finite fault inversion of dinsar coseismic displacement of the 2009 l aquila earthquake central italy 1 we define the geometric and kinematic characteristics of the fault activated during the mw 6 3 6 april 2009 l aquila earthquake from the modeling of envisat and cosmo skymed the first ever x band interferogram inverted for a coseismic dislocation study dinsar interferograms our best fit solution for the main shock is represented by a normal fault 16 km long and 12 km wide with a small right lateral component dipping 47 sw with a maximum slip of 90 cm although the seismic dislocation probably ended at 1 km depth the updip projection of the fault plane corresponds to the northern segment of the mapped paganica s demetrio fault where alignment of surface breaks was observed in the field the absence of this fault in existing seismic source catalogues suggests that an improved approach involving detailed surface and subsurface geological and geophysical investigations is needed for a better assessment of the seismic hazard at the local scale

glaciodynamically upthrusted bands of englacially transported debris in the pleistocene of central poland two kinds of buried structures are described from dzirzenin north east of warsaw where they occur within a glaciofluvial landform 1 narrow till ridges showing vertically oriented structures excavated from stratified gravel and sands and 2 a narrow vertical zone of massive gravelly sandy material involving vertically oriented lens like layers composed of massive sand with pebbles or of diamicton the gravelly sandy zone is also closely surrounded by stratified glaciofluvial sediments in spite of their vertical position and internal deformation the till ridges and gravelly sandy zone show non tectonic contacts with the surrounding stratified undisturbed sediments the glaciofluvial sediments that occur immediately next to the structures under discussion are characterized by the occurrence of comparatively coarse material and interbeddings of diamicton which wedge out away from these structures the gravelly sandy zone separates different kinds of water laid deposits the buried structures are interpreted as former debris laden bands thrust upwards within the frontal part of the ice sheet and then transformed into still frozen debris ridges projecting over the already dead ice further melting of the decaying ice resulted in abundant glaciofluvial sedimentation and the debris ridges also supplied material for the deposition of the neighbouring stratified deposits one of the ridges separated different glaciofluvial environments the glaciofluvial sediments completely buried the ice cemented ridges which were finally transformed by a melting out process into the till ridges and the gravelly sandy zone the former are interpreted as having been transformed from upturned debris laden bands with a high concentration of debris or from the bands composed of frozen up sediment slabs the gravelly sandy zone is interpreted as having most probably been deposited from upturned bands characterized by a lesser concentration of debris

imprint of foreland structure on the deformation of a thrust sheet the plio pleistocene gela nappe southern sicily italy 1 in sicily the progressive imbrication of the apenninic thrust belt above the pelagian african foreland is traced by the southward migration of marine basins that were progressively shortened during the late miocene pleistocene the outermost and youngest thrust sheet gela nappe displays a peculiar shortening with messinian to early pliocene e w folds refolded in the late pliocene early pleistocene by approximately n s folds subparallel to the transport direction of the thrust sheets this structural interference is documented in south sicily within localized belts of refolding spaced 5 8 km apart the significance of this fold interference pattern is highlighted by our analysis of the offshore seismic reflection line m23a crop mare project that intersects the gela nappe along a trace suborthogonal to the thrust transport direction migration and depth conversion of the line reveal multiple imbrications and draping of the allochthonous units above structural highs of the foreland delimited by inherited n s faults the largest faults bound mid late miocene extensional basins but were reactivated in compression during the late pliocene early pleistocene causing 1 superposed folding along discordant n s structural trends 2 compressional extrusion of the whole wedge of the gela nappe and 3 offset of its sole thrust the reactivation of faults subparallel to the transport direction accommodates differential flexure of the rigid foreland beneath the apenninic wedge and these late stage deformations in the foreland are responsible for the superposition of e w finite shortening onto n s shortening

