the rim of the ebro basin september 1995 previous workshops of the ilp task force had been in rueil malmaison france 1990 in matrahaza hungary 1991 on the rim of the pannonian basin in sundvollen norway 1992 in the oslo graben in benevento italy 1993 in the southern apennines fold andthrust belt and in the dead sea rift of israel 1994 the task force also organized a number of sessions during the 1992 and 1996 european geophysical society and the 1993 and 1995 european union of geosciences conferences reports of these meetings have been published in a number of special volumes and papers cloetingh et al 1993a b 1994 1995a b 1996 stephenson 1993 stephenson et al 1996 a position paper cloetingh sassi and task force team 1994 published in m a r i n e a n d p e t r o l e u m geo logy has outlined the task force strategy to pursue the development of a new generation of basin models using natural laboratories with high quality data sets obtained through close partnership with industry the 7th task force workshop was held on the faroe islands northern atlantic in 1996 with the aim of examining the dynamics of rifting

seismogenic stress field beneath mt etna south italy and possible relationships with volcano tectonic features abstract shallow shear type seismic activity occurring beneath the etna volcano during 1990 1995 has been analysed for hypocenter locations focal mechanisms and stress tensor inversion the results have been examined jointly with electronic distance measurements and tiltmeter data collected in the same period and reported in the literature significant seismicity located in the upper 10 km was found to be confined to the time intervals in which ground deformation data indicated inflation of the volcano edifice e g the periods preceding the december 1991 march 1993 and august 1995 march 1996 eruptive phases the shocks mostly occurred in a sector approximately centered on the crater area and elongated in the east west direction the causative seismogenic stress shows a low dip east west orientation of 1 in agreement with existing knowledge on relationships between local fault systems and magma uprise processes the shallow seismicity in question is tentatively explained as being due to lateral compression by magma inside a nearly north south system the volcano deflation phase revealed by electronic distance measurements and tilt data during the 1991 1993 major eruption was not accompanied by any significant shear type shallow event below the depth of 10 km the north south prevailing orientation of 1 reflects the dominant role of the regional stress

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

dynamics of mount etna volcano inferred from static and kinematic gps measurements 1 ground deformations measured on mount etna from late 1995 to mid 1998 using gps observations are analyzed four gps surveys were carried out during the considered period in 1995 the gps network consisted of 18 stations on the volcanic edifice and 6 stations around it during the 1996 survey 22 new monuments were added along a n s profile crossing the summit craters area this profile was surveyed by a semikinematic method allowing greater spatial detail to be achieved on the uppermost part of the volcano the comparisons between the gps surveys are reported here in terms of horizontal and vertical displacements for each station and also in terms of areal dilatation and strain distribution this last parameter continues its ascending trend at a rate of 5 strain yr 1 already shown in the previous period after the end of the 1991 1993 flank eruption inversion of the ground deformation patterns permits investigation of the evolution of both the position and dynamics of magma reservoirs beneath the volcano consistently associated with a general eastward sliding of its eastern sector this study allows us to define the nonuniqueness of ground deformation sources through the investigated period suggesting that the plumbing system of the volcano is made up of a complex system of single intrusions occurring at different times

continental margin large scale instability controlling the flank sliding of etna volcano abstract etna volcano is affected by a downward sliding of its eastern flank as rapid as a few cm year whose nature is highly debated recently collected marine geological and geophysical data allows a detailed image of the morphostructural setting of the continental margin facing the volcano here a large bulge offsets the margin that is deeply affected by widespread semicircular steps interpreted as evidence of large scale gravitational instability such features permeate the whole margin and extend inshore to the volcano sector where the larger ground deformations are measured both submarine instability and subaerial flank sliding are bounded by two regional tectonic lineaments interpreted as weakness lines these cross the coastline to accommodate the basinward movement of this large sector of the continental margin topped by the etna volcanic pile the new data allows re interpreting the tectonic setting of the coastal belt and proposing a novel structural model highlighting the active role of the continental margin instability to drive the seaward sliding of the volcano s eastern flank this model may suggest why a very active basaltic volcano has so unusually developed in front of an active thrust belt

fractal analysis of fractures in rocks the cantor s dust method abstract the cantor s dust method of fractal analysis has been used to describe the regularity of fracture patterns in geological materials seen on a two dimensional surface this linear method of analysis is well adapted to a determination of two dimensional phenomena the determination of the fractal dimension d indicates that it varies regularly as a function of the orientation of the analysis direction this is taken to indicate that there is a relation unexplained as yet between the regularity of the fracture pattern and the forces which produced it the use of the cantor s dust method on naturally fractured materials ranging in dimension from 3 mm to 45 m in maximum dimension indicates the fractal nature of the fractures found in natural materials the analysis method can also be used to identify local variations in the stress field which caused failure such as the fractures in a feldspar compared to those in the host granite etc the method appears to be a sensitive descriptive measure of the failure patterns in rocks