the deforming bed debris rich basal ice continuum and its implications for the formation of glacial landforms flutes and sediments melt out till abstract there are two potentially important shear zones at the base of the glacier the deforming layer and or the debris rich basal ice layer these two layers have a significant effect on glacier motion and glacial erosional depositional and sedimentary processes however it is shown that most of the processes operating within these two layers are very similar this includes compression at the ice margin longitudinal extension and simple shear upglacier similar styles of shear zone and associated fabric development and similar incorporation transport and depositional processes in the past many criterion have been developed to identify distinct deposition from the deforming layer and the debris rich basal ice layer however if the processes within these layers are similar then it makes the distinct identification of these two separate layers in the geological record very difficult however it is also shown that the main differences between the two layers include rates of sediment movement processes and preservation potential the later is very important as it appears that the two layers are interconnected and that material is melted out from the debris rich basal ice to form a significant component of the deforming layer in this way the final depositional imprint is from the deforming layer and there is little likelihood of the debris rich basal ice layer being preserved undeformed this is demonstrated from modern glacial environments pleistocene flute studies and studies of pleistocene melt out tills from the u k u s a and germany

structural setting of the adriatic basin and the main related petroleum exploration plays abstract most of the oil and gas resources located within the adriatic domain are genetically linked to the flexure of the adria continental margin and to the evolution of the apennines fold and thrust belt the source rocks contained in the pre flexure epi continental successions reached the maturity window during the flexural subsidence or alternatively the flexural accommodating siliciclastic flysch themselves generated and stored hydrocarbons the petroleum exploration plays of the adriatic domain are tentatively classified in this paper according to their geological evolution with respect to the apennines fold and thrust belt the description of the geological evolution of these structures and related petroleum plays are described including plays set in undeformed or poorly deformed foreland areas a new isochrones map showing the structural setting of the substratum at the level of the fucoidi fm is presented several different groups of structures can be recognized in the adriatic domain that can be connected to the final phases of deformation of the apennines or to the interaction with the dinarides fold and thrust belt front to the east

thrust front segmentation induced by differential slab retreat in the apennines italy new seismic reflection data reveal that the south eastward prolongation of the apennine thrust front in the central adriatic sea is most likely located in a more external position with respect to the traditional interpretation in this new interpretation the apennine thrust front shows a segmented geometry in correspondence to the tremiti lithospheric transfer zone the available data suggest that the north eastward flexural retreat of the subducting adriatic lithosphere and the related frontal accretion of the apennine accretionary prism have acted during the last 5 ma and may be considered still lively in both the po plain and in the central adriatic domain north of the tremiti lineament by analysing the tectonic evolution of the apulo adriatic areas it may be argued that the differential slab retreat between the central and southern sectors of the subducting adriatic plate has been able to induce the segmentation of the apennine thrust front

the continuity of active fault systems in greece summary evidence from geomorphology the distribution of large earthquakes and geodetic measurements suggests that the active faulting in mainland greece and the north aegean sea is concentrated into a small number of discrete linear zones that bound relatively rigid blocks on land the zones are most clearly identified where the faulting is associated with large escarpments particularly in hard footwall rocks the zones can become indistinct and diffuse near their ends sometimes because they enter high unstable topography where landsliding obscures the fault morphology but mostly because the extension rates decrease along strike as a consequence of the relative rotation of the blocks they bound the main graben systems of chalkidiki southern thessaly and the north gulf of evia all seem to connect with the strike slip faulting in the offshore aegean and to die out in the west a configuration related to clockwise rotations in east central greece by contrast the gulf of corinth which is the fastest opening graben system in greece opens more rapidly in the west than the east both these features of the gulf of corinth are consequences of the motion of the south aegean and peloponnese as a single block late pliocene and quaternary geology and geomorphology indicate that the boundaries of the rigid blocks in central greece have changed over that time with faulting migrating into the hanging walls sometimes changing in orientation these changes are probably related to the way faulting in the seismogenic layer adapts to block rotation so as to maintain the general features of a velocity field that is controlled by larger scale effects such as buoyancy forces and the seaward migration of the subducting slab beneath crete the image of greece as a mosaic of rigid blocks whose boundaries change with time is a useful framework for seismic hazard evaluation but we emphasize that some moderate sized earthquakes do occur away from the main fault zones within the relatively rigid blocks and especially near their diffuse ends

deformed pleistocene marine terraces along the ionian sea margin of southern italy unveiling blind fault related folds contribution to coastal uplift 1 morphotectonic analysis and fault numeric modeling of uplifted marine terraces along the ionian sea coast of the southern apennines allowed us to place quantitative constraints on middle pleistocene holocene deformation ten terrace orders uplifted to as much as 660 m were mapped along 80 km of the taranto gulf coastline the shorelines document both a regional and a local fault induced contribution to uplift the intermingling between the two deformation sources is attested by three 10 km scale undulations superimposed on a 100 km scale northeastward tilt the undulations spatially coincide with the trace of nw se striking transpressional faults that affected the coastal range during the early pleistocene to test whether fault activity continued to the present we modeled the differential uplift of marine terraces as progressive elastic displacement above blind oblique thrust ramps seated beneath the coast through an iterative and mathematically based procedure we defined the best geometric and kinematic fault parameters as well as the number and position of fault segments fault numerical models predict two fault propagation folds cored by blind thrusts with slip rates ranging from 0 5 to 0 7 mm yr and capable of generating an earthquake with a maximum moment magnitude of 5 9 6 3 notably we find that the locus of predominant activity has repeatedly shifted between the two fault systems during time and that slip rates on each fault have temporally changed it is not clear if the active deformation is seismogenic or dominated by aseismic creep however the modeled faults are embedded in an offshore transpressional belt that may have sourced historical earthquakes

coexisting tectonic settings the example of the southern tyrrhenian sea we performed geodetic strain rate analyses in southern italy using new gps velocities two dimensional strain and rotation rate fields were estimated and results show that most of the shortening is distributed in the northern sicily offshore extension becomes more evident and comparable with shortening on the eastern side of the same margin and greater in the eastern sicily offshore principal shortening and extension rate axes are consistent with long term geological features seismic reflection profiles show both active compressive and extensional faults affecting pleistocene strata we show evidence for contemporaneous extension and transtension in the cefalu basin combining geodetic data and geological features point to the coexistence of independent geodynamic processes i e the active e w backarc spreading in the hangingwall of the apennines subduction zone and shortening along the southern margin of the tyrrhenian backarc basin operated by the nnw motion of africa relative to eurasia

geometry segmentation pattern and displacement variations along a major apennine thrust zone central italy abstract hundreds of kilometres long arc shaped continuous thrust faults commonly imply very large displacements by detachment dominated thrusting therefore their occurrence has a large impact on fold thrust belt structure one of the major thrust faults of the central northern apennines the umbria marche sabina thrust zone is traditionally believed to represent one such feature characterised by displacements of several tens of kilometres however detailed studies of this structure revealed that it is actually composed of a series of partially overlapping fault segments rather than consisting of a single continuous thrust cross section balancing and restoration carried out by the integration of surface geological data with available sub surface information points out relatively limited amounts of thrust displacement

new insights into the 2012 emilia italy seismic sequence through advanced numerical modeling of ground deformation insar measurements 1 we provide new insights into the two main seismic events that occurred in 2012 in the emilia region italy we extend the results from previous studies based on analytical inversion modeling of gps and radarsat 1 insar measurements by exploiting radarsat 2 data moreover we benefit from the available large amount of geological and geophysical information through finite element method fem modeling implemented in a structural mechanical context to investigate the impact of known buried structures on the modulation of the ground deformation field we find that the displacement pattern associated with the 20 may event is consistent with the activation of a single fault segment of the inner ferrara thrust in good agreement with the analytical solution in contrast the interpretation of the 29 may episode requires the activation of three different fault segments and a block roto translation of the mirandola anticline the proposed fem based methodology is applicable to other seismic areas where the complexity of buried structures is known and plays a fundamental role in the modulation of the associated surface deformation pattern

coseismic fault slip of the 2008 mw 7 9 wenchuan earthquake estimated from insar and gps measurements 1 we infer co seismic fault slip during the 2008 mw 7 9 wenchuan earthquake from interferometric synthetic aperture radar insar and gps observations of ground deformation we use alos palsar data from ascending orbits on six tracks and we do not use data that are strongly affected by ionospheric perturbations we use a fault model composed of three planar fault segments of the beichuan fault and one planar segment representing the parallel pengguan fault maximum thrust slip is up to 6 7 m near the surface and occurs in two locations near yingxiu in the south and beichuan in the center of the rupture maximum strike slip is over 4 m and occurs near pingtong and nanba along the northern end of the rupture we find that the ratio of coseismic thrust to strike slip on the beichuan fault decreases from 1 5 to 0 7 from the sw to the ne citation feng g e a hetland x ding z li and l zhang 2010 coseismic fault slip of the 2008 mw 7 9 wenchuan earthquake estimated from insar and gps measurements geophys res lett 37 l01302 doi 10 1029 2009gl041213