dipping seismic reflectors electrically conductive zones and trapped water in the crust over a subducting plate the lithoprobe program across the northern cascadia subduction zone at vancouver island has obtained geophysical data that suggest a dipping zone of trapped free pore water in the overlying continental crust land and marine multichannel seismic reflection profiles show several bands of reflectors the primary one at a depth of about 30 km is about 5 km thick dips inland and appears to coincide with an electrically conductive layer defined by magnetotelluric data the downgoing oceanic crust is imaged as a thin reflector dipping at about 15 and 10 km deeper than the primary reflector a location that is consistent with seismicity and seismic refraction data both the reflectors and the conductor have been modeled by near horizontal lamellae with 1 4 saline water porosity detailed geothermal measurements defining heat flow that decreases inland indicate that the dipping bands are nearly isothermal at a temperature of 400 500 c it is suggested that free water generated by dehydration of the downgoing oceanic plate migrates upward until reduced temperature results in hydration reactions and mineral precipitation that forms an impermeable barrier low vertical permeability is required to keep the water from separating to the top of the layer this can be reconciled with the low electrical resistivity if pore interconnection is through thin grain boundary tubes as predicted by theoretical equilibrium pore geometry although very small effective grain size is necessary an abrupt transition from high permeability to very low permeability is predicted at a several percent porosity in agreement with the modeled porosity such pore geometry with low permeability may be restricted to temperatures above about 400 c i e in greenschist to amphibolite facies conditions where grains will deform to equilibrium geometry and cracks are annealed the region above the reflective and conductive band is estimated to be within blueschist conditions consistent with the inferred high seismic velocity from refraction data and high density from gravity data

the role of pre existing faults in basin evolution constraints from 2d finite element and 3d flexure models the lithospheric driving forces which cause intraplate basin deformation are relatively constant over large areas consequently lateral variations in deformation and stress and strain concentrations seem to be primarily caused by pre existing heterogenities in the rheological signature of the continental lithosphere underlying the sedimentary basins in this paper we explore the weak character of upper crustal faults and their control on basin shape for a number of case studies on intraplate phanerozoic basin settings using a 2d finite element and a 3d flexure model of key importance is the integration of seismic data and field observations with the tectonic modelling allowing the investigation of deformation processes and their expressions on different scales operating on different levels of the lithosphere finite element models for sub basin scales incorporating weak upper crustal faults predict strong control of these weak zones on local stress distributions and subsequent deformation in agreement with observed deformation patterns slip along upper crustal faults control stress distribution and subsequent faulting in overlying sedimentary rocks the effect of weak upper crustal fault movements on basin wide regional upper crustal flexure is looked at in two case studies on 1 extensional tectonics in the lake tanganyika rift zone east africa and 2 compressional tectonics in the central system and tajo basin central spain both settings indicate that basement warpings are controlled by large amounts of slip along so called weak crustal scale border faults which are mostly planar adopting border fault displacements in the 3d flexure model the results indicate low effective elastic thickness eet values in a range of 3 7 km for induced basement deflection patterns in accordance with observations the low eet values most likely reflect a partly decoupling of upper crustal and subcrustal deformation facilitated by the weak lower crust and in agreement with standard rheological assumptions for phanerozoic lithosphere in contrast the inferred weakness of upper crustal faults relative to surrounding rock is not evident from uniform rheological assumptions however observations of reactivations of faults which are not preferably aligned with the stress field and reactivations of basin deformation on long time scales are in support of this feature

dynamics of extensional basin formation and inversion introduction this volume contains a cohection of papers on the dynamics of extensional basin formation and inversion presented at the 3rd annual workshop of the international lithosphere program task force origin of sedimentary basins in sundvollen norway 18 23 august 1992 previous workshops of the ilp task force had been in rueil malmaison france 1990 and in matrahaza hungary 19911 on the rim of the pannonian basin the task force also organized a number of sessions during the 1992 european geophysical society and the 1993 european union of geosciences conferences reports of these meetings have been published in a number of special volumes and papers cloetingh et al 1993a b stephenson 1993 cloetingh sassi and task force team 1994 the 4th task force meeting focusing on the interplay of extension and compression was held in benevento southern italy in october 1993 a selection of papers presented at that task force workshop will be published in a forthcoming special volume of tectonophysics the emphasis of the 5th workshop of the task force taking place in the dead sea rift israel is on rifting and strike slip tectonics the 1995 workshop will be organized in the southern pyrenean foreland basin with the aim of examining the relationships between tectonics and eustasy in foreland fold and thrust belts the emphasis of the sundvollen workshop was on modelling studies as well as observational approaches to the dynamics of basin extension and inversion important elements of the meeting were the discussion of extensional tectonics rifting in passive margin settings and volcanism and magmatism in rifts and basins following the task force strategy to link subsurface data to field analogues an important part of the meeting was devoted to a thematic excursion in the oslo rift field guides have been published separately larsen et al 1992a

active thrusting as a possible seismogenic source in sicily southern italy some insights from integrated structural kinematic and seismological data abstract this paper proposes a new seismogenic interpretation of mainland and central southern sicily based on an integrated structural kinematic seismological approach through analysis of available structural and geophysical data the tectonic setting the major kinematic units and the crust geometry of the sicilian southward verging fold and thrust belt system are schematized in sections and in map form the depth contour lines of the outermost basal thrust plane which dates back to plio pleistocene times with some evidence of holocene activity are reconstructed this plane here named sicilian basal thrust sbt emerges along the southward convex sciacca gela catania front and reaches the base of the crust at a depth of about 30 km beneath northern sicily additionally an important regional upper crust splay with the same arched shape has been identified some kilometres northward in order to detect any possible indication of seismogenic activity linked to ongoing deformation of the sbt and its splay we analyzed the distribution and kinematics of the instrumental seismicity in the period between 1981 and 2006 particular attention was given to the background seismicity ml up to 4 6 located beneath the sedimentary cover at mt etna as it allows individuating a northward deepening seismogenic volume undergoing an average n s compression which corresponds well with the sbt geometry in section view a merged dataset of all the known major historical and instrumental events moment magnitude 4 5 that occurred above the sbt 0 to 30 km depth contour lines from 217 b c to 2006 was compiled and analyzed based on information from instrumental data and or on speculations on the shape and extent of the historical earthquake macroseismic fields two major ranges of hypocentral depths have been schematically identified within the merged dataset an upper crust range in average