tectonic evolution of a low angle extensional fault system from restored cross sections in the northern apennines italy 1 broad geological and geophysical documentation is available on regional extensional systems driven by low angle normal faults however little information exists about the three dimensional geometry and the offset distribution of such extensional structures we present a new set of balanced geological sections across the extensional fault system driven by the altotiberina low angle normal fault in the northern apennines of italy we document this extensional system throughout a large set of surface field surveys and geological maps and subsurface data seismic reflection profiles and boreholes the subsurface data allowed us to define the fault deep geometry and to obtain its structural contours the fault geometry is characterized by both along dip and along strike irregularities in cross section the fault displays a staircase trajectory with the shallowest part being dome shaped and flattened to horizontal this bending could be due to the footwall uplift triggered by a footwall uploading greater than about 115 mpa the sequential restoration of five geological cross sections yields a maximum extension of about 10 km accumulated over approximately 3 ma the resulting long term slip rate is about 3 mm yr which is of the same order as the present day extensional rate measured by gps 2 5 3 0 mm yr suggesting an almost steady state extension over the last 3 ma the distribution of the extension values along the fault strike is bell shaped as expected for a continuous surface

deep structure of the southern apennines italy thin skinned or thick skinned 1 the deep structure of the southern apennines sa accretionary wedge is still debated since industrial seismic reflection and well data provide reliable constraints only to a depth of about 10 km as a consequence two directly linked questions regard 1 the shortening in the accretionary prism particularly within the buried apulian thrust units and 2 the degree of involvement of the lower plate basement i e the apulian crystalline basement to address these issues we have constructed a regional section along a recently released deep seismic reflection profile crop 04 which intersects the entire sa the resulting cross section adequately constrained to a depth of about 15 km has been framed in a geodynamic scenario characterized by the eastward roll back of the westward subducting apulo adriatic lithosphere on the basis of this section we speculate on the deep structure building both thin and thick skinned thrust models a cross check of these end members models against documented tectonic geophysical and geochemical features shows that the thin skinned model is generally more consistent with the available data the development of basement slices with thicknesses of tens of kilometers is unlikely while it remains possible that the apulian basement could have been involved with its upper few kilometers in the thin skinned model the total shortening of the allochthonous units i e apennine and apulian carbonate platforms and lagonegro basin is estimated to be greater than 280 300 km some 90 km of shortening can be attributed to the apulian thrust units

late wisconsinan sub glacial clastic intrusive sheets along lake erie bluffs at bradtville ontario canada abstract numerous clastic intrusive sheets a few decimetres to more than 16 m long 1 120 cm thick and extending one to more than 25 m laterally occur along a 350 m long section of the late wisconsinan catfish creek drift in the lake erie bluffs at bradtville southwestern ontario most of them are downglacier dipping dikes the largest one terminating in the underlying middle wisconsinan tyrconnell formation most dikes strike nne ssw at right angles to the local direction of glacier movement during the deposition of catfish creek drift the tops of some of them are truncated or displaced downglacier by shearing the main concentration of clastic intrusive sheets is on the upglacier side of a glaciotectonically folded anticline of tyrconnell formation clays and silts underlying the catfish creek drift the host sediments are catfish creek till gravel sand and silt and tyrconnell formation silt and clay most intrusive sheets particularly the small to medium ones consist of massive to crudely laminated sand and silt intruded from below by a dewatering process the largest dike reflects in its composition mainly the adjoining or higher lying host sediment materials and its main part was formed by downward infilling or by gravity flows into an open fracture the large dike is flanked by small laminated silty sand sheets and several small apophyses some of them injected downward and sideways others upward by dewatering the clastic intrusive sheets were formed under a moving glacier the erie lobe probably both at the beginning and towards the end of the deposition of catfish creek till their location and position was predetermined by glaciotectonically induced listric planar structures and zones of weakness mainly tension fractures that strike transverse to glacier movement and dip downglacier and also by confinement of pore water in a permeable sediment wedge between the less pervious tyrconnell formation and massive catfish creek basal till

incipient extension along the active convergent margin of nubia in sicily italy cefalu etna seismic zone 1 recent geodetic data are compatible with nne ssw tectonic extension at a rate of 5 mm yr in sicily southern italy within a broader region of net active compression along the nubian plate margin northern africa the structures that accommodate such extensional regime and its cause are still unknown from field structural surveys and seismological analyses the geometry kinematics structural architecture and seismic potential of an extensional seismic zone linking cefalu and mount etna in central eastern sicily are defined the zone includes high angle wnw striking normal and right lateral strike slip faults and subordinate north and nne striking strike slip faults either right or left lateral the occurrence of small discontinuous faults and the absence of related depressions and sedimentary basins suggest that the extensional regime is still in an incipient stage the ongoing seismic activity possibly reactivates preexisting faults instrumentally and historically recorded earthquakes are lower than about 6 in magnitude and destructive events are historically unknown since at least 1300 a d this apparent upper bound of earthquake magnitudes is consistent with the maximum magnitude values estimated from the length of the longest mapped faults and sources of seismic swarms which all together suggest a value between 6 and 6 5 as the maximum expected magnitude that can be proposed at the present stage of investigation for earthquakes in the study area lateral extension on preexisting faults and upwelling of melt mantle material beneath mount etna are considered viable processes to explain at least in part the active extensional tectonics along the cefalu etna seismic zone strike slip seismic faulting beneath mount etna may be part of a previously proposed diffuse transfer zone affecting northeastern sicily and including the tindari fault

spatial variations of seismogenic stress orientations in sicily south italy abstract seismogenic stress orientations are estimated in the lithosphere of sicily by inversion of 131 local earthquake focal mechanisms fms selected from the literature an average misfit f 14 5 between stress tensor and fms indicates that the entire set of earthquakes is generated by a highly heterogeneous stress field detailed analysis of stress tensors and related earthquake misfits obtained for tens of subsets based on spatial separation of data allowed us to identify two main stress domains in the study region i a compressional domain including etna western sicily and the southern tyrrhenian sea offshore sicily where the 1 orientation roughly changes from nw se in the etna area and western sicily to nne ssw at the northeastern edge of the domain eolian islands and ii an extensional domain in northeastern sicily between the eolian islands and etna where 3 is oriented analogously to previously estimated in the easterly confining extensional area of the messina straits general agreement is found between this stress pattern and the gps crustal displacement vectors reported in the most recent literature for the study region moreover stress inversion enables us to locate the extensional domain more accurately than the presently available gps data finally the stress orientations estimated in the southern and western sectors of the study area etna and western sicily on and offshore match well with the displacement fields predicted for sicily by large scale models of plate motion conversely a mismatch is observed in the northeastern sector eolian islands and northeastern sicily we suggest that the joint action of africa eurasia convergence and ionian subduction trench retreat rollback of the subducting slab may explain the stress pattern detected in sicily in the present study work for computation of a finite element regional geodynamic model based on geophysical and geological data collected over the last few years has recently started with the purpose of quantitatively checking this hypothesis

a note on hydrodynamic instabilities and horizontal circulation in the surf zone the setup setdown of the mean water level induced by incident waves on a beach has been hypothesized to be unstable and thereby a source of horizontal circulation rip currents and rhythmic topography but a direct proof was lacking this paper examines the dynamics of a small amplitude circulation coupled with the subsequent perturbation on the mean water level and the wave radiation stress for normal regular wave incidence on a nonerodible and nonbarred beach two cases are considered in the first one the wave refraction by currents and depth variations is neglected whereas in the second one wave refraction is accounted for in the first case it is proved by analytical methods that there is no instability it is shown that the coupling between flow mean free surface and wave radiation stress provides a restoring force that reinforces gravity in the surf zone while in the shoaling zone the coupling opposes gravity this destabilizing effect in the shoaling zone is too small to overcome gravity force although this restoring destabilizing force cannot produce instability it causes a small correction on the classical long wave phase speed that becomes now anisotropic in contrast when wave refraction is included in the model the motionless basic equilibrium becomes unstable and circulation cells tend to develop it is argued that even without wave refraction if sediment transport and topographic evolution is accounted for the situation can be reversed and the basic equilibrium can be unstable therefore rip currents in nonbarred beaches cannot be explained from an instability originated only by the setup setdown unless wave refraction or topographic evolution is taken into account

fossil remnants of up turned debris bands in pleistocene glacial deposits of poland fossil remnants of up turned debris rich bands of glacial ice are recorded from three localities in the polish lowlands in each case the fossil debris bands occur in proximal parts of hills built of glacitectonically disturbed sediments the characteristics of these remnants and of the associated deposits and structures are described and they are compared to present day examples from spitsbergen

genesis of hummocky moraines by thrusting in glacier ice evidence from svalbard and britain irregular mounds of glacial debris commonly referred to as 9hummocky moraine9 until recently were linked to ice stagnation during rapid climatic amelioration however recent work in scotland has demonstrated that some hummocky moraine dating from the younger dryas event c 10 000 years bp was the product of deposition at active ice margins observations at modern high arctic glacier margins in svalbard 76 80 n indicate that some moraines of this type form under a dynamic glaciological regime mainly by thrusting in active polythermal ice undergoing strong longitudinal compression this situation is particularly common where there is a transition from warm based ice in the interior of a glacier to cold based ice at the margins or snout from their morphological similarity rectilinear slopes facing up glacier and irregular downglacier faces and apparent stacking of slabs of sediment of subglacial derivation it is concluded that some assemblages of british moraines are also the product of thrusting this process appears to be most dominant in polythermal glaciers rather than in temperate glaciers on this basis it is tentatively suggested that the younger dryas in britain was characterized by a climatic regime similar to that in svalbard today mean annual temperature 5 c 400 1000 mm precipitation and that the associated glaciers may have been of polythermal character

graviquakes in italy abstract we discuss the mechanics of crustal normal fault related earthquakes and show that they represent dissipation of gravitational potential energy graviquakes and their magnitude increases with the involved volume delimited by the seismogenic fault and an antithetic dilated wedge in its hangingwall and the fault dip the magnitude increases with the deepening of the brittle ductile transition bdt which in turn enlarges the involved volume the fault dip seems rather controlled by the static friction of the involved crustal layers we apply the model to the extensional area of the italian peninsula whose geodynamics is controlled by the alpine and apennines subduction zones the latter has a well developed backarc basin and a large part of the accretionary prism is affected by on going extensional tectonics which is responsible for most of peninsular italy seismicity analyzing the seismic record of the apennines the length of seismogenic normal faults tends to be at most about 3 times the hypocenter depth we compile a map of the brittle ductile transition depth and assuming a fixed 45 or 60 fault dip and a dilated wedge developed during the interseismic period almost perpendicular to the fault plane we compute the maximum volume of the hangingwall collapsing at the coseismic stage and estimate the maximum expected magnitude lower magnitude values are obtained in areas with thinner brittle layer and higher heat flow moreover lower magnitude relative to those theoretically expected may occur in areas of higher strain rate where faults may creep faster due to lower frictional values

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

on the relationships between slab dip back arc stress upper plate absolute motion and crustal nature in subduction zones 1 statistical analysis of modern oceanic subduction zone parameters such as the age of a downgoing plate or the absolute plate motions is performed in order to investigate which parameter controls the dip of a slab and conversely what the influence of slab geometry is on upper plate behavior for that purpose parameters have been determined from global databases along 159 transects from all subduction zones that are not perturbed by nearby collision or ridge plateau seamount subduction on the basis of tomographic images slabs that penetrate through or lie on the 670 km discontinuity are also identified the results of the statistical analysis are as follows 1 back arc stress correlates with slab dip i e back arc spreading is observed for deep dips deeper than 125 km larger than 50 whereas back arc shortening occurs only for deep dips less than 30 2 slab dip correlates with absolute motion of the overriding plate the correlation is even better when the slab lies on or even more penetrates through the 670 km discontinuity 3 slabs dip more steeply by about 20 on average beneath oceanic overriding plates than beneath continental ones 4 slabs dip more steeply on average by about 10 near edges 5 slab dip does not correlate with the magnitude of slab pull the age of subducting lithosphere at the trench the thermal regime of the subducting lithosphere the convergence rate or the subduction polarity east versus west the present study provides evidence that the upper plate absolute motion plays an important role on slab dip as well as on upper plate strain retreating overriding plates are often oceanic ones and thus may partially explain the steeper slab dips beneath oceanic upper plates one can infer that low slab dips correlate well with compression in continental advancing upper plates whereas steep dips are often associated with extension in oceanic retreating upper plates excess weight of old slabs is often counterbalanced by other forces probably asthenospheric in origin such as lateral mantle flow near slab edges or anchor forces to determine slab dip

ice flow directions of the last scandinavian ice sheet in central poland abstract the article presents the results of studies on the ice flow directions of the last scandinavian ice sheet sis in central poland at the southern periphery of the sis and particularly within the plock lobe the ice flow pattern was derived mainly from direct indices such as till fabric vergence of glaciotectonic compression structures orientation of small scale subglacial deformations formed beneath the flowing ice orientation of pavement stone longitudinal axes stone lee ends and clast surface striae the study is supplemented with a reconstruction of ice movement directions based on orientation analysis of both concave tunnel valley and convex eskers glacial morpholineaments linear glacial landforms till age was also determined using luminescence osl datings from sand deposits these were collected directly at numerous sites from under and above the last sis till unit combined with previously published data the results of the present investigation of the last ice sheet advance during the late weichselian ca 23 18 ka indicate that there were two different ice flow phases and that the maximum extent was asynchronous the western part of the said area experienced two advances during the leszno brandenburg and poznan frankfurt phases while during the earlier one the ice masses came from the nw presumably along the eastern limb of the odranian b2 after punkari 1997 ice stream and then from the n along the vistulian b3 stream the last sis occupied the eastern sector of the area only once during the younger poznan phase building the plock lobe the lobe shaped ice margin with a fan like flow pattern within the lobe may be indicative of a palaeo ice stream terminal zone

decollement depth versus accretionary prism dimension in the apennines and the barbados 1 along representative cross sections of the apennines and the northern barbados accretionary prisms we measured the area the decollement depth the angle a of the upper envelope and the angle b of the dip of the regional monocline the continental sections of the apennines accretionary prism have a deeper decollement than the oceanic sections of the northern barbados 6 10 km depth and 1 km depth respectively because the sediment pile is thinner on the incoming barbados plate and its denser oceanic structure is more easily subducted considering the frontal 50 km the apennines have an average cross sectional area of 500 km 2 and the northern barbados ridge of 100 km 2 the total area is a function of the depth of the decollement plane therefore at a given amount of subduction the deeper the decollement depth is the bigger the area of the wedge will result assuming negligible compaction and erosion as a consequence the larger area volume and higher elevation of the apennines with respect to the barbados is determined by the apenninic deeper decollement despite these differences the geometry of both decollements is in some cases comparable in particular close to the boundary between the crystalline crust and the sediment pile where the main density and strength contrasts are concentrated variations in depth of the decollement occur moving along strike in both accretionary prisms the geometry of the prisms is further controlled by the different values of a and b their sum and the distance of the accretionary prism relative to the subduction hinge index terms 8099 structural geology general or miscellaneous 8150 tectonophysics evolution of the earth plate boundary general 3040 8122 tectonophysics dynamics gravity and tectonics keywords decollement depth accretionary prism apennines barbados citation bigi s f lenci c doglioni j c moore e carminati and d scrocca decollement depth versus

till and moraine emplacement in a deforming bed surge an example from a marine environment the glacier sefstrombreen in spitsbergen surged across an arm of the sea between qsr 1882 and 1886 and rode up onto the island coraholmen marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location transported and smeared over the sea bed and coraholmen as a deformation till the glacier emplaced about 210sm 0 2 km 3 of drift in the terminal 2 km of its advance in a maximum of 14 years leaving a thickness of up to 20 m on coraholmen which was doubled in size as a result during the surge subglacial muds were characterised by high water pressures low effective pressures and low frictional resistance to glacier movement original sedimentary inhomogenities permit fold structures to be identified but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills the surge was probably shortlived and as the heavily crevassed glacier stagnated underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface reticulate crevasse intrusion ridges on coraholmen and the sea floor reflect the orientation of surge generated crevasses water and sediment was also extruded beyond the glacier at its maximum extent to form extensive flows producing till tongues both on coraholmen and the sea floor extending over 1 3 km from the glacier it is argued that subglacial deformation of pre existing sediment will almost invariably be associated with glaciation of marine areas and that this process will not only produce deformation tills through remoulding of pre existing sediments but will also play a fundamental role in glacier dynamics criteria which perrait glacial tills produced by such events from marine and glaciomarine muds are discussed copyright 1996 elsevier science ltd